© 1999 Oxford University Press
Article |
Effect of reduced body weight gain on the evaluation of chemopreventive agents in the methylnitrosourea-induced mammary cancer model
1 Chemoprevention Center, University of Alabama at Birmingham, 1675 University Boulevard, Birmingham, AL 35294,
2 National Cancer Institute, Division of Cancer Prevention, Bethesda, MD 20892 and
3 University of Florida, Department of Comparative and Experimental Pathology, Gainesville, FL 32610, USA
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
These studies examined whether the small to moderate reductions in body weight gain (
15%) affect mammary carcinogenesis. Beginning 1 week prior to methylnitrosourea (MNU) administration (experiment 1), rats received diets supplemented with 4-hydroxyphenylretinamide (4-HPR) (782 mg/kg of diet) and retinyl acetate (328 mg/kg of diet) or underwent food restrictions. Rats were administered an i.v. dose of MNU (50 mg/kg body wt) at 50 days of age. Although the final body weights were similarly depressed by 4-HPR (8%) and by retinyl acetate (11%) from rats fed ad libitum, the kinetics of inhibition were quite different. Whereas 4-HPR caused an acute decrease in body weight at the time it was administered, the effect of retinyl acetate was more chronic. At 110 days after the administration of MNU, the average number of mammary cancers per rat was 4.9 for rats fed ad libitum, 1.3 for rats fed 4-HPR, 3.1 when body weights were matched to 4-HPR-treated rats, 1.9 for retinyl acetate and 3.2 when body weights were matched to retinyl acetate. Experiment II was performed to determine the minimal degree of acute body weight gain reduction that would alter MNU-induced mammary carcinogenesis. Body weight gain depressions of 3, 6, 9, 12 and 15% were initiated at 43 days of age by dietary restrictions and MNU was administered at 50 days of age. At 120 days after MNU, the percentage decreases in mammary cancer multiplicity in the various groups were 14, 15, 41, 44 and 55%, respectively. These data demonstrate that moderate reductions (9–15%) in body weight gain, in particular when occurring during the initiation and early promotion stages can greatly affect cancer multiplicity.
Abbreviations: DMBA, 7,12-dimethylbenz[a]anthracene; 4-HPR, 4-hydroxyphenylretinamide; MNU, methylnitrosourea.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Depression of body weight gain is frequently employed as a non-specific indicator of toxicity in animal chemoprevention studies. In the evaluation of potential chemopreventive agents in rodent mammary cancer models, it has generally been accepted that a final body weight gain depression of 15% or less is tolerable in animals receiving the agent (i.e. cancer results are not affected). Various laboratories (1), including our own, have observed body weight gain depressions when the retinoids 4-hydroxyphenylretinamide (4-HPR) and retinyl acetate are fed at doses that prevent chemically induced mammary cancers. The administration of 4-HPR at a dose level of 782 mg/kg of diet causes an initial (within the first few days) decrease in body weight gain of 12–15% in rats. The body weights of the rats partially recover over the next month, but remain 7–10% below controls fed ad libitum for the remainder of the study. In contrast, the administration of retinyl acetate at a dose level of 328 mg/kg of diet results in an initial depression of body weight gain of only 2–3% compared with the controls. However, during the course of the study body weight gain reduction gradually increases such that an 8–12% difference is observed at the end of a 4–6 month study. Similar patterns of depression of body weight gain are observed in various degrees with several chemopreventive compounds (2,3).
In the last 50 years, there has been a large volume of literature indicating that calorie restriction (resulting in greatly depressed body weights), as compared with an ad libitum diet, significantly alters spontaneous and chemically induced cancers in rodents (4–8). Earlier studies have demonstrated that calorie restricted mice exhibit a decreased number of tumors in mammary, lung and skin cancer models as compared with mice fed ad libitum (9). More recent studies have focused on the degree of energy restriction necessary to reduce the incidence of cancers. For example, Klurfeld et al. (10) found that mammary tumor incidence can be reduced significantly by 20, 30 and 40% calorie restriction in female Sprague–Dawley rats receiving 7,12-dimethylbenz[a]anthracene (DMBA). Kritchevsky et al. (11) and Klurfeld et al. (12) also found that a 40% calorie-restricted diet inhibited chemically induced mammary and colon tumors in rats when compared with rats fed an ad libitum diet. Other recent studies have focused on the type of calories that are restricted (13). In most animal studies, calorie restriction seems to have a more striking effect on cancer incidence than the modification of specific fats in the diet (14).
The present studies were performed to determine the effects of limited body weight reductions (similar to those seen in chemoprevention studies) on the incidence and multiplicity of methylnitrosourea (MNU)-induced mammary cancers. In experiment I, the effects of 4-HPR, retinyl acetate and body weight alterations (to match the body weights observed in the retinoid-treated groups) on mammary cancers induced by MNU were determined. In experiment II, the objective was to determine the minimal levels of reduction in body weight necessary to significantly reduce the number of mammary cancers when compared with controls fed ad libitum. The effect of moderate reductions in body weight gain of 3, 6, 9, 12 and 15% on MNU-induced mammary cancers were determined.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Animals
Female Sprague–Dawley rats were obtained from Harlan Sprague–Dawley (Indianapolis, IN) (virus-free colony number 202). Upon arrival, Teklad (4% fat) rodent diet (Harlan Teklad, Madison, WI) and tap water were given ad libitum. All animals were housed individually in polycarbonate cages. The rats were kept in a room artificially lighted for 12 h.
Chemicals
Retinyl acetate was purchased from Sigma (St Louis, MO) and 4-hydroxyphenylretinamide (4-HPR) was supplied gratis by McNeil Pharmaceuticals (Spring House, PA). The vehicle for these retinoids consisted of 12 g ethanol, 19 g trioctanoin (a triglyceride), 0.05 ml Tenox-20 and 0.05 ml DL-
-tocopherol per kg of diet. The purity and stability of the agents in the diets were verified by photospectroscopy and HPLC. The analytical procedures used to assay 4-HPR and retinyl esters have been described previously (24). MNU was purchased from Ash Stevens (Detroit, MI). A preliminary study lasting 4 weeks was performed, using 10 rats per group, to verify that the procedures for measuring food consumption would be appropriate (Table I
).
|
Experiment I
Retinyl acetate and 4-HPR diet supplementation or feed restrictions were initiated when the rats were 43 days of age (Table II
). The control group (group 1) was fed Teklad (4% fat) mash diet ad libitum. The retinoid-treated rats also were fed ad libitum. The treatment groups were: group 2, 4-HPR (782 mg/kg of diet); group 3, feed restriction such that the body weights of the 4-HPR treated rats were matched; group 4, retinyl acetate (328 mg/kg of diet); group 5, feed restriction such that body weights of retinyl acetate-treated rats were matched. Food consumption and body weight measurements were taken weekly in group 1. The body weights and food consumption for rats in groups 2–5 were measured twice/week. In groups 3 and 5 (feed restriction groups), food consumption amounts were adjusted twice/week. Adjustments in feed intake were made according to the amount of food that was projected would keep the rats' body weight similar to the body weights of rats receiving the retinoids (groups 2 and 4). Since each animal was housed individually, one was assured that each rat received the appropriate amount of powdered diet. MNU was administered at 50 days of age by i.v. injection (50 mg/kg body wt) via the jugular vein. At 6 and 12 weeks after the initial retinoid treatment or feed restriction, vaginal smears were taken (10 rats/group) to determine estrus cycle lengths. All animals were palpated for mammary tumors twice each week. Palpable tumor location was recorded at the time of tumor appearance. The study was terminated 110 days after MNU administration.
|
Experiment II
The control group (group 1) was fed Teklad mash diet ad libitum (Table III
). The experimental groups included body weight gain reductions (as compared with group 1) of 3, 6, 9, 12 and 15% for groups 2, 3, 4, 5 and 6, respectively. Food restriction was initiated at 43 days of age and continued throughout the study. All rats were weighed three times per week (groups 1–6). Food consumption measurements were also taken three times per week for group 1. Adjustments in food intake for groups 2–6 were made three times/week and were made according to the level of percentage reduction in body weight gain required for each specified group as compared with group 1 (animals fed ad libitum). MNU was administered at 50 days of age by i.v. injection (50 mg/kg body wt) via the jugular vein. At 6 and 12 weeks after dietary restriction was initiated, vaginal smears were taken (10 rats/group) over a period of 2 weeks in order to determine estrus cycle lengths. All animals were palpated for mammary tumors twice each week. The study was terminated 130 days after MNU administration. Levels of serum progesterone and testosterone for group 1 (Teklad diet ad libitum), group 3 (6% reduction) and group 5 (12% reduction) were measured using solid phase 125I-radioimmunoassay coat-a-count kits from Diagnostic Products (Los Angeles, CA). Estradiol serum levels for these groups were determined using a solid phase 125I-double antibody kit from Diagnostic Products.
|
Histology and statistics
In each experiment, all mammary tumors were excised at necropsy and processed for histological classification (15). Mammary cancers were classified as adenocarcinomas. The log rank test (16) was used to analyze cancer incidence rates. The average number of cancers per rat was analyzed using the Armitage test (17). In experiment II, differences in the levels of serum estradiol, progesterone and testosterone were determined using the Mann–Whitney rank sum test (18).
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
A preliminary study was performed to verify that the food restriction procedures to be used would permit the matching of body weight gain depressions that are observed in retinoid-treated rats. The study lasted 4 weeks and demonstrated that it was feasible. By measuring food consumption, it was found that food consumed per day in the ad libitum fed control group was fairly constant (17–18 g/day) over the entire observation period. This was interesting since the body weights of the rats increased by 39%, from 150 g at 49 days to 209 g at 77 days of age (Table I
).
The body weights of the rats in each group in experiment I are presented in Figure 1. As shown, the body weights of the rats receiving the retinoids were depressed throughout the study. The administration of the carcinogen at 50 days of age caused a slight decrease in body weights of the rats for ~1 week. The patterns of body weight gain depression observed in the rats receiving 4-HPR and retinyl acetate were similar to those observed in earlier studies. Food consumption measurements throughout the study revealed that the average feed consumed per rat per day was 17.4 g for Teklad diet only (group 1), 16.9 g for 4-HPR (group 2) and 16.0 g for retinyl acetate (group 4). At the end of the study, the rats that received 4-HPR exhibited an 8% depression in body weight, whereas rats that received retinyl acetate had an 11% decrease (Table II). The depression of body weight gains did not affect the survival of the rats or cause any gross signs of toxicity. Estrus cycles were also not altered by these levels of body weight gain restrictions.
|
, Teklad diet ad libitum; • 4-HPR (782 mg/kg of diet); 
, food restricted to match body weights of 4-HPR-treated rats; 
, retinyl acetate (328 mg/kg of diet); 
, food restricted to match body weights of retinyl acetate-treated rats.The rats that received Teklad diet ad libitum (group 1) developed a 100% incidence of mammary cancers with an average of 4.9 cancers/rat (Table II
). In animals that received 4-HPR at a dose level of 782 mg/kg of diet (group 2), the number of mammary cancers was reduced to 1.3 cancers/rat (73%). Matching the body weight gain depression caused by 4-HPR (group 3) by restricting food intake caused a 37% decrease in the number of mammary cancers (to 3.1 cancers/rat). The administration of retinyl acetate (328 mg/kg of diet) decreased mammary cancer multiplicity by 61%. Matching the body weight gain pattern of the retinyl acetate-treated rats resulted in a 35% decrease in mammary cancer number. As shown in Figure 2, the administration of the retinoids, as well as similar depressions of body weight gain, increased the latency period of the mammary cancers.
|
In experiment II moderate reductions in body weight gain (3, 6, 9, 12 and 15%), induced at the time of carcinogen administration, were maintained throughout this study (Figure 3
). The actual percentage difference in body weights for each group versus the control group (group 1) was determined three times per week. The average percentage values over the entire study were 3.3% for group 2 (3% body weight gain reduction), 6.3% for group 3 (6% reduction), 8.6% for group 4 (9% reduction), 11.6% for group 5 (12% reduction) and 14.7% for group 6 (15% reduction). The average grams of food consumed per day by the rats in the various groups were 18.5 g for group 1, 18.1 g for group 2, 17.7 g for group 3, 16.8 g for group 4, 15.8 g for group 5 and 14.8 g for group 6. The depression of body weight gain did not affect the survival of the rats or cause any gross signs of toxicity. Estrus cycles were also not altered by these levels of body weight gain restrictions.
|
, 15% reduction.The rats in group 1 (Teklad diet ad libitum) developed a 100% incidence of mammary cancers with an average of 6.6 cancers/rat (Table III
). Although the latency of cancers was delayed in all restricted groups, there were no major differences in cancer incidence from the control group at the end of the study. Animals with reduced body weights of 3 and 6% showed a slight decrease in mammary cancer numbers (14–15%) as compared with the controls. Rats that were maintained at body weights of 9 and 12% below the controls had significant decreases in mammary cancer tumor multiplicity of 41 and 44%, respectively. A depression in body weight gain of 15% caused a 55% decrease in cancers as well as a large increase in the latency period of the cancers (Figure 4). Similarly, restricting body weight gain caused reductions in the average weight of the mammary cancers: Teklad diet ad libitum, 7.68 g; 3% body weight gain reduction, 5.33 g; 6% reduction, 3.59 g; 9% reduction, 2.99 g; 12% reduction, 2.85 g; and 15% reduction, 2.89 g. At the end of experiment II, serum levels of estradiol and progesterone (Table IV) in groups 3 (6% reduction) and 5 (12% reduction) were not significantly different from group 1 (Teklad diet ad libitum). Serum levels of testosterone in group 3 were significantly elevated (P < 0.01) when compared with group 1; however, a significant difference was not observed in the greater body weight reduced group (group 5).
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Numerous studies have shown that many retinoids are highly effective in preventing cancers in experimental animal models (19,20). Specifically, retinyl acetate and 4-HPR have been shown to be active in the prevention of mammary cancer (21–24). In chemoprevention studies, Welsch et al. (21) reported that feeding retinyl acetate depressed body weights by 13% and our laboratory previously found that feeding 4-HPR for a limited time depressed body weights by 7% (24). In this study, we confirmed that doses of these retinoids, which significantly decreased the number of mammary cancers induced by MNU, caused depressions in body weight gain of 8–11% from rats fed ad libitum that were only provided the Teklad (Table II
). Radcliffe and Moon (1) measured food consumption in rats fed 4-HPR at a dose level of 782 mg/kg of diet and reported that the observed depressed body weight during the first week of feeding was due entirely to reduced food intake. Our data also showed a 37% decrease in food intake during the first week in rats fed 4-HPR. In a preliminary study to verify that the body weight gain depressions observed in retinoid-treated rats could be matched by food restrictions, it was found that food consumed per day in rats fed ad libitum is fairly constant (17–18 g/day) even though body weights of the rats greatly increase with time. Thus, if a chemopreventive agent is mixed in the diet, the amount of the agent consumed by older rats is actually less when expressed on a `per g of body weight' basis. This is of importance when determining dose levels of an agent to be used in chemoprevention studies since the maximum tolerated dose is routinely determined in relatively young animals.
The mechanism by which moderate to severe dietary restrictions result in decreased chemically induced mammary cancers have been extensively investigated. In rats underfed (50% food restriction) for 1 week prior to and 1 week after DMBA administration, the resulting reduction in mammary tumors appears to be associated with suppression of prolactin and estrogen secretion (4). A 58% decrease in mammary tumor incidence was demonstrated in DMBA-treated rats fed 20% less food/day when compared with ad libitum-fed carcinogen treated controls (6). There were, however, no differences in plasma levels of estrogen or in the labeling index of mammary epithelial cells at the time of carcinogen treatment of the two groups of rats. Other mechanisms to explain the effects of severe (25% or greater) dietary restrictions in carcinogenesis have focused on decreased cellular proliferation (25), altered immune function (26), altered growth factor responsiveness (27), reduced insulin levels (28), enhanced DNA repair (29) and increased activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) (30). Birt et al. (31) have reported that calorie restriction reduces protein kinase C activity in a chemically induced skin cancer model. A recent study (32) found that adrenal cortical activity increased in proportion to the degree of calorie restriction, and that this increase parallels the level of cancer inhibition. Although severe body weight depressions alter various parameters, it is not known if the more limited body weight reductions observed in many chemoprevention studies cause similar changes.
The data demonstrate that at least part of the chemopreventive activity of agents that depress body weight gain can be attributed to factors other than the agent per se, and that this altered body weight effect is particularly striking when it occurs immediately at the time of carcinogen administration. When evaluating chemopreventive agents in chemically induced mammary cancer models, therefore, every effort should be made to use dose levels that do not depress body weight gains >5%. Our findings did not show any biologically significant alterations in serum levels of progesterone, testosterone or estradiol serum levels in the dietary restricted rats as compared with the ad libitum fed controls (when measured at the end of the study). Additional studies are warranted that will determine the effects of moderate body weight gain reduction during either the initiation or promotion stage of the mammary carcinogenic process, and that will determine if other in vivo cancer models are similarly affected by body weight gain depressions.
|
Notes |
|---|
4 To whom correspondence should be addressed Email: grubbsc{at}admin.shrp.uab.edu
|
Acknowledgments |
|---|
The authors would like to express their appreciation to the technicians for their excellent work, to Ms Mary Jo Hodges and Ms Kelly Noles for secretarial assistance, to Mr Harry Vaughn and Dr Mike Hardin for statistical analyses and to Ms Mattie Bandy for serum steroid analyses. This investigation was supported by NCI contracts N01-CN-25454-04 and N01-CN-55148-MAO., awarded by the National Cancer Institute, Division of Cancer Prevention (to C.J.G.).
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
- Radcliffe,J.D. and Moon,R.C. (1983) Effect of N-(4-hydroxyphenyl) retinamide on food intake, growth and mammary gland development in rats. Proc. Soc. Exp. Biol. Med., 174, 270–275.[Abstract]
- Anzano,M.A., Byers,S.W., Smith,J.M., Peer,C.W., Mullen,L.T., Brown,C.C., Roberts,A.B. and Sporn,M.B. (1994) Prevention of breast cancer in the rat with 9-cis-retinoic acid as a single agent and in combination with tamoxifen. Cancer Res., 54, 4614–4617.
[Abstract/Free Full Text] - Ratko,T.A., Detrisac,C.J., Mehta,R.G., Kelloff,G.J. and Moon,R.C. (1991) Inhibition of rat mammary gland chemical carcinogenesis by dietary dehydroepiandrosterone or a fluorinated analogue of dehydroepiandrosterone. Cancer Res., 51, 481–486.
[Abstract/Free Full Text] - Sylvester,P.W., Aylsworth,C.F., Van Vugt,D.A. and Meites,J. (1982) Influence of underfeeding during the `critical period' or thereafter on carcinogen-induced mammary tumors in rats. Cancer Res., 42, 4943–4947.
[Abstract/Free Full Text] - Cohen,L.A., Choi,K. and Wang,C.-X. (1988) Influence of dietary fat, calorie restriction and voluntary exercise on N-nitrosomethylurea-induced mammary tumorigenesis in rats. Cancer Res., 48, 4276–4283.
[Abstract/Free Full Text] - Sinha,D.K., Gebhard,R.L. and Pazik,J.E. (1988) Inhibition of mammary carcinogenesis in rats by dietary restriction. Cancer Lett., 40, 133–141.[ISI][Medline]
- Hart,R.W., Leakey,J.E., Chou,M., Duffy,P.H., Allaben,W.T. and Fevers,R.J. (1992) Modulation of chemical toxicity by modification of caloric intake. Adv. Exp. Med. Biol., 322, 73–81.[Medline]
- Rao,G.N., Piegorsch,W.W. and Haseman,J.K. (1987) Influence of body weight on the incidence of spontaneous tumors in rats and mice of long-term studies. Am. J. Clin. Nutr., 45, 252–260.
[Free Full Text] - Tannenbaum,A. (1940) The initiation and growth of tumors. Am. J. Cancer, 38, 335–350.
- Klurfeld,D.M., Welch,C.B., Davis,M.J. and Kritchevsky,D. (1989) Determination of degree of energy restriction necessary to reduce DMBA-induced mammary tumorigenesis in rats during the promotion phase. J. Nutr., 119, 286–291.
[Abstract/Free Full Text] - Kritchevsky,D., Weber,M.M. and Klurfeld,D.M. (1984) Dietary fat versus caloric content in initiation and promotion of 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis in rats. Cancer Res., 44, 3174–3177.
[Abstract/Free Full Text] - Klurfeld,D.M., Weber,M.M. and Kritchevsky,D. (1987) Inhibition of chemically-induced mammary and colon tumor promotion by caloric restriction in rats fed increased dietary fat. Cancer Res., 47, 2759–2762.
[Abstract/Free Full Text] - Boissonneault,G.A., Elson,C.E. and Pariza,M.W. (1986) Net energy effects of dietary fat on chemically-induced mammary carcinogenesis in F344 rats. J. Natl Cancer Inst., 76, 335–338.[ISI][Medline]
- Kritchevsky,D., Weber,M.M., Buck,C.L. and Klurfeld,D.M. (1986) Calories, fat and cancer. Lipids, 21, 272–274.[ISI][Medline]
- Young,S. and Hallowes,R.C. (1973) Tumors of the mammary gland. In Pathology of Tumors in Laboratory Animals, vol. 5. IARC Scientific Publications, Lyon, pp. 31–73.
- Peto,J. (1988) The calculation and interpretation of survival curves. In Buyse,M.E. (ed.) Cancer Clinical Trials: Methods and Practice. Oxford University Press, Oxford, pp. 361–380.
- Armitage,P. (1966) The chi-square test for heterogeneity of proportion after adjustment for stratification. J. R. Stat. Soc., B28, 150–163.
- Siegel,S. and Castellan,N.J. (1988) Nonparametric Statistics for the Behavioral Sciences, 2nd edn. McGraw–Hill, New York, NY.
- Hill,D.L. and Grubbs,C.J. (1992) Retinoids and cancer prevention. Annu. Rev. Nutr., 12, 161–181.[ISI][Medline]
- Wattenberg,L.W. (1992) Inhibition of carcinogenesis by minor dietary constituents. Cancer Res., 52 (suppl.), 2085s–2091s.[Medline]
- Welsch,C.W., Brown,C.K., Goodrich-Smith,M., Chivsano,J. and Moon,R.C. (1980) Synergistic effect of chronic prolactin suppression and retinoid treatment in the prophylaxis of N-methyl-N-nitrosourea-induced mammary tumorigenesis in female Sprague–Dawley rats. Cancer Res., 40, 3095–3098.
[Abstract/Free Full Text] - Moon,R.C., Grubbs,C.J. and Sporn,M.B. (1976) Inhibition of 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis by retinyl acetate. Cancer Res., 36, 2626–2630.[ISI]
- McCormick,D.L., Mehta,R.G., Thompson,C.A., Dinger,N., Caldwell,J.A. and Moon,R.C. (1982) Enhanced inhibition of mammary carcinogenesis by combined treatment with N-(4-hydroxyphenyl) retinamide and ovariectomy. Cancer Res., 42, 508–512.
[Abstract/Free Full Text] - Grubbs,C.J., Eto,I., Juliana,M.M., Hardin,J.M. and Whitaker,L.M. (1990) Effect of retinyl acetate and 4-hydroxyphenylretinamide on initiation of chemically-induced mammary tumors. Anticancer Res., 10, 661–666.[ISI][Medline]
- Lok,E., Nera,E.A., Iverson,F., Scott,F., So,Y. and Clayson,D.B. (1988) Dietary restriction, cell proliferation and carcinogenesis: a preliminary study. Cancer Lett., 38, 249–255.[ISI][Medline]
- Weindruch,R.H., Devens,B.H., Raff,H.V.and Walford,R.L. (1983) Influence of dietary restriction on aging and natural killer cell activity in mice. J. Immunol., 130, 993–996.[Abstract]
- Ruggeri,B.A., Klurfeld,D.M., Kritchevsky,D. and Furlanetto,R.W. (1989) Growth factor binding to 7,12-dimethylbenz[a]anthracene-induced mammary tumors from rats subjected to chronic caloric restriction. Cancer Res., 49, 4135–4141.
[Abstract/Free Full Text] - Ruggeri,B.A., Klurfeld,D.M., Kritchevsky,D. and Furlanetto,R.W. (1989) Caloric restriction and 7,12-dimethylbenz[a]anthracene-induced mammary tumor growth in rats: alterations in circulating insulin, insulin-like growth factors I and II and epidermal growth factor. Cancer Res., 49, 4130–4134.
[Abstract/Free Full Text] - Lipman,J.M., Turturro,A. and Hart,R.E. (1989) The influence of dietary restrictions on DNA repair in rodents: a preliminary study. Mech Aging Dev., 48, 135–144.
- Rao,G., Xia,E., Nadakavukaren,M.J. and Richardson,A. (1990) Effect of dietary restrictions on the age-dependent changes in the expression of antioxidant enzymes in rat liver. J. Nutr., 120, 602–609.
[Abstract/Free Full Text] - Birt,D.F., Kris,E.S., Choe,M. and Pelling,J.C. (1992) Dietary energy and fat effects on tumor promotion. Cancer Res., 52, 2035s–2039s.
- Zhu,Z., Haegele,A.D. and Thompson,H.F. (1997) Effect of caloric restriction on pre-malignant and malignant stages of mammary carcinogenesis. Carcinogenesis, 18, 1007–1012.
[Abstract/Free Full Text]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  B. Malewicz, Z. Wang, C. Jiang, J. Guo, M. P. Cleary, J. P. Grande, and J. Lu Enhancement of mammary carcinogenesis in two rodent models by silymarin dietary supplements Carcinogenesis, September 1, 2006; 27(9): 1739 - 1747. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Watanabe, Y. Kashida, M. Ueda, H. Onodera, T. Takizawa, M. Hirose, and K. Mitsumori Inhibition by Ethinylestradiol of N-Ethyl-N-Nitrosourea-Initiated Uterine Carcinogenesis in Transgenic Mice Carrying a Human Prototype C-Ha-ras Gene (rasH2 Mice) Toxicol Pathol, August 1, 2003; 31(5): 496 - 505. [Abstract] [PDF]
|
|
|
|
 |
|
 C. Zou, A.-T. Vlastos, L. Yang, J. Wang, M. Brewer, and M. Follen Effect of 4-Hydroxyphenylretinamide on Human Cervical Epithelial and Cancer Cell Lines Reproductive Sciences, January 1, 2003; 10(1): 41 - 48. [Abstract] [PDF]
|
|
|
|
 |
|
 T. R. Sutter, X.-R. He, P. Dimitrov, L. Xu, G. Narasimhan, E. O. George, C. H. Sutter, C. Grubbs, R. Savory, M. Stephan-Gueldner, et al. Multiple Comparisons Model-based Clustering and Ternary Pattern Tree Numerical Display of Gene Response to Treatment: Procedure and Application to the Preclinical Evaluation of Chemopreventive Agents Mol. Cancer Ther., December 1, 2002; 1(14): 1283 - 1292. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Murata and S. Kawanishi Oxidative DNA Damage by Vitamin A and Its Derivative via Superoxide Generation J. Biol. Chem., January 21, 2000; 275(3): 2003 - 2008. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||