AMPLIFICATION OF THE ATP-BINDING CASSETTE-2 TRANSPORTER GENE IS FUNCTIONALLY LINKED WITH ENHANCED EFFLUX OF ESTRAMUSTINE IN OVARIAN-CARCINOMA CELLS

An estramustine-resistant human ovarian carcinoma cell line, SKEM, was generated to explore resistance mechanisms associated with this agent , Cytogenetic analysis revealed that SKEM cells have a homogeneously s taining region (hsr) at chromosome 9q34, Mitrodissection of the hsr, f ollowed by fluorescence in situ hybridization to SKEM and normal metap hase spreads, confirmed that the amplified region was derived from seq uences from 9q34, In situ hybridization with a probe specific for ABC2 , a gene located at 9q34 that encodes an ATP binding cassette 2 (ABC2) transporter, indicated that this gene is amplified similar to 6-fold in the estramustine-resistant cells, Southern analysis confirmed that ABC2 was amplified in SKEM, and Northern analysis indicated that the A BC2 transcript was overexpressed similar to 5-fold. The ABC1 gene loca ted at 9q22-31 was not amplified in the resistant cells, and mRNA leve ls of several other ABC transporter genes were unaltered, Consistent w ith the concept that in creased ABC2 expression contributes to tile re sistant phenotype, we observed that the rate of emus of dansylated est ramustine was increased in SKEM compared with control cells, in additi on, antisense treatment directed toward ABC2 mRNA sensitized the resis tant cells to estramustine, Together, these results suggest that ampli fication and overexpression of ABC2 contributes to estramustine resist ance and provides the first indication of a potential cellular functio n for this product.