Post-initiation treatment of rats with indole-3-carbinol or beta-naphthoflavone does not suppress 7, 12-dimethylbenz[a]anthracene-induced mammary gland carcinogenesis

Indole-3-carbinol (I3C) and β-naphthoflavone (β-NF), blocking agents of 7,12-dimethylbenz[a]anthracene (DMBA)-initiated mammary gland carcinogenesis, were examined as potential post-initiation suppressing agents. Treatment of female Sprague–Dawley rats with I3C (250 mg/kg body weight (b.w.)), β-NF (20 mg/kg b.w.) or the vehicle ethanol:corn oil (2:3) (2.5 ml/kg b.w.), three times weekly by gavage, started 3 weeks after the initiation with one oral dose of DMBA (20 mg/rat at 7 weeks of age) and continued for up to 12 weeks. I3C- or β-NF- or vehicle-treated groups did not differ significantly in the overall outcome of mammary tumorigenesis including cumulative mammary tumor incidences and multiplicities, latent periods and number and weight of mammary tumors per tumor-bearing rat for malignant, benign and/or malignant + benign tumors. A tendency of the I3C-treated rats to develop fewer mammary adenocarcinomas with a greater average weight per tumor per rat (2.32±1.50 g) than in the β-NF- (1.52±1.58 g) or vehicle- (1.55±1.53 g) treated groups suggests an effect, yet to be confirmed, of I3C on tumor development and growth. A 12-week treatment with I3C or β-NF significantly increased the P450-dependent activities of ethoxy-, methoxy-, benzyloxy- and pentoxy-(with I3C only) resorufin O-dealkylase in hepatic microsomes indicating induction of several P450s. The alterations in the P450 complement may affect endogenous estrogen metabolism and mammary gland and tumor characteristics at the molecular level, e.g. estrogen receptor status and/or proliferative activity, which require further studies.     

Post-initiation treatment of rats with indole-3-carbinol or β-naphthoflavone does not suppress 7,12-dimethylbenz[a]anthracene-induced mammary gland carcinogenesis

Indole-3-carbinol (I3C) and β-naphthoflavone (β-NF), blocking agents of 7,12-dimethylbenz[a]anthracene (DMBA)-initiated mammary gland carcinogenesis, were examined as potential post-initiation suppressing agents. Treatment of female Sprague–Dawley rats with I3C (250 mg/kg body weight (b.w.)), β-NF (20 mg/kg b.w.) or the vehicle ethanol:corn oil (2:3) (2.5 ml/kg b.w.), three times weekly by gavage, started 3 weeks after the initiation with one oral dose of DMBA (20 mg/rat at 7 weeks of age) and continued for up to 12 weeks. I3C- or β-NF- or vehicle-treated groups did not differ significantly in the overall outcome of mammary tumorigenesis including cumulative mammary tumor incidences and multiplicities, latent periods and number and weight of mammary tumors per tumor-bearing rat for malignant, benign and/or malignant + benign tumors. A tendency of the I3C-treated rats to develop fewer mammary adenocarcinomas with a greater average weight per tumor per rat (2.32±1.50 g) than in the β-NF- (1.52±1.58 g) or vehicle- (1.55±1.53 g) treated groups suggests an effect, yet to be confirmed, of I3C on tumor development and growth. A 12-week treatment with I3C or β-NF significantly increased the P450-dependent activities of ethoxy-, methoxy-, benzyloxy- and pentoxy-(with I3C only) resorufin O-dealkylase in hepatic microsomes indicating induction of several P450s. The alterations in the P450 complement may affect endogenous estrogen metabolism and mammary gland and tumor characteristics at the molecular level, e.g. estrogen receptor status and/or proliferative activity, which require further studies.     

Nordihydroguaiaretic acid suppression of rat mammary carcinogenesis induced by N-methyl-N-nitrosourea

The activity of the lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), as a cancer chemopreventive agent in the rat mammary gland was determined. Beginning 1 week after a single i.v. dose of 20 or 50 mg N-methyl-N-nitrosourea (MNU)/kg body wt., female Sprague-Dawley rats were fed a semi-purified diet supplemented with 0 or 1000 mg NDGA/kg diet. At both MNU dose levels, groups receiving NDGA developed significantly fewer mammary cancers than did dietary controls; NDGA induced no gross or organ-specific toxicity. These data implicate lipoxygenase products in the process of mammary cancer induction, and suggest an additional enzymatic target for the design of chemopreventive drugs.     

Effect of PSC 833, an inhibitor of P-glycoprotein on N-methyl-N-nitrosourea induced mammary carcinogenesis in rats

Studies in our laboratory on the role of P-glycoprotein (Pgp, coded by mdr1 gene) have led to the hypothesis that over-expression of Pgp is closely associated with the development of cancer. It was conceived therefore that inhibitors of Pgp should inhibit the development of cancer. We have reported that PSC833 (PSC), a potent inhibitor of Pgp, inhibits the development of liver cancer in rats. Similarly, based on the intrinsic over-expression of Pgp in experimental mammary carcinogenesis, we studied the effect of PSC on N-methyl-N-nitrosourea induced mammary cancer in female Sprague-Dawley rats. The study indicates that PSC at daily dietary doses of 15 (PSC15) and 30 mg/kg (PSC30) body wt resulted in dose-dependent inhibition of the incidence as well as the growth of mammary tumors. Compared with controls, PSC15 and PSC30 inhibited: (i) mean tumor multiplicity by 32 and 67%, (ii) median tumor burden by 46 and 93% and (iii) incidence of ulcerated tumors by 40 and 82%, respectively. Most remarkably, PSC delayed median tumor incidence by 8 weeks, and exerted a 100% inhibitory effect on the incidence of large tumors, 4 cm(3) and greater. In all the cases, although the inhibitory effect of PSC was evident at both doses, only PSC30 exhibited statistical significance. A possible compounding effect that was also observed in PSC30-treated rats was a decrease in body weight gain not attributed to diminished food consumption. All in all, consistent with recent reports, which have demonstrated inhibition of cancer development by compromising Pgp function, this study introduces a novel role for Pgp in breast cancer and potentially an unexplored therapeutic approach in treating the disease.     

Suppression of mammary gland carcinogenesis by post-initiation treatment of rats with tamoxifen or indole-3-carbinol or their combination.

This study examined whether suppression of mammary gland carcinogenesis elicited by low doses of tamoxifen (TAM) can be enhanced by concomitant treatment of rats with indole-3-carbinol (I3C), a component of cruciferous vegetables and a dietary supplement used for its putative antiestrogenicity. Two weeks after one oral dose of 7,12-dimethylbenz[a]anthracene (DMBA) at 65 mg/kg body weight, female Sprague-Dawley rats started treatment with TAM (10 microg/rat) by subcutaneous injection, I3C (250 mg/kg body weight) by oral gavage, TAM+I3C or their respective vehicles three times per week, for up to 20 weeks. Significant increases in the median latency of malignant mammary tumors and decreases in the mean tumor mass per rat were due to TAM. Significant decreases in the mean tumor number per rat in TAM, I3C and TAM+I3C-treated rats indicated a cooperative effect of the two compounds. In both DMBA-initiated and uninitiated rats, significant increases in the ratios of liver to body weight in I3C and TAM+I3C-treated groups coincided with I3C-dependent increases of hepatic cytochrome P450 levels and activities (1A1, 1A2 and 2B1/2). The ratios of uterus to body weight decreased with the number of treatments and the decreases effected by TAM were greater than those by I3C. The levels of circulating estrone were increased in response to I3C treatment and were greater in DMBA-initiated rats than in uninitiated rats, which may contribute to the preventive effect of I3C. Chemoprevention may be accomplished through up-regulation of apoptotic enzyme (caspase) activities in the mammary gland or mammary tumors. Treatment with TAM, I3C or TAM+I3C had no effect on caspase-3&7, caspase-6, caspase-8 and caspase-9 activities in the mammary tumors or mammary gland of tumor-bearing rats or that of uninitiated rats. In the mammary gland of DMBA-initiated tumor-free rats, however, I3C treatment increased the levels of caspase-3&7 and caspase-9 activities, suggesting an I3C-mediated protective effect. Even though I3C alone is a much less effective suppressing agent of mammary carcinogenesis than TAM, I3C in combination with TAM does not weaken but may foster the benefits of chemoprevention with TAM.     

ras oncogene activation in mammary carcinomas induced by N-methyl-N-nitrosourea in Copenhagen rats.

The occurrence of Ha-ras and Ki-ras oncogenes was investigated in mammary tumors produced by treating genetically resistant Copenhagen (Cop) rats with N-methyl-N-nitrosourea. G35-->A codon 12 mutations in both Ha-ras and Ki-ras genes were analyzed by a polymerase chain reaction/liquid hybridization and gel retardation assay. More than half of the adenocarcinomas analyzed contained an activated Ha-ras gene. This was also the predominant mutation in similar tumors from susceptible Buf/N rats, suggesting a common mechanism of initiation. In contrast, only two of 15 mammary adenosquamous carcinomas from the Cop rats contained an activated Ha-ras gene, suggesting a different initiation mechanism for most of these tumors. Ki-ras activation was found in none of five and one of five adenocarcinomas from Buf/N and Cop rats, respectively, and in none of 13 adenosquamous carcinomas from Cop rats. These results suggest that Ki-ras activation does not play a major role in the initiation of the mammary tumors.     

Indole-3-carbinol synergistically sensitises ovarian cancer cells to bortezomib treatment

Background:

Bortezomib is a proteasome inhibitor with minimal clinical activity as a monotherapy in solid tumours, but its combination with other targeted therapies is being actively investigated as a way to increase its anticarcinogenic properties. Here, we evaluate the therapeutic potential of co-treatment with bortezomib and indole-3-carbinol (I3C), a natural compound found in cruciferous vegetables, in human ovarian cancer.

Methods:

We examined the effects of I3C, bortezomib and cisplatin in several human ovarian cancer cell lines. Synergy was determined using proliferation assays and isobologram analysis. Cell cycle and apoptotic effects were assessed by flow cytometry. The mechanism of I3C and bortezomib action was determined by RNA microarray studies, quantitative RT–PCR and western blotting. Antitumour activity of I3C and bortezomib was evaluated using an OVCAR5 xenograft mouse model.

Results:

I3C sensitised ovarian cancer cell lines to bortezomib treatment through potent synergistic mechanisms. Combination treatment with bortezomib and I3C led to profound cell cycle arrest and apoptosis as well as disruptions to multiple pathways, including those regulating endoplasmic reticulum stress, cytoskeleton, chemoresistance and carcinogen metabolism. Moreover, I3C and bortezomib co-treatment sensitised ovarian cancer cells to the standard chemotherapeutic agents, cisplatin and carboplatin. Importantly, in vivo studies demonstrated that co-treatment with I3C and bortezomib significantly inhibited tumour growth and reduced tumour weight compared with either drug alone.

Conclusion:

Together, these data provide a novel rationale for the clinical application of I3C and bortezomib in the treatment of ovarian cancer.     

吲哚-3-甲醇(I3C)抗肿瘤作用的研究进展

在传统的肿瘤治疗方法中化疗仍是主要的肿瘤治疗手段之一,现有化疗药物副反应大、难以耐受等缺点,因此迫切需要发现高效、低毒、乃至天然的化疗成分.吲哚-3-甲醇(indole-3-carbinol,I3C)广泛存在于十字化科蔬菜中,包括花茎甘蓝、抱子甘蓝、萝卜、辣根、大白菜、花椰菜、水田芥菜等,(分子式如图1所示),是十字花科蔬菜中研究最多和最重要的一种抗肿瘤成分.     

Post-initiation effects of chlorophyllin and indole-3-carbinol in rats given 1,2-dimethylhydrazine or 2-amino-3-methyl- imidazo

Chlorophyllin (CHL) is a water-soluble derivative of chlorophyll, the ubiquitous pigment in green and leafy vegetables, whereas indole-3-carbinol (I3C) is present in cruciferous vegetables such as cabbage, broccoli and cauliflower. In rats initiated with 1,2-dimethylhydrazine (DMH), CHL and I3C reportedly promoted or enhanced the incidence of colon tumors when they were administered after, or during and after the carcinogen exposure, respectively. The same compounds given post-initiation inhibited the formation of colonic aberrant crypts induced by heterocyclic amines, such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), but tumor suppression was not examined in the latter studies. In the present investigation, male F344 rats were treated with IQ or DMH during the first 5 weeks of a 1 year study; IQ was given in the diet (0.03%), whereas DMH was administered once a week by s.c. injection (20 mg/kg body wt). Beginning 1 week after the last dose of IQ or DMH until sacrifice, rats received 0.001, 0.01 or 0.1% (w/v) CHL in the drinking water or 0.001, 0.01 or 0.1% I3C in the diet. Compared with controls given carcinogen alone, 0.1% I3C treatment suppressed the multiplicity of IQ-induced colon tumors, and CHL inhibited in a dose-related manner the incidence of IQ-induced liver tumors. However, 0.001% CHL increased significantly the multiplicity of DMH-induced colon tumors while having no effect on the colon tumors induced by IQ. These results indicate that both the choice of carcinogen as well as the dose of the tumor modulator can be important determinants of the events that occur during post-initiation exposure to CHL or I3C. Based on the present findings and data in the literature, it is possible for CHL and I3C to act as tumor promoters or anticarcinogens, depending upon the test species, initiating agent and exposure protocol.     

Effects of indole-3-carbinol and phenethyl isothiocyanate on colon carcinogenesis induced by azoxymethane in rats

Indole-3-carbinol (I3C) and phenethyl isothiocyanate (PEITC) are breakdown products of the glucosinolates glucobrassicin and gluconasturtiin, respectively, and are thought to reduce carcinogen activation by P450 enzymes. To assess the effects of these compounds on colon cancer risk, rats were divided into five groups and fed the following diets: control diet (AIN-93G), or diets with PEITC or I3C added to the control diet: high-PEITC (3.37 mmols/kg diet-high level of PEITC), low-PEITC (0.67 mmols/kg-low level of PEITC), high-I3C (6.8 mmols/kg-high level of I3C) and low-I3C (1.36 mmols/kg-low level of I3C). Diets were fed for 2 weeks before and 10 weeks after administration of the colon carcinogen azoxymethane. Precancerous lesion (aberrant crypt foci, ACF) number in the distal colon was significantly lower in both high-I3C and low-I3C groups (6.9 +/- 0.8 and 5.9 +/- 0.59 per cm2, respectively) when compared with the control group (10.4 +/- 0.9). No significant difference in ACF number was found between the PEITC group and the control group. ACF expressing sialomucin, thought to indicate ACF more likely to progress to tumors, were greater in the high-PEITC group (13 +/- 3) than the control (5.6 +/- 2). Mucin-depleted ACF, suggested to have the greatest tumorigenic potential, tended to be lower in the low-I3C group (P < 0.06) compared with the control group. Mucosal apoptotic and cell proliferation labeling indices did not differ among groups, suggesting that reduction in the ACF number by I3C does not involve alterations in mucosal cell kinetics. No significant differences were found among the groups in hepatic cytochrome P450 2E1 (CYP2E1) activity, the first enzyme involved in activation of azoxymethane. However, there was increased activity of NADPH- and NADH reductases with high-I3C, which are the enzymes involved in the transfer of reducing equivalents to cytochrome P450. These results suggest that I3C lowers colon cancer risk through a mechanism not involving reduction of carcinogen activation by CYP2E1.     

Transgenic rats carrying human c-Ha-ras proto-oncogenes are highly susceptible to N-methyl-N-nitrosourea mammary carcinogenesis

A rat line carrying three copies of the human c-Ha-ras proto-oncogene, including its own promoter region, was established and designated Hras128. Expression of the transgene was detected in all organs examined from Hras128 rats by northern blot analysis. To examine its influence on susceptibility to N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis, female rats were treated with 50 mg/kg MNU i.v. at 50 days of age. All 22 Hras128 transgenic rats rapidly developed multiple and large mammary carcinomas within as little as 8 weeks after MNU treatment (14.1 tumors/rat, average diameter 16.4 mm). In contrast, 24 non-transgenic littermates developed no or only small tumors (0.46 tumors/rat, average diameter 7.4 mm) within this period. PCR-restriction fragment length polymorphism (RFLP) analysis and direct sequencing for the transduced human c-Ha-ras proto-oncogene indicated that 38 out of 44 tumors (86.4%) contained cells with mutations at codon 12 in exon 1. However, the signal densities of the mutated bands observed in the RFLP analyses revealed the presence of mixed populations of mutated and non-mutated cells in the tumors, the latter being in the majority. PCR-single strand conformation polymorphism analysis detected no mutations in codons 12 or 61 of the endogenous rat c-Ha-ras gene of Hras128 rat tumors. The results thus indicate that rats carrying the transduced human c-Ha-ras proto-oncogene are highly susceptible to MNU-induced mammary carcinogenesis and that this is not primarily due to mutations of the transgene or endogenous c-Ha-ras gene.     

吲哚-3-甲醇对DMBA诱导大鼠乳腺肿瘤的预防效果

背景与目的:近年来,乳腺癌化学预防成为热门研究方向,目前临床常用的化学预防药物,如他莫昔芬(三苯氧胺)在发挥防癌作用的同时,也出现了很多副作用.这样就促使人们从多方面寻找高效无毒的化学预防药物.通过流行病学的研究发现天然食物中有效成分与降低癌症的发病率存在着一定关系,如β-胡萝卜素、维甲酸、绿茶素等,从日常食物中提取防癌剂便为化学预防药物的发展指明了新的方向.本研究探讨了十字花科植物(花椰菜,结球甘蓝等)中的有效成分吲哚-3-甲醇(I3C)对大鼠乳腺癌的预防作用以及对大鼠乳腺肿瘤中ER受体表达抑制作用.方法:①将40只43 d龄SD大鼠40只按体重分层后随机分为不预防给药组(DMBA灌胃)、高剂量给药组(I3C,100 mg/d)、低剂量给药组(I3C,50 mg/d)、溶剂对照组,每组各10只.高剂量给药组与低剂给药量组预防性给予吲哚-3-甲醇1周,1周后不预防给药组、高剂量给药组与低剂量给药组分别30 mg/ml DMBA致癌剂一次性灌胃造模(1 ml/只),之后高剂量给药组与低剂量给药组分别给于吲哚-3-甲醇100 mg/d,与50 mg/d至实验结束(共100 d),观察各组乳腺肿瘤发生时间,记录数目并计算肿瘤体积,光镜下对乳腺肿瘤进行病理分类.②对各组大鼠乳腺肿瘤用免疫组化S-P方法测定ERα及ERβ的表达情况.结果:①各组大鼠乳腺肿瘤数目及体积均值(x±s):高剂量给药组荷瘤大鼠3只,低剂量给药组荷瘤大鼠3只,与不预防给药组荷瘤大鼠9只比较,差异有显著性(P〈0.05);高剂量给药组荷瘤7个,平均肿瘤体积(8±5)×102 mm3,低剂量给药组荷瘤总数13个,平均肿瘤体积(23±4)×102 mm3,与不预防给药组荷瘤总数21个,平均肿瘤体积(31±5)×102 mm3,差异有显著性(P〈0.05);而高剂量给药组与低剂量给药组之间进行比较P>0.05,差异无显著性.②光镜下组织学观察,高剂量给药组与低剂量给药组的乳腺肿瘤浸润性导管癌发生,分化程度高,侵袭性均明显低于不预防给药组.③ER受体在各组乳腺肿瘤中的表达:吲哚-3-甲醇高剂量给药组和低剂量给药组(高剂量给药组+低剂量给药组)ER受体阳性表达率为50%(10/20),不预防给药组ER受体阳性表达率85.7%(18/21);而高剂量给药组和低剂量给药组ER受体阴性表达率50%(10/20),不预防给药组的14.2%(3/21),它们之间比较均有显著差异(χ2=6.0341,P 〈0.05).其中ERα与ERβ在高剂量给药组和低剂量给药组中的阳性表达亦明显低于不预防给药组(P 〈0.05),有显著差异.结论:吲哚-3-甲醇在抑制乳腺肿瘤发生中有明显效果,但高剂量与低剂量之间并没有显著差异;并且能够有效阻断肿瘤中ER受体的表达,使其表达下调.     

4-Hydroxyandrostenedione in the prophylaxis of N-methyl-N-nitrosourea induced mammary tumourigenesis

We have examined the role of the aromatase inhibitor 4-hydroxyandrostenedione (4-OHA) in the prevention of mammary tumourigenesis in experiments involving 170 rats. We first demonstrated a prophylactic effect of 4-OHA (50 mg/week) in reducing tumour incidence over a 30 week period compared to controls (P = 0.04). We repeated the experiment to determine optimum dose and duration of therapy. Although 4-OHA again prevented tumour development (P less than 0.0005), there was no difference between the standard (50 mg/week) dose and the higher dose (100 mg/week). Rats were randomised at 30 weeks to either stop or to continue prophylactic therapy; marginal benefit in tumour free survival in continuing therapy was observed (P = 0.03). We conclude that 4-OHA is an effective agent in preventing carcinogen-induced mammary tumours in rats and further studies of the role of oestrogen synthesis inhibitors in the prevention of human mammary tumours may be indicated.     

Antitumour promoting activity of indole-3-carbinol in mouse skin carcinogenesis.

There has been growing interest in recent years in the potential of brassica vegetables (cabbage, cauliflower, brussels sprouts, etc.) as vectors for the introduction of anticarcinogenic compounds in the diet. Indole-3-carbinol, a major indole metabolite present in the cruciferous vegetables, has been found to inhibit various rodent tumours when administered prior to or during carcinogen exposure. In this study, the antitumour promoting potential of indole-3-carbinol was studied in a two-stage mouse skin model of carcinogenesis. The animals were initiated with a single subcarcinogenic dose of DMBA. After one week, 250 microg of indole-3-carbinol was applied topically to each animal prior to promotion with 5 microg TPA twice per week. Tumour development was significantly inhibited in indole-3-carbinol-supplemented animals in terms of cumulative numbers of tumours and average tumours per mouse. About 44% of male and 29% of female mice remained tumour-free in this group at the end of the experiment. A significant delay in the tumour induction time was also observed in indole-3-carbinol-supplemented animals. This evidence suggests that indole-3-carbinol, in the manner and dose given, inhibits the development of tumours in the two-stage mouse skin model of carcinogenesis.     

Indole-3-carbinol inhibits prostate cancer cell migration via degradation of beta-catenin

We determined whether indole-3-carbinol (I3C) could affect DU145 human prostate carcinoma cell migration to prevent the development and progression of prostate cancer. Although previous studies have shown anticancer properties of I3C in various cancer cell lines, it has not been determined how I3C regulates epidermal growth factor (EGF)-induced migration and related signaling pathways. DU145 cells were treated with I3C (100 microM) in the absence or presence of EGF (10 ng/ml). Our results showed that I3C significantly inhibited DU145 cell migration with and without EGF stimulation. It has been reported that the beta-catenin signaling pathway controls androgen receptor (AR)-mediated prostate cancer progression, which plays a key role in the metastasis of prostate cancer. Western blot analysis demonstrated that I3C led to the phosphorylation of beta-catenin and subsequent degradation of beta-catenin in the absence and presence of EGF. In contrast, I3C did not have any effect on the expression of beta-catenin mRNA. From these results, we suggest that I3C inhibits EGF (dependent or independent)-induced DU145 cell migration through beta-catenin degradation.     

Alteration of gene expression in rat mammary tumors induced by N-methyl-N-nitrosourea

Rodents are susceptible to the effects of chemical carcinogens and have been widely used in the study of mammary-gland carcinogenesis. However, little information is available regarding specific phenotypic changes that occur during mammary-gland carcinogenesis. In this study, subtraction hybridization was used to identify specific genes whose expression in N-methyl-N-nitrosourea (MNU)-induced rat mammary tumors had been altered. mRNA isolated from normal rat mammary tissue and tumors induced by treatment of 50-d-old female rats with MNU (50 mg/kg) was used to produce normal and tumor cDNA libraries. Total inserts prepared from each cDNA library were used to produce a subtracted tumor-normal probe. Differential screening of the tumor library with the subtracted probe and normal cDNA yielded 20 clones that appeared to be differentially expressed. Northern analysis of mRNA isolated from normal mammary tissue and tumor tissue confirmed that four of these clones were differentially expressed. The expression of clones 4 and 15 was greatly increased (13-fold and tenfold, respectively) in most MNU-induced mammary tumors, whereas the expression of clones 10 and 27 was decreased (13-fold and fourfold, respectively). Sequence analysis revealed that clones 15 and 27 were highly homologous to calcyclin and a cDNA isolated from HL-60 cells, respectively. The differential expression of clones 4 and 10 was due to the presence within these clones of retroviral sequences and a fragment of transferrin, respectively. These clones may represent markers useful for studying the development of MNU-induced mammary-gland neoplasias. © 1996 Wiley-Liss, Inc.     

Indole-3-carbinol inhibits the growth of human colon carcinoma cells but enhances the tumor multiplicity and volume of azoxymethane-induced rat colon carcinogenesis

Indole-3-carbinol (I3C) is a naturally occurring phytochemical which exerts a broad range of biological activities. The purpose of this study was to examine the effects of I3C on colon carcinogenesis, cell proliferation, cell-cycle progression and apoptosis, and on the levels of expression of several cell-cycle control molecules. We used a long-term rat model by using azoxymethane (AOM) to induce tumors (adenomas and adenocarcinomas) in the colon. In the present study, we found that after AOM injection, the treatment of male F344 rats with 0.01 and 0.05% I3C caused a significant increase in the tumor multiplicity of adenocarcinomas by 2.2- (P<0.05 for 0.01% I3C) and 2.1-fold (P<0.0002 for 0.05% I3C) respectively, when compared to the control rats. In addition, the tumor multiplicity of adenoma plus adenocarcinoma and the volume of adenocarcinoma were also increased by 2.0- (P<0.00001) and 2.1-fold (P<0.05) respectively, compared to the control. I3C significantly increased the proliferating cell nuclear antigen labeling index (PCNA LI) (P<0.008) and decreased the apoptotic index (P<0.05) of the colon adenocarcinoma. In contrast, in HCT 116 and HT29 human colon carcinoma cells, I3C inhibited growth and induced G1-phase cell-cycle arrest and apoptosis. Furthermore, I3C caused approximately a 2- to 4-fold increase in the cellular levels of p27KIP1 and p21CIP1 mRNA. These results suggest that I3C inhibits the growth of human colon carcinoma cells, at least in part, by inducing p27KIP1 and p21CIP1-mediated G1 cell-cycle arrest but dietary I3C promotes AOM-induced rat colon carcinogenesis by inhibiting the apoptosis of colon tumors. Therefore, the present study may provide further evidence for the ambivalent modulatory activity of I3C and this information may be useful when including I3C in cancer chemoprevention and/or extensive clinical therapy trials.     

Enhancement of carcinogenesis by the natural anticarcinogen indole-3-carbinol

Indole-3-carbinol (I3C), a natural constituent of cruciferous vegetables, is an inhibitor in several experimental animal models of carcinogenesis by polynuclear aromatic hydrocarbons or aflatoxin B1 (AFB1) when administered prior to or during carcinogen exposure. For assessment of the postinitiation effects of I3C, rainbow trout were exposed to dietary I3C in two different protocols--before and during AFB1 exposure or after AFB1 exposure only. Preinitiation exposure to I3C reduced AFB1-initiated hepatocellular carcinomas in trout as previously reported, but post-initiation I3C exposure strongly enhanced the tumor incidence above the positive AFB1 control. These results reveal the need for additional research to elucidate the overall effect of I3C on chemical carcinogenesis.