<prompt> Which of the following drugs is topoisomerase I inhibitor?DoxorubicinIrinotecanEtoposideVincristine  <response>: Camptothecin derivatives like topotecan and irinotecan act by inhibiting topoisomerase-I whereas Epipodophyllotoxins etoposide and teniposide and anthracyclines doxorubicin, daunorubicin etc. act by inhibiting topoisomerase-II. 