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PEA-15 as a Therapeutic Target for Enhanced Sensitization to Paclitaxel
Background: Inherent or acquired resistance of breast cancer to paclitaxel leads to treatment failure and progressive disease. One way in which cells may become resistant to paclitaxel is by activation of antiapoptotic pathways involving mitogen-activated protein kinases (MAPKs). PEA-15, a potential tumor suppressor, sequesters one such MAPK, ERK, in the cytoplasm, preventing its accumulation in the nucleus—which seems necessary for tumorigenicity. We propose to test a novel combination of paclitaxel and PEA-15 gene therapy, expecting that synergistic effects between these approaches will overcome paclitaxel resistance. Objectives/Hypothesis: The overall goal of this proposal is to define the mechanistic and functional significance of PEA-15 in the sensitivity or resistance of breast cancer cells to paclitaxel. Our hypothesis is that PEA-15 sensitizes breast cancer cells to paclitaxel by sequestering activated ERK in the cytoplasm. First, we will confirm that PEA-15 has antitumor effects on breast cancer cells (as it does on ovarian cancer cells) and clarify if those effects depend on ERK sequestration. Next, we will test PEA-15 gene therapy plus paclitaxel for potential synergistic effects in vitro and in a xenograft model of breast cancer. With this strategy, we hope to identify a way of reversing paclitaxel resistance in breast cancer. Specific Aims: 1. Confirm the antitumor effect of PEA-15 on breast cancer cells in vitro and in a breast cancer xenograft model and clarify the molecular mechanisms of that activity. 2. Test whether PEA-15 sensitizes breast cancer cells to paclitaxel in vitro and in a breast cancer xenograft model and establish the mechanism of sensitization. Study design: We will evaluate the in vitro activity of PEA-15 transfected into breast cancer cells by monitoring growth inhibition (MTT uptake), cell survival (trypan blue exclusion), DNA synthesis rate (BrdU incorporation), anchorage-independent growth (soft agar assay), and cell cycle distribution, G1 arrest, and apoptosis (flow cytometry) and intracellular location of ERK and phospho-ERK (pERK) in the PEA-15 transfectants. We will also use these tests to evaluate the effects of paclitaxel plus PEA-15 in vitro. Findings will be translated to in vivo conditions by testing if PEA-15 gene therapy, with or without paclitaxel, suppresses tumor cell growth in a xenograft model. Findings from these studies may form a novel molecular basis for future chemotherapeutic strategies that exploit inhibition of cell-proliferation signals by sequestering ERK. Potential outcomes and benefits: About 40% of advanced breast cancer cases do not respond to paclitaxel, and even those that do respond eventually develop resistance. The innovation of this proposal is its targeting paclitaxel-induced ERK as a mechanism of resistance—a novel therapeutic target for exploration in paclitaxel-resistant breast cancer.
Background: Understanding breast cancer at the molecular level is imperative for finding more effective treatment approaches. Anticancer drugs like paclitaxel kill breast cancer cells by inducing apoptosis (programmed cell death), but resistance to such drugs are a major hindrance to their use. Importantly, researchers have shown that the activation of the prosurvival ERK pathway by paclitaxel may reduce the efficiency of paclitaxel in inducing apoptosis. Therefore, effective combination therapies are needed to prevent or minimize the development of resistance to paclitaxel. We propose that combining paclitaxel with PEA-15 (a protein involved in cell proliferation and apoptosis) will significantly improve the effectiveness of paclitaxel to kill the cancer cells. We further speculate that the synergistic effect of this treatment results from PEA-15 suppressing ERK activity by sequestering the ERK induced by paclitaxel in the cytoplasm from nucleus, where it activates genes important for cancer growth and survival. Objectives/Hypothesis/Aims: We hypothesize that PEA-15 sensitizes breast cancer cells to paclitaxel by inactivating ERK. To test this hypothesis, we will, 1. Confirm the antitumor effect of PEA-15 in cultured breast cancer cells and in mice and clarify the molecular mechanisms of that activity, and 2.Test whether PEA-15 sensitizes breast cancer cells to paclitaxel in cultured cells and in mice and establish the mechanism by which this sensitization takes place. Study design: We have already shown that PEA-15 suppresses cellular proliferation in ovarian and breast cancer cell lines. Our first aim is to confirm the antitumor activity of PEA-15 in breast cancer by establishing and testing stable transfectants that overexpress PEA-15; determine whether ERK accumulates in the cytoplasm of those transfectants; and test the effect of PEA-15 gene therapy in a murine breast cancer model. Aim 2 involves testing the effects of the combination of PEA-15 and paclitaxel, first in breast cancer cells and next in a preclinical breast cancer model. Potential outcomes and benefits: The successful outcome of the proposed experiments will provide an important foundation for understanding paclitaxel resistance and targeting ERK to reverse the paclitaxel resistance by using PEA-15 gene therapy. We anticipate that the combination of PEA-15 gene therapy with paclitaxel to be more effective than currently available treatments for breast cancer. We expect that our preclinical data will allow us to conduct clinical trials within 5 to 7 years. Our strength is that the gene delivery system that we propose has been already used in clinical trials. Most significantly, we expect to see that this study will demonstrate an approach that prevents or minimizes the development of drug resistance of the tumor cells to paclitaxel, which would allow more patients with breast cancer to benefit from using this drug.