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A2aR antagonists: Next generation checkpoint blockade for cancer immunotherapy
Robert D Leone1, Ying-Chun Lo1, Jonathan D Powell1
1Sidney Kimmel Comprehensive Cancer Research Center, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
Abstract:
The last several years have witnessed exciting progress in the development of immunotherapy for the treatment of cancer. This has been due in great part to the development of so-called checkpoint blockade. That is, antibodies that block inhibitory receptors such as CTLA-4 and PD-1 and thus unleash antigen-specific immune responses against tumors. It is clear that tumors evade the immune response by usurping pathways that play a role in negatively regulating normal immune responses. In this regard, adenosine in the immune microenvironment leading to the activation of the A2a receptor has been shown to represent one such negative feedback loop. Indeed, the tumor microenvironment has relatively high concentrations of adenosine. To this end, blocking A2a receptor activation has the potential to markedly enhance anti-tumor immunity in mouse models. This review will present data demonstrating the ability of A2a receptor blockade to enhance tumor vaccines, checkpoint blockade and adoptive T cell therapy. Also, as several recent studies have demonstrated that under certain conditions A2a receptor blockade can enhance tumor progression, we will also explore the complexities of adenosine signaling in the immune response. Despite important nuances to the A2a receptor pathway that require further elucidation, studies to date strongly support the development of A2a receptor antagonists (some of which have already been tested in phase III clinical trials for Parkinson Disease) as novel modalities in the immunotherapy armamentarium.
Insights
Blocking the adenosine A2a receptor enhances anti-tumor immunity by boosting immunotherapy, including checkpoint blockade and vaccines. Further research is needed to understand adenosine signaling complexities for novel cancer treatments.
Area of Science:
- Immunology
- Oncology
- Pharmacology
Background:
- Cancer immunotherapy has advanced significantly, largely due to checkpoint blockade therapies targeting CTLA-4 and PD-1.
- Tumors evade immune responses by exploiting negative regulatory pathways, such as adenosine signaling via the A2a receptor in the tumor microenvironment.
- High adenosine concentrations in the tumor microenvironment contribute to immune suppression.
Purpose of the Study:
- To review the potential of blocking A2a receptor activation to enhance anti-tumor immunity.
- To present data on A2a receptor blockade's efficacy in combination with tumor vaccines, checkpoint blockade, and adoptive T cell therapy.
- To explore the complex role of adenosine signaling in immune responses, including instances where A2a receptor blockade may promote tumor progression.
Main Methods:
- Review of preclinical data and published studies on adenosine signaling and A2a receptor blockade in cancer.
- Analysis of the impact of A2a receptor antagonists on anti-tumor immune responses in various therapeutic settings.
- Examination of the complexities and nuances of adenosine-mediated immune regulation in the tumor microenvironment.
Main Results:
- A2a receptor blockade demonstrates potential to enhance the efficacy of cancer vaccines, checkpoint blockade, and adoptive T cell therapy in preclinical models.
- Adenosine signaling through the A2a receptor acts as a significant immunosuppressive mechanism within the tumor microenvironment.
- Certain conditions may lead to A2a receptor blockade paradoxically enhancing tumor progression, highlighting the complexity of this pathway.
Conclusions:
- A2a receptor antagonists represent a promising therapeutic strategy to augment anti-tumor immunity and enhance existing immunotherapies.
- Further elucidation of adenosine signaling complexities is crucial for optimizing the clinical application of A2a receptor antagonists.
- A2a receptor antagonists are being developed as novel immunotherapeutic agents, with some candidates already in late-stage clinical trials for other diseases.
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