Two drugs thought to only activate CB2 receptors were discovered to also block CB1, complicating past research | Research

The takeaway

GW405833 and AM1710, widely used as "selective CB2 agonists" in research, were found to also antagonize CB1 receptor signaling, meaning previous studies using these compounds may have misinterpreted their results.

Read this if you follow cannabinoid pharmacology and want to understand a major methodological caveat in the field.

GW405833 and AM1710 are not CB2-selective: they also antagonize CB1

What the researchers found

Two compounds (GW405833 and AM1710) that have been extensively used in research as selective CB2 receptor agonists were discovered to also antagonize CB1 receptor signaling. This makes them "Janus" ligands, named after the two-faced Roman god, as they simultaneously activate one receptor type while blocking the other.

GW405833 was the more potent CB1 antagonist of the two, noncompetitively blocking multiple CB1 signaling pathways including adenylyl cyclase, ERK phosphorylation, and receptor internalization. Its interaction with CB1/arrestin signaling was complex: it initially potentiated arrestin recruitment at 20 minutes but shifted to antagonism after 1 hour.

AM1710 behaved as a lower-potency competitive CB1 antagonist with some inverse agonist properties.

Why it matters

This is a critical methodological finding. Dozens of published studies have used GW405833 and AM1710 as "selective CB2" tools and attributed their effects solely to CB2 activation. The discovery of CB1 antagonism means those conclusions may need revision. Any experiment using these compounds must now account for their dual activity.

The numbers in context

GW405833: noncompetitive CB1 antagonist across multiple signaling pathways. AM1710: low-potency competitive CB1 antagonist/inverse agonist. Time-dependent arrestin modulation by GW405833: potentiation at 20 min, antagonism at 1 hour.

How the study worked

Autaptic hippocampal neurons (for endocannabinoid-mediated signaling), CB1-expressing HEK293 cells (for pathway-specific analysis), and multiple signaling readouts including adenylyl cyclase, ERK phosphorylation, PI(4,5)P2 signaling, receptor internalization, and arrestin recruitment.

What this study cannot tell us

In vitro study using cell cultures and isolated neurons. The relevance of these findings to in vivo pharmacology depends on drug concentrations achieved in tissues. The complex, time-dependent signaling profiles make it difficult to predict net effects in whole organisms.

How to read the evidence

Thorough in vitro pharmacological characterization using multiple signaling readouts. Provides definitive evidence of dual receptor activity for these tool compounds.

When this study was published

Published in 2017. The importance of confirming receptor selectivity for pharmacological tools continues to be recognized.

The bigger picture

The assumption that pharmacological tools are receptor-selective has led to conclusions that may be wrong. This discovery that "selective" CB2 agonists also block CB1 is a cautionary tale for the entire field. When a drug has dual effects, attributing outcomes to one receptor is scientifically unsound, and a body of CB2 research may need reinterpretation.

Questions still open

How many published findings attributed to "selective CB2 activation" are actually due to combined CB2 agonism and CB1 antagonism? Are there truly selective CB2 agonists, or do all compounds in this class have some CB1 activity? How should past studies be reinterpreted?

Common questions

Why does it matter that these drugs hit both receptors?

Many research studies used these compounds assuming they only affected CB2 receptors. If the drugs were also blocking CB1, the observed effects could be from CB1 antagonism, CB2 activation, or the combination. This means the conclusions of those studies about CB2's role may be partially or entirely wrong.

What is a "Janus" ligand?

Named after the two-faced Roman god Janus, a Janus ligand acts differently at two related receptors, in this case activating CB2 while blocking CB1. This dual action was not known when these compounds were first described and used in research.

Read the original research

Two Janus Cannabinoids That Are Both CB2 Agonists and CB1 Antagonists.

The Journal of pharmacology and experimental therapeutics, 360(2), 300-311

View on PubMed ↗Publisher’s paper ↗

Citation

Dhopeshwarkar, Amey; Murataeva, Natalia; Makriyannis, Alex; Straiker, Alex; Mackie, Ken. (2017). Two Janus Cannabinoids That Are Both CB2 Agonists and CB1 Antagonists.. The Journal of pharmacology and experimental therapeutics, 360(2), 300-311. https://doi.org/10.1124/jpet.116.236539