Technetium-99m spiperone dithiocarbamate: a potential radiopharmaceutical for dopamine receptor imaging with SPECT

Spiperone dithiocarbamate (SPDC) was prepared by reacting spiperone with carbon disulfide followed by sodium hydroxide. SPDC was labelled with 99mTc by reduction of pertechnetate with formamidine sulfinic acid or sodium dithionite at alkaline pH, resulting in approximately 40% incorporation of 99mTc. The lipophilic complex was conveniently isolated at high specific activity and high radiochemical purity by extraction into dichloromethane, which was then evaporated and the residue was redissolved in a 1:3 mixture of ethanol and saline containing 0.1 mg/mL gentisic acid. Biodistribution studies following i.p. injection in rats showed low uptake of radioactivity in the brain, but striatum/cortex and striatum/cerebellum ratios were reduced by pretreatment with haloperidol. This agent may allow imaging of dopamine D-2 receptors using single-photon emission computed tomography (SPECT).