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R G Mehta

Publications and source records attributed to R G Mehta.

At least 37 records · Page 2Linked to original sources
PubMed1998

Angoline and chelerythrine, benzophenanthridine alkaloids that do not inhibit protein kinase C.

Starting with an extract derived from the stem of Macleaya cordata (Papaveraceae) that was active in the process of inhibiting phorbol 12,13-dibutyrate binding to partially purified protein kinase C (PKC), the benzophenanthridine alkaloid angoline was isolated and identified. This discovery appeared in context, as a related benzophenanthridine alkaloid, chelerythrine, has been reported to mediate a variety of biological activities, including potent and selective inhibition of protein kinase C (PKC). However, in our studies, angoline was not observed to function as a potent inhibitor of PKC. Moreover, we were unable to confirm the reported inhibitory activity of chelerythrine. In a comprehensive series of studies performed with various PKC isozymes derived from a variety of mammalian species, neither chelerythrine nor angoline inhibited activity with high potency. To the contrary, chelerythrine stimulated PKC activity in the cytosolic fractions of rat and mouse brain in concentrations up to 100 microM. In addition, chelerythrine and angoline did not inhibit [3H]phorbol 12,13-dibutyrate binding to the regulatory domain of PKC at concentrations up to 40 microg/ml, and no significant alteration of PKC-alpha, -beta, or -gamma translocation was observed with human leukemia (HL-60) cells in culture. Further, chelerythrine did not inhibit 12-O-tetradecanoylphorbol 13-acetate-induced ornithine decarboxylase activity with cultured mouse 308 cells, but angoline was active in this capacity with an IC50 value of 1.0 microg/ml. A relatively large number of biological responses have been reported in studies conducted with chelerythrine, and alteration of PKC activity has been considered as a potential mechanism of action. In light of the current report, mechanisms independent of PKC inhibition should be considered as responsible for these effects.

Alkaloids↗
PubMed1998

Metabolism of N-[4-hydroxyphenyl]retinamide (4-HPR) to N-[4-methoxyphenyl]retinamide (4-MPR) may serve as a biomarker for its efficacy against human breast cancer and melanoma cells.

A clinical trial of N-[4-hydroxyphenyl]retinamide (4-HPR) has been in progress for the past 4 years to evaluate its role in chemoprevention of breast cancer. However, it is currently not known whether the effect of 4-HPR in breast cells is mediated by 4-HPR directly or through one of its metabolites. In this report, we investigated in vivo and in vitro effects of 4-HPR on three different breast carcinoma cells and two different melanoma cell lines. In vitro, the growth of all three breast carcinoma cell lines was inhibited by 4-HPR. Only one of two melanoma cell lines (UISO-Mel-1) showed growth inhibition to 4-HPR. The cell lines sensitive to 4-HPR in vitro also showed inhibition to 4-HPR in a xenograft model. Dietary 4-HPR (0.5 mmol/kg diet) reduced the growth of UISO-BCA-1 xenografts in female athymic mice, but had no effect on UISO-Mel-6 xenografts. Metabolism investigations of the 4-HPR-sensitive and insensitive cell lines indicated that N-[4-methoxyphenyl]retinamide (4-MPR), the major metabolite of 4-HPR, was detected only in cells sensitive to 4-HPR. Further in vitro studies with 4-MPR suggested that it is not an active metabolite of 4-HPR as it failed to inhibit growth of 4-HPR-resistant UISO-Mel-6 cells, and showed no dose-dependent inhibition of 4-HPR-sensitive breast carcinoma and melanoma cell lines. Our results in the present study indicate that, although 4-MPR is not an active metabolite of 4-HPR, detection of this metabolite in the malignant cells may serve as an indirect biomarker to predict response of cells to 4-HPR.

Animals↗
PubMed1998

Evaluation of the antioxidant potential of natural products.

Since reactive oxygen radicals play an important role in carcinogenesis and other human disease states, antioxidants present in consumable fruits, vegetables, and beverages have received considerable attention as cancer chemopreventive agents. Thus, in order to identify antioxidants in plant extracts, test materials were assessed for potential to scavenge stable 1,2-diphenyl-2-picrylhydrazyl (DPPH) free radicals, reduce TPA-induced free radical formation in cultured HL-60 human leukemia cells, and inhibit responses observed with a xanthine/xanthine oxidase assay system. Approximately 700 plant extracts were evaluated, and 28 were found to be active in the DPPH free radical scavenging assay. Based on secondary analyses performed to assess inhibition of 7,12-dimethylbenz(a)anthracene-induced preneoplastic lesion formation with a mouse mammary organ culture model, Chorizanthe diffusa Benth. (Polygonaceae), Mezoneuron cucullatum Roxb. (Leguminosae), Cerbera manghas L. (Apocynaceae) and Daphniphyllum calycinum Benth. (Daphniphyllaceae) were selected and subjected to bioassay-guided fractionation. 5,7,3',5'-Tetrahydroxy-8,4'-dimethoxyflavonol, 5,8,4'-trihydroxy-7,3'-dimethoxyflavonol, 5,3',4'-trihydroxy-7-methoxyflavonol, and 6,3',4'-trihydroxy-7-methoxyflavonol were identified as active principles from C. diffusa. Piceatannol, trans-resveratrol, apigenin and scirpusin A were found as the active principles of M. cucullatum, olivil, (-)-carinol, and (+)-cycloolivil were active principles from C. manghas, and 5,6,7,4'-tetrahydroxyflavone 3-O-rutinoside and kaempferol 3-O-neohesperidoside were active principles from D. calycinum. Of these substances, the hydroxystilbenes piceatannol and transresveratrol have thus far been shown to inhibit carcinogen-induced preneoplastic lesion formation in the mouse mammary gland organ culture model.

Animals↗
PubMed1997

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.

3T3 Cells↗
PubMed1997

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.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1997

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.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1997

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.

Animals↗
PubMed1997

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.

Animals↗
PubMed1995

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.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

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.

Adenocarcinoma↗
PubMed1992

Retinoid glucuronides do not interact with retinoid binding proteins.

Retinoid glucuronides have recently been described as water soluble, biologically active retinoids. In mouse mammary gland organ cultures retinoyl glucuronide, a retinoic acid counterpart, inhibited hormone induced differentiation. In this report we examined whether the effects of retinoyl and retinyl glucuronides are mediated by specific retinoid binding protein in mammary glands in organ culture. Results indicated that neither retinoyl nor retinyl glucuronide competed for cytosolic retinoic acid or retinol binding proteins respectively. These results indicate that either the effects of retinoid glucuronides are independent of retinoid binding proteins or they have to be metabolized to an active component which may in turn bind to retinoid binding protein for the glucuronide action.

Animals↗
PubMed1992

Retinoids as chemopreventive agents for breast cancer.

Although several retinoids have been evaluated for prevention of mammary carcinogenesis in rats and mice, retinyl acetate (RA) and N-(4-hydroxyphenyl)retinamide (4-HPR) proved most effective. In rats, dietary administration of the retinoids reduced the incidence and number, and increased the latency of N-methyl-N-nitrosourea (MNU)-induced mammary cancers. 4-HPR reduced the number of hyperplastic alveolar nodules (HAN) in MTV- mice and the number of tumors in MTV+ mice. Other studies indicate that the synergistic effect of retinoid administration and hormonal deprivation is more efficacious in prevention of MNU-induced mammary cancer than either modality alone. Furthermore, retinoids alone and the combination of retinoid and tamoxifen inhibit the appearance of mammary cancers following the surgical removal of the first cancer as well as inhibit the growth of established cancers. Again, the combined modality was the most effective. Retinoids also exert an antiproliferative effect upon the mammary epithelium in vivo, which is represented morphologically by a bare duct system with little branching, end buds, and few, if any, alveoli. In organ culture, retinoids inhibit mammary end bud differentiation and proliferation induced by insulin and prolactin or carcinogens.

Animals↗
PubMed1991

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.

Androstenes↗
PubMed1991

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.

Adipose Tissue↗
PubMed1991

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.

Animals↗