Diet modulates the gut microbiome, metabolism, and mammary gland inflammation to influence breast cancer risk

Several studies have indicated a strong link between obesity and the risk of breast cancer. Obesity decreases gut microbial biodiversity and modulates Bacteroidetes-to-Firmicutes proportional abundance, suggesting that increased energy-harvesting capacity from indigestible dietary fibers and elevated lipopolysaccharide bioavailability may promote inflammation. To address the limited evidence linking diet-mediated changes in the gut microbiota to breast cancer risk, we aimed to determine how diet affects the microbiome and breast cancer risk. Female 3-week-old BALB/c mice were fed six different diets (control, high-sugar, lard, coconut oil, lard+flaxseed oil, and lard+safflower oil) for 10 weeks. Fecal 16s sequencing was performed for each group. Diet shifted fecal microbiome populations and modulated mammary gland macrophage infiltration. Fecal conditioned media shifted macrophage polarity and inflammation. In our DMBA-induced breast cancer model, diet differentially modulated tumor and mammary gland metabolism. We demonstrated how dietary patterns change metabolic outcomes, and gut microbiota, which may contribute to breast tumor risk. Furthermore, we showed the influence of diet on metabolism, inflammation, and macrophage polarity. This study suggests that dietary-microbiome interactions are key mediators of breast cancer risk.

Anti-CD47 immunotherapy as a therapeutic strategy for the treatment of breast cancer brain metastasis

The presence of cell surface protein CD47 allows cancer cells to evade innate and adaptive immune surveillance resulting in metastatic spread. CD47 binds to and activates SIRPα on the surface of myeloid cells, inhibiting their phagocytic activity. On the other hand, CD47 binds the matricellular protein Thrombospondin-1, limiting T-cell activation. Thus, blocking CD47 is a potential therapeutic strategy for preventing brain metastasis. To test this hypothesis, breast cancer patient biopsies were stained with antibodies against CD47 to determine differences in protein expression. An anti-CD47 antibody was used in a syngeneic orthotopic triple-negative breast cancer model, and CD47 null mice were used in a breast cancer brain metastasis model by intracardiac injection of the E0771-Br-Luc cell line. Immunohistochemical staining of patient biopsies revealed an 89% increase in CD47 expression in metastatic brain tumors compared to normal adjacent tissue (p ≤ 0.05). Anti-CD47 treatment in mice bearing brain metastatic 4T1br3 orthotopic tumors reduced tumor volume and tumor weight by over 50% compared to control mice (p ≤ 0.05) and increased IBA1 macrophage/microglia marker 5-fold in tumors compared to control (p ≤ 0.05). Additionally, CD47 blockade increased the M1/M2 macrophage ratio in tumors 2.5-fold (p ≤ 0.05). CD47 null mice had an 89% decrease in metastatic brain burden (p ≤ 0.05) compared to control mice in a brain metastasis model. Additionally, RNA sequencing revealed several uniquely expressed genes and significantly enriched genes related to tissue development, cell death, and cell migration tumors treated with anti-CD47 antibodies. Thus, demonstrating that CD47 blockade affects cancer cell and tumor microenvironment signaling to limit metastatic spread and may be an effective therapeutic for triple-negative breast cancer brain metastasis.

Study design and methods for the pilot study of muscadine grape extract supplement to improve fatigue among older adult cancer survivors (FOCUS) trial

INTRODUCTION

Fatigue is a prevalent symptom among both cancer survivors and older adults. Negative consequences of fatigue include increased sedentary behavior, decreased physical activity and function, and lower quality of life. Few pharmacologic interventions improve fatigue. Our preclinical and clinical data show promising effects of a muscadine grape extract supplement (MGES) on oxidative stress, mitochondrial bioenergetics, the microbiome, and the symptom of fatigue. This pilot study seeks to translate these observations to cancer survivorship by testing the preliminary effect of MGE supplementation on older adult cancer survivors with self-reported fatigue.

MATERIALS AND METHODS

We designed a double-blinded placebo-controlled pilot study to evaluate preliminary efficacy of MGE supplementation versus placebo on fatigue among older adult cancer survivors (aged ≥65 years) who report baseline fatigue. Sixty-four participants will be enrolled and randomized 1:1 to twice daily MGES (four tablets twice daily) versus placebo for 12 weeks. The primary outcome is change in Patient-Reported Outcomes Measurement Information System (PROMIS) Fatigue score from baseline to 12 weeks. Secondary outcomes are change in self-reported physical function, physical fitness (6-min walk test), self-reported physical activity, global quality of life (QOL), and the Fried frailty index. Correlative biomarker assays will assess changes in 8-hydroxy-2 deoxyguanosine, peripheral blood mitochondrial function, inflammatory markers, and the gut microbiome.

DISCUSSION

This pilot study builds on preclinical and clinical observations to estimate effects of MGE supplementation on fatigue, physical function, QOL, and biologic correlates in older adult cancer survivors. Trial registration #: CT.govNCT04495751; IND 152908.

Abstract P5-08-14: Blockade of CD47/Thrombospondin-1 signaling increases glycolytic metabolism as a protective mechanism against chemotherapy-associated cardiac injury in a model of Triple-Negative Breast Cancer

Due to advances in diagnosis and treatment, cancer–related mortality has decreased, and by the year 2030, there will be 22 million cancer survivors in the United States. This success comes with an increased incidence of serious adverse effects, mainly in the cardiovascular system. While new treatment modalities are emerging for Triple-negative breast cancer (TNBC), most current strategies include anthracycline-based regimens to manage disease. Therefore, novel strategies are needed to overcome anthracycline-induced cardiotoxicities in this patient population. Activation of the TSP1/CD47 signaling axis is implicated in the progression of heart failure, with reported increases in TSP1 levels following myocardial infarction. Therefore, we examined the potential of CD47 blockade as a strategy to prevent cardiac injury as a consequence of cancer chemotherapy. Our data in a syngeneic orthotopic breast cancer model shows that blockade of CD47 using an in vivo anti-sense phosphodiesterase morpholino (PMO) preserved ejection fraction, fractional shortening, and cardiac output when compared to DOX treatment while preserving oncologic efficacy of chemotherapy. To determine a potential mechanism of cardioprotection, hearts of control and CD47 PMO-treated mice were subjected to RNA sequencing. Gene set enrichment analysis (GSEA) showed significant positive enrichment for metabolic pathways including pyruvate metabolism (NES= 2.3 , p< 0.002), and oxidative phosphorylation (NES=2.0, p< 0.01). During cardiac insult, metabolic flexibility of cardiomyocytes results in metabolic reprogramming from fatty acid oxidation to a glycolytic mechanism to overcome injury. Thus, DOX-associated cardiotoxicity may be mediated by an increase in TSP1 and a decrease in glycolysis, leading to the inability to overcome acute cellular stress. In vitro cellular bioenergetics, analysis revealed that TSP1 caused a dose-dependent reduction in glycolytic flux and glycolytic capacity in cardiac myoblast. This, coupled with preserved cardiac viability of cardiac cells treated with CD47 PMO in the presence of DOX, suggests that TSP1 may act through CD47 to prevent cardiac cell metabolic reprogramming needed to overcome injury. Furthermore, anti-sense experiments with siRNAs to Glut-4 and Hexokinase-II showed that the protection conferred by CD47 is mediated by activating these proteins. Therefore our studies suggest that the TSP1/CD47 axis may be central to the interplay of metabolism to preserve cardiac tissue integrity; thus, targeting this pathway may prevent the onset of chronic cardiac disease due to chemotherapy in cancer patients.

Citation Format: Steven M. Bronson, Jessica D. Mackert, Mitra Kooshki, Adam S. Wilson, Nildris Cruz-Diaz, Pierre L Triozzi, Alexandra Thomas, Katherine L. Cook, David R. Soto-Pantoja. Blockade of CD47/Thrombospondin-1 signaling increases glycolytic metabolism as a protective mechanism against chemotherapy-associated cardiac injury in a model of Triple-Negative Breast Cancer [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 P5-08-14.

Abstract P1-02-05: Endocrine-targeted therapies modify the gut microbiome affecting responsiveness in ER+ breast cancer

Background: The microbiome consists of the totality of microorganisms (bacteria, fungi, protist, viruses, and phages) that live on and within the body. Studies implicate the gut bacterial microbiome as a risk factor for estrogen receptor-positive (ER+) breast cancer. While diet is the main contributor to the gut microbiome, medications also shift the bacterial microbiome. We currently do not know whether oral endocrine targeting therapies, such as aromatase inhibitors or tamoxifen shift the gut microbiome. Furthermore, we do not know whether gut microbiome populations can influence drug efficacy. Methods: Fecal samples from human donors were placed into ex-vivo colonic bioreactors for stabilization (n=3). Bioreactors were untreated or treated with letrozole or tamoxifen citrate for 48 hours. Samples were collected, DNA isolated, and metagenomic sequencing performed to determine direct drug-bug interactions. C57BL/6 mice were placed on a healthy control (HC; 21% kcal from fat derived from olive oil and fish oil) or a Western diet (45% kcal from fat derived from corn oil, lard, and milkfat) for 6 weeks. Mice within dietary patterns were randomized and administered control, tamoxifen (TAM; 37 ppm tamoxifen citrate), or an aromatase inhibitor (AI; 5 ppm letrozole) for 16 weeks. Metagenomics sequencing were performed on fecal DNA samples at study endpoint. Female BALB/c mice fed a HC or Western diet were injected with bone metastatic 4T1.2ER+ breast cancer cells. Mice were administered tamoxifen citrate, oral probiotics, or a combination of TAM + probiotics for 3-weeks. Tumor volume, tumor weight, and lung weight were recorded at the end of the study. Hindlimbs were analyzed for metastatic lesions. Results: Metagenomic sequencing from the ex-vivo colonic bioreactors treated with aromatase inhibitors or tamoxifen display differential shifts in several β-glucuronidase-expressing and obesity-associated bacterial species suggesting AI and selective estrogen receptor modulators have varying effects in the gut microbiome that may influence estrogen bioavailability and metabolic parameters. C57BL/6 mice on HC or Western diet treated with AI or TAM also display differences in the microbiota and phage populations with TAM elevating Lactobacillus johnsonii and letrozole increasing Lactococcus lactis bacterial proportional abundance. In the tumor-bearing model, combination of oral Lactobacillus probiotics and TAM significantly reduced tumor weight when compared with the tumor weight in control, TAM, or probiotic treated mice fed a Western diet. Combination of probiotics and TAM also prevented the development of ER+ bone metastatic lesions. Conclusions: Our study indicates oral endocrine therapies differentially affect the gut microbiome and these drug-bug interactions are sensitive to dietary-influenced baseline microbiota populations, which may influence drug efficacy and metabolic outcomes. Furthermore, our preclinical studies suggest oral probiotic supplements may enhance tamoxifen efficacy to reduce tumor growth and metastatic development. Further clinical studies are needed on this topic.

Citation Format: Alana Arnone, Adam S. Wilson, Akiko Chiba, Bethany Kerr, David R. Soto-Pantoja, Alexandra Thomas, Katherine L. Cook. Endocrine-targeted therapies modify the gut microbiome affecting responsiveness in ER+ breast cancer [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 P1-02-05.

Early-life dietary exposures mediate persistent shifts in the gut microbiome and visceral fat metabolism

In utero dietary exposures are linked to the development of metabolic syndrome in adult offspring. These dietary exposures can potentially impact gut microbial composition and offspring metabolic health. Female BALB/c mice were administered a lard, lard + flaxseed oil, high sugar, or control diet 4 wk before mating, throughout mating, pregnancy, and lactation. Female offspring were offered low-fat control diet at weaning. Fecal 16S sequencing was performed. Untargeted metabolomics was performed on visceral adipose tissue (VAT) of adult female offspring. Immunohistochemistry was used to determine adipocyte size, VAT collagen deposition, and macrophage content. Hippurate was administered via weekly intraperitoneal injections to low-fat and high-fat diet-fed female mice and VAT fibrosis and collagen 1A (COL1A) were assessed by immunohistochemistry. Lard diet exposure was associated with elevated body and VAT weight and dysregulated glucose metabolism. Lard + flaxseed oil attenuated these effects. Lard diet exposures were associated with increased adipocyte diameter and VAT macrophage count. Lard + flaxseed oil reduced adipocyte diameter and fibrosis compared with the lard diet. Hippurate-associated bacteria were influenced by lard versus lard + flax exposures that persisted to adulthood. VAT hippurate was increased in lard + flaxseed oil compared with lard diet. Hippurate supplementation mitigated VAT fibrosis pathology. Maternal high-fat lard diet consumption resulted in long-term metabolic and gut microbiome programming in offspring, impacting VAT inflammation and fibrosis, and was associated with reduced VAT hippurate content. These traits were not observed in maternal high-fat lard + flaxseed oil diet-exposed offspring. Hippurate supplementation reduced VAT fibrosis. These data suggest that detrimental effects of early-life high-fat lard diet exposure can be attenuated by dietary omega-3 polyunsaturated fatty acid supplementation.

Targeting the CD47/thrombospondin-1 signaling axis regulates immune cell bioenergetics in the tumor microenvironment to potentiate antitumor immune response

BACKGROUND

CD47 is an integral membrane protein that alters adaptive immunosurveillance when bound to the matricellular glycoprotein thrombospondin-1 (TSP1). We examined the impact of the CD47/TSP1 signaling axis on melanoma patient response to anti-PD-1 therapy due to alterations in T cell activation, proliferation, effector function, and bioenergetics.

METHODS

A syngeneic B16 mouse melanoma model was performed to determine if targeting CD47 as monotherapy or in combination with anti-PD-1 impacted tumor burden. Cytotoxic (CD8+) T cells from Pmel-1 transgenic mice were used for T cell activation, cytotoxic T lymphocyte, and cellular bioenergetic assays. Single-cell RNA-sequencing, ELISA, and flow cytometry was performed on peripheral blood mononuclear cells and plasma of melanoma patients receiving anti-PD-1 therapy to examine CD47/TSP1 expression.

RESULTS

Human malignant melanoma tissue had increased CD47 and TSP1 expression within the tumor microenvironment compared with benign tissue. Due to the negative implications CD47/TSP1 can have on antitumor immune responses, we targeted CD47 in a melanoma model and observed a decrease in tumor burden due to increased tumor oxygen saturation and granzyme B secreting CD8+ T cells compared with wild-type tumors. Additionally, Pmel-1 CD8+ T cells exposed to TSP1 had reduced activation, proliferation, and effector function against B16 melanoma cells. Targeting CD47 allowed CD8+ T cells to overcome this TSP1 interaction to sustain these functions. TSP1 exposed CD8+ T cells have a decreased rate of glycolysis; however, targeting CD47 restored glycolysis when CD8+ T cells were exposed to TSP1, suggesting CD47 mediated metabolic reprogramming of T cells. Additionally, non-responding patients to anti-PD-1 therapy had increased T cells expressing CD47 and circulating levels of TSP1 compared with responding patients. Since CD47/TSP1 signaling axis negatively impacts CD8+ T cells and non-responding patients to anti-PD-1 therapy have increased CD47/TSP1 expression, we targeted CD47 in combination with anti-PD-1 in a melanoma model. Targeting CD47 in combination with anti-PD-1 treatment further decreased tumor burden compared with monotherapy and control.

CONCLUSION

CD47/TSP1 expression could serve as a marker to predict patient response to immune checkpoint blockade treatment, and targeting this pathway may preserve T cell activation, proliferation, effector function, and bioenergetics to reduce tumor burden as a monotherapy or in combination with anti-PD-1.

Discrete Correlation Summation Clustering Reveals Differential Regulation of Liver Metabolism by Thrombospondin-1 in Low-Fat and High-Fat Diet-Fed Mice

Thrombospondin-1 (TSP1) is a matricellular protein with many important roles in mediating carcinogenesis, fibrosis, leukocyte recruitment, and metabolism. We have previously shown a role of diet in the absence of TSP1 in liver metabolism in the context of a colorectal cancer model. However, the metabolic implications of TSP1 regulation by diet in the liver metabolism are currently understudied. Therefore Discrete correlation summation (DCS) was used to re-interrogate data and determine the metabolic alterations of TSP1 deficiency in the liver, providing new insights into the role of TSP1 in liver injury and the progression of liver pathologies such as nonalcoholic fatty liver disease (NAFLD). DCS analysis provides a straightforward approach to rank covariance and data clustering when analyzing complex data sets. Using this approach, our previous liver metabolite data was re-analyzed by comparing wild-type (WT) and Thrombospondin-1 null (Thbs1-/-) mice, identifying changes driven by genotype and diet. Principal component analysis showed clustering of animals by genotype regardless of diet, indicating that TSP1 deficiency alters metabolite handling in the liver. High-fat diet consumption significantly altered over 150 metabolites in the Thbs1-/- livers versus approximately 90 in the wild-type livers, most involved in amino acid metabolism. The absence of Thbs1 differentially regulated tryptophan and tricarboxylic acid cycle metabolites implicated in the progression of NAFLD. Overall, the lack of Thbs1 caused a significant shift in liver metabolism with potential implications for liver injury and the progression of NAFLD.

Intestinal Microbiota Influence Doxorubicin Responsiveness in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is highly aggressive with a poor 5-year survival rate. Targeted therapy options are limited and most TNBC patients are treated with chemotherapy. This study aimed to determine whether doxorubicin (Dox) shifts the gut microbiome and whether gut microbiome populations influence chemotherapeutic responsiveness. Female BALB/c mice (n = 115) were injected with 4T1-luciferase cells (a murine syngeneic TNBC model) and treated with Dox and/or antibiotics, high-fat diet-derived fecal microbiota transplant (HFD-FMT), or exogenous lipopolysaccharide (LPS). Metagenomic sequencing was performed on fecal DNA samples. Mice that received Dox were stratified into Dox responders or Dox nonresponders. Mice from the Dox responders and antibiotics + Dox groups displayed reduced tumor weight and metastatic burden. Metagenomic analysis showed that Dox was associated with increased Akkermansia muciniphila proportional abundance. Moreover, Dox responders showed an elevated proportional abundance of Akkermansia muciniphila prior to Dox treatment. HFD-FMT potentiated tumor growth and decreased Dox responsiveness. Indeed, lipopolysaccharide, a structural component of Gram-negative bacteria, was increased in the plasma of Dox nonresponders and FMT + Dox mice. Treatment with exogenous LPS increases intestinal inflammation, reduces Dox responsiveness, and increases lung metastasis. Taken together, we show that modulating the gut microbiota through antibiotics, HFD-FMT, or by administering LPS influenced TNBC chemotherapy responsiveness, lung metastasis, and intestinal inflammation.

Immuno-reactive cancer organoid model to assess effects of the microbiome on cancer immunotherapy

Immune checkpoint blockade (ICB) therapy has demonstrated good efficacy in many cancer types. In cancers such as non-resectable advanced or metastatic triple-negative breast cancer (TNBC), it has recently been approved as a promising treatment. However, clinical data shows overall response rates (ORRs) from ~ 3-40% in breast cancer patients, depending on subtype, previous treatments, and mutation status. Composition of the host-microbiome has a significant role in cancer development and therapeutic responsiveness. Some bacterial families are conducive to oncogenesis and progression, while others aid innate and therapeutically induced anti-tumor immunity. Modeling microbiome effects on anti-tumor immunity in ex vivo systems is challenging, forcing the use of in vivo models, making it difficult to dissect direct effects on immune cells from combined effects on tumor and immune cells. We developed a novel immune-enhanced tumor organoid (iTO) system to study factors affecting ICB response. Using the 4T1 TNBC murine cell line and matched splenocytes, we demonstrated ICB-induced response. Further administration of bacterial-derived metabolites from species found in the immunomodulatory host-microbiome significantly increased ICB-induced apoptosis of tumor cells and altered immune cell receptor expression. These outcomes represent a method to isolate individual factors that alter ICB response and streamline the study of microbiome effects on ICB efficacy.

Circulating Immune Bioenergetic, Metabolic, and Genetic Signatures Predict Melanoma Patients' Response to Anti-PD-1 Immune Checkpoint Blockade

PURPOSE

Immunotherapy with checkpoint inhibitors is improving the outcomes of several cancers. However, only a subset of patients respond. Therefore, predictive biomarkers are critically needed to guide treatment decisions and develop approaches to the treatment of therapeutic resistance.

EXPERIMENTAL DESIGN

We compared bioenergetics of circulating immune cells and metabolomic profiles of plasma obtained at baseline from patients with melanoma treated with anti-PD-1 therapy. We also performed single-cell RNA sequencing (scRNAseq) to correlate transcriptional changes associated with metabolic changes observed in peripheral blood mononuclear cells (PBMC) and patient plasma.

RESULTS

Pretreatment PBMC from responders had a higher reserve respiratory capacity and higher basal glycolytic activity compared with nonresponders. Metabolomic analysis revealed that responder and nonresponder patient samples cluster differently, suggesting differences in metabolic signatures at baseline. Differential levels of specific lipid, amino acid, and glycolytic pathway metabolites were observed by response. Further, scRNAseq analysis revealed upregulation of T-cell genes regulating glycolysis. Our analysis showed that SLC2A14 (Glut-14; a glucose transporter) was the most significant gene upregulated in responder patients' T-cell population. Flow cytometry analysis confirmed significantly elevated cell surface expression of the Glut-14 in CD3+, CD8+, and CD4+ circulating populations in responder patients. Moreover, LDHC was also upregulated in the responder population.

CONCLUSIONS

Our results suggest a glycolytic signature characterizes checkpoint inhibitor responders; consistently, both ECAR and lactate-to-pyruvate ratio were significantly associated with overall survival. Together, these findings support the use of blood bioenergetics and metabolomics as predictive biomarkers of patient response to immune checkpoint inhibitor therapy.

Abstract P1-09-03: Omega-3 polyunsaturated fatty acid supplementation shifts the gut and breast microbiome to influence inflammation

Obesity increases the risk of postmenopausal breast cancer. Obesity also influences the gut microbiome. The gut microbiome represents the totality of microorganisms living within the body and can influence the development of many different types of diseases, including breast cancer. Obesity is associated with an increase in the Firmicute-to-Bacteriodetes bacterial phyla ratio in the gut microbiome promoting dysbiosis and inflammation. We previously demonstrated that diet and obesity shift both the gut and breast tissue microbiome using a non-human primate model. To investigate the impact of omega-3 PUFA supplementation on the gut and breast microbiome, we used a combination of a preclinical murine model and human fecal samples collected from overweight and obese postmenopausal women enrolled in a weight loss clinical trial supplemented with placebo or high dose omega-3 PUFA (clinicaltrials.gov identifier: NCT02101970). Female C57BL/6 mice fed a Western (0.2% kcal from omega-3 PUFA) or a Western +omega-3 PUFA diet (1.3% kcal omega-3 PUFA) for 16 weeks demonstrate differences in intestinal permeability as measured by circulating plasma LPS, in vivo FITC-dextran permeability assay, and intestinal tight junction protein ZO-1 gene expression. Elevated LPS bioavailability associated with metabolic endotoxemia has been associated with breast cancer risk. Omega-3 PUFA supplementation shifts the gut and mammary gland (MG) microbiome. 16S sequencing of DNA isolated from matched fecal and MG samples demonstrate that omega-3 PUFA supplementation independently regulated both microbiomes. Moreover, omega-3 PUFA supplementation in a Western diet reduced Firmicute-to-Bacteriodetes ratio in the murine MG tissue. Obese and overweight postmenopausal women (n=46) were enrolled in a weight loss clinical trial (combination of calorie restriction and exercise) and were administered a placebo or 3.25 g/day combined eicosapentaenoic (EPA) and docosahexaenoic (DHA) fatty acids omega-3 PUFA supplements for 6 months. Bacterial sequencing of DNA isolated from fecal collections at baseline and after 6 months of intervention shows significant decrease in Firmicutes-to-Bacteriodetes ratio regardless of intervention group. However, when clustering subjects by relative weight loss and intervention (<10% weight loss on placebo; <10% weight loss on omega-3; >10% weight loss on placebo, or >10% weight loss on omega-3), women in the <10% weight loss on omega-3 PUFA group displayed significant reduction in the Firmicutes-to-Bacteriodetes ratio from baseline that was not observed in the <10% weight loss on placebo group. These data suggest that women who did not achieve substantial weight loss but were supplemented with omega-3 PUFA, show an improved gut microbiome for potential enhancement of health outcomes. Taken together, these data demonstrate that increasing omega-3 PUFA intake to approximately 2% of total daily calories can shift the gut and mammary gland microbiome to a pattern associated with improved intestinal permeability parameters and less chronic inflammation, which in turn is associated with reduced risk of postmenopausal breast cancer.

Citation Format: Katherine L. Cook, Adam S Wilson, David R Soto-Pantoja, Bruce F. Kimler, Shahid Umar, Carol J. Fabian. Omega-3 polyunsaturated fatty acid supplementation shifts the gut and breast microbiome to influence inflammation [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-09-03.

Metabolic Implications of Immune Checkpoint Proteins in Cancer

Expression of immune checkpoint proteins restrict immunosurveillance in the tumor microenvironment; thus, FDA-approved checkpoint inhibitor drugs, specifically PD-1/PD-L1 and CTLA-4 inhibitors, promote a cytotoxic antitumor immune response. Aside from inflammatory signaling, immune checkpoint proteins invoke metabolic reprogramming that affects immune cell function, autonomous cancer cell bioenergetics, and patient response. Therefore, this review will focus on the metabolic alterations in immune and cancer cells regulated by currently approved immune checkpoint target proteins and the effect of costimulatory receptor signaling on immunometabolism. Additionally, we explore how diet and the microbiome impact immune checkpoint blockade therapy response. The metabolic reprogramming caused by targeting these proteins is essential in understanding immune-related adverse events and therapeutic resistance. This can provide valuable information for potential biomarkers or combination therapy strategies targeting metabolic pathways with immune checkpoint blockade to enhance patient response.

Investigating the role of endogenous estrogens, hormone replacement therapy, and blockade of estrogen receptor-α activity on breast metabolic signaling

Purpose

Menopause is associated with an increased risk of estrogen receptor-positive (ER +) breast cancer. To characterize the metabolic shifts associated with reduced estrogen bioavailability on breast tissue, metabolomics was performed from ovary-intact and ovariectomized (OVX) female non-human primates (NHP). The effects of exogenous estrogen administration or estrogen receptor blockade (tamoxifen treatment) on menopause-induced metabolic changes were also investigated.

Methods

Bilateral ovariectomies were performed on female cynomolgus macaques (Macaca fascicularis) to model menopause. OVX NHP were then divided into untreated (n = 13), conjugated equine estrogen (CEE)-treated (n= 13), or tamoxifen-treated (n = 13) subgroups and followed for 3 years. Aged-matched ovary-intact female NHP (n = 12) were used as a premenopausal comparison group. Metabolomics was performed on snap-frozen breast tissue.

Results

Changes in several different metabolic biochemicals were noted, particularly in glucose and fatty acid metabolism. Specifically, glycolytic, Krebs cycle, acylcarnitines, and phospholipid metabolites were elevated in breast tissue from ovary-intact NHP and OVX + CEE in relation to the OVX and OVX + tamoxifen group. In contrast, treatment with CEE and tamoxifen decreased several cholesterol metabolites, compared to the ovary-intact and OVX NHP. These changes were accompanied by elevated bile acid metabolites in the ovary-intact group.

Conclusion

Alterations in estrogen bioavailability are associated with changes in the mammary tissue metabolome, particularly in glucose and fatty acid metabolism. Changes in these pathways may represent a bioenergetic shift in gland metabolism at menopause that may affect breast cancer risk.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10549-021-06354-w.

BSCI-17. Targeting SIRPα as a therapeutic strategy for the treatment of breast cancer brain metastasis

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer characterized by the lack of druggable targets and an incidence of brain metastasis from the primary site of approximately 35%. There is no standard treatment for managing brain metastasis associated with TNBC; therefore, new strategies are urgently needed to overcome disease mortality. The CD47/SIRPα signaling pathway is implicated in tumor progression due to bypassing innate and adaptive immune surveillance. Most strategies targeting this pathway focus on targeting the receptor CD47; however, targeting SIRPα as a potential strategy to mitigate tumor burden remains understudied. Analysis of gene expression database shows that SIRPα expression is significantly elevated in invasive breast cancer when compared to primary. Furthermore, single-cell data indicates that SIRPα is expressed in basal epithelial cells in TNBC tumors aside from the myeloid compartment. Our immune staining against SIRPα in patient biopsies shows a five-fold increase in SIRPα expression in metastatic brain tumors compared to the primary lesions. Therefore, targeting SIRPα may be a new immunotherapeutic strategy to treat breast cancer brain metastases. Anti-SIRPα treatment of mice bearing brain metastatic 4T1br3 orthotopic tumors showed reduced tumor volume and tumor weight by over 50% compared to isotype control-treated mice. Furthermore, in a model of intracardial brain metastasis, treatment with SIRPα antibody was associated with a 60% increase in survival compared to isotype control-treated mice. RNA sequencing of tumors indicated that SIRPα blockade is associated with a reduction in genes linked to mitochondrial respiratory chain and increases in negative regulation of the cell cycle. Furthermore, in vitro SIRPα targeting enhanced the cell-mediated cytotoxicity of microglia against 4T1Br3 breast cancer cells. This suggests that SIRPα blockade may influence both tumor and innate immune cells to limit brain metastatic breast cancer growth and enhance survival.

Diet Alters Entero-Mammary Signaling to Regulate the Breast Microbiome and Tumorigenesis

Obesity and poor diet often go hand-in-hand, altering metabolic signaling and thereby impacting breast cancer risk and outcomes. We have recently demonstrated that dietary patterns modulate mammary microbiota populations. An important and largely open question is whether the microbiome of the gut and mammary gland mediates the dietary effects on breast cancer. To address this, we performed fecal transplants between mice on control or high-fat diets (HFD) and recorded mammary tumor outcomes in a chemical carcinogenesis model. HFD induced protumorigenic effects, which could be mimicked in animals fed a control diet by transplanting HFD-derived microbiota. Fecal transplants altered both the gut and mammary tumor microbiota populations, suggesting a link between the gut and breast microbiomes. HFD increased serum levels of bacterial lipopolysaccharide (LPS), and control diet-derived fecal transplant reduced LPS bioavailability in HFD-fed animals. In vitro models of the normal breast epithelium showed that LPS disrupts tight junctions (TJ) and compromises epithelial permeability. In mice, HFD or fecal transplant from animals on HFD reduced expression of TJ-associated genes in the gut and mammary gland. Furthermore, infecting breast cancer cells with an HFD-derived microbiome increased proliferation, implicating tumor-associated bacteria in cancer signaling. In a double-blind placebo-controlled clinical trial of patients with breast cancer administered fish oil supplements before primary tumor resection, dietary intervention modulated the microbiota in tumors and normal breast tissue. This study demonstrates a link between the gut and breast that mediates the effect of diet on cancer. SIGNIFICANCE: This study demonstrates that diet shifts the microbiome in the gut and the breast tumor microenvironment to affect tumorigenesis, and oral dietary interventions can modulate the tumor microbiota in patients with breast cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/14/3890/F1.large.jpg.

Functions of Thrombospondin-1 in the Tumor Microenvironment

The identification of thrombospondin-1 as an angiogenesis inhibitor in 1990 prompted interest in its role in cancer biology and potential as a therapeutic target. Decreased thrombospondin-1 mRNA and protein expression are associated with progression in several cancers, while expression by nonmalignant cells in the tumor microenvironment and circulating levels in cancer patients can be elevated. THBS1 is not a tumor suppressor gene, but the regulation of its expression in malignant cells by oncogenes and tumor suppressor genes mediates some of their effects on carcinogenesis, tumor progression, and metastasis. In addition to regulating angiogenesis and perfusion of the tumor vasculature, thrombospondin-1 limits antitumor immunity by CD47-dependent regulation of innate and adaptive immune cells. Conversely, thrombospondin-1 is a component of particles released by immune cells that mediate tumor cell killing. Thrombospondin-1 differentially regulates the sensitivity of malignant and nonmalignant cells to genotoxic stress caused by radiotherapy and chemotherapy. The diverse activities of thrombospondin-1 to regulate autophagy, senescence, stem cell maintenance, extracellular vesicle function, and metabolic responses to ischemic and genotoxic stress are mediated by several cell surface receptors and by regulating the functions of several secreted proteins. This review highlights progress in understanding thrombospondin-1 functions in cancer and the challenges that remain in harnessing its therapeutic potential.

Platelet TSP-1 controls prostate cancer-induced osteoclast differentiation and bone marrow-derived cell mobilization through TGFβ-1

The development of distant metastasis is the leading cause of prostate cancer (CaP)-related death, with the skeleton being the primary site of metastasis. While the progression of primary tumors and the growth of bone metastatic tumors are well described, the mechanisms controlling pre-metastatic niche formation and homing of CaP to bone remain unclear. Through prior studies, we demonstrated that platelet secretion was required for ongoing tumor growth and pre-metastatic tumor-induced bone formation. Platelets stimulated bone marrow-derived cell (BMDC) mobilization to tumors supporting angiogenesis. We hypothesized that proteins released by the platelet α granules were responsible for inducing changes in the pre-metastatic bone niche. We found that the classically anti-angiogenic protein thrombospondin (TSP)-1 was significantly increased in the platelets of mice with RM1 murine CaP tumors. To determine the role of increased TSP-1, we implanted tumors in TSP-1 null animals and assessed changes in tumor growth and pre-metastatic niche. TSP-1 loss resulted in increased tumor size and enhanced angiogenesis by immunohistochemistry. Conversely, TSP-1 deletion reduced BMDC mobilization and enhanced osteoclast formation resulting in decreased tumor-induced bone formation as measured by microcomputed tomography. We hypothesized that changes in the pre-metastatic niche were due to the retention of TGF-β1 in the platelets of mice after TSP-1 deletion. To assess the importance of platelet-derived TGF-β1, we implanted RM1 CaP tumors in mice with platelet factor 4-driven deletion of TGF-β1 in platelets and megakaryocytes. Like TSP-1 deletion, loss of platelet TGF-β1 resulted in increased angiogenesis with a milder effect on tumor size and BMDC release. Within the bone microenvironment, platelet TGF-β1 deletion prevented tumor-induced bone formation due to increased osteoclastogenesis. Thus, we demonstrate that the TSP-1/TGF-β1 axis regulates pre-metastatic niche formation and tumor-induced bone turnover. Targeting the platelet release of TSP-1 or TGF-β1 represents a potential method to interfere with the process of CaP metastasis to bone.

Abstract PO-127: Single-cell liquid biopsy reveals circulating heterogeneity and converging subpopulations in relation to immunotherapy response in melanoma

Though treatment with immune checkpoint blockage (ICB) has greatly improved clinical outcomes, not all patients respond to this treatment. Being able to predict which patients are likely to respond would be a significant clinical advance. Thus there remains a need for predictive biomarkers to determine in advance those with the most potential to benefit from immune checkpoint blockade. To date, most biomarkers of response are identified in tumor tissue, whereas biomarkers that can be assessed from peripheral blood are more desirable, due to the ease of access and reproducibility of sampling. To identify biomarkers associated with ICB response from peripheral blood, we apply single cell RNA sequencing to 24 peripheral blood mononuclear cell (PBMC) samples, collected from 12 stage III and IV melanoma patients before and after treatment with anti-PD1 monotherapy. Among these 12 patients, 6 are responders and 6 are non-responders. After quality control, a total of 62,273 single cells remains for further analysis. To define the cell type landscape in an unbiased manner, unsupervised clustering is used. We identify 20 robust cell clusters, including two B cell clusters (B-cell_1; B-cell_2), three myeloid clusters (monocytes, myeloid-derived suppressor cells, and M2 macrophages), twelve clusters enriched for T/NK cells, two clusters of platelets, and Hematopoietic Stem and Progenitor Cells (HSPCs). Across all patients, cell composition differs between pre- and post-treatment samples. Strikingly, responders have significant greater proportions of B-cell_1 cells in their pre-treatment samples than non-responders. At gene level, our analysis identifies an individual overexpressed marker in B-cell_1, i.e. IGLC3, which is highly enriched in responders than non-responders before treatment. In summary, our analysis identifies specific cell type and gene within patients’ PBMC samples that can serve as predictive biomarkers for patient’s response to ICB.

Citation Format: Qianqian Song, Elizabeth Forbes, Lance D. Miller, Pierre L. Triozzi, Liang Liu, Wei Zhang, David R. Soto-Pantoja. Single-cell liquid biopsy reveals circulating heterogeneity and converging subpopulations in relation to immunotherapy response in melanoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-127.

TCR dependent metabolic programming regulates autocrine IL-4 production resulting in self-tuning of the CD8+ T cell activation setpoint

The ability of T cells to sense and respond to environmental cues by altering their functional capabilities is critical for a safe and optimally protective immune response. One of the important properties that contributes to this goal is the activation setpoint of the T cell. Here we report a new pathway through which CD8+ T cells can self-tune their activation threshold. We find that in the presence of a strong TCR engagement event, there is a shift in the metabolic programming of the cell where both glycolysis and oxidative phosphorylation are significantly increased. This diverges from the switch to a predominantly glycolytic profile that would be predicted following naïve T cell activation. This altered metabolic program results in the production of autocrine IL-4. Both metabolic pathways are required for this cytokine to be made. IL-4 signaling in the activated CD8+ T cell results in modulation of the sensitivity of the cell, establishing a higher activation setpoint that is maintained over time. Together these data demonstrate a novel mechanism for the regulation of IL-4 production in CD8+ T cells. Further, they reveal a new pathway for the self-tuning of peptide sensitivity. Finally, these studies uncover an unexpected role for oxidative phosphorylation in regulating differentiation in CD8+ T cells.

TCR Dependent Metabolic Programming Regulates Autocrine IL-4 Production Resulting in Self-Tuning of the CD8+ T Cell Activation Setpoint

The ability of T cells to sense and respond to environmental cues by altering their functional capabilities is critical for a safe and optimally protective immune response. One of the important properties that contributes to this goal is the activation set-point of the T cell. Here we report a new pathway through which TCR transgenic OT-I CD8⁺ T cells can self-tune their activation threshold. We find that in the presence of a strong TCR engagement event there is a shift in the metabolic programming of the cell where both glycolysis and oxidative phosphorylation are significantly increased. This diverges from the switch to a predominantly glycolytic profile that would be predicted following naïve T cell activation. Our data suggest this altered metabolic program results in the production of autocrine IL-4. Both metabolic pathways are required for this cytokine to be made. IL-4 signaling in the activated OT-I CD8⁺ T cell results in modulation of the sensitivity of the cell, establishing a higher activation setpoint that is maintained over time. Together these data demonstrate a novel mechanism for the regulation of IL-4 production in CD8⁺ T cells. Further, they reveal a new pathway for the self-tuning of peptide sensitivity. Finally, these studies uncover an unexpected role for oxidative phosphorylation in regulating differentiation in these cells.

Endoplasmic Reticulum Stress Pathway, the Unfolded Protein Response, Modulates Immune Function in the Tumor Microenvironment to Impact Tumor Progression and Therapeutic Response

Despite advances in cancer therapy, several persistent issues remain. These include cancer recurrence, effective targeting of aggressive or therapy-resistant cancers, and selective treatments for transformed cells. This review evaluates the current findings and highlights the potential of targeting the unfolded protein response to treat cancer. The unfolded protein response, an evolutionarily conserved pathway in all eukaryotes, is initiated in response to misfolded proteins accumulating within the lumen of the endoplasmic reticulum. This pathway is initially cytoprotective, allowing cells to survive stressful events; however, prolonged activation of the unfolded protein response also activates apoptotic responses. This balance is key in successful mammalian immune response and inducing cell death in malignant cells. We discuss how the unfolded protein response affects cancer progression, survival, and immune response to cancer cells. The literature shows that targeting the unfolded protein response as a monotherapy or in combination with chemotherapy or immunotherapies increases the efficacy of these drugs; however, systemic unfolded protein response targeting may yield deleterious effects on immune cell function and should be taken into consideration. The material in this review shows the promise of both approaches, each of which merits further research.

Metabolomic Analysis Reveals Unique Biochemical Signatures Associated with Protection from Radiation Induced Lung Injury by Lack of cd47 Receptor Gene Expression

The goal of this study was to interrogate biochemical profiles manifested in mouse lung tissue originating from wild type (WT) and cd47 null mice with the aim of revealing the in vivo role of CD47 in the metabolic response to ionizing radiation, especially changes related to the known association of CD47 deficiency with increased tissue viability and survival. For this objective, we performed global metabolomic analysis in mouse lung tissue collected from (C57Bl/6 background) WT and cd47 null mice with and without exposure to 7.6 Gy whole body radiation. Principal component analysis and hierarchical clustering revealed a consistent separation between genotypes following radiation exposure. Random forest analysis also revealed a unique biochemical signature in WT and cd47 null mice following treatment. Our data show that cd47 null irradiated lung tissue activates a unique set of metabolic pathways that facilitate the handling of reactive oxygen species, lipid metabolism, nucleotide metabolism and nutrient metabolites which may be regulated by microbial processing. Given that cd47 has pleiotropic effects on responses to ionizing radiation, we not only propose this receptor as a therapeutic target but postulate that the biomarkers regulated in this study associated with radioprotection are potential mitigators of radiation-associated pathologies, including the onset of pulmonary disease.

Identification of Schlafen-11 as a Target of CD47 Signaling That Regulates Sensitivity to Ionizing Radiation and Topoisomerase Inhibitors

Knockdown or gene disruption of the ubiquitously expressed cell surface receptor CD47 protects non-malignant cells from genotoxic stress caused by ionizing radiation or cytotoxic chemotherapy but sensitizes tumors in an immune competent host to genotoxic stress. The selective radioprotection of non-malignant cells is mediated in part by enhanced autophagy and protection of anabolic metabolism pathways, but differential H2AX activation kinetics suggested that the DNA damage response is also CD47-dependent. A high throughput screen of drug sensitivities indicated that CD47 expression selectively sensitizes Jurkat T cells to inhibitors of topoisomerases, which are known targets of Schlafen-11 (SLFN11). CD47 mRNA expression positively correlated with schlafen-11 mRNA expression in a subset of human cancers but not the corresponding non-malignant tissues. CD47 mRNA expression was also negatively correlated with SLFN11 promoter methylation in some cancers. CD47 knockdown, gene disruption, or treatment with a CD47 function-blocking antibody decreased SLFN11 expression in Jurkat cells. The CD47 signaling ligand thrombospondin-1 also suppressed schlafen-11 expression in wild type but not CD47-deficient T cells. Re-expressing SLFN11 restored radiosensitivity to a CD47-deficient Jurkat cells. Disruption of CD47 in PC3 prostate cancer cells similarly decreased schlafen-11 expression and was associated with a CD47-dependent decrease in acetylation and increased methylation of histone H3 in the SLFN11 promoter region. The ability of histone deacetylase or topoisomerase inhibitors to induce SLFN11 expression in PC3 cells was lost when CD47 was targeted in these cells. Disrupting CD47 in PC3 cells increased resistance to etoposide but, in contrast to Jurkat cells, not to ionizing radiation. These data identify CD47 as a context-dependent regulator of SLFN11 expression and suggest an approach to improve radiotherapy and chemotherapy responses by combining with CD47-targeted therapeutics.

Abstract P2007: Muscadine Grape Extract Prevents Cardiac Cell Cytotoxicity Due to Oxidative Stress by Enhancing Mitochondrial Function

Mitochondrial health is critical for the physiological function of tissues and responses to stress. During oxidative stress, failure to maintain mitochondrial respiration can ultimately lead to cell death and thus cardiac dysfunction. Agents that preserve mitochondrial integrity and maintain or increase mitochondrial respiratory capacity may prevent cardiac tissue damage due to oxidative stress. Muscadine grapes are rich in polyphenols, which are natural antioxidants, and are known to reduce cardiac damage. We treated cardiac cells with a proprietary muscadine grape extract (MGE), to prevent cardiac myoblast death due to reactive oxygen species (ROS) in the presence of the redox cycling agent 2,3 dimethoxynaphthoquinone (DMNQ), which generates both superoxide and hydrogen peroxide intracellularly, thus mimicking pathologies of elevated ROS. DMNQ increased cardiac cell cytotoxicity, as measured by LDH release, which was prevented by doses of MGE equivalent to 60 μg/mL of total phenolics (1.3 ± 0.023 DMNQ vs. 0.90 ± 0.030, n=3, *p<0.01). Moreover, cell respirometry measurements indicated that, while DMNQ reduced the oxygen consumption rate (OCR) by 50% (*p<0.05, n=3), treatment with MGE prevented this reduction, suggesting that the protective effect may be mediated by preservation of mitochondrial function. Furthermore, MGE treatment prevented the decrease in ATP-linked respiration (18.8 ±. 2.6 DMNQ vs. 34.0±.4.7 DMNQ + MGE, n=3, *p<0.01) and maximal respiratory capacity (31.6 ± 8.2 DMNQ vs. 48.91 ± 6.54 DMNQ + MGE, n=3, *p<0.01) observed with DMNQ treatment. Furthermore, the basal extracellular acidification rate (ECAR) was increased 2-fold with MGE pretreatment when compared to DMNQ alone (13.6 ± 2.3 DMNQ + MGE vs. 6.8 ±.0.88 DMNQ, n=3, *p<0.01), suggesting that MGE treatment may also increase glycolysis as a response to stress. These data suggest that MGE enhances mitochondrial function and cellular bioenergetics in cardiomyoblast cells during stress and thus may be used as a strategy to prevent tissue damage from oxidative stress observed in acute and chronic cardiac pathologies.

Targeting the Tumor Microenvironment in Radiation Oncology: Proceedings from the 2018 ASTRO-AACR Research Workshop

The development of cancers and their response to radiation are intricately linked to the tumor microenvironment (TME) in which they reside. Tumor cells, immune cells, and stromal cells interact with each other and are influenced by the microbiome and metabolic state of the host, and these interactions are constantly evolving. Stromal cells not only secrete extracellular matrix and participate in wound contraction, but they also secrete fibroblast growth factors (FGF), which mediate macrophage differentiation. Tumor-associated macrophages migrate to hypoxic areas and secrete vascular endothelial growth factor (VEGF) to promote angiogenesis. The microbiome and its byproducts alter the metabolic milieu by shifting the balance between glucose utilization and fatty acid oxidation, and these changes subsequently influence the immune response in the TME. Not only does radiation exert cell-autonomous effects on tumor cells, but it influences both the tumor-promoting and tumor-suppressive components in the TME. To gain a deeper understanding of how the TME influences the response to radiation, the American Society for Radiation Oncology and the American Association of Cancer Research organized a scientific workshop on July 26-27, 2018, to discuss how the microbiome, the immune response, the metabolome, and the stroma all shift the balance between radiosensitivity and radioresistance. The proceedings from this workshop are discussed here and highlight recent discoveries in the field, as well as the most important areas for future research.

Doxorubicin-Induced Myocardial Fibrosis Involves the Neurokinin-1 Receptor and Direct Effects on Cardiac Fibroblasts

BACKGROUND

Cancer patients receiving anthracycline-based chemotherapy (Anth-bC) may experience early cardiac fibrosis, which could be an important contributing mechanism to the development of impaired left ventricular (LV) function. Substance P, a neuropeptide that predominantly acts via the neurokinin 1 receptor (NK-1R), contributes to adverse myocardial remodelling and fibrosis in other cardiomyopathies. We sought to determine if NK-1R blockade is effective against doxorubicin (Dox - a frequently used Anth-bC)-induced cardiac fibrosis and cardiomyocyte apoptosis. In addition, we explored the direct effects of Dox on cardiac fibroblasts.

METHODS

Male Sprague-Dawley rats were randomised to receive saline, six cycles of Dox (1.5mg Dox/kg/cycle) or Dox with an NK-1R antagonist (L732138, 5mg/kg/daily through Dox treatment). At 8 weeks after the initial dose of Dox, LV function and histopathological myocardial fibrosis and cell apoptosis were assessed. Collagen secretion was measured in vitro to test direct Dox activation of cardiac fibroblasts.

RESULTS

Rats undergoing Dox treatment (9mg/kg cumulative dose) developed cardiac fibrosis and cardiomyocyte apoptosis. NK-1R blockade partially mitigated cardiac fibrosis while completely preventing cardiomyocyte apoptosis. This resulted in improved diastolic function. Furthermore, we found that Dox had direct effects on cardiac fibroblasts to cause increased collagen production and enhanced cell survival.

CONCLUSIONS

This study demonstrates that cardiac fibrosis induced by Anth-bC can be reduced by NK-1R blockade. The residual fibrotic response is likely due to direct Dox effects on cardiac fibroblasts to produce collagen.

Combination of anthracyclines and anti-CD47 therapy inhibit invasive breast cancer growth while preventing cardiac toxicity by regulation of autophagy

BACKGROUND

A perennial challenge in systemic cytotoxic cancer therapy is to eradicate primary tumors and metastatic disease while sparing normal tissue from off-target effects of chemotherapy. Anthracyclines such as doxorubicin are effective chemotherapeutic agents for which dosing is limited by development of cardiotoxicity. Our published evidence shows that targeting CD47 enhances radiation-induced growth delay of tumors while remarkably protecting soft tissues. The protection of cell viability observed with CD47 is mediated autonomously by activation of protective autophagy. However, whether CD47 protects cancer cells from cytotoxic chemotherapy is unknown.

METHODS

We tested the effect of CD47 blockade on cancer cell survival using a 2-dimensional high-throughput cell proliferation assay in 4T1 breast cancer cell lines. To evaluate blockade of CD47 in combination with chemotherapy in vivo, we employed the 4T1 breast cancer model and examined tumor and cardiac tissue viability as well as autophagic flux.

RESULTS

Our high-throughput screen revealed that blockade of CD47 does not interfere with the cytotoxic activity of anthracyclines against 4T1 breast cancer cells. Targeting CD47 enhanced the effect of doxorubicin chemotherapy in vivo by reducing tumor growth and metastatic spread by activation of an anti-tumor innate immune response. Moreover, systemic suppression of CD47 protected cardiac tissue viability and function in mice treated with doxorubicin.

CONCLUSIONS

Our experiments indicate that the protective effects observed with CD47 blockade are mediated through upregulation of autophagic flux. However, the absence of CD47 in did not elicit a protective effect in cancer cells, but it enhanced macrophage-mediated cancer cell cytolysis. Therefore, the differential responses observed with CD47 blockade are due to autonomous activation of protective autophagy in normal tissue and enhancement immune cytotoxicity against cancer cells.

Abstract 3528: Anti-CD47 immunotherapy regulates T cell metabolism and hypoxia in the tumor microenvironment

Dysfunction of infiltrating CD8+ effector T cells can be induced by hypoxia and aberrant tumor metabolite uptake in the microenvironment causing an “exhausted” T cell phenotype that limits anti-tumor immunosurveilance. Hence- therapeutic strategies aimed at improving T cell bioenergetics have the potential to reinvigorate T cell responses to reduce tumor burden. CD47 is a widely expressed receptor that controls phagocytic activity by engaging its counter receptor, SIRPα, in macrophages. Also autonomously or by binding to its ligand Thrombospondin-1 CD47 activation can control cell fate under stress. Our prior work shows that targeting CD47 on CD8+ T cells enhanced cytotoxicity against cancer cells. Moreover, depletion of CD8+ T cells in murine models reversed the anti-tumor effect of anti-CD47 therapy. Our new data shows that targeting CD47 reduced the growth of B16 melanoma tumors by approximately 50% (1607 ± 213.7, saline vs. 815.1 ± 67.8, CD47 (-) *p&lt;0.02 n=5-6). Further examination of tumors by live photoacoustic imaging showed that tumors of animals treated with anti-CD47 had reduction in oxygen tension and reduced vascularity when compared to control. This suggests that the reduction in tumor hypoxia by CD47 may shift metabolic competition in the microenvironment to increase metabolite availability allowing optimal activation of cytotoxic T cells. Cell respirometry measurements using an Agilent Seahorse bioanalyzer showed increased levels of mitochondrial function and glycolytic flux in CD47 null T cells when compared to WT. Moreover, these cells showed increased mitochondrial density and increased levels of the mitochondrial biogenesis regulator, PGC1-a. Treatment with CD47 antibody enhanced Pmel-1 CD8+ T cell effector function by reducing B16 melanoma target cell viability by over 60%. Anti-CD47 treatment of these T cells also resulted in upregulation of cell bioenergetics, suggesting that targeting CD47 may impact T cell metabolism to enhance cytotoxic activity against cancer cells. Therefore, our studies show a new role of CD47 immunotherapy regulating immunometabolism of T cells to enhance effector function which may lead to improvement of clinical outcomes in melanoma patients.

Citation Format: Yismelin R. Feliz-Mosquea, Elizabeth Stirling, Katherine L. Cook, Adam Wilson, Manish Bharadwaj, Anthony J. Molina, Liliya Yamaleyeva, Pierre L. Triozzi, David R. Soto-Pantoja. Anti-CD47 immunotherapy regulates T cell metabolism and hypoxia in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3528.

Abstract 449: Targeting PKR-like endoplasmic reticulum kinase modulates metabolism to promote T-cell effector function and PD1 immunotherapy responsiveness

The development of immunotherapy is a major recent advance in clinical oncology. However the majority of patients do not respond and those who do, experience resistance and relapse. Therefore, understanding the molecular mechanisms of immune checkpoint inhibitor resistance is critical to develop combinatorial drug strategies to potentiate therapeutic responsiveness to reduce mortality. Highly secretory cells, such as T-cells, have a larger endoplasmic reticulum (ER) to handle the increased protein translation capacity required by the cell. Therefore, T-cells may be highly sensitive to ER stress. The high nutrient needs of the tumor deplete resources in the microenvironment subjugating infiltrating T-cells to reduced nutrient availability resulting in stress. Our data indicate that co-culturing melanoma cells with T-cells increase T-cell specific unfolded protein response (UPR) signaling. Stimulating ER stress decreased cytolytic T-cell function in TALL-104 T-cells, enabling Mun2b melanoma survival. Knockdown of PERK restored T-cell killing capacity in ER stress induced cells. In an ex-vivo model of antigen-specific mediated T-cell death, Pmel-1 T-cells stimulated with gp100 displayed increased B16 melanoma killing when treated with GSK2606414 (a small molecule PERK inhibitor). PERK inhibition also elevated glycolysis proteins and mitochondrial bioenergetics in T-cells, suggesting PERK inhibition increases T-cell metabolism. As proof-of-concept, we determined the effect of PERK inhibition in a syngeneic B16 melanoma model. Male C57/Bl6 mice were inoculated with B16 melanoma cells. At 5 days post injection, mice were treated with a control IgG, antisense morpholino targeting PERK, PD1 antibody, or a combination of PERK morpholino and PD1 antibody. PERK morpholino treatment alone was sufficient to reduce tumor volume by 46.5%. PD1 antibody therapy alone reduced tumor volume by 47.4%. The combination of PD1 antibody and PERK targeting therapy significantly reduced B16 melanoma tumor volume by 64.5% demonstrating that targeting PERK in vivo enhanced immunocheckpoint therapy efficacy. Treated B16 tumors were homogenized and infiltrating T-cells isolated by flow cytometry. Gated CD3+ infiltrating leukocytes were then counted for CD8 and PD1 expression. Tumor infiltrating CD8+ T-cells doubled with PERK inhibition alone, giving further proof indicating that PERK may be a novel immune checkpoint target. Small molecule PERK inhibitors were previously shown to cause β-islet damage and insulin resistance; therefore we tested the effect of our PERK morpholino on glucose tolerance in the B16 melanoma model. PERK morpholino treatment had no overall impact on glucose tolerance and therefore may be a novel therapeutic to induce T-cell metabolism and potentiate immune checkpoint therapy efficacy with reduced off-target toxicities.

Citation Format: David R. Soto-Pantoja, Yismeilin R. Feliz-Mosquea, Kenysha YJ Clear, Adam S. Wilson, Katherine L. Cook. Targeting PKR-like endoplasmic reticulum kinase modulates metabolism to promote T-cell effector function and PD1 immunotherapy responsiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 449.

Mitochondrial autophagosomes as a mechanism of drug resistance in breast carcinoma

We have previously described the process by which mitochondria donate their membranes for the formation of autophagosomes, and in this study we show that the same process could be involved in drug sequestration and exocytosis resulting in multidrug-resistant cancerous cells. We examine the implications of mitochondrial vesicle formation of mitoautophagosomes (MAPS) in response to the cytotoxic drug MKT-077, which targets mortalin, in a drug-resistant breast carcinoma cell line overexpressing P-glycoprotein (P-gp). The breast cancer cell line MCF-7Adr is derived from MCF-7, but differs from its ancestral line in tolerance of MKT-077-induced mitochondrial toxicity. Our ultrastructural observations suggest that autophagy in the MCF-7Adr cells entails regional sequestration of MKT077 in multilamellar LC3-labeled MAPS, which then separate from their mitochondria, and fuse with or engulf each other. MAPS appeared to be migrating through the cytoplasm and fusing with the plasma membrane, thus carrying out exocytotic secretion. This mechanism, which seems ineffective in the ancestral cell line, provides a resistance mechanism for MKT-077 by enhancing the efflux process of the cells. After 8 hr of MKT-077 exposure, a fraction of the resistant cells appeared viable and contained larger number of smaller sized mitochondria. Mitoautophagosomes, therefore, provide a potentially novel model for multidrug resistance in cancerous cells and may contribute to the P-gp efflux process.

"UPRegulation" of CD47 by the endoplasmic reticulum stress pathway controls anti-tumor immune responses

We recently demonstrated that targeting the unfolded protein response (UPR) protein GRP78 down-regulates CD47 expression, resulting in increased tumor macrophage infiltration and inhibited resistance to anti-estrogen therapy. We now show new data indicating that anti-estrogen therapy regulates CD47 expression and implicates its ligand, thrombospondin-1, in regulation of tumor macrophage infiltration. Moreover, GRP78 and CD47 co-expression is associated with poor prognosis in breast cancer patients, suggesting the existence of crosstalk between UPR and immunity that regulates therapeutic responses in breast cancer.

Endoplasmic Reticulum Stress Protein GRP78 Modulates Lipid Metabolism to Control Drug Sensitivity and Antitumor Immunity in Breast Cancer

The unfolded protein response is an endoplasmic reticulum stress pathway mediated by the protein chaperone glucose regulated-protein 78 (GRP78). Metabolic analysis of breast cancer cells shows that GRP78 silencing increases the intracellular concentrations of essential polyunsaturated fats, including linoleic acid. Accumulation of fatty acids is due to an inhibition of mitochondrial fatty acid transport, resulting in a reduction of fatty acid oxidation. These data suggest a novel role of GRP78-mediating cellular metabolism. We validated the effect of GRP78-regulated metabolite changes by treating tumor-bearing mice with tamoxifen and/or linoleic acid. Tumors treated with linoleic acid plus tamoxifen exhibited reduced tumor area and tumor weight. Inhibition of either GRP78 or linoleic acid treatment increased MCP-1 serum levels, decreased CD47 expression, and increased macrophage infiltration, suggesting a novel role for GRP78 in regulating innate immunity. GRP78 control of fatty acid oxidation may represent a new homeostatic function for GRP78. Cancer Res; 76(19); 5657-70. ©2016 AACR.

Abstract 5661: Targeting CD47 expression on macrophages regulates immunometabolism enhancing tumoricidal activity against cancer cells

Macrophage mediated elimination of cancer cells is critical for control of tumor growth. Cancer cells evade immune recognition by expressing receptors that send inhibitory signals to prevent macrophage mediated cytotoxicity. Clinical studies show that overexpression of the cell surface receptor CD47 is a poor prognostic factor in cancer, allowing tumors to bypass immunosurveillance and activation pro-growth pathways. Prior studies have described that CD47 cell surface expression on cancer cells inhibits phagocytic activity through engagement of its counter receptor SIRPα on macrophages. However, the role of CD47 expression on macrophage function is not known. Here, we show that CD47 is expressed on primary mouse macrophages, RAW 264.7 and the U937 cell lines. Moreover, knockdown of CD47 on macrophages enhanced the tumoricidal capacity against melanoma and breast cancer cells as measured by cell impedance and LDH release. Blockade of CD47 enhanced the macrophage-mediated cytotoxicity against B16 melanoma and 4T1 cells when compared to untreated effector/target pairs. Blockade of CD47 on differentiated U937 human monocytes also enhanced tumoricidal activity against the triple-negative breast cancer cell line MDA-MB-231 by over 50% when compared to untreated co-cultures. This indicates that expression of CD47 on macrophages may play a role in polarization and macrophage tumoricidal capacity against cancer cells beyond the known interactions with SIRPα. Our previous studies show that blockade of CD47 preserves T cell viability under stress by increasing glycolytic flux. Activation of M1 cytotoxic macrophages requires a shift in metabolism from oxidative phosphorylation to glycolysis. Our data shows that blockade of CD47 on RAW 264.7 macrophages increases glycolytic flux when compared to untreated controls as measured by extracellular acidification rate (ECAR) using a Seahorse© XF analyzer. The increase in glycolysis was associated with a significant elevation of glucose uptake by macrophages treated with anti-sense CD47 morpholino, indicating that targeting this receptor regulates glucose metabolism to improve macrophage tumoricidal activity. Interestingly, blockade of CD47 in the 4T1 breast cancer cell line reduced ECAR and reduced glucose uptake indicating that targeting CD47 reverses Warburg metabolism in cancer cells. Overall, these results show a new role of CD47 expression that extends beyond suppressing macrophage mediated killing through engagement of SIRPα. Therefore, anti-CD47 immunotherapy may regulate immunometabolism to improve clinical outcomes of cancer patients.

Citation Format: Ashley A. Smith, Adam S. Wilson, David R. Soto-Pantoja. Targeting CD47 expression on macrophages regulates immunometabolism enhancing tumoricidal activity against cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5661. doi:10.1158/1538-7445.AM2017-5661

Abstract LB-213: Thrombospondin-1 regulates intestinal microbiota and bile acid metabolism in a murine model of colorectal cancer

Colon cancer is major public health concern with over 50,000 deaths annually in the US. Environmental and genetic factors influence colon cancer progression, and expression of thrombospondin-1 (TSP1) inversely correlates with colon cancer aggressiveness. TSP1 is a matricellular protein that regulates vascular physiology and tissue responses to stress. We previously demonstrated that deleting the TSP1 (Thbs1) gene in ApcMin/+ mice results in systemic metabolic changes as assessed in liver tissue, increased tumorigenesis, and lower survival of mice fed a low fat diet. We now show that TSP1 induces changes in intestinal microbiota that may cause shifts in secondary bile acid metabolism that influence colon carcinogenesis. Mice were maintained and bred at least two generations on a low fat western diet to equalize dietary effects on their epigenetic context and microbiomes. Mice were pair-fed a low fat or a 21% high-fat western diet beginning at weaning. Mouse fecal matter was collected 8 weeks after dietary exposures and subjected to 16S sequencing for bacterial population identification. Lactobacillaceae, Lachnopiraceae, Ruminococcacea, Verrucomicrobiaceae families were present in all groups. The family Verrucomicrobiaceae and its genus Akkemensi represented a high proportion of the bacterial population. The relative levels of Akkemensia were elevated in low fat fed mice in mice ApcMin/+ and Thbs1−/−:ApcMin/+ when compared to WT counterparts. Interestingly Akkenmensia abundance was reduced in ApcMin/+ mice fed a high-fat diet when compared to other groups. The relative population of the genus Ruminococcus was reduced in Thbs1−/− mice as well as in Thbs1−/−:ApcMin/+ mice fed low and high fat diets, suggesting that these population shifts are driven by genotype. Because intestinal bacteria can alter metabolism, particularly of bile acids, we collected large intestine tissue from mice and subjected it to metabolomics analysis. Our data showed primary and secondary bile metabolism were regulated by the absence of TSP1 in mice fed a high fat diet when compared to WT. High 6-beta-hydroxylithocholate levels were associated with onset of carcinogenesis since it was elevated in ApcMin/+ and Thbs1−/−:ApcMin/+ mice but not in WT or Thbs1−/−. 6-oxolithocholate, hyocholate and hyodeoxycholate were elevated only in ApcMin/+ mice fed a high fat diet but not in Thbs1−/−:ApcMin/+, suggesting that these metabolites contribute to the shift in survival and carcinogenesis observed between low and high fat diets. On the other hand levels of taurohyodeoxycholic acid, 3-dehydrocholate, 7-ketodeoxycholate were elevated in Thbs1−/−:ApcMin/+ and Thbs1−/− mice but not in ApcMin/+, indicating that changes in these metabolites are driven by the loss of Thbs1 and may pre-dispose mice to increased carcinogenesis when fed a high fat diet. Taken together our data shows an unexpected role of TSP1 in regulation of microbiota and bile acid metabolism and reveals potential targets for prevention and treatment of colorectal cancer.

Citation Format: David R. Soto-Pantoja, John M. Sipes, Brian Westwood, Nicole Morris, Nancy J. Emenaker, David D. Roberts. Thrombospondin-1 regulates intestinal microbiota and bile acid metabolism in a murine model of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-213. doi:10.1158/1538-7445.AM2017-LB-213

Abstract P2-04-06: Targeting of the unfolded protein response signaling arms differentially regulates macrophage proliferation, plasticity, and breast cancer cell clearance

The unfolded protein response (UPR) is an endoplasmic reticulum stress pathway controlled by the protein chaperone, glucose-regulated protein 78 (GRP78), to mediate inositol-requiring enzyme 1 (IRE1), PKR-like endoplasmic reticulum kinase (PERK), and activating transcription factor-6 (ATF6) signaling. UPR signaling has been shown to be upregulated in many different types of cancers, including breast cancer and melanoma, and is associated with the development of therapeutic resistance. These data suggest the importance of targeting UPR signaling as a possible cancer therapy. We have previously shown GRP78 to be upregulated in human breast tumor samples and leads to endocrine targeted therapy resistance. We recently showed inhibiting GRP78 in human orthotopic xenografts potentiates tamoxifen therapy effectiveness in sensitive tumors and restores endocrine therapy responsiveness in resistant tumors. In these GRP78-inhibited tumors there was a significant increase of CD68 positive macrophage population, suggesting that targeting UPR signaling has critical effects on the tumor microenvironment. Therefore, consideration of each UPR signaling component and how it effects the different cellular compartments of the tumor microenvironment need to be investigated to optimally induce both an antitumor immune effect and inhibit tumor epithelial cell growth. We now show deletion of GRP78, IRE1, and PERK through RNAi differentially regulates macrophage polarization. Specifically, PERK inhibition enhances macrophage proliferation and macrophage-mediated phagocytosis of 4T1 breast cancer cells, but not GRP78 or IRE1 inhibition. Targeting UPR signaling in the breast cancer cells also differentially affected macrophage cytolytic capacity; Specific breast cancer cell inhibition of IRE1 or GRP78 enhanced macrophage-mediated phagocytosis. Conditioned media from control or GRP78 silenced ZR-75-1 breast cancer cells indicated reciprocal regulation of CD206 and CD80; suggesting regulation of macrophage plasticity by GRP78-controlled secreted factors. GRP78 targeting in mice resulting in a cytokine shift and increased tumoral CD80+/CD68+ cells, suggesting that GRP78 inhibition favors a M1-like macrophage profile. Inhibition of UPR components in both macrophage and breast cancer cells, similar to what would be observed in systemic cancer therapies, indicated that either PERK or GRP78 inhibition enhances macrophage cytolytic clearance of breast cancer cells. Taken together, these data suggest that targeting GRP78 or PERK promotes an anti-tumor immune response by either directly promoting macrophage cytolytic activity (PERK targeting) or indirectly by shifting tumoral cytokine secretion (GRP78 targeting).

Citation Format: Cook KL, Wilson A, Westwood B, Soto-Pantoja DR. Targeting of the unfolded protein response signaling arms differentially regulates macrophage proliferation, plasticity, and breast cancer cell clearance [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-06.

Abstract 1352: High-throughput matrix screening reveals synergistic chemotherapeutic combinations with blockade of CD47 to enhance cytotoxicity in breast cancer

CD47 is a widely expressed cell surface receptor that serves as a counter-receptor for SIRPα in recognition of self by the innate immune system. On the other hand CD47 also serves as a signaling receptor for the matricellular protein thrombospondin-1 (TSP-1), regulating cell growth and survival. Clinical studies consistently show that increased expression of CD47 is an independent poor prognosis factor in several types of cancer, including breast cancer. Moreover elevated expression of CD47 is associated with development of resistance to chemotherapy by inhibiting cell death pathways. Therefore, agents targeting CD47 are attractive to overcome therapeutic resistance in breast cancer. Using a high-throughput assay in a 1536-well microplate format we screened a comprehensive set of approved and late stage development oncology drugs in combination with an anti-CD47 morpholino to find combinatorial strategies that are more cytotoxic against breast cancer cells. Potency and efficacy measurements during the primary screen identified compounds that synergized with anti-CD47 to augment their cytotoxicity effect. One of the compound groups that demonstrated increased synergism with CD47 were the anthracycline family of drugs. We further validated these results in a syngeneic model of breast cancer and demonstrated that blockade of CD47 in combination with doxorubicin improves chemotherapeutic response when compared to mice administered doxorubicin alone. Furthermore the anti-tumor response with anti-CD47 combination is associated with a reduction in glycolytic flux and a selective up regulation of mitophagy. Overall this indicates that blockade of CD47 in the clinic may synergize with chemotherapeutic strategies to improve patient curative responses.

Citation Format: David D. Roberts, Ashley Smith, John M. Sipes, Adam Wilson, Lesley Mathews-Griner, Rajarshi Guha, Craig J. Thomas, Marc Ferrer, David R. Soto-Pantoja. High-throughput matrix screening reveals synergistic chemotherapeutic combinations with blockade of CD47 to enhance cytotoxicity in breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1352.

Hydroxychloroquine inhibits autophagy to potentiate antiestrogen responsiveness in ER+ breast cancer

PURPOSE

Estrogen receptor-α (ERα)-targeted therapies including tamoxifen (TAM) or Faslodex (ICI) are used to treat ER(+) breast cancers. Up to 50% of tumors will acquire resistance to these interventions. Autophagy has been implicated as a major driver of antiestrogen resistance. We have explored the ability of hydroxychloroquine (HCQ), which inhibits autophagy, to affect antiestrogen responsiveness.

EXPERIMENTAL DESIGN

TAM-resistant MCF7-RR and ICI-resistant/TAM cross-resistant LCC9 ER(+) breast cancer cells were injected into mammary fat pads of female athymic mice and treated with TAM and/or ICI in combination with oral low-dose HCQ.

RESULTS

We show that HCQ can increase antiestrogen responsiveness in MCF7-RR and LCC9 cells and tumors, likely through the inhibition of autophagy. However, the combination of ICI+HCQ was less effective than HCQ alone in vivo, unlike the TAM+HCQ combination. Antiestrogen treatment stimulated angiogenesis in tumors but did not prevent HCQ effectiveness. The lower efficacy of ICI+HCQ was associated with ICI effects on cell-mediated immunity within the tumor microenvironment. The mouse chemokine KC (CXCL1) and IFNγ were differentially regulated by both TAM and ICI treatments, suggesting a possible effect on macrophage development/activity. Consistent with these observations, TAM+HCQ treatment increased tumor CD68(+) cells infiltration, whereas ICI and ICI+HCQ reduced peripheral tumor macrophage content. Moreover, macrophage elimination of breast cancer target cells in vitro was reduced following exposure to ICI.

CONCLUSION

HCQ restores antiestrogen sensitivity to resistant tumors. Moreover, the beneficial combination of TAM+HCQ suggests a positive outcome for ongoing neoadjuvant clinical trials using this combination for the treatment of ER(+) ductal carcinoma in situ lesions.

CD47 Receptor Globally Regulates Metabolic Pathways That Control Resistance to Ionizing Radiation

Modulating tissue responses to stress is an important therapeutic objective. Oxidative and genotoxic stresses caused by ionizing radiation are detrimental to healthy tissues but beneficial for treatment of cancer. CD47 is a signaling receptor for thrombospondin-1 and an attractive therapeutic target because blocking CD47 signaling protects normal tissues while sensitizing tumors to ionizing radiation. Here we utilized a metabolomic approach to define molecular mechanisms underlying this radioprotective activity. CD47-deficient cells and cd47-null mice exhibited global advantages in preserving metabolite levels after irradiation. Metabolic pathways required for controlling oxidative stress and mediating DNA repair were enhanced. Some cellular energetics pathways differed basally in CD47-deficient cells, and the global declines in the glycolytic and tricarboxylic acid cycle metabolites characteristic of normal cell and tissue responses to irradiation were prevented in the absence of CD47. Thus, CD47 mediates signaling from the extracellular matrix that coordinately regulates basal metabolism and cytoprotective responses to radiation injury.

Abstract 1202: Thrombospondin-1 regulates energy metabolism to increase carcinogenesis in an in vivo model of colorectal cancer

Over 140,000 people will be diagnosed with colorectal cancer in the United States this year, indicating an urgent need to develop therapeutic and dietary strategies to prevent and improve outcomes of this disease. The goal of this study was to determine the biochemical profiles of large intestine originating from wild type, thrombospondin-1 (thbs1) null, ApcMin/+ and ApcMin/+thbs1-/-mice, with the aim of identifying metabolic changes associated with variation in dietary lipids in the presence/absence of thrombospondin-1 (TSP1) as impacting tumorigenesis and tumor burden in ApcMin/+ animals. Our data indicates that expression of TSP1 in the APC-min mouse prevents the development of adenomas in the large intestine in mice fed low fat or high fat diets. On the other hand, lack of TSP1 increases tumor multiplicity in these mice, and up-regulates Ki67 in intestinal tissue. In the current study, general indications of greater uptake and utilization of glucose through glycolysis, as suggested by accumulation of glucose and lactate, in large intestine tissue were noted in the thbs1 null, ApcMin/+, and Apcmin/+thbs1-/- groups upon feeding of a high-fat diet. However, in high fat diet-fed Apcmin/+thbs1-/- mice, reductions in the pentose phosphate pathway (PPP) intermediates 6-phosphogluconate and the isobaric compounds ribulose/xylulose 5-phosphate, along with elevations in ribulose and ribose were also observed. These findings may be indicative of increased glucose utilization through the PPP in Apcmin/+thbs1-/- mice fed a high-fat diet, presumably to support nucleotide synthesis and anabolic processes related to tumor growth and proliferation in the large intestine. Moreover, while elevations in several amino sugars (UDP-glucose, UDP-galactose, UDP-N-acetylglucosamine, and UDP-N-acetylgalactosamine) were noted in WT mice fed a high-fat diet, a marked reduction in these metabolites was observed in Apcmin/+thbs1-/- mice fed a high-fat diet. As amino sugars are synthesized from glucose and play an important role in extracellular matrix structure and cellular communication, changes in these metabolites may be related to alterations in rates of synthesis and/or tumor growth and proliferation. While increased glucose utilization through glycolysis was apparent in large intestine tissue from all of the groups genetically predisposed to development of cancerous lesions and fed a high-fat diet, changes in PPP activity and amino sugars were limited to the Apcmin/+thbs1-/- group. Therefore, these findings may be indicative of metabolic changes that are unique to Apcmin/+thbs1-/- mice, which are particularly susceptible to tumor formation. Therefore these data suggest that TSP1 regulates progression of colon carcinogenesis and define metabolic targets of TSP1 that may contribute to prevention of colorectal cancer.

Citation Format: David R. Soto-Pantoja, John M. Sipes, Nicole Morris, Nancy J. Emmenaker, David D. Roberts. Thrombospondin-1 regulates energy metabolism to increase carcinogenesis in an in vivo model of colorectal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1202. doi:10.1158/1538-7445.AM2015-1202

NOS Inhibition Modulates Immune Polarization and Improves Radiation-Induced Tumor Growth Delay

Nitric oxide synthases (NOS) are important mediators of progrowth signaling in tumor cells, as they regulate angiogenesis, immune response, and immune-mediated wound healing. Ionizing radiation (IR) is also an immune modulator and inducer of wound response. We hypothesized that radiation therapeutic efficacy could be improved by targeting NOS following tumor irradiation. Herein, we show enhanced radiation-induced (10 Gy) tumor growth delay in a syngeneic model (C3H) but not immunosuppressed (Nu/Nu) squamous cell carcinoma tumor-bearing mice treated post-IR with the constitutive NOS inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME). These results suggest a requirement of T cells for improved radiation tumor response. In support of this observation, tumor irradiation induced a rapid increase in the immunosuppressive Th2 cytokine IL10, which was abated by post-IR administration of L-NAME. In vivo suppression of IL10 using an antisense IL10 morpholino also extended the tumor growth delay induced by radiation in a manner similar to L-NAME. Further examination of this mechanism in cultured Jurkat T cells revealed L-NAME suppression of IR-induced IL10 expression, which reaccumulated in the presence of exogenous NO donor. In addition to L-NAME, the guanylyl cyclase inhibitors ODQ and thrombospondin-1 also abated IR-induced IL10 expression in Jurkat T cells and ANA-1 macrophages, which further suggests that the immunosuppressive effects involve eNOS. Moreover, cytotoxic Th1 cytokines, including IL2, IL12p40, and IFNγ, as well as activated CD8(+) T cells were elevated in tumors receiving post-IR L-NAME. Together, these results suggest that post-IR NOS inhibition improves radiation tumor response via Th1 immune polarization within the tumor microenvironment.

Therapeutic targeting of the thrombospondin-1 receptor CD47 to treat liver cancer

CD47 is a signaling receptor for the matricellular protein thrombospondin-1 and a counter-receptor for signal regulatory protein-α (SIRPα) on macrophages. Following its initial discovery in 1992 as a cell surface protein that is over-expressed by ovarian carcinoma, elevated CD47 expression has emerged as a negative prognostic factor for a variety of cancers. CD47 is also a potential therapeutic target based on the ability of CD47 blockade to cause regression of tumors in mice, and a humanized CD47 antibody has recently entered phase I clinical trials. CD47 blockade may control tumor growth by inhibiting thrombospondin-1 signaling or by preventing inhibitory SIRPα signaling in tumor-associated macrophages. A recent publication by Lee et al. (Hepatology 60:179-191, 2014) provides evidence that blocking CD47 signaling specifically depletes tumor-initiating stem cells in hepatocellular carcinoma and implicates cathepsin-S/protease-activated receptor-2 signaling in mediating this therapeutic response.

CD47 signaling pathways controlling cellular differentiation and responses to stress

CD47 is a widely expressed integral membrane protein that serves as the counter-receptor for the inhibitory phagocyte receptor signal-regulatory protein-α (SIRPα) and as a signaling receptor for the secreted matricellular protein thrombospondin-1. Recent studies employing mice and somatic cells lacking CD47 have revealed important pathophysiological functions of CD47 in cardiovascular homeostasis, immune regulation, resistance of cells and tissues to stress and chronic diseases of aging including cancer. With the emergence of experimental therapeutics targeting CD47, a more thorough understanding of CD47 signal transduction is essential. CD47 lacks a substantial cytoplasmic signaling domain, but several cytoplasmic binding partners have been identified, and lateral interactions of CD47 with other membrane receptors play important roles in mediating signaling resulting from the binding of thrombospondin-1. This review addresses recent advances in identifying the lateral binding partners, signal transduction pathways and downstream transcription networks regulated through CD47 in specific cell lineages. Major pathways regulated by CD47 signaling include calcium homeostasis, cyclic nucleotide signaling, nitric oxide and hydrogen sulfide biosynthesis and signaling and stem cell transcription factors. These pathways and other undefined proximal mediators of CD47 signaling regulate cell death and protective autophagy responses, mitochondrial biogenesis, cell adhesion and motility and stem cell self-renewal. Although thrombospondin-1 is the best characterized agonist of CD47, the potential roles of other members of the thrombospondin family, SIRPα and SIRPγ binding and homotypic CD47 interactions as agonists or antagonists of signaling through CD47 should also be considered.

Tipping off endothelial tubes: nitric oxide drives tip cells

Angiogenesis, the formation of new blood vessels from pre-existing vessels, is a complex process that warrants cell migration, proliferation, tip cell formation, ring formation, and finally tube formation. Angiogenesis is initiated by a single leader endothelial cell called "tip cell," followed by vessel elongation by "stalk cells." Tip cells are characterized by their long filopodial extensions and expression of vascular endothelial growth factor receptor-2 and endocan. Although nitric oxide (NO) is an important modulator of angiogenesis, its role in angiogenic sprouting and specifically in tip cell formation is poorly understood. The present study tested the role of endothelial nitric oxide synthase (eNOS)/NO/cyclic GMP (cGMP) signaling in tip cell formation. In primary endothelial cell culture, about 40% of the tip cells showed characteristic sub-cellular localization of eNOS toward the anterior progressive end of the tip cells, and eNOS became phosphorylated at serine 1177. Loss of eNOS suppressed tip cell formation. Live cell NO imaging demonstrated approximately 35% more NO in tip cells compared with stalk cells. Tip cells showed increased level of cGMP relative to stalk cells. Further, the dissection of NO downstream signaling using pharmacological inhibitors and inducers indicates that NO uses the sGC/cGMP pathway in tip cells to lead angiogenesis. Taken together, the present study confirms that eNOS/NO/cGMP signaling defines the direction of tip cell migration and thereby initiates new blood vessel formation.

CD47 in the tumor microenvironment limits cooperation between antitumor T-cell immunity and radiotherapy

Although significant advances in radiotherapy have increased its effectiveness in many cancer settings, general strategies to widen the therapeutic window between normal tissue toxicity and malignant tumor destruction would still offer great value. CD47 blockade has been found to confer radioprotection to normal tissues while enhancing tumor radiosensitivity. Here, we report that CD47 blockade directly enhances tumor immunosurveillance by CD8(+) T cells. Combining CD47 blockade with irradiation did not affect fibrosarcoma growth in T cell-deficient mice, whereas adoptive transfer of tumor-specific CD8(+) T cells restored combinatorial efficacy. Furthermore, ablation of CD8(+) T cells abolished radiotherapeutic response in immunocompetent syngeneic hosts. CD47 blockade in either target cells or effector cells was sufficient to enhance antigen-dependent CD8(+) CTL-mediated tumor cell killing in vitro. In CD47-deficient syngeneic hosts, engrafted B16 melanomas were 50% more sensitive to irradiation, establishing that CD47 expression in the microenvironment was sufficient to limit tumor radiosensitivity. Mechanistic investigations revealed increased tumor infiltration by cytotoxic CD8(+) T cells in a CD47-deficient microenvironment, with an associated increase in T cell-dependent intratumoral expression of granzyme B. Correspondingly, an inverse correlation between CD8(+) T-cell infiltration and CD47 expression was observed in human melanomas. Our findings establish that blocking CD47 in the context of radiotherapy enhances antitumor immunity by directly stimulating CD8(+) cytotoxic T cells, with the potential to increase curative responses.

CD47 signaling regulates the immunosuppressive activity of VEGF in T cells

Thrombospondin-1 (TSP1) inhibits angiogenesis, in part, by interacting with the ubiquitous cell-surface receptor CD47. In endothelial cells, CD47 interacts directly with vascular endothelial growth factor receptor (VEGFR)-2, and TSP1 inhibits VEGFR2 phosphorylation and signaling by disrupting this association. We show that CD47 similarly associates with and regulates VEGFR2 in T cells. TSP1 inhibits phosphorylation of VEGFR2 and its downstream target Src in wild type but not in CD47-deficient human Jurkat and primary murine T cells. VEGFR2 signaling inhibits proliferation and TCR signaling in wild type T cells. However, ligation of CD47 by TSP1 or loss of CD47 expression reverses some inhibitory effects of VEGF on proliferation and T cell activation. We further found that VEGF and VEGFR2 expression are upregulated in CD47-deficient murine CD4(+) and human Jurkat T cells, and the resulting autocrine VEGFR2 signaling enhances proliferation and some TCR responses in the absence of CD47. Thus, CD47 signaling modulates the ability of VEGF to regulate proliferation and TCR signaling, and autocrine production of VEGF by T cells contributes to this regulation. This provides a mechanism to understand the context-dependent effects of TSP1 and VEGF on T cell activation, and reveals an important role for CD47 signaling in regulating T cell production of the major angiogenic factor VEGF.