Blockade of A _2A receptors potently suppresses the metastasis of CD73 ⁺ tumors

Abstract

CD73 inhibits antitumor immunity through the activation of adenosine receptors expressed on multiple immune subsets. CD73 also enhances tumor metastasis, although the nature of the immune subsets and adenosine receptor subtypes involved in this process are largely unknown. In this study, we revealed that A 2A /A 2B receptor antagonists were effective in reducing the metastasis of tumors expressing CD73 endogenously (4T1.2 breast tumors) and when CD73 was ectopically expressed (B16F10 melanoma). A 2A −/− mice were strongly protected against tumor metastasis, indicating that host A 2A receptors enhanced tumor metastasis. A 2A blockade enhanced natural killer (NK) cell maturation and cytotoxic function in vitro, reduced metastasis in a perforin-dependent manner, and enhanced NK cell expression of granzyme B in vivo, strongly suggesting that the antimetastatic effect of A 2A blockade was due to enhanced NK cell function. Interestingly, A 2B blockade had no effect on NK cell cytotoxicity, indicating that an NK cell-independent mechanism also contributed to the increased metastasis of CD73 + tumors. Our results thus revealed that CD73 promotes tumor metastasis through multiple mechanisms, including suppression of NK cell function. Furthermore, our data strongly suggest that A 2A or A 2B antagonists may be useful for the treatment of metastatic disease. Overall, our study has potential therapeutic implications given that A 2A /A 2B receptor antagonists have already entered clinical trials in other therapeutic settings.cancer metastasis | immunotherapy | tumor immunosuppression | innate immunity

CD73: A potential biomarker for anti-PD-1 therapy

“…Notably, our findings that A 2A blockade can enhance the activity of anti-PD-1 are supported by the recent study by Sitkovsky and colleagues who showed that the removal of the hypoxic (adenosine promoting) environment could enhance the activity of dual PD-1 and CTLA-4 blockade in an A 2A dependent manner. 7 Although our data supports a number of studies showing that blockade of the A 2A receptor enhances antitumor immunity, 3,[5][6][7] it has recently been observed that genetic ablation of A 2A can be deleterious in some tumor models due to reduced T cell effector memory differentiation/ survival. 8 Therefore, it may be that the pharmacodynamic and pharmacokinetic properties of A 2A antagonists are vital to their therapeutic outcome.…”

“…3 CD73 is an ectoenzyme which suppresses the antitumor immune response due to its conversion of AMP to adenosine which consequently suppresses immune responses due to the activation of A 2A and A 2B receptors on a wide range of immune cells including T lymphocytes. 5 Targeting this pathway by either direct inhibition of CD73 or the downstream A 2A /A 2B receptors has been shown to induce antitumor immunity 3,6,7 (and reviewed by Leone et al 5 ).…”

Adenosine Inhibits Tumor Cell Invasion via Receptor-Independent Mechanisms

“…At first sight, the inhibitory effects of adenosine are unexpected because high ecto-5 0 -nucleotidase activity is often considered as a poor prognostic factor, which allows the tumors to avoid immune destruction via the generation of immunosuppressive adenosine and deactivation of tumorinfiltrating inflammatory cells (5,10,12,32). This apparent discrepancy could be resolved on the basis of the following considerations.…”

“…Ã , P < 0.05, as compared with control. For complete densitometric analyses of phospho-kinases in control and adenosine-treated PC-3, cells see Supplementary Table. Therefore, local and transient generation of nanomolar adenosine by tumor-derived CD73 would indeed be sufficient for the failure of mounting effective immune responses via activation of the A 2A receptors on cytotoxic T lymphocytes and other inflammatory cells (14,32). On the other hand, the overall pattern of purine homeostasis is markedly deregulated in the tumor environment by hypoxia and metabolic stress, as ascertained by data on constitutively elevated levels of intratumoral ATP (7,34), the accelerated rate of nucleotide turnover (4,9,33), and the ability of solid tumors to maintain adenosine gradient, with the highest nucleoside concentrations being reported in the center (14).…”

“…Current research on the role of adenosine in tumor pathogenesis and inflammation is particularly focused on targeting the releasing pathways of the precursor nucleotide ATP (7,34), directional regulation of ecto-5 0 -nucleotidase/ CD73 activity by using selective enzyme inhibitors, siRNA gene silencing and anti-CD73 mAb therapies (10,12,32), synthesis of phosphorylated adenosine derivatives acting as site-specific CD73-activated prodrugs of A 2A receptors (40), as well as development of nonmetabolizable nucleoside analogues acting either as selective adenosine receptor agonists and antagonists (5,13) or as metabolic inhibitors of intracellular purine homeostasis (16,20). Yet another approach includes tumor treatment with adenosine as a "kindred" metabolite; however, most of the proapoptotic and antiproliferative effects of adenosine reported in studies with different malignant cells required continuous presence of supra-physiological nucleoside concentrations (0.1-20 mmol/L) in the assay mixture (15,(17)(18)(19).…”