Adenosine deaminase 2 (ADA2) is a human serum protein that catalyzes the reaction of deamination of adenosine to inosine. Besides catalytic activity, ADA2 has a heparin-binding domain and a growth factor-like domain. Adenosine accumulates in the tumor microenvironment and suppresses anti-tumor immune responses, while promoting tumor cell metastasis. Previously, we showed that treatment of mice with PEGylated forms of ADA2 (PEG ADA2) can decrease the accumulation of tumor-associated adenosine. Here, we analyzed the TCGA RNA-seq database using OncoLnc tool and observed that high expression of the ADA2 gene (CECR1) in certain immunotherapy responsive tumors correlated with increased survival of patients. We then tested different engineered ADA2 variants, using the inactive enzyme variant as a control, for the reversal of adenosine-mediated responses in human T cells, mouse peritoneal macrophages, and mouse and human tumor cell lines. ADA2 variants with higher catalytic activity were able to reverse adenosine-mediated suppression of human T-cell proliferation, cAMP accumulation in tumors and human T cells, and polarization of macrophages into an immunosuppressive, pro-tumor phenotype, whereas the inactive ADA2 variant failed to cause any of these effects. In addition, the variant that lacks the ability to bind to heparin but has improved catalytic activity (PEG NME8058) showed similar responses to those with the catalytically improved variant with intact heparin-binding domain (PEG NME8062). These results suggest that the improved immune cell activity with ADA2 in the presence of adenosine requires the enzyme activity of this molecule. Next, we assessed PEG NME8062 in MC38 and CT26 colon carcinoma syngeneic tumors in C57BL/6 and Balb/c mice, and observed delayed growth in both tumors. Using the inactive enzyme variant, we have shown that anti-tumor effect of PEG NME8062 depends on enzyme activity. Delayed tumor growth was also associated with increased density of key anti-tumor immune cell populations in both tumor models. These data suggest that PEG ADA2 can reduce tumor growth in an enzyme-activity-dependent manner and promote anti-tumor immune responses in vitro and in vivo. These findings have important implications for targeting purinergic signaling for cancer therapy.

Citation Format: Luz Marina Londoño-R, Jessica Cowell, Lin Wang, Qiping Zhao, Lei Huang, Chris Thanos, Michael J. LaBarre, Xiaoming Li, Caglar Cekic. PEGylated adenosine deaminase (ADA2) prevents adenosine-mediated increase in tumor growth and improves antitumor immune responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1755.