Cancer stem cells--an old idea that's new again: implications for the diagnosis and treatment of breast cancer

Cancer Stem Cells and their Management in Cancer Therapy

BACKGROUND

In the last decade, the proposed Cancer Stem Cell (CSC) hypothesis has steadily changed the way cancer treatment is approached. CSCs may be the source of the heterogeneous non-tumorigenic cell population included in a neoplasm. Intratumor and intertumoral heterogeneity is a well-known phenomenon that massively entangles the diagnosis and treatment of cancer. The literature seems to suggest that heterogeneity develops progressively within tumor-initiating stem cells. CSCs harbor genetic and/or epigenetic alterations that allow them to differentiate into multiple tumor cell types sequentially.

OBJECTIVE

The CSC hypothesis, cellular therapy, and the most recent patents on CSCs were reviewed.

METHODS

PubMed, Scopus, and Google Scholar were screened for this information. Also, an analysis of the most recent data targeting CSCs in pediatric cancer developed at two Canadian institutions is provided. The genes involved with the activation of CSCs and the drugs used to antagonize them are also highlighted.

RESULTS

It is underlined that (1) CSCs possess stem cell-like properties, including the ability for self-renewal; (2) CSCs can start carcinogenesis and are responsible for tumor recurrence after treatment; (3) Although some limitations have been raised, which may oppose the CSC hypothesis, cancer progression and metastasis have been recognized to be caused by CSCs.

CONCLUSION

The significant roles of cell therapy may include an auto-transplant with high-dose treatment, an improvement of the immune function, creation of chimeric antigen receptor T cells, and the recruitment of NK cell-based immunotherapy.

9-phenyl acridine photosensitizes A375 cells to UVA radiation

Acridines are an important class of bioactive molecules having varied uses. Its derivative, 9-phenylacridine (ACPH) had been found to exhibit antitumor activity both in cell lines and in vivo model. Its DNA binding ability and absorbance in the ultraviolet range encouraged us to investigate its role as a photosensitizer with UVA radiation. We investigated the effects of ACPH prior to UVA exposure on in vitro DNA through photo-cleavage assay. Effect of such treatment was also studied in cultured A375 melanoma cells. Endpoints studied included morphological changes, evaluation of cellular viability, scratch assay, intracellular reactive oxygen species (ROS) production, DNA damage, lipid peroxidation, glutathione (GSH) level, autophagy, cell cycle progression, depletion of mitochondrial membrane potential (ΔΨmt), induction of apoptosis and Hoechst dye efflux assay. Our findings indicated that ACPH could sensitize damage to DNA induced by UVA both in vitro and in cells. It could also potentiate cell killing by UVA. It arrested cells in G2/M phase and induced apoptotic death through mitochondria mediated pathway. This sensitization was through enhancement of intracellular ROS. Our findings also indicated that the stem cells side population was reduced on such treatment. The findings are important as it indicates ACPH as a promising photosensitizer and indicates its possible role in photodynamic therapy.

Notch Signaling Regulates Mitochondrial Metabolism and NF-κB Activity in Triple-Negative Breast Cancer Cells via IKKα-Dependent Non-canonical Pathways

Triple negative breast cancer (TNBC) patients have high risk of recurrence and metastasis, and current treatment options remain limited. Cancer stem-like cells (CSCs) have been linked to cancer initiation, progression and chemotherapy resistance. Notch signaling is a key pathway regulating TNBC CSC survival. Treatment of TNBC with PI3K or mTORC1/2 inhibitors results in drug-resistant, Notch-dependent CSC. However, downstream mechanisms and potentially druggable Notch effectors in TNBC CSCs are largely unknown. We studied the role of the AKT pathway and mitochondrial metabolism downstream of Notch signaling in TNBC CSC from cell lines representative of different TNBC molecular subtypes as well as a novel patient-derived model. We demonstrate that exposure of TNBC cells to recombinant Notch ligand Jagged1 leads to rapid AKT phosphorylation in a Notch1-dependent but RBP-Jκ independent fashion. This requires mTOR and IKKα. Jagged1 also stimulates mitochondrial respiration and fermentation in an AKT- and IKK-dependent fashion. Notch1 co-localizes with mitochondria in TNBC cells. Pharmacological inhibition of Notch cleavage by gamma secretase inhibitor PF-03084014 in combination with AKT inhibitor MK-2206 or IKK-targeted NF-κB inhibitor Bay11-7082 blocks secondary mammosphere formation from sorted CD90^hi or CD44⁺CD24^low (CSCs) cells. A TNBC patient-derived model gave comparable results. Besides mitochondrial oxidative metabolism, Jagged1 also triggers nuclear, NF-κB-dependent transcription of anti-apoptotic gene cIAP-2. This requires recruitment of Notch1, IKKα and NF-κB to the cIAP-2 promoter. Our observations support a model where Jagged1 triggers IKKα-dependent, mitochondrial and nuclear Notch1 signals that stimulate AKT phosphorylation, oxidative metabolism and transcription of survival genes in PTEN wild-type TNBC cells. These data suggest that combination treatments targeting the intersection of the Notch, AKT and NF-κB pathways have potential therapeutic applications against CSCs in TNBC cases with Notch1 and wild-type PTEN expression.

miR-372 and miR-373 enhance the stemness of colorectal cancer cells by repressing differentiation signaling pathways

miR‐372/373, a cluster of stem cell‐specific microRNAs transactivated by the Wnt pathway, has been reported to be dysregulated in various cancers, particularly colorectal cancer (CRC); however, the unique role of these microRNAs in cancer remains to be discovered. In the present study, we characterized the upregulation in expression of miR‐372/373 in CRC tissues from The Cancer Genome Atlas data, and then showed that overexpression of miR‐372/373 enhanced the stemness of CRC cells by enriching the CD26/CD24‐positive cell population and promoting self‐renewal, chemotherapy resistance and the invasive potential of CRC cells. To clarify the mechanism underlying microRNA‐induced stemness, we profiled 45 cell signaling pathways in CRC cells overexpressing miR‐372/373 and found that stemness‐related pathways, such as Nanog and Hedgehog, were upregulated. Instead, differentiation‐related pathways, such as NFκB, MAPK/Erk and VDR, were markedly repressed by miR‐372/373. Numerous new targets of miR‐372/373 were identified, including SPOP, VDR and SETD7, all of which are factors important for cell differentiation. Furthermore, in contrast to the increase in miR‐372/373 expression in CRC tissues, the expression levels of SPOP and VDR mRNA were significantly downregulated in these tissues, indicative of the poor differentiation status of CRC. Taken together, our findings suggest that miR‐372/373 enhance CRC cell stemness by repressing the expression of differentiation genes. These results provide new insights for understanding the function and mechanisms of stem cell‐specific microRNAs in the development of metastasis and drug resistance in CRC.

Functional Polymorphism in the MSI1 Gene Promoter Confers a Decreased Risk of Lung Cancer in Chinese by Reducing MSI1 Expression

Background:

Musashi1 (MSI1) is a characteristic stem cell marker that regulates the balance between cell self-renewal and differentiation. Evidence has identified MSI1 as a pivotal oncogenic regulator in diverse malignancies. However, little evidence uncovers the role of genetic variations of MSI1 gene in cancer etiology.

Objective:

The aim of this study was to investigate the association between genetic variants in the MSI1 gene and lung cancer risk.

Methods:

Based on a two-stage retrospective study with a total of 1559 patients with lung cancer and 1667 healthy controls, we evaluated the relevance between three putative functional SNPs in the MSI1 promoter (i.e., -2696T>C[rs7959801], -2297T>C[rs3742038] and -1081C>T[rs34570155]) and lung cancer risk.

Results:

We found that the SNP rs7959801T>C was significantly associated with lung cancer susceptibility. Compared to those with rs7959801TT wild-genotype, individuals with CT/CC variant genotypes exerted consistently beneficial roles in lung cancer risk in the discovery set (adjusted odd ratios [OR] = 0.67; 95% confidence interval [CI] = 0.57-0.80), and in the validation set (OR=0.69; 95%CI=0.54-0.88). Functional assays indicated that the allele transformation from T to C in rs7959801 of MSI1 gene arrestingly decreased its transcription activity in vitro. Furthermore, the expression levels of MSI1 were significantly lower in the patients with CT/CC variants than in those who were with TT genotype.

Conclusion:

Our findings suggested that the rs7959801T>C polymorphism in the MSI1 promoter conferred a decreased risk to lung cancer by reducing the expression of MSI1 and it may be a promising indicator for lung cancer predisposition.

The Ever-Evolving Concept of the Cancer Stem Cell in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), the most common type of pancreatic cancer, is the 4th most frequent cause of cancer-related death worldwide, primarily due to the inherent chemoresistant nature and metastatic capacity of this tumor. The latter is believed to be mainly due to the existence of a subpopulation of highly plastic “stem”-like cells within the tumor, known as cancer stem cells (CSCs), which have been shown to have unique metabolic, autophagic, invasive, and chemoresistance properties that allow them to continuously self-renew and escape chemo-therapeutic elimination. As such, current treatments for the majority of PDAC patients are not effective and do not significantly impact overall patient survival (<7 months) as they do not affect the pancreatic CSC (PaCSC) population. In this context, it is important to highlight the need to better understand the characteristics of the PaCSC population in order to develop new therapies to target these cells. In this review, we will provide the latest updates and knowledge on the inherent characteristics of PaCSCs, particularly their unique biological properties including chemoresistance, epithelial to mesenchymal transition, plasticity, metabolism and autophagy.

HCV nonstructural protein 4 is associated with aggressiveness features of breast cancer

BACKGROUND

Hepatitis C virus (HCV) has the lymphotropic feature that is supposed to be the reason of related extrahepatic manifestation. HCV viral oncoproteins may participate in the regulation of some gene expression that has been implicated in tumorigenesis. Our aim is to evaluate the HCV-NS4 circulating levels in breast cancer (BC) and to investigate its relation with BC tumor aggressiveness.

METHODS

This study was performed among 158 Egyptian women (120 with BC and 38 with benign breast diseases). ELISA was used for detection of anti-HCV antibodies, HCV-NS4, fibronectin, and CA 15-3.

RESULTS

No association between HCV detection in this group of BC patients (27.5% in BC vs. 23.7% in breast benign diseases, P = 0.687). Among HCV-infected patients, the mean HCV-NS4 serum level in BC was significantly higher than benign group (61.7 μg/mL vs. 33.9 μg/mL, P = 0.0005). Fibronectin levels were higher (P = 0.014) in patients infected with HCV than noninfected BC patients. Elevated HCV-NS4 levels were associated with tumor severity features like large size, late stages, high grades, and infiltrated lymph nodes. The elevated levels of HCV-NS4 (> 40 μg/mL) yielded an estimated odds ratio (95% confidence intervals) of 2.5 (0.98-6.36), 1.2 (0.44-3.33), 1.9 (0.53-7.00), and 2.5 (0.87-7.33) for developing large size, late stages, high grades, and infiltrated lymph nodes, respectively. Interestingly, HCV-NS4 levels significantly correlated with other BC tumor marker like CA15-3 (r = 0.535; P = 0.0009) and fibronectin (r = 0.432; P < 0.0001).

CONCLUSIONS

HCV-NS4 appears to be associated with BC progression features. Oncologists treating such BC patients should consider HCV screening to enable the early identification and to prevent progression of the disease.

Anti-cancer efficacy of nonthermal plasma dissolved in a liquid, liquid plasma in heterogeneous cancer cells

The therapeutic potential of nonthermal plasma for cancer treatment has been reported recently. The heterogeneity of cancer cells need to be addressed to design effective anticancer treatments. Here, we show that treatment with nonthermal atmospheric-pressure plasma dissolved in a liquid (liquid plasma) induces oxidative stress in heterogeneous populations of cancer cells and ultimately kills these cells via apoptosis, regardless of genetic status, e.g., mutations in p53 and other DNA-damage-response genes. We found that liquid plasma markedly increased the concentration of intracellular and mitochondrial reactive oxygen species (ROS), reflecting an influx from the extracellular milieu. Liquid plasma contributed to mitochondrial accumulation of ROS and depolarization of mitochondrial membrane potential with consequent cell death. Healthy normal cells, however, were hardly affected by the liquid-plasma treatment. The antioxidant N-acetylcysteine blocked liquid-plasma-induced cell death. A knockdown of CuZn-superoxide dismutase or Mn-SOD enhanced the plasma-induced cell death, whereas expression of exogenous CuZn-SOD, Mn-SOD, or catalase blocked the cell death. These results suggest that the mitochondrial dysfunction mediated by ROS production is a key contributor to liquid-plasma-induced apoptotic cell death, regardless of genetic variation. Thus, liquid plasma may have clinical applications, e.g., the development of therapeutic strategies and prevention of disease progression despite tumor heterogeneity.

Breast cancer stem-like cells: clinical implications and therapeutic strategies

Breast cancer is the most frequently diagnosed cancer in women, being also the leading cause of cancer death among female population, including in Romania. Resistance to therapy represents a major problem for cancer treatment. Current cancer treatments are both expensive and induce serious side effects; therefore ineffective therapies are both traumatic and pricy. Characterizing predictive markers that can identify high-risk patients could contribute to dedicated/personalized therapy to improve the life quality and expectancy of cancer patients. Moreover, there are some markers that govern specific tumor molecular features that can be targeted with specific therapies for those patients who are most likely to benefit. The identification of stem cells in both normal and malignant breast tissue have lead to the hypothesis that breast tumors arise from breast cancer stem-like cells (CSCs), and that these cells influence tumor’s response to therapy. CSCs have similar self-renewal properties to normal stem cells, however the balance between the signaling pathways is altered towards tumor formation In this review, we discuss the molecular aspects of breast CSCs and the controversies regarding their use in the diagnosis and treatment decision of breast cancer patients.

Cancer stem cells in drug resistant lung cancer: Targeting cell surface markers and signaling pathways

Lung cancer is the leading cause of cancer mortality worldwide. Despite advances in anti-cancer therapies such as chemotherapy, radiotherapy and targeted therapies, five-year survival rates remain poor (<15%). Inherent and acquired resistance has been identified as a key factor in reducing the efficacy of current cytotoxic therapies in the management of non-small cell lung cancer (NSCLC). There is growing evidence suggesting that cancer stem cells (CSCs) play a critical role in tumor progression, metastasis and drug resistance. Similar to normal tissue stem cells, CSCs exhibit significant phenotypic and functional heterogeneity. While CSCs have been reported in a wide spectrum of human tumors, the biology of CSCs in NSCLC remain elusive. Current anti-cancer therapies fail to eradicate CSC clones and instead, favor the expansion of the CSC pool and select for resistant CSC clones thereby resulting in treatment resistance and subsequent relapse in these patients. The identification of CSC-specific marker subsets and the targeted therapeutic destruction of CSCs remains a significant challenge. Strategies aimed at efficient targeting of CSCs are becoming increasingly important for monitoring the progress of cancer therapy and for evaluating new therapeutic approaches. This review focuses on the current knowledge of cancer stem cell markers in treatment-resistant lung cancer cells and the signaling cascades activated by these cells to maintain their stem-like properties. Recent progress in CSC-targeted drug development and the current status of novel agents in clinical trials are also reviewed.

Characterization of stem-like cells in mucoepidermoid tracheal paediatric tumor

Stem cells contribute to regeneration of tissues and organs. Cells with stem cell-like properties have been identified in tumors from a variety of origins, but to our knowledge there are yet no reports on tumor-related stem cells in the human upper respiratory tract. In the present study, we show that a tracheal mucoepidermoid tumor biopsy obtained from a 6 year-old patient contained a subpopulation of cells with morphology, clonogenicity and surface markers that overlapped with bone marrow mesenchymal stromal cells (BM-MSCs). These cells, designated as MEi (mesenchymal stem cell-like mucoepidermoid tumor) cells, could be differentiated towards mesenchymal lineages both with and without induction, and formed spheroids in vitro. The MEi cells shared several multipotent characteristics with BM-MSCs. However, they displayed differences to BM-MSCs in growth kinectics and gene expression profiles relating to cancer pathways and tube development. Despite this, the MEi cells did not possess in vivo tumor-initiating capacity, as proven by the absence of growth in situ after localized injection in immunocompromised mice. Our results provide an initial characterization of benign tracheal cancer-derived niche cells. We believe that this report could be of importance to further understand tracheal cancer initiation and progression as well as therapeutic development.

Enriched CD44(+)/CD24(-) population drives the aggressive phenotypes presented in triple-negative breast cancer (TNBC)

The mechanism underlying the aggressive behaviors of triple negative breast cancer (TNBC) is not well characterized yet. The association between cancer stem cell (CSC) population and the aggressive behaviors of TNBC has not been established. We found the CD44(+)/CD24(-) cell population was enriched in TNBC tissues and cell lines, with a higher capacity of proliferation, migration, invasion and tumorigenicity as well as lower adhesion ability. The CD44(+)/CD24(-) cell population with cancer stem cell-like properties may play an important role in the aggressive behaviors of TNBC. This discovery may lead to new therapeutic strategies targeting CD44(+)/CD24(-) cell population in TNBC.

Autophagy promotes resistance to photodynamic therapy-induced apoptosis selectively in colorectal cancer stem-like cells

Recent studies have indicated that cancer stem-like cells (CSCs) exhibit a high resistance to current therapeutic strategies, including photodynamic therapy (PDT), leading to the recurrence and progression of colorectal cancer (CRC). In cancer, autophagy acts as both a tumor suppressor and a tumor promoter. However, the role of autophagy in the resistance of CSCs to PDT has not been reported. In this study, CSCs were isolated from colorectal cancer cells using PROM1/CD133 (prominin 1) expression, which is a surface marker commonly found on stem cells of various tissues. We demonstrated that PpIX-mediated PDT induced the formation of autophagosomes in PROM1/CD133⁺ cells, accompanied by the upregulation of autophagy-related proteins ATG3, ATG5, ATG7, and ATG12. The inhibition of PDT-induced autophagy by pharmacological inhibitors and silencing of the ATG5 gene substantially triggered apoptosis of PROM1/CD133⁺ cells and decreased the ability of colonosphere formation in vitro and tumorigenicity in vivo. In conclusion, our results revealed a protective role played by autophagy against PDT in CSCs and indicated that targeting autophagy could be used to elevate the PDT sensitivity of CSCs. These findings would aid in the development of novel therapeutic approaches for CSC treatment.

A critical role of CD29 and CD49f in mediating metastasis for cancer-initiating cells isolated from a Brca1-associated mouse model of breast cancer

Cancer metastasis is a lethal problem that claims the lives of over 90% of cancer patients. In this study, we have investigated metastatic potential of cancer stem cells (CSCs) isolated from mammary tumors of a Brca1-mutant mouse model. Our data indicated that CSCs, which are enriched in CD24(+)CD29(+)/CD49f(+) cell population, displayed much higher migration ability than CD24(-)CD29(-)/CD49f(-) cells in tissue culture and enhanced metastatic potential in allograft-nude mice. CD24(+)CD29(+) cells maintained the ability to differentiate and reconstitute heterogeneity in the metastatic tumors whereas CD24(-)CD29(-) cells could not. Corresponding to their enhanced metastatic ability, CD24(+)CD29(+) cells exhibited features of the epithelial to mesenchymal transition. Finally, using short hairpin RNA to knock down CD29 and/or CD49f in metastatic cancer cells, we demonstrated that while acute knockdown of CD29 or CD49f alone slightly decreased cell migration ability, knockdown of both genes generated a profound effect to block their migration, revealing an overlapping, yet critical function of both genes in the migration of CSCs. Our findings indicate that in addition to serving as markers of CSCs, CD29 and CD49f may also serve as potential therapeutic targets for cancer metastasis.

Doublecortin-like kinase 1 exhibits cancer stem cell-like characteristics in a human colon cancer cell line

OBJECTIVE

Colon cancer stem cells (CSCs) are implicated in colorectal cancer carcinogenesis, metastasis, and therapeutic resistance. The identification of these cells could help to develop novel therapeutic strategies. Doublecortin-like kinase 1 (DCLK1) has been viewed as a marker for gastrointestinal stem cells that fuel the self-renewal process, however others view them as a marker of Tuft cells or as an enteroendocrine subtype. The purpose of this study was to use a colon cancer cell line to identify and characterize the stem-like characteristics of the DCLK1+ cell population.

METHODS

To enrich stem-like cells, HCT116 cells (derived from colon adenocarcinomas) were cultured using serum-free media to form spheres under both normal oxygen and hypoxia condition. DCLK1 transcript expression in the adherent parental cells and spheroids was quantified using quantitative real time reverse transcription- polymerase chain reaction [(q)RT-PCR]. DCLK1 protein expression was determined using flow cytometry. Self-renewal capability from adherent parental cells and spheroids was determined using extreme limiting dilution analysis (ELDA).

RESULTS

Under both normal oxygen and hypoxia condition, the adherent parental cells were composed of cells that express low levels of DCLK1. However, spheroids exhibited an increased frequency of cells expressing DCLK1 on both mRNA and protein levels. Cells derived from spheroids also possess stronger self-renewal capability.

CONCLUSIONS

The higher fraction of DCLK1+ cells exhibited by spheroids and hypoxia reflects the stem-like characteristics of these cells. DCLK1 may represent an ideal marker to study and develop effective strategies to overcome chemo-resistance and relapse of colon cancer.

Preclinical and clinical studies of gamma secretase inhibitors with docetaxel on human breast tumors

PURPOSE

Accumulating evidence supports the existence of breast cancer stem cells (BCSC), which are characterized by their capacity to self-renew and divide indefinitely and resistance to conventional therapies. The Notch pathway is important for stem cell renewal and is a potential target for BCSC-directed therapy.

EXPERIMENTAL DESIGN

Using human breast tumorgraft studies, we evaluated the impact of gamma secretase inhibitors (GSI) on the BCSC population and the efficacy of combining GSI with docetaxel treatment. The mouse experimental therapy paralleled a concurrent clinical trial in patients with advanced breast cancer, designed to determine the maximum-tolerated dose of the GSI, MK-0752, administered sequentially with docetaxel, and to evaluate BCSC markers in serial tumor biopsies.

RESULTS

Treatment with GSI reduced BCSCs in MC1 and BCM-2147 tumorgrafts by inhibition of the Notch pathway. GSI enhanced the efficacy of docetaxel in preclinical studies. In the clinical trial, 30 patients with advanced breast cancer were treated with escalating doses of MK-0752 plus docetaxel. Clinically, meaningful doses of both drugs were possible with manageable toxicity and preliminary evidence of efficacy. A decrease in CD44(+)/CD24(-), ALDH(+), and mammosphere-forming efficiency were observed in tumors of patients undergoing serial biopsies.

CONCLUSIONS

These preclinical data show that pharmacologic inhibition of the Notch pathway can reduce BCSCs in breast tumorgraft models. The clinical trial shows feasibility of combination GSI and chemotherapy, and together these results encourage further study of Notch pathway inhibitors in combination with chemotherapy in breast cancer.

Aldehyde dehydrogenase 1-positive cells in axillary lymph node metastases after chemotherapy as a prognostic factor in patients with lymph node-positive breast cancer

BACKGROUND

Aldehyde dehydrogenase 1 (ALDH1)-positive cells exhibit stem-like or progenitor ability and have been considered a clinically important diagnostic and therapeutic target in patients with breast cancer. In this study, the authors evaluated responsiveness to chemotherapy of ALDH1-positive cells in primary and metastatic lesions and its relation to prognosis for patients with lymph node-positive breast cancer.

METHODS

In total, 115 patients who had breast cancer with cytologically confirmed lymph node metastases and who underwent surgery after neoadjuvant chemotherapy (NAC) were evaluated. By using ALDH1 immunohistochemistry in core-needle biopsy specimens of the primary tumor, cytology samples of axillary lymph nodes before NAC, and pathologic samples of each after NAC, the clinical significance of ALDH1-positive cell status was evaluated in primary and metastatic lesions before and after NAC.

RESULTS

The presence of ALDH1-positive cancer cells, but not ALDH1-negative cancer cells, in primary and metastatic lesions after NAC was associated with a worse prognosis. In multivariate analysis, only ALDH1-positive cells in metastatic lesions after NAC correlated with overall survival. The responsiveness of ALDH1-positive cells to chemotherapy differed between primary and metastatic lesions, and the findings indicated that ALDH1-positive cells in metastatic lesions after NAC may clinically precede those in the primary lesion.

CONCLUSIONS

The responsiveness of ALDH1-positive cells to chemotherapy in primary and metastatic lesions and its prognostic significance were clarified in patients with breast cancer. The authors concluded that ALDH1-positive status may represent a surrogate marker as a new concept in patients with lymph node-positive breast cancer.

CD44(+)/CD24(-/low) cancer stem/progenitor cells are more abundant in triple-negative invasive breast carcinoma phenotype and are associated with poor outcome

Women classified as having triple-negative tumors have a poor prognosis. The importance of CD44(+)/CD24(-/low) (stem/progenitor cell-phenotype) in breast cancer patients has also been appreciated. However, correlation between triple negativity and CD44(+)/CD24(-/low) with tumor recurrence remains elusive. In the present study, we evaluated tumor specimens of 50 breast cancer patients with known hormone receptor status for whom we had follow-up information and outcome data available, and performed immunohistochemistry analysis to determine CD44 and CD24 expression. Gene expression arrays were also independently performed on 52 breast cancer specimens with banked frozen tissue. Lastly, we used FVBN202 transgenic mouse model of breast carcinoma and determined the hormone receptor status, the proportion of CD44(+)/CD24(-/low) breast cancer stem-like cells, and the behavior of the tumor. We determined that patients with triple-negative tumors had significantly higher incidence of recurrence or distant metastasis associated with increased frequency of breast cancer stem cell phenotypes compared with those with non-triple-negative tumors. Preclinical studies in FVBN202 transgenic mice confirmed these findings by showing that relapsed tumors were triple negative and had significantly higher frequency of breast cancer stem cells compared with their related primary tumors. Unlike non-triple-negative primary tumors, relapsed triple-negative tumors were tumorigenic at low doses when inoculated into FVBN202 transgenic mice. These findings suggest that CD44(+)/CD24(-/low) breast cancer stem-like cells play an important role in the clinical behavior of triple-negative breast cancer and that development of therapeutic targets directed to breast cancer stem-like cells may lead to reduction in the aggressiveness of triple-negative breast cancers.

Quantitative analyses of CD133 expression facilitate researches on tumor stem cells

CD133 is regarded as a marker of tumor initiating cells in many tumors, including colorectal cancer. O'Brien and Ricci et al. have proved that in primary colorectal tumors there are colorectal tumor stem cells (initiating cells) which are marked by CD133 antigen. Using a genetic knockin lacZ reporter mouse model, Shmelkov et al. challenged this increasingly influential viewpoint and drew two important conclusions that challenge former opinions. First, CD133 is widely distributed throughout the full range of tumor epithelial cells in the colon as opposed to being limited to a few cells. Second, CD133 negative cells of colon tumors are also tumorigenic, and are more inclined to metastasize. Based on these two opinions, we hypothesize that the expression of CD133 is different among tumor cells, and that quantitative but not qualitative analyses of CD133 abundance are necessary to determine the relationship between CD133 expression and tumor stem cell characteristics. To verify this hypothesis, colorectal cancer cell line SW620 was cultured and sorted into CD133(Hi), CD133(Mid) and CD133(Low) subgroups using magnetic microbeads to compare their xenograft biological characteristics. The results showed that the CD133(Hi) subgroup of SW620 is more close to the tumor initiating cells in terms of biological characteristics than CD133(Mid) and CD133(low) subgroups, but the CD133(low) subgroup still maintains the ability of tumorigenicity. It supported that tumor initiating cells are more correlated to the abundance of CD133.

Musashi1 regulates breast tumor cell proliferation and is a prognostic indicator of poor survival

Background

Musashi1 (Msi1) is a conserved RNA-binding protein that regulates the Notch and Wnt pathways, and serves as a stem cell marker in the breast and other tissues. It is unknown how Msi1 relates to other breast cancer markers, whether it denotes tumor initiating cells (TICs), and how it affects gene expression and tumor cell survival in breast cancer cells.

Results

Msi1 expression was analyzed in 20 breast cancer cell lines and in 140 primary breast tumors by western blotting and immunohistochemistry, respectively. Lentivirus RNA interference was used to reduce Msi1 expression in breast cancer cell lines MCF-7 and T47D grown as spheroid cultures and to assess stem cell gene expression and the growth of these cell lines as xenografts. In normal human breast tissue, Msi1 was expressed in 10.6% of myoepithelum and 1.2% of ductal epithelium in the terminal ductal lobular unit (TDLU), whereas, less than 0.05% of ductal epithelium and myoepithelium in large ducts outside the TDLU expressed Msi1. Msi1 was expressed in 55% of the breast cancer cell lines and correlated with ErbB2 expression in 50% of the cell lines. Msi1 was expressed in 68% of primary tumors and in 100% of lymph node metastases, and correlated with 5 year survival. Msi1 was enriched in CD133⁺ MCF-7 and T47D cells and in spheroid cultures of these cells, and Msi1 'knockdown' (KD) with a lentivirus-expressed shRNA decreased the number and size of spheroid colonies. Msi1 KD reduced Notch1, c-Myc, ErbB2 and pERK1/2 expression, and increased p21^CIP1 expression, which is consistent with known Msi1 target mRNAs. Msi1 KD also reduced the expression of the somatic and embryonic stem cell markers, CD133, Bmi1, Sox2, Nanog and Oct4. Xenografts of MCF-7 and T47D Msi1 KD cells resulted in a marked reduction of tumor growth, reduced Msi1 and Notch1 expression and increased p21^CIP1 expression.

Conclusion

Msi1 is a negative prognostic indicator of breast cancer patient survival, and is indicative of tumor cells with stem cell-like characteristics. Msi1 KD reduces tumor cell survival and tumor xenograft growth, suggesting that it may represent a novel target for drug discovery.

Targeting Notch to target cancer stem cells

The cellular heterogeneity of neoplasms has been at the center of considerable interest since the "cancer stem cell hypothesis", originally formulated for hematologic malignancies, was extended to solid tumors. The origins of cancer "stem" cells (CSC) or tumor-initiating cells (TIC; henceforth referred to as CSCs) and the methods to identify them are hotly debated topics. Nevertheless, the existence of subpopulations of tumor cells with stem-like characteristics has significant therapeutic implications. The stem-like phenotype includes indefinite self-replication, pluripotency, and, importantly, resistance to chemotherapeutics. Thus, it is plausible that CSCs, regardless of their origin, may escape standard therapies and cause disease recurrences and/or metastasis after apparently complete remissions. Consequently, the idea of selectively targeting CSCs with novel therapeutics is gaining considerable interest. The Notch pathway is one of the most intensively studied putative therapeutic targets in CSC, and several investigational Notch inhibitors are being developed. However, successful targeting of Notch signaling in CSC will require a thorough understanding of Notch regulation and the context-dependent interactions between Notch and other therapeutically relevant pathways. Understanding these interactions will increase our ability to design rational combination regimens that are more likely to prove safe and effective. Additionally, to determine which patients are most likely to benefit from treatment with Notch-targeting therapeutics, reliable biomarkers to measure pathway activity in CSC from specific tumors will have to be identified and validated. This article summarizes the most recent developments in the field of Notch-targeted cancer therapeutics, with emphasis on CSC.

Association of breast cancer stem cells identified by aldehyde dehydrogenase 1 expression with resistance to sequential Paclitaxel and epirubicin-based chemotherapy for breast cancers

PURPOSE

Breast cancer stem cells have been shown to be associated with resistance to chemotherapy in vitro, but their clinical significance remains to be clarified. The aim of this study was to investigate whether cancer stem cells were clinically significant for resistance to chemotherapy in human breast cancers.

EXPERIMENTAL DESIGN

Primary breast cancer patients (n = 108) treated with neoadjuvant chemotherapy consisting of sequential paclitaxel and epirubicin-based chemotherapy were included in the study. Breast cancer stem cells were identified by immunohistochemical staining of CD44/CD24 and aldehyde dehydrogenase 1 (ALDH1) in tumor tissues obtained before and after neoadjuvant chemotherapy. CD44(+)/CD24(-) tumor cells or ALDH1-positive tumor cells were considered stem cells.

RESULTS

Thirty (27.8%) patients achieved pathologic complete response (pCR). ALDH1-positive tumors were significantly associated with a low pCR rate (9.5% versus 32.2%; P = 0.037), but there was no significant association between CD44(+)/CD24(-) tumor cell proportions and pCR rates. Changes in the proportion of CD44(+)/CD24(-) or ALDH1-positive tumor cells before and after neoadjuvant chemotherapy were studied in 78 patients who did not achieve pCR. The proportion of ALDH1-positive tumor cells increased significantly (P < 0.001) after neoadjuvant chemotherapy, but that of CD44(+)/CD24(-) tumor cells did not.

CONCLUSIONS

Our findings suggest that breast cancer stem cells identified as ALDH1-positive, but not CD44(+)/CD24(-), play a significant role in resistance to chemotherapy. ALDH1-positive thus seems to be a more significantly predictive marker than CD44(+)/CD24(-) for the identification of breast cancer stem cells in terms of resistance to chemotherapy.

Tamoxifen prevents premalignant changes of breast, but not ovarian, cancer in rats at high risk for both diseases

Women at increased risk for breast cancer are at increased risk for ovarian cancer as well, reflecting common risk factors and intertwined etiology of the two diseases. We previously developed a rat model of elevated breast and ovarian cancer risk, allowing evaluation of dual-target cancer prevention strategies. Tamoxifen, a Food and Drug Administration-approved breast cancer chemoprevention drug, has been shown to promote ovarian cysts in premenopausal women; however, the effect of tamoxifen on ovarian cancer risk is still controversial. In the current experiment, Fischer 344 rats (n = 8 per treatment group) received tamoxifen (TAM) or vehicle (control) in factorial combination with combined breast and ovarian carcinogen (17beta-estradiol and 7,12 dimethylbenza[a]anthracene, respectively). Mammary and ovarian morphologies were normal in the control and TAM groups. Carcinogen (CARC) treatment induced mammary dysplasia with elevated cell proliferation and reduced estrogen receptor-alpha expression and promoted preneoplastic changes in the ovary. In the CARC + TAM group, tamoxifen reduced preneoplastic changes and proliferation rate in the mammary gland, but not in the ovary, compared with rats treated with carcinogen alone. Putative stem cell markers (Oct-4 and aldehyde dehydrogenase 1) were also elevated in the mammary tissue by carcinogen and this expansion of the stem cell population was not reversed by tamoxifen. Our study suggests that tamoxifen prevents early progression to mammary cancer but has no effect on ovarian cancer progression in this rat model.

CXCR4 receptor positive spheroid forming cells are responsible for tumor invasion in vitro

Stem cells have been found to be involved in breast cancer growth, but the specific contribution of cancer stem cells in tumor biology, including metastasis, is still uncertain. We found that murine breast cancer cell lines 4T1, 4TO7, 167Farn and 67NR contains cancer stem cells defined by CXCR4 expression and their capability of forming spheroids in suspension culture. Importantly, we showed that CXCR4 expression is essential for tumor invasiveness because both CXCR4 neutralizing antibody and shRNA knockdown of the CXCR4 receptor significantly reduced tumor cell invasion.

Review: the role of neural crest cells in the endocrine system

The neural crest is a pluripotent population of cells that arises at the junction of the neural tube and the dorsal ectoderm. These highly migratory cells form diverse derivatives including neurons and glia of the sensory, sympathetic, and enteric nervous systems, melanocytes, and the bones, cartilage, and connective tissues of the face. The neural crest has long been associated with the endocrine system, although not always correctly. According to current understanding, neural crest cells give rise to the chromaffin cells of the adrenal medulla, chief cells of the extra-adrenal paraganglia, and thyroid C cells. The endocrine tumors that correspond to these cell types are pheochromocytomas, extra-adrenal paragangliomas, and medullary thyroid carcinomas. Although controversies concerning embryological origin appear to have mostly been resolved, questions persist concerning the pathobiology of each tumor type and its basis in neural crest embryology. Here we present a brief history of the work on neural crest development, both in general and in application to the endocrine system. In particular, we present findings related to the plasticity and pluripotency of neural crest cells as well as a discussion of several different neural crest tumors in the endocrine system.

Rational targeting of Notch signaling in cancer

Accumulating preclinical and clinical evidence supports a pro-oncogenic function for Notch signaling in several solid tumors, particularly but not exclusively in breast cancer. Notch inhibitory agents, such as gamma-secretase inhibitors, are being investigated as candidate cancer therapeutic agents. Interest in therapeutic modulation of the Notch pathway has been increased by recent reports, indicating that its role is important in controlling the fate of putative 'breast cancer stem cells'. However, as is the case for most targeted therapies, successful targeting of Notch signaling in cancer will require a considerable refinement of our understanding of the regulation of this pathway and its effects in both normal and cancer cells. Notch signaling has bidirectional 'cross talk' interaction with multiple other pathways that include candidate therapeutic targets. Understanding these interactions will greatly increase our ability to design rational combination regimens. To determine which patients are most likely to benefit from treatment with Notch inhibitors, it will be necessary to develop molecular tests to accurately measure pathway activity in specific tumors. Finally, mechanism-based toxicities will have to be addressed by a careful choice of therapeutic agents, combinations and regimens. This article summarizes the current state of the field, and briefly describes opportunities and challenges for Notch-targeted therapies in oncology.

Gene expression profiling of breast cancer

DNA microarray platforms for gene expression profiling were invented relatively recently, and breast cancer has been among the earliest and most intensely studied diseases using this technology. The molecular signatures so identified help reveal the biologic spectrum of breast cancers, provide diagnostic tools as well as prognostic and predictive gene signatures, and may identify new therapeutic targets. Data are best presented in an open access format to facilitate external validation, the most crucial step in identifying robust, reproducible gene signatures suitable for clinical translation. Clinically practical applications derived from full expression profile studies already in use include reduced versions of microarrays representing key discriminatory genes and therapeutic targets, quantitative polymerase chain reaction assays, or immunohistochemical surrogate panels (suitable for application to standard pathology blocks). Prospective trials are now underway to determine the value of such tools for clinical decision making in breast cancer; these efforts may serve as a model for using such approaches in other tumor types.

Identification and characterization of cancer initiating cells from BRCA1 related mammary tumors using markers for normal mammary stem cells

It is hypothesized that cancer stem cells arise either from normal stem cells or from progenitor cells that have gained the ability to self-renew. Here we determine whether mammary cancer stem cells can be isolated by using antibodies that have been used for the isolation of normal mammary stem cells. We show that BRCA1 mutant cancer cell lines contained a subpopulation of CD24+CD29+ or CD24+CD49f+ cells that exhibited increased proliferation and colony forming ability in vitro, and enhanced tumor-forming ability in vivo. The purified CD24+CD29+ cells could differentiate and reconstitute the heterogeneity found in parental cells when plated as a monolayer. Under low-attachment conditions, we detected "tumorspheres" only in the presence of double positive cells, which maintained their ability to self-renew. Furthermore, CD24+CD29+ cells could form tubular structures reminiscent of the mammary ductal tree when grown in three-dimensional cultures, implying that these cancer cells maintain some of the characteristics of the normal stem cells. Nevertheless, they could still drive tumor formation since as low as 500 double positive cells immediately after sorting from BRCA1 mutant primary tumors were able to form tumors with the same heterogeneity found in the original tumors. These data provide evidence that breast cancer stem cells originate from normal stem cells and advance our understanding of BRCA1-associated tumorigenesis with possible implications for future cancer treatment.

A challenge for regenerative medicine: proper genetic programming, not cellular mimicry

Recent progress in stem cell biology and the reprogramming of somatic cells to a pluripotent phenotype has generated a new wave of excitement in regenerative medicine. Nonetheless, efforts aimed at understanding transdifferentiation, dedifferentiation, and the plasticity of cells, as well as the ability of somatic cells to be reprogrammed, has raised as many questions as those that have been answered. This review proffers the argument that many reports of transdifferentiation, dedifferentiation, and unexpected stem cell plasticity may be due to aberrant processes that lead to cellular look-alikes (cellular mimicry). In most cases, cellular look-alikes can now be identified readily by monitoring gene expression profiles, as well as epigenetic modifications of DNA and histone proteins of the cells involved. This review further argues that progress in regenerative medicine will be significantly hampered by failing to address the issue of cellular look-alikes.

Brca1 breast tumors contain distinct CD44+/CD24- and CD133+ cells with cancer stem cell characteristics

INTRODUCTION

Whether cancer stem cells occur in BRCA1-associated breast cancer and contribute to therapeutic response is not known.

METHODS

We generated and characterized 16 cell lines from five distinct Brca1deficient mouse mammary tumors with respect to their cancer stem cell characteristics.

RESULTS

All cell lines derived from one tumor included increased numbers of CD44+/CD24- cells, which were previously identified as human breast cancer stem cells. All cell lines derived from another mammary tumor exhibited low levels of CD44+/CD24- cells, but they harbored 2% to 5.9% CD133+ cells, which were previously associated with cancer stem cells in other human and murine tumors. When plated in the absence of attachment without presorting, only those cell lines that were enriched in either stem cell marker formed spheroids, which were further enriched in cells expressing the respective cancer stem cell marker. In contrast, cells sorted for CD44+/CD24- or CD133+ markers lost their stem cell phenotype when cultured in monolayers. As few as 50 to 100 CD44+/CD24- or CD133+ sorted cells rapidly formed tumors in nonobese diabetic/severe combined immunodeficient mice, whereas 50-fold to 100-fold higher numbers of parental or stem cell depleted cells were required to form few, slow-growing tumors. Expression of stem cell associated genes, including Oct4, Notch1, Aldh1, Fgfr1, and Sox1, was increased in CD44+/CD24- and CD133+ cells. In addition, cells sorted for cancer stem cell markers and spheroid-forming cells were significantly more resistant to DNA-damaging drugs than were parental or stem cell depleted populations, and they were sensitized to the drugs by the heat shock protein-90 inhibitor 17-DMAG (17-dimethylaminoethylamino-17-demethoxygeldanamycin hydrochloride).

CONCLUSION

Brca1-deficient mouse mammary tumors harbor heterogeneous cancer stem cell populations, and CD44+/CD24- cells represent a population that correlates with human breast cancer stem cells.

MR guided cancer treatment system for an elevated therapeutic index - a macroscopic approach

Adjuvant therapy for cancer usually refers to surgery followed by chemotherapy and/or radiation treatment to decrease the risk of recurrence. But still, the absolute benefit for survival obtained with adjuvant therapy compared with control is only approximately 6%. The objective of this analysis is to formulate a non-invasive multimodal cancer treatment system related to cancer stem cells and hypoxic fractions of solid tumors, emphasizing MRI monitoring and guidance, to elevate the therapeutic index. Tumor hypoxia is a therapeutic concern since it can reduce the effectiveness of drugs and radiotherapy, where well oxygenated cells requiring one third of the dose of hypoxic cells to achieve a given level of cell killing. Cancer stem cells might be the cause of tumor recurrence, sometimes many years after the appearance of the successful treatment of a primary tumor. Thus, the primary objective of such a treatment system will be to provide sufficient selective toxicity to both kill cancer stem cells and cells of hypoxic fractions of the tumor. Active tumor targeting with the use of liposomally encapsulated drugs is the starting point of the treatment procedure. The system facilitates quality assurance means by MR monitoring of drug accumulation and drug release, in real time. Cavitation involves the nucleation, growth and oscillation of gaseous cavities. Selective drug release and/or hyperthermia are achieved by ultrasound induced cavitation well defined to the tumor region. Hyperthermic effects, increased vascularization and subsequent increase in pO2 levels to hypoxic regions, can be monitored by MRI. MRI monitoring of key physiological parameters facilitates optimization related to approximate real time concomitant treatments, including correct timing and various combinations of drug therapy, hyperthermia, ionizing radiation, ablation, other treatment options, before or after surgery. The likelihood of an improved therapeutic index with the use of such a system seems compelling. Further research related to optimal timing, combinations of responses between liposomally encapsulated drug dosage, ultrasound exposure, hyperthermia, pO2 response time, ionizing radiation fractionation and treatment time, have to be conducted.

Pheochromocytomas in Nf1 knockout mice express a neural progenitor gene expression profile

Pheochromocytomas are adrenal medullary tumors that typically occur in adult patients, with increased frequency in multiple endocrine neoplasia type 2, von Hippel-Lindau disease, familial paraganglioma syndromes and neurofibromatosis type 1 (NF1). Pheochromocytomas arise in adult mice with a heterozygous knockout mutation of exon 31 of the murine Nf1 gene, providing a mouse model for pheochromocytoma development in NF1. We performed a microarray-based gene expression profiling study comparing mouse pheochromocytoma tissue to normal adult mouse adrenal medulla to develop a basis for studying the pathobiology of these tumors. The findings demonstrate that pheochromocytomas from adult neurofibromatosis knockout mice express multiple developmentally regulated genes involved in early development of both the CNS and peripheral nervous system. One of the most highly overexpressed genes is receptor tyrosine kinase Ret, which is known to be transiently expressed in the developing adrenal gland, down-regulated in adult adrenals and often overexpressed in human pheochromocytomas. Real-time polymerase chain reaction validated the microarray results and immunoblots confirmed the overexpression of Ret protein. Other highly expressed validated genes include Sox9, which is a neural crest determinant, and Hey 1, which helps to maintain the progenitor status of neural precursors. The findings are consistent with the recently proposed concept that persistent neural progenitors might give rise to pheochromocytomas in adult mouse adrenals and suggest that events predisposing to tumor development might occur before formation of the adrenal medulla or migration of cells from the neural crest. However, the competing possibility that developmentally regulated neural genes arise secondarily to neoplastic transformation cannot be ruled out. In either case, the unique profile of gene expression opens the mouse pheochromocytoma model to new applications pertinent to neural stem cells and suggests potential new targets for treatment of pheochromocytomas or eradication of their precursors.