Effects of Repeated Treatment with the Monoacylglycerol Lipase Inhibitor MJN110 on Pain-Related Depression of Nesting and Cannabinoid 1 Receptor Function in Male and Female Mice.

MJN110 inhibits the enzyme monoacylglycerol lipase (MAGL) to increase levels of the endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG), an endogenous high-efficacy agonist of cannabinoid 1 and 2 receptors (CB1/2R). MAGL inhibitors are under consideration as candidate analgesics, and we reported previously that acute MJN110 produced partial antinociception in an assay of pain-related behavioral depression in mice. Given the need for repeated analgesic administration in many pain patients and the potential for analgesic tolerance during repeated treatment, this study examined antinociceptive effects of repeated MJN110 on pain-related behavioral depression and CB1R-mediated G-protein function. Male and female ICR mice were treated daily for 7 days in a 2x2 design with (a) 1.0 mg/kg/day MJN110or its vehicle followed by (b) intraperitoneal injection of dilute lactic acid (IP acid) or its vehicle as a visceral noxious stimulus to depress nesting behavior. After behavioral testing, G-protein activity was assessed in lumbar spinal cord andfive brain regions using an assay of CP55,940-stimulated [35S]GTPÉ£S activation. As reported previously, acute MJN110 produced partial but significant relief of IP acid-induced nesting depression on Day 1. After 7 days, MJN110 continued to produce significant but partial antinociception in males, while antinociceptive tolerance developed in females. Repeated MJN110 also produced modest decreases in maximum levels of CP55,940-induced [35S]GTPÉ£S binding in spinal cord and most brain regions. These results indicate that repeated treatment with a relatively low antinociceptive MJN110 dose produces only partial and sex-dependent transient antinociception associated with the emergence of CB1R desensitization in this model of IP acid-induced nesting depression. Significance Statement The drug MJN110 inhibits monoacylglycerol lipase (MAGL) to increase levels of the endogenous cannabinoid 2-arachidonoylglycerol and produce potentially useful therapeutic effects including analgesia. This study used an assay of pain-related behavioral depression in mice to show that repeated MJN110 treatment produced (1) weak but sustained antinociception in male mice, (2) antinociceptive tolerance in females, and (3) modest cannabinoid-receptor desensitization that varied by region and sex. Antinociceptive tolerance may limit the utility of MJN110 for treatment of pain.

Molecular Pharmacology Profiling of Phenylfentanil and Its Analogues to Understand the Putative Involvement of an Adrenergic Mechanism in Fentanyl-Induced Respiratory Depression.

While there are approved therapeutics to treat opioid overdoses, the need for treatments to reverse overdoses due to ultrapotent fentanyls remains unmet. This may be due in part to an adrenergic mechanism of fentanyls in addition to their stereotypical mu-opioid receptor (MOR) effects. Herein, we report our efforts to further understanding of the functions these distinct mechanisms impart. Employing the known MOR neutral antagonist phenylfentanil as a lead, 17 analogues were designed based on the concept of isosteric replacement. To probe mechanisms of action, these analogues were pharmacologically evaluated in vitro and in vivo, while in silico modeling studies were also conducted on phenylfentanil. While it did not indicate MOR involvement in vivo, phenylfentanil yielded respiratory minute volumes similar to those caused by fentanyl. Taken together with molecular modeling studies, these results indicated that respiratory effects of fentanyls may also correlate to inhibition of both α1A- and α1B-adrenergic receptors.

Structural Alterations of the "Address" Moiety of NAN Leading to the Discovery of a Novel Opioid Receptor Modulator with Reduced hERG Toxicity.

The search for selective opioid ligands with desired pharmacological potency and improved safety profile has always been an area of interest. Our previous effort yielded a potent opioid modulator, NAN, a 6α-N-7'-indolyl-substituted naltrexamine derivative, which exhibited promising pharmacological activities both in vitro and in vivo. However, significant human ether-a-go-go-related gene (hERG) liability limited its further development. Therefore, a systematic structural modification on NAN was conducted in order to alleviate hERG toxicity while preserving pharmacological properties, which led to the discovery of 2'-methylindolyl derivative compound 21. Compared to NAN, compound 21 manifested overall improved pharmacological profiles. Follow-up hERG channel inhibition evaluation revealed a seven-fold decreased potency of compound 21 compared to NAN. Furthermore, several fundamental drug-like property evaluations suggested a reasonable ADME profile of 21. Collectively, compound 21 appeared to be a promising opioid modulator for further development as a novel therapeutic agent toward opioid use disorder treatments.

Rational Design, Chemical Syntheses, and Biological Evaluations of Peripherally Selective Mu Opioid Receptor Ligands as Potential Opioid Induced Constipation Treatment.

Opioid-induced constipation (OIC) is a common adverse effect of opioid analgesics. Peripherally acting µ opioid receptor antagonists (PAMORAs) can be applied in the treatment of OIC without compromising the analgesic effects. NAP, a 6ß-N-4-pyridyl-substituted naltrexamine derivative, was previously identified as a potent and selective MOR antagonist mainly acting peripherally but with some CNS effects. Herein, we introduced a highly polar aromatic moiety, for example, a pyrazolyl or imidazolyl ring to decrease CNS MPO scores in order to reduce passive BBB permeability. Four compounds 2, 5, 17, and 19, when administered orally, were able to increase intestinal motility during morphine-induced constipation in the carmine red dye assays. Among them, compound 19 (p.o.) improved GI tract motility by 75% while orally administered NAP and methylnaltrexone showed no significant effects at the same dose. Thus, this compound seemed a promising agent to be further developed as an oral treatment for OIC.

Design, Synthesis, and Biological Evaluation of NAP Isosteres: A Switch from Peripheral to Central Nervous System Acting Mu-Opioid Receptor Antagonists.

The µ opioid receptor (MOR) has been an intrinsic target to develop treatment of opioid use disorders (OUD). Herein, we report our efforts on developing centrally acting MOR antagonists by structural modifications of 17-cyclopropylmethyl-3,14-dihydroxy-4,5α-epoxy-6ß-[(4'-pyridyl) carboxamido] morphinan (NAP), a peripherally acting MOR-selective antagonist. An isosteric replacement concept was applied and incorporated with physiochemical property predictions in the molecular design. Three analogs, namely, 25, 26, and 31, were identified as potent MOR antagonists in vivo with significantly fewer withdrawal symptoms than naloxone observed at similar doses. Furthermore, brain and plasma drug distribution studies supported the outcomes of our design strategy on these compounds. Taken together, our isosteric replacement of pyridine with pyrrole, furan, and thiophene provided insights into the structure-activity relationships of NAP and aided the understanding of physicochemical requirements of potential CNS acting opioids. These efforts resulted in potent, centrally efficacious MOR antagonists that may be pursued as leads to treat OUD.

Exploring naltrexamine derivatives featuring azaindole moiety via nitrogen-walk approach to investigate their in vitro pharmacological profiles at the mu opioid receptor.

In the present work, we reported the application of a nitrogen-walk approach on developing a series of novel opioid ligands containing an azaindole moiety at the C6-position of the epoxymorphinan skeleton. In vitro study results showed that introducing a nitrogen atom around the indole moiety not only retained excellent binding affinity, but also led to significant functional switch at the mu opioid receptor (MOR). Further computational investigations provided corroborative evidence and plausible explanations of the results of the in vitro studies. Overall, our current work implemented a series of novel MOR ligands with high binding affinity and considerably low efficacy, which may shed light on rational design of low efficacy MOR ligands for opioid use disorder therapeutics.

Verifying the role of 3-hydroxy of 17-cyclopropylmethyl-4,5α-epoxy-3,14ß-dihydroxy-6ß-[(4'-pyridyl) carboxamido]morphinan derivatives via their binding affinity and selectivity profiles on opioid receptors.

In the present study, the role of 3-hydroxy group of a series of epoxymorphinan derivatives in their binding affinity and selectivity profiles toward the opioid receptors (ORs) has been investigated. It was found that the 3-hydroxy group was crucial for the binding affinity of these derivatives for all three ORs due to the fact that all the analogues 1a-e exhibited significantly higher binding affinities compared to their counterpart 3-dehydroxy ones 6a-e. Meanwhile most compounds carrying the 3-hydroxy group possessed similar selectivity profiles for the kappa opioid receptor over the mu opioid receptor as their corresponding 3-dehydroxy derivatives. [35S]-GTPγS functional assay results indicated that the 3-hydroxy group of these epoxymorphinan derivatives was important for maintaining their potency on the ORs with various effects. Further molecular modeling studies helped comprehend the remarkably different binding affinity and functional profiles between compound 1c (NCP) and its 3-dehydroxy analogue 6c.

Exploring the putative mechanism of allosteric modulations by mixed-action kappa/mu opioid receptor bitopic modulators.

The modulation and selectivity mechanisms of seven mixed-action kappa opioid receptor (KOR)/mu opioid receptor (MOR) bitopic modulators were explored. Molecular modeling results indicated that the 'message' moiety of seven bitopic modulators shared the same binding mode with the orthosteric site of the KOR and MOR, whereas the 'address' moiety bound with different subdomains of the allosteric site of the KOR and MOR. The 'address' moiety of seven bitopic modulators bound to different subdomains of the allosteric site of the KOR and MOR may exhibit distinguishable allosteric modulations to the binding affinity and/or efficacy of the 'message' moiety. Moreover, the 3-hydroxy group on the phenolic moiety of the seven bitopic modulators induced selectivity to the KOR over the MOR.