Effect of alkyl chain length on inhibition of N-nitrosomethylbenzylamine-induced esophageal tumorigenesis and DNA methylation by isothiocyanates

This study was undertaken to evaluate the inhibitory effectsof benzyl isothiocyanate (BITC), phenethyl isothiocyanate (PEITC),3-phenylpropyl isothiocyanate (PPITC) or 4- phenylbutyl isothiocyanate(PBITC) on N-nitrosomethylbenzylamine (NMBA)-induced esophagealtumorigenesis in male Fisher 344 rats. Groups of 15 male ratswere fed modified AIN-76A diet or diet containing the four isothiocyanatesat concentrations of 2.5, 1.0 and 0.4 µmol/g diet for25 weeks. After two weeks, rats were administered 0.5 mg/kgNMBA S.C. once weekly for 15 weeks. Additional controls receivedmodified AIN-76A diet only or diet containing the high concentrationof isothiocyanates (2.5 µmol/g) only. No tumors were foundin any of the groups that were not administered NMBA. Rats treatedwith NMBA only developed 6.7±0.8 tumors/animal. Tumorincidences in rats treated with 2.5 and 1.0 µmol PEITC/gdiet, and with all three dietary concentrations of PPITC wereinhibited by 60/100% compared to controls. Tumor multiplicitieswere inhibited by 83–100% by PEITC or PPITC at all dietaryconcentrations tested. PPITC clearly had a stronger inhibitoryeffect on NMBA tumorigenesis than did PEITC. Compared to PEITCand PPITC, BITC and PBITC had little inhibitory effect on tumormultiplicity and no effect on NMBA tumor incidence. In general,the occurrence of preneoplastic lesions (acanthoses, hyperkeratose,leukoplakias and leukokeratoses) was inhibited in a similarmanner as tumor incidence and multiplicity, except that no experimentaldiet resulted in a significant reduction of the incidence ofacanthoses and hyperkeratoses. As with their effects on tumorigenicityand formation of premalignant lesions, the inhibitory effectsof the isothiocyanates on NMBA-induced DNA methylation 24 hafter administration followed the order: PPITC > PEITC >PBITC > BITC.     

Structure-activity relationships for inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone lung tumorigenesis by arylalkyl isothiocyanates in A/J mice

Phenethyl isothiocyanate (PEITC), 3-phenylpropyl isothiocyanate (PPITC), 4-phenylbutyl isothiocyanate (PBITC), and the newly synthesized 5-phenylpentyl isothiocyanate (PPeITC), 6-phenylhexyl isothiocyanate (PHITC), and 4-(3-pyridyl)butyl isothiocyanate (PyBITC) were tested for their abilities to inhibit tumorigenicity and DNA methylation induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in the lungs of A/J mice. Mice were administered isothiocyanates by gavage for 4 consecutive days at doses of 5, 1, or 0.2 mumol/day prior to administration of 10 mumol of NNK by i.p. injection. Mice were sacrificed 16 weeks after NNK administration and pulmonary adenomas were quantitated, PEITC effectively inhibited NNK-induced lung tumors at a dose of 5 mumol/day but was not inhibitory at doses of 1 or 0.2 mumol/day. PPITC, PBITC, PPeITC, and PHITC were all considerably more potent inhibitors of NNK lung tumorigenesis than PEITC. While virtually no differences in inhibitory activity could be ascertained for PPITC, PBITC, and PPeITC, PHITC appeared to be the most potent tumor inhibitor of all of the compounds. At a dose of 0.2 mumol/day, PHITC pretreatment reduced tumor multiplicity by 85%. PyBITC, an analogue of both NNK and PBITC, was ineffective as an inhibitor. Using the same protocol, the compounds were found to have qualitatively similar inhibitory effects on NNK-induced DNA methylation when administered at 1 mumol/day. These results extend our previous findings that increased alkyl chain length enhances the inhibitory activity of an arylalkyl isothiocyanate toward NNK lung tumorigenesis and demonstrate the exceptional chemopreventive potentials of two new isothiocyanates, PPeITC and PHITC.     

Effects of NSAIDs on NNK-induced pulmonary and gastric tumorigenesis in A/J mice.

Non-steroidal anti-inflammatory drugs (NS-AIDs) are among the most widely prescribed drugs. In this study, we compared the efficacies of four NSAIDs to inhibit lung tumorigenesis in A/J mice. The tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), was given in drinking water between week 0 and week +7. Groups of 25 mice were fed sulindac (123 mg/kg diet), ibuprofen (263 mg/kg), piroxicam (25 mg/kg) or naproxen (230 mg/kg) in AIN-76A diet from week -2 to the end of the bioassay (week +23). Sulindac was the most effective inhibitor and reduced lung tumor multiplicity by 51%. Ibuprofen and piroxicam reduced lung multiplicity by 38% and 30%, respectively. Naproxen demonstrated no inhibitory capacity. Forestomach tumor multiplicity and incidence were both reduced by sulindac and ibuprofen. Sulindac administered from week -2 to week +7 was less effective (28% inhibition) than when given throughout the bioassay. Sulindac induced more intestinal adhesions than any other NSAID and was directly related to the cumulative dose of sulindac. These results show that chemoprevention of lung tumorigenesis by NSAIDs is not limited to sulindac although it is the most effective.     

Dose dependent inhibitory effects of dietary 8-methoxypsoralen on NNK-induced lung tumorigenesis in female A/J mice

We have reported that pretreatment by stomach tube with 8-methoxypsoralen (methoxsalen; 8-MOP), a potent human CYP2A6 inhibitor, strongly suppresses lung tumorigenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female A/J mice (Cancer Res. 2003). Here, we examined inhibitory effects with administration in the diet. When the mice were 7 weeks of age, they received dietary supplementation with 8-MOP at concentrations of 1, 10 or 100 ppm for 3 days prior to a single dose of NNK (2mg/0.1 ml saline/mouse, i.p.) or an equal volume of saline (vehicle control). The experiment was terminated 16 weeks after the first 8-MOP treatment and lung proliferative lesions were analyzed. The incidences and multiplicities in the 8-MOP 100 ppm-treated group were significantly reduced as compared with values for the NNK alone group (P<0.001). Multiplicities of NNK-induced lung proliferative lesions were also reduced in a dose dependent manner (Spearman rank correlation coefficient; rho=-0.806, correction P<0.0001). Mouse CYP2A4 and CYP2A5 differ from each other only 11 amino acids, and are closely related to the human CYP2A6. One hour after the last of three daily doses of 8-MOP (0.5, 5 or 50mg/kg body weight in 0.2 ml corn oil, given by stomach tube) or an equal volume of corn oil (vehicle control), given to the mice at 7 weeks of age, isolation of lung and liver RNAs demonstrated no effects on CYP2A4 and CYP2A5 mRNA levels with 8-MOP. In conclusion, the results of this study showed that clear dose response inhibitory effects of 8-MOP on NNK-induced lung tumorigenesis in female A/J mice fed diets containing 8-MOP, due to inhibition of enzyme activity of CYP2A4 and CYP2A5, rather than their gene expression.     

The essential role of the functional group in alkyl isothiocyanates for inhibition of tobacco nitrosamine-induced lung tumorigenesis

The importance of the isothiocyanate group in alkyl isothiocyanatefor inhibition of tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK)-induced lung tumorigenesis was examined in A/J mice. Ourprevious structure-activity relationship study of isothiocyanatesshowed that 1-dodecyl isothiocyanate [CH₃(CH₂)₁₁NCS], a simplealkyl isothiocyanate, is a potent inhibitor of NNK-induced lungtumorigenesis. It was chosenfor this study due to its structuralfeatures and potency. A single dose of 1-dodecyl isothiocyanategiven by gavage at 1 µmol/mouse 2 h prior to NNK administrationcompletely inhibited lung tumorigenesis, while removal of theisothiocyanate group or replacing it with a hydroxyl group abolishedthe inhibitory activity. These results demonstrate that theisothiocyanate functional group is critical for the inhibitoryactivity of isothiocyanates in NNK-induced lung tumorigenesis.To gain more insights into the relationship of in vivo inhibitionof tumorigenesis with the cytochrome P-450 enzyme inhibitoryactivity, the effects of these compounds on metabolism of NNKin mouse lung microsomes were studied. 1-Dodecyl isothiocyanateinhibited all three known oxidative pathways of NNK metabolism,with a stronger inhibitory activity toward NNK N-oxidation (IC₅₀430 nM) and keto alcohol formation (IC₅₀ 500 nM) than keto aldehydeformation (IC₅₀ 13 000 nM). 1-Dodecanol had a similar selectivityin inhibition of these metabolic pathways, but was less potentthan 1-dodecyl isothiocyanate. Dodecane showed little or noinhibitory activity in the same concentration range. These resultsindicate that the isothiocyanate group of 1-dodecyl isothiocyanateis important for inhibition of NNK-induced lung tumorigenesisand also for effective inhibition of cytochrome P-450 enzymesinvolved in NNK oxidation.     

A Cyp2a polymorphism predicts susceptibility to NNK-induced lung tumorigenesis in mice

Lung tumors from smokers as well as lung tumors from mice exposed to tobacco carcinogens such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), often carry mutations in K-ras, which activates downstream-signaling pathways such as PI3K/AKT/mTOR pathway. Mice with genetic deletion of one of three isoforms of AKT were used to investigate the role of AKT in mutant K-ras-induced lung tumorigenesis in mice. Although deletion of Akt1 or Akt2 decreased NNK-induced lung tumor formation by 90%, deletion of Akt2 failed to decrease lung tumorigenesis in two other mouse models driven by mutant K-ras. Genetic mapping showed that Akt2 was tightly linked to the cytochrome P450 Cyp2a locus on chromosome 7. Consequently, targeted deletion of Akt2 created linkage to a strain-specific Cyp2a5 polymorphism that decreased activation of NNK in vitro. Mice with this Cyp2a5 polymorphism had decreased NNK-induced DNA adduct formation in vivo and decreased NNK-induced lung tumorigenesis. These studies support human epidemiological studies linking CYP2A polymorphisms with lung cancer risk in humans and highlight the need to confirm phenotypes of genetically engineered mice in multiple mouse strains.     

Enhanced inhibition of lung adenocarcinoma by combinatorial treatment with indole-3-carbinol and silibinin in A/J mice

In earlier studies, we demonstrated the efficacy of indole-3-carbinol (I3C) against lung adenocarcinoma in A/J mice. However, these effects were accompanied by reductions in body weight gain. We therefore assessed if combinations of low doses of I3C with silibinin could inhibit lung tumorigenesis without causing undesirable side effects. In in vitro assays with A549 and H460 lung cancer cells, exposure of the cells to a mixture of low concentrations of I3C (50 μM) plus silibinin (50 μM) for 72 h caused inhibition of cell growth and extracellular signal-regulated kinase (ERK) and Akt activation and induction of apoptosis, whereas the individual agents did not have any effect. In mice pretreated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and given I3C (10 μmol/g diet) plus silibinin (7 μmol/g diet), multiplicities of tumors on the surface of the lung and adenocarcinoma were reduced by 60 and 95%, respectively. The individual effects of I3C and silibinin were relatively weaker: 43 and 36% reductions, respectively, in the multiplicity of tumors on the surface of the lung and 83 and 50% reductions, respectively, in the number of adenocarcinoma. Also, the expression of phospho-Akt, phospho-ERK and cyclin D1 and poly (ADP-ribose) polymerase cleavage were strongly modulated by I3C plus silibinin than by I3C or silibinin alone, suggesting that the chemopreventive activities of the mixture could be mediated, at least partly, via modulation of the level of these proteins. Taken together, our findings showed that mixtures of I3C and silibinin are more potent than the individual compounds for the chemoprevention of lung cancer in A/J mice.     

Studies of chemopreventive effects of budenoside on benzo[a]pyrene- induced neoplasia of the lung of female A/J mice

The objective of the present investigation was to determine conditions under which the synthetic glucocorticoid, budenoside, will inhibit benzo[a]pyrene (BaP)-induced pulmonary carcinogenesis when administered in the post-initiation period. For this purpose, female A/J mice were employed. The animals were given three administrations of 2 mg of BaP by oral intubation during a 1-week period. Budenoside was fed in the diet subsequent to the last dose of BaP. Using this format, two experiments were carried out to determine the effects of varying the time of administration of budenoside on the magnitude of the inhibition obtained. In both experiments, one group of mice was fed budenoside (1.5 mg/kg of diet) from 1 week after the last dose of BaP until the termination of the experiment, 15 weeks later. The reduction of pulmonary tumor formation under these conditions was 89% in the first experiment and 78% in the second (average 84%). In the first experiment the effects of feeding budenoside only during weeks 1-5 after BaP administration was studied. Under these conditions, inhibition of pulmonary tumor formation was 35%. In the second experiment, the effects of postponing the start of feeding budenoside was determined. In mice in which the budenoside feeding was delayed until 5 weeks after the last dose of BaP and then continued for the duration of the protocol, a 67% inhibition of tumor formation was found. The data obtained indicate that budenoside will produce inhibition of pulmonary adenoma formation when fed either early or late in the post-initiation stage of carcinogenesis, and that feeding throughout the entire post- initiation period gives maximum inhibition.      

Studies of chemopreventive effects of myo-inositol on benzo(a)pyrene-induced neoplasia of the lung and forestomach of female A/J mice

There is a continuing effort at identifying chemopreventiveagents that might be useful in preventing cancer of the lung.In the present study, the effects of myo-inositol and dexamethasoneon benzo[a]pyrene (B[a]P)-induced pulmonary adenoma formationin female A/J mice was investigated. A diet containing 3% myo-inositolfed beginning 1 week after B[a]P administration reduced thenumber of pulmonary adenomas by 40% but did not prevent forestomachtumors, which also occur in this experimental model. Under thesame conditions, dexamethasone, 0.5µg/g diet, inhibitedpulmonary adenoma formation by 57% and also inhibited forestomachtumor formation to a similar extent. Feeding a diet containingboth myo-inositol and dexamethasone resulted in an additiveeffect on the inhibition of pulmonary adenoma formation. Thecombination of myo-inositol plus dexamethasone produced almostidentical inhibition of forestomach tumor formation to thatof dexamethasone alone. The results of the present study arepreliminary, but may provide a basis for future investigationinto strategies for chemoprevention of pulmonary neoplasia.     

Effect of the length of alkyl chain on the cytochrome P450 dependent metabolism of N-dialkylnitrosamines

Liver microsomes from control and treated rats (P4501A, 2B, 2E1-induced) metabolize at variable metabolic rates eight N-nitroso-di-n-alkylamines, including five symmetrical (N-nitroso-dimethyl, -diethyl, -dipropyl, -dibutyl and -diamyl-amines) and four asymmetrical (N-nitroso-methylethyl, methylpropyl, methylbutyl, and methylamyl-amines), into aldehydes. Thus, the longer the alkyl chain of symmetrical N-nitrosamines, the smaller was the metabolic rate of the corresponding aldehyde formation. The chain length of the alkyl group of N-nitroso-methylalkylamines modified the oxidation of the alkyl moiety; the oxidation by CYP2E1 decreased as the n-alkyl chain length increased and conversely for the oxidation by CYP1A and CYP2B. Finally, the longer the n-alkyl chain of asymmetrical N-nitrosamines, the greater was the oxidation of methyl groups.     

Chemoprevention of lung carcinogenesis by the combination of aerosolized budesonide and oral pioglitazone in A/J mice

Budesonide, a synthetic glucocorticoid used for treating asthma, and pioglitazone, a synthetic peroxisome proliferator-activated receptors γ ligand used for the treatment of diabetes, were evaluated for their combinational chemopreventive efficacy on mouse lung cancer using female A/J mice with benzo(a)pyrene used as the carcinogen. All chemopreventive treatments began 2-wk post-carcinogen treatment and continued daily for 20 wk. Budesonide was administered by the aerosol route using an improved aerosol delivery system. Pioglitazone was introduced by oral gavage. The characterization of drug distribution showed that budesonide introduced by aerosol delivery accumulated only in the lung. Budesonide alone reduced tumor load by 78% and pioglitazone alone reduced tumor load by 63%. By combining aerosolized budesonide with pioglitazone, the inhibition on tumor load was 90%. In vitro experiments using human cancer cells showed that budesonide and pioglitazone exhibited independent, additive inhibitory effects on cell growth. Our results provide evidence that aerosolized budesonide and oral pioglitazone could be a promising drug combination for lung cancer chemoprevention.     

Point mutation of K-ras gene in cisplatin-induced lung tumours in A/J mice

The risks of secondary lung cancer in patients with early stage non-small and small cell lung cancers are estimated to be 1-2% and 2-10% per patient per year, respectively. Surprisingly, the incidence of second primary cancer in locally advanced non-small cell lung cancer at 10 years, following cisplatin-based chemotherapy with concurrent radiotherapy, increases to 61%. Those patients, on the road to being cured, cannot overlook the possibility of developing a second primary cancer. We developed a second primary lung cancer model using cisplatin as a carcinogen in A/J mice to screen for chemopreventive agents for a second malignancy. In the primary lung tumour model, 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), benzo(a)pyrene (BaP), urethane induces specific K-ras mutations in codon 12, codon 12, and codon 61, respectively, in the A/J mice. In this study, we investigated the mechanisms of carcinogenicity by cisplatin in the A/J mice. In the cisplatin-induced tumours, we found no K-ras codon 12 mutation, which is the major mutation induced by NNK or BaP. K-ras gene mutations in codon 13 and codon 61 were found in one tumour (4%) and five tumours (17.8%), respectively. These findings suggest that cisplatin is partially related to K-ras codon 61 mutations, and that the mechanism of carcinogenicity by cisplatin is different from that by NNK or BaP.     

Ki-ras mutation and cell proliferation of lung lesions induced by 1-nitropyrene in A/J mice

In this study, lung lesions were found in male A/J mice 24 wk after intraperitoneal injection of 1-nitropyrene (1-NP). The lesions were classified into three categories: alveolar/bronchiolar hyperplasia, adenoma, and adenocarcinoma. The proliferation kinetics of cells in the lesions were evaluated by assessing proliferating cell nuclear antigen (PCNA) expression and silver-staining nucleolar organizer regions (AgNORs). Furthermore, the role of the Ki-ras gene in tumorigenesis was studied by detecting point mutations in Ki-ras codons 12, 13, and 61 by polymerase chain reaction and sequence analysis. The PCNA-positive rates (± standard deviations) in various samples were as follows: 0% for specimens from six untreated animals and six uninvolved areas, 4.26 ± 3.94% for 19 hyperplasias (hyperplasias vs normal lung tissue, P < 0.01), 13.24 ± 6.35% for 25 adenomas (adenomas vs hyperplasias, P < 0.01), and 38.0 ± 9.63% for four adenocarcinomas (adenocarcinomas vs adenomas, P < 0.01). The corresponding mean AgNOR scores were as follows: 1.10 ± 0.05 for the untreated animals, 1.32 ± 0.09 for the uninvolved areas, 1.72 ± 0.59 for the hyperplasias (hyperplasias vs normal lung tissue, P < 0.05), 2.74 ± 0.70 for the adenomas (adenomas vs hyperplasias, P < 0.01), and 5.22 ± 0.62 for the adenocarcinomas (adenocarcinomas vs adenomas, P < 0.01). Ki-ras gene mutations were identified in three of four (75%) adenocarcinomas, six of 23 (26%) adenomas, and two of 17 (12%) hyperplasias. No mutations were found in normal lung tissue. The most frequent Ki-ras mutation was an arginine (CGA) AT → GC transition at codon 61 in exon 2. The PCNA-positive rates and AgNOR scores of cases with Ki-ras mutations were higher than those without an identified mutation (P < 0.05). Ki-ras mutations at codon 61 (Arg) may therefore influence the growth or development of 1-NP–induced lung lesions in A/J mice. Mol. Carcinog. 22:258–264, 1998. © 1998 Wiley-Liss, Inc.     

Thymosinalpha1 is chemopreventive for lung adenoma formation in A/J mice

The effects of thymosin (THN) alpha1 were investigated using the urethane injection carcinogenesis A/J mouse model. Lung adenomas were observed 2.5, 3, and 4 months after urethane injection (400 mg/kg i.p.) into female A/J mice. Daily administration of THNalpha1 (0.4 mg/kg, s.c.) reduced lung adenoma multiplicity significantly, by approximately 45, 40, and 17%, respectively, 2.5, 3, and 4 months after urethane injection. Animals treated with THNalpha1 had a significantly greater white cell density than control A/J mice. Endogenous THNalpha1-like peptides were detected in the mouse lung. By radioimmunoassay and by Western blot, prothymosin alpha was detected in the mouse lung. By immunocytochemistry, THNalpha1-like peptides were detected in all lung compartments including the bronchus, adenoma, bronchioles, and alveoli. These results indicate that exogenous THNalpha1 prevents lung carcinogenesis in A/J mice.     

SHORT COMMUNICATION: K-ras mutations in benzotrichloride-induced lung tumors of A/J mice

Benzotrichloride (BTC) is used extensively as a chemical intermediatein the synthesis of benzoyl chloride and benzoyl peroxide. Epidemiologkaldata suggest that BTC is a human lung carcinogen. BTC is alsoa carcinogen in the A/J mouse lung tumor bioassay. ActivatedK-ras protooncogenes were detected in BTC-induced lung tumorsfrom A/J mice. The polymerase chain reaction was used to amplifyspecific DNA segments likely to contain activating mutations,and the amplified DNAs were sequenced to identify the mutation.The activating mutation present in the K-ras gene from all BTC-inducedlung tumors (24/24) was a GC     

Chemopreventive efficacies of aspirin and sulindac against lung tumorigenesis in A/J mice

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs. In this study, we demonstrated the efficacy of aspirin to inhibit lung tumorigenesis in A/J mice. Lung tumors (9.9 tumors/mouse) were induced by the tobacco-specific nitrosamine, 4- (methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), administered in drinking water between week 0 and week +7. Groups of mice were fed sulindac (123 mg/kg diet), acetylsalicylic acid (ASA; 294 mg/kg), non- buffered Aspirin (294 mg/kg) or buffered Aspirin (294 mg/kg) in AIN-76A diet from week -2 to the end of the bioassay (week +23). These doses are comparable to the maximal doses recommended for humans. ASA and non- buffered Aspirin were the most effective inhibitors and reduced lung multiplicities by 60 and 62%, respectively. Sulindac inhibited lung tumor multiplicity by 52%. Inhibition by buffered Aspirin was not statistically significant. We evaluated the efficacies of NSAIDs to inhibit NNK activation by h1A2 v2 cells expressing human P-450 1A2. Salicylates, at doses of 500 microM and 1 mM, had no effect on NNK activation. Sulindac and its sulfide and sulfone metabolites (1 mM) inhibited NNK metabolism by 90, 92 and 65%, respectively. We observed a 76% inhibition with SKF 525A, a P-450 inhibitor. Taken together, these results indicate that salicylates and sulindac could be equally effective as chemopreventive agents, but they could differ in their mode of action.      

Structure-activity relationships of arylalkyl isothiocyanates for the inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone metabolism and the modulation of xenobiotic-metabolizing enzymes in rats and mice

Many arylalkyl isothiocyanates are potent inhibitors of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK)-induced lung tumorigenesis in rats and mice. In the mouse,4-phenylbutyl isothiocyanate (PBITC) and 6-phenylhexyl isothiocyanate(PHTTC) exhibited greater inhibition than benzyl isothiocyanate(BITC) and phenethyl isothiocyanate (PEITC). The present studywas conducted to investigate the structure-activity relationshipsof these four arylalkyl isothiocyanates for their inhibitionof NNK oxidation and effects on xenobiotic-metabolizing enzymesin rats and mice. A single dose (0.25 or 1.00 mmol/kg) of eachisothiocyanate was given to F344 rats 6 or 24 h before death.The rates of NNK oxidation were decreased in microsomes fromthe liver, lung and nasal mucosa of rats. Generally, PEITC wasmore potent than BITC but less potent than PBITC and PHlTC.The rates in rat liver microsomes were decreased at 6 h butrecovered or increased at 24 h; and the rates in rat lung microsomeswere markedly decreased at both 6 and 24 h; and the rates inrat nasal mucosa microsomes were also significantly decreased.The same treatment decreased the rat liver N-nitrosodimethyl-aminedemethylase activity dramatically and ethoxyresorufin O-dealkylaseand erythromycin N-demethylase activities moderately. However,the rat liver microsomal pentoxy-resorufin O-dealkylase activitywas decreased at 6 h but increased at 24 h, with PEITC showingthe most marked induction. The rat liver NAD(P)H: quinone oxidoreductaseactivity was increased 1.4- to 3.3-fold, with PEITC being mosteffective; and the glutathione S-transferase activity was increasedslightly. Similarly, at a single dose of 0.25 mmol/kg (5 µmol/mouse)24 h before death, PEITC, PBITC, PHlTC but not BITC, decreasedNNK oxidation in mouse lung microsomes by 40–85%, withPBITC and PHlTC showing greater inhibition. Furthermore, allfour isothiocyanates extensively inhibited NNK oxidation inrat lung and nasal mucosa microsomes as well as mouse lung microsomesin vitro, with PEITC (IC₅₀ of 120–300 nM) being more potentthan BITC (IC₅₀ of 500–1400 nM) but less potent than PBITCand PHITC (IC50 of 15–180 nM). PHITC was a very potentcompetitive inhibitor of NNK oxidation in mouse lung microsomeswith apparent K₁ values of 11–16 nM. These results indicatethat PBITC and PHITC are more potent inhibitors of NNK bioactivationin rats and mice than PEITC. In addition, these arylalkyl isothiocyanatescould be effective in protecting against the actions of a broadspectrum of carcinogenic or toxic compounds.     

Dietary selenium fails to influence cigarette smoke-induced lung tumorigenesis in A/J mice

The goal of the study was to determine if dietary selenium inhibited the induction of lung tumorigenesis by cigarette smoke in A/J mice. Purified diets containing 0.15, 0.5, or 2.0 mg/kg selenium in the form of sodium selenite were fed to female A/J mice. Half of the mice in each dietary group were exposed to cigarette smoke 6 h/day, 5 days/week for five months followed by a four month recovery period in ambient air, while the other half were used as controls. After the recovery period, the mice were euthanized, and their lungs were removed for further analysis. Mice exposed to smoke had a higher tumor incidence and a higher tumor multiplicity, whereas dietary Se did not affect either the tumor incidence or tumor multiplicity. An increase in dietary selenium led to increased levels of selenium in the lung as well as GPx protein levels, but dietary Se did not affect lung SOD protein levels. In conclusion, these data confirm the carcinogenic activity of cigarette smoke in mice but show that dietary Se provided as sodium selenite does not affect smoke-induced carcinogenesis in this model.     

Inhibition of spontaneous formation of lung tumors and rhabdomyosarcomas in A/J mice by black and green tea

We investigated the effects of black tea (BT) and green tea (GT) infusion on the spontaneous formation of lung tumors and rhabdomyosarcomas in A/J mice. Female A/J mice, 6 weeks of age, were allocated into five groups (50 per group) and were given the following as the sole source of drinking fluid: (i) deionized water (control group), (ii) 0.5% BT, (iii) 1% BT, (iv) 2% BT and (v) 1% GT. After 60 weeks, the mice were killed by decapitation. Lung tumor incidence, multiplicity and volume were significantly lower in the 2% BT group as compared with the controls (27 versus 52%, 0.33 versus 0.72 tumors/mouse and 4.27 versus 38.3 mm3, respectively). The 1% GT group had significantly lower lung tumor multiplicity (0.41/mouse), while the 1% BT group had significantly decreased tumor volume (7.17 mm3). Rhabdomyosarcomas were found in 34% of the mice in the control group, and both the 1 and 2% BT groups had significantly lower incidences at 13 and 14%, respectively. The mice in the 2% BT group weighed 16% less than those in the control group, although they consumed more food than the control group. The other tea-consuming groups also weighed less than the control group (7.8-11%) while consuming more food and fluid. In a separate experiment, similar carcinogenesis inhibition was also observed in female A/J mice that were given 0.6% and then 0.3% instant black tea for 52 weeks. These results demonstrate the inhibitory activity of BT against the spontaneous formation of lung tumors and rhabdomyosarcomas in mice.