Mechanism of the reversal reaction of platinated DNA with thiourea studied by platinated 5'-GMP

Interaction of liposome-encapsulated cisplatin with biomolecules

We prepared liposomes by hydrating 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid with aqueous solutions of three "probe" molecules-cis-diamminedichloroplatinum(II) (cis-[Pt(II)(NH(3))(2)Cl(2)], cisplatin), guanosine 5'-monophosphate (5'-GMP), and 9-ethylguanine (9-EtG)-in phosphate-buffered saline as well as N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer. The positively charged hydrolysis product of cisplatin, [Pt(II)(NH(3))(2)Cl(H(2)O)](+), is in the inner core of the liposomes and negatively charged 5'-GMP embeds in the lipid bilayer of liposomes. In the presence of cisplatin, the size of the liposomes remains unchanged, and for 5'-GMP-embedded liposomes the size increases significantly compared with that of empty or control liposomes. In contrast, the neutral biomolecule 9-EtG was found to be dispersed in the exterior bulk water and the size of the liposomes remained the same as that of empty or control liposomes. When cisplatin-containing liposomes mix with 5'-GMP-embedded liposomes or liposomes with 9-EtG, the N7 nitrogen atom of 5'-GMP or 9-EtG binds the cisplatin, thus replacing the "leaving groups" and forming a bisadduct. After 48 h of mixing, the size of the liposomes changes for the mixture of 5'-GMP-embedded liposomes and cisplatin-containing liposomes. We used (1)H and (31)P NMR spectroscopic techniques to monitor incorporation or association of cisplatin and biomolecules with liposomes and their subsequent reactions with each other. The dynamic light scattering technique provided the size distribution of the liposomes in the presence and absence of probe molecules.

Bis(acridinylthiourea)platinum(II) complexes: synthesis, DNA affinity, and biological activity in glioblastoma cells

The preparation of two novel bis(acridine)platinum(II) complexes is reported. The 4+ charged conjugates associate strongly with double-stranded native DNA (K(i)>10(6)), possibly through bisintercalation. A cell viability assay was used to demonstrate that both compounds are capable of mediating cytotoxicity at micromolar concentrations in SNB19 brain tumor cells.

Effects of thiourea and ammonium bicarbonate on the formation and stability of bifunctional cisplatin-DNA adducts: consequences for the accurate quantification of adducts in (cellular) DNA

Cisplatin reacts with DNA by forming mainly bifunctional adducts via reactive monofunctional intermediates. When freshly platinated DNA was postincubated with thiourea (10 mM, at 23 or 37 degrees C) for periods of up to 24 h, followed by determination of mono- and diadducts, a rapid initial decrease was seen in the fraction of diadducts, followed by a much slower decrease. About 40% diadducts were found after 10-min postincubation at 23 degrees C, which dropped to some 14% after 24 h at 37 degrees C; total platination was hardly affected. Postincubation of "aged" platinated DNA (no reactive monoadducts) only showed the slower decrease. The rapid process is likely to represent monoadduct inactivation, preventing the formation of diadducts, whereas the slow reaction must be interpreted as diadduct-to-monoadduct conversion. Similar reactions, but less efficient than with thiourea, occurred during dialysis against NH4HCO3 (0.1-1 M). Pt-containing (di)nucleotides in digested DNA were hardly affected by thiourea. Rapid reduction of the measured level of bifunctional adducts also occurred when cisplatin-treated Chinese hamster ovary cells were postincubated with thiourea, with concomitant increase in survival. It is concluded that quantification of the real levels of mono- and diadducts in freshly platinated DNA requires a posttreatment with thiourea of 30-60 min at 37 degrees C.

Interstrand cross-linking of the hexadeoxynucleotide d(TACGTA) upon reaction with trans-diamminedichloroplatinum(II)

The reaction of trans-diamminedichloroplatinum(II), an inactive isomer of cisplatin, with d(TACGTA) was performed in aqueous solution, and the interstrand cross-linked adduct was isolated on a preparative scale. This adduct was characterized by 1 M thiourea treatment, atomic absorption spectroscopy, enzymatic digestion and 1H NMR as platinum coordinated to two molecules of d(TACGTA) at the N7 atom of the guanine residue. This interstrand cross-linked adduct did not form a duplex structure in the conditions where the free hexanucleotide adopts it.