A search for monoclonal antibodies for the immunolocalisation of colorectal cancer

For the immunoscintigraphy or antibody targeting of colorectal cancer there is a need for monoclonal antibodies with better specificity and reactivity. The search for such antibodies forms the basis of this thesis. Two approaches were used. First, new monoclonal antibodies were produced against a crude membrane extract prepared from several colorectal cancers. Ten fusions were performed between immunised spleen cells from Balb C mice and the mouse myeloma cell line NSO, producing a total of 893 hybridomas of which 245 secreted antibodies positive on ELISA. Only 67 of these antibodies stained frozen sections of colorectal cancer. Five hybridomas (UC-ICR 12.1, 20.3, 40.1, 41.2 and 41.6) were cloned to monoclonal stage. UC-ICR 41.2 and 41.6 showed a favourable tissue distribution on immunocytochemistry and may be suitable for immunoscintigraphy. Second, immunoperoxidase technique was used to test 25 different monoclonal antibodies for cross-reactivity to colorectal cancer. Three monoclonals, M8, 77-1 and 8-30-3, which recognise epitopes of epithelial membrane antigen (EMA), showed a preferential affinity to the cancer when compared to normal colon. One of these, M8 has already been used for the immunoscintigraphy of breast cancer. The monoclonal antibody 77-1, radiolabelled with iodine-125 and indium-111, was found to retain immunoreactivity on live cell binding assays and xenograft localisation studies. In a clinical localisation study indium-111 labelled M8 detected 13 out of 21 (62%) tumour sites (13 primary tumours, 5 liver metastases and 3 recurrent tumours) in 16 patients. The uptake of the radiolabel as measured by the tumour to blood ratio was 5.3 ± 3.7 and the mean tumour to normal colon ratio was 2.5 ± 1.20. Indium-111 labelled 77-1 detected 10 of 17 (59%) tumour sites (12 primary, 3 liver metastases, and 2 recurrent tumours) in 14 patients. The tumour to blood ratio was 3.6 ± 1.43 and the mean tumour to normal colon ratio was 2.0 ± 0.81. These results showed that anti-EMA monoclonal antibodies have a role in the immunoscintigraphy of colorectal cancer. The new monoclonal antibodies UC-ICR 41.2 and 41.6 are worth further evaluation.