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Introduction
Resistance to ionizing radiation is one of the major obstacles for successful killing of cancer cells with radiotherapy. Indeed, radiation induces the activation of multiple signaling pathways, causing cancer cells to become inactivated and resulting in diverse types of stress responses, including apoptosis, cell cycle arrest, and senescence.1 However, a subset of human malignancies fails to respond to radiotherapy, as they are resistant to radiation-induced apoptosis.1,2 Thus, the identification of novel mechanisms of resistance to radiation may aid to overcome radioresistance, improve radiotherapy efficacy and, ultimately, personalize treatments.2
Preoperative chemoradiation is currently the standard of care for locally advanced rectal adenocarcinoma, obtaining tumor downstaging and lower rates of local failure.3 Indeed, total mesorectal excision is curative for small rectal tumors, but the risk of locoregional recurrence, distant metastasis, and death increases with tumors extending through the muscularis propria (tumor-nodes-metastasis (TNM), T3 or T4) or with nodal involvement (TNM, N1 or N2).3 In such a context, neoadjuvant chemoradiotherapy results in a wide spectrum of clinical responses and the magnitude of benefit is heterogeneous: while the achievement of pathological complete response is feasible in many patients, a subset of rectal carcinomas are not fully responsive to radiation.4 Thus, the identification of biomarkers predictive of resistance to preoperative chemoradiation and the characterization of novel targets to improve response to radiotherapy are area of active research in rectal cancer.
Advanced colorectal carcinomas (CRCs) bearing the BRAF V600E mutation are largely acknowledged as aggressive malignancies with poor prognosis and lack of response to anticancer therapies.5 By contrast, conflicting results have been proposed on the role of BRAF mutations in driving the sensitivity of rectal carcinoma cells to radiation, with some studies showing poor responses and others no influence.6–9 Thus, this study was designed to evaluate in vitro the radiosensitivity of CRC cells with different RAS/BRAF mutational profiles and exploit cyclin-dependent kinase 1 (CDK1) targeting as a strategy to improve efficacy of radiation therapy in BRAF V600E tumor cells.
Materials and methods
Cell lines, chemicals, constructs, and siRNAs
Human CRC RAS/BRAF wild-type COLO320, KRAS G13D HCT116, and BRAF V600E HT29 cells were purchased from the American Type Culture Collection (ATCC LGS Standards, Sesto San Giovanni, Milan, Italy). Cell line authentication was verified...