Long-term low-dose α-particle enhanced the potential of malignant transformation in human bronchial epithelial cells through MAPK/Akt pathway.

Since the wide usage of ionizing radiation, the cancer risk of low dose radiation (LDR) (<0.1 Gy) has become attractive for a long time. However, most results are derived from epidemiologic studies on atomic-bomb survivors and nuclear accidents surrounding population, and the molecular mechanism of this risk is elusive. To explore the potential of a long-term LDR-induced malignant transformation, human bronchial epithelial cells Beas-2B were fractionally irradiated with 0.025 Gy α-particles for 8 times in total and then further cultured for 1-2 months. It was found that the cell proliferation, the abilities of adhesion and invasion, and the protein expressions of p-ERK, p-Akt, especially p-P38 were not only increased in the multiply-irradiated cells but also in their offspring 1-2 months after the final exposure, indicating high potentiality of cell malignant transformation. On opposite, the expressions of p-JNK and p-P66 were diminished in the subcultures of irradiated cells and thus may play a role of negative regulation in canceration. When the cells were transferred with p38 siRNA, the LDR-induced enhancements of cell adhesion and invasion were significantly reduced. These findings suggest that long-term LDR of α-particles could enhance the potential of malignant transformation incidence in human bronchial epithelial cells through MAPK/Akt pathway.

Dose response of micronuclei induced by combination radiation of α-particles and γ-rays in human lymphoblast cells.

Combination radiation is a real situation of both nuclear accident exposure and space radiation environment, but its biological dosimetry is still not established. This study investigated the dose-response of micronuclei (MN) induction in lymphocyte by irradiating HMy2.CIR lymphoblast cells with α-particles, γ-rays, and their combinations. Results showed that the dose-response of MN induced by γ-rays was well-fitted with the linear-quadratic model. But for α-particle irradiation, the MN induction had a biphasic phenomenon containing a low dose hypersensitivity characteristic and its dose response could be well-stimulated with a state vector model where radiation-induced bystander effect (RIBE) was involved. For the combination exposure, the dose response of MN was similar to that of α-irradiation. However, the yield of MN was closely related to the sequence of irradiations. When the cells were irradiated with α-particles at first and then γ-rays, a synergistic effect of MN induction was observed. But when the cells were irradiated with γ-rays followed by α-particles, an antagonistic effect of MN was observed in the low dose range although this combination radiation also yielded a synergistic effect at high doses. When the interval between two irradiations was extended to 4h, a cross-adaptive response against the other irradiation was induced by a low dose of γ-rays but not α-particles.

DNA Nanoclusters Combined with One-Shot Radiotherapy Augment Cancer Immunotherapy Efficiency.

Immunotherapy shows immense promise for improving cancer treatment. Combining immunotherapy with radiotherapy provides a conspicuous advantage due to its enhanced abscopal effect. However, established immune tolerance mechanisms in the tumor microenvironment can hamper the generation of a sufficient abscopal effect. Herein, a type of DNA nanocluster (DNAnc) that is self-assembled by a CpG-ODNs-loaded Y-shaped double-stranded DNA vector based on the unique complementary base-pairing rules is designed. The unique structure of DNAnc makes it load more than ≈8125.5 ± 822.5 copies of CpG ODNs within one single nanostructure, which effectively increases resistance to nuclease degradation and elevates the efficiency of repolarizing macrophages to an M1-like phenotype. Mechanistic studies reveal that more DNAncs are endocytosed by macrophages in the cancer tissue and repolarized macrophages to elicit a robust abscopal effect with the accumulation of macrophages induced by radiotherapy, generating potent, long-term, and durable antitumor immunity for the inhibition of tumor metastasis and the prevention of tumor recurrence, which provides a novel strategy to boost cancer immunotherapy.

A DNA/DMXAA/Metal-Organic Framework Activator of Innate Immunity for Boosting Anticancer Immunity.

Immunotherapy has achieved revolutionary success in clinics, but it remains challenging for treating hepatocellular carcinoma (HCC) characterized by high vascularization. Here, it is reported that metal-organic framework-801 (MOF-801) can be employed as a stimulator of interferon genes (STING) through Toll-like receptor 4 (TLR4) not just as a drug delivery carrier. Notably, cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) and 5, 6-dimethylxanthenone-4-acetic acid (DMXAA) STING agonist with vascular disrupting function coordinates with MOF-801 to self-assemble into a nanoparticle (MOF-CpG-DMXAA) that effectively delivers CpG ODNs and DMXAA to cells for synergistically improving the tumor microenvironment by reprogramming tumor-associated macrophages (TAMs), promoting dendritic cells (DCs) maturation, as well as destroying tumor blood vessels. In HCC-bearing mouse models, it is demonstrated that MOF-CpG-DMXAA triggers systemic immune activation and stimulates robust tumoricidal immunity, resulting in a superior immunotherapeutic efficiency in orthotopic and recurrent HCC.

SirT1 regulates radiosensitivity of hepatoma cells differently under normoxic and hypoxic conditions.

Intratumoral hypoxic cells are more resistant to radiotherapy due to a reduction in lifespan of DNA-damaging free radicals and augmentation of post-irradiation molecular restoration. SirT1, a member of the mammalian sirtuin family, deacetylates various transcription factors to trigger cell defense and survival in response to stresses and DNA damage. In this study, we provide new evidence indicating that overexpression of SirT1 in hepatoma HepG2 cells allowed the cells to become much more resistant to irradiation under hypoxia than under normoxia. When SirT1 was knocked down in both HepG2 and SK-Hep-1 cells, the radiosensitivity was increased, especially under hypoxia. But this enhanced radiosensitivity in SirT1-deficient cells was extensively decreased by infecting cells with c-Myc siRNA. Furthermore, the expression of c-Myc protein and its acetylation were increased in the SirT1 knockdown cells and these increments under hypoxic conditions were much more notable than under normoxia. In addition, c-Myc interference significantly suppressed phosphorylated p53 protein expression after irradiation, especially under hypoxic conditions. The current findings indicate that SirT1 confers a higher radioresistance in hypoxic cells than in normoxic cells due to the decreased levels of c-Myc protein and its acetylation, and that a c-Myc-dependent radiation-induced phosphorylated p53 may be involved. SirT1 could serve as a novel target of radiation damage and thus as a potential strategy to advance the efficiency of radiotherapy in hepatoma entities.

Differential toxicity mechanism of gold nanoparticles in HK-2 renal proximal tubular cells and 786-0 carcinoma cells.

Aim: To research the influence and mechanism of gold nanoparticles (AuNPs) with different size for HK-2 cells (kidney normal cells) and 786-0 cells (kidney cancer cells). Materials & methods: HK-2 cells and 786-0 cells were treated with 5 and 200 nm AuNPs at 1 and 10 µg/ml. The cell viability, intracellular reactive oxygen species levels, cell apoptosis, cell autophagy, and related cell signaling pathways were analyzed. Results: In HK-2 cells, AuNPs reduced the activity of Akt and mTOR and upregulated the expression of LC3 II. In 786-0 cells, the activity of p38 was upregulated, which leaded to the increase of caspase 3 and initiated apoptosis. Conclusion: AuNPs of 5 and 200 nm at 10 µg/ml exerted antitumor effect by prompting apoptosis and inhibiting proliferation, while autophagy was activated to protect HK-2 cells from AuNPs-induced cytotoxicity.

Author Correction: PLGA-based dual targeted nanoparticles enhance miRNA transfection efficiency in hepatic carcinoma.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Iron Oxide Nanoparticles as Autophagy Intervention Agents Suppress Hepatoma Growth by Enhancing Tumoricidal Autophagy.

The combined treatment with nanoparticles and autophagy inhibitors, such as chloroquine (CQ) and hydroxychloroquine (HCQ), is extensively explored for cancer therapy. However, the toxicity of autophagy inhibitors and their unselective for tumoricidal autophagy have seriously hindered the application of the combined treatment. In this study, a carboxy-functional iron oxide nanoparticle (Fe2O3@DMSA) is designed and identified to significantly exert an antitumor effect without adding CQ or HCQ. Further investigation indicates that the effective inhibition effect of Fe2O3@DMSA alone on hepatoma growth is triggered by inhibiting the fusion of autophagosomes and lysosomes to enhance tumoricidal autophagy, which is induced by intracellular iron-retention-induced sustained reactive oxygen species (ROS) production. Furthermore, in two hepatoma-bearing mouse models, Fe2O3@DMSA alone effectively suppresses the growth of tumors without obvious toxic side effects. These studies offer a promising strategy for cancer therapy.

Potent anti-tumor immunostimulatory biocompatible nanohydrogel made from DNA.

Unmethylated CpG oligodeoxynucleotides are potent immunostimulatory motifs in activating both innate and acquired immune system by inducing Th1 type antigen-specific T cell responses, but their instability in serum greatly influences their immunostimulant efficiency. Here, we constructed a novel immuno-DNA nanohydrogels consisting of tandem repeat sequences of CpG units named CpG-MCA nanohydrogels through multi-primed chain amplification. CpG-MCA nanohydrogels were proved to resist degradation and increase the proliferation and migration of murine macrophage-like RAW264.7 cells. Furthermore, CpG-MCA nanohydrogels effectively induced high expression of tumor necrosis factor-α and interleukin-6, and remarkably inhibited the proliferation of U251 cells, suggesting that CpG-MCA nanohydrogels are expected to be employed as the potent anti-cancer immunostimulant.

PLGA-based dual targeted nanoparticles enhance miRNA transfection efficiency in hepatic carcinoma.

Hepatic carcinoma (HCC) is a lethal disease associated with high morbidity and poor prognosis. Recently years, gene therapies have offered novel modalities to improve the prognosis of HCC patients. MicroRNA-99a (miR-99a) is frequently down-regulated in HCC, where it acts as a tumor suppressor. Therefore, we constructed monomethoxy (polyethylene glycol)-poly(D,L-lactide-co-glycolide)-poly(L-lysine)-lactobionic acid- anti-vascular endothelial growth factor antibody (mPEG-PLGA-PLL-LA/VEGFab or PEAL-LA/VEGFab) nanoparticles (NPs) with highly specific targeting properties as carriers to restore the expression of miR-99a both in vitro and in vivo, to inhibit HCC progression. In vitro, PEAL-LA/VEGFab NPs showed more efficient delivery of miR-99a to HepG2 cells than the conventional transfection reagent LipofectamineTM2000 (Lip2000). The higher delivery efficiency associated with PEAL-LA/VEGFab NPs consequently resulted in down-regulation of target genes and suppression of the proliferation, migration and invasion of HepG2 cells. In vivo, miR-99a-PEAL-LA/VEGFab NPs inhibited tumor xenograft growth in HCC-bearing mice without causing obvious systemic toxicity. Our results demonstrate that PEAL-LA/VEGFab NPs selectively and effectively deliver miR-99a to HCC cells based on the double-targeting character of these nanoparticles, thereby offering potential for translation into effective clinical therapies for HCC.

Fe3O4 nanoparticles and cryoablation enhance ice crystal formation to improve the efficiency of killing breast cancer cells.

The key problem of cryoablation is that only freezing is often unable to kill the capillaries at tumor edges, leading to a high rate of recurrence. Here, we found that Fe3O4 nanoparticles were highly useful to improve the freezing capability of cryosurgery due to their ability to alter intracellular ice formation (IIF) and growth in tumor cells. The killing efficiency of cryoablation for MCF-7 breast cancer cells can be expected to be enhanced as the Fe3O4 nanoparticles concentration increased, it was mainly because that more IIF was induced by the participation of Fe3O4 nanoparticles during freezing, recrystallization and thawing. Furthermore, our results also showed that recrystallization contributed to the formation of extracellular embryonic crystals, which was capable of enhancing the efficiency of killing MCF-7 cells. This research is to develop an understanding of the mechanism of the cryoablation enhancing the killing efficiency in the presence of the Fe3O4 nanoparticles, and to promote their further application in tumor therapy.

The role of Dickkopf-1 as a potential prognostic marker in pancreatic ductal adenocarcinoma.

Dickkopf-1(DKK-1), the downstream target of ß-catenin/T-cell factor, participates in a negative feedback loop in the Wnt signaling and reported as an important biomarker in many tumors. In this study, we analyzed the expression of DKK-1 in pancreatic ductal adenocarcinoma (PDAC) patients at both mRNA and protein levels. We used real-time PCR to detect the expression of DKK-1 in 32 PDAC and paired adjacent non-tumor tissues, results suggested that the expression of DKK-1 was increased in PDAC tissues. We found the similar results in the analysis of 3 independent microarray data sets. Immunohistochemical staining of 311 pairs of PDAC tissues suggested that DKK-1 expression was significantly associated with T classification (P = 0.039) and lymph node metastasis (P = 0.035). Furthermore, Kaplan-Meier analysis for DKK-1 expression demonstrated that patients with higher DKK-1 level had shorter overall survival (OS) and relapse-free survival (RFS) time in Ren Ji cohort and online PDAC database at both mRNA and protein levels. Univariable and multivariable Cox regression analysis confirmed that DKK-1 as well as lymph node metastasis and histology were independent predictors of OS in patients with PDAC. This study demonstrated that DKK-1 may be a predictor for prognosis in PDAC patients.

Protective effect of mild endoplasmic reticulum stress on radiation-induced bystander effects in hepatocyte cells.

Radiation-induced bystander effect (RIBE) has important implications for secondary cancer risk assessment during cancer radiotherapy, but the defense and self-protective mechanisms of bystander normal cells are still largely unclear. The present study found that micronuclei (MN) formation could be induced in the non-irradiated HL-7702 hepatocyte cells after being treated with the conditioned medium from irradiated hepatoma HepG2 cells under either normoxia or hypoxia, where the ratio of the yield of bystander MN induction to the yield of radiation-induced MN formation under hypoxia was much higher than that of normoxia. Nonetheless, thapsigargin induced endoplasmic reticulum (ER) stress and dramatically suppressed this bystander response manifested as the decrease of MN and apoptosis inductions. Meanwhile, the interference of BiP gene, a major ER chaperone, amplified the detrimental RIBE. More precisely, thapsigargin provoked ER sensor of PERK to initiate an instantaneous and moderate ER stress thus defensed the hazard form RIBE, while BiP depletion lead to persistently destroyed homeostasis of ER and exacerbated cell injury. These findings provide new insights that the mild ER stress through BiP-PERK-p-eIF2α signaling pathway has a profound role in protecting cellular damage from RIBE and hence may decrease the potential secondary cancer risk after cancer radiotherapy.

Size-dependent cytotoxicity of Fe3O4 nanoparticles induced by biphasic regulation of oxidative stress in different human hepatoma cells.

The application of Fe3O4 nanoparticles (NPs) has made great progress in the diagnosis of disease and in the drug delivery system for cancer therapy, but the relative mechanisms of potential toxicity induced by Fe3O4 have not kept pace with its development in the application, which has hampered its further clinical application. In this article, we used two kinds of human hepatoma cell lines, SK-Hep-1 and Hep3B, to investigate the cytotoxic effects and the involved mechanisms of small Fe3O4 NPs with different diameters (6 nm, 9 nm, and 14 nm). Results showed that the size of NPs effectively influences the cytotoxicity of hepatoma cells: 6 nm Fe3O4 NPs exhibited negligible cytotoxicity and 9 nm Fe3O4 NPs affected cytotoxicity via cellular mitochondrial dysfunction and by inducing necrosis mediated through the mitochondria-dependent intracellular reactive oxygen species generation. Meanwhile, 14 nm Fe3O4 NPs induced cytotoxicity by impairing the integrity of plasma membrane and promoting massive lactate dehydrogenase leakage. These results explain the detailed mechanism of different diameters of small Fe3O4 NPs-induced cytotoxicity. We anticipate that this study will provide different insights into the cytotoxicity mechanism of Fe3O4 NPs, so as to make them safer to use in clinical application.

G(2)-M phase-correlative bystander effects are co-mediated by DNA-PKcs and ATM after carbon ion irradiation.

Accumulated evidence has shown that radiation-induced bystander effect (RIBE) may have significant implications to the efficiency of radiotherapy. Although cellular radiosensitivity relies on cell cycle status, it is largely unknown how about the relationship between RIBE and cell cycle distribution, much less the underlying mechanism. In the present study, the lung cancer A549 cells were synchronized into different cell cycle phases of G1, S and G2/M and irradiated with high linear energy transfer (LET) carbon ions. By treating nonirradiated cells with the conditioned medium from these irradiated cells, it was found that the G2-M phase cells had the largest contribution to RIBE. Meanwhile, the activity of DNA-PKcs but not ATM was increased in the synchronized G2-M phase cells in spite of both of them were activated in the asynchronous cells after carbon ion irradiation. When the G2-M phased cells were transferred with DNA-PKcs siRNA and ATM siRNA individually or treated with an inhibitor of either DNA-PKcs or ATM before carbon ion irradiation, the RIBE was effectively diminished. These results provide new evidence linking cell cycle to bystander responses and demonstrate that DNA-PKcs and ATM are two associated factors in co-regulating G2-M phase-related bystander effects.

Role of the MAPK pathway in the observed bystander effect in lymphocytes co-cultured with macrophages irradiated with γ-rays or carbon ions.

AIMS: The radiation-induced bystander effect (RIBE) has potential implications in cancer risks from space particle radiation; however, the mechanisms underlying RIBE are unclear. The role of the MAPK pathway in the RIBEs of different linear energy transfer (LET) was investigated. MAIN METHODS: Human macrophage U937 cells were irradiated with γ-rays or carbon ions and then co-cultured with nonirradiated HMy2.CIR (HMy) lymphocytes for different periods. The activation of MAPK proteins and the generation of intracellular nitric oxide (NO) and reactive oxygen species (ROS) in the irradiated U937 cells were measured. Micronuclei (MN) formation in the HMy cells was applied to evaluate the bystander damage. Some U937 cells were pretreated with different MAPK inhibitors before irradiation. KEY FINDINGS: Additional MN formation was induced in the HMy cells after co-culturing with irradiated U937 cells, and the yield of this bystander MN formation was dependent on the co-culture period with γ-ray irradiation but remained high after 1h of co-culture with carbon irradiation. Further investigations disclosed that the time response of the RIBEs had a relationship with LET, where ERK played a different role from JNK and p38 in regulating RIBEs by regulating the generation of the bystander signaling factors NO and ROS. SIGNIFICANCE: The finding that the RIBE of high-LET radiation could persist for a much longer period than that of γ-rays implies that particle radiation during space flight could have a high risk of long-term harmful effects. An appropriate intervention targeting the MAPK pathway may have significant implications in reducing this risk.

SirT1 knockdown potentiates radiation-induced bystander effect through promoting c-Myc activity and thus facilitating ROS accumulation.

Radiation-induced bystander effect (RIBE) has important implications for secondary cancer risk assessment during cancer radiotherapy, but the bystander signaling processes, especially under hypoxic condition, are still largely unclear. The present study found that micronuclei (MN) formation could be induced in the non-irradiated HL-7702 hepatocyte cells after being treated with the conditioned medium from irradiated hepatoma HepG2 and SK-Hep-1 cells under either normoxia or hypoxia. This bystander response was dramatically diminished or enhanced when the SirT1 gene of irradiated hepatoma cells was overexpressed or knocked down, respectively, especially under hypoxia. Meanwhile, SirT1 knockdown promoted transcriptional activity for c-Myc and facilitated ROS accumulation. But both of the increased bystander responses and ROS generation due to SirT1-knockdown were almost completely suppressed by c-Myc interference. Moreover, ROS scavenger effectively abolished the RIBE triggered by irradiated hepatoma cells even with SirT1 depletion. These findings provide new insights that SirT1 has a profound role in regulating RIBE where a c-Myc-dependent release of ROS may be involved.

The differential role of human macrophage in triggering secondary bystander effects after either gamma-ray or carbon beam irradiation.

The abscopal effect could be an underlying factor in evaluating prognosis of radiotherapy. This study established an in vitro system to examine whether tumor-generated bystander signals could be transmitted by macrophages to further trigger secondary cellular responses after different irradiations, where human lung cancer NCI-H446 cells were irradiated with either γ-rays or carbon ions and co-cultured with human macrophage U937 cells, then these U937 cells were used as a bystander signal transmitter and co-cultured with human bronchial epithelial cells BEAS-2B. Results showed that U937 cells were only activated by γ-irradiated NCI-H446 cells so that the secondary injuries in BEAS-2B cells under carbon ion irradiation were weaker than γ-rays. Both TNF-α and IL-1α were involved in the γ-irradiation induced secondary bystander effect but only TNF-α contributed to the carbon ion induced response. Further assay disclosed that IL-1α but not TNF-α was largely responsible for the activation of macrophages and the formation of micronucleus in BEAS-2B cells. These data suggest that macrophages could transfer secondary bystander signals and play a key role in the secondary bystander effect of photon irradiation, while carbon ion irradiation has conspicuous advantage due to its reduced secondary injury.

Role of DNA methylation in the adaptive responses induced in a human B lymphoblast cell line by long-term low-dose exposures to γ-rays and cadmium.

The possible involvement of epigenetic factors in health risks due to exposures to environmental toxicants and ionizing radiation is poorly understood. We have tested the hypothesis that DNA methylation contributes to the adaptive response (AR) to ionizing radiation or Cd. Human B lymphoblast cells HMy2.CIR were irradiated (0.032 Gy γ-rays) three times per week for 4 weeks or exposed to CdCl2 (0.005, 0.01, or 0.1 µM) for 3 months, and then challenged with a high dose of Cd (50 or 100 µM) or γ-rays (2 Gy). Long-term low-dose radiation (LDR) or long-term low-dose Cd exposure induced AR against challenging doses of Cd and irradiation, respectively. When the primed cells were treated with 5-aza-2'-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, the ARs were eliminated. These results indicate that DNA methylation is involved in the induction of AR in HMy2.CIR cells.

Reciprocal bystander effect between α-irradiated macrophage and hepatocyte is mediated by cAMP through a membrane signaling pathway.

Irradiated cells can induce biological effects on vicinal non-irradiated bystander cells, meanwhile the bystander cells may rescue the irradiated cells through a feedback signal stress. To elucidate the nature of this reciprocal effect, we examined the interaction between α-irradiated human macrophage cells U937 and its bystander HL-7702 hepatocyte cells using a cell co-culture system. Results showed that after 6h of cell co-culture, mitochondria depolarization corresponding to apoptosis was significantly induced in the HL-7702 cells, but the formation of micronuclei in the irradiated U937 cells was markedly decreased compared to that without cell co-culture treatment. This reciprocal effect was not observed when the cell membrane signaling pathway was blocked by filipin that inhibited cAMP transmission from bystander cells to irradiated cells. After treatment of cells with exogenous cAMP, forskolin (an activator of cAMP) or KH-7 (an inhibitor of cAMP), respectively, it was confirmed that cAMP communication from bystander cells to targeted cells could mitigate radiation damage in U739 cells, and this cAMP insufficiency in the bystander cells contributed to the enhancement of bystander apoptosis. Moreover, the bystander apoptosis in HL-7702 cells was aggravated by cAMP inhibition but it could not be evoked when p53 of HL-7702 cells was knocked down no matter of forskolin and KH-7 treatment. In conclusion, this study disclosed that cAMP could be released from bystander HL-7702 cells and compensated to α-irradiated U937 cells through a membrane signaling pathway and this cAMP communication played a profound role in regulating the reciprocal bystander effects.