Increased activity of amino acid transporters has been observed in a wide variety of cancers. However, whether amino acid metabolism is related to estrogen receptor-positive (ER⁺) breast cancer has been less well studied. We identified the rate-limiting enzyme involved in amino acid metabolism associated with ER⁺ breast cancer by integrating numerous bioinformatics tools and laboratory studies. The bioinformatics analysis revealed that highly expressed genes in ER⁺ breast cancer patients were correlated with breast cancer-related pathways, including ESR1 and PI3K signaling. The metabolic signaling and the amino acid metabolism were significantly regulated in breast neoplasms. We used the ER⁺ breast cancer cell line MCF-7 and breast cancer tissue from National Cheng Kung University Hospital to validate our findings in bioinformatics. In estradiol-treated MCF-7 cells, genes associated with anabolic metabolism of serine and methionine and genes associated with catabolic metabolism of tyrosine, phenylalanine and arginine were upregulated. Furthermore, the expression levels of ARG2, PSAT1, PSPH, TH, PAH, and MAT1A mRNA were increased in breast cancer patients relative to controls. The aforementioned genes were also found to be highly correlated with distant metastasis-free survival in breast cancer patients. High expression levels of ARG2, CBS, PHGDH, AHCY, HAL, TDO2, SHMT2, MAT1A, MAT2A, GLDC, GLS2, BCAT2, GLUD1, PAH and MTR contributed to poor prognoses, whereas high mRNA expression levels of HECA, CTH, PRODH, TAT, and MAT2B were correlated with good prognoses. FDA-approved drugs, including piperlongumine, ellipticine, etidronic acid, harmine, and meclozine, may have novel therapeutic effects in ER⁺ patients based on connectivity map (CMap) analyses. Collectively, our present study demonstrated that amino acid metabolism genes play crucial roles in tumor development and may serve as prospective drug targets or biomarkers for ER⁺ breast cancer.

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