am336 and ziconotide

Antagonists of the N-type voltage gated calcium channel (VGCC), Cav 2.2, have a potentially important role in the treatment of chronic neuropathic pain. ω-conotoxins, such MVIIA and CVID are effective in neuropathic pain models. CVID is reported to have a greater therapeutic index than MVIIA in neuropathic pain models, and it has been suggested that this is due to faster reversibility of binding, but it is not known whether this can be improved further.. We examined the potency of CVID, MVIIA and two intermediate hybrids ([K10R]CVID and [R10K]MVIIA) to reverse signs of neuropathic pain in a rat nerve ligation model in parallel with production of side effects. We also examined the potency and reversibility to inhibit primary afferent synaptic neurotransmission in rat spinal cord slices.. All ω-conotoxins produced dose-dependent reduction in mechanical allodynia. They also produced side effects on the rotarod test and in a visual side-effect score. CVID displayed a marginally better therapeutic index than MVIIA. The hybrids had a lesser effect in the rotarod test than either of their parent peptides. Finally, the conotoxins all presynaptically inhibited excitatory synaptic neurotransmission into the dorsal horn and displayed recovery that was largely dependent upon the magnitude of inhibition and not the conotoxin type.. These findings indicate that CVID provides only a marginal improvement over MVIIA in a preclinical model of neuropathic pain, which appears to be unrelated to reversibility from binding. Hybrids of these conotoxins might provide viable alternative treatments.

Topics: Analgesics, Non-Narcotic; Animals; Calcium Channel Blockers; Disease Models, Animal; Dose-Response Relationship, Drug; Hyperalgesia; Male; Neuralgia; omega-Conotoxins; Peptides; Rats; Rats, Sprague-Dawley; Rotarod Performance Test; Spinal Cord; Synaptic Transmission

Leconotide is an omega-conotoxin that blocks neuronal voltage sensitive calcium channels. This study compared the antihyperalgesic potencies of leconotide and ziconotide given intravenously alone and in combinations with a potassium channel modulator flupirtine, given intraperitoneally, in a rat model of diabetic neuropathic pain.. Rats were given streptozotocin (150 mg/kg ip) to induce diabetic neuropathy and hyperalgesia. Experiments were performed on diabetic rats with >or=30% hyperalgesia to noxious heat. Rats were given each conopeptide alone and with flupirtine. Open field activity monitoring and non-invasive blood pressure measurements were used to define the maximum doses and combinations that caused no side effects. Doses in a range up to maximum no side effect doses were tested for antihyperalgesic effects in rats with hyperalgesia.. The maximum no side effect dose of leconotide (2 mg/kg intravenously) caused 51.7% reversal of hyperalgesia compared with 0.4% for the highest no side effect dose of ziconotide (0.02 mg/kg; P < 0.001, one-way anova). Leconotide caused dose-related antihyperalgesic effects that were potentiated by coadministration with flupirtine at doses that were ineffective when given alone. Leconotide (0.02 mg/kg) and flupirtine (5 mg/kg) caused 25.3 +/- 7.6 and -6 +/- 9.5% reversal of hyperalgesia, respectively when given alone but in combination they caused 84.1 +/- 7.2% reversal of hyperalgesia (P < 0.01; one-way anova). No such interaction occurred with ziconotide.. Leconotide could have wider clinical applications than ziconotide. Unlike ziconotide, powerful antihyperalgesia without side effects can be achieved by intravenous administration of leconotide thus avoiding the need for an intrathecal injection.

Topics: Aminopyridines; Analgesics, Non-Narcotic; Animals; Blood Pressure; Calcium Channel Blockers; Diabetes Mellitus, Experimental; Diabetic Neuropathies; Dose-Response Relationship, Drug; Drug Interactions; Hemodynamics; Hot Temperature; Hyperalgesia; Injections, Intravenous; Male; Motor Activity; omega-Conotoxins; Pain Measurement; Rats; Rats, Wistar

Cone snails (Conidae) are marine predators with some extraordinary features. Their venom contains a hundred or more peptides that target numerous ion channels and receptors in mammals, including several that are involved in disease. omega-Conotoxins from fish hunting snails are 24-27 residue peptides with a rigid 4-loop cysteine framework that target the N-type voltage-gated calcium channel (VGCC). Two omega-conotoxins, MVIIA and CVID are currently in clinical development for chronic pain management (Ziconotide or Prialt, and AM336, respectively). In an attempt to develop small molecule equivalents of CVID, we defined the Calpha-Cbeta vectors of the residues believed to be important for binding to the N-type VGCC. Using these vectors, we undertook a virtual screening of virtual libraries approach to identify compounds that matched the pharmacophore. Cyclic pentapeptides containing residues of loop 2 of CVID, with one or more being a D-amino acid were designed and synthesised and were found to be active at the N-type VGCC (IC50 approximately 20 microM). Agreeing with the specificity profile of CVID, molecules were inactive at the P/Q-type VGCC.

Topics: Animals; Biochemistry; Calcium Channel Blockers; Calcium Channels, N-Type; Drug Design; Drug Evaluation, Preclinical; Ion Channel Gating; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Mimicry; omega-Conotoxins; Peptides, Cyclic; Protein Conformation; Rats; Structure-Activity Relationship; Venoms

Agents which decrease conductance of N-type voltage-gated Ca(2+) channels have been shown to attenuate measures of neuropathic pain in animal models and to provide symptom relief in humans. The omega-conotoxins have demonstrated efficacy but have a low therapeutic index. We have investigated the effects of a new omega-conotoxin, CVID (AM-336), and compared them with omega-conotoxin GVIA (SNX-124), omega-conotoxin MVIIA (SNX-111) and morphine in a spinal nerve ligation model of neuropathic pain in the rat. The ED(50) (and 95% CI) for attenuation of tactile allodynia by intrathecal administration for omega-conotoxin CVID, GVIA, MVIIA and morphine was 0.36 (0.27-0.48), 0.12 (0.06-0.24), 0.32 (0.23-0.45) and 4.4 (2.9-6.5) microg/kg, respectively. Only morphine significantly prolonged acute tail flick responses (ED(50) 2.3 (1.1-4.9) microg/kg). Of the omega-conotoxins, omega-conotoxin CVID showed the highest ratio of efficacy to behavioural toxicity. These observations show that intrathecal omega-conotoxins are effective in attenuating tactile allodynia in the rat without significantly affecting acute nociceptive responses. Omega-conotoxin CVID had similar potency to omega-conotoxin MVIIA but showed less toxicity in the therapeutic range.

Topics: Analysis of Variance; Animals; Calcium Channel Blockers; Dose-Response Relationship, Drug; Injections, Spinal; Male; Morphine; omega-Conotoxin GVIA; omega-Conotoxins; Pain; Rats; Rats, Sprague-Dawley; Venoms

N-type calcium channels modulate the release of key pro-nociceptive neurotransmitters such as glutamate and substance P (SP) in the central nervous system. Considerable research interest has focused on the therapeutic potential of the peptidic omega-conopeptides, GVIA and MVIIA as novel analgesic agents, due to their potent inhibition of N-type calcium channels. Recently, the novel peptidic N-type calcium channel blocker, AM336, was isolated from the venom of the cone snail, Conus catus. Thus, the aims of this study were to (i) document the antinociceptive effects of AM336 (also known as CVID) relative to MVIIA following intrathecal (i.t.) bolus dosing in rats with adjuvant-induced chronic inflammatory pain of the right hindpaw and to (ii) quantify the inhibitory effects of AM336 relative to MVIIA on K+-evoked SP release from slices of rat spinal cord. Both AM336 and MVIIA inhibited the K+-evoked release of the pro-nociceptive neurotransmitter, SP, from rat spinal cord slices in a concentration-dependent manner (EC50 values=21.1 and 62.9 nM, respectively), consistent with the antinociceptive actions of omega-conopeptides. Following acute i.t. dosing, AM336 evoked dose-dependent antinociception (ED50 approximately 0.110 nmol) but the doses required to produce side-effects were an order of magnitude larger than the doses required to produce antinociception. For i.t. doses of MVIIA0.07 nmol, produced a dose-dependent decrease in antinociception but the incidence and severity of the side-effects continued to increase for all doses of MVIIA investigated, suggesting that dose-titration with MVIIA in the clinical setting, may be difficult.

Topics: Animals; Calcium Channel Blockers; Calcium Channels, N-Type; Dose-Response Relationship, Drug; Injections, Spinal; Male; Nociceptors; omega-Conotoxins; Organ Culture Techniques; Pain Threshold; Potassium; Rats; Rats, Sprague-Dawley; Specific Pathogen-Free Organisms; Spinal Cord; Substance P; Venoms