Daniel Deaver

Naltrexone decreases D-amphetamine and ethanol self-administration in rhesus monkeys.

Amphetamines are the second most highly abused illicit drugs worldwide, yet there is no pharmacological treatment for amphetamine abuse and dependence. Preclinical studies and, more recently, human studies, suggest that the opioid receptor antagonist, naltrexone, might be useful in the treatment of amphetamine abuse. Naltrexone, an opioid receptor antagonist, is currently used for the treatment of alcohol dependence. The aim of this study was to explore the ability of naltrexone to modify self-administration of amphetamine or ethanol in rhesus monkeys. Monkeys were trained to respond to intravenous injections of either D-amphetamine (0.003 mg/kg/injection) or ethanol (0.05 g/kg/injection) on a fixed ratio 30 schedule. Naltrexone (0.01–1 mg/kg) was administered intramuscularly 30 min before the start of treatment test sessions. Naltrexone dose-dependently decreased both amphetamine and ethanol self-administration. These findings support the potential use of naltrexone as therapy for amphetamine and polydrug abuse.

Route of administration affects the ability of naltrexone to reduce amphetamine-potentiated brain stimulation reward in rats.

Opioid receptor antagonism has been shown to attenuate behavioral and neurochemical effects of amphetamine in humans and rodents. The effects of acute (oral or subcutaneous) or extended‐release naltrexone (XR‐NTX) were tested on the reward‐enhancing effects of amphetamine using the intracranial self‐stimulation (ICSS) paradigm. Acute exposure to drugs of abuse reduces the locus of rise (LOR) in the ICSS procedure, reflecting enhanced brain stimulation reward (BSR). Rats were treated once a day with naltrexone orally (PO; 5.0 mg/kg) or subcutaneously (SC; 0.5 mg/kg) for four consecutive days and tested with D‐amphetamine (0.5 mg/kg, intraperitoneal) in the ICSS paradigm 30 minutes later on days 1 and 4. Separate groups of rats received XR‐NTX (50 mg/kg, SC) or placebo microspheres (similar mass to XR‐NTX, SC) on day 0 and tested with D‐amphetamine in the ICSS paradigm on days 4, 14, 21, 28 and 41 after administration. Naltrexone plasma concentrations were determined for each amphetamine testing session using liquid chromatography‐mass spectrometry/mass spectrometry (LC‐MS/MS). In rats pretreated with naltrexone acutely, amphetamine‐potentiated BSR did not differ from vehicle‐pretreated rats on either day 1 or day 4 (25–30% decrease in LOR). In XR‐NTX‐pretreated rats, amphetamine‐potentiated BSR was reduced by 64 and 70% on days 4 and 14, respectively, compared to placebo microsphere‐treated controls. This effect dissipated by day 21. Naltrexone plasma concentrations were comparable across all treatment groups (14–30 ng/ml) on days 1, 4 and 14. In summary, an extended‐release formulation of naltrexone results in significant attenuation of psychostimulant‐enhanced BSR that is not observed with acute naltrexone.

Long-Acting Atypical Antipsychotics: Characterization of the Local Tissue Response

PurposeLong-acting injectables (LAIs) are increasingly recognized as an effective therapeutic approach for treating chronic conditions. Many LAIs are formulated to create a poorly soluble depot from which the active agent is delivered over time. This long residing depot can cause localized chronic-active inflammation in the tissue, which has not been well defined in the literature. The purpose of this work is to establish an experimental baseline for describing these responses.MethodsNon-human primates and rodents were used to examine the response to LAI formulations of two clinically relevant atypical antipsychotics, aripiprazole monohydrate and olanzapine pamoate monohydrate.ResultsA foreign body response develops with elevations of key cytokines such as IL-1α, IL-1β, TNFα, and IL6 at the site of injection. However, the tissue response for the two atypical antipsychotics compounds diverge as evidenced by quantitative differences observed in cytokine levels at various time points after dosing.ConclusionsOur studies show that, while the drugs are in the same therapeutic class, the response to each of these compounds can be distinguished qualitatively and quantitatively, supporting the idea that the injection site reaction involves a multiplicity of factors including the properties of the compound and cellular dynamics at the site of injection.

Overriding the blockade of antinociceptive actions of opioids in rats treated with extended-release naltrexone.

A monthly extended-release formulation of the opioid antagonist naltrexone (XR-NTX) is approved for treatment of alcohol dependence. There is little research regarding overriding chronic (>21 days) competitive opioid receptor blockade with opioids for acute pain. Using the hot plate test after XR-NTX or placebo microsphere administration, rats were treated with an opioid analgesic to determine the dose required to produce the maximum response latency (MRL; 60 s). Rats were later treated with the same opioid to determine any potential effects on respiration rate or locomotor activity. In naïve rats, 15 mg/kg morphine, 0.1 mg/kg fentanyl and 8 mg/kg hydrocodone produced MRL. In XR-NTX treated rats, morphine produced 36% and 46% MRL at 90 mg/kg on days 4 and 19 and 96% MRL at 45 mg/kg on day 39. Fentanyl produced 100% MRL at 2.0 mg/kg on days 4 and 19 and at 0.5 mg/kg on day 39. Hydrocodone (80 mg/kg) produced 69%, 80% and 100% MRL on days 4, 19 and 39. Compared to placebo, these doses did not further depress respiration or alter locomotor activity. Thus, opioid receptor blockade with XR-NTX can be overcome in rats with higher doses of opioids without further affecting respiration or locomotor activity.

Failed trials for central nervous system disorders do not necessarily invalidate preclinical models and drug targets

A recent article identified five key technical determinants that make substantial contributions to the outcome of drug R&D projects (Lessons learned from the fate of AstraZeneca’s drug pipeline: a five-dimensional framework. Nat. Rev. Drug Discov. 13, 419–431 (2014))1. Careful consideration of such determinants might be particularly valuable in the fields of neurology and psychiatry, in which successful drug development has declined precipitously over the past decade. This decline has largely been fuelled by a high failure rate in the translation of preclinical efficacy findings, caused by multiple factors (see Supplementary information S1 (table)), including limited training and poor protocol design, inadequate animal models, insufficiently validated therapeutic targets and problems with data handling and reporting. Here, we focus on three factors that can be addressed immediately in order to reevaluate the therapeutic potential of older drugs and targets and to increase the probability of success for future preclinical-to-clinical translation: data robustness, data generalizability and target engagement data, a factor that was also highlighted in the recent article1. We argue that the many failed clinical trials in neuropsychiatry do not necessarily invalidate the potential of a drug target or an animal model. Rather, these failures indicate a need for improved experimental designs and a robust translational strategy to better inform compound and dose selection for clinical trials. We conclude that many of the drugs and targets in neuropsychiatry that have been discarded because of negative clinical trial outcomes may deserve re-evaluation using contemporary knowledge, methodology and tools.

Translational potential of naloxone and naltrexone as TLR4 antagonists

In the recent TiPS review by Watkins et al. [1], as well as subsequent reports [2] and reviews [3], opiate antagonists (naloxone and naltrexone) are claimed to inhibit Toll-like receptor 4 (TLR4) signaling in a nonstereoselective fashion. These claims are based on the foundational in vitro finding that both enantiomers effect a ‘…dose dependent blockade of TLR4 by LPS [lipopolysaccharide], a classical TLR4 agonist, as indicated by suppression of LPS-induced reporter protein in a TLR4 expressing cell line’ [1].

Effects of oral loperamide on efficacy of naltrexone, baclofen and AM-251 in blocking ethanol self-administration in rats

Naltrexone is a μ-opioid receptor antagonist that has been extensively studied for its ability to block the rewarding effects of ethanol. Opioid receptors are widely distributed within the gastrointestinal tract (GIT). Typically, naltrexone is administered by parenteral routes in nonclinical studies. We initially tested if opioid receptors within the GIT would influence the ability of oral naltrexone to inhibit ethanol oral self-administration in rats using the co-administration of oral loperamide, a peripherally restricted opioid agonist. As expected, oral naltrexone only had modest effects on ethanol intake, and the response was not dose-dependent. However in rats, treatment with loperamide prior to the administration of naltrexone resulted in a suppression of ethanol intake which approached that observed with naltrexone given by the subcutaneous (SC) route. Importantly, administration of loperamide prior to administration of naltrexone did not alter blood concentrations of naltrexone. We then evaluated if oral loperamide would enhance effects of baclofen (a GABA(B) receptor agonist) and AM-251 (a CB-1 receptor antagonist) and found that pre-treatment with loperamide did potentiate the action of both drugs to reduce ethanol self-administration. Finally, the specific opioid receptor type involved was investigated using selective μ- and κ-receptor antagonists to determine if these would affect the ability of the AM-251 and loperamide combination to block ethanol drinking behavior. The effect of loperamide was blocked by ALKS 37, a peripherally restricted μ-receptor antagonist. These data suggest an important role for opioid receptors within the GIT in modulating central reward pathways and may provide new insights into strategies for treating reward disorders, including drug dependency.

Antidepressant-like effects of 3-carboxamido seco-nalmefene (3CS-nalmefene), a novel opioid receptor modulator, in a rat IFN-α-induced depression model

Patients receiving the cytokine immunotherapy, interferon-alpha (IFN-α) frequently present with neuropsychiatric consequences and cognitive impairments. Patients (25-80%) report symptoms of depression, including, anhedonia, irritability, fatigue and impaired motivation. Our lab has previously demonstrated treatment (170,000IU/kg sc, 3 times per week for 4weeks) of the pro-inflammatory cytokine, IFN-α, induced a depressive phenotype in rats in the forced swim test (FST). Here, we examine the biological mechanisms underlying behavioral changes induced by IFN-α, which may be reflective of mechanisms underlying inflammation associated depression. We also investigate the potential of 3-carboxamido seco-nalmefene (3CS-nalmefene), a novel opioid modulator (antagonist at mu and partial agonist at kappa and delta opioid receptors in vitro), to reverse IFN-α induced changes. In vitro radioligand receptor binding assays and the [35S] GTPγS were performed to determine the affinity of 3CS-nalmefene for the mu, kappa and delta opioid receptors. IFN-α treatment increased circulating and central markers of inflammation and hypothalamic-pituitaryadrenal (HPA) axis activity (IL-6, IL-1β and corticosterone) while increasing immobility in the FST, impairing of object displacement learning in the object exploration task (OET), and decreasing neuronal proliferation and brain-derived neurotrophic factor (BDNF) in the hippocampus. Treatment with 3CS-nalmefene (0.3mg/kg/sc twice per day, 3 times per week for 4weeks) prevented IFN-α-induced immobility in the FST and impaired object displacement learning. In addition, 3CS-nalmefene prevented IFN-α-induced increases in inflammation and hyperactivity of the HPA-axis, the IFN-α-induced reduction in both neuronal proliferation and BDNF expression in the hippocampus. Overall, these preclinical data would support the hypothesis that opioid receptor modulation is a relevant target for treatment of depression.

In Vitro Pharmacological Characterization of Buprenorphine, Samidorphan, and Combinations Being Developed as an Adjunctive Treatment of Major Depressive Disorder

A combination of buprenorphine (BUP) and samidorphan (SAM) at a 1:1 (mg/mg) fixed-ratio dose is being investigated as an adjunctive treatment of major depressive disorder (BUP/SAM, ALKS 5461). Both [3H]BUP and [3H]SAM bound to the μ-, κ-, and δ-opioid receptors (MOR, KOR, and DOR, respectively) with Kd values of 3 nM or less. [3H]BUP dissociated from the MOR more slowly than [3H]SAM did. In the [35S]GTPγS assay, BUP was a partial agonist at the MOR, KOR, and DOR. SAM was an antagonist at the MOR and a partial agonist at the KOR and DOR. The pharmacology of the combination of SAM and BUP was characterized at ratios like the molar ratios of both compounds at steady state in humans. In all assessments, SAM reduced the efficacy of BUP at the MOR without altering its potency. At the KOR, SAM had no significant effect on the activity of BUP. In bioluminescent resonance energy transfer assays, SAM, naltrexone, and naloxone were partial agonists when the MOR was coupled to the GαoB and Gαz, and were antagonists when coupled to Gαi. At the KOR, SAM was a partial agonist activating GαoA and GαoB and a full agonist in stimulating Gαz. SAM inhibited BUP’s recruitment of β-arrestin to the MOR, suggesting an attenuation of BUP’s efficacy in activating G proteins correlated with an inhibition of β-arrestin recruitment. The collective data suggest that SAM attenuates the efficacy of BUP under all conditions tested at the MOR and DOR but had little effect on BUP activity at the KOR.

Evaluation of samidorphan, a μ-opioid antagonist, in a drug discrimination assay in rats

Preclinical Research & Development