1. Introduction
Neuroblastoma (NB), a disease with survival rates below 50%, is the most common extracranial solid tumor appearing in the childhood. NB results from an uncommon development of neural crest progenitor cells of the sympathetic nervous system. Chemoradiation, autologous stem cell rescue, and surgical resection are current therapeutic tools to fight this disease [1]. Other anti-NB strategies are the use of phosphoinositide 3-kinase, fibroblast growth factor receptor, or cyclin-dependent kinase 3/6 inhibitors [2]; immunotherapy [3,4]; NB-extracellular vesicles targeting [5]; natural killer cells [6,7]; and retinoic acid therapy [8]. Moreover, a new stemness-related predictive model for NB by means of bioinformatics/machine learning examination has been suggested [9], and a recent review on precision medicine applications in NB has recently been published [10]. There is therefore a plethora of anti-NB strategies that are being developed. In addition, another promising line of research is the participation of the peptidergic systems in the progress of tumors because not only do peptides exert antitumor effects, they also favor tumor progression; that is, peptides act as anticancer or oncogenic factors [11]. Peptides contain less than 50 amino acids and can be synthesized and released from nerve cells, as well as from endothelial and epithelial cells, cells of the immune system (e.g., T cells, eosinophils, macrophages), and tumor cells [11,12]. This means that there are numerous sources where peptides are synthesized and released, and they are involved in numerous physiological (e.g., cardiovascular and respiratory mechanisms, learning, memory, bone metabolism, thermoregulation, food intake, immunoregulation, sleep, glucoregulation) and pathological (e.g., asthma, urinary tract dysfunction, nausea, vomiting, inflammation, pain, neurotrauma, stroke, Alzheimer’s disease, depression, stress, anxiety) actions. Tumor cells produce and release peptides that exert autocrine, paracrine, and endocrine actions as peptides are released into the bloodstream [11,12]. Moreover, tumor cell activity is regulated by peptides released from nerve endings, endothelial cells, and immune cells located in the tumor microenvironment [11,12]. Peptide receptor antagonists are potential anti-NB agents because they stimulate apoptosis in tumor cells and block the migration/invasion of these cells, as well as inhibiting angiogenesis [12]. Moreover, peptide receptor antagonists combined with radiotherapy/chemotherapy decreased the side-effects mediated by cytostatics and also exerted an anticancer synergic action [13,14]. Accordingly, this review is focused on the anticancer and oncogenic peptides involved in NB and on the therapeutic anti-NB strategies resulting from the actions mediated by the peptidergic systems. Finally, future research lines will be suggested.
2. Neuroblastoma and Peptidergic Systems
2.1. Oncogenic Peptides
2.1.1. Amylin
Human amylin promoted the release of factors (vascular endothelial growth factor, HspB5) by endothelial cells, favoring the proliferation and survival of human SH-SY5Y NB cells [15].
2.1.2. Angiotensin II
The expression of angiotensin II receptor 1 (ATR1) in human NB cell lines (CHP-404, CHP-134B, SMS-K-CNR) has been reported, but in others, this expression was not observed (CHP-100, GOTO, SK-N-AS) [16]. Moreover, in the same study, it was demonstrated that the vasoactive intestinal polypeptide increased the density of ATR1 in NB cells and that angiotensin II did not favor the synthesis of DNA in these cells [16]. However, angiotensin II acted as a growth factor in human SH-SY5Y NB cells and insulin (at high concentration), and insulin-like growth factor-1 (at low concentration) increased the proliferative effects mediated by angiotensin II on these cells [17]. The effect mediated by insulin was blocked with angiotensin II receptor antagonists such as DuP753 (ATR1 blocker) or PD123177 (ATR2 blocker) [17]. Moreover, in the human SK-N-MC NB cell line, the expression of the angiotensin 4 receptor has been described [18]. This receptor, after binding to angiotensin IV (an angiotensin II fragment), promoted the synthesis of DNA in SK-N-MC NB cells. This was also induced by the peptide LVV-hemorphin 7 [18].
Furthermore, angiotensin II promoted the differentiation of human SH-SY5Y NB cells by increasing the levels of reactive oxygen species and microtubule-associated protein (MAP) 2 without affecting viability. This increase was also mediated by the activation of NADPH oxidase [19]. SH-SY5Y NB cells, treated with angiotensin II, decreased in size, and when these cells were treated with the ATR2 inhibitor PD123319, a reduction in the level of MAP2 was found. This means that angiotensin II regulated the differentiation of NB cells by increasing MAP2 level via AT2R [19]. Moreover, angiotensin II, as well as the ATR2 agonist CGP42112A, favored neurite outgrowth/beta III-tubulin expression in SH-SY5Y NB cells [20]. This means that these mechanisms were mediated by ATR2, and in fact, the ATR2 antagonist PD123319 counteracted the effects mediated by angiotensin II or CGP42112A. Thus, the ATR2 signaling pathway plays an important role in neuronal differentiation. Neurite growth mediated by CGP42112A required the activation of c-Src, sphingosine kinase, and mitogen-activated protein kinase but not phosphatidylinositol 3-kinase stimulation [20]. The data reported in this study also suggested a transactivation of the nerve growth factor receptor tyrosine kinase A, since its inhibition decreased neurite outgrowth mediated by angiotensin II or CGP42112A.
2.1.3. Bradykinin
The effects mediated by bradykinin have been studied in human NB cell lines (CHP-100, CHP-134, IMR-32, SH-SY5Y) [21]. Bradykinin increased metalloproteinase activity and chemotactic response of NB cells, favored cell adhesion, and upregulated the expression of the vascular endothelial growth factor [21]. Moreover, bradykinin augmented the expression of the truncated purinergic P2X7B receptor (compared to the P2X7A full-length form expression) and promoted the proliferation of tumor cells, which was counteracted with purinergic P2X7 receptor antagonists. Mice transplanted with bradykinin-treated NB cells showed higher metastasis rates than animals administered with non-treated cells, and animals that received a purinergic P2X7 receptor antagonist (Brilliant blue G) did not show dissemination of NB cells to liver and bone marrow [21]. The data show that bradykinin and purines play a crucial role in NB dissemination, favoring metastasis.
Bradykinin also favored neurite outgrowth via myristoylated alanine-rich C kinase substrate phosphorylation involving the protein kinase C-dependent ROCK/RhoA pathway and protein phosphatase 2A in SH-SY5Y NB cells [22]. Bradykinin-potentiating peptides promoted the actions mediated by bradykinin because these peptides blocked angiotensin-converting enzyme activity. One of these peptides, named 10c (a synthetic bradykinin-potentiating peptide), protected SH-SY5Y NB cells against H2O2-induced oxidative stress [23]. Thus, 10c decreased the cell death promoted by H2O2, lipid peroxidation, reactive oxygen species generation, NF-κB expression, nitrate level, and inducible nitric oxide synthase expression, and it also protected mitochondrial membranes against oxidation [23].
2.1.4. Gastrin-Releasing Peptide/Bombesin
Gastrin-releasing peptide (GRP) acts as an autocrine growth factor in human NB, and the peptide is synthetized by NB cells [24,25]. GRP activated the phosphatidylinositol 3-kinase/Akt survival signaling pathway favoring DNA synthesis and cell cycle progression in NB cells; in fact, the silencing of the GRP receptor promoted cell cycle arrest [26,27]. GRP receptor was overexpressed in NB [1]. This overexpression downregulated phosphatase and tensin homologue (PTEN) expression, favoring NB cell growth [27]. The expression of both GRP and GRP receptor protein was reported in human NB tissues, and, importantly, an augmented receptor expression was observed in more aggressive and undifferentiated tumors in comparison with that reported in benign tumors [25]. Moreover, GRP receptor mRNA was found in human NB cell lines, and the treatment with GRP provoked the mobilization of intracellular calcium in SK-N-SH/LAN-1 NB cell lines and the growth of NB cells (SH-SY5Y, SK-N-SH, LAN-1, IMR-32) [25]. The latter effect was blocked when SK-N-SH NB cells were treated with anti-GRP antibodies. This means that immunotherapy could be a potential a promising therapeutic strategy against NB. In this sense, another study has reported the use of anti-GRP receptor monoclonal antibodies to treat NB; in this study, LAN-1, SK-N-DZ, SHEP, SH-SY5Y, SK-N-AS, and BE (2)-C NB cell lines were used [1]. Monoclonal antibodies inhibited the activation of GRP receptors by GRP and its downstream phosphatidylinositol 3-kinase/Akt signaling pathway. This blocked the proliferation of NB cells and promoted antibody-dependent cellular cytotoxicity in NB cells. Moreover, anti-GRP receptor monoclonal antibodies favored the release of interferon γ/cytotoxic granzyme B by natural killer cells and decreased the mitotic tumor cells in vivo [1].
GRP increased the migration of NB cells and matrix metalloproteinase-2 expression, whereas it decreased the level of TIMP metallopeptidase inhibitor-1 in human NB cells. The study in question was performed in IMR-32/LAN-1/SK-N-SH NB cells [28]. GRP receptor overexpression upregulated integrin α2/α3/β1 protein/mRNA expressions and favored SK-N-SH NB cell migration, whereas the silencing of integrin β1 blocked tumor cell migration [28]. Akt2 controls the metastatic potential of human NB cells (SK-N-BE (2), BE (2)-M17, BE (2)-C) [29]. The activation of the phosphatidylinositol 3-kinase/Akt signaling pathway has been correlated with a poor prognosis in patients suffering from NB [29]. This pathway plays a crucial role in NB oncogenic transformation, which is promoted by the GRP/GRP receptor system and requires the N-myc oncogene [29]. The expression of the latter oncogene was regulated by Akt2 in NB cells, and Akt2 attenuation favored anchorage-independent cell growth, decreased cell proliferation, and reduced the release of the angiogenic vascular endothelial growth factor [29]. Moreover, Akt2 silencing blocked the migration/invasion of NB cells, and Akt2 silencing NB cell xenografts resulted in fewer metastases in experimental animals compared to controls. The data suggest that the GRP/GRP receptor/Akt2 axis is involved in NB progression. Focal adhesion kinase (FAK), a downstream target of the GRP receptor signal, was involved in NB metastasis and tumorigenesis [30]. Its expression and that of GRP receptors were correlated in human NB, whereas in SK-N-SH NB cells, the overexpression of these receptors augmented integrin (α3/β1)/FAK expressions and cell migration [30]. GRP receptor silencing reduced Mycn/FAK levels in BE (2)-C NB cells; FAK overexpression favored cell growth in SK-N-SH NB cells; and FAK blockers (Y15) inhibited the NB cell growth and metastasis promoted by GRP [30]. Dichloroacetate (an acetic acid analog) reduced the proliferation of SK-N-AS/BE (2)-C NB cells and promoted cell death, and treatment with dichloroacetate and GRP receptor silencing synergistically blocked the proliferation of BE (2)-C NB cells [31]. RC-3095 reduced GRP release from NB cells and tubule formation by endothelial cells and increased the expression of pro-autophagic proteins in NB cell lines (BE (2)-M17, BE (2)-C) [32]. Moreover, the inhibition of GRP receptors increased the autophagy-mediated degradation of GRP in NB cells. Autophagy inhibited angiogenesis through GRP degradation in NB cells, and this means that autophagy activation is a potential and promising antivascular strategy in NB [32]. GRP receptor antagonists/GRP receptor knockdown blocked the growth of NB cells; however, depending on the administered dose of RC-3095, this GRP antagonist blocked (low concentration) or promoted (high concentration) the proliferation of murine neuro2a NB cells [33]. The proliferative effect mediated by RC-3095 was counteracted with sodium butyrate (a histone deacetylase inhibitor). The data suggest that GRP receptors could interact with epigenetic mechanisms regulating the growth of murine NB cells.
Changes in cell morphology, reduced cell proliferation and size, DNA synthesis inhibition, Akt downregulation, PTEN expression upregulation (inhibitor of the phosphatidylinositol 3-kinase/Akt signaling pathway; poorly differentiated NB shows reduced PTEN protein concentration), and anchorage-independent growth suppression was observed in GRP receptor knockdown BE (2)-C NB cells [34]. Moreover, GRP receptor deficiency reduced liver metastasis and deferred tumor growth in vivo [34]. GRP receptors control the metabolism of glucose by controlling hypoxia-inducible factor-1 alpha, pyruvate dehydrogenase phosphatase 2, and pyruvate dehydrogenase kinase 4; in addition, the latter controls glucose metabolism through the regulation of the hypoxia-inducible factor-1 alpha [31]. The silencing of the GRP receptor blocked key regulators of the aerobic glycolysis mechanisms in human NB cells (SK-N-AS, BE (2)-C) [31]. GRP receptor silencing reduced the expression of hypoxia-inducible factor-1 alpha and pyruvate dehydrogenase kinase 4 mRNA expression (both involved in aerobic glycolysis) and augmented the pyruvate dehydrogenase phosphatase 2 mRNA expression (involved in glucose oxidation) [31]. This is important since tumor cells, under normoxic conditions, use the aerobic glycolysis for energy production instead of glucose oxidation [31]. GRP silencing also regulated the cell signaling pathways involved in invasion and metastasis since NB cell migration (BE (2)-C, SH-SY5Y) in vitro and metastasis in vivo were blocked [24]. Furthermore, GRP silencing inhibited NB cell-mediated angiogenesis and reduced anchorage-independent growth and the mRNA levels of the oncogenes involved in NB progression. The study also reported that the PTEN/Akt signaling pathway is a key mediator of the tumorigenic properties of GRP in NB cells [24]. Cell migration mediated by GRP and angiogenesis decreased when PTEN was overexpressed, and Akt activation was positively correlated with NB progression. GRP, via GRP receptors, favored p21 (located in the nucleus)/p27 (cytoplasm) expressions in BE (2)-C NB cells, and the silencing of the GRP/GRP receptor signal augmented tumor suppressor PTEN expression/accumulation in the cytoplasm of NB cells [26]. The data suggest that cyclin-dependent kinase inhibitors (p21, p27) and tumor suppressors (PTEN) are involved in NB tumorigenesis. Finally, the overexpression of the transcription factor Ets 1 has been related to an upregulation of the GRP receptor promoter activity [35]. This factor is involved in the transcription of the GRP receptor in NB. This finding could serve to downregulate its expression; hence, the mitogenic action mediated by GRP on NB cells could be counteracted.
Bombesin and phorbol myristate acetate (a protein kinase C agonist) increased the release of vascular endothelial growth factor from BE (2)-C NB cells [36]. This effect was synergistic when GRP was administered. Thus, protein kinase C controlled the bombesin-mediated secretion of the vascular endothelial growth factor in NB cells, and when the secretion of this factor was inhibited, a reduced NB cell proliferation-induced by GRP was reported [36]. Bombesin mediated NB cell growth (BE (2)-C, SK-N-SH) and promoted the expression of angiogenic markers (vascular endothelial growth factor, platelet endothelial cell adhesion molecule (PECAM) 1), favoring angiogenesis [37]. The GRP receptor antagonists RC-3095 counteracted in vivo both the angiogenesis and tumor growth promoted by bombesin [37]. Bombesin increased Akt phosphorylation in NB cells (SK-H-SH, LAN-1, BE (2)-C), and this was counteracted when cells were treated with the GRP receptor antagonist H2756 [27]. The latter effect was also observed when NB cells were treated with LY-294002, a phosphatidylinositol 3-kinase signaling pathway inhibitor [27]. The data show that this pathway is important in NB cell growth mediated by bombesin.
2.1.5. Neuropeptide Y
A recent review dedicated on the involvement of neuropeptide Y in cancer development, including neuroblastoma, has been published [38]. Human NB cell lines (NB39, NB45, NB52, NB726) have been heterotransplanted into athymic nude mice: NB39 are undifferentiated cells; NB45 are poorly differentiated cells showing undifferentiated components; NB52 are poorly differentiated cells; and NB726 are differentiated cells [39]. In this study, the four mentioned NB cells expressed neuropeptide Y, NB45/NB52/NB726 displayed galanin, NB45/NB726 expressed calcitonin gene-related peptide, and NB726 showed vasoactive intestinal peptide and enkephalins (methionine- and leucine-enkephalin) [39]. Moreover, the average doubling time of tumors was two (NB39), ten (NB45), twenty-two (NB52), and forty-five (NB726) days [39]. The data show that human NB cells have different biological features. The neuropeptide Y receptor 2 is expressed in NB cells [40], and SK-N-MC NB cells expressed neuropeptide Y receptors 1, 4, and 5 [41]. The latter receptor was involved in cell proliferation [42].
Released neuropeptide Y from NB cells exerted via the neuropeptide Y receptor 2, an autocrine action favoring the proliferation of these cells and angiogenesis [40,43]. This proliferative action was increased when NB cells also expressed the neuropeptide Y receptor 5 [42,44], and the synthesis/release of neuropeptide Y from NB cells were mediated by protein kinase C-coupled M3 muscarinic receptors [45,46]. NPY increased SH-SY5Y NB cell survival and counteracted the toxic effect induced by β-amyloid on these cells [47] and also protected these cells against glutamate toxicity and endoplasmic reticulum stress. Neuropeptide Y exerted anti-apoptotic mechanisms, increasing the viability/survival of NB cells [48]. Neuropeptide Y, via the neuropeptide Y receptor 5/RhoA pathway, facilitated NB cell motility and invasiveness [49]. Poor survival, metastasis, and relapse have been associated with high serum concentrations of neuropeptide Y in NB [50]. The release of neuropeptide Y and neuropeptide Y/neuropeptide Y receptor 5 expression were favored in NB cells after treatment with the brain-derived neurotrophic factor (BDNF); the expression of the BDNF receptor, named tropomyosin-related kinase B receptor, has been associated with a worse prognosis in NB [43,44]. Neuropeptide Y receptor 5 antagonists inhibited the prosurvival actions induced by BDNF via the p44/p42 mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt pathways, favored apoptosis, and sensitized resistant NB cells to chemotherapy [43,44]. The neuropeptide Y receptor 2 antagonist, BIIE0246, blocked the activation of the p44/p42 mitogen-activated protein kinase pathway, reduced cell proliferation, and, mediated by Bim, favored apoptosis. These effects were also found with neuropeptide Y/neuropeptide Y receptor 2 small interfering RNA [40]. BIIE0246 exerted anti-angiogenic effects by reducing the proliferation of endothelial cells expressing the neuropeptide Y receptor 2; antagonists of this receptor, but not neuropeptide Y receptor 5 antagonists, reducing vascularization [40,42,43].
Pro-neuropeptide Y processing has been associated with inferior outcomes/clinically advanced stages in NB [51]. Neuropeptide Y gene expression was decreased in SH-SY5Y NB cells after treatment with retinoic acid, favoring the pro-neuropeptide Y procession to neuropeptide Y [52]. The neuropeptide Y receptor 2 mediated glycolysis in NB cells, and this process was essential for these cells to obtain ATP under hypoxia circumstances [53]. Finally, neuropeptide Y inhibited calcium channel currents in SH-SY5Y NB cells [54].
2.1.6. Neurotensin/Neuromedin U
Both peptides have been associated with the overall survival rate of patients with NB; neurotensin and neuromedin U levels were high in stage 4 NB individuals in which a less favorable outcome, in comparison with that observed in stage 4S NB patients, has been reported [55]. Both peptides favored the proliferation and invasion of SK-N-BE (2) NB cells, and it has been suggested that neurotensin and neuromedin U play an important role in regulating the tumor microenvironment, favoring NB development [55].
2.1.7. Oxytocin
Oxytocin increased the number of SK-N-SH and SY-SY5Y NB cells, as well as the viability of the latter cells, without the activation of neurotrophic factors (neurotrophic growth factor, brain-derived neurotrophic factor); in addition, cell death promoted by hydrogen peroxidase was not counteracted with oxytocin; hence, it did not exert protective effects against oxidative stress mechanisms [56]. Glutamate had a toxic action on cell viability/proliferation and blocked neurite development in SH-SY5Y NB cells, but oxytocin counteracted the latter effect, exerted anti-apoptotic and protective actions, and augmented cell viability [57]. Oxytocin promoted neurite outgrowth by inhibiting calcium voltage-gated channels in SH-SY5Y NB cells and increased the gene expression of SHANK 1 and 3 proteins and the intracellular calcium concentration in these cells [58]. Oxytocin promoted changes in the cytoskeleton of SK-N-SH NB cells, and the peptide did not affect nerve growth factor/brain-derived neurotrophic factor gene expressions, but increased mRNA levels for both factors were observed when these cells were treated with oxytocin and atosiban, an oxytocin receptor antagonist [59]. This antagonist decreased oxytocin receptor mRNA levels and increased MAP 2 gene expression [59]. A dense F-actin filament recruitment was reported in the filopodia apical parts of SK-N-SH NB cells treated with oxytocin [59]. Oxytocin favored non-coding RNA tumor marker expression (metastasis-associated lung adenocarcinoma transcript 1 (MALAT 1)) in SK-N-SH NB cells and the cyclic adenosine monophosphate-responsive element-binding protein bound to the proximal promoter of the MALAT 1 gene [60].
2.1.8. Prolactin-Releasing Peptide
This peptide binds to the GRP10 receptor [61]. PrRP31, a prolactin-releasing peptide analog, upregulated the extracellular signal-regulated kinase/cyclic adenyl monophosphate response element-binding protein and phosphoinositide-3 kinase-protein kinase B/Akt signaling pathways, promoting SH-SY5Y cell growth and survival [61].
2.1.9. sPEP1
sPEP1, a small 51-amino acid peptide, favored the self-renewal and aggressiveness of NB stem cells and exerted oncogenic actions by promoting the interaction of the SMAD family member 4 (SMAD4) and the eukaryotic translation elongation factor 1 alpha 1 (eEF1A1) [62]. sPEP1 interacted with the latter factor facilitating its binding to SMAD4, leading to SMAD4 transactivation repression and transcriptional upregulation of stem cell genes involved in tumor progression [62]. sPEP1 knockdown suppressed the in vivo metastasis and self-renewal of NB stem cells, and high levels of eEF1A1 or sPEP1 in the tissues of patients suffering from the disease have been related to poor survival [62]. Thus, sPEP1, via eEF1A1-suppressed SMAD4 transactivation, favored aggressiveness and self-renewal of NB stem cells.
2.1.10. Substance P
Substance P, via the neurokinin-1 receptor, promoted the proliferation of SKN-BE (2) NB cells, whereas cell growth was blocked when these cells were treated with L-733,060, a neurokinin-1 receptor antagonist [63,64]. The presence of neurokinin-1 receptors has also been reported in other NB cells (Kelly, SH-SY5Y, SK-N-AS, SK-N-BE, IMR-5), and, after targeting this receptor, cell viability was decreased, and apoptotic mechanisms were induced [65]. Neurokinin-1 receptor inhibition promoted TP53 signaling and suppressed the transcription factor E2F2 in NB cells, and aprepitant (a neurokinin-1 receptor antagonist) reduced the tumor size in vivo [65]. Septide (a neurokinin-1 receptor agonist) decreased 6-hydroxydopamine-induced toxicity and blocked apoptosis by triggering pro-survival signal pathways (protein kinase B/Akt) in SH-SY5Y NB cells [66]. NB cells (CHP-212, SH-SY5Y) expressed neurokinin-1 and -2 receptors and preprotachykinin I. Both receptors mediated the proliferation of NB cells; truncated and full-length neurokinin-1 receptors were observed in these cells; and neurokinin-1 receptor suppression decreased the proliferation of NB cells [67]. Moreover, the expression of neurokinin-1 receptors, studied in 59 patients, was independent of the NB stage and biology [68].
P2X7, a receptor for extracellular nucleotides, was expressed in NB cells (e.g., SK-SY5Y, SK-N-BE (2), LAN-1, Lan-5) and in NB tissues [69]. The activation of this receptor caused NB cell proliferation but not apoptosis/caspase 3 activation; the silencing of the P2X7 receptor led to pro-apoptotic mechanisms; and NB cell growth was mediated by the secretion of substance P from NB-activated cells by nucleotides [69].
2.1.11. Thyrotropin-Releasing Hormone
Thyrotropin-releasing hormone and three analogs (CG-3703 (montirelin), Z-thyrotropin-releasing hormone, and RGH-2202) exerted anti-apoptotic effects in SH-SY5Y NB cells, which were mediated by Bcl-2 protein (an increase was reported) and the activation of the phosphatidylinositol 3-kinase/Akt survival signaling pathway [70]. In fact, phosphatidylinositol 3-kinase inhibitors (LY-294002, wortmannin) counteracted the protective action exerted by thyrotropin-releasing hormone/RGH-2202 on tumor cells, but this action was not observed when PD-98059/U0126 (extracellular signal-regulated kinase 1/2/mitogen-activated protein kinase 1/2 inhibitors) were administered [70].
2.1.12. Vasopressin
Tolvaptan, a vasopressin receptor 2 antagonist, decreased the proliferation and invasion of SK-N-AS NB cells expressing such receptor, promoting apoptosis [71]. The antagonist decreased pAkt/Akt ratio, the catalytic alpha subunit of protein kinase A and cyclic adenosine monophosphate levels; diminished collagenase type IV activity and anchorage-independent growth; and counteracted the ROCK1/2-RhoA pathway involved in controlling cell movement [71]. Raloxifene, an estrogen receptor modulator, reduced vasopressin mRNA levels and increased phosphorylated extracellular signal-regulated kinase 1/2 levels in SH-SY5Y NB cells [72]. MAPK/extracellular signal-regulated kinase 1/2 or protein kinase C inhibitors blocked the actions mediated by raloxifene [72]. The data show that vasopressin expression is regulated by raloxifene through G protein-coupled estrogen receptor 1 by activating protein kinase C and the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Moreover, estradiol augmented vasopressin mRNA levels in SH-SY5Y NB cells, and this was also observed with estrogen receptor alpha agonists, but it was counteracted with estrogen receptor alpha antagonists (ICI 182,780) [73]. Estrogen receptor beta agonists reduced vasopressin expression, and estrogen receptor beta antagonists increased the action of estradiol on the expression of vasopressin [73]. Testosterone increased vasopressin expression in SH-SY5Y NB cells. This effect was blocked with estrogen receptor alpha antagonists, whereas estrogen receptor alpha agonists decreased the expression of the peptide [73]. Thus, testosterone and estradiol controlled vasopressin expression via estrogen receptors, exerting an inhibitory effect, through the estrogen receptor beta or a stimulatory action via the estrogen receptor alpha [73]. Finally, the stimulation of Akt mediated apoptosis in NB cells expressing a C98X vasopressin mutant following autophagy suppression [74]. The study in question also reported that autophagy-mediated degradation of mutated C98X peptides is needed because in the event that these peptides were not degraded, they will become toxic to cells [74]. Thus, Akt stimulation counteracted the autophagy beneficial actions, favoring cell death.
2.2. Anticancer Peptides
2.2.1. Adrenomedullin/Pro-Adrenomedullin N-Terminal 20 Peptide
Both adrenomedullin/pro-adrenomedullin N-terminal 20 peptide (PAMP) blocked DNA synthesis and cell growth in human TGW NB cells [75]. Calcitonin gene-related peptide antagonists blocked the effects mediated by adrenomedullin but not those induced by PAMP. The effects mediated by adrenomedullin were also counteracted using adrenomedullin antagonists [75]. PAMP inhibited NB cell growth by blocking calcium channels (N-type) via pertussis toxin-sensitive G protein-coupled receptors since pertussis toxin blocked the effects mediated by PAMP [75]. This mechanism was different from that involved in the cell growth inhibition promoted by adrenomedullin since pertussis toxin did not block the effects mediated by the peptide [75].
A high concentration of adrenomedullin has been reported by radioimmunoassay in human NB tissues [76], and this peptide promoted the release of nitric oxide from human SK-N-SH NB cells by regulating the mobilization of intracellular free calcium [77]. The latter was blocked with adrenomedullin receptor antagonists or nitric oxide synthase inhibitors. Adrenomedullin favored calcium influx via L-type calcium channels and ryanodine-sensitive calcium release from the endoplasmic reticulum, and it seems that this occurred through cAMP-protein kinase A-dependent processes [77]. The increased concentration of calcium led to nitric oxide synthase activation and, finally, the release of nitric oxide. NB69 and IMR-32 NB cells increased the expression of adrenomedullin during hypoxia, whereas the expression of the receptor activity modifying protein 2 was reduced in IMR-32 cells but was not changed in NB69 cells under hypoxia [78]. Adrenomedullin and calcitonin gene-related peptide (CGRP) interacted with the same CGRP receptor expressed in SK-N-MC NB cells; in adrenomedullin, but not in CGRP, the N-terminal ring organization is crucial for its binding to the CGRP receptor [79].
2.2.2. Corticotropin-Releasing Factor
Corticotropin-releasing factor/urocortin, after binding to the corticotropin releasing factor receptor 1, decreased both motility and proliferation in human SK-N-SH NB cells and favored the neuronal-like differentiation of these cells [80]. It seems that these mechanisms occurred after the activation of the cyclic adenosine monophosphate (cAMP)/protein kinase A/cAMP- responsive element binding protein pathway leading to reduced c-myc mRNA accumulation and increased levels of retinoblastoma protein and p27 (Kip1). Moreover, it has been reported that phospholipase C is not involved in the signaling pathways activated after the stimulation of corticotropin-releasing factor receptors in human SK-N-MC NB cells [81].
2.2.3. Exendin-4
The peptide exendin-4, a glucagon-like peptide-1 receptor agonist, promoted a more differentiated phenotype, counteracted anchorage-independent growth, increased cell adhesion, and decreased cell migration in NB cells (SK-N-AS, SH-SY5Y) [82].
2.2.4. Gonadotropin-Releasing Hormone
The activation of the gonadotropin-releasing hormone receptor blocked the growth of rat B35 NB cells, and apoptotic markers were expressed in these cells when they were treated with gonadotropin-releasing hormone [83]. Tumor xenograft growth (B35 NB cells) was slowed after gonadotropin-releasing hormone treatment [83].
2.2.5. Orexin
Orexin A/orexin mRNA have been reported in human NB tissues [84]. Orexins (A and B), through the orexin receptor 1, inhibited SK-N-MC NB cell growth by favoring apoptotic mechanisms [85], and the blockade of TRPC3/6 channels disrupted the orexin receptor 1 signaling via NCX in IMR32 NB cells [86]. In SH-SY5Y NB cells, orexin A showed a protective effect against 6-hydroxydopamine-induced toxicity by exerting anti-apoptotic and anti-oxidant effects and by decreasing cell death markers. This protective effect was mediated through phosphatidylinositol 3-kinase and protein kinase C signaling pathways [87,88]. SB-3344868 (orexin receptor 1 antagonist), LY-294002 (phosphatidylinositol 3-kinase inhibitor), and chelerythrine (protein kinase C inhibitor) blocked the protective actions mediated by orexin A in SH-SY5Y NB cells against 6-hydroxydopamine [88]. Orexin A also protected SH-SY5Y NB cells against H2O2-induced damage (viability/superoxide dismutase decrease, apoptosis) through the phosphatidylinositol 3-kinase/extracellular signal-regulated kinase 1 and 2/mitogen-activated protein kinase 1/2 signaling pathways [89]. Moreover, orexin A, by blocking endoplasmic reticulum stress-induced apoptosis through the combination of phosphatidylinositol 3-kinase and Gi signaling pathways, protected SH-SY5Y NB cells against oxygen–glucose deprivation/reoxygenation-induced processes [90].
2.2.6. SHPRH-146aa
circ-SHPRH (a unique circular RNA) and its derived peptide (SHPRH-146aa) are involved in NB pathogenesis and are promising therapeutic targets for NB treatment [91,92]. circ-SHPRH was overexpressed in NB samples, and this overexpression, like that of the SHPRH-146aa peptide, blocked the proliferation, migration, and invasion of NB cells (SK-N-AS, SH-SY5Y, SK-H-SH, IMR-32). Increased apoptosis was also reported, as well as caspase upregulation and Bcl-2 downregulation [92]. SHPRH-146aa peptide counteracted the malignancy traits of NB cells, and a SHPRH-146aa–RUNX1 protein interaction was found, leading to an increased expression of the protein coding gene NFKBIA. This interaction suggests a new pathway controlling apoptotic mechanisms in NB cells [92]. NFKBIA knockdown blocked the pro-apoptotic actions mediated by SHPRH-146aa on NB cells. circ-SHPRH expression in NB tissues and cell lines (SH-SY5Y, SK-N-BE (2)) has been studied [91]. circ-SHPRH upregulated the crucial cell cycle regulator p21 expression to block cyclin-dependent kinases in NB, and circ-SHPRH overexpression limited NB tumor growth in NOD scid gamma mice [91]. Figure 1 shows the peptidergic systems involved in NB development.
2.3. Other Peptides and Neuroblastoma
2.3.1. Adrenocorticotropin Hormone
Olfactory NB (esthesioneuroblastoma), a rare neuroectodermal tumor, arises from the olfactory neuroepithelium, and the release of adrenocorticotropin hormone (ACTH) from this tumor has rarely been observed; however, olfactory NB can cause ectopic ACTH syndrome (even long after the initial clinical treatment) because the presence/release of ACTH from olfactory NB cells has been reported [93,94,95,96]. Serum ACTH/cortisol levels were reduced after olfactory NB surgical removal [95], and it has been suggested that olfactory NB stimulation (e.g., chemotherapy, biopsy) triggers the onset of ectopic ACTH syndrome [94].
2.3.2. Melanin-Concentrating Hormone
Human NB tissues and cell lines (IMR-32, NB69) expressed melanin-concentrating hormone (MCH) receptor mRNA [97,98], whereas human Kelly NB cells expressed MCH and MCH receptor 1 but not MCH receptor 2 [99]. In the latter cells, MCH did not increase the level of free intracellular calcium but induced mitogen-activate protein kinase (MAPK) phosphorylation. This suggests that MCH acts via Galpha(i)/Galpha(o) in Kelly NB cells [99]. MCH, via MAPK and p53 signaling pathways, promoted neurite outgrowth in human SH-SY5Y NB cells [100]. These cells expressed MCH receptor 1 mRNA/protein, and the peptide regulated potassium currents, favored MAPK phosphorylation, and promoted the expression and nuclear localization of phosphorylated p53 protein. The peptide also augmented Elk-1 phosphorylation, upregulated Egr-1 expression (Elk-1 and Egr-1 are transcriptional factors), and favored neurite outgrowth [100]. The results suggest that MCH is involved in neuronal differentiation.
2.3.3. Neuropeptide FF
SH-SY5Y NB cells expressed neuropeptide FF receptor 2 [101]. The extracellular signal-regulated protein kinase pathway was activated after treatment with neuropeptide FF in these cells. Moreover, protein kinase A/nitric oxide synthases were involved in this activation, and neuropeptide FF also activated the NF-κB pathway [101]. SK-N-MC NB cells expressed both neuropeptide FF receptor 2 and neuropeptide YY [102]. The activation of this receptor by agonists led to the activation of the MAPK signaling pathway, actin cytoskeleton reorganization occurred, and the expression of neuropeptide FF receptor 2 mRNA/protein was upregulated by neuropeptide FF [102]. Other studies have reported that neuropeptide FF analogs antagonized opioid activities in neuropeptide FF receptor 2-transfected SH-SY5Y NB cells expressing mu/delta opioid receptors [103], and this antagonism was also observed in the same NB cell line regarding the neuropeptide FF receptor 1 [104]. The activation of the latter receptor blocked voltage-gated calcium current (N-type) and the activity of adenylyl cyclase but increased the release of intracellular calcium mediated by the stimulation of muscarinic receptors [104]. Thus, neuropeptide FF, via neuropeptide FF receptors 1/2, exerted anti-opioid effects; in addition, an interaction between neuropeptide FF and opioid receptors occurred. Moreover, peptides (SQA-neuropeptide FF, neuropeptide AF, neuropeptide FF) derived from the neuropeptide FF precursor were located in SH-SY5Y NB cells [105].
2.3.4. Somatostatin
A review focused on the current status of, and future perspectives on, nuclear medicine imaging and the treatment of NB has been published [106]. Olfactory NB cells express somatostatin receptor 2, which is a target for radionuclide imaging, for example, with 68Ga-DOTATATE [107,108,109]. A study has reported that 75% of patients with olfactory NB expressed somatostatin receptor 2, and 7.5% of them expressed somatostatin receptor 5 [108]. Moreover, the expression of the somatostatin receptor 2 has been also reported in NB tissue [110]. The therapeutic potential of combined chemotherapy and peptide receptor radionuclide therapy to treat refractory/relapsed metastatic NB has been suggested; however, the results are preliminary; hence, a more in-depth investigation is required [111]. Children with relapsed NB do not respond to I-meta-iodobenzylguanidine (MIBG) therapy, and other radiolabeled agents (e.g., DOTA-conjugated peptide) have been suggested to treat these patients expressing somatostatin receptors 2 [112].
Radiopharmaceuticals (177Lu-octreotide, 177Lu-octreotate) have been used for the treatment of human NB cell (CLB-BAR)-bearing mice [113]. After treatment with these somatostatin analogs, pro-apoptotic (TRADD, CASPS, TNSF8/10) and anti-apoptotic (IL10) genes were regulated. The antitumor effects observed were better with 177Lu-octreotide treatment than with 177Lu-octreotate [113]. The data confirm the activation of apoptotic mechanisms mediated by both somatostatin analogs and highlight the beneficial use of radiopharmaceuticals in nuclear medicine to detect and treat NB. The therapeutic potential of 177Lu-octreotate in NB xenograft models (BALB/c nude mice bearing IMR-32, CLB-GE, CLB-BAR tumor xenografts) has also been demonstrated, and the use of this radiopharmaceutical to fight metastatic NB has been suggested [114].
2.3.5. Vasoactive Intestinal Peptide/Pituitary Adenylate Cyclase-Activating Polypeptide
VIP level increased during NB differentiation [115], and NB can regress to a benign form or advance to a malignant metastatic tumor [116]. Vasoactive intestinal peptide (VIP) and PACAP promoted NB cell differentiation into a benign form by controlling vascular endothelial growth factor, vascular endothelial growth factor receptor, and hypoxia-inducible factor expressions [116]. The study showed that VIP and PACAP interfered with the cell differentiation regulating angiogenic and hypoxic mechanisms. This is important since hypoxia favored the activation of hypoxia-inducible factors, which promoted cell proliferation and metastasis and the release of the vascular endothelial growth factor [116]. VIP augmented dopamine transporter and synaptic vesicle glycoprotein 2C in IMR-32 NB cells [117].
Pituitary adenylate cyclase-activating polypeptide (PACAP), after binding to PAC-1 receptors, promoted its own expression in human NB-1 NB cells. This process was mediated by protein kinase A, extracellular signal-regulated kinase, and novel protein kinase isoforms [118]. NB-1 NB cells also expressed VPAC2 receptors [119], and PACAP, via the PAC1 receptor, favored VIP/fos gene expressions in these cells [120]. PACAP-38, via PAC-1 receptors, favored neuronal differentiation in SH-SY5Y NB cells through the cyclic adenyl monophosphate-induced activation of p38 mitogen-activated protein kinase and extracellular signal-regulated kinase pathways [121]. PACAP-38 did not promote the proliferation of SH-SY5Y NB cells; however, the leukemia inhibitory factor favored such proliferation, and SH-SY5Y cells treated with PACAP-38 increased Bcl-2 expression as well as resistance to hypoxic situations [122]. It seems that PACAP-27 protected murine neuro2a NB cells from apoptotic mechanisms, whereas VIP had no effect [123]. PAC-1 receptor-mediated neurite outgrowth and cytoprotection processes in murine neuro2a NB cells. These mechanisms were transglutaminase (TG2)-dependent [124]. Cytoprotection and TG2 activation were also observed in human SH-SY5Y NB cells, PACAP-27 augmented the activity of TG2, and the blockade of TG2 inhibited the PACAP-27-promoted attenuation of neurite outgrowth and hypoxia-induced cell death [124].
The effects of VIP/PACAP27/PACAP-38 and VIP/PACAP analogs on Mycn-amplified SK-N-DZ/IMR-32 NB cells and Kelly NB cells—presenting, in addition, a mutation (F1174L ALK)—have been studied [115]. The three NB cell lines expressed genes encoding the receptors (PAC-1, VPAC-1, VPAC-2) for VIP and PACAP. VIP promoted neuritogenesis in Kelly/SK-N-DZ cells and reduced Akt activity and Mycn expression in Kelly cells. These actions were dependent of protein kinase A [115]. Moreover, VIP blocked IMR-32/Kelly cell invasion [115]. The peptidergic systems involved in NB are shown in Table 1.
3. Perspectives and Future Research
Peptides such as amylin, angiotensin II, bradykinin, gastrin-releasing peptide, bombesin, neuropeptide Y, neurotensin, neuromedin U, prolactin-releasing peptide, oxytocin, sPEP1, thyrotropin-releasing hormone, and substance P, after binding to their respective receptors (e.g., GRP receptor, neuropeptide Y receptor 2/5, GRP10 receptor), favored NB progression (tumor cell proliferation, migration and invasion, anti-apoptotic effect, angiogenesis) [15,17,21,25,28,29,36,37,40,42,43,55,56,57,61,62,63,70]. This means that the use of peptide receptor antagonists is a promising anti-NB research line that must be fully developed because NB cells express/overexpress peptide receptors (e.g., neuropeptide Y, GRP), and antagonists of these receptors counteract NB growth (e.g., GRP receptor antagonists). On the contrary, other peptides exert anticancer effects (cell proliferation/migration inhibition, apoptosis) against NB. This is the case of adrenomedullin, PAMP, corticotropin-releasing factor, urocortin, exendin-4, gonadotropin-releasing hormone, orexin, and SHPRH-146aa peptide [75,80,82,83,85,92]. Accordingly, the therapeutic potential of combined peptide receptor radionuclide therapy and chemotherapy to fight NB has been proposed [111]. However, despite the existing data, basic research is needed in NB since, as mentioned in the previous section, the proliferative/antiproliferative and migration/antimigration activities exerted by many peptides (e.g., adrenocorticotropin hormone, MCH, neuropeptide FF, somatostatin, opioids, VIP, and PACAP) is unknown, as is whether NB cells synthesize and release peptides exerting autocrine proliferative actions and anti-apoptotic mechanisms, favoring NB cell viability and survival. The expression of many types of peptide receptors is currently unknown. It is also unknown as to whether peptide receptor antagonists elicit an antitumor action or not, as well as the tissue/serum concentrations of many peptides. This is important because a high level of peptides (e.g., neurotensin, neuromedin U) has been associated with a less-NB-favorable outcome [55], and peptide receptor overexpression (e.g., GRP receptor) favored NB cell migration and invasion [28]. Although some peptides (GRP, neuropeptide Y) have been more-thoroughly studied, unfortunately, much of the existing data regarding the above-mentioned aspects are fragmentary, scarce, or absent in many peptidergic systems; hence, there is still a lot of basic research work to be conducted in NB. The expression of peptide receptors is important since compared with that reported in benign tumors, an increased receptor expression (e.g., GRP receptor) was found in more aggressive and undifferentiated NB [25]. Poor survival, metastasis, and relapse have been related with a high serum peptide level (e.g., neuropeptide Y) in NB [50]. A high tissue level of sPEP1 has been associated to NB poor survival [62], and peptide precursor processing (e.g., pro-neuropeptide Y) has also been related in NB with clinically advanced stages and inferior outcomes [51]. To develop future anti-NB strategies, it must be taken into consideration that the expression of the same peptidergic receptor (e.g., ATR1) has been reported in some NB cell lines, but in others, this expression was not observed [16], and it was found that human NB cells have different biological features expressing different peptides [39].
A crucial research line is to determine the how peptidergic systems (peptides and receptors) are regulated. Currently, it is known that VIP augments ATR1 density in NB cells [16]; that insulin/insulin-like growth factor-1 potentiate the proliferative action mediated by angiotensin II on NB cells [17]; that BDNF, via the tropomyosin-related kinase B receptor, promotes the release of proliferative peptides/peptide receptor expression (e.g., neuropeptide Y and neuropeptide Y receptor 5, a high expression of this receptor has been related with a worse NB prognosis) [43,44]; that the retinoic acid decreases neuropeptide Y gene expression in NB [52]; and that the synthesis/release of peptides (e.g., neuropeptide Y) from NB cells are mediated muscarinic receptors [45,46]. The estrogen receptor modulator raloxifene decreases vasopressin mRNA levels in NB cells [72], and estradiol/testosterone increase such levels in the same cells [73]. CGRP antagonists block the anticancer effects mediated by adrenomedullin but not those induced by PAMP [75], and PACAP, via the PAC-1 receptor, favors its own expression in NB cells [118]. This is an important finding that merits further investigation in other peptidergic systems because PACAP favors NB cell differentiation into a benign form [116]. There is still much to do and much to learn; this research line is important and must be developed since by knowing the factors that regulate the synthesis and release of oncogenic or anticancer peptides, NB development could be controlled. It is known that several peptides originate from the same precursor; therefore, another important line of research is to understand how the gene expression of this precursor and the different peptides that originate from it are regulated in NB cells.
As mentioned in the previous section, a plethora of anti-NB strategies involving the peptidergic systems can be applied alone or in combination therapies. The beneficial actions exerted by the oncogenic peptides on NB development can be inhibited by using the following: (1) Peptide receptor antagonists: PD123319 (ATR2 antagonist) blocks the effects mediated by angiotensin II [20]. RC-3095 (GRP receptor antagonist) counteracts tumor growth/angiogenesis mediated by bombesin, increases pro-autophagic protein expression in NB cells, and decreases GRP release from NB cells and NB cell growth [32,33]. It is important to note that a low concentration of RC-3095 blocks murine NB cell proliferation (this was inhibited with a histone deacetylase inhibitor, suggesting the involvement of epigenetic mechanisms), but a high concentration promotes murine NB cell proliferation [33]. H2756 (GRP receptor antagonist) blocks Akt phosphorylation mediated by bombesin in NB cells [27]. Neuropeptide Y receptor 5 antagonists block the prosurvival actions mediated by BDNF, induce apoptosis, and sensitize resistant NB cells to chemotherapy [43,44]. BIIE0246 (neuropeptide Y receptor 2 antagonist) decreases NB cell proliferation, favors apoptosis, and promotes anti-angiogenic actions) [40,42,43]. The proliferative action promoted by insulin on NB cells is inhibited with the angiotensin II receptor antagonists DuP753 (ATR1) or PD123177 (ATR2) [17]. The oxytocin receptor antagonist atosiban reduces oxytocin receptor mRNA levels [59]. L-733,060 (neurokinin-1 receptor antagonist) induces apoptosis in NB cells [63,64]. Aprepitant (neurokinin-1 receptor antagonist) decreases NB tumor size [65]. And the vasopressin receptor 2 antagonist tolvaptan reduces the proliferation/invasion of NB cells and also promotes apoptosis [71]. (2) Purinergic P2X7 receptor antagonists block the proliferative action regulated by bradykinin [21]. (3) Anti-GRP antibodies inhibit the NB growth mediated by GRP [1,25]. (4) Integrin β1 silencing blocks NB cell migration; GRP receptor overexpression upregulates integrin α2/α3/β1 protein/mRNA expressions and favors NB cell migration [28]. (5) Phosphatidylinositol 3-kinase signaling pathway inhibitors (e.g., LY-294002, wortmannin) counteracts the Akt phosphorylation mediated by bombesin in NB cells [27] and the protective effects promoted by thyrotropin-releasing hormone on NB cells [70]. (6) Y15 (FAK inhibitor) blocks NB cell growth/metastasis mediated by GRP; NB cell growth is favored by FAK overexpression [30]. (7) GRP receptor knockdown in NB cells: cell proliferation/invasion/metastasis decrease, mRNA level decrease in oncogenes regulating NB progression, angiogenesis inhibition, PTEN expression upregulation (inhibitor of the phosphatidylinositol 3-kinase/Akt signaling pathway; a tumor suppressor), Akt downregulation, liver metastasis reduction, and aerobic glycolysis blockade [24,26,31,34]. (8) sPEP1 knockdown blocks self-renewal and metastasis of NB stem cells [62]. (9) The acetic acid analog dichloroacetate decreases NB cell proliferation and favors NB cell death, and dichloroacetate and GRP receptor silencing synergistically inhibit the proliferation of these cells [31]. (10) The transcription factor Ets 1 regulates GRP receptor transcription in NB cells; thus, by downregulating its expression, the mitogenic effect mediated by GRP on NB cells could be blocked [35]. (11) Anticancer peptides (adrenomedullin, PAMP, corticotropin-releasing factor, urocortins, exendin-4, gonadotropin-releasing hormone, orexin, SHPRH-146aa peptide) could be administered to counteract the effects exerted by the oncogenic peptides [75,80,82,83,85,92]. Many of the possible therapeutic strategies against NB must be confirmed and developed in the future; in many cases, the current data are preliminary, fragmentary, scarce, or absent. Figure 2 summarizes the anti-NB therapeutic strategies.
4. Conclusions
Surgical resection, chemoradiation, phosphoinositide 3-kinase inhibitors, autologous stem cell rescue, immunotherapy, cyclin-dependent kinase 3/6 inhibitors, and treatment with retinoic acid are some on the therapeutic strategies employed to fight NB [1,2,3,4,8]. In addition to the previous strategies, another has been focused on understanding how the peptidergic systems are involved in NB. In this sense, it is widely known that peptides are oncogenic and anticancer agents [11], and it is therefore a promising line of research that merits development for tumor diagnosis and treatment. In fact, some peptide drugs (e.g., gonadotropin-releasing hormone analogs, somatostatin analogs) have been approved by the FDA to fight some cancer types (e.g., breast, prostate, lung neuroendocrine), as well as for cancer diagnosis [125]. However, no antitumor drug involving the peptidergic systems is currently available in clinical practice to treat NB. This means that basic research (in vitro and in vivo experiments) is urgently needed to increase our knowledge concerning the involvement of peptides in NB and to transfer this knowledge into clinical practice. For example, although some peptidergic systems have been studied in NB, the oncogenic/anticancer effects (e.g., proliferative, antiproliferative, migration, apoptosis) mediated by other peptidergic systems have not yet been studied in NB and are currently unknown. It is important to understand, in depth, which peptides are synthetized and released from NB cells, the peptide receptors that express/overexpress these cells and whether the expression of these receptors is involved in the viability of NB cells, and the tissue/serum levels of peptides in NB. This is crucial because a high peptide concentration [55] and a peptide receptor overexpression [28] have, respectively, been related to a less-NB-favorable outcome and shown to favor NB cell migration and invasion. Moreover, this overexpression could be used as a tumor biomarker for NB. Peptide receptor overexpression in tumor cells is very useful for the diagnosis and treatment of tumors because this overexpression facilitates the delivery of chemotherapeutic drugs or compounds that promote apoptotic mechanisms in cancer cells; in fact, the therapeutic potential of combined chemotherapy and peptide receptor radionuclide therapy as an anti-NB strategy has been suggested [111]. Moreover, peptide receptor overexpression is important in developing anti-NB strategies using peptide receptor antagonists or agonists. Although some peptides (GRP, neuropeptide Y) have been more-thoroughly studied in NB, unfortunately, much of the data regarding this disease and the peptidergic systems are fragmentary, scarce, or absent; hence, there is still a lot of basic research work to be completed, and, in particular, in vivo experiments must be performed.
Oncogenic peptides promote NB progression, and this means that peptide receptor antagonists (PD123319, RC-3095, H2756, BIIE0246, DuP753, PD123177, L-733,060, aprepitant, tolvaptan) could be used as anti-NB agents since these compounds counteract NB growth and migration and angiogenesis. It is important to highlight that the same peptide (e.g., substance P) can bind to several G protein-coupled receptors, activating a variety of signaling pathways, which is crucial when studying the effect of a specific antagonist as an antitumor agent. This is an important point to investigate in NB. There are few studies on the use of peptide receptor antagonists in NB, and the number of antagonists tested is also scarce. Thus, studies on other peptide receptor antagonists, in addition to those already studied, to treat NB must be urgently developed in preclinical studies, and experiments using antagonists in combination with chemotherapy/radiotherapy must also be carried out that we might learn whether an anticancer synergic action occurs and whether the side-effects mediated by the cytostatics are reduced. Moreover, studies on P2X7 receptor antagonists, anti-oncogenic peptide antibodies, integrin β1 expression, signaling pathways involved and signaling pathway inhibitors (wortmannin, LY-294002), FAK inhibitors (Y15), peptide receptor knockdown, sPEP1 knockdown, acetic acid analogs (dichloroacetate), and the transcription factor Ets 1 must be fully developed to counteract the beneficial effects mediated by oncogenic peptides on NB. In the same way, the use of anticancer peptides to fight NB must be studied in depth; these peptides could counteract the effects mediated by the oncogenic peptides. However, peptides show a poor bioavailability, short half-life, and high solubility and safety. To increase the therapeutic option of anti-NB peptides, some strategies are currently available, such as amino acid sequence manipulation, peptide conjugation to polymers, peptide-loaded nanoparticles, peptide cyclization, cell-targeting peptides, and cell-penetrating peptides, to improve the delivery and stability of peptides [125,126]. The interactions between the peptidergic systems in NB must be investigated in depth. In this sense, it is crucial to understand the antitumor actions promoted by combining peptides or peptide receptor agonists exerting anti-NB actions and peptide receptor antagonists, as well as to determine the antitumor synergistic actions exerted by different peptide receptor antagonists favoring apoptotic mechanisms in NB cells. The involvement of oncogenic and anticancer peptides in NB progression shows the interactions between those peptides and the functional complexity of the mechanisms regulated by peptides in cancer development. Figure 3 shows the chemical structures of promising anti-NB effects.
The research line focusing on the mechanisms regulating the expression of oncogenic and anticancer peptides and their receptors in NB must also be potentiated. This is crucial because, for example, in NB cells, peptides control the expression of peptide receptors [16] and potentiate the effects mediated by other peptides [17]; some compounds favor the release of proliferative peptides and the expression of peptide receptors, as well as controlling the gene expression of peptides [43,44,52]; and peptides (PACAP) promote, after binding to their receptors, their own expression [118]. The latter must be highlighted because PACAP promotes the differentiation of NB cells into the benign form [116]. This research line must be potentiated in order to understand the mechanisms regulating both the synthesis and the release of oncogenic or anticancer peptides. This knowledge will assist in the development of therapeutic strategies to control NB progression. Moreover, the roles played by peptides in the tumor microenvironment must be elucidate, and it is especially important to understand how peptides control antitumor defenses by regulating the actions mediated by immune cells. Epigenetic mechanisms have been involved in the expression of peptide receptors, the recurrence rate, and carcinogenesis; thus, these mechanisms must also be studied in NB to understand how they control the peptidergic systems in NB.
In summary, many of the possible therapeutic strategies against NB must be confirmed and developed; in many cases, the current data are preliminary, fragmentary, scarce, or absent. However, peptidergic systems are potential and promising targets for the diagnosis and treatment of NB, and the current data suggest that drug cocktails including different compounds (anticancer peptides and peptide receptor antagonists) would be beneficial in treating the disease, either alone or in combination with conventional (radiotherapy/chemotherapy, surgery) or new (immunotherapy) anti-NB therapies. To develop clinical trials and increase the possibility of transversal research, basic research on the peptidergic systems in NB should be strengthened. Although the data regarding the involvement of the peptidergic systems in NB are, in many cases, fragmentary or very scarce for a particular peptidergic system, taken together, they are quite promising in terms of the potential development of this research line with the aim of developing new therapeutic strategies to treat NB in the future.
Conceptualization, M.L.S. and R.C.; resources, M.L.S. and R.C.; writing—original draft preparation, M.L.S. and R.C.; writing—review and editing, M.L.S. and R.C.; supervision, M.L.S. and R.C. All authors have read and agreed to the published version of the manuscript.
The authors thank Francisco David Rodríguez (University of Salamanca, Spain) for his help in preparing the chemical formulas.
The authors declare no conflicts of interest.
Footnotes
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
Figure 1 Oncogenic and anticancer peptides involved in NB. The experimental models used and the tumor effects mediated by these peptides are mentioned. Adrenomedullin/PAMP [
Figure 2 Anti-NB therapeutic strategies. Future research lines and interactions of the peptidergic system that must be investigated in depth are also mentioned.
Figure 3 Chemical structures of peptide receptor antagonists exerting an anti-NB action. The receptors involved and the anti-NB actions exerted are also indicated. Aprepitant [
Summary of the most important findings regarding the involvement of the peptidergic systems in NB.
| Peptides | Effects on Neuroblastoma | References |
|---|---|---|
| Adrenocorticotropin Hormone (ACTH) | - Olfactory NB releases ACTH. | [ |
| Adrenomedullin/Pro-Adrenomedullin N-terminal 20 Peptide (PAMP) | - Both peptides block DNA synthesis and cell growth in NB cells; | [ |
| Amylin | - Favors NB cell proliferation and survival; | [ |
| Angiotensin II | - NB cells express ATR1, ATR2, and ATR 4 receptors; | [ |
| Bradykinin | - Promotes NB cell proliferation and increases P2X7B receptor expression: bradykinin and purines are involved in NB dissemination, favoring metastasis; | [ |
| Corticotropin-Releasing Factor (CRF) | - CRF/urocortin reduce motility/proliferation in NB cells and favor neuronal-like differentiation; | [ |
| Exendin-4 | - Favors a more differentiated phenotype, counteracts anchorage-independent growth, increases cell adhesion, and decreases cell migration in NB cells. | [ |
| Gastrin-Releasing Peptide (GRP)/Bombesin | - GRP acts as an autocrine growth factor in NB cells; | [ |
| Gonadotropin-Releasing Hormone (GRH) | - Activation of GRH receptors inhibits NB cell growth and apoptotic markers are expressed in these cells after treatment with GRH; | [ |
| Melanin-Concentrating Hormone (MCH) | - NB tissues and cell lines express MCH and MCH receptor mRNA; | [ |
| Neuropeptide FF | - NB cells express neuropeptide YY and neuropeptide FF receptor 2; | [ |
| Neuropeptide Y | - NB cells express neuropeptide Y and neuropeptide Y receptors 1, 2, 4, and 5; | [ |
| Neurotensin/Neuromedin U | - Both peptides favor NB cell proliferation and invasion; | [ |
| Orexin | - Orexin A/orexin mRNA in NB tissue; | [ |
| Oxytocin | - Favors proliferation/viability and anti-apoptotic mechanisms in NB cells; | [ |
| Prolactin-Releasing Peptide (PrRP) | - Binds to GRP10 receptors; | [ |
| sPEP1 | - Favors self-renewal and aggressiveness of NB stem cells; | [ |
| SHPRH-146aa | - Its overexpression blocks NB cell proliferation, migration, and invasion; increases apoptosis; and conunteracts NB cell malignancy traits. | [ |
| Somatostatin | - Somatostatin receptor 2 located in NB tissue; | [ |
| Substance P | - Neurokinin-1 receptors expressed in NB cells; | [ |
| Thyrotropin-Releasing Hormone | - Exerts anti-apoptotic effects in NB cells. | [ |
| Vasoactive Intestinal Peptide (VIP)/Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) | - VIP level increased during NB differentiation; | [ |
| Vasopressin | - Tolvaptan decreases NB cell proliferation and invasion and induces apoptosis; | [ |
1. Qiao, J.; Liu, J.; Jacobson, J.C.; Clark, R.A.; Lee, S.; Liu, L.; An, Z.; Zhang, N.; Chung, D.H. Anti-GRP-R Monoclonal Antibody Antitumor Therapy against Neuroblastoma. PLoS ONE; 2022; 17, e0277956. [DOI: https://dx.doi.org/10.1371/journal.pone.0277956] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36525420]
2. Lukoseviciute, M.; Need, E.; Holzhauser, S.; Dalianis, T.; Kostopoulou, O.N. Combined Targeted Therapy with PI3K and CDK4/6, or FGFR Inhibitors Show Synergistic Effects in a Neuroblastoma Spheroid Culture Model. Biomed. Pharmacother.; 2024; 177, 116993. [DOI: https://dx.doi.org/10.1016/j.biopha.2024.116993] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/38889643]
3. Mao, C.; Poimenidou, M.; Craig, B.T. Current Knowledge and Perspectives of Immunotherapies for Neuroblastoma. Cancers; 2024; 16, 2865. [DOI: https://dx.doi.org/10.3390/cancers16162865]
4. Persaud, N.V.; Park, J.A.; Cheung, N.K.V. High-Risk Neuroblastoma Challenges and Opportunities for Antibody-Based Cellular Immunotherapy. J. Clin. Med.; 2024; 13, 4765. [DOI: https://dx.doi.org/10.3390/jcm13164765] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/39200906]
5. Dhamdhere, M.R.; Spiegelman, V.S. Extracellular Vesicles in Neuroblastoma: Role in Progression, Resistance to Therapy and Diagnostics. Front. Immunol.; 2024; 15, 1385875. [DOI: https://dx.doi.org/10.3389/fimmu.2024.1385875]
6. Rados, M.; Landegger, A.; Schmutzler, L.; Rabidou, K.; Taschner-Mandl, S.; Fetahu, I.S. Natural Killer Cells in Neuroblastoma: Immunological Insights and Therapeutic Perspectives. Cancer Metastasis Rev.; 2024; 43, pp. 1401-1417. [DOI: https://dx.doi.org/10.1007/s10555-024-10212-8]
7. Song, M.; Huang, Y.; Hong, Y.; Liu, J.; Zhu, J.; Lu, S.; Wang, J.; Sun, F.; Huang, J. PD-L1-Expressing Natural Killer Cells Predict Favorable Prognosis and Response to PD-1/PD-L1 Blockade in Neuroblastoma. OncoImmunology; 2024; 13, 2289738. [DOI: https://dx.doi.org/10.1080/2162402X.2023.2289738]
8. Makimoto, A.; Fujisaki, H.; Matsumoto, K.; Takahashi, Y.; Cho, Y.; Morikawa, Y.; Yuza, Y.; Tajiri, T.; Iehara, T. Retinoid Therapy for Neuroblastoma: Historical Overview, Regulatory Challenges, and Prospects. Cancers; 2024; 16, 544. [DOI: https://dx.doi.org/10.3390/cancers16030544]
9. Xia, Y.; Wang, C.; Li, X.; Gao, M.; Hogg, H.D.J.; Tunthanathip, T.; Hulsen, T.; Tian, X.; Zhao, Q. Development and Validation of a Novel Stemness-Related Prognostic Model for Neuroblastoma Using Integrated Machine Learning and Bioinformatics Analyses. Transl. Pediatr.; 2024; 13, pp. 91-109. [DOI: https://dx.doi.org/10.21037/tp-23-582]
10. Zhou, J.; Du, H.; Cai, W. Narrative Review: Precision Medicine Applications in Neuroblastoma—Current Status and Future Prospects. Transl. Pediatr.; 2024; 13, pp. 164-177. [DOI: https://dx.doi.org/10.21037/tp-23-557]
11. Sánchez, M.L.; Mangas, A.; Coveñas, R. Glioma and Peptidergic Systems: Oncogenic and Anticancer Peptides. Int. J. Mol. Sci.; 2024; 25, 7990. [DOI: https://dx.doi.org/10.3390/ijms25147990] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/39063232]
12. Sánchez, M.L.; Rodríguez, F.D.; Coveñas, R. Peptidergic Systems and Cancer: Focus on Tachykinin and Calcitonin/Calcitonin Gene-Related Peptide Families. Cancers; 2023; 15, 1694. [DOI: https://dx.doi.org/10.3390/cancers15061694]
13. Coveñas, R.; Muñoz, M. Involvement of the Substance P/Neurokinin-1 Receptor System in Cancer. Cancers; 2022; 14, 3539. [DOI: https://dx.doi.org/10.3390/cancers14143539] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35884599]
14. Robinson, P.; Coveñas, R.; Muñoz, M. Combination Therapy of Chemotherapy or Radiotherapy and the Neurokinin-1 Receptor Antagonist Aprepitant: A New Antitumor Strategy?. Curr. Med. Chem.; 2022; 29, pp. 1798-1812. [DOI: https://dx.doi.org/10.2174/0929867329666220811152602]
15. Caruso, G.; Fresta, C.G.; Lazzarino, G.; Distefano, D.A.; Parlascino, P.; Lunte, S.M.; Lazzarino, G.; Caraci, F. Sub-Toxic Human Amylin Fragment Concentrations Promote the Survival and Proliferation of SH-SY5Y Cells via the Release of VEGF and HspB5 from Endothelial RBE4 Cells. Int. J. Mol. Sci.; 2018; 19, 3659. [DOI: https://dx.doi.org/10.3390/ijms19113659]
16. Maggi, M.; Finetti, G.; Cioni, A.; Mancina, R.; Baldi, E.; Serio, M.; Catalioto, R.-M.; Renzetti, A.R. Identification and Characterization of Functional Angiotensin II Receptors in Human Neuroblastoma Cells. Regul. Pept.; 1995; 56, pp. 175-184. [DOI: https://dx.doi.org/10.1016/0167-0115(95)00016-5]
17. Chen, L.; Prakash, O.; Ré, R.N. The Interaction of Insulin and Angiotensin II on the Regulation of Human Neuroblastoma Cell Growth. Mol. Chem. Neuropathol.; 1993; 18, pp. 189-196. [DOI: https://dx.doi.org/10.1007/BF03160033] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/8466592]
18. Mustafa, T.; Chai, S.Y.; Mendelsohn, F.A.O.; Moeller, I.; Albiston, A.L. Characterization of the AT4 Receptor in a Human Neuroblastoma Cell Line (SK-N-MC). J. Neurochem.; 2001; 76, pp. 1679-1687. [DOI: https://dx.doi.org/10.1046/j.1471-4159.2001.00166.x] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/11259486]
19. Collazo, B.J.; Morales-Vázquez, D.; Álvarez-Del Valle, J.; Sierra-Pagan, J.E.; Medina, J.C.; Méndez-Álvarez, J.; Gerena, Y. Angiotensin II Induces Differentiation of Human Neuroblastoma Cells by Increasing MAP2 and ROS Levels. J. Renin Angiotensin Aldosterone Syst.; 2021; 2021, 6191417. [DOI: https://dx.doi.org/10.1155/2021/6191417] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/34285710]
20. Blanco, H.M.; Perez, C.N.; Banchio, C.; Alvarez, S.E.; Ciuffo, G.M. Neurite Outgrowth Induced by Stimulation of Angiotensin II AT2 Receptors in SH-SY5Y Neuroblastoma Cells Involves c-Src Activation. Heliyon; 2023; 9, e15656. [DOI: https://dx.doi.org/10.1016/j.heliyon.2023.e15656]
21. Ulrich, H.; Ratajczak, M.Z.; Schneider, G.; Adinolfi, E.; Orioli, E.; Ferrazoli, E.G.; Glaser, T.; Corrêa-Velloso, J.; Martins, P.C.M.; Coutinho, F. Kinin and Purine Signaling Contributes to Neuroblastoma Metastasis. Front. Pharmacol.; 2018; 9, 500. [DOI: https://dx.doi.org/10.3389/fphar.2018.00500] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/29867502]
22. Tanabe, A.; Shiraishi, M.; Negishi, M.; Saito, N.; Tanabe, M.; Sasaki, Y. MARCKS Dephosphorylation Is Involved in Bradykinin-induced Neurite Outgrowth in Neuroblastoma SH-SY5Y Cells. J. Cell. Physiol.; 2012; 227, pp. 618-629. [DOI: https://dx.doi.org/10.1002/jcp.22763]
23. Querobino, S.M.; Ribeiro, C.A.J.; Alberto-Silva, C. Bradykinin-Potentiating PEPTIDE-10C, an Argininosuccinate Synthetase Activator, Protects against H2O2-Induced Oxidative Stress in SH-SY5Y Neuroblastoma Cells. Peptides; 2018; 103, pp. 90-97. [DOI: https://dx.doi.org/10.1016/j.peptides.2018.03.017]
24. Paul, P.; Qiao, J.; Kim, K.W.; Romain, C.; Lee, S.; Volny, N.; Mobley, B.; Correa, H.; Chung, D.H. Targeting Gastrin-Releasing Peptide Suppresses Neuroblastoma Progression via Upregulation of PTEN Signaling. PLoS ONE; 2013; 8, e72570. [DOI: https://dx.doi.org/10.1371/journal.pone.0072570] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/24039782]
25. Kim, S.; Hu, W.; Kelly, D.R.; Hellmich, M.R.; Evers, B.M.; Chung, D.H. Gastrin-Releasing Peptide Is a Growth Factor for Human Neuroblastomas. Ann. Surg.; 2002; 235, pp. 621-630. [DOI: https://dx.doi.org/10.1097/00000658-200205000-00003]
26. Qiao, L.; Paul, P.; Lee, S.; Qiao, J.; Wang, Y.; Chung, D.H. Differential Regulation of Cyclin-Dependent Kinase Inhibitors in Neuroblastoma Cells. Biochem. Biophys. Res. Commun.; 2013; 435, pp. 295-299. [DOI: https://dx.doi.org/10.1016/j.bbrc.2013.04.023] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/23618860]
27. Ishola, T.; Kang, J.; Qiao, J.; Evers, B.; Chung, D. Phosphatidylinositol 3-Kinase Regulation of Gastrin-Releasing Peptide-Induced Cell Cycle Progression in Neuroblastoma Cells. Biochim. Biophys. Acta (BBA)-Gen. Subj.; 2007; 1770, pp. 927-932. [DOI: https://dx.doi.org/10.1016/j.bbagen.2007.02.002]
28. Lee, S.; Qiao, J.; Pritha, P.; Chung, D.H. Integrin Β1 Is Critical for Gastrin-Releasing Peptidereceptor-Mediated Neuroblastoma Cell Migration And Invasion. Surgery; 2013; 154, pp. 369-375. [DOI: https://dx.doi.org/10.1016/j.surg.2013.04.067]
29. Qiao, J.; Lee, S.; Paul, P.; Qiao, L.; Taylor, C.J.; Schlegel, C.; Colon, N.C.; Chung, D.H. Akt2 Regulates Metastatic Potential in Neuroblastoma. PLoS ONE; 2013; 8, e56382. [DOI: https://dx.doi.org/10.1371/journal.pone.0056382]
30. Lee, S.; Qiao, J.; Paul, P.; O’Connor, K.L.; Evers, B.M.; Chung, D.H. FAK Is a Critical Regulator of Neuroblastoma Liver Metastasis. Oncotarget; 2012; 3, pp. 1576-1587. [DOI: https://dx.doi.org/10.18632/oncotarget.732]
31. Rellinger, E.J.; Romain, C.; Choi, S.; Qiao, J.; Chung, D.H. Silencing Gastrin-Releasing Peptide Receptor Suppresses Key Regulators of Aerobic Glycolysis in Neuroblastoma Cells: GRP-R Signaling Regulates Glycolysis. Pediatr. Blood Cancer; 2015; 62, pp. 581-586. [DOI: https://dx.doi.org/10.1002/pbc.25348] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/25630799]
32. Kim, K.W.; Paul, P.; Qiao, J.; Lee, S.; Chung, D.H. Enhanced Autophagy Blocks Angiogenesis via Degradation of Gastrin-Releasing Peptide in Neuroblastoma Cells. Autophagy; 2013; 9, pp. 1579-1590. [DOI: https://dx.doi.org/10.4161/auto.25987]
33. Abujamra, A.L.; Almeida, V.R.; Brunetto, A.L.; Schwartsmann, G.; Roesler, R. A Gastrin-releasing Peptide Receptor Antagonist Stimulates Neuro2a Neuroblastoma Cell Growth: Prevention by a Histone Deacetylase Inhibitor. Cell Biol. Int.; 2009; 33, pp. 899-903. [DOI: https://dx.doi.org/10.1016/j.cellbi.2009.04.014] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/19426821]
34. Qiao, J.; Kang, J.; Ishola, T.A.; Rychahou, P.G.; Evers, B.M.; Chung, D.H. Gastrin-Releasing Peptide Receptor Silencing Suppresses the Tumorigenesis and Metastatic Potential of Neuroblastoma. Proc. Natl. Acad. Sci. USA; 2008; 105, pp. 12891-12896. [DOI: https://dx.doi.org/10.1073/pnas.0711861105] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/18753628]
35. Qiao, J.; Cree, J.; Kang, J.; Kim, S.; Evers, B.M.; Chung, D.H. Ets Transcriptional Regulation of Gastrin-Releasing Peptide Receptor in Neuroblastomas. Surgery; 2004; 136, pp. 489-494. [DOI: https://dx.doi.org/10.1016/j.surg.2004.05.030]
36. Schlegel, C.; Paul, P.; Lee, S.; Woon Kim, K.; Colon, N.C.; Qiao, J.; Chung, D.H. Protein Kinase C Regulates Bombesin-Induced Rapid VEGF Secretion in Neuroblastoma Cells. Anticancer Res.; 2012; 32, pp. 4691-4696.
37. Kang, J.; Ishola, T.A.; Baregamian, N.; Mourot, J.M.; Rychahou, P.G.; Evers, B.M.; Chung, D.H. Bombesin Induces Angiogenesis and Neuroblastoma Growth. Cancer Lett.; 2007; 253, pp. 273-281. [DOI: https://dx.doi.org/10.1016/j.canlet.2007.02.007]
38. Sánchez, M.L.; Rodríguez, F.D.; Coveñas, R. Neuropeptide Y Peptide Family and Cancer: Antitumor Therapeutic Strategies. Int. J. Mol. Sci.; 2023; 24, 9962. [DOI: https://dx.doi.org/10.3390/ijms24129962]
39. Hoshi, N.; Hitomi, J.; Kusakabe, T.; Fukuda, T.; Hirota, M.; Suzuki, T. Distinct Morphological and Immunohistochemical Features and Different Growth Rates among Four Human Neuroblastomas Heterotransplanted into Nude Mice. Med. Mol. Morphol.; 2008; 41, pp. 151-159. [DOI: https://dx.doi.org/10.1007/s00795-008-0407-x]
40. Lu, C.; Everhart, L.; Tilan, J.; Kuo, L.; Sun, C.-C.J.; Munivenkatappa, R.B.; Jönsson-Rylander, A.-C.; Sun, J.; Kuan-Celarier, A.; Li, L. Neuropeptide Y and Its Y2 Receptor: Potential Targets in Neuroblastoma Therapy. Oncogene; 2010; 29, pp. 5630-5642. [DOI: https://dx.doi.org/10.1038/onc.2010.301]
41. Li, A.; Ritter, S. Functional Expression of Neuropeptide Y Receptors in Human Neuroblastoma Cells. Regul. Pept.; 2005; 129, pp. 119-124. [DOI: https://dx.doi.org/10.1016/j.regpep.2005.02.003]
42. Kitlinska, J.; Abe, K.; Kuo, L.; Pons, J.; Yu, M.; Li, L.; Tilan, J.; Everhart, L.; Lee, E.W.; Zukowska, Z. Differential Effects of Neuropeptide Y on the Growth and Vascularization of Neural Crest–Derived Tumors. Cancer Res.; 2005; 65, pp. 1719-1728. [DOI: https://dx.doi.org/10.1158/0008-5472.CAN-04-2192] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/15753367]
43. Tilan, J.; Kitlinska, J. Neuropeptide Y (NPY) in Tumor Growth and Progression: Lessons Learned from Pediatric Oncology. Neuropeptides; 2016; 55, pp. 55-66. [DOI: https://dx.doi.org/10.1016/j.npep.2015.10.005]
44. Czarnecka, M.; Trinh, E.; Lu, C.; Kuan-Celarier, A.; Galli, S.; Hong, S.-H.; Tilan, J.U.; Talisman, N.; Izycka-Swieszewska, E.; Tsuei, J. Neuropeptide Y Receptor Y5 as an Inducible Pro-Survival Factor in Neuroblastoma: Implications for Tumor Chemoresistance. Oncogene; 2015; 34, pp. 3131-3143. [DOI: https://dx.doi.org/10.1038/onc.2014.253] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/25132261]
45. Magni, P.; Maggi, R.; Pimpinelli, F.; Motta, M. Cholinergic Muscarinic Mechanisms Regulate Neuropeptide Y Gene Expression via Protein Kinase C in Human Neuroblastoma Cells. Brain Res.; 1998; 798, pp. 75-82. [DOI: https://dx.doi.org/10.1016/S0006-8993(98)00471-5] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/9666082]
46. Dozio, E.; Ruscica, M.; Feltrin, D.; Motta, M.; Magni, P. Cholinergic Regulation of Neuropeptide Y Synthesis and Release in Human Neuroblastoma Cells. Peptides; 2008; 29, pp. 491-495. [DOI: https://dx.doi.org/10.1016/j.peptides.2007.11.001]
47. Croce, N.; Dinallo, V.; Ricci, V.; Federici, G.; Caltagirone, C.; Bernardini, S.; Angelucci, F. Neuroprotective Effect of Neuropeptide Y against β-Amyloid 25-35 Toxicity in SH-SY5Y Neuroblastomacells Is Associated with Increased Neurotrophinproduction. Neurodegener. Dis.; 2011; 8, pp. 300-309. [DOI: https://dx.doi.org/10.1159/000323468]
48. Palanivel, V.; Gupta, V.; Mirshahvaladi, S.S.O.; Sharma, S.; Gupta, V.; Chitranshi, N.; Mirzaei, M.; Graham, S.L.; Basavarajappa, D. Neuroprotective Effects of Neuropeptide Y on Human Neuroblastoma SH-SY5Y Cells in Glutamate Excitotoxicity and ER Stress Conditions. Cells; 2022; 11, 3665. [DOI: https://dx.doi.org/10.3390/cells11223665]
49. Abualsaud, N.; Caprio, L.; Galli, S.; Krawczyk, E.; Alamri, L.; Zhu, S.; Gallicano, G.I.; Kitlinska, J. Neuropeptide Y/Y5 Receptor Pathway Stimulates Neuroblastoma Cell Motility Through RhoA Activation. Front. Cell Dev. Biol.; 2021; 8, 627090. [DOI: https://dx.doi.org/10.3389/fcell.2020.627090]
50. Galli, S.; Naranjo, A.; Van Ryn, C.; Tilan, J.U.; Trinh, E.; Yang, C.; Tsuei, J.; Hong, S.-H.; Wang, H.; Izycka-Swieszewska, E. Neuropeptide Y as a Biomarker and Therapeutic Target for Neuroblastoma. Am. J. Pathol.; 2016; 186, pp. 3040-3053. [DOI: https://dx.doi.org/10.1016/j.ajpath.2016.07.019]
51. Bjellerup, P.; Theodorsson, E.; Jörnvall, H.; Kogner, P. Limited Neuropeptide Y Precursor Processing in Unfavourable Metastatic Neuroblastoma Tumours. Br. J. Cancer; 2000; 83, pp. 171-176. [DOI: https://dx.doi.org/10.1054/bjoc.2000.1234]
52. Magni, P.; Beretta, E.; Scaccianoce, E.; Motta, M. Retinoic Acid Negatively Regulates Neuropeptide Y Expression in Human Neuroblastoma Cells. Neuropharmacology; 2000; 39, pp. 1628-1636. [DOI: https://dx.doi.org/10.1016/S0028-3908(99)00231-2] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/10854907]
53. Wang, B.; Sheriff, S.; Balasubramaniam, A.; Kennedy, M.A. NMR Based Metabolomics Study of Y2 Receptor Activation by Neuropeptide Y in the SK-N-BE2 Human Neuroblastoma Cell Line. Metabolomics; 2015; 11, pp. 1243-1252. [DOI: https://dx.doi.org/10.1007/s11306-015-0782-y]
54. McDonald, R.L.; Vaughan, P.F.T.; Beck-Sickinger, A.G.; Peers, C. Inhibition of Ca2+ channel Currents in Human Neuroblastoma (SH-SY5Y) Cells by Neuropeptide Y and a Novel Cyclic Neuropeptide Y Analogue. Neuropharmacology; 1995; 34, pp. 1507-1514. [DOI: https://dx.doi.org/10.1016/0028-3908(95)00068-H] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/8606797]
55. Yang, D.; Zhang, X.; Li, Z.; Xu, F.; Tang, C.; Chen, H. Neuromedin U and Neurotensin May Promote the Development of the Tumour Microenvironment in Neuroblastoma. PeerJ; 2021; 9, e11512. [DOI: https://dx.doi.org/10.7717/peerj.11512]
56. Bakos, J.; Strbak, V.; Ratulovska, N.; Bacova, Z. Effect of Oxytocin on Neuroblastoma Cell Viability and Growth. Cell. Mol. Neurobiol.; 2012; 32, pp. 891-896. [DOI: https://dx.doi.org/10.1007/s10571-012-9799-1]
57. Gürbüz Özgür, B.; Vural, K.; Tuğlu, M.İ. Effects of Oxytocin on Glutamate Mediated Neurotoxicity in Neuroblastoma Cell Culture. Arch. Neuropsychiatry; 2023; 61, 24. [DOI: https://dx.doi.org/10.29399/npa.28377]
58. Zatkova, M.; Reichova, A.; Bacova, Z.; Strbak, V.; Kiss, A.; Bakos, J. Neurite Outgrowth Stimulated by Oxytocin Is Modulated by Inhibition of the Calcium Voltage-Gated Channels. Cell. Mol. Neurobiol.; 2018; 38, pp. 371-378. [DOI: https://dx.doi.org/10.1007/s10571-017-0503-3]
59. Bakos, J.; Strbak, V.; Paulikova, H.; Krajnakova, L.; Lestanova, Z.; Bacova, Z. Oxytocin Receptor Ligands Induce Changes in Cytoskeleton in Neuroblastoma Cells. J. Mol. Neurosci.; 2013; 50, pp. 462-468. [DOI: https://dx.doi.org/10.1007/s12031-013-9960-4]
60. Koshimizu, T.; Fujiwara, Y.; Sakai, N.; Shibata, K.; Tsuchiya, H. Oxytocin Stimulates Expression of a Noncoding RNA Tumor Marker in a Human Neuroblastoma Cell Line. Life Sci.; 2010; 86, pp. 455-460. [DOI: https://dx.doi.org/10.1016/j.lfs.2010.02.001]
61. Zmeškalová, A.; Popelová, A.; Exnerová, A.; Železná, B.; Kuneš, J.; Maletínská, L. Cellular Signaling and Anti-Apoptotic Effects of Prolactin-Releasing Peptide and Its Analog on SH-SY5Y Cells. Int. J. Mol. Sci.; 2020; 21, 6343. [DOI: https://dx.doi.org/10.3390/ijms21176343] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/32882929]
62. Song, H.; Wang, J.; Wang, X.; Yuan, B.; Li, D.; Hu, A.; Guo, Y.; Cai, S.; Jin, S. HNF4A-AS1-Encoded Small Peptide Promotes Self-Renewal and Aggressiveness of Neuroblastoma Stem Cells via eEF1A1-Repressed SMAD4 Transactivation. Oncogene; 2022; 41, pp. 2505-2519. [DOI: https://dx.doi.org/10.1038/s41388-022-02271-4] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35318442]
63. Muñoz, M.; Rosso, M.; Pérez, A.; Coveñas, R.; Rosso, R.; Zamarriego, C.; Piruat, J.I. The NK1 Receptor Is Involved in the Antitumoural Action of L-733,060 and in the Mitogenic Action of Substance P on Neuroblastoma and Glioma Cell Lines. Neuropeptides; 2005; 39, pp. 427-432. [DOI: https://dx.doi.org/10.1016/j.npep.2005.03.004] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/15939468]
64. Muñoz, M.; Pérez, A.; Coveñas, R.; Rosso, M.; Castro, E. Antitumoural Action of L-733,060 on Neuroblastoma and Glioma Cell Lines. Arch. Ital. Biol.; 2004; 142, pp. 105-112.
65. Henssen, A.G.; Odersky, A.; Szymansky, A.; Seiler, M.; Althoff, K.; Beckers, A.; Speleman, F.; Schäfers, S.; De Preter, K.; Astrahanseff, K. Targeting Tachykinin Receptors in Neuroblastoma. Oncotarget; 2017; 8, pp. 430-443. [DOI: https://dx.doi.org/10.18632/oncotarget.13440]
66. Chu, J.M.T.; Chen, L.W.; Chan, Y.S.; Yung, K.K.L. Neuroprotective Effects of Neurokinin Receptor One in Dopaminergic Neurons Are Mediated through Akt/PKB Cell Signaling Pathway. Neuropharmacology; 2011; 61, pp. 1389-1398. [DOI: https://dx.doi.org/10.1016/j.neuropharm.2011.08.027]
67. Mukerji, I.; Ramkissoon, S.H.; Reddy, K.K.R.; Rameshwar, P. Autocrine Proliferation of Neuroblastoma Cells Is Partly Mediated through Neurokinin Receptors: Relevance to Bone Marrow Metastasis. J. Neurooncol.; 2005; 71, pp. 91-98. [DOI: https://dx.doi.org/10.1007/s11060-004-9182-2]
68. Pohl, A.; Kappler, R.; Mühling, J.; Schweinitz, D.; Berger, M. Expression of Truncated Neurokinin-1 Receptor in Childhood Neuroblastoma Is Independent of Tumor Biology and Stage. Anticancer Res.; 2017; 37, pp. 6079-6085. [DOI: https://dx.doi.org/10.21873/anticanres.12056]
69. Raffaghello, L.; Chiozzi, P.; Falzoni, S.; Di Virgilio, F.; Pistoia, V. The P2X7 Receptor Sustains the Growth of Human Neuroblastoma Cells through a Substance P–Dependent Mechanism. Cancer Res.; 2006; 66, pp. 907-914. [DOI: https://dx.doi.org/10.1158/0008-5472.CAN-05-3185]
70. Jaworska-Feil, L.; Jantas, D.; Leskiewicz, M.; Budziszewska, B.; Kubera, M.; Basta-Kaim, A.; Lipkowski, A.W.; Lason, W. Protective Effects of TRH and Its Analogues against Various Cytotoxic Agents in Retinoic Acid (RA)-Differentiated Human Neuroblastoma SH-SY5Y Cells. Neuropeptides; 2010; 44, pp. 495-508. [DOI: https://dx.doi.org/10.1016/j.npep.2010.08.004]
71. Marroncini, G.; Anceschi, C.; Naldi, L.; Fibbi, B.; Baldanzi, F.; Maggi, M.; Peri, A. The V2 Receptor Antagonist Tolvaptan Counteracts Proliferation and Invasivity in Human Cancer Cells. J. Endocrinol. Investig.; 2022; 45, pp. 1693-1708. [DOI: https://dx.doi.org/10.1007/s40618-022-01807-5] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35604542]
72. Grassi, D.; Ghorbanpoor, S.; Acaz-Fonseca, E.; Ruiz-Palmero, I.; Garcia-Segura, L.M. The Selective Estrogen Receptor Modulator Raloxifene Regulates Arginine-Vasopressin Gene Expression in Human Female Neuroblastoma Cells Through G Protein-Coupled Estrogen Receptor and ERK Signaling. Endocrinology; 2015; 156, pp. 3706-3716. [DOI: https://dx.doi.org/10.1210/en.2014-2010]
73. Grassi, D.; Bellini, M.J.; Acaz-Fonseca, E.; Panzica, G.; Garcia-Segura, L.M. Estradiol and Testosterone Regulate Arginine-Vasopressin Expression in SH-SY5Y Human Female Neuroblastoma Cells through Estrogen Receptors-α and -β. Endocrinology; 2013; 154, pp. 2092-2100. [DOI: https://dx.doi.org/10.1210/en.2012-2137]
74. Castino, R.; Thepparit, C.; Bellio, N.; Murphy, D.; Isidoro, C. Akt Induces Apoptosis in Neuroblastoma Cells Expressing a C98X Vasopressin Mutant Following Autophagy Suppression. J. Neuroendocrinol.; 2008; 20, pp. 1165-1175. [DOI: https://dx.doi.org/10.1111/j.1365-2826.2008.01769.x] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/18673414]
75. Ando, K.; Omi, N.; Shimosawa, T.; Fujita, T. Proadrenomedullin N-terminal 20 Peptide (PAMP) Inhibits Proliferation of Human Neuroblastoma TGW Cells. FEBS Lett.; 1997; 413, pp. 462-466. [DOI: https://dx.doi.org/10.1016/S0014-5793(97)00958-7]
76. Satoh, F.; Takahashi, K.; Murakami, O.; Totsune, K.; Sone, M.; Ohneda, M.; Abe, K.; Miura, Y.; Hayashi, Y.; Sasano, H. Adrenomedullin in Human Brain, Adrenal Glands and Tumor Tissues of Pheochromocytoma, Ganglioneuroblastoma and Neuroblastoma. J. Clin. Endocrinol. Metab.; 1995; 80, pp. 1750-1752. [DOI: https://dx.doi.org/10.1210/jcem.80.5.7745031]
77. Xu, Y.; Krukoff, T.L. Adrenomedullin Stimulates Nitric Oxide Release from SK-N-SH Human Neuroblastoma Cells by Modulating Intracellular Calcium Mobilization. Endocrinology; 2005; 146, pp. 2295-2305. [DOI: https://dx.doi.org/10.1210/en.2004-1354] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/15677761]
78. Kitamuro, T.; Takahashi, K.; Totsune, K.; Nakayama, M.; Murakami, O.; Hida, W.; Shirato, K.; Shibahara, S. Differential Expression of Adrenomedullin and Its Receptor Component, Receptor Activity Modifying Protein (RAMP) 2 during Hypoxia in Cultured Human Neuroblastoma Cells. Peptides; 2001; 22, pp. 1795-1801. [DOI: https://dx.doi.org/10.1016/S0196-9781(01)00520-4]
79. Zimmermann, U.; Fischer, J.A.; Muff, R. Adrenomedullin and Calcitonin Gene-Related Peptide Interact with the Same Receptor in Cultured Human Neuroblastoma SK-N-MC Cells. Peptides; 1995; 16, pp. 421-424. [DOI: https://dx.doi.org/10.1016/0196-9781(94)00195-C]
80. Pozzoli, G.; De Simone, M.L.; Cantalupo, E.; Cenciarelli, C.; Lisi, L.; Boninsegna, A.; Dello Russo, C.; Sgambato, A.; Navarra, P. The Activation of Type 1 Corticotropin Releasing Factor Receptor (CRF-R1) Inhibits Proliferation and Promotes Differentiation of Neuroblastoma Cells in Vitro via p27Kip1 Protein up-Regulation and c-Myc mRNA down-Regulation. Mol. Cell. Endocrinol.; 2015; 412, pp. 205-215. [DOI: https://dx.doi.org/10.1016/j.mce.2015.05.004]
81. Dautzenberg, F.M. Stimulation of Neuropeptide Y-Mediated Calcium Responses in Human SMS-KAN Neuroblastoma Cells Endogenously Expressing Y2 Receptors by Co-Expression of Chimeric G Proteins. Biochem. Pharmacol.; 2005; 69, pp. 1493-1499. [DOI: https://dx.doi.org/10.1016/j.bcp.2005.02.014]
82. Luciani, P.; Deledda, C.; Benvenuti, S.; Squecco, R.; Cellai, I.; Fibbi, B.; Marone, I.M.; Giuliani, C.; Mordi, G.; Francini, F. Exendin-4 Induces Cell Adhesion and Differentiation and Counteracts the Invasive Potential of Human Neuroblastoma Cells. PLoS ONE; 2013; 8, e71716. [DOI: https://dx.doi.org/10.1371/journal.pone.0071716] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/23990978]
83. Morgan, K.; Stewart, A.J.; Miller, N.; Mullen, P.; Muir, M.; Dodds, M.; Medda, F.; Harrison, D.; Langdon, S.; Millar, R.P. Gonadotropin-Releasing Hormone Receptor Levels and Cell Context Affect Tumor Cell Responses to Agonist In Vitro and In Vivo. Cancer Res.; 2008; 68, pp. 6331-6340. [DOI: https://dx.doi.org/10.1158/0008-5472.CAN-08-0197] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/18676858]
84. Arihara, Z.; Takahashi, K.; Murakami, O.; Totsune, K.; Sone, M.; Satoh, F.; Ito, S.; Hayashi, Y.; Sasano, H.; Mouri, T. Orexin-A in the Human Brain and Tumor Tissues of Ganglioneuroblastoma and Neuroblastoma. Peptides; 2000; 21, pp. 565-570. [DOI: https://dx.doi.org/10.1016/S0196-9781(00)00184-4]
85. Rouet-Benzineb, P.; Rouyer-Fessard, C.; Jarry, A.; Avondo, V.; Pouzet, C.; Yanagisawa, M.; Laboisse, C.; Laburthe, M.; Voisin, T. Orexins Acting at Native OX1 Receptor in Colon Cancer and Neuroblastoma Cells or at Recombinant OX1 Receptor Suppress Cell Growth by Inducing Apoptosis. J. Biol. Chem.; 2004; 279, pp. 45875-45886. [DOI: https://dx.doi.org/10.1074/jbc.M404136200] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/15310763]
86. Louhivuori, L.M.; Jansson, L.; Nordström, T.; Bart, G.; Näsman, J.; Åkerman, K.E.O. Selective Interference with TRPC3/6 Channels Disrupts OX1 Receptor Signalling via NCX and Reveals a Distinct Calcium Influx Pathway. Cell Calcium; 2010; 48, pp. 114-123. [DOI: https://dx.doi.org/10.1016/j.ceca.2010.07.005]
87. Esmaeili-Mahani, S.; Vazifekhah, S.; Pasban-Aliabadi, H.; Abbasnejad, M.; Sheibani, V. Protective Effect of Orexin-A on 6-Hydroxydopamine-Induced Neurotoxicity in SH-SY5Y Human Dopaminergic Neuroblastoma Cells. Neurochem. Int.; 2013; 63, pp. 719-725. [DOI: https://dx.doi.org/10.1016/j.neuint.2013.09.022]
88. Pasban-Aliabadi, H.; Esmaeili-Mahani, S.; Abbasnejad, M. Orexin-A Protects Human Neuroblastoma SH-SY5Y Cells Against 6-Hydroxydopamine-Induced Neurotoxicity: Involvement of PKC and PI3K Signaling Pathways. Rejuvenation Res.; 2017; 20, pp. 125-133. [DOI: https://dx.doi.org/10.1089/rej.2016.1836]
89. Wang, C.-M.; Yang, C.-Q.; Cheng, B.-H.; Chen, J.; Bai, B. Orexin-A Protects SH-SY5Y Cells against H2O2-Induced Oxidative Damage via the PI3K/MEK1/2/ERK1/2 Signaling Pathway. Int. J. Immunopathol. Pharmacol.; 2018; 32, 2058738418785739. [DOI: https://dx.doi.org/10.1177/2058738418785739]
90. Kong, T.; Qiu, K.; Liu, M.; Cheng, B.; Pan, Y.; Yang, C.; Chen, J.; Wang, C. Orexin-A Protects against Oxygen-Glucose Deprivation/Reoxygenation-Induced Cell Damage by Inhibiting Endoplasmic Reticulum Stress-Mediated Apoptosis via the Gi and PI3K Signaling Pathways. Cell. Signal.; 2019; 62, 109348. [DOI: https://dx.doi.org/10.1016/j.cellsig.2019.109348]
91. Chang, S.; Ren, D.; Zhang, L.; Liu, S.; Yang, W.; Cheng, H.; Zhang, X.; Hong, E.; Geng, D.; Wang, Y. Therapeutic SHPRH-146aa Encoded by Circ-SHPRH Dynamically Upregulates P21 to Inhibit CDKs in Neuroblastoma. Cancer Lett.; 2024; 598, 217120. [DOI: https://dx.doi.org/10.1016/j.canlet.2024.217120] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/39002691]
92. Gao, J.; Pan, H.; Li, J.; Jiang, J.; Wang, W. A Peptide Encoded by the Circular Form of the SHPRH Gene Induces Apoptosis in Neuroblastoma Cells. PeerJ; 2024; 12, e16806. [DOI: https://dx.doi.org/10.7717/peerj.16806] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/38282862]
93. Familiar, C.; Azcutia, A. Adrenocorticotropic Hormone-Dependent Cushing Syndrome Caused by an Olfactory Neuroblastoma. Clin. Med. Insights Endocrinol. Diabetes; 2019; 12, 1179551419825832. [DOI: https://dx.doi.org/10.1177/1179551419825832] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/30728732]
94. Mikoshiba, T.; Sekimizu, M.; Saito, S.; Nakamura, S.; Nagai, R.; Kawaida, M.; Kurihara, I.; Kobayashi, S.; Ozawa, H. Ectopic Adrenocorticotropic Hormone Syndrome in Patients with Olfactory Neuroblastoma. Endocr. Relat. Cancer; 2024; 31, e240030. [DOI: https://dx.doi.org/10.1530/ERC-24-0030]
95. Alsarari, A.A.; Abdulkader, A.A.; Farooqi, W.A.; Al-Shibani, S.K.; Al Khuwaitir, T.S. Olfactory Neuroblastoma Causing Cushing’s Syndrome Due to the Ectopic Adrenocorticotropic Hormone (ACTH) Secretion: A Case Report. Cureus; 2024; 16, e56434. [DOI: https://dx.doi.org/10.7759/cureus.56434]
96. Kanno, K.; Morokuma, Y.; Tateno, T.; Hirono, Y.; Taki, K.; Osamura, R.Y.; Hirata, Y. Olfactory Neuroblastoma Causing Ectopic ACTH Syndrome. Endocr. J.; 2005; 52, pp. 675-681. [DOI: https://dx.doi.org/10.1507/endocrj.52.675]
97. Fry, D.; Dayton, B.; Brodjian, S.; Ogiela, C.; Sidorowicz, H.; Frost, L.J.; McNally, T.; Reilly, R.M.; Collins, C.A. Characterization of a Neuronal Cell Line Expressing Native Human Melanin-Concentrating Hormone Receptor 1 (MCHR1). Int. J. Biochem. Cell Biol.; 2006; 38, pp. 1290-1299. [DOI: https://dx.doi.org/10.1016/j.biocel.2006.01.007]
98. Takahashi, K.; Totsune, K.; Murakami, O.; Sone, M.; Satoh, F.; Kitamuro, T.; Noshiro, T.; Hayashi, Y.; Sasano, H.; Shibahara, S. Expression of Melanin-Concentrating Hormone Receptor Messenger Ribonucleic Acid in Tumor Tissues of Pheochromocytoma, Ganglioneuroblastoma, and Neuroblastoma1. J. Clin. Endocrinol. Metab.; 2001; 86, pp. 369-374. [DOI: https://dx.doi.org/10.1210/jcem.86.1.7158]
99. Schlumberger, S.E.; Jäggin, V.; Tanner, H.; Eberle, A.N. Endogenous Receptor for Melanin-Concentrating Hormone in Human Neuroblastoma Kelly Cells. Biochem. Biophys. Res. Commun.; 2002; 298, pp. 54-59. [DOI: https://dx.doi.org/10.1016/S0006-291X(02)02400-2]
100. Cotta-Grand, N.; Rovère, C.; Guyon, A.; Cervantes, A.; Brau, F.; Nahon, J.-L. Melanin-Concentrating Hormone Induces Neurite Outgrowth in Human Neuroblastoma SH-SY5Y Cells through P53 and MAPKinase Signaling Pathways. Peptides; 2009; 30, pp. 2014-2024. [DOI: https://dx.doi.org/10.1016/j.peptides.2009.06.015]
101. Sun, Y.; Zhang, X.; He, N.; Sun, T.; Zhuang, Y.; Fang, Q.; Wang, K.; Wang, R. Neuropeptide FF Activates ERK and NF Kappa B Signal Pathways in Differentiated SH-SY5Y Cells. Peptides; 2012; 38, pp. 110-117. [DOI: https://dx.doi.org/10.1016/j.peptides.2012.08.019] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/22981806]
102. Änkö, M.; Panula, P. Regulation of Endogenous Human NPFF2 Receptor by Neuropeptide FF in SK-N-MC Neuroblastoma Cell Line. J. Neurochem.; 2006; 96, pp. 573-584. [DOI: https://dx.doi.org/10.1111/j.1471-4159.2005.03581.x] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/16336216]
103. Mollereau, C.; Mazarguil, H.; Zajac, J.-M.; Roumy, M. Neuropeptide FF (NPFF) Analogs Functionally Antagonize Opioid Activities in NPFF2 Receptor-Transfected SH-SY5Y Neuroblastoma Cells. Mol. Pharmacol.; 2005; 67, pp. 965-975. [DOI: https://dx.doi.org/10.1124/mol.104.004614] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/15608144]
104. Kersanté, F.; Mollereau, C.; Zajac, J.-M.; Roumy, M. Anti-Opioid Activities of NPFF1 Receptors in a SH-SY5Y Model. Peptides; 2006; 27, pp. 980-989. [DOI: https://dx.doi.org/10.1016/j.peptides.2005.07.025]
105. Bonnard, E.; Burlet-Schiltz, O.; Monsarrat, B.; Girard, J.; Zajac, J. Identification of proNeuropeptide FFA Peptides Processed in Neuronal and Non-neuronal Cells and in Nervous Tissue. Eur. J. Biochem.; 2003; 270, pp. 4187-4199. [DOI: https://dx.doi.org/10.1046/j.1432-1033.2003.03816.x]
106. Feng, L.; Li, S.; Wang, C.; Yang, J. Current Status and Future Perspective on Molecular Imaging and Treatment of Neuroblastoma. Semin. Nucl. Med.; 2023; 53, pp. 517-529. [DOI: https://dx.doi.org/10.1053/j.semnuclmed.2022.12.004] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36682980]
107. Palmieri, D.E.; Tadokoro, K.S.; Valappil, B.; Pakala, T.; Muthukrishnan, A.; Seethala, R.R.; Snyderman, C.H. DOTATATE PET Imaging in Olfactory Neuroblastoma and Association with SSTR Expression. J. Neurol. Surg. Part B Skull Base; 2024; 85, pp. 439-444. [DOI: https://dx.doi.org/10.1055/a-2096-1802]
108. Czapiewski, P.; Kunc, M.; Gorczyński, A.; Haybaeck, J.; Okoń, K.; Reszec, J.; Lewczuk, A.; Dzierzanowski, J.; Karczewska, J.; Biernat, W. Frequent Expression of Somatostatin Receptor 2a in Olfactory Neuroblastomas: A New and Distinctive Feature. Hum. Pathol.; 2018; 79, pp. 144-150. [DOI: https://dx.doi.org/10.1016/j.humpath.2018.05.013]
109. Cracolici, V.; Wang, E.W.; Gardner, P.A.; Snyderman, C.; Gargano, S.M.; Chiosea, S.; Singhi, A.D.; Seethala, R.R. SSTR2 Expression in Olfactory Neuroblastoma: Clinical and Therapeutic Implications. Head Neck Pathol.; 2021; 15, pp. 1185-1191. [DOI: https://dx.doi.org/10.1007/s12105-021-01329-1]
110. Gains, J.E.; Sebire, N.J.; Moroz, V.; Wheatley, K.; Gaze, M.N. Immunohistochemical Evaluation of Molecular Radiotherapy Target Expression in Neuroblastoma Tissue. Eur. J. Nucl. Med. Mol. Imaging; 2018; 45, pp. 402-411. [DOI: https://dx.doi.org/10.1007/s00259-017-3856-4]
111. Fathpour, G.; Jafari, E.; Hashemi, A.; Dadgar, H.; Shahriari, M.; Zareifar, S.; Jenabzade, A.R.; Vali, R.; Ahmadzadehfar, H.; Assadi, M. Feasibility and Therapeutic Potential of Combined Peptide Receptor Radionuclide Therapy with Intensive Chemotherapy for Pediatric Patients with Relapsed or Refractory Metastatic Neuroblastoma. Clin. Nucl. Med.; 2021; 46, pp. 540-548. [DOI: https://dx.doi.org/10.1097/RLU.0000000000003577] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/33782280]
112. Alexander, N.; Marrano, P.; Thorner, P.; Naranjo, A.; Van Ryn, C.; Martinez, D.; Batra, V.; Zhang, L.; Irwin, M.S.; Baruchel, S. Prevalence and Clinical Correlations of Somatostatin Receptor-2 (SSTR2) Expression in Neuroblastoma. J. Pediatr. Hematol. Oncol.; 2019; 41, pp. 222-227. [DOI: https://dx.doi.org/10.1097/MPH.0000000000001326]
113. Romiani, A.; Simonsson, K.; Pettersson, D.; Al-Awar, A.; Rassol, N.; Bakr, H.; Lind, D.E.; Umapathy, G.; Spetz, J.; Palmer, R.H. Comparison of 177Lu-Octreotate and 177Lu-Octreotide for Treatment in Human Neuroblastoma-Bearing Mice. Heliyon; 2024; 10, e31409. [DOI: https://dx.doi.org/10.1016/j.heliyon.2024.e31409] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/38826727]
114. Romiani, A.; Spetz, J.; Shubbar, E.; Lind, D.E.; Hallberg, B.; Palmer, R.H.; Forssell-Aronsson, E. Neuroblastoma Xenograft Models Demonstrate the Therapeutic Potential of 177Lu-Octreotate. BMC Cancer; 2021; 21, 950. [DOI: https://dx.doi.org/10.1186/s12885-021-08551-8]
115. Boisvilliers, M.D.; Perrin, F.; Hebache, S.; Balandre, A.-C.; Bensalma, S.; Garnier, A.; Vaudry, D.; Fournier, A. VIP and PACAP Analogs Regulate Therapeutic Targets in High-Risk Neuroblastoma Cells. Peptides; 2016; 78, pp. 30-41. [DOI: https://dx.doi.org/10.1016/j.peptides.2016.01.014] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/26826611]
116. Maugeri, G.; D’Amico, A.G.; Rasà, D.M.; Saccone, S.; Federico, C.; Cavallaro, S.; D’Agata, V. PACAP and VIP Regulate Hypoxia-Inducible Factors in Neuroblastoma Cells Exposed to Hypoxia. Neuropeptides; 2018; 69, pp. 84-91. [DOI: https://dx.doi.org/10.1016/j.npep.2018.04.009]
117. Lekholm, E.; Ceder, M.M.; Forsberg, E.C.; Schiöth, H.B.; Fredriksson, R. Differentiation of Two Human Neuroblastoma Cell Lines Alters SV2 Expression Patterns. Cell. Mol. Biol. Lett.; 2021; 26, 5. [DOI: https://dx.doi.org/10.1186/s11658-020-00243-8]
118. Georg, B.; Falktoft, B.; Fahrenkrug, J. PKA, Novel PKC Isoforms, and ERK Is Mediating PACAP Auto-Regulation via PAC 1 R in Human Neuroblastoma NB-1 Cells. Neuropeptides; 2016; 60, pp. 83-89. [DOI: https://dx.doi.org/10.1016/j.npep.2016.09.004]
119. Falktoft, B.; Georg, B.; Fahrenkrug, J. Calmodulin Interacts with PAC1 and VPAC2 Receptors and Regulates PACAP-Induced FOS Expression in Human Neuroblastoma Cells. Neuropeptides; 2009; 43, pp. 53-61. [DOI: https://dx.doi.org/10.1016/j.npep.2009.02.001]
120. Falktoft, B.; Georg, B.; Fahrenkrug, J. Signaling Pathways in PACAP Regulation of VIP Gene Expression in Human Neuroblastoma Cells. Neuropeptides; 2009; 43, pp. 387-396. [DOI: https://dx.doi.org/10.1016/j.npep.2009.08.002]
121. Monaghan, T.K.; MacKenzie, C.J.; Plevin, R.; Lutz, E.M. PACAP-38 Induces Neuronal Differentiation of Human SH-SY5Y Neuroblastoma Cells via cAMP-mediated Activation of ERK and P38 MAP Kinases. J. Neurochem.; 2008; 104, pp. 74-88. [DOI: https://dx.doi.org/10.1111/j.1471-4159.2007.05018.x] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/17995938]
122. Monaghan, T.K.; Pou, C.; MacKenzie, C.J.; Plevin, R.; Lutz, E.M. Neurotrophic Actions of PACAP-38 and LIF on Human Neuroblastoma SH-SY5Y Cells. J. Mol. Neurosci.; 2008; 36, pp. 45-56. [DOI: https://dx.doi.org/10.1007/s12031-008-9082-6] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/18506635]
123. Deguil, J.; Jailloux, D.; Page, G.; Fauconneau, B.; Houeto, J.; Philippe, M.; Muller, J.; Pain, S. Neuroprotective Effects of Pituitary Adenylate Cyclase–Activating Polypeptide (PACAP) in MPP+-induced Alteration of Translational Control in Neuro-2a Neuroblastoma Cells. J. Neurosci. Res.; 2007; 85, pp. 2017-2025. [DOI: https://dx.doi.org/10.1002/jnr.21318] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/17492795]
124. Algarni, A.S.; Hargreaves, A.J.; Dickenson, J.M. Role of Transglutaminase 2 in PAC1 Receptor Mediated Protection against Hypoxia-Induced Cell Death and Neurite Outgrowth in Differentiating N2a Neuroblastoma Cells. Biochem. Pharmacol.; 2017; 128, pp. 55-73. [DOI: https://dx.doi.org/10.1016/j.bcp.2017.01.001]
125. Al Musaimi, O. Peptide Therapeutics: Unveiling the Potential against Cancer—A Journey through 1989. Cancers; 2024; 16, 1032. [DOI: https://dx.doi.org/10.3390/cancers16051032]
126. Li, C.M.; Haratipour, P.; Lingeman, R.G.; Perry, J.J.P.; Gu, L.; Hickey, R.J.; Malkas, L.H. Novel Peptide Therapeutic Approaches for Cancer Treatment. Cells; 2021; 10, 2908. [DOI: https://dx.doi.org/10.3390/cells10112908]
© 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.
Details
; Coveñas Rafael 2
1 Laboratory of Neuroanatomy of the Peptidergic Systems, Institute of Neurosciences of Castilla and León (INCYL), University of Salamanca, 37007 Salamanca, Spain; [email protected]
2 Laboratory of Neuroanatomy of the Peptidergic Systems, Institute of Neurosciences of Castilla and León (INCYL), University of Salamanca, 37007 Salamanca, Spain; [email protected], Group GIR USAL: BMD (Bases Moleculares del Desarrollo), University of Salamanca, 37007 Salamanca, Spain