Modulators of hedgehog signaling
Image-based assay for selective identification of novel modulators of the Hedgehog pathway
Unmet need: new drugs to overcome drug resistant mutations of the Hedgehog pathway
The Hedgehog (Hh) pathway plays a critical role in a number of cancers. In solid tumors, such as basal cell carcinoma (BCC), the most prevalent cancer in the Caucasian population, and medulloblastoma (MB), the most common childhood brain cancer, constitutive activation of the Hh pathway within tumor cells leads directly to the initiation of the tumor. In other cancers, Hh signals from tumor cells appear to condition the local environment to favor tumor growth. This category includes a broad spectrum of high incidence cancers, particularly those in breast, lung, liver, stomach, pancreas, prostate, and gastro-intestinal tract. Broad screens for small-molecule inhibitors of Hh signaling have identified an essential membrane protein, Smoothened (Smo), as a druggable target. Two inhibitors (GDC-0449 [Genentech] and HPI926 [Infinity Pharmaceuticals]) have entered clinical trials. Phase I trials with GDC-0449, examining invasive or metastatic forms of BCC and medullablastoma, clearly demonstrate the effectiveness of anti-Smo agents in a number of patients. The studies also highlight the need for additional drugs to overcome drug resistant mutations that occur within Smo.
Innovations and Advantages
• An image-based high content screen for novel modulators of the Hedgehog pathway.
• Direct analysis of drug effects on Smoothened (Smo) translocation and accumulation in the primary cilium.
• A pilot screen of 8,000 compounds identified 26 Smo antagonists
• Optimized screen in progress
• Secondary screens to explore toxicity, specificity, potency and inhibitory activity on both wild-type and mutant forms of Smo resistant to current treatments.
• Submicromolar hit identified
• Structure-activity relationship (SAR) data and analogs are available.
• Demonstration of direct interaction with Smo and inhibition of Hh signaling
Professors Andrew McMahon and Lee Rubin of Harvard University have jointly developed an image-based assay for selective identification of novel modulators of the Hedgehog pathway. This novel high content screen focuses on the critical biology of Smo action. Smo is only active when present within a specific cell organelle, the primary cilium. By tagging Smo, and a non-Hh regulated cilial protein, with distinct fluorescent tags, our scientists are able to directly observe Smo movement into or out of the primary cilium (Wang et al, 2009). A pilot screen of 8,000 compounds, primarily from annotated and natural product-like libraries, identified 26 Smo antagonists. One of the hits has an IC50 of 0.8 µM. Structure-activity relationships (SAR) data of this hit and its analogs that inhibit Smo translocation are available. Using secondary assays developed in the Harvard labs, our scientists have shown a direct interaction of the hit compound with Smo and inhibition of Hh signaling.
The scientists have optimized the screen and are screening additional compound libraries to to identify a larger set of compounds that block Hh ligand-dependent Smo accumulation within the primary cilium. Secondary screens are in place to explore toxicity, specificity, potency and inhibitory activity on both wild-type and mutant forms of Smo that are resistant to current treatments. SAR will be probed using analogs of hit compounds. In addition, Smo antagonists will be analyzed for the suitability of further medicinal chemistry optimization and analysis in animal studies.
Intellectual Property Status: Patent(s) pending
Wang Y, Zhou Z, Walsh CT, McMahon AP. 2009. Selective translocation of intracellular Smoothened to the primary cilium in response to Hedgehog pathway modulation. Proc Natl Acad Sci U S A. 106(8):2623-8.
McMahon, Andrew P.
Rubin, Lee L.
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Vivian Berlin, Director of Business Development
Reference Harvard Case #3741