Apoptosis, cancer and the p53 tumour suppressor gene

The link between relative stability constant of DNA- and BSA-chromenopyrimidine complexes and cytotoxicity towards human breast cancer cells (MCF-7)

In this study, we synthesized and characterized ten chromenopyrimidine derivatives using analytical and spectroscopic methods. Studies on DNA and albumin binding affinity, as well as cytotoxicity tests on human breast cancer (MCF-7) cells, of the chromenopyrimidines, were conducted. The natural logarithm of the relative stability constant of DNA- and BSA-chromenopyrimidine complexes [ln(K_DNA/K_BSA)] was used as a criterion for selecting compounds for cytotoxicity studies. We found that ln(K_DNA/K_BSA) was inversely related to IC₅₀ values of the compounds in MCF-7 cells. The antiproliferative effects of the compounds were found to induce apoptosis in MCF-7 cells, which is a desired mechanism of cell death. Correlations between the DNA and albumin binding affinities of chromenopyrimidines were established. We propose that this relationship approach can, for a given set of compounds, assist in predicting the cytotoxicity of potential drug candidates towards MCF-7 cells based on their experimentally determined CT-DNA and BSA binding affinities.

Target recognition assisted-primer exchange reaction (Ta-PER) for sensitive analysis of p53 gene and its application in analyzing amatoxin-treated samples

Sensitive and reliable detection of the p53 gene plays a significant role in precise cancer targeting and in fundamental research. However, the sensitivity of existing p53 gene detection approaches remains to be improved. Herein, we develop a target recognition assisted-primer exchange reaction (Ta-PER) for sensitive analysis of the p53 gene. Ta-PER was initiated by the recognition of a designed dumbbell structure probe by the p53 gene. In Ta-PER, the primer exchange reaction (PER) was combined with molecular beacon-based chain recycling to construct the signal amplification process. Through integrating target recognition with PER-based signal amplification, Ta-PER was established and exhibited a high detection sensitivity, with a limit of detection as low as 56 fM. In addition, the approach was also used to detect the p53 gene in normal HeLa cells and amatoxin-treated HeLa cells. The high level of the p53 gene in amatoxin-treated HeLa cells, which was approximately 1.67 times higher than that in HeLa cell extract, indicated the apoptosis of cells and suggested the promising prospect of the approach.

Reactive Oxygen Species Bridge the Gap between Chronic Inflammation and Tumor Development

According to numerous animal studies, adverse environmental stimuli, including physical, chemical, and biological factors, can cause low-grade chronic inflammation and subsequent tumor development. Human epidemiological evidence has confirmed the close relationship between chronic inflammation and tumorigenesis. However, the mechanisms driving the development of persistent inflammation toward tumorigenesis remain unclear. In this study, we assess the potential role of reactive oxygen species (ROS) and associated mechanisms in modulating inflammation-induced tumorigenesis. Recent reports have emphasized the cross-talk between oxidative stress and inflammation in many pathological processes. Exposure to carcinogenic environmental hazards may lead to oxidative damage, which further stimulates the infiltration of various types of inflammatory cells. In turn, increased cytokine and chemokine release from inflammatory cells promotes ROS production in chronic lesions, even in the absence of hazardous stimuli. Moreover, ROS not only cause DNA damage but also participate in cell proliferation, differentiation, and apoptosis by modulating several transcription factors and signaling pathways. We summarize how changes in the redox state can trigger the development of chronic inflammatory lesions into tumors. Generally, cancer cells require an appropriate inflammatory microenvironment to support their growth, spread, and metastasis, and ROS may provide the necessary catalyst for inflammation-driven cancer. In conclusion, ROS bridge the gap between chronic inflammation and tumor development; therefore, targeting ROS and inflammation represents a new avenue for the prevention and treatment of cancer.

Identification of a new benzophenone from Psidium guajava L. leaves and its antineoplastic effects on human colon cancer cells

Psidium guajava L. leaves have a long history of being consumed as herbal teas in many countries. The aim of this study was to identify compounds with anticancer potentials from Psidium guajava L. leaves. Utilizing various extraction and chromatographical techniques, we have isolated one new (2) and two known compounds (1, 3). Structural analyses by the spectroscopic methods of TOF-MS, 1H NMR, 13C NMR, HSQC, and HMBC identified these three compounds as guavinoside E (1), 3,5-dihydroxy-2,4-dimethyl-1-O-(6'-O-galloyl-β-d-glucopyranosyl)-benzophenone (2), and guavinoside B (3). Cell viability assays showed that compounds 2 and 3 inhibited the growth of HCT116 human colon cancer cells in a dose-dependent manner, where compound 2 was more potent than compound 3. Based on flow cytometry analysis, compound 2 showed stronger activity in inducing cellular apoptosis in cancer cells than compound 3. Furthermore, compounds 2 and 3 modulated expression levels of key proteins involved in cell proliferation and apoptotic signaling. Specifically, compound 2 increased the levels of p53, p-ERK1/2, p-JNK, and cleaved caspases 8 and 9, and compound 3 increased the levels of p53 and cleaved caspase 8. Overall, this study provided identities of three bioactive compounds from P. guajava L. leaves and their anti-cancer effects against human colon cancer cells, which could facilitate the utilization of these compounds and P. guajava L. leaves as potential chemoprevention agents against colon carcinogenesis.

Role of P53 Mutations in the Radiosensitivity Status of Tumor Cells

Wild-type p53 is involved in cellular response to DNA damage including cell cycle control, DNA repair and activation of apoptosis. Accumulation of p53 protein following DNA damage may initiate the apoptotic process, resulting in cell death. DNA damage induced by radiation is an example of apoptotic stimulus involving p53. Regulation of apoptosis by p53 can occur through transcriptional regulation of pro-apoptotic (e.g. bax) and anti-apoptotic (e.g. bel-2) factors. Although wild-type p53 usually sensitizes cells to radiation therapy, p53 mutations have a variable effect on radiation response. For example p53 mutations in bone or breast tumors have been found to be associated with resistance to chemotherapeutic drugs or ionizing radiation. Mutated p53 has has been reported to increase sensitivity to radiation and drugs in colorectal and bladder tumors. The present brief commentary tries to find an explanation at molecular level of these conflicting results.

A Mechanistic Basis for the Beneficial Effects of Caloric Restriction On Longevity and Disease: Consequences for the Interpretation of Rodent Toxicity Studies

Caloric restriction in rodents has been repeatedly shown to increase life span while reducing the severity and retarding the onset of both spontaneous and chemically induced neoplasms. These effects of caloric restriction are associated with a spectrum of biochemical and physiological changes that characterize the organism's adaptation to reduced caloric intake and provide the mechanistic basis for caloric restriction's effect on longevity. Here, we review evidence suggesting that the primary adaptation appears to be a rhythmic hypercorticism in the absence of elevated adrenocorticotropin (ACTH) levels. This characteristic hypercorticism evokes a spectrum of responses, including reduced body temperature and increased metabolic efficiency, decreased mitogenic response coupled with increased rates of apoptosis, reduced inflammatory response, reduced oxidative damage to proteins and DNA, reduced reproductive capacity, and altered drug-metabolizing enzyme expression. The net effect of these changes is to (1) decrease growth and metabolism in peripheral tissues to spare energy for central functions, and (2) increase the organism's capacity to withstand stress and chemical toxicity. Thus, caloric restriction research has uncovered an evolutionary mechanism that provides rodents with an adaptive advantage in conditions of fluctuating food supply. During periods of abundance, body growth and fecundity are favored over endurance and longevity. Conversely, during periods of famine, reproductive performance and growth are sacrificed to ensure survival of individuals to breed in better times. This phenomena can be observed in rodent populations that are used in toxicity testing. Improvements over the last 30 years in animal husbandry and nutrition, coupled with selective breeding for growth and fecundity, have resulted in several strains now exhibiting larger animals with reduced survival and increased incidence of background lesions. The mechanistic data from caloric restriction studies suggest that these large animals will also be more susceptible to chemically induced toxicity. This creates a problem in comparing tests performed on animals of different weights and comparing data generated today with the historical database. The rational use of caloric restriction to control body weight to within preset guidelines is a possible way of alleviating this problem.

AMPK and HIF signaling pathways regulate both longevity and cancer growth: the good news and the bad news about survival mechanisms

The AMP-activated protein kinase (AMPK) and hypoxia-inducible factor (HIF) signaling pathways are evolutionarily-conserved survival mechanisms responding to two fundamental stresses, energy deficiency and/or oxygen deprivation. The AMPK and HIF pathways regulate the function of a survival network with several transcription factors, e.g. FOXO, NF-κB, NRF2, and p53, as well as with protein kinases and other factors, such as mTOR, ULK1, HDAC5, and SIRT1. Given that AMPK and HIF activation can enhance not only healthspan and lifespan but also cancer growth in a context-dependent manner; it seems that cancer cells can hijack certain survival factors to maintain their growth in harsh conditions. AMPK activation improves energy metabolism, stimulates autophagy, and inhibits inflammation, whereas HIF-1α increases angiogenesis and helps cells to adapt to severe conditions. First we will review how AMPK and HIF signaling mechanisms control the function of an integrated survival network which is able not only to improve the regulation of longevity but also support the progression of tumorigenesis. We will also describe distinct crossroads between the regulation of longevity and cancer, e.g. specific regulation through the AMPKα and HIF-α isoforms, the Warburg effect, mitochondrial dynamics, and cellular senescence.

RG7386, a Novel Tetravalent FAP-DR5 Antibody, Effectively Triggers FAP-Dependent, Avidity-Driven DR5 Hyperclustering and Tumor Cell Apoptosis

Dysregulated cellular apoptosis and resistance to cell death are hallmarks of neoplastic initiation and disease progression. Therefore, the development of agents that overcome apoptosis dysregulation in tumor cells is an attractive therapeutic approach. Activation of the extrinsic apoptotic pathway is strongly dependent on death receptor (DR) hyperclustering on the cell surface. However, strategies to activate DR5 or DR4 through agonistic antibodies have had only limited clinical success. To pursue an alternative approach for tumor-targeted induction of apoptosis, we engineered a bispecific antibody (BsAb), which simultaneously targets fibroblast-activation protein (FAP) on cancer-associated fibroblasts in tumor stroma and DR5 on tumor cells. We hypothesized that bivalent binding to both FAP and DR5 leads to avidity-driven hyperclustering of DR5 and subsequently strong induction of apoptosis in tumor cells but not in normal cells. Here, we show that RG7386, an optimized FAP-DR5 BsAb, triggers potent tumor cell apoptosis in vitro and in vivo in preclinical tumor models with FAP-positive stroma. RG7386 antitumor efficacy was strictly FAP dependent, was independent of FcR cross-linking, and was superior to conventional DR5 antibodies. In combination with irinotecan or doxorubicin, FAP-DR5 treatment resulted in substantial tumor regression in patient-derived xenograft models. FAP-DR5 also demonstrated single-agent activity against FAP-expressing malignant cells, due to cross-binding of FAP and DR5 across tumor cells. Taken together, these data demonstrate that RG7386, a novel and potent antitumor agent in both mono- and combination therapies, overcomes limitations of previous DR5 antibodies and represents a promising approach to conquer tumor-associated resistance to apoptosis. Mol Cancer Ther; 15(5); 946-57. ©2016 AACR.

PTK6 Potentiates Gemcitabine-Induced Apoptosis by Prolonging S-phase and Enhancing DNA Damage in Pancreatic Cancer

Protein Tyrosine Kinase 6 (PTK6) is a non-receptor-type tyrosine kinase known to be expressed in various cancers, including pancreatic cancer. The role of PTK6 in cancer chemoresistance remains unclear. Therefore, it was hypothesized that PTK6 mechanistically regulates gemcitabine resistance in pancreatic cancer. Gemcitabine treatment stimulated endogenous PTK6 overexpression in MIAPaCa2 and Panc1 cells. PTK6 gene silencing increased cell survival after gemcitabine treatment and decreased apoptosis, whereas PTK6 overexpression decreased cell survival and increased apoptosis. Selection for gemcitabine resistance revealed substantially lower PTK6 expression in the gemcitabine-resistant subclones compared with the parental lines, while restoring PTK6 rescued gemcitabine sensitivity. Gemcitabine induced phosphorylation of H2AX (γ-H2AX) and ataxia-telangiectasia mutated kinase (pATM), specific markers for DNA double-strand breaks. Both gemcitabine-induced phosphorylation of H2AX and ATM were reduced by PTK6 knockdown and increased by PTK6 overexpression. PTK6 overexpression also increased the S-phase fraction 48 hours after gemcitabine treatment. Although gemcitabine activated both caspase-8 (CASP8) and caspase-9 (CASP9), the effect of PTK6 on gemcitabine-induced apoptosis required CASP8 but not CASP9. In mouse xenografts, PTK6 overexpression in subcutaneous tumors attenuated tumor growth after gemcitabine treatment. In conclusion, PTK6 prolongs S-phase and increases the ability of gemcitabine to cause DNA damage in vitro and in vivo.

IMPLICATIONS

PTK6 affects cell cycle and DNA damage, thus making it an important therapeutic target to improve the outcomes of patients with pancreatic cancer.

Cis-[RuCl(BzCN)(N-N)(P-P)]PF6 complexes: Synthesis and in vitro antitumor activity: (BzCN=benzonitrile; N-N=2,2'-bipyridine; 1,10-phenanthroline; P-P=1,4-bis(diphenylphosphino) butane, 1,2-bis(diphenylphosphino)ethane, or 1,1'-(diphenylphosphino)ferrocene)

The motivation to use ruthenium complexes in cancer treatment has led our research group to synthesize complexes with this metal and test them against several types of tumor cells, yielding promising results. In this paper the results of biological tests, assessed by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, were carried out on the complexes cis-[RuCl(BzCN)(bipy)(dppe)]PF6 (1), cis-[RuCl(BzCN)(bipy)(dppb)]PF6 (2), cis-[RuCl(BzCN)(bipy)(dppf)]PF6 (3) and cis-[RuCl(BzCN)(phen)(dppb)]PF6 (4) which are described [BzCN = b enzonitrile; bipy = 2,2'-bipyridine; phen = 1,10-phenanthroline; dppe = 1,2-bis(diphenylphosphino) ethane; dppb = 1,4-bis-(diphenylphosphino)butane; dppf = 1,1'-bis(diphenylphosphino)ferrocene]. The present study is focused on the cytotoxic activity of complexes (1)-(4) against four tumor cell lines and on the apoptosis and changes in the cell cycle and gene expression observed in the sarcoma 180 (S180) tumor cell line treated with complex (1). The results demonstrated that this complex inhibits S180 cell growth, with an IC50 of 17.02 ± 8.21 μM, while exhibiting lower cytotoxicity (IC50 = 53.73 ± 5.71 μM) towards lymphocytes (normal cells). Flow cytometry revealed that the complex inhibits the growth of tumor cells by inducing apoptosis as evidenced by an increase in the proportion of cells positive for annexin V staining and G0/G1 phase cell-cycle arrest. Further investigation showed that complex (1) induces a drop in the mitochondrial membrane potential and provokes a decrease in Bcl-2 protein expression and increase in caspase 3 activation, while the increased activation of caspase 8 caused a decrease in the gene expression in caspases 3 and 9. Increases in Tp53 and Bax expressions were also observed.

Human viruses and cancer

The first human tumor virus was discovered in the middle of the last century by Anthony Epstein, Bert Achong and Yvonne Barr in African pediatric patients with Burkitt's lymphoma. To date, seven viruses -EBV, KSHV, high-risk HPV, MCPV, HBV, HCV and HTLV1- have been consistently linked to different types of human cancer, and infections are estimated to account for up to 20% of all cancer cases worldwide. Viral oncogenic mechanisms generally include: generation of genomic instability, increase in the rate of cell proliferation, resistance to apoptosis, alterations in DNA repair mechanisms and cell polarity changes, which often coexist with evasion mechanisms of the antiviral immune response. Viral agents also indirectly contribute to the development of cancer mainly through immunosuppression or chronic inflammation, but also through chronic antigenic stimulation. There is also evidence that viruses can modulate the malignant properties of an established tumor. In the present work, causation criteria for viruses and cancer will be described, as well as the viral agents that comply with these criteria in human tumors, their epidemiological and biological characteristics, the molecular mechanisms by which they induce cellular transformation and their associated cancers.

Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors Part 4: p53 signaling pathway

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Loss of the tumor suppressor gene p53 and its encoded protein are the most common genetic events in human cancer and are a frequent occurrence in brain tumors. p53 functions as a transcription factor and is responsible for the transactivation and repression of key genes involved in cell growth, apoptosis and the cell cycle. Mutation of the p53 gene or dysfunction of its signaling pathway are early events in the transformation process of astrocytic gliomas. The majority of mutations are missense and occur in the conserved regions of the gene, within exons 5 through 8. Molecular therapeutic strategies to normalize p53 signaling in cells with mutant p53 include pharmacologic rescue of mutant protein, gene therapy approaches, small-molecule agonists of downstream inhibitory genes, antisense approaches and oncolytic viruses. Other strategies include activation of normal p53 activity, inhibition of mdm2-mediated degradation of p53 and blockade of p53 nuclear export. Further development of targeted therapies designed to restore or enhance p53 function, and evaluation of these new agents in clinical trials, will be needed to improve survival and quality of life for patients with brain tumors.

Upregulation of DR5 receptor by the diaminothiazole DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole] triggers an independent extrinsic pathway of apoptosis in colon cancer cells with compromised pro and antiapoptotic proteins

Mitochondria mediated signalling is the more common way of apoptosis induction exhibited by many chemotherapeutic agents in cancer cells. Death receptor mediated signalling for apoptosis in many cells also requires further amplification from the mitochondrial pathway activation through tBid. Thus the potential of most chemotherapeutic agents in tumours with intrinsic apoptosis resistance due to changes in molecules involved in the mitochondrial pathway is limited. Diaminothiazoles were shown earlier to bind to tubulin thereby exhibiting cytotoxicity towards different cancer cells. We observed that the lead diaminothiazole, DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole] could induce apoptosis in the colon cancer cell line HCT116 by both pathways. However, in contrast to many other chemotherapeutic agents, DAT1 triggered apoptosis where the intrinsic pathway was blocked by changing the pro and antiapoptotic proteins. An independent extrinsic pathway activation triggered by the upregulation of DR5 receptor accounted for that. The induction of DR5 occurred in the transcriptional level and the essential role of DR5 was confirmed by the fact that siRNA downregulation of DR5 significantly reduced DAT1 induced apoptosis. HCT116 cells were earlier shown to have a type II response for apoptosis induction where extrinsic pathway was connected to the intrinsic pathway via the mediator protein tBid. Our finding thus indicates that the signalling events in the manifestation of apoptosis depend not only on the cancer cell type, but also on the inducer. Our results also place diaminothiazoles in a promising position in the treatment of tumours with compromised apoptotic factors.

p53 mediates autophagy and cell death by a mechanism contingent on Bnip3

Myocardial ischemia and angiotensin II activate the tumor suppressor p53 protein, which promotes cell death. Previously, we showed that the Bcl-2 death gene Bnip3 is highly induced during ischemia, where it triggers mitochondrial perturbations resulting in autophagy and cell death. However, whether p53 regulates Bnip3 and autophagy is unknown. Herein, we provide new compelling evidence for a novel signaling axis that commonly links p53 and Bnip3 for autophagy and cell death. p53 overexpression increased endogenous Bnip3 mRNA and protein levels resulting in mitochondrial defects leading to loss of mitochondrial ΔΨ(m). This was accompanied by an increase in autophagic flux and cell death. Notably, genetic loss of function studies, such as Atg7 knock-down or pharmacological inhibition of autophagy with 3-methyl adenine, suppressed cell death induced by p53--indicating that p53 induces maladaptive autophagy. Our previous work demonstrated that Bnip3 induces mitochondrial defects and autophagic cell death. Conversely, loss of function of Bnip3 in cardiac myocytes or Bnip3(-/-) mouse embryonic fibroblasts prevented mitochondrial targeting of p53, autophagy, and cell death. To our knowledge, these data provide the first evidence for the dual regulation of autophagy and cell death of cardiac myocytes by p53 that is mutually dependent on and obligatorily linked to Bnip3 gene activation. Hence, our findings may explain more fundamentally, how, autophagy and cell death are dually regulated during cardiac stress conditions where p53 is activated.

Geminin functions downstream of p53 in K-ras-induced gene amplification of dihydrofolate reductase

DNA strand breakage and perturbation of cell-cycle progression contribute to gene amplification events that can drive cancer. In cells lacking p53, DNA damage does not trigger an effective cell-cycle arrest and in this setting promotes gene amplification. This is also increased in cells harboring oncogenic Ras, in which cell-cycle arrest is perturbed and ROS levels that cause DNA single strand breaks are elevated. This study focused on the effects of v-K-ras and p53 on Methotrexate (MTX)-mediated DHFR amplification. Rat lung epithelial cells expressing v-K-ras or murine lung cancer LKR cells harboring active K-ras continued cell-cycle progression when treated with MTX. However, upon loss of p53, amplification of DHFR and formation of MTX-resistant colonies occurred. Expression levels of cyclin A, Geminin, and Cdt1 were increased in v-K-ras transfectants. Geminin was sufficient to prevent the occurrence of multiple replications via interaction with Cdt1 after MTX treatment, and DHFR amplification proceeded in v-K-ras transfectants that possess a functional p53 in the absence of geminin. Taken together, our findings indicate that p53 not only regulates cell-cycle progression, but also functions through geminin to prevent DHFR amplification and protect genomic integrity.

Activating Death Receptor DR5 as a Therapeutic Strategy for Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. It is believed to arise from skeletal muscle progenitors, preserving the expression of genes critical for embryonic myogenic development such as MYOD1 and myogenin. RMS is classified as embryonal, which is more common in younger children, or alveolar, which is more prevalent in elder children and adults. Despite aggressive management including surgery, radiation, and chemotherapy, the outcome for children with metastatic RMS is dismal, and the prognosis has remained unchanged for decades. Apoptosis is a highly regulated process critical for embryonic development and tissue and organ homeostasis. Like other types of cancers, RMS develops by evading intrinsic apoptosis via mutations in the p53 tumor suppressor gene. However, the ability to induce apoptosis via the death receptor-dependent extrinsic pathway remains largely intact in tumors with p53 mutations. This paper focuses on activating extrinsic apoptosis as a therapeutic strategy for RMS by targeting the death receptor DR5 with a recombinant TRAIL ligand or agonistic antibodies directed against DR5.

Zerumbone, a Southeast Asian Ginger Sesquiterpene, Induced Apoptosis of Pancreatic Carcinoma Cells through p53 Signaling Pathway

Pancreatic carcinoma is one common cancer with gradually increasing incidence during the past several decades. However, currently the candidate drugs to suppress pancreatic cancer remain lacking. This research was carried out to investigate if zerumbone, a natural cyclic sesquiterpene isolated from Zingiber zerumbet Smith, will produce the anticancer effects on pancreatic carcinoma cell lines. The results showed that zerumbone concentration, and time, dependently produced inhibitory actions on cell viability of PANC-1 cells. In addition, Hoechst 33342, AO/EB, TUNEL staining, and caspase-3 activity assay further showed that zerumbone induced apoptosis of PANC-1 cells. The expression of p53 protein was markedly upregulated, and the p21 level was also obviously elevated in zerumbone-treated PANC-1 cells. Moreover, ROS production was increased by about 149% in PANC-1 cells treated by zerumbone 30 μM. Zerumbone also produced the same antitumor activity in pancreatic carcinoma cell lines SW1990 and AsPC-1. In summary, we found that zerumbone was able to induce apoptosis of pancreatic carcinoma cell lines, indicating to be a promising treatment for pancreatic cancer.

Multiple kinase pathways involved in the different de novo sensitivity of pancreatic cancer cell lines to 17-AAG

BACKGROUND

17-Allylamino-17-demethoxygeldanamycin (17-AAG) specifically targets heat shock protein (HSP)90 and inhibits its chaperoning functions for multiple kinases involved in cancer cell growth and survival. To select responsive patients, the molecular mechanisms underlying the sensitivity of cancer cells to 17-AAG must be elucidated.

MATERIALS AND METHODS

We used cytotoxicity assays and Western blotting to explore the effects of 17-AAG and sorafenib on cell survival and expression of multiple kinases in the pancreatic cancer cell lines AsPC-1 and Panc-1. Gene cloning and transfection, siRNA silencing, and immunohistochemistry were used to evaluate the effects of mutant p53 protein on 17-AAG sensitivity.

RESULTS

AsPC-1 and Panc-1 responded differently to 17-AAG, with half maximal inhibitory concentration (IC(50)) values of 0.12 and 3.18 μM, respectively. Comparable expression of HSP90, HSP70, and HSP27 was induced by 17-AAG in AsPC-1 and Panc-1 cells. P-glycoprotein and mutant p53 did not affect 17-AAG sensitivity in these cell lines. Multiple kinases are more sensitive to HSP90 inhibition in AsPC-1 than in Panc-1 cells. After 17-AAG treatment, p-Bad (S112) decreased in AsPC-1 cells and increased in Panc-1 cells. Sorafenib markedly increased p-Akt, p-ERK1/2, p-GSK-3β, and p-S6 in both cell lines. Accordingly, 17-AAG and sorafenib acted antagonistically in AsPC-1 and Panc-1 cells, except at high concentrations in AsPC-1 cells.

CONCLUSIONS

Differential inhibition of multiple kinases is responsible for the different de novo sensitivity of AsPC-1 and Panc-1 cells to HSP90 inhibition. P-glycoprotein and mutant p53 protein did not play a role in the sensitivity of pancreatic cancer cells to 17-AAG.

Disturbed flow: p53 SUMOylation in the turnover of endothelial cells

Disturbed blood flow induces apoptosis of vascular endothelial cells, which causes atherosclerosis. In this issue, Heo et al. (2011. J. Cell Biol. doi:10.1083/jcb.201010051) sheds light on p53’s role in this phenomenon. Disturbed flow induces peroxynitrite production, which activates protein kinase C ζ and it’s binding to the E3 SUMO (small ubiquitin-like modifier) ligase PIASy (protein inhibitor of activated STATy). This leads to p53 SUMOylation and its export to the cytosol, where it binds to the antiapoptotic protein Bcl-2 to induce apoptosis.

Drozitumab, a human antibody to death receptor 5, has potent antitumor activity against rhabdomyosarcoma with the expression of caspase-8 predictive of response

PURPOSE

Rhabdomyosarcoma (RMS) is a common pediatric soft-tissue tumor. In this study, we evaluated the efficacy and selectivity of drozitumab, a death receptor DR5-targeted therapeutic antibody, in RMS preclinical models.

EXPERIMENTAL DESIGN

A panel of 11 RMS cell lines was used for in vitro studies. The molecular marker predictive of response to drozitumab was interrogated. Selected RMS cell lines were injected into the gastrocnemius muscle of mice for in vivo assessment of the potency and selectivity of drozitumab.

RESULTS

We report that DR5, but not DR4, persisted at high levels and on the surface of all RMS cell lines. DR5 antibody drozitumab was effective in vitro against the majority of RMS cell lines. There was a strong correlation between caspase-8 expression and the sensitivity to drozitumab, which induced the rapid assembly of the death-induced signaling complex and the cleavage of caspase-8 only in sensitive cells. More importantly, caspase-8 catalytic activity was both necessary and sufficient for mediating the sensitivity to drozitumab. Furthermore, drozitumab had potent antitumor activity against established RMS xenografts with a specificity predicted from the in vitro analysis and with tumor-free status in half of the treated mice.

CONCLUSION

Our study provides the first preclinical evaluation of the potency and selectivity of a death receptor antibody in RMS. Drozitumab is effective, in vitro, against the majority of RMS cell lines that express caspase-8 and, in vivo, may provide long-term control of RMS.

A first-in-human study of conatumumab in adult patients with advanced solid tumors

PURPOSE

To determine the safety, tolerability, pharmacokinetics, and maximum tolerated dose (MTD) of conatumumab, an investigational, fully human monoclonal agonist antibody against human death receptor 5, in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

In the dose-escalation phase, patients received escalating intravenous doses of conatumumab (0.3, 1, 3, 10, or 20 mg/kg, 3-9 per cohort) every 2 weeks. In the dose-expansion phase, 10 patients with colorectal cancer (CRC) and 7 with non-small cell lung cancer (NSCLC) received 20 mg/kg of conatumumab every 2 weeks.

RESULTS

Thirty-seven patients received 1 or more doses of conatumumab. Conatumumab seemed to be well tolerated; there were no dose-limiting toxicities. Of adverse events possibly related to treatment, only 3 patients (8%) had a grade 3 event (fatigue and/or elevated lipase), and no anticonatumumab antibodies were detected. An MTD was not reached. Conatumumab exhibited dose linear kinetics from 3 to 20 mg/kg, with a mean terminal half-life of 13 to 19 days. One patient with NSCLC (0.3 mg/kg) had a confirmed partial response (PR) at week 32 (38% reduction in tumor size), with further reduction (48%) by week 96; this patient remains on conatumumab after 4.2 years with a sustained PR. Fourteen patients had a best response of stable disease, 2 for 32 weeks or more. One patient with CRC (0.3 mg/kg) and stable disease for 24 weeks had a 24% reduction in tumor size by RECIST (Response Evaluation Criteria in Solid Tumors) and a 35% reduction in the sum of standardized uptake values of all lesions measured by [18F]fluorodeoxyglucose positron emission tomographic scan. Changes in tumor levels of activated caspase-3 did not appear to be associated with tumor response.

CONCLUSIONS

Conatumumab can be administered safely up to the target dose of 20 mg/kg every 2 weeks.

Phase I dose-escalation study of recombinant human Apo2L/TRAIL, a dual proapoptotic receptor agonist, in patients with advanced cancer

PURPOSE

Apoptosis ligand 2/tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL)-a member of the tumor necrosis factor cytokine family-induces apoptosis by activating the extrinsic pathway through the proapoptotic death receptors DR4 and DR5. Recombinant human Apo2L/TRAIL (rhApo2L/TRAIL) has broad potential as a cancer therapy. To the best of our knowledge, this is the first in-human clinical trial to assess the safety, tolerability, pharmacokinetics, and antitumor activity of multiple intravenous doses of rhApo2L/TRAIL in patients with advanced cancer.

PATIENTS AND METHODS

This phase I, open-label, dose-escalation study treated patients with advanced cancer with rhApo2L/TRAIL doses ranging from 0.5 to 30 mg/kg/d, with parallel dose escalation for patients without liver metastases and with normal liver function (cohort 1) and for patients with liver metastases and normal or mildly abnormal liver function (cohort 2). Doses were given daily for 5 days, with cycles repeating every 3 weeks. Assessments included adverse events (AEs), laboratory tests, pharmacokinetics, and imaging to evaluate antitumor activity.

RESULTS

Seventy-one patients received a mean of 18.3 doses; seven patients completed all eight treatment cycles. The AE profile of rhApo2L/TRAIL was similar in cohorts 1 and 2. The most common AEs were fatigue (38%), nausea (28%), vomiting (23%), fever (23%), anemia (18%), and constipation (18%). Liver enzyme elevations were concurrent with progressive metastatic liver disease. Two patients with sarcoma (synovial and undifferentiated) experienced serious AEs associated with rapid tumor necrosis. Two patients with chondrosarcoma experienced durable partial responses to rhApo2L/TRAIL.

CONCLUSION

At the tested schedule and dose range, rhApo2L/TRAIL was safe and well tolerated. Dose escalation achieved peak rhApo2L/TRAIL serum concentrations equivalent to those associated with preclinical antitumor efficacy.

A phase I safety and pharmacokinetic study of the death receptor 5 agonistic antibody PRO95780 in patients with advanced malignancies

PURPOSE

PRO95780 is a fully human IgG1 monoclonal antibody that triggers the extrinsic apoptosis pathway through death receptor 5. This first-in-human study assessed the safety, tolerability, pharmacokinetics, and any early evidence of efficacy of PRO95780 in patients with advanced malignancies.

EXPERIMENTAL DESIGN

Target concentrations were predicted to occur at 10 mg/kg. Patients received up to eight cycles of PRO95780 i.v. using a 3+3 dose escalation design at 1 to 20 mg/kg every 14 days (every 28 days in cycle 1; stage 1), with cohort expansion at either the maximum tolerated dose or 10 mg/kg, whichever was lower (stage 2). Patients were evaluated for response every other cycle.

RESULTS

The maximum tolerated dose was not reached within this study. Four (8%) of 50 patients reported adverse events of greater than grade 2 at least possibly related to PRO95780, including 2 patients with reversible grade 3 transaminase elevation. The mean terminal half-life was 8.8 to 19.3 days, with dose-dependent increases in exposure (peak plasma concentration and area under the concentration) across 1 to 15 mg/kg. Most patients treated with 10 mg/kg or above achieved trough concentration above the target efficacious concentration at day 15 with moderate accumulation after multiple doses. No objective responses occurred, although three minor responses were observed in patients with colorectal and granulosa cell ovarian cancers (each treated with 4 mg/kg) and chondrosarcoma (10 mg/kg).

CONCLUSIONS

PRO95780 is safe and well tolerated at doses up to 20 mg/kg. Evidence of activity was noted in several different tumor types at 4 and 10 mg/kg. Pharmacokinetic analysis supports a dosing regimen of 10 to 15 mg/kg every 2 to 3 weeks.

Cellular stress response pathway system as a sentinel ensemble in toxicological screening

High costs, long test times, and societal concerns related to animal use have required the development of in vitro assays for the rapid and cost-effective toxicological evaluation and characterization of compounds in both the pharmaceutical and environmental arenas. Although the pharmaceutical industry has developed very effective, high-throughput in vitro assays for determining the therapeutic potential of compounds, the application of this approach to toxicological screening has been limited. A primary reason for this is that while drug candidate screens are directed to a specific target/mechanism, xenobiotics can cause toxicity through any of a myriad of undefined interactions with cellular components and processes. Given that it is not practical to design assays that can interrogate each potential toxicological target, an integrative approach is required if there is to be a rapid and low-cost toxicological evaluation of chemicals. Cellular stress response pathways offer a viable solution to the creation of a set of integrative assays as there is a limited and hence manageable set (a small ensemble of 10 or less) of major cellular stress response pathways through which cells mount a homoeostatic response to toxicants and which also participate in cell fate/death decisions. Further, over the past decades, these pathways have been well characterized at a molecular level thereby enabling the development of high-throughput cell-based assays using the components of the pathways. Utilization of the set of cellular stress response pathway-based assays as indicators of toxic interactions of chemicals with basic cellular machinery will potentially permit the clustering of chemicals based on biological response profiles of common mode of action (MOA) and also the inference of the specific MOA of a toxicant. This article reviews the biochemical characteristics of the stress response pathways, their common architecture that enables rapid activation during stress, their participation in cell fate decisions, the essential nature of these pathways to the organism, and the biochemical basis of their cross-talk that permits an assay ensemble screening approach. Subsequent sections describe how the stress pathway ensemble assay approach could be applied to screening potentially toxic compounds and discuss how this approach may be used to derive toxicant MOA from the biological activity profiles that the ensemble strategy provides. The article concludes with a review of the application of the stress assay concept to noninvasive in vivo assessments of chemical toxicants.

Ligand-based targeting of apoptosis in cancer: the potential of recombinant human apoptosis ligand 2/Tumor necrosis factor-related apoptosis-inducing ligand (rhApo2L/TRAIL)

Cancer is a leading cause of premature human death and commands considerable research attention. Apoptosis (type 1 programmed cell death) is critical in maintaining tissue homeostasis in metazoan organisms, and its dysregulation underpins the initiation and progression of cancer. Conventional chemotherapy and radiotherapy can induce apoptosis as a secondary consequence of inflicting cell damage. However, more direct and selective strategies to manipulate the apoptotic process in cancer cells are emerging as potential therapeutic tools. Genetic and biochemical understanding of the cellular signaling mechanisms that control apoptosis has increased substantially during the last decade. These advances provide a strong scientific framework for developing several types of targeted proapoptotic anticancer therapies. One promising class of agents is the proapoptotic receptor agonists. Of these, recombinant human apoptosis ligand 2/tumor necrosis factor-related apoptosis-inducing ligand (rhApo2L/TRAIL)-an optimized soluble form of an endogenous apoptosis-inducing ligand-is unique in that it activates two related proapoptotic receptors, DR4 and DR5. Preclinical data indicate that rhApo2L/TRAIL can induce apoptosis in a broad range of human cancer cell lines while sparing most normal cell types. In vitro, and in various in vivo tumor xenograft models, rhApo2L/TRAIL exhibits single-agent antitumor activity and/or cooperation with certain conventional and targeted therapies. Preclinical safety studies in nonhuman primates show rhApo2L/TRAIL to be well tolerated. Moreover, early clinical trial data suggest that rhApo2L/TRAIL is generally safe and provide preliminary evidence for potential antitumor activity. Clinical studies are ongoing to assess the safety and efficacy of this novel agent in combination with established anticancer therapies.

To kill a tumor cell: the potential of proapoptotic receptor agonists

Disturbances in mechanisms that direct abnormal cells to undergo apoptosis frequently and critically contribute to tumorigenesis, yielding a logical target for potential therapeutic intervention. There is currently heightened interest in the extrinsic apoptosis pathway, with several proapoptotic receptor agonists (PARAs) in development. The PARAs include the ligand recombinant human Apo2L/TRAIL and agonistic mAbs. Mechanistic and preclinical data with Apo2L/TRAIL indicate exciting opportunities for synergy with conventional therapies and for combining PARAs with other molecularly targeted agents. Novel molecular biomarkers may help identify those patients most likely to benefit from PARA therapy.

Targeting the extrinsic apoptosis pathway in cancer

Mutational inactivation of the p53 tumor-suppressor gene, which regulates apoptosis mainly via the cell-intrinsic pathway, reduces the sensitivity of many cancers to conventional treatments. Targeting the cell-extrinsic pathway, which triggers p53-independent apoptosis, offers a unique therapeutic strategy to induce apoptosis in cancer cells. This article focuses on two proapoptotic receptor agonists, recombinant human Apo2-ligand/TNF-related apoptosis-inducing ligand (rhApo2L/TRAIL) and Apomab, which activate death receptor (DR) 4 and/or DR5, thus stimulating the cell-extrinsic pathway. These agents are under investigation for the treatment of solid tumor and hematologic malignancies. Preclinical data indicate that both molecules cause significant regression or growth inhibition of malignant tumors without significant toxicity. Initial data on rhApo2L/TRAIL and Apomab from phase 1 safety trials also confirm that these agents are suitable for further clinical investigation.

Genotype-dependent radiosensitivity: clonogenic survival, apoptosis and cell-cycle redistribution

PURPOSE

We describe variations of three radiation-induced endpoints on the basis of cell genotype: Clonogenic survival, expression of apoptosis and cell-cycle redistribution.

METHODS

Clonogenic survival, apoptosis and cell-cycle redistribution are measured in multiple cell lines after exposure to radiation between 2 and 16 Gy. Cell lines varied in clonogenic radiosensitivity and expression of specific genes.

RESULTS

Clonal radiosensitivity is genotype-dependent, associating with four specific genes: A mutated form of Ataxia telangiectasia mutated (mutATM); with two forms of TP53, the gene that is template for tumor protein p53, wildtype TP53 (wtTP53) and mutated TP53 (mutTP53); and an unidentified gene in radioresistant glioblastoma cells. Apoptosis is also genotype-dependent showing elevated levels in cells that express mutATM and abrogated 14-3-3sigma (an isoform of the 14-3-3 gene) but less variation for different forms of TP53. Cell-cycle redistribution varied in mutATM cells. Kinetics of apoptosis are biphasic for both time and dose; cell lines did not express apoptosis at doses below 5 Gy or times before 24 hours. Kinetics of cell-cycle redistribution changed dynamically in the first 24 hours but showed little change after that time.

CONCLUSIONS

Clonogenic survival, radiation-induced apoptosis and radiation-induced redistribution in the cell-cycle vary with cell genotype, but not the same genotypes. There is temporal, not quantitative, correlation between apoptosis and clonal radiosensitivity with apoptosis suppressed by lower, less toxic doses of radiation (<5 Gy) but enabled after larger, more toxic doses. Kinetic patterns for apoptosis and redistribution show a common change at approximately 24 hours.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its therapeutic potential in breast and gynecologic cancers

OBJECTIVE

The relationship between the apoptotic pathway and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising area of scientific interest for cancer researchers. TRAIL-receptor-activating agents have demonstrated favorable in vitro and in vivo activity for the treatment of several malignancies including breast and gynecologic cancers.

METHODS

This article reviews the available peer-reviewed literature and our own institution's experience with specific TRAIL-receptor-activating agents. Emphasis was placed on the apoptotic/TRAIL mechanism, preclinical evaluation, and phase I studies in various malignancies.

RESULTS

Preclinical and early phase I studies indicate that these novel agents are safe with enhanced target specificity for malignancy. When these targeted agents are combined with conventional chemotherapy drugs or radiation therapy, they appear to increase cell death over single-agent modalities.

CONCLUSIONS

TRAIL-receptor-activating agents represent an exciting new class of targeted therapies that hold promise to improve the treatment of women with breast and gynecologic malignancies.

Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors. Part 5: apoptosis and cell cycle

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Abnormalities of the apoptotic and cell cycle signaling pathways are key molecular features of many brain tumors and are currently under evaluation for potential therapeutic intervention. The apoptosis pathway has numerous targets for molecular therapeutic development, including p53, Bax, Bcl-2, cFLIP, effector caspases, growth factor receptors, phosphatidylinositol-3-kinase, Akt and apoptosis inhibitors. Current molecular treatment approaches include antisense techniques, gene therapy and small-molecule modulators and inhibitors. Potential targets of the cell cycle pathway include the cyclins, cyclin-dependent kinases, p53, retinoblastoma, E2F and the cyclin-dependent kinase inhibitors. Developmental molecular therapeutics for this pathway include adenoviral and gene therapy, small-peptide cyclin-dependent kinase modulators, proteasomal inhibitors and small-molecule cyclin-dependent kinase inhibitors. Several of these recently identified agents have begun evaluation in clinical trials. Further development of targeted therapies designed to modulate apoptosis and the cell cycle, and evaluation of these new agents in clinical trials, will be needed to improve survival and quality of life for patients with brain tumors.

Targeted induction of apoptosis in cancer management: the emerging role of tumor necrosis factor-related apoptosis-inducing ligand receptor activating agents

Targeted induction of programmed cell death or apoptosis via the extrinsic apoptotic pathway represents an unexploited therapeutic strategy to destroy cancer cells. The activation of cell surface receptors by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) results in direct stimulation of apoptotic signaling pathways (extrinsic stimulation). Molecules that directly activate these receptors, such as agonistic monoclonal antibodies to the TRAIL receptors and recombinant TRAIL, are being developed as monotherapies and as part of combination therapies with existing chemotherapeutic drugs and other therapeutic modalities. This article examines the TRAIL receptors as potential targets for activating the TRAIL-mediated apoptosis pathway and presents the current status of novel therapeutics that exploit this pathway, particularly focusing on agonistic monoclonal antibodies to the TRAIL receptors. The preclinical activity, the status of ongoing evaluations, and the potential clinical impact of these novel agents are reviewed.

Increased Nox1 and hydrogen peroxide in prostate cancer

BACKGROUND

Reactive oxygen species (ROS) are emerging as candidate mediators of growth and angiogenesis in cancer. Increased ROS often correlates with cell growth, e.g., Ras-transformed cells and cells treated with growth factors. While non-transformed cells respond to growth factors/cytokines with the regulated production of ROS, tumor cells in culture frequently overproduce H(2)O(2). We propose that NADPH oxidases (Nox) account for increased levels of ROS in some cancers. Previously, transfection of Nox1 into a prostate cancer cell line dramatically enhanced tumor growth (Arbiser et al.: PNAS 99:715-720, 2001).

METHODS

Using immunohistochemistry, immunofluorescence, dihydroethidium staining, and Flow cytometry, we investigated the correlation between Nox1 and ROS in prostate cancer.

RESULTS

Here, we demonstrate that human prostate tumors show increased H(2)O(2) levels. Furthermore, 80% of human prostate tumor samples show markedly increased Nox1 protein levels and increased mRNA levels. In addition, a series of cell lines developed from LNCaP prostate cancer cells that demonstrate increasing tumor and metastatic potential, show increased Nox1 and a parallel increase in H(2)O(2) levels.

CONCLUSIONS

The results illustrate that human prostate cancer frequently show both increased H(2)O(2) and Nox1, and that in an animal model system increased Nox1/H(2)O(2) correlates with increased tumorigenicity.

Gene Expression Profiling in Seminoma and Nonseminoma

Purpose

Gene expression profiles of seminoma were compared with nonseminoma to get insights into tumorigenesis.

Materials and Methods

Eleven testicular tumor biopsies (five pure seminoma, six nonseminoma; pT1N0M0 to pT2N2M1) and biopsies from unaffected sites were analyzed once per patient using a macroarray (1,176 genes). On the same patients, six genes were validated using real-time quantitative (RTQ) polymerase chain reaction (PCR). Additionally, in a separate cohort of 19 patients, 24 genes selected from the macroarray were measured using RTQ-PCR.

Results

(1) The agreement in gene expression was 94% between the two methods and two different patient cohorts. (2) Two features in gene expression were independent of the tumor entity: Most changes of gene expression occurred in five functional groups like “cell cycle” and “apoptosis.” Genes within these groups were almost similarly (> 80%) up- or downregulated. (3) Nonseminoma were characterized by downregulated genes (75%), but in seminoma, upregulated genes (64%) prevailed. Furthermore, 64.4% of those genes that were differentially expressed in both tumor entities were usually upregulated in seminoma but downregulated in nonseminoma. A reverse pattern was found in 24.4% of such genes. Eleven percent of these genes showed a similar up- or downregulation in gene expression in both tumor entities.

Conclusion

Seminoma in this preliminary study can be differentiated from nonseminoma due to almost opposing gene expression profiles (89% of the significantly differentially expressed genes) and are in line with the histological discrimination of both tumor entities. Underlying mechanisms and implications regarding the origin and tumor progression of both entities are discussed.

Application of SELDI-TOF mass spectrometry for the identification of differentially expressed proteins in transformed follicular lymphoma

Completion of the human genome project has focused scientific attention on the development of methods that permit rapid characterization of proteins that are encoded by the genome. Recent improvements in two-dimensional separation techniques in combination with protein identification software/databases and mass spectrometry (MS) now permit rapid comprehensive large-scale analysis of individual proteins within complex protein mixtures. We have performed pairwise comparisons of low-grade and transformed follicular lymphomas (FLs) in order to identify proteins that may be involved in FL progression using surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometer (ProteinChip, Ciphergen Biosystems). This system utilizes preactivated differential binding surfaces to achieve multidimensional chromatography. The protein-bound chips were then analyzed by a SELDI-TOF mass spectrometer to generate protein profiles. In preliminary experiments, we established that the MS data obtained from SELDI-TOF MS were reproducible, and that reduction in sample complexity improved the ability to detect lower abundance proteins. With specific regard to FL transformation, we rapidly identified a number of potential candidate proteins involved in this process. These included an upregulated 32 kDa protein and a down-regulated 11.8 kDa protein. Protein database searches revealed several candidates, among them cyclin D3 (32.5 kDa) and caspase 3 (11.8 kDa) whose differential expression were confirmed by immunoblotting and/or immunohistochemical analysis on the primary tissue specimens. Our studies demonstrate the utility of SELDI-TOF-MS for the rapid discovery of differentially expressed proteins using femtomolar quantities of crude protein derived from biopsy material. The versatility of this methodology supports its application to the rapid discovery of potential biomarkers in a variety of cellular systems.

Comparative study of the toxic effects of fumonisin B1 in rat C6 glioma cells and p53-null mouse embryo fibroblasts

The present experiments have been carried out in order to study (comparatively) oxidative stress and its consequences (i.e. modifications of DNA bases and/or DNA fragmentation), cell cycle progression (through two generations) and apoptosis in C6 glioma cells (with normal p53 status) and p53-null mouse embryonic fibroblasts (MEF) after incubation with fumonisin B(1) (FB(1)). Further endpoints, including protein and DNA syntheses as well as cytotoxicity, have been also studied. The results show that FB(1) (incubation) produced a significant increase of malondialdehyde (MDA) production (suggestive of lipid peroxidation) which was prevented by antioxidant agents in both cell types. Moreover, FB(1) induced a significant and dose-related increase of 8-OH-dG and DNA fragmentation in both C6 glioma and MEF cells. Unlike MEF cells, apoptotic C6 glioma cells were observed after FB(1) incubation. Moreover, suppression of cell cycle progression was observed in C6 glioma but not in MEF cell incubated with FB(1). The results suggest a possible loss of protective mechanisms (such as p53-dependent apoptosis and cell cycle arrest) in FB(1)-damaged MEF cells and confirm that cells lacking of mechanisms governed by p53 gene would be more susceptible to neoplastic cascade or mutation following DNA lesions induced by this mycotoxin.