Several known indole compounds are not important precursors of direct mutagenic N-nitroso compounds in green cabbage

In this study we investigated the role of indole-3-acetonitrile, indole-3-carbinol, indole and tryptophan in the formation of N-nitroso compounds in green cabbage extracts. Green cabbage extracts were separated by gel permeation chromatography. Fractions were treated with nitrite, tested for mutagenicity and analysed for total N-nitroso content. Fractions in which spiked indole-3-acetonitrile, indole-3-carbinol, indole and tryptophan eluted appeared to be low in mutagenic activity and contained relatively small amounts of N-nitroso compounds. To detect indole compounds other than the ones used in the gel permeation chromatography experiments, high-performance liquid chromatography and gas chromatography-mass spectrometry analyses were performed of green cabbage extracts. Indole-3-carboxaldehyde was found to be the most commonly occurring indole compound, but it did not show direct mutagenic activity upon nitrite treatment. Indole-3-acetonitrile was the second most common compound; although it was mutagenic after nitrite treatment, its contribution to the mutagenicity of nitrite-treated green cabbage was roughly estimated to be only 2%. No other indole compounds were detected. From this study we conclude that neither the tested indole compounds nor indole-3-carboxaldehyde play a significant role in the formation of direct mutagenic N-nitroso compounds in nitrite-treated green cabbage extracts.     

Mutagenicities of nitrosated carboline derivatives

Food-borne amines have been considered as the potential precursors of endogenous carcinogenic N-nitroso compounds in humans. A compound which yields a direct mutagen after nitrite treatment was isolated from soy sauce and was identified as 1-methyl-1,2,3,4-tetrahydro-2-carboline-3-carboxylic acid (MTCA) (Wakabayashi, et al., 1983). The mutagenicities of other carboline derivatives such as harman, norharman, harmaline, harmalol, harmine, and harmol were studied. Like MTCA, the nitrosated carboline derivatives showed higher mutagenic activity as compared to their corresponding parent compounds. The demethylated analogue of MTCA, 1,2,3,4-tetrahydro-2-carboline-3-carboxylic acid was synthesized and its nitrosated products were shown to be mutagenic to Salmonella typhimurium TA 100 and TA 98. The potent mutagen Trp-P-2 is a typical 3-carboline derivative. The mutagenicity of Trp-P-2 was suppressed remarkably after nitrosation. Several 3-carboline derivatives also showed the similar property. Nitrosation of MTCA gave several derivatives which were isolated and showed direct mutagenicity to Salmonella typhimurium TA 98. Further characterization of these new carboline derivatives is in progress.     

Effects of 12-O-tetradecanoylphorbol-13-acetate (TPA), retinoic acid and diazepam on intercellular communication in a monolayer of rat liver epithelial cells

We have studied the influence of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), the vitamin A derivative retinoic acid and the benzodiazepine diazepam on intercellular communication via established gap junctions in a monolayer of rat liver epithelial cells (RLB) at various times of incubation. Intercellular communication was measured as the transfer of [3H]hypoxanthine-derived nucleotides between RLB hypoxanthine guanine phosphoribosyl transferase+ (HPRT+) and RLB HPRT- cells. TPA only showed transient inhibition of metabolic cooperation: after 4 h of treatment, intercellular communication was reduced to about 40% of the control and longer treatments showed progressively less effect until 24 h of treatment, when no difference was seen between TPA-treated and control preparations. Retinoic acid was a more effective inhibitor: both 3 X 10(-6) M applied for 24 h and 10(-4) M applied for 6.5 h, caused a 50% inhibition of label transfer. The junctional communication could only be blocked at very high concentrations (5 X 10(-4) M) in short-exposure experiments, but this is possibly a consequence of non-specific effects on the cell membrane. When the incubation time was 24 h, a considerable portion of the gap junctions appeared to persist in the 'open' state. Diazepam showed no significant inhibitory effect in the experiments performed.     

Bystander effects may modulate ultraviolet A and B radiation-induced delayed mutagenesis

Ultraviolet irradiation of cells can induce a state of genomic instability that can persist for several cell generations after irradiation. However, questions regarding the time course of formation, relative abundance for different types of ultraviolet radiation, and mechanism of induction of delayed mutations remain to be answered. In this paper, we have tried to address these questions using the hypoxanthine phosphoribosyl transferase (HPRT) mutation assay in V79 Chinese hamster cells irradiated with ultraviolet A or B radiation. Delayed HPRT(-) mutations, which are indications of genomic instability, were detected by incubating the cells in medium containing aminopterin, selectively killing HPRT(-) mutants, and then treating the cells with medium containing 6-thioguanine, which selectively killed non-mutant cells. Remarkably, the delayed mutation frequencies found here were much higher than reported previously using a cloning method. Cloning of cells immediately after irradiation prevents contact between individual cell clones. In contrast, with the present method, the cells are in contact and are mixed several times during the experiment. Thus the higher delayed mutation frequency measured by the present method may be explained by a bystander effect. This hypothesis is supported by an experiment with an inhibitor of gap junctional intercellular communication, which reduced the delayed mutation frequency. In conclusion, the results suggest that a bystander effect is involved in ultraviolet-radiation-induced genomic instability and that it may be mediated in part by gap junctional intercellular communication.     

Inhibition of gap-junctional intercellular communication between Chinese hamster lung fibroblasts by di(2-ethylhexyl) phthalate (DEHP) and trisodium nitrilotriacetate monohydrate (NTA)

Di(2-ethylhexyl)phthalate and trisodium nitrilotriacetate monohydrate, two apparently nongenotoxic carcinogens, were tested for effects on gap-junctional communication between Chinese hamster V79 lung fibroblasts. Both compounds inhibited gap-junctional communication in a concentration-dependent manner. The inhibiting effects of these chemicals on gap-junctional communication in vitro correlate with their tumor-promoting activity. Such results further support the hypothesis that inhibition of gap-junctional communication is an in vitro biomarker for some tumor-promoting chemicals.Abbreviations CAS Chemical Abstracts Service - DEHP di(2-ethylhexyl)phthalate - GJIC gap-junctional intercellular communication - NTA trisodium nitrilotriacetate monohydrate     

Synthesis and antimicrobial activity of 3-arylamino-1-chloropropan-2-ols

A series of nine 3-arylamino-1-chloropropan-2-ols 2a-2i were synthesized and their anti-fungal activity against pathogenic strains of Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger and Candida albicans, and antibacterial activity against four pathogenic bacterial strains of Salmonella typhi, Pseudomonas aeruginosa, Streptococcus pneumonae and Staphylococcus aureus were evaluated using different assay systems. 1-Chloro-3-(4'-chlorophenylamino)-propan-2-ol was found to be the most active anti-fungal compound against three pathogenic strains under study, i.e., A. fumigatus, A. flavus and A. niger; the compound showed more than 90% inhibition of growth of A. fumigatus at a concentration of 5.85 microg/ml in disc diffusion assay. Interestingly, 1-chloro-3-(4'-chlorophenylamino)-propan-2-ol did not show any toxicity up to a concentration of 4000 microg/ml. Although 1-chloro-3-(4'-chlorophenylamino)-propan-2-ol was about 8 times less active than the standard compound amphotericin B, its toxicity was many more fold less than the toxicity of amphotericin B. Further, 1-chloro-3-(2',6'-dichlorophenylamino)-propan-2-ol and 1-chloro-3-(3',5'-dichlorophenylamino)-propan-2-ol were found to be the most active compounds against C. albicans. In the anti-microbial assay, 1-chloro-3-(2',4'-dichlorophenylamino)-propan-2-ol and 1-chloro-3-(3',5'-dichlorophenylamino)-propan-2-ol were found to be the most active compounds against Salmonella typhi and 1-chloro-3-(3',4'-dichlorophenylamino)-propan-2-ol was found to be the most active compound against P. aeruginosa. Although, the activities of 1-chloro-3-(2',4'-dichlorophenylamino)-propan-2-ol and 1-chloro-3-(3',5'-dichlorophenylamino)-propan-2-ol are about half the activity of the standard anti-bacterial compound tetracycline, these compounds also were many fold less toxic than the standard drug.     

Interaction of cruciferous phytoanticipins with plant fungal pathogens: indole glucosinolates are not metabolized but the corresponding desulfo-derivatives and nitriles are

Glucosinolates represent a large group of plant natural products long known for diverse and fascinating physiological functions and activities. Despite the relevance and huge interest on the roles of indole glucosinolates in plant defense, little is known about their direct interaction with microbial plant pathogens. Toward this end, the metabolism of indolyl glucosinolates, their corresponding desulfo-derivatives, and derived metabolites, by three fungal species pathogenic on crucifers was investigated. While glucobrassicin, 1-methoxyglucobrassicin, 4-methoxyglucobrassicin were not metabolized by the pathogenic fungi Alternaria brassicicola, Rhizoctonia solani and Sclerotinia sclerotiorum, the corresponding desulfo-derivatives were metabolized to indolyl-3-acetonitrile, caulilexin C (1-methoxyindolyl-3-acetonitrile) and arvelexin (4-methoxyindolyl-3-acetonitrile) by R. solani and S. sclerotiorum, but not by A. brassicicola. That is, desulfo-glucosinolates were metabolized by two non-host-selective pathogens, but not by a host-selective. Indolyl-3-acetonitrile, caulilexin C and arvelexin were metabolized to the corresponding indole-3-carboxylic acids. Indolyl-3-acetonitriles displayed higher inhibitory activity than indole desulfo-glucosinolates. Indolyl-3-methanol displayed antifungal activity and was metabolized by A. brassicicola and R. solani to the less antifungal compounds indole-3-carboxaldehyde and indole-3-carboxylic acid. Diindolyl-3-methane was strongly antifungal and stable in fungal cultures, but ascorbigen was not stable in solution and displayed low antifungal activity; neither compound appeared to be metabolized by any of the three fungal species. The cell-free extracts of mycelia of A. brassicicola displayed low myrosinase activity using glucobrassicin as substrate, but myrosinase activity was not detectable in mycelia of either R. solani or S. sclerotiorum.     

Effect of biological toxins on gap-junctionai intercellular communication in Chinese hamster V79 cells

Since chemical modulation of gap junctional intercellular communication has been implicated in several toxicological endpoints, a study to examine the ability of several biological toxins to inhibit this process was undertaken. Eight biological toxins were tested for their ability to inhibit metabolic cooperation, a measure of gap-junctional intercellular communication, in the Chinese V79 cell system. Aplysiatoxin, anhydrodebromoaplysiatoxin and debromoaplysiatoxin showed the strongest ability to inhibit metabolic cooperation while T2-toxin and vomitoxin inhibited metabolic cooperation to a lesser degree. Afatoxin B₁, afatoxin B₂ and palytoxin were inactive in the Chinese V79 system. Palytoxin, which was extremely cytotoxic, might act as a tumor promoter if it induces compensatory hyperplasia in vivo.Abbreviations 6-TG 6-thioguanine - TPA 12-0-tetradecanoylphorbol-13-acetate     

On the mutagenic and recombinogenic activity of certain herbicides in Salmonella typhimurium and in Aspergillus nidulans

The plant growth-regulating hormones indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA), both strong recombinogens in Aspergillus nidulans, were tested in Salmonella typhimurium strains for his revertants at a range of concentrations from 1 to 2000 micrograms/plate with and without metabolic activation and were found negative. Also 3 herbicides of the chlorophenoxy group, 2,4-(dichlorophenoxy)acetic acid (2,4-D), 2,4-(dichlorophenoxy)butyric acid (2,4-DB) and 4-chloro-2-methylphenoxyacetic acid (MCPA), which show a plant growth hormone-like activity, and 2 of the triazine group, 2-ethylamino-4-chloro-6-isopropylamino-1,3,5-triazine (atrazine) and 2,4-bis(isopropylamino)6-chloro-1,3,5-triazine (propazine) were tested in S. typhimurium for point mutations and in A. nidulans for mitotic recombination. 2,4-D and MCPA were found to be weakly mutagenic at concentrations between 250 and 750 micrograms/plate in strain TA97a and only after metabolic activation and were recombinogens by inducing mainly mitotic crossing-over in A. nidulans at concentrations of 4-48 microM and 1500-3000 microM, respectively. 2,4-DB, atrazine and propazine were negative in both the Ames and the Aspergillus tests.     

Inactivation ofSalmonella enteritidis on shell eggs by novelN-halamine biocidal compounds

Summary Several newN-halamine compounds have been evaluated as potential replacements for free chlorine as disinfectants for the egg-processing industry. The compounds were tested againstSalmonella enteritidis on the surfaces of egg shells. Test procedure included spraying inoculated egg shells with solutions of several of theN-halamine compounds and free chlorine for comparison, suspending the most stableN-halamine compound in a thin coating of mineral oil on the egg shell and subsequent inoculation, and measuring the rates of diffusion of the compounds and free chlorine through the egg shells. Compounds DBC (1-bromo-3-chloro-2,2,5,5-tetramethylimidazolidin-4-one) and DC (1,3-dichloro-2,2,5,5,-tetramethylimidazolidin-4-one) were significantly more efficacious than free chlorine in inactivatingSalmonella in the spray experiments, while compound MC (1-chloro-2,2,5,5-tetramethylmidazolidin-4-one), in a mineral oil suspension, provided disinfection of the egg shells within 72 h of contact. None of the disinfectant compounds penetrated egg shells at a rate greater than 1 mg/l over a period of 6 h. Compound MC is recommended as a possible replacement for unstable, corrosive-free chlorine as a bactericide for the egg-processing industry.     

Bioavailability and Efficacy of a Gap Junction Enhancer (PQ7) in a Mouse Mammary Tumor Model

The loss of gap junctional intercellular communication is characteristic of neoplastic cells, suggesting that the restoration with a gap junction enhancer may be a new therapeutic treatment option with less detrimental effects than traditional antineoplastic drugs. A gap junction enhancer, 6-methoxy-8-[(2-furanylmethyl) amino]-4-methyl-5-(3-trifluoromethylphenyloxy) quinoline (PQ7), on the normal tissue was evaluated in healthy C57BL/6J mice in a systemic drug distribution study. Immunoblot analysis of the vital organs indicates a reduction in Cx43 expression in PQ7-treated animals with no observable change in morphology. Next the transgenic strain FVB/N-Tg(MMTV-PyVT) 634Mul/J (also known as PyVT) was used as a spontaneous mammary tumor mouse model to determine the biological and histological effects of PQ7 on tumorigenesis and metastasis at three stages of development: Pre tumor, Early tumor, and Late tumor formation. PQ7 was assessed to have a low toxicity through intraperitoneal administration, with the majority of the compound being detected in the heart, liver, and lungs six hours post injection. The treatment of tumor bearing animals with PQ7 had a 98% reduction in tumor growth, while also decreasing the total tumor burden compared to control mice during the Pre stage of development. PQ7 treatment increased Cx43 expression in the neoplastic tissue during Pre-tumor formation; however, this effect was not observed in Late stage tumor formation. This study shows that the gap junction enhancer, PQ7, has low toxicity to normal tissue in healthy C57BL/6J mice, while having clinical efficacy in the treatment of spontaneous mammary tumors of PyVT mice. Additionally, gap junctional intercellular communication and neoplastic cellular growth are shown to be inversely related, while treatment with PQ7 inhibits tumor growth through targeting gap junction expression.     

Phosphatases Involved in Modulation of Gap Junctional Intercellular Communication and Dephosphorylation of Connexin43 in Hamster Fibroblasts: 2B or Not 2B?

12-O-Tetradecanoylphorbol-13-acetate (TPA) caused strong suppression of gap junctional intercellular communication, altered phosphorylation status of the gap junction protein, connexin43, and disappearance of immunorecognizible connexin43-containing gap junction plaques in V79 fibroblasts. When TPA was removed, all parameters normalized during a 3- to 4-h period. The normalizations were independent of protein synthesis, suggesting the possible involvement of phosphatases. None of the phosphatase inhibitors okadaic acid, calyculin A, cyclosporin A, or FK506 affected intercellular communication or connexin43 phosphorylation status on their own. In sequential exposures to TPA and phosphatase inhibitors, only the protein-phosphatase 2B (PP2B) inhibitors cyclosporin A and FK506 delayed the recovery of the studied parameters. Rapamycin binds to the same set of proteins as does FK506, but without inhibiting PP2B. Rapamycin did not affect the recovery of intercellular communication, but it delayed the normalization of connexin43 band pattern and immunorecognition of gap junction plaques. Dephosphorylation of immunoprecipitated connexin43 was studied using PP1, 2A, 2B, and 2C. PP2A was the most efficient (by 100-fold on a molar basis). Connexin43 immunoprecipitated from TPA-exposed cells was a poor substrate for PP1, 2B, and 2C. Thus, PP2B appeared to play a role in normalization of intercellular communication, but not necessarily in direct dephosphorylation of connexin43. Peptidyl-prolyl isomerase activity of cyclosporin/FK506/rapamycin-binding proteins may promote the dephosphorylation of connexin43 in cells.     

Reversible Inhibition of Gap Junctional Intercellular Communication, Synchronous Contraction, and Synchronism of Intracellular Ca Fluctuation in Cultured Neonatal Rat Cardiac Myocytes by Heptanol

We analyzed by Fotonic Sensor, a fiber-optic displacement measurement instrument, the effects of heptanol on synchronized contraction of primary neonatal rat cardiac myocytes cultured at confluent density. We also examined the effect of heptanol on the changes in gap junctional intercellular communication by using the microinjection dye transfer method, and on intercellular Ca²⁺ fluctuation by confocal laser scanning microscopy of myocytes loaded with the fluorescent Ca²⁺ indicator fluo 3. In addition, we studied expression, phosphorylation, and localization of the major cardiac gap junction protein connexin 43 (Cx43) using immunofluorescence and Western blotting. At Day 6 of culture, numerous myocytes exhibited spontaneous, synchronous contractions, excellent dye coupling, and synchronized intracellular Ca²⁺ fluctuations. We treated the cells with 1.5, 2.0, 2.5, and 3.0 mmol/liter heptanol. With 1.5 mmol/liter heptanol, we could not observe significant effects on spontaneous contraction of myocytes. At 3.0 mmol/liter, the highest concentration used in the current experiment, heptanol inhibited synchronous contractions and even after washing out of heptanol, synchronous contraction was not rapidly recovered. On the other hand, at the intermediate concentrations of 2.0 and 2.5 mmol/liter, heptanol reversely inhibited synchronized contraction, gap junctional intercellular communication, and synchronization of intracellular Ca²⁺ fluctuations in the myocytes without preventing contraction and changes of intracellular Ca²⁺ in individual cells. Brief exposure (5-20 min) to heptanol (2.0 mmol/liter) did not cause detectable changes in the expression, phosphorylation, or localization of Cx43, despite strong inhibition of gap junctional intercellular communication. These results suggest that gap junctional intercellular communication plays an important role in synchronous intracellular Ca²⁺ fluctuations, which facilitate synchronized contraction of cardiac myocytes.     

Peroxynitrite diminishes gap junctional communication: protection by selenite supplementation

Loss of intercellular communication via gap junctions has been correlated with progression of cells to a malignant phenotype. Here, we show that peroxynitrite, a mediator of toxicity in inflammatory processes, diminishes gap junctional intercellular communication (GJIC) in WB-F344 rat liver epithelial cells, assayed by the scrapeloading dye-transfer technique as well as by microinjection of a fluorescent dye into single cells. Exposure of cultured cells to a steady-state concentration of peroxynitrite of 1.6 microM for 4 min or to 3-morpholinosydnonimine (SIN-1) at 0.5 mM strongly diminished GJIC. These concentrations of peroxynitrite or SIN-1 were not cytotoxic. When cells were grown in a medium supplemented with sodium selenite (0.1-1 microM) for 72 h, substantial protection was afforded against the decrease in GJIC by peroxynitrite. Thus, peroxynitrite can disrupt GJIC, and selenium-containing proteins protect.     

Indole-3-methylglucosinolate biosynthesis and metabolism in clubroot diseased plants

lndole-3-methylglucosinolate biosynthesis and metabolism in roots of Brassica napus (swede, cv. Danestone II) infected with Plasmodiophora brassicae Wor. were investigated with a pulse feeding technique developed to infiltrate intact tissue segments with labelled substrates. Infected root tissue metabolized [¹⁴C]-L-tryptophan to indole-3-methylglucosinolate, indole-3-acetonitrile, and some other lipophilic indole compounds. The incorporation of radioactivity into these compounds was significantly enhanced in infected tissue compared with control tissue. A time course study showed a high turnover of indole-3-methylglucosinolate and indole-3-acetonitrile in infected tissue. However, thioglucoside glucohydrolase activity was not changed in infected tissue compared with control tissue. Disc electrophoresis revealed the same isoenzyme in both tissues. Control and infected tissues both rapidly hydrolyzed [¹⁴C]-indole-3-acetonitrile in vivo. The possibility of a disease specific biosynthesis of indole-3-acetic acid from indole-3-methylglucosinolate as the result of a changed compartmentation is discussed.     

The actions of retinoids on cellular growth correlate with their actions on gap junctional communication

Retinoic acid (a possible morphogen), its biological precursor retinol, and certain synthetic derivatives of retinol profoundly change junctional intercellular communication and growth (saturation density) in 10T 1/2 and 3T3 cells and in their transformed counterparts. The changes correlate: growth decreases as the steady-state junctional permeability rises, and growth increases as that permeability falls. Retinoic acid and retinol exert quite different steady-state actions on communication at noncytotoxic concentrations in the normal cells: retinoic acid inhibits communication at 10(-10)-10(-9) M and enhances at 10(-9)-10(-7) M, whereas retinol only enhances (10(-8)-10(-6) M). In v-mos-transformed cells the enhancement is altogether lacking. But regardless of the retinoid or cell type, all growth responses show essentially the same dependence on junctional permeability. This is the expected behavior if the cell-to-cell channels of gap junctions disseminate growth-regulating signals through cell populations.     

Glucose metabolism and proliferation in glia: role of astrocytic gap junctions

Astrocytes play a well-established role in brain metabolism, being a key element in the capture of energetic compounds from the circulation and in their delivery to active neurons. Their metabolic status is affected in many pathological situations, such as gliomas, which are the most common brain tumors. This proliferative dysfunction is associated with changes in gap junctional communication, a property strongly developed in normal astrocytes studied both in vitro and in vivo. Here, we summarize and discuss the findings that have lead to the identification of a link between gap junctions, glucose uptake, and proliferation. Indeed, the inhibition of gap junctional communication is associated with an increase in glucose uptake due to a rapid change in the localization of both GLUT-1 and type I hexokinase. This effect persists due to the up-regulation of GLUT-1 and type I hexokinase and to the induction of GLUT-3 and type II hexokinase. In addition, cyclins D1 and D3 have been found to act as sensors of the inhibition of gap junctions and have been proposed to play the role of mediators in the mitogenic effect observed. Conversely, in C6 glioma cells, characterized by a low level of intercellular communication, an increase in gap junctional communication reduces glucose uptake by releasing type I and type II hexokinases from the mitochondria and decreases the exacerbated rate of proliferation due to the up-regulation of the Cdk inhibitors p21 and p27. Identification of the molecular actors involved in these pathways should allow the determination of potential therapeutic targets that could lead to the testing of alternative strategies to prevent, or at least slow down, the proliferation of glioma cells.     

Cell culture assays for chemicals with tumor-promoting or tumor-inhibiting activity based on the modulation of intercellular communication

The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication is reviewed. The two most extensively used types of assays for screening tests are (1) metabolic cooperation assays involving exchange between cells of precursors of nucleic acid synthesis and (2) dye-transfer assays that measure exchange of fluorescent dye from loaded cells to adjacent cells. About 300 substances of different biological activities have been studied using various assays. For tumor promoters/epigenetic carcinogens, metabolic cooperation assays have a sensitivity of 62% and dye-transfer assays 60%. Thirty percent of DNA-reactive carcinogens also possess the ability to uncouple cells. The complete estimation of the predictive power of these assays could not be made because the majority of the substances studied for intercellular communication effectsin vitro have not yet been studied for promoting activityin vivo. Both metabolic cooperation assays and dye transfer assays respond well to the following classes of substances: phorbol esters, organochlorine pesticides, polybrominated biphenyls, promoters for urinary bladder, some biological toxins, peroxisome proliferators, and some complex mixtures. Results ofin vitro assays for such tumor promoters/nongenotoxic carcinogens, such as some bile acids, some peroxides, alkanes, some hormones, mineral dusts, ascorbic acid, okadaic acid, and benz(e)pyrene, do not correlated with the data ofin vivo two-stage or complete carcinogenesis. Enhancement of intercellular communication was found for 18 chemicals. Among these, cAMP, retinoids, and carotenoids have demonstrated inhibition of carcinogenesis. We examine a number of factors that are important for routine screening, including the requirement for biotransformation for some agents to exert effects on gap junction. We also discuss the mechanisms of tumor promoter and tumor inhibitor effects on gap junctional permeability, including influences of protein kinase activation, changes in proton and Ca²⁺ intracellular concentrations, and effects of oxy radical production.Abbreviations DMBA 7,12-dimethylbenz(a)anthracene - DT dye transfer - DDT 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane - HGPRT hypoxanthine-guanine phosphoribosyl-transferase - MC metabolic cooperation - PAH polycyclic aromatic hydrocarbons - PKA protein kinase A - PKC protein kinase C - TG 6-thioguanine - TPA 12-O-tetradecanoylphorbol-13-acetate     

Synthesis and cytotoxicity evaluation of pyridin[2,3-f]indole-2,4,9-trione and benz[f]indole-2,4,9-trione derivatives

3-Ethoxycarbonyl-3-methyl-1N-substrituted-2,3-dihydro-pyridin[2,3-f]indole-2,4,9-trione [9(a-d)] and 3-ethoxycarbonyl-3-methyl-N-substrituted-2,3-dihydro-benz[f]indole-2,4,9-trione [10(a-i)] derivatives were synthesized from 7-chloro-6-(1,1-diethoxycarbonyl-ethyl)-5,8-quinolinedione (7) and 2-chloro-3-(1,1-diethoxycarbonyl-ethyl)-1,4-naphthoquinone (8), respectively, using a variety of alkyl- and arylamines. The cytotoxic activities of the synthesized compounds were evaluated by a Sulforhodamine B (SRB) assay against the following tumor cell lines: A459 (human non-small cell lung), SK-OV-3 (human ovarian), SK-MEL-2 (human melanoma), XF498 (human CNS), and HCT 15 (human colon). Almost all the derivatives mentioned above had a more potent cytotoxic effect against SK-OV-3 than etoposide. In particular, 3-ethoxycarbonyl-3-methyl-N-(4-aminophenyl)-2,3-dihydro-benz[f]indole-2,4,9-trione (10h) exhibited greater activity against all the tumor cell lines, and its cytotoxic effect against SK-OV-3 was especially higher than doxorubicin.     

Inhibition of metabolic cooperation in Chinese hamster V79 cells by various organic solvents and simple compounds

Gap-junctional intercellular communication is a biological process implicated in the regulation of cell proliferation and differentiation. Metabolic cooperation between 6-thioguanine-sensitive and resistant Chinese hamster cells, in vitro, has been used as a means to detect chemicals which can inhibit this form of intercellular communication. To further characterize this in vitro system as a potential screening assay for potential teratogens, tumor promoters and reproductive toxicants, a series of common solvents as well as other chemicals representing eight different functional groups, i.e., alcohols with straight or side chains, glycols, ketones, esters, ethers, phenols, aldehydes, amines and amino compounds and oxygen-heterocyclic compounds, were tested for their ability to inhibit colony-formation and to inhibit metabolic cooperation. A wide range of effects were observed which suggested a structure/activity relationship between a chemical's ability to inhibit gap junction-mediated intercellular communication and the cytotoxicity of a chemical. Possible mechanisms affecting the modulation of gap junctional communication by these chemicals are discussed.Abbreviations: Hypoxanthine guanine, phosphoribosyltranferase, HG-PRT; 6-thioguanine, 6-TG.On leave from: Beijing Municipal Research Institute of Environmental Protection, Beijing, People's Republic of China