The invention provides a method of inhibiting vascular hyperpermeability in an animal in need thereof. The method comprises administering an effective amount of a diketopiperazine, a prodrug of a diketopiperazine or a pharmaceutically-acceptable salt of either of them to the animal, wherein the diketopiperazine has the formula set forth in the specification.The invention also provides a method of modulating the cytoskeleton of an endothelial cell in an animal. The method comprises administering an effective amount of a diketopiperazine, a prodrug of a diketopiperazine or a pharmaceutically-acceptable salt of either of them to the animal, wherein the diketopiperazine has the formula set forth in the specification.The invention further provides a kit. The kit comprises a diketopiperazine, a prodrug of a diketopiperazine or a pharmaceutically-acceptable salt of either of them to the animal, wherein the diketopiperazine has the formula set forth in the specification.
