ABCC1 and osteosarcoma: To further verify the role of circPVT1 in DXR resistance in osteosarcoma cells, the apoptosis-related proteins (antiapoptotic factor: Bcl-2 and proapoptotic factor: c-caspase-3) and multidrug-resistant proteins (ABCB1 and MRP-1) were detected in KHOS/DXR and U2OS/DXR cells.