Which one of the following drugs is topoisomerase I inhibitor? (AIIMS Nov 2009)
a. During transcription and replication, DNA acquires conformational and topological changes that must be relieved. The enzymes topoisomerase I and topoisomerase II perform this function by introducing and then repairing single- or double-stranded DNA breaks
b. Camptothecin derivatives like topotecan and irinotecan act by inhibiting topoisomerase-I. These are used for the treatment of colo-rectal carcinoma. Diarrhea is the major adverse effect of irinotecan.
c. Epipodophyllotoxins (etoposide and teniposide) and anthracyclines (doxorubicin, daunorubicin etc.) act by inhibiting topoisomerase-II.