Senescent CAFs Mediate Immunosuppression and Drive Breast Cancer Progression

The tumor microenvironment (TME) profoundly influences tumorigenesis, with gene expression in the breast TME capable of predicting clinical outcomes. The TME is complex and includes distinct cancer-associated fibroblast (CAF) subtypes whose contribution to tumorigenesis remains unclear. Here, we identify a subset of myofibroblast CAFs (myCAF) that are senescent (senCAF) in mouse and human breast tumors. Utilizing the MMTV-PyMT;INK-ATTAC (INK) mouse model, we found that senCAF-secreted extracellular matrix specifically limits natural killer (NK) cell cytotoxicity to promote tumor growth. Genetic or pharmacologic senCAF elimination unleashes NK cell killing, restricting tumor growth. Finally, we show that senCAFs are present in HER2+, ER+, and triple-negative breast cancer and in ductal carcinoma in situ (DCIS) where they predict tumor recurrence. Together, these findings demonstrate that senCAFs are potently tumor promoting and raise the possibility that targeting them by senolytic therapy could restrain breast cancer development.

SIGNIFICANCE

senCAFs limit NK cell-mediated killing, thereby contributing to breast cancer progression. Thus, targeting senCAFs could be a clinically viable approach to limit tumor progression.

p38MAPKα Stromal Reprogramming Sensitizes Metastatic Breast Cancer to Immunotherapy

Metastatic breast cancer is an intractable disease that responds poorly to immunotherapy. We show that p38MAPKα inhibition (p38i) limits tumor growth by reprogramming the metastatic tumor microenvironment in a CD4+ T cell-, IFNγ-, and macrophage-dependent manner. To identify targets that further increased p38i efficacy, we utilized a stromal labeling approach and single-cell RNA sequencing. Thus, we combined p38i and an OX40 agonist that synergistically reduced metastatic growth and increased overall survival. Intriguingly, patients with a p38i metastatic stromal signature had better overall survival that was further improved by the presence of an increased mutational load, leading us to ask if our approach would be effective in antigenic breast cancer. The combination of p38i, anti-OX40, and cytotoxic T-cell engagement cured mice of metastatic disease and produced long-term immunologic memory. Our findings demonstrate that a detailed understanding of the stromal compartment can be used to design effective antimetastatic therapies.

SIGNIFICANCE

Immunotherapy is rarely effective in breast cancer. We dissected the metastatic tumor stroma, which revealed a novel therapeutic approach that targets the stromal p38MAPK pathway and creates an opportunity to unleash an immunologic response. Our work underscores the importance of understanding the tumor stromal compartment in therapeutic design. This article is highlighted in the In This Issue feature, p. 1275.

Abstract 2450: Investigating the intrinsic and extrinsic factors regulating breast cancer dormancy

Unfortunately, breast cancer can recur in patients upwards of 25 years after an initial diagnosis and “cure”. It was once thought that recurrence occurred within patients that harbored dormant breast disseminated tumor cells (DTCs) in distant organs that were not present in patients that did not recur. Interestingly, a significant percent of patients harbor DTCs, yet many do not recur, raising the critical question, what differentiates patients that experience a recurrence versus those who live with dormant DTCs for the rest of their lives? It is likely the answer lies in both cell intrinsic as well as extrinsic factors. Nevertheless, the extreme rarity of dormant DTCs has been the major obstacle to their study. To overcome this challenge, we developed an efficient system to isolate and study rare dormant tumor cells from metastatic organs. Using this system and single cell RNA-sequencing (scRNA-seq), we identified a group of genes differentially expressed in dormant breast cancer cells present in both bone and lung. While modulation of these genes individually had no impact on the metastatic behavior of breast cancer cells, we found that as a group, these genes predicted the dormancy phenotype in murine breast cancer models. Importantly, expression of these genes in primary human breast cancer tumors correlated with disease-free survival, suggesting these genes have predictive value in determining which patients are likely to recur. Moreover, we explored extrinsic mechanisms that impact dormancy and found that the chemotherapy reagent doxorubicin (Doxo) drastically changed the microenvironment in vivo, which allowed dormant breast cancer cells to grow robustly within the visceral fat and this was further exacerbated by a high fat diet. Further, we found that Doxo treatment induces significant adipose tissue dystrophy and macrophage infiltration, which may contribute to dormant metastatic outgrowth. Our study provides novel insight into breast cancer dormancy, and also reveals microenvironmental changes that impact dormant breast cancer cell outgrowth.

Citation Format: Qihao Ren, Weng Hua Khoo, Jiayu Ye, Douglas V. Faget, Peter I. Croucher, Sheila A. Stewart. Investigating the intrinsic and extrinsic factors regulating breast cancer dormancy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2450.

Abstract 244: Limiting metastatic breast cancer progression by targeting MK2 stromal signaling

Breast cancer is now the most common cancer among women in the US and metastasis to distant organs is the major cause of death in these patients. Among metastatic sites, bone is the most frequent destination of breast cancer metastasis and once the disease is found in the bone, it is often refractory to standard therapy. In addition, bone metastasis is associated with significant skeletal related events that greatly impact quality of life. Thus, there is a significant need to develop novel therapies that extend survival and improve quality of life. Previously we found that MK2 inhibition (MK2i) limits metastatic growth by targeting the tumor stromal compartment. To determine which stromal cells are targeted by MK2i we isolated stromal cells from within a metastatic bone lesion and carried out single cell RNA sequencing (scRNA-Seq). Using this approach, we found numerous gene expression changes in both the immune (CD45+) and non-immune (CD45-) populations upon MK2i. Indeed, we found significant numbers of p16+ senescent fibroblasts were present inside the metastatic lesion. We also found vascular cancer-associated fibroblasts (vCAF) and matrix CAFs (mCAF) inside the metastatic lesion suggesting that CAFs are not limited to primary disease. Numerous changes in gene expression in CD45+ cells were also observed, and these changes are being used to identify viable immunotherapies to deploy in our model. Finally, we are using conditional MK2 mice to establish the cell type targeted by MK2i. Our data demonstrate that MK2i is as effective as chemotherapy at limiting metastatic progression and our approach to leverage the scRNA-Seq data may allow us to optimize MK2i therapy to improve patient outcomes and quality of life.

Citation Format: Renata Ramalho Oliveira, Douglas V. Faget, Xianmin Luo, Jiayu Ye, Joseph B. Monahan, Sheila A. Stewart. Limiting metastatic breast cancer progression by targeting MK2 stromal signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 244.

Deconstructing tumor heterogeneity: the stromal perspective

Significant advances have been made towards understanding the role of immune cell-tumor interplay in either suppressing or promoting tumor growth, progression, and recurrence, however, the roles of additional stromal elements, cell types and/or cell states remain ill-defined. The overarching goal of this NCI-sponsored workshop was to highlight and integrate the critical functions of non-immune stromal components in regulating tumor heterogeneity and its impact on tumor initiation, progression, and resistance to therapy. The workshop explored the opposing roles of tumor supportive versus suppressive stroma and how cellular composition and function may be altered during disease progression. It also highlighted microenvironment-centered mechanisms dictating indolence or aggressiveness of early lesions and how spatial geography impacts stromal attributes and function. The prognostic and therapeutic implications as well as potential vulnerabilities within the heterogeneous tumor microenvironment were also discussed. These broad topics were included in this workshop as an effort to identify current challenges and knowledge gaps in the field.

Therapy-Induced Senescence Drives Bone Loss

Chemotherapy is important for cancer treatment, however, toxicities limit its use. While great strides have been made to ameliorate the acute toxicities induced by chemotherapy, long-term comorbidities including bone loss remain a significant problem. Chemotherapy-driven estrogen loss is postulated to drive bone loss, but significant data suggests the existence of an estrogen-independent mechanism of bone loss. Using clinically relevant mouse models, we showed that senescence and its senescence-associated secretory phenotype (SASP) contribute to chemotherapy-induced bone loss that can be rescued by depleting senescent cells. Chemotherapy-induced SASP could be limited by targeting the p38MAPK-MK2 pathway, which resulted in preservation of bone integrity in chemotherapy-treated mice. These results transform our understanding of chemotherapy-induced bone loss by identifying senescent cells as major drivers of bone loss and the p38MAPK-MK2 axis as a putative therapeutic target that can preserve bone and improve a cancer survivor's quality of life. SIGNIFICANCE: Senescence drives chemotherapy-induced bone loss that is rescued by p38MAPK or MK2 inhibitors. These findings may lead to treatments for therapy-induced bone loss, significantly increasing quality of life for cancer survivors.

Unmasking senescence: context-dependent effects of SASP in cancer

Cellular senescence plays a critical role in tumorigenesis. Once thought of as a tissue culture artefact by some researchers, senescence is now a major field of study. Although there are common molecular mechanisms that enforce the growth arrest that characterizes the phenotype, the impact of senescence is varied and can, in some instances, have opposite effects on tumorigenesis. It has become clearer that the cell of origin and the tissue in question dictate the impact of senescence on tumorigenesis. In this Review, we unravel this complexity by focusing on how senescence impacts tumorigenesis when it arises within incipient tumour cells versus stromal cells, and how these roles can change in different stages of disease progression. In addition, we highlight the diversity of the senescent phenotype and its functional output beyond growth arrest: the senescence-associated secretory phenotype (SASP). Fortunately, a number of new genetic and pharmacologic tools have been developed that are now allowing the senescence phenotype to be parsed further.

Inhibition of the Stromal p38MAPK/MK2 Pathway Limits Breast Cancer Metastases and Chemotherapy-Induced Bone Loss

The role of the stromal compartment in tumor progression is best illustrated in breast cancer bone metastases, where the stromal compartment supports tumor growth, albeit through poorly defined mechanisms. p38MAPKα is frequently expressed in tumor cells and surrounding stromal cells, and its expression levels correlate with poor prognosis. This observation led us to investigate whether inhibition of p38MAPKα could reduce breast cancer metastases in a clinically relevant model. Orally administered, small-molecule inhibitors of p38MAPKα or its downstream kinase MK2 each limited outgrowth of metastatic breast cancer cells in the bone and visceral organs. This effect was primarily mediated by inhibition of the p38MAPKα pathway within the stromal compartment. Beyond effectively limiting metastatic tumor growth, these inhibitors reduced tumor-associated and chemotherapy-induced bone loss, which is a devastating comorbidity that drastically affects quality of life for patients with cancer. These data underscore the vital role played by stromal-derived factors in tumor progression and identify the p38MAPK-MK2 pathway as a promising therapeutic target for metastatic disease and prevention of tumor-induced bone loss.Significance: Pharmacologically targeting the stromal p38MAPK-MK2 pathway limits metastatic breast cancer growth, preserves bone quality, and extends survival. Cancer Res; 78(19); 5618-30. ©2018 AACR.

Abstract A48: Apoptosis induced by NFAT1 in transformed cells is dependent on TNF-alpha sensitivity

The family of nuclear factor of activated T cells (NFAT) consists of four calcium-regulated members. NFAT proteins are largely known for playing a major role in gene expression regulation during T-cell activation. Nevertheless, NFAT members are also expressed in other cell types, such as adipocytes, neurons, cardiac muscle, breast, cartilage, pancreatic, and endothelial cells. Regulation of NFAT activity is essential to maintain homeostasis. Deregulation of NFAT is associated with many pathologies, such as cancer, neurodegenerative, and heart disorders. In cancer, different NFAT proteins were described for being involved in tumorigenesis and progression of the disease. However, some questions remain unanswered. NFAT1 deficient mice are more susceptible to chemical-induced carcinogenesis and develop spontaneous B-cell lymphomas and chondrosarcomas. Corroborating this data, NFAT1 is able to induce cell death in different cell types by the upregulation of apoptosis-inducing genes. Together, these studies suggest NFAT1 may act as tumor suppressor gene by inducing cell death. However, other studies point in the opposite direction by showing NFAT1's role in promoting migration and invasion of tumor cells in different types of cancer, contributing to the progression of the disease. Therefore, we aim to elucidate if NFAT1 is able to induce cell death in tumor cell lines to understand in which cell context NFAT1 may act as a tumor suppressor. Here, we show in our previous model that overexpression of constitutively active form of NFAT1 (NFAT1-ca) induces cell death in NIH3T3 H-RasV12 transformed fibroblasts. Gene expression analysis revealed that NFAT1-ca overexpression led to massive increase in TNF-alpha expression in these transformed fibroblasts. Deletion of Tnf gene, by CRISPR/Cas9 approach, turned NIH3T3 cells resistant to cell death induced by NFAT1-ca. Next, we addressed whether melanoma (B16F10), colon (HCT116, LoVo), and breast (4T1, MDA-MB-231) cancer cells are susceptible to apoptosis induced by NFAT1-ca. Both colon cancer cells underwent apoptosis when overexpressing NFAT1-ca. On the other hand, melanoma and breast cancer cells were not susceptible to cell death induced by NFAT1-ca. TNF-alpha expression was upregulated in melanoma and colon cancer cells and remains to be evaluated in breast cancer cells. Some studies show that B16F10 and MDA-MB-231 are resistant to TNF-alpha-induced apoptosis while HCT116 cells are susceptible. So far, our data suggest that NFAT1 may induce cell death mostly by TNF-alpha induction. Therefore, it is possible that cancer cells resistant to TNF-alpha are also resistant to NFAT1-ca.

Financial support: FAPERJ, CNPq, Ministry of Health – Brazil.

Citation Format: Douglas V. Faget, João P. B. Viola. Apoptosis induced by NFAT1 in transformed cells is dependent on TNF-alpha sensitivity [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr A48.

NFAT1 transcription factor regulates cell cycle progression and cyclin E expression in B lymphocytes

The NFAT family of transcription factors has been primarily related to T cell development, activation, and differentiation. Further studies have shown that these ubiquitous proteins are observed in many cell types inside and outside the immune system, and are involved in several biological processes, including tumor growth, angiogenesis, and invasiveness. However, the specific role of the NFAT1 family member in naive B cell proliferation remains elusive. Here, we demonstrate that NFAT1 transcription factor controls Cyclin E expression, cell proliferation, and tumor growth in vivo. Specifically, we show that inducible expression of NFAT1 inhibits cell cycle progression, reduces colony formation, and controls tumor growth in nude mice. We also demonstrate that NFAT1-deficient naive B lymphocytes show a hyperproliferative phenotype and high levels of Cyclin E1 and E2 upon BCR stimulation when compared to wild-type B lymphocytes. NFAT1 transcription factor directly regulates Cyclin E expression in B cells, inhibiting the G1/S cell cycle phase transition. Bioinformatics analysis indicates that low levels of NFAT1 correlate with high expression of Cyclin E1 in different human cancers, including Diffuse Large B-cell Lymphomas (DLBCL). Together, our results demonstrate a repressor role for NFAT1 in cell cycle progression and Cyclin E expression in B lymphocytes, and suggest a potential function for NFAT1 protein in B cell malignancies.

IRF2BP2 transcriptional repressor restrains naive CD4 T cell activation and clonal expansion induced by TCR triggering

CD4 T cell activation and differentiation mechanisms constitute a complex and intricate signaling network involving several regulatory proteins. IRF2BP2 is a transcriptional repressor that is involved in gene-expression regulation in very diverse biologic contexts. Information regarding the IRF2BP2 regulatory function in CD4 T lymphocytes is very limited and suggests a role for this protein in repressing the expression of different cytokine genes. Here, we showed that Irf2bp2 gene expression was decreased in CD4 T cells upon activation. To investigate the possible regulatory roles for IRF2BP2 in CD4 T cell functions, this protein was ectopically expressed in murine primary-activated CD4 T lymphocytes through retroviral transduction. Interestingly, ectopic expression of IRF2BP2 led to a reduction in CD25 expression and STAT5 phosphorylation, along with an impaired proliferative capacity. The CD69 expression was also diminished in IRF2BP2-overexpressing cells, whereas CD44 and CD62L levels were not altered. In vivo, transferred, IRF2BP2-overexpressing, transduced cells displayed an impaired expansion capacity compared with controls. Furthermore, overexpression of IRF2BP2 in differentiated Th cells resulted in slightly reduced IL-4 and pro-TGF-β production in Th2 and iT_regs but had no effect on IFN-γ or IL-17 expression in Th1 and Th17 cells, respectively. Taken together, our data suggest a role for IRF2BP2 in regulating CD4 T cell activation by repressing proliferation and the expression of CD25 and CD69 induced by TCR stimuli.

Osteopontin is a tumor autoantigen in prostate cancer patients

Anti-tumor antibodies act as biomarkers for the early diagnosis of prostate cancer (PCa). Osteopontin (OPN) is overexpressed in PCa cells and contributes to the progression of the disease. This study aimed to evaluate whether OPN evokes a humoral immune response in PCa patients and whether the reactivity levels of anti-OPN antibodies may be used to better differentiate PCa from benign and healthy donor plasma samples. Plasma samples from biopsy-proven PCa patients (29), benign prostate hyperplasia (BPH) (18) and control healthy donors (HD) (30) were tested by immunoblots using the recombinant human OPN. The frequency of anti-OPN antibodies was significantly higher in PCa (66%) plasma samples as compared to BPH (33%) and HD controls (10%). Anti-OPN antibodies were detected in a high proportion of plasma samples from patients with a Gleason score of less than 6 (57%), prostate-specific antigen levels lower than 10 ng/ml (67%) and pT2 organ-confined disease (70%), suggesting that anti-OPN antibodies may be used as an early serum marker for PCa. To the best of our knowledge, this is the first description of OPN as a tumor autoantigen and one of the most reactive individual autoantigens described thus far. These data support the inclusion of OPN in a multiplex of tumor antigens in order to perform antibody profiling in PCa as well as in other malignancies overexpressing OPN.