Abstract PR10: Novel hedgehog co-receptors in pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest human malignancies, with a dismal six month median survival. Currently there is inadequate understanding of the molecular mechanisms behind PDAC initiation and progression from pancreatic intraepithelial neoplasia (PanINs), the most common precursor lesions, to full blown carcinoma. Thus, there is a lack of effective treatment modalities. The Hedgehog (Hh) signaling pathway plays an important role in PDAC; 75% of PDAC cases display increased expression of Hh ligands. In fact, Hh signaling is found in early PanIN lesions and promotes tumor growth, and persists as the cancer progresses. Interestingly, Hh ligands do not act on the tumor cells themselves, but instead function in a paracrine manner, signaling to the surrounding tumor stroma, which in turn promotes tumor progression. PDAC is characterized by a highly desmoplastic stroma, however the mechanisms that activate Hh signaling in the stroma are currently not well understood, and represent potential therapeutic targets. Hh pathway activation involves the binding of Hh ligands to the canonical receptor, Patched1 (Ptch1). This terminates Ptch1-mediated repression of Smoothened (Smo) and furthers downstream effects through activation of the Gli family of transcription factors. Recently, new co-receptors were identified that play an essential role in Hh pathway function. CAMrelated/down-regulated by oncogenes (Cdo), Brother of Cdo (Boc), and Growth arrest-specific 1 (Gas1) all cooperate with Ptch1 to promote Hh signaling during development. A central question is to what degree these receptors act to mediate Hh pathway function in adult tissues, especially in Hh-driven diseases, such as PDAC. Our data reveals that in the healthy pancreas, Boc and Gas1 are expressed in a perivascular and periductal manner in both fibroblasts and stellate cells as shown by co-stains with αSMA and vimentin. We did not detect Cdo expression. Interestingly, during cancer progression, Gas1 and Boc expression is significantly increased throughout the cancer stroma. This finding is notable as expression of Gli2, a vital transcription factor in the Hh pathway, is also significantly increased in the stroma during tumorigenesis. Functional studies on Boc -/- ;Gas1 -/- mouse embryonic fibroblasts (MEFs) treated with Hh ligand showed a drastic reduction in Hh response compared to wild-type MEFs, indicating that these co-receptors are important for Hh signal transduction. To further functionally characterize these receptors, we performed co-injection experiments with wild-type pancreatic fibroblasts and tumor cells or Boc -/- ;Gas1 -/- fibroblasts and tumor cells to determine the effect of co-receptor loss on tumor growth. Strikingly, tumors co-injected with Boc -/- ;Gas1 -/- fibroblasts formed significantly larger tumors. Histological analysis revealed that these tumors had a higher degree of vascularity. Future studies include dissecting the manner in which mutant fibroblasts support increased vascularity and whether this increase renders these tumors more susceptible to chemotherapy. This abstract is also presented as poster B37. Citation Format: Esha Mathew, Benjamin L. Allen, Marina Pasca di Magliano. Novel hedgehog co-receptors in pancreatic cancer progression. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr PR10.