Characterization of 177Lu-Affibody-HSA bioconjugate for radionuclide therapy of EGFR-expressing head and neck carcinomas

Objectives The epidermal growth factor receptor (EGFR) is an attractive target for radionuclide therapy of disseminated head and neck carcinomas. EGFR specific Affibodies have shown excellent tumor localizations in PET and SPECT studies, but on the other hand, display extremely high kidney uptakes (>100%ID/g). This represents a critical concern for high doses to the radiation sensitive kidneys. We have recently demonstrated that a human serum albumin (HSA)-HER2 Affibody conjugate exhibits improved pharmacokinetics. The purpose of this study is to further explore whether radiolabeled EGFR-HSA bioconjugates could be suitable for radionuclide therapy of EGFR expressing tumors.

Methods HSA was modified by a site-specific conjugation with DOTA-NHS and the bifunctional crosslinker Sulfo-SMCC. The EGFR Affibody analog Ac-Cys-ZEGFR:1907 was then covalently conjugated with the HSA through the sulfo-SMCC, and the resulting bioconjugate DOTA-HSA-ZEGFR:1907 was further radiolabeled with 64Cu and 177Lu. Radiometal labeled DOTA-HSA-ZEGFR:1907 was subjected to in vitro cell uptake and internalization studies using the human oral squamous carcinoma cell line SAS (n=5). PET, SPECT and biodistribution studies were examined using SAS tumor-bearing mice (n=4).

Results Radiolabeling with 64Cu as well as with 177Lu resulted in high radiochemical yields (>70%). The in vitro stability of 177Lu-DOTA-HSA-ZEGFR:1907 in mouse serum was >80% at 168 h. Cell uptake studies displayed a significant (8.4% at 4 h) and specific uptake and the internalization of 177Lu-DOTA-HSA-ZEGFR:1907 could be verified. PET and SPECT using 64Cu-DOTA-HSA-ZEGFR:1907 and 177Lu-DOTA-HSA-ZEGFR:1907, respectively showed good tumor imaging contrasts. The imaging results were consistent with the biodistribution data: 177Lu-DOTA-HSA-ZEGFR:1907 displayed good tumor uptakes (5.1% ID/g) and high liver uptakes (31.5% ID/g) and relatively low kidney uptakes (8.5% ID/g) at 72 h p.i.

Conclusions 177Lu-DOTA-HSA-ZEGFR:1907 is a promising agent for radionuclide therapy of EGFR expressing head and neck carcinomas