The long term goal of this initiative is to identify novel antagonists that target hedgehog (Hh) binding interactions important for Hh activity as the basis for the development of novel anti-cancer therapeutics. Aberrant expression of the Hh pathway has been implicated in the growth of approximately 20-25% of all cancers, with many driven by the over-expression of Hh ligand. Several natural product and chemical inhibitors that block Hh signaling have anti-tumor effects in models of cancer. These compounds work predominantly by targeting the Hh co-receptor Smoothened (Smo) or Gli transcription factor. Resistance to Smo inhibitors has been observed in the clinic and hence inhibitors targeting other components of the pathway are greatly needed. There is compelling evidence that heparin sulfate proteoglycans (HSPGs) are critically involved in Hh ligand trafficking and signaling activity with a role for HSPGs implicated by restriction in the range of Hh signaling in cells lacking the function of the tout velu gene, which encodes a heparin sulfate copolymerase. The goal of this proposal is to identify novel inhibitors of the Hh pathway by targeting the interaction of Hh ligand with HSPGs. We propose to do this using a novel Hh/heparin binding assay we have developed to identify molecules that can modulate heparin-Hh interactions. In this assay, unlabeled heparin molecules and the small molecule suramin inhibit this interaction and also blocked Hh activity in a cell based assay of Hh function. This assay will be used in high throughput mode to screen a library of 60,000 small molecules to identify small molecule antagonists of Hh/heparin binding. Small molecule mediated disruption of protein- protein interactions involving extracellular proteins such as Hh and their binding partners is challenging and we expect aptamer selection to provide an alternative and complementary approach to identifying antagonists of Hh protein mediated activity whether at the heparin binding site on Hh or elsewhere on the protein. Hence, the goals of the current proposal are to use the Hh/heparin binding assay as a primary screen to identify compounds from large chemical libraries that block Hh binding to heparin and to map the heparin binding site of Hh using synthetic peptides and (Specific Aim 1). To isolate and characterize Hh binding aptamers (Specific Aim 2). Use a series of secondary/orthogonal assays to first confirm and verify hits from primary screening and aptamers from the selection, and secondly identify those that selectively block Hh/HSPG association and inhibit Hh signaling in bioassays and affect proliferation, survival and migration of Hh- dependent cancer cell lines (Specific Aim 3). The various secondary and counter screens will be employed to further characterize the selectivity and activity of the identified molecules, setting the stage for future chemical optimization and subsequent in vivo models of cancer. We believe the resulting molecules will be especially valuable as research tools to better understand HSPG contributions to Hh activity and as novel inhibitors to probe diseases associated with Hh-ligand driven cancers.

PUBLIC HEALTH RELEVANCE: The Hedgehog (Hh) pathway is a compelling therapeutic target as it plays a central role in the growth of a vast array of human cancer types including those such as pancreatic, liver and lung with few effective treatment options. The few current inhibitors identified to date for the Hh pathway almost exclusively bind to the smoothened co-receptor or target the Gli transcription factors and hence inhibitors targeting the Hh pathway by alternative mechanisms are of great interest. There is accumulating evidence that the ability of Hh protein to function is modulated by heparin sulfate proteoglycans (HSPG), and so we propose to identify small molecule and DNA-based compounds that selectively block Hh/HSPG interactions, test them as inhibitors in cancers models and so potentially identify a novel therapeutic avenue for hedgehog- dependent cancers.

R15CA159209

2011-03-01

2015-02-28