MYC overexpression or amplification is commonly seen in a wide variety of tumor types, including multiple myeloma. Although MYC appears to be an important driver of the oncogenic phenotype, the helix-loop-helix topology, short half-life, and rapid replenishment of its encoded protein make it a particularly challenging drug target. However, the promoter region of the MYC gene contains a G-quadruplex (G4) DNA secondary structure that can be stabilized to block transcription. Recently, we reported the identification of a compound from a small molecule microarray screen that selectively binds the MYC G4, compared with other oncogenes that also contain G4s, and inhibits MYC mRNA and protein expression, leading to cell cycle arrest in human multiple myeloma cell lines (ACS Chem Biol. 2015). Here we describe the in vitro and in vivo evaluation of a more potent analog that retains the selectivity of the original compound for the MYC G4 sequence. After observing strong growth inhibitory activity of this new compound in a diverse panel of human cancer cell lines, we evaluated its pharmacokinetic and toxicity profiles in mice. Preliminary pharmacokinetic studies showed promising serum bioavailability and exposure properties when administered either intravenously or intraperitoneally. The compound was well tolerated in a month long, dose-escalation toxicity study in mice receiving daily administration of the compound. No adverse effects were observed during the study. In an assessment of short term in vivo activity, MYC expression was inhibited in multiple myeloma xenografts. More long-term studies to evaluate the anti-tumor activity of the compound are currently in progress. Thus, our data provide evidence that small molecule stabilization of the MYC G4 can drive transcriptional silencing of oncogenic MYC expression both in vitro and in vivo.

Citation Format: Elena C. Leon, John K. Simmons, David Calabrese, Wendy DuBois, Kenneth Felsenstein, Lindsey B. Saunders, Shuling Zhang, Aleksandra Michalowski, Frank Gonzalez, Beverly A. Mock, John S. Schneekloth. Selective inhibition of MYC expression by a small molecule G-quadruplex stabilizer. [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 322.