Chemical form of tumor-tropic 99mTc-DL-homocysteine

Analyses of the chemical forms of 99mTc-complexes provide important information for the development of a new tumor-tropic 99mTc-labeled radiopharmaceutical. We attempted to determine the chemical form of 99mTc-DL-homocysteine (99mTc-Hcy) which was previously reported to be tumor-tropic. By analyzing the functional residues of Hcy in the 99mTc-Hcy molecule, it was estimated that the sulfhydryl and amino residues participated in the chelate formation. Gel filtration analysis of 99mTc-Hcy indicated that its molecular size was bigger than that of 99mTc-penicillamine monomer. The analysis also indicated that 99mTc-Hcy complex seemed to be a relatively small oligomer. Although an uncertainty remains on the valency of Tc in 99mTc-Hcy molecule and the accurate molecular size of this complex, its putative chemical form is described.