The effect of angiotensin receptor neprilysin inhibitor, sacubitril/valsartan, on central nervous system amyloid-ß concentrations and clearance in the cynomolgus monkey.

Sacubitril/valsartan (LCZ696) is the first angiotensin receptor neprilysin inhibitor approved to reduce cardiovascular mortality and hospitalization in patients with heart failure with reduced ejection fraction. As neprilysin (NEP) is one of several enzymes known to degrade amyloid-ß (Aß), there is a theoretical risk of Aß accumulation following long-term NEP inhibition. The primary objective of this study was to evaluate the potential effects of sacubitril/valsartan on central nervous system clearance of Aß isoforms in cynomolgus monkeys using the sensitive Stable Isotope Labeling Kinetics (SILK™)-Aß methodology. The in vitro selectivity of valsartan, sacubitril, and its active metabolite sacubitrilat was established; sacubitrilat did not inhibit other human Aß-degrading metalloproteases. In a 2-week study, sacubitril/valsartan (50mg/kg/day) or vehicle was orally administered to female cynomolgus monkeys in conjunction with SILK™-Aß. Despite low cerebrospinal fluid (CSF) and brain penetration, CSF exposure to sacubitril was sufficient to inhibit NEP and resulted in an increase in the elimination half-life of Aß1-42 (65.3%; p=0.026), Aß1-40 (35.2%; p=0.04) and Aßtotal (29.8%; p=0.04) acutely; this returned to normal as expected with repeated dosing for 15days. CSF concentrations of newly generated Aß (AUC(0-24h)) indicated elevations in the more aggregable form Aß1-42 on day 1 (20.4%; p=0.039) and day 15 (34.7%; p=0.0003) and in shorter forms Aß1-40 (23.4%; p=0.009), Aß1-38 (64.1%; p=0.0001) and Aßtotal (50.45%; p=0.00002) on day 15. However, there were no elevations in any Aß isoforms in the brains of these monkeys on day 16. In a second study cynomolgus monkeys were administered sacubitril/valsartan (300mg/kg) or vehicle control for 39weeks; no microscopic brain changes or Aß deposition, as assessed by immunohistochemical staining, were present. Further clinical studies are planned to address the relevance of these findings.

Structure of neprilysin in complex with the active metabolite of sacubitril.

Sacubitril is an ethyl ester prodrug of LBQ657, the active neprilysin (NEP) inhibitor, and a component of LCZ696 (sacubitril/valsartan). We report herein the three-dimensional structure of LBQ657 in complex with human NEP at 2 Å resolution. The crystal structure unravels the binding mode of the compound occupying the S1, S1' and S2' sub-pockets of the active site, consistent with a competitive inhibition mode. An induced fit conformational change upon binding of the P1'-biphenyl moiety of the inhibitor suggests an explanation for its selectivity against structurally homologous zinc metallopeptidases.

Plasma contact system activation drives anaphylaxis in severe mast cell-mediated allergic reactions.

BACKGROUND: Anaphylaxis is an acute, potentially lethal, multisystem syndrome resulting from the sudden release of mast cell-derived mediators into the circulation. OBJECTIVES AND METHODS: We report here that a plasma protease cascade, the factor XII-driven contact system, critically contributes to the pathogenesis of anaphylaxis in both murine models and human subjects. RESULTS: Deficiency in or pharmacologic inhibition of factor XII, plasma kallikrein, high-molecular-weight kininogen, or the bradykinin B2 receptor, but not the B1 receptor, largely attenuated allergen/IgE-mediated mast cell hyperresponsiveness in mice. Reconstitutions of factor XII null mice with human factor XII restored susceptibility for allergen/IgE-mediated hypotension. Activated mast cells systemically released heparin, which provided a negatively charged surface for factor XII autoactivation. Activated factor XII generates plasma kallikrein, which proteolyzes kininogen, leading to the liberation of bradykinin. We evaluated the contact system in patients with anaphylaxis. In all 10 plasma samples immunoblotting revealed activation of factor XII, plasma kallikrein, and kininogen during the acute phase of anaphylaxis but not at basal conditions or in healthy control subjects. The severity of anaphylaxis was associated with mast cell degranulation, increased plasma heparin levels, the intensity of contact system activation, and bradykinin formation. CONCLUSIONS: In summary, the data collectively show a role of the contact system in patients with anaphylaxis and support the hypothesis that targeting bradykinin generation and signaling provides a novel and alternative treatment strategy for anaphylactic attacks.

Fluorescence Lifetime-Based Competitive Binding Assays for Measuring the Binding Potency of Protease Inhibitors In Vitro.

Fluorescence lifetime (FLT)-based assays have developed to become highly attractive tools in drug discovery. All recently published examples of FLT-based assays essentially describe their use for monitoring enzyme-mediated peptide modifications, such as proteolytic cleavage or phosphorylation/dephosphorylation. Here we report the development of competitive binding assays as novel, inhibitor-centric assays, principally employing the FLT of the acridone dye Puretime 14 (PT14) as the readout parameter. Exemplified with two case studies on human serine proteases, the details of the rationale for both the design and synthesis of probes (i.e., active site-directed low-molecular-weight inhibitors conjugated to PT14) are provided. Data obtained from testing inhibitors with the novel assay format match those obtained with alternative formats such as FLT-based protease activity and time-resolved fluorescence resonance energy transfer-based competitive binding assays.

Novel 2,7-dialkyl-substituted 5(S)-amino-4(S)-hydroxy-8-phenyl-octanecarboxamide transition state peptidomimetics are potent and orally active inhibitors of human renin.

The action of renin is the rate-limiting step of the renin-angiotensin system (RAS), a key regulator of blood pressure. Effective renin inhibitors directly block the RAS entirely at source and, thus, may provide a vital weapon for hypertension therapy. Our efforts toward identifying novel small-molecule peptidomimetic renin inhibitors have resulted in the design of transition-state isosteres such as 1 bearing an all-carbon 8-phenyl-octanecarboxamide framework. Optimization of the extended P3 portion of 1 and extensive P2' modifications provided analogues with improved in vitro potencies in the presence of plasma. X-ray resolution of rh-renin/38a in the course of SAR work surprisingly unveiled the exploitation of a previously unexplored pocket (S3sp) important for strong binding affinities. Several inhibitors demonstrated oral efficacy in sodium-depleted marmosets. The most potent, 38a, induced dose-dependently a pronounced reduction in mean arterial blood pressure, paralleled by complete blockade of active plasma renin, up to 8 h post-dose. Oral bioavailability of 38a was 16% in marmosets.

Structure-based design of aliskiren, a novel orally effective renin inhibitor.

Hypertension is a major risk factor for cardiovascular diseases such as stroke, myocardial infarction, and heart failure, the leading causes of death in the Western world. Inhibitors of the renin-angiotensin system (RAS) have proven to be successful treatments for hypertension. As renin specifically catalyses the rate-limiting step of the RAS, it represents the optimal target for RAS inhibition. Several peptide-like renin inhibitors have been synthesized previously, but poor pharmacokinetic properties meant that these compounds were not clinically useful. We employed a combination of molecular modelling and crystallographic structure analysis to design renin inhibitors lacking the extended peptide-like backbone of earlier inhibitors, for improved pharmacokinetic properties. This led to the discovery of aliskiren, a highly potent and selective inhibitor of human renin in vitro, and in vivo; once-daily oral doses of aliskiren inhibit renin and lower blood pressure in sodium-depleted marmosets and hypertensive human patients. Aliskiren represents the first in a novel class of renin inhibitors with the potential for treatment of hypertension and related cardiovascular diseases.

Uncoupling of protein-3 induces an uncontrolled uncoupling of mitochondria after expression in muscle derived L6 cells.

The uncoupling proteins (UCPs) are thought to uncouple oxidative phosphorylation in the mitochondria and thus generate heat. One of the UCP isoforms, UCP3, is abundantly expressed in skeletal muscle, the major thermogenic tissue in humans. UCP3 has been overexpressed at high levels in yeast systems, where it leads to the uncoupling of cell respiration, suggesting that UCP3 may indeed be capable of dissipating the mitochondrial proton gradient. This effect, however, was recently shown to be a consequence of the high level of expression and incorrect folding of the protein and not to its intrinsic uncoupling activity. In the present study, we investigated the properties of UCP3 overexpressed in a relevant mammalian host system such as the rat myoblast L6 cell line. UCP3 was expressed in relatively low levels (< 1 microg x mg(-1) membrane protein) with the help of an adenovirus vector. Immunofluorescence microscopy of transduced L6 cells showed that UCP3 was expressed in more than 90% of the cells and that its staining pattern was characteristic for mitochondrial localization. The oxygen consumption of L6 cells under nonphosphorylating conditions increased concomitantly with the levels of UCP3 expression. However, uncoupling was associated with an inhibition of the maximal respiratory capacity of mitochondria and was not affected by purine nucleotides and free fatty acids. Moreover, recombinant UCP3 was resistant to Triton X-100 extraction under conditions that fully solubilize membrane bound proteins. Thus, UCP3 can be uniformly overexpressed in the mitochondria of a relevant muscle-derived cell line resulting in the expected increase of mitochondrial uncoupling. However, our data suggest that the protein is present in an incompetent conformation.