Evaluation of radiopharmaceuticals sequestered by acutely damaged myocardium

Eighteen radiopharmaceuticals were screened in a small-animal model as potential infarct-localizing agents. Twelve of the 18 compounds were labeled with 99mTc, four with 203Hg, one with 131I, and one with either 203Hg or 125I. The model used heat-induced myocardial lesions in the rat. The absolute concentration within the lesion and also the activity ratios of injured myocardium to normal heart tissue, blood, and muscle were determined for all compounds. Among the 99mTc-labeled agents, two bone-seekers [pyrophosphate (PPi) and 1-hydroxyethylidine-1,1-diphosphonate (HEDP)] showed the most promise; these were followed by 99mTc-tetracycline analogs and 99mTc-glucoheptonaate. The tracer showing the most favorable concentration in the lesion and the best target-to-nontarget ratios was an iodinated derivatives of hydroxymercurifluorescein labeled with either 125I or 203Hg. Consideration of the structure of these compounds suggests that the presence of mercury or of a polycyclic aromatic structure, such as that found is tetracycline and fluorescein, was associated with localization in damaged myocardial tissue. Mercury bound to such an aromatic moiety may produce an additive or even a synergistic effect.