Neurotransmitter serotonin or 5-Hydroxytryptamine (5-HT) is abundantly distributed in the central nervous system, including hippocampus and frontal cortex. 5-HT receptors are a family of G-protein coupled receptors, characterized with 7-transmembrane helices and presently have fourteen known receptor subtypes, some of which exist as multiple splice variants [D. L. Murphy, A. M. Andrews, C. H. Wichems, Q. Li, M. Tohda and B. Greenberg, J. Clin. Psychiatry, 1998, 59 (suppl. 15), 4]. 5-HT influences a number of physiological functions and is implicated in a large number of central nervous system disorders, vascular diseases, neurodegenerative diseases and others (Childers, W. E., et. al., Ann. Rep. Med. Chem. 2005, 40, 17).
5-HT2B receptors are widely distributed in mammalian peripheral tissues including lung, heart, pancreas, spleen, prostate, liver, vascular and skeletal muscle, adipose tissue, intestine, ovary, uterus, testis, and in the central nervous system (CNS) including brain and cerebral cortex. 5-HT2B receptors are expressed in pulmonary endothelial and smooth muscle cells in humans. 5-HT2B receptors stimulate calcium release in human endothelial cells from the pulmonary artery (Esteve, J. M., Launay, J. M., Kellerman, O., Maroteaux, L., Functions of serotonin in hypoxic pulmonary vascular remodeling. Cell Biochem. Biophys, 2007, 47, 33-44). The receptor was characterized in the rat gastric (fundus) smooth muscle cells initially as the receptor responsible mediating serotonin-induced contraction in this tissue.
Serotonin (5-HT) affects the pulmonary vasculature associated with PAH by vasoconstriction, platelet aggregation, and pulmonary arterial smooth muscle cell proliferation. Serotonin receptors subtypes, 5-HT1B, 5-HT2A and 5-HT1B have shown evidence for playing a role in the pathology of PAH. 5-HT2B receptors are expressed in pulmonary endothelial and smooth muscle cells and stimulate calcium release in human endothelial cells from the pulmonary artery. It has been demonstrated that 5-HT2B receptors are involved in the development of PH by mediating chronic hypoxic responses in wild-type mice compared with the complete lack of PH and vascular remodeling in the 5-HT2B receptor (−/−) knockout mice in the chronic hypoxic mouse model of PH (Launey et. al., Function of the serotonin 5-Hydroxytryptamine 2B receptor in pulmonary hypertension. Nat. Med 2002, 8, 1129-1135).
5-HT2B receptor modulators (antagonists, partial agonists, inverse agonists and agonists) have the potential to be selective for diseased pulmonary trachea, thymus, thyroid, salivary gland vasculature (i.e., vessels affected by hypoxic conditions) compared to normal pulmonary and systemic vessels. Due to this selectivity, 5-HT2B modulators particularly 5-HT2B antagonists offer a possible therapeutic advantage over the available agents for the treatment of pulmonary arterial hypertension, pulmonary hypertension associated with chronic obstructive pulmonary disease (COPD), right ventricular hypertrophy and related disease of the lung and vascular system.
Pulmonary hypertension (PH) is a progressive, debilitating and often fatal disease that results from an increase in pulmonary blood pressure associated with abnormal vascular proliferation. PH is estimated to affect 100,000 people worldwide. Pulmonary arterial hypertension (PAH) is an increase in the pulmonary vascular resistance due to vasoconstriction and pulmonary vascular remodeling that result in elevated pulmonary arterial pressure. The cause of idiopathic PAH is unknown. PAH can be developed as a consequence of existing diseases such as chronic obstructive pulmonary disease (COPD) hypoxia, portal hypertension, or HIV infection. PAH is progressive and fatal. The median survival time without treatment in adult PAH patients is 2.8 years after diagnosis, and is only 10 months in children. Although survival rates have improved with new drugs, the prognosis is still poor and development of safer and more effective drugs is needed. Current treatments include systemically administered intravenous and subcutaneous prostacyclin analogs and orally active endothelin receptor antagonists, which mainly cause pulmonary arterial dilation to relieve symptoms. There is only one approved orally active agent for PH available for patients, a non-selective endothelin A and B receptor antagonist which recquires liver toxicity monitoring.
The role of 5-HT2B in pulmonary hypertension was recognized by the observation that there may be a relationship between the PAH patients taking weight reducing agents such as dexfenfluramine, fenfluramine and aminorex which are 5-HT2B agonists; that the use of these agents may be contributing towards the elevation of pulmonary arterial hypertension (Kramer. M. S., and Lane, D. A Aminorex, dexfenfluramine, and primary pulmonary hypertension, J. Clin. Epidemiol. 1998, 51, 361-364). Both aminorex and fenfluramine elevates 5-HT levels by increasing the release of 5-HT from platelets and inhibiting the metabolism and the reuptake of 5-HT (Maclean, M. R., Pulmonary hypertension, anorexigens, and 5-HT: pharmacological synergism in action? Trends Pharmacology. Sci. 1999, 20, 490-495; Belohlavkova, S., Simok, J., Kokesova, A., Hnilickova, O., Hampl, V., Fenfluramine-induced pulmonary vasoconstriction: role of serotonin receptors and potassium channels. J. Appl. Physiol. 2001, 91, 755-761). Dexfenfluramine has binding affinity for 5-HT2 receptors and its major metabolite, N-deethylated dexfenfluramine is a potent agonist of the 5-HT2B receptor and thus is involved in the development of PAH.
A novel and potent 5-HT2B receptor antagonist, PRX-08066, has been shown to significantly reduce the elevation in pulmonary arterial pressure and right ventricular hypertrophy and also maintains cardiac function. Pulmonary vascular remodeling was also decreased in rats. The 5-HT2B antagonist PRX-08066 was shown to prevent the severity of PAH in the rat model (Porvasnik, S. L., Germain, S., Embury, J., Ganon, K. S., Jacques, V., Murray, J., Byrne, B. J., Shacham, S., Al-Mousily, F., PRX-08066, a novel 5-hydroxytryptamine receptor 2B antagonist, reduces monocrotaline-induced pulmonary arterial hypertension and right ventricular hypertrophy in rats., J. Pharmaco. Exp. Ther. 2010, 334, 364-372).
The 5-HT2B receptor has also been shown to play a key role in the regulation of neuroendocrine tumor cell proliferation and the modulation of the fibroblast component of the neoplastic microenvironment (Svejda, B., et. al. Cancer 2010, 116, 2902-12). Small intestinal neuroendocrine tumors (SI-NETs) are cancers originating from serotonin-producing enterochromaffm cells in the diffuse neuroendocrine system. The carcinoid syndrome reflects excessive serotonin release. Carcinoid syndrome symptomatology includes bronchoconstriction, flushing, diarrhea, and fibrosis in the local peritumoral tissue and at distant in the heart or lungs. 5-HT shows both mitogenic and fibrogenic effects in fibroblasts, smooth muscle cells, and endothelial cells. These effects are mediated via the G-protein coupled 5-HT receptors, which activate mitogenic pathways through the extracellular signal-regulated kinase (ERK) pathway and JNK activation. Other studies have reported that 5-HT modulates valvular subendocardial cell proliferation. The human heart valves express messenger ribonucleic acid (mRNA) for 5-HT agonists (fenfluramine, dexfenfluramine, pergolide, cabergoline, ergotamine) are associated with pulmonary fibrosis and valvular heart disease (Roth, B., Drugs and valvular heart disease. N. Engl. J. Med. 2007, 356, 6-9; Gustafsson, B, Hauso, O., Drozdov, I., Kidd, M., Modlin, I., Cacinoid heart disease. Int. J. Cardio. 2008, 129, 318-324). Significant evidence exists for involvement of 5-HT2B receptors in cellular pathways that culminate in fibrosis. It has been recognized that SI-NETs are often present with fibrosis in the peritumoral tissue, the adjacent mesentery and peritoneum as well as in the right side of the heart or lungs (Modlin, I., Moss, S., Chung, D., Jensen, R., Snyderwine, E., Priorities for improving the management of gastroentero-pancreatic neuroendocrine tumors. J. Natl. Cancer. Inst. 2008, 100, 1282).
The proliferative activity of 5-HT has been shown to be dependent on the expression of 5-HT2 receptor subtypes (Kidd, M., et. al. Inhibition of proliferation of small intestinal and bronchopulmonary neuroendocrine cell lines by using peptide analogs targeting receptors. Cancer. 2008, 112, 1404-1414). Similar proliferation effects have been observed in the 5-HT secreting prostate cancer cell line PC3 (Dizeyi, N., et. al. Expression of serotonin receptors 2B and 4 in human prostate cancer tissue and effects of their antagonists on prostate cancer cell lines. Eur. Urol. 2005, 47, 895-900), 5-HT2A receptor expressing breast cancer cell line MCF-7 (Sonier, B., et. al. The 5-HT2A serotoninergic receptor is expressed in the MCF-7 human breast cancer cell line and reveals a mitogenic effect of serotonin. Biochem. Biophys. Res. Commun. 2006, 343, 1053-1059), and in human choricarcinoma cell line JEG-3 and BeWO (Sonier, B., et. al. Expression of the 5-HT2A serotoninergic receptor in human placenta and choriocarcinoma cells: mitogenic implications of serotonin. Placenta. 2005, 26, 484-490).
During the investigation of signal transduction pathways involved in the antiproliferative effect of 5-HT2B receptor antagonist, by investigating phosphorylation of ERK, direct role of 5-HT2 receptor subtypes has been demonstrated in vascular and tracheal smooth muscle cell proliferation. The mechanism involves coupling of 5-HT2A receptors and the ERK pathway, while 5-HT2B receptors activate ERK through the RAS pathway (Nebigil, C. G., et. al. 5-hydroxytryptamine 2B receptor regulates cell-cycle progression: cross-talk with tryrosine kinase pathways. Proc. Natl. Acad. Sci. USA. 2000, 97, 2591-2596); Hershenson, M. B., et. al. Histamine antagonizes serotonin and growth factor-induced mitogen-activated protein kinase activation in bovine tracheal smooth muscle cells. J. Biol. Chem. 1995, 270, 19908-19913); Banes, A., et. al., Mechanisms of 5-hydroxytryptamine 2A receptor activation of the mitogen-activated protein kinase pathway in vascular smooth muscle. J. Pharmacol. Exp. Ther. 1999, 291, 1179-1187).
Fibrosis is an important key feature of small intestinal neuroendocrine tumor (SI-NETs) both in local peritumoral tissue and systemic (cardiac) sites. 5-HT is a well known inducer of fibrosis. The growth factors regulating fibrosis and proliferation in the tumor microenvironment and mechanisms are unclear. It has been shown that blocking 5-HT2B receptors on tumor cells inhibit SI-NET 5-HT release and in turn fibroblast activation in the tumor microenvironment. In the 5-HT2B expressing SI-NET cell line, KRJ-1, the 5-HT2B antagonist PRX-08066 has been shown to inhibit proliferation and 5-HT secretion and decreased ERK1/2 phosphorylation and profibrotic growth factor synthesis and secretion (transforming growth factor beta-1 {TGFβ1}), connective tissue growth factor (CTGF) and fibroblast growth factor (FGF2). The 5-HT2B antagonist PRx-08066 was also found to significantly decrease 5-HT release, TGFβ1, CTGF, and FGF2.
Blocking the 5-HT2B receptor with a 5-HT2B antagonist is an effective antiproliferative and antifibrotic strategy for SI-NETs because it inhibits tumor micronvironment fibroblasts as well as NET cells. Use of 5-HT2B receptor antagonists offers a possible effective therapeutic intervention to prevent tumor progression, fibrosis, and metastasis in the neuroendocrine neoplasia. It may also have therapeutic use in other fibrotic processes associated with neuroendocrine cell dysregulation such as Crohn's disease (Kidd, M., et. al. IL1beta- and LPS-induced serotonin secretion is increased in EC cells derived from Crohn's disease. Neurogastroenterol Motil. 2009; 21, 439-450).
The compounds of this invention represented by formula I are valuable in the prevention and treatment of various disease conditions regulated directly or indirectly by the inhibition (by serotonin receptors antagonist of compounds of formula I) or activation (by serotonin receptors partial or full agonist of compounds of formula I) of the neurotransmitter serotonin (5-Hydroxytryptamine, 5-HT). These diseases include cancer such as brain cancer, breast cancer, blood cancer, colorectal cancer, lung cancer, liver cancer, ovarian cancer, pancreas cancer, prostate cancer, stomach cancer, testicular cancer, uterus cancer, intestinal cancer, skin cancer, and other forms of cancer; tumor progression, metastasis and fibrosis in the neuroendocrine neoplasia, fibrotic processes associated with neuroendocrine cell dysregulation for example Crohn's disease, pulmonary arterial hypertension, pulmonary hypertension associated with chronic obstructive pulmonary disease (COPD), right ventricular hypertrophy, pulmonary vascular remodeling, asthma, cystic fibrosis, hypertension, ischemic stroke, angina pectoris, congestive heart failure, arrhythmia, arterial fibrillation, neurodenerative diseases, Alzheimer's disease, dementia, cognition impairment, memory decline, schizophrenia, dementia associated with Parkinson's and Huntington's disease, Pick's disease and Jacob disease.
These compounds may also have applications in the treatment of gastrointestinal disorders including irritable bowel syndrome, gastroesophageal reflux disease, Crohn's disease, gastric emptying disorders, gastritis, emesis, nausea, vomiting, prokinesia, non-ulcer dyspepcia, urinary incontinence, feeding disorders, bulimia, anorexia, obesity, constipation, constipation, and respiratory depression, stress disorders, post-traumatic stress disorder, acute stress disorder, delirium, anxiety, depression, biopolar depression, epilepsy, Down's syndrome, pain, migraine, panic disorders, social phobia, animal phobias, and obsessive compulsive disorders.
The compounds of formula I may also be valuable in substance-related disorders including dependence and abuse, intoxication, withdrawal, and delirium arising from the use of alcohol, amphetamines, cannabis, cocaine, hallucinogens, inhalants, nicotine, opioids, hypnotics, and anxiolytics.
These compounds of formula I may also be useful for the prevention and treatment of demyelinating diseases including multiple sclerosis, ALS, peripheral neuropathy, postherpetic neurolegia, cerebral vascular disorders, acute or chronic cerebrovascular damage, cerebral infarction, subarachanoid hemorrhage, and cerebral edema.
In addition, compounds of the invention may be used for the treatment of bronchoconstriction, vasodilation, smooth muscle contraction, brain disorders, vascular disorders, blood flow disorders as a result of vasodilation and vasospastic diseases such as angina, vascular headache, Reynaud's disease, pulmonary hypertension, and systemic hypertension; neuropathological diseases such as Alzheimer's diseases, Parkinson's disease, Huntington's disease; cardiovascular system regulation, prophylaxis and treatment of cerebral infarct, stroke, cerebral ischemia; as well as the treatment of diseases of the intestinal tract.
The compounds of the present invention may also be useful in the treatment of stress-related somatic disorders, bladder function disorders such as cystitis, stress-related urinary incontinence, urinary incontinence post prostate cancer-surgery, reflex sympathetic dystrophy including shoulder/hand syndrome, bladder function disorders such as cystitis, and any nociception, pain or migraine associated with the above mentioned conditions.