PGP and colonic neoplasm: For example, obacunone enhanced the effects of camptothecin (specifically proliferation inhibition and apoptosis activation [25 μM]) in human colon cancer cells [19] and reversed P-glycoprotein (P-gp)-induced multidrug resistance in drug-resistant human colon cancer HCT15 cells, thus significantly enhancing the cytotoxicity of paclitaxel [20].