The combination of external beam radiotherapy and experimental radioimmunotargeting with a monoclonal anticytokeratin antibody.

Abstract

Doses to tumors of up to 80 grays (Gy) have been postulated to eradicate solid experimental tumors with radiommunotargeting, but this value has proved difficult to reach. Combining two treatment modalities, external beam radiotherapy and radioimmunotargeting, could potentially give rise to a number of advantages. The purpose of this study was to detect potential benefits with different treatment timing strategies when combining external beam radiotherapy and radioimmunotargeting, with the anticytokeratin monoclonal antibody (MAb) TS1 injected into a nude mouse model carrying subcutaneous human HeLa Hep 2-cell tumors. Cytokeratins are present in necrotic regions within tumors, thereby providing a potential increase in binding sites for TS1 if combined with external beam radiotherapy. External beam radiotherapy was given before, after, and simultaneously with injection of radiolabeled MAb. The highest yields in terms of total accumulated dose (Gy), percentage of injected activity per gram of tumor tissue, and accumulated dose per injected activity (Gy/MBq) were seen in the group receiving external beam radiotherapy prior to MAb-injection. Enhanced effects may be achievable by combining external beam radiotherapy with experimental radioimmunotargeting using the monoclonal anticytokeratin antibody TS1, if the radiotherapy is given prior to MAb injection.