Gastrointestinal Inhibition of Sodium-Hydrogen Exchanger 3 Reduces Phosphorus Absorption and Protects against Vascular Calcification in CKD.

In CKD, phosphate retention arising from diminished GFR is a key early step in a pathologic cascade leading to hyperthyroidism, metabolic bone disease, vascular calcification, and cardiovascular mortality. Tenapanor, a minimally systemically available inhibitor of the intestinal sodium-hydrogen exchanger 3, is being evaluated in clinical trials for its potential to (1) lower gastrointestinal sodium absorption, (2) improve fluid overload-related symptoms, such as hypertension and proteinuria, in patients with CKD, and (3) reduce interdialytic weight gain and intradialytic hypotension in ESRD. Here, we report the effects of tenapanor on dietary phosphorous absorption. Oral administration of tenapanor or other intestinal sodium-hydrogen exchanger 3 inhibitors increased fecal phosphorus, decreased urine phosphorus excretion, and reduced [(33)P]orthophosphate uptake in rats. In a rat model of CKD and vascular calcification, tenapanor reduced sodium and phosphorus absorption and significantly decreased ectopic calcification, serum creatinine and serum phosphorus levels, circulating phosphaturic hormone fibroblast growth factor-23 levels, and heart mass. These results indicate that tenapanor is an effective inhibitor of dietary phosphorus absorption and suggest a new approach to phosphate management in renal disease and associated mineral disorders.

Discovery of Tenapanor: A First-in-Class Minimally Systemic Inhibitor of Intestinal Na+/H+ Exchanger Isoform 3.

We present herein the design, synthesis, and optimization of gut-restricted inhibitors of Na+/H+ exchanger isoform 3 (NHE3). NHE3 is predominantly expressed in the kidney and gastrointestinal tract where it acts as the major absorptive sodium transporter. We desired minimally systemic agents that would block sodium absorption in the gastrointestinal tract but avoid exposure in the kidney. Starting with a relatively low-potency highly bioavailable hit compound (1), potent and minimally absorbed NHE3 inhibitors were designed, culminating with the discovery of tenapanor (28). Tenapanor has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of irritable bowel syndrome with constipation in adults.

Benzimidazole and imidazole inhibitors of histone deacetylases: Synthesis and biological activity.

A series of N-hydroxy-3-[3-(1-substituted-1H-benzoimidazol-2-yl)-phenyl]-acrylamides (5a-5ab) and N-hydroxy-3-[3-(1,4,5-trisubstituted-1H-imidazol-2-yl)-phenyl]-acrylamides (12a-s) were designed, synthesized, and found to be nanomolar inhibitors of human histone deacetylases. Multiple compounds bearing an N1-piperidine demonstrate EC(50)s of 20-100 nM in human A549, HL60, and PC3 cells, in vitro and in vivo hyperacetylation of histones H3 and H4, and induction of p21(waf). Compound 5x displays efficacy in human tumor xenograft models.

Exploration of the HDAC2 foot pocket: Synthesis and SAR of substituted N-(2-aminophenyl)benzamides.

A series of N-(2-amino-5-substituted phenyl)benzamides (3-21) were designed, synthesized and evaluated for their inhibition of HDAC2 and their cytotoxicity in HCT116 cancer cells. Multiple compounds from this series demonstrated time-dependent binding kinetics that is rationalized using a co-complex crystal structure of HDAC2 and N-(4-aminobiphenyl-3-yl)benzamide (6).

Shared Platform for Antibiotic Research and Knowledge: A Collaborative Tool to SPARK Antibiotic Discovery.

The discovery of urgently needed antibiotics is hindered by challenges to information sharing. To help address this challenge, The Pew Charitable Trusts launched SPARK: the Shared Platform for Antibiotic Research and Knowledge. SPARK is an online, publicly available, interactive database designed to help scientists build on previous research and generate new insights to advance the field's understanding of Gram-negative permeability. This Viewpoint details how data are selected and integrated into the platform, how scientists can use SPARK to share their data, and the ways the scientific community can access and use these data to develop hypotheses.

Design of Gut-Restricted Thiazolidine Agonists of G Protein-Coupled Bile Acid Receptor 1 (GPBAR1, TGR5).

Bile acid signaling and metabolism in the gastrointestinal tract have wide-ranging influences on systemic disease. G protein-coupled bile acid receptor 1 (GPBAR1, TGR5) is one of the major effectors in bile acid sensing, with demonstrated influence on metabolic, inflammatory, and proliferative processes. The pharmacologic utility of TGR5 agonists has been limited by systemic target-related effects such as excessive gallbladder filling and blockade of gallbladder emptying. Gut-restricted TGR5 agonists, however, have the potential to avoid these side effects and consequently be developed into drugs with acceptable safety profiles. We describe the discovery and optimization of a series of gut-restricted TGR5 agonists that elicit a potent response in mice, with minimal gallbladder-related effects. The series includes 12 (TGR5 EC50: human, 143 nM; mouse, 1.2 nM), a compound with minimal systemic availability that may have therapeutic value to patients with type 2 diabetes mellitus, nonalcoholic steatohepatitis, or inflammatory bowel disease.

Discovery of alogliptin: a potent, selective, bioavailable, and efficacious inhibitor of dipeptidyl peptidase IV.

Alogliptin is a potent, selective inhibitor of the serine protease dipeptidyl peptidase IV (DPP-4). Herein, we describe the structure-based design and optimization of alogliptin and related quinazolinone-based DPP-4 inhibitors. Following an oral dose, these noncovalent inhibitors provide sustained reduction of plasma DPP-4 activity and a lowering of blood glucose in animal models of diabetes. Alogliptin is currently undergoing phase III trials in patients with type 2 diabetes.

Structural snapshots of human HDAC8 provide insights into the class I histone deacetylases.

Modulation of the acetylation state of histones plays a pivotal role in the regulation of gene expression. Histone deacetylases (HDACs) catalyze the removal of acetyl groups from lysines near the N termini of histones. This reaction promotes the condensation of chromatin, leading to repression of transcription. HDAC deregulation has been linked to several types of cancer, suggesting a potential use for HDAC inhibitors in oncology. Here we describe the first crystal structures of a human HDAC: the structures of human HDAC8 complexed with four structurally diverse hydroxamate inhibitors. This work sheds light on the catalytic mechanism of the HDACs, and on differences in substrate specificity across the HDAC family. The structure also suggests how phosphorylation of Ser39 affects HDAC8 activity.

Intestinal inhibition of the Na+/H+ exchanger 3 prevents cardiorenal damage in rats and inhibits Na+ uptake in humans.

The management of sodium intake is clinically important in many disease states including heart failure, kidney disease, and hypertension. Tenapanor is an inhibitor of the sodium-proton (Na(+)/H(+)) exchanger NHE3, which plays a prominent role in sodium handling in the gastrointestinal tract and kidney. When administered orally to rats, tenapanor acted exclusively in the gastrointestinal tract to inhibit sodium uptake. We showed that the systemic availability of tenapanor was negligible through plasma pharmacokinetic studies, as well as autoradiography and mass balance studies performed with (14)C-tenapanor. In humans, tenapanor reduced urinary sodium excretion by 20 to 50 mmol/day and led to an increase of similar magnitude in stool sodium. In salt-fed nephrectomized rats exhibiting hypervolemia, cardiac hypertrophy, and arterial stiffening, tenapanor reduced extracellular fluid volume, left ventricular hypertrophy, albuminuria, and blood pressure in a dose-dependent fashion. We observed these effects whether tenapanor was administered prophylactically or after disease was established. In addition, the combination of tenapanor and the blood pressure medication enalapril improved cardiac diastolic dysfunction and arterial pulse wave velocity relative to enalapril monotherapy in this animal model. Tenapanor prevented increases in glomerular area and urinary KIM-1, a marker of renal injury. The results suggest that therapeutic alteration of sodium transport in the gastrointestinal tract instead of the kidney--the target of current drugs--could lead to improved sodium management in renal disease.

Design and synthesis of pyrimidinone and pyrimidinedione inhibitors of dipeptidyl peptidase IV.

The discovery of two classes of heterocyclic dipeptidyl peptidase IV (DPP-4) inhibitors, pyrimidinones and pyrimidinediones, is described. After a single oral dose, these potent, selective, and noncovalent inhibitors provide sustained reduction of plasma DPP-4 activity and lowering of blood glucose in animal models of diabetes. Compounds 13a, 27b, and 27j were selected for development.

Characterization of the two catalytic domains in histone deacetylase 6.

Histone deacetylase 6 (HDAC6) is the only known HDAC with two potentially functional catalytic domains, yet the role towards substrate played by these two domains remains ambiguous. Most studies report HDAC6 activities measured using either immune complexes or in vitro translated products. Here, we characterize the activity of highly purified recombinant HDAC6, mutants with active site histidine mutations in each domain (H216A and H611A), and individual catalytic domains. The deacetylase activities of these proteins, as well as their kinetic parameters, were measured using histone, alpha-tubulin, and fluorogenic acetylated lysine as substrates. Mutant H216A only slightly lowers the catalytic rate. However, mutant H611A decreases the catalytic rate more than 5000-fold. The first domain expressed alone is not catalytically active. In contrast, the second domain shows only a modest decrease in substrate binding and product formation rate. Our results indicate that the in vitro deacetylase activity of HDAC6 resides in the C-terminal second catalytic domain.

Cell-based assay for screening 11beta-hydroxysteroid dehydrogenase inhibitors using liquid chromatography/tandem mass spectrometry detection.

Cortisol is an important glucocorticoid that regulates many physiological pathways by activating various intracellular receptors. The type 1 isozyme of 11beta-hydroxysteroid dehydrogenase (11beta-HSD1) functions in vivo predominantly as a reductase by converting cortisone into cortisol. A high-throughput liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed to screen for inhibitors of 11beta-HSD1 by monitoring cortisol and cortisone simultaneously. The injection cycle time can be as fast as 1 min/sample, making it amenable to the analysis of large numbers of the cell-assay samples in the screening of 11beta-HSD inhibitors. The reductase and dehydrogenase activities of 11beta-HSD1 are assessed separately.