Indeno[1,2- c]isoquinolin-5,11-diones conjugated to amino acids: Synthesis, cytotoxicity, DNA interaction, and topoisomerase II inhibition properties

Three series of indeno[1,2- c]isoquinolin-5,11-dione-amino acid conjugates were designed and synthesized. Amino acids were connected to the tetracycle through linkers with lengths of n = 2 and 3 atoms using ester (series I), amide (series II), and secondary amine (series III) functions. DNA binding was evaluated by thermal denaturation and fluorescence measurements. Lysine and arginine substituted derivatives with n = 3 provided the highest DNA binding. Arginine derivative 32 ( n = 2, series II) and glycine derivative 34 ( n = 2, series III) displayed high topoisomerase II inhibition. Incrementing the length of the N-6 side chain from two to three methylene units provided a significant increase in DNA affinity but a substantial loss in topoisomerase II inhibition. The most cytotoxic compounds toward HL60 leukemia cells were 19, 33, and 34 displaying micromolar IC 50 values. When tested with the topoisomerase II-mutated HL60/MX2 cell line, little variation of IC 50 values was found, suggesting that topoisomerase II might not be the main target of these compounds and that additional targets could be involved.