A Kinetic Study on the Reactions of Azolato-Bridged Dinuclear Platinum(II) Complexes with Guanosine 5?-Monophosphate

Kinetic analysis of and platinum(II) migration in the reactions of tetrazolato-bridged dinuclear platinum(II) complexes with nucleotides

The series of tetrazolato-bridged complexes with the formula [{cis‑Pt(NH₃)₂}₂(μ-OH)(μ-5-H-tetrazolato-N1,N2)]²⁺ (5-H-X) or [{cis‑Pt(NH₃)₂}₂(μ-OH)(μ-5-R-tetrazolato-N2,N3)]ⁿ⁺ (R=H (5-H-Y), CH₃ (1), CH₂COOCH₂CH₃ (2), CH₂COO^- (3), n=2 (5-H-Y, 1, 2) or 1 (3)) are promising candidate complexes for formulation as next-generation platinum-based anticancer drugs that form multimodal bindings with DNA molecules. These multimodal bindings involve both non-covalent and covalent interactions, the latter of which are acknowledged to be essential for platinum-based drugs to exert their anticancer activity. In the present study, the tetrazolato-bridged complexes reacted with two molar equivalents of guanosine-5'-monophosphate (GMP) to yield the 1:2 reaction products [{cis‑Pt(NH₃)₂(GMP-N7)}₂(μ-5-R-tetrazolato-N1,N3)]^{2- or 1-}. This reaction was accompanied by an intramolecular Pt(II) migration that contributed to the formation of diverse DNA crosslinking, such as interhelical crosslinks. The second-order reaction rate constants for the reactions performed in phosphate-buffered D₂O solution showed that the reactivity of the complexes decreased in the order 5-H-X≳5-H-Y>2≳1>3 and that reactivity was correlated with the cytotoxicity of the complexes. A similar result was obtained for the reaction of the complexes with calf thymus DNA in which the formation of covalent DNA adducts was quantified by means of inductively coupled plasma mass spectrometry. These results suggest that overall charge affects the kinetics of the reactions of platinum complexes with GMP and calf thymus DNA. Thus, the positive charge of the complexes affects not only the non-covalent but also the covalent interactions between the complexes and nucleotides and DNA, which are negatively charged molecules.

New bimetallic palladium(ii) and platinum(ii) complexes: studies of the nucleophilic substitution reactions, interactions with CT-DNA, bovine serum albumin and cytotoxic activity

Nucleophilic substitution reactions, interactions with CT-DNA, bovine serum albumin and cytotoxic activity of new bimetallic Pt(ii) and Pd(ii) complexes.

[Drug discovery research in in-vivo antitumor-active azolato-bridged dinuclear Pt(II) complexes]

Cis-diamminedichloridoplatinum(II) (cisplatin), which was first introduced as a clinical anticancer agent in the 1970s, is still among the most-utilized agents in current cancer chemotherapy. The discovery of cisplatin antitumor activity has catalyzed drug discovery research on antitumor platinum coordination compounds with improved efficacy. Some of new compounds show fewer side effects or expanded clinical applications. Apart from some clinical inconveniences, such as side effects, the high therapeutic efficacy of platinum-based agents implies that further modifications may lead to more effective anticancer platinum drugs which are effective against cancers that are typically resistant to chemotherapy, such as pancreatic cancer, and platinum-refractory cancer. Most of the cisplatin analogs cause cross-resistance to cisplatin, probably because of the similar biological consequences. It is suggested that platinum complexes which interact with DNA; the most probable target molecule, through a mechanism different from that of cisplatin can provide unique anticancer spectra required for next-generation anticancer drugs. Therefore, we synthesized a series of azolato-bridged dinuclear Pt(II) complexes with a general formula, [{cis-Pt(NH(3))(2)}(2)(µ-OH)(µ-azolato)](2+), which can form 1,2-intrastrand crosslinks with a minimal DNA distortion, whereas clinical platinum-based drugs provide 1,2-intrastrand crosslink with severe DNA distortion. Indeed, they exhibit much higher in vitro cytotoxicity than cisplatin, and we have recently found one of the dinuclear Pt(II) complexes exhibits markedly high in vivo antitumor efficacy against pancreatic cancer. Here, I update our drug-discovery research on the series of azolato-bridged dinuclear Pt(II) complexes that may be more effective and safer than current anticancer chemotherapeutic agents.

Substitution behaviour of novel dinuclear Pt(II) complexes with bio-relevant nucleophiles

The novel dinuclear Pt(II) complexes [{trans-Pt(NH(3))(2)Cl}(2)(μ-pyrazine)](ClO(4))(2) (Pt1), [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF (Pt2), and [{trans-Pt(NH(3))(2)Cl}(2)(μ-1,2-bis(4-pyridyl)ethane)](ClO(4))(2) (Pt3), were synthesized. Acid-base titrations, and temperature and concentration dependent kinetic measurements of the reactions with biologically relevant ligands such as thiourea (Tu), glutathione (GSH) and guanosine-5'-monophosphate (5'-GMP) were studied at pH 2.5 and 7.2. The reactions were followed under pseudo-first-order conditions by stopped-flow and UV-vis spectrophotometry. (1)H NMR spectroscopy was used to follow the substitution of chloride in the complex [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF by guanosine-5'-monophosphate (5'-GMP) under second-order conditions. The results indicate that the bridging ligand has an influence on the reactivity of the complexes towards nucleophiles. The order of reactivity of the investigated complexes is Pt1 > Pt2 > Pt3.

Mono- and dinuclear platinum(II) compounds with 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine. Structure, cytotoxic activity and reaction with 5'-GMP

Mono- and dinuclear platinum(II) coordination compounds of formula cis-[PtCl(2)(NH(3))(dmtp)], 1, cis-[PtCl(2)(dmtp)(2)], 2 and {H(+)[C(28)H(32)Cl(2)N(16)Pt(2)](2+)(NO(3))(3)(H(2)O)(6)}, 3, in which dmtp is 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine have been synthesized and characterized by infrared and by (1)H, (13)C, (195)Pt NMR spectroscopy. The coordination units of the cationic species of formula [Pt(2)(mu-dmtp)(2)Cl(2)(dmtp)(2)](2+) are built up by two platinum atoms in a square-planar environment. Two sites are occupied by two 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) bridging ligands which are linked to both metal atoms through their nitrogen atoms in positions 3 and 4. The other two positions are occupied by one monodentate 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) molecule and a coordinated chloride. This compound is the first in which the same triazolopyrimidine ligand (dmtp) coordinates to a metal ion in two different ways, i.e. bridging bidentate and non-bridging monodentate. In addition, the interaction of compounds 1 and 2 with 5'-GMP was investigated in solution by (1)H NMR spectroscopy. The cytotoxicity of all the new platinum(II) compounds were studied by using two different cell lines: T47D (breast cancer) and HCV29T (bladder cancer).

Substitution behaviour of amine-bridged dinuclear Pt(II) complexes with bio-relevant nucleophiles

Complexes of the type [Pt2(N,N,N',N'-tetrakis(2-pyridylmethyl)diamine(HO)2]4+ and [Pt2(N,N,N',N'-tetrakis(2-pyridylmethyl)diamine(Cl)2]2+ were used to study their reactions with a series of bio-relevant nucleophiles, viz. thiourea, L-methionine and guanosine-5'-monophosphate (5'-GMP2-) as a function of nucleophile concentration and temperature. The reactions with the sulfur containing nucleophiles (thiourea and L-methionine) were followed under pseudo-first-order conditions by stopped-flow and UV-Vis spectrophotometry. The reaction with 5'-GMP2- was carried out under second order conditions and studied by NMR spectroscopy. The results indicate that the bridged dinuclear complexes remain intact after coordination of the studied nucleophiles for an extended period of time, which differs significantly from that reported for other multinuclear platinum complexes in the literature.

A pyrazolato-bridged dinuclear platinum(II) complex induces only minor distortions upon DNA-binding

The cytotoxic, pyrazolato-bridged dinuclear platinum(II) complex [(cis-{Pt(NH3)2})2(mu-OH)(mu-pz)]2+ (pz=pyrazolate) has been found to cross-link two adjacent guanines of a double-stranded DNA decamer without destabilizing the duplex and without changing the directionality of the helix axis. A 1H NMR study of the oligonucleotide d(CTCTG*G*TCTC)-d(GAGACCAGAG), cross-linked at the two G* guanines by [(cis-{Pt(NH3)2})2(mu-pz)]3+, and molecular dynamics simulations of the explicitly solvated duplex were performed to characterize the structural details of the adduct. The dinuclear platinum cross-link unwinds the helix by approximately 15 degrees , that is, to a similar extent as the widely used antitumor drug cisplatin, but, in contrast to the latter, induces no significant bend in the helix axis. The Watson-Crick base-pairing remains intact, and the melting temperature of the duplex is unaffected by the cross-link. The helical twist is considerably reduced between the two platinated bases, as becomes manifest in an unusually short sequential H1'-H1' distance. This unwinding also affects the sugar ring of the guanosine in the 3'-position to the cross-link, which presents an N<-->S equilibrium. This is the first cytotoxic platinum complex that has been successfully designed by envisioning the structural consequences of its binding to DNA.

Modeling anticancer drug–DNA interactions via mixed QM/MM molecular dynamics simulations

The development of anticancer drugs started over four decades ago, with the serendipitous discovery of the antitumor activity of cisplatin and its successful use in the treatment of various cancer types. Despite the efforts made in unraveling the mechanism of the action of cisplatin, as well as in the rational design of new anticancer compounds, in many cases detailed structural and mechanistic information is still lacking. Many of these drugs exert their anticancer activity by covalently binding to DNA inducing a distortion or simply impeding replication, thus triggering a cellular response, which eventually leads to cell death. A detailed understanding of the structural and electronic properties of drug-DNA complexes and their mechanism of binding is the key step in elucidating the principles of their anticancer activity. At the theoretical level, the description of covalent drug-DNA complexes requires the use of state-of-the-art computer simulation techniques such as hybrid quantum/classical molecular dynamics simulations. In this review we provide a general overview on: drugs which covalently bind to DNA duplexes, the basic concepts of quantum mechanics/molecular mechanics (QM/MM), molecular dynamics methods and a list of selected applications of these simulations to the study of drug-DNA adducts. Finally, the potential and the limitations of this approach to the study of such systems are critically evaluated.