Atypical multidrug resistance may be associated with catalytically active mutants of human DNA topoisomerase II alpha

In human cells, atypical drug resistance was previously identified with red uced catalytic activity or nuclear localization efficiency of DNA topoisome rase II alpha (TOP2 alpha). We have shown two etoposide resistant hTOP2 alp ha mutants, K798L and K798P confer resistance to etoposide. In this work, w e showed these mutants are also resistant against doxorubicin and mAMSA in vivo in the yeast strain ISE2, rad52, top2-4 at the non-permissive temperat ure. We purified these mutants to characterize the drug resistant mechanism . Purified recombinant proteins were 8-to 12-fold more resistant to etoposi de and doxorubicin than wild type TOP2 alpha, and 2-fold more resistant to amsacrine, as measured by accumulation of cleavable DNA. These data show th at K798L and K798P may be intrinsically resistant against these drugs in vi tro and that this character may confer atypical multidrug resistant phenoty pe in vivo in yeast. (C) 2001 Elsevier Science B.V. All rights reserved.