Growth Of DMBA-induced Mammary Tumors Research Articles

In Vivo Inhibition of the Estrogen Sulfatase Enzyme and Growth of DMBA-Induced Mammary Tumors by Melatonin

Melatonin inhibits the growth of different kinds of neoplasias, especially breast cancer, by interacting with estrogen-responsive pathways, thus behaving as an antiestrogenic hormone. Recently, we described that melatonin reduces sulfatase expression and activity in MCF-7 human breast cancer cells, thus modulating the local estrogen biosynthesis. In this study, to investigate the in vivo sulfatase-inhibitory properties of melatonin, this indoleamine was administered to ovariectomized rats bearing DMBA-induced mammary tumors, and treated with estrone sulfate. In castrated animals, the growth of estrogen-sensitive mammary tumors depends on the local conversion of biologically inactive estrogens to bioactive unconjugated estrogens. Ovariectomy significantly reduced the size and the number of the tumors while the administration of estrone sulfate to ovariectomized animals stimulated tumor growth, an effect which was suppressed by melatonin. The uterine weight of ovariectomized rats, which depends on the local synthesis of estrogens, was increased by estrone sulfate, except in those animals which were also treated with melatonin. The growth-stimulatory effects of estrone sulfate on the uterus and tumors depend exclusively on locally formed estrogens, since no changes in serum estradiol were appreciated in estrone sulfate-treated rats. Melatonin counteracted the stimulatory effects of estrone sulfate on sulfatase activity and expression and incubation with melatonin decreased the sulfatase activity of tumors from control animals. Animals treated with melatonin had the same survival probability as the castrated animals and significantly higher than the uncastrated. We conclude that melatonin could exert its antitumoral effects on hormone-dependent mammary tumors by down-regulating the sulfatase pathway of the tumoral tissue.

Melatonin inhibits the growth of DMBA-induced mammary tumors by decreasing the local biosynthesis of estrogens through the modulation of aromatase activity

Melatonin inhibits the growth of breast cancer cells by interacting with estrogen-responsive pathways, thus behaving as an antiestrogenic hormone. Recently, we described that melatonin reduces aromatase expression and activity in MCF-7 human breast cancer cells, thus modulating the local estrogen biosynthesis. To investigate the in vivo aromatase-inhibitory properties of melatonin in our current study, this indoleamine was administered to rats bearing DMBA-induced mammary tumors, ovariectomized (ovx) and treated with testosterone. In these castrated animals, the growth of the estrogen-sensitive mammary tumors depends on the local aromatization of testosterone to estrogens. Ovariectomy significantly reduced the size of the tumors while the administration of testosterone to ovx animals stimulated tumor growth, an effect that was suppressed by administration of melatonin or the aromatase inhibitor aminoglutethimide. Uterine weight of ovx rats, which depends on the local synthesis of estrogens, was increased by testosterone, except in those animals that were also treated with melatonin or aminoglutethimide. The growth-stimulatory effects of testosterone on the uterus and tumors depend exclusively on locally formed estrogens, since no changes in serum estradiol were appreciated in testosterone-treated rats. Tumors from animals treated with melatonin had lower microsomal aromatase activity than tumors of animals from other groups, and incubation with melatonin decreased the aromatase activity of microsomal fractions of tumors. Animals treated with melatonin had the same survival probability as the castrated animals and significantly higher survival probability than the uncastrated. We conclude that melatonin could exert its antitumoral effects on hormone-dependent mammary tumors by inhibiting the aromatase activity of the tumoral tissue.

L-deprenyl inhibits tumor growth, reduces serum prolactin, and suppresses brain monoamine metabolism in rats with carcinogen-induced mammary tumors.

Previously, we have reported that L-deprenyl decreased the incidence of mammary tumors and pituitary tumors in old acyclic rats. The objective of the present study was to investigate the effects of L-deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, treatment on the development and growth of tumors and on the metabolism of catecholamines and indoleamine in the medial basal hypothalamus (MBH) and the striatum (ST) of rats bearing 7,12-dimethylbenzanthracene (DMBA)-induced mammary tumors. Female Sprague-Dawley rats with DMBA-induced mammary tumors were injected (sc) daily with 0.25 mg or 5.0 mg of deprenyl/kg BW or the vehicle (saline; control) for 12 wk. Tumor diameter, tumor number, body weight, and feed intake were measured every week of the treatment period. Serum PRL and the concentrations of catecholamines, indoleamine, and their metabolites were measured by RIA and HPLC, respectively. Treatment with 5.0 mg deprenyl decreased the tumor diameter, tumor number, and serum prolactin (PRL) level. Although the body weight increased in all three groups, the body weight gain in the 5.0 mg group was smaller than that in the control and 0.25 mg groups. Deprenyl treatment had no effect on feed intake. The concentrations of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were decreased in the MBH and the ST, and the concentration of 5-hydroxyindoleacetic acid (5-HIAA) was decreased in the MBH of deprenyl-treated rats. Treatment with 5.0 mg deprenyl enhanced the concentrations of norepinephrine (NE) and serotonin (5-HT) in the MBH and in the ST, and the concentration of dopamine (DA) in the MBH. These results suggest that the suppression of the development and growth of DMBA-induced mammary tumors by chronic deprenyl treatment may be mediated through alterations in the synthesis and metabolism of catecholamines and indoleamine in the MBH and inhibition of PRL secretion.

Inhibitory effects of medroxyprogesterone acetate (MPA) and the pure antiestrogen EM-219 on estrone (E1)-stimulated growth of dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in the rat

Estrogens are well known to play a predominant role in promoting the growth of DMBA-induced mammary tumors in the rat. Estrone (E1), a steroid having weak estrogenic activity, is one of most important estrogens in post-menopausal women, where it is converted into the potent estrogen estradiol (E2) by 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) in many peripheral tissues, including the mammary gland. In this report, we have studied the effect of a new antiestrogen (EM-219) (N-butyl, N-methyl-11-(3', 17'beta-dihydroxy-17'alpha-ethinyl-estra-1'3'5'(10'), 14'-tetraen-7'alpha-yl) undecanamide) on E1-stimulated growth of DMBA-induced mammary tumors and compared its effect with that of medroxyprogesterone acetate (MPA) alone or in combination. After 18 days, ovariectomy (OVX) reduced total tumor area to 29.6 +/- 7.1% of the original size, while E1 (1.0 microgram, twice daily) caused a 139 +/- 21% increase in tumor size in OVX animals. MPA (1.5 mg, twice daily) partially reversed the stimulatory effect of E1 to 66.0 +/- 9.0%, while the antiestrogen EM-219 (40 micrograms, twice daily) decreased tumor size to 70.0 +/- 10%. Combination of these two compounds led to a further inhibition of tumor size to 30.7 +/- 7.4% of the value found in OVX animals treated with E1. Tumor E2 levels decreased from 1688 +/- 155 pmoles/kg tissue in OVX animals receiving E1 to 709 +/- 92, 1347 +/- 98, and 184 +/- 11 pmoles/kg tissue in MPA-, EM-219-, and MPA+EM-219-treated OVX-E1 animals, respectively. Treatment of OVX animals with E1 increased by 69% the reductive activity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) while MPA abolished completely this effect of E1. In the oxidative direction, treatment with E1, E1 + MPA, or E1 + EM-219 had minimal or no significant effect on the activity of 17 beta-HSD (vs OVX), while the combined treatment with MPA+EM-219 induced a 2-fold increase in 17 beta-HSD activity, thus leading to an increased conversion of E2 into E1. The present data show that combination of the pure antiestrogen EM-219 with MPA exerts a greater reduction in DMBA-induced mammary tumor growth and intratumoral E2 levels stimulated by E1 than either compound used alone. This interactive effect of the antiestrogen and MPA could at least partially be related to the increased inactivation of E2 into E1.(ABSTRACT TRUNCATED AT 400 WORDS)

RU54115, a tight-binding aromatase inhibitor potentially useful for the treatment of breast cancer

RU54115 is a new potent inhibitor of aromatase. In vitro, it inhibits the enzyme from human placental microsomes with a K i of 0.5 nM, which places it among the tightest reported steroidal inhibitors of aromatase. In vivo, it lowers the amount of circulating estradiol in pregnant mare serum gonadotrophin (PMSG)-primed female rats with an ED 50 of 0.4 mg/kg when given s.c. and 4 mg/kg when given orally. An oral dose of 25 mg/kg when given once daily to female rats was able to inhibit the growth of DMBA-induced mammary tumors.

Antitumor effect of a specific aromatase inhibitor, 1 -methyl-androsta-1,4-diene-3,17-dione (Atamestane), in female rats bearing DMBA-induced mammary tumors

Atamestane is a potent competitive inhibitor of estrogen biosynthesis (aromatase) in several species, in vitro and in vivo, and has no endocrine side effects. In this study, the efficacy of atamestane in suppressing tumor growth was evaluated in comparing with that of a non-steroidal aromatase inhibitor (CGS 16949A, Ciba-Geigy) and ovariectomy. Female Sprague-Dawley rats bearing DMBA-tumors were treated s.c. once daily either with 30 or 150 mg/kg atamestane or with 0.1 or 0.5 mg/kg CGS 16949A for 4 weeks. At these biologically equivalent doses both aromatase inhibitors effectively inhibited tumor growth: at the end of treatment they caused a marked reduction in tumor size (up to 70%), while ovariectomy led to a complete remission of tumor growth. The histo-morphological pictures of the mammary tumors from treated animals were qualitatively almost similar to those of the control. In hosts, neither compound exerted any influence on the weight of genital organs (ovary, uterus and vagina), although the peripheral LH levels were significantly elevated by the higher dose of the aromatase inhibitors. This effect on LH levels is probably due to the elimination of the negative feed-back effect of estrogens on gonadotropin secretion (counter regulation). The serum prolactin levels were decreased by the aromatase inhibitors, indicating a diminution of estrogen levels in the treated animals. The present results clearly demonstrate that, in spite of the counter regulation, a pure aromatase inhibitor such as atamestane in sufficiently high doses is able to inhibit the growth of DMBA-induced mammary tumors in intact female rats.

Effect of an LHRH analog on growth and hormone receptor levels in DMBA-induced mammary tumors in the rat.

Dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in the rat are well known to be hormono-dependent. Daily injections of an LHRH agonist, [D-Ala6, des-Gly-NH2(10)]LHRH ethylamide (LHRH-A), 1 microgram daily, for 38 days results in a 35% decrease in the number of tumors present at the beginning of the experiment compared to a decline of 45% after ovariectomy and of 8% in the control group. This is accompanied by a marked reduction in ovarian LH and FSH receptors. LHRH-A treatment also resulted in reduction in the number of progesterone and prolactin receptors in the tumors. In addition, an increase in plasma LH and FSH and a decline in plasma prolactin (PRL) concentrations are observed. The mechanisms by which the LHRH agonist induces its antitumoral effect probably relate to an ovarian desensitization to LH and FSH with a concomitant decrease in circulating levels of estrogen and prolactin, two well known stimuli for the growth of DMBA-induced mammary tumors.

Effects of estradiol and prolactin on steroid receptor levels in 7,12-dimethylbenz(a)anthracene-induced mammary tumors and uterus in the rat

In order to eliminate changes of pituitary hormone secretion secondary to treatment and be able to assess the direct effect of 17β-estradiol and prolactin at the level of hormone-dependent mammary tumors induced in the rat by 7,12-dimethylbenz(a)anthracene (DMBA), the effects of the two hormones on steroid receptor levels were investigated in hypophysectomized-ovariectomized animals. Treatment with prolactin alone led to tumor estrogen receptor levels higher than those found after estrogen administration. When the level of progesterone receptors was measured as parameter of estrogen action, it was found that combined treatment with prolactin and 17β-estradiol led to levels much higher than those found after individual hormone treatment. Tissue specificity of this interaction between prolactin and 17β-estradiol is indicated by the absence of effect of prolactin on the estrogen-induced stimulation of the progesterone receptor in uterine tissue. These data demonstrate the direct stimulatory effect of prolactin on estrogen receptor levels in DMBA-induced mammary carcinoma and indicate the central role of this pituitary hormone as modulator of estrogen action and growth of DMBA-induced mammary tumors.

Potent inhibitory activity of a new antiestrogen, RU 16 117, on the development and growth of DMBA-induced rat mammary adenocarcinoma.

When initiated the same day as dimethylbenzanthracene (DMBA) administration, daily treatment with 8 or 24 mug of the new antiestrogen RU 16117 (11alpha-methoxy ethinyl estradiol) completely prevented the appearance of mammary tumors in all animals up to the last time interval studied (130 days after DMBA administration). At daily doses of 0.5 and 2.0 mug of RU 16117, the tumor incidence was reduced to 78.6% and 40.0%, respectively. The levels of receptors for estradiol, progesterone, and prolactin in tumor tissue were reduced after treatment with 2.0 mug RU 16117 while the binding of growth hormone and insulin was not affected. While plasma LH levels were decreased after treatment with 8 or 24 mug RU 16117, plasma prolactin levels were slightly increased in animals receiving the highest dose of the antiestrogen. When RU 16117 was given at the daily dose of 24 mug for a period of 4 weeks, RU 16117 led to 65% reduction of the number of already established DMBA-induced mammary tumors. Not only the tumor number but also the tumor size was reduced by RU 16117 in a manner similar to that following ovariectomy. That the inhibitory effect of RU 16117 was not due to its low estrogenic activity is indicated by the absence of inhibitory effect of similar treatment with a range of doses (0.1-12.5 mug per day) of estradiol-17beta which cover the low estrogenic activity of the doses of RU 16117 used. Decreased levels of receptors for estradiol-17beta, progesterone, and prolactin were found in the tumors remaining after ovariectomy while treatment with the dose (24 mug) of RU 16117, efficient to inhibit tumor growth, has a similar inhibitory effect on the levels of estradiol-17beta and prolactin receptors. The present data indicate that the potent inhibitory effect of RU 16117 on the development and growth of DMBA-induced mammary tumors results from actions at both the hypothalamic-pituitary and tumor levels. The action at the peripheral level would be possibly secondary to a reduced sensitivity of the tissue to circulating hormones through lowering of hormone receptor concentrations.