Topoisomerase levels determine chemotherapy response in vitro and in vivo
Darren J. Burgess*, Jason Doles†, Lars Zender*, Wen Xue*, Beicong Ma*‡, W. Richard McCombie*, Gregory J. Hannon*‡, Scott W. Lowe*‡§, and Michael T. Hemann*†
*Cold Spring Harbor Laboratory and ‡Howard Hughes Medical Institute, 1 Bungtown Road, Cold Spring Harbor, NY 11724; and †Center for Cancer Research,
Massachusetts Institute of Technology, Cambridge, MA 02139
Communicated by Michael H. Wigler, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, April 14, 2008 (received for review October 21, 2007)
Topoisomerase poisons are chemotherapeutic agents that are used extensively for treating human malignancies. These drugs can be highly effective, yet tumors are frequently refractory to treatment or become resistant upon tumor relapse. Using a pool-based RNAi screening approach and a well characterized mouse model of lymphoma, we explored the genetic basis for heterogeneous responses to topoisomerase poisons in vitro and in vivo. These experiments identified Top2A expression levels as major determinants of response to the topoisomerase 2 poison doxorubicin and showed that suppression of Top2A produces resistance to doxorubicin in vitro and in vivo. Analogously, using a targeted RNAi approach, we demonstrated that suppression of Top1 produces resistance to the topoisomerase 1 poison camptothecin yet hypersensitizes cancer cells to doxorubicin. Importantly, lymphomas relapsing after treatment display spontaneous changes in topoisomerase levels as predicted by in vitro gene knockdown studies. These results highlight the utility of pooled shRNA screens for identifying genetic determinants of chemotherapy response and suggest strategies for improving the effectiveness of topoisomerase poisons in the clinic.
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