Quantitative determination of the MDR-related P-glycoprotein, Pgp 170, by a rapid flow cytometric technique.

Pgp 170 is the main integral membrane protein involved in acquired or de novo multidrug resistance (MDR), frequently implicated in chemotherapeutic failure. Because there is at present no method for quantitating Pgp 170 levels, a new and convenient assay, using flow cytometry with a standard fluorescence curve and MRK 16, a mAb recognizing an external epitope of human Pgp 170, was developed. Assuming a 1:1 stoichiometry, we calculated for the first time the apparent number of Pgp 170 molecules per cell. The method was applied successfully to cells in suspension or grown as monolayers and their mixtures. All quality criteria were checked and proved the suitability of the method for quantifying Pgp 170.