Enhancement by retinyl acetate of hormone-induced mammary tumorigenesis in female GR/A mice

Feeding of retinyl acetate (82 mg/kg ration) for 13-16 weeks to estrone- and progesterone-treated nulliparous and multiparous inbred GR/A mice resulted in a substantial increase in the incidence of mammary carcinomas. Mammary carcinoma incidence in nulliparous control and retinoid-fed mice in experiment #1 was 22/65 (34%) and 37/65 (57%) (P less than 0.05), respectively; in experiment #2, 27/48 (56%) and 37/48 (77%) (P less than 0.05), respectively. Mammary carcinoma incidence in multiparous control and retinoid-fed mice in experiment #1 was 13/30 (43%) and 23/30 (77%) (P less than 0.05), respectively; in experiment #2, 19/19 (100%) and 19/19 (100%), respectively. The purported chemopreventive activities of retinyl acetate in murine mammary tumorigenesis were not demonstrated in this study; indeed, the vitamin A analog appeared to enhance this oncogenic process in the steroid hormone-treated GR mouse mammary cancer model.

The prophylaxis of rat and mouse mammary gland tumorigenesis by suppression of prolactin secretion: a reappraisal

The purpose of this study was to evaluate the effect of early and temporal CB-154 induced suppression of prolactin secretion on the genesis of mammary tumors in female Sprague-Dawley rats treated i.g. with 3 doses of 7,12-dimethylbenzanthracene (DMBA); doses which yield a high (20 mg), moderate (5 mg) and low (1.25 mg) mammary carcinoma incidence. In addition, the effect of prolactin suppression on the genesis of mammary tumors in strains of rodents which, when treated with maximally tolerated doses of DMBA, develop a moderate (female Lewis rats) and a low (female Long-Evans rats and female Balb/c mice) mammary carcinoma incidence was also evaluated. Daily suppression of prolactin secretion during DMBA treatment (30 days before, during and 30 days after) (series 1) or commencing 30 days after DMBA treatment (for 60-81 days) (series 2) significantly (P less than 0.05) reduced the number of mammary carcinomas in Sprague-Dawley rats treated with 20 and 5 mg DMBA and in Lewis rats (series 2); treatment with CB-154 did not significantly lower mammary carcinoma incidence in Sprague-Dawley rats treated with 1.25 mg DMBA, nor in Lewis rats (series 1), Long-Evans rats and Balb/c mice. These results provide evidence that the effectiveness of prolactin suppression in the prophylaxis of chemical carcinogenesis of the rodent mammary gland is enhanced when a moderate or large dose of the carcinogen is used, or a strain of rodent is used which is moderately or highly susceptible to the mammary oncogenic effects of the carcinogen. Low doses of the carcinogen or use of a rodent strain relatively resistant to the carcinogen nullifies the chemopreventive activities of early prolactin suppression.

Selenium and the genesis of murine mammary tumors

One hundred forty-seven female Sprague-Dawley rats were divided into 5 groups and at 60 days of age were treated i.g. with 5 mg of 7,12-dimethylbenzanthracene (DMBA) suspended in 1.0 ml of sesame oil. Selenium (Se), as selenium dioxide (SeO2), was administered in the drinking water to 4 of the 5 groups (30 rats/group) at 2 doses (2 and 4 mg/l) from 30-90 days of age (series 1) and from 90-150 days of age (series 2) prior to the onset of palpable mammary tumors. One group of rats (27 rats) served as controls. All rats were palpated weekly for mammary tumors and sacrificed 28 weeks after DMBA treatment. Total number of palpable mammary carcinomas which developed in each group were: controls, 60; series 1, 2 mg Se dose, 27, 4 mg Se dose, 29; series 2, 2 mg Se dose, 24, 4 mg Se dose, 32. Each dose level of Se in each series significantly (P less than 0.05) reduced the incidence of mammary carcinomas. These results provided evidence that Se can inhibit the early promoting phases of polycyclic hydrocarbon induced mammary carcinogenesis in female rats. Two hundred twenty-six nulliparous and 99 multiparous GR mice were treated daily with estrogen and progesterone for 13-16 weeks. Se (SeO2) was administered in the drinking water (2 mg/l) to one-half of these mice. Total number of mammary carcinomas in control nulliparous and multiparous mice were 119 and 90, respectively; in Se treated nulliparous and multiparous mice, 113 and 81, respectively. Se did not significantly effect mammary carcinoma incidence in hormone treated nulliparous and multiparous GR mice.

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

Two hundred forty Sprague-Dawley rats were treated i.v. with 2.5 or 1.25 mg of N-methyl-N-nitrosourea (MNU) per 100 g body weight at 50 and 57 days of age. At 60 days of age, rats given either dose were divided into 4 groups (30 rats/group) and treated as follows: Group 1, controls; Group 2, 0.4 mg 2-bromo-alpha-ergocryptine (CB-154) per 100 g body weight injected s.c. once daily; Group 3, retinyl acetate (328 mg/kg diet) fed daily; and Group 4, CB-154 and retinyl acetate treatments combined. Rats that received the 2.5-mg dose of MNU were treated for 129 days; those that received the 1.25-mg dose of MNU were treated for 175 days. The rats that were treated with the high dose of MNU were maintained without any treatment for an additional 13 weeks, after which they were sacrificed. The rats that were treated with the low dose of the carcinogen were sacrificed immediately after treatment. All rats were palpated once weekly for palpable mammary tumors. The number of rats with mammary tumors and the total number of mammary tumors at cessation of treatments were, respectively, as follows. MNU (2.5 mg): Group 1, 22 of 30 (73%), 82: Group 2, 11 of 30 (37%), 17; Group 3, 11 of 30 (37%), 19: Group 4, 2 of 30 (7%), 2. MNU (1.25 mg): Group 1, 8 of 30 (27%), 14; Group 2, 4 of 30 (13%), 5; Group 3, 3 of 30 (10%), 4; Group 4, 0 of 30, (0%), 0. Thus, chronic CB-154 treatment or retinyl acetate feeding markedly reduced the percentage of rates bearing mammary tumors and the total number of mammary tumors. The combined treatments were superior to either treatment alone, inasmuch as mammary tumorigenesis was nearly completely blocked in the rats of Group 4 that received the 2.5-mg dose of MNU and was totally blocked in the rats of Group 4 that received the 1.25-mg dose of MNU. Retinyl acetate feeding or CB-154-induced prolactin suppression appear to be equally effective treatments in the prophylaxis of MNU-induced mammary tumorigenesis in rats; the combined modality, however, appears to be far superior than either treatment alone.

Inhibition of mammary tumorigenesis in carcinogen-treated Lewis rats by suppression of prolactin secretion

One hundred sixty-eight female Lewis rats were treated intragastrically with 10 mg 7,12-dimethylbenz[a]anthracene at 56 and 63 days of age. Pituitary prolactin secretion was suppressed in one-half of these rats by daily sc administrations of 2-bromoergocryptine mesylate (CB-154; 0.4 mg/100 g body wt) from 29 to 90 days of age (series 1) and from 90 to 140 days of age (series 2). Treatment with CB-154 was initiated prior to the onset of palpable mammary carcinomas. Control rats were given injections of saline. Inguinal mammary glands were excised from 10 control and 10 CB-154-treated rats at the cessation of saline and CB-154 treatments and examined for hyperplastic nodules (HN). The remaining rats were palpated weekly for mammary carcinomas (MC) and killed at 200 days of age. Mean number of HN per rat, mean number of MC per rat, and percent of rats with MC were, respectively: series 1--controls, 0.6, 1.5, and 68; CB-154 treatment, 0.5, 1.1, and 62; series 2--controls, 10.4, 2.0, and 94; CB-154 treatment, 5.1, 1.1, and 56. The number of HN and MC was only slightly reduced in rats when prolactin was suppressed during carcinogen treatment (series 1) but markedly reduced when prolactin was suppressed after carcinogen treatment (series 2). These results provide evidence that prolactin is involved in the early development of mammary dysplasias in the carcinogen-treated female Lewis rat.

Inhibition of mammary tumorigenesis in GR mice with 2-bromo-alpha-ergocryptine

A high incidence of mammary tumors is found in multiparous GR mice during the 2nd and 3rd pregnancies and in nulliparous GR mice treated with estrone/progesterone. The purpose of this study was to determine if prolactin is a contributing hormone in the genesis of these neoplasms. In one series of experiments, 238 15-week-old nulliparous GR mice were treated with estrone (drinking water, 0.5 mg/liter) plus progesterone (30 mg progesterone pellet with cholesterol, implanted SC once monthly) for a period of 13 weeks. Half of these mice were injected SC once daily with 100 micrograms of the prolactin-suppressing drug 2-bromo-alpha-ergocryptine (CB-154) for the duration of hormone treatment, and the other half were injected SC once daily with 0.9% NaCl solution (controls). In another series of experiments, 87 pregnant GR mice were divided into two groups and injected SC once daily from day 7 to 21 of pregnancy with 0.9% NaCl solution (controls) or CB-154 (100 micrograms/mouse). In the first series, the numbers of mice with mammary tumors and total number of mammary tumors were: controls, 58/119 (49%) and 73; CB-154 treatment, 34/119 (29%) and 37, respectively. In the second series, the numbers were: controls, 39/44 (89%) and 73; CB-154 treatment, 24/43 (56%) and 43, respectively. In both studies, CB-154 treatment significantly (p less than 0.05-0.005) reduced the percentage of mice with mammary tumors and total number of mammary tumors. These results provide evidence that prolactin is a contributing hormone in the genesis of estrone/progesterone and pregnancy-induced mammary tumors in female GR mice.