The purpose of the study was to investigate whether carvedilol has an antiproliferative effect alone and whether carvedilol provides an additive, synergistic or antagonistic effect on imatinib mesylate-induced cytotoxicity in both C6 glioma monolayer and spheroid culture. The C6 rat glioma chemoresistant experimental brain tumour cell line, that is notoriously difficult to treat with combination chemotherapy, was used both in monolayer and spheroid cultures. We treated C6 glioma cells with carvedilol alone and a combination of carvedilol and imatinib mesylate at a concentration of 10 µM. Following treatment, we evaluated cell proliferation index, bromodeoxyuridine labelling index (BrDU-LI), cell cycle distributions, apoptotic cell percentages, cAMP levels and three dimensional cell morphology at monolayer cultures. In addition BrDU-LI, volume and morphology of spheroids were also assessed. Carvedilol and imatinib mesylate alone reduced cell number, BrDU-LI, cAMP levels and spheroid volume. Carvedilol and imatinib mesylate arrested cells at G0/G1 phase in a time-dependent manner and time-independent manner, respectively. Carvedilol increased apoptosis rate only at the 24th h, but imatinib mesylate did for all time intervals. Interestingly carvedilol, drug with well-known protective effect on mitochondria, induced severe mitochondria damage, and imatinib mesylate induced autophagy confirmed only by transmission electron microscopy. These results suggest that carvedilol showed antitumour activity against rat C6 glioma cells and a combination of carvedilol with imatinib mesylate resulted in enhanced in vitro antitumour activity.

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