The invention provides novel peptide prodrugs which contain cleavage sites specifically cleaved by prostate specific membrane antigen (PSMA). These prodrugs are useful for substantially inhibiting the non-specific toxicity of a variety of therapeutic drugs. PSMA is secreted by prostatic glandular cells. Upon cleavage of the prodrug by PSMA, the therapeutic drugs are activated and exert their toxicity. Sesquiterpene-γ-lactones form part of the prodrugs, and are designed to be linked to carrier moieties such as the peptides of the invention. Methods for treating cell proliferative disorders are also featured in the invention.