Promotion Of Mammary Carcinogenesis Research Articles

Abstract P5-03-09: Ovarian Hormones Promote Mammary Carcinogenesis by Altering Growth Factor Receptor Signaling

Abstract Study of carcinogenesis in rat models plays an important role in understanding the nature of neoplastic transformation. Identification of biological, cellular and molecular alterations involved in the carcinogen induced preneoplastic transformation has vital importance in mammary cancer development. Copenhagen rats are resistant to the carcinogen, N-methyl-N-nitrosourea (MNU) induced mammary carcinogenesis. Our previous studies indicate that MNU induced preneoplastic lesions were promoted to mammary cancer by the hormones estrogen and progesterone. The purpose of this study is to delineate the molecular mechanisms of hormonal promotion of mammary carcinogenesis. Seven week old female Copenhagen rats were administered a single dose of 50 mg/kg body weight MNU intraperitoneally. Four weeks post carcinogen administration, rats were divided into 4 groups, 1) Control, 2) rats treated with 30 mg estradiol, 3) rats treated with 30 mg progesterone, 4) rats treated with 30 mg estradiol plus 30 mg of progesterone. Two weeks after the implantation rats were killed and mammary glands were excised and used for further experiments. Quantitative RT-PCR experiments showed up-regulation of growth factor receptors such as Igf-1r, Egfr and growth factor signaling members Grb2, Pi3k and Ras mRNA expression. Immuno histochemical studies showed strong staining to growth factor receptors and western blotting studies showed increased protein levels of growth factor receptors such as IGF-1R and EGFR and active form of proliferative signaling molecules Akt and SAPK/JNK were up-regulated in combination of estradiol and progesterone treated rats. Phosphorylated p38 was reduced in the combination of hormones treated rat preneoplastic lesions when compared to control. Combination of ovarian hormones treatment provided enhanced growth factor signaling environment and promoted the mammary lesions through activation of SAPK/JNK and growth factor signaling pathways. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-03-09.

Unsuspected Consequences of the Adolescent Overweight Epidemic

We read with great interest the article entitled “Weight Status in Young Girls and the Onset of Puberty,” which was published in the March issue of Pediatrics.1 The authors showed, from longitudinal follow-up of 354 girls, that a higher BMI z score at 36 months of age and a higher rate of change of BMI between 36 months of age and first grade were associated with earlier puberty. They concluded that increasing rates of obesity in the United States may result in an earlier average age of onset of puberty and in a number of adverse outcomes, in particular reproductive cancers. That early menarche is predictive of elevated breast carcinoma risk is well known.2 More unexpected and, indeed, paradoxical are the results of a number of studies, including our prospective cohort study (the E3N cohort) of 98 995 French women (mainly teachers, aged 40–65 years at recruitment in 1990–1991) who were followed, on average, for 12 years.3 We showed that, indeed, women who had breast cancer had significantly earlier menarche than controls; however, when adjusting for age at menarche, significant trends of decreasing risk with increasing body silhouettes at age 8 and at menarche were observed (P trend: <.001 to <.0005, respectively, with relative risks of 0.86 [95% confidence interval: 0.75–0.99] and 0.89 [95% confidence interval: 0.80–0.99]) for women who were overweight (ie, who reported a silhouette equal or greater than the fifth silhouette according to the drawings of Sorensen et al4) at age 8 and at menarche, respectively. We observed no clear effect modification according to menopausal status, age at menarche, delay between age at menarche and regular cycling, regularity of cycles in adult life, or BMI at baseline. Our results suggest that overweight during childhood or adolescence reduces breast cancer risk and that this reduction is not fully explained by menstrual characteristics after menarche or by adult BMI but, rather, by hormonal mechanisms in the peripubertal period, when mammary tissue develops. Several contradictory explanations may be put forward. According to Stoll,5 excess adiposity around menarche can alter the production of ovarian hormones and increase the frequency of anovulatory cycles, notably through insulin pathways, which lead to a decrease in the promotion of mammary carcinogenesis. However, others have shown that the leanest body silhouette at age 10 was associated with both higher peak growth velocities during adolescence and elevated breast carcinoma risk.6 Baer et al7 concluded that rapid adolescent growth may increase breast cancer risk by increasing levels of growth hormones and epithelial proliferation in the breast or by decreasing the amount of time for repair of DNA damage. Finally, alternative explanations have been proposed. Obesity in preadolescent and adolescent girls is associated with higher basal insulin levels, hyperandrogenia, decreased plasma levels of sex hormone–binding globulin, and, consequently, increased levels of unbound testosterone and estradiol.7 Higher prepubertal estrogenic exposures might paradoxically reduce breast cancer risk through differentiation of terminal end buds, mammary gland structures that are known to be the sites for malignant transformation.8 Additional research is required, therefore, to fully assess the consequences of the adolescent overweight epidemic.

High-Fat Corn Oil Diet Promotes the Development of High Histologic Grade Rat DMBA-Induced Mammary Adenocarcinomas, While High Olive Oil Diet Does Not

Effects of a high corn oil and a high olive oil diet on the histopathologic characteristics of rat dimethylbenz(alpha)anthracene-induced mammary adenocarcinomas were investigated in comparison with those of a control low-fat diet. Two experimental series (A and B) studied the influence of a high corn oil diet on the initiation and the promotion of mammary carcinogenesis, while another one (C) assessed the effects of the two dietary lipids on the promotion. Nine parameters have been analyzed and a new histologic grading method, adapted to rat tumors, has been applied in each carcinoma. High corn oil diets, particularly when acting as promoters, associated with higher-grade carcinomas than control (p < 0.05) and high olive oil groups. Stromal invasion and tumoral necrosis were more prominent and a prevailing cribriform pattern was observed (p < 0.05). High olive oil diet adenocarcinomas exhibited a predominantly low histologic grade and few necrotic and invasive areas, similar to the control, and they presented the highest percentage of papillary areas. Lymphoplasmacytic and mast cell infiltration were also influenced by the dietary lipids. Thus, high corn oil diet adenocarcinomas presented a higher degree of morphological malignancy than control and high olive oil tumors, which is in line with the greater clinical malignancy described in rats from the former group and the non-promoting effect of the high olive oil diet. As far as we are concerned, a similar histopathologic approach of the effects of the dietary lipids on experimental breast cancer has not been carried out up to now.

Upper abdominal obesity, insulin resistance and breast cancer risk.

A majority of prospective studies show breast cancer risk to be higher in obese postmenopausal women with upper abdominal adiposity than in those with overall adiposity. The evidence is more limited and inconsistent in the case of premenopausal women. The review examines evidence that aberrant insulin signalling may be involved in the promotion of mammary carcinogenesis. The aetiology and concomitants of abdominal visceral obesity are examined. Clinical and experimental evidence suggests that the higher breast cancer risk associated with greater abdominal visceral obesity may be related to aberrant insulin signalling through the insulin receptor substrate 1 pathway, leading to insulin resistance, hyperinsulinaemia and increased concentrations of endogenous oestrogen and androgen. The putative role of aberrant insulin signalling in the promotion of mammary carcinogenesis may help to explain clinical relationships between breast cancer risk and age at menarche, pregnancies and onset of obesity. Overall adiposity in women adversely affects breast cancer risk mainly by greater exposure of mammary epithelial tissue to endogenous oestrogen. Upper abdominal adiposity appears to involve an additional effect related to the presence of insulin resistance. Aetiological factors in the development of hyperinsulinaemic insulin resistance are still uncertain but may involve aberrant susceptibility genes in adipocyte insulin receptors or in the insulin receptor substrate 1 pathway. Epigenetic factors are also likely to contribute, including high free fatty acid levels and obesity. Dietary fatty acids, particularly polyunsaturated fatty acids, are known to regulate adipocyte differentiation through the nuclear peroxisome proliferator-activated receptor gamma, and may also have a role in insulin resistance. These aetiological factors are likely to be relevant to the high risk of postmenopausal breast cancer in industrialised Western populations.

Conjugated Linoleic Acid Does Not Inhibit Development of Aberrant Crypt Foci in Colons of Male Sprague-Dawley Rats

Conjugated linoleic acid (CLA) is a potent inhibitor of the initiation and promotion of mammary carcinogenesis in animal models, but its role in colon carcinogenesis remains unclear. The objective of this study was to determine whether CLA inhibits the promotion of colon carcinogenesis. Forty male Sprague-Dawley rats were given a single dose of azoxymethane (20 mg/kg body wt ip). After 1 wk, the animals were randomized into two groups (n = 20) and fed a control AIN-93G diet or the control diet supplemented with 1% CLA at the expense of the soybean oil. After 12 wk, the animals were killed, and their colons were stained with methylene blue for aberrant crypt foci (ACF) analysis by light microscopy. The total number of ACF per animal did not differ between the control (174 ±11) and CLA (170 ± 10) groups. Furthermore, CLA did not affect the average crypt multiplicity (crypts/ACF) or the average number of ACF in any size category. However, rats fed the 1% CLA diet had significantly higher serum insulin levels at the time of sacrifice than those fed the control diet. Thus it is possible that the promoting effects of elevated serum insulin on colon carcinogenesis may have counteracted an inhibitory effect of CLA.

Effects of a long-chain fatty amine on mammary carcinogenesis induced in female Sprague-Dawley rats by DMBA.

Reports that protein kinase C is inhibited by sphingosine and other long-chain amines and the suggestion that promotion of mammary carcinogenesis by dietary fat is mediated by protein kinase C prompted us to investigate the effects of a long-chain amine, 1-octadecylamine, on mammary carcinogenesis induced by 7,12-dimethylbenz[a]anthracene in rats fed a high-fat diet. Rats fed the amine sulfate at a level of 0.01% in a semipurified diet containing 20% corn oil developed more tumors than those fed the high-fat diet alone, although body weight gain was inhibited slightly. Rats fed the amine sulfate at 0.1% of the diet developed very few tumors compared with those fed either the high-fat diet or a low-fat diet containing 5% corn oil. At the higher level, the C18 amine also caused a marked inhibition of body weight gain.

Effect of energy intake on the promotion of mammary carcinogenesis by dietary fat.

The effect of low-fat and high-fat diets on the induction of mammary carcinomas by 1-methyl-1-nitrosourea (MNU) was studied in female Sprague-Dawley rats. All rats were given MNU (25 mg/kg body wt) at 50 days of age. For the first 17 weeks after carcinogen administration, they were fed a purified diet containing either 5 or 20% fat incorporated into agar gel. Food intake was restricted, so that the amounts fed provided the same amount of net utilizable energy each day for both groups, regardless of the fat content of the diets. From 17 to 32 weeks, the diets were fed ad libitum. During the restricted feeding period, there was no significant difference in tumor incidence or in the number of tumors detected between the groups. During the weeks in which animals were fed ad libitum, significantly more tumors appeared in the high-fat group than in the low-fat group. The data provide support for the hypothesis that consumption of a high-fat diet can lead to an enhancement of mammary carcinogenesis. It appears, however, that diets must be consumed ad libitum for the stimulatory effect on tumor occurrence to be exhibited.