Restriction of telomerase capping by short non-toxic peptides via arresting telomeric G-quadruplex

The stabilization of a G-quadruplex structure in human telomeric DNA has become a promising strategy in the development of cancer therapeutics. Here, we report FK13 (a small fragment of human cathelicidin peptide LL37, residues 17-29) and its mutant peptides (KR12A, KR12B and KR12C) inhibiting telomerase activity by stabilizing the telomeric G-quadruplex structures. An array of biophysical studies like fluorescence anisotropy, circular dichroism spectroscopy, circular dichroism melting, isothermal titration calorimetry, and high resolution nuclear magnetic resonance spectroscopy, in conjunction with molecular dynamics simulations, are employed to examine the interaction of peptides with the G-quadruplex structure. Furthermore, the peptide-quadruplex interaction is monitored in ex vivo systems, the telomerase over-expressed MCF7 breast adeno-carcinoma cell line. MTT assay and flow cytometry studies indicate selective antiproliferative activities of the peptides towards cancer cells over normal kidney epithelial cell line. Confocal microscopy evidenced nuclear transport and localisation of the peptides. A telomerase repeat amplification protocol assay further evidences telomere uncapping and abrogation of telomerase catalysing activity upon administration of peptides. Hence, arresting G-quadruplex structures using short peptides brings in a new mechanistic insight for the development of future peptide based therapeutics against cancer.