Pyridostatin (RR82) is a highly selective small molecule that stabilizes telomeric DNA G-quadruplex with a Kd of 490 nM, promoting their folding and inducing dysfunctional telomeres by uncapping POT1 and activating DNA damage signaling. It also modulates gene expression, reducing SRC protein levels and SRC-dependent motility in breast cancer cells, contributing to its anti-proliferative effects.