γ-
Aminobutyric acid (
GABA) is the major inhibitory
neurotransmitter in the central nervous system. Inhibition of
GABA aminotransferase (
GABA-AT), a
pyridoxal 5'-phosphate (PLP)-dependent
enzyme that degrades
GABA, has been established as a possible strategy for the treatment of
substance abuse. The raised
GABA levels that occur as a consequence of this inhibition have been found to antagonize the rapid release of
dopamine in the ventral striatum (nucleus accumbens) that follows an acute challenge by an addictive substance. In addition, increased
GABA levels are also known to elicit an
anticonvulsant effect in patients with
epilepsy. We previously designed the mechanism-based inactivator (1S,3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic
acid (2), now called
CPP-115, that is 186 times more efficient in inactivating
GABA-AT than
vigabatrin, the only FDA-approved
drug that is an inactivator of
GABA-AT.
CPP-115 was found to have high therapeutic potential for the treatment of
cocaine addiction and for a variety of
epilepsies, has successfully completed a Phase I safety clinical trial, and was found to be effective in the treatment of
infantile spasms (
West syndrome). Herein we report the design, using molecular dynamics simulations, synthesis, and
biological evaluation of a new mechanism-based inactivator, (S)-3-amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic
acid (5), which was found to be almost 10 times more efficient as an inactivator of
GABA-AT than
CPP-115. We also present the unexpected crystal structure of 5 bound to
GABA-AT, as well as computational analyses used to assist the structure elucidation process. Furthermore, 5 was found to have favorable pharmacokinetic properties and low off-target activities. In vivo studies in freely moving rats showed that 5 was dramatically superior to
CPP-115 in suppressing the release of
dopamine in the corpus striatum, which occurs subsequent to either an acute
cocaine or
nicotine challenge. Compound 5 also attenuated increased metabolic demands (neuronal
glucose metabolism) in the hippocampus, a brain region that encodes spatial information concerning the environment in which an animal receives a reinforcing or aversive
drug. This multidisciplinary computational design to preclinical efficacy approach should be applicable to the design and improvement of mechanism-based inhibitors of other
enzymes whose crystal structures and inactivation mechanisms are known.