Multidrug resistance (MDR) is a salient feature of
chemotherapy failure in pediatric patients. One of the most common and well-studied mechanisms implicated in causing MDR is
P-glycoprotein (Pgp), an
ATP-dependent, transmembrane
drug efflux pump. Accurate and reproducible detection of this MDR
protein is necessary as it may have important clinical implications. In this study comparing the directly conjugated anti-Pgp
monoclonal antibodies UIC2-PE and 15D3-PE to the unconjugated anti-Pgp mAb MRK16, we analyzed cell lines, normal peripheral blood cells, and bone marrow cells from pediatric patients diagnosed with
acute myeloid leukemia and
acute lymphoblastic leukemia; all samples were also analyzed for Pgp function using
rhodamine 123 in order to correlate results from antibody staining with functional activity. For all patient samples evaluated, only MRK16 correlated well with the
rhodamine 123 assay. Both the directly conjugated
antibodies UIC2-PE and 15D3-PE failed to detect Pgp in almost all cases. Pre-treatment of cells with
neuraminidase did not provide a consistent enhancement of
antigen detection. Based on these results, we suggest that while UIC2-PE and 15D3-PE may be able to detect the very high levels of Pgp expressing laboratory-cultured cell lines, they are not suitable for clinical application in their currently available conjugated form. When assaying patient samples for Pgp expression and function using flow cytometry, the
rhodamine 123 functional assay should be performed in concert with staining with MRK16.