Human cancer: etiologic agents/dose responses/DNA repair/cellular and animal models

Emergence of nutrigenomics and dietary components as a complementary therapy in cancer prevention

Cancer is an illness characterized by abnormal cell development and the capability to infiltrate or spread to rest of the body. A tumor is the term for this abnormal growth that develops in solid tissues like an organ, muscle, or bone and can spread to other parts of the body through the blood and lymphatic systems. Nutrition is a critical and immortal environmental component in the development of all living organisms encoding the relationship between a person's nutrition and their genes. Nutrients have the ability to modify gene expression and persuade alterations in DNA and protein molecules which is researched scientifically in nutrigenomics. These interactions have a significant impact on the pharmacokinetic properties of bioactive dietary components as well as their site of action/molecular targets. Nutrigenomics encompasses nutrigenetics, epigenetics, and transcriptomics as well as other "omic" disciplines like proteomics and metabolomics to explain the vast disparities in cancer risk among people with roughly similar life style. Clinical trials and researches have evidenced that alternation of dietary habits is potentially one of the key approaches for reducing cancer risk in an individual. In this article, we will target how nutrigenomics and functional food work as preventive therapy in reducing the risk of cancer.

Advanced Computational Methodologies Used in the Discovery of New Natural Anticancer Compounds

Natural chemical compounds have been widely investigated for their programmed necrosis causing characteristics. One of the conventional methods for screening such compounds is the use of concentrated plant extracts without isolation of active moieties for understanding pharmacological activity. For the last two decades, modern medicine has relied mainly on the isolation and purification of one or two complicated active and isomeric compounds. The idea of multi-target drugs has advanced rapidly and impressively from an innovative model when first proposed in the early 2000s to one of the popular trends for drug development in 2021. Alternatively, fragment-based drug discovery is also explored in identifying target-based drug discovery for potent natural anticancer agents which is based on well-defined fragments opposite to use of naturally occurring mixtures. This review summarizes the current key advancements in natural anticancer compounds; computer-assisted/fragment-based structural elucidation and a multi-target approach for the exploration of natural compounds.

Analysis of DNA damage induced by aflatoxin B1 in Dunkin–Hartley guinea pigs

Aflatoxin B1 (AFB1) is among the most potent naturally occurring carcinogens and classified as a group I carcinogen. Since the ingestion of aflatoxin-contaminated food is associated with several liver diseases, the aim of the present study was to evaluate the effect of 2, 20, and 200 ppb of AFB1 on DNA damage in peripheral blood lymphocytes and liver cells in Dunkin-Hartley guinea pigs. The animals were divided into four groups according to the given diet. After the treatment the lymphocytes and liver cells were isolated and DNA damage determined by Comet assay. The levels of DNA damage in lymphocytes were higher animals treated with 200 ppb of AFB1-enriched diet (P = 0.02). In the liver cells there were a relationship between the levels of DNA damage and the consumption of AFB1 in all studied groups. These results suggest that Comet assay performed on lymphocytes is a valuable genotoxic marker for high levels of exposure to AFB1 in guinea pig. Additionally our results indicate that the exposure to this toxin increases significantly and increases the level of DNA damage in liver cells, which is a key step on liver cancer development. We also suggest that the Comet assay is an useful tool for monitoring the genotoxicity of AFB1 in liver.

Malondialdehyde, a major endogenous lipid peroxidation product, sensitizes human cells to UV- and BPDE-induced killing and mutagenesis through inhibition of nucleotide excision repair

Aldehydes are ubiquitous contaminants in the human environment. Intracellular aldehydes are mainly derived from the metabolism of polyunsaturated fatty acids and from lipid peroxidation, which is significantly elevated under oxidative stress conditions. Oxidative stress has long been suspected to be involved in many disease processes, including carcinogenesis, neurodegeneration and aging, but its mechanisms are largely unknown. Aldehydes are reactive not only toward nucleic acids but also to many amino acids, and these aldehyde-protein interactions have been suspected of affecting many cellular functions, including DNA repair. To test this possibility we determined the effect of malondialdehyde (MDA), one of the most abundant intracellular aldehyde, on ultraviolet (UV) light- and benzo(a)pyrene diol epoxide (BPDE)-induced cytotoxicity and mutagenesis in human cells. We found that MDA treatment greatly sensitized cells to both UV- and BPDE-induced cell killing and that, MDA pre-treatment significantly enhanced UV-induced mutagenesis. Using in vitro DNA repair synthesis and host cell reactivation assays we found that MDA treatment of cells greatly inhibited nucleotide excision repair for both and UV light- and BPDE-induced DNA damage. Further experiments raise the possibility that the inhibitory effect on nucleotide excision repair is mainly caused by the direct interaction of MDA with cellular repair proteins. Together these results strongly suggest that intracellular aldehydes play an important role in oxidative stress-related mutagenesis and carcinogenesis through their inhibitory effect on DNA repair mechanisms as well as on induction of DNA damage.

A carcinogenic western diet does not induce somatic mutations in various target tissues of transgenic C56BL/6 mice

Although the importance of diet in human cancer is clear, most dietary studies of carcinogenesis in laboratory rodents have involved the use of large doses of a carcinogen, which is not comparable to the human situation. The use of carcinogens has been necessary because laboratory rodents have extremely low spontaneous rates of colon cancer. Newmark et al. (2001) showed, however, that a radical dietary manipulation sufficed to induce high rates of colon cancer in C57BL/6 mice. Here we report an investigation into whether or not this dietary manipulation acts by altering somatic mutation rates. We used the transgenic lambda cII locus of F1 pups (C57BL/6 x Big Blue with the same C57BL/6 genetic background. The same diet (ND), high in fat, and low in calcium, vitamin D, folic acid, choline, and fibre, that was used by Newmark et al. (2001) was fed ad libitum to dams during pregnancy and lactation in order to examine its effect on mutagenesis in development and growth. There was no significant difference in mutant frequency in the small intestine (P = 0.82), or bone marrow (P = 0.95) of pups fed a ND versus the control diet. To investigate the effect of a ND during adulthood, 6-week-old F1 pups were fed a ND ad libitum for 6, 12 and 19 weeks. There was no significant difference in mutant frequency in the small intestine (P = 0.66) or colon (P = 0.49) at the cII locus with no significant difference in body weight. These results indicate that Western diet-induced carcinogenesis is not mediated by alterations in mutation rate and thus may act at the promotion rather than at the initiation stage of carcinogenesis.

Cell cycle progression in G1 and S phases is CCR4 dependent following ionizing radiation or replication stress in Saccharomyces cerevisiae

To identify new nonessential genes that affect genome integrity, we completed a screening for diploid mutant Saccharomyces cerevisiae strains that are sensitive to ionizing radiation (IR) and found 62 new genes that confer resistance. Along with those previously reported (Bennett et al., Nat. Genet. 29:426-434, 2001), these genes bring to 169 the total number of new IR resistance genes identified. Through the use of existing genetic and proteomic databases, many of these genes were found to interact in a damage response network with the transcription factor Ccr4, a core component of the CCR4-NOT and RNA polymerase-associated factor 1 (PAF1)-CDC73 transcription complexes. Deletions of individual members of these two complexes render cells sensitive to the lethal effects of IR as diploids, but not as haploids, indicating that the diploid G1 cell population is radiosensitive. Consistent with a role in G1, diploid ccr4Delta cells irradiated in G1 show enhanced lethality compared to cells exposed as a synchronous G2 population. In addition, a prolonged RAD9-dependent G1 arrest occurred following IR of ccr4Delta cells and CCR4 is a member of the RAD9 epistasis group, thus confirming a role for CCR4 in checkpoint control. Moreover, ccr4Delta cells that transit S phase in the presence of the replication inhibitor hydroxyurea (HU) undergo prolonged cell cycle arrest at G2 followed by cellular lysis. This S-phase replication defect is separate from that seen for rad52 mutants, since rad52Delta ccr4Delta cells show increased sensitivity to HU compared to rad52Delta or ccr4Delta mutants alone. These results indicate that cell cycle transition through G1 and S phases is CCR4 dependent following radiation or replication stress.

DNA repair in human fibroblasts, as reflected by host-cell reactivation of a transfected UV-irradiated luciferase gene, is not related to donor age

The effect of donor age on the ability of mammalian cells to repair ultraviolet (UV)-induced DNA damage has been studied using several approaches, most recently via assays that measure the host-cell reactivation (HCR) of UV-irradiated reporter gene-containing plasmid vectors following their transfection into cells. Plasmid HCR assays indirectly quantify a cell line's ability to perform nucleotide excision repair (NER) by measuring the enzyme activity of the repaired reporter gene, e.g., chloramphenical acetyltransferase (cat) or luciferase (luc), and are useful in studies investigating whether increasing age may be a risk factor for the deficient repair of potentially cancer-causing, sunlight-induced, DNA lesions in skin cells. In our study, we quantified the DNA repair ability of cultured, nontransformed, human skin fibroblast lines through their HCR of a transfected UV-C-irradiated plasmid containing luc. HCR was measured at various times after transfection in five lines from normal donors of ages 21-96 years, and from one donor who had xeroderma pigmentosum (XP). The normal lines displayed increasing HCR at successive post-transfection time points and showed no significant correlation between HCR and donor age. The XP-A line, known to be markedly deficient in NER of UV-induced DNA damage, showed minimal evidence of HCR compared to the normal lines. To further assess potential variation in HCR with donor age, fibroblast lines from five old donors, ages 84-94 years, were compared with lines from five young donors, ages 17-26 years. While significant differences in HCR were found between some lines, no significant difference was found between the young and old age groups (P = 0.44). Our study provides no indication that the higher incidence of skin cancer observed with increasing age is due to an age-related decrease in the ability to repair UV-induced DNA damage.

A second life in science—working after the age of 65

I was born in January, 1921 and was fortunate in working for a research organization that had no fixed retirement age. I was permitted to continue Science as long as there were some resources to support research that had some relevance to the organization's goals. A number of projects on which I worked were continuations of ones begun before the age of 65 (1986) and several new ones were based on both previous interests and ideas and some on new ideas. A number of the ideas arose from participation on Committees of the US National Research Council. I was able to extend my earlier interests in DNA repair to include experiments on the variations in DNA repair among apparently normal humans. In collaborations with other researchers we showed that the repair abilities following exposures to chemicals or to ionizing or ultraviolet (UV) radiation did not follow Poisson distributions. I participated in experiments, using a fish model to estimate the wavelength ranges in sunlight responsible for inducing melanoma and another fish model to estimate the germ cell mutations that might arise from exposures to the heavily ionizing particles in cosmic rays beyond low Earth orbit. A transgenic fish model was used to investigate the possibilities of using the fish to assay for mutagens in sediments in Long Island Sound. These Reflections summarize the atmosphere necessary for a second life and the scientific results of this life.

Guanosine Distribution and Oxidation Resistance in Eight Eukaryotic Genomes

Reactive oxygen species that attack DNA are continuously generated in living cells. Both the guanosine (G) mole fraction and its distribution should affect the stability of genomes and their parts to oxidation. At a lesser G content, genomes should be more oxidation resistant or "ennobled". Oxidant scavenging by G's in nonessential parts of introns and intergenic domains should decrease G oxidation in the essential exons. To determine whether genomes are indeed ennobled and whether oxidant-scavenging domains exist in genomes, the relative rates of guanosine oxidation in average exons, introns, and intergenic domains were estimated. Comparison among genomes indicated that average exons are ennobled in the genomes of Caenorhabditis (worm), Arabidopsis (plant), Saccharomyces (yeast), Schizosaccharomyces (yeast), and Plasmodium (malaria parasite), and that average introns and intergenic domains are ennobled in these genomes and in the genome of Drosophila (fly). The exon oxidation rates estimated for these genomes were less than the rate for the hypothetical "standard" genome, with a 0.25 mole fraction of uniformly distributed G. For Plasmodium the rate was half of that estimated for the standard genome. Average exons were not ennobled in the human or fly genomes; their G distributions were comparable to that in the standard genome. Instead, their exons were situated between introns and intergenic domains that could protect them by oxidant scavenging, the G's of their introns and intergenic domains outnumbering those of their exons 50-fold in humans and 4-fold in flies. The G distribution in the Encephalitozoon (parasite) genome was not protective relative to that of the standard genome.

DNA repair and cancer: lessons from mutant mouse models

DNA damage, if the repair process, especially nucleotide excision repair (NER), is compromised or the lesion is repaired by some other error-prone mechanism, causes mutation and ultimately contributes to neoplastic transformation. Impairment of components of the DNA damage response pathway (e.g., p53) is also implicated in carcinogenesis. We currently have considerable knowledge of the role of DNA repair genes as tumor suppressors, both clinically and experimentally. The deleterious clinical consequences of inherited defects in DNA repair system are apparent from several human cancer predisposition syndromes (e.g., NER-compromised xeroderma pigmentosum [XP] and p53-deficient Li-Fraumeni syndrome). However, experimental studies to support the clinical evidence are hampered by the lack of powerful animal models. Here, we review in vivo experimental data suggesting the protective function of DNA repair machinery in chemical carcinogenesis. We specifically focus on the three DNA repair genes, O(6)-methylguanine-DNA methyltransferase gene (MGMT ), XP group A gene (XPA) and p53. First, mice overexpressing MGMT display substantial resistance to nitrosamine-induced hepatocarcinogenesis. In addition, a reduction of spontaneous liver tumors and longer survival times were evident. However, there are no known mutations in the human MGMT and therefore no associated cancer syndrome. Secondly, XPA mutant mice are indeed prone to spontaneous and carcinogen-induced tumorigenesis in internal organs (which are not exposed to sunlight). The concomitant loss of p53 resulted in accelerated onset of carcinogenesis. Finally, p53 null mice are predisposed to brain tumors upon transplacental exposure to a carcinogen. Accumulated evidence in these three mutant mouse models firmly supports the notion that the DNA repair system is vital for protection against cancer.

The role of DNA breaks in genomic instability and tumorigenesis

DNA double-strand breaks (DSBs) represent dangerous chromosomal lesions that can lead to mutation, neoplastic transformation, or cell death. DSBs can occur by extrinsic insult from environmental sources or may occur intrinsically as a result of cellular metabolism or a genetic program. Mammalian cells possess potent and efficient mechanisms to repair DSBs, and thus complete normal development as well as mitigate oncogenic potential and prevent cell death. When DSB repair (DSBR) fails, chromosomal instability results and can be associated with tumor formation or progression. Studies of mice deficient in various components of the non-homologous end joining pathway of DSBR have revealed key roles in both the developmental program of B and T lymphocytes as well as in the maintenance of general genome stability. Here, we review the current thinking about DSBs and DSBR in chromosomal instability and tumorigenesis, and we highlight the implications for understanding the karyotypic features associated with human tumors.

Divide and conquer: nucleotide excision repair battles cancer and ageing

Protection from cancer and ensured longevity are tightly linked in mammals. One of the fundamental mechanisms contributing to both is the cellular response to DNA damage. The appropriate response is an initial attempt at repair, but if the damage is too extensive or compromises DNA metabolism, a signalling cascade triggers cellular senescence or death. Evidence in mice and humans suggests a division of tasks amongst DNA repair pathways: transcription-coupled repair and interstrand crosslink repair of cytotoxic lesions are predominantly responsible for longevity assurance, whereas excision repair of mutagenic lesions provides protection against cancer. Similarly, the signalling component of the DNA-damage response might contribute unequally to organismal outcomes depending on its set point: an inadequate response to DNA damage sanctions carcinogenesis but might limit local ageing, whereas overzealous signalling provides cancer protection but accelerates ageing.

Genetic and environmental factors in cancer and neurodegenerative diseases

The aim of this review is to summarise the recent findings in the fields of carcinogenesis and neurodegenerative diseases, the both disorders are characterised by the contribution of different factors including the inheritance of mutated genes, and the exposure to endogenous or exogenous agents during the life. We first analysed the causative genes until now discovered in both processes, then we focused our attention on the role of environmental exposure, susceptibility factors, oxidative stress, apoptosis and aging to the development of such disorders. The genotype at a particular locus may account for an inter-individual susceptibility that can both increase or decrease the risk to develop the pathology especially after the exposure to environmental agents. The mechanism of apoptosis, that is an excellent strategy in order to eliminate damaged cells, seems to be lost during carcinogenesis, while it seems to be involved in the neuronal death in a lot of neurodegenerative disorders. Oxidative stress can both lead to DNA mutations or to the formation of damaged proteins, so being an important risk factor for the initiation and the progression of a disease: in fact it may be one of the causes or can arise as a consequence of a damage caused by other factors increasing then the first damage. It is well established that carcinogenesis is a multi-step process caused by series of successive mutations occurring into a cell and conferring to this cell a growth advantage, so that age is the largest risk factor for cancer in humans. Pathophysiology of neurodegenerative diseases is complex and likely involves multiple overlapping and perhaps redundant pathways of neuronal damage, characterised by the generation of anomalous proteins, often due to mutations in the corresponding gene, and by their subsequent accumulation into or outside specific areas of the brain.