Preclinical evaluation of [18F]FB-A20FMDV2 as a selective marker for measuring αVβ6 integrin occupancy using positron emission tomography in rodent lung

Abstract

Purpose Integrin α v β 6 belongs to the RGD subset of the integrin family, and its expression levels are a prognostic and theranostic factor in some types of cancer and pulmonary fibrosis. This paper describes the GMP radiolabelling of the synthetic 20 amino acid peptide A20FMDV2 (NAVPNLRGDLQVLAQKVART), derived from the foot-and-mouth disease virus, and characterises the use of [ 18 F]FB-A20FMDV2 as a high affinity, specific and selective PET radioligand for the quantitation and visualisation of α v β 6 in rodent lung to support human translational studies. Methods The synthesis of [ 18 F]FB-A20FMDV2 was performed using a fully automated and GMP-compliant process. Sprague-Dawley rats were used to perform homologous (unlabelled FB-A20FMDV2) and heterologous (anti-α v β 6 antibody 8G6) blocking studies. In order to generate a dosimetry estimate, tissue residence times were generated, and associated tissue exposure and effective dose were calculated using the Organ Level Internal Dose Assessment/Exponential Modelling (OLINDA/EXM) software. Results [ 18 F]FB-A20FMDV2 synthesis was accomplished in 180 min providing~800 MBq of [ 18 F]FB-A20FMDV2 with a molar activity of up to 150 GBq/μmol and high radiochemical purity (> 97%). Following i.v. administration to rats, [ 18 F]FB-A20FMDV2 was rapidly metabolised with intact radiotracer representing 5% of the total radioactivity present in rat plasma at 30 min. For the homologous and heterologous block in rats, lung-to-heart SUV ratios at 30-60 min post-administration of [ 18 F]FB-A20FMDV2 were reduced by 38.9 ± 6.9% and 56 ± 19.2% for homologous and heterologous block, respectively. Rodent biodistribution and dosimetry calculations using OLINDA/EXM provided a whole body effective dose in humans 33.5 μSv/MBq. Conclusion [ 18 F]FB-A20FMDV2 represents a specific and selective PET ligand to measure drug-associated αvβ6 integrin occupancy in lung. The effective dose, extrapolated from rodent data, is in line with typical values for compounds labelled with fluorine-18 and combined with the novel fully automated and GMP-compliant synthesis and allows for clinical use in translational studies.

A stapled chromogranin A-derived peptide homes in on tumors that express αvβ6 or αvβ8 integrins

“…However, the notion that αvβ6 expression in mouse kidney is negligible [27], and the observation that 5a-IRDye and control 5a-Scr-IRDye accumulated in this organ to similar extents suggests that most uptake in the kidney was related to renal clearance and not to a specific targeting mechanism. The uptake of 5a-IRDye by the lung was possibly related to the fact that this organ expresses αvβ6 and αvβ8 integrins [28,29].…”

Clinical quantification of the integrin αvβ6 by [18F]FB-A20FMDV2 positron emission tomography in healthy and fibrotic human lung (PETAL Study)

“…Preclinical data was available to conduct a preliminary estimate of the number of subjects that may be required to achieve this precision. Coefficients of variation (CV) for standardised uptake values (SUV) in rat tissues at various timepoints (n = 3 per timepoint) following administration of [ 18 F]FB-A20FMV2 ranged between 3 and 150% for different tissues and incubation timepoints [19]. The mean CVs across all rodent tissues were 39-58%; for the lung, the mean CV ranged from 3 to 26%.…”

“…A20FMDV2 was labelled with fluorine-18 by conjugation of the resin bound precursor (A20FMDV2) to the prosthetic group [18F]-fluorobenzoic acid ([18F]FB), followed by acidic cleavage from the resin, purification by semi-preparative HPLC and reformulation in saline. The synthetic procedure of [18F]-FB-A20FMDV2 was adapted from a previously described method [19,25]. An automated procedure was developed in-house using an Eckert and Ziegler Modular Lab system coupled with a semi-preparative HPLC system.…”

“…A venous cannula was inserted into a cubital or forearm vein and an arterial cannula was inserted into the radial artery under local anaesthesia. GMP grade [ 18 F]FB-A20FMVD2 [19] was injected via the venous cannula and emission data acquired for up to 240 min. The arterial cannula was used to collect blood samples throughout the scan to enable the quantification of the total and unmetabolised [ 18 F]FB- A20FMDV2-related radioactivity in whole blood and plasma throughout the duration of the scan.…”

“…The envelope protein of foot and mouth disease virus (FMDV) contains a 20 amino acid peptide sequence, NAVPNLRGDLQVLAQKVART (A20FMDV2) that binds the αvβ6 integrin with high affinity and selectivity [15][16][17][18]. Automated GMP-compatible radiochemistry non-clinical radiodosimetry of the A20FMDV2 peptide is described in the accompanying article [19]. [ 1 9 F]FB-labelled A20FMDV2 has an acceptable toxicology profile, showed no adverse effects in healthy subjects and has an effective dose (0.0217 mSv/MBq) that permits multiple scans in a single subject [20].…”