OT1-03-03: Effect of Tamoxifen Therapy on Inhibition of Tumor Suppressor p53 by Estrogen Receptor.

Background: A large number of patients with estrogen receptor (ER)-positive tumors are resistant to tamoxifen (TAM). Although several plausible reasons for such resistance have been suggested, the mechanisms remain unclear. ER mediates effects of estrogen by promoting proliferation of breast cancer cells. Tumor suppressor protein p53 guards against tumorigenesis by preventing proliferation of cells with genomic damage. Dr. Das9s laboratory previously reported that ER binds and functionally suppresses wild type p53 in human breast cancer cells and xenograft tumor tissue, and TAM is capable of inhibiting this interaction. We hypothesize that relieving suppression of wild type p53 by ER could be an important mechanism underlying TAM action in breast cancer. To test this hypothesis, we have initiated a pilot randomized clinical trial of 50 women with newly diagnosed ERa-positive breast cancer. Specific Aims: 1) To investigate the effect of a short pre-surgical intervention with TAM on the ER-p53 interaction in ER-positive, p53 wild type breast tumors and 2) To confirm the wild type status of p53 and analyze the functional status of the p53 pathway by monitoring expression of selected p53 target genes in tumors that have and have not been treated with TAM. Trial design: A randomized clinical trial in the pre-surgical setting was proposed with either TAM 20mg for four weeks vs. no intervention. Patients randomized to the TAM arm will undergo multiple pharmacokinetic and phamacodynamic measurements of TAM metabolites and genotyping for common polymorphisms of TAM metabolism genes, CYP2D6 and CYP3A4/5. Fresh tumor tissue will be harvested from all patients at the time of surgery for analysis of ER-p53 protein interaction using tissue chromatin immunoprecipitation (tissue ChIP) assay. p53 gene status will be determined by sequencing. RNA and protein expression of ER, p53, and a selected group of ER and p53 target genes in the diagnostic core biopsy and surgical specimens will be analyzed by quantitative real-time PCR (qRTPCR) and immunohistochemistry (IHC). TAM metabolites will also be measured in the tumor and the surrounding benign tissue. Eligibility criteria: Women greater or equal to eighteen years of age diagnosed with ER-positive invasive breast cancer (approximately 1cm in size) who will undergo primary surgical excision for their initial therapy are eligible. Women must not be pregnant, be on current hormonal therapy, or have a history of hypercoagulable syndrome or prior arterial or venous thrombosis. Statistical methods: Descriptive statistics such as frequencies and relative frequencies will be computed for all categorical variables. Numeric variables will be summarized using simple descriptive statistics such as mean, standard deviation, and quartiles. Ninety-five percent confidence intervals will be computed. ChIP data will be subjected to Fisher9s Exact Test. IHC date will be analyzed by Wilcoxon-Mann-Whitney test. Present accrual and target accrual: We have accrued 17 patients to date and plan to accrue a total of 50 patients, 25 in each arm. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr OT1-03-03.