A novel Re-[186/188]-labelled porphyrin for targeted radiotherapy

The concept of labelling a porphyrin, a tumour-avid agent, with a radionucl ide to evaluate its potential as a therapeutic modality is reported. A nove l water-soluble porphyrin, namely meso-tetrakis[3,4-bis carboxymethyleneoxy )phenyl]porphyrin, with suitable dicarboxylic acid groups as aromatic subst ituents in the periphery, was synthesized and characterized. The labelling of this porphyrin with Re-186/186, a beta (-) emitter, was optimized by var ying the reaction conditions. The complexation yield was >98% as estimated by paper chromatography in acetone and in saline. The radiochemical purity was found to remain at > 98% when stored at 4 degreesC for 24 h. Biodistrib ution studies in Swiss mice bearing fibrosarcomas showed an uptake of simil ar to 3.5% per gram of tumour at 30 min post-injection. This uptake in the tumour was retained until 24 h post-injection with major activity showing r enal clearance; no significant activity was present in other organs of inte rest. The tumour/blood and tumour/muscle ratios were observed to be 38 and 5, respectively, at 24 h post-injection, thereby indicating a possible ther apeutic potential for tumours. ((C), 2002 Lippincott Williams & Wilkins).