Extrato de chá verde (Camellia sinensis): um potencial agente antitumoral em células de câncer de mama

Abstract

Green tea (GT), a beverage derived from Camellia sinensis, has been extensively studied for its antioxidant property, which is attributed to catechins. These phenolic compounds have been shown to inhibit carcinogenesis, but its mechanisms are still poorly understood. Additionally, most studies perform assays using isolated polyphenols from GT. We aimed to obtain a catechin-rich green tea extract (GTE) and to evaluate its antitumor potential on human breast cancer. Tea infusion was prepared on a ratio of 1 g: 40 mL of boiling distilled water using a combination of temperature and time (70, 75, 80, 85, 90, 95 and 100 ºC/5, 10, 15 min). Infusions were evaluated by polyphenols content (Folin Ciocalteu s reagent) and antioxidant potential (FRAP). Breast cancer cells (MDA-MB-231 and MCF-7) and non-tumoral cells (MCF-10A), were exposed to different concentrations of GTE (31.5 μg/mL to 1.0 mg/mL) during 24 h-48 h, and cell viability was assessed by Alamar Blue® and Trypan Blue assays. Viability was also acessed in the presence of p53 inhibitor, pifithrin-α. Immunocytochemistry and Western blotting analysis were performed to access the expression of p53. Our results demonstrated no influence of extraction condition in the total content of polyphenols and antioxidant potential of GT, and a new extract was obtained at 80 ºC/5 min, then freeze dried to be used in cell culture. After exposure for 24h, GTE already promoted a cytotoxic effect, reducing viability of both breast cancer cell lines (IC50 MDA-MB-231 = 138,8 μg/mL; IC50 MCF-7 = 324,5 μg/mL) without cytotoxic effect on normal cells (IC50 MCF-10A = 10097 μg/mL). In addition, GTE promotes an increase of p53 levels on treated MCF-7 cells, which express the wild-type form of the protein. Interestingly, an opposite phenomenon was evidenced in MDA-MB-231 cells, that express the mutated form of p53, in which protein levels seem to be lower in the presence of the extract. Our data suggests that GTE has anticarcinogenic potential on breast cancer and it is possible that this capacity might be related with the modulation of p53