Abstract
Multidrug-resistant clones of a drug-sensitive human malignant melanoma cell line were isolated by single-step selection in culture medium containing either vincristine (4.5 ng/ml or 7.5 ng/ml), vinblastine (3 ng/ml), or colchicine (8 ng/ml). This protocol yielded primary colonies showing relatively low (4- to 24-fold) levels of drug resistance. These clones exhibit the classical multidrug resistance (MDR) phenotype, being cross-resistant to Vinca alkaloids, anthracyclines, colchicine, and actinomycin D. The appearance of an MDR phenotype in these cells was linked to a decreased accumulation and increased efflux of the drug [3H]vinblastine when compared to the drug-sensitive melanoma cell line. This increased drug efflux was dependent on the presence of cellular ATP and could be reduced by treatment of the cells with rotenone and deoxyglucose. A partial human mdr complementary DNA clone was used to monitor the degree of amplification and the level of transcription of this gene in the cloned lines. All 5 MDR sublines expressed increased levels of the specific 4.5-kilobase mdr mRNA, but did not show mdr gene amplification. Our results indicate that relatively low levels of drug resistance, similar to those observed clinically and in experimental xenografts, can be achieved by single-step drug selection and result from increased expression of at least one member of the mdr gene family.
Footnotes
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↵1 Supported by National Cancer Institute Contract N43-CM-73717 to Integrated Genetics and by grants from the National Cancer Institute and the Medical Research Council of Canada to P. G.
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↵2 To whom requests for reprints should be addressed, at Integrated Genetics, Inc., One Mountain Road, Framingham, MA 01701.
- Received April 28, 1988.
- Revision received August 15, 1988.
- Accepted August 18, 1988.
- ©1988 American Association for Cancer Research.