Cellular responses to etoposide: cell death despite cell cycle arrest and repair of DNA damage

Harnessing the therapeutic potential of phytochemicals in neuroblastoma

Neuroblastomas are the most common solid tumors outside of the brain that originate from immature neural crest cells, accounting for about 10% of all pediatric malignancies. The treatment for neuroblastomas involves a multimodal schedule, including surgery, radiation, chemotherapy, and immunotherapy. All these modalities are limited by side effects that might be severe, poor prognosis, and a high risk of recurrence. In the quest for additional therapeutic approaches, phytochemicals have attracted attention owing to their reported antitumor properties, safety, and multimechanistic mode of action. Several studies have used plant-derived bioactive compounds such as phenolics and flavonoids, suggesting modulation of biomolecules and signal transduction pathways involved in neuroblastoma. We reviewed the findings of recent preclinical and clinical studies demonstrating the effects of phytochemicals on neuroblastoma, shedding light on their molecular mechanism of action and potential therapeutic applications.

Multiparametric in vitro genotoxicity assessment of different variants of amorphous silica nanomaterials in rat alveolar epithelial cells

The hazard posed to human health by inhaled amorphous silica nanomaterials (aSiO2 NM) remains uncertain. Herein, we assessed the cyto- and genotoxicity of aSiO2 NM variants covering different sizes (7, 15, and 40 nm) and surface modifications (unmodified, phosphonate-, amino- and trimethylsilyl-modified) on rat alveolar epithelial (RLE-6TN) cells. Cytotoxicity was evaluated at 24 h after exposure to the aSiO2 NM variants by the lactate dehydrogenase (LDH) release and WST-1 reduction assays, while genotoxicity was assessed using different endpoints: DNA damage (single- and double-strand breaks [SSB and DSB]) by the comet assay for all aSiO2 NM variants; cell cycle progression and γ-H2AX levels (DSB) by flow cytometry for those variants that presented higher cytotoxic and DNA damaging potential. The variants with higher surface area demonstrated a higher cytotoxic potential (SiO2_7, SiO2_15_Unmod, SiO2_15_Amino, and SiO2_15_Phospho). SiO2_40 was the only variant that induced significant DNA damage on RLE-6TN cells. On the other hand, all tested variants (SiO2_7, SiO2_15_Unmod, SiO2_15_Amino, and SiO2_40) significantly increased total γ-H2AX levels. At high concentrations (28 µg/cm2), a decrease in G0/G1 subpopulation was accompanied by a significant increase in S and G2/M sub-populations after exposure to all tested materials except for SiO2_40 which did not affect cell cycle progression. Based on the obtained data, the tested variants can be ranked for its genotoxic DNA damage potential as follows: SiO2_7 = SiO2_40 = SiO2_15_Unmod > SiO2_15_Amino. Our study supports the usefulness of multiparametric approaches to improve the understanding on NM mechanisms of action and hazard prediction.

PD-1/PD-L1 and DNA Damage Response in Cancer

The application of immunotherapy for cancer treatment is rapidly becoming more widespread. Immunotherapeutic agents are frequently combined with various types of treatments to obtain a more durable antitumor clinical response in patients who have developed resistance to monotherapy. Chemotherapeutic drugs that induce DNA damage and trigger DNA damage response (DDR) frequently induce an increase in the expression of the programmed death ligand-1 (PD-L1) that can be employed by cancer cells to avoid immune surveillance. PD-L1 exposed on cancer cells can in turn be targeted to re-establish the immune-reactive tumor microenvironment, which ultimately increases the tumor's susceptibility to combined therapies. Here we review the recent advances in how the DDR regulates PD-L1 expression and point out the effect of etoposide, irinotecan, and platinum compounds on the anti-tumor immune response.

Curvicollide D Isolated from the Fungus Amesia sp. Kills African Trypanosomes by Inhibiting Transcription

Sleeping sickness or African trypanosomiasis is a serious health concern with an added socio-economic impact in sub-Saharan Africa due to direct infection in both humans and their domestic livestock. There is no vaccine available against African trypanosomes and its treatment relies only on chemotherapy. Although the current drugs are effective, most of them are far from the modern concept of a drug in terms of toxicity, specificity and therapeutic regime. In a search for new molecules with trypanocidal activity, a high throughput screening of 2000 microbial extracts was performed. Fractionation of one of these extracts, belonging to a culture of the fungus Amesia sp., yielded a new member of the curvicollide family that has been designated as curvicollide D. The new compound showed an inhibitory concentration 50 (IC₅₀) 16-fold lower in Trypanosoma brucei than in human cells. Moreover, it induced cell cycle arrest and disruption of the nucleolar structure. Finally, we showed that curvicollide D binds to DNA and inhibits transcription in African trypanosomes, resulting in cell death. These results constitute the first report on the activity and mode of action of a member of the curvicollide family in T. brucei.

Tight association of autophagy and cell cycle in leukemia cells

Background

Autophagy plays an essential role in maintaining cellular homeostasis and in the response to cellular stress. Autophagy is also involved in cell cycle progression, yet the relationship between these processes is not clearly defined.

Results

In exploring this relationship, we observed that the inhibition of autophagy impaired the G2/M phase-arresting activity of etoposide but enhanced the G1 phase-arresting activity of palbociclib. We further investigated the connection of basal autophagy and cell cycle by utilizing the autophagosome tracer dye Cyto-ID in two ways. First, we established a double-labeling flow-cytometric procedure with Cyto-ID and the DNA probe DRAQ5, permitting the cell cycle phase-specific determination of autophagy in live cells. This approach demonstrated that different cell cycle phases were associated with different autophagy levels: G1-phase cells had the lowest level, and G2/M-phase cells had the highest one. Second, we developed a flow-cytometric cell-sorting procedure based on Cyto-ID that separates cell populations into fractions with low, medium, and high autophagy. Cell cycle analysis of Cyto-ID-sorted cells confirmed that the high-autophagy fraction contained a much higher percentage of G2/M-phase cells than the low-autophagy fraction. In addition, Cyto-ID-based cell sorting also proved to be useful for assessing other autophagy-related processes: extracellular flux analysis revealed metabolic differences between the cell populations, with higher autophagy being associated with higher respiration, higher mitochondrial ATP production, and higher glycolysis.

Conclusion

This work provides clear evidence of high autophagy in G2/M-phase cells by establishing a novel cell sorting technique based on Cyto-ID.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00334-8.

N-2-(phenylamino) benzamide derivatives as novel anti-glioblastoma agents: Synthesis and biological evaluation

Glioblastoma is one of the most lethal brain tumors. The crucial chemotherapy is mainly alkylating agents with modest clinical success. Given this desperate need and inspired by the encouraging results of a phase II trial via concomitant Topo I inhibitor plus COX-2 inhibitor, we designed a series of N-2-(phenylamino) benzamide derivatives as novel anti-glioblastoma agents based on structure modification on 1,5-naphthyridine derivatives (Topo I inhibitors). Notably, the target compounds I-1 (33.61 ± 1.15 μM) and I-8 (45.01 ± 2.37 μM) were confirmed to inhibit COX-2, while a previous reported compound (1,5-naphthyridine derivative) resulted nearly inactive towards COX-2 (IC₅₀ > 150 μM). Besides, I-1 and I-8 exhibited higher anti-proliferation, anti-migration, anti-invasion effects than the parent compound 1,5-naphthyridine derivative, suggesting the success of modification based on the parent. Moreover, I-1 obviously repressed tumor growth in the C6 glioma orthotopic model (TGI = 66.7%) and U87MG xenograft model (TGI = 69.4%). Besides, I-1 downregulated PGE₂, VEGF, MMP-9, and STAT3 activation, upregulated E-cadherin in the orthotopic model. More importantly, I-1 showed higher safety than temozolomide and different mechanism from temozolomide in the C6 glioma orthotopic model. All the evidence demonstrated that N-2-(phenylamino) benzamide derivatives as novel anti-glioblastoma agents could be promising for the glioma management.

Cell survival after DNA damage in the comet assay

The comet assay is widely used in basic research, genotoxicity testing, and human biomonitoring. However, interpretation of the comet assay data might benefit from a better understanding of the future fate of a cell with DNA damage. DNA damage is in principle repairable, or if extensive, can lead to cell death. Here, we have correlated the maximally induced DNA damage with three test substances in TK6 cells with the survival of the cells. For this, we selected hydrogen peroxide (H2O2) as an oxidizing agent, methyl methanesulfonate (MMS) as an alkylating agent and etoposide as a topoisomerase II inhibitor. We measured cell viability, cell proliferation, apoptosis, and micronucleus frequency on the following day, in the same cell culture, which had been analyzed in the comet assay. After treatment, a concentration dependent increase in DNA damage and in the percentage of non-vital and apoptotic cells was found for each substance. Values greater than 20-30% DNA in tail caused the death of more than 50% of the cells, with etoposide causing slightly more cell death than H2O2 or MMS. Despite that, cells seemed to repair of at least some DNA damage within few hours after substance removal. Overall, the reduction of DNA damage over time is due to both DNA repair and death of heavily damaged cells. We recommend that in experiments with induction of DNA damage of more than 20% DNA in tail, survival data for the cells are provided.

Cytotoxicity of Poupartone B, an Alkyl Cyclohexenone Derivative from Poupartia borbonica, against Human Cancer Cell Lines

Poupartia borbonica is an endemic tree from the Mascarene Islands that belongs to the Anacardiaceae family. The leaves of this plant were phytochemically studied previously, and isolated alkyl cyclohexenone derivatives, poupartones A - C, demonstrated antiplasmodial and antimalarial activities. In addition to their high potency against the Plasmodium sp., high toxicity on human cells was also displayed. The present study aims to investigate in more detail the cytotoxicity and pharmacological interest of poupartone B, one of the most abundant derivatives in the leaves of P. borbonica. For that purpose, real-time live-cell imaging of different human cancer cell lines and normal fibroblasts, treated or not treated with poupartone B, was performed. A potent inhibition of cell proliferation associated with the induction of cell death was observed. A detailed morphological analysis of different adherent cell lines exposed to high concentrations of poupartone B (1 - 2 µg/mL) demonstrated that this compound induced an array of cellular alterations, including a rapid retraction of cellular protrusions associated with cell rounding, massive cytoplasmic vacuolization, loss of plasma membrane integrity, and plasma membrane bubbling, ultimately leading to paraptosis-like cell death. The structure-activity relation of this class of compounds, their selective toxicity, and pharmacological potential are discussed.

Ouabain Induces DNA Damage in Human Osteosarcoma U-2 OS Cells and Alters the Expression of DNA Damage and DNA Repair-associated Proteins

BACKGROUND/AIM

Ouabain, isolated from natural plants, exhibits anticancer activities; however, no report has presented its mechanism of DNA damage induction in human osteosarcoma cancer cells in vitro. The aim of this study was to investigate whether ouabain induces DNA damage and repair, accompanied with molecular pathways in human osteosarcoma cancer U-2 OS cells in vitro.

MATERIALS AND METHODS

The percentage of viable cell number was measured by flow cytometric assay; DNA damage was assayed by DAPI staining, comet assay, and agarose gel electrophoresis. DNA damage and repair associated protein expressions were assayed by western blotting assays.

RESULTS

Ouabain reduced total cell viability, induced chromatin condensation, DNA fragmentation, and DNA damage in U-2 OS cells. Ouabain increased p-ATM^Ser1981, p-ATR^Ser428, and p53 at 2.5-10 μM, increased p-p53^Ser15 at 10 μM; however, it decreased p-MDM2^Ser166 at 2.5-10 μM. Ouabain increased p-H2A.X^Ser139, MDC-1, and PARP at 2.5-10 μM and BRCA1 at 5-10 μM; however, it decreased DNA-PK and MGMT at 2.5-10 μM in U-2 OS cells at 48 h treatment. Ouabain promoted expression and nuclear translocation of p-H2A.X^Ser139 in U-2 OS cells and this was confirmed by confocal laser microscopy.

CONCLUSION

Ouabain reduced total viable cell number through triggering DNA damage and altering the protein expression of DNA damage and repair system in U-2 OS cells in vitro.

PLAC8 promotes the autophagic activity and improves the growth priority of human trophoblast cells

Autophagy plays an important role in the normal development and function of trophoblast cells and is precisely regulated during pregnancy. Dysregulated autophagy contributes to the abnormal proliferation of trophoblasts, which is closely related to the occurrence of pregnancy-related diseases. Placenta specific 8 (PLAC8, Onzin) is a multifaceted protein proven to promote autophagy and potentiate various tumor progression. Its role in trophoblasts remains elusive. In our present study, PLAC8 expression was detected in tissues of first-trimester placentas (n = 5), term placentas (n = 5), choriocarcinoma (n = 5), and placental site trophoblastic tumor (n = 5). PLAC8 expression was increased in gestational neoplasms compared with normal pregnancies. mCherry-EGFP-LC3B reporter and transmission electron microscopy confirmed PLAC8 promoted the autophagic flux of human trophoblast cells. Both gain-of-function and loss-of-function experiments demonstrated PLAC8-regulated autophagy-related genes, including ATG5, ATG12, and Beclin-1. In addition, our data showed that PLAC8 co-localized with p53 and promoted its degradation, and p53 re-expression partially abrogated the PLAC8-induced autophagy activity. Furthermore, the overexpression of PLAC8 promoted cell viability and proliferation, acting as a protective mechanism of trophoblasts against the cytotoxicity of etoposide (VP-16). Such a phenomenon was effectively abrogated by autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ). In conclusion, PLAC8-induced autophagy to promote the proliferation of trophoblasts. This study provided insights into the mechanism of PLAC8-induced autophagy in trophoblasts, which is significant for a wide range of gestational diseases and may contribute to developing novel treatment strategies for trophoblastic diseases.

Thio-substituted derivatives of 4-amino-pyrazolo[3,4-d]pyrimidine-6-thiol as antiproliferative agents

The current study was designed to identify new compounds as potential antiproliferative drug candidates. Synthesis of heteroaromatic bicyclic and monocyclic derivatives as purine bioisosters was employed. Their antiproliferative activity was studied against U937 cancer cells. The most effective compounds were evaluated for their selectivity against cancer cells, the possible mechanism of cell death, and their interference with DNA replication. Among the synthesized compounds, only three (4b, 4j and 4l) demonstrated a value of IC₅₀ less than 20 μM. However, two of them (4b and 4l) were specific against cancer cells, with 4l presenting high selectivity. The presence of substituted pyrazolo[3,4-d]pyrimidine core is as essential for this activity as the presence of substituents at the thiol function in 6-position.

The Role of Posttranslational Modifications in DNA Repair

The human body is a complex structure of cells, which are exposed to many types of stress. Cells must utilize various mechanisms to protect their DNA from damage caused by metabolic and external sources to maintain genomic integrity and homeostasis and to prevent the development of cancer. DNA damage inevitably occurs regardless of physiological or abnormal conditions. In response to DNA damage, signaling pathways are activated to repair the damaged DNA or to induce cell apoptosis. During the process, posttranslational modifications (PTMs) can be used to modulate enzymatic activities and regulate protein stability, protein localization, and protein-protein interactions. Thus, PTMs in DNA repair should be studied. In this review, we will focus on the current understanding of the phosphorylation, poly(ADP-ribosyl)ation, ubiquitination, SUMOylation, acetylation, and methylation of six typical PTMs and summarize PTMs of the key proteins in DNA repair, providing important insight into the role of PTMs in the maintenance of genome stability and contributing to reveal new and selective therapeutic approaches to target cancers.

Checkpoint kinase‑1 inhibition and etoposide exhibit a strong synergistic anticancer effect on chronic myeloid leukemia cell line K562 by impairing homologous recombination DNA damage repair

Leukemia, a malignant hematological disease, has poor therapeutic outcomes due to chemotherapeutic resistance. Increasing evidence has confirmed that the elevated capacity for DNA damage repair in cancer cells is a major mechanism of acquired chemotherapeutic resistance. Thus, combining chemotherapy with inhibitors of DNA damage repair pathways is potentially an ideal strategy for treating leukemia. Checkpoint kinase 1 (CHK1) is an important component of the DNA damage response (DDR) and is involved in the G₂/M DNA damage checkpoint. In the present study, we demonstrated that shRNA-mediated CHK1 silencing suppressed cell proliferation and enhanced the cytotoxic effects of etoposide (VP16) in the chronic myeloid leukemia (CML) cell line K562 through the results of CCK-8, and comet assay. The results demonstrated that shRNA-induced CHK1 silencing can override G₂/M arrest and impair homologous recombination (HR) repair by reducing breast cancer susceptibility gene 1 (BRCA1) expression. Cells had no time, and thus limited ability, to repair the damage and were thus more sensitive to chemotherapy after CHK1 downregulation. Second, we tested the therapeutic effect of VP16 combined with CCT245737, an orally bioavailable CHK1 inhibitor, and observed strong synergistic anticancer effects in K562 cells. Moreover, we discovered that CCT245737 significantly prevented the G₂/M arrest caused by acute exposure to VP16. Interestingly, CCT245737 inhibited both BRCA1 and Rad51, the most important component of the HR repair pathway. In conclusion, these results revealed that CHK1 is potentially an ideal therapeutic target for the treatment of CML and that CCT245737 should be considered a candidate drug.

Downregulation of the inflammatory network in senescent fibroblasts and aging tissues of the long-lived and cancer-resistant subterranean wild rodent, Spalax

The blind mole rat (Spalax) is a wild, long‐lived rodent that has evolved mechanisms to tolerate hypoxia and resist cancer. Previously, we demonstrated high DNA repair capacity and low DNA damage in Spalax fibroblasts following genotoxic stress compared with rats. Since the acquisition of senescence‐associated secretory phenotype (SASP) is a consequence of persistent DNA damage, we investigated whether cellular senescence in Spalax is accompanied by an inflammatory response. Spalax fibroblasts undergo replicative senescence (RS) and etoposide‐induced senescence (EIS), evidenced by an increased activity of senescence‐associated beta‐galactosidase (SA‐β‐Gal), growth arrest, and overexpression of p21, p16, and p53 mRNAs. Yet, unlike mouse and human fibroblasts, RS and EIS Spalax cells showed undetectable or decreased expression of the well‐known SASP factors: interleukin‐6 (IL6), IL8, IL1α, growth‐related oncogene alpha (GROα), SerpinB2, and intercellular adhesion molecule (ICAM‐1). Apparently, due to the efficient DNA repair in Spalax, senescent cells did not accumulate the DNA damage necessary for SASP activation. Conversely, Spalax can maintain DNA integrity during replicative or moderate genotoxic stress and limit pro‐inflammatory secretion. However, exposure to the conditioned medium of breast cancer cells MDA‐MB‐231 resulted in an increase in DNA damage, activation of the nuclear factor κB (NF‐κB) through nuclear translocation, and expression of inflammatory mediators in RS Spalax cells. Evaluation of SASP in aging Spalax brain and intestine confirmed downregulation of inflammatory‐related genes. These findings suggest a natural mechanism for alleviating the inflammatory response during cellular senescence and aging in Spalax, which can prevent age‐related chronic inflammation supporting healthy aging and longevity.

Accumulated cytotoxicity of CDK inhibitor dinaciclib with first-line chemotherapy drugs in salivary adenoid cystic carcinoma cells

Adenoid cystic carcinoma (ACC) is one of the most common salivary gland malignant tumors. Its treatment failure is partly due to the limitations of chemotherapeutic agents and their adverse effects. The objective of this study was to determine the potential additive anti-cancer effect of a novel CDK inhibitor dinaciclib with first-line chemotherapy drugs in ACC. Protein expression of phosphorylated CDK2 (p-CDK2) in paraffin-embedded tissue specimens of ACC from 17 patients was investigated by immunohistochemistry (IHC). Cell Counting Kit (CCK-8), clone formation assay, and flow cytometry were used to test the proliferation and apoptosis of ACC-2 cells treated with dinaciclib with or without other first-line chemotherapy drugs. Protein expression was also determined by Western blot. Interestingly, we discovered that p-CDK2 protein was expressed in both cytoplasmic and nucleus in salivary ACC tissues, which was higher than that in normal salivary tissues, indicating that agents targeting CDK2 may be potential therapeutic strategies against this type of tumor. As expected, CDK inhibitor dinaciclib significantly induced ACC-2 cells apoptosis. Moreover, it sensitized cells to the chemotherapeutic agents such as cisplatin, pemetrexed, and etoposide (VP-16), and this effect by dinaciclib may induce cell cycle arrest via abrogating CDK2 activity. Therefore, combinational therapy of CDK inhibitor dinaciclib with first-line chemotherapy drugs may be a promising strategy in the treatment of salivary ACC.

Comparison of CHOP vs CHOPE for treatment of peripheral T-cell lymphoma: a meta-analysis

Objective

To compare cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) and CHOP plus etoposide (CHOPE) with regard to outcomes including efficacy and safety for patients with peripheral T-cell lymphoma (PTCL).

Methods

Relevant literature was searched using PubMed, Embase, Wanfang, and CNKI for eligible trials comparing CHOP with CHOPE for treatment of PTCL. The following outcomes of PTCL patients were considered: complete response (CR), partial response (PR), overall response rate (ORR), and adverse events (AEs; grade >3). Risk ratios (RRs) were appropriately derived from fixed-effects or random-effects models.

Results

A total of five prospective or retrospective articles with 1,560 patients were elected for the meta-analysis. There were no significant differences in CR (RR =1.11, 95% CI: 0.73–1.67, P=0.632), PR (RR =1.40, 95% CI: 0.52–3.76, P=0.504), and ORR (RR =1.25, 95% CI: 0.93–1.69, P=0.146) between the CHOP and CHOPE groups. However, AEs including anemia (RR =1.69, 95% CI: 1.33–2.16, P<0.001) and thrombocytopenia (RR =1.43, 95% CI: 1.15–1.77, P=0.001) were significantly increased in CHOPE group compared to that in CHOP group.

Conclusion

Meta-analysis suggested that there were no differences in therapeutic effect for patients with PTCL between CHOP and CHOPE groups with regards to CR, PR, and ORR, whereas the CHOPE group had significantly increased AEs (anemia and thrombocytopenia) compared to CHOP group.

TLP-mediated global transcriptional repression after double-strand DNA breaks slows down DNA repair and induces apoptosis

Transcription and DNA damage repair act in a coordinated manner. Recent studies have shown that double-strand DNA breaks (DSBs) are repaired in a transcription-coupled manner. Active transcription results in a faster recruitment of DSB repair factors and expedites DNA repair. On the other hand, transcription is repressed by DNA damage through multiple mechanisms. We previously reported that TLP, a TATA box-binding protein (TBP) family member that functions as a transcriptional regulator, is also involved in DNA damage-induced apoptosis. However, the mechanism by which TLP affects DNA damage response was largely unknown. Here we show that TLP-mediated global transcriptional repression after DSBs is crucial for apoptosis induction by DNA-damaging agents such as etoposide and doxorubicin. Compared to control cells, TLP-knockdown cells were resistant to etoposide-induced apoptosis and exhibited an elevated level of global transcription after etoposide exposure. DSBs were efficiently removed in transcriptionally hyperactive TLP-knockdown cells. However, forced transcriptional shutdown using transcriptional inhibitors α-amanitin and 5,6-dichloro-1-ß-D-ribofuranosylbenzimidazole (DRB) slowed down DSB repair and resensitized TLP-knockdown cells to etoposide. Taken together, these results indicate that TLP is a critical determinant as to how cells respond to DSBs and triggers apoptosis to cells that have sustained DNA damage.

Ionizing radiation manifesting DNA damage response in plants: An overview of DNA damage signaling and repair mechanisms in plants

Plants orchestrate various DNA damage responses (DDRs) to overcome the deleterious impacts of genotoxic agents on genetic materials. Ionizing radiation (IR) is widely used as a potent genotoxic agent in plant DDR research as well as plant breeding and quarantine services for commercial uses. This review aimed to highlight the recent advances in cellular and phenotypic DDRs, especially those induced by IR. Various physicochemical genotoxic agents damage DNA directly or indirectly by inhibiting DNA replication. Among them, IR-induced DDRs are considerably more complicated. Many aspects of such DDRs and their initial transcriptomes are closely related to oxidative stress response. Although many key components of DDR signaling have been characterized in plants, DDRs in plant cells are not understood in detail to allow comparison with those in yeast and mammalian cells. Recent studies have revealed plant DDR signaling pathways including the key regulator SOG1. The SOG1 and its upstream key components ATM and ATR could be functionally characterized by analyzing their knockout DDR phenotypes after exposure to IR. Considering the potent genotoxicity of IR and its various DDR phenotypes, IR-induced DDR studies should help to establish an integrated model for plant DDR signaling pathways by revealing the unknown key components of various DDRs in plants.

CtIP promotes G2/M arrest in etoposide-treated HCT116 cells in a p53-independent manner

Acquired resistance to cytotoxic antineoplastic agents is a major clinical challenge in tumor therapy; however, the mechanisms involved are still poorly understood. In this study, we show that knockdown of CtIP, a corepressor of CtBP, promotes cell proliferation and alleviates G2/M phase arrest in etoposide (Eto)-treated HCT116 cells. Although the expression of p21 and growth arrest and DNA damage inducible α (GADD45a), which are important targets of p53, was downregulated in CtIP-deficient HCT116 cells, p53 deletion did not affect G2/M arrest after Eto treatment. In addition, the phosphorylation levels of Ser317 and Ser345 in Chk1 and of Ser216 in CDC25C were lower in CtIP-deficient HCT116 cells than in control cells after Eto treatment. Our results indicate that CtIP may enhance cell sensitivity to Eto by promoting G2/M phase arrest, mainly through the ATR-Chk1-CDC25C pathway rather than the p53-p21/GADD45a pathway. The expression of CtIP may be a useful biomarker for predicting the drug sensitivity of colorectal cancer cells.

Orthosiphon stamineus Extracts Inhibits Proliferation and Induces Apoptosis in Uterine Fibroid Cells

Objectives: The effects of water and 50% ethanolic-water extracts of Orthosiphon stamineus Benth (OS) on cell proliferation and apoptotic activity against uterine leiomyosarcoma (SK-UT-1) cells were investigated. Methods: Anti-proliferation effect was evaluated through cell cycle analysis whereas apoptotic activity was determined via screening and quantifying using fluorescence microscopy and flow cytometric analysis, respectively. The effect of extracts on molecular mechanism was studied using real-time reverse transcription polymerase chain reaction and Western blotting. Results: Cell cycle flow cytometric analysis showed the induction of cell cycle arrests were behaves in a p53-independent manner. The examination using fluorescence microscopy and Annexin V flow cytometry revealed the presence of morphological features of apoptotic bodies. Downregulation of anti-apoptotic gene (Bcl-2) supports the apoptotic activity of OS extracts although poorly induce PARP-1 cleavage in Western blot analysis. The extracts also inhibit the SK-UT-1 growth by suppressing VEGF-A, TGF-β1 and PCNA genes, which involved in angiogenesis and cell proliferation. Conclusion: This study demonstrates that O. stamineus extracts are able to inhibit proliferation and induced apoptosis of uterine fibroid cells and is worth further investigation.

Etoposide radiosensitizes p53-defective cholangiocarcinoma cell lines independent of their G2 checkpoint efficacies

Radiotherapy has been accounted as the most comprehensive cancer treatment modality over the past few decades. However, failure of this treatment modality occurs in several malignancies due to the resistance of cancer cells to radiation. It was previously reported by the present authors that defective cell cycle checkpoints could be used as biomarkers for predicting the responsiveness to radiation in individual patients with cholangiocarcinoma (CCA). However, identification of functional defective cell cycle checkpoints from cells from a patient's tissues is cumbersome and not applicable in the clinic. The present study evaluated the radiosensitization potential of etoposide in p53-defective CCA KKU-M055 and KKU-M214 cell lines. Treatment with etoposide enhanced the responsiveness of two p53-defective CCA cell lines to radiation independent of G₂ checkpoint function. In addition, etoposide treatment increased radiation-induced cell death without altering the dominant mode of cell death of the two cell lines. These findings indicate that etoposide could be used as a radiation sensitizer for p53-defective tumors, independent of the function of G₂ checkpoint.

Both p62/SQSTM1-HDAC6-dependent autophagy and the aggresome pathway mediate CDK1 degradation in human breast cancer

Cyclin-dependent kinase 1 (CDK1) is the central mammalian regulator of cell proliferation and a promising therapeutic target for breast cancer. In fact, CDK1 inhibition downregulates survival and induces apoptosis. Due to its essential role, CDK1 expression and activity are strictly controlled at various levels. We previously described that CDK1 stability is also regulated and that SCF(βTrCP) ubiquitinates CDK1, which is degraded via the lysosomal pathway. In addition, in breast tumors from patients, we found a negative correlation between CDK1 accumulation and βTrCP levels, and a positive correlation with the degree of tumor malignancy. This prompted us to study the molecular mechanism involved in CDK1 clearance. In this report, we determine that both chemotherapeutic agents and proteolytic stress induce CDK1 degradation in human breast cancer MCF7 cells through p62/HDAC6-mediated selective autophagy. On the one hand, CDK1 binds to p62/SQSTM1-LC3 and, on the other hand, it interacts with HDAC6. Both complexes are dependent on the presence of an intact βTrCP-binding motif on CDK1. Furthermore, we also show that CDK1 is recruited to aggresomes in response to proteasome inhibition for an extended period. We propose CDK1 clearance as a potential predictive biomarker of antitumor treatment efficacy.

Pleomorphism and drug resistant cancer stem cells are characteristic of aggressive primary meningioma cell lines

Background

Meningioma tumors arise in arachnoid membranes, and are the most reported central nervous system (CNS) tumors worldwide. Up to 20% of grade I meningioma tumors reoccur and currently predictive cancer stem cells (CSCs) markers for aggressive and drug resistant meningiomas are scarce.

Methods

Meningioma tissues and primary cell lines were investigated using whole transcriptome microarray analysis, immunofluorescence staining of CSCs markers (including CD133, Sox2, Nestin, and Frizzled 9), and drug treatment with cisplatin or etoposide.

Results

Unsupervised hierarchical clustering of six meningioma samples separated tissues into two groups. Analysis identified stem cells related pathways to be differential between the two groups and indicated the de-regulation of the stem cell associated genes Reelin (RELN), Calbindin 1 (CALB1) and Anterior Gradient 2 Homolog (AGR2). Immunofluorescence staining for four tissues confirmed stemness variation in situ. Biological characterization of fifteen meningioma primary cell lines concordantly separated cells into two functionally distinct sub-groups. Pleomorphic cell lines (NG type) grew significantly faster than monomorphic cell lines (G type), had a higher number of cells that express Ki67, and were able to migrate aggressively in vitro. In addition, NG type cell lines had a lower expression of nuclear Caspase-3, and had a significantly higher number of CSCs co-positive for CD133+ Sox2+ or AGR2+ BMI1+. Importantly, these cells were more tolerant to cisplatin and etoposide treatment, showed a lower level of nuclear Caspase-3 in treated cells and harbored drug resistant CSCs.

Conclusion

Collectively, analyses of tissues and primary cell lines revealed stem cell associated genes as potential targets for aggressive and drug resistant meningiomas.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-017-0441-7) contains supplementary material, which is available to authorized users.

Deleterious role of trace elements - Silica and lead in the development of chronic kidney disease

Chronic-Kidney-Disease of Unknown-etiology (CKDu) has been reported in developing-countries like Sri-Lanka, India and Central-America without sparing the Indian sub-district (namely Canacona) located in south-Goa. The disease etiology is unlinked to common causes of diabetes and hypertension and assumed to be environmentally induced due to its asymptomatic-nature and occurrence in groundwater relying communities. This study aimed to understand environmental risk-factors underlying CKDu-etiology using Indian sub-district (Canacona) as case-study. Biochemical-analysis of CKDu-affected and non-affected individual's blood and detailed hydro-geochemical analyses of CKDu-affected and non-affected region's groundwater (drinking-water)were conducted. Trace geogenic-element-silica was highly dominant in affected-region's groundwater, thus its nephrotoxic-potential was analysed via in-vitro cytotoxicity-assays on human-kidney-cell-lines. All CKDu-affected-subjects showed increased-levels of serum-urea (52.85 mM),creatinine (941.5 μM),uric-acid (1384.5 μM), normal blood-glucose (4.65 mM), being distinct biomarkers of environmentally-induced CKD-'chronic-tubulo-interstitial-nephritis'. Affected-subjects reported high blood-lead levels (1.48 μM)suggesting direct-nephrotoxicity resulting in impaired blood-clearance and also exhibits indirect-nephrotoxicity by disrupting calcium-homeostasis causing skeletal-disorders and prolonged-consumption of NSAID's (pain-alleviation), indirectly causing renal-damage. Affected-region's groundwater was acidic (pH-5.6), resulting in borderline-lead (9.98 μgL^-1) and high-silica (115.5 mgL^-1)contamination. Silica's bio-availability (determining its nephrotoxicity) was enhanced at groundwater's acidic-pH and Ca-Mg-deficient-composition (since these cations complex with silica reducing bioavailability). Silica exhibited renal-proximal-tubular-cytotoxicity on long-term exposure comparable with affected-region's groundwater silica-levels, by apoptosis-mediated-cell-death resulting in tubular-atrophy, interstitial-fibrosis and irreversible renal-damage (CKD). Thus this study provides novel-insights into nephrotoxic-potential of trace-geogenic-element-silica in CKDu causation. It highlights direct-indirect nephrotoxicity exhibited by lead at low-levels due to its bio-accumulative-capacity. Silica's nephrotoxic-potential can be considered when deciphering etiology of CKDu-problem in developing-countries (relying on groundwater).

Nuclear α-catenin mediates the DNA damage response via β-catenin and nuclear actin

α-Catenin is an F-actin-binding protein widely recognized for its role in cell-cell adhesion. However, a growing body of literature indicates that α-catenin is also a nuclear protein. In this study, we show that α-catenin is able to modulate the sensitivity of cells to DNA damage and toxicity. Furthermore, nuclear α-catenin is actively recruited to sites of DNA damage. This recruitment occurs in a β-catenin-dependent manner and requires nuclear actin polymerization. These findings provide mechanistic insight into the WNT-mediated regulation of the DNA damage response and suggest a novel role for the α-catenin-β-catenin complex in the nucleus.

Combined Effect of Silica Nanoparticles and Benzo[a]pyrene on Cell Cycle Arrest Induction and Apoptosis in Human Umbilical Vein Endothelial Cells

Particulate matter (PM) such as ultrafine particulate matter (UFP) and the organic compound pollutants such as polycyclic aromatic hydrocarbon (PAH) are widespread in the environment. UFP and PAH are present in the air, and their presence may enhance their individual adverse effects on human health. However, the mechanism and effect of their combined interactions on human cells are not well understood. We investigated the combined toxicity of silica nanoparticles (SiNPs) (UFP) and Benzo[a]pyrene (B[a]P) (PAH) on human endothelial cells. Human umbilical vascular endothelial cells (HUVECs) were exposed to SiNPs or B[a]P, or a combination of SiNPs and B[a]P. The toxicity was investigated by assessing cellular oxidative stress, DNA damage, cell cycle arrest, and apoptosis. Our results show that SiNPs were able to induce reactive oxygen species generation (ROS). B[a]P, when acting alone, had no toxicity effect. However, a co-exposure of SiNPs and B[a]P synergistically induced DNA damage, oxidative stress, cell cycle arrest at the G2/M check point, and apoptosis. The co-exposure induced G2/M arrest through the upregulation of Chk1 and downregulation of Cdc25C, cyclin B1. The co-exposure also upregulated bax, caspase-3, and caspase-9, the proapoptic proteins, while down-regulating bcl-2, which is an antiapoptotic protein. These results show that interactions between SiNPs and B[a]P synergistically potentiated toxicological effects on HUVECs. This information should help further our understanding of the combined toxicity of PAH and UFP.

Fluorescein hydrazones: A series of novel non-intercalative topoisomerase IIα catalytic inhibitors induce G1 arrest and apoptosis in breast and colon cancer cells

Fluorescein hydrazones (5 and 7) were synthesized in three/four steps with 82-92% yields. All synthesized compounds were evaluated by topoisomerase I (topo I) and topoisomerase IIα (topo IIα)-mediated relaxation and cell viability assays. Among them, most of the compounds showed topo I & IIα inhibitory activity and nineteen compounds showed strong anti-proliferative activity against various cell lines. In brief, 5e inhibited 53% topo IIα (etoposide 29%) at 20 μM and showed excellent antiproliferative activity against DU145 (1.43 ± 0.04 μM), HCT15 (2.4 ± 0.03 μM) and MCF7 (11.4 ± 0.5 μM) cell lines in comparison with adriamycin, etoposide, and camptothecin. Compounds 5e, 5g and 5h were further evaluated to determine their mode of action. Compounds 5e, 5g and 5h functioned as non-intercalative topo IIα catalytic inhibitor with induction of G1 arrest and activation of apoptotic proteins in dose-dependent manner.

Collision of Trapped Topoisomerase 2 with Transcription and Replication: Generation and Repair of DNA Double-Strand Breaks with 5' Adducts

Topoisomerase 2 (Top2) is an essential enzyme responsible for manipulating DNA topology during replication, transcription, chromosome organization and chromosome segregation. It acts by nicking both strands of DNA and then passes another DNA molecule through the break. The 5′ end of each nick is covalently linked to the tyrosine in the active center of each of the two subunits of Top2 (Top2cc). In this configuration, the two sides of the nicked DNA are held together by the strong protein-protein interactions between the two subunits of Top2, allowing the nicks to be faithfully resealed in situ. Top2ccs are normally transient, but can be trapped by cancer drugs, such as etoposide, and subsequently processed into DSBs in cells. If not properly repaired, these DSBs would lead to genome instability and cell death. Here, I review the current understanding of the mechanisms by which DSBs are induced by etoposide, the unique features of such DSBs and how they are repaired. Implications for the improvement of cancer therapy will be discussed.

Mangiferin and Cancer: Mechanisms of Action

Mangiferin, a bioactive compound derived primarily from Anacardiaceae and Gentianaceae families and found in mangoes and honeybush tea, has been extensively studied for its therapeutic properties. Mangiferin has shown promising chemotherapeutic and chemopreventative potential. This review focuses on the effect of mangiferin on: (1) inflammation, with respect to NFκB, PPARү and the immune system; (2) cell cycle, the MAPK pathway G₂/M checkpoint; (3) proliferation and metastasis, and implications on β-catenin, MMPs, EMT, angiogenesis and tumour volume; (4) apoptosis, with a focus on Bax/Bcl ratios, intrinsic/extrinsic apoptotic pathways and telomerase activity; (5) oxidative stress, through Nrf2/ARE signalling, ROS elimination and catalase activity; and (6) efficacy of chemotherapeutic agents, such as oxaliplatin, etoposide and doxorubicin. In addition, the need to enhance the bioavailability and delivery of mangiferin are briefly addressed, as well as the potential for toxicity.

Suberoylanilide hydroxamic acid synergistically enhances the antitumor activity of etoposide in Ewing sarcoma cell lines

Ewing sarcomas (ES) are highly malignant tumors arising in bone and soft tissues. Given the poor outcome of affected patients with primary disseminated disease or at relapse, there is a clear need for new targeted therapies. The HDAC inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA, Vorinostat) inhibits ES tumor growth and induces apoptosis in vitro and in vivo. Thus, SAHA may be considered a novel treatment. However, it is most likely that not a single agent but a combination of agents with synergistic mechanisms will help improve the prognosis in high-risk ES patients. Therefore, the aim of the present study was to assess a putative synergistic effect of SAHA in combination with conventional chemotherapeutic agents. The antitumor activity of SAHA in combination with conventional chemotherapeutics (doxorubicin, etoposide, rapamycin, topotecan) was assessed using an MTT cell proliferation assay on five well-characterized ES cell lines (CADO-ES-1, RD-ES, TC-71, SK-ES-1, SK-N-MC) and a newly established ES cell line (DC-ES-15). SAHA antagonistically affected the antiproliferative effect of doxorubicin and topotecan in the majority of the ES cell lines, but synergistically enhanced the antiproliferative activity of etoposide. In functional analyses, pretreatment with SAHA significantly increased the effects of etoposide on apoptosis and clonogenicity. The in-vitro analyses presented in this work show that SAHA synergistically enhances the antitumor activity of etoposide in ES cells. Sequential treatment with etoposide combined with SAHA may represent a new therapeutic approach in ES.

Genotoxicity of Superparamagnetic Iron Oxide Nanoparticles in Granulosa Cells

Nanoparticles that are aimed at targeting cancer cells, but sparing healthy tissue provide an attractive platform of implementation for hyperthermia or as carriers of chemotherapeutics. According to the literature, diverse effects of nanoparticles relating to mammalian reproductive tissue are described. To address the impact of nanoparticles on cyto- and genotoxicity concerning the reproductive system, we examined the effect of superparamagnetic iron oxide nanoparticles (SPIONs) on granulosa cells, which are very important for ovarian function and female fertility. Human granulosa cells (HLG-5) were treated with SPIONs, either coated with lauric acid (SEONLA) only, or additionally with a protein corona of bovine serum albumin (BSA; SEON^LA-BSA), or with dextran (SEON^DEX). Both micronuclei testing and the detection of γH2A.X revealed no genotoxic effects of SEON^LA-BSA, SEON^DEX or SEON^LA. Thus, it was demonstrated that different coatings of SPIONs improve biocompatibility, especially in terms of genotoxicity towards cells of the reproductive system.

p53 protein-mediated up-regulation of MAP kinase phosphatase 3 (MKP-3) contributes to the establishment of the cellular senescent phenotype through dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2)

Growth arrest is one of the essential features of cellular senescence. At present, the precise mechanisms responsible for the establishment of the senescence-associated arrested phenotype are still incompletely understood. Given that ERK1/2 is one of the major kinases controlling cell growth and proliferation, we examined the possible implication of ERK1/2. Exposure of normal rat epithelial cells to etoposide caused cellular senescence, as manifested by enlarged cell size, a flattened cell body, reduced cell proliferation, enhanced β-galactosidase activity, and elevated p53 and p21. Senescent cells displayed a blunted response to growth factor-induced cell proliferation, which was preceded by impaired ERK1/2 activation. Further analysis revealed that senescent cells expressed a significantly higher level of mitogen-activated protein phosphatase 3 (MKP-3, a cytosolic ERK1/2-targeted phosphatase), which was suppressed by blocking the transcriptional activity of the tumor suppressor p53 with pifithrin-α. Inhibition of MKP-3 activity with a specific inhibitor or siRNA enhanced basal ERK1/2 phosphorylation and promoted cell proliferation. Apart from its role in growth arrest, impairment of ERK1/2 also contributed to the resistance of senescent cells to oxidant-elicited cell injury. These results therefore indicate that p53-mediated up-regulation of MKP-3 contributes to the establishment of the senescent cellular phenotype through dephosphorylating ERK1/2. Impairment of ERK1/2 activation could be an important mechanism by which p53 controls cellular senescence.

Chaetoglobosin K induces apoptosis and G2 cell cycle arrest through p53-dependent pathway in cisplatin-resistant ovarian cancer cells

Adverse side effects and acquired resistance to conventional platinum based chemotherapy have become major impediments in ovarian cancer treatment, and drive the development of more selective anticancer drugs. Chaetoglobosin K (ChK) was shown to have a more potent growth inhibitory effect than cisplatin on two cisplatin-resistant ovarian cancer cell lines, OVCAR-3 and A2780/CP70, and was less cytotoxic to a normal ovarian cell line, IOSE-364, than to the cancer cell lines. Hoechst 33342 staining and Flow cytometry analysis indicated that ChK induced preferential apoptosis and G2 cell cycle arrest in both ovarian cancer cells with respect to the normal ovarian cells. ChK induced apoptosis through a p53-dependent caspase-8 activation extrinsic pathway, and caused G2 cell cycle arrest via cyclin B1 by increasing p53 expression and p38 phosphorylation in OVCAR-3 and A2780/CP70 cells. DR5 and p21 might play an important role in determining the sensitivity of normal and malignant ovarian cells to ChK. Based on these results, ChK would be a potential compound for treating platinum-resistant ovarian cancer.

Potent cytotoxic arylnaphthalene lignan lactones from Phyllanthus poilanei

Two new (1 and 2) and four known arylnaphthalene lignan lactones (3-6) were isolated from different plant parts of Phyllanthus poilanei collected in Vietnam, with two further known analogues (7 and 8) being prepared from phyllanthusmin C (4). The structures of the new compounds were determined by interpretation of their spectroscopic data and by chemical methods, and the structure of phyllanthusmin D (1) was confirmed by single-crystal X-ray diffraction analysis. Several of these arylnaphthalene lignan lactones were cytotoxic toward HT-29 human colon cancer cells, with compounds 1 and 7-O-[(2,3,4-tri-O-acetyl)-α-L-arabinopyranosyl)]diphyllin (7) found to be the most potent, exhibiting IC50 values of 170 and 110 nM, respectively. Compound 1 showed activity when tested in an in vivo hollow fiber assay using HT-29 cells implanted in immunodeficient NCr nu/nu mice. Mechanistic studies showed that this compound mediated its cytotoxic effects by inducing tumor cell apoptosis through activation of caspase-3, but it did not inhibit DNA topoisomerase IIα activity.

Cell cycle modulation by Marek's disease virus: the tegument protein VP22 triggers S-phase arrest and DNA damage in proliferating cells

Marek's disease is one of the most common viral diseases of poultry affecting chicken flocks worldwide. The disease is caused by an alphaherpesvirus, the Marek's disease virus (MDV), and is characterized by the rapid onset of multifocal aggressive T-cell lymphoma in the chicken host. Although several viral oncogenes have been identified, the detailed mechanisms underlying MDV-induced lymphomagenesis are still poorly understood. Many viruses modulate cell cycle progression to enhance their replication and persistence in the host cell, in the case of some oncogenic viruses ultimately leading to cellular transformation and oncogenesis. In the present study, we found that MDV, like other viruses, is able to subvert the cell cycle progression by triggering the proliferation of low proliferating chicken cells and a subsequent delay of the cell cycle progression into S-phase. We further identified the tegument protein VP22 (pUL49) as a major MDV-encoded cell cycle regulator, as its vector-driven overexpression in cells lead to a dramatic cell cycle arrest in S-phase. This striking functional feature of VP22 appears to depend on its ability to associate with histones in the nucleus. Finally, we established that VP22 expression triggers the induction of massive and severe DNA damages in cells, which might cause the observed intra S-phase arrest. Taken together, our results provide the first evidence for a hitherto unknown function of the VP22 tegument protein in herpesviral reprogramming of the cell cycle of the host cell and its potential implication in the generation of DNA damages.

Nonhomologous DNA end joining and chromosome aberrations in human embryonic lung fibroblasts treated with environmental pollutants

In order to evaluate the ability of a representative polycyclic aromatic hydrocarbon (PAH) and PAH-containing complex mixtures to induce double strand DNA breaks (DSBs) and repair of damaged DNA in human embryonic lung fibroblasts (HEL12469 cells), we investigated the effect of benzo[a]pyrene (B[a]P) and extractable organic matter (EOM) from ambient air particles <2.5μm (PM2.5) on nonhomologous DNA end joining (NHEJ) and induction of stable chromosome aberrations (CAs). PM2.5 was collected in winter and summer 2011 in two Czech cities differing in levels and sources of air pollutants. The cells were treated for 24h with the following concentrations of tested chemicals: B[a]P: 1μM, 10μM, 25μM; EOMs: 1μg/ml, 10μg/ml, 25μg/ml. We tested several endpoints representing key steps leading from DSBs to the formation of CAs including histone H2AX phosphorylation, levels of proteins Ku70, Ku80 and XRCC4 participating in NHEJ, in vitro ligation activity of nuclear extracts of the HEL12469 cells and the frequency of stable CAs assessed by whole chromosome painting of chromosomes 1, 2, 4, 5, 7 and 17 using fluorescence in situ hybridization. Our results show that 25μM of B[a]P and most of the tested doses of EOMs induced DSBs as indicated by H2AX phosphorylation. DNA damage was accompanied by induction of XRCC4 expression and an increased frequency of CAs. Translocations most frequently affected chromosome 7. We observed only a weak induction of Ku70/80 expression as well as ligation activity of nuclear extracts. In summary, our data suggest the induction of DSBs and NHEJ after treatment of human embryonic lung fibroblasts with B[a]P and complex mixtures containing PAHs.

26,26,26,27,27,27-Hexadeuterated-1,25-Dihydroxyvitamin D3 (1,25D-d6) As Adjuvant of Chemotherapy in Breast Cancer Cell Lines

It has been demonstrated that 1,25-dihydroxyvitamin D₃ (1,25D) and some of its analogues have antitumor activity. 1,25D labeled with deuterium (26,26,26,27,27,27-hexadeuterated 1α,25-dihydroxyvitamin D₃, or 1,25D-d₆) is commonly used as internal standard for 1,25D liquid chromatography-mass spectrometry (LC-MS) quantification. In the present study using human breast cancer cell lines, the biological activity of 1,25D-d₆ administered alone and in combination with two commonly used antineoplastic agents, 5-fluorouracil and etoposide, was evaluated. Using an MTT assay, flow cytometry, and western blots, our data demonstrated that 1,25D-d₆ has effects similar to the natural hormone on cell proliferation, cell cycle, and apoptosis. Furthermore, the combination of 1,25D-d₆ and etoposide enhances the antitumoral effects of both compounds. Interestingly, the antitumoral effect is higher in the more aggressive MDA-MB-231 breast cancer cell line. Our data indicate that 1,25D-d₆ administered alone or in combination with chemotherapy could be a good experimental method for accurately quantifying active 1,25D levels in cultures or in biological fluids, on both in vitro breast cancer cell lines and in vivo animal experimental models.

Replication-dependent and transcription-dependent mechanisms of DNA double-strand break induction by the topoisomerase 2-targeting drug etoposide

Etoposide is a DNA topoisomerase 2-targeting drug widely used for the treatment of cancer. The cytoxicity of etoposide correlates with the generation of DNA double-strand breaks (DSBs), but the mechanism of how it induces DSBs in cells is still poorly understood. Catalytically, etoposide inhibits the re-ligation reaction of Top2 after it nicks the two strands of DNA, trapping it in a cleavable complex consisting of two Top2 subunits covalently linked to the 5' ends of DNA (Top2cc). Top2cc is not directly recognized as a true DSB by cells because the two subunits interact strongly with each other to hold the two ends of DNA together. In this study we have investigated the cellular mechanisms that convert Top2ccs into true DSBs. Our data suggest that there are two mechanisms, one dependent on active replication and the other dependent on proteolysis and transcription. The relative contribution of each mechanism is affected by the concentration of etoposide. We also find that Top2α is the major isoform mediating the replication-dependent mechanism and both Top2α and Top2 mediate the transcription-dependent mechanism. These findings are potentially of great significance to the improvement of etoposide's efficacy in cancer therapy.

Multiplexed in vivo fluorescence optical imaging of the therapeutic efficacy of photodynamic therapy

In our study we wanted to elucidate a time frame for in vivo optical imaging of the therapeutic efficacy of photodynamic therapy (PDT) by using a multiplexed imaging approach for detecting apoptosis and vascularization. The internalization of the photosensitizer Foslip(®) into tongue-squamous epithelium carcinoma cells (CAL-27) was examined in vitro and in vivo. For detecting apoptosis, annexin V was covalently coupled to the near-infrared dye DY-734 and the spectroscopic properties and binding affinity to apoptotic CAL-27 cells were elucidated. CAL-27 tumor bearing mice were treated with PDT and injected 2 days and 2 weeks thereafter with DY-734-annexin V. PDT-induced changes in tumor vascularization were detected with the contrast agent IRDye(®) 800CW RGD up to 3 weeks after PDT. A perinuclear enrichment of Foslip(®) could be seen in vitro which was reflected in an accumulation in CAL-27 tumors in vivo. The DY-734-annexin V (coupling efficiency 30-50%) revealed a high binding affinity to apoptotic compared to non-apoptotic cells (17.2% vs. 1.2%) with a KD-value of 20 nm. After PDT-treatment, the probe showed a significantly higher (p <0.05) contrast in tumors at 2 days compared to 2 weeks after therapy (2-8 h post injection). A reduction of the vascularization could be detected after PDT especially in the central tumor areas. To detect the therapeutic efficacy of PDT, a multiplexed imaging approach is necessary. A detection of apoptotic cells is possible just shortly after therapy, whereas at later time points the efficacy can be verified by investigating the vascularization.

Dual regulatory roles of human AP-endonuclease (APE1/Ref-1) in CDKN1A/p21 expression

The human AP-endonuclease (APE1/Ref-1), an essential multifunctional protein involved in repair of oxidative DNA damage as well as in transcriptional regulation, is often overexpressed in tumor cells. APE1 was earlier shown to stimulate p53's DNA binding and its transactivation function in the expression of cyclin-dependent kinase inhibitor p21 (CDKN1A) gene. Here, we show APE1's stable binding to p53 cis elements which are required for p53-mediated activation of p21 in p53-expressing wild type HCT116 cells. However, surprisingly, we observed APE1-dependent repression of p21 in isogenic p53-null HCT116 cells. Ectopic expression of p53 in the p53-null cells abrogated this repression suggesting that APE1's negative regulatory role in p21 expression is dependent on the p53 status. We then identified APE1's another binding site in p21's proximal promoter region containing cis elements for AP4, a repressor of p21. Interestingly, APE1 and AP4 showed mutual dependence for p21 repression. Moreover, ectopic p53 in p53-null cells inhibited AP4's association with APE1, their binding to the promoter and p21 repression. These results together establish APE1's role as a co-activator or co-repressor of p21 gene, dependent on p53 status. It is thus likely that APE1 overexpression and inactivation of p53, often observed in tumor cells, promote tumor cell proliferation by constitutively downregulating p21 expression.

Toxic effect of silica nanoparticles on endothelial cells through DNA damage response via Chk1-dependent G2/M checkpoint

Silica nanoparticles have become promising carriers for drug delivery or gene therapy. Endothelial cells could be directly exposed to silica nanoparticles by intravenous administration. However, the underlying toxic effect mechanisms of silica nanoparticles on endothelial cells are still poorly understood. In order to clarify the cytotoxicity of endothelial cells induced by silica nanoparticles and its mechanisms, cellular morphology, cell viability and lactate dehydrogenase (LDH) release were observed in human umbilical vein endothelial cells (HUVECs) as assessing cytotoxicity, resulted in a dose- and time- dependent manner. Silica nanoparticles-induced reactive oxygen species (ROS) generation caused oxidative damage followed by the production of malondialdehyde (MDA) as well as the inhibition of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Both necrosis and apoptosis were increased significantly after 24 h exposure. The mitochondrial membrane potential (MMP) decreased obviously in a dose-dependent manner. The degree of DNA damage including the percentage of tail DNA, tail length and Olive tail moment (OTM) were markedly aggravated. Silica nanoparticles also induced G2/M arrest through the upregulation of Chk1 and the downregulation of Cdc25C, cyclin B1/Cdc2. In summary, our data indicated that the toxic effect mechanisms of silica nanoparticles on endothelial cells was through DNA damage response (DDR) via Chk1-dependent G2/M checkpoint signaling pathway, suggesting that exposure to silica nanoparticles could be a potential hazards for the development of cardiovascular diseases.

Inhibition of ATM blocks the etoposide-induced DNA damage response and apoptosis of resting human T cells

It is believed that normal cells with an unaffected DNA damage response (DDR) and DNA damage repair machinery, could be less prone to DNA damaging treatment than cancer cells. However, the anticancer drug, etoposide, which is a topoisomerase II inhibitor, can generate DNA double strand breaks affecting not only replication but also transcription and therefore can induce DNA damage in non-replicating cells. Indeed, we showed that etoposide could influence transcription and was able to activate DDR in resting human T cells by inducing phosphorylation of ATM and its substrates, H2AX and p53. This led to activation of PUMA, caspases and to apoptotic cell death. Lymphoblastoid leukemic Jurkat cells, as cycling cells, were more sensitive to etoposide considering the level of DNA damage, DDR and apoptosis. Next, we used ATM inhibitor, KU 55933, which has been shown previously to be a radio/chemo-sensitizing agent. Pretreatment of resting T cells with KU 55933 blocked phosphorylation of ATM, H2AX and p53, which, in turn, prevented PUMA expression, caspase activation and apoptosis. On the other hand, KU 55933 incremented apoptosis of Jurkat cells. However, etoposide-induced DNA damage in resting T cells was not influenced by KU 55933 as revealed by the FADU assay. Altogether our results show that KU 55933 blocks DDR and apoptosis induced by etoposide in normal resting T cells, but increased cytotoxic effect on proliferating leukemic Jurkat cells. We discuss the possible beneficial and adverse effects of drugs affecting the DDR in cancer cells that are currently in preclinical anticancer trials.

A novel topoisomerase inhibitor, daurinol, suppresses growth of HCT116 cells with low hematological toxicity compared to etoposide

We report that daurinol, a novel arylnaphthalene lignan, is a promising potential anticancer agent with adverse effects that are less severe than those of etoposide, a clinical anticancer agent. Despite its potent antitumor activity, clinical use of etoposide is limited because of its adverse effects, including myelosuppression and the development of secondary leukemia. Here, we comprehensively compared the mechanistic differences between daurinol and etoposide because they have similar chemical structures. Etoposide, a topoisomerase II poison, is known to attenuate cancer cell proliferation through the inhibition of DNA synthesis. Etoposide treatment induces G(2)/M arrest, severe DNA damage, and the formation of giant nuclei in HCT116 cells. We hypothesized that the induction of DNA damage and nuclear enlargement due to abnormal chromosomal conditions could give rise to genomic instability in both tumor cells and in actively dividing normal cells, resulting in the toxic adverse effects of etoposide. We found that daurinol is a catalytic inhibitor of human topoisomerase IIa, and it induces S-phase arrest through the enhanced expression of cyclins E and A and by activation of the ATM/Chk/Cdc25A pathway in HCT116 cells. However, daurinol treatment did not cause DNA damage or nuclear enlargement in vitro. Finally, we confirmed the in vivo antitumor effects and adverse effects of daurinol and etoposide in nude mice xenograft models. Daurinol displayed potent antitumor effects without any significant loss of body weight or changes in hematological parameters, whereas etoposide treatment led to decreased body weight and white blood cell, red blood cell, and hemoglobin concentration.