Ga-68-Trivehexin

Like most precursors used for radiolabeling with radioactive metal cations, Trivehexin is composed of a dedicated complex ligand (a so-called chelator) for kinetically inert binding of the ⁶⁸Ga^III ion, and the bioligand(s) for binding to αvβ6-integrin. The chelator comprised in Trivehexin is a triazacycloalkane with 3 phosphinic acid substituents, with the basic structure 1,4,7-triazacyclononane-1,4,7-triphosphinate{{cite journal | vauthors = Notni J, Šimeček J, Wester HJ | title = Phosphinic acid functionalized polyazacycloalkane chelators for radiodiagnostics and radiotherapeutics: unique characteristics and applications | journal = ChemMedChem | volume = 9 | issue = 6 | pages = 1107–1115 | date = June 2014 | pmid = 24700633 | doi = 10.1002/cmdc.201400055 }} (frequently abbreviated TRAP).{{cite journal | vauthors = Notni J, Šimeček J, Hermann P, Wester HJ | title = TRAP, a powerful and versatile framework for gallium-68 radiopharmaceuticals | journal = Chemistry | volume = 17 | issue = 52 | pages = 14718–14722 | date = December 2011 | pmid = 22147338 | doi = 10.1002/chem.201103503 }}{{cite journal | vauthors = Steiger K, Quigley NG, Groll T, Richter F, Zierke MA, Beer AJ, Weichert W, Schwaiger M, Kossatz S, Notni J | title = There is a world beyond αvβ3-integrin: Multimeric ligands for imaging of the integrin subtypes αvβ6, αvβ8, αvβ3, and α5β1 by positron emission tomography | journal = EJNMMI Research | volume = 11 | issue = 1 | pages = 106 | date = October 2021 | pmid = 34636990 | pmc = 8506476 | doi = 10.1186/s13550-021-00842-2 | doi-access = free }}{{cite journal | vauthors = Baranyai Z, Reich D, Vágner A, Weineisen M, Tóth I, Wester HJ, Notni J | title = A shortcut to high-affinity Ga-68 and Cu-64 radiopharmaceuticals: one-pot click chemistry trimerisation on the TRAP platform | journal = Dalton Transactions | volume = 44 | issue = 24 | pages = 11137–11146 | date = June 2015 | pmid = 25999035 | doi = 10.1039/C5DT00576K | hdl = 2437/234748 | hdl-access = free }} The αvβ6-integrin binding molecular unit is a cyclic nonapeptide with the amino acid sequence cyclo(YRGDLAYp(NMe)K).

In the Trivehexin molecule, three of these cyclopeptides are attached by covalent bonds to a single TRAP chelator core. Since TRAP possesses three equivalent carboxylic acids for conjugation of other molecular units via amide formation, Trivehexin is a C3-symmetrical molecule with its three peptide bioligands being fully equivalent. The peptides are attached to the chelator core via the terminal amine group of the side chains of N-methyl lysine. Actually, the conjugation is not done by amide bonding directly, but involves prior functionalization of the peptide with a short molecular extension (a linker) bearing a terminal alkyne, and of TRAP with three linkers bearing terminal azides. These components are assembled by means of copper(I) catalyzed alkyne-azide cycloaddition (CuAAC, also known as Huisgen reaction, a Click chemistry reaction), giving rise to the three 1,3-triazole linkages in the ⁶⁸Ga-Trivehexin structure.

⁶⁸Ga-Trivehexin is a radioactive drug. The radioactive atom, gallium-68 (⁶⁸Ga), decays with a half-life of approximately 68 min to the stable isotope zinc-68 (⁶⁸Zn), to 89% by β⁺ decay whereby a positron with a maximum kinetic energy of 1.9 MeV is emitted (the remaining 11% are EC decays). Due to the short half life, ⁶⁸Ga-Trivehexin can not be manufactured long before use but the ⁶⁸Ga has to be introduced into the molecule shortly before application. This process is referred to as radiolabeling, and is done by complexation of the trivalent cation ⁶⁸Ga^III by the TRAP chelator in Trivehexin.

⁶⁸Ga^III is usually obtained from a dedicated mobile radionuclide source, a Gallium-68 generator, in form of a solution in dilute (0.04–0.1 M) hydrochloric acid (frequently and imprecisely referred to as "⁶⁸Ga chloride solution in HCl" despite it contains no species with a Ga–Cl bond but [⁶⁸Ga(H₂O)₆]³⁺ complex hydrate cations).{{Cite journal |date=2008-02-20 |title=Gallium(III) Ion Hydrolysis under Physiological Conditions |url=http://koreascience.or.kr/journal/view.jsp?kj=JCGMCS&py=2008&vnc=v29n2&sp=372 |journal=Bulletin of the Korean Chemical Society |language=en |volume=29 |issue=2 |pages=372–376 |doi=10.5012/bkcs.2008.29.2.372 |issn=0253-2964}} For radiolabeling, the pH of the ⁶⁸Ga containing generator eluate has to be raised from its initial value (depending on HCl concentration, pH 1–1.5) to pH 2–3.5 using suitable buffers, such as sodium acetate. Then, Trivehexin (5–10 nmol) is added to the buffered ⁶⁸Ga-containing solution, and the mixture is briefly heated to 50–100 °C (usually 2–3 min) to finalize the complexation reaction.

The abundance of αvβ6-integrin on most adult human cell types and respective tissues is low. It is however overexpressed in the context of several medical conditions, such as cancer{{cite journal | vauthors = Nieberler M, Reuning U, Reichart F, Notni J, Wester HJ, Schwaiger M, Weinmüller M, Räder A, Steiger K, Kessler H | title = Exploring the Role of RGD-Recognizing Integrins in Cancer. | journal = Cancers | volume = 9 | issue = 9 | pages = 116 | date = September 2017 | pmid = 28869579 | doi = 10.3390/cancers9090116 | doi-access = free | pmc = 5615331 }} or fibrosis,{{cite journal | vauthors = Munger JS, Huang X, Kawakatsu H, Griffiths MJ, Dalton SL, Wu J, Pittet JF, Kaminski N, Garat C, Matthay MA, Rifkin DB, Sheppard D | title = The integrin alpha v beta 6 binds and activates latent TGF beta 1: a mechanism for regulating pulmonary inflammation and fibrosis | journal = Cell | volume = 96 | issue = 3 | pages = 319–28 | date = February 1999 | pmid = 10025398 | doi = 10.1016/s0092-8674(00)80545-0 | doi-access = free }} particularly idiopathic pulmonary fibrosis.{{cite journal | vauthors = Maher TM, Simpson JK, Porter JC, Wilson FJ, Chan R, Eames R, Cui Y, Siederer S, Parry S, Kenny J, Slack RJ, Sahota J, Paul L, Saunders P, Molyneaux PL, Lukey PT, Rizzo G, Searle GE, Marshall RP, Saleem A, Kang'ombe AR, Fairman D, Fahy WA, Vahdati-Bolouri M | title = A positron emission tomography imaging study to confirm target engagement in the lungs of patients with idiopathic pulmonary fibrosis following a single dose of a novel inhaled αvβ6 integrin inhibitor. | journal = Respiratory Research | volume = 21 | issue = 1 | pages = 75 | date = March 2020 | pmid = 32216814 | doi = 10.1186/s12931-020-01339-7 | doi-access = free | pmc = 7099768 }}

In line with the finding that αvβ6-integrin is expressed by epithelial cells,{{cite journal | vauthors = Breuss JM, Gallo J, DeLisser HM, Klimanskaya IV, Folkesson HG, Pittet JF, Nishimura SL, Aldape K, Landers DV, Carpenter W | title = Expression of the beta 6 integrin subunit in development, neoplasia and tissue repair suggests a role in epithelial remodeling | journal = Journal of Cell Science | volume = 108 | issue = Pt 6 | pages = 2241–51 | date = June 1995 | doi = 10.1242/jcs.108.6.2241 | pmid = 7673344 }} an elevated density of the protein is observed on the cell surfaces of many carcinomas (synonymous to cancers of epithelial origin).{{cite journal | vauthors = Niu J, Li Z | title = The roles of integrin αvβ6 in cancer. | journal = Cancer Letters | volume = 403 | pages = 128–137 | date = September 2017 | pmid = 28634043 | doi = 10.1016/j.canlet.2017.06.012 }} Hence, ⁶⁸Ga-Trivehexin can be used for PET imaging of αvβ6-integrin positive cancers (i.e., those whose cells possess a sufficiently high density of αvβ6 on their surface), including but not limited to pancreatic ductal adenocarcinoma,{{cite journal | vauthors = Steiger K, Schlitter AM, Weichert W, Esposito I, Wester HJ, Notni J | title = Perspective of αvβ6-Integrin Imaging for Clinical Management of Pancreatic Carcinoma and Its Precursor Lesions. | journal = Molecular Imaging | volume = 16 | issue = 1 | pages = 1536012117709384 | date = January 2017 | pmid = 28627323 | doi = 10.1177/1536012117709384 | doi-access = free | pmc = 5480625 }} non-small cell lung cancer, squamous cell carcinomas (SCC) of different origin (most notably, oral and esophageal SCC), as well as breast, ovarian, and bladder cancer.

⁶⁸Ga-Trivehexin has a high binding affinity to αvβ6-integrin (IC₅₀ = 0.047 nM). Its affinity to other RGD-binding integrins is much lower (IC₅₀ for αvβ3, αvβ8, and α5β1 are 2.7, 6.2, and 22 nM, respectively; note that for IC₅₀, higher values mean lower affinity), resulting in a high selectivity for αvβ6-integrin.

Since ⁶⁸Ga is a positron emitter, ⁶⁸Ga-Trivehexin is applicable for PET imaging. However, PET is rarely used as a standalone imaging technique these days. Most clinics use PET/CT or even PET/MRI systems that acquire morphological and functional images in a single workflow and thus, provide more detailed and useful medical information to the physician.

For clinical PET/CT diagnostics, an activity in the range of 80–150 MBq ⁶⁸Ga-Trivehexin is injected intravenously (i.v.). The tracer then distributes with the blood flow and moves into tissues by diffusion, where it specifically binds to its target αvβ6-integrin, while an excess is excreted via the kidneys and the urine. As a result, ⁶⁸Ga-Trivehexin and, therefore, the positron-emitting radionuclide ⁶⁸Ga, is preferably accumulated by αvβ6-integrin abundant tissues (for example, tumor tissue). Next, a PET/CT scanner is used to detect the gamma radiation which is generated by the annihilation of the positrons emitted by ⁶⁸Ga (not the actual positrons, which do not leave the body but travel only a few millimetres through the tissue). The spatial distribution of the annihilation events is reconstructed from the raw detector data (referred to as listmode data), which eventually delivers a 3-dimensional data set of radioactivity distribution in the body. These data allow the visualization of αvβ6-integrin positive tissues as 2-dimensional tomographic images or 3-dimensional volume rendering. Typically, the PET/CT imaging is performed 45–60 minutes after the i.v. administration of ⁶⁸Ga-Trivehexin.

⁶⁸Ga-Trivehexin has not yet obtained a marketing approval. It is used for clinical imaging of αvβ6-integrin expression in experimental settings. First-in-human application of different αvβ6-integrin radiotracers has demonstrated that ⁶⁸Ga-Trivehexin performed especially well in detecting pancreatic cancer, showing high uptake in tumor lesions and low background in the gastrointestinal tract (GI tract).{{cite journal | vauthors = Kimura RH, Iagaru A, Guo HH | title = Mini review of first-in-human integrin αvβ6 PET tracers | journal = Frontiers in Nuclear Medicine | volume = 9 | issue = 3 | pages = 1271208 | date = October 2023 | pmid = 39355045 | doi = 10.3389/fnume.2023.1271208 | doi-access = free | pmc = 11440954 }} ⁶⁸Ga-Trivehexin has been used for clinical PET/CT imaging in single cases {{cite journal | vauthors = Quigley NG, Czech N, Sendt W, Notni J | title = PET/CT imaging of pancreatic carcinoma targeting the "cancer integrin" αvβ6 | journal = European Journal of Nuclear Medicine and Molecular Imaging | volume = 48 | issue = 12 | pages = 4107–4108 | date = June 2021 | language = EN | pmid = 34109438 | doi = 10.1007/s00259-021-05443-8 | doi-access = free | pmc = 8484182 }}{{cite journal | vauthors = Rehm J, Winzer R, Notni J, Hempel S, Distler M, Folprecht G, Kotzerke J | title = Concomitant metastatic head-and-neck cancer and pancreatic cancer assessed by αvβ6-integrin PET/CT using ⁶⁸Ga-Trivehexin: incidental detection of a brain metastasis. | journal = European Journal of Nuclear Medicine and Molecular Imaging | volume = 51 | issue = 11 | pages = 3469–3471 | date = September 2024 | pmid = 38771514 | doi = 10.1007/s00259-024-06750-6 | doi-access = free | pmc = 11368998 }} and two cohorts (12 and 44 patients, respectively) {{cite journal | vauthors = Das SS, Ahlawat S, Thakral P, Malik D, Simecek J, Cb V, Koley M, Gupta J, Sen I | title = Potential Efficacy of ⁶⁸Ga-Trivehexin PET/CT and Immunohistochemical Validation of αvβ6 Integrin Expression in Patients With Head and Neck Squamous Cell Carcinoma and Pancreatic Ductal Adenocarcinoma. | journal = Clinical Nuclear Medicine | volume = 49 | issue = 8 | pages = 733–740 | date = May 2024 | language = EN | pmid = 38768077 | doi = 10.1097/RLU.0000000000005278 }}{{cite journal | vauthors = Rehm J, Winzer R, Pretze M, Mueller J, Notni J, Hempel S, Distler M, Folprecht G, Kotzerke J | title = αvβ6-integrin targeted PET/CT imaging in pancreatic cancer patients using ⁶⁸Ga-Trivehexin | journal = Frontiers in Nuclear Medicine | volume = 15 | issue = 4 | pages = 148602 | date = November 2024 | pmid = 39618940 | doi = 10.3389/fnume.2024.1487602 | doi-access = free | pmc = 11604418 }}

of suspected or known pancreatic ductal adenocarcinoma, as well as in cases of tonsillar carcinoma metastasized to the brain,

of bronchial mucoepidermoid carcinoma{{cite journal | vauthors = Wu H, Li L, Xiao Z, Li C, He Y | title = αvβ6-integrin targeted [⁶⁸Ga]Ga-Trivehexin PET/CT imaging of a rare bronchial mucoepidermoid carcinoma | journal = European Journal of Nuclear Medicine and Molecular Imaging | date = November 2024 | pmid = 39500808 | doi = 10.1007/s00259-024-06974-6 | doi-access = free }}

and mucinous lung adenocarcinoma,{{cite journal | vauthors = Wu H, Li L, Xiao Z, Chen Q, Li C, He Y | title = [⁶⁸Ga]Ga-Trivehexin PET/CT imaging of integrin-αvβ6 expression in concomitant mucinous lung adenocarcinoma and idiopathic pulmonary fibrosis | journal = European Journal of Nuclear Medicine and Molecular Imaging | date = March 2025 | pmid = 40042637 | doi = 10.1007/s00259-025-07146-w }}

of disseminated parathyroid adenoma in the context of the diagnosis of primary hyperparathyroidism (PHPT),{{cite journal | vauthors = Kuyumcu S, Denizmen D, Has-Simsek D, Poyanli A, Uzum AK, Buyukkaya F, Isik EG, Onder S, Aksakal N, Ozkan ZG, Sanli Y | title = ⁶⁸Ga-Trivehexin PET/CT: a promising novel tracer for primary hyperparathyroidism | journal = European Journal of Nuclear Medicine and Molecular Imaging | volume = 51 | issue = 13 | pages = 3912–3923 | date = July 2024 | pmid = 39028425 | doi = 10.1007/s00259-024-06846-z | doi-access = free | pmc = 11527967 }}

of papillary thyroid carcinoma,{{cite journal | vauthors = Singhal T, Agrawal K, Mandal S, Parida GK | title = Cancer-Specific Integrin Imaging With ⁶⁸Ga-Trivehexin: A Potential Imaging for Accurate Staging of Thyroid Malignancy. | journal = Clinical Nuclear Medicine | date = November 2024 | pmid = 39499025 | doi = 10.1097/RLU.0000000000005557 | doi-access = free }}

and of breast cancer.{{cite journal | vauthors = Kömek H, Güzel Y, Kaplan İ, Yilmaz EE, Can C | title = Superiority of 68 Ga-Trivehexin PET/CT Over 18 F-FDG PET/CT in the Evaluation of Lymph Nodes in Patients With Breast Cancer | journal = Clinical Nuclear Medicine | date = November 2024 | pmid = 39601487 | doi = 10.1097/RLU.0000000000005585 }} In a cohort of 20 suspected (19 confirmed) head-and-neck squamous cell carcinoma (HNSCC) cases, ⁶⁸Ga-Trivehexin PET had a higher sensitivity (92.5%), positive predictive value (PPV, 100%), and accuracy (93%) than the standard ¹⁸F-FDG PET, for which sensitivity, PPV, and accuracy were 90%, 93.1%, and 84.3%, respectively.

In accordance with the known expression of αvβ6-integrin in early lung fibrosis, ⁶⁸Ga-Trivehexin was used for PET/CT imaging of idiopathic pulmonary fibrosis (IPF).{{Cite web |title=Lung fibrosis: radiopharmaceutical improves diagnosis and monitoring |url=https://healthcare-in-europe.com/en/news/lung-fibrosis-radiopharmaceutical-diagnosis-monitoring.html |access-date=2025-03-24 |website=healthcare-in-europe.com |language=en}} In explorative studies, ⁶⁸Ga-Trivehexin could generate an IPF-specific PET signal while the same tissue areas were PET-negative using the standard metabolic PET tracer ¹⁸F-FDG.{{cite journal | vauthors = Kuyumcu S, Denizmen Zorba D, Özkan ZG | title = ⁶⁸Ga-Trivehexin PET/CT uptake in malignant and fibrotic lung tissue: refining diagnostic applications | journal = European Journal of Nuclear Medicine and Molecular Imaging | date = March 2025 | pmid = 40082263 | doi = 10.1007/s00259-025-07193-3 | doi-access = free }} ⁶⁸Ga-Trivehexin PET scans displayed an uptake of SUV_max = 5.53 in fibrotic lung areas and thus enabled clear differentiation of fibrotic from non-fibrotic lung tissue.

Like for other radioactive imaging agents in medicine, the applied amounts of radioactivity are so low that radiation-related adverse effects are very unlikely to occur, and have not been observed in practice. Consistent with the "tracer principle", the amount of pharmacologically active compound injected to a patient in the course of such an examination is extremely low. Adverse events, such as toxicity or allergic reactions, are thus highly improbable. No adverse or clinically detectable pharmacologic effects were observed following intravenous administration of ⁶⁸Ga-Trivehexin when administered to cancer patients, and there were no significant changes in vital signs, laboratory study results, or electrocardiograms. In a study involving healthy volunteers, researchers again reported no adverse or clinically detectable pharmacologic effects and no significant changes in vital signs.{{cite journal | vauthors = Wang B, Jiang Y, Zhu J, Wu H, Wu J, Li L, Huang J, Xiao Z, He Y | title = Fully-automated production of [⁶⁸Ga]Ga-Trivehexin for clinical application and its biodistribution in healthy volunteers. | journal = Frontiers in Oncology | volume = 14 | pages = 1445415 | date = August 2024 | pmid = 39156699 | doi = 10.3389/fonc.2024.1445415 | doi-access = free | pmc = 11327152 }}

{{reflist}}

Category:Positron emission tomography

Category:Amides

Category:Chelating agents

Category:Nine-membered rings

Category:Gallium

Category:Phosphinates

Category:Isotopes of gallium

Category:Nonapeptides

Category:Triazoles