Indoleamine 2,3-dioxygenase activity and L-tryptophan transport in human breast cancer cells. (9/72)

The activity and expression of indoleamine 2,3-dioxygenase together with L-tryptophan transport has been examined in cultured human breast cancer cells. MDA-MB-231 but not MCF-7 cells expressed mRNA for indoleamine 2,3-dioxygenase. Kynurenine production by MDA-MB-231 cells, which was taken as a measure of enzyme activity, was markedly stimulated by interferon-gamma (1000 units/ml). Accordingly, L-tryptophan utilization by MDA-MB-231 cells was enhanced by interferon-gamma. 1-Methyl-DL-tryptophan (1 mM) inhibited interferon-gamma induced kynurenine production by MBA-MB-231 cells. Kynurenine production by MCF-7 cells remained at basal levels when cultured in the presence of interferon-gamma. L-Tryptophan transport into MDA-MB-231 cells was via a Na(+)-independent, BCH-sensitive pathway. It appears that system L (LAT1/CD98) may be the only pathway for l-tryptophan transport into these cells. 1-Methyl-D,L-tryptophan trans-stimulated l-tryptophan efflux from MDA-MB-231 cells and thus appears to be a transported substrate of system L. The results suggest that system L plays an important role in providing indoleamine-2,3-dioxygenase with its main substrate, L-tryptophan, and suggest a mechanism by which estrogen receptor-negative breast cancer cells may evade the attention of the immune system.  (+info)

Catalytic hydroamination of alkynes and norbornene with neutral and cationic tantalum imido complexes. (10/72)

[reaction: see text] Several tantalum imido complexes have been synthesized and shown to efficiently catalyze the hydroamination of internal and terminal alkynes. An unusual hydroamination/hydroarylation reaction of norbornene catalyzed by a highly electrophilic cationic tantalum imido complex is also reported. Factors affecting catalyst activity and selectivity are discussed along with mechanistic insights gained from stoichiometric reactions.  (+info)

Preparation of enantiopure norbornane ligands bearing both (2S,3S)-bis(phosphinomethyl) and 7-syn-oxygen functional groups and an application to rhodium-catalyzed asymmetric hydrogenation. (11/72)

Enantiopure bicyclo[2.2.1]heptane derivatives having both (2S,3S)-bis[(diphenylphosphino)methyl] and 7-syn-oxygen functional groups were synthesized by using diastereoselective Diels-Alder reaction of di-(1R)-menthyl fumarate and 5-trimethylsilylcyclopentadiene followed by silver-promoted stereospecific frame rearrangement of a bromolactone intermediate. Rhodium-catalyzed asymmetric hydrogenations were carried out using the diphosphines as a chiral ligand.  (+info)

The climacteric-like behaviour of young, mature and wounded citrus leaves. (12/72)

Although leaves and other vegetative tissues are generally considered as non-climacteric, citrus leaves show a climacteric system II behaviour after detachment. Upon harvest, young, fully expanded 'Valencia' orange (Citrus sinensis) leaves ( approximately 60-d-old) exhibited two phases of ethylene production. The first phase, up to 6 d after detachment, was characterized by a low and constant ethylene production (system I pathway), associated with a constitutive expression of ACC synthase 2 (CsACS2), CsERS1, and CsETR1. ACC synthase 1 (CsACS1) was not expressed during this phase and autoinhibition of ethylene production was apparent following treatment with exogenous ethylene or propylene. The second phase, 7-12 d after detachment, was characterized by a climacteric rise in ethylene production, preceded by the induction of CsACS1 and ACC oxidase 1 (CsACO1) gene expression in the system II pathway. This induction was accelerated and augmented by exogenous ethylene or propylene, indicating an autocatalytic system II ethylene biosynthesis. Mature leaves (6-8-months-old) behaved similarly, except that the climacteric peak in ethylene production occurred earlier (day 5). Young and mature leaves varied in the timing of the climacteric ethylene rise and CsACS1 and CsACO1 induction. The two phases of ethylene production, system I and system II, were also detected in wounded leaf discs of both young and mature leaves. The first phase peaked 15 min after excision and the second phase peaked after 6 h.  (+info)

5-FU uptake in peritoneal metastases after pretreatment with radioimmunotherapy or vasoconstriction: an autoradiographic study in the rat. (13/72)

This study was conducted to test if tumour drug uptake could be increased in experimental colorectal cancer peritoneal metastases, by using pretreatment with peritoneal vasoconstriction or radioimmunotherapy. A total of 29 nude rats with peritoneal metastases were injected intraperitoneally (i.p.) with 14C-labelled 5-FU. The animals were randomly allocated to 5 groups. Six days prior to 5-FU, group I (control) received i.p. NaCl, group II was subjected to i.p. radioimmunotherapy (RIT) 131I-labelled anti-CEA monoclonal antibody (150 MBq) and group III received i.p. Norbormide 10 minutes before 5-FU. Two days prior to 5-FU group IV and V received i.p. NaCl (control) and RIT, respectively. 5-FU uptake was visualised with autoradiography and quantified by computer-based image analysis. Tumours in group III showed a higher uptake (mean+/-SD, 21.4+/-17) than in group I (11.8+/-10, p=0.04). This was also true when the analysis was restricted to larger tumours (> or = median 627 pixels) group III (23.2+/-19) vs. group I (11.8+/-7, p=0.002). Peritoneal tumours in group II were of smaller size (median area 308 pixels) than in group I (619 pixels), in group III (901 pixels), in group IV (769 pixels) and in group V (808 pixels). RIT decreased the tumour size whereas it did not affect 5-FU uptake. The uptake of 5-FU was potentiated by pretreating the animals with Norbormide. These results demonstrate that 5-FU uptake in experimental peritoneal metastases is increased when the peritoneal absorption of the drug is blocked using pretreatment with a vasoconstrictive agent. This principle may also be relevant when treating patients with colorectal cancer peritoneal metastases.  (+info)

Species-specific modulation of the mitochondrial permeability transition by norbormide. (14/72)

In the present study, we show that norbormide stimulates the opening of the permeability transition pore (PTP) in mitochondria from various organs of the rat but not of guinea pig and mouse. Norbormide does not affect the basic parameters that modulate the PTP activity since the proton electrochemical gradient, respiration, phosphorylation and Ca(2+) influx processes are only partially affected. On the other hand, norbormide induces rat-specific changes in the fluidity of the lipid interior of mitochondrial membranes, as revealed by fluorescence anisotropy of various reporter molecules. Such changes increase the PTP open probability through the internal Me(2+) regulatory site. The lack of PTP opening by norbormide is matched by a negligible perturbation of internal lipid domains in guinea pig and mouse, suggesting that the drug does not gain access to the matrix in the mitochondria from these species. Consistent with this interpretation, we demonstrate a preferential interaction of norbormide with the mitochondrial surface leading to alterations of the Me(2+) binding affinity for the external PTP regulatory site. Our findings indicate that norbormide affects Me(2+) binding to the regulatory sites of the PTP, and suggest that the drug could be taken up by a mitochondrial transport system unique to the rat. The characterization of the norbormide target may lead to a better understanding of the mechanisms underlying the mitochondrial PTP as well as to the identification of species-specific drugs that affect mitochondrial function.  (+info)

Metabolism of (+)-fenchone by CYP2A6 and CYP2B6 in human liver microsomes. (15/72)

The in vitro metabolism of (+)-fenchone was examined in human liver microsomes and recombinant enzymes. Biotransformation of (+)-fenchone was investigated by gas chromatography-mass spectrometry. (+)-Fenchone was found to be oxidized to 6-exo-hydroxyfenchone, 6-endo-hydroxyfenchone and 10-hydroxyfenchone by human liver microsomal P450 enzymes. The formation of metabolite of (+)-fenchone was determined by relative abundance of mass fragments and retention time with GC. CYP2A6 and CYP2B6 in human liver microsomes were major enzymes involved in the hydroxylation of (+)-fenchone, based on the following lines of evidence. First, of eleven recombinant human P450 enzymes tested, CYP2A6 and CYP2B6 catalyzed oxidation of (+)-fenchone. Second, oxidation of (+)-fenchone was inhibited by thioTEPA, (+)-menthofuran anti-CYP2A6 and anti-CYP2B6 antibodies. Finally, there was a good correlation between CYP2A6, CYP2B6 contents and (+)-fenchone hydroxylation activities in liver microsomes of 8 human samples.  (+info)

Amphetamine, cocaine, and fencamfamine: relationship between locomotor and stereotypy response profiles and caudate and accumbens dopamine dynamics. (16/72)

Using in vivo microdialysis, the caudate and nucleus accumbens dopamine (DA) responses to the psychomotor stimulants amphetamine (AMPH), cocaine (COC), and fencamfamine (FCF) were evaluated in rats concurrent with characterization of their behavioral response profiles. Doses of each stimulant that produced either enhanced locomotion or a prolonged period of intense focused stereotypies were examined to evaluate the quantitative relationships between stimulant-induced behaviors and changes in DA dynamics and to test the hypothesis that a balance between mesostriatal and mesolimbic DA activity contributes to the appearance of specific stimulant-induced behaviors. Although 10 mg/kg COC and 1.7 mg/kg FCF promoted levels of locomotor activity substantially greater than 0.5 mg/kg AMPH, the magnitude of the DA increases in both caudate and accumbens were markedly less than was obtained following AMPH. Thus, stimulant-induced locomotion appears to be dissociated from the quantitative DA response in both brain regions. This behavioral/DA dissociation was also apparent at higher doses of AMPH (2.5 mg/kg), COC (40 mg/kg), and FCF (6 mg/kg), doses that promoted a behavioral pattern that included a prolonged period of intense stereotypy. Indeed, the regional DA responses to these high doses of COC and FCF were substantially less than the response to 0.5 mg/kg AMPH. Furthermore, there were no differences in the ratio of the caudate and accumbens DA responses as a function of dose for any of the three drugs. Thus, the balance between the regional DA activation does not appear to regulate the expression of the behavioral response. Additionally, the effects of these stimulants on regional DA metabolite concentrations were compared. The results indicate that AMPH promoted an identical pattern of effects on caudate and accumbens DA metabolites, suggesting that similar mechanisms govern the dynamics of DA in response to AMPH in both brain regions. In contrast, the DA uptake blockers promoted some region-specific effects on DA metabolites that may be due to regional differences in the DA metabolism and rates of impulse flow.  (+info)