Abstract 4853: BMVC specifically binds the major G-quadruplex structure formed in the c-MYC promoter to lower c-MYC levels

The c-MYC proto-oncogene is one of the most deregulated genes in human cancers. Transcriptional repression of c-MYC is considered as one of the attractive strategies in targeting c-MYC. Previous studies revealed that the c-MYC promoter nuclease hypersensitive element (NHE) III1 region, which regulates 80-95% of total c-MYC transcription, can form DNA G-quadruplex (G4) and that stabilization of the c-MYC G4 could repress c-MYC gene expression. We have previously determined the molecular structure of the major G-quadruplex formed in the c-MYC promoter NHE (MycG4), which is an intramolecular parallel-stranded structure. BMVC, a carbazole derivative, was designed as a fluorescent probe for recognizing telomeric G4. However, we found that BMVC binds to MycG4 with much greater affinity and specificity. Cellular studies showed that BMVC was enriched in the nucleus at 48 hr after treatment, leading to markedly reduced c-MYC expression levels. Promoter-driven luciferase assays revealed that BMVC could enhance the inhibitory effects of MycG4, suggesting BMVC can repress c-MYC expression in vivo through stabilization of MycG4. To understand the molecular interactions between BMVC and MycG4, we have determined the molecular structure of the complexes of BMVC with MycG4 by NMR. BMVC appears to bind the 5’-end of the MycG4 with very high affinity, as shown by the slow-exchange binding on the NMR timescale. The structure of the 5’-end complex of BMVC and MycG4 shows that BMVC is paired to the flanking adenine with specific hydrogen bonding interactions, while the BMVC-adenine plane stacks nicely on the 5’-end G-tetrad of MycG4. Compared to the previous MycG4 complex with a quindoline compound, the tighter and more specific binding of BMVC appears to be imparted by the novel arched shape of BMVC and specific pairing recognition of BMVC with the flanking bases of MycG4. BMVC can also bind to the 3’-end of MycG4 with lower affinity to form a second complex. However, the 3’-end complex shows much more dynamic conformation and less specific interactions. Our results indicated that the cellular targets of BMVC include not only telomeric G4, but also the c-MYC promoter G4. Because of the inherent fluorescence and novel binding mode of BMVC, our study provides useful information for future design of improved carbazole-based anticancer agents or specific cellular fluorescent probes, as well as insights into specific recognition of MycG4 by small molecules. Citation Format: Wenting Liu, Guanhui Wu, Clement Lin, Buket Onel, Ding Chen, Ta-Chau Chang, Danzhou Yang. BMVC specifically binds the major G-quadruplex structure formed in the c-MYC promoter to lower c-MYC levels. [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 4853.