Abstract 2752: Recognition of the hybrid-1 human telomeric G-quadruplex by a platinum(II)-based compound

The human telomeric DNA, which consists of tandem repeat sequences of d(TTAGGG)n, plays an important role in cancers and cell aging. Previous studies in human cancer cells have demonstrated DNA G-quadruplex (G4) structure formation in telomeres. G-quadruplexes are four-stranded structures formed in guanine-rich sequences that are held together by guanine-guanine Hoogsteen hydrogen bonding, and G-quadruplex stabilization by small molecules induces tumor cell senescence and apoptosis by repressing telomerase activity and the DNA damage response pathway. Additionally, telomeric-overhang DNA can form biologically relevant higher-order DNA structures containing consecutive G-quadruplexes which provides additional binding sites for small molecules. Thus, telomeric DNA G-quadruplexes have attracted increasing interest as potential drug targets for cancer therapy. Here, we found that a novel platinum (II)-based tripod (Pt-tripod) specifically recognizes the hybrid-1 human telomeric G4, which is formed in the physiologically relevant K+ solution. Pt-tripod strongly represses telomerase activity and exhibits DNA-targeted photodynamic therapy anticancer activity. Using NMR, we show that Pt-tripod binds the hybrid-1 human telomeric G4 over other G-quadruplex structures and dsDNA. We determined solution structures of the 1:1 and the dimeric 4:2 Pt-tripod-hybrid-1 telomeric G4 complexes by NMR. Our 1:1 complex structure shows preferential binding of the Pt-tripod to the 5′-end of hybrid-1 telomeric G4. At higher ligand ratio, Pt-tripod binds to the 3′-end of the hybid-1 G4 and induces an unprecedented dimeric 4:2 structure interlocked by a non-canonical A:A pair at the 3′-end. The specific binding of the Pt-tripod with the hybrid-1 G4 is achieved by unique interaction modes including the π-π stacking, hydrogen bonding, and electrostatic interactions with the loop and flanking segments. The non-planar tertiary amine conformation and three properly sized cationic platinum arms are critical for the specific and strong binding. Our structures provide significant insights into understanding the dynamic binding of small molecules with G-quadruplexes, and a structural basis for future rational anticancer drug design of non-planar small molecules targeting the human telomeric G4. Our studies also provide a potential handle to study the specific protein interactions and biological functions of hybrid-1 human telomeric G4. Citation Format: Wenting Liu, Clement Lin, Zong-wan Mao, Danzhou Yang. Recognition of the hybrid-1 human telomeric G-quadruplex by a platinum(II)-based compound [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2752.