SYNTHESIS AND TESTING OF NEW ANTILEUKEMIC SCHIFF-BASES OF N-HYDROXY-N'-AMINOGUANIDINE AGAINST CCRF-CEM/0 HUMAN LEUKEMIA-CELLS INVITRO AND SYNERGISM STUDIES WITH CYTARABINE (ARA-C)

A series of eight new N-hydroxy-N'-aminoguanidine (HAG) Schiff bases [ArCH = NNHC(= NH)NHOH . tosylate] was synthesized as potential antitumor agents through the inhibition of the enzyme ribonucleotide reductase (EC 1.17.4.1). Five of the HAG derivatives (LK02 through LK06) were designed to contain an orthohydroxy group on the phenyl ring of ArCH = to increase the stability of the Schiff base formed. In addition, two compounds with a substituted quinoline [LK10; ArCH=(4-hydroxy-7-trifluoromethylquinolin-3-yl) methylene] or isoquinoline (LK11; ArCH=(5-nitroisoquinolin-1-yl)methylene] moiety were synthesized through multiple-step reactions involving reduction and/or oxidation. The IC50 values of the newly synthesized HAG Schiff bases were determined against human leukemic CCRF-CEM/0 cells in culture. The IC50 values of two previously reported HAG derivatives [ATL25; ArCH=(5-nitroisoquinolin-1-yl)methylene] and [LW02; ArCH=2-hydroxy-3-allyl-benzylidene)] were also determined for the first time against CCRF-CEM/0 cells. Among the compounds tested, LK11 was found to be the most potent (IC50, 2.95 +/- 0.1 muM) and the 4-methoxy-2-hydroxyphenyl derivative (LK02) to be the least potent (IC50, 121 +/- 16 muM). LK11 was about 15-fold more potent against CCRF-CEM/0 cells compared to the parent compound hydroxyguanidine sulfate (IC50, 46 +/- 7.1 muM) and was about 32 times more potent than LK10 (IC50, 97.6 +/- 0.9 muM). LK11 in combination was incubated in sequence with cytarabine (ara-C) at various molar ratios against CCRF-CEM/0 cells for 48 hr. The results were analyzed using both the isobologram and the median-effect methods. This combination at a 1:1 molar ratio was about 6-fold more potent (IC50, 0.16 muM) compared to ara-C alone (IC50, 1.05 muM and about 18-fold more potent compared to LK11 alone (IC50, 2.95 +/- 0.1 muM. In summary, the antileukemic potency of certain HAG derivatives can be improved by the presence of orthohydroxy groups of the phenyl ring, and a 1:1 molar combination of an isoquinoline HAG compound and ara-C leads to significant synergistic antileukemic activity against CCRF-CEM/0 cells in vitro.