Abstract 1202: ERG344: A novel IRG1 inhibitor for the treatment of colon cancer

Abstract

Abstract Immune responsive gene 1 (Irg1) is an LPS-inducible gene within macrophages (MF) whose protein product is responsible for the synthesis of itaconate from aconitate through a break in the TCA cycle. Although primarily present in proinflammatory macrophages, IRG1 expression has been linked with certain cancers (glioblastoma, ovarian carcinoma) and its tumor-driven upregulation in peritoneal resident macrophages (pResMF) has been shown to contribute to peritoneal tumor growth. Here, we report Irg1 gene expression at the single cell level (scRNAseq) in samples obtained from colorectal cancer patients (n=7; ~11,000 single cells). Transcriptomic analysis showed that Irg1 was primarily expressed by cancer cells, although other tumoral cell types also showed substantial levels of the gene. To determine if IRG1 is a druggable target in cancer, we synthesized a series of small MW inhibitors and selected ERG344 for in vivo testing based on its ability to inhibit itaconate synthesis in a rat glioblastoma cell line (C6) engineered to stably express Irg1. The IC50 value of inhibition was ~150 μM. In vivo, ERG344 suppressed tumor growth and increased survival probability in a syngeneic colon cancer model (CT26). Drug administration was initiated when the tumors reached an average tumor volume of ~100 mm3 and involved daily ERG344 doses of 0.2 mg/kg ip or 0.3 mg/kg po. Complete tumor regressions (~17%) were observed in the same model when ERG344 was administered ip at 3 mg/kg. Immunophenotyping of CT26 tumors treated with either vehicle or 0.2 mg/kg ERG344 ip indicated that IRG1 inhibition renders the tumor microenvironment less immunosuppressive by decreasing the frequency of monocytic myeloid suppressor cells (m-MDSCs), increasing the frequency of cytotoxic CD8+ T cells, and decreasing the CD8+ expression of the negative co-stimulatory molecule PD-1. To determine if ERG344 is also able to reduce pResMF-driven peritoneal tumor growth, murine melanoma B16F15 cells were injected into the peritoneal cavity of C57BL/6 mice treated with vehicle or 1 mg/kg ERG344 (n=8/group). Seven days after tumor inoculation, mice treated with ERG344 showed reduced tumor growth in the peritoneal cavity, which led to increased survival probability of the animals. The studies collectively suggest that IRG1 is a novel target for the treatment of primary and metastatic tumor growth in colorectal cancer and highlight the therapeutic potential of ERG344. Citation Format: Adonia E. Papathanassiu, Francesca Lodi, Hong A. Vu, Diether Lambrechts. ERG344: A novel IRG1 inhibitor for the treatment of colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1202.