Sulfated etoposide and nitrogen mustard prodrugs and their activation by streptomyces arylsulfatase

Abstract

Etoposide sulfate (ES) and p-di-2-chloroethylaminophenyl sulfate (CAPS) were designed as nontoxic anticancer prodrugs of etoposide and p-di-2-chloroethylaminophenol (CAP) that could be activated on tumor cell surfaces by monoclonal antibody (mAb)-arylsulfatase conjugates. In vitro assays indicated that CAPS and ES were nontoxic to the H2981 human lung adenocarcinoma cell line, while etoposide and CAP had IC50 values of 1–2 μM. Several commercially available arylsulfatases, as well as the arylsulfatases from human liver and urine, were either unable or poorly able to effect the hydrolysis of ES and CAPS. In contrast, arylsulfatase from Streptomyces (SAS) hydrolyzed ES and CAPS with specific activities of 3.0 and 4.8 μmol/min/ mg, respectively. SAS was conjugated to the L6 mono-clonal antibody and was able to activate ES in an immunologically specific manner on H2981 cells (L6 antigen positive). ES and CAPS were stable in mouse serum and were at least 9–13 times less toxic to mice on a molar basis than etoposide and CAP. Thus, ES and CAPS may have significant potential as prodrugs for site-specific activation by mAb-SAS conjugates.