Adenosine signaling via the A2A and A2B receptors is emerging as an important regulatory mechanism of immune responses. While A2AR has high affinity for adenosine, A2BR is a low-affinity receptor that becomes activated only under pathological conditions when adenosine concentration reaches micromolar ranges. Besides high levels of adenosine (up to 100 μM), the tumor microenvironment (TME) is characterized by hypoxia. Hypoxia upregulates A2BR on tumors and on immune cells. TT-702 is a novel, selective and highly potent, orally active A2BR antagonist. Here we show that TT-702 inhibits tumor growth through multiple mechanisms including enhancement of dendritic cell (DC) function and T-cell activation, reduction of MDSCs and Tregs, and suppression of cancer cell growth, fibrosis and angiogenesis. The cellular potency of TT-702 was assessed in NECA induced cAMP production. The ability of TT-702 to reverse NECA-mediated immune suppression was evaluated using standard human DC differentiation and MLR assays. The effects of TT-702 on tumor growth were determined in B16F10 melanoma and MC38 and CT26 colorectal cancers in mice treated with TT-702 at 0.3, 1, 3 or 10 mg/kg (BID), anti-PD-1 (RMP1-14, 5 mg/kg, Q2D) or TT-702+RMP1-14 intraperitoneally. TT-702 binds to human A2BR with Ki value of 8.3 nM and exhibits greater than 100x selectivity for A1, A2A and A3 receptors. It potently inhibited NECA-stimulated cAMP production (IC50=2.8 nM). TT-702 dose-dependently inhibited the growth of human prostate cancer cells LNCaP and PC-3 (IC50=1.4 μM). Combination of TT-702 with enzalutamide showed an additive and synergistic effects to inhibit LNCaP and PC-3 growth, respectively. TT-702 prevented NECA-induced suppression of human DC differentiation and completely reversed NECA-induced T cell inactivation (EC50=0.45 μM). By contrast, preladenant, an A2AR antagonist, had no effect on cancer cell growth and DC differentiation. Moreover, TT-702 increased MC38 tumor-infiltrating immune stimulatory cells (DCs, CD4+ and CD8+ T cells) and reduced immunosuppressive cells (MDSCs and Tregs). TT-702 dose-dependently inhibited the growth of mouse MC38 and CT26 colorectal cancers. Interestingly, TT-702 also inhibited the growth of mouse B16F10 melanoma cold tumor. Furthermore, combination of TT-702 with anti-PD-1 synergistically inhibited both B16F10 and CT26 tumor growth. Most importantly, TT-702 significantly reduced tumor fibrosis and angiogenesis, suggesting that TT-702 may improve the TME for T cell penetration, cancer killing and prevention of metastasis. TT-702, a novel, selective and potent A2B receptor antagonist, has the potential to treat a diverse range of hard-to-treat and aggressive tumors (including cold ones) as a monotherapy, and in combination with anti-PD-1, enzalutamide and other anticancer therapies. TT-702 exhibits excellent safety and PK profiles in animals and is slated to enter clinical development in 2021.

Citation Format: Peidong Fan, Filomena Housley, Helena Haberstock, Ken Horne, Jim Liu, Elfatih Elzein, Lina Yao. TT-702, a selective and potent A2B receptor antagonist for the treatment of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 55.