Quarfloxin is a first-in-class small-molecule targeted cancer therapeutic derived from the validated fluoroquinolone class of drugs. Quarfloxin was rationally designed to target a G-quadruplex (QPLX) DNA structure and disrupt protein-DNA interactions essential to cancer cells. The QPLX targeted by quarfloxin forms within ribosomal DNA (rDNA) and the QPLX is bound by the nucleolin protein.