Search

T cells play a critical role in the control of cancer. The development of immune checkpoint blockers (ICB) aimed at enhancing antitumor T-cell responses has revolutionized cancer treatment. However, durable clinical benefit is observed in only a subset of patients, prompting research efforts to focus on strategies that target multiple inhibitory signals within the tumor microenvironment (TME) to limit tumor evasion and improve patient outcomes. Adenosine has emerged as a potent immune suppressant within the TME, and CD73 is the major enzyme responsible for its extracellular production. CD73 can be co-opted within the TME to impair T-cell–mediated antitumor immunity and promote tumor growth. To target this pathway and block the formation of adenosine, we designed a novel, selective, and potent class of small-molecule inhibitors of CD73, including AB680 (quemliclustat), which is currently being tested in patients with cancer. AB680 effectively restored T-cell proliferation, cytokine secretion, and cytotoxicity that were dampened by the formation of immunosuppressive adenosine by CD73. Furthermore, in an allogeneic mixed lymphocyte reaction where CD73-derived adenosine had a dominant suppressive effect in the presence of PD-1 blockade, AB680 restored T-cell activation and function. Finally, in a preclinical mouse model of melanoma, AB680 inhibited CD73 in the TME and increased the antitumor activity of PD-1 blockade. Collectively, these data provide a rationale for the inhibition of CD73 with AB680 in combination with ICB, such as anti–PD-1, to improve cancer patient outcomes.

Supplementary Data from Targeting CD73 with AB680 (Quemliclustat), a Novel and Potent Small-Molecule CD73 Inhibitor, Restores Immune Functionality and Facilitates Antitumor Immunity

Supplementary Figure from Targeting CD73 with AB680 (Quemliclustat), a Novel and Potent Small-Molecule CD73 Inhibitor, Restores Immune Functionality and Facilitates Antitumor Immunity

T cells play a critical role in the control of cancer. The development of immune checkpoint blockers (ICB) aimed at enhancing antitumor T-cell responses has revolutionized cancer treatment. However, durable clinical benefit is observed in only a subset of patients, prompting research efforts to focus on strategies that target multiple inhibitory signals within the tumor microenvironment (TME) to limit tumor evasion and improve patient outcomes. Adenosine has emerged as a potent immune suppressant within the TME, and CD73 is the major enzyme responsible for its extracellular production. CD73 can be co-opted within the TME to impair T-cell–mediated antitumor immunity and promote tumor growth. To target this pathway and block the formation of adenosine, we designed a novel, selective, and potent class of small-molecule inhibitors of CD73, including AB680 (quemliclustat), which is currently being tested in patients with cancer. AB680 effectively restored T-cell proliferation, cytokine secretion, and cytotoxicity that were dampened by the formation of immunosuppressive adenosine by CD73. Furthermore, in an allogeneic mixed lymphocyte reaction where CD73-derived adenosine had a dominant suppressive effect in the presence of PD-1 blockade, AB680 restored T-cell activation and function. Finally, in a preclinical mouse model of melanoma, AB680 inhibited CD73 in the TME and increased the antitumor activity of PD-1 blockade. Collectively, these data provide a rationale for the inhibition of CD73 with AB680 in combination with ICB, such as anti–PD-1, to improve cancer patient outcomes.

INTRODUCTION: Tumors employ many strategies to attenuate immune responses. High levels of extracellular adenosine generated in the tumor microenvironment engage A2a and A2b adenosine receptors on immune cells, resulting in immunosuppression. Expression of A2aR and A2bR can vary by cell type, with T cells predominantly expressing A2aR while myeloid cells express both A2aR and A2bR. We have previously shown that etrumadenant, a dual A2aR/A2bR antagonist, blocks the immunosuppressive effects of adenosine in immune cells and enhances anti-tumor immune responses in mouse syngeneic tumors. Using dual and selective adenosine receptor antagonists, we assessed the contribution of these receptors to adenosine-mediated phenotypes in immune and cancer cells. METHODS: Human CD8+ T cells were isolated from healthy human blood and activated using CD3/CD28/CD2 stimulation and cytokines were analyzed by cytokine bead array at 72 hours. Primary human dendritic cells (DC) were isolated from healthy blood and matured with LPS/IFN-γ for 24 hours. Cancer cell lines were purchased from ATCC. The adenosine analogue NECA was used to stimulate A2aR/A2bR-mediated signaling. RESULTS: Activated human CD8+ T cells stimulated in the presence of NECA showed suppression of activation markers (CD69) and cytokine production (IFN-γ, IL-2 and granzyme B). As expected, we observed similar rescue of this phenotype with both etrumadenant and an A2aR-specific antagonist owing to the sole expression of A2aR on T cells. In contrast, primary DC have comparable expression of A2aR and A2bR, suggesting that dual blockade may provide greater resistance to adenosine-mediated suppression than A2aR antagonism. Indeed, etrumadenant was able to attenuate the adenosine-mediated upregulation of IL-10 and enhance IL-12p70 production, whereas a comparable A2aR-specific antagonist showed no significant rescue versus NECA-stimulated controls. These observations may be extended to suppressive myeloid populations as well as tumor-resident macrophages and myeloid-derived suppressor cells isolated from mouse syngeneic tumors, which have very high expression of both A2aR and A2bR. RNA-sequencing identified a cassette of genes regulated by adenosine-signaling in these cells, which were largely reversed by etrumadenant. Finally, cultured human cancer cell lines have high expression of A2bR, which has been implicated in driving their tumorigenesis. Etrumadenant reversed adenosine-stimulated gene expression changes in non-small cell lung cancer cell lines, restoring enriched pathways driven by adenosine signaling. CONCLUSIONS: Taken together, these results show an important role for A2aR/A2bR in adenosine-mediated immunosuppression and provide a mechanistic rationale for stimulation of anti-tumor immune responses with the dual adenosine receptor antagonist etrumadenant. Citation Format: Sachie Marubayashi, Bindi Patel, Livia Yamashiro, Dana Piovesan, Sean Cho, Jenna Jeffrey, Manmohan Leleti, Jay Powers, Matt Walters, Daniel DiRenzo. Dual A2aR/A2bR antagonism with etrumadenant (AB928) eliminates the suppressive effects of adenosine on immune and cancer cells in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 256.