Molecular mechanisms in Alzheimer's disease and related potential treatments such as structural target convergence of antibodies and simple organic molecules.

The amyloid cascade is the most frequently accepted hypothesis of Alzheimer's Disease (AD). According to this hypothesis, the formation of plaques precedes the appearance of fibrillary tangles. Therapeutic agents able to inhibit the formation of plaques are therefore considered as potential disease-modifying treatments (DMT) that could prevent or limit the progression of AD. Plaques are deposits formed by aggregates of amyloid-ß (Aß)-peptides. These peptides are metabolites of amyloid precursor protein (APP) first mediated by two enzymes: ß-secretase 1 (BACE1) and γ-secretase. Molecular identification of these two enzymes has stimulated the development of their inhibitors. The clinical testing of these two classes of molecules has not been successful to date. The oligomerization of Aß-peptides into plaques is now targeted by immunological approaches such as antibodies and vaccines. Structural consideration of the Aß-peptide sequence led to the launch of the antibody Aducanumab. Several other antibodies are in late clinical phases. Progress in the understanding of the effects of N-truncated Aß-peptides such as pE3-42, formed by the action of recently well characterized enzymes (aminopeptidase A, dipeptidylpeptidase-4 and glutaminyl cyclase) suggests that oligomerization can be limited either by enzyme inhibitors or antibody approaches. This strategy associating two structurally interconnected mechanisms is focused in this review.

Positive allosteric modulation of the mu-opioid receptor produces analgesia with reduced side effects.

Positive allosteric modulators (PAMs) of the mu-opioid receptor (MOR) have been hypothesized as potentially safer analgesics than traditional opioid drugs. This is based on the idea that PAMs will promote the action of endogenous opioid peptides while preserving their temporal and spatial release patterns and so have an improved therapeutic index. However, this hypothesis has never been tested. Here, we show that a mu-PAM, BMS-986122, enhances the ability of the endogenous opioid Methionine-enkephalin (Met-Enk) to stimulate G protein activity in mouse brain homogenates without activity on its own and to enhance G protein activation to a greater extent than ß-arrestin recruitment in Chinese hamster ovary (CHO) cells expressing human mu-opioid receptors. Moreover, BMS-986122 increases the potency of Met-Enk to inhibit GABA release in the periaqueductal gray, an important site for antinociception. We describe in vivo experiments demonstrating that the mu-PAM produces antinociception in mouse models of acute noxious heat pain as well as inflammatory pain. These effects are blocked by MOR antagonists and are consistent with the hypothesis that in vivo mu-PAMs enhance the activity of endogenous opioid peptides. Because BMS-986122 does not bind to the orthosteric site and has no inherent agonist action at endogenously expressed levels of MOR, it produces a reduced level of morphine-like side effects of constipation, reward as measured by conditioned place preference, and respiratory depression. These data provide a rationale for the further exploration of the action and safety of mu-PAMs as an innovative approach to pain management.

Aminopeptidase A contributes to biochemical, anatomical and cognitive defects in Alzheimer's disease (AD) mouse model and is increased at early stage in sporadic AD brain.

One of the main components of senile plaques in Alzheimer's disease (AD)-affected brain is the Aß peptide species harboring a pyroglutamate at position three pE3-Aß. Several studies indicated that pE3-Aß is toxic, prone to aggregation and serves as a seed of Aß aggregation. The cyclisation of the glutamate residue is produced by glutaminyl cyclase, the pharmacological and genetic reductions of which significantly alleviate AD-related anatomical lesions and cognitive defects in mice models. The cyclisation of the glutamate in position 3 requires prior removal of the Aß N-terminal aspartyl residue to allow subsequent biotransformation. The enzyme responsible for this rate-limiting catalytic step and its relevance as a putative trigger of AD pathology remained yet to be established. Here, we identify aminopeptidase A as the main exopeptidase involved in the N-terminal truncation of Aß and document its key contribution to AD-related anatomical and behavioral defects. First, we show by mass spectrometry that human recombinant aminopeptidase A (APA) truncates synthetic Aß1-40 to yield Aß2-40. We demonstrate that the pharmacological blockade of APA with its selective inhibitor RB150 restores the density of mature spines and significantly reduced filopodia-like processes in hippocampal organotypic slices cultures virally transduced with the Swedish mutated Aß-precursor protein (ßAPP). Pharmacological reduction of APA activity and lowering of its expression by shRNA affect pE3-42Aß- and Aß1-42-positive plaques and expressions in 3xTg-AD mice brains. Further, we show that both APA inhibitors and shRNA partly alleviate learning and memory deficits observed in 3xTg-AD mice. Importantly, we demonstrate that, concomitantly to the occurrence of pE3-42Aß-positive plaques, APA activity is augmented at early Braak stages in sporadic AD brains. Overall, our data indicate that APA is a key enzyme involved in Aß N-terminal truncation and suggest the potential benefit of targeting this proteolytic activity to interfere with AD pathology.

Contribution of Delta-Opioid Receptors to Pathophysiological Events Explored by Endogenous Enkephalins.

Very few discoveries in the neurosciences have triggered clinical speculation and experimentation regarding the etiology of psychiatric illness to the same extent as that following identification of the opiate receptor(s) and subsequent isolation of endogenous morphine-like peptides. There is overwhelming evidence in animals and in human that opioids are involved in behaviorally relevant issues such as the modulation of pain, the response to stress, motivation, addiction, sexuality, food intake, etc., but our knowledge on the possible relation between opioids and mental illness is still very limited.These responses could be explored eitheir by using higlhy selective delta agonist or by emphasizing the effects of phasically secreted endogenous opioid peptides, enkephalin. Both approaches were investigated in particular through protection of enkephalin degradation by dual enkephalinase ihibitors DENKIs such as RB101, PL37 or PL265.

Obligatory Metabolism of Angiotensin II to Angiotensin III for Zona Glomerulosa Cell-Mediated Relaxations of Bovine Adrenal Cortical Arteries.

Hyperaldosteronism is associated with hypertension, cardiac hypertrophy, and congestive heart failure. Steroidogenic factors facilitate aldosterone secretion by increasing adrenal blood flow. Angiotensin (Ang) II decreases adrenal vascular tone through release of zona glomerulosa (ZG) cell-derived vasodilatory eicosanoids. However, ZG cell-mediated relaxation of bovine adrenal cortical arteries to Ang II is not altered by angiotensin type 1 or 2 receptor antagonists. Because traditional Ang II receptors do not mediate these vasorelaxations to Ang II, we investigated the role of Ang II metabolites. Ang III was identified by liquid chromatography-mass spectrometry as the primary ZG cell metabolite of Ang II. Ang III stimulated ZG cell-mediated relaxation of adrenal arteries with greater potency than did Ang II. Furthermore, ZG cell-mediated relaxations of adrenal arteries by Ang II were attenuated by aminopeptidase inhibition, and Ang III-stimulated relaxations persisted. Ang IV had little effect compared with Ang II. Moreover, ZG cell-mediated relaxations of adrenal arteries by Ang II were attenuated by an Ang III antagonist but not by an Ang (1-7) antagonist. In contrast, Ang II and Ang III were equipotent in stimulating aldosterone secretion from ZG cells and were unaffected by aminopeptidase inhibition. Additionally, aspartyl and leucyl aminopeptidases, which convert Ang II to Ang III, are the primary peptidase expressed in ZG cells. This was confirmed by enzyme activity. These data indicate that intra-adrenal metabolism of Ang II to Ang III is required for ZG cell-mediated relaxations of adrenal arteries but not aldosterone secretion. These studies have defined an important role of Ang III in the adrenal gland.

Synergistic combinations of the dual enkephalinase inhibitor PL265 given orally with various analgesic compounds acting on different targets, in a murine model of cancer-induced bone pain.

BACKGROUND: The first line pharmacological treatment of cancer pain is morphine and surrogates but a significant pain relief and a reduction of the side-effects of these compounds makes it necessary to combine them with other drugs acting on different targets. The aim of this study was to measure the antinociceptive effect on cancer-induced bone pain resulting from the association of the endogenous opioids enkephalin and non-opioid analgesic drugs. For this purpose, PL265 a new orally active single dual inhibitor of the two degrading enkephalins enzymes, neprilysin (NEP) and aminopeptidase N (APN) was used. It strictly increased the levels of enkephalin at their sites of releases. The selected non-opioid compounds are: gabapentin, A-317491 (P2X3 receptor antagonist), ACEA (CB1 receptor antagonist), AM1241 (CB2 receptor antagonist), JWH-133 (CB2 receptor antagonist), URB937 (FAAH inhibitor), and NAV26 (Nav1.7 channel blocker). METHODS: Experiments. Experiments were performed in 5-6 weeks old (26-33g weight) C57BL/6 mice. Cell culture and cell inoculation. B16-F10 melanoma cells were cultured and when preconfluent, treated and detached. Finally related cells were resuspended to obtain a concentration of 2×106 cells/100µL. Then 105 cells were injected into the right tibial medullar cavity. Control mice were treated by killed cells by freezing. Behavioural studies. Thermal withdrawal latencies were measured on a unilatered hot plate (UHP) maintained at 49±0.2°C. Mechanical threshold values were obtained by performing the von Frey test using the "up and down" method. To evaluate the nature (additive or synergistic) of the interactions between PL265 and different drugs, an isobolographic analysis following the method described by Tallarida was performed. RESULTS: The results demonstrate the ability of PL265, a DENKI that prevents the degradation of endogenous ENKs, to counteract cancer-induced bone thermal hyperalgesia in mice, by exclusively stimulating peripheral opioid receptors as demonstrated by used of an opioid antagonist unable to enter the brain. The development of such DENKIs, endowed with druggable pharmacokinetic characteristics, such as good absorption by oral route, can be considered as an important step in the development of much needed novel antihyperalgesic drugs. Furthermore, all the tested combinations resulted in synergistic antihyperalgesic effects. As shown here, the greatest synergistic antinociceptive effect (doses could be lowered by 70%) was produced by the combination of PL265 with the P2X3 receptor antagonist (A-317491), cannabinoid CB1 receptor agonist (exogenous, ACEA and endogenous URB937-protected-AEA) and Nav1.7 blocker (NAV26) whose mechanism of action involves the direct activation of the enkephalinergic system. CONCLUSIONS: These multi-target-based antinociceptive strategies using combinations of non-opioid drugs with dual inhibitors of enkephalin degrading enzymes may bring therapeutic advantages in terms of efficacy and safety by allowing the reduction of doses of one of the compounds or of both, which is of the utmost interest in the chronic treatment of cancer pain. IMPLICATIONS: This article presents synergistic antinociceptive effect produced by the combination of PL265 with non-opioid analgesic drugs acting via unrelated mechanisms. These multi-target-based antinociceptive strategies may bring therapeutic advantages by allowing the reduction of doses, which is of great interest in the chronic treatment of cancer pain.

Substituted α-mercaptoketones, new types of specific neprilysin inhibitors.

New neprilysin inhibitors containing an α-mercaptoketone HSC(R1R2)CO group, as zinc ligand were designed. Two parameters were explored for potency optimization: the size of the inhibitor which could interact with the S1, S1' or S2' domain of the enzyme and the nature of the substituents R1, R2 of the mercaptoketone group. Introduction of a cyclohexyl chain in R1, R2 position and a (3-thiophen)benzyl group in position R3 (compound 12n) yielded to the most potent inhibitor of this series with a Ki value of 2±0.3nM. This result suggests that this new inhibitor interacts within the S1, S1' domain of NEP allowing a pentacoordination of the catalytic Zn2+ ion by the mercaptoketone moiety.

Preventive and alleviative effects of the dual enkephalinase inhibitor (Denki) PL265 in a murine model of neuropathic pain.

Neuropathic pain remains difficult to treat due to the involvement of various pathophysiological mechanisms in its pathogeny. Among the different opioidergic systems the enkephalinergic one is primarily recruited via activation of delta opioid receptor (DOP) in chronic pain and of mu opioid receptor (MOP) in acute pain. To investigate the role of their endogenous ligands Met and Leu-enkephalin in neuropathic pain control, a dual inhibitor of their degrading enzymes, PL265, which acts restrictively at the level of peripheral nociceptors, was administered per os to assess its efficacy in pain prevention and alleviation using a partial sciatic nerve ligation model (PSNL) in mice. We demonstrated here that the pre-injury oral administration of PL265 (50mg/kg) during the 9 days of neuropathy development reduces thermal hyperalgesia and mechanical allodynia for two weeks after the end of treatment. The repeated administration (50mg/kg daily, during 10 days) does not induce tolerance. Therefore, protecting the enkephalins released at the peripheral level during neuropathic pain with oral PL265 seems to be a promising approach to prevent and alleviate the painful symptoms of neuropathic pain in humans without the unwanted effects of exogenous opiates such as morphine.

Modulation of disulfide dual ENKephalinase inhibitors (DENKIs) activity by a transient N-protection for pain alleviation by oral route.

The endogenous opioid system, essentially constituted by two opioid receptors which are stimulated by the natural internal effectors enkephalins (Met-enkephalin and Leu-enkephalin), is present at the different sites (peripheral, spinal, central) of the control of pain. We have demonstrated that the protection of the enkephalin inactivation by the two metallopeptidases (neprilysin and neutral aminopeptidase) increases their local concentration selectively induced by pain stimuli triggering analgesic responses. With the aim of increasing the orally antinociceptive responses of the previously described disulfide DENKIs ( [Formula: see text] CH(R1)CH2-S-S-CH2-C(R2R3)CONHCH(R4)COOR5), we designed new pro-drugs, in the same chemical series, with a transient protection of the free amino group by an acyloxyalkyl carbamate, giving rise to ((CH3)2CHCO2CH(CH3)OCONHCH(R1)CH2-S-S-CH2-C(R2R3)CONHCH(R4)COOR5) pro-drugs 2a-2g. These compounds were easily prepared from their parent analogs, with a good yield. They were tested per os and shown to be highly efficient in peripherally-controlled inflammatory and neuropathic pain with long lasting effects but completely inactive in the acute centrally-controlled hot plate test, a model of pain by excess of nociception. This demonstrates that DENKIs are able to relieve pain at its source thanks to the increase of enkephalin levels.

Long-lasting oral analgesic effects of N-protected aminophosphinic dual ENKephalinase inhibitors (DENKIs) in peripherally controlled pain.

The peripheral endogenous opioid system is critically involved in neuropathic and inflammatory pain generation as suggested by the modulation of opioid receptors expression and enkephalins (ENKs) release observed in these painful conditions. Accordingly, an innovative approach in the treatment of these nocifensive events is to increase and maintain high local concentrations of extracellular pain-evoked ENKs, by preventing their physiological enzymatic inactivation by two Zn metallopeptidases, the neutral endopeptidase (NEP, neprilysin, EC 3.4.24.11) and the neutral aminopeptidase (APN, EC 3.4.11.2). With this aim, new orally active dual ENKephalinase inhibitors (DENKIs) were designed as soluble prodrugs by introducing a N-terminal cleavable carbamate in the previously described aminophosphinic inhibitors. This induces long-lasting antinociceptive responses after oral administration, in various rodent models of inflammatory and neuropathic pain. These responses are mediated through stimulation of peripheral opioid receptors by DENKIs-protected ENKs as demonstrated by naloxone methiodide reversion. In all tested models, the most efficient prodrug 2a (PL265) was active, at least during 150-180 min, after single oral administration of 25-50 mg/kg in mice and of 100-200 mg/kg in rats. In models of neuropathic pain, both hyperalgesia and allodynia were markedly reduced. Interestingly, combination of inactive doses of 2a (PL265) and of the anti-epileptic drug gabapentin had synergistic effect on neuropathic pain. Pharmacokinetic studies of 2a (PL265) in rats show that the active drug is the only generated metabolite produced. These encouraging results have made 2a (PL265) a suitable candidate for clinical development.

New orally active dual enkephalinase inhibitors (DENKIs) for central and peripheral pain treatment.

Protecting enkephalins, endogenous opioid peptides released in response to nociceptive stimuli, is an innovative approach for acute and neuropathic pain alleviation. This is achieved by inhibition of their enzymatic degradation by two membrane-bound Zn-metallopeptidases, neprilysin (NEP, EC 3.4.24.11) and aminopeptidase N (APN, EC 3.4.11.2). Selective and efficient inhibitors of both enzymes, designated enkephalinases, have been designed that markedly increase extracellular concentrations and half-lives of enkephalins, inducing potent antinociceptive effects. Several chemical families of Dual ENKephalinase Inhibitors (DENKIs) have previously been developed but devoid of oral activity. We report here the design and synthesis of new pro-drugs, derived from co-drugs combining a NEP and an APN inhibitor through a disulfide bond with side chains improving oral bioavailability. Their pharmacological properties were assessed in various animal models of pain targeting central and/or peripheral opioid systems. Considering its efficacy in acute and neuropathic pain, one of these new DENKIs, 19-IIIa, was selected for clinical development.

TGF-ß and opioid receptor signaling crosstalk results in improvement of endogenous and exogenous opioid analgesia under pathological pain conditions.

Transforming growth factor-ß1 (TGF-ß1) protects against neuroinflammatory events underlying neuropathic pain. TGF-ß signaling enhancement is a phenotypic characteristic of mice lacking the TGF-ß pseudoreceptor BAMBI (BMP and activin membrane-bound inhibitor), which leads to an increased synaptic release of opioid peptides and to a naloxone-reversible hypoalgesic/antiallodynic phenotype. Herein, we investigated the following: (1) the effects of BAMBI deficiency on opioid receptor expression, functional efficacy, and analgesic responses to endogenous and exogenous opioids; and (2) the involvement of the opioid system in the antiallodynic effect of TGF-ß1. BAMBI-KO mice were subjected to neuropathic pain by sciatic nerve crash injury (SNI). Gene (PCR) and protein (Western blot) expressions of µ- and δ-opioid receptors were determined in the spinal cord. The inhibitory effects of agonists on the adenylyl cyclase pathway were investigated. Two weeks after SNI, wild-type mice developed mechanical allodynia and the functionality of µ-opioid receptors was reduced. By this time, BAMBI-KO mice were protected against allodynia and exhibited increased expression and function of opioid receptors. Four weeks after SNI, when mice of both genotypes had developed neuropathic pain, the analgesic responses induced by morphine and RB101 (an inhibitor of enkephalin-degrading enzymes, which increases the synaptic levels of enkephalins) were enhanced in BAMBI-KO mice. Similar results were obtained in the formalin-induced chemical-inflammatory pain model. Subcutaneous TGF-ß1 infusion prevented pain development after SNI. The antiallodynic effect of TGF-ß1 was naloxone-sensitive. In conclusion, modulation of the endogenous opioid system by TGF-ß signaling improves the analgesic effectiveness of exogenous and endogenous opioids under pathological pain conditions.

Cocaine dysregulates opioid gating of GABA neurotransmission in the ventral pallidum.

The ventral pallidum (VP) is a target of dense nucleus accumbens projections. Many of these projections coexpress GABA and the neuropeptide enkephalin, a δ and µ opioid receptor (MOR) ligand. Of these two, the MOR in the VP is known to be involved in reward-related behaviors, such as hedonic responses to palatable food, alcohol intake, and reinstatement of cocaine seeking. Stimulating MORs in the VP decreases extracellular GABA, indicating that the effects of MORs in the VP on cocaine seeking are via modulating GABA neurotransmission. Here, we use whole-cell patch-clamp on a rat model of withdrawal from cocaine self-administration to test the hypothesis that MORs presynaptically regulate GABA transmission in the VP and that cocaine withdrawal changes the interaction between MORs and GABA. We found that in cocaine-extinguished rats pharmacological activation of MORs no longer presynaptically inhibited GABA release, whereas blocking the MORs disinhibited GABA release. Moreover, MOR-dependent long-term depression of GABA neurotransmission in the VP was lost in cocaine-extinguished rats. Last, GABA neurotransmission was found to be tonically suppressed in cocaine-extinguished rats. These substantial synaptic changes indicated that cocaine was increasing tone on MOR receptors. Accordingly, increasing endogenous tone by blocking the enzymatic degradation of enkephalin inhibited GABA neurotransmission in yoked saline rats but not in cocaine-extinguished rats. In conclusion, our results indicate that following withdrawal from cocaine self-administration enkephalin levels in the VP are elevated and the opioid modulation of GABA neurotransmission is impaired. This may contribute to the difficulties withdrawn addicts experience when trying to resist relapse.

Randomised, double-blind, placebo-controlled, dose-escalating phase I study of QGC001, a centrally acting aminopeptidase a inhibitor prodrug.

BACKGROUND AND OBJECTIVES: Inhibition of brain aminopeptidase A (APA), which converts angiotensin II into angiotensin III, has emerged as a novel antihypertensive treatment, as demonstrated in several experimental animal models. QGC001 (originally named RB150) is a prodrug of the specific and selective APA inhibitor EC33, and as such it is the prototype of a new class of centrally acting antihypertensive agents. Given by the oral route in hypertensive rats, it enters the brain and generates EC33, which blocks the brain renin-angiotensin system activity and normalises blood pressure. The aim of the present study was to evaluate the safety, pharmacokinetics and pharmacodynamic effects of QGC001 in humans. DESIGN AND METHODS: Fifty-six healthy male volunteers were randomly assigned to receive in double-blind and fasted conditions single oral doses of 10, 50, 125, 250, 500, 750, 1,000 and 1,250 mg of QGC001 (n = 6/dose) or placebo (n = 2/dose). We measured plasma and urine concentrations of both QGC001 and EC33 by liquid chromatography-tandem mass spectrometry, plasma renin concentrations (PRC), plasma and free urine aldosterone (PAldo and UAldo), plasma copeptine (PCop), and plasma and urine cortisol (PCort and UCort) concentrations, and supine systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) at various time points. RESULTS: All doses of QGC001 were clinically and biologically well-tolerated. Peak plasma concentrations (Cmax) of QGC001 and EC33 increased linearly with the dose, with a median time to reach Cmax (tmax) of 1.5 h for QGC001 and 3.0 h for EC33. The median plasma elimination half-life of QGC001 was 1.6 h consistently throughout doses. Urinary excretion of QGC001 and EC33 was below 2% of the administered dose. When compared with placebo, QGC001 did not significantly change PRC, PAldo, UAldo, PCop, PCort or UCort. No significant change was observed for supine HR, SBP and DBP in any treatment group. CONCLUSION: Single oral administration of QGC001 up to 1,250 mg in healthy volunteers was well-tolerated. Following oral administration, QGC001 is absorbed via the gastrointestinal tract and converted partially into its active metabolite EC33 in plasma. As in animal experiments, in normotensive subjects QGC001 had no effect on the systemic renin-angiotensin-aldosterone parameters and on PCop concentrations, a marker of vasopressin release. In normotensive subjects, a single dose of QCG001 had no effect on SBP, DBP or HR. These data support further evaluation of multiple oral doses of QGC001 in human volunteers and its clinical efficacy in hypertensive patients.

A sensitive fluorigenic substrate for selective in vitro and in vivo assay of leukotriene A4 hydrolase activity.

Leukotriene A4 hydrolase (LTA4H) is a bifunctional zinc-dependent metalloprotease bearing both an epoxide hydrolase, producing the pro-inflammatory LTB4 leukotriene, and an aminopeptidase activity, whose physiological relevance has long been ignored. Distinct substrates are commonly used for each activity, although none is completely satisfactory; LTA4, substrate for the hydrolase activity, is unstable and inactivates the enzyme, whereas aminoacids ß-naphthylamide and para-nitroanilide, used as aminopeptidase substrates, are poor and nonselective. Based on the three-dimensional structure of LTA4H, we describe a new, specific, and high-affinity fluorigenic substrate, PL553 [L-(4-benzoyl)phenylalanyl-ß-naphthylamide], with both in vitro and in vivo applications. PL553 possesses a catalytic efficiency (k(cat)/K(m)) of 3.8±0.5×104 M⁻¹ s⁻¹ using human recombinant LTA4H and a limit of detection and quantification of less than 1 to 2 ng. The PL553 assay was validated by measuring the inhibitory potency of known LTA4H inhibitors and used to characterize new specific amino-phosphinic inhibitors. The LTA4H inhibition measured with PL553 in mouse tissues, after intravenous administration of inhibitors, was also correlated with a reduction in LTB4 levels. This authenticates the assay as the first allowing the easy measurement of endogenous LTA4H activity and in vitro specific screening of new LTA4H inhibitors.

Comparison of fluorigenic peptide substrates PL50, SNAPTide, and BoTest A/E for BoNT/A detection and quantification: exosite binding confers high-assay sensitivity.

Detection and quantification of low doses of botulinum toxin serotype A (BoNT/A) in medicinal preparations require precise and sensitive methods. With mounting pressure from governmental authorities to replace the mouse LD50 assay, interest in alternative methods such as the endopeptidase assay, quantifying the toxin active moiety, is growing. Using internal collision-induced fluorescence quenching, Pharmaleads produced peptides encompassing the SNAP-25 cleavage site: a 17-mer (PL63) and a 48-mer (PL50) reaching the previously identified α-exosite, with PL50 showing higher apparent affinity for BoNT/A. Peptide mapping experiments revealed that this increased affinity is mainly due to a connecting peptide sequence between the N-terminus of PL63 and the α-exosite, identifying a new cooperative exosite on BoNT/A. Other endopeptidase substrates available, including SNAPTide and BoTest A/E, are both based on fluorescent resonance energy transfer (FRET) technology. To compare these assays, their limits of detection and quantification were determined using light chain or 150-kDa BoNT/A. Detection limits of PL50 and BoTest were over 100 times better than those using SNAPtide in standard conditions. Although the BoTest possessed a detection limit around 0.2 pM for either BoNT/A form, its quantification limit (9.7 pM) using purified BoNT/A was 12 times inferior to PL50, estimated at 0.8 pM, suitable for medicinal preparation quantification.

Pain inhibition by blocking leukocytic and neuronal opioid peptidases in peripheral inflamed tissue.

Inflammatory pain can be controlled by endogenous opioid peptides. Here we blocked the degradation of opioids in peripheral injured tissue to locally augment this physiological system. In rats with hindpaw inflammation, inhibitors of aminopeptidase N (APN; bestatin) or neutral endopeptidase (NEP; thiorphan), and a dual inhibitor, NH(2)-CH-Ph-P(O)(OH)CH(2)-CH-CH(2)Ph(p-Ph)-CONH-CH-CH(3)-COOH (P8B), were applied to injured paws. Combined bestatin (1.25-5 mg)/thiorphan (0.2-0.8 mg) or P8B (0.0625-1 mg) alone elevated mechanical nociceptive thresholds to 307 and 227% of vehicle-treated controls, respectively. This analgesia was abolished by antibodies to methionine-enkephalin, leucine-enkephalin, and dynorphin A 1-17, by peripherally restricted and by selective µ-, δ-, and κ-opioid receptor antagonists. Flow cytometry and photospectrometry revealed expression and metabolic activity of APN and NEP on macrophages, granulocytes, and sciatic nerves from inflamed tissue. Radioimmunoassays showed that inhibition of leukocytic APN and NEP by bestatin (5-500 µM)/thiorphan (1-100 µM) combinations or by P8B (1-100 µM) prevented the degradation of enkephalins. Blockade of neuronal peptidases by bestatin (0.5-10 mM)/thiorphan (0.1-5 mM) or by P8B (0.1-10 mM) additionally hindered dynorphin A 1-17 catabolism. Thus, leukocytes and peripheral nerves are important sources of APN and NEP in inflamed tissue, and their blockade promotes peripheral opioid analgesia.

Central antihypertensive effects of orally active aminopeptidase A inhibitors in spontaneously hypertensive rats.

Brain renin-angiotensin system hyperactivity has been implicated in the development and maintenance of hypertension. We reported previously in the brain that aminopeptidase A and aminopeptidase N are involved in the metabolism of angiotensin II and angiotensin III, respectively. By using in vivo specific and selective aminopeptidase A and aminopeptidase N inhibitors, we showed that angiotensin III is one of the main effector peptides of the brain renin-angiotensin system, exerting a tonic stimulatory control more than blood pressure in hypertensive rats. Aminopeptidase A, the enzyme generating brain angiotensin III, thus represents a potential target for the treatment of hypertension. We demonstrated here the antihypertensive effects of RB150, a prodrug of the specific and selective aminopeptidase A inhibitor, EC33, in spontaneously hypertensive rats, a model of human essential hypertension. Oral administration of RB150 in conscious spontaneously hypertensive rats inhibited brain aminopeptidase A activity, demonstrating the central bioavailability of RB150 and its ability to generate EC33 into the brain. Oral RB150 treatment dose-dependently reduced blood pressure in spontaneously hypertensive rats with an ED(50) of 30 mg/kg, lasting for several hours. This decrease in blood pressure is partly attributed to a decrease in sympathetic tone, reducing vascular resistance. This treatment did not modify systemic renin-angiotensin system activity. Concomitant oral administration of RB150 with a systemic renin-angiotensin system blocker, enalapril, potentiated the RB150-induced blood pressure decrease achieved in <2 hours. Thus, RB150 may be the prototype of a new class of centrally active antihypertensive agents that might be used in combination with classic systemic renin-angiotensin system blockers to improve blood pressure control.

Inhibiting the breakdown of endogenous opioids and cannabinoids to alleviate pain.

Chronic pain remains unsatisfactorily treated, and few novel painkillers have reached the market in the past century. Increasing the levels of the main endogenous opioid peptides - enkephalins - by inhibiting their two inactivating ectopeptidases, neprilysin and aminopeptidase N, has analgesic effects in various models of inflammatory and neuropathic pain. Stemming from the same pharmacological concept, fatty acid amide hydrolase (FAAH) inhibitors have also been found to have analgesic effects in pain models by preventing the breakdown of endogenous cannabinoids. Dual enkephalinase inhibitors and FAAH inhibitors are now in early-stage clinical trials. In this Review, we compare the effects of these two potential classes of novel analgesics and describe the progress in their rational design. We also consider the challenges in their clinical development and opportunities for combination therapies.