Aging-related repositioned drugs, donepezil and sildenafil citrate, increase apoptosis of anti-mitotic drug-resistant KBV20C cells through different molecular mechanisms

Background/Aim: The study focused on identifying the mechanisms or drugs that could sensitize P-glycoprotein (P-gp)-overexpressing resistant KBV20C cancer cells to halaven (HAL) or vincristine (VIC) treatment. Materials and Methods: Based on the relatively low dose or IC₅₀ values for sensitizing anti-mitotic drug-resistant KBV20C cells, the aging-related drugs donepezil (DON) and sildenafil citrate (SID) were selected. Fluorescence-activated cell sorting (FACS), western blotting, and annexin V analyses were performed to investigate the mechanism of action of DON and SID in HAL-treated KBV20C cells. Results: DON or SID reduced cell viability, increased G₂ arrest, and up-regulated the expression of the DNA damaging protein pH2AX when used as co-treatment with HAL. DON and SID induced both early and late apoptosis in KBV20C cells in response to HAL treatment, without increasing autophagy. VIC-DON and VIC-SID co-treatments increased sensitization of KBV20C cells, suggesting that DON and SID can be combined with other anti-mitotic drugs for sensitizing resistant cancer cells. When the sensitization efficacies of DON and SID were compared to that of the anti-psychotic repositioned drug fluphenazine (FLU), HAL-SID or HAL-FLU co-treatments were found to have better sensitization effects than HAL-DON suggesting that HAL-SID sensitization mechanism is different from that of HAL-DON. In addition, DON was found to have higher P-gp inhibitory activity than FLU or SID. Conclusion: These results suggest that HAL-FLU or HAL-SID sensitization in KBV20C cells involves both cytotoxic and P-gp inhibitory effects, whereas HAL-DON sensitization may involve only P-gp inhibitory activity of DON.