Etoposide is an antitumor agent that complexes with topoisomerase II and DNA to enhance double-strand and single-strand cleavage of DNA and reversibly inhibit religation. Blocks the cell cycle in in S-phase and G2-phase of the cell cycle; induces apoptosis in normal and tumor cell lines; inhibits synthesis of the oncoprotein Mdm2 and induces apoptosis in tumor lines that overexpress Mdm2.