Tissue-specific promoters active in CD44+CD24-/low breast cancer cells

Improvement of current immunotherapies with engineered oncolytic viruses that target cancer stem cells

The heterogeneity of the solid tumor microenvironment (TME) impairs the therapeutic efficacy of standard therapies and also reduces the infiltration of antitumor immune cells, all of which lead to tumor progression and invasion. In addition, self-renewing cancer stem cells (CSCs) support tumor dormancy, drug resistance, and recurrence, all of which might pose challenges to the eradication of malignant tumor masses with current therapies. Natural forms of oncolytic viruses (OVs) or engineered OVs are known for their potential to directly target and kill tumor cells or indirectly eradicate tumor cells by involving antitumor immune responses, including enhancement of infiltrating antitumor immune cells, induction of immunogenic cell death, and reprogramming of cold TME to an immune-sensitive hot state. More importantly, OVs can target stemness factors that promote tumor progression, which subsequently enhances the efficacy of immunotherapies targeting solid tumors, particularly the CSC subpopulation. Herein, we describe the role of CSCs in tumor heterogeneity and resistance and then highlight the potential and remaining challenges of immunotherapies targeting CSCs. We then review the potential of OVs to improve tumor immunogenicity and target CSCs and finally summarize the challenges within the therapeutic application of OVs in preclinical and clinical trials.

Oncolytic Adenovirus for the Targeting of Paclitaxel-Resistant Breast Cancer Stem Cells

Adjuvant systemic therapies effectively reduce the risk of breast cancer recurrence and metastasis, but therapy resistance can develop in some patients due to breast cancer stem cells (BCSCs). Oncolytic adenovirus (OAd) represents a promising therapeutic approach as it can specifically target cancer cells. However, its potential to target BCSCs remains unclear. Here, we evaluated a Cox-2 promoter-controlled, Ad5/3 fiber-modified OAd designed to encode the human sodium iodide symporter (hNIS) in breast cancer models. To confirm the potential of OAds to target BCSCs, we employed BCSC-enriched estrogen receptor-positive (ER+) paclitaxel-resistant (TaxR) cells and tumorsphere assays. OAd-hNIS demonstrated significantly enhanced binding and superior oncolysis in breast cancer cells, including ER+ cells, while exhibiting no activity in normal mammary epithelial cells. We observed improved NIS expression as the result of adenovirus death protein deletion. OAd-hNIS demonstrated efficacy in targeting TaxR BCSCs, exhibiting superior killing and hNIS expression compared to the parental cells. Our vector was capable of inhibiting tumorsphere formation upon early infection and reversing paclitaxel resistance in TaxR cells. Importantly, OAd-hNIS also destroyed already formed tumorspheres seven days after their initiation. Overall, our findings highlight the promise of OAd-hNIS as a potential tool for studying and targeting ER+ breast cancer recurrence and metastasis.

Tumor matrix stiffness provides fertile soil for cancer stem cells

Matrix stiffness is a mechanical characteristic of the extracellular matrix (ECM) that increases from the tumor core to the tumor periphery in a gradient pattern in a variety of solid tumors and can promote proliferation, invasion, metastasis, drug resistance, and recurrence. Cancer stem cells (CSCs) are a rare subpopulation of tumor cells with self-renewal, asymmetric cell division, and differentiation capabilities. CSCs are thought to be responsible for metastasis, tumor recurrence, chemotherapy resistance, and consequently poor clinical outcomes. Evidence suggests that matrix stiffness can activate receptors and mechanosensor/mechanoregulator proteins such as integrin, FAK, and YAP, modulating the characteristics of tumor cells as well as CSCs through different molecular signaling pathways. A deeper understanding of the effect of matrix stiffness on CSCs characteristics could lead to development of innovative cancer therapies. In this review, we discuss how the stiffness of the ECM is sensed by the cells and how the cells respond to this environmental change as well as the effect of matrix stiffness on CSCs characteristics and also the key malignant processes such as proliferation and EMT. Then, we specifically focus on how increased matrix stiffness affects CSCs in breast, lung, liver, pancreatic, and colorectal cancers. We also discuss how the molecules responsible for increased matrix stiffness and the signaling pathways activated by the enhanced stiffness can be manipulated as a therapeutic strategy for cancer.

Targeting autophagy and lipid metabolism in cancer stem cells

Cancer stem cells (CSCs) are a subset of cancer cells with self-renewal ability and tumor initiating properties. Unlike the other non-stem cancer cells, CSCs resist traditional therapy and remain a major cause of disease relapse. With the recent advances in metabolomics, various studies have demonstrated that CSCs have distinct metabolic properties. Metabolic reprogramming in CSCs contributes to self-renewal and maintenance of stemness. Accumulating evidence suggests that rewiring of energy metabolism is a key player that enables to meet energy demands, maintains stemness, and sustains cancer growth and invasion. CSCs use various mechanisms such as increased glycolysis, redox signaling and autophagy modulation to overcome nutritional deficiency and sustain cell survival. The alterations in lipid metabolism acquired by the CSCs support biomass production through increased dependence on fatty acid synthesis and β-oxidation and contribute to oncogenic signaling pathways. This review summarizes our current understanding of lipid metabolism in CSCs and how pharmacological regulation of autophagy and lipid metabolism influences CSC phenotype. Increased dependence on lipid metabolism appears as an attractive strategy to eliminate CSCs using therapeutic agents that specifically target CSCs based on their modulation of lipid metabolism.

Oncolytic Viruses and Cancer, Do You Know the Main Mechanism?

The global rate of cancer has increased in recent years, and cancer is still a threat to human health. Recent developments in cancer treatment have yielded the understanding that viruses have a high potential in cancer treatment. Using oncolytic viruses (OVs) is a promising approach in the treatment of malignant tumors. OVs can achieve their targeted treatment effects through selective cell death and induction of specific antitumor immunity. Targeting tumors and the mechanism for killing cancer cells are among the critical roles of OVs. Therefore, evaluating OVs and understanding their precise mechanisms of action can be beneficial in cancer therapy. This review study aimed to evaluate OVs and the mechanisms of their effects on cancer cells.

Epigenetic Silencing of HER2 Expression during Epithelial-Mesenchymal Transition Leads to Trastuzumab Resistance in Breast Cancer

HER2 receptor tyrosine kinase (encoded by the ERBB2 gene) is overexpressed in approximately 25% of all breast cancer tumors (HER2-positive breast cancers). Resistance to HER2-targeting therapies is partially due to the loss of HER2 expression in tumor cells during treatment. However, little is known about the exact mechanism of HER2 downregulation in HER2-positive tumor cells. Here, by analyzing publicly available genomic data we investigate the hypothesis that epithelial-mesenchymal transition (EMT) abrogates HER2 expression by epigenetic silencing of the ERBB2 gene as a mechanism of acquired resistance to HER2-targeted therapies. As result, HER2 expression was found to be positively and negatively correlated with the expression of epithelial and mesenchymal phenotype marker genes, respectively. The ERBB2 chromatin of HER2-high epithelial-like breast cancer cells and HER2-low mesenchymal-like cells were found to be open/active and closed/inactive, respectively. Decreased HER2 expression was correlated with increased EMT phenotype, inactivated chromatin and lower response to lapatinib. We also found that induction of EMT in the HER2-positive breast cancer cell line BT474 resulted in downregulated HER2 expression and reduced trastuzumab binding. Our results suggest that ERBB2 gene silencing by epigenetic regulation during EMT may be a mechanism of de novo resistance of HER2-positive breast cancer cells to trastuzumab and lapatinib.

Paclitaxel-Based Chemotherapy Targeting Cancer Stem Cells from Mono- to Combination Therapy

Paclitaxel (PTX) is a chemotherapeutical agent commonly used to treat several kinds of cancer. PTX is known as a microtubule-targeting agent with a primary molecular mechanism that disrupts the dynamics of microtubules and induces mitotic arrest and cell death. Simultaneously, other mechanisms have been evaluated in many studies. Since the anticancer activity of PTX was discovered, it has been used to treat many cancer patients and has become one of the most extensively used anticancer drugs. Regrettably, the resistance of cancer to PTX is considered an extensive obstacle in clinical applications and is one of the major causes of death correlated with treatment failure. Therefore, the combination of PTX with other drugs could lead to efficient therapeutic strategies. Here, we summarize the mechanisms of PTX, and the current studies focusing on PTX and review promising combinations.

CXCL12 Retargeting of an Oncolytic Adenovirus Vector to the Chemokine CXCR4 and CXCR7 Receptors in Breast Cancer

Breast cancer is the most frequently diagnosed cancer in women under 60, and the second most diagnosed cancer in women over 60. While significant progress has been made in developing targeted therapies for breast cancer, advanced breast cancer continues to have high mortality, with poor 5-year survival rates. Thus, current therapies are insufficient in treating advanced stages of breast cancer; new treatments are sorely needed to address the complexity of advanced-stage breast cancer. Oncolytic virotherapy has been explored as a therapeutic approach capable of systemic administration, targeting cancer cells, and sparing normal tissue. In particular, oncolytic adenoviruses have been exploited as viral vectors due to their ease of manipulation, production, and demonstrated clinical safety profile. In this study, we engineered an oncolytic adenovirus to target the chemokine receptors CXCR4 and CXCR7. The overexpression of CXCR4 and CXCR7 is implicated in the initiation, survival, progress, and metastasis of breast cancer. Both receptors bind to the ligand, CXCL12 (SDF-1), which has been identified to play a crucial role in the metastasis of breast cancer cells. This study incorporated a T4 fibritin protein fused to CXCL12 into the tail domain of an adenovirus fiber to retarget the vector to the CXCR4 and CXCR7 chemokine receptors. We showed that the modified virus targets and infects CXCR4- and CXCR7-overexpressing breast cancer cells more efficiently than a wild-type control vector. In addition, the substitution of the wild-type fiber and knob with the modified chimeric fiber did not interfere with oncolytic capability. Overall, the results of this study demonstrate the feasibility of retargeting adenovirus vectors to chemokine receptor-positive tumors.

Viroimmunotherapy for breast cancer: promises, problems and future directions

Virotherapy, a strategy to use live viruses as therapeutics, is a relatively novel field in the treatment of cancer. With the advancements in molecular biology and virology, there has been a huge increase in research on cancer virotherapy. For the treatment of cancer, viruses could be used either as vectors in gene therapy or as oncolytic agents. A variety of viruses have been studied for their potential usage in gene therapy or oncolytic therapy. In this review, we discuss virotherapy with a special focus on breast cancer. Breast cancer is the most common cancer and the leading cause of cancer-related deaths in women worldwide. Current treatments are insufficient to cure metastatic breast cancer and are often associated with severe side effects that further deteriorates patients' quality of life. Therefore, novel therapeutic approaches such as virotherapy need to be developed for the treatment of breast cancer. Here we summarize the current treatments for breast cancer and the potential use of virotherapy in the treatment of the disease. Furthermore, we discuss the use of oncolytic viruses as immunotherapeutics and the rational combination of oncolytic viruses with other therapeutics for optimal treatment of breast cancer. Finally, we outline the progress made in virotherapy for breast cancer and the shortcomings that need to be addressed for this novel therapy to move to the clinic for better treatment of breast cancer.

Eradicating the Roots: Advanced Therapeutic Approaches Targeting Breast Cancer Stem Cells

Accumulating evidences have demonstrated that the existence of breast cancer-initiating cells, which drives the original tumorigenicity, local invasion and migration propensity of breast cancer. These cells, termed as breast cancer stem cells (BCSCs), possess properties including self-renewal, multidirectional differentiation and proliferative potential, and are believed to play important roles in the intrinsic drug resistance of breast cancer. One of the reasons why BCBCs cause difficulties in breast cancer treating is that BCBCs can control both genetic and non-genetic elements to keep their niches safe and sound, which allows BCSCs for constant self-renewal and differentiation. Therapeutic strategies designed to target BCSCs may ultimately result in effective interventions for the treatment of breast cancer. Novel strategies including nanomedicine, oncolytic virus therapy, immunotherapy and induced differentiation therapy are emerging and proved to be efficient in anti-BCSCs therapy. In this review, we summarized breast tumor biology and the current challenges of breast cancer therapies, focused on breast cancer stem cells, and introduced promising therapeutic strategies targeting BCSCs.

Cancer Stem Cells and Combination Therapies to Eradicate Them

Cancer stem cells (CSCs) show self-renewal ability and multipotential differentiation, like normal stem or progenitor cells, and which proliferate uncontrollably and can escape the effects of drugs and phagocytosis by immune cells. Traditional monotherapies, such as surgical resection, radiotherapy and chemotherapy, cannot eradicate CSCs, however, combination therapy may be more effective at eliminating CSCs. The present review summarizes the characteristics of CSCs and several promising combination therapies to eradicate them.

Investigation of multicellular tumor spheroids enriched for a cancer stem cell phenotype

Background

Cancer stem cells (CSCs) provide self-renewal of the tumor after radiation and chemotherapy. These cells are important during tumor development. The in vitro model of avascular tumor that enriched of cells with stem like characteristics is critical to understanding of the role CSCs in the tumor.

Methods

Cell viability was evaluated by MTT assay. The expression of cancer stem cells markers (CD133, CD44, CD24 and bmi-1) in 2D cell culture and multicellular tumor spheroids (MCTS) of MCF-7 cells was evaluated. The Stemi2000 software AxioVisionRed 4.7 was used for image processing. The volume of spheroids was calculated by Bjerkvig formula.

Results

The highest expression of CD133, CD44, CD24 and bmi-1 receptors was detected in MCTS, enriched with cancer stem cells (eMCTS). Cell aggregates of eMCTS culture were returned from suspension to adhesive conditions. It was found that the cells of the MCTS surface layers were enriched with CD133, CD44, CD24, bmi-1, EpCAM, vim markers, but not adherent cells. eMCTS are less sensitive to anticancer drugs (cisplatin, methotrexate and doxorubicin), than adhesive cell culture and MCTS cultured under standard conditions in a complete nutrient medium (P<0.05).

Conclusions

We observed that eMCTS population possesses aggressive phenotypic characteristics such as invasion, cancer stem cell markers and chemoresistance. eMCTS model could improve the screening efficiency of therapeutical agents against CSCs.

CD24 isoform a promotes cell proliferation, migration and invasion and is downregulated by EGR1 in hepatocellular carcinoma

Introduction

CD24 is known as a heavily glycosylated cell surface molecule that is highly expressed in a wide variety of human malignancies. Previous studies have shown that CD24 plays an important role in self-renewal, proliferation, migration, invasion and drug resistance of hepatocellular carcinoma (HCC). However, little is known about the expression and function of CD24 isoform a (CD24A) and CD24 isoform b (CD24B) in HCC.

Materials and methods

Quantitative real-time polymerase chain reaction (qPCR) and Western blotting were performed to detect CD24 and EGR1 expression in HCC cells and tissue. The function of CD24 in cell proliferation was verified with MTT assays, colony formation assays and tumor xenograft models. Wound healing assays and invasion assays were performed to clarify the function of CD24 in the regulation of cell migration and invasion in HCC. A dual luciferase reporter assay and chromatin immunoprecipitation assay were used to analyze the regulation mechanism of CD24A.

Results

CD24A but not CD24B, which was barely detected by qPCR and Western blotting, is significantly upregulated in HCC tissue. Both CD24A and CD24B contribute to HCC cell proliferation, migration and invasion, but CD24A is more effective than CD24B. EGR1 downregulates CD24A and exerts transcription-promoting activity on the CD24A promoter. Furthermore, EGR1 represses HCC cell proliferation via downregulation of CD24A.

Conclusion

CD24A is the predominant CD24 isoform in HCC and plays a major role in cell proliferation, migration, and invasion. EGR1 can exert its antitumor effect through transcriptional downregulation of CD24A in HCC.

Emerging functional markers for cancer stem cell-based therapies: Understanding signaling networks for targeting metastasis

Metastasis is one of the most challenging issues in cancer patient management, and effective therapies to specifically target disease progression are missing, emphasizing the urgent need for developing novel anti-metastatic therapeutics. Cancer stem cells (CSCs) gained fast attention as a minor population of highly malignant cells within liquid and solid tumors that are responsible for tumor onset, self-renewal, resistance to radio- and chemotherapies, and evasion of immune surveillance accelerating recurrence and metastasis. Recent progress in the identification of their phenotypic and molecular characteristics and interactions with the tumor microenvironment provides great potential for the development of CSC-based targeted therapies and radical improvement in metastasis prevention and cancer patient prognosis. Here, we report on newly uncovered signaling mechanisms controlling CSC's aggressiveness and treatment resistance, and CSC-specific agents and molecular therapeutics, some of which are currently under investigation in clinical trials, gearing towards decisive functional CSC intrinsic or surface markers. One special research focus rests upon subverted regulatory pathways such as insulin-like growth factor 1 receptor signaling and its interactors in metastasis-initiating cell populations directly related to the gain of stem cell- and EMT-associated properties, as well as key components of the E2F transcription factor network regulating metastatic progression, microenvironmental changes, and chemoresistance. In addition, the study provides insight into systems biology tools to establish complex molecular relationships behind the emergence of aggressive phenotypes from high-throughput data that rely on network-based analysis and their use to investigate immune escape mechanisms or predict clinical outcome-relevant CSC receptor signaling signatures. We further propose that customized vector technologies could drastically enhance systemic drug delivery to target sites, and summarize recent progress and remaining challenges. This review integrates available knowledge on CSC biology, computational modeling approaches, molecular targeting strategies, and delivery techniques to envision future clinical therapies designed to conquer metastasis-initiating cells.

Oncolytic Virotherapy versus Cancer Stem Cells: A Review of Approaches and Mechanisms

A growing body of evidence suggests that a subset of cells within tumors are resistant to conventional treatment modalities and may be responsible for disease recurrence. These cells are called cancer stem cells (CSC), which share properties with normal stem cells including self-renewal, pluripotency, drug resistance, and the ability to maintain quiescence. While most conventional therapies can efficiently destroy rapidly dividing cancer cells comprising the bulk of a tumor, they often fail to kill the less abundant and quiescent CSCs. Furthermore, killing of only differentiated cells in the tumor may actually allow for enrichment of CSCs and thereby portend a bad prognosis. Therefore, targeting of CSCs is important to achieve long-term success in cancer therapy. Oncolytic viruses represent a completely different class of therapeutics that can kill cancer cells in a variety of ways, which differ from those of conventional therapies. Hence, CSCs that are inherently resistant to conventional therapies may be susceptible to oncolytic virus-mediated killing. Recent studies have shown that oncolytic viruses can efficiently kill CSCs in many types of cancer. Here, we discuss the mechanism through which CSCs can escape conventional therapies and how they may still be susceptible to different classes of oncolytic viruses. Furthermore, we provide a summary of recent studies that have tested oncolytic viruses on CSCs of different origins and discuss possible future directions for this fascinating subset of oncolytic virus research.

shRNA-armed conditionally replicative adenoviruses: a promising approach for cancer therapy

The small-interfering RNAs (siRNAs) have been employed to knockdown the expression of cancer-associated genes and shown some promise in cancer therapy. However, synthetic siRNA duplexes or plasmid mediated delivery of siRNAs have several problems, such as short half-life, low transfection efficiency and cytotoxicity associated with transfection. Conditionally replicating adenovirus (CRAds) as the delivery vector for short hairpin RNAs (shRNAs) could overcome these limitations and have shown augmented anti-tumor effects in experimental studies and preclinical trials. In this review, we summarize recent progress in the development of CRAds-shRNA for cancer treatment. Combination of CRAds-shRNA with chemotherapeutics, radiation, dendritic cells, monoclonal antibodies and small-molecule inhibitors will be necessary to eradicate cancer cells and cancer stem cells and achieve superior outcomes. The use of CRAd platform for efficient delivery of shRNAs and foreign genes will open a new avenue for cancer therapy.

Oncolytic Virotherapy for Breast Cancer Treatment

Breast cancer continues to be a leading cause of mortality among women. While at an early stage, localized breast cancer is easily treated; however, advanced stages of disease continue to carry a high mortality rate. The discrepancy in treatment success highlights that current treatments are insufficient to treat advanced-stage breast cancer. As new and improved treatments have been sought, one therapeutic approach has gained considerable attention. Oncolytic viruses are uniquely capable of targeting cancer cells through intrinsic or engineered means. They come in many forms, mainly from four major virus groups as defined by the Baltimore classification system. These vectors can target and kill cancer cells, and even stimulate immunotherapeutic effects in patients. This review discusses not only individual oncolytic viruses pursued in the context of breast cancer treatment but also the emergence of combination therapies with current or new therapies, which has become a particularly promising strategy for treatment of breast cancer. Overall, oncolytic virotherapy is a promising strategy for increased treatment efficacy for advanced breast cancer and consequently provides a unique platform for personalized treatments in patients.

HER2 in Breast Cancer Stemness: A Negative Feedback Loop towards Trastuzumab Resistance

HER2 receptor tyrosine kinase that is overexpressed in approximately 20% of all breast cancers (BCs) is a poor prognosis factor and a precious target for BC therapy. Trastuzumab is approved by FDA to specifically target HER2 for treating HER2+ BC. However, about 60% of patients with HER2+ breast tumor develop de novo resistance to trastuzumab, partially due to the loss of expression of HER2 extracellular domain on their tumor cells. This is due to shedding/cleavage of HER2 by metalloproteinases (ADAMs and MMPs). HER2 shedding results in the accumulation of intracellular carboxyl-terminal HER2 (p95HER2), which is a common phenomenon in trastuzumab-resistant tumors and is suggested as a predictive marker for trastuzumab resistance. Up-regulation of the metalloproteinases is a poor prognosis factor and is commonly seen in mesenchymal-like cancer stem cells that are risen during epithelial to mesenchymal transition (EMT) of tumor cells. HER2 cleavage during EMT can explain why secondary metastatic tumors with high percentage of mesenchymal-like cancer stem cells are mostly resistant to trastuzumab but still sensitive to lapatinib. Importantly, many studies report HER2 interaction with oncogenic/stemness signaling pathways including TGF-β/Smad, Wnt/β-catenin, Notch, JAK/STAT and Hedgehog. HER2 overexpression promotes EMT and the emergence of cancer stem cell properties in BC. Increased expression and activation of metalloproteinases during EMT leads to proteolytic cleavage and shedding of HER2 receptor, which downregulates HER2 extracellular domain and eventually increases trastuzumab resistance. Here, we review the hypothesis that a negative feedback loop between HER2 and stemness signaling drives resistance of BC to trastuzumab.

Intravenously usable fully serotype 3 oncolytic adenovirus coding for CD40L as an enabler of dendritic cell therapy

Vaccination with dendritic cells (DCs), the most potent professional antigen-presenting cells in the body, is a promising approach in cancer immunotherapy. However, tumors induce immunosuppression in their microenvironment that suppresses and impairs the function of DCs. Therefore, human clinical trials with DC therapy have often been disappointing. To improve the therapeutic efficacy and to overcome the major obstacles of DC therapy, we generated a novel adenovirus, Ad3-hTERT-CMV-hCD40L, which is fully serotype 3 and expresses hCD40L for induction of antitumor immune response. The specific aim is to enhance DCs function. Data from a human cancer patient indicated that this capsid allows effective transduction of distant tumors through the intravenous route. Moreover, patient data suggested that virally produced hCD40L can activate DCs in situ. The virus was efficient in vitro and had potent antitumor activity in vivo. In a syngeneic model, tumors treated with Ad5/3-CMV-mCD40L virus plus DCs elicited greater antitumor effect as compared with either treatment alone. Moreover, virally coded CD40L induced activation of DCs, which in turn, lead to the induction of a Th1 immune response and increased tumor-specific T cells. In conclusion, Ad3-hTERT-CMV-hCD40L is promising for translation into human trials. In particular, this virus could enable successful dendritic cell therapy in cancer patients.

miR-199a-5p confers tumor-suppressive role in triple-negative breast cancer

Background

Triple-negative breast cancer (TNBC) remains a poor prognostic factor for breast cancer since no effective targeted therapy is readily available. Our previous studies confirmed miR-199a-5p is a TNBC-specific circulating biomarker, however, its functional roles in breast cancer is largely unknown. Thus, we investigated the functional implication of miR-199a-5p in TNBC and its potential underlying mechanisms.

Methods

MTT assay was performed to investigate the cell proliferation after transient transfection of miR-199a-5p in MDA-MB-231 cell line, followed by cell cycle analysis. Transwell invasion assay and wound healing assay were used to study the invasion and migration ability respectively. To further investigate the stemness-related characteristics of miR-199a-5p in breast cancer cells, single-cell clonogenic assay and aldehyde dehydrogenase (ALDH) assay were performed. 32 normal and 100 breast cancer patients’ plasma were recruited to identify the potential circulating markers by qPCR.

Results

Cell proliferation assay revealed significant inhibition after miR-199a-5p ectopic expression (p < 0.0001), as a result of decreased S phase (p = 0.0284), increased G0/G1 phase (p = 0.0260) and apoptosis (p = 0.0374). Invasiveness (p = 0.0005) and wound healing ability were also decreased upon miR-199a-5p overexpression. It significantly altered EMT-related genes expression, namely CDH1, ZEB1 and TWIST. Single-cell clonogenic assay showed decreased colonies in miR-199a-5p (p = 0.0182). Significant downregulation (p = 0.0088) and inhibited activity (p = 0.0390) of ALDH was observed in miR-199a-5p. ALDH1A3, which is the dominant isoform of ALDH, is significantly upregulated in breast cancer plasma especially in TNBC (p = 0.0248). PIK3CD was identified as a potential downstream target of miR-199a-5p.

Conclusions

Taken together, we unraveled, for the first time, the tumor-suppressive role of miR-199a-5p in TNBC, which attributed to EMT and cancer stemness properties, providing a novel therapeutic options towards this aggressive disease.

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.

Let-7a regulates mammosphere formation capacity through Ras/NF-κB and Ras/MAPK/ERK pathway in breast cancer stem cells

Breast cancer stem cells (BCSCs) have the greatest potential to maintain tumorigenesis in all subtypes of tumor cells and were regarded as the key drivers of tumor. Recent evidence has demonstrated that BCSCs contributed to a high degree of resistance to therapy. However, how BCSCs self renewal and tumorigenicity are maintained remains obscure. Herein, our study illustrated that overexpression of let-7a reduced cell proliferation and mammosphere formation ability of breast cancer stem cells(BCSCs) in a KRas-dependent manner through different pathways in vitro and in vivo. To be specific, we provided the evidence that let-7a was decreased, and reversely the expression of KRas was increased with moderate expression in early stages (I/II) and high expression in advanced stages (III/IV) in breast cancer specimens. In addition, the negative correlation between let-7a and KRas was clearly observed. In vitro, we found that let-7a inhibited mammosphere-forming efficiency and the mammosphere-size via NF-κB and MAPK/ERK pathway, respectively. The inhibitory effect of let-7a on mammosphere formation efficiency and the size of mammospheres was abolished after the depletion of KRas. On the contrary, enforced expression of KRas rescued the effect of let-7a. In vivo, let-7a inhibited the growth of tumors, whereas the negative effect of let-7a was rescued after overexpressing KRas. Taken together, our findings suggested that let-7a played a tumor suppressive role in a KRas-dependent manner.

What common biomarkers characterize a triple-negative profile in breast cancer?

Triple-negative breast cancers are not a homogeneous subgroup. There is substantial intra-subgroup diversity in tumor biology, prognosis and treatment sensitivity. Then, these triple-negative phenotype (TNP) groups, having specific features, can be again divided into subclasses based on an added immunohistochemical markers. The challenge in treating TNP breast cancers is that they are not responsive to antiestrogens or trastuzumab secondary to negative receptor status, and as a result have a poor prognosis. Therefore, the presence or absence of supplementary markers could help predict which therapies are best suited for patients based on the pattern that their disease markers show. In this review, we will recapitulate the major supplementary biomarkers related to triple-negative breast cancer, which could give new therapeutic options.

miRNA therapy targeting cancer stem cells: a new paradigm for cancer treatment and prevention of tumor recurrence

Cancer stem cells (CSCs) are a small subpopulation of cells within tumors that retain the properties of self-renewal and tumorigenicity in vivo. Although CSCs have been reported in multiple cancers, the regulation of CSCs has not been described at the molecular level. miRNAs are endogenous small noncoding RNAs that post-transcriptionally regulate the expression of their target genes via RNA interference and are involved in almost all cellular processes. Since aberrant miRNA expression occurs in CSCs, such dysregulated miRNAs may be promising therapeutic targets. In this review, we summarize the current knowledge regarding miRNAs that regulate CSC properties and discuss an in vivo delivery system for synthetic miRNA mimics and miRNA inhibitors for the development of innovative miRNA therapy against CSCs.

Regulation of stem cells-related signaling pathways in response to doxorubicin treatment in Hs578T triple-negative breast cancer cells

Different molecular changes have been previously associated with therapeutic response and recurrent disease, however, the detailed mechanism of action in triple-negative breast cancer subtype remains elusive. In this study, we investigated the cellular and molecular signaling of two claudin-low triple-negative breast cancer cells to doxorubicin and docetaxel treatment. Whole human transcriptomic evaluation was used to identify the subsequent changes in gene expression, while biological effects were measured by means of proliferation and anchorage-independent growth assays. Microarray analysis revealed changes in stem cell-related signaling pathways, suggesting that doxorubicin treatment affects the balance between self-renewal and differentiation. While the treatment reduced the proliferation, aggregation and mammosphere forming ability of stem-like cells derived from Hs578T cell line, stem-like cells derived from MDA-MB-231 cells were not significantly affected. Our results suggest that claudin-low triple-negative breast cancer cells might predominantly alter stem cell-related signaling pathways to promote stem-like cells activity as an innate resistance mechanism to doxorubicin treatment.

Impact of kinesin Eg5 inhibition by 3,4-dihydropyrimidin-2(1H)-one derivatives on various breast cancer cell features

Background

Breast cancer is a complex heterogeneous disease and is one of the leading causes of death among women. In addressing the need for treatments of this life-threatening illness, we studied 3,4-dihydropyrimidin-2(1H)-one (or thione) derivatives (DHPMs), a class of inhibitor molecules of the Eg5 motor spindle protein that shows pronounced antitumor activity against several cancer cell lines.

Methods

An in vitro screening was performed for identification of DHPMs with potent antitumor effects on MCF-7 and MDA-MB-231 cells and the selected DHPMs were evaluated for their inhibitory activity on Eg5 both in silico, using Molecular dynamics, and in vitro Eg5 inhibition assays. Analysis of cell death induction, proliferation, cell cycle and cancer stem cells (CSC) profile were performed by flow cytometry to assess the influence of the selected DPHMs on these important tumor features. Finally, the effects of DHPM treatment on tube formation were evaluated in vitro using HUVEC cells, and in vivo using a model on chorioallantoic membrane (CAM) of fertilized eggs.

Results

We identified five DHPMs with pronounced inhibitory activity on Eg5 motor protein interfering with the proper mitotic spindle assembly during cell division. These compounds impair the correct conclusion of cell cycle of the breast cancer cells and showed to be selective for tumor cells. Moreover, DHPMs modulate the CD44⁺/CD24⁻ phenotype leading to a decrease in the CSC population in MDA-MB-231 cells, an important effect since CSC are resistant to many conventional cancer therapies and play a pivotal role in tumor initiation and maintenance. This observation was confirmed by the results which demonstrated that DHPM treated cells had impaired proliferation and were unable to sustain angiogenesis events. Finally, the DHMP treated cells were induced to apoptosis, which is one of the most pursued goals in drug development.

Conclusions

The results of our study strongly suggest that DHPMs inhibit important tumorigenic features of breast cancer cells leading them to death by apoptosis. These findings firmly point to DHPM molecular architecture as a promising alternative against breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1274-1) contains supplementary material, which is available to authorized users.

Targeting lung cancer stem-like cells with TRAIL gene armed oncolytic adenovirus

Lung cancer stem cell (LCSC) is critical in cancer initiation, progression, drug resistance and relapse. Disadvantages showed in conventional lung cancer therapy probably because of its existence. In this study, lung cancer cell line A549 cells propagated as spheroid bodies (named as A549 sphere cells) in growth factors-defined serum-free medium. A549 sphere cells displayed CSC properties, including chemo-resistance, increased proportion of G0/G1 cells, slower proliferation rate, ability of differentiation and enhanced tumour formation ability in vivo. Oncolytic adenovirus ZD55 carrying EGFP gene, ZD55-EGFP, infected A549 sphere cells and inhibited cell growth. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) armed oncolytic adenovirus, ZD55-TRAIL, exhibited enhanced cytotoxicity and induced A549 sphere cells apoptosis through mitochondrial pathway. Moreover, small molecules embelin, LY294002 and resveratrol improved the cytotoxicity of ZD55-TRAIL. In the A549 sphere cells xenograft models, ZD55-TRAIL significantly inhibited tumour growth and improved survival status of mice. These results suggested that gene armed oncolytic adenovirus is a potential approach for lung cancer therapy through targeting LCSCs.

Adenoviral vectors for prodrug activation-based gene therapy for cancer

Cancer cell heterogeneity is a common feature - both between patients diagnosed with the same cancer and within an individual patient's tumor - and leads to widely different response rates to cancer therapies and the potential for the emergence of drug resistance. Diverse therapeutic approaches have been developed to combat the complexity of cancer, including individual treatment modalities designed to target tumor heterogeneity. This review discusses adenoviral vectors and how they can be modified to replicate in a cancer-specific manner and deliver therapeutic genes under multi-tiered regulation to target tumor heterogeneity, including heterogeneity associated with cancer stem cell-like subpopulations. Strategies that allow for combination of prodrug-activation gene therapy with a novel replication-conditional, heterogeneous tumor-targeting adenovirus are discussed, as are the benefits of using adenoviral vectors as tumor-targeting oncolytic vectors. While the anticancer activity of many adenoviral vectors has been well established in preclinical studies, only limited successes have been achieved in the clinic, indicating a need for further improvements in activity, specificity, tumor cell delivery and avoidance of immunogenicity.

CD123 targeting oncolytic adenoviruses suppress acute myeloid leukemia cell proliferation in vitro and in vivo

We report here a novel strategy to redirect oncolytic adenoviruses to CD123 by carry a soluble coxsackie-adenovirus receptor (sCAR)-IL3 expression cassette in the viral genome to form Ad.IL3, which sustainably infected acute myeloid leukemia (AML) cells through CD123. Ad.IL3 was further engineered to harbor gene encoding manganese superoxide dismutase (MnSOD) or mannose-binding plant lectin Pinellia pedatisecta agglutinin (PPA), forming Ad.IL3-MnSOD and Ad.IL3-PPA. As compared with Ad.IL3 or Ad.sp-E1A control, Ad.IL3-MnSOD and Ad.IL3-PPA significantly suppressed in vitro proliferation of HL60 and KG-1 cells. Elevated apoptosis was detected in HL60 and KG-1 cells treated with either Ad.IL3-MnSOD or Ad.IL3-PPA. The caspase-9–caspase-7 pathway was determined to be activated by Ad.IL3-MnSOD as well as by Ad.IL3-PPA in HL60 cells. In an HL60/Luc xenograft nonobese diabetic/severe-combined immunodeficiency mice model, Ad.IL3-MnSOD and Ad.IL3-PPA suppressed cancer cell growth as compared with Ad.IL3. A significant difference of cancer cell burden was detected between Ad.IL3 and Ad.IL3-PPA groups at day 9 after treatment. Furthermore, Ad.IL3-MnSOD significantly prolonged mouse survival as compared with Ad.sp-E1A. These findings demonstrated that Ad.IL3-gene could serve as a novel agent for AML therapy. Harboring sCAR-ligand expression cassette in the viral genome may provide a universal method to redirect oncolytic adenoviruses to various membrane receptors on cancer cells resisting serotype 5 adenovirus infection.

The anti-tumor activity of E1A and its implications in cancer therapy

The adenovirus type 5 E1A protein (E1A) plays a critical role in anti-cancer gene therapy and has been tested in clinical trials. The expression of E1A significantly reduces tumorigenesis, promotes cell death, and inhibits cancer cell mobility. Chemosensitization is one of the anti-tumor effects of E1A, increasing in vitro and in vivo sensitization of anti-cancer drugs, including cisplatin, gemcitabine, etoposide, doxorubicin, paclitaxel, and tumor necrosis factor-related apoptosis-inducing ligand and histone deacetylase inhibitors in different types of cancer cells. E1A also demonstrates anti-metastasis activity through various molecular mechanisms such as the repression of protease expression, suppression of HER2/neu and downregulation of microRNA (miR-520h). Moreover, E1A has been reported to reprogram transcription in tumor cells and stabilize tumor suppressors such as PP2A/C, p21 and p53. Because E1A plays a potentially significant role in anti-tumor therapy, there exists an urgent need to study the anti-cancer activities of E1A. This paper presents a review of our current understanding of the tumor-suppressive functions and molecular regulation of E1A, as well as the potential clinical applications of E1A.

Oncolytic viral therapy: targeting cancer stem cells

Cancer stem cells (CSCs) are defined as rare populations of tumor-initiating cancer cells that are capable of both self-renewal and differentiation. Extensive research is currently underway to develop therapeutics that target CSCs for cancer therapy, due to their critical role in tumorigenesis, as well as their resistance to chemotherapy and radiotherapy. To this end, oncolytic viruses targeting unique CSC markers, signaling pathways, or the pro-tumor CSC niche offer promising potential as CSCs-destroying agents/therapeutics. We provide a summary of existing knowledge on the biology of CSCs, including their markers and their niche thought to comprise the tumor microenvironment, and then we provide a critical analysis of the potential for targeting CSCs with oncolytic viruses, including herpes simplex virus-1, adenovirus, measles virus, reovirus, and vaccinia virus. Specifically, we review current literature regarding first-generation oncolytic viruses with their innate ability to replicate in CSCs, as well as second-generation viruses engineered to enhance the oncolytic effect and CSC-targeting through transgene expression.

Targeting CSCs in tumor microenvironment: the potential role of ROS-associated miRNAs in tumor aggressiveness

Reactive oxygen species (ROS) have been widely considered as critical cellular signaling molecules involving in various biological processes such as cell growth, differentiation, proliferation, apoptosis, and angiogenesis. The homeostasis of ROS is critical to maintain normal biological processes. Increased production of ROS, namely oxidative stress, due to either endogenous or exogenous sources causes irreversible damage of bio-molecules such as DNA, proteins, lipids, and sugars, leading to genomic instability, genetic mutation, and altered gene expression, eventually contributing to tumorigenesis. A great amount of experimental studies in vitro and in vivo have produced solid evidence supporting that oxidative stress is strongly associated with increased tumor cell growth, treatment resistance, and metastasis, and all of which contribute to tumor aggressiveness. More recently, the data have indicated that altered production of ROS is also associated with cancer stem cells (CSCs), epithelial-to-mesenchymal transition (EMT), and hypoxia, the most common features or phenomena in tumorigenesis and tumor progression. However, the exact mechanism by which ROS is involved in the regulation of CSC and EMT characteristics as well as hypoxia- and, especially, HIF-mediated pathways is not well known. Emerging evidence suggests the role of miRNAs in tumorigenesis and progression of human tumors. Recently, the data have indicated that altered productions of ROS are associated with deregulated expression of miRNAs, suggesting their potential roles in the regulation of ROS production. Therefore, targeting ROS mediated through the deregulation of miRNAs by novel approaches or by naturally occurring anti-oxidant agents such as genistein could provide a new therapeutic approach for the prevention and/or treatment of human malignancies. In this article, we will discuss the potential role of miRNAs in the regulation of ROS production during tumorigenesis. Finally, we will discuss the role of genistein, as a potent anti-tumor agent in the regulation of ROS production during tumorigenesis and tumor development.

Overview of cancer stem cells (CSCs) and mechanisms of their regulation: implications for cancer therapy

The identification of small subpopulations of cancer stem cells (CSCs) from blood mononuclear cells in human acute myeloid leukemia (AML) in 1997 was a landmark observation that recognized the potential role of CSCs in tumor aggressiveness. Two critical properties contribute to the functional role of CSCs in the establishment and recurrence of cancerous tumors: their capacity for self-renewal and their potential to differentiate into unlimited heterogeneous populations of cancer cells. These findings suggest that CSCs may represent novel therapeutic targets for the treatment and/or prevention of tumor progression, since they appear to be involved in cell migration, invasion, metastasis, and treatment resistance-all of which lead to poor clinical outcomes. The identification of CSC-specific markers, the isolation and characterization of CSCs from malignant tissues, and targeting strategies for the destruction of CSCs provide a novel opportunity for cancer research. This overview describes the potential implications of several common CSC markers in the identification of CSC subpopulations that are restricted to common malignant diseases, e.g., leukemia, and breast, prostate, pancreatic, and lung cancers. The role of microRNAs (miRNAs) in the regulation of CSC function is also discussed, as are several methods commonly used in CSC research. The potential role of the antidiabetic drug metformin- which has been shown to have effects on CSCs, and is known to function as an antitumor agent-is discussed as an example of this new class of chemotherapeutics.

Understanding glioma stem cells: rationale, clinical relevance and therapeutic strategies

Glioblastoma multiforme is one of the most aggressive brain tumors in adults. Despite the use of the best available multimodal therapeutic approaches, the prognosis remains dismal. The identification of glioma stem cells (GSCs) has offered new hope to affected patients, since it could explain, in part, the highly heterogeneous nature of this tumor and its chemo- and radio-resistance. Although still in its infancy, GSC research has unveiled many of its complexities and the theory itself remains controversial. GSC phenotype can significantly vary between patients and a single tumor may present several distinct GSCs. New therapeutic solutions that effectively target this population are of utmost importance, since they may be able to decrease neoplastic recurrence and improve patient survival. Here, we discuss the mechanisms by which GSCs lead to glioma relapse, the main controversies in this field and the most recent treatments that could successfully target this population.

Targeting CSC-related miRNAs for cancer therapy by natural agents

The theory of cancer stem cells (CSCs) has provided evidence on fundamental clinical implications because of the involvement of CSCs in cell migration, invasion, metastasis, and treatment resistance, which leads to the poor clinical outcome of cancer patients. Therefore, targeting CSCs will provide a novel therapeutic strategy for the treatment and/or prevention of tumors. However, the regulation of CSCs and its signaling pathways during tumorigenesis are not well understood. MicroRNAs (miRNAs) have been proved to act as key regulators of the post-transcriptional regulation of genes, which involve in a wide array of biological processes including tumorigenesis. The altered expressions of miRNAs are associated with poor clinical outcome of patients diagnosed with a variety of tumors. Therefore, emerging evidence strongly suggest that miRMAs play critical roles in tumor development and progression. Emerging evidence also suggest that miRNAs participate in the regulation of tumor cell growth, migration, invasion, angiogenesis, drug resistance, and metastasis. Moreover, miRNAs such as let-7, miR-21, miR-22, miR-34, miR-101, miR-146a, and miR-200 have been found to be associated with CSC phenotype and function mediated through targeting oncogenic signaling pathways. In this article, we will discuss the role of miRNAs in the regulation of CSC phenotype and function during tumor development and progression. We will also discuss the potential role of naturally occurring agents (nutraceuticals) as potent anti-tumor agents that are believed to function by targeting CSC-related miRNAs.

uPAR-controlled oncolytic adenoviruses eliminate cancer stem cells in human pancreatic tumors

Pancreatic tumors contain cancer stem cells highly resistant to chemotherapy. The identification of therapies that can eliminate this population of cells might provide with more effective treatments. In the current work we evaluated the potential of oncolytic adenoviruses to act against pancreatic cancer stem cells (PCSC). PCSC from two patient-derived xenograft models were isolated from orthotopic pancreatic tumors treated with saline, or with the chemotherapeutic agent gemcitabine. An enrichment in the number of PCSC expressing the cell surface marker CD133 and a marked enhancement on tumorsphere formation was observed in gemcitabine treated tumors. No significant increase in the CD44, CD24, and epithelial-specific antigen (ESA) positive cells was observed. Neoplastic sphere-forming cells were susceptible to adenoviral infection and exposure to oncolytic adenoviruses resulted in elevated cytotoxicity with both Adwt and the tumor specific AduPARE1A adenovirus. In vivo, intravenous administration of a single dose of AduPARE1A in human-derived pancreatic xenografts led to a remarkable anti-tumor effect. In contrast to gemcitabine AduPARE1A treatment did not result in PCSC enrichment. No enrichment on tumorspheres neither on the CD133(+) population was detected. Therefore our data provide evidences of the relevance of uPAR-controlled oncolytic adenoviruses for the elimination of pancreatic cancer stem cells.

The art of gene therapy for glioma: a review of the challenging road to the bedside

Glioblastoma multiforme (GBM) is a highly invasive brain tumour that is unvaryingly fatal in humans despite even aggressive therapeutic approaches such as surgical resection followed by chemotherapy and radiotherapy. Unconventional treatment options such as gene therapy provide an intriguing option for curbing glioma related deaths. To date, gene therapy has yielded encouraging results in preclinical animal models as well as promising safety profiles in phase I clinical trials, but has failed to demonstrate significant therapeutic efficacy in phase III clinical trials. The most widely studied antiglioma gene therapy strategies are suicide gene therapy, genetic immunotherapy and oncolytic virotherapy, and we have attributed the challenging transition of these modalities into the clinic to four major roadblocks: (1) anatomical features of the central nervous system, (2) the host immune system, (3) heterogeneity and invasiveness of GBM and (4) limitations in current GBM animal models. In this review, we discuss possible ways to jump these hurdles and develop new gene therapies that may be used alone or in synergy with other modalities to provide a powerful treatment option for patients with GBM.

Therapeutic strategies targeting cancer stem cells

Increasing studies have demonstrated a small proportion of cancer stem cells (CSCs) exist in the cancer cell population. CSCs have powerful self-renewal capacity and tumor-initiating ability and are resistant to chemotherapy and radiation. Conventional anticancer therapies kill the rapidly proliferating bulk cancer cells but spare the relatively quiescent CSCs, which cause cancer recurrence. So it is necessary to develop therapeutic strategies acting specifically on CSCs. In recent years, studies have shown that therapeutic agents such as metformin, salinomycin, DECA-14, rapamycin, oncostatin M (OSM), some natural compounds, oncolytic viruses, microRNAs, cell signaling pathway inhibitors, TNF-related apoptosis inducing ligand (TRAIL), interferon (IFN), telomerase inhibitors, all-trans retinoic acid (ATRA) and monoclonal antibodies can suppress the self-renewal of CSCs in vitro and in vivo. A combination of these agents and conventional chemotherapy drugs can significantly inhibit tumor growth, metastasis and recurrence. These strategies targeting CSCs may bring new hopes to cancer therapy.

Drug Resistant Breast Cancer Cell Line Displays Cancer Stem Cell Phenotype and Responds Sensitively to Epigenetic Drug SAHA

Cancer stem cell (CSC) population in solid human breast tumor was identified by CD44(+)/CD24(-) phenotype, characterized by high tumorigenicity, invasiveness and drug resistance. In this study, we characterized drug resistant breast cancer cell line-MCF-7/Adr and a number of breast cancer cell lines using flow cytometry, immunofluorescence, mammosphere formation assay and migration assay, examining their CSC immunophenotypes, presence of CSC proteins, tumorigenicity in vitro and migratory rates, respectively. Our results show that MCF-7/Adr cells uniformly display CSC characteristics yet retain low migratory rate. They are also able to self-renew and differentiate under floating culture conditions. Furthermore, MCF-7/Adr is selectively sensitive to epigenetic drug, suberoylanilide hydroxamic acid (SAHA), losing drug resistance and changes morphology yet retaining CSC immunophenotypes. In conclusion, we show that resistant breast cancer cell line MCF-7/Adr demonstrates uniform CSC like characteristics and are sensitive to epigenetic drug treatment.

Breast cancer stem cells: new therapeutic approaches

SUMMARY Breast cancer stem cells are defined as a small subset of cells within a cancer that constitutes a reservoir of self-sustaining cells; they are low-dividing, have a reduced ability to undergo apoptosis and a higher ability of DNA repair, making them more resistant to conventional radiation and chemotherapy. The recent better understanding of the mechanisms of resistance to therapy related to stem cells has opened new scenarios and perspectives for therapeutic approaches. Some drugs active against breast cancer stem cells have been used in cancer therapy for years, other approaches are currently under clinical trials and many drugs are still in a preclinical phase. Only controlled clinical trials will answer the question whether or not these new therapeutical approaches alone or combined with the ongoing treatments significantly improve the outcome of breast cancer patients.

The hTERT promoter enhances the antitumor activity of an oncolytic adenovirus under a hypoxic microenvironment

Hypoxia is a microenvironmental factor that contributes to the invasion, progression and metastasis of tumor cells. Hypoxic tumor cells often show more resistance to conventional chemoradiotherapy than normoxic tumor cells, suggesting the requirement of novel antitumor therapies to efficiently eliminate the hypoxic tumor cells. We previously generated a tumor-specific replication-competent oncolytic adenovirus (OBP-301: Telomelysin), in which the human telomerase reverse transcriptase (hTERT) promoter drives viral E1 expression. Since the promoter activity of the hTERT gene has been shown to be upregulated by hypoxia, we hypothesized that, under hypoxic conditions, the antitumor effect of OBP-301 with the hTERT promoter would be more efficient than that of the wild-type adenovirus 5 (Ad5). In this study, we investigated the antitumor effects of OBP-301 and Ad5 against human cancer cells under a normoxic (20% oxygen) or a hypoxic (1% oxygen) condition. Hypoxic condition induced nuclear accumulation of the hypoxia-inducible factor-1α and upregulation of hTERT promoter activity in human cancer cells. The cytopathic activity of OBP-301 was significantly higher than that of Ad5 under hypoxic condition. Consistent with their cytopathic activity, the replication of OBP-301 was significantly higher than that of Ad5 under the hypoxic condition. OBP-301-mediated E1A was expressed within hypoxic areas of human xenograft tumors in mice. These results suggest that the cytopathic activity of OBP-301 against hypoxic tumor cells is mediated through hypoxia-mediated activation of the hTERT promoter. Regulation of oncolytic adenoviruses by the hTERT promoter is a promising antitumor strategy, not only for induction of tumor-specific oncolysis, but also for efficient elimination of hypoxic tumor cells.