Synthesis and evaluation of 2,4-diaminoquinazoline antifolates with activity against methotrexate-resistant human tumor cells.

In an attempt to find potent antifolates with selectivity against tumor cells with intrinsic or acquired resistance to methotrexate, eleven nonclassical 2,4-diaminoquinazoline antifolates were synthesized and tested as inhibitors of dihydrofolate reductase from L5178Y cells. Several compounds appeared to be good enzyme inhibitors, with I50 values around 1 nM. Two of the compounds were also good inhibitors of cell growth in vitro. One of these (PKC-32, 9-(2,4-diamino-5-methylquinazoline-6-methylene)aminophenanthren e) appeared to be 100-fold more potent than methotrexate as an inhibitor of growth of a methotrexate-resistant cell line with impaired transport for methotrexate. PKC-32 and PKC-155 were also tested against mouse tumors in vivo. PKC-32 was modestly active in vivo as compared with methotrexate. This drug may be a useful agent in the treatment of methotrexate-resistant tumors.