Abstract PR12: Selective targeting of MYC mRNA by chemically stabilized antisense oligonucleotides

Despite its well-characterized properties as a proto-oncogene in numerous cancers, direct potent and selective inhibition of MYC or its protein product c-Myc with cell-permeable synthetic agents remains a significant challenge. Systemic inhibition of c-Myc activity in mice by expression of dominant negative MYC transgenes has been shown to dramatically decrease tumor burden with apparently tolerable side effects (Soucek et al, Nature 2008). In order to ultimately realize the goal of therapeutic MYC inhibition in cancer, we have initiated discovery chemistry efforts aimed at inhibiting MYC at the transcriptional, translational, and post-translational level. Here we describe the application of synthetic antisense oligonucleotides designed to target specific sequences of the MYC mRNA (MYCASOs). We have incorporated several chemical features into MYCASOs, including the addition of locked nucleic acid (LNA) bases at the 59 and 39 ends, phosphorothioate linkers, and internal DNA bases in order to increase mRNA target affinity and cleavage, cellular permeability, stability, and systemic distribution in vivo. Treatment of MYC¬-expressing cancer cells with MYCASOs leads to a potent decrease in MYC mRNA and c-Myc protein levels. Cleaved MYC mRNA in MYCASO-treated cells is detected with a sensitive 59 rapid amplification of cDNA ends (RACE) assay. MYCASO-treatment of cancer cell lines leads to significant inhibition of cellular proliferation and induces apoptosis in c-Myc-dependent myeloma and leukemia cell lines while decreasing c-Myc-mediated gene expression. In vivo administration of MYCASOs simply dissolved in saline was performed in mice by tail vein injection. MYCASOs are well tolerated up to 25 mg per kg on a twice-weekly dosing regimen. In a MYC-induced model of hepatocellular carcinoma, MYCASO treatment leads to detectable cleavage of the MYC transcript, decreases c-Myc levels within tumors, and significantly decreases tumor burden. MYCASOs represent a new chemical tool for in vitro and in vivo modulation of c-Myc activity, and promising therapeutic agents for MYC-driven tumors. Citation Format: Christopher J. Ott, Raj Bandaru, Taylor Gill, Junyan Tao, Xin Chen, Yixian Zhang, James E. Bradner. Selective targeting of MYC mRNA by chemically stabilized antisense oligonucleotides. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr PR12.