ici-198583 and Leukemia

2-Deamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI 198583) is a potent inhibitor of thymidylate synthase. Its analogue, N(alpha)-[4-[N-[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinyl)methyl]-N-propargylamino]phenylacetyl]-L-glutamic acid, containing p-aminophenylacetic acid residue substituting p-aminobenzoic acid residue, was synthesized. The new analogue exhibited a moderately potent thymidylate synthase inhibition, of linear mixed type vs. the cofactor, N(5,10)-methylenetetrahydrofolate. The Ki value of 0.34 microM, determined with a purified recombinant rat hepatoma enzyme, was about 30-fold higher than that reported for inhibition of thymidylate synthase from mouse leukemia L1210 cells by ICI 198583 (Hughes et al., 1990, J. Med. Chem. 33, 3060). Growth of mouse leukemia L5178Y cells was inhibited by the analogue (IC50 = 1.26 mM) 180-fold weaker than by ICI 198583 (IC50 = 6.9 microM).

Topics: Animals; Folic Acid; Glutamic Acid; Leukemia; Mice; Rats

N10-Propargyl-5,8-dideazafolic acid (CB3717) and 2-desamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI-198,583) are potent folate-based inhibitors of thymidylate synthase. We studied the membrane transport and the growth-inhibitory effects of the two thymidylate synthase inhibitors on human CCRF-CEM leukemia cells with different transport properties for folic acid, reduced folates, and methotrexate (MTX). Membrane transport of [3H]ICI-198,583 can proceed via the high affinity/low capacity reduced folate carrier as supported by findings that (a) uptake of [3H]ICI-198,583 was significantly impaired in CEM cells which have a transport defect for MTX, (b) variants of CEM cells which overproduce the reduced folate carrier system showed a concomitant increase in the uptake of [3H]ICI-198,583 as for [3H]MTX, (c) MTX inhibited transport of [3H]ICI-198,583, and (d) uptake of [3H]ICI-198,583 was inhibited after treatment of CEM cells with an N-hydroxysuccinimide ester of MTX, which is a potent inhibitor of MTX transport. However, a membrane-associated folate-binding protein (FBP) offers another route for entry of CB3717 and ICI-198,583. CEM-FBP cells that have an elevated amount of FBP and do not have a functional reduced folate carrier were 640- and 61-fold more sensitive to CB3717 and ICI-198,583, respectively, compared to control CEM cells expressing the reduced folate/MTX carrier. This high sensitivity was related to a high affinity of the FBP for CB3717 and ICI-198,583 (Kd 2-3 nM), which is only 3-fold lower than for folic acid (Kd 1 nM) but significantly higher than for MTX (Kd 100 nM). Furthermore, after incubation of CEM-FBP cells for 24 h at 10 nM [3H]ICI-198,583, the high affinity binding of the FBP for ICI-198,583 allowed a 600-fold concentrative uptake of [3H]ICI-198,583 and its conversion to polyglutamate forms. These results indicate that multiple folate transport systems may be involved in the uptake of folate-based thymidylate synthase inhibitors.

Topics: Antineoplastic Agents; Biological Transport; Cell Division; Cells, Cultured; Drug Carriers; Folic Acid; Folic Acid Antagonists; Humans; In Vitro Techniques; Leukemia; Methotrexate; Quinazolines; Thymidylate Synthase