Tumor and Stem Cell Biology Nitric Oxide Mediates Metabolic Coupling of Omentum-Derived Adipose Stroma to Ovarian and Endometrial Cancer Cells

Omental adipose stromal cells (O-ASC) are a multipotent population of mesenchymal stem cells contained in the omentum tissue that promote endometrial and ovarian tumor proliferation, migration, and drug resistance. The mechanistic underpinnings of O-ASCs' role in tumor progression and growth are unclear. Here, we propose a novel nitric oxide (NO)–mediated metabolic coupling between O-ASCs and gynecologic cancer cells in which O-ASCs support NO homeostasis in malignant cells. NO is synthesized endogenously by the conversion of L-arginine into citrulline through nitric oxide synthase (NOS). Through arginine depletion in the media using L-arginase and NOS inhibition in cancer cells using N-nitro-L-arginine methyl ester (L-NAME), we demonstrate that patientderived O-ASCs increase NO levels in ovarian and endometrial cancer cells and promote proliferation in these cells. O-ASCs and cancer cell cocultures revealed that cancer cells use O-ASC– secreted arginine and in turn secrete citrulline in the microenvironment. Interestingly, citrulline increased adipogenesis potential of the O-ASCs. Furthermore, we found that O-ASCs increased NO synthesis in cancer cells, leading to decrease in mitochondrial respiration in these cells. Our findings suggest that O-ASCs upregulate glycolysis and reduce oxidative stress in cancer cells by increasing NO levels through paracrine metabolite secretion. Significantly, we found that O-ASC– mediated chemoresistance in cancer cells can be deregulated by altering NO homeostasis. A combined approach of targeting secreted arginine through L-arginase, along with targeting microenvironment-secreted factors using L-NAME, may be a viable therapeutic approach for targeting ovarian and endometrial cancers. Cancer Res; 75(2); 456–71. 2014 AACR. Introduction The omentum, the fatty pad of adipose tissue that covers the bowel, is a frequent site ofmetastasis for ovarian cancer (1–3). The omentum contains a population of stromal cells, adipose stromal cells (ASC), which are multipotent mesenchymal stem cells that engraft in tumors and can support cancer progression (4–7). Omentum-derived ASCs (O-ASC) may contribute to the formation of a hospitable environment for the development of ovarian cancer metastasis (8, 9). Recently, we showed that O-ASCs promoted proliferation, migration, chemotherapy, and radiation response of ovarian cancer cells (8). Furthermore, O-ASCs recruited to tumors expressed factors that enhanced tumor vascularization, promoted survival, and proliferation of endometrial cancer cells (9). However, the mechanism by which O-ASCs regulate tumor growth and induce chemoresistance is unknown. We hypothesize that "nitric oxide homeostasis" is a key player in regulating reciprocal communication between O-ASCs and gynecologic cancers (ovarian cancer and endometrial cancer). O-ASCs can differentiate into adipocytes lineage, promote tumor initiation, growth, vascularization, metastasis, and resistance to chemotherapy in many tumor models (2, 10). Recently, we showed that O-ASCs promoted proliferation, migration, chemotherapy, and radiation response of ovarian cancer cells (8). Omentum has been shown to promote colonization of ovarian cancer cells (11). Mounting evidence suggests that bidirectional communication between ovarian cancer and its microenvironment is critical for tumor growth (12). One critically important, yet often overlooked, contributor to ovarian cancer and endometrial cancer tumor growth, progression, and metastasis to omentum is nitric oxide (NO). Cancer cells' high affinity for NO could explain the proximity of many carcinomas to fatty tissue, and thus the high positive correlation between obesity and cancer (13). NO is an intracellular signalingmolecule that plays pleiotropic roles in cellular physiology and diseases (14) by regulating cellular levels of pH, blood flow, oxygen, and nutrients (15). NO is synthesized endogenously by the conversion of L-arginine into citrulline through nitric oxide synthase (NOS). NOS is differentially expressed in obese and nonobese individuals and is overexpressed in many tumors (16, 17). It has been shown that high levels of NOS activity exist in malignant tissue from gynecologic cancers (18) and higher NOS expressions were correlated to the Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas. Department of Bioengineering, Rice University, Houston, Texas. University of Texas, MD Anderson Cancer Center, Houston, Texas. GE Power & Water, Boulder, Colorado. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Corresponding Author: Deepak Nagrath, Department of Chemical and Biomolecular Engineering, MS-362, Rice University, 6100 Main Street, Houston, TX 77005. Phone: 713-348-6408; Fax: 713-348-5478; E-mail: [email protected] doi: 10.1158/0008-5472.CAN-14-1337 2014 American Association for Cancer Research. Cancer Research Cancer Res; 75(2) January 15, 2015 456 on May 28, 2017. © 2015 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from Published OnlineFirst November 25, 2014; DOI: 10.1158/0008-5472.CAN-14-1337