Strategies to stimulate dendritic cell (DC) activity, such as ex vivo generation and priming of DC vaccines, have been explored as cancer immunotherapies owing to their potential to elicit antitumor T cell responses. Despite decades of research, the success of DC vaccines has been limited, potentially because of unidentified tolerance-enforcing mechanisms. Here we show that GM-CSF-IL-4-induced differentiating DCs express ALDH1A2 and produce retinoic acid, inhibiting DC maturation. Genetic knockout of Aldh1a2 releases this natural brake and enhances DC function. We further develop an ALDH1A2 inhibitor with high potency, favorable drug-like properties and no evidence of off-target effects. Treatment with this inhibitor promotes DC activity, which in turn enhances antigen-specific T cell responses, improving the efficacy of DC vaccines. Our study demonstrates the unique role of the ALDH1A2-retinoic acid axis in regulating DC functions and further presents a new small-molecule inhibitor of ALDH1A2 as a potential immunotherapeutic agent for cancer.

Stem cell populations employ cell-intrinsic and niche-mediated mechanisms to preserve long-term self-renewal and regenerative potential. We propose that tumor-initiating cells (TICs) hijack this developmental circuitry to sustain their growth and establish an early immunosuppressive microenvironment during malignant progression. Recent work implicates CXCR4 tissue-resident macrophages (TRMs) in the mammary gland as a central orchestrator of this process. Conserved CXCL12/CXCR4-AKT-β-catenin signaling links CXCR4 TRM support of normal mammary stem cells to TIC maintenance, underscoring how developmental niches are exploited in malignancy. During tumorigenesis, aberrant CXCL12 production from tumor-associated fibroblasts promotes the expansion of CXCR4 TRMs, while CXCR4 signaling enhances ALDH1A2-dependent retinoic acid production, which induces regulatory T cells and thereby suppresses anti-tumor immunity at the earliest stages of tumor development. From this perspective, early immune evasion is not only a hallmark of cancer but also a therapeutic window. Targeting TRMs early in cancer development could delay, or even prevent, malignant initiation. More broadly, we propose that TIC-niche crosstalk constitutes a tractable vulnerability, and that incorporating TRM-directed interventions alongside conventional and immune-based therapies may shift the balance toward durable tumor control.

Metastatic cancer cell fate is shaped by the local microenvironment niches. To unbiasedly define the cellular and molecular features of metastatic niches, we developed sortase A-based microenvironment niche tagging (SAMENT), which selectively labels cells encountered by cancer cells during metastasis. Applying SAMENT across multiple cancer models and target organs revealed shared niche features, including macrophage enrichment and T cell depletion, alongside marked organ-specific phenotype heterogeneity in niche macrophages. In bone, metastatic niches are enriched for macrophages expressing estrogen receptor alpha (ERα) with active ERα signaling. Conditional deletion of Esr1 in macrophages significantly impaired bone colonization by enabling T cell infiltration. ERα⁺ macrophages were also identified in human bone metastases across multiple cancer types. Together, these findings define a distinct ERα⁺ macrophage niche and establish macrophage ERα signaling as a key driver of T cell exclusion during metastatic colonization.

Epithelial-to-mesenchymal transition (EMT) is known to play roles in orchestrating cellular plasticity across many physiological and pathological contexts. Partial EMT, wherein cells maintain both epithelial and mesenchymal features, is gaining recognition for its functional importance in cancer in recent years. There are many factors regulating both partial and full EMT, and the precise mechanisms underlying these processes vary depending on the biological context. Furthermore, how different EMT states cooperate to create a heterogeneous tumor population and promote different pro-malignant features remains largely undefined. In a recent study published in Nature Cancer, Youssef and colleagues described how two disparate EMT programs, active in either organ fibrosis or embryonic development, are utilized within different cells within the same murine mammary tumor model. This work provides mechanistic insight into the development of intratumoral heterogeneity, providing evidence for the cooperation between the two EMT trajectories.

Aldehyde dehydrogenase 1a3 (ALDH1A3) activity is recognized as a pathogenic trait in cardiometabolic diseases and cancer, though the mechanisms by which ALDH1A3 promotes disease are unclear and effective therapeutic inhibitors of ALDH1A3 are lacking. Whereas the function of the ALDH1A enzymes in development is the conversion of retinaldehyde into all- retinoic acid (atRA) to activate retinoid nuclear receptor signaling, this pathway is paradoxically hypothesized as a cell-intrinsic tumor suppressor pathway. We resolve this paradox by showing that while ALDH1A3 is overexpressed across diverse cancers, ALDH1A3-expressing tumor cells lose sensitivity to retinoid signaling. Instead, atRA produced by ALDH1A3 acts in a paracrine fashion to activate retinoid nuclear receptor signaling in immune cells to suppress anti-tumor immunity. To inhibit ALDH1A3, we developed a hybrid and high-throughput screening approach followed by medicinal optimization to identify first-in-class, oral and safe antagonists of ALDH1A3 with potent anti-tumor immunotherapeutic activity and an optimized drug development profile.

Bone marrow is both a primary site for hematopoiesis and a fertile niche for metastasis. The mechanism of the common occurrence of anemia among patients with bone metastasis remains poorly understood. Here, we show that a specialized population of VCAM1CD163CCR3 macrophages, normally essential for erythropoiesis by transporting iron to erythroblasts, are highly enriched in the bone metastatic niche in mouse models. Tumor cells hijack these macrophages for iron supply, reducing iron availability for erythroblasts, impairing erythropoiesis, and contributing to anemia. Increased iron supply enables tumor cells to produce hemoglobin in response to hypoxia, mimicking erythroblasts. We identify macrophages with similar iron-transporting features in human bone metastases and show that elevated HBB expression correlates with increased risk of bone metastasis. These findings establish iron-transporting macrophages as an essential component of the metastatic bone niche, revealing a critical interplay between immune cells, metal metabolism, and tumor cell plasticity in driving metastasis and anemia.

Cells are compartmentalized into different organelles to ensure precise spatial temporal control and efficient operation of cellular processes. Membraneless organelles, also known as biomolecular condensates, are emerging as previously underappreciated ways of organizing cellular functions. Condensates allow local concentration of protein, RNA, or DNA molecules with shared functions, thus facilitating spatiotemporal control of biochemical reactions spanning a range of cellular processes. Studies discussed herein have shown that aberrant formation of condensates is associated with various diseases such as cancers. Here, we summarize how condensates mechanistically contribute to malignancy-related cellular processes, including genomic instability, epigenetic rewiring, oncogenic transcriptional activation, and signaling. An improved understanding of condensate formation and dissolution will enable development of new cancer therapies. Finally, we address the remaining challenges in the field and suggest future efforts to better integrate condensates into cancer research.

Cancer evolves through dynamic exchanges with its environment, harnessing these interactions to grow, adapt, and transcend the constraints that would otherwise limit its progress. A new collection of articles explores this tumor-environment crosstalk across temporal and spatial scales.

Tumor-initiating cells (TICs) share features and regulatory pathways with normal stem cells, yet how the stem cell niche contributes to tumorigenesis remains unclear. Here, we identify CXCR4 macrophages as a niche population enriched in normal mammary ducts, where they promote the regenerative activity of basal cells in response to luminal cell-derived CXCL12. CXCL12 triggers AKT-mediated stabilization of β-catenin, which induces Wnt ligands and pro-migratory genes, enabling intraductal macrophage infiltration and supporting regenerative activity of basal cells. Notably, these same CXCR4 niche macrophages regulate the tumor-initiating activity of various breast cancer subtypes by enhancing TIC survival and tumor-forming capacity, while promoting early immune evasion through regulatory T cell induction. Furthermore, a CXCR4 niche macrophage gene signature correlates with poor prognosis in human breast cancer. These findings highlight the pivotal role of the CXCL12-CXCR4 axis in orchestrating interactions between niche macrophages, mammary epithelial cells, and immune cells, thereby establishing a supportive niche for both normal tissue regeneration and mammary tumor initiation.

UNLABELLED: Immune checkpoint blockade (ICB) has transformed cancer treatment, but success rates remain limited. Recent research suggests that dietary fiber enhances ICB efficacy through microbiome-dependent mechanisms. However, prior studies in mice compared grain-based chow (high fiber) with low-fiber-purified diet, but these diets also differed in other dimensions, including phytochemicals. Therefore, further work is needed to establish the robustness of the effect of fiber on ICB across cancer types and dietary contexts. In this study, we investigated gut microbiome composition, metabolite levels, and ICB activity in mice fed with grain-based chow or purified diets with differing quantities of isolated fibers (cellulose and inulin). Compared with dietary fiber content, consumption of chow versus purified diet had a greater effect on the gut microbiome and a much stronger impact on the metabolome. Studies in multiple tumor models revealed that fiber has a weaker impact on ICB (anti-PD-1) efficacy than previously reported. Although diet affected ICB in some models, the effect was not directionally consistent. None of the models tested displayed the pattern expected if fiber controlled ICB efficacy: strong efficacy in both chow and high-fiber-purified diet but low efficacy in low-fiber-prified diet. Thus, dietary fiber seems to have limited or inconsistent effects on ICB efficacy in mouse models, and other dietary factors that correlate with fiber intake may underlie clinical correlations between fiber consumption and immunotherapy efficacy.

SIGNIFICANCE: Clinical associations between high-fiber diets and improved immunotherapy efficacy may be driven by dietary factors correlated with fiber intake rather than fiber itself, which could impact dietary recommendations for patients undergoing immunotherapy.

Phosphatidylinositol 3-kinase (PI3K) signaling is both the effector pathway of insulin and among the most frequently activated pathways in human cancer. In murine cancer models, the efficacy of PI3K inhibitors is dramatically enhanced by a ketogenic diet, with a proposed mechanism involving dietary suppression of insulin. Here, we confirm profound diet-PI3K anticancer synergy but show that it is, surprisingly, unrelated to diet macronutrient composition. Instead, the diet-PI3K interaction involves microbiome metabolism of ingested phytochemicals. Specifically, murine ketogenic diet lacks the complex spectrum of phytochemicals found in standard chow, including the soy phytochemicals soyasaponins. We find that soyasaponins are converted by the microbiome into inducers of hepatic cytochrome P450 enzymes, and thereby lower PI3K inhibitor blood levels and anticancer activity. A high-carbohydrate, low-phytochemical diet synergizes with PI3K inhibition to treat cancer in mice, as do antibiotics that curtail the gut microbiome. Thus, diet impacts anticancer drug activity through phytochemical-microbiome-liver interactions.

Cancer stem cells (CSCs) often exhibit stem-like attributes that depend on an intricate stemness-promoting cellular ecosystem within their niche. The interplay between CSCs and their niche has been implicated in tumor heterogeneity and therapeutic resistance. Normal stem cells (NSCs) and CSCs share stemness features and common microenvironmental components, displaying significant phenotypic and functional plasticity. Investigating these properties across diverse organs during normal development and tumorigenesis is of paramount research interest and translational potential. Advancements in next-generation sequencing (NGS), single-cell transcriptomics, and spatial transcriptomics have ushered in a new era in cancer research, providing high-resolution and comprehensive molecular maps of diseased tissues. Various spatial technologies, with their unique ability to measure the location and molecular profile of a cell within tissue, have enabled studies on intratumoral architecture and cellular cross-talk within the specific niches. Moreover, delineation of spatial patterns for niche-specific properties such as hypoxia, glucose deprivation, and other microenvironmental remodeling are revealed through multilevel spatial sequencing. This tremendous progress in technology has also been paired with the advent of computational tools to mitigate technology-specific bottlenecks. Here we discuss how different spatial technologies are used to identify NSCs and CSCs, as well as their associated niches. Additionally, by exploring related public data sets, we review the current challenges in characterizing such niches, which are often hindered by technological limitations, and the computational solutions used to address them.

Triple-negative breast cancer (TNBC) is the most challenging subtype of the disease due to its aggressive nature and lack of targeted therapy options. To identify regulators of TNBC, we conducted a genome-wide CRISPR knockout screen in both three-dimensional (3D) tumor spheroid and two-dimensional cell culture models. The 3D spheroid model displayed unique potential in identifying putative tumor suppressors because of its closer mimicry of in vivo tumor growth conditions. Notably, the chromatin remodeling SWI/SNF complex emerged as a potent suppressor of tumor spheroid growth. Specifically, loss of the SWI/SNF ATPase subunit SMARCA4 promoted tumor spheroid growth with reduced compactness and enhanced primary tumor growth and metastasis across multiple TNBC models. SMARCA4 was required for the transcription of the Rho GTPase-activating factor ARHGAP29 by enhancing DNA accessibility through direct binding to its promoter. SMARCA4 loss resulted in reduced ARHGAP29 levels and hyperactive RHOA signaling, subsequently disrupting cell adhesion, facilitating the formation of a loose spheroid structure in vitro, and enhancing breast cancer growth and metastasis in vivo. These results establish SMARCA4 and SWI/SNF as tumor suppressors of TNBC through suppression of RHOA activity. Significance: CRISPR-knockout screen in 3D tumor spheroid revealed that SMARCA4, a SWI/SNF ATPase subunit, suppresses triple-negative breast cancer growth and metastasis by increasing ARHGAP29 transcription and inhibiting the RHOA signaling pathway.

Immune checkpoint blockade (ICB) therapy, which has revolutionized cancer treatment, has been approved for the treatment of triple-negative breast cancer (TNBC). Unfortunately, most patients with TNBC are either not eligible for treatment or exhibit resistance, resulting in limited overall survival benefits. There is an urgent need to elucidate the mechanisms of resistance and enhance therapeutic efficacy. Here, via CRISPR activation (CRISPRa) screening, we identified family with sequence similarity 114 member A1 (FAM114A1) as a key mediator of immune evasion and ICB resistance in TNBC. Mechanistically, FAM114A1 binds p85α to disrupt the p85α/p110α protein complex, thus activating the PI3K/AKT pathway and simultaneously preventing condensate formation of E2F Transcription Factor 4 (E2F4) to promote E2F4-driven Metadherin (MTDH) transcription. Upregulation of these FAM114A1-mediated pathways suppresses tumor antigen presentation and consequently attenuates antitumor immunity in TNBC. Moreover, targeting FAM114A1 improves the therapeutic effectiveness of anti-PD-1 therapy in mouse models, and a FAM114A1-based signature shows strong predictive performance for identifying patients with TNBC who may benefit from ICB. Collectively, our findings not only reveal that FAM114A1 is an immune evasion driver but also highlight it as a promising biomarker and therapeutic target. Our study provides new insights into TNBC immune evasion and outlines a potential avenue to improve the effectiveness of ICB.

Recent evidence has revealed that cancer is not solely driven by genetic abnormalities but also by significant metabolic dysregulation. Cancer cells exhibit altered metabolic demands and rewiring of cellular metabolism to sustain their malignant characteristics. Metabolic reprogramming has emerged as a hallmark of cancer, playing a complex role in breast cancer initiation, progression, and metastasis. The different molecular subtypes of breast cancer exhibit distinct metabolic genotypes and phenotypes, offering opportunities for subtype-specific therapeutic approaches. Cancer-associated metabolic phenotypes encompass dysregulated nutrient uptake, opportunistic nutrient acquisition strategies, altered utilization of glycolysis and TCA cycle intermediates, increased nitrogen demand, metabolite-driven gene regulation, and metabolic interactions with the microenvironment. The tumor microenvironment, consisting of stromal cells, immune cells, blood vessels, and extracellular matrix components, influences metabolic adaptations through modulating nutrient availability, oxygen levels, and signaling pathways. Metastasis, the process of cancer spread, involves intricate steps that present unique metabolic challenges at each stage. Successful metastasis requires cancer cells to navigate varying nutrient and oxygen availability, endure oxidative stress, and adapt their metabolic processes accordingly. The metabolic reprogramming observed in breast cancer is regulated by oncogenes, tumor suppressor genes, and signaling pathways that integrate cellular signaling with metabolic processes. Understanding the metabolic adaptations associated with metastasis holds promise for identifying therapeutic targets to disrupt the metastatic process and improve patient outcomes. This chapter explores the metabolic alterations linked to breast cancer metastasis and highlights the potential for targeted interventions in this context.

Epithelial-to-mesenchymal transition (EMT), a biological phenomenon of cellular plasticity initially reported in embryonic development, has been increasingly recognized for its importance in cancer progression and metastasis. Despite tremendous progress being made in the past 2 decades in our understanding of the molecular mechanism and functional importance of EMT in cancer, there are several mysteries around EMT that remain unresolved. In this Unsolved Mystery, we focus on the variety of EMT types in metastasis, cooperative and collective EMT behaviors, spatiotemporal characterization of EMT, and strategies of therapeutically targeting EMT. We also highlight new technical advances that will facilitate the efforts to elucidate the unsolved mysteries of EMT in metastasis.

Triple-negative breast cancer is one of the most prevalent malignant cancers worldwide. Disrupting the MTDH-SND1 protein-protein interaction has recently been shown to be a promising strategy for breast cancer therapy. In this work, a novel potent stabilized peptide with a stronger binding affinity was obtained through rational structure-based optimization. Furthermore, a sulfonium-based peptide delivery system was established to improve the cell penetration and antitumor effects of stabilized peptides in metastatic breast cancer. Our study further broadens the in vivo applications of the stabilized peptides for blocking MTDH-SND1 interaction and provides promising opportunities for breast cancer therapy.

The retinoid nuclear receptor pathway, activated by the vitamin A metabolite retinoic acid, has been extensively investigated for over a century. This study has resulted in conflicting hypotheses about how the pathway regulates health and how it should be pharmaceutically manipulated. These disagreements arise from a fundamental contradiction: retinoid agonists offer clear benefits to select patients with rare bone growth disorders, acute promyelocytic leukemia, and some dermatologic diseases, yet therapeutic retinoid pathway activation frequently causes more harm than good, both through acute metabolic dysregulation and a delayed cancer-promoting effect. In this review, we discuss controlled clinical, mechanistic, and genetic data to suggest several disease settings where inhibition of the retinoid pathway may be a compelling therapeutic strategy, such as solid cancers or metabolic syndromes, and also caution against continued testing of retinoid agonists in cancer patients. Considerable evidence suggests a central role for retinoid regulation of immunity and metabolism, with therapeutic opportunities to antagonize retinoid signaling proposed in cancer, diabetes, and obesity.

Metastasis is a major contributor to cancer patient mortality. Tumour cells often develop phenotypic plasticity to successfully metastasize to different target organs. Recent progress in the study of bone metastasis has provided novel insight into the biological processes that drive the spread and growth of cancer cells in the bone. In this review, we provide a summary of how the bone marrow microenvironment promotes phenotypic plasticity of metastatic tumour cells and alters therapeutic responses. We highlight pivotal transformations in cellular status driven by plasticity, including mesenchymal-epithelial transition, acquisition of stem-like traits, and awakening from dormancy. Additionally, we describe the phenomenon of host-organ mimicry and metabolic rewiring that collectively serve as key attributes of disseminated tumour cells, enabling their successful colonization and growth within the bone marrow microenvironment.

Dysregulation of lipid metabolism is a key characteristic of the tumor microenvironment, where tumor cells utilize lipids for proliferation, survival, metastasis, and evasion of immune surveillance. Lipid metabolism has become a critical regulator of CD8+ T-cell-mediated antitumor immunity, with excess lipids in the tumor microenvironment impeding CD8+ T-cell activities. Considering the limited efficacy of immunotherapy in many solid tumors, targeting lipid metabolism to enhance CD8+ T-cell effector functions could significantly improve immunotherapy outcomes. In this review, we examine recent findings on how lipid metabolic processes, including lipid uptake, synthesis, and oxidation, regulate CD8+ T cells within tumors. We also assessed the impact of different lipids on CD8+ T-cell-mediated antitumor immunity, with a particular focus on how lipid metabolism affects mitochondrial function in tumor-infiltrating CD8+ T cells. Furthermore, as cancer is a systemic disease, we examined systemic factors linking lipid metabolism to CD8+ T-cell effector function. Finally, we summarize current therapeutic approaches that target lipid metabolism to increase antitumor immunity and enhance immunotherapy. Understanding the molecular and functional interplay between lipid metabolism and CD8+ T cells offers promising therapeutic opportunities for cancer treatment.

Tissues derive ATP from two pathways-glycolysis and the tricarboxylic acid (TCA) cycle coupled to the electron transport chain. Most energy in mammals is produced via TCA metabolism. In tumours, however, the absolute rates of these pathways remain unclear. Here we optimize tracer infusion approaches to measure the rates of glycolysis and the TCA cycle in healthy mouse tissues, Kras-mutant solid tumours, metastases and leukaemia. Then, given the rates of these two pathways, we calculate total ATP synthesis rates. We find that TCA cycle flux is suppressed in all five primary solid tumour models examined and is increased in lung metastases of breast cancer relative to primary orthotopic tumours. As expected, glycolysis flux is increased in tumours compared with healthy tissues (the Warburg effect), but this increase is insufficient to compensate for low TCA flux in terms of ATP production. Thus, instead of being hypermetabolic, as commonly assumed, solid tumours generally produce ATP at a slower than normal rate. In mouse pancreatic cancer, this is accommodated by the downregulation of protein synthesis, one of this tissue's major energy costs. We propose that, as solid tumours develop, cancer cells shed energetically expensive tissue-specific functions, enabling uncontrolled growth despite a limited ability to produce ATP.

Cancer metastasis, or the development of secondary tumors in distant tissues, accounts for the vast majority of fatalities in patients with breast cancer. Breast cancer cells show a striking proclivity to metastasize to distinct organs, specifically the lung, liver, bone, and brain, where they face unique environmental pressures and a wide variety of tissue-resident cells that together create a strong barrier for tumor survival and growth. As a consequence, successful metastatic colonization is critically dependent on reciprocal cross talk between cancer cells and host cells within the target organ, a relationship that shapes the formation of a tumor-supportive microenvironment. Here, we discuss the mechanisms governing organ-specific metastasis in breast cancer, focusing on the intricate interactions between metastatic cells and specific niche cells within a secondary organ, and the remarkable adaptations of both compartments that cooperatively support cancer growth. More broadly, we aim to provide a framework for the microenvironmental prerequisites within each distinct metastatic site for successful breast cancer metastatic seeding and outgrowth.

Development of cancer therapeutics has traditionally focused on targeting driver oncogenes. Such an approach is limited by toxicity to normal tissues and treatment resistance. A class of 'cancer fitness genes' with crucial roles in metastasis have been identified. Elevated or altered activities of these genes do not directly cause cancer; instead, they relieve the stresses that tumor cells encounter and help them adapt to a changing microenvironment, thus facilitating tumor progression and metastasis. Importantly, as normal cells do not experience high levels of stress under physiological conditions, targeting cancer fitness genes is less likely to cause toxicity to noncancerous tissues. Here, we summarize the key features and function of cancer fitness genes and discuss their therapeutic potential.

Type 2 diabetes (T2D) is associated with β-cell dedifferentiation. Aldehyde dehydrogenase 1 isoform A3 (ALHD1A3) is a marker of β-cell dedifferentiation and correlates with T2D progression. However, it is unknown whether ALDH1A3 activity contributes to β-cell failure, and whether the decrease of ALDH1A3-positive β-cells (A+) following pair-feeding of diabetic animals is due to β-cell restoration. To tackle these questions, we (i) investigated the fate of A+ cells during pair-feeding by lineage-tracing, (ii) somatically ablated ALDH1A3 in diabetic β-cells, and (iii) used a novel selective ALDH1A3 inhibitor to treat diabetes. Lineage tracing and functional characterization show that A+ cells can be reconverted to functional, mature β-cells. Genetic or pharmacological inhibition of ALDH1A3 in diabetic mice lowers glycemia and increases insulin secretion. Characterization of β-cells following ALDH1A3 inhibition shows reactivation of differentiation as well as regeneration pathways. We conclude that ALDH1A3 inhibition offers a therapeutic strategy against β-cell dysfunction in diabetes.

The SOX9 transcription factor ensures proper tissue development and homeostasis and has been implicated in promoting tumor progression. However, the role of SOX9 as a driver of lung adenocarcinoma (LUAD), or any cancer, remains unclear. Using CRISPR/Cas9 and Cre-LoxP gene knockout approaches in the Kras-driven mouse LUAD model, we found that loss of Sox9 significantly reduces lung tumor development, burden and progression, contributing to significantly longer overall survival. SOX9 consistently drove organoid growth in vitro, but SOX9-promoted tumor growth was significantly attenuated in immunocompromised mice compared to syngeneic mice. We demonstrate that SOX9 suppresses immune cell infiltration and functionally suppresses tumor associated CD8 T, natural killer and dendritic cells. These data were validated by flow cytometry, gene expression, RT-qPCR, and immunohistochemistry analyses in Kras-driven murine LUAD, then confirmed by interrogating bulk and single-cell gene expression repertoires and immunohistochemistry in human LUAD. Notably, SOX9 significantly elevates collagen-related gene expression and substantially increases collagen fibers. We propose that SOX9 increases tumor stiffness and inhibits tumor-infiltrating dendritic cells, thereby suppressing CD8 T cell and NK cell infiltration and activity. Thus, SOX9 drives Kras-driven lung tumor progression and inhibits anti-tumor immunity at least partly by modulating the tumor microenvironment.

Metastasis is responsible for a large majority of death from malignant solid tumors. Bone is one of the most frequently affected organs in cancer metastasis, especially in breast and prostate cancer. Development of bone metastasis requires cancer cells to successfully complete a number of challenging steps, including local invasion and intravasation, survival in circulation, extravasation and initial seeding, and finally, formation of metastatic colonies after a period of dormancy or indolent growth. During this process, cancer cells often undergo a series of cellular and molecular changes to gain cellular plasticity that helps them adapt to various environments they encounter along the journey of metastasis. Understanding the mechanisms behind cellular plasticity and adaptation during the formation of bone metastasis is crucial for the development of novel therapies.

Immune checkpoint inhibitor (ICI) therapy is generating remarkable responses in individuals with cancer, but only a small portion of individuals with breast cancer respond well. Here we report that tumor-derived Jagged1 is a key regulator of the tumor immune microenvironment. Jagged1 promotes tumorigenesis in multiple spontaneous mammary tumor models. Through Jagged1-induced Notch activation, tumor cells increase expression and secretion of multiple cytokines to help recruit macrophages into the tumor microenvironment. Educated macrophages crosstalk with tumor-infiltrating T cells to inhibit T cell proliferation and tumoricidal activity. In individuals with triple-negative breast cancer, a high expression level of Jagged1 correlates with increased macrophage infiltration and decreased T cell activity. Co-administration of an ICI PD-1 antibody with a Notch inhibitor significantly inhibits tumor growth in breast cancer models. Our findings establish a distinct signaling cascade by which Jagged1 promotes adaptive immune evasion of tumor cells and provide several possible therapeutic targets.

Ligand-dependent corepressor (LCOR) mediates normal and malignant breast stem cell differentiation. Cancer stem cells (CSCs) generate phenotypic heterogeneity and drive therapy resistance, yet their role in immunotherapy is poorly understood. Here we show that immune-checkpoint blockade (ICB) therapy selects for LCOR CSCs with reduced antigen processing/presentation machinery (APM) driving immune escape and ICB resistance in triple-negative breast cancer (TNBC). We unveil an unexpected function of LCOR as a master transcriptional activator of APM genes binding to IFN-stimulated response elements (ISREs) in an IFN signaling-independent manner. Through genetic modification of LCOR expression, we demonstrate its central role in modulation of tumor immunogenicity and ICB responsiveness. In TNBC, LCOR associates with ICB clinical response. Importantly, extracellular vesicle (EV) Lcor-messenger RNA therapy in combination with anti-PD-L1 overcame resistance and eradicated breast cancer metastasis in preclinical models. Collectively, these data support LCOR as a promising target for enhancement of ICB efficacy in TNBC, by boosting of tumor APM independently of IFN.

Metastatic breast cancer is a leading health burden worldwide. Previous studies have shown that metadherin (MTDH) promotes breast cancer initiation, metastasis and therapy resistance; however, the therapeutic potential of targeting MTDH remains largely unexplored. Here, we used genetically modified mice and demonstrate that genetic ablation of Mtdh inhibits breast cancer development through disrupting the interaction with staphylococcal nuclease domain-containing 1 (SND1), which is required to sustain breast cancer progression in established tumors. We performed a small-molecule compound screening to identify a class of specific inhibitors that disrupts the protein-protein interaction (PPI) between MTDH and SND1 and show that our lead candidate compounds C26-A2 and C26-A6 suppressed tumor growth and metastasis and enhanced chemotherapy sensitivity in preclinical models of triple-negative breast cancer (TNBC). Our results demonstrate a significant therapeutic potential in targeting the MTDH-SND1 complex and identify a new class of therapeutic agents for metastatic breast cancer.

Despite increased overall survival rates, curative options for metastatic breast cancer remain limited. We have previously shown that metadherin (MTDH) is frequently overexpressed in poor prognosis breast cancer, where it promotes metastasis and therapy resistance through its interaction with staphylococcal nuclease domain-containing 1 (SND1). Through genetic and pharmacological targeting of the MTDH-SND1 interaction, we reveal a key role for this complex in suppressing antitumor T cell responses in breast cancer. The MTDH-SND1 complex reduces tumor antigen presentation and inhibits T cell infiltration and activation by binding to and destabilizing Tap1/2 messenger RNAs, which encode key components of the antigen-presentation machinery. Following small-molecule compound C26-A6 treatment to disrupt the MTDH-SND1 complex, we showed enhanced immune surveillance and sensitivity to anti-programmed cell death protein 1 therapy in preclinical models of metastatic breast cancer, in support of this combination therapy as a viable approach to increase immune-checkpoint blockade therapy responses in metastatic breast cancer.

Immunotherapy has limited success in triple-negative breast cancer (TNBC). In this issue of Cell Metabolism, Wang et al. found that microbial metabolite TMAO boosts CD8 T cell-mediated antitumor immunity by inducing pyroptosis in tumor cells, enhancing the efficacy of immunotherapy in TNBC (Wang et al., 2022).

The bone marrow has been widely recognised to host a unique microenvironment that facilitates tumour colonisation. Bone metastasis frequently occurs in the late stages of malignant diseases such as breast, prostate and lung cancers. The biology of bone metastasis is determined by tumour-cell-intrinsic traits as well as their interaction with the microenvironment. The bone marrow is a dynamic organ in which various stages of haematopoiesis, osteogenesis, osteolysis and different kinds of immune response are precisely regulated. These different cellular components constitute specialised tissue microenvironments-niches-that play critical roles in controlling tumour cell colonisation, including initial seeding, dormancy and outgrowth. In this review, we will dissect the dynamic nature of the interactions between tumour cells and bone niches. By targeting certain steps of tumour progression and crosstalk with the bone niches, the development of potential therapeutic approaches for the clinical treatment of bone metastasis might be feasible.

The systemic spread of tumor cells is the ultimate cause of the majority of deaths from cancer, yet few successful therapeutic strategies have emerged to specifically target metastasis. Here we discuss recent advances in our understanding of tumor-intrinsic pathways driving metastatic colonization and therapeutic resistance, as well as immune activating strategies to target metastatic disease. We focus on therapeutically exploitable mechanisms, promising strategies in preclinical and clinical development, and emerging areas with potential to become innovative treatments.

The complexity of intracellular signalling requires both a diversity of molecular players and the sequestration of activity to unique compartments within the cell. Recent findings on the role of liquid-liquid phase separation provide a distinct mechanism for the spatial segregation of proteins to regulate signalling pathway crosstalk. Here, we discover that DACT1 is induced by TGFβ and forms protein condensates in the cytoplasm to repress Wnt signalling. These condensates do not localize to any known organelles but, rather, exist as phase-separated proteinaceous cytoplasmic bodies. The deletion of intrinsically disordered domains within the DACT1 protein eliminates its ability to both form protein condensates and suppress Wnt signalling. Isolation and mass spectrometry analysis of these particles revealed a complex of protein machinery that sequesters casein kinase 2-a Wnt pathway activator. We further demonstrate that DACT1 condensates are maintained in vivo and that DACT1 is critical to breast and prostate cancer bone metastasis.

Loss of E-cadherin expression has been well known as a hallmark of epithelial-mesenchymal transition (EMT), which is linked to increased risk of cancer metastasis. However, it was less clear whether E-cadherin and its downstream signaling pathways are functionally involved in driving EMT and the prometastatic phenotype. A study by Onder and colleagues in 2008 discovered that E-cadherin loss not only helps tumor cells detach from each other by breaking down cell-cell junctions but also elicits intracellular signaling events to confer a mesenchymal cell state and metastatic phenotype. This study established E-cadherin as an important global regulator, rather than just a marker, of EMT. The discovery inspired further investigation in the following decade that significantly deepened our understanding of E-cadherin and its diverse functions and more broadly of cellular plasticity in different stages and contexts of cancer metastasis..

Selective pressure and signals from the tissue microenvironment drive metastasis and determine the survival of metastatic tumor cells at distant organs. Zhang et al. and Bado et al. apply CRISPR-mediated evolving barcode technology to elucidate the role of the bone microenvironment in the evolution of breast cancer metastasis.

Development of chemoresistance in breast cancer patients greatly increases mortality. Thus, understanding mechanisms underlying breast cancer resistance to chemotherapy is of paramount importance to overcome this clinical challenge. Although activated Notch receptors have been associated with chemoresistance in cancer, the specific Notch ligands and their molecular mechanisms leading to chemoresistance in breast cancer remain elusive. Using conditional knockout and reporter mouse models, we demonstrate that tumor cells expressing the Notch ligand Dll1 is important for tumor growth and metastasis and bear similarities to tumor-initiating cancer cells (TICs) in breast cancer. RNA-seq and ATAC-seq using reporter models and patient data demonstrated that NF-κB activation is downstream of Dll1 and is associated with a chemoresistant phenotype. Finally, pharmacological blocking of Dll1 or NF-κB pathway completely sensitizes Dll1 tumors to chemotherapy, highlighting therapeutic avenues for chemotherapy resistant breast cancer patients in the near future.

Combining single-cell lineage tracing with RNA sequencing has provided unprecedented opportunities to prospectively explore metastatic dynamics in vivo. In this issue of Cancer Cell, Simeonov et al. developed the macsGESTALT lineage recording system to reveal that hybrid EMT states and S100 expression are associated with elevated metastatic abilities in a pancreatic cancer model.

Colorectal and lung cancers account for one-third of all cancer-related deaths worldwide. Previous studies suggested that metadherin (MTDH) is involved in the development of colorectal and lung cancers. However, how MTDH regulates the pathogenesis of these cancers remains largely unknown. Using genetically modified mouse models of spontaneous colorectal and lung cancers, we found that MTDH promotes cancer progression by facilitating Wnt activation and by inducing cytotoxic T-cell exhaustion, respectively. Moreover, we developed locked nucleic acid-modified (LNA) MTDH antisense oligonucleotides (ASO) that effectively and specifically suppress MTDH expression and . Treatments with MTDH ASOs in mouse models significantly attenuated progression and metastasis of colorectal, lung, and breast cancers. Our study opens a new avenue for developing therapies against colorectal and lung cancers by targeting MTDH using LNA-modified ASO. SIGNIFICANCE: This study provides new insights into the mechanism of MTDH in promoting colorectal and lung cancers, as well as genetic and pharmacologic evidence supporting the development of MTDH-targeting therapeutics.

Estrogen receptor-negative (ER-negative) breast cancer is thought to be more malignant and devastating than ER-positive breast cancer. ER-negative breast cancer exhibits elevated NF-κB activity, but how this abnormally high NF-κB activity is maintained is poorly understood. The importance of linear ubiquitination, which is generated by the linear ubiquitin chain assembly complex (LUBAC), is increasingly appreciated in NF-κB signaling, which regulates cell activation and death. Here, we showed that epsin proteins, a family of ubiquitin-binding endocytic adaptors, interacted with LUBAC via its ubiquitin-interacting motif and bound LUBAC's bona fide substrate NEMO via its N-terminal homolog (ENTH) domain. Furthermore, epsins promoted NF-κB essential modulator (NEMO) linear ubiquitination and served as scaffolds for recruiting other components of the IκB kinase (IKK) complex, resulting in the heightened IKK activation and sustained NF-κB signaling essential for the development of ER-negative breast cancer. Heightened epsin levels in ER-negative human breast cancer are associated with poor relapse-free survival. We showed that transgenic and pharmacological approaches eliminating epsins potently impeded breast cancer development in both spontaneous and patient-derived xenograft breast cancer mouse models. Our findings established the pivotal role epsins played in promoting breast cancer. Thus, targeting epsins may represent a strategy to restrain NF-κB signaling and provide an important perspective into ER-negative breast cancer treatment.

Bone is one of the most preferred sites of metastatic spread from different cancer types, including breast cancer. However, different breast cancer subtypes exhibit distinct metastatic behavior in terms of kinetics and anatomic sites of relapse. Despite advances in the diagnosis, the identification of patients at high-risk of bone recurrence is still an unmet clinical need. We conducted a retrospective analysis, by gene expression and immunohistochemical assays, on 90 surgically resected breast cancer samples collected from patients who experienced no evidence of distant metastasis, bone or visceral metastasis in order to identify a primary tumor-derived marker of bone recurrence. We identified trefoil factor-1 (pS2 or TFF1) as strictly correlated to bone metastasis from ER+ breast cancer. In silico analysis was carried out to confirm this observation, linking gene expression data with clinical characteristics available from public clinical datasets. Then, we investigated TFF1 function in ER+ breast cancer tumorigenesis and bone metastasis through xenograft in vivo models of MCF 7 breast cancer with gain and loss of function of TFF1. As a response to microenvironmental features in primary tumors, TFF1 expression could modulate ER+ breast cancer growth, leading to a less proliferative phenotype. Our results showed it may not play a role in late stages of bone metastasis, however further studies are warranted to understand whether it could contribute in the early-stages of the metastatic cascade. In conclusion, TFF1 upregulation in primary ER+ breast cancer could be useful to identify patients at high-risk of bone metastasis. This could help clinicians in the identification of patients who likely can develop bone metastasis and who could benefit from personalized treatments and follow-up strategies to prevent metastatic disease.

Transcription factor SNAI2 plays key roles during development and has also been known to promote metastasis by inducing invasive phenotype and tumor-initiating activity of cancer cells. However, the post-translational regulation of SNAI2 is less well studied. We performed a dual-luciferase-based, genome-wide E3 ligase siRNA library screen and identified ASB13 as an E3 ubiquitin ligase that targets SNAI2 for ubiquitination and degradation. ASB13 knockout in breast cancer cells promoted cell migration and decreased F-actin polymerization, while overexpression of ASB13 suppressed lung metastasis. Furthermore, ASB13 knockout decreased YAP expression, and such regulation is dependent on an increased protein level of SNAI2, which in turn represses YAP transcription. YAP suppresses tumor progression in breast cancer, as YAP knockout increases tumorsphere formation, anchorage-independent colony formation, cell migration in vitro, and lung metastasis in vivo. Clinical data analysis reveals that ASB13 expression is positively correlated with improved overall survival in breast cancer patients. These findings establish ASB13 as a suppressor of breast cancer metastasis by promoting degradation of SNAI2 and relieving its transcriptional repression of YAP.

The enzyme glucose-6-phosphate dehydrogenase (G6PD) is a major contributor to NADPH production and redox homeostasis and its expression is upregulated and correlated with negative patient outcomes in multiple human cancer types. Despite these associations, whether G6PD is essential for tumor initiation, growth, or metastasis remains unclear. Here, we employ modern genetic tools to evaluate the role of G6PD in lung, breast, and colon cancer driven by oncogenic K-Ras. Human HCT116 colorectal cancer cells lacking G6PD exhibited metabolic indicators of oxidative stress, but developed into subcutaneous xenografts with growth comparable with that of wild-type controls. In a genetically engineered mouse model of non-small cell lung cancer driven by K-Ras G12D and p53 deficiency, G6PD knockout did not block formation or proliferation of primary lung tumors. In MDA-MB-231-derived human triple-negative breast cancer cells implanted as orthotopic xenografts, loss of G6PD modestly decreased primary site growth without ablating spontaneous metastasis to the lung and moderately impaired the ability of breast cancer cells to colonize the lung when delivered via tail vein injection. Thus, in the studied K-Ras tumor models, G6PD was not strictly essential for tumorigenesis and at most modestly promoted disease progression. SIGNIFICANCE: K-Ras-driven tumors can grow and metastasize even in the absence of the oxidative pentose pathway, a main NADPH production route.

There is an unmet clinical need for improved tissue and liquid biopsy tools for cancer detection. We investigated the proteomic profile of extracellular vesicles and particles (EVPs) in 426 human samples from tissue explants (TEs), plasma, and other bodily fluids. Among traditional exosome markers, CD9, HSPA8, ALIX, and HSP90AB1 represent pan-EVP markers, while ACTB, MSN, and RAP1B are novel pan-EVP markers. To confirm that EVPs are ideal diagnostic tools, we analyzed proteomes of TE- (n = 151) and plasma-derived (n = 120) EVPs. Comparison of TE EVPs identified proteins (e.g., VCAN, TNC, and THBS2) that distinguish tumors from normal tissues with 90% sensitivity/94% specificity. Machine-learning classification of plasma-derived EVP cargo, including immunoglobulins, revealed 95% sensitivity/90% specificity in detecting cancer. Finally, we defined a panel of tumor-type-specific EVP proteins in TEs and plasma, which can classify tumors of unknown primary origin. Thus, EVP proteins can serve as reliable biomarkers for cancer detection and determining cancer type.

SNAI2/SLUG, a metastasis-promoting transcription factor, is a labile protein that is degraded through the ubiquitin proteasome degradation system. Here, we conducted comprehensive gain- and loss-of-function screens using a human DUB cDNA library of 65 genes and an siRNA library of 98 genes, and identified USP20 as a deubiquitinase (DUB) that regulates SNAI2 ubiquitination and stability. Further investigation of USP20 demonstrated its function in promoting migration, invasion, and metastasis of breast cancer. USP20 positively correlates with SNAI2 protein level in breast tumor samples, and higher USP20 expression is associated with poor prognosis in ER breast cancer patients.