Establishment and evaluation of MRK16-magnetic cell sorting assays for detecting low expression of multidrug resistance P-glycoprotein using human leukemia cell lines and peripheral blood cells from healthy donors.

Two types of magnetic cell sorting assays, termed MRK16-MACS and MRK16-MACS-FACS, have been established to detect low expression level of P-glycoprotein (P-gp) using a monoclonal antibody MRK16, which recognizes a cell surface epitope of P-gp. With K-562 and U-937 cell lines, which are known to express low levels of P-gp and hence routinely used as negative control cell lines in conventional flow cytometry, both assays gave significantly positive reactivities indicating improved specificity and sensitivity of these assays. The findings in the dilution test, where P-gp-positive cells were added to P-gp-negative cells at various ratios, demonstrated that the MRK16-MACS assay is quantitative and capable of detecting small numbers of P-gp-positive cells as few as 2.5% of the total cells tested. Furthermore, specific enrichment of P-gp-expressing cells in magnetic cell sorting assays was verified by reverse transcription-polymerase chain reaction (RT-PCR) analysis and functional assay for P-gp with Rhodamine 123. The availability of such magnetic cell sorting assays may offer an approach to quantitate low level of P-gp expression.