Biodistribution of¹³¹I-labeled anti-CK8 monoclonal antibody in HNSCC in xenotransplanted SCID mice

Background: A new promising approach to improve the outcome of head and neck squamous cell carcinoma (HNSCC) is the application of radio-labeled antibodies directed against tumor-associated antigens. Cytokeratin 8 (CK8), an intermediate filament forming protein, is shown to be de novo expressed in dysplastic lesions as well as in HNSCC. Therefore like the epithelial cell adhesion molecule CK8 seems to be a suitable anchor molecule for targeted radioimmunotherapy (RIT). The aim of this study was to investigate the biodistribution of a radiolabeled Cytokeratin 8-specific monoclonal antibody (mAb) in a SCID (severe combined immunodeficiency disease) mouse model. Materials and Methods: The mAb against CK8 was labeled with ¹³¹I and biodistribution was tested in established HNSCC xenografts in SCID mice. The biodistribution of the mAb in the tumor and different organs was determined with a gamma counter and was calculated as % injected dose/gram tissue. Results: Initially, after systemic administration of ¹³¹I-anti CK8 monoclonal antibody high activity was seen in all the organs. Over time the general activity decreased, whereas activity accumulated in the tumor. This activity decayed compared to the other tissues with a two- to threefold prolonged radioactive half-life. Conclusion: Specific antibody-antigen-binding is probably responsible for the prolonged radioactive half-life in the tumor and the resulting cumulative activity due to enrichment of the ¹³¹I-anti CK8 mAb, so that Cytokeratin 8 seems to be a suitable anchor molecule for radioimmunotherapy in HNSCC.