Measurement of P-glycoprotein expression in human neuroblastoma xenograftsusing in vitro quantitative autoradiography

P-glycoprotein (P-gp) has a role in multidrug resistance (MDR) encountered in human cancers. In this study, we used the colchicine-resistant cell line BE(2)-C/CHCb(0.2), a strain of neuroblastoma cell line BE(2)-C, as a model to measure variations of P-gp expression in cells grown in vitro and in vi vo. Cells were cultured in the medium supplemented with colchicine. At the beginning of the study the drug was withdrawn and, after 22 days, added bac k to the culture medium. Cells were harvested at various time points and xe nografted in nude mice. P-gp content in cells was measured by self-competit ive binding assay and in tumors, by quantitative autoradiography (QAR). Bot h assays were tarried out using I-125-labeled monoclonal antibody MRK16, re active with P-gp. Concentration of P-gp in cells varied from a maximum of 1 ,361 pmol/g in the presence of colchicine to a minimum of 374 pmol/g in the absence of colchicine in the culture medium. P-gp concentration in the tum ors ranged from 929 to 188 pmol/g, which correlated with P-gp content in th e cells at the time of their injection in the mice. QAR is an accurate and reliable method to quantify P-gp expression in tumors. Changes in colchicin e concentration in the ambient medium of BE(2) C/CHCb(0.2) cells growing in vitro resulted in a change in phenotype of P-gp expression, which was stab le under conditions of in vivo growth over approximately 9 cell divisions i n nude mice xenografts. Therefore, P-gp content in xenografts depends only on the level of resistance of the cells at the time of their injection in t he mice. NUCL MED BIOL 26;1:35-41 1999. (C) 1998 Elsevier Science Inc.