Scientists Designed a New Drug That Blocks CB1 Receptors Without Entering the Brain to Treat Liver Fibrosis | Research

The takeaway

Researchers created novel dual-action compounds that block peripheral CB1 receptors and inhibit inflammatory iNOS without crossing the blood-brain barrier, showing antifibrotic effects in animal models of liver fibrosis.

Read this if you are interested in how cannabinoid receptor science is being applied to develop new treatments for liver disease.

Novel compounds block CB1 receptors without entering the brain, avoiding psychiatric side effects

What the researchers found

This medicinal chemistry study designed and synthesized a new class of compounds that combine two therapeutic mechanisms: blocking CB1 cannabinoid receptors and inhibiting inducible nitric oxide synthase (iNOS), both of which are implicated in liver fibrosis.

The key innovation was engineering these compounds to stay out of the brain, avoiding the psychiatric side effects (depression, anxiety, suicidality) that doomed the first-generation CB1 blocker rimonabant.

A series of 3,4-diarylpyrazolinecarboximidamides were synthesized and tested. The lead compound (compound 7) demonstrated potent CB1 receptor binding, iNOS inhibition, and reduced food intake (via peripheral CB1 blockade). In animal models of liver fibrosis, it showed antifibrotic effects through the combined action of iNOS inhibition and CB1 receptor antagonism.

Why it matters

Liver fibrosis is a major global health burden with few effective treatments. This study demonstrates that the endocannabinoid system can be targeted therapeutically without the psychiatric risks that ended rimonabant's clinical use. The dual-mechanism approach could be more effective than targeting either pathway alone.

The numbers in context

Lead compound 7 showed potent CB1 receptor binding affinity, iNOS inhibition, reduced food intake, and antifibrotic effects in animal models. The specific binding affinities are reported in the full text.

How the study worked

Structure-activity relationship study involving synthesis and testing of a series of 3,4-diarylpyrazolinecarboximidamides. Compounds were evaluated in CB1 receptor binding assays, iNOS activity assays, food intake studies, and animal models of liver fibrosis. Brain penetrance was assessed to confirm peripheral restriction.

What this study cannot tell us

Preclinical study with no human data. The long-term safety of chronic peripheral CB1 blockade combined with iNOS inhibition has not been established. Animal models of fibrosis may not fully predict human therapeutic outcomes. Only one lead compound was tested in vivo.

How to read the evidence

Preclinical drug design and animal study. Preliminary evidence for a novel therapeutic approach requiring human clinical trials.

When this study was published

Published in 2017.

The bigger picture

After rimonabant was withdrawn from the European market in 2008 due to psychiatric adverse effects, peripheral CB1 receptor blockers have been pursued as a safer alternative. This dual-target approach represents a new generation of cannabinoid-based drug design that leverages receptor biology while avoiding central nervous system risks.

Questions still open

Will peripheral CB1 blockers prove safe in long-term human use? Could this dual-mechanism approach work for other liver diseases beyond fibrosis? Would combination of existing drugs (a CB1 blocker plus an iNOS inhibitor) achieve the same effect?

Common questions

What does the CB1 receptor have to do with liver disease?

CB1 receptors in the liver contribute to fibrosis (scarring). Blocking these receptors has antifibrotic effects, but earlier drugs that also blocked CB1 in the brain caused depression and suicidal thoughts. This study designed compounds that only block CB1 outside the brain.

What happened to rimonabant?

Rimonabant was a CB1 receptor blocker approved in Europe for obesity but withdrawn in 2008 due to psychiatric side effects including depression and suicidality. This study represents a new generation of CB1 blockers designed to avoid the brain entirely.

Read the original research

Design, Synthesis, and Biological Evaluation of Novel, Non-Brain-Penetrant, Hybrid Cannabinoid CB1R Inverse Agonist/Inducible Nitric Oxide Synthase (iNOS) Inhibitors for the Treatment of Liver Fibrosis.

Journal of medicinal chemistry, 60(3), 1126-1141

View on PubMed ↗Publisher’s paper ↗

Citation

Iyer, Malliga R; Cinar, Resat; Katz, Alexis; Gao, Michael; Erdelyi, Katalin; Jourdan, Tony; Coffey, Nathan J; Pacher, Pal; Kunos, George. (2017). Design, Synthesis, and Biological Evaluation of Novel, Non-Brain-Penetrant, Hybrid Cannabinoid CB1R Inverse Agonist/Inducible Nitric Oxide Synthase (iNOS) Inhibitors for the Treatment of Liver Fibrosis.. Journal of medicinal chemistry, 60(3), 1126-1141. https://doi.org/10.1021/acs.jmedchem.6b01504