Abstract 2890: Investigating dynamic IDO-Kyn-Ahr pathway induced tumor immunosuppression using imaging modality to optimize therapeutic Intervention
Authors: Bah Mamadou Alpha , Serganova Inna , Budhu Sadna , Schild Tanya , Khan Jonathan F. , Keshari Kayvan R. , Wolchok Jedd D. , Merghoub Taha 
Published: June 2023

Abstract
Despite great clinical responses in several cancers to immune checkpoint blockade (ICB) intervention, there persist many mechanisms of tumor evasion. Tryptophan catabolism by enzymes Indoleamine-2,3-dioxygenase 1 (IDO1) and tryptophan-2,3-dioxygenase 2 (TDO2) into metabolite L-Kynurenine (Kyn) has been shown to drive an immunosuppressive tumor microenvironment (TME). We have shown tumors overexpressing IDO1 recruit and activate the Treg/macrophage suppressive axis and blockade of aryl hydrocarbon receptor (AHR) activation abrogates this. Preclinical models demonstrate inhibition of IDO1 delayed tumor growth and increased T cell function. However, a phase III clinical trial in melanoma patients combining IDO1 inhibition with anti-PD-1 blockade showed no improved efficacy when compared to anti-PD-1 blockade. Kyn can act as a key signaling molecule through activation of AHR. We hypothesize that AHR engagement by kyn within the TME is highly dynamic and elevated AHR engagement must coincide with intervention to maximize therapeutic response. Using an AHR biosensor, we designed a construct with a dioxin response element (DRE) promoter that is engaged upon AHR-ligand complex, translocated to the nucleus, and drives a luciferase gene with a luminescence readout. This allows us to use an image-guided approach to track AHR bioactivity in real-time. In-vitro, we were able to validate our construct using transduced murine B16 melanoma and 4T1 breast cancer models. We treated transduced cells with endogenous AHR ligands, kynurenine, and AHR agonist (FICZ), and observed a significant dose-dependent increase in AHR reporter readout. Additionally, the AHR inhibitor (CH-223191) abrogated AHR activity and subsequent luminescence below control threshold. We implanted both DRE transduced B16 (B16-DRE) and 4T1 (4T1-DRE) intradermally and intramammary fat pad respectively. Tumors were imaged and we observed total luminescence flux corresponding to increased tumor growth. After three weeks, we assessed IDO, AHR, and HIF1a expression which all converge on the IDO-Kyn-AhR pathway using a broad panel of lymphocyte and myeloid markers from tumors and spleen. We identified high expression of IDO, AHR, and HIF1a markers in myeloid cells with an increased frequency of dendritic cells and macrophages. Future experiments will focus on using our reporter construct in the context of ICB treatment and assessing AHR activity overtime as well as sampling peripheral blood to assess the magnitude of tryptophan, kyn, and other polycyclic hydrocarbons including gut microbiome-derived indoles. The characterization of the IDO-Kyn-AhR modulation after therapeutic intervention will inform the rational design of treatment regimens to abrogate immune suppression associated with AHR activity in combination with ICB treatment.
Citation Format: Mamadou Alpha Bah, Inna Serganova, Sadna Budhu, Tanya Schild, Jonathan F. Khan, Kayvan R. Keshari, Jedd D. Wolchok, Taha Merghoub. Investigating dynamic IDO-Kyn-Ahr pathway induced tumor immunosuppression using imaging modality to optimize therapeutic Intervention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2890.