To cite some examples, exposure to mahanine, a carbazole alkaloid from Micromelum minutum, was found to be responsible for the negative modulation of the cellular levels of selected DNA methyltransferases in prostate tumor cells, thereby restoring the expression of the epigenetically silenced tumor suppressor gene RASSF1A (Ras Association Domain Family Member 1). The gene discussed is RASSF1; the disease is prostate neoplasm.