Broad-scope Syntheses of [11 C/18 F]Trifluoromethylarenes from Aryl(mesityl)iodonium Salts.

Efficient methods for labeling aryl trifluoromethyl groups to provide novel radiotracers for use in biomedical research with positron emission tomography (PET) are keenly sought. We report a broad-scope method for labeling trifluoromethylarenes with either carbon-11 (t1/2 =20.4 min) or fluorine-18 (t1/2 =109.8 min) from readily accessible aryl(mesityl)iodonium salts. In this method, the aryl(mesityl)iodonium salt is treated rapidly with no-carrier-added [11 C]CuCF3 or [18 F]CuCF3 . The mesityl group acts as a spectator allowing radiolabeled trifluoromethylarenes to be obtained with very high chemoselectivity. Radiochemical yields from aryl(mesityl)iodonium salts bearing either electron-donating or electron-withdrawing groups at meta- or para- position are good to excellent (67-96 %). Ortho-substituted and otherwise sterically hindered trifluoromethylarenes still give good yields (15-34 %). Substituted heteroaryl(mesityl)iodonium salts are also viable substrates. The broad scope of this method was further exemplified by labeling a previously inaccessible target, [11 C]p-trifluoromethylphenyl boronic acid, as a potentially useful labeling synthon. In addition, fluoxetine, leflunomide, and 3-trifluoromethyl-4-aminopyridine, as examples of small drug-like molecules and candidate PET radioligands, were successfully labeled in high yields (69-81 %).

E2730, an uncompetitive γ-aminobutyric acid transporter-1 inhibitor, suppresses epileptic seizures in a rat model of chronic mesial temporal lobe epilepsy.

OBJECTIVE: More than one third of mesial temporal lobe epilepsy (MTLE) patients are resistant to current antiseizure medications (ASMs), and half experience mild-to-moderate adverse effects of ASMs. There is therefore a strong need to develop and test novel ASMs. The objective of this work is to evaluate the pharmacokinetics and neurological toxicity of E2730, a novel uncompetitive inhibitor of γ-aminobutyric acid transporter-1, and to test its seizure suppression effects in a rat model of chronic MTLE. METHODS: We first examined plasma levels and adverse neurological effects of E2730 in healthy Wistar rats. Adult male rats were implanted with osmotic pumps delivering either 10, 20, or 100 mg/kg/day of E2730 subcutaneously for 1 week. Blood sampling and behavioral assessments were performed at several timepoints. We next examined whether E2730 suppressed seizures in rats with chronic MTLE. These rats were exposed to kainic acid-induced status epilepticus, and 9 weeks later, when chronic epilepsy was established, were assigned to receive one of the three doses of E2730 or vehicle for 1 week in a randomized crossover design. Continuous video-electroencephalographic monitoring was acquired during the treatment period to evaluate epileptic seizures. RESULTS: Plasma levels following continuous infusion of E2730 showed a clear dose-related increase in concentration. The drug was well tolerated at all doses, and any sedation or neuromotor impairment was mild and transient, resolving within 48 h of treatment initiation. Remarkably, E2730 treatment in chronically epileptic rats led to seizure suppression in a dose-dependent manner, with 65% of rats becoming seizure-free at the highest dose tested. Mean seizure class did not differ between the treatment groups. SIGNIFICANCE: This study shows that continuous subcutaneous infusion of E2730 over 7 days results in a marked, dose-dependent suppression of spontaneous recurrent seizures, with minimal adverse neurological effects, in a rat model of chronic MTLE. E2730 shows strong promise as an effective new ASM to be translated into clinical trials.

Effective Preparation of [18F]Flumazenil Using Copper-Mediated Late-Stage Radiofluorination of a Stannyl Precursor.

(1) Background: [18F]Flumazenil 1 ([18F]FMZ) is an established positron emission tomography (PET) radiotracer for the imaging of the gamma-aminobutyric acid (GABA) receptor subtype, GABAA in the brain. The production of [18F]FMZ 1 for its clinical use has proven to be challenging, requiring harsh radiochemical conditions, while affording low radiochemical yields. Fully characterized, new methods for the improved production of [18F]FMZ 1 are needed. (2) Methods: We investigate the use of late-stage copper-mediated radiofluorination of aryl stannanes to improve the production of [18F]FMZ 1 that is suitable for clinical use. Mass spectrometry was used to identify the chemical by-products that were produced under the reaction conditions. (3) Results: The radiosynthesis of [18F]FMZ 1 was fully automated using the iPhase FlexLab radiochemistry module, affording a 22.2 ± 2.7% (n = 5) decay-corrected yield after 80 min. [18F]FMZ 1 was obtained with a high radiochemical purity (>98%) and molar activity (247.9 ± 25.9 GBq/µmol). (4) Conclusions: The copper-mediated radiofluorination of the stannyl precursor is an effective strategy for the production of clinically suitable [18F]FMZ 1.

Imaging Somatostatin Positive Tumors with Tyr3-Octreotate/Octreotide Conjugated to Desferrioxamine B Squaramide Radiolabeled with either Zirconium-89 or Gallium-68.

Radiolabeled derivatives of Tyr3-octreotide and Tyr3-octreotate, synthetic analogues of the peptide hormone somatostatin, can be used for positron emission tomography (PET) imaging of somatostatin receptor expression in neuroendocrine tumors. In this work, a squaramide ester derivative of desferrioxamine B (H3DFOSq) was used attach either Tyr3-octreotide or Tyr3-octreotate to the metal binding ligand to give H3DFOSq-TIDE and H3DFOSq-TATE. These new peptide-H3DFOSq conjugates form stable complexes with either of the positron-emitting radionuclides gallium-68 (t1/2 = 68 min) or zirconium-89 (t1/2 = 3.3 days). The new complexes were evaluated in an AR42J xenograft model that has endogenous expression of SSTR2. All four agents displayed good tumor uptake and produced high-quality PET images. For both radionuclides, the complexes formed with H3DFOSq-TATE performed better, with higher tumor uptake and retention than the complexes formed with H3DFOSq-TIDE. The versatile ligands presented here can be radiolabeled with either gallium-68 or zirconium-89 at room temperature. The long radioactive half-life of zirconium-89 makes distribution of pre-synthesized tracers produced to certified standards feasible and could increase the number of clinical centers that can perform diagnostic PET imaging of neuroendocrine tumors.

A Bivalent Inhibitor of Prostate Specific Membrane Antigen Radiolabeled with Copper-64 with High Tumor Uptake and Retention.

Molecules containing lysine-ureido-glutamate functional groups bind to the active site of prostate specific membrane antigen, which is overexpressed in prostate cancer. To prepare copper radiopharmaceuticals for the diagnosis and therapy of prostate cancer, macrobicyclic sarcophagine ligands tethered to either one or two lysine-ureido-glutamate functional groups through an appropriate linker have been prepared. Sarcophagine ligands can be readily radiolabeled with positron-emitting copper-64 at room temperature. The bivalent agent, in which two targeting groups are tethered to a single copper complex, dramatically outperforms the monomeric agent with respect to tumor uptake and retention. The high tumor uptake, low background, and prolonged tumor retention, even at 24 hours post injection, suggest the bivalent agent is a promising diagnostic for prostate cancer and could be used for prospective dosimetry for therapy with a copper-67 variant.

Automated preparation of 2-[18 F]fluoropropionate labeled peptides using a flexible, multi-stage synthesis platform (iPHASE Flexlab).

Radiolabelled peptides are vital tools used in positron emission tomography imaging for the diagnosis of disease, drug discovery, and biomedical research. Peptides are typically labeled through conjugation to a radiolabelled prosthetic group, which usually necessitates complex, multi-step procedures, especially for fluorine-18 labeled peptides. Herein, we describe the automated synthesis and formulation of 2-[18 F]fluoropropionate labeled RGD-peptides through use of the iPHASE Flexlab as an effective dual-stage radiochemical synthesis module. The fully automated preparation of the monomeric RGD-peptides, [18 F]FP-GalactoRGD and [18 F]FP-c(RGDy(SO3 )K), was accomplished in under 90 minutes with n.d.c. radiochemical yields ca. 7% from fluoride. Similarly, the automated preparation of the dimeric RGD-peptides, [18 F]F-PRGD2 and [18 F]FP-E(RGDy(SO3 )K)2 , was accomplished in under 105 minutes with n.d.c. yields ca. 4% from fluoride.

[11 C]Fluoroform, a Breakthrough for Versatile Labeling of PET Radiotracer Trifluoromethyl Groups in High Molar Activity.

Positron-emission tomography (PET) is an immensely important imaging modality in biomedical research and drug development but must use selective radiotracers to achieve biochemical specificity. Such radiotracers are usually labeled with carbon-11 (t1/2 =20 min) or fluorine-18 (t1/2 =110 min), but these are only available from cyclotrons in a few simple chemical forms. [18 F]Fluoroform has emerged for labeling tracers in trifluoromethyl groups but is severely limited in utility by low radioactivity per mass (low molar activity). Here, the synthesis of [11 C]fluoroform is described, based on CoF3 -mediated fluorination of cyclotron-produced [11 C]methane. This process is efficient and repetitively reliable. [11 C]Fluoroform shows versatility for labeling small molecules in very high molar activity (>200 GBq µmol-1 ), far exceeding that possible by using [18 F]fluoroform. Therefore, [11 C]fluoroform represents a major breakthrough for labeling prospective PET tracers in trifluoromethyl groups at high molar activity.

Sulfonation of Tyrosine as a Method To Improve Biodistribution of Peptide-Based Radiotracers: Novel 18F-Labeled Cyclic RGD Analogues.

Control of the biodistribution of radiolabeled peptides has proven to be a major challenge in their application as imaging agents for positron emission tomography (PET). Modification of peptide hydrophilicity in order to increase renal clearance has been a common endeavor to improve overall biodistribution. Herein, we examine the effect of site-specific sulfonation of tyrosine moieties in cyclic(RGDyK) peptides as a means to enhance their hydrophilicity and improve their biodistribution. The novel sulfonated cyclic(RGDyK) peptides were conjugated directly to 4-nitrophenyl 2-[18F]fluoropropionate, and the biodistribution of the radiolabeled peptides was compared with that of their nonsulfonated, clinically relevant counterparts, [18F]GalactoRGD and [18F]FPPRGD2. Site-specific sulfonation of the tyrosine residues was shown to increase hydrophilicity and improve biodistribution of the RGD peptides, despite contributing just 79 Da toward the MW, compared with 189 Da for both the "Galacto" and mini-PEG moieties, suggesting this may be a broadly applicable approach to enhancing biodistribution of radiolabeled peptides.

An Investigation of (Diacetoxyiodo)arenes as Precursors for Preparing No-Carrier-Added [(18)F]Fluoroarenes from Cyclotron-Produced [(18)F]Fluoride Ion.

Treatment of (diacetoxyiodo)arenes (1a-1u) with cyclotron-produced [(18)F]fluoride ion rapidly affords no-carrier-added [(18)F]fluoroarenes (2a-2u) in useful yields and constitutes a new method for converting substituted iodoarenes into substituted [(18)F]fluoroarenes in just two steps.

Precision peptide theranostics: developing N- to C-terminus optimized theranostics targeting cholecystokinin-2 receptor.

Peptides are ideal for theranostic development as they afford rapid target accumulation, fast clearance from background tissue, and exhibit good tissue penetration. Previously, we developed a novel series of peptides that presented discreet folding propensity leading to an optimal candidate [68Ga]Ga-DOTA-GA1 ([D-Glu]6-Ala-Tyr-NMeGly-Trp-NMeNle-Asp-Nal-NH2) with 50 pM binding affinity against cholecystokinin-2 receptors (CCK2R). However, we were confronted with challenges of unfavorably high renal uptake. Methods: A structure activity relationship study was undertaken of the lead theranostic candidate. Prudent structural modifications were made to the peptide scaffold to evaluate the contributions of specific N-terminal residues to the overall biological activity. Optimal candidates were then evaluated in nude mice bearing transfected A431-CCK2 tumors, and their biodistribution was quantitated ex vivo. Results: We identified and confirmed that D-Glu3 to D-Ala3 substitution produced 2 optimal candidates, [68Ga]Ga-DOTA-GA12 and [68Ga]Ga-DOTA-GA13. These radiopeptides presented with high target/background ratios, enhanced tumor retention, excellent metabolic stability in plasma and mice organ homogenates, and a 4-fold reduction in renal uptake, significantly outperforming their non-alanine counterparts. Conclusions: Our study identified novel radiopharmaceutical candidates that target the CCK2R. Their high tumor uptake and reduced renal accumulation warrant clinical translation.

First-in-Human Safety, Imaging, and Dosimetry of a Carbonic Anhydrase IX-Targeting Peptide, [68Ga]Ga-DPI-4452, in Patients with Clear Cell Renal Cell Carcinoma.

[68Ga]Ga-DPI-4452, a first-in-class carbonic anhydrase IX-binding radiolabeled peptide, is the imaging agent of a theranostic pair with [177Lu]Lu-DPI-4452, developed for selecting and treating patients with carbonic anhydrase IX-expressing tumors. Here, [68Ga]Ga-DPI-4452 imaging characteristics, dosimetry, pharmacokinetics, and safety were assessed in 3 patients with clear cell renal cell carcinoma. Methods: After [68Ga]Ga-DPI-4452 administration, patients underwent serial full-body PET/CT imaging. Blood and urine were sampled. Safety was monitored for 7 d after injection. Results: Tumor uptake was observed at all time points (15 min to 4 h). Across 36 lesions, the SUVmax at 1 h after administration ranged from 6.8 to 211.6 (mean, 64.6 [SD, 54.8]). The kidneys, liver, and bone marrow demonstrated low activity. [68Ga]Ga-DPI-4452 was rapidly eliminated from blood and urine. No clinically significant toxicity was observed. Conclusion: [68Ga]Ga-DPI-4452 showed exceptional tumor uptake in patients with clear cell renal cell carcinoma, with very high tumor-to-background ratios and no significant adverse events, suggesting potential diagnostic and patient selection applications.

Administering [177Lu]Lu-PSMA-617 Prior to Radical Prostatectomy in Men with High-risk Localised Prostate Cancer (LuTectomy): A Single-centre, Single-arm, Phase 1/2 Study.

BACKGROUND: High-risk localised prostate cancer (HRCaP) has high rates of biochemical recurrence; [177Lu]Lu-PSMA-617 is effective in men with advanced prostate cancer. OBJECTIVE: To investigate the dosimetry, safety, and efficacy of upfront [177Lu]Lu-PSMA-617 in men with HRCaP prior to robotic radical prostatectomy (RP). DESIGN, SETTING, AND PARTICIPANTS: In this single-arm, phase I/II trial, we recruited men with HRCaP (any of prostate-specific antigen [PSA] >20 ng/ml, International Society of Urological Pathology (ISUP) grade group [GG] 3-5, and ≥cT2c), with high tumour uptake on [68Ga]Ga-PSMA-11 positron emission tomography/computed tomography (PSMA PET/CT), and scheduled for RP. INTERVENTION: Cohort A (n = 10) received one cycle and cohort B (n = 10) received two cycles of [177Lu]Lu-PSMA-617 (5 GBq) followed by surgery 6 weeks later. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary endpoint was tumour radiation absorbed dose. Adverse events (AEs; Common Terminology Criteria for Adverse Events (CTCAE) version 5.0), surgical safety (Clavien-Dindo), imaging, and biochemical responses were evaluated (ClinicalTrials.gov: NCT04430192). RESULTS AND LIMITATIONS: Between May 29, 2020 and April 28, 2022, 20 patients were enrolled. The median PSA was 18 ng/ml (interquartile range [IQR] 11-35), Eighteen (90%) had GG ≥3, and six (30%) had N1 disease. The median (IQR) highest tumour radiation absorbed dose after cycle 1 for all lesions was 35.5 Gy (19.5-50.1), with 19.6 Gy (11.3-48.4) delivered to the prostate. Five patients received radiation to lymph nodes. Nine (45%) patients achieved >50% PSA decline. The most common AEs related to [177Lu]Lu-PSMA-617 were grade 1 fatigue in eight (40%), nausea in seven (35%), dry mouth in six (30%), and thrombocytopenia in four (20%) patients. No grade 3/4 toxicities or Clavien 3-5 complications occurred. Limitations include small a sample size. CONCLUSIONS: In men with HRCaP and high prostate-specific membrane antigen (PSMA) expression, [177Lu]Lu-PSMA-617 delivered high levels of targeted radiation doses with few toxicities and without compromising surgical safety. Further studies of [177Lu]Lu-PSMA-617 in this population are worthwhile to determine whether meaningful long-term oncological benefits can be demonstrated. PATIENT SUMMARY: In this study, we demonstrate that up to two cycles of [177Lu]Lu-PSMA-617 given prior to radical prostatectomy in patients with high-risk localised prostate cancer are safe and deliver targeted doses of radiation to tumour-affected tissues. It is tolerated well with minimal treatment-related adverse events, and surgery is safe with a low rate of complications. Activity measured through PSA reduction, repeat PSMA PET/CT, and histological response is promising.

One-step radiosynthesis of 4-nitrophenyl 2-[(18) F]fluoropropionate ([(18) F]NFP); improved preparation of radiolabeled peptides for PET imaging.

The versatile (18) F-labeled prosthetic group, 4-nitrophenyl 2-[(18) F]fluoropropionate ([(18) F]NFP), was synthesized in a single step in 45 min from 4-nitrophenyl 2-bromopropionate, with a decay corrected radiochemical yield of 26.2% ± 2.2%. Employing this improved synthesis of [(18) F]NFP, [(18) F]GalactoRGD - the current 'gold standard' tracer for imaging the expression of αV ß3 integrin - was prepared with high specific activity in 90 min and 20% decay corrected radiochemical yield from [(18) F]fluoride.

Development of Highly Potent Clinical Candidates for Theranostic Applications against Cholecystokinin-2 Receptor Positive Cancers.

Peptide receptor radionuclide therapy (PRRT) is a promising form of systemic radiation therapy designed to eradicate cancer. Cholecystokinin-2 receptor (CCK2R) is an important molecular target that is highly expressed in a range of cancers. This study describes the synthesis and in vivo characterization of a novel series of 177Lu-labeled peptides ([177Lu]Lu-2b-4b) in comparison with the reference CCK2R-targeting peptide CP04 ([177Lu]Lu-1b). [177Lu]Lu-1b-4b showed high chemical purity (HPLC ≥ 94%), low Log D7.4 (-4.09 to -4.55) with strong binding affinity to CCK2R (KD 0.097-1.61 nM), and relatively high protein binding (55.6-80.2%) and internalization (40-67%). Biodistribution studies of the novel 177Lu-labeled peptides in tumors (AR42J and A431-CCK2R) showed uptake one- to eight-fold greater than the reference compound CP04 at 1, 24, and 48 h. Rapid clearance and high tumor uptake and retention were established for [177Lu]Lu-2b-4b, making these compounds excellent candidates for theranostic applications against CCK2R-expressing tumors.

The Protein Landscape of Mucinous Ovarian Cancer: Towards a Theranostic.

MOC is a rare histotype of epithelial ovarian cancer, and current management options are inadequate for the treatment of late stage or recurrent disease. A shift towards personalised medicines in ovarian cancer is being observed, with trials targeting specific molecular pathways, however, MOC lags due to its rarity. Theranostics is a rapidly evolving category of personalised medicine, encompassing both a diagnostic and therapeutic approach by recognising targets that are expressed highly in tumour tissue in order to deliver a therapeutic payload. The present review evaluates the protein landscape of MOC in recent immunohistochemical- and proteomic-based research, aiming to identify potential candidates for theranostic application. Fourteen proteins were selected based on cell membrane localisation: HER2, EGFR, FOLR1, RAC1, GPR158, CEACAM6, MUC16, PD-L1, NHE1, CEACAM5, MUC1, ACE2, GP2, and PTPRH. Optimal proteins to target using theranostic agents must exhibit high membrane expression on cancerous tissue with low expression on healthy tissue to afford improved disease outcomes with minimal off-target effects and toxicities. We provide guidelines to consider in the selection of a theranostic target for MOC and suggest future directions in evaluating the results of this review.

Region- and voxel-based quantification in human brain of [18F]LSN3316612, a radioligand for O-GlcNAcase.

BACKGROUND: Previous studies found that the positron emission tomography (PET) radioligand [18F]LSN3316612 accurately quantified O-GlcNAcase in human brain using a two-tissue compartment model (2TCM). This study sought to assess kinetic model(s) as an alternative to 2TCM for quantifying [18F]LSN3316612 binding, particularly in order to generate good-quality parametric images. METHODS: The current study reanalyzed data from a previous study of 10 healthy volunteers who underwent both test and retest PET scans with [18F]LSN3316612. Kinetic analysis was performed at the region level with 2TCM using 120-min PET data and arterial input function, which was considered as the gold standard. Quantification was then obtained at both the region and voxel levels using Logan plot, Ichise's multilinear analysis-1 (MA1), standard spectral analysis (SA), and impulse response function at 120 min (IRF120). To avoid arterial sampling, a noninvasive relative quantification (standardized uptake value ratio (SUVR)) was also tested using the corpus callosum as a pseudo-reference region. Venous samples were also assessed to see whether they could substitute for arterial ones. RESULTS: Logan and MA1 generated parametric images of good visual quality and their total distribution volume (VT) values at both the region and voxel levels were strongly correlated with 2TCM-derived VT (r = 0.96-0.99) and showed little bias (up to - 8%). SA was more weakly correlated to 2TCM-derived VT (r = 0.93-0.98) and was more biased (~ 16%). IRF120 showed a strong correlation with 2TCM-derived VT (r = 0.96) but generated noisier parametric images. All techniques were comparable to 2TCM in terms of test-retest variability and reliability except IRF120, which gave significantly worse results. Noninvasive SUVR values were not correlated with 2TCM-derived VT, and arteriovenous equilibrium was never reached. CONCLUSIONS: Compared to SA and IRF, Logan and MA1 are more suitable alternatives to 2TCM for quantifying [18F]LSN3316612 and generating good-quality parametric images.

A New Turn in Peptide-Based Imaging Agents: Foldamers Afford Improved Theranostics Targeting Cholecystokinin-2 Receptor-Positive Cancer.

Proteins adopt unique folded secondary and tertiary structures that are responsible for their remarkable biological properties. This structural complexity is key in designing efficacious peptides that can mimic the three-dimensional structure needed for biological function. In this study, we employ different chemical strategies to induce and stabilize a ß-hairpin fold of peptides targeting cholecystokinin-2 receptors for theranostic application (combination of a targeted therapeutic and a diagnostic companion). The newly developed peptides exhibited enhanced folding capacity as demonstrated by circular dichroism (CD) spectroscopy, ion-mobility spectrometry-mass spectrometry, and two-dimensional (2D) NMR experiments. Enhanced folding characteristics of the peptides led to increased biological potency, affording four optimal Ga-68 labeled radiotracers ([68Ga]Ga-4b, [68Ga]Ga-11b-13b) targeting CCK-2R. In particular, [68Ga]Ga-12b and [68Ga]Ga-13b presented improved metabolic stability, enhanced cell internalization, and up to 6 fold increase in tumor uptake. These peptides hold great promise as next-generation theranostic radiopharmaceuticals.

4-Nitrophenyl activated esters are superior synthons for indirect radiofluorination of biomolecules.

Indirect radiolabelling has for a long time been the mainstay strategy for radiofluorination of biomolecules. Acylation of biomolecules through the use of an 18F-labelled activated ester is a standard method for indirect radiolabelling. However, the preparation of 18F-labelled activated esters is typically a complex and multistep procedure. Herein, we describe the use of 4-nitrophenyl (PNP) activated esters to rapidly prepare 18F-labelled acylation synthons in one step. Furthermore, we present a comparative study of PNP activated esters and the commonly utilised 2,3,5,6-tetrafluorphenyl (TFP) activated esters under direct radiofluorination conditions and demonstrate their relative acylation behaviour. We demonstrate the superiority of PNP esters under direct radiofluorination conditions with favourable acylation kinetics.

Rapid Syntheses of [11C]Arylvinyltrifluoromethanes through Treatment of (E)-Arylvinyl(phenyl)iodonium Tosylates with [11C]Trifluoromethylcopper(I).

We report a method for labeling arylvinyltrifluoromethanes with carbon-11 (t1/2 = 20.4 min) as representatives of a new radiolabeled chemotype that has potential for developing radiotracers for biomedical imaging with positron emission tomography. Treatment of (E)-arylvinyl(phenyl)iodonium tosylates (1a-1k) with [11C[CuCF3 gave the corresponding [11C]arylvinyltrifluoromethanes ([11C]2a-[11C]2k) in high radiochemical yields (90-97%) under rapid (2 min) and mild (60 °C) conditions.