Glycoalkaloid Solasonine Targets SHH Signaling to Block MED12 Mutant Breast Cancer Oncogenesis

Abstract

As breast cancer is the second leading cause of cancer deaths among American women, there is a strong need to find improved treatment strategies for this disease. Radiation and chemotherapy are the frontline choice of treatment; however, personalized treatment is rapidly on the rise as a superior treatment method. Through prior studies, it has been found that 67% of breast cancer tumors carry a mutation in the Mediator subunit MED12 thus indicating that MED12 likely has a critical tumor suppressive role in the breast. Interestingly, previous results from our lab, and others, have indicated that MED12 plays a role in restricting GLI3‐dependent SHH signaling. This finding is of importance to this study as hyper‐activated SHH signaling is known to play a role in promoting breast cancer oncogenesis. We thus hypothesize that MED12 mutations cause breast cancer oncogenenesis through hyperactivated SHH signaling, and furthermore, that drugs which target the SHH signaling pathway could prove to be beneficial for MED12 mutant breast cancer. Through proliferation assays and quantitative PCR analysis, we were able to conclude that MED12 mutations, as mimicked by a MED12 knockdown setting, enhance breast cancer cell growth and promote GLI3‐dependent SHH signaling. Through a MTT screening strategy, we found that the natural compound Solasonine can differentially target MED12 knockdown breast cancer cells. Solasonine is a known glycoalkaloid that has previously been shown to potentially target anti‐inflammatory signaling pathways. To study the effect of Solasonine on MED12 knockdown breast cancer cells, quantitative PCR was used to measure the levels of GLI3 target genes in cells treated with either vehicle or Solasonine. We found that Solasonine treatment significantly decreased the GLI3 target genes GLI1 and CREB 5 thus suggesting that Solasonine could target the GLI3‐dependent SHH signaling pathway to block breast cancer oncogenesis. These findings were further complemented by colony formation assays which showed that Solasonine treatment leads to a significant reduction in the formation of colonies in vitro. Overall, our findings suggest that Solasonine targets the SHH signaling pathway to block breast cancer oncogenesis and may therefore prove to be a superior treatment method for MED12 mutant breast cancer.