Regorafenib

BEZ235 was purchased from LC laboratories (Woburn, MA, USA) and regorafenib was obtained from Toronto Research Chemicals (North York, ON, Canada). Other chemicals were purchased from Sigma Chemical Co. (St. Louis, MO, USA). The antibodies were all purchased from Cell Signaling Technology, Inc. (Danvers, MA, USA). Bradford protein assay kit was purchased from Bio-Rad (Hercules, CA, USA). PVDF membranes were purchased from Merck Millipore (Bedford, MA, USA). The Western blot chemiluminescence reagents were purchased from Amersham Biosciences (Arlington Heights, IL, USA).

Compounds were dissolved in 100% dimethyl sulfoxide (DMSO; Sigma, St. Louis, MO, USA) and used at the concentrations indicated. Sorafenib Tosylate (purity > 98%, purchased from ApexBio (Houston, TX, USA)) and regorafenib (Toronto Research Chemicals, Toronto, Canada) were dissolved in 100% DMSO and used at the concentrations indicated. The coefficient of drug interaction (CDI) was used to analyze effects of drug combinations [58 (link),59 (link)]. CDI is calculated as follows: CDI = AB/(A × B). According to the absorbance of each group, AB is the ratio of the combination groups to control group, where A or B is the ratio of the single agent group to the control group. Thus, CDI values less than, equal to, or greater than 1 indicates that the drugs are synergistic, additive, or antagonistic, respectively. CDI less than 0.7 indicates a significantly synergistic effect.