Comparison of three commercially available antibodies for flow cytometric monitoring of P-glycoprotein expression in tumor cells.

Cellular drug resistance to natural products is often due to the presence of an efflux pump which reduces intracellular drug content and chemosensitivity. A 170 kD cell surface resident P-glycoprotein is believed to act as the efflux pump. In the present report, we have compared three commercially available antibodies C-219, JSB-1, and mdr(Ab-1) for use in flow cytometric detection of P-glycoprotein positive cells. Our data show that C219 gives uniformly good results in a variety of murine and human tumor cell lines for detection of P-glycoprotein positive cells. We have also compared data of C219 stained cells analyzed in parallel on a flow cytometer equipped with a small laser (15 mW) and a large laser (5 watt) cell sorter. Data obtained on these two instruments are comparable. A staining protocol and data on dual staining of cells for DNA content by propidium iodide and P-glycoprotein expression after FITC labeling are also presented.