Glutathione-activated anti-tumor prodrugs of 6-mercaptopurine and 6-thioguanine

The present invention relates to a method for treating a tumor in a tissue of a human or non-human animal, the tumor having an elevated level of glutathione relative to the tissue, the method comprising the steps of administering to the animal a prodrug comprising a thiopurine having a sulfur heteroatom conjugated to an alpha-, beta-unsaturated carbonyl moiety, in combination with a pharmaceutically acceptable carrier, the moiety comprising a double bond having an alpha end and a beta end, the beta end being accessible to glutathione in an addition-elimination reaction, the prodrug lacking an ionizable carboxylic acid group; and observing a reduction in growth of the tumor.