The risk of recurrence of estrogen receptor-positive breast cancer remains constant, even 20 years after diagnosis. Recurrence may be more likely in patients pre-programmed for it already in the womb, such as in the daughters born to obese mothers. Maternal obesity persistently alters offspring’s gut microbiota and impairs tumor immune responses. To investigate if the gut dysbiosis is linked to increased risk of mammary cancer recurrence in the offspring of obese rat dams, we fed adult offspring genistein which is known to have beneficial effects on the gut bacteria. However, the effects of genistein on breast cancer remain controversial. We found that genistein intake after tamoxifen response prevented the increased risk of local recurrence in the offspring of obese dams but had no effect on the control offspring. A significant increase in the abundance of inflammatory Prevotellaceae and Enterobacteriaceae, and a reduction in short-chain fatty acid producing Clostridiaceae was observed in the offspring of obese dams. Genistein supplementation reversed these changes as well as reversed increased gut metabolite N-acetylvaline levels which are linked to increased all-cause mortality. Genistein supplementation also reduced genotoxic tyramine levels, increased metabolites improving pro-resolving phase of inflammation, and reversed the elevated tumor mRNA expression of multiple immunosuppressive genes in the offspring of obese dams. If translatable to breast cancer patients, attempts to prevent breast cancer recurrences might need to focus on dietary modifications which beneficially modify the gut microbiota.

Although multifactorial in origin, one of the most impactful consequences of social isolation is an increase in breast cancer mortality. How this happens is unknown, but many studies have shown that social isolation increases circulating inflammatory cytokines and impairs mitochondrial metabolism. Using a preclinical Sprague Dawley rat model of estrogen receptor-positive breast cancer, we investigated whether social isolation impairs the response to tamoxifen therapy and increases the risk of tumors emerging from dormancy, and thus their recurrence. We also studied which signaling pathways in the mammary glands may be affected by social isolation in tamoxifen treated rats, and whether an anti-inflammatory herbal mixture blocks the effects of social isolation. Social isolation increased the risk of dormant mammary tumor recurrence after tamoxifen therapy. The elevated recurrence risk was associated with changes in multiple signaling pathways including an upregulation of IL6/JAK/STAT3 signaling in the mammary glands and tumors and suppression of the mitochondrial oxidative phosphorylation (OXPHOS) pathway. In addition, social isolation increased the expression of receptor for advanced glycation end-products (RAGE), consistent with impaired insulin sensitivity and weight gain linked to social isolation. In socially isolated animals, the herbal product inhibited IL6/JAK/STAT3 signaling, upregulated OXPHOS signaling, suppressed the expression of RAGE ligands S100a8 and S100a9, and prevented the increase in recurrence of dormant mammary tumors. Increased breast cancer mortality among socially isolated survivors may be most effectively prevented by focusing on the period following the completion of hormone therapy using interventions that simultaneously target several different pathways including inflammatory and mitochondrial metabolism pathways.

Background: About 50 000 new cases of cancer in the United States are attributed to obesity. The adverse effects of obesity on breast cancer may be most profound when affecting the early development; that is, in the womb of a pregnant obese mother. Maternal obesity has several long‐lasting adverse health effects on the offspring, including increasing offspring's breast cancer risk and mortality. Gut microbiota is a player in obesity as well as may impact breast carcinogenesis. Gut microbiota is established early in life and the microbial composition of an infant's gut becomes permanently dysregulated because of maternal obesity. Metabolites from the microbiota, especially short chain fatty acids (SCFAs), play a critical role in mediating the effect of gut bacteria on multiple biological functions, such as immune system, including tumor immune responses.Recent Findings: Maternal obesity can pre‐program daughter's breast cancer to be more aggressive, less responsive to treatments and consequently more likely to cause breast cancer related death. Maternal obesity may also induce poor response to immune checkpoint inhibitor (ICB) therapy through increased abundance of inflammation associated microbiome and decreased abundance of bacteria that are linked to production of SCFAs. Dietary interventions that increase the abundance of bacteria producing SCFAs potentially reverses offspring's resistance to breast cancer therapy.Conclusion: Since immunotherapies have emerged as highly effective treatments for many cancers, albeit there is an urgent need to enlarge the patient population who will be responsive to these treatments. One of the factors which may cause ICB refractoriness could be maternal obesity, based on its effects on the microbiota markers of ICB therapy response among the offspring. Since about 40% of children are born to obese mothers in the Western societies, it is important to determine if maternal obesity impairs offspring's response to cancer immunotherapies.

Maternal high fat diet (HFD) and obesity during pregnancy increase female offspring${}^{\prime }$s mammary cancer risk in animal studies. We aimed to observe whether the consumption of grape juice during pregnancy can reverse this risk. During pregnancy and lactation, female Wistar rats were fed either a control or HFD and also received grape juice or tap water. At the age of 50 days, female offspring were euthanized, and mammary glands were collected to assess changes in biomarkers of increased mammary cancer risk. Maternal HFD increased the number of terminal end buds in offspring’s mammary glands and promoted cell proliferation (ki67). Maternal grape consumption blocked these effects. Apoptosis marker caspase 7, but not caspase 3, was reduced in the HFD offspring. HFD offspring also exhibited a reduction in the indicators of cell cycle regulation (p27, p21) and an ability to maintain DNA integrity (reduced p53). Maternal grape juice did not have any effect on these endpoints in the HFD offspring but reduced caspase 7 and p53 levels in the control offspring, perhaps reflecting reduced cellular stress. Maternal HFD increased oxidative stress marker GPx1 mRNA expression, and grape juice increased the levels of GPx2 in both the control and HFD offspring. HFD increased XBP1/Xbp1s, Atf4 and Atf6 mRNA expression and reduced ATF6 and CHOP protein levels. Maternal grape juice reversed the increase in XBP1/Xbp1s, Atf4 and Atf6 in the HFD offspring. PPAR was downregulated in the HFD group, and grape juice reversed this effect. Grape juice also reduced the levels of HER2 and IRS, both in the control and HFD offspring. In conclusion, maternal grape juice supplementation reversed some of the biomarkers that are indicative of increased breast cancer risk in the HFD offspring.

Endocrine therapy can lead to nutrient deprivation by reducing glucose and glutamine uptake and total cellular ATP production. The ability of cells to bypass this metabolic stress is fundamental to how they regulate BC growth and acquire endocrine resistance. Sirtuins (SIRTs) are NAD+-dependent deacylases and regulate a widerange of intracellular processes including metabolism. SIRT3, activated by calorie restriction, modulates mitochondrial adaptation to low energy input. It has a key role in mitochondrial integrity and function, regulating cell survival, death and metabolic pathways, regulating the shift to amino-acid and fatty-acid catabolism. SIRT3 can maintain ROS levels at the appropriate levels for sustaining a proliferative phenotype, preventing apoptosis and promoting carcinogenesis. A role of SIRT3 in epigenetic regulation has also been reported. We used Differential Dependency Network analysis to compare the wiring of the SIRTs and key metabolism-related genes in matched antiestrogen- sensitive vs. resistant breast cancer (BC) cells, which identified several novel signaling hubs including CDKN2A (p16), linking SIRT3 to cell proliferation. The ability of SIRTs to sense and respond to changes in energy, coupled with their deacetylase/deacylase functions, could provide a mechanism for the cell to rewire signaling and maintain a newly acquired drug-resistant phenotype. Using endocrine sensitive (LCC1) and resistant (LCC9) BC cells, we confirmed the higher expression of SIRT3 in LCC9, compared to LCC1 cells. Upregulation of SIRT3 expression within 24 hrs of Fulvestrant (ICI 1 µM) treatment (p=0.0176) in LCC1 was shown, but no effect was observed in LCC9 cells. Conversely, treatment with 17β-estradiol (E2- 10 nM) did not significantly affect SIRT3 expression in either LCC1 or LCC9 cells. Inhibition of SIRT3 acitivity, using the LC0296 inhibitor (15 µM), reduced growth rate in LCC1 and SIRT3-silenced LCC9 cells under treatment with ICI (1 nM and 1 µM, respectively) (p< 0.0001, p< 0.001 respectively). Treatment with SIRTUIN 3 inhibitor and ICI induced apoptosis in LCC1 and SIRT3-silenced LCC9 cells compared to the untreated control and ICI only treated cells (p< 0.001). The combination SIRT3 inhibitor (15 µM) plus ICI (0.5 µM) increased ROS production in LCC9-SIRT3 silenced cells in 24 hours of treatment compared to the untreated control and ICI only treated cells (p< 0.001). SIRT3 inhibitor (15 µM) decreased LCC1 cell spheroid formation (p< 0.05), however it didn’t show additive effect to the effect of ICI (0.5 µM) in the same conditions. The combination of SIRT3 inhibitor (15 µM) and ICI (1 µM) reduced the growth of LCC9 SIRT3-silenced cells in detached condition compared to untreated control and ICI only treated cells (p< 0.001). The results show that SIRT3 may have a role in Fulvestrant response in BC cells; the mechanism is under investigation in our laboratory. Citation Format: Karla Andrade de Oliveira, Surojeet Sengupta, Lu Jin, Fabia de Oliveira Andrade, Melike Ozgu-Onal, Anil Yadav, Robert Clarke. Inhibition of Sirtuin 3 Sensitizes Breast Cancer Cells to Fulvestrant [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-11-08.

Disclosure: K.A. de Oliveira: None. F.D. Andrade: None. M. Ozgul-Onal: None. A. Yadav: None. T. Onal: None. L. Jin: None. S. Sengupta: None. R. Clarke: None. Endocrine therapy can lead to cellular nutrient deprivation by reducing glucose and glutamine uptake and total cellular ATP production in breast cancer cells. The ability to bypass this metabolic stress is fundamental to how breast cancer cells regulate growth and acquire endocrine resistance. SIRT3, which can be activated by calorie restriction, modulates mitochondrial adaptation to low energy input. It has a key role in mitochondrial integrity and function, regulating cell survival, death, and metabolism, regulating the shift to amino-acid and fatty-acid catabolism. SIRT3 can maintain ROS levels at the appropriate levels for sustaining a proliferative phenotype, preventing apoptosis and promoting carcinogenesis. A role of SIRT3 in epigenetic regulation has also been reported. The ability of SIRTs to sense and respond to changes in energy, coupled with their intrinsic deacetylase/deacylase functions, could provide a mechanism for the cell to rewire signaling and maintain a newly acquired drug-resistant phenotype. Using antiestrogen sensitive (LCC1) and cross-resistant (LCC9) breast cancer cells, we confirmed higher expression of SIRT3 in LCC9, compared with LCC1 cells. Upregulation of SIRT3 expression within 24 hrs of Fulvestrant (ICI 1 µM) treatment (p=0.0176) in LCC1 was shown, whereas no effect was observed in LCC9 cells. Inhibition of SIRT3 activity, using the inhibitor LC0296 (15 µM), reduced growth rate in both LCC1 and SIRT3-silenced LCC9 cells under treatment with ICI (p<0.0001, p<0.001 respectively). Treatment with SIRTUIN 3 inhibitor and ICI induced caspase-independent cell death in LCC1 and SIRT3-silenced LCC9 cells compared to the untreated control and ICI only treated cells (p<0.001). The combination of SIRT3 inhibition (LC0296, 15 µM) and ICI treatment (0.5 µM) increased ROS production in LCC9-SIRT3 silenced cells in 24 hrs compared with the untreated control and ICI only treated cells (p<0.001). The combination of LC0296 and ICI induced a decrease in mitochondrial membrane potential and ATP production, and a decrease in glycolytic capacity and glycolytic reserve in both LCC1 and SIRT3-silenced LCC9 cells, compared with the untreated control (p<0.001). Moreover, ICI significantly reduced ATP production in the mitochondria of the SIRT3-silenced LCC9 cells (p<0.001) but not in the non-silenced (control) LCC9 cells. Taken together, these results show that SIRT3 may have a key role in determining the response to fulvestrant response in ER+ breast cancer cells; a more detailed understanding of this role for SIRT3 is under investigation in our laboratory. Presentation: Thursday, June 15, 2023