Abstract A15: Fatty acid binding protein 4 is indispensable for ovarian cancer metastasis
Authors: Mukherjee Abir , Coscia Fabian , Fahrmann Johannes , Chiang Chun-Yi , Smith Justin , Nieman Kristin , Ladanyi Andras , Romero Iris , Fiehn Oliver , Mann Matthias , Lengyel Ernst 
Published: August 2018

Abstract
Introduction: Omental metastasis is a defining feature of ovarian cancer and other cancers with peritoneal spread. We and others have previously shown that ovarian cancer (OvCa) cells readily home to the omentum in an adipokine-dependent manner and take up lipids from omental adipocytes to fuel metastasis. The complex interactions between omental adipocytes and OvCa cells, and the mechanisms by which OvCa cells adapt to this unique lipid-rich microenvironment, are still unclear and warrant further study. Here we used multiple omics platforms to study adipocyte-induced alterations in OvCa cells.
Methods: We cocultured human primary adipocytes (HPA) with OvCa cell lines and then used mass spectrometry-based proteomic and global untargeted metabolomic analysis to study the altered cellular physiology of cancer cells upon encountering omental adipocytes. Stable cell lines were generated using lentivirus-mediated gene silencing and, subsequently, functional characterization was carried out using microarray and cell-based metabolic analysis. Since fatty acid binding protein 4 (FABP4) was identified in this analysis, we used a small-molecule inhibitor against FABP4 in an orthotopic xenograft mouse model to determine its role in promoting metastatic tumor burden.
Results: Proteomic analysis revealed that HPA increases the expression of several proteins, especially those involved in lipid metabolism, such as cluster of differentiation 36 (CD36), FABP4, and alcohol dehydrogenase 1 (ADH1) in OvCa cancer cells. While we found that CD36 was essential for lipid uptake by the cancer cells, we determined that FABP4 was indispensable for their retention of intracellular lipid accumulation. Corollary metabolomic analysis showed that FABP4 knockdown dramatically reduced intracellular triacylglycerol levels induced by adipocyte coculture. We also found that FABP4 was responsible for the increased rate of β-oxidation observed in adipocyte cocultured cancer cells. Moreover, cancer cells exhibited increased oxidative stress when cultured with adipocytes or adipocyte conditioned media as evidenced by flow-cytometry analysis of reactive oxygen species. These observations were corroborated by detection of elevated oxidative stress markers such as oxidized lipids (15-HETE, 9-HODE, and 2-hydroxypalmitate), oxidized cholesterol (7-beta-hydroxy cholesterol), and oxidized glutathione. This increase in reactive oxygen species was found to be dependent on the levels of adipocyte-induced FABP4, suggesting that FABP4 plays a critical role in the alteration of cancer cells in contact with adipocytes. To determine the functional consequence of FABP4 inhibition in cancer cells, we carried out microarray and ingenuity pathway analysis (IPA) analysis after FABP4 knockdown, which revealed that FABP4 makes a significant contribution to proliferative and metastatic signatures in cancer cells. Knockdown of FABP4 also reduced colony-forming capacity in clonogenic assays and targeting FABP4 using a small-molecule inhibitor led to a significant reduction of metastatic burden in an orthotopic xenograft mouse model.
Conclusions: Cancer cells in close proximity to adipocytes increase lipid-utilization genes. These genes enhance the ability of the cancer cells to use fatty acids, which are in abundance at the omentum, as an additional fuel source. FABP4, a lipid chaperon protein, was found to play a key role in regulating lipid utilization and redox-balance in cancer cells, helping them adapt to the omental microenvironment. Therefore, FABP4 may have potential as a therapeutic target against metastatic ovarian cancer.
Citation Format: Abir Mukherjee, Fabian Coscia, Johannes Fahrmann, Chun-Yi Chiang, Justin Smith, Kristin Nieman, Andras Ladanyi, Iris Romero, Oliver Fiehn, Matthias Mann, Ernst Lengyel. Fatty acid binding protein 4 is indispensable for ovarian cancer metastasis. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A15.