Synthesis and stereochemical preference of peptide 4-aminocyclophosphamide conjugates as potential prodrugs of phosphoramide mustard for activation by prostate-specific antigen (PSA)

Abstract In an effort to develop proteolytically activated prodrugs of phosphoramide mustard by prostate-specific antigen (PSA), a series of tetrapeptide (Cbz-Ser-Ser-Phe-Tyr)-conjugated 4-aminocyclophosphamide (4-NH 2 -CPA) isomers were synthesized and evaluated as substrates of PSA. The cleavage of the conjugates by PSA were found to be stereoselective as only the two isomers with 4 R -configuration were efficiently cleaved by PSA. The cis - ( 2R , 4R ) - isomer was the best substrate of PSA with a half-life of 12 min. LC/MS analysis of the incubation solution of this isomer with PSA suggests that 4-NH 2 -CPA is released upon proteolysis and quickly degrades to cytotoxic phosphoramide mustard. These results clarified the stereochemical requirements of PSA on the peptide conjugates of 4-NH 2 -CPA and demonstrated the potential of these conjugates as potential PSA-activated prodrugs targeting prostate cancer.