Discovery of a Novel Piperidine-Based Inhibitor of Cholesteryl Ester Transfer Protein (CETP) That Retains Activity in Hypertriglyceridemic Plasma.

Herein we describe the discovery and characterization of a novel, piperidine-based inhibitor of cholesteryl ester transfer protein (CETP) with a core structure distinct from other reported CETP inhibitors. A versatile synthesis starting from 4-methoxypyridine enabled an efficient exploration of the SAR, giving a lead molecule with potent CETP inhibition in human plasma. The subsequent optimization focused on improvement of pharmacokinetics and mitigation of off-target liabilities, such as CYP inhibition, whose improvement correlated with increased lipophilic efficiency. The effort led to the identification of an achiral, carboxylic acid-bearing compound 16 (TAP311) with excellent pharmacokinetics in rats and robust efficacy in hamsters. Compared to anacetrapib, the compound showed substantially reduced lipophilicity, had only modest distribution into adipose tissue, and retained potency in hypertriglyceridemic plasma in vitro and in vivo. Furthermore, in contrast to torcetrapib, the compound did not increase aldosterone secretion in human adrenocortical carcinoma cells nor in chronically cannulated rats. On the basis of its preclinical efficacy and safety profile, the compound was advanced into clinical trials.

Phagocytosis by human monocytes is required for the secretion of presepsin.

BACKGROUND: Presepsin, a soluble CD14 subtype, is increasingly recognized as a useful biomarker for sepsis. However, little is known about the biological characteristics of presepsin in humans. Furthermore, there are no studies evaluating clinical validity of measuring the presepsin levels in patients after allogeneic hematopoietic cell transplantation, irrespective of the high frequency of sepsis. METHODS: For in vitro assays, neutrophils and monocytes were isolated from the peripheral blood of healthy controls and treated with bacteria or inflammatory stimuli. Presepsin levels in the culture supernatants were measured by enzyme linked immunosorbent assay (ELISA). For a cohort study of patients undergoing allogeneic hematopoietic cell transplantation, serum samples were subjected to ELISA for presepsin, and the relationship of presepsin levels with the incidence of transplantation-related complications was statistically analyzed. RESULTS: We found that monocytes were the main source of presepsin in humans. Presepsin secretion by human monocytes was triggered by bacterial phagocytosis or sterile phagocytic stimulus, such as monosodium urate crystals, rather than soluble inflammatory stimuli. Elastase, a serine protease in human monocytes, mediated CD14 cleavage to produce presepsin. The cohort study demonstrated that high presepsin values were significantly associated with an increased incidence of hemophagocytic syndrome, as well as bacteremia. Moreover, patients with higher presepsin values revealed inferior overall survival, suggesting that presepsin can also be a prognostic marker for transplantation. CONCLUSIONS: In this study, we clarified the biological features of presepsin in humans. Our study may be useful for increasing the clinical application of presepsin as a biomarker.

Insulin down-regulates specific activity of ATP-binding cassette transporter A1 for high density lipoprotein biogenesis through its specific phosphorylation.

Insulin resistance/hyperinsulinism is one of the major risks for atherosclerotic vascular diseases and low HDL may be involved in pathogenesis. We examined direct effects of insulin on HDL biosynthesis focusing on the activity of ATP-binding cassette transporter A1 (ABCA1) in culture cells and in experimental animals. Insulin impairs HDL biosynthesis through modulation of ABCA1 activity by two different mechanisms. Insulin enhances degradation of ABCA1. However, even after this effect was cancelled by blocking its specific signal, insulin still reduces HDL biogenesis. This effect was found due to phosphorylation of ABCA1 that leads to decrease of its specific activity. We identified a novel insulin-specific phosphorylation site Tyr1206 of ABCA1 to regulate its specific activity. The observation in a rat model of insulin resistance was consistent with these results. The findings demonstrate a new mechanism for regulation of ABCA1 activity and provide new insights into the link between development of atherosclerosis, and insulin resistance/hyperinsulinism.

Hurdles in the drug discovery of cathepsin K inhibitors.

There were many hurdles in the drug discovery of cathepsin K inhibitors such as species differences not only in bone metabolism but also in amino acid sequences in the critical site of the target enzyme, discrepancies between PK/PD due to unique tissue distribution of the inhibitor affecting both efficacy and side effects originated from a characteristic intracellular or tissue distribution of some classes of compounds. The value of this new therapeutic approach over the launched indirect competitors should be further clarified from the efficacy and side effect point of view. The cathepsin K inhibitor drug discovery was initiated based on a strong and osteoclast-specific expression of this enzyme. However, the tissues and cells expressing cathepsin K have been expanding as the investigation on pathological conditions progressed with respect to side effects as well as new possible indications.

Effect of cathepsin K inhibitors on bone resorption.

On the basis of the pyrrolopyrimidine core structure that was previously discovered, cathepsin K inhibitors having a spiro amine at the P3 have been explored to enhance the target, bone marrow, tissue distribution. Several spiro structures were identified with improved distribution toward bone marrow. The representative inhibitor 7 of this series revealed in vivo reduction in C-terminal telopeptide of type I collagen in rats and monkeys.

Discovery of orally bioavailable cathepsin S inhibitors for the reversal of neuropathic pain.

Cathepsin S inhibitors are well-known to be an attractive target as immunological therapeutic agents. Recently, our gene expression analysis identified that cathepsin S inhibitors could also be effective for neuropathic pain. Herein, we describe the efficacy of selective cathepsin S inhibitors as antihyperalgesics in a model of neuropathic pain in rats after oral administration.

Discovery of selective and nonpeptidic cathepsin S inhibitors.

Nonpeptidic, selective, and potent cathepsin S inhibitors were derived from an in-house pyrrolopyrimidine cathepsin K inhibitor by modification of the P2 and P3 moieties. The pyrrolopyrimidine-based inhibitors show nanomolar inhibition of cathepsin S with over 100-fold selectivity against other cysteine proteases, including cathepsin K and L. Some of the inhibitors showed cellular activities in mouse splenocytes as well as oral bioavailabilities in rats.

New chemotypes for cathepsin K inhibitors.

Cyano pyrimidine acetylene and cyano pyrimidine t-amine, which belong to a new chemical class, were prepared and tested for inhibitory activities against cathepsin K and the highly homologous cathepsins L and S. The use of novel chemotypes in the development of cathepsin K inhibitors has been demonstrated by derivatives of compounds 1 and 8.

Novel scaffold for cathepsin K inhibitors.

Pyrrolopyrimidine, a novel scaffold, allows to adjust interactions within the S3 subsite of cathepsin K. The core intermediate 10 facilitated the P3 optimization and identified highly potent and selective cathepsin K inhibitors 11-20.

Preservation of endothelial function by the HMG-CoA reductase inhibitor fluvastatin through its lipid-lowering independent antioxidant properties in atherosclerotic rabbits.

Recent evidence suggests that the beneficial effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on entothelial function and cardiovascular ischemic events may be attributed not only to their lipid-lowering effects but also to cholesterol-lowering independent (direct) effects on the atherosclerotic vessel wall. This study was designed to test the hypothesis that fluvastatin (Flu) preserves the endothelial function by its cholesterol-lowering independent actions. Rabbits were fed a 0.5% high-cholesterol (HC) diet for 12 weeks (progression phase) and then fed the HC diet either containing or not containing Flu 2 mg/kg/day for an additional 8 weeks (treatment phase). Rabbits fed a normal diet were used as controls. Plasma total and low-density lipoprotein cholesterol concentrations did not differ during the treatment phase: Endothelium-dependent/NO-mediated relaxation (acetylcholine and A23187) was impaired in the HC diet group, whereas it was preserved in the HC plus Flu treatment group. The endothelium-independent relaxation (sodium nitroprusside) was similar between the three groups. Interestingly, aortic oxidative stress (lipid peroxides and isoprostane F(2alpha)-III contents) and NADPH oxidase component (p22phox and gp91phox) mRNA expression were increased in the HC group but not in the HC plus Flu group. The A23187-induced nitric oxide production from the aorta was increased in both HC and HC plus Flu groups. There was no significant difference in tissue endothelial-type nitric oxide synthase mRNA expression. Plaque area and intimal thickening of the aorta were significantly lowered in the HC plus Flu group. Flu treatment preserved the endothelial function associated with the decrease in markers of oxidative stress in this experiment. These beneficial endothelial effects of Flu are likely to occur independently of plasma lipid concentrations and to be mediated by its antioxidant action.

Comparison of heat- and pressure-induced unfolding of ribonuclease a: the critical role of Phe46 which appears to belong to a new hydrophobic chain-folding initiation site.

To clarify the structural role of Phe46 inside the hydrophobic core of bovine pancreatic ribonuclease A (RNase A), thermal and pressure unfolding of wild-type RNase A and three mutant forms (F46V, F46E, and F46K) were analyzed by fourth-derivative UV absorbance spectroscopy. All the mutants, as well as the wild type, exhibited a two-state transition during both thermal and pressure unfolding, and both T(m) and P(m) decreased markedly when Phe46 was replaced with valine, glutamic acid, or lysine. The strongest effect was on the F46K mutant and the weakest on F46V. Both unfolding processes produced identical blue shifts in the fourth-derivative spectra, indicating that the tyrosine residues are similarly exposed in the temperature- and pressure-induced unfolded states. A comparison of Gibbs free energies determined from the pressure and temperature unfoldings, however, gave DeltaG(p)/DeltaG(t) ratios (r) of 1.7 for the wild type and 0.92 +/- 0.03 for the mutants. Furthermore, the DeltaV value for each mutant was larger than that for the wild type. CD spectra and activity measurements showed no obvious major structural differences in the folded state, indicating that the structures of the Phe46 mutants and wild type differ in the unfolded state. We propose a model in which Phe46 stabilizes the hydrophobic core at the boundary between two structural domains. Mutation of Phe46 decreases protein stability by weakening the unfolding cooperativity between these domains. This essential function of Phe46 in RNase A stability indicates that it belongs to a chain-folding initiation site.