Regulation of ornithine decarboxylase induction by deguelin, a natural product cancer chemopreventive agent

Deguelin, a plant-derived rotenoid, mediates potent chemopreventive responses through transcriptional regulation of phorbol ester-induced ornithine decarboxylase (ODC) activity. To explore the mechanism of this effect, the activity of this compound was evaluated with a number of model systems. Using cultured mouse epidermal 308 cells, the steady-state levels of both 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ODC mRNA and c-fos were decreased by treatment with deguelin. ODC activity was also inhibited by bullatacin and various antimitotic agents (podophyllotoxin, vinblastine, and colchicine), but only deguelin and bullatacin were active as inhibitors of ODC levels in a TPA-independent c-Myc-mediated induction system using cultured BALB/c c-MycER cells. These results suggest that antimicrotubule effects, as mediated by rotenone, for example, are not responsible for inhibitory activity facilitated by deguelin. This was confirmed by use of an in vitro model of tubulin polymerization in which deguelin and a variety of other rotenoids were investigated and found to be inactive. As anticipated, however, NADH dehydrogenase was inhibited by these rotenoids. Moreover, inhibition of this enzyme correlated with a rapid depletion of ATP levels and potential to inhibit either TPA- or c-Myc-induced ODC activity. It therefore seems that deguelin-mediated interference with transient requirements for elevated energy can inhibit the induction of ODC activity and thereby yield a cancer chemopreventive response.

Prevention of preneoplastic mammary lesion development by a novel vitamin D analogue, 1alpha-hydroxyvitamin D5

BACKGROUND

The form of vitamin D (vitamin D3) in fortified milk and the provitamin D produced by the body undergo metabolic activation to a biologically active form, 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. This compound can induce cell differentiation and can prevent proliferation of cancer cells. However, because 1alpha,25(OH)2D3 is hypercalcemic (effective in increasing serum calcium level), it is not suitable for use in cancer prevention or cancer therapy trials.

PURPOSE

We synthesized a vitamin D5 series analogue, 1alpha-hydroxy, 24-ethyl-cholecalciferol, or 1alpha-hydroxyvitamin D5 [1alpha(OH)D5], and evaluated its chemopreventive activity in carcinogen-treated mammary glands in organ culture experiments.

METHODS

The analogue 1alpha(OH)D5 was synthesized from sitosterol acetate and was characterized by nuclear magnetic resonance. Its purity was evaluated by high-pressure liquid chromatography. The calcemic activities of vitamin D3 and D5 analogues were determined in vitamin D-deficient Sprague-Dawley rats. Mammary glands of BALB/c mice were placed in organ culture and treated with the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) to induce preneoplastic lesions. Vitamin D analogues were added to the culture medium at four different concentrations, and formation of mammary lesions was evaluated. The effects of 1alpha(OH)D5 and 1alpha,25(OH)2D3 on the expression of vitamin D receptors (VDRs) and transforming growth factor-beta1 (TGF-beta1) were studied by immunohistochemistry. Statistical significance was determined by the chi-squared test. All reported P values were two-sided.

RESULTS

1alpha,25(OH)2D3 was fourfold more calcemic than 1alpha(OH)D5 at a dose of 0.042 microg/kg per day in rats. Both 1alpha,25(OH)2D3 and 1alpha(OH)D5 inhibited the development of DMBA-induced preneoplastic lesions in mouse mammary glands compared with untreated glands. The effect of the vitamin D3 analogue was observed at a much lower concentration (0.01 microM). Treatment with 1alpha(OH)D5 resulted in a dose-related (0.01-10.0 microM) inhibition without any toxicity, whereas the vitamin D3 analogue was highly potent but toxic at concentrations of 1.0 microM or higher. Normal mouse mammary glands poorly express VDR and TGF-beta1; incubation with 1alpha(OH)D5 or 1alpha,25(OH)2D3 dramatically induced their expression.

CONCLUSIONS

This is the first report showing the possibility of chemoprevention by a vitamin D5 series compound. We conclude that 1alpha(OH)D5 is less calcemic than 1alpha,25(OH)2D3. It is nontoxic at a wide range of concentrations, but it is potent in inhibiting the development of preneoplastic lesions in mammary glands in organ culture. In addition, we show for the first time the induction of TGF-beta1 in normal mammary tissues by a chemopreventive agent.

IMPLICATIONS

1alpha(OH)D5 is a good candidate for in vivo chemoprevention studies. It may mediate its action by inducing expression of VDR and of TGF-beta1, as is seen in other systems.

Cancer chemopreventive potential of sulforamate, a novel analogue of sulforaphane that induces phase 2 drug-metabolizing enzymes

Chemoprevention involves the use of natural or synthetic substances to reduce the risk of developing cancer. Two dietary components capable of mediating chemopreventive activity in animal models by modulation of drug-metabolizing enzymes are sulforaphane, an aliphatic isothiocyanate, and brassinin, an indole-based dithiocarbamate, both found in cruciferous vegetables. We currently report the synthesis and activity of a novel cancer chemopreventive agent, (+/-)-4-methylsulfinyl-1-(S-methyldithiocarbamyl)-butane (trivial name, sulforamate), an aliphatic analogue of brassinin with structural similarities to sulforaphane. This compound was shown to be a monofunctional inducer of NAD(P)H:quinone oxidoreductase [quinone reductase (QR)], a Phase II enzyme, in murine Hepa 1c1c7 cell culture and two mutants thereof. Induction potential was comparable to that observed with sulforaphane (concentration required to double the specific activity of QR, approximately 0.2 microM), but cytotoxicity was reduced by about 3-fold (IC50 approximately 30 microm). In addition, sulforaphane, as well as the analogue, increased glutathione levels about 2-fold in cultured Hepa 1c1c7 cells. Induction of QR was regulated at the transcriptional level. Using Northern blotting techniques, time- and dose-dependent induction of QR mRNA levels were demonstrated in Hepa 1c1c7 cell culture. To further investigate the mechanism of induction, HepG2 human hepatoma cells were transiently transfected with QR-chloramphenicol acetyltransferase plasmid constructs containing various portions of the 5'-region of the QR gene. Sulforaphane and the analogue significantly induced (P < 0.0001) CAT activity at a concentration of 12.5 microM by interaction with the antioxidant responsive element (5-14-fold induction) without interacting with the xenobiotic responsive element. Moreover, both compounds significantly induced mouse mammary QR and glutathione S-transferase activity (feeding of 3 mg/mouse intragastric for 4 days), whereas the elevation of hepatic enzyme activities was less pronounced. Both sulforaphane and the analogue were identified as potent inhibitors of preneoplastic lesion formation in carcinogen-treated mouse mammary glands in organ culture (84 and 78% inhibition at 1 microm, respectively). On the basis of these results, the sulforaphane analogue can be regarded as a readily available promising new cancer chemopreventive agent.

Sulfone metabolite of sulindac inhibits mammary carcinogenesis

Sulindac sulfoxide, a commonly prescribed anti-inflammatory drug, has cancer chemopreventive activity. During its metabolism, the inactive prodrug sulindac sulfoxide undergoes either reduction to the active anti-inflammatory metabolite sulindac sulfide or irreversible oxidation to sulindac sulfone, which lacks prostaglandin synthetase inhibitory activity. Interestingly, sulindac sulfone has been reported to have cancer chemopreventive activity. The objective of the experiments reported here was to investigate the chemopreventive activity of sulindac sulfone against mammary carcinogenesis and to study its mechanism. Rats were injected with either 12.5 or 37.5 mg of 1-methyl-1-nitrosourea (MNU)/kg body weight at 50 days of age. Sulindac sulfone was incorporated into a purified diet at a concentration of either 0.03 or 0.06% (w/w) and fed to rats beginning 7 days after the injection of MNU. Sulindac sulfoxide at a level of 0.06% (w/w) was fed as a reference for comparison. Thirty rats were assigned to each dietary group treated with the high dose of MNU, and 44 rats were assigned to each dietary group treated with the low dose of MNU. The sulfone reduced cancer incidence and the number of cancers per rat irrespective of the dose of MNU injected, and its chemopreventive activity was comparable to that of sulindac sulfoxide. Cancer latency was also prolonged significantly by sulindac sulfone; the effect was particularly notable at the low dose of carcinogen, at which the prolongation of latency was >8 weeks. The sulfone inhibited the occurrence of mammary carcinomas that were classified as having either a wild-type or a mutant codon 12 in the Ha-ras gene; however, the inhibitory effect was greater against carcinomas with a mutant Ha-ras genotype. Using a mammary gland organ culture transformation assay, it was observed that sulindac sulfone also inhibited the formation of 7,12-dimethylbenz(a)anthracene-induced hyperplastic alveolar nodules and that the inhibitory activity of the sulfone was comparable to that of the sulfoxide. These data indicate that the observed effect of the sulfone on mammary carcinogenesis in vivo is likely to be due to a tissue-specific effect rather than to other systemic effects. The findings that both the prodrug and the sulfone inhibited carcinogenesis in vivo and nodule formation in organ culture and that the sulfone lacks inhibitory activity on prostaglandin synthesis suggest a mechanism(s) of chemoprevention that is independent of the prostaglandin pathway. A candidate mechanism for the apparent clonal selection pressure exerted by the sulfone against mammary carcinogenesis is apoptosis. To test this hypothesis, MCF-7 cells were exposed to a range of concentrations of sulindac sulfone and sulfoxide. Both compounds inhibited cell growth and induced apoptosis in the absence of necrosis. Collectively, these data support a specific chemopreventive effect of sulindac sulfone against mammary carcinogenesis and indicate that this compound may have a selective effect against carcinogenesis involving alterations in the signal transduction cascade of which Ha-ras is a component. Evidence is consistent with the involvement of apoptosis in the cancer-inhibitory activity observed.

Cancer chemopreventive activity of resveratrol, a natural product derived from grapes

Resveratrol, a phytoalexin found in grapes and other food products, was purified and shown to have cancer chemopreventive activity in assays representing three major stages of carcinogenesis. Resveratrol was found to act as an antioxidant and antimutagen and to induce phase II drug-metabolizing enzymes (anti-initiation activity); it mediated anti-inflammatory effects and inhibited cyclooxygenase and hydroperoxidase functions (antipromotion activity); and it induced human promyelocytic leukemia cell differentiation (antiprogression activity). In addition, it inhibited the development of preneoplastic lesions in carcinogen-treated mouse mammary glands in culture and inhibited tumorigenesis in a mouse skin cancer model. These data suggest that resveratrol, a common constituent of the human diet, merits investigation as a potential cancer chemopreventive agent in humans.

Cancer Chemopreventive Activity of Resveratrol, a Natural Product Derived from Grapes

Resveratrol, a phytoalexin found in grapes and other food products, was purified and shown to have cancer chemopreventive activity in assays representing three major stages of carcinogenesis. Resveratrol was found to act as an antioxidant and antimutagen and to induce phase II drug-metabolizing enzymes (anti-initiation activity); it mediated anti-inflammatory effects and inhibited cyclooxygenase and hydroperoxidase functions (antipromotion activity); and it induced human promyelocytic leukemia cell differentiation (antiprogression activity). In addition, it inhibited the development of preneoplastic lesions in carcinogen-treated mouse mammary glands in culture and inhibited tumorigenesis in a mouse skin cancer model. These data suggest that resveratrol, a common constituent of the human diet, merits investigation as a potential cancer chemopreventive agent in humans.

Inhibition of N-methyl-N-nitrosourea-induced mammary tumors in rats by the soybean isoflavones

Soy-based diets, rich in the isoflavones genistein and daidzein, are thought to protect against breast and prostate cancer. We used the N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis animal model to test the effectiveness of these two isoflavones as chemopreventive agents. Each isoflavone was injected daily into 35-day-old rats for six months while we monitored the animals' body weight and mammary tumor appearance. Genistein was effective in reducing tumor multiplicity, but it reduced tumor incidence only marginally. Daidzein was less effective in reducing both tumor incidence and multiplicity. To investigate genistein's mechanism of action, we determined the topoisomerase II (topo II) activity and detected the phosphotyrosine-containing peptides in the extracts of mammary tissues isolated from control and isoflavone-treated animals. Mammary tumors contained over 60-fold higher topo II enzymatic activity than the mammary glands. Similarly, more tyrosine phosphopeptides were detectable in mammary tumors than in mammary glands. Tissue samples from genistein treated animals contained similar topo II and protein tyrosine kinase (PTK) activities as the control group. These data suggest that mammary tumorigenesis is accompanied by an extensive increase in topo II and PTK activities. The mechanism of chemoprevention by genistein, however, is independent of topo II or PTK inhibition.

Cancer chemopreventive activity of brassinin, a phytoalexin from cabbage

Brassinin [3-(S-methyldithiocarbamoyl)aminomethyl indole], a phytoalexin first identified as a constituent of cabbage, was synthesized and evaluated for cancer chemopreventive activity. Dose-dependent inhibition of 7,12-dimethylbenz[a]anthracene (DMBA)-induced preneoplastic lesion formation was observed with mouse mammary glands in organ culture, as was dose-dependent inhibition of DMBA-induced mouse skin tumors that were promoted by treatment with 12-O-tetradecanoylphorbol-13-acetate. Cyclobrassinin is a biologically derived product of the oxidative cyclization of brassinin, and was as active as the parent compound in inhibiting the formation of preneoplastic mammary lesions in culture; however, 2-methylbrassinin was not significantly active in this process. Therefore, oxidative cyclization may be an effective metabolic activation step. As judged by these tumor inhibition studies in conjunction with potential to induce phase II enzymes in mice or cell culture, brassinin may be effective as a chemopreventive agent during both the initiation and promotion phases of carcinogenesis. This is the first report documenting the chemopreventive potential of structurally novel indole-based phytoalexins that are naturally occurring in cruciferous vegetables, and the synthetic route described herein has proven amenable for scale-up production. The bifunctional structural nature of brassinin, bearing both an indole nucleus and a dithiocarbamoyl-aminomethyl moiety, is notably similar to the individual structural elements of other known chemopreventive agents such as indole-3-carbinol or benzylisothiocyanate. The favorable biological activity demonstrated by the compound may originate from the presence of these two moieties.

A correlative approach for the identification of antimutagens that demonstrate chemopreventive activity

Seventy natural and synthetic compounds were tested for potential to inhibit mutation induced by 7,12-dimethylbenz(a)anthracene (DMBA) in Salmonella typhimurium strain TM677. Results were compared with their ability to inhibit DMBA-induced preneoplastic lesions in a mouse mammary gland organ culture system. The response mediated by fifty-five of the test compounds was either positive or negative in both test systems, indicating that the combined use of these assays should aid in the discovery of antimutagenic agents that have cancer chemopreventive potential.

Chemoprevention of MNU-induced mammary tumorigenesis by hormone response modifiers: toremifene, RU 16117, tamoxifen, aminoglutethimide and progesterone

The effects of structurally different antiestrogens, progesterone and the aromatase inhibitor aminoglutethimide, were evaluated for chemopreventive activity in the N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis model. Treatment with either RU 16117, progesterone or aminoglutethimide resulted in a significant decrease in cancer multiplicity [> or = 50%; P < .05] when administered individually at doses 80% of the maximally tolerated dose [MID]. Toremifene was also remarkably effective in inhibiting MNU-induced mammary tumorigenesis although this inhibition was achieved at a dose which caused a significant decrease in body weight gain. Aminoglutethimide, RU 16117 and toremifene citrate, in addition to their effects on tumor multiplicity, caused significant increases in the latency period for tumor development. Combinations of aminoglutethimide, progesterone and/or a suboptimal dose of tamoxifen citrate also proved to be effective in inhibiting the development of MNU-induced mammary cancers; however, the combination regimen was no more effective than either aminoglutethimide or progesterone administered alone. These results suggested that agents altering the hormonal environment, regardless of their mechanism of action, may provide protection against the development of hormone responsive mammary cancer.

Structure-activity relationships of brassinin in preventing the development of carcinogen-induced mammary lesions in organ culture

Brassinin, a phytoalexin, is found in Chinese cabbage. Previously, we showed that brassinin significantly inhibited dimethylbenz(a)anthracene (DMBA)-induced mammary lesions in organ culture. Moreover, it was an effective inhibitor against two stage skin carcinogenesis. In the present study, we synthesized several analogs of brassinin and evaluated their effectiveness in the mouse mammary gland organ culture model. Results showed that cyclobrassinin, also a naturally occurring brassinin analog, was more effective than brassinin. Spirobrassinin and N-ethyl-2,3-dihydrobrassinin also significantly inhibited mammary lesion formation. However, none of the methyl substituted analogs were effective. The effects of brassinin may, in part, be mediated by induction of phase II detoxifying enzymes such as quinone reductase.

Phase I/II trial of tamoxifen with or without fenretinide, an analog of vitamin A, in women with metastatic breast cancer

PURPOSE

Considerable attention has been focused on the chemopreventive properties of fenretinide against carcinogen-induced rodent mammary cancer. Less is known about its direct antitumor effects. The combination of tamoxifen and fenretinide is more effective than tamoxifen or fenretinide alone in prevention of rat mammary cancer. However, the combined toxicity of tamoxifen plus fenretinide in humans is unknown. Therefore, we performed a phase I/II trial in women with estrogen receptor (ER)-positive or progesterone receptor (PR)-positive, previously untreated metastatic breast cancer.

PATIENTS AND METHODS

Groups of three patients received tamoxifen 20 mg/d, or tamoxifen plus fenretinide 100, 200, 300, or 400 mg/d. Patients who received fenretinide enjoyed a 3-day "drug holiday" every 4 weeks. Serum levels of fenretinide and its major metabolites were monitored. Patients were monitored for known toxicities of tamoxifen and vitamin A analogs, as well as for response.

RESULTS

There were no significant adverse effects on renal, hepatic, hematologic, or lipid values. Nyctalopia, photophobia, cheilitis, and pruritus were not observed. Improvement or stabilization of disease occurred in 12 of 15 patients.

CONCLUSION

We conclude that tamoxifen administered with fenretinide is nontoxic. Phase III trials of tamoxifen versus tamoxifen plus fenretinide are warranted.

Influence of thiols and inhibitors of prostaglandin biosynthesis on the carcinogen-induced development of mammary lesions in vitro

Mouse mammary gland undergoes physiological changes, comparable to that in the animal, under appropriate hormonal conditions in organ culture. Moreover, they form mammary lesions when exposed to the carcinogen, dimethylbenz(a)anthracene (DMBA) for a short duration. This organ culture system was utilized in the present of study to evaluate activity of two groups of potential chemopreventive agents. Activity of inhibitors of prostaglandin synthesis and thiols was determined at five concentrations. The average incidence of mammary lesions induced by DMBA was 60%, oltipraz oxithiazolidine, thioctic acid and N-acetylcysteine were effective at different concentrations, whereas diallyldisulfide, sulfasalazine and ajoene were marginally effective. Within the inhibitors of prostaglandin synthesis category, aspirin, ibuprofen and indomethacin were effective, whereas dipyridamol, piroxicam and pentoxyphyllin were ineffective. The results correlated well with the known in vivo effects of these agents on chemically induced carcinogenesis of mammary gland. The study provides evidence for the use of mammary gland organ culture as a screening total system for prediction of effective chemopreventive agents against mammary carcinogenesis.

Characterization of effective chemopreventive agents in mammary gland in vitro using an initiation-promotion protocol

Mouse mammary glands respond to carcinogen stimulus to form mammary lesions in organ culture. Prevention of the formation of mammary lesion has been utilized as a test to evaluate the effectiveness of a variety of classes of agents. In the present study we determined whether the effective chemopreventive agents are active against initiation or the promotion phase of lesion development. Mammary glands were subjected to 24 hours exposure to 2 mg/ml dimethylbenz (a) anthracene (DMBA) followed by a 5 day exposure to 7,12-tetradecanoyl phorbol - 13 - acetate (TPA). This treatment protocol allows one to study initiation and promotion aspects of lesion development. Chemopreventive agents effective when present prior to the carcinogen were considered as anti-initiators, whereas agents effective when present after the DMBA treatment along with TPA were considered as anti-promoters. Within the chemopreventive agents evaluated, limonene, oltipraz, aspirin, curcumin and b-sitosterol were anti-initiators. Esculatin, thiolutin, silymarin, DHEA and a few others were found to be anti-promoters. Results presented in this report can be utilized to study the efficacy of these agents in vivo.

Inhibition of rat mammary gland chemical carcinogenesis by dietary dehydroepiandrosterone or a fluorinated analogue of dehydroepiandrosterone

The chemopreventive efficacy of p.o. administered dehydroepiandrosterone (DHEA), DHEA plus N-(4-hydroxyphenyl)retinamide (4-HPR), or 16 alpha-fluoro-5-androsten-17-one (DHEA analogue 8354) was examined in rats treated with N-methyl-N-nitrosourea (MNU; 50 mg/kg body weight, i.v.) at 50 days of age. Semipurified diet (AIN-76A) containing each steroid alone, or DHEA plus 4-HPR, was administered during initiation (-1 week to +1 week post-MNU), promotion/progression (+1 week post-MNU to termination), or both phases (-1 week post-MNU to termination) of the carcinogenic process. Neither DHEA nor DHEA analogue 8354 (0.2%, w/w) significantly affected the initiation of mammary cancer when administered alone; however, DHEA (0.2%, w/w) plus 4-HPR (1 mmol/kg diet) significantly reduced cancer multiplicity (26%) when given during initiation. All three treatments were strongly effective when given during promotion/progression, significantly reducing mammary cancer multiplicity by 77% (DHEA), 84% (DHEA/4-HPR), and 66% (DHEA analogue 8354), relative to carcinogen controls. Cancer incidence was significantly inhibited by DHEA (33% inhibition) and DHEA/4-HPR (24% reduction) during promotion/progression. However, the most effective chemopreventive treatment encompassed both phases of carcinogenesis. Thus, under these conditions, DHEA (0.2% or 0.1%, w/w) reduced cancer incidence (52% and 32% reductions, respectively) and multiplicity (91% and 86% reductions, respectively). Further reduction in mammary cancer incidence was observed in animals that received DHEA (both doses) plus 4-HPR (1 and 0.5 mmol/kg diet, respectively). DHEA analogue 8354 (0.2% or 0.1%, w/w) given for the duration of the study reduced only cancer multiplicity (61% and 56% reductions, respectively). Tumor-related mortality was significantly lower in rats that received long-term treatment with DHEA or DHEA/4-HPR, when compared with carcinogen controls. Except for a slight, but significant, postcarcinogen decrease in the mean body weights of rats treated concomitantly with DHEA (plus or minus 4-HPR) and MNU, additional gross manifestations of steroid-induced toxicity were not observed.

Distribution of fenretinide in the mammary gland of breast cancer patients

Fenretinide has been used orally as a chemopreventive retinoid in a trial for women at risk of developing contralateral breast cancer. The levels of fenretinide and its metabolites were measured in the breast tissue obtained at surgery from women in the trial. Fenretinide was concentrated by breast tissue. Two major metabolites were detected in the tissue extract, one co-eluting with N-(4-methoxyphenyl)retinamide (4-MPR), and the other, more polar, eluting at 17 min under the conditions used. This metabolite remains unidentified. Division of the breast tissue into epithelial cells and fat fractions revealed that fenretinide and the metabolite at the 17 min peak were concentrated in the epithelial cells, whereas 4-MPR was principally localised in the fat compartment. Thus fat may serve as a storage compartment for the retinoid.

Effects of retinoid glucuronides on mammary gland development in organ culture

Retinoyl beta-glucuronide (RAG) and retinyl beta-glucuronide (ROG) inhibit prolactin-induced morphological developments in cultured mouse mammary gland, and are equally effective in depressing prolactin and steroid hormone-induced DNA synthesis in the same tissue. Retinol is essentially inactive by both assay methods. Although RAG and ROG show little or no toxicity in several cell and animal models, some possibly toxic manifestations were seen at higher concentrations in cultured mammary tissue. Nonetheless, because of the strong correlation between the actions of chemopreventive agents in culture mouse mammary glands and their effectiveness in vivo, the retinoid glucuronides may well prove to be useful cancer chemopreventive agents.

Therapeutic effect of N-(4-hydroxyphenyl)retinamide on N-methyl-N-nitrosourea-induced rat mammary cancer

Virgin Sprague--Dawley rats received a single i.v. injection of 40 mg N-methyl-N-nitrosourea (MNU)/kg body wt. at 50 days of age. After the first palpable mammary tumor reached 10 mm in size, the animals were sequentially allocated to one of 4 groups: (I) placebo diet, (II) 10 micrograms tamoxifen s.c. 3 times per week, (III) 3 mmol N-(4-hydroxyphenyl)retinamide (4-HPR)/kg diet, or (IV) both (II) and (III). Weekly measurements of initial tumors and subsequent tumors were made throughout the study. 4-HPR administration resulted in a complete regression (non-palpable state) of the first mammary tumor in 6 animals (22%) and partial regression or nonprogression in 5 others (19%). Tamoxifen alone induced only partial response in 9 animals (33%). 4-HPR and tamoxifen resulted in 19% total and 26% partial response. The data suggests therapeutic value of 4-HPR in MNU-induced rat mammary carcinoma.

Chemoprevention of experimental carcinogenesis in animals

Retinoids are well-established chemopreventive agents for experimental carcinogenesis of many target organs including mammary glands, urinary bladder, lung, skin, liver, pancreas, colon, and esophagus. Modification of the basic retinoid structure has produced analogs with enhanced target organ specificity, increased inhibitory activity, and reduced toxicity. N-(4-hydroxyphenyl)retinamide (4-HPR) currently appears to be the most efficacious retinoid against carcinogen-induced breast, urinary bladder, and lung cancer in rodents. Retinoids are most effective when administered shortly after the carcinogen treatment; however, the treatment can be delayed significantly while maintaining its chemopreventive effect. Under various experimental conditions combining retinoid treatment with other modifiers of growth enhances its chemopreventive activity; for example retinoid plus hormonal modulation can provide better protection against mammary cancer than either treatment alone. More recently chemopreventive activity of various other classes of agents, such as thiols, phenols, antioxidants, inhibitors of prostaglandin synthesis, etc., have been investigated in experimental mammary, urinary bladder, and lung cancer models.

Suppression of rat mammary cancer development by N-(4-hydroxyphenyl)retinamide (4-HPR) following surgical removal of first palpable tumor

A study was conducted to determine whether N-(4-hydroxyphenyl)retinamide (4-HPR) affects the development of new mammary tumors subsequent to the surgical removal of the first palpable tumor. Sprague-Dawley female rats were injected i.v. with 35 mg N-methyl-N-nitrosourea (MNU) per killogram body weight at 50 days of age. The first palpable tumor was removed when 0.3-0.5 cm in diameter, and the animals placed on diets containing either 1, 2 or 3 mmol 4-HPR/kg diet. Placebo diet without 4-HPR served as control. Some animals were killed at the time of surgical removal of the first tumor and whole mounts of the mammary glands were prepared. Moreover, five animals per group were bled at 1, 3 and 6 months after commencing the 4-HPR diet and the levels of 4-HPR and N-(4-methoxyphenyl)retinamide (4-MPR) were determined. 4-HPR decreased tumor multiplicity in a dose-related manner, but cancer formation was only inhibited at the 2 and 3 mmol levels of 4-HPR. Whole mounts of mammary glands of rats treated with MNU demonstrated the presence of nonpalpable microscopic tumors in addition to the palpable tumor which was excised. Plasma levels of 4-HPR and 4-MPR increased with increasing dietary dose levels, but a linear relationship was not evident. However, the increase in plasma 4-HPR was directly correlated with an increased survival of the tumor-bearing animals. The results indicate that 4-HPR effectively inhibits the appearance of subsequent mammary tumors following excision of the first palpable tumor, and thus may be suitable for use as a chemopreventive agent in patients at increased risk for breast disease.

Metabolism of the chemopreventive retinoid N-(4-hydroxyphenyl)retinamide by mammary gland in organ culture

N-(4-Hydroxyphenyl)retinamide (4-HPR) is considered to be the most effective chemopreventive retinoid for chemically induced mammary carcinogenesis in rats. However, the mechanism of 4-HPR action in mammary cells is poorly understood. In the present study we examined the metabolism of 4-HPR in the mouse mammary gland in organ culture. Mammary glands excised from BALB/c mice were incubated with 4-HPR in the presence of insulin, prolactin and steroid hormones for 6 days. The glands were extracted with chloroform/methanol (2:1, v/v), and the metabolites were separated on a reversed-phase h.p.l.c. column. Three metabolites were separated in addition to 4-HPR; one of the metabolites, M2, was co-eluted with 13-cis-4-HPR, M3 was co-eluted with N-(4-methoxyphenyl)retinamide (4-MPR) and M1 remains unidentified. There appeared to be some hormonal regulation in the distribution of metabolites in the glands. Increased levels of 4-MPR and M1 were observed in insulin-plus-prolactin-treated glands as compared with the glands incubated with steroid hormones. Furthermore, it was observed that M1 isolated from the livers of 4-HPR-treated rats competed for the cellular retinoic acid-binding protein (CRABP) sites; however, 4-HPR did not bind to CRABP. These results indicate that mouse mammary gland can metabolize 4-HPR and that the metabolites which compete for CRABP sites may have physiological significance in the retinoid inhibition of mammary carcinogenesis.

Effect of all-trans-retinoic acid on nuclear RNA polymerase activity in chemically-induced rat mammary tumors

In the present study the effect of all-trans-retinoic acid (RA) on nuclear RNA polymerase activity in N-methyl-N-nitrosourea (MNU)-induced mammary tumors was investigated. Three experimental protocols were used. (1) The tumor mince was incubated with 1 microM RA for 30 min at 30 degrees C; the RNA polymerase activity was measured in the purified nuclei and compared with control nuclei. (2) In order to evaluate the influence of retinoic binding protein on enzyme activity, mammary tumor nuclei were incubated with RA bound cytosolic retinoic acid binding protein complex (RA-CRABP) at 25 degrees C for 30 min. This step allows the complex to translocate into the nuclei. The enzyme activity in these nuclei was compared with the nuclei pre-incubated with buffer or cytosol. (3) Finally, the influence of the addition of RA-CRABP complex directly into the RNA polymerase reaction mixture was determined and compared with appropriate controls. Results indicated that the RNA polymerase activity in the nuclei of RA treated tissue as well as in the nuclei subsequent to the translocation step was significantly reduced. However, the addition of RA-CRABP into the reaction mixture did not alter the enzyme activity. These results suggest that alteration of RNA polymerase activity may be an essential step in the retinoid action in mammary tissues.

Effects of 12-O-tetradecanoylphorbol-13-acetate on carcinogen-induced mouse mammary lesions in organ culture

Mammary glands of young female BALB/c mice develop hyperplastic nodule-like alveolar lesions (NLAL) in response to a 24-h exposure to 7,12-dimethylbenz(a)anthracene (DMBA; 2 micrograms/ml) on Day 3 during a 24-day organ culture. Experiments were conducted to determine if 12-O-tetradecanoylphorbol-13-acetate (TPA), a known tumor promoter, can influence the development of DMBA-induced NLAL in mammary gland organ culture. Mammary glands were incubated with TPA (25 ng/ml) for various periods of time in the presence of appropriate hormone combinations. Results indicated that the presence of TPA in the medium between Days 9 to 14 of the culture period enhanced both the incidence and multiplicity of DMBA-induced NLAL; however, it was ineffective when included in the medium between Days 4 to 9 or 19 to 24 of the organ culture. Toxicity of TPA was evident when it was present during the entire culture period subsequent to DMBA treatment. Computer-assisted image analysis of NLAL in the glands determined the area covered by these lesions within the gland. It was observed that 7.8% of the area was covered by NLAL in DMBA plus TPA-treated glands as compared to 2.5% by DMBA treatment alone. These results provide a model for initiation-promotion studies of mammary carcinogenesis in vitro, as well as a modified approach for quantitative analysis of structural alterations.

Anticarcinogenic effects of retinoids in animals

Retinoids are effective inhibitors of chemical carcinogenesis in the skin, mammary gland, esophagus, respiratory tract, pancreas, and urinary bladder of experimental animals. Modification of the basic retinoid structure has produced retinoids with enhanced target organ specificity, resulting in increased anticancer activity with reduced systemic toxicity. Newer retinoidal benzoic acid derivatives are even more active. Combining retinoid treatment with other modulators of carcinogenesis results in a synergistic inhibition of tumor development. Retinoids in combination with hormonal manipulation are much more effective in inhibiting mammary carcinogenesis than is either treatment alone; this combination approach also inhibits mammary tumor recurrence following surgical removal of the first tumor. Retinoids are most effective when administered shortly after the carcinogenic insult. However, even when retinoid treatment is delayed, the compounds are still effective cancer chemopreventive agents for the mammary gland and urinary bladder. The time that retinoid exposure can be delayed and retain an anticancer effect is directly related to tumor latency, with a longer delay permissible against tumors with long latent periods. The mechanism(s) by which retinoids inhibit carcinogenesis is unknown; however, in the mammary gland, retinoids inhibit differentiation and proliferation, DNA synthesis, and RNA polymerase activity. Cytosolic retinoid-retinoid receptor complexing is apparently a prerequisite for the nuclear interaction of retinoids, at least in mammary cells.

Role of hormones on the induction of retinoic acid binding protein in mouse mammary gland organ culture

Influence of various hormones on the induction of cellular retinoic acid binding protein (CRABP) was investigated in the mouse mammary gland organ cultures. Thoracic pairs of mammary glands from the BALB/c mice were cultured for seven days in the presence of various hormones in CMRL medium at 37 degrees C under 50% O2, 5% CO2 and 45% N2 atmosphere. There was a modest increase of mammary CRABP by insulin (I) + prolactin (P), however, addition of progesterone (Pg) or estrogen (E) + Pg to the medium resulted in a dramatic increase in the CRABP. Aldosterone (A) + hydrocortisone (F), in addition to I + P, which promotes differentiation to an extent similar to that of I + P + E + Pg did not have any influence on the induction of CRABP. These results indicate that prolactin and/or Pg in the medium can increase the concentration of CRABP in the mammary gland in vitro. From the results presented in this report, as well as previous work by other investigators, it is concluded that the biological response to retinoids in the mammary tissues cannot be correlated with the absolute concentration of CRABP in the cells. However, the biological response may be dependent upon both the ability of the target organ cells to metabolize the retinoid and to have minimal concentration of CRABP for binding to the active metabolite. The functional significance of hormone-induced CRABP is presently unknown.

Cell kinetics in normal and neoplastic mammary tissues by flow cytometric analyses

The cell cycle kinetics of normal mammary tissue and cancer mammary tissues were studied by flow cytometry to determine the effect of estrogen and progesterone and antiestrogens on proliferative activity. The proliferative activity was higher in rat mammary tissue during the estrus and pregnant stages compared to the nonestrus or lactational stages. Upon 5 days administration of estrogen and progesterone to the lactating animal, the low proliferative activity was increased to the values found in the pregnant stage. Steroidal effect on proliferative activity was also shown using organ cultures of normal rat tissues and the increase in proliferative activity can be reversed by the addition of 10(-6) M retinoic acid but not by retinyl acetate. In a human mammary tumor cell line (MCF-7), the cell kinetic activity was significantly depressed by antiestrogens (i.e., tamoxifen) as determined by both flow cytometry and tritiated thymidine uptake studies. Finally, a human tumor model system was developed with the MCF-7 cell line in estrogenized nude mice. Flow cytometry of the resulting tumor indicates a tetraploid tumor similar to the cell culture. Cell kinetic analysis of these nude mice tumor cells demonstrates the high proliferative activity of the estrogenized animals compared to the tamoxifen-treated animals. In conclusion, the use of flow cytometry to rapidly measure cell kinetic activity of mammary tissue has been demonstrated. The effects of estrogen or estrogen and progesterone hormones seem to increase the proliferative activity, while antiestrogens decrease this activity. Findings are observed in both in vivo and in vitro conditions or normal tissues, mammary cancer tissue, and cultured cells.

Retinoic-acid-binding protein in normal and neoplastic human esophagus

The concentration of cellular retinoic acid binding proteins (CRABP) was determined in the cytosol of normal esophageal tissue and in esophageal carcinomas. Unlike the reported results for human breast, colon, melanoma, or oropharynx cancers, the CRABP levels in esophageal cancers were either undetectable or contained levels of CRABP which were significantly lower than that of adjacent histologically disease-free tissue (P less than 0.005). Moreover, there was no difference between the normal mucosa of cancer or noncancer patients with regards to the CRABP concentration. The absence of CRABP in the cancer tissue was not dependent on the degree of differentiation. These results indicate that the CRABP disappears when the normal mucosa becomes malignant. If such a change is also demonstrated in known premalignant conditions of the esophagus, CRABP could serve as a diagnostic biochemical marker for early detection of this cancer.

Distribution of antiestrogen-specific binding sites in normal and neoplastic mammary gland

Recently, several investigators have demonstrated the presence of triphenylethylene antiestrogen binding sites in the cytoplasm of many tissues, which specifically bind to radioactive tamoxifen with high affinity. Although mammary gland is one of the principal target organs for antiestrogen action, the characterization of antiestrogen binding in mammary tissues has not been reported. We have studied the antiestrogen binding properties of [3H]tamoxifen in the mammary glands of virgin, pregnant and lactating rats as well as in the N-methyl-N-nitrosourea-induced mammary tumors. Tritium labeled tamoxifen bound specifically and with high affinity (Kd = 10(-9) M) to components present in 25,000 g supernatant. Unlabeled estradiol or DES did not compete for these sites, whereas unlabeled tamoxifen showed competitive inhibition. The mammary glands contained threefold higher levels of cytoplasmic binding sites as compared to the mammary tumors. Mammary glands from the pregnant rats bound tamoxifen to a greater extent than that of either virgin or lactating rats. The functional relevance of these binding sites is still unknown.

Inhibition of carcinogenesis by retinoids

Retinoids are effective inhibitors of chemical carcinogenesis in the mammary gland and urinary bladder of experimental animals. Modification of the basic retinoid structure has produced retinoids with increased target organ specificity, resulting in increased anticancer activity with reduced systemic toxicity. Combining retinoid treatment with hormonal manipulation results in a synergistic inhibition of mammary carcinogenesis; this combination approach also inhibits development of additional mammary cancers following surgical removal of the first mammary cancer. Retinoids are most effective when administered shortly after the carcinogenic insult. However, even when retinoid treatment is delayed, the compounds are still effective cancer chemopreventive agents for the mammary gland and urinary bladder. The length of time that retinoid exposure can be delayed and retain an anticancer effect is directly related to tumor latency, with a longer delay permissible against tumors with long latent periods.

Retinoids inhibit prolactin-induced development of the mammary gland in vitro

Mouse mammary gland organ culture technique was utilized to determine the effects of retinoids on the prolactin-induced structural differentiation of the mammary gland. Thoracic glands from BALB/c mice pretreated with steroids differentiate in 6 days into alveolar structures in presence of insulin and prolactin. All-trans-retinoic acid and N-(-4-hydroxyphenyl)retinamide inhibit prolactin-induced structural changes in the glands. Retinyl acetate, which is effective against mammary carcinogenesis in the rat, but is ineffective against mouse mammary carcinogenesis, failed to inhibit such proliferation. These results were correlated with inhibition of [3H]thymidine incorporation into DNA in a dose related manner by retinoids effective in inhibiting mammary development.

Nuclear interactions of retinoic acid-binding protein in chemically induced mammary adenocarcinoma

Cellular retinoic acid-binding protein (CRABP) was detected in the nuclear fraction of N-methyl-N-nitrosourea-induced mammary cancers after the incubation of cytosol containing [3H]retinoic acid (RA)-bound CRABP with isolated nuclei. CRABP extracted from the nuclei in buffer containing 0.4 M-KCl sedimented as a 2 S component when subjected to sucrose-density-gradient analysis. [3H]RA-CRABP was found to be a prerequisite for the detection of nuclear binding, since the incubation of isolated nuclei or 0.4 M-KCl extract of the nuclei with [3H]RA did not result in any significant binding. Incubation of [3H]RA-CRABP at 25 or 30 degrees C before incubation with the nuclei neither altered the sedimentation coefficient nor enhanced the nuclear binding compared with 0 degrees C incubation. The tumour nuclei contained a saturable number of binding sites with a dissociation constant of 1.6 x 10(-9) M. These results indicate that the action of retinoic acid in the target organ may be mediated by its interaction with the nuclei.

Retinoic acid binding proteins and steroid receptor levels in human breast cancer

Samples of 31 human breast cancer tissues were examined for the presence or absence of cytosolic retinoic acid binding proteins (cRABP), estrogen receptors (ER) and progesterone receptors (PR). cRABP were detected as specifically sedimenting 2S components on sucrose density gradient. Specific binding under the 2S region for cRABP and under the 8S region for ERR and PR were determined. The levels of cRABP ranged from less than 1 pmol to 14 pmol per mg of cytosol protein. Tumors containing less than 3 pmol cRABP were designed as low cRABP; tissues were considered ER- and PR- when the receptor levels were less than 10 fmol/mg protein. Approximately 60% of primary and metastatic tumors examined contained high cRABP. Tumors with well differentiated histopathology exhibited increased levels of cRABP. There was no significant correlation between the presence or absence of steroid receptors and cRABP in human mammary tumors.

Temporal association between arterial cholesterol deposition, thymidine incorporation into DNA, and atherosclerosis in Japanese quail fed an atherogenic diet

Male Japanese quail (strain SEA) rapidly develop atherosclerotic lesions in the aorta and brachiocephalic arteries when fed an atherogenic diet containing 1.0% cholesterol and 0.5% cholic acid. The present study was conducted to determine the parameters of the atherosclerotic response. Groups of 20 quail fed the atherogenic diet were killed at 0 days, 1 day, 3 days, or weekly from 1 to 12 weeks. Quail fed the atherogenic diet for 1 day showed a significant increase in serum cholesterol; a plateau was reached by 2 weeks. A significant increase in arterial cholesterol was seen after 2 weeks on the atherogenic diet, and arterial cholesterol showed a linear increase with time from 2 to 12 weeks. Increased incorporation of tritiated thymidine into the DNA of arterial cells was first seen at 2 weeks; thymidine incorporation increased to a maximum value at 9 weeks, then declined to 50-60% of the 9-week value at weeks 11 and 12. Grossly visible atherosclerotic lesions were first seen at 3 weeks, and 90% of birds showed gross atherosclerotic lesions by 8 weeks. Atherosclerosis induced in Japanese quail by feeding cholesterol and cholic acid is characterized initially by lipid deposition in the arterial wall, followed by increased incorporation of tritiated thymidine and the appearance of gross lesions.

Enhanced inhibition of mammary carcinogenesis by combined treatment with N-(4-hydroxyphenyl)retinamide and ovariectomy

Bilateral ovariectomy and dietary administration of the retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) are both effective inhibitors of chemical carcinogenesis in the rat mammary gland. The present study was designed to determine whether an enhanced inhibitory effect is obtained with combined ovariectomy and 4-HPR administration, compared to either treatment alone. In separate experiments, 50-day-old virgin female Sprague-Dawley rats received either a single i.v. injection of 50 mg N-methyl-N-nitrosourea per kg body weight or a single intragastric dose of 20 mg 7,12-dimethylbenz(a)anthracene. The experimental design was the same in both the N-methyl-N-nitrosourea and 7,12-dimethylbenz(a)anthracene experiments: Group 1, 25 intact rats, placebo diet; Group 2, 25 intact rats, supplement of 782 mg 4-HPR per kg diet; Group 3, 50 ovariectomized rats, placebo diet; Group 4, 50 ovariectomized rats, supplement of 782 mg 4-HPR per kg diet. Feeding of the 4-HPR supplement was begun 7 days after carcinogen administration; ovariectomy was performed 7 days post-7,12-dimethylbenz(a)anthracene or 14 days post-N-methyl-N-nitrosourea. In both experiments, combined ovariectomy plus 4-HPR was significantly more active in suppressing mammary cancer induction than was either manipulation alone. 4-HPR was a more effective inhibitor of carcinogenesis in ovariectomized rats than in intact animals. These data indicate that 4-HPR is highly effective in inhibiting ovarian hormone-independent cancers and suggest that retinoid inhibition of mammary carcinogenesis does not involve an influence on ovarian hormone action.

Retinoid binding in normal and neoplastic mammary tissue

The inhibitory effect of dietary supplementation of certain retinoids on mammary carcinogenesis in the rat has been reported from our laboratory. Specific cytosolic retinoic acid binding proteins (cRABP) as well as retinol binding proteins sedimenting as 2S components have been detected in the mammary tissue during normal and neoplastic differentiation. Relatively higher levels of cRABP were observed in the mammary glands from pregnant animals as well as in ovarian hormone independent tumors; whereas in glands obtained from lactating rats and in hormone dependent tumors, lower levels of cRABP were evident. Exogenous treatment of such animals with estradiol-17 beta enhanced the levels of cRABP. The results indicate a possible correlation between endocrine and retinoid function in both normal and neoplastic differentiation of mammary tissue. [3H]retinoic acid-RABP complex, under appropriate conditions, translocates into th nucleus. Unbound [3H]retinoic acid, however, failed to associate with the nuclear sites. Additional studies indicate a possible selective inhibition of ovarian hormones independent tumors by the retinoids.

Correlation between retinoid inhibition of N-methyl-N-nitrosourea-induced mammary carcinogenesis and levels of retinoic acid binding proteins

A correlation was made between the ability of retinoids to suppress N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis and the levels of cytosolic retinoic acid binding proteins (cRABP) in the cytosol of MNU-induced mammary tumors. Although retinyl acetate and N-(4-hydroxyphenyl)-retinamide were found to be effective inhibitors of mammary carcinogenesis in intact hosts, both retinoids were significantly more active in ovariectomized rats than in intact animals. Quantitative analysis of cRABP in the tumors indicated that mammary cancers arising in animals which were ovariectomized one week after MNU administration contained significantly increased concentrations of cRABP compared to cancers appearing in intact rats. In addition, when animals bearing palpable mammary tumors were ovariectomized, the tumors which continued to grow contained significantly higher levels of cRABP than did tumors which stopped growing or regressed. These data suggest that the selective inhibition of ovarian hormone-independent mammary cancer by retinyl acetate and N-(4-hydroxyphenyl)retinamide may be mediated through an increased level of cRABP in tumor cells of ovariectomized hosts.

Hormonal regulation of retinoic acid-binding proteins in the mammary gland

A cytosolic retinoic acid-binding (RAB) protein that sediments specifically as a 2S component on sucrose density gradients was detected in the mammary glands of virgin, pregnant and lactating rats. Mammary cytosol from pregnant rats contained significantly higher concentrations of cytosolic RAB protein than did cytosol from either virgin or lactating rats. The glands of pregnant animals exhibited increased concentration of cytosolic RAB protein during the first 5 days of pregnancy, and a steady decline was observed thereafter. The concentration of cytosolic RAB protein dropped to the value observed during lactation on the day 20 of pregnancy. Moreover, throughout lactation, low concentrations of cytosolic RAB protein were maintained. Daily treatment of virgin and lactating animals with 5 micrograms of oestradiol-17 beta for 1 week increased cytosolic RAB protein to concentrations comparable with those seen in pregnant rats. Progesterone, however, did not affect the mammary cytosolic RAB protein content of virgin rats. These results suggest hormonal involvement in the regulation of cytosolic RAB protein concentration of mammary gland during differentiation.

Inhibition of DNA synthesis by retinyl acetate during chemically induced mammary carcinogenesis

The effect of retinoids on DNA synthesis was studied in the female Sprague-Dawley rat. Animals were treated with either solvent, 7,12-dimethylbenz(a)anthracene, or 1-methyl-1-nitro-sourea at 50 days of age and were placed on either placebo or retinyl acetate diet at 57 days of age. [3H]Thymidine incorporation into purified DNA isolated from mammary parenchymal cells was determined. Retinyl acetate effectively inhibited mammary cell DNA synthesis in both 1-methyl-1-nitrosourea- and 7,12-dimethylbenz(a)anthracene-treated animals; however, DNA synthesis in solvent-treated animals was unaffected.

Androgen receptors in chemically-induced colon carcinogenesis

Cytoplasmic extracts (105,000 x g supernatants) prepared from the colon of 1,2-dimethylhydrazine hydrochloride (DMH) treated male BD-IX rats bound 3H-5 alpha-dihydrotestosterone (DHT) with high affinity (Kd = 3 x 10(-9) M) and low capacity (n = 20 fmoles/mg protein). Unoccupied saturable binding sites were not detected in normal intact colon but were observed in colons from gonadectomized rats. DHT receptors were present in both the ascending and descending segments of the colon. The DHT binding components sedimented as 7--8S species on linear sucrose density gradients and were effectively displaced by cyproterone acetate, but not by progesterone. Forty percent of the DMH-induced colon tumors also bound DHT with high affinity and limited capacity. These results suggest that the sex steroids are involved in carcinogen-induced colon tumorigenesis, and the action is mediated by their association with sex steroid specific receptors.

Distribution of retinoic acid-binding proteins in normal and neoplastic mammary tissues

Cellular retinoic acid-binding proteins were detected in chemically induced mammary tumors using sucrose density gradient analysis. Unlabeled retinoic acid did not displace nonspecific binding in the 5S region but was, however, a competitive inhibitor for the specifically binding 2S component. Mammary gland cytosol fractions from both 1-methyl-1-nitrosourea-treated and untreated as well as from lactating rats contained low levels of retinoic acid-binding proteins. 1-Methyl-1-nitrosourea treatment did not result in the increased number of binding sites. Thus, the increase in the levels of binding proteins in tumors most probably occurred during tumor development and probably was not a result of the carcinogen per se. Retinoids which have been shown to be effective in the chemoprevention of mammary carcinogenesis only partially competed for the binding sites, indicating that they may be metabolized prior to their action as an active chemopreventive agent.

Nuclear interaction of Fusarium mycotoxins with estradiol binding sites in the mouse uterus

By using cell-free preparations of uteri obtained from immature BALB/c mice, it was demonstrated that zearalenone and zearalanol, Fusarium mycotoxins, inhibited [3H]estradiol-17 beta binding to specific sites in cytosol. Significant inhibition was noted from zearalenone at 4 x 10(-6) M and from zearalanol at 4 x 10(-7) M. Unlabeled mycotoxins (5 x 10(-6) M) incubated with intact uteri caused translocation of specific estrogen binding sites into nuclei that were exchangeable with [3H]estradiol-17 beta. Zearalanol was more effective in this regard than zearalenone. Ability of the mycotoxins to compete with estradiol-17 beta for the cytosol receptor and to cause translocation of the receptor to the nucleus in general is correlated with their biological activity. These data suggest that the uterotrophic effects of Fusarium mycotoxins are mediated through their association with estrogen receptors in the uterus.

Action of growth-promoting hormones on macromolecular biosynthesis during lobulo-alveolar development of the entire mammary gland in organ culture

The entire 2nd thoracic mammary gland of the immature virgin BALB/c mouse was stimulated to full lobulo-alveolar (LA) growth after 120 h organ culture in hormone supplemented medium. The minimal hormonal combination required was insulin (I) + prolactin (Prl) + aldosterone (A). The corticosteroid was replaceable by oestradiol-17beta (E) + progesterone (P). The combination I alone or I + the steroid hormone(s) failed to induce the LA development and similar results were also evident in presence of Prl + the steroids. Incubation of the glands in medium with I + Prl + A activated a sequential rise of RNA, protein and DNA synthesis. A near maximal increase of RNA synthesis was present at 48 h in the medium with I + Prl, addition of the steroid hormones did not show further stimulatory effect. Supplementation of the medium with I + Prl and the adrenal or the ovarian steroids was needed for maximal activation of protein synthesis at 72 h and DNA replication at 96 h. The medium with I alone did not show a substantial rise of macromolecular biosynthesis in the mammary gland in organ culture. The highest level of DNA polymerase activity was observed at 72 h in glands cultivated in medium with I + Prl and A or E + P. Only a modest increase of DNA polymerase activity was present in glands cultivated with I alone or I + Prl. Prior treatment of the glands (cultivated with I + Prl + A) with actinomycin D or puromycin resulted into 44 and 40% reduction of DNA polymerase activity suggesting hormone-induced synthesis of the enzyme before the rise of DNA synthesis in the mammary cells at 96 h in organ culture. Significance of these results with respect to the action of the "growth-promoting" hormones in the mammary gland in organ culture and in the animal has been discussed.