CD133+ cells contribute to radioresistance via altered regulation of DNA repair genes in human lung cancer cells

DNA repair in tumor radioresistance: insights from fruit flies genetics

BACKGROUND

Radiation therapy (RT) is a key anti-cancer treatment that involves using ionizing radiation to kill tumor cells. However, this therapy can lead to short- and long-term adverse effects due to radiation exposure of surrounding normal tissue. The type of DNA damage inflicted by radiation therapy determines its effectiveness. High levels of genotoxic damage can lead to cell cycle arrest, senescence, and cell death, but many tumors can cope with this damage by activating protective mechanisms. Intrinsic and acquired radioresistance are major causes of tumor recurrence, and understanding these mechanisms is crucial for cancer therapy. The mechanisms behind radioresistance involve processes like hypoxia response, cell proliferation, DNA repair, apoptosis inhibition, and autophagy.

CONCLUSION

Here we briefly review the role of genetic and epigenetic factors involved in the modulation of DNA repair and DNA damage response that promote radioresistance. In addition, leveraging our recent results on the effects of low dose rate (LDR) of ionizing radiation on Drosophila melanogaster we discuss how this model organism can be instrumental in the identification of conserved factors involved in the tumor resistance to RT.

Musashi-2 (MSI2) regulation of DNA damage response in lung cancer

Lung cancer is one of the most common types of cancer worldwide. Non-small cell lung cancer (NSCLC), typically caused by KRAS and TP53 driver mutations, represents the majority of all new lung cancer diagnoses. Overexpression of the RNA-binding protein (RBP) Musashi-2 (MSI2) has been associated with NSCLC progression. To investigate the role of MSI2 in NSCLC development, we compared the tumorigenesis in mice with lung-specific Kras-activating mutation and Trp53 deletion, with and without Msi2 deletion (KPM2 versus KP mice). KPM2 mice showed decreased lung tumorigenesis in comparison with KP mice. In addition, KPM2 lung tumors showed evidence of decreased proliferation, but increased DNA damage, marked by increased levels of phH2AX (S139) and phCHK1 (S345), but decreased total and activated ATM. Using cell lines from KP and KPM2 tumors, and human NSCLC cell lines, we found that MSI2 directly binds ATM mRNA and regulates its translation. MSI2 depletion impaired DNA damage response (DDR) signaling and sensitized human and murine NSCLC cells to treatment with PARP inhibitors in vitro and in vivo. Taken together, we conclude that MSI2 supports NSCLC tumorigenesis, in part, by supporting repair of DNA damage by controlling expression of DDR proteins. These results suggest that targeting MSI2 may be a promising strategy for lung cancers treated with DNA-damaging agents.

Cancer cell cycle heterogeneity as a critical determinant of therapeutic resistance

Intra-tumor heterogeneity is now arguably one of the most-studied topics in tumor biology, as it represents a major obstacle to effective cancer treatment. Since tumor cells are highly diverse at genetic, epigenetic, and phenotypic levels, intra-tumor heterogeneity can be assumed as an important contributing factor to the nullification of chemotherapeutic effects, and recurrence of the tumor. Based on the role of heterogeneous subpopulations of cancer cells with varying cell-cycle dynamics and behavior during cancer progression and treatment; herein, we aim to establish a comprehensive definition for adaptation of neoplastic cells against therapy. We discuss two parallel and yet distinct subpopulations of tumor cells that play pivotal roles in reducing the effects of chemotherapy: "resistant" and "tolerant" populations. Furthermore, this review also highlights the impact of the quiescent phase of the cell cycle as a survival mechanism for cancer cells. Beyond understanding the mechanisms underlying the quiescence, it provides an insightful perspective on cancer stem cells (CSCs) and their dual and intertwined functions based on their cell cycle state in response to treatment. Moreover, CSCs, epithelial-mesenchymal transformed cells, circulating tumor cells (CTCs), and disseminated tumor cells (DTCs), which are mostly in a quiescent state of the cell cycle are proved to have multiple biological links and can be implicated in our viewpoint of cell cycle heterogeneity in tumors. Overall, increasing our knowledge of cell cycle heterogeneity is a key to identifying new therapeutic solutions, and this emerging concept may provide us with new opportunities to prevent the dreadful cancer recurrence.

Cancer stem cells: a target for overcoming therapeutic resistance and relapse

Cancer stem cells (CSCs) are a small subset of cells in cancers that are thought to initiate tumorous transformation and promote metastasis, recurrence, and resistance to treatment. Growing evidence has revealed the existence of CSCs in various types of cancers and suggested that CSCs differentiate into diverse lineage cells that contribute to tumor progression. We may be able to overcome the limitations of cancer treatment with a comprehensive understanding of the biological features and mechanisms underlying therapeutic resistance in CSCs. This review provides an overview of the properties, biomarkers, and mechanisms of resistance shown by CSCs. Recent findings on metabolic features, especially fatty acid metabolism and ferroptosis in CSCs, are highlighted, along with promising targeting strategies. Targeting CSCs is a potential treatment plan to conquer cancer and prevent resistance and relapse in cancer treatment.

Mutual regulation of TGFβ-induced oncogenic EMT, cell cycle progression and the DDR

TGFβ signaling and the DNA damage response (DDR) are two cellular toolboxes with a strong impact on cancer biology. While TGFβ as a pleiotropic cytokine affects essentially all hallmarks of cancer, the multifunctional DDR mostly orchestrates cell cycle progression, DNA repair, chromatin remodeling and cell death. One oncogenic effect of TGFβ is the partial activation of epithelial-to-mesenchymal transition (EMT), conferring invasiveness, cellular plasticity and resistance to various noxae. Several reports show that both individual networks as well as their interface affect chemo-/radiotherapies. However, the underlying mechanisms remain poorly resolved. EMT often correlates with TGFβ-induced slowing of proliferation, yet numerous studies demonstrate that particularly the co-activated EMT transcription factors counteract anti-proliferative signaling in a partially non-redundant manner. Collectively, evidence piled up over decades underscore a multifaceted, reciprocal inter-connection of TGFβ signaling / EMT with the DDR / cell cycle progression, which we will discuss here. Altogether, we conclude that full cell cycle arrest is barely compatible with the propagation of oncogenic EMT traits and further propose that 'EMT-linked DDR plasticity' is a crucial, yet intricate facet of malignancy, decisively affecting metastasis formation and therapy resistance.

DNA Damage Responses, the Trump Card of Stem Cells in the Survival Game

Stem cells, as a group of undifferentiated cells, are enriched with self-renewal and high proliferative capacity, which have attracted the attention of many researchers as a promising approach in the treatment of many diseases over the past years. However, from the cellular and molecular point of view, the DNA repair system is one of the biggest challenges in achieving therapeutic goals through stem cell technology. DNA repair mechanisms are an advantage for stem cells that are constantly multiplying to deal with various types of DNA damage. However, this mechanism can be considered a trump card in the game of cell survival and treatment resistance in cancer stem cells, which can hinder the curability of various types of cancer. Therefore, getting a deep insight into the DNA repair system can bring researchers one step closer to achieving major therapeutic goals. The remarkable thing about the DNA repair system is that this system is not only under the control of genetic factors, but also under the control of epigenetic factors. Therefore, it is necessary to investigate the role of the DNA repair system in maintaining the survival of cancer stem cells from both aspects.

The Warburg effect on radioresistance: Survival beyond growth

The Warburg effect is a phenomenon in which cancer cells rely primarily on glycolysis rather than oxidative phosphorylation, even in the presence of oxygen. Although evidence of its involvement in cell proliferation has been discovered, the advantages of the Warburg effect in cancer cell survival under treatment have not been fully elucidated. In recent years, the metabolic characteristics of radioresistant cancer cells have been evaluated, enabling an extension of the original concept of the Warburg effect. In this review, we focused on the role of the Warburg effect in redox homeostasis and DNA damage repair, two critical factors contributing to radioresistance. In addition, we highlighted the metabolic involvement in the radioresistance of cancer stem cells, which is the root cause of tumor recurrence. Finally, we summarized radiosensitizing drugs that target the Warburg effect. Insights into the molecular mechanisms underlying the Warburg effect and radioresistance can provide valuable information for developing strategies to enhance the efficacy of radiotherapy and provide future directions for successful cancer therapy.

Mitochondria in Cancer Stem Cells: From an Innocent Bystander to a Central Player in Therapy Resistance

Cancer continues to rank among the world's leading causes of mortality despite advancements in treatment. Cancer stem cells, which can self-renew, are present in low abundance and contribute significantly to tumor recurrence, tumorigenicity, and drug resistance to various therapies. The drug resistance observed in cancer stem cells is attributed to several factors, such as cellular quiescence, dormancy, elevated aldehyde dehydrogenase activity, apoptosis evasion mechanisms, high expression of drug efflux pumps, protective vascular niche, enhanced DNA damage response, scavenging of reactive oxygen species, hypoxic stability, and stemness-related signaling pathways. Multiple studies have shown that mitochondria play a pivotal role in conferring drug resistance to cancer stem cells, through mitochondrial biogenesis, metabolism, and dynamics. A better understanding of how mitochondria contribute to tumorigenesis, heterogeneity, and drug resistance could lead to the development of innovative cancer treatments.

Predicting tumor repopulation through the gene panel derived from radiation resistant colorectal cancer cells

BACKGROUND

Tumor cells with the capability of radiation resistance can escape the fate of cell death after radiotherapy, serving as the main cause of treatment failure. Repopulation of tumors after radiotherapy is dominated by this group of residual cells, which greatly reduce the sensitivity of recurrent tumors to the therapy, resulting in poor clinical outcomes. Therefore, revealing the mechanism of radiation resistant cells participating in tumor repopulation is of vital importance for cancer patients to obtain a better prognosis.

METHODS

Co-expressed genes were searched by using genetic data of radiation resistant cells (from GEO database) and TCGA colorectal cancer. Univariate and multivariate Cox regression analysis were performed to define the most significant co-expressed genes for establishing prognostic indicator. Logistic analysis, WGCNA analysis, and other types of tumors were included to verify the predictive ability of the indicator. RT-qPCR was carried out to test expression level of key genes in colorectal cancer cell lines. Colongenic assay was utilized to test the radio-sensitivity and repopulation ability of key gene knockdown cells.

RESULTS

Prognostic indicator based on TCGA colorectal cancer patients containing four key radiation resistance genes (LGR5, KCNN4, TNS4, CENPH) was established. The indicator was shown to be significantly correlated with the prognosis of colorectal cancer patients undergoing radiotherapy, and also had an acceptable predictive effect in the other five types of cancer. RT-qPCR showed that expression level of key genes was basically consistent with the radiation resistance level of colorectal cancer cells. The clonogenic ability of all key gene knockdown cells decreased after radiation treatment compared with the control groups.

CONCLUSIONS

Our data suggest that LGR5, KCNN4, TNS4 and CENPH are correlated with radiation sensitivity of colorectal cancer cells, and the indicator composed by them can reflect the prognosis of colorectal cancer patients undergoing radiation therapy. Our data provide an evidence of radiation resistant tumor cells involved in tumor repopulation, and give patients undergoing radiotherapy an approving prognostic indicator with regard to tumor progression.

Molecular mechanisms of tumor resistance to radiotherapy

BACKGROUND

Cancer is the most prevalent cause of death globally, and radiotherapy is considered the standard of care for most solid tumors, including lung, breast, esophageal, and colorectal cancers and glioblastoma. Resistance to radiation can lead to local treatment failure and even cancer recurrence.

MAIN BODY

In this review, we have extensively discussed several crucial aspects that cause resistance of cancer to radiation therapy, including radiation-induced DNA damage repair, cell cycle arrest, apoptosis escape, abundance of cancer stem cells, modification of cancer cells and their microenvironment, presence of exosomal and non-coding RNA, metabolic reprogramming, and ferroptosis. We aim to focus on the molecular mechanisms of cancer radiotherapy resistance in relation to these aspects and to discuss possible targets to improve treatment outcomes.

CONCLUSIONS

Studying the molecular mechanisms responsible for radiotherapy resistance and its interactions with the tumor environment will help improve cancer responses to radiotherapy. Our review provides a foundation to identify and overcome the obstacles to effective radiotherapy.

Tissue-specific cancer stem/progenitor cells: Therapeutic implications

Surgical resection, chemotherapy, and radiation are the standard therapeutic modalities for treating cancer. These approaches are intended to target the more mature and rapidly dividing cancer cells. However, they spare the relatively quiescent and intrinsically resistant cancer stem cells (CSCs) subpopulation residing within the tumor tissue. Thus, a temporary eradication is achieved and the tumor bulk tends to revert supported by CSCs' resistant features. Based on their unique expression profile, the identification, isolation, and selective targeting of CSCs hold great promise for challenging treatment failure and reducing the risk of cancer recurrence. Yet, targeting CSCs is limited mainly by the irrelevance of the utilized cancer models. A new era of targeted and personalized anti-cancer therapies has been developed with cancer patient-derived organoids (PDOs) as a tool for establishing pre-clinical tumor models. Herein, we discuss the updated and presently available tissue-specific CSC markers in five highly occurring solid tumors. Additionally, we highlight the advantage and relevance of the three-dimensional PDOs culture model as a platform for modeling cancer, evaluating the efficacy of CSC-based therapeutics, and predicting drug response in cancer patients.

APEX1 predicts poor prognosis of gallbladder cancer and affects biological properties of CD133+ GBC-SD cells via upregulating Jagged1

Although APEX1 is associated with the tumorigenesis and progression of some human cancer types, the function of APEX1 in gallbladder cancer (GBC) is unclear. In this study, we found that APEX1 expression is up-regulated in GBC tissues, and APEX1 positive expression is related to aggressive clinicopathological features and poor prognosis of GBC. APEX1 was an independent risk factor of GBC prognosis, and presented some pathological diagnostic significance in GBC. Furthermore, APEX1 was overexpressed in CD133⁺ GBC-SD cells in comparison with GBC-SD cells. APEX1 knockdown increased the sensitivity of CD133⁺ GBC-SD cells to 5-Fluorouracil via facilitating cell necrosis and apoptosis. APEX1 knockdown in CD133⁺ GBC-SD cells dramatically inhibited cell proliferation, migration, and invasion, and promoted cell apoptosis in vitro. APEX1 knockdown in CD133⁺ GBC-SD cells accelerated tumor growth in the xenograft models. Mechanistically, APEX1 affected these malignant properties via upregulating Jagged1 in CD133⁺ GBC-SD cells. Thus, APEX1 is a promising prognostic biomarker, and a potential therapeutic target for GBC.

An Image-Based Identification of Aggressive Breast Cancer Circulating Tumor Cell Subtypes

Using previously established CTC lines from breast cancer patients, we identified different morphometric subgroups of CTCs with one of them having the highest tumorigenic potential in vivo despite the slowest cell proliferation in vitro. This subgroup represents 32% of all cells and contains cells with small cell volume, large nucleus to cell, dense nuclear areas to the nucleus, mitochondria to cell volume ratios and rough texture of cell membrane and termed "Small cell, Large mitochondria, Rough membrane" (SLR). RNA-seq analyses showed that the SLR group is enriched in pathways and cellular processes related to DNA replication, DNA repair and metabolism. SLR upregulated genes are associated with poor survival in patients with ER+ breast cancer based on the KM Plotter database. The high tumorigenic potential, slow proliferation, and enriched DNA replication/repair pathways suggest that the SLR subtype is associated with stemness properties. Our new findings provide a simple image-based identification of CTC subpopulations with elevated aggressiveness, which is expected to provide a more accurate prediction of patient survival and therapy response than total CTC numbers. The detection of morphometric and transcriptomic profiles related to the SLR subgroup of CTCs also opens opportunities for potential targeted cancer treatment.

Review: Mechanisms and perspective treatment of radioresistance in non-small cell lung cancer

Radiotherapy is the major treatment of non-small cell lung cancer (NSCLC). The radioresistance and toxicity are the main obstacles that leading to therapeutic failure and poor prognosis. Oncogenic mutation, cancer stem cells (CSCs), tumor hypoxia, DNA damage repair, epithelial-mesenchymal transition (EMT), and tumor microenvironment (TME) may dominate the occurrence of radioresistance at different stages of radiotherapy. Chemotherapy drugs, targeted drugs, and immune checkpoint inhibitors are combined with radiotherapy to treat NSCLC to improve the efficacy. This article reviews the potential mechanism of radioresistance in NSCLC, and discusses the current drug research to overcome radioresistance and the advantages of Traditional Chinese medicine (TCM) in improving the efficacy and reducing the toxicity of radiotherapy.

Epigenetic regulation of stem cells in lung cancer oncogenesis and therapy resistance

Epigenetics plays an important role in regulating stem cell signaling, as well as in the oncogenesis of lung cancer and therapeutic resistance. Determining how to employ these regulatory mechanisms to treat cancer is an intriguing medical challenge. Lung cancer is caused by signals that cause aberrant differentiation of stem cells or progenitor cells. The different pathological subtypes of lung cancer are determined by the cells of origin. Additionally, emerging studies have demonstrated that the occurrence of cancer treatment resistance is connected to the hijacking of normal stem cell capability by lung cancer stem cells, especially in the processes of drug transport, DNA damage repair, and niche protection. In this review, we summarize the principles of the epigenetic regulation of stem cell signaling in relation to the emergence of lung cancer and resistance to therapy. Furthermore, several investigations have shown that the tumor immune microenvironment in lung cancer affects these regulatory pathways. And ongoing experiments on epigenetics-related therapeutic strategies provide new insight for the treatment of lung cancer in the future.

Tumor microenvironment enriches the stemness features: the architectural event of therapy resistance and metastasis

Cancer divergence has many facets other than being considered a genetic term. It is a tremendous challenge to understand the metastasis and therapy response in cancer biology; however, it postulates the opportunity to explore the possible mechanism in the surrounding tumor environment. Most deadly solid malignancies are distinctly characterized by their tumor microenvironment (TME). TME consists of stromal components such as immune, inflammatory, endothelial, adipocytes, and fibroblast cells. Cancer stem cells (CSCs) or cancer stem-like cells are a small sub-set of the population within cancer cells believed to be a responsible player in the self-renewal, metastasis, and therapy response of cancer cells. The correlation between TME and CSCs remains an enigma in understanding the events of metastasis and therapy resistance in cancer biology. Recent evidence suggests that TME dictates the CSCs maintenance to arbitrate cancer progression and metastasis. The immune, inflammatory, endothelial, adipocyte, and fibroblast cells in the TME release growth factors, cytokines, chemokines, microRNAs, and exosomes that provide cues for the gain and maintenance of CSC features. These intricate cross-talks are fueled to evolve into aggressive, invasive, migratory phenotypes for cancer development. In this review, we have abridged the recent developments in the role of the TME factors in CSC maintenance and how these events influence the transition of tumor progression to further translate into metastasis and therapy resistance in cancer.

The EMT transcription factor ZEB1 governs a fitness-promoting but vulnerable DNA replication stress response

The DNA damage response (DDR) and epithelial-to-mesenchymal transition (EMT) are two crucial cellular programs in cancer biology. While the DDR orchestrates cell-cycle progression, DNA repair, and cell death, EMT promotes invasiveness, cellular plasticity, and intratumor heterogeneity. Therapeutic targeting of EMT transcription factors, such as ZEB1, remains challenging, but tumor-promoting DDR alterations elicit specific vulnerabilities. Using multi-omics, inhibitors, and high-content microscopy, we discover a chemoresistant ZEB1-high-expressing sub-population (ZEB1^hi) with co-rewired cell-cycle progression and proficient DDR across tumor entities. ZEB1 stimulates accelerated S-phase entry via CDK6, inflicting endogenous DNA replication stress. However, DDR buildups involving constitutive MRE11-dependent fork resection allow homeostatic cycling and enrichment of ZEB1^hi cells during transforming growth factor β (TGF-β)-induced EMT and chemotherapy. Thus, ZEB1 promotes G1/S transition to launch a progressive DDR benefitting stress tolerance, which concurrently manifests a targetable vulnerability in chemoresistant ZEB1^hi cells. Our study thus highlights the translationally relevant intercept of the DDR and EMT.

The role of stem cells in small-cell lung cancer: evidence from chemoresistance to immunotherapy

Small cell lung cancer (SCLC) is the most aggressive subtype of lung cancer, accounting for approximately 15% among all lung cancers. Despite the ability of chemotherapy, the first-line treatment for SCLC, to rapidly shrink tumors, nearly all patients experience recurrence and metastasis within a few months. Cancer stem cells (CSCs) are a small population of tumor cells responsible for tumorigenesis, metastasis, and recurrence after treatment, which play a crucial role in chemoresistance by promoting DNA repair and expression of drug resistance-associated proteins. Thus, targeting CSCs has been successful in certain malignancies. Tumor therapy has entered the era of immunotherapy and numerous preclinical trials have demonstrated the effectiveness of immunotherapeutic approaches targeting CSCs, such as tumor vaccines and chimeric antigen receptor (CAR) T cell, and the feasibility of combining them with chemotherapy. Therefore, a deeper understanding of the interaction between CSCs and immune system is essential to facilitate the advances of new immunotherapies approaches targeting CSCs as well as combination with standard drugs such as chemotherapy. This narrative review summarizes the mechanisms of chemoresistance of CSCs in SCLC and the latest advances in targeted therapies. Thereafter, we discuss the effects of CSCs on tumor immune microenvironment in SCLC and corresponding immunotherapeutic approaches. Eventually, we propose that the combination of immunotherapy targeting CSCs with standard drugs is a promising direction for SCLC therapies.

Upregulation of Long Noncoding RNA MALAT1 in Colorectal Cancer Promotes Radioresistance and Aggressive Malignance

BACKGROUND

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), a conserved transcript with 8000 nt, is highly associated with malignancy of numerous cancer types. However, the function of MALAT1 plays in regulating the response to radiotherapy in colorectal cancer (CRC) remains unclear. Thus, the object of this study is to investigate the functions of MALAT1 in CRC radioresistance.

METHODS

First, the expression of MALAT1 in colon adenocarcinoma (COAD) was analyzed through the Cancer Genome Atlas (TCGA) database. Then, we detected the expression level of MALAT1 in tumor tissues and CRC cell lines and analyzed the relevance of MALAT1 and clinicopathological parameters. In the end, the effect of silencing MALAT1 on the radiosensitivity of CRC cells was investigated, and its potential mechanism was preliminarily illustrated.

RESULTS

The analysis of TCGA data showed that MALAT1 was closely related to the type of tumor, and high expression of MALAT1 was remarkably relevant to poor outcome. MALAT1 was highly expressed in CRC tissues and cell lines and related to tumor stages. Knockdown of MALAT1 could significantly suppress colony survival, proliferation, and migration and increase apoptosis, G2/M phase arrest, and formation of gamma-H2AX foci in HCT116, whether in combination with X-rays or not. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated that the regulated proteins were principally enriched in the glycosaminoglycan degradation pathway after silencing MALAT1.

CONCLUSION

Our results implied that MALAT1 was highly expressed in CRC and associated with tumor stage and prognosis. Silencing MALAT1 can increase HCT116 cell radiosensitivity, which may be potentially influenced by glycosaminoglycan degradation pathway.

The Molecular and Cellular Strategies of Glioblastoma and Non-Small-Cell Lung Cancer Cells Conferring Radioresistance

Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLC). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLC. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.

Aldehyde Dehydrogenase 1B1 Is Implicated in DNA Damage Response in Human Colorectal Adenocarcinoma

Aldehyde dehydrogenase 1B1 (ALDH1B1) has been correlated with colorectal tumorigenesis and is considered a potential biomarker for colon cancer. Its expression has been associated with attenuation of the cell cycle in the G2/M phase and resistance to DNA damaging agents. The present study examines the role of ALDH1B1 in DNA damage response (DDR) in human colorectal adenocarcinoma. To this end, we utilized an isogenic HT29 cell line pair differing in the expression of ALDH1B1. The overexpression of ALDH1B1 was related to the translational upregulation of the total and phosphorylated (at ser15) p53. Comet and apoptosis assays revealed that the expression of ALDH1B1 protected HT29 cells from etoposide-induced DNA damage as well as apoptosis, and its overexpression led to increased constitutive phosphorylation of H2AX (at ser139). Furthermore, the expression profile of a variety of DNA damage signaling (DDS)-related genes was investigated by utilizing the RT2 profiler™ PCR array. Our results demonstrated that ALDH1B1 triggered a transcriptional activation of several DNA repair-related genes (MRE11A, PMS1, RAD18 and UNG). Finally, Spearman’s rank correlation coefficient analysis in 531 publicly available colorectal adenocarcinoma clinical samples indicated the statistically significant positive correlation between ALDH1B1 and DDR and repair genes or proteins, such as APEX1, FEN1, MPG, UNG, XRCC1, DDB1, XPC, CIB1, MRE11, PRKDC, RAD50, RAD21, TP53BP1, XRCC6 and H2AX. Collectively, our results suggest that ALDH1B1 may play an essential role in the DDR and DNA repair processes. Further studies on ALDH1B1 will elucidate its precise role in DDR.

The Role of Tumor Stem Cell Exosomes in Cancer Invasion and Metastasis

Exosomes are lipid membrane bilayer-encapsulated vesicles secreted by cells into the extracellular space. They carry abundant inclusions (such as nucleic acids, proteins, and lipids) that play pivotal roles in intercellular communication. Tumor stem cells are capable of self-renewal and are crucial for survival, proliferation, drug resistance, metastasis, and recurrence of tumors. The miRNAs (microRNAs) in exosomes have various functions, such as participating in inflammatory response, cell migration, proliferation, apoptosis, autophagy, and epithelial-mesenchymal transition. Tumor stem cells secrete exosomes that act as important messengers involved in various tumor processes and several studies provide increasing evidence supporting the importance of these exosomes in tumor recurrence and metastasis. This review primarily focuses on the production and secretion of exosomes from tumors and tumor stem cells and their effects on cancer progression. Cancer stem cancer derived exosome play an important massager in the tumor microenvironment. It also emphasizes on the study of tumor stem cell exosomes in the light of cancer metastasis and recurrence aiming to provide valuable insights and novel perspectives, which could be beneficial for developing effective diagnostic and treatment strategies.

Anticancer Activities of 9-chloro-6-(piperazin-1-yl)-11H-indeno[1,2-c] quinolin-11-one (SJ10) in Glioblastoma Multiforme (GBM) Chemoradioresistant Cell Cycle-Related Oncogenic Signatures

Simple Summary

Glioblastoma multiforme (GBM) remains to be the most frequent malignant tumor of the central nervous system (CNS), which accounts for approximately 54% of all primary brain gliomas. Current treatment modalities for GBM include surgical resection, followed by radiotherapy and chemotherapy with temozolomide (TMZ). However, due to its genetic heterogeneity, GBM tumors always recur, due to treatment reasistance. The aim of this study was to identify molecular gene signatures, responsible for cancer initiation, progression, resistances and to treatment, metastasis, and also evaluate the potency of our novel compounds SJ10 as potential target for CCNB1/CDC42/MAPK7/CD44 oncogenic signatures. Accordingly, we used computational simulation and identify these signatures as regulators of the cell cycle in GBM, which leads to cancer development and metastasis. We also showed the antiproliferative and cytotoxic effects of SJ10 compound against a panel of NCI-60 cancer cell lines. This suggests the potential of the compounds to inhibit CCNB1/CDC42/MAPK7/CD44 in GBM.

Abstract

Current anticancer treatments are inefficient against glioblastoma multiforme (GBM), which remains one of the most aggressive and lethal cancers. Evidence has shown the presence of glioblastoma stem cells (GSCs), which are chemoradioresistant and associated with high invasive capabilities in normal brain tissues. Moreover, accumulating studies have indicated that radiotherapy contributes to abnormalities in cell cycle checkpoints, including the G₁/S and S phases, which may potentially lead to resistance to radiation. Through computational simulations using bioinformatics, we identified several GBM oncogenes that are involved in regulating the cell cycle. Cyclin B1 (CCNB1) is one of the cell cycle-related genes that was found to be upregulated in GBM. Overexpression of CCNB1 was demonstrated to be associated with higher grades, proliferation, and metastasis of GBM. Additionally, increased expression levels of CCNB1 were reported to regulate activation of mitogen-activated protein kinase 7 (MAPK7) in the G₂/M phase, which consequently modulates mitosis; additionally, in clinical settings, MAPK7 was demonstrated to promote resistance to temozolomide (TMZ) and poor patient survival. Therefore, MAPK7 is a potential novel drug target due to its dysregulation and association with TMZ resistance in GBM. Herein, we identified MAPK7/extracellular regulated kinase 5 (ERK5) genes as being overexpressed in GBM tumors compared to normal tissues. Moreover, our analysis revealed increased levels of the cell division control protein homolog (CDC42), a protein which is also involved in regulating the cell cycle through the G₁ phase in GBM tissues. This therefore suggests crosstalk among CCNB1/CDC42/MAPK7/cluster of differentiation 44 (CD44) oncogenic signatures in GBM through the cell cycle. We further evaluated a newly synthesized small molecule, SJ10, as a potential target agent of the CCNB1/CDC42/MAPK7/CD44 genes through target prediction tools and found that SJ10 was indeed a target compound for the above-mentioned genes; in addition, it displayed inhibitory activities against these oncogenes as observed from molecular docking analysis.

Cancer Stem Cells: An Ever-Hiding Foe

Cancer stem cells are a population of cells enable to reproduce the original phenotype of the tumor and capable to self-renewal, which is crucial for tumor proliferation, differentiation, recurrence, and metastasis, as well as chemoresistance. Therefore, the cancer stem cells (CSCs) have become one of the main targets for anticancer therapy and many ongoing clinical trials test anti-CSCs efficacy of plenty of drugs. This chapter describes CSCs starting from general description of this cell population, through CSCs markers, signaling pathways, genetic and epigenetic regulation, role of epithelial-mesenchymal transition (EMT) transition and autophagy, cooperation with microenvironment (CSCs niche), and finally role of CSCs in escaping host immunosurveillance against cancer.

Golgi Phosphoprotein 3 Confers Radioresistance via Stabilizing EGFR in Lung Adenocarcinoma

PURPOSE

Radioresistance is a major cause of treatment failure in tumor radiotherapy and the underlying mechanisms of radioresistance are still elusive. Golgi phosphoprotein 3 (GOLPH3) has been reported to associate tightly with cancer progression and chemoresistance. Herein, we explored whether GOLPH3 mediated radioresistance of lung adenocarcinoma (LUAD) and whether targeted suppression of GOLPH3 sensitized LUAD to radiotherapy.

METHODS AND MATERIALS

The aberrant expression of GOLPH3 was evaluated by immunohistochemistry in LUAD clinical samples. To evaluate the association between GOLPH3 and radioresistance, colony formation and apoptosis were assessed in control and GOLPH3 knockdown cells. γ-H2AX foci/level determination and micronucleus test were used to analyze DNA damage production and repair. The rescue of GOLPH3 knockdown was then performed by exogenous expression of siRNA-resistant mutant GOLPH3 to confirm the role of GOLPH3 in DNA damage repair. Mechanistically, the effect of GOLPH3 on regulating stability and nuclear accumulation of epidermal growth factor receptor (EGFR) and the activation of DNA-PK were investigated by qRT-PCR, western blot, immunofluorescence and co-immunoprecipitation. The role of GOLPH3 in vivo in radioresistance was determined in a xenograft model.

RESULTS

In tumor tissues of 33 patients with LUAD, the expression of GOLPH3 showed significantly increases compared with those in matched normal tissues. Knocking down GOLPH3 reduced the clonogenic capacity, impaired DSB repair and enhanced apoptosis after irradiation. In contrast, reversal of GOLPH3 depletion rescued the impaired repair of radiation-induced DSBs. Mechanistically, loss of GOLPH3 accelerated the degradation of EGFR in lysosome, causing the reduction in EGFR levels, thereby weakening nuclear accumulation of EGFR and attenuating the activation of DNA-PK. Furthermore, adenovirus-mediated GOLPH3 knockdown could enhance the ionizing-radiation response in LUAD xenograft model.

CONCLUSIONS

GOLPH3 conferred resistance of LUAD to ionizing-radiation via stabilizing EGFR and targeted suppression of GOLPH3 might be considered as a potential therapeutic strategy for sensitizing LUAD to radiotherapy.

MEOX2 Transcription Factor Is Involved in Survival and Adhesion of Glioma Stem-like Cells

Simple Summary

Glioblastoma is the most common and lethal primary brain tumor for which no curative treatment currently exists. In our previous work, we showed that MEOX2 was associated with a poor patient prognosis but its biological involvement in tumor development remains ill defined. To this purpose, the aim of our study was to investigate the role of MEOX2 in patient-derived glioblastoma cell cultures. We unraveled the MEOX2 contribution to cell viability and growth and its potential involvement in phenotype and adhesion properties of glioblastoma cells. This work paves the way toward a better understanding of the role of MEOX2 in the pathophysiology of primary brain tumors.

Abstract

The high expression of MEOX2 transcription factor is closely associated with poor overall survival in glioma. MEOX2 has recently been described as an interesting prognostic biomarker, especially for lower grade glioma. MEOX2 has never been studied in glioma stem-like cells (GSC), responsible for glioma recurrence. The aim of our study was to investigate the role of MEOX2 in GSC. Loss of function approach using siRNA was used to assess the impact of MEOX2 on GSC viability and stemness phenotype. MEOX2 was localized in the nucleus and its expression was heterogeneous between GSCs. MEOX2 expression depends on the methylation state of its promoter and is strongly associated with IDH mutations. MEOX2 is involved in cell proliferation and viability regulation through ERK/MAPK and PI3K/AKT pathways. MEOX2 loss of function correlated with GSC differentiation and acquisition of neuronal lineage characteristics. Besides, inhibition of MEOX2 is correlated with increased expression of CDH10 and decreased pFAK. In this study, we unraveled, for the first time, MEOX2 contribution to cell viability and proliferation through AKT/ERK pathway and its potential involvement in phenotype and adhesion properties of GSC.

Beyond the Double-Strand Breaks: The Role of DNA Repair Proteins in Cancer Stem-Cell Regulation

Simple Summary

Cancer stem cells (CSCs) are a tumor cell population maintaining tumor growth and promoting tumor relapse if not wholly eradicated during treatment. CSCs are often equipped with molecular mechanisms making them resistant to conventional anti-cancer therapies whose curative potential depends on DNA damage-induced cell death. An elevated expression of some key DNA repair proteins is one of such defense mechanisms. However, new research reveals that the role of critical DNA repair proteins is extending far beyond the DNA repair mechanisms. This review discusses the diverse biological functions of DNA repair proteins in CSC maintenance and the adaptation to replication and oxidative stress, anti-cancer immune response, epigenetic reprogramming, and intracellular signaling mechanisms. It also provides an overview of their potential therapeutic targeting.

Abstract

Cancer stem cells (CSCs) are pluripotent and highly tumorigenic cells that can re-populate a tumor and cause relapses even after initially successful therapy. As with tissue stem cells, CSCs possess enhanced DNA repair mechanisms. An active DNA damage response alleviates the increased oxidative and replicative stress and leads to therapy resistance. On the other hand, mutations in DNA repair genes cause genomic instability, therefore driving tumor evolution and developing highly aggressive CSC phenotypes. However, the role of DNA repair proteins in CSCs extends beyond the level of DNA damage. In recent years, more and more studies have reported the unexpected role of DNA repair proteins in the regulation of transcription, CSC signaling pathways, intracellular levels of reactive oxygen species (ROS), and epithelial–mesenchymal transition (EMT). Moreover, DNA damage signaling plays an essential role in the immune response towards tumor cells. Due to its high importance for the CSC phenotype and treatment resistance, the DNA damage response is a promising target for individualized therapies. Furthermore, understanding the dependence of CSC on DNA repair pathways can be therapeutically exploited to induce synthetic lethality and sensitize CSCs to anti-cancer therapies. This review discusses the different roles of DNA repair proteins in CSC maintenance and their potential as therapeutic targets.

Molecular mechanisms of chemo- and radiotherapy resistance and the potential implications for cancer treatment

Cancer is a leading cause of death worldwide. Surgery is the primary treatment approach for cancer, but the survival rate is very low due to the rapid progression of the disease and presence of local and distant metastasis at diagnosis. Adjuvant chemotherapy and radiotherapy are important components of the multidisciplinary approaches for cancer treatment. However, resistance to radiotherapy and chemotherapy may result in treatment failure or even cancer recurrence. Radioresistance in cancer is often caused by the repair response to radiation-induced DNA damage, cell cycle dysregulation, cancer stem cells (CSCs) resilience, and epithelial-mesenchymal transition (EMT). Understanding the molecular alterations that lead to radioresistance may provide new diagnostic markers and therapeutic targets to improve radiotherapy efficacy. Patients who develop resistance to chemotherapy drugs cannot benefit from the cytotoxicity induced by the prescribed drug and will likely have a poor outcome with these treatments. Chemotherapy often shows a low response rate due to various drug resistance mechanisms. This review focuses on the molecular mechanisms of radioresistance and chemoresistance in cancer and discusses recent developments in therapeutic strategies targeting chemoradiotherapy resistance to improve treatment outcomes.

Messing Up the Cancer Stem Cell Chemoresistance Mechanisms Supported by Tumor Microenvironment

Despite the recent advances in cancer patient management and in the development of targeted therapies, systemic chemotherapy is currently used as a first-line treatment for many cancer types. After an initial partial response, patients become refractory to standard therapy fostering rapid tumor progression. Compelling evidence highlights that the resistance to chemotherapeutic regimens is a peculiarity of a subpopulation of cancer cells within tumor mass, known as cancer stem cells (CSCs). This cellular compartment is endowed with tumor-initiating and metastasis formation capabilities. CSC chemoresistance is sustained by a plethora of grow factors and cytokines released by neighboring tumor microenvironment (TME), which is mainly composed by adipocytes, cancer-associated fibroblasts (CAFs), immune and endothelial cells. TME strengthens CSC refractoriness to standard and targeted therapies by enhancing survival signaling pathways, DNA repair machinery, expression of drug efflux transporters and anti-apoptotic proteins. In the last years many efforts have been made to understand CSC-TME crosstalk and develop therapeutic strategy halting this interplay. Here, we report the combinatorial approaches, which perturb the interaction network between CSCs and the different component of TME.

DNA damage and mitochondria in cancer and aging

Age and DNA repair deficiencies are strong risk factors for developing cancer. This is reflected in the comorbidity of cancer with premature aging diseases associated with DNA damage repair deficiencies. Recent research has suggested that DNA damage accumulation, telomere dysfunction and the accompanying mitochondrial dysfunction exacerbate the aging process and may increase the risk of cancer development. Thus, an area of interest in both cancer and aging research is the elucidation of the dynamic crosstalk between the nucleus and the mitochondria. In this review, we discuss current research on aging and cancer with specific focus on the role of mitochondrial dysfunction in cancer and aging as well as how nuclear to mitochondrial DNA damage signaling may be a driving factor in the increased cancer incidence with aging. We suggest that therapeutic interventions aimed at the induction of autophagy and mediation of nuclear to mitochondrial signaling may provide a mechanism for healthier aging and reduced tumorigenesis.

Oncolytic virotherapy promotes radiosensitivity in soft tissue sarcoma by suppressing anti-apoptotic MCL1 expression

Soft tissue sarcoma (STS) is a rare cancer that develops from soft tissues in any part of the body. Despite major advances in the treatment of STS, patients are often refractory to conventional radiotherapy, leading to poor prognosis. Enhancement of sensitivity to radiotherapy would therefore improve the clinical outcome of STS patients. We previously revealed that the tumor-specific, replication-competent oncolytic adenovirus OBP-301 kills human sarcoma cells. In this study, we investigated the radiosensitizing effect of OBP-301 in human STS cells. The in vitro antitumor effect of OBP-301 and ionizing radiation in monotherapy or combination therapy was assessed using highly radiosensitive (RD-ES and SK-ES-1) and moderately radiosensitive (HT1080 and NMS-2) STS cell lines. The expression of markers for apoptosis and DNA damage were evaluated in STS cells after treatment. The therapeutic potential of combination therapy was further analyzed using SK-ES-1 and HT1080 cells in subcutaneous xenograft tumor models. The combination of OBP-301 and ionizing radiation showed a synergistic antitumor effect in all human STS cell lines tested, including those that show different radiosensitivity. OBP-301 was found to enhance irradiation-induced apoptosis and DNA damage via suppression of anti-apoptotic myeloid cell leukemia 1 (MCL1), which was expressed at higher levels in moderately radiosensitive cell lines. The combination of OBP-301 and ionizing radiation showed a more profound antitumor effect compared to monotherapy in SK-ES-1 (highly radiosensitive) and HT1080 (moderately radiosensitive) subcutaneous xenograft tumors. OBP-301 is a promising antitumor reagent to improve the therapeutic potential of radiotherapy by increasing radiation-induced apoptosis in STS.

Targeting Genome Stability in Melanoma-A New Approach to an Old Field

Despite recent groundbreaking advances in the treatment of cutaneous melanoma, it remains one of the most treatment-resistant malignancies. Due to resistance to conventional chemotherapy, the therapeutic focus has shifted away from aiming at melanoma genome stability in favor of molecularly targeted therapies. Inhibitors of the RAS/RAF/MEK/ERK (MAPK) pathway significantly slow disease progression. However, long-term clinical benefit is rare due to rapid development of drug resistance. In contrast, immune checkpoint inhibitors provide exceptionally durable responses, but only in a limited number of patients. It has been increasingly recognized that melanoma cells rely on efficient DNA repair for survival upon drug treatment, and that genome instability increases the efficacy of both MAPK inhibitors and immunotherapy. In this review, we discuss recent developments in the field of melanoma research which indicate that targeting genome stability of melanoma cells may serve as a powerful strategy to maximize the efficacy of currently available therapeutics.

Reactive oxygen species produced by altered tumor metabolism impacts cancer stem cell maintenance

Controlling reactive oxygen species (ROS) at sustainable levels can drive multiple facets of tumor biology, including within the cancer stem cell (CSC) population. Tight regulation of ROS is one key component in CSCs that drives disease recurrence, cell signaling, and therapeutic resistance. While ROS are well-appreciated to need oxygen and are a product of oxidative phosphorylation, there are also important roles for ROS under hypoxia. As hypoxia promotes and sustains major stemness pathways, further consideration of ROS impacts on CSCs in the tumor microenvironment is important. Furthermore, glycolytic shifts that occur in cancer and may be promoted by hypoxia are associated with multiple mechanisms to mitigate oxidative stress. This altered metabolism provides survival advantages that sustain malignant features, such as proliferation and self-renewal, while producing the necessary antioxidants that reduce damage from oxidative stress. Finally, disease recurrence is believed to be attributed to therapy resistant CSCs which can be quiescent and have changes in redox status. Effective DNA damage response pathways and/or a slow-cycling state can protect CSCs from the genomic catastrophe induced by irradiation and genotoxic agents. This review will explore the delicate, yet complex, relationship between ROS and its pleiotropic role in modulating the CSC.

Linking Serine/Glycine Metabolism to Radiotherapy Resistance

Simple Summary

Hyperactivation of the de novo serine/glycine biosynthesis across different cancer types and its critical contribution in tumor initiation, progression, and therapy resistance indicate the relevance of serine/glycine metabolism-targeted therapies as therapeutic intervention in cancer. In this review, we specifically focus on the contribution of the de novo serine/glycine biosynthesis pathway to radioresistance. We provide a future perspective on how de novo serine/glycine biosynthesis inhibition and serine-free diets may improve the outcome of radiotherapy. Future research in this field is needed to better understand serine/glycine metabolic reprogramming of cancer cells in response to radiation and the influence of this pathway in the tumor microenvironment, which may provide the rationale for the optimal combination therapies.

Abstract

The activation of de novo serine/glycine biosynthesis in a subset of tumors has been described as a major contributor to tumor pathogenesis, poor outcome, and treatment resistance. Amplifications and mutations of de novo serine/glycine biosynthesis enzymes can trigger pathway activation; however, a large group of cancers displays serine/glycine pathway overexpression induced by oncogenic drivers and unknown regulatory mechanisms. A better understanding of the regulatory network of de novo serine/glycine biosynthesis activation in cancer might be essential to unveil opportunities to target tumor heterogeneity and therapy resistance. In the current review, we describe how the activation of de novo serine/glycine biosynthesis in cancer is linked to treatment resistance and its implications in the clinic. To our knowledge, only a few studies have identified this pathway as metabolic reprogramming of cancer cells in response to radiation therapy. We propose an important contribution of de novo serine/glycine biosynthesis pathway activation to radioresistance by being involved in cancer cell viability and proliferation, maintenance of cancer stem cells (CSCs), and redox homeostasis under hypoxia and nutrient-deprived conditions. Current approaches for inhibition of the de novo serine/glycine biosynthesis pathway provide new opportunities for therapeutic intervention, which in combination with radiotherapy might be a promising strategy for tumor control and ultimately eradication. Further research is needed to gain molecular and mechanistic insight into the activation of this pathway in response to radiation therapy and to design sophisticated stratification methods to select patients that might benefit from serine/glycine metabolism-targeted therapies in combination with radiotherapy.

The CD44high Subpopulation of Multifraction Irradiation-Surviving NSCLC Cells Exhibits Partial EMT-Program Activation and DNA Damage Response Depending on Their p53 Status

Ionizing radiation (IR) is used for patients diagnosed with unresectable non-small cell lung cancer (NSCLC). However, radiotherapy remains largely palliative due to the survival of specific cell subpopulations. In the present study, the sublines of NSCLC cells, A549IR (p53wt) and H1299IR (p53null) survived multifraction X-ray radiation exposure (MFR) at a total dose of 60 Gy were investigated three weeks after the MFR course. We compared radiosensitivity (colony formation), expression of epithelial-mesenchymal transition (EMT) markers, migration activity, autophagy, and HR-dependent DNA double-strand break (DSB) repair in the bulk and entire CD44high/CD166high CSC-like populations of both parental and MFR survived NSCLC cells. We demonstrated that the p53 status affected: the pattern of expression of N-cadherin, E-cadherin, Vimentin, witnessing the appearance of EMT-like phenotype of MFR-surviving sublines; 1D confined migratory behavior (wound healing); the capability of an irradiated cell to continue to divide and form a colony of NSCLC cells before and after MFR; influencing the CD44/CD166 expression level in MFR-surviving NSCLC cells after additional single irradiation. Our data further emphasize the impact of p53 status on the decay of γH2AX foci and the associated efficacy of the DSB repair in NSCLC cells survived after MFR. We revealed that Rad51 protein might play a principal role in MFR-surviving of p53 null NSCLC cells promoting DNA DSB repair by homologous recombination (HR) pathway. The proportion of Rad51 + cells elevated in CD44high/CD166high population in MFR-surviving p53wt and p53null sublines and their parental cells. The p53wt ensures DNA-PK-mediated DSB repair for both parental and MFR-surviving cells irrespectively of a subsequent additional single irradiation. Whereas in the absence of p53, a dose-dependent increase of DNA-PK-mediated non-homologous end joining (NHEJ) occurred as an early post-irradiation response is more intensive in the CSC-like population MFR-surviving H1299IR, compared to their parental H1299 cells. Our study strictly observed a significantly higher content of LC3 + cells in the CD44high/CD166high populations of p53wt MFR-surviving cells, which enriched the CSC-like cells in contrast to their p53null counterparts. The additional 2 Gy and 5 Gy X-ray exposure leads to the dose-dependent increase in the proportion of LC3 + cells in CD44high/CD166high population of both parental p53wt and p53null, but not MFR-surviving NSCLC sublines. Our data indicated that autophagy is not necessarily associated with CSC-like cells’ radiosensitivity, emphasizing that careful assessment of other milestone processes (such as senescence and autophagy-p53-Zeb1 axis) of primary radiation responses may provide new potential targets modulated for therapeutic benefit through radiosensitizing cancer cells while rescuing normal tissue. Our findings also shed light on the intricate crosstalk between autophagy and the p53-related EMT, by which MFR-surviving cells might obtain an invasive phenotype and metastatic potential.

Targeting NPM1 in irradiated cells inhibits NPM1 binding to RAD51, RAD51 foci formation and radiosensitizes NSCLC

The ability of chemo-radiation therapy to control locally advanced stage III non-small cell lung cancer (NSCLC) is poor. While addition of consolidation immunotherapy has improved outcomes in subsets of patients there is still an urgent need for new therapeutic targets. Emerging research indicates that nucleophosmin1 (NPM1) is over-expressed in NSCLC, promotes tumor growth and that over-expression correlates with a lower survival probability. NPM1 is critical for APE1 base excision activity and for RAD51-mediated repair of DNA double strand breaks (DSBs). YTR107 is a small molecule radiation sensitizer that has been shown to bind to NPM1, suppressing pentamer formation. Here we show that in irradiated cells YTR107 inhibits SUMOylated NPM1 from associating with RAD51, RAD51 foci formation and repair of DSBs. YTR107 acts synergistically with the PARP1/2 inhibitor ABT 888 to increase replication stress and radiation-induced cell lethality. YTR107 was found to radiosensitize tumor initiating cells. Congruent with this knowledge, adding YTR107 to a fractionated irradiation regimen diminished NSCLC xenograft growth and increased overall survival. These data support the hypothesis that YTR107 represents a therapeutic target for control of NSCLC.

Making radiation therapy more effective in the era of precision medicine

Cancer has become a leading cause of death and constitutes an enormous burden worldwide. Radiation is a principle treatment modality used alone or in combination with other forms of therapy, with 50%–70% of cancer patients receiving radiotherapy at some point during their illness. It has been suggested that traditional radiotherapy (daily fractions of approximately 1.8–2 Gy over several weeks) might select for radioresistant tumor cell sub-populations, which, if not sterilized, give rise to local treatment failure and distant metastases. Thus, the challenge is to develop treatment strategies and schedules to eradicate the resistant subpopulation of tumorigenic cells rather than the predominant sensitive tumor cell population. With continued technological advances including enhanced conformal treatment technology, radiation oncologists can increasingly maximize the dose to tumors while sparing adjacent normal tissues, to limit toxicity and damage to the latter. Increased dose conformality also facilitates changes in treatment schedules, such as changes in dose per treatment fraction and number of treatment fractions, to enhance the therapeutic ratio. For example, the recently developed large dose per fraction treatment schedules (hypofractionation) have shown clinical advantage over conventional treatment schedules in some tumor types. Experimental studies suggest that following large acute doses of radiation, recurrent tumors, presumably sustained by the most resistant tumor cell populations, may in fact be equally or more radiation sensitive than the primary tumor. In this review, we summarize the related advances in radiotherapy, including the increasing understanding of the molecular mechanisms of radioresistance, and the targeting of these mechanisms with potent small molecule inhibitors, which may selectively sensitize tumor cells to radiation.

Oxidative stress associated metabolic adaptations regulate radioresistance in human lung cancer cells

Differential inherent and acquired radioresistance of human lung cancer cells contribute to poor therapeutic outcome and tumor recurrence after radiotherapy. Inherent radioresistance of lung cancer cells is known to be associated with ROS^Low cancer stem cells (CSCs). However, mechanism of acquired radioresistance in lung cancer cells is poorly understood. Here, we exposed human lung cancer cells (A549) to a cumulative dose of 40Gy and allowed the radioresistant (RR) survivors to divide and form macroscopic colonies after each fraction of 5Gy dose. The RR subline exhibited enrichment of cytosolic ROS^High cells without specific increase in mitochondrial ROS levels. We found a concomitant increase in the expression of redox regulatory transcription factor Nrf2 and its dependent antioxidant genes in RR cells and cell cycle delay as compared to parental cells. The treatment of RR cells with Nrf2 inhibitor resulted in decreased clonogenic survival indicating their addiction to Nrf2 for metabolic adaptations under high levels of cytosolic ROS. A causal role of inherent ROS levels in conferring radioresistance was established by sorting ROS^High and ROS^Low populations from parental and RR cells. It was observed that ROS^High population from both parental and RR cells exhibited radioresistance as observed by clonogenic assay. Interestingly, ROS^High population of cells exhibited higher levels of cellular thiols in both parental and RR cells. Thus, our observations highlight presence of a novel subpopulation in lung cancer cells, which exhibits radioresistance by maintaining 'oxidative stress' and Nrf2 dependent metabolic adaptations. We also posit Nrf2 pathway as a druggable target for radiosensitization of RR A549 cells.

Characterization of sphere cells derived from a patient-derived xenograft model of lung adenocarcinoma treated with ionizing radiation

PURPOSE

Cancer stem cells (CSCs) are relatively resistant to radiation compared to their non-tumorigenic progeny. Ionizing radiation (IR) can expand the pool of CSCs that leads to more aggressive cancers, but the reason underlying CSC-induced cancer aggressiveness after radiation therapy remains unclear. To understand this, we investigated the phenotypic and molecular characteristics of sphere cells formed from IR-treated patient-derived xenograft (PDX) lung adenocarcinoma tumors.

MATERIALS AND METHODS

After treatment with various modes of IR, we collected tumors from PDX mice and successfully obtained sphere cells. To compare tumorigenicity, we performed migration, invasion, and mouse transplantation assays with sphere cells from each group. To investigate the molecular features, we used a cDNA microarray and compared gene expression among groups.

RESULTS AND CONCLUSIONS

Tumorigenicity assays revealed that sphere cells from 2- or 5-Gy IR-treated tumors more aggressive than sphere cells from non-IR treated tumors. Microarray results showed that SERPIB4 and CCL2 were upregulated in sphere cells from IR-treated tumors compared to that in sphere cells from non-IR treated tumors. Interestingly, these genes are related to immune reactions in cancer. Taken together, our results suggest that the aggressiveness of sphere cells obtained after IR treatment is related to resistance, and provide new opportunities for exploring targeted therapies to overcome common radioresistance.

Stem cell programs in cancer initiation, progression, and therapy resistance

Over the past few decades, substantial evidence has convincingly revealed the existence of cancer stem cells (CSCs) as a minor subpopulation in cancers, contributing to an aberrantly high degree of cellular heterogeneity within the tumor. CSCs are functionally defined by their abilities of self-renewal and differentiation, often in response to cues from their microenvironment. Biological phenotypes of CSCs are regulated by the integrated transcriptional, post-transcriptional, metabolic, and epigenetic regulatory networks. CSCs contribute to tumor progression, therapeutic resistance, and disease recurrence through their sustained proliferation, invasion into normal tissue, promotion of angiogenesis, evasion of the immune system, and resistance to conventional anticancer therapies. Therefore, elucidation of the molecular mechanisms that drive cancer stem cell maintenance, plasticity, and therapeutic resistance will enhance our ability to improve the effectiveness of targeted therapies for CSCs. In this review, we highlight the key features and mechanisms that regulate CSC function in tumor initiation, progression, and therapy resistance. We discuss factors for CSC therapeutic resistance, such as quiescence, induction of epithelial-to-mesenchymal transition (EMT), and resistance to DNA damage-induced cell death. We evaluate therapeutic approaches for eliminating therapy-resistant CSC subpopulations, including anticancer drugs that target key CSC signaling pathways and cell surface markers, viral therapies, the awakening of quiescent CSCs, and immunotherapy. We also assess the impact of new technologies, such as single-cell sequencing and CRISPR-Cas9 screening, on the investigation of the biological properties of CSCs. Moreover, challenges remain to be addressed in the coming years, including experimental approaches for investigating CSCs and obstacles in therapeutic targeting of CSCs.

CSC Radioresistance: A Therapeutic Challenge to Improve Radiotherapy Effectiveness in Cancer

Radiotherapy (RT) is a modality of oncologic treatment that can be used to treat approximately 50% of all cancer patients either alone or in combination with other treatment modalities such as surgery, chemotherapy, immunotherapy, and therapeutic targeting. Despite the technological advances in RT, which allow a more precise delivery of radiation while progressively minimizing the impact on normal tissues, issues like radioresistance and tumor recurrence remain important challenges. Tumor heterogeneity is responsible for the variation in the radiation response of the different tumor subpopulations. A main factor related to radioresistance is the presence of cancer stem cells (CSC) inside tumors, which are responsible for metastases, relapses, RT failure, and a poor prognosis in cancer patients. The plasticity of CSCs, a process highly dependent on the epithelial–mesenchymal transition (EMT) and associated to cell dedifferentiation, complicates the identification and eradication of CSCs and it might be involved in disease relapse and progression after irradiation. The tumor microenvironment and the interactions of CSCs with their niches also play an important role in the response to RT. This review provides a deep insight into the characteristics and radioresistance mechanisms of CSCs and into the role of CSCs and tumor microenvironment in both the primary tumor and metastasis in response to radiation, and the radiobiological principles related to the CSC response to RT. Finally, we summarize the major advances and clinical trials on the development of CSC-based therapies combined with RT to overcome radioresistance. A better understanding of the potential therapeutic targets for CSC radiosensitization will provide safer and more efficient combination strategies, which in turn will improve the live expectancy and curability of cancer patients.

Radiobiologically derived biphasic fractionation schemes to overcome the effects of tumour hypoxia

OBJECTIVE

As a fractionated course of radiotherapy proceeds tumour shrinkage leads to resolution of hypoxia and the initiation of accelerated proliferation of radioresistant cancer cells with better repair capacity. We hypothesise that, in tumours with significant hypoxia, improved tumour control could be achieved with biphasic fractionation schedules that either use acceleration after 3-4 weeks of conventional radiotherapy or deliver a higher proportional dose towards the end of a course of treatment. We conducted a modelling study based on the concept of biological effective dose (BED) comparing such novel regimens with conventional fractionation.

METHODS

The comparator conventional fractionation schedule 70 Gy in 35 fractions delivered over 7 weeks was tested against the following novel regimens, both of which were designed to be isoeffective in terms of late normal tissue toxicity.40 Gy in 20 fractions over 4 weeks followed by 22.32 Gy in 6 consecutive daily fractions (delayed acceleration)30.4 Gy in 27 fractions over 4 weeks followed by 40 Gy in 15 fractions over 3 weeks (temporal dose redistribution)The delayed acceleration regimen is exactly identical to that of the comparator schedule over the first 28 days and the BED gains with the novel schedule are achieved during the second phase of treatment when reoxygenation is complete. For the temporal redistribution regimen, it was assumed that the reoxygenation fraction progressively increases during the first 4 weeks of treatment and an iterative approach was used to calculate the final tumour BED for varying hypoxic fractions.

RESULTS

Novel fractionation with delayed acceleration or temporal fractionation results in tumour BED gains equivalent to 3.5-8 Gy when delivered in 2 Gy fractions.

CONCLUSION

In hypoxic tumours, novel fractionation strategies result in significantly higher tumour BED in comparison to conventional fractionation.

ADVANCES IN KNOWLEDGE

We demonstrate that novel biphasic fractionation regimens could overcome the effects of tumour hypoxia resulting in biological dose escalation.

XRCC1 Is a Promising Predictive Biomarker and Facilitates Chemo-Resistance in Gallbladder Cancer

Gallbladder cancer is a relatively uncommon human malignant tumor with an extremely poor prognosis. Currently, no biomarkers can accurately diagnose gallbladder cancer and predict patients' prognosis. XRCC1 is involved in tumorigenesis, progression, and chemo-resistance of several human cancers, but the role of XRCC1 in gallbladder cancer is never reported. In this study, we investigated the expression of XRCC1 and its clinicopathological and prognostic significance in gallbladder cancer, and explored the biological role of XRCC1 in gallbladder cancer cells. We found that XRCC1 was significantly up-regulated in gallbladder cancer in protein and mRNA levels. Positive XRCC1 expression was correlated with aggressive clinicopathological features and was an independent poor prognostic factor in gallbladder cancer. The ROC curves suggested that XRCC1 expression had potential clinicopathological diagnostic value in gallbladder cancer. In vitro, XRCC1 was overexpression in CD133⁺GBC-SD cells compared to GBC-SD cells. In functional experiment, XRCC1 knockdown had a non-significant impact on proliferation, migration, invasion, and apoptosis of CD133⁺GBC-SD cells. But, XRCC1 knockdown could significantly improve the sensitivity of CD133⁺GBC-SD cells to 5-Fluorouracil via promoting cell necrosis and apoptosis. Thus, this study indicates that XRCC1 may be a promising predictive biomarker of gallbladder cancer and a potential therapeutic target for gallbladder cancer.

The Role of Cancer Stem Cells in Radiation Resistance

Cancer stem cells (CSC) are a distinct subpopulation within a tumor. They are able to self-renew and differentiate and possess a high capability to repair DNA damage, exhibit low levels of reactive oxygen species (ROS), and proliferate slowly. These features render CSC resistant to various therapies, including radiation therapy (RT). Eradication of all CSC is a requirement for an effective antineoplastic treatment and is therefore of utmost importance for the patient. This makes CSC the prime targets for any therapeutic approach. Albeit clinical data is still scarce, experimental data and first clinical trials give hope that CSC-targeted treatment has the potential to improve antineoplastic therapies, especially for tumors that are known to be treatment resistant, such as glioblastoma. In this review, we will discuss CSC in the context of RT, describe known mechanisms of resistance, examine the possibilities of CSC as biomarkers, and discuss possible new treatment approaches.

DNA damage response and resistance of cancer stem cells

The cancer stem cell (CSC) model defines tumors as hierarchically organized entities, containing a small population of tumorigenic CSC, or tumour-initiating cells, placed at the apex of this hierarchy. These cells may share common qualities with chemo- and radio-resistant cancer cells and contribute to self-renewal activities resulting in tumour formation, maintenance, growth and metastasis. Yet, it remains obscure what self-defense mechanisms are utilized by these cells against the chemotherapeutic drugs or radiotherapy. Recently, attention has been focused on the pivotal role of the DNA damage response (DDR) in tumorigenesis. In line with this note, an increased DDR that prevents CSC and chemoresistant cells from genotoxic pressure of chemotherapeutic drugs or radiation may be responsible for cancer metastasis. In this review, we focus on the current knowledge concerning the role of DDR in CSC and resistant cancer cells and describe the existing opportunities of re-sensitizing such cells to modulate therapeutic treatment effects.

Approaches to Targeting Cancer Stem Cells in Solid Tumors

CSCs are a population of self-renewing and tumor repopulating cells that have been observed in hematologic and solid tumors and their presence contributes to the development of drug resistance. The failure to eliminate CSCs with conventional therapy is one of major obstacles in the successful treatment of cancer. Several mechanisms have been described to contribute to CSCs chemoresistance properties that include the adoption of drug-efflux pumps, drug detoxification pathways, changes in metabolism, improved DNA repair mechanisms, and deregulated survival and pro-apoptotic pathways. Thus, CSCs are therefore an attractive target to develop new anti-cancer therapies.

Difference in Acquired Radioresistance Induction Between Repeated Photon and Particle Irradiation

In recent years, advanced radiation therapy techniques, including stereotactic body radiotherapy and carbon–ion radiotherapy, have progressed to such an extent that certain types of cancer can be treated with radiotherapy alone. The therapeutic outcomes are particularly promising for early stage lung cancer, with results matching those of surgical resection. Nevertheless, patients may still experience local tumor recurrence, which might be exacerbated by the acquisition of radioresistance after primary radiotherapy. Notwithstanding the risk of tumors acquiring radioresistance, secondary radiotherapy is increasingly used to treat recurrent tumors. In this context, it appears essential to comprehend the radiobiological effects of repeated photon and particle irradiation and their underlying cellular and molecular mechanisms in order to achieve the most favorable therapeutic outcome. However, to date, the mechanisms of acquisition of radioresistance in cancer cells have mainly been studied after repeated in vitro X-ray irradiation. By contrast, other critical aspects of radioresistance remain mostly unexplored, including the response to carbon-ion irradiation of X-ray radioresistant cancer cells, the mechanisms of acquisition of carbon-ion resistance, and the consequences of repeated in vivo X-ray or carbon-ion irradiation. In this review, we discuss the underlying mechanisms of acquisition of X-ray and carbon-ion resistance in cancer cells, as well as the phenotypic differences between X-ray and carbon-ion-resistant cancer cells, the biological implications of repeated in vivo X-ray or carbon-ion irradiation, and the main open questions in the field.

Cancer Stem Cells and Radioresistance: DNA Repair and Beyond

The current preclinical and clinical findings demonstrate that, in addition to the conventional clinical and pathological indicators that have a prognostic value in radiation oncology, the number of cancer stem cells (CSCs) and their inherent radioresistance are important parameters for local control after radiotherapy. In this review, we discuss the molecular mechanisms of CSC radioresistance attributable to DNA repair mechanisms and the development of CSC-targeted therapies for tumor radiosensitization. We also discuss the current challenges in preclinical and translational CSC research including the high inter- and intratumoral heterogeneity, plasticity of CSCs, and microenvironment-stimulated tumor cell reprogramming.

Therapeutic considerations of PARP in stem cell biology: Relevance in cancer and beyond

Cancer stem cells (CSCs) are of fundamental importance in tumor progression because of their tumor-initiating properties, their resistance to radio- and chemotherapy, their invasive properties and their propensity to escape immune responses that together contribute to tumor relapse. These highly aggressive features underscore the importance of constantly identifying new and innovative therapeutic solutions to eradicate these cells. In this narrative review we discuss recent findings on the involvement of PARP family members in cancer stem cell biology and the benefit of their inhibition. Nonetheless, an important limitation in the use of PARP inhibitors is the emergence of a prominent function of PARP1 in non-cancer stem cell biology including stem cell maintenance and differentiation during development, neurogenesis or adipogenesis. Thus, we also summarize the dominant discoveries revealing the importance of PARP1 in normal stem cell biology.

BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were linked to genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.