Acute toxicity of CCl4 but not of paracetamol induces a transcriptomic signature of fibrosis in precision-cut liver slices

In rat in vivo, both paracetamol (APAP) and carbon tetrachloride (CCl4) induce liver necrosis, but long-term treatment with CCl4, in contrast to paracetamol, causes liver fibrosis. The aim of this study was to perform transcriptomic analysis to compare the early changes in mRNA expression profiles induced by APAP and CCl4 in the rat precision-cut liver slice model (PCLS) and to identify early markers that could predict fibrosis-inducing potential. Microarray data of rat PCLS exposed to APAP andCCl4was generated using a toxic dose based on decrease in ATP levels. Toxicity pathway analysis using a custom made fibrosis-related gene list showed fibrosis as one of the predominant toxic endpoints in CCl4-treated, but not in APAP-treated PCLS. Moreover, genes which have a role in fibrosis such as alpha-B crystallin, jun proto-oncogene, mitogen-activated protein kinase 6, serpin peptidase inhibitor and also the transcription factor Kruppel-like-factor-6 were up-regulated by CCl4, but not by APAP. Predicted activation or inhibition of several upstream regulators due to CCl4 is in accordance with their role in fibrosis. In conclusion, transcriptomic analysis of PCLS successfully identified the fibrotic potential of CCl4 as opposed to APAP. The application of PCLS as an ex vivo model to identify early biomarkers to predict the fibrogenic potential of toxic compounds should be further explored.

Org 214007-0: a novel non-steroidal selective glucocorticoid receptor modulator with full anti-inflammatory properties and improved therapeutic index

Glucocorticoids (GCs) such as prednisolone are potent immunosuppressive drugs but suffer from severe adverse effects, including the induction of insulin resistance. Therefore, development of so-called Selective Glucocorticoid Receptor Modulators (SGRM) is highly desirable. Here we describe a non-steroidal Glucocorticoid Receptor (GR)-selective compound (Org 214007-0) with a binding affinity to GR similar to that of prednisolone. Structural modelling of the GR-Org 214007-0 binding site shows disturbance of the loop between helix 11 and helix 12 of GR, confirmed by partial recruitment of the TIF2-3 peptide. Using various cell lines and primary human cells, we show here that Org 214007-0 acts as a partial GC agonist, since it repressed inflammatory genes and was less effective in induction of metabolic genes. More importantly, in vivo studies in mice indicated that Org 214007-0 retained full efficacy in acute inflammation models as well as in a chronic collagen-induced arthritis (CIA) model. Gene expression profiling of muscle tissue derived from arthritic mice showed a partial activity of Org 214007-0 at an equi-efficacious dosage of prednisolone, with an increased ratio in repression versus induction of genes. Finally, in mice Org 214007-0 did not induce elevated fasting glucose nor the shift in glucose/glycogen balance in the liver seen with an equi-efficacious dose of prednisolone. All together, our data demonstrate that Org 214007-0 is a novel SGRMs with an improved therapeutic index compared to prednisolone. This class of SGRMs can contribute to effective anti-inflammatory therapy with a lower risk for metabolic side effects.

Cytotoxic effects of 109 reference compounds on rat H4IIE and human HepG2 hepatocytes. III: Mechanistic assays on oxygen consumption with MitoXpress and NAD(P)H production with Alamar Blue™

In vitro toxicity screening can reduce the attrition rate of drug candidates in the pharmaceutical industry in the early development process. The focus in this study is to compare the sensitivity for cytotoxicity of a time-resolved fluoro metric oxygen probe with that of a fluoro metric Alamar Blue™ (AB) assay. Both assays measure mitochondrial activity by either oxygen consumption (LUX-A65N-1 (MitoXpress, Luxcel) probe) or NADH/FADH conversion (AB). Both assays were carried out with increasing concentrations of 109 reference compounds using rat H4IIE and human HepG2 hepatocytes at incubation periods of 24, 48 and 72 h. Prior to this study, the influence on medium with either glucose or galactose was studied to analyze the rate of glycolysis and oxygen consumption, which latter process may be impaired in hepatoma cells. Inhibitors of oxygen consumption in combination with a glucose up-take inhibitor showed the largest consumption rate differences in the presence of 5mM of glucose. The choice for the 109 reference compounds was based on the so-called Multicentre Evaluation for In vitro Cytotoxicity (MEIC) and on diverse drug categories. For 59 toxic reference compounds, an evaluation for both assays was carried up to 10(-3)M. Toxicity was demonstrated with MitoXpress for 23 (39%) and 36 (61%) compounds in H4IIE and HepG2 cells, respectively, and with AB for 44 (75%) and 40 (68%) compounds. For 50 more pharmaceutical drugs more physiological concentrations were used up to 3.16×10(-5)M, and only 19 (38%) of these compounds appeared to be toxic in both assays. In conclusion, overall 63 (58%) and 60 (55%) compounds showed toxic effects with the MitoXpress and AB assays on rat H4IIE and human HepG2 hepatocytes, respectively. AB assays were more sensitive with respect to H4IIE cells and MitoXpress assays with respect to HepG2 cells. At all tested time intervals, MitoXpress showed its sensitivity, while AB is more sensitive at 48 and 72 h. With AB more toxic compounds were identified, whereas MitoXpress was more sensitive for a few compounds. A species specific difference was clearly found with digoxin, a human specific potassium channel inhibitor. Thus both assays are valuable identifiers of early toxicity with discrimination in time, compounds and species.

SERMs and SARMs: detection of their activities with yeast based bioassays

Selective estrogen receptor modulators (SERMs) and selective androgen receptor modulators (SARMs) are compounds that activate their cognate receptor in particular target tissues without affecting other organs. Many of these compounds will find their use in therapeutic treatments. However, they also will have a high potential for misuse in veterinary practice and the sporting world. Here we demonstrate that yeast estrogen and androgen bioassays can be used to detect SERMs and SARMs, and are also useful screening tools to investigate their mode of action. Six steroidal 11beta-substituents of E2 (SERMs) and some arylpropionamide- and quinoline-based SARMs were tested. In addition, 7 compounds previously tested on AR agonism and determined as inactive in the yeast androgen bioassay, while QSAR modelling revealed strong binding to the human androgen receptor, are now shown to act as AR antagonists.

Evaluation of the Vitotox and RadarScreen assays for the rapid assessment of genotoxicity in the early research phase of drug development

The Vitotox and RadarScreen assays were evaluated as early screens for mutagenicity and clastogenicity, respectively. The Vitotox assay is a bacterial reporter assay in Salmonella typhimurium based on the SOS-response, and it contains a luciferase gene under control of the recN promoter. The RadarScreen assay is a RAD54 promoter-linked beta-galactosidase reporter assay in yeast. The expression of this beta-galactosidase can easily be quantified by use of the substrate d-luciferin-o-beta-galactopyranoside, which is converted into galactose and luciferin that can be measured luminometrically. Recently, an ECVAM workgroup defined a list of 20 genotoxic and 42 non-genotoxic compounds [D. Kirkland, P. Kasper, L. Muller, R. Corvi, G. Speit, Recommended lists of genotoxic and non-genotoxic chemicals for assessment of the performance of new or improved genotoxicity tests: a follow-up to an ECVAM workshop, Mutat. Res. 653 (2008) 99-108.] that can be used for the validation and/or optimization of in vitro genotoxicity assays. In the present study, this compound set was used for the validation of the assays. Moreover, an additional set of 192 compounds was used to broaden this validation study. The compounds of this additional set can be classified as non-genotoxins and genotoxins and consists of both in-house and reference compounds. In case of the ECVAM compound list, the results from the Vitotox and RadarScreen assays were compared to the genotoxic/non-genotoxic classification of the compounds in this list. In case of the additionally tested compounds, the results of the Vitotox and RadarScreen assays were compared, respectively, with bacterial mutagenicity (Ames) results or in vitro clastogenicity data obtained in-house or from the literature. The validation with respect to the ECVAM compound list resulted in a sensitivity for both the Vitotox and RadarScreen assay of 70% (14/20). If both assays were combined the sensitivity increased to 85% (17/20). Both tests also gave a low number of false positive results. The specificity of the Vitotox and RadarScreen assays was 93% (39/42) and 83% (35/42), respectively. This resulted in a predictivity of the Vitotox and RadarScreen assay of 85% (53/62) and 79% (49/62), respectively. In case both tests were combined the specificity and the predictivity of the Vitotox and RadarScreen assay turned out to be 81% (34/42) and 82% (51/62), respectively. The results from the additional list of 192 compounds confirmed the results found with the ECVAM compound list. The results from the Vitotox assay showed a high correlation with Ames test of 91% (132/145). Subsequently, the RadarScreen assay had a correlation with in vitro clastogenicity of 76% (93/123). The specificity of the Vitotox assay was 94% (90/96) for Ames test results and that of the RadarScreen assay was 74% (34/46) for clastogenicity. Moreover, the sensitivities of the Vitotox and RadarScreen assays were 86% (42/49) and 77% (59/77), respectively. Implementation of the Vitotox and RadarScreen assays in the early research phase of drug development can lead to fast de-selection for genotoxicity. It is expected that this application will reduce the number of compounds that have a positive score in the regulatory Ames and clastogenicity tests. Moreover, problems with a complete compound class can be foreseen at an early time point in the research phase, which gives more time for issue resolution than late detection of these problems with the regulatory tests.

Predictive models for carcinogenicity and mutagenicity: frameworks, state-of-the-art, and perspectives

Mutagenicity and carcinogenicity are endpoints of major environmental and regulatory concern. These endpoints are also important targets for development of alternative methods for screening and prediction due to the large number of chemicals of potential concern and the tremendous cost (in time, money, animals) of rodent carcinogenicity bioassays. Both mutagenicity and carcinogenicity involve complex, cellular processes that are only partially understood. Advances in technologies and generation of new data will permit a much deeper understanding. In silico methods for predicting mutagenicity and rodent carcinogenicity based on chemical structural features, along with current mutagenicity and carcinogenicity data sets, have performed well for local prediction (i.e., within specific chemical classes), but are less successful for global prediction (i.e., for a broad range of chemicals). The predictivity of in silico methods can be improved by improving the quality of the data base and endpoints used for modelling. In particular, in vitro assays for clastogenicity need to be improved to reduce false positives (relative to rodent carcinogenicity) and to detect compounds that do not interact directly with DNA or have epigenetic activities. New assays emerging to complement or replace some of the standard assays include Vitotox, GreenScreenGC, and RadarScreen. The needs of industry and regulators to assess thousands of compounds necessitate the development of high-throughput assays combined with innovative data-mining and in silico methods. Various initiatives in this regard have begun, including CAESAR, OSIRIS, CHEMOMENTUM, CHEMPREDICT, OpenTox, EPAA, and ToxCast. In silico methods can be used for priority setting, mechanistic studies, and to estimate potency. Ultimately, such efforts should lead to improvements in application of in silico methods for predicting carcinogenicity to assist industry and regulators and to enhance protection of public health.

High-throughput screening for analysis of in vitro toxicity

The influence of combinatorial chemistry and high-throughput screening (HTS) technologies in the pharmaceutical industry during the last 10 years has been enormous. However, the attrition rate of drugs in the clinic due to toxicity during this period still remained 40-50%. The need for reduced toxicity failure led to the development of early toxicity screening assays. This chapter describes the state of the art for assays in the area of genotoxicity, cytotoxicity, carcinogenicity, induction of specific enzymes from phase I and II metabolism, competition assays for enzymes of phase I and II metabolism, embryotoxicity as well as endocrine disruption and reprotoxicity. With respect to genotoxicity, the full Ames, Ames II, Vitotox, GreenScreen GC, RadarScreen, and non-genotoxic carcinogenicity assays are discussed. For cytotoxicity, cellular proliferation, calcein uptake, oxygen consumption, mitochondrial activity, radical formation, glutathione depletion as well as apoptosis are described. For high-content screening (HCS), the possibilities for analysis of cytotoxicity, micronuclei, centrosome formation and phospholipidosis are examined. For embryotoxicity, endocrine disruption and reprotoxicity alternative assays are reviewed for fast track analysis by means of nuclear receptors and membrane receptors. Moreover, solutions for analyzing enzyme induction by activation of nuclear receptors, like AhR, CAR, PXR, PPAR, FXR, LXR, TR and RAR are given.

Evaluation of cytotoxic, genotoxic and CYP450 enzymatic competition effects of Tanzanian plant extracts traditionally used for treatment of fungal infections

HIV-infected patients in sub-Saharan countries highly depend on traditional medicines for the treatment of opportunistic oral infections as candidiasis. Previous investigations on antifungal activity of medicinal plant extracts utilized by traditional healers in Tanzania have revealed 12 extracts with potent antifungal activity. Although the plants may be good candidates for new treatment opportunities, they can be toxic or genotoxic and could cause pharmacokinetic interactions when used concomitantly with antiretroviral agents. Therefore, we investigated the cytotoxicity, genotoxicity and cytochrome P450 interaction potential of these medicinal plants. Cytotoxicity was tested by Hoechst 33342, Alamar Blue, calcein-AM, glutathione depletion and O(2)-consumption assays and genotoxicity by a Vitotox assay. Competition of the 12 extracts on substrate metabolism by CYP3A4, 2C9, 2C19 and 2D6 was tested with high-throughput CYP inhibition screening. Pregnane X receptor (PXR) activation was tested using Chinese hamster ovary cell lines expressing human PXR. Herbal extracts inducing high human PXR activation were tested for enhanced CYP3A4 mRNA levels with quantitative polymerase chain reaction. Genotoxicity was found for Jatropha multifida, Sterculia africana and Spirostachys africana. All plant extracts showed high cytotoxic effects in almost all tests. Potent competition with CYP3A4, 2D6, 2C9 and 2C19 was found for 75% of the herbal extracts. Spirostachys africana did not affect CYP2D6 and for S. africana and Turraea holstii no effect on CYP2D6 and CYP3A4 (DBF) was found. Nine plant extracts showed significant activation of human PXR, but only Agaura salicifolia, Turraea holstii and S. africana significantly induced CYP3A4 mRNA levels. These results indicate the possibility of potential medicinal plant-antiretroviral interactions.

Screening of synthetic and plant-derived compounds for (anti)estrogenic and (anti)androgenic activities

Recently we constructed yeast cells that either express the human estrogen receptor alpha or the human androgen receptor in combination with a consensus ERE or ARE repeat in the promoter region of a green fluorescent protein (yEGFP) read-out system. These bioassays were proven to be highly specific for their cognate agonistic compounds. In this study the value of these yeast bioassays was assessed for analysis of compounds with antagonistic properties. Several pure antagonists, selective estrogen receptor modulators (SERMs) and plant-derived compounds were tested. The pure antiestrogens ICI 182,780 and RU 58668 were also classified as pure ER antagonists in the yeast estrogen bioassay and the pure antiandrogen flutamide was also a pure AR antagonist in the yeast androgen bioassay. The plant-derived compounds flavone and guggulsterone displayed both antiestrogenic and antiandrogenic activities, while 3,3'-diindolylmethane (DIM) and equol combined an estrogenic mode of action with an antiandrogenic activity. Indol-3-carbinol (I3C) only showed an antiandrogenic activity. Coumestrol, genistein, naringenin and 8-prenylnaringenin were estrogenic and acted additively, while the plant sterols failed to show any effect. Although hormonally inactive, in vitro and in vivo metabolism of the aforementioned plant sterols may still lead to the formation of active metabolites in other test systems.

Phase II enzyme levels in HepG2 cells and cryopreserved primary human hepatocytes and their induction in HepG2 cells

The HepG2 cell line is a valuable tool for screening for cytotoxicity in the early phase of pharmaceutical development. Some compounds which produce reactive and toxic metabolites, are classified as being toxic in HepG2 cells. In contrast, other compounds, which are toxic in primary human hepatocytes, are not toxic in HepG2 cells. A difference in metabolism between HepG2 cells and primary human hepatocytes might be the reason. To investigate this, cytochrome P450 and Phase II enzyme levels were characterized. In the present study the focus is on Phase II enzyme metabolism. Transcript levels of UDP-glucuronosyl transferases (UGTs), sulfotransferases (SULTs), glutathione S-transferases (GSTs), N-acetyltransferase-1 (NAT1) and epoxide hydrolase (EPHX1) were measured with quantitative PCR in HepG2 cells and cryopreserved primary human hepatocytes. Levels of SULT1A1, 1A2, 1E1, 1A2, and 2A1, microsomal GST 1, GST mu1, NAT1, and EPHX1 in HepG2 cells were almost similar to levels in primary human hepatocytes. In contrast, levels of UGT1A1 and 1A6 transcripts were between 10- and more than 1000-fold higher in the primary hepatocytes. The regulatory processes of Phase II enzymes by the aryl hydrocarbon receptor, pregnane X receptor and constitutive androstane receptor were studied in HepG2 cells and appeared quite similar to those in primary human hepatocytes. Due to the involvement of Phase II enzymes in the toxication of some compounds, HepG2 cells can be a valuable cellular system to predict toxicity for these compounds. On the other hand, the normal expression of most Phase II enzymes in combination with the lower expression of cytochrome P450 enzymes in HepG2 cells might result in an underestimation of toxicity for several compounds. Compared to primary human hepatocytes, HepG2 cells are a relatively easy-to-handle tool to study the up-regulation of Phase II enzymes.

Cytochrome P450 enzyme levels in HepG2 cells and cryopreserved primary human hepatocytes and their induction in HepG2 cells

Early in vitro toxicity screening might improve the success rate of new chemical entities in pharmaceutical development. In previous studies, the advantage of cytotoxicity screening with the HepG2 cell line was shown. Cytotoxicity could be identified for 70% of the compounds in these assays as compared with known toxicity in either in vitro assays in primary hepatocytes, in in vivo assays in rats, or in (pre-)clinical development in humans. The low Phase I and II enzyme levels in HepG2 cells might have been responsible for the fact that 30% of the compounds scored negative. Therefore, we performed two follow-up studies in which Cytochrome P450 (CYP) enzymes and Phase II metabolism were examined. In the present study, the transcript levels of CYP1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 were measured with quantitative PCR. Results showed that transcripts of all CYPs were present in HepG2 cells, however, mRNA levels of most CYPs were dramatically lower than in primary human hepatocytes. These results were confirmed with luminometric assays which were used to measure the enzyme activities of CYP1A1, 1A2, 2C9, and 3A4. Regulation of CYP1A1, 1A2, 2B6, 2C8, 2D6, 2E1, and 3A4 by the aryl hydrocarbon receptor, pregnane X receptor and constitutive androstane receptor was studied in HepG2 cells at the mRNA and/or enzyme level. Regulation of CYP1A1, 1A2, 2B6, and 3A4 mRNA levels was similar to the regulation in primary human hepatocytes. In contrast, CYP2C8 mRNA levels are inducible in primary human hepatocytes, but not in HepG2 cells, after treatment with PXR/CAR activators. Consistent with other studies, CYP2D6 and 2E1 transcript levels were not changed after treatment with AhR, PXR, and CAR activators. Moreover, CYP1A1 and 1A2 enzyme levels could be induced by AhR agonists and CYP3A4 by PXR agonists. As a consequence of the low levels of CYPs in HepG2 cells, cytotoxicity of several compounds might have been missed or underestimated as compared with cytotoxicity in primary human hepatocytes. Inducing HepG2 cells with particular receptor stimulators might lead to higher toxicity for several of the tested compounds. Compared to primary human hepatocytes, HepG2 cells are a relatively easy-to-handle tool to study the up-regulation of CYP1A1, 1A2, 2B6, and 3A4.

Sensitivity of 1H NMR Analysis of Rat Urine in Relation to Toxicometabonomics. Part I: Dose-Dependent Toxic Effects of Bromobenzene and Paracetamol

(1)H nuclear magnetic resonance (NMR) spectroscopy of rat urine in combination with pattern recognition analysis was evaluated for early noninvasive detection of toxicity of investigational chemical entities. Bromobenzene (B) and paracetamol (P) were administered at five single oral dosages between 2 and 500 mg/kg and between 6 and 1800 mg/kg, respectively. The sensitivity of the proposed method to detect changes in the NMR spectra 24 and 48 h after single dosing was compared with histopathology and biochemical parameters in plasma and urine. Both B and P applied at the highest dosages induced liver necrosis and markedly increased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) plasma levels. At dosages of 125 mg/kg B and 450 mg/kg P, liver necrosis and changes in AST and ALT were less pronounced, while at lower dose levels these effects could not be detected. Changes in kidney pathology or standard urine biochemistry were not observed at any of these dosages. Evaluation of the total NMR dataset showed 80 signals to be sensitive for B and P dosing. Principal component analysis on the reduced dataset revealed that NMR spectra were significantly different at dosages above 8 mg/kg (B) and 110 mg/kg (P) at both sampling times. This implies a 4- to 16-fold increased sensitivity of NMR versus histopathology and clinical chemistry in recognizing early events of liver toxicity.

Uniform Procedure of 1H NMR Analysis of Rat Urine and Toxicometabonomics Part II: Comparison of NMR Profiles for Classification of Hepatotoxicity

A procedure of nuclear magnetic resonance (NMR) urinalysis using pattern recognition is proposed for early detection of toxicity of investigational compounds in rats. The method is applied to detect toxicity upon administration of 13 toxic reference compounds and one nontoxic control compound (mianserine) in rats. The toxic compounds are expected to induce necrosis (bromobenzene, paracetamol, carbon tetrachloride, iproniazid, isoniazid, thioacetamide), cholestasis (alpha-naphthylisothiocyanate (ANIT), chlorpromazine, ethinylestradiol, methyltestosterone, ibuprofen), or steatosis (phenobarbital, tetracycline). Animals were treated daily for 2 or 4 days except for paracetamol and bromobenzene (1 and 2 days) and carbon tetrachloride (1 day only). Urine was collected 24 h after the first and second treatment. The animals were sacrificed 24 h after the last treatment, and NMR data were compared with liver histopathology as well as blood and urine biochemistry. Pathology and biochemistry showed marked toxicity in the liver at high doses of bromobenzene, paracetamol, carbon tetrachloride, ANIT, and ibuprofen. Thioacetamide and chlorpromazine showed less extensive changes, while the influences of iproniazid, isoniazid, phenobarbital, ethinylestradiol, and tetracycline on the toxic parameters were marginal or for methyltestosterone and mianserine negligible. NMR spectroscopy revealed significant changes upon dosing in 88 NMR biomarker signals preselected with the Procrustus Rotation method on principal component discriminant analysis (PCDA) plots. Further evaluation of the specific changes led to the identification of biomarker patterns for the specific types of liver toxicity. Comparison of our rat NMR PCDA data with histopathological changes reported in humans and/or rats suggests that rat NMR urinalysis can be used to predict hepatotoxicity.

A portrait of cisplatin-induced transcriptional changes in mouse embryonic stem cells reveals a dominant p53-like response

Accumulation of damage in undifferentiated cells may threaten homeostasis and regenerative capacity. Remarkably, p53 has been suggested to be transcriptionally inactive in these cells. To gain insight in the kinetics and interplay of the predominant transcriptional responses of DNA damage signalling pathways in undifferentiated cells, mouse embryonic stem cells were exposed to cisplatin at four different time points (2, 4, 8 and 24h) and concentrations (1, 2, 5 and 10 microM). RNA was isolated and subjected to genome-wide expression profiling. Up to one fourth of the tested genes could be identified as being differentially expressed (false discovery rate=10%) after the cisplatin treatment. Clustering of the expression changes showed a strong time dependency. To investigate the relationship between affected genes, a gene set analysis method was used. Functionally related gene sets were defined using gene ontologies or transcription factor binding sites and were tested for overrepresentation within the differentially expressed genes. A variety of gene sets were clearly enriched among which 'apoptosis' and 'cell cycle' were the most pronounced. Furthermore, there was a strong enrichment of genes with a p53-binding motif. The involvement of the 'cell cycle' and 'apoptosis' gene sets in the cisplatin response was detected at concentrations and time points where the respective biological assays were still negative. The results reveal novel insights into the mechanisms which maintain the genomic integrity in undifferentiated cells. Additionally the results illustrate that gene set analysis of genome-wide expression changes provides a sensitive instrument to detect cellular stress responses to DNA damage.

Cytotoxic effects of 110 reference compounds on HepG2 cells and for 60 compounds on HeLa, ECC-1 and CHO cells. II mechanistic assays on NAD(P)H, ATP and DNA contents

In this study the focus is on the comparison of fluorometric assays, using Alamar Blue (AB) and Hoechst 33342 coloration, and luminometric assays, using Cyto-Lite and ATP-Lite, for toxicity measurements. With AB, ATP-Lite and Cyto-Lite the energy status of the cell is measured and with Hoechst 33342 the amount of DNA. These assays were carried out with different dosages of several toxic compounds with the following permanent cell lines: human liver (Hep G2), human endometrium (ECC-1), human cervix (HeLa) and Chinese hamster ovary (CHO) cells. In these assays toxicity of 110 compounds was assessed in Hep G2 cells. With 60 of those, toxicity was assessed in Hela, ECC-1 and CHO cells. These compounds were non-narcotic antitussives, nasal decongestants, narcotic analgesics, hypnotics, vasodilators, specific cellular energy blockers, cellular proliferation inhibitors, ion channel blockers, estrogens, antiestrogens, androgens, progestagens and others. The outcome of this study is that all four cell lines were responsive to the same set of 60 drugs with a comparable indication of toxicity. Hep G2 cells appear slightly more sensitive, as compared to the other three cell lines. Evaluation up to dosages of 3.2 x 10(-4) or even 3.2 x 10(-3)M for some of the compounds for these four assays in Hep G2 cells demonstrated toxicity for 45 of the 60 (75%) reference compounds with known toxicity in these assays. With a new set of 50 compounds, among which there were estrogens, androgens, progestagens and antiestrogens, 18 (36%) were identified as toxic up to a concentration of 3.2 x 10(-5)M. In conclusion, many of the 60 tested reference compounds gave similar dose and toxicity effects on these permanent cell lines. Therefore, all these cell lines can be used for toxicity screening with AB, ATP-Lite, Cyto-Lite and Hoechst 33342. However, species specific cell lines may reveal species specific effects, as shown with digoxin.

Cytotoxic effects of 100 reference compounds on Hep G2 and HeLa cells and of 60 compounds on ECC-1 and CHO cells. I Mechanistic assays on ROS, glutathione depletion and calcein uptake

In this study fluorometric assays have been used for medium throughput screening on toxicity. Dichlorofluorescein diacetate, monochlorobimane and calcein-AM were fluorophores for the measurement of the formation of reactive oxygen species (ROS), the quantification of glutathione and the membrane stability, respectively. These assays have been carried out in the presence or absence of toxic compounds and with four different cell lines, i.e. human liver (Hep G2), human endometrium (ECC-1), human cervix (HeLa) and Chinese hamster ovary cells (CHO). In these assays the toxic dose of 60 reference compounds was assessed for Hep G2, HeLa, ECC-1 and CHO cells and of 40 pharmaceutical compounds for Hep G2 (ROS, glutathione) or HeLa (calcein) cells, only. These compounds were narcotic analgesics, hypnotics, vasodilators, specific cellular energy blockers, cellular proliferation inhibitors, ion channel blockers, estrogens, antiestrogens, androgens, progestagens and others. The outcome of this study revealed that all four cell lines were responsive to the same set of drugs. Only for some drugs Hep G2 cells appear slightly more sensitive, as compared to the other three cell lines. In general the HeLa cell line was the most sensitive cell line for the calcein uptake, while the Hep G2 cell line shows slightly more sensitivity for dichorofluorescein and monochlorobimane assays than the other three cell lines. Further evaluation at higher toxic dosages with Hep G2 cells for ROS and glutathione depletion and HeLa cells for calcein uptake, demonstrated toxic effects for 56 of the 100 reference compounds in these assays, among which there were estrogens, androgens, progestagens and antiestrogens. In conclusion, almost all tested compounds gave similar dose and toxicity effects on the permanent cell lines used in this study. Only three compounds showed more tissue specific cell responses. This shows that in principle all four cell lines can be used for toxicity screening.

Receptor profiling and endocrine interactions of tibolone

The receptor profiles and in vivo activity of tibolone, and its primary metabolites, Delta(4)-isomer, and 3alpha- and 3beta-hydroxytibolone, were studied and compared to those of structurally related compounds. The Delta(4)-isomer was the strongest binder and activator of the progesterone receptor (PR); tibolone was 10 times weaker in binding and half as potent in transactivation of PR; 3alpha- and 3beta-hydroxytibolone did not bind or activate PR. In rabbits oral tibolone produced a minor progestagenic effect in the endometrium, whereas co-administration of tibolone and the anti-estrogen ICI 164,384 unmasked tibolone's progestagenic effect. 3-Hydroxytibolones were the strongest binders and activators of the estrogen receptors (ERs), with greater affinity for ERalpha than for ERbeta. Tibolone showed weaker binding and activation of both ERs and the Delta(4)-isomer has a binding and activation activity of less than 0.1% of E2 for ERalpha or ERbeta. Tamoxifen and 4-hydroxytamoxifen showed partial ERalpha agonistic effects with a maximal response of 12% and raloxifene of 3-5%. Oral administration of 1mg tibolone to ovariectomized rats induced an estrogenic effect on vaginal epithelium. The Delta(4)-isomer was a stronger binder and activator of the androgen receptor (AR) than tibolone; both 3-hydroxytibolones did not bind or activate AR. Introducing a 7alpha-methyl group decreased progestagenic and increased androgenic activity. We conclude that the progestagenic and androgenic activities of tibolone are mediated by the Delta(4)-isomer, and the estrogenic activity, by the 3-hydroxytibolones. The estrogenic activity of the 3-hydroxytibolones masked the progestagenic activity of tibolone in rabbit endometrium. Full estrogenic response was observed in rat vaginal tissue after oral administration of tibolone.