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

Cancer interception by interceptor molecules: mechanistic, preclinical and human translational studies with chlorophylls

Before 'cancer interception' was first advocated, 'interceptor molecules' had been conceived as a sub-category of preventive agents that interfered with the earliest initiation steps in carcinogenesis. Three decades ago, a seminal review cataloged over fifty synthetic agents and natural products that were known or putative interceptor molecules. Chlorophylls and their derivatives garnered much interest based on the potent antimutagenic activity in the Salmonella assay, and the subsequent mechanistic work that provided proof-of-concept for direct molecular complexes with planar aromatic carcinogens. As the 'interceptor molecule' hypothesis evolved, mechanistic experiments and preclinical studies supported the view that chlorophylls can interact with environmental heterocyclic amines, aflatoxins, and polycyclic aromatic hydrocarbons to limit their uptake and bioavailability in vivo. Support also came from human translational studies involving ultralow dose detection in healthy volunteers, as well as intervention in at-risk subjects. Antimutagenic and antigenotoxic effects of natural and synthetic chlorophylls against small alkylating agents also highlighted the fact that non-interceptor mechanisms existed. This gave impetus to investigations broadly related to free radical scavenging, anti-inflammatory effects, immune modulation and photodynamic therapy. Therapeutic aspects of chlorophylls also were investigated, with evidence for cell cycle arrest and apoptosis in human cancer cells. As the science has evolved, new mechanistic leads continue to support the use and development of chlorophylls and their porphyrin derivatives for cancer interception, beyond the initial interest as interceptor molecules.

Optimization of Erlotinib Plus Sulindac Dosing Regimens for Intestinal Cancer Prevention in an Apc-Mutant Model of Familial Adenomatous Polyposis (FAP)

A clinical trial in patients with familial adenomatous polyposis (FAP) demonstrated that sulindac plus erlotinib (SUL+ERL) had good efficacy in the duodenum and colon, but toxicity issues raised concerns for long-term prevention. We performed a biomarker study in the polyposis in rat colon (Pirc) model, observing phosphorylated Erk inhibition in colon polyps for up to 10 days after discontinuing ERL+SUL administration. In a follow-up study lasting 16 weeks, significant reduction of colon and small intestine (SI) tumor burden was detected, especially in rats given 250 ppm SUL in the diet plus once-a-week intragastric dosing of ERL at 21 or 42 mg/kg body weight (BW). A long-term study further demonstrated antitumor efficacy in the colon and SI at 52 weeks, when 250 ppm SUL was combined with once-a-week intragastric administration of ERL at 10, 21, or 42 mg/kg BW. Tumor-associated matrix metalloproteinase-7 (Mmp7), tumor necrosis factor (Tnf), and early growth response 1 (Egr1) were decreased at 16 weeks by ERL+SUL, and this was sustained in the long-term study for Mmp7 and Tnf. Based on the collective results, the optimal dose combination of ERL 10 mg/kg BW plus 250 ppm SUL lacked toxicity, inhibited molecular biomarkers, and exhibited effective antitumor activity. We conclude that switching from continuous to once-per-week ERL, given at one-quarter of the current therapeutic dose, will exert good efficacy with standard-of-care SUL against adenomatous polyps in the colon and SI, with clinical relevance for patients with FAP before or after colectomy. PREVENTION RELEVANCE: This investigation concludes that switching from continuous to once-per-week erlotinib, given at one-quarter of the current therapeutic dose, will exert good efficacy with standard-of-care sulindac against adenomatous polyps in the colon and small intestine, with clinical relevance for patients with FAP before or after colectomy.

Epigenetic Regulation of NRF2/KEAP1 by Phytochemicals

Epigenetics has provided a new dimension to our understanding of nuclear factor erythroid 2–related factor 2/Kelch-like ECH-associated protein 1 (human NRF2/KEAP1 and murine Nrf2/Keap1) signaling. Unlike the genetic changes affecting DNA sequence, the reversible nature of epigenetic alterations provides an attractive avenue for cancer interception. Thus, targeting epigenetic mechanisms in the corresponding signaling networks represents an enticing strategy for therapeutic intervention with dietary phytochemicals acting at transcriptional, post-transcriptional, and post-translational levels. This regulation involves the interplay of histone modifications and DNA methylation states in the human NFE2L2/KEAP1 and murine Nfe2l2/Keap1 genes, acetylation of lysine residues in NRF2 and Nrf2, interaction with bromodomain and extraterminal domain (BET) acetyl “reader” proteins, and non-coding RNAs such as microRNA (miRNA) and long non-coding RNA (lncRNA). Phytochemicals documented to modulate NRF2 signaling act by reversing hypermethylated states in the CpG islands of NFE2L2 or Nfe2l2, via the inhibition of DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), through the induction of ten-eleven translocation (TET) enzymes, or by inducing miRNA to target the 3′-UTR of the corresponding mRNA transcripts. To date, fewer than twenty phytochemicals have been reported as NRF2 epigenetic modifiers, including curcumin, sulforaphane, resveratrol, reserpine, and ursolic acid. This opens avenues for exploring additional dietary phytochemicals that regulate the human epigenome, and the potential for novel strategies to target NRF2 signaling with a view to beneficial interception of cancer and other chronic diseases.

1-Methoxy-3-indolylmethyl DNA adducts in six tissues, and blood protein adducts, in mice under pak choi diet: time course and persistence

We previously showed that purified 1-methoxy-3-indolylmethyl (1-MIM) glucosinolate, a secondary plant metabolite in Brassica species, is mutagenic in various in vitro systems and forms DNA and protein adducts in mouse models. In the present study, we administered 1-MIM glucosinolate in a natural matrix to mice, by feeding a diet containing pak choi powder and extract. Groups of animals were killed after 1, 2, 4 and 8 days of pak choi diet, directly or, in the case of the 8-day treatment, after 0, 8 and 16 days of recovery with pak choi-free diet. DNA adducts [N²-(1-MIM)-dG, N⁶-(1-MIM)-dA] in six tissues, as well as protein adducts [τN-(1-MIM)-His] in serum albumin (SA) and hemoglobin (Hb) were determined using UPLC-MS/MS with isotopically labeled internal standards. None of the samples from the 12 control animals under standard diet contained any 1-MIM adducts. All groups receiving pak choi diet showed DNA adducts in all six tissues (exception: lung of mice treated for a single day) as well as SA and Hb adducts. During the feeding period, all adduct levels continuously increased until day 8 (in the jejunum until day 4). During the 14-day recovery period, N²-(1-MIM)-dG in liver, kidney, lung, jejunum, cecum and colon decreased to 52, 41, 59, 11, 7 and 2%, respectively, of the peak level. The time course of N⁶-(1-MIM)-dA was similar. Immunohistochemical analyses indicated that cell turnover is a major mechanism of DNA adduct elimination in the intestine. In the same recovery period, protein adducts decreased more rapidly in SA than in Hb, to 0.7 and 37%, respectively, of the peak level, consistent with the differential turnover of these proteins. In conclusion, the pak choi diet lead to the formation of high levels of adducts in mice. Cell and protein turnover was a major mechanism of adduct elimination, at least in gut and blood.

Indole-3-Carbinol and Its Role in Chronic Diseases

Indole-3-carbinol (I3C), a common phytochemical in cruciferous vegetables, and its condensation product, 3,3'-diindolylmethane (DIM) exert several biological activities on cellular and molecular levels, which contribute to their well-recognized chemoprevention potential. Initially, these compounds were classified as blocking agents that increase drug-metabolizing enzyme activity. Now it is widely accepted that I3C and DIM affect multiple signaling pathways and target molecules controlling cell division, apoptosis, or angiogenesis deregulated in cancer cells. Although most of the current data support the role of I3C and DIM in prevention of hormone-dependent cancers, it seems that their application in prevention of the other cancer as well as cardiovascular disease, obesity, and diabetes reduction is also possible. This chapter summarizes the current experimental data on the I3C and DIM activity and the results of clinical studies indicating their role in prevention of chronic diseases.

Mammalian models of chemically induced primary malignancies exploitable for imaging-based preclinical theragnostic research

Compared with transplanted tumor models or genetically engineered cancer models, chemically induced primary malignancies in experimental animals can mimic the clinical cancer progress from the early stage on. Cancer caused by chemical carcinogens generally develops through three phases namely initiation, promotion and progression. Based on different mechanisms, chemical carcinogens can be divided into genotoxic and non-genotoxic ones, or complete and incomplete ones, usually with an organ-specific property. Chemical carcinogens can be classified upon their origins such as environmental pollutants, cooked meat derived carcinogens, N-nitroso compounds, food additives, antineoplastic agents, naturally occurring substances and synthetic carcinogens, etc. Carcinogen-induced models of primary cancers can be used to evaluate the diagnostic/therapeutic effects of candidate drugs, investigate the biological influential factors, explore preventive measures for carcinogenicity, and better understand molecular mechanisms involved in tumor initiation, promotion and progression. Among commonly adopted cancer models, chemically induced primary malignancies in mammals have several advantages including the easy procedures, fruitful tumor generation and high analogy to clinical human primary cancers. However, in addition to the time-consuming process, the major drawback of chemical carcinogenesis for translational research is the difficulty in noninvasive tumor burden assessment in small animals. Like human cancers, tumors occur unpredictably also among animals in terms of timing, location and the number of lesions. Thanks to the availability of magnetic resonance imaging (MRI) with various advantages such as ionizing-free scanning, superb soft tissue contrast, multi-parametric information, and utility of diverse contrast agents, now a workable solution to this bottleneck problem is to apply MRI for noninvasive detection, diagnosis and therapeutic monitoring on those otherwise uncontrollable animal models with primary cancers. Moreover, it is foreseeable that the combined use of chemically induced primary cancer models and molecular imaging techniques may help to develop new anticancer diagnostics and therapeutics.

High mutagenic activity of juice from pak choi (Brassica rapa ssp. chinensis) sprouts due to its content of 1-methoxy-3-indolylmethyl glucosinolate, and its enhancement by elicitation with methyl jasmonate

Cruciferous vegetables have the reputation to protect against cancer, an effect attributed to glucosinolates (GLS) and their breakdown products. However, some GLS are mutagenic, an activity associated with cancer initiation rather than chemoprevention. We show that juices from steamed pak choi sprouts are strongly mutagenic in Salmonella typhimurium TA100 upon addition of fresh myrosinase. Growth of the plants in the presence of methyl jasmonate, a hormone eliciting defence factors, led to 20-fold enhanced mutagenic activity. The level of 1-methoxy-3-indolylmethyl (1-MIM)-GLS was similarly increased, whereas those of other GLS were only elevated 0.8- to 3.2-fold. 1-MIM-GLS is a potent mutagen, whose activity is further enhanced by human sulphotransferase 1A1 (hSULT1A1), an activation not observed with other GLS. The mutagenicity of the pak choi juices was increased 20-fold in bacteria expressing hSULT1A1. A tiny level of juice from elicitated sprouts, 0.04% in the mutagenicity assay, was sufficient to double the number of revertants above the spontaneous level. We conclude that pak choi juice is mutagenic, an activity that can be strongly affected by the growth conditions. It is owed essentially to a single component, 1-MIM-GLS. We recommend using cultivars, growth conditions and/or food preparations that keep the level of this GLS congener low.

A Further Study of the Role of Copper in Regard to the Antimutagenic Action of Sodium Copper Chlorophyllin (SCC) in Somatic Cells of Drosophila melanogaster

Previous findings suggest that copper plays a crucial role in the antimutagenic effect of sodium copper chlorophyllin (SCC). The objective of the current research was to compare the antimutagenic effects of two SCC compounds with different amounts of copper (3.7% and 5.4%, respectively) on the genetic damage induced by gamma rays in somatic cells of Drosophila. Data indicate that an increase in copper content of 31.5% in SCC-5.4 resulted in a greater inhibition of gamma ray genetic damage of 49% whereas only a 2% inhibition with SCC-3.7 occurred. Of greater interest is the association of SCC with a variety of uses in humans, such as a chemo preventive agent and food supplement. A greater attention to the concentration of copper in the SCC product in use should be required.

Sodium copper chlorophyllin (SCC) induces genetic damage in postmeiotic and somatic wing cells of Drosophila melanogaster

There is no apparent evidence to indicate that sodium copper chlorophyllin (SCC) is mutagenic. The aim of the present study was thus to determine the mutagenic effect of SCC, in postmeiotic germ cells of the adult male Drosophila. This investigation was based on the ability to examine whether SCC induced sex-linked recessive lethal mutations (SLRL), as well as the somatic mutation and recombination test (SMART). Four different SCC concentrations were used: 0, 45, 69, 80, and 100 mM. For SLRL, two broods were generated to test sperm and primarily spermatids. Results showed a significant frequency of recessive lethal mutations compared with control sperm cells with SCC at 69, 80, and 100 mM. In contrast, the frequency of somatic mutations rose by 0.21 only with 100 mM of SCC. These findings provide evidence that SCC is a weak mutagen in both cell lines. The differential response may be attributed to repair mechanisms that are active in somatic cells but almost absent in germ cells.

The rainbow trout liver cancer model: response to environmental chemicals and studies on promotion and chemoprevention

Rainbow trout (Oncorhynchus mykiss) are an outstanding model of liver cancer induction by environmental chemicals and development of strategies for chemoprevention. Trout have critical and unique advantages allowing for cancer studies with 40,000 animals to determine dose-response at levels orders of magnitude lower than possible in rodents. Examples of two promoters in this model, the dietary supplement dehydroepiandrosterone (DHEA) and industrial chemical perfluorooctanoic acid (PFOA), are presented. In addition, indole-3-carbinol (I3C) and chlorophyllin (CHL) inhibit initiation following exposure to potent human chemical carcinogens (e.g., aflatoxin B(1) (AFB(1))). Two "ED(001)" cancer studies have been conducted, utilizing approximately 40,000 trout, by dietary exposure to AFB(1) and dibenzo[d,e,f,p]chrysene (DBC). These studies represent the two largest cancer studies ever performed and expand the dose-response dataset generated by the 25,000 mouse "ED(01)" study over an order of magnitude. With DBC, the liver tumor response fell well below the LED(10) line, often used for risk assessment, even though the biomarker (liver DBC-DNA adducts) remained linear. Conversely, the response with AFB(1) remained relatively linear throughout the entire dose range. These contributions to elucidation of mechanisms of liver cancer, induced by environmental chemicals and the remarkable datasets generated with ED(001) studies, make important contributions to carcinogenesis and chemoprevention.

A study of the inhibition/promotion effects of sodium-copper chlorophyllin (SCC)-mediated mutagenesis in somatic cells of Drosophila

Sodium-copper chlorophyllin (SCC), a copper-porphyrin complex, has been shown to act as an inhibitor as well as a promoter of DNA-damage induction by a variety of mutagens in several test systems. In order to investigate the basis of this dual effect, experiments were carried out to compare the influence of pretreatment with intact SCC and that of its constituents, the metal-free protoporphyrin (PP-IX) and copper as CuCl(2). The wing-spot test was employed to monitor mutational events in somatic cells of Drosophila melanogaster. Heterozygous mwh+/+flr(3) larvae were treated for 24h with SCC, PP-IX, CuCl(2) or sucrose. Following this treatment, one group of larvae were immediately allowed to feed on instant medium containing 0.5mM N-nitroso-N-ethylurea (ENU) dissolved in phosphate buffer to reach pH 6. The remaining larvae received treatment with ENU with a delay of 1, 2 or 3days (DTD). Results revealed an (a) overall inhibitory effect for 0-DTD and 1-DTD after pretreatment with SCC, (b) only in 0-DTD after PP-IX, and (c) in all DTDs after treatment with CuCl(2). These results provide evidence that the copper ion plays a central role in the antimutagenic effect of SCC, and for a sustained period of time. Pretreatment with SCC and PP-IX produced a promoter effect at 2-DTD and 3-DTD. The results could be explained as an effect of the accumulation of metal-free porphyrin following the dissociation of the copper-porphyrin complex (SCC), the copper-ion reaching proteins to form complexes and participated in anabolic pathways.

Glucosinolates in Brassica vegetables: the influence of the food supply chain on intake, bioavailability and human health

Glucosinolates (GLSs) are found in Brassica vegetables. Examples of these sources include cabbage, Brussels sprouts, broccoli, cauliflower and various root vegetables (e.g. radish and turnip). A number of epidemiological studies have identified an inverse association between consumption of these vegetables and the risk of colon and rectal cancer. Animal studies have shown changes in enzyme activities and DNA damage resulting from consumption of Brassica vegetables or isothiocyanates, the breakdown products (BDP) of GLSs in the body. Mechanistic studies have begun to identify the ways in which the compounds may exert their protective action but the relevance of these studies to protective effects in the human alimentary tract is as yet unproven. In vitro studies with a number of specific isothiocyanates have suggested mechanisms that might be the basis of their chemoprotective effects. The concentration and composition of the GLSs in different plants, but also within a plant (e.g. in the seeds, roots or leaves), can vary greatly and also changes during plant development. Furthermore, the effects of various factors in the supply chain of Brassica vegetables including breeding, cultivation, storage and processing on intake and bioavailability of GLSs are extensively discussed in this paper.

Single-dose pharmacokinetics and tolerability of absorption-enhanced 3,3'-diindolylmethane in healthy subjects

We have completed a single ascending dose clinical study of the proposed chemopreventive agent 3,3'-diindolylmethane (DIM). The study agent was nutritional-grade, absorption-enhanced BioResponse 3,3'-diindolylmethane (BR-DIM). We determined the safety, tolerability, and pharmacokinetics of single doses of BR-DIM in drug-free, non-smoking, healthy men and women. Groups of four subjects were enrolled for each dose level. After randomization, one subject in each group received placebo whereas three received active BR-DIM. The doses administered were 50, 100, 150, 200, and 300 mg, with the 300-mg dose repeated in an additional group. No BR-DIM-related adverse effects were reported at doses up to 200 mg. At the 300-mg dose, one of six subjects reported mild nausea and headache and one also reported vomiting. Only the latter effect was judged as probably related to the study agent. Analysis of serial plasma samples showed that only one subject at the 50-mg dose had detectable concentrations of DIM. The single 100-mg dose of BR-DIM resulted in a mean maximum plasma concentration (C(max)) of 32 ng/mL and a mean area under the curve (AUC) of 128 h ng/mL, and a single 200-mg dose produced a mean C(max) of 104 ng/mL and a mean AUC of 553 h ng/mL. The single 300-mg dose of BR-DIM resulted in a mean C(max) of 108 ng/mL and a mean AUC of 532 h ng/mL. We conclude that BR-DIM is well tolerated at single doses of up to 200 mg, and that increasing the dose to 300 mg did not result in an increase in C(max).

A New Medium-term Rat Colorectal Bioassay Applying Neoplastic Lesions as End Points for Detection of Carcinogenesis Modifiers Effects with Weak or Controversial Modifiers

We have established a two-stage, medium-term rat colorectal carcinogenesis model featuring induction of neoplastic lesions within ten weeks. In the present study, we examined the ability of this model to detect weak modifiers. F344 male rats were given three subcutaneous (sc) injections of 1,2-dimethyl-hydrazine (DMH, 40 mg/kg b.w.) in one week followed by drinking water containing 1% dextran sodium sulfate (DSS) for a second week. One week after this regimen, basal diet alone, or diets containing 10% perilla oil, 10% corn oil, 10% dextrin, or 0.1% indole-3-carbinol (I3C) were supplied. The perilla oil and corn oil groups did not show significant differences in the numbers of aberrant crypt foci (ACF) and incidences or multiplicity of proliferative lesions as compared to the controls at either time point. In the dextrin group, the total number of ACF at week ten was significantly increased. With I3C, the total number of ACF and incidence and multiplicities of adenocarcinomas at week ten and the incidence of invasive tumors at week twenty were significantly increased. These data essentially correspond with earlier reported results, except in the vegetable oil cases. Thus, the system is suitable for detection of colorectal carcinogenesis modifiers with advantages over previous models using ACF alone as end points.

Low-dose dietary chlorophyll inhibits multi-organ carcinogenesis in the rainbow trout

We recently reported that chlorophyll (Chl) strongly inhibits aflatoxin B(1) preneoplasia biomarkers in rats when administered by co-gavage (Simonich et al., 2007. Natural chlorophyll inhibits aflatoxin B1-induced multi-organ carcinogenesis in the rat. Carcinogenesis 28, 1294-1302.). The present study extends this by examining the effects of dietary Chl on tumor development, using rainbow trout to explore ubiquity of mechanism. Duplicate groups of 140 trout were fed diet containing 224 ppm dibenzo[a,l]pyrene (DBP) alone, or with 1000-6000 ppm Chl, for 4 weeks. DBP induced high tumor incidences in liver (51%) and stomach (56%), whereas Chl co-fed at 2000, 4000 or 6000 ppm reduced incidences in stomach (to 29%, 23% and 19%, resp., P<0.005) and liver (to 21%, 28% and 26%, resp., P<0.0005). Chlorophyllin (CHL) at 2000 ppm gave similar protection. Chl complexed with DBP in vitro (2Chl:DBP, K(d1)=4.44+/-0.46 microM, K(d2)=3.30+/-0.18 microM), as did CHL (K(d1)=1.38+/-0.32 microM, K(d2)=1.17+/-0.05 microM), possibly explaining their ability to inhibit DBP uptake into the liver by 61-63% (P<0.001). This is the first demonstration that dietary Chl can reduce tumorigenesis in any whole animal model, and that it may do so by a simple, species-independent mechanism.

Allelochemical induction of cytochrome P450 monooxygenases and amelioration of xenobiotic toxicity in Helicoverpa zea

Polyphagous herbivores encounter allelochemicals as complex mixtures in their host plants, and the toxicity of an individual compound may be influenced by the chemical matrix in which it is encountered. Certain plant constituents may reduce toxicity of cooccurring compounds by inducing detoxification systems, including cytochrome P450s, which can metabolize a broad range of substances. The polyphagous corn earworm Helicoverpa zea encounters a diversity of plant allelochemicals in its many host plants and, as well, can encounter aflatoxins, mycotoxins produced by Aspergillus flavus and Aspergillus parasiticus that infect damaged grains. Dietary supplementation of each of three plant allelochemicals that are frequently (coumarin, COU), occasionally (indole-3-carbinol, 13C), or rarely (xanthotoxin, XAN) encountered by H. zea larvae substantially reduced the toxicity of aflatoxin B1 (AFB1) to H. zea. Compared to fourth instars on diets containing 1 microg/g AFB1 that failed to develop and pupate, fourth instars on diets containing I3C and XAN increased in mass by 216.1 and 700% after 6 days, and pupated at rates of 40 and 88%, respectively. Diets containing COU or XAN also significantly reduced the mortality rates of caterpillars exposed to the insecticides, diazinon and carbaryl. Diets containing COU and XAN increased CYP6B8 transcripts 2.6-fold; CYP321A1 transcripts increased 20.7, 8.3, and 10.6-fold in response to COU, I3C, and XAN, respectively. These results indicate that consumption of plant allelochemicals can ameliorate toxicity of natural and synthetic toxins encountered by insects, and they suggest that P450s induced by these allelochemicals contribute to detoxification of these chemicals in H. zea.

Single-Dose and Multiple-Dose Administration of Indole-3-Carbinol to Women: Pharmacokinetics Based on 3,3′-Diindolylmethane

We have completed a phase I trial in women of the proposed chemopreventive natural product indole-3-carbinol (I3C). Women received oral doses of 400, 600, 800, 1,000, and 1,200 mg I3C. Serial plasma samples were analyzed by high-performance liquid chromatography-mass spectrometry for I3C and several of its condensation products. I3C itself was not detectable in plasma. The only detectable I3C-derived product was 3,3'-diindolylmethane (DIM). Mean Cmax for DIM increased from 61 ng/mL at the 400-mg I3C dose to 607 ng/mL following a 1,000-mg dose. No further increase was observed following a 1,200-mg dose. A similar result was obtained for the area under the curve, which increased from 329 h ng/mL at the 400-mg dose to 3,376 h ng/mL after a 1,000-mg dose of I3C. Significant interindividual quantitative variation was seen in plasma DIM values within each dosing group, but the overall profiles were qualitatively similar, with no quantifiable DIM before dosing, tmax at approximately 2 h, and DIM levels near or below 15 ng/mL (the limit of quantitation), by 24 h. Different results were obtained for 14 subjects who received a 400-mg dose of I3C after 8 weeks of twice-daily I3C dosing. Although the predose sampling occurred at least 12 h after the last known ingestion of I3C, 6 of 14 subjects exhibited Cmax for DIM in their predose plasma. Despite this high initial value, plasma DIM for all subjects decreased to near or below the limit of quantitation within the 12-h sampling period. Possible reasons for this disparity between apparent t1/2 of DIM and the high predose values are discussed.

Tumors from rats given 1,2-dimethylhydrazine plus chlorophyllin or indole-3-carbinol contain transcriptional changes in beta-catenin that are independent of beta-catenin mutation status

Tumors induced in the rat by 1,2-dimethylhydrazine (DMH) contain mutations in beta-catenin, but the spectrum of such mutations can be influenced by phytochemicals such as chlorophyllin (CHL) and indole-3-carbinol (I3C). In the present study, we determined the mutation status of beta-catenin in more than 50 DMH-induced colon tumors and small intestine tumors, and compared this with the concomitant expression of beta-catenin mRNA using quantitative real-time RT-PCR analysis. In total, 19/57 (33%) of the tumors harbored mutations in beta-catenin, and 14/19 (74%) of the genetic changes substituted amino acids adjacent to Ser33, a key site for phosphorylation and beta-catenin degradation. These tumors were found to express a 10-fold range of beta-catenin mRNA levels, independent of the beta-catenin mutation status and phytochemical exposure, i.e. CHL or I3C given post-initiation. However, beta-catenin mRNA levels were strongly correlated with mRNA levels of c-myc, c-jun and cyclin D1, which are targets of beta-catenin/Tcf signaling. Tumors with the highest levels of beta-catenin mRNA often had over-expressed beta-catenin protein, and those with lower beta-catenin mRNA typically had low beta-catenin protein expression, but there were exceptions (high beta-catenin mRNA/low beta-catenin protein, or vice versa). We conclude that DMH-induced mutations stabilize beta-catenin protein in tumors, which increase c-myc, c-jun and cyclin D1, but there also can be over-expression of beta-catenin itself at the mRNA level, contributing to high beta-catenin protein levels. Similar findings have been reported in primary human colon cancers and their liver metastases, compared with matched normal-looking tissue. Thus, further studies are warranted on the mechanisms that upregulate beta-catenin at the transcriptional level in human and rodent colon cancers.

Cruciferous vegetables and colo-rectal cancer

Cruciferous vegetables have been studied extensively for their chemoprotective effects. Although they contain many bioactive compounds, the anti-carcinogenic actions of cruciferous vegetables are commonly attributed to their content of glucosinolates. Glucosinolates are relatively biologically inert but can be hydrolysed to a range of bioactive compounds such as isothiocyanates (ITC) and indoles by the plant-based enzyme myrosinase, or less efficiently by the colonic microflora. A number of mechanisms whereby ITC and indoles may protect against colo-rectal cancer have been identified. In experimental animals cruciferous vegetables have been shown to inhibit chemically-induced colon cancer. However, the results of recent epidemiological cohort studies have been inconsistent and this disparity may reflect a lack of sensitivity of such studies. Possible explanations for the failure of epidemiological studies to detect an effect include: assessment of cruciferous vegetable intake by methods that are subject to large measurement errors; the interaction between diet and genotype has not been considered: the effect that post-harvest treatments may have on biological effects of cruciferous vegetables has not been taken into account.

Post-initiation chlorophyllin exposure does not modulate aflatoxin-induced foci in the liver and colon of rats

Chlorophyllin (CHL) is a promising chemopreventive agent believed to block cancer primarily by inhibiting carcinogen uptake through the formation of molecular complexes with the carcinogens. However, recent studies suggest that CHL may have additional biological effects particularly when given after the period of carcinogen treatment. This study examines the post-initiation effects of CHL towards aflatoxin B1 (AFB₁)-induced preneoplastic foci of the liver and colon. The single concentration of CHL tested in this study (0.1% in the drinking water) had no significant effects on AFB₁-induced foci of the liver and colons of rats.

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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.

The dietary phytochemical chlorophyllin alters E-cadherin and beta-catenin expression in human colon cancer cells

Chlorophyllin (CHL), an anticarcinogenic and antimutagenic water-soluble derivative of chlorophyll, has been reported to induce apoptosis in human colon cancer cells via a pathway involving cell differentiation. Induction of differentiation markers may be important in limiting cancer-cell invasion and metastasis, and there is much interest in understanding the underlying mechanisms, because this might provide insights for cancer chemotherapy. In the present study, human HCT116 colon-cancer cells were treated with CHL, and the expression levels of E-cadherin and beta-catenin were examined using immunocytochemistry and laser scanning confocal microscopy. E-cadherin was detected almost exclusively at the cell periphery of cancer cells treated with or without CHL, but the expression of E-cadherin in the plasma membrane was markedly elevated in the cells treated with CHL. beta-Catenin also was strongly expressed in the plasma membrane, especially after CHL treatment. No change in the expression of beta-catenin mRNA was detected across a broad range of CHL concentrations (10-500 micromol/L), but there was a concentration-dependent decrease in nuclear beta-catenin protein levels without overt changes in the cytosolic pool of beta-catenin. Our interpretation of these findings is that CHL induces E-cadherin expression, and this facilitates trafficking of beta-catenin away from the nucleus and into the plasma membrane, possibly for destruction via the adherins junction remodeling (Hakai) pathway.

Effect of common Brassica vegetables (Brussels sprouts and red cabbage) on the development of preneoplastic lesions induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in liver and colon of Fischer 344 rats

Aim of the present study was the investigation of effects of juices from commonly consumed Brassica vegetables (two cultivars of Brussels sprouts and two cultivars of red cabbage) on formation and development of preneoplastic lesions in colons (aberrant crypt foci, ACF) and livers (glutathione-S-transferase placental form, GST-P+) in male F344 rats. The foci were induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a widespread carcinogenic heterocyclic aromatic amine which is found in fried meats. Recently, we reported on pronounced protective effects in the two-organ foci model when the vegetable juices were given during the carcinogen treatment but several findings by other groups indicated that breakdown products of glucosinolates contained in Brassica vegetables cause tumour promotion in various organs of laboratory rodents. In the present study, the animals received the juices in the drinking water (5%) over a period of 20 days after treatment with IQ (100 mg/kg bw on 10 alternate days). To increase the foci yield (which facilitates the detection of modifying effects), the animals were fed with a modified (high fat, fibre free) AIN-76 diet. With exception of the sprout variety "Cyrus", all juices lowered the number of GST-P+ foci as well as the foci area in the liver, but none of these effects was statistically significant. In the colon, none of the juices had an impact on crypt multiplicity (number of crypts/focus), whereas the number of ACF was decreased; only with the sprout variety Maximus the protective effect was significant (reduction 49%). The present findings show that administration of vegetable juices to the animals after the carcinogen does not increase the number and size of IQ-induced preneoplastic lesions in liver and colon.

Characterization of senescence-associated proteases in postharvest broccoli florets

We characterized the senescence-associated proteases of postharvest broccoli (Brassica oleracea L. var Green King) florets, using class-specific protease inhibitors and gelatin-polyacrylamide gel electrophoresis. Different classes of senescence-associated proteases in broccoli florets were partially characterized for the first time. Protease activity of broccoli florets was depressed by all the inhibitors and showed different inhibition curves during postharvest. The hydrolytic activity of metalloprotease (EC 3.4.24. - ) and serine protease (EC 3.4.21. - ) reached a maximum, 1 day after harvest (DAH), then decreased, while the hydrolytic activity of cysteine protease (EC 3.4.22. - ) and aspartic protease (EC 3.4.23. - ) increased throughout the postharvest senescence based on the calculated inhibition percentage of protease activity. The senescence-associated proteases were separated into seven endoprotease (EP) groups by gelatin-polyacryamide gel electrophoresis and classified into EP1 (metalloprotease), EP2 (metalloprotease and cysteine protease), EP3 (serine protease and aspartic protease), EP4, EP5, EP7 (cysteine protease), and EP6 (serine protease) based on the sensitivity of class-specific protease inhibitors. The proteases EP2, EP3, and EP4 were present throughout the postharvest stages. EP3 was the major EP at all times during senescence; EP4 intensity of activity increased after 2 DAH; EP6 and EP7 clearly increased after 4 DAH. Our results suggest that serine protease activity contributes to early stage (0-1 DAH) and late stage (4-5 DAH) of senescence; metalloprotease activity was involved in the early and intermediate stages (0-3 DAH) of senescence; and cysteine protease and aspartic protease activities participated in the whole process of broccoli senescence.

Tailoring cancer chemoprevention regimens to the individual

The present article, which is a tribute to the memory of Dr. Edward Bresnick, emphasizes the importance of environmental and life-style factors for cancer causation in the human population and points out approaches to cancer prevention. These approaches include vaccinations for the prevention of cancers that are caused by infectious agents as well as the use of cancer chemopreventive agents. The use of tamoxifen and letrozole to prevent breast cancer, finasteride to prevent prostate cancer, sunscreens or topical applications of 5-fluorouracil to prevent sunlight-induced skin cancer, and aspirin or calcium to prevent colon cancer are a few examples of cancer chemoprevention in high risk individuals and in the general population. An underdeveloped area of cancer chemoprevention is the use of combinations of agents that work by different mechanisms. It was pointed out that animal studies indicate that many cancer chemopreventive agents inhibit carcinogenesis under one set of experimental conditions but enhance carcinogenesis under another set of experimental conditions. These observations suggest that tailoring the chemopreventive regimen to the individual or to groups of individuals living under different environmental conditions or with different mechanisms of carcinogenesis may be an important aspect of cancer chemoprevention in human populations. How to tailor cancer chemoprevention regimens to the individual is an important challenge for the future.

Inhibitory effects of chlorophyllin, hemin and tetrakis(4-benzoic acid)porphyrin on oxidative DNA damage and mouse skin inflammation induced by 12-O-tetradecanoylphorbol-13-acetate as a possible anti-tumor promoting mechanism

Reactive oxygen species (ROS) from both endogenous and exogenous sources can cause oxidative DNA damage and dysregulated cell signaling, which are involved in the multistage process of carcinogenesis such as tumor initiation, promotion and progression. A number of structurally different anticarcinogenic agents inhibit inflammation and tumor promotion as they reduce ROS production and oxidative DNA damage. Evidence suggests that porphyrins can interfere with the actions of various carcinogens and mutagens by forming face-to-face complexes and their antimutagenic or antigenotoxic effects may also be attributed to their antioxidant activities. However, little is known regarding the anti-tumor promoting potential and mechanism of the porphyrin compounds. Based on our previous results on the inhibitory effects of chlorophyllin (CHL), hemin and tetrakis(4-benzoic acid)porphyrin (TBAP) against two-stage mouse skin carcinogenesis, we have investigated their anti-tumor promoting mechanisms. In the present work, CHL, hemin and TBAP reduced superoxide anion generation by 12-O-tetradecanoylphorbol-13-acetate (TPA) in differentiated HL-60 cells and the production of hydroxyl radicals by Fenton reaction. Porphyrins exert a dose-related inhibition of his(+) reversion in Salmonella typhimurium TA102 induced by tert-butylhydroperoxide (t-BOOH). DNA strand breaks by ROS derived from H(2)O(2)/Cu(II) and the formation of 8-hydroxydeoxyguanosine (8-OH-dG) in calf thymus DNA treated with H(2)O(2)/UV also were inhibited markedly by porphyrins in a concentration-dependent manner. Furthermore, CHL, hemin and TBAP decreased myeloperoxidase (MPO) activity and H(2)O(2) formation as well as epidermal ornithine decarboxylase (ODC) activity in mouse skin treated with TPA. These results demonstrate that the antioxidative properties of porphyrins are important for inhibiting TPA-induced tumor promotion.

The disposition and metabolism of 2-amino-3-methylimidazo-[4,5-f]quinoline in the F344 rat at high versus low doses of indole-3-carbinol

Indole-3-carbinol (I3C), a compound found in cruciferous vegetables, inhibits the formation of DNA adducts, colonic aberrant crypts, and tumors in rats given heterocyclic amines, such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Previous mechanism studies indicated that I3C induces cytochromes P4501A1 (CYP1A1) and CYP1A2, as well as phase 2 pathways, leading to enhanced metabolism and excretion of IQ. However, the chemopreventive activity is dependent on the dose of I3C, and at low doses which do not induce CYP1A activity, there is evidence for increased IQ-DNA adduct formation in vivo. The present study examined the fate of IQ in the rat and the profile of urinary metabolites across a broad range of I3C doses. Male F344 rats were given a single injection of I3C by oral gavage, at a dose equivalent to that received from a single daily exposure to 0, 5, 10, 25, 50, 100, 200, 500 or 1000 ppm I3C in the diet, or they were given the 1000-ppm-equivalent dose of I3C for 14 consecutive days. Subsequently, each rat was given 14C-labeled IQ (5 mg/kg; 0.1 mCi/kg) and the animal was sacrificed 8 h later. With increasing I3C, there was a dose-dependent decrease in IQ-associated radiolabel in several systemic tissues, and an increase in the radiolabel eliminated via the feces. In the urine, there was a dose-dependent increase in IQ-5-O-glucuronide and IQ-5-O-sulfate metabolites, and a concomitant decrease in the IQ-sulfamate at intermediate and high doses of I3C. However, 5- and 10 ppm-equivalent doses of I3C enhanced the levels of IQ-sulfamate compared with controls, possibly due to the high ratio of hepatic CYP1A2 versus CYP1A1 activities at these I3C doses. The possible significance of the low versus high dose effects are discussed in the context of ongoing clinical trials with I3C and the reported chemopreventive mechanisms in vivo.

Mutational analysis of Ctnnb1 and Apc in tumors from rats given 1,2-dimethylhydrazine or 2-amino-3-methylimidazo[4,5-f]quinoline: mutational 'hotspots' and the relative expression of beta-catenin and c-jun

There is growing interest in beta-catenin and its role in various human cancers. We recently reported that 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)- and 1,2-dimethylhydrazine (DMH)-induced colon tumors in the rat contain mutations in Ctnnb1, the gene for beta-catenin, but the mutation spectrum was influenced by postinitiation exposure to chlorophyllin (CHL) and indole-3-carbinol (I3C) [Blum et al., Carcinogenesis 2001;22:315-320]. The present paper describes a follow-up study in which all of the target organs for IQ- and DMH-induced tumorigenesis were screened; Ctnnb1 mutations were found in 44 of 119 DMH-induced colon tumors, six of 13 IQ-induced colon tumors, 28 of 81 DMH-induced small intestine tumors, none of five IQ-induced small intestine tumors, four of 106 IQ-induced liver tumors, none of 14 DMH-induced Zymbal's gland tumors, none of 24 IQ-induced Zymbal's gland tumors, and none of 29 IQ-induced skin tumors. In tumors from rats given carcinogen alone, or carcinogen plus CHL or I3C, Ctnnb1 mutations frequently substituted amino acids adjacent to Ser33, a critical Ser/Thr residue in the glycogen synthase kinase-3beta regulatory domain of beta-catenin. However, substitution of critical Ser/Thr residues themselves was detected in only three of 24 (12.5%) of the tumors from rats given carcinogen alone, compared with 23 of 58 (40%) of the tumors from rats given carcinogen and treated postinitiation with I3C or CHL (P < 0.02). More than 50 of the colon tumors with wild-type beta-catenin were examined further for their Apc status; the overall frequency of Apc mutations was <10%, and these genetic changes occurred exclusively in the 'Mutation Cluster Region' of Apc. A subset of colon tumors also was examined for expression of beta-catenin and c-jun; these proteins were overexpressed in all tumors containing Ctnnb1 mutations, but the expression was highest in tumors with Ctnnb1 mutations affecting Thr41 and Ser45 residues in the glycogen synthase kinase-3beta region of beta-catenin. Thus, Ctnnb1 mutations occurred more frequently than Apc mutations in colon and small intestine tumors of the rat, and certain mutations upregulated beta-catenin/T-cell factor target genes more effectively than others, perhaps influencing the response to phytochemicals administered postinitiation.

Growth-inhibitory effects of the chemopreventive agent indole-3-carbinol are increased in combination with the polyamine putrescine in the SW480 colon tumour cell line

BACKGROUND

Many tumours undergo disregulation of polyamine homeostasis and upregulation of ornithine decarboxylase (ODC) activity, which can promote carcinogenesis. In animal models of colon carcinogenesis, inhibition of ODC activity by difluoromethylornithine (DFMO) has been shown to reduce the number and size of colon adenomas and carcinomas. Indole-3-carbinol (I3C) has shown promising chemopreventive activity against a range of human tumour cell types, but little is known about the effect of this agent on colon cell lines. Here, we investigated whether inhibition of ODC by I3C could contribute to a chemopreventive effect in colon cell lines.

METHODS

Cell cycle progression and induction of apoptosis were assessed by flow cytometry. Ornithine decarboxylase activity was determined by liberation of CO2 from 14C-labelled substrate, and polyamine levels were measured by HPLC.

RESULTS

I3C inhibited proliferation of the human colon tumour cell lines HT29 and SW480, and of the normal tissue-derived HCEC line, and at higher concentrations induced apoptosis in SW480 cells. The agent also caused a decrease in ODC activity in a dose-dependent manner. While administration of exogenous putrescine reversed the growth-inhibitory effect of DFMO, it did not reverse the growth-inhibition following an I3C treatment, and in the case of the SW480 cell line, the effect was actually enhanced. In this cell line, combination treatment caused a slight increase in the proportion of cells in the G2/M phase of the cell cycle, and increased the proportion of cells undergoing necrosis, but did not predispose cells to apoptosis. Indole-3-carbinol also caused an increase in intracellular spermine levels, which was not modulated by putrescine co-administration.

CONCLUSION

While indole-3-carbinol decreased ornithine decarboxylase activity in the colon cell lines, it appears unlikely that this constitutes a major mechanism by which the agent exerts its antiproliferative effect, although accumulation of spermine may cause cytotoxicity and contribute to cell death. The precise mechanism by which putrescine enhances the growth inhibitory effect of the agent remains to be elucidated, but does result in cells undergoing necrosis, possibly following accumulation in the G2/M phase of the cell cycle.

Food and cancer

Food is an important factor in determining cancer incidence in many countries and regions. Food components relevant to cancer development can be divided into macro- and microcomponents. The former tends to act indirectly. The latter usually has a clearly defined action, for example as genotoxic agents. Food can have both positive (carcinogenic) and negative (preventive) effects. Total calory intake appears to have a strong positive influence on cancer incidence. Food typical of advanced nations including fat-rich food is associated with increases in breast, colon and prostate cancers. Vegetables rich in antioxidants and fibers tend to reduce cancer incidence. Carcinogenic plant alkaloids, myctoxins and other food contaminants frequently enter our bodies. Heat-cooking generates genotoxicants, including aromatic hydrocarbons (via combustion) and heterocyclic amines (HCAs) through reactions involving creatin(in)e, sugar and amino acids in meat. HCAs are relatively newcomers as food genotoxicants and can produce breast, colon and prostate cancers in rodents. Some epidemiological investigations positively correlate HCA intake and cancer incidence. HCAs can produce other toxicological effects including salivary gland atrophy and myocardial degeneration. Improved food, better life styles and developments in the functional food industry are all crucila to cancer prevention.

Development of a multi-organ rat model for evaluating chemopreventive agents: efficacy of indole-3-carbinol

Indole-3-carbinol (I-3-C) is among the most widely and popularly known antiestrogens. Due to its putative chemopreventive action, I-3-C is being marketed to the general public in health food establishments. Although it has been demonstrated to prevent cancer in animal bioassays, I-3-C also acts as a promoter in the liver and colon. Because of this potential dual biological activity, it is important to investigate both the inhibitory and promotional activities of I-3-C in multi-organ tumorigenesis animal models. 7,12-Dimethylbenz[a]anthracene, aflatoxin B1 and azoxymethane were used to initiate mammary, liver and colon carcinogenesis, respectively in female Sprague-Dawley rats. The rats were fed continuously on a diet containing I-3-C for 25 weeks after initiation. I-3-C treatment was begun one week after the last carcinogen treatment had been administered. I-3-C treatment resulted in a delay in latency of mammary tumor formation, but did not alter tumor incidence or multiplicity among survivors. In the colon, the protocol produced a 40% decrease in aberrant colon crypt foci. However, in the liver, it strongly-induced GST-P foci in carcinogen-treated (a four-fold increase in volume percent foci) and in the vehicle controls (a 69-fold increase). These data support previous findings in other rodent and fish tumor models that I-3-C both inhibits and promotes carcinogenesis. The results of this study clearly demonstrate that I-3-C is not an appropriate chemoprotective agent for human use, in spite of its effects in the breast and colon in this rat animal model.

Sequencing of the rat beta-catenin gene (Ctnnb1) and mutational analysis of liver tumors induced by 2-amino-3-methylimidazo[4,5-f]quinoline

beta-Catenin, a protein that functions in cadherin-mediated cell-cell adhesion as well as in signal transduction, has received increasing attention in recent years due to its role as an oncogene in various human cancers. The primary sequence of the human beta-catenin gene (CTNNB1) has been known for some time, but that of the rat beta-catenin gene (Ctnnb1) has not heretofore been studied in detail. We report here the primary structure of Ctnnb1 using PCR-based methods and direct sequencing. The size of the complete Ctnnb1 gene was determined to be 9082 bp. We found the rat Ctnnb1 gene to contain 14 exons, ranging in size from 61 to 356 bp, and 13 introns ranging in size from 76 to 2524 bp. The transcription start site appears to be 157 bp upstream of the ATG codon located in exon 1. The resulting transcript is 2650 nucleotides long (encoding a protein of 781 amino acids). We found the 5' UTR to consist of 157 nucleotides and the 3' UTR to be 147 nucleotides long. The region coding for the glycogen synthase kinase-3beta domain of beta-catenin is located in exon 2 of rat Ctnnb1, in contrast to human CTNNB1 in which it is found in exon 3. Based on the newly acquired knowledge of the primary sequence, more than a dozen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced rat liver tumors were screened for the presence or absence of mutations in all 14 exons of rat Ctnnb1. Surprisingly, no mutations were found. The results are discussed in the context of the organ-specificity of IQ-induced mutations in beta-catenin, being highly prevalent in colon tumors, but much less common in liver tumors.

Predominant mutation of codon 41 of the beta-catenin proto-oncogene in rat colon tumors induced by 1,2-dimethylhydrazine using a complete carcinogenic protocol

Constitutive activation of the wnt-signaling pathway plays an important role during both human and rat colon carcinogenesis and can be brought through mutations in either the adenomatous polyposis coli or the beta-catenin gene. Mutations found in the beta-catenin gene typically affect one out of four regulatory phosphorylation sites near the N-terminus of the beta-catenin protein. Whereas in human colon cancers, however, the majority of beta-catenin mutations directly alter threonine 41 or serine 45; the beta-catenin mutations found in chemically induced rat colon tumors seemed to cluster around codon 33 instead. Unlike previous studies, that have used relatively short-term (2-5 weeks) treatment with one of the alkylating agents 1,2,-dimethylhydrazine (DMH) or azoxymethane, we have investigated the mutational spectrum of the beta-catenin gene in a panel of rat colon tumors induced by long-term (20 weeks) DMH-treatment. We detected beta-catenin mutations in 12 of 33 (36%) tumors. Interestingly, only one of the beta-catenin mutations found affected the previously implicated codon 33 cluster region (Asp32Asn), whereas 11 of 12 (>90%) mutations represented identical C-->T transitions within codon 41 resulting in the common replacement of threonine by isoleucine. We propose a model in which codon 41 mutations bear higher oncogenic potential but are induced by DMH less frequently than mutations in the codon 33 cluster region. Consequently, only after sustained carcinogenic treatment, as is achieved in the long-term DMH-protocol, codon 41 mutations will be induced frequently enough to be present in all developing malignant lesions and, then, because of their higher oncogenic potential, these are selected for.

Colonic cell proliferation, apoptosis and aberrant crypt foci development in rats given 2-amino-3-methylimidaz

Sodium-copper chlorophyllin (CHL) inhibits the formation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)- and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced colonic aberrant crypt foci (ACF) and tumours in the F344 rat when it is given simultaneously with either carcinogen. However, CHL reportedly increased the incidence of dimethylhydrazine (DMH)-induced colon tumours in the same species when administered post-initiation. In the present study, rats were given IQ (130 mg/kg body weight, by oral gavages on alternating days) for 2 weeks, starting in experiment week 3, and one week after the final IQ dose rats received CHL treatment until the study was terminated at 16 weeks. Compared with animals given carcinogen alone, the mean number of IQ-induced ACF per colon was reduced significantly by 1% (w/v) CHL in the drinking water (P < 0.05), whereas 0.1% and 0.01% CHL had no effect. These CHL concentrations increased in a dose-related manner both the terminal deoxynucleotidyl transferase-mediated nick end labelling (TUNEL) and bromodeoxyuridine (BrdU) labelling indices in the distal colon. However, the lowest concentration tested, 0.001% CHL, increased the mean number of IQ-induced ACF per colon (P < 0.05), and increased the BrdU labelling index without a concomitant change in TUNEL. These studies indicated that 0.001% CHL promoted IQ-ACF due to deregulation of the homeostatic balance between cell birth and apoptosis in the colonic mucosa, whereas higher concentrations of CHL had either no effect or protected against IQ-induced ACF by causing dose-related increases in the overall rate of cell turnover in the colon.