Disclosed herein are methods for suppressing an immune response in a subject, treating a neoplasm in a subject, or treating a fibroproliferative vascular disease in a subject, that includes administering to the subject a therapeutically effective amount of a 2-(4-piperazinyl)-substituted 4H-1-benzopyran-4-one compound, or a pharmaceutically acceptable salt thereof, having the structure of wherein the presence of each of R.sub.1 and R.sub.2 is optional and R.sub.1 and R.sub.2 are each independently selected from alkyl, substituted alkyl, heteroalkyl, cycloalkyl, substituted cycloalkyl, heterocycloalkyl, substituted heterocycloalkyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, halogen, hydroxy, or amino.