Rhenium-188 Labelled Meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl] Porphyrin for Targeted Radiotherapy: Preliminary Biological Evaluation in Mice

Purpose: This study focusses on a promising carrier system for therapeutic and imaging purposes using meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl] porphyrin (T(3,4)CPP). To assess its potential for clinical use, we labelled T(3,4)CPP with (188)Re and analysed some kinetic biodistribution parameters after intravenous injection in mice.

Materials And Methods: T(3,4)CPP was synthesized and labelled with (188)Re. Normal Kunming (KM) mice and melanoma- or hepatoma-bearing BALB/c nude mice were injected intravenously with 5.55 MBq (188)Re-labelled T(3,4)CPP and sacrificed at 0.5, 2, 4, and 24 h and 8, and 24 h, respectively.

Results: The (188)Re-T(3,4)CPP yield was more than 95% with specific activity 16.9 GBq (mol)(-1), and Vitamin C (VC) could increase its stability in vitro. In normal KM mice, (188)Re-T(3,4)CPP had fast blood clearance (approximately 99%, 24 h postinjection), low retention in the vital organs and hepatotropic characteristics. In nude mice, more than 4.4 and 6.1% uptake per gram of tumour (%ID g(-1)) at 8 h postinjection was in melanoma and hepatoma, respectively; this remained as high levels after 24 h as 4.6 and 6.5%, respectively. At 8 h, the tumour/blood and tumour/muscle (T/M) ratios in melanomas and hepatoma bearing mice were 7.3, 13,and 7.0, 20, respectively. Twenty-four hours later, these high ratios still continued in existence which were 9.6, 19 and 10, 25, respectively.

Conclusion: The results obtained in this study indicate that (188)Re-T(3,4)CPP has better tumour affinity and retainable accumulation characteristics in carcinoma which can potentially be used for tumour-targeted radiotherapy.