Understanding the unique pathways of IBC cell survival and motility

Abstract

Inflammatory breast cancer (IBC) is a dreadful disease because of its rapid onset, highly invasive nature and lack of definitive treatment strategies. The underlying differences between conventional breast cancer and IBC have identified that IBC carries a unique identity, which needs to be explored and researched extensively to achieve better prognosis and disease free survival rate. Working towards the same goal, this project focuses on deciphering two unique molecular pathways that regulate IBC cell invasion and survival.

The first part of this dissertation studies the overall distribution of upregulated caveolin-1 in IBC cells in vitro and identifies the role of caveolin-1 in decreasing IBC cell invasion by manipulating either the expression by siRNA specific against caveolin-1, function by treatment of exogenous caveolin-1 scaffolding domain or the assembly of caveolin-1 with methyl-β-cyclodextrine (MβCD) treatment. Due to the scaffolding nature of caveolin-1 and previous data suggesting the involvement of RhoC GTPase in the invasive and metastatic phenotype of IBC, this project seeks to determine the co-localization of caveolin-1 and RhoC GTPase. Based on the data, I speculate that caveolin-1 regulation of RhoC GTPase activity requires presence of intermediate modulators such as Rho specific GEFs or GAPs in caveolae that ultimately cause RhoC GTPase activation and cell invasion.

The later part of this project concentrates on targeting Platelet Derived Growth Factor Receptor α (PDGFRα) by small molecule inhibitors namely, Imatinib and Crenolanib. This study is based on the earlier data that reports higher expression and signaling of PDGFRα in IBC patients when compared to non-IBC patients. The overall goals of this part of the project are to characterize PDGFRα in IBC cell lines in vitro and evaluate the efficacy of two receptor tyrosine kinase inhibitor molecules against PDGFRα in regulating IBC cell survival in vitro and in vivo. Intracellular localization pattern of PDGFRα and presence of PDGF ligands in SUM149 IBC cells indicated involvement of the autocrine activation mechanism. PDGFRα targeting by Crenolanib was found to affect IBC cell survival, growth, emboli formation and thus exhibits cytostatic effect on IBC tumor in vivo. On the other hand, Imatinib treatment over a wide concentration range failed to render any response on IBC survival. I further extended Crenolanib studies to determine if Crenolanib treatment can make IBC cells chemosensitive (reduction in the dose of current systemic chemotherapy). This was tested by treating IBC cells with Crenolanib and Docetaxel (systemic chemotherapy) either alone or in combination to evaluate the changes in cell survival. I found significant decrease in cell survival upon combination treatment of Crenolanib and Docetaxel as compared to individual treatments. Further research with respect to the mutational status and structure of PDGRα needs to be undertaken to address the possible reasons for intracellular localization of PDGRα and Imatinib resistance in IBC.

Thus, this project studies two potential biomarkers, caveolin-1 and PDGFRα that would benefit patients with early IBC detection. Understanding the role of caveolin-1 in RhoC GTPase mediated IBC invasion provides an insight into the IBC molecular pecularities. On the other hand, targeting PDGFRα by Crenolanib offers promising neoadjuvant or adjuvant chemotherapy to minimize the loco-regional spread and to achieve longer disease free survival by preventing the IBC recurrence.