Ganoderma Lucidum Polysaccharides Potentiate Low-Dose Gemcitabine Against 4T1 Breast Tumors, Associated With Immune Activation and Gut Microbiota Remodeling.

Gemcitabine (GEM), a first-line chemotherapeutic agent, may fail to prevent recurrence in some settings. Traditional Chinese medicine emphasizes Yin-Yang balance and "fuzheng" approaches and may offer complementary strategies. Ganoderma lucidum polysaccharides (GLP) exhibit immune-enhancing activity, but evidence for direct anti-tumor efficacy, either alone or in combination with low-dose GEM, remains limited. Using a murine 4T1 breast cancer model, we integrated flow cytometry, 16S rRNA gene sequencing, and gas chromatography-mass spectrometry to evaluate the anti-tumor activity of GLP combined with low-dose GEM. GLP alone enhanced immune parameters but did not significantly suppress tumor growth, whereas low-dose GEM reduced tumor volume and activated anti-tumor immunity. Notably, the GLP plus GEM combination produced greater tumor inhibition than either treatment alone and was associated with increased IFN-γ and TNF-α levels, enhanced CD8+ T-cell infiltration, and enrichment of Ligilactobacillus, Duncaniella, and Faecalibaculum in the gut microbiota, and elevated serum levels of short-chain fatty acids and tryptophan. Notably, the antitumor effect in the combination group was accompanied by reduced tumoral IDO expression and elevated serum tryptophan, which were statistically correlated; however, as kynurenine levels were not quantified in this study, we cannot attribute this correlation to altered IDO enzymatic activity or establish a direct functional link along the IDO-tryptophan metabolic pathway. Thus, the combination of GLP and low-dose GEM exerts a synergistic anti-tumor effect.