The long-term goal of this research is to design new compounds to inactivate GABA aminotransferase (GABA- AT), the enzyme that degrades the inhibitory neurotransmitter GABA, for the treatment of chemical addiction and epilepsy. Inhibition of GABA-AT, which raises GABA levels, has been shown to effectively dampen excessive neural activity without affecting basal neuronal firing. When the concentration of GABA diminishes below a threshold level in the brain, convulsions result; raising the brain GABA levels terminates the seizure. Increasing GABA levels also blocks cocaine, nicotine, methamphetamine, alcohol, and heroin addiction in rats and cocaine addiction in humans without affecting the craving for food. The neurochemical response to drugs of abuse is a sharp increase in dopamine levels in the nucleus accumbens, which activates the neurons responsible for pleasure and reward responses. The rise in dopamine and associated behaviors can be antagonized by an increase in the concentration of GABA. Vigabatrin (trade name SabrilTM), an irreversible inhibitor of GABA-AT, is currently marketed as a monotherapy for pediatric patients and as an adjunctive therapy for adults with refractory seizures. It was shown by positron emission tomography (PET) in primates that vigabatrin inhibits these cocaine-induced dopamine increases. The acceptance of vigabatrin for the treatment of both epilepsy and stimulant addiction, however, has been hampered by concerns about visual field defects (VFDs) in 25-50% of patients following chronic administration of large amounts of vigabatrin; the typical dose is 1-3 grams a day. The mechanism leading to the VFDs is not known; nonetheless, if the prevailing belief that VFDs arise from prolonged exposure to large doses of drug is correct, and if much lower doses of a drug can be used, there may be no untoward consequences. We previously designed a GABA-AT inactivator, (1S,3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (2), which was found to be 300 times more potent than vigabatrin in modulation of the dopamine increase induced by addictive substances and in reversal of cocaine addiction in rats as well in a model for infantile spasms. Compound 2 is currently being evaluated for safety in a clinical trial. In the last budget period we designed a new compound (17) that is 10 times more potent than 2.
An aim of this proposal is to synthesize new inactivators of GABA-AT, based on 2, and study their inactivation mechanisms, including the inactivation mechanism of 17, which will be very beneficial to future inhibitor design.
A third aim i s to determine the structure of the new inactivators bound to GABA-AT by crystallography in collaboration with Dr. Dali Liu.
A fourth aim will involve studies by collaborator Dr. Stephen Dewey on the effect of these new compounds on dopamine release in rat brains using positron emission tomography (PET) and their effect on addiction in rats and studies on their anticonvulsant activity by the Anticonvulsant Screening Program at the NIH.
The aim of this research is to design new compounds to block GABA aminotransferase, the enzyme that catalyzes the destruction of the inhibitory neurotransmitter GABA, thereby increasing the brain levels of GABA. When the concentration of GABA diminishes below a threshold level in the brain, convulsions result; raising the brain GABA levels, for example by blocking GABA aminotransferase, terminates the seizure. Increasing GABA levels also blocks cocaine, nicotine, methamphetamine, alcohol, and heroin addiction in rats and cocaine addiction in humans without affecting the craving for food.
|Juncosa, Jose I; Takaya, Kenji; Le, Hoang V et al. (2018) Design and Mechanism of (S)-3-Amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic Acid, a Highly Potent ?-Aminobutyric Acid Aminotransferase Inactivator for the Treatment of Addiction. J Am Chem Soc 140:2151-2164|
|Moschitto, Matthew J; Silverman, Richard B (2018) Synthesis of ( S)-3-Amino-4-(difluoromethylenyl)-cyclopent-1-ene-1-carboxylic Acid (OV329), a Potent Inactivator of ?-Aminobutyric Acid Aminotransferase. Org Lett 20:4589-4592|
|Mascarenhas, Romila; Le, Hoang V; Clevenger, Kenneth D et al. (2017) Selective Targeting by a Mechanism-Based Inactivator against Pyridoxal 5'-Phosphate-Dependent Enzymes: Mechanisms of Inactivation and Alternative Turnover. Biochemistry 56:4951-4961|
|Wu, Rui; Sanishvili, Ruslan; Belitsky, Boris R et al. (2017) PLP and GABA trigger GabR-mediated transcription regulation in Bacillus subtilis via external aldimine formation. Proc Natl Acad Sci U S A 114:3891-3896|
|Le, Hoang V; Hawker, Dustin D; Wu, Rui et al. (2015) Design and mechanism of tetrahydrothiophene-based ?-aminobutyric acid aminotransferase inactivators. J Am Chem Soc 137:4525-33|
|Lee, Hyunbeom; Le, Hoang V; Wu, Rui et al. (2015) Mechanism of Inactivation of GABA Aminotransferase by (E)- and (Z)-(1S,3S)-3-Amino-4-fluoromethylenyl-1-cyclopentanoic Acid. ACS Chem Biol 10:2087-98|
|Lee, Hyunbeom; Juncosa, Jose I; Silverman, Richard B (2015) Ornithine aminotransferase versus GABA aminotransferase: implications for the design of new anticancer drugs. Med Res Rev 35:286-305|
|Lee, Hyunbeom; Doud, Emma H; Wu, Rui et al. (2015) Mechanism of inactivation of ?-aminobutyric acid aminotransferase by (1S,3S)-3-amino-4-difluoromethylene-1-cyclopentanoic acid (CPP-115). J Am Chem Soc 137:2628-40|
|Juncosa, Jose I; Lee, Hyunbeom; Silverman, Richard B (2013) Two continuous coupled assays for ornithine-?-aminotransferase. Anal Biochem 440:145-9|
|Juncosa Jr, Jose I; Groves, Andrew P; Xia, Guoyao et al. (2013) Probing the steric requirements of the ýý-aminobutyric acid aminotransferase active site with fluorinated analogues of vigabatrin. Bioorg Med Chem 21:903-11|
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