Inhibition of chemically induced mammary and colon tumor promotion by caloric restriction in rats fed increased dietary fat

Tumor promotion associated with increased dietary fat may be inhibited by reduction in total caloric intake. This hypothesis was tested in rats given either 7,12-dimethylbenz(a)anthracene to induce mammary tumors or 1,2-dimethylhydrazine to induce colon tumors. One week after dosage with either carcinogen, the rats were fed semipurified diets that provided 4% fat with ad libitum calories or 13.1% fat with a reduction of calories by 40% from ad libitum intake. Rats treated with 7,12-dimethylbenz(a)anthracene and subjected to caloric restriction weighed 40% less than those fed ad libitum; rats treated with 1,2-dimethylhydrazine were heavier at the onset of caloric restriction and lost weight and weighed approximately 40% less than animals fed ad libitum. At 20 weeks after 7,12-dimethylbenz(a)anthracene administration, rats fed ad libitum had 80% tumor incidence while in those fed restricted calories, 20% had tumors (P less than 0.001). All other measures of mammary tumor growth were significantly reduced in rats given restricted calories. Six months after 1,2-dimethylhydrazine administration, colon tumor incidence was 100% in rats fed ad libitum and 53% in those fed the calorie-restricted diet (P less than 0.001). This reduction of colonic carcinogenesis was seen despite a significant increase in mucosal labeling index following [3H]thymidine autoradiography. This paradoxical finding may be due to the increased fat content of the calorie-restricted diet. These data demonstrate that the tumor-promoting effects of dietary fat can be more than offset by a reduction in total caloric intake and that the promoting effect of fat may be due, at least in part, to its greater caloric density.     

Influence of dietary fat, caloric restriction, and voluntary exercise on N-nitrosomethylurea-induced mammary tumorigenesis in rats

The effect of dietary fat, energy restriction, and exercise on N-nitrosomethylurea (NMU:CAS:684-93-5)-induced mammary tumorigenesis in female F344 rats was investigated. Rats were fed the NIH-07 diet until N-nitrosomethylurea administration on Day 50 of age, when they were transferred to six treatment groups. Three sedentary groups were fed either high-fat (20%, w/w), medium-fat (10%), or low-fat (5%) diets ad libitum (HFAL, MFAL, LFAL, respectively); two sedentary groups were fed high fat and medium fat diets restricted to 75% of the food consumed by their ad libitum counterparts (HFR, MFR), and one group was fed a HFAL diet but allowed free access to an activity wheel (HFEX). Tumor yields among the three ad libitum sedentary groups were significantly greater in the HFAL and MFAL groups when compared to the LFAL group. Dietary restriction reduced tumor yields by more than 90% of ad libitum controls regardless of fat intake. Voluntary exercise reduced tumor yields and delayed time of tumor appearance in HFEX animals to levels similar to those found in LFAL animals. Animals with voluntary access to exercise wheels averaged between 1.03 and 2.85 miles/day, consumed more food (+18%), and exhibited greater weight gain (+13%) than their sedentary counterparts. Restricted animals exhibited significantly decreased body weight gains (-15%) compared to their ad libitum counterparts, but no differences in weight gains were detected among the HFAL, MFAL, and LFAL groups, despite widely varying amounts of fat intake. Body composition studies indicated that body fat content was not influenced by the quantity of fat consumed in the diet, but was significantly reduced by caloric restriction (-20 to 26%) and exercise (-20%). While the precise mechanisms underlying the tumor-promoting effects of HFAL diets and the antipromoting effects of energy restriction and exercise remain to be elucidated, available evidence suggests that these effects are not due to alterations in energy homeostasis per se, but may instead be exerted indirectly, and perhaps independently via endocrine, paracrine, or neurohormonal mechanisms.     

Combinations of tomato and broccoli enhance antitumor activity in dunning r3327-h prostate adenocarcinomas

The consumption of diets containing 5 to 10 servings of fruits and vegetables daily is the foundation of public health recommendations for cancer prevention, yet this concept has not been tested in experimental models of prostate cancer. We evaluated combinations of tomato and broccoli in the Dunning R3327-H prostate adenocarcinoma model. Male Copenhagen rats (n=206) were fed diets containing 10% tomato, 10% broccoli, 5% tomato plus 5% broccoli (5:5 combination), 10% tomato plus 10% broccoli (10:10 combination) powders, or lycopene (23 or 224 nmol/g diet) for approximately 22 weeks starting 1 month prior to receiving s.c. tumor implants. We compared the effects of diet to surgical castration (2 weeks before termination) or finasteride (5 mg/kg body weight orally, 6 d/wk). Castration reduced prostate weights, tumor areas, and tumor weight (62%, P<0.001), whereas finasteride reduced prostate weights (P<0.0001), but had no effect on tumor area or weight. Lycopene at 23 or 224 nmol/g of the diet insignificantly reduced tumor weights by 7% or 18%, respectively, whereas tomato reduced tumor weight by 34% (P<0.05). Broccoli decreased tumor weights by 42% (P<0.01) whereas the 10:10 combination caused a 52% decrease (P<0.001). Tumor growth reductions were associated with reduced proliferation and increased apoptosis, as quantified by proliferating cell nuclear antigen immunohistochemistry and the ApopTag assay. The combination of tomato and broccoli was more effective at slowing tumor growth than either tomato or broccoli alone and supports the public health recommendations to increase the intake of a variety of plant components.     

Oncodevelopmental enzymes of the Dunning rat prostatic adenocarcinoma

In this paper, data are presented which demonstrate that adenylate kinase and creatine kinase are oncodevelopmental enzymes in the rat prostate. The Dunning tumor (dorsal rat prostate) was used as a model system; four sublines of the tumor (R3327-H, R3327-AT, MAT Lu, and MAT LyLu) were studied. The tumor lines were maintained as solid tumors in syngeneic rats (Copenhagen) and as monolayers in tissue culture. The appearance of adenylate kinase with malignant transformation of the dorsal prostate was demonstrated. The disappearance of the CK-M subunit of creatine kinase and decreasing levels of creatine kinase were demonstrated with increasing anaplasia. The lactate dehydrogenase (LDH) concentration increased with increasing anaplasia, and the LDH isoenzyme pattern shifted to a more glycolytic pattern (LDH-4, LDH-5). The malignant isoenzyme pattern was reversible with the use of a differentiating agent (dimethyl sulfoxide). Prostates from neonatal rats and castrated adult male rats exhibited patterns of creatine kinase and adenylate kinase similar to those of the undifferentiated tumor. The oncofetal isoenzyme pattern of the castrated rat prostate was reversible with physiological levels of exogenous testosterone.     

R3327 prostate adenocarcinoma clonogenic cells: epithelial properties and hormone response

Cell colonies derived from the clonogenic tumor cell [colony-forming cell, prostate adenocarcinoma (CFC-PA)] assayed in vitro from the R3327 rat prostate adenocarcinoma demonstrate prostate acid phosphatase activity when assayed histochemically and convert testosterone to stanolone. The number of CFC-PA/10(4) cells plated in steroid-free cultures was increased following the addition of testosterone or stanolone and decreased following the addition of 17 beta-estradiol. The decreased rate of growth of the R3327 tumor in castrated male inbred Copenhagen rats when compared to the growth measured in normal (intact) male and female inbred Copenhagen rats was reflected in a large decrease in the number of CFC-PA/10(4) cells plated from tumors grown in castrated male rats when compared to the values obtained from tumors that were grown in normal male and female rats. Furthermore, the replacement of fetal calf serum with normal male or castrated male rat serum resulted in little change in CFC-PA/10(4) cells plated in cultures established from tumors grown in castrated rats, although significant increases in CFC-PA were observed in cultures established from tumors grown in normal male or female rats.     

Dietary restriction reduces angiogenesis and growth in an orthotopic mouse brain tumour model

Diet and lifestyle produce major effects on tumour incidence, prevalence, and natural history. Moderate dietary restriction has long been recognised as a natural therapy that improves health, promotes longevity, and reduces both the incidence and growth of many tumour types. Dietary restriction differs from fasting or starvation by reducing total food and caloric intake without causing nutritional deficiencies. No prior studies have evaluated the responsiveness of malignant brain cancer to dietary restriction. We found that a moderate dietary restriction of 30-40% significantly inhibited the intracerebral growth of the CT-2A syngeneic malignant mouse astrocytoma by almost 80%. The total dietary intake for the ad libitum control group (n=9) and the dietary restriction experimental group (n=10) was about 20 and 13 Kcal x day(-1), respectively. Overall health and vitality was better in the dietary restriction-fed mice than in the ad libitum-fed mice. Tumour microvessel density (Factor VIII immunostaining) was two-fold less in the dietary restriction mice than in the ad libitum mice, whereas the tumour apoptotic index (TUNEL assay) was three-fold greater in the dietary restriction mice than in the ad libitum mice. CT-2A tumour cell-induced vascularity was also less in the dietary restriction mice than in the ad libitum mice in the in vivo Matrigel plug assay. These findings indicate that dietary restriction inhibited CT-2A growth by reducing angiogenesis and by enhancing apoptosis. Dietary restriction may shift the tumour microenvironment from a proangiogenic to an antiangiogenic state through multiple effects on the tumour cells and the tumour-associated host cells. Our data suggest that moderate dietary restriction may be an effective antiangiogenic therapy for recurrent malignant brain cancers.     

Interrelationships between dietary restriction, the IGF-I axis, and expression of vascular endothelial growth factor by prostate adenocarcinoma in rats

Human studies suggest that excessive energy intake and obesity may influence prostate cancer progression. Rodent experiments demonstrate that diet restriction attenuates tumor growth in parallel with reduced vascular density. The present study examines changes in the insulin-like growth factor I (IGF-I) axis caused by dietary restriction and their association with the expression of vascular endothelial growth factor (VEGF) in prostate cancer. Weanling male Copenhagen rats were randomized into control or 40% dietary restricted groups (n = 5). After 8 wk, rats were implanted with rat AT6.3 prostate adenocarcinoma cells. Two weeks later, the animals were sacrificed and serum, normal prostate, liver, and prostate tumor samples were collected for analyses. Dietary restriction reduced serum concentrations of IGF-I by 35% (P < 0.05) and increased IGF-binding protein-3 (IGFBP3) by sevenfold (P < 0.0001). Lower circulating IGF-I concentrations were correlated with reduced IGF-I mRNA expression in the liver, the primary source of circulating IGF-I. Dietary restriction also lowered mRNA expression of IGF-I (45%, P = 0.0242) and its receptor IGFIR (40%, P = 0.0083) in prostate tumors. Similarly, reduced VEGF mRNA (30%, P = 0.0176) and secreted VEGF protein (33%, P = 0.0003) were observed in prostate cancer of restricted rats. An in vitro study employing AT6.3 prostate cancer cells demonstrated dose- and time-dependent stimulation of VEGF expression by IGF-I. These results suggest that dietary restriction reduces endocrine and prostate tumor autocrine/paracrine IGF-I expression, which contributes to reduced VEGF expression and signaling, to inhibit tumor angiogenesis associated with prostate tumorigenesis.     

Cancer progression in the transgenic adenocarcinoma of mouse prostate mouse is related to energy balance, body mass, and body composition, but not food intake

Calorie restriction can inhibit or delay carcinogenesis, reportedly due to a reduction in calorie intake rather than by concurrent changes in body mass and/or composition. Our objective was to test the hypothesis that body mass and/or composition have an important effect, independent of energy intake, on the benefits or hazards associated with calorie restriction or overeating, respectively. In the first experiment, transgenic mice that spontaneously develop prostate cancer [transgenic adenocarcinoma of mouse prostate (TRAMP)] were housed at 27 degrees C or 22 degrees C and pair fed the same diet for 21 weeks (95% of ad libitum intake at 27 degrees C). In the second experiment, TRAMP mice were housed at 27 degrees C or 22 degrees C and fed the same diet ad libitum for 21 weeks. Despite a similar calorie intake, pair-fed mice at 27 degrees C (PF27) were heavier (28.3 +/- 3.3 versus 17.6 +/- 1.6 g at 21 weeks; P < 0.001; mean +/- SD) and had greater fat (6.4 +/- 2.1 versus 1.9 +/- 0.3 g; P < 0.001) and lean mass (P < 0.001) than pair-fed mice at 22 degrees C. Furthermore, PF27 mice had greater levels of serum leptin (P < 0.001), lower levels of adiponectin (P < 0.05), and a greater frequency of prostatic adenocarcinoma (P < 0.05). In contrast, ad libitum-fed mice housed at 22 degrees C consumed approximately 30% more calories than ad libitum-fed mice at 27 degrees C, but there was no difference between groups in body composition or cancer progression. These results imply that the ability of calorie restriction to inhibit or delay cancer incidence and progression is mediated in part by changes in energy balance, body mass, and/or body composition rather than calorie intake per se, suggesting that excess calorie retention, rather than consumption, confers cancer risk.     

Dietary fat versus caloric content in initiation and promotion of 7,12-dimethylbenz(a)anthracene-induced mammary tumorigenesis in rats

Enhancement of mammary tumor formation by dietary fat may be mediated via increased caloric intake. Three experiments were performed to study this relationship in 7,12-dimethyl-benz(a)anthracene (DMBA)-treated female Sprague-Dawley rats: (a) high- or low-fat isocaloric diets were fed in a crossover design; (b) low-fat, high-calorie and high-fat, low-calorie diets were fed in a crossover design; (c) pair-fed rats were restricted to 60% of the calories of controls with ad libitum access to food beginning 10 days after DMBA administration. The pair-fed rats received daily 60% of calories, the same level of fiber, and 115% more fat than did rats fed ad libitum. Tumor yield but not tumor incidence was greater in rats fed high-fat rather than low-fat isocaloric diets prior to initiation of tumorigenesis. A low-fat, high-calorie diet led to more tumor incidence and yield than was associated with feeding of a high-fat, low-calorie diet. Caloric restriction (although with concomitant intake of more fat) led to complete inhibition of tumor formation. These results indicate that both high-fat and high-calorie diets exhibit cocarginogenic, not merely promotional, properties. Caloric intake may be a greater determinant than dietary fat of a tumor-enhancing regimen. Finally, restriction of caloric intake during promotion markedly suppresses tumor formation, despite the increased fat content of the restricted diet, suggesting a permissive role for calories in tumor formation. The possibility remains that alterations in levels of other dietary components could also have contributed to the observed effects.     

Estrogen-induced pituitary tumor development in the ACI rat not inhibited by dietary energy restriction

We have demonstrated that a 40% restriction of dietary energy consumption virtually abolishes the development of prolactin (PRL)-producing pituitary tumors in Fischer 344 (F344) rats treated chronically with estrogen, apparently by inhibiting the ability of estrogen to enhance survival within a rapidly proliferating lactotroph population. The purpose of the study reported here was to determine whether energy restriction exerts a similar antitumorigenic action in another rat strain, August x Copenhagen-Irish (ACI), in which PRL-producing pituitary tumors develop in response to estrogen treatment. Ovariectomized female ACI rats were either allowed to consume a control diet ad libitum or were fed a modified diet that restricted energy consumption by 40% relative to the amount of energy consumed by animals fed the control diet. We also examined the ability of 17beta-estradiol (E2) administered for 20 wk via subcutaneous Silastic implants to induce development of PRL-producing pituitary tumors. Treatment with E2 increased pituitary weight as well as the pituitary weight-to-body weight ratio and induced gross hyperprolactinemia to the same extent in ACI rats fed either the control or the energy-restricted diet. Moreover, dietary energy restriction did not affect the ability of E2 to induce pituitary cell proliferation or inhibit apoptosis, as evidenced by quantification of two surrogate markers. These data provide compelling evidence that a 40% restriction of energy consumption does not inhibit the ability of E2 to induce pituitary tumor development in the ACI rat. In conjunction with our published studies of the F344 rat strain, the data presented herein indicate that the inhibitory effects of dietary energy restriction on estrogen-induced pituitary tumor development are rat-strain specific and suggest that sensitivity to specific antitumorigenic actions of energy restriction is strongly affected by genetic background.     

The combined effects of dietary fat, protein, and energy intake on azoxymethane-induced intestinal and renal carcinogenesis.

Two 3 x 3 factorial experiments were conducted to examine the effects of dietary protein (8, 16, and 32% of energy from casein) and dietary fat (12, 24, and 48% of energy from corn oil) on the initiation and promotion of azoxymethane-induced carcinogenesis in rats. For the initiation study, 33 weanling male Sprague-Dawley rats were randomized to each of nine diets fed ad libitum. Azoxymethane was administered s.c. between the fourth to sixth weeks of feeding, providing a total dose of 6 mg/100 g body weight. All rats were subsequently fed a common diet containing 16% energy from protein and 24% energy from fat for an additional 30 to 38 weeks. For the promotion study, all rats were fed a common diet containing 16% of energy from protein and 12% of energy from fat until the completion of azoxymethane administration, when 33 rats were randomized to each of nine diets varying in fat and protein content and fed these diets until sacrifice. Low-protein diets during the initiation phase were associated with increased risk of renal adenocarcinomas (P less than 0.001) and mesenchymal (P = 0.005) malignancies. No other statistically significant relationships were found between the levels of dietary fat or protein and the prevalence of malignant lesions of the small intestine, colon, or kidney in either the initiation or promotion study (although polypoid adenocarcinoma of the colon increased suggestively from 13 to 19 to 26% of rats with increasing dietary protein during initiation). Results of a multiple logistic regression analysis, combining both studies, showed that ad libitum energy intake was significantly associated with intestinal carcinogenesis. The odds of finding an intestinal adenocarcinoma increased by 6.2 +/- 2.6% (SE) for each additional kilocalorie of mean daily ad libitum intake (P = 0.014). The quintile of rats which consumed the least averaged 60 kcal/day, while the most voracious quintile averaged 74 kcal/day. This 14 kcal/day difference in mean ad libitum intake corresponded to more than a doubling (146% increase) of the odds of developing an intestinal adenocarcinoma. These studies suggest that ad libitum energy intake is a critical factor modulating experimental colon carcinogenesis.     

NE-10 neuroendocrine cancer promotes the LNCaP xenograft growth in castrated mice

Increases in neuroendocrine (NE) cells and their secretory products are closely correlated with tumor progression and androgen-independent prostate cancer. However, the mechanisms by which NE cells influence prostate cancer growth and progression, especially after androgen ablation therapy, are poorly understood. To investigate the role of NE cells on prostate cancer growth, LNCaP xenograft tumors were implanted into nude mice. After the LNCaP tumors were established, the NE mouse prostate allograft (NE-10) was implanted on the opposite flank of these nude mice to test whether NE tumor-derived systemic factors can influence LNCaP growth. Mice bearing LNCaP tumors with or without NE allografts were castrated 2 weeks after NE tumor inoculation, and changes in LNCaP tumor growth rate and gene expression were investigated. After castration, LNCaP tumor growth decreased in mice bearing LNCaP tumors alone, and this was accompanied by a loss of nuclear androgen receptor (AR) localization. In contrast, in castrated mice bearing both LNCaP and NE-10 tumors, LNCaP tumors continued to grow, had increased levels of nuclear AR, and secreted prostate-specific antigen. Therefore, in the absence of testicular androgens, NE secretions were sufficient to maintain LNCaP cell growth and androgen-regulated gene expression in vivo. Furthermore, in vitro experiments showed that NE secretions combined with low levels of androgens activated the AR, an effect that was blocked by the antiandrogen bicalutamide. Because an increase in AR level has been reported to be sufficient to account for hormone refractory prostate cancers, the NE cell population ability to increase AR level/activity can be another mechanism that allows prostate cancer to escape androgen ablation therapy.     

Flow cytometric analysis of R3327 rat prostate adenocarcinoma grown in vivo and in vitro

The Dunning R3327 transplantable prostate adenocarcinoma in the Copenhagen rat is an acceptable model for the human disease. The G-subline (a rapidly growing carcinoma) and the H-subline (a slow-growing, well-differentiated adenocarcinoma) represent the extremes of differentiation and growth rate of this tumor. Both sublines were found to have one population that was diploid and a second aneuploid population that was hyperdiploid in DNA content. The percentage of hyperdiploid cells was significantly higher in R3327-G tumors than in R3327-H tumors. The tumor cell population ratios were stable in vivo, but the in vitro culture conditions supported only cells with diploid DNA content following four to five subcultures. These predominantly diploid cultured cells, when injected into intact male rats, resulted in tumors that had both diploid and aneuploid cells.     

Inhibition of DMBA-induced mammary tumorigenesis by caloric restriction in rats fed high-fat diets

Most previous studies on the inhibiting effect of caloric restriction during promotion of DMBA-induced mammary carcinogenesis have used low to moderate levels of dietary fat, i.e., about 4 to 14% by weight. The current study was designed to test whether a moderate degree of caloric restriction, 25%, would inhibit tumor growth in rats fed the equivalent of 20% dietary fat which approximates human consumption in affluent countries. Rats were fed diets ad libitum that contained 5, 15 or 20% corn oil. Groups of rats were pair-fed to the last 2 groups, but subjected to a 25% caloric restriction. These groups were fed 20 or 26.7% corn oil so that absolute fat intake in the paired groups was identical. Significant inhibition of tumor incidence, tumor weight, tumor burden, body fat deposition, and fasting serum insulin were observed in the 2 calorically restricted groups. We conclude that moderate caloric restriction is significantly more effective in inhibiting tumor growth than is the promoting effect of diets high in fat. Total body weight, body fat and serum insulin concentrations may be better correlates of risk of developing mammary tumors than is dietary fat.     

Tumor progression in serial passages of the Dunning R3327-G rat prostatic adenocarcinoma: growth rate response to endocrine manipulation

Serial passages of the poorly differentiated, androgen-sensitive R3327-G prostatic adenocarcinoma were used to study the progressive changes that occur in tumor growth rate and androgen sensitivity. Different in vivo transplant generations (21st to 28th) were compared. The tumor doubling and animal survival times resulting from the implantation of the 21st to 22nd generation (21-22G) tumor cells in intact male rats were significantly greater than those resulting from the implantation of 23-28G tumor cells. The most dramatic difference between early (21-23G) and late (26-28G) tumor generations, however, was in androgen sensitivity. The 26-28G tumors displayed androgen sensitivity only when implanted into animals castrated 2 to 7 days previously. Tumors grown in the pretreated castrates grew at a significantly slower rate than those in intact rats and the pretreated castrates had longer survival times than the intact rats. When 26-28G tumors were allowed to grow in intact rats to approximately 1 cu cm and then the rats were castrated, no significant difference in the growth rate between these tumors and tumors grown in intact rats was observed. In contrast, the androgen sensitivity of 21-23G tumors could be demonstrated, regardless of whether treatment was started before or after implantation. The fact that androgen sensitivity was still evident under certain conditions in late-generation R3327-G tumors demonstrates that the basic mechanism involving androgen response was still present, although functioning at a much reduced level.     

5alpha-dihydrotestosterone-binding proteins and androgen sensitivity in prostatic cancers of Copenhangen rats.

A line (R-3327-A) of androgen-insensitive squamous cell carcinomas of the prostate of Copenhagen rats has been derived from an established line (R-3327) of androgen-responsive tumors R-3327 A tummors have a growth rate of approximately 10 times that of R-3327. The response of R=3327 A to hormonal environment has been determined by measuring the growth rate of the tumor transplanted to males, females, and castrated males. No great differences were observed. The metabolism of testosterone by tumore samples was studied following s.c. injections of the labeled steroid. The results show very little 5alpha-reduction of testosterone compared with that obtained in the prostate gland itself, as well as in the androgen-sensitive R-3327 tumors. A comparison of the presence of 17beta-hydroxy-5alpha-androstan-3-one-binding proteins in cytoplasmic extracts from both lines of tumors shows that the receptor proteins are present only in the androgen-sensitive R-3327 and not in the androgen-insensitive R-3327 A. The levels of the receptor proteins in R-3327 tumors are higher in tumors borne by male than by female animals, and castration of males decreases the amount of 17beta-hydroxy-5alpha-androstan-3-one binding.     

Effect of dietary energy restriction on vascular density during mammary carcinogenesis

Inhibition of mammary carcinogenesis by dietary energy restriction is associated with a decrease in cell proliferation and the induction of apoptosis. Although changes in the metabolism of insulin-like growth factor I and glucocorticoids have been proposed to modulate these cellular processes, limitations in blood supply could induce similar effects. To investigate this possibility, female Sprague Dawley rats were given an injection of 1-methyl-1-nitrosourea and fed purified diets ad libitum or at 60% ad libitum intake, i.e., 40% dietary energy restriction. Premalignant mammary pathologies and mammary adenocarcinomas obtained from these rats were processed for vascular density analysis via CD-31 immunostaining. Vascular density, measured as vessels/unit area, of premalignant mammary pathologies and adenocarcinomas from dietary energy restriction rats was reduced 31 and 39%, respectively (P < 0.01). This effect, which was observed in a 50-microm wide band of tissue surrounding each pathology, was exerted on blood vessels > 25 microm2. Conversely, intratumoral vascular density was unaffected by dietary energy restriction. cDNA microarray and Western blot analyses of adenocarcinomas for evidence of dietary energy restriction-mediated effects on vascularization revealed that only the level of vascular endothelial growth factor receptor protein Flk-1 was significantly reduced (P < 0.001). It appears that dietary energy restriction imposes limitations in the supply of blood to developing pathologies, an effect that could directly inhibit the carcinogenic process. The vascular density data imply that dietary energy restriction inhibited the growth of endothelial cells but leave unresolved the question of whether dietary energy restriction had a specific effect on angiogenesis. The factors that account for the failure of dietary energy restriction to limit intratumoral vascularization are not obvious and merit additional investigation.     

The effects of cholestyramine, colestipol, and ADR-132 on the rat prostate and dunning R-3327 adenocarcinoma

The effects of three compounds known to have hypocholesterolemic activity in several species were investigated on the rat prostate and the hormone-dependent R-3327 rat prostatic adenocarcinoma. Cholestyramine, colestipol, and ADR-132 are bile acid-sequestering anion exchange resins which were fed to separate groups of adult male Copenhagen X Fischer (F1) hybrid rats in doses of 0.25%, 1.00%, and 2.00% of diet. The results indicate that serum cholesterol levels in tumor-bearing rats and controls fed these compounds for 29 days were not reduced. The body and organ weights as well as the histological features of the prostate gland, seminal vesicles, and the R-3327 tumor were unaffected by these agents.     

Low zinc intake suppressed N-methyl-N-nitrosourea-induced mammary tumorigenesis in Sprague-Dawley rats

Zinc has been shown to be accumulated in N-methyl-N-nitrosourea (MNU)-induced rat mammary tumors. Zinc is required for cell proliferation and tumorigenesis is characterized by dysregulation of cell proliferation. An accumulation of zinc in mammary tumors perhaps indicates a reliance on zinc to sustain tumor growth. Limiting zinc supply by means such as reduced zinc intake should negatively modulate mammary tumorigenesis. Our objective was to determine the effects of zinc status on MNU-induced mammary tumorigenesis in sexually mature female rats. Twenty-one-day-old Sprague-Dawley rats were assigned to low-zinc (3 mg zinc/kg diet) or adequate-zinc (12 mg zinc/kg diet) ad libitum or pair-fed control group (n = 25-33 rats/group). On day 50 of age, all rats were intraperitoneally injected with MNU (50 mg/kg body wt) to induce mammary tumorigenesis. Rats were further maintained on their assigned diet until 14 weeks post-MNU injection. Total food intake and overall body weight gain were lower in low-zinc rats than in adequate-zinc ad libitum control rats, but were similar to adequate-zinc pair-fed control rats. Plasma zinc concentration was lower in low-zinc rats than in adequate-zinc ad libitum and pair-fed control rats, confirming moderately low-zinc status in low-zinc rats. Tumor incidence (46 versus 84 and 80%; P < 0.05) and tumor multiplicity (0.8 versus 5.0 and 2.6 tumors/rat; P < 0.05) and tumor number (28 versus 123 and 66 tumors) were reduced in low-zinc rats compared with that in adequate-zinc ad libitum and pair-fed control rats, respectively. Tumor latency in low-zinc and adequate-zinc pair-fed control rats was not significantly different, but was longer than in adequate-zinc ad libitum control rats (P < 0.05), suggesting that reduced food intake associated with low-zinc intake prolonged tumor latency. Tumor burden and size were not affected by zinc intake. Overall, our observations showed that moderately low-zinc status suppressed MNU-induced rat mammary tumorigenesis.