Reversal of multi-drug resistance in human KB cell lines by structural analogs of verapamil.

Several structural analogs of verapamil were studied for their ability to reverse multi-drug resistance (MDR) in human KB cell lines. D595, D792 and verapamil completely reversed resistance to colchicine and adriamycin. D595 and D792 had a higher reversing potency than verapamil. Devapamil, gallopamil, emopamil and D528 partially reversed MDR. The reversing potency of a drug did not correlate with its calcium antagonistic activity. No differences in reversing potency between (R)-isomers, (L)-isomers and the racemic forms were observed in the case of both verapamil and emopamil. (R)-verapamil, which has less calcium antagonistic activity and less in vivo toxicity than racemic verapamil, and D792, which has higher reversing potency and less in vivo toxicity than racemic verapamil, should be suitable for clinical applications to overcome drug resistance in cancer patients.