LAUSR

We have generated a mouse model of Superficial Basal Cell Carcinoma (BCC) to study the effect of the Smoothened inhibitor vismodegib in vivo. Despite the potency of vimodegib in blocking Hedgehog (Hh) signaling and efficacy in treatment of BCC, residual disease persists in the mouse model. To better understand the Biology of BCC and the potential mechanisms maintaining BCC during treatment, we profiled isolated untreated as well as residual tumors. We found that treated tumors change their transcriptional program to resemble the cells of skin and hair follicle structures like the Interfollicular Epidermis (IFE) and Isthmus, both of which harbor stem cell compartments. Consistent with these findings, residual disease lacks expression of epidermal differentiation markers and initiates growth upon cessation of treatment. While Wnt signaling is clearly required for BCC initiation in mouse models, we show that Wnt signaling is down-regulated in untreated full-blown disease and subsequently strongly induced in the treated tumors. We hypothesize that re-initiation of the Wnt pathway maintains BCC and study the effect of blocking both Wnt and Hh pathways with combined treatment of vismodegib and Wnt inhibitors. Citation Format: Brian Biehs, Gerrit J. Dijkgraaf, Bruno Alicke, Franklin Peale, Stephen E. Gould, Frederic J. de Sauvage. Characterization of residual Basal Cell Carcinoma after vismodegib treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-136. doi:10.1158/1538-7445.AM2017-LB-136