Adenovirus-mediated human topoisomerase IIα gene transfer increases the sensitivity of etoposide-resistant human and mouse breast cancer cells

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Abstract
Cellular resistance to chemotherapeutic agents is attributable to several mechanisms, including alteration of topoisomerase IIa gene expression. Our previous studies have shown that transient transfection with a vector containing either Drosophila or human topoisomerase IIalpha gene into drug-resistant tumor cells enhanced their drug sensitivity. Furthermore, we constructed a recombinant adenovirus, Ad-hTopoIIalpha, containing the human topoisomerase IIa gene that was able to selectively increase etoposide sensitivity in drug-resistant tumor cells. We also examined Ad-hTopoIIalpha for therapeutic efficacy in vitro using additional etoposide-resistant cell lines, including a mouse breast cancer cell line and a human leukemia cell line. The etoposide-resistant mouse breast cancer cell line FvP, which is derived from FM3A, and etoposide-resistant human breast cancer cell line, MDA-VP, which derived from MDA-P cells showed increased sensitivity to etoposide as well as increased expression of human Topoisomerase IIa mRNA, but this was not seen in FM3A and MDA-P cells. On the other hand, the etoposide-resistant human leukemia cell line K562/MX2 and the parental cell line K562/P did not show enhanced sensitivity against etoposide or an increase in human Topoisomerase IIa mRNA. Using a recombinant adenovirus containing beta-galactosidase gene (Ad-beta-gal), K562 cells were not transducted by the recombinant adenovirus, while both etoposide-sensitive FM3A cells and etoposide resistant FvP cells were transducted by recombinant adenovirus. Ad-hTOP2alpha and etopside treatment showed reduced inoculated tumor weight in the mice. We concluded that a recombinant adenovirus containing the human Topoisomerase IIalpha gene might be a powerful tool for overcoming drug resistance in breast cancer cells, but not in leukemia cells.