Lectin conjugates as biospecific contrast agents for MRI. Coupling of Lycopersicon esculentum agglutinin to linear water-soluble DTPA-loaded oligomers.

Magnetic resonance imaging (MRI) requires synthesis of contrast media bearing targeting groups and numerous gadolinium chelating groups generating high relaxivity. This paper explores the results of linking the gadolinium chelates to the targeting group, a protein molecule, via various types of linkers. Polycondensates of diethylenetriaminepentaacetic acid (DTPA) with either diols or diamines were synthesised and coupled to the targeting group, a lectin (Lycopersicon esculentum agglutinin, tomato lectin) which binds with high affinity to specific oligosaccharide configurations in the endothelial glycocalyx. The polycondensates bear up to four carboxylic groups per constitutive unit. Gd-chelate bonds are created through dative interactions with the unshared pair of electrons on each oxygen and nitrogen atom on DTPA. This is mandatory for complexation of Gd(III) and avoidance of the severe toxicity of free gadolinium ions. The polymer-DTPA compounds were characterised by (1)H NMR and mass spectrometry. The final lectin-DTPA-polycondensate conjugates were purified by fast protein liquid chromatography (FPLC). The capacity for specific binding was assessed, and the MRI properties were examined in order to evaluate the use of these oligomers as components of selective perfusional contrast agents.

Redox behavior of tumor-inhibiting ruthenium(III) complexes and effects of physiological reductants on their binding to GMP.

Biotransformation of ruthenium(III) anticancer complexes as hypothesized in the activation-by-reduction theory is the central topic of the present paper. The redox behavior of tetrachlorobis(azole)ruthenate(III)-type complexes was studied by NMR spectroscopy and square wave voltammetry. The influence of reducing agents on the binding behavior toward the DNA-modeling nucleotide GMP was determined by capillary electrophoresis, accompanied by identification of arising peaks by online coupling to electrospray ionization mass spectrometry. The determination of redox potentials revealed that the biologically relevant reductants ascorbic acid and glutathione are capable of reducing the studied Ru(III) complexes under physiological conditions. Characteristic differences in reduction kinetics dependent on the pH value can be explained by higher reduction strength of ascorbic acid and glutathione at higher pH compared to the pH-independent redox response of ruthenium(III) complexes. Binding behavior of (H2ind)[trans-RuCl4(Hind)2] (Hind = 1H-indazole) toward GMP was found to be increased upon addition of two equivalents of glutathione but not of ascorbic acid. In contrast, only a minor influence on the GMP-binding under reductive conditions was found for (H2im)[trans-RuCl4(Him)2] (KP418, Him = 1H-imidazole).

Tumour-inhibiting platinum(II) complexes with aminoalcohol ligands: biologically important transformations studied by micellar electrokinetic chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry.

(SP-4-2)-Bis[(R)-(-)-2-aminobutanol-kappaN]dichloroplatinum(II) and (SP-4-2)-bis[(R)-(-)-2-aminobutanolato-kappa2N,O]platinum(II) are promising cytotoxic agents exhibiting a strongly pH-dependent rate of reaction with the DNA-modeling nucleotide guanosine 5'-monophosphate (GMP). This potential mode-of-action binding, directly correlating with cytotoxicity, is influenced by the intramolecular chelation of bifunctional aminoalcohol ligands which was examined by means of micellar electrokinetic chromatography (MEKC) and nuclear magnetic resonance (NMR). While NMR clearly proves the existence of equilibrium between the ring-opened and ring-closed species, no such transformation was observed under MEKC conditions. In a kinetic study performed by MEKC, the half-lives of GMP bound to the platinum complexes were determined and compared to the kinetic data acquired by capillary zone electrophoresis. An appreciable increase in binding in the presence of sodium dodecyl sulfate (SDS) micelles was explained in terms of activation of (SP-4-2)-bis[(R)-(-)-2-aminobutanol-kappaN]dichloroplatinum(II). This apparently takes place due to the shifting of the equilibrium towards the ring-opened species, induced by adduct formation between SDS and the platinum complex that was confirmed by electrospray ionization mass spectrometry.

Tumor-inhibiting platinum(II) complexes with aminoalcohol ligands: comparison of the mode of action by capillary electrophoresis and electrospray ionization-mass spectrometry.

Capillary electrophoresis (CE) was used as an assay for studying the interaction of (SP-4-2)-bis[(R)-(-)-2-aminobutanol)dichloroplatinum(II) (1) and (SP-4-2)bis(4-aminobutanol)dichloroplatinum(II) (2) with guanosine 5'-monophosphate (GMP). CE kinetic measurements carried out at two physiological pH levels indicated that upon increasing the pH, 1 showed an appreciable change in binding behavior, with the rate of binding increased for more than 10 times as expressed by apparent half-life values of GMP (6.1 and 62.2 h at pH 6.0 and 7.4, respectively). The rate of GMP binding for 2 remained comparatively less affected by pH (half-lives of 8.5 and 10.6 h, respectively). Regardless of the nature of platinum complex and pH, the reaction with GMP tends to be decelerated at increased chloride concentrations in solution, this effect being particularly pronounced when changing from 4 mM (intracellular level) to 100 mM (extracellular level). The kinetic differences of platinum complexes were characterized in terms of the respective GMP-adducts structure, independently identified by means of off-line electrospray ionization-mass spectrometry. Also addressed was the interpretation of binding behavior as based on the structural features of the intact complexes, namely differing inclination to intramolecular chelation.