Factors Affecting Chemistry of Reduction - Mediated
99mTc-Labelling of Monoclonal Antibodies and Poly
clonal Human Immunoglobulins
VIPA BOONKITTICHAROEN, Ph.D.*, DUANGPEN PUCHINDA, M.Sc. *,
ANNA NGONRATH NA AYUDHYA,B.Sc.*, PUANGTONG KRAIPHIBUL, M.D.*
Affiliation : * Division of Radiotherapy and Nuclear Medicine, Department of Radiology, Faculty of Medicine, Ramathibodi
Hospital, Mahidol University, Bangkok 10400, Thailand.
AbstractIn developing a new method for preparing a radiopharmaceutical for clinical investigation, a thorough understanding of reaction stoichiometry is crucial in optimizing the labelling
chemistry. Factors determining labelling efficiency of the 2 - mercaptoethanol (2-ME) - mediated
99mTc-labelling of antibody molecules were elucidated using anti-tumor monoclonal antibodies
of different lgG subclasses (i.e. IOR-CEA(IgG 1), Ml70(1gG 1), 3F8(IgG3) and EMD (lgG2.)) and
polyclonal human immunoglobulins (Sandoglobulin). Antibodies which were sensitive to 2-ME
reduction (i.e. required 500-1000 molar excess of 2-ME) could tag 99mTc with high efficiency since
they possessed abundant reactive sites (i.e. sulfydryl groups) for 99mTc binding. Reduction sensitivity of antibodies was unlikely to be affected by IgG subclass and could be rated as follows :
Sandoglobulin > IOR-CEA > 3F8 > Ml70 > EMD. Concentrations of the reduced antibodies for
effective labelling appeared to be related to the reduction sensitivity, i.e. 0.2, 0.4 and 0.6 mg/ml
were required for labelling of IOR-CEA, 3F8 and Ml70 respectively. In addition, susceptibility to
2-ME reduction seemed to reflect the rate of antibody labelling. For 2-ME resistant molecules, i.e.
M 170 and EMD, successful labelling could be achieved by using a slow 99mTc reducing agent such
as SnC1
2 instead of SnF2 which reacted more rapidly. Since 2-ME generates reactive sulfhydryl
groups that are distal to antigen binding sites, the immunoreactivity of the modified antibody was
not affected by the effect of reduction.
Keywords : 99mTc-Labelling, Labelling Chemistry, Anti-Tumor Monoclonal Antibody, Human Immunoglobulin
All Articles
Download
