Radiation resistance of cancer stem cells: the 4 R's of radiobiology revisited

The changing paradigm of tumour response to irradiation

Tumours contain multiple different cell populations, including cells derived from the bone marrow as well as cancer-associated fibroblasts and various stromal populations including the vasculature. The microenvironment of the tumour cells plays a significant role in the response of the tumour to radiation treatment. Low levels of oxygen (hypoxia) caused by the poorly organized vasculature in tumours have long been known to affect radiation response; however, other aspects of the microenvironment may also play important roles. This article reviews some of the old literature concerning tumour response to irradiation and relates this to current concepts about the role of the tumour microenvironment in tumour response to radiation treatment. Included in the discussion are the role of cancer stem cells, radiation damage to the vasculature and the potential for radiation to enhance immune activity against tumour cells. Radiation treatment can cause a significant influx of bone marrow-derived cell populations into both normal tissues and tumours. Potential roles of such cells may include enhancing vascular recovery as well as modulating immune reactivity.

Radiation-Induced Reprogramming of Pre-Senescent Mammary Epithelial Cells Enriches Putative CD44(+)/CD24(-/low) Stem Cell Phenotype

The enrichment of putative CD44(+)/CD24(-/low) breast stem cell populations following exposure to ionizing radiation (IR) has been ascribed to their inherent radioresistance and an elevated frequency of symmetric division during repopulation. However, recent studies demonstrating radiation-induced phenotypic reprogramming (the transition of non-CD44(+)/CD24(-/low) cells into the CD44(+)/CD24(-/low) phenotype) as a potential mechanism of CD44(+)/CD24(-/low) cell enrichment have raised the question of whether a higher survival and increased self-renewal of existing CD44(+)/CD24(-/low) cells or induced reprogramming is an additional mode of enrichment. To investigate this question, we combined a cellular automata model with in vitro experimental data using both MCF-10A non-tumorigenic human mammary epithelial cells and MCF-7 breast cancer cells, with the goal of identifying the mechanistic basis of CD44(+)/CD24(-/low) stem cell enrichment in the context of radiation-induced cellular senescence. Quantitative modeling revealed that incomplete phenotypic reprogramming of pre-senescent non-stem cells (reprogramming whereby the CD44(+)/CD24(-/low) phenotype is conveyed, along with the short-term proliferation capacity of the original cell) could be an additional mode of enriching the CD44(+)/CD24(-/low) subpopulation. Furthermore, stem cell enrichment in MCF-7 cells occurs both at lower doses and earlier time points, and has longer persistence, than that observed in MCF-10A cells, suggesting that phenotypic plasticity appears to be less regulated in breast cancer cells. Taken together, these results suggest that reprogramming of pre-senescent non-stem cells may play a significant role in both cancer and non-tumorigenic mammary epithelial populations following exposure to IR, a finding with important implications for both radiation therapy and radiation carcinogenesis.

Evaluating biomarkers to model cancer risk post cosmic ray exposure

Robust predictive models are essential to manage the risk of radiation-induced carcinogenesis. Chronic exposure to cosmic rays in the context of the complex deep space environment may place astronauts at high cancer risk. To estimate this risk, it is critical to understand how radiation-induced cellular stress impacts cell fate decisions and how this in turn alters the risk of carcinogenesis. Exposure to the heavy ion component of cosmic rays triggers a multitude of cellular changes, depending on the rate of exposure, the type of damage incurred and individual susceptibility. Heterogeneity in dose, dose rate, radiation quality, energy and particle flux contribute to the complexity of risk assessment. To unravel the impact of each of these factors, it is critical to identify sensitive biomarkers that can serve as inputs for robust modeling of individual risk of cancer or other long-term health consequences of exposure. Limitations in sensitivity of biomarkers to dose and dose rate, and the complexity of longitudinal monitoring, are some of the factors that increase uncertainties in the output from risk prediction models. Here, we critically evaluate candidate early and late biomarkers of radiation exposure and discuss their usefulness in predicting cell fate decisions. Some of the biomarkers we have reviewed include complex clustered DNA damage, persistent DNA repair foci, reactive oxygen species, chromosome aberrations and inflammation. Other biomarkers discussed, often assayed for at longer points post exposure, include mutations, chromosome aberrations, reactive oxygen species and telomere length changes. We discuss the relationship of biomarkers to different potential cell fates, including proliferation, apoptosis, senescence, and loss of stemness, which can propagate genomic instability and alter tissue composition and the underlying mRNA signatures that contribute to cell fate decisions. Our goal is to highlight factors that are important in choosing biomarkers and to evaluate the potential for biomarkers to inform models of post exposure cancer risk. Because cellular stress response pathways to space radiation and environmental carcinogens share common nodes, biomarker-driven risk models may be broadly applicable for estimating risks for other carcinogens.

Irradiation of primary human gliomas triggers dynamic and aggressive survival responses involving microvesicle signaling

Malignant gliomas are heterogeneous populations of dynamically interacting cells. Genomic and transcriptional changes define this cellular hierarchy and allow certain tumor cells to co-opt metabolic machinery and adopt gene expression profiles that promote cellular reprogramming. Resultant expansion of privileged subpopulations can then rapidly adapt to microenvironmental stress that ultimately influence tumor response to therapeutic intervention. In this study, primary gliomas were subjected to acute or chronic irradiation and analyzed for changes in survival parameters, oxidative stress, gene expression, and cell invasion before and after treatment with secreted microvesicles isolated from irradiated and nonirradiated glioma cells. We found that primary gliomas exposed to ionizing radiation undergo metabolic changes that increase oxidative stress, alter gene expression, and affect the contents of and response to cellular secreted microvesicles. Radiation-induced changes were exacerbated under chronic as compared to acute irradiation paradigms and promoted cellular reprogramming through enhanced expression of key transcription factors and regulators involved in differentiation and pluripotency (SOX2, POU3F2, SALL2, OLIG2, NANOG, POU5F1v1, MSI1). Irradiation also affected changes in paracrine signaling mediated by cellular secreted microvesicles that significantly altered target cell phenotype. Primary gliomas treated with microvesicles exhibited increased radioresistance and treatment with microvesicles from chronically irradiated gliomas promoted invasion via induction of increased matrix metalloproteinase II activity. Together, our data describe a complex radiation response of primary glioma cells involving metabolic and transcriptional changes that alter radiation sensitivity and induce invasive behavior. These important changes can contribute to tumor growth and recurrence, and confound interventions designed to forestall disease progression. Environ. Mol. Mutagen. 57:405-415, 2016. © 2015 Wiley Periodicals, Inc.

K+ channel signaling in irradiated tumor cells

K⁺ channels crosstalk with biochemical signaling cascades and regulate virtually all cellular processes by adjusting the intracellular K⁺ concentration, generating the membrane potential, mediating cell volume changes, contributing to Ca²⁺ signaling, and directly interacting within molecular complexes with membrane receptors and downstream effectors. Tumor cells exhibit aberrant expression and activity patterns of K⁺ channels. The upregulation of highly "oncogenic" K⁺ channels such as the Ca²⁺-activated IK channel may drive the neoplastic transformation, malignant progression, metastasis, or therapy resistance of tumor cells. In particular, ionizing radiation in doses used for fractionated radiotherapy in the clinic has been shown to activate K⁺ channels. Radiogenic K⁺ channel activity, in turn, contributes to the DNA damage response and promotes survival of the irradiated tumor cells. Tumor-specific overexpression of certain K⁺ channel types together with the fact that pharmacological K⁺ channel modulators are already in clinical use or well tolerated in clinical trials suggests that K⁺ channel targeting alone or in combination with radiotherapy might become a promising new strategy of anti-cancer therapy. The present article aims to review our current knowledge on K⁺ channel signaling in irradiated tumor cells. Moreover, it provides new data on molecular mechanisms of radiogenic K⁺ channel activation and downstream signaling events.

MET inhibition overcomes radiation resistance of glioblastoma stem-like cells

Glioblastoma (GBM) contains stem-like cells (GSCs) known to be resistant to ionizing radiation and thus responsible for therapeutic failure and rapidly lethal tumor recurrence. It is known that GSC radioresistance relies on efficient activation of the DNA damage response, but the mechanisms linking this response with the stem status are still unclear. Here, we show that the MET receptor kinase, a functional marker of GSCs, is specifically expressed in a subset of radioresistant GSCs and overexpressed in human GBM recurring after radiotherapy. We elucidate that MET promotes GSC radioresistance through a novel mechanism, relying on AKT activity and leading to (i) sustained activation of Aurora kinase A, ATM kinase, and the downstream effectors of DNA repair, and (ii) phosphorylation and cytoplasmic retention of p21, which is associated with anti-apoptotic functions. We show that MET pharmacological inhibition causes DNA damage accumulation in irradiated GSCs and their depletion in vitro and in GBMs generated by GSC xenotransplantation. Preclinical evidence is thus provided that MET inhibitors can radiosensitize tumors and convert GSC-positive selection, induced by radiotherapy, into GSC eradication.

Tumor Cells Surviving Exposure to Proton or Photon Radiation Share a Common Immunogenic Modulation Signature, Rendering Them More Sensitive to T Cell-Mediated Killing

PURPOSE

To provide the foundation for combining immunotherapy to induce tumor antigen-specific T cells with proton radiation therapy to exploit the activity of those T cells.

METHODS AND MATERIALS

Using cell lines of tumors frequently treated with proton radiation, such as prostate, breast, lung, and chordoma, we examined the effect of proton radiation on the viability and induction of immunogenic modulation in tumor cells by flow cytometric and immunofluorescent analysis of surface phenotype and the functional immune consequences.

RESULTS

These studies show for the first time that (1) proton and photon radiation induced comparable up-regulation of surface molecules involved in immune recognition (histocompatibility leukocyte antigen, intercellular adhesion molecule 1, and the tumor-associated antigens carcinoembryonic antigen and mucin 1); (2) proton radiation mediated calreticulin cell-surface expression, increasing sensitivity to cytotoxic T-lymphocyte killing of tumor cells; and (3) cancer stem cells, which are resistant to the direct cytolytic activity of proton radiation, nonetheless up-regulated calreticulin after radiation in a manner similar to non-cancer stem cells.

CONCLUSIONS

These findings offer a rationale for the use of proton radiation in combination with immunotherapy, including for patients who have failed radiation therapy alone or have limited treatment options.

The insights of Let-7 miRNAs in oncogenesis and stem cell potency

The ability of the classic tumour‐suppressive let‐7 family to inhibit carcinogenesis, tumour progression, recurrence and pluripotency of cancer stem cells has generated significant interest in the field of cancer research. Through suppressing and degrading downstream‐targeted mRNAs, let‐7 affected most aspects of cell biology. It is perplexing how let‐7 affects oncogenesis, as the large influx of new miRNAs and other kinds of non‐coding RNAs are continuously defined. In this review, we delineate the complex functions of let‐7 and discuss the future direction of let‐7 research.

Impacts of Ionizing Radiation on the Different Compartments of the Tumor Microenvironment

Radiotherapy (RT) is one of the most important modalities for cancer treatment. For many years, the impact of RT on cancer cells has been extensively studied. Recently, the tumor microenvironment (TME) emerged as one of the key factors in therapy resistance. RT is known to influence and modify diverse components of the TME. Hence, we intent to review data from the literature on the impact of low and high single dose, as well as fractionated RT on host cells (endothelial cells, fibroblasts, immune and inflammatory cells) and the extracellular matrix. Optimizing the schedule of RT (i.e., dose per fraction) and other treatment modalities is a current challenge. A better understanding of the cascade of events and TME remodeling following RT would be helpful to design optimal treatment combination.

Snail-induced epithelial-to-mesenchymal transition of MCF-7 breast cancer cells: systems analysis of molecular changes and their effect on radiation and drug sensitivity

Background

Epithelial-to-mesenchymal transition (EMT) has been associated with the acquisition of metastatic potential and the resistance of cancer cells to therapeutic treatments. MCF-7 breast cancer cells engineered to constitutively express the zinc-finger transcriptional repressor gene Snail (MCF-7-Snail cells) have been previously shown to display morphological and molecular changes characteristic of EMT. We report here the results of a comprehensive systems level molecular analysis of changes in global patterns of gene expression and levels of glutathione and reactive oxygen species (ROS) in MCF-7-Snail cells and the consequence of these changes on the sensitivity of cells to radiation treatment and therapeutic drugs.

Methods

Snail-induced changes in global patterns of gene expression were identified by microarray profiling using the Affymetrix platform (U133 Plus 2.0). The resulting data were processed and analyzed by a variety of system level analytical methods. Levels of ROS and glutathione (GSH) were determined by fluorescent and luminescence assays, and nuclear levels of NF-κB protein were determined by an ELISA based method. The sensitivity of cells to ionizing radiation and anticancer drugs was determined using a resazurin-based cell cytotoxicity assay.

Results

Constitutive ectopic expression of Snail in epithelial-like, luminal A-type MCF-7 cells induced significant changes in the expression of >7600 genes including gene and miRNA regulators of EMT. Mesenchymal-like MCF-7-Snail cells acquired molecular profiles characteristic of triple-negative, claudin-low breast cancer cells, and displayed increased sensitivity to radiation treatment, and increased, decreased or no change in sensitivity to a variety of anticancer drugs. Elevated ROS levels in MCF-7-Snail cells were unexpectedly not positively correlated with NF-κB activity.

Conclusions

Ectopic expression of Snail in MCF-7 cells resulted in morphological and molecular changes previously associated with EMT. The results underscore the complexity and cell-type dependent nature of the EMT process and indicate that EMT is not necessarily predictive of decreased resistance to radiation and drug-based therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2274-5) contains supplementary material, which is available to authorized users.

Re-sensitization of radiation resistant colorectal cancer cells to radiation through inhibition of AMPK pathway

Radiotherapy (RT) is commonly used to treat multi-tumors to attenuate the risk of recurrence. Despite impressive initial clinical responses, a large proportion of patients experience resistance to RT. Therefore, identification of functionally relevant biomarkers would be beneficial for radioresistant patients. Adenosine monophosphate-activated kinase (AMPK) is recognized as a mediator of tumor suppressor gene function. In the present study, radio-sensitive and -resistant colon cancer patient samples were compared and the AMPK pathway was observed to be highly activated in radioresistant patients. In addition, the protein and mRNA levels of AMPK were upregulated in radioresistant colon cancer cells in comparison to radiosensitive colon cancer cells. The present study provides evidence that activation of AMPK by metformin contributes to radioresistance. Inhibition of AMPK by either small interfering RNA or Compound C, which is a specific inhibitor of AMPK, re-sensitized radiation resistant cells. The data presented indicates a synergistic effect on radiation resistant cancer cells by the combination of Compound C and radiation. In summary, the present study proposes that inhibition of the AMPK pathway is a potential strategy for reversing radiation resistance and may contribute to the development of therapeutic anticancer drugs.

Cancer stem cells and chemoresistance: The smartest survives the raid

Chemoresistant metastatic relapse of minimal residual disease plays a significant role for poor prognosis of cancer. Growing evidence supports a critical role of cancer stem cell (CSC) behind the mechanisms for this deadly disease. This review briefly introduces the basics of the conventional chemotherapies, updates the CSC theories, highlights the molecular and cellular mechanisms by which CSC smartly designs and utilizes multiple lines of self-defense to avoid being killed by chemotherapy, and concisely summarizes recent progress in studies on CSC-targeted therapies in the end, with the hope to help guide future research toward developing more effective therapeutic strategies to eradicate tumor cells in the patients.

Targeting Notch to overcome radiation resistance

Radiotherapy represents an important therapeutic strategy in the treatment of cancer cells. However, it often fails to eliminate all tumor cells because of the intrinsic or acquired treatment resistance, which is the most common cause of tumor recurrence. Emerging evidences suggest that the Notch signaling pathway is an important pathway mediating radiation resistance in tumor cells. Successful targeting of Notch signaling requires 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 be safe and effective. Here we summarize the role of Notch in mediating resistance to radiotherapy, the different strategies to block Notch in cancer cells and how treatment scheduling can improve tumor response. Finally, we discuss a need for reliable Notch related biomarkers in specific tumors to measure pathway activity and to allow identification of a subset of patients who are likely to benefit from Notch targeted therapies.

Effects of Charged Particles on Human Tumor Cells

The use of charged particle therapy in cancer treatment is growing rapidly, in large part because the exquisite dose localization of charged particles allows for higher radiation doses to be given to tumor tissue while normal tissues are exposed to lower doses and decreased volumes of normal tissues are irradiated. In addition, charged particles heavier than protons have substantial potential clinical advantages because of their additional biological effects, including greater cell killing effectiveness, decreased radiation resistance of hypoxic cells in tumors, and reduced cell cycle dependence of radiation response. These biological advantages depend on many factors, such as endpoint, cell or tissue type, dose, dose rate or fractionation, charged particle type and energy, and oxygen concentration. This review summarizes the unique biological advantages of charged particle therapy and highlights recent research and areas of particular research needs, such as quantification of relative biological effectiveness (RBE) for various tumor types and radiation qualities, role of genetic background of tumor cells in determining response to charged particles, sensitivity of cancer stem-like cells to charged particles, role of charged particles in tumors with hypoxic fractions, and importance of fractionation, including use of hypofractionation, with charged particles.

Enhancement of tumor initiation and expression of KCNMA1, MORF4L2 and ASPM genes in the adenocarcinoma of lung xenograft after vorinostat treatment

Cancer stem cells (CSCs) are usually tolerant to chemotherapy and radiotherapy and associated with tumor relapse. Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor (HDACI), is currently being used in clinical trials of lung cancer. However, SAHA facilitates the formation of induced pluripotent stem cells from somatic cells. We hypothesized that SAHA would mediate the CSCs properties and subsequently confer a more malignant phenotype in lung cancer. Transfected H1299 lung cancer cells, which stably expresses a triple fused reporter gene (DsRedm-Fluc-tTKsr39) under the control of CMV promoter was used to establish a xenograft mouse model. After the treatment of SAHA, H1299 cell line and tumor xenografts were sorted by fluorescence-activated cell sorting (FACS) based on aldehyde dehydrogenase (ALDH) activity. We found that SAHA could suppress the growth of xenografted H1299 tumors with decreased proportion of ALDH^br lung cancer cells indicating that SAHA may target CSCs. However, SAHA significantly enhanced the tumor initiating capacity and the expression of malignant genes such as KCNMA1, MORF4L2 and ASPM in the remaining living ALDH^br cells. These findings suggested that SAHA treatment created a more drug-resistant state in residual ALDH^br cells. The in vivo imaging technique may facilitate searching and characterization of CSCs.

Evolving Strategies for Therapeutically Targeting Cancer Stem Cells

Cancer is a multifactor and multistep process that is affected intrinsically by the genetic and epigenetic makeup of tumor cells and extrinsically by the host microenvironment and immune system. A key component of cancer involves a unique subpopulation of highly malignant cancerous cells referred to as cancer stem cells (CSCs). CSCs are positioned at the apex of the tumor hierarchy with an ability to both self-renew and also generate non-CSC/differentiated progeny, which contribute to the majority of the tumor mass. CSCs undergo functional changes and show plasticity that is stimulated by specific microenvironmental cues and interactions in the tumor niche, which contribute to the complexity and heterogeneity of the CSC population. The prognostic value of CSCs in the clinic is evident since there are many examples in which CSCs serve as markers for poor patient prognosis. CSCs are innately resistant to many standard therapies and they display anoikis resistance, immune evasion, tumor dormancy, and field cancerization, which may result in metastasis and relapse. Many academic laboratories and biotechnology companies are currently focusing on strategies that target CSCs. Combination therapies, epigenetic modifiers, stemness inhibitors, CSC surface marker-based therapies, and immunotherapy-based CSC-targeting drugs are currently undergoing clinical trials. Potential new targets/strategies in CSC-targeted therapy include MDA-9/Syntenin (SDCBP), Patched (PTCH), epigenetic targets, noncoding RNAs, and differentiation induction. Defining ways of targeting and destroying CSCs holds potential to impact significantly on cancer therapy, including prevention of metastasis and cancer recurrence.

Inhibition of mTOR sensitizes breast cancer stem cells to radiation-induced repression of self-renewal through the regulation of MnSOD and Akt

The sensitization of breast cancer stem cells (BrCSCs) to the inhibitive effects of radiotherapy through adjuvant therapy which targets oncogenic pathways represents a prospective strategy for improving the effect of radiation in patients with triple-negative breast cancer (TNBC). Mammalian target of rapamycin (mTOR) activation is one of the most frequent events in human malignancies, and is critical for sustaining the self-renewing ability of cancer stem cells (CSCs); inhibition by rapamycin is an effective and promising strategy in anticancer treatments. In the present study, we found that mTOR activity was closely related to the self-renewal ability of BrCSCs, and in triple negative MDA-MB-453 and MDA-MB-468 cells, rapamycin repression of mTOR phosphorylation decreased the number of mammospheres and helped to sensitize the resistant CSCs to low-dose radiation therapy. By inhibiting mTOR and mitochondrial manganese superoxide dismutase (MnSOD), we confirmed that rapamycin functioned through the mTOR/MnSOD/reactive oxygen species (ROS) signaling pathway, and the existence of Akt governed the rapamycin-induced asymmetric division (AD) of stem cells in cases of radiation-treated breast cancer. The synergic effects of rapamycin and low-dose radiation induced the AD of stem cells, which then resulted in a decrease in the number of mammospheres, and both were mediated by MnSOD. Governed by Akt, the consequent inhibition of ROS formation and oxidative stress preserved the AD mode of stem cells, which is critical for an improved radiotherapy response in clinical treatment, as the tumor group is thus easier to eliminate with radiation therapy. We posit that an in-depth understanding of the interaction of radiation with CSCs has enormous potential and will make radiation even better and more effective.

Re-irradiation of recurrent anaplastic ependymoma using radiosurgery or fractionated stereotactic radiotherapy

PURPOSE

Recurrent ependymomas were retreated with stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT). The efficacy, toxicities, and differences between SRS and FSRT were analyzed.

METHODS

Eight patients with recurrent ependymomas fulfilling the criteria described below were evaluated. Inclusion criteria were: (1) the patient had previously undergone surgery and conventional radiotherapy as first-line treatment; (2) targets were located in or adjacent to the eloquent area or were deep-seated; and (3) the previously irradiated volume overlapped the target lesion.

RESULTS

FSRT was delivered to 18 lesions, SRS to 20 lesions. A median follow-up period was 23 months. The local control rate was 76 % at 3 years. No significant differences in local control were observed due to tumor size or fractionation schedule. Lesions receiving >25 Gy/5 fr or 21 Gy/3 fr did not recur within 1 year, whereas no dose-response relationship was observed in those treated with SRS. No grade ≥2 toxicity was observed.

CONCLUSION

Our treatment protocol provided an acceptable LC rate and minimal toxicities. Because local recurrence of tumors may result in patient death, a minimum dose of 21 Gy/3 fr or 25 Gy/5 fr or higher may be most suitable for treatment of these cases.

[Cancer stem cells: Radiotherapeutic features and therapeutic targets]

Recent evidences suggest that many types of cancers contain a cell population presenting stem cell properties. While the great majority of tumor cells are destined to differentiate, and eventually stop dividing, only a minority population of cells, termed cancer stem cells (CSCs), possesses extensive self-renewal capability and can recapitulate tumor pathophysiology in an immune-compromised animal model. Tumor initiating cells have been identified and isolated in many tumor types including brain, colon and prostate. They are virtually resistant to radiation and may contribute to treatment resistance and recurrence. Therefore, therapies specifically targeting CSCs will likely be needed for complete tumor eradication. The present study reviews published reports identifying the mechanisms of radioresistance of CSCs and potential targets based on the pathways of self-renewal. Further elucidation of pathways that regulate CSCs may provide insights into the development of novel innovative therapies.

Hypoxia imaging in gliomas with 18F-fluoromisonidazole PET: toward clinical translation

There is significant interest in the development of improved image-guided therapy for neuro-oncology applications. Glioblastomas (GBM) in particular present a considerable challenge because of their pervasive nature, propensity for recurrence, and resistance to conventional therapies. MRI is routinely used as a guide for planning treatment strategies. However, this imaging modality is not able to provide images that clearly delineate tumor boundaries and affords only indirect information about key tumor pathophysiology. With the emergence of PET imaging with new oncology radiotracers, mapping of tumor infiltration and other important molecular events such as hypoxia is now feasible within the clinical setting. In particular, the importance of imaging hypoxia levels within the tumoral microenvironment is gathering interest, as hypoxia is known to play a central role in glioma pathogenesis and resistance to treatment. One of the hypoxia radiotracers known for its clinical utility is (18)F-fluoromisodazole ((18)F-FMISO). In this review, we highlight the typical causes of treatment failure in gliomas that may be linked to hypoxia and outline current methods for the detection of hypoxia. We also provide an overview of the growing body of studies focusing on the clinical translation of (18)F-FMISO PET imaging, strengthening the argument for the use of (18)F-FMISO hypoxia imaging to help optimize and guide treatment strategies for patients with glioblastoma.

Radiosensitization of TPGS-emulsified docetaxel-loaded poly(lactic-co-glycolic acid) nanoparticles in CNE-1 and A549 cells

Docetaxel is among the most effective radiosensitizers. It is widely used as radiosensitizer in many tumors, including head and neck carcinoma. Nevertheless, poor solubility and severe hypersensitivity limit its clinical use and its therapeutic effect remains to be improved. In this study, docetaxel-loaded polymeric nanoparticles were prepared by nanoprecipitation method to be new radiosensitizer with lower side effects and higher efficacy. The physiochemical characteristics of the nanoparticles were studied. Two human tumor cell lines which are resistant to radiotherapy were used in this research. We have compared the radioenhancement efficacy of docetaxel-loaded nanoparticles with docetaxel in A549 and CNE-1 cells. Compared with docetaxel, radiosensitization of docetaxel-loaded nanoparticles was improved significantly (sensitization enhancement ratio in A549 increased 1.24-fold to 1.68-fold when the radiation was applied 2 h after the drug, p < 0.01, sensitization enhancement ratio in CNE-1 increased 1.32-fold to 1.61-fold, p < 0.05). We explored the mechanisms for the radiosensitization efficiency and the difference between docetaxel and docetaxel-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles. The improved radiosensitization efficacy was associated with enhanced G2/M arrest, promoted apoptosis and the role of D-alpha-tocopheryl polyethylene glycol 1000 succinate which will enhance the cell uptake and inhibit the multiple drug resistance. Moreover, the radiosensitization efficacy of docetaxel-loaded nanoparticles was more prominent than docetaxel. In conclusion, tocopheryl polyethylene glycol 1000 succinate-emulsified docetaxel-loaded PLGA nanoparticles were more efficacious and fewer adverse effects were observed than with the commercial docetaxel formulation. Thus, PLGA nanoparticles hold promise as a radiosensitizing agent.

IL-6 signaling promotes DNA repair and prevents apoptosis in CD133+ stem-like cells of lung cancer after radiation

BACKGROUND

Local tumor control by standard fractionated radiotherapy (RT) remains poor because of tumor resistance to radiation (radioresistance). It has been suggested that cancer stem cells (CSCs) are more radioresistant than non-CSCs. In previous studies, we have shown IL-6 promotes self-renewal of CD133+ CSC-like cells. In this study, we investigated whether IL-6 plays roles not only in promoting self-renewal of CD133+ cells after radiation, but also in conferring radioresistance of CD133+ cells in NSCLC.

MATERIALS AND METHODS

To compare radiation sensitivity of CSCs and non-CSCs, CD133+ CSC-like and CD133- cell populations were isolated from two NSCLC cell lines, A549 and H157, by immunomagnetic separation and their sensitivities to ionizing radiation were investigated using the clonogenic survival assay. To further study the IL-6 effect on the radiosensitivity of CD133+ CSC-like cells, CD133+ cells were isolated from A549IL-6si/sc and H157IL-6si/sc cells whose intracellular IL-6 levels were manipulated via the lentiviral transduction with IL-6siRNA. Post-irradiation DNA damage was analyzed by γ-H2AX staining and Comet assay. Molecular mechanisms by which IL-6 regulates the molecules associated with DNA repair and anti-apoptosis after radiation were analyzed by Western blot and immunofluoresecence (IF) staining analyses.

RESULTS

NSCLC CD133+ CSC-like cells were enriched upon radiation. Survival of NSCLC CD133+ cells after radiation was higher than that of CD133- cells. Survival of IL-6 expressing NSC LC CD133+ cells (sc) was higher than that of IL-6 knocked-down cells (IL-6si) after radiation. IL-6 played a role in protecting NSCLC CD133+ cells from radiation-induced DNA damage and apoptosis.

CONCLUSIONS

IL-6 signaling promotes DNA repair while protecting CD133+ CSC-like cells from apoptotic death after radiation for lung cancer. A combined therapy of radiation and agents that inhibit IL-6 signaling (or its downstream signaling) is suggested to reduce CSC-mediated radioresistance in lung cancer.

IL-6 signaling promotes DNA repair and prevents apoptosis in CD133+ stem-like cells of lung cancer after radiation

Background

Local tumor control by standard fractionated radiotherapy (RT) remains poor because of tumor resistance to radiation (radioresistance). It has been suggested that cancer stem cells (CSCs) are more radioresistant than non-CSCs. In previous studies, we have shown IL-6 promotes self-renewal of CD133+ CSC-like cells. In this study, we investigated whether IL-6 plays roles not only in promoting self-renewal of CD133+ cells after radiation, but also in conferring radioresistance of CD133+ cells in NSCLC.

Materials and methods

To compare radiation sensitivity of CSCs and non-CSCs, CD133+ CSC-like and CD133- cell populations were isolated from two NSCLC cell lines, A549 and H157, by immunomagnetic separation and their sensitivities to ionizing radiation were investigated using the clonogenic survival assay. To further study the IL-6 effect on the radiosensitivity of CD133+ CSC-like cells, CD133+ cells were isolated from A549IL-6si/sc and H157IL-6si/sc cells whose intracellular IL-6 levels were manipulated via the lentiviral transduction with IL-6siRNA. Post-irradiation DNA damage was analyzed by γ-H2AX staining and Comet assay. Molecular mechanisms by which IL-6 regulates the molecules associated with DNA repair and anti-apoptosis after radiation were analyzed by Western blot and immunofluoresecence (IF) staining analyses.

Results

NSCLC CD133+ CSC-like cells were enriched upon radiation. Survival of NSCLC CD133+ cells after radiation was higher than that of CD133- cells. Survival of IL-6 expressing NSC LC CD133+ cells (sc) was higher than that of IL-6 knocked-down cells (IL-6si) after radiation. IL-6 played a role in protecting NSCLC CD133+ cells from radiation-induced DNA damage and apoptosis.

Conclusions

IL-6 signaling promotes DNA repair while protecting CD133+ CSC-like cells from apoptotic death after radiation for lung cancer. A combined therapy of radiation and agents that inhibit IL-6 signaling (or its downstream signaling) is suggested to reduce CSC-mediated radioresistance in lung cancer.

Metabolic activation of mitochondria in glioma stem cells promotes cancer development through a reactive oxygen species-mediated mechanism

Introduction

Cancer stem cells (CSCs) possess characteristics associated with normal stem cells, specifically the abilities to renew themselves and to give rise to all cell types (differentiation). It is assumed that induction of differentiation in CSCs would reduce their ability to form tumors. What triggers CSC differentiation and the role of “differentiation” in tumorigenesis remain elusive.

Methods

Glioma stem cell (GSC) lines and subcutaneous as well as orthotopic xenografts established from fresh surgical specimens of glioblastoma multiforme were used.

Results

Exposure of GSCs to serum activates mitochondrial respiration and causes an increase in mitochondrial reactive oxygen species (ROS) as well as oxidative stress responses, leading to the appearance of differentiation morphology and a deceased expression of CSC markers. Chemical perturbation of the mitochondrial electron transport chain causes ROS increase and further downregulation of stem cell markers, while antioxidant N-acetyl-cysteine reduces ROS and suppresses the differentiation of GSCs. Surprisingly, the serum-induced differentiated GSCs exhibit greater ability to form tumor in both orthotopic and subcutaneous xenograft models, which can be suppressed by N-acetyl-cysteine. Mitochondrial ROS from the serum-stimulated cells triggered the activation of nuclear factor-kappa-B (NFκB) pathway, which is a potential mechanism for the promotion of tumorigenesis.

Conclusion

This study suggests that ROS generated from active mitochondrial respiration in the presence of serum is critical in CSCs activation, which promotes tumor development in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0174-2) contains supplementary material, which is available to authorized users.

Increased activity of CHK enhances the radioresistance of MCF-7 breast cancer stem cells

The resistance of breast cancer to radiotherapy remains a major obstacle to successful cancer management. Radiotherapy may result in DNA damage and activate breast cancer stem cells. DNA damage may lead to activation of the checkpoint kinase (CHK) signaling pathway, of which debromohymenialdisine (DBH) is a specific inhibitor. Radiotherapy also increases the expression of phosphorylated CHK1/2 (pCHK1/2) in the breast cancer cell line, MCF-7, in vitro in a dose-dependent manner. DBH is a relatively stable effective inhibitor that significantly reduces pCHK1/2 expression and MCF-7 proliferation. Low-dose radiotherapy combined with DBH resulted in a higher MCF-7 inhibition rate compared with high-dose radiation alone. This result indicates that the inhibition of the CHK1/2 signal pathway may significantly reduce DNA damage within radiated cells. Radiotherapy may also regulate the proportion of CD44⁺/CD24⁻ MCF-7 cancer stem cells in a dose- and time-dependent manner. However, the stem cell proportion of MCF-7 cells was significantly reduced by treatment with DBH. The inhibition is relatively stable and time dependent. Significant reductions were observed after 3 days of culture (P<0.01). The results of the present study indicate that the DBH-induced downregulation of CHK may provide a novel method of enhancing the effect of radiotherapy and reducing stem cell survival in the MCF-7 cell line.

Radiation responses of stem cells: targeted and non-targeted effects

Stem cells are fundamental to the development of any tissue or organism via their ability to self-renew, which is aided by their unlimited proliferative capacity and their ability to produce fully differentiated offspring, often from multiple lineages. Stems cells are long lived and have the potential to accumulate mutations, including in response to radiation exposure. It is thought that stem cells have the potential to be induced into a cancer stem cell phenotype and that these may play an important role in resistance to radiotherapy. For radiation-induced carcinogenesis, the role of targeted and non-targeted effects is unclear with tissue or origin being important. Studies of genomic instability and bystander responses have shown consistent effects in haematopoietic models. Several models of radiation have predicted that stem cells play an important role in tumour initiation and that bystander responses could play a role in proliferation and self-renewal.

Stem cell-like gene expression signature identified in ionizing radiation-treated cancer cells

Recent studies have reported that embryonic stem (ES) cell-associated gene expression signatures have been identified in poorly differentiated tumors, revealing a link between ES cell identity and cancer cells. Cancer cells originate from cancer stem cells (CSCs). Both types of cells share common properties such as self-renewal and heterogeneity. CSCs are also resistant to conventional chemotherapy and radiotherapy. Here, we show similar gene expression patterns between ES cells and ionizing radiation (IR)-treated cancer cells. Using genome-wide transcriptome analysis, we compared the gene expression profiles among ES cells, cancer cells, and irradiated cancer cells, and identified a subset of similar gene expression patterns between ES cells and irradiated cancer cells, indicated by hierarchical clustering. These gene expression patterns were then confirmed by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analyses. Using bioinformatic analyses, these candidate genes are also associated with various biological pathways related to stemness in cancer. Taken together, our data suggest that identification of common molecular characteristics between ES cells and irradiated cancer cells is important to understand the properties of cancer stem cells and their resistance to radiotherapy.

MicroRNA-144 affects radiotherapy sensitivity by promoting proliferation, migration and invasion of breast cancer cells

Radiotherapy resistance remains a major obstacle for patients with breast cancer. miRNAs are important regulators in many biological processes including proliferation, apoptosis, invasion and metastasis and response to treatment in different types of tumors. Here, we describe the role of miRNA-144 in the regulation of radiotherapy sensitivity, migration and invasion of breast cancer cells. The cell survival rate of breast cancer cells was measured by WST-1 assay after irradiation. The caspase-3/-7 activity and apoptotic proteins were analyzed by Caspase-Glo3/7 assay and western blot analysis, respectively. The migration and invasion of breast cancer cells were evaluated by BD Transwell migration and Matrigel invasion assays. The EMT markers were detected by western blot analysis. We found that overexpression of miR-144 increased the proliferation rate of MDA-MB-231 cells without radiation. Both MDA-MB‑231 and SKBR3 cells exhibited significantly increased radiation resistance after overexpression of miR-144. Meanwhile, the migration and invasion of both MDA-MB-231 and SKBR3 cells were changed by altered miR-144 expression. In addition, the overexpression of miR-144 inhibited E-cadherin expression and promoted Snail expression. miR-144 activated AKT by downregulation of PTEN in breast cancer cells. Our results strongly suggest that miR-144 acts as an important regulator of tumorigenesis and tumor progression of breast cancer. These results indicate that miR-144 might serve as a potential molecular target for breast cancer treatment.

Analysis of immune cell populations and cytokine profiles in murine splenocytes exposed to whole-body low-dose irradiation

PURPOSE

In contrast to high-dose therapeutic irradiation, definitive research detailing the physiological effects of low-dose irradiation is limited. Notably, the immunological response elicited after low-dose irradiation remains controversial.

MATERIALS AND METHODS

Female C57BL/6 mice were whole- body-irradiated with a single or three daily fractions up to a total dose of 0.1, 1, or 10 cGy. Blood and spleen were harvested 2, 7 and 14 days after irradiation.

RESULTS

The splenic CD4(+) T cell subpopulations were temporarily increased at 2 days after single or fractionated irradiation, whereas the percentage of dendritic cells (DC) and macrophages was decreased. Whereas CD8(+) T cell populations were decreased in single-dose irradiated mice at day 7, early and sustained reduction of CD8(+) T cell numbers was observed in fractionated- dose-irradiated mice from day 2 until day 14. In addition, single-dose irradiation resulted in a Th1 cytokine expression profile, whereas fractionated-dose irradiation drove a Th2 shift. Additionally, increased expression of immune-related factors was observed at early time-points with single-dose irradiation, in contrast to the dose-independent induction following fractionated-dose irradiation.

CONCLUSIONS

Our results demonstrate that low-dose irradiation modulates the immune response in mice, where the sensitivity and kinetics of the induced response vary according to the dosing method.

Genotoxic Damage to Glioblastoma Cells Treated with 6 MV X-Radiation in The Presence or Absence of Methoxy Estradiol, IUDR or Topotecan

Objective

To explore the cumulative genotoxic damage to glioblastoma (GBM) cells, grown as multicellular spheroids, following exposure to 6 MV X-rays (2 Gy, 22 Gy) with or without, 2- methoxy estradiol (2ME2), iododeoxyuridine (IUDR) or topotecan (TPT), using the Picogreen assay.

Materials and Methods

The U87MG cells cultured as spheroids were treated with 6 MV X-ray using linear accelerator. Specimens were divided into five groups and irradiated using X-ray giving the dose of 2 Gy after sequentially incubated with one of the following three drug combinations: TPT, 2-ME2/TPT, IUDR/TPT or 2ME2/IUDR/ TPT. One specimen was used as the irradiated only sample (R). The last group was also irradiated with total dose of 22 Gy (each time 2 Gy) of 6 MV X-ray in 11 fractions and treated for three times. DNA damage was evaluated using the Picogreen method in the experimental study.

Results

R/TPT treated group had more DNA damage [double strand break (DSB)/single strand break (SSB)] compared with the untreated group (P<0.05). Moreover the R/ TPT group treated with 2ME2 followed by IUDR had maximum DNA damage in spheroid GBM indicating an augmented genotoxicity in the cells. The DNA damage was induced after seven fractionated irradiation and two sequential treatments with 2ME2/IUDR/TPT. To ensure accuracy of the slope of dose response curve the fractionated radiation was calculated as 7.36 Gy with respect to α/β ratio based on biologically effective dose (BED) formulae.

Conclusion

Cells treated with 2ME2/IUDR showed more sensitivity to radiation and accumulative DNA damage. DNA damage was significantly increased when GBM cells treated with TPT ceased at S phase due to the inhibition of topoisomerase enzyme and phosphorylation of Chk1 enzyme. These results suggest that R/TPT- treated cells increase sensitivity to 2ME2 and IUDR especially when they are used together. Therefore, due to an increase in the level of DNA damage (SSB vs. DSB) and impairment of DNA repair machinery, more cell death will occur. This in turn may improve the treatment of GBM.

Optimization of radiation dosing schedules for proneural glioblastoma

Glioblastomas are the most aggressive primary brain tumor. Despite treatment with surgery, radiation and chemotherapy, these tumors remain uncurable and few significant increases in survival have been observed over the last half-century. We recently employed a combined theoretical and experimental approach to predict the effectiveness of radiation administration schedules, identifying two schedules that led to superior survival in a mouse model of the disease (Leder et al., Cell 156(3):603-616, 2014). Here we extended this approach to consider fractionated schedules to best minimize toxicity arising in early- and late-responding tissues. To this end, we decomposed the problem into two separate solvable optimization tasks: (i) optimization of the amount of radiation per dose, and (ii) optimization of the amount of time that passes between radiation doses. To ensure clinical applicability, we then considered the impact of clinical operating hours by incorporating time constraints consistent with operational schedules of the radiology clinic. We found that there was no significant loss incurred by restricting dosage to an 8:00 a.m. to 5:00 p.m. window. Our flexible approach is also applicable to other tumor types treated with radiotherapy.

Breast Cancer Stem Cell Correlates as Predicative Factors for Radiation Therapy

In today's era of personalized medicine, the use of radiation therapy for breast cancer is still tailored to the type of surgery and the stage of the cancer. The future of breast radiation oncology would hopefully entail selecting patients for whom there is a clear benefit for the use of radiation therapy. To get to this point we need reliable predictors of radiation response. Cancer stem cells have been correlated to radiation resistance and outcome for patients with breast cancer, and there is considerable interest in whether cancer stem cell markers or biologic surrogates may be predictive of response to radiation therapy. We review the data or in some cases lack of data regarding stem cell correlates as predictors of radiation resistance as well as the correlation of known predictors with stem cell biology. More research is certainly needed to investigate potential predictors of radiation response, stem cell or otherwise, to move us toward the goal of personalized radiation therapy.

Niche signaling promotes stem cell survival in the Drosophila testis via the JAK-STAT target DIAP1

Tissue-specific stem cells are thought to resist environmental insults better than their differentiating progeny, but this resistance varies from one tissue to another, and the underlying mechanisms are not well-understood. Here, we use the Drosophila testis as a model system to study the regulation of cell death within an intact niche. This niche contains sperm-producing germline stem cells (GSCs) and accompanying somatic cyst stem cells (or CySCs). Although many signals are known to promote stem cell self-renewal in this tissue, including the highly conserved JAK-STAT pathway, the response of these stem cells to potential death-inducing signals, and factors promoting stem cell survival, have not been characterized. Here we find that both GSCs and CySCs resist cell death better than their differentiating progeny, under normal laboratory conditions and in response to potential death-inducing stimuli such as irradiation or starvation. To ask what might be promoting stem cell survival, we characterized the role of the anti-apoptotic gene Drosophila inhibitor of apoptosis 1 (diap1) in testis stem cells. DIAP1 protein is enriched in the GSCs and CySCs and is a JAK-STAT target. diap1 is necessary for survival of both GSCs and CySCs, and ectopic up-regulation of DIAP1 in somatic cyst cells is sufficient to non-autonomously rescue stress-induced cell death in adjacent differentiating germ cells (spermatogonia). Altogether, our results show that niche signals can promote stem cell survival by up-regulation of highly conserved anti-apoptotic proteins, and suggest that this strategy may underlie the ability of stem cells to resist death more generally.

Incorporating cancer stem cells in radiation therapy treatment response modeling and the implication in glioblastoma multiforme treatment resistance

PURPOSE

To perform a preliminary exploration with a simplistic mathematical cancer stem cell (CSC) interaction model to determine whether the tumor-intrinsic heterogeneity and dynamic equilibrium between CSCs and differentiated cancer cells (DCCs) can better explain radiation therapy treatment response with a dual-compartment linear-quadratic (DLQ) model.

METHODS AND MATERIALS

The radiosensitivity parameters of CSCs and DCCs for cancer cell lines including glioblastoma multiforme (GBM), non-small cell lung cancer, melanoma, osteosarcoma, and prostate, cervical, and breast cancer were determined by performing robust least-square fitting using the DLQ model on published clonogenic survival data. Fitting performance was compared with the single-compartment LQ (SLQ) and universal survival curve models. The fitting results were then used in an ordinary differential equation describing the kinetics of DCCs and CSCs in response to 2- to 14.3-Gy fractionated treatments. The total dose to achieve tumor control and the fraction size that achieved the least normal biological equivalent dose were calculated.

RESULTS

Smaller cell survival fitting errors were observed using DLQ, with the exception of melanoma, which had a low α/β = 0.16 in SLQ. Ordinary differential equation simulation indicated lower normal tissue biological equivalent dose to achieve the same tumor control with a hypofractionated approach for 4 cell lines for the DLQ model, in contrast to SLQ, which favored 2 Gy per fraction for all cells except melanoma. The DLQ model indicated greater tumor radioresistance than SLQ, but the radioresistance was overcome by hypofractionation, other than the GBM cells, which responded poorly to all fractionations.

CONCLUSION

The distinct radiosensitivity and dynamics between CSCs and DCCs in radiation therapy response could perhaps be one possible explanation for the heterogeneous intertumor response to hypofractionation and in some cases superior outcome from stereotactic ablative radiation therapy. The DLQ model also predicted the remarkable GBM radioresistance, a result that is highly consistent with clinical observations. The radioresistance putatively stemmed from accelerated DCC regrowth that rapidly restored compartmental equilibrium between CSCs and DCCs.

Tumor Induction in Mice After Localized Single- or Fractionated-Dose Irradiation: Differences in Tumor Histotype and Genetic Susceptibility Based on Dose Scheduling

PURPOSE

To investigate differences in tumor histotype, incidence, latency, and strain susceptibility in mice exposed to single-dose or clinically relevant, fractioned-dose γ-ray radiation.

METHODS AND MATERIALS

C3Hf/Kam and C57BL/6J mice were locally irradiated to the right hindlimb with either single large doses between 10 and 70 Gy or fractionated doses totaling 40 to 80 Gy delivered at 2-Gy/d fractions, 5 d/wk, for 4 to 8 weeks. The mice were closely evaluated for tumor development in the irradiated field for 800 days after irradiation, and all tumors were characterized histologically.

RESULTS

A total of 210 tumors were induced within the radiation field in 788 mice. An overall decrease in tumor incidence was observed after fractionated irradiation (16.4%) in comparison with single-dose irradiation (36.1%). Sarcomas were the predominant postirradiation tumor observed (n=201), with carcinomas occurring less frequently (n=9). The proportion of mice developing tumors increased significantly with total dose for both single-dose and fractionated schedules, and latencies were significantly decreased in mice exposed to larger total doses. C3Hf/Kam mice were more susceptible to tumor induction than C57BL/6J mice after single-dose irradiation; however, significant differences in tumor susceptibilities after fractionated radiation were not observed. For both strains of mice, osteosarcomas and hemangiosarcomas were significantly more common after fractionated irradiation, whereas fibrosarcomas and malignant fibrous histiocytomas were significantly more common after single-dose irradiation.

CONCLUSIONS

This study investigated the tumorigenic effect of acute large doses in comparison with fractionated radiation in which both the dose and delivery schedule were similar to those used in clinical radiation therapy. Differences in tumor histotype after single-dose or fractionated radiation exposures provide novel in vivo evidence for differences in tumor susceptibility among stromal cell populations.

MicroRNA in radiotherapy: miRage or miRador?

At least half of all cancer patients will receive radiation therapy. Tumour radioresistance, or the failure to control certain tumours with this treatment, can result in locoregional recurrence; thus there is great interest in understanding the underlying biology and developing strategies to overcome this problem. The expanding investigation of microRNA in cancer suggests that these regulatory factors can influence the DNA damage response, the microenvironment and survival pathways, among other processes, and thereby may affect tumour radioresistance. As microRNA are readily detectable in tumours and biofluids, they hold promise as predictive biomarkers for therapy response and prognosis. This review highlights the current insights on the major ways that microRNA may contribute to tumour radiation response and whether their levels reflect treatment success. We conclude by applying the potential framework of future roles of miR in personalised radiotherapy using prostate cancer clinical management as an example.

Regulation of miRNAs affects radiobiological response of lung cancer stem cells

Radiotherapy (RT) is a key therapeutic strategy for lung cancer, the most common cause of cancer-related deaths worldwide, but radioresistance often occurs and leads to failure of RT. It is therefore important to clarify the mechanism underlying radioresistance in lung cancer. Cancer stem cells (CSCs) are considered the fundamental reason for radioresistance. MicroRNAs (miRNAs) have been regarded as important regulatory molecules of CSCs, carcinogenesis, and treatment response of cancers. It is crucial to clarify how regulation of miRNAs affects repair of DNA damage, redistribution, repopulation, reoxygenation, and radiosensitivity (5R) of lung cancer stem cells (LCSCs). A thorough understanding of the regulation of miRNAs affecting 5R of LCSCs has potential impact on identifying novel targets and thus may improve the efficacy of lung cancer radiotherapy.

Abnormal expression of the Notch and Wnt/β-catenin signaling pathways in stem-like ALDHhiCD44+ cells correlates highly with Ki-67 expression in breast cancer

Previous studies have reported that breast cancer stem cells may be closely associated with tumor metastasis, recurrence, and even the failure of chemotherapy and radiotherapy. The aim of the present study was to investigate whether important cell signaling pathways associated with drug resistance are activated in stem-like acetaldehyde dehydrogenase (ALDH)^hi cluster of differentiation (CD)44⁺ cells, and to analyze the association between ALDH^hiCD44⁺ cells and specific pathological features. ALDH^hiCD44⁺ cells and non-stem-like ALDH^lowCD44⁺ cells were separated from MDA-MB-231 cells by fluorescence-activated cell sorting, and the mRNA expression levels of Notch1 and β-catenin were estimated by performing quantitative polymerase chain reaction in the stem-like and non-stem-like cells. Line correlation analysis was used to evaluate the correlation between an immunohistochemical panel of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and Ki-67, and ALDH^hiCD44⁺ cells from patients with invasive breast carcinoma. The mRNA levels of Notch1 and β-catenin were significantly higher in the ALDH^hiCD44⁺ cells compared with those in the ALDH^lowCD44⁺ cells (P<0.05); furthermore, the present study determined a high correlation (P<0.05) between the ALDH^hiCD44⁺ cells and Ki-67 expression (P=0.007), but no correlation (P≥0.05) with ER (P=0.065), PR (P=0.107) and HER2 (P=0.050). Overall, these data clearly indicate that ALDH^hiCD44⁺ cells may serve as novel diagnostic and prognostic factors in breast cancer.

Elimination of ALDH+ breast tumor initiating cells by docosahexanoic acid and/or gamma tocotrienol through SHP-1 inhibition of Stat3 signaling

Study investigated the ability of docosahexaenoic acid (DHA) alone and in combination with gamma-tocotrienol (γT3) to eliminate aldehyde dehydrogenase positive (ALDH+) cells and to inhibit mammosphere formation, biomarker and functional assay for tumor initiating cells (TICs), respectively, in human triple negative breast cancer cells (TNBCs), and investigated possible mechanisms of action. DHA upregulated Src homology region 2 domain-containing protein tyrosine phosphatase-1 (SHP-1) protein levels and suppressed levels of phosphorylated signal transducer and activator of transcription-3 (pStat3) and its downstream mediators c-Myc, and cyclin D1. siRNA to SHP-1 enhanced the percentage of ALDH+ cells and Stat-3 signaling, as well as inhibited, in part, the ability of DHA to reduce the percentage of ALDH+ cells and Stat-3 signaling. γT3 alone and in combination with DHA reduced ALDH+ TNBCs, up-regulated SHP-1 protein levels, and suppressed Stat-3 signaling. Taken together, data demonstrate the anti-TIC potential of achievable concentrations of DHA alone as well as in combination with γT3.