Changes in the intestinal microbiota of female Wistar rats with chemically induced breast cancer

Breast cancer (BC) is the leading cancer in terms of incidence and is among the five most lethal malignant tumors in the world and in Russia. The number of studies revealing the relationship between microbiota and the occurrence and/or progression of BC, as well as other oncological diseases, is increasing. Intestinal microbiota is considered as a potential diagnostic and prognostic oncobiomarker. The aim of the study was to conduct a metagenomic analysis of the intestinal microbiota composition using 16S rRNA gene sequencing in female Wistar rats with chemically induced BC and subsequent chemotherapy, surgery, and a combination of these treatment methods.

Material and methods. The studies were performed on mature female Wistar rats. At the beginning of the experiment, the age of female Wistar rats was 3 months, and the weight of the animals was 250–300 g. For the study, 5 groups were formed: intact rats (n = 6); rats with BC without treatment (n = 7); rats with BC that received chemotherapy alone (n = 8); rats with BC that received only surgical removal of the tumor (n = 10); rats with BC that received surgical removal of the tumor and chemotherapy (n = 9). Fecal samples from the studied groups of rats were collected for subsequent metagenomic analysis by 16S rRNA gene sequencing, which was performed using the MiSeq System (Illumina, USA) with the MiSeq Reagent Kit v2 (500-cycles) with 2×250 bp double-ended reads.

Results and discussion. The most of the isolated bacteria in the experimental groups belonged to the Firmicutes and Bacteroidetes types, typical representatives of the gastrointestinal tract microbiota of Wistar rats. In the group with ВС without treatment, dysbiosis was observed in the intestinal microflora due to an increase in the level of Bacteroidetes and the number of bacteria such as Actinobacteria. After chemotherapy, a decrease in the level of Firmicutes with an increase in the number of Bacteroidetes and Proteobacteria was found, after surgical treatment an increase in Verrucomicrobia was revealed, due to the effect of Verrucomicrobia on the reparation of the surgical wound. With chemically induced ВС, as well as with different treatment methods, a decrease in the Firmicutes /(Firmicutes + Bacteroidetes) ratio was found in the intestines of rats compared to the intact animals. Further studies in breast cancer patients are needed to understand whether this ratio can be used as an additional diagnostic biomarker for ВС.

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