Gefitinib is an ATP-competitive inhibitor of receptor tyrosine kinases known to repress the progression of various types of cancers. Emerging evidence has shown that this molecule modulates endothelial cells to inhibit angiogenesis. However, the biological effects of gefitinib have not been comprehensively investigated in endothelial cells. In this study, gefitinib-mediated regulation of cell proliferation, migration, cell attachment, cytoskeletal actin filament reorganization, tubular-like structure formation and angiogenesis in vivo was examined along with the corresponding mechanisms. G1-phase cell cycle arrest was detected and led to a decrease in H-3-labeled thymidine incorporation under sublethal doses of gefitinib. Endothelial cell migration was blocked in both wound-healing and transwell assays. In addition, gefitinib simultaneously inhibited collagen- and fibronectin-dependent cell attachment. Importantly, we first observed that the gefitinib-induced phenotypes might be partially due to the abnormal retrograde flow of actin filaments. The results of this study revealed the antivasculogenic effects of gefitinib at sublethal doses and indicated that the treatment of cancer patients with this drug might impair angiogenesis in the tumor microenvironment to reduce the cancer metastasis rate in addition to the direct therapeutic benefits of repressing epidermal growth factor receptor signaling in cancer cells. (C) 2020 The Author. Published by Elsevier Inc.