Abstract P5-07-03: Small molecule inhibition of smoothened in triple negative breast cancer-associated fibroblasts depletes cancer stem cells and sensitizes to cytotoxic chemotherapy in mice and humans

Abstract

Abstract The cellular and molecular basis of stromal cell recruitment, activation and crosstalk in carcinomas is poorly understood, limiting the development of targeted anti-stromal therapies. In mouse models of triple negative breast cancer (TNBC), we use single cell genomics to show that Hh ligand produced by neoplastic cells reprograms cancer-associated fibroblast (CAF) gene expression, driving tumor growth and metastasis. Hh-activated CAFs upregulated expression of FGF5 and deposition of fibrillar collagen, leading to FGFR and FAK activation in adjacent neoplastic cells and the acquisition of a stem-like, drug-resistant phenotype. Treatment with smoothened inhibitors (SMOi) reversed these phenotypes. Stromal treatment of TNBC patient-derived xenograft (PDX) models with SMOi downregulated the expression of cancer stem cell markers and sensitized tumors to docetaxel, leading to markedly improved survival and reduced metastatic burden. In the phase I clinical trial EDALINE, 3 patients with metastatic TNBC derived clinical benefit from combination therapy with the SMOi Sonedigib and docetaxel chemotherapy, with one patient experiencing a complete radiological response. Responders also exhibited high baseline FGFR activation and ECM deposition, suggesting a mechanism of action consistent with findings from the animal models. These studies identify Hh signaling to CAFs as a novel mediator of cancer stem cell plasticity and drug resistance and an exciting new therapeutic target in TNBC. Citation Format: Swarbrick A, Cazet A, Hui M, O'Toole S, Lim E, Martin M. Small molecule inhibition of smoothened in triple negative breast cancer-associated fibroblasts depletes cancer stem cells and sensitizes to cytotoxic chemotherapy in mice and humans [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-07-03.