Impact of Adenosine Analogue, Adenosine-5'-N-Ethyluronamide (NECA), on Insulin Signaling in Skeletal Muscle Cells

Overcoming high level adenosine-mediated immunosuppression by DZD2269, a potent and selective A2aR antagonist

BACKGROUND

Adenosine is a potent immunosuppressant whose levels in the tumor microenvironment (TME) are often much higher than those in normal tissues. Binding of adenosine to its receptor A2aR activates a cascade of genes and leads to immunosuppression. In addition, immune checkpoint blockage markedly increases A2aR expression in T cells, which could dampen their anti-tumor response. Several A2aR antagonists are under clinical development, but with limited clinical benefit reported so far. These A2aR antagonists showed much diminished activity at high adenosine levels found in TME, which may explain their clinical underperformance. We report the discovery and early clinical development of DZD2269, a novel A2aR antagonist which can fully block A2aR mediated immunosuppression commonly found in TME. Adenosine stimulates phosphorylation of cyclic AMP response element binding protein (CREB) in T cells and inhibits anti-tumor cytokine secretion in PBMCs in a dose-dependent manner. DZD2269 was able to reverse the immunosuppression induced by high concentrations of adenosine, as demonstrated by inhibiting CREB phosphorylation in T cells, restoring Th1 cytokine secretion in PBMCs, and stimulating dendritic cells (DCs) maturation. As a single agent, DZD2269 showed anti-tumor growth in multiple syngeneic mouse tumor models, and more profound anti-tumor effects were observed when DZD2269 was in combination with immune checkpoint inhibitors, radiotherapy, or chemotherapy. A good PK/PD relationship was observed in these animal models. In the phase 1 clinical study, downregulation of pCREB was detected in human T cells, consistent with preclinical prediction. Our data support further clinical development of DZD2269 in patients with cancer.

METHODS

The selectivity of DZD2269 for adenosine receptors was tested in engineered cell lines, and its efficacy in blocking A2aR signaling and reversing adenosine-mediated immunosuppression was assessed in human T cells and peripheral blood mononuclear cells (PBMCs). The anti-tumor effects of DZD2269 were evaluated in multiple syngeneic mouse models as a single agent as well as in combination with chemotherapy, radiotherapy, or immune checkpoint inhibitors. A phase 1 study in healthy volunteers (NCT04932005) has been initiated to assess safety, pharmacokinetics (PK) and pharmacodynamics (PD) of DZD2269.

RESULTS

Adenosine stimulates phosphorylation of cyclic AMP response element binding protein (CREB) in T cells and inhibits anti-tumor cytokine secretion in PBMCs in a dose-dependent manner. DZD2269 was able to reverse the immunosuppression induced by high concentrations of adenosine, as demonstrated by inhibiting CREB phosphorylation in T cells, restoring Th1 cytokine secretion in PBMCs, and stimulating dendritic cells (DCs) maturation. As a single agent, DZD2269 showed anti-tumor growth in multiple syngeneic mouse tumor models, and more profound anti-tumor effects were observed when DZD2269 was in combination with immune checkpoint inhibitors, radiotherapy, or chemotherapy. A good PK/PD relationship was observed in these animal models. In the phase 1 clinical study, downregulation of pCREB was detected in human T cells, consistent with preclinical prediction.

CONCLUSION

DZD2269 is a novel A2aR antagonist which can fully block A2aR mediated immunosuppression commonly found in TME. Clinical development of DZD2269 in patients with cancer is warranted (NCT04634344).

Molecular networks underlying cannabinoid signaling in skeletal muscle plasticity

The cannabinoid system is ubiquitously present and is classically considered to engage in neural and immunity processes. Yet, the role of the cannabinoid system in the whole body and tissue metabolism via central and peripheral mechanisms is increasingly recognized. The present review provides insights in (i) how cannabinoid signaling is regulated via receptor-independent and -dependent mechanisms and (ii) how these signaling cascades (might) affect skeletal muscle plasticity and physiology. Receptor-independent mechanisms include endocannabinoid metabolism to eicosanoids and the regulation of ion channels. Alternatively, endocannabinoids can act as ligands for different classic (cannabinoid receptor 1 [CB₁ ], CB₂ ) and/or alternative (e.g., TRPV1, GPR55) cannabinoid receptors with a unique affinity, specificity, and intracellular signaling cascade (often tissue-specific). Antagonism of CB₁ might hold clues to improve oxidative (mitochondrial) metabolism, insulin sensitivity, satellite cell growth, and muscle anabolism, whereas CB₂ agonism might be a promising way to stimulate muscle metabolism and muscle cell growth. Besides, CB₂ ameliorates muscle regeneration via macrophage polarization toward an anti-inflammatory phenotype, induction of MyoD and myogenin expression and antifibrotic mechanisms. Also TRPV1 and GPR55 contribute to the regulation of muscle growth and metabolism. Future studies should reveal how the cannabinoid system can be targeted to improve muscle quantity and/or quality in conditions such as ageing, disease, disuse, and metabolic dysregulation, taking into account challenges that are inherent to modulation of the cannabinoid system, such as central and peripheral side effects.

The Impact of CB1 Receptor on Nuclear Receptors in Skeletal Muscle Cells

Cannabinoids are abundant signaling compounds; their influence predominantly arises via engagement with the principal two G-protein-coupled cannabinoid receptors, CB1 and CB2. One suggested theory is that cannabinoids regulate a variety of physiological processes within the cells of skeletal muscle. Earlier publications have indicated that expression of CB1 receptor mRNA and protein has been recognized within myotubes and tissues of skeletal muscle from both murines and humans, thus representing a potentially significant pathway which plays a role in the control of skeletal muscular activities. The part played by CB1 receptor activation or inhibition with respect to these functions and relevant to targets in the periphery, especially skeletal muscle, is not fully delineated. Thus, the aim of the current research was to explore the influence of CB1 receptor stimulation and inhibition on downstream signaling of the nuclear receptor, NR4A, which regulates the immediate impacts of arachidonyl-2′-chloroethylamide (ACEA) and/or rimonabant in the cells of skeletal muscle. Murine L6 skeletal muscle cells were used in order to clarify additional possible molecular signaling pathways which contribute to alterations in the CB1 receptor. Skeletal muscle cells have often been used; it is well-documented that they express cannabinoid receptors. Quantitative real-time probe-based polymerase chain reaction (qRT-PCR) assays are deployed in order to assess the gene expression characteristics of CB1 receptor signaling. In the current work, it is demonstrated that skeletal muscle cells exhibit functional expression of CB1 receptors. This can be deduced from the qRT-PCR assays; triggering CB1 receptors amplifies both NR4A1 and NR4A3 mRNA gene expression. The impact of ACEA is inhibited by the selective CB1 receptor antagonist, rimonabant. The present research demonstrated that 10 nM of ACEA notably amplified mRNA gene expression of NR4A1 and NR4A3; this effect was suppressed by the addition of 100 nM rimonabant. Furthermore, the CB1 receptor antagonist led to the downregulation of mRNA gene expression of NR4A1, NR4A2 and NR4A3. In conclusion, in skeletal muscle, CB1 receptors were recognized to be important moderators of NR4A1 and NR4A3 mRNA gene expression; these actions may have possible clinical benefits. Thus, in skeletal muscle cells, a possible physiological expression of CB1 receptors was identified. It is as yet unknown whether these CB1 receptors contribute to pathways underlying skeletal muscle biological function and disease processes. Further research is required to fully delineate their role(s).

The Impact of CB1 Receptor on Inflammation in Skeletal Muscle Cells

Background

Various factors trigger the inflammatory response and cytokine activation in skeletal muscle. Inflamed muscle will exhibit significant levels of inflammation and cytokine activity. Interleukin-6 (IL-6), a pro-inflammatory cytokine, exerts pleiotropic effects on skeletal muscle. Endocannabinoid produced by all cell types binds to a class of G protein-coupled receptors, in particular cannabinoid CB1 receptors, to induce skeletal muscle actions.

Objective

The purpose of this research was to discover whether activation of cannabinoid CB1 receptors in L6 skeletal muscle cells may promote IL-6 gene expression.

Materials and Methods

L6 skeletal muscle cells were cultured in 25 cm² flasks and quantitative reverse transcription-polymerase chain reaction (probe-based) utilised to quantify IL-6 gene expression levels among different treatment settings.

Results

Arachidonyl-2'-chloroethylamide (ACEA) 10 nM, a persistent selective CB1 receptor agonist, promotes IL-6 gene expression in a time-dependent manner. Rimonabant 100 nM, a selective cannabinoid CB1 receptor antagonist, blocks the impact of ACEA. However, insulin does not change IL-6 gene expression.

Conclusion

For the first time, a unique link between ACEA and IL-6 up-regulation has been established; IL-6 up-regulation generated by ACEA is mediated in skeletal muscle through cannabinoid CB1 receptor activation. As a result, cannabinoid CB1 receptors may be useful pharmaceutical targets in the treatment of inflammation and related disorders in skeletal muscle tissues.