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    Research Grants Awarded

    Role of Mitotic Checkpoint in the Sensitivity of Breast Cancer to Paclitaxel

    Study Section:
    Tumor Cell Biology IV

    Scientific Abstract:
    Background. To date, only limited pathologic, phenotypic, or genotypic tumor characteristics are available to predict whether a particular patient with breast cancer (BC) would benefit from paclitaxel. We propose that measurement of mitotic (M) checkpoint functionality could be used as a marker of paclitaxel sensitivity. This idea is based on the following evidence: (1) paclitaxel stabilizes microtubules and activates the M checkpoint, which is involved in regulation of the G 2 /M transition; (2) knocking down MAD2 or BubR1, 2 major components of the M checkpoint that regulate CDK1, results in dysfunction of the M checkpoint and confers resistance to paclitaxel. These findings, plus our ability to measure MAD2, BubR1, and CDK1 rapidly with a novel cell-cycle profiling device, led us to develop this translational research proposal. Objective/Hypothesis. A d ysfunctional M checkpoint predicts paclitaxel resistance . Specific Aims 1. Determine whether a dysfunctional M checkpoint can be used as a biomarker of paclitaxel resistance in breast cancer in vitro . 2. Validate that a dysfunctional M checkpoint contributes to paclitaxel resistance in vivo . Study Design. We designed 2 interdependent specific aims to assess M checkpoint function and its relationship to paclitaxel sensitivity in BC. Aim 1, we will quantitatively define M checkpoint status (functional or not) by statistically analyzing CDK1 activity and MAD2/BubR1 expression, and we will verify the relationship between M checkpoint status (measured conventionally and with our novel cell-cycle profiling device) and paclitaxel sensitivity in BC cell lines. Aim 2, we will evaluate the relationship between M checkpoint status and paclitaxel sensitivity in a xenograft model and in human breast tumor samples. Our goal is to confirm that a dysfunctional M checkpoint is associated with lack of response to paclitaxel. Potential Outcomes and Benefits. This hypothesis-driven study will uniquely define a mechanism-based endpoint for evaluating the biological responses of BC to paclitaxel. We expect that the M checkpoint will be a biomarker for predicting paclitaxel sensitivity in patients with BC. We expect that accomplishing these aims will provide the necessary foundation for developing a large prospective clinical trial to identify patients who are not likely to respond to paclitaxel so as to spare such patients unnecessary treatment, with its attendant side effects and cost.

    Lay Abstract:
    Background. Paclitaxel is used to treat early and metastatic breast cancer, but it is not effective in all cases, and it is difficult to identify in advance who will respond to it. Paclitaxel acts by disrupting the cell-division process in a way that eventually leads to cell death. The cell-division process is regulated at several checkpoints; one such checkpoint (the mitotic [M] checkpoint) is controlled by the coordinated action of cyclin-dependent kinases (CDKs) and molecules that regulate CDK1 (MAD2, BubR1). Objective/Hypothesis. We hypothesize that being able to identify breast cancer cells that have nonfunctional M checkpoints will allow us to identify which tumors will not respond to paclitaxel. Specific Aims Aim 1. Confirm that breast cancer cells with a nonfunctional M checkpoint are resistant to paclitaxel. Aim 2. Test if a nonfunctional M checkpoint can be used as a marker of paclitaxel resistance in mouse and human tumors . Study Design. Aim 1 comprises statistical analyses of CDK1 activity and MAD2/BubR1 expression to define cutpoints for M checkpoint status and tests of those cutpoints with cultured breast cancer cells known to be sensitive or resistant to paclitaxel. We will also use a novel cell-cycle profiling device to measure M checkpoint status in those cells. We expect that cells with low MAD2 or BubR1 will be resistant to paclitaxel via inactivation of CDK1 . For aim 2, we will inject mice with human breast cancer cells and test whether M checkpoint status predicts the response of the resulting tumors to paclitaxel (assessed by tumor shrinkage and extended survival). Finally, we will test samples of breast cancer tissue from patients treated with paclitaxel to confirm that a nonfunctional M checkpoint is associated with lack of response to paclitaxel. Potential Outcomes and Benefits. Our long-term goal is to find a way of identifying patients who will not respond to paclitaxel before treatment is begun, so that patients with tumors that do not respond can be spared an ineffective and perhaps toxic treatment. We believe that M checkpoint abnormalities in tumor cells are one way of seeing whether those tumors will respond or will not respond to the drug—that the M checkpoint is a biomarker for predicting paclitaxel sensitivity in breast cancer. Accomplishing our aims will provide the foundation for a large prospective clinical trial to identify which patients will benefit from paclitaxel treatment.