BackgroundAngiogenesis plays an important role in tumor growth and metastasis; therefore, inhibition of angiogenesis is a promising strategy for developing new anticancer drugs. Type 2 methionine aminopeptidase (MetAP2) protein is likely a molecular target of angiogenesis inhibitors. Methods Nitroxoline, an antibiotic used to treat urinary tract infections, was identified from a high-throughput screen of a library of 175000 compounds for MetAP2 inhibitors and from a parallel screen using the Johns Hopkins Drug Library to identify currently used clinical drugs that can also inhibit human umbilical vein endothelial cells (HUVEC) proliferation. To investigate the mechanism of action of nitroxoline, inhibition of MetAP2 activity and induction of senescence were assessed in HUVEC. To test the antiangiogenic activity of nitroxoline, endothelial tube formation in Matrigel and microvessel formation in Matrigel plugs in vivo were assessed. Antitumor efficacy of nitroxoline was evaluated in mouse models of human breast cancer xenograft (n = 10) and bladder cancer orthotopic xenograft (n = 11). Furthermore, the mechanism of action of nitroxoline was investigated in vivo. Results Nitroxoline inhibited MetAP2 activity in vitro (half maximal inhibitory concentration [IC50] = 54.8 nM, 95% confidence interval [CI] = 22.6 to 132.8 nM) and HUVEC proliferation (IC50 = 1.9 μM, 95% CI = 1.54 to 2.39 μM). Nitroxoline inhibited MetAP2 activity in HUVEC in a dose-dependent manner and induced premature senescence in a biphasic manner. Nitroxoline inhibited endothelial tube formation in Matrigel and reduced microvessel density in vivo. Mice (five per group) treated with nitroxoline showed a 60% reduction in tumor volume in breast cancer xenografts (tumor volume on day 30, vehicle vs nitroxoline, mean = 215.4 vs 86.5 mm, difference = 128.9 mm, 95% CI = 32.9 to 225.0 mm, P =. 012) and statistically significantly inhibited growth of bladder cancer in an orthotopic mouse model (tumor bioluminescence intensities of vehicle [n = 5] vs nitroxoline [n = 6], P =. 045). Conclusion Nitroxoline shows promise as a potential therapeutic antiangiogenic agent.