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P-Glycoprotein Expression in Human Breast Cancer Cells¹

Department of Medicine/Oncology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284

Multidrug resistance in Chinese hamster ovary cells is associated with the M_r 170,000 surface glycoprotein. Using our monoclonal antibody to this protein, we have isolated a complementary DNA clone from an expression vector library. This complementary DNA recognizes a 4.5-kilobase mRNA in drug-resistant but not -sensitive Chinese hamster ovary cells; it also recognizes a 5.0-kilobase mRNA in our Adriamycin-resistant subline of the MDA-231 human breast cancer cell line which is not expressed in the drug-sensitive parent line. Southern blot analysis shows that the P-glycoprotein sequences are greatly amplified in resistant Chinese hamster ovary cells but not in the resistant human breast cancer cells, indicating that amplification and expression of the M_r 170,000 P-glycoprotein gene are not necessarily coordinate events. Amplification of this gene may not be required for multidrug resistance in human cells.

¹ This work was supported in part by CA 30195 and by the Robert A. Welch Foundation.

² To whom requests for reprints should be addressed, at Department of Medicine/Oncology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78284.

Received 8/12/86. Revised 11/10/86. Accepted 1/14/87.