From Automated Synthesis to In Vivo Application in Multiple Types of Cancer-Clinical Results with [68Ga]Ga-DATA5m.SA.FAPi

Abstract

Radiolabeled FAPI (fibroblast activation protein inhibitors) recently gained attention as widely applicable imaging and potential therapeutic compounds targeting CAF (cancer-associated fibroblasts) or DAF (disease-associated fibroblasts in benign disorders). Moreover, the use of FAPI has distinct advantages compared to FDG (e.g., increased sensitivity in regions with high glucose metabolism, no need for fasting, and rapid imaging). In this study, we wanted to evaluate the radiochemical synthesis and the clinical properties of the new CAF-targeting tracer [⁶⁸Ga]Ga-DATA^5m.SA.FAPi. The compound consists of a (radio)chemically easy to use hybrid chelate DATA.SA, which can be labeled at low temperatures, making it an interesting molecule for 'instant kit-type' labeling, and a squaric acid moiety that provides distinct advantages for synthesis and radiolabeling. Our work demonstrates that automatic synthesis of the FAP inhibitor [⁶⁸Ga]Ga-DATA^5m.SA.FAPi is feasible and reproducible, providing convenient access to this new hybrid chelator-based tracer. Our studies demonstrated the diagnostic usability of [⁶⁸Ga]Ga-DATA^5m.SA.FAPi for the unambiguous detection of cancer-associated fibroblasts of various carcinomas and their metastases (NSCLC, liposarcoma, parotid tumors, prostate cancer, and pancreas adenocarcinoma), while physiological uptake in brain, liver, intestine, bone, and lungs was very low.

Keywords: DATA; FAP; FAPI; Ga-68; PET; chelator; first-in-human study; molecular imaging; nuclear medicine; squaric acid.

Figure 1

Schematic representation of the relevant chemical structures. (A): Gly-2-cyanopyrrolidine FAP inhibitors: (N-(1-naphthyl)-gly-2-cyanopyrrolidine; (4-quinolinyl)glycyl-2-cyanopyrrolidine and the quinoline-gly-2-cyano-4,4-difluoroPro-based FAPi, UAMC1110; (B) DOTA-conjugated FAPI conjugates FAPI-04 (top) and FAPI-46 (bottom); (C) DATA^5m (D) DATA^5m. SA.FAPi.

Figure 2

Quality control of [⁶⁸Ga]Ga-DATA^5m.SA.FAPi. (A) radio-HPLC; (B) radio-TLC in citric acid buffer; (C) radio-TLC in ammoniumacetate buffer and methanol (1:1 v/v).

Figure 3

Maximum-intensity projection (MIP) of [⁶⁸Ga]Ga-DATA^5m.SA.FAPi in a patient without any disease-related tumor uptake. Gp: glandula parotis; Gsm: glandula submandibularis; T: thyroid; L: liver; Ph: pancreas head; Pt: pancreas tail; Gb: gall bladder; Rp: renal pelvis; U: uterus; B: urinary bladder.

Figure 4

MIPs and transversal images of [⁶⁸Ga]Ga-DATA^5m.SA.FAPi in cancer patients. Crosshair indicates target lesion (highest tumor SUV_max); (A) hepatic metastases of parotid gland tumor; target lesion (primary tumor/liver metastasis): 5.0; (B) metastasized prostate cancer; target lesion (bone metastasis in L1 vertebra): 12.7; (C) metastasized liposarcoma; target lesion (peritoneal metastases): 10.6; (D) primary pancreatic head adenocarcinoma tumor: 10.1.

Figure 5

(A) MIP and transversal image of [⁶⁸Ga]Ga-DATA^5m.SA.FAPi in a NSCLC patient. Crosshair indicates target lesion with a SUV_max of 7.3. (B) Cerebral (left) and bone (right) metastases demonstrated by FAPI-PET/CT. (C,D) MIPs, FDG scan performed two weeks before imaging with [⁶⁸Ga]Ga-DATA^5m.SA.FAPi; the upper picture in (D) is the enlarged image of the head shown in (B).