Metformin prevents aggressive ovarian cancer growth driven by high-energy diet: similarity with calorie restriction

Caloric restriction (CR) was recently demonstrated by us to restrict ovarian cancer growth in vivo. CR resulted in activation of energy regulating enzymes adenosine monophosphate activated kinase (AMPK) and sirtuin 1 (SIRT1) followed by downstream inhibition of Akt-mTOR. In the present study, we investigated the effects of metformin on ovarian cancer growth in mice fed a high energy diet (HED) and regular diet (RD) and compared them to those seen with CR in an immunocompetent isogeneic mouse model of ovarian cancer. Mice either on RD or HED diet bearing ovarian tumors were treated with 200 mg/kg metformin in drinking water. Metformin treatment in RD and HED mice resulted in a significant reduction in tumor burden in the peritoneum, liver, kidney, spleen and bowel accompanied by decreased levels of growth factors (IGF-1, insulin and leptin), inflammatory cytokines (MCP-1, IL-6) and VEGF in plasma and ascitic fluid, akin to the CR diet mice. Metformin resulted in activation of AMPK and SIRT1 and inhibition of pAkt and pmTOR, similar to CR. Thus metformin can closely mimic CR''s tumor suppressing effects by inducing similar metabolic changes, providing further evidence of its potential not only as a therapeutic drug but also as a preventive agent.     

Caloric restriction reduces growth of mammary tumors and metastases

We investigated the effects of caloric restriction (CR) on growth of tumors and metastases in the 4T1 mammary tumor model and found that CR, compared with normal diet, reduced the growth of mammary tumors and metastases and the total number of metastases that originated both spontaneously from the primary tumor and also experimentally from i.v. injection of the tumor cells. CR also decreased proliferation and angiogenesis and increased apoptosis in tumors. CR reduced levels of insulin, leptin, insulin-like growth factor 1, insulin-like growth factor binding protein 3 and increased adiponectin in tumors. We also demonstrated that tumors from CR mice possessed lower levels of transforming growth factor-β, lower intratumor deposition of collagen IV and reduced invasiveness due to a decrease in tumor secretion of active matrix metalloproteinase 9. Our results suggest that CR-induced metabolic and signaling changes affect the stroma and the tumor cells resulting in a microenvironment that prevents proliferation of breast tumors and their metastases.     

Both dietary calorie and fat affect the growth of transplanted mammary-tumors in riii/sa mice - the effect of calorie is more profound than the effect of fat

The effects of dietary calories and/or fat on the growth of mammary tumor transplants, their expression of mouse mammary tumor virus (MMTV) and the incidence of lung metastasis were examined in RIII/Sa mice. Starting at 3-4 weeks of age, groups of female mice were fed either high isocaloric diets (16 kcal/day/mouse) containing 25% or 5% corn or fish oil or low isocaloric (10 kcal/day/mouse) diets containing 25% or 5% fish or corn oil. After one week, small pieces (2x2x2 mm) of tumor tissue, prepared from a transplantable mammary tumor, were inserted into the fourth pair of mammary glands of mice, and the mice maintained on their respective diets until sacrifice. All mice developed palpable tumors during a period of 3-4 weeks. After 12 weeks, all those mice that were assessed for tumor burden were sacrificed, tumor weight in each mouse determined, and the level of the expression of MMTV in the tumors evaluated by dot blot hybridization. Our results show that low isocalorie diets, regardless of the type or amount of fat, inhibited tumor growth by at least 60% in comparison to high isocalorie diets. However, mice fed low isocaloric diets containing fish oil were also found to produce smaller tumors (20-40%) as opposed to those mice fed similar, but corn oil containing diets. Fatty acid analyses of mammary tumors and liver tissue of mice fed corn oil and fish oil containing diets revealed that while normal and tumor tissues from both groups contained high levels of polyunsaturated fatty acids, the tissues of mice fed corn oil had the n-6, whereas the mice fed fish oil had the n-3 family of fatty acids. The levels of MMTV expression were found to be unaffected by either caloric or fat content in the diet. In a separate set of experiments, the effect of a low calorie diet on lung metastasis was determined, It was found that mice fed a low calorie diet produced significantly less metastatic lung nodules than those mice fed a high calorie diet: the mean survival time for the former group of mice was 106 days, as compared to only 71 days for the latter group of mice. In conclusion, we suggest that the amount of calories in a diet is more important than the amount or the type of fat in suppressing the growth of transplanted tumors and that a low calorie diet may also lower the incidence of lung metastasis.     

Metformin prevents cancer metastasis by inhibiting M2-like polarization of tumor associated macrophages

Accumulated evidence suggests that M2-like polarized tumor associated macrophages (TAMs) plays an important role in cancer progression and metastasis, establishing TAMs, especially M2-like TAMs as an appealing target for therapy intervention. Here we found that metformin significantly suppressed IL-13 induced M2-like polarization of macrophages, as illustrated by reduced expression of CD206, down-regulation of M2 marker mRNAs, and inhibition of M2-like macrophages promoted migration of cancer cells and endothelial cells. Metformin triggered AMPKα1 activation in macrophage and silencing of AMPKα1 partially abrogated the inhibitory effect of metformin in IL-13 induced M2-like polarization. Administration of AICAR, another activator of AMPK, also blocked the M2-like polarization of macrophages. Metformin greatly reduced the number of metastases of Lewis lung cancer without affecting tumor growth. In tumor tissues, the percentage of M2-like macrophage was decreased and the area of pericyte-coated vessels was increased. Further, the anti-metastatic effect of metformin was abolished when the animals were treated with macrophages eliminating agent clodronate liposome. These findings suggest that metformin is able to block the M2-like polarization of macrophages partially through AMPKα1, which plays an important role in metformin inhibited metastasis of Lewis lung cancer.     

Purification and some properties of a lung-derived growth factor that differentially stimulates the growth of tumor cells metastatic to the lung

The ability of malignant cells to respond to growth factor(s) present in or secreted by a distant target organ may be important in tumor metastasis. We used metastatic cell lines and clones of the rat 13762NF mammary adenocarcinoma that show reproducible spontaneous metastatic behavior from the mammary fat pad to regional lymph nodes and lung sites. Whereas poorly lung metastatic MTPa and MTC cells did not grow in response to lung-conditioned medium, highly lung-metastatic MTLn3 cells responded and grew rapidly in lung-conditioned medium. The major growth-promoting factor for MTLn3 cells from porcine and rat lung-conditioned media was purified by using hydroxylapatite affinity and anion exchange chromatography, chromatofocusing, size exclusion chromatography, and preparative native gel electrophoresis. The activity in each of the purification fractions was measured by determining their ability to increase the number of MTLn3 cells in serum-deprived culture. The major component that differentially stimulated the growth of highly metastatic MTLn3 cells was a glycoprotein of Mr approximately 66,000. Under reducing conditions, its apparent Mr was approximately 72,000. This lung-derived mitogen was stable at pH 4.0-9.0, possessed a pI of 6.9-7.0, and preferentially promoted the growth of lung-metastasizing tumor lines over their poorly lung-metastasizing counterparts in rat 13762NF mammary adenocarcinoma and murine B16 melanoma tumor systems. The activity of porcine lung-derived growth factor was not affected by pretreatment with antisera to porcine insulin, human granulocyte-macrophage colony-stimulating factor, human platelet-derived growth factor, or murine epidermal growth factor. It was inactivated by reduction with dithiothreitol or exposure to high temperature (95 degrees C). The results suggest that specific organ-derived growth factors are important in metastatic colonization and organ growth of particular malignant cells.     

Dietary energy restriction inhibits estrogen-induced mammary, but not pituitary, tumorigenesis in the ACI rat.

Because of the suggested role of energy consumption and the well-documented role of estrogens in the etiology of breast cancer, we have examined the effect of a 40% restriction of dietary energy consumption on the ability of administered 17beta-estradiol (E2) to induce mammary tumorigenesis in female ACI rats. Experiments herein test the hypothesis that at least part of the inhibitory effect of energy restriction on mammary tumorigenesis is exerted downstream of potential effects of dietary manipulation on the production of estrogens by the ovaries. Ovary-intact ACI rats were fed a control or a 40% energy-restricted diet and were either treated continuously with E2 from subcutaneous Silastic tubing implants or received no hormone treatment. Mammary cancers rapidly developed in E2-treated rats fed the control diet; within 216 days of initiation of E2 treatment 100% of the population at risk exhibited palpable mammary tumors. Dietary energy restriction markedly inhibited E2-induced mammary tumorigenesis, as evidenced by significant reductions in cancer incidence and tumor burden as well as a significant increase in the latency to the appearance of the first palpable cancer. The inhibitory actions of dietary energy restriction on E2-induced mammary tumorigenesis were associated with an inhibition of E2-stimulated mammary cell proliferation. However, this inhibition was insufficient to block induction of lobuloalveolar hyperplasia or appearance of focal regions of atypical epithelial hyperplasia. These data suggest that dietary energy restriction inhibits E2-induced mammary cancer by attenuating or retarding the progression of atypical hyperplasia to carcinoma. Expression of progesterone receptor (PR) was up-regulated within the focal regions of atypical hyperplasia and the carcinomas induced by E2, regardless of whether the rats were fed the control or energy-restricted diet. However, circulating progesterone was reduced by dietary energy restriction, suggesting a possible mechanism for inhibition of mammary tumorigenesis. Dietary energy restriction did not inhibit the ability of administered E2 to induce prolactin (PRL)-producing pituitary tumors and associated hyperprolactinemia, indicating that the inhibitory effects of dietary energy restriction on mammary tumorigenesis are tissue specific and independent of circulating E2 and PRL.     

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.     

Short-term dietary administration of celecoxib enhances the efficacy of tumor lysate-pulsed dendritic cell vaccines in treating murine breast cancer

Cyclooxygenase-2 (COX-2) is a rate-limiting enzyme in the synthesis of prostaglandins. It is over-expressed in multiple cancers and has been associated with diminished tumor immunity. Dendritic cells (DCs) are considered candidates for cancer immunotherapy due to their ability to process and present antigens to T cells and stimulate immune responses. However, DC-based vaccines have exhibited minimal effectiveness against established tumors. In this study, we evaluated the effect of short-term administration of the selective COX-2 inhibitor celecoxib on the efficacy of DC-based vaccines in preventing and treating established 4T1 murine mammary tumors. We show that dietary celecoxib alone significantly suppresses the growth of primary tumors and the incidence of lung metastases in the prophylactic setting but is less effective against pre-established tumors. However, we demonstrate that celecoxib administered after primary tumor establishment synergizes with tumor lysate-pulsed DC and the adjuvant, GM-CSF, to improve the antitumor immune response by suppressing primary tumor growth and markedly reducing the occurrence of lung metastases. This triple combination therapy elicits a tumor-specific immune response evidenced by elevated IFN-gamma and IL-4 secretion by CD4+ T cells and results in increased infiltration of CD4+ and CD8+ T cells to the tumor site. In addition, dietary celecoxib inhibits angiogenesis evidenced by decreased vascular proliferation within the tumor and serum vascular endothelial growth factor levels. These studies suggest that short-term celecoxib therapy in combination with DC vaccines may be safely used for treating metastatic breast cancer.     

Comparison of 'spontaneous' and 'experimental' metastasis using rat 13762 mammary adenocarcinoma metastatic cell clones

Rat 13762NF mammary adenocarcinoma cloned cell lines were assayed at different in vitro passage numbers and compared for their abilities to form 'spontaneous' metastases by subcutaneous injection of cells and 'experimental' metastases by intravenous injection of cells. Tumor cell clones were established from locally growing tumor and spontaneous lung metastases, and these clones were found to possess heterogeneous metastatic potentials in both metastasis assays. The rank order of clonal metastatic potentials based on either the average number of lung tumor colonies or the average total lung tumor volume was generally equivalent for 'spontaneous' and 'experimental' metastases, but some differences were noted. Ranking of 'spontaneous' metastasis by average total lung tumor volumes more closely resembled the rank order of 'experimental' metastasis than by the average number of spontaneous metastases. The results demonstrated that in the 13762NF mammary adenocarcinoma system (i) there is heterogeneity in tumor cell clonal metastatic potential using either 'spontaneous' or 'experimental' assays; (ii) these two assay methods yield generally the same rank order of metastatic potential; (iii) the metastatic potential of each of the tumor cell clones drifts with time (passage number) in cell culture, and (iv) ranking by average tumor burden calculated from total lung tumor volumes may yield a better estimate of metastatic potential than ranking by the average number of lung tumor colonies.     

The role of intratumor environment in determining spontaneous metastatic activity of a B16 melanoma clone

B16 melanoma-derived cell lines and clones that initiate rapid-growing and nonmetastatic tumors in normal young (2-month-old) mice were previously shown to form slower-growing and highly metastatic tumors in normal mature or aged (greater than 10-month-old) mice. Similarly, slower tumor growth and enhanced metastasis occurred in young mice hyperimmunized against tumor-associated antigens. The metastatic characteristics of subcutaneous tumors initiated by one B16 melanoma clone, G3.26, were examined in normal young mice, normal mature mice, young mice immunized against G3.26 cells, and young mice maintained on a diet of 50% less food than usual. In normal young mice, tumors rarely disseminated viable lung metastases, even at very large sizes, and viable tumor cells were not detected in blood obtained by whole-body vascular perfusion. In contrast, tumors in mature, in immunized, and in calorie-restricted mice gave rise to visible lung metastases in 60-90% of mice, with dissemination beginning at relatively small tumor sizes. These tumors grew 27-78% slower than tumors in normal young mice, but in no case was expression of metastatic activity dependent on longer host survival. In all three experimental hosts, metastatic activity was transient and not expressed during subsequent growth of metastases in young mice. Different host mechanisms operating in mature, immune, and calorie-restricted mice were probably responsible for suppressing tumor growth. However, the consistent generation of metastatic activity under such diverse conditions suggests a common basis for promotion of metastasis, possibly related to intratumor environment alterations resulting from slower tumor growth.     

Downregulation of IFN-gammaR in association with loss of Fas function is linked to tumor progression

The host immune system functions as an intrinsic surveillance network in the recognition and destruction of tumor cells, and it has been demonstrated that lymphocytes and IFN-gamma are the primary tumor suppressors of the immune system. However, the immune system can concurrently select for tumor variants with reduced immunogenicity and aggressive phenotypes. We report here that tumor escape variants that have survived CTL adoptive immunotherapy exhibited decreased expression levels of both Fas and IFN-gammaR in vitro. Furthermore, examination of spontaneously arising mouse primary mammary carcinoma and lung metastases revealed that both Fas and IFN-gammaR protein levels were dramatically lower in lung metastases than in primary tumors in vivo. Functional disruption of either the Fas- or the IFN-gamma signaling pathway enhanced the colonization efficiency of preexisting metastatic tumor cells, whereas disruption of both Fas and IFN-gammaR pathways resulted in synergistic augmentation of the colonization efficiency of the preexisting metastatic tumor cells, as determined by experimental lung metastases assay. Gene expression profiling revealed that altered expression of genes involved in immediate IFN-gammaR signaling, the interferon primary response, apoptosis and tumor colonization is associated with loss of IFN-gammaR function and enhanced metastatic potential. Interestingly, disruption of IFN-gammaR function did not alter tumor cell susceptibility to CTL-mediated cytotoxicity, but is linked to enhanced infiltration of endogenous T cells in the tumor microenvironment in vivo. These findings suggest that coordinate downregulation of Fas and IFN-gammaR, 2 key components of cancer immunosurveillance system on tumor cells, leads to a more aggressive metastatic phenotype.     

二甲双胍相关性自噬与肿瘤的关系

二甲双胍是最广泛使用的双胍类抗糖尿病药物,其通过需肝激酶B1的机制降低肝葡萄糖,该酶为控制体内代谢的要点,二甲双胍通过该机制引起蛋白合成减少、细胞增殖减慢,这激发了人们研究其在肿瘤细胞增殖、自噬和凋亡调控方面作用的兴致,其中二甲双胍相关性自噬在不同的肿瘤及其肿瘤细胞的不同时期,对肿瘤发生发展的影响并不相同。目前,已有大量的实验致力于二甲双胍能否作为抗肿瘤药物应用于临床,二甲双胍有望成为新一代抗肿瘤药物或辅助用药。     

Dietary fat modulation of murine mammary tumor metabolism studied by in vivo 31P-nuclear magnetic resonance spectroscopy

The effect of dietary fat concentration and saturation on high energy phosphate metabolites and phospholipid turnover in transplanted line 168 murine mammary tumors was studied using surface coil 31P-nuclear magnetic resonance spectroscopy. Female BALB/c mice were fed one of five diets each containing at least the minimum of essential fatty acids (EFA). Four diets contained additional safflower or palm oil for a total fat concentration of 5 or 20% by weight. The growth rate of tumors from mice fed the high safflower oil diet was significantly greater than the growth rate of tumors for mice fed all other diets including the one which contained the minimal EFA. 31P-nuclear magnetic resonance-observable phosphate metabolite ratios. ATP/Pi, ATP/phosphomonoester (ATP/PME), and PME/Pi, and tumor pH of line 168 tumors decreased with increasing tumor volume, indicating a shift from active to inactive tumor metabolism. The rates of those decreases with progressive tumor growth differed significantly among tumors of mice fed the different diets. Decreases in ATP/Pi, ATP/PME, and pH were the most rapid in the tumors of mice fed the high safflower oil diet and significantly faster than tumors of mice fed the diet containing minimum EFA. In addition, the decrease in the PME/Pi ratio of tumors was significantly greater in mice fed the high fat (high palm oil and high safflower oil) diets than mice fed the diet containing the minimum of EFA. The rate of decline of ATP/Pi and ATP/PME with progressive tumor growth was directly correlated with levels of linoleic acid as well as total unsaturated fat. High levels of a polyunsaturated fat had a significant effect on mammary tumor metabolism particularly during early stages of tumor growth. Differences in high energy phosphate metabolite dynamics relative to dietary fat were present in tumors of equal volume. Thus, dietary fat influences on mammary tumorigenesis may be related to high energy phosphate metabolites.     

Differential-effects of omega-3 and omega-6 Fatty-acids on primary tumor-growth and metastasis

The amount and type of dietary lipid can significantly influence spontaneous tumor development and tumor progression. To determine the effect of fish oil (rich in omega-3 polyunsaturated fatty acids) and corn oil (rich in omega-6 polyunsaturated fatty acids) on primary tumor growth, metastasis and carcass weight, 45 female Lewis/Wistar rats with subcutaneous mammary tumor implants (MAC-33) were randomized to 1 of 3 diets with 30% lipid consisting of: (i) corn oil alone, (ii) combined 50%:50% corn oil:fish oil, or (iii) fish oil alone. Primary tumor weight was significantly reduced in animals which were fed fish oil or corn oil alone compared to animals given combined corn oil:fish oil diet. Biochemical analysis (protein, DNA, RNA) of the primary revealed no difference between dietary groups. Cell cycle analysis of the primary tumor showed no difference in percent G(0)-G(1), S, G(2)-M or growth fraction (% S + G(2)-M) between dietary groups. In contrast, lung metastasis, was reduced in animals fed the combined corn oil:fish oil diet. Thus, dietary, lipid intake can significantly influence primary tumor growth and tumor metastasis. Differential effects of omega-3 and omega-6 polyunsaturated fatty acids occur on primary tumor growth and development of distant pulmonary metastases in this animal model.     

A role of estrogens and insulin binding in the dietary lipid alteration of R3230AC mammary carcinoma growth in rats

The importance of estrogens in the dietary lipid alteration of R3230AC mammary carcinoma growth and insulin binding was studied. Animals were divided into three groups [intact, ovariectomized, and ovariectomized treated with estradiol valerate (EV)] and were fed diets containing either 0% fat (fat free), 0.5% corn oil (low fat), or 20% corn oil (high fat). An alteration of tumor burden between animals fed high-fat versus either low-fat or fat-free diets was observed and appeared to be influenced by the estrogen status of the animal. The difference in tumor burden attributed to dietary lipid seen in intact rats was less in ovariectomized rats and greater in ovariectomized rats treated with EV, despite the fact that absolute tumor burden was reduced by this treatment. A similar relationship was observed for dietary lipid-induced differences in insulin binding to plasma membranes from these tumors. Reduction of tumor growth resulting from estrogen treatment was greater in low-fat- and fat-free-fed animals than in high-fat-fed rats. Again, tumor growth behavior appeared to be related to the reduction of insulin binding induced by estrogen treatment; insulin binding to plasma membranes from animals fed a low unsaturated lipid diet was decreased to a greater extent by EV treatment than in membranes from high-fat-fed rats. Altered tumor growth and membrane insulin binding, resulting from dietary perturbations and/or EV treatment, were not invariably related to serum insulin levels, nor to differences in membrane preparation, as reflected by 5'-nucleotidase activity, nor to membrane fatty acid composition or uptake of proline. Taken together, these results suggest a potential role of estrogens and insulin receptors as mediators of the dietary lipid alterations of growth of the R3230AC mammary carcinoma.     

Effect of dietary fat on human breast cancer growth and lung metastasis in nude mice

Results from epidemiological studies have generally indicated an association of dietary saturated animal fats with human breast cancer risk. Some studies, however, have suggested a similar association for some polyunsaturated vegetable fats shown to promote both rodent mammary carcinogenesis and metastasis. This study was performed to evaluate the effects of corn oil on growth and metastasis of MDA-MB-435 human breast cancer cells, which have a propensity for metastasis. Corn oil is rich in the omega-6 fatty acid linoleic acid. Fifty-eight female athymic nude mice (NCr-nu/nu) were fed a high-fat diet (23% wt/wt corn oil; 12% linoleic acid) or a low-fat diet (5% wt/wt corn oil; 2.7% linoleic acid). Seven days after diets were started, tumor cells (1 x 10(6) were injected into a mammary fat pad. The time to appearance of solid tumors and the tumor size were recorded. After 15 weeks, the study was terminated, and autopsies were performed to determine the weight of the primary tumor and the extent of metastasis. The latent interval for tumor appearance in the animals fed the high-fat diet was shorter than that in the low-fat diet group, and the tumor growth rate in the high-fat diet group showed a small but statistically significant increase compared with the low-fat diet group. Primary tumors developed in 27 of the 29 mice on the high-fat diet and in 21 of the 29 on the low-fat diet. Of the mice with palpable primary tumors, 18 of 27 in the high-fat diet group and eight of 21 in the low-fat diet group had macroscopic lung metastases. The extent of metastasis in the high-fat diet group was independent of the primary tumor weight, but only those in the low-fat diet group with primary tumors weighing more than 2 g developed metastases. These results suggest that a high-fat diet rich in omega-6 polyunsaturated fatty acid can enhance metastasis of human breast cancer cells in this mouse model. The findings support the need for further study of the relationship between dietary polyunsaturated fats and breast cancer risk and for experiments to determine the effect on metastasis of only a 50% difference in fat intake--the dietary goal of the proposed clinical trials of low-fat dietary intervention in breast cancer patients.     

Influence of dietary retinyl acetate on normal rat mammary gland development and on the enhancement of 7,12-dimethylbenz[a]anthracene-induced rat mammary tumorigenesis by high levels of dietary fat

The effect of high levels of dietary fat and retinyl acetate (ROA) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat mammary tumor development and growth was examined. Female Sprague-Dawley rats, 51-53 days of age, were treated ig with 5 mg DMBA. At 55-57 days of age, the animals were divided into the following dietary treatment groups: A) 4.5% fat [control fat (CF)]; B) CF + 1.0 mmol ROA/kg diet (CF + ROA); C) 20.0% fat [high fat (HF)]; and D) HF + ROA. HF diets significantly increased mammary tumor multiplicity, with or without ROA, but did not significantly influence mammary tumor growth. ROA treatment reduced mammary tumor multiplicity regardless of the level of dietary fat and inhibited mammary tumor growth in the presence of normal levels of dietary fat. High levels of dietary fat did not significantly influence normal mammary gland growth and development. ROA significantly decreased normal mammary gland growth and development regardless of the level of dietary fat. Blood retinoids in rats fed ROA were primarily in the form of retinyl esters, i.e., retinyl linoleate, retinyl palmitate-oleate, and retinyl stearate. Free retinol levels in blood were not significantly influenced by ROA feeding. Blood retinyl ester levels were lower in rats fed the HF + ROA diet as compared to rats fed the CF + ROA diet.     

Effect of dietary calorie and fat restriction on mammary tumor growth and hepatic as well as tumor glutathione in rats

Effect of dietary calorie restriction and fat reduction on growth of established mammary carcinoma in rats and on glutathione levels in liver and tumor tissue was investigated. Reduced (GSH) and oxidized (GSSG) glutathione were determined enzymatically. Female Sprague-Dawley rats were injected with 25 mg/kg methylnitrosourea (MNU) on day 50 of life for tumor induction, and subsequently fed a diet containing 50 kcal/day with 45% (energy %) fat. When tumors reached approximately 1 cm3, the diet was changed for 10 +/- 2 weeks. Four dietary groups were formed: two high calorie groups (50 kcal/day) with 45% or 25% fat and two calorie restricted groups (35 kcal/day) with 45% or 25% fat, respectively. Tumor growth was significantly inhibited by the 30% calorie restriction, and the inhibition was most effective in the calorie restricted group with low fat level. However, reduction of fat, alone, had no significant inhibitory effect. GSSG levels in both liver and tumor showed no differences among the groups. Hepatic GSH levels tended to be lower in the calorie-restricted groups, and showed no difference between isocaloric groups with different fat levels. In contrast, GSH in tumor tissue tended to be lower in the low fat groups, independently of calorie levels.     

Factors that affect metastasis in virus-induced mouse mammary tumors

Two hundred and forty-one mammary tumor-bearing breeding female mice of the BALB/cf C3H and BALB/ cfRIII strains, carrying milk-transmitted murine mammary tumor virus (MuMTV) of C3H and RIII origin, respectively, were studied to evaluate the factors that affect tumor metastasis. Only lung metastases were considered and the following factors taken in account: MuMTV inducing variant (C3H, RIII), number of deliveries, tumor histotype , number of tumors per mouse, clinical duration of tumors, tumor size, and tumor growth rate. Only the number of deliveries, the tumor size and the number of tumors per mouse were found to significantly influence the rate of metastasis. The tumor growth rate affects concurrently with tumor size the metastatic process. In fact, the larger the tumor the higher the tumor growth rate. This direct relationship is significant (P less than 0.01) and, in case of lung metastases at autopsy, there was a prevalence of large tumors (greater than 2 cm) and high growth rate (greater than 0.3 mm/day). The discordance of these data with those concerning mammary tumor metastasis in virgin females of the same two strains, the enhancing effect of pregnancies on metastatic spread of tumors, and the significance of results for the understanding of the general mechanisms of tumor metastasis are discussed.