Efficacy and safety of the first-in-class imidazoline-2 receptor ligand CR4056 in pain from knee osteoarthritis and disease phenotypes: a randomized, double-blind, placebo-controlled phase 2 trial

A comprehensive review of phase 2/3 trials in osteoarthritis: an expert opinion

INTRODUCTION

Osteoarthritis (OA) is a chronic, degenerative, and debilitating disease associated with significant long-term morbidity and disability. The pathogenesis of OA is not completely understood but involves an interplay between environmental risk factors, joint mechanics, abnormal pain pathways and upregulation of inflammatory signaling pathways. Current therapeutic options for patients are limited to conservative management, minimal pharmacological options or surgical management, with significant caveats to all approaches.

AREAS COVERED

In this review, we have set out to investigate current phase II/III clinical trials by undertaking a PubMed search. Examined clinical trials have explored a myriad of potential therapeutics from conventional disease-modifying anti-rheumatic drugs and biologics usually used in the treatment of inflammatory arthritides, to more novel approaches targeting inflammatory pathways implicated in OA, cartilage degeneration or pain pathways.

EXPERT OPINION

Unfortunately, most completed phase II/III clinical trials have shown little impact on patient pain scores, with the exception of the traditional DMARD methotrexate and Sprifermin. Methotrexate has been shown to be beneficial when used in the correct patient cohort (MRI proven synovitis). Sprifermin has the longest follow-up data of 5 years and has been shown to reduce loss of MRI-measured cartilage thickness and pain scores.

The imidazoline I2 receptor agonist 2-BFI reduces abuse-related effects of morphine: self-administration and drug discrimination

RATIONALE

Increasing evidence shows that imidazoline I2 receptor agonists enhance opioid-induced analgesia, suggesting that the combination of I2 receptor agonists with opioids could be a favorable strategy for pain control. However, the effect of I2 receptor agonists on the abuse liability of opioids is unknown. This study examined the impact of the I2 receptor agonist 2-BFI on some abuse-related behavioral effects of the opioid morphine in rats.

OBJECTIVES

The von Frey filament test was used to determine the antinociceptive effects of 2-BFI (intravenous, i.v.) in a rat model of complete Freund's adjuvant (CFA)-induced inflammatory pain. IV self-administration was used to assess the reinforcing effects of 2-BFI alone and to assess the effects of non-contingent injections of 2-BFI (i.p.) on morphine self-administration. A two-lever drug discrimination paradigm in which rats were trained to discriminate 3.2 mg/kg morphine (i.p.) from saline was used to examine whether 2-BFI or another I2 receptor agonist 2-(4,5-dihydroimidazol-2-yl)quinoline hydrochloride (BU224) affected the discriminative stimulus effects of morphine.

RESULTS

2-BFI could not maintain reliable self-administration behavior in rats with no pain or CFA-treated inflammatory pain. However, pretreatment with 2-BFI (i.p.) produced dose-dependent decreases in the dose-effect curve of morphine self-administration. Both 2-BFI and BU224 did not substitute for morphine but significantly attenuated the discriminative stimulus effects of morphine.

CONCLUSIONS

These results suggest that I2 receptor agonists do not enhance, but in fact appear to decrease, the abuse liability of opioids, further supporting the potential utility of I2 receptor agonist-opioid combination therapy for pain control.

Preclinical Evaluation of an Imidazole-Linked Heterocycle for Alzheimer's Disease

Humanity is facing a vast prevalence of neurodegenerative diseases, with Alzheimer's disease (AD) being the most dominant, without efficacious drugs, and with only a few therapeutic targets identified. In this scenario, we aim to find molecular entities that modulate imidazoline I2 receptors (I2-IRs) that have been pointed out as relevant targets in AD. In this work, we explored structural modifications of well-established I2-IR ligands, giving access to derivatives with an imidazole-linked heterocycle as a common key feature. We report the synthesis, the affinity in human I2-IRs, the brain penetration capabilities, the in silico ADMET studies, and the three-dimensional quantitative structure-activity relationship (3D-QSAR) studies of this new bunch of I2-IR ligands. Selected compounds showed neuroprotective properties and beneficial effects in an in vitro model of Parkinson's disease, rescued the human dopaminergic cell line SH-SY5Y from death after treatment with 6-hydroxydopamine, and showed crucial anti-inflammatory effects in a cellular model of neuroinflammation. After a preliminary pharmacokinetic study, we explored the action of our representative 2-(benzo[b]thiophen-2-yl)-1H-imidazole LSL33 in a mouse model of AD (5xFAD). Oral administration of LSL33 at 2 mg/Kg for 4 weeks ameliorated 5XFAD cognitive impairment and synaptic plasticity, as well as reduced neuroinflammation markers. In summary, this new I2-IR ligand that promoted beneficial effects in a well-established AD mouse model should be considered a promising therapeutic strategy for neurodegeneration.

Modulation of NMDA receptor activity by CR4056, an imidazoline-2 receptor ligand with analgesic properties

CR4056 is an imidazoline-2 receptor ligand having potent analgesic activity and synergistic effect with opioids. Very recently it has been found that CR4056 can revert the cognitive impairment in animal models of Alzheimer's disease (AD). Since several lines of evidence highlight the importance of NMDAR modulators in nociceptive signaling and in AD progression, we considered as important to investigate the effects of CR4056 on NMDAR activity. In primary culture of cortical neurons, application of NMDA and glycine elicits a current that is decreased in a dose-dependent fashion by CR4056 (IC50 5.3 ± 0.1 µM). CR4056 antagonism is reversible, not competitive and voltage-independent and it is not blocked by pertussis toxin. CR4056 interacts with the co-agonist glycine site in a competitive way, indeed high glycine concentrations diminish its effect. Fibroblasts expressing different recombinant NMDA receptors are differently modulated by CR4056: the potency and the efficacy of the compound are higher in GluN1- GluN2B than in GluN1-GluN2A containing receptors. In lamina II neurons of spinal cord slices, single stimulation of afferent fibers evokes an NMDA-mediated current that is inhibited by 10 µM CR4056. Repetitive stimulation of the dorsal root at high frequency and high intensity produces a firing activity that is significatively depressed by CR4056. Taken together, our results broad the understanding of the molecular mechanisms of CR4056 analgesic activity, involving the modulation of NMDAR activity. Therefore, we propose that the analgesic action of CR4056 and the neuroprotective effects in AD models may be mediated also by NMDAR inhibition.

I2-Imidazoline Ligand CR4056 Improves Memory, Increases ApoE Expression and Reduces BBB Leakage in 5xFAD Mice

Recent evidence suggests that I2-imidazoline ligands have neuroprotective properties in animal models of neurodegeneration, such as Alzheimer's disease (AD). We recently demonstrated that the I2-ligand BU224 reversed memory impairments in AD transgenic mice and this effect was not because of reductions in amyloid-β (Aβ) deposition. In this study, our aim was to determine the therapeutic potential of the powerful analgesic I2-imidazoline ligand CR4056 in the 5xFAD model of AD, since this ligand has been proven to be safely tolerated in humans. Sub-chronic oral administration of CR4056 (30 mg/kg for 10 days) led to an improvement in recognition memory in 6-month-old 5xFAD mice, but not in wild-type littermates, without affecting Aβ levels or deposition. Our results also revealed a change in the profile of microglia by CR4056, resulting in a suppression of pro-inflammatory activated microglia, but increased the density of astrocytes and the expression of ApoE, which is mainly produced by these glial cells. In addition, CR4056 restored fibrinogen extravasation, affecting the distribution of markers of astrocytic end feet in blood vessels. Therefore, these results suggest that CR4056 protects against Aβ-mediated neuroinflammation and vascular damage, and offers therapeutic potential at any stage of AD.

Heterocycle-Based Multicomponent Reactions in Drug Discovery: From Hit Finding to Rational Design

In the context of the structural complexity necessary for a molecule to selectively display a therapeutical action and the requirements for suitable pharmacokinetics, a robust synthetic approach is essential. Typically, thousands of relatively similar compounds should be prepared along the drug discovery process. In this respect, heterocycle-based multicomponent reactions offer advantages over traditional stepwise sequences in terms of synthetic economy, as well as the fast access to chemsets to study the structure activity relationships, the fine tuning of properties, and the preparation of larger amounts for preclinical phases. In this account, we briefly summarize the scientific methodology backing the research line followed by the group. We comment on the main results, clustered according to the targets and, finally, in the conclusion section, we offer a general appraisal of the situation and some perspectives regarding future directions in academic and private research.

Insights into the Pharmacokinetics and In Vitro Cell-Based Studies of the Imidazoline I2 Receptor Ligand B06

The impact of neurodegenerative diseases (ND) is becoming unbearable for humankind due to their vast prevalence and the lack of efficacious treatments. In this scenario, we focused on imidazoline I₂ receptors (I₂-IR) that are widely distributed in the brain and are altered in patients with brain disorders. We took the challenge of modulating I₂-IR by developing structurally new molecules, in particular, a family of bicyclic α-iminophosphonates, endowed with high affinity and selectivity to these receptors. Treatment of two murine models, one for age-related cognitive decline and the other for Alzheimer's disease (AD), with representative compound B06 ameliorated their cognitive impairment and improved their behavioural condition. Furthermore, B06 revealed beneficial in vitro ADME-Tox properties. The pharmacokinetics (PK) and metabolic profile are reported to de-risk B06 for progressing in the preclinical development. To further characterize the pharmacological properties of B06, we assessed its neuroprotective properties and beneficial effect in an in vitro model of Parkinson's disease (PD). B06 rescued the human dopaminergic cell line SH-SY5Y from death after treatment with 6-hydroxydopamine (6-OHDA) and showed a crucial anti-inflammatory effect in a cellular model of neuroinflammation. This research reveals B06 as a putative candidate for advancing in the difficult path of drug discovery and supports the modulation of I₂-IR as a fresh approach for the therapy of ND.

Fentanyl Structure as a Scaffold for Opioid/Non-Opioid Multitarget Analgesics

One of the strategies in the search for safe and effective analgesic drugs is the design of multitarget analgesics. Such compounds are intended to have high affinity and activity at more than one molecular target involved in pain modulation. In the present contribution we summarize the attempts in which fentanyl or its substructures were used as a μ-opioid receptor pharmacophoric fragment and a scaffold to which fragments related to non-opioid receptors were attached. The non-opioid ‘second’ targets included proteins as diverse as imidazoline I₂ binding sites, CB₁ cannabinoid receptor, NK₁ tachykinin receptor, D₂ dopamine receptor, cyclooxygenases, fatty acid amide hydrolase and monoacylglycerol lipase and σ₁ receptor. Reviewing the individual attempts, we outline the chemistry, the obtained pharmacological properties and structure-activity relationships. Finally, we discuss the possible directions for future work.

New developments in osteoarthritis pharmacological therapies

OA is an increasingly common, painful condition with complex aetiology and limited therapies. Approaches to expanding our therapeutic armamentarium have included repurposing existing therapies used for other rheumatological conditions, modifying existing OA preparations to enhance their benefits, and identifying new therapeutics. HCQ and low-dose MTX have been unsuccessful in improving hand OA pain or reducing structural progression. Anti-IL-6 and anti-GM-CSF also did not improve symptoms in hand OA trials, but IL-1 remains an intriguing target for large-joint OA, based on reduced joint replacements in a post hoc analysis from a large cardiovascular disease trial. The peripheral nociceptive pathway appears an attractive target, with mAbs to nerve growth factor and IA capsaicin demonstrating efficacy; tropomyosin receptor kinase A inhibitors are at an earlier stage of development. Limited evidence suggests pharmacological therapies can modify cartilage and bone structural progression, though evidence of synchronous symptom benefits are lacking.

An up to date on clinical prospects and management of osteoarthritis

The rising prevalence of osteoarthritis (OA) in the general population has necessitated the development of novel treatment options. It is critical to recognize the joint as a separate entity participating in degenerative processes, as well as the multifaceted nature of OA. OA is incurable because there is currently no medication that can stop or reverse cartilage or bone loss. As this point of view has attracted attention, more research is being directed toward determining how the various joint components are impacted and how they contribute to OA pathogenesis. Over the next few years, several prospective therapies focusing on inflammation, cartilage metabolism, subchondral bone remodelling, cellular senescence, and the peripheral nociceptive pathway are predicted to transform the OA therapy landscape. Stem cell therapies and the use of various biomaterials to target articular cartilage (AC) and osteochondral tissues are now being investigated in considerable detail. Currently, laboratory-made cartilage tissues are on the verge of being used in clinical settings. This review focuses on the update of clinical prospects and management of osteoarthritis, as well as future possibilities for the treatment of OA.

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Osteoarthritis (OA) is a general term that incorporates several different joint diseases.

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The exact pathophysiology of OA remains unclear.

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OA is incurable because there is currently no medication that can stop or reverse cartilage or bone loss.

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Nonsteroidal anti-inflammatory drugs are the most frequently prescribed medications to alleviate arthritic discomfort.

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Stem cell therapies to target articular cartilage and osteochondral tissues are now under investigation.

Benzofuranyl-2-imidazoles as imidazoline I2 receptor ligands for Alzheimer's disease

Recent findings unveil the pharmacological modulation of imidazoline I₂ receptors (I₂-IR) as a novel strategy to face unmet medical neurodegenerative diseases. In this work, we report the chemical characterization, three-dimensional quantitative structure-activity relationship (3D-QSAR) and ADMET in silico of a family of benzofuranyl-2-imidazoles that exhibit affinity against human brain I₂-IR and most of them have been predicted to be brain permeable. Acute treatment in mice with 2-(2-benzofuranyl)-2-imidazole, known as LSL60101 (garsevil), showed non-warning properties in the ADMET studies and an optimal pharmacokinetic profile. Moreover, LSL60101 induced hypothermia in mice while decreased pro-apoptotic FADD protein in the hippocampus. In vivo studies in the familial Alzheimer's disease 5xFAD murine model with the representative compound, revealed significant decreases in the protein expression levels of antioxidant enzymes superoxide dismutase and glutathione peroxidase in hippocampus. Overall, LSL60101 plays a neuroprotective role by reducing apoptosis and modulating oxidative stress.

Osteoarthritis year in review 2020: epidemiology & therapy

This personal choice of research themes and highlights from within the past year (1 May 2019 to 14 April 2020) spans descriptive, analytical-observational, and intervention studies. Descriptive estimates of the burden of osteoarthritis continue to underscore its position as a leading cause of disability worldwide, but whose burden is often felt greatest among disadvantaged and marginalised communities. Many of the major drivers of that burden are known but epidemiological studies continue the important work of elaborating on their timing, dose, specificity, and reversibility and placing them within an appropriate multi-level framework. A similar process of elaboration is seen also in studies (re-)estimating the relative benefits and risks of existing interventions, in some cases helping to identify low-value care, unwarranted variation, and initiating processes of deprescribing and decommissioning. Such research need not engender therapeutic nihilism. Our review closes by highlighting some emerging evidence on the efficacy and safety of novel therapeutic interventions and with a selective roll-call of methodological and meta-research in OA illustrating the continued commitment to improving research quality.

Improved efficacy, tolerance, safety, and abuse liability profile of the combination of CR4056 and morphine over morphine alone in rodent models

BACKGROUND AND PURPOSE

Prolonged use of opioids causes analgesic tolerance and adverse effects including constipation and dependence. Compounds targeting imidazoline I2 receptors are known to potentiate opioid analgesia in rodents. We investigated whether combination with the I2 receptor ligand CR4056 could improve efficacy and safety of morphine and explored the mechanisms of the CR4056-opioid interaction.

EXPERIMENTAL APPROACH

We used the complete Freund's adjuvant (CFA) model in rats to study the effects of treatments on hyperalgesia, morphine tolerance and microglia activation as measured by immunofluorescence. Opioid-induced adverse effects were assessed in rodent models of morphine-induced constipation, sedation (open field, sedation rating scale, and rotarod), physical dependence (naloxone-induced withdrawal), and abuse (conditioned place preference-associated reward). Chemiluminescence assays tested CR4056 as allosteric modulator of μ-opioid receptors.

KEY RESULTS

CR4056 (ED50 = 4.88 mg·kg-1 ) and morphine (ED50 = 2.07 mg·kg-1 ) synergized in reducing CFA-induced hyperalgesia (ED50 = 0.52 mg·kg-1 ; 1:1 combination). Consistently, low doses of CR4056 (1 mg·kg-1 ) spared one third of the cumulative morphine dose administered during 4 days and prevented/reversed the development of tolerance to morphine anti-hyperalgesia. These opioid-sparing effects were associated with decreased activation of microglia, independent of CR4056 interactions on μ-opioid receptors. Importantly, the low doses of CR4056 and morphine that synergize in analgesia did not induce constipation, sedation, physical dependence, or place preference.

CONCLUSION AND IMPLICATIONS

We showed selective synergism between CR4056 and morphine as analgesics. Their combination showed an improved safety and abuse liability profile over morphine alone. CR4056 could be developed as an opioid-sparing drug in multimodal analgesia.

Recent advances in the treatment of osteoarthritis

Osteoarthritis (OA) is one of the most debilitating diseases and is associated with a high personal and socioeconomic burden. So far, there is no therapy available that effectively arrests structural deterioration of cartilage and bone or is able to successfully reverse any of the existing structural defects. Efforts to identify more tailored treatment options led to the development of strategies that enabled the classification of patient subgroups from the pool of heterogeneous phenotypes that display distinct common characteristics. To this end, the classification differentiates the structural endotypes into cartilage and bone subtypes, which are predominantly driven by structure-related degenerative events. In addition, further classifications have highlighted individuals with an increased inflammatory contribution (inflammatory phenotype) and pain-driven phenotypes as well as senescence and metabolic syndrome phenotypes. Most probably, it will not be possible to classify individuals by a single definite subtype, but it might help to identify groups of patients with a predominant pathology that would more likely benefit from a specific drug or cell-based therapy. Current clinical trials addressed mainly regeneration/repair of cartilage and bone defects or targeted pro-inflammatory mediators by intra-articular injections of drugs and antibodies. Pain was treated mostly by antagonizing nerve growth factor (NGF) activity and its receptor tropomyosin-related kinase A (TrkA). Therapies targeting metabolic disorders such as diabetes mellitus and senescence/aging-related pathologies are not specifically addressing OA. However, none of these therapies has been proven to modify disease progression significantly or successfully prevent final joint replacement in the advanced disease stage. Within this review, we discuss the recent advances in phenotype-specific treatment options and evaluate their applicability for use in personalized OA therapy.

The influence of sample size and gender composition on the meta-analysis conclusion of platelet-rich plasma treatment for osteoarthritis

Objective

The magnitude of the therapeutic effects of intra-articular injection of platelet-rich plasma (PRP) on osteoarthritis (OA) is still under debate. The goal of this study that was a systematic review of randomised controlled trials ​of PRP injections for the treatment of OA was to elucidate the therapeutic efficacy of PRP.

Methods

Electronic databases of PubMed, CENTRAL, EMBASE, EBSCO, ClinicalTrials.gov, and International Clinical Trials Registry Platform ​were searched from inception to June 2018 for RCTs that compared PRP injections to controls in patients with OA. A random-effects approach was used to compile data and subgroups according to trial size (large trials versus small trials), patient profile (age and gender), and PRP preparation method was performed.

Results

Thirty trials met the inclusion criteria and were analysed. All results had unexplained statistical heterogeneity. Patients treated with PRP compared with control showed statistically relevant pain relief and function improvement at short term (standardised mean difference [SMD] ​= ​−0.62, 95% confidence interval [CI]: −0.98 to −0.27, P ​= ​0.0006, SMD ​= ​−0.74, 95% CI: −1.11 to 0.36, P ​= ​0.0001, respectively), medium term (SMD ​= ​−0.53, 95% CI: −0.83 to −0.23, P ​= ​0.0006, SMD ​= ​−0.50, 95% CI: −0.75 to −0.25, P ​= ​0.0006), and long term (SMD ​= ​−0.69, 95% CI: −1.08 to −0.30, P ​= ​0.0006, SMD ​= ​−0.68, 95% CI: −0.1.09 to −0.27, P ​= ​0.001, respectively). A subgroup analysis of the data from large trials and from trials composed of less than 50% female patients revealed that therapeutic effects of the treatment are insignificant.

Conclusions

According to the currently available data, PRP injections are beneficial for pain relief and function improvement in patients with OA. This meta-analysis, however, demonstrated that the efficacy of PRP is related to sample size and gender composition. Thus, more randomised controlled trials of high quality and larger patient size, also including gender aspects, are required to understand this phenomenon.

The translational potential of this article

The translation potential of this meta-analysis is that provided another perspective to analyse the treatment effect of PRP for OA. In future research, phenotypes subpopulation and gender difference of OA patient should be considered for PRP treatment.

CR4056, a powerful analgesic imidazoline-2 receptor ligand, inhibits the inflammation-induced PKCε phosphorylation and membrane translocation in sensory neurons

BACKGROUND AND PURPOSE

CR4056 is a first-in-class imidazoline-2 (I₂ ) receptor ligand characterized by potent analgesic activity in different experimental animal models of pain. In a recent phase II clinical trial, CR4056 effectively reduced pain in patients with knee osteoarthritis. In the present study, we investigated the effects of CR4056 on PKCε translocation in vitro and on PKCε activation in vivo in dorsal root ganglia (DRG) neurons.

EXPERIMENTAL APPROACH

Effects of CR4056 on bradykinin-induced PKCε translocation were studied in rat sensory neurons by immunocytochemistry. PKCε activation was investigated by immunohistochemistry analysis of DRG from complete Freund's adjuvant-treated animals developing local hyperalgesia. The analgesic activity of CR4056 was tested on the same animals.

KEY RESULTS

CR4056 inhibited PKCε translocation with very rapid and long-lasting activity. CR4056 decreased hyperalgesia and phospho-PKCε immunoreactivity in the DRG neurons innervating the inflamed paw. The effect of CR4056 on PKCε translocation was blocked by pertussis toxin, implying that the intracellular pathways involved G_i proteins. The inhibition of PKCε translocation by CR4056 was independent of the α₂ -adrenoeceptor and, surprisingly, was also independent of idazoxan-sensitive I₂ binding sites. The I₂ agonist 2BFI had no effect alone but potentiated the activity of low concentrations of CR4056.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that CR4056 shares the ability to inhibit PKCε translocation with other analgesics. Whether the inhibition of PKCε involves binding to specific subtype(s) of I₂ receptors should be further investigated. If so, this would be a new mode of action of a highly specific I₂ receptor ligand.