Lysophosphatidate Induces Chemo-Resistance by Releasing Breast Cancer Cells from Taxol-Induced Mitotic Arrest Nasser Samadi, Raie T. Bekele, Ing Swie Goping, Luis M. Schang, David N. Brindley* Department of Biochemistry (Signal Transduction Research Group), School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada Abstract Background: Taxol is a microtubule stabilizing agent that arrests cells in mitosis leading to cell death. Taxol is widely used to treat breast cancer, but resistance occurs in 25–69% of patients and it is vital to understand how Taxol resistance develops to improve chemotherapy. The effects of chemotherapeutic agents are overcome by survival signals that cancer cells receive. We focused our studies on autotaxin, which is a secreted protein that increases tumor growth, aggressiveness, angiogenesis and metastasis. We discovered that autotaxin strongly antagonizes the Taxol-induced killing of breast cancer and melanoma cells by converting the abundant extra-cellular lipid, lysophosphatidylcholine, into lysophosphatidate. This lipid stimulates specific G-protein coupled receptors that activate survival signals. Methodology/Principal Findings: In this study we determined the basis of these antagonistic actions of lysophosphatidate towards Taxol-induced G2/M arrest and cell death using cultured breast cancer cells. Lysophosphatidate does not antagonize Taxol action in MCF-7 cells by increasing Taxol metabolism or its expulsion through multi-drug resistance transporters. Lysophosphatidate does not lower the percentage of cells accumulating in G2/M by decreasing exit from S- phase or selective stimulation of cell death in G2/M. Instead, LPA had an unexpected and remarkable action in enabling MCF-7 and MDA-MB-468 cells, which had been arrested in G2/M by Taxol, to normalize spindle structure and divide, thus avoiding cell death. This action involves displacement of Taxol from the tubulin polymer fraction, which based on inhibitor studies, depends on activation of LPA receptors and phosphatidylinositol 3-kinase. Conclusions/Significance: This work demonstrates a previously unknown consequence of lysophosphatidate action that explains why autotaxin and lysophosphatidate protect against Taxol-induced cell death and promote resistance to the action of this important therapeutic agent. Citation: Samadi N, Bekele RT, Goping IS, Schang LM, Brindley DN (2011) Lysophosphatidate Induces Chemo-Resistance by Releasing Breast Cancer Cells from Taxol-Induced Mitotic Arrest. PLoS ONE 6(5): e20608. doi:10.1371/journal.pone.0020608 Editor: Hava Karsenty Avraham, Beth Israel Deaconess Medical Center, United States of America Received January 24, 2011; Accepted May 5, 2011; Published May 27, 2011 Copyright: 2011 Samadi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The work was supported by the Canadian Institutes of Health Research. This agency had no role in the study design, data collection and analysis, decision to publish, provided the original author and source are credited. Competing Interests: The authors have declared that no competing interests exist. * E-mail: david.brindley@ualberta.ca Introduction Breast cancer is the most common malignancy among women in Western societies and approximately 30% of breast cancer patients develop metastases and die [1]. Taxol is widely used for treating metastatic and early-stage breast cancer. Taxol interacts with b-tubulin [2] causing lateral polymerization and microtubule stability resulting in mitotic arrest and cell death [3]. Resistance to Taxol is common with response rates of only 25 to 69% when used as a first-line treatment. There is an urgent need to identify patients who will respond to treatment [4] and to understand how to overcome chemo-resistance. The efficacy of chemotherapy is often compromised by survival signals received by tumor cells [5,6]. We showed that extracellular lysophosphatidate (LPA) provides such a survival signal. LPA strongly antagonizes Taxol-induced death in MCF-7 breast cancer and MDA-MB-435 melanoma cells [7]. This effect requires the activation of phosphatidylinositol 3-kinase (PI3K) and it is accompanied by a reversal of the Taxol-induced increase in ceramide concentrations. These latter results are compatible with earlier studies where ceramides were shown to antagonize the stimulation of cell division by LPA [8]. Ceramides are bioactive lipids that cause increased apoptosis in most cells [9]. They accumulate in cancer cells in response to a large variety of chemotherapeutic agents and radiation therapy as part of the process leading to caspase activation and cell death [10,11,12]. Therefore, a combination of ceramides with traditional chemo- therapy drugs may have the potential to be used as a new therapeutic intervention against multiple cancers [13]. The present studies deal mainly with another novel effect of LPA, namely its ability to antagonize the Taxol-induced accumulation of cancer cells in the G2/M phase of the cell cycle [7]. The signaling effects of extracellular LPA are mediated by at least eight G-protein coupled receptors [14,15,16]. Most of the LPA in extracellular fluids is produced by the secreted enzyme, autotaxin (ATX), which converts the abundant extracellular lysophosphatidylcholine to LPA and thus controls LPA concen- trations [6,16,17,18]. Circulating LPA is turned over rapidly with PLoS ONE | www.plosone.org 1 May 2011 | Volume 6 | Issue 5 | e20608