Cellular determinants of oxaliplatin sensitivity in colon cancer cell lines.

Oxaliplatin (L-OHP) is a new platinum analogue that has shown antitumour activity against colon cancer both in vitro and in vivo and is now used in the chemotherapeutic treatment of metastatic colon and rectal cancer. L-OHP like cisplatin (CDDP), is detoxified by glutathione (GSH)-related enzymes and forms platinum (Pt)-DNA adducts lesions that are repaired by the nucleotide excision repair system (NER). We investigated the cytotoxicity and the pharmacology of L-OHP and CDDP on a panel of six colon cell lines in vitro. We showed that GSH and glutathione S-transferase (GST) activity were not correlated to oxaliplatin cytotoxicity. Pt-DNA adducts formation and repair were correlated with CDDP, but not with L-OHP cytotoxicity. The determination of ERCC1 and XPA expression, two enzymes of the NER pathway, by reverse transcriptase-polymerase chain reaction (RT-PCR), demonstrated that ERCC1 expression was predictive of L-OHP sensitivity (r(2)=0.67, P=0.02) and XPA level after oxaliplatin exposure was also correlated to L-OHP IC(50) (r(2)=0.5; P=0.04). The knowledge of such correlations could help predict the sensitivity of patients with colon cancer to L-OHP.

The I-CreI meganuclease and its engineered derivatives: applications from cell modification to gene therapy.

Meganucleases (MNs) are highly specific enzymes that can induce homologous recombination in different types of cells, including mammalian cells. Consequently, these enzymes are used as scaffolds for the development of custom gene-targeting tools for gene therapy or cell-line development. Over the past 15 years, the high resolution X-ray structures of several MNs from the LAGLIDADG family have improved our understanding of their protein-DNA interaction and mechanism of DNA cleavage. By developing and utilizing high-throughput screening methods to test a large number of variant-target combinations, we have been able to re-engineer scores of I-CreI derivatives into custom enzymes that target a specific DNA sequence of interest. Such customized MNs, along with wild-type ones, have allowed for exploring a large range of biotechnological applications, including protein-expression cell-line development, genetically modified plants and animals and therapeutic applications such as targeted gene therapy as well as a novel class of antivirals.

The domain structure of protoporphyrinogen oxidase, the molecular target of diphenyl ether-type herbicides.

Protoporphyrinogen oxidase (EC 1-3-3-4), the 60-kDa membrane-bound flavoenzyme that catalyzes the final reaction of the common branch of the heme and chlorophyll biosynthesis pathways in plants, is the molecular target of diphenyl ether-type herbicides. It is highly resistant to proteases (trypsin, endoproteinase Glu-C, or carboxypeptidases A, B, and Y), because the protein is folded into an extremely compact form. Trypsin maps of the native purified and membrane-bound yeast protoporphyrinogen oxidase show that this basic enzyme (pI > 8.5) was cleaved at a single site under nondenaturing conditions, generating two peptides with relative molecular masses of 30,000 and 35,000. The endoproteinase Glu-C also cleaved the protein into two peptides with similar masses, and there was no additional cleavage site under mild denaturing conditions. N-terminal peptide sequence analysis of the proteolytic (trypsin and endoproteinase Glu-C) peptides showed that both cleavage sites were located in putative connecting loop between the N-terminal domain (25 kDa) with the betaalphabeta ADP-binding fold and the C-terminal domain (35 kDa), which possibly is involved in the binding of the isoalloxazine moiety of the FAD cofactor. The peptides remained strongly associated and fully active with the Km for protoporphyrinogen and the Ki for various inhibitors, diphenyl-ethers, or diphenyleneiodonium derivatives, identical to those measured for the native enzyme. However, the enzyme activity of the peptides was much more susceptible to thermal denaturation than that of the native protein. Only the C-terminal domain of protoporphyrinogen oxidase was labeled specifically in active site-directed photoaffinity-labeling experiments. Trypsin may have caused intramolecular transfer of the labeled group to reactive components of the N-terminal domain, resulting in nonspecific labeling. We suggest that the active site of protoporphyrinogen oxidase is in the C-terminal domain of the protein, at the interface between the C- and N-terminal domains.

Stability of recombinant yeast protoporphyrinogen oxidase: effects of diphenyl ether-type herbicides and diphenyleneiodonium.

Protoporphyrinogen oxidase catalyzes the oxygen-dependent aromatization of protoporphyrinogen IX to protoporphyrin IX and is the molecular target of diphenyl ether-type herbicides. Structural features of yeast protoporphyrinogen oxidase were assessed by circular dichroism studies on the enzyme purified from E. coli cells engineered to overproduce the protein. Coexpression of the bacterial gene ArgU that encodes tRNAAGA,AGG and a low induction temperature for protein synthesis were critical for producing protoporphyrinogen oxidase as a native, active, membrane-bound flavoprotein. The secondary structure of the protoporphyrinogen oxidase was 40.0 +/- 1. 5% alpha helix, 23.5 +/- 2.5% beta sheet, 18.0 +/- 2.0% beta turn, and 18.5 +/- 2.5% random-coil. Purified protoporphyrinogen oxidase appeared to be a monomeric protein that was relatively heat-labile (Tm of 44 +/- 0.5 degreesC). Acifluorfen, a potent inhibitor that competes with the tetrapyrrole substrate, and to a lower extent FAD, the cofactor of the enzyme, protected the protein from thermal denaturation, raising the Tm to 50.5 +/- 0.5 degreesC (acifluorfen) and 46.5 +/- 0.5 degreesC (FAD). However, diphenyleneiodonium, a slow tight-binding inhibitor that competes with dioxygen, did not protect the enzyme from heat denaturation. Acifluorfen binding to the protein increased the activation energy for the denaturation from 15 to 80 kJ.mol-1. The unfolding of the protein was a two-step process, with an initial fast reversible unfolding of the native protein followed by slow aggregation of the unfolded monomers. Functional analysis indicated that heat denaturation caused a loss of enzyme activity and of the specific binding of radiolabeled inhibitor. Both processes occurred in a biphasic manner, with a transition temperature of 45 degreesC.

Acylation stabilizes a protease-resistant conformation of protoporphyrinogen oxidase, the molecular target of diphenyl ether-type herbicides.

Protein acylation is an important way in which a number of proteins with a variety of functions are modified. The physiological role of the acylation of cellular proteins is still poorly understood. Covalent binding of fatty acids to nonintegral membrane proteins is thought to produce transient or permanent enhancement of the association of the polypeptide chains with biological membranes. In this paper, we investigate the functional role for the palmitoylation of an atypical membrane-bound protein, yeast protoporphyrinogen oxidase, which is the molecular target of diphenyl ether-type herbicides. Palmitoylation stabilizes an active heat- and protease-resistant conformation of the protein. Palmitoylation of protoporphyrinogen oxidase has been demonstrated to occur in vivo both in yeast cells and in a heterologous bacterial expression system, where it may be inhibited by cerulenin leading to the accumulation of degradation products of the protein. The thiol ester linking palmitoleic acid to the polypeptide chain was shown to be sensitive to hydrolysis by hydroxylamine and also by the widely used serine-protease inhibitor phenylmethylsulfonyl fluoride.

Combination of oxaliplatin and irinotecan on human colon cancer cell lines: activity in vitro and in vivo.

The in vitro and in vivo combination of oxaliplatin and irinotecan was investigated in a panel of four human colon cancer cell lines and their counterpart xenografts. In vitro and in vivo experiments demonstrated a synergistic or additive interaction in three cell lines (HCT-116, HCT-8 and HT-29) and an antagonism in SW-620 cells. Since there were clearly opposite interactions depending on the cell line, we further investigated cellular determinants possibly involved in the interaction between the two drugs in HCT-8 and SW-620 cells. Irinotecan slowed down the early platinum-DNA adducts repair (1 h after oxaliplatin exposure) in the presence of irinotecan only in HCT-8 cells (p=0.03, n=3). Moreover, a decrease of the expression of two proteins of the nucleotide excision repair (NER) system, ERCC1 and XPA, was observed. None of these effects was seen in SW-620 cells. Irinotecan induced apoptosis with an increase of poly(ADP-ribose) polymerase (PARP) cleavage in SW-620 cells (60 versus 7% basal level). Pretreatment of these cells with oxaliplatin abolished the increase in PARP cleavage induced by irinotecan (29%). In HCT-8 cells, a very little PARP cleavage was observed whatever the drug treatment. The persistence of platinum-DNA adducts in the presence of irinotecan could be due to a direct impact of irinotecan on NER gene expression or to an indirect effect on topoisomerase I activity. Complementary studies are required to determine if the cellular parameters identified in this study could be translated at the clinical level to predict clinical response after combined treatment with oxaliplatin and irinotecan in humans.

[Treatment of bacterial infections by ofloxacin. 42 cases]. / Traitement des infections bactériennes par l'ofloxacine. Quarante-deux observations.

Fourty-two patients with 44 infective sites were treated with ofloxacin alone (22) or associated with an other antibiotic (20). Thirty-five patients (83%) and 37 infective localisations (84%) were cured. The treatment efficacy was similar for ofloxacin alone or associated, and for treatments given with first or second intent. All non-documented infections were cured. Two of the 4 failures were pneumococcal. So, the non-documented infections, the genital and urinary tract infections, the pulmonary infections (second intent) and osteitis seem to be the best indications of ofloxacin therapy.

[Epilepsy with rolandic paroxysms and migraine, a non-fortuitous association. Results of a controlled study]. / Epilepsie à paroxysmes rolandiques et migraine, une association non fortuite. Résultats d'une étude contrôlée.

The incidence of migraine was studied in 4 groups of patients: patients with centro-temporal epilepsy, patients with absence of epilepsy, patients with partial epilepsy, and non-epileptic patients with a history of cranial trauma. Migraines were present in 62% of the patients with centro-temporal epilepsy, 34% of the patients with absence of epilepsy, 8% of the patients with partial epilepsy and 6% of the patients with cranial trauma. These results suggest that the association of centro-temporal epilepsy and migraine is non-fortuitous as well as, to a lesser degree, absence of epilepsy and migraine. The authors discuss the role of serotonin in the association epilepsy-migraine and suggest that centro-temporal epilepsy might be a feature for the diagnosis of migraine.

Kinetics of protoporphyrinogen oxidase inhibition by diphenyleneiodonium derivatives.

Protoporphyrinogen oxidase, the last enzyme of the common branch of the heme and chlorophyll pathways in plants, is the molecular target of diphenyl ether-type herbicides. These compounds inhibit the enzyme competitively with respect to the tetrapyrrole substrate, protoporphyrinogen IX. We used the flavinic nature of protoporphyrinogen oxidase to investigate the reactivity of the enzyme toward the 2,2'-diphenyleneiodonium cation, a known inhibitor of several flavoproteins. Diphenyleneiodonium inhibited the membrane-bound yeast protoporphyrinogen oxidase competitively with molecular oxygen. The typical slow-binding kinetics suggested that the enzyme with a reduced flavin rapidly combined with the inhibitor to form an initial complex which then slowly isomerized to a modified enzyme-inhibitor complex (Ki = 6.75 x 10(-8) M, Ki* = 4.1 x 10(-9) M). This inhibition was strongly pH-dependent and was maximal at pH 8. Substituted diphenyleneiodoniums were synthesized and shown to be even better inhibitors than 2,2'-diphenyleneiodonium: Ki = 4.4 x 10(-8) M and Ki* = 1.3 x 10(-9) M for 4-methyl-2,2'-diphenyleneiodonium, Ki = 2.2 x 10(-8) M and Ki * = 1.1 x 10(-9) M for 6-methyl-2,2'-diphenyleneiodonium, and Ki = 6.4 x 10(-9) M and Ki* = 1.2 x 10(-1)2 M for 4-nitro-2,2'-diphenyleneiodonium. The 4-nitro-2,2'-diphenyleneiodonium was a quasi irreversible inhibitor (k5/k6 > 5000). Diphenyleneiodoniums are a new class of protoporphyrinogen oxidase inhibitors that act via a mechanism very different from that of diphenyl ether-type herbicides and appear to be promising tools for studies on the structure-function relationships of this agronomically important enzyme.