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The poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) have demonstrated efficacy in ovarian, breast, and prostate cancers, but current biomarkers do not consistently predict clinical benefit. 18 F-fluorthanatrace ( 18 F-FTT) is an analog to rucaparib, a clinically approved PARPi, and is a candidate biomarker for PARPi response. This study intends to characterize 18 F-FTT pharmacokinetics in breast cancer and optimize image timing for clinical trials. A secondary aim is to determine whether 18 F-FTT uptake in breast cancer correlates with matched frozen surgical specimens as a reference standard for PARP-1 protein. Methods: Thirty prospectively enrolled women with a new diagnosis of breast cancer were injected with 18 F-FTT and imaged dynamically 0-60 min after injection over the chest, with an optional static scan over multiple bed positions starting around 70 min. Kinetic analysis of lesion uptake was performed using blood-pool activity with population radiometabolite corrections. Normal breast and normal muscle reference tissue models were compared with PARP-1 protein expression in 10 patients with available tissue. Plasma radiometabolite concentrations and uptake in tumor and normal muscle were investigated in mouse xenografts. Results: Pharmacokinetics of 18 F-FTT were well fit by Logan plot reference region models of reversible binding. However, fits of 2-tissue compartment models assuming negligible metabolite uptake were unstable. Rapid metabolism of 18 F-FTT was demonstrated in mice, and similar uptake of radiometabolites was found in tumor xenografts and normal muscle. Tumor 18 F-FTT distribution volume ratios relative to normal muscle reference tissue correlated with tissue PARP-1 expression ( P < 0.02, n = 10). The tumor-to-normal muscle ratio from a 5-min frame between 50 and 60 min after injection, a potential static scan protocol, closely corresponded to the distribution volume ratio relative to normal muscle and correlated to PARP-1 expression ( P < 0.02, n = 10). Conclusion: This study of PARPi analog 18 F-FTT showed that uptake kinetics in vivo corresponded to expression of PARP-1 and that 18 F-FTT quantitation is influenced by radiometabolites that are increasingly present late after injection. Radiometabolites can be controlled by using optimal image acquisition timing or normal muscle reference tissue modeling in dynamic imaging or a tumor-to-normal muscle ratio. Optimal image timing for tumor-to-normal muscle quantification in humans appears to be between 50 and 60 min after injection. Therefore, a clinically practical static imaging protocol commencing 45-55 min after injection may sufficiently balance 18 F-FTT uptake with background clearance and radiometabolite interference for quantitative interpretation of PARP-1 expression in vivo., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Although the precise molecular mechanisms responsible for neuronal death and motor dysfunction in late-onset Parkinson's disease (PD) are unknown, evidence suggests that mitochondrial dysfunction and neuroinflammation occur early, leading to a collective increase in reactive oxygen species (ROS) production and oxidative stress. However, the lack of methods for tracking oxidative stress in the living brain has precluded its use as a potential biomarker. The goal of the current study is to address this need through the evaluation of the first superoxide (O 2 •- )-sensitive radioactive tracer, [ 18 F]ROStrace, in a model of late-onset PD. To achieve this goal, MitoPark mice with a dopaminergic (DA) neuron-specific deletion of transcription factor A mitochondrial ( Tfam ) were imaged with [ 18 F]ROStrace from the prodromal phase to the end-stage of PD-like disease. Our data demonstrate [ 18 F]ROStrace was sensitive to increased oxidative stress during the early stages of PD-like pathology in MitoPark mice, which persisted throughout the disease course. Similarly to PD patients, MitoPark males had the most severe parkinsonian symptoms and metabolic impairment. [ 18 F]ROStrace retention was also highest in MitoPark males, suggesting oxidative stress as a potential mechanism underlying the male sex bias of PD. Furthermore, [ 18 F]ROStrace may provide a method to identify patients at risk of Parkinson's before irreparable neurodegeneration occurs and enhance clinical trial design by identifying patients most likely to benefit from antioxidant therapies.

The opioid crisis is a catastrophic health emergency catalyzed by the misuse of opioids that target and activate the mu opioid receptor. Traditional radioligands used to study the mu opioid receptor are often tightly regulated owing to their abuse and respiratory depression potential. In the present study, we sought to design and characterize a library of 24 non-agonist ligands for the mu opioid receptor. Ligands were evaluated for the binding affinity, intrinsic activity, and predicted blood-brain barrier permeability. Several ligands demonstrated single-digit nM binding affinity for the mu opioid receptor while also demonstrating selectivity over the delta and kappa opioid receptors. The antagonist behavior of 1A and 3A at the mu opioid receptor indicate that these ligands would likely not induce opioid-dependent respiratory depression. Therefore, these ligands can enable a safer means to interrogate the endogenous opioid system. Based on binding affinity, selectivity, and potential off-target binding, [ 11 C] 1A was prepared via metallophotoredox of the aryl-bromide functional group to [ 11 C]methyl iodide. The nascent radiotracer demonstrated brain uptake in a rhesus macaque model and accumulation in the caudate and putamen. Naloxone was able to reduce [ 11 C] 1A binding, though the interactions were not as pronounced as naloxone's ability to displace [ 11 C]carfentanil. These results suggest that GSK1521498 and related congeners are amenable to radioligand design and can offer a safer way to query opioid neurobiology.

Clostridioides difficile infection (CDI) is an urgent public health threat with limited preventative options. In this work, we developed a messenger RNA (mRNA)-lipid nanoparticle (LNP) vaccine targeting C. difficile toxins and virulence factors. This multivalent vaccine elicited robust and long-lived systemic and mucosal antigen-specific humoral and cellular immune responses across animal models, independent of changes to the intestinal microbiota. Vaccination protected mice from lethal CDI in both primary and recurrent infection models, and inclusion of non-toxin cellular and spore antigens improved decolonization of toxigenic C. difficile from the gastrointestinal tract. Our studies demonstrate mRNA-LNP vaccine technology as a promising platform for the development of novel C. difficile therapeutics with potential for limiting acute disease and promoting bacterial decolonization.

Direct fluorination of a tosylate or mesylate precursor has been a wide-spread and reliable way for radio-fluorination. This approach can be difficult to achieve when the precursor cannot be easily obtained or is chemically unstable. A possible alternative method is to radiolabel ethylene ditosylate or 1,3-propanediol di-p-tosylate to form a radiofluorinated synthon. Here we present the automation of a simplified and reliable approach for the two-step fluorination using [ 18 F]FP-TMP, an analog of antibacterial agent trimethoprim. We demonstrate the feasibility of purifying the fluorinated synthon via filtration, and one final HPLC purification on a commercially available Trasis AllinOne module. The overall reaction time for the two-step reaction is around 90 min andthe decay-corrected yield for more than fifty preparations of [ 18 F]FP-TMP is 22 ± 5 % with high radiochemical purity (≥ 90 %) and specific activities (147 ± 107 GBq/μmol). All batches passed pre-established quality control specifications, demonstrating the utility of using this method in tracer syntheses that meet good manufacturing practice (GMP) requirement. This method can be adopted to the syntheses of other radiotracers, such as [ 18 F]FE-TMP, (+)-[ 18 F]F-PHNO and [ 18 F]FFMZ., Competing Interests: Declaration of competing interest Mark Sellmyer and Robert Mach have filed US patent US20180104365A1, assigned to the University of Pennsylvania, on radiotracer derivatives of trimethoprim for medical imaging. Both hold equity in Vellum Biosciences, a corporate entity that is commercializing trimethoprim radiotracers. Hsiaoju Lee has a consulting agreement with Vellum Biosciences. All others have no conflict of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Purpose: Mu-opioid receptors (MORs) are widely expressed in the central nervous system (CNS), peripheral organs, and immune system. This study measured the whole body distribution of MORs in rhesus macaques using the MOR selective radioligand [ 11 C]carfentanil ([ 11 C]CFN) on the PennPET Explorer. Both baseline and blocking studies were conducted using either naloxone or GSK1521498 to measure the effect of the antagonists on MOR binding in both CNS and peripheral organs., Methods: The PennPET Explorer was used for MOR total-body PET imaging in four rhesus macaques using [ 11 C]CFN under baseline, naloxone pretreatment, and naloxone or GSK1521498 displacement conditions. Logan distribution volume ratio (DVR) was calculated by using a reference model to quantitate brain regions, and the standard uptake value ratios (SUVRs) were calculated for peripheral organs. The percent receptor occupancy (%RO) was calculated to establish the blocking effect of 0.14 mg/kg naloxone or GSK1521498., Results: The %RO in MOR-abundant brain regions was 75-90% for naloxone and 72-84% for GSK1521498 in blocking studies. A higher than 90% of %RO were observed in cervical spinal cord for both naloxone and GSK1521498. It took approximately 4-6 min for naloxone or GSK1521498 to distribute to CNS and displace [ 11 C]CFN from the MOR. A smaller effect was observed in heart wall in the naloxone and GSK1521498 blocking studies., Conclusion: [ 11 C]CFN total-body PET scans could be a useful approach for studying mechanism of action of MOR drugs used in the treatment of acute and chronic opioid use disorder and their effect on the biodistribution of synthetic opioids such as CFN. GSK1521498 could be a potential naloxone alternative to reverse opioid overdose., (© 2024. The Author(s).)

The synucleinopathies are a diverse group of neurodegenerative disorders characterized by the accumulation of aggregated alpha-synuclein (aSyn) in vulnerable populations of brain cells. Oxidative stress is both a cause and a consequence of aSyn aggregation in the synucleinopathies; however, noninvasive methods for detecting oxidative stress in living animals have proven elusive. In this study, we used the reactive oxygen species (ROS)-sensitive positron emission tomography (PET) radiotracer [ 18 F]ROStrace to detect increases in oxidative stress in the widely-used A53T mouse model of synucleinopathy. A53T-specific elevations in [ 18 F]ROStrace signal emerged at a relatively early age (6-8 months) and became more widespread within the brain over time, a pattern which paralleled the progressive development of aSyn pathology and oxidative damage in A53T brain tissue. Systemic administration of lipopolysaccharide (LPS) also caused rapid and long-lasting elevations in [ 18 F]ROStrace signal in A53T mice, suggesting that chronic, aSyn-associated oxidative stress may render these animals more vulnerable to further inflammatory insult. Collectively, these results provide novel evidence that oxidative stress is an early and chronic process during the development of synucleinopathy and suggest that PET imaging with [ 18 F]ROStrace holds promise as a means of detecting aSyn-associated oxidative stress noninvasively.

Aggregated α-synuclein (α-syn) protein is a pathological hallmark of Parkinson's disease (PD) and Lewy body dementia (LBD). Development of positron emission tomography (PET) radiotracers to image α-syn aggregates has been a longstanding goal. This work explores the suitability of a pyridothiophene scaffold for α-syn PET radiotracers, where 47 derivatives of a potent pyridothiophene (asyn-44; K d =1.85 nM) were synthesized and screened against [ 3 H]asyn-44 in competitive binding assays using post-mortem PD brain homogenates. Equilibrium inhibition constant (K i ) values of the most potent compounds were determined, of which three had K i 's in the lower nanomolar range (12-15 nM). An autoradiography study confirmed that [ 3 H]asyn-44 is promising for imaging brain sections from multiple system atrophy and PD donors. Fluorine-18 labelled asyn-44 was synthesized in 6±2 % radiochemical yield (decay-corrected, n=5) with a molar activity of 263±121 GBq/μmol. Preliminary PET imaging of [ 18 F]asyn-44 in rats showed high initial brain uptake (>1.5 standardized uptake value (SUV)), moderate washout (~0.4 SUV at 60 min), and low variability. Radiometabolite analysis showed 60-80 % parent tracer in the brain after 30 and 60 mins. While [ 18 F]asyn-44 displayed good in vitro properties and acceptable brain uptake, troublesome radiometabolites precluded further PET imaging studies. The synthesis and in vitro evaluation of additional pyridothiophene derivatives are underway, with the goal of attaining improved affinity and metabolic stability., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Introduction: Dopamine D3 receptor (D3R) ligands have been studied for the possible treatment of neurological and neuropsychiatric disorders. However, selective D3R radioligands for in vitro binding studies have been challenging to identify due to the high structural similarity between the D2R and D3R. In a prior study, we reported a new conformationally-flexible benzamide scaffold having a high affinity for D3R and excellent selectivity vs. D2R. In the current study, we characterized the in vitro binding properties of a new radioiodinated ligand, [ 125 I]HY-3-24., Methods: In vitro binding studies were conducted in cell lines expressing D3 receptors, rat striatal homogenates, and rat and non-human primate (NHP) brain tissues to measure regional brain distribution of this radioligand., Results: HY-3-24 showed high potency at D3R ( K i  = 0.67 ± 0.11 nM, IC 50  = 1.5 ± 0.58 nM) compared to other D2-like dopamine receptor subtypes (D2R K i  = 86.7 ± 11.9 nM and D4R K i  > 1,000). The K d (0.34 ± 0.22 nM) and B max (38.91 ± 2.39 fmol/mg) values of [ 125 I]HY-3-24 were determined. In vitro binding studies in rat striatal homogenates using selective D2R and D3R antagonists confirmed the D3R selectivity of [ 125 I]HY-3-24. Autoradiography results demonstrated that [ 125 I]HY-3-24 specifically binds to D3Rs in the nucleus accumbens, islands of Calleja, and caudate putamen in rat and NHP brain sections., Conclusion: These results suggest that [ 125 I]HY-3-24 appears to be a novel radioligand that exhibits high affinity binding at D3R, with low binding to other D2-like dopamine receptors. It is anticipated that [ 125 I]HY-3-24 can be used as the specific D3R radioligand., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Lee, Kim, Martorano, Riad, Taylor, Luedtke and Mach.)

A series of bitopic ligands based on Fallypride with a flexible secondary binding fragment (SBF) were prepared with the goal of preparing a D 3 R-selective compound. The effect of the flexible linker ( ( R , S ) -trans -2a - d ), SBFs ( ( R , S ) -trans -2h - j ), and the chirality of orthosteric binding fragments (OBFs) ( ( S , R ) -trans -d , ( S , R ) -trans -i , ( S , S ) -trans -d , ( S , S ) -trans -i, ( R , R ) -trans -d, and ( R , R ) -trans -i ) were evaluated in in vitro binding assays. Computational chemistry studies revealed that the interaction of the fragment binding to the SBF increased the distance between the pyrrolidine nitrogen and ASP110 3.32 of the D 3 R, thereby reducing the D 3 R affinity to a suboptimal level.

The difference in the secondary binding site (SBS) between the dopamine 2 receptor (D 2 R) and dopamine 3 receptor (D 3 R) has been used in the design of compounds displaying selectivity for the D 3 R versus D 2 R. In the current study, a series of bitopic ligands based on Fallypride were prepared with various secondary binding fragments (SBFs) as a means of improving the selectivity of this benzamide analog for D 3 R versus D 2 R. We observed that compounds having a small alkyl group with a heteroatom led to an improvement in D 3 R versus D 2 R selectivity. Increasing the steric bulk in the SBF increase the distance between the pyrrolidine N and Asp110, thereby reducing D 3 R affinity. The best-in-series compound was (2S,4R)-trans-27 which had a modest selectivity for D 3 R versus D 2 R and a high potency in the β-arrestin competition assay which provides a measure of the ability of the compound to compete with endogenous dopamine for binding to the D 3 R. The results of this study identified factors one should consider when designing bitopic ligands based on Fallypride displaying an improved affinity for D 3 R versus D 2 R., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

Background: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development., Main Body: This selection of highlights provides commentary on 21 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first-in-human application of novel radiopharmaceuticals., Conclusion: Trends in radiochemistry and radiopharmacy are highlighted. Hot topics cover the entire scope of EJNMMI Radiopharmacy and Chemistry, demonstrating the progress in the research field in many aspects., (© 2023. The Author(s).)

Abnormal α-synuclein (α-syn) aggregation characterizes α-synucleinopathies, including Parkinson's disease (PD) and multiple system atrophy (MSA). However, no suitable positron emission tomography (PET) radiotracer for imaging α-syn in PD and MSA exists currently. Our structure-activity relationship studies identified 4-methoxy- N -(4-(3-(pyridin-2-yl)-3,8-diazabicyclo[3.2.1]octan-8-yl)phenyl)benzamide ( 4i ) as a PET radiotracer candidate for imaging α-syn. In vitro assays revealed high binding of 4i to recombinant α-syn fibrils (inhibition constant ( K i ) = 6.1 nM) and low affinity for amyloid beta (Aβ) fibrils in Alzheimer's disease (AD) homogenates. However, [ 3 H]4i also exhibited high specific binding to AD, progressive supranuclear palsy, and corticobasal degeneration tissues as well as PD and MSA tissues, suggesting notable affinity to tau. Nevertheless, the specific binding to pathologic α-syn aggregates in MSA post-mortem brain tissues was significantly higher than in PD tissues. This finding demonstrated the potential use of [ 11 C]4i as a PET tracer for imaging α-syn in MSA patients. Nonhuman primate PET studies confirmed good brain uptake and rapid washout for [ 11 C]4i .

A chemical fingerprint search identified Z3777013540 (1-(5-(6-fluoro-1 H -indol-2-yl)pyrimidin-2-yl)piperidin-4-ol; 1 ) as a potential 4R-tau binding ligand. Binding assays in post-mortem Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) brain with [ 3 H] 1 provided K D (nM) values in AD = 4.0, PSP = 5.1, and CBD = 4.5. In vivo positron emission tomography (PET) imaging in rats with [ 18 F] 1 demonstrated good brain penetration and rapid clearance from normal brain tissues. A subsequent molecular similarity search using 1 as the query revealed an additional promising compound, Z4169252340 (4-(5-(6-fluoro-1 H -indol-2-yl)pyrimidin-2-yl)morpholine; 21 ). Binding assays with [ 3 H] 21 provided K D (nM) values in AD = 1.2, PSP = 1.6, and CBD = 1.7 and lower affinities for binding aggregated α-synuclein and amyloid-beta. PET imaging in rats with [ 18 F] 21 demonstrated a higher brain penetration than [ 18 F] 1 and rapid clearance from normal brain tissues. We anticipate that 1 and 21 will be useful for the identification of other potent novel 4R-tau radiotracers.

Purpose: Previous studies from our lab utilized an ultra-high throughput screening method to identify compound 1 as a small molecule that binds to alpha-synuclein (α-synuclein) fibrils. The goal of the current study was to conduct a similarity search of 1 to identify structural analogs having improved in vitro binding properties for this target that could be labeled with radionuclides for both in vitro and in vivo studies for measuring α-synuclein aggregates., Methods: Using 1 as a lead compound in a similarity search, isoxazole derivative 15 was identified to bind to α-synuclein fibrils with high affinity in competition binding assays. A photocrosslinkable version was used to confirm binding site preference. Derivative 21, the iodo-analog of 15, was synthesized, and subsequently radiolabeled isotopologs [ 125 I]21 and [ 11 C]21 were successfully synthesized for use in in vitro and in vivo studies, respectively. [ 125 I]21 was used in radioligand binding studies in post-mortem Parkinson's disease (PD) and Alzheimer's disease (AD) brain homogenates. In vivo imaging of an α-synuclein mouse model and non-human primates was performed with [ 11 C]21., Results: In silico molecular docking and molecular dynamic simulation studies for a panel of compounds identified through a similarity search, were shown to correlate with K i values obtained from in vitro binding studies. Improved affinity of isoxazole derivative 15 for α-synuclein binding site 9 was indicated by photocrosslinking studies with CLX10. Design and successful (radio)synthesis of iodo-analog 21 of isoxazole derivative 15 enabled further in vitro and in vivo evaluation. K d values obtained in vitro with [ 125 I]21 for α-synuclein and Aβ 42 fibrils were 0.48 ± 0.08 nM and 2.47 ± 1.30 nM, respectively. [ 125 I]21 showed higher binding in human postmortem PD brain tissue compared with AD tissue, and low binding in control brain tissue. Lastly, in vivo preclinical PET imaging showed elevated retention of [ 11 C]21 in PFF-injected mouse brain. However, in PBS-injected control mouse brain, slow washout of the tracer indicates high non-specific binding. [ 11 C]21 showed high initial brain uptake in a healthy non-human primate, followed by fast washout that may be caused by rapid metabolic rate (21% intact [ 11 C]21 in blood at 5 min p.i.)., Conclusion: Through a relatively simple ligand-based similarity search, we identified a new radioligand that binds with high affinity (<10 nM) to α-synuclein fibrils and PD tissue. Although the radioligand has suboptimal selectivity for α-synuclein towards Aβ and high non-specific binding, we show here that a simple in silico approach is a promising strategy to identify novel ligands for target proteins in the CNS with the potential to be radiolabeled for PET neuroimaging studies., (© 2023. The Author(s), under exclusive licence to World Molecular Imaging Society.)

Introduction: Right ventricular (RV) function is a major determinant of outcome in patients with precapillary pulmonary hypertension (PH). We studied the effect of ranolazine on RV function over 6 months using multi-modality imaging and biochemical markers in patients with precapillary PH (groups I, III, and IV) and RV dysfunction [CMR imaging ejection fraction (EF) < 45%] in a longitudinal, randomized, double-blinded, placebo-controlled, multicenter study of ranolazine treatment., Methods: Enrolled patients were assessed using cardiac magnetic resonance (CMR) imaging, 11 C-acetate and 18 -F-FDG positron emission tomography (PET), and plasma metabolomic profiling, at baseline and at the end of treatment., Results: Twenty-two patients were enrolled, and 15 patients completed all follow-up studies with 9 in the ranolazine arm and 6 in the placebo arm. RVEF and RV/Left ventricle (LV) mean glucose uptake were significantly improved after 6 months of treatment in the ranolazine arm. Metabolomic changes in aromatic amino acid metabolism, redox homeostasis, and bile acid metabolism were observed after ranolazine treatment, and several changes significantly correlated with changes in PET and CMR-derived fluid dynamic measurements., Discussion: Ranolazine may improve RV function by altering RV metabolism in patients with precapillary PH. Larger studies are needed to confirm the beneficial effects of ranolazine., Competing Interests: SC has served as a consultant for Acceleron Pharma and United Therapeutics; SC is a director, officer, and shareholder in Synhale Therapeutics; SC holds research grants from Actelion and Pfizer. SC has filed patent applications regarding the targeting of metabolism in pulmonary hypertension. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Han, Forfia, Vaidya, Ramani, deKemp, Mach, Mankoff, Bravo, DiCarli, Chan, Waxman and Han.)

D3 receptors, a key component of the dopamine system, have emerged as a potential target of therapies to improve motor symptoms across neurodegenerative and neuropsychiatric conditions. In the present work, we evaluated the effect of D3 receptor activation on the involuntary head twitches induced by 2,5-dimethoxy-4-iodoamphetamine (DOI) at behavioral and electrophysiological levels. Mice received an intraperitoneal injection of either a full D3 agonist, WC 44 [4-(2-fluoroethyl)-N-[4-[4-(2-methoxyphenyl)piperazin 1-yl]butyl]benzamide] or a partial D3 agonist, WW-III-55 [N-(4-(4-(4-methoxyphenyl)piperazin-1-yl)butyl)-4-(thiophen-3-yl)benzamide] five minutes before the intraperitoneal administration of DOI. Compared to the control group, both D3 agonists delayed the onset of the DOI-induced head-twitch response and reduced the total number and frequency of the head twitches. Moreover, the simultaneous recording of neuronal activity in the motor cortex (M1) and dorsal striatum (DS) indicated that D3 activation led to slight changes in a single unit activity, mainly in DS, and increased its correlated firing in DS or between presumed cortical pyramidal neurons (CPNs) and striatal medium spiny neurons (MSNs). Our results confirm the role of D3 receptor activation in controlling DOI-induced involuntary movements and suggest that this effect involves, at least in part, an increase in correlated corticostriatal activity. A further understanding of the underlying mechanisms may provide a suitable target for treating neuropathologies in which involuntary movements occur.

Förster resonance energy transfer (FRET) is a valuable method for monitoring protein conformation and biomolecular interactions. Intrinsically fluorescent amino acids that can be genetically encoded, such as acridonylalanine (Acd), are particularly useful for FRET studies. However, quantitative interpretation of FRET data to derive distance information requires careful use of controls and consideration of photophysical effects. Here we present two case studies illustrating how Acd can be used in FRET experiments to study small molecule induced conformational changes and multicomponent biomolecular complexes., (© 2023 The Protein Society.)

Electronic cigarette (EC) use has increased dramatically, particularly among adolescents and young adults, and, like cigarette use, can cause pulmonary inflammation and increase the risk of lung disease. Methods: This preliminary study used PET with 18 F-6-(1/2)(2-fluoro-propyl)-4-methylpyridin-2-amine ( 18 F-NOS) to quantify inducible nitric oxide synthase expression to characterize oxidative stress and inflammation in the lungs in vivo in 3 age- and sex-matched groups: 5 EC users, 5 cigarette smokers, and 5 controls who had never smoked or vaped. Results: EC users showed greater 18 F-NOS nondisplaceable binding potential (BP ND ) than cigarette smokers ( P = 0.03) and controls ( P = 0.01), whereas BP ND in cigarette smokers did not differ from that in controls ( P > 0.1). 18 F-NOS lung tissue delivery and inducible nitric oxide synthase distribution volume did not significantly differ among groups. Although there were no group differences in peripheral inflammatory biomarker concentrations, 18 F-NOS BP ND correlated with the proinflammatory cytokine tumor necrosis factor-α concentrations ( r s = 0.87, P = 0.05) in EC users. Additionally, when EC users and cigarette smokers were pooled together, number of vaping episodes or cigarettes per day correlated with interleukin-6 levels ( r s = 0.86, P = 0.006). Conclusion: This is the first PET imaging study to compare lung inflammation between EC and cigarette users in vivo. We found preliminary evidence that EC users have greater pulmonary inflammation than cigarette smokers and controls, with a positive association between pulmonary and peripheral measures of inflammation., (© 2023 by the Society of Nuclear Medicine and Molecular Imaging.)

Sigma-2 receptor (S2R) is a S2R ligand-binding site historically associated with reportedly 21.5 kDa proteins that have been linked to several diseases, such as cancer, Alzheimer's disease, and schizophrenia. The S2R is highly expressed in various tumors, where it correlates with the proliferative status of the malignant cells. Recently, S2R was reported to be the transmembrane protein TMEM97. Prior to that, we had been investigating the translocator protein (TSPO) as a potential 21.5 kDa S2R candidate protein with reported heme and sterol associations. Here, we investigate the contributions of TMEM97 and TSPO to S2R activity in MCF7 breast adenocarcinoma and MIA PaCa-2 (MP) pancreatic carcinoma cells. Additionally, the role of the reported S2R-interacting partner PGRMC1 was also elucidated. Proximity ligation assays and co-immunoprecipitation show a functional association between S2R and TSPO. Moreover, a close physical colocalization of TMEM97 and TSPO was found in MP cells. In MCF7 cells, co-immunoprecipitation only occurred with TMEM97 but not with PGRMC1, which was further confirmed by confocal microscopy experiments. Treatment with the TMEM97 ligand 20-( S )-hydroxycholesterol reduced co-immunoprecipitation of both TMEM97 and PGRMC1 in immune pellets of immunoprecipitated TSPO in MP cells. To the best of our knowledge, this is the first suggestion of a (functional) interaction between TSPO and TMEM97 that can be affected by S2R ligands.

Reduced haloperidol ( 1 ) was previously reported to act as a potent sigma-1 receptor (S1R) ligand with substantially lower affinity to the dopamine D2 receptor (D2R) compared to haloperidol. It was also found to facilitate brain-derived neurotrophic factor (BDNF) secretion from astrocytic glial cell lines in a sigma-1 receptor (S1R)-dependent manner. Although an increase in BDNF secretion may have beneficial effects in some neurological conditions, the therapeutic utility of reduced haloperidol ( 1 ) is limited because it can be oxidized back to haloperidol in the body, a potent dopamine D2 receptor antagonist associated with well-documented adverse effects. A difluorinated analogue of reduced haloperidol, (±)-4-(4-chlorophenyl)-1-(3,3-difluoro-4-(4-fluorophenyl)-4-hydroxybutyl)piperidin-4-ol ( 2 ), was synthesized in an attempt to minimize the oxidation. Compound (±)- 2 was found to exhibit high affinity to S1R and facilitate BDNF release from mouse brain astrocytes. It was also confirmed that compound 2 cannot be oxidized back to the corresponding haloperidol analogue in liver microsomes. Furthermore, compound 2 was distributed to the brain following intraperitoneal administration in mice and reversed the learning deficits in active avoidance tasks. These findings suggest that compound 2 could serve as a promising S1R ligand with therapeutic potential for the treatment of cognitive impairments.

The use of computer-aided drug design (CADD) for the identification of lead compounds in radiotracer development is steadily increasing. Traditional CADD methods, such as structure-based and ligand-based virtual screening and optimization, have been successfully utilized in many drug discovery programs and are highlighted throughout this review. First, we discuss the use of virtual screening for hit identification at the beginning of drug discovery programs. This is followed by an analysis of how the hits derived from virtual screening can be filtered and culled to highly probable candidates to test in in vitro assays. We then illustrate how CADD can be used to optimize the potency of experimentally validated hit compounds from virtual screening for use in positron emission tomography (PET). Finally, we conclude with a survey of the newest techniques in CADD employing machine learning (ML)., Competing Interests: The authors declare no conflict of interest.

We have developed and characterized a novel D2R antagonist with exceptional GPCR selectivity - ML321. In functional profiling screens of 168 different GPCRs, ML321 showed little activity beyond potent inhibition of the D2R and to a lesser extent the D3R, demonstrating excellent receptor selectivity. The D2R selectivity of ML321 may be related to the fact that, unlike other monoaminergic ligands, ML321 lacks a positively charged amine group and adopts a unique binding pose within the orthosteric binding site of the D2R. PET imaging studies in non-human primates demonstrated that ML321 penetrates the CNS and occupies the D2R in a dose-dependent manner. Behavioral paradigms in rats demonstrate that ML321 can selectively antagonize a D2R-mediated response (hypothermia) while not affecting a D3R-mediated response (yawning) using the same dose of drug, thus indicating exceptional in vivo selectivity. We also investigated the effects of ML321 in animal models that are predictive of antipsychotic efficacy in humans. We found that ML321 attenuates both amphetamine- and phencyclidine-induced locomotor activity and restored pre-pulse inhibition (PPI) of acoustic startle in a dose-dependent manner. Surprisingly, using doses that were maximally effective in both the locomotor and PPI studies, ML321 was relatively ineffective in promoting catalepsy. Kinetic studies revealed that ML321 exhibits slow-on and fast-off receptor binding rates, similar to those observed with atypical antipsychotics with reduced extrapyramidal side effects. Taken together, these observations suggest that ML321, or a derivative thereof, may exhibit ″atypical″ antipsychotic activity in humans with significantly fewer side effects than observed with the currently FDA-approved D2R antagonists., Competing Interests: The authors declare no competing financial interest., (© 2022 American Chemical Society.)

Previous studies have confirmed that the binding of D 3 receptor antagonists is competitively inhibited by endogenous dopamine despite excellent binding affinity for D 3 receptors. This result urges the development of an alternative scaffold that is capable of competing with dopamine for binding to the D 3 receptor. Herein, an SAR study was conducted on metoclopramide that incorporated a flexible scaffold for interaction with the secondary binding site of the D 3 receptor. The alteration of benzamide substituents and secondary binding fragments with aryl carboxamides resulted in excellent D 3 receptor affinities ( K i = 0.8-13.2 nM) with subtype selectivity to the D 2 receptor ranging from 22- to 180-fold. The β-arrestin recruitment assay revealed that 21c with 4-(pyridine-4-yl)benzamide can compete well against dopamine with the highest potency (IC 50 = 1.3 nM). Computational studies demonstrated that the high potency of 21c and its analogs was the result of interactions with the secondary binding site of the D 3 receptor. These compounds also displayed minimal effects for other GPCRs except moderate affinity for 5-HT 3 receptors and TSPO. The results of this study revealed that a new class of selective D 3 receptor antagonists should be useful in behavioral pharmacology studies and as lead compounds for PET radiotracer development.

The sigma-2 receptor/transmembrane protein 97 (σ2R/TMRM97) is a promising biomarker of tumor proliferation and a target for cancer therapy. [ 3 H]DTG has been used to evaluate σ2R/TMEM97 binding affinity in compound development studies. However, [ 3 H]DTG has equal and moderate binding affinities to both sigma 1 receptor (σ1R) and σ2R/TMEM97. Furthermore, co-administration with the σ1R masking compound (+)-pentazocine may cause bias in σ2R/TMEM97 binding affinity screening experiments. We have developed a radioiodinated ligand, [ 125 I]RHM-4, which has high affinity and selectivity for σ2R/TMEM97 versus σ1R. In this study, a head-to-head comparison between [ 3 H]DTG and [ 125 I]RHM-4 on the binding affinity and their effectiveness in σ2R/TMEM97 compound screening studies was performed. The goal of these studies was to determine if this radioiodinated ligand is a suitable replacement for [ 3 H]DTG for screening new σ2R/TMEM97 compounds. Furthermore, to delineate the binding properties of [ 125 I]RHM-4 to the σ2R/TMEM97, the structure of RHM-4 was split into two fragments. This resulted in the identification of two binding regions in the σ2R, the "DTG" binding site, which is responsible for binding to the σ2R/TMEM97, and the secondary binding site, which is responsible for high affinity and selectivity for the σ2R/TMEM97 versus the σ1R. The results of this study indicate that [ 125 I]RHM-4 is an improved radioligand for in vitro binding studies of the σ2R/TMEM97 versus [ 3 H]DTG.

Astatine-211-parthanatine ([ 211 At]PTT) is an alpha-emitting radiopharmaceutical therapeutic that targets poly(adenosine-diphosphate-ribose) polymerase 1 (PARP1) in cancer cells. High-risk neuroblastomas exhibit among the highest PARP1 expression across solid tumors. In this study, we evaluated the efficacy of [ 211 At]PTT using 11 patient-derived xenograft (PDX) mouse models of high-risk neuroblastoma, and assessed hematological and marrow toxicity in a CB57/BL6 healthy mouse model. We observed broad efficacy in PDX models treated with [ 211 At]PTT at the maximum tolerated dose (MTD 36 MBq/kg/fraction x4) administered as a fractionated regimen. For the MTD, complete tumor response was observed in 81.8% (18 of 22) of tumors and the median event free survival was 72 days with 30% (6/20) of mice showing no measurable tumor >95 days. Reversible hematological and marrow toxicity was observed 72 hours post-treatment at the MTD, however full recovery was evident by 4 weeks post-therapy. These data support clinical development of [ 211 At]PTT for high-risk neuroblastoma., (© 2022. The Author(s).)

Neuroinflammation is implicated as a key pathologic mechanism in many neurodegenerative diseases and is thought to be mediated in large part by microglia, native phagocytic immune cells of the CNS. Abnormal aggregation of the protein α-synuclein after phagocytosis by microglia is one possible neuropathophysiological mechanism driving Parkinson's disease (PD). We conducted a human pilot study to evaluate the feasibility of targeting the inducible isoform of nitric oxide synthase using the [ 18 F]NOS radiotracer to measure neuroinflammation in idiopathic PD. Ten adults consisting of 6 PD patients and 4 healthy controls (HC) underwent one hour of dynamic [ 18 F]NOS positron emission tomography (PET) brain imaging with arterial blood sampling. We observed increased [ 18 F]NOS whole brain distribution volume (V T ) in PD patients compared to age-matched healthy controls ( p < 0.008) via a 1-tissue compartment (TC) model. The rate constant K1 for transport from blood into tissue did not differ between groups ( p = 0.72). These findings suggest elevated oxidative stress, a surrogate marker of inflammation, is present in early-stage idiopathic PD and indicate that [ 18 F]NOS PET imaging is a promising, non-invasive method to measure neuroinflammation.

BACKGROUNDSeveral molecular imaging strategies can identify bacterial infections in humans. PET affords the potential for sensitive infection detection deep within the body. Among PET-based approaches, antibiotic-based radiotracers, which often target key bacterial-specific enzymes, have considerable promise. One question for antibiotic radiotracers is whether antimicrobial resistance (AMR) reduces specific accumulation within bacteria, diminishing the predictive value of the diagnostic test.METHODSUsing a PET radiotracer based on the antibiotic trimethoprim (TMP), [11C]-TMP, we performed in vitro uptake studies in susceptible and drug-resistant bacterial strains and whole-genome sequencing (WGS) in selected strains to identify TMP resistance mechanisms. Next, we queried the NCBI database of annotated bacterial genomes for WT and resistant dihydrofolate reductase (DHFR) genes. Finally, we initiated a first-in-human protocol of [11C]-TMP in patients infected with both TMP-sensitive and TMP-resistant organisms to demonstrate the clinical feasibility of the tool.RESULTSWe observed robust [11C]-TMP uptake in our panel of TMP-sensitive and -resistant bacteria, noting relatively variable and decreased uptake in a few strains of P. aeruginosa and E. coli. WGS showed that the vast majority of clinically relevant bacteria harbor a WT copy of DHFR, targetable by [11C]-TMP, and that despite the AMR, these strains should be "imageable." Clinical imaging of patients with [11C]-TMP demonstrated focal radiotracer uptake in areas of infectious lesions.CONCLUSIONThis work highlights an approach to imaging bacterial infection in patients, which could affect our understanding of bacterial pathogenesis as well as our ability to better diagnose infections and monitor response to therapy.TRIAL REGISTRATIONClinicalTrials.gov NCT03424525.FUNDINGInstitute for Translational Medicine and Therapeutics, Burroughs Wellcome Fund, NIH Office of the Director Early Independence Award (DP5-OD26386), and University of Pennsylvania NIH T32 Radiology Research Training Grant (5T32EB004311-12).

The intrinsic photochemistry of the isoxazole, a common heterocycle in medicinal chemistry, can be applied to offer an alternative to existing strategies using more perturbing, extrinsic photo-crosslinkers. The utility of isoxazole photo-crosslinking is demonstrated in a wide range of biologically relevant experiments, including common proteomics workflows.

A series of σ2R compounds containing benzimidazolone and diazacycloalkane cores was synthesized and evaluated in radioligand binding assays. Replacing the piperazine moiety in a lead compound with diazaspiroalkanes and the fused octahydropyrrolo[3,4-b] pyrrole ring system resulted in a loss in affinity for the σ2R. On the other hand, the bridged 2,5-diazabicyclo[2.2.1]heptane, 1,4-diazepine, and a 3-aminoazetidine analog possessed nanomolar affinities for the σ2R. Computational chemistry studies were also conducted with the recently published crystal structure of the σ2R/TMEM97 and revealed that hydrogen bond interactions with ASP29 and π-stacking interactions with TYR150 were largely responsible for the high binding affinity of small molecules to this protein.

Background: Oxidative stress is implicated in the pathogenesis of the most common neurodegenerative diseases, such as Alzheimer's disease (AD). However, tracking oxidative stress in the brain has proven difficult and impeded its use as a biomarker. Herein, we investigate the utility of a novel positron emission tomography (PET) tracer, [ 18 F]ROStrace, as a biomarker of oxidative stress throughout the course of AD in the well-established APP/PS1 double-mutant mouse model. PET imaging studies were conducted in wild-type (WT) and APP/PS1 mice at 3 different time points, representing early (5 mo.), middle (10 mo.), and advanced (16 mo.) life (n = 6-12, per sex). Semi-quantitation SUVRs of the plateau phase (40-60 min post-injection; SUVR 40-60 ) of ten brain subregions were designated by the Mirrione atlas and analyzed by Pmod. Statistical parametric mapping (SPM) was used to distinguish brain regions with elevated ROS in APP/PS1 relative to WT in both sexes. The PET studies were validated by ex vivo autoradiography and immunofluorescence with the parent compound, dihydroethidium., Results: [ 18 F]ROStrace retention was increased in the APP/PS1 brain compared to age-matched controls by 10 mo. of age (p < 0.0001) and preceded the accumulation of oxidative damage in APP/PS1 neurons at 16 mo. (p < 0.005). [ 18 F]ROStrace retention and oxidative damages were higher and occurred earlier in female APP/PS1 mice as measured by PET (p < 0.001), autoradiography, and immunohistochemistry (p < 0.05). [ 18 F]ROStrace differences emerged midlife, temporally and spatially correlating with increased Aβ burden (r 2  = 0.36; p = 0.0003), which was also greatest in the female brain (p < 0.001)., Conclusions: [ 18 F]ROStrace identifies increased oxidative stress and neuroinflammation in APP/PS1 female mice, concurrent with increased amyloid burden midlife. Differences in oxidative stress during this crucial time may partially explain the sexual dimorphism in AD. [ 18 F]ROStrace may provide a long-awaited tool to stratify at-risk patients who may benefit from antioxidant therapy prior to irreparable neurodegeneration., (© 2022. The Author(s).)

In this study, a panel of 46 compounds containing five different scaffolds known to have high σ 2 receptor affinity were screened. 6,7-Dimethoxy-2-[4-(4-methoxyphenyl)butan-2-yl]-1,2,3,4-tetrahydroisoquinoline [(±)- 7 ] ( K i for σ 1 = 48.4 ± 7.7 nM, and K i for σ 2 = 0.59 ± 0.02 nM) and its desmethyl analogue, (±)- 8 ( K i for σ 1 = 108 ± 35 nM, and K i for σ 2 = 4.92 ± 0.59 nM), showed excellent binding affinity and subtype selectivity for σ 2 receptors. In vitro cell binding indicated that σ 2 receptor binding of [ 11 C]-(±)- 7 and [ 11 C]-(±)- 8 was dependent on TMEM97 protein expression. In PET studies, the peak brain uptake of [ 11 C]-(±)- 7 (8.28 ± 2.52%ID/cc) was higher than that of [ 11 C]-(±)- 8 (4.25 ± 0.97%ID/cc) with specific distribution in the cortex and hypothalamus. Brain uptake or tissue binding was selectively inhibited by ligands with different σ 2 receptor binding affinities. The results suggest [ 11 C]-(±)- 7 can be used as a PET radiotracer for imaging the function of σ 2 receptors in central nervous system disorders.

Our understanding of the progression and mechanisms underlying the onset of Parkinson's disease (PD) has grown enormously in the past few decades. There is growing evidence suggesting that poly (ADP-ribose) polymerase 1 (PARP-1) hyperactivation is involved in various neurodegenerative disorders, including PD, and that poly (ADP-ribose) (PAR)-dependent cell death is responsible for neuronal loss. In this review, we discuss the contribution of PARP-1 and PAR in the pathological process of PD. We describe the potential pathways regulated by the enzyme, review clinically relevant PARP-1 inhibitors as potential disease-modifying therapeutics for PD, and outline important factors that need to be considered for repurposing PARP-1 inhibitors for use in PD., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Fluorine 18 ( 18 F) fluorthanatrace ( 18 F-FTT) is a PET radiotracer for imaging poly (adenosine diphosphate-ribose) polymerase-1 (PARP-1), an important target for a class of drugs known as PARP inhibitors, or PARPi. This article describes the stepwise development of this radiotracer from its design and preclinical evaluation to the first-in-human imaging studies and the initial validation of 18 F-FTT as an imaging-based biomarker for measuring PARP-1 expression levels in patients with breast and ovarian cancer. A detailed discussion on the preparation and submission of an exploratory investigational new drug application to the Food and Drug Administration is also provided. Additionally, this review highlights the need and future plans for identifying a commercialization strategy to overcome the major financial barriers that exist when conducting the multicenter clinical trials needed for approval in the new drug application process. The goal of this article is to provide a road map that scientists and clinicians can follow for the successful clinical translation of a PET radiotracer developed in an academic setting. Keywords : Molecular Imaging-Cancer, PET, Breast, Genital/Reproductive, Chemistry, Radiotracer Development, PARPi, 18 F-FTT, Investigational New Drug © RSNA, 2022.

The poly-(adenosine diphosphate-ribose) polymerase (PARP) family of proteins participates in numerous functions, most notably the DNA damage response. Cancer vulnerability to DNA damage has led to development of several PARP inhibitors (PARPi). This class of drugs has demonstrated therapeutic efficacy in ovarian, breast, and prostate cancers, but with variable response. Consequently, clinics need to select patients likely to benefit from these targeted therapies. In vivo imaging of 18 F-fluorthanatrace uptake has been shown to correspond to PARP-1 expression in tissue. This study characterized the pharmacokinetics of 18 F-fluorthanatrace and tested kinetic and static models to guide metric selection in future studies assessing 18 F-fluorthanatrace as a biomarker of response to PARPi therapy. Methods: Fourteen prospectively enrolled ovarian cancer patients were injected with 18 F-fluorthanatrace and imaged dynamically for 60 min after injection followed by up to 2 whole-body scans, with venous blood activity and metabolite measurements. SUV max and SUV peak were extracted from dynamic images and whole-body scans. Kinetic parameter estimates and SUVs were assessed for correlations with tissue PARP-1 immunofluorescence ( n = 7). Simulations of population kinetic parameters enabled estimation of measurement bias and precision in parameter estimates. Results: 18 F-fluorthanatrace blood clearance was variable, but labeled metabolite profiles were similar across patients, supporting use of a population parent fraction curve. The total distribution volume from a reversible 2-tissue-compartment model and Logan reference tissue distribution volume ratio (DVR) from the first hour of PET acquisition correlated with tumor PARP-1 expression by immunofluorescence ( r = 0.76 and 0.83, respectively; P < 0.05). DVR bias and precision estimates were 6.4% and 29.1%, respectively. SUV max and SUV peak acquired from images with midpoints of 57.5, 110 ± 3, and 199 ± 4 min highly correlated with PARP-1 expression (mean ± SD, r ≥ 0.79; P < 0.05). Conclusion: Tumor SUV max and SUV peak at 55-60 min after injection and later and DVR from at least 60 min appear to be robust noninvasive measures of PARP-1 binding. 18 F-fluorthanatrace uptake in ovarian cancer was best described by models of reversible binding. However, pharmacokinetic patterns of tracer uptake were somewhat variable, especially at later time points., (© 2022 by the Society of Nuclear Medicine and Molecular Imaging.)

Repurposing PARP-1 inhibitors (PARPi) for non-oncological applications offers an attractive therapeutic strategy for pathological conditions characterized by PARP-1 hyperactivity. In the context of Parkinson's disease (PD), PARP-1 hyperactivity has been linked to neuronal death and disease progression. From a therapy perspective, the evaluation of PARPi as neuroprotective agents may offer a new therapeutic alternative for neurodegenerative disorders. An ideal PARPi needs to inhibit PARP-1 hyperactivity while also limiting downstream DNA damage and cellular toxicity-an effect that is attractive in cancer but far from ideal in neurological disease applications. Consequently, in this study, we set out to evaluate the neuroprotective properties of a previously reported low-toxicity PARPi (10e) using in vitro neuronal models of PD. 10e is a structural analogue of FDA-approved PARPi olaparib, with high PARP-1 affinity and selectivity. Our studies revealed that 10e protects neuronal cells from oxidative stress and DNA damage. In addition, 10e exhibits neuroprotective properties against α-synuclein pre-formed fibrils (αSyn PFF) mediated effects, including reduction in the levels of phosphorylated αSyn and protection against abnormal changes in NAD + levels. Our in vitro studies with 10e provide support for repurposing high-affinity and low-toxicity PARPi for neurological applications and lay the groundwork for long-term therapeutic studies in animal models of PD., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Poly (ADP-ribose) (PAR) is a negatively charged polymer that is biosynthesized by Poly (ADP-ribose) Polymerase-1 (PARP-1) and regulates various cellular processes. Alpha-synuclein (αSyn) is an intrinsically disordered protein (IDP) that has been directly implicated with driving the onset and progression of Parkinson's disease (PD). The mechanisms by which α-synuclein (αSyn) elicits its neurotoxic effects remain unclear, though it is well established that the main components of Lewy bodies (LBs) and Lewy neurites (LNs) in PD patients are aggregated hyperphosphorylated (S129) forms of αSyn (pαSyn). In the present study, we used immunofluorescence-based assays to explore if PARP-1 enzymatic product (PAR) promotes the aberrant cytoplasmic accumulation of pαSyn. We also performed quantitative measurements using in situ proximity ligation assays (PLA) on a transgenic murine model of α-synucleinopathy (M83-SNCA ∗ A53T) and post mortem PD/PDD patient samples to characterize PAR-pαSyn interactions. Additionally, we used bioinformatic approaches and site-directed mutagenesis to identify PAR-binding regions on αSyn. In summary, our studies show that PAR-pαSyn interactions are predominantly observed in PD-relevant transgenic murine models of αSyn pathology and post mortem PD/PDD patient samples. Moreover, we confirm that the interactions between PAR and αSyn involve electrostatic forces between negatively charged PAR and lysine residues on the N-terminal region of αSyn., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Puentes, Lengyel-Zhand, Lee, Hsieh, Schneider, Edwards, Luk, Lee, Trojanowski and Mach.)

The genetic code to life is balanced on a string of DNA that is under constant metabolic and physical stress from environmental forces. Nearly all diseases have a genetic component caused by or resulting in DNA damage that alters biology to drive pathogenesis. Recent advancements in DNA repair biology have led to the development of imaging tools that target DNA damage response and repair proteins. PET has been used for early detection of oncogenic processes and monitoring of tumor response to chemotherapeutics that target the DNA repair machinery. In the field of precision medicine, imaging tools provide a unique opportunity for patient stratification by directly measuring drug target expression or monitoring therapy to identify early responders. This overview discusses the state of the art on molecular imaging of DNA damage and repair from the past 5 years, with an emphasis on poly[adenosine diphosphate ribose]polymerase-1 as an imaging target and predictive biomarker of response to therapy., (© 2021 by the Society of Nuclear Medicine and Molecular Imaging.)

N- phenylpiperazine analogs can bind selectively to the D3 versus the D2 dopamine receptor subtype despite the fact that these two D2-like dopamine receptor subtypes exhibit substantial amino acid sequence homology. The binding for a number of these receptor subtype selective compounds was found to be consistent with their ability to bind at the D3 dopamine receptor subtype in a bitopic manner. In this study, a series of the 3-thiophenephenyl and 4-thiazolylphenyl fluoride substituted N -phenylpiperazine analogs were evaluated. Compound 6a was found to bind at the human D3 receptor with nanomolar affinity with substantial D3 vs. D2 binding selectivity (approximately 500-fold). Compound 6a was also tested for activity in two in-vivo assays: (1) a hallucinogenic-dependent head twitch response inhibition assay using DBA/2J mice and (2) an L-dopa-dependent abnormal involuntary movement (AIM) inhibition assay using unilateral 6-hydroxydopamine lesioned (hemiparkinsonian) rats. Compound 6a was found to be active in both assays. This compound could lead to a better understanding of how a bitopic D3 dopamine receptor selective ligand might lead to the development of pharmacotherapeutics for the treatment of levodopa-induced dyskinesia (LID) in patients with Parkinson's disease.

[ 18 F]Fallypride and [ 18 F]Fluortriopride (FTP) are two different PET radiotracers that bind with sub-nanomolar affinity to the dopamine D3 receptor (D 3 R). In spite of their similar D 3 affinities, the two PET ligands display very different properties for labeling the D 3 R in vivo: [ 18 F]Fallypride is capable of binding to D 3 R under "baseline" conditions, whereas [ 18 F]FTP requires the depletion of synaptic dopamine in order to image the receptor in vivo. These data suggest that [ 18 F]Fallypride is able to compete with synaptic dopamine for binding to the D 3 R, whereas [ 18 F]FTP is not. The goal of this study was to conduct a series of docking and molecular dynamic simulation studies to identify differences in the ability of each molecule to interact with the D 3 R that could explain these differences with respect to competition with synaptic dopamine. Competition studies measuring the ability of each ligand to compete with dopamine in the β-arrestin assay were also conducted. The results of the in silico studies indicate that FTP has a weaker interaction with the orthosteric binding site of the D 3 R versus that of Fallypride. The results of the in silico studies were also consistent with the IC50 values of each compound in the dopamine β-arrestin competition assays. The results of this study indicate that in silico methods may be able to predict the ability of a small molecule to compete with synaptic dopamine for binding to the D 3 R.

Background: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to update the readership on trends in the field of radiopharmaceutical development., Results: This commentary of highlights has resulted in 23 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals., Conclusion: Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

The response to poly(ADP-ribose) polymerase inhibitors (PARPi) is dictated by homologous recombination (HR) DNA repair and the abundance of lesions that trap PARP enzymes. It remains unclear, however, if the established role of PARP in promoting chromatin accessibility impacts viability in these settings. Using a CRISPR-based screen, we identified the PAR-binding chromatin remodeller ALC1/CHD1L as a key determinant of PARPi toxicity in HR-deficient cells. ALC1 loss reduced viability of breast cancer gene (BRCA)-mutant cells and enhanced sensitivity to PARPi by up to 250-fold, while overcoming several resistance mechanisms. ALC1 deficiency reduced chromatin accessibility concomitant with a decrease in the association of base damage repair factors. This resulted in an accumulation of replication-associated DNA damage, increased PARP trapping and a reliance on HR. These findings establish PAR-dependent chromatin remodelling as a mechanistically distinct aspect of PARPi responses and therapeutic target in HR-deficient cancers.