Reprogramming of non-genomic estrogen signaling by the stemness factor SOX2 enhances the tumor-initiating capacity of breast cancer cells

Adipocyte-conditioned medium induces tamoxifen resistance by activating PI3K/Akt/mTOR pathway in estrogen receptor-positive breast cancer cells

Resistance to endocrine therapy is a major clinical challenge in estrogen receptor (ER)-positive breast cancer. Obesity is associated with the clinical response to ER-positive breast cancers; however, the mechanism underlying obesity-induced resistance to endocrine therapy in ER-positive breast cancers remains unclear. In this study, we investigated the molecular mechanisms underlying obesity-induced resistance to tamoxifen (TAM), an anti-estrogen agent, in the ER-positive breast cancer cell line MCF-7 using differentiated adipocyte-conditioned medium (D-CM). Treatment of the cells with D-CM promoted TAM resistance by reducing TAM-induced apoptosis. The expression levels of the ERα target genes were higher in D-CM-treated cells than those in untreated ones. In contrast, when the cells were cultured in the presence of TAM, the expression levels were decreased, with or without D-CM. Moreover, the expression of the markers for cancer stem-like cells (CSCs) and mammosphere formation was enhanced by co-treating with D-CM and TAM, compared with TAM alone. The phosphatidylinositol-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was activated in MCF-7 cells by D-CM treatment, even in the presence of TAM. Inhibition of the PI3K/Akt/mTOR pathway decreased the expression levels of the CSC markers, suppressed mammosphere formation, and resensitized to TAM via inducing apoptosis in D-CM-treated cells. These results indicate that the conditioned medium of differentiated adipocytes promoted TAM resistance by inducing the CSC phenotype through activation of the PI3K/Akt/mTOR pathway in ER-positive breast cancer cells. Thus, the PI3K/Akt/mTOR pathway may be a therapeutic target in obese patients with ER-positive breast cancers.

The multifaceted role of SOX2 in breast and lung cancer dynamics

Breast and lung cancers are leading causes of death among patients, with their global mortality and morbidity rates increasing. Conventional treatments often prove inadequate due to resistance development. The alteration of molecular interactions may accelerate cancer progression and treatment resistance. SOX2, known for its abnormal expression in various human cancers, can either accelerate or impede cancer progression. This review focuses on examining the role of SOX2 in breast and lung cancer development. An imbalance in SOX2 expression can promote the growth and dissemination of these cancers. SOX2 can also block programmed cell death, affecting autophagy and other cell death mechanisms. It plays a significant role in cancer metastasis, mainly by regulating the epithelial-to-mesenchymal transition (EMT). Additionally, an imbalanced SOX2 expression can cause resistance to chemotherapy and radiation therapy in these cancers. Genetic and epigenetic factors may affect SOX2 levels. Pharmacologically targeting SOX2 could improve the effectiveness of breast and lung cancer treatments.

Role of hydroxymethylglutharyl-coenzyme A reductase in the induction of stem-like states in breast cancer

PURPOSE

De novo synthesis of cholesterol and its rate-limiting enzyme, 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMGCR), is deregulated in tumors and critical for tumor cell survival and proliferation. However, the role of HMGCR in the induction and maintenance of stem-like states in tumors remains unclear.

METHODS

A compiled public database from breast cancer (BC) patients was analyzed with the web application SurvExpress. Cell Miner was used for the analysis of HMGCR expression and statin sensitivity of the NCI-60 cell lines panel. A CRISPRon system was used to induce HMGCR overexpression in the luminal BC cell line MCF-7 and a lentiviral pLM-OSKM system for the reprogramming of MCF-7 cells. Comparisons were performed by two-tailed unpaired t-test for two groups and one- or two-way ANOVA.

RESULTS

Data from BC patients showed that high expression of several members of the cholesterol synthesis pathway were associated with lower recurrence-free survival, particularly in hormone-receptor-positive BC. In silico and in vitro analysis showed that HMGCR is expressed in several BC cancer cell lines, which exhibit a subtype-dependent response to statins in silico and in vitro. A stem-like phenotype was demonstrated upon HMGCR expression in MCF-7 cells, characterized by expression of the pluripotency markers NANOG, SOX2, increased CD44 +/CD24low/ -, CD133 + populations, and increased mammosphere formation ability. Pluripotent and cancer stem cell lines showed high expression of HMGCR, whereas cell reprogramming of MCF-7 cells did not increase HMGCR expression.

CONCLUSION

HMGCR induces a stem-like phenotype in BC cells of epithelial nature, thus affecting tumor initiation, progression and statin sensitivity.

Isoliensinine augments the therapeutic potential of paclitaxel in multidrug-resistant colon cancer stem cells and induced mitochondria-mediated cell death

Previously we have reported the isoliensinine (ISO) potentates the therapeutic potential of cisplatin in cisplatin resistant colorectal cancer stem cells. The present study evaluates the chemo-sensitizing potential of the combinatorial regimen of ISO and Paclitaxcel (PTX) on multidrug-resistant (MDR)-HCT-15 cells to reduce the dose requirement of both ISO and PTX. The results of the present study suggest that treatment with the combinatorial regimen of ISO and PTX enhanced the cytotoxic effect with resultant increase in apoptosis in MDR-HCT-15 cells as evident from the altered cellular morphology, G2/M cell cycle arrest, propidium iodide uptake, Annexin V, increased intracellular Ca2+ accumulation, decreased mitochondrial membrane potential, diminished ATP production, PARP-1 cleavage, altered expression of ERK1/2, and apoptotic proteins. Treatment with combinatorial regimen of ISO and PTX also modulated the expression of the transcription factors SOX2, OCT4 which determine the stemness of cancer cells. Thus, results of the present study suggest that ISO and PTX combination regimen induces apoptosis in MDR-HCT-15 in a synergistic manner.

Gel-Free Single-Cell Culture Arrays on a Microfluidic Chip for Highly Efficient Expansion and Recovery of Colon Cancer Stem Cells

The microgel single-cell culture approach we developed to expand tumor stem cells (TSCs) is associated with limited TSC production, which can be attributable to cell viability loss in microgel formation and tumorsphere expansion limitation caused by hydrogel stiffness. In this work, we developed a gel-free single-cell culture array on a microfluidic chip to overcome these issues. The microfluidic chip used in the study has a 16,000 hydrophilic microchamber array, which can capture ∼2000 single cells at a time. After cell capturing, the cell culture chambers were enclosed by forming a chitosan layer through interactions between chitosan and alginate, thus preventing cell loss in the gel-free culture. The hydrophilic coating prevented cell adhesion, so only TSCs with anti-apoptosis and self-renewal properties can survive the harsh culture and form tumorspheres. After a 7 day culture, 19.04% of the HCT116 colon cancer cells formed single-cell-derived tumorspheres with an average size of 46.59 ± 10.58 μm. Compared with the microgel single-cell culture, sphere-forming rate and TSC expansion efficiency were significantly improved by using this gel-free single-cell culture array. After cell culture, the chitosan layer could be destabilized easily, thus allowing recovery of the tumorspheres from the microchip by applying a reverse flow. Approximately 13,600 cells could be obtained in a single culture, which can be used for off-chip cell assays. Flow cytometry analysis indicated high proportions of LGR5(+) and SOX2(+) cells within the single-cell-derived tumorspheres. Moreover, the differentiation experiments confirmed the multi-lineage differentiation potential of single-cell-derived tumorspheres. The gel-free single-cell culture offers a label-free approach to obtain sufficient amounts of TSCs, which is valuable for tumor biology research and the development of TSC-specific therapeutic strategies.

Breast Cancer Stem-Like Cells in Drug Resistance: A Review of Mechanisms and Novel Therapeutic Strategies to Overcome Drug Resistance

Breast cancer is the most frequent type of malignancy in women worldwide, and drug resistance to the available systemic therapies remains a major challenge. At the molecular level, breast cancer is heterogeneous, where the cancer-initiating stem-like cells (bCSCs) comprise a small yet distinct population of cells within the tumor microenvironment (TME) that can differentiate into cells of multiple lineages, displaying varying degrees of cellular differentiation, enhanced metastatic potential, invasiveness, and resistance to radio- and chemotherapy. Based on the expression of estrogen and progesterone hormone receptors, expression of human epidermal growth factor receptor 2 (HER2), and/or BRCA mutations, the breast cancer molecular subtypes are identified as TNBC, HER2 enriched, luminal A, and luminal B. Management of breast cancer primarily involves resection of the tumor, followed by radiotherapy, and systemic therapies including endocrine therapies for hormone-responsive breast cancers; HER2-targeted therapy for HER2-enriched breast cancers; chemotherapy and poly (ADP-ribose) polymerase inhibitors for TNBC, and the recent development of immunotherapy. However, the complex crosstalk between the malignant cells and stromal cells in the breast TME, rewiring of the many different signaling networks, and bCSC-mediated processes, all contribute to overall drug resistance in breast cancer. However, strategically targeting bCSCs to reverse chemoresistance and increase drug sensitivity is an underexplored stream in breast cancer research. The recent identification of dysregulated miRNAs/ncRNAs/mRNAs signatures in bCSCs and their crosstalk with many cellular signaling pathways has uncovered promising molecular leads to be used as potential therapeutic targets in drug-resistant situations. Moreover, therapies that can induce alternate forms of regulated cell death including ferroptosis, pyroptosis, and immunotherapy; drugs targeting bCSC metabolism; and nanoparticle therapy are the upcoming approaches to target the bCSCs overcome drug resistance. Thus, individualizing treatment strategies will eliminate the minimal residual disease, resulting in better pathological and complete response in drug-resistant scenarios. This review summarizes basic understanding of breast cancer subtypes, concept of bCSCs, molecular basis of drug resistance, dysregulated miRNAs/ncRNAs patterns in bCSCs, and future perspective of developing anticancer therapeutics to address breast cancer drug resistance.

Unexplored Functions of Sex Hormones in Glioblastoma Cancer Stem Cells

Biological sex impacts a wide array of molecular and cellular functions that impact organismal development and can influence disease trajectory in a variety of pathophysiological states. In nonreproductive cancers, epidemiological sex differences have been observed in a series of tumors, and recent work has identified previously unappreciated sex differences in molecular genetics and immune response. However, the extent of these sex differences in terms of drivers of tumor growth and therapeutic response is less clear. In glioblastoma (GBM), the most common primary malignant brain tumor, there is a male bias in incidence and outcome, and key genetic and epigenetic differences, as well as differences in immune response driven by immune-suppressive myeloid populations, have recently been revealed. GBM is a prototypic tumor in which cellular heterogeneity is driven by populations of therapeutically resistant cancer stem cells (CSCs) that underlie tumor growth and recurrence. There is emerging evidence that GBM CSCs may show a sex difference, with male tumor cells showing enhanced self-renewal, but how sex differences impact CSC function is not clear. In this mini-review, we focus on how sex hormones may impact CSCs in GBM and implications for other cancers with a pronounced CSC population. We also explore opportunities to leverage new models to better understand the contribution of sex hormones vs sex chromosomes to CSC function. With the rising interest in sex differences in cancer, there is an immediate need to understand the extent to which sex differences impact tumor growth, including effects on CSC function.

SOX2 mediates metabolic reprogramming of prostate cancer cells

New strategies are needed to predict and overcome metastatic progression and therapy resistance in prostate cancer. One potential clinical target is the stem cell transcription factor SOX2, which has a critical role in prostate development and cancer. We thus investigated the impact of SOX2 expression on patient outcomes and its function within prostate cancer cells. Analyses of SOX2 expression among a case-control cohort of 1028 annotated tumor specimens demonstrated that SOX2 expression confers a more rapid time to metastasis and decreased patient survival after biochemical recurrence. SOX2 ChIP-Seq analyses revealed SOX2-binding sites within prostate cancer cells which differ significantly from canonical embryonic SOX2 gene targets, and prostate-specific SOX2 gene targets are associated with multiple oncogenic pathways. Interestingly, phenotypic and gene expression analyses after CRISPR-mediated deletion of SOX2 in castration-resistant prostate cancer cells, as well as ectopic SOX2 expression in androgen-sensitive prostate cancer cells, demonstrated that SOX2 promotes changes in multiple metabolic pathways and metabolites. SOX2 expression in prostate cancer cell lines confers increased glycolysis and glycolytic capacity, as well as increased basal and maximal oxidative respiration and increased spare respiratory capacity. Further, SOX2 expression was associated with increased quantities of mitochondria, and metabolomic analyses revealed SOX2-associated changes in the metabolism of purines, pyrimidines, amino acids and sugars, and the pentose phosphate pathway. Analyses of SOX2 gene targets with central functions metabolism (CERK, ECHS1, HS6SDT1, LPCAT4, PFKP, SLC16A3, SLC46A1, and TST) document significant expression correlation with SOX2 among RNA-Seq datasets derived from patient tumors and metastases. These data support a key role for SOX2 in metabolic reprogramming of prostate cancer cells and reveal new mechanisms to understand how SOX2 enables metastatic progression, lineage plasticity, and therapy resistance. Further, our data suggest clinical opportunities to exploit SOX2 as a biomarker for staging and imaging, as well as a potential pharmacologic target.

Targeting CDK7 reverses tamoxifen resistance through regulating stemness in ER+ breast cancer

BACKGROUND

Although tamoxifen is the mainstay endocrine therapy for estrogen receptor-positive (ER+) breast cancer patients, the emergence of tamoxifen resistance is still the major challenge that results in treatment failure. Tamoxifen is very effective in halting breast cancer cell proliferation; nonetheless, the ability of tamoxifen to target cancer stem and progenitor cell populations (CSCs), a major key player for the emergence of tamoxifen resistance, has not been adequately investigated yet. Thus, we explored whether targeting CDK7 modulates CSCs subpopulation and tamoxifen resistance in ER+ breast cancer cells.

METHODS

Mammosphere-formation assay, stem cell biomarkers and tamoxifen sensitivity were analyzed in MCF7 tamoxifen-sensitive cell line and its resistant counterpart, LCC2, following CDK7 targeting by THZ1 or siRNA.

RESULTS

Analysis of clinically relevant data indicated that expression of stemness factor, SOX2, was positively correlated with CDK7 expression in tamoxifen-treated patients. Moreover, overexpression of the stemness gene, SOX2, was associated with shorter overall survival in those patients. Importantly, the number of CSC populations and the expression of CDK7, P-Ser118-ER-α and c-MYC were significantly higher in LCC2 cells compared with parental MCF-7 cells. Moreover, targeting CDK7 inhibited mammosphere formation, CSC-regulating genes, and CSC biomarkers expression in MCF-7 and LCC2 cells.

CONCLUSION

Our data indicate, for the first time, that CDK7-targeted therapy in ER+ breast cancer ameliorates tamoxifen resistance, at least in part, by inhibiting cancer stemness. Thus, targeting CDK7 might represent a potential approach for relieving tamoxifen resistance in ER+ breast cancer.

The Breast Cancer Stem Cells Traits and Drug Resistance

Drug resistance is a major challenge in breast cancer (BC) treatment at present. Accumulating studies indicate that breast cancer stem cells (BCSCs) are responsible for the BC drugs resistance, causing relapse and metastasis in BC patients. Thus, BCSCs elimination could reverse drug resistance and improve drug efficacy to benefit BC patients. Consequently, mastering the knowledge on the proliferation, resistance mechanisms, and separation of BCSCs in BC therapy is extremely helpful for BCSCs-targeted therapeutic strategies. Herein, we summarize the principal BCSCs surface markers and signaling pathways, and list the BCSCs-related drug resistance mechanisms in chemotherapy (CT), endocrine therapy (ET), and targeted therapy (TT), and display therapeutic strategies for targeting BCSCs to reverse drug resistance in BC. Even more importantly, more attention should be paid to studies on BCSC-targeted strategies to overcome the drug resistant dilemma of clinical therapies in the future.

Unfavorable Prognostic Effects of the Stem Cell Pluripotency Factor Sox2 in Feline Invasive Mammary Carcinomas

Background: Sex-determining Region Y (SRY)-box transcription factor-2 (Sox2) belongs to the "Yamanaka's factors," necessary and sufficient to convert somatic cells into pluripotent stem cells. In breast cancers, Sox2 expression has been associated with poor prognosis, and resistance to therapy. The aims of this study were to determine the frequency of Sox2 positivity in feline invasive mammary carcinomas (FMCs), its relationships with other clinical-pathologic variables, and with patient outcomes. Materials and Methods: This study relies on a previously described retrospective cohort of 180 FMCs, diagnosed in female cats treated by mastectomy alone, with 2-year follow-up. Sox2 (clone SP76), Estrogen Receptor alpha (ER), Progesterone Receptor (PR), Ki-67, Human Epidermal growth factor Receptor 2 (HER2), Androgen Receptor (AR), Bcl-2, Forkhead box protein A1 (FOXA1), basal markers and FoxP3-positive regulatory T cells (Tregs) were detected by automated immunohistochemistry. Sox2 expression was quantitated as an index (percentage of neoplastic cells demonstrating a positive nuclear signal). The FMCs were considered Sox2-positive at threshold >42%. Results: Sox2 was not expressed in the normal mammary gland or in mammary hyperplasia without atypia, but was occasionally detected in atypical hyperplasia. In FMCs, the mean Sox2 index was 38 ± 30%, and 79/180 FMCs (44%) were Sox2-positive. Sox2 expression was associated with older age at diagnosis, lymphovascular invasion, high Ki-67 proliferation indexes, low PR and FOXA1 expression, and increased numbers of tumor-associated Tregs, but was not significantly associated with the clinical stage, histological types, and histological grade. By multivariate survival analysis, Sox2 was associated with poor cancer-specific survival (Hazard Ratio = 1.48, 95% confidence interval 1.04-2.11, p = 0.0292), independently of the pathologic tumor size, pathologic nodal stage, distant metastasis, and AR expression. A rare subgroup of FMCs characterized by an AR+Sox2-phenotype (19/180 cases, 11%) was associated with very favorable outcomes. Conclusion: Sox2 expression was associated with poor cancer-specific survival of female cats with invasive mammary carcinomas, as previously reported in human breast cancer, but was more commonly expressed in cats than reported in breast cancers. Sox2 showed complementarity with AR in FMC prognostication.

Carcinoma-Associated Fibroblasts Promote Growth of Sox2-Expressing Breast Cancer Cells

Simple Summary

The tumor microenvironment has a strong impact on the behavior of tumor cells. One major cell type residing in the tumor microenvironment is the carcinoma-associated fibroblast (CAF). We were interested in the effect of CAFs on Sox2 (sex determining region Y (SRY)-box 2), which not only is an essential embryonal stem cell transcription factor, but also plays a role in cancer stem cell activity. We found that long-term exposure of ERα-positive breast cancer cells to the cocktail of CAF-secreted factors strongly increased Sox2 expression involving tumor-related proteins and signaling pathways. However, Sox2 was not only present in those tumor cells that express stem cell markers, but was equally abundant in other tumor cells. By being widely expressed, Sox2 may have functions in non-stem cells. In fact, Sox2 was found to regulate ERα expression, to act anti-apoptotically, to promote cellular growth and to protect cells against the anti-estrogen fulvestrant.

Abstract

CAFs (Carcinoma-associated fibroblasts) play an important role in cancer progression. For instance, they promote resistance to anti-estrogens, such as fulvestrant. Here, we show that, in ERα-positive breast cancer cell lines, the cocktail of factors secreted by CAFs (CAF-CM) induce the expression of the embryonal stem cell transcription factor Sox2 (sex determining region Y (SRY)-box 2). Long-term exposure to CAF-CM was able to give rise to very high Sox2 levels both in the absence and presence of fulvestrant. IL-6 (interleukin-6), a major component of CAF-CM, failed to raise Sox2 expression. In MCF-7 sublines established in the presence of CAF-CM, almost all cells showed Sox2 expression, whereas long-term treatment of T47D cells with CAF-CM resulted in a ~60-fold increase in the proportions of two distinct populations of Sox2 high and low expresser cells. Exposure of BT474 cells to CAF-CM raised the fraction of Sox2 high expresser cells by ~3-fold. Cell sorting based on CD44 and CD24 expression or ALDH (aldehyde dehydrogenase) activity revealed that most Sox2 high expresser cells were not CD44^hi/CD24^lo- or ALDH-positive cells suggesting that they were not CSCs (cancer stem cells), though CD44 played a role in Sox2 expression. Functionally, Sox2 was found to protect CAF-CM-treated cells against apoptosis and to allow higher growth activity in the presence of fulvestrant. Mechanistically, the key drivers of Sox2 expression was found to be STAT3 (Signal transducer and activator of transcription 3), Bcl-3 (B-cell lymphoma 3) and the PI3K (Phosphoinositide 3-kinase)/AKT pathway, whose activities/expression can all be upregulated by CAF-CM. These data suggest that CAF-CM induces Sox2 expression in non-CSCs by activating proteins involved in growth control and drug resistance, leading to higher protection against apoptosis.

MCF7 Spheroid Development: New Insight about Spatio/Temporal Arrangements of TNTs, Amyloid Fibrils, Cell Connections, and Cellular Bridges

Human breast adenocarcinoma cells (MCF7) grow in three-dimensional culture as spheroids that represent the structural complexity of avascular tumors. Therefore, spheroids offer a powerful tool for studying cancer development, aggressiveness, and drug resistance. Notwithstanding the large amount of data regarding the formation of MCF7 spheroids, a detailed description of the morpho-functional changes during their aggregation and maturation is still lacking. In this study, in addition to the already established role of gap junctions, we show evidence of tunneling nanotube (TNT) formation, amyloid fibril production, and opening of large stable cellular bridges, thus reporting the sequential events leading to MCF7 spheroid formation. The variation in cell phenotypes, sustained by dynamic expression of multiple proteins, leads to complex networking among cells similar to the sequence of morphogenetic steps occurring in embryogenesis/organogenesis. On the basis of the observation that early events in spheroid formation are strictly linked to the redox homeostasis, which in turn regulate amyloidogenesis, we show that the administration of N-acetyl-l-cysteine (NAC), a reactive oxygen species (ROS) scavenger that reduces the capability of cells to produce amyloid fibrils, significantly affects their ability to aggregate. Moreover, cells aggregation events, which exploit the intrinsic adhesiveness of amyloid fibrils, significantly decrease following the administration during the early aggregation phase of neutral endopeptidase (NEP), an amyloid degrading enzyme.

PreImplantation Factor immunohistochemical expression correlates with prostate cancer aggressiveness

BACKGROUND

The PreImplantation Factor (PIF)-a peptide secreted by viable embryos-exerts autotrophic protective effects, promotes endometrial receptivity and controls trophoblast invasion. Synthetic PIF (sPIF) has both immune-protective and regenerative properties, and reduces oxidative stress and protein misfolding. PIF is detected by immunohistochemistry (IHC) in hyperplastic endometriotic lesions and advanced uterine cancer. sPIF reduces graft-versus-host disease while maintaining a graft-versus-leukemia effect.

METHODS

PIF detection in prostate cancer was assessed in 50 human prostate samples following radical prostatectomy using tumor-microarray-based IHC correlating PIF immune staining with Gleason score (GS) and cancer aggressiveness.

RESULTS

PIF was detected in moderate-to-high risk prostate cancer (GS 4+3 and beyond, prognostic groups 3 to 5). In prostate cancer (GS (WHO Grade Group (GG)5), PIF was detected in 50% of cases; in prostate cancer (GS 4+4 GG4), PIF was observed in 62.5% of cases; in prostate cancer (GS 4+3 GG3), PIF immunostaining was observed in 57.1% of cases. In prostate cancer, (GS 3+4 GG2) and (GS 3+3 GG1) cases where PIF staining was negative to weak, membranous staining was observed in 20% of cases (staining pattern considered negative). High-grade prostate intraepithelial neoplasia PIF positive stain in 28.57% of cases (6 of 21) was observed. In contrast, PIF was not detected in normal prostate glands. Importantly, sPIF added to the PC3 cell line alone or combined with prostate cancer fibroblast feeder-cells did not affect proliferation. Only when peripheral blood mononuclear cells were added to the culture, a minor increase in cell proliferation was noted, reflecting local proliferation control.

CONCLUSIONS

Collectively, PIF assessment could be a valuable, simple-to-use immunohistochemical biomarker to evaluate aggressiveness/prognosis in specimens from prostate cancer patients.

The LSD1 inhibitor iadademstat (ORY-1001) targets SOX2-driven breast cancer stem cells: a potential epigenetic therapy in luminal-B and HER2-positive breast cancer subtypes

SOX2 is a core pluripotency-associated transcription factor causally related to cancer initiation, aggressiveness, and drug resistance by driving the self-renewal and seeding capacity of cancer stem cells (CSC). Here, we tested the ability of the clinically proven inhibitor of the lysine-specific demethylase 1 (LSD1/KDM1A) iadademstat (ORY-100) to target SOX2-driven CSC in breast cancer. Iadademstat blocked CSC-driven mammosphere formation in breast cancer cell lines that are dependent on SOX2 expression to maintain their CSC phenotype. Iadademstat prevented the activation of an LSD1-targeted stemness-specific SOX2 enhancer in CSC-enriched 3-dimensional spheroids. Using high-throughput transcriptional data available from the METABRIC dataset, high expression of SOX2 was significantly more common in luminal-B and HER2-enriched subtypes according to PAM50 classifier and in IntClust1 (high proliferating luminal-B) and IntClust 5 (luminal-B and HER2-amplified) according to integrative clustering. Iadademstat significantly reduced mammospheres formation by CSC-like cells from a multidrug-resistant luminal-B breast cancer patient-derived xenograft but not of those from a treatment-naïve luminal-A patient. Iadademstat reduced the expression of SOX2 in luminal-B but not in luminal-A mammospheres, likely indicating a selective targeting of SOX2-driven CSC. The therapeutic relevance of targeting SOX2-driven breast CSC suggests the potential clinical use of iadademstat as an epigenetic therapy in luminal-B and HER2-positive subtypes.

Sox2 promotes expression of the ST6Gal-I glycosyltransferase in ovarian cancer cells

Background

The ST6Gal-I glycosyltransferase, which adds α2–6-linked sialic acids to N-glycosylated proteins is upregulated in a wide range of malignancies including ovarian cancer. Prior studies have shown that ST6Gal-I-mediated sialylation of select surface receptors remodels intracellular signaling to impart cancer stem cell (CSC) characteristics. However, the mechanisms that contribute to ST6Gal-I expression in stem-like cancer cells are poorly understood.

Results

Herein, we identify the master stem cell transcription factor, Sox2, as a novel regulator of ST6Gal-I expression. Interestingly, SOX2 and ST6GAL1 are located within the same tumor-associated amplicon, 3q26, and these two genes exhibit coordinate gains in copy number across multiple cancers including ~ 25% of ovarian serious adenocarcinomas. In conjunction with genetic co-amplification, our studies suggest that Sox2 directly binds the ST6GAL1 promoter to drive transcription. ST6Gal-I expression is directed by at least four distinct promoters, and we identified the P3 promoter as the predominant promoter utilized by ovarian cancer cells. Chromatin Immunoprecipitation (ChIP) assays revealed that Sox2 binds regions proximal to the P3 promoter. To confirm that Sox2 regulates ST6Gal-I expression, Sox2 was either overexpressed or knocked-down in various ovarian cancer cell lines. Sox2 overexpression induced an increase in ST6Gal-I mRNA and protein, as well as surface α2–6 sialylation, whereas Sox2 knock-down suppressed levels of ST6Gal-I mRNA, protein and surface α2–6 sialylation.

Conclusions

These data suggest a process whereby SOX2 and ST6GAL1 are coordinately amplified in cancer cells, with the Sox2 protein then binding the ST6GAL1 promoter to further augment ST6Gal-I expression. Our collective results provide new insight into mechanisms that upregulate ST6Gal-I expression in ovarian cancer cells, and also point to the possibility that some of the CSC characteristics commonly attributed to Sox2 may, in part, be mediated through the sialyltransferase activity of ST6Gal-I.

The Central Contributions of Breast Cancer Stem Cells in Developing Resistance to Endocrine Therapy in Estrogen Receptor (ER)-Positive Breast Cancer

Breast cancer stem cells (BCSC) play critical roles in the acquisition of resistance to endocrine therapy in estrogen receptor (ER)-positive (ER + ve) breast cancer (BC). The resistance results from complex alterations involving ER, growth factor receptors, NOTCH, Wnt/β-catenin, hedgehog, YAP/TAZ, and the tumor microenvironment. These mechanisms are likely converged on regulating BCSCs, which then drive the development of endocrine therapy resistance. In this regard, hormone therapies enrich BCSCs in ER + ve BCs under both pre-clinical and clinical settings along with upregulation of the core components of “stemness” transcriptional factors including SOX2, NANOG, and OCT4. SOX2 initiates a set of reactions involving SOX9, Wnt, FXY3D, and Src tyrosine kinase; these reactions stimulate BCSCs and contribute to endocrine resistance. The central contributions of BCSCs to endocrine resistance regulated by complex mechanisms offer a unified strategy to counter the resistance. ER + ve BCs constitute approximately 75% of BCs to which hormone therapy is the major therapeutic approach. Likewise, resistance to endocrine therapy remains the major challenge in the management of patients with ER + ve BC. In this review we will discuss evidence supporting a central role of BCSCs in developing endocrine resistance and outline the strategy of targeting BCSCs to reduce hormone therapy resistance.

Phase I trial to evaluate the addition of alisertib to fulvestrant in women with endocrine-resistant, ER+ metastatic breast cancer

PURPOSE

In estrogen receptor-positive (ER+) breast cancer models, activation of Aurora A kinase (AURKA) is associated with downregulation of ERα expression and resistance to endocrine therapy. Alisertib is an oral selective inhibitor of AURKA. The primary objectives of this phase I trial were to determine the recommended phase II dose (RP2D) and evaluate the toxicities and clinical activity of alisertib combined with fulvestrant in patients with ER+ metastatic breast cancer (MBC).

METHODS

In this standard 3 + 3 dose-escalation phase I study, postmenopausal patients with endocrine-resistant, ER+ MBC previously treated with endocrine therapy were assigned to one of two dose levels of alisertib (40 or 50 mg) in combination with fixed-dose fulvestrant.

RESULTS

Ten patients enrolled, of which nine were evaluable for the primary endpoint. The median patient age was 59. All patients had secondary (acquired) endocrine resistance, and all had received prior aromatase inhibitor. Six had experienced disease progression on fulvestrant. There were no severe (grade 3+) toxicities reported during cycle 1 at either dose level. The median progression-free survival time was 12.4 months (95% CI 5.3-not met), and the 6-month clinical benefit rate was 77.8% (95% CI 40.0-87.2%).

CONCLUSIONS

In patients with endocrine-resistant, ER+ MBC, alisertib in combination with fulvestrant was well tolerated. A favorable safety profile was observed. The RP2D is 50 mg twice daily on days 1-3, 8-10, and 15-17 of a 28-day cycle with standard dose fulvestrant. Promising antitumor activity was observed, including activity among patients with prior progression on fulvestrant.

SOX2 is required to maintain cancer stem cells in ovarian cancer

Ovarian cancer cells can form spheroids under serum‐free suspension culture conditions. The spheroids, which are enriched in cancer stem cells, can result in tumor dissemination and relapse. To identify new targetable molecules in ovarian cancer spheroids, we investigated the differential expression of genes in spheroids compared with that under monolayer culture conditions by qPCR microarray. We identified that SOX2 is overexpressed in spheroids. We then proved that SOX2 expression was increased in successive spheroid generations. Besides, knockdown of SOX2 expression in SKOV3 or HO8910 ovarian cancer spheroid cells decreased spheroid formation, cell proliferation, cell migration, resistance to Cisplatin treatment, tumorigenicity, and the expression of stemness‐related genes and epithelial to mesenchymal transition‐related genes, whereas overexpression of SOX2 in SKOV3 or HO8910 ovarian cancer cells showed the opposite effects. In addition, we found that SOX2 expression was closely associated with chemo‐resistance and poor prognosis in EOC patients. These results strongly suggest that SOX2 is required to maintain cancer stem cells in ovarian cancer. Targeting SOX2 in ovarian cancer may be therapeutically beneficial.

MicroRNAs, a subpopulation of regulators, are involved in breast cancer progression through regulating breast cancer stem cells

Cancer stem cells (CSCs; also known as tumor-initiating cells) are essential effectors of tumor progression due to their self-renewal capacity, differentiation potential, tumorigenic ability and resistance to chemotherapy, all of which contribute to cancer relapse, metastasis and a poor prognosis. Breast cancer stem cells (BCSCs) have been identified to be involved in the processes of BC initiation, growth and recurrence. MicroRNAs (miRNAs) are a class of non-coding small RNAs of 19-23 nucleotides in length that regulate gene expression at the post-transcriptional level through various mechanisms, and serve critical roles in cancer progression. miRNAs have been demonstrated to elicit effects on BCSCs characteristics via the targeting of oncogenes or tumor suppressor genes. The present study focused on the effect of miRNAs on BCSC, including BCSC formation, self-renewal and differentiation, by which miRNAs may inhibit BCSC invasion and metastasis, modulate clonogenicity and tumorigenicity of BCSCs as well as regulate chemotherapy resistance to BC. Through an improved understanding of the association between BCSCs and miRNAs, a novel and safer therapeutic target for BC may be identified.

Nuclear receptors outside the nucleus: extranuclear signalling by steroid receptors

Steroid hormone receptors mediate numerous crucial biological processes and are classically thought to function as transcriptional regulators in the nucleus. However, it has been known for more than 50 years that steroids evoke rapid responses in many organs that cannot be explained by gene regulation. Mounting evidence indicates that most steroid receptors in fact exist in extranuclear cellular pools, including at the plasma membrane. This latter pool, when engaged by a steroid ligand, rapidly activates signals that affect various aspects of cellular biology. Research into the mechanisms of signalling instigated by extranuclear steroid receptor pools and how this extranuclear signalling is integrated with responses elicited by nuclear receptor pools provides novel understanding of steroid hormone signalling and its roles in health and disease.

Cardamonin reduces chemotherapy-enriched breast cancer stem-like cells in vitro and in vivo

The failure of cytotoxic chemotherapy in breast cancers has been closely associated with the presence of drug resistant cancer stem cells (CSCs). Thus, screening for small molecules that selectively inhibit growth of CSCs may offer great promise for cancer control, particularly in combination with chemotherapy. In this report, we provide the first demonstration that cardamonin, a small molecule, selectively inhibits breast CSCs that have been enriched by chemotherapeutic drugs. In addition, cardamonin also sufficiently prevents the enrichment of CSCs when simultaneously used with chemotherapeutic drugs. Specifically, cardamonin effectively abolishes chemotherapeutic drug-induced up-regulation of IL-6, IL-8 and MCP-1 and activation of NF-κB/IKBα and Stat3. Furthermore, in a xenograft mouse model, co-administration of cardamonin and the chemotherapeutic drug doxorubicin significantly retards tumor growth and simultaneously decreases CSC pools in vivo. Since cardamonin has been found in some herbs, this work suggests a potential new approach for the effective treatment of breast CSCs by administration of cardamonin either concurrent with or after chemotherapeutic drugs.

Novel AKT phosphorylation sites identified in the pluripotency factors OCT4, SOX2 and KLF4

The four OSKM factors OCT4, SOX2, KLF4 and c-MYC are key transcription factors modulating pluripotency, self-renewal and tumorigenesis in stem cells. However, although their transcriptional targets have been extensively studied, little is known about how these factors are regulated at the posttranslational level. In this study, we established an in vitro system to identify phosphorylation patterns of the OSKM factors by AKT kinase. OCT4, SOX2, KLF4 and c-MYC were expressed in Sf9 insect cells employing the baculoviral expression system. OCT4, SOX2 and KLF4 were localized in the nucleus of insect cells, allowing their easy purification to near homogeneity upon nuclear fractionation. All transcription factors were isolated as biologically active DNA-binding proteins. Using in vitro phosphorylation and mass spectrometry-based phosphoproteome analyses several novel and known AKT phosphorylation sites could be identified in OCT4, SOX2 and KLF4.

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.

The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.

Metabolic control of cancer cell stemness: Lessons from iPS cells

The Nobel prized discovery of nuclear reprogramming is swiftly providing mechanistic evidence of a role for metabolism in the generation of cancer stem cells (CSC). Traditionally, the metabolic demands of tumors have been viewed as drivers of the genetic programming detected in cancer tissues. Beyond the energetic requirements of specific cancer cell states, it is increasingly recognized that metabolism per se controls epi-transcriptional networks to dictate cancer cell fate, i.e., metabolism can define CSC. Here I review the CSC-related metabolic features found in induced pluripotent stem (iPS) cells to provide an easily understandable framework in which the infrastructure and functioning of cellular metabolism might control the efficiency and kinetics of reprogramming in the re-routing of non-CSC to CSC-like cellular states. I suggest exploring how metabolism-dependent regulation of epigenetics can play a role in directing CSC states beyond conventional energetic demands of stage-specific cancer cell states, opening a new dimension of cancer in which the "physiological state" of CSC might be governed not only by cell-autonomous cues but also by local micro-environmental and systemic metabolo-epigenetic interactions. Forthcoming studies should decipher how specific metabolites integrate and mediate the overlap between the CSC-intrinsic "micro-epigenetics" and the "upstream" local and systemic "macro-epigenetics," thus paving the way for targeted epigenetic regulation of CSCs through metabolic modulation including "smart foods" or systemic "metabolic nichotherapies."

Information-dependent enrichment analysis reveals time-dependent transcriptional regulation of the estrogen pathway of toxicity

The twenty-first century vision for toxicology involves a transition away from high-dose animal studies to in vitro and computational models (NRC in Toxicity testing in the 21st century: a vision and a strategy, The National Academies Press, Washington, DC, 2007). This transition requires mapping pathways of toxicity by understanding how in vitro systems respond to chemical perturbation. Uncovering transcription factors/signaling networks responsible for gene expression patterns is essential for defining pathways of toxicity, and ultimately, for determining the chemical modes of action through which a toxicant acts. Traditionally, transcription factor identification is achieved via chromatin immunoprecipitation studies and summarized by calculating which transcription factors are statistically associated with up- and downregulated genes. These lists are commonly determined via statistical or fold-change cutoffs, a procedure that is sensitive to statistical power and may not be as useful for determining transcription factor associations. To move away from an arbitrary statistical or fold-change-based cutoff, we developed, in the context of the Mapping the Human Toxome project, an enrichment paradigm called information-dependent enrichment analysis (IDEA) to guide identification of the transcription factor network. We used a test case of activation in MCF-7 cells by 17β estradiol (E2). Using this new approach, we established a time course for transcriptional and functional responses to E2. ERα and ERβ were associated with short-term transcriptional changes in response to E2. Sustained exposure led to recruitment of additional transcription factors and alteration of cell cycle machinery. TFAP2C and SOX2 were the transcription factors most highly correlated with dose. E2F7, E2F1, and Foxm1, which are involved in cell proliferation, were enriched only at 24 h. IDEA should be useful for identifying candidate pathways of toxicity. IDEA outperforms gene set enrichment analysis (GSEA) and provides similar results to weighted gene correlation network analysis, a platform that helps to identify genes not annotated to pathways.

Small cell lung cancer: Circulating tumor cells of extended stage patients express a mesenchymal-epithelial transition phenotype

Small cell lung cancer (SCLC) is distinguished by aggressive growth, early dissemination and a poor prognosis at advanced stage. The remarkably high count of circulating tumor cells (CTCs) of SCLC allowed for the establishment of permanent CTC cultures at our institution for the first time. CTCs are assumed to have characteristics of cancer stem cells (CSCs) and an epithelial-mesenchymal transition (EMT) phenotype, but extravasation of tumors at distal sites is marked by epithelial features. Two SCLC CTC cell lines, namely BHGc7 and BHGc10, as well as SCLC cell lines derived from primary tumors and metastases were analyzed for the expression of pluripotent stem cell markers and growth factors. Expression of E-cadherin and β-Catenin were determined by flow cytometry. Stem cell-associated markers SOX17, α-fetoprotein, OCT-3/4, KDR, Otx2, GATA-4, Nanog, HCG, TP63 and Goosecoid were not expressed in the 2 CTC lines. In contrast, high expression was found for HNF-3β/FOXA2, SOX2, PDX-1/IPF1 and E-cadherin. E-cadherin expression was restricted to the 2 CTCs and 2 cell lines derived from pleural effusion (SCLC26A) and bone metastases (NCI-H526), respectively. Thus, these SCLC CTCs established from extended disease SCLC patients lack expression of stem cell markers which suppress the epithelial phenotype. Instead they express high levels of E-cadherin consistent with a mesenchymal-epithelial transition (MET or EMrT) and form large tumorospheres possibly in response to the selection pressure of first-line chemotherapy. HNF-3β/FOXA2 and PDX-1/IPF1 expression seem to be related to growth factor dependence on insulin/IGF-1 receptors and IGF-binding proteins.

Regulation of steroid hormone receptors and coregulators during the cell cycle highlights potential novel function in addition to roles as transcription factors

Cell cycle progression is tightly controlled by several kinase families including Cyclin-Dependent Kinases, Polo-Like Kinases, and Aurora Kinases. A large amount of data show that steroid hormone receptors and various components of the cell cycle, including cell cycle regulated kinases, interact, and this often results in altered transcriptional activity of the receptor. Furthermore, steroid hormones, through their receptors, can also regulate the transcriptional expression of genes that are required for cell cycle regulation. However, emerging data suggest that steroid hormone receptors may have roles in cell cycle progression independent of their transcriptional activity. The following is a review of how steroid receptors and their coregulators can regulate or be regulated by the cell cycle machinery, with a particular focus on roles independent of transcription in G2/M.

Embryonic Stem Cell-Related Protein L1TD1 Is Required for Cell Viability, Neurosphere Formation, and Chemoresistance in Medulloblastoma

Misexpression of stem cell-related genes may occur in some cancer cells, influencing patient's prognosis. This is the case of medulloblastoma, a common and clinically challenging malignant tumor of the central nervous system, where expression of the pluripotency factor, OCT4, is correlated with poor survival. A downstream target of OCT4, L1TD1 (LINE-1 type transposase domain-containing protein 1 family member), encodes a novel embryonic stem cell (ESC)-related protein involved in pluripotency and self-renewal of ESCs. L1TD1 is still poorly characterized and its expression pattern and function in cancer cells are virtually unknown. Although normally restricted to non-neoplastic undifferentiated cells and germ cells, we found that high L1TD1 expression also occurs in medulloblastoma cells, reaching levels similar to those found in ESCs, and is correlated with poor prognosis. Conversely to what is reported during normal cell differentiation, when differentiated cells remain healthy, despite L1TD1 downregulation, depletion of L1TD1 protein levels by targeted gene silencing significantly reduced medulloblastoma cell viability, inhibiting cell proliferation and inducing apoptosis. More strikingly, L1TD1 depletion downregulated expression of the neural stem cell markers, CD133 and Nestin, inhibited neurosphere generation capability, and sensitized medulloblastoma cells to temozolomide and cisplatin, two chemotherapeutic agents of clinical relevance in medulloblastoma treatment. Our findings provide insights about the contribution of pluripotency-related genes to a more aggressive tumor phenotype through their involvement in the acquisition of stem-like properties by cancer cells and point out L1TD1 as a potential therapeutic target in malignant brain tumors.

Long noncoding RNA linc00617 exhibits oncogenic activity in breast cancer

Protein-coding genes account for only 2% of the human genome, whereas the vast majority of transcripts are noncoding RNAs including long noncoding RNAs. LncRNAs are involved in the regulation of a diverse array of biological processes, including cancer progression. An evolutionarily conserved lncRNA TUNA, was found to be required for pluripotency of mouse embryonic stem cells. In this study, we found the human ortholog of TUNA, linc00617, was upregulated in breast cancer samples. Linc00617 promoted motility and invasion of breast cancer cells and induced epithelial-mesenchymal-transition (EMT), which was accompanied by generation of stem cell properties. Moreover, knockdown of linc00617 repressed lung metastasis in vivo. We demonstrated that linc00617 upregulated the expression of stemness factor Sox2 in breast cancer cells, which was shown to promote the oncogenic activity of breast cancer cells by stimulating epithelial-to-mesenchymal transition and enhancing the tumor-initiating capacity. Thus, our data indicate that linc00617 functions as an important regulator of EMT and promotes breast cancer progression and metastasis via activating the transcription of Sox2. Together, it suggests that linc00617 may be a potential therapeutic target for aggressive breast cancer. © 2015 Wiley Periodicals, Inc.

The other face of TLR3: A driving force of breast cancer stem cells

Activation of TLR3 has long been studied in the field of anticancer immunotherapy. Our recent work revealed that TLR3 also promotes the induction of breast cancer stem cells (CSCs) through co-activation of β-catenin and NF-κB signaling. Targeting these 2 pathways simultaneously instead of individually allows for effective inhibition of CSCs that are enhanced by TLR3 activation.

The Activation of the Sox2 RR2 Pluripotency Transcriptional Reporter in Human Breast Cancer Cell Lines is Dynamic and Labels Cells with Higher Tumorigenic Potential

The striking similarity displayed at the mechanistic level between tumorigenesis and the generation of induced pluripotent stem cells and the fact that genes and pathways relevant for embryonic development are reactivated during tumor progression highlights the link between pluripotency and cancer. Based on these observations, we tested whether it is possible to use a pluripotency-associated transcriptional reporter, whose activation is driven by the SRR2 enhancer from the Sox2 gene promoter (named S4+ reporter), to isolate cancer stem cells (CSCs) from breast cancer cell lines. The S4+ pluripotency transcriptional reporter allows the isolation of cells with enhanced tumorigenic potential and its activation was switched on and off in the cell lines studied, reflecting a plastic cellular process. Microarray analysis comparing the populations in which the reporter construct is active versus inactive showed that positive cells expressed higher mRNA levels of cytokines (IL-8, IL-6, TNF) and genes (such as ATF3, SNAI2, and KLF6) previously related with the CSC phenotype in breast cancer.

Histone deacetylase 1/Sp1/microRNA-200b signaling accounts for maintenance of cancer stem-like cells in human lung adenocarcinoma

The presence of cancer stem-like cells (CSCs) is one of the mechanisms responsible for chemoresistance that has been a major hindrance towards lung adenocarcinoma (LAD) treatment. Recently, we have identified microRNA (miR)-200b as a key regulator of chemoresistance in human docetaxel-resistant LAD cells. However, whether miR-200b has effects on regulating CSCs remains largely unclear and needs to be further elucidated. Here, we showed that miR-200b was significantly downregulated in CD133+/CD326+ cells that exhibited properties of CSCs derived from docetaxel-resistant LAD cells. Also, restoration of miR-200b could inhibit maintenance and reverse chemoresistance of CSCs. Furthermore, suppressor of zeste-12 (Suz-12) was identified as a direct and functional target of miR-200b, and silencing of Suz-12 phenocopied the effects of miR-200b on CSCs. Additionally, overexpression of histone deacetylase (HDAC) 1 was identified as a pivotal mechanism responsible for miR-200b repression in CSCs through a specificity protein (Sp) 1-dependent mechanism, and restoration of miR-200b by HDAC1 repression significantly suppressed CSCs formation and reversed chemoresistance of CSCs by regulating Suz-12-E-cadherin signaling. Also, downregulation of HDAC1 or upregulation of miR-200b reduced the in vivo tumorigenicity of CSCs. Finally, Suz-12 was inversely correlated with miR-200b, positively correlated with HDAC1 and up-regulated in docetaxel-resistant LAD tissues compared with docetaxel-sensitive tissues. Taken together, the HDAC1/miR-200b/Suz-12-E-cadherin signaling might account for maintenance of CSCs and formation of chemoresistant phenotype in docetaxel-resistant LAD cells.

Targeting breast cancer initiating cells: advances in breast cancer research and therapy

Over the past 10 years there have been significant advances in our understanding of breast cancer and the important roles that breast cancer initiating cells (CICs) play in the development and resistance of breast cancer. Breast CICs endowed with self-renewing and tumor-initiating capacities are believed to be responsible for the relapses which often occur after various breast cancer therapies. In this review, we will summarize some of the key developments in breast CICs which will include discussion of some of the key genes implicated: estrogen receptor (ER), HER2, BRCA1, TP53, PIK3CA, RB, P16INK1 and various miRs as well some drugs which are showing promise in targeting CICs. In addition, the concept of combined therapies will be discussed. Basic and clinical research is resulting in novel approaches to improve breast cancer therapy by targeting the breast CICs.

SOX2 and cancer: current research and its implications in the clinic

SOX2 is a gene that encodes for a transcription factor belonging to the SOX gene family and contains a high-mobility group (HMG) domain, which permits highly specific DNA binding. Consequently, SOX2 functions as an activator or suppressor of gene transcription. SOX2 has been described as an essential embryonic stem cell gene and moreover, a necessary factor for induced cellular reprogramming. SOX2 research has only recently switched focus from embryogenesis and development to SOX2’s function in disease. Particularly, the role of SOX2 in cancer pathogenesis has become of interest in the field. To date, studies have shown SOX2 to be amplified in various cancer types and affect cancer cell physiology via involvement in complicated cell signaling and protein-protein interactions. Recent reviews in this field have highlighted SOX2 in mammalian physiology, development and pathology. In this review, we comprehensively compile what is known to date about SOX2’s involvement in cancer biology, focusing on the most recent findings in the fields of cellular signaling and cancer stem cells. Lastly, we underscore the role of SOX2 in the clinic and highlight new findings, which may provide novel clinical applications for SOX2 as a prognostic marker, indicator of metastasis, biomarker or potential therapeutic target in some cancer types.

Xenopatients 2.0: reprogramming the epigenetic landscapes of patient-derived cancer genomes

In the science-fiction thriller film Minority Report, a specialized police department called "PreCrime" apprehends criminals identified in advance based on foreknowledge provided by 3 genetically altered humans called "PreCogs". We propose that Yamanaka stem cell technology can be similarly used to (epi)genetically reprogram tumor cells obtained directly from cancer patients and create self-evolving personalized translational platforms to foresee the evolutionary trajectory of individual tumors. This strategy yields a large stem cell population and captures the cancer genome of an affected individual, i.e., the PreCog-induced pluripotent stem (iPS) cancer cells, which are immediately available for experimental manipulation, including pharmacological screening for personalized "stemotoxic" cancer drugs. The PreCog-iPS cancer cells will re-differentiate upon orthotopic injection into the corresponding target tissues of immunodeficient mice (i.e., the PreCrime-iPS mouse avatars), and this in vivo model will run through specific cancer stages to directly explore their biological properties for drug screening, diagnosis, and personalized treatment in individual patients. The PreCog/PreCrime-iPS approach can perform sets of comparisons to directly observe changes in the cancer-iPS cell line vs. a normal iPS cell line derived from the same human genetic background. Genome editing of PreCog-iPS cells could create translational platforms to directly investigate the link between genomic expression changes and cellular malignization that is largely free from genetic and epigenetic noise and provide proof-of-principle evidence for cutting-edge "chromosome therapies" aimed against cancer aneuploidy. We might infer the epigenetic marks that correct the tumorigenic nature of the reprogrammed cancer cell population and normalize the malignant phenotype in vivo. Genetically engineered models of conditionally reprogrammable mice to transiently express the Yamanaka stemness factors following the activation of phenotypic copies of specific cancer diseases might crucially evaluate a "reprogramming cure" for cancer. A new era of xenopatients 2.0 generated via nuclear reprogramming of the epigenetic landscapes of patient-derived cancer genomes might revolutionize the current personalized translational platforms in cancer research.