This study was designed to evaluate a direct method of 99mTc labeling using β-mercaptoethanol as a reducing agent, and to investigate whether 99mTc labeled specific monoclonal antibody against carcinoembryonic antigen (CEA-92) can be used for
the
scintigraphic localization of human colon cancer xenograft. Purified CEA-92 IgG was fragmented into F (ab')2 and then labeled with 99mTc by transchelation method using glucarate as a chelator. Labeling efficiency, immunological reactivity and in
vitro
stability of 99mTc CEA-92 F (ab')2 were measured and then injected intravenously into nude mice bearing human colon cancer (SNU-C4). Scintigrams were obtained at 24 hour after injection. Then nude mice were sacrificed and the radioactivity was
measured.
Labeling efficiency of injected 99mTc CEA-92 F (ab')2, immunoreative fraction and in vitro stability at 24 hour of injected 99mTc CEA-92 F (ab')2 was 45.2%, 32.8% and 57.4%, respectively. At 24 hour after injection, % ID/g in kidney (46.77)
showed
high
uptake, but %ID/g in tumor (1.65) was significantly higher than spleen (0.69), muscle (0.16), intestine (0.45), stomach (0.75), heart (0.48) and blood (0.45). There was no significant difference between tumor and liver (1.81). Tumor contrast as
quantitated by tumor to blood ratio of 99mTc CEA-92 F (ab')2 was increased significantly (p<0.005) until 24 hours (3.70), and there was no statistical differece from tumor to blood ratio of I-131 CEA-92 F (ab')2.
The scintigram demonstrated localization of radioactivity over transplanted tumor, but significant background radioactivity was also noted over kidney and abdomen.
It is concluded that CEA-92 F (ab')2 can be labeled with 99mTc by a direct transchelation method using β-mercaptoethanol as a reducing agent and 99mTc labeled CEA-92 F (ab')2 can be used for the scintigraphic localization of human colon cancer
xenograft in nude mice model.
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