P-Glycoprotein expression by human colonic tumor cells influences the growth of tumor cells in vitro

The stability of P-glycoprotein expression by high and low expressing cells obtained by flow sorting from two cell lines established from colonic tumors was assessed. Low expressing cells rapidly recovered expression to a level that was comparable to that determined for uncloned cells. High expressing cells maintained a high level of expression relative to the parental uncloned lines, although there was continuous reversion to a level of expression determined for the parental line with time. The population growth rates for high expressing cells was greater than that of parental and low expressing cells when assessed immediately following plating of sorted cells. The data suggest that high expression of P-glycoprotein confers a growth advantage which may increase repopulation and dissemination of tumor cells following drug therapy.