Chemotherapy increases transgene expression in leukemic cells

Background Patients with acute myeloid leukemia (AML) often obtain complete remission with chemotherapy but the majority of patients relapse. Combining chemotherapy and gene therapy appears to be a promising approach; however, the effects of chemotherapy on transgene expression in leukemic cells have not yet been investigated. Methods DA1‐3b leukemic cells were transfected with pCDNA3 plasmids carrying GM‐CSF or LacZ cDNA. The leukemic K562 cell line and primary cultured AML cells were transduced with an Ad5.CMV‐LacZ adenoviral vector. Cells were then incubated with various concentrations of daunorubicin (DNR) and cytosine arabinoside (Ara‐C), and expression of the transgene was measured. Murine DA1‐3b‐pCDNA3/LacZ leukemic cells were also injected into syngeneic C3H/Hej mice. Results In the cells carrying pCDNA3, DNR and Ara‐C dramatically increased expression of the LacZ and GM‐CSF transgenes. Over‐expression depended on drug dose and was due to increased transcription. Enhancement was also observed in K562 cells and in some primary cultured AML samples transduced with the Ad5.CMV‐LacZ adenovirus. Addition of N ‐acetyl‐ L ‐cysteine inhibited the over‐expression, suggesting that reactive oxygen species were involved in activating the CMV promoter. In the A549 lung carcinoma cell line transduced with Ad5.CMV‐LacZ, Ara‐C had only a minor effect, and DNR had a detrimental effect, suggesting that expression depends on cell type. In vivo experiments in which mice received DA1‐3b‐pCDNA3/LacZ leukemic cells, and were then treated with Ara‐C, also showed increased transgene expression in these leukemic cells. Conclusions In leukemic cells, chemotherapeutic agents can induce over‐expression of transgenes. This suggests a promising combined strategy for the treatment of acute leukemia. Copyright © 2003 John Wiley & Sons, Ltd.