Enzastaurin (Enz) is a potent and selective inhibitor of PKCβ with antiproliferative activity (IC₅₀= ~6 nM). Enz suppresses VEGF-induced angiogenesis in the rat corneal micropocket assay, decreases microvessel density, and prevents VEGF secretion from human tumor cell xenografts in nude mice. Prolonged courses of Enz increase chemotherapy or radiation tumor growth delay of glioma, breast, and small cell lung cancer xenografts.