A Study on the Mechanism of Resistance to Nitrogen Mustard (HN2) in Ehrlich Ascites Tumor Cells: Comparison of Uptake of HN2-14C into Sensitive and Resistant Cells

Summary Uptake of nitrogen mustard (HN2)- 14 C into cell suspensions containing equal packed cell volumes of sensitive or resistant Ehrlich ascites tumor cells was determined by incubating the suspensions in modified Krebs-Ringer phosphate media (pH 7.6) at 37°C in the presence of the labeled drug. Sensitive cells accumulated approximately twice as much drug as the resistant cells over a concentration range of 10 -6 to 10 -4 m. The difference in uptake occurred within 5 min of incubation and persisted for 24 hours. Uptake was inhibited at 0°C, by ouabain (5 × 10 -4 m), N -ethylmaleimide (10 -3 m), 2,4-dinitrophenol (10 -3 m), and iodoacetate (10 -2 m). It was not inhibited by malonate (10 -3 m), fluoride (10 -3 m), or cyanide (10 -3 m). Sensitive cells precipitated in trichloroacetic acid retained 80–90% of the drug, whereas resistant cells retained only 50–60%. Intact cell membranes were required for the differential uptake since cell homogenates of the two cell lines bound approximately equal amounts of drug. These results suggest that the development of resistance to HN2 in Ehrlich ascites tumor cells may be accompanied by an alteration in the properties of the cellular binding sites for HN2, which enables the resistant cells to exclude the drug.