ARQ-501 is a naphthoquinone compound derived from bark of Tabebuia sp., with antitumor, antibacterial, antifungal and antitrypanosomal activities. Beta-lapachone exerts its anti-tumor effect by indirect actions of inducing p53-independent apoptosis and cell cycle arrest mediated through altered activities of cell cycle control regulatory proteins; including down-regulating retinoblastoma protein (pRB), a transcriptional repressor target at transcription factor E2F-1, as well as induces expression of cyclin dependent kinase inhibitor 1A (CDKN1A or p21). Both E2F-1 and p21 are required for G1/S-phase transition during cell cycle. This agent also inhibits DNA topoisomerase I by a mechanism distinct from that of camptothecin, and thereby blocks the formation of a cleavable complex leading to enzyme inhibition and prevent DNA repair. Furthermore, beta-lapachone could induce reactive oxygen species in vivo, and result in cytotoxicity.