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    Awarded Grants
    Epoxygenase Mechanisms of Breast Cancer Progression

    Scientific Abstract:
    Three enzymatic pathways of arachidonic acid metabolism, cyclooxygenases, lipoxygenases and epoxygenases have been identified in mammalian cells, but only the first two pathways have been linked to human cancer. We have found that the oral HIV protease inhibitor, ritonavir, a potent inhibitor of epoxygenases, inhibits the growth of breast cancer xenografts. Epoxygenases promote the production of epoxyeicosatrienoic acids (EET’s) that activate Akt kinase. What is not known is whether epoxygenases promote the proliferation and survival of breast cancer cells and if so how. This gap in knowledge is preventing us from clinically developing epoxygenases as therapeutic targets in breast cancer. Objective/Hypothesis: This project seeks to determine whether epoxygenases are therapeutic targets in breast cancer. The hypothesis to be tested is that epoxygenase activation promotes breast cancer progression by promoting Akt phosphorylation and cancer cell survival. The specific aims are: 1. To establish the molecular mechanisms by which epoxygenases cause growth dysregulation in breast cancer, 2. To establish that epoxygenases enhance the oncogenic potential of the v-Ha-ras oncogene in mammary carcinoma, and 3. To establish that the epoxygenase pathway activates and requires Hsp90, a potential downstream mediator of epoxygenase signaling, for cancer cell survival. Study Design: For Aim 1, we will determine whether EET promotes ERK activation through a MEK pathway and Akt activation through a PI3-kinase pathway and whether the MDA-MB-231 is dependent upon EET for proliferation and survival. Inhibition of EET production by ritonavir will be determined, as will be the degree of dependence of the MDA-MB-231 line on EET for proliferation and survival. Targeted lipidomics using the method of electron capture APCI-MS/MS will be used to profile EET regio- and stereoisomers. In Aim 2, a bacterial epoxygenase will be tested for cooperation with activated Ha-ras in an MCF10A xenograft model of breast cancer progression. In Aim 3 we will determine whether the Hsp90 inhibitor, 17-allyl aminogeldanamycin, inhibits Akt activation and cell survival induced by bacterial epoxygenase. Potential Outcomes and Benefits of the Research: The proposed studies will provide evidence that epoxygenases can play a role in breast cancer etiology and progression. This area is largely unexplored and these studies may lead to the identification of epoxygenases as a novel therapeutic target in breast cancer.

    Lay Abstract:
    It is well recognized that the progression of breast cancer requires resistance to cell death, but the mechanisms by which breast cancer cells acquire this attribute is not well understood. One way in which breast cancer cells accomplish this resistance to cell death is to activate a protein called Akt. Activated Akt then acts through multiple pathways to promote resistance to cell death and is therefore considered to be a master regulator of cancer cell survival. The molecular mechanisms by which Akt is activated are not well understood. We have recently discovered that an oral HIV protease inhibitor drug, ritonavir, FDA approved to treat AIDS, also has activity against breast cancer in a mouse model of mammary cancer and blocks Akt activation. A lack of understanding of the molecular mechanisms by which ritonavir blocks mammary cancer growth and Akt activation prevents us from developing this drug clinically. To overcome this gap in knowledge, we have recently found evidence that ritonavir may block the production of an Akt activator called EET, by inhibiting enzymes called epoxygenases. We have also found that ritonavir inhibits heat shock protein 90 (Hsp90), a protein that is important for breast cancer progression and potentially regulated by EET. Our rationale for the proposed studies is that if we can determine the molecular targets of ritonavir, we will be able to further develop ritonavir for breast cancer therapeutics. Knowledge of the relevant molecular targets of ritonavir will allow us to monitor their inhibition in clinical studies. The hypothesis that we will test in the proposed studies is that epoxygenase activation promotes breast cancer progression by promoting Akt phosphorylation and cancer cell survival. For Aim 1, we will determine the molecular mechanisms by which EET promotes breast cancer proliferation and survival. The effects of ritonavir on EET production by breast cancer cells will be determined by targeted lipidomics. In Aim 2, a bacterial epoxygenase that produces EET will be tested for cooperation with activated Ha-Ras in an MCF10A mouse model of mammary cancer. In Aim 3 we will determine whether the Hsp90 inhibitor, 17-allyl aminogeldanamycin, inhibits Akt activation and cell survival induced by bacterial epoxygenase. In summary, the proposed studies will provide evidence that epoxygenases can play a role in breast cancer etiology and progression. This area is largely unexplored and these studies may lead to the identification of epoxygenases as a novel therapeutic target in breast cancer.