J. Grant Collins

Multi-nuclear platinum complexes as anti-cancer drugs

Abstract This article reviews investigations over the last 15 years into the development of multi-nuclear platinum complexes as anti-cancer agents, with the purpose of providing an insight into the benefits of, and reasons for, their success. The cytotoxicity of multi-nuclear platinum complexes is compared, as is their ability to overcome both natural and acquired drug resistance. Possible structure-activity relationships are outlined. While the multi-nuclear platinum complexes exhibit excellent anti-cancer activity, the associated toxicity could limit their clinical use. Given that these complexes derive their activity from the novel adducts they form with DNA, three important aspects of their binding are discussed; their DNA pre-association, the DNA adducts formed and the DNA conformational changes induced.

DNA intercalators in cancer therapy : organic and inorganic drugs and their spectroscopic tools of analysis

Since the discovery of the DNA intercalation process by Lerman in 1961 thousands of organic, inorganic octahedral (particularly ruthenium(II) and rhodium(III)) and square-planar (particularly platinum(II)) compounds have been developed as potential anticancer agents and diagnostic agents. The design and synthesis of new drugs is focused on bis-intercalators which have two intercalating groups linked via a variety of ligands, and synergistic drugs, which combine the anticancer properties of intercalation with other functionalities, such as covalent binding or boron-cages (for radiation therapy). Advances in spectroscopic techniques mean that the process of DNA intercalation can be examined in far greater detail than ever before, yielding important information on structure-activity relationships. In this review we examine the history and development of DNA intercalators as anticancer agents and advances in the analysis of DNA-drug interactions.

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.

Structure of a marsupial-milk trisaccharide.

Abstract A trisaccharide, which is a major carbohydrate component of the milk of the tammar wallaby and the grey kangaroo, has been identified by chemical, enzymic, g.l.c.-m.s., and n.m.r. methods as O-β- d -galactopyranosyl-(1→3)-O-β- d -galactopyranosyl-(1→4)- d -glucose (3′-galactosyl-lactose).

Sorbitol production by Zymomonas mobilis

SummaryHigh resolution 13C Nuclear Magnetic Resonance (NMR) spectroscopy has been employed to determine the chemical composition of the unknown major products in a sucrose or fructose plus glucose fermentation to ethanol by the bacterium Zymmonas mobilis. When grown on these sugars Z.mobilis was found to produce significant amounts of sorbitol, up to 43 g·l-1 for strain ZM31 when grown on 250 g·l-1 sucrose.The production of sorbitol and decrease of glucose, fructose, or sucrose was followed throughout batch fermentations by NMR and HPLC. Sorbitol was shown to be derived only from fructose by [14C]-feeding experiments. Additionally 31P NMR spectroscopy was utilized to determine the concentrations of both glucose 6-phosphate and fructose 6-phosphate relative to their respective concentrations in Z.mobilis cells fermenting glucose or fructose alone.It is suggested that free glucose inside the cell inhibits fructokinase. Free intracellular fructose may then be reduced to sorbitol via a dehydrogenase type enzyme. Attempts to grow Z.mobilis on sorbitol were unsuccessful, as were experiments to induce growth via mutagenesis.

Mechanism of Cytotoxicity and Cellular Uptake of Lipophilic Inert Dinuclear Polypyridylruthenium(II) Complexes

The accumulation, uptake mechanism, cytotoxicity, cellular localisation of—and mode of cell death induced by—dinuclear ruthenium(II) complexes ΔΔ/ΛΛ‐[{Ru(phen)2}2{μ‐bbn}]4+ (Rubbn), where phen is 1,10‐phenanthroline, bbn is bis[4(4′‐methyl‐2,2′‐bipyridyl)]‐1,n‐alkane (n=2, 5, 7, 10, 12 or 16), and the corresponding mononuclear complexes containing the bbn ligands, were studied in L1210 murine leukaemia cells. Cytotoxicity increased with linker chain length, and the ΔΔ‐Rubb16 complex displayed the highest cytotoxicity of the series, with an IC50 value of 5 μM, similar to that of carboplatin in the L1210 murine leukaemia cell line. Confocal microscopy and flow cytometry studies indicated that the complexes accumulate in the mitochondria of L1210 cells, with the magnitude of cellular uptake and accumulation increasing with linking chain length in the bbn bridge of the metal complex. ΔΔ‐Rubb16 entered the L1210 cells by passive diffusion (with a minor contribution from protein‐mediated active transport), inducing cell death via apoptosis. Additionally, metal‐complex uptake in leukaemia cells was approximately 16‐times that observed in healthy B cells highlighting that the bbn series of complexes may have potential as selective anticancer drugs.

Cucurbituril binding of trans-[{PtCl(NH3)2}2(µ-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.

In vitro susceptibility and cellular uptake for a new class of antimicrobial agents: dinuclear ruthenium(II) complexes

OBJECTIVES To determine the in vitro susceptibility and cellular uptake for a series of dinuclear ruthenium(II) complexes [{Ru(phen)(2)}(2){μ-bb(n)}](4+) (Rubb(n)), and the mononuclear complexes [Ru(Me(4)phen)(3)](2+) and [Ru(phen)(2)(bb(7))](2+) against Staphylococcus aureus, methicillin-resistant S. aureus, Escherichia coli and Pseudomonas aeruginosa. METHODS The in vitro susceptibility was determined by MIC and MBC assays, and time-kill curve experiments, while the cellular uptake was evaluated by monitoring the fluorescence of the complexes remaining in the supernatant of the cultures after incubation for various periods of time, flow cytometry and confocal microscopy. RESULTS Rubb(12) and Rubb(16) are highly active, with MIC and MBC values of 1-2 mg/L (0.5-1 μM) for the two Gram-positive strains and 2-4 mg/L for E. coli and 16-32 mg/L for P. aeruginosa. Rubb(16) showed equal or better activity (on a molar basis) to gentamicin and ampicillin for all strains apart from P. aeruginosa. The relative MBC to MIC values indicated that Rubb(12) and Rubb(16) are bactericidal, and from the time-kill curve experiments, the ruthenium complexes can kill the bacteria within 2-6 h. The cellular uptake studies demonstrated that the observed antimicrobial activity is correlated with the level of uptake of the ruthenium complexes. Confocal microscopy confirmed the cellular uptake of Rubb(16), and tentatively suggested that the ruthenium complex is localized in the bacteria. CONCLUSIONS The inert dinuclear ruthenium(II) complexes Rubb(12) and Rubb(16) have potential as new antimicrobial agents. The structure of the dinuclear ruthenium complexes can be readily further modified in order to increase their selectivity for bacteria over human cells.

Inclusion complexes of the antitumour metallocenes Cp2MCl2 (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.

Enhanced cytotoxicity of benzimidazole carbamate derivatives and solubilisation by encapsulation in cucurbit[n]uril

The albendazole derivatives (2-methoxyethyl) 5-propylthio-1H-benzimidazole-2-yl carbamate (MEABZ), N1-(2-methoxyethoxycarbonyl)-2-amino-5-propylthiobenzimidazole and N1-(2-methoxyethoxycarbonyl)-2-amino-6-propylthiobenzimidazole (MEABZ isomers A and B) and (2-hydroxyethyl) 5-propylthio-1H-benzimidazole-2-yl carbamate (HEABZ) have been synthesised. The cytotoxicity of these compounds was evaluated against a human colorectal cancer cell line (HT-29) and a human prostate cancer cell line (PC-3). The results demonstrate MEABZ, a new benzimidazole, is up to ten times more cytotoxic than the parent drug albendazole, whereas the MEABZ isomers A and B and HEABZ show no activity. A comparison of the cytotoxicity of these compounds, relative to ABZ, provides structure-activity data for this important class of anticancer agents. The aqueous solubilities of MEABZ encapsulated in Q[n] have been determined by (1)H NMR spectroscopy. The aqueous solubility of MEABZ at a physiologically relevant pH increased by 1200-fold by encapsulation in Q[8], from 8 microM to 9.4 mM, while Q[6,7] encapsulation substantially increased the solubility to more than 2 mM. Encapsulation in Q[7] and Q[8] induced significant upfield shifts for the MEABZ propyl and benzimidazole resonances. The upfield shifts indicate that the propyl and benzimidazole protons are located within the Q[7] and Q[8] cavity upon encapsulation. By contrast, encapsulation in Q[6] induced large upfield shifts for the (1)H resonances from the carbamate functional group, indicating that MEABZ associates with Q[6] at its portals, with only the carbamate group binding within the cavity.