Radioimmunoimaging of colorectal cancer using (99m)Tc labeled monoclonal antibody

Abstract

AIM:To determine whether Hb3 and its fragment F(ab')(2) have practical value in radioimmunoimaging of colorectal cancer.METHODS:Intact Hb3 was purified by hydroxylapatite chromatography.The fragment F(ab') (2) was prepared by cold digestion and purified as intact Hb3.Hb3 and its fragment F(ab') (2) were labeled with 99mTc by direct labeling method using SnCl(2) as reducing agent. The radioactive doses ranged from 15 to 40 mCi.The imaging was accomplished by single photon emission computered tomograph (SPECT) with imaging time ranging from 2.5 to 48 hours. In this study, 10 patients were selected. Among them, 7 were administered with intact Hb3, and 3 with F(ab') (2) fragment. All the patients were diagnosed as having colorectal adenocarcinoma.RESULTS:After purification, intact Hb3 and its fragment F(ab') (2) were fit for radioimmunoimaging. The percentage of labeling of (99m)Tc to Hb3 or F(ab') (2) was 80.6%-91.5%. Among the 10 patients, 3 of 7 patients administered with intact Hb3 had positive scans, the other 4 had negative scans, and 2 of 3 patients administered with F(ab') (2)had positive scans, the other 1 had negative scans.CONCLUSION:The results showed that both intact Hb3 and its F(ab') (2) have some practical value in radioimmunoimaging of colorectal cancer, and the effects of imaging with F(ab') (2) was better than that with intact Hb3.

Figure 1

Chromatogram of digested Hb3. OD₂₈₀ (·-·) shows concentration of protein. OD₄₀₅ (+ - +) shows immunoreactivity.

Figure 2

SDS-PAGE results of antibody electrophoresis. Lane 1: low molecular weight marker; lane 2-3: intact Hb3; lane 4-5: intact Hb3 (1/10 concentration); lane 6: Hb3 fragments F(ab’)₂ (broken); lane 7: Hb3 fragments F(ab’)₂ (unbroken); lane 8: high molecular weight marker; lane 9: low molecular weight marker.

Figure 3

Chromatogram of ^99mTc labeled antibody, OD₄₀₅ shows immunoreactivity. ·-· radioactivity, + - + immunoreactivity.

Figure 4

Images of Patient 4. Rectal cancer complicated with liver metastasis. Anterior scan (6 h) shows an unclear abnormal radiation concentration under the bladder (upper left). Anterior scan (24 h) shows a clear abnormal radiation concentration in the left lobe of liver (lower left).