Novel recombinant Fab fragments of the TAG-72 monoclonal antibody cc49 containing an integrated radiometal binding site for radioimmunoguided surgery of DCIS

Abstract

Abstract : 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 (9mm)Tc 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 (99m)Tc through its incorporated His6. The tumor targeting properties of (9mm)Tc-rFab will also be evaluated in the xenograft model.