Chemosensitization activities of scutellarin and 5-fluorouracil: the roles of caspase-6 activation and centrosome amplification Free

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We have recently reported that resveratrol (200 μM, 24 hours) evokes apoptosis of the HCT116 colon cancer cells through caspase-6 activation and lamin A cleavage (Proteomics, 2006). In the present study using the experimental model, we investigated apoptosis sensitization activities of scutellarin and 5-fluorouracil. Scutellarin, a natural compound from Chinese herbs, is under clinical trials for vascular protection. We found that scutellarin (50 to 100 μM) promoted resveratrol-elicited caspase-6 activation, lamin A cleavage and apoptosis in the cancer cells wild type for p53 (p53+/+). The sensitization effects were not detected in p53 knockout (p53-/-) cells. At the sensitizing doses, scutellarin alone did not cause caspase-6 activation or cell death. 5-fluorouracil (20 to 50 nM) also enhanced the resveratrol-evoked caspase-6 activation, lamin A cleavage and apoptosis of the cancer cells, but irrespective to their p53 status. Similarly, 5-fluorouracil alone did not trigger caspase-6 activation or apoptosis at the potent sensitizing doses. Moreover, we observed that spontaneous centrosome amplification was more frequent in the p53-/- cells, compared to their p53+/+ counterparts. The low doses of 5-fluorouracil significantly elicited centrosome amplification in both HCT116 cell lines, p53+/+ or p53-/-, to a comparable level. More interestingly, the cancer cells with centrosome amplification were more susceptible to death triggering by resveratrol, in the presence or absence of p53. The p53-/- cells without centrosome amplification were highly resistant to the death induction by resveratrol, while the p53+/+ cells without centrosome amplification still showed a moderate sensitivity. A higher level of caspase-6 activation was noted in the cancer cells (p53+/+ or p53-/-) with centrosome amplification, compared to those without multiple centrosomes. Taken together, the data imply that scutellarin and 5-fluorouracil sensitized resveratrol-evoked apoptosis of the colon cancer cells by promoting resveratrol-triggered death signalling (i.e., caspase-6 activation), in p53-dependent and p53-independent manners respectively. Centrosome amplification was also underlying the sensitization effect of 5-fluorouracil. We have, for the first time, documented the chemosensitization activity of scutellarin as well as a functional link between centrosome amplification and cell death sensitivity. Our results would benefit the pharmacological development of resveratrol, scutellarin and 5-fluorouracil as chemotherapeutic or chemosensitizing agents, and provide an initial trigger for the developments of novel cancer therapeutic plans involving induction of centrosome amplification.