Discovery of ( R)-8-(6-Methyl-4-oxo-1,4,5,6-tetrahydropyrrolo[3,4- b]pyrrol-2-yl)-3-(1-methylcyclopropyl)-2-((1-methylcyclopropyl)amino)quinazolin-4(3 H)-one, a Potent and Selective Pim-1/2 Kinase Inhibitor for Hematological Malignancies

Pim kinases are a family of constitutively active serine/threonine kinases that are partially redundant and regulate multiple pathways important for cell growth and survival. In human disease, high expression of the three Pim isoforms has been implicated in the progression of hematopoietic and solid tumor cancers, which suggests that Pim kinase inhibitors could provide patients with therapeutic benefit. Herein, we describe the structure-guided optimization of a series of quinazolinone-pyrrolodihydropyrrolone analogs leading to the identification of potent pan-Pim inhibitor 28 with improved potency, solubility, and drug-like properties. Compound 28 demonstrated on-target Pim activity in an in vivo pharmacodynamic assay with significant inhibition of BAD phosphorylation in KMS-12-BM multiple myeloma tumors for 16 h postdose. In a 2-week mouse xenograft model, daily dosing of compound 28 resulted in 33% tumor regression at 100 mg/kg.

Small Molecule Disruptors of the Glucokinase-Glucokinase Regulatory Protein Interaction: 5. A Novel Aryl Sulfone Series, Optimization Through Conformational Analysis

The glucokinase-glucokinase regulatory protein (GK-GKRP) complex plays an important role in controlling glucose homeostasis in the liver. We have recently disclosed a series of arylpiperazines as in vitro and in vivo disruptors of the GK-GKRP complex with efficacy in rodent models of type 2 diabetes mellitus (T2DM). Herein, we describe a new class of aryl sulfones as disruptors of the GK-GKRP complex, where the central piperazine scaffold has been replaced by an aromatic group. Conformational analysis and exploration of the structure-activity relationships of this new class of compounds led to the identification of potent GK-GKRP disruptors. Further optimization of this novel series delivered thiazole sulfone 93, which was able to disrupt the GK-GKRP interaction in vitro and in vivo and, by doing so, increases cytoplasmic levels of unbound GK.

Small molecule disruptors of the glucokinase-glucokinase regulatory protein interaction: 4. Exploration of a novel binding pocket

Structure-activity relationship investigations conducted at the 5-position of the N-pyridine ring of a series of N-arylsulfonyl-N'-2-pyridinyl-piperazines led to the identification of a novel bis-pyridinyl piperazine sulfonamide (51) that was a potent disruptor of the glucokinase-glucokinase regulatory protein (GK-GKRP) interaction. Analysis of the X-ray cocrystal of compound 51 bound to hGKRP revealed that the 3-pyridine ring moiety occupied a previously unexplored binding pocket within the protein. Key features of this new binding mode included forming favorable contacts with the top face of the Ala27-Val28-Pro29 ("shelf region") as well as an edge-to-face interaction with the Tyr24 side chain. Compound 51 was potent in both biochemical and cellular assays (IC50=0.005 μM and EC50=0.205 μM, respectively) and exhibited acceptable pharmacokinetic properties for in vivo evaluation. When administered to db/db mice (100 mg/kg, po), compound 51 demonstrated a robust pharmacodynamic effect and significantly reduced blood glucose levels up to 6 h postdose.

Small molecule disruptors of the glucokinase-glucokinase regulatory protein interaction: 3. Structure-activity relationships within the aryl carbinol region of the N-arylsulfonamido-N'-arylpiperazine series

We have recently reported a novel approach to increase cytosolic glucokinase (GK) levels through the binding of a small molecule to its endogenous inhibitor, glucokinase regulatory protein (GKRP). These initial investigations culminated in the identification of 2-(4-((2S)-4-((6-amino-3-pyridinyl)sulfonyl)-2-(1-propyn-1-yl)-1-piperazinyl)phenyl)-1,1,1,3,3,3-hexafluoro-2-propanol (1, AMG-3969), a compound that effectively enhanced GK translocation and reduced blood glucose levels in diabetic animals. Herein we report the results of our expanded SAR investigations that focused on modifications to the aryl carbinol group of this series. Guided by the X-ray cocrystal structure of compound 1 bound to hGKRP, we identified several potent GK-GKRP disruptors bearing a diverse set of functionalities in the aryl carbinol region. Among them, sulfoximine and pyridinyl derivatives 24 and 29 possessed excellent potency as well as favorable PK properties. When dosed orally in db/db mice, both compounds significantly lowered fed blood glucose levels (up to 58%).

Optimization of potency and pharmacokinetic properties of tetrahydroisoquinoline transient receptor potential melastatin 8 (TRPM8) antagonists

Transient receptor potential melastatin 8 (TRPM8) is a nonselective cation channel expressed in a subpopulation of sensory neurons in the peripheral nervous system. TRPM8 is the predominant mammalian cold temperature thermosensor and is activated by cold temperatures ranging from 8 to 25 °C and cooling compounds such as menthol or icilin. TRPM8 antagonists are being pursued as potential therapeutics for treatment of pain and bladder disorders. This manuscript outlines new developments in the SAR of a lead series of 1,2,3,4-tetrahydroisoquinoline derivatives with emphasis on strategies to improve pharmacokinetic properties and potency. Selected compounds were profiled in two TRPM8 target-specific in vivo coverage models in rats (the icilin-induced wet dog shake model and the cold pressor test). Compound 45 demonstrated robust efficacy in both pharmacodynamic models with ED90 values <3 mg/kg.

Small molecule disruptors of the glucokinase-glucokinase regulatory protein interaction: 2. Leveraging structure-based drug design to identify analogues with improved pharmacokinetic profiles

In the previous report , we described the discovery and optimization of novel small molecule disruptors of the GK-GKRP interaction culminating in the identification of 1 (AMG-1694). Although this analogue possessed excellent in vitro potency and was a useful tool compound in initial proof-of-concept experiments, high metabolic turnover limited its advancement. Guided by a combination of metabolite identification and structure-based design, we have successfully discovered a potent and metabolically stable GK-GKRP disruptor (27, AMG-3969). When administered to db/db mice, this compound demonstrated a robust pharmacodynamic response (GK translocation) as well as statistically significant dose-dependent reductions in fed blood glucose levels.

Selective class I phosphoinositide 3-kinase inhibitors: optimization of a series of pyridyltriazines leading to the identification of a clinical candidate, AMG 511

The phosphoinositide 3-kinase family catalyzes the phosphorylation of phosphatidylinositol-4,5-diphosphate to phosphatidylinositol-3,4,5-triphosphate, a secondary messenger which plays a critical role in important cellular functions such as metabolism, cell growth, and cell survival. Our efforts to identify potent, efficacious, and orally available phosphatidylinositol 3-kinase (PI3K) inhibitors as potential cancer therapeutics have resulted in the discovery of 4-(2-((6-methoxypyridin-3-yl)amino)-5-((4-(methylsulfonyl)piperazin-1-yl)methyl)pyridin-3-yl)-6-methyl-1,3,5-triazin-2-amine (1). In this paper, we describe the optimization of compound 1, which led to the design and synthesis of pyridyltriazine 31, a potent pan inhibitor of class I PI3Ks with a superior pharmacokinetic profile. Compound 31 was shown to potently block the targeted PI3K pathway in a mouse liver pharmacodynamic model and inhibit tumor growth in a U87 malignant glioma glioblastoma xenograft model. On the basis of its excellent in vivo efficacy and pharmacokinetic profile, compound 31 was selected for further evaluation as a clinical candidate and was designated AMG 511.

Abstract 2805: In vitro characterization of AMG 511, a potent and selective class I PI3K inhibitor for the treatment of cancer

The PI3K signaling pathway is frequently activated in cancer and has been implicated in many aspects of tumor growth and survival. Inhibition of this pathway represents a potential therapeutic path for the treatment of cancer. This study evaluated the in vitro characteristics of AMG 511, a potent and selective pan class I PI3K inhibitor exhibiting IC50 values of 8, 11, 2, and 6 nM against the PI3K β, α, β, and ≤ isoforms respectively. AMG 511 was shown to be inactive against members of the closely related phosphoinositide 3 kinase related kinases (PIKK) family of kinases and did not inhibit mTOR, hVPS34, PI4Kα or PI4Kα in-vitro (IC50 values &gt; 1 μM). In addition, AMG 511 was inactive against a majority of protein kinases (372) in the human kinome as measured by in-vitro binding assays. AMG 511 inhibited PI3K pathway signaling in U87 MG glioblastoma cells as determined by dose-dependent reduction in AKT S473 phosphorylation (IC50 = 4 nM). AKT inhibition resulted in a concomitant reduction in PRAS40 phosphorylation (IC50 = 23 nM), a downstream effector of AKT. Reduced phosphorylation of mTORC1 substrates p70S6K (IC50 = 30 nM) and S6 (IC50 = 70 nM) but not 4EBP1 (T37/46), was also detected in U87 MG cells, suggesting that upstream blockade of PI3K pathway signaling with AMG 511 treatment leads to a selective reduction in downstream mTORC1 activity. Given the well documented role of mTORC1 in cap-dependent translation we profiled AMG 511 in a methionine-analog incorporation assay in U87 MG cells. However, no significant inhibition of bulk translation was observed following treatment with AMG 511 in U87 MG cells. Treatment of U87 MG cells with AMG 511 revealed a pronounced G1 arrest with a concurrent reduction in BrdU+ cells, detectable within 8 hours of treatment. This anti-proliferative effect was fully reversible by 18 hours following washout. In line with these anti-proliferative effects, reduced cyclin D1 levels and elevated p27 levels were detected within 4 hours of treatment. Minimal cell killing effects were detected with AMG 511 treatment in U87 MG cells as measured by induction of cleaved caspase-3 and DNA content &lt; 2N. AMG 511 was profiled across a large panel of tumor cell lines encompassing several tumor types including breast and lung. A majority of the cell lines tested exhibited sensitivity to AMG 511 with a subset exhibiting evidence for cell death upon treatment with AMG 511. Breast cancer cell lines harboring activating mutations in PI3Kα, loss of PTEN, or amplification of Her2 tended to show greater sensitivity to AMG 511 treatment. In conclusion, AMG 511 is a potent and selective pan class I PI3K inhibitor, capable of inhibiting PI3K signaling and inducing robust anti-proliferative effects via a G1 arrest in many tumor cell lines, with evidence of cell killing in a subset of lines.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2805. doi:1538-7445.AM2012-2805

Structure-based design of novel class II c-Met inhibitors: 2. SAR and kinase selectivity profiles of the pyrazolone series

As part of our effort toward developing an effective therapeutic agent for c-Met-dependent tumors, a pyrazolone-based class II c-Met inhibitor, N-(4-((6,7-dimethoxyquinolin-4-yl)oxy)-3-fluorophenyl)-1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxamide (1), was identified. Knowledge of the binding mode of this molecule in both c-Met and VEGFR-2 proteins led to a novel strategy for designing more selective analogues of 1. Along with detailed SAR information, we demonstrate that the low kinase selectivity associated with class II c-Met inhibitors can be improved significantly. This work resulted in the discovery of potent c-Met inhibitors with improved selectivity profiles over VEGFR-2 and IGF-1R that could serve as useful tools to probe the relationship between kinase selectivity and in vivo efficacy in tumor xenograft models. Compound 59e (AMG 458) was ultimately advanced into preclinical safety studies.

Fused piperidines as a novel class of potent and orally available transient receptor potential melastatin type 8 (TRPM8) antagonists

The transient receptor potential melastatin type 8 (TRPM8) is a nonselective cation channel primarily expressed in a subpopulation of sensory neurons that can be activated by a wide range of stimuli, including menthol, icilin, and cold temperatures (<25 °C). Antagonism of TRPM8 is currently under investigation as a new approach for the treatment of pain. As a result of our screening efforts, we identified tetrahydrothienopyridine 4 as an inhibitor of icilin-induced calcium influx in CHO cells expressing recombinant rat TRPM8. Exploration of the structure-activity relationships of 4 led to the identification of a potent and orally bioavailable TRPM8 antagonist, tetrahydroisoquinoline 87. Compound 87 demonstrated target coverage in vivo after oral administration in a rat pharmacodynamic model measuring the prevention of icilin-induced wet-dog shakes (WDS).

Structure-activity relationships of phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitors: investigations of various 6,5-heterocycles to improve metabolic stability

N-(6-(6-Chloro-5-(4-fluorophenylsulfonamido)pyridin-3-yl)benzo[d]thiazol-2-yl)acetamide (1) is a potent and efficacious inhibitor of PI3Kα and mTOR in vitro and in vivo. However, in hepatocyte and in vivo metabolism studies, 1 was found to undergo deacetylation on the 2-amino substituent of the benzothiazole. As an approach to reduce or eliminate this metabolic deacetylation, a variety of 6,5-heterocyclic analogues were examined as an alternative to the benzothiazole ring. Imidazopyridazine 10 was found to have similar in vitro potency and in vivo efficacy relative to 1, while only minimal amounts of the corresponding deacetylated metabolite of 10 were observed in hepatocytes.

Phospshoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitors: discovery and structure-activity relationships of a series of quinoline and quinoxaline derivatives

The phosphoinositide 3-kinase (PI3K) family catalyzes the ATP-dependent phosphorylation of the 3'-hydroxyl group of phosphatidylinositols and plays an important role in cell growth and survival. There is abundant evidence demonstrating that PI3K signaling is dysregulated in many human cancers, suggesting that therapeutics targeting the PI3K pathway may have utility for the treatment of cancer. Our efforts to identify potent, efficacious, and orally available PI3K/mammalian target of rapamycin (mTOR) dual inhibitors resulted in the discovery of a series of substituted quinolines and quinoxalines derivatives. In this report, we describe the structure-activity relationships, selectivity, and pharmacokinetic data of this series and illustrate the in vivo pharmacodynamic and efficacy data for a representative compound.

Discovery and optimization of a series of benzothiazole phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitors

Phosphoinositide 3-kinase α (PI3Kα) is a lipid kinase that plays a key regulatory role in several cellular processes. The mutation or amplification of this kinase in humans has been implicated in the growth of multiple tumor types. Consequently, PI3Kα has become a target of intense research for drug discovery. Our studies began with the identification of benzothiazole compound 1 from a high throughput screen. Extensive SAR studies led to the discovery of sulfonamide 45 as an early lead, based on its in vitro cellular potency. Subsequent modifications of the central pyrimidine ring dramatically improved enzyme and cellular potency and led to the identification of chloropyridine 70. Further arylsulfonamide SAR studies optimized in vitro clearance and led to the identification of 82 as a potent dual inhibitor of PI3K and mTOR. This molecule exhibited potent enzyme and cell activity, low clearance, and high oral bioavailability. In addition, compound 82 demonstrated tumor growth inhibition in U-87 MG, A549, and HCT116 tumor xenograft models.

Structure-activity relationship (SAR) investigations of tetrahydroquinolines as BKCa agonists

The membrane bound large-conductance, calcium-activated potassium channel (BKCa) is an important regulator of neuronal activity. Here we describe the identification and structure-activity relationship of a novel class of potent tetrahydroquinoline BKCa agonists. An example from this class of BKCa agonists was shown to depress the spontaneous neuronal discharges in an electrophysiological model of migraine.

The transient receptor potential vanilloid-1 channel in thermoregulation: a thermosensor it is not

The development of antagonists of the transient receptor potential vanilloid-1 (TRPV1) channel as pain therapeutics has revealed that these compounds cause hyperthermia in humans. This undesirable on-target side effect has triggered a surge of interest in the role of TRPV1 in thermoregulation and revived the hypothesis that TRPV1 channels serve as thermosensors. We review literature data on the distribution of TRPV1 channels in the body and on thermoregulatory responses to TRPV1 agonists and antagonists. We propose that two principal populations of TRPV1-expressing cells have connections with efferent thermoeffector pathways: 1) first-order sensory (polymodal), glutamatergic dorsal-root (and possibly nodose) ganglia neurons that innervate the abdominal viscera and 2) higher-order sensory, glutamatergic neurons presumably located in the median preoptic hypothalamic nucleus. We further hypothesize that all thermoregulatory responses to TRPV1 agonists and antagonists and thermoregulatory manifestations of TRPV1 desensitization stem from primary actions on these two neuronal populations. Agonists act primarily centrally on population 2; antagonists act primarily peripherally on population 1. We analyze what roles TRPV1 might play in thermoregulation and conclude that this channel does not serve as a thermosensor, at least not under physiological conditions. In the hypothalamus, TRPV1 channels are inactive at common brain temperatures. In the abdomen, TRPV1 channels are tonically activated, but not by temperature. However, tonic activation of visceral TRPV1 by nonthermal factors suppresses autonomic cold-defense effectors and, consequently, body temperature. Blockade of this activation by TRPV1 antagonists disinhibits thermoeffectors and causes hyperthermia. Strategies for creating hyperthermia-free TRPV1 antagonists are outlined. The potential physiological and pathological significance of TRPV1-mediated thermoregulatory effects is discussed.

Delayed administration of a potent cyclin dependent kinase and glycogen synthase kinase 3 beta inhibitor produces long-term neuroprotection in a hypoxia-ischemia model of brain injury

We compared the neuroprotective efficacy of a potent and CNS-penetrant cyclin dependent kinase (CDK) and glycogen synthase kinase 3 beta (GSK3beta) inhibitor (Compound 1) in juvenile (postnatal day 21; P21) and adult C57Bl/6 mice (postnatal day 60; P60) using a model of hypoxic-ischemic brain injury (HI). Neuronal cell counts and density measures from brain sections stained with Cresyl Violet revealed that exposure of P21 mice to 60 min of HI resulted in extensive damage to the ipsilateral cornu ammonis 1 (CA1) region of the hippocampus (40% cell loss) and striatum (30% cell loss) 7 days later. Exposure of P60 mice to 40 min of HI produced a similar pattern of cell loss. Intraperitoneal administration of Compound 1 (3 mg/kg) 1, 5 and 9 h after 60 min of HI did not reduce brain injury in P21 mice relative to vehicle controls. By contrast, in P60 mice, this treatment significantly decreased cell loss in the ipsilateral hippocampus (10% cell loss) and striatum (15% loss) relative to vehicle controls. Terminal uridine deoxynucleotidyl transferase (TUNNEL) positive cell counts and infarct volume were also substantially reduced in P60 mice treated with Compound 1. A motor coordination test performed twice weekly until 5 weeks post-HI confirmed that Compound 1 produced long lasting functional recovery. Our results indicate that Compound 1 produced long lasting neuroprotective effects in adult but not juvenile mice suggesting that inhibition of the CDKs and GSK3beta plays a distinct neuroprotective role in the juvenile and adult brain.

Structure–activity relationship (SAR) investigations of substituted imidazole analogs as TRPV1 antagonists

A novel series of 4,5-biarylimidazoles as TRPV1 antagonists were designed based on the previously reported 4,6-disubstituted benzimidazole series. The analogs were evaluated for their ability to block capsaicin- or acid-induced calcium influx in TRPV1-expressing CHO cells. These studies led to the identification of a highly potent and orally bioavailable TRPV1 antagonist, imidazole 33.

Nonthermal activation of transient receptor potential vanilloid-1 channels in abdominal viscera tonically inhibits autonomic cold-defense effectors

An involvement of the transient receptor potential vanilloid (TRPV) 1 channel in the regulation of body temperature (T(b)) has not been established decisively. To provide decisive evidence for such an involvement and determine its mechanisms were the aims of the present study. We synthesized a new TRPV1 antagonist, AMG0347 [(E)-N-(7-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl)-3-(2-(piperidin-1-yl)-6-(trifluoromethyl)pyridin-3-yl)acrylamide], and characterized it in vitro. We then found that this drug is the most potent TRPV1 antagonist known to increase T(b) of rats and mice and showed (by using knock-out mice) that the entire hyperthermic effect of AMG0347 is TRPV1 dependent. AMG0347-induced hyperthermia was brought about by one or both of the two major autonomic cold-defense effector mechanisms (tail-skin vasoconstriction and/or thermogenesis), but it did not involve warmth-seeking behavior. The magnitude of the hyperthermic response depended on neither T(b) nor tail-skin temperature at the time of AMG0347 administration, thus indicating that AMG0347-induced hyperthermia results from blockade of tonic TRPV1 activation by nonthermal factors. AMG0347 was no more effective in causing hyperthermia when administered into the brain (intracerebroventricularly) or spinal cord (intrathecally) than when given systemically (intravenously), which indicates a peripheral site of action. We then established that localized intra-abdominal desensitization of TRPV1 channels with intraperitoneal resiniferatoxin blocks the T(b) response to systemic AMG0347; the extent of desensitization was determined by using a comprehensive battery of functional tests. We conclude that tonic activation of TRPV1 channels in the abdominal viscera by yet unidentified nonthermal factors inhibits skin vasoconstriction and thermogenesis, thus having a suppressive effect on T(b).

Design and synthesis of quinolin-2(1H)-one derivatives as potent CDK5 inhibitors

Cyclin-dependent kinase 5 (CDK5) is a serine/threonine protein kinase and its deregulation is implicated in a number of neurodegenerative disorders such as Alzheimer's disease, amyotrophic lateral sclerosis, and ischemic stroke. Using active site homology modeling between CDK5 and CDK2, we explored several different chemical series of potent CDK5 inhibitors. In this report, we describe the design, synthesis, and CDK5 inhibitory activities of quinolin-2(1H)-one derivatives.

Structure-activity relationships of 3,4-dihydro-1H-quinazolin-2-one derivatives as potential CDK5 inhibitors

Cyclin-dependent kinase 5 (CDK5) is a serine/threonine kinase that plays a critical role in the early development of the nervous system. Deregulation of CDK5 is believed to contribute to the abnormal phosphorylation of various cellular substrates associated with neurodegenerative disorders such as Alzheimer's disease, amyotrophic lateral sclerosis, and ischemic stroke. Acyclic urea 3 was identified as a potent CDK5 inhibitor and co-crystallographic data of urea 3/CDK2 enzyme were used to design a novel series of 3,4-dihydroquinazolin-2(1H)-ones as CDK5 inhibitors. In this investigation we present our synthetic studies toward this series of compounds and discuss their biological relevance as CDK5 inhibitors.

Repeated administration of vanilloid receptor TRPV1 antagonists attenuates hyperthermia elicited by TRPV1 blockade

Capsaicin, the active ingredient in some pain-relieving creams, is an agonist of a nonselective cation channel known as the transient receptor potential vanilloid type 1 (TRPV1). The pain-relieving mechanism of capsaicin includes desensitization of the channel, suggesting that TRPV1 antagonism may be a viable pain therapy approach. In agreement with the above notion, several TRPV1 antagonists have been reported to act as antihyperalgesics. Here, we report the in vitro and in vivo characterization of a novel and selective TRPV1 antagonist, N-(4-[6-(4-trifluoromethyl-phenyl)-pyrimidin-4-yloxy]-benzothiazol-2-yl)-acetamide I (AMG 517), and compare its pharmacology with that of a closely related analog, tert-butyl-2-(6-([2-(acetylamino)-1,3-benzothiazol-4-yl]oxy)pyrimidin-4-yl)-5-(trifluoromethyl)phenylcarbamate (AMG8163). Both AMG 517 and AMG8163 potently and completely antagonized capsaicin, proton, and heat activation of TRPV1 in vitro and blocked capsaicin-induced flinch in rats in vivo. To support initial clinical investigations, AMG 517 was evaluated in a comprehensive panel of toxicology studies that included in vivo assessments in rodents, dogs, and monkeys. The toxicology studies indicated that AMG 517 was generally well tolerated; however, transient increases in body temperature (hyperthermia) were observed in all species after AMG 517 dosing. To further investigate this effect, we tested and showed that the antipyretic, acetaminophen, suppressed the hyperthermia caused by TRPV1 blockade. We also showed that repeated administration of TRPV1 antagonists attenuated the hyperthermia response, whereas the efficacy in capsaicin-induced flinch model was maintained. In conclusion, these studies suggest that the transient hyperthermia elicited by TRPV1 blockade may be manageable in the development of TRPV1 antagonists as therapeutic agents. However, the impact of TRPV1 antagonist-induced hyperthermia on their clinical utility is still unknown.

Novel Vanilloid Receptor-1 Antagonists: 1. Conformationally Restricted Analogues of trans-Cinnamides

The vanilloid receptor-1 (VR1 or TRPV1) is a member of the transient receptor potential (TRP) family of ion channels and plays a role as an integrator of multiple pain-producing stimuli. From a high-throughput screening assay, measuring calcium uptake in TRPV1-expressing cells, we identified an N-aryl trans-cinnamide (AMG9810, compound 9) that acts as a potent TRPV1 antagonist. We have demonstrated the antihyperalgesic properties of 9 in vivo and have also reported the discovery of novel, orally bioavailable cinnamides derived from this lead. Herein, we expand our investigations and describe the synthesis and biological evaluation of a series of conformationally constrained analogues of the s-cis conformer of compound 9. These investigations resulted in the identification of 4-amino- and 4-oxopyrimidine cores as suitable isosteric replacements for the trans-acrylamide moiety. The best examples from this series, pyrimidines 79 and 74, were orally bioavailable and exhibited potent antagonism of both rat (IC50 = 4.5 and 0.6 nM, respectively) and human TRPV1 (IC50 = 7.4 and 3.7 nM, respectively). In addition, compound 74 was shown to be efficacious at blocking a TRPV1-mediated physiological response in vivo in the capsaicin-induced hypothermia model in rats; however, it was ineffective at preventing thermal hyperalgesia induced by complete Freund's adjuvant in rats.

Novel Vanilloid Receptor-1 Antagonists: 2. Structure−Activity Relationships of 4-Oxopyrimidines Leading to the Selection of a Clinical Candidate

A series of novel 4-oxopyrimidine TRPV1 antagonists was evaluated in assays measuring the blockade of capsaicin or acid-induced influx of calcium into CHO cells expressing TRPV1. The investigation of the structure-activity relationships in the heterocyclic A-region revealed the optimum pharmacophoric elements required for activity in this series and resulted in the identification of subnanomolar TRPV1 antagonists. The most potent of these antagonists were thoroughly profiled in pharmacokinetic assays. Optimization of the heterocyclic A-region led to the design and synthesis of 23, a compound that potently blocked multiple modes of TRPV1 activation. Compound 23 was shown to be effective in a rodent "on-target" biochemical challenge model (capsaicin-induced flinch, ED50 = 0.33 mg/kg p.o.) and was antihyperalgesic in a model of inflammatory pain (CFA-induced thermal hyperalgesia, MED = 0.83 mg/kg, p.o.). Based on its in vivo efficacy and pharmacokinetic profile, compound 23 (N-{4-[6-(4-trifluoromethyl-phenyl)-pyrimidin-4-yloxy]-benzothiazol-2-yl}-acetamide; AMG 517) was selected for further evaluation in human clinical trials.

Novel Vanilloid Receptor-1 Antagonists: 3. The Identification of a Second-Generation Clinical Candidate with Improved Physicochemical and Pharmacokinetic Properties

Based on the previously reported clinical candidate, AMG 517 (compound 1), a series of related piperazinylpyrimidine analogues were synthesized and evaluated as antagonists of the vanilloid 1 receptor (VR1 or TRPV1). Optimization of in vitro potency and physicochemical and pharmacokinetic properties led to the discovery of (R)-N-(4-(6-(4-(1-(4-fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16p), a potent TRPV1 antagonist [rTRPV1(CAP) IC50 = 3.7 nM] with excellent aqueous solubility (>or=200 microg/mL in 0.01 N HCl) and a reduced half-life (rat t1/2 = 3.8 h, dog t1/2 = 2.7 h, monkey t1/2 = 3.2 h) as compared to AMG 517. In addition, compound 16p was shown to be efficacious at blocking a TRPV1-mediated physiological response in vivo (ED50 = 1.9 mg/kg, p.o. in the capsaicin-induced flinch model in rats) and was also effective at reducing thermal hyperalgesia induced by complete Freund's adjuvant in rats (MED = 1 mg/kg, p.o). Based on its improved overall profile, compound 16p (AMG 628) was selected as a second-generation candidate for further evaluation in human clinical trials as a potential new treatment for chronic pain.

Potent Nonpeptide Antagonists of the Bradykinin B1 Receptor: Structure−Activity Relationship Studies with Novel Diaminochroman Carboxamides

The bradykinin B1 receptor is induced following tissue injury and/or inflammation. Antagonists of this receptor have been studied as promising candidates for treatment of chronic pain. We have identified aryl sulfonamides containing a chiral chroman diamine moiety that are potent antagonists of the human B1 receptor. Our previously communicated lead, compound 2, served as a proof-of-concept molecule, but suffered from poor pharmacokinetic properties. With guidance from metabolic profiling, we performed structure-activity relationship studies and have identified potent analogs of 2. Variation of the sulfonamide moiety revealed a preference for 3- and 3,4-disubstituted aryl sulfonamides, while bulky secondary and tertiary amines were preferred at the benzylic amine position for potency at the B1 receptor. Modifying the beta-amino acid core of the molecule lead to the discovery of highly potent compounds with improved in vitro pharmacokinetic properties. The most potent analog at the human receptor, compound 38, was also active in a rabbit B1 receptor cellular assay. Furthermore, compound 38 displayed in vivo activity in two rabbit models, a pharmacodynamic model with a blood pressure readout and an efficacy model of inflammatory pain.

The vanilloid receptor TRPV1 is tonically activated in vivo and involved in body temperature regulation

The vanilloid receptor TRPV1 (transient receptor potential vanilloid 1) is a cation channel that serves as a polymodal detector of pain-producing stimuli such as capsaicin, protons (pH <5.7), and heat. TRPV1 antagonists block pain behaviors in rodent models of inflammatory, neuropathic, and cancer pain, suggesting their utility as analgesics. Here, we report that TRPV1 antagonists representing various chemotypes cause an increase in body temperature (hyperthermia), identifying a potential issue for their clinical development. Peripheral restriction of antagonists did not eliminate hyperthermia, suggesting that the site of action is predominantly outside of the blood-brain barrier. Antagonists that are ineffective against proton activation also caused hyperthermia, indicating that blocking capsaicin and heat activation of TRPV1 is sufficient to produce hyperthermia. All TRPV1 antagonists evaluated here caused hyperthermia, suggesting that TRPV1 is tonically activated in vivo and that TRPV1 antagonism and hyperthermia are not separable. TRPV1 antagonists caused hyperthermia in multiple species (rats, dogs, and monkeys), demonstrating that TRPV1 function in thermoregulation is conserved from rodents to primates. Together, these results indicate that tonic TRPV1 activation regulates body temperature.

Identification of a Nonpeptidic and Conformationally Restricted Bradykinin B1 Receptor Antagonist with Anti-Inflammatory Activity

We report the discovery of chroman 28, a potent and selective antagonist of human, nonhuman primate, rat, and rabbit bradykinin B1 receptors (0.4-17 nM). At 90 mg/kg s.c., 28 decreased plasma extravasation in two rodent models of inflammation. A novel method to calculate entropy is introduced and ascribed approximately 30% of the gained affinity between "flexible" 4 (Ki = 132 nM) and "rigid" 28 (Ki = 0.77 nM) to decreased conformational entropy.

Design of Potent, Orally Available Antagonists of the Transient Receptor Potential Vanilloid 1. Structure−Activity Relationships of 2-Piperazin-1-yl-1H-benzimidazoles

The vanilloid receptor-1 (VR1 or TRPV1) is a membrane-bound, nonselective cation channel that is predominantly expressed by peripheral neurons sensing painful stimuli. TRPV1 antagonists produce antihyperalgesic effects in animal models of inflammatory and neuropathic pain. Herein, we describe the synthesis and the structure-activity relationships of a series of 2-(4-pyridin-2-ylpiperazin-1-yl)-1H-benzo[d]imidazoles as novel TRPV1 antagonists. Compound 46ad was among the most potent analogues in this series. This compound was orally bioavailable in rats and was efficacious in blocking capsaicin-induced flinch in rats in a dose-dependent manner. Compound 46ad also reversed thermal hyperalgesia in a model of inflammatory pain, which was induced by complete Freund's adjuvant (CFA).

Synthesis and evaluation of thiazole carboxamides as vanilloid receptor 1 (TRPV1) antagonists

A thiazole derivative, 2-(2,6-dichlorobenzyl)-N-(4-isopropylphenyl) thiazole-4-carboxamide (1), was identified as a TRPV1 antagonist. We synthesized various thiazole analogs and evaluated them for their ability to block capsaicin- or acid-induced calcium influx in TRPV1-expressing CHO cells. The IC(50) values of the most potent antagonists were ca. 0.050microM in these assays.

Proton Activation Does Not Alter Antagonist Interaction with the Capsaicin-Binding Pocket of TRPV1

Vanilloid receptor 1 (TRPV1) is activated by chemical ligands (e.g., capsaicin and protons) and heat. In this study, we show that (2E)-3-[2-piperidin-1-yl-6-(trifluoromethyl)pyridin-3-yl]-N-quinolin-7-ylacrylamide (AMG6880), 5-chloro-6-[(3R)-3-methyl-4-[6-(trifluoromethyl)-4-(3,4,5-trifluorophenyl)-1H-benzimidazol-2-yl]piperazin-1-yl]pyridin-3-yl)methanol (AMG7472), and N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carboxamide (BCTC) are potent antagonists of rat TRPV1 activation by either capsaicin or protons (pH 5) (defined here as group A antagonists), whereas (2E)-3-(6-tert-butyl-2-methylpyridin-3-yl)-N-(1H-indol-6-yl)acrylamide (AMG0610), capsazepine, and (2E)-3-(4-chlorophenyl)-N-(3-methoxyphenyl)acrylamide (SB-366791) are antagonists of capsaicin, but not proton, activation (defined here as group B antagonists). By using capsaicin-sensitive and insensitive rabbit TRPV1 channels, we show that antagonists require the same critical molecular determinants located in the transmembrane domain 3/4 region to block both capsaicin and proton activation, suggesting the presence of a single binding pocket. To determine whether the differential pharmacology is a result of proton activation-induced conformational changes in the capsaicin-binding pocket that alter group B antagonist affinities, we have developed a functional antagonist competition assay. We hypothesized that if group B antagonists bind at the same or an overlapping binding pocket of TRPV1 as group A antagonists, and proton activation does not alter the binding pocket, then group B antagonists should compete with and prevent group A antagonism of TRPV1 activation by protons. Indeed, we found that each of the group B antagonists competed with and prevented BCTC, AMG6880 or AMG7472 antagonism of rat TRPV1 activation by protons with pA2 values similar to those for blocking capsaicin, indicating that proton activation does not alter the conformation of the TRPV1 capsaicin-binding pocket. In conclusion, group A antagonists seem to lock the channel conformation in the closed state, blocking both capsaicin and proton activation.

Melanocortin subtype-4 receptor agonists containing a piperazine core with substituted aryl sulfonamides

The biological activity for a set of melanocortin-4 receptor (MC4R) agonists containing a piperazine core with an ortho-substituted aryl sulfonamide is described. Compounds from this set had binding and functional activities at MC4R less than 30 nM. The most selective compound in this series was >25,000-fold more potent at MC4R than MC3R, and 490-fold more potent at MC4R than MC5R. This compound also reduced food intake after oral dosing at 25, 50, and 100 mg kg(-1) in fasted mice.