Intensification of tumor affinity of 99mTc-DL-homocysteine by cooperative use of SH-containing compounds.

The enhancement of tumor-specific distribution was investigated on 99mTc-DL-homocysteine (99mTc-Hcy), a possible tumor-imaging agent. In vitro HPLC analysis showed that 99mTc-Hcy did not bind to nonmercaptalbumin but to mercaptalbumin in blood. When glutathione, homocysteine or cysteine, which converts albumin from the mercapto- to nonmercapto-form, was intravenously injected into 99mTc-Hcy predosed mice bearing Ehrlich solid tumor, the SH-containing compounds did not affect the radioactivity distribution in tumor, but decreased that in blood to less than half that of untreated animals. In vitro gel filtration analysis showed that glutathione released 99mTc-Hcy from albumin. Free 99mTc-Hcy produced in blood by the treatment was rapidly excreted into urine. These results suggest that the combination of 99mTc-Hcy and SH-containing compounds is useful for tumor-imaging.