Evaluation of ribociclib drug application in addition to TMZ-radiotherapy combined treatment in temozolomide (TMZ) sensitive U87MG glioblastoma cell line in terms of cell cycle

Objective: Glioblastoma Multiform (GBM) is known as the most common malignant brain tumor, accounting for 54% of gliomas and approximately 16% of all brain tumors. Ribociclib, one of the CDK4/6 inhibitors; It prevents the transition from G1 to S phase in the cell cycle. Our study aims to evaluate Ribociclib application in addition to TMZ and radiotherapy treatment in terms of cell survival and cell cycle, using the U87MG cell line. Method: TMZ-sensitive U87MG GBM cell line was used. The experimental plan was designed as control, TMZ, Ribociclib, vehicle and TMZ+Ribociclib groups. The experimental groups in which radiotherapy was applied were also included in the groups. The effect of TMZ and Ribociclib on the viability of U87MG cells was evaluated by MTT assay and IC50 (half maximum inhibitory concentration) values were found. Cells were irradiated at 2 Gray (Gy) per day for 5 consecutive days for a total of 10Gy. The effect of the determined effective doses on cell cycle and apoptosis was evaluated by analyzing cyclin D, p53, p21, Tap73, pRB and active caspase-3 protein levels by western blot. Results: IC50 values of Ribociclib and TMZ in U87MG cells, respectively; It was determined as 10 and 120μM. A decrease in cell viability was observed with the addition of radiotherapy 1 hour after the application of Ribociclib and TMZ alone and together (p<0.001). Additionally, our study revealed for the first time that their colony-forming potential is limited. The effects of ribociclib and TMZ on the cell cycle were interpreted with the determined proteins, and in addition, whether the apoptotic mechanism was mediated by TAp73 was evaluated for the first time. Conclusion: It has been demonstrated that Ribociclib in combination with TMZ can reduce the viability of aggressive GBM cells. In addition, our study shows that Ribociclib has the potential to be a new therapeutic for the treatment of GBM as an adjunct to TMZ.