Incidence Of Spontaneous Cancer Research Articles

Lack of telomerase reduces cancer incidence and increases lifespan of zebrafish tp53M214K mutants

Telomerase activity is restricted in humans and telomere attrition occurs in several tissues accompanying natural aging. Critically short telomeres trigger DNA damage responses and activate p53 which leads to apoptosis or replicative senescence. These processes reduce cell proliferation and disrupt tissue homeostasis, thus contributing to systemic aging. Similarly, zebrafish have restricted telomerase expression, and telomeres shorten to critical length during their lifespan. Telomerase-deficient zebrafish (tert −/−) is a premature model of aging that anticipates aging phenotypes due to early telomere shortening. tert −/− zebrafish have impaired cell proliferation, accumulation of DNA damage markers and p53 response. These cellular defects lead to disruption of tissue homeostasis, resulting in premature infertility, gastrointestinal atrophy, sarcopenia and kyphosis. Such consequences contribute to its premature death. Here we reveal a genetic interdependence between tp53 and telomerase function. Mutation of tp53 abrogates premature aging of tert −/− zebrafish, prolonging male fertility and lifespan. However, it does not fully rescue healthspan. tp53mut tert −/− zebrafish retain high levels of inflammation and increased spontaneous cancer incidence. Conversely, loss of telomerase prolongs the lifespan of tp53mut single mutants. Lack of telomerase reduces two-fold the cancer incidence in double mutants and increases lifetime survival. Thus, we observe a reciprocal rescue of tp53mut and tert −/− that ameliorates lifespan but not spontaneous cancer incidence of tp53mut, likely due to higher levels of inflammation.

Analysis of approaches to the formation of a control group in radon epidemiological case-control studies

Objectives: Studying the influence of the method of selecting a control group in the radon case-control study on assessment of dose-effect dependence. Study the effect of additional additive or multiplicative risk factors on the results of the study. Materials and Methods: Simulation of a large-scale radon epidemiological case-control study. Analyzing of the influence of the representative value of the comparison subgroup on the results of calculating the odds ratio of the incidence of radiation-induced lung cancer. Analysis of different variants of standardization of the control group on the correctness of the dose-effect dependence. Development of methods for identifying risk factors that affect the incidence of lung cancer and determining the mechanism of their influence (additive or multiplicative). Results: It is shown that the insufficient representativeness of the comparison subgroup used in calculating the odds ratio can significantly distort the estimates of dose-effect dependence. In the presence of factors (sex, smoking, etc.), correlating both with the incidence of lung cancer and of radon concentration, complete standardization of such factors is necessary. Multiplicative risk factors without such correlation do not require additional standardization in the selection of a control group. Calculation of the odds ratio for various risk factors in subgroups differing in the levels of spontaneous cancer incidence allows to determine the significance of this factor for the incidence of lung cancer, and to establish the preferential mechanism of the influence of this factor (multiplicative or additive). Conclusions. When carrying out the radon case-control study, it is necessary to identify risk factors that correlate both with the incidence of lung cancer, and with the radon concentration, to assess the mechanism of action of these factors and to made the complete standardization of the control group for them.

Targeted p16(Ink4a) epimutation causes tumorigenesis and reduces survival in mice.

Cancer has long been viewed as a genetic disease; however, epigenetic silencing as the result of aberrant promoter DNA methylation is frequently associated with cancer development, suggesting an epigenetic component to the disease. Nonetheless, it has remained unclear whether an epimutation (an aberrant change in epigenetic regulation) can induce tumorigenesis. Here, we exploited a functionally validated cis-acting regulatory element and devised a strategy to induce developmentally regulated genomic targeting of DNA methylation. We used this system to target DNA methylation within the p16(Ink4a) promoter in mice in vivo. Engineered p16(Ink4a) promoter hypermethylation led to transcriptional suppression in somatic tissues during aging and increased the incidence of spontaneous cancers in these mice. Further, mice carrying a germline p16(Ink4a) mutation in one allele and a somatic epimutation in the other had accelerated tumor onset and substantially shortened tumor-free survival. Taken together, these results provide direct functional evidence that p16(Ink4a) epimutation drives tumor formation and malignant progression and validate a targeted methylation approach to epigenetic engineering.

N-acetyltransferase 2 (Nat2) polymorphism in the sand rat Psammomys obesus

Human arylamine N-acetyltransferase 1 (NAT1) and its homologue in rodents (Nat2) are polymorphic xenobiotic metabolizing enzymes and also seem to play a role in endogenous metabolism. NAT1 and Nat2 polymorphism was associated to cancers under xenobiotic procarcinogens metabolism as well as under endogenous substrate metabolism. This study investigated the p-aminobenzoic acid (PABA) -Nat2 catalytic activity and its polymorphism in liver homogenates of adult sand rats Psammomys obesus Cretzschmar, 1828. These Saharian sand rats develop high incidence of spontaneous cancers under standard laboratory diet. The average value of PABA-Nat2 specific activity tested in nine sand rats was significant (2.96 ± 2.16 nmoles/min/mg). The N-acetylation exhibited a bimodal distribution. There was a significant difference (p < 0.01) between PABA-Nat2 activity in the fast acetylators group (4.10 ± 1.67 nmol/min/mg) and slow acetylators group (0.7 ± 0.27 nmol/min/mg). The percentage of the fast acetylator group was 66.66%. These results support the presence of Nat2 polymorphism in the liver of the strain sand rats Psammomys obesus. This strain is useful for investigating the role of Nat2 polymorphisms in susceptibility to cancers related to arylamine carcinogen exposures as well as to endogenous substrate metabolism.

Quantification of plasma DNA as a prognostic indicator in canine lymphoid neoplasia

Dogs have a similar incidence of spontaneous cancers as people, and a noninvasive test to monitor disease status in dogs would be of great value. Humans with cancer often have increased levels of cell-free circulating DNA in their plasma, which has shown promise for diagnosis, prognosis and detection of residual disease. We hypothesized that dogs with cancer have increased circulating DNA compared with healthy dogs or dogs with non-neoplastic diseases. Plasma DNA was measured in 40 healthy dogs, 20 dogs with non-neoplastic diseases and 80 dogs with cancer. The reference interval for plasma DNA in healthy dogs was 1-15 ng mL(-1). Dogs with lymphoma and lymphoid leukaemia had significantly higher concentrations (range: 0-91 ng mL(-1), P < 0.0001). Antigen receptor rearrangement assays suggest that plasma DNA had the same clonality as the primary lymphoid tumours. Dogs with lymphoid neoplasia and plasma DNA >25 ng mL(-1) had shorter remission times than those with < 25 ng mL(-1) (P = 0.0116). In contrast to humans, where increased plasma DNA is seen in many diseases, dogs with nonlymphoid malignancies and non-neoplastic diseases had plasma DNA concentrations similar to healthy dogs. This study shows that a portion of dogs with lymphoid neoplasia have increased tumour-derived plasma DNA, which serves as a negative prognostic indicator.

A Population-Based Analysis of Second Primary Cancers After Irradiation for Rectal Cancer

To investigate the possible association between pelvic irradiation for rectal cancer and subsequent second primary cancers. A population-based analysis of 20,910 individuals with rectal cancer from the Surveillance, Epidemiology, and End Results registry, for whom follow-up times were at least 5 years, was performed. Kaplan-Meier estimates for the development of second cancers within irradiated and nonirradiated cohorts provided a comparison that accounted for censored data. Cox proportional hazards analyses were further conducted to compensate for patient and tumor-related factors. A total of 656 (12%) and 2368 (16%) second primary cancers were enumerated from the irradiated and nonirradiated cohorts, respectively, with the proportion of second primary cancers within the irradiated cohort being significantly decreased (P < 0.001) on crude analysis. However, Kaplan-Meier and Cox analyses revealed no significant difference between the 2 cohorts when all second primary cancer sites were considered together (hazard ratio = 1.02; 95% confidence interval [CI], 0.92-1.12). Proportional hazards analysis for specific second primary sites revealed a decreased risk after pelvic irradiation for cancer of the prostate (hazard ratio = 0.63; 95% CI, 0.48-0.84), and an increased risk for cancers of the uterine corpus & cervix (hazard ratio = 2.5; 95% CI, 1.6-4.0). Second primary cancers after irradiation for rectal cancers appear relatively infrequent compared with the background incidence of spontaneous cancers, and should not factor into treatment decisions for this older population. We hypothesize that the incidence of second primary tumors within adjacent organs could represent a balance between the radiation-induction of tumors and the radiation-inhibition of spontaneously occurring tumors.

Zebrafish Genomic Instability Mutants and Cancer Susceptibility

Somatic loss of tumor suppressor gene function comprising the second hit of Knudson's two-hit hypothesis is important in human cancer. A genetic screen was performed in zebrafish (Danio rerio) to find mutations that cause genomic instability (gin), as scored by Streisinger's mosaic-eye assay that models this second hit. The assay, based on a visible test for loss of wild-type gene function at a single locus, golden, is representative of genomewide events. Twelve ENU-induced genomic instability (gin) mutations were isolated. Most mutations showed weak dominance in heterozygotes and all showed a stronger phenotype in homozygotes. Trans-heterozygosity for 7 of these mutations showed greatly enhanced instability. A variety of spontaneous tumors were found in heterozygous adults from all gin lines, consistent with the expectation that genomic instability (mutator) mutations can accelerate carcinogenesis. The incidence of spontaneous cancer at 30-34 months was increased 9.6-fold in heterozygotes for the mutant with the strongest phenotype, gin-10. Tumors were seen in skin, colon, kidney, liver, pancreas, ovary, testis, and neuronal tissues, with multiple tumors in some fish. The study of these mutants will add to our understanding of the mechanisms of somatic loss of gene function and how those mechanisms contribute to cancer susceptibility.

Human cytochrome P450 reductase can act as a source of endogenous oxidative DNA damage and genetic instability

Studies with repair-deficient mice and other experiments suggest that oxidative DNA modifications are generated in all types of cells even under physiological conditions and that this type of endogenous DNA damage contributes to spontaneous cancer incidence. However, the cellular sources of reactive oxygen species that are relevant for nuclear oxidative DNA damage are largely unknown. Here, we report that expression of human NADPH-cytochrome P450 reductase (hOR) in cultured V79 Chinese hamster cells gives rise to elevated basal levels of oxidative purine modifications after depletion of glutathione. Also, the basal levels of micronuclei are increased in the hOR-expressing cells, and again the effect is enhanced when the antioxidant defense system of the cells is diminished by depletion of glutathione. The oxidative DNA damage is increased when duroquinone, a substrate of hOR, is added, both in the presence and absence of glutathione. In contrast, hOR-expressing cells are similarly sensitive as the parental cells when oxidative DNA damage and micronuclei are induced by a mechanism independent of hOR, i.e., exposure to bromate. The results identify hOR as a potential source of endogenous oxidative DNA damage and subsequent genetic instability in mammalian cells.

Cooperation between p53 mutation and high telomerase transgenic expression in spontaneous cancer development.

Telomerase reintroduction in adult somatic tissues is envisioned as a way to extend their proliferative capacity. It is still a question, however, whether constitutive telomerase expression in adult tissues impacts the normal aging and spontaneous cancer incidence of an organism. Here, we studied the aging and spontaneous cancer incidence of mice with transgenic telomerase expression in a wide range of adult tissues, K5-Tert mice. For this, we maintained large colonies of K5-Tert mice for more than 2 years. K5-Tert mice showed a decreased life span compared to wild-type cohorts associated with a higher incidence of preneoplastic and neoplastic lesions in various tissue types. Neoplasias in K5-Tert mice were coincident with transgene expression in the affected tissues. These observations suggest that high telomerase activity may cooperate with genetic alterations that occur with age to promote tumorigenesis. Indeed, we demonstrate here that increased cancer incidence and the reduced viability of K5-Tert mice are aggravated in a p53(+/-) genetic background, indicating that telomerase cooperates with loss of p53 function in inducing tumorigenesis. Altogether, these results demonstrate that constitutive high levels of telomerase activity result in a decreased life span associated with an increased incidence of neoplasias as the organism ages.

Role of endogenous oxidative DNA damage in carcinogenesis: what can we learn from repair-deficient mice?

Basal steady-state levels of oxidative DNA base modifications such as 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxoG) are observed in all types of cells, most probably due to a continuous generation of reactive oxygen species (ROS) in the cellular oxygen metabolism, and it has long been suspected that they might play an important role in the initiation of carcinogenesis. Experimental evidence for this assumption can be obtained by studying the effects of a modulation of the steady-state levels, either by in- or decreasing the generation of oxidative DNA damage, on spontaneous mutation rates and cancer incidence. However, clear answers have not yet been obtained by these strategies. It is still doubtful whether an efficient reduction of the in vivo steady-state levels can be achieved by application of antioxidants, and effects observed under oxidative stress conditions (i.e. increased oxidative DNA damage) are inconclusive due to the pronounced epigenetic effects of ROS on signal transduction and gene expression (tumor promotion). In addition, the reliable quantification of the basal levels of oxidative DNA modifications is still a major problem. Recently, the generation of mice deficient in the repair 8-oxoG (ogg1-/- mice) has opened the door for an alternative approach. Results obtained so far indicate that an increase by less than five 8-oxoG residues per 106 bp in the liver of the knockout animals is associated with a two- to threefold higher spontaneous mutation frequency in transgenic genes. However, the increase in the ogg1-/- mice of the steady-state level of 8-oxoG and the spontaneous mutation frequency was only observed in the liver and apparently too small to enhance the spontaneous cancer incidence significantly. The limited effect seems to be due to a back-up repair system for 8-oxoG in the ogg1-/- mice, and it can be expected that the inactivation of this pathway in double-knockout mice will lead to higher effects and a better assessment of the risk associated with endogenous oxidative DNA damage.

Dietary Restriction in Mice Beginning at One Year of Age: Effect on Life-Span and Spontaneous Cancer Incidence

Lifelong dietary restriction beginning at 3 to 6 weeks of age in rodents is known to decelerate the rate of aging, increase mean and maximum life-spans, and inhibit the occurrence of many spontaneous cancers. Little is known about the effects of dietary restriction started in middle age. In the experiments now reported, the food intake of 12- to 13-month-old mice of two long-lived strains was restricted by using nutrient-enriched diets in accordance with the concept of “undernutrition without malnutrition.” The mice on the restricted diet averaged 10 to 20% increases in mean and maximum survival times as compared with the control mice. Spontaneous lymphoma was inhibited by the food restriction. Reproduced with permission from Science . Copyright 1982 American Association for the Advancement of Science. Richard Weindruch, Roy L. Walford, Dietary Restriction in Mice Beginning at One Year of Age: Effect on Life-Span and Spontaneous Cancer Incidence. Science 215 , 1415-1418 (1982).

Dose–response relationships in chemical carcinogenesis: superposition of different mechanisms of action, resulting in linear–nonlinear curves, practical thresholds, J-shapes

The shape of a carcinogen dose–cancer incidence curve is discussed as the result of a superposition of dose–response relationships for various effects of the carcinogen on the process of carcinogenesis. Effects include direct DNA damage, e.g., by covalent binding, indirect DNA damage, e.g., by increased formation of reactive oxygen species or interaction with DNA replication or chromosome integrity. The `fixation' of a DNA adduct as a heritable mutation depends on its pro-mutagenic potency and on the rates of DNA repair and DNA replication. Endogenous and unavoidable DNA damage is responsible for a background rate of the process of mutagenesis and carcinogenesis and forms the basis of spontaneous cancer incidence. For DNA-reactive carcinogens, linearity of the dose response at the low-dose end is expected. With increasing dose, saturation of DNA repair can introduce a sublinearity (example: dimethylnitrosamine). Stimulation of cell division as a result of high-dose toxicity and regenerative proliferation also results in a sublinear deviation from low-dose linearity. If the DNA-damaging potency of the carcinogen is low in comparison with the high-dose effects, the linear part of the low dose–cancer incidence curve might be hidden within the background variability. Under such conditions, `practical thresholds' could be discussed (formaldehyde). If a carcinogen increases the rate of cell division or the level of oxidative stress at high dose but has an antimitogenic or antioxidative effect at low dose, a J-shaped (or: U-shaped) curve with a decrease of the spontaneous tumor incidence at low dose could result (caffeic acid; TCDD). This phenomenon has been observed even under conditions of a genotoxic contribution (ionizing radiation; diesel exhaust particles). For a mechanism-based assessment of a low-dose cancer risk, information on the various modes of action and modulations should be available over the full dose range, and models should be refined to incorporate the respective information.

Multistage carcinogenesis modeling and the initiation event.

Carcinogenesis is generally considered to be a multistage process classified under "initiation," "promotion," and "progression," and it is therefore of interest to know how radiation might affect them. Models which are currently being used with some success to analyze a variety of data are based on the two-mutation with clonal expansion model developed by Moolgavkar and Knudson [J Natl Cancer Inst 66:1037-1052, 1981]. These models imply that the "initiation" event would be a mutation but also imply that "progression" also involves mutation and that both these events could be influenced by radiation. The models offer the possibility of calculating the incidence of cancer over lifetime and can simultaneously provide the age and dose dependence of cancer. The models have implications for radiation protection and imply that radiation risk is related to spontaneous cancer incidence and that spontaneously induced "initiation" may also be associated with radiation-induced cancer.

Relevance of maximum tolerated dose to human carcinogenic risk

The shape of a carcinogen dose–cancer incidence curve is discussed as the result of a superposition of dose–response relationships for various effects of the carcinogen on the process of carcinogenesis. Effects include direct DNA damage, e.g., by covalent binding, indirect DNA damage, e.g., by increased formation of reactive oxygen species or interaction with DNA replication or chromosome integrity. The `fixation' of a DNA adduct as a heritable mutation depends on its pro-mutagenic potency and on the rates of DNA repair and DNA replication. Endogenous and unavoidable DNA damage is responsible for a background rate of the process of mutagenesis and carcinogenesis and forms the basis of spontaneous cancer incidence. For DNA-reactive carcinogens, linearity of the dose response at the low-dose end is expected. With increasing dose, saturation of DNA repair can introduce a sublinearity (example: dimethylnitrosamine). Stimulation of cell division as a result of high-dose toxicity and regenerative proliferation also results in a sublinear deviation from low-dose linearity. If the DNA-damaging potency of the carcinogen is low in comparison with the high-dose effects, the linear part of the low dose–cancer incidence curve might be hidden within the background variability. Under such conditions, `practical thresholds' could be discussed (formaldehyde). If a carcinogen increases the rate of cell division or the level of oxidative stress at high dose but has an antimitogenic or antioxidative effect at low dose, a J-shaped (or: U-shaped) curve with a decrease of the spontaneous tumor incidence at low dose could result (caffeic acid; TCDD). This phenomenon has been observed even under conditions of a genotoxic contribution (ionizing radiation; diesel exhaust particles). For a mechanism-based assessment of a low-dose cancer risk, information on the various modes of action and modulations should be available over the full dose range, and models should be refined to incorporate the respective information.

Dietary restriction in mice beginning at 1 year of age: effect on life-span and spontaneous cancer incidence.

Lifelong dietary restriction beginning at 3 to 6 weeks of age in rodents is known to decelerate the rate of aging, increase mean and maximum life-spans, and inhibit the occurrence of many spontaneous cancers. Little is known about the effects of dietary restriction started in middle age. In the experiments now reported the food intake of 12- to 13-month-old mice of two long-lived strains was restricted by using nutrient-enriched diets in accordance with the concept of "undernutrition without malnutrition." The mice on the restricted diet averaged 10 to 20 percent increases in mean and maximum survival times compared to the control mice. Spontaneous lymphoma was inhibited by the food restriction.

Biochemical and histochemical study of lactate dehydrogenase activity in ovaries of mice with high and low incidence of spontaneous cancer

Biochemical and histochemical study of lactate dehydrogenase activity in ovaries of mice with high and low incidence of spontaneous cancer

Influence of Irradiated Bacon Lipids on Body Growth, Incidence of Cancer, and Other Pathologic Changes in Micea

SUMMARYUncured bacon, irradiated with 5.58 megarads of gamma rays was compared with similar uncured unirradiated bacon by feeding to 757 mice. There were no major differences between the control and experimental groups. No gross or histopathological lesions attributable to irradiation of the lipid were observed. The incidence of spontaneous cancers showed no significant differences among the diet groups and indicates that irradiation of the bacon did not produce carcinogens or growth‐altering substances demonstrable under the conditions of these experiments.

The Relative Incidence of Oophorectomy in Women with and without Carcinoma of the Breast

In the past two decades numerous discussions and some evidence have appeared regarding the possible effect of ovarian-hormonal activities on the normally functioning as well as on the abnormally functioning breast. It is further true, however, that a close relationship between the activity of the ovary and that of the breast was widely recognized long before an attempt was made to explain such a relationship by modern hormonology. Most of the present conceptions concerning the possible role of the ovarian hormones in normal and abnormal activity of the breast are based on the results of animal experimentation. The very nature of the problem prevents, to some degree, the prosecution of studies on human beings. However, convincing results have been obtained in animals, especially mice. The investigations of Lathrop and Loeb (1916) and later of Cori (1927) are especially outstanding as regards an “ovarian-mammary” mechanism in the development of spontaneous carcinoma of female mice. Lathrop and Loeb, working with a strain of mice in which the incidence of spontaneous cancer in the female was high, found that castration of the females when they were less than six months of age led to marked decrease in the incidence of mammary tumors. In a later report Loeb (1919) was able to confirm and enlarge his previous results. He concluded that the hereditary factors which determine the development of mammary carcinoma in mice depend on the cooperation of a definite quantity of ovarian hormones if cancer is to develop. Such a conclusion was justifiable since the results showed that if the quantity of hormone that was acting exceeded a certain limit, mammary cancer appeared as frequently in the castrated animals as in those which were not castrated.

Possible Effect of Oil of Thyme on the Incidence of Spontaneous Cancer in Mice

In 1932 (1), a report was made on the possible effect of natural oil of Gaultheria on the incidence of cancer. The observations suggested the possibility that small amounts of that oil in a basic diet consisting of rolled oats, meat scrap, powdered milk, and salt delayed the time at which spontaneous tumors occurred in a series of mice belonging to the highly inbred dilute brown stock. The question arose whether this observation would also apply to other of the essential oils. To test out this idea, a number of mice were given oil of thyme in addition to their otherwise standard diet. The oil was given daily, in the ratio of one drop of oil to 20 gms. of the basic oatmeal diet.

Influence of Sex and Heredity on the Development of Tar Tumors

The influence of heredity on the induction of tar tumors in mice has been studied, according to Woglom (1), by Parodi (2), who concluded as a result of his experiments on a small number of animals, that heredity has no influence. Miss Lynch (3) extended this work, using two strains of mice in which the incidence of spontaneous mammary cancer was 65 per cent and 28 per cent respectively. These animals, 20 in each group, were painted with coal tar. No variation was detected between the two strains. Murray (4), working with mice having spontaneous tumors, endeavored to determine the influence these tumors would have on the artificial induction of tumors with tar. He makes the statement: “If there is a difference, it is in the direction of a more rapid induction of tumors in cancer mice.” For our purposes we have selected two strains of mice in which the incidence of spontaneous cancer is markedly different: a strain of albino mice (strain 3) in which the incidence of mammary cancer is 93 per cent of the bred females, and a hybrid strain resulting from crossing an albino with the common house mouse, having a low or delayed tumor incidence. Ninety-two animals of strain 3 and 32 of the hybrid strain were chosen for the experiment. They were kept in individual cages, and painted twice weekly with tar obtained from the Barrett Company, over an area approximately 1 cm. in diameter, in the interscapular region, from which the hair had previously been removed by sodium sulphide. After two weeks of tarring it was no longer necessary to remove the hair.