Roles of DNA topoisomerase II isozymes in chemotherapy and secondary malignancies

doi:10.1073/pnas.0704002104

Roles of DNA topoisomerase II isozymes in chemotherapy and secondary malignancies

*Department of Pharmacology, University of Medicine and Dentistry of New Jersey, 675 Hoes Lane, Piscataway, NJ 08854;
^†Avagenex Pharmaceuticals, 6 Dey Farm Drive, Princeton Junction, NJ 08550; and
^‡Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138

Contributed by James C. Wang, May 13, 2007 (received for review April 5, 2007)

Abstract

Drugs that target DNA topoisomerase II (Top2), including etoposide (VP-16), doxorubicin, and mitoxantrone, are among the most effective anticancer drugs in clinical use. However, Top2-based chemotherapy has been associated with higher incidences of secondary malignancies, notably the development of acute myeloid leukemia in VP-16-treated patients. This association is suggestive of a link between carcinogenesis and Top2-mediated DNA damage. We show here that VP-16-induced carcinogenesis involves mainly the β rather than the α isozyme of Top2. In a mouse skin carcinogenesis model, the incidence of VP-16-induced melanomas in the skin of 7,12-dimethylbenz[a]anthracene-treated mice is found to be significantly higher in TOP2β⁺ than in skin-specific top2β-knockout mice. Furthermore, VP-16-induced DNA sequence rearrangements and double-strand breaks (DSBs) are found to be Top2β-dependent and preventable by cotreatment with a proteasome inhibitor, suggesting the importance of proteasomal degradation of the Top2β-DNA cleavage complexes in VP-16-induced DNA sequence rearrangements. VP-16 cytotoxicity in transformed cells expressing both Top2 isozymes is, however, found to be primarily Top2α-dependent. These results point to the importance of developing Top2α-specific anticancer drugs for effective chemotherapy without the development of treatment-related secondary malignancies.

Footnotes

^§To whom correspondence may be addressed. E-mail: jcwang{at}fas.harvard.edu or lliu{at}umdnj.edu
Author contributions: A.M.A. and Y.L.L. contributed equally to this work; A.M.A., Y.L.L., J.C.W., and L.F.L. designed research; A.M.A., Y.L.L., C.-P.L., and Y.-C.T. performed research; Y.L.L. and J.C.W. contributed new reagents/analytic tools; A.M.A., Y.L.L., C.-P.L., and L.F.L. analyzed data; and A.M.A., Y.L.L., J.Y.-N.L., J.C.W., and L.F.L. wrote the paper.
The authors declare no conflict of interest.
Abbreviations:

DMBA,

7,12-dimethylbenz[a]anthracene;

TPA,

phorbol 12-tetradecanoate 13-acetate;

VP-16,

etoposide;

Top2,

DNA topoisomerase II;

TOP2β+,

mouse with phenotype of wild-type Top2β;

TOP2β−,

mouse with phenotype of mutant Top2β;

DSBs,

double-strand breaks;

MEFs,

mouse embryonic fibroblasts;

bcr,

breakpoint cluster region;

t-AML,

treatment-related acute myeloid leukemia;

SV40,

simian virus 40;

shRNA,

short hairpin RNA.