Human Cancer Biology Synergistic Antitumor Effect of the Activated PPARγ and Retinoid Receptors on Human Osteosarcoma Bai-Cheng He 1,2,4 , Liang Chen 1,4 , Guo-Wei Zuo 1,4 , Wenli Zhang 4,5 , Yang Bi 1,4 , Jiayi Huang 1,4 , Yi Wang 1,4 , Wei Jiang 4 , Qing Luo 1,4 , Qiong Shi 1,4 , Bing-Qiang Zhang 1,4 , Bo Liu 1,4 , Xia Lei 4,3 , Jinyong Luo 1,4 , Xiaoji Luo 1,4 , Eric R. Wagner 4 , Stephanie H. Kim 4 , Connie J. He 4 , Yawen Hu 4 , Jikun Shen 4 , Qixin Zhou 2 , Farbod Rastegar 4 , Zhong-Liang Deng 1,4 , Hue H. Luu 4 , Tong-Chuan He 1,4 , and Rex C. Haydon 4 Abstract Purpose: Osteosarcoma is the most common primary malignancy of bone. The long-term survival of osteosarcoma patients hinges on our ability to prevent and/or treat recurrent and metastatic lesions. Here, we investigated the activation of peroxisome proliferator-activated receptor γ (PPARγ) and retinoid receptors as a means of differentiation therapy for human osteosarcoma. Experimental Design: We examined the endogenous expression of PPARγ and retinoid receptors in a panel of osteosarcoma cells. Ligands or adenovirus-mediated overexpression of these receptors were test- ed to inhibit proliferation and induce apoptosis of osteosarcoma cells. Osteosarcoma cells overexpressing the receptors were introduced into an orthotopic tumor model. The effect of these ligands on osteoblastic differentiation was further investigated. Results: Endogenous expression of PPARγ and isotypes of retinoic acid receptor (RAR) and retinoid X receptor (RXR) is detected in most osteosarcoma cells. Troglitazone, 9-cis retinoic acid (RA), and all-trans RA, as well as overexpression of PPARγ, RARα, and RXRα, inhibit osteosarcoma cell proliferation and induce apoptosis. A synergistic inhibitory effect on osteosarcoma cell proliferation is observed between troglitazone and retinoids, as well as with the overexpression pairs of PPARγ/RARα, or PPARγ/RXRα. Overexpression of PPARγ, RARα, RXRα, or in combinations inhibits osteosarcoma tumor growth and cell proliferation in vivo. Retinoids (and to a lesser extent, troglitazone) are shown to promote osteogenic differentiation of osteosarcoma cells and mesenchymal stem cells. Conclusions: Activation of PPARγ, RARα, and RXRα may act synergistically on inhibiting osteosarco- ma cell proliferation and tumor growth, which is at least partially mediated by promoting osteoblastic differentiation of osteosarcoma cells. Clin Cancer Res; 16(8); 2235–45. ©2010 AACR. Osteosarcoma is the most common nonhematologic malignant tumor of bone in children and adults, with its peak incidence in the teens (1–4). Osteosarcoma is char- acterized by a high propensity for lung metastasis, with 10% to 20% having detectable metastases at diagnosis (5). Without systemic treatment, few patients with osteo- sarcoma achieve long-term disease-free status, even with optimal local treatment (6). Certain genetic or acquired conditions increase the risk for osteosarcoma (1–4). Pa- tients with hereditary retinoblastoma have a high risk for osteosarcoma (7). We have shown that Wnt/β-catenin and S100A6 are frequently upregulated in human osteosarco- ma tumors (8–12). Cytogenetic studies on osteosarcoma have documented a variety of genetic alterations resulting in inactivation of tumor suppressor genes and overexpres- sion of oncogenes (1–4). However, it is unclear how much these genetic changes contribute to osteosarcoma develop- ment (3, 4). Increasing evidence suggests that disruptions of osteo- genic differentiation may lead to osteosarcoma develop- ment (3, 4, 13). Mesenchymal stem cells are adherent bone marrow stromal cells that can differentiate into oste- ogenic, chondrogenic, adipogenic, and myogenic lineages (14–16). Osteogenic differentiation is a multistep process that requires a balanced regulation of proliferation and Authors' Affiliations: 1 Key Laboratory of Diagnostic Medicine designated by the Chinese Ministry of Education and the Affiliated Hospitals; 2 Department of Pharmacology, School of Pharmacy, Chongqing Medical University; 3 Department of Dermatology, Daping Hospital of the Third Military Medical University, Chongqing, China; 4 Molecular Oncology Laboratory, Department of Surgery, The University of Chicago Medical Center, Chicago, Illinois; and 5 Department of Orthopaedic Surgery, Huaxi Hospital Affiliated with Sichuan University School of Medicine, Chengdu, Sichuan, China Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/). Corresponding Authors: Rex C. Haydon, Molecular Oncology Laboratory, The University of Chicago Medical Center, 5841 South Maryland Avenue, MC 3079, Chicago, IL 60637. Phone: 773-702-5263; Fax: 773-834-4598; E-mail: rhaydon@surgery.bsd.uchicago.edu and Tong-Chuan He, Molecu- lar Oncology Laboratory, The University of Chicago Medical Center, 5841 South Maryland Avenue, MC 3079, Chicago, IL 60637. Phone: 773-702- 5263; Fax: 773-834-4598; E-mail: tche@surgery.bsd.uchicago.edu. doi: 10.1158/1078-0432.CCR-09-2499 ©2010 American Association for Cancer Research. Clinical Cancer Research www.aacrjournals.org 2235 Downloaded from http://aacrjournals.org/clincancerres/article-pdf/16/8/2235/1995027/2235.pdf by guest on 20 June 2022