Selective sensitization of adriamycin-resistant P388 murine leukemia cells to antineoplastic agents following transfection with human DNA topoisomerase II alpha.

Previous studies have demonstrated decreased levels of DNA topoisomerase IIα protein and messenger RNA in the Adriamycin-resistant P388 murine leukemia cell line P388/ADR/7 compared to the sensitive P388/4 cell line. An allelic fusion event involving the topoismerase IIα and the retinoic acid receptor α genes has been identified in these cells that probably contributes to the decreased topoisomerase II activity in P388/ADR/7 cells. However this allelic mutation may be a minor contributor or even incidental to the resistance phenotype, since these cells display other candidate mechanisms of resistance, including increased P-glycoprotein, increased glutathione-S-transferase activity and an increased onset of DNA repair. To establish a role for topoisomerase IIα in mediating the Adriamycin resistance phenotype, complementation of the mutant allele was attempted by transfecting the murine P388/ADR/7 cells with a human topoisomerase IIα expression construct under the control of the human metallothionein IIA promoter. The majority of transfected cell lines that were obtained by selection in hygromycin B contained copies of the integrated expression construct that were rearranged. Only two of thirty-two transfected cell lines were found to contain a single, unrearranged copy of the human topoisomerase IIα cDNA. P388/ADR/7 cell lines carrying an integrated, intact human topoisomerase IIα expression vector were more sensitive to Adriamycin, daunorubicin, mitoxantrone, and etoposide, but not to actinomycin D and vincristine compared to control cells transfected with vector alone or cell lines with rearranged topoisomerase IIα expression constructs. These findings suggest that topoisomerase IIα is a selective and significant contributor to multifactorial resistance.