mGlu2 and mGlu3 receptor negative allosteric modulators attenuate the interoceptive effects of alcohol in male and female rats

RATIONALE

The subjective effects of alcohol are associated with alcohol use disorder (AUD) vulnerability and treatment outcomes. The interoceptive effects of alcohol are part of these subjective effects and can be measured in animal models using drug discrimination procedures. The newly developed mGlu2 and mGlu3 negative allosteric modulators (NAMs) are potential therapeutics for AUD and may alter interoceptive sensitivity to alcohol.

OBJECTIVES

To determine the effects of mGlu2 and mGlu3 NAMs on the interoceptive effects of alcohol in rats.

METHODS

Long-Evans rats were trained to discriminate the interoceptive stimulus effects of alcohol (2.0 g/kg, i.g.) from water using both operant (males only) and Pavlovian (male and female) drug discrimination techniques. Following acquisition training, an alcohol dose-response (0, 0.5, 1.0, 2.0 g/kg) experiment was conducted to confirm stimulus control over behavior. Next, to test the involvement of mGlu2 and mGlu3, rats were pretreated with the mGlu2-NAM (VU6001966; 0, 3, 6, 12 mg/kg, i.p.) or the mGlu3-NAM (VU6010572; 0, 3, 6, 12 mg/kg, i.p.) before alcohol administration (2.0 g/kg, i.g.).

RESULTS

In Pavlovian discrimination, male rats showed greater interoceptive sensitivity to 1.0 and 2.0 g/kg alcohol compared to female rats. Both mGlu2-NAM and mGlu3-NAM attenuated the interoceptive effects of alcohol in male and female rats using Pavlovian and operant discrimination. There may be a potential sex difference in response to the mGlu2-NAM at the highest dose tested.

CONCLUSIONS

Male rats may be more sensitive to the interoceptive effects of the 2.0 g/kg alcohol training dose compared to female rats. Both mGlu2-and mGlu3-NAM attenuate the interoceptive effects of alcohol in male and female rats. These drugs may have potential for treatment of AUD in part by blunting the subjective effects of alcohol.

Design and Synthesis of mGlu2 NAMs with Improved Potency and CNS Penetration Based on a Truncated Picolinamide Core

Herein, we detail the optimization of the mGlu₂ negative allosteric modulator (NAM), VU6001192, by a reductionist approach to afford a novel, simplified mGlu₂ NAM scaffold. This new chemotype not only affords potent and selective mGlu₂ inhibition, as exemplified by VU6001966 (mGlu₂ IC₅₀ = 78 nM, mGlu₃ IC₅₀ > 30 μM), but also excellent central nervous system (CNS) penetration (K_p = 1.9, K_p,uu = 0.78), a feature devoid in all previously disclosed mGlu₂ NAMs (K_ps ≈ 0.3, K_p,uus ≈ 0.1). Moreover, this series, based on overall properties, represents an exciting lead series for potential mGlu₂ PET tracer development.