Evidence for a transport carrier of nitrogen mustard in nitrogen mustard-sensitive and -resistant L5178Y lymphoblasts.

Abstract

Summary Uptake of nitrogen mustard (HN2)- 14 C by HN2-sensitive and -resistant L5178Y lymphoblasts followed simple Michaelis-Menten kinetics and demonstrated chemical specificity. Hydrolyzed HN2 and the monofunctional analog, dimethyl 2-chloroethylamine, inhibited uptake of HN2- 14 C, and the kinetics were those of competitive inhibition. Other structural analogs of HN2 such as chlorambucil, melphalan, and cyclophosphamide did not inhibit drug uptake. Transport proceeded against a concentration gradient as high as 35-fold and was almost completely inhibited at 4° and partially inhibited by ouabain and 2,4-dinitrophenol. These findings suggest that transport of HN2 is carrier-mediated and is an active process. The K m for resistant cells was higher than that of sensitive cells, suggesting a decreased affinity of the transport carrier for drug. The V max of resistant cells was lower than that of sensitive lymphoblasts, suggesting decreased transport capacity in resistant cells. The binding of HN2- 14 C to DNA, RNA, and protein of resistant lymphoblasts was significantly lower than that observed in each of the corresponding fractions of HN2-sensitive cells. The data suggest that resistance to HN2 is multifactorial, one factor being decreased uptake of HN2 by resistant cells.