Correction: Zanin et al. Analysis of Radiation Toxicity in Mammalian Cells Stably Transduced with Mitochondrial Stat3. Int. J. Mol. Sci. 2023, 24, 8232.

In the original publication [...].

Analysis of Radiation Toxicity in Mammalian Cells Stably Transduced with Mitochondrial Stat3.

A coordinated action between nuclear and mitochondrial activities is essential for a proper cellular response to genotoxic stress. Several nuclear transcription factors, including STAT3, translocate to mitochondria to exert mitochondrial function regulation; however, the role of mitochondrial STAT3 (mitoSTAT3) under stressed conditions is still poorly understood. In this study, we examined whether the stable expression of mitoSTAT3 wild-type or mutated at the conserved serine residue (Ser727), which is involved in the mitochondrial function of STAT3, can affect the DNA damage response to UVC radiation. To address this issue, we generated mammalian cells (NIH-3T3 and HCT-116 cells) stably transduced to express the mitochondrial-targeted Stat3 gene in its wild-type or Ser727 mutated forms. Our results show that cell proliferation is enhanced in mitoStat3-transduced cells under both non-stressed and stressed conditions. Once irradiated with UVC, cells expressing wild-type mitoSTAT3 showed the highest cell survival, which was associated with a significant decrease in cell death. Low levels of oxidative stress were detected in UVC-irradiated NIH-3T3 cells expressing mitoSTAT3 wild-type or serine-related dominant active form (Ser727D), confirming a role of mitochondrial STAT3 in minimizing oxidant cellular stress that provides an advantage for cell survival.

Biological Mechanisms to Reduce Radioresistance and Increase the Efficacy of Radiotherapy: State of the Art.

Cancer treatment with ionizing radiation (IR) is a well-established and effective clinical method to fight different types of tumors and is a palliative treatment to cure metastatic stages. Approximately half of all cancer patients undergo radiotherapy (RT) according to clinical protocols that employ two types of ionizing radiation: sparsely IR (i.e., X-rays) and densely IR (i.e., protons). Most cancer cells irradiated with therapeutic doses exhibit radio-induced cytotoxicity in terms of cell proliferation arrest and cell death by apoptosis. Nevertheless, despite the more tailored advances in RT protocols in the last few years, several tumors show a relatively high percentage of RT failure and tumor relapse due to their radioresistance. To counteract this extremely complex phenomenon and improve clinical protocols, several factors associated with radioresistance, of both a molecular and cellular nature, must be considered. Tumor genetics/epigenetics, tumor microenvironment, tumor metabolism, and the presence of non-malignant cells (i.e., fibroblast-associated cancer cells, macrophage-associated cancer cells, tumor-infiltrating lymphocytes, endothelial cells, cancer stem cells) are the main factors important in determining the tumor response to IR. Here, we attempt to provide an overview of how such factors can be taken advantage of in clinical strategies targeting radioresistant tumors.

Genomic Changes Driven by Radiation-Induced DNA Damage and Microgravity in Human Cells.

The space environment consists of a complex mixture of different types of ionizing radiation and altered gravity that represents a threat to humans during space missions. In particular, individual radiation sensitivity is strictly related to the risk of space radiation carcinogenesis. Therefore, in view of future missions to the Moon and Mars, there is an urgent need to estimate as accurately as possible the individual risk from space exposure to improve the safety of space exploration. In this review, we survey the combined effects from the two main physical components of the space environment, ionizing radiation and microgravity, to alter the genetics and epigenetics of human cells, considering both real and simulated space conditions. Data collected from studies on human cells are discussed for their potential use to estimate individual radiation carcinogenesis risk from space exposure.

Robust and Biocompatible Functionalization of ZnS Nanoparticles by Catechol-Bearing Poly(2-methyl-2-oxazoline)s.

Zinc sulfide (ZnS) nanoparticles (NPs) are particularly interesting materials for their electronic and luminescent properties. Unfortunately, their robust and stable functionalization and stabilization, especially in aqueous media, has represented a challenging and not yet completely accomplished task. In this work, we report the synthesis of colloidally stable, photoluminescent and biocompatible core-polymer shell ZnS and ZnS:Tb NPs by employing a water-in-oil miniemulsion (ME) process combined with surface functionalization via catechol-bearing poly-2-methyl-2-oxazoline (PMOXA) of various molar masses. The strong binding of catechol anchors to the metal cations of the ZnS surface, coupled with the high stability of PMOXA against chemical degradation, enable the formation of suspensions presenting excellent colloidal stability. This feature, combined with the assessed photoluminescence and biocompatibility, make these hybrid NPs suitable for optical bioimaging.

Analysis of DNA-damage response to ionizing radiation in serum-shock synchronized human fibroblasts.

Many aspects of cellular physiology, including cellular response to genotoxic stress, are related to the circadian rhythmicity induced by the molecular clock. The current study investigated if the cellular response to DNA damage is in relation to endogenous expression levels of the PER2 protein, a key component of the molecular regulatory system that confers rhythmicity in mammalian cells. Human normal fibroblasts (CCD-34Lu) were subjected to serum shock to induce circadian oscillations of the PER2 protein and then irradiated with γ- rays at times corresponding to the trough and peak expression of the PER2 protein. To better examine cellular response to DNA damage, the experiments performed in this study were carried out in non-proliferating CCD-34Lu fibroblasts in order to maintain the cell and circadian cycles separated while they were being exposed to genotoxic stress. Study results demonstrated that clonogenic cell survival, double-strand break repair kinetics, and TP53 protein levels were affected in the cells irradiated at the trough than in those irradiated at peak expression of the PER2 protein.

PEGylation of ORMOSIL nanoparticles differently modulates the in vitro toxicity toward human lung cells.

ORganically MOdified SILica (ORMOSIL) nanoparticles (NPs) appear promising carriers for the delivery of drugs to target tissues but concerns on possible cytotoxic effects exist. Here, we studied the in vitro responses to ORMOSIL NPs in different types of human lung cells to determine the effects of polyethylene glycol (PEG) coating on NP cytotoxicity. Non-PEG NPs caused a concentration-dependent decrease of viability of all types of cells, while PEG NPs induced deleterious effects and death in carcinoma alveolar type II A549 cells but not in CCD-34Lu fibroblasts and NCI-H2347 adenocarcinoma cells. Reactive oxygen species were detected in cells incubated with PEG NPs, but their deactivation by superoxide dismutase and catalase did not protect A549 cells from death, suggesting that the oxidative stress was not the main determinant of cytotoxicity. Only in A549 cells PEG NPs modulated the transcription of genes involved in inflammation, signal transduction and cell death. Transmission electron microscopy evidenced a unique intracellular localization of PEG NPs in the lamellar bodies of A549 cells, which could be the most relevant factor leading to cytotoxicity by reducing the production of surfactant proteins and by interfering with the pulmonary surfactant system.

The DNA-damage response to γ-radiation is affected by miR-27a in A549 cells.

Perturbations during the cell DNA-Damage Response (DDR) can originate from alteration in the functionality of the microRNA-mediated gene regulation, being microRNAs (miRNAs), small non-coding RNAs that act as post-transcriptional regulators of gene expression. The oncogenic miR-27a is over-expressed in several tumors and, in the present study, we investigated its interaction with ATM, the gene coding for the main kinase of DDR pathway. Experimental validation to confirm miR-27a as a direct regulator of ATM was performed by site-direct mutagenesis of the luciferase reporter vector containing the 3'UTR of ATM gene, and by miRNA oligonucleotide mimics. We then explored the functional miR-27a/ATM interaction under biological conditions, i.e., during the response of A549 cells to ionizing radiation (IR) exposure. To evaluate if miR-27a over-expression affects IR-induced DDR activation in A549 cells we determined cell survival, cell cycle progression and DNA double-strand break (DSB) repair. Our results show that up-regulation of miR-27a promotes cell proliferation of non-irradiated and irradiated cells. Moreover, increased expression of endogenous mature miR-27a in A549 cells affects DBS rejoining kinetics early after irradiation.

The toxicity outcome of silica nanoparticles (Ludox®) is influenced by testing techniques and treatment modalities.

We analyzed the influence of the kind of cytotoxicity test and its application modality in defining the level of hazard of the in vitro exposures to nanostructures. We assessed the cytotoxicity induced by two different Ludox® silica nanoparticles (NPs), AS30 and SM30, on three human cell lines, CCD-34Lu, A549, and HT-1080. Dynamic light scattering measurements showed particle agglomeration when NPs are diluted in culture medium supplemented with fetal calf serum. We examined the impact of such particle aggregation on the cytotoxicity by exposing the cells to NPs under different treatment modalities: short incubation (2 h) in serum-free medium or long incubation (24-72 h) in serum-containing medium. Under this last modality, NP suspensions tended to form aggregates and were toxic at concentrations five- to tenfold higher than in serum-free medium. The results of cell survival varied considerably when the long-term clonogenic assay was performed to validate the data of the short-term MTS assay. Indeed, the half maximum effective concentrations (EC(50)) in all the three cell lines were four- to fivefold lower when calculated from the data of clonogenic assay than of MTS. Moreover, the mechanisms of NP toxicity were cell-type-specific, showing that CCD-34Lu are prone to the induction of plasma membrane damages and HT-1080 are prone to DNA double-strand break and apoptosis induction. Taken together, our results demonstrate that the choice of testing strategy and treatment conditions plays an important role in assessing the in vitro toxicity of NPs.

Interplay between DNA replication stress, chromatin dynamics and DNA-damage response for the maintenance of genome stability.

DNA replication stress is a major source of DNA damage, including double-stranded breaks that promote DNA damage response (DDR) signaling. Inefficient repair of such lesions can affect genome integrity. During DNA replication different factors act on chromatin remodeling in a coordinated way. While recent studies have highlighted individual molecular mechanisms of interaction, less is known about the orchestration of chromatin changes under replication stress. In this review we attempt to explore the complex relationship between DNA replication stress, DDR and genome integrity in mammalian cells, taking into account the role of chromatin disposition as an important modulator of DNA repair. Recent data on chromatin restoration and epigenetic re-establishment after DNA replication stress are reviewed.

Microfluidic Crystallization of Surfactant-Free Doped Zinc Sulfide Nanoparticles for Optical Bioimaging Applications.

The room-temperature controlled crystallization of monodispersed ZnS nanoparticles (average size of 5 nm) doped with luminescent ions (such as Mn2+, Eu3+, Sm3+, Nd3+, and Yb3+) was achieved via a microfluidic approach. The preparation did not require any stabilizing ligands or surfactants, minimizing potential sources of impurities. The synthesized nanomaterials were characterized from a structural (XRD and XAS at lanthanide L3 edges), morphological (TEM), and compositional (XPS, ICP-MS) perspective, giving complementary information on the materials' features. In view of potential applications in the field of optical bioimaging, the optical emission properties of the doped nanoparticles were assessed, and samples showed strong luminescent properties while being less affected by self-quenching mechanisms. Furthermore, in vitro cytotoxicity experiments were conducted, showing no negative effects and evidencing the appeal of the synthesized materials for potential applications in the field of optical bioimaging.

The cellular uptake of meta-tetra(hydroxyphenyl)chlorin entrapped in organically modified silica nanoparticles is mediated by serum proteins.

Nanosized objects made of various materials are gaining increasing attention as promising vehicles for the delivery of therapeutic and diagnostic agents for cancer. Photodynamic therapy (PDT) appears to offer a very attractive opportunity to implement drug delivery systems since no release of the sensitizer is needed to obtain the therapeutic effect and the design of the nanovehicle should be much easier. The aim of our study was to investigate the use of organic-modified silica nanoparticles (NPs) for the delivery of the second-generation photosensitizer meta-tetra(hydroxyphenyl)chlorin (mTHPC) to cancer cells in vitro. mTHPC was entrapped in NPs (approximately 33 nm diameter) in a monomeric form which produced singlet oxygen with a high efficiency. In aqueous media with high salt concentrations, the NPs underwent aggregation and precipitation but their stability could be preserved in the presence of foetal bovine serum. The cellular uptake, localization and phototoxic activity of mTHPC was determined comparatively in human oesophageal cancer cells after its delivery by the NPs and the standard solvent ethanol/poly(ethylene glycol) 400/water (20:30:50, by vol). The NP formulation reduced the cellular uptake of mTHPC by about 50% in comparison to standard solvent while it did not affect the concentration-dependent photokilling activity of mTHPC and its intracellular localization. Fluorescence resonance energy transfer measurements, using NPs with mTHPC physically entrapped and a cyanine covalently linked, and ultracentrifugation experiments indicated that mTHPC is transferred from NPs to serum proteins when present in the medium. However, the coating of the NP surface with poly(ethylene glycol) largely prevented the transfer to proteins. In conclusion, mTHPC is rapidly transferred from the uncoated nanoparticles to the serum proteins and then internalized by the cells as a protein complex, irrespective of its modality of delivery.

DNA repair in modeled microgravity: double strand break rejoining activity in human lymphocytes irradiated with gamma-rays.

Cell response to ionising radiation depends, besides on genetic and physiological features of the biological systems, on environmental conditions occurring during DNA repair. Many data showed that microgravity, experienced by astronauts during space flights or modeled on Earth, causes apoptosis, cytoskeletal alteration, cell growth inhibition, increased frequency of mutations and chromosome aberrations. In this study, we analysed the progression of the rejoining of double strand breaks (DSBs) in human peripheral blood lymphocytes (PBLs) irradiated with gamma-rays and incubated in static condition (1 g) or in modeled microgravity (MMG). gamma-H2AX foci formation and disappearance, monitored during the repair incubation, showed that the kinetics of DSBs rejoining was different in the two gravity conditions. The fraction of foci-positive cells decreased slower in MMG than in 1 g at 6 and 24 h after irradiation (P<0.01) and the mean number of gamma-H2AX foci per nucleus was significantly higher in MMG than in 1g at the same time-points (P<0.001). In the same samples we determined apoptotic level and the rate of DSB rejoining during post-irradiation incubation. A significant induction of apoptosis was observed in MMG at 24 h after irradiation (P<0.001), whereas at shorter times the level of apoptosis was slightly higher in MMG respect to 1 g. In accordance with the kinetics of gamma-H2AX foci, the slower rejoining of radiation-induced DSBs in MMG was observed by DNA fragmentation analyses during the repair incubation; the data of pulsed-field gel electrophoresis assay showed that the fraction of DNA released in the gel was significantly higher in PBL incubated in MMG after irradiation with respect to cells maintained in 1 g. Our results provide evidences that MMG incubation during DNA repair delayed the rate of radiation-induced DSB rejoining, and increased, as a consequence, the genotoxic effects of ionising radiation.

Tumor-facing hepatocytes significantly contribute to mild hyperthermia-induced targeting of rat liver metastasis by PLGA-NPs.

The effect of mild hyperthermia (MHT) on nanoparticle (NP) accumulation in rat model liver metastasis and the contribution of neoplastic and non-neoplastic cells were characterized. CdSe/ZnS QD-doped poly(lactic-co-glycolic acid) (PLGA) NPs (155 ±â€¯10 nm) were delivered via the ileocolic vein to metastatic livers 15 min after localized MW irradiation (1 min, 41 °C) or in normothermia (37 °C, NT). Quantitative analysis of tissue sections by confocal fluorescence microscopy 1 h after NP injection showed no NP tumor accumulation in NT. On the contrary, MHT increased NP association with tumor, compared to normal tissue. Counterstaining of specific markers showed that the MHT effect is due to an increased NP endocytosis not only by tumor cells, but also by hepatocytes at the growing tumor edge and, to a minor extent, by tumor-associated macrophages. High-NP capturing hepatocytes, close to the tumor, may be a relevant phenomenon in MHT-induced increased targeting of NPs to liver metastasis, influencing their therapeutic efficacy.

Individual Radiosensitivity in Oncological Patients: Linking Adverse Normal Tissue Reactions and Genetic Features.

Introduction: Adverse effects of radiotherapy (RT) significantly affect patient's quality of life (QOL). The possibility to identify patient-related factors that are associated with individual radiosensitivity would optimize adjuvant RT treatment, limiting the severity of normal tissue reactions, and improving patient's QOL. In this study, we analyzed the relationships between genetic features and toxicity grading manifested by RT patients looking for possible biomarkers of individual radiosensitivity. Methods: Early radiation toxicity was evaluated on 143 oncological patients according to the Common Terminology Criteria for Adverse Events (CTCAE). An individual radiosensitivity (IRS) index defining four classes of radiosensitivity (highly radiosensitive, radiosensitive, normal, and radioresistant) was determined by a G2-chromosomal assay on ex vivo irradiated, patient-derived blood samples. The expression level of 15 radioresponsive genes has been measured by quantitative real-time PCR at 24 h after the first RT fraction, in blood samples of a subset of 57 patients, representing the four IRS classes. Results: By applying univariate and multivariate statistical analyses, we found that fatigue was significantly associated with IRS index. Interestingly, associations were detected between clinical radiation toxicity and gene expression (ATM, CDKN1A, FDXR, SESN1, XPC, ZMAT3, and BCL2/BAX ratio) and between IRS index and gene expression (BBC3, FDXR, GADD45A, and BCL2/BAX). Conclusions: In this prospective cohort study we found that associations exist between normal tissue reactions and genetic features in RT-treated patients. Overall, our findings can contribute to the identification of biological markers to predict RT toxicity in normal tissues.

Functional validation of miRNAs targeting genes of DNA double-strand break repair to radiosensitize non-small lung cancer cells.

DNA-Double strand breaks (DSBs) generated by radiation therapy represent the most efficient lesions to kill tumor cells, however, the inherent DSB repair efficiency of tumor cells can cause cellular radioresistance and impact on therapeutic outcome. Genes of DSB repair represent a target for cancer therapy since their down-regulation can impair the repair process making the cells more sensitive to radiation. In this study, we analyzed the combination of ionizing radiation (IR) along with microRNA-mediated targeting of genes involved in DSB repair to sensitize human non-small cell lung cancer (NSCLC) cells. MicroRNAs are natural occurring modulators of gene expression and therefore represent an attractive strategy to affect the expression of DSB repair genes. As possible IR-sensitizing targets genes we selected genes of homologous recombination (HR) and non-homologous end joining (NHEJ) pathway (i.e. RAD51, BRCA2, PRKDC, XRCC5, LIG1). We examined these genes to determine whether they may be real targets of selected miRNAs by functional and biological validation. The in vivo effectiveness of miRNA treatments has been examined in cells over-expressing miRNAs and treated with IR. Taken together, our results show that hsa-miR-96-5p and hsa-miR-874-3p can directly regulate the expression of target genes. When these miRNAs are combined with IR can decrease the survival of NSCLC cells to a higher extent than that exerted by radiation alone, and similarly to radiation combined with specific chemical inhibitors of HR and NHEJ repair pathway.

Bystander response in human lymphoblastoid TK6 cells.

The mechanisms of the medium-mediated bystander response induced by gamma-rays in non-irradiated TK6 cells were investigated. Cell cultures were irradiated and the culture medium discarded immediately after irradiation and replaced with a fresh one. In cells incubated with conditioned medium from irradiated cells (CM), a significant decrease in cell viability and cloning efficiency was observed, together with a significant increase in apoptosis, also in directly irradiated cells. To examine whether bystander apoptosis involved the extrinsic pathway, an inhibitor of caspase-8 was added to CM cultures, which significantly decreased apoptosis to control levels. The addition to CM of ROS scavengers, Cu-Zn superoxide dismutase and N-acetylcysteine did not affect the induction of apoptosis. To assess whether CM treatment activates a DNA damage response, also the formation of gamma-H2AX foci, as markers of double-strand breaks and their colocalisation with 53-binding protein 1 (53BP1) and the protein mutated in the Nijmegen breakage syndrome 1 (NBS1) was analysed. In cultures treated for 2h with CM, 9-11% of cells showed gamma-H2AX foci, which partially or totally lacked colocalisation with 53BP1 and NBS1 foci. About 85% of irradiated cells were positive for gamma-H2AX foci, which colocalised with 53BP1 and NBS1 proteins. At 24h from irradiation, very few irradiated cells retained foci, fitting DNA repair kinetics. The number of foci-positive bystander cells also decreased to background values 24h after CM incubation. Our results suggest that irradiated TK6 cells release into the medium some soluble factors, not ROS, which are responsible for the cytotoxic effects induced in bystander cells. In our experimental system, the role of ROS appeared to be of minor importance in inducing cell mortality, but probably critical in activating the DNA damage response in the responsive fraction of bystander cells.

"Modeled microgravity" affects cell response to ionizing radiation and increases genomic damage.

The aim of this work was to assess whether "modeled microgravity" affects cell response to ionizing radiation, increasing the risk associated with radiation exposure. Lymphoblastoid TK6 cells were irradiated with various doses of gamma rays and incubated for 24 h in a modeled microgravity environment obtained by the Rotating Wall Vessel bioreactor. Cell survival, induction of apoptosis and cell cycle alteration were compared in cells irradiated and then incubated in 1g or modeled microgravity conditions. Modulation of genomic damage induced by ionizing radiation was evaluated on the basis of HPRT mutant frequency and the micronucleus assay. A significant reduction in apoptotic cells was observed in cells incubated in modeled microgravity after gamma irradiation compared with cells maintained in 1g. Moreover, in irradiated cells, fewer G2-phase cells were found in modeled microgravity than in 1g, whereas more G1-phase cells were observed in modeled microgravity than in 1g. Genomic damage induced by ionizing radiation, i.e. frequency of HPRT mutants and micronucleated cells, increased more in cultures incubated in modeled microgravity than in 1g. Our results indicate that modeled microgravity incubation after irradiation affects cell response to ionizing radiation, reducing the level of radiation-induced apoptosis. As a consequence, modeled microgravity increases the frequency of damaged cells that survive after irradiation.

Modeled microgravity affects cell survival and HPRT mutant frequency, but not the expression of DNA repair genes in human lymphocytes irradiated with ionising radiation.

We analysed the possibility that a reduced gravitational force impairs the efficiency of DNA repair, increasing the risk of the exposure to conditions occurring during spaceflight: i.e., ionising radiation and microgravity. To obtain information on the effects of the reduced gravity in repairing DNA damage induced by radiation, we compared cell survival and mutant frequency at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus in human peripheral blood lymphocytes (PBL) irradiated and subsequently incubated for 24h in 1g or modeled microgravity. A weak decrease of the surviving fraction and a significant increase of the HPRT mutant frequency were observed in PBL incubated in modeled microgravity after irradiation compared with those maintained in 1g. Given the increase of HPRT mutants observed in MMG, we investigated whether modeled microgravity can alter the transcription of 14 genes representative of the main DNA repair pathways: non-homologous end joining (NHEJ), homologous recombination (HR), base excision repair (BER) and nucleotide excision repair (NER). The transcriptional profiles of almost all BER and NER genes were up-regulated in irradiated PBL, whereas the expression of HR and NHEJ genes was only slightly or not affected by radiation. Incubation in modeled microgravity after irradiation did not significantly change the expression of genes involved in DNA repair, suggesting that transcriptional impairment was not responsible for the increase of mutant frequency observed in irradiated cells incubated in microgravity in comparison to the static 1g condition.

MicroRNAs Used in Combination with Anti-Cancer Treatments Can Enhance Therapy Efficacy.

MicroRNAs (miRNAs), a recently discovered class of small non-coding RNAs, constitute a promising approach to anti-cancer treatments when they are used in combination with other agents. MiRNAs are evolutionarily conserved non-coding RNAs that negatively regulate gene expression by binding to the complementary sequence in the 3'-untranslated region (UTR) of target genes. MiRNAs typically suppress gene expression by direct association with target transcripts, thus decreasing the expression levels of target proteins. The delivery to cells of synthetic miRNAs that mimic endogenous miRNA targeting genes involved in the DNA-Damage Response (DDR) can perturb the process, making cells more sensitive to chemotherapy or radiotherapy. This review examines how cells respond to combined therapy and it provides insights into the role of miRNAs in targeting the DDR repair pathway when they are used in combination with chemical compounds or ionizing radiation to enhance cellular sensitivity to treatments.