Copper(II) complexes of L-arginine as netropsin mimics showing DNA cleavage activity in red light.

Copper(II) complexes [Cu(L-arg)(2)](NO(3))(2) (1) and [Cu(L-arg)(B)Cl]Cl (2-5), where B is a heterocyclic base, namely, 2,2'-bipyridine (bpy, 2), 1,10-phenanthroline (phen, 3), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz, 5), are prepared and their DNA binding and photoinduced DNA cleavage activity studied. Ternary complex 3, structurally characterized using X-ray crystallography, shows a square-pyramidal (4 + 1) coordination geometry in which the N,O-donor L-arginine and N,N-donor 1,10-phenanthroline form the basal plane with one chloride at the elongated axial site. The complex has a pendant cationic guanidinium moiety. The one-electron paramagnetic complexes display a metal-centered d-d band in the range of 590-690 nm in aqueous DMF. They show quasireversible cyclic voltammetric response due to the Cu(II)/Cu(I) couple in the range of -0.1 to -0.3 V versus a saturated calomel electrode in a DMF-Tris HCl buffer (pH 7.2). The DNA binding propensity of the complexes is studied using various techniques. Copper(II) bis-arginate 1 mimics the minor groove binder netropsin by showing preferential binding to the AT-rich sequence of double-strand (ds) DNA. DNA binding study using calf thymus DNA gives an order: 5 (L-arg-dppz) > or = 1 (bis-L-arg) > 4 (L-arg-dpq) > 3 (L-arg-phen) >> 2 (L-arg-bpy). Molecular docking calculations reveal that the complexes bind through extensive hydrogen bonding and electrostatic interactions with ds-DNA. The complexes cleave supercoiled pUC19 DNA in the presence of 3-mercaptopropionic acid as a reducing agent forming hydroxyl ((*)OH) radicals. The complexes show oxidative photoinduced DNA cleavage activity in UV-A light of 365 nm and red light of 647.1 nm (Ar-Kr mixed-gas-ion laser) in a metal-assisted photoexcitation process forming singlet oxygen ((1)O(2)) species in a type-II pathway. All of the complexes, barring complex 2, show efficient DNA photocleavage activity. Complexes 4 and 5 exhibit significant double-strand breaks of DNA in red light of 647.1 nm due to the presence of two photosensitizers, namely, L-arginine and dpq or dppz in the molecules.

Novel cytotoxic DNA sequence and minor groove targeted photosensitizers: conjugates of pyrene and netropsin analogues.

The design, syntheses, photochemical and biological properties of conjugates of pyrene with pyrrole- (1) and imidazole-containing (2) analogues of netropsin are reported. The results of an ethidium displacement assay and circular dichroism (CD) titration studies show both compounds bind with a higher affinity to poly(dA-dT) than to poly(dG-dC). In addition they bind as strongly to T4 coliphage DNA as to calf thymus DNA suggesting the binding occurs in the minor groove. The quenching rate constants of the singlet excited states of agents 1 and 2 by molecular oxygen were found to be 8.5 x 10(9) M-1S-1 and 7.7 x 10(9) M-1S-1, suggesting the involvement of singlet oxygen. Both compounds showed some cytotoxicity to human chronic myeloid leukemia K562 cells in the dark. Upon irradiation the activities were significantly enhanced resulting in photoinduced dose modifications of 8 and 14 for 1 and 2, respectively under the conditions employed. Both agents were markedly more phototoxic than 1-pyrenebutyric acid 8. To address the mechanism of action of compounds 1 and 2 their photoactivated abilities to produce DNA strand breaks were measured. Both agents caused increased single strand breakage with increasing UV exposure. The concentrations (EC50) of 1 and 2 needed to cause 50% single-strand cleavage of pBR322 DNA upon UV-A activation were found to be 40 microM and 45 microM, respectively. In contrast, no DNA strand breaks were observed in the dark with either conjugate or with 8 following irradiation. DNA strand breaks were measured in drug treated K562 cells using alkaline elution.(ABSTRACT TRUNCATED AT 250 WORDS)