Wild-type p53-dependent etoposide-induced apoptosis mediated by caspase-3 activation in human glioma cells

Etoposide Induces Apoptosis in Activated Human Hepatic Stellate Cells via ER Stress

The activation of hepatic stellate cells (HSCs) plays a vital role in the progression of liver fibrosis, and the induction of HSCs apoptosis may attenuate or reverse fibrogenesis. The therapeutic effects of etoposide(VP-16), a widely used anticancer agent, on HSCs apoptosis and liver fibrosis resolution are still unclear. Here, we report that VP-16 reduced the proliferation of LX-2 cells and led to significantly high levels of apoptosis, as indicated by Annexin V staining and the proteolytic cleavage of the executioner caspase-3 and PARP. Additionally, the unfolded protein response regulators CHOP, BIP, caspase-12, p-eIF2α and IRE1α, which are considered endoplasmic reticulum (ER) stress markers, were upregulated by VP-16. The strong inhibitory effect of VP-16 on LX-2 cells was mainly dependent on ER stress, which activated JNK signaling pathway. Remarkably, VP-16 treatment decreased the expression of α-SMA and type I collagen and simultaneously increased the ratio of matrix metalloproteinases (MMPs) to tissue inhibitor of matrix metalloproteinases (TIMPs). In contrast, VP-16 induced significantly more apoptosis in HSCs than in normal hepatocytes. Taken together, our findings demonstrate that VP-16 exerts a proapoptotic effect on LX-2 cells and has an antifibrogenic effect on collagen deposition, suggesting a new strategy for the treatment of liver fibrosis.

Inhibition of PTTG1 expression by microRNA suppresses proliferation and induces apoptosis of malignant glioma cells

The present study aimed to investigate the role of pituitary tumor-transforming gene 1 (PTTG1) in the proliferation, invasion and apoptosis of human malignant glioma U251 cells. Firstly, 2 microRNAs (miRNAs) targeting PTTG1 messenger (m)RNA were ligated into a pcDNA6.2-GW/EmGFP-miR expression vector. The recombinant plasmids, miRNA-1 and miRNA-2 (miR-2), were transfected into U251 cells using the liposome method. PTTG1 mRNA and protein levels were evaluated using quantitative polymerase chain reaction and western blot analysis. The proliferation and invasion abilities of U251 cells were determined using methylthiazol tetrazolium and Matrigel assays. Flow cytometry analysis with Annexin V/propidium iodide double staining was used to determine the percentage of apoptotic cells. PTTG1 expression was effectively suppressed by miR-2. U251 cell growth was inhibited between 10.7 and 34.7% in the miR-2 group compared with the blank group. The Matrigel assay demonstrated that the percentage of infiltrating U251 cells was significantly lower in the miR-2 group (12.3±1.0%) compared to the blank group (24.7±1.4%; P<0.001) and the negative control group (24.0±2.0%; P<0.05). A higher percentage of apoptotic U251 cells were observed in the miR-2 group compared with the blank group (53.6 vs. 32.4%) using flow cytometry due to cycle arrests at the G2/M phase. The miR-2-transfected U251 cells were subcutaneously injected into nude mice, and these mice possessed a decreased tumor tissue growth rate and higher percentage of apoptotic cells compared with the blank and negative control groups. In conclusion, PTTG1 gene expression in human malignant glioma U251 cells was effectively suppressed by exogenous miR-2. The downregulation of PTTG1 induced glioma cell apoptosis and cell cycle arrest at the G2/M phase, which inhibited cell proliferation, reverse invasion and infiltration of glioma cells.

Tanshinone IIA inhibits viral oncogene expression leading to apoptosis and inhibition of cervical cancer

Human papilloma virus (HPV) is the well-established etiological factor of cervical cancer. E6 and E7 oncoproteins expressed by HPV are known to inactivate tumor suppressor proteins p53 and pRb, respectively. Tanshinone IIA (Tan IIA) is a diterpenoid naphthoquinone found in the traditional Chinese medicine Danshen (Salvia sp.). Tan IIA has been shown to possess anti-tumor activity against several cancer types. In this study we show that Tan IIA potently inhibited proliferation of the human cervical cancer CaSki, SiHa, HeLa and C33a cells. Mechanistically in HPV positive CaSki cells, Tan IIA was found to (i) downregulate expression of HPV E6 and E7 genes and modulate associated proteins E6AP and E2F1, (ii) cause S phase cell cycle arrest, (iii) induce accumulation of p53 and alter expression of p53-dependent targets, (iv) modulate pRb and related proteins, and (v) cause p53-mediated apoptosis by moderating Bcl2, Bax, caspase-3, and PARP cleavage expressions. In vivo, Tan IIA resulted in over 66% reduction in tumor volume of cervical cancer xenograft in athymic nude mice. Tan IIA treated tumor tissues had lower expression of proliferation marker PCNA and changes in apoptosis targets were in agreement with in vitro studies, further confirming reduced proliferation and involvement of multiple targets behind anti-cancer effects. This is the first demonstration of Tan IIA to possess significant anti-viral activity by repressing HPV oncogenes leading to inhibition of cervical cancer. Together, our data suggest that Tan IIA can be exploited as a potent therapeutic agent for the prevention and treatment of cervical and other HPV-related cancers.

Ablation of dihydroceramide desaturase confers resistance to etoposide-induced apoptosis in vitro

Sphingolipid biosynthesis is potently upregulated by factors associated with cellular stress, including numerous chemotherapeutics, inflammatory cytokines, and glucocorticoids. Dihydroceramide desaturase 1 (Des1), the third enzyme in the highly conserved pathway driving sphingolipid biosynthesis, introduces the 4,5-trans-double bond that typifies most higher-order sphingolipids. Surprisingly, recent studies have shown that certain chemotherapeutics and other drugs inhibit Des1, giving rise to a number of sphingolipids that lack the characteristic double bond. In order to assess the effect of an altered sphingolipid profile (via Des1 inhibition) on cell function, we generated isogenic mouse embryonic fibroblasts lacking both Des1 alleles. Lipidomic profiling revealed that these cells contained higher levels of dihydroceramide than wild-type fibroblasts and that complex sphingolipids were comprised predominantly of the saturated backbone (e.g. sphinganine vs. sphingosine, dihydrosphingomyelin vs. sphingomyelin, etc.). Des1 ablation activated pro-survival and anabolic signaling intermediates (e.g. Akt/PKB, mTOR, MAPK, etc.) and provided protection from apoptosis caused by etoposide, a chemotherapeutic that induces sphingolipid synthesis by upregulating several sphingolipid biosynthesizing enzymes. These data reveal that the double bond present in most sphingolipids has a profound impact on cell survival pathways, and that the manipulation of Des1 could have important effects on apoptosis.

Trichostatin A sensitizes HBx-expressing liver cancer cells to etoposide treatment

Agents commonly used in cancer chemotherapy rely on the induction of cell death via apoptosis, mitotic catastrophe, premature senescence and autophagy. Chemoresistance is the major factor limiting long-term treatment success in patients with hepatocellular carcinoma (HCC). Recent studies have revealed that the hepatitis B virus X protein (HBx) exerts anti-apoptotic effects, resulting in an increased drug resistance in HCC cells. In this study, we showed that etoposide treatment activated caspase-8 and caspase-3, leading to cleavages of p53, Bid and PARP, which subsequently induced apoptosis. Furthermore, p53 and Bid were accumulated in cytoplasm following etoposide treatment. However, HBx significantly attenuated etoposide-induced cell death. In HBx-expressing cells, despite the translocation of p53 and Bid to cytoplasm, the activation of caspases was inhibited. Furthermore, the phosphorylation of extracellular-signal-regulated kinase (ERK) was markedly increased in HBx-expressing cells. Moreover, the pretreatment with trichostatin A (TSA, a histone deacetylase inhibitor) or TSA in combination with etoposide significantly sensitized HCC cells to apoptosis by inhibiting ERK phosphorylation, reactivating caspases and PARP, and inducing translocation of p53 and Bid to cytoplasm. Collectively, HBx reduces the sensitivity of HCC cells to chemotherapy. TSA in combination with etoposide can significantly overcome the increased resistance of HBx-expressing HCC cells to chemotherapy.

Upregulation of topoisomerase IIalpha expression in advanced gallbladder carcinoma: a potential chemotherapeutic target

PURPOSE

The lack of treatment options other than surgical resection results in unfavourable prognosis of advanced gallbladder carcinoma. The aim of this study was to identify cancer-specific cellular targets that would form the basis for some therapeutic approaches for this disease.

METHODS

Twelve advanced gallbladder carcinoma tissue samples and three samples of normal gallbladder epithelium were screened to identify differentially expressed genes by DNA microarray analysis. The results obtained were validated in an independent sample set by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). Among the genes picked-up, one molecule, topoisomerase IIalpha (TOPO IIalpha), was further assessed immunohistochemically as a potential chemotherapeutic target, and the growth inhibitory effects of etoposide, doxorubicin and idarubicin, representative TOPO IIalpha inhibitors, on two different gallbladder carcinoma cell lines were compared with that of gemcitabine and 5-fulorouracil.

RESULTS

Five upregulated genes were identified: four cell cycle-related genes (TOPO IIalpha, cyclin B2, CDC28 protein kinase regulatory subunit 2, ubiquitin-conjugating enzyme E2C) and a metabolism-related gene (gamma-glutamyl hydrolase). Immunohistochemically, TOPO IIalpha was expressed in gallbladder cancer cells, and 16 of 35 cases (46%) had strong TOPO IIalpha expression defined as having a labeling index of >50%. In in vitro growth inhibition assay, etoposide, as well as doxorubicin and idarubicin, was the most effective for OCUG-1 cells that had strong TOPO IIalpha expression, while gemicitabine was the most effective for NOZ cells with weak TOPO IIalpha expression. Etoposide induced apoptosis of OCUG-1 cells.

CONCLUSIONS

TOPO IIalpha might be an effective chemotherapeutic target in advanced gallbladder carcinoma, especially when it is expressed strongly.

p53 is required for etoposide-induced apoptosis of human embryonic stem cells

The molecular mechanisms controlling DNA-damage-induced apoptosis of human embryonic stem cells (hESC) are poorly understood. Here we investigate the role of p53 in etoposide-induced apoptosis. We show that p53 is constitutively expressed at high levels in the cytoplasm of hESC. Etoposide treatment results in a rapid and extensive induction of apoptosis and leads to a further increase in p53 and PUMA expression as well as Bax processing. p53 both translocates to the nucleus and associates with the mitochondria, accompanied by colocalization of Bax with Mcl1. hESC stably transduced with p53 shRNA display 80% reduction of endogenous p53 and exhibit an 80% reduction in etoposide-induced apoptosis accompanied by constitutive downregulation of Bax and an attenuated upregulation of PUMA. Our data further show that undifferentiated hESC that express Oct4 are much more sensitive to etoposide-induced apoptosis than their more differentiated progeny. Our study demonstrates that p53 is required for etoposide-induced apoptosis of hESC and reveals, at least in part, the molecular mechanism of DNA-damage-induced apoptosis in hESC.

Comparative analysis of xanafide cytotoxicity in breast cancer cell lines

Xanafide, a DNA-intercalating agent and topoisomerase II inhibitor, has previously demonstrated comparable cytotoxicity to the parent drug amonafide (NSC 308847). The current study was conducted to investigate further the anti-proliferative effects of xanafide in human breast cancer cell lines, in vitro and in vivo. The in vitro activity of xanafide against MCF-7, MDA-MB-231, SKBR-3 and T47D cell lines was compared to that of paclitaxel, docetaxel, gemcitabine, vinorelbine and doxorubicin. In MCF-7, xanafide demonstrated comparable total growth inhibition (TGI) concentrations to the taxanes and lower TGI values than gemcitabine, vinorelbine and doxorubicin. MCF-7 (oestrogen receptor (ER)+/p53 wild-type) was the most sensitive cell line to xanafide. MDA-MB-231 and SKBR-3 exhibited similar sensitivity to xanafide. T47 D (ER+/p53 mutated), showed no response to this agent. The in vivo activity of xanafide was further compared to that of docetaxel in MCF-7 and MDA-MB-231 cell lines using the hollow fibre assay. Xanafide was slightly more potent than docetaxel, at its highest dose in MCF-7 cell line, whereas docetaxel was more effective than xanafide in MDA-MB-231 cell line. Our results show that there is no relationship between sensitivity of these cell lines to xanafide and cellular levels of both isoforms of topoisomerase II and suggest that ER and p53 status and their crosstalk may predict the responsiveness or resistance of breast cancer patients to xanafide.

Down-regulation of beta1,4-galactosyltransferase V is a critical part of etoposide-induced apoptotic process and could be mediated by decreasing Sp1 levels in human glioma cells

beta1,4-Galactosyltransferase V (beta1,4GalT V; EC 2.4.1.38) is considered to be very important in glioma for expressing transformation-related highly branched N-glycans. Recently, we have characterized beta1,4GalT V as a positive growth regulator in several glioma cell lines. However, the role of beta1,4GalT V in glioma therapy has not been clearly reported. In this study, interfering with the expression of beta1,4GalT V by its antisense cDNA in SHG44 human glioma cells markedly promoted apoptosis induced by etoposide and the activation of caspases as well as processing of Bid and expression of Bax and Bak. Conversely, the ectopic expression of beta1,4GalT V attenuated the apoptotic effect of etoposide on SHG44 cells. In addition, both the beta1,4GalT V transcription and the binding of total or membrane glycoprotein with Ricinus communis agglutinin-I (RCA-I) were partially reduced in etoposide-treated SHG44 cells, correlated well with a decreased level of Sp1 that has been identified as an activator of beta1,4GalT V transcription. Collectively, our results suggest that the down-regulation of beta1,4GalT V expression plays an important role in etoposide-induced apoptosis and could be mediated by a decreasing level of Sp1 in SHG44 cells, indicating that inhibitors of beta1,4GalT V may enhance the therapeutic efficiency of etoposide for malignant glioma.

Synthetic Smac peptide enhances the effect of etoposide-induced apoptosis in human glioblastoma cell lines

Smac/DIABLO is a mitochondrial protein released into cytosol during the progression of apoptosis. Smac/DIABLO promotes apoptosis by neutralizing the inhibitory effect of the inhibitor of apoptosis proteins (IAPs) on the processing and activity of the effecter of caspase. Here, we generated synthetic Smac peptide which possesses an IAP-binding domain and Drosophila antennapaedia penetration sequence, and examined whether it enhances the effect of the chemotherapeutic agent etoposide in the human glioblastoma cell line. Cellular uptake of Smac peptide in several glioma cell lines was most prominent at 6-12 h after addition. Caspase activity assay showed that our peptide successfully increased the activity of caspase-3 and caspase-9 in etoposide-induced apoptosis. In addition, Smac peptide increased the amount of cleaved PARP (poly ADP-ribose polymerase), but control peptides did not. Moreover, the addition of z-VAD-fmk, a caspase inhibitor, counterbalanced the effect of Smac peptide. Finally, we demonstrated that Smac peptide could enhance the growth inhibition effect of etoposide compared with control peptides. These results suggest that synthetic Smac peptide may be a new molecular targeting anti-tumor therapy for human glioblastoma.

Insulin-like growth factor-I decreased etoposide-induced apoptosis in glioma cells by increasing bcl-2 expression and decreasing CPP32 activity

AIMS

In a variety of tumors, the susceptibility of the tumor cells to apoptotic cell death following chemotherapy is a major determinant of therapeutic outcome. Gliomas are resistant to most chemotherapeutic agents, and its mechanism is not known in detail. In an attempt to understand the mechanism of chemo-resistance, we investigated the roles of insulin-like growth factor-I (IGF-I), IGF-I receptors (IGF-IR), and their relationship with the apoptotic response of two glioma cell lines to etoposide, a chemotherapeutic agent for malignant gliomas.

METHODS

Two human glioma cell lines, U-87MG and KNS-42, were used. Etoposide-induced cell growth inhibition was quantified using a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide), colorimetric assay. Hoechst 33258 staining, DNA fragmentation assay, and western blot were used for the evaluation of apoptosis. ApoAlert caspase assay was used for measuring the activity of caspase-3 (CPP32) and interleukin-1 beta -converting enzyme (ICE) protease. In addition, the effect of IGF-IR antisense was tested in U-87MG and KNS-42 glioma cell lines.

RESULTS

Etoposide inhibited the growth of U-87MG and KNS-42 cells in a concentration-dependent manner. Etoposide increased the expression of wild-type p53, activated CPP32 (but not ICE) activity, and induced apoptosis in these cells. IGF-I prevented etoposide-induced apoptosis by increasing the expression of bcl-2 and decreasing the activity of CPP32. IGF-IR antisense enhanced the apoptotic effect of etoposide.

CONCLUSIONS

IGF-I decreased etoposide-induced apoptosis in glioma cells by increasing the expression of bcl-2 and decreasing the activity of CPP32. The antisense of IGF-IR increased etoposide-induced apoptosis. The anti-apoptotic effect of IGF-I and IGF-IR might be related to the chemo-resistance of glioma to chemotherapeutic agents.

Apoptosis in Hep2 cells treated with etoposide and colchicine

When malignant cells undergo apoptosis, they exhibit many distinct patterns of behavior, with blebbing being one of the most spectacular and mysterious features. Despite huge advancements in our understanding of cell death, the mechanisms of apoptosis associated blebbing have not been elucidated. In order to verify the putative involvement of actin and tubulin in this process, Hep2 cells were treated with a combination of etoposide (10 microg/ml) and colchicine (0.2 microg/ml) for 24 h. Blebbing was analyzed using immunofluorescence staining of actin and tubulin, and the course of apoptosis was followed by time-lapse videomicroscopy, immunofluorescence detection of caspase-3 and cytokeratin fragment 18. The results indicate that microfilaments (actin) and not microtubules (tubulin) are involved in blebbing of Hep2 cells. Furthermore, despite the different mechanisms by which both chemicals act, their combined effects are not additive, but rather eliminate each other.

Inverse correlation of epidermal growth factor receptor messenger RNA induction and suppression of anchorage-independent growth by OSI-774, an epidermal growth factor receptor tyrosine kinase inhibitor, in glioblastoma multiforme cell lines

OBJECT

Quantitative and qualitative alterations in the epidermal growth factor receptor (EGFR) commonly occur in many cancers in humans, including malignant gliomas. The aim of the current study was to evaluate molecular and cellular effects of OSI-774, a novel EGFR tyrosine kinase inhibitor, on nine glioblastoma multiforme (GBM) cell lines.

METHODS

The effects of OSI-774 on expression of EGFR messenger (m)RNA and protein, proliferation, anchorage-independent growth, and apoptosis were examined using semiquantitative reverse transcription-polymerase chain reaction, immunocytochemical analysis, Coulter counting, soft agar cloning, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling/fluorescence-activated cell sorting, respectively. All p53 genes were completely and bidirectionally sequenced. Suppression of anchorage-independent growth by OSI-774 was inversely correlated to the induction of EGFR mRNA during relative serum starvation (r = -0.74) and was unrelated to p53 status. Overall, suppression of anchorage-independent growth was a considerably stronger effect of OSI-774 than inhibition of proliferation. The extent of OSI-774-induced apoptosis positively correlated with both proliferation and anchorage-independent growth of GBM cell lines (r = 0.75 and 0.79, respectively). In a single cell line derived from a secondary GBM, exposure to concentrations of greater than or equal to 1 micromol/L resulted in a substantial net cell loss during proliferation studies.

CONCLUSIONS

The induction of EGFR mRNA may constitute a cellular mechanism to counteract the inhibitory effect of OSI-774 on the anchorage-independent growth of GBM cells. In contrast, no considerable correlation could be established between baseline expression levels of EGFR (both mRNA and protein) in GBM cell lines and their biological response to OSI-774. The OSI-774 induced greater (p53-independent) apoptosis in more malignant GBM phenotypes and may be a promising therapeutic agent against secondary GBM.

Inverse correlation of epidermal growth factor receptor messenger RNA induction and suppression of anchorage-independent growth by OSI-774, an epidermal growth factor receptor tyrosine kinase inhibitor, in glioblastoma multiforme cell lines

Object

Quantitative and qualitative alterations in the epidermal growth factor receptor (EGFR) commonly occur in many cancers in humans, including malignant gliomas. The aim of the current study was to evaluate molecular and cellular effects of OSI-774, a novel EGFR tyrosine kinase inhibitor, on nine glioblastoma multiforme (GBM) cell lines.

Methods

The effects of OSI-774 on expression of EGFR messenger (m)RNA and protein, proliferation, anchorage-independent growth, and apoptosis were examined using semiquantitative reverse transcription–polymerase chain reaction, immunocytochemical analysis, Coulter counting, soft agar cloning, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling/fluorescence-activated cell sorting, respectively. All p53 genes were completely and bidirectionally sequenced.

Suppression of anchorage-independent growth by OSI-774 was inversely correlated to the induction of EGFR mRNA during relative serum starvation (r = −0.74) and was unrelated to p53 status. Overall, suppression of anchorage-independent growth was a considerably stronger effect of OSI-774 than inhibition of proliferation. The extent of OSI-774–induced apoptosis positively correlated with both proliferation and anchorage-independent growth of GBM cell lines (r = 0.75 and 0.79, respectively). In a single cell line derived from a secondary GBM, exposure to concentrations of greater than or equal to 1 μmol/L resulted in a substantial net cell loss during proliferation studies.

Conclusions

The induction of EGFR mRNA may constitute a cellular mechanism to counteract the inhibitory effect of OSI-774 on the anchorage-independent growth of GBM cells. In contrast, no considerable correlation could be established between baseline expression levels of EGFR (both mRNA and protein) in GBM cell lines and their biological response to OSI-774. The OSI-774 induced greater (p53-independent) apoptosis in more malignant GBM phenotypes and may be a promising therapeutic agent against secondary GBM.

Apoptosis in glioma cells: review and analysis of techniques used for study with focus on the laser scanning cytometer

Traditional approaches to the treatment of brain tumors are based on the hypothesis that tumors arise and grow because of the disordered regulation of cell proliferation. More recently, it has become apparent that tumor growth depends not only on the rate of cell proliferation but also on the rate of apoptosis (programmed cell death). Genomic alterations that occur in malignancy may limit the cell's ability to undergo apoptosis. Many new treatment strategies for gliomas stem from the use of techniques aimed at manipulating apoptosis. Being able to assess the efficacy of experimental treatments with refined techniques and being able to use instruments that can provide accurate measurements of the apoptotic markers will open the door for discovering novel strategies with the potential to induce effective and selective cytotoxicity. We discuss here in detail the major traditional techniques of assessing apoptosis. We provide an overview of cytometric techniques, including flow cytometry (FC), and will compare it with the laser scanning cytometer (LSC). This is a powerful new tool with potential for obtaining a fast and objective analysis of apoptosis through multiple mechanisms, as well as for assessing proliferation and DNA ploidy in solid malignant tumors.

Apoptotic effect in the glioma cells induced by specific protein extracted from Okinawa Habu (Trimeresurus flavoviridis) venom in relation to oxidative stress

Okinawa Habu (Trimeresurus flavoviridis) venom is well known for its toxic efficacy, from which one kind of specific protein, Okinawa Habu apoxin protein-1 (OHAP-1) has been extracted. The purpose of this study was to investigate whether OHAP-1 could induce apoptosis in some glioma cells, and if so, to elucidate the possible mechanism involved. Three malignant glioma cell lines were tested. The malignant glioma cell lines were rat C6 and human RBR 17T, U251. OHAP-1 inhibited growth of all cell lines. Whether or not the apoptosis had been induced was determined by using DNA gel electrophoresis, DNA flow cytometry and TUNEL assay. After OHAP-1 treatment, DNA fragmentation, an increase in the percentage of subdiploid DNA content, and TUNEL positive cells were found in the C6, RBR17T, and U251 cells. Furthermore, OHAP-1 showed L-amino acid oxidase (LAAO) activity. In order to study the mechanism of apoptosis induced by OHAP-1, the changes of intracellular reactive oxygen species (ROS) were measured using flow cytometry, and the expression of p53 protein was examined using immunohistochemistry. OHAP-1 was found to generate ROS and increase the expression of p53 protein in glioma cells. The inhibiting effect of OHAP-1 on three tested cells was reversed when an antioxidant of either catalase or reduced glutathione (GSH) was added; its apoptotic effect correspondingly became weaker. In this study, the apoptotic effect of OHAP-1 on some malignant glioma cells was confirmed, and it could be that this effect might be mediated through promoting the generation of intracellular ROS and p53 protein expression in glioma cells. It was suggested that OHAP-1 is promising as a potential candidate for clinical tumor therapy.

Tumor p53 status and response to topoisomerase II inhibitors

It is thought that when tumor cells are treated with anticancer drugs, they die through the apoptotic pathway and that cell resistance to cancer chemotherapy is mainly a resistance to apoptosis commitment. p53 is not functional in nearly half of the tumors examined and because of its involvement (directly or through its target genes) in the apoptotic pathway, drug resistance to chemotherapy has been largely attributed to the status of this "tumor suppressor protein". Topoisomerase II (topo II) inhibitors are widely used not only as single agents, but also in the majority of combination treatment protocols for hematologic malignancies and solid tumors. The relationship between p53 and topo II raises many questions about basic regulatory, biochemical, structural and functional characteristics that could be different in cells in different tissues, and most importantly, between different tumor cell types and their normal tissue counterpart. Understanding these relationships may lead to strategies for chemotherapy optimization and further precision targeting of tumor cells in order to avoid drug resistance and thereby chemotherapy failure.

Implication of p53 and caspase-3 in kainic acid but not in N-methyl-D-aspartic acid-induced apoptosis in organotypic hippocampal mouse cultures

Apoptotic death is known to be an active process requiring the activation of several apoptotic proteins. Depending on the tissue studied and the stimulus used, these processes are distinct. In this work, we studied if there is a putative implication of the p53 and the caspase-3 proteins in kainic acid (KA) and N-methyl-D-aspartic acid (NMDA)-induced apoptosis in organotypic cultures and if there is any relationship between their respective expressions. We found that KA and NMDA both induce apoptosis but only KA-induced apoptosis is p53- and caspase-3-dependent. This demonstrates that KA and NMDA induce apoptosis following different intracellular pathways.

The diversity of p53 mutations among human brain tumors and their functional consequences

The p53 tumor suppressor is implicated in cell cycle control, DNA repair, replicative senescence and programmed cell death. Inactivation of the p53 contributes to the wide range of human tumors, including glial neoplasms. In this review, we describe the regulation and biochemical properties of p53 protein that may explain its ability to activate various genetic programs underlying cellular responses to stress conditions. The overall spectrum of p53 mutations is rather shared between tumor types indicating that these mutations are not tumor type-specific. However, there is one example of germ-line mutation of p53 gene (the deletion of the codon 236) that is associated with a familiar brain tumor syndrome. We compare the frequency and type of most common mutations among various brain tumours (focusing on glioblastomas) and their consequences on protein functions. Furthermore, we discuss the most promising approaches of potential brain tumor therapy, including an adenovirus-mediated p53 gene transfer. Human glioblastomas are highly sensitive to the effects of p53 activity when the wild-type p53 is introduced ectopically. It suggests that the genetic or pharmacological modulation of the p53 pathway is potentially important strategy in the treatment of human cancers.

Apoptosis induced by box jellyfish (Chiropsalmus quadrigatus) toxin in glioma and vascular endothelial cell lines

This study was made to investigate whether Chiropsalmus Quadrigatus toxins (CqTX), which isolated from box jellyfish C. Quadrigatus venom, could induce apoptosis in human U251 and rat C6 malignant glioma cells and transformed vascular endothelial ECV 304 cell lines. Cell viability was estimated by MTT assay. Apoptosis was evaluated using TdT (terminal deoxynucleotidyl transferase)-mediated dUTP nick-end labeling (TUNEL) method and DNA gel electrophoresis. Furthermore, the expression of p53 protein was examined immunohistochemically in the U251 cells. After the CqTX treatment, the growth of all cell lines was inhibited, the fragmented DNA was observed and some cells became TUNEL positive. The expression of p53 protein was increased in the tested U251 cells. The results suggested that CqTX induced apoptosis in these cell lines. The promotion of the p53 expression might be one mechanism of apoptosis induced by CqTX in the glioma cells.

Caspase-9 transduction overrides the resistance mechanism against p53-mediated apoptosis in U-87MG glioma cells

OBJECTIVE

Conflicting reports have been published with regard to the relationship between the efficacy of p53 gene therapy and the p53 status of gliomas. In this study, we evaluated whether U-87MG glioma cells harboring wild-type p53 and U251 and U-373MG glioma cells harboring mutated p53 demonstrate different sensitivities to p53-induced apoptosis. In addition, we tested whether transduction of Bax or caspase-9, which are downstream components of p53-induced apoptosis, can override the resistance mechanism of U-87MG cells to apoptosis.

METHODS

We transduced U-87MG, U251, and U-373MG glioma cells with p53, Bax, or caspase-9 genes via adenovirus (Adv) vectors, to induce the same level of respective proteins, and evaluated the degree of apoptosis.

RESULTS

U-87MG cells were highly resistant to Adv for p53 (Adv-p53)-mediated apoptosis, whereas U251 and U-373 cells underwent extensive apoptosis after Adv-p53 infection. In U-87MG cells, the elevation of Bax and Fas was not as marked as that observed in U251 and U-373MG cells after Adv-p53 infection. Endogenous expression of Bcl-XL and Bcl-2 in U-87MG cells was greater than that in U251 and U-373MG cells. U-87MG cells were more resistant to Bax-mediated apoptosis than were U251 or U-373MG cells. In contrast, U-87MG cells were more sensitive to caspase-9-mediated apoptosis than were U251 or U-373MG cells, suggesting that transduction of caspase-9 may override the resistance mechanism of U-87MG to p53-mediated apoptosis.

CONCLUSION

These results demonstrate that proapoptotic function induced by p53 transduction in U-87MG cells was repressed at several steps and that induction of caspase-9 may circumvent this resistance mechanism.

Diazepam enhances etoposide-induced cytotoxicity in U-87 MG human glioma cell line

Various approaches might be employed in an effort to increase efficacy of the chemotherapeutic treatment of cancer. Recently, various modulators of anticancer therapy effectiveness have been studied. Antiproliferative effects of peripheral benzodiazepine receptor (PBR) ligands might be exploited to enhance cytotoxic effect of a chemotherapeutic drug towards cancer cells. In this work, we sought to enhance cytotoxic effect of etoposide (VP-16) by a PBR ligand, diazepam (DZ) in U-87 MG human glioma cells. Cytotoxicity of VP-16, DZ and their combinations was assessed by using the microculture MTT assay. Cell survival, effective concentrations (EC) and the onset of cytotoxic effect were determined. After 72 h of cultivation, survival of U-87 MG cells was reduced to 57 +/- 7% in the presence of VP-16 at 12.5 microg/mL alone, whereas DZ at 10-4 mol/L alone caused 28 +/- 6% reduction in cell survival. Coincubation of VP-16 at 12.5 microg/mL with DZ at 10-4 mol/L led to a further decrease in cell survival to 45 +/- 6%. Furthermore, DZ at 10-4 mol/L significantly decreased effective concentrations, EC10, EC30 and EC50, of VP-16 and the dose-response curves were shifted to the left. Addition of DZ at 10-4 mol/L to VP-16 also facilitated the onset of its cytotoxic effect. The same decrease in survival was thus achieved approximately 30 h earlier in comparison with VP-16 alone. However, DZ at 10-9 mol/L failed both to exert any effect on glioma cells survival and enhance cytotoxic effect of VP-16. DZ at 10-4 mol/L was capable of both reducing U-87 MG glioma cells survival when applied alone and also enhancing the cytotoxic effect of VP-16. No such observation was made for the lower concentrations of DZ. Potential implementation of diazepam in the antiglioma/anticancer armamentarium awaits further experimentation but phase I and phase II clinical trials could be suggested.