Molecular Modeling Revealed a "No-Go Zone" on the Cannabinoid Receptor That Blocks Inactive Compounds | Research

The takeaway

Using computational modeling of active and inactive cannabinoids, researchers identified a specific region near the cannabinoid receptor where extra molecular volume prevents binding, explaining why some cannabinoid compounds are inactive.

Read this if you are interested in the molecular science behind how cannabinoids interact with their brain receptors.

A physical "no-go zone" at the receptor explained activity differences among cannabinoids

What the researchers found

Building on their earlier work on cannabinoid structure-activity relationships, researchers used the "active analog approach" to model a previously unknown feature of the cannabinoid receptor.

By comparing the three-dimensional shapes of four active cannabinoids with two inactive ones, they identified a region of "steric interference" near the receptor, essentially a physical space where extra molecular bulk prevents a compound from binding. They termed this the "receptor essential volume" (REV).

The REV was located near the top of the carbocyclic ring on the bottom face of the cannabinoid molecule. Active compounds had conformations that cleared this zone; inactive compounds could not avoid it.

The model was validated by testing it against additional cannabinoids: a minimally active classical cannabinoid, an active benzofuran cannabinoid, and the nonclassical cannabinoid CP-47,497. In each case, the compound's activity could be explained by whether its accessible conformations could clear the REV.

Why it matters

This study provided a molecular-level explanation for why some cannabinoid compounds are active and others are not, knowledge essential for designing new therapeutic cannabinoids with specific properties.

The numbers in context

Four active cannabinoids, two inactive cannabinoids used to define the model. Three additional compounds used for validation. The REV was mapped in three-dimensional space near the carbocyclic ring.

How the study worked

Computational molecular mechanics study using MMP2(85) for structure optimization and Chem-X MAP facility for calculating the receptor essential volume. Four active and two inactive cannabinoids were used to define the model, with three additional compounds used for validation.

What this study cannot tell us

Computational modeling predicts but does not directly observe receptor interactions. The cannabinoid receptor structure was not yet experimentally determined at this time. Only a small set of compounds was used to define and test the model.

How to read the evidence

A computational chemistry study with internal validation. Provides molecular insight but requires experimental confirmation of predictions.

When this study was published

Published in 1993. The CB1 receptor crystal structure was not solved until 2016, which ultimately confirmed many structural predictions from studies like this.

The bigger picture

This work contributed to the rational drug design approach for cannabinoid therapeutics. Understanding the physical constraints of the receptor binding site helps chemists design molecules that either fit (for therapeutic purposes) or are blocked (to create receptor antagonists).

Questions still open

Does the receptor essential volume model predict the activity of synthetic cannabinoids? How does this model compare to the actual receptor structure determined by X-ray crystallography? Can this approach guide design of non-psychoactive therapeutic cannabinoids?

Common questions

Why are some cannabinoids inactive?

This study found that inactive cannabinoids have extra molecular volume that physically prevents them from fitting into a critical region near the receptor binding site.

How does this help drug development?

By mapping the physical constraints of receptor binding, chemists can design new compounds that either fit precisely (for therapeutic effects) or are deliberately blocked (for antagonist drugs).

Read the original research

Characterization of a region of steric interference at the cannabinoid receptor using the active analog approach.

Journal of medicinal chemistry, 36(12), 1761-71

View on PubMed ↗

Citation

Reggio, P H; Panu, A M; Miles, S. (1993). Characterization of a region of steric interference at the cannabinoid receptor using the active analog approach.. Journal of medicinal chemistry, 36(12), 1761-71.