Inhibitory effects of gallic acid on the activity of exosomal secretory pathway in breast cancer cell lines: A possible anticancer impact.

Introduction: Breast cancer cells produce exosomes that promote tumorigenesis. The anticancer properties of gallic acid have been reported. However, the mechanism underlying its anticancer effect on the exosomal secretory pathway is still unclear. We investigated the effect of gallic acid on exosome biogenesis in breast cancer cell lines. Methods: The cytotoxic effect of gallic acid on MCF-10a, MCF-7, and MDA-MD-231 cells was measured by MTT assay after 48 hours treatment. Expression of miRNAs including miRNA-21, -155, and 182 as well as exosomal genes such as Rab27a, b, Rab11, Alix, and CD63; along with HSP-70 (autophagy gene), was determined using Q-PCR. The subcellular distribution of it was monitored by flow cytometry analysis. Isolated exosomes were characterized by transmission and scanning electron microscopes and flow cytometry. Acetylcholinesterase activity is used to measure the number of exosomes in supernatants. In addition, autophagy markers including LC3 and P62 were measured by ELISA. Results: Data showed that gallic acid was cytotoxic to cells (P < 0.05). Gallic acid modulated expression of miRNAs and down-regulated transcript levels of exosomal genes and up-regulated the HSP-70 gene in three cell lines (P < 0.05). The surface CD63/total CD63 ratio as well as acetylcholinesterase activity decreased in treated cells (P < 0.05). The protein level of LC3 was increased in three cell lines, while the expression of P62 increased in MCF-7 and MDA-MB-231 cancer cell lines. Conclusion: Together, gallic acid decreased the activity of the exosomal secretory pathway in breast cancer cell lines, providing evidence for its anti-cancer effects.