Preclinical Characterization of Novel FAP-2286-Based Radioligand with Albumin Binder for Improved Tumor Retention

Fibroblast activation protein (FAP) is an attractive biomarker for tumor-targeting agents in cancer diagnosis and therapy. FAP-2286 shows retention in FAP-expressing tumors and is known as a promising FAP-targeting radioligand. In this study, we aimed to develop a FAP-2286 derivative that demonstrates higher tumor retention than FAP-2286. We designed DOTAGA-FAP-2286 and DOTAGA-FAP-2286-ALB by replacing DO3A with 2-(4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-1-yl)pentanedioic acid (DOTAGA) and introducing an albumin binder. Both compounds were successfully radiolabeled with ¹¹¹In. Compared with [¹¹¹In]In-DOTAGA-FAP-2286, [¹¹¹In]In-DOTAGA-FAP-2286-ALB showed higher stability in murine plasma. In the cell competition binding study, In-DOTAGA-FAP-2286-ALB exhibited a higher FAP-binding affinity than In-DOTAGA-FAP-2286. In the albumin-binding assay, [¹¹¹In]In-DOTAGA-FAP-2286-ALB showed a high binding rate in the solution with albumin. The biodistribution assay revealed marked tumor retention of [¹¹¹In]In-DOTAGA-FAP-2286-ALB, resulting in the enhancement of predicted tumor AUC values of [²²⁵Ac]Ac-DOTAGA-FAP-2286-ALB. These results suggest advantages of the introduction of an albumin binder to FAP-2286.