Piperafizine A is a natural methylated diketopiperazine first isolated from an actinomycete, Streptoverticillium. It potentiates the cytotoxicity of vincristine , an anti-cancer alkaloid known to be exported from cells by P-glycoprotein. Piperafizine A directs the intracellular accumulation of vincristine in cancer cells to a similar degree as verapamil , a P-glycoprotein inhibitor. The effects of piperafizine A on vincristine accumulation in cancer cells is dose-dependent over a range of 1 to 20 μg/ml.
