Analysis of urine samples from metastatic bone cancer patients administered 153Sm-EDTMP

153Sm-EDTMP is currently undergoing clinical evaluation as a radiotherapeutic agent for the relief of pain associated with cancer metastatic to bone. These clinical studies have demonstrated biodistributions similar to those seen earlier in animals, namely, rapid clearance from blood, selective uptake in bone and in particular metastatic bone lesions. The radioactivity not deposited in bone is cleared through the kidneys into the urine. In this study, urine samples collected from 9 patients injected with 153Sm-EDTMP underwent complexation analysis via Pharmacia SP-Sephadex C25 cation exchange chromatography. The results showed 96.9 +/- 1.7% of the radioactivity in the urine to be present as a complex of 153Sm. An HPLC method was developed and it was demonstrated that different complexes of 153Sm could be separated. A non-radioactive analytical standard of the Sm-EDTMP chelate was synthesized, characterized and shown to have the same HPLC retention profile as the 153Sm-EDTMP drug product. HPLC analysis was performed on six urine samples and in each case a single radioactivity peak with an elution profile the same as that of a 153Sm-EDTMP standard was observed. These results indicate that the 153Sm-EDTMP chelate is excreted intact in the urine of patients.