Ryodipine-induced enhancement of farmarubicin cytotoxicity against human leukemia cells in vitro.

Ryodipine is a recently developed dihydropyridine calcium channel blocker, chemically similar to nifedipine but with some advantages: light stability, low toxicity, etc. In recent years calcium antagonists have attracted attention not only with their cardiovascular activity but also as drugs increasing the antitumor effect of some cytostatics. In the present work the potentiating effect of ryodipine on the farmarubicin-induced cytotoxicity against K 562 human leukemia cells in vitro was evaluated. The cells were exposed to farmarubicin, ryodipine and combination of both drugs. The results obtained clearly demonstrated that a nontoxic concentration (0.5 microgram/ml) of ryodipine increased (about 5 times) farmarubicin cytotoxicity as the IC50 of the cytostatic was shifted from 1,86 ng/ml on single treatment to 0.37 ng/ml on combined treatment of the cells. The data presented suggest a role for ryodipine in the enhancement of the antitumor activity of some cytostaticts.