Radioimmunoscintigraphy of Breast Tumor Xenografts in Mouse Model by 99mTc Direct Radiolabeling of a Monoclonal Antibody PR81

Authors

1 Ph.D. Student in Medical Physics, Medical Physics Dept., Tarbiat Modarres University, Tehran, Iran

2 Assistant Professor, Medical Physics Dept., Tarbiat Modarres University, Tehran, Iran.

3 Assistant Professor, Radioisotope Dept., Nuclear Research Center, Atomic Energy Organization of Iran, Tehran, Iran.

4 Professor, Medical Biotechnology Dept., Tarbiat Modarres University, Tehran, Iran.

5 -Associate Professor, Radioisotope Dept., Nuclear Research Center, Atomic Energy Organization of Iran, Tehran, Iran.

6 B. Sc. Radioisotope Dept., Nuclear Research Center, Atomic Energy Organization of Iran, Tehran, Iran.

7 M. Sc. Radioisotope Dept., Nuclear Research Center, Atomic Energy Organization of Iran, Tehran, Iran.

8 Professor, Immunology Dept., Tarbiat Modarres University, Tehran, Iran.

9 Ph.D. Student in Medical Physics, Medical Physics Dept., Tarbiat Modarres University, Tehran, Iran.

10 Ph.D. Student in Medical Biotechnology, Medical Physics Dept., Tarbiat Modarres University, Tehran, Iran

11 Professor, Pathology Dept., Tarbiat Modarres University, Tehran, Iran.

12 Assistant Professor,Laboratory Animal Sciences Dept., Institue Pastor, Tehran, Iran.

Abstract

Introduction: The radioimmunoscintigraphy (RIS) has found widespread clinical applications in 
tumor  diagnosis.  Human  epithelial  mucin,  MUC1,  is  commonly  over  expressed  in 
adenocarcinoma including 80% of breast cancers and represents a useful target for RIS. The PR81 
is  a  new  murine  anti-MUC1  monoclonal  antibody  that  was  found  to  react  with  the  membrane 
extracts of several human breast cancerous tissues and the cell surface of some MUC1 positive 
cell lines. In this study, a direct method which is very simple, rapid and efficient for the labeling 
of this MAb with 99mTc, particularly suitable for the development of a ‘kit’, was developed. The 
quality  control  of  new  radiopharmaceutical  and  immunoscintigraphy  studies  in  BALB/c  mice 
bearing breast tumor xenografts were also performed. 
Materials and Methods: The Ab reduction was performed with 2-mercaptoethanol (2-ME) at a 
molar  ratio  of  2000:1  (2-ME:MAb)  and  reduced  Ab  was  labeled  with 99mTc  via  methylene 
diphosphonate (MDP) as a transchelator. The labeling efficiency was determined by ITLC. The 
amount  of  radiocolloids  was  measured  by  cellulose  nitrate  electrophoresis.  The  stability  of  the 
labeled product was checked in fresh human serum by gel filtration chromatography (FPLC) over 
24 hrs. The integrity of the labeled MAb was checked by the means of SDS-PAGE. Cell-binding 
assay  was  used  to  test  the  binding  ability  of 99mTc-PR81  to  MCF7  cells.  Biodistribution  was 
studied in normal BALB/c mice at 4 and 24 hrs post-injection. The tumor imaging was performed 
in female BALB/c mice with breast tumor xenografts 24 hrs after the new complex injection. 
Results:  The  labeling  efficiency  was  94.2%±2.3  and  radiocolloids  were  2.5%±1.7.  In  vitro 
stability  was  70%±5.7  in  fresh  human  serum  over  24  hrs.  There  was  no  significant  Ab 
fragmentation due to the labeling procedure. Both the labeled and unlabeled PR81 were able to 
compete for binding to MCF7 cells. The biodistribution studies in normal BALB/c mice showed 
that  there  was  no  important  accumulation  in  any  organ.  The  immunoscintigraphy  studies 
demonstrated definite localization of the preparation at the site of tumors with high sensitivity. 
Discussion and Conclusion: The results show that by using the Schwarz method of radiolabeling 
MAb PR81, a labeling yield higher than 90% with high stability of the complex in human serum 
can be obtained. These findings demonstrated that the new radiopharmaceutical can be considered 
as a promising candidate for imaging of human breast cancer. 

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