β Lapachone blocks the cell cycle and induces apoptosis in canine osteosarcoma cells

Osteosarcoma is a malignant tumor of primitive bone cells with a high incidence in dogs and humans. The need for more effective drugs with less adverse consequences has pushed the development of chemotherapeutic agents from plants and other natural sources. The aim of this study was to verify the cytotoxic effects of p-lapachone, a compound present in the sawdust of Tabebuia sp. (popularly known as ipe) wood, on canine osteosarcoma cells subcultured and treated in different concentrations (0.1 mu m, 0.3 mu m e 1.0 mu m) and exposure times (24h, 48h e 72h). Results were obtained through Trypan blue dye exclusion, tetrazolium reducing method, cell survival assay, Annexin V-FITC and Propidium Iodine labeling, JC-1 dye labeling and cell cycle kinetics e analysis. The group treated with 0.3 mu m P-lapachone presented higher decrease in cell viability (80.27%, 24h, 47.41%, 48h and 35.19%, 72h) and greater progression of cytotoxicity (19.73%, 24h, 52.59%, 48h and 64.81%, 72h). The lower IC50 (0.180 mu m) was verified in the group treated for 72 hours. Cell growth after treatment decreased as concentration and time of exposure increased, with 0.50% survival fraction at the concentration of 1.0 mu m. Initial apoptosis was the most frequent type of cell death in all groups, reaching bottom in the 24-hour group treated with 0.1 mu m (4.26%) and peaking in the 72-hour group treated with 1.0 mu m (85.89%). Mitochondrial depolarization demonstrated a dose-dependent phenomenon, indicating the intrinsic apoptosis. Cell growth inhibition by blocking cell cycle in the G0/G1 phase related to the exposure the time. p-lapachone is cytotoxic for canine osteosarcoma cells, induces apoptosis and promotes cell cycle arrest in G0/G1 phase.