Novel Kraft Softwood Lignin-Derived Carbon Quantum Dots: Synthesis, Characterization, and In Vitro Cytocompatibility.

Carbon quantum dots (CQDs) have been investigated for biomedical applications in medical imaging due to their fluorescent properties, overall long-term stability, and excellent cytocompatibility and biocompatibility. Lignin is an organic polymer in the tissues of woody plants. It is also considered a byproduct of the wood and pulp industries. Hence, it presents as a renewable source of carbon nanoparticles. In this study, we report the synthesis and material and biological characterization of two colloidal suspensions of CQDs in water derived from lignin-based carbon. One was the native form of CQDs derived from lignin carbon, and the second was doped with nitrogen to evaluate material differences. Material characterization was carried out using various commonly used techniques, including Fourier transform infrared spectroscopy (FTIR), emission and absorbance spectra, zeta potential, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Thin films of CQDs were formed on glass and silicon substrates to assess the in vitro cytocompatibility with human mesenchymal stem cells (hMSCs). Observations suggest that the two forms of CQDs promote cell attachment within 24 h and sustain it for at least 7 days. The overall structure and shape of cells suggest a lack of any adverse or toxic effects of CQDs. The data lay down the novel foundation to support the use of lignin-derived CQDs in tissue engineering applications.

High-Throughput Screening Strategy Identifies Allosteric, Covalent Human D-Amino Acid Oxidase Inhibitor.

Genome-wide association studies have linked polymorphisms in the gene G72 to schizophrenia risk in several human populations. Although controversial, biochemical experiments have suggested that the mechanistic link of G72 to schizophrenia is due to the G72 protein product, pLG72, exerting a regulatory effect on human D-amino acid oxidase (hDAAO) activity. In an effort to identify hDAAO inhibitors of novel mechanism of action, we designed a pLG72-directed hDAAO activity assay suitable for high-throughput screening (HTS). During assay development, we confirmed that pLG72 was an inhibitor of hDAAO. Thus, our assay employed an IC20 pLG72 concentration that was high enough to allow dynamic pLG72-hDAAO complexes to form but with sufficient remaining hDAAO activity to measure during an HTS. After conducting an approximately 150,000-compound HTS, we further characterized a class of compound hits that were less potent hDAAO inhibitors when pLG72 was present. Focusing primarily on compound 2: [2-(2,5-dimethylphenyl)-6-fluorobenzo[d]isothiazol-3(2H)-on], we demonstrated that these compounds inhibited hDAAO via an allosteric, covalent mechanism. Although there is significant interest in the therapeutic potential of compound 2: and its analogues, their sensitivity to reducing agents and their capacity to bind cysteines covalently would need to be addressed during therapeutic drug development.

Novel human D-amino acid oxidase inhibitors stabilize an active-site lid-open conformation.

The NMDAR (N-methyl-D-aspartate receptor) is a central regulator of synaptic plasticity and learning and memory. hDAAO (human D-amino acid oxidase) indirectly reduces NMDAR activity by degrading the NMDAR co-agonist D-serine. Since NMDAR hypofunction is thought to be a foundational defect in schizophrenia, hDAAO inhibitors have potential as treatments for schizophrenia and other nervous system disorders. Here, we sought to identify novel chemicals that inhibit hDAAO activity. We used computational tools to design a focused, purchasable library of compounds. After screening this library for hDAAO inhibition, we identified the structurally novel compound, 'compound 2' [3-(7-hydroxy-2-oxo-4-phenyl-2H-chromen-6-yl)propanoic acid], which displayed low nM hDAAO inhibitory potency (Ki=7 nM). Although the library was expected to enrich for compounds that were competitive for both D-serine and FAD, compound 2 actually was FAD uncompetitive, much like canonical hDAAO inhibitors such as benzoic acid. Compound 2 and an analog were independently co-crystalized with hDAAO. These compounds stabilized a novel conformation of hDAAO in which the active-site lid was in an open position. These results confirm previous hypotheses regarding active-site lid flexibility of mammalian D-amino acid oxidases and could assist in the design of the next generation of hDAAO inhibitors.

Structural, kinetic, and pharmacodynamic mechanisms of D-amino acid oxidase inhibition by small molecules.

We characterized the mechanism and pharmacodynamics of five structurally distinct inhibitors of d-amino acid oxidase. All inhibitors bound the oxidized form of human enzyme with affinity slightly higher than that of benzoate (Kd ≈ 2-4 µM). Stopped-flow experiments showed that pyrrole-based inhibitors possessed high affinity (Kd ≈ 100-200 nM) and slow release kinetics (k < 0.01 s(-1)) in the presence of substrate, while inhibitors with pendent aromatic groups altered conformations of the active site lid, as evidenced by X-ray crystallography, and showed slower kinetics of association. Rigid bioisosteres of benzoic acid induced a closed-lid conformation, had slower release in the presence of substrate, and were more potent than benzoate. Steady-state d-serine concentrations were described in a PK/PD model, and competition for d-serine sites on NMDA receptors was demonstrated in vivo. DAAO inhibition increased the spatiotemporal influence of glial-derived d-serine, suggesting localized effects on neuronal circuits where DAAO can exert a neuromodulatory role.

Design, synthesis, and structure-activity relationships of novel bicyclic azole-amines as negative allosteric modulators of metabotropic glutamate receptor 5.

A novel series of diaryl bicyclic azole-amines that are potent selective negative modulators of metabotropic glutamate receptor 5 (mGluR5) were identified through rational design. An initial hit compound 5a of modest potency (IC(50) = 1.2 µM) was synthesized. Evaluation of structure-activity relationships (SAR) on the left-hand side of the molecule revealed a preference for a 2-substituted pyridine group linked directly to the central heterocycle. Variation of the central azolo-amine portion of the molecule revealed a preference for the [4,5-c]-oxazoloazepine scaffold, while right-hand side variants showed a preference for ortho- and meta-substituted benzene rings linked directly to the tertiary amine of the saturated heterocycle. These iterations led to the synthesis of 29b, a potent (IC(50) = 16 nM) and selective negative modulator that showed good brain penetrance, high receptor occupancy, and a duration of action greater than 1 h in rat when administered intraperitoneally. Formal PK studies in rat and Rhesus monkey revealed a short half-life that was attributable to high first-pass clearance.