Abstract 5570: A novel approach to targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine
Authors: Zhang Michelle , Stone Everett , Triplett Todd A. , Triplett Kendra , Lamb Candice , Karamitros Christos S. , Blazek John , Georgiou George , Manfredi Mark G. 
Published: July 2017

Abstract
Checkpoint inhibitors have become the cornerstone for new innovation in immune-based oncology therapy. Several orthogonal immune pathways are currently being investigated to relieve suppression or boost activity of the innate and adaptive immune system. The IDO immune-metabolism pathway was recently clinically validated in melanoma in combination with checkpoint inhibition. This opens up a new approach to relieving suppressive mediators and lends credence to the tumor microenvironment containing small molecule metabolites that induce immune tolerance. Both indoleamine-pyrrole 2,3-dioxygenase 1 (IDO1) and Tryptophan 2,3-dioxygenase (TDO) enzymes metabolize tryptophan, forming Kynurenine which binds the aryl hydrocarbon receptor (AHR) in multiple innate and adaptive immune cell types causing a net immunosuppressive effect. Both enzymes are upregulated across many tumor types, however, only the IDO1 enzyme has thus far been addressed in the clinic with small molecule inhibitors. We have postulated that enzyme-mediated depletion of Kynurenine into safe and immunologically inert metabolites can alleviate tumor immunosuppression. We have cloned and characterized several bacterial Kynureninases (KYNase) which preferentially degrade Kynurenine with a &gt;1,000 higher kcat/KM as opposed to mammalian enzymes that cleave 3-OH Kynurenine. We show that PEGylated bacterial KYNases can deplete Kynurenine produced by IDO1+, TDO+ and IDO1/TDO+ dual positive human cancer cells whereas, the IDO1 inhibitor epacadostat or TDO inhibitor 680C91 only selectively inhibited Kyn production in IDO1+ or TDO+ cells respectively. In vivo, a single subcutaneous dose of KYNase in B16F10 tumor-bearing mice was able to deplete Kynurenine in both the plasma and tumors and increase effector T-cells in the tumor. KYNase demonstrated significant tumor growth inhibition and survival benefit either as a single agent or in combination with checkpoint inhibitors (anti-PD1 or anti-CTLA4) in B16F10, CT26 and 4T1 models. Interestingly, KYNase combined with anti-PD1, showed greater efficacy than epacadostat / anti-PD1 combination in CT26 tumor bearing mice. A pharmacologically optimized human KYNase is currently moving toward clinical development for the treatment of cancers where both IDO/TDO pathways play a significant immunosuppressive role through kynurenine production.
Citation Format: Michelle Zhang, Everett Stone, Todd A. Triplett, Kendra Triplett, Candice Lamb, Christos S. Karamitros, John Blazek, George Georgiou, Mark G. Manfredi. A novel approach to targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5570. doi:10.1158/1538-7445.AM2017-5570