MD-354 potentiates the antinociceptive effect of clonidine in the mouse tail-flick but not hot-plate assay

Targeting Alpha7 Nicotinic Acetylcholine Receptors in Lung Cancer: Insights, Challenges, and Therapeutic Strategies

Alpha7 nicotinic acetylcholine receptor (α7 nAChR) is an ion-gated calcium channel that plays a significant role in various aspects of cancer pathogenesis, particularly in lung cancer. Preclinical studies have elucidated the molecular mechanism underlying α7 nAChR-associated lung cancer proliferation, chemotherapy resistance, and metastasis. Understanding and targeting this mechanism are crucial for developing therapeutic interventions aimed at disrupting α7 nAChR-mediated cancer progression and improving treatment outcomes. Drug research and discovery have determined natural compounds and synthesized chemical antagonists that specifically target α7 nAChR. However, approved α7 nAChR antagonists for clinical use are lacking, primarily due to challenges related to achieving the desired selectivity, efficacy, and safety profiles required for effective therapeutic intervention. This comprehensive review provided insights into the molecular mechanisms associated with α7 nAChR and its role in cancer progression, particularly in lung cancer. Furthermore, it presents an update on recent evidence about α7 nAChR antagonists and addresses the challenges encountered in drug research and discovery in this field.

A Novel Mu-Delta Opioid Agonist Demonstrates Enhanced Efficacy With Reduced Tolerance and Dependence in Mouse Neuropathic Pain Models

Numerous studies have demonstrated a physiological interaction between the mu opioid receptor (MOR) and delta opioid receptor (DOR) systems. A few studies have shown that dual MOR-DOR agonists could be beneficial, with reduced tolerance and addiction liability, but are nearly untested in chronic pain models, particularly neuropathic pain. In this study, we tested the MOR-DOR agonist SRI-22141 in mice in the clinically relevant models of HIV Neuropathy and Chemotherapy-Induced Peripheral Neuropathy (CIPN). SRI-22141 was more potent than morphine in the tail flick pain test and had equal or enhanced efficacy versus morphine in both neuropathic pain models, with significantly reduced tolerance. SRI-22141 also produced no jumping behavior during naloxone-precipitated withdrawal in CIPN or naïve mice, suggesting that SRI-22141 produces little to no dependence. SRI-22141 also reduced tumor necrosis factor-α and cyclooxygenase-2 in CIPN in the spinal cord, suggesting an anti-inflammatory mechanism of action. The DOR-selective antagonist naltrindole strongly reduced CIPN efficacy and anti-inflammatory activity in the spinal cord, without affecting tail flick antinociception, suggesting the importance of DOR activity in these models. Overall, these results provide compelling evidence that MOR-DOR agonists could have strong efficacy with reduced side effects and an anti-inflammatory mechanism in the treatment of neuropathic pain. PERSPECTIVE: This study demonstrates that a MOR-DOR dual agonist given chronically in chronic neuropathic pain models has enhanced efficacy with strongly reduced tolerance and dependence, with a further anti-inflammatory effect in the spinal cord. This suggests that MOR-DOR dual agonists could be effective treatments for neuropathic pain with reduced side effects.

MD-354 selectively antagonizes the antinociceptive effects of (-)nicotine in the mouse tail-flick assay

RATIONALE

(-)Nicotine produces antinociceptive effects in rodents. meta-Chlorophenylguanidine (MD-354), an analgesia-enhancing agent, binds at 5-HT(3) and alpha(2)-adrenoceptors and potentiates the antinociceptive effects of an "inactive" dose of clonidine. The present study examined the actions of MD-354 on (-)nicotine-induced antinociception.

MATERIALS AND METHODS

Mouse tail-flick and other assays were employed.

RESULTS

In the tail-flick assay, (-)nicotine (ED(50) = 1.66 mg/kg) but not MD-354 produced dose-related antinociceptive effects. Administered in combination with (-)nicotine (2.5 mg/kg), MD-354 (AD(50) = 3.4 mg/kg) did not potentiate, but effectively antagonized the antinociceptive actions of (-)nicotine. In a mouse hot-plate assay, MD-354 failed to modify (-)nicotine responses. In combination with a locomotor activity-suppressing dose of (-)nicotine, MD-354 (up to 17 mg/kg) failed to antagonize (-)nicotine-induced hypolocomotion. In a rat drug discrimination paradigm using (-)nicotine as training drug, MD-354 produced saline-appropriate responding; in combination with the training dose of (-)nicotine, MD-354 failed to antagonize the nicotine cue.

CONCLUSIONS

MD-354 selectively antagonizes the antinociceptive actions of (-)nicotine in the tail-flick, but not in the hot-plate assay, or either the motor effects, or discriminative stimulus effects of (-)nicotine. The most parsimonious explanation is that MD-354 might act as a negative allosteric modulator of alpha 7 nACh receptors, and radioligand binding and functional data are provided to support this conclusion.

MD-354: what is it good for?

MD-354 (meta-chlorophenylguanidine) has been identified as a member of a novel class of 5-HT(3) serotonin receptor agonists. MD-354 is a 5-HT(3) receptor partial agonist that has been shown to behave as an agonist in some assays, and as an antagonist in others. MD-354 also binds at alpha-adrenoceptors (ARs) and displays an affinity for alpha(2B)-ARs comparable to its affinity for 5-HT(3) receptors. Although devoid of antinociceptive actions following systemic administration alone, MD-354 markedly enhances the antinociceptive actions of clonidine in the mouse tail-flick assay without potentiating the sedative side effects of clonidine. Although studies with MD-354 are still in progress, some pharmacological findings are described here. MD-354-related agents may represent drug adjuvants for the relief of severe pain.

The 5-HT3 receptor partial agonist MD-354 (meta-chlorophenylguanidine) enhances the discriminative stimulus actions of (+)amphetamine in rats

The effect of the 5-HT3 receptor partial agonist MD-354 (meta-chlorophenylguanidine) was examined on the discriminative stimulus produced by (+)amphetamine. Using male Sprague-Dawley rats trained to discriminate 1.0 mg/kg (i.p.) of (+)amphetamine from saline vehicle (VI 15-s schedule of reinforcement) in a two-lever operant procedure for appetitive reward, tests of stimulus generalization (substitution) and antagonism showed that MD-354 neither substituted for, nor antagonized, the amphetamine stimulus at the doses evaluated. Administration of (+)amphetamine doses in combination with a fixed (i.e., 1.0 mg/kg) dose of MD-354 shifted the (+)amphetamine dose-response curve to the left such that, following 0.3 mg/kg of (+)amphetamine, stimulus generalization occurred. Furthermore, MD-354 doses of 0.1, 0.3 and 1.0 mg/kg, but not doses of 0.01, 0.5, 1.5 or 3.0 mg/kg (i.p.), administered in combination with the ED(50) dose (0.33 mg/kg) of (+)amphetamine resulted in stimulus generalization (i.e., >80% drug-appropriate responding). It is concluded that even though MD-354 lacks amphetamine-like central stimulant actions of its own it can modulate the discriminative stimulus effects of (+)amphetamine in rats.

Antinociception: Mechanistic studies on the action of MD-354 and clonidine. Part 1. The 5-HT3 component

MD-354 (m-chlorophenylguanidine) is a 5-HT3/alpha2B-adrenoceptor ligand. Both receptors play a role in antinociception. In the mouse tail-flick assay, subcutaneously administered MD-354 was inactive as an analgesic. However, a combination of an inactive dose of clonidine (0.25 mg/kg) with an inactive dose of MD-354 (6 mg/kg) produced a substantial antinociceptive effect (maximal possible effect=66%). Considering the 5-HT3 receptor partial agonist properties of MD-354, the analgesia enhancing effect of MD-354 on clonidine might be associated, at least in part, with its 5-HT3 receptor agonist or antagonist activity. Combinations of an inactive dose of clonidine (0.25 mg/kg) with 5-HT3 receptor antagonists (tropisetron, zacopride and ondansetron) were examined. Saline-like doses of tropisetron, zacopride and ondansetron significantly enhanced the antinociceptive effect of clonidine (combinations: maximal possible effect=86%, 82% and 79% respectively), suggesting that MD-354 may enhance the analgesic actions of clonidine, at least in part, through a 5-HT3 receptor antagonist mechanism.