Immunohistochemical detection of P‐glycoprotein in human tumor cells with a low degree of drug resistance

Abstract

We report the immunohistochemical detection of the 170–180 kDa multi-drug-resistance-related P-glycoprotein in human tumor cells with a low level of resistance. A series of human squamous lung cancer cell lines with increasing levels of resistance to doxorubicin (DOX) was developed and stained for P-glycoprotein, using the JSB-lMAb. Subline SW1573/50A with a 4- to 6-fold cross-resistance to daunorubicin (DNR) and vincristine (VCR) showed rather uniform positive staining for P-glycoprotein apparently at cytoplasmic sites. Only in cells with higher degrees of resistance (> 10-fold) could plasmamembrane-associated P-glycoprotein be made visible. DNR efflux was increased in SW1573I50A as compared to the parent line SWl573 (52 and 70% DNR were retained during 3 min efflux respectively). Verapamil partially reversed DNR and VCR resistance in SWl573/50A. Cells obtained from a metastasized renal cell carcinoma and cultured in vitro stained in a similar way to SWl573/50A and showed some sensitivity to verapamil modulation of VCR cytotoxicity. Our results suggest that weakly resistant cancer cells obtained from patients can be routinely detected with JSB-l on cytospins, and Implicate that in such weakly resistant cells P-glycoprotein may be present, while plasma membrane expression is not yet readily detectable.