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Annexin/lipocortin I as a unique target of mechanism-based chemoprevention of breast cancer: computer biology and in vitro new gene mutation assays.
RISK and Prevention, Epidemiology
DNA damage-induced gene mutation is a major mechanism of cancer initiation, whether the damage arises from environmental chemicals or endogenous reactive metabolites. Since the generation of gene mutations occurs via tolerance of DNA lesions rather than error-prone repair, error-prone damage bypassing DNA synthesis and its underlying molecular biology offer an intriguing potential target for cancer prevention. Annexin (anx)/lipocortin I is a major substrate of the oncogenic tyrosine kinases, and is involved in signal transduction of various growth factors. Nuclear anx I plays a key role in cell transformation, thereby being involved in an early stage of various cancers including human breast ductal epithelial cancer. Our laboratory has recently characterized nuclear anx I as a helicase with higher affinity for damaged DNA. Anx I helicase is regulated by the DNA damage signaling enzymes, and stimulates in vitro DNA synthesis bypassing the damaged sites via error-prone DNA polymerases. Anx I, indeed, plays an important role in chemical induced mutagenesis of the hprt gene in MCF10F human breast epithelial cells. Some cancer-preventive flavonoids such as silymarin are relatively good inhibitors of anx I helicase. In the proposed research, we will search more potent dietary compounds and/or drugs for breast cancer prevention by the aids of the computer biology. The flavonoids bind to the “diazepam pocket” of the anx I molecule, and computer screening of chemicals that interact to this site revealed a new series (approximately 300) of chemicals. These small molecules resemble many cancer preventive dietary compounds. To determine whether these candidate compounds serve as prototype drugs for breast cancer prevention, our Specific Aims are to test them for the in vitro anx I helicase assay as well as for the hprt mutation and transformation assays of high anx I MCF10F cells. From detailed computer analysis of the interaction between the best inhibitors and anx I together with the proposed assay data, we will chemically modify them to increase their potency for cancer prevention with less toxicity. This proposed research will facilitate the translation of leads from in vitro and/or epidemiological observations into intervention strategies, since the computer biology together with experimental data of the target protein promotes the structure-based design of drugs for breast cancer prevention that otherwise is not offered.
While conventional treatments with anti-cancer drugs and surgical operations have recently improved the survival of patients, they do not influence the incidence of breast cancer. Prevention of breast cancer among populations of risks by using simple compounds such as diets and anti-hormone agents is an urgent and important issue. Inhibition of cancer initiation rather than inhibition of malignant transformation of cancer is the most effective target for cancer prevention. Since cancer is initiated by gene mutations resulting from DNA damage by environmental chemicals and/or by reactive metabolites in the body, the best target of cancer prevention exists in the process of gene mutation. While the protein called as annexin /lipocortin I is absent in normal breast tissues, its cellular levels parallel degrees of malignancy of breast cancer. Our laboratory demonstrated that this protein plays an important role in chemical induced gene mutation, thereby in the early stage of breast cancer development. Flavonoids, compounds that are present in vegetables and soy products reduce the incidence of breast cancer among women with risks of breast cancer, and delay the cancer formation in animal models. To test our hypothesis that annexin I is a unique target of breast cancer prevention, we investigated if cancer preventive flavonoids inhibit annexin I, thereby reducing gene mutation. Genistein, quercetin and silymarin, flavonoids that are preventive against cancers in animals, inhibit annexin I, while flavone and flavonol, inactive flavonoids, do not. To find a more potent drug(s) for breast cancer prevention, we will employ the computer biology to analyze the interaction between chemicals and annexin I. Since computer analysis identified a new series (approximately 300) of small molecules, we will test them for annexin I and for gene mutation and transformation in MCF10F cells, normal human breast epithelial cells. By the aids of the computer biology, we will chemically modify them to produce drugs with more potent cancer preventive effects and less toxicity. Our proposed research will stimulate the translation of leads from in vitro and/or epidemiological observations into clinical intervention, since computer analysis of the interaction between chemicals and annexin I promotes the structure-based design of drugs for breast cancer prevention that is not offered by most of cancer prevention studies.