Ga-68-Trivehexin
68Ga-Trivehexin is a radiotracer for positron emission tomography, obtained by labeling the peptide conjugate Trivehexin with the positron emitting radionuclide gallium-68. 68Ga-Trivehexin targets the cell surface receptor αvβ6-integrin and accumulates in αvβ6-integrin-abundant tissues after intravenous application. 68Ga-Trivehexin is thus applied for PET imaging of medical conditions associated with elevated αvβ6-integrin expression.
αvβ6-Integrin, the biological target of 68Ga-Trivehexin, is a heterodimeric transmembrane cell adhesion receptor whose primary natural ligand is latency associated peptide in its complex with transforming growth factor beta 1. Binding of αvβ6-integrin to LAP releases and thus, activates TGF-β1. In early-stage cancer, TGF-β1 acts as a tumor suppressor but can turn into a tumor promoter as cancers develop, and furthermore induces fibrosis, particularly of the lung. As the likely most important activator of TGF-β1, αvβ6-integrin is often found overexpressed in tumors and fibrosis, which is why 68Ga-Trivehexin PET imaging is primarily relevant in this medical context.
Chemistry
Trivehexin precursor
Like most precursors used for radiolabeling with radioactive metal cations, Trivehexin is composed of a dedicated complex ligand for kinetically inert binding of the 68GaIII ion, and the bioligand 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. The αvβ6-integrin binding molecular unit is a cyclic nonapeptide with the amino acid sequence cyclo.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 bearing a terminal alkyne, and of TRAP with three linkers bearing terminal azides. These components are assembled by means of copper catalyzed alkyne-azide cycloaddition, giving rise to the three 1,3-triazole linkages in the 68Ga-Trivehexin structure.
Trivehexin is manufactured and distributed by the German company TRIMT GmbH.
68Ga radiolabeling
68Ga-Trivehexin is a radioactive drug. The radioactive atom, gallium-68, decays with a half-life of approximately 68 min to the stable isotope zinc-68, to 89% by β+ decay whereby a positron with a maximum kinetic energy of 1.9 MeV is emitted. 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 68GaIII by the TRAP chelator in Trivehexin.68GaIII is usually obtained from a dedicated mobile radionuclide source, a Gallium-68 generator, in form of a solution in dilute hydrochloric acid. For radiolabeling, the pH of the 68Ga containing generator eluate has to be raised from its initial value to pH 2–3.5 using suitable buffers, such as sodium acetate. Then, Trivehexin is added to the buffered 68Ga-containing solution, and the mixture is briefly heated to 50–100 °C to finalize the complexation reaction.
Use as medical imaging agent
αvβ6-Integrin target
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 or fibrosis, particularly idiopathic pulmonary fibrosis.In line with the finding that αvβ6-integrin is expressed by epithelial cells, an elevated density of the protein is observed on the cell surfaces of many carcinomas. Hence, 68Ga-Trivehexin can be used for PET imaging of αvβ6-integrin positive cancers, including but not limited to pancreatic ductal adenocarcinoma, non-small cell lung cancer, squamous cell carcinomas of different origin, as well as breast, ovarian, and bladder cancer. In colorectal cancer, expression of αvβ6-integrin is higher in the more aggressive forms and correlated with reduced overall survival.
68Ga-Trivehexin has a high binding affinity to αvβ6-integrin. Its affinity to other RGD-binding integrins is much lower, resulting in a high selectivity for αvβ6-integrin.
Imaging procedure
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. 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. Next, a PET/CT scanner is used to detect the gamma radiation which is generated by the annihilation of the positrons emitted by 68Ga. The spatial distribution of the annihilation events is reconstructed from the raw detector 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.
Cancers imaging
68Ga-Trivehexin has not yet obtained a marketing approval. It is used for clinical imaging of αvβ6-integrin expression in experimental settings.Pancreatic cancer
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 . Since its introduction, 68Ga-Trivehexin has been used predominantly for PET/CT imaging of pancreatic ductal adenocarcinoma, for example, in single cases and two cohorts of suspected or known PDAC.Breast cancer
The feasibility of 68Ga-Trivehexin PET imaging of breast cancer was demonstrated in a case of triple-negative BC. Another report suggested that 68Ga-Trivehexin PET/CT might offer superior detection efficacy for breast cancer compared to 18F-FDG PET/CT. Furthermore, in progesterone- and estrogen-receptor negative BC with elevated Ki67 proliferation index and strong E-cadherin, 68Ga-Trivehexin PET identified several 18F-FDG-avid lymph nodes as false positives. In a patient with lobular BC and pancreatic neuroendocrine tumor, 68Ga-Trivehexin selectively showed a PET signal only in the lobular carcinoma, while the metabolic tracer 18F-FGD and the neuroendocrine tumor tracer 68Ga-DOTATATE yielded PET signals for both the BC and PNET lesions.File:Ga-68-Trivehexin vs FDG Non Small Cell Lung Cancer Brain Metastases AdvSci 2025 He-et-al.png|thumb|Representative 68Ga-Trivehexin PET/CT of a 55-year-old woman with lung adenocarcinoma and multiple metastatic lesions, compared with 18F-FDG PET/CT. Both images show maximum intensity projections. Yellow arrows: Primary tumor. Red arrows: Metastatic lesions including lymph node metastases. Blue arrows: Brain metastases. Green arrows: Liver metastases. Pink arrows: Bone metastases.
Lung Cancer
A prospective clinical study involving 58 participants with non-small cell lung cancer compared the diagnostic performance of 68Ga-Trivehexin PET/CT with 18F-FDG PET/CT. Both radiotracers showed similar diagnostic accuracy for the detection of primary tumors. The sensitivity for detection of lymph node metastases was comparable for 68Ga-Trivehexin and 18F-FDG, but 68Ga-Trivehexin showed a higher specificity and accuracy than 18F-FDG. Sensitivity for detecting brain metastasis was 92.3% for 68Ga-Trivehexin and 38.5% for 18F-FDG, mainly because of the high glucose consumption of normal brain tissue, which usually results in a high physiological uptake of 18F-FDG in the brain, generating a strong background signal which frequently obscures brain metastases in PET images.Application of 68Ga-Trivehexin PET was reported for single cases of other, rare forms of lung cancer, such as bronchial mucoepidermoid carcinoma and mucinous lung adenocarcinoma.