We examined the antitumor effects of two antifolate inhibitors of thymidylate synthesis, N-(5-[N-(3, 4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N-methylamino ]-2-theno yl-L-glutamic acid (D1694; Tomudex) and 1843U89 as well as a folate-based inhibitor of purine synthesis, 5,