PHYSIOLOGICAL LIGANDS FOR GPR139

TECHNICAL FIELD

This application relates to physiological ligands for the orphan receptor GPR139, methods of using those ligands to activate the receptor in a physiological environment, and methods of modulating neurological functions or conditions by changing the activation state of GPR139.

BACKGROUND

G-protein coupled receptors (GPCRs) are compelling targets for drug discovery. Currently, about 30% of drugs on the market are targeting GPCRs. Sequencing of the human genome revealed thousands of new genes, including hundreds of new G-protein coupled receptors, offering many new opportunities for drug discovery. However, these new GPCRs were identified based on their sequence and structural similarities to known GPCRs and their ligands, and thus their biological significance remains unknown. Without the ligands for these receptors, it is difficult to understand their physiological function. Furthermore, finding the ligands for the receptors will certainly help to establish assays for screening for agonists, antagonists, and modulators of the receptors.

GPR139 is an orphan G-protein coupled receptor that is predominantly expressed in the brain (Vanti et al., Biochem. Biophys. Res. Commun. 305(1):67-71 (2003); Gloriam et al., Biochim Biophys Acta. 1722(3):235-46 (2005); Matsuo et al., Biochem. Biophys. Res. Commun. 331(1):363-9 (2005)). It is coupled with Gq signaling and appears to be constitutively active when recombinantly expressed in mammalian cells (Matsuo et al., 2005). GPR139 is highly conserved among different species. For example, human, mouse and rat GPR139 protein sequences share greater than 94% identity at amino acid level (FIG. 1). In addition, human GPR139 also shares 94% and 72% identity to a putative protein encoded by chicken and zebrafish genomes, respectively. GPR139's predominant expression in the brain and high degree of sequence homology across different species, suggest it has an important role in vertebrate physiology; however, no physiological ligand for GPR139 has been identified to date.

SUMMARY

Provided herein are methods of activating GPR139 by contacting the receptor with L-tryptophan (L-Trp), L-phenylalanine (L-Phe), or derivatives thereof

Also described are methods for reducing the activity of GPR139 in a subject by identifying a subject in need of reduced GPR139 activation, and administering an amount of one or more compounds sufficient to reduce the activity of GPR139 to the subject, which in turn will decrease the level of GPR139 activation relative to the native activation state.

Methods for modulating a neurological function or condition in a subject by administering an amount of one or more compounds sufficient to modulate the activity GPR139 to the subject are also described herein.

Also provided are methods for modulating a disease condition of the pancreas in a subject by administering an amount of one or more compounds sufficient to modulate the activity GPR139 to the subject.

In addition, provided herein are methods of administering any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds to a subject.

Described herein is chimeric G protein, designated GO2Q, and methods for using it to detect activation of GPCRs. Also described are methods for detecting GPR139 activation by co-expressing GO2Q chimeric G-protein and GPR139 in a cell, by exposing the cell or a membrane obtained from the cell to a compound, and determining whether or not GPR139 is activated by the compound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Provides an alignment of the human, mouse, and rat GPR139 amino acid sequences. The sequences shown are identical to the sequences reported in Genbank for accession numbers: AK291384 (human) (SEQ ID NO: 3), NM_—001024138 (mouse) (SEQ ID NO: 4), and NM_—001024241 (rat) (SEQ ID NO: 5). A consensus sequence (SEQ ID NO: 6) is also provided.

FIG. 2-FIG. 2F: Tryptophan, phenylalanine, and their derivatives activate GPR139. Human (FIG. 2A and FIG. 2B) or mouse (FIG. 2C and FIG. 2D) GPR139 were co-transfected with chimeric G-protein GO2Q into COS7 cells. Cell membranes from transfected cells were used in GTPγS binding studies using various ligands at different concentrations to stimulate GPR139. FIG. 2E and FIG. 2F show control experiments in the dose response studies of Example 1.

FIG. 3A and FIG. 3B: Provides the results of experiments conducted to determine whether Trp and its derivatives (FIG. 3A) and Phe and its derivatives (FIG. 3B) stimulate Ca²⁺ mobilization in HEK293 cells expressing GPR139.

FIG. 4A and FIG. 4B: Shows microscopic images of HEK-293 cells transiently transfected with GPR139 in the absence (FIG. 4A) or presence (FIG. 4B) of L-Phe and L-Trp.

FIG. 5: Shows the presence of GPR142 mRNA (lanes 1 and 2) and GPR139 mRNA (lanes 4 and 5) in murine brain cells and murine pancreatic cells (Min6), respectively.

FIGS. 6 (A) and (B): Shows the detection of GPR139 in rat brain sections by ribo-probe hybridization using an 35S-labeled antisense sequence.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various terms relating to aspects of the description are used throughout the specification and claims. Such terms are to be given their ordinary meaning in the art unless otherwise indicated. Other specifically defined terms are to be construed in a manner consistent with the definitions provided herein.

“Effective amount” and amount “sufficient” are used interchangeably herein, and mean an amount or dose sufficient to generally bring about the desired therapeutic or prophylactic benefit in patients in need of such treatment for the designated disease, disorder, or condition. Effective amounts or doses of the compounds of the present invention may be ascertained by routine methods such as modeling, dose escalation studies or clinical trials, and by taking into consideration routine factors, e.g., the mode or route of administration or drug delivery, the pharmacokinetics of the compound, the severity and course of the disease, disorder, or condition, the subject's previous or ongoing therapy, the subject's health status and response to drugs, and the judgment of the treating physician. An example of a dose is in the range of from about 0.001 to about 200 mg of compound per kg of subject's body weight per day, preferably about 0.05 to 100 mg/kg/day, or about 1 to 35 mg/kg/day, in single or divided dosage units (e.g., BID, TID, QID). For a 70-kg human, an illustrative range for a suitable dosage amount is from about 0.05 to about 7 g/day, or about 0.2 to about 2.5 g/day.

The term “a neurological function or condition” as used herein may refer to any one of a sleep disorder, depressive disorders such as major depressive disorder, treatment-resistant depression, bipolar disorder, schizophrenia, Parkinson's Disease, a cognitive impairment, Alzheimer's Disease, attention deficit disorders, neurotransmitter release or absorption, short-term memory, long term memory, or post-traumatic stress disorder, and similar such functions and disorders.

“Pharmaceutically acceptable” means approved or approvable by a regulatory agency of the Federal or a state government or the corresponding agency in countries other than the United States, or that is listed in the U.S. Pharmacopoeia or other generally recognized pharmacopoeia for use in animals, and more particularly, in humans.

“Pharmaceutically acceptable carrier” refers to a medium that does not interfere with the effectiveness of the biological activity of the active ingredient(s), for example, compounds disclosed herein, and is not toxic to the host to which it is administered.

“Specific binding” refers to the ability of an antibody, or antigen-binding fragment, to bind to a particular biomolecule or compound with an affinity that is greater than that with which it may bind other biomolecules or compounds.

The term “subject” as used herein may refer to an animal, and preferably is a mammal such as a mouse, rat, hamster, guinea pig, rabbit, cat, dog, monkey, donkey, cow, horse, pig, and the like. Most preferably, the mammal is a human.

Provided herein are methods for activating GPR139 in a subject by identifying a subject in need of GPR139 activation, and administering an amount of one or more compounds sufficient to activate GPR139 to the subject, which in turn will increase the level of GPR139 activation relative native activation state. In some embodiments the compounds that can be administered for this purpose are provided in Table 4, such that any one of the compounds listed in Table 4 could be administered to a subject to activate GPR139. In some embodiments the compounds that can be administered for this purpose are any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine or a derivative thereof. In some embodiments the compounds that can be administered for this purpose are any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine. In an alternative embodiment a combination of any of the compounds listed in Table 4 could be administered to a subject to activate GPR139. More specifically, any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine or a derivative thereof could be administered to a subject to activate GPR139.

Provided herein are methods for reducing the activity of GPR139 in a subject by identifying a subject in need of reduced GPR139 activation, and administering an amount of one or more compounds sufficient to reduce the activity of GPR139 to the subject, which in turn will decrease the level of GPR139 activation relative native activation state. In some embodiments the compounds that can be administered for this purpose are compounds capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds. In some embodiments the interfering compound may be a protein, protein fragment, or a small molecule capable of interacting with any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds, or GPR139. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to GPR139 and inhibits or prevents its interaction with an activating compound. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds and inhibits or prevents its interaction with GPR139. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, and inhibits or prevents its interaction with GPR139.

Also described herein are methods for modulating a neurological function or condition in a subject by administering an amount of one or more compounds sufficient to modulate the activity GPR139 to the subject. In some embodiments the neurological function or condition may be modulated by increasing the activity of GPR139. In some embodiments a neurological function or condition may be modulated by increasing the activity of GPR139 by administering to a subject any one of the compounds listed in Table 4 in order to activate GPR139. In some embodiments a neurological function or condition may be modulated by increasing the activity of GPR139 by administering to a subject any one of the compounds listed in Table 4 in order to increase the activation level of GPR139. In some embodiments a neurological function or condition may be modulated by increasing the activity of GPR139 by administering to a subject any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine or a derivative thereof in order to activate GPR139. In some embodiments a neurological function or condition may be modulated by increasing the activity of GPR139 by administering to a subject any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine or a derivative thereof in order to increase the activation level of GPR139. In some embodiments the neurological function or condition may be modulated by decreasing the activity of GPR139. In some embodiments a neurological function or condition may be modulated by decreasing the activity of GPR139 by administering to a subject a compound capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds. In some embodiments a neurological function or condition may be modulated by decreasing the activity of GPR139 by administering to a subject a compound capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, or a compound listed in Table 4. In some embodiments a neurological function or condition may be modulated by decreasing the activity of GPR139 by administering to a subject a compound capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine. In some embodiments the interfering compound may be a protein, protein fragment, or a small molecule capable of interacting with any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds, or GPR139. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to GPR139 and inhibits or prevents its interaction with an activating compound. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds and inhibits or prevents its interaction with GPR139. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, and inhibits or prevents its interaction with GPR139.

Described herein are methods for modulating a disease condition of the pancreas in a subject by administering an amount of one or more compounds sufficient to modulate the activity GPR139 to the subject. In some embodiments the disease condition of the pancreas may be modulated by increasing the activity of GPR139. In some embodiments a disease condition of the pancreas may be modulated by increasing the activity of GPR139 by administering to a subject any one of the compounds listed in Table 4 in order to activate GPR139. In some embodiments a disease condition of the pancreas may be modulated by increasing the activity of GPR139 by administering to a subject any one of the compounds listed in Table 4 in order to increase the activation level of GPR139. In some embodiments a disease condition of the pancreas may be modulated by increasing the activity of GPR139 by administering to a subject any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine or a derivative thereof in order to activate GPR139. In some embodiments a disease condition of the pancreas may be modulated by increasing the activity of GPR139 by administering to a subject any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine, β-phenylethylamine or a derivative thereof in order to increase the activation level of GPR139. In some embodiments the disease condition of the pancreas may be modulated by decreasing the activity of GPR139. In some embodiments a disease condition of the pancreas may be modulated by decreasing the activity of GPR139 by administering to a subject a compound capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds. In some embodiments a disease condition of the pancreas may be modulated by decreasing the activity of GPR139 by administering to a subject a compound capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, or a compound listed in Table 4. In some embodiments a disease condition of the pancreas may be modulated by decreasing the activity of GPR139 by administering to a subject a compound capable of interfering with the interaction of GPR139 and any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine. In some embodiments the interfering compound may be a protein, protein fragment, or a small molecule capable of interacting with any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds, or GPR139. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to GPR139 and inhibits or prevents its interaction with an activating compound. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds and inhibits or prevents its interaction with GPR139. In some embodiments the interfering compound may be an antibody, or an antibody fragment, that specifically binds to L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine or β-phenylethylamine, and inhibits or prevents its interaction with GPR139.

Also provided herein are methods of administering any one of L-tryptophan, L-phenylalanine, tryptamine, amphetamine, D-tryptophan, D-phenylalanine β-phenylethylamine, a compound listed in Table 4 or a derivative of any one of these compounds to a subject. Any one of the compounds described herein may be administered to a subject orally in any acceptable dosage form such as capsules, tablets, aqueous suspensions, solutions or the like. Any one of the compounds may also be administered to a subject parenterally including but not limited to: subcutaneous, intravenous, intramuscular, intra-articular, intra-synovial, intrasternal, intranasal, topically, intrathecal, intrahepatic, intralesional, and intracranial injection or infusion techniques. Alternatively, any one of the compounds can be administered to a subject intravenously or intraperitoneally, for example, by injection. Administration of the compounds described herein to a subject may be carried out using a pharmaceutically acceptable formulation that includes the any one of the compounds for activating or inhibiting the activation of GPR139 described herein. Such formulations may also include a pharmaceutically acceptable carrier, as are commonly known in the art.

Chimeric G-Protein GO2Q

Historically, the Gi, Go coupled GPCRs offer a much greater signal-to-noise ratio in GTPγS binding studies. For Gs and Gq coupled GPCRs, although ligand-stimulated specific signals can be detected in GTPγS binding assay, the signal-to-noise ratios are often very small. Described herein is a chimeric G-protein that can be co-expressed with a GPCR in a cell to increase the signal-to-noise ratio in a GTPγS binding assay and thereby allow for detection of GPCR activity. In some embodiments the chimeric G-protein has an N-terminus from a Go2 protein and a C-terminus from a Gq protein in about any one of the ratio combinations shown in Table 1.

TABLE 1

Proportions of a Go2/Gq chimeric G-protein

Portion of total chimeric G-protein
Portion of total chimeric G-protein

from the N-terminus from Go2 protein
from the C-terminus from Gq protein

95
5

90
10

85
15

80
20

75
25

70
30

65
35

60
40

55
45

50
50

45
55

40
60

35
65

30
70

25
75

20
80

15
85

10
90

5
95

In some embodiments the chimeric G-protein has the amino acid sequence:

(SEQ ID NO: 1)

MGCTLSAEERAALERSKAIEKNLKEDGISAAKDVKLLLLGAGESGKSTIV

KQMKIIHEDGFSGEDVKQYKPVVYSNTIQSLAAIVRAMDTLGIEYGDKER

KADAKMVCDVVSRMEDTEPFSAELLSAMMRLWGDSGIQECFNRSREYQLN

DSAKYYLDSLDRIGAADYQPTEQDILRTRVKTTGIVETHFTFKNLHFRLF

DVGGQRSERKKWIHCFEDVTAIIFCVALSGYDQVLHEDETTNRMHESLKL

FDSICNNKWFTDTSIILFLNKKDIFEEKIKKSPLTICFPEYTGPSAFTEA

VAYIQAQYESKNKSAHKEIYTHVTCATDTNNIrfvfaavkdtilqlnlke

ynlv,

where the capitalized residues are from the N-terminus from Go2 protein and the lower-case residues are from the C-terminus from Gq protein. The chimeric G-protein GO2Q disclosed herein consists of the sequence of SEQ ID NO:1. In some aspects the sequence of SEQ ID NO:1 is encoded by the following DNA sequence:

(SEQ ID NO: 2)

ATGGGATGTACTCTGAGCGCAGAGGAGAGAGCCGCCCTCGAGCGGAGCAA

GGCGATTGAGAAAAACCTCAAAGAGGATGGCATCAGCGCCGCCAAAGACG

TGAAATTACTCCTGCTCGGGGCTGGAGAATCAGGAAAAAGCACCATTGTG

AAGCAGATGAAGATCATCCATGAAGATGGCTTCTCCGGAGAAGACGTGAA

ACAGTACAAGCCTGTTGTCTACAGCAACACTATCCAGTCCCTGGCAGCCA

TCGTCCGGGCCATGGACACTTTGGGCATCGAATATGGTGATAAGGAGAGA

AAGGCTGACGCCAAGATGGTGTGTGATGTGGTGAGTCGGATGGAAGACAC

CGAGCCCTTCTCTGCAGAGCTGCTTTCTGCCATGATGCGGCTCTGGGGCG

ACTCAGGAATCCAAGAGTGCTTCAACCGGTCCCGGGAGTATCAGCTCAAC

GACTCTGCCAAATACTACCTGGACAGCCTGGATCGGATTGGGGCCGCCGA

CTACCAGCCCACCGAGCAGGACATCCTCCGAACCAGGGTCAAAACCACTG

GCATCGTAGAAACCCACTTCACATTCAAGAACCTCCACTTCAGGCTGTTT

GACGTCGGAGGCCAGCGATCTGAACGCAAGAAGTGGATCCATTGCTTCGA

GGACGTCACGGCCATCATTTTCTGTGTCGCGCTCAGCGGCTATGACCAGG

TGCTCCACGAAGACGAAACCACGAACCGCATGCACGAATCCCTGAAGCTT

TTTGACAGCATCTGCAACAACAAATGGTTCACAGACACGTCCATCATCCT

GTTTCTTAACAAGAAGGACATATTTGAAGAGAAGATCAAGAAGTCCCCGC

TCACCATCTGCTTTCCTGAATATACAGGCCCCAGCGCCTTCACAGAAGCC

GTGGCTTACATCCAGGCCCAGTACGAGAGCAAGAACAAGTCAGCCCACAA

GGAGATCTACACCCACGTCACCTGCGCCACGGACACCAACAACATCcgct

ttgtctttgctgccgtcaaggacaccatcctccagttgaacctgaaggag

tacaatctggtctaa,

where the capitalized residues represent the sequence that encodes the N-terminus from Go2 protein and the lower-case residues represent the sequence that encodes the C-terminus from Gq protein.

Also described herein is a method for detecting activation of a GPCR using a chimeric Go2/Gq G-protein. The described method capitalizes on the preferred signal-to-noise ratio provided by chimeric G-proteins of this sort. In some embodiments the described method is conducted by co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has an N-terminus from a Go2 protein and a C-terminus from a Gq protein in about any one of the ratio combinations shown in Table 1. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has the amino acid sequence of SEQ ID NO: 1. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein is GO2Q. In some embodiments the described method is conducted by co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the GPCR is GPR139. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has an N-terminus from a Go2 protein and a C-terminus from a Gq protein in about any one of the ratio combinations shown in Table 1 and the GPCR is GPR139. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has the amino acid sequence of SEQ ID NO: 1 and the GPCR is GPR139. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, contacting the cell with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein is GO2Q and the GPCR is GPR139.

In some embodiments the method can be carried out with a cell membrane obtained from a cell co-expressing a chimeric Go2/Gq G-protein and a GPCR in a cell. In some embodiments the described method is conducted by co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has an N-terminus from a Go2 protein and a C-terminus from a Gq protein in about any one of the ratio combinations shown in Table 1. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has the amino acid sequence of SEQ ID NO: 1. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein is GO2Q. In some embodiments the described method is conducted by co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the GPCR is GPR139. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has an N-terminus from a Go2 protein and a C-terminus from a Gq protein in about any one of the ratio combinations shown in Table 1 and the GPCR is GPR139. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein has the amino acid sequence of SEQ ID NO: 1 and the GPCR is GPR139. In some embodiments the method involves co-expressing a chimeric Go2/Gq G-protein with a GPCR in a cell, isolating a segment of the cell membrane of the cell, contacting the cell membrane with a compound, and determining whether the compound activates the GPCR, where the chimeric Go2/Gq G-protein is GO2Q and the GPCR is GPR139.

The described methods for assessing activation of GPCR using a chimeric Go2/Gq G-protein expressed in the same cell can make use of a variety of cell types. In some embodiments, the described method can be carried out using a mammalian cell line modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest. In some embodiments the cell line used for the described method may be a fibroblast cell, a kidney cell, a monkey kidney cell (such as a COS cell) or other similar type of cell commonly used to assess GPCR activity. IN addition, cells that natively express a GPCR of interest could be modified to express a chimeric Go2/Gq G-protein in order to better assess GPRC activation. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to transiently express either a chimeric Go2/Gq G-protein or a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to transiently express both a chimeric Go2/Gq G-protein and a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to stably express either a chimeric Go2/Gq G-protein or a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to stably express a chimeric Go2/Gq G-protein and a GPCR of interest. In one embodiment a mammalian cell line may be modified to stably express a chimeric Go2/Gq G-protein to allow for further modification by either transient or stable expression of any GPCR of interest to produce a cell for use in the described method.

In some embodiments, the described method can be carried out using a mammalian cell line modified to co-express a chimeric Go2/Gq G-protein described in Table 1 with a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein described in Table 1 with a GPCR of interest may be modified to transiently express either a chimeric Go2/Gq G-protein described in Table 1 or a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to transiently express both a chimeric Go2/Gq G-protein described in Table 1 and a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to stably express either a chimeric Go2/Gq G-protein described in Table 1 or a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to stably express a chimeric Go2/Gq G-protein described in Table 1 and a GPCR of interest. In one embodiment a mammalian cell line may be modified to stably express a chimeric Go2/Gq G-protein described in Table 1 to allow for further modification by either transient or stable expression of any GPCR of interest to produce a cell for use in the described method.

In some embodiments, the described method can be carried out using a mammalian cell line modified to co-express a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 and a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 with a GPCR of interest may be modified to transiently express either a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 or a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to transiently express both a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 and a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to stably express either a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 or a GPCR of interest. In some embodiments the cell modified to co-express a chimeric Go2/Gq G-protein with a GPCR of interest may be modified to stably express a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 and a GPCR of interest. In one embodiment a mammalian cell line may be modified to stably express a chimeric Go2/Gq G-protein having the amino acid sequence of SEQ ID NO: 1 to allow for further modification by either transient or stable expression of any GPCR of interest to produce a cell for use in the described method.

The following examples are provided to describe the embodiments described herein with greater detail. They are intended to illustrate, not to limit, the embodiments.

Example 1
Tryptophan, Phenylalanine, and their Derivatives Activate GPR139

In order identify the ligands for GPR139 two improvements in the detection assay were made to allow for the ligands to be detected. First, we chose to use a GTPγS binding assay instead of using live cultured cells. The GTPγS binding assay is a cell free system that uses the cell membrane of the cell(s) of interest rather than the live cell(s). One advantage of this assay is that potential ligands present in the cell culture media are washed away when the cell membrane is prepared. This reduces the basal level of signal and increase the chance of detecting receptor ligands when assessing compounds that activate the receptor. Second, a GO2Q chimeric G-protein was created to be co-expressed with GPR139 in order to increase the signal-to-noise ratio in the GTPγS binding assay. Historically, the Gi, Go coupled GPCRs offer much greater signal-to-noise ratio in GTPγS binding studies. For Gs and Gq coupled GPCRs, although ligand-stimulated specific signals can be detected in a GTPγS binding assay, the signal-to-noise ratios are often very small. To address this a chimeric GO2-Gq chimeric G-protein, GO2Q, with the N-terminus from Go2 protein and the C-terminus from Gq protein. This chimeric G-protein, when co-expressed with Gq-coupled GPCRs, for instance histamine H1 receptor, was able to increase the signal-to-noise ratio to 3:1 when histamine was used as the ligand.

To test for compounds that activate GPR139, different amino acids and their derivatives (Table 2) were tested as ligands in the GTPγS binding assay using cell membranes from COS7 cells co-expressing GPR139 and GO2Q. Cell membrane from COS7 cells expressing GO2Q alone or co-expressing other GPCRs were also tested in GTPγS binding assay in parallel as controls. Each compound was tested in triplicate. The results show L-tryptophan (Trp) and L-phenylalanine (L-Phe) are able to activate GPR139 at the concentration tested (1 mM). In addition, a few tryptophan and phenylalanine derivatives, including tryptamine, β-phenylethylamine, and amphetamine also activated GPR139 at a 1 mM concentration in the GTPγS binding assay (Table 3, lower panel, positive results are bolded and correspond to the position of compounds shown in Table 2). The activation of GPR139 by L-Trp and L-Phe and their derivatives appeared to be specific since in the same assay, these compounds did not activate membranes from cells expressing GO2Q alone (Table 3, upper panel) or from cells co-expressing GO2Q and other GPCRs such as GPR21, GPR52, GPCR119, GPCR132, GPCR134, or GPR182 (data not shown).

TABLE 2

Compounds tested for activating of GPR139

Ligand plate 1 mM for final concentration

1
2
3
4
5
6
7
8
9
10
11
12

A
Ala
Arg
Asn
Asp

B
Cys
Cystine
Gln
Glu

C
Gly
His
Ile
Met

D
Leu
Lys
Phe
Pro

E
Ser
Thr
Trp
Tyr

F
Val
Adrenaline
DA
HA

G
Octopamine
b-phenylethylamine
Seretonin
Tyramine

H
Tryptamine
Amphetamine
HO-Pro
Buffer

TABLE 3

Activation levels of GPR139 by amino acids and their derivatives

1
2
3
4
5
6
7
8
9
10
11
12

Ct-GO2Q

A
1903
2049
2139
2171
2131
2255
2195
2142
2133
2177
2137
2132

B
1928
2132
2114
2242
2149
2229
2181
2327
2336
2242
2310
2311

C
1936
2133
2289
2308
2259
2197
2266
2222
2253
2173
2307
2276

D
2194
2213
2167
2400
2138
2041
2190
2215
2345
2256
2235
2329

E
1975
2036
2164
2210
2213
2008
2172
2234
2272
2192
2191
2186

F
2072
2083
1977
2240
2117
2045
2250
2213
2319
2186
2204
2199

G
2087
2140
2142
2334
2065
2024
2356
2154
2332
2132
2277
2369

H
2025
2048
2088
2331
2132
2001
2166
2152
2189
2200
2247
2259

GPR139-GO2Q

A
2363
2348
2439
2806
2783
2528
2806
2483
2547
2758
2922
2925

B
2168
2458
2336
2501
2652
2258
2583
2525
2766
2847
2837
2841

C
2560
2505
2414
2640
2499
2499
2760
2542
2903
2657
2829
2802

D
2621
2544
2437
2433
2617
2589
8697
6925
8417
2719
2657
2786

E
2605
2458
2545
2547
2507
2558
8141
9121
9149
2752
2715
2921

F
2632
2689
2533
2721
2624
2670
2688
2825
2708
2737
2863
2899

G
2554
2675
2831
6705
7099
6634
2839
2852
2920
2883
2932
2873

H
6757
7686
7742
7242
6744
7263
2825
2797
3109
2819
2769
2970

To assess the manner in which L-Trp and L-Phe and their derivatives including L-Trp, D-Trp, 1-methy-L-Trp, 1-methy-D-Try, L-Phe, D-Phe, Tryptamine, 13-Phenylethylamine, and amphetamine activated GPR139, dose response studies were performed for activation of GPR139. The results show that all these compounds specifically activate GPR139 in a dose-responsive manner (FIG. 2).

The active compounds were also tested in a calcium mobilization assay (FLIPR® assay). For these experiments human GPR139 was transiently expressed in HEK293 cells and calcium mobilization was stimulated using L-Trp, L-Phe or their derivatives. The results showed that L-Trp, L-Phe, and their derivatives also specifically stimulate calcium mobilization (FIG. 3). For GPR139 expressing cells, L-Trp and L-Phe demonstrated EC₅₀(half maximal effective concentration) values from 100-200 μM. Similar to GTPγS binding studies, 1-methyl-L-Trp, and 1-methyl-D-Trp demonstrated higher potencies. The concentrations of L-Trp and L-Phe in many cell culture media (for instance DMEM is about 80 μM and 750 μM respectively) are close to the EC50 values of L-Trp and L-Phe for GPR139. When GPR139 is recombinantly expressed in mammalian cells and cultured in these media, the accumulated GPR139 agonist concentrations in the media would be significantly above the EC₅₀values of L-Trp and L-Phe, therefore the receptor, GPR139, would be constantly activated in the tissue culture conditions. This may explain why GPR139 appeared constitutively active when recombinantly expressed in mammalian cells.

Many GPCRs are internalize by the cell when they are activated. To determine whether GPR139 was internalized when activated, internalization experiments were conducted using an N-terminally V-tagged mouse GPR139. These experiments showed that upon stimulation with L-Trp and L-Phe, VS-tagged GPR139 was internalized (FIG. 4).

About 300 additional phenylalanine analogues have been tested for GPR139 activation using a calcium mobilization (FLIPR®) assay. The results of these experiments indicate that many of these analogues can also activate GPR139. Table 4 lists certain phenylalanine analogues that have been determined to activate GPR139 by calcium mobilization at a concentration of 300 μM (calcium mobilization is expressed as percentage of that observed for L-phenylalanine).

TABLE 4

Phenylalanine derivatives as ligands for GPR139

% L-phenylalanine

Compound description
at 300 μM (average)

3-Bromo-D-phenylalanine
172

Styryl-L-alanine
169

2-Bromo-L-phenylalanine
168

3-Bromo-L-phenylalanine
167

3-Nitro-D-Phenylalanin
164

2-Naphthyl-L-alanine
161

3-Benzothienyl-L-alanine
161

1-Naphthyl-D-alanine
157

(3R)-2-tert-butoxycarbony 1-3,4- dihydro-1H-
155

isoquinoline-3-carboxylic acid

2-Naphthyl-D-alanine
155

S-(5-bromothienyl)-D-alanine
154

4-Bromo-L-phenylalanine
153

L-1,2,3,4-tetrahydronorharman-3-carboxylic acid
151

2-(5-bromothienyl)-L-alanine
151

3-Methyl-D-phenylalanine
150

4-Trifluoromethyl-L-phenylalanine
150

S-Nitro-L-phenylalanine
150

4-Methyl-L-phenylalanine
149

3,4-Dichloro-L-phenylalanine
149

3,4-Dichloro-D-phenylalanine
149

3-Chloro-D-phenylalanine
147

3-Methyl-L-phenylalanine
147

1-Naphthyl-L-alanine
147

4-Chloro-L-phenylalanine
146

3-Chloro-L-phenylalanine
145

2,3,4,5,6-P entafluoro-D-phenylalanine
145

3-Benzothienyl-D-alanine
143

4-Bromo-D-phenylalanine
139

2,4-Dichloro-D-phenylalanine
135

2-Bromo-D-phenylalanine
135

2-Methyl-L-phenylalanine
134

3-Trifluoromethyl-L-phenylalanine
133

4-Fluoro-L-phenylalanine
132

3-Nitro-L-phenylalanine
131

D-2-Amino-5-phenyl-pentanoic acid
129

4-Methoxy-L-phenylalanine
128

4-Iodo-D-phenylalanine
125

α-methyl-4-Fluoro-L-phenylalanine
125

2,4-Dichloro-L-phenylalanine
122

3,4-Difluoro-D-phenylalanine
121

2-Fluoro-L-phenylalanine
119

3,3-Diphenyl-L-alanine
117

4-Iodo-L-phenylalanine
116

3-Cyano-L-phenylalanine
115

4-tert-Butyl-L-phenylalanine
115

3-Fluoro-L-phenylalanine
114

2,4-Dimethyl-L-phenylalanine
113

4-Nitro-D-phenylalanine
111

4-Chloro-D-phenylalanine
110

2-Trifluoromethyl-L-phenylalanine
110

2-Methyl-D-phenylalanine
109

d-Homo-phenylalanine
105

4-Methyl-D-phenylalanine
102

3,5-Difluoro-D-phenylalanine
102

2,4-Dimethyl-D-phenylalanine
101

2,4-Dinitro-L-phenylalanine
95

3-Fluoro-D-phenylalanine
94

3-Cyano-D-phenylalanine
93

4-Fluoro-D-phenylalanine
91

Example 2
Expression Profile of GPR139

Experiments were conducted to assess tissues or cell types that expressed GPR139. Initial RT-PCR studies focused on assessing expression in mouse brain and mouse pancreatic cells (min6 cells). These studies showed that GPR139 and GPR142 (another orphan GPCR that is closely related to GPR139) are expressed in mouse brain as well as in mouse pancreatic beta cells as detected by RT-PCR (FIG. 5). The expression of GPR139 in rat brain was also confirmed by in situ hybridization (FIGS. 6A and 6B).

PHYSIOLOGICAL LIGANDS FOR GPR139

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