Apatinib,a small-molecule Inhibitor of VEGFR-2,has attracted much attention due to its encouraging anticancer activity in third-line clinical treatment for many malignancies,including non-small cell lung cancer (NSCLC).Its usage in second-line therapy with chemotherapeutic drugs is still under exploration.In this study we investigated the antitumor effect of apatinib combined with docetaxel against NSCLC and its cellular pharmacokinetic basis.A549 xenograft nude mice were treated with apatinib (100 mg/kg every day for 20 days) combined with docetaxel (8 mg/kg,ip,every four days for 5 times).Apatinib significantly enhanced the antitumor effect of docetaxel and alleviated docetaxel-induced liver damage as well as decreased serum transaminases (ALT and AST).LC-MS/MS analysis revealed that apatinib treatment significantly increased the docetaxel concentration in tumors (up to 1.77 times) without enhancing the docetaxel concentration in the serum,heart,liver,lung and kidney.Furthermore,apatinib decreased docetaxel-induced upregulation of P-glycoprotein in tumors.The effects of apatinib on the uptake,efflux and subcellular distribution of docetaxel were investigated in A549 and A549/DTX (docetaxel-resistant) cells in vitro.A cellular pharmacokinetic study revealed that apatinib significantly increased cellular/subcellular accumulation (especially in the cytosol) and decreased the efflux of docetaxel in A549/DTX cells through P-gp,while apatinib exerted no significant effect on the cellular pharmacokinetics of docetaxel in A549 cells.Consequently,the IC50 value of docetaxel in A549/DTX cells was more significantly decreased by apatinib than that in A549 cells.These results demonstrate that apatinib has potential for application in second-line therapy combined with docetaxel for NSCLC patients,especially for docetaxel-resistant or multidrug-resistant patients.