Tumorigenic transformation of rat bone cells by benzo(a)pyrene: An <i>in vitro</i> osteosarcoma model.

Abstract

Bone is a specialized connective tissue composed of intercellular calcified material, bone matrix and several types of cells. These mineralized, cellular structures are richly supplied with blood vessels and nerves. To investigate the possibility of tumorigenic conversion of normal bone cells by tobacco-related chemical carcinogens, primary normal rat osteoblast-enriched cells were exposed to benzo(a)pyrene, a tobacco-related chemical carcinogen, alone or in conjunction with 12-O-tetradecanoylphorbol-13-acetate(TPA). Chemically treated (PTRCC-BaP) and chemically transformed cells (RCC-BaP and Rcc-BaP-TPA) were established and their biological properties, in vitro and in vivo tumorigenicity, and expression of c-myc, c-fos, c-jun, p53, and Rb were studied. The chemically transformed cells demonstrated anchorage-independent growth and developed tumors in nude mice. They showed higher proliferation rate than normal cells and morphological alteration from normal cells. The chemically treated and chemically transformed cells possessed high alkaline phosphatase activities and a low acid phosphatase/alkaline phosphatase ratio, and expressed osteonectin protein. They expressed higher levels of c-myc transcripts compared to the parental cells. However, the levels of c-jun and c-fos transcripts were notably decreased in chemically transformed cells and these cells also contained lower levels of p53 and Rb proteins than normal cells, These results indicate that malignant transformation of rat bone cells can be induced by benzo(a)pyrene and that overexpression of c-myc messages, together with the downregulation of p53 and Rb proteins, may be associated with malignant progression of rat bone cells.