A metabolic-immune subtype of breast cancer defined by G6PD and SHMT2: From single‑cell dissection to dual-targeted therapy.

Breast cancer heterogeneity limits the precision of current prognostic and therapeutic strategies, underscoring the need for molecular frameworks that capture underlying metabolic drivers. Here, we systematically dissected the landscape of amino acid metabolism (AAM) in breast cancer through integrated bulk and single‑cell transcriptomics, machine learning, in silico knockout, and computational drug screening. From 379 AAM-related genes, we identified 48 survival‑associated AAM genes, which were genomically altered in 53% of patients. Unsupervised consensus clustering defined three stable subtypes with distinct metabolic-immune phenotypes. Among these, the aggressive CL2 subtype exhibited a hyper‑anabolic state tightly coupled with an immunosuppressive microenvironment characterized by M2 macrophage enrichment and CD8⁺ T cell exclusion. An 11‑gene prognostic signature was developed and validated across independent cohorts, quantitatively capturing the CL2 phenotype with 77.8% concordance in anabolic pathways and 93.8% in catabolic pathways. Single‑cell dissection revealed that this metabolic program is epithelial‑intrinsic and actively orchestrates immune exclusion: high‑risk epithelial cells preferentially engage macrophages via APP signaling while exhibiting minimal crosstalk with cytotoxic lymphocytes. Within this circuitry, G6PD and SHMT2 emerged as dual‑functional hubs linking anabolic output to immune evasion, with their overexpression confirmed by qPCR and immunohistochemistry. Finally, molecular docking and dynamics simulations identified piceid as a putative dual inhibitor of G6PD and SHMT2, with favorable binding free energies (-35.53 and -56.49 kcal/mol, respectively). Our study establishes a previously unrecognized AAM‑driven subtype, provides a robust prognostic tool, and proposes a first‑in‑class dual‑targeting strategy, highlighting the therapeutic potential of targeting metabolic vulnerabilities in aggressive breast cancer.