Bariatric surgery is associated with improved breast cancer (BC) outcomes, including greater immunotherapy effectiveness in a preclinical BC model. A potential mechanism of bariatric surgery–associated protection is the gut microbiota. Here, we demonstrate the dependency of improved immunotherapy response on the post–bariatric surgery gut microbiome via fecal microbiota transplantation (FMT). Response to αPD-1 immunotherapy was significantly improved following FMT from formerly obese bariatric surgery–treated mice. When stool from post–bariatric surgery patients was transplanted into recipient mice and compared to the patients’ presurgery transplants, postsurgery microbes significantly reduced tumor burden and doubled immunotherapy effectiveness. Microbes impact tumor burden through microbially derived metabolites, including branched-chain amino acids (BCAAs). Circulating BCAAs correlated significantly with natural killer T (NKT) cell content in the tumor microenvironment in donor mice after bariatric surgery and FMT recipients of donor cecal content after bariatric surgery compared with obese controls. BCAA supplementation replicated improved αPD-1 effectiveness in 2 BC models, supporting the role of BCAAs in increased immunotherapy effectiveness after bariatric surgery. Ex vivo exposure increased primary NKT cell expression of antitumor cytokines, demonstrating direct activation of NKT cells by BCAAs. Together, the findings suggest that reinvigorating antitumor immunity may depend on bariatric surgery–associated microbially derived metabolites, namely BCAAs.

Mononuclear phagocytes (MPs) play a crucial role in tissue homeostasis; however, MPs also contribute to tumor progression and resistance to immune checkpoint blockade (ICB). Targeting MPs could be an effective strategy to enhance ICB efficacy. We report that protein kinase C delta (PKCδ), a serine/threonine kinase, is abundantly expressed by MPs in human and mouse tumors. PKCδ ^−/− mice displayed reduced tumor progression compared to wild types, with increased response to anti–PD-1. Tumors from PKCδ ^−/− mice demonstrated T _H 1-skewed immune response including increased antigen presentation and T cell activation. Depletion of MPs in vivo altered tumor growth in control but not PKCδ ^−/− mice. Coinjection of PKCδ ^−/− M2-like macrophages with cancer cells into wild-type mice markedly delayed tumor growth and significantly increased intratumoral T cell activation compared to PKCδ ^+/+ controls. PKCδ deficiency reprogrammed MPs by activating type I and type II interferon signaling. Thus, PKCδ might be targeted to reprogram MPs to augment ICB efficacy.

Medical therapeutics for weight loss are changing the landscape of obesity but impacts on obesity-associated cancer remain unclear. We report that in pre-clinical models with significant retatrutide (RETA, LY3437943)-induced weight loss, pancreatic cancer engraftment was reduced, tumor onset was delayed, and progression was attenuated resulting in a 14-fold reduction in tumor volume compared to only 4-fold reduction in single agonist semaglutide-treated mice. Despite weight re-gain after RETA withdrawal, the anti-tumor benefits of RETA persisted. Remarkably, RETA-induced protection extends to a lung cancer model with 50% reduced tumor engraftment, significantly delayed tumor onset, and mitigated tumor progression, with a 17-fold reduction in tumor volume compared to controls. RETA induced immune reprogramming systemically and in the tumor microenvironment with durable anti-tumor immunity evidenced by elevated circulating IL-6, increased antigen presenting cells, reduced immunosuppressive cells, and activation of pro-inflammatory pathways. In sum, our findings suggest that patients with RETA-mediated weight loss may also benefit from reduced cancer risk and improved outcomes.

Bariatric surgery is associated with improved outcomes for several cancers, including breast cancer (BC), although the mechanisms mediating this protection are unknown. We hypothesized that elevated bile acid pools detected after bariatric surgery may be factors that contribute to improved BC outcomes. Patients with greater expression of the bile acid receptor FXR displayed improved survival in specific aggressive BC subtypes. FXR is a nuclear hormone receptor activated by primary bile acids. Therefore, we posited that activating FXR using an established FDA-approved agonist would induce anticancer effects. Using in vivo and in vitro approaches, we determined the anti-tumor potential of bile acid receptor agonism. Indeed, FXR agonism by the bile acid mimetic known commercially as Ocaliva (“OCA”), or Obeticholic acid (INT-747), significantly reduced BC progression and overall tumor burden in a pre-clinical model. The transcriptomic analysis of tumors in mice subjected to OCA treatment revealed differential gene expression patterns compared to vehicle controls. Notably, there was a significant down-regulation of the oncogenic transcription factor MAX (MYC-associated factor X), which interacts with the oncogene MYC. Gene set enrichment analysis (GSEA) further demonstrated a statistically significant downregulation of the Hallmark MYC-related gene set (MYC Target V1) following OCA treatment. In human and murine BC analyses in vitro, agonism of FXR significantly and dose-dependently inhibited proliferation, migration, and viability. In contrast, the synthetic agonism of another common bile acid receptor, the G protein-coupled bile acid receptor TGR5 (GPBAR1) which is mainly activated by secondary bile acids, failed to significantly alter cancer cell dynamics. In conclusion, agonism of FXR by primary bile acid memetic OCA yields potent anti-tumor effects potentially through inhibition of proliferation and migration and reduced cell viability. These findings suggest that FXR is a tumor suppressor gene with a high potential for use in personalized therapeutic strategies for individuals with BC.

Obesity is one of the most prevalent chronic diseases and has become a global epidemic. Obesity leads to a greater risk of breast cancer (BC), metastases, recurrence, and decreased survival. For sustained weight loss, bariatric surgery is effective as a long-term solution. Bariatric surgery is associated with improved outcomes of several cancers including BC, although the mechanisms mediating this protection are unknown. We hypothesized that elevated bile acid pools detected after bariatric surgery may be factors that contribute to improved BC outcomes. Indeed, patients with greater expression of the bile acid receptor FXR displayed improved survival in specific BC subtypes. Patients with tumors that are estrogen receptor negative (ER-) displayed significantly elevated survival with higher FXR (NR1H4) expression compared to lower expression. FXR is a nuclear hormone receptor activated by bile acids. Therefore, we posited that activating FXR using an established FDA-approved agonist would display anticancer effects. Indeed, FXR agonism by the bile acid mimetic known commercially as OCALIVA (“OCA”), or Obeticholic acid (INT-747), significantly reduced BC progression and overall tumor burden in a pre-clinical model. In human and murine BC analyses in vitro, agonism of FXR significantly and dose-dependently inhibited proliferation, migration, and viability. In contrast, synthetic agonism of another common bile acid receptor, the G protein-coupled bile acid receptor (GPBAR1, TGR5) which is mainly activated by secondary bile acids, failed to significantly alter cancer cell dynamics. In conclusion, agonism of FXR by primary bile acid memetic OCA yields potent anti-tumor effects potentially through inhibition of proliferation and migration and reduced cell viability. Findings suggest that FXR is a tumor suppressor gene with high potential for personalized therapeutic strategies for individuals with BC.

Breast cancer (BC) is the most common cancer and the second cause of death in US women. Our lack of understanding of how genetic variants affect molecular mechanisms that mediate BC aggression poses a substantial obstacle to advancements in cancer diagnosis and therapy. To examine genetic variants on BC traits, a novel murine model was created with robust phenotypic and genomic variation. The FVB C3(1)-T-antigen (“C3Tag”) mouse develops spontaneous tumors in the mammary glands of female mice with a mean latency of 4-5 months of age. This genetically engineered mouse model (GEMM) is well established to resemble human basal-like TNBC. TNBC is an aggressive subtype with few clinical approaches and poor patient outcomes. Thus, to model human heterogeneity in BC outcomes, we systematically crossed the C3Tag GEMM into the BXD recombinant inbred family – the largest and best characterized genetic reference population. The new model is termed “BXD-BC” and F1 hybrids of the cross have isogenic genomes that are reproducible. BXD-BCs are a potent tool to determine the impact of genetic modifiers on BC tumor traits. We hypothesized that examination of BXD-BC GEMMs will enable the identification of susceptibility loci, candidate genes, and molecular networks that underlie variation of multiple BC phenotypes. Using N=29 BXD-BC strains, we demonstrated significant heritable variations in the severity of TNBC characteristics such as tumor latency, multiplicity, and survival. Interestingly, 2 BXD-BC strains never developed tumors out to 1 year of age. Thus, BXD-BC strains demonstrate variance in cancer susceptibility and progression compared to the parent C3Tag GEMM, indicating the presence of genetic modifiers. Through an unbiased systematic quantification of breast cancer severity across BXD-BC hybrids, we identified several significant quantitative trait loci (QTL) and candidate genes for specific tumor traits. In combination with public human GWAS datasets, we defined syntenic regions, candidate genes, and underlying networks through cross-species systems genetics analyses to demonstrate the translational validity of conserved, biologically relevant, and targetable candidates. Our findings suggest conserved candidates predicting TNBC patient survival. In sum, the BXD-BC resource is an innovative, reliable, and robust preclinical model that reflects robust genetic heterogeneity. Using cutting edge systems genetics, we have identified genetic modifiers of BC phenotypic variation that could be targeted to advance therapeutic limitations or as biomarkers of risk or response to therapy.