Activation mechanism and novel binding sites of the BKCa channel activator CTIBD.

The large-conductance calcium-activated potassium (BKCa) channel, which is crucial for urinary bladder smooth muscle relaxation, is a potential target for overactive bladder treatment. Our prior work unveiled CTIBD as a promising BKCa channel activator, altering V 1/2 and G max This study investigates CTIBD's activation mechanism, revealing its independence from the Ca2+ and membrane voltage sensing of the BKCa channel. Cryo-electron microscopy disclosed that two CTIBD molecules bind to hydrophobic regions on the extracellular side of the lipid bilayer. Key residues (W22, W203, and F266) are important for CTIBD binding, and their replacement with alanine reduces CTIBD-mediated channel activation. The triple-mutant (W22A/W203A/F266A) channel showed the smallest V 1/2 shift with a minimal impact on activation and deactivation kinetics by CTIBD. At the single-channel level, CTIBD treatment was much less effective at increasing P o in the triple mutant, mainly because of a drastically increased dissociation rate compared with the WT. These findings highlight CTIBD's mechanism, offering crucial insights for developing small-molecule treatments for BKCa-related pathophysiological conditions.

PDK4-mediated metabolic reprogramming is a potential therapeutic target for neovascular age-related macular degeneration.

Age-related macular degeneration (AMD) causes severe blindness in the elderly due to choroidal neovascularization (CNV), which results from the dysfunction of the retinal pigment epithelium (RPE). While normal RPE depends exclusively on mitochondrial oxidative phosphorylation for energy production, the inflammatory conditions associated with metabolic reprogramming of the RPE play a pivotal role in CNV. Although mitochondrial pyruvate dehydrogenase kinase (PDK) is a central node of energy metabolism, its role in the development of CNV in neovascular AMD has not been investigated. In the present study, we used a laser-induced CNV mouse model to evaluate the effects of Pdk4 gene ablation and treatment with pan-PDK or specific PDK4 inhibitors on fluorescein angiography and CNV lesion area. Among PDK isoforms, only PDK4 was upregulated in the RPE of laser-induced CNV mice, and Pdk4 gene ablation attenuated CNV. Next, we evaluated mitochondrial changes mediated by PDK1-4 inhibition using siRNA or PDK inhibitors in inflammatory cytokine mixture (ICM)-treated primary human RPE (hRPE) cells. PDK4 silencing only in ICM-treated hRPE cells restored mitochondrial respiration and reduced inflammatory cytokine secretion. Likewise, GM10395, a specific PDK4 inhibitor, restored oxidative phosphorylation and decreased ICM-induced upregulation of inflammatory cytokine secretion. In a laser-induced CNV mouse model, GM10395 significantly alleviated CNV. Taken together, we demonstrate that specific PDK4 inhibition could be a therapeutic strategy for neovascular AMD by preventing mitochondrial metabolic reprogramming in the RPE under inflammatory conditions.

Discovery of a peripheral 5HT2A antagonist as a clinical candidate for metabolic dysfunction-associated steatohepatitis.

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is currently the leading cause of chronic liver disease worldwide. Metabolic Dysfunction-Associated Steatohepatitis (MASH), an advanced form of MASLD, can progress to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Based on recent findings by our team that liver 5HT2A knockout male mice suppressed steatosis and reduced fibrosis-related gene expression, we developed a peripheral 5HT2A antagonist, compound 11c for MASH. It shows good in vitro activity, stability, and in vivo pharmacokinetics (PK) in rats and dogs. Compound 11c also shows good in vivo efficacy in a diet-induced obesity (DIO) male mice model and in a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) male mice model, effectively improving histologic features of MASH and fibrosis. According to the tissue distribution study using [14C]-labeled 11c, the compound was determined to be a peripheral 5HT2A antagonist. Collectively, first-in-class compound 11c shows promise as a therapeutic agent for the treatment of MASLD and MASH.

Inhibition of pyruvate dehydrogenase kinase 4 ameliorates kidney ischemia-reperfusion injury by reducing succinate accumulation during ischemia and preserving mitochondrial function during reperfusion.

Ischemia-reperfusion (IR) injury, a leading cause of acute kidney injury (AKI), is still without effective therapies. Succinate accumulation during ischemia followed by its oxidation during reperfusion leads to excessive reactive oxygen species (ROS) and severe kidney damage. Consequently, the targeting of succinate accumulation may represent a rational approach to the prevention of IR-induced kidney injury. Since ROS are generated primarily in mitochondria, which are abundant in the proximal tubule of the kidney, we explored the role of pyruvate dehydrogenase kinase 4 (PDK4), a mitochondrial enzyme, in IR-induced kidney injury using proximal tubule cell-specific Pdk4 knockout (Pdk4ptKO) mice. Knockout or pharmacological inhibition of PDK4 ameliorated IR-induced kidney damage. Succinate accumulation during ischemia, which is responsible for mitochondrial ROS production during reperfusion, was reduced by PDK4 inhibition. PDK4 deficiency established conditions prior to ischemia resulting in less succinate accumulation, possibly because of a reduction in electron flow reversal in complex II, which provides electrons for the reduction of fumarate to succinate by succinate dehydrogenase during ischemia. The administration of dimethyl succinate, a cell-permeable form of succinate, attenuated the beneficial effects of PDK4 deficiency, suggesting that the kidney-protective effect is succinate-dependent. Finally, genetic or pharmacological inhibition of PDK4 prevented IR-induced mitochondrial damage in mice and normalized mitochondrial function in an in vitro model of IR injury. Thus, inhibition of PDK4 represents a novel means of preventing IR-induced kidney injury, and involves the inhibition of ROS-induced kidney toxicity through reduction in succinate accumulation and mitochondrial dysfunction.

Inhibition of Pyruvate Dehydrogenase Kinase 4 in CD4+ T Cells Ameliorates Intestinal Inflammation.

BACKGROUND & AIMS: Despite recent evidence supporting the metabolic plasticity of CD4+ T cells, it is uncertain whether the metabolic checkpoint pyruvate dehydrogenase kinase (PDK) in T cells plays a role in the pathogenesis of colitis. METHODS: To investigate the role of PDK4 in colitis, we used dextran sulfate sodium (DSS)-induced colitis and T-cell transfer colitis models based on mice with constitutive knockout (KO) or CD4+ T-cell-specific KO of PDK4 (Pdk4fl/flCD4Cre). The effect of PDK4 deletion on T-cell activation was also studied in vitro. Furthermore, we examined the effects of a pharmacologic inhibitor of PDK4 on colitis. RESULTS: Expression of PDK4 increased during colitis development in a DSS-induced colitis model. Phosphorylated PDHE1α, a substrate of PDK4, accumulated in CD4+ T cells in the lamina propria of patients with inflammatory bowel disease. Both constitutive KO and CD4+ T-cell-specific deletion of PDK4 delayed DSS-induced colitis. Adoptive transfer of PDK4-deficient CD4+ T cells attenuated murine colitis, and PDK4 deficiency resulted in decreased activation of CD4+ T cells and attenuated aerobic glycolysis. Mechanistically, there were fewer endoplasmic reticulum-mitochondria contact sites, which are responsible for interorganelle calcium transfer, in PDK4-deficient CD4+ T cells. Consistent with this, GM-10395, a novel inhibitor of PDK4, suppressed T-cell activation by reducing endoplasmic reticulum-mitochondria calcium transfer, thereby ameliorating murine colitis. CONCLUSIONS: PDK4 deletion from CD4+ T cells mitigates colitis by metabolic and calcium signaling modulation, suggesting PDK4 as a potential therapeutic target for IBD.

Synthesis and biological evaluation of tyrosine derivatives as peripheral 5HT2A receptor antagonists for nonalcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD), attributed to excessive fat accumulation in the liver, is reportedly prevalent worldwide. NAFLD is one of the leading causes of chronic liver disease, including non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatic cellular carcinoma (HCC). The peripheral roles of serotonin (5-hydroxytryptamine, 5HT) were found to regulate hepatic lipid metabolism. Among serotonin receptor subtypes, 5HT2A receptor is known to regulate hepatic lipid metabolism. Hepatic lipid accumulation and hepatic triglyceride (TG) were reduced in liver-specific 5HT2A receptor knockout (5HT2A receptor LKO) mice upon high-fat diet (HFD) feeding. In the present study, we explored a series of new peripherally acting 5HT2A receptor antagonists. Compound 14a displayed good in vitro activity, with an IC50 value of 0.17 nM. Compound 14a exhibited good microsomal stability, no significant CYP and hERG inhibition, and 5HT receptor subtype selectivity. The brain-to-plasma ratio of 14a was below the lower limit of quantification, indicating limited blood-brain barrier (BBB) penetration. HFD-fed 14a treated mice showed decreased liver steatosis and lobular inflammation. These results demonstrate the potential of newly synthesized peripheral 5HT2A receptor antagonists for treating NAFLD.

Identification of New Non-BBB Permeable Tryptophan Hydroxylase Inhibitors for Treating Obesity and Fatty Liver Disease.

Serotonin (5-hydroxytryptophan) is a hormone that regulates emotions in the central nervous system. However, serotonin in the peripheral system is associated with obesity and fatty liver disease. Because serotonin cannot cross the blood-brain barrier (BBB), we focused on identifying new tryptophan hydroxylase type I (TPH1) inhibitors that act only in peripheral tissues for treating obesity and fatty liver disease without affecting the central nervous system. Structural optimization inspired by para-chlorophenylalanine (pCPA) resulted in the identification of a series of oxyphenylalanine and heterocyclic phenylalanine derivatives as TPH1 inhibitors. Among these compounds, compound 18i with an IC50 value of 37 nM was the most active in vitro. Additionally, compound 18i showed good liver microsomal stability and did not significantly inhibit CYP and Herg. Furthermore, this TPH1 inhibitor was able to actively interact with the peripheral system without penetrating the BBB. Compound 18i and its prodrug reduced body weight gain in mammals and decreased in vivo fat accumulation.

Peripheral Selective Oxadiazolylphenyl Alanine Derivatives as Tryptophan Hydroxylase 1 Inhibitors for Obesity and Fatty Liver Disease.

Tryptophan hydroxylase 1 (TPH1) has been recently suggested as a promising therapeutic target for treating obesity and fatty liver disease. A new series of 1,2,4-oxadiazolylphenyl alanine derivatives were identified as TPH1 inhibitors. Among them, compound 23a was the most active in vitro, with an IC50 (half-maximal inhibitory concentration) value of 42 nM, showed good liver microsomal stability, and showed no significant inhibition of CYP and hERG. Compound 23a inhibited TPH1 in the peripheral tissue with limited BBB penetration. In high-fat diet-fed mice, 23a reduced body weight gain, body fat, and hepatic lipid accumulation. Also, 23a improved glucose intolerance and energy expenditure. Taken together, compound 23a shows promise as a therapeutic agent for the treatment of obesity and fatty liver diseases.

Identification and Characterization of a Novel Large-Conductance Calcium-Activated Potassium Channel Activator, CTIBD, and Its Relaxation Effect on Urinary Bladder Smooth Muscle.

The large-conductance calcium-activated potassium channel (BKCa channel) is expressed on various tissues and is involved in smooth muscle relaxation. The channel is highly expressed on urinary bladder smooth muscle cells and regulates the repolarization phase of the spontaneous action potentials that control muscle contraction. To discover novel chemical activators of the BKCa channel, we screened a chemical library containing 8364 chemical compounds using a cell-based fluorescence assay. A chemical compound containing an isoxazolyl benzene skeleton (compound 1) was identified as a potent activator of the BKCa channel and was structurally optimized through a structure-activity relationship study to obtain 4-(4-(4-chlorophenyl)-3-(trifluoromethyl)isoxazol-5-yl)benzene-1,3-diol (CTIBD). When CTIBD was applied to the treated extracellular side of the channel, the conductance-voltage relationship of the channel shifted toward a negative value, and the maximum conductance increased in a concentration-dependent manner. CTIBD altered the gating kinetics of the channel by dramatically slowing channel closing without effecting channel opening. The effects of CTIBD on bladder muscle relaxation and micturition function were tested in rat tissue and in vivo. CTIBD concentration-dependently reduced acetylcholine-induced contraction of urinary bladder smooth muscle strips. In an acetic acid-induced overactive bladder (OAB) model, intraperitoneal injection of 20 mg/kg CTIBD effectively restored frequent voiding contraction and lowered voiding volume without affecting other bladder function parameters. Thus, our results indicate that CTIBD and its derivatives are novel chemical activators of the bladder BKCa channel and potential candidates for OAB therapeutics. SIGNIFICANCE STATEMENT: The novel BKCa channel activator CTIBD was identified and characterized in this study. CTIBD directly activates the BKCa channel and relaxes urinary bladder smooth muscle of rat, so CTIBD can be a potential candidate for overactive bladder therapeutics.

Structural basis for the inhibition of PDK2 by novel ATP- and lipoyl-binding site targeting compounds.

Pyruvate dehydrogenase kinase (PDK) controls the activity of pyruvate decarboxylase complex (PDC) by phosphorylating key serine residues on the E1 subunit, which leads to a decreased oxidative phosphorylation in mitochondria. Inhibition of PDK activity by natural/synthetic compounds has been shown to reverse the Warburg effect, a characteristic metabolism in cancer cells. PDK-PDC axis also has been associated with diabetes and heart disease. Therefore, regulation of PDK activity has been considered as a promising strategy to treat related diseases. Here we present the X-ray crystal structure of PDK2 complexed with a recently identified PDK4 inhibitor, compound 8c, which has been predicted to bind at the lipoyl-binding site and interrupt intermolecular interactions with the E2-E3bp subunits of PDC. The co-crystal structure confirmed the specific binding location of compound 8c and revealed the remote conformational change in the ATP-binding pocket. In addition, two novel 4,5-diarylisoxazole derivatives, GM10030 and GM67520, were synthesized and used for structural studies, which target the ATP-binding site of PDK2. These compounds bind to PDK2 with a sub-100nM affinity as determined by isothermal titration calorimetry experiments. Notably, the crystal structure of the PDK2-GM10030 complex displays unprecedented asymmetric conformation of human PDK2 dimer, especially in the ATP-lids and C-terminal tails.

Design, Synthesis, and Biological Evaluation of New Peripheral 5HT2A Antagonists for Nonalcoholic Fatty Liver Disease.

Nonalcoholic fatty liver disease (NAFLD) is increasingly prevalent worldwide, causing serious liver complications, including nonalcoholic steatohepatitis. Recent findings suggest that peripheral serotonin (5-hydroxytryptamine, 5HT) regulates energy homeostasis, including hepatic lipid metabolism. More specifically, liver-specific 5HT2A knockout mice exhibit alleviated hepatic lipid accumulation and hepatic steatosis. Here, structural modifications of pimavanserin (CNS drug), a 5HT2A antagonist approved for Parkinson's disease, led us to synthesize new peripherally acting 5HT2A antagonists. Among the synthesized compounds, compound 14a showed good in vitro activity, good liver microsomal stability, 5HT subtype selectivity, and no significant inhibition of CYP and hERG. The in vitro and in vivo blood-brain barrier permeability study proved that 14a acts peripherally. Compound 14a decreased the liver weight and hepatic lipid accumulation in high-fat-diet-induced obesity mice. Our study suggests new therapeutic possibilities for peripheral 5HT2A antagonists in NAFLD.

Optimization of cyclic sulfamide derivatives as 11ß-hydroxysteroid dehydrogenase 1 inhibitors for the potential treatment of ischemic brain injury.

The 11ß-hydroxysteroiddehydrogenase type 1(11ß-HSD1), acortisolregenerating enzyme that amplifies tissue glucocorticoidlevels, plays an important role in diabetes, obesity, and glaucoma and is recognized as a potential therapeutic target for various disease conditions. Moreover, a recent study demonstrated that selective 11ß-HSD1 inhibitor can attenuate ischemic brain injury. This prompted us to optimize cyclic sulfamide derivative for aiming to treat ischemic brain injury. Among the synthesized compounds, 6e has an excellent in vitro activivity with an IC50 value of 1 nM toward human and mouse 11ß-HSD1 and showed good 11ß-HSD1 inhibition in ex vivo study using brain tissue isolated from mice. Furthermore, in the transient middle cerebral artery occlusion model in mice, 6e treatment significantly attenuated infarct volume and neurological deficit following cerebral ischemia/reperfusion injury. Additionally, binding modes of 6e for human and mouse 11ß-HSD1 were suggested.

Dopamine neuron induction and the neuroprotective effects of thyroid hormone derivatives.

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive movement disturbances caused by the selective loss of dopamine (DA) neurons in the substantia nigra. Despite the identification of the causal mechanisms underlying the pathogenesis of PD, effective treatments remain elusive. In this study, we observed that a low level of fetal bovine serum (FBS) effectively induced DA neurons in rat neural precursor cells (NPCs) by enhancing nuclear receptor-related 1 protein (NURR1) expression. Among the various components of FBS, the thyroid hormones triiodothyronine (T3) and thyroxine (T4) were identified as key factors for the induction of DA neurons. Since an overdose of thyroid hormones can cause hyperthyroidism, we synthesized several thyroid hormone derivatives that can partially activate thyroid hormone receptors and induce the complete differentiation of NPCs into DA neurons. Two derivatives (#3 and #9) showed positive effects on the induction and maturation of DA neurons without showing significant affinity for the thyroid hormone receptor. They also effectively protected and restored DA neurons from neurotoxic insults. Taken together, these observations demonstrate that thyroid hormone derivatives can strongly induce DA neuron differentiation while avoiding excessive thyroid stimulation and might therefore be useful candidates for PD treatment.

Discovery of Novel Pyruvate Dehydrogenase Kinase 4 Inhibitors for Potential Oral Treatment of Metabolic Diseases.

Pyruvate dehydrogenase kinase 4 (PDK4) activation is associated with metabolic diseases including hyperglycemia, insulin resistance, allergies, and cancer. Structural modifications of hit anthraquinone led to the identification of a new series of allosteric PDK4 inhibitors. Among this series, compound 8c showed promising in vitro activity with an IC50 value of 84 nM. Good metabolic stability, pharmacokinetic profiles, and possible metabolites were suggested. Compound 8c improved glucose tolerance in diet-induced obese mice and ameliorated allergic reactions in a passive cutaneous anaphylaxis mouse model. Additionally, compound 8c exhibited anticancer activity by controlling cell proliferation, transformation, and apoptosis. From the molecular docking studies, compound 8c displayed optimal fitting in the lipoamide binding site (allosteric) with a full fitness, providing a new scaffold for drug development toward PDK4 inhibitors.

ENOblock inhibits the pathology of diet-induced obesity.

Obesity is a medical condition that impacts on all levels of society and causes numerous comorbidities, such as diabetes, cardiovascular disease, and cancer. We assessed the suitability of targeting enolase, a glycolysis pathway enzyme with multiple, secondary functions in cells, to treat obesity. Treating adipocytes with ENOblock, a novel modulator of these secondary 'moonlighting' functions of enolase, suppressed the adipogenic program and induced mitochondrial uncoupling. Obese animals treated with ENOblock showed a reduction in body weight and increased core body temperature. Metabolic and inflammatory parameters were improved in the liver, adipose tissue and hippocampus. The mechanism of ENOblock was identified as transcriptional repression of master regulators of lipid homeostasis (Srebp-1a and Srebp-1c), gluconeogenesis (Pck-1) and inflammation (Tnf-α and Il-6). ENOblock treatment also reduced body weight gain, lowered cumulative food intake and increased fecal lipid content in mice fed a high fat diet. Our results support the further drug development of ENOblock as a therapeutic for obesity and suggest enolase as a new target for this disorder.

Design, synthesis and biological evaluation of glutamic acid derivatives as anti-oxidant and anti-inflammatory agents.

A series of glutamic acid derivatives was synthesized and evaluated for their antioxidant activity and stability. We found several potent and stable glutamic acid derivatives. Among them, compound 12b exhibited good in vitro activity, chemical stability and cytotoxicity. A prototype compound 12b showed an anti-inflammatory effect in LPS-stimulated RAW 264.7 cell lines and in a zebrafish model.

Design, synthesis, and biological evaluation of aryl N-methoxyamide derivatives as GPR119 agonists.

A series of N-methoxyamide derivatives was identified and evaluated as GPR119 agonists. Several N-methoxyamides with thienopyrimidine and pyridine scaffolds showed potent GPR119 agonistic activities. Among them, compound 9c displayed good in vitro activity and potency. Moreover, compound 9c lowered glucose excursion in mice in an oral glucose tolerance test and increased GLP-1 secretion in intestinal cells.

Discovery and optimization of adamantane carboxylic acid derivatives as potent diacylglycerol acyltransferase 1 inhibitors for the potential treatment of obesity and diabetes.

We have developed a series of adamantane carboxylic acid derivatives exhibiting potent diacylglycerol acyltransferase 1 (DGAT1) inhibitory activities. Optimization of the series led to the discovery of E-adamantane carboxylic acid compound 43c, which showed excellent in vitro activity with an IC50 value of 5 nM against human and mouse DGAT1, also good druggability as well as microsomal stability and safety profiles such as hERG, CYP and cytotoxicity. Compound 43c significantly reduced plasma triglyceride levels in vivo (in rodents and zebrafish) and also showed bodyweight gain reduction and glucose area under curve (AUC) lowering efficacy in diet-induced obesity (DIO) mice.

Synthesis and biological evaluation of aminobenzimidazole derivatives with a phenylcyclohexyl acetic acid group as anti-obesity and anti-diabetic agents.

A series of benzimidazole derivatives with a phenylcyclohexyl acetic acid group as DGAT-1 inhibitors was developed. Among the benzimidazole series, compound 5k showed submicromolar in vitro activity toward human and mouse DGAT-1, good selectivity toward DGAT-2, human liver metabolic stability, and pharmacokinetic (PK) and safety profiles such as hERG, CYP and acute toxicity. Additionally, 5k showed good in vivo efficacy in 4weeks study with DIO mouse model.