Targeting the Inhibition of Tryptophan 2,3-Dioxygenase (TDO-2) for Cancer Treatment

Patent Application Title:	Novel 3-Indol Substituted Derivatives, Pharmaceutical Compositions, and Methods for Use
Patent Application Number:	US 2016/0272628 A1	Publication date:	September 22, 2016
Priority Application:	US 62/203,032	Priority date:	August 10, 2015.
Inventors:	Ninkovic, S.; Crosignani, S.; McAlpine, I. J.; Collins, M. R.; Scales, S. A.; Maderna, A.; Wythes, M.
Applicants:	Pfizer Inc., New York, NY, USA
	iTeos Therapeutics, Charleroi (BE)
Disease Area:	Cancer, neurodegenerative disorders, and chronic viral infections	Biological Target:	Tryptophan 2,3-dioxygenase (TDO-2)

Summary:	The invention in this patent application relates to novel 3-(indol-3-yl)pyridine derivatives represented generally by Formula (I) that possess activities as TDO2 inhibitors. These compounds may be useful for the treatment and/or prevention of cancer, neurodegenerative disorders such as Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease, chronic viral infections such as HCV and HIV, depression, and obesity.
	Some sites in the human body (e.g., the brain, the eye, the testis, and the placenta) can tolerate the presence of foreign antigens without causing an inflammatory immune response. This behavior is known as immune privilege. Thus, tissue grafts, which are normally attacked by the immune system, can survive in these immune privileged sites for extended periods of time without being rejected. It is believed that immune privilege occurs in these sites because their tissues perform unique functions and cannot be regenerated if they were damaged by a responsive immune reaction.
	L-Tryptophan (Trp) is an essential amino acid that performs a variety of important functions within the cell. Besides its typical role in protein synthesis, it is also utilized in the biosynthesis of nicotinamide adenine dinucleotide (NAD+), the neurotransmitter serotonin, and the hormone melatonin in the pineal gland. Earlier studies have indicated that Trp catabolism is essential to maintaining the immune privilege of the placenta, but recent growing evidence implicates Trp catabolism in survival of cancer cells and immune evasion.
	Tryptophan is catabolized in the local microenvironment of tumors, immune-privileged sites, or sites of inflammation. The degradation and depletion of Trp and accumulation of its metabolites in these sites create an immunosuppressive environment that shuts down antitumor immune responses in tumors and in tumor-draining lymph nodes by inducing T-cell anergy and apoptosis.
	The major Trp catabolism pathway in mammals is known as the kynurenine pathway. The first and rate limiting step in this pathway, which converts Trp into N-formylkynurenine is catalyzed by specific enzymes that may vary in their expression levels or with the cell type. These enzymes include indoleamine-2,3-dioxygenases (IDO1 and IDO2) and tryptophan 2,3-dioxygenase (TDO2). TDO2 is a member of the oxidoreductases family, and it is normally expressed in the liver to regulate systemic Trp levels. Recent studies have revealed that TDO2 is constitutively expressed in a wide variety of cancer cells, such as bladder carcinoma, hepatocarcinoma, melanoma, mesothelioma, neuroblastoma, sarcoma, breast carcinoma, leukemia, renal cell carcinoma, colorectal carcinoma, head and neck carcinoma, lung carcinoma, brain tumor, glioblastoma, astrocytoma, myeloma, and pancreatic carcinoma. The TDO2-catalyzed catabolism of Trp in tumor cells is responsible for immune response suppression and consequently prevention of tumor rejection. This in turn promotes the survival, growth, invasion, and metastasis of malignant cells. Studies using the P815 mastocytoma tumor model provided the first clear evidence of the role of TDO2 in regulating tumor growth. These studies have shown that inhibition of TDO2 decreases tumor growth in P815 mTDO2 implanted tumors.
	The following observations provide additional evidence on the role of TDO2 and Trp catabolism in immune response suppression in different tumors and cancers:
	TDO2 is highly expressed in hepatocellular carcinoma (HCC). The inhibition of TDO2 could lead to increased Trp concentration and decreased downstream production of Trp metabolites and hence may be useful for the treatment of liver diseases that can progress to the stage of liver carcinoma. Evidence shows that increased Trp concentration can benefit conditions such as cirrhotic livers. Evidence also shows that increased levels of serum Trp metabolites causes negative effects, for example, increased levels of the Trp metabolite, quinolinic acid correlates with hepatic dysfunction in patients with liver cirrhosis, while indole-3-lactic acid is associated with alcohol-induced liver disease in mice. TDO2 is also expressed in neurons, microglia, and astrocytes. Overexpression of TDO2 in the glioma cells produces the Trp metabolite kynurenine (Kyn) that activates the aryl hydrocarbon receptor (AHR). This TDO-AHR pathway is active in brain tumors, and it is implicated in malignant progression and poor patient survival. In addition, tryptophan catabolism occurs in microglia cells and causes the accumulation of quinolinic acid, which is believed to be associated with a malignant phenotype. TDO2 mRNA is found in tumors such as breast carcinoma, bladder, renal cell, pancreatic, colorectal, head and neck carcinoma, lung carcinoma, and melanoma. Enhanced Trp catabolism is observed in different forms of gynecological cancers such as ovarian carcinoma, cervical cancer, and endometrial cancer. Inflammatory mediators, particularly IFN-gamma, induce Trp catabolism as an endogenous mechanism to restrict excessive immune responses and prevent immunopathology. However, there is a mounting evidence that suppression of antitumor immune responses in precancerous lesions and established cancers by Trp catabolism promotes tumor growth.
	These studies and observation provide a compelling rational that shows the great potential and increased importance of the inhibition of Trp catabolism as an attractive biological target for therapeutic intervention against cancer. Therefore, a considerable research has been directed toward achieving this goal through identifying selective and efficient inhibitors of TDO2 that may be used to block the Trp catabolism and possibly provide effective treatment for cancer.
	In addition to their potential as novel cancer treatment, TDO2 inhibitors may also provide promising and needed treatments for neurological and brain disorders. TDO2 is expressed in neurons and brain vasculature and additionally in astroglial cells in the case of schizophrenia. The inhibition of the kynurenine pathway has become a viable therapeutic target to develop medications to treat cognitive diseases such as bipolar disorder and Tourette syndrome, neurodegenerative disorders such as Alzheimer’s disease, and motor neuron diseases including Amyotrophic lateral sclerosis, Multiple sclerosis, and Huntington’s and Parkinson’s diseases.
	HIV-associated neurocognitive disorders (HAND) are caused by cognitive changes related to Trp catabolism in patients infected with human immunodeficiency virus type-1 (HIV-1). In addition, T cell hyporesponsiveness has been recently associated with the Trp catabolic pathway in HIV-infected patients, and this may also be associated with other chronic viral infectious diseases such as Hepatitis C.
	While there are several known TDO2 inhibitors, they either suffer from limited affinity for the target or possess unfavorable pharmacokinetic properties that make them unsuitable to be developed as drugs for human use.
	Therefore, there exists a need for the discovery and development of new TDO2 inhibitors with improved efficacy such as the compounds described in this patent application for the treatment and/or prevention of cancer and possibly for the treatment of several neurodegenerative disorders and chronic viral infections such as HIV and HCV.
Important Compound Classes:
Key Structures:	The inventors described the structures and methods of synthesis of 153 compounds of Formula (I) including the following representative examples:
Biological Assay:	1.Assay for TDO2 Enzymatic Activity Determination 2.Cellular Assay for TDO2 Activity Determination 3.Pharmacodynamic Assay for TDO2 in Vivo Activity Determination: Increase of Blood Tryptophan Levels in Mice
Biological Data:	The biological data obtained from testing the above representative compounds in human brain glioblastoma cells using the Cellular Assay for TDO2 Activity Determination are summarized in the following table:
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The author declares no competing financial interest.