Automated radiosynthesis and preclinical evaluation of two new PSMA-617 derivatives radiolabelled via [18F]AlF2+ method.

BACKGROUND: In the last decade the development of new PSMA-ligand based radiopharmaceuticals for the imaging and therapy of prostate cancer has been a highly active and important area of research. The most promising derivative in terms of interaction with the antigen and clinical properties has been found to be "PSMA-617", and its lutetium-177 radiolabelled version has recently been approved by EU and USA regulatory agencies for therapeutic purposes. For the above reasons, the development of new derivatives of PSMA-617 radiolabelled with fluorine-18 may still be of great interest. This paper proposes the comparison of two different PSMA-617 derivatives functionalized with NODA and RESCA chelators, respectively, radiolabelled via [18F]AlF2+ complexation. RESULTS: The organic synthesis of two PSMA-617 derivatives and their radiolabelling via [18F]AlF2+ complexation resulted to proceed efficiently and successfully. Moreover, stability in solution and in plasma has been evaluated. The whole radiosynthesis procedure has been fully automated, and the final products have been obtained with radiochemical yield and purity potentially suitable for clinical studies. The biodistribution of the two derivatives was performed both in prostate cancer and glioma tumour models. Compared with the reference [18F]F-PSMA-1007 and [18F]F-PSMA-617-RESCA, [18F]F-PSMA-617-NODA derivative showed a higher uptake in both tumors, faster clearance in non-target organs, and lower uptake in salivary glands. CONCLUSION: PSMA-617 NODA and RESCA derivatives were radiolabelled successfully via [18F]AlF2+ chelation, the former being more stable in solution and human plasma. Moreover, preclinical biodistribution studies showed that [18F]F-PSMA-617-NODA might be of potential interest for clinical applications.

The "digital biopsy" in non-small cell lung cancer (NSCLC): a pilot study to predict the PD-L1 status from radiomics features of [18F]FDG PET/CT.

PURPOSE: The present pilot study investigates the putative role of radiomics from [18F]FDG PET/CT scans to predict PD-L1 expression status in non-small cell lung cancer (NSCLC) patients. METHODS: In a retrospective cohort of 265 patients with biopsy-proven NSCLC, 86 with available PD-L1 immunohistochemical (IHC) assessment and [18F]FDG PET/CT scans have been selected to find putative metabolic markers that predict PD-L1 status (< 1%, 1-49%, and ≥ 50% as per tumor proportion score, clone 22C3). Metabolic parameters have been extracted from three different PET/CT scanners (Discovery 600, Discovery IQ, and Discovery MI) and radiomics features were computed with IBSI compliant algorithms on the original image and on images filtered with LLL and HHH coif1 wavelet, obtaining 527 features per tumor. Univariate and multivariate analysis have been performed to compare PD-L1 expression status and selected radiomic features. RESULTS: Of the 86 analyzed cases, 46 (53%) were negative for PD-L1 IHC, 13 (15%) showed low PD-L1 expression (1-49%), and 27 (31%) were strong expressors (≥ 50%). Maximum standardized uptake value (SUVmax) demonstrated a significant ability to discriminate strong expressor cases at univariate analysis (p = 0.032), but failed to discriminate PD-L1 positive patients (PD-L1 ≥ 1%). Three radiomics features appeared the ablest to discriminate strong expressors: (1) a feature representing the average high frequency lesion content in a spherical VOI (p = 0.009); (2) a feature assessing the correlation between adjacent voxels on the high frequency lesion content (p = 0.004); (3) a feature that emphasizes the presence of small zones with similar grey levels inside the lesion (p = 0.003). The tri-variate linear discriminant model combining the three features achieved a sensitivity of 81% and a specificity of 82% in the test. The ability of radiomics to predict PD-L1 positive patients was instead scarce. CONCLUSIONS: Our data indicate a possible role of the [18F]FDG PET radiomics in predicting strong PD-L1 expression; these preliminary data need to be confirmed on larger or single-scanner series.

Synthesis and automated fluorine-18 radiolabeling of new PSMA-617 derivatives with a CuAAC radiosynthetic approach.

In the last decade, the development of new radiopharmaceuticals for the imaging and therapy of prostate cancer has been a highly active and important area of research, especially focusing on the prostate-specific membrane antigen (PSMA), an antigen which is upregulated in prostate, as well as in other tumor cells. A large variety of PSMA ligands have been radiolabeled, to date. Among the various derivatives, PSMA-617 resulted to be one of the most interesting in terms of interaction with the antigen and clinical properties, and its lutetium-177 labeled version has recently been approved by regulatory agencies for therapeutic purposes. For this reasons, the radiolabeling with fluorine-18 of a PSMA-617 derivative might be of interest. Beside other methodologies to radiolabel macromolecules with fluorine-18, the "click-chemistry" approach resulted to be very useful, and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) is considered one of most efficient and reliable. This paper proposes the synthesis of a suitable precursor for the radiolabeling with fluorine-18 of a new PSMA-617 derivative. The whole radiosynthetic procedure has been fully automated, and the final product, which proved to be stable in plasma, has been obtained with radiochemical yield and purity suitable for subsequent preclinical studies.

Treatment response assessment in [18F]FDG-PET/CT oncology scans: Impact of count statistics variation and reconstruction protocol.

PURPOSE: To investigate influences of reconstruction algorithms and count statistics variation on quantification and treatment response assessment in cancer patients, by using a large field of view-FOV scanner. METHODS: 54 cancer patients underwent PET/CT scan: 1) at baseline: 1.5 min/FOV, reconstructed by ordered-subset expectation maximization + point-spread-function-OSEM-PSF and bayesian penalised-likelihood-BPL algorithm 2) at restaging: 2 min/FOV, reconstructed also at 1.5 and 1 min/FOV, using OSEM-PSF and BPL. SUL (lean-body mass SUV) peak and max were measured for each target-lesion (n = 59). Differences in quantification obtained from datasets with different reconstruction algorithms and different time/FOV were evaluated. For any pair of PET datasets, metabolic response was assessed by using SULpeak, with a threshold of 30% in variation considered as significant. RESULTS: Both at baseline and restaging, SULpeak and max values were higher in BPL reconstructions than in OSEM-PSF (p < 0.0001). SULpeak at different time/FOV reconstructions showed no statistically significant differences both with OSEM-PSF and BPL; SULmax depended on acquisition time (p < 0.05). In 56/59 lesions (95%) therapy response was concordant regardless count statistics variation and reconstruction algorithm; 2/59 (3%) showed different responses according to count statistics, both for OSEM-PSF and BPL; in 1/59 lesion (2%) response was different depending on reconstruction algorithm used. CONCLUSIONS: BPL provided higher SULpeak and max than OSEM-PSF. With a large FOV/high sensitivity scanner, variation of time/FOV in restaging PET scans gave stable and reproducible results in terms of SULpeak, both for OSEM-PSF and BPL. Thus, metabolic response defined by SULpeak variation proved to be quite independent from count statistics.

Study of the Tissue Distribution of TLQP-21 in Mice Using [18F]JMV5763, a Radiolabeled Analog Prepared via [18F]Aluminum Fluoride Chelation Chemistry.

TLQP-21 is a neuropeptide that is involved in the control of several physiological functions, including energy homeostasis. Since TLQP-21 could oppose the early phase of diet-induced obesity, it has raised a huge interest, but very little is known about its mechanisms of action on peripheral tissues. Our aim was to investigate TLQP-21 distribution in brain and peripheral tissues after systemic administration using positron emission tomography. We report here the radiolabeling of NODA-methyl phenylacetic acid (MPAA) functionalized JMV5763, a short analog of TLQP-21, with [18F]aluminum fluoride. Labeling of JMV5763 was initially performed manually, on a small scale, and then optimized and implemented on a fully automated radiosynthesis system. In the first experiment, mice were injected in the tail vein with [18F]JMV5763, and central and peripheral tissues were collected 13, 30, and 60 min after injection. Significant uptake of [18F]JMV5763 was found in stomach, intestine, kidney, liver, and adrenal gland. In the CNS, very low uptake values were measured in all tested areas, suggesting that the tracer does not efficiently cross the blood-brain barrier. Pretreatment with non-radioactive JMV5763 caused a significant reduction of tracer uptake only in stomach and intestine. In the second experiment, PET analysis was performed in vivo 10-120 min after i.v. [18F]JMV5763 administration. Results were consistent with those of the ex vivo determinations. PET images showed a progressive increase of [18F]JMV5763 uptake in intestine and stomach reaching a peak at 30 min, and decreasing at 120 min. Our results demonstrate that 18F-labeling of TLQP-21 analogs is a suitable method to study its distribution in the body.

Non-peptide NK1 receptor ligands based on the 4-phenylpyridine moiety.

The quinoline nucleus of the previously described 4-phenylquinoline-3-carboxamides NK(1) receptor ligands 7 has been transformed into either substituted or azole-(i.e., triazole or tetrazole) fused pyridine moieties of compounds 9 and 10, respectively, in order to obtain NK(1) receptor ligands showing lower molecular weight or higher hydrophilicity. The program of molecular manipulations produced NK(1) receptor ligands showing affinity in the nanomolar range. In particular, 4-methyl-1-piperazinyl derivative 9j showed an IC(50) value of 4.8 nM and was proved to behave as a NK(1) antagonist blocking Sar(9)-SP-sulfone induced proliferation and migration of microvascular endothelial cells. Therefore, compound 9j has been labeled with [(11)C]CH(3)I (t(1/2)=20.4 min, ß(+)=99.8%) starting from the corresponding des-methyl precursor 9i using with a radiochemical yield of about 10% (not decay corrected) and a specific radioactivity>1 Ci/µmol in order to be used as a radiotracer in next PET studies.

Monitoring disease evolution and treatment response in lysosomal disorders by the peripheral benzodiazepine receptor ligand PK11195.

Microglia activation and neuroinflammation play a pivotal role in the pathogenesis of lysosomal storage disorders (LSD) affecting the central nervous system (CNS), which are amenable to treatment by hematopoietic stem cell transplantation (HSCT). HSCT efficacy relies on replacing the intra- and extra-vascular hematopoietic cell compartments, including CNS microglia, with a cell population expressing the functional enzyme. Non-invasive and quantitative assessment of microglia activation and of its reduction upon HSCT might allow for evaluation of disease evolution and response to treatment in LSD. We here demonstrate that microglia activation can be quantified ex vivo and in vivo by PET using the peripheral benzodiazepine receptor ligand PK11195 in two models of LSD. Furthermore, we show a differential PBR binding following microglia replacement by donor cells in mice undergoing HSCT. Our data indicates that PBR ligands constitute valuable tools for monitoring the evolution and the response to treatment of LSD with CNS involvement, and enable us to evaluate whether the turnover between endogenous and donor microglia following HSCT could be adequate enough to delay disease progression.

Synthesis and carbon-11 labeling of (R)- and (S)-thionisoxetine, norepinephrine reuptake inhibitors, potential radioligands for positron emission tomography.

Standards and des-methyl precursors of (R)- and (S)-thionisoxetine, potent and selective norepinephrine reuptake inhibitors, were synthesized and radiolabeled with carbon-11. Both enantiomers of the N-methyl-3-(2-thiomethylphenoxy)-3-phenylpropanamine and the 3-(2-thiomethylphenoxy)-3-phenylpropylamine were obtained via multi-step syntheses, while the radiosyntheses were carried out using [11C]CH3I. The radiochemical yields were 26%, decay corrected and the specific radioactivity ranging from 2 to 3 Ci/micromol. The HPLC analyses were performed using a chiral column: during the radiolabeling, no racemization occurred and the isomers were synthesized with high enantiomeric purity.

Synthesis, labeling, and biological evaluation of halogenated 2-quinolinecarboxamides as potential radioligands for the visualization of peripheral benzodiazepine receptors.

The previous exploration of the structure-affinity relationships concerning 4-phenyl-2-quinolinecarboxamide peripheral benzodiazepine receptor (PBR) ligands 6 showed as an interesting result the importance of the presence of a chlorine atom in the methylene carbon at position 3 of the quinoline nucleus. The subnanomolar PBR affinity shown by N-benzyl-3-chloromethyl-N-methyl-4-phenyl-2-quinolinecarboxamide (6b) suggested its chlorine atom to be replaced with other halogens in order to optimize the interaction of the quinolinecarboxamide derivatives with PBR and to develop suitable candidates for positron emission tomography (PET) or single photon emission computed tomography (SPECT) studies. The binding studies led to the discovery of fluoromethyl derivative 6a, which showed an IC50 value of 0.11 nM and is, therefore, one of the most potent PBR ligands so far described. Fluoromethyl derivative 6a has been labeled with 11C (t1/2=20.4 min, beta+=99.8%) starting from the corresponding des-methyl precursor (14) using [11C]CH3I in the presence of tetrabutylammonium hydroxide in DMF with a 35-40% radiochemical yield (corrected for decay) and 1.5 Ci/micromol of specific radioactivity. Ex vivo rat biodistribution and inhibition (following intravenous pre-administration of PK11195) studies showed that [11C]6a rapidly and specifically accumulated in PBR-rich tissues such as heart, lung, kidney, spleen, and adrenal, and at a lower level in other peripheral organs and in the brain. The images obtained in mouse with small animal YAP-(S)PET essentially confirmed the result of the ex vivo biodistribution experiments. The biological data suggest that [11C]6a is a promising radioligand for peripheral benzodiazepine receptor PET imaging in vivo.

11C-labeling of n-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]arylcarboxamide derivatives and evaluation as potential radioligands for PET imaging of dopamine D3 receptors.

The selective dopamine D(3) receptor ligands N-4-[4-[(2,3-dichlorophenyl)piperazin-1-yl]butyl]1-methoxy-2-naphthalencarboxamide (1) and N-4-[4-[(2,3-dichlorophenyl)piperazin-1-yl]butyl]-7-methoxy-2-benzofurancarboxamide (2) were labeled with (11)C (t(1/2) = 20.4 min) as potential radioligands for the noninvasive assessment of the dopamine D(3) neurotransmission system in vivo with positron emission tomography (PET). The radiosynthesis consisted in an O-methylation of the des-methyl precursors N-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]-1-hydroxy-2-naphthalenecarboxamide (3) and N-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]-7-hydroxy-2-benzofurancarboxamide (4) with [(11)C]methyl iodide using tBuOK/HMPA and KOH/DMSO, respectively. The radiotracers [(11)C]1 and [(11)C]2 were obtained in 35 min with over 99% radiochemical purity, 74 +/- 37 GBq/mumol of specific radioactivity, 13% and 26% radiochemical yield (EOB, decay-corrected). Distribution studies in rats demonstrated that the new tracers [(11)C]1 and [(11)C]2 cross the blood-brain barrier and localize in the brain. However, the kinetics of cerebral uptake did not reflect the regional expression of the D(3) receptors. Despite their in vitro pharmacological profile, [(11)C]1 and [(11)C]2 do not display an in vivo behavior suitable to image D(3) receptor expression using PET.

11C-Radiosynthesis and preliminary human evaluation of the disposition of the ACE inhibitor [11C]zofenoprilat.

(4S)-1-[(S)-3-Mercapto-2-methylpropanoyl]-4-phenylthio-L-proline (Zofenoprilat, 2), the active metabolite of the potent ACE inhibitor Zofenopril Calcium (1), was labelled with carbon-11 (t1/2=20.4 min) to evaluate its pharmacokinetics behaviour in human body using Positron Emission Tomography (PET). [11C]2 labelling procedures were based on the use of immobilized Grignard reagent and the acylation of (S)-4-phenylthio-L-proline methyl ester (5) with 11C-labelled methacryloyl chloride, followed by a Michael addition with thiobenzoic acid. The radiochemical yield was 5-10% (EOB, decay corrected) and specific radioactivity ranged from 0.5 to 1.5 Ci/micromol (18.5-55.5 GBq/micromol). Preliminary in vivo human evaluation of [11C]2 showed that the drug accumulates in organs which express high levels of ACE, like lungs and kidneys, and in organs involved in drug metabolism such as the liver and gall bladder. Results of the distribution of [11C]2 showed a measurable concentration of the drug in the target tissues such as the kidney and to a minor extent, the heart, where it can afford organ protection.

Automation of [11C]acyl chloride syntheses using commercially available 11C-modules.

In implementing published procedures for the incorporation of [11C]carbon dioxide on the immobilized Grignard reagents for the radiosynthesis of [11C]acyl chlorides, several modifications on a commercial PET tracer synthesizer module for 11C-methylations were made to obtain reliable and reproducible production processes for routine clinical applications. High yields of [carbonyl-11C]WAY-100635 and [11C]zofenoprilat were obtained via 11C-carboxylation using [carbonyl-11C]cyclohexanecarbonyl chloride and 2-methyl-[l-11C]acryloyl chloride prepared with the modified module.

[11C]RN5: a new agent for the in vivo imaging of myocardial alpha1-adrenoceptors.

The radiolabelling with the positron-emitter Carbon-11 and the biological evaluation in rats of 3-[2-[4-(2-[11C]methoxyphenyl)piperazin-1-yl]ethyl]pyrimido[5,4-b]indole-2,4-dione ([11C]RN5), alpha1-adrenoceptor antagonist (K(i)=0.21 nM), as a putative radioligand for the non-invasive assessment of alpha1-adrenoceptors with positron emission tomography (PET) is reported. The radiosynthesis procedure consisted of O-methylation of des-methyl precursor with [11C]methyl iodide in the presence of potassium hydroxide in dimethylformamide (DMF) at 80 degrees C. [11C]RN5 was obtained in >99% radiochemical purity in 25 min with a radiochemical yield in the 20-30% range, end of synthesis (EOS) (non-decay corrected) and a specific radioactivity of 92.5+/-18.5 GBq/micromol. Pre-clinical studies in rats showed a high uptake of [11C]RN5 in heart, spleen, adrenal gland, lung and kidney but not in the brain. Inhibition studies with high doses of different adrenergic antagonists indicate that more than 70% of myocardial uptake of [11C]RN5 is due to specific binding to alpha1-adrenoceptors. Our results indicate that [11C]RN5 is suitable to be further developed as a potential radioligand for the in vivo PET imaging of myocardial alpha1-adrenoceptors in humans.