Arabella Young

Targeting Cancer-Derived Adenosine:New Therapeutic Approaches

UNLABELLED CD73 generation of immunosuppressive adenosine within the hypoxic tumor microenvironment causes dysregulation of immune cell infiltrates, resulting in tumor progression, metastases, and poor disease outcomes. Therapies targeted toward the adenosinergic pathway, such as antibodies targeting CD73 and CD39, have proven efficacy in mouse tumor models; however, humanized versions are only in preliminary development. In contrast, A(2A) adenosine receptor antagonists have progressed to late-stage clinical trials in Parkinson disease, yet evidence of their role in oncology is limited. This review will compare the merits and challenges of these therapeutic approaches, identifying tumor indications and combinations that may be fruitful as they progress to the clinic. SIGNIFICANCE High concentrations of immunosuppressive adenosine have been reported in cancers, and adenosine is implicated in the growth of tumors. This brief review delineates the current treatment strategies and tumor subtypes that will benefit from targeting adenosinergic pathways, alone or in combination with contemporary approaches to cancer treatment.

Antimetastatic Effects of Blocking PD-1 and the Adenosine A2A Receptor

Adenosine targeting is an attractive new approach to cancer treatment, but no clinical study has yet examined adenosine inhibition in oncology despite the safe clinical profile of adenosine A2A receptor inhibitors (A2ARi) in Parkinson disease. Metastasis is the main cause of cancer-related deaths worldwide, and therefore we have studied experimental and spontaneous mouse models of melanoma and breast cancer metastasis to demonstrate the efficacy and mechanism of a combination of A2ARi in combination with anti-PD-1 monoclonal antibody (mAb). This combination significantly reduces metastatic burden and prolongs the life of mice compared with either monotherapy alone. Importantly, the combination was only effective when the tumor expressed high levels of CD73, suggesting a tumor biomarker that at a minimum could be used to stratify patients that might receive this combination. The mechanism of the combination therapy was critically dependent on NK cells and IFNγ, and to a lesser extent, CD8(+) T cells and the effector molecule, perforin. Overall, these results provide a strong rationale to use A2ARi with anti-PD-1 mAb for the treatment of minimal residual and metastatic disease.

A Threshold Level of Intratumor CD8+ T-cell PD1 Expression Dictates Therapeutic Response to Anti-PD1

Despite successes, thus far, a significant proportion of the patients treated with anti-PD1 antibodies have failed to respond. We use mouse tumor models of anti-PD1 sensitivity and resistance and flow cytometry to assess tumor-infiltrating immune cells immediately after therapy. We demonstrate that the expression levels of T-cell PD1 (PD1(lo)), myeloid, and T-cell PDL1 (PDL1(hi)) in the tumor microenvironment inversely correlate and dictate the efficacy of anti-PD1 mAb and function of intratumor CD8(+) T cells. In sensitive tumors, we reveal a threshold for PD1 downregulation on tumor-infiltrating CD8(+) T cells below which the release of adaptive immune resistance is achieved. In contrast, PD1(hi) T cells in resistant tumors fail to be rescued by anti-PD1 therapy and remain dysfunctional unless intratumor PDL1(lo) immune cells are targeted. Intratumor Tregs are partly responsible for the development of anti-PD1-resistant tumors and PD1(hi) CD8(+) T cells. Our analyses provide a framework to interrogate intratumor CD8(+) T-cell PD1 and immune PDL1 levels and response in human cancer.

Tumor immunoevasion by the conversion of effector NK cells into type 1 innate lymphoid cells

Avoiding destruction by immune cells is a hallmark of cancer, yet how tumors ultimately evade control by natural killer (NK) cells remains incompletely defined. Using global transcriptomic and flow-cytometry analyses and genetically engineered mouse models, we identified the cytokine-TGF-β-signaling-dependent conversion of NK cells (CD49a−CD49b+Eomes+) into intermediate type 1 innate lymphoid cell (intILC1) (CD49a+CD49b+Eomes+) populations and ILC1 (CD49a+CD49b−Eomesint) populations in the tumor microenvironment. Strikingly, intILC1s and ILC1s were unable to control local tumor growth and metastasis, whereas NK cells favored tumor immunosurveillance. Experiments with an antibody that neutralizes the cytokine TNF suggested that escape from the innate immune system was partially mediated by TNF-producing ILC1s. Our findings provide new insight into the plasticity of group 1 ILCs in the tumor microenvironment and suggest that the TGF-β-driven conversion of NK cells into ILC1s is a previously unknown mechanism by which tumors escape surveillance by the innate immune system.

Improved Efficacy of Neoadjuvant Compared to Adjuvant Immunotherapy to Eradicate Metastatic Disease

Immunotherapy has recently entered a renaissance phase with the approval of multiple agents for the treatment of cancer. Immunotherapy stands ready to join traditional modalities, including surgery, chemotherapy, radiation, and hormone therapy, as a pillar of cancer treatment. Although immunotherapy has begun to have success in advanced cancer treatment, its scheduling and efficacy with surgery to treat earlier stages of cancer and prevent distant metastases has not been systematically examined. Here, we have used two models of spontaneously metastatic breast cancers in mice, to illustrate the significantly greater therapeutic power of neoadjuvant, compared with adjuvant immunotherapies in the context of primary tumor resection. Elevated and sustained peripheral tumor-specific immune responses underpinned the outcome, and blood sampling of tumor-specific CD8+ T cells immediately prior and post surgery may provide a predictor of outcome. These data now provide strong rationale to extensively test and compare neoadjuvant immunotherapy in humans.

NK cells require IL-28R for optimal in vivo activity

Significance Natural killer (NK) cells are naturally circulating innate lymphocytes that sense altered cells, including pathogen-activated and early-transformed cells. The signals that prime the NK cell to respond are not completely understood, but cytokines, such as IL-12, IL-18, and type I interferon (IFN-αβ) from antigen-presenting cells, are appreciated to be key to NK cell effector functions in response to bacteria, viruses, and tumors. In this light, another class of IFN, IFN type III (IFN-λ), has been described that shares some common functions with IFN-αβ, but with a more restricted cellular expression. Here, we demonstrate for the first time, to our knowledge, the ability of IFN-λ to directly regulate NK cell effector functions in vivo, alone and in the context of IFN-αβ. Natural killer (NK) cells are naturally circulating innate lymphoid cells that protect against tumor initiation and metastasis and contribute to immunopathology during inflammation. The signals that prime NK cells are not completely understood, and, although the importance of IFN type I is well recognized, the role of type III IFN is comparatively very poorly studied. IL-28R–deficient mice were resistant to LPS and cecal ligation puncture-induced septic shock, and hallmark cytokines in these disease models were dysregulated in the absence of IL-28R. IL-28R–deficient mice were more sensitive to experimental tumor metastasis and carcinogen-induced tumor formation than WT mice, and additional blockade of interferon alpha/beta receptor 1 (IFNAR1), but not IFN-γ, further enhanced metastasis and tumor development. IL-28R–deficient mice were also more susceptible to growth of the NK cell-sensitive lymphoma, RMAs. Specific loss of IL-28R in NK cells transferred into lymphocyte-deficient mice resulted in reduced LPS-induced IFN-γ levels and enhanced tumor metastasis. Therefore, by using IL-28R–deficient mice, which are unable to signal type III IFN-λ, we demonstrate for the first time, to our knowledge, the ability of IFN-λ to directly regulate NK cell effector functions in vivo, alone and in the context of IFN-αβ.

Targeting immunosuppressive adenosine in cancer

Despite the success of anti-programmed cell death protein 1 (PD1), anti-PD1 ligand 1 (PDL1) and anti-cytotoxic T lymphocyte antigen 4 (CTLA4) therapies in advanced cancer, a considerable proportion of patients remain unresponsive to these treatments (known as innate resistance). In addition, one-third of patients relapse after initial response (known as adaptive resistance), which suggests that multiple non-redundant immunosuppressive mechanisms coexist within the tumour microenvironment. A major immunosuppressive mechanism is the adenosinergic pathway, which now represents an attractive new therapeutic target for cancer therapy. Activation of this pathway occurs within hypoxic tumours, where extracellular adenosine exerts local suppression through tumour-intrinsic and host-mediated mechanisms. Preclinical studies in mice with adenosine receptor antagonists and antibodies have reported favourable antitumour immune responses with some definition of the mechanism of action. Currently, agents targeting the adenosinergic pathway are undergoing first-in-human clinical trials as single agents and in combination with anti-PD1 or anti-PDL1 therapies. In this Review, we describe the complex interplay of adenosine and adenosine receptors in the development of primary tumours and metastases and discuss the merits of targeting one or more components that compose the adenosinergic pathway. We also review the early clinical data relating to therapeutic agents inhibiting the adenosinergic pathway.

Adenosine 2B Receptor Expression on Cancer Cells Promotes Metastasis

Adenosine plays an important role in inflammation and tumor development, progression, and responses to therapy. We show that an adenosine 2B receptor inhibitor (A2BRi) decreases both experimental and spontaneous metastasis and combines with chemotherapy or immune checkpoint inhibitors in mouse models of melanoma and triple-negative breast cancer (TNBC) metastasis. Decreased metastasis upon A2BR inhibition is independent of host A2BR and lymphocytes and myeloid cells. Knockdown of A2BR on mouse and human cancer cells reduces their metastasis in vivo and decreases their viability and colony-forming ability, while transiently delaying cell-cycle arrest in vitro The prometastatic activity of adenosine is partly tumor A2BR dependent and independent of host A2BR expression. In humans, TNBC cell lines express higher A2BR than luminal and Her2(+) breast cancer cell lines, and high expression of A2BR is associated with worse prognosis in TNBC. Collectively, high A2BR on mouse and human tumors promotes cancer metastasis and is an ideal candidate for therapeutic intervention. Cancer Res; 76(15); 4372-82. ©2016 AACR.

MAPK signaling and inflammation link melanoma phenotype switching to induction of CD73 during immunotherapy

Evolution of tumor cell phenotypes promotes heterogeneity and therapy resistance. Here we found that induction of CD73, the enzyme that generates immunosuppressive adenosine, is linked to melanoma phenotype switching. Activating MAPK mutations and growth factors drove CD73 expression, which marked both nascent and full activation of a mesenchymal-like melanoma cell state program. Proinflammatory cytokines like TNFα cooperated with MAPK signaling through the c-Jun/AP-1 transcription factor complex to activate CD73 transcription by binding to an intronic enhancer. In a mouse model of T-cell immunotherapy, CD73 was induced in relapse melanomas, which acquired a mesenchymal-like phenotype. We also detected CD73 upregulation in melanoma patients progressing under adoptive T-cell transfer or immune checkpoint blockade, arguing for an adaptive resistance mechanism. Our work substantiates CD73 as a target to combine with current immunotherapies, but its dynamic regulation suggests limited value of CD73 pretreatment expression as a biomarker to stratify melanoma patients. Cancer Res; 77(17); 4697-709. ©2017 AACR.

Co-blockade of immune checkpoints and adenosine A2A receptor suppresses metastasis

Immunosuppressive pathways active within the tumor microenvironment must be targeted in combination to sufficiently bolster antitumor immune defenses. Inhibition of A2A adenosine receptor signaling in combination with immune checkpoint blockade enhances CD8+ T and NK cell anti-metastatic activity. This results in reduced metastatic burden and improved survival in pre-clinical models.