Illustration of the molecular structure of the anticancer drug etoposide. Etoposide inhibits the enzyme topoisomerase II, which is essential to DNA (deoxyribonuclease) replication, and by extension cell division. Cancer cells divide rapidly, so causing errors in their DNA synthesis in this manner can promote apoptosis (cell death) of the cancer cells. Etoposide is used to treat a variety of cancers. It can cause side effects including alopecia, constipation, diarrhoea, nausea and vomiting. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (light grey, smaller) and oxygen (red).