(530b) Developing an Enzyme to Alleviate Adenosine-Mediated Immunosuppression in Cancer

A small metabolite, adenosine, accumulates in tumors at concentrations up to 100-times normal levels. Under normal conditions, adenosine calms immune responses to allow the body to heal following trauma or infection. However, high concentrations within tumors suppress immune cells from responding properly. Further, adenosine signaling amongst the tumor cells potentiates a positive feedback loop which supports tumor growth and encourages production of more adenosine. Tumors produce adenosine by multiple pathways and the metabolite acts on up to four receptors, thus, preventing either generation or signaling mediated by adenosine has proven challenging.

We report a novel approach to prevent adenosine-mediate immune suppression: the development of an enzyme to directly target adenosine itself. Adenosine deaminase (ADA), a naturally occurring enzyme, converts adenosine into nontoxic inosine so efficiently that the process is limited by substrate transport rather than the kinetic mechanism. We present here the optimization of an Escherichia coli production process and a single purification step to yield 15 milligrams of pure ADA per liter of culture. Prior to our work, this ADA variant had not yet been evaluated in pure form or produced at scale. In concert, we report the Michaelis-Menten kinetic parameters of the pure enzyme and will present its crystal structure. Most importantly, we will describe how tumor mouse models treated with ADA benefitted from a statistically significant survival advantage versus control mice. We will further discuss ongoing efforts to characterize the mechanistic in vivo impact of ADA on the murine immune system, including pharmacodynamic and pharmacokinetics studies, as well as phenotyping of immune cell subsets. From a 30,000-foot view, we intend to demonstrate the efficacy of adenosine depletion as therapeutic strategy for the treatment of solid cancers and to present ADA as an efficient means of doing so.