FAP (fibroblast activation protein)

Of 15 synthesized FAPIs, FAPI-04 was identified as the most promising tracer for clinical application. Compared with the previously published ligand, FAPI-02, FAPI-04 showed excellent stability in human serum, higher affinity for FAP as opposed to CD26, and slower excretion in vitro. https://pubmed.ncbi.nlm.nih.gov/29626119/

In vivo, a higher SUV was reached in tumor-bearing animals, leading to larger areas under the curve as calculated from biodistribution experiments. Finally, PET/CT scans with 68Ga-FAPI-04 in 2 patients with metastasized breast cancer revealed high tracer uptake in metastases and a reduction in pain symptoms after therapy with a considerably low dose of 90Y-FAPI-04. Conclusion: FAPI-04 represents a promising tracer for both diagnostic imaging and, possibly, targeted therapy of malignant tumors with a high content of activated fibroblasts, such as breast cancer.https://pubmed.ncbi.nlm.nih.gov/29626119/

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Results: Similar to literature values for 18F-FDG, 68Ga-DOTATATE, and 68Ga-PSMA-11, an examination with 200 MBq of 68Ga-FAPI-2 or 68Ga-FAPI-4 corresponds to an equivalent dose of approximately 3-4 mSv. After a fast clearance via the kidneys, the normal organs showed a low tracer uptake with only minimal changes between 10 min and 3 h after injection. In 68Ga-FAPI-2, the tumor uptake from 1 to 3 h after injection decreased by 75%, whereas the tumor retention was prolonged with 68Ga-FAPI-4 (25% washout). Regarding tumor-to-background ratios, at 1 h after injection both 68Ga-FAPI tracers performed equally. In comparison to 18F-FDG, the tumor uptake was almost equal (average SUVmax, 7.41 for 18F-FDG and 7.37 for 68Ga-FAPI-2; not statistically significant); the background uptake in brain (11.01 vs. 0.32), liver (2.77 vs. 1.69), and oral/pharyngeal mucosa (4.88 vs. 2.57) was significantly lower with 68Ga-FAPI. Other organs did not relevantly differ between 18F-FDG and 68Ga-FAPI. Conclusion: FAPI PET/CT is a new diagnostic method in imaging cancer patients. In contrast to 18F-FDG, no diet or fasting in preparation for the examination is necessary, and image acquisition can potentially be started a few minutes after tracer application. Tumor-to-background contrast ratios were equal to or even better than those of 18F-FDG.[1]

FAPIs based on a quinoline structure were synthesized and characterized with respect to binding, internalization, and efflux in cells expressing human and murine FAP as well as CD26.https://pubmed.ncbi.nlm.nih.gov/29626119/

Preclinical pharmacokinetics were determined in tumor-bearing animals with biodistribution experiments and small-animal PET. Finally, a proof-of-concept approach toward imaging and therapy was chosen for 2 patients with metastasized breast cancer. https://pubmed.ncbi.nlm.nih.gov/29626119/

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Methods: A preliminary dosimetry estimate for 68Ga-FAPI-2 and 68Ga-FAPI-4 was based on 2 patients examined at 0.2, 1, and 3 h after tracer injection using the QDOSE dosimetry software suit. Further PET/CT scans of tumor patients were acquired 1 h after injection of either 68Ga-FAPI-2 (n = 25) or 68Ga-FAPI-4 (n = 25); for 6 patients an intraindividual related 18F-FDG scan (also acquired 1 h after injection) was available. For the normal tissue of 16 organs, a 2-cm spheric volume of interest was placed in the parenchyma; for tumor lesions, a threshold-segmented volume of interest was used to quantify SUVmean and SUVmax[1]

[1]. 68Ga-FAPI PET/CT: Biodistribution and Preliminary Dosimetry Estimate of 2 DOTA-Containing FAP-Targeting Agents in Patients with Various Cancers. J Nucl Med. 2019 Mar;60(3):386-392.

[2]. Fibroblast Activation Protein (FAP) targeting homodimeric FAP inhibitor radiotheranostics: a step to improve tumor uptake and retention time. Am J Nucl Med Mol Imaging. 2021 Dec 15;11(6):476-491.

[3]. Clinical summary of fibroblast activation protein inhibitor-based radiopharmaceuticals: cancer and beyond. Eur J Nucl Med Mol Imaging. 2022 Jul;49(8):2844-2868. doi: 10.1007/s00259-022-05706-y. Epub 2022 Jan 31. Erratum in: Eur J Nucl Med Mol Imaging. 2022 Jul;49(8):3007.

Currently, several radiopharmaceuticals targeting fibroblast activation proteins (FAPs) based on the highly effective FAP inhibitor UAMC1110 are under investigation. Preclinical and clinical studies have shown the potential of these imaging agents. However, the monomeric small molecules have short retention times in tumors and high renal clearance. Therefore, our strategy is to develop a homodimer system containing two FAP inhibitors to prolong retention time and enhance tumor accumulation. We synthesized the homodimers DOTA·(SA·FAPi)₂ and DOTAGA·(SA·FAPi)₂, which contain two squaramide-conjugated FAP inhibitors, and evaluated them radiochemically using gallium-68. We tested the in vitro stability, lipophilicity, and affinity of [⁶⁸Ga]Ga-DOTAGA·(SA·FAPi)₂. Furthermore, [68Ga]Ga-DOTAGA.(SA.FAPi)2 was subjected to human PET/CT scans and directly compared with [68Ga]Ga-DOTA.SA.FAPi and [18F]FDG. Gallium-68 labeling showed a higher radiochemical yield. Inhibition experiments demonstrated that the compound exhibits excellent affinity and selectivity for FAP, with IC50 values down to the nanomolar level. In human PET/CT studies, [68Ga]Ga-DOTAGA.(SA.FAPi)2 showed significantly higher tumor uptake and longer tumor retention time compared to [68Ga]Ga-DOTA.SA.FAPi. Therefore, the introduction of the dimer has advanced human PET imaging technology, manifested in increased tumor accumulation and prolonged in vivo retention time. Thus, the application of the dimer structure may be the next step in prolonging the uptake time of FAP inhibitors, thereby developing radiotherapy analogs of FAP inhibitors. [2]

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Fibroblast activating protein (FAP) is a type II membrane-bound glycoprotein that is overexpressed in cancer-associated fibroblasts and activated fibroblasts at wound healing/inflammatory sites. Since the first clinical application of quinoline-based FAP ligands in 2018, FAP inhibitor-based PET imaging and radiotherapy have been used to study a variety of diseases, including malignant and non-malignant ones. Therefore, remarkable progress has been made, especially in deepening the understanding of FAPI-based PET imaging and the potential value of FAPI-based tumor radiotherapy. This article provides a comprehensive review of radiolabeled FAPIs and their clinical translation, aiming to elucidate the current and future potential roles of such molecules in nuclear medicine. In particular, this article highlights the value of FAPI radiopharmaceuticals in the diagnosis and treatment of tumors or benign diseases. However, current research limitations hinder the accurate evaluation of FAPI radiopharmaceuticals. Nevertheless, it remains important to further explore the clinical value of FAPIs in diagnosis and treatment through the design of more sophisticated and larger-sample clinical trials in the future. [3]

C40H56N10O10

836.93

836.418

2370952-98-8

138454802

White to off-white solid powder

1.43±0.1 g/cm3(Predicted)

1143.9±65.0 °C(Predicted)

-7.2

4

17

16

60

1490

1

C1C[C@H](N(C1)C(=O)CNC(=O)C2=C3C=C(C=CC3=NC=C2)OCCCN4CCN(CC4)C(=O)CN5CCN(CCN(CCN(CC5)CC(=O)O)CC(=O)O)CC(=O)O)C#N

CRWOFMLXEOYIEP-PMERELPUSA-N

InChI=1S/C40H56N10O10/c41-24-30-3-1-9-50(30)35(51)25-43-40(59)32-6-7-42-34-5-4-31(23-33(32)34)60-22-2-8-44-18-20-49(21-19-44)36(52)26-45-10-12-46(27-37(53)54)14-16-48(29-39(57)58)17-15-47(13-11-45)28-38(55)56/h4-7,23,30H,1-3,8-22,25-29H2,(H,43,59)(H,53,54)(H,55,56)(H,57,58)/t30-/m0/s1

2-[4,7-bis(carboxymethyl)-10-[2-[4-[3-[4-[[2-[(2S)-2-cyanopyrrolidin-1-yl]-2-oxoethyl]carbamoyl]quinolin-6-yl]oxypropyl]piperazin-1-yl]-2-oxoethyl]-1,4,7,10-tetrazacyclododec-1-yl]acetic acid

FAPI-2; 2370952-98-8; UNII-54MD7EU3MC; 54MD7EU3MC; FAPI-02; SCHEMBL21257060;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: 100 mg/mL (119.48 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (2.99 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (2.99 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (2.99 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)