WO2009109334A1

WO2009109334A1 - (s)-(+)-2-[4-fluorbenzyloxy)benzylamino]propanamide for use in the treatment of mixed or combined pain

Info

Publication number: WO2009109334A1
Application number: PCT/EP2009/001407
Authority: WO
Inventors: Laura Faravelli; Paolo Marchettini; Rodolfo Giuliani; Stefano Rossetti; Luca Benatti
Original assignee: Newron Pharmaceuticals S.P.A.
Priority date: 2008-03-07
Filing date: 2009-02-27
Publication date: 2009-09-11

Abstract

(S)-(+)-2-[4-(2-Fluorobenzyloxy) benzylamino] propanamide (ralfϊnamide) and the salts thereof with pharmaceutically acceptable acids for use in the treatment of mixed or combined pain where a nociceptive component is combined with a neuropathic component, such as nerve compression and/or nerve entrapment syndromes, in particular, neuropathic low back pain (NLBP) or radicular low back pain (RLBP), alone or in combination with other therapeutic agents.

Description

(S)-(+)-2-[4-(2-FLUOROBENZYLOXY)BENZYLAMINO]PROPANAMIDE FOR USE IN THE TREATMENT OF MIXED OR COMBINED PAIN

FIELD OF THE INVENTION

The present invention relates to an α-aminoamide derivative, (S)-(+)-2-[4-(2- fluorobenzyloxy)benzylamino]propanamide, i.e. ralfinamide, and its salts with pharmaceutically acceptable acids, in particular its methanesulfonate, for the use in treating mixed or combined pain, comprising both a nociceptive and neuropathic component, such as nerve compression and/or nerve entrapment syndromes.

BACKGROUND OF THE INVENTION

Pain, that is classified on the basis of its presumed underlying pathophysiology, is broadly categorized as nociceptive or neuropathic.

However, there are some particular pathological pain conditions in which neuropathic and nociceptive components are both simultaneously involved and this is the case of a mixed or combined pain (Hansson PT et al. Neuropathic Pain: Pathophysiology and Treatment". Progress in Pain Research and Management. Edited by PT Hansson, HL Fields, RG Hill, and P Marchettini Eds, IASP press, Seattle 2001, VoI 21, Chapt 1, Page 1).

Chronic pain patients examined in the real life of the clinical setting, rarely complain of a single painful entity and conversely more likely exhibit a combination of pain symptoms/syndromes. Nerve compression and nerve entrapment syndromes such as nerve root compression from an herniated disk, or ulnar nerve entrapment but also other forms of nerve entrapment and/or compression, present a combination of nociceptive and neuropathic pain. The terms nerve compression and nerve entrapment refer to isolated peripheral nerve injuries occurring at specific locations where a nerve is mechanically constricted in a fibrous or fibro-osseous tunnel or deformed by a fibrous band. In some instances the nerve is injured by chronic direct compression, and in other instances angulation or stretching forces cause mechanical damage to the nerve. ( J. D. England "Entrapment Neuropathies " http://neuropathvmd.org/pdf/44/Entrapment%20Neuropathies.pdf) This repetitive injury and localized trauma to a nerve may result in microvascular (ischemic) changes, oedema, injury to the outside layers of the nerve (myelin sheath) that aid in the transmission of the nerve's messages, and structural alterations in membranes at the organelle levels in both the myelin sheath and the nerve axon. Focal segmental demyelination at the area of compression is a constant feature of compression syndromes (J-S Harrop "Nerve Entrapment Syndromes " eMedicine Dec 7, 2007; http://www. emedicine. com/med/fulltopic/toyic2909. htm ). Common examples of nerve compression in a fibro-osseous tunnel are the carpal tunnel syndrome and ulnar neuropathy at the cubital tunnel. Angulation and stretch injury are important mechanisms of nerve injury for ulnar neuropathies associated with gross deformity of the elbow joint ("tardy ulnar palsy") and neurogenic thoracic outlet syndrome. Recurrent compression of nerves by external forces may also cause focal nerve injuries such as ulnar neuropathy at the elbow and deep branch lesions of the ulnar nerve in the hand (J. D. England "Entrapment Neuropathies" http://neuropathymd.org/pdf/44/Entrapment%20Neuropathies.pdf) The symptoms of nerve compression vary, based on the particular nerve involved. In general, however, most entrapment syndromes involve mixed sensory and motor nerves and the temporal sequence of neurological manifestations includes: irritative or inflammation (sensory nerves), pain, parestesia, numbness (sensory nerves), weakness and atrophy (motor nerves).

Signs of sympathetic dystrophy may be prominent features in chronic cases due to the compression of a major mixed nerve (both sensory and motor), such as the sciatic or median nerves (J-S Harrop " Nerve Entrapment Syndromes " eMedicine Dec 7, 2007; http://www. emedicine. com/med/fulltopic/topic2909. htm.).

Among these clinical manifestations one component of pain, due to nerve compression/nerve entrapment, is nociceptive and it is localized at the site of disturbance.

Nociceptive pain is caused by the ongoing activation of Aδ and C-nociceptors in response to noxious stimulus, which is in this case a compressive stimulation. Generally there is a close correspondence between pain perception and stimulus intensity and the pain is indicative of real or potential tissue damage. Following a continuous compression injury, an aberrant signal processing in the peripheral or central nervous system may develop, yielding a neuropathic component of pain that is projected within the area corresponding to the affected roots. Example of projected pain, is pain perceived into the ulnar part of the hand in ulnar nerve entrapment.

These types of pain, showing the symptomatology of neuropathic pain originated from external compression (both for peripheral nerve and roots), are defined as "Combined

Pain" (Hansson PT et al. Neuropathic Pain: Pathophysiology and Treatment".

Progress in Pain Research and Management. Edited by PT Hansson, HL Fields, RG

Hill, and P Marchettini Eds, IASP press, Seattle 2001, VoI 21 , Chapt 1, Page 1).

These authors, in dealing specifically with pain in radiculopathies, underline that nerve root compression usually involves a combination of nociceptive pain and projected neuropathic pain.

A particular example of pain deriving from nerve root compression is neuropathic low back pain (NLBP) or radicular low back pain (RLBP).

NLBP/RLBP, including both the neuropathic and nociceptive components is characterized by a dorsal root compression or by a herniated disk or spinal stenosis that can compress the dorsal root ganglions. (Audette J. F. et al.(2005) "Neuropathic low back pain ", Current Pain and Headache Reports, 9: 168-177; McCaIl IW. (2000) "

Lumbar herniated disk" , Radiol Clin North Am. 38(6): 1293-1309 and Atlas SJ and al. (2003) "Evaluation and treatment of low back pain: an evidence-based approach to clinical care ", Muscle Nerve 27(3):265-284).

Common clinical pain management consists of the prescription of drugs specifically addressed to neuropathic or nociceptive types of pain. For example for neuropathic pain the typical treatment includes antiepileptic drugs such as gabapentin, pregabalin, carbamazepine, lamotrigine or antidepressants combining noradrenergic and ion channels blocker activity such as amitriptyline and nortriptyline, whereas for nociceptive pain the most used drugs are tramadol, codeine or the typical NSAIDs.

These latter are not particularly effective against neuropathic pain, while the former conversely are not particularly active against nociceptive pain.

To our knowledge there are no pharmacological treatment specific for "Combined Pain", and in particular for patients suffering from nerve compression and/or entrapment.

PRIOR ART WO90/14334 discloses substituted α-aminoamide derivatives, including ralfinamide, active on the central nervous system (CNS) that are useful in the treatment of epilepsy, of Parkinson's disease and as neuroprotective agents in degenerative processes associated with normal ageing or pathological situations, such as brain ischemia; they can also be used as antidepressants, hypnotics and/or antispastic agents (see also Pevarello P. et al. (1998), "Synthesis and anticonvulsant activity of a new class of 2-[(arylalkyl)amino]alkanamide derivatives ", J. Med. Chemistry, 41 : 579- 590). WO99/26614 discloses substituted α-aminoamide derivatives active for the treatment of neuronal damages following global and focal ischemia, for the treatment or prevention of neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS) and for treatment, prevention or amelioration of pain, as anticonvulsant, and as antimanic depressants, as local anesthetics, as antiarrhythmics and for the treatment or prevention of diabetic neuropathy. WO 99/35125 discloses the use of α-aminoamide derivatives as analgesics.

WO 03/020273 discloses a pharmaceutical composition comprising an α-aminoamide, such as ralfinamide, in combination with gabapentin for analgesic use.

WO 04/062655 discloses α-aminoamide derivatives as antimigraine agents.

WO 05/018627 discloses α-aminoamide derivatives useful as antiinflammatory agents. WO 05/070405 discloses α-aminoamide derivatives useful in the treatment of lower urinary tract disorders.

WO 06/027052 specifically discloses and claims the use of the single R-enantiomer of ralfinamide and its salts with pharmaceutically acceptable acids as a selective sodium and calcium channel modulator for the selective treatment of pathological affections wherein sodium or calcium channel mechanism(s) play(s) a pathological role, including pain, migraine, inflammatory processes affecting all body systems, disorders affecting skin and related tissue, disorders of the respiratory system, disorders of the immune and endocrinological systems, gastrointestinal, and urogenital disorders, wherein the therapeutical activity of said compound is substantially free from any MAO inhibitory side effect or exhibits significantly reduced MAO inhibitory side effect.

WO 07/147491 discloses a process for the production of ralfinamide with high purity degree. WO 07/144153 discloses α-aminoamide derivatives useful in the treatment of cognitive disorders.

Veneroni et al. report, in "Anti-allodynic effect of NW- 1029, a novel Na+ channel blocker, in experimental animal models of inflammatory and neuropathic pain" - Pain (2003);102: 17-25, that ralfϊnamide was active in an in vivo model of neuropathic pain, such as the "Chronic constriction injury - CCI", but not in animal models, predictive of nociceptive pain, such as the "hot-plate" and the "tail-flick" tests.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the α-aminoamide derivative (S)-(+)-2-[4-(2- fluorobenzyloxy)benzylamino]propanamide, i.e. ralfϊnamide and the salts thereof with pharmaceutically acceptable acids, in particular with methanesulfonic acid, for the use as in claim 1. Ralfinamide is a compound showing a multiple mechanism of action, including NMDA antagonism, MAO-B inhibition, glutamate release inhibition, Substance P release inhibition and sodium and calcium channel blockade. (Stummann TC et al., "The anti-nociceptive agent ralfinamide inhibits tetrodotoxin- resistant and tetrodotoxin-sensitive Na+ currents in dorsal root ganglion neurons. " Eur J Pharmacol 2005;510: 197-208. Colombo E et al., "Ralfinamide acts through NMDA receptor complex: A central role or chronic pain treatment. " Euro J Pain 2007; 1 l(Suppl 1): 152-153. Izzo E et al., "Anti-inflammatory effect of ralfinamide on carraggeenan-induced paw oedema in rat and on spinal cord synaptosomes substance P release. " Society for Neuroscience, 34^th Annual Meeting, San Diego, CA, USA, 2004.) Ralfinamide is effective in animal models of neuropathic pain such as a model of partial denervation in the rat produced by the L5-L6 spinal nerve ligation (Example 1). In this model ralfϊnamide methanesulfoante at the dose of 10 mg/kg (as a salt) decreases pain response evaluated as increase in withdrawal thresholds in response to mechanical stimuli and increase in withdrawal latency of the injured paw in response to thermal stimuli, respectively.

Potential effect of ralfϊnamide on the nociceptive pain has been evaluated in naϊve rats using the hot plate (Example 4) and tail flick (Example 3) tests, two models of acute pain induced by noxious heat stimulus. Ralfinamide methanesulfonate at 30 mg/kg (as a salt) did not modify the nociceptive threshold to noxious stimuli in naive rat neither in the hot plate nor in the tail flick tests, showing to be devoid of any activity on nociception.

A Phase II study, randomized, double-blind, placebo-controlled, multi-center, multinational study has been conducted to determine preliminary evidence of efficacy and evaluate the safety, tolerability and maximum tolerated dose of escalating doses of ralfϊnamide (administered as the methanesulfonate salt) from 80 to 320 mg/day (40- 160 mg b.i.d.; as a salt), compared to placebo, in patients with different types of neuropathic pain (Example 5). In this clinical trial that included patients with diverse types of chronic neuropathic pain, unexpectedly two clusters of patients peculiarly stand out from the comprehensive population examined, for their striking positive response to ralfinamide.

At a closer scrutiny, the two subpopulation clusters of chronic pain patients, composed by patients with nerve compression and/or entrapment neuropathy (including carpal tunnel syndrome, tarsus tunnel syndrome, ulnar nerve entrapment, compression radiculopathy, lumbar spinal stenosis, sciatic nerve compression, spinal root compression and intercostal neuralgia), have been found to share the peculiarity of presenting a dual mechanism of nerve injury. In fact, the entrapped peripheral nerves and compressed spinal roots combine a pain mechanism due to axonal damage (neuropathic injury) and, in addition, an external injury on the nerve or root (nociceptive injury) due to mechanical compression/entrapment.

Since preclinical data provided strong evidence of an excellent effect of ralfinamide in several neuropathic animal pain models (such as the Spinal Nerve Ligation model), but no response in nociceptive pain models (such as the Tail Flick or the Hot Plate), the finding of a highly positive response in these subpopulations of patients suffering of combined nociceptive and neuropathic pain, was absolutely unexpected. Unpredictably from previous preclinical data in animal models, the clinical data presented hereinafter show that ralfinamide and its salts with pharmaceutically acceptable acids can be advantageously used for treating populations of patients having pain of the combined nociceptive and neuropathic type, such as Nerve Compression/Entrapment syndromes (NCET).

As a further evidence of the activity of ralfinamide in the treatment of mixed or combined pain, ralfinamide has been proved to show a surprisingly analgesic activity in preclinical animal models of NLBP/RLBP such as "Chronic compression of the Dorsal root ganglion - CCD" in rats, as described in Example 2, (Hu Sj et al. (1998) "An experimental model for chronic compression of dorsal root ganglion produced by intravertebral foramen stenosis in the rat" Pain, 77:15-23 and Song XJ et al. (1999) "Mechanical and thermal hyperalgesia and ectopic neuronal discharge after chronic compression of dorsal root ganglia"- J Neurophysiol; 82:3347-58).

Moreover the above said activity of ralfinamide in the treatment of NLBP/RLBP has been shown in a 12-week, randomized, double-blind, international phase Ilb/III trial randomizing approximately 400 patients with NLBP of at least moderate severity as judged by the patients. Patients were diagnosed in accordance with the diagnostic criteria proposed by the International Association for the Study of Pain (IASP). Patients were randomized to treatment with ralfinamide at a daily dose from 160 to 320 mg as methanesulfonate salt, or placebo.

According to the object of this invention, ralfinamide is effective in the treatment of patients suffering of combined nociceptive and neuropathic pain conditions, when it is administered in the range of 10 to 1000 mg per day, preferably in the range of 30 to 500 mg per day, more preferably from 60 to 350 mg per day, most preferably from 80 to 320 mg per day (if not otherwise specified, the above ranges refer to ralfinamide methanesulfonate; these values should be stoichiometrically adjusted if ralfinamide is administered as the free base or the salt with another pharmaceutically acceptable acid).

According to a further object of this invention, ralfinamide or the salt thereof with pharmaceutically acceptable acids may optionally be administered to the patients in need thereof in conjunction with one or more other therapeutic agents. Examples of suitable agents for adjunctive therapy include a serotonin receptor modulator including a 5HT1B/1D agonist, such as a triptan (e.g. sumatriptan or naratriptan); an adenosine Al agonist; an adenosine A2 antagonist; a purinergic P2X antagonist, an EP ligand; an NMDA receptor modulator, such as a glycine antagonist; an AMPA modulator; a substance P antagonist (e.g. an NKl antagonist); a cannabinoid; a nicotinic receptor agonist; an alpha- 1 or 2 adrenergic agonist; paracetamol or phenacetin; a 5-lipoxygenase inhibitor; a leukotriene receptor antagonist; DMARDs - Disease Modifying Anti-Rheumatic Drugs (e.g. methotrexate); gabapentin, pregabalin and related compounds; a neurone stabilising antiepileptic drugs such as lamotrigine or valproate; a monoaminergic uptake inhibitor (e.g. venlafaxine); a nitric oxide synthase (NOS) inhibitor, such as an iNOS or an nNOS inhibitor; a free radical scavenger; an inhibitor of the release, or action, of tumor necrosis factor alpha (TNFα); an antibody therapy, such as monoclonal antibody therapy; an antiviral agent, such as a nucleoside inhibitor (e.g. lamivudine) or an immune system modulator (e.g. interferon); an opioid analgesic, such as morphine; a vanilloid receptor agonist and antagonist; NSAIDs such as a cyclooxygenase-1 and/or cyclooxygenase-2 inhibitor ; a local anaesthetic such as lidocaine and derivatives; a stimulant, including caffeine; antitussive (e.g. codeine, hydrocodone, carmiphen, carbetapentane, or dextramethorphan); an antipsychotic agent, including typical and atypical antipsychotics (e.g. haloperidol, risperidone, clozapine); an anti-depressant, such as a selective serotonin re-uptake inhibitors , serotonin and noradrenaline reuptake inhibitors, tryciclic antidepressant drugs (e.g. amitryptiline); a mood stabilizer (e.g. lithium); an anxiolytic agent (e.g. benzodiazepines, duloxetine, buspirone, beta- adrenergic receptors antagonists); other calcium or sodium channel blockers. The suitable agents for the adjunctive therapy mentioned above may be administered concomitantly with ralfinamide or sequentially, depending on the nature of the agent(s) and the pharmacological target which may be determined according to the common knowledge and experience of the practitioner. It is to be understood that as used herein the terms "treatment" or "treating" whenever not specifically defined otherwise, include prevention, alleviation and cure of pathological affection, in particular, they include both treatment of established symptoms and prophylactic treatment. The compounds of the present invention for their therapeutic and/or preventive use in the above mentioned pathologies will be preferably used as active ingredients in a pharmaceutical composition. Therefore, a further object of the present invention are pharmaceutical compositions containing a therapeutically effective amount of ralfinamide, preferably as a salt with a pharmaceutically acceptable acid, more preferably a salt with methanesulfonic acid, in a mixture with a pharmaceutically acceptable carrier.

The above said compositions may contain ralfinamide or the salt thereof with a pharmaceutically acceptable acid as a single therapeutically effective agent or may optionally contain an additional agent suitable for the above described adjunctive therapy.

Accordingly, the expression "therapeutically effective" when referred to an "amount", a "dose" or "dosage" of the compounds of this invention is intended as an "amount", a "dose" or "dosage" of said compound sufficient for use in both treatment of the established symptoms and the prophylactic treatment of the above said pathological affections.

The pharmaceutical compositions object of the present invention may be administered in a variety of immediate and modified release dosage forms, e.g. orally, in the form of tablets, troches, capsules, sugar or film coated tablets, liquid solutions, emulsions, suspensions or syrups; rectally, in the form of suppositories; parenterally, e.g. by intramuscular and/ or depot formulations; intravenous injection or infusion; intranasally; locally and transdermally in form of patch and gel and cream.

Suitable pharmaceutically acceptable, therapeutically inert organic and/or inorganic carrier materials useful in the preparation of such composition include, for example, water, gelatin, gum arabic, lactose, starch, cellulose, magnesium stearate, talc, vegetable oils, cyclodextrins, polyalkyleneglycols and the like.

The composition comprising ralfinamide or a salt thereof with a pharmaceutically acceptable acid, optionally in combination with one or more additional therapeutic agent(s) suitable for adjunctive therapy, as mentioned above, can be sterilized and may contain further well known auxiliary components, such as, for example, preservatives, stabilizers, wetting or emulsifying agents, e.g. paraffin oil, mannide monooleate, salts to adjust osmotic pressure, buffers and the like.

For example, the solid oral forms may contain, together with the active ingredient, diluents, e.g. lactose, dextrose, saccharose, cellulose, corn starch or potato starch; lubricants, e.g. silica, talc, stearic acid, magnesium or calcium stearate, and/or polyethylene glycols; binding agents, e.g. starches, arabic gums, gelatin, methylcellulose, carboxymethylcellulose or polyvinyl pyrrolidone; disgregating agents, e.g. a starch, alginic acid, alginates or sodium starch glycolate; effervescing mixtures; dyestuffs; sweeteners; wetting agents such as lecithin, polysorbates, laurylsulphates; and, in general, non-toxic and pharmacologically inactive substances used in pharmaceutical formulations. Said pharmaceutical preparations may be manufactured according to common techniques, for example, by means of mixing, granulating, tabletting, sugar-coating, or film-coating processes. The oral formulations comprise sustained release formulations that can be prepared in conventional manner, for instance by applying an enteric coating to tablets and granules.

The liquid dispersion for oral administration may be e.g. syrups, emulsions and suspensions. The syrups may contain as carrier, for example, saccharose or saccharose with glycerine and/or mannitol and/or sorbitol.

Suspensions and emulsions may contain as a carrier, for example, a natural gum, agar, sodium alginate, pectin, methylcellulose, carboxymethyl-cellulose, or polyvinyl alcohol. The suspensions or solutions for intramuscular injections may contain, together with the active compound, a pharmaceutically acceptable carrier, e.g. sterile water, olive oil, ethyl oleate, glycols, e.g. propylene glycol, and, if desired, a suitable amount of lidocaine hydrochloride. The solutions for intravenous injections or infusion may contain as carrier, for example, sterile water or preferably they may be in the form of sterile, aqueous, isotonic saline solutions.

The suppositories may contain, together with the active ingredient, a pharmaceutically acceptable carrier, e.g. cocoa butter, polyethylene glycol, a polyoxyethylene sorbitan, fatty acid ester, surfactants or lecithin. The pharmaceutical compositions as above defined will contain, per dosage unit, e.g., capsule, tablet, powder injection, teaspoonful, suppository and the like from 10 to 500 mg , preferably from 20 to 250 mg, more preferably from 30 to 125 mg of ralfinamide or a salt thereof with a pharmaceutically acceptable acid, if not otherwise specified (these values refer to the content of ralfinamide as a salt with methanesulfonic acid). Optimal therapeutically effective doses to be administered may be readily determined by those skilled in the art and will vary, basically, with the strength of the preparation, with the mode of administration and with the advancement of the condition or disorder treated. In addition, factors associated with the particular subject being treated, including subject age, weight, diet and time of administration, will result in the need to adjust the dose to an appropriate therapeutically effective level.

EXAMPLE 1

SPINAL NERVE LIGATION SURGERY (SNL)

SNL injury was produced on Sprague Dawley rats as described by Chung and colleagues (Kim S. H., Chung JM. "An experimental model for peripheral neuropathy produced by spinal nerve ligation in the rat" . Pain 1992; 50: 355-363).

Anesthesia was induced with 2% halothane in O₂ at 2 1/min and maintained with 0.5% halothane in O₂. The dorsal vertebral column from L4 to S2 was exposed, and the L5 and L6 spinal nerves were identified and carefully isolated. The L5 and L6 spinal nerves were tightly ligated distal to the dorsal root ganglion with 4-0 silk suture. The incision was closed, and the animals were observed for uneventful recoveries. Rats that exhibited motor deficiency (10%) were excluded from additional testing. Sham SNL rats underwent the same surgery and handling as the experimental animals but without SNL.

Behavioral tests

Baseline mechanical and thermal sensitivity were determined for all experimental subjects before sham or L5/L6 spinal nerve ligation (SNL) surgery. The level of the experimental neuropathic pain and the effects of ralfinamide in SNL and sham rats were measured at day 7 after surgery.

Evaluation of tactile and thermal sensitivity

Mechanical threshold was determined by measuring the paw withdrawal threshold to probing with a series of calibrated (0.4-15 gm) von Frey filaments (Chaplan SR, Bach FW, Pogrel JW, Chung JM and Yaksh TL. "Quantitative assessment of tactile allodynia in the rat paw ". J Neurosci Method. 1994; 53: 55-63).

A significant reduction in paw withdrawal threshold from the pre-SNL baseline value indicated tactile hypersensitivity (data are expressed as mean paw-withdrawal threshold in grams) Thermal threshold was determined by measuring paw withdrawal latencies to a radiant heat source applied to the plantar surface of the affected paw of nerve-injured or sham- operated rats (Hargreaves K, Dubner R, Brown F, Flores C, Joris J. "A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia ". Pain. 1988 Jan;32(l):77-88). A significant reduction in paw-withdrawal latency from the pre-SNL baseline value was interpreted as thermal hyperalgesia.

Experimental protocol

On experiment day (day 7 after surgery), baseline thresholds were determined 30 minutes before compound treatment. Neuropathic rats and sham-operated rats were then assigned to groups of 8 animals each, receiving oral administration of three different doses of ralfinamide methanesulfonate (1, 3, and 10 mg/kg, as a salt). The thermal and mechanical thresholds in neuropathic and sham rats were determined at 30, 60, 90, 120, 150, 180, 210, 240 minutes after ralfinamide treatment. Results

The tight ligation of spinal nerves produced a marked reduction in the thermal and the mechanical stimuli which were necessary to evoke paw withdrawal. In spinal nerves-ligated rats, oral administration of ralfϊnamide methanesulfonate at 10 mg/kg (as a salt) increased significantly the withdrawal thresholds in response to mechanical stimuli. The maximal effects were observed within 30 min (-85% recovery of the pre SNL threshold) and returned to pre-treatment neuropathic levels within 240 min. In sham-operated rats, however, oral administration of ralfϊnamide methanesulfonate did not increase the withdrawal threshold in response to mechanical stimuli, showing the compound to be uneffective on normal nociceptions at this dose. In spinal nerves-ligated rats, oral administration of ralfinamide methanesulfonate at 10 mg/kg (as a salt) also increased significantly the withdrawal times of the injured paw in response to thermal stimuli. The maximum possible effect developed in 30 minutes and decreased to the basal neuropathic latency within 240 min.

These results clearly show the efficacy of ralfinamide against pain of neuropathic type.

EXAMPLE 2

CHRONIC COMPRESSION OF THE DORSAL ROOT GANGLIONS (CCD)

In the CCD model of nerve compression the L4 and L5 dorsal root ganglia (DRG) are compressed by a stainless steel rod. This chronic compression leads to an ipsilateral cutaneous allodynia and hyperalgesia associated with increased excitability of neurons in the compressed ganglion.

The surgical procedure for CCD has been performed as described by Song XJ et al. in "Mechanical and thermal hyperalgesia and ectopic neuronal discharge after chronic compression of dorsal root ganglia"- J Neurophysiol (1999); 82:3347-58. Briefly, Sprague Dawley rats were anesthetized with intraperitoneal pentobarbital sodium (40 mg/kg). On the left side, the paraspinal muscles were separated from the mammillary process and the transverse process and intervertebral foramina Of L₄ and L₅ exposed. An L-shaped rod, made of stainless steel, (about 3.5x2mm in length and 0.6mm in diameter) was carefully inserted into each foramen at an angle of 30° to the midline.

After the rod was in place, thus producing the nerve compression, the muscle and skin layers were sutured.

Foot withdrawal treshold to punctate mechanical stimuli (mechanical allodynia) and foot withdrawal threshold to heat stimuli (thermal hyperalgesia) were evaluated on the 7^th post-CCD day as described in the Example 1.

The analgesic effect of ralfinamide, orally administered in a a dose range of 10 to 60 mg/Kg, was evaluated.

The results show that ralfinamide is effective in this animal model for treatment of NLBP/RLBP.

EXAMPLE 3 TAIL FLICK TEST Methods The rat tail flick test was performed according to the method described by D 'Amour FE, Smith DL. "A method for determining loss of pain sensation " . J Pharmacol Exp Ther 1941 ;72:74-79 using an analgesiometer. Two groups of rats were treated p.o. with distilled water (vehicle) or ralfinamide methanesulfonate (30 mg/kg, as a salt), respectively, and 90 min after drug administration, each animal was placed on a platform and the tail was exposed to a focused beam of radiant heat approximately 3 cm from the tip. The thermal nociceptive threshold was defined as the latency required to elicit a flick of the tail in response to the thermal stimulus. The beam light intensity was adjusted to produce a reaction latency of 3-5 sec in control rats. A 20 sec cut-off was used to prevent tissue damage. Data were evaluated by analysis of variance followed by Dunnett's t-test. The latencies, were converted from reaction latencies (sec) to a percentage of the Maximum possible Effect (%MPE) according to the following formula:

post-drug latency - pre-drug latency %MPE = X 100 cut-off(20 sec) - pre-drug latency

Results In the control group the tail flick response latency to noxious heat stimuli was 3.9±0.4 sec. In the treated group, the latency was not statistically different (4.1±0.4 sec) 90 min after administration.

These results show the ineffectiveness of ralfϊnamide against pain of the nociceptive type.

EXAMPLE 4 HOT-PLATE TEST Methods The hot-plate test in the rat was performed according to the method described by Woolfe G and MacDonald AD "The evaluation of the analgesic action of pethidine hydrochloride (Demerol) ". J Pharmacol Exp Ther 1944; 80: 300-307 using an electrically heated and thermostatically controlled aluminum surface (25x25 cm), set to a temperature of 56°C ± 0.05 (U. Basile, Italy). Two groups of rats were treated p.o. with distilled water (vehicle) or ralfinamide methanesulfonate (30 mg/kg, as a salt) and 60 and 120 min later were placed on the hot-plate within a transparent observation cylinder. The thermal nociceptive threshold was defined as the latency (sec) required for eliciting paw licking, repeated shaking of the hind-paw or jumping. A 30 sec cut-off time was used to prevent tissue damage. Data were evaluated by analysis of variance followed by Dunnett's t-test. The latency measurements were converted from reaction latencies (sec) to a percentage of the Maximum possible Effect (%MPE) according to the following formula:

post-drug latency - pre-drug latency %MPE = X 100 cut-off(30 sec) — pre-drug latency

Results

In the vehicle group the hind paw licking/jumping thresholds to noxious heat stimuli was 17.9±1.6 sec. Ralfinamide methanesulfonate did not change nociceptive threshold, neither 60 min (18.411.2 sec) nor 120.

These results confirm the ineffectiveness of ralfinamide against pain of the nociceptive pain. EXAMPLE 5 CLINICAL TRIAL

A Phase II study, randomized, double-blind, placebo-controlled, multi-center, multinational study has been conducted to determine preliminary evidence of efficacy and evaluate the safety, tolerability and maximum tolerated dose of escalating doses of ralfϊnamide methanesulfonate from 80 to 320 mg/day (40-160 mg b.i.d.; as a salt), compared to placebo, in patients with different types of neuropathic pain. A total of 272 patients were randomized (ralfinamide methanesulfonate: 177; placebo: 95), but one patient on the ralfinamide group did not receive the treatment. 56 patients (31.6 %) in the ralfinamide methanesulfonate group and 22 patients (23%) in the placebo group discontinued the trial prematurely.

The demographic characteristics of the study population (respectively, ralfinamide methanesulfoante, and placebo) are as follows: mean age: 58.1 ± 11.4 and 56.8 ± 9.7; gender (% male): 53.1% and 54.7%, and mean body weight (kg): 75.5 ± 14.7 and 76.5 ± 15.8, respectively.

The proportion of the recruited patients, with each sub-type of neuropathic pain, was as follow (ralfinamide methanesulfonate; placebo): NCET - Nerve Compression/Entrapment (33.4%; 41.1%), diabetic neuropathy (25%; 22%), traumatic neuropathy (15%; 11%), post-herpetic neuropathy (7.3%; 7.4%), ischaemic nerve roots (5.6%; 5.3%), and other sub-types (14%; 14%).

Ralfinamide methanesulfonate at a dose of 320 mg/day (as a salt) was well tolerated; approximately 75% of patients were able to reach and maintain the maximum prescribed dose (320 mg/day for ralfinamide methanesulfonate). The proportion of patients discontinuing, due to Adverse Events (AEs) was comparable in the two groups (ralfinamide methanesulfonate: 6.8%; placebo: 5.3%). No clinically significant or relevant pattern of adverse effects of ralfinamide on vital signs, laboratory values or ECG parameters was noted. In addition, the proportion of patients with a new abnormality noted on the ophthalmological examination at endpoint, as compared to the screening evaluation, was similar in both groups (ralfinamide methanesulfonate: 1 1.5%; placebo: 10.4%).

The primary efficacy analysis was based on the change from baseline to week 8 (day 56) or end-point (in case of premature termination) on the Visual Analogue Scale for pain assessment (VAS) as rated by the patient. The secondary efficacy analysis was based on the assessment of the improvement, in the daily pain score, using the daily pain diary on the 11 -point Likert categorical scale as reported in the EMEA Guidelines, particularly in the " Reccommandation of Committee for Medical Products or Human Use (CHMP) Guideline on Clinical Medicinal Products intended for the treatment of Neuropathic Pain ". London, 24 January 2007 Doc. Ref. CPMP/EWP/252/03 Rev. 1. See also G. Cruccu et al. "EFNS guidelines on Neuropathic Pain assessment". European Journal of Neurology 2004, 11 : 153-162. The following Table 1 shows the comparison between the change in the VAS score of the group of patients receiving ralfinamide methanesulfonate and the change in the VAS score of the group of patients receiving placebo TABLE 1

Primary efficacy measure (VAS) in all recruited patients

(-) Treatments were compared by using ANCOVA (analysis of covariance) with mean baseline VAS, treatment and centre as covariates. Missing data were substituted with LOCF method.

LOCF = Last Observation Carried Forward; n= number of patients;

Baseline= values at the start of the study;

Endpoint= values at the end of the study, the missing values are replaced by LOCF; Adjusted= mean adjusted for the covariates of the ANCOVA model;

Treatment Difference Estimate= difference between the adjusted change from Baseline to the Endpoint;

ITT = intent-to-treat: primary analysis conducted on all randomized subjects with at least one post treatment evaluation; 95% CI = 95% Confidence Interval; SE= Standard Error; SD= Standard Deviation.

The comparison between ralfinamide methanesulfonate and placebo groups for the VAS (mean change from baseline to endpoint) showed a positive trend (p<0.075) indicating a benefit with ralfinamide treatment in patients with any type of neuropathic pain. Additionaly, efficacy analysis were conducted on different category of neurophatic pain ( eg. NCET, diabetic neuropathy etc).

When data from a subpopulation of patients with the NCET pain ("NCET patients"), where a combination of nociceptive and neurophatic components is involved, 96 patients (35.6%), respectively, 57 on ralfinamide methanesulfonate and 39 on placebo), were analyzed separately the improvement noted on the VAS with ralfinamide methanesulfonate treatment was significantly greater than in the placebo group (p=0.037; adjusted change from Baseline to Endpoint of -22.1( 95 % CI of -29.0 to -15.3) for ralfinamide methanesulfonate and - 12.2 (95% CI -19.9; -4.4) for placebo.

The anatomical/etiological classification of NCET syndromes characterized by painful focal neuropathies (mono neuropathies, plexopathies and radiculopathies) did include, for instance: carpal tunnel syndrome, tarsus tunnel syndrome, ulnar nerve entrapment, compression radiculopathy, lumbar spinal stenosis, sciatic nerve compression, spinal root compression and intercostal neuralgia.

The following Table 2 shows the comparison between the VAS rating of the group of NCET patients receiving ralfinamide methanesulfonate and the VAS rating of the group of NCET patients receiving placebo.

TABLE 2 Primary efficacy measure (VAS) in patients with Nerve Compression/Entrapment

(-) Factorial analysis of covariance (treatment by neuropathic pain) using Baseline as a covariate. Missing data were substituted with LOCF. Adjusted = mean adjusted for the covariates of the ANCOVA model; Treatment Difference Estimate = difference between the adjusted change from Baseline to the Endpoint;

NCET patients showed statistically significant (p=0.037) improvement in mean change in VAS scores with ralfinamide methanesulfonate treatment, with respect to placebo. In addition, the proportion of patients showing at least 50% improvement in the VAS score was significantly higher (p=0. 012) for the ralfinamide methanesulfonate group

(45.6%), compared to the placebo group (20.5 %).

In a further analysis (Table 3) regarding patients with NCET pain, the improvement noted on the 11 -point Likert pain rating scale in the group of patients receiving ralfinamide methanesulfonate was significantly greater than in the placebo group (p=0.0418; adjusted change from Baseline to Endpoint of -1.84 (95% CI -2.52, -1.16) for ralfinamide and -0.98

(95% CI -1.68, -0.29) for placebo.

TABLE 3 Secondary efficacy measure (Likert) in patients with Nerve

Compression/Entrapment

(-) Factorial analysis of covariance (treatment by neuropathic pain) using Baseline as a covariate. Missing data were substituted with LOCF. Adjusted= mean adjusted for the covariates of the ANCOVA model; Treatment Difference Estimate= difference between the adjusted change from Baseline to the Endpoint;

Overall, ralfinamide was significantly superior to placebo in reducing the severity of mixed or combined pain, with a greater number of patient responders. The superiority of ralfinamide was particular significant in patients with nerve compression and/or nerve entrapment (NCET) syndromes. Statistically significant benefit was measured on the VAS and 11 -point Likert pain scale, both in terms of mean change from baseline and in the proportion of responders (>50% improvement) to the treatment with ralfinamide methanesulfonate.

Claims

1. The compound (S)-(+)-2-[4-(2-fluorobenzyloxy) benzylamino] propanamide (ralfϊnamide) or a salt thereof with a pharmaceutically acceptable acid for use in the treatment of mixed or combined pain where a nociceptive component is combined with a neurophatic component.

2. The compound of claim 1 which is the salt of (S)-(+)-2-[4-(2-fluorobenzyloxy) benzylamino] propanamide (ralfinamide) with methanesulfonic acid.

3. The compound of any of claims 1 and 2 for use in the treatment of mixed or combined pain where the mixed or combined pain comprises nerve compression and/or nerve entrapment syndromes.

4. The compound of claim 3 for use in the treatment of nerve compression and/or nerve entrapment syndromes where the nerve compression and/or nerve entrapment syndrome is one or more of the following syndromes: carpal tunnel syndrome, tarsus tunnel syndrome, ulnar nerve entrapment, compression radiculopathy, lumbar spinal stenosis, sciatic nerve compression, spinal root compression and intercostal neuralgia.

5. The compound of claim 4 for use in the treatment of a nerve compression and/or nerve entrapment syndrome which is carpal tunnel syndrome and/or compression radiculopathy.

6. A compound of any of claims 1 to 3 for use in the treatment of neuropathic low back pain (NLBP) or radicular low back pain (RLBP).

7. A compound of any of claims 1 to 6 for use in the treatment as in any of claims 1 to 6 wherein the said compound is administered to a patient in need thereof in a daily dosage (as the salt with methanesulfonic acid) from 10 to 1000 mg per day, preferably from 30 to 500 mg per day, more preferably from 60 to 350 mg per day, most preferably from 80 to 320 mg per day.

8. A compound of claim 6 for use in the treatment of neuropathic low back pain (NLBP) or radicular low back pain (RLBP) characterized in that said compound is administered to a patient in a daily dosage (as the salt with methanesulfonic acid) from 160 to 320 mg.

9. A compound according to any of claims 1 to 8 for use in the treatment of mixed or combined pain in combination with one or more other therapeutic agents.

10. A compound according to claim 9 wherein the other therapeutic agent(s) is/are selected from gabapentin, pregabalin, paracetamol, phenacetin, lamotrigine, valproate, venlafaxine, amitryptiline, duloxetine, haloperidol and benzodiazepine anxiolytic derivatives

11. Use of a compound of any of claims 1 to 6 for the manufacture of a medicament for the treatment of patients suffering of a mixed or combined pain where a nociceptive component is combined with a neurophatic component, optionally in combination with one or more other therapeutic agents.

12. Use of a compound according to claim 11 wherein the patient is suffering of neurophatic low back pain (NLBP) or radicular low back pain (RLBP).

13. Use of a compound according to claim 12 characterized in that the compound is embodied into a pharmaceutical dosage form suitable for administering from 160 to 320 mg per day to the patient affected by neurophatic low back pain (NLBP) or radicular low back pain (RLBP).

14. A pharmaceutical formulation for use in the treatment of mixed or combined pain where a nociceptive component is combined with a neuropathic component, comprising a compound as defined in any of claims 1 to 8 as the active ingredient, optionally in conjunction with another therapeutic agent, together with one or more pharmaceutically acceptable excipients, carriers or diluents.

15. A method for treating a patient suffering of a mixed or combined pain where a nociceptive component is combined with a neuropathic component which comprises administering to said patient a therapeutically effective amount of (S)-(+)-2-[4-(2- fluorobenzyloxy) benzylamino] propanamide (ralfinamide) or a salt thereof with a pharmaceutically acceptable acid, optionally in combination with one or more other therapeutic agents.

16. A method as in claim 15 wherein the salt of (S)-(+)-2-[4-(2-fluorobenzyloxy) benzylamino] propanamide (ralfinamide) is a salt with methanesulfonic acid.

17. A method as in claim 15 wherein the mixed or combined pain comprises nerve compression and/or nerve entrapment syndromes.

18. A method as in claim 15 where the syndrome is one or more of the following syndromes: carpal tunnel syndrome, tarsus tunnel syndrome, ulnar nerve entrapment, compression radiculopathy, lumbar spinal stenosis, sciatic nerve compression, spinal root compression and intercostal neuralgia.

19. A method as in claim 18 where the syndrome is carpal tunnel syndrome and/or compression radiculopathy.

20. A method as in claim 15 wherein the patient is suffering of neuropathic low back pain (NLBP) or radicular low back pain (RLBP).

21. A method as in any of claims 15 to 20 wherein the compound is administered to a patient in need thereof in a dosage (as the salt with methanesulfonic acid) from 10 to 1000 mg per day, preferably from 30 to 500 mg per day, more preferably from 60 to 350 mg per day, most preferably from 80 to 320 mg per day.

22. A method as in claim 20 wherein the compound is administered to the patient in need thereof in a daily dosage (as the salt with methanesulfonic acid) from 160 to 320 mg.