Novel Recombinant Fab Fragments of the Tag-72 Monoclonal Antibody CC49 Containing an Integrated Radiometal Binding Site for Radioimmunoguided Surgery for DCIS
Annual summary 1 May 2003-30 Apr 2004
UNIVERSITY HEALTH NETWORK TORONTO (ONTARIO) GRANT AND CONTRACT SERVICES
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Ductal carcinoma in situ DCIS is an early form of breast cancer. Surgical treatment of DCIS is currently inadequate due to the inability to define accurately the extent of the disease. Radioimmunoguided surgery RIGS employing radionuclide-conjugated monoclonal antibodies against breast cancer antigens and a sensitive gamma-detecting probe may improve the surgical management of DCIS by more clearly identifying malignant tissue. TAG-72 antigen is overexpressed in 81 of NCIS by immunohistochemical staining with monoclonal antibody CC49. Our objective was to construct a novel recombinant Fab rFab of CC49 containing an integrated radiometal-binding site that can be directly labeled with 9mmTc through the C-terminal hexahistidine His6 for RIGS of DCIS. In the first year of the project, I have cloned the genes of Fab L and Fd from CC49 hybridoma cells, constructed a co-expression plasmid to express rFab of CC49 in Pichia pastoris, and purified the rFab to homogeneity. This rFab was immunoreactive to TAG-72 in vitro rFab labeled with 1231 localized specifically in TAG-72 positive s.c. LS174T cancer xenografts in athymic mice. In the second year, rFab will be labeled with 99mTc through its incorporated His6. The tumor targeting properties of 9mmTc-rFab will also be evaluated in the xenograft model.
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