The lack of effects of alkylating agents on mammalian cell membranes

The importance of cell membrane components as target sites for the action of 2,3,5-tris(ethyleneimino)-benzoquinone (Trenimon), mechlorethamine hydrochloride (HN2) and tris(2-chloroethyl) amine hydrochloride (HN3) was investigated. Uptake of 2-aminoisobutyric acid (AIBA) was studied under nonsaturating conditions where the transport system was rate-limiting for the uptake. Uptake of AIBA into L5178Y leukaemic cells was either inhibited or stimulated, depending on the type of the drug, the drug concentration and the length of incubation. Treatment of human erythrocytes with 10(-3) M HN3 produced new high-molecular-weight protein bands on SDS-polyacrylamide gel electrophoresis. Conversely, HN3 had no effect on L5178Y cell membrane proteins. Neither HN2 nor Trenimon produced any detectable changes in membrane proteins of L5178Y cells or human erythrocytes. None of the three drugs at concentrations and incubation conditions which inhibited cell replication changed the stoichiometry or dissociation constant of concanavalin A (Con A) binding sites on L5178Y cells. Trenimon at highly toxic concentrations had no effect on the fluidity of phospholipid membranes or of membranes of Ehrlich ascites tumour cells as analysed by ESR spin-label methods. The results presented here do not support the hypothesis that cell membranes are the primary target sites for alkylating drugs.