Abstract 5155: BMP-2 inhibits the tumorigenicity of human osteosarcoma tumor-initiating cells

Abstract

Abstract Bone morphogenetic proteins (BMPs), members of the transforming growth factor (TGF)-β superfamily, were originally identified as molecules that induce bone and cartilage formation and are now considered as multifunctional cytokines. More recently, there have been a number of studies showing the inhibitory effects of BMP-2 on tumorigenesis in many cancers. However, very little has been investigated to date about the role of BMP-2 in human osteosarcoma. In the present study we show that BMP-2 inhibits the tumorigenicity of an aggressive human osteosarcoma cell line, OS99-1. Based on the stem cell theory of cancer, a subpopulation of cells showing characteristics of stem cells was identified using high aldehyde dehydrogenase (ALDH) activity (ALDHbr cells) from xenografts. These stem-like cells were found to be highly tumorigenic and were classified as tumor initiating cells. In vitro, the growth of the sorted tumorigenic ALDHbr cells was significantly inhibited by the addition of 300 ng/ml of BMP-2 in the presence of 0.5% fetal bovine serum (FBS) for 48h, as evaluated by cell proliferation assay. In addition, using RT-PCR analysis, we found BMP-2 down-regulated the expressions of embryonic stem cell markers Oct3/4, Nanog, and Sox-2. Conversely there was an increase in the transcription of osteogenic markers Runx-2 and Collagen Type I in the sorted tumorigenic ALDHbr cells treated with the same BMP-2 solution for 48h compared with the same volume of vehicle. In vivo, tumor formation in animals was compared to a control receiving ALDHbr cells maintained under identical conditions without BMP-2. All animals receiving untreated ALDHbr cells developed large tumor masses that showed characteristic osteosarcoma features, including nuclear atypia, extensive neovascularization, and high mitotic activity. Conversely, ALDHbr cells treated with 30μg/animal of BMP-2 did not form significant tumors. Further immunostaining confirmed most Ki-67 positive cells were shown in the tumor sections from mice injected with ALDHbr cells without BMP-2, whereas few Ki-67 positive cells were present in the sections of tumor from ALDHbr cells treated with BMP-2. Based on these results, it appears that BMP-2 may suppress tumor growth by inducing the differentiation of tumor -initiating cells. BMP-2 or BMP-2-mimetic drugs, if properly delivered to tumor and combined with traditional therapies, may therefore provide a new therapeutic option. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5155.