Concurrent inhibition of GLI and SMO is a novel therapeutic strategy to control Breast Cancer Stem Cells

Abstract

Background: Hedgehog (Hh) signalling pathway is implicated in pathogenesis in a variety of solid and hematologic malignancies. Smoothened (SMO) plays a critical role in regulation of the Hh pathway, however, noncanonical mechanisms can activate the pathway in SMO independent manner. Even there are available drugs to target Hh pathway, its clinical application in breast cancer is limited at this moment. Hh pathway is a significant contributor to survival and maintenance of cancer stem cells (CSCs). In this study, we revealed prognostic meanings of Hh pathway upregulation and effective strategies to target Hh pathway in breast cancer. Results: The systematic review showed that Hh upregulation, especially GLI1 overexpression, increased recurrence risk and worsened overall survival outcome. Hh upregulation is found in adherent cell lines of breast cancer and the tendency became enhanced in their sphere pairs. Hh inhibition by GANT61 (GLI1/2 inhibitor) or by glasdegib (SMO inhibitor) suppressed cell viability, breast cancer stem cell (BCSC) properties and cell invasion. Concurrent inhibition of GLIs and SMO synergistically reduced viability and sphere formation of breast cancer cells. Methods: Publications searched as of July 31st 2015

3 studies were pooled to evaluate odds ratio of recurrence risk and 3 studies were summarized to evaluate hazard ratios of overall survival in GLI1 overexpressed group. mRNA expression level was analysed in ZR-75-1, MCF7, Hs578T, MDA-MB-231, MDA-MB-436 and there sphere cells. The rate of CD44 and CD24 expression is analysed by FACS. GANT61 or siRNA against GLI1 and glasdegib were treated in adherent cells or sphere cells of breast cancer. Antagonistic effects and inhibitory doses in adherent cells were calculated in standard curves. Combination indexes were calculated following Chou-Talay model. Conclusions: Hh pathway is activated in breast cancer and the activation is associated with unfavourable prognosis in breast cancer patients according to systematic review and meta-analysis with published data. This study revealed concurrent inhibition of GLI and SMO is an effective strategy to target Hh pathway. Validating investigation in vivo is warranted.