ENHANCED HOST-CELL REACTIVATION CAPACITY AND EXPRESSION OF DNA-REPAIRGENES IN HUMAN BREAST-CANCER CELLS RESISTANT TO BI-FUNCTIONAL ALKYLATING-AGENTS

Human breast carcinoma (MCF7-MLNr) cells resistant to the bifunctional drugs L-phenylalanine mustard (L-PAM, 5-fold resistance), mechloretha mine (9-fold), cisplatin (3-fold), and BCNU (3-fold) were used to inve stigate the role of DNA repair in the development of resistance to alk ylating agents. We have previously shown that neither L-PAM transport and metabolism nor glutathione-associated enzymes were altered in MCF7 -MLNr cells, compared to the sensitive cells MCF7-WT. This study shows that treatment of pRSV-CAT plasmid with L-PAM at concentrations up to 1 mu M proportionally inhibit the expression of chloramphenicol acety l transferase (CAT) activity, while higher concentrations abolished CA T activity. pRSV-CAT reactivation was significantly increased when pla smid was transfected into MCF7-MLNr cells, compared to MCF-WT cells. T his indicates that resistant cells have more efficient capacity to rec ognize and repair L-PAM induced DNA damage. The mRNA expression of DNA nucleotide excision repair genes ERCC1, XPD (ERCC2), XPB (ERCC3), and polymerase beta was found to be similar in both the MCF7-WT and MCF7- MLNr cells. Western blot analysis also reveals no difference in the ex pression of ERCC1, AP endonuclease, poly (ADP-ribose) polymerase, and alkyl-N-purine-DNA glycosylase proteins. The lack of correlation betwe en enhanced host cell reactivation capacity in resistant cells, and th e expression of these specific DNA repair genes suggests that proteins encoded by these genes are not rate limiting steps for resistance to bi-functional alkylating drugs in human breast cancer cells.