PubMed · 9551213
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J A Moscow, E Schneider, S P Ivy, K H Cowan. 1997. Multidrug resistance.. https://pubmed.ncbi.nlm.nih.gov/9551213/
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BACKGROUND: Multidrug resistance (MDR) is mediated by the drug resistance proteins, the multidrug resistance-associated protein (MRP) and P-glycoprotein, both of which confer resistance by the active efflux of chemotherapeutic drugs from the cell. Reduced Fas (CD95/APO-1) expression and resistance to Fas-mediated apoptosis have also been correlated with P-glycoprotein-mediated MDR. METHODS: We investigated cell surface Fas expression (using anti-Fas monoclonal antibody DX2.1) in a series of MRP-expressing drug-resistant leukemia sublines, and P-glycoprotein-expressing leukemia sublines, and their susceptibility to apoptosis induced by anti-Fas treatment (CH-11 monoclonal antibody). Caspase-3 activation was detected by Western blot and apoptosis was determined by flow cytometry with 7-aminoactinomycin D (7-AAD) staining of cells. RESULTS: Fas expression was not reduced in either the MRP- or P-glycoprotein-expressing drug-resistant cell lines, although expression was reduced by 15% in one low-level drug-resistant subline. Expression of MRP or P-glycoprotein did not confer resistance to caspase-3 activation or to anti-Fas-induced cell death. CONCLUSIONS: MDR mediated by the drug transport proteins MRP and P-glycoprotein does not correlate with resistance to Fas-mediated cell death or resistance to caspase-3 activation.
A significant problem in the clinical treatment of cancer relates to the development of tumor resistance to many chemotherapeutic agents. Acquired drug resistance is often mediated through overexpression of membrane transport proteins that effectively efflux anticancer agents. Two of the best-studied transporters, P-glycoprotein (Pgp) and MRP1, have pharmacological properties that only partially overlap. In our search for improved drug-resistance antagonists, we have identified a family of substituted quinoxalines that selectively antagonizes Pgp over MRP1. Consequently, a focused library of congeners was designed and synthesized starting with a parent bromomethylquinoxalinone. This parent quinoxalinone was then condensed with a series of phenols to yield a family of substituted phenoxymethylquinoxalinones. These compounds were evaluated for their toxicity toward drug-sensitive MCF-7 breast carcinoma cells and for their abilities to antagonize Pgp and MRP1 in drug-resistant cell lines (NCI/ADR and MCF-7/VP, respectively). The results of this structure-activity study indicate that compounds with carbonyl substitutions of the phenoxy group (ester, amide, or ketone moieties) demonstrate excellent antagonism of Pgp while having relatively low toxicity toward drug-sensitive cells. Importantly, none of these compounds antagonized MRP1. Because of their transporter selectivity, we predict that substituted quinoxalinones may be more effective MDR modulators in vivo than are nonselective transporter antagonists.
MDR1 P-glycoprotein (P-gp), the multidrug resistance-associated transmembrane transporter, is physiologically expressed by human peripheral immune cells, but its role in cell-mediated immunity remains poorly understood. Here, we demonstrate a novel role for P-gp in alloantigen-dependent human T cell activation. The pharmacologic P-gp inhibitor tamoxifen (1-10 microM) and the MDR1 P-gp-specific mAb Hyb-241 (1-20 microg/ml), which detected surface P-gp on 21% of human CD3(+) T cells and 84% of CD14(+) APCs in our studies, inhibited alloantigen-dependent, but not mitogen-dependent, T cell proliferation in a dose-dependent manner from 40-90% (p < 0.01). The specific inhibitory effect on alloimmune T cell activation was associated with >85% inhibition (p < 0.01) of IL-2, IFN-gamma, and TNF-alpha production in 48-h MLR coculture supernatants. Addition of recombinant human IL-2 (0.1-10 ng/ml) restored proliferation in tamoxifen-treated cocultures. Pretreatment of purified CD4(+) T cells with Hyb-241 mAb before coculture resulted in inhibition of CD4(+) T cellular IFN-gamma secretion. Also, blockade of P-gp on allogeneic APCs inhibited IL-12 secretion. Taken together these results demonstrate that P-gp is functional on both CD4(+) T cells and CD14(+) APCs, and that P-gp blockade may attenuate both IFN-gamma and IL-12 through a positive feedback loop. Our results define a novel role for P-gp in alloimmunity and thus raise the intriguing possibility that P-gp may represent a novel therapeutic target in allograft rejection.