Abstract 1472: Enzymatic depletion of adenosine by pegylated, engineered adenosine deaminase 2 (PEG-ADA2): A novel immunotherapeutic approach to treat solid tumors

Proceedings: AACR 107th Annual Meeting 2016; April 16-20, 2016; New Orleans, LA Adenosine is an endogenous immunosuppressant that binds to adenosine receptor checkpoints and protects tissue from immune-mediated rejection. Abnormally high adenosine levels (up to 100-fold greater than other tissues) contribute to a highly immunosuppressive tumor microenvironment (TME). We hypothesized that adenosine deaminase 2 (ADA2), a human enzyme that catalyzes the deamination of adenosine, could be administered at therapeutic levels to deplete high levels of TME adenosine and stimulate anti-tumor immune activity. Recombinant wild-type ADA2 (wtADA2) was cleared extremely rapidly from circulation (t1/2 = 69 min, 7.5 mg/kg iv, n = 9 mice), rendering it unsuitable for therapeutic testing. Therefore, a series of variants was designed to attenuate the heparin binding properties of ADA2 to improve bio-distribution and conjugated with 20K PEG to improve pharmacokinetics (PK). The variant PEG-ADA2-K374D displayed 94% less binding to heparin compared to wtADA2, enzymatic activity comparable to wtADA2, and 33-fold improved PK (t1/2 = 2,256 min); and consistently induced at least 60% (p 40-fold increase). This variant induced a maximum TGI of 69% (p<0.05) in the MH194/PSC4 model at 0.003 mg/kg, a 100-fold lower dose than PEG-ADA2-K374D (n = 8). A third variant, PEG-ADA2-E182T lacked detectable enzymatic activity and displayed no tumor growth inhibition, suggesting that ADA2 enzyme activity is required for efficacy. These data suggest that engineered PEG-ADA2 variants induce significant tumor growth inhibition activity in several syngeneic solid tumor models, validating enzymatic depletion of high TME adenosine levels as novel immunotherapeutic approach to treat solid tumors. Citation Format: Lin Wang, Jessica Cowell, Sanna Rosengren, Lei Huang, Xiaoming Li, Qiping Zhao, Jennifer Souratha, Mathieu Marella, Barbara Blouw, Keri Cannon, Chunmei Zhao, Kim Phan, Curtis Thompson, Michael Shepard, Christopher Thanos. Enzymatic depletion of adenosine by pegylated, engineered adenosine deaminase 2 (PEG-ADA2): A novel immunotherapeutic approach to treat solid tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1472.