Image-guided Trp-IDO/TDO-Kyn-AHR pathway inhibition, combined with immunotherapy

ABSTRACT Despite recent progress in immunotherapy (checkpoint blockade and adoptive T cell transfer), most patients with solid tumors still do not respond or subsequently develop acquired resistance to therapy. Our group and others have described an immune resistance mechanism mediated by the metabolic dysregulation of

Tryptophan (Trp) catabolism through the Kynurenine (Kyn) - aryl hydrocarbon receptor (AHR) pathway. The production of Kyn and signaling through the AHR suppresses CD8+ and CD4+ effector T cells and enhances the generation of immunosuppressive cell types, including FoxP3+CD4+ T cells (Tregs), myeloid-derived

suppressor cells (MDSCs) and M2-polarised tumor-associated macrophages (TAMs) - cells which play a critical role in limiting anti-tumor immunity. We propose to image signaling activity through the IDO/TDO-Kyn- AHR pathway, in order to optimize the timing (scheduling) of combination drug treatment (treatments targeting

this pathway along with immune based therapies). In this proposal, we plan to: use imaging to better understand signaling through the Trp–Kyn-AHR pathway in the tumor microenvironment, by monitoring AHR transcriptional activity using dual reporter systems. We have successfully developed a DRE (dioxin responsive enhancers)-AHR reporter system in order to: 1) quantify the

kinetics of engagement of the AHR upon in vitro stimulation with different agonists/antagonists and its correlation with phenotypic changes in different components of the TME: cancer cells, macrophage and T cells; 2); to monitor the dynamic of activation of the AHR pathway in vivo using a biosensor system during tumor

progression in IDO/TDO-expressing cancer models 3) to evaluate the in vivo dynamics of AHR activation after response to therapeutic interventions (PD-1/CTLA-4 blockade, T cell therapy) in the same models 4) design therapies combining the inhibition of the Trp-Kyn-AHR axis with immune therapy based on reporter assays of

the AHR activity over time; and 4) evaluate the potential for clinical translation. This approach addresses an unmet need and the proposed strategy is strongly supported by 4 experts in the field and our recent publication in Nature Communication– see letters of support.