Dormant Tumor Cells Research Articles

Abstract C033: The circadian rhythm gene Dec2 promotes pancreatic cancer dormancy by facilitating immune evasion

Abstract Metastatic recurrence following curative-intent pancreatic cancer surgery is a major clinical problem as nearly all die of this at both early and latent periods following surgery. Latent recurrences are due to reactivation of dormant tumor cells that disseminate before the primary tumor has been removed. The mechanisms that drive cancer dormancy are poorly understood in part because of the lack of animal models that recapitulate the biology of the resected patient. Here we introduce a novel mouse model of pancreatic cancer dormancy in which we establish distal pancreatic tumors by orthotopic injection, resect them four weeks later and then follow the mice for recurrence. We observed recurrence patterns and survival outcomes that mimic human patients undergoing surgery for pancreatic cancer where two thirds of the mice succumb to early metastatic recurrence (median survival 26 days) and one third of the mice (called dormant mice) live substantially long (median survival 554 days) without clinical evidence of disease yet harbor disseminated tumor cells in most organs of the body. Disseminated tumor cells isolated from the livers of dormant mice were quiescent, exhibited stem cell properties and upregulated the expression of Dec2, a transcriptional repressor previously best known for its importance in maintaining circadian rhythms. Dec2 enabled the dormant tumor cells to evade the immune system by reducing the amount of MHC1 on their surfaces, and thereby lowered the number of CD8+ T cells within the tumor microenvironment. Knocking out Dec2 significantly improved the overall survival of immunocompetent mice and increased CD8+ T cell tumor infiltration. The decrease in cell surface MHCI was likely due to impaired surface localization of the protein. RNA-seq analysis demonstrated a loss of antigen presentation pathway genes in Dec2 WT cells, particularly in genes encoding subunits of the proteasome. Proper localization of MHC1 is known to depend upon proteasome-generated peptides. By cut-and-run analysis, Dec2 bound directly to the promoters of a number of proteasomal genes, lowered expression of these genes, and decreased proteasomal activity. These studies describe a new mechanism for Dec2 in regulating cancer dormancy through its downregulation of proteasomal activity which in turn converts a hot to a cold TME by decreasing cell surface MHC1. Citation Format: Lan Wang, Orjola Prela, Ching-Hua Shih, Juliana Cazarin de Menezes, Brian Altman, Paula Vertino, Chris Harris, Darren Carpizo. The circadian rhythm gene Dec2 promotes pancreatic cancer dormancy by facilitating immune evasion [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C033.

MALAT1 protects dormant tumor cells from immune elimination.

MALAT1 protects dormant tumor cells from immune elimination.

Unveiling the role of cellular dormancy in cancer progression and recurrence.

Cellular dormancy is a major contributor to cancer progression and recurrence. This review explores recent findings on the molecular mechanisms implicated in cancer dormancy and investigates potential strategies to improve therapeutic interventions. Research on cancer dormancy reveals a complex and multifaceted phenomenon. Providing a latent reservoir of tumor cells with reduced proliferation and enhanced drug-tolerance, dormant cancer cells emerge from a clonally diverse population after therapy or at metastatic sites. These cells exhibit distinct transcriptional and epigenetic profiles, involving the downregulation of Myc and mechanistic target of rapamycin (mTOR) pathways, and the induction of autophagy. Senescence traits, under the control of factors such as p53, also contribute significantly. The tumor microenvironment can either promote or prevent dormancy establishment, notably through the involvement of T and NK cells within the dormant tumor niche. Strategies to combat dormancy-related relapse include direct elimination of dormant tumor cells, sustaining dormancy to prolong survival, or awakening dormant cells to re-sensitize them to antiproliferative drugs. Improving our understanding of cancer dormancy at primary and secondary sites provides valuable insights into patient care and relapse prevention.

13C Tracer Analysis and Metabolomics in Dormant Cancer Cells.

Over the last two decades, major advances in the field of tumor dormancy have been made. Yet, it is not completely understood how dormant disseminated tumor cells survive and transition to a proliferative state to generate a metastatic lesion. On the other hand, metabolic rewiring has been shown to influence metastasis development through the modulation of both intracellular signaling and the crosstalk between metastatic cells and their microenvironment. Thus, studying the metabolic features of dormant disseminated tumor cells has gained importance in understanding the dormancy process. Here, we describe a method to perform metabolomics and 13C tracer analysis in 3D cultures of dormant breast cancer cells.

Immune evasion of dormant disseminated tumor cells is due to their scarcity and can be overcome by T cell immunotherapies

The period between "successful" treatment of localized breast cancer and the onset of distant metastasis can last many years, representing an unexploited window to eradicate disseminated disease and prevent metastases. We find that the source of recurrence-disseminated tumor cells (DTCs) -evade endogenous immunity directed against tumor neoantigens. Although DTCs downregulate major histocompatibility complex I, this does not preclude recognition by conventional Tcells. Instead, the scarcity of interactions between two relatively rare populations-DTCs and endogenous antigen-specific Tcells-underlies DTC persistence. This scarcity is overcome by any one of three immunotherapies that increase the number of tumor-specific Tcells: Tcell-based vaccination, or adoptive transfer of Tcell receptor or chimeric antigen receptor Tcells. Each approach achieves robust DTC elimination, motivating discovery of MHC-restricted and -unrestricted DTC antigens that can be targeted with Tcell-based immunotherapies to eliminate the reservoir of metastasis-initiating cells in patients.

A Live Tracker of Dormant Disseminated Tumor Cells.

The high prevalence of dormant disseminated tumor cells (DTCs) persisting systemically in patients with metastatic cancer is a major threat to long-lasting cure (Aguirre-Ghiso, Nat Rev Cancer 7:834-846, 2007; Klein, Nat Rev Cancer 20(11):681-694, 2020; Lyden et al. Cancer Cell 40:787-791, 2022). Despite its clinical significance, the study of what drives DTCs in and out of dormancy while they linger in distant sites has been challenged by the lack of tools to find and follow dormant DTCs inside a living organism. Here, leveraging the fact that dormant DTCs are mostly quiescent, we describe a live cell reporter to distinguish dormant from cycling DTCs (Correia, Nat Rev Cancer 22(7):379, 2022; Correia et al. Nature 594(7864):566-571, 2021). Cancer cell lines are engineered to coexpress a luciferase-tdTomato reporter and a fluorescent fusion protein of mVenus with a mutant form of the cell cycle inhibitor p27 (mVenus-p27K-) that identifies quiescent cells. When implanted in animal models or assembled in cocultures in vitro, labeled cells can be imaged longitudinally over time or retrieved alive alongside their surrounding microenvironment for downstream gene, protein, and metabolite profiling, allowing the mapping of tissue-specific determinants of cancer dormancy and metastasis.

Establishing and Characterizing Chemotherapy-Induced Immunological Dormant Tumor Cell Lines.

Chemotherapy, together with radiotherapy, targeted therapies, and immunotherapy, is the main option to treat cancer patients in neoadjuvant/adjuvant setting to reduce the risk of disease progression and metastasis formation from disseminated tumor cells. Cancer cells that survived chemotherapy treatment may emerge with novel characteristics, one of which is the ability to stimulate the native and adaptive immune systems. Models allowing the characterization of chemotherapy-induced tumor cell plasticity and induction of immune response or adaptation are needed to identify novel mechanisms and devise novel therapeutic strategies to prevent relapses. Here we describe a protocol for selecting chemotherapy-resistant cancer cells and testing the in vivo effects on the local and systemic immune responses. While originally developed to characterize the effects of methotrexate and doxorubicin on murine 4T1 breast cancer cells and the relative immune response, the method can be broadened to other chemotherapies and syngeneic cancer models.

Modeling Tumor Cell Dormancy in an Ex Vivo Liver Metastatic Niche.

Despite decades of research into metastatic disease, our knowledge of the mechanisms governing dormancy are still limited. Unraveling the process will aid in developing effective therapies to either maintain or eliminate these dormant cells and thus prevent them from emerging into overt metastatic disease. To study the behavior of dormant tumor cells-mechanisms that promote, maintain, and disrupt this state-we utilize the Legacy LiverChip®, an all-human ex vivo hepatic microphysiological system. This complex, bioengineered system is able to recreate metastatic disease that is reflective of the human situation and is among only a handful of systems able to mimic spontaneous tumor cell dormancy. The dormant subpopulation reflects the defining traits of cellular dormancy-survival in a foreign microenvironment, chemoresistance, and reversible growth arrest. This microphysiological system has and continues to provide critical insights into the biology of dormant tumor cells. It also serves as an accessible tool to identify new therapeutic strategies targeting dormancy and concurrently evaluate the efficacy of therapeutic agents as well as their metabolism and dose-limiting toxicity.

Dormant tumors circumvent tumor-specific adaptive immunity by establishing a Treg-dominated niche via DKK3.

Approximately 30% of breast cancer survivors deemed free of disease will experience locoregional or metastatic recurrence even up to 30 years after initial diagnosis, yet how residual/dormant tumor cells escape immunity elicited by the primary tumor remains unclear. We demonstrate that intrinsically dormant tumor cells are indeed recognized and lysed by antigen-specific T cells in vitro and elicit robust immune responses in vivo. However, despite close proximity to CD8+ killer T cells, dormant tumor cells themselves support early accumulation of protective FoxP3+ T regulatory cells (Tregs), which can be targeted to reduce tumor burden. These intrinsically dormant tumor cells maintain a hybrid epithelial/mesenchymal state that is associated with immune dysfunction, and we find that the tumor-derived, stem cell/basal cell protein Dickkopf WNT signaling pathway inhibitor 3 (DKK3) is critical for Treg inhibition of CD8+ T cells. We also demonstrate that DKK3 promotes immune-mediated progression of proliferative tumors and is significantly associated with poor survival and immunosuppression in human breast cancers. Together, these findings reveal that latent tumors can use fundamental mechanisms of tolerance to alter the T cell microenvironment and subvert immune detection. Thus, targeting these pathways, such as DKK3, may help render dormant tumors susceptible to immunotherapies.

244MO A phase II trial targeting disseminated dormant tumor cells with hydroxychloroquine, everolimus or the combination to prevent recurrent breast cancer (“CLEVER”)

244MO A phase II trial targeting disseminated dormant tumor cells with hydroxychloroquine, everolimus or the combination to prevent recurrent breast cancer (“CLEVER”)

PROGNOSTIC VALUE OF LIQUID BIOPSY IN CRC: A LITERATURE REVIEW

Relevance: Liquid biopsy is a modern, quite appropriate, and promising method for diagnosing malignant neoplasms for oncology. The method allows us to determine the level of freely circulating tumor cells – micrometastases, tumor DNA, microRNA, and exosomes in blood plasma- and detect various genetic changes. A literature review of current scientific publications on liquid biopsy techniques, indexed in Medline, PubMed, and Medscape, was carried out as part of the work.
 The study aimed to review is to assess the prognostic significance of liquid biopsy, to determine the place of the method in current recommendations, and its expediency from the point of view of the practice.
 Methods: The information search was conducted in the Medline, PubMed, and Medscape databases, with a search depth of 8 years. Data from randomized controlled trials, clinical trials, reviews, systematic reviews, and meta-analyses were analyzed. The review includes both full-fledged articles in the public domain and abstracts to obtain complete information on the problem.
 Results: Liquid biopsy surpasses tissue biopsy in simplicity and speed of research, easy repeatability, and minimal invasiveness, as well as the possibility of dynamic monitoring of progression – the overall clonal transformation of the tumor and the emergence of resistance to treatment.
 The disadvantages of this method are low sensitivity, difficulty in correctly interpreting biomarkers and determining their specificity, and high risk of false positive and false negative results due to dormant tumor cells.
 Conclusion: At present, the Liquid biopsy method is relevant and in demand, but it needs to be tested on a validated sample of the main population, and in order to achieve effective clinical use, important work needs to be done to standardize both preanalytical and analytical procedures and generalize them for all components of liquid biopsy.

PROGNOSTIC VALUE OF LIQUID BIOPSY IN CRC: A LITERATURE REVIEW

Relevance: Liquid biopsy is a modern, quite appropriate, and promising method for diagnosing malignant neoplasms for oncology. The method allows us to determine the level of freely circulating tumor cells – micrometastases, tumor DNA, microRNA, and exosomes in blood plasma- and detect various genetic changes. A literature review of current scientific publications on liquid biopsy techniques, indexed in Medline, PubMed, and Medscape, was carried out as part of the work.
 The study aimed to review is to assess the prognostic significance of liquid biopsy, to determine the place of the method in current recommendations, and its expediency from the point of view of the practice.
 Methods: The information search was conducted in the Medline, PubMed, and Medscape databases, with a search depth of 8 years. Data from randomized controlled trials, clinical trials, reviews, systematic reviews, and meta-analyses were analyzed. The review includes both full-fledged articles in the public domain and abstracts to obtain complete information on the problem.
 Results: Liquid biopsy surpasses tissue biopsy in simplicity and speed of research, easy repeatability, and minimal invasiveness, as well as the possibility of dynamic monitoring of progression – the overall clonal transformation of the tumor and the emergence of resistance to treatment.
 The disadvantages of this method are low sensitivity, difficulty in correctly interpreting biomarkers and determining their specificity, and high risk of false positive and false negative results due to dormant tumor cells.
 Conclusion: At present, the Liquid biopsy method is relevant and in demand, but it needs to be tested on a validated sample of the main population, and in order to achieve effective clinical use, important work needs to be done to standardize both preanalytical and analytical procedures and generalize them for all components of liquid biopsy.

Abstract B038: Prostate cancer (PCa) cell dormancy in bone depends on physical contacts between PCa cells and osteoblasts and can be induced via FAK inhibition

Abstract Advanced prostate cancer (PCa) in patients still progresses to metastatic relapse after curative treatment such as primary tumor removal. This is likely due to the early disseminated PCa cells that stayed dormant initially and got reactivated to proliferate into overt metastases. However, we don’t know when and to which organs PCa cells disseminate, whether and how primary tumor removal affects the dissemination and dormancy. To answer these, we injected C4-2B cells subcutaneously into immunodeficient NSG mice and randomized the mice for either having the tumors removed at week 2 or keeping the tumors till the endpoints. We then euthanized the mice and semi-quantified the disseminated C4-2B cells in various mouse organs via human-specific genomic PCR at weeks 2/6/8. We serendipitously found PCa metastatic recurrence at a distant site in one mouse at 5 weeks post removal of the C4-2B PCa subcutaneous tumor, suggesting that the mice without observed recurrence may have dormant disseminated tumor cells (DTC). We further observed that tumor removal limited DTC in the bones, specifically, in the bone cortex. In clinic, metastatic PCa tumors were found in patient bone marrows and bone marrow DTC presence was associated with poor prognosis. Therefore, we hypothesized that cells in the bone cortex induce and maintain DTC dormancy. We first explored the dormancy-inducing effects of various types of cells in bone. We co-cultured C4-2B cells in direct contact with osteoblasts MC3T3-E1, macrophages Raw264.7, mesenchymal progenitors OP-9, fibroblasts NIH3T3, or endothelial cells HUVEC. The dormancy phenotypes such as proliferation and marker gene changes of the co-cultured C4-2B cells were compared to C4-2B cells cultured alone. We found that only MC3T3-E1 cells, but not other cells, inhibited C4-2B proliferation, increased the expression of dormancy markers such as NR2F1, and decreased the expressions of proliferation markers such as Ki67 and Cyclin D1, suggesting that osteoblasts induced C4-2B dormancy. Direct physical contacts were necessary as dormancy phenotypes were not observed in C4-2B cells treated with the conditioned media of MC3T3-E1 cells cultured alone, nor in C4-2B cells in transwell co-culture with MC3T3-E1 cells. We then performed RNA-Seq in C4-2B/MC3T3-E1 co-culture to profile the dormancy signature, which was loaded into a novel artificial intelligence (AI) platform to screen for drugs mimicking this signature. One candidate from the AI pipeline, PF-562271, a focal adhesion kinase (FAK) inhibitor, was validated with dormancy-mimicking effect for C4-2B cells in vitro. Further studies are focusing on the in vivo effects and the mechanisms of action of PF-562271. Our study profiled the C4-2B PCa cell disseminations post primary tumor removal. We defined a unique osteoblast-induced dormancy signature and revealed physical contact requirement in dormancy. We also recapitulated osteoblast-induced PCa cell dormancy in vitro using an FAK inhibitor, which could potentially inhibit PCa bone metastatic progression and recurrence clinically. Citation Format: Ruihua Liu, Shang Su, Ke Liu, Jing Xing, Mary Stangis, Diego P. Jacho, Eda D. Yildirim-Ayan, Cara M. Gatto-Weis, Haiquan Yu, Bin Chen, Xiaohong Li. Prostate cancer (PCa) cell dormancy in bone depends on physical contacts between PCa cells and osteoblasts and can be induced via FAK inhibition [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B038.

Advances in the Mechanism of Action of Neutrophil Extracellular Traps in Gastrointestinal Tumors: A Review.

Neutrophils are important immune cells in the body, extremely abundant, phagocytic and bactericidal, and usually involved in the defense against infectious diseases as immune become. However, a new reticulum structure has been discovered: neutrophil extracellular traps (NETs), which consists of various components such as DNA and proteins, etc. Current studies have found that NETs are closely associated with various diseases such as immune diseases, inflammation and tumors, and the study of the development and metastasis of gastrointestinal tumors has become a recent research hotspot. The clinical significance of NETs has been gradually highlighted, especially in the area of immunosuppression. We reviewed a large amount of relevant literature, summarized the latest detection methods of NETs, explored the mechanism of NETs in gastrointestinal tumors and summarized the latest hotspot directions. NETs are involved in the development of gastrointestinal tumors, and are closely related to the proliferation and metastasis of gastrointestinal tumors. Higher levels of NETs are associated with poor prognosis of gastrointestinal tumors, promote local growth of tumors through various pathways, participate in tumor-related systemic injury, and promote tumor growth and metastasis by enhancing the mitochondrial function of tumor cells and awakening dormant tumor cells. NETs are highly expressed in tumors, and tumors and their microenvironment can promote the production of NETs, providing new ideas for the clinical diagnosis and treatment of gastrointestinal tumors. In this paper, we describe the basic information about NETs, explore the research mechanisms related to NETs in gastrointestinal tumors, and prospectively explore the clinical potential of hotspots and inhibitors related to NETs for gastrointestinal tumors, in order to provide new ideas and targets for the diagnosis and treatment of gastrointestinal tumors.

The metastatic niche formation: focus on extracellular vesicle-mediated dialogue between lung cancer cells and the microenvironment.

Lung cancer is the deadliest cancer in the world, with the majority of patients presenting with advanced or metastatic disease at first diagnosis. The lungs are also one of the most common sites of metastasis from lung cancer and other tumors. Understanding the mechanisms that regulate metastasis formation from primary lung cancer and in the lungs is therefore fundamental unmet clinical need. One of the first steps during the establishment of lung cancer metastases includes the formation of the pre-metastatic niche (PMN) at distant organs, which may occur even during the early phases of cancer development. The PMN is established through intricate cross-talk between primary tumor-secreted factors and stromal components at distant sites. Mechanisms controlling primary tumor escape and seeding of distant organs rely on specific properties of tumor cells but are also tightly regulated by interactions with stromal cells at the metastatic niche that finally dictate the success of metastasis establishment. Here, we summarize the mechanisms underlying pre-metastatic niche formation starting from how lung primary tumor cells modulate distant sites through the release of several factors, focusing on Extracellular Vesicles (EVs). In this context, we highlight the role of lung cancer-derived EVs in the modulation of tumor immune escape. Then, we illustrate the complexity of Circulating Tumor Cells (CTCs) that represent the seeds of metastasis and how interactions with stromal and immune cells can help their metastatic dissemination. Finally, we evaluate the contribution of EVs in dictating metastasis development at the PMN through stimulation of proliferation and control of disseminated tumor cell dormancy. Overall, we present an overview of different steps in the lung cancer metastatic cascade, focusing on the EV-mediated interactions between tumor cells and stromal/immune cells.

The aging lung reawakens dormant tumor cells.

The aging lung reawakens dormant tumor cells.

Abstract 4500: Enedione derivates as a potential cancer treatment through the inhibition of COPZ1

Abstract Cancer is a leading cause of death worldwide; it was responsible for approximately 10 million deaths in 2020. Besides surgery for tumor removal, the most common treatments available are chemotherapy and radiation, which are not selective, resulting in side effects such as pain, hair loss, nausea, and vomiting. They are also ineffective against stem-like and dormant tumor cells, which could lead to a relapse and/or metastasis. Consequently, the development of drugs with tumor-specific targets is needed. COPI is a coatomer responsible for the retrograde transport from Golgi complex (GC) to the endoplasmic reticulum (ER). In this context, we developed four compounds targeting disruption of GC through inhibition of COPI and previous results showed that compounds 1-4 significantly decrease cell viability of pancreatic cancer cell lines MIA PaCa-2 and AsPC-1, compared to hTERT-HPNE normal pancreatic cell line. In the present work, RT q-PCR confirmed that the two isoforms of the COPI ζ subunit COPZ1 and COPZ2 are expressed at similar levels in normal cells while COPZ2 is downregulated in tumor cell lines. Our in vitro results demonstrated that compounds 1-4 decreased cell viability of breast cancer (HCC1143) and melanoma (A-395) cell lines. The tested compounds are able to target COPZ1-dependent tumor cells, therefore they are great candidates for further studies aiming to develop a selective treatment for cancer. Citation Format: Allana C. Martins, Barbara Mitsuyasu Barbosa, Ingridhy O. Maia Freitas da Silveira, Roberto Gomes. Enedione derivates as a potential cancer treatment through the inhibition of COPZ1. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4500.

Abstract 1242: Single cell multiomic map reveals regulatory landscape of human brain metastases

Abstract Capturing comprehensive brain metastasis landscape is critical to the establishment of effective anti-tumor strategies. This study took advantage of single-cell multiomics sequencing to profile the molecular and cellular dynamics in tumor cells and associated microenvironment during brain metastasis. Among different primary cancer types, our data suggest that there are conserved yet distinct tumor cell subpopulations, governed by specific changes in gene expression, chromatin accessibility and tumor-stroma interactions. We characterized the conserved tumor subpopulations of brain metastasis with features of: (1) dormancy, (2) enhanced translation and migration, (3) cell death and (4) high proliferation rate. Dormant tumor cells in brain metastasis appear to limit cell-cell interactions with the surrounding microenvironment. In line with previous observations, dormant cells exhibit distinct stimulation for interferon, oxidative phosphorylation and HIPPO signaling. Despite a pronounced cell plasticity, trajectory analysis uncovered a cell progression pattern and its major sequential states and driving genes. Importantly, the tumor trajectory provides new insights into the regulatory landscape controlling the transition from dormant to proliferating tumor cells. Our findings also point to a valuable use of matched isolated circulating tumor cells and cell-free DNA to map the molecular and cellular dynamics of brain metastases. This work demonstrated that despite a pronounced intratumoral heterogeneity, brain metastases present conserved tumor subpopulations regardless of the patient and primary type. A novel and key finding in this study is the multiomics characterization of the regulatory landscape shaping human brain metatastases. Thus, we believe further understanding of these key regulatory elements could lead to novel tumor targets with broad translational potential. Citation Format: Remi Klotz, Alexis Zukowski, Mohamed Kamal, Frank Attenelo, Srinivas Ramachandran, Min Yu. Single cell multiomic map reveals regulatory landscape of human brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1242.

Abstract 86: Chemotherapy-induced microenvironmental changes promote dormant breast cancer cell outgrowth in adipose tissue

Abstract Despite the high 5-year survival rate for early-stage breast cancer patients, late recurrence of the disease remains a major challenge. Breast cancer can recur in approximately 20-25% of patients months to decades after an initial diagnosis, and there are few biomarkers that predict which patients will suffer from the recurrent disease. Unfortunately, this means clinicians and their patients must take a frustrating wait-and-see approach. Notably, disseminated tumor cells (DTCs) are frequently detected in early-stage breast cancer patients, and their presence predicts a higher chance of recurrence. However, why some patients with DTCs recur while others do not remains a mystery. Previous work has suggested that changes in the tumor microenvironment (TME) play an important role in the maintenance of tumor cell dormancy. When assessing the impact of doxorubicin (DOXO), a chemotherapeutic agent often used to treat breast cancer patients, on the TME, we noted that DOXO treatment led to the activation of dormant breast cancer cells in the visceral adipose tissue. Moreover, in accordance with the clinical observation that obese patients suffer a higher risk of cancer recurrence, we found that diet-induced obesity further exacerbated DOXO ability to reactivate dormant breast cancer cells in adipose tissue and this reactivation was associated with robust macrophage infiltration. These findings were interesting in light of our observation that tumor cells can metastasize to visceral fat depots in breast cancer patients. To understand why macrophages were recruited to the adipose tissue and how they led to tumor cell reactivation, we profiled the microenvironmental changes in visceral fat from Veh- and Doxo- treated mice using single-cell RNA-sequencing and found that the infiltrating macrophages exhibited unique pro-inflammatory and lipid-regulatory phenotypes. Our study provides novel insights into how TME impacts breast cancer dormancy and also highlights the importance of adipose tissue as a unique reservoir that potentiates cancer relapse. Citation Format: Qihao Ren, Jiayu Ye, Xiaoyu Yuan, Sheila Stewart. Chemotherapy-induced microenvironmental changes promote dormant breast cancer cell outgrowth in adipose tissue [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 86.

Age-associated microenvironmental changes highlight the role of PDGF-C in ER+ breast cancer metastatic relapse

Patients with estrogen receptor (ER)-positive breast cancer are at risk of metastatic relapse for decades after primary tumor resection and treatment, a consequence of dormant disseminated tumor cells (DTCs) reawakening at secondary sites. Here we use syngeneic ER+ mouse models in which DTCs display a dormant phenotype in young mice but accelerated metastatic outgrowth in an aged or fibrotic microenvironment. In young mice, low-level Pdgfc expression by ER+ DTCs is required for their maintenance in secondary sites but is insufficient to support development of macrometastases. By contrast, the platelet-derived growth factor (PDGF)-Chi environment of aging or fibrotic lungs promotes DTC proliferation and upregulates tumor cell Pdgfc expression stimulating further stromal activation, events that can be blocked by pharmacological inhibition of PDGFRα or with a PDGF-C-blocking antibody. These results highlight the role of the changing microenvironment in regulating DTC outgrowth and the opportunity to target PDGF-C signaling to limit metastatic relapse in ER+ breast cancer.