Monascus Pigment Rubropunctatin: A Potential Dual Agent for Cancer Chemotherapy and Phototherapy

The Monascus pigment, rubropunctatin, was extracted and purified from red mold rice (RMR), and its cytotoxic activities against human cervical carcinoma HeLa cells were studied under the conditions with or without light irradiation. The IC50 value of rubropunctatin against HeLa cells in the dark was 93.71 ± 1.96 μM (24 h), while the cytotoxic activity was enhanced more than 3 times (IC50 = 24.02 ± 2.17 μM) under light irradiation (halogen lamp, 500 W; wavelength, 597-622 nm; and fluence rate, 15 mW cm(-2), for 30 min). However, the IC50 value of rubropunctatin against the immortalized human cervical epithelial H8 cells was more than 300 μM, even under light irradiation, indicating that rubropunctatin has a favorable selectivity index (SI). Treatment of HeLa cells with rubropunctatin in the dark or under light irradiation resulted in a dose-dependent apoptosis, as validated by the increase in the percentage of cells in the sub-G1 phase and phosphatidylserine externalization, and the inductive effect on HeLa cell apoptosis was boosted by the light irradiation. In addition, treatment with rubropunctatin alone or under light irradiation was found to induce apoptosis in HeLa cells via the mitochondrial pathway, including loss of mitochondrial membrane potential, activation of caspase-3, caspase-8, and caspase-9, and increase of the level of intracellular reactive oxygen species (ROS). It was suggested that rubropunctatin could be a promising natural dual anticancer agent for photodynamic therapy and chemotherapy.