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  • 1
    ISSN: 1524-4741
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Chemoprevention, or intervention with chemical agents at the precancer stage to avoid or slow the development of the carcinogenic process, is one strategy to reduce both the incidence of breast cancer and its mortality. Systematic development of cancer chemopreventive drugs calls for evaluation of pre-clinical efficacy in well-characterized in vitro screens and animal cancer models. Highly promising agents are also included in traditional pre-clinical toxicity tests performed in two species. The most promising and least toxic agents enter clinical trials, including both phase I safety and pharmacokinetics evaluations and phase II and III efficacy studies. The use of populations with defined, measurable biologic alterations in tissue occurring prior to cancer development, i.e. intermediate biomarkers, is important to successful phase II chemoprevention trials. The intermediate biomarkers may be of several types, such as histological/premalignant lesions, proliferative, genetic/regulatory, differentiation-related, or biochemical. For example, ductal and lobular carcinoma in situ are premalignant lesions in the human breast. These lesions are tissue at very high risk of malignant progression and also have the potential to be modulated by chemopreventive agents. In addition, other types of biomarkers may be identified within the lesions. These biomarkers could then serve as surrogate trial end-points, instead of cancer incidence, for use in shorter, less costly trials.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-0603
    Keywords: Chemopreventive agent ; Ornithine decarboxylase ; Tracheal epithelial cells ; Tumor promoter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A unique assay method to detect ornithine decarboxylase (ODC) activity in normal tracheal epithelial cells induced by a classic tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) has been developed. Using this new assay, the inhibition of induced ODC activity is measured, thereby providing a screening system to identify potential chemopreventive or therapeutic agents. The assay is designed to be specific as it detects a radioactively labeled reaction product, putrescine from the decarboxylation of ornithine by ODC. As TPA is a classical tumor promoter, inhibition TPA-induced ODC activity can also be used to select antitumor promoter agents. Since the assay requires only 2 days to complete, it can be used to screen a large number of compounds for chemopreventive activity in a relatively short period of time.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-0603
    Keywords: Carcinogen biomarker ; Chemoprevention ; Growth inhibition ; Human keratinocytes ; In vitro toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methods are described for a human keratinocyte assay for screening cancer preventive agents. Normal human keratinocytes at the first or second subculture are seeded into multi-well dishes. Cultures are repeatedly exposed to the carcinogen, propane sultone, and nontoxic concentrations of potential chemopreventive agents. At the end of the exposure period, the cultures are evaluated for growth and involucrin expression. Data are analyzed to determine the potential for test agents to inhibit propane sultone induced growth or to induce involucrin expression relative to that in propane sultone treated controls.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-0603
    Keywords: Glutathione-S-transferase ; Human liver cells ; Phase II enzyme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract For selection and identification of potential chemopreventive agents, a biochemical assay using induction of a phase II enzyme, glutathione-S-transferase (GST) in a liver cell culture is described. A normal human liver cell line (Chang liver cells) was selected as the candidate cell line for induction of GST (liver tissues are abundant in GST) by a known chemopreventive agent, oltipraz. Exponentially growing cells plated for 24 hours are exposed to various doses of a chemopreventive agent for an additional 24 hours, homogenized by sonication, and the homogenate is assayed for GST in a modified microplate enzyme assay using CDNB (1-chloro-2,4-dinitrobenzene) as a substrate. A concurrent protein assay is performed to determine the specific enzyme activity. As the assay is modified from a spectrophotometric assay to a microplate assay, it is reliable, sensitive and fast, a significant number of test agents can be screened in a short time.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-0603
    Keywords: Chemoprevention ; In vitro assays ; Drug screening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This issue reports the methods of twelve in vitro assays currently being used to screen potential chemopreventive agents for activity. These assays provide quantitative data to help determine the efficacy and prioritize agents for further development in whole animal screening. It is essential that such in vitro assays provide accurate, consistent, and relevant data to identify and prioritize agents with the most promise to prevent human cancer. The twelve assays presented in this volume are currently providing such data to the National Cancer Institute's Chemoprevention Program.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-0603
    Keywords: Anchorage-independent growth ; Chemoprevention ; Human lung tumor cells ; In vitro model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An in vitro model for screening potential chemopreventive agents using inhibition of anchorage-independent growth of a human lung tumor cell line, A427, is described. A427 cells were selected for the model development, as they are known to be tumorigenic in animals, can grow in soft agarose, and their growth can be inhibited by a well-known chemopreventive agent, 13-cis-retinoic acid. Cells are plated on agarose, allowed to develop colonies for 28 days, the stained colonies are enumerated, and the inhibition of spontaneous colony formation measured. A cytotoxicity test is used concurrently with anchorage independent assay for measuring the relative survival of cells to ensure that any observed inhibition of anchorage independent growth is due to the biological activity of the chemopreventive agents, as it uses human cells as substrates rendering the efficacy data feasible for direct extrapolation to humans.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-0603
    Keywords: Antineoplastic agents ; Cell transformation ; Chemoprevention ; Epithelial cells ; Respiratory tract
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This rat tracheal epithelial (RTE) focus inhibition assay is designed to provide information on the anticarcinogenic properties of potential chemopreventive (CP) agents. The assay uses cultured primary RTE cells and measures the inhibition of morphological transformation induced by the carcinogen, benzo[a]pyrene (B[a]P). RTE cells are used as a model for human respiratory epithelial cells, a major target tissue of carcinogens, to provide data to help evaluate the anticarcincogenic potential of CP agents. In the assay, primary RTE cells are treated with the carcinogen B[a]P for 24 hours in the presence of the test CP agent. After 30 days, foci of morphologically transformed, precancerous cells are identified and inhibition is scored as a decrease in the number of these foci compared to the B[a]P-alone treated cultures. The RTE assays provides important data for agent selection prior to whole animal screening assays in the development of chemoprevention drugs.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-0603
    Keywords: Albumin ; Bronchial cells ; Chemoprevention ; Ecto-cervical cells ; Growth inhibition ; Hepatocytes ; Human ; In vitro ; Keratinocytes ; Mammary epithelial cells ; Mitochondrial function ; Normal ; Oral mucosal cells ; PCNA ; Prostate epithelial cells ; Renal cells ; Toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Human Epithelial Cell Cytotoxicity (HECC) Assay for determining organ specific cytotoxicity uses human epithelial cells from eight different human tissues, including: skin, mammary, prostate, renal, bronchial, oral, ecto-cervix, and liver. Although the initial studies using this assay were conducted using cancer chemopreventive agents, the HECC Assay can also be used to evaluate other types of drugs, personal care products, environmental chemicals, and potential toxicants. Human epithelial cells at an early passage are seeded into multi-well dishes. The cells are exposed to multiple concentrations of a test agent for a three day period. The concentration ranges for test agents in the assay are determined in a preliminary assay using an exposure of five days and log dilutions from the highest soluble concentration. At the end of the exposure period, the cultures are evaluated for inhibition of growth. In the HECC Assay, cultures are exposed for three days. At the end of the exposure period, the cultures are evaluated for inhibition of growth, mitochondrial function, and PCNA expression or albumin synthesis (hepatocytes). Data are analyzed to determine the concentration that inhibited and point by 50 percent (TC50). Values for each agent in each target epithelial cell line or culture and the target tissue specific sensitivity are compared to determine the relative sensitivity of each epithelial cell line to the test agent.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0730-2312
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: A major determinant of progress in human breast cancer prevention is the identification of agents with significant anticarcinogenic activity and acceptable levels of toxicity in experimental animals. Over the past 20 years, more than 50 experimental regimens have been shown to have significant chemopreventive activity in the rat mammary gland. The most effective approaches to mammary cancer chemoprevention in rats involve surgical endocrine ablations such as bilateral ovariectomy. However, prophylactic surgical ablations are unlikely to be acceptable to the majority of the general public. All chemicals evaluated to date are less effective, and none has been shown to reduce mammary cancer incidence to zero. As a result, efforts continue to identify chemical agents whose protective activity is comparable to that of endocrine ablation. DHEA is an adrenal steroid with chemopreventive activity in several animal models for human cancer. In the present studies, the chemopreventive efficacy of DHEA was evaluated in rats exposed to the mammary gland carcinogen, N-methyl-N-nitrosourea (MNU). Groups of 20 female Sprague-Dawley rats were fed an AIN-76A diet supplemented with 0, 400, or 800 mg DHEA per kg diet; one week later, all rats received a single i.p. injection of 35 mg MNU per kg body weight. Animals were palpated weekly to monitor mammary tumor development, and all mammary tumors were histologically confirmed. When administered at 800 mg/kg diet, DHEA reduced mammary cancer incidence in controls from 95% to 15%; carcinoma multiplicity in rats receiving 800 mg DHEA per kg diet was reduced by more than 85% from control levels. In a separate study, the 400 mg/kg diet dose of DHEA reduced the incidence of mammary cancer to 5% from 80% found in controls fed the basal diet. Reductions in mammary cancer incidence and multiplicity associated with DHEA administration were accompanied by large increases in cancer latency. Evaluation of mammary gland wholemounts from animals fed DHEA demonstrated a massive induction of lobuloalveolar differentiation. These results indicate the dietary supplementation with non-toxic dose levels of DHEA has chemopreventive efficacy approaching that of endocrine ablation. This protection may be mediated by the induction of differentiation in the mammary gland, during which sensitive mammary parenchymal structures (terminal end buds) are stimulated to develop into structures (alveolar buds) less sensitive to carcinogenic insult.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0730-2312
    Keywords: Animal models ; carcinogenesis ; chemoprevention ; drug development ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: In the NCI, Chemoprevention Branch drug development program, potential chemopreventive agents are evaluated for efficacy against chemical carcinogen-induced tumors in animal models. This paper summarizes the results of 144 agents in 352 tests using various animal efficacy models. Of these results, 146 were positive, representing 85 different agents.The target organs selected for the animals model are representative of high-incidence human cancers. The assays include inhibition of tumors induced by MNU in hamster trachea, DEN in hamster lung, AOM in rat colon (including inhibition of AOM-induced aberrant crypts), MAM in mouse colon, DMBA and MNU in rat mammary glands, DMBA promoted by TPA in mouse skin, and OH-BBN in mouse bladder.The agents tested may be classified into various pharmacological and chemical structural categories that are relevant to their chemopreventive potential. These categories include antiestrogens, antiinflammatories (e. g., NSAIDs), antioxidants, arachidonic acid metabolism inhibitors, GST and GSH enhancers, ODC inhibitors, protein kinase C inhibitors, retinoids and carotenoids, organosulfur compounds, calcium compounds, vitamin D3 and analogs, and phenolic compounds (e. g., flavonoids). The various categories of compounds have different spectra of efficacy in animal models. In hamster lung, GSH-enhancing agents and antioidants appear to have high potential for inhibiting carcinogenesis. In the colon, NSAIDs and other antiinflammatory agents appear particularly promising. Likewise, NSAIDs are very active in mouse bladder. In rat mammary glands, retinoids and antiestrogens (as would be expected) are efficacious. Several of the chemicals evaluated also appear to be promising chemopreventive agents based on their activity in several of the animal models. Particularly, the ODC inhibitor DFMO was active in the colon, mammary glands, and bladder models, while the dithiolthione, oltipraz, was efficacious in all the models listed above (i. e., lung, colon, mammary glands, skin, and bladder). 1994 Wiley-Liss, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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