RT Journal Article
SR Electronic
T1 Murine Transgenic Cells Lacking DNA Topoisomerase IIβ Are Resistant to Acridines and Mitoxantrone: Analysis of Cytotoxicity and Cleavable Complex Formation
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1309
OP 1316
DO 10.1124/mol.56.6.1309
VO 56
IS 6
A1 F. Errington
A1 E. Willmore
A1 M. J. Tilby
A1 L. Li
A1 G. Li
A1 W. Li
A1 B. C. Baguley
A1 C. A. Austin
YR 1999
UL http://molpharm.aspetjournals.org/content/56/6/1309.abstract
AB Murine transgenic cell lines lacking DNA topoisomerase II (topo II)β have been used to assess the importance of topo IIβ as a drug target. Western blot analysis confirmed that the topo IIβ −/− cell lines did not contain topo IIβ protein. In addition, both the topo IIβ +/+ and topo IIβ −/− cell lines contained similar levels of topo IIα protein. The trapped in agarose DNA immunostaining assay (TARDIS) was used to detect topo IIα and β cleavable complexes in topo IIβ −/− and topo IIβ +/+ cells. These results show that both topo IIα and β are in vivo targets for etoposide, mitoxantrone, and amsacrine (mAMSA) in topo IIβ +/+ cells. As expected, only the α-isoform was targeted in topo IIβ −/− cells. Clonogenic assays comparing the survival of topo IIβ −/− and topo IIβ +/+ cells were carried out to establish whether the absence of topo IIβ caused drug resistance. Increased survival of topo IIβ −/− cells compared with topo IIβ +/+ cells was observed after treatment with amsacrine (mAMSA), methylN-(4′-[9-acridinylamino]-2-methoxyphenyl) carbamate hydrochloride (AMCA), methylN-(4′-[9-acridinylamino]-2-methoxyphenyl)carbamate hydrochloride (mAMCA), mitoxantrone, and etoposide. These studies showed that topo IIβ −/− cells were significantly more resistant to mAMSA, AMCA, mAMCA, and mitoxantrone, than topo IIβ +/+ cells, indicating that topo IIβ is an important target for the cytotoxic effects of these compounds.