LAUSR

1) Background and Objective: Musashi-1(Msi1) is an RNA-binding protein that negatively regulates translation by binding to the 3′-UTRs of target mRNAs including Numb, APC and p21WAF-1, key regulators of Notch, Wnt signaling and cell cycle progression, respectively. We aim to identify small molecule inhibitors of Msi1’s mRNA-binding activity thus blocking the growth of a broad range of cancer cells. 2) Methods: Fluorescence polarization assay was used to screen for small molecules that disrupt the binding of Msi1 to its consensus RNA binding site. Hits were validated by surface plasmon resonance, amplified luminescent proximity homogeneous assay and nuclear magnetic resonance. 3) Results: Among ~2,000 small molecules we screened, we found several clusters of compounds that disrupt the Msi1-numb RNA binding potently, including natural products, herbal extracts and fungal metabolites. One of the clusters is the derivatives of the secondary metabolites from Aspergillus nidulans. The top hit, Aza-9, from this cluster was validated by amplified luminescent proximity homogeneous assay. Further validation by surface plasmon resonance and nuclear magnetic resonance indicate that Aza-9 binds to Msi1 directly, in the RNA binding pocket. 4) Discussion and Conclusions: Our study supports the hypothesis that Msi1 inhibition is a viable and effective anti-cancer strategy. More target validation assays will be carried out for the compounds from other clusters. Citation Format: Lan Lan, Amber Smith, Xiaoqing Wu, Anuradha Roy, Ragul Gowthaman, John Karanicolas, Amber D. Somoza, Clay C.C. Wang, Berl Oakley, Roberto De Guzman, Kristi Neufeld, Liang Xu. Discovery of novel small molecule inhibitors of RNA-binding protein Musashi-1 [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 1133. doi:10.1158/1538-7445.AM2017-1133