Inhibitory effect of calcium channel blockers on growth of pancreatic cancer cells.

Calcium, which binds to calmodulin inside the cells, is an important mediator of various intracellular processes, including cell proliferation. We speculated that blockade of Ca2+ influx into the cells by Ca(2+)-channel blockers, such as phenytoin and verapamil, might affect the Ca(2+)-calmodulin pathway leading to suppression of cell growth. In this study, we examined the effect of phenytoin and verapamil on growth of two human pancreatic cancer cell lines, MIA PaCa-2 and CAV, in vitro and in vivo. Both phenytoin and verapamil inhibited growth of the two cell lines in a dose-dependent fashion. Phenytoin and verapamil each significantly prolonged doubling time of MIA PaCa-2 and the combination of the two drugs acted synergistically. The activity of ornithine decarboxylase, which is a rate-limiting enzyme of the polyamine pathway that is closely related to cell proliferation, was significantly inhibited by both drugs in a time-dependent fashion. Phenytoin, but not verapamil, inhibited growth of MIA PaCa-2 tumors xenotransplanted into nude mice, whereas both phenytoin and verapamil inhibited the growth of CAV tumors. Since phenytoin and verapamil are known to have fewer side effects than conventional antineoplastic drugs, these results suggest their possible use in novel therapeutic strategies.