The Dog as a Second Species for Toxicology Testing Provides Value to Drug Development.

The objective of the pharmaceutical industry is to develop new drugs that are safe for human use. In many cases, the accepted approach codified in guidance from regulatory authorities to assess the nonclinical safety profile of potential pharmaceuticals is to perform toxicity testing in two species. However, the use of a second species to establish the safety of new pharmaceuticals has been the subject of much scrutiny in recent years and the industry has been repeatedly challenged to reduce, refine, or replace some or all of the animals used to establish the safety of these pharmaceutical candidates. Specifically, the value of the dog in this testing paradigm has been questioned. Publications reviewing available data for marketed drugs suggest that for many drugs, the dog does not identify unique toxicities critical to human safety. The weakness of this approach, however, is that many of the cases where the dog (or any other species) has the greatest impact on drug development are cases for which development decisions based on safety concerns are not shared publicly. The European Federation of Pharmaceutical Industries and Associations (EFPIA) Preclinical Development Expert Group (PDEG) decided to share case studies collected from its membership and the literature to illustrate the value of the dog in drug development decision-making and clinical monitoring practices to protect the safety of trial subjects.

Time for a Fully Integrated Nonclinical-Clinical Risk Assessment to Streamline QT Prolongation Liability Determinations: A Pharma Industry Perspective.

Defining an appropriate and efficient assessment of drug-induced corrected QT interval (QTc) prolongation (a surrogate marker of torsades de pointes arrhythmia) remains a concern of drug developers and regulators worldwide. In use for over 15 years, the nonclinical International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) S7B and clinical ICH E14 guidances describe three core assays (S7B: in vitro hERG current & in vivo QTc studies; E14: thorough QT study) that are used to assess the potential of drugs to cause delayed ventricular repolarization. Incorporating these assays during nonclinical or human testing of novel compounds has led to a low prevalence of QTc-prolonging drugs in clinical trials and no new drugs having been removed from the marketplace due to unexpected QTc prolongation. Despite this success, nonclinical evaluations of delayed repolarization still minimally influence ICH E14-based strategies for assessing clinical QTc prolongation and defining proarrhythmic risk. In particular, the value of ICH S7B-based "double-negative" nonclinical findings (low risk for hERG block and in vivo QTc prolongation at relevant clinical exposures) is underappreciated. These nonclinical data have additional value in assessing the risk of clinical QTc prolongation when clinical evaluations are limited by heart rate changes, low drug exposures, or high-dose safety considerations. The time has come to meaningfully merge nonclinical and clinical data to enable a more comprehensive, but flexible, clinical risk assessment strategy for QTc monitoring discussed in updated ICH E14 Questions and Answers. Implementing a fully integrated nonclinical/clinical risk assessment for compounds with double-negative nonclinical findings in the context of a low prevalence of clinical QTc prolongation would relieve the burden of unnecessary clinical QTc studies and streamline drug development.

Outcomes of the European Federation of Pharmaceutical Industries and Associations Oligonucleotide Working Group Survey on Nonclinical Practices and Regulatory Expectations for Therapeutic Oligonucleotide Safety Assessment.

The Oligonucleotide Working Group of the European Federation of Pharmaceutical Industries and Associations (EFPIA) conducted a survey of companies to understand the trends in nonclinical practices and regulatory expectations for oligonucleotide drug safety assessment. Twenty-two companies of different types, with varying oligonucleotide experience levels in the field, participated. The survey identified key regulatory challenges and areas of perceived health authority (HA) concern regarding nonclinical safety strategies for oligonucleotides, such as the choice of toxicology species, approaches to dose setting in toxicity studies, dose scaling from animals to humans, the implementation (and regulatory acceptability) of lean packages, and methods for dealing with impurities and human-specific off-targets. The perceived oligonucleotide experience of HAs and the relevance of guidance to oligonucleotide development were also assessed. The results showed a general lack of consensus on nonclinical safety assessment approaches being used for this growing class of medicines and highlight the need for continuing collaboration between sponsors and HAs to better define best practices.

Adverse vacuolation in multiple tissues in cynomolgus monkeys following repeat-dose administration of a PEGylated protein.

PEGylation is considered a safe mechanism to enhance the pharmacokinetics (PK) and pharmacodynamics (PD) of biotherapeutics. Previous studies using PEGylation as a PK enhancement tool have reported benign PEG-related vacuolation in multiple tissues. This paper establishes a threshold for PEG burden beyond which there are alterations in tissue architecture that could potentially lead to dysfunction. As part of the nonclinical safety assessment of Compound A, a 12 kDa protein conjugated to a 40 kDa branched PEG molecule, monkeys were dosed subcutaneously twice weekly for 3 months at protein doses resulting in weekly PEG doses of 8, 24, 120, or 160 mg/kg. Consistent with previous reports with PEGylated biomolecules, Compound A administration resulted in intracellular vacuoles attributed to the PEG moiety in macrophages in numerous tissues and epithelial cells in the choroid plexus and kidney. Vacuolation occurred at all doses with dose-dependent severity and no evidence of recovery up to 2 months after dosing cessation. The vacuolation was considered nonadverse at PEG doses ≤120 mg/kg/week. However, at 160 mg/kg/week PEG, the vacuolation in choroid plexus, pituitary gland, kidney, and choroid of the eye was considered adverse due to significant alterations of tissue architecture that raised concern for the possibility of compromised tissue function. To our knowledge, this is the first report of potentially adverse cellular consequences of PEG accumulation in tissues other than kidney. Furthermore, the lack of reversibility of vacuolation coupled with the lack of a biomarker for intracellular PEG accumulation highlights a potential risk that should be weighed against the benefits of PK/PD enhancement for long-term administration of PEGylated compounds at high doses.

Evaluation of microRNAs-208 and 133a/b as differential biomarkers of acute cardiac and skeletal muscle toxicity in rats.

Conventional circulating biomarkers of cardiac and skeletal muscle (SKM) toxicity lack specificity and/or have a short half-life. MicroRNAs (miRNAs) are currently being assessed as biomarkers of tissue injury based on their long half-life in blood and selective expression in certain tissues. To assess the utility of miRNAs as biomarkers of cardiac and SKM injury, male Sprague-Dawley rats received a single dose of isoproterenol (ISO); metaproterenol (MET); allylamine (AAM); mitoxantrone (MIT); acetaminophen (APAP) or vehicle. Blood and tissues were collected from rats in each group at 4, 24 and 48h. ISO, MET, and AAM induced cardiac and SKM lesions and APAP induced liver specific lesions. There was no evidence of tissue injury with MIT by histopathology. Serum levels of candidate miRNAs were compared to conventional serum biomarkers of SKM/cardiac toxicity. Increases in heart specific miR-208 only occurred in rats with cardiac lesions alone and were increased for a longer duration than cardiac troponin and FABP3 (cardiac biomarkers). ISO, MET and AAM induced increases in MyL3 and skeletal muscle troponin (sTnl) (SKM biomarkers). MIT induced large increases in sTnl indicative of SKM toxicity, but sTnl levels were also increased in APAP-treated rats that lacked SKM toxicity. Serum levels of miR-133a/b (enriched in cardiac and SKM) increased following ISO, MET, AAM and MIT treatments but were absent in APAP-treated rats. Our results suggest that miR-133a/b are sensitive and specific markers of SKM and cardiac toxicity and that miR-208 used in combination with miR-133a/b can be used to differentiate cardiac from SKM toxicity.

PEGylated Biopharmaceuticals: Current Experience and Considerations for Nonclinical Development.

PEGylation (the covalent binding of one or more polyethylene glycol molecules to another molecule) is a technology frequently used to improve the half-life and other pharmaceutical or pharmacological properties of proteins, peptides, and aptamers. To date, 11 PEGylated biopharmaceuticals have been approved and there is indication that many more are in nonclinical or clinical development. Adverse effects seen with those in toxicology studies are mostly related to the active part of the drug molecule and not to polyethylene glycol (PEG). In 5 of the 11 approved and 10 of the 17 PEGylated biopharmaceuticals in a 2013 industry survey presented here, cellular vacuolation is histologically observed in toxicology studies in certain organs and tissues. No other effects attributed to PEG alone have been reported. Importantly, vacuolation, which occurs mainly in phagocytes, has not been linked with changes in organ function in these toxicology studies. This article was authored through collaborative efforts of industry toxicologists/nonclinical scientists to address the nonclinical safety of large PEG molecules (>10 kilo Dalton) in PEGylated biopharmaceuticals. The impact of the PEG molecule on overall nonclinical safety assessments of PEGylated biopharmaceuticals is discussed, and toxicological information from a 2013 industry survey on PEGylated biopharmaceuticals under development is summarized. Results will contribute to the database of toxicological information publicly available for PEG and PEGylated biopharmaceuticals.

Quantitative analysis of polyethylene glycol (PEG) and PEGylated proteins in animal tissues by LC-MS/MS coupled with in-source CID.

The covalent conjugation of polyethylene glycol (PEG, typical MW > 10k) to therapeutic peptides and proteins is a well-established approach to improve their pharmacokinetic properties and diminish the potential for immunogenicity. Even though PEG is generally considered biologically inert and safe in animals and humans, the slow clearance of large PEGs raises concerns about potential adverse effects resulting from PEG accumulation in tissues following chronic administration, particularly in the central nervous system. The key information relevant to the issue is the disposition and fate of the PEG moiety after repeated dosing with PEGylated proteins. Here, we report a novel quantitative method utilizing LC-MS/MS coupled with in-source CID that is highly selective and sensitive to PEG-related materials. Both (40K)PEG and a tool PEGylated protein (ATI-1072) underwent dissociation in the ionization source of mass spectrometer to generate a series of PEG-specific ions, which were subjected to further dissociation through conventional CID. To demonstrate the potential application of the method to assess PEG biodistribution following PEGylated protein administration, a single dose study of ATI-1072 was conducted in rats. Plasma and various tissues were collected, and the concentrations of both (40K)PEG and ATI-1072 were determined using the LC-MS/MS method. The presence of (40k)PEG in plasma and tissue homogenates suggests the degradation of PEGylated proteins after dose administration to rats, given that free PEG was absent in the dosing solution. The method enables further studies for a thorough characterization of disposition and fate of PEGylated proteins.

DPP8 and DPP9 expression in cynomolgus monkey and Sprague Dawley rat tissues.

Dipeptidyl peptidases (DPPs) are proteolytic enzymes that regulate many physiological systems by degrading signaling peptides. DPP8 and DPP9 are distinct from DPP4 in sequence, cellular localization and expression levels, thus implying distinct functions. However, DPP8 and DPP9 expression needs further delineation. We evaluated DPP4, DPP8 and DPP9 expression using three independent methods at the mRNA, protein, and functional levels to better understand the local physiological contribution of each enzyme. Sprague Dawley rats and cynomolgus monkeys were selected for DPP4, DPP8 and DPP9 expression profiling to represent animal species commonly utilized for drug preclinical safety evaluation. A novel Xhibit assay of DPP protease activity was applied in addition to newly available antibodies for immunohistochemical localization. This combined approach can facilitate a functional evaluation of protease expression, which is important for understanding physiological relevance. Few inter-species differences were observed. Tissue mRNA and protein levels generally correlated to functional DPP4 and DPP8/9 enzymatic activity. All three proteins were seen in epithelial cells, lymphoid cells and some endothelial and vascular smooth muscle cells. Combined DPP8/DPP9 enzymatic activity was uniformly intracellular across tissues at approximately 10-fold lower levels than non-renal DPP4. Consistent levels of each DPP were detected among most non-renal tissues in rats and monkeys. DPP4 was ubiquitous, principally detected on cell membranes of epithelial and endothelial cells and was greatest in the kidney. The expression patterns suggest that DPP8 and DPP9 may act similarly across tissues, and that their actions might in part overlap with DPP4.

Cannabinoid receptor antagonist-induced striated muscle toxicity and ethylmalonic-adipic aciduria in beagle dogs.

Ibipinabant (IBI), a potent cannabinoid-1 receptor (CB1R) antagonist, previously in development for the treatment of obesity, causes skeletal and cardiac myopathy in beagle dogs. This toxicity was characterized by increases in muscle-derived enzyme activity in serum and microscopic striated muscle degeneration and accumulation of lipid droplets in myofibers. Additional changes in serum chemistry included decreases in glucose and increases in non-esterified fatty acids and cholesterol, and metabolic acidosis, consistent with disturbances in lipid and carbohydrate metabolism. No evidence of CB1R expression was detected in dog striated muscle as assessed by polymerase chain reaction, immunohistochemistry, Western blot analysis, and competitive radioligand binding. Investigative studies utilized metabonomic technology and demonstrated changes in several intermediates and metabolites of fatty acid metabolism including plasma acylcarnitines and urinary ethylmalonate, methylsuccinate, adipate, suberate, hexanoylglycine, sarcosine, dimethylglycine, isovalerylglycine, and 2-hydroxyglutarate. These results indicated that the toxic effect of IBI on striated muscle in beagle dogs is consistent with an inhibition of the mitochondrial flavin-containing enzymes including dimethyl glycine, sarcosine, isovaleryl-CoA, 2-hydroxyglutarate, and multiple acyl-CoA (short, medium, long, and very long chain) dehydrogenases. All of these enzymes converge at the level of electron transfer flavoprotein (ETF) and ETF oxidoreductase. Urinary ethylmalonate was shown to be a biomarker of IBI-induced striated muscle toxicity in dogs and could provide the ability to monitor potential IBI-induced toxic myopathy in humans. We propose that IBI-induced toxic myopathy in beagle dogs is not caused by direct antagonism of CB1R and could represent a model of ethylmalonic-adipic aciduria in humans.

Production of metallothionein polyclonal antibodies using chickens as model.

The production of polyclonal antibodies (pAbs) against metallothioneins (MT) has been done in mammals. In this work, we describe a model where pAbs against rat liver MT were produced in chickens. Liver MT-1 and MT-2 isoforms isolated from rats were used as immunogens. MT was purified by exclusion chromatography and MT isoforms isolated by ionic exchange chromatography. Chickens were immunized with each isoform emulsified with Freund adjuvant over 6 weeks. MT-pAbs obtained from egg yolk were purified by ammonium sulfate precipitation followed by thiophilic interaction chromatography. MT-pAbs were characterized by ELISA, SDS-PAGE electrophoresis, and Western blot assays. Results showed significant titers (1:1,000) of MT-1 and MT-2 IgY in the eggs collected 30 days after the first immunization as determined by a direct ELISA assay; results also show a cross-reaction between MT-1 and MT-2 isoforms: however, the Abs obtained did not react with other non-MT proteins in hepatic homogenates. Sensitivity assays showed that MT-pAbs detected MT-1 and MT-2 at nanogram levels. These data suggest that chickens are an alternative model for producing pAbs against mammal high-homology proteins such as MT.

Genetic and gene expression studies implicate renin and endothelin-1 in edema caused by peroxisome proliferator-activated receptor gamma agonists.

OBJECTIVE: Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists can cause peripheral edema in susceptible individuals. To investigate the mechanistic basis underlying this adverse event, we performed a candidate gene analysis of patients enrolled in clinical trials of muraglitazar, an investigational PPARalpha/gamma dual agonist, and developed a cell culture-based gene expression assay and nonhuman primate model of edema to study the edemagenic properties of PPARgamma agonists. METHODS: A total of 213 single nucleotide polymorphisms (SNPs) in 63 genes were genotyped in 730 participants. Chi-square and logistic regression analyses were used to test for association with edema. Transcriptional responses to PPARgamma agonists were evaluated in Calu-6 cells using quantitative real-time PCR. Male Cynomolgus monkeys were treated with PPAR agonists and were evaluated for edema using MRI. RESULTS: SNPs in renin (rs2368564) and endothelin-1 (rs5370) were associated with reduced risk of edema (P=0.003 and P=0.028, respectively) and an SNP in beta1 adrenergic receptor (rs1801253) was associated with increased susceptibility to edema (P=0.034). Gene expression studies revealed that renin and endothelin-1 were regulated by PPARgamma in Calu-6 cells. A survey of 10 PPARgamma agonists further revealed that a compound's in vitro potency was correlated with its edemagenic potential leading to the prediction that one of three previously uncharacterized PPARgamma agonists would cause less edema. This prediction was validated in a nonhuman primate model of PPARgamma agonist-induced edema. CONCLUSION: Our results implicate a key role for renin and endothelin-1 in the edema caused by PPARgamma agonists and demonstrate how knowledge gained from pharmacogenetic studies can be applied in drug discovery.

Urine acidification has no effect on peroxisome proliferator-activated receptor (PPAR) signaling or epidermal growth factor (EGF) expression in rat urinary bladder urothelium.

We previously reported prevention of urolithiasis and associated rat urinary bladder tumors by urine acidification (via diet acidification) in male rats treated with the dual peroxisome proliferator-activated receptor (PPAR)alpha/gamma agonist muraglitazar. Because urine acidification could potentially alter PPAR signaling and/or cellular proliferation in urothelium, we evaluated urothelial cell PPARalpha, PPARdelta, PPARgamma, and epidermal growth factor receptor (EGFR) expression, PPAR signaling, and urothelial cell proliferation in rats fed either a normal or an acidified diet for 5, 18, or 33 days. A subset of rats in the 18-day study also received 63 mg/kg of the PPARgamma agonist pioglitazone daily for the final 3 days to directly assess the effects of diet acidification on responsiveness to PPARgamma agonism. Urothelial cell PPARalpha and gamma expression and signaling were evaluated in the 18- and 33-day studies by immunohistochemical assessment of PPAR protein (33-day study only) and quantitative real-time polymerase chain reaction (qRT-PCR) measurement of PPAR-regulated gene expression. In the 5-day study, EGFR expression and phosphorylation status were evaluated by immunohistochemical staining and egfr and akt2 mRNA levels were assessed by qRT-PCR. Diet acidification did not alter PPARalpha, delta, or gamma mRNA or protein expression, PPARalpha- or gamma-regulated gene expression, total or phosphorylated EGFR protein, egfr or akt2 gene expression, or proliferation in urothelium. Moreover, diet acidification had no effect on pioglitazone-induced changes in urothelial PPARgamma-regulated gene expression. These results support the contention that urine acidification does not prevent PPARgamma agonist-induced bladder tumors by altering PPARalpha, gamma, or EGFR expression or PPAR signaling in rat bladder urothelium.

Molecular events associated with arsenic-induced malignant transformation of human prostatic epithelial cells: aberrant genomic DNA methylation and K-ras oncogene activation.

Numerous studies link arsenic exposure to human cancers in a variety of tissues, including the prostate. Our prior work showed that chronic arsenic exposure of the non-tumorigenic, human prostate epithelial cell line, RWPE-1, to low levels of (5 microM) sodium arsenite for 29 weeks resulted in malignant transformation and produced the tumorigenic CAsE-PE cell line. The present work focuses on the molecular events occurring during this arsenic-induced malignant transformation. Genomic DNA methylation was significantly reduced in CAsE-PE cells. A time course experiment showed that during malignant transformation DNA methyltransferase activity was markedly reduced by arsenic. However, DNA methyltransferase mRNA levels were not affected by arsenic exposure. Microarray screening showed that K-ras was highly overexpressed in CAsE-PE cells, a result further confirmed by Northern blot and Western blot analyses. Since ras activation is thought to be a critical event in prostate cancer progression, further detailed study was performed. Time course experiments also showed that increased K-ras expression preceded malignant transformation. Mutational analysis of codons 12, 13, and 61 indicated the absence of K-ras mutations. The K-ras gene can be activated by hypomethylation, but our study showed that CpG methylation in K-ras promoter region was not altered by arsenic exposure. Arsenic metabolism studies showed RWPE-1, CAsE-PE, and primary human prostate cells all had a very poor capacity for arsenic methylation. Thus, inorganic arsenic-induced transformation in human cells is associated with genomic DNA hypomethylation and K-ras overexpression. However, overexpression of K-ras occurred without mutations and through a mechanism other than promoter region hypomethylation.

Interferon alpha induction of metallothionein in rat liver is not linked to interleukin-1, interleukin-6, or tumor necrosis factor alpha.

Synthesis of metallothionein (MT) is induced by interferon-alpha (IFN-alpha) in vitro and in vivo. In addition, IFN-alpha promotes redistribution of zinc (Zn) from the plasma to the liver in mice. However, it is not clear if IFN-alpha induces hepatic MT synthesis directly or indirectly via liberation of other cytokines. In order to address this issue, we determined hepatic MT levels, Zn concentration in plasma, liver, and urine, and plasma levels interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNFalpha) in rats following intramuscular injection of human IFN-alpha (1.5 x 10(6) UI/m(2)). Animals were housed in metabolic cages and sacrificed at various times after IFN-alpha administration. Zn concentrations in serum, urine, and hepatic tissue were determined by atomic absorption spectrophotometry. MT protein was measured using the MT silver saturation method and expression of MT-1 and MT-2 mRNA was measured by RT-PCR. Plasma levels of rat IL-1, IL-6, and TNFalpha were determined using an ELISA method. Hepatic MT levels began to increase at 2 h following IFN-alpha administration and reached maximum levels at 12 h post-treatment. Induction of MT gene expression was confirmed by increases in MT-1 and MT-2 mRNA levels 6, 12, and 18 h after IFN-alpha administration. IFN-alpha treatment also resulted in biphasic increases in hepatic Zn, with levels peaking at 2 h, the time-point when MT levels are first increased, and again at 18 h. Concurrently, there were decreases in serum Zn levels at these time points, suggesting IFN-alpha induced movement of Zn from the blood to hepatic tissue. The decrease in serum Zn was not due to increased excretion since urinary Zn levels were unaffected following IFN-alpha treatment. IFN-alpha administration had no effect on plasma IL-1, IL-6, and TNFalpha levels. These results show that IFN-alpha promotes the increase of hepatic MT levels and plasma/liver redistribution directly, without IL-1, IL-6, or TNFalpha participation.

Estrogen signaling in livers of male mice with hepatocellular carcinoma induced by exposure to arsenic in utero.

BACKGROUND: Exposure of pregnant mice to inorganic arsenic induces a spectrum of tumors, including hepatocellular carcinoma (HCC), in their adult offspring similar to that induced by exposing adult mice to estrogenic compounds. To investigate whether arsenic exposure in utero causes altered estrogen signaling, we examined expression of estrogen receptor-alpha (ER-alpha), cyclin D1 (an estrogen-responsive hepatic oncogene), and several cytochrome P450 genes (with sexually dimorphic liver expression patterns) in livers from adult male mice with in utero arsenic-induced HCC. METHODS: Quantitative real-time reverse transcription-polymerase chain reaction was used to evaluate gene expression in livers of adult male mice that had (i.e., exposed mice; n = 8) or had not (i.e., control mice; n = 5) been exposed to arsenic in utero. DNA methylation status of portions of the ER-alpha and cyclin D1 gene promoters in liver tissue was measured using methylation-specific polymerase chain reaction. Statistical tests were two-sided. RESULTS: ER-alpha mRNA levels were 3.1-fold (95% confidence interval [CI] = 2.0-fold to 4.3-fold) higher in livers of exposed mice than in those of control mice, and cyclin D1 levels were 3.0-fold (95% CI = 1.7-fold to 4.3-fold) higher. Exposed mice showed a feminized expression pattern of several cytochrome P450 genes, expressing the female-dominant CYP2A4 (P =.017 versus control) and CYP2B9 (P<.001) genes at 8.7 and 10.5 times, respectively, the level in control mice and expressing the male-dominant CYP7B1 at approximately one-fourth the level in control mice(P =.0012). Exposed mice exhibited reduced (by approximately 90%) methylation of the ER-alpha gene promoter in liver DNA as compared with control mice; the cyclin D1 gene promoter was not methylated in either exposed or control mice. CONCLUSION: Altered estrogen signaling may play a role in induction of HCC by arsenic exposure in utero. Specifically, overexpression of ER-alpha, potentially through promoter region hypomethylation, in livers of such mice may be linked to the hepatocarcinogenicity of arsenic.

Effects of cadmium on DNA-(Cytosine-5) methyltransferase activity and DNA methylation status during cadmium-induced cellular transformation.

Cadmium is a human carcinogen that likely acts via epigenetic mechanisms. Since DNA methylation alterations represent an important epigenetic event linked to cancer, the effect of cadmium on DNA methyltransferase (MeTase) activity was examined using in vitro (TRL1215 rat liver cells) and ex vivo (M.SssI DNA MeTase) systems. Cadmium effectively inhibited DNA MeTases in a manner that was noncompetitive with respect to substrate (DNA), indicating an interaction with the DNA binding domain rather than the active site. Based on these results, the effects of prolonged cadmium exposure on DNA MeTase and genomic DNA methylation in TRL1215 cells were studied. After 1 week of exposure to 0-2.5 microM cadmium, DNA MeTase activity was reduced (up to 40%) in a concentration-dependent fashion, while genomic DNA methylation showed slight but significant reductions at the two highest concentrations. After 10 weeks of exposure, the cells exhibited indications of transformation, including hyperproliferation, increased invasiveness, and decreased serum dependence. Unexpectedly, these cadmium-transformed cells exhibited significant increases in DNA methylation and DNA MeTase activity. These results indicate that, while cadmium is an effective inhibitor of DNA MeTase and initially induces DNA hypomethylation, prolonged exposure results in DNA hypermethylation and enhanced DNA MeTase activity.

Metallothionein is a potential negative regulator of apoptosis.

Apoptotic resistance can either be desirable or undesirable, depending on the conditions. In cancer chemotherapy, it is critical that tumor cells are selectively and effectively killed while leaving normal cells undamaged. Since acquisition of apoptotic resistance appears to be a common occurrence during malignant transformation, elucidating the mechanisms underlying apoptotic resistance is an area of intense study. Previous studies have revealed that metallothionein (MT) can protect cells from apoptosis induced by oxidative stress and metals. In the present study, we tested the hypothesis that the presence of MT may somehow modulate apoptosis. Our results revealed a strong linear negative correlation between basal MT levels and etoposide-induced apoptosis in the human tumor cell lines PLC/PRF/5, H460, and HepG2 (r = -0.991). In HepG2 cells, 24 h pretreatment with cadmium resulted in concentration-dependent increases in MT levels and marked decreases in etoposide-induced apoptosis. Zinc pretreatment also resulted in increased MT synthesis and decreased etoposide-induced apoptosis. More importantly, induced MT levels were negatively correlated with sensitivity to etoposide-induced apoptosis (r = -0.965). These suggest that MT may play a role in regulating apoptosis and that modulating MT expression may provide a strategy for altering cellular resistance to chemotherapeutic compounds.

Inorganic arsenite-induced malignant transformation of human prostate epithelial cells.

Although several epidemiologic studies show an association between arsenic exposure and prostate cancer, it is still unknown whether human prostate epithelial cells are directly susceptible to arsenic-induced transformation. This study was designed to determine whether the nontumorigenic human prostate epithelial cell line RWPE-1 could be malignantly transformed in vitro by arsenite. RWPE-1 cells were continuously exposed to 5 micro M arsenite and monitored for signs of transformation, assessed as changes in matrix metalloproteinase-9 levels. After 29 weeks of exposure, the arsenite-exposed RWPE-1 cells (referred to as CAsE-PE) showed a marked increase in matrix metalloproteinase-9 secretion, a common finding in prostate malignancies. Malignant transformation was confirmed when CAsE-PE cells produced aggressive undifferentiated malignant epithelial tumors in nude mice. The tumors stained positive for human prostate-specific antigen, confirming their origin. These results are the first report of arsenite-induced malignant transformation of a human epithelial cell line and provide an important in vitro model for studying the mechanisms underlying arsenic-induced carcinogenesis in humans.

Chronic arsenic-exposed human prostate epithelial cells exhibit stable arsenic tolerance: mechanistic implications of altered cellular glutathione and glutathione S-transferase.

Acquisition of stable arsenic tolerance in human cells following chronic arsenic exposure has not been previously reported. In the present work, we describe acquisition of stable arsenic tolerance in the human prostate epithelial cell line RWPE-1 following chronic arsenic exposure in vitro. RWPE-1 cells continuously exposed to 5 microM sodium arsenite for > or =18 weeks exhibited dramatic resistance to acute arsenite toxicity. The LC50 for acute arsenite exposure in these chronic arsenic-exposed prostate epithelial (CAsE-PE) cells was 43.8 microM versus 17.6 microM in control cells. Similar results were obtained using the antineoplastic agent arsenic trioxide. This tolerance was stable, as CAsE-PE cells grown in arsenic-free medium for 5 weeks retained their resistant phenotype. Compared to control cells, CAsE-PE cells showed a 90% reduction in arsenic accumulation over 24 h coupled with a 2.6-fold increase in the rate of arsenic efflux. CAsE-PE cells had increased basal GSH levels (4.9-fold) and increased GST activity (2.4-fold) and both GSH depletion and inhibition of GST activity abolished arsenic tolerance. Arsenic tolerance was also abolished by treatment with inhibitors of the Mdr1 and Mrp1 transporters, although no increases in mdr1 or mrp1 gene expression were observed. Our results indicate that this tolerance in human cells involves increases in GSH levels and GST activity that allow for more efficient arsenic efflux by MRP1 and MDR1. This study represents the first report of stable acquired arsenic tolerance in human cells, which could have important implications for both the toxicology and the pharmacology of arsenic.

Altered apoptotic gene expression and acquired apoptotic resistance in cadmium-transformed human prostate epithelial cells.

BACKGROUND: Cadmium is a suspected prostatic carcinogen, although the underlying mechanisms are unclear. To investigate these mechanisms, we performed molecular comparisons between the cadmium-transformed prostate epithelial cell line CTPE and the nontumorigenic parental line RWPE-1. METHODS: Gene expression patterns were compared by using cDNA arrays, RNase protection assays, and Western blots. Apoptosis was analyzed by using flow cytometry to quantify apoptotic nuclei and an enzyme-linked immunosorbent assay method to measure DNA fragmentation. Caspase-3 activity was measured colorimetrically. RESULTS: Among the genes down-regulated in CTPE cells were those encoding several members of the caspase family of apoptotic proteases as well as the apoptotic regulator Bax. Ribonuclease protection assays confirmed global down-regulation of caspase gene expression in CTPE. Decreased Bax expression in CTPE was confirmed by Western blots, which also revealed increased expression of anti-apoptotic Bcl-2. Consistent with these changes, CTPE cells exhibited increased resistance to apoptosis induced by cadmium, cisplatin, and etoposide. CTPE cells also exhibited lower caspase-3 activity vs. RWPE-1 after etoposide treatment. CONCLUSIONS: CTPE cells exhibited altered expression of important apoptotic regulators as well as resistance to several apoptotic stimuli. We hypothesize that acquired apoptotic resistance may be a key aspect of cadmium-induced malignant transformation of prostate epithelial cells and that this may contribute to both tumor initiation and the acquisition of aggressive characteristics subsequent to tumor formation.