Enhancement of the mutagenicity of anticancer drugs by the calcium antagonists verapamil and fendiline.

The enhancement of the mutagenicity of anticancer drugs by the calcium antagonists verapamil (CAS 52-53-9) and fendiline (CAS 13042-18-7) is reviewed. Both calcium antagonists enhance synergistically the induction of chromosome aberrations (dicentric and ring chromosomes) in cultured human lymphocytes by the antitumor agent bleomycin. Since two other calcium antagonists, nifedipine and diltiazem, when tested with the same system, did not show this effect, the comutagenicity of verapamil and fendiline does not seem to be related with calcium antagonism per se. Verapamil furthermore potentiates the induction of various chromosome and chromatid aberrations in Chinese hamster ovary (CHO) cells in vitro by the antitumor agent mitomycin C. In bacteria (Salmonella typhimurium) verapamil enhances synergistically the induction of gene mutations (frameshifts) by several anticancer drugs, including various anilinoacridine derivatives. When applied alone, neither verapamil which was tested in each of the three studies (human lymphocytes, CHO-cells, and bacteria) nor fendiline, which was tested only in human lymphocytes, proved to be mutagenic. To explain the comutagenicity of verapamil and fendiline, it is assumed that they prevent the mutagen (e.g., bleomycin) to be extruded from the cell. Consequently, the mutagen would be accumulated intracellularly and this would enhance its efficiency.