Effects of cytotoxic cis- and trans-diammine monochlorido platinum(II) complexes on selenium-dependent redox enzymes and DNA.

Here we present the preparation of 14 pairs of cis- and trans-diammine monochlorido platinum(II) complexes, coordinated to heterocycles (i.e., imidazole, 2-methylimidazole and pyrazole) and linked to various acylhydrazones, which were designed as potential inhibitors of the selenium-dependent enzymes glutathione peroxidase 1 (GPx-1) and thioredoxin reductase 1 (TrxR-1). However, no inhibition of bovine GPx-1 and only weak inhibition of murine TrxR-1 was observed in in vitro assays. Nonetheless, the cis configured diammine monochlorido Pt(II) complexes exhibited cytotoxic and apoptotic properties on various human cancer cell lines, whereas the trans configured complexes generally showed weaker potency with a few exceptions. On the other hand, the trans complexes were generally more likely to lack cross-resistance to cisplatin than the cis analogues. Platinum was found bound to the nuclear DNA of cancer cells treated with representative Pt complexes, suggesting that DNA might be a possible target. Thus, detailed in vitro binding experiments with DNA were conducted. Interactions of the compounds with calf thymus DNA were investigated, including Pt binding kinetics, circular dichroism (CD) spectral changes, changes in DNA melting temperatures, unwinding of supercoiled plasmids and ethidium bromide displacement in DNA. The CD results indicate that the most active cis configured pyrazole-derived complex causes unique structural changes in the DNA compared to the other complexes as well as to those caused by cisplatin, suggesting a denaturation of the DNA structure. This may be important for the antiproliferative activity of this compound in the cancer cells.

Microwave-assisted synthesis and evaluation of acylhydrazones as potential inhibitors of bovine glutathione peroxidase.

Glutathione peroxidases (GPx) were the first selenocysteine enzymes identified. They play critical roles in cellular defense to excessH(2)O(2) and lipid peroxides, with GPx1 contributing the most cellular activity. In the treatment of cancer, for example, in lymphomas and leukaemias, evidence has been accumulating that up-regulation of the GPx system may serve to protect cancer cells from oxidative stress caused by anticancer drugs. We hypothesize that small molecules which block GPx1 could help overcome acquired resistance to anticancer drugs by raising the level of oxidative stress in cancer cells. Our previous efforts identified an acylhydrazone as a lead structure for the inhibition of GPx1. Now we report the microwave-supported synthesis and inhibitory screening of a series of 78 analogs. The special conformational isomerism resulting of the acylhydrazone functionality was investigated by the analysis of distinct NMR data and crystal structures, indicating that conformers at the C(O)-N hydrazide bond are responsible for this phenomena. Though some of the analogs showed poor aqueous solubility and could not be tested in the enzyme assay, the combinatorial approach led to the identification of a closely related isomer of the lead compound with increased inhibitory activity: N'-[1-(4-hydroxyphenyl)ethylidene]-2-(1H-imidazol-1-yl)acetohydrazide. This success supports the idea that novel GPx1 inhibitors can be developed by drug-design methods and paves the way for a new class of GPx1 inhibitors.

Evaluation of (S)- and (R)-misonidazole as GPX inhibitors: synthesis, characterization including circular dichroism and in vitro testing on bovine GPx-1.

Racemic misonidazole, a radiosensitizer formally used in radiation therapy of cancer and to date still applied, was once reported to exhibit strong inhibitory effects on mouse glutathione peroxidases (GPX). This appeared to qualify misonidazole as a lead structure for the development of novel GPX inhibitors to cause oxidative stress in chemotherapy-resistant tumors. A unique feature of misonidazole as an inhibitor of GPX is the absence of a thiol functionality. Therefore, it was expected to selectively target inhibition devoid of promiscuous interactions with cations and sulfhydryl groups. We synthesized the isomers of misonidazole and analyzed the ability of chiroptical high-performance liquid chromatography (HPLC) to identify the particular enantiomers. Due to the chiral pool synthesis, the assignment of the correct configuration could be verified. Finally, we evaluated both isomers for their inhibitory activities on bovine erythrocyte GPx-1, which is 87% homologous to the human enzyme. Despite the previously reported inhibition of racemic misonidazole on the less homologous mouse GPx-1, we did not find any significant inhibitory activity on the bovine enzyme for either isomer. Though misonidazole appears unlikely to be an inhibitor of human GPx-1 activity, we still spotlight misonidazole as a promising fragment-like lead structure in general.

Identification of a glutathione peroxidase inhibitor that reverses resistance to anticancer drugs in human B-cell lymphoma cell lines.

Cancer cells isolated from two patients with malignant non-Hodgkin B-cell lymphomas that became resistant to chemotherapy during clinical treatment were made ≥fourfold resistant in culture to anticancer drugs, that is cisplatin, etoposide, methotrexate and bortezomib. Because most resistant lines showed significantly increased expression of the anti-oxidative enzyme glutathione peroxidase 1 (GPx1), GPx1 was investigated as a target for inhibitor development. Virtual screening of a library of diverse structures by docking them to the active site of the X-ray crystal structure of bovine GPx1 uncovered compounds that might block the enzyme. An enzyme assay confirmed an acylhydrazone heterocycle (3) with GPx inhibitory activity. Combinations of 3 with the anticancer drugs listed above led to reversal of resistance in the lymphoma cell lines.

Modifiers of von Willebrand factor identified by natural variation in inbred strains of mice.

Type 1 von Willebrand disease (VWD) is the most common inherited human bleeding disorder. However, diagnosis is complicated by incomplete penetrance and variable expressivity, as well as wide variation in von Willebrand factor (VWF) levels among the normal population. Previous work has exploited the highly variable plasma VWF levels among inbred strains of mice to identify 2 major regulators, Mvwf1 and Mvwf2 (modifier of VWF). Mvwf1 is a glycosyltransferase and Mvwf2 is a natural variant in Vwf that alters biosynthesis. We report the identification of an additional alteration at the Vwf locus (Mvwf5), as well as 2 loci unlinked to Vwf (Mvwf6-7) using a backcross approach with the inbred mouse strains WSB/EiJ and C57BL/6J. Through positional cloning, we show that Mvwf5 is a cis-regulatory variant that alters Vwf mRNA expression. A similar mechanism could potentially explain a significant percentage of human VWD cases, especially those with no detectable mutation in the VWF coding sequence. Mvwf6 displays conservation of synteny with potential VWF modifier loci identified in human pedigrees, suggesting that its ortholog may modify VWF in human populations.

Enhanced VWF biosynthesis and elevated plasma VWF due to a natural variant in the murine Vwf gene.

Both genetic and environmental influences contribute to the wide variation in plasma von Willebrand factor (VWF) levels observed in humans. Inbred mouse strains also have highly variable plasma VWF levels, providing a convenient model in which to study genetic modifiers of VWF. Previously, we identified a major modifier of VWF levels in the mouse (Mvwf1) as a regulatory mutation in murine Galgt2. We now report the identification of an additional murine VWF modifier (Mvwf2). Mvwf2 accounts for approximately 16% of the 8-fold plasma VWF variation (or approximately 25% of the genetic variation) observed between the A/J and CASA/RkJ strains and maps to the murine Vwf gene itself. Twenty SNPs were identified within the coding regions of the A/J and CASA/RkJ Vwf alleles, and in vitro analysis of recombinant VWF demonstrated that a single SNP (+7970G>A) and the associated nonsynonymous amino acid change (R2657Q) confers a significant increase in VWF biosynthesis from the CASA/RkJ Vwf allele. This change appears to represent a unique gain of function that likely explains the mechanism of Mvwf2 in vivo. The identification of a natural Vwf gene variant among inbred mice affecting biosynthesis suggests that similar genetic variation may contribute to the wide range of VWF levels observed in humans.