HIGH-AFFINITY MONOCLONAL-ANTIBODIES AGAINST P-GLYCOPROTEIN

Cancer patients treated with one anticancer agent often develop resist ance to a broad spectrum of chemotherapeutic agents. This type of mult iple drug resistance (MDR) is often accompanied by a decrease in drug accumulation and an increase in expression of a 170,000-Da plasma memb rane glycoprotein (P-170) that can effectively pump various anticancer agents out of cytoplasm. A panel of 12 IgG1, IgG(2a), or IgG(2b) mono clonal antibodies was generated against the extracellular portion of P -glycoprotein by immunizing mice with a human MDR1 gene-transfected BA 3T3 fibroblast line. We have characterized two of the anti-P-glycoprot ein monoclonal antibodies, 15D3 and 17F9, in some detail. Both antibod ies immunoprecipitate a 170- to 180-kDa protein hom MDR cells, but do not block binding of the known anti-P-glycoprotein antibody MRK16, sug gesting that 15D3 and 17F9 bind to a different epitope on the extracel lular domain of P-glycoprotein than MRK16. Scatchard analysis revealed that 15D3 and 17F9 had association constants of 1.3 and 1.1 x 10(8) M (-1), respectively. 15D3 and 17F9 had little effect on MDR cell growth except for a minor inhibition of KB-V1 cells when the cells were incu bated in the presence of vinblastine. Neither antibody inhibited the e fflux of P-glycoprotein substrates from MDR cells. Because of their st rong binding activity, these antibodies may be useful for diagnostic d etection of MDR in patients undergoing chemotherapy or as targeting co mponents of immunotherapeutic agents. (C) 1995 Academic Press, Inc.