75,77Br- and 123I-analogues of D-glucose as potential tracers for glucose utilisation in heart and brain

A number of D-glucose analogues labelled with either the positron emitter 75Br (T 1/2 = 1.6 h) or the single photon emitter 123I (T 1/2 = 13.3 h) were studied as potential tracers for glucose utilisation in heart and brain. Of these, 3-deoxy-3-bromo-D-glucose, 3-deoxy-3-iodo-D-glucose, methyl 2-deoxy-2-bromo-beta-D-glucoside and methyl 2-deoxy-2-iodo-beta-D-glucoside showed little uptake of radioactivity into brain and an unfavourable ratio of heart-to-blood and heart-to-lung concentrations. In contrast, methyl 3,4,6-tri-O-acetyl-2-deoxy-2-iodo-beta-D-glucoside (MTIG) and methyl 3,4,6-tri-O-acetyl-2-deoxy-2-bromo-beta-D-glucoside (MTBG) showed promising brain uptake (160% MBC for MTBG) with a good brain-to-blood concentration ratio of 0.8. MTBG is not metabolically altered in the brain. Thus, this compound may be a promising tracer for measuring glucose transport if it proves to be a substrate for the hexose carrier at the blood-brain-barrier.