Inhibition of Glutamine Uptake Improves the Efficacy of Cetuximab on Gastric Cancer

Abstract

Treatment for advanced gastric cancer is challenging. Epidermal growth factor receptor (EGFR) contributes to the proliferation and development of gastric cancer (GC), and its overexpression is associated with unfavorable prognosis in GC. Cetuximab, a monoclonal antibody targeting EGFR, failed to improve the overall survival of gastric cancer patients indicated in phase III randomized trials. Glutamine is a vital nutrient for tumor growth and its metabolism contributes to therapeutic resistance, making glutamine uptake an attractive target for cancer treatment. The aim of the present study was to investigate whether intervention of glutamine uptake could improve the effect of cetuximab on GC. The results of MTT assay showed that by glutamine deprivation or inhibition of glutamine uptake, the viability of gastric carcinoma cells was inhibited more severely than that of human immortal gastric mucosa epithelial cells (GES-1). The expression of the key glutamine transporter alanine-serine-cysteine (ASC) transporter 2 (ASCT2; SLC1A5) was significantly higher in gastric carcinoma tissues and various gastric carcinoma cell lines than in normal gastric tissues and cells, as shown by immunohistochemistry and western blotting, while silencing ASCT2 significantly inhibited the viability and proliferation of gastric carcinoma cells. Consistent with previous studies, it was shown herein by MTT and EdU assays that cetuximab had a weak inhibitory effect on the cell viability of gastric carcinoma cells. However, inhibiting glutamine uptake by blockade of ASCT2 with l-γ-glutamyl- p-nitroanilide (GPNA) significantly enhanced the inhibitory effect of cetuximab on suppressing the proliferation of gastric cancer both in vitro and in vivo. Moreover, combining cetuximab and GPNA induced cell apoptosis considerably in gastric carcinoma cells, as shown by flow cytometry, and had a higher depressing effect on gastric cancer proliferation both in vitro and in vivo, as compared to either treatment alone. The present study suggested that inhibition of glutamine uptake may be a promising strategy for improving the inhibitory efficacy of cetuximab on advanced gastric cancer.

Targeting glutamine metabolism as a therapeutic strategy for cancer

“…L-γ-glutamyl-p-nitroanilide (GPNA) suppresses the growth of TNBC, different types of lung cancer, and neuroblastoma cells 73 , 77 , 81 . In addition, combined treatment with GPNA and a monoclonal antibody (cetuximab) targeting EGFR effectively suppressed the growth of gastric cancer cells in vitro and in vivo 86 . However, amino acid analogs are unsuitable for clinical use due to their low affinity, lack of specificity, and toxicity 87 .…”

Exploiting the Achilles’ heel of cancer: disrupting glutamine metabolism for effective cancer treatment

“…In breast cancer, RNF5 loss is associated with increased ASCT2 expression, finally leading to poor patient outcomes, and poor response to paclitaxel ( Jeon et al, 2015 ). ASCT2 is overexpressed on the surface of various tumor cells, such as gastric cancer ( Ma et al, 2021 ), colon cancer ( Ma et al, 2018 ), pancreatic cancer ( Wang et al, 2022 ), and TNBC ( Van Geldermalsen et al, 2016 ). Small molecule inhibitors targeting ASCT2 and other glutamine transporters have been shown to inhibit glutamine uptake and consumption and exhibit antitumor effects in various cancer models.…”

“…It is unclear whether the delayed cell growth after GPNA treatment is caused by ASCT2 inhibition. Ma et al demonstrated that blocking ASCT2 with GPNA significantly enhanced the anti-proliferative effect of trastuzumab in gastric cancer in vitro and in vivo ( Ma et al, 2021 ). GPNA treatment also inhibited cell growth in pancreatic cancer ( Wang et al, 2022 ).…”

Enzymatic depletion of circulating glutamine is immunosuppressive in cancers

“…Small molecules used to prevent glutamine uptake by inhibiting the primary glutamine transporters, ASCT2, SNAT2, and SNAT1, have suffered from poor affinity, lack of specificity, and toxicity. 10 , 11 , 12 For example, V-9302 was reported as a high-affinity inhibitor of ASCT2, but other studies suggest that it preferentially inhibits SNAT2 and LAT1, the latter being the primary transporter for essential amino acid uptake. 13 , 14 The naturally occurring glutamine analog 6-diazo-5-oxo-L-norleucine (DON) inhibits multiple enzymes that utilize glutamine, including mitochondrial glutaminases, but has translated poorly as a therapeutic primarily due to a narrow therapeutic index leading to gastrointestinal toxicity.…”