Combined blockade of EGFR and glutamine metabolism in preclinical models of colorectal cancer

Abstract

Improving response to epidermal growth factor receptor (EGFR)-targeted therapies in patients with advanced wild-type (WT) RAS colorectal cancer (CRC) remains an unmet need. In this preclinical work, we evaluated a new therapeutic combination aimed at enhancing efficacy by targeting cancer cell metabolism in concert with EGFR. We hypothesized that combined blockade of glutamine metabolism and EGFR represents a promising treatment approach by targeting both the “fuel” and “signaling” components that these tumors need to survive. To explore this hypothesis, we combined CB-839, an inhibitor of glutaminase 1 (GLS1), the mitochondrial enzyme responsible for catalyzing conversion of glutamine to glutamate, with cetuximab, an EGFR-targeted monoclonal antibody in preclinical models of CRC. 2D and 3D in vitro assays were executed following treatment with either single agent or combination therapy. The combination of cetuximab with CB-839 resulted in reduced cell viability and demonstrated synergism in several cell lines. In vivo efficacy experiments were performed in cell-line xenograft models propagated in athymic nude mice. Tumor volumes were measured followed by immunohistochemical (IHC) analysis of proliferation (Ki67), mechanistic target of rapamycin (mTOR) signaling (pS6), and multiple mechanisms of cell death to annotate molecular determinants of response. In vivo , a significant reduction in tumor growth and reduced Ki67 and pS6 IHC staining were observed with combination therapy, which was accompanied by increased apoptosis and/or necrosis. The combination showed efficacy in cetuximab-sensitive as well as resistant models. In conclusion, this therapeutic combination represents a promising new precision medicine approach for patients with refractory metastatic WT RAS CRC.

The cancer metabolic reprogramming and immune response

“…Under conditions of nutritional deficiencies, cancer cells can obtain glutamine by breaking down large molecules. For example, excessive activation of the oncogene RAS can promote endocytosis, and cancer cells clear extracellular proteins and degrade into amino acids including glutamine, providing nutrients for cancer cells [72]. In addition to tumor cells, glutamine has a high utilization rate in immune cells to support cell fate determination and immune responses, such as lymphocytes, macrophages, and neutrophils [73][74][75].…”

Novel Regulators of the IGF System in Cancer

“…In hepatoblastoma cells, circHMGCS1 exerts its oncogenic role by sponging the tumor suppressing action of miR-503-5p, thus upregulating IGF2 and the PI3K-Akt signaling pathway [ 106 ]. In that cancer model, the circRNA/IGF2/Akt axis induced increased expression of the mRNA and protein for glutaminase, an enzyme that converts glutamine to glutamate, which is a major carbon source for ATP production in tumor cells [ 106 , 107 ]. Please refer to Figure 1 for a schematic representation of circRNAs controlling IGF system components in cancer.…”

New insights into molecules and pathways of cancer metabolism and therapeutic implications

“…The oral glutaminase inhibitor CB-839 was reported to suppress Gln-derived metabolite production during tumor development [84,85]. Cohen et al [86] found that cetuximab (which targets EGFR) in combination with CB-839 improved therapeutic efficacy in cetuximab-resistant CRC (Table 2 and Figure 1D). Gregory et al [87] reported that combining CB-839 with arsenic trioxide or homoharringtonine decreased Gln synthesis in hematologic malignancies, upregulated ROS in the mitochondria, and triggered tumor cell death ( Table 2).…”

“…Cohen et al . [86] found that cetuximab (which targets EGFR) in combination with CB‐839 improved therapeutic efficacy in cetuximab‐resistant CRC (Table 2 and Figure 1D). Gregory et al .…”