Phenyl 123-Triazole-Thymidine Ligands Stabilize G-Quadruplex DNA Inhibit DNA Synthesis and Potentially Reduce Tumor Cell Proliferation over 3′-Azido Deoxythymidine

摘要

Triazoles are known for their non-toxicity, higher stability and therapeutic activity. Few nucleoside (>L1, >L2 and >L3) and non-nucleoside 1,2,3-triazoles (>L4–L14) were synthesised using click chemistry and they were screened for tumor cell cytotoxicity and proliferation. Among these triazole ligands studied, nucleoside ligands exhibited higher potential than non-nucleoside ligands. The nucleoside triazole analogues, 3′-Phenyl-1,2,3- triazole-thymidine (>L2) and 3′-4-Chlorophenyl-1,2,3-triazole-thymidine (>L3), demonstrated higher cytotoxicity in tumor cells than in normal cells. The IC50 value for >L3 was lowest (50 µM) among the ligands studied. >L3 terminated cell cycle at S, G2/M phases and enhanced sub-G1 populations, manifesting induction of apoptosis in tumor cells. Confocal studies indicated that nucleoside triazole ligands (>L2/L3) cause higher DNA fragmentation than other ligands. Preclinical experiments with tumor-induced mice showed greater reduction in tumor size with >L3. In vitro DNA synthesis reaction with >L3 exhibited higher DNA synthesis inhibition with quadruplex forming DNA (QF DNA) than non quadruplex forming DNA (NQF DNA). Tm of quadruplex DNA increased in the presence of >L3, indicating its ability to enhance stability of quadruplex DNA at elevated temperature and the results indicate that it had higher affinity towards quadruplex DNA than the other forms of DNA (like dsDNA and ssDNA). From western blot experiment, it was noticed that telomerase expression levels in the tissues of tumor-induced mice were found to be reduced on >L3 treatment. Microcalorimetry results emphasise that two nucleoside triazole ligands (>L2/>L3) interact with quadruplex DNA with significantly higher affinity (Kd≈10⁻⁷ M). Interestingly the addition of an electronegative moiety to the phenyl group of >L2 enhanced its anti-proliferative activity. Though IC50 values are not significantly low with >L3, the studies on series of synthetic 1,2,3-triazole ligands are useful for improving and building potential pro-apoptotic ligands.