A novel acetylated derivative of vitexin improves the immunogenic profile of breast cancer through tuning miR-20a/MICA Axis

Abstract

Background: The activating immune ligand, MICA, acts as a "kill me" signal through the NKG2D receptor expressed on natural killer (NK) cells that are key players in the fight against breast cancer (BC). Shedding of MICA during BC progression acts as a formidable barrier against NK cells' immune-surveillance. Recently, miR-20a was found to mediate immune escape through repressing MICA levels on BC cells. However, targeting miR-20a/MICA using natural compounds has seldomly been investigated. Vitexin, a flavone Cglycoside, showed potent anticancer properties. It was reported that acetylation of glycosides increases their cytotoxic activity, with an unknown impact on immunogenicity. Our group has successfully isolated 3'-O-acetylvitexin from Ocimum basilicum which showed potent cytotoxic effects against colon cancer cells but has never been investigated in BC. Our aim is to unravel the role of the immunogenic miR-20a/MICA axis in BC patients and its regulation by vitexin and 3'-O-acetylvitexin. Methods: Breast tissues were collected from 26 BC patients. ER, PR and HER2 expression was quantified using immunohistochemistry. MDA-MB-231 TNBC cells and MCF-7 HRþ BC cells were treated with serial dilutions of vitexin and 3'-O-acetylvitexin. Their cytotoxic activities were assessed using MTT, colony forming and migration assays. Total RNA was extracted, reverse transcribed, then MICA and miR-20a were quantified using qRT-PCR. Results: miR-20a is upregulated in BC patients, while MICA was downregulated in MDA-MB-231 compared to MCF7 cells. Vitexin decreased MDA-MB-231 cellular viability and migration capacity. 3'-O-acetylvitexin resulted in a more pronounced dosedependent repression of TNBC cellular viability, colonogenicity and migration capacity. Treatment with vitexin didn't show any alteration in miR-20a but showed only 2 folds increase in MICA. However, 3'-O-acetylvitexin markedly decreased miR-20a with a concomitant increase in MICA by 12 folds. Conclusions: 3'-O-acetylvitexin displays more pronounced anticancer properties against TNBC through halting their progression and immune suppressive nature by modulating miR-20a/MICA axis. This highlights miR-20a/MICA axis as a potential therapeutic target in BC.