RESUMO
BACKGROUND: Osteosarcoma is the most common type of bone cancer in adolescents. There have been no significant improvements in outcomes since chemotherapy was first introduced. Bupivacaine and lidocaine have been shown to be toxic to certain malignancies. This study evaluates the effect of these medications on two osteosarcoma cell lines. QUESTIONS/PURPOSES: (1) Does incubation of osteosarcoma cells with bupivacaine or lidocaine result in cell death? (2) Does this result from an apoptotic mechanism? (3) Is a specific apoptotic pathway implicated? METHODS: Two cell lines were chosen to account for the inherent heterogeneity of osteosarcoma. UMR-108 is a transplantable cell line that has been used in multiple studies as a primary tumor. MNNG/HOS has a high metastatic rate in vivo. Both cell lines were exposed bupivacaine (0.27, 0.54, 1.08, 2.16, 4.33 and 8.66 mM) and lidocaine (0.66, 1.33, 5.33, 10.66, 21.32 and 42.64 mM) for 24 hours, 48 hours, and 72 hours. These concentrations were determined by preliminary experiments that found the median effective dose was 1.4 mM for bupivacaine and 7.0 mM for lidocaine in both cell lines. Microculture tetrazolium and colony formation assay determined whether cell death occurred. Apoptosis induction was evaluated by phase-contrast micrographs, flow cytometry, DNA fragmentation and reactive oxygen species (ROS). The underlying pathways were analyzed by protein electrophoresis and Western blot. All testing was performed in triplicate and compared with pH-adjusted controls. Quantitative results were analyzed without blinding. RESULTS: Both medications caused cell death in a dose- and time-dependent manner. Exposure to bupivacaine for 24 hours reduced viability of UMR-108 cells by 6 ± 0.75% (95% CI 2.9 to 9.11; p = 0.01) at 1.08 mM and 89.67 ± 1.5% (95% CI 82.2 to 95.5; p < 0.001) at 2.16 mM. Under the same conditions, MNNG/HOS viability was decreased in a similar fashion. After 24 hours, the viability of UMR-108 and MNNG/HOS cells exposed to 5.33 mM of lidocaine decreased by 25.33 ± 8.3% (95% CI 2.1 to 48.49; p = 0.03) and 39.33 ± 3.19% (95% CI 30.46 to 48.21; p < 0.001), respectively, and by 90.67 ± 0.66% (95% CI 88.82 to 92.52; p < 0.001) and 81.6 ± 0.47% (95% CI 79.69 to 82.31; p < 0.001) at 10.66 mM, respectively. After 72 hours, the viability of both cell lines was further reduced. Cell death was consistent with apoptosis based on cell morphology, total number of apoptotic cells and DNA fragmentation. The percentage increase of apoptotic UMR-108 and MNNG/HOS cells confirmed by Annexin-V positivity compared with controls was 21.3 ± 2.82 (95% CI 16.25 to 26.48; p < 0.001) and 21.23 ± 3.23% (95% CI 12.2 to 30.2; p = 0.003) for bupivacaine at 1.08 mM and 25.15 ± 4.38 (95% CI 12.9 to 37.3; p = 0.004) and 9.11 ± 1.74 (95% CI 4.35 to 13.87; p = 0.006) for lidocaine at 5.33 mM. The intrinsic apoptotic pathway was involved as the expression of Bcl-2 and survivin were down-regulated, and Bax, cleaved caspase-3 and cleaved poly (ADP-ribose) polymerase-1 were increased. ROS production increased in the UMR-108 cells but was decreased in the MNNG/HOS cells. CONCLUSION: These findings provide a basis for evaluating these medications in the in vivo setting. Studies should be performed in small animals to determine if clinically relevant doses have a similar effect in vivo. In humans, biopsies could be performed with standard doses of these medications to see if there is a difference in biopsy tract contamination on definitive resection. CLINICAL RELEVANCE: Bupivacaine and lidocaine could potentially be used for their ability to induce and enhance apoptosis in local osteosarcoma treatment. Outcome data when these medications are used routinely during osteosarcoma treatment can be evaluated compared with controls. Further small animal studies should be performed to determine if injection into the tumor, isolated limb perfusion, or other modalities of treatment are viable.
