Chemical and biological properties of verapamil labeled with technetium-99m: A potential myocardial imaging agents

On the base of property to enter into myocardial cells as a calcium channel blocker, verapamil was labeled with technetium-99m in order to investigate the possibility to obtain new radiopharmaceutical for myocardial imaging. The conditions of labeling verapamil with technetium-99m for different ammounts of stannous(II) ion, mannitol, cystein and pH range 2.5–3.5 were examined. Investigation of radiochemical purity (>95%) and biodistribution of 99mTc-verapamil in rats showed that it was stable during 2 hours after labeling. Accumulation of 99mTc-verapamil in heart was 1.2% and in liver 9.4%, 5 minutes after injection. Biodistribution of 99mTc-verapamil in rats in conditions of stress, pharmacologically caused by dipiridamol, showed that the elimination of 99mTc-verapamil from the heart was slower related to the control group. In the group of rats previously treated with isoproterenol uptake of 99mTc-verapamil in heart was lower related to the control group (0.7% versus 1.0%) 5 minutes after injection. Lipophilicity of 99mTc-verapamil was examined by determination of partition coefficient (log P = 0.62) and protein binding (79%). Imaging studies on dogs provided relatively good myocardial images with partially overlap of activity in the lung and liver.