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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.

BCAT1, the enzyme responsible for the reversible transamination of leucine in the cytosol, has recently been implicated in the development and growth of various types of cancer. The limited expression of BCAT1 in adult tissues under physiological conditions suggests that the enzyme is a sensible target for drug development. To better understand the role of BCAT1 in cancer, we examined its gene expression at the single cell level (scRNAseq) in specimens obtained from lung, colorectal, breast, and ovarian cancer patients (n=36; >200,000 single cells). In those samples, Bcat1 gene expression was primarily associated with myeloid cells and fibroblasts with the exception of ovarian cancer in which robust Bcat1 presence was also seen in cancer cells. In tumor infiltrating lymphocytes (TILs), enrichment in Bcat1 gene expression was observed in exhausted CD4+ and CD8+ T cells compared to other T cell subtypes; this was independent of the cancer type examined. We speculated that inhibition of BCAT1 in TILs reverses exhaustion and has a therapeutic impact in cancer. In the syngeneic CT26 colon cancer model, combination treatment of a BCAT1 inhibitor (ERG245; ip administration of 5 mg/kg, given at days 7, 8 and 9 after tumor cell inoculation) and an anti-PD1 antibody (ab) (clone RMP1-14; ip administration given at days 7, 11, 14, and 18) led to eradication of established tumors. In the same model, limited treatment of large tumors (average size of ~600 mm3) with ERG245+anti-PD1 ab suppressed tumor growth and increased the frequency of CD8+ T cells expressing Granzyme B and IFNγ by ~50% compared to anti-PD1 monotherapy. Mechanistically, in vitro treatment of newly activated hCD8+ T cells with ERG245 impaired translocation of the lactate transporter MCT1 to the cell surface and increased the levels of intracellular lactate within 30 min of activation leading to upregulation of transcription factor ATF3. ERG245-driven metabolic reprogramming of CD8+ T cells towards an oxidative phenotype (increased OXPHOS) was also observed at 24h of treatment. Withdrawal of ERG245 restored intracellular lactate levels without reversing the metabolic reprogramming of the cells. We propose that these are elements of a mechanism that links temporal inhibition of BCAT1 to the rise of highly energetic CD8+ T cells with increased cytotoxicity and proliferative capacity in vitro and in vivo. Citation Format: Adonia E. Papathanassiu, Francesca Lodi, Hagar Elkafrawy, Michelangelo Certo, Hong Vu, Jeong Hun Ko, Jacques Behmoaras, Claudio Mauro, Diether Lambrechts. BCAT1 as a druggable target in immuno-oncology [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3402.

Efrapeptins (EF), a family of fungal peptides, inhibit proteasomal enzymatic activities and the in vitro and in vivo growth of HT-29 cells. They are also known inhibitors of F(1)F(0)-ATPase, a mitochondrial enzyme that functions as an Hsp90 co-chaperone. We have previously shown that treatment of cancer cells with EF results in disruption of the Hsp90:F(1)F(0)-ATPase complex and inhibition of Hsp90 chaperone activity. The present study examines the effect of EF on breast cancer growth in vitro and in vivo. As a monotherapy, EF inhibited cell proliferation in vitro with an IC(50) value ranging from 6 nM to 3.4 μM. Inhibition of Hsp90 chaperone function appeared to be the dominant mechanism of action and the factor determining cellular sensitivity to EF. In vitro inhibition of proteasome became prominent in the absence of adequate levels of Hsp90 and F(1)F(0)-ATPase as in the case of the relatively EF-resistant MDA-MB-231 cell line. In vivo, EF inhibited MCF-7 and MDA-MB-231 xenograft growth with a maximal inhibition of 60% after administration of 0.15 and 0.3 mg/kg EF, respectively. 2-Deoxyglucose (2DG), a known inhibitor of glycolysis, acted synergistically with EF in vitro and antagonistically in vivo. In vitro, the synergistic effect was attributed to a prolonged endoplasmic reticulum (ER) stress. In vivo, the antagonistic effect was ascribed to the downregulation of tumoral and/or stromal F(1)F(0)-ATPase by 2DG.

Recent evidence suggests that the cytosolic presence of branched chain amino acid aminotransferase (BCAT1) in adult tissues is associated with diverse pathological conditions including cancer and inflammatory diseases such as rheumatoid arthritis; in these diseases, BCAT1 appears to modulate the expression of many key proteins and to be a new druggable target. In cancer, BCAT1 physically associates with CD147 and regulates the levels and the cellular localization of the protein in a number of different cell lines in vitro and in vivo. Silencing of Bcat1 gene downregulates the total expression of CD147 in MDA-MB-435 cells, while inhibition of BCAT1 by sodium 4-methyl-5-oxo-hexanoate (ERG240) leads to suppression of the extracellular CD147 in the same cells. In turn, suppression of extracellular CD147 results in downregulation of CD147-associated proteins such as MCT4, matrix metalloproteinases (MMPs), cyclophilin A, and GAPDH. Furthermore, inhibition of BCAT1 is associated with prevention of cancer cell migration and reduction in secretion of metabolic by-products such as lactate. Surprisingly, treatment of MDA-MB-231 tumor-bearing animals with 2-deoxyglucose (2DG), a well-known inhibitor of glycolysis, leads to a decrease in the levels of c-MYC and BCAT1, an increase in the total expression of CD147, and the increased shedding of the extracellular CD147 into the circulation. This observation suggests that BCAT1-driven regulation of CD147 in cancer cells involves a complex mechanism. Inhibition of tumoral BCAT1 is expected to adversely affect the metastatic potential of various tumors not only through a reduction in cell motility but also through alterations in the tumor microenvironment, driven by inhibition of extracellular CD147. Citation Format: Adonia E. Papathanassiu, Hong A. Vu. Inhibition of BCAT1 suppresses the expression of pro-metastatic proteins and reduces cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2683. doi:10.1158/1538-7445.AM2014-2683