A Low Dose of Aripiprazole Has the Strongest Sensitization Effect Among 19 Repositioned Bipolar Drugs in P-gp-overexpressing Drug-resistant Cancer Cells.

Background/aim We investigated drugs that could sensitize P-glycoprotein (P-gp)-overexpressing drug-resistant cancer cells to vincristine (VIC) or eribulin treatment and assessed their associated mechanisms of action. Materials and methods We investigated 15 bipolar drugs (quetiapine, risperidone, clozapine, asenapine, iloperidone, paliperidone, ziprasidone, trifluoperazine, loxapine succinate, pilocarpine, valproic acid, carbamazepine, levetiracetam, topiramate, and felbamate) to identify drugs with a sensitizing effect on VIC-resistant KBV20C cells at relatively low doses. Fluorescence-activated cell sorting (FACS), annexin V analyses, and rhodamine uptake tests were performed to further investigate the mechanism of action. Results We found that co-treatment with half the tested drugs (quetiapine, iloperidone, trifluoperazine, loxapine, risperidone, ziprasidone, or felbamate) at low doses could highly sensitize VIC-resistant KBV20C cells. With lower amounts of the bipolar drugs or VIC, we found that among the 15 bipolar drugs tested, 2 combinations (VIC-quetiapine and VIC-trifluoperazine) had much higher sensitization effects, suggesting that lower effective doses were sufficient for sensitizing P-gp-overexpressing resistant cells compared to those required with the other drugs. Furthermore, when we compared quetiapine and trifluoperazine to previously known bipolar drugs (fluphenazine, thioridazine, pimozide, or aripiprazole), we found that aripiprazole, administered at lower doses, had a much higher sensitization effect. We also demonstrated that co-treatment with another anti-mitotic drug (eribulin) increased the sensitization of KBV20C cells similar to VIC. We also found that aripiprazole had higher P-gp-inhibitory activity than the other bipolar drugs, indicating that this activity was involved in the higher level of VIC-aripiprazole sensitization. Conclusion Co-treatment of anti-mitotic drug-resistant cancer cells with a low dose of aripiprazole had the strongest sensitization effect and is highly dependent on P-gp-inhibitory activity.