The characteristic binding of catechol estrogens to estrogen receptors in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors

The binding of catechol estrogens (2-hydroxyestrone, 4-hydroxyestrone, 2-hydroxyestradiol, and 4-hydroxyestradiol) to estrogen receptors in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor cytosols was investigated. Cytosol estrogen receptors exhibited high affinities (Ka = 1.12-1.88 X 10(8) M-1) for all catechol estrogens as well as estradiol. The receptor level of catechol estrogens (46.1-97.5 fmol/mg protein) was 1.6-3.0 times higher than that of estradiol; especially the binding of 4-hydroxyestrone to estrogen receptors was the highest of all catechol estrogens and estradiol. In judging the receptor level of more than 20 fmol/mg protein to be positive, the binding of catechol estrogens to estrogen receptors was approximately correlated with that of estradiol. The positive receptor level of catechol estrogens was found in a half of tumor cytosols which showed the negative receptor level of estradiol. These results suggested that characteristic estrogen receptors indicating high affinities for catechol estrogens might be present in rat mammary tumor cytosols.     

Relationship between estrogen receptors, 17 beta-hydroxysteroid dehydrogenase and estrogen content in human breast cancer.

Estrone and estradiol levels in tumor tissue cytosols were determined in 11 premenopausal and 20 postmenopausal women at the same time that 17 beta-hydroxysteroid dehydrogenase and estrogen receptors (ER) were carried out on their breast cancers. Estrogen receptor positive tumors showed significantly higher levels of estrone and estradiol. However, all ER negative tumors contained measurable amounts of both estradiol and estrone. Higher levels of estrone were observed in ER negative tumors which correlates well with high 17 beta-hydroxysteroid dehydrogenase activity. These results suggest that false negative receptor assays in the premenopausal women is not likely to be due to occupancy of receptors by endogenous estrogens. Furthermore, the higher estrone content in the ER negative group is probably due to high 17 beta-hydroxysteroid dehydrogenase activity inherent to these tumor cells.     

Regulation of estrogen-stimulated lordosis behavior and hypothalamic progestin receptor induction by antiestrogens in female rats

Two estrogen antagonists, CI-628 (CI) and tamoxifen (TX), were used to examine the relationship between estrogen priming of lordosis behavior and progestin receptor induction in the hypothalamus-preoptic area (HPOA) of ovariectomized female rats. Lordosis behavior was assessed by measuring lordosis quotients (LQ) in response to injection of 2 micrograms of estradiol benzoate (EB) followed 48 hr later by 500 micrograms of progesterone (P). Behavior testing began 4 hr after P injection. The effects of antiestrogens were assessed by injecting CI and TX (1-2 mg) from 0 to 48 hr prior to EB. Levels of cytosol progestin receptor in the HPOA were determined by quantifying the specific binding of 0.5 nM [3H]R5020 to cytosols from animals receiving the same EB and antiestrogen treatments used in behavioral testing. TX given concurrently with or CI given 2 hr before EB abolished both lordosis behavior and induction of HPOA progestin receptors. In contrast, CI given 12 hr prior to EB abolished lordosis but permitted a 95% elevation in the concentration of progestin binding sites in the HPOA. TX or CI given 48 hr before EB resulted in moderate levels of lordosis (mean LQs from 56 to 69) and induction of HPOA progestin receptors from 85 to 130% above noninjected controls. However, CI given 24 hr prior to EB produced less than a 40% increase in brain R5020 binding even though lordosis behavior was equivalent to that seen in the 48-hr animals (mean LQ = 53). These data indicate that the effects of antiestrogens on female sexual behavior and on the synthesis of brain progestin receptors depend on which antiestrogen is used and the time interval between administration of estrogen and antiestrogen. They also demonstrate that under some conditions estrogen induction of cytosol progestin receptors in the HPOA can be dissociated from estrogen priming of lordosis behavior in rats.     

Effects of diabetes on the dietary lipid alteration of R3230AC mammary carcinoma growth in rats

To examine the effects of diabetes on the alteration of R3230AC mammary tumor growth by dietary lipids, streptozotocin-induced diabetic rats were fed diets containing either 20% corn oil (HF), 20% hydrogenated cottonseed oil (HCTO), or 0% fat (FF). Diabetes resulted in lower tumor weights and body weights compared to those of intact animals. Unlike intact animals, relative tumor weight (g tumor/100 g body wt) of diabetic animals fed HF diets were not greater than those from animals fed FF diets. However, in these diabetic animals, growth of tumors in HF-fed rats was faster than in HCTO-fed rats, a relationship similar to that seen in intact rats. A surprising result was the almost twofold greater tumor weight/100 g body wt observed in diabetic FF-fed rats compared to those fed HCTO diets. Insulin binding to tumor plasma membranes from diabetic animals was higher in rats fed HF diets than in rats fed FF or HCTO diets. The tumor plasma membrane fatty acid composition of diabetic rats fed FF and HCTO diets displayed higher proportions of the monounsaturates (C18:1 and C21:1) and decreased amounts of the polyunsaturates (C18:2 and C20:4) compared to the levels observed in membranes from HF-fed rats. These results, as well as the insulin binding data, were similar to those obtained using intact animals. The data presented here indicate that the more rapid growth of the R3230AC mammary tumor seen in intact animals fed high polyunsaturated fat vs fat-free diets did not occur in diabetic animals.     

Effects of temperature, storage and sodium molybdate on the analysis of estrogen and progesterone receptors in rabbit uterine tissue and gynecologic tumor

The cytoplasmic estrogen receptor (ERc) and progesterone receptor (PRc) in mammary tumors have been recognized as useful biochemical markers for predicting the objective response of patients with advanced breast cancers to endocrine therapy. These proteins are also useful in the prognosis of gynecologic carcinoma. This report presents data showing the effect of sodium molybdate in the stabilization of estrogen and progesterone receptors. In rabbit uterine tissue, molybdate (20 mM) increased the binding of progesterone and estrogen to the receptors in several ways: (a) the apparent loss of detectable receptors during lengthy sucrose gradient analysis and at elevated temperature (30 degrees C) was reduced; (b) the instability of receptors due to storage at -70 degrees C was lessened, and (c) the conversion of the 7S PRc to the 3.5S form was minimized. Similarly, molybdate caused a qualitative and/or a statistically significant quantitative difference in receptor values for some human gynecologic tumors presented herein; the molybdate-associated changes vary with tumor specimen. Of the 8 tumors for which receptor values in the presence of molybdate (M+) and its absence (M-) can be compared, detectable ERc of 6 and PRc of 7 tumors increased with molybdate, and ERc of 2 and PRc of 1 tumor showed no change. In addition to the increase in receptor values, a concomitant shift of the 3-4S molecules to the 7-8S moieties was noted for some tumors (1 of 6 for ERc and 3 of 7 for PRc). In 2 receptor-poor tumor samples, ERc was only detected in M+ cytosols. These results show that molybdate is effective in reducing receptor degradation and stabilizes the 7-8S molecules from converting to 4S moieties. The addition of molybdate may be helpful for better quantitation of steroid receptors in clinical specimens.     

Human adenovirus type 9-induced rat mammary tumors.

Following subcutaneous inoculation of newborn Wistar-Furth rats with human adenovirus type 9 (Ad9), 16 of 16 female and 0 of 11 male rats developed mammary tumors. Tumor-positive animals usually developed tumors in multiple glands. Histopathological analyses indicated that three general categories of tumor could be identified. Mammary fibroadenomas were the most common tumor type encountered, but phyllodeslike tumors and solid sarcomas were also frequently found. In situ hybridization and immunohistochemical techniques established that benign fibroadenomas were derived from mammary fibroblasts (collagen type I- and vimentin-positive cells) and that malignant tumors were derived from myoepithelial cells (collagen type IV-, vimentin-, and muscle-specific actin-positive cells). The fact that mammary tumors were limited to female rats suggested that female hormones are essential for tumor growth and development. In this regard, ovariectomy of Ad9-infected female rats prevented tumor development, while subsequent diethylstilbestrol (DES) treatment elicited tumor formation. In addition, Ad9-infected and castrated male rats which received DES also developed mammary tumors. Established male mammary tumors regressed when DES treatment was stopped and reappeared after DES treatment was resumed. Together, these results indicate that estrogen is required for both initiation and maintenance of Ad9-induced mammary tumors. Southern blot analysis of high-molecular-weight tumor DNA showed that mammary tumor cells contained single or multiple integrated copies of the entire Ad9 genome. RNase protection experiments established that estrogen receptor as well as Ad9 E1a and E4 mRNAs were expressed in mammary tumors, but Ad9 E3 and, surprisingly, E1b mRNAs were not expressed at detectable levels.     

Estrogen receptors in the adrenal cortex of the possum (Trichosurus vulpecula)

1. Specific [3H]estradiol binding activity with characteristics of estrogen receptors was found in the cytosols and nuclear extracts of the adrenal cortex proper and special zone of the brushtail possum (Trichosurus vulpecula). 2. The specific estradiol receptor had a sedimentation coefficient on sucrose gradients of approximately 9S and a molecular weight on gel filtration of more than 200,000. The adrenal cortex cytosol binds [3H]estradiol with high affinity (Ka 5.5 X 10(9) M-1), and limited capacity (Bmax 62.7 fmol/mg cytosol prot). In competition experiments with different steroids the receptor showed a high affinity for four estrogens and a very low affinity to androgens, progesterone and cortisol. 3. There was no difference in the affinity and maximum binding capacity of the cytosols from cortex proper in male and female animals, but the binding capacity of the special zone of females was half that of cortex proper. Estradiol receptors were found in the kidney, liver, lung, testis and muscle but only in the adrenal and prostate was the binding capacity relatively high compared with the uterus. 4. The specific binding capacity of [3H]estradiol to cytosols of adrenal cortex at different stages of the estrus cycle and pregnancy was unrelated to that of the uterus. In the adrenal the receptor concentration was lowest at estrus, when uterine concentration was high, while in late pregnancy the binding of adrenal cortex and uterus cytosols was almost the same. 5. The possible physiological significance of the presence of a specific estrogen receptor in male and female possums is discussed.     

The role of food intake on gastric mucosal growth and gastrin receptors during pregnancy and lactation

We examined the effects of pregnancy and lactation on mucosal growth and the numbers and affinity of gastrin receptors in the oxyntic gland mucosa in rats and compared these with changes in serum gastrin levels and food consumption. Gastric mucosal DNA, RNA, and protein contents were significantly increased during lactation. These changes were not observed in either pregnant or nonlactating rats which had given birth at the same time as the lactating animals. The gastrin-binding capacity of a membrane fraction of the oxyntic mucosa was also increased at the corresponding periods in lactating rats (Days 7, 15, 20). Scatchard plot analysis revealed that the number of gastrin receptors was significantly increased without any change in affinity. Food consumption and levels of serum gastrin remained unaltered in pregnant and non-lactating rats compared to virgin controls, but were significantly increased in lactating rats. Increased serum gastrin levels and gastrin binding capacities in lactating rats (Day 15) were abolished by preventing increased food consumption by means of pair feeding. The results demonstrate that the number of gastrin receptors in the oxyntic mucosa increases during lactation in rats. This increase is probably due to hypergastrinemia caused by increased food intake. The increased number of gastrin receptors may be involved in the mechanism of hypertrophic responses of the gastric mucosa in lactating rats.     

Prolactin receptors in mammary tumors of GR mice.

Prolactin receptors have been identified in estrone-progesterone induced mammary tumors from GR mice. 125I-labeled ovine prolactin binding to tumor homogenates reached a steady state in 12 hours at 22 degrees and was specific for prolactin. Prolactin receptors were highest (16 fmoles/mg protein) in primary, hormone-dependent tumors and declined progressively in transplanted hormone-dependent and transplanted hormone-responsive tumors. In autonomous tumors, binding was approximately 5% of that found in primary tumors. Scatchard analysis of binding to selected tumors indicated that the observed decrease in bound hormone was due to a loss in the number of receptor sites; binding affinity was unaltered (kd approximately 1 X 10(-10) M). Since receptors for estrogen and progesterone as well as those for prolactin decline in a concerted manner with the transition to autonomy, autonomous growth may result from a loss of receptors or an increase in the relative proportion of autonomous cells present in the tumor.     

Antitumor activity of naltrexone and correlation with steroid hormone receptors.

We have evaluated the opiate peptide antagonist, naltrexone, for its effectiveness as an antitumor agent. For this evaluation, we tested the effect of naltrexone given daily in the diet on the growth of established 7,12-dimethylbenz(a)anthracene-induced mammary tumors. Tumors continued to grow actively in rats fed chow diet only (control group). In contrast, the naltrexone-supplemented diet (75 mg/kg diet) significantly decreased the size of the established mammary tumors in rats over the 25 day observation period, resulting in an average decrease in tumor volume by approximately 23% compared with their sizes at the beginning of the treatment. Tumor regression occurred in 70% of the rats. Tumors that respond to naltrexone showed appreciable amounts of estrogen and progesterone receptors while unresponsive tumors were negative for estrogen and progesterone receptors. For the first time, we report that naltrexone can regress established mammary tumors and that the inhibitory effect of naltrexone appears to be restricted to the hormonally responsive mammary tumors.     

Dopamine receptors in rat pituitary and estradiol-induced pituitary tumor: effect of chronic treatment with bromocriptine

We have investigated dopamine (DA) receptors in estradiol-induced PRL-secreting pituitary tumors and intact pituitary tissue. Female rats were injected at 3-week intervals with 2 mg estradiol valerate (EV) or with diluent. After 21 weeks, adenomatous changes in the pituitary gland of EV-treated rats were seen and plasma PRL concentrations reached 2 micrograms/ml. Bromocriptine (2.5 mg/kg) was then administered for 1 month to half of the control rats and half of the rats bearing tumors. Anterior pituitary weight was increased in EV-treated rats compared to controls while the affinity and the density of DA receptors as assessed by [3H]spiperone binding remained unchanged. Bromocriptine (CB-154) induced a 70% decrease in the density of DA receptors without any change in affinity both in normal pituitaries and in tumors. Concurrently, the elevated plasma concentrations of PRL in the tumor bearing rats were decreased to control values following the CB-154 treatment. Our data suggest that rats with primary estrogen-induced PRL secreting tumors have normal pituitary DA receptors.     

雌激素受体与脑肿瘤

雌激素通过其受体对脑结构与功能具有重要的调节作用,如调节脑结构的性别差异、生殖行为、神经可塑性与学习记忆等。脑肿瘤是一种危害严重的肿瘤,研究表明肿瘤细胞表达的雌激素受体的种类、水平与脑肿瘤的生长过程相关。雌激素受体可通过直接作用或与部分其它受体相互作用,调控相关基因的转录,进而调节肿瘤的生长、增殖、转移、扩散以及凋亡等生理、生化过程。本文就雌激素受体在肿瘤细胞的表达水平、表达种类以及雌激素受体参与的信号通路做一简要综述。     

Increased glucagon receptors in chronically hypersomatotrophic and hyperglucagonemic rats

The effect of increased levels of growth hormone on glucagon binding by isolated hepatocytes and on the cellular cyclic AMP response to glucagon was evaluated in rats bearing growth hormone-secreting tumor (Mt-T-W15) and in rats treated with rat growth hormone. An increased binding, due to an increased number of receptors, was observed in both groups of animals. Glucagon binding did not correlate with plasma glucagon levels, suggesting a failure of down regulation, possibly due to an effect of growth hormone and insulin on the number of receptors. Tumor-bearing and growth hormone-treated rats had larger hepatocytes so that, when hormone binding was expressed in terms of square micrometer of membrane surface, it appeared decreased. When the tumor was removed the increase in the number of glucagon receptors per cell persisted, even though the average cell size returned toward normal. It is suggested that this retention of the receptors may have been the result of continuing hyperinsulinism. Basal cAMP levels were elevated in hepatocytes of tumor-bearing and growth hormone-treated animals, possibly due to cell hypertrophy. On the other hand, the maximum cAMP response to glucagon was not altered by the experimental procedures. A negative effect of insulin on cAMP accumulation may explain this apparent paradox. Indeed, hepatocytes isolated from rats following tumor removal, but with continuing hyperinsulinemia, had a lower maximum cAMP response, even though the glucagon binding per cell or per unit of cell surface was increased.     

A transplantable rat Leydig cell tumor--1. LH and prolactin receptors and effects of the endocrine status of the host animal

We have examined the binding capacity and properties (affinity, specificity) of LH and prolactin (Prl) receptors in a transplantable rat Leydig cell tumor (H-540) grown in intact, castrated and hypophysectomized rats. LH receptors in adult rat testis and Prl receptors in the rat ventral prostate were examined simultaneously for comparison. The results can be summarized as follows: The qualitative properties (affinity, specificity) of LH and Prl receptors in tumor Leydig cells appear to be identical to those of corresponding receptors in non-tumor tissues. The levels of LH receptors in tumor Leydig cells are only some 1% of that present in normal Leydig cells from adult rats. Tumor Leydig cells grown in hypophysectomized rats had even lower levels of LH receptors; ca. 1/3 of that found in tumors from intact rats. The levels of Prl receptors in the tumor Leydig cells are almost as high as in normal Leydig cells from adult rats. In tumors grown in hypophysectomized rats, the levels of Prl receptors were much lower (ca. 20%) than in tumors from intact or castrated rats. There were great variations in the number of LH and Prl receptors in individual tumors, and there was a positive correlation (r = 0.88; P less than 0.01) between LH and Prl receptors in individual tumors. No differentiation toward a "LH receptor tumor" or "Prl receptor tumor" was observed. Thus, receptors for LH and Prl in tumor cells are qualitatively normal, but the number is greatly (LH) or moderately (Prl) reduced. These receptors in the tumor Leydig cells are stimulated by pituitary hormones.     

Endogenous estrogen mediates vascular reactivity and distensibility in pregnant rat mesenteric arteries

The role of estrogen in the maternal systemic cardiovascular adaptations during pregnancy is still controversial. Female Sprague-Dawley rats were implanted at day 14 of pregnancy with either a 50-mg tamoxifen pellet (estrogen receptor blocker, n = 10) or placebo pellet (n = 10). Virgin female rats were a nonpregnant control (n = 7). At days 20-22 of pregnancy, resistance-sized mesenteric arteries were mounted onto a dual-chamber arteriograph system. Pregnancy significantly blunted the pressor response to phenylephrine [measurement of the effective concentration that yielded 50% maximum response (EC(50)) values were 1.5 +/- 0.22 vs. 0.69 +/- 0.16 microM (P < 0.05)] and enhanced vasodilation to ACh [EC(50) = 1.13 +/- 2.53 vs. 3.13 +/- 6.04 nM (P < 0.05)] compared with nonpregnant rats. However, tamoxifen treatment during pregnancy reversed these effects. Inhibition of nitric oxide (NO) synthase with N(G)-monomethyl-L-arginine (250 microM) shifted only the responses of the placebo-treated pregnant group to both phenylephrine and ACh. Arterial distensibility in the placebo-treated pregnant group was also significantly increased (P < 0.05) compared with nonpregnant and tamoxifen-treated pregnant animals. In summary, endogenous estrogen during pregnancy increases NO-dependent modulation of vessel tone and arterial distensibility.     

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.     

Endocrine aging in C57 BL mice--II. Dynamics of estrogen receptors in the hypothalamic-pituitary axis

Specific cytosolic and nuclear binding sites for estrogens were measured in the hypothalamic-pituitary axis (HPA) of young (4-8 months) and old (16-18 months) C57 BL mice in order to determine any age-related alteration in hormone-receptor interaction. Our results indicated no age differences in the affinity (KD = 0.89 +/- 0.03 (SEM) vs 1.09 +/- 0.2 X 10(-9) M), the specificity, the sedimentation profile (6 s) or in the number (98.9 +/- 4.9 vs 84.4 +/- 2.3 fmol/mg protein) of unoccupied estrogen binding sites in the cytosols. Estradiol administration to young mice induced a complete translocation of cytosolic estrogen receptors to the nucleus, and two types of nuclear binding sites were observed: Type I were specific for estrogens with high affinity (KD = 0.51 +/- 0.06 X 10(-9) M) and low binding capacity (115.1 +/- 22.7 fmol/mg DNA) and sedimented in the 4.0 s area, while Type II binding sites showed a much higher capacity and lower affinity for R2858. HPA nuclear suspensions of aged untreated mice showed undetectable (less than 50 fmol/mg DNA) levels of nuclear estrogen receptors and E2 pre-treatment resulted in a significant increase in both types of binding sites. While no significant changes in the physicochemical characteristics of these nuclear receptors were observed, when compared to young animals, aging was manifested by a translocation defect in the HPA of C57 BL mice. These results suggest aging changes in the endocrine regulating centers of the brain with defective activation of estrogen receptors.     

Equivalent affinity of aldosterone and corticosterone for type I receptors in kidney and hippocampus: direct binding studies

In studies from several laboratories evidence has been adduced that renal Type I (mineralocorticoid) receptors and hippocampal "corticosterone-preferring" high affinity glucocorticoid receptors have similar high affinity for both aldosterone and corticosterone. In all these studies the evidence for renal mineralocorticoid receptors is indirect, inasmuch as the high concentrations of transcortin (CBG) in renal cytosol make studies with [3H]corticosterone as a probe difficult to interpret, given its high affinity for CBG. We here report direct binding studies, with [3H]aldosterone and [3H]corticosterone as probes, on hippocampal and renal cytosols from adrenalectomized rats, in which tracer was excluded from Type II dexamethasone binding glucocorticoid receptors with excess RU26988, and from CBG by excess cortisol 17 beta acid. In addition, we have compared the binding of [3H]aldosterone and [3H]corticosterone in renal cytosols from 10-day old rats, in which CBG levels in plasma and kidney are extremely low. Under conditions where neither tracer binds to type II sites or CBG, they label an equal number of sites (kidney 30-50 fmol/mg protein, hippocampus approximately 200 fmol/mg protein) with equal, high affinity (Kd 4 degrees C 0.3-0.5 nM). Thus direct tracer binding studies support the identity of renal Type I mineralocorticoid receptors and hippocampal Type I (high affinity, corticosterone preferring) glucocorticoid receptors.     

Increase of estrogen receptor level by thyroxine in estrogen dependent pituitary tumor (MtT/F84) in rats

A rat transplantable pituitary tumor, MtT/F84, grows much faster in E2 treated rats than in normal females, but is much retarded in thyroidectomized rats. Triiodothyronine (T3) administration in a drinking water increased the tumor growth by the dose dependent manner. The tumor contained both estrogen receptor (ER) and T3 receptor. ER levels both in the nuclei and cytosols elevated 2 to 3 times by the T3 administration compared to those of control. E2 administration promotes the growth of MtT/F84 through elevation of nuclear ER level. T3 may directly elevate cellular ER level and thus it may enhance estrogenic actions including the tumor growth.     

Effect of amphotericin B and its combination with 5-fluorouracil on the development of transplantable rat lymphosarcoma]

The studies were carried out on rats with subcutaneously transplanted metastizing Pliss lymphosarcoma. The animals were treated with amphotericin B administered intravenously in complex with sodium desoxycholate in doses of 336 and 20 Units/kg for 7 days beginning from 24th hour after the tumor transplantation. The treatment resulted in a statistically reliable inhibition of the tumor metastasizing as compared to the control animals. When the animals with the tumors were subjected to combined therapy with 5-fluoruracyl and amphotericin B, the antitumor and antimetastatic effect of 5-fluoruracyl significantly increased. Determination of amphotericin B binding with the organ homogenates showed that the antibiotic bound with the homogenates or the organs of the rats with the tumors to a greater extent than with those of the intact animals. The levels of the antibiotics in the tumor metastases were higher than those in the primary tumors.