Pharmacological properties of NK433, a new centrally acting muscle relaxant

RESUME-1: a Phase III study of tolperisone in the treatment of painful, acute muscle spasms of the back

Tolperisone is a nonopioid, centrally acting muscle relaxant in clinical development in the USA for the treatment of symptoms associated with acute, painful muscles spasms of the back. CLN-301, RESUME-1, is a 14-day double-blind, randomized, placebo-controlled, parallel-group Phase III study of the efficacy and safety of tolperisone administered orally three-times daily in 1000 male and female subjects at approximately 70 clinical sites in the USA experiencing back pain due to or associated with muscle spasm of acute onset. Tolperisone is a promising therapeutic for managing acute, painful muscle spasms of the back as it appears to lack the off-target CNS effects often seen with conventional skeletal muscle relaxants. Clinical Trials Registration: NCT04671082.

Basic aspects of the pharmacodynamics of tolperisone, a widely applicable centrally acting muscle relaxant

Tolperisone (2-methyl-1-(4-methylphenyl)-3-piperidin-1-ylpropan-1-one hydro-chloride) was introduced in the clinical practice more than forty years ago and is still evaluated as a widely applicable compound in pathologically elevated skeletal muscle tone (spasticity) and related pains of different origin. In the present review, basic pharmacodynamic effects measured on whole animals, analyses of its actions on cell and tissue preparations and molecular mechanism of action on sodium and calcium channels are summarized as recently significantly new data were reported.

Khat and synthetic cathinones: a review

For centuries, 'khat sessions' have played a key role in the social and cultural traditions among several communities around Saudi Arabia and most East African countries. The identification of cathinone as the main psychoactive compound of khat leaves, exhibiting amphetamine-like pharmacological properties, resulted in the synthesis of several derivatives structurally similar to this so-called natural amphetamine. Synthetic cathinones were primarily developed for therapeutic purposes, but promptly started being misused and extensively abused for their euphoric effects. In the mid-2000's, synthetic cathinones emerged in the recreational drug markets as legal alternatives ('legal highs') to amphetamine, 'ecstasy', or cocaine. Currently, they are sold as 'bath salts' or 'plant food', under ambiguous labels lacking information about their true contents. Cathinone derivatives are conveniently available online or at 'smartshops' and are much more affordable than the traditional illicit drugs. Despite the scarcity of scientific data on these 'legal highs', synthetic cathinones use became an increasingly popular practice worldwide. Additionally, criminalization of these derivatives is often useless since for each specific substance that gets legally controlled, one or more structurally modified analogs are introduced into the legal market. Chemically, these substances are structurally related to amphetamine. For this reason, cathinone derivatives share with this drug both central nervous system stimulating and sympathomimetic features. Reports of intoxication and deaths related to the use of 'bath salts' have been frequently described over the last years, and several attempts to apply a legislative control on synthetic cathinones have been made. However, further research on their pharmacological and toxicological properties is fully required in order to access the actual potential harm of synthetic cathinones to general public health. The present work provides a review on khat and synthetic cathinones, concerning their historical background, prevalence, patterns of use, legal status, chemistry, pharmacokinetics, pharmacodynamics, and their physiological and toxicological effects on animals and humans.

Tolperisone: a typical representative of a class of centrally acting muscle relaxants with less sedative side effects

Tolperisone, a piperidine derivative, is assigned to the group of centrally acting muscle relaxants and has been in clinical use now for decades. The review summarizes the known pharmacokinetics, pharmacodynamics, toxicology and side effects in humans and the clinical use of tolperisone. A future perspective for further exploration of this drug is given.

Silperisone: a centrally acting muscle relaxant

Silperisone is a tolperisone like organosilicon compound with centrally acting muscle relaxant properties. Studies in mice showed that silperisone may have less propensity to cause CNS depressant or motor side effects than tolperisone or other antispastic drugs. In cats and rats, silperisone was an effective suppressant of monosynaptic and polysynaptic spinal reflexes and decerebrate rigidity. Its suppressant effect on the spinal reflexes was also demonstrated in the isolated hemisected rat spinal cord in vitro. The in vivo potency and efficacy of silperisone by i.v administration were similar to those of tolperisone and eperisone. However, in cats by intraduodenal administration and in mice by oral administration its duration of action was much longer and its functional bioavailability much higher than of the other two drugs. With regard to its profile of actions silperisone was similar to tolperisone with minor differences. The most striking difference was in pontine facilitation and bulbar inhibition of the patellar reflex. Tolperisone depressed both, whereas silperisone inhibited only the former. The mechanism underlying the spinal reflex depressant effects of silperisone involves the blockade of voltage gated neuronal sodium and calcium channels leading to a decreased release of excitatory transmitter and reduced neuronal excitability. In addition, silperisone has potassium channel blocking effect, which is stronger than that of tolperisone. Silperisone is absorbed rapidly and is extensively metabolized in rats. However, its metabolism in dogs and particularly in humans is much less extensive. The elimination half-life of silperisone in humans is 12 to 16 h, so that it can be administered once or twice daily. Phase I clinical studies with silperisone at doses up to 150 mg/day failed to detect any adverse effects at plasma concentrations considered to be effective in the preclinical tests. These findings suggested that silperisone might be a useful antispastic drug. However, findings in chronic animal toxicity studies led to the discontinuation of silperisone's development.

Simple pharmacological test battery to assess efficacy and side effect profile of centrally acting muscle relaxant drugs

INTRODUCTION

Centrally muscle relaxants (CMRs) are used mainly for treating muscle spasticities of neurological origin, and painful muscle spasms due to rheumatologic conditions. Their use is frequently associated with dose-limiting adverse effects. New drugs with improved side-effect characteristics are badly needed. However, there is no general agreement in the pharmacological literature on what methods are adequate to assess CMR effect and side effects in behaving rodents, which may hinder the development of new drugs. Here we report on the establishment of a simple pharmacological test battery, which was used to compare efficacies and side effect profiles of 11 compounds with central muscle relaxant action, in mice (intraperitoneal application).

METHODS

For measuring muscle relaxant activity, (1) a new tremor model (GYKI 20039-induced tremor) and (2) the morphine-induced Straub-tail assay were used. The former, newly developed method has advantages over harmaline- or LON-954-induced tremor. For detecting side effect liability (ataxia, sedation, impairment of voluntary motor functions), (1) the rota-rod test, (2) measurement of spontaneous motility, (3) the weight-lifting test and (4) the thiopental sleep test were used.

RESULTS

Among the 11 muscle relaxant compounds tested (tolperisone, eperisone, silperisone, diazepam, baclofen, tizanidine, afloqualon, mephenesin, zoxazolamine, memantine and carisoprodol), the calculated safety ratios (i.e. ID50 for side effect/ID50 for muscle relaxant effect) varied in a wide range. Silperisone seems to have the most advantageous profile (safety ratios range between 1.7 and 3.3 in the different pairs of assays) compared to the other tested drugs with lower (one or more ratios below 1.5, and often far below 1) and more varying ratios.

DISCUSSION

Therapeutic indices calculated from the results of these in vivo experiments for the clinically used muscle relaxants are in agreement with their adverse effect profiles in humans. Thus the present test battery seems to be suitable for predicting the possible clinical utility of newly synthesized compounds.

Antinociceptive Effects of Sodium Channel-Blocking Agents on Acute Pain in Mice

The effects of various sodium channel blocking agents on acute thermal and mechanical nociception, as assessed using the plantar and tail pressure tests, respectively, were compared with the effects of morphine. The drugs used were mexiletine, lidocaine, carbamazepine, phenytoin, eperisone, tolperisone, and zonisamide. The sodium channel blocking agents exhibited a rather preferential elevation of the threshold for thermal nociception. By contrast, morphine produced similar analgesic effects on thermal and mechanical nociception. In the sciatic nerve isolated from mice, mexiletine, lidocaine, eperisone, and tolperisone impaired the propagation of low frequency action potentials (evoked at 0.2 Hz). Carbamazepine, phenytoin, and zonisamide generated a more frequency-dependent local anesthetic action with their obvious effects on higher frequency action potentials (evoked at 5 and/or 10 Hz). Our results show that sodium channel blocking agents have a preferential antinociceptive action against thermal stimulation that is likely to be attributed to their local anesthetic action.

Effects of a new centrally acting muscle relaxant, NK433 (lanperisone hydrochloride) on spinal reflexes

(-)-(R)-2-methyl-3-(1-pyrrolidinyl)-4'-trifluoromethylpropiophenone++ + monohydrochloride, lanperisone hydrochloride (NK433) administered intravenously or orally depressed the mono- and polysynaptic reflex potential, dorsal root reflex potential, flexor reflex mediated by group II afferent fibers, patellar and flexor reflexes. These effects were reduced by spinal transection. NK433 inhibited the facilitation of the flexor reflex mediated by group II afferent fibers that was induced by intrathecal administration of noradrenaline-HCl. (+)-(1R,2R)-2-methyl-3-(1-pyrrolidinyl)-1-(4-trifluoromethylphenyl)-1-pr opanol (LPS-9)-HCl, a metabolite of NK433, also inhibited the spinal reflexes. Given orally, NK433 had effects more than three times stronger and tending to be longer-lasting than those of eperisone-HCl. These results suggest that NK433 exerts a non-selective inhibition on spinal reflexes and that inhibition of the descending noradrenergic tonic facilitation within the spinal cord is involved in the mechanism of spinal reflex depression by NK433. LPS-9 could contribute to the potent activity of NK433 after oral administration.

Effects of NK433, a new centrally acting muscle relaxant, on masticatory muscle reflexes in rats

The effects of (-)-(R)-2-methyl-3-(1-pyrrolidinyl)-4'- trifluoromethylpropiophenone monohydrochloride (NK433), a novel centrally acting muscle relaxant, on masticatory muscle reflexes were investigated in rats. NK433 inhibited the monosynaptic tonic vibration reflex of the masseter muscle and the polysynaptic tonic periodontal masseteric reflex. These reflexes are increased by gamma-motor activity. NK433 had a weak inhibitory effect on the polysynaptic jaw opening reflex evoked by electrical stimulation of the tooth pulp, which is little related with gamma-motor activity. Eperisone-HCl depressed the three types of masticatory muscle reflexes. When intravenously administered, eperisone-HCl was equipotent to NK433, but the effect of eperisone-HCl was shorter-lasting than that of NK433. The effect of intragastrically administered NK433 on the periodontal masseteric reflex was about three times stronger than that of eperisone-HCl. These results suggest that NK433 inhibits masticatory muscle reflexes controlled by the gamma-motor system and thus may ameliorate the temporomandibular joint syndrome in man.