methods and compositions for improving the angiogenesis - inhibitory effect of an anti - angiogenic serpin , or anti - angiogenic fragment thereof , by covalently linking a polymer moiety to the serpin such that the biological half - life of the serpin is extended for inhibition of diseases having a pathological angiogenic component including diabetic retinopathy , age - related macular degeneration , rheumatoid arthritis , endometriosis , psoriasis , juvenile hemangioma , and cancer .