Dual-Nuclide Biodistribution and Therapeutic Evaluation of a Novel Antibody-Based Radiopharmaceutical in Anaplastic Thyroid Cancer Xenografts.

Abstract

Anaplastic thyroid cancer (ATC) is a rare but severe form of thyroid cancer responsible for approximately 50% of thyroid cancer deaths. Consequently, the identification of innovative therapies remains crucial for the effective treatment of ATC. Molecular radiotherapy is a rapidly growing field within oncology and the cell surface antigen CD44v6, which is overexpressed in several cancers, is a plausible target for molecular radiotherapy of ATC. Immunohistochemistry (IHC) of 39 ATC patient samples were evaluated for CD44v6 expression. Biodistribution and dosimetry of 125I/177Lu-labeled UU-40, a CD44v6 specific antibody, followed by in vivo efficacy in two ATC xenograft models with varying target expression levels (ACT-1 and BHT-101) accompanied by SPECT-imaging evaluated radiolabeled UU-40 for therapeutic efficiency in ATC xenografts. The IHC revealed CD44v6 immunoreactivity in 46% of ATC patient samples. The biodistribution favored 177LuUU-40 over the 125I-labeled antibody and confirmed in vivo specificity of both radioconjugates. The in vivo efficacy and accompanied SPECT imaging of a moderate CD44v6-expressing xenograft model (BHT-101) verified the tumor specificity as well as the target-specific effect of 177Lu -UU-40 on tumor growth and survival. A 100% complete response rate was demonstrated as a result of therapy using a single dose of 16 MBq 177Lu -UU-40 in a high CD44v6-expressing xenograft model (ACT-1), and SPECT-imaging revealed excellent tumor uptake of the radioconjugate at 14 days post-injection. This study verifies the expression of CD44v6 in ATC and cements the superiority and promise of 177Lu -UU-40 over 131I-UU-40 for antibody-based molecular radiotherapy of CD44v6-positive ATC.