In vitro myotoxic effects of bupivacaine on rhabdomyosarcoma cells, immortalized and primary muscle cells

Background: Rhabdomyosarcoma is a rare malignant skeletal muscle tumor. It mainly occurs in children and young adults and has an unsatisfactory prognosis. Prior studies showed a direct myotoxic effect of bupivacaine on differentiated muscle cells in vitro and in vivo. Exact mechanisms of this myotoxicity are still not fully understood, but a myotoxic effect on malignant muscle tumor cells has not been examined so far. Thus, the aim of this study was to examine if bupivacaine has cytotoxic effects on rhabdomyosarcoma cells, immortalized muscle cells and differentiated muscle cells. Methods: Cell lines of rhabdomyosarcoma cells, immortalized muscle cells and differentiated muscle cells were established. After microscopic identification, cells were exposed to various concentrations of bupivacaine ( 500, 1,000, 1,750, 2,500 and 5,000 ppm) for 1 and 2 h, respectively. 24 and 28 h after incubation the cultures were stained with propidium iodid and analyzed by flow cytometry. The fraction of dead cells was calculated for each experiment and the concentration with 50% cell survival (IC50) was computed. Cell groups as well as incubation and recovery time were compared (ANOVA/Bonferroni p < 0.01). Results: The total number of cultured cells was similar for the different local anesthetics and examined concentrations. Increasing concentrations of bupivacaine led to a decrease in survival of muscle cells. IC50 was highest for immortalized cells, followed by rhabdomyosarcoma cells and differentiated cells. Exposure time, but not recovery time, had an influence on survival. Conclusion: Bupivacaine has clear but different cytotoxic effects on various muscle cell types in vitro. Differentiated primary cells seem to be more vulnerable than tumor cells possibly because of more differentiated intracellular structures.