Comparison of (99m)Tc-labeled PR81 and its F(ab')₂ fragments as radioimmunoscintigraphy agents for breast cancer imaging.
OBJECTIVE
We digested anti-MUC1 monoclonal antibody PR81 to produce F(ab')₂ fragments. A comparison was performed between the two radiolabeled PR81 and F(ab')₂ 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')₂ 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')₂ 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')₂ 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.


CONCLUSIONS
The results showed that F(ab')₂ fragment of PR81 is more suitable than intact PR81 for safer and more rapid detection of human breast cancer.
Department of Biology, Faculty of Sciences, Islamic Azad University, Zanjan Branch, 45156-58145 Zanjan, Iran. saloutim@yahoo.com
Mojtaba
M
Salouti
Mohammad Hossein
MH
Babaei
Hossein
H
Rajabi
Haleh
H
Foroutan
Mohammad Javad
MJ
Rasaee
Ahmad Bitarafan
AB
Rajabi
Javad
J
Mohammadnejad
Mohammad
M
Shafiee
Mohammad
M
Mazidi
Fariba Johari
FJ
Daha
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007553:Isotope Labeling; D051379:Mice; D008807:Mice, Inbred BALB C; D015609:Organotechnetium Compounds; D010434:Pepsin A / Q000378:metabolism; D016719:Radioimmunodetection / Q000379:methods*
D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D015609:Organotechnetium Compounds; D010434:Pepsin A