The role of histone acetylation versus DNA damage in drug-induced senescence and apoptosis

Mechanisms of carboplatin- and paclitaxel-dependent induction of premature senescence and pro-cancerogenic conversion of normal peritoneal mesothelium and fibroblasts

Carboplatin (CPT) and paclitaxel (PCT) are the optimal non-surgical treatment of epithelial ovarian cancer (EOC). Although their growth-restricting influence on EOC cells is well known, their impact on normal peritoneal cells, including mesothelium (PMCs) and fibroblasts (PFBs), is poorly understood. Here, we investigated whether, and if so, by what mechanism, CPT and PCT induce senescence of omental PMCs and PFBs. In addition, we tested whether PMC and PFB exposure to the drugs promotes the development of a pro-cancerogenic phenotype. The results showed that CPT and PCT induce G2/M growth arrest-associated senescence of normal peritoneal cells and that the strongest induction occurs when the drugs act together. PMCs senesce telomere-independently with an elevated p16 level and via activation of AKT and STAT3. In PFBs, telomeres shorten along with an induction of p21 and p53, and their senescence proceeds via the activation of ERK1/2. Oxidative stress in CPT + PCT-treated PMCs and PFBs is extensive and contributes causatively to their premature senescence. Both PMCs and PFBs exposed to CPT + PCT fuel the proliferation, migration, and invasion of established (A2780, OVCAR-3, SKOV-3) and primary EOCs, and this activity is linked with an overproduction of multiple cytokines altering the cancer cell transcriptome and controlled by p38 MAPK, NF-κB, STAT3, Notch1, and JAK1. Collectively, our findings indicate that CPT and PCT lead to iatrogenic senescence of normal peritoneal cells, which paradoxically and opposing therapeutic needs alters their phenotype towards pro-cancerogenic. It cannot be excluded that these adverse outcomes of chemotherapy may contribute to EOC relapse in the case of incomplete tumor eradication and residual disease initiation. © 2023 The Pathological Society of Great Britain and Ireland.

Exploring the Antioxidant Potential of Tragia volubilis L.: Mitigating Chemotherapeutic Effects of Doxorubicin on Tumor Cells

Several plants of the genus Tragia L. have shown antibacterial, fungicidal, and antiproliferative activity, among other types of activities; however, most species of the genus have not been investigated. Tragia volubilis L. is native to tropical America and Africa, and although it has been reported as medicinal in the literature, it has not been thoroughly investigated. In this study, the phytochemical screening, isolation, and identification of compounds and the determination of the antioxidant activity of the aqueous extract of Tragia volubilis L. and its partitions were carried out. Ethyl acetate and n-butanol partitions of the extract present high antioxidant activity according to the Antioxidant Activity Index. Due to their activity, these partitions were tested on RKO cells as a representative model, both individually and in combination with Doxorubicin. It was found that the partitions significantly reduced the effect of Doxorubicin, as well as the expression of proteins involved in DNA damage and cell death. While the reduction of the chemotherapeutic effect of Doxorubicin on tumor cells may not be a desired outcome in therapeutic settings, the findings of the study are valuable in revealing the antioxidant potential of Tragia volubilis L. and its partitions. This highlights the importance of carefully regulating the application of antioxidants, especially in the context of cancer chemotherapy.

Fast assay to predict multipotent mesenchymal stromal cell replicative senescence dynamics

The major obstacle to the application of mesenchymal stromal cells (MSCs) in regenerative medicine is the expansion of the donor-derived cells in vitro to obtain high cell numbers in the shortest possible time. However, MSCs gradually undergo replicative senescence after a variable number of divisions that reduce their therapeutic efficacy, which needs to be determined before administration. The authors developed a fast and simple evaluation assay testing two senescence inducers, mitoxantrone (Mxt) and trichostatin A (TSA), to predict the onset of spontaneous replicative senescence of adipose-derived mesenchymal stromal cells (ASCs) and have confirmed the correlation between induced senescence and spontaneous replicative senescence in the assay using Mxt. This protocol facilitates the standardization of therapeutic ASCs and MSCs from other origins before application.

NCOR1 Sustains Colorectal Cancer Cell Growth and Protects against Cellular Senescence

Simple Summary

NCOR1 is a scaffold protein that interacts with multiple partners to repress gene transcription. NCOR1 controls immunometabolic functions in several tissues and has been recently shown to protect against experimental colitis in mice. Our laboratory has observed a pro-proliferative role of NCOR1 in normal intestinal epithelial cells. However, it is unclear whether NCOR1 is functionally involved in colon cancer. This study demonstrated that NCOR1 is required for colorectal cancer cell growth. Depletion of NCOR1 caused these cells to become senescent. Transcriptomic signatures confirmed these observations but also predicted the potential for these cells to become pro-invasive. Thus, NCOR1 plays a novel role in preventing cancer-associated senescence and could represent a target for controlling colon cancer progression.

Abstract

NCOR1 is a corepressor that mediates transcriptional repression through its association with nuclear receptors and specific transcription factors. Some evidence supports a role for NCOR1 in neonatal intestinal epithelium maturation and the maintenance of epithelial integrity during experimental colitis in mice. We hypothesized that NCOR1 could control colorectal cancer cell proliferation and tumorigenicity. Conditional intestinal epithelial deletion of Ncor1 in Apc^Min/+ mice resulted in a significant reduction in polyposis. RNAi targeting of NCOR1 in Caco-2/15 and HT-29 cell lines led to a reduction in cell growth, characterized by cellular senescence associated with a secretory phenotype. Tumor growth of HT-29 cells was reduced in the absence of NCOR1 in the mouse xenografts. RNA-seq transcriptome profiling of colon cancer cells confirmed the senescence phenotype in the absence of NCOR1 and predicted the occurrence of a pro-migration cellular signature in this context. SOX2, a transcription factor essential for pluripotency of embryonic stem cells, was induced under these conditions. In conclusion, depletion of NCOR1 reduced intestinal polyposis in mice and caused growth arrest, leading to senescence in human colorectal cell lines. The acquisition of a pro-metastasis signature in the absence of NCOR1 could indicate long-term potential adverse consequences of colon-cancer-induced senescence.

Cellular Responses to Platinum-Based Anticancer Drugs and UVC: Role of p53 and Implications for Cancer Therapy

Chemotherapy is intended to induce cancer cell death through apoptosis and other avenues. Unfortunately, as discussed in this article, moderate doses of genotoxic drugs such as cisplatin typical of those achieved in the clinic often invoke a cytostatic/dormancy rather than cytotoxic/apoptosis response in solid tumour-derived cell lines. This is commonly manifested by an extended apoptotic threshold, with extensive apoptosis only being seen after very high/supralethal doses of such agents. The dormancy response can be associated with senescence-like features, polyploidy and/or multinucleation, depending in part on the p53 status of the cells. In most solid tumour-derived cells, dormancy represents a long-term survival mechanism, ultimately contributing to disease recurrence. This review highlights the nonlinearity of key aspects of the molecular and cellular responses to bulky DNA lesions in human cells treated with chemotherapeutic drugs (e.g., cisplatin) or ultraviolet light-C (a widely used tool for unraveling details of the DNA damage-response) as a function of the level of genotoxic stress. Such data highlight the growing realization that targeting dormant cancer cells, which frequently emerge following conventional anticancer treatments, may represent a novel strategy to prevent or, at least, significantly suppress cancer recurrence.

Natural Polyphenols Targeting Senescence: A Novel Prevention and Therapy Strategy for Cancer

Cancer is one of the most serious diseases endangering human health. In view of the side effects caused by chemotherapy and radiotherapy, it is necessary to develop low-toxic anti-cancer compounds. Polyphenols are natural compounds with anti-cancer properties and their application is a considerable choice. Pro-senescence therapy is a recently proposed anti-cancer strategy and has been shown to effectively inhibit cancer. It is of great significance to clarify the mechanisms of polyphenols on tumor suppression by inducing senescence. In this review, we delineated the characteristics of senescent cells, and summarized the mechanisms of polyphenols targeting tumor microenvironment and inducing cancer cell senescence for cancer prevention and therapy. Although many studies have shown that polyphenols effectively inhibit cancer by targeting senescence, it warrants further investigation in preclinical and clinical studies.

Targeted elimination of senescent Ras-transformed cells by suppression of MEK/ERK pathway

The Ras-Raf-MEK-ERK pathway plays a central role in tumorigenesis and is a target for anticancer therapy. The successful strategy based on the activation of cell death in Ras-expressing cells is associated with the suppression of kinases involved in Ras pathway. However, activation of cytoprotective autophagy overcomes antiproliferative effect of the inhibitors and develops drug resistance. We studied whether cellular senescence induced by HDAC inhibitor sodium butyrate in E1a+cHa-Ras-transformed rat embryo fibroblasts (ERas) and A549 human Ki-Ras mutated lung adenocarcinoma cells would enhance the tumor suppressor effect of MEK/ERK inhibition. Treatment of control ERas cells with PD0325901 for 24 h results in mitochondria damage and apoptotic death of a part of cellular population. However, the activation of AMPK-dependent autophagy overcomes pro-apoptotic effects of MEK/ERK inhibitor and results in restoration of the mitochondria and rescue of viability. Senescent ERas cells do not develop cytoprotective autophagy upon inhibition of MEK/ERK pathway due to spatial dissociation of lysosomes and autophagosomes in the senescent cells. Senescent cells are unable to form the autophagolysosomes and to remove the damaged mitochondria resulting in apoptotic death. Our data show that suppression of MEK/ERK pathway in senescent cells provides a new strategy for elimination of Ras-expressing cells.

Cypermethrin: Oxidative stress and genotoxicity in retinal cells of the adult zebrafish

Cypermethrin (CM), widely used for control of indoor and field pests, is one of the most common contaminants in freshwater aquatic systems. We evaluated CM genotoxicity and the activities of superoxide dismutase (SOD) and catalase (CAT) in retinal cells of adult zebrafish. Histological and immunofluorescence techniques show the presence of apoptotic cells in the zebrafish retina after 9 d of treatment with 0.6 μg/L CM. Histone γ-H2AX, a marker of DNA damage, was detected in both outer and inner nuclear layers; caspase-3, an apoptotic marker, was detected in the outer nuclear layer. In the comet assay, the cells were sensitive to hydrogen peroxide-induced DNA damage, showing a dose-dependent response. We observed a positive comet assay response to CM that was dose- and time-dependent. Following exposure to CM, SOD and CAT enzyme activities, and sod and cat mRNA levels, increased. These results indicate that CM causes DNA damage and oxidative stress and can induce apoptosis in retinal cells.

Therapeutic doses of doxorubicin induce premature senescence of human mesenchymal stem cells derived from menstrual blood, bone marrow and adipose tissue

Doxorubicin (Dox) is an effective anticancer drug with known activity against a wide spectrum of malignancies, hematologic malignancies in particular. Despite extensive clinical use, the mechanisms of its side effects and negative action on normal cells remain under study. The aim of this study was to investigate the effect of Dox on cultured human mesenchymal stem cells (MSCs) derived from menstrual blood (eMSCs), bone marrow (BMSCs) and adipose tissue (AMSCs). Dox treatment in high doses decreased the survival of MSCs in a dose-dependent manner. Clinically relevant low doses of Dox induced premature senescence of eMSCs, BMSCs and AMSCs, but did not kill the cells. Dox caused cell cycle arrest and formation of γ-H2AX foci, and increased the number of SA-β-gal-positive cells. BMSCs entered premature senescence earlier than other MSCs. It has been reported that neural-like cells differentiated from MSCs of various origins are more sensitive to Dox than their parent cells. Dox-treated differentiated MSCs exhibited lower viability and earlier generation of γ-H2AX foci. Dox administration inhibited secretory activity in neural-like cells. These findings suggest that a clinically relevant Dox dose damages cultured MSCs, inducing their premature senescence. MSCs are more resistant to this damage than differentiated cells.

Proteomic analysis of the vitamin C effect on the doxorubicin cytotoxicity in the MCF-7 breast cancer cell line

PURPOSE

Doxorubicin is an anthracycline drug which inhibits the growth of breast cancer cell lines. However, a major factor limiting its use is a cumulative, dose-dependent cardiotoxicity, resulting in a permanent loss of cardiomyocytes. Vitamin C was found to potentiate the cytotoxic effects of a variety of chemotherapeutic drugs including doxorubicin. The aim of the study was to describe the changes in protein expression and proliferation of the MCF-7 cells induced by the vitamin C applied with doxorubicin.

METHODS

Label-free quantitative proteomics and real-time cell analysis methods were used to search for proteome and cell proliferation changes. These changes were induced by the pure DOX and by DOX combined with vitamin C applied on the MCF-7 cell line.

RESULTS

From the real-time cell analysis experiments, it is clear that the highest anti-proliferative effect occurs with the addition of 200 µM of vitamin C to 1 µM of doxorubicin. By applying both the label-free protein quantification method and total ion current assay, we found statistically significant changes (p ≤ 0.05) of 26 proteins induced by the addition of vitamin C to doxorubicin on the MCF-7 cell line. These differentially expressed proteins are involved in processes such as structural molecule activity, transcription and translation, immune system process and antioxidant, cellular signalling and transport.

CONCLUSION

The detected proteins may be capable of predicting response to DOX therapy. This is a key tool in the treatment of breast cancer, and the combination with vit C seems to be of particular interest due to the fact that it can potentiate anti-proliferative effect of DOX.

DNA damage in the oligodendrocyte lineage and its role in brain aging

Myelination is a recent evolutionary addition that significantly enhances the speed of transmission in the neural network. Even slight defects in myelin integrity impair performance and enhance the risk of neurological disorders. Indeed, myelin degeneration is an early and well-recognized neuropathology that is age associated, but appears before cognitive decline. Myelin is only formed by fully differentiated oligodendrocytes, but the entire oligodendrocyte lineage are clear targets of the altered chemistry of the aging brain. As in neurons, unrepaired DNA damage accumulates in the postmitotic oligodendrocyte genome during normal aging, and indeed may be one of the upstream causes of cellular aging - a fact well illustrated by myelin co-morbidity in premature aging syndromes arising from deficits in DNA repair enzymes. The clinical and experimental evidence from Alzheimer's disease, progeroid syndromes, ataxia-telangiectasia and other conditions strongly suggest that oligodendrocytes may in fact be uniquely vulnerable to oxidative DNA damage. If this damage remains unrepaired, as is increasingly true in the aging brain, myelin gene transcription and oligodendrocyte differentiation is impaired. Delineating the relationships between early myelin loss and DNA damage in brain aging will offer an additional dimension outside the neurocentric view of neurodegenerative disease.

The Growing Complexity of Cancer Cell Response to DNA-Damaging Agents: Caspase 3 Mediates Cell Death or Survival?

It is widely stated that wild-type p53 either mediates the activation of cell cycle checkpoints to facilitate DNA repair and promote cell survival, or orchestrates apoptotic cell death following exposure to cancer therapeutic agents. This reigning paradigm has been challenged by numerous discoveries with different human cell types, including solid tumor-derived cell lines. Thus, activation of the p53 signaling pathway by ionizing radiation and other DNA-damaging agents hinders apoptosis and triggers growth arrest (e.g., through premature senescence) in some genetic backgrounds; such growth arrested cells remain viable, secrete growth-promoting factors, and give rise to progeny with stem cell-like properties. In addition, caspase 3, which is best known for its role in the execution phase of apoptosis, has been recently reported to facilitate (rather than suppress) DNA damage-induced genomic instability and carcinogenesis. This observation is consistent with an earlier report demonstrating that caspase 3 mediates secretion of the pro-survival factor prostaglandin E₂, which in turn promotes enrichment of tumor repopulating cells. In this article, we review these and related discoveries and point out novel cancer therapeutic strategies. One of our objectives is to demonstrate the growing complexity of the DNA damage response beyond the conventional “repair and survive, or die” hypothesis.

Phosphorylation of Tip60 by p38α regulates p53-mediated PUMA induction and apoptosis in response to DNA damage

Tip60 is a multifunctional acetyltransferase involved in multiple cellular functions. Acetylation of p53 at K120 by Tip60 promotes p53-mediated apoptosis after DNA damage. We previous showed that Tip60 activity is induced by phosphorylation at T158 by p38. In this study, we investigated the role of p38-mediated Tip60 phosphorylation in p53-mediated, DNA damage-induced apoptosis. We found that DNA damage induces p38 activation, Tip60-T158 phosphorylation, and p53-K120 acetylation with similar kinetics. p38α is essential for DNA damage-induced Tip60-T158 phosphorylation. In addition, both p38α and Tip60 are essential for p53-K120 acetylation, binding of p53 to PUMA promoter, PUMA expression and apoptosis induced by DNA damage. Moreover, DNA damage induces protein kinase activity of p38α towards Tip60-T158, and constitutive activation of p38 in cells leads to increases in Tip60-T158 phosphorylation, p53-K120 acetylation, PUMA expression and apoptosis. Furthermore, the Tip60-T158A mutant that cannot be phosphorylated by p38 fails to mediate p53-K120 acetylation, PUMA induction, and apoptosis following DNA damage. These results establish that Tip60-T158 phosphorylation by p38 plays an essential role in stimulating Tip60 activity required for inducing the p53-PUMA pathway that ultimately leads to apoptosis in response to DNA damage, which provides a mechanistic basis for the tumor-suppressing function of p38 and Tip60.

Gallotannin is a DNA damaging compound that induces senescence independently of p53 and p21 in human colon cancer cells

The plant secondary metabolite gallotannin (GT) is the simplest hydrolyzable tannin shown to have anti-carcinogenic properties in several cell lines and to inhibit tumor development in different animal models. Here, we determined if GT induces senescence and DNA damage and investigated the involvement of p53 and p21 in this response. Using HCT116 human colon cancer cells wildtype for p53(+/+) /p21(+/+) and null for p53(+/+) /p21(-/-) or p53(-/-) /p21(+/+) , we found that GT induces senescence independently of p21 and p53. GT was found to increase the production of reactive oxygen species (ROS) by altering the redox balance in the cell, mainly by reducing the levels of glutathione and superoxide dismutase (SOD). Using the key antioxidants N-acetyl cysteine, dithiothreitol, SOD, and catalase, we showed that ROS were partially involved in the senescence response. Furthermore, GT-induced cell cycle arrest in S-phase in all HCT116 cell lines. At later time points, we noticed that p53 and p21 null cells escaped complete arrest and re-entered cell cycle provoking higher rates of multinucleation. The senescence induction by GT was irreversible and was accompanied by significant DNA damage as evidenced by p-H2AX staining. Our findings indicate that GT is an interesting anti colon cancer agent which warrants further study.

HIPK2 restricts SIRT1 activity upon severe DNA damage by a phosphorylation-controlled mechanism

Upon severe DNA damage a cellular signalling network initiates a cell death response through activating tumour suppressor p53 in association with promyelocytic leukaemia (PML) nuclear bodies. The deacetylase Sirtuin 1 (SIRT1) suppresses cell death after DNA damage by antagonizing p53 acetylation. To facilitate efficient p53 acetylation, SIRT1 function needs to be restricted. How SIRT1 activity is regulated under these conditions remains largely unclear. Here we provide evidence that SIRT1 activity is limited upon severe DNA damage through phosphorylation by the DNA damage-responsive kinase HIPK2. We found that DNA damage provokes interaction of SIRT1 and HIPK2, which phosphorylates SIRT1 at Serine 682 upon lethal damage. Furthermore, upon DNA damage SIRT1 and HIPK2 colocalize at PML nuclear bodies, and PML depletion abrogates DNA damage-induced SIRT1 Ser682 phosphorylation. We show that Ser682 phosphorylation inhibits SIRT1 activity and impacts on p53 acetylation, apoptotic p53 target gene expression and cell death. Mechanistically, we found that DNA damage-induced SIRT1 Ser682 phosphorylation provokes disruption of the complex between SIRT1 and its activator AROS. Our findings indicate that phosphorylation-dependent restriction of SIRT1 activity by HIPK2 shapes the p53 response.

Exploiting tumor cell senescence in anticancer therapy

Cellular senescence is a physiological process of irreversible cell-cycle arrest that contributes to various physiological and pathological processes of aging. Whereas replicative senescence is associated with telomere attrition after repeated cell division, stress-induced premature senescence occurs in response to aberrant oncogenic signaling, oxidative stress, and DNA damage which is independent of telomere dysfunction. Recent evidence indicates that cellular senescence provides a barrier to tumorigenesis and is a determinant of the outcome of cancer treatment. However, the senescence-associated secretory phenotype, which contributes to multiple facets of senescent cancer cells, may influence both cancer-inhibitory and cancer-promoting mechanisms of neighboring cells. Conventional treatments, such as chemo- and radiotherapies, preferentially induce premature senescence instead of apoptosis in the appropriate cellular context. In addition, treatment-induced premature senescence could compensate for resistance to apoptosis via alternative signaling pathways. Therefore, we believe that an intensive effort to understand cancer cell senescence could facilitate the development of novel therapeutic strategies for improving the efficacy of anticancer therapies. This review summarizes the current understanding of molecular mechanisms, functions, and clinical applications of cellular senescence for anticancer therapy.

Histone deacetylases and their inhibitors in cancer, neurological diseases and immune disorders

Epigenetic aberrations, which are recognized as key drivers of several human diseases, are often caused by genetic defects that result in functional deregulation of epigenetic proteins, their altered expression and/or their atypical recruitment to certain gene promoters. Importantly, epigenetic changes are reversible, and epigenetic enzymes and regulatory proteins can be targeted using small molecules. This Review discusses the role of altered expression and/or function of one class of epigenetic regulators--histone deacetylases (HDACs)--and their role in cancer, neurological diseases and immune disorders. We highlight the development of small-molecule HDAC inhibitors and their use in the laboratory, in preclinical models and in the clinic.

Sustained activation of DNA damage response in irradiated apoptosis-resistant cells induces reversible senescence associated with mTOR downregulation and expression of stem cell markers

Cells respond to genotoxic stress by activating the DNA damage response (DDR). When injury is severe or irreparable, cells induce apoptosis or cellular senescence to prevent transmission of the lesions to the daughter cells upon cell division. Resistance to apoptosis is a hallmark of cancer that challenges the efficacy of cancer therapy. In this work, the effects of ionizing radiation on apoptosis-resistant E1A + E1B transformed cells were investigated to ascertain whether the activation of cellular senescence could provide an alternative tumor suppressor mechanism. We show that irradiated cells arrest cell cycle at G₂/M phase and resume DNA replication in the absence of cell division followed by formation of giant polyploid cells. Permanent activation of DDR signaling due to impaired DNA repair results in the induction of cellular senescence in E1A + E1B cells. However, irradiated cells bypass senescence and restore the population by dividing cells, which have near normal size and ploidy and do not express senescence markers. Reversion of senescence and appearance of proliferating cells were associated with downregulation of mTOR, activation of autophagy, mitigation of DDR signaling, and expression of stem cell markers.

A new p53 target gene, RKIP, is essential for DNA damage-induced cellular senescence and suppression of ERK activation

p53, a strong tumor suppressor protein, is known to be involved in cellular senescence, particularly premature cellular senescence. Oncogenic stresses, such as Ras activation, can initiate p53-mediated senescence, whereas activation of the Ras-mitogen-activated protein kinase (MAPK) pathway can promote cell proliferation. These conflicting facts imply that there is a regulatory mechanism for balancing p53 and Ras-MAPK signaling. To address this, we evaluated the effects of p53 on the extracellular signal-regulated kinase (ERK) activation and found that p53 could suppress ERK activation through de novo synthesis. Through several molecular biologic analyses, we found that RKIP, an inhibitor of Raf kinase, is responsible for p53-mediated ERK suppression and senescence. Overexpression of RKIP can induce cellular senescence in several types of cell lines, including p53-deficient cells, whereas the elimination of RKIP by siRNA or forced expression of ERK blocks p53-mediated cellular senescence. These results suggested that RKIP is an essential protein for cellular senescence. Moreover, modification of the p53 serine 46 residue was critical for RKIP induction and ERK suppression as well as cellular senescence. These results indicated that RKIP is a novel p53 target gene that is responsible for p53-mediated cellular senescence and tumor suppressor protein expression.

The effect of systemic chemotherapy on neurogenesis, plasticity and memory

Chemotherapy has been enormously successful in treating many forms of cancer and improving patient survival rates. With the increasing numbers of survivors, a number of cognitive side effects have become apparent. These have been called "chemobrain" or "chemofog" among patient groups, who describe the symptoms as a decline in memory, concentration and executive functions. Changes which, although subtle, can cause significant distress among patients and prevent a return to the quality of life experienced before treatment. This cognitive side effect of chemotherapy was not anticipated as it had been assumed that chemotherapy agents, administered systematically, could not cross the blood-brain barrier and that the brain was therefore protected from their action. It is now realised that low concentrations of many chemotherapy agents cross the blood-brain barrier and even those that are completely prevented from doing so, can induce the production of inflammatory cytokines in peripheral tissues which in turn can cross the blood-brain barrier and impact on the brain. A large number of patient studies have shown that cognitive decline is found in a proportion of patients treated with a variety of chemotherapy agents for different types of cancer. The deficits experienced by these patients can last for up to several years and have a deleterious effect on educational attainment and ability to return to work. Imaging studies of patients after systemic chemotherapy show that this treatment produces structural and functional changes in the brain some of which seem to persist even when the cognitive deficits have ceased. This suggests that, with time, brain plasticity may be able to compensate for the deleterious effects of chemotherapy treatment. A number of mechanisms have been suggested for the changes in brain structure and function found after chemotherapy. These include both central and peripheral inflammatory changes, demyelination of white matter tracts, a reduction in stem cell proliferation in both the hippocampal neurogenic region and by oligodendrocyte precursors as well as changes in hormonal or growth factor levels. A number of possible treatments have been suggested which range from pharmacological interventions to cognitive behavioural therapies. Some of these have only been tested in animal models while others have produced varying degrees of improvement in patient populations. Currently, there is no recognised treatment and a greater understanding of the causes of the cognitive decline experienced after chemotherapy will be key to finding ways of preventing or treating the effects of chemobrain.

Dexamethasone reduces sensitivity to cisplatin by blunting p53-dependent cellular senescence in non-small cell lung cancer

Introduction

Dexamethasone (DEX) co-treatment has proved beneficial in NSCLC patients, improving clinical symptoms by the reduction of side effects after chemotherapy. However, recent studies have shown that DEX could render cancer cells more insensitive to cytotoxic drug therapy, but it is not known whether DEX co-treatment could influence therapy-induced senescence (TIS), and unknown whether it is in a p53-dependent or p53-independent manner.

Methods

We examined in different human NSCLC cell lines and detected cellular senescence after cisplatin (DDP) treatment in the presence or absence of DEX. The in vivo effect of the combination of DEX and DDP was assessed by tumor growth experiments using human lung cancer cell lines growing as xenograft tumors in nude mice.

Results

Co-treatment with DEX during chemotherapy in NSCLC resulted in increased tumor cell viability and inhibition of TIS compared with DDP treated group. DEX co-treatment cells exhibited the decrease of DNA damage signaling pathway proteins, the lower expression of p53 and p21^CIP1, the lower cellular secretory program and down-regulation of NF-κB and its signaling cascade. DEX also significantly reduced DDP sensitivity in vivo.

Conclusions

Our results underscore that DEX reduces chemotherapy sensitivity by blunting therapy induced cellular senescence after chemotherapy in NSCLC, which may, at least in part, in a p53-dependent manner. These data therefore raise concerns about the widespread combined use of gluocorticoids (GCs) with antineoplastic drugs in the clinical management of cancer patients.

PTTG1 attenuates drug-induced cellular senescence

As PTTG1 (pituitary tumor transforming gene) abundance correlates with adverse outcomes in cancer treatment, we determined mechanisms underlying this observation by assessing the role of PTTG1 in regulating cell response to anti-neoplastic drugs. HCT116 cells devoid of PTTG1 (PTTG1^−/−) exhibited enhanced drug sensitivity as assessed by measuring BrdU incorporation in vitro. Apoptosis, mitosis catastrophe or DNA damage were not detected, but features of senescence were observed using low doses of doxorubicin and TSA. The number of drug-induced PTTG1^−/− senescent cells increased ∼4 fold as compared to WT PTTG1-replete cells (p<0.001). p21, an important regulator of cell senescence, was induced ∼3 fold in HCT116 PTTG1^−/− cells upon doxorubicin or Trichostatin A treatment. Binding of Sp1, p53 and p300 to the p21 promoter was enhanced in PTTG1^−/− cells after treatment, suggesting transcriptional regulation of p21. p21 knock down abrogated the observed senescent effects of these drugs, indicating that PTTG1 likely suppresses p21 to regulate drug-induced senescence. PTTG1 also regulated SW620 colon cancer cells response to doxorubicin and TSA mediated by p21. Subcutaneously xenografted PTTG1^−/− HCT116 cells developed smaller tumors and exhibited enhanced responses to doxorubicin. PTTG1^−/− tumor tissue derived from excised tumors exhibited increased doxorubicin-induced senescence. As senescence is a determinant of cell responses to anti-neoplastic treatments, these findings suggest PTTG1 as a tumor cell marker to predict anti-neoplastic treatment outcomes.

Curcumin enhances the effect of cisplatin in suppression of head and neck squamous cell carcinoma via inhibition of IKKβ protein of the NFκB pathway

Previous experiments have shown that curcumin or cisplatin treatment suppresses growth of head and neck squamous cell carcinoma (HNSCC). To study the potential cooperative effect of both agents, two HNSCC cell lines were treated with curcumin or cisplatin alone or in combination. In vivo studies consisted of intravenous tail vein injection of liposomal curcumin, with intraperitoneal cisplatin, into nude mice growing xenograft HNSCC tumors. Introduction of curcumin and suboptimal concentrations of cisplatin showed a significant suppressive effect compared with treatment with either agent alone. Reduced expression of cyclin D1, IκBα, phospho-IκBα, and IKKβ occurred in cisplatin- and curcumin-treated cell lines. Confocal microscopy showed expression of IKKβ in the nucleus of the cell lines. Chromatin immunoprecipitation assay on DNA isolated from IKKβ immunoprecipitated samples showed PCR amplification of interleukin-8 promoter sequences, a binding site of NFκB, indicating an interaction between IKKβ and NFκB. Curcumin inhibited IKKβ in the cytoplasm and nucleus, leading to reduced NFκB activity, with no effect on phospho-AKT. In vivo studies showed significant growth inhibition of xenograft tumors treated with a combination of liposomal curcumin and cisplatin. The suppressive effect of curcumin was mediated through inhibition of cytoplasmic and nuclear IKKβ, resulting in inhibition of NFκB activity. Cisplatin treatment led to cellular senescence, indicating an effect mediated by p53 activation. The mechanisms of the two agents through different growth signaling pathways suggest potential for the clinical use of subtherapeutic doses of cisplatin in combination with curcumin, which will allow effective suppression of tumor growth while minimizing the toxic side effects of cisplatin.

New biomarkers probing depth of cell senescence assessed by laser scanning cytometry

The imaging analytical capabilities of laser scanning cytometer (LSC) have been used to assess morphological features considered to be typical of the senescent phenotype. The characteristic “flattening” of senescent cells was reflected by the decline in the density of staining (intensity of maximal pixel) of DNA-associated fluorescence [4,6-diamidino-2-phenylindole (DAPI)] paralleled by an increase in nuclear size (area). The decrease in ratio of maximal pixel to nuclear area was even more sensitive senescence biomarker than the change in maximal pixel or nuclear area, each alone. The saturation cell density at plateau phase of growth recorded by LSC was found to be dramatically decreased in cultures of senescent cells, thereby also serving as an additional marker. The induction of cyclin dependent kinase inhibitors p21^WAF1 and p27^KIP1 and γH2AX and activation of ATM markers of DNA damage response were measured in parallel with DNA/DAPI maximal pixel and nuclear area. These biomarker indices were expressed in quantitative terms by reporting them as a fraction of the respective controls. The effect of treatment of A549 and WI-38 cells with different concentrations of mitoxantrone (Mxt) and trichostatin A for various time periods was studied to assess the degree (depth) of cell senescence. Also assessed was the effect of 2-deoxy-d-glucose, the agent attenuating metabolic cell activity, on the depth of senescence induced by Mxt. A relationship between the ability of cells to synthesize RNA (incorporate 5-ethynyluridine) that leads to growth imbalance and induction of cell senescence was also studied. The data show that morphometric analysis of cellular attributes by LSC offers an attractive tool to detect cell senescence and measure its degree particularly in assessing effects of the factors that enhance or attenuate this process. This methodology is of importance in light of the evidence that cellular senescence is not only a biological process that is fundamental for organismal aging but also impedes formation of induced-pluripotent stem cells providing the barrier for neoplastic transformation and is the major mechanism of induction of reproductive cell death during treatment of solid tumors. © 2010 International Society for Advancement of Cytometry.

DNMT3a plays a role in switches between doxorubicin-induced senescence and apoptosis of colorectal cancer cells

The DNA-damaging drug doxorubicin (Dox) induces cell senescence at concentrations significantly lower than those required for induction of apoptosis. At low Dox concentrations, tumor suppressor p53 is activated, which enhances the expression of p21(Waf1/Cip1) (p21). At high concentrations, Dox activates p53 leading to apoptosis without enhancing p21 expression. The underlying mechanisms and factors that govern the differential effects of Dox in inducing senescence and apoptosis are unclear. Here, we report that the DNA methyltransferase (DNMT) DNMT3a was upregulated by Dox especially at concentrations that induced apoptosis in HCT116 colorectal cancer cells, and this process was regulated by p53. Meanwhile, p21 expression was significantly upregulated at senescence-inducing concentrations and kept low on treatment with apoptosis-inducing concentrations of Dox. The differential expression of DNMT3a and p21 in response to Dox suggests that DNMT3a may be a key factor in switches between Dox-induced senescence and apoptosis. Moreover, when DNMT3a was silenced, treatment of HCT116 cells with apoptosis-inducing concentration of Dox increased the percentage of cells undergoing senescence, accompanied by upregulation of p21. Contrarily, senescence-inducing concentration of Dox promoted apoptosis rate, and p21 expression was repressed. Surprisingly, no changes in DNA methylation status at p21 promoter were detected at either ranges of Dox, although DNMT3a and HDAC1 were recruited to p21 promoter at apoptosis-inducing Dox concentration, where they were present in the same complex. Overall, these data demonstrate that DNMT3a impacts the expression of p21 and plays a role in determining the Dox-induced senescence and apoptosis in HCT116 cells.

Quantitative proteomic analysis reveals the perturbation of multiple cellular pathways in jurkat-T cells induced by doxorubicin

Doxorubicin remains an important part of chemotherapy regimens in the clinic and is considered an effective agent in the treatment of acute lymphoblastic leukemia (ALL). Although the cellular responses induced by doxorubicin treatment have been investigated for years, the precise mechanisms underlying its cytotoxicity and therapeutic activity remain unclear. Here we utilized mass spectrometry, together with stable isotope labeling by amino acids in cell culture (SILAC), to analyze comparatively the protein expression in Jurkat-T cells before and after treatment with a clinically relevant concentration of doxorubicin. We were able to quantify 1066 proteins in Jurkat-T cells with both forward and reverse SILAC measurements, among which 62 were with significantly altered levels of expression induced by doxorubicin treatment. These included the up-regulation of core histones, heterogeneous nuclear ribonucleoproteins, and superoxide dismutase 2 as well as the down-regulation of hydroxymethylglutaryl-CoA synthase and farnesyl diphosphate synthase. The latter two are essential enzymes for cholesterol biosynthesis. We further demonstrated that the doxorubicin-induced growth inhibition of Jurkat-T cells could be rescued by treatment with cholesterol, supporting that doxorubicin exerts its cytotoxic effect, in part, by suppressing the expression of hydroxymethylglutaryl-CoA synthase and farnesyl diphosphate synthase, thereby inhibiting the endogenous production of cholesterol. The results from the present study provide important new knowledge for gaining insights into the molecular mechanisms of action of doxorubicin.

DNA methylation-related vitamin D receptor insensitivity in breast cancer

Calcitriol (1α, 25(OH)(2)-Vitamin D3) binds to the vitamin D receptor (VDR) and regulates differentiation of the normal mammary gland, and may therefore be useful in breast cancer treatment or prevention. Many breast cancer cells are, however, resistant to Calcitriol. In this study, we investigated the resistance mechanism and the role of epigenetic silencing of VDR by promoter hypermethylation. Bisulfite sequencing of the VDR promoter region revealed methylated CpG islands at -700 base pairs (bp) upstream and near the transcription start site. VDR CpG islands were demethylated by 5'deoxy-azacytidine treatment, and this was accompanied by a parallel increase in VDR mRNA levels in breast cancer cell lines. Quantitative methylation-specific PCR analyses confirmed hypermethylation of these CpG islands in primary tumors, and its absence in normal breast tissue. VDR transcripts detected in breast cancers were predominantly 5'-truncated, while normal breast tissue expressed full-length transcripts. Consistent with this observation, genes containing the VDR-responsive element (VDRE), such as cytochrome p450 hydroxylases, p21 or C/EBP were underexpressed in breast cancers compared to normal breast samples. Expression of the active longer transcripts of VDR was restored with 5'deoxy-Azacytidine (AZA) treatment, with a concurrent increase in expression of VDRE-containing genes. Thus, promoter methylation-mediated silencing of expression of the functional variants of VDR may contribute to reduced expression of downstream effectors of the VDR pathway and subsequent Calcitriol insensitivity in breast cancer. These data suggest that pharmacological reversal of VDR methylation may re-establish breast cancer cell susceptibility to differentiation therapy using Calcitriol.

Single-cell analysis of p16(INK4a) and p21(WAF1) expression suggests distinct mechanisms of senescence in normal human and Li-Fraumeni Syndrome fibroblasts

Herein we used single-cell observation methods to gain insight into the roles of p16(INK4A) and p21(WAF1) (hereafter p16 and p21) in replicative senescence and ionizing radiation-induced accelerated senescence in human [normal, ataxia telangiectasia (AT) and Li-Fraumeni syndrome (LFS)] fibroblast strains. Cultures of all strains entered a state of replicative senescence at late passages, as evident from inhibition of growth, acquisition of flattened and enlarged cell morphology, and positive staining for senescence-associated beta-galactosidase. In addition, proliferating early-passage cultures of these strains exhibited accelerated senescence in response to ionizing radiation. Immunofluorescence microscopy revealed the heterogeneous expression of p16 in normal and AT fibroblast strains, with the majority of the cells exhibiting undetectable levels of p16 irrespective of in vitro culture age. Importantly, replicative senescence as well as accelerated senescence triggered by ionizing radiation were accompanied by sustained nuclear accumulation of p21, but did not correlate with p16 expression in p53-proficient (normal and AT) fibroblasts. In p53-deficient (LFS) fibroblasts, on the other hand, replicative senescence and ionizing radiation-triggered accelerated senescence strongly correlated with expression of p16 but not of p21. Furthermore, senescence in LFS fibroblasts was associated with genomic instability encompassing polyploidy. Our findings are compatible with a model in which p16 serves as a backup regulator of senescence, triggering this response preferentially in the absence of wild-type p53 activity. The possibility that one of the tumor-suppressor functions of p16 may be associated with genomic instability, preventing the emergence of malignant progeny from polyploid giant cells, is also supported by these results.

Accelerated lung aging: a novel pathogenic mechanism of chronic obstructive pulmonary disease (COPD)

An enhanced or abnormal inflammatory response to the lungs to inhaled particles and gases, usually from cigarette smoke, is considered to be a general pathogenic mechanism in COPD (chronic obstructive pulmonary disease). Activation of leucocytes and the development of oxidant-antioxidant and protease-anti-protease imbalances are thought to be important aspects of this enhanced inflammatory response to cigarette smoke. The mechanisms involved in the perpetuation of the inflammatory response in the lungs in patients who develop COPD, even after smoking cessation, are not fully established and are key to our understanding of the pathogenic mechanisms in COPD and may be important for the development of new therapies. There is a relationship between chronic inflammatory diseases and aging, and the processes involved in aging may provide a novel mechanism in the pathogenesis of COPD. There is good evidence linking aging and COPD. During normal aging, pulmonary function deteriorates progressively and pulmonary inflammation increases, accompanied in the lungs by the features of emphysema. These features are accelerated in COPD. Emphysema is associated with markers of accelerated aging in the lungs, and COPD is also associated with features of accelerated aging in other organs, such as the cardiovascular and musculoskeletal systems. Cigarette smoke and other oxidative stresses result in cellular senescence and accelerate lung aging. There is also evidence that anti-aging molecules such as histone deacetylases and sirtuins are decreased in the lungs of COPD patients, compared with smokers without COPD, resulting in enhanced inflammation and further progression of COPD. The processes involved in accelerated aging may provide novel targets for therapy in COPD. The present article reviews the evidence for accelerated aging as a mechanism in the pathogenesis of COPD.

Relationships between cancer and aging: a multilevel approach

The incidence of cancer increases with age in humans and in laboratory animals alike. There are different patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer in two ways: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine systems. Increased susceptibility to the effects of tumor promoters is found both in aged animals and aged humans, as predicted by the multistage model of carcinogenesis. Aging is associated with a number of events at the molecular, cellular and physiological levels that influence carcinogenesis and subsequent cancer growth. An improved understanding of age-associated variables impacting on the tumor microenvironment, as well as the cancer cells themselves, will result in improved treatment modalities in geriatric oncology.

Non-DNA-binding platinum anticancer agents: Cytotoxic activities of platinum-phosphato complexes towards human ovarian cancer cells

DNA is believed to be the molecular target for the cytotoxic activities of platinum (Pt) anticancer drugs. We report here a class of platinum(II)- and platinum(IV)-pyrophosphato complexes that exhibit cytotoxicity comparable with and, in some cases, better than cisplatin in ovarian cell lines (A2780, A2780/C30, and CHO), yet they do not show any evidence of covalent binding to DNA. Moreover, some of these compounds are quite effective in cisplatin- and carboplatin-resistant cell line A2780/C30. The lack of DNA binding was demonstrated by the absence of a detectable Pt signal by atomic absorption spectroscopy using isolated DNA from human ovarian cells treated with a platinum(II)-pyrophosphato complex, (trans-1,2-cyclohexanediamine)(dihydrogen pyrophosphato) platinum(II), (pyrodach-2) and from NMR experiments using a variety of nucleotides including single- and double-stranded DNA. Furthermore, pyrodach-2 exhibited reduced cellular accumulations compared with cisplatin in cisplatin- and carboplatin-resistant human ovarian cells, yet the IC(50) value for the pyrophosphato complex was much less than that of cisplatin. Moreover, unlike cisplatin, pyrodach-2 treated cells overexpressed fas and fas-related transcription factors and some proapoptotic genes such as Bak and Bax. Data presented in this report collectively indicate that pyrodach-2 follows different cytotoxic mechanisms than does cisplatin. Unlike cisplatin, pyrodach-2 does not undergo aquation during 1 week and is quite soluble and stable in aqueous solutions. Results presented in this article represent a clear paradigm shift not only in expanding the molecular targets for Pt anticancer drugs but also in strategic development for more effective anticancer drugs.

Aging and induced senescence as factors in the pathogenesis of lung emphysema

Classically, the development of emphysema in chronic obstructive pulmonary disease is believed to involve inflammation induced by cigarette smoke and leukocyte activation, including oxidant-antioxidant and protease-antiprotease imbalances. While there is substantial evidence for this, additional aspects have been suggested by a number of clinical and experimental observations. Smokers exhibit signs of premature aging, particularly obvious in the skin. The link between aging and chronic disease is well-known, e.g., for the brain and musculoskeletal or cardiovascular system, as well as the clinical link between malnutrition and emphysema, and the experimental link to caloric restriction. Interestingly, this intervention also increases lifespan, in parallel with alterations in metabolism, oxidant burden and endocrine signaling. Of special interest is the observation that, even in the absence of an inflammatory environment, lung fibroblasts from patients with emphysema show persistent alterations, possibly based on epigenetic mechanisms. The importance of these mechanisms for cellular reprogramming and response patterns, individual risk profile and therapeutic options is becoming increasingly recognized. The same applies to cellular senescence. Recent findings from patients and experimental models open novel views into the arena of gene-environment interactions, including the role of systemic alterations, cellular stress, telomeres, CDK inhibitors such as p16, p21, pRb, PI3K, mTOR, FOXO transcription factors, histone modifications, and sirtuins. This article aims to outline this emerging picture and to stimulate the identification of challenging questions. Such insights also bear implications for the long-term course of the disease in relation to existing or future therapies and the exploration of potential lung regeneration.

Death in the AIRE

When thymic epithelia begin to synthesize peripheral tissue antigens such as insulin, we are seeing the result of autoimmune regulator (AIRE) activity and the workings of central tolerance. AIRE is an extraordinary protein that repatterns the transcriptome of medullary thymic epithelia (mTECs) to produce a stroma decorated with peripheral self-peptides. These peptidic arrays are used to purge self-reactive T cells, thereby averting autoimmunity. We now propose that an inherently cytotoxic event such as global chromatin modification paves the way for AIRE action. This injury stimulus might impose temporal restrictions for the T-cell education process and is endured, at least transiently, by the unique cellular environment provided by the medullary thymic epithelia.

Induction of senescence with doxorubicin leads to increased genomic instability of HCT116 cells

Induction of senescence has been proposed as a possible in vivo tumor response to anticancer treatment. Senescent cancer cells are often polyploid, however, their route to polyploidy is poorly recognized (endoreduplication versus aberrant mitoses). We showed that after treatment of HCT116 cells with a low dose of doxorubicin most of them stopped proliferation as documented by SA-beta-galactosidase activity and the lack of Ki67 expression. Increased expression of other common senescence markers, p53, p21 and cyclin D1, was also observed. The cells became giant, polyploid and polymorphic, with multinucleated cells comprising a substantial fraction. The vast majority of the doxorubicin-treated cells did not enter mitoses, as evidenced by mitotic index analysis, as well as by the predominantly cytoplasmic localization of cyclin B1 and a lack of separation of multiplied centrosomes. This allowed us to conclude that doxorubicin-treated HCT116 cells underwent endoreduplication. However, the rare events of aberrant mitoses of polyploid cells observed by us led to aneuploid progeny as was documented by cytogenetic analysis of survivors. Thus, a senescence-inducing treatment of HCT116 cancer cells had a dual effect-it stopped the proliferation of the majority of the cells, but also led to the appearance of proliferating aneuploid ones.

Ultraviolet light exposure triggers nuclear accumulation of p21(WAF1) and accelerated senescence in human normal and nucleotide excision repair-deficient fibroblast strains

Induction of the p21(WAF1) protein (hereafter called p21) following genotoxic stress is known to inhibit proliferating cell nuclear antigen (PCNA)-dependent DNA repair, downregulate apoptosis, and trigger a sustained growth-arrested phenotype called accelerated senescence. Studies with immortalized human and murine cell lines have revealed that exposure to ultraviolet light (UVC; 254 nm) results in the degradation of p21 to facilitate DNA repair and promote cell survival, or may lead to apoptotic cell death. The objective of the present study was to determine whether exposure of non-transformed human fibroblast strains to relatively low fluences of UVC (i.e., fluences typically used in the clonogenic survival assay) might induce sustained nuclear accumulation of p21, leading to accelerated senescence. We have evaluated the responses of normal human fibroblast (NHF) strains and nucleotide excision repair (NER)-deficient fibroblast strains representing xeroderma pigmentosum (XP) complementation groups A and G and Cockayne syndrome (CS) complementation groups A and B. We report that exposure of NHFs to < or =15 J/m(2) of UVC, and NER-deficient fibroblasts to < or =5 J/m(2) of UVC, results in sustained nuclear accumulation of p21 and growth arrest through accelerated senescence. With each fibroblast strain examined, exposure to UVC fluences that resulted in approximately 90% loss of clonogenic potential triggered significant (>60%) accelerated senescence, but only marginal (<5%) apoptosis. We conclude that nuclear accumulation of p21 accompanied by accelerated senescence may be an integral component of the response of human fibroblasts to UVC-induced DNA damage, irrespective of their DNA repair capabilities.

Mdm2 as a sensitive and mechanistically informative marker for genotoxicity induced by benzo[a]pyrene and dibenzo[a,l]pyrene

Mdm2 is an oncoprotein interacting with p53 and maintaining low p53 levels in unstressed cells. Here we investigated the effect of genotoxic compounds on Mdm2 phosphorylation levels. Employing the Mdm2 2A10 antibody and phosphatase treatment we found that Mdm2 accumulated in HepG2 cells when exposed to low concentrations of genotoxic compounds such as mitomycin C, etoposide, 5-fluorouracil, and benzo[a]pyrene (BP). The low-dose responses were not accompanied by p53 accumulation and the effect of low concentrations of BP on Mdm2 was not affected by small interfering RNA for p53. In human lymphoblasts 10nM BP induced an Mdm2 response. Low concentrations of BP also induced binding of Mdm2 to chromatin in HepG2 cells, but no p53 binding or H2AX phosphorylation. The more mutagenic dibenzo[a,l]pyrene as well as higher BP concentrations instead induced gammaH2AX and p53 Ser15 association with chromatin. Acrolein potentiated the effect of BP on p53 stabilization and chromatin binding. Taken together, these data suggest that (1) Mdm2 is a sensitive biomarker for certain types of genotoxicity, and (2) that polycyclic aromatic hydrocarbons-induced Mdm2 binding to chromatin reflects repairable damage, whereas chromatin binding of p53 Ser15 and gammaH2AX indicates more persistent DNA damage. The analysis of Mdm2 and related endpoints might be useful for evaluating mutagenic potentials of DNA damages. It is suggested that patterns documented here can be used for separating BP doses that induce readily repaired DNA adducts from doses that overwhelm this capacity.

Autophagy induced by suberoylanilide hydroxamic acid in Hela S3 cells involves inhibition of protein kinase B and up-regulation of Beclin 1

Histone deacetylase inhibitors are promising chemotherapeutic agents and some are in clinical trials. Several molecular mechanisms have been invoked to describe their effects on cancer cells in vivo and in vitro. Autophagy has been observed in response to several anticancer reagents and has been demonstrated to be responsible for cell death. However, the exact mechanism of this phenomenon is still not clear. Here we demonstrated that suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, induces nonapoptotic cell death with several specific features characteristic of autophagy in Hela S3 cells. Suberoylanilide hydroxamic acid inhibits the activity of the mammalian target of rapamycin, a negative regulator of macroautophagy which induces the formation of autophagosomes in a Beclin 1- and autophagy-related 7-dependent manner. This process is mediated by Akt and tuberous sclerosis 2 as is demonstrated by inhibition by continuous active Akt plasmid transfection and RNA interference of tuberous sclerosis 2. Our data provide the first evidence that suberoylanilide hydroxamic acid induces autophagy in Hela S3 cells through interference with the mammalian target of rapamycin signaling pathway. These findings suggest that suberoylanilide hydroxamic acid may induce autophagic cancer cell death via its specific pathway, and invite further investigation into the detailed mechanism of this pathway to explore this compound's full potential as a chemotherapeutic agent.

Utilization of chromatin remodeling agents for lung cancer therapy

Lung cancer is a disease with enormous global medical and economic impact that remains refractory to conventional treatment modalities. Recent insights regarding mechanisms pertaining to epigenetic regulation of gene expression during malignant transformation, together with the identification of agents that modulate chromatin structure provide new opportunities for the treatment and prevention of this lethal disease.

Cellular senescence and cancer treatment

Cellular senescence, an irreversible cell-cycle arrest, reflects a safeguard program that limits the proliferative capacity of the cell exposed to endogenous or exogenous stress signals. A number of recent studies have clarified that an acutely inducible form of cellular senescence may act in response to oncogenic activation as a natural barrier to interrupt tumorigenesis at a premalignant level. Paralleling the increasing insights into premature senescence as a tumor suppressor mechanism, a growing line of evidence identifies cellular senescence as a critical effector program in response to DNA damaging chemotherapeutic agents. This review discusses molecular pathways to stress-induced senescence, the interference of a terminal arrest condition with clinical outcome, and the critical overlap between premature senescence and apoptosis as both tumor suppressive and drug-responsive cellular programs.