Ming-Shiu Hung

Important Hydrogen Bond Networks in Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitor Design Revealed by Crystal Structures of Imidazoleisoindole Derivatives with IDO1

Indoleamine 2,3-dioxygenase 1 (IDO1), promoting immune escape of tumors, is a therapeutic target for the cancer immunotherapy. A number of IDO1 inhibitors have been identified, but only limited structural biology studies of IDO1 inhibitors are available to provide insights on the binding mechanism of IDO1. In this study, we present the structure of IDO1 in complex with 24, a NLG919 analogue with potent activity. The complex structure revealed the imidazole nitrogen atom of 24 to coordinate with the heme iron, and the imidazoleisoindole core situated in pocket A with the 1-cyclohexylethanol moiety extended to pocket B to interact with the surrounding residues. Most interestingly, 24 formed an extensive hydrogen bond network with IDO1, which is a distinct feature of IDO1/24 complex structure and is not observed in the other IDO1 complex structures. Further structure-activity relationship, UV spectra, and structural biology studies of several analogues of 24 demonstrated that extensive hydrophobic interactions and the unique hydrogen bonding network contribute to the great potency of imidazoleisoindole derivatives. These results are expected to facilitate the structure-based drug design of new IDO inhibitors.

Discovery of Novel N-β-d-Xylosylindole Derivatives as Sodium-Dependent Glucose Cotransporter 2 (SGLT2) Inhibitors for the Management of Hyperglycemia in Diabetes

A novel series of N-linked β-D-xylosides were synthesized and evaluated for inhibitory activity against sodium-dependent glucose cotransporter 2 (SGLT2) in a cell-based assay. Of these, the 4-chloro-3-(4-cyclopropylbenzyl)-1-(β-D-xylopyranosyl)-1H-indole 19m was found to be the most potent inhibitor, with an EC(50) value similar to that of the natural SGLT2 inhibitor phlorizin. Further studies in Sprague-Dawley (SD) rats indicated that 19m significantly increased urine glucose excretion in a dose-dependent manner with oral administration. The antihyperglycemic effect of 19m was also observed in streptozotocin (STZ) induced diabetic SD rats. These results described here are a good starting point for further investigations into N-glycoside SGLT2 inhibitors.

Discovery of 2-[5-(4-chloro-phenyl)-1-(2,4-dichloro-phenyl)-4-ethyl-1H-pyrazol-3-yl]-1,5,5-trimethyl-1,5-dihydro-imidazol-4-thione (BPR-890) via an active metabolite. A novel, potent and selective cannabinoid-1 receptor inverse agonist with high antiobesity efficacy in DIO mice.

By using the active metabolite 5 as an initial template, further structural modifications led to the identification of the titled compound 24 (BPR-890) as a highly potent CB1 inverse agonist possessing an excellent CB2/1 selectivity and remarkable in vivo efficacy in diet-induced obese mice with a minimum effective dose as low as 0.03 mg/kg (po qd) at the end of the 30-day chronic study. Current SAR studies along with those of many existing rimonabant-mimicking molecules imply that around the pyrazole C3-position, a rigid and deep binding pocket should exist for CB1 receptor. In addition, relative to the conventional carboxamide carbonyl, serving as a key hydrogen-bond acceptor during ligand-CB1 receptor interaction, the corresponding polarizable thione carbonyl might play a more critical role in stabilizing the Asp366-Lys192 salt bridge in the proposed CB1-receptor homology model and inducing significant selectivity for CB1R over CB2R.

Discovery and structure–activity relationships of phenyl benzenesulfonylhydrazides as novel indoleamine 2,3-dioxygenase inhibitors

A novel class of phenyl benzenesulfonylhydrazides has been identified as potent inhibitors of indoleamine 2,3-dioxygenase (IDO), and their structure-activity relationship was explored. Coupling reactions between various benzenesulfonyl chlorides and phenylhydrazides were utilized to synthesize the sulfonylhydrazides bearing various substituents. Compound 3i exhibited 61 nM of IC50 in enzymatic assay and 172 nM of EC50 in the HeLa cell. The computational study of 3i suggested that the major interactions between 3i and IDO protein are the coordination of sulfone and heme iron, the hydrogen bonding and hydrophobic interactions between 3i and IDO. This novel class of IDO inhibitor provides a new direction to discover effective anti-cancer agents.

Discovery of 1‐(2,4‐Dichlorophenyl)‐4‐ethyl‐5‐(5‐(2‐(4‐(trifluoromethyl)phenyl)ethynyl)thiophen‐2‐yl)‐N‐(piperidin‐1‐yl)‐1H‐pyrazole‐3‐carboxamide as a Potential Peripheral Cannabinoid‐1 Receptor Inverse Agonist

Cannabinoid-1 receptor (CB1R) is one of the most abundant neuroregulatory receptors in the brain, and it is involved in regulating feeding and appetite. In addition to expression in brain, this receptor is also found in the peripheral organs, such as adipose tissues, muscle, and liver. In sharp contrast, the structurally closely related cannabinoid-2 receptor (CB2R) is expressed almost exclusively in the immune system and is primarily involved in immune regulation and neurodegeneration. The therapeutic potential of CB1R antagonists has been extensively reviewed, and at least one compound (1; also called rimonabant or SR141716A) has shown clinical evidence of weight reducing action. However, after its launch in 2006, it was subsequently withdrawn (2008) in Europe due to severe psychiatric effects including depression, anxiety and stress disorders. Currently, only two drugs, orlistat and sibutramine, are available for the long-term treatment of obesity; however, both have met with moderate success because of their limited weight-loss efficacy and many accompanying adverse effects, including high blood pressure and flatulence.

Bioisosteric Replacement of the Pyrazole 5-Aryl Moiety of N-(Piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A). A Novel Series of Alkynylthiophenes as Potent and Selective Cannabinoid-1 Receptor Antagonists

Replacing the conventional pyrazole 5-aryl substituent of 1 (SR141716A) with the 2-thienyl moiety appended with an appropriate alkynyl unit, a novel class of 5-(5-alkynyl-2-thienyl)pyrazole derivatives, behaving as highly potent CB1 receptor antagonists with good CB1/2 selectivity, was discovered, many of which, as typified by compound 18, showed significant weight reduction in diet-induced obese mouse model, thus pharmacologically validating that the bioisosteric replacement described above is viable. Also encouraging was the finding that a subtle structural modification of the newly developed series could result in a distinct difference in the intrinsic property, as demonstrated by compounds 12 (NA) and its methylated structural isomers 15 (PA) and 18 (IA). Moreover, current structure-activity relationship studies revealed that around the pyrazole 5-position of 1, a deep and flat crevice surrounded by a sequence of hydrophobic/aromatic residues as indicated by the CB1-receptor homology model might exist in the binding site.

Discovery of 1-(2,4-Dichlorophenyl)-N-(piperidin-1-yl)-4-((pyrrolidine-1-sulfonamido)methyl)-5-(5-((4-(trifluoromethyl)phenyl)ethynyl)thiophene-2-yl)-1H-pyrazole-3-carboxamide as a Novel Peripherally Restricted Cannabinoid-1 Receptor Antagonist with Significant Weight-Loss Efficacy in Diet-Induced Obese Mice

After extensive synthetic efforts, we found that many structurally diverse bioisosteres could be generated via derivatizing the C-4 alkyl chain on the pyrazole ring of compound 3 (B/P = 1/33) with different electronegative groups. Especially when a sulfonamide or sulfamide moiety was added, resulting compounds exhibited not only potent CB1R activity but also a desired tPSA value over 90 Å(2), a threshold considered to possess a low probability to cross BBB, leading to the identification of compound 4 (B/P = 1/64) as a peripherally restricted CB1R antagonist. Apart from its significant weight-loss efficacy in DIO mice, compound 4 also displays 163 clean off-target profiles and is currently under development for treating obesity and the related metabolic syndrome.

Identification of substituted naphthotriazolediones as novel tryptophan 2,3-dioxygenase (TDO) inhibitors through structure-based virtual screening

A structure-based virtual screening strategy, comprising homology modeling, ligand-support binding site optimization, virtual screening, and structure clustering analysis, was developed and used to identify novel tryptophan 2,3-dioxygenase (TDO) inhibitors. Compound 1 (IC50 = 711 nM), selected by virtual screening, showed inhibitory activity toward TDO and was subjected to structural modifications and molecular docking studies. This resulted in the identification of a potent TDO selective inhibitor (11e, IC50 = 30 nM), making it a potential compound for further investigation as a cancer therapeutic and other TDO-related targeted therapy.

A novel peripheral cannabinoid receptor 1 antagonist, BPR0912, reduces weight independently of food intake and modulates thermogenesis

To investigate the in vivo metabolic effects of treatment with BPR0912, a novel and potent peripheral cannabinoid receptor 1 (CB1R) antagonist, on both normal mice and diet‐induced obese (DIO) mice.

Biphasic suppression of appetite by cannabinoid CB1 receptor antagonists with distinct functional activities.

A novel alkynylthiophene series of cannabinoid CB1 receptor antagonists has been described to exhibit distinct intrinsic activities with minimal substructure modifications. The three representatives, BPR0432, BPR0568 and BPR0569, functioning as a neutral antagonist, an inverse agonist and a partial agonist, respectively, in GTP binding assay, were further characterized for their downstream signaling activities in relation to in vivo efficacy in appetite suppression to diets of different macronutrients. Interestingly, these three derivatives all behaved as inverse agonists with the potency of BPR0432>BPR0568>BPR0569 in cAMP assay. After administered to non-deprived rats, the potency in appetite suppression was positively related to their strength in intrinsic activity in the first hour of intake. The preferential suppression to high fat and high carbohydrate diets was revealed after 6h and only appeared in the treatment of BPR0568, presumably due to its metabolic stability in addition to its intrinsic activity. These results indicated the suppression of appetite was controlled in a biphasic manner, and these three structurally close but functionally distinct compounds are invaluable tools in elucidating the mechanism of neuronal response to appetite and palatability.