K-RAS transformation in prostate epithelial cell overcomes H2O2-induced apoptosis via upregulation of gamma-glutamyltransferase-2

Glutathione‑degrading enzymes in the complex landscape of tumors (Review)

Glutathione (GSH)‑degrading enzymes are essential for starting the first stages of GSH degradation. These enzymes include extracellular γ‑glutamyl transpeptidase (GGT) and intracellular GSH‑specific γ‑glutamylcyclotransferase 1 (ChaC1) and 2. These enzymes are essential for cellular activities, such as immune response, differentiation, proliferation, homeostasis regulation and programmed cell death. Tumor tissue frequently exhibits abnormal expression of GSH‑degrading enzymes, which has a key impact on the development and spread of malignancies. The present review summarizes gene and protein structure, catalytic activity and regulation of GSH‑degrading enzymes, their vital roles in tumor development (including regulation of oxidative and endoplasmic reticulum stress, control of programmed cell death, promotion of inflammation and tumorigenesis and modulation of drug resistance in tumor cells) and potential role as diagnostic biomarkers and therapeutic targets.

Antioxidants prevent particulate matter-induced senescence of lung fibroblasts

Particulate matter (PM) contributes to human diseases, particularly lung disease; however, the molecular mechanism of its action is yet to be determined. Herein, we found that prolonged PM exposure induced the cellular senescence of normal lung fibroblasts via a DNA damage-mediated response. This PM-induced senescence (PM-IS) was only observed in lung fibroblasts but not in A549 lung adenocarcinoma cells. Mechanistic analysis revealed that reactive oxygen species (ROS) activate the DNA damage response signaling axis, increasing p53 phosphorylation, ultimately leading to cellular senescence via an increase in p21 expression without affecting the p16-pRB pathway. A549 cells, instead, were resistant to PM-IS due to the PM-induced ROS production suppression. Water-soluble antioxidants, such as vitamin C and N-Acetyl Cysteine, were found to alleviate PM-IS by suppressing ROS production, implying that antioxidants are a promising therapeutic intervention for PM-mediated lung pathogenesis.

Base excision repair accessory factors in senescence avoidance and resistance to treatments

Cancer cells, in which the RAS and PI3K pathways are activated, produce high levels of reactive oxygen species (ROS), which cause oxidative DNA damage and ultimately cellular senescence. This process has been documented in tissue culture, mouse models, and human pre-cancerous lesions. In this context, cellular senescence functions as a tumour suppressor mechanism. Some rare cancer cells, however, manage to adapt to avoid senescence and continue to proliferate. One well-documented mode of adaptation involves increased production of antioxidants often associated with inactivation of the KEAP1 tumour suppressor gene and the resulting upregulation of the NRF2 transcription factor. In this review, we detail an alternative mode of adaptation to oxidative DNA damage induced by ROS: the increased activity of the base excision repair (BER) pathway, achieved through the enhanced expression of BER enzymes and DNA repair accessory factors. These proteins, exemplified here by the CUT domain proteins CUX1, CUX2, and SATB1, stimulate the activity of BER enzymes. The ensued accelerated repair of oxidative DNA damage enables cancer cells to avoid senescence despite high ROS levels. As a by-product of this adaptation, these cancer cells exhibit increased resistance to genotoxic treatments including ionizing radiation, temozolomide, and cisplatin. Moreover, considering the intrinsic error rate associated with DNA repair and translesion synthesis, the elevated number of oxidative DNA lesions caused by high ROS leads to the accumulation of mutations in the cancer cell population, thereby contributing to tumour heterogeneity and eventually to the acquisition of resistance, a major obstacle to clinical treatment.

Lipid Metabolism Regulates Oxidative Stress and Ferroptosis in RAS-Driven Cancers: A Perspective on Cancer Progression and Therapy

HRAS, NRAS and KRAS, collectively referred to as oncogenic RAS, are the most frequently mutated driver proto-oncogenes in cancer. Oncogenic RAS aberrantly rewires metabolic pathways promoting the generation of intracellular reactive oxygen species (ROS). In particular, lipids have gained increasing attention serving critical biological roles as building blocks for cellular membranes, moieties for post-translational protein modifications, signaling molecules and substrates for ß-oxidation. However, thus far, the understanding of lipid metabolism in cancer has been hampered by the lack of sensitive analytical platforms able to identify and quantify such complex molecules and to assess their metabolic flux in vitro and, even more so, in primary tumors. Similarly, the role of ROS in RAS-driven cancer cells has remained elusive. On the one hand, ROS are beneficial to the development and progression of precancerous lesions, by upregulating survival and growth factor signaling, on the other, they promote accumulation of oxidative by-products that decrease the threshold of cancer cells to undergo ferroptosis. Here, we overview the recent advances in the study of the relation between RAS and lipid metabolism, in the context of different cancer types. In particular, we will focus our attention on how lipids and oxidative stress can either promote or sensitize to ferroptosis RAS driven cancers. Finally, we will explore whether this fine balance could be modulated for therapeutic gain.

Development and Validation of a Machine Learning Prognostic Model for Hepatocellular Carcinoma Recurrence After Surgical Resection

Surgical resection remains primary curative treatment for patients with hepatocellular carcinoma (HCC) while over 50% of patients experience recurrence, which calls for individualized recurrence prediction and early surveillance. This study aimed to develop a machine learning prognostic model to identify high-risk patients after surgical resection and to review importance of variables in different time intervals. The patients in this study were from two centers including Eastern Hepatobiliary Surgery Hospital (EHSH) and Mengchao Hepatobiliary Hospital (MHH). The best-performed model was determined, validated, and applied to each time interval (0-1 year, 1-2 years, 2-3 years, and 3-5 years). Importance scores were used to illustrate feature importance in different time intervals. In addition, a risk heat map was constructed which visually depicted the risk of recurrence in different years. A total of 7,919 patients from two centers were included, of which 3,359 and 230 patients experienced recurrence, metastasis or died during the follow-up time in the EHSH and MHH datasets, respectively. The XGBoost model achieved the best discrimination with a c-index of 0.713 in internal validation cohort. Kaplan-Meier curves succeed to stratify external validation cohort into different risk groups (p < 0.05 in all comparisons). Tumor characteristics contribute more to HCC relapse in 0 to 1 year while HBV infection and smoking affect patients' outcome largely in 3 to 5 years. Based on machine learning prediction model, the peak of recurrence can be predicted for individual HCC patients. Therefore, clinicians can apply it to personalize the management of postoperative survival.

KRAS, BRAF, PIK3CA mutation frequency of radical prostatectomy samples and review of the literature

OBJECTIVE

The molecular basis of prostate cancer is highly heterogeneous. Our study aimed to perform the mutation analysis of KRAS, BRAF, PIK3CA, and immunohistochemical (IHC) evaluation of EGFR, HER2, p16, and PTEN to demonstrate new areas for targeted therapies.

METHODS

A total of 24 prostatectomy samples diagnosed with adenocarcinoma were analyzed by microarray hybridization. Also, these samples were IHC stained for EGFR, HER2, P16, and PTEN. The cases were divided into two groups based on low and high Gleason scores. All findings were compared with the clinicopathological parameters of the patients.

RESULTS

While KRAS mutation was in 3/24 (12.5%) of our cases, BRAF and PIK3CA mutations were not detected. There was no significant difference between the groups in terms of KRAS mutation frequency. HER2 was immunohistochemically negative in all samples. There was no correlation between EGFR, P16 immunopositivity, and clinicopathological features.

CONCLUSION

KRAS mutation frequency is similar to those in Asian populations. BRAF and PIK3CA mutation frequencies have been reported in the literature in the range of 0-15% and 0-10.4%, respectively, consistent with our study findings. HER2 immunoexpression is a controversial issue in the literature. EGFR and p16 expressions may not correlate with the stage.

Intrinsic Oncolytic Activity of Hoshino Mumps Virus Vaccine Strain Against Human Fibrosarcoma and Cervical Cancer Cell Lines

Background: The use of oncolytic viruses as therapeutic agents is a promising treatment for various human cancers. Several viruses have been extensively examined to achieve tumor cell death. Objectives: This study aimed at evaluating the natural oncolytic activity of mumps Hoshino vaccine strain against two human cancer cell lines, that is, HT1080 fibrosarcoma and HeLa cervical adenocarcinoma cell lines. Methods: The cytolytic activity of the virus was evaluated using an MTT assay. Apoptosis was detected by Annexin-V/propidium iodide (PI) staining and analyzed via flow cytometry. To indicate viral replication in vivo, nude mice with HeLa heterografts were treated with the Hoshino strain of mumps virus. Results: It was found that human fibrosarcoma and cervical cells were more sensitive to the mumps Hoshino strain, even at a very low multiplicity of infection (MOI) compared to normal human diploid cells. The results also showed that the Hoshino strain induced apoptosis in both cancer cells. A preliminary in vivo study revealed the significant suppression of tumor growth in the group treated with the mumps Hoshino strain compared to the control group. Conclusions: The Hoshino vaccine strain of mumps virus showed promising oncolytic activities against human fibrosarcoma and cervical adenocarcinoma cells.

The impact of oncogenic RAS on redox balance and implications for cancer development

The RAS family of proto-oncogenes comprises HRAS, KRAS, and NRAS, which are among the most mutated genes in human cancers. The RAS family genes encode small GTPases that coordinate key signaling pathways in response to growth factors. Mutations in RAS result in a constitutively active form of the protein that supports cellular transformation and tumorigenesis. The mechanisms of oncogenic RAS-mediated transformation encompass uncontrolled proliferation and inhibition of cell death through overactivation of the RAF-MEK-ERK and the PI3K-AKT pathways, respectively. In addition, the control of redox balance by RAS has also been proposed to play a role in its oncogenic properties. However, the exact role of redox balance in mediating mutant RAS transformation is still under debate. Here, we present, on one hand, the involvement of pro-oxidant components in oncogenic RAS transformation, such as NADPH oxidases and mitochondrial reactive oxygen species, and how these promote transformation. On the other hand, we describe the contribution of antioxidant components to mutant RAS transformation, including Nrf2, glutathione biosynthesis and xCT, as well as the mechanisms by which antioxidant programs drive transformation. Finally, we aim to reconcile the seemingly opposite effects of oncogenic RAS on redox balance and discuss a model for the complementary role of both pro-oxidant and antioxidant pathways in mutant RAS-driven tumor progression.

The prognostic significance of pretreatment serum γ-glutamyltranspeptidase in primary liver cancer: a meta-analysis and systematic review

Aim: To assess the prognostic value of the pretreatment serum γ-glutamyltranspeptidase (GGT) level in patients with primary liver cancer (PLC). Methods: Relevant studies were systematically searched online on Web of Science, PubMed, and Embase databases published until 9 October 2018. The end points were overall survival (OS), recurrence-free survival (RFS), and disease-free survival (DFS). Meta-analysis was conducted using hazard ratio (HR), and its 95% confidence interval (CI) as effect measure. Results: A total of 33 eligible studies with 9238 patients with PLC were included in this meta-analysis. The synthesized analysis showed that that higher serum GGT level was significantly related to poorer OS (HR: 1.79, 95% CI: 1.66–1.93, P<0.01), RFS (HR: 1.60, 95% CI: 1.46–1.77, P<0.01), and DFS (HR: 1.52, 95% CI: 1.33–1.73, P<0.01) of patients with PLC. Subgroup analyses demonstrated that the negative prognostic impact of higher serum GGT level on OS and RFS was still of significance regardless of ethnicity, pathological type, sample size, cut-off value, first-line treatment, and analysis type. Conclusion: The pretreatment serum GGT might be a predictive factor of poor prognosis for PLC patients.

Non enzymatic upregulation of tissue factor expression by gamma-glutamyl transferase in human peripheral blood mononuclear cells

Background

Besides maintaining intracellular glutathione stores, gamma-glutamyltransferase(GGT) generates reactive oxygen species and activates NFkB, a redox-sensitive transcription factor key in the induction of Tissue Factor (TF) gene expression, the principal initiator of the clotting cascade. Thus, GGT might be involved in TF-mediated coagulation processes, an assumption untested insofar.

Methods

Experiments were run with either equine, enzymatically active GGT or human recombinant (hr) GGT, a wheat germ-derived protein enzymatically inert because of missing post-translational glycosylation. TF Procoagulant Activity (PCA, one-stage clotting assay), TF antigen(ELISA) and TFmRNA(real-time PCR) were assessed in unpooled human peripheral blood mononuclear cell(PBMC) suspensions obtained from healthy donors through discontinuous Ficoll/Hystopaque density gradient.

Results

Equine GGT increased PCA, an effect insensitive to GGT inhibition by acivicin suggesting mechanisms independent of its enzymatic activity, a possibility confirmed by the maintained stimulation in response to hrGGT, an enzymatically inactive molecule. Endotoxin(LPS) contamination of GGT preparations was excluded by heat inactivation studies and direct determination(LAL method) of LPS concentrations <0.1 ng/mL practically devoid of procoagulant effect. Inhibition by anti-GGT antibodies corroborated that conclusion. Upregulation by hrGGT of TF antigen and mRNA and its downregulation by BAY-11-7082, a NFkB inhibitor, and N-acetyl-L-cysteine, an antioxidant, was consistent with a NFkB-driven, redox-sensitive transcriptional site of action.

Conclusions

GGT upregulates TF expression independent of its enzymatic activity, a cytokine-like behaviour mediated by NFκB activation, a mechanism contributing to promote acute thrombotic events, a possibility in need, however, of further evaluation.

Advances of diagnostic and mechanistic studies of γ-glutamyl transpeptidase in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer and the second major cause of cancerous deaths in the world, accounting for 80-90% of all cases of liver cancer with an assessed global incidence of 782,000 new cases and approximate 746,000 deaths in 2012. Preoperative laboratory data (des-γ carboxyprothrombin (DCP), α-fetoprotein (AFP), Indocyanine green retention 15 min (ICG-R15), and γ-glutamyl transferase (GGT)) should be completely assessed before deciding a treatment and predicting prognosis in order to improve the prognosis for patients with HCC. A few recent studies have suggested GGT as an independent prognostic indicator in cases with HCC. And the data of our and other research teams revealed that combination of GGT and ICG-R15 or other factors may improve the efficiency of GGT as a prognostic predictor. In addition of clinical studies, a few mechanistic studies had been performed and GGT was suggested to promote tumor progression and poor prognosis through inducing DNA damage and genome instability, releasing reactive oxygen species to activating invasion-related signaling pathway, blocking chemotherapy, regulating microRNAs, and managing CpG island methylation. Although there were a few mechanistic studies, further and accurate researches were still in need.

High Levels of Gamma-Glutamyl Transferase and Indocyanine Green Retention Rate at 15 min as Preoperative Predictors of Tumor Recurrence in Patients With Hepatocellular Carcinoma

This study investigated the preoperative independent risk factors associated with survival and recurrence for patients with hepatocellular carcinoma (HCC) who underwent hepatic resection. In total, 384 consecutive patients who underwent curative hepatic resection for single primary HCC were studied. Predictive factors associated with 1-, 3-, and 5-year survival and recurrence-free survival (RFS) were assessed using a univariate log-rank test and multivariate Cox proportional hazards regression model. Gamma-glutamyl transferase (GGT) > 100 U/L was identified as a preoperative independent risk factor affecting 1-, 3-, and 5-year survival whereas GGT > 50 U/L and indocyanine green retention 15 min (ICG-R15) > 10% were identified as preoperative independent risk factors affecting 1-, 3-, and 5-year RFS. The 384 patients studied had a 1-, 3-, and 5-year RFS rate of 72.8%, 43.3%, and 27%, respectively. Patients with GGT > 50 U/L had a 1-, 3-, and 5-year RFS rate of 64.5%, 36.0%, and 21.7%. These patients had lower survival rates than did patients with GGT ≤ 50 U/L (P < 0.05). Patients with GGT > 50 U/L and ICG-R15 > 10% had a 1-, 3-, and 5-year RFS rate of 62.4%, 29.5%, and 14.1%, respectively. These patients had lower survival rates than did patients in the other 2 groups with different levels of GGT and ICG (P < 0.05, respectively). The same was also true for patients with a tumor < 5 cm in size. Combined information in the form of high levels of GGT and ICG-R15 is a preoperative predictor that warrants full attention when evaluating tumor recurrence postoperatively.

Can gamma-glutamyl transferase levels contribute to a better prognosis for patients with hepatocellular carcinoma?

Hepatocellular carcinoma (HCC) is the most common type of liver cancer. Hepatic resection has long been considered a main treatment option for HCC, but the high rate of recurrence after hepatic resection remains a problem that impacts the prognosis and survival of patients with HCC. Thus, clarifying the factors for survival and risk factors for tumor recurrence after hepatic resection is crucial. Imaging studies are currently emphasized before selecting a treatment and predicting the prognosis for patients with HCC. Recently, laboratory testing of des-gamma-carboxyprothrombin (DCP), alpha-fetoprotein (AFP), indocyanine green 15 min after administration (ICG-R15), and γ-glutamyl transpeptidase (γ-GTP) has garnered attention as a way to select treatment and predict the prognosis of patients with HCC. γ-GTP in particular has critical clinical significance as an indicator of prognosis. This indicator helps to predict prognosis and it helps with the selection of further treatment, as was revealed by studies based on different subgroups of patients published in the past 5 years. The reason for the association between γ-GTP and early recurrence and poor survival is being investigated. Preoperative laboratory results (DCP, AFP, ICG-R15, and γ-GTP) may warrant attention and need to be fully evaluated before selecting a treatment and predicting prognosis in order to improve the prognosis for patients with HCC.

Gamma-glutamyl transpeptidase: redox regulation and drug resistance

The expression of gamma-glutamyl transpeptidase (GGT) is essential to maintaining cysteine levels in the body. GGT is a cell surface enzyme that hydrolyzes the gamma-glutamyl bond of extracellular reduced and oxidized glutathione, initiating their cleavage into glutamate, cysteine (cystine), and glycine. GGT is normally expressed on the apical surface of ducts and glands, salvaging the amino acids from glutathione in the ductal fluids. GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress. The induction of GGT is observed in tumors with elevated levels of intracellular glutathione. Studies in models of hepatocarcinogenesis show that GGT expression in foci of preneoplastic hepatocytes provides a selective advantage to the cells during tumor promotion with agents that deplete intracellular glutathione. Similarly, expression of GGT in tumors enables cells to maintain elevated levels of intracellular glutathione and to rapidly replenish glutathione during treatment with prooxidant anticancer therapy. In the clinic, the expression of GGT in tumors is correlated with drug resistance. The inhibitors of GGT block GGT-positive tumors from accessing the cysteine in extracellular glutathione. They also inhibit GGT activity in the kidney, which results in the excretion of GSH in the urine and a rapid decrease in blood cysteine levels, leading to depletion of intracellular GSH in both GGT-positive and GGT-negative tumors. GGT inhibitors are being developed for clinical use to sensitize tumors to chemotherapy.

Glutathione S-conjugates as prodrugs to target drug-resistant tumors

Living organisms are continuously exposed to xenobiotics. The major phase of enzymatic detoxification in many species is the conjugation of activated xenobiotics to reduced glutathione (GSH) catalyzed by the glutathione-S-transferase (GST). It has been reported that some compounds, once transformed into glutathione S-conjugates, enter the mercapturic acid pathway whose end products are highly reactive and toxic for the cell responsible for their production. The cytotoxicity of these GSH conjugates depends essentially on GST and gamma-glutamyl transferases (γGT), the enzymes which initiate the mercapturic acid synthesis pathway. Numerous studies support the view that the expression of GST and γGT in cancer cells represents an important factor in the appearance of a more aggressive and resistant phenotype. High levels of tumor GST and γGT expression were employed to selectively target tumor with GST- or γGT-activated drugs. This strategy, explored over the last two decades, has recently been successful using GST-activated nitrogen mustard (TLK286) and γGT-activated arsenic-based (GSAO and Darinaparsin) prodrugs confirming the potential of GSH-conjugates as anticancer drugs.

Oncolytic activity of avian influenza virus in human pancreatic ductal adenocarcinoma cell lines

Pancreatic ductal adenocarcinoma (PDA) is the most lethal form of human cancer, with dismal survival rates due to late-stage diagnoses and a lack of efficacious therapies. Building on the observation that avian influenza A viruses (IAVs) have a tropism for the pancreas in vivo, the present study was aimed at testing the efficacy of IAVs as oncolytic agents for killing human PDA cell lines. Receptor characterization confirmed that human PDA cell lines express the alpha-2,3- and the alpha-2,6-linked glycan receptor for avian and human IAVs, respectively. PDA cell lines were sensitive to infection by human and avian IAV isolates, which is consistent with this finding. Growth kinetic experiments showed preferential virus replication in PDA cells over that in a nontransformed pancreatic ductal cell line. Finally, at early time points posttreatment, infection with IAVs caused higher levels of apoptosis in PDA cells than gemcitabine and cisplatin, which are the cornerstone of current therapies for PDA. In the BxPC-3 PDA cell line, apoptosis resulted from the engagement of the intrinsic mitochondrial pathway. Importantly, IAVs did not induce apoptosis in nontransformed pancreatic ductal HPDE6 cells. Using a model based on the growth of a PDA cell line as a xenograft in SCID mice, we also show that a slightly pathogenic avian IAV significantly inhibited tumor growth following intratumoral injection. Taken together, these results are the first to suggest that IAVs may hold promise as future agents of oncolytic virotherapy against pancreatic ductal adenocarcinomas.

IMPORTANCE

Despite intensive studies aimed at designing new therapeutic approaches, PDA still retains the most dismal prognosis among human cancers. In the present study, we provide the first evidence indicating that avian IAVs of low pathogenicity display a tropism for human PDA cells, resulting in viral RNA replication and a potent induction of apoptosis in vitro and antitumor effects in vivo. These results suggest that slightly pathogenic IAVs may prove to be effective for oncolytic virotherapy of PDA and provide grounds for further studies to develop specific and targeted viruses, with the aim of testing their efficacy in clinical contexts.

Human GGT2 does not autocleave into a functional enzyme: A cautionary tale for interpretation of microarray data on redox signaling

AIMS

Human γ-glutamyltranspeptidase 1 (hGGT1) is a cell-surface enzyme that is a regulator of redox adaptation and drug resistance due to its glutathionase activity. The human GGT2 gene encodes a protein that is 94% identical to the amino-acid sequence of hGGT1. Transcriptional profiling analyses in a series of recent publications have implicated the hGGT2 enzyme as a modulator of disease processes. However, hGGT2 has never been shown to encode a protein with enzymatic activity. The aim of this study was to express the protein encoded by hGGT2 and each of its known variants and to assess their stability, cellular localization, and enzymatic activity.

RESULTS

We discovered that the proteins encoded by hGGT2 and its variants are inactive propeptides. We show that hGGT2 cDNAs are transcribed with a similar efficiency to hGGT1, and the expressed propeptides are N-glycosylated. However, they do not autocleave into heterodimers, fail to localize to the plasma membrane, and do not metabolize γ-glutamyl substrates. Substituting the coding sequence of hGGT1 to conform to alterations in a CX3C motif encoded by hGGT2 mRNAs disrupted autocleavage of the hGGT1 propeptide into a heterodimer, resulting in loss of plasma membrane localization and catalytic activity.

INNOVATION AND CONCLUSIONS

This is the first study to evaluate hGGT2 protein. The data show that hGGT2 does not encode a functional enzyme. Microarray data which have reported induction of hGGT2 mRNA should not be interpreted as induction of a protein that has a role in the metabolism of extracellular glutathione and in maintaining the redox status of the cell.

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 (EC₅₀) 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.

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