Immunohistochemical localization of phosphodiesterase 10A in multiple mammalian species

Phosphodiesterase Type 5 Inhibitors in Male Reproduction: Molecular Mechanisms and Clinical Implications for Fertility Management

Phosphodiesterases, particularly the type 5 isoform (PDE5), have gained recognition as pivotal regulators of male reproductive physiology, exerting significant influence on testicular function, sperm maturation, and overall fertility potential. Over the past several decades, investigations have expanded beyond the original therapeutic intent of PDE5 inhibitors for erectile dysfunction, exploring their broader reproductive implications. This narrative review integrates current evidence from in vitro studies, animal models, and clinical research to clarify the roles of PDEs in effecting the male reproductive tract, with an emphasis on the mechanistic pathways underlying cyclic nucleotide signaling, the cellular specificity of PDE isoform expression, and the effects of PDE5 inhibitors on Leydig and Sertoli cell functions. Although certain findings suggest potential improvements in sperm motility, semen parameters, and a more favorable biochemical milieu for spermatogenesis, inconsistencies in study design, limited sample sizes, and inadequate long-term data temper definitive conclusions. Addressing these gaps through standardized protocols, larger and more diverse patient cohorts, and explorations of mechanistic biomarkers could pave the way for incorporating PDE5 inhibitors into evidence-based fertility treatment strategies. In the future, such targeted approaches may inform individualized regimens, optimize male reproductive outcomes, and refine the clinical application of PDE5 inhibitors as part of comprehensive male fertility management.

THPP-1 PDE10A inhibitor reverses the cognitive deficits and hyperdopaminergic state in a neurodevelopment model of schizophrenia

Schizophrenia (SCZ) is a complex neuropsychiatric disorder characterized by positive, negative, and cognitive symptoms. The neurodevelopmental methylazoxy-methanol acetate (MAM) rodent model replicates key neurobiological features of SCZ which includes hyperdopaminergic states in the ventral tegmental area (VTA) and cognitive deficits. Typical and atypical antipsychotics are primarily effective in treating the positive symptoms of SCZ but often fall short of addressing cognitive deficits. A promising therapeutic approach for treating all symptoms of SCZ has emerged through the inhibition of phosphodiesterase 10 A (PDE10A). Our study aim was to investigate the impact of acute and chronic THPP-1 (PDE10A inhibitor) treatment, in MAM rats, focusing on cognitive deficits and VTA dopamine (DA) activity. Adult offspring of pregnant rats treated with Saline or MAM (20 mg/kg) on gestational day 17 were treated with THPP-1 acutely (male/female rats; 3 mg/kg) at postnatal day (PD) 70-80 or chronically (males; 3 weeks; 2-3 mg/kg) from PD 70-91 and tested in the novel object recognition test and electrophysiological recording of DA neurons in the VTA. Acute THPP-1 treatment reversed cognitive impairments and normalized the increased number of active DA neurons in the VTA of male and female MAM rats, without affecting control rats. Also, chronic THPP-1 treatment reversed cognitive deficits and normalized DA hyperactivity in the VTA of male MAM rats. The efficacy of THPP-1 in reversing MAM-induced impairments underscores its ability to target disease-specific circuitry without affecting normal regulated systems in control rats. Our findings highlight the therapeutic potential of THPP-1 for addressing cognitive deficits and DA dysregulation in SCZ.

Synthesis of Tryptamine-Thiazolidin-4-one Derivatives and the Combined In Silico and In Vitro Evaluation of their Biological Activity and Cytotoxicity

Tryptamine, a monoamine alkaloid with an indole ring structure, is derived from the decarboxylation of the amino acid tryptophan, which is present in fungi, plants, and animals. Tryptamine analogues hold significant therapeutic potential due to their broad pharmacological activities, including roles as neurotransmitters and potential therapeutic agents for various diseases. Structural modifications of tryptamine enhance receptor selectivity and metabolic stability, improving therapeutic efficacy. These modifications are crucial for optimizing pharmacokinetic and pharmacodynamic properties, making the analogues more effective and safer for clinical use. In this study, novel tryptamine-thiazolidin-4-one (YS1-12) derivatives were synthesized via a one-pot three-component condensation reaction. The synthesized compounds are characterized by different spectroscopy techniques such as FT-IR, 1H NMR, 13C NMR, and HR-NMS. The synthesized compounds were subjected to binary QSAR disease models for bioactivity prediction and a target prediction model for target analysis. Potential targets were identified, and physics-based molecular simulations were conducted. Additionally, MM/GBSA binding free energy analysis was performed to calculate the average binding free energies of YS1-12 compared to reference molecules. Our computational results indicated promising biological activities for these new compounds. To further investigate these activities, the compounds were tested in vitro using two different cancer cell lines: YKG-1 glioblastoma and SH-SY5Y neuroblastoma cells. The results confirmed the potential activities of these novel compounds. Notably, compounds YS4 and YS10 exhibited favorable activities compared to the control compounds 5-FU and Temozolomide. YS4 demonstrated an IC50 value of 20 nM against YKG-1 cells, while YS10 exhibited an IC50 value of 0.44 nM against SH-SY5Y cells.

Aberrant activity at rest of the associative striatum in schizophrenia: Meta-analyses of the amplitude of low frequency fluctuations

Schizophrenia is a severe psychiatric disorder associated with brain alterations at rest. Amplitude of low-frequency fluctuations (ALFF) and its fractional version (fALFF) have been widely used to investigate alterations in spontaneous brain activity in schizophrenia. However, results are still inconsistent. Furthermore, while these measurements are similar, they showed some differences, and no meta-analysis has been yet performed to compare them in schizophrenia. Thus, we conducted systematic research in five databases and in the grey literature to find articles investigating fALFF and/or ALFF alterations in schizophrenia. Two separate meta-analyses were performed using the SDM-PSI software to identify fALFF and ALFF alterations separately. Then, a conjunction analysis was conducted to determine congruent results between the two approaches. We found that patients with schizophrenia showed altered fALFF activity in the left insula/putamen, the right paracentral lobule and the left middle occipital gyrus compared to healthy individuals. Patients with schizophrenia exhibited ALFF alterations in the bilateral putamen, the bilateral caudate nucleus, the bilateral inferior frontal gyrus, the right precuneus, the right precentral gyrus, the left postcentral gyrus, the right posterior cingulate gyrus, compared to healthy controls. ALFF increased activity in the left putamen was higher in drug-naïve patients and was correlated with positive symptoms. The conjunction analysis revealed a spatial convergence between fALFF and ALFF studies in the left putamen. This left putamen cluster is part of the associative striatum. Its alteration in schizophrenia provides additional support to the influential aberrant salience hypothesis of psychosis.

New Drug Treatments for Schizophrenia: A Review of Approaches to Target Circuit Dysfunction

Schizophrenia is a leading cause of global disease burden. Current drug treatments are associated with significant side effects and have limited efficacy for many patients, highlighting the need to develop new approaches that target other aspects of the neurobiology of schizophrenia. Preclinical, in vivo imaging, postmortem, genetic, and pharmacological studies have highlighted the key role of cortical GABAergic (gamma-aminobutyric acidergic)-glutamatergic microcircuits and their projections to subcortical dopaminergic circuits in the pathoetiology of negative, cognitive, and psychotic symptoms. Antipsychotics primarily act downstream of the dopaminergic component of this circuit. However, multiple drugs are currently in development that could target other elements of this circuit to treat schizophrenia. These include drugs for GABAergic or glutamatergic targets, including glycine transporters, D-amino acid oxidase, sodium channels, or potassium channels. Other drugs in development are likely to primarily act on pathways that regulate the dopaminergic system, such as muscarinic or trace amine receptors or 5-HT2A receptors, while PDE10A inhibitors are being developed to modulate the downstream consequences of dopaminergic dysfunction. Our review considers where new drugs may act on this circuit and their latest clinical trial evidence in terms of indication, efficacy, and side effects. Limitations of the circuit model, including whether there are neurobiologically distinct subgroups of patients, and future directions are also considered. Several drugs based on the mechanisms reviewed have promising clinical data, with the muscarinic agonist KarXT most advanced. If these drugs are approved for clinical use, they have the potential to revolutionize understanding of the pathophysiology and treatment of schizophrenia.

Alterations of striatal phosphodiesterase 10 A and their association with recurrence rate in bipolar I disorder

Phosphodiesterase 10 A (PDE10A), a pivotal element of the second messenger signaling downstream of the dopamine receptor stimulation, is conceived to be crucially involved in the mood instability of bipolar I disorder (BD-I) as a primary causal factor or in response to dysregulated dopaminergic tone. We aimed to determine whether striatal PDE10A availability is altered in patients with BD-I and assessed its relationship with the clinical characteristics of BD-I. This case-control study used positron emission tomography (PET) with 2-(2-(3-(4-(2-[18F]fluoroethoxy)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione ([18F]MNI-659), a radioligand that binds to PDE10A, to examine the alterations of the striatal PDE10A availability in the living brains of individuals with BD-I and their association with the clinical characteristics of BD-I. [18F]MNI-659 PET data were acquired from 25 patients with BD-I and 27 age- and sex-matched healthy controls. Patients with BD-I had significantly lower PDE10A availability than controls in the executive (F = 8.86; P = 0.005) and sensorimotor (F = 6.13; P = 0.017) subregions of the striatum. Lower PDE10A availability in the executive subregion was significantly associated with a higher frequency of mood episodes in patients with BD-I (r = -0.546; P = 0.007). This study provides the first evidence of altered PDE10A availability in patients with BD-I. Lower PDE10A availability in the executive subregion of the striatum is associated with an increased recurrence risk, suggesting that PDE10A may prevent BD-I relapse. Further studies are required to elucidate the role of PDE10A in BD-I pathophysiology and explore its potential as a treatment target.

Age-Related Effects of Inhalational Anesthetics in B4galnt1-Null and Cuprizone-Treated Mice: Clinically Relevant Insights into Demyelinating Diseases

Anesthetics are essential agents that are frequently used in clinical practice to induce a reversible loss of consciousness and sensation by depressing the central nervous system. The inhalational anesthetics isoflurane and sevoflurane are preferred due to their rapid induction and recovery times and ease of administration. Despite their widespread use, the exact molecular mechanisms by which these anesthetics induce anesthesia are not yet fully understood. In this study, the age-dependent effects of inhalational anesthetics on two demyelination models were investigated: congenital (B4galnt1-null) and chemically induced (cuprizone). Various motor and cognitive tests were used to determine sensitivity to isoflurane and sevoflurane anesthesia. B4galnt1-null mice, which exhibit severe motor deficits due to defects in ganglioside synthesis, showed significant impairments in motor coordination and balance in all motor tests, which were exacerbated by both anesthetics. Cuprizone-treated mice, which mimic the demyelination in B4galnt1-null mice, also showed altered, age-dependent sensitivity to anesthesia. The study showed that older mice exhibited more pronounced deficits, with B4galnt1-null mice showing the greatest susceptibility to sevoflurane. These differential responses to anesthetics suggest that age and underlying myelin pathology significantly influence anesthetic effects.

A Novel PDE10A Inhibitor for Tourette Syndrome and Other Movement Disorders

BACKGROUND

Tourette syndrome is a neurodevelopmental movement disorder involving basal ganglia dysfunction. PDE10A inhibitors modulate signaling in the striatal basal ganglia nuclei and are thus of interest as potential therapeutics in treating Tourette syndrome and other movement disorders.

METHODS

The preclinical pharmacology and toxicology, human safety and tolerability, and human PET striatal enzyme occupancy data for the PDE10A inhibitor EM-221 are presented.

RESULTS

EM-221 inhibited PDE10A with an in vitro IC50 of 9 pM and was >100,000 selective vs. other PDEs and other CNS receptors and enzymes. In rats, at doses of 0.05-0.50 mg/kg, EM-221 reduced hyperlocomotion and the disruption of prepulse inhibition induced by MK-801, attenuated conditioned avoidance, and facilitated novel object recognition, consistent with PDE10A's inhibition. EM-221 displayed no genotoxicity and was well tolerated up to 300 mg/kg in rats and 100 mg/kg in dogs. In single- and multiple-day ascending dose studies in healthy human volunteers, EM-221 was well tolerated up to 10 mg, with a maximum tolerated dose of 15 mg. PET imaging indicated that a PDE10A enzyme occupancy of up to 92.8% was achieved with a ~24 h half-life.

CONCLUSIONS

The preclinical and clinical data presented here support the study of EM-221 in phase 2 trials of Tourette syndrome and other movement disorders.

Targeting Striatal Glutamate and Phosphodiesterases to Control L-DOPA-Induced Dyskinesia

A large body of work during the past several decades has been focused on therapeutic strategies to control L-DOPA-induced dyskinesias (LIDs), common motor complications of long-term L-DOPA therapy in Parkinson's disease (PD). Yet, LIDs remain a clinical challenge for the management of patients with advanced disease. Glutamatergic dysregulation of striatal projection neurons (SPNs) appears to be a key contributor to altered motor responses to L-DOPA. Targeting striatal hyperactivity at the glutamatergic neurotransmission level led to significant preclinical and clinical trials of a variety of antiglutamatergic agents. In fact, the only FDA-approved treatment for LIDs is amantadine, a drug with NMDAR antagonistic actions. Still, novel agents with improved pharmacological profiles are needed for LID therapy. Recently other therapeutic targets to reduce dysregulated SPN activity at the signal transduction level have emerged. In particular, mechanisms regulating the levels of cyclic nucleotides play a major role in the transduction of dopamine signals in SPNs. The phosphodiesterases (PDEs), a large family of enzymes that degrade cyclic nucleotides in a specific manner, are of special interest. We will review the research for antiglutamatergic and PDE inhibition strategies in view of the future development of novel LID therapies.

Phosphodiesterase 10A inhibitor PF-2545920 as a prospective agent for the clinical promotion of sperm motility

Phosphodiesterase (PDE) inhibitors can improve sperm motility in patients with asthenozoospermia. However, the most commonly reported nonselective PDE inhibitor pentoxifylline and PDE5 inhibitor sildenafil have the disadvantages of requiring a high concentration and destroying sperm integrity. We examined the PDE10A inhibitor PF-2545920 to compare its ability to promote sperm motility with that of pentoxifylline and sildenafil. After seminal plasma was discarded, several semen samples were subjected to four treatments (control, PF-2545920, pentoxifylline, and sildenafil) to evaluate their ability to affect motility, viability, and spontaneous acrosome reactions. Intracellular calcium and adenosine triphosphate (ATP), mitochondrial membrane potential, and penetration through viscous medium were assessed by flow cytometry, luciferase, and hyaluronic acid after treatment with PF-2545920. Statistical analyses were performed using the analysis of variance statistical test. PF-2545920 elevated the percentage of motile spermatozoa compared to the control, pentoxifylline, and sildenafil groups at 10 µmol l -1 ( P < 0.01). It is less toxic to GC-2spd mouse spermatocytes cells and spermatozoa and causes fewer spontaneous acrosomal reactions ( P < 0.05). PF-2545920 also increased mitochondrial membrane potential ( P < 0.001) and altered intracellular calcium ( P < 0.05) in a dose-dependent manner, including increasing sperm hyaluronic acid penetrating ability ( P < 0.05). Therefore, PF-2545920 might be an excellent choice for stimulating the sperm motility.

Expanding the genotype-phenotype landscape of PDE10A-associated movement disorders

BACKGROUND

Phosphodiesterase 10A (PDE10A) controls body movements by regulating cyclic adenosine monophosphate signaling in the basal ganglia. Two classes of PDE10A variants are reported with distinctive genotype-phenotype correlation. The autosomal recessive mutations in the GAF-A and catalytic domains are associated with compromised membrane localization, and manifest with infantile onset chorea, developmental, and cognition delay with normal brain MRI. Conversely, autosomal dominant mutations in the GAF-B domain cause protein aggregates which results in childhood onset chorea in the context of normal cognition and development, with striatal lesions.

METHODS

Phenotypic characteristics of affected individuals with PDE10A mutations belonging to a single family were recorded. In addition, Sanger sequencing and in silico analysis were used to identify the mutations. Homozygosity mapping was applied together with whole exome sequencing.

RESULTS

Four individuals from a consanguineous family affected with PDE10A mutations were observed for up to 40 years. Although these individuals displayed a clinical phenotype attributed to the recessive GAF-A mutations, they revealed a bi-allelic GAF-B mutation (c.883G > A:p. D295 N; p.Asp295Asn) that was segregated with all affected individuals. In addition to chorea, we observed peculiar foot deformities and pronounced social phobia, with normal brain MRI. In silico structural analysis suggested that the GAF-B mutation blocked allosteric PDE10A activation. The resulting lack of PDE10A activity likely phenocopies GAF-A mutations, and this is achieved through a distinct mechanism.

CONCLUSIONS

Collectively, our findings demonstrate the association of recessive and dominant phenotypes of known variants, and further expands the genotype-phenotype landscape of PDE10A-associated movement disorders.

Inhibition of CXCR2 enhances CNS remyelination via modulating PDE10A/cAMP signaling pathway

CXC chemokine receptor 2 (CXCR2) plays an important role in demyelinating diseases, but the detailed mechanisms were not yet clarified. In the present study, we mainly investigated the critical function and the potential molecular mechanisms of CXCR2 on oligodendrocyte precursor cell (OPC) differentiation and remyelination. The present study demonstrated that inhibiting CXCR2 significantly enhanced OPC differentiation and remyelination in primary cultured OPCs and ethidium bromide (EB)-intoxicated rats by facilitating the formation of myelin proteins, including PDGFRα, MBP, MAG, MOG, and Caspr. Further investigation identified phosphodiesterase 10A (PDE10A) as a main downstream protein of CXCR2, interacting with the receptor to regulate OPC differentiation, in that inhibition of CXCR2 reduced PDE10A expression while suppression of PDE10A did not affect CXCR2. Furthermore, inhibition of PDE10A promoted OPC differentiation, whereas overexpression of PDE10A down-regulated OPC differentiation. Our data also revealed that inhibition of CXCR2/PDE10A activated the cAMP/ERK1/2 signaling pathway, and up-regulated the expression of key transcription factors, including SOX10, OLIG2, MYRF, and ZFP24, that ultimately promoted remyelination and myelin protein biosynthesis. In conclusion, our findings suggested that inhibition of CXCR2 promoted OPC differentiation and enhanced remyelination by regulating PDE10A/cAMP/ERK1/2 signaling pathway. The present data also highlighted that CXCR2 may serve as a potential target for the treatment of demyelination diseases.

Inhibition of PDE10A in a New Rat Model of Severe Dopamine Depletion Suggests New Approach to Non-Dopamine Parkinson's Disease Therapy

Parkinson's disease is the second most common neurodegenerative pathology. Due to the limitations of existing therapeutic approaches, novel anti-parkinsonian medicines with non-dopamine mechanisms of action are clearly needed. One of the promising pharmacological targets for anti-Parkinson drug development is phosphodiesterase (PDE) 10A. The stimulating motor effects of PDE10A inhibition were detected only under the conditions of partial dopamine depletion. The results raise the question of whether PDE10A inhibitors are able to restore locomotor activity when dopamine levels are very low. To address this issue, we (1) developed and validated the rat model of acute severe dopamine deficiency and (2) tested the action of PDE10A inhibitor MP-10 in this model. All experiments were performed in dopamine transporter knockout (DAT-KO) rats. A tyrosine hydroxylase inhibitor, α-Methyl-DL-tyrosine (αMPT), was used as an agent to cause extreme dopamine deficiency. In vivo tests included estimation of locomotor activity and catalepsy levels in the bar test. Additionally, we evaluated the tissue content of dopamine in brain samples by HPLC analysis. The acute administration of αMPT to DAT-KO rats caused severe depletion of dopamine, immobility, and catalepsy (Dopamine-Deficient DAT-KO (DDD) rats). As expected, treatment with the L-DOPA and carbidopa combination restored the motor functions of DDD rats. Strikingly, administration of MP-10 also fully reversed immobility and catalepsy in DDD rats. According to neurochemical studies, the action of MP-10, in contrast to L-DOPA + carbidopa, seems to be dopamine-independent. These observations indicate that targeting PDE10A may represent a new promising approach in the development of non-dopamine therapies for Parkinson's disease.

Positron Emission Tomography Assessments of Phosphodiesterase 10A in Patients With Schizophrenia

BACKGROUND AND HYPOTHESIS

Phosphodiesterase 10A (PDE10A) is a highly expressed enzyme in the basal ganglia, where cortical glutamatergic and midbrain dopaminergic inputs are integrated. Therapeutic PDE10A inhibition effects on schizophrenia have been reported previously, but the status of this molecule in the living patients with schizophrenia remains elusive. Therefore, this study aimed to investigate the central PDE10A status in patients with schizophrenia and examine its relationship with psychopathology, cognition, and corticostriatal glutamate levels.

STUDY DESIGN

This study included 27 patients with schizophrenia, with 5 antipsychotic-free cases, and 27 healthy controls. Positron emission tomography with [18F]MNI-659, a specific PDE10A radioligand, was employed to quantify PDE10A availability by measuring non-displaceable binding potential (BPND) of the ligand in the limbic, executive, and sensorimotor striatal functional subregions, and in the pallidum. BPND estimates were compared between patients and controls while controlling for age and gender. BPND correlations were examined with behavioral and clinical measures, along with regional glutamate levels quantified by the magnetic resonance spectroscopy.

STUDY RESULTS

Multivariate analysis of covariance demonstrated a significant main effect of diagnosis on BPND (p = .03). A posthoc test showed a trend-level higher sensorimotor striatal BPND in patients, although it did not survive multiple comparison corrections. BPND in controls in this subregion was significantly and negatively correlated with the Tower of London scores, a cognitive subtest. Striatal or dorsolateral prefrontal glutamate levels did not correlate significantly with BPND in either group.

CONCLUSIONS

The results suggest altered striatal PDE10A availability and associated local neural dysfunctions in patients with schizophrenia.

PDE5 inhibitors and male reproduction: Is there a place for PDE5 inhibitors in infertility clinics or andrology laboratories?

The objective of this review study is to evaluate the therapeutic role of PDE5 inhibitors (PDE5is) in the amelioration of oligoasthenospermia in infertile males. PDE5is have a beneficial influence on the secretory function of the Leydig and Sertoli cells, the biochemical environment within the seminiferous tubule, the contractility of the testicular tunica albuginea, and the prostatic secretory function. In several studies, the overall effect of sildenafil and vardenafil increased quantitative and qualitative sperm motility. Furthermore, some studies indicate that PDE5is influence positively the sperm capacity to undergo capacitation under biochemical conditions that are known to induce the sperm capacitation process. Additional research efforts are necessary in order to recommend unequivocally the usage of sildenafil, vardenafil, or avanafil for the alleviation of male infertility.

Easily automated radiosynthesis of [18F]P10A-1910 and its clinical translation to quantify phosphodiesterase 10A in human brain

Our previous work showed that [18F]P10A-1910 was a potential radioligand for use in imaging phosphodiesterase 10A (PDE10A). Specifically, it had high brain penetration and specific binding that was demonstrated in both rodents and non-human primates. Here, we present the first automatic cGMP-level production of [18F]P10A-1910 and translational PET/MRI study in living human brains. Successful one-step radiolabeling of [18F]P10A-1910 on a GE TRACERlab FX2N synthesis module was realized via two different methods. First, formulated [18F]P10A-1910 was derived from heating spirocyclic iodonium ylide in a tetra-n-butyl ammonium methanesulfonate solution. At the end of synthesis, it was obtained in non-decay corrected radiochemical yields (n.d.c. RCYs) of 12.4 ± 1.3%, with molar activities (MAs) of 90.3 ± 12.6 μmol (n = 7) (Method I). The boronic pinacol ester combined with copper and oxygen also delivered the radioligand with 16.8 ± 1.0% n. d.c. RCYs and 77.3 ± 20.7 GBq/μmol (n = 7) MAs after formulation (Method II). The radiochemical purity, radionuclidic purity, solvent residue, sterility, endotoxin content and other parameters were all validated for human use. Consistent with the distribution of PDE10A in the brain, escalating uptake of [18F]P10A-1910 was observed in the order of cerebellum (reference region), substantial nigra, caudate and putamen. The non-displaceable binding potential (BPND) was estimated by simplified reference-tissue model (SRTM); linear regressions demonstrated that BPND was well correlated with the most widely used semiquantitative parameter SUV. The strongest correlation was observed with SUV(50–60 min) (R2 = 0.966, p &lt; 0.01). Collectively, these results indicated that a static scan protocol could be easily performed for PET imaging of PDE10A. Most importantly, that [18F]P10A-1910 is a promising radioligand to clinically quantify PDE10A.

Motor, epileptic, and developmental phenotypes in genetic disorders affecting G protein coupled receptors-cAMP signaling

Over the last years, a constantly increasing number of genetic diseases associated with epilepsy and movement disorders have been recognized. An emerging group of conditions in this field is represented by genetic disorders affecting G-protein-coupled receptors (GPCRs)–cAMP signaling. This group of postsynaptic disorders includes genes encoding for proteins highly expressed in the central nervous system and involved in GPCR signal transduction and cAMP production (e.g., GNAO1, GNB1, ADCY5, GNAL, PDE2A, PDE10A, and HPCA genes). While the clinical phenotype associated with ADCY5 and GNAL is characterized by movement disorder in the absence of epilepsy, GNAO1, GNB1, PDE2A, PDE10A, and HPCA have a broader clinical phenotype, encompassing movement disorder, epilepsy, and neurodevelopmental disorders. We aimed to provide a comprehensive phenotypical characterization of genetic disorders affecting the cAMP signaling pathway, presenting with both movement disorders and epilepsy. Thus, we reviewed clinical features and genetic data of 203 patients from the literature with GNAO1, GNB1, PDE2A, PDE10A, and HPCA deficiencies. Furthermore, we delineated genotype–phenotype correlation in GNAO1 and GNB1 deficiency. This group of disorders presents with a highly recognizable clinical phenotype combining distinctive motor, epileptic, and neurodevelopmental features. A severe hyperkinetic movement disorder with potential life-threatening exacerbations and high susceptibility to a wide range of triggers is the clinical signature of the whole group of disorders. The existence of a distinctive clinical phenotype prompting diagnostic suspicion and early detection has relevant implications for clinical and therapeutic management. Studies are ongoing to clarify the pathophysiology of these rare postsynaptic disorders and start to design disease-specific treatments.

Phosphodiesterase 9 inhibition prolongs the antiparkinsonian action of l-DOPA in parkinsonian non-human primates

Phosphodiesterase 9 (PDE9) degrades selectively the second messenger cGMP, which is an important molecule of dopamine signaling pathways in striatal projection neurons (SPNs). In this study, we assessed the effects of a selective PDE9 inhibitor (PDE9i) in the primate model of Parkinson's disease (PD). Six macaques with advanced parkinsonism were used in the study. PDE9i was administered as monotherapy and co-administration with l-DOPA at two predetermined doses (suboptimal and threshold s.c. doses of l-Dopa methyl ester plus benserazide) using a controlled blinded protocol to assess motor disability, l-DOPA -induced dyskinesias (LID), and other neurologic drug effects. While PDE9i was ineffective as monotherapy, 2.5 and 5 mg/kg (s.c.) of PDE9i significantly potentiated the antiparkinsonian effects of l-DOPA with a clear prolongation of the "on" state (p < 0.01) induced by either the suboptimal or threshold l-DOPA dose. Co-administration of PDE9i had no interaction with l-DOPA pharmacokinetics. PDE9i did not affect the intensity of LID. These results indicate that cGMP upregulation interacts with dopamine signaling to enhance the l-DOPA reversal of parkinsonian motor disability. Therefore, striatal PDE9 inhibition may be further explored as a strategy to improve motor responses to l-DOPA in PD.

In Vitro Effects of Papaverine on Cell Migration and Vascular Endothelial Growth Factor in Cancer Cell Lines

Papaverine (PPV) is a benzylisoquinoline alkaloid isolated from Papaver somniferum that exerts antiproliferative activity. However, several questions remain regarding the biochemical pathways affected by PPV in tumourigenic cells. In this study, the influence of PPV on cell migration (light microscopy), expression of vascular endothelial growth factor (VEGF) B, VEGF R1, VEGF R2, and phosphorylated focal adhesion kinase (pFAK) were investigated using spectrophotometry in MDA-MB-231-, A549- and DU145 cell lines. The migration assay revealed that, after 48 h, PPV (100 µM) reduced cell migration to 81%, 91%, and 71% in MDA-MB-231-, A549-, and DU145 cells, respectively. VEGF B expression was reduced to 0.79-, 0.71-, and 0.73-fold after 48 h of exposure to PPV in MDA-MB-231-, A549- and DU145 cells, while PPV exposure of 48 h increased VEGF R1 expression in MDA-MB-231- and DU145 cells to 1.38 and 1.46. A fold decrease in VEGF R1 expression was observed in A549 cells to 0.90 after exposure to 150 µM. No statistically significant effects were observed on VEGF R2- and FAK expression after exposure to PPV. This study contributes to the understanding of the effects of a phytomedicinal alkaloid compound in cancer cells and may provide novel approaches to the application of non-addictive alkaloids.

Discovery of a highly specific 18F-labeled PET ligand for phosphodiesterase 10A enabled by novel spirocyclic iodonium ylide radiofluorination

As a member of cyclic nucleotide phosphodiesterase (PDE) enzyme family, PDE10A is in charge of the degradation of cyclic adenosine (cAMP) and guanosine monophosphates (cGMP). While PDE10A is primarily expressed in the medium spiny neurons of the striatum, it has been implicated in a variety of neurological disorders. Indeed, inhibition of PDE10A has proven to be of potential use for the treatment of central nervous system (CNS) pathologies caused by dysfunction of the basal ganglia–of which the striatum constitutes the largest component. A PDE10A-targeted positron emission tomography (PET) radioligand would enable a better assessment of the pathophysiologic role of PDE10A, as well as confirm the relationship between target occupancy and administrated dose of a given drug candidate, thus accelerating the development of effective PDE10A inhibitors. In this study, we designed and synthesized a novel ¹⁸F-aryl PDE10A PET radioligand, codenamed [¹⁸F]P10A-1910 ([¹⁸F]9), in high radiochemical yield and molar activity via spirocyclic iodonium ylide-mediated radiofluorination. [¹⁸F]9 possessed good in vitro binding affinity (IC₅₀ = 2.1 nmol/L) and selectivity towards PDE10A. Further, [¹⁸F]9 exhibited reasonable lipophilicity (logD = 3.50) and brain permeability (P_app > 10 × 10⁻⁶ cm/s in MDCK-MDR1 cells). PET imaging studies of [¹⁸F]9 revealed high striatal uptake and excellent in vivo specificity with reversible tracer kinetics. Preclinical studies in rodents revealed an improved plasma and brain stability of [¹⁸F]9 when compared to the current reference standard for PDE10A-targeted PET, [¹⁸F]MNI659. Further, dose–response experiments with a series of escalating doses of PDE10A inhibitor 1 in rhesus monkey brains confirmed the utility of [¹⁸F]9 for evaluating target occupancy in vivo in higher species. In conclusion, our results indicated that [¹⁸F]9 is a promising PDE10A PET radioligand for clinical translation.

Antiparkinsonian-like effects of CPL500036, a novel selective inhibitor of phosphodiesterase 10A, in the unilateral rat model of Parkinson's disease

Phosphodiesterase 10A (PDE10A), the enzyme which catalyzes hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), is located almost exclusively in striatal γ-amino-butyric acid (GABA)ergic medium spiny neurons (MSNs). Since dopaminergic deficiency in Parkinson's disease (PD) leads to functional imbalance of striatal direct and indirect output pathways formed by MSNs, PDE10A seems to be of special interest as a potential therapeutic target in PD. The aim of the present study was to examine the influence of 7-{5,8-dimethyl-[1,2,4]triazolo[1,5-a]pyrazin-2-yl}-2-phenylimidazo[1,2-a]pyrimidine (CPL500036), a novel selective inhibitor of PDE10A, on sensorimotor deficits and therapeutic effects of L-3,4-dihydroxyphenylalanine (L-DOPA) in hemiparkinsonian rats. Animals were unilaterally lesioned with 6-hydroxydopamine, and their sensorimotor deficits were examined in the stepping, cylinder, vibrissae and catalepsy tests. CPL500036 (0.1 and 0.3 mg/kg) was administered either acutely or chronically (2 weeks), alone or in combination with L-DOPA/benserazide (6 mg/kg/6 mg/kg). Acute treatment with CPL500036 reversed the lesion-induced impairments of contralateral forelimb use in the stepping and cylinder tests but did not influence deficits in the vibrissae test and the lesion-induced catalepsy. Moreover, CPL500036 did not diminish the therapeutic effects produced by acute and chronic treatment with L-DOPA in these tests. The present study suggests a potential use of CPL500036 as a co-treatment to L-DOPA in PD therapy.

Suppression of Colon Tumorigenesis in Mutant Apc Mice by a Novel PDE10 Inhibitor that Reduces Oncogenic β-Catenin

Previous studies have reported that phosphodiesterase 10A (PDE10) is overexpressed in colon epithelium during early stages of colon tumorigenesis and essential for colon cancer cell growth. Here we describe a novel non-COX inhibitory derivative of the anti-inflammatory drug, sulindac, with selective PDE10 inhibitory activity, ADT 061. ADT 061 potently inhibited the growth of colon cancer cells expressing high levels of PDE10, but not normal colonocytes that do not express PDE10. The concentration range by which ADT 061 inhibited colon cancer cell growth was identical to concentrations that inhibit recombinant PDE10. ADT 061 inhibited PDE10 by a competitive mechanism and did not affect the activity of other PDE isozymes at concentrations that inhibit colon cancer cell growth. Treatment of colon cancer cells with ADT 061 activated cGMP/PKG signaling, induced phosphorylation of oncogenic β-catenin, inhibited Wnt-induced nuclear translocation of β-catenin, and suppressed TCF/LEF transcription at concentrations that inhibit cancer cell growth. Oral administration of ADT 061 resulted in high concentrations in the colon mucosa and significantly suppressed the formation of colon adenomas in the Apc^+/min-FCCC mouse model of colorectal cancer without discernable toxicity. These results support the development of ADT 061 for the treatment or prevention of adenomas in individuals at risk of developing colorectal cancer. PREVENTION RELEVANCE: PDE10 is overexpressed in colon tumors whereby inhibition activates cGMP/PKG signaling and suppresses Wnt/β-catenin transcription to selectively induce apoptosis of colon cancer cells. ADT 061 is a novel PDE10 inhibitor that shows promising cancer chemopreventive activity and tolerance in a mouse model of colon cancer.

Pivotal role of phosphodiesterase 10A in the integration of dopamine signals in mice striatal D1 and D2 medium-sized spiny neurones

BACKGROUND AND PURPOSE

Dopamine in the striatum plays a crucial role in reward processes and action selection. Dopamine signals are transduced by D₁ and D₂ dopamine receptors which trigger mirror effects through the cAMP/PKA signalling cascade in D1 and D2 medium-sized spiny neurones (MSNs). Phosphodiesterases (PDEs), which determine the profile of cAMP signals, are highly expressed in MSNs, but their respective roles in dopamine signal integration remain poorly understood.

EXPERIMENTAL APPROACH

We used genetically-encoded FRET biosensors to monitor at the single cell level the functional contribution of PDE2A, PDE4 and PDE10A in the changes of the cAMP/PKA response to transient and continuous dopamine in mouse striatal brain slices.

KEY RESULTS

We found that PDE2A, PDE4 and PDE10A operate on the moderate to high cAMP levels elicited by D₁ or A_2A receptor stimulation. In contrast, only PDE10A is able to reduce cAMP down to baseline in both type of neurones, leading to the dephosphorylation of PKA substrates.

CONCLUSION AND IMPLICATIONS

In both MSN types, PDE10A inhibition blunts the responsiveness to dopamine, whereas PDE2A or PDE4 inhibition reinforces dopamine action.

Cellular context shapes cyclic nucleotide signaling in neurons through multiple levels of integration

Intracellular signaling with cyclic nucleotides are ubiquitous signaling pathways, yet the dynamics of these signals profoundly differ in different cell types. Biosensor imaging experiments, by providing direct measurements in intact cellular environment, reveal which receptors are activated by neuromodulators and how the coincidence of different neuromodulators is integrated at various levels in the signaling cascade. Phosphodiesterases appear as one important determinant of cross-talk between different signaling pathways. Finally, analysis of signal dynamics reveal that striatal medium-sized spiny neuron obey a different logic than other brain regions such as cortex, probably in relation with the function of this brain region which efficiently detects transient dopamine.

Advances in Cyclic Nucleotide Phosphodiesterase-Targeted PET Imaging and Drug Discovery

Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.

Challenges on Cyclic Nucleotide Phosphodiesterases Imaging with Positron Emission Tomography: Novel Radioligands and (Pre-)Clinical Insights since 2016

Cyclic nucleotide phosphodiesterases (PDEs) represent one of the key targets in the research field of intracellular signaling related to the second messenger molecules cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP). Hence, non-invasive imaging of this enzyme class by positron emission tomography (PET) using appropriate isoform-selective PDE radioligands is gaining importance. This methodology enables the in vivo diagnosis and staging of numerous diseases associated with altered PDE density or activity in the periphery and the central nervous system as well as the translational evaluation of novel PDE inhibitors as therapeutics. In this follow-up review, we summarize the efforts in the development of novel PDE radioligands and highlight (pre-)clinical insights from PET studies using already known PDE radioligands since 2016.

PDE10A Inhibitors-Clinical Failure or Window Into Antipsychotic Drug Action?

PDE10A, a phosphodiesterase that inactivates both cAMP and cGMP, is a unique signaling molecule in being highly and nearly exclusively expressed in striatal medium spiny neurons. These neurons dynamically integrate cortical information with dopamine-signaled value to mediate action selection among available behavioral options. Medium spiny neurons are components of either the direct or indirect striatal output pathways. Selective activation of indirect pathway medium spiny neurons by dopamine D2 receptor antagonists is putatively a key element in the mechanism of their antipsychotic efficacy. While PDE10A is expressed in all medium spiny neurons, studies in rodents indicated that PDE10A inhibition has behavioral effects in several key assays that phenocopy dopamine D2 receptor inhibition. This finding gave rise to the hypothesis that PDE10A inhibition also preferentially activates indirect pathway medium spiny neurons, a hypothesis that is consistent with electrophysiological, neurochemical, and molecular effects of PDE10A inhibitors. These data underwrote industry-wide efforts to investigate and develop PDE10A inhibitors as novel antipsychotics. Disappointingly, PDE10A inhibitors from 3 companies failed to evidence antipsychotic activity in patients with schizophrenia to the same extent as standard-of-care D2 antagonists. Given the notable similarities between PDE10A inhibitors and D2 antagonists, gaining an understanding of why only the latter class is antipsychotic affords a unique window into the basis for this therapeutic efficacy. With this in mind, we review the data on PDE10A inhibition as a step toward back-translating the limited antipsychotic efficacy of PDE10A inhibitors, hopefully to inform new efforts to develop better therapeutics to treat psychosis and schizophrenia.

Phosphodiesterase type 1 inhibition alters medial prefrontal cortical activity during goal-driven behaviour and partially reverses neurophysiological deficits in the rat phencyclidine model of schizophrenia

Positive modulation of cAMP signalling by phosphodiesterase (PDE) inhibitors has recently been explored as a potential target for the reversal of cognitive and behavioural deficits implicating the corticoaccumbal circuit. Previous studies show that PDE type 1 isoform B (PDE1B) inhibition may improve memory function in rodent models; however, the contribution of PDE1B inhibition to impulsivity, attentional and motivational functions as well as its neurophysiological effects have not been investigated. To address this, we recorded single unit activity in medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) in Lister Hooded rats treated with the PDE1B inhibitor Lu AF64386 and tested in the 5-choice serial reaction time task (5-CSRTT). We also asked whether PDE1B inhibition modulates neurophysiological deficits produced by subchronic phencyclidine (PCP) treatment, a rat pharmacological model of schizophrenia. Lu AF64386 significantly affected behavioural parameters consistent with a reduction in goal-directed behaviour, however without affecting accuracy. Additionally, it reduced mPFC neuronal activity. Pre-treatment with PCP did not affect behavioural parameters, however it significantly disrupted overall neuronal firing while increasing phasic responses to reward-predicting cues and disrupting mPFC-NAc cross-talk. The latter two effects were reversed by Lu AF64386. These findings suggest PDE1B inhibition may be beneficial in disorders implicating a dysfunction of the mPFC-NAc network.

Interplay between APC and ALDH1B1 in a newly developed mouse model of colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is a leading cause of cancer mortality worldwide. Mutations in the adenomatous polyposis coli (APC) gene are pivotal in colorectal tumorigenesis. Recently, we demonstrated that aldehyde dehydrogenase 1B1 (ALDH1B1) knockdown dramatically reduced colon tumor growth in a mouse xenograft model. The purpose of the present preliminary study is to examine the effect of loss of ALDH1B1 in CRC development in an inducible colon-specific Apc mouse model.

METHODS

Apc^W/FCdx2^ERT2-Cre mice develop uni-allelic inactivation of Apc specifically in colon epithelial cells following tamoxifen treatment. Aldh1b1^-/- KO mice were crossed with Apc^W/FCdx2^ERT2-Cre mice. Six-month-old male Apc^W/FCdx2^ERT2-Cre/Aldh1b1^-/-, and Apc^W/FCdx2^ERT2-Cre/Aldh1b1^+/+ mice were treated with tamoxifen (50 mg/kg, i.p.) for three consecutive days. Apc^W/F/Aldh1b1^-/- and Apc^W/F/Aldh1b1^+/+ mice were treated with corn oil (i.e., tamoxifen vehicle control) for three consecutive days. Eighteen days later, mice were sacrificed and their colons examined microscopically, macroscopically and histologically for the presence of adenoma.

RESULTS

All Apc^W/FCdx2^ERT2-Cre/Aldh1b1^+/+ and Apc^W/FCdx2^ERT2-Cre/Aldh1b1^-/- mice treated with tamoxifen developed colorectal adenoma. The Apc^W/FCdx2^ERT2-Cre/Aldh1b1^-/- mice showed a significant decrease in the total volume of all ileal and colonic adenomas, and decreased incidence of large colonic adenoma compared to Apc^W/FCdx2^ERT2-Cre/Aldh1b1^+/+ mice. Immunohistochemical analysis of p53 and β-catenin showed a trend toward decreased expression score in colonic adenomas of Apc^W/FCdx2^ERT2-Cre/Aldh1b1^-/- mice.

CONCLUSION

The present preliminary study suggests that deletion of ALDH1B1 may protect against the full development of colorectal cancer. Further mechanistic studies are required to elucidate how ALDH1B1 contributes for colorectal cancer.

Advances in the Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 2: Focus on Schizophrenia

Schizophrenia is a debilitating mental disorder with relatively high prevalence (~1%), during which positive manifestations (such as psychotic states) and negative symptoms (e.g., a withdrawal from social life) occur. Moreover, some researchers consider cognitive impairment as a distinct domain of schizophrenia symptoms. The imbalance in dopamine activity, namely an excessive release of this neurotransmitter in the striatum and insufficient amounts in the prefrontal cortex is believed to be partially responsible for the occurrence of these groups of manifestations. Second-generation antipsychotics are currently the standard treatment of schizophrenia. Nevertheless, the existent treatment is sometimes ineffective and burdened with severe adverse effects, such as extrapyramidal symptoms. Thus, there is an urgent need to search for alternative treatment options of this disease. This review summarizes the results of recent preclinical and clinical studies on phosphodiesterase 10A (PDE10A), which is highly expressed in the mammalian striatum, as a potential drug target for the treatment of schizophrenia. Based on the literature data, not only selective PDE10A inhibitors but also dual PDE2A/10A, and PDE4B/10A inhibitors, as well as multifunctional ligands with a PDE10A inhibitory potency are compounds that may combine antipsychotic, precognitive, and antidepressant functions. Thus, designing such compounds may constitute a new direction of research for new potential medications for schizophrenia. Despite failures of previous clinical trials of selective PDE10A inhibitors for the treatment of schizophrenia, new compounds with this mechanism of action are currently investigated clinically, thus, the search for new inhibitors of PDE10A, both selective and multitarget, is still warranted.

Specific phosphodiesterase type-10 inhibitor, papaverine, added after the cooling period improves canine sperm quality

The use of chilled semen has gained increasing interest in canine reproductive services. The addition of phosphodiesterase (PDE) inhibitors that increase the intracellular cyclic adenosine monophosphate levels may improve sperm motility. The purpose of this study was to examine the quality of sperm under the effect of the specific PDE-10 inhibitor (papaverine) added after storage for 1, 2, and 3 days at 5 °C. The ejaculates were obtained from 5 healthy Beagle dogs by digital manipulation. After collection, ejaculates were pooled, extended and cooled at 5 °C during 3 days. Sperm parameters were tested 30 min after the addition of different papaverine (PA) concentrations: 0, 5, 10 and 20 µM. Sperm motility (CASA), viability (PI/FITC-PNA) and capacitation status (chlortetracycline assay) were evaluated. The results showed that the addition of PA has no effect on sperm samples at day 0. However, concentrations of 5 and 10 µM increased (p < .05) sperm motility kinetics and viability significantly compared to the control at day 1, day 2 and day 3 of cooling. The addition of 20 μM PA decreased (p < .05) sperm quality parameters significantly and increased the percentage of capacitated/acrosome-reacted spermatozoa. In conclusion, the addition of 5 and 10 μM PA concentrations after cooled storage improved canine sperm quality.

PDE5 and PDE10 inhibition activates cGMP/PKG signaling to block Wnt/β-catenin transcription, cancer cell growth, and tumor immunity

Although numerous reports conclude that nonsteroidal anti-inflammatory drugs (NSAIDs) have anticancer activity, this common drug class is not recommended for long-term use because of potentially fatal toxicities from cyclooxygenase (COX) inhibition. Studies suggest the mechanism responsible for the anticancer activity of the NSAID sulindac is unrelated to COX inhibition but instead involves an off-target, phosphodiesterase (PDE). Thus, it might be feasible develop safer and more efficacious drugs for cancer indications by targeting PDE5 and PDE10, which are overexpressed in various tumors and essential for cancer cell growth. In this review, we describe the rationale for using the sulindac scaffold to design-out COX inhibitory activity, while improving potency and selectivity to inhibit PDE5 and PDE10 that activate cGMP/PKG signaling to suppress Wnt/β-catenin transcription, cancer cell growth, and tumor immunity.

Combination of the phosphodiesterase 10A inhibitor, MR1916 with risperidone shows additive antipsychotic-like effects without affecting cognitive enhancement and cataleptic effects in rats

AIM

Phosphodiesterase 10A (PDE10A) inhibitors not only have antipsychotic-like effects but also cause cognitive enhancement without affecting extrapyramidal side effects in rodents, suggesting that PDE10A may be a novel approach for the treatment of schizophrenia. However, how a combination of PDE10A inhibitor with a currently available antipsychotic drug, risperidone contributes to the effect of each compound in rats remains unclear. The purpose of the present study was to examine the combination effects of MR1916 with a currently available antipsychotic drug, risperidone, in rats.

METHODS

We examined the combination effects of the PDE10A inhibitor, MR1916 with risperidone on conditioned avoidance response (CAR) to assess antipsychotic-like effects in rats. We also examined them on catalepsy as extrapyramidal side effects and novel object recognition test in cognitive functions in rats.

RESULTS

MR1916 (0.025-0.2 mg/kg, p.o.) and risperidone (0.75-6 mg/kg, p.o.) alone attenuated the CAR in a dose-dependent manner. The combination of MR1916 (0.025 mg/kg, p.o.) with risperidone (0.75 mg/kg, p.o.) significantly enhanced the attenuation of CAR without increasing the escape failure response. At the same dosage, the cataleptic effects were not enhanced by combined treatment of MR1916 with risperidone. Furthermore, the enhancement of object recognition memory induced by MR1916 (0.3 mg/kg, p.o.) was not affected by the combination with risperidone (0.75 mg/kg, p.o.).

CONCLUSION

The combination of MR1916 with risperidone may have additive antipsychotic-like effects without affecting extrapyramidal side effects, and the cognitive-enhancing effect of MR1916 may not be interfered with the addition of risperidone.

Phosphodiesterase 10A Inhibitor Monotherapy Is Not an Effective Treatment of Acute Schizophrenia

BACKGROUND

Current treatments for psychotic symptoms associated with schizophrenia often provide inadequate efficacy with unacceptable adverse effects. Improved therapeutics have long been a goal of research. Preclinical testing suggests that phosphodiesterase 10A (PDE10A) inhibitors may provide a novel approach to treating psychosis associated with schizophrenia.

METHODS

The efficacy and safety of a highly selective PDE10A inhibitor, PF-02545920, was evaluated in a phase 2 multicenter, randomized, double-blind, placebo-controlled, parallel-group study. Eligible patients (18-65 years) with an acute exacerbation of schizophrenia were randomized 2:2:1:2 to PF-02545920 (5 or 15 mg every 12 hours [Q12H] titrated), risperidone (3 mg Q12H), or placebo for 28 days (n = 74:74:37:74). The primary objectives were to evaluate the efficacy of PF-02545920 using the Positive and Negative Syndrome Scale (PANNS) and safety/tolerability.

RESULTS

At day 28, PF-02545920 (either dose) was not significantly different from placebo for mean change from baseline in the PANNS total score (primary end point) or most other end points. Pharmacokinetics exposures seemed adequate for binding/inhibiting PDE10A enzyme. Risperidone was statistically different from placebo for the PANNS total score, demonstrating study sensitivity. Incidence rates for adverse events were similar among the groups. Both doses of PF-02545920 were generally well tolerated. Dystonia occurred in 1, 6, 0, and 3 patients in the PF-02545920 5 mg Q12H, PF-02545920 15 mg Q12H, risperidone, and placebo groups, respectively.

CONCLUSIONS

Neither dose of PF-02545920 was superior to placebo for the primary and most secondary end points. This indicates that PDE10A inhibition does not produce an antipsychotic effect in patients with acute exacerbation of schizophrenia.

Advances in Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 1: Overview of the Chemical and Biological Research

Phosphodiesterase 10A (PDE10A) is a double substrate enzyme that hydrolyzes second messenger molecules such as cyclic-3',5'-adenosine monophosphate (cAMP) and cyclic-3',5'-guanosine monophosphate (cGMP). Through this process, PDE10A controls intracellular signaling pathways in the mammalian brain and peripheral tissues. Pharmacological, biochemical, and anatomical data suggest that disorders in the second messenger system mediated by PDE10A may contribute to impairments in the central nervous system (CNS) function, including cognitive deficits as well as disturbances of behavior, emotion processing, and movement. This review provides a detailed description of PDE10A and the recent advances in the design of selective PDE10A inhibitors. The results of preclinical studies regarding the potential utility of PDE10A inhibitors for the treatment of CNS-related disorders, such as schizophrenia as well as Huntington's and Parkinson's diseases are also summarized.

PET Molecular Imaging of Phosphodiesterase 10A: An Early Biomarker of Huntington's Disease Progression

BACKGROUND

Changes in phosphodiesterase 10A enzyme levels may be a suitable biomarker of disease progression in Huntington's disease.

OBJECTIVES

To evaluate phosphodiesterase 10A PET imaging as a biomarker of HD progression using the radioligand, [¹⁸ F]MNI-659.

METHODS

The cross-sectional study (NCT02061722) included 45 Huntington's disease gene-expansion carriers stratified into four disease stages (early and late premanifest and Huntington's disease stages 1 and 2) and 45 age- and sex-matched healthy controls. The primary analysis compared striatal and pallidal phosphodiesterase 10A availability between Huntington's disease gene-expansion carriers and healthy controls as assessed by [¹⁸ F]MNI-659 binding. We assessed changes in phosphodiesterase 10A expression using several PET methodologies and compared with previously proposed measures of Huntington's disease progression (PET imaging of D_2/3 receptors and anatomical volume loss on MRI). The longitudinal follow-up study (NCT02956148) continued evaluation of phosphodiesterase 10A availability in 35 Huntington's disease gene-expansion carriers at a mean of 18 months from baseline of the cross-sectional study.

RESULTS

Primary analyses revealed that phosphodiesterase 10A availability in caudate, putamen, and globus pallidus was significantly lower in Huntington's disease gene-expansion carriers versus healthy controls across all stages. Striatal and pallidal phosphodiesterase 10A availability progressively declined in the premanifest stages and appeared to plateau between stages 1 and 2. The percentage decline of phosphodiesterase 10A availability measured cross-sectionally between Huntington's disease gene-expansion carriers and healthy controls was greater than that demonstrated by D_2/3 receptor availability or volumetric changes. Annualized rates of phosphodiesterase 10A change showed a statistically significant decline between the cross-sectional study and follow-up.

CONCLUSIONS

[¹⁸ F]MNI-659 PET imaging is a biologically plausible biomarker of Huntington's disease progression that is more sensitive than the dopamine-receptor and volumetric methods currently used. © 2020 International Parkinson and Movement Disorder Society.

Phosphodiesterase 10A levels are related to striatal function in schizophrenia: a combined positron emission tomography and functional magnetic resonance imaging study

Pharmacological inhibition of phosphodiesterase 10A (PDE10A) is being investigated as a treatment option in schizophrenia. PDE10A acts postsynaptically on striatal dopamine signaling by regulating neuronal excitability through its inhibition of cyclic adenosine monophosphate (cAMP), and we recently found it to be reduced in schizophrenia compared to controls. Here, this finding of reduced PDE10A in schizophrenia was followed up in the same sample to investigate the effect of reduced striatal PDE10A on the neural and behavioral function of striatal and downstream basal ganglia regions. A positron emission tomography (PET) scan with the PDE10A ligand [¹¹C]Lu AE92686 was performed, followed by a 6 min resting-state magnetic resonance imaging (MRI) scan in ten patients with schizophrenia. To assess the relationship between striatal function and neurophysiological and behavioral functioning, salience processing was assessed using a mismatch negativity paradigm, an auditory event-related electroencephalographic measure, episodic memory was assessed using the Rey auditory verbal learning test (RAVLT) and executive functioning using trail-making test B. Reduced striatal PDE10A was associated with increased amplitude of low-frequency fluctuations (ALFF) within the putamen and substantia nigra, respectively. Higher ALFF in the substantia nigra, in turn, was associated with lower episodic memory performance. The findings are in line with a role for PDE10A in striatal functioning, and suggest that reduced striatal PDE10A may contribute to cognitive symptoms in schizophrenia.

Perinatal Bisphenol A Exposure and Reprogramming of Imprinted Gene Expression in the Adult Mouse Brain

Genomic imprinting, a phenomenon by which genes are expressed in a monoallelic, parent-of-origin-dependent fashion, is critical for normal brain development. Expression of imprinted genes is regulated via epigenetic mechanisms, including DNA methylation (5-methylcytosine, 5mC), and disruptions in imprinting can lead to disease. Early-life exposure to the endocrine disrupting chemical bisphenol A (BPA) is associated with abnormalities in brain development and behavior, as well as with disruptions in epigenetic patterning, including 5mC and DNA hydroxymethylation (5-hydroxymethylcytosine, 5hmC). Using an established mouse model of perinatal environmental exposure, the objective of this study was to examine the effects of perinatal BPA exposure on epigenetic regulation of imprinted gene expression in adult mice. Two weeks prior to mating, dams were assigned to control chow or chow containing an environmentally relevant dose (50 µg/kg) of BPA. Exposure continued until offspring were weaned at post-natal day 21, and animals were followed until 10 months of age. Expression of three imprinted genes—Pde10a, Ppp1r9a, and Kcnq1, as well as three genes encoding proteins critical for regulation of 5mC and 5hmC—Dnmt1, Tet1, and Tet2, were evaluated in the right cortex and midbrain using qRT-PCR. Perinatal BPA exposure was associated with a significant increase in adult Kcnq1 (p = 0.04) and Dnmt1 (p = 0.02) expression in the right cortex, as well as increased expression of Tet2 in the midbrain (p = 0.03). Expression of Tet2 and Kcnq1 were positively correlated in the midbrain. Analysis of 5mC and 5hmC at the Kcnq1 locus was conducted in parallel samples using standard and oxidative bisulfite conversion followed by pyrosequencing. This analysis revealed enrichment of both 5mC and 5hmC at this locus in both brain regions. No significant changes in 5mC and 5hmC at Kcnq1 were observed with perinatal BPA exposure. Together, these data suggest that perinatal BPA exposure results in altered expression of Kcnq1, Dnmt1, and Tet2 in the adult mouse brain. Further studies with larger sample sizes are necessary to understand the mechanistic basis for these changes, as well as to determine the implications they have for brain development and function.

Phosphodiesterase inhibitors say NO to Alzheimer's disease

Phosphodiesterases (PDEs) consisted of 11 subtypes (PDE1 to PDE11) and over 40 isoforms that regulate levels of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), the second messengers in cell functions. PDE inhibitors (PDEIs) have been attractive therapeutic targets due to their involvement in diverse medical conditions, e.g. cardiovascular diseases, autoimmune diseases, Alzheimer's disease (AD), etc. Among them; AD with a complex pathology is a progressive neurodegenerative disorder which affect mostly senile people in the world and only symptomatic treatment particularly using cholinesterase inhibitors in clinic is available at the moment for AD. Consequently, novel treatment strategies towards AD are still searched extensively. Since PDEs are broadly expressed in the brain, PDEIs are considered to modulate neurodegenerative conditions through regulating cAMP and cGMP in the brain. In this sense, several synthetic or natural molecules inhibiting various PDE subtypes such as rolipram and roflumilast (PDE4 inhibitors), vinpocetine (PDE1 inhibitor), cilostazol and milrinone (PDE3 inhibitors), sildenafil and tadalafil (PDE5 inhibitors), etc have been reported showing encouraging results for the treatment of AD. In this review, PDE superfamily will be scrutinized from the view point of structural features, isoforms, functions and pharmacology particularly attributed to PDEs as target for AD therapy.

Antipsychotics: Mechanisms underlying clinical response and side-effects and novel treatment approaches based on pathophysiology

Antipsychotic drugs are central to the treatment of schizophrenia and other psychotic disorders but are ineffective for some patients and associated with side-effects and nonadherence in others. We review the in vitro, pre-clinical, clinical and molecular imaging evidence on the mode of action of antipsychotics and their side-effects. This identifies the key role of striatal dopamine D2 receptor blockade for clinical response, but also for endocrine and motor side-effects, indicating a therapeutic window for D2 blockade. We consider how partial D2/3 receptor agonists fit within this framework, and the role of off-target effects of antipsychotics, particularly at serotonergic, histaminergic, cholinergic, and adrenergic receptors for efficacy and side-effects such as weight gain, sedation and dysphoria. We review the neurobiology of schizophrenia relevant to the mode of action of antipsychotics, and for the identification of new treatment targets. This shows elevated striatal dopamine synthesis and release capacity in dorsal regions of the striatum underlies the positive symptoms of psychosis and suggests reduced dopamine release in cortical regions contributes to cognitive and negative symptoms. Current drugs act downstream of the major dopamine abnormalities in schizophrenia, and potentially worsen cortical dopamine function. We consider new approaches including targeting dopamine synthesis and storage, autoreceptors, and trace amine receptors, and the cannabinoid, muscarinic, GABAergic and glutamatergic regulation of dopamine neurons, as well as post-synaptic modulation through phosphodiesterase inhibitors. Finally, we consider treatments for cognitive and negative symptoms such dopamine agonists, nicotinic agents and AMPA modulators before discussing immunological approaches which may be disease modifying. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Comparison of phosphodiesterase 10A and dopamine transporter levels as markers of disease burden in early Parkinson's disease

BACKGROUND

Recent work has shown loss of phosphodiesterase 10A levels in middle-stage and advanced treated patients with PD, which was associated with motor symptom severity.

OBJECTIVES

To assess phosphodiesterase 10A levels in early PD and compare with loss of dopamine transporter as markers of disease burden.

METHODS

Seventy-eight subjects were included in this study (17 early de novo, 15 early l-dopa-treated, 24 moderate-advanced l-dopa-treated patients with PD, and 22 healthy controls). All participants underwent [¹¹ C]IMA107 PET, [¹¹ C]PE2I PET, and 3-Tesla MRI scan.

RESULTS

Early de novo PD patients showed loss of [¹¹ C]IMA107 and of [¹¹ C]PE2I binding in caudate and putamen (P < 0.001); early l-dopa-treated PD patients showed additional loss of [¹¹ C]IMA107 in the caudate (P < 0.001; annual decline 3.6%) and putamen (P < 0.001; annual decline 2.8%), but loss of [¹¹ C]PE2I only in the putamen (P < 0.001; annual decline 6.8%). Lower [¹¹ C]IMA107 correlated with lower [¹¹ C]PE2I in the caudate (rho = 0.51; P < 0.01) and putamen (rho = 0.53; P < 0.01). Longer disease duration correlated with lower [¹¹ C]IMA107 in the caudate (rho = -0.72; P < 0.001) and putamen (rho = -0.48; P < 0.01), and with lower [¹¹ C]PE2I only in the putamen (rho = -0.65; P < 0.001). Higher burden of motor symptoms correlated with lower [¹¹ C]IMA107 in the caudate (rho = -0.42; P < 0.05) and putamen (rho = -0.41; P < 0.05), and with lower [¹¹ C]PE2I only in the putamen (rho = -0.69; P < 0.001).

CONCLUSION

Our findings demonstrate loss of phosphodiesterase 10A levels very early in the course of PD and is associated with the gradual and progressive increase of motor symptoms. Phosphodiesterase 10A imaging shows similar potential with dopamine transporter imaging to follow disease progression. © 2019 International Parkinson and Movement Disorder Society.

PDE10A mutations help to unwrap the neurobiology of hyperkinetic disorders

The dual-specific cAMP/cGMP phosphodiesterase PDE10A is exclusively localised to regions of the brain and specific cell types that control crucial brain circuits and behaviours. The downside to this expression pattern is that PDE10A is also positioned to be a key player in pathology when its function is perturbed. The last decade of research has seen a clear role emerge for PDE10A inhibition in modifying behaviours in animal models of psychosis and Huntington's disease. Unfortunately, this has not translated to the human diseases as expected. More recently, a series of families with hyperkinetic movement disorders have been identified with mutations altering the PDE10A protein sequence. As these mutations have been analysed and characterised in other model systems, we are beginning to learn more about PDE10A function and perhaps catch a glimpse into how PDE10A activity could be modified for therapeutic benefit.

In vitro phosphodiesterase 10A (PDE10A) binding in whole hemisphere human brain using the PET radioligand [18F]MNI-659

Highly specific and sensitive biomarkers for pathologies related to dysfunctions in the basal ganglia circuit are of great value to assess therapeutic efficacy not only clinically to establish an early diagnosis, but also in terms of monitoring the efficacy of therapeutic interventions and decelerated neurodegeneration. The phosphodiesterase 10A (PDE10A) enzyme plays a central role in striatal signaling and is implicated in several neuropsychiatric disorders involving striatal pathology, such as Huntingtońs disease (HD) and schizophrenia. Inhibition of PDE10A activates the neurons in the striatum and consequently leads to alteration of behavioral aspects modulated by the striatal circuit. [¹⁸F]MNI-659, (2-(2-(3-(4-(2-[¹⁸F]fluoroethoxy)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione), is a newly developed PET radioligand that shows a high binding to PDE10A in the human brain in vivo. In the present study, we examined the in vitro binding of [¹⁸F]MNI-659 in human postmortem brain to gain a better understanding of the presence, density, disease-related alterations and therapy related to changes in PDE10A expression. The results show high specific binding of [¹⁸F]MNI-659 in the caudate nucleus, putamen and the hippocampal formation. Low specific [¹⁸F]MNI-659 binding was detected in nucleus accumbens in comparison to the caudate nucleus and putamen. In vitro binding studies with [¹⁸F]MNI-659 will facilitate in elucidating better understanding of the role of PDE10A activity in health and disease that may lead to new diagnostic opportunities in HD.

Development of 2-(2-(3-(4-([18F]Fluoromethoxy- d2)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione for Positron-Emission-Tomography Imaging of Phosphodiesterase 10A in the Brain

Phosphodiesterase 10A (PDE10A) is a newly identified therapeutic target for central-nervous-system disorders. 2-(2-(3-(4-([¹⁸F]Fluoroethoxy)phenyl)-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione ([¹⁸F]MNI-659, [¹⁸F]5) is a useful positron-emission-tomography (PET) ligand for imaging of PDE10A in the human brain. However, the radiolabeled metabolite of [¹⁸F]5 can accumulate in the brain. In this study, using [¹⁸F]5 as a lead compound, we designed four new ¹⁸F-labeled ligands ([¹⁸F]6-9) to find one more suitable than [¹⁸F]5. Of these, 2-(2-(3-(4-([¹⁸F]fluoromethoxy- d₂)phenyl)-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione ([¹⁸F]9) exhibited high in vitro binding affinity ( K_i = 2.9 nM) to PDE10A and suitable lipophilicity (log D = 2.2). In PET studies, the binding potential (BP_ND) of [¹⁸F]9 (5.8) to PDE10A in the striatum of rat brains was significantly higher than that of [¹⁸F]5 (4.6). Furthermore, metabolite analysis showed much lower levels of contamination with radiolabeled metabolites in the brains of rats given [¹⁸F]9 than in those given [¹⁸F]5. In conclusion, [¹⁸F]9 is a useful PET ligand for PDE10A imaging in brain.

Molecular Imaging in Huntington's Disease

Huntington's disease (HD) is a rare monogenic neurodegenerative disorder caused by a trinucleotide CAG repeat expansion in the huntingtin gene resulting in the formation of intranuclear inclusions of mutated huntingtin. The accumulation of mutated huntingtin leads to loss of GABAergic medium spiny neurons (MSNs); subsequently resulting in the development of chorea, cognitive dysfunction and psychiatric symptoms. Premanifest HD gene expansion carriers, provide a unique cohort to examine very early molecular changes, occurring before the development of overt symptoms, to elucidate disease pathophysiology and identify reliable biomarkers of HD progression. Positron emission tomography (PET) is a non-invasive molecular imaging technique allowing the evaluation of specific molecular targets in vivo. Selective PET radioligands provide invaluable tools to investigate the role of the dopaminergic system, brain metabolism, microglial activation, phosphodiesterase 10A, and cannabinoid, GABA, adenosine and opioid receptors in HD. PET has been employed to monitor disease progression aiming to identify a reliable biomarker to predict phenoconversion from premanifest to manifest HD.

Postsynaptic movement disorders: clinical phenotypes, genotypes, and disease mechanisms

Movement disorders comprise a group of heterogeneous diseases with often complex clinical phenotypes. Overlapping symptoms and a lack of diagnostic biomarkers may hamper making a definitive diagnosis. Next-generation sequencing techniques have substantially contributed to unraveling genetic etiologies underlying movement disorders and thereby improved diagnoses. Defects in dopaminergic signaling in postsynaptic striatal medium spiny neurons are emerging as a pathogenic mechanism in a number of newly identified hyperkinetic movement disorders. Several of the causative genes encode components of the cAMP pathway, a critical postsynaptic signaling pathway in medium spiny neurons. Here, we review the clinical presentation, genetic findings, and disease mechanisms that characterize these genetic postsynaptic movement disorders.