Raltitrexed is an inhibitor of thymidylate synthase (Ki = 62 nM).[1] It inhibits the growth of L1210 mouse lymphocytic leukemia cells in vitro (IC50 = 8 nM) as well as reduces thymidylate synthase activity and completely eliminates tumors in a mouse L1210:ICR ascitic tumor model when administered at a dose of 4 mg/kg, effects that can be reversed by administration of thymidine. It also reduces tumor growth and the number of metastases in an HCT116-luc mouse xenograft model.[2] Formulations containing raltitrexed have been used in the treatment of advanced colorectal cancers.