Abstract C45: Validation of thromboxane A2 receptor (TP) as a target to block breast cancer metastasis.

Abstract

Abstract The receptor of thromboxane A2 (TXA2), TP, is a seven transmembrane, G-protein-coupled receptor. Increased expression of TP at RNA level was found to correlate with a poor prognosis in breast cancer patients but it is unknown how TP expression and activities are involved in breast cancer progression. Here we report that TP is expressed in metastatic breast cancer cells at both RNA and protein levels. Treatment of breast cancer MDA-MB-231 cells by U46619, a TP agonist, induced cell body contraction. The U46619-induced contraction was blocked by SQ29548, a high-affinity TP antagonist. Further studies found that small GTPase RhoA was activated by TP activation and that pretreatment of MDA-MB-231 cells with Y27632, a Rho kinase (ROCK) inhibitor, blocked U46619-induced cell contraction. The requirement of RhoA activation in U46619 induced cell contraction was further confirmed by the ability of dominant negative RhoA to block cell contraction induced by U46619. MDA-MB-231 cells with TP knockdown displayed a reduced percentage of contraction under the treatment of U46619 and TXA2 agonist I-BOP as well as attenuated invasion ability. When injected into mice, MDA-MB-231 cells with TP depleted did not present significant changes in primary tumor formation or growth. However, TP depletion reduced the ability of MDA-MB-231 cells to metastasize to the lung and the liver in an experimental metastasis model. We further demonstrated that TP depletion reduced the lung colonization ability of MDA-MB-231 cells by blocking active extravasation. Taken together, TP is expressed in breast cancer and that activation of TP has profound effects on tumor cell cytoskeleton and contraction through activation of RhoA. Inhibition or depletion of TP reduces the metastatic dissemination of breast cancer cells in vivo by blocking the extravasation of tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C45.