Methods for treating pain

Abstract

The present invention features methods and compositions for preventing, reducing, or treating a traumatic, metabolic or toxic peripheral nerve lesion or pain including, for example, neuropathic pain, inflammatory and nociceptive pain by administering to a mammal in need thereof a compound that reduces the expression or activity of BH4. According to this invention, this reduction may be achieved by reducing the enzyme activity of any of the BH4 synthetic enzymes, such as GTP cyclohydrolase (GTPCH), sepiapterin reductase (SPR), or dihydropteridine reductase (DHPR); by antagonizing the cofactor function of BH4 on BH4-dependent enzymes; or by blocking BH4 binding to membrane bound receptors. The compounds of the invention may be administered alone or in combination with a second therapeutic agent. The invention also provides methods for diagnosing pain or a peripheral nerve lesion in a mammal by measuring the levels of BH4 or its metabolites in biological sample. Alternatively, pain or a peripheral nerve lesion may be diagnosed by measuring the levels or activity of any one of the BH4 synthetic enzymes in tissue samples of a mammal. Also disclosed are screening methods that make use of BH4 or BH4 synthetic enzymes, BH4-dependent enzymes, and BH4-binding receptors for the identification of novel therapeutics for the treatment, prevention, or reduction of pain.

1 . A method of treating, reducing, or preventing pain or the consequences or development of a peripheral nerve lesion in a mammal, said method comprising administering to said mammal a composition that reduces the tetrahydrobiopterin (BH4) biological activity in an amount sufficient to treat, reduce, or prevent pain or the exacerbation of a peripheral nerve lesion due to overproduction of BH4. 
     
     
         2 . The method of  claim 1 , wherein said mammal is a human. 
     
     
         3 . The method of  claim 1 , wherein the pain is reduced by reducing the BH4 levels in primary sensory neurons or dorsal horn neurons. 
     
     
         4 . The method of  claim 3 , wherein said primary sensory neurons are in a dorsal root ganglion or a trigeminal ganglion. 
     
     
         5 . The method of  claim 4 , wherein said dorsal horn neurons are in the spinal cord or spinal nucleus of the trigeminal in the brainstem. 
     
     
         6 . The method of  claim 1 , wherein the reduction in BH4 biological activity is the result of a reduction in BH4 synthesis or recycling. 
     
     
         7 . The method of  claim 1 , wherein said BH4 biological activity is reduced by increasing the expression, GTPCH-binding, or activity of GTP cyclohydrolase feedback regulatory protein (GFRP). 
     
     
         8 . The method of  claim 6 , wherein said reduction in BH4 synthesis is the result of a reduction in the level or biological activity of at least one enzyme selected from the group consisting of sepiapterin reductase (SPR), Pyruvoyltetrahydropterin Synthase (PTPS), GTP cyclohydrolase (GTPCH), Pterin-4α-carbinolamine dehydratase, and dihydropteridine reductase (DHPR). 
     
     
         9 . The method of  claim 8 , wherein said reduction in BH4 synthesis is the result of a reduction in the biological activity of at least one enzyme selected from the group consisting of sepiapterin reductase (SPR), GTP cyclohydrolase (GTPCH), and dihydropteridine reductase (DHPR). 
     
     
         10 . The method of  claim 8 , wherein the biological activity of at least two of said enzymes is reduced. 
     
     
         11 . The method of  claim 10 , wherein the biological activity of at least three of said enzymes is reduced. 
     
     
         12 . The method of  claim 8 , wherein said biological activity is reduced by at least 10%. 
     
     
         13 . The method of  claim 12 , wherein said biological activity is reduced by at least 40%. 
     
     
         14 . The method of  claim 1 , wherein said composition comprises methotrexate. 
     
     
         15 . The method of  claim 1 , wherein said composition comprises at least one compound selected from the group consisting of 2,4 diamino 6-hydroxypyrimidine (DAHP), Tetrahydro-L-biopterin, L-Sepiapterin, 7,8-dihydro-L-Biopterin, 6,7-dimethyltetrahydropterin hydrochloride, and 8-bromo-cGMP. 
     
     
         16 . The method of  claim 1 , wherein said composition comprises at least one compound selected from the group consisting of N-acetyl-serotonin (NAS), N-Chloroacetylserotonin, N-Methoxyacetylserotonin, and N-Chloroacetyldopamine. 
     
     
         17 . The method of  claim 1 , wherein said composition comprises a compound having the formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1  is H, C 1-6  alkyl, halo, NO 2 , CN, CO 2 R 4 , CONR 4 R 5 , SO 2 R 4 , SO 2 NR 4 R 5 , OR 4 , or NR 4 R 5 , wherein each of R 4  and R 5  is, independently, H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl, 
 R 2  is H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl, and R 3  is H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, C 1-4  alkheteroaryl, CO 2 R 6 , CONR 7 R 8 , SO 2 R 6 , or SO 2 NR 7 R 8 , wherein R 6  is C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl and each of R 7  and R 8  is, independently, H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl; 
 R 3  is as above and R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N, O, or S of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring and each of R 9 , R 10 , R 11 , R 12 , and R 13  is, independently H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl;
 R 3  is as above and R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring, each of R 12  and R 13  is as above, and R 14  is OR 4 , halo, NO 2 , CN, CO 2 R 7 , CONR 7 R 8 , SO 2 R 7 , SO 2 NR 7 R 8 , C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl, wherein each of R 4 , R 7  and R 8  is, independently, H, C 1 -C 6  alkyl, C 6 -C 12  aryl, C 1 -C 4  alkaryl, heteroaryl, or C 1 -C 4  alkheteroaryl; or
 R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring, each of R 9 , R 10 , R 11 , and R 14  are as above, R 3  does not exist, and a double bond is formed between the carbon bearing R 14  and the nitrogen bearing R 2 . 
     
     
         18 . The method of  claim 17 , wherein said composition comprises a compound of formula (I), wherein
 R 1  is H, C 1-6  alkyl, halo, NO 2 , CN, CO 2 R 4 , CONR 4 R 5 , SO 2 R 4 , SO 2 NR 4 R 5 , OR 4 , or NR 4 R 5 , wherein each of R 4  and R 5  is, independently, H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl,   R 2  is H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C i-4  alkheteroaryl, and   R 3  is H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, C 1-4  alkheteroaryl, CO 2 R 6 , CONR 7 R 8 , SO 2 R 6 , or SO 2 NR 7 R 8 , wherein R 6  is C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl and each of R 7  and R 8  is, independently, H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl.   
     
     
         19 . The method of  claim 1 , wherein said composition comprises a compound of formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N, O, or S of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring and each of R 9 , R 10 , R 11 , R 12 , and R 13  is, independently H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, alkaryl, or C 1-4  alkheteroaryl. 
     
     
         20 . The method of  claim 1 , wherein said composition comprises a compound of formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 3  is as above and R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring, each of R 12  and R 13  is as above, and R 14  is OR 4 , halo, NO 2 , CN, CO 2 R 7 , CONR 7 R 8 , SO 2 R 7 , SO 2 NR 7 R 8 , C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl, wherein each of R 4 , R 7  and R 8  is, independently, H, C 1 -C 6  alkyl, C 6-12  C 12  aryl, C 1 -C 4  alkaryl, heteroaryl, or C 1 -C 1  alkheteroaryl. 
     
     
         21 . The method of  claim 1 , wherein said composition comprises a compound of formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring, each of R 9 ,R 10 , R 11 , R 12 , and R 14  are as above, R 3  does not exist, and a double bond is formed between the carbon bearing R 14  and the nitrogen bearing R 2 . 
     
     
         22 . The method of  claim 1 , wherein said composition comprises a compound of formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N, O, or S of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring and each of R 9 , R 10 , R 11 , R 12 , and R 13  is, independently H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl. 
     
     
         23 . The method of  claim 1 , wherein said composition comprises a compound of formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 3  is as above and R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring, each of R 12  and R 13  is as above, and R 14  is OR 4 , halo, NO 2 , CN, CO 2 R 7 , CONR 7 R 8 , SO 2 R 7 , SO 2 NR 7 R 8 , C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl, wherein each of R 4 , R 7  and R 8  is, independently, H, C 1 -C 6  alkyl, C 6 -C 12  aryl, C 1 -C 4  alkaryl, heteroaryl, or C 1 -C 4  alkheteroaryl. 
     
     
         24 . The method of  claim 1 , wherein said composition comprises a compound of formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1  and R 2  together are represented by 
 
       
         
           
           
               
               
           
         
       
       wherein the N of the R 1 /R 2  linkage forms a bond to the pyrimidinone ring, each of R 9 , R 10 , R 11 , and R 14  are as above, R 3  does not exist, and a double bond is formed between the carbon bearing R 14  and the nitrogen bearing R 2 . 
     
     
         25 . The method of  claim 18 , wherein said composition comprises a compound selected from the group consisting of 
       
         
           
           
               
               
           
         
       
     
     
         26 . The method of  claim 1 , wherein said composition comprises a compound having the formula: 
       
         
           
           
               
               
           
         
       
       wherein
 R 15  is H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl; and 
 R 16  is H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, C 1-4  alkheteroaryl, CO 2 R 17 , CONR 18 R 19 , SO 2 R 17  or SO 2 NR 18 R 19 , wherein R 17  is C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl and each of R 18  and R 19  is, independently, H, C 1-6  alkyl, C 6-12  aryl, heteroaryl, C 1-4  alkaryl, or C 1-4  alkheteroaryl. 
 
     
     
         27 . The method of  claim 1 , wherein said pain is acute pain. 
     
     
         28 . The method of  claim 1 , wherein said pain is chronic pain. 
     
     
         29 . The method of  claim 1 , wherein said pain is selected from the group consisting of peripheral and central neuropathic pain, inflammatory pain, functional pain nociceptive pain, and headache. 
     
     
         30 . The method of  claim 1 , further comprising a second therapeutic agent. 
     
     
         31 . The method of  claim 30 , wherein said second therapeutic agent is an analgesic agent. 
     
     
         32 . The method of  claim 30 , wherein said analgesic agent is a non-steroidal anti-inflammatory agent (NSAIDs), opioid receptor agonist, tricyclic antidepressant, SSRI, anticonvulsant, clonidine, sodium or calcium channel blocker, potassium channel opener, 5-HT1D receptor agonist. 
     
     
         33 . The method of  claim 32 , wherein said second therapeutic agent is an inhibitor of an enzyme selected from the group consisting of nitric oxide synthase (NOS), tyrosine hydroxylase, tryptophan hydroxylase I (non-neuronal TphI), tryptophan hydroxylase II (neuronal Tph II), phenylalanine hydroxylase, dopamine-β-hydroxylase, N-methyltransferase, and ether lipid oxidase. 
     
     
         34 . The method of  claim 30 , wherein said therapeutic agent that reduces the levels of tetrahydrobiopterin (BH4) and said second therapeutic agent are administered within one hour of each other. 
     
     
         35 . The method of  claim 30 , wherein said therapeutic agent that reduces the levels of tetrahydrobiopterin (BH4) and said second therapeutic agent are administered simultaneously. 
     
     
         36 . The method of  claim 30 , wherein said therapeutic agent that reduces the levels of tetrahydrobiopterin (BH4) and said second analgesia-inducing compound are administered in the same pharmaceutical formulation. 
     
     
         37 . A method of diagnosing pain or a peripheral nerve lesion in a mammal, said method comprising detecting an increase in BH4, BH4 metabolite, BH4 precursor, or BH4 intermediate in a biological sample from said mammal. 
     
     
         38 . The method of  claim 37 , wherein said BH4 metabolite is pterin, biopterin, 7,8 dihydropterin, 7,8-dihydroxanthopterin, xanthopterin, isoxanthopterin, leucopterin, 7,8-dihydroneopterin, or neopterin. 
     
     
         39 . The method of  claim 37 , wherein said BH4 intermediate is 7,8-dihydroneopterin triphosphate, neopterin, or 6-pyruvoyl tetrahydropterin. 
     
     
         40 . The method of  claim 37 , wherein said biological sample is selected from the group consisting of blood, serum, plasma, tissue sample, urine, cerebrospinal fluid, synovial fluid, tissue exudate, or tissue sample. 
     
     
         41 . The method of  claim 37 , wherein said increase is at least a 20% increase relative to control conditions. 
     
     
         42 . A method of diagnosing pain or a peripheral nerve lesion in a mammal, said method comprising detecting an increase in the activity or level of a BH4 synthetic enzyme in primary sensory neurons or dorsal horn neurons of said mammal. 
     
     
         43 . The method of  claim 42 , wherein said BH4 synthetic enzyme is selected from the group consisting of sepiapterin reductase (SPR), Pyruvoyltetrahydropterin Synthase (PTPS), GTP cyclohydrolase (GTPCH), Pterin-4α-carbinolamine dehydratase, and dihydropteridine reductase (DHPR). 
     
     
         44 . The method of  claim 42 , wherein said detecting is performed by imaging techniques. 
     
     
         45 . The method of  claim 44 , wherein said imaging is positron emission tomography (PET). 
     
     
         46 . The method of  claim 42 , wherein said increase is at least a 20% increase relative to control conditions.