Histone deacetylase (HDAC) inhibitors and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) show promise for the treatment of cancers. The purpose of this study was to examine the molecular mechanisms by which HDAC inhibitor MS-275 sensitizes TRAIL-resistant breast cancer cells in vivo, inhibits angiogenesis and metastasis, and reverses epithelial-mesenchymal transition (EMT). BALB/c nude mice were orthotopically implanted with TRAIL-resistant invasive breast cancer MDA-MB-468 cells and treated intravenously with MS-275, TRAIL, or MS-275 followed by TRAIL, 4 times during first 3 weeks. Treatment of mice with TRAIL alone had no effect on tumor growth, metastasis, angiogenesis, and EMT. In comparison, MS-275 sensitized TRAIL-resistant xenografts by inducing apoptosis, inhibiting tumor cell proliferation, angiogenesis, metastasis, and reversing EMT. Treatment of nude mice with MS-275 resulted in downregulation of NF-κB and its gene products (cyclin D1, Bcl-2, Bcl-X(L), VEGF, HIF-1α, IL-6, IL-8, MMP-2, and MMP-9) and upregulation of DR4, DR5, Bax, Bak, and p21(/CIP1) in tumor cells. Furthermore, MS-275-treated mice showed significantly reduced tumor growth and decreased circulating vascular VEGFR2-positive endothelial cells, CD31-positive or von Willebrand factor-positive blood vessels, and lung metastasis compared with control mice. Interestingly, MS-275 caused "cadherin switch" and reversed EMT as shown by the upregulation of E-cadherin and downregulation of N-cadherin and transcription factors Snail, Slug, and ZEB1. In conclusion, sequential treatments of mice with MS-275 followed by TRAIL may target multiple pathways to reverse EMT and inhibit tumor progression, angiogenesis, and metastasis and represent a novel therapeutic approach to treat cancer.