Radioimmunodiagnosis of Head and Neck Squamous Cell Carcinomas : Preclinical Studies

Abstract: Despite improvements in treatment, the prognosis for patients with advanced head and neck squamous cell carcinomas (HNSCC) has only improved to a minor degree. To raise the success rate and minimize morbidity further developments in diagnostics are highly desired. Radioimmunodiagnosis could offer a more specific and sensitive diagnostic method. Herein, we have evaluated different radioimmunoconjugates directed against CD44v6 and epidermal growth factor receptor (EGFR) for imaging of HNSCC. The studies were performed in a murine HNSCC xenograft model.Initially, the 111In-labeled anti CD44v6 chimeric monoclonal antibody U36 (cMAb U36) was evaluated. The novel radioimmunoconjugate showed high and accumulating tumor uptake. Since small molecules might be advantageous for imaging, due mainly to their shorter circulation half-life in the bloodstream, we then investigated antibody fragments F(ab’)2 and Fab’ derived from cMAb U36. The highest tumor-to-blood ratio was achieved with the dimeric antibody fragment F(ab’)2, compared with both the intact anti-body and monomeric Fab’.Furthermore, the possibility of improving EGFR-targeted imaging was explored by pre-blocking EGFR. The liver uptake of injected labeled human epidermal growth factor (hEGF) was significantly reduced when an excess of unlabeled hEGF was injected 30 minutes in advance. However, as hEGF stimulates cell proliferation it may be inadvisable to treat cancer patients with large amounts. Alternatively, pre-blocking with an anti-EGFR Affibody molecule (ZEGFR:955)2 demonstrated similar decrease in liver uptake as unlabeled hEGF. Finally, (ZEGFR:955)2 was compared with other Affibody molecules with higher affinity to EGFR, ZEGFR:1907 and (ZEGFR:1907)2, as pre-blocking agents. In addition, a novel hEGF radioimmunoconjugate, [67Ga]Ga-NOTA-Bn-NCS-hEGF was used for EGFR targeting. The dimeric (ZEGFR:1907)2 showed greatest reduction in non-tumor uptake, and highest tumor-to-organ ratio in EGFR expressing organs, when injected in advance of the radioimmunoconjugate.To summarize, the results presented here demonstrate how different radioimmunoconjugates as well as pre-blocking EGFR can improve the radioimmunodiagnosis of head and neck squamous cell carcinomas.