WO2016071511A1

WO2016071511A1 - Treatment of mast cell activation syndrome (mcas) with masitinib

Info

Publication number: WO2016071511A1
Application number: PCT/EP2015/075977
Authority: WO
Inventors: Alain Moussy; Jean-Pierre Kinet; Colin Mansfield
Original assignee: Ab Science
Priority date: 2014-11-07
Filing date: 2015-11-06
Publication date: 2016-05-12

Abstract

The present invention relates to a method for treating mast cell activation syndrome (MCAS) in human patients comprising administering a tyrosine kinase inhibitor to patients in need of, wherein said tyrosine kinase inhibitor is an inhibitor of wild-type c-Kit, Lyn and Fyn kinase activity and is preferably masitinib.

Description

TREATMENT OF MAST CELL ACTIVATION SYNDROME (MCAS)

WITH MASITINIB

FIELD OF INVENTION

The present invention relates to a method for treating mast cell activation syndrome (MCAS), and more particularly MCAS associated with severe handicap, comprising administering a tyrosine kinase inhibitor, preferably masitinib, to patients in need thereof.

BACKGROUND OF INVENTION

Mast cells are characterized by their heterogeneity, not only regarding tissue location and structure but also at functional and histochemical levels. Mast cell activation is followed by the controlled release of a variety of mediators that are essential for the defense of the organism against invading pathogens. By contrast, in the case of hyperactivation of mast cells, uncontrolled hypersecretion of these mediators is deleterious for the body. Mast cells produce a large variety of mediators categorized here into three groups:

Preformed granule-associated mediators (histamines, proteoglycans, and neutral proteases);

Lipid-derived mediators (prostaglandins, thromboxanes and leucotrienes); Various cytokines (including the interleukins: IL-1 , IL-2, IL-3, IL-4, IL-5, IL- 6, IL-8 and tumor necrosis factor alpha TNF-a, GM-CSF, ΜΓΡ-Ι , ΜΓΡ-1β and IFN-γ).

Human mast cells constitutively express a number of receptors for different biological molecules. Among these receptors, whose ligation induces the activation of mast cells, the best known is the high affinity receptor for IgE (FcsRI). Binding of IgE- multivalent antigen complexes to FcsRI leads to receptor aggregation and internalization, signaling, and de granulation. This can be accompanied by the transcription of cytokine genes, thus, perpetuating the inflammatory response. Moreover, triggering of mast cells leads to the secretion of diverse pre-formed and/or de novo synthesized mediators, such as vasoactive amines (histamine, serotonin), sulfated proteoglycans, lipid mediators (prostaglandin D2, leucotrienes), growth factors, proteases, cytokines and chemokines as described previously. These mediators can, alone or in synergy with macrophage-derived and T cell-derived cytokines, generate a complex inflammatory response and induce the recruitment and activation of inflammatory cells to the site of degranulation.

Inappropriate activation of mast cells, without proliferation or otherwise accumulation of mast cells, results in a syndrome named mast cell activation syndrome (MCAS).

The marked clinical heterogeneity of clinical signs and symptoms encompassed by the term MCAS renders the diagnosis and therapeutic treatment of patients suffering from MCAS complex and particularly challenging for the physician or the diagnostician.

In 2011, Molderings et al. (Molderings et al., Journal of Hematology & Oncology, 2011, 4:10) have nevertheless proposed a method allowing MCAS to be diagnosed, and comprising a set of two major and four minor criteria, as described in the present invention (modified from the World Health Organization 2008 consensus diagnostic criteria for systemic mastocytosis).

Patients suffering from MCAS often experience symptoms resulting from the constitutive activation of mast cells and release of their mediators. Collectively, these are referred to as "mast cell mediator release symptoms". Systemic symptoms may include: asthenia, pruritus, food intolerance, erythematous crisis, muscle and joint pain, pollakiuria (micturition frequency), epigastric pain, aerophagia/eructation, memory loss, and psychological impact of the disease, particularly depression (Hermine O, et al., PLoS ONE. 2008;3:e2266). Each clinical symptom can be objectively measured by frequency or via an appropriate rating scale, although these do not form any part of formal diagnosis of MCAS. However, no formally established thresholds for categorizing the burden and severity of disability in MCAS related to mast cell mediator release associated handicaps exist. This is in part because the perception of handicap is highly dependent on the patient's lifestyle and environment; that is to say, identical symptoms may be perceived as a handicap resulting in significant detriment to quality- of- life for one patient, yet impact on another patient merely as a minor annoyance. Thus, beyond the method of Molderings et al. for diagnosing MCAS, diagnosis mast cell mediator release associated handicap relies upon the patient' s and physician's assessment of handicap severity.

To make the patient's and physician's assessment of handicap severity objective and measurable, it is usually relied on the following measuring methods/rating scales:

- for flushes: number of flushes per week;

for diarrhea: number of stools per day;

for pollakiuria: number of micturitions per day;

for depression: the score on the Hamilton rating scale (Hamilton M. J Neurol Neurosurg Psychiatry. 1960;23:56-62 ; Hedlund JL, et al. J Oper Psychiatry. 1979;10: 149-161). The Hamilton rating scale (Ham-D17) remains a reference measure to evaluate depression in research concerning somatic patients. Ham-D17 is composed of 17 items scored 0-4 (depressed mood, guilt, suicide, psychic and somatic anxiety, psychomotor retardation, agitation, hypochondriasis, work and interests impairment) or 0-2 (early, middle and late insomnia, gastrointestinal, somatic general, genital, loss of weight and loss of insight items) according to the absence, presence and seriousness of the symptom;

for fatigue: the score on the Fatigue Impact scale (FIS) (The Fatigue Impact Scale was designed as a fatigue- specific measure for patients in primary care setting and also as a research tool (Fisk JD, et al. Clin Infect Dis. 1994;18:S79-83). It can be used as a clinical measure to guide intervention or treatment, and to assess change over time. FIS consists of 40 questions within these three groups: cognitive, physical, and psychosocial functioning. The person who is taking the test rates the extent to which fatigue causes problems in his/her life. The Fatigue Impact Scale (FIS) is one of the most widely used tools, although there now exist modified versions [the modified Fatigue Impact Scale (MFIS), the daily FIS, the unidimensional FIS and the abbreviated MFIS]). Other scores for measuring fatigue include, but are not limited to, Fatigue Severity Scale (FSS), Fatigue Symptom Inventory (FSI), Brief Fatigue Inventory (BFI) or Multidimensional Assessment of Fatigue (MAF), as described by Whitehead (Journal of Pain and Symptom Management, 2009, 37(1): 107-128); for pruritus: the score on a numerically amended version of the scale taught in Hermine O, et al., PLoS ONE. 2008;3:e2266 (The presence of pruritus and its score can be assessed in compliance with Hermine O, et al., PLoS ONE. 2008;3:e2266);

for pain: the Visual Analog Scale for Pain ( VAS) score or the Brief Pain Inventory (BPI) score may be used for assessing pain. Pain assessment tools may be unidimensional or multidimensional. For simple assessment of changes in pain intensity and for assessment of pain intensity in clinical settings, VAS based tools have been proven to be psychometrically satisfactory. VASs consist of a line, usually 10 cm long, whose ends are labeled as the extremes of pain (for example, "no pain" to "pain as bad as it could be"). Patients are simply asked to indicate which point along the line best represents their pain intensity. The distance from the no pain end to the mark made by the patient is that patient's pain intensity score. VASs are directly correlated with other self-report measures of pain intensity, as well as to observed pain behavior [Jensen, MP, et al., J Pain 2003;4(1): 2e21]. The BPI is a medical questionnaire used to measure pain, developed by the Pain Research Group of the world health organization (WHO) Collaborating Centre for Symptom Evaluation in Cancer Care [Cleeland CS, et al., (March 1994). "Pain assessment: global use of the Brief Pain Inventory". Ann. Acad. Med. Singap. 23 (2): 129-38].

Depending on the score and thus on the severity of the handicap, MCAS may be thus be classified as mild, moderate or severe (or as MCAS associated with mild, moderate or severe handicap), with the latter category representing a disabling even life-threatening problem.

The treatment of MCAS, and more specifically of MCAS with severe mast cell mediator release associated handicap remains a challenge to clinicians because of the diversity and complexity of the syndrome itself and the lack of standard and highly effective therapy. None of the known approved drugs appear to represent a cure for the syndrome, and no available therapy appears to regulate the activation of mast cells responsible for MCAS. Moreover, the efficacy of known drugs is limited and may decrease over time, with undesirable side effects reported. A retrospective of the possible drugs used for treating MCAS and its symptoms is provided in Afrin, "Presentation, diagnosis, and management of mast cell activation syndrome", Mast Cells, 2013, Nova Science Publishers, Ed. David B. Murray. Among the available drugs, Glucocorticoids may be used for controlling MCAS chronically and emergently, since they are inexpensive, but the well-known toxicities from chronic use render them less preferable.

The most inexpensive sustainable therapies for MCAS generally include histamine HI and H2, such as diphenhydramine, or receptor blockers, such as loratadine, fexofenadine, cetirizine and levocitirizine; further, benzodiazepines may also be administered, such as diazepam, clonazepam, alprazolam or flunitrazepam; imidazopyridines such as Zolpidem may also be used for targeting the benzodiazepine receptor.

Non-steroidal anti-inflammatory drugs (NSAIDs) may also be very helpful in some MCAS patients, but these drugs (and many narcotic analgesics, too) can trigger flares of mast cells activation, even to the point of anaphylaxis, and even at ordinarily trivial doses. Among NSAIDs, aspirin remains the least expensive compound, but where aspirin remains intolerable or ineffective, the use of COX2-selective inhibitors such as celecoxib can be considered. Further, considering that leukotrienes are synthesized and released by mast cells and clearly drive a wide variety of events categorized as inflammatory in nature, leukotriene receptor antagonists such as montelukast and zafirlukast may be used for treating some forms of MCAS.

Cromolyn has also been reported for its mast-cell-stabilizing activity in some patients, and though its specific mechanism of action remains unclear, it has recently been discovered to be a potent agonist of the G-protein-coupled receptor 35, whose expression in human mast cells, eosinophils and basophils is upregulated upon challenge with IgE antibodies.

Finally, Pentosan, Quercetin, pancreatic enzyme supplements or antibodies binding the Fc portion of IgE, such as omalizumab may also provide beneficial effects in patients suffering from MCAS. The use of masitinib, a small molecular weight tyrosine kinase inhibitor capable of inhibiting the tyrosine kinase activity of c-Kit, or of a pharmaceutical salt or solvate thereof has shown promising results in the treatment of mastocytosis and more specifically in the treatment of cutaneous or systemic mastocytosis, indolent systemic mastocytosis or smoldering systemic mastocytosis in human patients, optionally in combination with at least one other cytoreductive or disease modifying drug, with an overall patient assessment (OPA)>l (see e.g. the patent application US 13/881,043). Nevertheless, masitinib, or any other similar tyrosine kinase inhibitors, including imatinib, dasatinib, midostaurin has never been reported as to possess a beneficial effect on patients suffering from mast cell activation syndrome.

It therefore results that there is no indication, in the prior art, that any of the known drugs could actually provide a reliable treatment for alleviating the symptoms of patients suffering from MCAS, and more specifically of MCAS with severe mast cell mediator release associated handicap. Thus, there exists a continuing need to identify new targeted drugs that possess greater inhibitory action against the uncontrolled activation of mast cells which results in the occurrence of MCAS, while being also capable of minimizing side effects.

SUMMARY This invention thus relates to a method for treating MCAS, and more particularly MCAS associated to severe handicap, by administering a tyrosine kinase inhibitor.

The present invention thus relates to a method for treating mast cell activation syndrome (MCAS) in human patients comprising administering a tyrosine kinase inhibitor. In one embodiment, said tyrosine kinase inhibitor is an inhibitor of wild-type c-Kit, Lyn and Fyn kinase activity. In one embodiment, said tyrosine kinase inhibitor is masitinib or a pharmaceutically acceptable salt thereof. In one embodiment, said tyrosine kinase inhibitor is masitinib mesilate.

In one embodiment, said MCAS is as defined by the Molderings diagnostic criteria, or the Valent diagnostic criteria, or the Akin diagnostic criteria. In one embodiment, said mast cell activation syndrome comprises at least one mast cell mediator release associated handicap, wherein said handicap is a mild, moderate or severe handicap.

In one embodiment, said at least one mast cell mediator release associated handicap is selected from the list comprising asthenia, pruritus, food intolerance, erythematous crisis, bone, muscle and joint pain, pollakiuria, epigastric pain, aerophagia/eructation, memory loss and psychological impact of the disease, particularly depression, anaphylaxis, faintness, fatigue, flushing, rashes, itching, hives, blood pressure changes and shock, chest pain, rapid heart rate, wheezing, degenerative disc disease, osteoporosis/osteopenia, nausea, vomiting, abdominal pain, gastroesophageal reflux, diarrhea, inflammation of the esophagus, intestinal cramping and bloating, malabsorption, cognitive difficulties/brain fog, dizziness/vertigo, lightheadedness, migraine headache, paresthesia, and peripheral neuropathy.

In one embodiment, said severe handicap comprises at least one of pruritus, flushes, depression, fatigue, pain, pollakiuria and diarrhea, and if present handicaps are considered as being severe on an appropriate scale of said handicap, preferably having the following scores: pruritus score between 6 and 10, preferably 9 or > 9; number of flushes per week between 7 and 9, preferably 8 or > 8; depression measured by the Hamilton rating scale between 14 and 24, preferably 19 or > 19; fatigue score measured by FIS between 65 and 90, preferably 75 or > 75 (or any equivalent cut-off determined using the FSS, FSI, BFI or MAF); pain measured by VAS between 15 and 25, preferably 20 or > 20 (or any equivalent cut-off determined using the BPI or unidimensional or multidimensional pain assessment tool); number of stools per day between 3 and 5, preferably 4 or > 4; number of micturition per day between 7 and 9, preferably 8 or > 8. In one embodiment, said tyrosine kinase inhibitor is to be administered at a starting daily dose of 3.0 to 6.0 mg/kg/day, preferably reaching a stable treatment dose of 4.5 to 6.0 mg/kg/day. In one embodiment, said tyrosine kinase inhibitor is dose escalated by increments of 1.5 mg/kg/day to reach a maximum of 9.0 mg/kg/day.

In one embodiment, said tyrosine kinase inhibitor is administered orally. In one embodiment, said tyrosine kinase inhibitor is administered twice a day.

In one embodiment, said tyrosine kinase inhibitor is comprised in a pharmaceutical composition in an amount of at least 50 mg and less than 600 mg, preferably of at least 100 mg and less than 400 mg. The present invention also relates to a tyrosine kinase inhibitor for use in the treatment of mast cell activation syndrome (MCAS) in human patients.

In one embodiment, said tyrosine kinase inhibitor is an inhibitor of wild-type c-Kit, Lyn and Fyn kinase activity.

In one embodiment, said tyrosine kinase inhibitor is masitinib or a pharmaceutically acceptable salt thereof, and preferably masitinib mesilate.

In one embodiment, said MCAS treated by the method of the invention is as defined by the Molderings diagnostic criteria, or the Valent diagnostic criteria, or the Akin diagnostic criteria.

In one embodiment, said MCAS comprises at least one mast cell mediator release associated handicap, wherein said handicap is a mild, moderate or severe handicap, and is preferably severe handicap.

In one embodiment, said at least one mast cell mediator release associated handicap is selected from the list comprising asthenia, pruritus, food intolerance, erythematous crisis, bone, muscle and joint pain, pollakiuria, epigastric pain, aerophagia/eructation, memory loss and psychological impact of the disease, particularly depression, anaphylaxis, faintness, fatigue, flushing, rashes, itching, hives, blood pressure changes and shock, chest pain, rapid heart rate, wheezing, degenerative disc disease, osteoporosis/osteopenia, nausea, vomiting, abdominal pain, gastroesophageal reflux, diarrhea, inflammation of the esophagus, intestinal cramping and bloating, malabsorption, cognitive difficulties/brain fog, dizziness/vertigo, lightheadedness, migraine headache, paresthesia, and peripheral neuropathy. In one embodiment, said severe handicap comprises at least one of pruritus, flushes, depression, fatigue, pain, pollakiuria and diarrhea, and if present handicaps are considered as being severe on an appropriate scale of said handicap, preferably having the following scores: pruritus score between 6 and 10, preferably 9 or > 9; number of flushes per week between 7 and 9, preferably 8 or > 8; depression measured by the Hamilton rating scale between 14 and 24, preferably 19 or > 19; fatigue score measured by FIS between 65 and 90, preferably 75 or > 75 (or any equivalent cut-off determined using the FSS, FSI, BFI or MAF); pain measured by VAS between 15 and 25, preferably 20 or > 20 (or any equivalent cut-off determined using the BPI or unidimensional or multidimensional pain assessment tool); number of stools per day between 3 and 5, preferably 4 or > 4; number of micturition per day between 7 and 9, preferably 8 or > 8.

In one embodiment, said tyrosine kinase inhibitor is administered orally, preferably at a starting daily dose of 3.0 to 6.0 mg/kg/day, preferably reaching a stable treatment dose of 4.5 to 6.0 mg/kg/day, and is preferably dose escalated by increments of 1.5 mg/kg/day to reach a maximum of 9.0 mg/kg/day.

DEFINITIONS

In the present invention, the following terms have the following meanings:

As disclosed above, the expression "mast cell activation syndrome" (MCAS), as used in the present application, encompasses a collection of clinical signs and symptoms resulting from the inappropriate activation of mast cells, wherein no proliferation or otherwise accumulation of mast cells is observed. According to an embodiment, MCAS corresponds to the syndrome defined by the Molderings criteria, or the Valent diagnostic criteria, or the Akin diagnostic criteria, as defined below. In a first embodiment, MCAS is defined according to Molderings et al. (Molderings et al., Journal of Hematology & Oncology, 2011, 4:10), and thus relates to a syndrome for which both hereinafter major criteria or the second hereinafter major criterion and at least one hereinafter minor criterion are fulfilled: Major criteria:

o Multifocal or disseminated dense infiltrates of mast cells in bone marrow biopsies and/or in sections of other extracuteanous organ(s), e.g. gastrointestinal tract biopsies; CD117-, tryptase- and CD25-stained; o Unique constellation of clinical complaints as a result of a pathologically increased mast cell activity (mast cell mediator release syndrome).

Minor criteria:

o Mast cells in bone marrow or other extracutaneous organ(s) show an abnormal morphology (>25%) in bone marrow smears or in histologies; o Mast cells in bone marrow express CD2 and/or CD25;

o Detection of genetic changes in mast cells from blood, bone marrow or extracutaneous organs for which an impact on the state of activity of affected mast cells in terms of an increased activity has been proved; o Evidence of a pathologically increased release of mast cell mediators by determination of the content of: tryptase in blood, N-methylhistamine in urine, heparin in blood, chromogranin A in blood, other mast cell- specific mediators (e.g. leukotrienes, prostaglandin D₂).

In a second embodiment, the term MCAS is defined by the Valent diagnostic criteria (Valent et al, Int Arch Allergy Immunol 2012, 157:215-225), and thus relates to a syndrome for which the following criteria are fulfilled:

1. typical clinical signs and symptoms, including: flushing, pruritus, urticaria, angioedema, nasal congestion, nasal pruritus, wheezing, throat swelling, headache, hypotension, and diarrhea.

2. Substantial and transient increase in a mast cell (MC)-derived mediator in biological fluids [preferably serum total tryptase, but also histamine/histamine metabolites and prostaglandin D2 (PGD2)/PGD2 urinary metabolites] during or shortly after the acute event compared to a baseline level recorded either before the acute event or at least 24 h after all clinical signs and symptoms of the event have completely resolved.

3. An objective major response of clinical symptoms to agents that attenuate the production or activity of MC-derived mediators. According to the definition of Valent et al, all three criteria should be met to define MCAS. However, in some circumstances, a patient may not respond to a drug and may even require intensive care and epinephrine administration. In such a patient, the condition may still be considered as MCAS if typical symptoms (1) and an increase in MC mediators (2) are present, and a primary underlying MC disease (e.g. SM) or an underlying IgE-mediated disease (e.g. allergy) is known.

In a third embodiment, the term MCAS is defined by the Akin diagnostic criteria (Akin et al, J Allergy Clin Immunol, 2010, 126(6): 1099- 1104), and thus relates to a syndrome for which the following criteria are fulfilled:

- episodic symptoms consistent with mast cell mediator release affecting two or more organ systems evidenced as follows:

o skin: urticaria, angioedema, flushing;

o gastrointestinal: nausea, vomiting, diarrhea, abdominal cramping;

o cardiovascular: hypotensive syncope or near syncope, tachycardia;

o respiratory: wheezing;

o naso-ocular: conjunctival injection, pruritus, nasal stuffiness; a decrease in the frequency or severity, or resolution of symptoms with anti- mediator therapy: HI and H2 histamine receptor antagonists, anti-leukotriene medications (cysLT receptor blockers or 5-LO inhibitor), or mast cell stabilizers (cromolyn sodium);

evidence of an elevation in a validated urinary or serum marker of mast cell activation: documentation of elevation of the marker above the patient's baseline during a symptomatic period on at least two occasions; or if baseline tryptase levels are persistently > 15ng, documentation of elevation of the tryptase above baseline in one occasion. Total serum tryptase is recommended as the markers of choice; less specific (also from basophils) 24 hours urine histamine metabolites or 11-beta-prostaglandin F2;

primary (clonal) and secondary disorders of mast cell activation ruled out. Primary disorders of mast cell activation include: anaphylaxis with an associated clonal mast cell disorder, and monoclonal mast cell activation syndrome (MMAS).

Secondary disorders of mast cell activation include: allergic disorders, mast cell activation associated with chronic inflammatory or neoplastic disorders, physical urticarias, chronic autoimmune urticaria.

The term "subject" refers to a mammal, preferably a human. In one embodiment, a subject may be a "patient", i.e. a warm-blooded animal, more preferably a human, who/which is awaiting the receipt of, or is receiving medical care or was/is/will be the object of a medical procedure, or is monitored for the development of MCAS.

The terms "treating" or "treatment" refers to both therapeutic treatment and prophylactic or preventative measures; wherein the object is to prevent or slow down (lessen) MCAS. Those in need of treatment include those already with MCAS as well as those prone to have MCAS or those in whom MCAS is to be prevented. A subject is successfully "treated" for MCAS if, after receiving a therapeutic amount of a tyrosine kinase inhibitor according to the methods of the present invention, the subject shows observable and/or measurable reduction in or absence of one or more of the following: reduction in the number of pathogenic cells; reduction in the percent of total cells that are pathogenic; and/or relief to some extent, of one or more of the symptoms associated with MCAS; reduced morbidity and mortality, and improvement in quality of life issues. The above parameters for assessing successful treatment and improvement in the disease are readily measurable by routine procedures familiar to a physician.

The term "therapeutically effective amount" means the level or amount of agent that is aimed at, without causing significant negative or adverse side effects to the target, (1) delaying or preventing the onset of MCAS; (2) slowing down or stopping the progression, aggravation, or deterioration of one or more symptoms of MCAS; (3) bringing about ameliorations of the symptoms of MCAS; (4) reducing the severity or incidence of MCAS; or (5) curing MCAS. A therapeutically effective amount may be administered prior to the onset of MCAS, for a prophylactic or preventive action. Alternatively or additionally, the therapeutically effective amount may be administered after initiation of MCAS, for a therapeutic action or maintenance of a therapeutic action.

The term "pharmaceutically acceptable carrier or excipient" refers to an excipient or carrier that does not produce an adverse, allergic or other untoward reaction when administered to an animal, preferably a human. It includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. For human administration, injected preparations should meet sterility, pyrogenicity, general safety and purity standards as required by regulatory offices, such as, for example, FDA Office or EMA.

The term "about" preceding a figure means plus or less 10% of the value of said figure.

As used herein, the term an "aryl group" means a monocyclic or polycyclic-aromatic radical comprising carbon and hydrogen atoms. Examples of suitable aryl groups include, but are not limited to, phenyl, tolyl, anthracenyl, fluorenyl, indenyl, azulenyl, and naphthyl, as well as benzo-fused carbocyclic moieties such as 5,6,7,8-tetrahydronaphthyl. An aryl group can be unsubstituted or substituted with one or more substituents. In one embodiment, the aryl group is a monocyclic ring, wherein the ring comprises 6 carbon atoms, referred to herein as "(C6)aryl".

As used herein, the term "alkyl group" means a saturated straight chain or branched non- cyclic hydrocarbon having from 1 to 10 carbon atoms. Representative saturated straight chain alkyls include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl and n-decyl; while saturated branched alkyls include isopropyl, sec-butyl, isobutyl, tert-butyl, isopentyl, 2-methylbutyl, 3-methylbutyl, 2-methylpentyl, 3- methylpentyl, 4-methylpentyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, 5- methylhexyl, 2,3-dimethylbutyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 2,3- dimethylhexyl, 2,4-dimethylhexyl, 2,5-dimethylhexyl, 2,2-dimethylpentyl, 2,2- dimethylhexyl, 3,3-dimtheylpentyl, 3,3-dimethylhexyl, 4,4-dimethylhexyl, 2- ethylpentyl, 3-ethylpentyl, 2-ethylhexyl, 3-ethylhexyl, 4-ethylhexyl, 2-methyl-2- ethylpentyl, 2-methyl-3-ethylpentyl, 2-methyl-4-ethylpentyl, 2-methyl- 2-ethylhexyl, 2- methyl-3-ethylhexyl, 2-methyl-4-ethylhexyl, 2,2-diethylpentyl, 3,3-diethylhexyl, 2,2- diethylhexyl, 3,3-diethylhexyl and the like. Alkyl groups included in compounds of this invention may be optionally substituted with one or more substituents.

As used herein, the term "alkoxy" refers to an alkyl group which is attached to another moiety by an oxygen atom. Examples of alkoxy groups include methoxy, isopropoxy, ethoxy, tert-butoxy, and the like. Alkoxy groups may be optionally substituted with one or more substituents.

As used herein, the term "heteroaryl" or like terms means a monocyclic or polycyclic heteroaromatic ring comprising carbon atom ring members and one or more heteroatom ring members (such as, for example, oxygen, sulfur or nitrogen). Typically, a heteroaryl group has from 1 to about 5 heteroatom ring members and from 1 to about 14 carbon atom ring members. Representative heteroaryl groups include pyridyl, 1-oxo-pyridyl, furanyl, benzo[l,3]dioxolyl, benzo[l,4]dioxinyl, thienyl, pyrrolyl, oxazolyl, imidazolyl, thiazolyl, isoxazolyl, quinolinyl, pyrazolyl, isothiazolyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, triazolyl, thiadiazolyl, isoquinolinyl, indazolyl, benzoxazolyl, benzofuryl, indolizinyl, imidazopyridyl, tetrazolyl, benzimidazolyl, benzothiazolyl, benzothiadiazolyl, benzoxadiazolyl, indolyl, tetrahydroindolyl, azaindolyl, imidazopyridyl, quinazolinyl, purinyl, pyrrolo[2,3]pyrimidinyl, pyrazolo[3,4]pyrimidinyl, imidazo[l,2-a]pyridyl, and benzo(b)thienyl. A heteroatom may be substituted with a protecting group known to those of ordinary skill in the art, for example, the hydrogen on a nitrogen may be substituted with a tert-butoxycarbonyl group. Heteroaryl groups may be optionally substituted with one or more substituents. In addition, nitrogen or sulfur heteroatom ring members may be oxidized. In one embodiment, the heteroaromatic ring is selected from 5-8 membered monocyclic heteroaryl rings. The point of attachment of a heteroaromatic or heteroaryl ring to another group may be at either a carbon atom or a heteroatom of the heteroaromatic or heteroaryl rings.

The term "heterocycle" as used herein, refers collectively to heterocycloalkyl groups and heteroaryl groups. As used herein, the term "heterocycloalkyl" means a monocyclic or polycyclic group having at least one heteroatom selected from O, N or S, and which has 2-11 carbon atoms, which may be saturated or unsaturated, but is not aromatic. Examples of heterocycloalkyl groups including (but not limited to): piperidinyl, piperazinyl, 2-oxopiperazinyl, 2- oxopiperidinyl, 2-oxopyrrolidinyl, 4-piperidonyl, pyrrolidinyl, hydantoinyl, valerolactamyl, oxiranyl, oxetanyl, tetrahydropyranyl, tetrahydrothiopyranyl, tetrahydropyrindinyl, tetrahydropyrimidinyl, tetrahydrothiopyranyl sulfone, tetrahydrothiopyranyl sulfoxide, morpholinyl, thiomorpholinyl, thiomorpholinyl sulfoxide, thiomorpholinyl sulfone, 1,3-dioxolane, tetrahydrofuranyl, dihydrofuranyl-2- one, tetrahydrothienyl, and tetrahydro-l,l-dioxothienyl. Typically, monocyclic heterocycloalkyl groups have 3 to 7 members. Preferred 3 to 7 membered monocyclic heterocycloalkyl groups are those having 5 or 6 ring atoms. A heteroatom may be substituted with a protecting group known to those of ordinary skill in the art, for example, the hydrogen on a nitrogen may be substituted with a tert-butoxycarbonyl group. Furthermore, heterocycloalkyl groups may be optionally substituted with one or more substituents. In addition, the point of attachment of a heterocyclic ring to another group may be at either a carbon atom or a heteroatom of a heterocyclic ring. Only stable isomers of such substituted heterocyclic groups are contemplated in this definition.

As used herein the term "substituent" or "substituted" means that a hydrogen radical on a compound or group is replaced with any desired group that is substantially stable to reaction conditions in an unprotected form or when protected using a protecting group. Examples of preferred substituents are those found in the exemplary compounds and embodiments disclosed herein, as well as halogen (chloro, iodo, bromo, or fluoro); alkyl; alkenyl; alkynyl; hydroxy; alkoxy; nitro; thiol; thioether; imine; cyano; amido; phosphonato; phosphine; carboxyl; thiocarbonyl; sulfonyl; sulfonamide; ketone; aldehyde; ester; oxygen (-0); haloalkyl (e.g., trifluoromethyl); cycloalkyl, which may be monocyclic or fused or non-fused polycyclic (e.g., cyclopropyl, cyclobutyl, cyclopentyl, or cyclohexyl), or a heterocycloalkyl, which may be monocyclic or fused or non-fused polycyclic (e.g., pyrrolidinyl, piperidinyl, piperazinyl, morpholinyl, or thiazinyl), monocyclic or fused or non-fused polycyclic aryl or heteroaryl (e.g., phenyl, naphthyl, pyrrolyl, indolyl, furanyl, thiophenyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, triazolyl, tetrazolyl, pyrazolyl, pyridyl, quinolinyl, isoquinolinyl, acridinyl, pyrazinyl, pyridazinyl, pyrimidinyl, benzimidazolyl, benzothiophenyl, or benzofuranyl); amino (primary, secondary, or tertiary); C0₂CH₃; CONH₂; OCH₂CONH₂; NH₂; S0₂NH₂; OCHF₂; CF3; OCF3; and such moieties may also be optionally substituted by a fused-ring structure or bridge, for example -OCH₂0-. These substituents may optionally be further substituted with a substituent selected from such groups. In certain embodiments, the term "substituent" or the adjective "substituted" refers to a substituent selected from the group consisting of an alkyl, an alkenyl, an alkynyl, an cycloalkyl, an cycloalkenyl, a heterocycloalkyl, an aryl, a heteroaryl, an aralkyl, a heteraralkyl, a haloalkyl, - C(0)NRiiRi2, -NRi₃C(0)Ri4, a halo, -ORi , cyano, nitro, a haloalkoxy, -C(0)Ri₃, - NR11R12, -SR13, -C(0)ORi3, -OC(0)Ri3, -NRi C(0)NRnRi₂, -OC(0)NRnRi₂, - NRi₃C(0)ORi4, -S(0)rRi3, -NRi₃S(0)rRi₄, -OS(0)rRi₄, S(0)rNRnRi₂, -O, -S, and -N- Ri3, wherein r is 1 or 2; Rn and R12, for each occurrence are, independently, H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocycloalkyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; or Rn and R12 taken together with the nitrogen to which they are attached is optionally substituted heterocycloalkyl or optionally substituted heteroaryl; and Ri₃ and Ri4 for each occurrence are, independently, H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocycloalkyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl. In certain embodiments, the term "substituent" or the adjective "substituted" refers to a solubilising group.

The term "solubilising group" means any group which can be substantially ionized and that enables the compound to be soluble in a desired solvent, such as, for example, water or water-containing solvent. Furthermore, the solubilising group can be one that increases the compound or complex's lipophilicity. Typically, the solubilising group is selected from alkyl group substituted with one or more heteroatoms such as N, O, S, each optionally substituted with alkyl group substituted independently with alkoxy, amino, alkylamino, dialkylamino, carboxyl, cyano, or substituted with cycloheteroalkyl or heteroaryl, or a phosphate, or a sulfate, or a carboxylic acid. For example, by "solubilising group" it is referred herein to one of the following: - an alkyl, cycloalkyl, aryl, heretoaryl group comprising either at least one nitrogen or oxygen heteroatom or which group is substituted by at least one amino group or oxo group;

- an amino group which may be a saturated cyclic amino group which may be substituted by a group consisting of alkyl, alkoxycarbonyl, halogen, haloalkyl, hydroxyalkyl, amino, monoalkylamino, dialkylamino, carbamoyl, monoalkylcarbamoyl and dialkylcarbamoyl;

- one of the structures a) to i) shown below, wherein the wavy line and the arrow line correspond to the point of attachment to core structure of formula I

d e f g h i

The term "cycloalkyl" means a saturated cyclic alkyl radical having from 3 to 10 carbon atoms. Representative cycloalkyls include cyclopropyl, l-methylcyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl. Cycloalkyl groups can be optionally substituted with one or more substituents.

The term "halogen" means -F, -CI, -Br or -I.

DETAILED DESCRIPTION

The present invention therefore relates to a method for treating mast cell activation syndrome (MCAS) in a subject, preferably in human patients comprising administering a tyrosine kinase inhibitor to subjects or patients in need of. Preferably, a therapeutically effective amount of a tyrosine kinase inhibitor is administered to the subject. The term "mast cell activation syndrome" (MCAS) in this invention is to be fully distinguished from the term "mast cell activation disease" (MCAD). The term "mast cell activation disease" (MCAD) encompasses a collection of disorders or syndromes characterized by the accumulation of pathological mast cells in potentially any or all organs and tissues and/or the aberrant release of variable subsets of mast cell mediators.

MCAD encompasses more specifically diseases such as systemic mastocytosis (SM), mast cell activation syndrome (MCAS) or mast cell leukemia (MCL). Whereas SM and MCL appear to share a rare occurrence but can advantageously be diagnosed according to some specific criteria defined by the World Health Organization (WHO), MCAS on the contrary presents a complex clinical picture of multiple mast cell mediator-induced symptoms that do not meet the WHO criteria for diagnosis of SM.

This invention aims at providing a method for treating MCAS, preferably with severe mast cell mediator release associated handicap. This invention does not aim at providing any further treatment, especially excludes the treatment of MCAD as a whole, excludes the treatment of systemic mastocytosis and excludes the treatment of mast cell leukemia. It is emphasized herein that the MCAS patient is not a systemic mastocytosis patient or a mast cell leukemia patient.

Tyrosine Kinase Inhibitors for use in the present invention

Tyrosine kinases are receptor type or non-receptor type proteins, which transfer the terminal phosphate of ATP to tyrosine residues of proteins thereby activating or inactivating signal transduction pathways. These proteins are known to be involved in many cellular mechanisms, which in case of disruption, lead to disorders such as abnormal cell proliferation and migration as well as inflammation. Within the meaning of the present invention, a "tyrosine kinase inhibitor" is thus a drug that inhibits tyrosine kinases, thereby interfering with signaling processes within cells. Blocking such processes can stop the cell growing and dividing.

In one embodiment, the tyrosine kinase inhibitor for use in the method for treating MCAS of the invention has the following formula [A] :

wherein Ri and R₂, are selected independently from hydrogen, halogen, a linear or branched alkyl, cycloalkyl group containing from 1 to 10 carbon atoms, trifluoromethyl, alkoxy, cyano, dialkylamino, and a solubilising group, m is 0-5 and n is 0-4; the group R₃ is one of the following :

(i) an aryl group such as phenyl or a substituted variant thereof bearing any combination, at any one ring position, of one or more substituents such as halogen, alkyl groups containing from 1 to 10 carbon atoms, trifluoromethyl, cyano and alkoxy;

(ii) a heteroaryl group such as 2, 3, or 4-pyridyl group, which may additionally bear any combination of one or more substituents such as halogen, alkyl groups containing from 1 to 10 carbon atoms, trifluoromethyl and alkoxy;

(iii) a five-membered ring aromatic heterocyclic group such as for example 2-thienyl, 3- thienyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, which may additionally bear any combination of one or more substituents such as halogen, an alkyl group containing from 1 to 10 carbon atoms, trifluoromethyl, and alkoxy; or a pharmaceutically acceptable salt or solvate thereof.

In a particular embodiment the tyrosine kinase inhibitor for use in the method for treating MCAS of the invention has general formula [B],

wherein:

Ri is selected independently from hydrogen, halogen, a linear or branched alkyl, cycloalkyl group containing from 1 to 10 carbon atoms, trifluoromethyl, alkoxy, amino, alkylamino, dialkylamino, solubilising group. m is 0-5, or a pharmaceutically acceptable salt or solvate thereof.

Pharmaceutically acceptable salts preferably are pharmaceutically acceptable acid addition salts, like for example with inorganic acids, such as hydrochloric acid, sulfuric acid or a phosphoric acid, or with suitable organic carboxylic or sulfonic acids, for example aliphatic mono- or di-carboxylic acids, such as trifluoroacetic acid, acetic acid, propionic acid, glycolic acid, succinic acid, maleic acid, fumaric acid, hydroxymaleic acid, malic acid, tartaric acid, citric acid or oxalic acid, or amino acids such as arginine or lysine, aromatic carboxylic acids, such as benzoic acid, 2-phenoxy-benzoic acid, 2- acetoxy-benzoic acid, salicylic acid, 4-aminosalicylic acid, aromatic-aliphatic carboxylic acids, such as mandelic acid or cinnamic acid, heteroaromatic carboxylic acids, such as nicotinic acid or isonicotinic acid, aliphatic sulfonic acids, such as methane-, ethane- or 2-hydroxyethane- sulfonic, in particular methanesulfonic acid, or aromatic sulfonic acids, for example benzene-, p-toluene- or naphthalene-2-sulfonic acid. Unless otherwise indicated, references to "mesilate" are used in the present invention to refer to a salt of methanesulfonic acid with a named pharmaceutical substance (such as compounds of formula [A] or [B]). Use of mesilate rather than mesylate is in compliance with the INNM (International nonproprietary names modified) issued by WHO (e.g. World Health Organization (February 2006). International Nonproprietary Names Modified. INN Working Document 05.167/3. WHO.). For example, masitinib or imatinib mesilate mean the methanesulfonic acid salt of masitinib or imatinib, respectively. Masitinib as tyrosine kinase inhibitor for use in the present invention

In one highly preferred embodiment, the tyrosine kinase inhibitor of formula [B] for use in the method of the invention is masitinib or a pharmaceutically acceptable salt or solvate thereof, more preferably masitinib mesilate. Preferably, "masitinib mesilate" means the orally bioavailable mesilate salt of masitinib - CAS 1048007-93-7 (MsOH); C28H30N6OS.CH3SO3H; MW 594.76:

The chemical name for masitinib is 4-(4-methylpiperazin-l-ylmethyl)-N-[4-methyl-3-(4- pyridin-3ylthiazol-2-ylamino) phenyl]benzamide - CAS number 790299-79-5.

Masitinib was described in US 7,423,055 and EP 1 525 200 Bl . A detailed procedure for the synthesis of masitinib mesilate is given in WO 2008/098949.

Tyrosine kinase inhibitors, preferably of formula [A] or [B] or masitinib mesilate can preferably be used as c-Kit inhibitors.

In a particular embodiment, the tyrosine kinase inhibitor for use in the method for treating MCAS of the invention is an inhibitor of wild-type c-Kit, Lyn and Fyn kinase activity. Stem cell factor (SCF), the ligand of the c-Kit receptor, was indeed shown to be a major growth factor for mast cell survival, proliferation, differentiation, adhesion and degranulation processes (Reber et al., Eur J Pharmacol 2008;533:327-340), with SCF- dependent activation of c-Kit critical for mast cell homeostasis and function. Binding of SCF to the c-Kit receptor was shown to induce c-Kit dimerization followed by its transphosphorylation, leading to the recruitment and activation of various intracytoplasmic substrates. These activated substrates were also shown to induce multiple intracellular signaling pathways responsible for cell proliferation and activation. The symptoms of MCAS are in particular resulting from the inappropriate enhanced release of mast cells mediators. In a particular embodiment, the tyrosine kinase inhibitor for use in the method of the present invention is thus capable of inhibiting specifically the SCF/c-Kit pathway. Similarly, Lyn and Fyn kinases were shown to play the role of key components of the transduction pathway leading to IgE induced degranulation (Gilfillan & Tkaczyk, 2006, Nat Rev Immunol, 6:218-230; Gilfillan et al., 2009, Immunological Reviews, 228:149-169). In a particular embodiment, the tyrosine kinase inhibitor for use in the method for treating MCAS of the present invention is thus capable of inhibiting specifically the activity Lyn and Fyn kinases.

Masitinib is a small molecule selectively inhibiting specific tyrosine kinases such as c- Kit, PDGFR, Lyn, Fyn and to a lesser extent the fibroblast growth factor receptor 3 (FGFR3), without inhibiting, at therapeutic doses, kinases associated with known toxicities (i.e. those tyrosine kinases or tyrosine kinase receptors attributed to possible tyrosine kinase inhibitor cardiac toxicity, including ABL, KDR and Src) (Dubreuil et al., 2009, PLoS ONE 2009.4(9):e7258). Masitinib' s strong inhibitory effect on wild-type and juxtamembrane-mutated c-Kit receptors, results in cell cycle arrest and apoptosis of cell lines dependent on c-Kit signaling (Dubreuil et al., 2009, PLoS ONE, 4(9):e7258). Stem cell factor, the ligand of the c-Kit receptor, is a critical growth factor for mast cells; thus, masitinib is an effective antimastocyte, exerting a direct antiproliferative and pro- apoptotic action on mast cells through its inhibition of c-Kit signaling. Moreover, in vitro, masitinib demonstrated greater activity and selectivity against c-Kit than imatinib, inhibiting recombinant human wild-type c-Kit with an half inhibitory concentration (IC50) of 200 ± 40 tiM and blocking stem cell factor-induced proliferation and c-Kit tyrosine phosphorylation with an IC50 of 150 + 80 nM in Ba/F3 cells expressing human or mouse wild-type c-Kit. In contrast, masitinib only weakly inhibited the proliferation of Ba/F3 cells expressing the D816V c-Kit mutation with an IC50 of 5.0 + 2.0 μΜ, and by consequence is inactive, at therapeutically viable doses, against the D816V mutation of c-Kit.

In addition to its antiproliferative properties, masitinib can also regulate the activation of mast cells through its targeting of Lyn and Fyn, key components of the transduction pathway leading to IgE induced degranulation. Treatment of MCAS with Masitinib

Molecules able to inhibit the survival and/or activation of mast cells may be able to control the symptoms and progression of MCAS. In connection to the present invention we consider that a tyrosine kinase inhibitor, notably as defined above, especially masitinib, through its inhibition of mast cell proliferation and activation, is fulfilling this role in the treatment of MCAS, via but not limited to, reducing the overall mast cell burden and inhibiting the global activity of mast cells.

In connection with the present invention, it would seem, without willing to be bound by the theory, that surprisingly a tyrosine kinase inhibitor, notably as defined above, especially masitinib, could also be of further therapeutic benefit against MCAS by inhibiting mast cell degranulation via inhibition of Lyn and Fyn. This is significant as it represents a mechanism of action that is independent from the c-Kit signaling pathway or survival of mast cells. It follows that the subsequent decrease in mast cell degranulation would lead to a lessening of mast cell mediator release symptoms and MCAS related handicap. In addition, a reduction in release of various chemoattractants associated with mast cell migration will lessen the rate of mast cell recruitment and accumulation, further lessening the symptoms of MCAS patients dampening their cascade effect. For example, SCF is a chemotactic factor for mast cells, with mast cells themselves possessing the capacity to synthesize, store and release SCF. Thus, expression of SCF is increased in the activation of mast cells, with subsequent migration of other mast cells towards this source of SCF, cumulating in mast cell accumulation. If the mast cell mediator release encountered in MCAS is due to an intrinsic defect that lowers the activation threshold of mast cells, then masitinib' s inhibition of degranulation would help compensate or restore normal function, with respect to mediator hypersecretion and release of the mast cell chemoattractants, such as SCF.

A reduction of mast cell activity via the inhibitory action of masitinib on c-Kit, Lyn and Fyn tyrosine kinase activity, thus impacts the overall mast cell burden and inflammatory cascade as well as the threshold of mast cell degranulation and migration/recruitment of mast cells. Unexpectedly, without willing to be bound by the theory, it is through this multifaceted mechanism of action that the use of a tyrosine kinase inhibitor according to the invention can elicit a response in MCAS patients.

In a particular embodiment, the method of the invention allows a mast cell activation syndrome patient to be treated, wherein MCAS is as defined by the Molderings diagnostic criteria, or the Valent diagnostic criteria, or the Akin diagnostic criteria, as defined hereinabove.

Further, in a particular embodiment, the method of the invention, comprising administering a tyrosine kinase inhibitor, notably as defined above, and more specifically masitinib, also allows MCAS with mast cell mediator release associated handicap to be treated. In a particular embodiment, the method of the invention allows mild, moderate and preferably severe handicap to be treated.

As exposed above, it indeed appears that patients suffering from MCAS often experience symptoms resulting from the enhanced or inappropriate activation of mast cells and release of their mediators. These symptoms are collectively referred to as "mast cell mediator release symptoms" or "mast cells mediator release associated handicap". These symptoms may in particular comprise, but are not limited to, asthenia, pruritus, food intolerance, erythematous crisis, bone, muscle and joint pain, pollakiuria (micturition frequency), epigastric pain, aerophagia/eructation, memory loss and psychological impact of the disease, particularly depression, anaphylaxis, faintness, fatigue, flushing, rashes, itching, hives, blood pressure changes and shock, chest pain, rapid heart rate, wheezing, degenerative disc disease, osteoporosis/osteopenia, nausea, vomiting, abdominal pain, gastroesophageal reflux, diarrhea, inflammation of the esophagus, intestinal cramping and bloating, malabsorption, cognitive difficulties/brain fog, dizziness/vertigo, lightheadedness, migraine headache, paresthesia, and peripheral neuropathy.

The method of the present invention was advantageously shown to provide a significant beneficial effect on MCAS patients with severe mast cell mediator release associated handicap. According to the present invention, it is considered that the expression "severe handicap" actually refers to a clinical situation wherein the treated patients suffering from MCAS present at least one mast cell mediator release associated handicap selected from the group comprising at least one of the symptoms listed hereinabove, preferably at least one of pruritus, flushes, depression, fatigue, pain, pollakiuria and diarrhea, more preferably at least one of pruritus, flushes and depression. Further, in a particular embodiment, the method of the invention allows patients suffering from MCAS to be treated when the severe handicapped status of MCAS is defined as at least one of the following handicaps: pruritus score between 6 and 10, preferably 9 or > 9; number of flushes per week between 7 and 9, preferably 8 or > 8; depression measured by the Hamilton rating scale between 14 and 24, preferably 19 or > 19; fatigue score measured by FIS between 65 and 90, preferably 75 or > 75 (or any equivalent cut-off determined using the FSS, FSI, BFI or MAF); pain measured by VAS between 15 and 25, preferably 20 or > 20 (or any equivalent cut-off determined using the BPI or unidimensional or multidimensional pain assessment tool); number of stools per day between 3 and 5, preferably 4 or > 4; number of micturition per day between 7 and 9, preferably 8 or > 8. In a particular embodiment, the method of the present invention in particular advantageously demonstrated a treatment response as a > 75% improvement of the handicap from baseline for pmritus, flushes or HAMD- 17. The level of response obtained with the method of the invention thus represents a highly clinically relevant improvement not only for depression, but also for pruritus, and flushes, since it provides a good approximation to the situation of complete response, for a given parameter.

Considering the above reported efficacy and safety of oral masitinib in a subpopulation of patients diagnosed with MCAS with severe mast cell mediator release associated handicap, masitinib can thus be regarded as the first viable therapeutic strategy for treating MCAS, and capable of reducing symptoms and severity of mast cell mediator release associated handicap in MCAS patients.

In a particular embodiment, the present invention thus relates to the use of at least one tyrosine kinase inhibitor as described above, and more particularly masitinib or a pharmaceutically acceptable salt thereof, for the preparation of a medicament for the treatment of MCAS, and in particular MCAS with severe mast cell mediator release associated handicap, in human patients. Dosage regimen

Regarding best dosage regimen, the tyrosine kinase inhibitor for use in the method of the invention, especially masitinib or a pharmaceutically acceptable salt thereof, is to be administered at a starting daily dose of about 3.0 to 6.0 mg/kg/day. Nonetheless said tyrosine kinase inhibitor, especially masitinib or a pharmaceutically acceptable salt thereof, can be dose escalated by increments of about 1.5 mg/kg/day to reach a maximum of about 9.0 mg/kg/day in low responder patients.

Indeed, depending on age, individual condition, mode of administration, and the clinical setting, effective doses of said tyrosine kinase inhibitor, especially masitinib or a pharmaceutically acceptable salt thereof, in human patients with MCAS, and more particularly with MCAS with mast cell mediator release associated handicap, are about 3.0 to 6.0 mg/kg/day per os, preferably in two daily intakes. For adult human patients with MCAS, and more particularly with MCAS with mast cell mediator release associated handicap, a starting dose of said tyrosine kinase inhibitor, especially masitinib or a pharmaceutically acceptable salt thereof, of 3.0 to 6.0 mg/kg/day has been found to be the preferred embodiment according to the invention, preferably reaching a stable treatment dose of 4.5 to 6.0 mg/kg/day. For patients with an inadequate response after an assessment of response to therapy and in the absence of limiting toxicities, dose escalation of said tyrosine kinase inhibitor, especially masitinib or a pharmaceutically acceptable salt thereof, to a maximum of about 9.0 mg/kg/day can be safely considered and patients may be treated as long as they benefit from treatment and in the absence of limiting toxicities.

Dose adjustment can be considered a dynamic process, with a patient undergoing multiple increases and/or decreases to optimize the balance between response and toxicity throughout treatment, both of which are likely to vary over time and duration of drug exposure. If dose escalation is undertaken, it is suggested that the starting dose of about 3.0 to 6.0 + 1.5 mg/kg/day be incremented by 1 to 2 mg/kg/day up to a maximum dose of about 9.0 mg/kg/day, over a period which depends upon clinical observations. For example, a single dose escalation of said tyrosine kinase inhibitor, especially masitinib or a pharmaceutically acceptable salt thereof, and preferably masitinib mesilate may take from 1 to 2 months. It is also contemplated herein that to fully obtain the therapeutic benefits of a patient-optimized dose of said tyrosine kinase inhibitor or mast cell inhibitor, especially masitinib or a pharmaceutically acceptable salt thereof, dose increments smaller than 1 to 2 mg kg/day could be implemented. Dose reduction is to be considered to reduce toxicity in appropriate cases.

Any dose indicated herein refers to the amount of active ingredient as such, not to its salt form.

Given that the masitinib dose in mg/kg/day used in the described dose regimens refers to the amount of active ingredient masitinib, compositional variations of a pharmaceutically acceptable salt of masitinib mesilate will not change the said dose regimens.

In a particular embodiment, masitinib may further be administered via different routes of administration but oral administration is preferred. Thus, in still another preferred embodiment, in the use or the method above, masitinib or salts thereof, is administered orally; preferably twice a day for long term period such as over more than 6 months, preferably more than 12 months. Masitinib can be administered in the form of 100 and 200 mg tablets.

According to a particular embodiment, the pharmaceutical composition or medicament for use in the method for treating MCAS of the invention is thus an oral composition.

As is known to the person skilled in the art, various forms of excipients can be used adapted to the mode of administration and some of them can promote the effectiveness of the active molecule, e.g. by promoting a release profile rendering this active molecule overall more effective for the treatment desired.

Pharmaceutical compositions, medicaments or compositions for use in the method of the invention are thus able to be administered in various forms, more specially for example in an injectable, pulverizable or ingestible form, for example via the intramuscular, intravenous, subcutaneous, intradermal, oral, topical, rectal, vaginal, ophthalmic, nasal, transdermal or parenteral route. A preferred route is oral administration. The present invention notably covers the use of a compound according to the present invention for the manufacture of pharmaceutical composition or medicament.

Such medicament or pharmaceutical composition can take the form of a medicament or pharmaceutical composition adapted for oral administration, which can be formulated using pharmaceutically acceptable carriers well known in the art in suitable dosages. Such carriers enable the pharmaceutical compositions to be formulated as tablets, pills, dragees, capsules, liquids, gels, syrups, slurries, suspensions, and the like, for ingestion by the patient. In addition to the active ingredients, these pharmaceutical compositions may contain suitable pharmaceutically-acceptable carriers comprising excipients and auxiliaries which facilitate processing of the active compounds into preparations which can be used pharmaceutically. Further details on techniques for formulation and administration may be found in the latest edition of Remington's Pharmaceutical Sciences (Maack Publishing Co., Easton, Pa.). EXAMPLES

The present invention is further illustrated by the following examples. Example 1

Proof-of-concept for masitinib's efficacy in treatment of patients suffering from MCAS with severe handicap is provided by post-hoc analysis of data from two phase II clinical trials conducted in a relevant patient population.

Two phase II previous studies assessed the efficacy of masitinib in MCAS patients. Assessment of treatment response on a handicap was defined as a > 75% improvement of the handicap from baseline for pruritus, flushes, or Hamilton rating scale for depression.

These two studies included 31 patients meeting the following criteria for severe handicap at baseline; i.e. pruritus score>9; flushes frequency per week>8; Hamilton score>19. Note that a given patient may present more than one handicap. Tables 1 and 2 show results from post-hoc analysis of the first and second studies, respectively.

Table 1: First Study - Response to the treatment defined as a 75% improvement in patients

Patient handicap* response (N=16)

WEEK 8 WEEK 12

Number of severe handicaps at 18 18

baseline

Response rate 10 (56%) 7 (39%) *Handicap severity at baseline: pruritus score≥9; flushes frequency per week>8; Hamilton score>19 Analysis performed on patient handicap response. Missing data equal to failure - replacement of missing data was performed for patients who withdrawn because of an adverse event occurrence, a lack of efficacy or an unknown reason.

In the first study, 16 patients reported 18 severe handicaps (pruritus score>9; flushes frequency per week>8; Hamilton score>19) at baseline. For patients treated with masitinib a response level of 56% was reached after 8 weeks of treatment, then 39% after 12 weeks of treatment.

Table 2: Second Study - Response to the treatment defined as a 75% improvement in patients

Patient handicap response (N=15)

WEEK 8 WEEK 12

N 21 21

Response 9 (43%) 6 (29%)

^Handicap severity at baseline: pruritus score≥9; flushes frequency per week>8; Hamilton score>19 Analysis performed on patient handicap response. Missing data equal to failure - replacement of missing data was performed for patients who withdrawn because of an adverse event occurrence, a lack of efficacy or an unknown reason.

In the second study, 15 patients reported 21 severe handicaps (pruritus score>9; flushes frequency per week>8; Hamilton score>19) at baseline. For patients treated with masitinib a response level of 43% was reached after 8 weeks of treatment, then 29% after 12 weeks of treatment. Table 3 shows pooled results from post-hoc analysis of the first and second studies. A total of 31 patients with mast cell activation disease reported 39 severe handicaps (pruritus score>9; flushes frequency per week>8; Hamilton score>19) at baseline. For patients treated with masitinib a response level of 49% was reached after 8 weeks of treatment, then 33% after 12 weeks of treatment.

Table 3: Pooled populations of the first and second studies - Response to the treatment defined as a 75% improvement in patients

Patient handicap* response (N=31)

WEEK 8 WEEK 12

Number of severe handicaps at 39 39

baseline

Response rate 19 (49%) 13 (33%)

^Handicap severity at baseline: pruritus score≥9; flushes frequency per week>8; Hamilton score>19 Analysis performed on patient handicap response. Missing data equal to failure - replacement of missing data was performed for patients who withdrawn because of an adverse event occurrence, a lack of efficacy or an unknown reason

Example 2

Methods

Study design A prospective, multicenter, randomised, double-blind, placebo controlled, parallel groups, phase 2/3 study is being conducted to compare the efficacy and safety of masitinib versus placebo in the treatment of patients suffering from mast cell activation syndrome with severe handicap. The trial lasted 48 weeks.

Masitinib was given orally at the dose of 3 mg/kg/day during 4 weeks, then 4.5 mg/kg/day during 4 weeks, and then 6 mg/kg/day with possible dose adjustments. Masitinib was supplied as 100 and 200 mg tablets (AB Science, France) and was administered orally in two daily intakes. The dose of masitinib was increase provided that no severe suspected (or not assessable) adverse event was reported and no suspected (or not assessable) adverse event led to treatment interruption and no suspected (or not assessable) adverse event was ongoing at the time of the dose increase, regardless of its severity. At the week 4 visit, the daily dose of masitinib was increased to 4.5 mg/kg/day provided that the patient did not present a suspected or not assessable adverse event which was either severe, or leading to masitinib interruption, and provided that no suspected or not assessable adverse event was ongoing at week 4, regardless of its severity. The patients presenting with non-severe suspected adverse event at the time of the dose increase were allowed to pursue the dose progression schedule with one month delay.

At the week 8 visit, if the patient did not present with a suspected or not assessable adverse event which was either severe, or leading to masitinib interruption, and if no suspected or not assessable adverse event was ongoing at week 8, regardless of its severity, the daily dose of masitinib was increased to 6 mg/kg/day. Eligible patients were suffering from mast cell activation syndrome with severe handicap. Patients with mast cell activation syndrome with severe handicap have been randomized in two treatment groups including: Group 1 : patients received masitinib 3 mg/kg/day during 4 weeks then 4.5 mg/kg/day during 4 weeks and then 6 mg/kg/day (each switch being subjected to a toxicity control), and Group 2: patients received placebo with the same administration plan as masitinib.

The two treatment groups were defined such as to equally balance handicap/scores at baseline regarding pruritus, flushes, depression and fatigue, which might influence the study outcome. The randomization procedures included a minimization process aimed at reducing any difference in the distribution of the handicaps/scores at baseline and country in patients with mast cell activation syndrome.

Patients were classified as suffering mast cell activation syndrome with severe handicap when they fulfilled the following criteria: a diagnosis of mast cell activation syndrome (MCAS) with handicap was established as per Molderings et al. (Journal of Hematology and Oncology 2011). For patients in whom diagnostic criteria included elevation in mast cell mediator(s), at least two elevations (at the same or different points in time) had to be documented among one or more of serum tryptase, serum chromogranin A, plasma prostaglandin D₂, plasma histamine, plasma heparin (upper limit of normal 0.02 anti- Factor Xa units/ml per Seidel et al., Journal of Thrombosis and Haemostasis 2011), and random or 24-hour urinary prostaglandin D₂, 11-β-prostaglandin F_2a, N-methylhistamine, and leukotriene E4. Semm chromogranin A levels were disregarded in patients in whom the specimen for testing was obtained at a time when the patient was clinically judged to have any degree or extent of cardiac or renal failure, or neuroendocrine malignancy, or proton pump inhibitor use within the prior five days. Patients were warned to avoid all NSAID use in the five days prior to submitting specimens for prostaglandin testing, unless a non-steroidal anti-inflammatory drug (NSAID) was already a regular component of the patient's regimen.

Patients were considered as suffering from mast cell activation syndrome when both following major criteria or the second following criterion and at least one minor following criterion were fulfilled (Molderings et al. Journal of Hematology & Oncology 2011 4: 10 doi: 10.1186/1756-8722-4-10):

Major criteria :

1. Multifocal or disseminated dense infiltrates of mast cells in bone marrow biopsies and/or in sections of other extracutaneous organ(s) (e.g., gastrointestinal tract biopsies; CD117-, tryptase- and CD25-stained);

2. Unique constellation of clinical complaints as a result of a pathologically increased mast cell activity (mast cell mediator release syndrome).

Minor criteria :

1. Mast cells in bone marrow or other extracutaneous organ(s) show an abnormal morphology (>25%) in bone marrow smears or in histologies;

2. Mast cells in bone marrow express CD2 and/or CD25;

3. Detection of genetic changes in mast cells from blood, bone marrow or extracutaneous organs for which an impact on the state of activity of affected mast cells in terms of an increased activity has been proved; 4. Evidence of a pathologically increased release of mast cell mediators by determination of the content of: tryptase in blood, N-methylhistamine in urine, heparin in blood, chromogranin A in blood, other mast cell-specific mediators (e.g., leukotrienes, prostaglandin D₂). Patients were considered as handicapped when they fulfilled at least one of the following handicaps: a Pruritus score > 9; a number of flushes per week > 8 or a Hamilton rating scale for depression (HAMD-17) score > 19.

Patients with any form of mastocytosis (including mast cell leukemia) were excluded from the study. C-kit sequencing for detecting c-kit polymorphism and mast cell counting was performed centrally in order to ensure consistency in the study results.

Response and safety assessment

Masitinib safety profile was compared to placebo on the following parameters: Occurrence of Adverse Events (AEs), Changes in physical examination including vital signs (blood pressure, pulse rate) and weight, and Clinical laboratory tests (biochemistry, haematology, urinalysis, ECG).

Analysis datasets:

Intention-To-Treat (ITT) dataset - The ITT population was defined as all patients randomized. Patients were classified according to the treatment arm to which they have been randomized, irrespective of the actual treatment received.

Modified Intent- To-Treat (mITT) dataset - The mITT dataset included all ΓΓΤ patients but patients withdrawing prematurely from the study for a well-documented non treatment-related cause were excluded. The said causes comprised withdrawal of consent for other reason than lack of efficacy or toxicity related to treatment, death for reason not related to treatment or no treatment intake. Per Protocol (PP) dataset - The PP data set consisted of all patients of the mITT data set without any major protocol deviation. This was the set of patients who participated in the study as intended. Patients terminating the study prematurely were included in the PP data set provided that there was no protocol deviation. Before locking the data base, the precise reasons for excluding patients from the PP data set were fully defined and documented by the Data Review Committee.

Protocol deviations were defined as: inclusion and non-inclusion criteria were not met, intake of forbidden medication, non-respect of visit dates, missing value for main criterion without premature termination, non-respect of protocol design, any other deviations during the course of the study.

Safety population - The safety population consisted of all patients randomized and who took at least one dose of study medication (masitinib or placebo).

Statistical Methods:

Primary analysis: The primary analysis was done on the mITT population. It was based on the cumulative response by patient x handicap:

- Handicaps were defined as: pruritus score > 9, number of flushes per week > 8, HAMD-17 score > 19;

- Response on a handicap was defined as an improvement > 75% for pruritus, flushes, Hamilton;

- For all the patients, the response at each study visit (4 visits from week 12 to week 24) was calculated on each handicap present at Baseline (among pruritus, flushes, Hamilton);

- So, from 4 to 12 responses were calculated by patient: 4 if the patients presented only 1 handicap at Baseline corresponding to the 4 visits and 12 if the patients presented the 3 handicaps at Baseline corresponding to the 3 handicaps x the 4 visits. The difference between treatment- arms (masitinib versus placebo) was tested using a Generalized Estimating Equations (GEE) model using Logit as link function. This statistical model included all the responses (yes/no) on handicaps observed from week 12 to week 24: so from 4 to 12 responses by patient (as described above). Beside the treatment, the following factors and covariates were included in the model: handicap, visit and randomization stratification factors. It was concluded in a difference between masitinib and placebo if the p-value associated to treatment was < 5%.

If data were not available for assessment at a visit because a patient left the study prematurely, as primary analysis, missing data were replaced according to following rules:

- Case 1 : discontinuation before week 24 for toxicity, lack of efficacy, or unknown reason: in this case, missing data was imputed as failure (missing = failure).

- Case 2: discontinuation before week 24 for a documented reason excluding toxicity or lack of efficacy: in this case, non-observed values were considered as Missing At Random (MAR), and no imputation was done (Observed Cases).

Secondary analysis:

Cumulative response on pruritus, from W12 to W24 - Analysis on the cumulative response on pruritus among patients with the handicap at Baseline, was done on the mITT population:

- Handicap was defined as: pruritus score > 9.

- Response on a handicap was defined as an improvement > 75% for pruritus.

- For the patients presenting the handicap at Baseline (i.e. score > 9), the response at each study visited (4 visits from week 12 to week 24) was calculated as defined above.

- So, 4 responses were calculated by patient.

The difference between treatment- arms (masitinib versus placebo) was tested using a Generalized Estimating Equations (GEE) model using Logit as link function. This statistical model included all the responses (yes/no) on handicaps observed from week 12 to week 24: so 4 responses by patient (as described above). Beside the treatment, the following factor and covariates were included in the model: visit and randomization stratification factors. It was concluded in a difference between masitinib and placebo if the p-value associated to treatment was < 5%. If data were not available for assessment at a visit because a patient left the study prematurely, as primary analysis, missing data were imputed as failure (missing = failure). Missing data were replaced according the same rales as for the primary criterion depending of the study discontinuation reason.

Cumulative response on flushes, from W12 to W24 - The same analysis and sensitivity analyses as applied on cumulative response on pruritus was performed on the cumulative response on flushes. Cumulative response on HAMD-17 score, from W12 to W24 - The same analysis and sensitivity analyses as applied on cumulative response on pruritus was performed on the cumulative response on HAMD-17 score.

Cumulative AFIRMM (Association Francaise pour les Initiatives de Recherche sur le Mastocyte et les Mastocytoses) questionnaire symptom reduction responses, from W12 to W24:

Cumulative Global symptoms reduction response from W12 to W24, defined as a decrease of at least 50% in total score from baseline, in patients with a baseline score of at least 50% of the maximum possible score.

Cumulative Global symptoms reduction response from W12 to W24, defined as a decrease of at least 75% in total score from baseline, in patients with a baseline score of at least 75% of the maximum possible score.

Cumulative System-specific symptoms reduction response from W12 to W24, defined as a decrease of at least 50% of the maximum possible score in each system category, in patients with a baseline score of at least 50% of the maximum possible score for the category.

Cumulative System-specific symptoms reduction response from W12 to W24, defined as a decrease of at least 75% of the maximum possible score in each system category, in patients with a baseline score of at least 75% of the maximum possible score for the category.

The same analysis and sensitivity analyses as applied on cumulative response on pruritus was performed on the cumulative AFIRMM questionnaire symptom reduction responses (Global with decrease of 50%, Global with decrease of 75%, System-specific with decrease of 50% and System- specific with decrease of 75%).

Change from Baseline in Global score, from W12 to W24 - Difference between treatment groups (masitinib versus placebo) from W12 to W24, was tested using a Mixed Model for Repeated Measures (MMRM). Beside the treatment, the following factors and covariates were included in the model: visit and randomization stratification factors. The baseline value was also included in the model as a covariate. It was concluded in a difference between masitinib and placebo if the p-value associated to treatment was < 5%. Missing data were imputed with the LOCF method according the same rules as for the primary criterion depending of the study discontinuation reason. Same sensitivity analyses as the primary criterion were performed. If the underlying hypotheses for the use of Gaussian mixed model were not fulfilled, semi-parametric or non-parametric methods could be used.

Cumulative OLO-C30 (Quality of Life) response in total score, from W12 to W24 - Response was defined as an improvement of at least 25% in total score from baseline. The same analysis and sensitivity analyses as applied on cumulative response on pruritus were performed on the cumulative QLQ-C30 response.

Change from Baseline in OLO-C30 (Quality of Life) response, from W12 to W24 - Change from Baseline, from W12 to W24, were assessed for each scale (functional scales i.e. physical, role, cognitive, emotional and social; symptom scales i.e. fatigue, nausea/vomiting, pain and global scale) and each individual items (8, 11, 13, 16, 17 and 28). Difference between treatment groups (masitinib versus placebo) from W12 to W24, were tested using a Mixed Model for Repeated Measures (MMRM). Beside the treatment, the following factors and covariates were included in the model: visit and randomization stratification factors. The baseline value was also included in the model as a covariate. It was concluded in a difference between masitinib and placebo if the p-value associated to treatment was < 5%. The analysis was done on the mITT population as primary population. Missing data were imputed with the LOCF method according the same rules as for the primary criterion depending of the study discontinuation reason. Same sensitivity analyses as the primary criterion were performed. If the underlying hypotheses for the use of Gaussian mixed model were not fulfilled, semi-parametric or non- parametric methods could be used.

Cumulative response in mast cell mediators, from W12 to W24 - Response was defined as a decrease by at least 50% from baseline in mast cell mediators found elevated at baseline. Elevated mast cell mediator values cut-off were defined in the statistical analysis plan before breaking the blind. The same analysis and sensitivity analyses as applied on cumulative response on pruritus was performed on the cumulative response in mast cell mediators.

Change from baseline in mast cell mediators, from W12 to W24 - The same analysis and sensitivity analyses as applied on AFIRMM global score and QLQ-C30 scores change from baseline was performed on the change from baseline in mast cell mediators. The number of patients with elevated mast cell mediators, at each assessment points, was also displayed.

Claims

1. A method for treating mast cell activation syndrome (MCAS) in human patients comprising administering a tyrosine kinase inhibitor.

2. The method according to claim 1 wherein said tyrosine kinase inhibitor is an inhibitor of wild-type c-Kit, Lyn and Fyn kinase activity.

3. The method according to claim 1 or claim 2 wherein said tyrosine kinase inhibitor is masitinib or a pharmaceutically acceptable salt thereof.

4. The method according to anyone of claims 1 to 3, wherein said tyrosine kinase inhibitor is masitinib mesilate.

5. The method according to anyone of claims 1 to 4, wherein said MCAS is as defined by the Molderings diagnostic criteria, or the Valent diagnostic criteria, or the Akin diagnostic criteria.

6. The method according to anyone of claims 1 to 5, wherein said mast cell activation syndrome comprises at least one mast cell mediator release associated handicap, wherein said handicap is a mild, moderate or severe handicap.

7. The method according to claim 6, wherein said at least one mast cell mediator release associated handicap is selected from the list comprising asthenia, pruritus, food intolerance, erythematous crisis, bone, muscle and joint pain, pollakiuria, epigastric pain, aerophagia/eructation, memory loss and psychological impact of the disease, particularly depression, anaphylaxis, faintness, fatigue, flushing, rashes, itching, hives, blood pressure changes and shock, chest pain, rapid heart rate, wheezing, degenerative disc disease, osteoporosis/osteopenia, nausea, vomiting, abdominal pain, gastroesophageal reflux, diarrhea, inflammation of the esophagus, intestinal cramping and bloating, malabsorption, cognitive difficulties/brain fog, dizziness/vertigo, lightheadedness, migraine headache, paresthesia, and peripheral neuropathy.

8. The method according to claim 6 or claim 7, wherein said severe handicap comprises at least one of pruritus, flushes, depression, fatigue, pain, pollakiuria and diarrhea, and wherein if present handicaps are considered as being severe on an appropriate scale of said handicap, preferably have the following scores: pruritus score between 6 and 10, preferably 9 or > 9; number of flushes per week between 7 and 9, preferably

8 or > 8; depression measured by the Hamilton rating scale between 14 and 24, preferably 19 or > 19; fatigue score measured by FIS between 65 and 90, preferably 75 or > 75 (or any equivalent cut-off determined using the FSS, FSI, BFI or MAF); pain measured by VAS between 15 and 25, preferably 20 or > 20 (or any equivalent cut-off determined using the BPI or unidimensional or multidimensional pain assessment tool); number of stools per day between 3 and 5, preferably 4 or > 4; number of micturition per day between 7 and 9, preferably 8 or > 8.

9. The method according to anyone of claims 1 to 8, wherein said tyrosine kinase inhibitor is to be administered at a starting daily dose of 3.0 to 6.0 mg/kg/day, preferably reaching a stable treatment dose of 4.5 to 6.0 mg kg/day.

10. The method according to claim 9, wherein said tyrosine kinase inhibitor is dose escalated by increments of 1.5 mg/kg/day to reach a maximum of 9.0 mg/kg/day.

11. The method according to anyone of claims 1 to 10, wherein said tyrosine kinase inhibitor is administered orally.

12. The method according to anyone of claims 1 to 11, wherein said tyrosine kinase inhibitor is administered twice a day.

13. The method according to anyone of claims 1 to 12, wherein said tyrosine kinase inhibitor is comprised in a pharmaceutical composition in an amount of at least 50 mg and less than 600 mg, preferably of at least 100 mg and less than 400 mg.

14. A tyrosine kinase inhibitor for use in the treatment of mast cell activation syndrome (MCAS) in human patients.

15. The tyrosine kinase inhibitor according to claim 14, wherein said tyrosine kinase inhibitor is an inhibitor of wild-type c-Kit, Lyn and Fyn kinase activity.

16. The tyrosine kinase inhibitor according to claim 14 or 15, wherein said tyrosine kinase inhibitor is masitinib or a pharmaceutically acceptable salt thereof, and preferably masitinib mesilate.

17. The tyrosine kinase inhibitor according to any one of claims 14 to 16, wherein said MCAS treated by the method of the invention is as defined by the Molderings diagnostic criteria, or the Valent diagnostic criteria, or the Akin diagnostic criteria.

18. The tyrosine kinase inhibitor according to any one of claims 14 to 17, wherein said MCAS comprises at least one mast cell mediator release associated handicap, wherein said handicap is a mild, moderate or severe handicap, and is preferably severe handicap.

19. The tyrosine kinase inhibitor according to claim 18, wherein said at least one mast cell mediator release associated handicap is selected from the list comprising asthenia, pruritus, food intolerance, erythematous crisis, bone, muscle and joint pain, pollakiuria, epigastric pain, aerophagia/emctation, memory loss and psychological impact of the disease, particularly depression, anaphylaxis, faintness, fatigue, flushing, rashes, itching, hives, blood pressure changes and shock, chest pain, rapid heart rate, wheezing, degenerative disc disease, osteoporosis/osteopenia, nausea, vomiting, abdominal pain, gastroesophageal reflux, diarrhea, inflammation of the esophagus, intestinal cramping and bloating, malabsorption, cognitive difficulties/brain fog, dizziness/vertigo, lightheadedness, migraine headache, paresthesia, and peripheral neuropathy.

20. The tyrosine kinase inhibitor according to claim 18 or claim 19, wherein said severe handicap comprises at least one of pruritus, flushes, depression, fatigue, pain, pollakiuria and diarrhea, and wherein if present handicaps are considered as being severe on an appropriate scale of said handicap, preferably have the following scores: pruritus score between 6 and 10, preferably 9 or > 9; number of flushes per week between 7 and 9, preferably 8 or > 8; depression measured by the Hamilton rating scale between 14 and 24, preferably 19 or > 19; fatigue score measured by FIS between 65 and 90, preferably 75 or > 75 (or any equivalent cut-off determined using the FSS, FSI, BFI or MAF); pain measured by VAS between 15 and 25, preferably 20 or > 20 (or any equivalent cut-off determined using the BPI or unidimensional or multidimensional pain assessment tool); number of stools per day between 3 and 5, preferably 4 or > 4; number of micturition per day between 7 and 9, preferably 8 or > 8.

21. The tyrosine kinase inhibitor according to any one of claims 14 to 20, wherein said tyrosine kinase inhibitor is administered orally, preferably at a starting daily dose of 3.0 to 6.0 mg kg/day, preferably reaching a stable treatment dose of 4.5 to 6.0 mg/kg/day, and is preferably dose escalated by increments of 1.5 mg/kg/day to reach a maximum of 9.0 mg/kg/day.