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

Calcium, which binds to calmodulin inside the cell, is an important mediator of various intracellular pro-cesses, including cell proliferation. We speculated that blockade of Ca²⁺influx into the cells by Ca²⁺-channel blockers, such as phenytoin and verapamil, might affect the Ca²⁺-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 drugsacted synergistically. The activity of ornithine decarbox-ylase, 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.