DNA G-quadruplexes (G4s) have become increasingly present in modern drug discovery efforts. The main focus centers on cancer therapeutic development, as G4s are more concentrated in oncogenic promoters than the rest of the genome. Two of the most well described G4s to date are within the MYC and the VEGF promoters; stabilization of either structure fosters transcriptional silencing. Downregulation of MYC decreases cell proliferation and alters metabolism; it is promising for a number of cancers, such lymphomas, leukemia, colorectal cancer and more. VEGF downregulation would modulate angiogenesis, which is of therapeutic benefit for almost all solid tumors. The physiological structure of both of these promoter G4s has been elucidated using plasmid DMS footprinting, which incorporates DNA supercoiling in addition to stabilizing cations or molecules. The current study examines a variety of anhydrous or crowding co-solvents for their ability to recapitulate the physiological structure in single-stranded ex vivo conditions. The co-solvents tested included glucose, acetonitrile, polyethylene glycol, dextran sulfate, sucrose, ficoll, and extracted nucleoplasm, ranging from 0-40%. Significant changes in structure, including loop directionality and number of competing isoforms, were examined by electronic circular dichroism. Electromobility shift assays differentiated inter- and intra-molecular structures, further distinguishing the distribution of isoforms. DMS footprinting with select molecular crowding and dehydrating agents was performed and compared to plasmid footprints, to validate physiological mimicry ex vivo. Ongoing studies examining the physiological conditions regulating G4 stability and function include moving from plasmid to in cell DMS footprinting in order to most completely identify the physiologic isoform, and to using optimized co-solvents to examine the effects of small molecules ex vivo and better predict active hits for in vitro evaluation. Overall the VEGF and MYC promoter G4 structures are promising therapeutic targets for anti-angiogenic and anti-proliferative therapy, respectively. This comprehensive understanding of physiological principles governing the above G4 formation will best inform future drug discovery efforts for these and other oncogenic promoters.
Citation Format: Rhianna K. Morgan, Tracy A. Brooks. Physiological mimicry to characterize the average topology of the MYC and VEGF promoter G-quadruplexes. [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 3092.