A CB2 receptor drug suppressed neuropathic pain without tolerance and prevented morphine tolerance in mice
A mouse study found that the CB2 cannabinoid agonist LY2828360 suppressed chemotherapy-induced neuropathic pain for 12 days without tolerance, prevented morphine tolerance when co-administered, and remained effective in mice already tolerant to morphine.
Quick Facts
What This Study Found
Researchers characterized LY2828360, a CB2 cannabinoid receptor agonist that had previously failed in a clinical trial for osteoarthritis due to lack of efficacy.
In vitro, LY2828360 was identified as a "G protein-biased" agonist: it activated G protein signaling but did not recruit arrestin, a pattern that may explain its sustained efficacy.
In mice with chemotherapy-induced neuropathic pain (from paclitaxel), LY2828360 at 3 mg/kg/day for 12 days suppressed pain without developing tolerance. The effect was absent in CB2 knockout mice, confirming it worked through CB2 receptors.
When co-administered with morphine, LY2828360 prevented morphine tolerance from developing. LY2828360 also remained effective in mice that were already tolerant to morphine.
There was a trend toward reduced morphine dependence (fewer naloxone-precipitated withdrawal jumps) in mice receiving both drugs.
Key Numbers
LY2828360 at 3 mg/kg/day for 12 days: sustained pain relief without tolerance. Co-administration with morphine (10 mg/kg/day): morphine tolerance blocked in wild-type but not CB2 knockout mice. Trend toward reduced withdrawal signs (p = 0.055).
How They Did This
Mouse study using CB2 knockout and wild-type mice. Paclitaxel-induced neuropathic pain model. In vitro receptor characterization (cAMP, ERK1/2, arrestin recruitment, inositol phosphate, receptor internalization). 12-day chronic dosing paradigms.
Why This Research Matters
Opioid tolerance is a major clinical problem: patients need escalating doses for the same pain relief, increasing addiction and overdose risk. A drug that both treats neuropathic pain independently and prevents opioid tolerance could transform pain management, particularly for cancer patients on chemotherapy.
The Bigger Picture
The failure of LY2828360 in an osteoarthritis trial does not mean it is a failed drug. This study suggests it may be effective for a different pain type (neuropathic) and as an adjunct to opioids. The G protein-biased signaling mechanism is increasingly recognized as important for sustained drug efficacy.
What This Study Doesn't Tell Us
Mouse model of chemotherapy pain may not translate directly to human neuropathic pain. LY2828360 previously failed in a human osteoarthritis trial. The trend toward reduced morphine dependence did not reach statistical significance (p = 0.055). CB2 agonists can have immunosuppressive effects not assessed here.
Questions This Raises
- ?Would LY2828360 show efficacy in human neuropathic pain trials?
- ?Can the G protein-biased mechanism be leveraged to develop more effective CB2 drugs?
- ?Would combining a CB2 agonist with opioids in human pain management actually reduce opioid tolerance?
Trust & Context
- Key Stat:
- 12 days of pain relief without tolerance, and morphine tolerance blocked by co-administration
- Evidence Grade:
- Moderate. Well-designed preclinical study with knockout controls and mechanistic characterization, though clinical translation from mouse to human is uncertain.
- Study Age:
- Published in 2018. G protein-biased CB2 agonism has continued to be an active area of cannabinoid pharmacology research.
- Original Title:
- Slowly Signaling G Protein-Biased CB2 Cannabinoid Receptor Agonist LY2828360 Suppresses Neuropathic Pain with Sustained Efficacy and Attenuates Morphine Tolerance and Dependence.
- Published In:
- Molecular pharmacology, 93(2), 49-62 (2018)
- Authors:
- Lin, Xiaoyan(3), Dhopeshwarkar, Amey S(2), Huibregtse, Megan, Mackie, Ken, Hohmann, Andrea G
- Database ID:
- RTHC-01732
Evidence Hierarchy
Tests effects in animals (usually mice or rats), not humans.
What do these levels mean? →Frequently Asked Questions
What does "G protein-biased" mean?
Receptors can activate multiple signaling pathways inside cells. A G protein-biased drug activates the G protein pathway but not the arrestin pathway. This matters because arrestin signaling is often responsible for tolerance (the drug stops working over time). By avoiding arrestin, LY2828360 may provide sustained pain relief.
If this drug failed for arthritis pain, why test it for neuropathic pain?
Different types of pain involve different mechanisms. Osteoarthritis pain is primarily inflammatory, while chemotherapy-induced neuropathic pain involves nerve damage. CB2 receptors play different roles in these contexts, so a drug that fails for one pain type may succeed for another.
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Cite This Study
https://rethinkthc.com/research/RTHC-01732APA
Lin, Xiaoyan; Dhopeshwarkar, Amey S; Huibregtse, Megan; Mackie, Ken; Hohmann, Andrea G. (2018). Slowly Signaling G Protein-Biased CB2 Cannabinoid Receptor Agonist LY2828360 Suppresses Neuropathic Pain with Sustained Efficacy and Attenuates Morphine Tolerance and Dependence.. Molecular pharmacology, 93(2), 49-62. https://doi.org/10.1124/mol.117.109355
MLA
Lin, Xiaoyan, et al. "Slowly Signaling G Protein-Biased CB2 Cannabinoid Receptor Agonist LY2828360 Suppresses Neuropathic Pain with Sustained Efficacy and Attenuates Morphine Tolerance and Dependence.." Molecular pharmacology, 2018. https://doi.org/10.1124/mol.117.109355
RethinkTHC
RethinkTHC Research Database. "Slowly Signaling G Protein-Biased CB2 Cannabinoid Receptor A..." RTHC-01732. Retrieved from https://rethinkthc.com/research/lin-2018-slowly-signaling-g-proteinbiased
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.