Treatment of diseases

A method of inhibiting vascular hyperpermeability in an animal in need thereof comprising administering to the animal an effective amount of an active ingredient, wherein the active ingredient comprises a diketopiperazine, a prodrug of a diketopiperazine or a pharmaceutically-acceptable salt of either of them, wherein the diketopiperazine has the following formula:

• wherein:
• R1 and R2, which may be the same or different, each is:
• (a) a side chain of an amino acid, wherein the amino acid is glycine, alanine, valine, norvaline, α-aminoisobutyric acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, leucine, isoleucine, norleucine, serine, homoserine, threonine, aspartic acid, asparagine, glutamic acid, glutamine, lysine, hydroxylysine, histidine, arginine, homoarginine, citrulline, phenylalanine, p-aminophenylalanine, tyrosine, tryptophan, thyroxine, cysteine, homocysteine, methionine, penicillamine or ornithine;
• (b) R1 is —CH2—CH2—CH2— or —CH2—CH(OH)—CH2— and together with the adjacent ring nitrogen forms proline or hydroxyproline and/or R2 is —CH2—CH2—CH2— or —CH2—CH(OH)—CH2— and together with the adjacent ring nitrogen forms proline or hydroxyproline;
• or
• (c) a derivative of a side chain of an amino acid, wherein the amino acid is one of those recited in (a), and the derivatized side chain has:
• (i) an —NH2 group replaced by an —NHR3 or —N(R3)2 group, wherein each R3 may independently be a substituted or unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl, arylalkyl or heteroaryl;
• (ii) an —OH group replaced by an —O—PO3H2 or —OR3 group, wherein each R3 may independently be a substituted or unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl, arylalkyl or heteroaryl;
• (iii) a —COOH group replaced by a —COOR3 group, wherein each R3 may independently be a substituted or unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl, arylalkyl or heteroaryl;
• (iv) a —COOH group replaced by a —CON(R4)2 group, wherein each R4 may independently be H or a substituted or unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl, arylalkyl or heteroaryl;
• (v) an —SH group replaced by —S—S—CH2—CH(NH2)—COOH or —S—S—CH2—CH2—CH(NH2)—COOH;
• (vi) a —CH2— group replaced by a —CH(NH2)— or a —CH(OH)— group;
• (vii) a —CH3 group replaced by a —CH2—NH2 or a —CH2—OH group;
• and/or
• (viii) an H which is attached to a carbon atom replaced by a halogen.