Combinatorial cytotoxic effects of Curcuma longa and Zingiber officinale on the PC-3M prostate cancer cell line

Background: Many plant-derived products exhibit potent chemopreventive activity against animal tumor models as well as rodent and human cancer cell lines. They have low side effects and toxicity and presumably modulate the factors that are critical for cell proliferation, differentiation, senescence and apoptosis. The present study investigates the effects of some medicinal plant extracts from generally recognized as safe plants that may be useful in the prevention and treatment of cancer. Methods: Clonogenic assays using logarithmically-growing cells were performed to test the effect. The cytotoxic effects of Curcuma longa and Zingiber offi cinale were studied using sulforhodamine B assay, tetrazolium dye assay, colony morphology and microscopic analysis. Results: Out of the 13 lyophilized plant-derived extracts evaluated for growth-inhibitory effects on the PC-3M prostate cancer cell line, two extracts derived from C. longa and Z. offi cinale showed signifi cant inhibitory effects on colonyforming ability. The individual and augmentative effects of these two extracts were tested for their narrow range effective lower concentration on PC-3M in clonogenic assays. At relatively lower concentrations, C. longa showed signifi cant inhibition of colony formation in clonogenic assays; whereas at same concentrations Z. offi cinale showed only moderate inhibitory effects. However, when both the agents were tested together at the same concentrations, the combined effects were much more signifi cant than their individual ones. On normal prostate epithelial cells both C. longa and Z. offi cinale had similar effects but at a lower magnitude. These observations were confi rmed by several cytotoxicity assays involving the morphological appearance of the colonies, microscopic observations, per cent inhibition in comparison to control by sulforhodamine B and tetrazolium dye assay. Conclusions: From these observations, it was concluded that the combined effects of C. longa and Z. offi cinale are much greater than their individual effects, suggesting the role of multiple components and their synergistic mode of actions to elicit stronger benefi cial effects.