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The study aimed to disclose the anti-cancer activity of Pluchea indica tea leaves by evaluating the cytotoxicity on breast and cervical cancer cells, compared with non-cancer cells.

Two P. indica extracts were prepared using two solvents, namely hot water (PA) and ethanol (PE). MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) and clonogenic assays were applied to determine cytotoxic effect of both extracts toward cancer cells from human breast (MDA-MB-231 and MCF7) and cervix (SiHa, HeLa and C-33A) and also non-cancer Vero cells. Dichlorofluorescein diacetate (DCFDA)-staining assay was used to quantify the intracellular level of the reactive oxygen species (ROS). Correlation between the quantity of compounds present and the cytotoxicity of the extracts was analyzed by Pearson's method and a possible class of bioactive compounds was proposed based on the highest correlation coefficient (r).

Significant reduction in cell viability and proliferation capability was observed in all cancer cells after treatment with either PA or PE extract albeit PE was more effective. Lower toxicity was detected in Vero cells, indicating the selectivity and safety of extracts. The intracellular ROS level was augmented in treated cancer cells which were inversely correlated to cell viability, suggesting the cancer toxicity was likely induced by intracellular oxidative stress. As flavonoids were found abundantly in the extracts and flavonoids' content was the most related to the activity (r = 0.815), it was hypothesized that the flavonoids might play crucial roles in cancer cytotoxicity.

P. indica tea-leaf extracts can be a good source of promising anti-cancer agents with reduced side effects for breast and cervical cancer treatment.