VK4-40, a Novel D3R Partial Agonist, Attenuates Cocaine Reward and
Relapse in Rodents
Abstract
Background and Purpose. Despite widespread abuse of cocaine, there are
no approved treatments for cocaine use disorder. Chronic cocaine use is
associated with upregulated dopamine D3 receptor (D3R) expression in the
brain, and therefore, most D3R-based medication development has focused
on D3R antagonists. However, D3R antagonists do not attenuate cocaine
intake under “easy” self-administration conditions when response
requirements are low. Here we evaluated a novel, highly selective and
metabolically stable D3R partial agonist, VK4-40, for its efficacy in
reducing cocaine intake and relapse to drug seeking. Experimental
Approach. The impact of VK4-40 on cocaine intake and relapse were
evaluated using intravenous self-administration procedures under a
fixed-ratio 2 reinforcement schedule and cocaine-primed reinstatement
conditions in rats. Optogenetic brain-stimulation reward procedures were
used to evaluate the interaction of VK4-40 and cocaine in the mesolimbic
dopamine system. Sucrose self-administration and a conditioned place
preference paradigm was used to evaluate the abuse potential of VK4-40
alone and other unwanted effects. Key Results. VK4-40 dose-dependently
reduced cocaine self-administration and cocaine-primed reinstatement of
drug-seeking behavior. In addition, VK4-40 inhibited cocaine-enhanced
brain-stimulation reward caused by optogenetic stimulation of dopamine
neurons in the ventral tegmental area. VK4-40 alone decreased
brain-stimulation reward, and produced neither conditioned place
preference nor place aversion. This new D3R partial agonist also failed
to alter oral sucrose self-administration. Conclusions and Implications.
The novel D3R partial agonist, VK4-40, attenuates cocaine reward and
relapse in rodents, without significant unwanted effects. These findings
support further investigation of D3R partial agonists as putative
treatments for cocaine use disorder.