A critical discussion on diet, genomic mutations and repair mechanisms in colon carcinogenesis

Toxicology Letters 265 (2017) 106–116

Contents lists available at ScienceDirect

Toxicology Letters journal homepage: www.elsevier.com/locate/toxlet

A critical discussion on diet, genomic mutations and repair mechanisms in colon carcinogenesis Juliana Yumi Sakitaa,1 , Bianca Gasparottoa,1 , Sergio Britto Garciab , Sergio Akira Uyemuraa , Vinicius Kannena,* a b

Department of Toxicology, Bromatology, and Clinical Analysis, University of Sao Paulo, Ribeirao Preto, Brazil Department of Pathology, University of Sao Paulo, Ribeirao Preto, Brazil

H I G H L I G H T S

G R A P H I C A L A B S T R A C T


Western diet has an uncountable number of chemicals that affect humans.
Combining low concentrations of various chemicals leads to more powerful effects than an isolated exposure.
Low and late-cell cycle expressed genes are prone to undergo mutation.
Detection and repair mechanisms have a specific threshold to be activated throughout the G2/M phase.
Reactivation of these mechanisms during the M phase promotes genomic instability.

A R T I C L E I N F O

Article history: Received 19 August 2016 Received in revised form 9 November 2016 Accepted 27 November 2016 Available online 28 November 2016 Keywords: Xenobiotics Pollutants Environment Bowels Proliferation

A B S T R A C T

Colon cancer is one of the most common malignancies and its etiology closely tied to dietary habits. Recent epidemiological data shows that colon cancer incidence is shifting to a much younger population. In this regard, some dietary components from a regular human meal might have various DNA-damaging compounds. Given that not every person endure cancer, the colonic malignancy develops throughout decades, and persistent DNA damage promotes cancer when induced at the proper intensity, a critical discussion of possible novel mechanisms by which carcinogens promote these tumors is urgently needed. Robust genomic sequencing analyses showed that low and late cell cycle expressed genes are prone to undergo mutation. Moreover, detection and repair mechanisms have a particular threshold to be activated throughout the G2/M phase, and reactivation of these devices during the M phase promotes genomic instability. Conditions of combined exposure to non-genotoxic concentrations of various

* Corresponding author at: Department of Toxicology, Bromatology, and Clinical Analysis, University of Sao Paulo, 14040-903, Brazil. E-mail address: [email protected] (V. Kannen). These authors contributed equally to this work.

1

http://dx.doi.org/10.1016/j.toxlet.2016.11.020 0378-4274/© 2016 Elsevier Ireland Ltd. All rights reserved.

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

107

carcinogens seem to act effectively through these weaknesses in genomic repair mechanisms. Therefore, we suggest that the natural tolerance of body defence mechanisms eventually become overwhelmed by the chronic exposure to different combinations and intensities of dietary mutagens leading to the high incidence of colon cancer in modern society. © 2016 Elsevier Ireland Ltd. All rights reserved.

1. Introduction The latest prospective data on cancer suggest that 1 in 21 people will die from colorectal cancer (CRC) in the United States of America. This cancer ranks at the third place for the most common malignancies and cause of tumor-related deaths, and at the first position for diagnosis and deaths from gastrointestinal tumors (Arnold et al., 2016). Previous reports suggested that 75% of cancers are related to chronic exposure to environmental factors (David and Zimmerman, 2010; Nebert and Dalton, 2006). Humans have never been exposed to such wide range of exogenous and endogenous damaging compounds, which in multiple and different combinations interact synergistically to promote mutations, and cancer (David and Zimmerman, 2010; Kravchenko et al., 2015). For instance, an average 70 kg American seemed to intake daily 1.8 mg of diet-related carcinogens that promote the risk of colon cancer (Layton et al., 1995). Colon carcinogenesis is a complex disease and its risk closely tied to dietary habits and lifestyle (Bouvard et al., 2015). We showed that dietary habits modulated the intensity of early colon carcinogenic events (Kannen et al., 2013, 2014). Whether a slight increase in the dietary fat content enhanced colonic preneoplasia (Kannen et al., 2014), reducing food intake did not protect from colon carcinogenesis either (Kannen et al., 2013). Moreover, DNAdamaging events seemed to occur together with microenvironment tissue changes throughout the development of preneoplastic lesions in the colon (Frajacomo et al., 2014). Diet appears to provide the most direct route by which various carcinogens challenge daily the DNA repair machinery of humans (Jeffrey and Williams, 2005). It means that metabolic mechanisms might be a critical step throughout the mutational process since

genetic polymorphisms modulate the cancer risk by the activity of xenobiotic-metabolizing enzymes (Jeffrey and Williams, 2005; Nebert and Dalton, 2006). Kravchenko et al. suggested that the synergetic activity of multiple low dose carcinogens could increase the cancer risk more than that exposure to a single carcinogen (Kravchenko et al., 2015). To understand the principles that govern the risk of sporadic CRC in humans, we should consider which factors favor sustained genomic damage leading to mutations in a cell. We thus reviewed the current understanding on CRC to show that there is still little known about the effects of dietary compounds on DNA damageinduced repair mechanisms. We suggest that the selective pressures of continuous exposure to a broad diversity of environmental carcinogens in different concentrations and combinations might overwhelm the natural tolerance of protective mechanisms in humans. It might help to clarify the current shifting incidence of CRC from old patients towards a much younger population (Siegel et al., 2014). 2. A brief historical review on environmental carcinogenesis Modern research methods revealed that the King of Naples Ferrante I (1423–1494) endured an invasive colon adenocarcinoma. Based on stable carbon isotope (d13C) and stable nitrogen isotope (d15N) isotope analyses, paleopathologists reported that he had a meat-rich but fish-poor diet, exposing the colon to natural alkylating compounds largely (Ottini et al., 2011). Studying the development of squamous cell carcinoma in chimney sweeps, Sir Percival Pot hypothesized first this connection between environmental factors and cancer in 1775 (Dobson, 1972). About a century and a half later, Whitman suggested that several carcinogenic hits

Fig. 1. Timeline for environmental carcinogenesis and colon cancer. Sir Percivall Pott recognized the role of carcinogens in the development of squamous cell carcinomas in 1775. Spencer (1891) further refined Pott’s initial observations and showed that a genetic susceptibility to the carcinogens present in soot could account for the elevated cancer incidence in some families. Virchow, besides being the father of the modern pathology was also the first to hypothesize in 1855 that cancer stem cells give rise to tumors. A century later, Richards suggested that genetic mutations inducing tumors occur in stem cell niches. Professor Virchow’s assistant Hansemann (1890) observed that an asymmetric epithelial cell division takes place in tumors. Then, Boveri (1902) connected the dots between Hansemann’s previous notes on asymmetric cell division and anaplasia, suggesting the causal role of aneuploidy in cancer. Hansemann’s idea on anaplasia and dedifferentiation yet abetted Whitman (1919) to hypothesize that several carcinogenic hits drive a cell away from its original phenotype, as it becomes mutated. Foulds (1958) suggested that ‘widespread “initiation” can occur without gross or histologic change and that the added stimulus of “promotion” evokes visible focal lesions of varied kinds.' Whitman’s and Foulds’ ideas on cancer initiation indeed lead Ashley and Knudson to build mathematical assumptions on how many carcinogenic hits would be required for tumors to arise. Remarkably, Tyzzer (1916) was first to suggest that the immune system protects the human body against tumors. Fearon and Volgestein hypothesized the adenoma-adenocarcinoma model to explain colon carcinogenesis.

108

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

drive a cell away from its original phenotype, as it becomes genomically mutated (Whitman, 1919). In 1955, Richards then observed that genetic mutations in stem cell niches induce tumors to occur (Richards, 1955), a hypothesis first proposed by Virchow in 1855 (Huntly and Gilliland, 2005). Foulds compressed such background suggesting that the “widespread ‘initiation’ can occur without gross or histologic change and that the added stimulus of ‘promotion’ evokes visible focal lesions of varied kinds” (Foulds, 1958). Whitman’ and Foulds’ ideas on cancer initiation indeed led Ashley and Knudson to hypothesize mathematically the number of carcinogenic hits required to induce a tumor (Ashley, 1969; Knudson, 1971). Neither Ashley nor Knudson was, however, aware that gastric cancer and retinoblastoma have a different etiology. For instance, retinoblastoma is an inheritable disease, whereas gastric cancer is related to either inheritable or somatic mutations. These ideas thus fostered the development of the adenomaadenocarcinoma sequence model (Fearon and Vogelstein, 1990). A timeline shows main discoveries on cancer related to this discussion (Fig. 1). 3. The adenoma-adenocarcinoma sequence model The adenoma-adenocarcinoma hypothesis suggests that a specific genomic mutation induces high proliferative activity and facilitates the acquisition of a malignant phenotype by colonocytes. Because DNA mutations are not the solely event that promotes cancer, proliferation becomes the cornerstone for either cancer initiation or inhibition. Boveri’s ideas, indeed, provided the background to show that aneuploidy hampers an oncogenic adaptive potential in genomically mutated cells, which enables them to survive facing additional DNA damage (Fearon and Vogelstein, 1990; Holland and Cleveland, 2009). Alberici et al. demonstrated that adenomatous polyposis coli (APC) mutations

promote aneuploidy-related chromosomal instability throughout cancer initiation and progression steps (Alberici et al., 2007). Given that Fearon’s and Volgestein’s original words are closely tied to Willet’s notes on environmental factors promoting colon cancer (Willett, 1989), they asked “... In addition to hereditary factors, environmental factors have been shown to be involved in determining colorectal tumor incidence . . . What is the relationship between these environmental factors and the genetic alterations . . . ?” (Fearon and Vogelstein, 1990). 4. Activity of damaging compounds in the colon Little doubt currently remains that dietary compounds increase the risk of colon cancer. Studying the potential for cancer in immigrants moving from low- to high-incidence cancer countries revealed that new dietary habits increased the colon cancer incidence among them (McMichael et al., 1980). Recent reports have shown that 75% of cancers are related to chronic exposure to environmental factors (David and Zimmerman, 2010; Nebert and Dalton, 2006), and colon cancer incidence is increasing in patients with less than 50-years old (Siegel et al., 2014). The International Agency for Research on Cancer reported that the dietary intake of red meat enhances the risk of colon cancer (Bouvard et al., 2015). Interestingly, vegetarians have the lowest risk of this malignancy (Orlich et al., 2015). We should briefly remember the classification of dietary damaging compounds into naturally occurring toxicants (Table 1), cooking-produced carcinogens (Table 2), and synthetic compounds [Table 3; (Carnero et al., 2015; Casey et al., 2015; Engstrom et al., 2015; Hu et al., 2015; Kravchenko et al., 2015; Langie et al., 2015; Nahta et al., 2015; Narayanan et al., 2015; Ochieng et al., 2015; Robey et al., 2015; Thompson et al., 2015)]. For instance, Agent Orange is an herbicide that was used in the Korean-Vietnam

Table 1 Activity of naturally occurring toxicants (NOT) in food. Type

Name

Food source

Toxic concentration

Cancer inducer

Ref

NOT

Acetaldehyde methylformyl-hydrazone Aflatoxin

Gyromitra esculenta

50 mg/kg

Yes

Aspergillus flavus and Aspergillus parasiticus 20 mg/kg

Yes

Agaritine

Agaricus bisporus and Agaricus elvensis

Yes

Amygdalin Asarone

Malus pumila 0.6 g/kg Asarum europaeum, Acorus calamus, Acorus 20,000 ppm gramineus, and Acorus tatarinowii Cinnamomum verum 0.01-3000 ppm Cycas revoluta and Zamia pumila 12.5 mg/g

Anon (1996), Michelot and Toth (1991) Anon (1996), De Ruyck et al. (2015), Schwartzbord et al. (2013) Schulzova et al. (2009), Walton et al. (1997) Anon (1996), Lerner (1981) Anon (1996), Berg et al. (2016)

Benzaldehyde Cycasin Estragole

Goitrin Indole acetonitrile Mycotoxins Ptaquiloside (contamination of water and milk) Safrole Solanin 4-Hydrazino benzoic acid

Ocimum basilicum, Syzygium anisatum, Clausena anisata, Foeniculum vulgare, Pinus sylvestris, Artemisia dracunculus, and Pimpinella anisum Brassica oleracea, Brassica oleracea, and Brassica napus Brassicaceae family Aspergillus genus Leptosporangiate ferns

200-10,000 mg/kg

Yes Yes Yes Yes

0.03–100 ppm

Yes

Imprecise

Yes

Imprecise Yes 0.1–80 ng/kg Yes Detection in the milk of 8.5% from the Yes total amount intook by the animal

Sassafras genus

0.09-4.6 mg/tea cup

Yes

Solanaceae family Agaricus bisporus

0.2 g/kg Imprecise

Yes Yes

Anon (1996), Feron et al. (1991) Kisby et al. (1992), Sieber et al. (1980) Anon (1996), Ding et al. (2015)

Higdon et al. (2007), Luthy et al. (1984) Reddy et al. (1983) Anon (1996) Gomes et al. (2012), Potter and Baird (2000) Carlson and Thompson (1997), Chen et al. (1999) Anon (1996) Anon (1996), Oikawa et al. (2006)

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

109

Table 2 Activity of cooking-produced carcinogens (CPC). Type

Symbol

Name

Food concentration ng/g

Cancer inducer

Ref.

CPC

AaC Acrolein BaP

2-amino-9H-pyridol[2,3-b]indole Propenal Benzo[a]pyrene

0.21–2.50 Imprecise 0.9–36

Yes Yes Yes

0.18–1.40

Yes

Nagao and Sugimura (1993) Stevens and Maier (2008) Nagao and Sugimura (1993), Szterk et al. (2012), Wakabayashi et al. (1992) Nagao and Sugimura (1993), Szterk et al. (2012)

Yes

Nagao and Sugimura (1993), Takayama et al. (1984)

1.78–5.89 0.16–0.19 0.1–0.35 0.13–0.20

Yes Yes Yes Yes Yes

Nagao Szterk Nagao Nagao Nagao

0.64–6.44

Yes

Nagao and Sugimura (1993)

0.39–2.1 0.15–0.57 0.56–69.2

Yes Yes Yes

Szterk et al. (2012) Nagao and Sugimura (1993), Szterk et al. (2012) Nagao and Sugimura (1993)

0.2–42.7

Yes

0.12–0.21

Yes

Nagao and Sugimura (1993), Szterk et al. (2012), Wakabayashi et al. (1992) Nagao and Sugimura (1993)

0.15–0.25

Yes

Nagao and Sugimura (1993)

4,8DiMeIQx Glu-P-1

2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f] quinoxaline 2-amino-6-methyldipyrido[1,2- a:30 ,20 -d] imidazole 2-aminodipyrido[1,2-a:30 ,20 -d]imidazole Glu-P-2 Harmane 1-Methyl- 9H-pyrido[3,4-b]indole IQ 2-amino-3-methylimidazo[4,5-f]quinoline MeAaC 2-amino-3-methyl-9H-pyridol[2,3-b]indole MeIQ 2-amino-3,4-dimethylimidazo[4,5-f] quinoline 2-amino-3,8-dimethylimidazo[4,5-f] MeiQx quinoxaline Norharmane b-Carboline (9H-pyrido[3,4-b]indole) Phe-P-1 2-amino-5-phenylpyridine PhIP 2-amino-L-methyl- 6-phenylimidazo[4,5-b] pyridine Benz[a]anthracene Tetracene

Trp-P-1 Trp-P-2

3-amino-1,4-dimethyl-5H-pyrido[4,3-b] indole 3-amino-1-methyl-5H-pyrido[4,3-b]indole

War and one of many synthetic compounds that increase the incidence of colon cancer (Yi, 2013). Another carcinogenic crop herbicide is the Imazethapyr, which promoted bladder and colon cancers (Koutros et al., 2009). Mycotoxins are natural chemicals produced by fungi living in food crops (Richard, 2007). After these compounds are bioactivated, they react with DNA advancing the formation of many different DNA adducts whereby each one of them requires distinct mechanisms for genomic repair (Jeffrey and Williams, 2005). Aflatoxin also increased the risk of colon cancer in human samples (Harrison et al., 1993). Furthermore, common household cooking methods produce carcinogens at low levels, but prolonged-time and high-temperature cooking practices promote mutagens to levels of 500 parts-per-billion of meat (Turesky, 2007). Hepatic and extrahepatic cytochromes usually activate these compounds in several powerful carcinogens (Magagnotti et al., 2003), which promote DNA adducts, sister chromatid exchange, chromosomal aberrations, microsatellite instability, and mutations in Kirsten rat sarcoma viral oncogene homolog (KRAS), tumor protein p53 (TP53), and APC genes in the colon (Nagao and Sugimura, 1993; Turesky, 2007). Considering the Tables 1–3 seems possible that carcinogens contaminate human food altering the risk of cancer. 5. Genomic mutations in the colon It has recently been suggested that ‘the lifetime risk of colorectal cancer would be very low, . . . , if colonic epithelial stem cells were not constantly dividing’ (Tomasetti and Vogelstein, 2015). It seems that acquisition of mutations in three driver genes is enough to transit a cell from normal towards malignant and invasive phenotypes. Whereas the first hit in a proliferation control-related gene, such as APC, would facilitate that a second strike induces benign tumors (i.e., KRAS), the third and last mutation might produce malignancy and invasion (Vogelstein and Kinzler, 2015). A novel in vitro dataset just provided mechanistic evidence that this sequence of events leads to the development of CRC (Matano et al., 2015). Furthermore, engineering transgenic mice to harbor APC and KRAS mutations in colonic epithelial cells, Fearon’s research group demonstrated that early proliferative

and Sugimura et al. (2012) and Sugimura and Sugimura and Sugimura

(1993), Takayama et al. (1984) (1993), Wakabayashi et al. (1992) (1993), Szterk et al. (2012) (1993), Szterk et al., (2012)

changes take place within the cryptal stem cell niche right after mutations were activated (Feng et al., 2013). Experiments with Pms2cre/creApcCKO/CKO and Lgr5EGFP-IRES-creERT2Apc580S/ 580S mice then revealed that APC mutations are time-dependent and hitchhike in the crypt fission even before a microadenoma develops (Fischer et al., 2014). An R26R-Confetti tracing strategy in the leucine-rich repeat containing G protein-coupled receptor 5 (Lgr5) cellular lineage revealed that KRAS mutations enhance crypt fission, and these cells are potential tumor-initiating units (Snippert et al., 2014). Genomic mutations might rule the cancer initial steps and, thus, the development of colon carcinogenesis [Table 4; (Chang et al., 2016; Ogino et al., 2007; Vogelstein and Kinzler, 2015)]. 6. Effects of DNA damage in cancer initiation DNA repair mechanisms work synchronically to cell-cycle activities (Bieging et al., 2014). Damaging the cellular genome augments exponentially throughout the whole human life in close resemblance to the cancer incidence (de Magalhaes, 2013). Based on a mathematical modeling where human aging was the carcinogenic trigger, Michor and colleagues observed that high mutation rates are related to the worsening of DNA repair mechanisms (Foo et al., 2011). Indeed, DNA double-strand breaks activate the ataxia telangiectasia mutated (ATM)-H2A histone family member X (H2AX)/checkpoint kinase 2 (Chk2)-TP53 pathway even before genomic instability and malignant conversion developed in patients. Although activating the DNA repair delays lesions to develop, the natural selection takes place gearing genomically unstable clones towards proliferation (Bartkova et al., 2005; Foo et al., 2015). Whereas a battle of the body against the survival of DNA-damaged cells might best illustrate the concept of cancer initiation (Bartkova et al., 2005; Bieging et al., 2014; de Magalhaes, 2013; Lobrich and Jeggo, 2007), a cancer initiated cell probably is that unit that escaped its intracellular anticarcinogenic mechanisms, as well as later tissue barriers, against abnormal growth (Foo et al., 2015). Fig. 2 shows the complexity of genomic response activated by DNA damage. We should thus focus on what damages the DNA, as well as how this damage might be processed.

110

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

Table 3 Effects of synthetic compounds in cancer. Chemicals

Hallmarks of cancer

2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane 12-O-tetradecanoylphorbol-13-acetate Acetaminophen Acrolein Acrylamide Atrazine Azamethiphos Benomyl Biphenyl Bisphenol A Butyltins C.I. solvent yellow 14 Cabendazim Carbon Black Chlorothalonil Cobalt Cotinie Cypermethrin DDT Dibutyl phthalate Dichlorvos Diethylhexyl phthalate Diniconazole Fluoxastrobin Folpet Hexachlorobenzene Imazalil Iron Lactofen Lead Lindane Linuronx Maneb Mercury Methoxychlor Methylene bis(thiocyanate) Methylmercury Na-selenite Nickel chloride Nitric oxide Nonylphenol Organophosphates Oxyfluorfen Paraquat Perfluorooctane sulfonate Phosalone Polybrominated diphenyl ethers Pyraclostrobin Pyridaben Quinones Rotenone Sulfur dioxide Titanium dioxide Tributyltin chloride Triclosan Tungsten Vinclozolin Ziram

" # " " " " " " "

" " " " " "

" " " " "

" " " # " " # " " # # " " " " " " "

" "

" "

" #

"

"

" " # "

# " # #

" " " # " " "

"

" " " " " " "

# # # #

#

# # # " "

# # # # # # # #

#

" " " " "

#

"

"

"

" "

"

" " " " " "

" "

#

#

# # #

"

" " " "

# #

"

" "

" #

"

" # " #

"

# # #

" "

" " "

#

" "

"

"

" "

# # #

"

" "

" "

"

"

# " # # " # # # #

" "

" " " # " " " "

" "

# " "

" # # "

" " " " " " # " " " " " " " " " " " " " " " " " " " " " " " " " " " " " # " "

#

" " " " "

" "

" " " "

" " " # " " " " "

"

"

# "

# # "

"

" # "

# "

" " "

" "

" #

# # "

" # " # # # " "

# " "

" #

#

# #

" " #

Chemicals were previously selected by the ‘The Halifax Project’. Genome Instability & Mutation, ; Sustaining Proliferative Signaling, ; Evading Growth Suppressors, Resisting Cell Death, ; Avoiding Immune Destruction, ; Deregulating Cellular Energetics, ; Enabling Replicative Immortality, ; Tumor Promoting Inflammation, Inducing Angiogenesis, ; Activating Invasion & Metastasis, .

7. Understanding the safe genomic code of cancer initiation Whether random genomic errors throughout replication phase might induce intrinsic mutations, extrinsic risk factors promote carcinogenic changes in human DNA. Based on a large collection of human data and well-designed calculations, Hannun and colleagues determined the power of intrinsic and extrinsic factors promoting several types of cancer. Rather than supported by intrinsic factors, the development of CRC is closely tight to the

; ;

effects of extrinsic mutations in at least 70% of cases (Wu et al., 2016). Diet might be one of many external risk factors promoting cancer (McMichael, 2002). Previous authors notably suggested that the correlation between diet and CRC range from 16% to 90% of cases (Aleksandrova et al., 2014; Doll and Peto, 1981; Johnson and Lund, 2007). According to Bernstein and colleagues, following the genomic damage by diet-related compounds, a cell might activate pro-survival stress-response pathways that alter chromosomal stability and activity of mitosis-related mechanisms leading to the

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

111

Table 4 Most common genomic mutations in the colon. Genomic Target

Type of Genomic Mutation

APC

Missense Nonsense

Protein Mutation Transition

Transversion Transition

Missense Deletion Nonsense Deletion Nonsense

KRAS

Transversion Deletion/Deamination Transversion Deletion/Depurination Transversion Transition

Unknown

Transversion Transition

Missense

Transversion Transition Transversion

TP53

Missense

Transversion

Nonsense Missense Transition Nonsense Missense

Nonsense Missense

Transversion Transition Transversion Transition Transversion Transition Transversion Transition Transversion Transition

SMAD4

Nonsense Missense

PIK3CA

Missense

Transversion Transversion Transition

Transversion Transition

c.95A > G c.646C > T c.694C > T c.799G > T c.832C > T c.904C > T c.3907C > T c.3914C > A c.3914delC c.3934G > T c.3935delG c.3944C > A c.3982C > T c.4012C > T c.4031C > A c.465A > G c.573T > C c.1005A > G c.34G > C c.34G > T c.35G > A c.35G > C c.35G > T c.38G > C c.318C > G c.423C > G c.440T > G c.511G > T c.514G > T c.524G > A c.536A > G c.586C > T c.638G > T c.646G > A c.700T > G c.734G > A c.742C > T c.761T > G c.772G > A c.772G > T c.817C > T c.818G > A c.841G > C c.844C > T c.853G > A c.856G > A c.857A > G c.1015G > T c.1067C > G c.1069T > C c.1081C > T c.1624G > A c.1633G > A c.1636C > G c.3140A > G

p.Asn32Ser p.Arg216Stop p.Arg232Stop p.Gly267Stop p.Gln278Stop p.Arg302Stop p.Gln1303Stop p.Ala1305Glu p.Ala1305Glufs p.Gly1312Stop p.Gly1312Glufs p.Ser1315Stop p.Gln1328Stop p.Gln1338Stop p.Ser1344Stop p.Lys155= p.Tyr191= p.Leu335= p.Gly12Cys p.Gly12Ser p.Gly12Ala p.Gly12Asp p.Gly12Val p.Gly13Asp p.Ser106Arg p.Cys141Trp p.Val147Gly p.Glu171Stop p.Val172Phe p.Arg175His p.His179Arg p.Arg196Stop p.Arg213Leu p.Val216Met p.Tyr234Asp p.Gly245Asp p.Arg248Trp p.Ile254Ser p.Glu258Lys p.Glu258Stop p.Arg273Cys p.Arg273His p.Asp281His p.Arg282Trp p.Glu285Lys p.Glu286Lys p.Glu286Gly p.Glu339Stop p.Pro356Arg p.Ser357Pro p.Arg361Cys p.Glu542Lys p.Glu545Lys p.Gln546Lys p.His1047Arg

Mutations found in 103 patients diagnosed with colorectal cancer, and previously reported by Chang et al. (2016). Targeted genes were selected according to Vogelstein and Kinzler (2015). Selected mutations were classified as reported by Ogino et al. (2007).

acquisition of genomic fluidity, in a Darwinian selection-dependent manner (Payne et al., 2008). Additionally, Swanton and colleagues provided a remarkable collection of experimental data that DNA damage repair (DDR) mechanisms must protect the genome against mutations before natural selection drives genomically unstable clones on towards proliferation (Dewhurst et al., 2014). If genomic instability, an event that occurs in mutated cells, promotes adaptive potential in cancer-initiating cells, enabling them to endure more DNA damage and survive (Holland and Cleveland, 2009), one of the earliest carcinogenic events could be the occurrence of light-genomic damage events that fails to activate either apoptosis or intracellular repair mechanisms (Baker et al., 2013; Dewhurst et al., 2014).

Although DDR activity during early cell-cycle phases protects from cancer, genomic damage-induced DDR activation throughout mitosis hampers aneuploidy in a cell because impaired chromosome segregation promotes telomere fusion (Bartkova et al., 2005). Chromosomal instability could even promote tetraploidy at an early tumorigenic stage (Shackney et al., 1989). Tetraploid cells can arise from a variety of mechanisms, including mitotic slippage, cytokinetic failure, and virus-induced cell fusion. It seems probable that the abnormal segregation of chromosomes that leads to aneuploidy as tetraploid cells proliferate may not only be better tolerated than their diploid progenitors, but the process of tetraploidization may itself facilitate further genetic changes leading to more aggressive aneuploid cancers. Aneuploidy is thus

112

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

Fig. 2. Proliferation and DNA damage response. High-proliferation favours the frequency of DNA damage in a cell. Either activation or inactivation of the DNA damage response (DDR) hangs on the intensity of the DNA damage. Whereas a successful DDR activation averts a cell from malignant transformation (that cell could either undergo apoptosis or have its DNA repaired), its failure promotes development of cancer. DNA mutations render the cell genome unstable before malignant transformation takes place, since cellular defence mechanisms would not be as effective as they were before and the genome would be prone to easily process errors. Aneuploidy is thus a known feature in tumors. Two types of DNA damage activates two main DDR pathways: single-strand breaks (SSBs) promotes the phosphorylation of ataxia telangiectasia and Rad3 related (ATR) by the activation of its upstream elements named ATR-interacting protein (ATRIP), HUS1 checkpoint homolog (HUS1), and replication protein A (RPA), whilst doublestrand breaks (DSBs) activates ataxia telangiectasia mutated (ATM) through the phosphorylation of its upstream proteins nibrin (NBS1), meiotic recombination 11 (MRE11), and GTP-binding proteins (RADs). DSB-related phosphorylation of that H2A histone family member X (gH2AX) promotes the activation of both ATM and ATR pathways. Although ATR signalling is mainly related to the checkpoint kinase 1 (CHK1) phosphorylation, whereas ATM activates CHK2, both pathways rely on several transducer elements for the activation of those proteins (CHK1/2), named: DNA topoisomerase 2-binding protein 1 (TOPBP1), breast cancer 1 (BRCA1), mediator of DNA-damage checkpoint 1 (MDC1), tumor suppressor p53-binding protein 1 (53BP1), and ring finger protein 8 (RNF8). CHK1/2 could induce either a direct apoptosis or a cell-cycle checkpoint arrest, which could be reinforced by 53BP1/CHK2 signalling on the tumor protein 53 (TP53). Considering that repaired DNA enables a cell to undergo mitosis, an unrepaired genome could promote either apoptosis or genomic instability. Such a fate is settled by the activation of the complex polo-like kinase 1 (PLK1), cyclin-dependent kinase 1 (CDK1), replication timing regulatory factor 1 (RIF1), and Aurora B kinase (AURKB) through DNA damage-related signalling that yet promotes the inhibition of 53BP1, RNF8, and TP53. AURKB has a pivotal role in promoting tumors, since it inhibits the shelterin complex (which protects telomeres from fusion) from promoting genomic instability, which facilitates the tumor development.

related to the genomic instability that facilitates cancer initiation and development (Orthwein et al., 2014). For instance, increased number of tetraploid cells has been related to a less favorable outcome in colon cancer (Dewhurst et al., 2014). Aneuploidization has, however, been restrained by budding uninhibited by benzimidazoles 1-related kinase (BubR1), which is a crucial surveillance piece in the spindle-assembly checkpoint controlling chromosome segregation. Whereas inhibiting BubR1 gene expression induced premature cellular senescence, microtubule-kinetochore attachment defects leading to chromosome missegregation, and aneuploidy, mice overexpressing BubR1 showed reduced signs of aging and cancer (Baker et al., 2013). Aneuploidy has been found enhanced in the progeny of tetraploid

cells, in which the whole-genome was doubled, and genomic instability increased (Dewhurst et al., 2014). Also, growth factors can increase proliferation that disposes an even larger number of cells to the formation of double-strand break (DSB) foci, from which either proliferation-related events or genome-damaging compounds could easily induce genomic instability and cancer initiation (Nikolova et al., 2012; Orthwein et al., 2014). Hence, red meat cooked at high temperatures, rich in carcinogens such as polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs), increased the risk of colon cancer by impairing nucleotide excision repair (NER) through nonsynonymous single nucleotide polymorphisms (nsSNPs) in its molecular elements (Steck et al., 2014). A recent investigation

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

revealed that persistent organic pollutants (POPs) unbalance DDR mechanisms in humans, mainly that nonhomologous end-joining (NHEJ) pathway induced by DSB (He et al., 2015). Environmental carcinogens such as PAHs have been demonstrated to promote hypomethylation in non-smoking coke oven workers (Pavanello et al., 2010). HCAs were also found promoting microsatellite instability (MSI) in sporadic colon cancer patients (Wu et al., 2001). Bayani et al. helped to clarify this idea suggesting that interactions between cumulative DNA damage and epigenetic changes, i.e. either hyper- or hypomethylation, promote the development of structural chromosomal instability [(S)-CIN] at first and malignant transformation afterward (Bayani et al., 2007). In colon cancer, DNA hypomethylation preceded (S)-CIN (Rodriguez et al., 2006). Understanding some potential interactions among diet, genomic damage, and the activity of DDR in the intestinal colon helps to clarify some current ideas. 8. Effects of cell-cycle and genomic repair mechanisms on cancer Although it is quite clear that proliferation is the key event in which mutations happen (Lawrence et al., 2013; Tomasetti and Vogelstein, 2015), proven that diet impacts on it are not that simple. For instance, Zoetendal and colleagues demonstrated that as much as African-Americans have a higher risk of CRC than South Africans their high intestinal proliferation index was reduced altering their diet to a South African style, which decreased their risk for CRC (O'Keefe et al., 2015). Previously, we reported that either food restriction or high-fat diet increases the risk of CRC. Fat, besides to induce stronger carcinogenic effects than malnutrition, promoted proliferation of carcinogenically exposed cells (Kannen et al., 2013, 2014, 2012). We should, however, notice that fat remains unproven to damage the DNA directly, but rather it promotes cancer triggering alternative procarcinogenic mechanisms, such as immunological deregulation and dysbiosis (Schulz et al., 2014). Hence, benzo[a]pyrene (BaP), which is a PAH, seems to be a good example of dietary carcinogens promoting genomic damage. Diggs et al. analyzed data from 22 developed and developing countries and suggested that the mean daily intake of BaP was about 1.3  2.6 mg per person (Diggs et al., 2011). PAHs are metabolically activated by cytochrome P450 (CYP; types 1A1/2 and 1B1) before a second phase metabolism finally delivers the ultimate carcinogen that directly binds to DNA mutating it. Indeed, BaP seemed to promote DNA damage and alter HR and NHEJ pathways in vitro and in vivo models (Tung et al., 2014). Classified as an HCA, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) also induced DNA adducts (PhIP-C8-dG) in the colon of exposed mice. Notably, the transformation related protein 53 (Trp53) modulated this event (Krais et al., 2016). Because DNA damage usually occurs in the cryptal stem cell niche, the failure of cell-cycle checkpoints will potentially enable mutations to induce tumor-initiating cells (O'Brien et al., 2012; Vermeulen and Snippert, 2014). Indeed, cyclin D2 (Ccnd2)- cyclindependent kinase (Cdk) 4/6 complexes hyperphosphorylate retinoblastoma protein (RB) proteins allowing the progression of intestinal Apc-mutated cells throughout the G1/S cell cycle phase (Cole et al., 2010). During the G2/M genomic repair by the homologous recombination (HR) pathway, the heterozygous but not homozygous loss of that checkpoint kinase 1 (Chk1) promoted intestinal tumors to develop (Greenow et al., 2014). Either induction or suppression of HR events, triggered by inherited or somatic genomic mutations, have been both related to genomic instability in tumor-initiating cells (Sukup-Jackson et al., 2014). Given that mutation in APC promotes either inherited or sporadic colon cancers (Cancer Genome Atlas, 2012), the gene sequence encoding APC proteins was shown to undergo higher

113

Fig. 3. DNA damage, cell cycle and cancer. This hypothetical graph illustrates that DNA damage response (DDR) effectively repairs genomically damaged sites throughout G1/S rather than G2/M cell-cycle phases. Damaging the DNA in late cell-cycle phases would thus enhance the chances of cancer initiation to succeed.

levels of DNA damage than TP53 in colonocytes but not in a tumor cell line (Glei et al., 2007). After DNA damage, transcription of the APC encoding gene was found dependent on the activity of TP53, since knocking out strategies on it decreased APC gene expression in cells exposed to an alkylating agent (Jaiswal and Narayan, 1998). Whether losing the Trp53 activity has been shown to enhance the survival of DNA-damaged cells during the colon cancer initiation (Schwitalla et al., 2013), reactivation of its endogenous activity in Trp53-deficient aggressive liver carcinoma revealed that it upregulates inflammatory cytokines triggering an immune response against cancer (Xue et al., 2007). The ATM-related DNA damaging/repair response was not only shown to arrest the cell cycle for genetic repair but also to induce the expression of killer cell lectin-like receptor subfamily K (NKG2D) ligands that signal potential cellular threats to be killed by immune cells (Gasser et al., 2005). Moreover, mutations in ATPdependent DNA helicase (Ku-70)/NHEJ factor and Trp53 have recently been found to promote the b-catenin nuclear activity that leads to high-epithelial cellular proliferation, chronic inflammation, and tumorigenesis (Puebla-Osorio et al., 2014). Tschopp and colleagues revealed that TP53-inducible death-domain-containing protein (PIDD) promotes genotoxic-stress-induced nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-kB) activation and cell survival after genomic damage (Janssens et al., 2005). Whether dietary compounds might impact directly on the initial phases of colon carcinogenesis, their effects on G2/M genomic repair mechanisms should be better explored (Fig. 3). 9. Conclusion Taken together, the natural tolerance of intrinsic protective cellular and systemic mechanisms seems to be prey to particular levels and timing of carcinogenic environmental insults. It seems plausible that: (1) if DNA damage occurs in the late G1 phase, but not in its early steps, checkpoint activity fails to detect genomic errors allowing the cell cycle to progress towards its S phase (Deckbar et al., 2010); (2) G2/M checkpoints and repair mechanisms are only activated after a certain DNA damage threshold is bypassed (Deckbar et al., 2007); (3) weakly expressed genes are amplified late in the cell cycle and prone to undergo mutation (Lawrence et al., 2013; Sulli et al., 2012); (4) reactivation of DNA repair throughout the M phase promotes genomic instability (Orthwein et al., 2014); and, (5) genomically mutated cells might induce changes in the tissue microenvironment enabling their survival and expansion. Indeed, diet provides a significant number of mixed chemicals that could promote the perfect condition for cancer development, as well as it is the most direct route by which harmful compounds access the human body. This combined effect of multiple low doses of dietary carcinogens seems to promote

114

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

genomic damage, building the perfect niche that cancer-initiating cells can survive and expand. It is possible that cumulative genotoxic and non-genotoxic exposures to multiple compounds might induce DNA damages or methylation alterations in such lowintensity that would not be enough to activate genomic protective components. A better understanding of both the cellular causes and the long-term consequences of genomic damage from diet and our environment is urgently needed, which requires new experimental approaches to detail how environmental carcinogens impact cell-cycle control and promote colon cancer in the human population. Conflict of interest statement The authors have no conflicts of interest to disclosure. Acknowledgements The authors also disclose receipt of financial support for the development of this investigation from the following organizations: the National Council for Scientific and Technological Development (CNPQ; 443376/2014-0) and the Sao Paulo Research Foundation (FAPESP; 2014/06428-5). The funders had no role in the study design, decision to publish, or preparation of the manuscript. References Alberici, P., de Pater, E., Cardoso, J., Bevelander, M., Molenaar, L., Jonkers, J., Fodde, R., 2007. Aneuploidy arises at early stages of Apc-driven intestinal tumorigenesis and pinpoints conserved chromosomal loci of allelic imbalance between mouse and human. Am. J. Pathol. 170, 377–387. Aleksandrova, K., Pischon, T., Jenab, M., Bueno-de-Mesquita, H.B., Fedirko, V., Norat, T., Romaguera, D., Knuppel, S., Boutron-Ruault, M.C., Dossus, L., Dartois, L., Kaaks, R., Li, K., Tjonneland, A., Overvad, K., Quiros, J.R., Buckland, G., Sanchez, M. J., Dorronsoro, M., Chirlaque, M.D., Barricarte, A., Khaw, K.T., Wareham, N.J., Bradbury, K.E., Trichopoulou, A., Lagiou, P., Trichopoulos, D., Palli, D., Krogh, V., Tumino, R., Naccarati, A., Panico, S., Siersema, P.D., Peeters, P.H., Ljuslinder, I., Johansson, I., Ericson, U., Ohlsson, B., Weiderpass, E., Skeie, G., Borch, K.B., Rinaldi, S., Romieu, I., Kong, J., Gunter, M.J., Ward, H.A., Riboli, E., Boeing, H., 2014. Combined impact of healthy lifestyle factors on colorectal cancer: a large European cohort study. BMC Med. 12, 168. 1996. Carcinogens and Anticarcinogens in the Human Diet: A Comparison of Naturally Occurring and Synthetic Substances, Washington (DC). Arnold, M., Sierra, M.S., Laversanne, M., Soerjomataram, I., Jemal, A., Bray, F., 2016. Global patterns and trends in colorectal cancer incidence and mortality. Gut Epub ahead of print. Ashley, D.J., 1969. The two hit and multiple hit theories of carcinogenesis. Br. J. Cancer 23, 313–328. Baker, D.J., Dawlaty, M.M., Wijshake, T., Jeganathan, K.B., Malureanu, L., van Ree, J.H., Crespo-Diaz, R., Reyes, S., Seaburg, L., Shapiro, V., Behfar, A., Terzic, A., van de Sluis, B., van Deursen, J.M., 2013. Increased expression of BubR1 protects against aneuploidy and cancer and extends healthy lifespan. Nat. Cell Biol. 15, 96–102. Bartkova, J., Horejsi, Z., Koed, K., Kramer, A., Tort, F., Zieger, K., Guldberg, P., Sehested, M., Nesland, J.M., Lukas, C., Orntoft, T., Lukas, J., Bartek, J., 2005. DNA damage response as a candidate anti-cancer barrier in early human tumorigenesis. Nature 434, 864–870. Bayani, J., Selvarajah, S., Maire, G., Vukovic, B., Al-Romaih, K., Zielenska, M., Squire, J. A., 2007. Genomic mechanisms and measurement of structural and numerical instability in cancer cells. Semin.Cancer Biol. 17, 5–18. Berg, K., Bischoff, R., Stegmuller, S., Cartus, A., Schrenk, D., 2016. Comparative investigation of the mutagenicity of propenylic and allylic asarone isomers in the Ames fluctuation assay. Mutagenesis 31, 443–451. Bieging, K.T., Mello, S.S., Attardi, L.D., 2014. Unravelling mechanisms of p53mediated tumour suppression. Nat. Rev. Cancer 14, 359–370. Bouvard, V., Loomis, D., Guyton, K.Z., Grosse, Y., Ghissassi, F.E., Benbrahim-Tallaa, L., Guha, N., Mattock, H., Straif, K., International Agency for Research on Cancer Monograph Working, G., 2015. Carcinogenicity of consumption of red and processed meat. Lancet Oncol. 16, 1599–1600. Cancer Genome Atlas, N., 2012. Comprehensive molecular characterization of human colon and rectal cancer. Nature 487, 330–337. Carlson, M., Thompson, R.D., 1997. Liquid chromatographic determination of safrole in sassafras-derived herbal products. J. AOAC Int. 80, 1023–1028. Carnero, A., Blanco-Aparicio, C., Kondoh, H., Lleonart, M.E., Martinez-Leal, J.F., Mondello, C., Ivana Scovassi, A., Bisson, W.H., Amedei, A., Roy, R., Woodrick, J., Colacci, A., Vaccari, M., Raju, J., Al-Mulla, F., Al-Temaimi, R., Salem, H.K., Memeo, L., Forte, S., Singh, N., Hamid, R.A., Ryan, E.P., Brown, D.G., Wise Sr., J.P., Wise, S.S.,

Yasaei, H., 2015. Disruptive chemicals, senescence and immortality. Carcinogenesis 36 (Suppl. 1), S19–S37. Casey, S.C., Vaccari, M., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Barcellos-Hoff, M.H., Brown, D.G., Chapellier, M., Christopher, J., Curran, C., Forte, S., Hamid, R.A., Heneberg, P., Koch, D.C., Krishnakumar, P.K., Laconi, E., Maguer-Satta, V., Marongiu, F., Memeo, L., Mondello, C., Raju, J., Roman, J., Roy, R., Ryan, E.P., Ryeom, S., Salem, H.K., Scovassi, A.I., Singh, N., Soucek, L., Vermeulen, L., Whitfield, J.R., Woodrick, J., Colacci, A., Bisson, W.H., Felsher, D.W., 2015. The effect of environmental chemicals on the tumor microenvironment. Carcinogenesis 36 (Suppl. 1), S160–183. Chang, Y.C., Chang, J.G., Liu, T.C., Lin, C.Y., Yang, S.F., Ho, C.M., Chen, W.T., Chang, Y.S., 2016. Mutation analysis of 13 driver genes of colorectal cancer-related pathways in Taiwanese patients. World J. Gastroenterol. 22, 2314–2325. Chen, C.L., Chi, C.W., Chang, K.W., Liu, T.Y., 1999. Safrole-like DNA adducts in oral tissue from oral cancer patients with a betel quid chewing history. Carcinogenesis 20, 2331–2334. Cole, A.M., Myant, K., Reed, K.R., Ridgway, R.A., Athineos, D., Van den Brink, G.R., Muncan, V., Clevers, H., Clarke, A.R., Sicinski, P., Sansom, O.J., 2010. Cyclin D2cyclin-dependent kinase 4/6 is required for efficient proliferation and tumorigenesis following Apc loss. Cancer Res. 70, 8149–8158. David, A.R., Zimmerman, M.R., 2010. Cancer: an old disease, a new disease or something in between? Nat. Rev. Cancer 10, 728–733. De Ruyck, K., De Boevre, M., Huybrechts, I., De Saeger, S., 2015. Dietary mycotoxins, co-exposure, and carcinogenesis in humans: short review. Mutat. Res. Rev. Mutat. Res. 766, 32–41. Deckbar, D., Birraux, J., Krempler, A., Tchouandong, L., Beucher, A., Walker, S., Stiff, T., Jeggo, P., Lobrich, M., 2007. Chromosome breakage after G2 checkpoint release. J. Cell Biol. 176, 749–755. Deckbar, D., Stiff, T., Koch, B., Reis, C., Lobrich, M., Jeggo, P.A., 2010. The limitations of the G1-S checkpoint. Cancer Res. 70, 4412–4421. Dewhurst, S.M., McGranahan, N., Burrell, R.A., Rowan, A.J., Gronroos, E., Endesfelder, D., Joshi, T., Mouradov, D., Gibbs, P., Ward, R.L., Hawkins, N.J., Szallasi, Z., Sieber, O.M., Swanton, C., 2014. Tolerance of whole-genome doubling propagates chromosomal instability and accelerates cancer genome evolution. Cancer Discov. 4, 175–185. Diggs, D.L., Huderson, A.C., Harris, K.L., Myers, J.N., Banks, L.D., Rekhadevi, P.V., Niaz, M.S., Ramesh, A., 2011. Polycyclic aromatic hydrocarbons and digestive tract cancers: a perspective. J. Environ. Sci. Health C Environ. Carcinog. Ecotoxicol. Rev. 29, 324–357. Ding, W., Levy, D.D., Bishop, M.E., Pearce, M.G., Davis, K.J., Jeffrey, A.M., Duan, J.D., Williams, G.M., White, G.A., Lyn-Cook, L.E., Manjanatha, M.G., 2015. In vivo genotoxicity of estragole in male F344 rats. Environ. Mol. Mutagen. 56, 356–365. Dobson, J., 1972. Percivall pott. Ann. R. Coll. Surg. Engl. 50, 54–65. Doll, R., Peto, R., 1981. The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today. J. Natl. Cancer Inst. 66, 1191–1308. Engstrom, W., Darbre, P., Eriksson, S., Gulliver, L., Hultman, T., Karamouzis, M.V., Klaunig, J.E., Mehta, R., Moorwood, K., Sanderson, T., Sone, H., Vadgama, P., Wagemaker, G., Ward, A., Singh, N., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Colacci, A.M., Vaccari, M., Mondello, C., Scovassi, A.I., Raju, J., Hamid, R.A., Memeo, L., Forte, S., Roy, R., Woodrick, J., Salem, H.K., Ryan, E.P., Brown, D.G., Bisson, W.H., 2015. The potential for chemical mixtures from the environment to enable the cancer hallmark of sustained proliferative signalling. Carcinogenesis 36 (Suppl. 1), S38–60. Fearon, E.R., Vogelstein, B., 1990. A genetic model for colorectal tumorigenesis. Cell 61, 759–767. Feng, Y., Sentani, K., Wiese, A., Sands, E., Green, M., Bommer, G.T., Cho, K.R., Fearon, E. R., 2013. Sox9 induction, ectopic Paneth cells, and mitotic spindle axis defects in mouse colon adenomatous epithelium arising from conditional biallelic Apc inactivation. Am. J. Pathol. 183, 493–503. Feron, V.J., Til, H.P., de Vrijer, F., Woutersen, R.A., Cassee, F.R., van Bladeren, P.J., 1991. Aldehydes: occurrence, carcinogenic potential, mechanism of action and risk assessment. Mutat. Res. 259, 363–385. Fischer, J.M., Schepers, A.G., Clevers, H., Shibata, D., Liskay, R.M., 2014. Occult progression by Apc-deficient intestinal crypts as a target for chemoprevention. Carcinogenesis 35, 237–246. Foo, J., Leder, K., Michor, F., 2011. Stochastic dynamics of cancer initiation. Phys. Biol. 8, 015002. Foo, J., Liu, L.L., Leder, K., Riester, M., Iwasa, Y., Lengauer, C., Michor, F., 2015. An evolutionary approach for identifying driver mutations in colorectal cancer. PLoS Comput. Biol. 11, e1004350. Foulds, L., 1958. The natural history of cancer. J. Chronic Dis. 8, 2–37. Frajacomo, F.T., de Paula Garcia, W., Fernandes, C.R., Garcia, S.B., Kannen, V., 2014. Pineal gland function is required for colon antipreneoplastic effects of physical exercise in rats. Scand. J. Med. Sci. Sports 25, e451–458. Gasser, S., Orsulic, S., Brown, E.J., Raulet, D.H., 2005. The DNA damage pathway regulates innate immune system ligands of the NKG2D receptor. Nature 436, 1186–1190. Glei, M., Schaeferhenrich, A., Claussen, U., Kuechler, A., Liehr, T., Weise, A., Marian, B., Sendt, W., Pool-Zobel, B.L., 2007. Comet fluorescence in situ hybridization analysis for oxidative stress-induced DNA damage in colon cancer relevant genes. Toxicol. Sci. 96, 279–284. Gomes, J., Magalhaes, A., Michel, V., Amado, I.F., Aranha, P., Ovesen, R.G., Hansen, H. C., Gartner, F., Reis, C.A., Touati, E., 2012. Pteridium aquilinum and its ptaquiloside toxin induce DNA damage response in gastric epithelial cells, a link with gastric carcinogenesis. Toxicol. Sci. 126, 60–71.

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116 Greenow, K.R., Clarke, A.R., Williams, G.T., Jones, R., 2014. Wnt-driven intestinal tumourigenesis is suppressed by Chk1 deficiency but enhanced by conditional haploinsufficiency. Oncogene 33, 4089–4096. Harrison, J.C., Carvajal, M., Garner, R.C., 1993. Does aflatoxin exposure in the United Kingdom constitute a cancer risk? Environ. Health Perspect. 99, 99–105. He, X., Jing, Y., Wang, J., Li, K., Yang, Q., Zhao, Y., Li, R., Ge, J., Qiu, X., Li, G., 2015. Significant accumulation of persistent organic pollutants and dysregulation in multiple DNA damage repair pathways in the electronic-waste-exposed populations. Environ. Res. 137, 458–466. Higdon, J.V., Delage, B., Williams, D.E., Dashwood, R.H., 2007. Cruciferous vegetables and human cancer risk: epidemiologic evidence and mechanistic basis. Pharmacol. Res. 55, 224–236. Holland, A.J., Cleveland, D.W., 2009. Boveri revisited: chromosomal instability, aneuploidy and tumorigenesis. Nat. Rev. Mol. Cell Biol. 10, 478–487. Hu, Z., Brooks, S.A., Dormoy, V., Hsu, C.W., Hsu, H.Y., Lin, L.T., Massfelder, T., Rathmell, W.K., Xia, M., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Brown, D.G., Prudhomme, K.R., Colacci, A., Hamid, R.A., Mondello, C., Raju, J., Ryan, E.P., Woodrick, J., Scovassi, A.I., Singh, N., Vaccari, M., Roy, R., Forte, S., Memeo, L., Salem, H.K., Lowe, L., Jensen, L., Bisson, W.H., Kleinstreuer, N., 2015. Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: focus on the cancer hallmark of tumor angiogenesis. Carcinogenesis 36 (Suppl. 1), S184–202. Huntly, B.J., Gilliland, D.G., 2005. Leukaemia stem cells and the evolution of cancerstem-cell research. Nat. Rev. Cancer 5, 311–321. Jaiswal, A.S., Narayan, S., 1998. Protein synthesis and transcriptional inhibitors control N-methyl-N'-nitro-N-nitrosoguanidine-induced levels of APC mRNA in a p53-dependent manner. Int. J. Oncol. 13, 733–740. Janssens, S., Tinel, A., Lippens, S., Tschopp, J., 2005. PIDD mediates NF-kappaB activation in response to DNA damage. Cell 123, 1079–1092. Jeffrey, A.M., Williams, G.M., 2005. Risk assessment of DNA-reactive carcinogens in food. Toxicol. Appl. Pharmacol. 207, 628–635. Johnson, I.T., Lund, E.K., 2007. Review article: nutrition, obesity and colorectal cancer. Aliment. Pharmacol. Ther. 26, 161–181. Kannen, V., Zanette, D.L., Fernandes, C.R., Ferreira, F.R., Marini, T., Carvalho, M.C., Brandao, M.L., Elias Junior, J., Mauad, F.M., Silva Jr., W.A., Stopper, H., Garcia, S.B., 2012. High-fat diet causes an imbalance in the colonic serotonergic system promoting adipose tissue enlargement and dysplasia in rats. Toxicol. Lett. 213, 135–141. Kannen, V., Fernandes, C.R., Stopper, H., Zanette, D.L., Ferreira, F.R., Frajacomo, F.T., Carvalho, M.C., Brandao, M.L., Elias Junior, J., Jordao Junior, A.A., Uyemura, S.A., Waaga-Gasser, A.M., Garcia, S.B., 2013. Colon preneoplasia after carcinogen exposure is enhanced and colonic serotonergic system is suppressed by food deprivation. Toxicology 312, 123–131. Kannen, V., Moreira, M.C., Waaga-Gasser, A.M., Modiano, P., Elias Junior, J., Fernandes, C.R., Garcia, S.B., 2014. Partial lipectomy reduces dimethylhydrazineinduced carcinogenic initiation in the colon of rats. Toxicology 316, 9–13. Kisby, G.E., Ellison, M., Spencer, P.S., 1992. Content of the neurotoxins cycasin (methylazoxymethanol beta-D-glucoside) and BMAA (beta-N-methylamino-Lalanine) in cycad flour prepared by Guam Chamorros. Neurology 42, 1336–1340. Knudson Jr., A.G., 1971. Mutation and cancer: statistical study of retinoblastoma. Proc. Natl. Acad. Sci. U. S. A. 68, 820–823. Koutros, S., Lynch, C.F., Ma, X., Lee, W.J., Hoppin, J.A., Christensen, C.H., Andreotti, G., Freeman, L.B., Rusiecki, J.A., Hou, L., Sandler, D.P., Alavanja, M.C., 2009. Heterocyclic aromatic amine pesticide use and human cancer risk: results from the U.S. Agric. Health Stud. Int J. Cancer 124, 1206–1212. Krais, A.M., Speksnijder, E.N., Melis, J.P., Singh, R., Caldwell, A., Gamboa da Costa, G., Luijten, M., Phillips, D.H., Arlt, V.M., 2016. Metabolic activation of 2-amino-1methyl-6-phenylimidazo [4,5-b]pyridine and DNA adduct formation depends on p53: Studies in Trp53(+/+),Trp53(+/) and Trp53(-/-) mice. Int. J. Cancer 138, 976–982. Kravchenko, J., Corsini, E., Williams, M.A., Decker, W., Manjili, M.H., Otsuki, T., Singh, N., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Colacci, A.M., Vaccari, M., Mondello, C., Scovassi, A.I., Raju, J., Hamid, R.A., Memeo, L., Forte, S., Roy, R., Woodrick, J., Salem, H.K., Ryan, E.P., Brown, D.G., Bisson, W.H., Lowe, L., Lyerly, H.K., 2015. Chemical compounds from anthropogenic environment and immune evasion mechanisms: potential interactions. Carcinogenesis 36 (Suppl.1), S111–127. Langie, S.A., Koppen, G., Desaulniers, D., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Azqueta, A., Bisson, W.H., Brown, D., Brunborg, G., Charles, A.K., Chen, T., Colacci, A., Darroudi, F., Forte, S., Gonzalez, L., Hamid, R.A., Knudsen, L.E., Leyns, L., Lopez de Cerain Salsamendi, A., Memeo, L., Mondello, C., Mothersill, C., Olsen, A.K., Pavanello, S., Raju, J., Rojas, E., Roy, R., Ryan, E., Ostrosky-Wegman, P., Salem, H. K., Scovassi, I., Singh, N., Vaccari, M., Van Schooten, F.J., Valverde, M., Woodrick, J., Zhang, L., van Larebeke, N., Kirsch-Volders, M., Collins, A.R., 2015. Causes of genome instability: the effect of low dose chemical exposures in modern society. Carcinogenesis 36 (Suppl. 1), S61–S88. Lawrence, M.S., Stojanov, P., Polak, P., Kryukov, G.V., Cibulskis, K., Sivachenko, A., Carter, S.L., Stewart, C., Mermel, C.H., Roberts, S.A., Kiezun, A., Hammerman, P.S., McKenna, A., Drier, Y., Zou, L., Ramos, A.H., Pugh, T.J., Stransky, N., Helman, E., Kim, J., Sougnez, C., Ambrogio, L., Nickerson, E., Shefler, E., Cortes, M.L., Auclair, D., Saksena, G., Voet, D., Noble, M., DiCara, D., Lin, P., Lichtenstein, L., Heiman, D. I., Fennell, T., Imielinski, M., Hernandez, B., Hodis, E., Baca, S., Dulak, A.M., Lohr, J., Landau, D.A., Wu, C.J., Melendez-Zajgla, J., Hidalgo-Miranda, A., Koren, A., McCarroll, S.A., Mora, J., Lee, R.S., Crompton, B., Onofrio, R., Parkin, M., Winckler, W., Ardlie, K., Gabriel, S.B., Roberts, C.W., Biegel, J.A., Stegmaier, K., Bass, A.J., Garraway, L.A., Meyerson, M., Golub, T.R., Gordenin, D.A., Sunyaev, S., Lander, E.

115

S., Getz, G., 2013. Mutational heterogeneity in cancer and the search for new cancer-associated genes. Nature 499, 214–218. Layton, D.W., Bogen, K.T., Knize, M.G., Hatch, F.T., Johnson, V.M., Felton, J.S., 1995. Cancer risk of heterocyclic amines in cooked foods: an analysis and implications for research. Carcinogenesis 16, 39–52. Lerner, I.J., 1981. Laetrile: a lesson in cancer quackery. CA Cancer J. Clin. 31, 91–95. Lobrich, M., Jeggo, P.A., 2007. The impact of a negligent G2/M checkpoint on genomic instability and cancer induction. Nat. Rev. Cancer 7, 861–869. Luthy, J., Carden, B., Friederich, U., Bachmann, M., 1984. Goitrin–a nitrosatable constitutent of plant foodstuffs. Experientia 40, 452–453. Magagnotti, C., Pastorelli, R., Pozzi, S., Andreoni, B., Fanelli, R., Airoldi, L., 2003. Genetic polymorphisms and modulation of 2-amino-1-methyl-6phenylimidazo[4,5-b]pyridine (PhIP)-DNA adducts in human lymphocytes. Int. J. Cancer 107, 878–884. Matano, M., Date, S., Shimokawa, M., Takano, A., Fujii, M., Ohta, Y., Watanabe, T., Kanai, T., Sato, T., 2015. Modeling colorectal cancer using CRISPR-Cas9-mediated engineering of human intestinal organoids. Nat. Med. 21, 256–262. McMichael, A.J., McCall, M.G., Hartshorne, J.M., Woodings, T.L., 1980. Patterns of gastro-intestinal cancer in European migrants to Australia: the role of dietary change. Int. J. Cancer 25, 431–437. McMichael, A.J., 2002. A global perspective on food, environment and health, with particular reference to diet and cancer. IARC Sci. Publ. 156, 525–530. Michelot, D., Toth, B., 1991. Poisoning by Gyromitra esculenta–a review. J. Appl. Toxicol. 11, 235–243. Nagao, M., Sugimura, T., 1993. Carcinogenic factors in food with relevance to colon cancer development. Mutat. Res. 290, 43–51. Nahta, R., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Andrade-Vieira, R., Bay, S.N., Brown, D.G., Calaf, G.M., Castellino, R.C., Cohen-Solal, K.A., Colacci, A., Cruickshanks, N., Dent, P., Di Fiore, R., Forte, S., Goldberg, G.S., Hamid, R.A., Krishnan, H., Laird, D.W., Lasfar, A., Marignani, P.A., Memeo, L., Mondello, C., Naus, C.C., Ponce-Cusi, R., Raju, J., Roy, D., Roy, R., Ryan, E.P., Salem, H.K., Scovassi, A.I., Singh, N., Vaccari, M., Vento, R., Vondracek, J., Wade, M., Woodrick, J., Bisson, W.H., 2015. Mechanisms of environmental chemicals that enable the cancer hallmark of evasion of growth suppression. Carcinogenesis 36 (Suppl. 1), S2–18. Narayanan, K.B., Ali, M., Barclay, B.J., Cheng, Q., D'Abronzo, L., Dornetshuber-Fleiss, R., Ghosh, P.M., Gonzalez Guzman, M.J., Lee, T.J., Leung, P.S., Li, L., Luanpitpong, S., Ratovitski, E., Rojanasakul, Y., Romano, M.F., Romano, S., Sinha, R.K., Yedjou, C., Al-Mulla, F., Al-Temaimi, R., Amedei, A., Brown, D.G., Ryan, E.P., Colacci, A., Hamid, R.A., Mondello, C., Raju, J., Salem, H.K., Woodrick, J., Scovassi, I., Singh, N., Vaccari, M., Roy, R., Forte, S., Memeo, L., Kim, S.Y., Bisson, W.H., Lowe, L., Park, H. H., 2015. Disruptive environmental chemicals and cellular mechanisms that confer resistance to cell death. Carcinogenesis 36 (Suppl. 1), S89–S110. Nebert, D.W., Dalton, T.P., 2006. The role of cytochrome P450 enzymes in endogenous signalling pathways and environmental carcinogenesis. Nat. Rev. Cancer 6, 947–960. Nikolova, T., Hennekes, F., Bhatti, A., Kaina, B., 2012. Chloroethylnitrosoureainduced cell death and genotoxicity: cell cycle dependence and the role of DNA double-strand breaks, HR and NHEJ. Cell Cycle 11, 2606–2619. O'Brien, C.A., Kreso, A., Ryan, P., Hermans, K.G., Gibson, L., Wang, Y., Tsatsanis, A., Gallinger, S., Dick, J.E., 2012. ID1 and ID3 regulate the self-renewal capacity of human colon cancer-initiating cells through p21. Cancer Cell 21, 777–792. O'Keefe, S.J., Li, J.V., Lahti, L., Ou, J., Carbonero, F., Mohammed, K., Posma, J.M., Kinross, J., Wahl, E., Ruder, E., Vipperla, K., Naidoo, V., Mtshali, L., Tims, S., Puylaert, P.G., DeLany, J., Krasinskas, A., Benefiel, A.C., Kaseb, H.O., Newton, K., Nicholson, J.K., de Vos, W.M., Gaskins, H.R., Zoetendal, E.G., 2015. Fat, fibre and cancer risk in African Americans and rural Africans. Nat. Commun. 6, 6342. Ochieng, J., Nangami, G.N., Ogunkua, O., Miousse, I.R., Koturbash, I., Odero-Marah, V., McCawley, L.J., Nangia-Makker, P., Ahmed, N., Luqmani, Y., Chen, Z., Papagerakis, S., Wolf, G.T., Dong, C., Zhou, B.P., Brown, D.G., Colacci, A.M., Hamid, R.A., Mondello, C., Raju, J., Ryan, E.P., Woodrick, J., Scovassi, A.I., Singh, N., Vaccari, M., Roy, R., Forte, S., Memeo, L., Salem, H.K., Amedei, A., Al-Temaimi, R., Al-Mulla, F., Bisson, W.H., Eltom, S.E., 2015. The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis. Carcinogenesis 36 (Suppl. 1), S128–159. Ogino, S., Gulley, M.L., den Dunnen, J.T., Wilson, R.B., Association for Molecular Patholpogy, T., Education, C., 2007. Standard mutation nomenclature in molecular diagnostics: practical and educational challenges. J. Mol. Diagn. 9,1–6. Oikawa, S., Ito, T., Iwayama, M., Kawanishi, S., 2006. Radical production and DNA damage induced by carcinogenic 4-hydrazinobenzoic acid, an ingredient of mushroom Agaricus bisporus. Free Radic. Res. 40, 31–39. Orlich, M.J., Singh, P.N., Sabate, J., Fan, J., Sveen, L., Bennett, H., Knutsen, S.F., Beeson, W. L., Jaceldo-Siegl, K., Butler, T.L., Herring, R.P., Fraser, G.E., 2015. Vegetarian dietary patterns and the risk of colorectal cancers. JAMA Intern. Med. 175, 767–776. Orthwein, A., Fradet-Turcotte, A., Noordermeer, S.M., Canny, M.D., Brun, C.M., Strecker, J., Escribano-Diaz, C., Durocher, D., 2014. Mitosis inhibits DNA doublestrand break repair to guard against telomere fusions. Science 344, 189–193. Ottini, L., Falchetti, M., Marinozzi, S., Angeletti, L.R., Fornaciari, G., 2011. Geneenvironment interactions in the pre-Industrial Era: the cancer of King Ferrante I of Aragon (1431–1494). Human Pathol. 42, 332–339. Pavanello, S., Pesatori, A.C., Dioni, L., Hoxha, M., Bollati, V., Siwinska, E., Mielzynska, D., Bolognesi, C., Bertazzi, P.A., Baccarelli, A., 2010. Shorter telomere length in peripheral blood lymphocytes of workers exposed to polycyclic aromatic hydrocarbons. Carcinogenesis 31, 216–221. Payne, C.M., Bernstein, C., Dvorak, K., Bernstein, H., 2008. Hydrophobic bile acids, genomic instability, Darwinian selection, and colon carcinogenesis. Clin Exp Gastroenterology 1, 19–47.

116

J.Y. Sakita et al. / Toxicology Letters 265 (2017) 106–116

Potter, D.M., Baird, M.S., 2000. Carcinogenic effects of ptaquiloside in bracken fern and related compounds. Br. J. Cancer 83, 914–920. Puebla-Osorio, N., Kim, J., Ojeda, S., Zhang, H., Tavana, O., Li, S., Wang, Y., Ma, Q., Schluns, K.S., Zhu, C., 2014. A novel Ku70 function in colorectal homeostasis separate from nonhomologous end joining. Oncogene 33, 2748–2757. Reddy, B.S., Hanson, D., Mathews, L., Sharma, C., 1983. Effect of micronutrients, antioxidants and related compounds on the mutagenicity of 3,2'-dimethyl-4aminobiphenyl, a colon and breast carcinogen. Food Chem. Toxicol. 21, 129–132. Richard, J.L., 2007. Some major mycotoxins and their mycotoxicoses–an overview. Int. J. Food Microbiol. 119, 3–10. Richards, B.M., 1955. Deoxyribose nucleic acid values in tumour cells with reference to the stem-cell theory of tumour growth. Nature 175, 259–261. Robey, R.B., Weisz, J., Kuemmerle, N.B., Salzberg, A.C., Berg, A., Brown, D.G., Kubik, L., Palorini, R., Al-Mulla, F., Al-Temaimi, R., Colacci, A., Mondello, C., Raju, J., Woodrick, J., Scovassi, A.I., Singh, N., Vaccari, M., Roy, R., Forte, S., Memeo, L., Salem, H.K., Amedei, A., Hamid, R.A., Williams, G.P., Lowe, L., Meyer, J., Martin, F. L., Bisson, W.H., Chiaradonna, F., Ryan, E.P., 2015. Metabolic reprogramming and dysregulated metabolism: cause, consequence and/or enabler of environmental carcinogenesis? Carcinogenesis 36 (Suppl. 1), S203–231. Rodriguez, J., Frigola, J., Vendrell, E., Risques, R.A., Fraga, M.F., Morales, C., Moreno, V., Esteller, M., Capella, G., Ribas, M., Peinado, M.A., 2006. Chromosomal instability correlates with genome-wide DNA demethylation in human primary colorectal cancers. Cancer Res. 66, 8462–9468. Schulz, M.D., Atay, C., Heringer, J., Romrig, F.K., Schwitalla, S., Aydin, B., Ziegler, P.K., Varga, J., Reindl, W., Pommerenke, C., Salinas-Riester, G., Bock, A., Alpert, C., Blaut, M., Polson, S.C., Brandl, L., Kirchner, T., Greten, F.R., Polson, S.W., Arkan, M. C., 2014. High-fat-diet-mediated dysbiosis promotes intestinal carcinogenesis independently of obesity. Nature 514, 508–512. Schulzova, V., Hajslova, J., Peroutka, R., Hlavasek, J., Gry, J., Andersson, H.C., 2009. Agaritine content of 53 Agaricus species collected from nature. Food Addit. Contam. A Chem. Anal. Control Expo. Risk Assess. 26, 82–93. Schwartzbord, J.R., Emmanuel, E., Brown, D.L., 2013. Haiti's food and drinking water: a review of toxicological health risks. Clin. Toxicol. 51, 828–833. Schwitalla, S., Ziegler, P.K., Horst, D., Becker, V., Kerle, I., Begus-Nahrmann, Y., Lechel, A., Rudolph, K.L., Langer, R., Slotta-Huspenina, J., Bader, F.G., Prazeres da Costa, O., Neurath, M.F., Meining, A., Kirchner, T., Greten, F.R., 2013. Loss of p53 in enterocytes generates an inflammatory microenvironment enabling invasion and lymph node metastasis of carcinogen-induced colorectal tumors. Cancer Cell 23, 93–106. Shackney, S.E., Smith, C.A., Miller, B.W., Burholt, D.R., Murtha, K., Giles, H.R., Ketterer, D.M., Pollice, A.A., 1989. Model for the genetic evolution of human solid tumors. Cancer Res. 49, 3344–3354. Sieber, S.M., Correa, P., Dalgard, D.W., McIntire, K.R., Adamson, R.H., 1980. Carcinogenicity and hepatotoxicity of cycasin and its aglycone methylazoxymethanol acetate in nonhuman primates. J. Natl. Cancer Inst. 65, 177–189. Siegel, R., Desantis, C., Jemal, A., 2014. Colorectal cancer statistics, 2014. CA. Cancer J. Clin. 64, 104–117. Snippert, H.J., Schepers, A.G., van Es, J.H., Simons, B.D., Clevers, H., 2014. Biased competition between Lgr5 intestinal stem cells driven by oncogenic mutation induces clonal expansion. EMBO Rep. 15, 62–69. Steck, S.E., Butler, L.M., Keku, T., Antwi, S., Galanko, J., Sandler, R.S., Hu, J.J., 2014. Nucleotide excision repair gene polymorphisms, meat intake and colon cancer risk. Mutat. Res. 762, 24–31. Stevens, J.F., Maier, C.S., 2008. Acrolein: sources, metabolism, and biomolecular interactions relevant to human health and disease. Mol. Nutr. Food Res. 52, 7–25.

Sukup-Jackson, M.R., Kiraly, O., Kay, J.E., Na, L., Rowland, E.A., Winther, K.E., Chow, D. N., Kimoto, T., Matsuguchi, T., Jonnalagadda, V.S., Maklakova, V.I., Singh, V.R., Wadduwage, D.N., Rajapakse, J., So, P.T., Collier, L.S., Engelward, B.P., 2014. Rosa26-GFP direct repeat (RaDR-GFP) mice reveal tissue- and age-dependence of homologous recombination in mammals in vivo. PLoS Genet. 10, e1004299. Sulli, G., Di Micco, R., d'Adda di Fagagna, F., 2012. Crosstalk between chromatin state and DNA damage response in cellular senescence and cancer. Nat. Rev. Cancer 12, 709–720. Szterk, A., Roszko, M., Malek, K., Kurek, M., Zbiec, M., Waszkiewicz-Robak, B., 2012. Profiles and concentrations of heterocyclic aromatic amines formed in beef during various heat treatments depend on the time of ripening and muscle type. Meat Sci. 92, 587–595. Takayama, S., Masuda, M., Mogami, M., Ohgaki, H., Sato, S., Sugimura, T., 1984. Induction of cancers in the intestine, liver and various other organs of rats by feeding mutagens from glutamic acid pyrolysate. Gan 75, 207–213. Thompson, P.A., Khatami, M., Baglole, C.J., Sun, J., Harris, S., Moon, E.Y., Al-Mulla, F., Al-Temaimi, R., Brown, D., Colacci, A., Mondello, C., Raju, J., Ryan, E., Woodrick, J., Scovassi, I., Singh, N., Vaccari, M., Roy, R., Forte, S., Memeo, L., Salem, H.K., Amedei, A., Hamid, R.A., Lowe, L., Guarnieri, T., Bisson, W.H., 2015. Environmental immune disruptors, inflammation and cancer risk. Carcinogenesis 36 (Suppl.1), S232–S253. Tomasetti, C., Vogelstein, B., 2015. Cancer etiology: variation in cancer risk among tissues can be explained by the number of stem cell divisions. Science 347, 78– 81. Tung, E.W., Philbrook, N.A., Belanger, C.L., Ansari, S., Winn, L.M., 2014. Benzo[a] pyrene increases DNA double strand break repair in vitro and in vivo: a possible mechanism for benzo[a]pyrene-induced toxicity. Mutat. Res. Genet. Toxicol. Environ. Mutagen. 760, 64–69. Turesky, R.J., 2007. Formation and biochemistry of carcinogenic heterocyclic aromatic amines in cooked meats. Toxicol. Lett. 168, 219–227. Vermeulen, L., Snippert, H.J., 2014. Stem cell dynamics in homeostasis and cancer of the intestine. Nat. Rev. Cancer 14, 468–480. Vogelstein, B., Kinzler, K.W., 2015. The path to cancer three strikes and you're out. New Eng. J. Med. 373, 1895–1898. Wakabayashi, K., Nagao, M., Esumi, H., Sugimura, T., 1992. Food-derived mutagens and carcinogens. Cancer Res. 52, 2092–2098. Walton, K., Coombs, M.M., Catterall, F.S., Walker, R., Ioannides, C., 1997. Bioactivation of the mushroom hydrazine, agaritine, to intermediates that bind covalently to proteins and induce mutations in the Ames test. Carcinogenesis 18, 1603–1608. Whitman, R., 1919. Somatic mutation as a factor in the production of cancer: a critical review of v. Hansemann's theory of anaplasia in the light of modern knowledge of genetics. J. Cancer Res. 181, 181–202. Willett, W., 1989. The search for the causes of breast and colon cancer. Nature 338, 389–394. Wu, A.H., Shibata, D., Yu, M.C., Lai, M.Y., Ross, R.K., 2001. Dietary heterocyclic amines and microsatellite instability in colon adenocarcinomas. Carcinogenesis 22, 1681–1684. Wu, S., Powers, S., Zhu, W., Hannun, Y.A., 2016. Substantial contribution of extrinsic risk factors to cancer development. Nature 529, 43–47. Xue, W., Zender, L., Miething, C., Dickins, R.A., Hernando, E., Krizhanovsky, V., Cordon-Cardo, C., Lowe, S.W., 2007. Senescence and tumour clearance is triggered by p53 restoration in murine liver carcinomas. Nature 445, 656–660. Yi, S.W., 2013. Cancer incidence in Korean Vietnam veterans during 1992–2003: the Korean veterans health study. J. Prev. Med. Public Health 46, 309–318. de Magalhaes, J.P., 2013. How ageing processes influence cancer. Nat. Rev. Cancer 13, 357–365.