Different forms of the breast cancer drug tamoxifen and its metabolites bind to cannabinoid receptors with varying selectivity, suggesting this drug's chemical structure could serve as a blueprint for developing new cannabinoid-based medicines.
Read this if you follow cannabinoid pharmacology research or drug development pipelines for new cannabinoid-based medicines.
Tamoxifen scaffold binds to both CB1 and CB2 receptors with isomer-specific selectivity
What the researchers found
Tamoxifen is primarily known as a breast cancer drug, but this study revealed that its chemical structure interacts with cannabinoid receptors in ways that could be therapeutically useful.
The researchers tested tamoxifen's two mirror-image forms (isomers) and their metabolic breakdown products at both CB1 and CB2 cannabinoid receptors. They found that different forms showed different receptor preferences. One metabolite (Z-4OHT) had notably higher affinity for both receptor types, while another (endoxifen) was relatively CB1-selective.
All tested forms acted as inverse agonists at both CB1 and CB2 receptors, meaning they reduce the baseline activity of these receptors. One form (Z-tamoxifen) was more potent than a well-known reference compound (AM630) at CB2 receptors.
Why it matters
This research opens a new avenue for cannabinoid drug development. Rather than starting from scratch, medicinal chemists could use tamoxifen's chemical scaffold as a starting point to design drugs that precisely target cannabinoid receptors, potentially avoiding the psychoactive effects of THC while harnessing therapeutic benefits.
The numbers in context
Z-4OHT showed higher affinity for both CB1 and CB2 receptors compared to E-isomers. Endoxifen isomers were relatively CB1-selective. Z-tamoxifen exceeded the efficacy of the full inverse agonist AM630 at CB2 receptors. Z-tamoxifen and Z-endoxifen showed insurmountable antagonism at CB1 and CB2 receptors respectively.
How the study worked
Laboratory study using cell-based assays to measure binding affinity, G-protein activation, and effects on adenylyl cyclase signaling at human CB1 and CB2 cannabinoid receptors. Different isomers and metabolites of tamoxifen were systematically compared.
What this study cannot tell us
All experiments were conducted in cell cultures, not in living organisms. The concentrations needed for cannabinoid receptor effects may differ from those achieved during normal tamoxifen therapy. The therapeutic relevance of these interactions remains to be tested in animal models.
How to read the evidence
Cell-based laboratory study demonstrating receptor binding and functional activity. No in vivo data yet.
When this study was published
Published in 2016. This line of research represents early-stage drug discovery that typically takes years to translate to clinical applications.
The bigger picture
The discovery that existing FDA-approved drug structures interact with cannabinoid receptors could accelerate drug development. This approach of repurposing known chemical scaffolds has successfully produced new medicines in other therapeutic areas.
Questions still open
- Do patients taking tamoxifen for breast cancer experience any effects mediated through cannabinoid receptors? Could tamoxifen-derived compounds be designed to selectively target one cannabinoid receptor type?
Common questions
Why is a breast cancer drug relevant to cannabinoid research?
Could this lead to new medicines?
Read the original research
Tamoxifen Isomers and Metabolites Exhibit Distinct Affinity and Activity at Cannabinoid Receptors: Potential Scaffold for Drug Development.
PloS one, 11(12), e0167240
Citation
Ford, Benjamin M; Franks, Lirit N; Radominska-Pandya, Anna; Prather, Paul L. (2016). Tamoxifen Isomers and Metabolites Exhibit Distinct Affinity and Activity at Cannabinoid Receptors: Potential Scaffold for Drug Development.. PloS one, 11(12), e0167240. https://doi.org/10.1371/journal.pone.0167240
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