Abstract B72: Identification of hedgehog signaling between ovarian tumors and carcinoma associated mesenchymal stem cells

Introduction: Mesenchymal stem cells (MSCs) are emerging as an important component of the tumor microenvironment. However, controversy surrounds their effect on tumor growth. We characterized human ovarian carcinoma associated mesenchymal stem cells (CA-MSCs). These CA-MSCs significantly promote tumor growth and increase the cancer stem cell population. CA-MSCs have a unique expression profile with increased BMP expression. Hedgehog (HH) signaling, which is critical in development, stem cell function and cancer, is an important regulator of BMP expression. Interestingly, HH signaling may promote tumor growth through paracrine activation of the tumor stroma. We therefore hypothesize that the induction of BMP expression in CA-MSCs may be mediated through hedgehog signaling. Methods: We used primary ovarian tumors, SKOV3, and ID8 ovarian cancer cell lines, and a Gli-1/LacZ reporter mouse model, to evaluate the presence of HH and HH signaling molecules in ovarian tumors and stroma. Adipose derived MSCs (Ad-MSC) and primary human ovarian CA-MSCs were used to determine HH signaling responsiveness. Results: Consistent with previous reports, we found that HH and HH receptors/signaling/response proteins (SMO, PTCH, GLI1, GLI3) are present in primary ovarian tumors. Response to HH signaling in normal ovary (as assessed through Gli-1/LacZ reporter mice) was largely seen in the stromal cells rather than epithelial cells. Stromal HH signaling was also observed in ID8 tumors injected in Gli-1/LacZ reporter mice. Hedgehog treatment of Ad-MCS and CA-MSCs resulted in clear dose dependent activation of HH responsive transcriptional targets including expression of hedgehog itself. BMP4 expression was induced in both Ad-MSC and CA-MSCs, however CA-MSCs had higher baseline BMP4 expression and demonstrated a 1000-fold increase in BMP4 expression with HH treatment. In addition, CA-MSCs treated with HH had increased expression of the HH receptor SMO, leading to an altered SMO:PTCH/receptor:inhibitor ratio. Thus a positive feedback loop may explain the hyper-responsiveness of CA-MSC to HH signaling. Treatment of MSCs with tumor conditioned media can induce similar expression patterns indicating the tumor is signaling to its stroma through HH. Conclusions: Hedgehog is present in ovarian cancer and high levels have been associated with poor prognosis. We demonstrate that ovarian cancer cells make HH and MSCs respond to HH signaling with increased expression of BMP4. We previously demonstrated BMP4 can then feedback to influence tumor ‘stemness’. The increased BMP4 expression in CA-MSCs is in conjunction with hyper-responsiveness to HH signaling, possibly through altered levels of HH signaling pathway components. Experiments are ongoing to determine if this finding may explain the lack of clinical benefit observed with HH inhibitors in epithelial tumors; CA-MSCs may be a mechanism of resistance through increased sensitivity to HH signaling. Citation Format: Lan Coffman, Yunjung Choi, Ronald Buckanovich. Identification of hedgehog signaling between ovarian tumors and carcinoma associated mesenchymal stem cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B72.