Quality Control of Multidrug Resistance Assays in Adult Acute Leukemia: Correlation Between Assays for P-Glycoprotein Expression and Activity

We have compared multiple assays for the P-glycoprotein (PgplMDRl) phenotype in fresh and thawed adult acute leu-kemia t o validate and quantitate measures for the expres-sion and function of Pgp. The results are related t o the Pgp-expressing KB8 and KB8-5 cell lines. The most sensitive assay was the measurement of modulation of the rhodamine 123 (R123) fluorescence by 2 pmol/L PSC833, followed by the modulation of the probe calcein-AM. We also found a good intralaboratory and interlaboratory correlation be-tween the values of the R123/PSC833 assay for fresh as well as thawed samples. In addition, the effects of PSC833 on ’HH-daunorubicin (DNR) accumulation, DNR fluorescence, and ’H-vincristine accumulation were very similar. The correla-tion between the DNRIPSC833 and R123/PSC833 test was r =.86 IN = 51). The modulation of drug accumulation by