Characteristics of human tumour cell lines after induction of multidrug resistance

A colorimetric technique was used to investigate some aspects of multidrug resistant (MDR)-induced cell lines. Continuous contact of the inducing agent with cells was necessary for MDR induction and this was followed by a series of phases i.e., a selection phase (ESP) lasted up to 6 days, a conditioning phase (CP) lasted up to 14 days and an expansion phase (EP) lasted up to 7 days. Gene transfection to correct missing MHC class I antigens on the Fen cell line did not affect cell behaviour. Of particular interest was the finding that the withdrawal of the MDR inducing agent did not reverse MDR phenotype immediately.