Etoposide

Structure of etoposide

Mechanism of action

Etoposide forms a ternary complex with DNA and the topoisomerase II enzyme, which is an enzyme that aids in relaxing negative or positive supercoils in DNA. Topoisomerase II normally will form a double-stranded break in one DNA double-strand, allow another to pass through, and re-ligate the broken strands. Etoposide’s binding prevents topoisomerase II from re-ligating the broken DNA strands, which causes the DNA breaks made by topoisomerase II to stay broken, and also prevents the topoisomerase II molecule from leaving the site and relieving tension elsewhere. This results in a double-strand break in the DNA that can have various deleterious effects on the cell, and depletion of topoisomerase II available to relieve further tension.