A ternary supramolecular system containing a boronated DNA-metallointercalator, ß-cyclodextrin and the hexanucleotide d(GTCGAC)2.

Solution NMR studies of the interaction between the hexanucleotide d(GTCGAC)(2), ß-cyclodextrin and a boronated 2,2':6',2''-terpyridineplatinum(II) complex containing 1,12-dicarba-closo-dodecaborane(12) (1,12-closo-carborane) reveal the formation of a remarkable ternary supramolecular system in which the terpyridine ligand is intercalated between the C(3) and G(4) bases, whilst the closo-carborane moiety is encapsulated by the cyclic sugar.

Oligonuclear polypyridylruthenium(II) complexes incorporating flexible polar and non-polar bridges: synthesis, DNA-binding and cytotoxicity.

The paper reports the synthesis and characterisation of a series of flexible di-bidentate bridging ligands in which two 4-methyl-2,2'-bipyridine groups are linked at the 4'-position by polymethylene (bb(n)), linear polyether (bbO(n)) or linear alkylamine (bbN(n)) chains of varying length (n). The enantiomers (ΔΔ/ΛΛ) of the rac forms of the ruthenium(ii) dinuclear complexes incorporating these ligands -i.e. [{Ru(phen)(2)}(2)(µ-BL)](4+) (phen = 1,10-phenanthroline; BL = bb(n), bbO(n) or bbN(n)) - have been isolated by reaction of Δ- or Λ-[Ru(phen)(2)(py)(2)](2+) (py = pyridine) with the respective bridging ligands. Mononuclear species - in which only one of the bidentate moieties of the bridging ligand is coordinated - have also been isolated, as well as trinuclear and tetranuclear species involving the bb(7) bridge. Fluorescence displacement studies of the DNA-binding of the dinuclear complexes containing the bbO(n) and bbN(n) bridges generally revealed a lower affinity than their bb(n) analogues for an oligonucleotide containing a single bulge site; the mononuclear complexes showed a lower affinity - and the trinuclear and tetranuclear complexes a higher affinity - than the dinuclear species, revealing an interesting interplay of lipophilicity, electrostatics and size in the complex/nucleic acid interaction. Cytotoxicity studies of these complexes against a murine leukaemia cell line revealed that the presence of the polyether or polyamine links in the chain lowered the cytotoxicity compared with their polymethylene analogues, and that the bb(7)-bridged trinuclear and tetranuclear complexes showed considerably enhanced cytotoxicity compared with the dinuclear Rubb(7) analogue.

New anthracenedione derivatives with improved biological activity by virtue of stable drug-DNA adduct formation.

Mitoxantrone is an anticancer agent that acts as a topoisomerase II poison, however, it can also be activated by formaldehyde to form DNA adducts. Pixantrone, a 2-aza-anthracenedione with terminal primary amino groups in its side chains, forms formaldehyde-mediated adducts with DNA more efficiently than mitoxantrone. Molecular modeling studies indicated that extension of the "linker" region of anthracenedione side arms would allow the terminal primary amino greater flexibility and thus access to the guanine residues on the opposite DNA strand. New derivatives based on the pixantrone and mitoxantrone backbones were synthesized, and these incorporated primary amino groups as well as extended side chains. The stability of DNA adducts increased with increasing side chain length of the derivatives. A mitoxantrone derivative bearing extended side chains (7) formed the most stable adducts with ∼100-fold enhanced stability compared to mitoxantrone. This finding is of great interest because long-lived drug-DNA adducts are expected to perturb DNA-dependent functions at all stages of the cell cycle.

DNA binding by pixantrone.

The binding of the anticancer drug pixantrone (6,9-bis[(2-aminoethyl)amino]benzo[g]isoquinoline-5,10-dione dimaleate) to the octanucleotide duplexes d(ACGATCGT)(2) and the corresponding C-5 methylated cytosine ((5Me)C) analogue d(A(5Me)CGAT(5Me)CGT)(2) has been studied by NMR spectroscopy and molecular modelling. The large upfield shifts observed for the resonances from the aromatic protons of pixantrone upon addition to either d(ACGATCGT)(2) or the corresponding (5Me)C analogue is consistent with the drug binding the octanucleotides by intercalation. The selective reduction in the sequential NOEs between the C(2)-G(3) and C(6)-G(7) nucleotides in NOESY spectra of either octanucleotide with added pixantrone confirms the intercalative binding mechanism. Strong NOEs from the side-chain ethylene protons of pixantrone to the H5 protons and the 5-CH(3) protons of the C(2) and C(6) residues of d(ACGATCGT)(2) and d(A(5Me)CGAT(5Me)CGT)(2), respectively, indicate that pixantrone predominantly intercalates from the DNA major groove at the 5'-CG and 5'-(5Me)CG sites. Simple molecular models based on the conclusions from the NMR experiments indicated that the (5Me)C groups do not represent a steric barrier to intercalation from the major groove. However, the observation of weak NOEs from the ethylene protons of pixantrone to a variety of minor groove protons from either octanucleotide suggests that the drug can also associate in the minor groove.

Electrochemical method applicable to treatment of wastewater from nitrotriazolone production.

Laboratory studies show that electrochemical oxidation of acidic nitrotriazolone (NTO) solutions results in complete mineralization, with ammonium nitrate as the only solution product Other products (carbon dioxide, carbon monoxide, and nitrous oxide) are eliminated as gases from the working electrode. No additional chemical loading is required for the process, and electricity isthe only input The process maytherefore represent a cost-effective and environmentally friendly method of remediation for wastewater from NTO manufacture. Electrolyses were carried out at different applied voltages and at NTO concentrations of 0.01 and 0.05 mol/L, and the results indicate that a higher oxidation rate results in a greater charge passed per mole of NTO oxidized and increased production of nitrous oxide. Mechanisms are proposed on the basis of competing oxidative pathways that account for all products formed and the total charge passed during the reaction.

Solubilisation and cytotoxicity of albendazole encapsulated in cucurbit[n]uril.

The aqueous solubilities of albendazole encapsulated in cucurbit[6, 7 and 8]urils (Q[6], Q[7] and Q[8]) have been determined by (1)H NMR spectroscopy, and the effect of encapsulation on their cytotoxicities evaluated. Encapsulation in Q[6] and Q[7] increased the aqueous solubility of albendazole by 2000-fold, from 3 microM to 6 mM at pH 6.6, while Q[8]-encapsulation increased the solubility to over 2 mM. Encapsulation in Q[7] and Q[8] induced significant upfield shifts for the albendazole propyl and benzimidazole resonances, compared to those observed for Q[6]-binding and what would normally be expected for the respective functional groups. The upfield shifts indicate that the albendazole propyl and benzimidazole protons are located within the Q[7] and Q[8] cavity upon encapsulation. Alternatively, encapsulation in Q[6] only induced a large upfield shift for the albendazole carbamate methyl resonance, indicating that the drug associates with Q[6] at its portals, with only the carbamate group within the cavity. Simple molecular models based on the observed relative changes in chemical shift could be constructed that were consistent with the conclusions from the NMR experiments. Cytotoxicity assays against human colorectal cells (HT-29), human ovarian cancer cells (1A9) and the human T-cell acute lymphoblastic leukaemia cells (CEM) indicated that encapsulation in Q[7] did not significantly reduce the in vitro anti-cancer activity of albendazole.

Binding of a dinuclear ruthenium(ii) complex to the TAR region of the HIV-AIDS viral RNA.

Molecular modelling has identified a new RNA conformational feature created by the insertion of bulge residues into duplex regions that may act as a recognition site for small molecule binding, in particular for inert dinuclear ruthenium complexes.

Inclusion complexes of the antitumour metallocenes Cp(2)MCl(2) (M = Mo, Ti) with cucurbit[n]urils.

The encapsulation of the aquated forms of molybdocene dichloride and titanocene dichloride by cucurbit[n]uril (Q[n], where n = 7 and 8) at different pD values has been studied by (1)H NMR spectroscopy and molecular modelling. (1)H NMR titration experiments indicate that both metallocenes form 1 : 1 host-guest complexes with both Q[7] and Q[8]. In these complexes, both the cyclopentadienyl ligands and metal centre are positioned deep within the cucurbituril cavity. In vitro cell proliferation studies using the cancer cell lines MCF-7 and 2008 showed that the encapsulated molybdocene complex was more active than the corresponding free metallocene, with GI(50) values of 210 and 400 muM respectively. However, unexpectedly the encapsulation of Cp(2)MoCl(2(aq))at pD 7 catalysed significant degradation of the cucurbituril framework in the presence of oxygen. Encapsulation of Cp(2)TiCl(2(aq)) by Q[7] greatly slowed the protonolysis of the cyclopentadienyl ligands in aqueous phosphate buffer (pD 7), while encapsulation in Q[8] only slightly retarded the hydrolytic degradation of the metallocene.

Dinuclear ruthenium(ii) complexes with flexible bridges as non-duplex DNA binding agents.

The stereoisomers of a series of dinuclear ruthenium(ii) complexes [{Ru(phen)(2)}(2)(micro-BL)](4+) (phen = 1,10-phenanthroline) with flexible bridging ligands (BL) bb2 {1,2-bis[4(4'-methyl-2,2'-bipyridyl)]ethane}, bb5 {1,5-bis[4(4'-methyl-2,2'-bipyridyl)]pentane}, bb7 {1,7-bis[4(4'-methyl-2,2'-bipyridyl)]heptane}, and bb10 {1,10-bis[4(4'-methyl-2,2'-bipyridyl)]decane} have been synthesised. Their binding to a control dodecanucleotide, d(CCGGAATTCCGG)(2), and a tridecanucleotide, d(CCGAGAATTCCGG)(2), which contains a single adenine bulge have been studied using fluorescence displacement assays involving intercalating and groove-binding dyes, equilibrium dialysis and binding affinity chromatography. The fluorescence intercalator displacement (FID) assay indicated that LambdaLambda-[{Ru(phen)(2)}(2)(micro-bb7)](4+) had the greatest binding affinity with all the oligonucleotides, whereas an analogous fluorescence technique using a minor-groove binding dye, equilibrium dialysis and affinity binding chromatography showed that DeltaDelta-[{Ru(phen)(2)}(2)(micro-bb7)](4+) had the strongest binding. An (1)H NMR study of the binding of the DeltaDelta-enantiomer of [{Ru(phen)(2)}(2)(micro-bb7)](4+) to d(CCGAGAATTCCGG)(2) confirmed the selectivity of the metal complex for the bulge site and provided the basis for an energy-minimised binding model of the dinuclear ruthenium complex with the single adenine bulge containing trinucleotide. The binding model demonstrated the ability of the flexibly-linked complex to follow the curvature of the DNA minor groove.

The effect of ancillary ligand chirality and phenanthroline functional group substitution on the cytotoxicity of platinum(II)-based metallointercalators.

Fifteen platinum(II)-based metallointercalators have been synthesised that utilise substituted 1,10-phenanthroline (phen) ligands, including 5-chloro-1,10-phenanthroline (5-Cl-phen), 5-methyl-1,10-phenanthroline (5-CH3-phen), 5-amino-1,10-phenanthroline (5-NH2-phen), 5-nitro-1,10-phenanthroline (5-NO2-phen) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), and achiral ethylenediamine (en) and the chiral ancillary ligands 1S,2S-diaminocyclohexane (S,S-dach) and 1R,2R-diaminocyclohexane (R,R-dach). Their cytotoxicity in the L1210 murine leukaemia cell line was determined using growth inhibition assays. The most cytotoxic metal complexes are those that contain S,S-dach ancillary ligands and 5-CH3-phen intercalating ligands. One metallointercalator [Pt(5-CH3-phen)(S,S-dach)]Cl2 (5MESS), displays a 5-10-fold increase in cytotoxicity compared to the clinical agent cisplatin. From DNA binding experiments there appears to be no significant difference between any of the metal complexes, indicating that neither DNA binding affinity nor the mode of binding/DNA adduct formed is the sole determinant of the cytotoxicity of this family of platinum(II)-based metallointercalators.

Dinuclear ruthenium(II) complexes as potential probes for RNA bulge sites.

1H NMR spectroscopy and molecular modelling have been used to investigate the binding of the DeltaDelta-and LambdaLambda-enantiomers of the dinuclear ruthenium(II) complex [[Ru(Me2bpy)2]2(mu-bpm)]4+ [Me2bpy = 4,4'-dimethyl-2,2'-bipyridine; bpm = 2,2'-bipyrimidine] to an RNA tridecanucleotide duplex containing a single-base bulge [r(CCGAGAAUUCCGG)2]], and the corresponding control dodecanucleotide [r(CCGGAAUUCCGG)2]. Both enantiomers bound the control RNA sequence weakly. From upfield shifts of the metal complex H3 and H3' protons throughout the titration of the control dodecanucleotide with DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+, a binding constant of 1 x 10(3) M(-1) was determined. In NOESY spectra of the control sequence with added DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+, NOEs were only observed to protons from the terminal base-pair residues. No significant changes in chemical shift were observed for either the metal complex or RNA protons upon addition of the LambdaLambda-enantiomer to the control dodecanucleotide. The DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+ complex bound the bulge-containing RNA with a significantly greater affinity (6 x 10(4) M(-1)) than the non-bulge control RNA duplex. Competition binding experiments indicated that the LambdaLambda-isomer bound the tridecanucleotide with similar affinity to the DeltaDelta-enantiomer. Addition of DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+ to the bulge-containing tridecanucleotide induced selective changes in chemical shift for the base H8 and sugar H1' resonances from the adenine bulge residue, and resonances from nucleotide residues adjacent to the bulge site. Intermolecular NOEs observed in NOESY spectra of the tridecanucleotide with added DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+ confirmed the selective binding of the ruthenium complex at the bulge site. Preliminary binding models, consistent with the NMR data, showed that the ruthenium complex could effectively associate in the RNA minor groove at the bulge site.

Cucurbituril binding of trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ and the effect on the reaction with cysteine.

The effect of encapsulation by cucurbiturils Q[7] and Q[8] on the rate of reaction of the anti-cancer dinuclear platinum complex trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ with the model biological nucleophiles glutathione and cysteine has been examined by NMR spectroscopy. It was expected that the octamethylene linking chain would fold inside the cucurbituril host and hence position the reactive platinum centres close to the cucurbituril portals, and thereby, confer resistance to degradation by biological nucleophiles. The upfield shifts of the resonances from the methylene protons in the linking ligand observed in 1H NMR spectra of the platinum complex upon addition of either Q[7] or Q[8] indicate that the cucurbituril is positioned over the linking ligand, with the Pt(II) centres projecting out of the portal. Furthermore, the relative changes in chemical shift of the methylene resonances suggest that the octamethylene linking chain folds within the cucurbituril cavity, particularly in Q[8]. Simple molecular models, based on the observed relative changes in chemical shift, could be constructed that were consistent with the proposed folding of the linking ligand within the cucurbituril cavity. Encapsulation by Q[7] was found to reduce the rate of reaction of the platinum complex with glutathione. Encapsulation by Q[7] and Q[8] was also found to reduce the rate of reaction of the platinum complex with cysteine, with Q[8] slowing the reaction to a greater extent than Q[7], consistent with the inferred encapsulation geometries. Encapsulation of dinuclear platinum complexes within the cucurbituril cavity may provide a novel way of reducing the reactivity and degradation of these promising chemotherapeutic agents with blood plasma proteins.

Selectivity at a three-base bulge site in the DNA binding of DeltaDelta-[{Ru(phen)2} 2(mu-dppm)]4+ [dppm is 4,6-bis(2-pyridyl)pyrimidine; phen is 1,10-phenanthroline].

The binding of the stereoisomers of [{Ru(phen)2}2(mu-bpm)]4+, [{Ru(phen)2}2(mu-dppm)]4+ and [{Ru(phen)2}2(mu-bb)]4+ {phen is 1,10-phenanthroline; bpm is 2,2'-bipyrimidine, dppm is 4,6-bis(2-pyridyl)pyrimidine, bb is 1,2-bis[4-(4'-methyl-2,2'-bipyridyl)]ethane} to an oligonucleotide duplex [d(GCATCGAAAGCTACG).d(CGTAGCCGATGC)] containing a three-base bulge has been studied using a fluorescence intercalator displacement assay. Of the dinuclear ruthenium complexes, the dppm-linked species showed the strongest binding to the oligonucleotide, with the DeltaDelta isomer binding slightly more strongly than the meso isomer and the LambdaLambda isomer exhibiting the weakest binding. In order to determine whether the DeltaDelta-[{Ru(phen)2}2(mu-dppm)]4+ metal complex specifically bound at the three-base bulge site, a 1H NMR study of the binding of the metal complex to the oligonucleotide duplex d(GCATCGAAAGCTACG)*d(CGTAGCCGATGC) was carried out. Although a detailed picture of the metal complex-oligonucleotide association could not be determined from the NMR results owing to the broadening of the resonances from the metal complex and nucleotide residues at the bulge site, the NMR results do indicate that the metal complex specifically binds at the three-base bulge site. The combined results of this study suggest that the dppm-bridged dinuclear ruthenium complexes have considerable potential as probes for the unusual secondary structure obtained by the insertion of a three-base bulge within duplex DNA.

Cucurbit[n]uril binding of platinum anticancer complexes.

The encapsulation of cisplatin by cucurbit[7]uril (Q[7]) and multinuclear platinum complexes linked via a 4,4'-dipyrazolylmethane (dpzm) ligand by Q[7] and cucurbit[8]uril (Q[8]) has been studied by NMR spectroscopy and molecular modelling. The NMR studies suggest that some cisplatin binds in the cucurbituril cavity, while cis-[PtCl(NH3)2(H2O)]+ only binds at the portals. Alternatively, the dpzm-linked multinuclear platinum complexes are quantitatively encapsulated within the cavities of both Q[7] and Q[8]. Upon encapsulation, the non-exchangeable proton resonances of the multinuclear platinum complexes show significant upfield shifts in 1H NMR spectra. The H3/H3* resonances shift upfield by 0.08 to 0.55 ppm, the H5/H5* shift by 0.9 to 1.6 ppm, while the methylene resonances shift by 0.74 to 0.88 ppm. The size of the resonance shift is dependent on the cavity size of the encapsulating cucurbituril, with Q[7] encapsulation producing larger shifts than Q[8]. The upfield shifts of the dpzm resonances observed upon cucurbituril encapsulation indicate that the Q[7] or Q[8] is positioned directly over the dpzm linking ligand. The terminal platinum groups of trans-[{PtCl(NH3)2}2 mu-dpzm]2+ (di-Pt) and trans-[trans-{PtCl(NH3)2}2-trans-{Pt(dpzm)2(NH3)2}]4+ (tri-Pt) provide a barrier to the on and off movement of cucurbituril, resulting in binding kinetics that are slow on the NMR timescale for the metal complex. Although the dpzm ligand has relatively few rotamers, encapsulation by the larger Q[8] resulted in a more compact di-Pt conformation with each platinum centre retracted further into each Q[8] portal. Encapsulation of the hydrolysed forms of di-Pt and tri-Pt is considerably slower than for the corresponding Cl forms, presumably due to the high-energy cost of passing the +2 platinum centres through the cucurbituril portals. The results of this study suggest that cucurbiturils could be suitable hosts for the pharmacological delivery of multinuclear platinum complexes.