Roles of gut-breast axis in breast pathophysiology

Microbiome impacts cancer development and therapeutic efficacy. In addition to the guts, microbes reside in different tissues influencing the pathophysiology of the tissue microenvironment. These tissue-resident microbes are largely attributed to translocation of gut microbes. In the breast, such passage is termed ‘gut-

breast axis’, helping establish microbiotas of breast tissue and milk. Nevertheless, gut-breast axis has been mostly conceptualized around pregnancy, and it is completely unknown whether this axis indeed exists outside pregnancy to impact breast health and carcinogenesis. Our long-term goal is to dissect how microbiome

contributes to breast pathophysiology. Especially, the objectives of the present study are to determine i) whether gut-breast axis occurs on a regular basis; ii) whether this involves discrete sets of bacteria for healthy cohorts vs. cancer patients, and iii) what are their roles. Our central hypothesis is that gut-breast axis takes

place on a regular basis, involving distinct sets of bacteria to confer anti-tumor effects on healthy cohorts vs. pro-tumor effects on cancer patients. The proposed research is based on our preliminary studies allowing us to harvest specific gut microbiotas from tumor-protected or -susceptible animals. We reported that supplementing

sepiapterin (SEP)—the endogenous precursor of tetrahydrobiopterin (the cofactor of nitric oxide (NO) synthase)—normalized arginine metabolism and improved the immunogenicity of HER2-positive mammary tumors. We then orally applied SEP to mice prone to HER2-positive mammary tumors and saw strong tumor

prevention. These mice also showed increases in NO levels and NO-producing bacteria in the guts. Besides, extracts of these gut bacteria activated innate immune cells, suggesting the roles of these gut bacteria in anti- tumor immunity. Here, we will determine whether these gut bacteria physically translocate to the breast to exert

tumor preventative effects. Our hypothesis will be tested through two SPECIFIC AIMS: 1) Determine whether gut microbiotas of a) tumor-protected vs. b) -susceptible mice exert anti-tumor vs, pro-tumor effects; and 2) determine whether distinct sets of gut microbes are translocated to mammary glands to exert anti-tumor vs.

pro-tumor effects. In Aim 1, we will transplant gut microbiota of a) tumor-protected (SEP-treated) or b) - susceptible (DMSO-treated) HER2 mice into recipients and give the inverse drug treatments. We will test whether the transplanted microbiotas antagonize the treatments. In Aim 2, gut microbiota of a) tumor-protected

(SEP) vs b) -susceptible (DMSO) mice are differentially labeled, and the 50:50 mixture is given to the recipients undergoing SEP or DMSO treatment. Labeled microbes are analyzed for their gut-breast translocation; their ratios in the breast; and the contributions of breast microbiota to the drug effects. The proposed study is

innovative because this is the first time to corroborate gut-breast axis and its contributions to breast pathophysiology. The study is significant because it will have a positive translational impact by justifying the development of a new breast cancer treatment or prevention strategy focused on breast microbiota.