Preparation of a 153Sm-5,10,15,20-tetrakis(4-methoxyphenyl) porphyrin complex as a possible therapeutic agent

Introduction: Porphyrins are interesting derivatives with low toxicity, tumor avidity and rapid wash-out suggested as potential radiopharmaceuticals in radiolabeled form. In this work we report, synthesis, radiolabeling, quality control, stability, partition coefficient determination and biodistribution studies of 153Sm-5,10,15,20-tetrakis(4-methoxyphenyl) porphyrin (153Sm-4-MPP) in wild-type rats. Methods: [153Sm]-4MPP was prepared using [153Sm]SmCl3 and 5,10,15,20-tetrakis(4-methoxyphenyl) porphyrin (H2-4MPP) for 18 h at 80-90°C. Stability of the complex was checked in final formulation and in presence of human serum for 24 h. The biodistribution of the labeled compound in vital organs of wild-type rats was studied. A detailed comparative pharmacokinetic study performed for 153Sm cation and [153Sm]-4-MPP up to 24h. Results: The radiochemical purity of [153Sm]-4MPP was reported >97±2% and >99±0.5% by ITLC and HPLC, respectively. The specific activity was 220-230 MBq/mmol. The calculated partition coefficient for the compound was (log P=-1.09). The complex is mostly cleared from the circulation through kidneys and liver. The kidney:blood and  kidney:muscle ratios 24 h post injection were 14.75 and 42.4, respectively.  kidney/liver ratio was almost constant at all time intervals (0.6). Conclusion: [153Sm]-4MPP was prepared at the optimized conditions and suitable characteristics. Further investigations such as biological studies of this agent on tumor-bearing models are needed.