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Objective: Polo‐like kinase 1 (PLK1), a serine/threonine‐protein kinase, functions as a potent oncogene in the initiation and progression of tumor. The aim of this study is to assess potential correlations between PLK1 expression and immune infiltration in breast cancer (BRCA) and construct a PLK1‐based immune risk model applicable for prognosis and treatment response prediction in BRCA. Methods: We collected data on PLK1 gene expression in BRCA patients from The Cancer Genome Atlas (TCGA) database. Thereafter, we analyzed the associations of PLK1 expression with immune cell infiltration and immunomodulators, and established a prognostic risk model based on seven PLK1‐associated immunomodulator genes and a nomogram for survival prediction. Results: BRCA prognosis, clinical stage progression, and tumor classification were all shown to be substantially correlated with PLK1 expression. The PLK1 gene was significantly enriched in T cell and B cell receptors and molecules of the chemokine signaling pathways. Specifically, PLK1 expression was positively correlated with the CD8+ T cell and regulatory T cell (Tregs) activation and negatively correlated with M2 macrophage infiltration. The seven‐genes‐based risk model could serve as an independent prognostic factor of BRCA. The risk model was markedly correlated with the expression of programmed cell death protein 1/programmed cell death ligand 1 (PD‐1/PD‐L1; both p < 0.001) immune checkpoints, and tumor mutation burden (TMB). High‐ and low‐risk BRCA patients identified by the risk model responded differently to anti‐PD‐1 and/or anti‐CTLA4 therapy, as well as common chemotherapy drugs, like cisplatin, paclitaxel, and gemcitabine. Conclusion: This PLK1‐based immune risk model can effectively predict the prognosis and tumor progression of BRCA, identify gene mutations, and evaluate patient's response toward immunotherapy and chemotherapy regimens. [ABSTRACT FROM AUTHOR]

Gene therapy with adenoviral vectors is a promising new approach for the treatment of refractory advanced breast cancer. Strategies to restrict adenoviral-mediated therapeutic gene expression are important to avoid harming normal cells. Fatty acid synthase (FAS) is overexpressed in several human cancers. FAS is highly expressed in infiltrating breast cancer tissue, and always associated with malignant phenotypes and poor prognosis. In this study, expression of the FAS was evaluated in three breast cancer cell lines. A 680 bp-FAS promoter was cloned and its transcriptional activity was analyzed in breast cancer cell lines. We made a recombinant adenovirus construct carrying herpes simplex virus thymidine kinase (HSV-TK) driven by human FAS promoter (Ad-FAS-TK) and analyzed its target cytotoxicity in vitro and in vivo against human breast cancer cells combined with prodrug ganciclovir (GCV). The results show that the expression of FAS varies in the three breast cancer cell lines examined (respectively, SK-Br3>MCF-7>MDA-MB-231), but FAS promoter can initiate relative high transcriptional activities in all three kinds of cancer cells while little in normal fibroblast cells. Furthermore, FAS promoter can drive the therapeutic gene in a wider range of human breast cancers than cerbB2 promoter and exhibit a stronger activity than midkine (MK) promoter. Combination of Ad-FAS-TK and GCV treatment exhibited strong-targeted cytotoxic effect on breast cancer cells but showed little activity in normal fibroblast cells. The tumorigenic capability of breast cancer cells treated with Ad-FAS-TK/GCV was completely inhibited in vitro and in vivo assays. In conclusion, adenoviral-mediated suicide gene therapy controlled by tumor associated-FAS promoter can induce specific cytotoxic effect on human breast cancer cells in vitro and in vivo. So it is a promising target for the development of gene therapy against breast cancers. [ABSTRACT FROM AUTHOR]