Tumor blood vessels are often leaky because of poor covering by mural cells and loose cell-to-cell contacts. Leaky vessels result in hemorrhage and limited vascular perfusion, which lead to hypoxic tumor microenvironment. Antiangiogenic agents have been shown to normalize the tumor blood vessels, albeit temporarily. Continued administration has been found to be associated with increased tumor hypoxia, a major driving force behind chemoresistance and metastasis. Sac-1004 was recently demonstrated to prevent vascular leakage, normalize tumor vessels and prevent metastasis in sustained manner. Here, we sought that combining antiangiogenic agent, sunitinib with Sac-1004 could have better inhibitory effect upon tumor growth. We found that B16F10 tumor growth was significantly reduced and tumor-bearing mice survival was increased upon combining sunitinib therapy with Sac-1004. In concordance with this observation, tumor vascular perfusion was substantially improved in tumors receiving combination therapy. In addition, tumor vascular leakage was reduced to higher extent in combination treatment group as compared to either therapy alone, an effect attributed to improved vascular junction. Interestingly, hypoxia in tumor environment was significantly reduced, when sunitinib was combined with Sac1004. Taken together, our data demonstrates that combining antiangiogenic therapy with vascular-leakage inhibiting agent might be a beneficial strategy to combat cancer. (C) 2014 Elsevier Inc. All rights reserved.