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Objective: We digested anti-MUC1 monoclonal antibody PR81 to produce F(ab′) fragments. A comparison was performed between the two radiolabeled PR81 and F(ab′) fragments for breast tumor imaging in a mouse model. Methods: The optimum conditions for pepsin digestion of PR81 were investigated in terms of enzymes: antibody ratio, digestion time duration and preserved immunoreactivity of the produced fragments. The F(ab′) fragments were labeled with Technetium-99m using HYNIC as a chelator and tricine as a co-ligand. The immunoreactivity of the complexes was assessed by radioimmunoassay using MCF7 cells. Biodistribution and imaging studies were performed in female BALB/c mice with breast tumor xenograft at 4, 8 and 24 h post-administration. The PR81 was labeled with technetium-99m in the same way for comparison. Results: The optimum time duration for PR81 digestion was found to be 28 h at an enzyme:antibody weight ratio of 1:20 that resulted in 95.2 ± 4.7% purity. The labeling of intact PR81 and its F(ab′) fragments were 87.6 ± 4.2 and 76.1 ± 3.3% after 1 h, respectively ( p value <0.05). The percentage of immunoreactivity of F(ab′) fragments and intact PR81 were 75.4 ± 2.1% and 85.7 ± 2.9%, respectively ( p value <0.05). The biodistribution and imaging studies demonstrated localization of the fragments at 4 h post-administration with high sensitivity and specificity. Conclusion: The results showed that F(ab′) fragment of PR81 is more suitable than intact PR81 for safer and more rapid detection of human breast cancer. [ABSTRACT FROM AUTHOR]

Radioimmunoscintigraphy (RIS) has found widespread clinical application in tumor diagnosis. The antibody (Ab) PR81 is a new murine anti-MUC1 monoclonal antibody (MAb) against human breast carcinoma. In this study a very simple, rapid and efficient method for labeling of this MAb with 99mTc, particularly suitable for development of a 'kit'is described. The reduction of Ab was performed with 2- mercaptoethanol (2-ME) at a molar ratio of 2000:1 (2-ME:MAb) and the reduced Ab was labeled with 99mTc via methylene diphosphonate (MDP) as a transchelator. The labeling efficiency which was determined by instant thin layer chromatography (ITLC) was 94.2%±2.3. Radiocolloides measured by cellulose nitrate electrophoresis were 2.5%±1.7. In vitro stability of the labeled product in human serum which was measured by gel filtration chromatography (FPLC) was 70%±5.7 over 24 hr. The integrity of labeled MAb was checked by means of SDS-PAGE and no significant fragmentation was observed. The results of the cell-binding studies showed that both labeled and unlabeled PR81 were able to compete for binding to MCF 7 cells. Biodistribution studies were performed in normal BALB/c mice at 4 and 24 hrs post-injection and no important accumulation was observed in vital organs. These results show that the new radiopharmaceutical may be considered as a promising candidate for imaging of breast cancer. [ABSTRACT FROM AUTHOR]