Development of an .sup.111In-labeled dihydropyridine complex for L-type calcium channel imaging

[.sup.111In]-DTPA-Amlodipine complex ([.sup.111In]-DTPA-AMLO) was prepared starting high purity [.sup.111In]indium chloride and conjugated DTPA-AMLO in 30 min at room temperature in acetate buffer in high radiochemical purity (>99 %, RTLC/HPLC; specific activity: 8-10 GBq/mmol). The log P, stability, biodistribution studies and imaging studies in untreated and amlodipine-pretreated rats were determined. The tracer is mostly washed out through kidneys as expected for a dihydropyridine compound. Blocking studies demonstrated high specific binding of the tracer in calcium channel-rich organs including intestine, heart and colon. SPECT images fully supported above results in normal and treated rats.