Bicinchoninic acid bca assay

Sorafenib, regorafenib and lenvatinib were from Cayman Chemical Company (Michigan, United States); DMSO and bicinchoninic acid (BCA) assay were from Solarbio Science and Technology Company (Beijing, China); fetal bovine serum (FBS), Dulbecco’s modified essential media (DMEM) and trypsin-EDTA were from Gibco (California, United States); cell counting kit-8 (CCK-8) was from Dojindo Corporation (Shanghai, China); penicillin-streptomycin was from MedChem Express (New Jersey, United States); dithiothreitol (DTT) and Tris were from BBI Life Sciences (Shanghai, China); rLys-C and trypsin were from Promega Corporation (Madison, United States); triethylammonium bicarbonate (TEAB) buffer, iodoacetamide (IAM) and bovine serum albumin (BSA) were from Sigma-Aldrich Corporation (St Louis, MO, United States); Annexin V-FITC apoptosis detection kit was from Becton, Dickinson and Company (New Jersey, United States); cell cycle analysis kit was from Beyotime Biotechnology (Shanghai, China); acetonitrile (ACN), formic acid (FA) and TMT 6-plex reagent kit were from Thermo Fisher Scientific (Waltham, MA, United States); protease inhibitor cocktail was from Bimake (Houston, Texas, United States).

The exosome-free DMEM cultured BMSCs or UC-MSCs for 2 days was collected. The collected medium was centrifuged first at 3000 g for 20 min, second at 20,000 g for 30 min. The supernatant was collected and filtered with a 0.22-μm filter (Millex), then the supernatant was ultracentrifugated at 100,000 g for 90 min, the precipitation was resuspended by 100 μl PBS after washed with PBS. The total protein concentration of exosomes was quantified by the bicinchoninic acid (BCA) assay (Solarbio).