IDO1, an enzyme that initiates tryptophan metabolism along the kynurenine pathway (KP), is commonly overexpressed in IBD and colorectal cancer (CRC). We previously demonstrated that global knockout of IDO1 reduced tumorigenesis in the AOM/DSS model of colitis-associated cancer (CAC). The aim of the current investigation was to define how IDO1 and KP metabolites interact with epithelial signaling pathways relevant to neoplastic (CAC and CRC) growth.Methods:
The AOM/DSS protocol was used for in vivo modeling of CAC with an epithelial specific (Villin-Cre) IDO1−/− mouse (IDO1-iKO). CRC was modeled in vitro using human CRC cell lines (HT29 and DLD1). These studies were confirmed in matched colonoid (organoid) and tumoroid cultures derived from the same CRC patient. Inhibitors to Wnt/LRP, AKT and PI3K were used. Proliferation was measure by CDK-8 (in vitro) and BrdU incorporation (in vivo). An IDO1 specific inhibitor currently in Phase II clinical trials was used for in vitro assays (INCB24360).Results:
In vivo CRC/CAC modeling demonstrated that epithelial specific knockout of IDO1 was sufficient to reduce tumorigenesis and the tumor proliferation index in AOM/DSS exposed mice (IDO1-iKO versus WT). IDO1-iKO mice did not exhibit more severe colitis in this model. In vitro studies using CRC cell lines illustrated that kynurenine, the initial KP metabolite, rapidly activated (<5 minutes) pivotal signaling pathways relevant to both genetically driven CRC (Canonical Wnt/GSKB/β-catenin) as well as inflammation-associated CAC (PI3K-AKT) resulting in augmented proliferation. These findings extended robustly to human tumoroids, but not to non-transformed colonoids. Finally, in translationally relevant experiments, we found that INCB24360 significantly reduced proliferation in neoplastic cells, but did not impact viability of non-transformed colonoids.Conclusions:
IDO1 and tryptophan derived metabolites promote epithelial β-catenin signaling and neoplastic growth by rapidly activating canonical Wnt and PI3K/AKT pathways. In vitro and in vivo studies suggest that these pathway preferentially impact neoplastic cells over the non-transformed epithelium. These studies highlight the potential for IDO1 or KP pathway inhibition as a therapeutic target for colitis associated or genetically driven colon cancer.