Researchers Create First Chemical Tools to Map the CB1 Receptor's Allosteric Binding Site | Research

The takeaway

Scientists designed and synthesized the first covalent chemical probes capable of permanently binding to the CB1 receptor's allosteric site, with the lead compound GAT100 showing exceptional potency as a negative allosteric modulator.

Read this if you follow cannabinoid receptor pharmacology and drug development research.

First covalent probes for the CB1 allosteric site, with GAT100 as lead compound

What the researchers found

The CB1 receptor has a primary (orthosteric) binding site where THC and most cannabinoid drugs bind, and a secondary (allosteric) site where modulators can fine-tune receptor activity. But the exact location and structure of this allosteric site has been unknown.

This study created the first chemical tools to map this site. Researchers designed covalent probes, compounds that permanently attach to specific amino acids, based on two known allosteric modulators (Org27569 and PSNCBAM-1).

The lead compound, GAT100, emerged as a highly potent negative allosteric modulator that, unlike its parent compounds, did not exhibit inverse agonism (reducing baseline receptor activity). It also enhanced binding of orthosteric agonists. These properties make GAT100 a valuable research tool for understanding allosteric modulation and a potential starting point for drug development.

Why it matters

Mapping the CB1 allosteric site is essential for designing next-generation cannabinoid drugs that could modulate the receptor with more precision and fewer side effects than current drugs. GAT100 is the key that could unlock this understanding.

The numbers in context

GAT100 identified as lead compound from a focused library. Most potent negative allosteric modulator in GTPgammaS and beta-arrestin assays. Reduced inverse agonism compared to Org27569. Positive allosteric modulation of CP55,940 binding.

How the study worked

Medicinal chemistry study involving rational design, synthesis, and pharmacological characterization of covalent CB1 allosteric ligands. Compounds were tested in radioligand binding, GTPgammaS functional assays, and beta-arrestin recruitment assays.

What this study cannot tell us

In vitro study with no in vivo validation. Covalent probes permanently modify the receptor, which limits their therapeutic potential but makes them valuable research tools. The allosteric site structure remains to be fully characterized.

How to read the evidence

Novel medicinal chemistry achievement with thorough pharmacological characterization, but entirely in vitro.

When this study was published

Published in 2016. GAT100 and related probes have since been used in further structural and functional studies of the CB1 receptor.

The bigger picture

Allosteric modulators represent the next frontier in cannabinoid pharmacology. By developing tools to map exactly where and how these modulators bind, researchers can move from serendipitous discovery to rational drug design for conditions ranging from pain to neurodegeneration.

Questions still open

Will GAT100 successfully map the allosteric site through structural studies? Could non-covalent analogs of GAT100 be developed as therapeutic drugs? What is the three-dimensional structure of the CB1 allosteric site?

Common questions

What is an allosteric site and why does it matter?

It's a secondary binding pocket on the CB1 receptor, separate from where THC binds. Drugs targeting this site could fine-tune receptor activity more precisely than THC or other direct-acting drugs, potentially with fewer side effects.

What makes GAT100 special?

It's the first tool capable of permanently attaching to the CB1 allosteric site, allowing researchers to map its exact location. It also has improved properties compared to previous allosteric modulators, including reduced unwanted inverse agonism.

Read the original research

Novel Electrophilic and Photoaffinity Covalent Probes for Mapping the Cannabinoid 1 Receptor Allosteric Site(s).

Journal of medicinal chemistry, 59(1), 44-60

View on PubMed ↗Publisher’s paper ↗

Citation

Kulkarni, Pushkar M; Kulkarni, Abhijit R; Korde, Anisha; Tichkule, Ritesh B; Laprairie, Robert B; Denovan-Wright, Eileen M; Zhou, Han; Janero, David R; Zvonok, Nikolai; Makriyannis, Alexandros; Cascio, Maria G; Pertwee, Roger G; Thakur, Ganesh A. (2016). Novel Electrophilic and Photoaffinity Covalent Probes for Mapping the Cannabinoid 1 Receptor Allosteric Site(s).. Journal of medicinal chemistry, 59(1), 44-60. https://doi.org/10.1021/acs.jmedchem.5b01303