Effects of geometric isomerism and ligand substitution in bifunctional dinuclear platinum complexes on binding properties and conformational changes in DNA

Characterization, modes of interactions with DNA/BSA biomolecules and anti-tumor activity of newly synthesized dinuclear platinum(II) complexes with pyridazine bridging ligand

Platinum-based drugs are widely recognized efficient anti-tumor agents, but faced with multiple undesirable effects. Here, four dinuclear platinum(II) complexes, [{Pt(1,2-pn)Cl}2(μ-pydz)]Cl2 (C1), [{Pt(ibn)Cl}2(μ-pydz)]Cl2 (C2), [{Pt(1,3-pn)Cl}2(μ-pydz)]Cl2 (C3) and [{Pt(1,3-pnd)Cl}2(μ-pydz)]Cl2 (C4), were designed (pydz is pyridazine, 1,2-pn is ( ±)-1,2-propylenediamine, ibn is 1,2-diamino-2-methylpropane, 1,3-pn is 1,3-propylenediamine, and 1,3-pnd is 1,3-pentanediamine). Interactions and binding ability of C1-C4 complexes with calf thymus DNA (CT-DNA) has been monitored by viscosity measurements, UV-Vis, fluorescence emission spectroscopy and molecular docking. Binding affinities of C1-C4 complexes to the bovine serum albumin (BSA) has been monitored by fluorescence emission spectroscopy. The tested complexes exhibit variable cytotoxicity toward different mouse and human tumor cell lines. C2 shows the most potent cytotoxicity, especially against mouse (4T1) and human (MDA-MD468) breast cancer cells in the dose- and time-dependent manner. C2 induces 4T1 and MDA-MD468 cells apoptosis, further documented by the accumulation of cells at sub-G1 phase of cell cycle and increase of executive caspase 3 and caspase 9 levels in 4T1 cells. C2 exhibits anti-proliferative effect through the reduction of cyclin D3 and cyclin E expression and elevation of inhibitor p27 level. Also, C2 downregulates c-Myc and phosphorylated AKT, oncogenes involved in the control of tumor cell proliferation and death. In order to measure the amount of platinum(II) complexes taken up by the cells, the cellular platinum content were quantified. However, C2 failed to inhibit mouse breast cancer growth in vivo. Chemical modifications of tested platinum(II) complexes might be a valuable approach for the improvement of their anti-tumor activity, especially effects in vivo.

New minor groove covering DNA binding mode of dinuclear Pt(II) complexes with various pyridine-linked bridging ligands and dual anticancer-antiangiogenic activities

New anticancer platinum(II) compounds simultaneously targeting tumor cells and tumor-derived neoangiogenesis, with new DNA interacting mode and large therapeutic window are appealing alternative to improve efficacy of clinical platinum chemotherapeutics. Herein, we describe three novel dinuclear [{Pt(en)Cl}₂(μ-L)]²⁺ complexes with different pyridine-like bridging ligands (L), 4,4'-bipyridine (Pt1), 1,2-bis(4-pyridyl)ethane (Pt2) and 1,2-bis(4-pyridyl)ethene (Pt3), which highly, positively charged aqua derivatives, [{Pt(en)(H₂O)}₂(μ-L)]⁴⁺, interact with the phosphate backbone forming DNA-Pt adducts with an unique and previously undescribed binding mode, called a minor groove covering. The results of this study suggested that the new binding mode of the aqua-Pt(II) complexes with DNA could be attributed to the higher anticancer activities of their chloride analogues. All three compounds, particularly complex [{Pt(en)Cl}₂(μ-4,4'-bipy)]Cl₂·2H₂O (4,4'-bipy is 4,4'-bipyridine) (Pt1), overcame cisplatin resistance in vivo in the zebrafish-mouse melanoma xenograft model, showed much higher therapeutic potential than antiangiogenic drug sunitinib malate, while effectively blocking tumor neovascularization and melanoma cell metastasis. Overall therapeutic profile showed new dinuclear Pt(II) complexes could be novel, effective and safe anticancer agents. Finally, the correlation with the structural characteristics of these complexes can serve as a useful tool for developing new and more effective anticancer drugs.

Influence of geometric isomerism on the binding of platinum anticancer agents with phospholipids

Reported herein is a detailed NMR and DFT study of the interaction of the 15N-labelled dinuclear platinum anticancer compound [{cis-PtCl(NH3)2}2{μ-H2N(CH2)6NH2}]2+ (15N-1, 1,1/c,c) with 1,2-dihexanoyl-sn-glycero-3-phosphate (DHPA), as a comparison with an earlier study of the interaction of the same water-soluble phospholipid fragment with the geometric trans isomer (1,1/t,t). The reaction of 15N-1 with the sodium salt of DHPA was studied at 298 K, pH ∼ 5.6, by [1H,15N] HSQC 2D NMR spectroscopy. The NMR data, supported by DFT models, provide evidence that the monofunctional DHPA adduct of 15N-1 exists in two conformational forms, with different orientation of the (CH2)6 linker; one has an interaction between the unbound {PtN3Cl} moiety and the coordinated DHPA molecule. Similarly, two bifunctional adduct conformers are identified, in which one has an interaction between the phosphate groups of the two bound DHPA molecules. When compared to the previously reported reactions of 1,1/t,t with DHPA, equilibrium conditions of the 1,1/c,c reaction are reached more slowly (120 h), similar to the reaction with phosphate. The rate constant for the first step of DHPA binding (kL) is slightly lower (1.6 fold) for the cis-compared to the trans-isomer, whereas the rate constant for the reverse reaction is 4-fold lower, resulting in a much greater proportion of DHPA bound species at equilibrium.

Element 78 – Platinum

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Computational investigations of trans‑platinum(II) oxime complexes used as anticancer drug

Some platinum oxime complexes are optimized at HF/CEP-31G level which has been reported as the best level for these type complexes in the gas phase. IR spectrum is calculated and the new scale factor is derived. NMR spectrum is calculated at the same level of theory and examined in detail. Quantum chemical parameters which have been mainly used are investigated and their formulas are given in detail. Additionally, selected quantum chemical parameters of studied complexes are calculated. New theoretical IC₅₀% formulas are derived and biological activity rankings of mentioned complexes are investigated.

Cyclometalated Pt(ii) complexes with a bidentate Schiff-base ligand displaying unexpected cis/trans isomerism: synthesis, structures and electronic properties

Unexpected cis/trans isomerism in a bis-cyclometalated Pt(ii) complex is investigated by NMR, X-ray diffraction, optical, electrochemical and computational methods and rationalized.

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.

Synthesis and evaluation of series of diazine-bridged dinuclear platinum(II) complexes through in vitro toxicity and molecular modeling: correlation between structure and activity of Pt(II) complexes

Polynuclear Pt(II) complexes are a novel class of promising anticancer agents with potential clinical significance. A series of pyrazine (pz) bridged dinuclear Pt(II) complexes with general formulas {[Pt(L)Cl]2(μ-pz)}(2+) (L, ethylenediamine, en; (±)-1,2-propylenediamine, 1,2-pn; isobutylenediamine, ibn; trans-(±)-1,2-diaminocyclohexane, dach; 1,3-propylenediamine, 1,3-pd; 2,2-dimethyl-1,3-propylenediamine, 2,2-diMe-1,3-pd) and one pyridazine (pydz) bridged {[Pt(en)Cl]2(μ-pydz)}(2+) complex were prepared. The anticancer potential of these complexes were determined through in vitro cytotoxicity assay in human fibroblasts (MRC5) and two carcinoma cell lines (A375 and HCT116), interaction with double stranded DNA through in vitro assay, and molecular docking study. All complexes inhibited cell proliferation with inhibitory concentrations in the 0.5-120 μM range. While {[Pt(1,3-pd)Cl]2(μ-pz)}(2+) showed improved activity and {[Pt(en)Cl]2(μ-pydz)}(2+) showed comparable activity to that of clinically relevant cisplatin, {[Pt(en)Cl]2(μ-pydz)}(2+) was less toxic in an assay with zebrafish (Danio rerio) embryos, causing no adverse developmental effects. The in vitro cytotoxicity of all diazine-bridged dinuclear Pt(II) complexes is discussed in correlation to their structural characteristics.

Toxicity in tumor cells, DNA binding mode, and resistance to decomposition by sulfur nucleophiles of new dinuclear bifunctional trans-PtII complexes containing long alkane linkers

In an effort to design dinuclear PtII compounds that maintain the target (DNA) binding profile of the trans-oriented dinuclear bifunctional PtII complexes containing aliphatic linker chains but are less susceptible to metabolic decomposition, the new, long-chain dinuclear PtII complexes—[{trans-PtCl(dien)}2-μ-(CH2)n]2+ (n = 7,10,12, dien = diethylenetriamine)—were synthesized. The toxicity of these metallodrugs was examined in ovarian tumor cell lines. The results showed that the activity of these complexes increased with growing length of the linker; the activity of complex containing the longest linker (n = 12) was comparable with that of cis-diamminedichloridoplatinum(II) (cisplatin). This observation correlated with the results of DNA binding studies performed in cell-free media. The results of these studies demonstrated that the growing length of the aliphatic bridge promoted more distorting conformational alterations induced in DNA. Attention was also paid to the reactivity of {[Pt(dien)Cl]2-alkane} compounds with glutathione (GSH). The results of these experiments support the thesis that the dinuclear structure of {[Pt(dien)Cl]2-alkane} complexes remains stable in the presence of S-containing compounds without undergoing chemical degradation as previously observed for some di/trinuclear bifunctional PtII complexes. This enhanced stability represents a favorable property which may contribute to reduce side effects and increase therapeutic efficacy of the dinuclear {[Pt(dien)Cl]2-alkane} compounds.

Novel oximato-bridged platinum(II) di- and trimer(s): synthetic, structural, and in vitro anticancer activity studies

Novel platinum complexes of trans geometry [PtCl(2){(Z)-R(H)C═NOH}(2)] [R = Me (1), Et (3)] and [PtCl(2){(E)-R(H)C═NOH}{(Z)-R(H)C═NOH}] [R = Me (2), Et (4)] as well as the classic trans-[PtCl(2)(R(2)C═NOH)(2)] [R = Me, Et] were reacted with an equivalent amount of silver acetate in acetone solution at ambient temperature, resulting in formation of unprecedented head-to-tail-oriented oximato-bridged dimers [PtCl{μ-(Z)-R(H)C═NO}{(Z)-R(H)C═NOH}](2) [R = Me (5), Et (7)], [PtCl{μ-(Z)-R(H)C═NO}{(E)-R(H)C═NOH}](2) [R = Me (6), Et (8)], and [PtCl(μ-R(2)C═NO)(R(2)C═NOH)](2) [R = Me (9), Et (10)], correspondingly. The dimeric species feature a unique six-membered diplatinacycle and represent the first example of oxime ligands coordinated to platinum via the oxygen atom. All complexes were characterized by elemental analyses, electrospray ionization mass spectrometry, IR and multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, as well as X-ray diffraction in the cases of dimers 6 and 9. Furthermore, the crystal and molecular structures of a trimeric oximato-bridged complex 11 comprising three platinum units connected in a chain way were established. The cytotoxicity of both dimers and the respective monomers was comparatively evaluated in three human cancer cell lines: cisplatin-sensitive CH1 cells as well as cisplatin-resistant SW480 and A549 cells, whereupon structure-activity relationships were drawn. Thus, it was found that dimerization results in a substantial (up to 7-fold) improvement of IC(50) values of (aldoxime)Pt(II) compounds, whereas for the analogous complexes featuring ketoxime ligands the reverse trend was observed. Remarkably, the novel dimers yielded no cross-resistance with cisplatin in SW480 cells, exhibiting up to 2-fold enhanced cytotoxicity in comparison with the CH1 cell line and thereby possessing a promising potential to overcome resistance toward platinum anticancer drugs. The latter point was also confirmed by investigating the potency of apoptosis induction in the case of one monomer as well as one dimer; the investigated complexes proved to be strong apoptotic agents which could induce cell death even in the cisplatin-resistant SW480 cell line.

Excursions in polynuclear platinum DNA binding

Polynuclear platinum agents are a structurally unique class of anti-cancer drugs, distinct from the cisplatin family. To describe the chemistry and biology of this class, it was necessary to challenge the accepted paradigms for the structure-activity relationships; design new chemotypes and delineate the structures and consequences of their DNA binding modes. This article summarizes the structural changes induced in DNA by both covalent (bond-forming) and non-covalent (ligand recognition) adducts. Solution (Nuclear Magnetic Resonance), solid state (crystallography) and gas-phase (Electrospray Ionization Mass Spectrometry) techniques have all been used to describe the new DNA structures along with molecular biological techniques. The combined approaches allow molecular description of hitherto unobserved adducts such as long-range major-groove interstrand crosslinks; directional isomers on DNA and a third class of ligand-DNA binding, the phosphate clamp. The phosphate recognition is distinct from ''classic'' minor-groove recognition or intercalation.

Effects of geometric isomerism and anions on the kinetics and mechanism of the stepwise formation of long-range DNA interstrand cross-links by dinuclear platinum antitumor complexes

Reported herein is a detailed study of the kinetics and mechanism of formation of a 1,4-GG interstrand cross-link by the dinuclear platinum anticancer compound [15N][{cis-PtCl(NH3)2}2{mu-NH2(CH2)6NH2}]2+ (1,1/c,c (1)). The reaction of [15N]1 with 5'-{d(ATATGTACATAT)2} (I) has been studied by [1H,15N] HSQC NMR spectroscopy in the presence of different concentrations of phosphate. In contrast with the geometric trans isomer (1,1/t,t), there was no evidence for an electrostatic preassociation of 1,1/c,c with the polyanionic DNA surface, and the pseudo-first-order rate constant for the aquation of [(15)N]1 was actually slightly higher (rather than lower) than that in the absence of DNA. When phosphate is absent, the overall rate of formation of the cross-link is quite similar for the two geometric isomers, occurring slightly faster for 1,1/t,t. A major difference in the DNA binding pathways is the observation of phosphate-bound intermediates only in the case of 1,1/c,c. 15 mM phosphate causes a dramatic slowing in the overall rate of formation of DNA interstrand cross-links due to both the slow formation and slow closure of the phosphate-bound monofunctional adduct. A comparison of the molecular models of the bifunctional adducts of the two isomers shows that helical distortion is minimal and globally the structures of the 1,4 interstrand cross-links are quite similar. The effect of carrier ligand was investigated by similar studies of the ethylenediamine derivative [15N]1-en. A pKa value of 5.43 was determined for the [15N]1,1/c,c-en diaquated species. The rate of reaction of [15N]1-en with duplex I is similar to that of 1,1/c,c and the overall conformation of the final adduct appears to be similar. The significance of these results to the development of "second-generation" polynuclear platinum clinical candidates based on the 1,1/c,c chelate (dach) series is discussed.

Dinuclear Platinum Complexes with Biological Relevance Based on the 1,2-Diaminocyclohexane Carrier Ligand

The synthesis of bifunctional dinuclear platinum complexes, [{PtCl(dach)}(2)-mu-Y](n+)Cl(n) (1-3; Y = H(2)N(CH(2))(3)NH(2)(CH(2))(4)NH(2), H(2)N(CH(2))(6)NH(2)(CH(2))(6)NH(2), and H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2), respectively; Figure 1) is reported. There was no labilization of the polyamine linker groups of the cis-1,2-diaminocyclohexane complexes in the presence of sulfur-containing species at physiological pH, in contrast to previous studies preformed on trans complexes. Metabolism reactions are somewhat dependent on the nature of the polyamine: at physiological pH, the spermidine complex 1 forms an inert (tetraamine)platinum species in which one platinum is chelated by a central and terminal amino group. The stability of cis-geometry complexes may make them viable second-generation polynuclear platinum clinical candidates.

Vibrational spectroscopy studies on linear polyamines

Vibrational spectroscopy [both Raman and INS (inelastic neutron scattering)], coupled to quantum mechanical calculations, was used in order to perform a thorough structural analysis of linear polyamines and polynuclear polyamine metal chelates [e.g. with Pt(II) and Pd(II)] with potential anticancer activity. The complementarity of the Raman and INS spectroscopies was exploited in order to gain a better knowledge of the conformational behaviour of these systems. Moreover, the conjugation of the experimental spectroscopic data to the theoretical results allows us to obtain valuable information on the structural preferences of this kind of system, which may lead to the establishment of SARs (structure–activity relationships) ruling their biological activity. Some of the most significant results obtained by the ‘Molecular Physical-Chemistry’ Research Group of the University of Coimbra (Portugal) are reviewed here.

A dinuclear monofunctional platinum(II) complex with an aromatic linker shows low reactivity towards glutathione but high DNA binding ability and antitumor activity

Multinuclear Pt(II) complexes represent a novel class of antitumor agents. In this work, a dinuclear monofunctional Pt(II) complex {[cis-Pt(NH(3))(2)Cl](2)(4,4'-methylenedianiline)}(NO(3))(2) (1) was synthesized and characterized by (1)H NMR, electrospray mass spectrometry, and elemental analysis. The 2D [(1)H,(15)N] heteronuclear single quantum coherence NMR spectra of (15)N-labeled 1 revealed that the cationic core of this water-soluble complex hardly hydrolyzes in aqueous solution and reacts very slowly with glutathione. Hydrolysis appears not to be an essential step for the formation of Pt-guanosine-5'-monophosphate (5'-GMP) or Pt-DNA adducts because the complex can react readily with 5'-GMP and partially transform B-DNA into its Z form. Such properties are desired to achieve the goal of enhancing cytotoxicity and lowering side effects of Pt(II) complexes. In fact, complex 1 is highly cytotoxic against the murine leukemia (P-388) and the human non-small-cell lung cancer (A-549) cell lines, and it is more cytotoxic than cisplatin at most concentrations tested.

trans-Platinum reporting for duty

HIV infects millions of people worldwide; however, no cures for this AIDS-causing retrovirus exist. A new approach using trans-platinum-nucleobase complexes to inhibit viral replication by disrupting the nucleocapsid protein-RNA interaction is presented in this issue of Chemistry & Biology.

Structure–toxicity relationships for different types of dinuclear platinum complexes

Nine structurally distinct dinuclear platinum complexes have been evaluated in a novel model system for the investigation of renal epithelial toxicity of platinum drugs. The results showed that these compounds are toxic when applied at the basolateral side of renal epithelia, whereas their toxic effects on the apical side are negligible. Such a difference in toxicity of the complexes has been found to result from their poor uptake through the apical membrane, as compared to the basolateral membrane. Toxicity of the compounds on the basolateral side varies depending on their structure. Structure-toxicity relationships for the group of complexes with rigid ligands and for the group of complexes with flexible ligands are discussed. Among the dinuclear complexes with rigid ligands, sterically hindered complexes are less toxic, due to their poor uptake and low reactivity towards glutathione. Within the group of complexes with flexible ligands, cis-configured isomers are more toxic than their trans-counterparts.

Structural characterization and DNA interactions of new cytotoxic transplatin analogues containing one planar and one nonplanar heterocyclic amine ligand

trans-Diaminedicholoroplatinum(II) complexes with one planar and one non-planar heterocyclic amine ligand were designed as new potential antitumor drugs. The X-ray crystallographic structures of trans-[PtCl2(4-picoline)(piperidine)] and trans-[PtCl2(4-picoline)(piperazine)].HCl revealed that the piperidine and piperazine ligands bind to the platinum through the equatorial position and that the ligands adopt the chair conformation. The nonplatinated amine of the piperazine can form hydrogen bonds with atoms that are approximately 7.5 A away from the Pt binding site. DNA is considered a major pharmacological target of platinum compounds. Hence, to expand the database correlating structural features of platinum compounds and DNA distortions induced by these compounds, which may facilitate identification of more effective anticancer platinum drugs, we describe the DNA binding mode in a cell-free medium of trans-[PtCl2(4-picoline)(piperidine)] and trans-[PtCl2(4-picoline)(piperazine)].HCl. Interestingly, the overall impact of the replacement of the second ammine group in transplatin by the heterocyclic ligands appears to change the character of the global conformational changes induced in DNA towards that induced by cisplatin. The clinical ineffectiveness of the parent transplatin has been proposed to be also associated with its reduced capability to form bifunctional adducts in double-helical DNA. The results of the present work support the view that replacement of both ammine groups of transplatin by heterocyclic ligands enhances cytotoxicity probably due to the marked enhancement of the stability of intrastrand cross-links in double-helical DNA.

Effects of geometric isomerism in dinuclear platinum antitumor complexes on aquation reactions in the presence of perchlorate, acetate and phosphate

The aquation and subsequent reactions of the dinuclear Pt antitumor complexes [{trans-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1,1/t,t) and [{cis-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1,1/c,c) in 15 mM perchlorate, acetate or phosphate solutions were followed at 298 K by [(1)H,(15)N] HSQC 2D NMR spectroscopy. Rate and equilibrium constants for the initial reversible aquation and the subsequent reversible reaction with phosphate or acetate are reported. The rate constant for the first aquation step is two-fold lower for 1,1/c,c than 1,1/t,t but the anation rate constants are similar so that the equilibrium lies further towards the chloro form for the 1,1/c,c compound. A pK (a) value of 6.01+/-0.03 was determined for the diaquated species [{cis-Pt(NH(3))(2)(H(2)O)}(2)(mu-NH(2)(CH(2))(6)NH(2))](4+) (1,1/c,c-3) which is 0.4 units higher than that of the 1,1/t,t compound. The rate constants for the binding of acetate and phosphate to 1,1/t,t are similar, but the rate constant for the reverse reaction is close to ten-fold higher in the case of phosphate so that equilibrium conditions are attained more rapidly (12 h compared with 64 h). On the other hand, for 1,1/c,c the rate constants for the forward and reverse reactions with acetate and phosphate are quite similar so that equilibrium conditions are reached very slowly (80-100 h) and a greater proportion of phosphate-bound species are present. The reduced lability of the bound phosphate for 1,1/c,c is attributed to the formation of a macrochelate phosphate-bridged species which was characterized by (31)P NMR and ESI-MS. The speciation profiles of 1,1/t,t and 1,1/c,c under physiological conditions are explored.

Application of fluorescence microscopy for investigation of cellular distribution of dinuclear platinum anticancer drugs

The dinuclear platinum complexes with aliphatic diamines [{cis-Pt(NH(3))(2)Cl}(2)(mu-H(2)N(CH(2))(6)NH(2))](NO(3))(2) (1,1/c,c) and [{trans-Pt(NH(3))(2)Cl}(2)(mu-H(2)N(CH(2))(4)NH(2))](NO(3))(2) (1,1/t,t), which are known to be highly active in vitro against several cancer cell lines, have been modified with a fluorogenic reporter (carboxyfluorescein diacetate, CFDA) and a hapten (dinitrophenyl, DNP). These labeled complexes have been designed for fluorescence microscopy investigation of cellular pathways of promising dinuclear platinum anticancer drugs and present the first example of labeling biologically active dinuclear platinum complexes with a fluorescent reporter. The modified compounds interact with a guanine model base similarly to the label-free parent complexes. The uptake of the complexes with a fluorescent label and the respective unlabeled complexes in the U2-OS human osteosarcoma cell line and its cisplatin-resistant derivative, U2-OS/Pt cell line has been investigated. Cellular processing of the CFDA- and DNP-modified dinuclear platinum complexes in U2-OS and U2-OS/Pt cells has been studied.

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

In this study, the reactions of N-acetyl-L-methionine (AcMet) with [{trans-PtCl(NH(3))(2)}(2)-mu-H(2)N(CH(2))(6)NH(2)](NO(3))(2) (BBR3005: 1,1/t,t 1) and its cis analog [{cis-PtCl(NH(3))(2)}(2)-mu-{H(2)N(CH(2))(6)NH(2)}]Cl(2) (1,1/c,c 2) were analyzed to determine the rate and reaction profile of chloride substitution by methionine sulfur. The reactions were studied in PBS buffer at 37 degrees C by a combination of multinuclear ((195)Pt, {(1)H-(15)N} HSQC) magnetic resonance (NMR) spectroscopy and electrospray ionization time of flight mass spectrometry (ESITOFMS). The diamine linker of the 1,1/t,t trans complex was released as a result of the trans influence of the coordinated sulfur atom, producing trans-[PtCl(AcMet)(NH(3))(2)](+) (III) and trans-[Pt(AcMet)(2)(NH(3))(2)](2+) (IV). In contrast the cis geometry of the dinuclear compound maintained the diamine bridge intact and a number of novel dinuclear platinum compounds obtained by stepwise substitution of sulfur on both platinum centers were identified. These include (charges omitted for clarity): [{cis-PtCl(NH(3))(2)}-mu-NH(2)(CH(2))(6)NH(2)-{cis-Pt(AcMet)(NH(3))(2)}] (V); [{cis-Pt(AcMet)(NH(3))(2)}(2)-mu-NH(2)(CH(2))(6)NH(2)] (VI); [{cis-PtCl(NH(3))(2)}-mu-NH(2)(CH(2))(6)NH(2)-{PtCl(AcMet)NH(3)] (VII); [{PtCl(AcMet)(NH(3))}(2)-mu-NH(2)(CH(2))(6)NH(2)] (VIII); [{trans-Pt(AcMet)(2)(NH(3))}-mu-NH(2)(CH(2))(6)NH(2)-{PtCl(AcMet)(NH(3))] (IX) and the fully substituted [{trans-Pt(AcMet)(2)(NH(3))}(2)-mu-{NH(2)(CH(2))(6)NH(2)] (X). For both compounds the reactions with methionine were slower than those with glutathione (Inorg Chem 2003, 42:5498-5506). Further, the 1,1/c,c geometry resulted in slower reaction than the trans isomer, because of steric hindrance of the bridge, as observed previously in reactions with DNA and model nucleotides.

A Surprisingly Stable Macrochelate Formed from the Reaction of Cis Dinuclear Platinum Antitumor Compounds with Reduced Glutathione

The structurally unique macrochelate [{Pt(en)}2-mu-{H2N(CH2)6 NH2}-mu-(SG)] (I) is the principal product of the reaction of the dinuclear compound [{PtCl(en)}2-mu-{H2N(CH2)6 NH2}]Cl2 (1) with reduced glutathione (GSH) in a stoichiometric 1:1 ratio in phosphate buffered saline (PBS) (pH 7.35). The macrochelate is formed through simultaneous bridging of the hexanediamine linker and glutathione thiolate. This represents a novel structure for glutathione adducts of platinum. At higher (1:4) ratios of Pt complex to GSH, an interesting interchange between bridged Pt-(SG)-Pt and terminal Pt-SG species is observed with the diamine linker still remaining intact in all cases. The integrity of I is further evident when reaction ratios are increased to 1:4 (Pt complex/GSH), and additional minor products are identified as [{Pt(en)SG}2-mu-{NH2(CH2)6 NH2}] (II), which transforms to [{Pt{NH2(CH2)2 NH2}(SG)}2-mu-{H2N(CH2)6 NH2}-mu-(SG)] (III), where the chelate ring is broken to produce a dangling monodentate ethylenediamine. The chemical shifts of the Pt-NH2 linker in all compounds are explained by consideration of the enhanced rigidity of the macrochelate (I) leading to shielding in comparison to the "open" monodentate structures (II, III). The remarkable stability of I is discussed in terms of possible biological implications.

Cytotoxic activity of metal complexes of biogenic polyamines: polynuclear platinum(II) chelates

Several polynuclear Pt(II) chelates with biogenic polyamines were synthesized and screened for their potential antiproliferative and cytotoxic activity in different human cancer cell lines. To gather information regarding the structure-activity relationships underlying their biological activity, the complexes studied were designed to differ in geometrical parameters such as the nature of the ligand and the number and chemical environment of the metal centers. Distinct effects were found for different cell lines and different structural characteristics of the complexes; chelates II, III, and IV displayed specificity toward the HeLa and HSC-3 epithelial-type cells, while V, VI, and VII were clearly more effective against the THP-1, MOLT-3, and CCRF-CEM leukemia cell lines. The toxicity of these Pt(II) complexes on noncancer cells was, in all cases, found to be reversed upon drug removal.

DNA interactions of new antitumor platinum complexes with trans geometry activated by a 2-metylbutylamine or sec-butylamine ligand

The global modification of mammalian and plasmid DNAs by novel platinum compounds, trans-[PtCl(2)(NH(3))(Am)], where Am=2 -methylbutylamine or sec-butylamine was investigated in cell-free media using various biochemical and biophysical methods. These modifications were analyzed in the context of the activity of these new compounds in several tumor cell lines including those resistant to antitumor cis-diamminedichloroplatinum(II) (cisplatin). The results showed that the replacement of one amine group by 2-methylbutylamine or sec-butylamine ligand in clinically ineffective trans-diamminedichloroplatinum(II) (transplatin) resulted in a radical enhancement of its activity in tumor cell lines so that they are more cytotoxic than cisplatin and exhibited significant antitumor activity including activity in cisplatin-resistant tumor cells. Importantly, this replacement also markedly altered DNA binding mode of transplatin and reduced the efficiency of repair systems to remove the adducts of the new analogues from DNA. The results support the view that one strategy to activate trans geometry in bifunctional platinum(II) compounds including circumvention of resistance to cisplatin may consist in a chemical modification of the ineffective transplatin which results in an increased efficiency to form DNA interstrand cross-links.

Induced-fit recognition of DNA by organometallic complexes with dynamic stereogenic centers

Organometallic chemistry offers novel concepts in structural diversity and molecular recognition that can be used in drug design. Here, we consider DNA recognition by eta 6-arene Ru(II) anticancer complexes by an induced-fit mechanism. The stereochemistry of the dinuclear complex [((eta 6-biphenyl)RuCl(en))2-(CH2)6]2 + (3, en = ethylenediamine) was elucidated by studies of the half unit [(eta 6-biphenyl)RuCl(Et-en)]+ (2, where Et-en is Et(H)NCH2CH2NH2). The structures of the separated RRu*RN* and SRu*RN* diastereomers of 2 were determined by x-ray crystallography; their slow interconversion in water (t(1/2) approximately 2 h, 298 K, pH 6.2) was observed by NMR spectroscopy. For 2 and 3 the RRu*RN* configurations are more stable than SRu*RN* (73:27). X-ray and NMR studies showed that reactions of 2 and 3 with 9-ethylguanine gave rise selectively to SRu*RN* diastereomers. Dynamic chiral recognition of guanine can lead to high diastereoselectivity of DNA binding. The dinuclear complex 3 induced a large unwinding (31 degrees) of plasmid DNA, twice that of mononuclear 2 (14 degrees), and effectively inhibited DNA-directed RNA synthesis in vitro. This dinuclear complex gave rise to interstrand cross-links on a 213-bp plasmid fragment with efficiency similar to bifunctional cisplatin, and to 1,3-GG interstrand and 1,2-GG and 1,3-GTG intrastrand cross-links on site-specifically ruthenated 20-mers. Complex 3 blocked intercalation of ethidium considerably more than mononuclear 2. The concept of induced-fit recognition of DNA by organometallic complexes containing dynamic stereogenic centers via dynamic epimerization, intercalation, and cross-linking may be useful in the design of anticancer drugs.

Platinum-based anticancer agents: innovative design strategies and biological perspectives

The impact of cisplatin on cancer chemotherapy cannot be denied. Over the past 20 years, much effort has been dedicated to discover new platinum-based anticancer agents that are superior to cisplatin or its analogue, carboplatin. Most structural modifications are based on changing one or both of the ligand types coordinated to platinum. Altering the leaving group can influence tissue and intracellular distribution of the drug, whereas the carrier ligand usually determines the structure of adducts formed with DNA. DNA-Pt adducts produced by cisplatin and many of its classical analogues are almost identical, and would explain their similar patterns of tumor sensitivity and susceptibility to resistance. Recently some highly innovative design strategies have emerged, aimed at overcoming platinum resistance and/or to introduce novel mechanisms of antitumor action. Platinum compounds bearing the 1,2-diaminocyclohexane carrier ligand; and those of multinuclear Pt complexes giving rise to radically different DNA-Pt adducts, have resulted in novel anticancer agents capable of circumventing cisplatin resistance. Other strategies have focused on integrating biologically active ligands with platinum moieties intended to selectively localizing the anticancer properties. With the rapid advance in molecular biology, combined with innovation, it is possible new Pt-based anticancer agents will materialize in the near future.

Tumour-inhibiting platinum complexes--state of the art and future perspectives

Thirty years after the onset of the first clinical studies with cisplatin, the development of antineoplastic platinum drugs continues to be a productive field of research. This article reviews the current preclinical and clinical status, including a discussion of the molecular basis for the activity of the parent drug cisplatin and platinum drugs of the second and third generation, in particular their interaction with DNA. Further emphasis is laid on the development of third generation platinum drugs with activity in cisplatin-resistant tumours, particularly on chelates containing 1,2-diaminocyclohexane (DACH) and on the promising and more recently evolving field of non-classic ( trans- and multinuclear) platinum complexes. The development of oral platinum drugs and drug targeting strategies using liposomes, polymers or low-molecular-weight carriers in order to improve the therapeutic index of platinum chemotherapy are also covered.

High nuclearity nickel compounds with three, four or five metal atoms showing antibacterial activity

The effect on DNA and the antibacterial activity of a series of high nuclearity nickel compounds with three, four and five metal atoms were examined. The compounds have a mixed ligand composition with salicylhydroxamic acid and di-2-pyridyl-ketonoxime as chelate agents. In the trinuclear compound Ni(3)(shi)(2)(Hpko)(2)(py)(2)(1), two metal ions show a square planar geometry while the third one is in an octahedral environment. The compounds with four and five nickel atoms construct metallacrown cores with two distinct connectivities. The tetranuclear vacant metallacrown [12-MC(Ni(II)N(Hshi)2(pko)2)-4](2+) shows the connectivity pattern [-O-Ni-O-N-Ni-N-](2), while the pentanuclear ([Ni(II)][12-MC(Ni(II)N(shi)2(pko)2)-4])(2+) follows the pattern [-Ni-O-N-](4). Two distinct arrangements of the chelates around the ring metal ions were observed; a 6-5-6-5-6-5-6-5 arrangement for the [12-MC(Ni(II)N(Hshi)2(pko)2)-4] core and a 6-6-5-5-6-6-5-5 arrangement for the [12-MC(Ni(II)N(shi)2(pko)2)-4] core. Magnetic variable temperature susceptibility study of the trinuclear compound revealed the presence of one paramagnetic nickel(II) ion with strong crystal field dependence, with D=5.0(4) cm(-1), g(xy)=2.7(3) and g(z)=2.3(3). The effect of the synthesized Ni(II) complexes on the integrity and electrophoretic mobility of nucleic acids was examined. Only compounds 2, 3 and 4 altered the mobility of pDNA, forming high molecular weight concatamers at low concentrations or precipitates at higher concentrations. Antibacterial activity screening of the above compounds suggests that nickel compounds 2, 3 and 4 were the most active and can act as potent antibacterial agents.

Apoptosis and growth arrest induced by platinum compounds in U2-OS cells reflect a specific DNA damage recognition associated with a different p53-mediated response

Mononuclear and multinuclear platinum complexes are known to induce distinct types of DNA lesions and exhibit different profiles of antitumor activity, in relation to p53 mutational status. In this study, we investigated the cellular effects of exposure to two platinum compounds (cisplatin and the multinuclear platinum complex BBR 3464), in the osteosarcoma cell line, U2-OS, carrying the wild-type p53 gene and capable of undergoing apoptosis or cell cycle arrest in response to diverse genotoxic stresses. In spite of the ability of both compounds to up-regulate p53 at cytotoxic concentrations, exposure to BBR 3464 resulted in cell cycle arrest but only cisplatin was capable of inducing significant levels of apoptosis and phosphorylation at the Ser15 residue of p53. The cisplatin-induced protein phosphorylation, not detectable in cells treated with BBR 3464, was associated with RPA phosphorylation, a specific up-regulation of Bax and down-regulation of p21(WAF1). Cells treated with BBR 3464 displayed a different cellular response with evidence of cytostasis associated with a high induction of p21(WAF1). The regulation of p21(WAF1) after cisplatin or BBR 3464 exposure required a p53 signal, as documented using stable transfectants expressing a dominant-negative form of p53 (175(his)). Taken together, these results indicate that cellular response to different genotoxic lesions (i.e. apoptosis or growth arrest) is associated with a specific recognition of DNA damage and a different p53-mediated signaling pathway. Multinuclear platinum complexes could be regarded as useful tools for investigating the p53-mediated process of cell cycle arrest in response to DNA damage.