Kynurenine-3-monooxygenase (KMO) inhibitors to treat pulmonary hypertension

Abstract

There was a need for safe and effective treatments for pulmonary hypertension, especially pulmonary arterial hypertension (PAH). The inventors discovered dysregulation of the kynurenine pathway (KP) in the lungs of PAH patients, marked by an imbalance of KP metabolites and upregulation of key enzymes, particularly kynurenine 3-monooxygenase (KMO). This disclosure pertains to a kynurenine-3-monooxygenase inhibitor for use in the treatment or prevention of pulmonary hypertension, in particular pulmonary arterial hypertension. The kynurenine-3- monooxygenase inhibitor is effective in reducing vascular and cardiac remodeling, decreasing right ventricular systolic pressure, reducing pulmonary ventricular resistance, decreasing medial hypertrophy of large arteries, lowering the proportion of muscularized and occluded small arteries and decreasing right ventricular hypertrophy.

Description

DescriptionKYNURENINE-3-MONOOXYGENASE (KMO) INHIBITORS TO TREAT PULMONARY HYPERTENSIONTechnical Field

[0001] This disclosure pertains to compounds for their use in the treatment or the prevention of pulmonary hypertension (PH), in particular of pulmonary arterial hypertension (PAH).Backg ound Art

[0002] Pulmonary hypertension (PH) defines a group of clinical conditions presenting with abnormal elevation in the pulmonary circulation pressure. Thus, a normal mean pulmonary artery pressure (mPAP) at rest is 14 ± 3.3 mm Hg, and PH is commonly defined as an increase of mPAP > 20 mm Hg, as assessed by right heart catheterization. The PH diseases are classified into five classes: class 1 to class 5. In particular, pulmonary hypertension diseases include pulmonary arterial hypertension (group 1 ), such as idiopathic PAH, heritable PAH, PAH associated with drugs and toxins, PAH associated to other conditions, pulmonary veno-occlusive disease and / or pulmonary capillary hemangomatosis etc..., PH associated with left heart disease (group 2), PH associated to lung diseases and / or hypoxia (group 3), PH associated with pulmonar artery obstruction such as chronic thrombo-embolic pulmonary hypertension (group 4), and PH with unclear and / or multifactorial mechanisms (group 5)1.

[0003] Among pulmonary hypertension diseases, pulmonary arterial hypertension is a devastating pulmonary vascular disease, causing breathlessness, loss of exercise capacity, right heart failure and ultimately death. Pulmonary arterial hypertension (PAH) is a rare, chronic, and devastating disease defined by progressive occlusion of distal pulmonary arteries caused by vascular remodeling. According to the European Respiratory Society (ERS) guidelines, PAH is characterized by pulmonary vascular resistance (PVR) > 2 Wood Units, pulmonary mean pulmonary arterial pressure (mPAP) > 20 mmHg, and pulmonary capillary wedge pressure (PAWP) < 15 mmHg at rest, which ultimately leads to right ventricle hypertrophy and then heart failure and death1. These parameters may be measured in the subject at rest by right-heart catheterization.

[0004] The vascular remodeling is due to the dysfunction of pulmonary arterial vascular cells, affecting both smooth muscle cells (hPASMCs) and pulmonary arterial endothelial cells (hPAECs), and involving vascular cell proliferation and migration, associated with perivascular inflammation and vasoconstriction2. The current pharmacological treatments mainly target vasoconstriction through multiple pathways, yet they all have inconveniences. Examples of treatment options can be:- Endothelin Receptor Antagonists (ERAs): these drugs, such as bosentan and ambrisentan, block endothelin effects, leading to improved exercise capacity and hemodynamics. However, they come with potential liver toxicity and drug interaction risks.- Phosphodiesterase Type 5 Inhibitors (PDE-5ls): Sildenafil and tadalafil fall into this category. By inhibiting cGMP breakdown, they enhance vasodilation, improving exercise tolerance. Side effects include headaches and contraindications with nitrates.Prostacyclin Derivatives: Epoprostenol, treprostinil, and iloprost are potent vasodilators administeredvia continuous infusion or inhalation. While effective, their complex administration and side effects (jaw pain, flushing) pose challenges.- Soluble Guanylate Cyclase Stimulators (sGCs): Riociguat, an oral sGC stimulator, improves exercise capacity and hemodynamics. However, careful dose titration is necessary due to hypotension risk.- The current standards being combination therapy that improves the quality of life and patient survival3. Combining medications (e.g., ERA + PDE-5I) targets multiple pathways, enhancing efficacy.- Recently, in 2024, biotherapeutic drug Sotatercept was approved by the FDA as a treatment for Adults with Pulmonary Arterial Hypertension. Sotatercept is a fusion protein that traps and regulates molecules involved in vascular remodeling and acts as an inhibitor of activin signaling.

[0005] Lung transplantation remains the definitive treatment for patients with disease refractory to - or not progressing on - best medical therapy.

[0006] A need remains for additional safe and effective treatments of pulmonary hypertension and particularly pulmonary arterial hypertension.Detailed description

[0007] The present invention relates to a kynurenine-3-monooxygenase inhibitor for use in the treatment and prevention of pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0008] The term "treatment" is used herein according to its ordinary meaning, i.e. to cure, heal, alleviate, relieve, alter, remedy, ameliorate, improve or affect the disease, to reduce the symptoms of the disease or to help to manage the condition or its symptoms.

[0009] The term "prevention " is used herein according to its ordinary meaning, i.e. to preclude, stop, or hinder a disease or a condition.

[0010] As mentioned above, pulmonary hypertension (PH) covers five groups of diseases1, categorized according to similar pathophysiological mechanisms, clinical presentation, haemodynamic characteristics, and therapeutic management.

[0011] Group 1 is Pulmonary Arterial Hypertension (PAH), which includes various subtypes. Idiopathic PAH consists of cases with no identifiable cause, further divided into non-responders and acute responders at vasoreactivity testing. Heritable PAH is linked to genetic factors. PAH can also be associated with the use of certain drugs and toxins. Additionally, PAH may develop in connection with conditions such as connective tissue disease, HIV infection, portal hypertension, congenital heart disease, and schistosomiasis. Another subtype of PAH includes those with features of venous or capillary involvement (PVOD / PCH). Persistent PH of the newborn is also categorized under Group 1 .

[0012] Group 2 encompasses PH associated with left heart disease. This includes heart failure, which can present with either preserved ejection fraction or reduced / mildly reduced ejection fraction.Valvular heart disease and congenital or acquired cardiovascular conditions that lead to postcapillary PH are also part of this group.

[0013] Group 3 is PH associated with lung diseases and / or hypoxia. This group includes obstructive lung disease or emphysema, restrictive lung disease, and lung diseases with a mixed restrictive / obstructive pattern. Hypoventilation syndromes and hypoxia without lung disease, such as that experienced at high altitudes, are included as well. Developmental lung disorders are also part of Group 3.

[0014] Group 4 comprises PH associated with pulmonary artery obstructions. Chronic thromboembolic PH and other types of pulmonary artery obstructions fall under this category.

[0015] Group 5 includes PH with unclear and / or multifactorial mechanisms. This group involves haematological disorders, systemic disorders, metabolic disorders, and chronic renal failure with or without haemodialysis. Pulmonary tumor thrombotic microangiopathy and fibrosing mediastinitis are also included in Group 5.

[0016] Of course, it is understood that this recent classification is constantly evolving, and new groups and / or subgroups, also covered in the context of the present invention, are regularly discovered.

[0017] Kynurenine-3-monooxygenase (KMO) is an enzyme that is involved in the kynurenine pathway (KP)4. KP is initiated by tryptophan, an essential amino acid that is quickly converted into kynurenine (KYN) followed by successive production of metabolites to end up with NAD+ co-enzyme synthesis. It is divided into three major routes thanks to enzyme activities. KYN can be degraded (1 ) through the principal path by the kynurenine 3-monooxygenase (KMO) enzyme, generating several toxic metabolites, including 3-hydroxy-kynurenine (3-OH-Kynurenine), and quinolinic acid (QA)5,(2) by the kynurenine-aminotransferase (KAT) and (3) by the kynureninase to produce protective kynurenic acid (KA)5and anthranilic acid (AA), respectively. Some KMO inhibitors have been proposed as therapeutic agents for the treatment of neurodegenerative disease such Huntington's disease or Alzheimer's disease (WO2010 / 01 1302).

[0018] Surprisingly, the inventors have found that KMO inhibitors may be effective in the treatment and the prevention of pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0019] The invention therefore relates to a kynurenine-3-monooxygenase inhibitor for use in the treatment and prevention of pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0020] The inventors have found that there is a dysregulation of KP in the lungs of PAH patients. As a matter of fact, they have found an imbalance of KP metabolites reflected by the upregulation of the main KP enzymes, particularly kynurenine 3-monooxygenase (KMO) in the lungs of PAH patients.

[0021] It is believed that KMO inhibitors are able to decrease the proliferation and migration of human lung vascular cells and promote pulmonary artery relaxation. It is believed that KMO blockadedecreases right ventricular systolic pressure, and vascular and cardiac remodeling, decreasing vascular cell proliferation namely through the IL-6 / STAT3 pathway.

[0022] In an embodiment, the KMO inhibitor is effective in reducing vascular and cardiac remodeling in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0023] In an embodiment, the KMO inhibitor is effective in decreasing in right ventricular systolic pressure in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0024] In an embodiment, the KMO inhibitor is effective in reducing pulmonary ventricular resistance in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0025] In an embodiment, the KMO inhibitor is effective in decreasing medial hypertrophy of large arteries in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0026] In an embodiment, the KMO inhibitor is effective in lowering the proportion of muscularized and occluded small arteries in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0027] In an embodiment, the KMO inhibitor is effective in decreasing right ventricular hypertrophy in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0028] In an embodiment, the KMO inhibitor is effective in decreasing cardiac fibrosis in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0029] In an embodiment, the KMO inhibitor is effective in improving pulmonary artery vasomotricity in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0030] In an embodiment, the KMO inhibitor is effective in relaxing or delaying contraction of pulmonary arteries in a patient suffering from pulmonary hypertension (PH) and particularly pulmonary arterial hypertension (PAH).

[0031] An inhibitor of the enzyme kynurenine 3-monooxygenase (KMO) refers to a compound that causes an inhibition of the activity or expression of KMO. "Inhibition of the activity of KMO" refers in particular to a significant decrease in KMO activity as a direct or indirect response to the presence of at least one KMO inhibitor, relative to the activity of KMO in the absence of said at least one KMO inhibitor. The decrease in activity may be due to the direct interaction of the KMO inhibitor with KMO, or due to the interaction of the KMO inhibitor with one or more other factors that in turn affect KMO activity. For example, the presence of the KMO inhibitor may decrease KMO activity by directly binding to the KMO, by causing (directly or indirectly) another factor to decrease KMO activity, or by (directly or indirectly) decreasing the amount of KMO present in the cell or organism. "Inhibition ofthe expression of KMO" refers in particular to a to a significant decrease in KMO expression within the cell, as a direct or indirect response to the presence of at least one KMO inhibitor, relative to the expression of KMO in the absence of said at least one KMO inhibitor. The skilled person knows how to recognize inhibitors of the activity and / or expression of KMO.

[0032] In one embodiment, KMO activity is reduced by at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%.

[0033] In one embodiment, KMO expression is reduced by at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%.

[0034] Inhibition of KMO activity can be measured as described in the Examples (Supplemental Method 4).

[0035] In an embodiment, the inhibitor of human KMO has an IC50 value less than or equal to 1 micromolar, in particular less than 0.9 micromolar, in particular less than 0.8 micromolar, in particular less than 0.7 micromolar.

[0036] In an embodiment, the inhibitor of rat KMO has an IC50 value less than or equal to 0.1 micromolar, less than or equal to 0.09 micromolar, less than or equal to 0.08 micromolar, less than or equal to 0.07 micromolar, less than or equal to 0.06 micromolar, less than or equal to 0.05 micromolar, less than or equal to 0.04 micromolar, less than or equal to 0.03 micromolar.

[0037] In an embodiment, the kynurenine-3-monooxygenase inhibitor for use according to the invention is a compound of formula (I):wherein:RT is chosen from aryl and heteroaryl, each of which is substituted with one, two, or three groups chosen from halo, lower alkyl, alkoxy, and hydroxy;R2’ is chosen from hydrogen and optionally substituted lower alkyl;R3’ and R4’ are independently chosen from hydrogen, halo, hydroxy, lower alkyl, and lower alkoxy;R5’ and R6’ are independently chosen from hydrogen and lower alkyl; or R3’ and R5’, taken together with the atoms to which they are attached, form an optionally substituted cycloalkyl ring,n is one or two;R7’ is chosen from -C(O)OR8’, -C(O)R8’, optionally substituted amino, -(C=N-OR1 1 ’)R8’, - C(O)NR9’R10’ , cyano, and optionally substituted heteroaryl;R8’ is chosen from hydrogen, optionally substituted lower alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, and glycosyl; and R9’ and R10’ are independently chosen from hydrogen, optionally substituted lower alkyl, optionally substituted lower alkoxy, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocycloalkyl, and optionally substituted heteroaryl; or R9’ and R1 O’, together with the nitrogen to which they are bound, form an optionally substituted heterocycloalkyl or optionally substituted heteroaryl ring;R1 1 ’ is chosen from hydrogen and optionally substituted lower alkyl; or an enantiomer, diastereoisomer, hydrate, solvate, tautomer, racemic mixture or pharmaceutically acceptable salt thereof.

[0038] In an embodiment, the kynurenine-3-monooxygenase inhibitor for use according to the invention is a compound of formula (la):wherein:R1 and R2 independently from each another are hydrogen or (C1 -C6) alkyl, in particular a methyl; n is 1 or 2;R3 represents an -OH group; an -O(C1 -C6 alkyl) group, in particular -OEt or -OiPr; an -O(C3-C6 cycloalkyl) group, in particular an -O-cyclopentyl; an -O(C3-C7 heterocyclic) group, in particular an -O-tetrahydropyran-4-yl; an -O-heteroaryl group, in particular an -O-pyridyl; an -O-aryl group, in particular an -O-phenyl; an -0(C1 -C6 alkyl) aryl group, in particular -O-benzyl; an -NR7R8 group, in whichR7 represents a hydrogen atom or a (C1 -C6) alkyl group and R8 represents a hydrogen atom; a heteroaryl group, in particular containing one or more nitrogen atoms; a (C1 -C6) alkyl group, in particular an ethyl group, optionally substituted with an -NR9 R10 group in which R9 and R10 represent, independently of one another, a hydrogen atom or a (C1 -C6) alkyl group, in particular a group methyl; a (C1 -C6) alkyl group, in particular an ethyl group, optionally substituted with a group -OR10 in which R1 1 represents a hydrogen atom or a (C1 -C6) alkyl group, in particular a methyl group; or R7 and R8 form with the nitrogen atom which provides them with a heterocycle, in particular a pyrrolidine, a piperidine, a morpholine, a piperazine, the heterocycle being optionally substituted with a (C1 -C6) alkyl group, in particular a methyl group;R4 represents a hydrogen atom or a (C1 -C6) alkyl group, in particular -Me or -Et;R5 and R6 represent, independently from each other, a hydrogen atom, a halogen atom, in particular Cl, or a group chosen from: a — CN group; an — OH group; an — O(C1 -C6) alkyl group, in particular — OMe, the alkyl group being optionally substituted by one or more halogen atoms, in particular F; a (C1 -C6) alkyl group, in particular methyl, optionally substituted with one or more halogen atoms, in particular F; an -O(C3-C6 cycloalkyl) group, in particular an -O-cyclopropyl; or an enantiomer, diastereoisomer, hydrate, solvate, tautomer, racemic mixture or pharmaceutically acceptable salt thereof.

[0039] In an embodiment, the kynurenine-3-monooxygenase inhibitor of formula (la) for use according to the invention is such that R5 and R6 represent independently from each other a halogen atom, preferably R5 and R6 are chlorine atoms.

[0040] In an embodiment, the kynurenine-3-monooxygenase inhibitor of formula (la) for use according to the invention is such that R4 represents a (C1 -C6) alkyl group, in particular -ethyl.

[0041] In an embodiment, the kynurenine-3-monooxygenase inhibitor of formula (la) for use according to the invention is such that n=1 .

[0042] In an embodiment, the kynurenine-3-monooxygenase inhibitor of formula (la) for use according to the invention is such that R3 represents an -OH group or an -O(C1 -C6 alkyl) group, in particular -OEt or -OiPr.

[0043] In an embodiment, the kynurenine-3-monooxygenase inhibitor of formula (la) for use according to the invention is such that R1 and R2 both represent a hydrogen atom.

[0044] In a particular embodiment, the kynurenine-3-monooxygenase inhibitor of formula (la) for use according to the invention is 4-(3,4-dichloro-phenyl)-4-ethoxyimino-butyric acid.

[0045] The 4-(3,4-dichloro-phenyl)-4-ethoxyimino-butyric acid is a compound of formula (lb):

[0046] In an embodiment, the KMO inhibitor of formula (I) is chosen among the following compounds:4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyric acid;4-(3,4-dichloro-phenyl)-4-ethoxyimino-butyric acid;4-Benzyloxyimino-4-(3 ,4-dichloro-phenyl)-butyric acid;4-Cyclopropylmethoxyimino-4-(3 ,4-dichloro-phenyl)-butyric acid;4-(3,5-Dichloro-phenyl)-4-methoxyimino-butyric acid;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-2-methyl -butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-3-methyl-butyric acid;4-Methoxyimino-4-pyridin-2-yl-butyric acid;4-Methoxyimino-4-pyridin-3-yl-butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid methyl ester;4-(3,4-Dichloro-phenyl)-4-ethoxyimino-butyric acid methyl ester;4-Benzyloxyimino-4-(3,4-dichloro-phenyl)-butyric acid methyl ester;4-(3,4-Dichloro-phenyl)-4-hydroxyimino-butyric acid methyl ester;5-(3,4-Dichloro-phenyl)-5-methoxyimino-pentanoic acid methyl ester;5-(3,4-Dichloro-phenyl)-5-methoxyimino-pentanoic acid;1 -(3,4-Dichloro-phenyl)-5-methoxy-pentan- 1 -one O-methyl-oxime;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-phenyl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-3-yl-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(2-morpholin-4-yl-ethyl)- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-[l,3,4]thiadiazol-2-yl- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-4-yl-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-2-yl-butyr amide;4-(3,4-Dichloro-phenyl)-N-isoxazol-3-yl-4-methoxyimino-butyramide;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-N-( 1 -methyl- 1 H-pyrazol-4-yl)- butyramide;1 -(3 ,4-Dichloro-phenyl)-4-morpholin-4-yl-butane- 1 ,4-dione 1 -(O-methyl- oxime);4-(3,4-Dichloro-phenyl)-N-ethyl-4-methoxyimino-butyr amide;4-(3,4-Dichloro-phenyl)-N-isopropyl-4-methoxyimino-butyramide;N-Cyclopropyl-4-(3,4-dichloro-phenyl)-4-methoxyimino-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-methyl-butyr amide;4-[4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino]-piperidine-1 -carboxylic acid tert-butyl ester;4-[4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino]-piperidinium trifluoroacetate;{2-[4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino]-ethyl}-dimethyl-ammonium trifluoroacetate;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N,N-dimethyl-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-2-methyl-N-phenyl-butyramide;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-2-methyl-N-pyridin-3 -yl- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid isopropyl ester;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid cyclopentyl ester;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid cyclobutyl ester;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid pyridin-3-yl ester;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyric acid tetrahydro-pyran-4-yl ester;1 -(3,4-Dichloro-phenyl)-3-(3-methyl-[l,2,4]oxadiazol-5-yl)-propan-1 -one O- methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(2H-tetrazol-5-yl)-propan- 1 -one O-methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-imidazol- 1 -yl-propan- 1 -one O-methyl-oxime;1 -(3 ,4-Dichloro-phenyl)-4-imidazol- 1 -yl-butan- 1 -one O-methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(5-methyl-isoxazol-3-yl)-propan- 1 -one O-methyl- oxime;(1S, 2S)-trans-2-[(3,4-Dichloro-phenyl)-methoxyimino-methyl]- cyclopropanecarboxylic acid methyl ester;(1 S, 2S)-trans-2-[(3,4-Dichloro-phenyl)-methoxyimino-methyl]- cyclopropanecarboxylic acid; and4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyric acid 3 ,4,5 ,6-tetrahydroxy- tetrahydro-pyran-2- ylmethyl ester,4-[2-tert-Butoxycarbonylamino-ethoxyimino]-4-(3,4-dichloro-phenyl)-butyric acid;4-[2-Amino-ethoxyimino]-4-(3,4-dichloro-phenyl)-butyric acid;4-(3,4-Dichloro-phenyl)-4-(2-dimethylamino-ethoxyimino)-butyric acid;4-(4,5-Dichloro-2-hydroxy-phenyl)-4-hydroxyimino-butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyronitrile;4-(3-Chloro-phenyl)-4-methoxyimino-butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrazin-2-yl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-3-ylmethyl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(4-methyl-pyridin-3-yl)- butyramide;1 -(3,4-Dichloro-phenyl)-3-(2-methyl-2H-tetrazol-5-yl)-propan-1 -one O- methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(2-methyl-2H-tetrazol-5-yl)-propan- 1 -one O- methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(5-methyl-[1 ,2,4]oxadiazol-3-yl)-propan-1 -one O- methyl-oxime;1 -(3 ,4-Dichloro-phenyl)-3-[ 1 ,2,4]triazol- 1 -yl-propan- 1 -one O-methyl-oxime;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrimidin-5-yl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(5-methyl-pyridin-3-yl)- butyramide;4-(3,4-Dichloro-phenyl)-N-(2,6-dimethyl-pyridin-3-yl)-4-methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(2-methyl-pyrimidin-5-yl)- butyramide;1 -(3,4-Dichloro-phenyl)-3-(3-hydroxy-isoxazol-5-yl)-propan-l -one O-methyl- oxime;4-(3,4-Dichloro-phenyl)-N-(5-fluoro-pyridin-3-yl)-4-methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridazin-3-yl-butyr amide;4-(3,4-Dichloro-phenyl)-N-(3,5-dimethyl-pyrazin-2-yl)-4-methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(6-trifluoromethyl-pyridin-3-yl)- butyramide;1 -(3 ,4-Dichloro-phenyl)-4-piperidin- 1 -yl-butane- 1 ,4-dione 1 -(O-methyl- oxime);1 -(3,4-Dichloro-phenyl)-4-(4-methyl-piperidin- 1 -yl)-butane- 1 ,4-dione 1 -(O- methyl-oxime);4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(6-methyl-pyridazin-3-yl)- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(6-methyl-pyridin-3-yl)- butyramide;1 -(3 ,4-Dichloro-phenyl)-4-(3-hydroxy-pyrrolidin- 1 -yl)-butane- 1 ,4-dione 1 -(O- methyl-oxime);4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrimidin-2-yl-butyramide;Pyrimidine-5-carboxylic acid {3-(3,4-dichloro-phenyl)-3-methoxyimino- propyl} -amide;4-(3,4-Dichloro-phenyl)-N-(2-hydroxy-ethyl)-4-methoxyimino-butyramide;5-(3,4-Dichloro-phenyl)-5-methoxyimino-pentanoic acid amide;1 -(3 ,4-Dichloro-phenyl)-4-(4-hydroxy-piperidin- 1 -yl)-butane- 1 ,4-dione 1 -(O- methyl-oxime);3- {4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino } -pyrrolidine- 1 - carboxylic acid tert-butyl ester;4-(3,4-Dichloro-phenyl)-N-(2-hydroxy-propyl)-4-methoxyimino-butyramide;4-(3,4-Dichloro-phenyl)-N-(2,4-dimethyl-pyridin-3-yl)-4-methoxyimino- butyramide;5 -(3 ,4-Dichloro-phenyl)-5 -methoxyimino-pentanenitrile;4-(3,4-Dichloro-phenyl)-N-(2,3-dihydroxy-propyl)-4 — methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrrolidin-3-yl-butyramide;4-(3,4-Dichloro-phenyl)-N-methoxy-4-methoxyimino-N-methyl-butyramide;1 -(3 ,4-Dichloro-phenyl)-pentane-1 ,4-dione l-(O-methyl-oxime);4-(3,4-Dichloro-phenyl)-N-(6-fluoro-pyridin-3-yl)-4-methoxyimino- butyramide;N- {3-(3 ,4-Dichloro-phenyl)-3-methoxyimino-propyl} -methanesulfonamide;1 -(3,4- Dichloro-phenyl)-pentane-1 ,4-dione bis-(O-methyl-oxime);4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(2,4,6-trimethyl-pyridin-3-yl)- butyramide;Pyridine-3-sulfonic acid {3-(3,4-dichloro-phenyl)-3-methoxyimino-propyl}-amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid (S)-2-((R)-3,4-dihydroxy-5-oxo-2,5-dihydro- furan-2-yl)-2-hydroxy-ethyl ester; and1 -(3,4-Dichloro-phenyl)-3-(1 H-imidazo[4,5-c]pyridin-2-yl)-propan-1 -one O-methyl-oxime ester; or an enantiomer, diastereoisomer, hydrate, solvate, tautomer, racemic mixture or pharmaceutically acceptable salt thereof.

[0047] The synthesis of the above compounds of formula (I) and (la), in particular of 4-(3,4-dichloro- phenyl)-4-ethoxyimino-butyric acid (lb), is described in the prior art. As a matter of fact, patent application WO 2010 / 011302 describes the synthesis of compound of formula (I) and its application in the field of neurodegenerative diseases treatment without, however, describing activity on pulmonary hypertension. Thus, the inventors have surprisingly discovered that this compound has activity in the treatment and prevention of pulmonary hypertension, in particular pulmonary arterial hypertension.

[0048] In another aspect, the invention relates to a method of treatment and prevention of pulmonary hypertension, in particular pulmonary arterial hypertension, comprising administering a therapeutically effective amount of a KMO inhibitor to a subject in need thereof.

[0049] The therapeutically effective amount of a KMO inhibitor will be adapted according to the nature and severity of the pathology to be treated, the route of administration and also the weight and age of the subject. In general, the dosage unit will vary between 0.5 mg and 2000 mg per day, in one or more doses, preferably between 1 and 1000 mg when the subject is human.

[0050] In the context of this invention, the term “aryl group” means an aromatic ring having 5 to 8 carbon atoms or several fused aromatic rings having 5 to 14 carbon atoms. In particular, the aryl groups may be monocyclic or bicyclic groups, preferably phenyl or naphthyl. In particular it would be a phenyl group (Ph).

[0051] In the context of this invention, the term “heteroaryl group” means any aromatic hydrocarbon group of 3 to 9 atoms containing one or more heteroatoms, in particular one or two, such as, for example, sulfur, nitrogen or oxygen atoms, in particular, one or more nitrogen atoms. The heteroaryl according to this invention may consist of one or more fused rings. Examples of heteroaryl groups are furyl, isoxazyl, pyridyl, thiazolyl, pyrimidyl, pyridazinyl, benzimidazole, benzoxazole, benzothiazole, pyrazole. In particular, the heteroaryl group is chosen from pyridazinyl pyrazole and pyridyl groups.

[0052] In the context of this invention, the term “halogen atom” is understood to mean any halogen atom, in particular chosen from Cl, Br, I or F, in particular chosen from F, Cl or Br, in particular F or Cl, more specifically, Cl.

[0053] In the context of this invention, the term “C1 -C6 alkyl group” means any alkyl group of 1 to 6 carbon atoms, linear or branched, in particular methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl, n-pentyl, n-hexyl. In particular, it is a methyl (Me), ethyl (Et), isopropyl (iPr) or t- butyl (tBu) group, in particular a methyl, ethyl or isopropyl group, more particularly a methyl or ethyl group.

[0054] In the context of the present invention, the terms “C3-C6 cycloalkyl group” means any saturated and hydrocarbon-based cycle comprising from 3 to 6 carbon atoms, in particular the cyclopropyl cyclobutyl, cyclopentyl or cyclohexyl group. In particular it is a cyclopentyl or cyclohexyl group.

[0055] In the context of this invention, the term “heterocyclic group” means any saturated cyclic hydrocarbon group of 3 to 9 atoms containing one or more heteroatoms, such as, for example, sulfur, nitrogen or oxygen atoms, in particular atoms of nitrogen and oxygen, more particularly one or more nitrogen atoms. The heterocyclic group according to this invention may consist of one or more fused rings. Examples of heterocyclic groups are tetrahydrofuran, tetrahydropyran, pyrrolidine, piperazine, piperidine, thiolane, oxirane, oxine, thiane, thiazolidine, morpholine groups. In particular, the heterocyclic group is chosen from tetrahydropyran, piperidine, pyrrolidine, piperazine and morpholine groups.

[0056] Within the scope of this invention, the term “pharmaceutically acceptable” is meant to be useful in the preparation of a pharmaceutical composition which is generally safe, non-toxic and neither biologically nor otherwise undesirable and which is acceptable for veterinary use as well as in human pharmaceuticals.

[0057] Within the scope of this invention, the term “pharmaceutically acceptable salts of a compound” means salts which are pharmaceutically acceptable, as defined herein, and which possess the desired pharmacological activity of the parent compound. Such salts include: (1 ) acid addition salts formed with mineral acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like; or formed with organic acids such as acetic acid, benzenesulfonic acid, benzoic acid, camphorsulfonic acid, citric acid, ethanesulfonic acid, fumaric acid, glucoheptonic acid, gluconic acid, glutamic acid, glycolic acid hydroxynaphthoic acid, 2-hydroxyethanesulfonic acid, lactic acid, maleic acid, malic acid, mandelic acid, acid methanesulfonic acid, muconic acid, 2- naphthalenesulfonic acid, propionic acid, salicylic acid, succinic acid, dibenzoyl-L-tartaric acid, tartaric acid, p-toluenesulphonic acid, trimethylacetic acid, trifluoroacetic acid and the like; or(2) salts formed when an acidic proton present in the parent compound is replaced by a metal ion, for example an alkali metal ion, an alkaline earth metal ion or an aluminum ion; or coordinates with an organic or inorganic base. Acceptable organic bases include diethanolamine, ethanolamine, N- methylglucamine, triethanolamine, tromethamine and the like. Acceptable inorganic bases include aluminum hydroxide, calcium hydroxide, potassium hydroxide, sodium carbonate and sodium hydroxide.

[0058] In the context of this invention, the term “solvate of a compound” is understood to mean any compound obtained by adding an inert solvent molecule to the compound according to the invention, the solvate being formed because of their mutual attractive force. The solvates are, for example, alcoholates of the compound. A hydrate is a solvate in which the inert solvent used is water. It can be a mono, di or trihydrate.

[0059] In the context of this invention, the term “tautomer” is intended to mean any constituent isomer of the compounds according to this invention which are interconvertible by the reversible chemical reaction known as tautomerization. In most cases, the reaction is produced by the migration of a hydrogen atom accompanied by a change of location of a double bond. In a solution of a compound capable of tautomerization, an equilibrium between the two tautomers is created. The ratio between the tautomers is then a function of the solvent, the temperature and the pH. The tautomerism is therefore the transformation of one functional group into another, most often by concomitant displacement of a hydrogen atom and a IT bond (double or triple bond). Common tautomers are, for example, aldehyde / ketone-alcohol pairs or more precisely enol pairs; amides — imidic acids; lactams — lactims; imines — enamines; enamines — enamines. Ire particular, it may include a cyclechain tautomerism that takes place when the movement of the proton is accompanied by the transformation of an open structure to a cycle.

[0060] The kynurenine-3-monooxygenase inhibitor according to the invention can be administered in the form of a pharmaceutical composition comprising a pharmaceutically acceptable excipient.

[0061] In an embodiment, the pharmaceutical composition comprising a kynurenine-3- monooxygenase inhibitor according to the invention and a pharmaceutically acceptable excipient is for use in the treatment or prevention of pulmonary hypertension, in particular pulmonary arterial hypertension.

[0062] These compositions may be formulated for administration to mammals, including humans. The posology varies according to the treatment and the condition in question. These pharmaceutical compositions are suitable for administration by any suitable route, for example orally (including buccal and sublingual route), rectally, nasally (including inhaled), topically (including transdermal), vaginal, intraocular or parenteral (including subcutaneous), intramuscular or intravenous). In particular, the pharmaceutical compositions are adapted for oral administration. These formulations can be prepared using any of the methods known to those skilled in the art by combining the active ingredients with the appropriate pharmaceutically acceptable excipients. The unit forms of suitable oral administrations include tablets, capsules, powders, granules and oral solutions or suspensions in aqueous or non-aqueous liquids, comestible or edible foams, or liquid water- in -water emulsions or oil or oil-in-water. When preparing a solid composition in tablet form, the main active ingredient, in particular in powder form, is mixed with a suitable pharmaceutical excipient such as gelatin, starch, lactose, magnesium stearate, talc, arabic gum or the like. The tablets may be coated with sucrose or other suitable materials or they may be treated in such a way that they will have prolonged or delayed activity and continuously release a predetermined amount of active ingredient.

[0063] A preparation in capsules is obtained by mixing the active ingredient, in particular in powder form, with a diluent and pouring the resulting mixture into soft or hard gelatin capsules, in particular gelatin capsules. Lubricants such as, for example, talc, magnesium stearate, calcium stearate or polyethylene glycol in solid form can be added to the composition before it is filled into capsules. A disintegrant or solubilizer such as for example calcium carbonate or 0.15 sodium carbonate may also be added in order to improve the availability of the drug after taking the capsule.

[0064] In addition, suitable binders, lubricants and disintegrants as well as colorants may be added if necessary to the mixture. Suitable binders may be for example starch, gelatin, natural sugars such as for example glucose or beta-lactose, sweetening agents made from corn, synthetic or natural rubber such as acacia for example or sodium alginate, carboxymethylcellulose, polyethylene glycol, waxes and the like. Lubricants useful in these dosage forms include sodium oleate, sodium stearate, magnesium stearate, sodium benzoate, sodium acetate, sodium chloride, and the like. Disintegrants include starch, methylcellulose, agar, bentonite, xanthan gum and the like. The tablets are formulated for example by preparing a powder mixture, granulating or dry pressing the mixture, adding a lubricant and a disintegrant and pressing the mixture to give the tablets. A powder mixture is prepared by mixing the active ingredient suitably added with a diluent or a base and optionally with a binder such as, for example, carboxymethylcellulose, alginate, gelatin or polyvinylpyrrolidone, a dissolution retardant such as paraffin, an absorption accelerator such as, for example, a quaternary salt and / or an absorbent such as, for example, bentonite, kaolin or dicalcium phosphate. The powder mixtures can be, granulated by wetting with a binder such as for example a syrup, a starch paste, acaciamucilage or solutions of cellulose or polymeric materials and pressing them through a sieve. The granules may be lubricated by the addition of stearic acid, stearate salt, talc or mineral oil so as to prevent them from sticking to the molds used for manufacturing the tablets. The lubricated mixture is then pressed to produce the tablets. An opaque or transparent protective layer consisting of a shellac layer, a layer of sugar or polymeric materials may be optionally present. Dyes may be added to these coatings to differentiate them from other tablets.

[0065] A syrup or elixir preparation may contain the active ingredient together with a sweetener, an antiseptic, as well as a flavoring agent and a suitable colorant. In general, the syrup preparations are obtained by dissolving the compound in an aqueous solution with an agent giving an appropriate taste while the elixirs are prepared using a nontoxic alcoholic vehicle.

[0066] The water-dispersible powders or granules may contain the active ingredient in a mixture with dispersing agents or wetting agents, or suspending agents, such as, for example, ethoxylated isostearyl alcohols and polyoxyethylene sorbitol ethers, and with taste correctors or sweeteners. For rectal administration, suppositories are used which are prepared with binders that melt at rectal temperature, for example cocoa butter or polyethylene glycols.

[0067] For parenteral, intranasal or intraocular administration, aqueous suspensions, isotonic saline solutions or sterile and injectable solutions containing dispersing agents and / or pharmacologically compatible wetting agents are used.

[0068] The active ingredient may also be formulated as microcapsules, optionally with one or more additives.

[0069] The pharmaceutical compositions adapted for topical administration may be formulated as a cream, ointment, suspension, lotion, powder, solution, paste, gel, spray, aerosol or oil.

[0070] Pharmaceutical compositions adapted for nasal administration in which the excipient is in the solid state including powders having particle sizes for example in the range of 20 to 500 microns, administered by inhalation from a container holding the powder and placed near the nose.

[0071] Pharmaceutical formulations adapted for vaginal administration may be administered in the form of a buffer, cream, gel, paste, mousse or spray.

[0072] In another embodiment, the pharmaceutical composition according to this invention further comprises another active ingredient, in particular having a complementary or synergistic effect.

[0073] This second active ingredient can be administered in the same pharmaceutical composition as the compound of formula (I) of this invention. It may also be administered separately, either at the same time or over time.

[0074] The invention will be better understood in the light of the description of the figures and examples which follow, which are given by way of non-limiting description.Brief Description of DrawingsFig. 1

[0075] Figure 1 . Imbalance of the kynurenine pathway in the lungs of PAH patients(A) simplified schema of the kynurenine pathway; (B) assessment of KMO, Kynureninase, and KAT 1 mRNA expression by qPCR in lungs from iPAH, hPAH and MVO patients vs. controls normalized to (3-Actin (Actb) gene expression (n=5 to 6 per group); (C) western blot (upper image) and quantification (lower graphs) of KMO, Kynureninase and KAT1 protein expression in the lungs from PAH patients vs. controls with normalization relative to actin (ACTB) (n=6 to 7 in each group); (D) KMO enzymatic activity in lungs of PAH patients vs. controls, (n=6 for control group and 6 to7 for PAH groups). Statistical analyses were performed using an ordinary one-way ANOVA followed by a Dunnett’s test. *P< 0.05; **P<0.01 ; ***P<0.001 versus Control. The values shown are means ± SEMFig. 2

[0076] Figure 2. Imbalance of the kynurenine pathway in the monocrotaline (MCT) rat model of pulmonary hypertension.(A) five groups of rats were compared: saline-treated controls (Control), MCT (60mg / kg sc) exposed groups =after three days (MCT D3), seven days (MCT D7), fourteen days (MCT D14) and twenty- one days (MCT D 21 ); (B) quantitative RT-PCR evaluation of mRNA of KMO, Kynureninase, and KAT1 in total RNA of lungs from control and MCT (D3, D7, D14, and D21 ) rats, with normalization relative to Actb gene expression (n=6 in each group); (C) western blot (upper image) and quantification (lower graphs) of KMO, Kynureninase and KAT1 proteins in lysates of lungs from control and MCT (D3, D7, D14, and D21 ) rats, with normalization relative to ACTB (n=4 in each group); (D) KMO enzymatic activity in lungs from control and MCT (D3, D7, D14, and D21 ) rats (n=2- 3 in each group). Statistical significances were determined with an ordinary one-way ANOVA followed by a Dunnett’s test (A through D). *P< 0.05; **P<0.01 ; ***P<0.001 versus Control. The values shown are means ± SEM.Fig. 3

[0077] Figure 3. The KMO inhibitor 1506 can reverse experimental pulmonary hypertension, decreasing hemodynamics parameters, and vascular and cardiac remodeling in the MCT rat model. (A) three groups of rats were compared: Control, MCT and MCT-exposed to 1506 group treated from day 14 to 21 with 1506 (25 mg. kg1.day1per os) (MCT + 1506). In vivo effects of 1506, measured 3 weeks after MCT injection; (B) right ventricular systolic pressure (RVSP, mmHg) and representative traces of pressure in right hearts of Control, MCT, MCT + 1506 rats (n=8 to1 1 rats per group) scale bar: 200 ms; (C) calculated total pulmonary vascular resistance (PVR was evaluated by the RVSP / CO ratio, mmHg. min. mL-1 ) in Control, MCT and MCT + 1506 groups (n= 8 to1 1 rats); (D) quantification of medial thickness of pulmonary arteries (PA) with external diameter > 50 pm; (E) muscularization analysis of small arteries (external diameter < 50pm) classified into three groups: non-muscularized, muscularized, and occluded arterioles, percentage representative for each group; (F) Fulton’s index of right ventricular hypertrophy, calculated as the ratio weight of right ventricle[RV] / left ventricle [LV]+septum [S] in Control, MCT, MCT + 1506 rat groups (n=8 to10 rats); (G) measurement of cardiac fibrosis in the right ventricle (RV); Statistical analyses were assessed with an ordinary one-way ANOVA followed by Tukey’s multiple comparisons test to compare Control, MCT and MCT + 1506 groups (A through G). *P<0.05; **P<0.01 ; ***P<0.001 ; ****P<0,0001 . The values shown are means ± SEM.Fig. 4

[0078] Figure 4. KMO inhibitor 1506 regulates the vascular tone of the pulmonary arteries (PAs) from MCT rats.

[0079] Concentration-relaxation response curves of vehicle (DMSO) and increasing concentrations of 1506 (10 nmol. L1to 500pM.L-1) on isolated segments of precontracted PAs by U46619 (1 pM). (A) Representative graph on the left and percentage of PAs relaxation with 1506 (100pM) or DMSO (n=7 control rats for each group) and (B) in PAs from MCT rats (n=7 MCT rats for each group); (C) A normalized dose-response curve was established by applying an increasing concentration of KCI (10 to 90 mmol. L1) on isolated pulmonary arteries from control rats. Graphics show the quantification of EC50 values (n=5 control rats) and (D) in PAs from MCT rats (n= 3 to 5 MCT rats); (E) A normalized dose-response curve was established by applying an increasing concentration of U46619 (1 nmol. L1to 100pmol.L'1) (n=5 control rats). Quantification of EC50 values in PAs from control rats (n= 5 control rats) and (F) in PAs from MCT rats (n=3 to 5 MCT rats). Statistical differences between DMSO and 1506 treatments were determined with an unpaired Student’s t-tests or a Mann-Whitney tests. *P< 0.05; **P<0.01 ; ***P<0.001 ; ****P<0,0001 versus Control. The values shown are means ± SEM.Fig. 5

[0080] Figure 5. 1506 inhibits the increased proliferation of pulmonary vascular cells exposed to PDGF in vitro and in vivo in MCT rats

[0081] In vitro, control human pulmonary artery smooth muscle cells (hPASMCs) were stimulated with PDGF in the presence or the absence of 1506. (A) Measurement of control hPASMCs proliferation (BrdU incorporation) after 24h exposure to PDGF-BB (20 ng. ml-1) in the presence or in the absence of 1506 (100pM). Values are expressed as fold change of the mean value relative to Control; (B) percentage wound closure in hPASMCs after 24h exposure to PDGF-BB (20 ng. ml-1) in the presence or the absence 1506 (100pM) (n=3 donors), then control human endothelial cells isolated from pulmonary arteries (hPAECs) were stimulated with VEGF in the presence or the absence of 1506; (C) Measurement of control hPAECs proliferation (BrdU incorporation) after 24h exposure to VEGF (20 ng. mF1) in the presence or absence of 1506 (100pM). Values are expressed as fold changes of the mean value relative to Control; (D) percentage wound closure in hPAECs after 24h exposure to VEGF (20 ng. ml-1) in the presence or in absence of 1506 (1 OOpM) (n=2 13 donors,), In vivo, three groups of rats were compared: Control, MCT, and MCT + 1506; (E) quantitative RT- PCR of PCNA on total RNA from lungs from Control, MCT, and MCT + 1506 rats with a normalization relative to actb ; (F) Western blot (left) and quantification (right) of PCNA with a normalization relative to ACTB in the lung section of each group of rats (n=4 rats). Statistical analysis was performed withan ordinary-one-way ANOVA followed by a Dunnett’s test. *P<0.05; **P<0.01 ; ***P<0.001 ;****P<0,0001 . The values shown are means ± SEM.Fig. 6

[0082] Figure 6. Downregulation of KMO activity using the 1506 inhibitor reduces the IL-6 and STAT3 pathway engagement.Three groups of rats were compared: Control, MCT, and MCT + 1506. (D) Graph representation of the first 10 enriched terms derived from Gene ontology: Biological Process and Canonical pathway: Kyoto Encyclopedia of Genes and Genomes (KEGG); (E) Representative RT-qPCR of IL-6 and STAT3 mRNA expression measured in total RNA form rat lungs , with normalization relative to Actb gene expression (n=6 rats per group); (F) Western blot showing protein expression of IL-6 and P- TYR705 STAT3 and STAT3 and quantification of protein expression with normalization relative to actin in rat lung protein extracts (n=4 rats per group). Statistical differences between Control, MCT, and MCT + 1506 groups were assessed with ordinary-one-way ANOVA followed by a post-hoc Dunnett’s test. ns= non-significant, *P<0.05; **P<0.01 ; ***P<0.001. The values show are means ± SEM.Fig. 7

[0083] Figure 7. Imbalance of the kynurenine pathway enzymes in the lungs of PAH patients(A) assessment of KAT2 and KAT3 mRNA expression by qPCR in lungs from PAH patients vs. controls normalized with p-Actin (Actb) gene expression (n=5 to7 per group); western blot and quantification of KAT2 and KAT3 in the lungs from PAH patients vs. controls with normalization relative to actin (ACTB) (n=6 to7 in each group). Statistical significances were determined using an ordinary one-way ANOVA followed by a Dunnett’s test. *P< 0.05; **P<0.01 ; ***P<0.001 versus Control. The values shown are means ± SEM.Fig. 8

[0084] Figure 8. Kinetics study of the kynurenine pathway enzymes in the monocrotaline (MCT) rat modelAssessment of hemodynamics and cardiac parameters, and expression of KAT2 and KAT3. Five groups of rats were compared: saline-treated controls (Control), MCT (60mg / kg sc), pulmonary hypertension model (MCT) exposed group after three days (MCT D3), seven days (MCT D7), fourteen days (MCT D14) and twenty-one days (MCT D 21 ) and hemodynamic parameters are measured: (A) right ventricular systolic pressure (RVSP, mmHg); (B) Fulton index; (C) cardiac output (CO, min / mL); (D) systemic pressure and; (E) heart rate in Control and MCT groups (n=8 to11 rats), then (F) Western blot and quantification of KAT2 and KAT3 proteins in lysates of lungs from control and MCT rats (D3, D7, D14, and D21 ) rats with normalization relative to ACTB (n=4 in each group). Statistical significances were determined with an ordinary one-way ANOVA followed by a Dunnett’s test. *P< 0.05; **P<0.01 ; ***P<0.001 versus Control. The values shown are means ± SEM.Fig. 9

[0085] Figure 9. The KMO inhibitor 1506 can reverse experimental pulmonary hypertension, decreasing vascular and cardiac remodeling in the MCT rat modelPreliminary experiment to assess 150 dosing for further experiments. Four groups of rats were compared: Control, MCT and MCT-exposed group treated from 14 to 21 days with 1506 (25 mg.kg- 1 .day-1 or 50 mg.kg-1 .day-1 per os) (n=7-13 rats), In vivo effects of 15063 weeks after MCT injection. (A) right ventricular systolic pressure (RVSP, mmHg); (B) Fulton’s index of right ventricular hypertrophy, calculated as the ratio weight of right ventricle [RV] / left ventricle [LV]+septum [S] in Control, MCT, MCT + 1506 (25 mg.kg-1 .day-1 ), MCT + 1506 (50 mg.kg-1 .day-1 ) rat groups; (C) systemic pressure (mmHg); (D) cardiac output (CO, min / mL); (E) cardiac rate (mL / min) in Control, MCT and MCT + 1506. Statistical differences were determined between Control, MCT, and MCT+1506 groups and were assessed with an ordinary one-way ANOVA followed by a Tukey’s test (A through E) *P<0.05; **P<0.01 ; ***P<0.001 ; ****P<0,0001 . The values shown are means ± SEM.Fig. 10

[0086] Figure 10. 1506 inhibited PDGF-induced proliferation in control hPASMCs in a dosedependent manner, using two different tests.(A) MTS at 24h using 1506 from 25 pM to 100 pM (n=4 donors). Significance relative to untreated and 20 ng. ml-1 PDGF-induced cells is shown (n=4 donors); (B) BrdU incorporation after 24h exposure to PDGF (20 ng. ml-1 ) in the presence or absence of increasing concentrations of 1506 (10, 50 and 100pM). Values are expressed as fold change of the mean value relative to Control. Statistical analysis was performed using an ordinary-one-way ANOVA followed by Dunnett’s test. *P<0.05; **P<0.01 ; ***P<0.001 ; ****P<0,0001 . The values shown are means ± SEM.Fig. 11

[0087] Figure 1 1 . Downregulation of KMO activity could inhibit p-catenin and GSK3p expressions(A) Protein expression of f3-catenin and GSK3f3 with normalization relative to actin in the lung of each group of rats (n=4 rats), western blot. Statistical differences between Control, MCT, and MCT + 1506 groups were assessed with an ordinary-one-way ANOVA followed by Dunnett’s test. *P<0.05; **P<0.01 ; ***P<0.001 . The values shown are means ± SEM.Fig. 12

[0088] Figure 12. Analysis of selected pathways and genes regulated by KMO blockade using RNAseq analysis(C) quantification of selected gene expression known to be associated with PAH and affected by MCT, and regulated by 1506; (D) representative pathways extracted from supplemental enrichment lists explored from the data bases: hallmark, canonical pathway, -pid (pathway interaction database), -wiki (wikipedia) and -biocarta.Examples

[0089] MATERIALS AND METHODS

[0090] Study strategy

[0091] Several approaches were used to assess the impact of the kynurenine pathway impairment in PAH: in vivo measurement of the dysregulation of KP enzymes in PAH patient and rat PH lungs, in vitro analysis of the role of KP inhibition in the human pulmonary arterial smooth muscle cells (hPASMCs) and the human pulmonary arterial endothelial cells (hPAECs) proliferation and migration, ex vivo, analyses of vascular tone in isolated control and MCT rat pulmonary arteries (PAs) exposed to a KP inhibitor, in vivo blockade of KP enzyme in the monocrotaline (MCT) rat model of PH with evaluation of cardiac and vascular remodeling, and identification of key impacted pathways through RNAseq. Detailed descriptions of all materials and standard methods used in this study, including a listing of chemicals, primers, and antibodies used, animal model, surgical procedures, RT-qPCR, Western blot, in vitro culture, cell proliferation, cell migration assay, isometric tension measurement, and statistical analyses are presented in the following Supplemental Methods.

[0092] Human tissues, choice of the rat model and ethical considerations

[0093] Human lungs were collected from PAH patients during lung transplantation and from control patients upon lobectomy or pneumonectomy for localized lung cancer. Human control lungs were sampled far away from the area of the tumor and validated as normal tissue by the local pathologist. Patients were part of the French Network on Pulmonary Hypertension, a program approved by the inventors’ institutional ethics committee (Comite de Protection des Personnes Ile-de-France VII) and lung tissues were used for research provided written informed consent from transplant recipients or families of organ donors (Protocol N8CO-08- 003, ID RCB: 2008A00485-50, approved on June 18th, 2008). PAH patients were diagnosed and followed up at the inventors’ National Referral Center for Pulmonary Hypertension (Pulmotension, Hopital Kremlin Bicetre), according to all standards and ERS / ESC guidelines 2022. The clinical data for the patients are listed in Supplemental Table 1 . In animal studies, the sample size was based on general knowledge and experience with the Monocrotaline (MCT) model. The inventors have decided to use MCT rat model, that was the most appropriate for in vivo studies of the mechanisms underlying the kynurenine pathway blockade using a KMO inhibitor, mainly because it is a relevant model to explore features of metabolic dysregulation of the Kynurenine pathway. Importantly, in MCT rats and not Sugen / hypoxia rats the KP metabolic profile in the circulation, was similar to that observed in human PAH16. Animals were randomized to experimental groups based on weight at treatment initiation and for data collection. The endpoint (day 21 ) was selected in advance for the measurement of all parameters. All animals were used in strict accordance with European Union regulations (directive 2010 / 63 / UE) for animal experiments and the inventors’institution’s guidelines for animal care and handling. The procedures performed on rats were approved by the local ethics committee, CEEA26 (Animal Experimentation Ethics Committee no. 26), and the French Ministry of Higher Education and Research. To evaluate the effects of a rebalancing of the KP, MCT rats were treated with a KP blocker, more precisely with an inhibitor of the KMO enzyme called MBR-01506 (compound (lb)) developed by METABRAINRESEARCH SAS. The assessments of vascular remodeling, cardiac fibrosis, and the in vivo 1506 experiment were performed blind.

[0094] SUPPLEMENTAL METHODS

[0095] Supplemental Method 1 : Chemicals

[0096] All chemicals used are listed in the Supplemental Table 2. The compound 1506 (compound (lb)) is a KMO inhibitor disclosed in patent application WO2010 / 01 1302 Al filed by CHDI initially developed to target Huntington's disease.

[0097] Supplemental Method 2: RNA extraction and real-time PCR

[0098] Total RNA was isolated from human and rat lung samples using the RNeasy mini kit (Qiagen). 1 pg of RNA was used for reverse transcription (4368814; ThermoFisher). Gene expression was quantified using qPCR TaqMan gene expression assay (4324018; Life Technologies). The selective primers used for experiments are listed in Supplemental Table 3. The qPCR was performed on a StepOnePlus real-time PCR system and results were analyzed with the StepOne software v2.0 (Life Technologies). Results were considered for interpretation if the Ct value was less than 35. Fold change of gene expression was determined with the formula (2- AACt), normalized to housekeeping gene p-actin expression.

[0099] Supplemental Method 3: Western blot

[0100] Total proteins from human and rat lung samples were lysed in RIPA buffer (50 mM Tris-HCI pH 8, 150 mM NaCI, 1 % NP-40, 0.5% sodium deoxycholate, 0.1 % SDS) supplemented with HaltTM protease and phosphatase inhibitor cocktail (Thermo Fisher Scientific) using a GentleMACS device according to the manufacturer’s procedures. After sonication, the protein lysates were centrifugated for 10min at 16000 x g. Protein quantity was determined by the bicinchoninic acid (BCA) assay. Loading of 20-50pg of total proteins per well, was separated by electrophoresis in 4-15% acrylamide gradient gels (Bio-Rad) at 120V for 1 h30, then transferred on nitrocellulose membrane (GE Healthcare) at 100V for 1 h. The membranes were blocked with poly (vinyl alcohol) (PVA) 1 X in TBS with 0.1 % Tween 20 (TBST) for 5 min. Finally, the membrane was incubated with adequate primary antibodies (cf. Supplemental Table 4) diluted in TBST with 5% BSA overnight at 4°C. The day after, membranes were washed three times in TBST for 10 min then incubated with secondary anti-rabbit or anti-mouse antibodies for 1 h at room temperature, then revealed with enhanced chemiluminescence (ECL) prime detection kit (GE Healthcare) and ChemiDoc (Bio-rad). Band intensities were measured with Image Lab software. All results were normalized to p-actin protein expression.

[0101] Supplemental Method 4: KMO activity

[0102] KMO activity was enzymatically evaluated from washed human or rat total lung mitochondrial extracts. Washed mitochondria were prepared at 4°C from frozen human or rat lungs. A 700pL volume of isolation buffer (10 mM HEPES, 200 mM D-Mannitol, 70 mM sucrose, 1 mM EGTA pH 7.4) was added to 100pg of frozen human or rat lungs. Homogenization was carried out with thePrecellys Evolution®, 2x40 sec 6000 RPM at 4°C. The suspension was centrifuged 1000 g for 10 min at 4°C. The pellet was discarded, and the post-nuclear supernatant was centrifuged at 10 000 g for 20 min at 4°C. The supernatant was discarded, and the pellet was resuspended with 100pL of DTT Buffer (42 mM Trizma HCI, 8mM Trizma Base, 250 mM Sucrose, 1 mM EDTA, 100mM DTT at pH 7.4). The suspension was centrifuged for 10 min, 15000 g at 4°C. The supernatant contained mitochondria suspension. Mitochondria protein quantity was determined by the Bovine Serum Albumin (BSA) assay (Ci= 2mg / mL). The day after, a 200 pl reaction mixture containing 2,3 mM kynurenine (Sigma-Aldrich, Saint-Quentin Fallavier, France), 0.5 mM NADPH and 10 pg of mitochondrial extracts protein was prepared in a 50 mM HEPES buffer including 4 mM MgCI2 at pH 7.4. The KMO enzyme activity was monitored by measuring the oxidation of NADPH. A 96 wells microplate (P96) was seeded in two conditions: blank and 100% activity. In blank condition, 10pg of mitochondrial extract protein were added to 10OpL HEPES buffer containing 900pL NADPH (0.5mM). In 100%, 10pg of mitochondrial extract protein was added to 100pL Kynurenine (0.3mM) and 900pL NADPH (0.5mM). In each condition, a positive (rat liver mitochondria XENOTECH.IIC ref.1000. M at 20mg / ml, batch 1 1 10056) and negative control (R0 61 -8048 Roche, 0.01 M) were added. In P96, 200pL of the mixture was incubated at 37 °C and the absorbance was monitored spectrophotometrically C with a microreader (Ceres900; Bio-Tek Instruments Inc., Highland Park, Winooski, VT, USA) at 340 nm for NADPH concentration decrease.

[0103] Supplemental Method 5: In v / fro studiesThe control human pulmonary arterial smooth muscle cells (hPASMCs) were purchased from LONZA and obtained at passage 3. The control human pulmonary arterial endothelial cells (hPAECs) were purchased from Promocell and obtained at passage 2. The cell donors were healthy non-smokers, with no alcohol dependence and no hypertension. Each cell type was cultured in the corresponding medium kits LONZA (SmBM Basal Medium 500 ml ref: CC-3181 supplemented with SmGM-2 Single Quot Suppl&Growth Factors, ref: CC-4149) or Promocell (Endothelial Cell Basal Medium 500 ml ref: C-22210 supplemented with Supplement Mix / Endothelial Cell Growth Medium ref: C-39215 and Endothelial Cell Growth Medium ref: C-22010B) that contained basal medium, serum and growth factors with the exact composition advised by the manufacturer. The passage of PASMCs and PAECs used in cellular biology experiments was between P4 and P6.

[0104] Supplemental Method 6: Proliferation assay

[0105] Pulmonary vascular cell proliferation was measured by BrdU incorporation in the nucleus of cells undergoing DNA replication using the DELFIA cell proliferation kit (ref: AD0200, Perkin Elmer). Briefly, 5000 cells were seeded per well, and 24h after cell adhesion the hPASMCs or hPAECs cells were starved for 24h and then exposed to PDGF-BB (20ng / ml) or VEGF (20ng / ml), respectively, with or without the 1506 compound (1 OOpM) in the presence of 1 pmol / L BrdU for 24h. The fluorescence signal was read with an Envision 2103 plate reader (Perkin Elmer).

[0106] Supplemental Method 7: Migration assay or Wound healing

[0107] To evaluate migration, the wound-healing test was performed using the I Bl DI technology on hPASMCs and hPAECs. Cells were plated in a culture insert (Cat. No. 90209, IBIDI) at a density of 1 .2 x 104cells per well in a complete medium. After 24h, the culture insert was removed, and the plates were washed briefly with phosphate-buffered saline (PBS) to remove non-adherent cells. Then, the cells were incubated in a complete medium containing cytosine arabinose (1 pmol / L) to prevent cell proliferation for 24h and exposed to PDGF (20ng / mL) or VEGF (20ng / mL) with or without the 1506 compound (100pM) for 24h. The inventors photographed the wound at 0 and 24h and quantified the cell migration using the Image J software.

[0108] Supplemental Method 8: Animal model

[0109] Male Wistar rats were purchased from Janvier Labs (53940, Le Genest Saint Isle, France), rats were 4 weeks-old when transferred to Metabrain Research animal facilities. The study was carried out by the Council Directive 2010 / 63 / EU and the French guidelines (Directive 87 / 148, Ministere de (’Agriculture et de la Peche) and was approved in project request #30523. All experiments on animals were carried out by the European animal care guidelines (ETS 123). Animals were acclimatized to the environment and trained for manipulation for 1 week before the experiment. Animals were housed in a temperature-controlled (22 ± 2°C) area under constant humidity (50 ± 20%) and with a 12-hour light-dark cycle (light on at 7.00 am). The rats were divided into groups of 3 rats per cage. The dimensions of the cage were 48 x 37.5 x 21 cm. All rats were allowed to eat normal growth diet A04 from SAFE (Scientific Animal Food and Engineering - Route de Saint-Bris - 89290 AUGY - France) and drink ad libitum. The litter (sterile sawdust) was changed every other day. General signs were observed and only animals without any abnormal signs were included. Briefly, monocrotaline (MCT)-induced PH rats received a unique subcutaneous injection of MCT (60mg / kg) at six-week-old. Oral treatments consisted of either the vehicle (0.5% carboxy-methyl-cellulose (CMC)ZTween) or 1506 (25mg / kg) resuspended in 0.5% CMC / Tween and was administered daily in a curative protocol from day 14 to day 21 . Twenty-one days after the MCT injection, rats were anesthetized under isoflurane to perform left and right catheterizations using a 3.5 French umbilical vessel catheter connected to the pressure detector. Several hemodynamic parameters were measured, including right ventricular systolic pressure (RVSP), systolic systemic pressure, heart rate, and cardiac output (CO) by thermodilution principle to determine the pulmonary vascular resistance (PVR=RVSP / CO). Fulton index was defined by the ratio of right ventricle weight to the addition of left ventricle and septum weight, normalized with the total rat body weight. For lung processing, three technics were applied including formol conservation, OCT inflating, and microdissected pulmonary arteries (up to the 3rd order). The unilobed left lung was divided into three equal parts for biochemistry and molecular biology experiments (ARN, proteins, and metabolites), and the right lung was inflated with the mixture OCT:NaCI (1 :1 ). Some pulmonary arteries (PAs) were isolated from lungs. Left lungs, PAs, and superior right inflated lungs were frozen in liquid nitrogen and then stored at -80°C. The inferior right inflated lungs were stored in formol at room temperature. The fluctuation in the animal count for these in vivo experiments can be solely attributed to the invasive nature ofhemodynamic measurements. Hemodynamic data may be absent either due to the inability to obtain them during right heart catheterization or because of animal mortality during the procedures. It is important to note that there is no separate mortality rate, as all cases of missing animals occurred during right heart catheterization.

[0110] Supplemental Method 9: Measurement of Medial thickness

[0111] Paraffin-embedded 6pm lung slices were stained with hematein-eosin-Safran (HES). The vascular remodeling was evaluated on 80 arteries with a diameter between 50 and 100pm. The medial thickness was calculated according to the formula: (medial diameter) / (total diameter) x100 (%). The images were analyzed by conventional light microscopy using quantitative semi-automated software (NIS-BR; Nikon).

[0112] Supplemental Method 10: Assessment of muscularization and occlusion of distal pulmonary arteries

[0113] Muscularization and occlusion of rat pulmonary arteries was evaluated after double immunostaining of 6pm slices cut from frozen inflated lungs, with alpha-smooth muscle actin (a-SMA, F3777 Sigma) and Von Willebrand factor (VWF, A0082 DAKO) to identify smooth muscle cells and endothelial cells, respectively. Pulmonary arteries (diameters < 50pM) were classified into three groups, non-muscularized, muscularized, and occluded. Anti-Von Willebrand factor (VWF) and antialpha smooth muscle cell-FITC antibodies were incubated with the sections, in the presence of 2% rat serum overnight at 4°C. Sections were incubated for 1 h with the secondary antibody, in the presence of 2% rat serum. 4',6'-Diamidino-2-phenylindole (DAPI, 10 pg.ml-1 ) (Life Technologies) diluted 1 / 500 was added and the sections were incubated for one minute to visualize the nuclei. The slices were then mounted on glass slides, in Dako Fluorescent mounting medium (Dako). Once the arteries were detected with red fluorescence, the fluorescence channel was turned on green staining to evaluate the presence of muscularization or occlusion. From one slice, in total, 100 distal pulmonary arteries were counted for 6 rats per group.

[0114] Supplemental Method 1 1 : Quantification of cardiac fibrosis

[0115] The rat right ventricles (RV) were fixed in 4% of paraformaldehyde (PFA), embedded in paraffin, and then cut into 6pm sections. Slices were stained with Picrosirius Red (F3BA), and fibrosis was measured on 8 sections per rat for 6 animals per group. Pictures were photographed at 10X on an EVOS confocal (Carl Zeiss). The images were analyzed using the Imaged software.

[0116] Supplemental Method 12: Isometric tension measurement

[0117] Control and MCT Rat pulmonary arteries (PAs) were isolated and then mounted in a bath system (EMKA Technologies, Paris) coupled to IOX software (EMKA Technologies). Briefly, PAs were calibrated at 0.3 g for optimal length. For each experimental condition, 4-6 PAs were used from 4-6 control or MCT rats. PAs were conserved in Krebs solution containing NaCI (1 19 mmol / L), KCI (4.7 mmol / L), CaCI2 (2.5 mmol / L), MgSO4 (1 .17 mmol / L), KH2PO4 (1 .18 mmol / L), NaHCO3 (25 mmol / L) and glucose (1 1 mmol / L) at 37°C and gas mixture 5%C02 / 95%02. Firstly, 100 mmol / L of KCI (K100) was applied to check for the contraction of PAs in basal settings followed by two washesin Krebs solution. For the relaxation protocol, the vessels were preconstructed using the thromboxane A2 analog U46619 (I pmol / L), then followed by injection of increasing doses of 1506 (from 100 nmol. L-1to 500 pmol. L-1) or vehicle (DMSO) (from 100 nmol. L-1to 500 pmol. L-1). For the contraction protocol, basal vessels were pretreated with 1506 (100 pM) or DMSO followed by KCI (10-90 mmol / L) or U46619 (1 nmol / L to 100pmol / L) to trigger the contractile response.

[0118] Supplemental Method 13: Transcriptomic analysis

[0119] Total RNA was extracted from rat lung tissue using RNeasy Mini kit 74106 (Qiagen) with DNase digestion. RNA was qualified for purity on a NanoDrop (Thermo Scientific) spectrophotometer and integrity on a Bioanalyzer 2100 using RNA 6000 Nano kit (Agilent Technologies). RNA concentration was measured on a Xenius (Safas) fluorimeter using a Quantiluor® RNA kit (Promega). Directional RNA-Seq Libraries were constructed using the TruSeq Stranded mRNA library prep kit (Illumina), following the manufacturer’s instructions, 1 pg of total RNA was used. Final library quality was assessed on an Agilent Bioanalyzer 2100, using an Agilent High Sensitivity DNA Kit, and library concentration was measured on a Xenius (Safas) fluorimeter using PicoGreenTM kit (invitrogen), and by qPCR. Libraries were pooled in equimolar proportions and sequenced in 3 paired-end 2x100 bp runs on an Illumina NovaSeq instrument. Sequencing was done by Integragen (Evry, France). Demultiplexing has been done with bcl2fastq2 tools (V2.15.0) and trimming reads adapters with Cutadapt (v1 .3). All downstream analysis was performed using R and RStudio51. Reads were independently mapped to the rat genome mRatBN7.2 and counted with gtf ensemble release 108 at gene level using Rsubread52. Genes with a count mean lower than 10 were discarded for downstream analyses. TMM normalization was done using edgeR53and data were linearized with the voom function from Limma54. Then the inventors used a bioanalysis pipeline to find differentially expressed gene patterns across the 3 treatment groups and make functional enrichment analysis55. Briefly, the inventors applied a one-way analysis of variance for the TREATMENT factor for each gene and made pairwise Tukey's post hoc tests between groups. The inventors found two lists of genes corresponding to the two patterns of interest. Each selected gene has at least two significant p-values (< 0.05) across contrasts and fold-change >1 .01 for upregulation or fold-change <-1 .01 for downregulation. For functional enrichment analysis the inventors used MSigDB v7.556and applied Fisher exact test with FDR correction for multiple testing to find significant overlap. All raw and processed data have been submitted on GEO NCBI database with the accession number GSExxxx.

[0120] Supplemental Method 14: Statistical analyses

[0121] All results were analyzed with the GraphPad Prism software (GraphPad, version 9.3.0 for Windows). Unpaired t-tests followed by Mann-Whitney tests were performed to compare the PAH and control groups or the MCT and control rats. For more than 6 samples, normality was assessed with Shapiro-Wilk tests followed by Ordinary one-way ANOVA. All data were presented as mean ± SEM. Differences were considered significant if P<0.05.

[0122] RESULTS

[0123] Imbalance of the kynurenine pathway in PAH

[0124] According to preclinical research, the catabolism of kynurenine is a key step in driving the kynurenine pathway (KP) either to the main pathway leading to the synthesis of the toxic quinolinic acid (QA), or to the protective kynurenic acid (KA), or to the anthranilic acid (AA)4(Figure 1 A). Thus, the inventors evaluated the gene and protein expression of the three major enzymes responsible for this catabolism, Kynurenine-3-monooxygenase (KMO), Kynureninase, and Kynurenineaminotransferase (KAT1 ) in the lungs of patients with idiopathic PAH (iPAH), heritable PAH (hPAH) and in patients with Pulmonary vein-occlusive disease (PVOD) patients (Figure 7). mRNA expression of KMO, Kynureninase, and KAT1 were similar in the lungs of all PAH patient’s groups compared to those of control subjects due to a significant disparity in intra-group expression (Figure 1 B). There was a trend towards an increase in KMO protein expression for hPAH and PVOD patient’s groups and a trend towards an increase in Kynureninase expression in iPAH patient group. KAT1 protein expression was significantly increased in the PVOD patient group. Evaluation of KAT2 and KAT3 mRNA and protein expression showed decreased expression in PAH and PVOD patients (Figure 7). Next, the inventors proceeded to focus on KMO a flavin adenine dinucleotide enzyme located in the outer mitochondrial membrane, which is the pivotal enzyme in the kynurenine pathway, dysregulated in several central18and peripheral diseases19. Here the inventors observed a significant increase in the KMO enzymatic activity in the lung mitochondrial lysates of all three groups of PAH patients compared to controls, iPAH patients, hPAH patients, and PVOD patients (Figure 1 D). iPAH patients showed a significative increase but hPAH and PVO patients showed the highest levels of KMO activity compared to the controls. These data establish that KMO activity is deregulated in PAH and PVOD patients with potential consequences on metabolites profiles.

[0125] The Kynurenine pathway is dysregulated in the Monocrotaline rat model of Pulmonary Hypertension

[0126] In a translational perspective and to validate the monocrotaline (MCT) rat model of Pulmonary Hypertension (PH), the inventors first checked the hemodynamic parameters at end point (Figure 8) and then if the imbalance of the kynurenine pathway (KP) occurs in a kinetics study. The inventors sampled lung tissues after 3, 7, 14, and 21 days of exposure to MCT (Figure 2A). Thanks to the hemodynamic data, the inventors validated the MCT model with a significant increase in right ventricular systolic pressure (RVSP), cardiac output (CO), and a progressive rise in the Fulton index, which becomes significantly different from day 14 onwards, with no alteration in heart rate and systemic pressure. The inventors observed a significant decrease in mRNA expression of the main KP enzymes (KMO, Kynureninase, and KAT 1 ) in the lungs of MCT rats from day 3 to day 21 (Figure 2B). KAT2 and KAT3 mRNA and protein expression have also been evaluated (Figure 8) and the inventors didn’t observe significant differences. KMO, Kynureninase, and KAT1 protein expression showed a trend toward an increase 7 to 14 days after MCT administration (Figure 2C), and differences were significant 14 to 21 days after MCT administration, depending on the enzyme. Focusing on KMO enzymatic activity, the inventors demonstrated that the lungs of MCT-exposedrats exhibited significantly higher KMO activity than control rat lungs, as soon as day 7 after the MCT injection (Figure 2D). These data suggest deregulated KMO activity in the lung of MCT rats, with early substantial increase of KMO activity concomitant with the progression of vascular remodeling.

[0127] KMO inhibition have beneficial effects in vivo, reducing vascular and cardiac remodeling in the Pulmonary Hypertension rat model

[0128] The findings showing deregulated KMO activity in the lungs of both PAH patients and MCT rats, led us focusing on the potential therapeutic effects of the KMO-inhibitor 1506 in the MCT rat model. Initial dosing experiments allowed selecting the lower dose of mg. kg1per day (Figure 9).

[0129] The KMO inhibitor-1506 (25 mg. kg1per day) or vehicle were administered by daily oral route in a curative protocol from day 14 to 21 in MCT rats (Figure 3A). In comparison with MCT rats, the MCT-treated rats receiving the 1506 compound showed a significant decrease in right ventricular systolic pressure (RVSP) (P=0.0017 versus MCT) (Figure 3B) and reduced pulmonary ventricular resistance (PVR) (P=0.0124 versus MCT) (Figure 3C). Hemodynamic effects of 1506 were associated with decreased medial hypertrophy of large arteries as assessed by the pulmonary vessel wall thickness (Figure 3D) and a lower proportion of muscularized and occluded small arteries in MCT-treated rats (Figure 3E). With regards to the cardiac parameters, right ventricular hypertrophy was significantly reduced (Figure 3F) and was associated with a decrease in cardiac fibrosis (Figure 3G) in 1506-treated MCT rats. The cardiac output and the heart rate were unchanged in 1506-treated MCT rats (Figure 9). These results highlight that the KMO inhibitor-1506 has beneficial effects on PH development in vivo.

[0130] Pharmacological inhibition of the kynurenine pathway regulates rat pulmonary artery vasomotricity

[0131] The significant effects on hemodynamics in the 1506-treated MCT rats could be secondary to the decreased vascular remodeling. To assess if 1506 could have direct effects on pulmonary artery vasomotricity, the inventors investigated the effects of KMO inhibition, on relaxation and contraction of isolated-pulmonary arteries (PAs) from both control and MCT rats (Figure 4). For relaxation experiments, PAs were pre-contracted with the thromboxane A2 analog U46619 (1 pmol. L-1), and then exposed to increasing concentrations of dimethyl sulfoxide (DMSO, vehicle) or 1506 (100 nmol. L1to 500 pmol. L1). As shown in Figure 4A, the contraction of control PAs decreased progressively in response to increasing 1506 doses compared to vehicle. Notably, the same effects were observed in stiff PAs isolated from diseased MCT rats (Figure 4B). For the contractility experiments, the response to increasing concentration of potassium chloride (KCL, 10 to 90 mmol. L'1) was shifted significantly to the right in the presence of 1506, as correlated with a significant increase of EC50 values in the PAs from control (Figure 4C) and MCT rats (Figure 4D). These results were validated with increasing concentrations of the thromboxane A2 analog U46619 (100 nmol. L'1to 100 pmol. L-1) used as positive control. A significant shift to the right was observed in the presence of U46619 in control and MCT PAs rats (Figures 4E and 4F). Thus, KMO inhibition induced potent relaxation and delayed contraction in PAs from control rats and more importantly in PAs fromMCT rats, suggesting direct effects of 1506 on vasomotricity, even in remodeled and stiff pulmonary arteries from diseased rats.

[0132] Blocking KMO contributes to the decreased proliferation of pulmonary vascular cells in vitro and in vivo

[0133] According to preclinical research in cancer, KMO is involved in tumor cell proliferation and metastasis and might be a biomarker of poor survival prognosis20. Excessive proliferation and migration are major hallmarks of cancer and are critical in pulmonary artery vascular remodeling in PAH21. The inventors hypothesized that blocking KMO could affect vascular cell proliferation and migration processes in vascular cells. Thus, the inventors explored the effects of KMO blockade on human pulmonary artery smooth muscle cells (hPASMCs) in response to platelet-derived growth factor (PDGF, 20 ng. mL-1) after exposure to 1506 for 24h. In preliminary experiments the inventors used the cell viability assay based on the reduction of a tetrazolium compounds (MTT) and the Bromodeoxyuridine (BrdU) (Figure 10), to determine 1506 (100pM) as an optimal concentration, in dose-dependent manner. Pharmacological blockade of KMO significantly inhibited hPASMCs proliferation (P=0.0002 versus PDGF) (Figure 5A) and significantly reduced hPASMCs migration (P=0.0016 versus PDGF) (Figure 5B). Then, the inventors focused on human pulmonary artery endothelial cells (hPAECs) stimulated with vascular endothelial growth factor (VEGF, 20 ng. mL-1) and exposed to 1506 (100pM) for 24h. The inventors observed similar results in hPAECs as in PASMCs (Figure 5C et 5D). The inventors also evaluated in vivo the antiproliferative effect of KMO inhibition in lung tissue from control, MCT, and 1506-treated MCT rats. The inventors measured the gene and protein levels of the proliferation marker, proliferating cell nuclear antigen (PCNA). The inventors didn’t notice any difference in mRNA levels in the lungs of MCT rats treated with 1506, (Figure 5E), but the inventors observed a significant decrease in PCNA protein expression (PcO.0001 versus MCT) (Figure 5F). All these findings suggest that the blockade of KMO has antiproliferative effects in vitro and in vivo.

[0134] KMO inhibition could act on the proliferation of vascular cells through the IL-6 / STAT3 pathway

[0135] To investigate the molecular pathways involved in KMO inhibition in MCT rats, the inventors conducted an RNAseq transcriptomic analysis. The results of the principal component analysis (PCA) showed significant variation in transcripts between Control, MCT and MCT + 1506, with a total variance of 49% on the X axis, separating control rats from other rat groups. The Y axis separated MCT rats and MCT + 1506 rats with a total variance of 6%. Analysis of differentially expressed genes (DEGs) revealed 393 genes regulated by 1506. According to the heatmap, among theses 393 genes, 225 were up-regulated and 168 were down-regulated by the 1506 treatment. The enrichment analysis identified several pathways (Figure 6D and Figure 12) regulated by 1506. Two main pathways emerged from this enrichment analysis, the IL-6 / STAT3 pathway and the p-catenin pathway. The literature pointed to the involvement of the II-6 / STAT3 pathway in cancer and vascular remodeling including proliferation22, inflammation23, and resistance to apoptosis24. This pathway is initiated in response to IL-6 binding to its specific receptor. Quickly after its phosphorylation on thetyrosine 705 residue (PY705) STAT3 is translocated in the nucleus allowing DNA binding. The inventors also investigated the p-catenin pathway by western-blotting (Figure 11 ). According to the RNAseq analysis, IL-6 mRNA expression was increased in MCT rats compared to controls and significantly decreased in MCT rats treated by 1506 (dire le p), while STAT 3 mRNA expression was unchanged (Figure 6E). To validate the RNAseq data the inventors then assessed the gene and protein expression of IL-6 and STAT3 (Figure 6F). The inventors found a significant increase of IL- 6 gene expression in the lungs of MCT rats (P=0.0009 versus control) which was reversed by treatment of MCT rats with 1506 (P=0.0031 versus MCT). Similar significant effects are observed in the IL-6 protein expression, with P=0.0294 and P=0.0026 for MCT versus control and MCT + 1506 versus MCT respectively. Then, the inventors assessed the gene and protein levels of STAT3. The inventors didn’t observe any difference between each group. However, the protein level of phosphoTyrosine 705 STAT3 is significantly increased in the lungs of MCT (P=0.0123 versus control), this expression is reversed in the lung of 1506-treated MCT rats (P=0.0106 versus MCT). The inventors found that KMO inhibition in vivo significantly decreased STAT3 phosphorylation in the lungs of MCT rats. Together, these results suggest that KMO inhibition decreased proliferation through regulation of the IL-6 / STAT3 pathway in the lungs of MCT rats.Citation List1 . 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Claims

Claims

1. A kynurenine-3-monooxygenase inhibitor for use in the treatment or prevention of pulmonary hypertension.

2. A kynurenine-3-monooxygenase inhibitor for use according to claim 1 , wherein said pulmonary hypertension is pulmonary arterial hypertension.

3. A kynurenine-3-monooxygenase inhibitor for use according to claim 1 or claim 2, wherein said kynurenine-3-monooxygenase inhibitor is a compound of formula (I):wherein :R1 ’ is chosen from aryl and heteroaryl, each of which is substituted with one, two, or three groups chosen from halo, lower alkyl, alkoxy, and hydroxy;R2’ is chosen from hydrogen and optionally substituted lower alkyl;R3’ and R4’ are independently chosen from hydrogen, halo, hydroxy, lower alkyl, and lower alkoxy;R5’ and R6’ are independently chosen from hydrogen and lower alkyl; or R3’ and R5’, taken together with the atoms to which they are attached, form an optionally substituted cycloalkyl ring, n is one or two;R7’ is chosen from -C(O)OR8’, -C(O)R8’, optionally substituted amino, -(C=N-OR1 1 ’)R8’, - C(O)NR9’R10’, cyano, and optionally substituted heteroaryl;R8’ is chosen from hydrogen, optionally substituted lower alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, and glycosyl; and R9’ and R10’ are independently chosen from hydrogen, optionally substituted lower alkyl, optionally substituted lower alkoxy, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocycloalkyl, and optionally substituted heteroaryl; or R9’ and R1 O’, together with the nitrogen to which they are bound, form an optionally substituted heterocycloalkyl or optionally substituted heteroaryl ring;R11 ’ is chosen from hydrogen and optionally substituted lower alkyl; or an enantiomer, diastereoisomer, hydrate, solvate, tautomer, racemic mixture or pharmaceutically acceptable salt thereof.

4. A kynurenine-3-monooxygenase inhibitor for use according to any one of claims 1 to 3 wherein said kynurenine-3-monooxygenase inhibitor is a compound of formula (la):wherein:R1 and R2 independently from each another are hydrogen or (C1 -C6) alkyl, in particular a methyl; n is 1 or 2;R3 represents an -OH group; an -O(C1 -C6 alkyl) group, in particular -OEt or -OiPr; an -O (C3-C6 cycloalkyl) group, in particular an -O-cyclopentyl; an -O (C3 -C7 heterocyclic) group, in particular an -O-tetrahydropyran-4-yl; an -O-heteroaryl group, in particular an -O-pyridyl; an -O-aryl group, in particular an -O-phenyl; an -O(C1 -C6 alkyl) aryl group, in particular -O-benzyl; an -NR7R8 group, in whichR7 represents a hydrogen atom or a (C1 -C6) alkyl group and R8 represents a hydrogen atom; a heteroaryl group, in particular containing one or more nitrogen atoms; a (C1 -C6) alkyl group, in particular an ethyl group, optionally substituted with an -NR9 R10 group in which R9 and R10 represent, independently of one another, a hydrogen atom or a (C1 -C6) alkyl group, in particular a group methyl;a (C1 -C6) alkyl group, in particular an ethyl group, optionally substituted with a group -OR10 in which R1 1 represents a hydrogen atom or a (C1 -C6) alkyl group, in particular a methyl group; or R7 and R8 form with the nitrogen atom which provides them with a heterocycle, in particular a pyrrolidine, a piperidine, a morpholine, a piperazine, the heterocycle being optionally substituted with a (C1 -C6) alkyl group, in particular a methyl group;R4 represents a hydrogen atom or a (C1 -C6) alkyl group, in particular -Me or -Et;R5 and R6 represent, independently from each other, a hydrogen atom, a halogen atom, in particular Cl, or a group chosen from: a — CN group; an — OH group; an — O(C1 -C6) alkyl group, in particular — OMe, the alkyl group being optionally substituted by one or more halogen atoms, in particular F; a (C1 -C6) alkyl group, in particular methyl, optionally substituted with one or more halogen atoms, in particular F; an -O(C3-C6 cycloalkyl) group, in particular an -O-cyclopropyl; or an enantiomer, diastereoisomer, hydrate, solvate, tautomer, racemic mixture or pharmaceutically acceptable salt thereof.

5. A kynurenine-3-monooxygenase inhibitor for use according to claim 4 wherein R5 and R6 represent independently from each other a halogen atom, preferably R5 and R6 are chlorine atoms.

6. A kynurenine-3-monooxygenase inhibitor for use according to claim 4 or claim 5 wherein R4 represents a (C1 -C6) alkyl group, in particular -ethyl.

7. A kynurenine-3-monooxygenase inhibitor for use according to any one of claims 4 to 6 wherein n=1 .

8. A kynurenine-3-monooxygenase inhibitor for use according to any one of claims 4 to 7 wherein R3 represents an -OH group or an -O(C1 -C6 alkyl) group, in particular -OEt or -OiPr.

9. A kynurenine-3-monooxygenase inhibitor for use according to any one of claims 4 to 8 wherein R1 and R2 both represent a hydrogen atom.

10. A kynurenine-3-monooxygenase inhibitor for use according to any one of claims 4 to 9 wherein the compound of formula (I) is 4-(3,4-dichloro-phenyl)-4-ethoxyimino-butyric acid.

11. A kynurenine-3-monooxygenase inhibitor for use according to claim 3 wherein the compound of formula (I) is chosen from:4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyric acid;4-Benzyloxyimino-4-(3 ,4-dichloro-phenyl)-butyric acid;4-Cyclopropylmethoxyimino-4-(3 ,4-dichloro-phenyl)-butyric acid;4-(3,5-Dichloro-phenyl)-4-methoxyimino-butyric acid;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-2-methyl -butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-3-methyl-butyric acid;4-Methoxyimino-4-pyridin-2-yl-butyric acid;4-Methoxyimino-4-pyridin-3-yl-butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid methyl ester;4-(3,4-Dichloro-phenyl)-4-ethoxyimino-butyric acid methyl ester;4-Benzyloxyimino-4-(3,4-dichloro-phenyl)-butyric acid methyl ester;4-(3,4-Dichloro-phenyl)-4-hydroxyimino-butyric acid methyl ester;5-(3,4-Dichloro-phenyl)-5-methoxyimino-pentanoic acid methyl ester;5-(3,4-Dichloro-phenyl)-5-methoxyimino-pentanoic acid;1 -(3,4-Dichloro-phenyl)-5-methoxy-pentan- 1 -one O-methyl-oxime;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-phenyl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-3-yl-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(2-morpholin-4-yl-ethyl)- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-[l,3,4]thiadiazol-2-yl- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-4-yl-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-2-yl-butyr amide;4-(3,4-Dichloro-phenyl)-N-isoxazol-3-yl-4-methoxyimino-butyramide;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-N-( 1 -methyl- 1 H-pyrazol-4-yl)- butyramide;1 -(3 ,4-Dichloro-phenyl)-4-morpholin-4-yl-butane- 1 ,4-dione 1 -(O-methyl- oxime);4-(3,4-Dichloro-phenyl)-N-ethyl-4-methoxyimino-butyr amide;4-(3,4-Dichloro-phenyl)-N-isopropyl-4-methoxyimino-butyramide;N-Cyclopropyl-4-(3,4-dichloro-phenyl)-4-methoxyimino-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-methyl-butyr amide;4-[4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino]-piperidine-1 -carboxylic acid tert-butyl ester;4-[4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino]-piperidinium trifluoroacetate;{2-[4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino]-ethyl}-dimethyl- ammonium trifluoroacetate;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N,N-dimethyl-butyr amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-2-methyl-N-phenyl-butyramide;4-(3 ,4-Dichloro-phenyl)-4- methoxyimino-2-methyl-N-pyridin-3 -yl- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid isopropyl ester; 4-(3,4-Dichloro-phenyl)-4- methoxyimino-butyric acid cyclopentyl ester; 4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid cyclobutyl ester;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid pyridin-3-yl ester;4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyric acid tetrahydro-pyran-4-yl ester; l-(3,4-Dichloro- phenyl)-3-(3-methyl-[l,2,4]oxadiazol-5-yl)-propan-l-one O- methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(2H-tetrazol-5-yl)-propan- 1 -one O-methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-imidazol- 1 -yl-propan- 1 -one O-methyl-oxime;1 -(3 ,4-Dichloro-phenyl)-4-imidazol- 1 -yl-butan- 1 -one O-methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(5-methyl-isoxazol-3-yl)-propan- 1 -one O-methyl- oxime;(1S, 2S)-trans-2-[(3,4-Dichloro-phenyl)-methoxyimino-methyl]- cyclopropanecarboxylic acid methyl ester;(1 S, 2S)-trans-2-[(3,4-Dichloro-phenyl)-methoxyimino-methyl]- cyclopropanecarboxylic acid; and4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyric acid 3 ,4,5 ,6-tetrahydroxy- tetrahydro-pyran-2- ylmethyl ester,4-[2-tert-Butoxycarbonylamino-ethoxyimino]-4-(3,4-dichloro-phenyl)-butyric acid;4-[2-Amino-ethoxyimino]-4-(3,4-dichloro-phenyl)-butyric acid;4-(3,4-Dichloro-phenyl)-4-(2-dimethylamino-ethoxyimino)-butyric acid;4-(4,5-Dichloro-2-hydroxy-phenyl)-4-hydroxyimino-butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyronitrile;4-(3-Chloro-phenyl)-4-methoxyimino-butyric acid;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrazin-2-yl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridin-3-ylmethyl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(4-methyl-pyridin-3-yl)- butyramide;1 -(3,4-Dichloro-phenyl)-3-(2-methyl-2H-tetrazol-5-yl)-propan-1 -one O- methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(2-methyl-2H-tetrazol-5-yl)-propan- 1 -one O- methyl-oxime;1 -(3,4-Dichloro-phenyl)-3-(5-methyl-[1 ,2,4]oxadiazol-3-yl)-propan-1 -one O- methyl-oxime;1 -(3 ,4-Dichloro-phenyl)-3-[ 1 ,2,4]triazol- 1 -yl-propan- 1 -one O-methyl-oxime;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrimidin-5-yl-butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(5-methyl-pyridin-3-yl)- butyramide;4-(3,4-Dichloro-phenyl)-N-(2,6-dimethyl-pyridin-3-yl)-4-methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(2-methyl-pyrimidin-5-yl)- butyramide;1 -(3,4-Dichloro-phenyl)-3-(3-hydroxy-isoxazol-5-yl)-propan-l -one O-methyl- oxime;4-(3,4-Dichloro-phenyl)-N-(5-fluoro-pyridin-3-yl)-4-methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyridazin-3-yl-butyr amide;4-(3,4-Dichloro-phenyl)-N-(3,5-dimethyl-pyrazin-2-yl)-4-methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(6-trifluoromethyl-pyridin-3-yl)- butyramide;1 -(3 ,4-Dichloro-phenyl)-4-piperidin- 1 -yl-butane- 1 ,4-dione 1 -(O-methyl- oxime);1 -(3,4-Dichloro-phenyl)-4-(4-methyl-piperidin- 1 -yl)-butane- 1 ,4-dione 1 -(O- methyl-oxime);4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(6-methyl-pyridazin-3-yl)- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(6-methyl-pyridin-3-yl)- butyramide;1 -(3 ,4-Dichloro-phenyl)-4-(3-hydroxy-pyrrolidin- 1 -yl)-butane- 1 ,4-dione 1 -(O- methyl-oxime);4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrimidin-2-yl-butyramide;Pyrimidine-5-carboxylic acid {3-(3,4-dichloro-phenyl)-3-methoxyimino- propyl} -amide;4-(3,4-Dichloro-phenyl)-N-(2-hydroxy-ethyl)-4-methoxyimino-butyramide;5-(3,4-Dichloro-phenyl)-5-methoxyimino-pentanoic acid amide;1 -(3 ,4-Dichloro-phenyl)-4-(4-hydroxy-piperidin- 1 -yl)-butane- 1 ,4-dione 1 -(O- methyl-oxime);3- {4-(3 ,4-Dichloro-phenyl)-4-methoxyimino-butyrylamino } -pyrrolidine- 1 - carboxylic acid tert-butyl ester;4-(3,4-Dichloro-phenyl)-N-(2-hydroxy-propyl)-4-methoxyimino-butyramide;4-(3,4-Dichloro-phenyl)-N-(2,4-dimethyl-pyridin-3-yl)-4-methoxyimino- butyramide;5 -(3 ,4-Dichloro-phenyl)-5 -methoxyimino-pentanenitrile;4-(3,4-Dichloro-phenyl)-N-(2,3-dihydroxy-propyl)-4 — methoxyimino- butyramide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-pyrrolidin-3-yl-butyramide;4-(3,4-Dichloro-phenyl)-N-methoxy-4-methoxyimino-N-methyl-butyramide;1 -(3 ,4-Dichloro-phenyl)-pentane-1 ,4-dione l-(O-methyl-oxime);4-(3,4-Dichloro-phenyl)-N-(6-fluoro-pyridin-3-yl)-4-methoxyimino- butyramide;N- {3-(3 ,4-Dichloro-phenyl)-3-methoxyimino-propyl} -methanesulfonamide;1 -(3,4- Dichloro-phenyl)-pentane-1 ,4-dione bis-(O-methyl-oxime);4-(3,4-Dichloro-phenyl)-4-methoxyimino-N-(2,4,6-trimethyl-pyridin-3-yl)- butyramide;Pyridine-3-sulfonic acid {3-(3,4-dichloro-phenyl)-3-methoxyimino-propyl}-amide;4-(3,4-Dichloro-phenyl)-4-methoxyimino-butyric acid (S)-2-((R)-3,4-dihydroxy-5-oxo-2,5-dihydro- furan-2-yl)-2-hydroxy-ethyl ester; and1 -(3,4-Dichloro-phenyl)-3-(1 H-imidazo[4,5-c]pyridin-2-yl)-propan-1 -one O-methyl-oxime ester; or an enantiomer, diastereoisomer, hydrate, solvate, tautomer, racemic mixture or pharmaceutically acceptable salt thereof.

12. A pharmaceutical composition comprising a kynurenine-3-monooxygenase inhibitor as defined in any one of claims 1 to 11 and a pharmaceutically acceptable excipient, for use in the treatment or prevention of pulmonary hypertension.

13. A pharmaceutical composition for use according to claim 12 wherein the pulmonary hypertension is pulmonary arterial hypertension.

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