CASP3 and osteosarcoma: The data showed that co-treatment with doxycycline at non-toxic dose could significantly increase the anti-viability effect of ZOL in osteosarcoma HOS and MG-63 cells in MTT assay and colony formation assay, and largely increased the levels of apoptotic markers, cleaved caspase 3 and PARP, in ZOL-treated cells.