Combined Effects of Bisphosphonate and Radiation on Osteosarcoma

Antitumour effects of third-generation bisphosphonates (BPs), such as zoledronic acid (ZOL), and the combined effects of ZOL with other anticancer agents against osteosarcoma cells have been reported previously. The aim of this study was to identify further combined antitumour effects using BPs and radiation in osteosarcoma cell lines. Materials and Methods: Cell proliferation, cell cycle analysis, and nuclear morphology were examined in each osteosarcoma cell line divided into three groups (ZOL alone, radiation alone and the ZOL/radiation combination). Results: Combined therapy (low-concentration ZOL and lowdose radiation) had significant growth inhibitory effects compared to the use of ZOL or radiation individually. Flow cytometric analysis revealed an increase in cells in the subG1 phase by combined treatment, and apoptotic cells were also observed. Conclusion: These findings suggest that combination therapy using BPs and radiation may be a promising therapy for osteosarcoma, producing fewer side effects and complications in the near future. Osteosarcoma is a high-grade malignant bone neoplasm that commonly occurs in juvenile patients. Although the prognosis of these patients has improved substantially through the development of effective adjuvant or neoadjuvant regimens of chemotherapy, >20% patients still die as a result of tumour metastasis and unresectable tumour (1-5). Chemotherapy for bone and soft tissue tumours is problematic since high-dose drugs are required compared with other tumour types due to the low concentration of drug reaching the tissue, and serious adverse drug reactions often oblige chemotherapy to be halted in patients such as those with elderly onset tumours. Therefore, new antitumour drugs and new therapy methods are urgently needed for bone and soft tissue tumours. Various new osteosarcoma therapies have been investigated worldwide, with many clinical trials performed on novel agents. Among these agents, the antitumour effects of bisphosphonates (BPs) have been recently reported (6-8). BPs are effective inhibitors of bone resorption and have been used for the past three decades in the treatment of metabolic bone diseases (9). BPs can be divided into two classes based on differences in the structure of the R2 sidechain. Nitrogen-containing BPs (N-BPs), or so-called secondand third-generation BPs, have a basic nitrogencontaining moiety in the R2 side-chain. Non-nitrogencontaining BPs (Non N-BPs), or so-called first-generation BPs, do not contain a nitrogen in the R2 side-chain and are less potent antiresorptive agents than N-BPs. N-BPs induce apoptosis in osteoclasts by inhibiting protein prenylation in small G-proteins through inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway (10). It has previously been reported that third-generation BPs, such as zoledronic acid (ZOL) and minodronic acid (YM529), show direct antitumour effects and synergistically augment the effects of anticancer agents in various cancer cell lines (11-15). Recently, several investigators have 2713 Correspondence to: Hiroaki Murata, MD, Ph.D., Department of Orthopaedics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, 465 Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan. Tel: +81 752515549, Fax: +81 752515841, e-mail: [email protected]