Polyphenol-Rich Muscadine Grape Extract Reduces Triple Negative Breast Cancer Metastasis in Mice with Changes in the Gut Microbiome

Abstract Background Triple negative breast cancer (TNBC) has a high propensity to metastasize and no treatments are available to slow or prevent metastatic progression. The goal of this study is to determine whether a proprietary high-polyphenol content muscadine grape extract (MGE) inhibits TNBC metastasis. Methods 4T1 TNBC cells were injected into the mammary fat pad of 6-week-old female Balb/c mice. After 2 weeks, tumors were surgically removed and mice were placed into a control (n=8) or treatment group that received 0.1 mg/mL total phenolics MGE in the drinking water (n=8) for 4 weeks. Immunohistochemistry (Ki67, α-SMA) and hemotoxylin and eosin staining were used to quantify metastases. Gut microbial composition was determined by 16S rRNA sequencing and short chain fatty acids (SCFAs) were detected by gas chromatography. MDA-MB-231, BT-549 and 4T1 TNBC cell motility and cytoskeletal organization was assessed in vitr o by scratch wound migration and confocal microscopy, respectively. Data were evaluated by student’s t -test. Results MGE reduced metastatic proliferation in mouse lungs (33.3%) and livers (58.3%) and decreased the number (51.1%) and size (17.4%) of liver metastases, resulting in a 55.7% reduction in metastatic tumor burden ( P < 0.01). Serum IL-6 was reduced 99.6% in MGE-treated mice ( P = 0.06). MGE attenuated migration, altered cytoskeletal organization, and reduced RHAMM expression in TNBC cells ( P < 0.05). The gut microbiota, a mediator of polyphenolic bioactivities, was altered significantly in MGE-treated mice; MGE increased the alpha diversity (7.14%), Firmicutes/Bacteroidetes ratio (2-fold), relative abundance of butyrate-producing genera, and butyrate (3-fold) ( P < 0.05). Butyrate inhibited 4T1 cell proliferation and migration, suggesting butyrate contributes to MGE’s anti-metastatic activities ( P < 0.05). Conclusion Our results indicate that MGE may be an effective adjuvant therapy to reduce TNBC metastatic progression.