Identification and biological characterization of 6-aryl-7-isopropylquinazolinones as novel TRPV1 antagonists that are effective in models of chronic pain

Vanilloid receptor 1 (VR1, TRPV1) is a cation-selective ion channel that is expressed on primary afferent neurons and is upregulated following inflammation and nerve damage. Blockers of this channel may have utility in the treatment of chronic nociceptive and neuropathic pain. Here, we describe the optimization from a high throughput screening hit, of a series of 6-aryl-7-isopropylquinazolinones that are TRPV1 antagonists in vitro. We also demonstrate that one compound is active in vivo against capsaicin-induced hyperalgesia and in models of neuropathic and nociceptive pain in the rat.

Potent and Orally Bioavailable Non-Peptide Antagonists at the Human Bradykinin B1 Receptor Based on a 2-Alkylamino-5-sulfamoylbenzamide Core

The bradykinin B(1) receptor is rapidly induced after inflammation or tissue trauma and appears to play an important role in the maintenance of hyperalgesia in inflammatory conditions. Here, we describe the optimization process to identify novel, potent non-peptide human B(1) receptor antagonists based on a 2-alkylamino-5-sulfamoylbenzamide core. Optimized derivatives are selective, functional B(1) antagonists with low nanomolar affinity and exhibit oral bioavailability in animals.

Design of non-peptide CCK2 and NK1 peptidomimetics using 1-(2-nitrophenyl)thiosemicarbazide as a novel common scaffold

A beta-turn overlay hypothesis has been used to transform the core scaffold of a selective non-peptide bradykinin B2 receptor antagonist into ligands specifically recognized by the CCK2 or NK1 receptors.

Bradyzide, a potent non-peptide B(2) bradykinin receptor antagonist with long-lasting oral activity in animal models of inflammatory hyperalgesia

Bradyzide is from a novel class of rodent-selective non-peptide B(2) bradykinin antagonists (1-(2-Nitrophenyl)thiosemicarbazides). Bradyzide has high affinity for the rodent B(2) receptor, displacing [(3)H]-bradykinin binding in NG108-15 cells and in Cos-7 cells expressing the rat receptor with K(I) values of 0.51+/-0.18 nM (n=3) and 0.89+/-0.27 nM (n=3), respectively. Bradyzide is a competitive antagonist, inhibiting B(2) receptor-induced (45)Ca efflux from NG108-15 cells with a pK(B) of 8.0+/-0.16 (n=5) and a Schild slope of 1.05. In the rat spinal cord and tail preparation, bradyzide inhibits bradykinin-induced ventral root depolarizations (IC(50) value; 1.6+/-0.05 nM (n=3)). Bradyzide is much less potent at the human than at the rodent B(2) receptor, displacing [(3)H]-bradykinin binding in human fibroblasts and in Cos-7 cells expressing the human B(2) receptor with K(I) values of 393+/-90 nM (n=3) and 772+/-144 nM (n=3), respectively. Bradyzide inhibits bradykinin-induced [(3)H]-inositol trisphosphate (IP(3)) formation with IC(50) values of 11.6+/-1.4 nM (n=3) at the rat and 2.4+/-0.3 microM (n=3) at the human receptor. Bradyzide does not interact with a range of other receptors, including human and rat B(1) bradykinin receptors. Bradyzide is orally available and blocks bradykinin-induced hypotension and plasma extravasation. Bradyzide shows long-lasting oral activity in rodent models of inflammatory hyperalgesia, reversing Freund's complete adjuvant (FCA)-induced mechanical hyperalgesia in the rat knee joint (ED(50), 0.84 micromol kg(-1); duration of action >4 h). It is equipotent with morphine and diclofenac, and 1000 times more potent than paracetamol, its maximal effect exceeding that of the non-steroidal anti-inflammatory drugs (NSAIDs). Bradyzide does not exhibit tolerance when administered over 6 days. In summary, bradyzide is a potent, orally active, antagonist of the B(2) bradykinin receptor, with selectivity for the rodent over the human receptor. British Journal of Pharmacology (2000) 129, 77 - 86

2-Nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-N - methylamide (SDZ NKT 343), a potent human NK1 tachykinin receptor antagonist with good oral analgesic activity in chronic pain models

A lead compound which had sub-micromolar affinity for the rabbit NK1 receptor but negligible affinity for rat NK1 receptors, 3a, was discovered by directed screening. 2-Substitution in the ring of the benzylthiourea substituent in the initial lead was found to be important, and halogens (Cl, Br) in this position were found to improve affinity for the human receptor. The activity of a series of 2-halo-substituted benzylthioureas was then optimized by modification of the proline diphenylmethyl amide, guided by a simple conceptual model based on structural overlay between these early antagonists and NK1 selective peptides. In this way, aromatic amino acid amides were identified which had improved affinity with respect to the starting diphenylmethyl (DPM) amides. The first sub-nanomolar ligand for the human NK1 receptor which arose from this series, 4af, combined a 2-chlorobenzylthiourea unit with a 2-naphthylalanine amide. Contemporaneously it was discovered that the benzylthiourea unit could be simplified to a phenylthiourea providing that an appropriate 2-substituent was also incorporated. Combination of these two series gave 2-NO2 phenylthiourea analogues which led directly to the analogous urea, 5f (2-nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benz yl- N-methylamide, SDZ NKT 343), a highly potent ligand for the human NK1 receptor (Ki = 0.16 nM). In addition to its high in vitro potency, 5f proved to be a potent orally active analgesic in guinea pig models of chronic inflammatory and neuropathic pain. The nature of the 2-aryl substituent was found to be critical for oral activity in this series. Clinical evaluation of 5f as a novel analgesic agent is currently underway.

Analogues of capsaicin with agonist activity as novel analgesic agents: structure-activity studies. 4. Potent, orally active analgesics

Structural features of three regions of the capsaicin molecule necessary for agonist properties were delineated by a previously reported modular approach. These in vitro agonist effects were shown to correlate with analgesic potency in rodent models. Combination of optimal structural features from each of these regions of the capsaicin molecule have led to highly potent agonists (eg., 1b). Evaluation in vivo established that 1b had analgesic properties but poor oral activity, short duration of action, and excitatory side effects which precluded further development of this compound. Preliminary metabolism studies had shown that the phenol moiety of 1b was rapidly glucuronidated in vivo, providing a possible explanation for the poor pharmacokinetic profile. Subsequent specific modification of the phenol group led to compounds 2a-j, which retained in vitro potency. The in vivo profiles of two representatives of this series, 2a,h, were much improved over the "parent" phenol series, and they are candidates for development as analgesic agents.

Detection of reverse transcriptase in culture medium for mammary tumour cell lines: a comparison of an established radio-labelling technique and a contemporary non-isotopic technique

Classically, radio-label techniques have been employed to analyse biological samples for reverse transcriptase (RT) activity. More recently, however, non-isotopic kits have been developed for retroviral quantification. Nevertheless, until the present investigation it has not been known if these contemporary methods are more sensitive at detecting reverse transcriptase activity. In our study, a non-isotopic ELISA method was shown to be considerably more sensitive than the radio-label technique at detecting reverse transcriptase in growth medium used to culture the murine breast cancer cell line GR/A. Using the ELISA, less reverse transcriptase activity was demonstrated in growth medium from human mammary adenocarcinoma MCF-7 cells than the murine source. This ELISA did not detect reverse transcriptase activity from a pure source of Moloney murine leukaemia virus. In light of this, the broad applicability of this ELISA for reverse transcriptase from different viral sources must be investigated before it can be used to monitor biological supernatants for the presence of retroviruses.

The discovery of capsazepine, the first competitive antagonist of the sensory neuron excitants capsaicin and resiniferatoxin

Capsaicin and resiniferatoxin are natural products which act specifically on a subset of primary afferent sensory neurons to open a novel cation-selective ion channel in the plasma membrane. These sensory neurons are involved in nociception, and so, these agents are targets for the design of a novel class of analgesics. Although synthetic agonists at the capsaicin receptor have been described previously, competitive antagonists at this receptor would be interesting and novel pharmacological agents. Structure-activity relationships for capsaicin agonists have previously been rationalized, by ourselves and others, by dividing the capsaicin molecule into three regions--the A (aromatic ring)-, B (amide bond)-, and C (hydrophobic side chain)-regions. In this study, the effects on biological activity of conformational constraint of the A-region with respect to the B-region are discussed. Conformational constraint was achieved by the introduction of saturated ring systems of different sizes. The resulting compounds provided agonists of comparable potency to unconstrained analogues as well as a moderately potent antagonist, capsazepine. This compound is the first competitive antagonist of capsaicin and resiniferatoxin to be described and is active in various systems, in vitro and in vivo. It has recently attracted considerable interest as a tool for dissecting the mechanisms by which capsaicin analogues evoke their effects. NMR spectroscopy and X-ray crystallography experiments, as well as molecular modeling techniques, were used to study the conformational behavior of a representative constrained agonist and antagonist. The conformation of the saturated ring contraint in the two cases was found to differ markedly, dramatically affecting the relative disposition of the A-ring and B-region pharmacophores. In agonist structures, the A- and B-regions were virtually coplanar in contrast to those in the antagonist, in which they were approximately orthogonal. A rationale for agonist and antagonist activity at the capsaicin receptor is proposed, based on the consideration of these conformational differences.

Neural modulation of bovine mesenteric lymph node contraction

Spontaneous isometric contractions and field-evoked responses were recorded in vitro from strips of bovine mesenteric lymph node capsule. Field stimulation (0.3 ms pulses, 60 V nominal, 2 min trains) at frequencies > or = 2 Hz evoked a frequency-dependent increase in baseline tension which was maximum at frequencies > or = 16 Hz. Evoked contractions were significantly reduced (P = 0.02) by the neurotoxin tetrodotoxin (10(-6) M) although they were unaffected by the alpha-adrenoceptor antagonists phentolamine, rauwolscine and prazosin (3 x 10(-6) M). Similarly, responses were unaffected by the beta-adrenoceptor antagonist propranolol (10(-6) M), the cholinergic antagonist atropine (10(-6) M) or the uptake blocker cocaine (10(-6) M). Field-evoked contraction was also unaffected by a 30 min exposure to alpha,beta-methylene ATP (10(-6) M). The results suggest that bovine lymph node capsular smooth muscle is innervated by excitatory nerves which are non-adrenergic, non-cholinergic and non-purinergic in nature.

Glucocorticoid-dependent oncogenic transformation by type 16 but not type 11 human papilloma virus DNA

Squamous cell carcinoma of the uterine cervix is one of the most common cancers among women. Correlation between human papilloma virus (HPV) infection of the uterine cervix and the development of cervical neoplasia has been established. More recent studies have shown the presence and expression of integrated HPV types 16 and 18 DNA sequences in 70-80% of cervical tumours and tumour cell lines. It has been suggested that, in addition to HPVs, other agents such as hormones and tobacco products act as cofactors in cervical neoplasia (for review see ref. 15). The presence and expression of a glucocorticoid-responsive element in HPV-16 has been reported. Here we provide evidence for the oncogenic transformation of primary cells with a combination of HPV-16 DNA, but not HPV-11 DNA, and the activated form of the human Ha-ras oncogene only in the presence of the glucocorticoid hormone dexamethasone.