Development Of Radioresistance Research Articles

Abstract 2887: Impact of ionizing radiation on the energy metabolism of normal and tumor cells in the brain

Abstract This study aims to analyze irradiation-induced metabolic alterations in glioblastoma cells and astrocytes to enhance understanding of cellular responses and facilitate the development of more effective radiotherapeutic strategies. Metabolic reprogramming of tumor cells is considered one of the hallmarks of cancer. Studies have shown that abnormal activation of oncogenes and cancer-related signaling pathways, as well as the inactivation of tumor suppressor genes can induce metabolic reprogramming. These metabolic aberrations facilitate rapid proliferation, continuous growth, invasion, metastasis, and immune evasion. Following the application of radiotherapy, the activity of several metabolic pathways significantly changes, potentially leading to the development of radioresistance. However, a differential effect of ionizing radiation on tumor and normal cells is not well understood. Hence, quantifying irradiation-induced metabolic changes in glioblastoma cells and astrocytes is of high importance. We have developed a novel approach to measure dynamic metabolite changes upon irradiation, in vivo, in situ, and in real-time. This tool combines imaging of recently developed fluorescent biosensors via 2-photon microscopy and millimeter-scaled irradiation. Murine glioblastoma cells and astrocytes were generated with stable expression of biosensors for the quantification of intracellular concentrations of various metabolites, including lactate. Cytosolic concentrations of lactate depend on the balance between glycolytic production, mitochondrial consumption of pyruvate and lactate, and the exchange with the extracellular lactate pool via monocarboxylate transporters. Many cancer cells are characterized by an excessive conversion of glucose to lactate even under normoxic conditions. We quantified this so-called Warburg Effect in glioblastoma cells and astrocytes as the ratio between basal lactate production and the lactate increase after OXPHOS inhibition and determined irradiation-induced metabolic changes on the single-cell level. Complementarily, we used metabolomics and Seahorse analyses before and after irradiation. Our data indicate that irradiation increases oxygen consumption in glioblastoma cells but not in astrocytes. Also, we established an orthotopic glioblastoma mouse model via injection of sensor-expressing tumor cells for in vivo measurements of metabolite changes during and after irradiation. These data are expected to significantly advance the understanding of the cellular response to irradiation on a molecular level in situ and in real-time. This knowledge will help to develop combination treatments and increase the efficiency of radiotherapy. Citation Format: Marvin Kreuzer, Pascal Imseng, Bruno Weber, Martin Pruschy. Impact of ionizing radiation on the energy metabolism of normal and tumor cells in the brain [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2887.

PITPNC1 Suppress CD8+ T cell immune function and promote radioresistance in rectal cancer by modulating FASN/CD155

BackgroundRadioresistance is a primary factor contributing to the failure of rectal cancer treatment. Immune suppression plays a significant role in the development of radioresistance. We have investigated the potential role of phosphatidylinositol transfer protein cytoplasmic 1 (PITPNC1) in regulating immune suppression associated with radioresistance.MethodsTo elucidate the mechanisms by which PITPNC1 influences radioresistance, we established HT29, SW480, and MC38 radioresistant cell lines. The relationship between radioresistance and changes in the proportion of immune cells was verified through subcutaneous tumor models and flow cytometry. Changes in the expression levels of PITPNC1, FASN, and CD155 were determined using immunohistochemistry and western blotting techniques. The interplay between these proteins was investigated using immunofluorescence co-localization and immunoprecipitation assays. Additionally, siRNA and lentivirus-mediated gene knockdown or overexpression, as well as co-culture of tumor cells with PBMCs or CD8+ T cells and establishment of stable transgenic cell lines in vivo, were employed to validate the impact of the PITPNC1/FASN/CD155 pathway on CD8+ T cell immune function.ResultsUnder irradiation, the apoptosis rate and expression of apoptosis-related proteins in radioresistant colorectal cancer cell lines were significantly decreased, while the cell proliferation rate increased. In radioresistant tumor-bearing mice, the proportion of CD8+ T cells and IFN-γ production within immune cells decreased. Immunohistochemical analysis of human and animal tissue specimens resistant to radiotherapy showed a significant increase in the expression levels of PITPNC1, FASN, and CD155. Gene knockdown and rescue experiments demonstrated that PITPNC1 can regulate the expression of CD155 on the surface of tumor cells through FASN. In addition, co-culture experiments and in vivo tumor-bearing experiments have shown that silencing PITPNC1 can inhibit FASN/CD155, enhance CD8+ T cell immune function, promote colorectal cancer cell death, and ultimately reduce radioresistance in tumor-bearing models.ConclusionsPITPNC1 regulates the expression of CD155 through FASN, inhibits CD8+ T cell immune function, and promotes radioresistance in rectal cancer.

FBW7/GSK3β mediated degradation of IGF2BP2 inhibits IGF2BP2-SLC7A5 positive feedback loop and radioresistance in lung cancer

BackgroundThe development of radioresistance seriously hinders the efficacy of radiotherapy in lung cancer. However, the underlying mechanisms by which radioresistance occurs are still incompletely understood. The N6-Methyladenosine (m6A) modification of RNA is involved in cancer progression, but its role in lung cancer radioresistance remains elusive. This study aimed to identify m6A regulators involved in lung cancer radiosensitivity and further explore the underlying mechanisms to identify therapeutic targets to overcome lung cancer radioresistance.MethodsBioinformatic mining was used to identify the m6A regulator IGF2BP2 involved in lung cancer radiosensitivity. Transcriptome sequencing was used to explore the downstream factors. Clonogenic survival assays, neutral comet assays, Rad51 foci formation assays, and Annexin V/propidium iodide assays were used to determine the significance of FBW7/IGF2BP2/SLC7A5 axis in lung cancer radioresistance. Chromatin immunoprecipitation (ChIP)-qPCR analyses, RNA immunoprecipitation (RIP) and methylated RNA immunoprecipitation (MeRIP)-qPCR analyses, RNA pull-down analyses, co-immunoprecipitation analyses, and ubiquitination assays were used to determine the feedback loop between IGF2BP2 and SLC7A5 and the regulatory effect of FBW7/GSK3β on IGF2BP2. Mice models and tissue microarrays were used to verify the effects in vivo.ResultsWe identified IGF2BP2, an m6A “reader”, that is overexpressed in lung cancer and facilitates radioresistance. We showed that inhibition of IGF2BP2 impairs radioresistance in lung cancer both in vitro and in vivo. Furthermore, we found that IGF2BP2 enhances the stability and translation of SLC7A5 mRNA through m6A modification, resulting in enhanced SLC7A5-mediated transport of methionine to produce S-adenosylmethionine. This feeds back upon the IGF2BP2 promoter region by further increasing the trimethyl modification at lysine 4 of histone H3 (H3K4me3) level to upregulate IGF2BP2 expression. We demonstrated that this positive feedback loop between IGF2BP2 and SLC7A5 promotes lung cancer radioresistance through the AKT/mTOR pathway. Moreover, we found that the ubiquitin ligase FBW7 functions with GSK3β kinase to recognize and degrade IGF2BP2.ConclusionsCollectively, our study revealed that the m6A “reader” IGF2BP2 promotes lung cancer radioresistance by forming a positive feedback loop with SLC7A5, suggesting that IGF2BP2 may be a potential therapeutic target to control radioresistance in lung cancer.

Upregulation of CoQ shifts ferroptosis dependence from GPX4 to FSP1 in acquired radioresistance

Acquired radioresistance is the primary contributor to treatment failure of radiotherapy, with ferroptosis is identified as a significant mechanism underlying cell death during radiotherapy. Although resistance to ferroptosis has been observed in both clinical samples of radioresistant cells and cell models, its mechanism remains unidentified. Herein, our investigation revealed that radioresistant cells exhibited greater tolerance to Glutathione Peroxidase 4 (GPX4) inhibitors and, conversely, increased sensitivity to ferroptosis suppressor protein 1 (FSP1) inhibitors compared to their sensitive counterparts. This observation suggested that FSP1 might play a dominant role in the development of radioresistance. Notably, the knockout of FSP1 demonstrated considerably superior efficacy in resensitizing cells to radiotherapy compared to the knockout of GPX4. To elucidate the driving force behind this functional shift, we conducted a metabolomic assay, which revealed an upregulation of Coenzyme Q (CoQ) synthesis and a downregulation of glutathione synthesis in the acquired radioresistance cells. Mechanistically, CoQ synthesis was found to be supported by aarF domain containing kinase 3-mediated phosphorylation of CoQ synthases, while the downregulation of Solute carrier family 7 member 11 led to decreased glutathione synthesis. Remarkably, our retrospective analysis of clinical response data further validated that the additional administration of statin during radiotherapy, which could impede CoQ production, effectively resensitized radioresistant cells to radiation. In summary, our findings demonstrate a dependency shift from GPX4 to FSP1 driven by altered metabolite synthesis during the acquisition of radioresistance. Moreover, we provide a promising therapeutic strategy for reversing radioresistance by inhibiting the FSP1-CoQ pathway.

Insights on the radiation-induced adaptive response at the cellular level and its implications in cancer therapy.

Development of resistance upon exposure to small doses of ionizing radiation followed by higher doses is known as radiation-induced adaptive response (RIAR). Traditionally, the induction of the RIAR phenomenon at the cellular level has been examined in cell lines, animal models, and epidemiological studies where people live in high natural background radiation. The primary intention of the earlier studies was to corroborate the existence of RIAR and the mechanism involved in mediating the response surveyed by exposure to a low dose of radiation (<500 mGy) as priming dose towards the radiation protection point of view. However, the investigation has shifted the focus to understand the relevance of this phenomenon at clinically relevant set-ups (high doses in the order of Gy) and can be exploited during radiotherapy as RIAR is considered a mechanism for the development of radioresistance. Although the knowledge of molecular mechanisms at the cellular level has evolved significantly in multi-fractionated radiotherapy regimes, its relevance in developing radioresistance at low doses remains elusive. The authors recapitulate the existing knowledge on RIAR at cellular levels, specifically after low-dose exposure as an adaptive dose, and discussed its potential implications in clinical radiotherapy outcomes. Recent studies contributed to understand the signaling molecules, pathways, and inhibitors to mitigate RIAR-mediated radiation resistance and persistent radio-tolerance at the cellular level. Monitoring the disease progression in tumor samples or liquid biopsies before, during, and after therapy with suitable biomarkers has been proposed as a strategy to translate the phenomena into clinical scenario.

Polymerase iota (POLI) confers radioresistance of esophageal squamous cell carcinoma by regulating RAD51 stability and facilitating homologous recombination

Radiotherapy resistance is an important and urgent challenge in the clinical management of esophageal squamous carcinoma (ESCC). However, the factors mediating the ESCC resistance to radiotherapy and its underlying molecular mechanisms are not fully clarified. Our previous studies have demonstrated the critical role of DNA polymerase iota (POLI) in ESCC development and progression, here, we aimed to investigate the involvement of POLI in ESCC radiotherapy resistance and elucidate the underlying molecular mechanism. We found that highly expressed POLI was correlated with shorter overall survival of ESCC patients received radiotherapy. Down-regulation of POLI sensitized ESCC to IR, prolonged γH2AX foci in nuclei and comet tails after IR. HR but not NHEJ repair is inhibited in POLI-deficient ESCC cells. POLI stabilizes RAD51 protein via competitively binding with and blocking the interaction between RAD51 and E3 ligase XIAP and XIAP-mediated ubiquitination. Furthermore, loss of POLI leads to the activation of GAS signaling. Our findings provide novel insight into the role of POLI in the development of radioresistance mediated by stabilizing RAD51 protein in ESCC.

The multifaceted role of extracellular vesicles in prostate cancer-a review.

Prostate cancer is the second most prominent form of cancer in men and confers the highest mortality after lung cancer. The term "extracellular vesicles" refers to minute endosomal-derived membrane microvesicles and it was demonstrated that extracellular vesicles affect the environment in which tumors originate. Extracellular vesicles' involvement is also established in the development of drug resistance, angiogenesis, stemness, and radioresistance in various cancers including prostate cancer. Extracellular vesicles influence the general environment, processes, and growth of prostate cancer and can be a potential area that offers a significant lead in prostate cancer therapy. In this review, we have elaborated on the multifaceted role of extracellular vesicles in various processes involved in the development of prostate cancer, and their multitude of applications in the diagnosis and treatment of prostate cancer through the encapsulation of various bioactives.

Cyclin D1 promotes radioresistance through regulation of RAD51 in melanoma.

Melanoma is a notoriously radioresistant type of skin cancer. Elucidation of the specific mechanisms underlying radioresistance is necessary to improve the clinical efficacy of radiation therapy. To identify the key factors contributing to radioresistance, five melanoma cell lines were selected for study and genes that were upregulated in relatively radioresistant melanomas compared with radiosensitive melanoma cells determined via RNA sequencing technology. In particular, we focused on cyclin D1 (CCND1), a well known cell cycle regulatory molecule. In radiosensitive melanoma, overexpression of cyclin D1 reduced apoptosis. In radioresistant melanoma cell lines, suppression of cyclin D1 with a specific inhibitor or siRNA increased apoptosis and decreased cell proliferation in 2D and 3D spheroid cultures. In addition, we observed increased expression of γ-H2AX, a molecular marker of DNA damage, even at a later time after γ-irradiation, under conditions of inhibition of cyclin D1, with a response pattern similar to that of radiosensitive SK-Mel5. In the same context, expression and nuclear foci formation of RAD51, a key enzyme for homologous recombination (HR), were reduced upon inhibition of cyclin D1. Downregulation of RAD51 also reduced cell survival to irradiation. Overall, suppression of cyclin D1 expression or function led to reduced radiation-induced DNA damage response (DDR) and triggered cell death. Our collective findings indicate that the presence of increased cyclin D1 potentially contributes to the development of radioresistance through effects on RAD51 in melanoma and could therefore serve as a therapeutic target for improving the efficacy of radiation therapy.

Transcriptional pausing induced by ionizing radiation enables the acquisition of radioresistance in nasopharyngeal carcinoma.

Lesions on the DNA template can impact transcription via distinct regulatory pathways. Ionizing radiation (IR) as the mainstay modality for many malignancies elicits most of the cytotoxicity by inducing a variety of DNA damages in the genome. How the IR treatment alters the transcription cycle and whether it contributes to the development of radioresistance remain poorly understood. Here, we report an increase in the paused RNA polymerase II (RNAPII), as indicated by the phosphorylation at serine 5 residue of its C-terminal domain, in recurrent nasopharyngeal carcinoma (NPC) patient samples after IR treatment and cultured NPC cells developing IR resistance. Reducing the pool of paused RNAPII by either inhibiting TFIIH-associated CDK7 or stimulating the positive transcription elongation factor b, a CDK9-CycT1 heterodimer, attenuates IR resistance of NPC cells. Interestingly, the poly(ADP-ribosyl)ation of CycT1, which disrupts its phase separation, is elevated in the IR-resistant cells. Mutation of the major poly(ADP-ribosyl)ation sites of CycT1 decreases RNAPII pausing and restores IR sensitivity. Genome-wide chromatin immunoprecipitation followed by sequencing analyses reveal that several genes involved in radiation response and cell cycle control are subject to the regulation imposed by the paused RNAPII. Particularly, we identify the NIMA-related kinase NEK7 under such regulation as a new radioresistance factor, whose downregulation results in the increased chromosome instability, enabling the development of IR resistance. Overall, our results highlight a novel link between the alteration in the transcription cycle and the acquisition of IR resistance, opening up new opportunities to increase the efficacy of radiotherapy and thwart radioresistance in NPC.

Biological and therapeutic viewpoints towards role of miR-218 in human cancers: Revisiting molecular interactions and future clinical translations

Understanding the exact pathogenesis of cancer is difficult due to heterogenous nature of tumor cells and multiple factors that cause its initiation and development. Treatment of cancer is mainly based on surgical resection, chemotherapy, radiotherapy and their combination, while gene therapy has been emerged as a new kind of therapy for cancer. Post-transcriptional regulation of genes has been of interest in recent years and among various types of epigenetic factors that can modulate gene expression, short non-coding RNAs known as microRNAs (miRNAs) have obtained much attention. The stability of mRNA decreases by miRNAs to repress gene expression. miRNAs can regulate tumor malignancy and biological behavior of cancer cells and understanding their function in tumorigenesis can pave the way towards developing new therapeutics in future. One of the new emerging miRNAs in cancer therapy is miR-218 that increasing evidence highlights its anti-cancer activity, while a few studies demonstrate its oncogenic function. The miR-218 transfection is promising in reducing progression of tumor cells. miR-218 shows interactions with molecular mechanisms including apoptosis, autophagy, glycolysis and EMT, and the interaction is different. miR-218 induces apoptosis, while it suppresses glycolysis, cytoprotective autophagy and EMT. Low expression of miR-218 can result in development of chemoresistance and radio-resistance in tumor cells and direct targeting of miR-218 as a key player is promising in cancer therapy. LncRNAs and circRNAs are nonprotein coding transcripts that can regulate miR-218 expression in human cancers. Moreover, low expression level of miR-218 can be observed in human cancers such as brain, gastrointestinal and urological cancers that mediate poor prognosis and low survival rate.

Radiotherapy and radio-sensitization in H3K27M -mutated diffuse midline gliomas.

H3K27M mutated diffuse midline gliomas (DMGs) are extremely aggressive and the leading cause of cancer-related deaths in pediatric brain tumors with 5-year survival <1%. Radiotherapy is the only established adjuvant treatment of H3K27M DMGs; however, the radio-resistance is commonly observed. We summarized current understandings of the molecular responses of H3K27M DMGs to radiotherapy and provide crucial insights into current advances in radiosensitivity enhancement. Ionizing radiation (IR) can mainly inhibit tumor cell growth by inducing DNA damage regulated by the cell cycle checkpoints and DNA damage repair (DDR) system. In H3K27M DMGs, the aberrant genetic and epigenetic changes, stemness genotype, and epithelial-mesenchymal transition (EMT) disrupt the cell cycle checkpoints and DDR system by altering the associated regulatory signaling pathways, which leads to the development of radio-resistance. The advances in mechanisms of radio-resistance in H3K27M  DMGs promote the potential targets to enhance the sensitivity to radiotherapy.

Circ_0085616 contributes to the radio-resistance and progression of cervical cancer by targeting miR-541-3p/ARL2 signaling.

Circular RNAs (circRNAs) play crucial regulatory roles in cancer progression and the development of radio-resistance. Here, we intended to explore the role of circ_0085616 in cervical cancer progression and its associated mechanism. Colony formation assay was employed to analyze the radio-resistance and proliferation of cervical cancer cells. Cell proliferation ability was also assessed by 5-ethynyl-2'-deoxyuridine (EdU) assay. Cell apoptosis was analyzed by flow cytometry. Tube formation assay was performed to analyze cell angiogenesis ability. Transwell assays were conducted to measure cell migration and invasion abilities. Dual-luciferase reporter assay was utilized to verify the target relationships. Xenograft mice model was used to analyze the role of circ_0085616 in tumor growth in vivo. Circ_0085616 expression was elevated in cervical cancer tissues and cell lines. Circ_0085616 interference suppressed the radio-resistance, proliferation, tube formation, migration, and invasion and elevated the apoptosis rate of cervical cancer cells. Circ_0085616 acted as a sponge for microRNA-541-3p (miR-541-3p), and miR-541-3p was negatively regulated by circ_0085616 in cervical cancer cells. Circ_0085616 absence-induced changes in the behaviors of cervical cancer cells were largely overturned by anti-miR-541-3p. miR-541-3p negatively regulated ADP ribosylation factor like GTPase 2 (ARL2) expression by binding to its 3' untranslated region (3'UTR). miR-541-3p mimic-induced effects were largely reversed by pcDNA-ARL2 in cervical cancer cells. Circ_0085616 positively regulated ARL2 expression by sequestering miR-541-3p. Circ_0085616 absence significantly inhibited the tumor growth in vivo. Circ_0085616 contributed to the radio-resistance and progression of cervical cancer partly through mediating the miR-541-3p/ARL2 axis.

Role of ionizing radiation activated NRF2 in lung cancer radioresistance

Radiotherapies are commonly used to target remaining tumor niches after surgery of solid tumors but are restricted due to therapeutic resistance. Several pathways of radioresistance have been reported in various cancers. This study investigates the pivotal role of Nuclear factor-erythroid 2–related factor 2 (NRF2) in the activation of DNA damage repair in lung cancer cells after x-rays exposure. To explore the NRF2 activation after ionizing irradiations, this study uses a knockdown of NRF2, which shows potential DNA damage after x-rays irradiation in lung cancers. This work further shows that NRF2 knockdown disrupts damaged DNA repair by inhibiting DNA-dependent protein kinase catalytic subunit. At the same time, NRF2 knockdown by shRNA considerably disparate homologous recombination by interfering with Rad51 expression. Further investigation of the associated pathway reveals that NRF2 activation mediates DNA damage response via the mitogen-activated protein kinase (MAPK) pathway as the knockout of NRF2 directly enhances intracellular MAPK phosphorylation. Similarly, both N-acetylcysteineand constitutive knockout of NRF2 disrupt DNA-dependent protein kinase catalytic subunit, while NRF2 knockout failed to upregulate Rad51 expression after irradiation in-vivo. Taken together, these findings advocate NRF2 plays a critical role in the development of radioresistance by upregulating DNA damage response via the MAPK pathway, which can be of great significance.

Abstract 5793: Met confers radioresistance-associated aggressiveness through enhancing PLXDC2-mediated cancer stem cell plasticity

Abstract The development of radioresistance in head and neck squamous cell carcinoma (HNSCC) remains a significant problem in cancer treatment, contributing to the lack of improvement in survival trends in the past decades. One of the clinical challenges is that radioresistance often promotes tumor aggressiveness. However, the underlying mechanisms and molecular determinants are largely unknown. We report here that radioresistance-associated HNSCC aggressiveness is effectively exacerbated by c-Met but can be suppressed by its genetic knockdown and pharmacological inactivation. Through unbiased RNAseq data, we further uncovered that the resulting upregulation of c-Met signaling increases the expression of PLXDC2. a critical gene associated with the tumor microenvironment. Mechanistically, PLXDC2 is upregulated in radioresistant HNSCC cells through c-Met mediated activation of ERK1/2-ELK1 signaling cascade. Most importantly, PLXDC2 modulates cancer cell plasticity by inducing epithelial-mesenchymal transition (EMT) and the emergence of cancer stem cell (CSC) subpopulation. Additionally, depletion of PLXDC2 overcomes c-Met-mediated radioresistance by reversing the EMT progress and blunting the self-renewal capacity of CSCs. Therapeutically, a combination of the c-Met selective inhibitor SU11274 with radiation remarkably induces tumor shrinkage and constrains tumor metastasis to lymph nodes in vivo. Our study is novel in being the first to explore the role and mechanism of the c-Met-PLXDC2 axis in radioresistance-associated HNSCC aggressiveness and the first to our knowledge to evaluate how to take advantage of blocking this signaling to overcome radioresistance in preclinical mouse models of HNSCC. Citation Format: Fanghui Chen, Liwei Lang, Chloe Shay, Georgia Chen, Nabil Saba, Yong Teng. Met confers radioresistance-associated aggressiveness through enhancing PLXDC2-mediated cancer stem cell plasticity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5793.

Insights into the characteristics of primary radioresistant cervical cancer using single-cell transcriptomics

Radioresistance is a major cause of radiotherapy failure among patients with cervical cancer (CC), the fourth most common cause of cancer mortality in women worldwide. Traditional CC cell lines lose intra-tumoral heterogeneity, posing a challenge for radioresistance research. Meanwhile, conditional reprogramming (CR) maintains intra-tumoral heterogeneity and complexity, as well as the genomic and clinical characteristics of original cells and tissues. Three radioresistant and two radiosensitive primary CC cell lines were developed under CR conditions from patient specimens, and their characteristics were verified via immunofluorescence, growth kinetics, clone forming assay, xenografting, and immunohistochemistry. The CR cell lines had homogenous characteristics with original tumor tissues and maintained radiosensitivity in vitro and in vivo, while also maintaining intra-tumoral heterogeneity according to single-cell RNA sequencing analysis. Upon further investigation, 20.83% of cells in radioresistant CR cell lines aggregated in the G2/M cell cycle phase, which is sensitive to radiation, compared to 38.1% of cells in radiosensitive CR cell lines. This study established three radioresistant and two radiosensitive CC cell lines through CR, which will benefit further research investigating radiosensitivity in CC. Our present study may provide an ideal model for research on development of radioresistance and potential therapeutic targets in CC.

Depletion of SOD2 enhances nasopharyngeal carcinoma cell radiosensitivity via ferroptosis induction modulated by DHODH inhibition

BackgroundRecurrence due to the development of radioresistance remains a major challenge in the clinical management of nasopharyngeal carcinoma. The objective of this study was to increase the sensitivity of nasopharyngeal carcinoma cells to ionizing radiation by enhancing oxidative stress and ferroptosis caused by disrupting the mitochondrial anti-oxidant enzyme system.MethodsOxidative stress cell model was constructed by SOD2 knockdown using shRNA. The expression and activity of DHODH was suppressed by siRNA and brequinar in SOD2 depleted cells. Protein levels were determined by western blotting and ferroptosis was assessed by C11 BODIPY and malondialdehyde assay. Cell viability was evaluated using CCK-8 assay while radiotoxicity was assessed by colony formation assay. Cellular ATP level was determined by ATP assay kits, ROS was determined by DCFD and DHE, while mitochondrial oxygen consumption was determined by seahorse assay. Data were analyzed by two-tailed independent t-test.ResultsRadiation upregulated SOD2 expression and SOD2 depletion increased cellular O2.−, malondialdehyde, and the fluorescence intensity of oxidized C11 BODIPY. It also resulted in mitochondrial damage. Its depletion decreased colony formation both under ionizing and non-ionizing radiation conditions. The ferroptosis inhibitor, deferoxamine, rescued cell viability and colony formation in SOD2 depleted cells. Cellular level of malondialdehyde, fluorescence intensity of oxidized C11 BODIPY, O2.− level, ATP, and mitochondrial oxygen consumption decreased following DHODH inhibition in SOD2 depleted cells. Cell viability and colony formation was rescued by DHODH inhibition in SOD2 depleted cells.ConclusionInducing oxidative stress by SOD2 inhibition sensitized nasopharyngeal carcinoma cells to ionizing radiation via ferroptosis induction. This was found to be dependent on DHODH activity. This suggests that DHODH inhibitors should be used with caution during radiotherapy in nasopharyngeal carcinoma patients.

Oxymatrine inhibits the development of radioresistance in NSCLC cells by reversing EMT through the DcR3/AKT/GSK-3β pathway

IntroductionLung cancer is the leading cause of cancer-associated mortality globally. In particular, non-small cell lung cancer (NSCLC) constitutes the largest percentage of all cases of lung cancer. In clinical practice, radioresistance contributes to poor responses to radiotherapy. Therefore, the demand remains to explore potential novel and effective mechanism underlying radioresistance to improve the efficacy of radiotherapy for NSCLC.Material and methodsWestern blotting was conducted to quantify the protein expression of epithelial-mesenchymal transition markers E-cadherin and vimentin in the A549 cell line. The proliferation of A549 cells was measured using the Cell Counting Kit-8 and colony forming assays. In addition, the apoptosis of A549 cells was analyzed by flow cytometry. Invasion and migration by NSCLC cells was quantified using Transwell and wound healing assays. Plasmids were used to overexpress decoy receptor 3 (DcR3) in A549 cells. Xenograft models were established to measure the extent of NSCLC tumor growth in vivo.ResultsOur study clarified the activation of the DcR3/protein kinase B (AKT)/glycogen synthase kinase 3β (GSK-3β) pathway in radioresistant NSCLC cells. Oxymatrine (OMT) treatment restored radiosensitivity and inhibited irradiation-induced epithelial-mesenchymal transition (EMT), invasion and migration in NSCLC cells through the DcR3/AKT/GSK-3β pathway in vitro. By contrast, OMT treatment promoted the suppressive effects of radiation on the weight and volume of the xenograft tumors in animal models.ConclusionsIn conclusion, OMT suppressed the development of radioresistance in NSCLC cells by promoting radiosensitivity, through the reversal of EMT process by inhibiting the DcR3/AKT/GSK-3β pathway.

Mechanisms of radioresistance and the underlying signaling pathways in colorectal cancer cells

Radiotherapy is one of the most common modalities for the treatment of a wide range of tumors, including colorectal cancer (CRC); however, radioresistance of cancer cells remains a major limitation for this treatment. Following radiotherapy, the activities of various cellular mechanisms and cell signaling pathways are altered, resulting in the development of radioresistance, which leads to therapeutic failure and poor prognosis in patients with cancer. Furthermore, even though several inhibitors have been developed to target tumor resistance, these molecules can induce side effects in nontumor cells due to low specificity and efficiency. However, the role of these mechanisms in CRC has not been extensively studied. This review discusses recent studies regarding the relationship between radioresistance and the alterations in a series of cellular mechanisms and cell signaling pathways that lead to therapeutic failure and tumor recurrence. Our review also presents recent advances in the in vitro/in vivo study models aimed at investigating the radioresistance mechanism in CRC. Furthermore, it provides a relevant biochemical basis in theory, which can be useful to improve radiotherapy sensitivity and prolong patient survival.

The miR-34a-5p-c-MYC-CHK1/CHK2 Axis Counteracts Cancer Stem Cell-Like Properties and Enhances Radiosensitivity in Hepatocellular Cancer Through Repression of the DNA Damage Response.

Radiotherapy has become an increasingly widespread modality for treating hepatocellular cancer (HCC); however, the development of radioresistance significantly limits its effectiveness and invariably leads to tumor recurrence. Cancer stem cell (CSC) theory offers a potential explanation for tumor relapse and radioresistance, but the underlying mechanism remains unknown. Herein we investigate the role of miRNA in molecular regulation of stemness and radioresistance in HCC. Two HCC radiation-resistant cell lines (Huh7-RR and SMMC-7721-RR) were established by selecting the radioresistant subpopulation from HCC cells via clonogenic survival assays. MiRNA Sequencing was used to identify potential radiosensitivity involved miRNA in HCC-RR cells. Xenograft tumor mouse model was established for in vivo study. CSC properties were assessed using sphere formation assay and side population (SP) cells analysis. We found that miR-34a-5p was significantly downregulated in HCC-RR cells. Overexpression of miR-34a-5p counteracts CSC properties and enhances radiosensitivity in HCC. Mechanistic investigation revealed that c-MYC is the direct target of miR-34a-5p. Overexpression of miR-34a-5p reversed c-MYC-induced radioresistance. Moreover, we found that the specific molecular mechanism was that c-MYC activated CHK1 and CHK2, which are two key DNA damage checkpoint kinases, and facilitated the DNA damage response to radiation. Repression of the miR-34a-5p-cMYC-CHK1/CHK2 axis contributes to the acquisition of radioresistance in HCC cells. In summary, the miR-34a-5p-c-MYC-CHK1/CHK2 axis counteracts cancer stem cell-like properties and enhances radiosensitivity in hepatocellular cancer through repression of the DNA damage response.

Enzymatic Digestion of Cell-surface Heparan Sulfate Alters the Radiation Response in Triple-negative Breast Cancer Cells

Radiation resistance represents a major challenge in the treatment of breast cancer. As heparan sulfate (HS) chains are known to contribute to tumorigenesis, we aimed to investigate the interplay between HS degradation and radiation response in triple-negative breast cancer (TNBC) cells. HS chains were degraded in vitro as TNBC cells MDA-MB-231 and HCC1806 were treated with heparinase I and III. Subsequently, radioresistance was determined via colony formation assay after doses of 2, 4 and 6 Gy. Cell cycle profile, stem cell characteristics, expression of HS, activation of beta integrins, and apoptosis were determined by flow cytometry. Additionally, cell motility was analyzed via wound-healing assays, and expression and activation of FAK, CDK-6, Src, and Erk1/2 were quantified by western blot pre- and post-irradiation. Finally, the expression of cytokines was analyzed using a cytokine array. Radiation promoted cell cycle changes, while heparinase treatment induced apoptosis in both cell lines. Colony formation assays showed significantly increased radio-resistance for both cell lines after degradation of HS. Cell migration was similarly upregulated after degradation of HS compared to controls. This effect was even more prominent after irradiation. Interestingly, FAK, a marker of radioresistance, was significantly activated in the heparinase-treated group. Additionally, we found Src to be dysregulated in MDA-MB-231 cells. Finally, we observed differential secretion of GRO, CXCL1, IGFBP1, IL8, Angiogenin, and Osteoprotegerin after HS degradation and radiotherapy. Our results suggest an influence of HS chains on the development of radioresistance in TNBC.