Pyridostatin decreases the proliferation of MRC-5–SV40 cells and various cancer cell lines, and induces cell-cycle arrest by DNA-damage checkpoint activation. Pyridostatin also reduces SRC-dependent cell motility in MDA-MB-231 cells by interacting with G-quadruplex motifs in SRC. Pyridostatin decreases EBNA1 synthesis via inhibition of G-quadruplexes.