The Opioid Crisis and the Future of Addiction and Pain Therapeutics

Self-Medication for Chronic Pain Using Classic Psychedelics: A Qualitative Investigation to Inform Future Research

Background: Chronic Pain is among the leading causes of disability worldwide with up to 60% of patients suffering from comorbid depression. Psychedelic-assisted therapy has recently been found effective in treating a host of mental health issues including depression and has historically been found to be useful in treating pain. Reports of self-medication for chronic pain using psychedelic drugs have been widely documented, with anecdotal evidence indicating widespread success in a range of pathologies. Aims: In preparation for an upcoming trial, to better understand how those with lived experience of chronic pain self-medicate with psychedelic drugs, and to establish, in detail, their therapeutic protocols and practices for success. Methods: As part of patient-involvement (PI) for an upcoming trial in this population, 11 individuals who reported self-medicating with psychedelic drugs took part in a 1-h semi-structured discussion, which was then transcribed and thematically analyzed. Results: Across a range of psychedelic substances and doses, reported pain scores improved substantially during and after psychedelic experiences. Two processes, Positive Reframing and Somatic Presence, were reliably identified as playing a role in improvements in mental wellbeing, relationship with pain, and physical (dis)comfort. Inclusion of other strategies such as mindfulness, breathwork, and movement were also widely reported. Due to the data's subjective nature, this paper is vulnerable to bias and makes no claims on causality or generalisability. Together, these results have been used to inform study design for a forthcoming trial. Conclusion: This pre-trial PI work gives us confidence to test psychedelic therapy for chronic pain in a forthcoming controlled trial. The results presented here will be instrumental in improving our ability to meet the needs of future study participants.

Optimized Opioid-Neurotensin Multitarget Peptides: From Design to Structure-Activity Relationship Studies

Fusion of nonopioid pharmacophores, such as neurotensin, with opioid ligands represents an attractive approach for pain treatment. Herein, the μ-/δ-opioid agonist tetrapeptide H-Dmt-d-Arg-Aba-β-Ala-NH2 (KGOP01) was fused to NT(8-13) analogues. Since the NTS1 receptor has been linked to adverse effects, selective MOR-NTS2 ligands are preferred. Modifications were introduced within the native NT sequence, particularly a β3-homo amino acid in position 8 and Tyr11 substitutions. Combination of β3hArg and Dmt led to peptide 7, a MOR agonist, showing the highest NTS2 affinity described to date (Ki = 3 pM) and good NTS1 affinity (Ki = 4 nM), providing a >1300-fold NTS2 selectivity. The (6-OH)Tic-containing analogue 9 also exhibited high NTS2 affinity (Ki = 1.7 nM), with low NTS1 affinity (Ki = 4.7 μM), resulting in an excellent NTS2 selectivity (>2700). In mice, hybrid 7 produced significant and prolonged antinociception (up to 8 h), as compared to the KGOP01 opioid parent compound.

GRKs as Key Modulators of Opioid Receptor Function

Understanding the link between agonist-induced phosphorylation of the mu-opioid receptor (MOR) and the associated physiological effects is critical for the development of novel analgesic drugs and is particularly important for understanding the mechanisms responsible for opioid-induced tolerance and addiction. The family of G protein receptor kinases (GRKs) play a pivotal role in such processes, mediating phosphorylation of residues at the C-tail of opioid receptors. Numerous strategies, such as phosphosite specific antibodies and mass spectrometry have allowed the detection of phosphorylated residues and the use of mutant knock-in mice have shed light on the role of GRK regulation in opioid receptor physiology. Here we review our current understanding on the role of GRKs in the actions of opioid receptors, with a particular focus on the MOR, the target of most commonly used opioid analgesics such as morphine or fentanyl.

The α2,3-selective potentiators of GABAA receptors, KRM-II-81 and MP-III-80, produce anxiolytic-like effects and block chemotherapy-induced hyperalgesia in mice without tolerance development

Opiate analgesics are one of the treatment options for severe chronic pain, including late-stage cancer, chronic back pain and other disorders. The recent resurgence in opioid overdose has highlighted the serious need for alternative medicines for pain management. While a role for potentiators of α2/3-containing GABA_A receptors in the modulation of pain has been known for several years, advancements in this area required data from selective compounds. KRM-II-81(5-(8-ethynyl-6-(pyridin-2-yl)-4H-benzo[f]imidazo[1,5-a][1,4]diazepin-3- yl)oxazole) and analogs selectively potentiate GABA_A receptors containing α2/3 subunits and have recently been shown to attenuate pain behaviors in several acute and chronic pain models in rodents. The present study was designed to ascertain whether KRM-II-81 and the structural analog MP-III-80 (3-ethyl-5-(8-ethynyl-6-(pyridin-2-yl)-4H-benzo[f]imidazo[1,5-a][1,4]diazepin-3-yl)-1,2,4-oxadiazole) would block chemotherapeutic agent paclitaxel-induced pain in male, C57BL/6 mice. Both compounds significantly inhibited pain behaviors evoked by cold and tactile stimulation in paclitaxel-treated mice as did the neuropathic pain drug gabapentin. Subchronic dosing for 22 days with KRM-II-81 and MP-III-80 demonstrated enduring analgesic efficacy without tolerance development, while the effects of gabapentin showed evidence of tolerance development. KRM-II-81 and MP-III-80 also decreased marble-burying behavior in this mouse strain as did the anxiolytic drug chlordiazepoxide. In contrast to KRM-II-81 and MP-III-80, chlordiazepoxide had motor-impairing effects at anxiolytic-like doses. The data add to the literature documenting that these selective potentiators of α2/3-containing GABA_A receptors are effective in a host of animal models used to detect novel analgesic drugs. The anxiolytic-like efficacy of these compounds fits well with the comorbidity of anxiety in patients with chronic pain and cancer.

R-(-)-ketamine modifies behavioral effects of morphine predicting efficacy as a novel therapy for opioid use disorder1

Substance abuse disorder continues to have devastating consequences for individuals and society and current therapies are not sufficient to provide the magnitude of medical impact required. Although some evidence suggests the use of ketamine in treating various substance use related- symptoms, its adverse event profile including dissociation, dysphoria, and abuse liability limit its potential as a therapy. Here, we outline experiments to test our hypothesis that (R)-ketamine can both alleviate withdrawal symptoms and produce effects that help sustain abstinence. In morphine-dependent rats, (R)-ketamine alleviated naloxone-precipitated withdrawal signs. (R)-ketamine also blocked morphine-induced place preference in mice without inducing place preference on its own. We also evaluated whether (R)-ketamine would induce anhedonia, a counter-indicated effect for a drug abuse treatment agent. S-(+)- but not R-(-)-ketamine produced anhedonia-like responses in rats that electrically self-stimulated the medial forebrain bundle (ICSS). However, time-course studies of ICSS are needed to fully appreciate these differences. These data begin to support the claim that (R)-ketamine will dampen withdrawal symptoms and drug liking, factors known to contribute to the cycle of drug addiction. In addition, these data suggest that (R)-ketamine would not produce negative mood or anhedonia that could interfere with treatment. It is suggested that continued investigation of (R)-ketamine as a novel therapeutic for substance abuse disorder be given consideration by the preclinical and clinical research communities. This suggestion is further encouraged by a recent report on the efficacy of (R)-ketamine in treatment-resistant depressed patients at a dose with little measurable dissociative side-effects.