SYNTHESIS OF GLUCOSE-CHLORAMBUCIL DERIVATIVES AND THEIR RECOGNITION BY THE HUMAN GLUT1 GLUCOSE-TRANSPORTER

A limitation of the use of chemotherapeutic agents against intracerebr al tumors lies on their poor uptake into the central nervous system. A n approach to enhance brain delivery is to design agents that are tran sported into the brain by one of the saturable nutrient carriers of th e blood-brain barrier, the highly efficient brain and erythrocyte gluc ose transporter isoform GLUT1. Since the GLUT1 hexose transporter of t he blood-brain barrier is also present on erythrocytes, new compounds designed to be transported by the GLUT1 transporter were studied on hu man erythrocytes, which represent unique, easily accessible human GLUT 1 expressing cells. In this paper we describe the synthesis of four gl ucose-chlorambucil derivatives, namely methyl 6-O-4[bis(2-chloroethyl) amino] benzenebutanoyl-beta-D-glucopyranoside (3), -chloroethyl)amino] benzenebutanoyl-D-glucopyranose (6), methyl 6-{4-[bis(2-chloroethyl)am ino] nzenebutanoylamido}-6-deoxy-beta-D-glucopyranoside (9) and 6-{4-[ bis(2-chloroethyl)amino]benzenebutanoyl amido}-6-deoxy-D-glucopyranose (10), and the study of their interactions with the GLUT1 transporter of the human erythrocytes. All four compounds were able to inhibit [C- 14]glucose uptake in a concentration-dependent manner. One of them, co mpound 6, exhibited an approximately 160-fold higher inhibition of [C- 14]glucose uptake by the GLUT1 transporter than glucose itself. Compou nd 6 was also able to inhibit [H-3]cytochalasin B binding to erythrocy tes with approximately 1000-fold higher efficacy than does glucose. Th e inhibition of glucose uptake was entirely reversible, indicating tha t it was not due to alkylation of a nucleophilic group of the hexose t ransporter. The above results suggested specific interactions of compo und 6 with the hexose transporter protein. Uptake studies of [C-14]com pound 6 indicated, in addition, some non-specific interactions with in tact and open erythrocyte membranes: only a small amount of the bound [C-14]compound 6 can be displaced by cytochalasin B. Collectively, the se findings led us to conclude that the interactions of compound 6 wit h GLUT1 are presumably that of a non-transported inhibitor.