Cebranopadol: a novel potent analgesic nociceptin/orphanin FQ peptide and opioid receptor agonist.

Cebranopadol (trans-6'-fluoro-4',9'-dihydro-N,N-dimethyl-4-phenyl-spiro[cyclohexane-1,1'(3'H)-pyrano[3,4-b]indol]-4-amine) is a novel analgesic nociceptin/orphanin FQ peptide (NOP) and opioid receptor agonist [Ki (nM)/EC50 (nM)/relative efficacy (%): human NOP receptor 0.9/13.0/89; human mu-opioid peptide (MOP) receptor 0.7/1.2/104; human kappa-opioid peptide receptor 2.6/17/67; human delta-opioid peptide receptor 18/110/105]. Cebranopadol exhibits highly potent and efficacious antinociceptive and antihypersensitive effects in several rat models of acute and chronic pain (tail-flick, rheumatoid arthritis, bone cancer, spinal nerve ligation, diabetic neuropathy) with ED50 values of 0.5-5.6 µg/kg after intravenous and 25.1 µg/kg after oral administration. In comparison with selective MOP receptor agonists, cebranopadol was more potent in models of chronic neuropathic than acute nociceptive pain. Cebranopadol's duration of action is long (up to 7 hours after intravenous 12 µg/kg; >9 hours after oral 55 µg/kg in the rat tail-flick test). The antihypersensitive activity of cebranopadol in the spinal nerve ligation model was partially reversed by pretreatment with the selective NOP receptor antagonist J-113397[1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one] or the opioid receptor antagonist naloxone, indicating that both NOP and opioid receptor agonism are involved in this activity. Development of analgesic tolerance in the chronic constriction injury model was clearly delayed compared with that from an equianalgesic dose of morphine (complete tolerance on day 26 versus day 11, respectively). Unlike morphine, cebranopadol did not disrupt motor coordination and respiration at doses within and exceeding the analgesic dose range. Cebranopadol, by its combination of agonism at NOP and opioid receptors, affords highly potent and efficacious analgesia in various pain models with a favorable side effect profile.

Further investigations into the genotoxicity of 2,6-xylidine and one of its key metabolites.

The metabolite of several amide anaesthetics, 2,6-xylidine, is a possible human (Group 2B) carcinogen and induced nasal tumours in rats after dietary administration. However, published papers on the genotoxicity of 2,6-xylidine in vitro have given inconsistent results. It has been proposed that the genotoxicity of 2,6-xylidine is dependent on its metabolism to a key metabolite dimethylphenyl N-hydroxylamine (DMHA), which would then be further converted to form a reactive nitrenium ion by phase 2 (mainly acetylation) metabolism. In order to study whether the inconsistent results could be explained by different systems having different potential for DMHA to be formed and to induce genotoxicity in vitro, we have tested 2,6-xylidine in conventional Ames bacteria, and strains engineered to overexpress acetyltransferase, in the presence of different concentrations of induced rat liver and human liver S9. All tests gave consistently negative results. The formation of DMHA by induced rat liver S9 and human S9 was clearly shown to occur, and to be concentration- and time-dependent. The potential inhibitory effects of the solvent DMSO were also studied, but it was clearly not responsible for the negative results with 2,6-xylidine. Thus, whatever is the mode of action of 2,6-xylidine carcinogenicity in rodents, it has proven impossible to detect mutagenic effects in Ames tests with numerous variations of metabolic conditions, or even using acetyltransferase overexpressing strains of bacteria.

Differential contribution of opioid and noradrenergic mechanisms of tapentadol in rat models of nociceptive and neuropathic pain.

The novel analgesic tapentadol combines mu-opioid receptor agonism and noradrenaline reuptake inhibition in a single molecule and shows potent analgesia in various rodent models of pain. We analyzed the contribution of opioid and monoaminergic mechanisms to the activity of tapentadol in rat models of nociceptive and neuropathic pain. Antinociceptive efficacy was inferred from tail withdrawal latencies of experimentally naive rats using a tail flick test. Antihypersensitive efficacy was inferred from ipsilateral paw withdrawal thresholds toward an electronic von Frey filament in a spinal nerve ligation model of mononeuropathic pain. Dose-response curves of tapentadol (intravenous) were determined in combination with vehicle or a fixed dose (intraperitoneal) of the mu-opioid receptor antagonist naloxone (1mg/kg), the alpha2-adrenoceptor antagonist yohimbine (2.15 mg/kg), or the serotonin 5-HT(2A) receptor antagonist ritanserin (0.316 mg/kg). Tapentadol showed clear antinociceptive and antihypersensitive effects (>90% efficacy) with median effective dose (ED(50)) values of 3.3 and 1.9 mg/kg, respectively. While the antinociceptive ED(50) value of tapentadol was shifted to the right 6.4-fold by naloxone (21.2mg/kg) and only 1.7-fold by yohimbine (5.6 mg/kg), the antihypersensitive ED(50) value was shifted to the right 4.7-fold by yohimbine (8.9 mg/kg) and only 2.7-fold by naloxone (5.2mg/kg). Ritanserin did not affect antinociceptive or antihypersensitive ED(50) values of tapentadol. Activation of both mu-opioid receptors and alpha2-adrenoceptors contribute to the analgesic effects of tapentadol. The relative contribution is, however, dependent on the particular pain indication, as mu-opioid receptor agonism predominantly mediates tapentadol's antinociceptive effects, whereas noradrenaline reuptake inhibition predominantly mediates its antihypersensitive effects.

Tapentadol hydrochloride: a next-generation, centrally acting analgesic with two mechanisms of action in a single molecule.

Tapentadol exerts its analgesic effects through micro opioid receptor agonism and noradrenaline reuptake inhibition in the central nervous system. Preclinical studies demonstrated that tapentadol is effective in a broad range of pain models, including nociceptive, inflammatory, visceral, mono- and polyneuropathic models. Moreover, clinical studies showed that tapentadol effectively relieves moderate to severe pain in various pain care settings. In addition, it was reported to be associated with significantly fewer treatment discontinuations due to a significantly lower incidence of gastrointestinal-related adverse events compared with equivalent doses of oxycodone. The combination of these reduced treatment discontinuation rates and tapentadol efficacy for the relief of moderate to severe nociceptive and neuropathic pain may offer an improvement in pain therapy by increasing patient compliance with their treatment regimen.

(-)-(1R,2R)-3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol hydrochloride (tapentadol HCl): a novel mu-opioid receptor agonist/norepinephrine reuptake inhibitor with broad-spectrum analgesic properties.

(-)-(1R,2R)-3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol hydrochloride (tapentadol HCl) is a novel micro-opioid receptor (MOR) agonist (Ki = 0.1 microM; relative efficacy compared with morphine 88% in a [35S]guanosine 5'-3-O-(thio)triphosphate binding assay) and NE reuptake inhibitor (Ki = 0.5 microM for synaptosomal reuptake inhibition). In vivo intracerebral microdialysis showed that tapentadol, in contrast to morphine, produces large increases in extracellular levels of NE (+450% at 10 mg/kg i.p.). Tapentadol exhibited analgesic effects in a wide range of animal models of acute and chronic pain [hot plate, tail-flick, writhing, Randall-Selitto, mustard oil colitis, chronic constriction injury (CCI), and spinal nerve ligation (SNL)], with ED50 values ranging from 8.2 to 13 mg/kg after i.p. administration in rats. Despite a 50-fold lower binding affinity to MOR, the analgesic potency of tapentadol was only two to three times lower than that of morphine, suggesting that the dual mode of action of tapentadol may result in an opiate-sparing effect. A role of NE in the analgesic efficacy of tapentadol was directly demonstrated in the SNL model, where the analgesic effect of tapentadol was strongly reduced by the alpha2-adrenoceptor antagonist yohimbine but only moderately attenuated by the MOR antagonist naloxone, whereas the opposite was seen for morphine. Tolerance development to the analgesic effect of tapentadol in the CCI model was twice as slow as that of morphine. It is suggested that the broad analgesic profile of tapentadol and its relative resistance to tolerance development may be due to a dual mode of action consisting of both MOR activation and NE reuptake inhibition.

Differential effects of human ether-a-go-go-related gene (HERG) blocking agents on QT duration variability in conscious dogs.

The effects of drugs that inhibit human ether-a-go-go-related gene (HERG) related cardiac potassium channels on the variability of QT duration as a sign of repolarisation instability were evaluated in conscious telemetered dogs. QT duration variability was determined using a beat-to-beat analysis before and after the infusions of HERG channel blocking agents. Variability was evaluated as increased mean width (P(width)) and length (P(length)) of Poincaré plots of 100 consecutive beats. As HERG channel blockers which are associated with arrhythmias of the torsades de pointes (TdP) type, dofetilide and sotalol were infused. Verapamil was used as an HERG channel blocker that is not associated with TdP. Dofetilide (0.01 and 0.03 mg/kg) dose-dependently prolonged QT(c) duration (12% and 16%). Dofetilide also induced an increase of QT variability that reached statistical significance for P(length) at the higher dose (64%). A dose of 3 mg/kg sotalol neither prolonged QT(c) duration nor QT duration variability. In contrast, at 10 mg/kg sotalol prolonged QT(c) duration (15%) and increased P(length) (33%). Doses of 0.1 and 0.3 mg/kg verapamil did not increase QT(c) duration nor QT time variability. QT duration variability in conscious dogs may be a useful preclinical marker to discriminate pro-arrhythmogenic and non-arrhythmogenic activities of HERG blocking agents.