A comparative study of the interactions of cationic hetarenes with quadruplex-DNA forming oligonucleotide sequences of the insulin-linked polymorphic region (ILPR)

The interactions of the ILPR sequence (ILPR = insulin- linked polymorphic region) a2 [d(ACAG(4)TGTG(4)ACAG(4)TGTG(4))] with [2.2.2] heptamethinecyanine derivatives 1a-e and with the already established quadruplex ligands coralyne (2), 3,3'-[2,6pyridinediylbis(carbonylimino)]bis[1-methylquinolinium] (3), 4,4',4 '',4'''-(21H, 23H-porphine-5,10,15,20-tetrayl) tetrakis[1-methylpyridinium] (4), naphtho[2,1-b:3,4-b':6,5-b '':7,8-b''']tetraquinolizinium (5) and thiazole orange (6) were studied. It is demonstrated with absorption, fluorescence and CD spectroscopy that all investigated ligands bind with relatively high affinity to the ILPR-quadruplex DNA a2 (0.2-5.5 x 10(6) M-1) and that in most cases the binding parameters of ligand-ILPR complexes are different from the ones observed with other native quadruplex-forming DNA sequences.