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Radiolabeled porphyrins are potential tumor avid radiopharmaceuticals because of their behaviour in the human body, ability to complex various radionuclides, water solubility, low toxicity etc., in this work radio ytterbium/samarium porphyrin complexes have been developed. 175 Yb and 153 Sm labeled 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrins ([ 175 Yb]-TDMPP/[ 153 Sm]-TDMPP) were prepared using 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrin (H 2 TDMPP) and [ 175 Yb]YbCl 3 or [ 153 Sm]SmCl 3 in 12-24 h at 60 ∘ C. Stability of the complexes were checked in final formulation and human serum for 24 h, followed by partition coefficient determination and biodistribution studies in wild type and breast carcinoma-bearing mice. The radiocomplexes were obtained with acceptable radiochemical purity (> 95% (paper chromatography) and > 96% (HPLC) for [ 175 Yb]-TDMPP and > 97% (paper chromatography) and >98% (HPLC) for [ 153 Sm]-TDMPP) with specific activities of 12-15 GBq/mmol and 278 GBq/mmol at the end of bombardment for [ 175 Yb]-TDMPP and [ 153 Sm]-TDMPP respectively. The partition coefficients were determined for [ 175 Yb]-TDMPP and [ 153 Sm]-TDMPP) (log = 0.63 and log = 0.96 respectively). The [ 175 Yb]-TDMPP complex is mostly washed out from the circulation through kidneys. Liver and spleen also demonstrated significant activity uptake in 72 h post injection. Also [ 153 Sm]-TDMPP, is mostly washed out from the circulation through kidneys, however lungs are the major accumulation sites. The [ 153 Sm]-TDMPP complex demonstrated significant targeted uptake in breast carcinoma xenografts with tumor: blood ratios of 10.67, 10.47 and 19.01 in 24, 48 and72 h respectively. Also interesting tumor: kidney/liver ratios were obtained. 153 Sm-TDMPP properties suggest an efficient tumor targeting agent with high tumor-avidity. Further investigation on the therapeutic properties must be conducted.

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