Effective Targeting of Glutamine Synthetase with Amino Acid Analogs as a Novel Therapeutic Approach in Breast Cancer

Cancer cells undergo metabolic rewiring to support rapid proliferation and survival in challenging environments. Glutamine is a preferred resource for cancer metabolism, as it provides both carbon and nitrogen for cellular biogenesis. Recent studies suggest the potential anticancer activity of amino acid analogs. Some of these analogs disrupt cellular nucleotide synthesis, thereby inhibiting the formation of DNA and RNA in cancer cells. In the present study, we investigated the anticancer properties of Acivicin and Azaserine in the breast cancer MCF-7 cell line, comparing their effects to those on the non-tumorigenic MCF-10 epithelial cell line in vitro. Interestingly, at lower concentrations, both Acivicin and Azaserine showed potent inhibition of MCF-7 cell proliferation, as assessed by the MTT assay, without detectable toxicity to normal cells. In contrast, Sorafenib (Nexavar), a commonly used drug for solid tumors, showed harmful effects on normal cells, as indicated by increased lactate dehydrogenase (LDH) production in treated cells. Furthermore, unlike Sorafenib, treatment with Acivicin and Azaserine significantly affected apoptotic signaling in treated cells, indicating the role of both amino acid analogs in activating programmed cell death (PCD), as assessed by the Annexin-V assay, DAPI staining, and the relative expression of tumor suppressor genes PTEN and P53. ELISA analysis of MCF-7 cells revealed that both Acivicin and Azaserine treatments promoted the production of anti-inflammatory cytokines, including IL-4 and IL-10, while significantly reducing the production of tumor necrosis factor alpha (TNF-α). Mechanistically, both Acivicin and Azaserine treatment led to a significant reduction in the expression of glutamine synthetase (GS) at both the RNA and protein levels, resulting in a decrease in intracellular glutamine concentrations over time. Additionally, both treatments showed comparable effects on Raf-1 gene expression and protein phosphorylation when compared with Sorafenib, a Raf-1 inhibitor. Moreover, docking studies confirmed the strong binding affinity between Acivicin, Azaserine, and glutamine synthetase, as evidenced by their docking scores and binding interactions with the enzyme crystal. Collectively, these findings provide evidence for the anticancer activity of the two amino acid analogs Acivicin and Azaserine as antagonists of glutamine synthetase, offering novel insights into potential therapeutic strategies for breast cancer.