WP1066 is a cell-permeable inhibitor of STAT3 that directs dephosphorylation and nuclear export of constitutively phosphorylated STAT3 in U87-MG and U373-MG malignant glioma cells when given at a concentration of 10 μM. It also induces apoptosis in U87-MG (IC50 = 5.6 μM) and U373-MG (IC50 = 3.7 μM) cells. WP1066 is orally bioavailable, crosses the blood-brain barrier, and demonstrates in vivo activity, including immune activation as indicated by the up-regulation of CD80 and CD86 and the induction of proliferation of effector T cells. In addition to inducing apoptosis in cancer cells, WP1066 suppresses vascular smooth muscle cell proliferation after vascular injury in mice and prevents seizures following brain injury in rats.