Abstract: The present invention relates to Glutathione S-transferase (GST)/Reduced Glutathione (GSH) as a means for the in-vivo release of a drug that has been conjugated to specific electrophilic moieties via a sulfonamide bond. The drug may be an anticancer agent (or one with other therapeutic properties) carrying a free —NH— which has been derivatized by the attachment of an electrophile containing a moiety, such as p-CN— or p-NO2-pyridinylsulfonyl groups, or p-NO2- or 2,4 dinitrophenylsulfonyl groups, or suitable derivatives thereof, to make a prodrug. Optionally, the sulfonamide moiety may have attached to it a targeting molecule. The present invention also provides Glutathione S-transferase (GST)/Reduced Glutathione (GSH) as a means for the release of a protected amino derivative that has been conjugated to specific electrophilic moieties via a sulfonamide bond.