Background: Protein kinase C frequently plays a central role in the intracellular signal transduction of growth factors and cytokines. Methods: The acyclic bisindolylmaleimide 317615·2HCl was identified as a potent selective inhibitor of protein kinase Cβ. The compound 317615·2HCl was tested in culture and in vivo in the rat corneal micropocket and in the SW2 small-cell lung carcinoma human tumor xenograft. Results: In cell culture, 317615·2HCl was a more potent inhibitor of VEGF-stimulated HUVEC proliferation (IC50 150 nM, 72 h) than of human SW2 small-cell lung carcinoma cell proliferation (IC50 3.5 µM, 72 h). When administered orally twice daily for 10 days, the compound 317615·2HCl markedly decreased the neoangiogenesis induced by VEGF or bFGF in the rat corneal micropocket assay. To assess antitumor efficacy, 317615·2HCl was administered orally twice daily to nude mice bearing SW2 xenograft tumors on days 14 through 30 after tumor implantation. The number of countable intratumoral vessels was decreased in a dose-dependent manner reaching as low as one-quarter the number in the control tumors. The decrease in intratumoral vessels was paralleled by increases in tumor growth delay. Treatment of the tumor-bearing animals with paclitaxel or carboplatin followed by treatment with 317615·2HCl resulted in a 2.5- to 3.0-fold increase in tumor growth delay compared with the standard chemotherapeutic agents alone. Conclusions: 317615·2HCl represents a new approach to antiangiogenic therapy in cancer-blocking multiple growth factor signaling pathways in endothelial cells with a single agent. 317615·HCl is in early clinical testing.