Recruitment of CD11b(+)Ly6C(+) monocytes in non-small cell lung cancer xenografts challenged by anti-VEGF antibody

A series of antibodies against vascular endothelial growth factor (VEGF) have been developed for the treatment of various types of cancer, including non-small cell lung cancer (NSCLC) in recent years. However, tumors frequently demonstrate resistance to these strategies of VEGF inhibition. Efforts to better understand the mechanism underlying the acquired resistance to anti-VEGF antibodies are warranted. In the present study, in order to develop a xenograft model of acquired resistance to anti-VEGF antibody, xenografts of human adenocarcinoma A549 cells were generated through the successive inoculation of tumor tissue explants into first (F1), second (F2) and third (F3) generations of mice treated with the anti-VEGF antibody B20. Tumor growth rate and vessel-forming ability, assessed via cluster of differentiation (CD) 31 staining, were significantly lower in the F1, F2 and F3 groups compared with in the F0 control group (P<0.01), suggesting that drug resistance was not successfully acquired. The percentages of CD11b(+) myeloid-derived suppressor cells and lymphocyte antigen 6C (Ly6C)(+) subsets were significantly smaller in F1, F2 and F3 groups compared with in F0 (P<0.01). However, the ratio of Ly6C(+) to CD11b(+) cells was significantly higher in the F3 group compared with in F0 and F1 groups (P<0.01), indicating increasing recruitment of the Ly6C(+) subset with successive challenges with the anti-VEGF antibody. In conclusion, the recruitment of CD11b(+)Ly6C(+) monocytes increased with successive generations of NSCLC-xenografted mice challenged by B20, an anti-VEGF agent.