This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Cancer, Subject name: Pharmacology
What enzyme is inhibited by etoposide - 
Select and explain. 
A. Topoisomerase I, B. Topoismerase II, C. Dihydrofolate reductase, D. Dihydro orotate oxidase
B: Topoismerase II
Answer: B: Topoismerase II 
Explanation: Ans. is 'b' i.e., Topoismerase II Etoposide* It is a semisynthetic derivative of podophyllotoxin, a plant glycoside.* It is not a mitotic inhibitor, but arrests cells in the G2 phase and causes DNA breaks by affecting DNA topoisomerase-2 function.* While the cleaving of double stranded DNA is not interfered, the subsequent resealing of the strand is prevented.* Etoposide is used in testicular tumours, lung cancer, Hodgkin's and other lymphomas, carcinoma bladder and stomach. Alopecia, leucopenia and g.i.t. disturbances are the main toxicity. Oral bioavailability is 50%; oral dose is double than i.v. dose.