SDI-118, a novel procognitive SV2A modulator: First-in-human randomized controlled trial including PET/fMRI assessment of target engagement.

Background: Current treatments for progressive neurodegenerative disorders characterized by cognitive impairment either have limited efficacy or are lacking altogether. SDI-118 is a small molecule which modulates the activity of synaptic vesicle glycoprotein 2A (SV2A) in the brain and shows cognitive enhancing effects in a range of animal models of cognitive deficit. Methods: This first-in-human study evaluated safety, tolerability, and pharmacokinetics/pharmacodynamics of SDI-118 in single ascending oral doses up to 80 mg administered to 32 healthy male subjects. Brain target occupancy was measured in eight subjects using positron emission tomography with PET-ligand [11C]-UCB-J. Food effect was assessed in seven subjects. Mood state was regularly evaluated using standardized questionnaires, and resting state fMRI data were analyzed as exploratory objectives. Key Results: At all doses tested, SDI-118 was well tolerated and appeared safe. Adverse events were mainly dizziness, hypersomnia, and somnolence. All were mild in intensity and increased in frequency with increasing administered dose. No dose-limiting adverse reactions were observed at any dose. SDI-118 displayed a linear pharmacokinetic profile with no significant food effect. Brain penetration and target engagement were demonstrated by a dose-proportional SV2A occupancy. Conclusion: Single oral doses of SDI-118 up to 80 mg were very well tolerated in healthy male subjects. Dose-proportional SV2A occupancy in the brain was demonstrated with brain imaging. Adverse effects in humans mainly occurred in higher dose ranges, with high occupancy levels, and were all mild and self-limiting. These data support further clinical exploration of the compound in patients with cognitive disorders. Clinical Trial Registration: https://clinicaltrials.gov/, identifier NCT05486195.

Sembragiline: A Novel, Selective Monoamine Oxidase Type B Inhibitor for the Treatment of Alzheimer's Disease.

Monoamine oxidase B (MAO-B) has been implicated in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Increased MAO-B expression in astroglia has been observed adjacent to amyloid plaques in AD patient brains. This phenomenon is hypothesized to lead to increased production of hydrogen peroxide and reactive oxygen species (ROS), thereby contributing to AD pathology. Therefore, reduction of ROS-induced oxidative stress via inhibition of MAO-B activity may delay the progression of the disease. In the present study we report the pharmacological properties of sembragiline, a novel selective MAO-B inhibitor specifically developed for the treatment of AD, and on its effect on ROS-mediated neuronal injury and astrogliosis in MAO-B transgenic animals. Sembragiline showed potent and long-lasting MAO-B-selective inhibition and did not inhibit MAO-A at doses where full inhibition of MAO-B was observed. Such selectivity should translate into a favorable clinical safety profile. Indeed, sembragiline neither induced the serotonin syndrome when administered together with the serotonin precursor l-5-hydroxytryptophan in combination with antidepressants such as fluoxetine, nor potentiated the pressor effect of tyramine. Additionally, in experiments using a transgenic animal model conditionally overexpressing MAO-B in astroglia, sembragiline protected against neuronal loss and reduced both ROS formation and reactive astrogliosis. Taken together, these findings warrant further investigation of the potential therapeutic benefit of MAO-B inhibitors in patients with AD and other neurologic disorders.

The structure of mammalian serine racemase: evidence for conformational changes upon inhibitor binding.

Serine racemase is responsible for the synthesis of D-serine, an endogenous co-agonist for N-methyl-D-aspartate receptor-type glutamate receptors (NMDARs). This pyridoxal 5'-phosphate-dependent enzyme is involved both in the reversible conversion of L- to D-serine and serine catabolism by alpha,beta-elimination of water, thereby regulating D-serine levels. Because D-serine affects NMDAR signaling throughout the brain, serine racemase is a promising target for the treatment of disorders related to NMDAR dysfunction. To provide a molecular basis for rational drug design the x-ray crystal structures of human and rat serine racemase were determined at 1.5- and 2.1-A resolution, respectively, and in the presence and absence of the orthosteric inhibitor malonate. The structures revealed a fold typical of beta-family pyridoxal 5'-phosphate enzymes, with both a large domain and a flexible small domain associated into a symmetric dimer, and indicated a ligand-induced rearrangement of the small domain that organizes the active site for specific turnover of the substrate.

Fragment-based discovery of BACE1 inhibitors using functional assays.

Novel nonpeptidic inhibitors of beta-secretase (BACE1) have been discovered by employing a fragment-based biochemical screening approach. A diverse library of 20000 low-molecular weight compounds were screened and yielded 26 novel hits that were confirmed by biochemical and surface plasmon resonance secondary assays. We describe here fragment inhibitors cocrystallized with BACE1 in a flap open and flap closed conformation as determined by X-ray crystallography.

The histamine H3 receptor as a therapeutic drug target for CNS disorders.

The histamine H3 receptor plays a regulatory role in the pre-synaptic release of histamine and other neurotransmitters, making it an attractive target for CNS indications including cognitive disorders, narcolepsy, ADHD and pain. As more and more H3 antagonists/H3 inverse agonists progress through the clinic, knowledge is gained to define the profile of the 'ideal' compound in terms of specificity, pharmacokinetic parameters and both duration and magnitude of receptor occupancy. Whether a single compound profile for the treatment of different disorders can be defined remains to be seen.

The mitochondrial effects of small organic ligands of BCL-2: sensitization of BCL-2-overexpressing cells to apoptosis by a pyrimidine-2,4,6-trione derivative.

We have investigated the mitochondrial effects of BH3I-2', Chelerythrine, and HA14-1, small organic molecules that share the ability to bind the BH3 domain of BCL-2. All compounds displayed a biphasic effect on mitochondrial respiration with uncoupling at low concentrations and respiratory inhibition at higher concentrations, the relative uncoupling potency being BH3I-2' (half-maximal uncoupling at about 80 nm) > Chelerythrine (half-maximal uncoupling at about 2 microm) > HA14-1 (half-maximal uncoupling at about 20 microm). At concentrations lower than required for uncoupling all compounds sensitized the permeability transition pore (PTP) to opening both in isolated mitochondria and intact cells. To assess whether the effects on BCL-2 binding, PTP induction and respiration could be due to different structural determinants we have tested a set of HA14-1 analogs from the Hoffmann-La Roche chemical library. We have identified 5-(6-chloro-2,4-dioxo-1,3,4,10-tetrahydro-2H-9-oxa-1,3-diaza-anthracen-10-yl)-pyrimidine-2,4,6-trione (EM20-25) as a molecule devoid of effects on respiration that is able to induce PTP opening, to disrupt the BCL-2/BAX interactions in situ and to activate caspase-9 in BCL-2-overexpressing cells. EM20-25 neutralized the antiapoptotic activity of overexpressed BCL-2 toward staurosporine and sensitized BCL-2-expressing cells from leukemic patients to the killing effects of staurosporine, chlorambucil, and fludarabine. These results provide a proof of principle that the potentially toxic effects of BCL-2 ligands on mitochondrial respiration are not essential for their antiapoptotic activity and represent an important step forward in the development of tumor-selective drugs acting on BCL-2.

Crystal engineering yields crystals of cyclophilin D diffracting to 1.7 A resolution.

In the pharmaceutical industry, knowledge of the three-dimensional structure of a specific target facilitates the drug-discovery process. Despite possessing favoured analytical properties such as high purity and monodispersion in light scattering, some proteins are not capable of forming crystals suitable for X-ray analysis. Cyclophilin D, an isoform of cyclophilin that is expressed in the mitochondria, was selected as a drug target for the treatment of cardiac disorders. As the wild-type enzyme defied all attempts at crystallization, protein engineering on the enzyme surface was performed. The K133I mutant gave crystals that diffracted to 1.7 A resolution using in-house X-ray facilities and were suitable for soaking experiments. The crystals were very robust and diffraction was maintained after soaking in 25% DMSO solution: excellent conditions for the rapid analysis of complex structures including crystallographic fragment screening.

The voltage-dependent anion channel is the target for a new class of inhibitors of the mitochondrial permeability transition pore.

The relevance of the mitochondrial permeability transition pore (PTP) in Ca2+ homeostasis and cell death has gained wide attention. Yet, despite detailed functional characterization, the structure of this channel remains elusive. Here we report on a new class of inhibitors of the PTP and on the identification of their molecular target. The most potent among the compounds prepared, Ro 68-3400, inhibited PTP with a potency comparable to that of cyclosporin A. Since Ro 68-3400 has a reactive moiety capable of covalent modification of proteins, [3H]Ro 68-3400 was used as an affinity label for the identification of its protein target. In intact mitochondria isolated from rodent brain and liver and in SH-SY5Y human neuroblastoma cells, [3H]Ro 68-3400 predominantly labeled a protein of approximately 32 kDa. This protein was identified as the isoform 1 of the voltage-dependent anion channel (VDAC). Both functional and affinity labeling experiments indicated that VDAC might correspond to the site for the PTP inhibitor ubiquinone0, whereas other known PTP modulators acted at distinct sites. While Ro 68-3400 represents a new useful tool for the study of the structure and function of VDAC and the PTP, the results obtained provide direct evidence that VDAC1 is a component of this mitochondrial pore.

Novel hexahydrospiro[piperidine-4,1'-pyrrolo[3,4-c]pyrroles]: highly selective small-molecule nociceptin/orphanin FQ receptor agonists.

Novel hexahydrospiro[piperidine-4,1'-pyrrolo[3,4-c]pyrroles that act as potent and selective orphanin FQ/nociceptin (N/OFQ) receptor (NOP) agonists were identified. The best compound, (+)-5a, potently inhibited 3H-N/OFQ binding to the NOP receptor (K(i) = 0.49 nM) but was >1000-fold less potent in binding to MOP, KOP, and DOP opiate receptors. Further, (+)-5a potently stimulated GTP gamma S binding to NOP membranes (EC50 = 65 nM) and inhibited forskolin-mediated cAMP accumulation in NOP-expressing cells (EC50 = 9.1 nM) with a potency comparable to that of the natural peptide agonist N/OFQ. These results indicate that (+)-5a is a highly selective and potent small-molecule full agonist of the NOP receptor.