Abstract 1665: Targeting phosphatases for the treatment of ER-negative breast cancer

Abstract Background: ER-negative breast cancers are poorly responsive to anti-estrogen therapies. Currently, the only available treatment for ER-negative tumors is either chemotherapy or for a subset of ER-negative breast cancer is herceptin. Thus, there is an urgent need to developed targeted therapy to prevent these life-threatening cancers. In this project, we are investigating whether other signaling molecules, phosphatases, are differentially expressed in ER-negative as compared to ER-positive breast cancers. We hypothesize that: (1) the specific phosphatases that govern the growth of ER-negative cancers are different from those of ER-positive breast cancers, (2) identification of the specific phosphatases that regulate the growth of ER-negative cancer is possible using genomic and proteomic approaches, and (3) inhibition of some of the phosphatases activated in ER-negative cancers, and over-expression of some of the phosphatases under-expressed in ER-negative breast cancers, will suppress the growth of ER-negative breast cancers. Methods: Affymetrix microarray studies: cDNA was synthesized from total RNA isolated from tumor samples followed by Biotin-labeled cRNA and was then hybridized onto an Affymetrix HGU133A GeneChipTM and data analysis as described previously. Analysis was limited by the phosphatase list found using gene ontology annotation. Statistical analysis was done with dChip software. Differentially expressed genes were found using t-test. QRT-PCR: All Taqman assays run on ABI7900HT. siRNA knock-down assay and cell growth: siRNA knockdown was performed using Dharmafect and cell growth was measured by MTS assay. Results: We have identified 22 phosphatases that were upregulated (>1.2 fold with p-value of <0.05), and 19 phosphatases that were downregulated (<0.8-fold with a p-value <0.05). Among them, validation studies showed that PPM1A is significantly downregulated and ACP1 is upregulated in ER-negative cells. ACP1 knock-down inhibits the growth of ER-negative breast cancer cell lines but not the growth of ER-positive cells. Studies of breast cancer cells in which under-expressed phosphatases are over-expressed and over-expressed phosphatases are inhibited are underway to investigate the effect of modulation of phosphatase activity on invasion, xenograft growth, and metastasis. Conclusion: Several over and under-expressed phosphatases identified in our microarray analysis have been shown to critically regulate the growth of ER-negative breast cancer cells. Our results demonstrate that PPM1A and ACP1 knockdown inhibit ER-negative breast cancer cells growth. By identifying the molecules that regulate breast cancer cell growth we will identify potential new targets for the treatment and prevention of these aggressive breast cancers. Supported by Komen Promise grant KG081694 & Komen SAB grant SAB08-00006 (PB). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1665. doi:10.1158/1538-7445.AM2011-1665