High throughput screening of a new fluorescent G-quadruplex ligand having telomerase inhibitory activity in human A549 cells

Abstract

Genome-wide analysis showed that putative G-quadruplex DNA structures are prevalent in the human genome. The presence of G-quadruplex structure in the telomere and promoter region of certain oncogenes inspired people to use G-quadruplex ligand as anti-cancer agents. G-quadruplex structures, stabilized by ligand at telomere are resolved by telomerase making the cancer cells resistant to G-quadruplex ligand. So, identification of a new G-quadruplex ligand having anti-telomerase activity would be a promising strategy for cancer therapy as about 85% of human cancers are telomerase positive. A set of the drug-like compounds were screened from the ZINC database randomly and 2284 ligands were chosen following Lipinskis rule of five that were docked with five different G-quadruplex DNA sequences in idock. We screened 43 potential G-quadruplex binders using Z-score as a normalization scoring function. The compound (ZINC ID-05220992) gave the best score (average idock = -10.17 kcal/mol, average normalized idock = -3.42). We performed G4 FID assay, CD analysis to understand its binding with three different G-quadruplex DNA sequences, and checked its anti-telomerase activity in A549 cells using TRAP assay. We observed that this compound had an intrinsic fluorescence, capability to stain live cells with a blue fluorescence, and a specific affinity to only 22AG out of three different G-quadruplex DNA sequences under study. It showed cytotoxicity, good permeability to live cells, and a significant reduction of telomerase activity in human A549 cells at a very low dose. So, this compound has strong potential to be an anti-cancer drug. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/470216v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@116cce1org.highwire.dtl.DTLVardef@1e500c1org.highwire.dtl.DTLVardef@194a0b3org.highwire.dtl.DTLVardef@c258fe_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIA set of compounds were screened randomly by a High throughput method and Lipinskis rule of five from ZINC database to identify potential G4-binders. C_LIO_LIThe compound (ZINC ID-05220992) was screened after docking with five G-quadruplex DNA C_LIO_LIIt binds G-quadruplex DNA 22AG as detected by TO displacement and CD spectroscopy. C_LIO_LIIt inhibits telomerase activity in A549 cells and also cytotoxic to this cell. C_LIO_LIIt penetrates live A549 cell in culture and stains it with blue fluorescence C_LI