Preclinical evaluation of FAP-2286 for fibroblast activation protein targeted radionuclide imaging and therapy

Purpose Fibroblast activation protein (FAP) is a membrane-bound protease that has limited expression in normal adult tissues but is highly expressed in the tumor microenvironment of many solid cancers. FAP-2286 is a FAP-binding peptide coupled to a radionuclide chelator that is currently being investigated in patients as an imaging and therapeutic agent. The potency, selectivity, and efficacy of FAP-2286 were evaluated in preclinical studies. Methods FAP expression analysis was performed by immunohistochemistry and autoradiography on primary human cancer specimens. FAP-2286 was assessed in biochemical and cellular assays and in in vivo imaging and efficacy studies, and was further evaluated against FAPI-46, a small molecule–based FAP-targeting agent. Results Immunohistochemistry confirmed elevated levels of FAP expression in multiple tumor types including pancreatic, breast, and sarcoma, which correlated with FAP binding by FAP-2286 autoradiography. FAP-2286 and its metal complexes demonstrated high affinity to FAP recombinant protein and cell surface FAP expressed on fibroblasts. Biodistribution studies in mice showed rapid and persistent uptake of 68 Ga-FAP-2286, 111 In-FAP-2286, and 177 Lu-FAP-2286 in FAP-positive tumors, with renal clearance and minimal uptake in normal tissues. 177 Lu-FAP-2286 exhibited antitumor activity in FAP-expressing HEK293 tumors and sarcoma patient-derived xenografts, with no significant weight loss. In addition, FAP-2286 maintained longer tumor retention and suppression in comparison to FAPI-46. Conclusion In preclinical models, radiolabeled FAP-2286 demonstrated high tumor uptake and retention, as well as potent efficacy in FAP-positive tumors. These results support clinical development of 68 Ga-FAP-2286 for imaging and 177 Lu-FAP-2286 for therapeutic use in a broad spectrum of FAP-positive tumors.