Sp1 inhibition-mediated upregulation of VEGF165b induced by rh-endostatin enhances antiangiogenic and anticancer effect of rh-endostatin in A549

Recombinant human endostatin (rh-endostatin), a potential antiangiogenic agent, is used in non-small cell lung carcinoma treatment and represses vascular endothelial cell growth factor (VEGF) levels in tumor cell. However, precise affection of rh-endostatin on the proangiogenic VEGF isoforms (VEGF(165)) or antiangiogenic VEGF isoforms (VEGF(165)b) is not clear. We therefore tested the hypothesis that rh-endostatin could alter expression of these isoforms to regulate tumor growth. A549 cells were exposed to rh-endostatin, and the expression of VEGF(165) and VEGF(165)b was detected. The role of SP1 as a regulator of isoform expression was investigated. We then examined the anticancer and antiangiogenic efficacy of rh-endostatin in combination with exogenous VEGF(165)b against A549 cells, EA.HY 926 cells and xenograft model of human lung cancer. rh-Endostatin reduced VEGF(165) and induced VEGF(165)b as well as inhibited SP1 in A549 cells. SP1 inhibitor (betulinic acid) also developed those changes. VEGF(165)b-rh-endostatin combination was highly synergistic and inhibited growth, survival, and migration of A549 cells, VEGF-mediated VEGFR2 phosphorylation in EA.HY 926 cells, and tumor growth in xenograft model of human lung cancer. rh-Endostatin downregulates proangiogenic vascular endothelial growth factor A (VEGFA) isoform and upregulates antiangiogenic VEGFA isoform, possibly through inhibition of SP1. Furthermore, VEGF(165)b sensitizes A549 to rh-endostatin treatment and enhances the anticancer effect of rh-endostatin.