Mechanism of action of the dual topoisomerase-I and -II inhibitor TAS-103 and activity against (multi)drug resistant cells.
TAS-103 is a recently developed dual inhibitor of topoisomerase-I (topo-I) and topoisomerase-II (topoII). TAS-103 has documented cytotoxicity in vitro and antitumor activity against a variety of mouse, rat, and human xenografts in vivo.


OBJECTIVE
To determine TAS-103 activity against (multi)drug resistant cells in vitro and to delineate its mechanism of action.


METHODS
TAS-103 was evaluated for activity against three human multidrug-resistant cell lines representing resistance mediated by P-glycoprotein (Pgp)-, multidrug resistance protein (MRP), and lung resistance protein (LRP) as well as one camptothecin-resistant cell line associated with a mutated topo-I enzyme. Drug sensitivity following short (2 h), intermediate (6-8 h) and long term (24 h) exposures were compared. The mechanism of action was studied by evaluating inhibition of topoisomerase-I and -II specific DNA relaxation assays, drug-induced DNA/protein cross-link formation, and competitive DNA intercalation with ethidium bromide.


RESULTS
Increasing the exposure time only modestly potentiated TAS-103 cytotoxicity (3-5 fold) demonstrating a lack of strong exposure duration dependency. TAS-103 cytotoxicity was not affected by the presence of any of the drug resistance mechanisms studied. TAS-103 inhibits topo-I and -II activity in DNA relaxation assays, but in our assay system TAS-103 was found to have only a weak ability to induce DNA-protein crosslinks. DNA migration patterns in agarose gel electrophoresis indicate that TAS-103 can interact directly with DNA. Also its ability to displace ethidium bromide which has intercalated into the DNA provides an indication on the nature of drug-DNA interaction.


CONCLUSIONS
TAS-103 cytotoxicity is not affected by the presence of Pgp, MRP, LRP or mutations in the CAM binding region of the topo-I enzyme and its growth-inhibitory effect appears to be weakly dependent on exposure duration. The presented evidence suggest that the inhibitory effects of TAS-103 on topo-I and -II may in part be related to its DNA binding rather than primarily through stabilization of topo-I or -II intermediates with DNA through specific binding to the enzymes.
Minderman
H
H
Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA. minderman@sc3101.med.buffalo.edu
Wrzosek
C
C
Cao
S
S
Utsugi
T
T
Kobunai
T
T
Yamada
Y
Y
Rustum
Y M
YM
D000634:Aminoquinolines / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007192:Indenes / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured
D000634:Aminoquinolines; D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D007192:Indenes; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D004247:DNA; D002166:Camptothecin; C106647:6-((2-(dimethylamino)ethyl)amino)-3-hydroxy-7H-indeno(2,1-c)quinolin-7-one