Radiation-induced signaling pathways that promote cancer cell survival (review)

Iodine-125 seed inhibits proliferation and promotes apoptosis of cholangiocarcinoma cells by inducing the ROS/p53 axis

With advances in radioactive particle implantation in clinical practice, Iodine-125 (125I) seed brachytherapy has emerged as a promising treatment for cholangiocarcinoma (CCA), showing good prognosis; however, the underlying molecular mechanism of the therapeutic effect of 125I seed is unclear. To study the effects of 125I seed on the proliferation and apoptosis of CCA cells. CCA cell lines, RBE and HCCC-9810, were treated with reactive oxygen species (ROS) scavenger acetylcysteine (NAC) or the p53 functional inhibitor, pifithrin-α hydrobromide (PFTα). Cell counting kit-8 (CCK-8) assay, 5-bromo-2-deoxy-uridine (BrdU) staining, and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay and flow cytometry assay were performed to test the radiation-sensitivity of 125I seed toward CCA cells at different radiation doses (0.4 mCi and 0.8 mCi). 2,7-dichlorofluorescein diacetate (DCF-DA) assay, real-time quantitative polymerase chain reaction (RT-qPCR), and western blot analysis were performed to assess the effect of 125I seed on the ROS/p53 axis. A dose-dependent inhibitory effect of 125I seeds on the proliferation of CCA cells was observed. The 125I seed promoted apoptosis of CCA cells and induced the activation of the ROS/p53 pathway in a dose-dependent manner. NAC or PFTα treatment effectively reversed the stimulatory effect of 125I seed on the proliferation of CCA cells. NAC or PFTα suppressed apoptosis and p53 protein expression induced by the 125I seed. 125I seed can inhibit cell growth mainly through the apoptotic pathway. The mechanism may involve the activation of p53 and its downstream apoptotic pathway by up-regulating the level of ROS in cells.

Radiosensitizing effects of heparinized magnetic iron oxide nanoparticles in colon cancer

The combination of radiation treatment and chemotherapy is currently the standard for management of cancer patients. However, safe doses do not often provide effective therapy, then pre-treated patients are forced to repeat treatment with often already increased tumor resistance to drugs and irradiation. One of the solutions we suggest is to improve primary course of radiation treatment via enhancing radiosensitivity of tumors by magnetic-guided iron oxide nanoparticles (magnetite). We obtained spherical heparinized iron oxide nanoparticles (hIONPs, ∼20 nm), characterized it by TEM, Infrared spectroscopy and DLS. Then hIONPs cytotoxicity was assessed for colon cancer cells (XTT assay) and cellular uptake of nanoparticles was analyzed with X-ray fluorescence. Combination of ionizing radiation (IR) and hIONPs in vitro caused an increase of G2/M arrest of cell cycle, mitotic errors and decrease in survival (compared with samples exposed to IR and hIONPs separately). The promising results were shown for magnetic-guided hIONPs in CT26-grafted BALB/C mice: the combination of intravenously administrated hIONPs and IR showed 20,8% T/C ratio (related to non-treated mice), while single radiation had no shown significant decrease in tumor growth (72,4%). Non-guided by magnets hIONPs with IR showed 57,9% of T/C. This indicates that ultra-small size and biocompatible molecule are not the key to successful nano-drug design, in each case, delivery technologies need to be improved when transferred to in vivo model.

Possibility of nanostructured lipid carriers encapsulating astaxanthin from Haematococcus pluvialis to alleviate skin injury in radiotherapy

PURPOSE

The study aimed to protect patients' skin against ionizing irradiation during radiotherapy by using astaxanthin-encapsulated nanostructured lipid carriers (NLC-ATX).

MATERIALS AND METHODS

NLC-ATX was prepared by a combined method of hot homogenization and sonication. Cytotoxicity of NLC-ATX was evaluated by MTT colorimetric assay. The in vitro radioprotection of NLC-ATX for human fibroblast (HF) cells was investigated based on the level of ROS (reactive oxygen species), DNA damage, and cell death caused by X-irradiation. In addition, the in vivo radioprotection was evaluated based on the appearance and histological structure of the irradiated skin.

RESULTS

NLC-ATX was successfully prepared, with a mean particle size, zeta potential, and encapsulation efficiency of 114.4 nm, -34.1 mV, and 85.67%, respectively. Compared to the control, NLC-ATX, at an optimum ATX concentration under in vitro condition, reduced the amount of generated ROS and DNA damage of 81.6% and 41.6%, respectively, after X-radiation, resulting in a significant decrease in cell death by 62.69%. Under in vivo condition, after the 9th day of X-irradiation (equivalent to an accumulated dose of 14 Gy), the dorsal skin of five out of six NLC-ATX-untreated mice exhibited grade-1 skin damage, according to CTCAE v5.0, while treatment with NLC-ATX protected 6/6 mice from acute skin damage. Moreover, on the 28th day after the first X-irradiation, the histological images illustrated that NLC-ATX at an ATX concentration of 0.25 µg/mL exhibited good recovery of the skin, with barely any difference noted in the collagen fibers and sebaceous glands compared to normal skin.

CONCLUSIONS

NLC-ATX shows potential for application in skin protection against adverse effects of ionizing rays during radiotherapy.

Crosstalk between Oxidative Stress and Inflammation Induced by Ionizing Radiation in Healthy and Cancerous Cells

Radiotherapy (RT) is a unique modality in cancer treatment with no replacement in many cases and uses a tumoricidal dose of various ionizing radiation (IR) types to kill cancer cells. It causes oxidative stress through reactive oxygen species (ROS) production or the destruction of antioxidant systems. On the other hand, RT stimulates the immune system both directly and indirectly by releasing danger signals from stress-exposed and dying cells. Oxidative stress and inflammation are two reciprocal and closely related mechanisms, one induced and involved by the other. ROS regulates the intracellular signal transduction pathways, which participate in the activation and expression of pro-inflammatory genes. Reciprocally, inflammatory cells release ROS and immune system mediators during the inflammation process, which drive the induction of oxidative stress. Oxidative stress or inflammation-induced damages can result in cell death (CD) or survival mechanisms that may be destructive for normal cells or beneficial for cancerous cells. The present study has focused on the radioprotection of those agents with binary effects of antioxidant and anti-inflammatory mechanisms IR-induced CD.

Long noncoding RNA LINC00173 induces radioresistance in nasopharyngeal carcinoma via inhibiting CHK2/P53 pathway

Radiotherapy is the backbone of nasopharyngeal carcinoma (NPC), nearly 11-17% NPC patients suffered local relapse and 18-37% suffered distant metastasis mainly due to radioresistance. Therefore, the key of improving patients' survivals is to investigate the mechanism of radioresistance. In this study, we revealed that the expression level of long intergenic nonprotein coding RNA 173 (LINC00173) was significantly increased in the radioresistant NPC patients' tumour tissues compared with the radiosensitive patients by RNA-sequencing, which also predict poor prognosis in NPC. Overexpression of LINC00173 induced radioresistance of NPC cells in vitro and in vivo. Mechanistically, LINC00173 bound with checkpoint kinase 2 (CHK2) in nucleus, and impaired the irradiation-induced CHK2 phosphorylation, then suppressed the activation of P53 signalling pathway, which eventually inhibiting apoptosis and leading to radioresistance in NPC cells. In summary, LINC00173 decreases the occurrence of apoptosis through inhibiting the CHK2/P53 pathway, leads to NPC radioresistance and could be considered as a novel predictor and therapeutic target in NPC.

Emulsion Technology in Nuclear Medicine: Targeted Radionuclide Therapies, Radiosensitizers, and Imaging Agents

Radiopharmaceuticals serve as a major part of nuclear medicine contributing to both diagnosis and treatment of several diseases, especially cancers. Currently, most radiopharmaceuticals are based on small molecules with targeting ability. However, some concerns over their stability or non-specific interactions leading to off-target localization are among the major challenges that need to be overcome. Emulsion technology has great potential for the fabrication of carrier systems for radiopharmaceuticals. It can be used to create particles with different compositions, structures, sizes, and surface characteristics from a wide range of generally recognized as safe (GRAS) materials, which allows their functionality to be tuned for specific applications. In particular, it is possible to carry out surface modifications to introduce targeting and stealth properties, as well as to control the particle dimensions to manipulate diffusion and penetration properties. Moreover, emulsion preparation methods are usually simple, economic, robust, and scalable, which makes them suitable for medical applications. In this review, we highlight the potential of emulsion technology in nuclear medicine for developing targeted radionuclide therapies, for use as radiosensitizers, and for application in radiotracer delivery in gamma imaging techniques.

Gold nanoparticles enhances radiosensitivity in glioma cells by inhibiting TRAF6/NF-κB induced CCL2 expression

Gliomas are inherently difficult to treat by radiotherapy because glioma cells become radioresistant over time. However, combining radiotherapy with a radiosensitizer could be an effective strategy to mitigate the radioresistance of glioma cells. Gold nanoparticles (AuNPs) have emerged as a promising nanomaterial for cancer therapy, but little is known about whether AuNPs and X-ray radiation have cytotoxic synergistic effects against tumors. In this study, we found that the combination of AuNPs and X-ray irradiation significantly reduced the viabilities, as well as the migration and invasion, of glioma cells. Mechanistically, we observed that the AuNPs inhibited radiation-induced CCL2 expression by inhibiting the TRAF6/NF-κB pathway, which likely manifested the synergistic therapeutic effect between the AuNPs and X-ray radiation. The AuNPs also re-sensitized radioresistant glioma cells by inhibiting CCL2 expression. These results were also observed in another tumor cell line with a different molecular pattern, indicating that the underlying mechanism may be ubiquitous through cancer cells. Lastly, using the glioma mouse model, we observed that AuNPs significantly reduced tumor growth in the presence of X-ray radiation compared to radiotherapy alone.

Identification of a three-gene prognostic signature for radioresistant esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is causing a high mortality rate due to the lack of efficient early prognosis markers and suitable therapeutic regimens. The prognostic role of genes responsible for the acquisition of radioresistance in ESCC has not been fully elucidated.

AIM

To establish a prognostic model by studying gene expression patterns pertinent to radioresistance in ESCC patients.

METHODS

Datasets were obtained from the Gene Expression Omnibus and The Cancer Genome Atlas databases. The edgeR, a Bioconductor package, was used to analyze mRNA expression between different groups. We screened genes specifically responsible for radioresistance to estimate overall survival. Pearson correlation analysis was performed to confirm whether the expression of those genes correlated with each other. Genes contributing to radioresistance and overall survival were assessed by the multivariate Cox regression model through the calculation of βi and risk score using the following formula: .

RESULTS

We identified three prognostic mRNAs (cathepsin S [CTSS], cluster of differentiation 180 [CD180], and SLP adapter and CSK-interacting membrane protein [SCIMP]) indicative of radioresistance. The expression of the three identified mRNAs was related to each other (r > 0.70 and P < 0.05). As to 1-year and 3-year overall survival prediction, the area under the time-dependent receiver operating characteristic curve of the signature consisting of the three mRNAs was 0.716 and 0.841, respectively. When stratifying patients based on the risk score derived from the signature, the high-risk group exhibited a higher death risk and shorter survival time than the low-risk group (P < 0.0001). Overall survival of the low-risk patients was significantly better than that of the high-risk patients (P = 0.018).

CONCLUSION

We have developed a novel three-gene prognostic signature consisting of CTSS, CD180, and SCIMO for ESCC, which may facilitate the prediction of early prognosis of this malignancy.

MicroRNAs Contribute to Host Response to Coxiella burnetii

MicroRNAs (miRNAs), a class of small noncoding RNAs, are critical to gene regulation in eukaryotes. They are involved in modulating a variety of physiological processes, including the host response to intracellular infections. Little is known about miRNA functions during infection by Coxiella burnetii, the causative agent of human Q fever. This bacterial pathogen establishes a large replicative vacuole within macrophages by manipulating host processes such as apoptosis and autophagy. We investigated miRNA expression in C. burnetii-infected macrophages and identified several miRNAs that were down- or upregulated during infection. We further explored the functions of miR-143-3p, an miRNA whose expression is downregulated in macrophages infected with C. burnetii, and show that increasing the abundance of this miRNA in human cells results in increased apoptosis and reduced autophagy-conditions that are unfavorable to C. burnetii intracellular growth. In sum, this study demonstrates that C. burnetii infection elicits a robust miRNA-based host response, and because miR-143-3p promotes apoptosis and inhibits autophagy, downregulation of miR-143-3p expression during C. burnetii infection likely benefits the pathogen.

Chrysophanol-Induced Autophagy Disrupts Apoptosis via the PI3K/Akt/mTOR Pathway in Oral Squamous Cell Carcinoma Cells

Background and Objectives: Natural products are necessary sources for drug discovery and have contributed to cancer chemotherapy over the past few decades. Furthermore, substances derived from plants have fewer side effects. Chrysophanol is an anthraquinone derivative that is isolated from rhubarb. Although the anticancer effect of chrysophanol on several cancer cells has been reported, studies on the antitumor effect of chrysophanol on oral squamous-cell carcinoma (OSCC) cells have yet to be elucidated. Therefore, in this study, we investigated the anticancer effect of chrysophanol on OSCC cells (CAL-27 and Ca9-22) via apoptosis and autophagy, among the cell death pathways. Results: It was found that chrysophanol inhibited the growth and viability of CAL-27 and Ca9-22 and induced apoptosis through the intrinsic pathway. It was also found that chrysophanol activates autophagy-related factors (ATG5, beclin-1, and P62/SQSTM1) and LC3B conversion. That is, chrysophanol activated both apoptosis and autophagy. Here, we focused on the roles of chrysophanol-induced apoptosis and the autophagy pathway. When the autophagy inhibitor 3-MA and PI3K/Akt inhibitor were used to inhibit the autophagy induced by chrysophanol, it was confirmed that the rate of apoptosis significantly increased. Therefore, we confirmed that chrysophanol induces apoptosis and autophagy at the same time, and the induced autophagy plays a role in interfering with apoptosis processes. Conclusions: Therefore, the potential of chrysophanol as an excellent anticancer agent in OSCC was confirmed via this study. Furthermore, the combined treatment of drugs that can inhibit chrysophanol-induced autophagy is expected to have a tremendous synergistic effect in overcoming oral cancer.

Targeting Na-H exchanger 1 overcomes nuclear factor kappa B-mediated tumor resistance to radiotherapy

Intrinsic or acquired radioresistance often limits the efficacy of radiation therapy (RT), thereby leading to local control failure. Cancerous cells have abnormal pH dynamics due to high metabolic demands, but it is unclear how pH dynamics contribute to radioresistance. In this study, we investigated the role of Na-H exchange 1 (NHE1), the major intracellular pH (pH_i) regulator, in RT response. We observed that RT increased NHE1 expression and modulated pH_i in MDA-MB-231 human breast cancer cells. When combined with RT, pharmacological NHE1 inhibition by 5-(N-Ethyl-N-isopropyl)amiloride (EIPA) reduced pH_i and clonogenic survival. EIPA attenuated radiation-damaged DNA repair, increasing G2/M cell cycle arrest. The combination of EIPA and RT increased apoptotic cell death while decreasing phosphorylation of NF-κB p65. Similarly, the knockdown of NHE1 increased radiosensitivity with lower pH_i and increased apoptosis. Consistent with in vitro data, the EIPA plus RT inhibited the growth of MDA-MB-231 xenograft tumors in mice to a greater extent than either EIPA or RT alone. EIPA abrogated the RT-induced increase in NHE1 and phospho-NF-κB p65 expression in tumor tissues. Such coincidence of increased NHE1 level, pH_i, and NF-κB activation was also found in radioresistant MDA-MB-231 cells, which were reversed by EIPA treatment. Bioinformatics analysis of RNA sequencing data revealed that inhibiting NHE1 reversed three core gene networks that were up-regulated in radioresistant cells and correlated with high NHE1 expression in patient samples: NF-κB, senescence, and extracellular matrix. Taken together, our findings suggest that NHE1 contributes to RT resistance via NF-κB-mediated signaling networks, and NHE1 may be a promising target for improving RT outcomes.

Glioblastoma cells have increased capacity to repair radiation-induced DNA damage after migration to the olfactory bulb

BACKGROUND

The invasive nature of GBM combined with the diversity of brain microenvironments creates the potential for a topographic heterogeneity in GBM radioresponse. Investigating the mechanisms responsible for a microenvironment-induced differential GBM response to radiation may provide insights into the molecules and processes mediating GBM radioresistance.

METHODS

Using a model system in which human GBM stem-like cells implanted into the right striatum of nude mice migrate throughout the right hemisphere (RH) to the olfactory bulb (OB), the radiation-induced DNA damage response was evaluated in each location according to γH2AX and 53BP1 foci and cell cycle phase distribution as determined by flow cytometry and immunohistochemistry. RNAseq was used to compare transcriptomes of tumor cells growing in the OB and the RH. Protein expression and neuron-tumor interaction were defined by immunohistochemistry and confocal microscopy.

RESULTS

After irradiation, there was a more rapid dispersal of γH2AX and 53BP1 foci in the OB versus in the RH, indicative of increased double strand break repair capacity in the OB and consistent with the OB providing a radioprotective niche. With respect to the cell cycle, by 6 h after irradiation there was a significant loss of mitotic tumor cells in both locations suggesting a similar activation of the G2/M checkpoint. However, by 24 h post-irradiation there was an accumulation of G2 phase cells in the OB, which continued out to at least 96 h. Transcriptome analysis showed that tumor cells in the OB had higher expression levels of DNA repair genes involved in non-homologous end joining and genes related to the spindle assembly checkpoint. Tumor cells in the OB were also found to have an increased frequency of soma-soma contact with neurons.

CONCLUSION

GBM cells that have migrated to the OB have an increased capacity to repair radiation-induced double strand breaks and altered cell cycle regulation. These results correspond to an upregulation of genes involved in DNA damage repair and cell cycle control. Because the murine OB provides a source of radioresistant tumor cells not evident in other experimental systems, it may serve as a model for investigating the mechanisms mediating GBM radioresistance.

Molecular mechanisms underlying the action of carcinogens in gastric cancer with a glimpse into targeted therapy

BACKGROUND

Gastric cancer imposes a substantial global health burden despite its overall incidence decrease. A broad spectrum of inherited, environmental and infectious factors contributes to the development of gastric cancer. A profound understanding of the molecular underpinnings of gastric cancer has lagged compared to several other tumors with similar incidence and morbidity rates, owing to our limited knowledge of the role of carcinogens in this malignancy. The International Agency for Research on Cancer (IARC) has classified gastric carcinogenic agents into four groups based on scientific evidence from human and experimental animal studies. This review aims to explore the potential comprehensive molecular and biological impacts of carcinogens on gastric cancer development and their interactions and interferences with various cellular signaling pathways.

CONCLUSIONS

In this review, we highlight recent clinical trial data reported in the literature dealing with different ways to target various carcinogens in gastric cancer. Moreover, we touch upon other multidisciplinary therapeutic approaches such as surgery, adjuvant and neoadjuvant chemotherapy. Rational clinical trials focusing on identifying suitable patient populations are imperative to the success of single-agent therapeutics. Novel insights regarding signaling pathways that regulate gastric cancer can potentially improve treatment responses to targeted therapy alone or in combination with other/conventional treatments. Preventive strategies such as control of H. pylori infection through eradication or immunization as well as dietary habit and lifestyle changes may reduce the incidence of this multifactorial disease, especially in high prevalence areas. Further in-depth understanding of the molecular mechanisms involved in the role of carcinogenic agents in gastric cancer development may offer valuable information and update state-of-the-art resources for physicians and researchers to explore novel ways to combat this disease, from bench to bedside. A schematic outlining of the interaction between gastric carcinogenic agents and intracellular pathways in gastric cancer H. pylori stimulates multiple intracellular pathways, including PI3K/AKT, NF-κB, Wnt, Shh, Ras/Raf, c-MET, and JAK/STAT, leading to epithelial cell proliferation and differentiation, apoptosis, survival, motility, and inflammatory cytokine release. EBV can stimulate intracellular pathways such as the PI3K/Akt, RAS/RAF, JAK/STAT, Notch, TGF-β, and NF-κB, leading to cell survival and motility, proliferation, invasion, metastasis, and the transcription of anti-apoptotic genes and pro-inflammatory cytokines. Nicotine and alcohol can lead to angiogenesis, metastasis, survival, proliferation, pro-inflammatory, migration, and chemotactic by stimulating various intracellular signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, ROS, and JAK/STAT. Processed meat contains numerous carcinogenic compounds that affect multiple intracellular pathways such as sGC/cGMP, p38 MAPK, ERK, and PI3K/AKT, leading to anti-apoptosis, angiogenesis, metastasis, inflammatory responses, proliferation, and invasion. Lead compounds may interact with multiple signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, DNA methylation-dependent, and epigenetic-dependent, leading to tumorigenesis, carcinogenesis, malignancy, angiogenesis, DNA hypermethylation, cell survival, and cell proliferation. Stimulating signaling pathways such as PI3K/Akt, RAS/RAF, JAK/STAT, WNT, TGF-β, EGF, FGFR2, and E-cadherin through UV ionizing radiation leads to cell survival, proliferation, and immortalization in gastric cancer. The consequence of PI3K/AKT, NF-κB, Ras/Raf, ROS, JAK/STAT, and WNT signaling stimulation by the carcinogenic component of Pickled vegetables and salted fish is the Warburg effect, tumorigenesis, angiogenesis, proliferation, inflammatory response, and migration.

Radioresistance Mechanisms in Prostate Cancer Cell Lines Surviving Ultra-Hypo-Fractionated EBRT: Implications and Possible Clinical Applications

The use of a higher dose per fraction to overcome the high radioresistance of prostate cancer cells has been unsuccessfully proposed. Herein, we present PC3 and DU-145, castration-resistant prostate cancer cell lines that survived a clinically used ultra-higher dose per fraction, namely, radioresistant PC3 and DU-145 cells (PC3RR and DU-145RR). Compared to PC3, PC3RR showed a higher level of aggressive behaviour, with enhanced clonogenic potential, DNA damage repair, migration ability and cancer stem cell features. Furthermore, compared to PC3, PC3RR more efficiently survived further radiation by increasing proliferation and down-regulating pro-apoptotic proteins. No significant changes of the above parameters were described in DU-145RR, suggesting that different prostate cancer cell lines that survive ultra-higher dose per fraction do not display the same grade of aggressive phenotype. Furthermore, both PC3RR and DU-145RR increased antioxidant enzymes and mesenchymal markers. Our data suggest that different molecular mechanisms could be potential targets for future treatments plans based on sequential strategies and synergistic effects of different modalities, possibly in a patient-tailored fashion. Moreover, PC3RR cells displayed an increase in specific markers involved in bone remodeling, indicating that radiotherapy selects a PC3 population capable of migrating to secondary metastatic sites. Finally, PC3RR cells showed a better sensitivity to Docetaxel as compared to native PC3 cells. This suggests that a subset of patients with castration-resistant metastatic disease could benefit from upfront Docetaxel treatment after the failure of radiotherapy.

Silibinin Radiosensitizes EGF Receptor-knockdown Prostate Cancer Cells by Attenuating DNA Repair Pathways

Emergence of radioresistance in prostate cancer (PCa) cells is a major obstacle in cancer therapy and contributes to the relapse of the disease. EGF receptor (EGFR) signaling plays an important role in the development of radioresistance. Herein, we have assessed the modulatory effects of silibinin on radiation-induced resistance via DNA repair pathways in EGFR-knockdown DU145 cells. shRNA-based silencing of EGFR was done in radioresistant human PCa DU145 cells and effects of ionizing radiation (IR) and silibinin were assessed using clonogenic and trypan blue assays. Furthermore, radiosensitizing effects of silibinin on PCa in context with EGFR were analyzed using flow cytometry, comet assay, and immunoblotting. Silibinin decreased the colony formation ability with an increased death of DU145 cells exposed to IR (5 Gray), with a concomitant decrease in Rad51 protein expression. Silibinin (25 μM) augmented the IR-induced cytotoxic effect in EGFR-knockdown PCa cells, along with induction of G2/M phase cell cycle arrest. Further, we studied homologous recombination (HR) and non-homologous end joining (NHEJ) pathways in silibinin-induced DNA double-strand breaks in EGFR-knockdown DU145 cells. Silibinin down-regulated the expression of Rad51 and DNA-dependent protein kinase proteins without any considerable effect on Ku70 and Ku80 in IR-exposed EGFR-knockdown PCa cells. The pro-survival signaling proteins, phospho-extracellular signal-regulated kinases (ERK)1/2, phospho-Akt and phospho-STAT3 were decreased by silibinin in EGFR-deficient PCa cells. These findings suggest a novel mechanism of silibinin-induced radiosensitization of PCa cells by targeting DNA repair pathways, HR and NHEJ, and suppressing the pro-survival signaling pathways, ERK1/2, Akt and STAT3, in EGFR-knockdown PCa cells.

A calpain-6/YAP axis in sarcoma stem cells that drives the outgrowth of tumors and metastases

Sarcomas include cancer stem cells, but how these cells contribute to local and metastatic relapse is largely unknown. We previously showed the pro-tumor functions of calpain-6 in sarcoma stem cells. Here, we use an osteosarcoma cell model, osteosarcoma tissues and transcriptomic data from human tumors to study gene patterns associated with calpain-6 expression or suppression. Calpain-6 modulates the expression of Hippo pathway genes and stabilizes the hippo effector YAP. It also modulates the vesicular trafficking of β-catenin degradation complexes. Calpain-6 expression is associated with genes of the G2M phase of the cell cycle, supports G2M-related YAP activities and up-regulated genes controlling mitosis in sarcoma stem cells and tissues. In mouse models of bone sarcoma, most tumor cells expressed calpain-6 during the early steps of tumor out-growth. YAP inhibition prevented the neoformation of primary tumors and metastases but had no effect on already developed tumors. It could even accelerate lung metastasis associated with large bone tumors by affecting tumor-associated inflammation in the host tissues. Our results highlight a specific mechanism involving YAP transcriptional activity in cancer stem cells that is crucial during the early steps of tumor and metastasis outgrowth and that could be targeted to prevent sarcoma relapse.

Proton-induced DNA damage promotes integration of foreign plasmid DNA into human genome

High-risk human papillomaviruses (HPVs) cause virtually all cervical cancer cases and are also associated with other types of anogenital and oropharyngeal cancers. Normally, HPV exists as a circular episomal DNA in the infected cell. However, in some instances, it integrates into the human genome in such a way as to enable increased expression of viral oncogenes, thereby leading to carcinogenesis. Since viral integration requires breaks in both viral and human genomes, DNA damage likely plays a key role in this critical process. One potentially significant source of DNA damage is exposure to elevated doses of ionizing radiation. Natural background radiation is ubiquitous; however, some populations, including radiological workers, radiotherapy patients, and astronauts, are exposed to significantly higher radiation doses, as well as to different types of radiation such as particle radiation. We hypothesize that ionizing radiation-induced DNA damage facilitates the integration of HPV into the human genome, increasing the risk of developing HPV-related cancers in the exposed population. To test this, we first determined the kinetics of DNA damage in keratinocytes exposed to ionizing radiation (protons) by assessing γ-H2AX foci formation using immunofluorescence (direct damage), and also measured ROS and 8-oxoG levels via DCFDA and Avidin-FITC (indirect damage).As anticipated, direct DNA damage was observed promptly, within 30 min, whereas indirect DNA damage was delayed due to the time required for ROS to accumulate and cause oxidative damage. Although radiation was lethal at high doses, we were able to establish an experimental system where radiation exposure (protons and X-rays) induced DNA damage dose-dependently without causing major cytotoxic effects as assessed by several cytotoxicity assays. Most importantly, we explored the impact of radiation exposure on integration frequency using a clonogenic assay and demonstrated that as predicted, proton-induced DNA damage promotes the integration of HPV-like foreign DNA in oral keratinocytes. Overall, the insights gained from this work enable us to better understand the contribution of radiation exposure and DNA damage to HPV-mediated carcinogenesis and direct us toward strategies aimed at preventing malignancies in HPV-infected individuals.

Novel mechanisms underlying inhibition of inflammation-induced angiogenesis by dexamethasone and gentamicin via PI3K/AKT/NF-κB/VEGF pathways in acute radiation proctitis

Acute radiation proctitis (ARP) is one of the most common complications of pelvic radiotherapy attributed to radiation exposure. The mechanisms of ARP are related to inflammation, angiogenesis, and so on. In this study we evaluated the effect of dexamethasone (DXM) combined with gentamicin (GM) enema on ARP mice, and explored its possible mechanisms by transcriptome sequencing, western blot and immunohistochemistry. C57BL/6 mice were randomly divided into 3 groups: healthy control group, ARP model group, and DXM + GM enema treatment group. ARP mice were established by using a single 6 MV X-ray dose of 27 Gy pelvic local irradiation. Transcriptome sequencing results showed that 979 genes were co-upregulated and 445 genes were co-downregulated in ARP mice compared to healthy mice. According to gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis, we firstly found that PI3K/AKT/NF-κB/VEGF pathways were mostly correlated with the inflammation-induced angiogenesis in ARP mice. PI3K/AKT pathway leads to the activation of NF-κB, which promotes the transcription of VEGF and Bcl-2. Interestingly, symptoms and pathological changes of ARP mice were ameliorated by DXM + GM enema treatment. DXM + GM enema inhibited inflammation by downregulating NF-κB and upregulating AQP3, as well as inhibited angiogenesis by downregulating VEGF and AQP1 in ARP mice. Moreover, DXM + GM enema induced apoptosis by increasing Bax and suppressing Bcl-2. The novel mechanisms may be related to the downregulation of PI3K/AKT/NF-κB/VEGF pathways.

A Study on the Radiosensitivity of Radiation-Induced Lung Injury at the Acute Phase Based on Single-Cell Transcriptomics

Background and Aims

Radiation-induced lung injury (RILI) is the most common complication associated with chest tumors, such as lung and breast cancers, after radiotherapy; however, the pathogenic mechanisms are unclear. Single-cell RNA sequencing has laid the foundation for studying RILI at the cellular microenvironmental level. This study focused on changes during the acute pneumonitis stage of RILI at the cellular microenvironmental level and investigated the interactions between different cell types.

Methods

An acute RILI model in mice and a single-cell transcriptional library were established. Intercellular communication networks were constructed to study the heterogeneity and intercellular interactions among different cell types.

Results

A single-cell transcriptome map was established in a mouse model of acute lung injury. In total, 18,500 single-cell transcripts were generated, and 10 major cell types were identified. The heterogeneity and radiosensitivity of each cell type or subtype in the lung tissues during the acute stage were revealed. It was found that immune cells had higher radiosensitivity than stromal cells. Immune cells were highly heterogeneous in terms of radiosensitivity, while some immune cells had the characteristics of radiation resistance. Two groups of radiation-induced Cd8⁺Mki67⁺ T cells and Cd4⁺Cxcr6⁺ helper T cells were identified. The presence of these cells was verified using immunofluorescence. The ligand-receptor interactions were analyzed by constructing intercellular communication networks. These explained the origins of the cells and revealed that they had been recruited from endothelial cells to the inflammatory site.

Conclusions

This study revealed the heterogeneity of in vivo radiosensitivity of different cell types in the lung at the initial stage post irradiation

Chronically Radiation-Exposed Survivor Glioblastoma Cells Display Poor Response to Chk1 Inhibition under Hypoxia

Glioblastoma is the most malignant primary brain tumor, and a cornerstone in its treatment is radiotherapy. However, tumor cells surviving after irradiation indicates treatment failure; therefore, better understanding of the mechanisms regulating radiotherapy response is of utmost importance. In this study, we generated clinically relevant irradiation-exposed models by applying fractionated radiotherapy over a long time and selecting irradiation-survivor (IR-Surv) glioblastoma cells. We examined the transcriptomic alterations, cell cycle and growth rate changes and responses to secondary radiotherapy and DNA damage response (DDR) modulators. Accordingly, IR-Surv cells exhibited slower growth and partly retained their ability to resist secondary irradiation. Concomitantly, IR-Surv cells upregulated the expression of DDR-related genes, such as CHK1, ATM, ATR, and MGMT, and had better DNA repair capacity. IR-Surv cells displayed downregulation of hypoxic signature and lower induction of hypoxia target genes, compared to naïve glioblastoma cells. Moreover, Chk1 inhibition alone or in combination with irradiation significantly reduced cell viability in both naïve and IR-Surv cells. However, IR-Surv cells’ response to Chk1 inhibition markedly decreased under hypoxic conditions. Taken together, we demonstrate the utility of combining DDR inhibitors and irradiation as a successful approach for both naïve and IR-Surv glioblastoma cells as long as cells are refrained from hypoxic conditions.

Involvement of the NF-κB and PI3K/Akt/mTOR pathways in cell death triggered by stypoldione, an o-quinone isolated from the brown algae Stypopodium zonale

Multiple myeloma (MM) is a clonal plasma cell malignancy that remains incurable to date. Thus, the aims of this study were to evaluate the involvement of the NF-κB and PI3K/Akt/mTOR pathways in the cytotoxicity of stypoldione, an o-quinone isolated from the brown algae Stypopodium zonale, in MM cells (MM1.S). The cytotoxic effect was evaluated in MM1.S cells and peripheral blood mononuclear cells (PBMCs) by MTT assay. The stypoldione reduced the cell viability of MM1.S cells in a concentration and time-dependent manner (IC50 in MM.1S from 2.55 to 5.38 μM). However, it was also cytotoxic to PBMCs, but at a lower range. Additionally, no significant hemolysis was observed even at concentration up to 10 times the IC50 . Apoptotic cell death was confirmed by cell morphology and Annexin V-FITC assay. Stypoldione induced intrinsic and extrinsic apoptosis by increasing FasR expression and reactive oxygen species (ROS) production, inverting the Bax/Bcl-2 ratio, and inducing ΔΨm loss, which resulted in AIF release and caspase-3 activation. It also increased Ki-67 and survivin expression and inhibited the NF-κB and PI3K/Akt/mTOR pathways. These results suggest that stypoldione is a good candidate for the development of new drugs for MM treatment.

Cell Signaling Pathways That Promote Radioresistance of Cancer Cells

Radiation therapy (RT) is a standard treatment for solid tumors and about 50% of patients with cancer, including pediatric cancer, receive RT. While RT has significantly improved the overall survival and quality of life of cancer patients, its efficacy has still been markedly limited by radioresistance in a significant number of cancer patients (intrinsic or acquired), resulting in failure of the RT control of the disease. Radiation eradicates cancer cells mainly by causing DNA damage. However, radiation also concomitantly activates multiple prosurvival signaling pathways, which include those mediated by ATM, ATR, AKT, ERK, and NF-κB that promote DNA damage checkpoint activation/DNA repair, autophagy induction, and/or inhibition of apoptosis. Furthermore, emerging data support the role of YAP signaling in promoting the intrinsic radioresistance of cancer cells, which occurs through its activation of the transcription of many essential genes that support cell survival, DNA repair, proliferation, and the stemness of cancer stem cells. Together, these signaling pathways protect cancer cells by reducing the magnitude of radiation-induced cytotoxicity and promoting radioresistance. Thus, targeting these prosurvival signaling pathways could potentially improve the radiosensitivity of cancer cells. In this review, we summarize the contribution of these pathways to the radioresistance of cancer cells.

Biosensor for deconvolution of individual cell fate in response to ion beam irradiation

Clonogenic survival assay constitutes the gold standard method for quantifying radiobiological effects. However, it neglects cellular radiation response variability and heterogeneous energy deposition by ion beams on the microscopic scale. We introduce "Cell-Fit-HD4D" a biosensor that enables a deconvolution of individual cell fate in response to the microscopic energy deposition as visualized by optical microscopy. Cell-Fit-HD4D enables single-cell dosimetry in clinically relevant complex radiation fields by correlating microscopic beam parameters with biological endpoints. Decrypting the ion beam's energy deposition and molecular effects at the single-cell level has the potential to improve our understanding of radiobiological dose concepts as well as radiobiological study approaches in general.

Features of the cytoprotective effect of selenium nanoparticles on primary cortical neurons and astrocytes during oxygen-glucose deprivation and reoxygenation

The study is aimed at elucidating the effect of selenium nanoparticles (SeNPs) on the death of cells in the primary culture of mouse cerebral cortex during oxygen and glucose deprivation (OGD). A primary cell culture of the cerebral cortex containing neurons and astrocytes was subjected to OGD and reoxygenation to simulate cerebral ischemia-like conditions in vitro. To evaluate the neuroprotective effect of SeNPs, cortical astrocytes and neurons were incubated for 24 h with SeNPs, and then subjected to 2-h OGD, followed by 24-h reoxygenation. Vitality tests, fluorescence microscopy, and real-time PCR have shown that incubation of primary cultured neurons and astrocytes with SeNPs at concentrations of 2.5–10 µg/ml under physiological conditions has its own characteristics depending on the type of cells (astrocytes or neurons) and leads to a dose-dependent increase in apoptosis. At low concentration SeNPs (0.5 µg/ml), on the contrary, almost completely suppressed the processes of basic necrosis and apoptosis. Both high (5 µg/ml) and low (0.5 µg/ml) concentrations of SeNPs, added for 24 h to the cells of cerebral cortex, led to an increase in the expression level of genes Bcl-2, Bcl-xL, Socs3, while the expression of Bax was suppressed. Incubation of the cells with 0.5 µg/ml SeNPs led to a decrease in the expression of SelK and SelT. On the contrary, 5 µg/ml SeNPs caused an increase in the expression of SelK, SelN, SelT, SelP. In the ischemic model, after OGD/R, there was a significant death of brain cells by the type of necrosis and apoptosis. OGD/R also led to an increase in mRNA expression of the Bax, SelK, SelN, and SelT genes and suppression of the Bcl-2, Bcl-xL, Socs3, SelP genes. Pre-incubation of cell cultures with 0.5 and 2.5 µg/ml SeNPs led to almost complete inhibition of OGD/R-induced necrosis and greatly reduced apoptosis. Simultaneously with these processes we observed suppression of caspase-3 activation. We hypothesize that the mechanisms of the protective action of SeNPs involve the activation of signaling cascades recruiting nuclear factors Nrf2 and SOCS3/STAT3, as well as the activation of adaptive pathways of ESR signaling of stress arising during OGD and involving selenoproteins SelK and SelT, proteins of the Bcl-2 family ultimately leading to inactivation of caspase-3 and inhibition of apoptosis. Thus, our results demonstrate that SeNPs can act as neuroprotective agents in the treatment of ischemic brain injuries.

OUP accepted manuscript

Radioresistance is one of the key obstacles that may lead to the failure of cancer treatment. The underlying mechanisms of radioresistance remain largely unknown; however, increasing evidence has shown that long noncoding RNAs (lncRNAs) are involved in radiotherapy resistance of several cancers. In the present study, we demonstrated that radiation-elevated transcript (RET), a newly identified lnRNA, was highly expressed in cancer cells. Knockdown of RET significantly inhibited the proliferation and colony formation of cancer cells and markedly inhibited apoptosis. Furthermore, downregulation of RET in cancer cells significantly inhibited cell growth, decreased colony survival fractions, and promoted apoptosis in response to radiation treatment, indicating a role in radiation resistance. Moreover, RET knockdown significantly increased the expression of γ-H2AX, an indicator of DNA double strand damage, and reversed radiation-induced EMT, both of which contributed to its radiation resistance. In addition, a negative correlation was found between the expression of RET and PTEN. Rescue assays confirmed RET knockdown enhanced radiosensitivity of cancer cells by upregulating the expression of PTEN. Mechanistically, RET positively regulated Slug, a repressor of PTEN transcription, by acting as a molecular sponge of miR-3179. Our present study showed that RET conferred radioresistance by regulating miR-3179/Slug/PTEN axis, indicating that RET may be a potential target for the clinical application in cancer patients with radioresistance.

The ADAM17-directed Inhibitory Antibody MEDI3622 Antagonizes Radiotherapy-induced VEGF Release and Sensitizes Non-Small Cell Lung Cancer for Radiotherapy

The cellular response to ionizing radiation (IR) depends on tumor cell and microenvironmental factors. Here, we investigated the role of IR-induced ADAM17 matrix metalloproteinase activity for the intercellular communication between tumor cells and the tumor vasculature in non-small cell lung cancer (NSCLC) tumor models. Factors shed by ADAM17 from NSCLC tumor cells (A549, H358) and relevant for endothelial cell migration were investigated using transwell migration assays, ELISA, and flow cytometry. Tumor angiogenesis-related endpoints were analyzed with the chorio-allantoic membrane assay and in murine NSCLC tumor models. Efficacy-oriented experiments were performed in a murine orthotopic NSCLC tumor model using irradiation with an image-guided small-animal radiotherapy platform alone and in combination with the novel ADAM17-directed antibody MEDI3622. In vitro, VEGF was identified as the major factor responsible for IR-induced and ADAM17-dependent endothelial cell migration toward attracting tumor cells. IR strongly enhanced tumor cell-associated ADAM17 activity, released VEGF in an ADAM17-dependent manner, and thereby coordinated the communication between tumor and endothelial cells. In vivo, tumor growth and microvessel size and density were strongly decreased in response to the combined treatment modality of IR and MEDI3622 but not by either treatment modality alone and thus suggest that the supra-additive effect of the combined treatment modality is in part due to abrogation of the ADAM17-mediated IR-induced protective effect on the tumor vasculature. Furthermore, we demonstrate that the novel ADAM17-inhibitory antibody MEDI3622 potently improves the radiotherapy response of NSCLC.

Significance

The tumor response to radiotherapy is influenced by several factors of the tumor microenvironment. We demonstrate that inhibition of the sheddase ADAM17 by the novel antibody MEDI3622 reduces IR-induced VEGF release from tumor cells relevant for endothelial cell migration and vasculature protection, thereby enhancing radiotherapy treatment outcome of NSCLC.

Activation of efficient DNA repair mechanisms after photon and proton irradiation of human chondrosarcoma cells

Although particle therapy with protons has proven to be beneficial in the treatment of chondrosarcoma compared to photon-based (X-ray) radiation therapy, the cellular and molecular mechanisms have not yet been sufficiently investigated. Cell viability and colony forming ability were analyzed after X-ray and proton irradiation (IR). Cell cycle was analyzed using flow cytometry and corresponding regulator genes and key players of the DNA repair mechanisms were measured using next generation sequencing, protein expression and immunofluorescence staining. Changes in metabolic phenotypes were determined with nuclear magnetic resonance spectroscopy. Both X-ray and proton IR resulted in reduced cell survival and a G2/M phase arrest of the cell cycle. Especially 1 h after IR, a significant dose-dependent increase of phosphorylated γH2AX foci was observed. This was accompanied with a reprogramming in cellular metabolism. Interestingly, within 24 h the majority of clearly visible DNA damages were repaired and the metabolic phenotype restored. Involved DNA repair mechanisms are, besides the homology directed repair (HDR) and the non-homologous end-joining (NHEJ), especially the mismatch mediated repair (MMR) pathway with the key players EXO1, MSH3, and PCNA. Chondrosarcoma cells regenerates the majority of DNA damages within 24 h. These molecular mechanisms represent an important basis for an improved therapy.

DNA repair inhibitors sensitize cells differently to high and low LET radiation

The aim of this study was to investigate effects of high LET α-radiation in combination with inhibitors of DDR (DNA-PK and ATM) and to compare the effect with the radiosensitizing effect of low LET X-ray radiation. The various cell lines were irradiated with α-radiation and with X-ray. Clonogenic survival, the formation of micronuclei and cell cycle distribution were studied after combining of radiation with DDR inhibitors. The inhibitors sensitized different cancer cell lines to radiation. DNA-PKi affected survival rates in combination with α-radiation in selected cell lines. The sensitization enhancement ratios were in the range of 1.6–1.85 in cancer cells. ATMi sensitized H460 cells and significantly increased the micronucleus frequency for both radiation qualities. ATMi in combination with α-radiation reduced survival of HEK293. A significantly elicited cell cycle arrest in G₂/M phase after co-treatment of ATMi with α-radiation and X-ray. The most prominent treatment effect was observed in the HEK293 by combining α-radiation and inhibitions. ATMi preferentially sensitized cancer cells and normal HEK293 cells to α-radiation. DNA-PKi and ATMi can sensitize cancer cells to X-ray, but the effectiveness was dependent on cancer cells itself. α-radiation reduced proliferation in primary fibroblast without G₂/M arrest.

Radiotherapy in Medulloblastoma-Evolution of Treatment, Current Concepts and Future Perspectives

Simple Summary

Craniospinal irradiation (CSI) is the backbone of medulloblastoma treatment and the first treatment to achieve a cure in many patients. Within the last decades, significant efforts have been made to enhance efficacy in combination with chemotherapy. With this approach, a majority of low- and standard-risk patients can be cured. In parallel, many clinical trials have dealt with CSI-dose reduction and reduction of boost volume in order to decrease long-term toxicity, particularly neurotoxicity. Within these trials, standardized quality assurance has helped to increase the accuracy of treatment and improve prognosis. More recently, advances of radiotherapy techniques such as proton treatment allowed for better sparing of healthy tissue in order to further diminish detrimental long-term effects. Major future challenges are the adaption of radiotherapy regimens to different molecularly defined disease groups alone or together with new targeted agents. Moreover, and even more importantly, innovative combinatorial treatments are needed in high- and very-high risk situations.

Abstract

Medulloblastoma is the most frequent malignant brain tumor in children. During the last decades, the therapeutic landscape has changed significantly with craniospinal irradiation as the backbone of treatment. Survival times have increased and treatments were stratified according to clinical and later molecular risk factors. In this review, current evidence regarding the efficacy and toxicity of radiotherapy in medulloblastoma is summarized and discussed mainly based on data of controlled trials. Current concepts and future perspectives based on current risk classification are outlined. With the introduction of CSI, medulloblastoma has become a curable disease. Due to combination with chemotherapy, survival rates have increased significantly, allowing for a reduction in radiation dose and a decrease of toxicity in low- and standard-risk patients. Furthermore, modern radiotherapy techniques are able to avoid side effects in a fragile patient population. However, high-risk patients remain with relevant mortality and many patients still suffer from treatment related toxicity. Treatment needs to be continually refined with regard to more efficacious combinatorial treatment in the future.

A novel role for apatinib in enhancing radiosensitivity in non-small cell lung cancer cells by suppressing the AKT and ERK pathways

Background

Radioresistance is still the major cause of radiotherapy failure and poor prognosis in patients with non-small cell lung cancer (NSCLC). Apatinib (AP) is a highly selective inhibitor of vascular endothelial growth factor receptor 2 (VEGFR2). Whether and how AP affects radiosensitivity in NSCLC remains unknown. The present study aimed to explore the radiosensitization effect of AP in NSCLC and its underlying mechanism as a radiosensitizer.

Methods

The NSCLC cell lines A549 and LK2 were treated with AP, ionizing radiation (IR), or both AP and IR. Expression of VEGFR2 was analyzed by western blot and RT-PCR. Cell proliferation was measured using CCK-8 and colony formation assays. Apoptosis and cell cycle distribution in NSCLC cells were analyzed by flow cytometry. Nuclear phosphorylated histone H2AX foci immunofluorescence staining was performed to evaluate the efficacy of the combination treatment. Western blot was used to explore the potential mechanisms of action.

Results

AP inhibited cell proliferation in a dose- and time-dependent manner. Flow cytometry analysis indicated that AP significantly increased radiation-induced apoptosis. Colony formation assays revealed that AP enhanced the radiosensitivity of NSCLC cells. AP strongly restored radiosensitivity by increasing IR-induced G2/M phase arrest. AP effectively inhibited repair of radiation-induced DNA double-strand breaks. Western blot analysis showed that AP enhanced radiosensitivity by downregulating AKT and extracellular signal-regulated kinase (ERK) signaling.

Conclusion

Our findings suggest that AP may enhance radiosensitivity in NSCLC cells by blocking AKT and ERK signaling. Therefore, AP may be a potential clinical radiotherapy synergist and a novel small-molecule radiosensitizer in NSCLC. Our study fills a gap in the field of anti-angiogenic drugs and radiosensitivity.

Activation of G protein coupled estrogen receptor prevents chemotherapy-induced intestinal mucositis by inhibiting the DNA damage in crypt cell in an extracellular signal-regulated kinase 1- and 2- dependent manner

Chemotherapy-induced intestinal mucositis (CIM) is a common adverse reaction to antineoplastic treatment with few appropriate, specific interventions. We aimed to identify the role of the G protein coupled estrogen receptor (GPER) in CIM and its mechanism. Adult male C57BL/6 mice were intraperitoneally injected with 5-fluorouracil to establish the CIM model. The selective GPER agonist G-1 significantly inhibited weight loss and histological damage in CIM mice and restored mucosal barrier dysfunction, including improving the expression of ZO-1, increasing the number of goblet cells, and decreasing mucosal permeability. Moreover, G-1 treatment did not alter the antitumor effect of 5-fluorouracil. In the CIM model, G-1 therapy reduced the expression of proapoptotic protein and cyclin D1 and cyclin B1, reversed the changes in the number of TUNEL+ cells, Ki67+ and bromodeoxyuridine+ cells in crypts. The selective GPER antagonist G15 eliminated all of the above effects caused by G-1 on CIM, and application of G15 alone increased the severity of CIM. GPER was predominantly expressed in ileal crypts, and G-1 inhibited the DNA damage induced by 5-fluorouracil in vivo and vitro, as confirmed by the decrease in the number of γH2AX+ cells in the crypts and the comet assay results. Referring to the data from GEO dataset we verified GPER activation restored ERK1/2 activity in CIM and 5-fluorouracil-treated IEC-6 cells. Once the effects of G-1 on ERK1/2 activity were abolished with the ERK1/2 inhibitor PD0325901, the effects of G-1 on DNA damage both in vivo and in vitro were eliminated. Correspondingly, all of the manifestations of G-1 protection against CIM were inhibited by PD0325901, such as body weight and histological changes, the mucosal barrier, the apoptosis and proliferation of crypt cells. In conclusion, GPER activation prevents CIM by inhibiting crypt cell DNA damage in an ERK1/2-dependent manner, suggesting GPER might be a target preventing CIM.

Disulfiram Sensitizes a Therapeutic-Resistant Glioblastoma to the TGF-β Receptor Inhibitor

Despite neurosurgery following radiation and chemotherapy, residual glioblastoma (GBM) cells develop therapeutic resistance (TR) leading to recurrence. The GBM heterogeneity confers TR. Therefore, an effective strategy must target cancer stem cells (CSCs) and other malignant cancer cells. TGF-β and mesenchymal transition are the indicators for poor prognoses. The activity of aldehyde dehydrogenases (ALDHs) is a functional CSC marker. However, the interplay between TGF-β and ALDHs remains unclear. We developed radiation-resistant and radiation-temozolomide-resistant GBM models to investigate the underlying mechanisms conferring TR. Galunisertib is a drug targeting TGF-β receptors. Disulfiram (DSF) is an anti-alcoholism drug which functions by inhibiting ALDHs. The anti-tumor effects of combining DSF and Galunisertib were evaluated by in vitro cell grow, wound healing, Transwell assays, and in vivo orthotopic GBM model. Mesenchymal-like phenotype was facilitated by TGF-β in TR GBM. Additionally, TR activated ALDHs. DSF inhibited TR-induced cell migration and tumor sphere formation. However, DSF did not affect the tumor growth in vivo. Spectacularly, DSF sensitized TR GBM to Galunisertib both in vitro and in vivo. ALDH activity positively correlated with TGF-β-induced mesenchymal properties in TR GBM. CSCs and mesenchymal-like GBM cells targeted together by combining DSF and Galunisertib may be a good therapeutic strategy for recurrent GBM patients.

Macrophage migration inhibitory factor (MIF) inhibitor 4-IPP downregulates stemness phenotype and mesenchymal trans-differentiation after irradiation in glioblastoma multiforme

Radiation therapy is among the most essential treatment methods for glioblastoma multiforme (GBM). Radio-resistance and cancer stem cell properties can cause therapeutic resistance, cancer heterogeneity, and poor prognoses in association with GBM. Furthermore, the GBM subtype transition from proneural to the most malignant mesenchymal subtype after radiation therapy also accounts for high resistance to conventional treatments. Here, we demonstrate that the inhibition of macrophage migration inhibitory factor (MIF) and D-dopachrome tautomerase (DDT) by 4-iodo-6-phenylpyrimidine (4-IPP), a dual inhibitor targeting MIF and DDT, downregulates stemness phenotype, intracellular signaling cascades, mesenchymal trans-differentiation, and induces apoptosis in proneural glioma stem cells (GSCs). In an analysis of The Cancer Genome Atlas, high MIF and DDT expression were associated with poor prognosis. GSC growth was effectively inhibited by 4-IPP in a time- and dose-dependent manner, and 4-IPP combined with radiation therapy led to significantly reduced proliferation compared with radiation therapy alone. The expression of stemness factors, such as Olig2 and SOX2, and the expression of pAKT, indicating PI3K signaling pathway activation, were decreased in association with both 4-IPP monotherapy and combination treatment. The expression of mesenchymal markers, TGM2 and NF-κB, and expression of pERK (indicating MAPK signaling pathway activation) increased in association with radiation therapy alone but not with 4-IPP monotherapy and combination therapy. In addition, the combination of 4-IPP and radiation therapy significantly induced apoptosis compared to the monotherapy of 4-IPP or radiation. In vivo results demonstrated a significant tumor-suppressing effect of 4-IPP when combined with radiation therapy. Collectively, our results showed that the targeted inhibition of MIF and DDT has the potential to strengthen current clinical strategies by enhancing the anticancer effects of radiation therapy.

Understanding the Radiobiology of Vestibular Schwannomas to Overcome Radiation Resistance

Vestibular schwannomas (VS) are benign tumors arising from cranial nerve VIII that account for 8-10% of all intracranial tumors and are the most common tumors of the cerebellopontine angle. These tumors are typically managed with observation, radiation therapy, or microsurgical resection. Of the VS that are irradiated, there is a subset of tumors that are radioresistant and continue to grow; the mechanisms behind this phenomenon are not fully understood. In this review, the authors summarize how radiation causes cellular and DNA injury that can activate (1) checkpoints in the cell cycle to initiate cell cycle arrest and DNA repair and (2) key events that lead to cell death. In addition, we discuss the current knowledge of VS radiobiology and how it may contribute to clinical outcomes. A better understanding of VS radiobiology can help optimize existing treatment protocols and lead to new therapies to overcome radioresistance.

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.

MT1-MMP-dependent ECM processing regulates laminB1 stability and mediates replication fork restart

Radiotherapy remains a mainstay of treatment for a majority of cancer patients. We have previously shown that the membrane bound matrix metalloproteinase MT1-MMP confers radio- and chemotherapy resistance to breast cancer via processing of the ECM and activation of integrinβ1/FAK signaling. Here, we further discovered that the nuclear envelope protein laminB1 is a potential target of integrinβ1/FAK. FAK interacts with laminB1 contributing to its stability. Stable laminB1 is found at replication forks (RFs) where it is likely to allow the proper positioning of RF protection factors, thus preventing RF degradation. Indeed, restoration of laminB1 expression rescues replication fork stalling and collapse that occurs upon MT1-MMP inhibition, and reduces DNA damage in breast cancer cells. Together, these data highlight a novel mechanism of laminB1 stability and replication fork restart via MT1-MMP dependent extracelluar matrix remodeling.

A radiosensitizer, gallotannin-rich extract from Bouea macrophylla seeds, inhibits radiation-induced epithelial-mesenchymal transition in breast cancer cells

Background

Radioresistance can pose a significant obstacle to the effective treatment of breast cancers. Epithelial–mesenchymal transition (EMT) is a critical step in the acquisition of stem cell traits and radioresistance. Here, we investigated whether Maprang seed extract (MPSE), a gallotannin-rich extract of seed from Bouea macrophylla Griffith, could inhibit the radiation-induced EMT process and enhance the radiosensitivity of breast cancer cells.

Methods

Breast cancer cells were pre-treated with MPSE before irradiation (IR), the radiosensitizing activity of MPSE was assessed using the colony formation assay. Radiation-induced EMT and stemness phenotype were identified using breast cancer stem cells (CSCs) marker (CD24^−/low/CD44⁺) and mammosphere formation assay. Cell motility was determined via the wound healing assay and transwell migration. Radiation-induced cell death was assessed via the apoptosis assay and SA-β-galactosidase staining for cellular senescence. CSCs- and EMT-related genes were confirmed by real-time PCR (qPCR) and Western blotting.

Results

Pre-treated with MPSE before irradiation could reduce the clonogenic activity and enhance radiosensitivity of breast cancer cell lines with sensitization enhancement ratios (SERs) of 2.33 and 1.35 for MCF7 and MDA-MB231cells, respectively. Pretreatment of breast cancer cells followed by IR resulted in an increased level of DNA damage maker (γ-H2A histone family member) and enhanced radiation-induced cell death. Irradiation induced EMT process, which displayed a significant EMT phenotype with a down-regulated epithelial marker E-cadherin and up-regulated mesenchymal marker vimentin in comparison with untreated breast cancer cells. Notably, we observed that pretreatment with MPSE attenuated the radiation-induced EMT process and decrease some stemness-like properties characterized by mammosphere formation and the CSC marker. Furthermore, pretreatment with MPSE attenuated the radiation-induced activation of the pro-survival pathway by decrease the expression of phosphorylation of ERK and AKT and sensitized breast cancer cells to radiation.

Conclusion

MPSE enhanced the radiosensitivity of breast cancer cells by enhancing IR-induced DNA damage and cell death, and attenuating the IR-induced EMT process and stemness phenotype via targeting survival pathways PI3K/AKT and MAPK in irradiated breast cancer cells. Our findings describe a novel strategy for increasing the efficacy of radiotherapy for breast cancer patients using a safer and low-cost natural product, MPSE.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03363-6.

Targeting the Y-box Binding Protein-1 Axis to Overcome Radiochemotherapy Resistance in Solid Tumors

Multifunctional Y-box binding protein-1 (YB-1) is highly expressed in different human solid tumors and is involved in various cellular processes. DNA damage is the major mechanism by which radiochemotherapy (RCT) induces cell death. On induction of DNA damage, a multicomponent signal transduction network, known as the DNA damage response, is activated to induce cell cycle arrest and initiate DNA repair, which protects cells against damage. YB-1 regulates nearly all cancer hallmarks described to date by participating in DNA damage response, gene transcription, mRNA splicing, translation, and tumor stemness. YB-1 lacks kinase activity, and p90 ribosomal S6 kinase and AKT are the key kinases within the RAS/mitogen-activated protein kinase and phosphoinositide 3-kinase pathways that directly activate YB-1. Thus, the molecular targeting of ribosomal S6 kinase and AKT is thought to be the most effective strategy for blocking the cellular function of YB-1 in human solid tumors. In this review, after describing the prosurvival effect of YB-1 with a focus on DNA damage repair and cancer cell stemness, clinical evidence will be provided indicating an inverse correlation between YB-1 expression and the treatment outcome of solid tumors after RCT. In the interest of being concise, YB-1 signaling cascades will be briefly discussed and the current literature on YB-1 posttranslational modifications will be summarized. Finally, the current status of targeting the YB-1 axis, especially in combination with RCT, will be highlighted.

Interfering with Tumor Hypoxia for Radiotherapy Optimization

Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.

Cilostazol eliminates radiation-resistant glioblastoma by re-evoking big conductance calcium-activated potassium channel activity

In spite of radio- and chemotherapy, glioblastoma (GBM) develops therapeutic resistance leading to recurrence and poor prognosis. Therefore, understanding the underlying mechanisms of resistance is important to improve the treatment of GBM. To this end, we developed a radiation-resistant cell model by exposure to consecutive periods of irradiation. Simultaneously, single high-dose irradiation was introduced to determine "when" GBM developed consecutive irradiation-induced resistance (CIIR). We found that CIIR promoted TGF-β secretion, activated pro-survival Akt, and downregulated p21 in a p53-independent manner. Furthermore, CIIR upregulated multidrug-resistant proteins, resulting in temozolomide resistance. CIIR GBM also enhanced cell mobility and accelerated cell proliferation. The big-conductance calcium-activated potassium channel (BK channel) is highly expressed and activated in GBM. However, CIIR diminishes BK channel activity in an expression-independent manner. Cilostazol is a phosphodiesterase-3 inhibitor for the treatment of intermittent claudication and was able to reverse CIIR-induced BK channel inactivation. Paxilline, a BK channel blocker, promoted cell migration and proliferation in parental GBM cells. In contrast, Cilostazol inhibited CIIR-induced cell motility, proliferation, and the ability to form tumor spheres. Moreover, we established a radiation-resistant GBM in vivo model by intracranially injecting CIIR GBM cells into the brains of NOD/SCID mice. We found that Cilostazol delayed tumor in vivo growth and prolonged survival. As such, inactivation of the BK channel assists GBM in developing radiation resistance. Accordingly, restoring BK channel activity may be an effective strategy to improve therapeutic efficacy, and cilostazol could be repurposed to treat GBM.

Enhanced KRT13 gene expression bestows radiation resistance in squamous cell carcinoma cells

Cancer metastasis and recurrence are potentially lethal. A small number of cancer cell groups called cancer stem cells (CSCs) have both stem cell capacity and cancer-forming ability and are reported to play important roles in cancer metastasis and recurrence. These CSCs are considered to be radiation-resistant (RR). Therefore, understanding the biological effects of radiation on squamous cell carcinoma (SCC) cell lines in vitro and in vivo might be worthwhile to circumvent radiation resistance. Currently, there are no reports on the establishment of RR-SCC cells in serum-free defined culture, which mimics biological mechanisms and prevents instability of using serum in the culture medium. We isolated radiation-resistant strains, designated A431-LDR and A431-HDR, from A431 cells derived from vulval SCC and irradiated them with a total dose of 60 Gy at a low-dose rate (2.2 Gy/d) (RM1000) and a high-dose rate (5 Gy/5.75min) in serum-free defined culture. These cells exhibited high sphere-forming and migration ability in vitro and high tumor-forming ability in nude mice xenografts. Overexpression of KRT13 in A431-RR cells might play a role in its radiation-resistant characteristics. These cells might be useful not only to study cancer stem cells but also to study the circumvention of radiation resistance by novel cancer treatment modalities.

Prospects for Radiopharmaceuticals as Effective and Safe Therapeutics in Oncology and Challenges of Tumor Resistance to Radiotherapy

The rapid advances in nuclear medicine have resulted in significant advantages for the field of oncology. The focus is on the application of radiopharmaceuticals as therapeuticals. In addition, the latest developments in cell biology (the understanding of the cell structure, function, metabolism, genetics, signaling, transformation) have given a strong scientific boost to radiation oncology. In this regard, the article discusses what is soon going to be a new jump in radiation oncology based on the already accumulated considerable knowledge at the cellular level about the mechanisms of cell transformation and tumor progression, cell response to radiation, cell resistance to apoptosis and radiation and cell radio-sensitivity. The mechanisms of resistance of tumor cells to radiation and the genetically determined individual sensitivity to radiation in patients (which creates the risk of radiation-induced acute and late side effects) are the 2 major challenges to overcome in modern nuclear medicine. The paper focuses on these problems and makes a detailed summary of the significance of the differences in the ionizing properties of radiopharmaceuticals and the principle of their application in radiation oncology that will shed additional light on how to make the anti-cancer radiotherapies more efficient and safe, giving some ideas for optimizations.

Chronic exposure of humans to high level natural background radiation leads to robust expression of protective stress response proteins

Understanding exposures to low doses of ionizing radiation are relevant since most environmental, diagnostic radiology and occupational exposures lie in this region. However, the molecular mechanisms that drive cellular responses at these doses, and the subsequent health outcomes, remain unclear. A local monazite-rich high level natural radiation area (HLNRA) in the state of Kerala on the south-west coast of Indian subcontinent show radiation doses extending from ≤ 1 to ≥ 45 mGy/y and thus, serve as a model resource to understand low dose mechanisms directly on healthy humans. We performed quantitative discovery proteomics based on multiplexed isobaric tags (iTRAQ) coupled with LC–MS/MS on human peripheral blood mononuclear cells from HLNRA individuals. Several proteins involved in diverse biological processes such as DNA repair, RNA processing, chromatin modifications and cytoskeletal organization showed distinct expression in HLNRA individuals, suggestive of both recovery and adaptation to low dose radiation. In protein–protein interaction (PPI) networks, YWHAZ (14-3-3ζ) emerged as the top-most hub protein that may direct phosphorylation driven pro-survival cellular processes against radiation stress. PPI networks also identified an integral role for the cytoskeletal protein ACTB, signaling protein PRKACA; and the molecular chaperone HSPA8. The data will allow better integration of radiation biology and epidemiology for risk assessment [Data are available via ProteomeXchange with identifier PXD022380].

The future potential of Annona muricata L. extract and its bioactive compounds as radiation sensitizing agent: proposed mechanisms based on a systematic review

Despite technological advances in cancer treatment, especially in radiotherapy, many efforts are being made in improving cancer cell radio-sensitivity to increase therapeutic ratio and overcome cancer cell radio-resistance. In the present review, we evaluated the anticancer mechanism of Annona muricata L. (AM) leaves extract and its bioactive compounds such as annonaceous acetogenins, annomuricin, annonacin, or curcumin; and further correlated them with the potential of the mechanism to increase or to reduce cancer cells radio-sensitivity based on literature investigation. We see that AM has a promising future potential as a radio-sensitizer agent.

Inhibition of cell proliferation and radioresistance by miR-383-5p through targeting RNA binding protein motif (RBM3) in nasopharyngeal carcinoma

Background

RNA binding protein motif (RBM3) is associated with radioresistance in nasopharyngeal carcinoma (NPC), and miR-383-5p was predicted to target the 3'-untranslated region (3'UTR) of RBM3 messenger RNA (mRNA). Our study aimed to investigate the role and the mechanisms of miR-383-5p targeting RBM3 in NPC cell proliferation and radioresistance (RR).

Methods

The expression of miR-383-5p was detected by Real-time quantitative PCR (qRT-PCR) between RS (Radiosensitivity) and RR (Radioresistance) NPC patient- tissue specimens and cell lines. Cell Counting Kit-8 (CCK-8) and Clonogenic survival assay were applied to analyze the effect of miR-383-5p on NPC cell proliferation and radioresistance. Possible downstream target of miR-383-5p in NPC cells, RBM3was evaluated by luciferase assay and qRT-PCR. miR-383-5p inhibited NPC cell proliferation and radioresistance through RBM3 by rescue experiments. The effect of miR-383-5p on radiation-induced apoptosis was explored through Flow cytometric analysis and Western blotting. Western blotting was analyzed the molecular of RBM3-mediated Jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) signaling pathways

Results

The expression of miR-383-5p was decreased in radioresistant NPC tissues and cells. miR-383-5p inhibited cell proliferation and radioresistance in CNE1/IR cells. We also observed that therapeutic administration of a miR-383-5p agomir dramatically sensitized NPC xenografts to radiation in a mouse model. Conversely, in the same xenograft model, administration of a miR-383-5p antagomir dramatically increased NPC resistance to radiation. miR-383-5p targeted the 3'UTR of RBM3. miR-383-5p inhibited NPC cell proliferation and radioresistance through RBM3. Finally, we found that miR-383-5p increased radiation-induced apoptosis, activated JNK signaling, and inhibited ERK signaling.

Conclusions

Our study revealed that miR-383-5p targeted the 3'UTR of RBM3 and contributed to the efficacy of NPC radiation therapy by altering the RBM3-mediated JNK and ERK signaling pathways.

A Novel PDE4D Inhibitor BPN14770 Reverses Scopolamine-Induced Cognitive Deficits via cAMP/SIRT1/Akt/Bcl-2 Pathway

A global, quantitative proteomics/systems-biology analysis of the selective pharmacological inhibition of phosphodiesterase-4D (PDE4D) revealed the differential regulation of pathways associated with neuroplasticity in memory-associated brain regions. Subtype selective inhibitors of PDE4D bind in an allosteric site that differs between mice and humans in a single amino acid (tyrosine vs. phenylalanine, respectively). Therefore to study selective inhibition of PDE4D by BPN14770, a subtype selective allosteric inhibitor of PDE4D, we utilized a line of mice in which the PDE4D gene had been humanized by mutating the critical tyrosine to phenylalanine. Relatively low doses of BPN14770 were effective at reversing scopolamine-induced memory and cognitive deficits in humanized PDE4D mice. Inhibition of PDE4D alters the expression of protein kinase A (PKA), Sirt1, Akt, and Bcl-2/Bax which are components of signaling pathways for regulating endocrine response, stress resistance, neuronal autophagy, and apoptosis. Treatment with a series of antagonists, such as H89, sirtinol, and MK-2206, reversed the effect of BPN14770 as shown by behavioral tests and immunoblot analysis. These findings suggest that inhibition of PDE4D enhances signaling through the cAMP-PKA-SIRT1-Akt -Bcl-2/Bax pathway and thereby may provide therapeutic benefit in neurocognitive disorders.

Lead and cadmium exposure induces male reproductive dysfunction by modulating the expression profiles of apoptotic and survival signal proteins in tea-garden workers

The aim of this study was to evaluate the impact of Lead (Pb) and Cadmium (Cd) exposure at the molecular level on the reproductive status of tea garden workers in North-East India. Using semen samples, we experimentally determined sperm analysis as well as oxidative stress parameters in all samples and evaluated the expression levels of apoptotic and cell survival proteins [p53, phospho-Akt, nuclear factor-κB (NF-κB, p50 subunit) and B cell lymphoma 2 (Bcl2)]. Our data revealed significant differences in the average heavy metal concentrations and various semen analysis profile between the infertile and normal groups. Increasing Pb and Cd concentrations in semen samples of patients showed positive associations with increasing number of multiple defects in sperm and the level of seminal oxidative stress markers in the high Pb and Cd concentration groups. These groups also exhibited positive correlations between high metal concentrations and the average p53 expression levels, but negative correlations with the mean p-Akt cascade protein levels in sperm cells. In the low Pb and Cd concentrations groups, we also observed reverse mean range and correlation patterns. Therefore, our findings may suggest that graded levels of metal exposure significantly influence the relative fluctuation in the levels of p53 and Akt cascade proteins in the sperm cells of infertile subjects. Furthermore, this may be a regulating factor of sperm cell fate, in turn, determining the fertility outcome of the men working in the tea gardens.

Radiation-Related Deregulation of TUBB3 and BRCA1/2 and Risk of Secondary Lung Cancer in Women With Breast Cancer

INTRODUCTION

Breast cancer survivors are at increased risk of developing unrelated primary cancers, particularly lung cancer. Evidence indicates that sex hormones as well as a deregulation of DNA-repair pathways may contribute to lung cancer onset. We investigated whether the hormone status and expression of markers involved in DNA repair (BRCA1/2, ERCC1, and P53R2), synthesis (TS and RRM1), and cell division (TUBB3) might be linked to lung cancer risk.

PATIENTS AND METHODS

Thirty-seven breast cancer survivors with unrelated lung cancer and 84 control subjects comprising women with breast cancer (42/84) or lung cancer (42/84) were enrolled. Immunohistochemistry on tumor tissue was performed. Geometric mean ratio was used to assess the association of marker levels with patient groups.

RESULTS

Estrogen receptor was expressed in approximately 90% of the breast cancer group but was negative in the majority of the lung cancer group, a result similar to the lung cancer control group. Likewise, ER isoform β was weakly expressed in the lung cancer group. Protein analysis of breast cancer versus control had a significantly lower expression of BRCA1, P53R2, and TUBB3. Likewise, a BRCA1 reduction was observed in the lung cancer group concomitant with a BRCA2 increase. Furthermore, BRCA2 and TUBB3 increased in ipsilateral lung cancer in women who had previously received radiotherapy for breast cancer.

CONCLUSION

The decrease of DNA-repair proteins in breast cancer could make these women more susceptible to therapy-related cancer. The increase of BRCA2 and TUBB3 in lung cancer from patients who previously received radiotherapy for breast cancer might reflect a tissue response to exposure to ionizing radiation.

Targeting Cullin-RING E3 Ligases for Radiosensitization: From NEDDylation Inhibition to PROTACs

As a dynamic regulator for short-lived protein degradation and turnover, the ubiquitin-proteasome system (UPS) plays important roles in various biological processes, including response to cellular stress, regulation of cell cycle progression, and carcinogenesis. Over the past decade, research on targeting the cullin-RING (really interesting new gene) E3 ligases (CRLs) in the UPS has gained great momentum with the entry of late-phase clinical trials of its novel inhibitors MLN4924 (pevonedistat) and TAS4464. Several preclinical studies have demonstrated the efficacy of MLN4924 as a radiosensitizer, mainly due to its unique cytotoxic properties, including induction of DNA damage response, cell cycle checkpoints dysregulation, and inhibition of NF-κB and mTOR pathways. Recently, the PROteolysis TArgeting Chimeras (PROTACs) technology was developed to recruit the target proteins for CRL-mediated polyubiquitination, overcoming the resistance that develops inevitably with traditional targeted therapies. First-in-class cell-permeable PROTACs against critical radioresistance conferring proteins, including the epidermal growth factor receptor (EGFR), androgen receptor (AR) and estrogen receptor (ER), cyclin-dependent kinases (CDKs), MAP kinase kinase 1 (MEK1), and MEK2, have emerged in the past 5 years. In this review article, we will summarize the most important research findings of targeting CRLs for radiosensitization.