Non-toxic Efficacy of the Combination of Caffeine and Valproic Acid on Human Osteosarcoma Cells In Vitro and in Orthotopic Nude-mouse Models.

BACKGROUND/AIM We have previously reported that caffeine can enhance chemotherapy efficacy of bone and soft-tissue sarcoma via cell-cycle perturbation. Valproic acid has histone deacetylase (HDAC) inhibitory activity. The present study aimed to investigate the efficacy of the combination of valproic acid and caffeine on human osteosarcoma cells in vitro and in orthotopic nude-mouse models. MATERIALS AND METHODS Human osteosarcoma cell lines (MG63, 143B and SaOS2) were used. Cell survival after a 72 h exposure to valproic acid and caffeine was assessed with a WST-8 assay. Half maximal inhibitory concentration (IC50) values and combination indices (CIs) were calculated. Caspase 3 activity was measured by a fluorochrome inhibitor of caspase (FLICA) assay. 143B cells were also transplanted to the tibia of nude mice and treated with these drugs. RESULTS Both valproic acid and caffeine caused concentration-dependent cell death of the osteosarcoma cell lines in vitro. Apoptosis induction was observed with the Caspase 3 assay. The combination was synergistic. The combination of valproic acid and caffeine showed effective anti-tumor activity in vivo without the need for conventional anticancer drugs or any observable toxicity Conclusion: Efficacy of combination therapy with caffeine and valproic acid in osteosarcoma was observed in vitro and in vivo without toxicity, suggesting that either or both drugs can be effectively combined with appropriate chemotherapy in the future.