Structure-based design of cyclooxygenase-2 selectivity into ketoprofen

We have recently described how to achieve COX-2 selectivity from the non-selective inhibitor indomethacin (1) using a combination of a pharmacophore and computer 3-D models based on the known X-ray crystal structures of cyclooxygenases. In the present study we have focused on the design of COX-2 selective analogues of the NSAID ketoprofen (2). The design is similarly based on the combined use of the previous pharmacophore together with traditional medicinal chemistry techniques motivated by the comparative modeling of the 3-D structures of 2 docked into the COX active sites. The analysis includes use of the program GRID to detect isoenzyme differences near the active site region and is aimed at suggesting modifications of the basic benzophenone frame of the lead compound 2. The resulting series of compounds bearing this central framework is exemplified by the potent and selective COX-2 inhibitor 17 (LM-1669).     

Cyanide bystander effect of the linamarase/linamarin killer-suicide gene therapy system

Background

The killer‐suicide system linamarase/linamarin (lis/lin) uses the plant gene linamarase (β‐glucosidase) to convert the cyanogenic glucoside substrate, linamarin, into glucose and cyanide. We have studied the bystander effect associated with this new system mediated by the production of the cyanide ion that diffuses freely across membranes.

Methods

Immunofluorescent staining of cells treated with an anti‐linamarase antibody allowed us to localize the enzyme within the cells. Flow cytometry was used to determine the sensitivity of different mixtures of cells, C6lis and C6gfp (green), to linamarin as a percentage of cell survival.

Results

We demonstrate here that rat glioblastoma C6 cells carrying the linamarase gene (lis), mixed with naive C6 cells and exposed to linamarin, induce generalized cell death. Cells expressing lis efficiently export linamarase, whereas linamarin enters cells poorly by endocytosis; as a result most of the cyanide is produced outside the cells. The study was facilitated by the presence of the green fluorescent protein (gfp) gene in the bystander population. As few as 10% C6lis‐positive cells are sufficient to eliminate the entire cell culture in 96 h.

Conclusions

This bystander mechanism does not preferentially kill toxic metabolite producer cells compared with bystander cells, thus allowing production of sufficient cyanide to cause tumor regression. In this report we confirm the potential of the lis/lin gene therapy system as a powerful tool to eliminate tumors in vivo. Copyright © 2002 John Wiley & Sons, Ltd.

     

Altered elemental profile as indicator of homeostatic imbalance in pathogenesis of oral submucous fibrosis

Oral submucous fibrosis (OSF) is a potential precancerous condition of the oral cavity and oropharynx. The etiopathogenesis of this complex precancerous condition is still obscure. In addition to deleterious oral habits, malnutrition, and possible genetic predisposition, altered bioelemental status is also likely to play an important role in its pathogenesis. The present study analyzed 68 elements by inductively coupled plasma-mass spectroscopy in oral mucosa of normal and OSF individuals and some interesting alterations in elemental profile in the diseased tissue have been noted, indicating a homeostatic imbalance. These bioelemental alterations leading to homeostatic imbalance might be considered as an important biological event in the pathogenesis of OSF.     

Reactive oxygen species, antioxidant systems and nitric oxide in peroxisomes

Peroxisomes are subcellular organelles with an essentially oxidative type of metabolism. Like chloroplasts and mitochondria, plant peroxisomes also produce superoxide radicals (O2*(-)) and there are, at least, two sites of superoxide generation: one in the organelle matrix, the generating system being xanthine oxidase, and another site in the peroxisomal membranes dependent on NAD(P)H. In peroxisomal membranes, three integral polypeptides (PMPs) with molecular masses of 18, 29 and 32 kDa have been shown to generate radicals O2*(-). Besides catalase, several antioxidative systems have been demonstrated in plant peroxisomes, including different superoxide dismutases, the ascorbate-glutathione cycle, and three NADP-dependent dehydrogenases. A CuZn-SOD and two Mn-SODs have been purified and characterized from different types of peroxisomes. The four enzymes of the ascorbate-glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase) as well as the antioxidants glutathione and ascorbate have been found in plant peroxisomes. The recycling of NADPH from NADP(+) can be carried out in peroxisomes by three dehydrogenases: glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and isocitrate dehydrogenase. In the last decade, different experimental evidence has suggested the existence of cellular functions for peroxisomes related to reactive oxygen species (ROS), but the recent demonstration of the presence of nitric oxide synthase (NOS) in plant peroxisomes implies that these organelles could also have a function in plant cells as a source of signal molecules like nitric oxide (NO*), superoxide radicals, hydrogen peroxide, and possibly S-nitrosoglutathione (GSNO).     

High-affinity HLA-A(*)02.01 peptides from parathyroid hormone-related protein generate in vitro and in vivo antitumor CTL response without autoimmune side effects

Parathyroid hormone-related protein (PTH-rP), a protein produced by prostate carcinoma and other epithelial cancers, is a key agent in the development of bone metastases. We investigated whether the protein follows the self-tolerance paradigm or can be used as a target Ag for anticancer immunotherapy by investigating the immunogenicity of two HLA-A(*)02.01-binding PTH-rP-derived peptides (PTR-2 and -4) with different affinity qualities. PTH-rP peptide-specific CTL lines were generated from the PBMC of two HLA-A(*)02.01(+) healthy individuals, stimulated in vitro with PTH-rP peptide-loaded autologous dendritic cells and IL-2. The peptide-specific CTLs were able to kill PTH-rP(+)HLA-A(*)02.01(+) breast and prostate carcinoma cell lines. The two peptides were also able to elicit a strong antitumor PTH-rP-specific CTL response in HLA-A(*)02.01 (HHD) transgenic mice. The vaccinated mice did not show any sign of side effects due to cell-mediated autoimmunity or toxicity. In this study we describe two immunogenic and toxic-free PTH-rP peptides as valid candidates for the design of peptide-based vaccination strategies against prostate cancer and bone metastases from the most common epithelial malignancies.     

Genome properties of the diatom Phaeodactylum tricornutum

Diatoms are a ubiquitous class of microalgae of extreme importance for global primary productivity and for the biogeochemical cycling of minerals such as silica. However, very little is known about diatom cell biology or about their genome structure. For diatom researchers to take advantage of genomics and post-genomics technologies, it is necessary to establish a model diatom species. Phaeodactylum tricornutum is an obvious candidate because of its ease of culture and because it can be genetically transformed. Therefore, we have examined its genome composition by the generation of approximately 1,000 expressed sequence tags. Although more than 60% of the sequences could not be unequivocally identified by similarity to sequences in the databases, approximately 20% had high similarity with a range of genes defined functionally at the protein level. It is interesting that many of these sequences are more similar to animal rather than plant counterparts. Base composition at each codon position and GC content of the genome were compared with Arabidopsis, maize (Zea mays), and Chlamydomonas reinhardtii. It was found that distribution of GC within the coding sequences is as homogeneous in P. tricornutum as in Arabidopsis, but with a slightly higher GC content. Furthermore, we present evidence that the P. tricornutum genome is likely to be small (less than 20 Mb). Therefore, this combined information supports the development of this species as a model system for molecular-based studies of diatom biology. The nucleotide sequence data reported has been deposited in GenBank Nucleotide Sequence Database (dbEST section) under accession nos. BI306757 through BI307753.     

Differential expression of a metallothionein gene during the presymbiotic versus the symbiotic phase of an arbuscular mycorrhizal fungus

A full-length cDNA encoding a metallothionein (MT)-like polypeptide, designated GmarMT1, was identified in an expressed sequence tag collection from germinated spores of the arbuscular mycorrhizal fungus Gigaspora margarita (BEG34). The GmarMT1 gene is composed of two exons separated by an 81-bp intron. It codes for a 65-amino acid polypeptide comprising a plant type 1 MT-like N-terminal domain and a C-terminal domain that is most closely related to an as-yet-uncharacterized fungal MT. As revealed by heterologous complementation assays in yeast, GmarMT1 encodes a functional polypeptide capable of conferring increased tolerance against Cd and Cu. The GmarMT1 RNA is expressed in both presymbiotic spores and symbiotic mycelia, even in the absence of metal exposure, but is significantly less abundant in the latter stage. An opposite pattern was observed upon Cu exposure, which up-regulated GmarMT1 expression in symbiotic mycelia but not in germinated spores. Together, these data provide the first evidence, to our knowledge, for the occurrence in an arbuscular mycorrhizal fungus of a structurally novel MT that is modulated in a metal and life cycle stage-dependent manner and may afford protection against heavy metals (and other types of stress) to both partners of the endomycorrhizal symbiosis.