Evaluation of cannabimimetic effects of selected minor cannabinoids and Terpenoids in mice

BACKGROUND

The cannabis plant contains several cannabinoids, and many terpenoids that give cannabis its distinctive flavoring and aroma. Δ9-Tetrahydrocannabinol (Δ9-THC) is the plant's primary psychoactive constituent. Given the abuse liability of Δ9-THC, assessment of the psychoactive effects of minor cannabinoids and other plant constituents is important, especially for compounds that may be used medicinally. This study sought to evaluate select minor cannabinoids and terpenes for Δ9-THC-like psychoactivity in mouse Δ9-THC drug discrimination and determine their binding affinities at CB1 and CB2 receptors.

METHODS

Δ9-THC, cannabidiol (CBD), cannabinol (CBN), cannabichromene (CBC), cannabichromenevarin (CBCV), Δ8-tetrahydrocannabinol (Δ8-THC), (6aR,9R)-Δ10-tetrahydrocannabinol [(6aR,9R)-Δ10-THC], Δ9-tetrahydrocannabinol varin (THCV), β-caryophyllene (BC), and β-caryophyllene oxide (BCO) were examined.

RESULTS

All minor cannabinoids showed measurable cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptor binding, with CBC, CBCV, and CBD, showing the weakest CB1 receptor binding affinity. BC and BCO exhibited negligible affinity for both CB1 and CB2 receptors. In drug discrimination, only Δ8-THC fully substituted for Δ9-THC, while CBN and (6aR,9R)-Δ10-THC partially substituted for Δ9-THC. THCV and BCO did not alter the discriminative stimulus effects of Δ9-THC.

CONCLUSION

In summary, only some of myriad cannabinoids and other chemicals found in the cannabis plant bind potently to the identified cannabinoid receptors. Further, only four of the compounds tested herein [Δ9-THC, Δ8-THC, (6aR,9R)-Δ10-THC, and CBN] produced Δ9-THC-like discriminative stimulus effects, suggesting they may possess cannabimimetic subjective effects. Given that the medicinal properties of phytocannabinoids and terpenoids are being investigated scientifically, delineation of their potential adverse effects, including their ability to produce Δ9-THC-like intoxication, is crucial.

mGlu2 and mGlu3 receptor negative allosteric modulators attenuate the interoceptive effects of alcohol in male and female rats

RATIONALE

The subjective effects of alcohol are associated with alcohol use disorder (AUD) vulnerability and treatment outcomes. The interoceptive effects of alcohol are part of these subjective effects and can be measured in animal models using drug discrimination procedures. The newly developed mGlu2 and mGlu3 negative allosteric modulators (NAMs) are potential therapeutics for AUD and may alter interoceptive sensitivity to alcohol.

OBJECTIVES

To determine the effects of mGlu2 and mGlu3 NAMs on the interoceptive effects of alcohol in rats.

METHODS

Long-Evans rats were trained to discriminate the interoceptive stimulus effects of alcohol (2.0 g/kg, i.g.) from water using both operant (males only) and Pavlovian (male and female) drug discrimination techniques. Following acquisition training, an alcohol dose-response (0, 0.5, 1.0, 2.0 g/kg) experiment was conducted to confirm stimulus control over behavior. Next, to test the involvement of mGlu2 and mGlu3, rats were pretreated with the mGlu2-NAM (VU6001966; 0, 3, 6, 12 mg/kg, i.p.) or the mGlu3-NAM (VU6010572; 0, 3, 6, 12 mg/kg, i.p.) before alcohol administration (2.0 g/kg, i.g.).

RESULTS

In Pavlovian discrimination, male rats showed greater interoceptive sensitivity to 1.0 and 2.0 g/kg alcohol compared to female rats. Both mGlu2-NAM and mGlu3-NAM attenuated the interoceptive effects of alcohol in male and female rats using Pavlovian and operant discrimination. There may be a potential sex difference in response to the mGlu2-NAM at the highest dose tested.

CONCLUSIONS

Male rats may be more sensitive to the interoceptive effects of the 2.0 g/kg alcohol training dose compared to female rats. Both mGlu2-and mGlu3-NAM attenuate the interoceptive effects of alcohol in male and female rats. These drugs may have potential for treatment of AUD in part by blunting the subjective effects of alcohol.

Structure-activity relationships for locomotor stimulant effects and monoamine transporter interactions of substituted amphetamines and cathinones

Substitutions to the phenethylamine structure give rise to numerous amphetamines and cathinones, contributing to an ever-growing number of abused novel psychoactive substances. Understanding how various substitutions affect the pharmacology of phenethylamines may help lawmakers and scientists predict the effects of newly emerging drugs. Here, we established structure-activity relationships for locomotor stimulant and monoamine transporter effects of 12 phenethylamines with combinations of para-chloro, β-keto, N-methyl, or N-ethyl additions. Automated photobeam analysis was used to evaluate effects of drugs on ambulatory activity in mice, whereas in vitro assays were used to determine activities at transporters for dopamine (DAT), norepinephrine (NET), and 5-HT (SERT) in rat brain synaptosomes. In mouse studies, all compounds stimulated locomotion, except for 4-chloro-N-ethylcathinone. Amphetamines were more potent stimulants than their β-keto counterparts, while para-chloro amphetamines tended to be more efficacious than unsubstituted amphetamines. Para-chloro compounds also produced lethality at doses on the ascending limbs of their locomotor dose-effect functions. The in vitro assays showed that all compounds inhibited uptake at DAT, NET, and SERT, with most compounds also acting as substrates (i.e., releasers) at these sites. Unsubstituted compounds displayed better potency at DAT and NET relative to SERT. Para-chloro substitution or increased N-alkyl chain length augmented relative potency at SERT, while combined para-chloro and N-ethyl substitutions reduced releasing effects at NET and DAT. These results demonstrate orderly SAR for locomotor stimulant effects, monoamine transporter activities, and lethality induced by phenethylamines. Importantly, 4-chloro compounds produce toxicity in mice that suggests serious risk to humans using these drugs in recreational contexts.

Contingent administration of typical and biased kappa opioid agonists reduces cocaine and oxycodone choice in a drug vs. food choice procedure in male rhesus monkeys

RATIONALE

Combinations of mu and kappa-opioid receptor (KOR) agonists have been proposed as analgesic formulations with reduced abuse potential. The feasibility of this approach has been increased by the development of KOR agonists with biased signaling profiles that produce KOR-typical antinociception with fewer KOR-typical side effects.

OBJECTIVE

The present study determined if the biased KOR agonists, nalfurafine and triazole 1.1, could reduce choice for oxycodone in rhesus monkeys as effectively as the typical KOR agonist, salvinorin A.

METHODS

Adult male rhesus monkeys (N = 5) responded under a concurrent schedule of food delivery and intravenous cocaine injections (0.018 mg/kg/injection). Once trained, cocaine (0.018 mg/kg/injection) or oxycodone (0.0056 mg/kg/injection) was tested alone or in combination with contingent injections of salvinorin A (0.1-3.2 µg/kg/injection), nalfurafine (0.0032-0.1 µg/kg/injection), triazole 1.1 (3.2-100.0 µg/kg/injection), or vehicle. In each condition, the cocaine or oxycodone dose, as well as the food amount, was held constant across choice components, while the dose of the KOR agonist was increased across choice components.

RESULTS

Cocaine and oxycodone were chosen over food on more than 80% of trials when administered alone or contingently with vehicle. When KOR agonists were administered contingently with either cocaine or oxycodone, drug choice decreased in a dose-dependent manner. Salvinorin A and triazole 1.1 decreased drug-reinforcer choice without altering total trials completed (i.e., choice allocation shifted to food), while nalfurafine dose dependently decreased total trials completed.

CONCLUSIONS

These results demonstrate that salvinorin A and triazole 1.1, but not nalfurafine, selectively reduce cocaine and oxycodone self-administration independent of nonspecific effects on behavior, suggesting that G-protein bias does not appear to be a moderating factor in this outcome. Triazole 1.1 represents an important prototypical compound for developing novel KOR agonists as deterrents for prescription opioid abuse.

Cognitive-enhancing effects of acetylcholine receptor agonists in group-housed cynomolgus monkeys who drink ethanol

The cognitive impairments that are often observed in patients with alcohol use disorder (AUD) partially contribute to the extremely low rates of treatment initiation and adherence. Brain acetylcholine receptors (AChR) mediate and modulate cognitive and reward-related behavior and their distribution can be altered by long-term heavy drinking. Therefore, AChRs are promising pharmacotherapeutic targets for treating the cognitive symptoms of AUD. In the present study, the pro-cognitive efficacy of two AChR agonists, xanomeline and varenicline, were evaluated in group-housed monkeys who self-administered ethanol for more than one year. The muscarinic AChR antagonist scopolamine was used to disrupt performance of a serial stimulus discrimination and reversal (SDR) task designed to probe cognitive flexibility, defined as the ability to modify a previously learned behavior in response to a change in reinforcement contingencies. The ability of xanomeline and varenicline to remediate the disruptive effects of scopolamine was compared between dominant and subordinate monkeys, with lighter and heavier drinking histories, respectively. We hypothesized that subordinate monkeys would be more sensitive to all three drugs. Scopolamine dose-dependently impaired performance on the serial SDR task in all monkeys at doses lower than those that produced non-specific impairments (e.g, sedation); its potency did not differ between dominant and subordinate monkeys. However, both AChR agonists were effective in remediating the scopolamine-induced deficit in subordinate monkeys, but not in dominant monkeys. These findings suggest xanomeline and varenicline may be effective for enhancing cognitive flexibility in individuals with a history of heavy drinking. Significance Statement Pro-cognitive effects of two acetylcholine (Ach) receptor agonists were assessed in group-housed monkeys who had several years' experience drinking ethanol. The muscarinic ACh receptor agonist xanomeline and the nicotinic ACh receptor agonist varenicline reversed a cognitive deficit induced by the muscarinic ACh receptor antagonist scopolamine. However, this effect was observed only in lower-ranking (subordinate) monkeys and not higher-ranking (dominant monkeys). Results suggest that ACh agonists may effectively remediate alcohol-induced cognitive deficits in a subpopulation of those with alcohol use disorder.

The development of diphenyleneiodonium analogs as GPR3 agonists

G protein-coupled receptor 3 (GPR3) is an orphan receptor potentially involved in many important physiological processes such as drug abuse, neuropathic pain, and anxiety and depression related disorders. Pharmacological studies of GPR3 have been limited due to the restricted number of known agonists and inverse agonists for this constitutively active receptor. In this medicinal chemistry study, we report the discovery of GPR3 agonists based off the diphenyleneiodonium (DPI) scaffold. The most potent full agonist was the 3-trifluoromethoxy analog (32) with an EC50 of 260 nM and 90% efficacy compared to DPI. Investigation of a homology model of GPR3 from multiple sequence alignment resulted in the finding of a binding site rich in potential π-π and π-cation interactions stabilizing DPI-scaffold agonists. MMGBSA free energy analysis showed a good correlation with trends in observed EC50s. DPI analogs retained the same high receptor selectivity for GPR3 over GPR6 and GPR12 as observed with DPI. Collectively, the DPI analog series shows that order of magnitude improvements in potency with the scaffold were attainable; however, attempts to replace the iodonium ion to make the scaffold more druggable failed.

Methamphetamine and Designer Stimulants Modulate Tonic Human Cerebrovascular Smooth Muscle Contractility: Relevance to Drug-Induced Neurovascular Stress

To avoid criminal prosecution, clandestine chemists produce designer stimulants that mimic the pharmacological and psychoactive effects of conventional stimulants, such as methamphetamine. Following persistent or high-dose exposure, both acute vasoconstriction and loss of vascular homeostasis are reported dangers of conventional stimulants, and designer stimulants may pose even greater dangers. To compare the effects of a conventional stimulant and two designer stimulants on vascular contraction, this study examined the direct effects of 1,3-benzodioxolylbutanamine (BDB) and N-butylpentylone in comparison to methamphetamine on the function of human brain vascular smooth muscle cells (HBVSMCs). HBVSMCs suspended in collagen gels were exposed to varying concentrations of each drug, and the degree of constriction was assessed over one week. The MTT assay was used to measure the impact of the three drugs on the cellular metabolic activity as a marker of cellular toxicity. The highest concentration tested of either methamphetamine or N-butylpentylone produced a loss of HBVSMC contractility and impaired cellular metabolism. BDB showed a similar pattern of effects, but, uniquely, it also induced vasoconstrictive effects at substantially lower concentrations. Each drug produced direct effects on HBVSMC contraction that may be a mechanism by which the cardiovascular system is damaged following high-dose or persistent exposure, and this could be exacerbated by any sympathomimetic effects of these compounds in whole organisms. BDB appears to impact HBVSMC function in ways distinct from methamphetamine and N-butylpentylone, which may present unique dangers.

Distinct Effects of Methamphetamine Isomers on Limbic Norepinephrine and Dopamine Transmission in the Rat Brain

Methamphetamine (METH) is a psychostimulant that primarily exerts its effects on the catecholamine (dopamine (DA) and norepinephrine (NE)) systems, which are implicated in drug addiction. METH exists as two distinct enantiomers, dextrorotatory (d) and levorotatory (l). In contrast to d-METH, the major component of illicit METH used to induce states of euphoria and alertness, l-METH is available without prescription as a nasal decongestant and has been highlighted as a potential agonist replacement therapy to treat stimulant use disorder. However, little is known regarding l-METH's effects on central catecholamine transmission and behavior. In this study, we used fast-scan cyclic voltammetry to elucidate how METH isomers impact NE and DA transmission in two limbic structures, the ventral bed nucleus of the stria terminalis (vBNST) and nucleus accumbens (NAc), respectively, of anesthetized rats. In addition, the dose-dependent effects of METH isomers on locomotion were characterized. d-METH (0.5, 2.0, 5.0 mg/kg) enhanced both electrically evoked vBNST-NE and NAc-DA concentrations and locomotion. Alternatively, l-METH increased electrically evoked NE concentration with minimal effects on DA regulation (release and clearance) and locomotion at lower doses (0.5 and 2.0 mg/kg). Furthermore, a high dose (5.0 mg/kg) of d-METH but not l-METH elevated baseline NE and DA concentrations. These results suggest mechanistic differences between NE and DA regulation by the METH isomers. Moreover, l-METH's asymmetric regulation of NE relative to DA may have distinct implications in behaviors and addiction, which will set the neurochemical framework for future studies examining l-METH as a potential treatment for stimulant use disorders.

Effect of TRV130 and methadone on fentanyl-vs.-food choice and somatic withdrawal signs in opioid-dependent and post-opioid-dependent rats

The high efficacy mu-opioid receptor (MOR) agonist methadone is an effective opioid use disorder (OUD) medication used exclusively in opioid-dependent patients. However, methadone has undesirable effects that limit its clinical efficacy. Intermediate efficacy MOR agonists may treat OUD with fewer undesirable effects. We compared the effects of methadone with the intermediate efficacy MOR agonist TRV130 (oliceridine) on fentanyl-vs.-food choice and somatic withdrawal signs in opioid-dependent and post-opioid-dependent rats. Male rats (n = 20) were trained under a fentanyl-vs.-food choice procedure. Rats were then provided extended fentanyl (3.2 µg/kg/infusion) access (6 p.m.-6 a.m.) for 10 days to produce opioid dependence/withdrawal. Rats were treated with vehicle (n = 7), TRV130 (3.2 mg/kg; n = 8), or methadone (3.2 mg/kg; n = 5) three times per day after each extended-access session (8:30 a.m., 11 a.m., 1:30 p.m.). Withdrawal sign scoring (1:55 p.m.) and choice tests (2-4 p.m.) were conducted daily. Vehicle, TRV130, and methadone effects on fentanyl choice were redetermined in post-opioid-dependent rats. Vehicle-, TRV130-, and methadone-treated rats had similar fentanyl intakes during extended access. Vehicle-treated rats exhibited increased withdrawal signs and decreased bodyweights. Both methadone and TRV130 decreased these withdrawal signs. TRV130 was less effective than methadone to decrease fentanyl choice and increase food choice in opioid-dependent rats. Neither methadone nor TRV130 decreased fentanyl choice in post-opioid-dependent rats. Results suggest that higher MOR activation is required to reduce fentanyl choice than withdrawal signs in fentanyl-dependent rats. Additionally, given that TRV130 did not precipitate withdrawal in opioid-dependent rats, intermediate efficacy MOR agonists like TRV130 may facilitate the transition of patients with OUD from methadone to lower efficacy treatments like buprenorphine.

Tanshinone IIA exerts autophagic cell death through down-regulation of β-catenin in renal cell carcinoma cells

Renal cell carcinoma (RCC), also called kidney cancer, is one of the most common malignancies worldwide, including the United States and China. Because of the characteristics of RCC that are both insidious and largely insensitive to chemo-radiation, the incidence and mortality of RCC are increasing every year. However, there are few studies describing anti-cancer effects of the natural compounds on RCC as compared to other cancers. Here, we analyzed the anti-neoplastic impact of Tanshinone IIA (TSN) on RCC cells. We noted that TSN increased the expression of LC3 proteins while having little effect on PARP and Alix protein expression. We found that TSN up-regulated the expression of autophagy-related proteins such as Atg7 and Beclin-1. Moreover, TSN promoted the formation of autophagic vacuoles such as autophagosomes and autolysosomes. However, treatment with 3-Methyladenine (3-MA) or Chloroquine (CQ), slightly decreased the ability of TSN to induce autophagy, but still autophagy occurred. In addition, TSN inhibited translocation of β-catenin into the nucleus, and β-catenin deletion and TSN treatment in RCC increased the expression of LC3 protein. Overall our findings indicate that TSN can exert significant anti-tumor effects through down-regulation of β-catenin to induce autophagic cell death.

Identification of a Potent Human Trace Amine-Associated Receptor 1 Antagonist

Human trace amine-associated receptor subtype 1 (hTAAR1) is a G protein-coupled receptor that has therapeutic potential for multiple diseases, including schizophrenia, drug addiction, and Parkinson's disease (PD). Although several potent agonists have been identified and have shown positive results in various clinical trials for schizophrenia, the discovery of potent hTAAR1 antagonists remains elusive. Herein, we report the results of structure-activity relationship studies that have led to the discovery of a potent hTAAR1 antagonist (RTI-7470-44, 34). RTI-7470-44 exhibited an IC₅₀ of 8.4 nM in an in vitro cAMP functional assay, a K_i of 0.3 nM in a radioligand binding assay, and showed species selectivity for hTAAR1 over the rat and mouse orthologues. RTI-7470-44 displayed good blood-brain barrier permeability, moderate metabolic stability, and a favorable preliminary off-target profile. Finally, RTI-7470-44 increased the spontaneous firing rate of mouse VTA dopaminergic neurons and blocked the effects of the known TAAR1 agonist RO5166017. Collectively, this work provides a promising hTAAR1 antagonist probe that can be used to study TAAR1 pharmacology and the potential therapeutic role in hypodopaminergic diseases such as PD.

Sex differences in inflammatory cytokine levels following synthetic cathinone self-administration in rats

Synthetic cathinones are used as stimulants of abuse. Many abused drugs, including stimulants, activate nuclear factor-κB (NF-κB) transcription leading to increases in NF-κB-regulated pro-inflammatory cytokines, and the level of inflammation appears to correlate with length of abuse. The purpose of this study was to measure the profile of IL-1α, IL-1β, IL-6, CCL2 and TNF-α in brain and plasma to examine if drug exposure alters inflammatory markers. Male and female Sprague-Dawley rats were trained to self-administer α-pyrrolidinopentiophenone (α-PVP) (0.1 mg/kg/infusion), 4-methylmethcathinone (4MMC) (0.5 mg/kg/infusion), or saline through autoshaping, and then self-administered for 21 days during 1 h (short access; ShA) or 6 h (long access; LgA) sessions. Separate rats were assigned to a naïve control group. Cytokine levels were examined in amygdala, hippocampus, hypothalamus, prefrontal cortex, striatum, thalamus, and plasma. Rats acquired synthetic cathinone self-administration, and there were no sex differences in drug intake. Synthetic cathinone self-administration produced sex differences in IL-1α, IL-1β, IL-6, CCL2 and TNF-α levels. There were widespread increases in inflammatory cytokines in the brains of male rats compared to females, particularly for 4MMC, whereas females were more likely to show increased inflammatory cytokines in plasma compared to saline groups than males. Furthermore, these sex differences in cytokine levels were more common after LgA access to synthetic cathinones than ShA. These results suggest that synthetic cathinone use likely produces sex-selective patterns of neuroinflammation during the transition from use to abuse. Consequently, treatment need may differ depending on the progression of synthetic cathinone abuse and based on sex.

The kappa-opioid receptor agonist, triazole 1.1, reduces oxycodone self-administration and enhances oxycodone-induced thermal antinociception in male rats

RATIONALE

Triazole 1.1 is a novel kappa-opioid receptor (KOR) agonist reported to produce antinociception without KOR-typical adverse effects. When combined with the mu-opioid receptor (MOR) agonist, oxycodone, triazole 1.1 blocks oxycodone-induced pruritis without producing sedation-like effects in nonhuman primates. However, it is unknown if triazole 1.1 can reduce the abuse-related effects or enhance the antinociceptive effects of oxycodone similarly to other KOR agonists.

OBJECTIVES

The aim of the present study was to quantitatively compare the behavioral effects of triazole 1.1 to the KOR agonists, U50,488h and nalfurafine, on oxycodone self-administration and oxycodone-induced thermal antinociception when administered as mixtures with oxycodone.

METHODS

In the self-administration study, male Sprague-Dawley (SD) rats (n = 6) self-administered intravenous (i.v.) oxycodone alone (0.056 mg/kg/inj) or combined with U50,488 h (0.032-0.32 mg/kg/inj), nalfurafine (0.00032-0.0032 mg/kg/inj), or triazole 1.1 (0.32-1.8 mg/kg/inj) under a progressive-ratio schedule of reinforcement. In a hot plate assay, male SD rats (n = 6) received i.v. injections of oxycodone (1.0-5.6 mg/kg), U50,488h (1.0-18.0 mg/kg), nalfurafine (0.01-1.0 mg/kg), or triazole 1.1 (3.2-32.0 mg/kg) alone or in combinations of fixed proportion with oxycodone based on the relative potencies of the single drugs. Each study concluded with administration of the KOR antagonist nor-BNI and some degree of retesting of the previous conditions to verify that the behavioral effects were mediated by KOR activation.

RESULTS

All KOR agonists reduced oxycodone self-administration in a dose-dependent manner. Moreover, all single drugs and drug combinations produced dose-dependent, fully efficacious thermal antinociception. All KOR agonist:oxycodone combinations produced either additive or super-additive thermal antinociception. Finally, each KOR agonist was blocked in effect by nor-BNI in both behavioral measures.

CONCLUSION

This study demonstrates that triazole 1.1 reduces oxycodone's reinforcing effects and enhances oxycodone-induced antinociception to degrees that are comparable to typical KOR agonists. Given triazole 1.1's mild adverse-effect profile, developing MOR-KOR agonist combinations from the triazole 1.1 series may render new pain therapeutics with reduced abuse liability.

Potential function of oxymatrine as a novel suppressor of epithelial-to-mesenchymal transition in lung tumor cells

AIMS

Tumor cells metastasis as well as proliferation are important factors that can substantially determines the prognosis of cancer. In particular, epithelial-mesenchymal transition (EMT) is key phenomena which can cause tumor cell transition into other organs by promoting the disruption of the cell-cell junctions. Because oxymatrine (OMT) have been reported to attenuate the tumor growth, we investigated whether OMT can down-regulate EMT process in tumor cells. We also focused on transforming growth factor-β (TGF-β)-induced EMT process because EMT process can be significantly induced by this growth factor.

MAIN METHODS

The cell viability was measured by MTT and real time cell analysis (RTCA) assay. The expression levels of various proteins involved in the regulation of EMT and Akt/mTOR/PI3K signaling pathway were evaluated by Western blot analysis. mRNA levels of several important EMT markers were analyzed by reverse transcription polymerase chain reaction (RT-PCR). The effects of OMT on the cellular invasion and migration were evaluated by RTCA, wound healing assay, and boyden chamber assays.

KEY FINDINGS

OMT suppressed the expression of both constitutive and TGF-β-induced mesenchymal markers, such as fibronectin, vimentin, MMP-9, MMP-2, N-cadherin, Twist, and Snail, but induced the levels of epithelial markers. Moreover, OMT down-regulated oncogenic PI3K/Akt/mTOR pathways which lead to a significant attenuation of invasive and migratory potential of lung cancer cells.

SIGNIFICANCE

Overall, our study established a novel anti-metastatic role of OMT against human lung cancer cells.

Some effects of putative G-protein biased mu-opioid receptor agonists in male rhesus monkeys

G-protein-biased mu-opioid receptor (GPB-MOR) agonists are an emerging class of compounds being evaluated as candidate analgesics and agonist medications for opioid use disorder. Most of the basic pharmacology of GPB-MOR agonists has been conducted in rodents and much less is known how the basic behavioral pharmacology of these compounds translates to nonhuman primates. The present study determined the antinociceptive potency and time course of three putative GPB-MOR agonists: (+)-oliceridine (i.e. TRV130), SR14968, and SR17018 in male rhesus monkeys (n = 3). In addition, the respiratory effects of these compounds were also indirectly determined using a pulse oximeter to measure percent peripheral oxygen saturation (%SpO2). The largest intramuscular oliceridine dose (3.2 mg/kg) produced significant antinociception at 50°C, but not 54°C, and peak effects were between 10 and 30 min. Oliceridine also decreased SpO2 below the 90% threshold that would be clinically categorized as hypoxia in two out of three monkeys. The largest intramuscular SR14968 dose (0.32 mg/kg) produced 100% MPE at 50°C, but not 54°C, in two out of three monkeys, and peak effects were between 30 and 100 min. The largest intravenous SR17018 dose (1 mg/kg) produced 100% MPE at 50°C, but not 54°C, in the same two out of three monkeys, and peak effects were between 30 and 100 min. Solubility limitations for both SR14968 and SR17018 impaired our ability to determine in-vivo potency and effectiveness on antinociceptive and %SpO2 measures for these two compounds.

Overcoming reduced antibiotic susceptibility in intracellular Salmonella enterica serovar Typhimurium using AR-12

Host-directed therapies (HDTs) could enhance the activity of traditional antibiotics. AR-12 is a promising HDT against intracellular pathogens including Salmonella enterica serovar Typhimurium, and has been shown to act through modulation of autophagy and the Akt kinase pathway. Since AR-12 does not inhibit the growth of planktonic bacteria but only works in conjunction with the infected host-cell, we hypothesized that AR-12 could enhance the activity of antibiotics in less-susceptible strains in the intracellular host environment. We found that repetitive passaging of S. typhimurium in macrophages in the absence of antibiotics led to a 4-fold reduction in their intracellular susceptibility to streptomycin (STR), but had no effect on the bacteria's sensitivity to AR-12. Moreover, when the host-passaged strains were treated with a combined therapy of AR-12 and STR, there was a significant reduction of intracellular bacterial burden compared to STR monotherapy. Additionally, co-treatment of macrophages infected with multi-drug resistant S. typhimurium with AR-12 and STR or ampicillin showed enhanced clearance of the intracellular bacteria. The drug combination did not elicit this effect on planktonic bacteria. Overall, AR-12 enhanced the clearance of less susceptible S. typhimurium in an intracellular environment.

α-PPP and its derivatives are selective partial releasers at the human norepinephrine transporter: A pharmacological characterization of interactions between pyrrolidinopropiophenones and high and low affinity monoamine transporters

While classical cathinones, such as methcathinone, have been shown to be monoamine releasing agents at human monoamine transporters, the subgroup of α-pyrrolidinophenones has thus far solely been characterized as monoamine transporter reuptake inhibitors. Herein, we report data from previously undescribed α-pyrrolidinopropiophenone (α-PPP) derivatives and compare them with the pharmacologically well-researched α-PVP (α-pyrrolidinovalerophenone). Radiotracer-based in vitro uptake inhibition assays in HEK293 cells show that the investigated α-PPP derivatives inhibit the human high-affinity transporters of dopamine (hDAT) and norepinephrine (hNET) in the low micromolar range, with α-PVP being ten times more potent. Similar to α-PVP, no relevant pharmacological activity was found at the human serotonin transporter (hSERT). Unexpectedly, radiotracer-based in vitro release assays reveal α-PPP, MDPPP and 3Br-PPP, but not α-PVP, to be partial releasing agents at hNET (EC50 values in the low micromolar range). Furthermore, uptake inhibition assays at low-affinity monoamine transporters, i.e., the human organic cation transporters (hOCT) 1-3 and human plasma membrane monoamine transporter (hPMAT), bring to light that all compounds inhibit hOCT1 and 2 (IC50 values in the low micromolar range) while less potently interacting with hPMAT and hOCT3. In conclusion, this study describes (i) three new hybrid compounds that efficaciously block hDAT while being partial releasers at hNET, and (ii) highlights the interactions of α-PPP-derivatives with low-affinity monoamine transporters, giving impetus to further studies investigating the interaction of drugs of abuse with OCT1-3 and PMAT.

Reinforcing and Stimulant-Like Effects of Methamphetamine Isomers in Rhesus Macaques

Monoamine releasers such as d-methamphetamine (d-MA) can reduce cocaine use in laboratory studies and have been forwarded for the management of cocaine use disorder (CUD). However, the proven abuse liability of d-MA has limited enthusiasm for clinical use. The levorotatory isomer of MA, l-MA, appears to have lesser stimulant effects, possibly due to its preferential norepinephrine-releasing properties compared with dopamine. The present study evaluated the abuse potential of l-MA by comparing its reinforcing effects with known stimulant drugs of abuse in nonhuman primates. Adult rhesus macaques (N = 4) responded for intravenous injections of cocaine, d-MA, methcathinone (MCAT), or l-MA under a fixed-ratio (FR) schedule of reinforcement; reinforcing effectiveness was evaluated using behavioral economic demand procedures. In a separate cohort (N = 9), daily activity and food-reinforced responding were assessed during 100 days of treatment with daily dosages of l-MA (2.3 mg/kg per day, i.v.) or d-MA (0.74 mg/kg per day, i.v.) previously shown to decrease cocaine self-administration. Results show that all drugs maintained self-administration, with peak injections reaching ∼100 inj per session for cocaine, MCAT, and d-MA and ∼50 inj per session for l-MA . In demand studies, self-administration of each drug gradually decreased as FR size increased. The exponential model of demand indicated that the reinforcing effectiveness of l-MA was significantly less than the other drugs studied. Chronic l-MA treatment did not appreciably alter daily activity and only transiently suppressed food-reinforced responding. These data, coupled with previous findings that l-MA effectively reduces stimulant self-administration, suggest that l-MA, or other norepinephrine-preferring releasers, may serve as agonist medication for CUD with lesser abuse liability than common psychostimulants. SIGNIFICANCE STATEMENT: Development of pharmacotherapies for cocaine use disorder remains a formidable challenge. Agonist-based therapies show promise, but enthusiasm is tempered by the abuse liability of previously proposed medications. This study evaluated the abuse liability and chronic treatment effects of methamphetamine's levorotatory isomer (l-MA). l-MA demonstrated lower abuse liability compared with commonly abused stimulants and produced few untoward effects. In the context of recent studies demonstrating that l-MA attenuates stimulant self-administration, these findings support l-MA's potential as a pharmacotherapy for stimulant addiction.

Alpha-pyrrolidinopentiophenone and mephedrone self-administration produce differential neurochemical changes following short- or long-access conditions in rats

Stimulant-induced neurochemical changes may occur at different times for different brain regions or neurotransmitter systems. This study sought to examine the behavioral and neurochemical effects of extended access to α-pyrrolidinopentiophenone (α-PVP) and 4-methylmethcathinone (4MMC). Male and female Sprague-Dawley rats were trained to self-administer α-PVP (0.1 mg/kg/infusion) or 4MMC (0.5 mg/kg/infusion) through autoshaping, and then self-administered for 21 days during 1 h (short access; ShA) or 6 h (long access; LgA) sessions. Separate rats were assigned to a naïve control group. Amygdala, hippocampus, hypothalamus, prefrontal cortex (PFC), striatum, and thalamus were extracted, and tissue was analyzed with electrochemical detection and liquid chromatography mass spectrometry. Rats acquired self-administration of α-PVP and 4MMC, and LgA rats showed more escalation of self-administration than ShA rats. Synthetic cathinone administration produced several effects on neurotransmitters. LgA self-administration of α-PVP increased 5-HIAA levels in all brain regions, compared to control. In contrast, both LgA and ShA 4MMC self-administration decreased 5-HT and 5-HIAA levels in most brain regions. LgA exposure to both synthetic cathinones increased DOPAC levels in hypothalamus and striatum, and increased HVA levels in striatum compared to control. LgA self-administration of either synthetic cathinone produced region-specific increases in NE levels, whereas ShA self-administration lowered NE levels in select locations compared to control. These alterations in neurotransmitter levels indicate that synthetic cathinone use may produce differential neurochemical changes during the transition from use to abuse, and that 21 days of self-administration only models the beginning stages of dysregulated drug intake.

Chronic phenmetrazine treatment promotes D2 dopaminergic and α2-adrenergic receptor desensitization and alters phosphorylation of signaling proteins and local cerebral glucose metabolism in the rat brain

Phenmetrazine (PHEN) is a putative treatment for cocaine and psychostimulant recidivism; however, neurochemical changes underlying its activity have not been fully elucidated. We sought to characterize brain homeostatic adaptations to chronic PHEN, specifically on functional brain activity (local cerebral glucose utilization), G-Protein Coupled Receptor-stimulated G-protein activation, and phosphorylation of ERK1/2Thr202/Tyr204, GSK3βTyr216, and DARPP-32Thr34. Male Sprague-Dawley rats were implanted with sub-cutaneous minipumps delivering either saline (vehicle), acute (2-day) or chronic (14-day) low dose (25 mg/kg/day) or high dose (50 mg/kg/day) PHEN. Acute administration of high dose PHEN increased local cerebral glucose utilization measured by 2-[14C]-deoxyglucose uptake in basal ganglia and motor-related regions of the rat brain. However, chronically treated animals developed tolerance to these effects. To identify the neurochemical changes associated with PHEN's activity, we performed [35S]GTPγS binding assays on unfixed and immunohistochemistry on fixed coronal brain sections. Chronic PHEN treatment dose-dependently attenuated D2 dopamine and α2-adrenergic, but not 5-HT1A, receptor-mediated G-protein activation. Two distinct patterns of effects on pERK1/2 and pDARPP-32 were observed: 1) chronic low dose PHEN decreased pERK1/2, and also significantly increased pDARPP-32 levels in some regions; 2) acute and chronic PHEN increased pERK1/2, but chronic high dose PHEN treatment tended to decrease pDARPP-32. Chronic low dose, but not high dose, PHEN significantly reduced pGSK3β levels in several regions. Our study provides definitive evidence that extended length PHEN dosage schedules elicit distinct modes of neuronal acclimatization in cellular signaling. These pharmacodynamic modifications should be considered in drug development for chronic use.

In a Rat Model of Opioid Maintenance, the G Protein-Biased Mu Opioid Receptor Agonist TRV130 Decreases Relapse to Oxycodone Seeking and Taking and Prevents Oxycodone-Induced Brain Hypoxia

BACKGROUND

Maintenance treatment with opioid agonists (buprenorphine, methadone) is effective for opioid addiction but does not eliminate opioid use in all patients. We modeled maintenance treatment in rats that self-administered the prescription opioid oxycodone. The maintenance medication was either buprenorphine or the G protein-biased mu opioid receptor agonist TRV130. We then tested prevention of oxycodone seeking and taking during abstinence using a modified context-induced reinstatement procedure, a rat relapse model.

METHODS

We trained rats to self-administer oxycodone (6 hours/day, 14 days) in context A; infusions were paired with discrete tone-light cues. We then implanted osmotic pumps containing buprenorphine or TRV130 (0, 3, 6, or 9 mg/kg/day) and performed 3 consecutive tests: lever pressing reinforced by oxycodone-associated discrete cues in nondrug context B (extinction responding), context-induced reinstatement of oxycodone seeking in context A, and reacquisition of oxycodone self-administration in context A. We also tested whether TRV130 maintenance would protect against acute oxycodone-induced decreases in nucleus accumbens oxygen levels.

RESULTS

In male rats, buprenorphine and TRV130 decreased extinction responding and reacquisition of oxycodone self-administration but had a weaker (nonsignificant) effect on context-induced reinstatement. In female rats, buprenorphine decreased responding in all 3 tests, while TRV130 decreased only extinction responding. In both sexes, TRV130 prevented acute brain hypoxia induced by moderate doses of oxycodone.

CONCLUSIONS

TRV130 decreased oxycodone seeking and taking during abstinence in a partly sex-specific manner and prevented acute oxycodone-induced brain hypoxia. We propose that G protein-biased mu opioid receptor agonists, currently in development as analgesics, should be considered as relapse prevention maintenance treatment for opioid addiction.

The psychoactive aminoalkylbenzofuran derivatives, 5-APB and 6-APB, mimic the effects of 3,4-methylenedioxyamphetamine (MDA) on monoamine transmission in male rats

RATIONALE

The nonmedical use of new psychoactive substances (NPS) is a worldwide public health concern. The so-called "benzofury" compounds, 5-(2-aminopropyl)benzofuran (5-APB) and 6-(2-aminopropyl)benzofuran (6-APB), are NPS with stimulant-like properties in human users. These substances are known to interact with monoamine transporters and 5-HT receptors in transfected cells, but less is known about their effects in animal models.

METHODS

Here, we used in vitro monoamine transporter assays in rat brain synaptosomes to characterize the effects of 5-APB and 6-APB, together with their N-methyl derivatives 5-MAPB and 6-MAPB, in comparison with 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA). In vivo neurochemical and behavioral effects of 5-APB (0.3 and 1.0 mg/kg, i.v.) and 6-APB (0.3 and 1.0 mg/kg, i.v.) were assessed in comparison with MDA (1.0 and 3.0 mg/kg, i.v.) using microdialysis sampling in the nucleus accumbens of conscious male rats.

RESULTS

All four benzofuran derivatives were substrate-type releasers at dopamine transporters (DAT), norepinephrine transporters (NET), and serotonin transporters (SERT) with nanomolar potencies, similar to the profile of effects produced by MDA and MDMA. However, the benzofurans were at least threefold more potent than MDA and MDMA at evoking transporter-mediated release. Like MDA, both benzofurans induced dose-related elevations in extracellular dopamine and serotonin in the brain, but benzofurans were more potent than MDA. The benzofuran derivatives also induced profound behavioral activation characterized by forward locomotion which lasted for at least 2 h post-injection.

CONCLUSIONS

Overall, benzofurans are more potent than MDA in vitro and in vivo, producing sustained stimulant-like effects in rats. These data suggest that benzofuran-type compounds may have abuse liability and could pose risks for adverse effects, especially if used in conjunction with abused drugs or medications which enhance monoamine transmission in the brain.

Effects of chronic treatment with bupropion on self-administration of nicotine + cocaine mixtures in nonhuman primates

Chronic health problems associated with long-term nicotine use are the leading cause of preventable death in the United States. The use of tobacco products is 3-4 times greater among individuals with cocaine use disorder than that observed in the general population. This may reflect the propensity of nicotine to augment the reinforcing effects of cocaine. However, the mechanism of action of nicotine differs from that of cocaine, which presents a significant challenge for the development of pharmacotherapeutic interventions for the management of nicotine + cocaine polydrug abuse. Bupropion, an FDA-approved smoking cessation aid, has pharmacological actions at both monoamine transporters and nicotinic receptors, suggesting that it may be effective at decreasing nicotine + cocaine coabuse. Here, rhesus monkeys (n = 4) responded for food pellets and, separately, intravenous injections of nicotine, cocaine, or nicotine + cocaine mixtures under a second-order FR2(VR16:S) schedule of reinforcement during 7- to 10-day continuous treatment with saline or bupropion (1.0 and 1.8 mg/kg/hr). Results show that bupropion treatment dose-dependently decreased self-administration of nicotine combined with a low dose of cocaine (0.0032 mg/kg/inj); however, when the dose of cocaine in the mixture was higher (i.e., 0.01 mg/kg/inj), bupropion attenuated self-administration in only a subset of subjects. The effective dosage of bupropion increased responding for cocaine alone, nicotine alone, and for saline injections and significantly increased measures of daily activity. The apparent stimulant-like effects of bupropion at the dosage required to decrease cocaine + nicotine self-administration does not support its clinical use for the management of nicotine + cocaine polydrug abuse. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Validation of a High-Throughput Calcium Mobilization Assay for the Human Trace Amine-Associated Receptor 1

The human trace amine-associated receptor 1 (hTAAR1) is a G protein-coupled receptor (GPCR) that is widely expressed in monoaminergic nuclei in the central nervous system and has therapeutic potential for multiple diseases, including drug addiction and schizophrenia. Thus, identification of novel hTAAR1 ligands is critical to advancing our knowledge of hTAAR1 function and to the development of therapeutics for a wide range of diseases. Herein we describe the development of a robust, 3-addition high-throughput screening (HTS) calcium mobilization assay using stable CHO-Gα_q16-hTAAR1 cells, which functionally couple hTAAR1 to the promiscuous Gα_q16 protein and thus allow signal transduction to occur through mobilization of internal calcium. Our previously established 96-well hTAAR1 assay was first miniaturized to the 384-well format and optimized to provide an assay with a Z' factor of 0.84, which is indicative of a robust HTS assay. Using the 3-addition protocol, 22,000 compounds were screened and yielded a ~1% agonist hit rate and a ~0.2% antagonist hit rate. Of the antagonist hits, two confirmed hits are the most potent hTAAR1 antagonists identified to date (IC₅₀ = 206 and 281 nM). While scientists have been studying hTAAR1 for years, the lack of suitable hTAAR1 antagonists has been a major roadblock for studying the basic pharmacology of hTAAR1. Thus, these new ligands will serve as valuable tools to study hTAAR1-mediated signaling mechanisms, therapeutic potential, and in vivo functions.

Berbamine Analogs Exhibit Differential Protective Effects From Aminoglycoside-Induced Hair Cell Death

Hearing loss is the third most common chronic health condition in the United States and largely results from damage to sensory hair cells. Major causes of hair cell damage include aging, noise exposure, and medications such as aminoglycoside antibiotics. Due to their potent antibacterial properties and low cost, aminoglycosides are often used for the treatment of gram-negative bacterial infections, surpassing expensive antibiotics with fewer harmful side effects. However, their use is coupled with permanent hearing loss in over 20% of patients requiring these life-sustaining antibiotics. There are currently no FDA-approved drugs that prevent hearing loss from aminoglycosides. A previous study by our group identified the plant alkaloid berbamine as a strong protectant of zebrafish lateral line hair cells from aminoglycoside damage. This effect is likely due to a block of the mechanotransduction channel, thereby reducing aminoglycoside entry into hair cells. The present study builds on this previous work, investigating 16 synthetic berbamine analogs to determine the core structure underlying their protective mechanisms. We demonstrate that nearly all of these berbamine analogs robustly protect lateral line hair cells from ototoxic damage, with ED₅₀ values nearing 20 nM for the most potent analogs. Of the 16 analogs tested, nine strongly protected hair cells from both neomycin and gentamicin damage, while one conferred strong protection only from gentamicin. These data are consistent with prior research demonstrating that different aminoglycosides activate somewhat distinct mechanisms of damage. Regardless of the mechanism, protection required the entire berbamine scaffold. Phenolic alkylation or acylation with lipophilic groups appeared to improve protection compared to berbamine, implying that these structures may be responsible for mitigating damage. While the majority of analogs confer protection by blocking aminoglycoside uptake, 18% of our analogs also confer protection via an uptake-independent mechanism; these analogs exhibited protection when delivered after aminoglycoside removal. Based on our studies, berbamine analogs represent a promising tool to further understand the pathology of aminoglycoside-induced hearing loss and can serve as lead compounds to develop otoprotective drugs.

Quantification of observable behaviors induced by typical and atypical kappa-opioid receptor agonists in male rhesus monkeys

RATIONALE

Kappa-opioid receptor (KOR) agonists are antinociceptive but have side effects that limit their therapeutic utility. New KOR agonists have been developed that are fully efficacious at the KOR but may produce fewer or reduced side effects that are typical of KOR agonists.

OBJECTIVES

We determined behavioral profiles for typical and atypical KOR agonists purported to differ in intracellular-signaling profiles as well as a mu-opioid receptor (MOR) agonist, oxycodone, using a behavioral scoring system based on Novak et al. (Am J Primatol 28:124-138, 1992, Am J Primatol 46:213-227, 1998) and modified to quantify drug-induced effects (e.g., Duke et al. J Pharmacol Exp Ther 366:145-157, 2018).

METHODS

Six adult male rhesus monkeys were administered a range of doses of the typical KOR agonists, U50-488H (0.0032-0.1 mg/kg) and salvinorin A (0.00032-0.01 mg/kg); the atypical KOR agonists, nalfurafine (0.0001-0.001 mg/kg) and triazole 1.1 (0.01-0.32 mg/kg); the MOR agonist, oxycodone (0.0032-0.32 mg/kg); and as controls, cocaine (0.032-0.32 mg/kg) and ketamine (0.32-10 mg/kg). For time-course determinations, the largest dose of each KOR agonist or MOR agonist was administered across timepoints (10-320 min). In mixture conditions, oxycodone (0.1 mg/kg) was followed by KOR-agonist administration.

RESULTS

Typical KOR agonists produced sedative-like and motor-impairing effects. Nalfurafine was similar to typical KOR agonists on most outcomes, and triazole 1.1 produced no effects on its own except for reducing scratch during time-course determinations. In the mixture, all KOR agonists reduced oxycodone-induced scratching, U50-488H and nalfurafine reduced species-typical activity, and U50-488H increased rest/sleep posture.

CONCLUSIONS

Atypical "biased" KOR agonists produce side-effect profiles that are relatively benign (triazole 1.1) or reduced (nalfurafine) compared to typical KOR agonists.

Evaluation of the Reinforcing Strength of Phendimetrazine Using a Progressive-Ratio Schedule of Reinforcement in Rhesus Monkeys

Stimulant abuse is a persistent public health problem with no Food and Drug Administration-approved pharmacotherapy. Although monoamine-releasing drugs such as d-amphetamine can decrease cocaine self-administration in human and animal laboratory studies, their potential for abuse limits clinical utility. "Abuse-deterrent" formulations of monoamine releasers, such as prodrugs, hold greater clinical promise if their abuse potential is, as theorized, lower than that of cocaine. In these studies, we determined the reinforcing strength of phendimetrazine (PDM), a prodrug for the amphetamine-like monoamine releaser phenmetrazine; both drugs have been shown to decrease cocaine self-administration in laboratory animals. To date, no study has directly compared PDM (Schedule III) with cocaine (Schedule II) under progressive-ratio (PR) schedules of reinforcement, which are better suited than fixed-ratio schedules to directly compare reinforcing strength of drugs. Dose-response curves for cocaine (saline, 0.001-0.3 mg/kg per injection) and PDM (0.1-1.0 mg/kg per injection) were generated in six cocaine-experienced male rhesus monkeys during 4-hour sessions with a 20-minute limited hold (LH). Under these conditions, the maximum number of injections was not significantly different between cocaine and PDM. The reinforcing strength of doses situated on the peaks of the cocaine and PDM dose-effect curves were redetermined with a 60-minute LH. The mean number of injections increased for both drugs, but not for saline. Cocaine presentations resulted in significantly higher peak injections than PDM with a 60-minute LH, which is consistent with the lower scheduling of PDM. These results support PDM as Schedule III and highlight the importance of schedule parameters when comparing reinforcing strength of drugs using a PR schedule of reinforcement. SIGNIFICANCE STATEMENT: One strategy for reducing cocaine use is to identify a treatment that substitutes for cocaine but has lower abuse potential. In a rhesus monkey model of drug abuse, this study compared the reinforcing strength of cocaine and phendimetrazine, a drug that has been shown to decrease cocaine use in some studies.

Transdermal Delivery of the Free Base of 3-Fluoroamphetamine: In Vitro Skin Permeation and Irritation Potential

This work aimed to continue our effort in establishing the feasibility of 3-fluoroamphetamine (also known as PAL-353) to be a transdermal drug candidate by studying the delivery of the base form through the human cadaver skin in lieu of the previously investigated salt form, and for the first time using an EPIDERM™-reconstructed human epidermal model to predict the skin irritation potential of PAL-353, in support of development for a matrix-type transdermal delivery system. Passive and enhanced (with chemical permeation enhancers) transdermal delivery were investigated via in vitro permeation studies that were performed on Franz diffusion cells with dermatomed human cadaver skin. After 24 h, PAL-353 free base revealed high passive permeation of 417.49 ± 30.12, 1577.68 ± 165.41, and 4295.16 ± 264.36 μg/cm², with applied formulation concentrations of 5.5 (F1), 20 (F2), and 40 (F3) mg/mL, respectively. Oleyl alcohol produced an approximately threefold steady-state flux enhancement at 5% or 10% w/w but may not be needed as the free base alone provided therapeutically relevant permeation. Further, it was predicted that therapeutically relevant delivery would be unlikely to cause skin irritation using the EPIDERM™-reconstructed human epidermal model. In conclusion, the present study further supported the development of PAL-353 transdermal delivery systems.

The pharmacokinetics of 3-fluoroamphetamine following delivery using clinically relevant routes of administration

3-Fluoroamphetamine (also called PAL-353) is a synthetic amphetamine analog that has been investigated for cocaine use disorder (CUD), yet no studies have characterized its pharmacokinetics (PK). In the present study, we determined the PK of PAL-353 in male Sprague Dawley rats following intravenous bolus injection (5 mg/kg). Plasma samples were analyzed using a novel bioanalytical method that coupled liquid-liquid extraction and LC-MS/MS. The primary PK parameters determined by WinNonlin were a C0 (ng/mL) of 1412.09 ± 196.12 and a plasma half-life of 2.27 ± 0.67 h. As transdermal delivery may be an optimal approach to delivering PAL-353 for CUD, we assessed its PK profile following application of 50 mg of transdermal gel (10% w/w drug over 5 cm2). The 10% w/w gel resulted in a short lag time, sustained delivery, and a rapid clearance in plasma immediately after removal. The rodent PK data were verified by examining in vitro permeation through human epidermis mounted on Franz diffusion cells. An in vitro-in vivo correlation (IVIVC) analysis was performed using the Phoenix IVIVC toolkit to assess the predictive relationship between rodent and human skin absorption/permeation. The in vitro permeation study revealed a dose-proportional cumulative and steady-state flux with ~ 70% of drug permeated. The fraction absorbed in vivo and fraction permeated in vitro showed a linear relationship. In conclusion, we have characterized the PK profile of PAL-353, demonstrated that it has favorable PK properties for transdermal administration for CUD, and provided preliminary evidence of the capacity of rodent data to predict human skin flux.

Effects of the mGluR2/3 receptor agonist LY379268 on the reinforcing strength of cocaine in rhesus monkeys

RATIONALE

Because chronic cocaine exposure produces profound effects on brain glutamate function, this system has been investigated as a target for novel medications for cocaine use disorder. Studies in animal models have provided encouraging results for drugs that target metabotropic glutamate receptors (mGluR), particularly group II mGluRs which includes mGluR2 and mGluR3 receptors.

OBJECTIVE

The present study examined the effects of the mGluR2/3 receptor-selective agonist, (-)-2-oxa-4-aminobicylco hexane-4,6-dicarboxylic acid (LY379268), in male rhesus monkeys self-administering cocaine under two procedures that assess the strength of cocaine as a reinforcer.

METHODS AND RESULTS

In four monkeys, acute effects of LY379268 on food and cocaine self-administration were characterized using a multiple 10-response fixed-ratio food, progressive-ratio cocaine schedule of reinforcement. Maximum injections were delivered when the available cocaine dose was 0.01-0.1 mg/kg. When monkeys self-administered 0.03 mg/kg per injection cocaine, LY379268 (0.001-0.56 mg/kg, i.v.), increased cocaine injections and disrupted food-maintained responding. Another group of monkeys (n = 3) responded under a food-cocaine choice procedure in which a dose-effect curve for self-administered cocaine (0.0, 0.003-0.1 mg/kg per injection) was generated daily. Acute LY379268 (0.01-0.1 mg.kg, i.v.) produced a shift in allocation of responding towards cocaine without affecting the total reinforcers delivered. When treatment was extended to 5 consecutive days, tolerance developed to LY379268-induced increases in cocaine choice.

CONCLUSIONS

These data from two complimentary nonhuman primate models of cocaine use disorder are consistently negative with respect to the potential of LY379268 as a pharmacotherapy for reducing ongoing cocaine use.

Synthetic cathinone self-administration in female rats modulates neurotransmitter levels in addiction-related brain regions

Synthetic cathinones are used for their stimulant-like properties. Stimulant-induced neurochemical changes are thought to occur at different times in different brain regions and neurotransmitter systems. This study sought to examine the behavioral and neurochemical effects of α-pyrrolidinopentiophenone (α-PVP) and mephedrone (4MMC) in female rats. Methods probed the chronology of effects of synthetic cathinone exposure. Female rats were trained to self-administer α-PVP, 4MMC, or saline. Drug exposure ceased after 7 days of autoshaping for half of each drug group; the other half self-administered for another 21 days. Amygdala, hippocampus, hypothalamus, PFC, striatum, and thalamus were extracted, and tissue was analyzed with electrochemical detection and liquid chromatography mass spectrometry. Responding was minimal during autoshaping; thus, most infusions were delivered noncontingently in the autoshaping phase. Rats acquired self-administration of α-PVP and 4MMC. Synthetic cathinone administration, and duration of exposure produced several effects on neurotransmitters. α-PVP primarily increased serotonin, 5-hydroxy-3-acetic acid (5-HIAA), norepinephrine, and glutamate in hypothalamus. In contrast, 4MMC decreased serotonin and 5-HIAA in several brain regions. Longer durations of exposure to both synthetic cathinones increased 5-HIAA, norepinephrine, and glutamate in multiple brain regions compared to the short exposure during autoshaping. Notably, both α-PVP and 4MMC produced minimal changes in dopamine levels, suggesting that the dopaminergic effects of these synthetic cathinones are transient. These alterations in neurotransmitter levels indicate that synthetic cathinone use may produce differential neurochemical changes during the transition from use to abuse.

Effects of methamphetamine isomers on d-methamphetamine self-administration and food-maintained responding in male rats

RATIONALE

Methamphetamine (METH) abuse is generally attributed to the d-isomer. Self-administration of l-METH has been examined only in rhesus monkeys with a history of cocaine self-administration or drug-naïve rats using high toxic doses.

OBJECTIVES

In this study, the ability of l-METH and, for comparison, d-METH to engender self-administration in experimentally naïve rats, as well as to decrease d-METH self-administration and food-maintained responding, was examined.

METHODS

Male Sprague-Dawley rats were used in 3 separate experiments. In experiment 1, the acquisition of l- or d-METH self-administration followed by dose-response determinations was studied. In experiment 2, rats were trained to self-administer d-METH (0.05 mg/kg/infusion) and, then, various doses of l- or d-METH were given acutely prior to the session; the effect of repeated l-METH (30 mg/kg) also was examined. In experiment 3, rats were trained to respond for food reinforcement and, then, various doses of l- or d-METH were given acutely prior to the session; the effect of repeated l-METH (3 mg/kg) also was examined.

RESULTS

Reliable acquisition of l- and d-METH self-administration was obtained at unit doses of 0.5 and 0.05 mg/kg/infusion respectively. The dose-response function for l-METH self-administration was flattened and shifted rightward compared with d-METH self-administration, with peak responding for l- and d-METH occurring at unit doses of 0.17 and 0.025 respectively. l-METH also was approximately 10-fold less potent than d-METH in decreasing d-METH self-administration and 2-fold lower in decreasing food-maintained responding. Tolerance did not occur to repeated l-METH pretreatments on either measure.

CONCLUSIONS

As a potential pharmacotherapeutic, l-METH has less abuse liability than d-METH and its efficacy in decreasing d-METH self-administration and food-maintained responding is sustained with repeated treatment.

Metabolites of the ring-substituted stimulants MDMA, methylone and MDPV differentially affect human monoaminergic systems

BACKGROUND

Amphetamine analogs with a 3,4-methylenedioxy ring-substitution are among the most popular illicit drugs of abuse, exerting stimulant and entactogenic effects. Enzymatic N-demethylation or opening of the 3,4-methylenedioxy ring via O-demethylenation gives rise to metabolites that may be pharmacologically active. Indeed, previous studies in rats show that specific metabolites of 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxymethcathinone (methylone) and 3,4-methylenedioxypyrovalerone (MDPV) can interact with monoaminergic systems.

AIM

Interactions of metabolites of MDMA, methylone and MDPV with human monoaminergic systems were assessed.

METHODS

The ability of parent drugs and their metabolites to inhibit uptake of tritiated norepinephrine, dopamine and serotonin (5-HT) was assessed in human embryonic kidney 293 cells transfected with human monoamine transporters. Binding affinities and functional activity at monoamine transporters and various receptor subtypes were also determined.

RESULTS

MDMA and methylone displayed greater potency to inhibit norepinephrine uptake as compared to their effects on dopamine and 5-HT uptake. N-demethylation of MDMA failed to alter uptake inhibition profiles, whereas N-demethylation of methylone decreased overall transporter inhibition potencies. O-demethylenation of MDMA, methylone and MDPV resulted in catechol metabolites that maintained norepinephrine and dopamine uptake inhibition potencies, but markedly reduced activity at 5-HT uptake. O-methylation of the catechol metabolites significantly decreased norepinephrine uptake inhibition, resulting in metabolites lacking significant stimulant properties.

CONCLUSIONS

Several metabolites of MDMA, methylone and MDPV interact with human transporters and receptors at pharmacologically relevant concentrations. In particular, N-demethylated metabolites of MDMA and methylone circulate in unconjugated form and could contribute to the in vivo activity of the parent compounds in human users.

The sesquiterpene beta-caryophyllene oxide attenuates ethanol drinking and place conditioning in mice

Approximately 20 million adults in the United States have an alcohol use disorder. In recent years, modulation of the behavioral effects of ethanol by phytochemicals has been explored. In this study, we used the ethanol-induced loss of righting reflex (LORR) assay to assess potency differences between the sesquiterpene phytochemical beta-caryophyllene (BCP) and its derivative caryophyllene oxide (BCPO). We also investigated the effects of BCPO on two bottle-choice ethanol drinking and the ethanol-induced conditioned place preference (CPP). We then determined whether there are any pharmacokinetic or pharmacodynamic interactions between BCPO and ethanol, using blood ethanol analysis and pretreatments with the selective cannabinoid receptor 2 (CB2) antagonist AM630, respectively. BCPO augmented the ethanol-induced LORR at a dose (30 mg/kg) tenfold lower than BCP (300 mg/kg). Swiss-Webster mice were found to split into stable high and low drinking groups. This same dose (30 mg/kg) of BCPO significantly decreased ethanol intake and preference for ethanol over water in mice that consumed high amounts of ethanol, without any effect on total fluid intake. BCPO had limited effects in mice that consumed low amounts of ethanol. BCPO also significantly attenuated the ethanol-induced CPP. Blood ethanol analysis showed no significant effect of ethanol on the pharmacokinetics of ethanol. Furthermore, the enhancement of the ethanol-induced LORR by BCPO was reversed by AM630. These findings demonstrate that BCPO more potently modulates the behavioral effects of ethanol than the parent compound BCP. Moreover, they suggest that BCPO modulates the behavioral effects of ethanol through pharmacodynamic rather than pharmacokinetic mechanisms.

Skin Delivery and Irritation Potential of Phenmetrazine as a Candidate Transdermal Formulation for Repurposed Indications

Phenmetrazine, a selective dopamine and norepinephrine releaser, previously available as an oral anorectic, is prone to be abused. This study aimed to assess the feasibility of delivering phenmetrazine via the transdermal route for a new indication, while also minimizing its abuse potential. The passive permeation of phenmetrazine through dermatomed human cadaver skin was evaluated using static Franz diffusion cells at 10 mg/mL for the fumarate salt, and at 20, 40, and 80 mg/mL for the free base in propylene glycol for 24 h. Further, oleic acid (5% w/w), oleyl alcohol (5% and 10% w/w), and lauric acid (10% w/w) were investigated as chemical permeation enhancers to enhance the delivery. Skin irritation potential was assessed using EpiDerm™ in vitro reconstructed human epidermal model. The free base showed superior 24-h delivery (8.13 ± 4.07%, 10.6 ± 2.5%, and 10.4 ± 1.4% for groups with 20, 40, and 80 mg/mL of the free base, respectively) to phenmetrazine fumarate salt (undetectable). The successful screening of effective chemical enhancers, oleyl alcohol (5% and 10% w/w), oleic acid (5% w/w), and lauric acid (10% w/w) resulted in significant enhancement of delivery. The calculated therapeutic relevant flux for the potential indication, attention deficit hyperactivity disorder, 20 μg/cm²/h was met, where a 24-mg daily dose from a 50-cm² patch was projected to be delivered to a 60-kg individual. Irritation study results suggest that formulations with therapeutically relevant delivery are likely to be non-irritant. In conclusion, it is feasible to deliver therapeutically relevant amounts of phenmetrazine via the transdermal route.

The synthetic cathinone psychostimulant α-PPP antagonizes serotonin 5-HT2A receptors: In vitro and in vivo evidence

Synthetic cathinones (SCs) are β-keto analogs of amphetamines. Like amphetamines, SCs target monoamine transporters; however, unusual neuropsychiatric symptoms have been associated with abuse of some SCs, suggesting SCs might possess additional pharmacological properties. We performed radioligand competition binding assays to assess the affinities of nine SCs at human 5-HT_2A receptors (5-HT_2A R) and muscarinic M₁ receptors (M₁ R) transiently expressed in HEK293 cells. None of the SCs exhibited affinity at M₁ R (minimal displacement of [~K_d ] [³ H]scopolamine up to 10 μM). However, two SCs, α-pyrrolidinopropiophenone (α-PPP) and 4-methyl-α-PPP, had low μM K_i values at 5-HT_2A R. In 5-HT_2A R-phosphoinositide hydrolysis assays, α-PPP and 4-methyl-α-PPP displayed inverse agonist activity. We further assessed the 5-HT_2A R functional activity of α-PPP, and observed it competitively antagonized 5-HT_2A R signaling stimulated by the 5-HT₂ R agonist (±)-2,5-dimethoxy-4-iodoamphetamine (DOI; K_b  = 851 nM). To assess in vivo 5-HT_2A R activity, we examined the effects of α-PPP on the DOI-elicited head-twitch response (HTR) in mice. α-PPP dose-dependently blocked the HTR with maximal suppression at 10 mg/kg (P < 0.0001), which is a moderate dose used in studies investigating psychostimulant properties of α-PPP. To corroborate a 5-HT_2A R mechanism, we also tested 3,4-methylenedioxy-α-PPP (MDPPP) and 3-bromomethcathinone (3-BMC), SCs that we observed had 5-HT_2A R K_i s > 10 μM. Neither MDPPP nor 3-BMC, at 10 mg/kg doses, attenuated the DOI HTR. Our results suggest α-PPP has antagonist interactions at 5-HT_2A R in vitro that may translate at physiologically-relevant doses in vivo. Considering 5-HT_2A R antagonism has been shown to mitigate effects of psychostimulants, this property may contribute to α-PPPs unpopularity compared to other monoamine transporter inhibitors.

Analysis of neurotransmitter levels in addiction-related brain regions during synthetic cathinone self-administration in male Sprague-Dawley rats

RATIONALE

Synthetic cathinones are used as stimulants of abuse. Different stimulants may induce distinct rates of disease progression, yielding neurochemical changes that may vary across brain regions or neurotransmitter systems.

OBJECTIVES

This research sought to behaviorally and chemically differentiate stages of synthetic cathinone abuse through rodent self-administration and measurement of the neurotransmitter profile in multiple brain regions.

METHODS

Male rats were trained to self-administer α-PVP, mephedrone (4MMC), or saline. Half of each drug group stopped self-administering after autoshaping; the other half self-administered for another 21 days. Brain tissue from amygdala, hippocampus, hypothalamus, PFC, striatum, and thalamus was profiled with electrochemical detection to assess neurotransmitter levels.

RESULTS

During autoshaping, the majority of infusions were delivered noncontingently. In the self-administration phase, rats responded more for α-PVP and 4MMC than for saline, demonstrating that both synthetic cathinones were reinforcing. Longer durations of exposure elevated 5-HIAA in hypothalamus, PFC, and hippocampus, indicating that learning may produce changes in addiction-related brain regions. Both synthetic cathinones decreased norepinephrine in hippocampus, while α-PVP decreased glutamate in hippocampus and PFC, and 4MMC decreased glutamate in thalamus. Furthermore, α-PVP increased dopaminergic metabolites in striatum, whereas 4MMC decreased serotonin in the amygdala, hippocampus, and PFC. Interestingly, neither synthetic cathinone affected dopamine levels despite their functional effects on the dopaminergic system.

CONCLUSIONS

In summary, the neurotransmitter changes observed here suggest that synthetic cathinone use likely produces sequential neurochemical changes during the transition from use to abuse. Consequently, treatment need may differ depending on the progression of synthetic cathinone abuse.

Effectiveness comparisons of G-protein biased and unbiased mu opioid receptor ligands in warm water tail-withdrawal and drug discrimination in male and female rats

One emerging strategy to address the opioid crisis is the development of mu opioid receptor (MOR) ligands that preferentially signal the G-protein vs. β-arrestin pathway. The present study compared the relative potency and effectiveness of two G-protein biased (GPB)-MOR ligands TRV130 and SR-14968 to five unbiased MOR ligands (NAQ, nalbuphine, buprenorphine, morphine, and methadone) on therapeutic-related (e.g. antinociception) and abuse-related (e.g. discriminative stimulus effects) endpoints. Male and female rats were tested in a warm water tail-withdrawal procedure (50 °C) or trained to discriminate fentanyl (0.04 mg/kg, SC) from saline in a two-lever food-reinforced discrimination procedure. TRV130 and SR-14968 were approximately two-fold more potent to produce fentanyl stimulus effects vs. antinociception. Morphine, fentanyl, and methadone were significantly more potent in the fentanyl discrimination vs. tail withdrawal procedure. In addition, maximum antinociceptive and discriminative stimulus effects of fixed-proportion fentanyl/naltrexone mixtures (1:0.018, 1:0.054, 1:0.18, 1:0.3, and 1:0.54) were used to quantify 1) the relative in vivo efficacy of the two GPB-MOR agonists and five unbiased MOR ligands, and 2) potential species differences in MOR ligand effects between rats and monkeys. The efficacy-effect function generated from the fentanyl/naltrexone mixtures stratified the five unbiased ligands consistent with agonist-stimulated GTPγS binding (NAQ = nalbuphine < buprenorphine < morphine < methadone). However, TRV130 and SR-14968 produced greater antinociception and less fentanyl-like stimulus effects than was predicted. Furthermore, there was a significant positive correlation between rat and monkey antinociceptive effects. Overall, these results demonstrate GPB-MOR agonists produce undesirable abuse-related effects, albeit with slightly better potency and efficacy ratios compared to unbiased agonists. This article is part of the Special Issue entitled 'Opioid Neuropharmacology: Advances in treating pain and opioid addiction'.

Oxymatrine Attenuates Tumor Growth and Deactivates STAT5 Signaling in a Lung Cancer Xenograft Model

Oxymatrine (OMT) is a major alkaloid found in radix Sophorae flavescentis extract and has been reported to exhibit various pharmacological activities. We elucidated the detailed molecular mechanism(s) underlying the therapeutic actions of OMT in non-small cell lung cancer (NSCLC) cells and a xenograft mouse model. Because the STAT5 signaling cascade has a significant role in regulating cell proliferation and survival in tumor cells, we hypothesized that OMT may disrupt this signaling cascade to exert its anticancer effects. We found that OMT can inhibit the constitutive activation of STAT5 by suppressing the activation of JAK1/2 and c-Src, nuclear localization, as well as STAT5 binding to DNA in A549 cells and abrogated IL-6-induced STAT5 phosphorylation in H1299 cells. We also report that a sub-optimal concentration of OMT when used in combination with a low dose of paclitaxel produced significant anti-cancer effects by inhibiting cell proliferation and causing substantial apoptosis. In a preclinical lung cancer mouse model, OMT when used in combination with paclitaxel produced a significant reduction in tumor volume. These results suggest that OMT in combination with paclitaxel can cause an attenuation of lung cancer growth both in vitro and in vivo.

The G-protein biased mu-opioid agonist, TRV130, produces reinforcing and antinociceptive effects that are comparable to oxycodone in rats

Mu-opioid agonists (e.g., oxycodone) are highly effective therapeutics for pain. However, they also produce reinforcing effects that increase their likelihood of abuse. Recent strategies in drug development have focused on opioids with biased receptor-signaling profiles that favor activation of specific intracellular pathways over others with the aim of increasing therapeutic selectivity. TRV130, a mu agonist biased towards G-protein signaling, produces antinociceptive effects comparable to the mu agonist, morphine, but exhibits reduced side effects. However, in terms of abuse potential, we know of no published preclinical data investigating the effects of TRV130 as a reinforcer. In the present study, we assessed the relative reinforcing effects of TRV130 and oxycodone, a commonly-prescribed mu agonist, in rats self-administering the drugs under a progressive-ratio (PR) schedule of reinforcement. In addition, we assessed the relative potency and efficacy of TRV130 and oxycodone in rats in a test of thermal antinociception (Hot Plate). For self-administration, male Sprague-Dawley rats (n = 7) self-administered intravenous infusions of TRV130 or oxycodone (0.01-0.32 mg/kg/inj) under a PR schedule of reinforcement. For the Hot-Plate test, male rats (n = 7) received subcutaneous injections of TRV130 (0.1-3.2 mg/kg/inj) or oxycodone (0.1-5.6 mg/kg/inj), and nociceptive response latencies were measured. TRV130 and oxycodone were equi-potent and equi-effective in self-administration and thermal antinociception. This study demonstrates that TRV130 produces reinforcing and antinociceptive effects that are quantitatively similar to oxycodone, and that a biased-signaling profile does not necessarily reduce abuse potential.

Formulation and evaluation of 4-benzylpiperidine drug-in-adhesive matrix type transdermal patch

The objective of our study was to develop a transdermal patch of 4-benzylpiperidine and to evaluate its in vitro transdermal permeation profile. Appropriate pressure sensitive adhesives and additives were selected based on solubility and slide crystallization studies. Release liners and backing membranes were selected based on their ability to peel without leaving a residue and their affinity to formulation respectively. Drug-in-adhesive patches developed were investigate for their in vitro drug permeation over 48 h across dermatomed human skin using Franz diffusion cells. Silicone based pressure sensitive adhesive along with colloidal silicon dioxide as viscosity builder, fluoropolymer coated membranes as the release liner and polyester based membranes as backing were chosen to develop a drug in silicone adhesive patch. Polyisobutylene adhesive based patch was developed with drug in polyisobutylene adhesive, along with oleic acid and oleyl alcohol as permeation enhancers, polyester for the release liner and polyethylene as backing. Among the patches developed, polyisobutylene adhesive based patch with higher drug concentration exhibited superior transdermal permeation (1608.5 ± 53.4 µg/cm² over 48 h). The final patch was further tested for uniformity in coat weight, shear strength, tack and peel adhesion.

Anti-myeloma Effects of Icariin Are Mediated Through the Attenuation of JAK/STAT3-Dependent Signaling Cascade

Because of the essential role of signal transducer and activator of transcription 3 (STAT3) in proliferation, anti-apoptosis, and chemoresistance of multiple myeloma (MM), we investigated whether icariin, a prenylated flavonol glycoside, inhibits both constitutive and inducible STAT3 activation in human myeloma cell lines. We noted that icariin could block constitutive STAT3 phosphorylation as well as its nuclear translocation and DNA binding ability in U266 cells. Icariin also suppressed IL-6-induced STAT3 activation through the inhibition of upstream kinases (Janus activated kinase-1 and -2, and c-Src). We found that icariin downregulated the protein expression of STAT3 downstream target gene products such as Bcl-2, Bcl-xl, survivin, IAP-1/2, COX-2, VEGF, and matrix metallopeptidase 9 (MMP-9) in a concentration-dependent manner. Moreover, this flavonoid also exhibited the capacity to significantly induce apoptosis and suppress proliferation of MM cells. Interestingly, this agent also significantly potentiated the apoptotic effects of bortezomib through the suppression of STAT3 activation in MM cells. Altogether, our data indicates that the potential application of icariin as a STAT3 blocker in myeloma therapy.