The BET degrader ZBC260 suppresses stemness and tumorigenesis and promotes differentiation in triple-negative breast cancer by disrupting inflammatory signaling.

BACKGROUND: Breast cancer stem cells (BCSCs) are resistant to standard therapies, facilitate tumor dissemination, and contribute to relapse and progression. Super-enhancers are regulators of stemness, and BET proteins, which are critical for super-enhancer function, are a potential therapeutic target. Here, we investigated the effects of BET proteins on the regulation of breast cancer stemness using the pan-BET degrader ZBC260. METHODS: We evaluated the effect of ZBC260 on CSCs in TNBC cell lines. We assessed the effect of ZBC260 on cellular viability and tumor growth and measured its effects on cancer stemness. We used RNA sequencing and stemness index to determine the global transcriptomic changes in CSCs and bulk cells and further validated our findings by qPCR, western blot, and ELISA. RESULTS: ZBC260 potently inhibited TNBC growth both in vitro and in vivo. ZBC260 reduced stemness as measured by cell surface marker expression, ALDH activity, tumorsphere number, and stemness index while increasing differentiated cells. GSEA analysis indicated preferential downregulation of stemness-associated and inflammatory genes by ZBC260 in ALDH+ CSCs. CONCLUSIONS: The BET degrader ZBC260 is an efficient degrader of BET proteins that suppresses tumor progression and decreases CSCs through the downregulation of inflammatory genes and pathways. Our findings support the further development of BET degraders alone and in combination with other therapeutics as CSC targeting agents.

Natural killer cell regulation of breast cancer stem cells mediates metastatic dormancy.

Breast cancer patients with estrogen receptor positive tumors face a constant risk of disease recurrence for the remainder of their lives. Dormant tumor cells residing in tissues such as the bone marrow may generate clinically significant metastases many years after initial diagnosis. Previous studies suggest that dormant cells display "stem like" properties (CSCs), which may be regulated by the immune system. Although many studies have examined tumor cell intrinsic characteristics of dormancy, the role of the immune system in controlling dormancy and its escape is not well understood. This scientific gap is due, in part, to a lack of immunocompetent mouse models of breast cancer dormancy with many studies involving human xenografts in immunodeficient mice. To overcome this limitation, we studied dormancy in immunocompetent, syngeneic mouse breast cancer models. We find that PyMT, Met-1 and D2.0R cell lines contain CSCs that display both short- and long-term metastatic dormancy in vivo, which is dependent on the host immune system. Natural killer cells were key for the metastatic dormancy phenotype observed for D2.0R and the role of NK cells in regulating CSCs was further investigated.Quiescent D2.0R CSC are resistant to NK cytotoxicity, while proliferative D2.0R CSC were sensitive to NK cytotoxicity both in vitro and in vivo. This resistance was mediated, in part, by the expression of Bach1 and Sox2 transcription factors. NK killing was enhanced by the STING agonist MSA-2. Collectively, our findings demonstrate the important role of immune regulation of breast tumor dormancy and highlight the importance of utilizing immunocompetent models to study this phenomenon.

Tumor microenvironment interactions with cancer stem cells in pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer in the United States. Additionally, the low survival rate makes PDAC the third-leading cause of cancer-related mortality in the United States, and it is projected that by 2030, it will become the second-leading cause of cancer mortality. Several biological factors contribute to PDAC aggressiveness, and their understanding will narrow the gap from biology to clinical care of PDAC, leading to earlier diagnoses and the development of better treatment options. In this review, we describe the origins of PDAC highlighting the role of cancer stem cells (CSC). CSC, also known as tumor initiating cells, which exhibit a unique metabolism that allows them to maintain a highly plastic, quiescent, immune- and therapy-evasive state. However, CSCs can exit quiescence during proliferation and differentiation, with the capacity to form tumors while constituting a small population in tumor tissues. Tumorigenesis depends on the interactions between CSCs and other cellular and non-cellular components in the microenvironment. These interactions are fundamental to support CSC stemness and are maintained throughout tumor development and metastasis. PDAC is characterized by a massive desmoplastic reaction, which result from the deposition of high amounts of extracellular matrix components by stromal cells. Here we review how this generates a favorable environment for tumor growth by protecting tumor cells from immune responses and chemotherapy and inducing tumor cell proliferation and migration, leading to metastasis formation ultimately leading to death. We emphasize the interactions between CSCs and the tumor microenvironment leading to metastasis formation and posit that better understanding and targeting of these interactions will improve patient outcomes.

LncRNA XIST regulates breast cancer stem cells by activating proinflammatory IL-6/STAT3 signaling.

Aberrant expression of XIST, a long noncoding RNA (lncRNA) initiating X chromosome inactivation (XCI) in early embryogenesis, is a common feature of breast cancer (BC). However, the roles of post-XCI XIST in breast carcinogenesis remain elusive. Here we identify XIST as a key regulator of breast cancer stem cells (CSCs), which exhibit aldehyde dehydrogenase positive (ALDH+) epithelial- (E) and CD24loCD44hi mesenchymal-like (M) phenotypes. XIST is variably expressed across the spectrum of BC subtypes, and doxycycline (DOX)-inducible knockdown (KD) of XIST markedly inhibits spheroid/colony forming capacity, tumor growth and tumor-initiating potential. This phenotype is attributed to impaired E-CSC in luminal and E- and M-CSC activities in triple-negative (TN) BC. Gene expression profiling unveils that XIST KD most significantly affects cytokine-cytokine receptor interactions, leading to markedly suppressed expression of proinflammatory cytokines IL-6 and IL-8 in ALDH- bulk BC cells. Exogenous IL-6, but not IL-8, rescues the reduced sphere-forming capacity and proportion of ALDH+ E-CSCs in luminal and TN BC upon XIST KD. XIST functions as a nuclear sponge for microRNA let-7a-2-3p to activate IL-6 production from ALDH- bulk BC cells, which acts in a paracrine fashion on ALDH+ E-CSCs that display elevated cell surface IL-6 receptor (IL6R) expression. This promotes CSC self-renewal via STAT3 activation and expression of key CSC factors including c-MYC, KLF4 and SOX9. Together, this study supports a novel role of XIST by derepressing let-7 controlled paracrine IL-6 proinflammatory signaling to promote CSC self-renewal.

Cancer stem cell antigen nanodisc cocktail elicits anti-tumor immune responses in melanoma.

One of the major reasons for poor cancer outcomes is the existence of cancer stem cells (CSCs). CSCs are a small subpopulation of tumor cells that can self-renew, differentiate into the majority of tumor cells, and maintain tumorigenicity. As CSCs are resistant to traditional chemotherapy and radiation, they contribute to metastasis and relapse. Thus, new approaches are needed to target and eliminate CSCs. Here, we sought to target and reduce the frequency of CSCs in melanoma by therapeutic vaccination against CSC-associated transcription factors, such as Sox2 and Nanog, and aldehyde dehydrogenase (ALDH). Toward this goal, we have identified novel immunogenic peptide epitopes derived from CSC-associated Sox2 and Nanog and synthesized synthetic high-density lipoprotein (sHDL) nanodisc vaccine formulated with Sox2, Nanog, and ALDH antigen peptides together with CpG, a Toll-like receptor 9 agonist. Vaccination with nanodiscs containing six CSC antigen peptides elicited robust T cell responses against CSC-associated antigens and promoted intratumoral infiltration of CD8+ T cells, while reducing the frequency of CSCs and CD4+ regulatory T cells within melanoma tumors. Nanodisc vaccination effectively reduced tumor growth and significantly extended animal survival without toxicity toward normal stem cells. Overall, our therapeutic strategy against CSCs represents a cost-effective, safe, and versatile approach that may be applied to melanoma and other cancer types, as well as serve as a critical component in combined therapies to target and eliminate CSCs.

p53 Inhibits Bmi-1-driven Self-Renewal and Defines Salivary Gland Cancer Stemness.

PURPOSE: Mucoepidermoid carcinoma (MEC) is a poorly understood salivary gland malignancy with limited therapeutic options. Cancer stem cells (CSC) are considered drivers of cancer progression by mediating tumor recurrence and metastasis. We have shown that clinically relevant small molecule inhibitors of MDM2-p53 interaction activate p53 signaling and reduce the fraction of CSC in MEC. Here we examined the functional role of p53 in the plasticity and self-renewal of MEC CSC. EXPERIMENTAL DESIGN: Using gene silencing and therapeutic activation of p53, we analyzed the cell-cycle profiles and apoptosis levels of CSCs in MEC cell lines (UM-HMC-1, -3A, -3B) via flow cytometry and looked at the effects on survival/self-renewal of the CSCs through sphere assays. We evaluated the effect of p53 on tumor development (N = 51) and disease recurrence (N = 17) using in vivo subcutaneous and orthotopic murine models of MEC. Recurrence was followed for 250 days after tumor resection. RESULTS: Although p53 activation does not induce MEC CSC apoptosis, it reduces stemness properties such as self-renewal by regulating Bmi-1 expression and driving CSC towards differentiation. In contrast, downregulation of p53 causes expansion of the CSC population while promoting tumor growth. Remarkably, therapeutic activation of p53 prevented CSC-mediated tumor recurrence in preclinical trials. CONCLUSIONS: Collectively, these results demonstrate that p53 defines the stemness of MEC and suggest that therapeutic activation of p53 might have clinical utility in patients with salivary gland MEC.

Metabolic collateral lethal target identification reveals MTHFD2 paralogue dependency in ovarian cancer.

Recurrent loss-of-function deletions cause frequent inactivation of tumour suppressor genes but often also involve the collateral deletion of essential genes in chromosomal proximity, engendering dependence on paralogues that maintain similar function. Although these paralogues are attractive anticancer targets, no methodology exists to uncover such collateral lethal genes. Here we report a framework for collateral lethal gene identification via metabolic fluxes, CLIM, and use it to reveal MTHFD2 as a collateral lethal gene in UQCR11-deleted ovarian tumours. We show that MTHFD2 has a non-canonical oxidative function to provide mitochondrial NAD+, and demonstrate the regulation of systemic metabolic activity by the paralogue metabolic pathway maintaining metabolic flux compensation. This UQCR11-MTHFD2 collateral lethality is confirmed in vivo, with MTHFD2 inhibition leading to complete remission of UQCR11-deleted ovarian tumours. Using CLIM's machine learning and genome-scale metabolic flux analysis, we elucidate the broad efficacy of targeting MTHFD2 despite distinct cancer genetic profiles co-occurring with UQCR11 deletion and irrespective of stromal compositions of tumours.

Single-cell RNA-sequencing identifies anti-cancer immune phenotypes in the early lung metastatic niche during breast cancer.

Microenvironmental changes in the early metastatic niche may be exploited to identify therapeutic targets to inhibit secondary tumor formation and improve disease outcomes. We dissected the developing lung metastatic niche in a model of metastatic, triple-negative breast cancer using single-cell RNA-sequencing. Lungs were extracted from mice at 7-, 14-, or 21 days after tumor inoculation corresponding to the pre-metastatic, micro-metastatic, and metastatic niche, respectively. The progression of the metastatic niche was marked by an increase in neutrophil infiltration (5% of cells at day 0 to 81% of cells at day 21) and signaling pathways corresponding to the hallmarks of cancer. Importantly, the pre-metastatic and early metastatic niche were composed of immune cells with an anti-cancer phenotype not traditionally associated with metastatic disease. As expected, the metastatic niche exhibited pro-cancer phenotypes. The transition from anti-cancer to pro-cancer phenotypes was directly associated with neutrophil and monocyte behaviors at these time points. Predicted metabolic, transcription factor, and receptor-ligand signaling suggested that changes in the neutrophils likely induced the transitions in the other immune cells. Conditioned medium generated by cells extracted from the pre-metastatic niche successfully inhibited tumor cell proliferation and migration in vitro and the in vivo depletion of pre-metastatic neutrophils and monocytes worsened survival outcomes, thus validating the anti-cancer phenotype of the developing niche. Genes associated with the early anti-cancer response could act as biomarkers that could serve as targets for the treatment of early metastatic disease. Such therapies have the potential to revolutionize clinical outcomes in metastatic breast cancer.

Targeting ESR1 mutation-induced transcriptional addiction in breast cancer with BET inhibition.

Acquired mutations in the ligand-binding domain (LBD) of the gene encoding estrogen receptor α (ESR1) are common mechanisms of endocrine therapy resistance in patients with metastatic ER+ breast cancer. The ESR1 Y537S mutation, in particular, is associated with development of resistance to most endocrine therapies used to treat breast cancer. Employing a high-throughput screen of nearly 1,200 Federal Drug Administration-approved (FDA-approved) drugs, we show that OTX015, a bromodomain and extraterminal domain (BET) inhibitor, is one of the top suppressors of ESR1 mutant cell growth. OTX015 was more efficacious than fulvestrant, a selective ER degrader, in inhibiting ESR1 mutant xenograft growth. When combined with abemaciclib, a CDK4/6 inhibitor, OTX015 induced more potent tumor regression than current standard-of-care treatment of abemaciclib + fulvestrant. OTX015 has preferential activity against Y537S mutant breast cancer cells and blocks their clonal selection in competition studies with WT cells. Thus, BET inhibition has the potential to both prevent and overcome ESR1 mutant-induced endocrine therapy resistance in breast cancer.

Effects of iron modulation on mesenchymal stem cell-induced drug resistance in estrogen receptor-positive breast cancer.

Patients with estrogen receptor-positive (ER+) breast cancer, the most common subtype, remain at risk for lethal metastatic disease years after diagnosis. Recurrence arises partly because tumor cells in bone marrow become resistant to estrogen-targeted therapy. Here, we utilized a co-culture model of bone marrow mesenchymal stem cells (MSCs) and ER+ breast cancer cells to recapitulate interactions of cancer cells in bone marrow niches. ER+ breast cancer cells in direct contact with MSCs acquire cancer stem-like (CSC) phenotypes with increased resistance to standard antiestrogenic drugs. We confirmed that co-culture with MSCs increased labile iron in breast cancer cells, a phenotype associated with CSCs and disease progression. Clinically approved iron chelators and in-house lysosomal iron-targeting compounds restored sensitivity to antiestrogenic therapy. These findings establish iron modulation as a mechanism to reverse MSC-induced drug resistance and suggest iron modulation in combination with estrogen-targeted therapy as a promising, translatable strategy to treat ER+ breast cancer.

In Vitro Quantification of Cancer Stem Cells Using a Mammosphere Formation Assay.

Cancer stem cells (CSCs) are a small subpopulation of self-renewing cancer cells that are present within tumors. In this chapter, we provide a detailed method for the quantification of CSCs in vitro through mammosphere formation.

Efficacy of an ALDH peptide-based dendritic cell vaccine targeting cancer stem cells.

Cancer immunotherapies may be limited by their failure to target cancer stem cells (CSCs). We previously described an approach to target these cells using a dendritic cell (DC) vaccine primed with lysates of CSCs identified by aldehyde dehydrogenase (ALDH). However, its clinical application is limited by the difficulty of obtaining adequate amounts of tumor from patient to make CSC lysate for vaccine preparation. To address this issue, we evaluated targeting ALDHhigh CSCs using two antigenic peptides derived from ALDH in D5 melanoma model in both protection and therapeutic settings. ALDH 1A1 or 1A3 peptide-DC vaccines primed cytotoxic T lymphocytes (CTLs) that specifically killed ALDHhigh D5 CSCs, with ALDH 1A1 + 1A3 dual peptides-DC vaccine mediating an additive CTL effect compared to single peptide-DC vaccines. In a tumor challenge model, ALDH peptide-DC vaccines induced significant protective immunity suppressing D5 tumor growth with the dual peptides-DC vaccine being superior to each peptide individually. In a therapeutic model, dual peptide-DC vaccine resulted in significant tumor growth suppression with anti-PD-L1 administration significantly augmenting this effect. Immune monitoring studies revealed that ALDH dual peptides-DC vaccination elicited strong T cell (CTL & IFNγ Elispot) and antibody immunity targeting ALDHhigh CSCs, resulting in significant reduction of ALDHhigh D5 CSCs. ALDH dual peptides-DC vaccination plus anti-PD-L1 administration resulted in increased recruitment of CD3+ TILs in the residual tumors and further reduction of ALDHhigh D5 CSCs. ALDH peptide(s)-based vaccine may allow for clinical translation via immunological targeting of ALDHhigh CSCs. Furthermore, this vaccine augments the efficacy of immune checkpoint blockade.

A Dual-Filtration System for Single-Cell Sequencing of Circulating Tumor Cells and Clusters in HCC.

Hepatocellular carcinoma (HCC) is a leading cause of cancer death worldwide. Identification and sequencing of circulating tumor (CT) cells and clusters may allow for noninvasive molecular characterization of HCC, which is an unmet need, as many patients with HCC do not undergo biopsy. We evaluated CT cells and clusters, collected using a dual-filtration system in patients with HCC. We collected and filtered whole blood from patients with HCC and selected individual CT cells and clusters with a micropipette. Reverse transcription, polymerase chain reaction, and library preparation were performed using a SmartSeq2 protocol, followed by single-cell RNA sequencing (scRNAseq) on an Illumina MiSeq V3 platform. Of the 8 patients recruited, 6 had identifiable CT cells or clusters. Median age was 64 years old; 7 of 8 were male; and 7 of 8 had and Barcelona Clinic Liver Cancer stage C. We performed scRNAseq of 38 CT cells and 33 clusters from these patients. These CT cells and clusters formed two distinct groups. Group 1 had significantly higher expression than group 2 of markers associated with epithelial phenotypes (CDH1 [Cadherin 1], EPCAM [epithelial cell adhesion molecule], ASGR2 [asialoglycoprotein receptor 2], and KRT8 [Keratin 8]), epithelial-mesenchymal transition (VIM [Vimentin]), and stemness (PROM1 [CD133], POU5F1 [POU domain, class 5, transcription factor 1], NOTCH1, STAT3 [signal transducer and activator of transcription 3]) (P < 0.05 for all). Patients with identifiable group 1 cells or clusters had poorer prognosis than those without them (median overall survival 39 vs. 384 days; P = 0.048 by log-rank test). Conclusion: A simple dual-filtration system allows for isolation and sequencing of CT cells and clusters in HCC and may identify cells expressing candidate genes known to be involved in cancer biology. Presence of CT cells/clusters expressing candidate genes is associated with poorer prognosis in advanced-stage HCC.

Mitochondrial complex II in intestinal epithelial cells regulates T cell-mediated immunopathology.

Intestinal epithelial cell (IEC) damage by T cells contributes to graft-versus-host disease, inflammatory bowel disease and immune checkpoint blockade-mediated colitis. But little is known about the target cell-intrinsic features that affect disease severity. Here we identified disruption of oxidative phosphorylation and an increase in succinate levels in the IECs from several distinct in vivo models of T cell-mediated colitis. Metabolic flux studies, complemented by imaging and protein analyses, identified disruption of IEC-intrinsic succinate dehydrogenase A (SDHA), a component of mitochondrial complex II, in causing these metabolic alterations. The relevance of IEC-intrinsic SDHA in mediating disease severity was confirmed by complementary chemical and genetic experimental approaches and validated in human clinical samples. These data identify a critical role for the alteration of the IEC-specific mitochondrial complex II component SDHA in the regulation of the severity of T cell-mediated intestinal diseases.

Flower lose, a cell fitness marker, predicts COVID-19 prognosis.

Risk stratification of COVID-19 patients is essential for pandemic management. Changes in the cell fitness marker, hFwe-Lose, can precede the host immune response to infection, potentially making such a biomarker an earlier triage tool. Here, we evaluate whether hFwe-Lose gene expression can outperform conventional methods in predicting outcomes (e.g., death and hospitalization) in COVID-19 patients. We performed a post-mortem examination of infected lung tissue in deceased COVID-19 patients to determine hFwe-Lose's biological role in acute lung injury. We then performed an observational study (n = 283) to evaluate whether hFwe-Lose expression (in nasopharyngeal samples) could accurately predict hospitalization or death in COVID-19 patients. In COVID-19 patients with acute lung injury, hFwe-Lose is highly expressed in the lower respiratory tract and is co-localized to areas of cell death. In patients presenting in the early phase of COVID-19 illness, hFwe-Lose expression accurately predicts subsequent hospitalization or death with positive predictive values of 87.8-100% and a negative predictive value of 64.1-93.2%. hFwe-Lose outperforms conventional inflammatory biomarkers and patient age and comorbidities, with an area under the receiver operating characteristic curve (AUROC) 0.93-0.97 in predicting hospitalization/death. Specifically, this is significantly higher than the prognostic value of combining biomarkers (serum ferritin, D-dimer, C-reactive protein, and neutrophil-lymphocyte ratio), patient age and comorbidities (AUROC of 0.67-0.92). The cell fitness marker, hFwe-Lose, accurately predicts outcomes in COVID-19 patients. This finding demonstrates how tissue fitness pathways dictate the response to infection and disease and their utility in managing the current COVID-19 pandemic.

The Roles of the Let-7 Family of MicroRNAs in the Regulation of Cancer Stemness.

Cancer has long been viewed as a disease of normal development gone awry. Cancer stem-like cells (CSCs), also termed as tumor-initiating cells (TICs), are increasingly recognized as a critical tumor cell population that drives not only tumorigenesis but also cancer progression, treatment resistance and metastatic relapse. The let-7 family of microRNAs (miRNAs), first identified in C. elegans but functionally conserved from worms to human, constitutes an important class of regulators for diverse cellular functions ranging from cell proliferation, differentiation and pluripotency to cancer development and progression. Here, we review the current state of knowledge regarding the roles of let-7 miRNAs in regulating cancer stemness. We outline several key RNA-binding proteins, long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) involved in the regulation of let-7 biogenesis, maturation and function. We then highlight key gene targets and signaling pathways that are regulated or mutually regulated by the let-7 family of miRNAs to modulate CSC characteristics in various types of cancer. We also summarize the existing evidence indicating distinct metabolic pathways regulated by the let-7 miRNAs to impact CSC self-renewal, differentiation and treatment resistance. Lastly, we review current preclinical studies and discuss the clinical implications for developing let-7-based replacement strategies as potential cancer therapeutics that can be delivered through different platforms to target CSCs and reduce/overcome treatment resistance when applied alone or in combination with current chemo/radiation or molecularly targeted therapies. By specifically targeting CSCs, these strategies have the potential to significantly improve the efficacy of cancer therapies.

Targeting cancer stem cells via integrin ß4.

Integrins mediate cell-cell interactions and communication with the extracellular matrix (ECM). These transmembrane protein receptors allow binding between a cell and its surroundings, initiating a breadth of intracellular signaling resulting in proliferation, differentiation, survival, or migration. Such responses have made integrins an attractive target for cancer therapy. Self-renewing and highly tumorigenic cancer stem cells (CSCs) are most resistant to traditional radiation treatment and chemotherapy, and therefore may contribute directly to the metastasis and relapse of the disease. In both the 4T1 mouse metastatic mammary tumor model and SCC7 head and neck squamous cell carcinoma model, integrin ß4 (ITGB4) was expressed on ALDHhigh 4T1 and SCC7 CSCs. Using two immunological approaches, we targeted ITGB4 through 1) ITGB4 protein-pulsed dendritic cell (ITGB4-DC) vaccination or 2) via anti-CD3/anit-ITGB4 bispecific antibody (ITGB4 BiAb)-armed T cell adoptive transfer. These two therapies reduced ITGB4-expressing CSCs and inhibited local tumor growth and lung metastasis through ITGB4 specific cellular and humoral immune responses. Additionally, the combination of anti-PD-L1 immunotherapy with our two ITGB4-targeted approaches significantly improved treatment efficacy. We also found increased concentrations of serum IFN-γ and IL-6 in the 4T1 and SCC7 models which may help define future directions of this ITGB4-targeted study. Together, these results emphasize ITGB4 as a practical CSC immunological target with possible therapeutic benefits across tumor types with high ITGB4 expression.

A randomized, placebo-controlled phase 2 study of paclitaxel in combination with reparixin compared to paclitaxel alone as front-line therapy for metastatic triple-negative breast cancer (fRida).

PURPOSE: CXCR1, one of the receptors for CXCL8, has been identified as a druggable target on breast cancer cancer stem cells (CSC). Reparixin (R), an investigational oral inhibitor of CXCR1, was safely administered to metastatic breast cancer patients in combination with paclitaxel (P) and appeared to reduce CSC in a window-of-opportunity trial in operable breast cancer. The fRida trial (NCT02370238) evaluated the addition of R to weekly as first-line therapy for metastatic (m) TNBC. SUBJECTS AND METHODS: Subjects with untreated mTNBC were randomized 1:1 to R or placebo days 1-21 in combination with weekly P 80 mg/m2 on days 1, 8, 15 of 28-day cycles. The primary endpoint was PFS by central review. RESULTS: 123 subjects were randomized (62 to R + P and 61 to placebo + P). PFS was not different between the 2 groups (median 5.5 and 5.6 months for R + P and placebo + P, respectively; HR 1.13, p = 0.5996). ALDH+ and CD24-/CD44+ CSC centrally evaluated by IHC were found in 16 and 34 of the 54 subjects who provided a metastatic tissue biopsy at study entry. Serious adverse events (21.3 and 20% of subjects) and grade ≥ 3 adverse reactions (ADR) (9.1 and 6.3% of all ADRs) occurred at similar frequency in both groups. CONCLUSION: fRida is the first randomized, double-blind clinical trial of a CSC-targeting agent in combination with chemotherapy in breast cancer. The primary endpoint of prolonged PFS was not met. CLINICAL TRIAL REGISTRATION/DATE OF REGISTRATION: NCT01861054/February 24, 2015.

Breast cancer dormancy: need for clinically relevant models to address current gaps in knowledge.

Breast cancer is the most commonly diagnosed cancer in the USA. Although advances in treatment over the past several decades have significantly improved the outlook for this disease, most women who are diagnosed with estrogen receptor positive disease remain at risk of metastatic relapse for the remainder of their life. The cellular source of late relapse in these patients is thought to be disseminated tumor cells that reactivate after a long period of dormancy. The biology of these dormant cells and their natural history over a patient's lifetime is largely unclear. We posit that research on tumor dormancy has been significantly limited by the lack of clinically relevant models. This review will discuss existing dormancy models, gaps in biological understanding, and propose criteria for future models to enhance their clinical relevance.