Inhibition of P2X7 receptors by Lu AF27139 diminishes colonic hypersensitivity and CNS prostanoid levels in a rat model of visceral pain.

Visceral pain is a prominent feature of various gastrointestinal diseases. The P2X7 receptor is expressed by multiple cell types including dorsal root ganglion satellite glial cells, macrophages, and spinal microglia, all of which have been implicated in nociceptive sensitization. We have used the selective and CNS penetrant P2X7 receptor antagonist Lu AF27139 to explore this receptor's role in distinct rat models of inflammatory and visceral hypersensitivity. Rats injected with CFA in the hindpaw displayed a marked reduction in hindpaw mechanical threshold, which was dose-dependently reversed by Lu AF27139 (3-30 mg/kg, p.o.). In rats injected with TNBS in the proximal colon, the colorectal distension threshold measured distally was significantly lower than sham treated rats at 7 days post-injection (P < 0.001), indicative of a marked central sensitization. Colonic hypersensitivity was also reversed by Lu AF27139 (10-100 mg/kg) and by the κ-opioid receptor agonist U-50,488H (3 mg/kg, s.c.). Moreover, both Lu AF27139 and U-50,488H prevented a TNBS-induced increase in spinal and brain levels of PGE2 and LTB4, as well as an increase in brain levels of PGF2α and TXB2. Lu AF27139 was well tolerated as revealed by a lack of significant effect on rotarod motor function and coordination at all doses tested up to 300 mg/kg. Thus, P2X7 receptor antagonism is efficacious in a rat model of visceral pain, via a mechanism which potentially involves attenuation of microglial function within spinal and/or supraspinal pain circuits, albeit a peripheral site of action cannot be excluded.

P2X7 receptor-mediated release of microglial prostanoids and miRNAs correlates with reversal of neuropathic hypersensitivity in rats.

BACKGROUND: P2X7 receptor antagonists have potential for treating various central nervous system (CNS) diseases, including neuropathic pain, although none have been approved for clinical use. Reasons may include insufficient understanding of P2X7 receptor signalling in pain, and the lack of a corresponding preclinical mechanistic biomarker. METHODS: Lu AF27139 is a highly selective and potent small molecule antagonist at rat, mouse and human forms of the P2X7 receptor, with excellent pharmacokinetic and CNS permeability properties. In the current experiments, we probed the utility of previously characterized and novel signalling cascades exposed to Lu AF27139 using cultured microglia combined with release assays. Subsequently, we assessed the biomarker potential of identified candidate molecules in the rat chronic constriction injury (CCI) model of neuropathic pain; study design limitations precluded their assessment in spared nerve injury (SNI) rats. RESULTS: Lu AF27139 blocked several pain-relevant pathways downstream of P2X7 receptors in vitro. At brain and spinal cord receptor occupancy levels capable of functionally blocking P2X7 receptors, it diminished neuropathic hypersensitivity in SNI rats, and less potently in CCI rats. Although tissue levels of numerous molecules previously linked to neuropathic pain and P2X7 receptor function (e.g. IL-6, IL-1ß, cathepsin-S, 2-AG) were unaffected by CCI, Lu AF27139-mediated regulation of spinal PGE2 and miRNA (e.g. rno-miR-93-5p) levels increased by CCI aligned with its ability to diminish neuropathic hypersensitivity. CONCLUSIONS: We have identified a pain-relevant P2X7 receptor-regulated mechanism in neuropathic rats, which could hold promise as a translatable biomarker and by association enhance the clinical progression of P2X7 receptor antagonists in neuropathic pain. SIGNIFICANCE: Sub-optimal translation of preclinical molecules has hindered the clinical development of novel mechanism of action analgesics. We have undertaken a comprehensive in vitro analysis of migroglial signalling mechanisms recruited upon P2X7 receptor activation, a number of which were shown to be modulated by a selective P2X7 receptor antagonist in a well characterized animal model of neuropathic pain. Subject to further confirmation in other neuropathic models, this opens up the possibility to investigate their clinical utility as potential pain biomarkers in patients.

Synthesis and Characterization of the Novel Rodent-Active and CNS-Penetrant P2X7 Receptor Antagonist Lu AF27139.

There remains an insufficient number of P2X7 receptor antagonists with adequate rodent potency, CNS permeability, and pharmacokinetic properties from which to evaluate CNS disease hypotheses preclinically. Herein, we describe the molecular pharmacology, safety, pharmacokinetics, and functional CNS target engagement of Lu AF27139, a novel rodent-active and CNS-penetrant P2X7 receptor antagonist. Lu AF27139 is highly selective and potent against rat, mouse, and human forms of the receptors. The rat pharmacokinetic profile is favorable with high oral bioavailability, modest clearance (0.79 L/(h kg)), and good CNS permeability. In vivo mouse CNS microdialysis studies of lipopolysaccharide (LPS)-primed and 2'(3')-O-(benzoylbenzoyl)adenosine-5'-triphosphate (BzATP)-induced IL-1ß release demonstrate functional CNS target engagement. Importantly, Lu AF27139 was without effect in standard in vitro and in vivo toxicity studies. Based on these properties, we believe Lu AF27139 will be a valuable tool for probing the role of the P2X7 receptor in rodent models of CNS diseases.

Effects of CYP46A1 Inhibition on Long-Term-Depression in Hippocampal Slices ex vivo and 24S-Hydroxycholesterol Levels in Mice in vivo.

The manipulation of cholesterol and its metabolites has been hypothesized to be therapeutically beneficial for mood disorders, neurodegenerative disorders, and epilepsies. A major regulator of cholesterol clearance and turnover in the central nervous system is CYP46A1, a brain enriched enzyme responsible for metabolism of cholesterol into 24S-hydroxycholesterol. Inhibition of this enzyme may negatively modulate NMDARs as 24S-hydroxycholesterol was shown to enhance NMDAR function. In addition, alterations of local cholesterol or other changes mediated by CYP46A1 activity could have important influences on central nervous system function. Here we demonstrate that humans and mice display brain region specific and similar CYP46A1 and 24S-hydroxycholesterol distribution. Treatment with distinct classes of CYP46A1 inhibitors led to central 24S-hydroxycholesterol reduction in vivo and ablation of long term depression in hippocampal slices. Our results suggest that rodents show similarity to humans for studying the impact of CYP46A1 inhibitors and that rapid, local modulation of oxysterols can be achieved through CYP46A1 inhibition.

Optimizing Pyrazolopyrimidine Inhibitors of Calcium Dependent Protein Kinase 1 for Treatment of Acute and Chronic Toxoplasmosis.

Calcium dependent protein kinase 1 (CDPK1) is an essential Ser/Thr kinase that controls invasion and egress by the protozoan parasite Toxoplasma gondii. The Gly gatekeeper of CDPK1 makes it exquisitely sensitive to inhibition by small molecule 1H-pyrazolo[3,4-d]pyrimidine-4-amine (PP) compounds that are bulky ATP mimetics. Here we rationally designed, synthesized, and tested a series of novel PP analogs that were evaluated for inhibition of CDPK1 enzyme activity in vitro and parasite growth in cell culture. Optimal substitution on the PP scaffold included 2-pyridyl ethers directed into the hydrophobic pocket and small carbocyclic rings accessing the ribose-binding pocket. Further optimization of the series led to identification of the lead compound 3a that displayed excellent potency, selectivity, safety profile, and efficacy in vivo. The results of these studies provide a foundation for further work to optimize CDPK1 inhibitors for the treatment of acute and chronic toxoplasmosis.

Allosteric Modalities for Membrane-Bound Receptors: Insights from Drug Hunting for Brain Diseases.

Medicinal chemists are accountable for embedding the appropriate drug target profile into the molecular architecture of a clinical candidate. An accurate characterization of the functional effects following binding of a drug to its biological target is a fundamental step in the discovery of new medicines, informing the translation of preclinical efficacy and safety observations into human trials. Membrane-bound proteins, particularly ion channels and G protein-coupled receptors (GPCRs), are biological targets prone to allosteric modulation. Investigations using allosteric drug candidates and chemical tools suggest that their functional effects may be tailored with a high degree of translational alignment, making them molecular tools to correct pathophysiological functional tone and enable personalized medicine when a causative target-to-disease link is known. We present select examples of functional molecular fine-tuning of allosterism and discuss consequences relevant to drug design.

Discovery of Selective Toxoplasma gondii Dihydrofolate Reductase Inhibitors for the Treatment of Toxoplasmosis.

A safer treatment for toxoplasmosis would be achieved by improving the selectivity and potency of dihydrofolate reductase (DHFR) inhibitors, such as pyrimethamine (1), for Toxoplasma gondii DHFR ( TgDHFR) relative to human DHFR ( hDHFR). We previously reported on the identification of meta-biphenyl analog 2, designed by in silico modeling of key differences in the binding pocket between TgDHFR and hDHFR. Compound 2 improves TgDHFR selectivity 6.6-fold and potency 16-fold relative to 1. Here, we report on the optimization and structure-activity relationships of this arylpiperazine series leading to the discovery of 5-(4-(3-(2-methoxypyrimidin-5-yl)phenyl)piperazin-1-yl)pyrimidine-2,4-diamine 3. Compound 3 has a TgDHFR IC50 of 1.57 ± 0.11 nM and a hDHFR to TgDHFR selectivity ratio of 196, making it 89-fold more potent and 16-fold more selective than 1. Compound 3 was highly effective in control of acute infection by highly virulent strains of T. gondii in the murine model, and it possesses the best combination of selectivity, potency, and prerequisite drug-like properties to advance into IND-enabling, preclinical development.

Fused thiazolyl alkynes as potent mGlu5 receptor positive allosteric modulators.

A new series of potent fused thiazole mGlu5 receptor positive allosteric modulators (PAMs) (10, 11 and 27-31) are disclosed and details of the SAR and optimization are described. Optimization of alkynyl thiazole 9 (Lu AF11205) led to the identification of potent fused thiazole analogs 10b, 27a, 28j and 31d. In general, substituted cycloalkyl, aryl and heteroaryl carboxamides, and carbamate analogs are mGlu5PAMs, whereas smaller alkyl carboxamide, sulfonamide and sulfamide analogs tend to be mGlu5 negative allosteric modulators (NAMs).

Antidepressant-like effects of PDE4 inhibitors mediated by the high-affinity rolipram binding state (HARBS) of the phosphodiesterase-4 enzyme (PDE4) in rats.

RATIONALE: Phosphodiesterase-4 (PDE4) has two conformation states based on rolipram binding, the high-affinity rolipram binding state (HARBS) and the low-affinity rolipram binding state (LARBS); their functions remain to be fully explained. OBJECTIVE: Experiments were carried out to determine the roles of the HARBS and LARBS in the mediation of antidepressant-like effects on behavior. MATERIALS AND METHODS: Two animal models sensitive to antidepressant drugs, the forced-swim test (FST), and the differential-reinforcement-of-low-rate (DRL) 72-s operant schedule, were used to examine the antidepressant-like effects of rolipram, CDP840, and piclamilast, PDE4 inhibitors that interact differentially with the HARBS and LARBS, and MEM1018 and MEM1091, two novel PDE4 inhibitors. Drug discrimination vs rolipram and rolipram competition binding assays also were carried out. RESULTS: In the FST, rolipram and piclamilast, both at 0.1 mg/kg, produced an antidepressant-like effect, i.e., reduced immobility and increased swimming, whereas, 1 mg/kg of CDP840 or 0.5 mg/kg of MEM1018 or MEM1091 was required to produce a similar effect. Consistent with this, only rolipram and piclamilast produced antidepressant-like effects in rats under the DRL schedule of reinforcement, as evidenced by decreased response rates and increased reinforcement rates. In addition, in rats trained to discriminate rolipram from its vehicle, only rolipram and piclamilast substituted. Finally, [(3)H]rolipram and [(3)H]piclamilast binding analysis revealed that CDP840 and the two novel PDE4 inhibitors MEM1018 and MEM1091 exhibited a lower affinity for the HARBS than did rolipram. CONCLUSION: These results suggest that the HARBS of PDE4 is the primary conformation important for antidepressant-like effects on behavior.

Phosphodiesterase inhibitors for cognitive enhancement.

An effective treatment for age-related cognitive deficits remains an unmet medical need. Currently available drugs for the symptomatic treatment of Alzheimer's disease or other dementias have limited efficacy. This may be due to their action at only one of the many neurotransmitter systems involved in the complex mechanisms that underlie cognition. An alternative approach would be to target second messenger systems that are utilized by multiple neurotransmitters. Cyclic adenosine monophosphate (cAMP) is a second messenger that plays a key role in biochemical processes that regulate the cognitive process of memory consolidation. Prolongation of cAMP signals can be accomplished by inhibiting phosphodiesterases (PDEs). Eleven PDE families, comprised of more than 50 distinct members, are currently known. This review summarizes the evidence demonstrating that rolipram, a selective inhibitor of cAMP-selective PDE4 enzymes, has positive effects on learning and memory in animal models. These data provide support for the general approach of second messenger modulation as a potential therapy for cognitive dysfunction, and specifically suggest that PDE4 inhibitors may have utility for improving the symptoms of cognitive decline associated with neurodegenerative and psychiatric diseases.

Effects of the novel PDE4 inhibitors MEM1018 and MEM1091 on memory in the radial-arm maze and inhibitory avoidance tests in rats.

RATIONALE: Inhibition of cyclic AMP (cAMP)-specific phosphodiesterase (PDE4) enhances memory in rodents. MEM1018 and MEM1091 are newly developed PDE4 inhibitors that had not been evaluated as yet for their effects on working and reference memory. OBJECTIVE: Experiments were carried out to determine whether these two drugs alter memory and if these effects are associated with changes in intracellular cAMP in the brain. METHODS: The effects of MEM1018 and MEM1091 on memory deficits induced by the N-methyl-D-: aspartate (NMDA) receptor antagonist MK-801 were determined in the eight-arm radial maze and step-through inhibitory avoidance tasks in rats. Their effects on cAMP concentrations in primary cultures of rat cerebral cortical neurons and their potency for inhibiting recombinant PDE4 subtypes were examined. RESULTS: In the radial-arm maze, MEM1018 and MEM1091 (0.1-2.5 mg/kg, IP) enhanced working and reference memory impaired by MK-801 (0.1 mg/kg). In addition, both drugs antagonized the amnesic effect of MK-801 on passive avoidance behavior. Overall, the behavioral effects of MEM1018 and MEM1091 were similar to the prototypic PDE4 inhibitor rolipram (0.1 mg/kg). Consistent with this, and similar to the effects of rolipram, both MEM1018 (10-30 microM) and MEM1091 (10 microM) enhanced the ability of NMDA (30 microM) to increase cAMP concentrations in rat cerebral cortical neurons, in vitro. MEM1018 and MEM1091 showed greater relative selectivity for PDE4D than rolipram, although the general profiles of the three compounds were similar. CONCLUSIONS: The novel PDE4 inhibitors MEM1018 and MEM1091 enhance memory in a manner generally similar to rolipram. PDE4D may be the primary target for the PDE4 inhibitors in the mediation of memory.