Nanoparticle mediated microvascular embolization (NME) of tumor tissue may occur after systemic administration of PEM, leading to widespread shutdown of vascular flow, hemorrhage, and necrosis. PEM constructs are developed that incorporate large amounts of iron-containing protein, possess high oxygen affinities, and demonstrate delayed nitric oxide binding. Such properties induce selective NME of tumors after extravasation, and will likely enhance the effect of VEGFR TKIs and/or mTOR inhibitors.