Abstract 4817: Molecular cancer therapy targeting RNA-binding protein Musashi-1

Abstract

Abstract Musashi-1 (MSI1) is an evolutionarily conserved RNA-binding protein best studied for its role in post-transcriptional regulation of target mRNAs. Elevated MSI1 levels in a variety of human cancers including colon cancer are associated with up-regulation of Notch/Wnt signaling. MSI1 binds to and negatively regulates translation of Numb and APC (adenomatous polyposis coli), negative regulators of Notch and Wnt signaling respectively. Our hypothesis is that, small molecules disrupting MSI1-RNA binding will remove translational control of MSI1 over Numb/APC, which will in turn inhibit Notch/Wnt signaling. Previously we have shown natural product (-)-gossypol as the first small molecule inhibitor of MSI1 that down-regulates Notch/Wnt signaling and inhibits tumor xenograft growth in vivo. Here we identified gossypolone (Gn), a major metabolite of gossypol, as a more potent MSI1inhibitor with more than 20-fold increase in Ki value in our fluorescence polarization binding assay. Further validation of Gn-MSI1 binding was carried out by surface plasmon resonance and nuclear magnetic resonance. In colon cancer cells, Gn reduced Notch/Wnt signaling and induced apoptosis. However, the same concentration of Gn is less active than that of (-)-gossypol in all of the cell assays tested. In order to increase Gn bioavailability, we used the PEGylated liposome in our in vivo studies. Properties of gossypolone-liposome (Gn-lip) were evaluated by transmission electron microscopy and a Zetasizer Nano ZS90 instrument; cytotoxicity of free liposomes as compared to Gn-lip and Gn was also evaluated. To further characterize the in vivo tumor-specific accumulation of liposomes, a near-infrared (NIR) fluorescent dye DiR was used. NIR imaging demonstrated tumor-targeted delivery of DiR-loaded liposomes in DLD-1 xenografts in SCID mice. Gn-lip via tail vein injection twice weekly inhibited the growth of human colon cancer DLD-1 xenografts in nude mice, as compared to the untreated control (P < 0.01, n = 10). Our data suggest that Gn-lip improved the bioavailability of Gn as well as achieved tumor-targeted delivery and controlled release of Gn, which enhances its overall biocompatibility and drug efficacy in vivo. Our study provides a proof-of-concept to develop the Gn-lip as a novel molecular therapy for colon cancer with MSI1 overexpression. Citation Format: Lan Lan, Hao Liu, Amber Smith, Carl Appelman, Jia Yu, Sarah Larsen, Rebecca Marquez, Xiaoqing Wu, Philip Gao, Ragul Gowthaman, John Karanicolas, Roberto De Guzman, Steven Rogers, Jeffrey Aubé, Kristi Neufeld, Liang Xu. Molecular cancer therapy targeting RNA-binding protein Musashi-1. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4817.