The quantification of erlotinib (OSI-774) and OSI-420 in human plasma by liquid chromatography-tandem mass spectrometry

An accurate and precise method was developed using HPLC-MS/MS to quantify erlotinib (OSI-774) and its O-desmethyl metabolite, OSI-420, in plasma. The advantages of this method include the use of a small sample volume, liquid-liquid extraction with high extraction efficiency and short chromatographic run times. The analytes were extracted from 100 microL plasma volume using hexane:ethyl acetate after midazolam was added to the sample for internal standardization. The compounds were separated on a Phenomenex C-18 Luna analytical column with acetonitrile:5 mM ammonium acetate as the mobile phase. All compounds were monitored by tandem mass spectrometry with electrospray positive ionization. The intra-day accuracy and precision (% coefficient of variation, % CV) estimates for erlotinib at 10 ng/mL were 90% and 9%, respectively. The intra-day accuracy and precision estimates for OSI-420 at 5 ng/mL were 80% and 4%, respectively. This method was used to quantify erlotinib and OSI-420 in plasma of patients (n=21) administered 150 mg erlotinib per day for non-small cell lung cancer.     

Comparative visual acuity of coleoid cephalopods

The pelagic realm of the ocean is characterized by extremelyclear water and a lack of surfaces. Adaptations to the visualecology of this environment include transparency, fluorescence,bioluminescence, and deep red or black pigmentation. While thesignals that pelagic organisms send are increasingly well-understood,the optical capabilities of their viewers, especially for predatorswith camera-like vision such as fish and squid, are almost unknown.Aquatic camera-like vision is characterized by a spherical lensfocusing an image on the retina. Here, we measured the resolvingpower of the lenses of eight species of pelagic cephalopodsto obtain an approximation of their visual capabilities. Wedid this by focusing a standard resolution target through dissectedlenses and calculating their modulation transfer functions.The modulation transfer function (MTF) is the single most completeexpression of the resolving capabilities of a lens. Since theoptical and retinal capabilities of an eye are generally well-matched,we considered our measurements of cephalopod lens MTF to bea good proxy for their visual capabilities in vivo. In general,squid have optical capabilities comparable to other organismsgenerally assumed to have good vision, such as fish and birds.Surprisingly, the optical capability of the eye of Vampyroteuthisinfernalis rivals that of humans.     

Synthesis and analysis of the enantiomers of calmidazolium,and a 1H NMR demonstration of a chiral interaction with calmodulin

Calmidazolium {R24571, 1-[bis(4-chlorophenyl)methyl]-3-[2-(2,4-dichlorophenyl)-2-[(2,4-dichlorophenyl)methoxy]ethyl]-1H-imidazolium chloride} is a potent calmodulin inhibitor. This paper describes the synthesis and properties of the enantiomers of calmidazolium from the enantiomers of miconazole {1(N)-(2-(2,4-dichlorobenzyloxy)-2-(2,4-dichlorophenyl))-ethyl imidazole}, prepared from the racemate by chiral preparative scale high performance liquid chromatography. Overlap between ligand and protein resonances in the aromatic region of the ¹H NMR spectrum of the calmidazolium-calmodulin complexes has been obviated by preparation of the protein with all of its nine phenylalanine rings deuterated (Phe-d₅ calmodulin). This has been accomplished by the overexpression of calmodulin derived from Trypanosoma brucei rhodiesiense in E. coli in a medium supplemented with ring-deuterated phenylalanine. The kinetics of binding of each enantiomer are slow on the ¹H NMR time scale as judged by the behaviour of the H2 resonance of Histidine-107, which is clearly visible under the sample conditions used. The aromatic spectral regions of the protein-bound (+) and (−) enantiomers contrast strikingly, reflecting differences in bound environment and/or conformation. Chirality 8:545–500, 1996. © 1997 Wiley-Liss, Inc.     

Regulation of bile acid synthesis. Isolation and characterization of microsomal phosphatases

In preliminary experiments, we have shown that rat liver microsomes possess phosphatase activity which was inhibited in the presence of sodium fluoride. We have now separated six microsomal phosphatase fractions appearing to be isoenzymes. They all possess different kinetic constants and are not equally inhibited by tartrate and fluoride ions, inhibitors of phosphatase activity. One phosphatase fraction, in fact, is almost completely unaffected by fluoride ion. More pertinent to our interest, these isoenzymes exhibit differing abilities to modulate the activities of hydroxymethylglutaryl CoA reductase, acyl-CoA:cholesterol O-acetyltransferase, and cholesterol 7 alpha-hydroxylase. Interaction of four of the fractions with rat liver microsomes resulted in a decrease in cholesterol 7 alpha-hydroxylase activity; two were without effect.     

A theoretical expression for the protection associated with stoichiometric and catalytic scavengers in a single compartment model of organophosphorus poisoning

The ability of certain organophosphorus (OP) compounds to inhibit acetylcholinesterase (AChE) has made them useful for industrial (insecticides) and military (nerve agents) purposes. We have previously published a single compartment mathematical model of the interactions between OP nerve agents and the enzymes affected by these agents. That model, which could be used to predict the LD50 of seven nerve agents in rats, has been extended to include the protective actions of stoichiometric and catalytic OP-scavenger enzymes (delivered as pretreatments) so that protective ratios attributable to the scavengers may be predicted. Prediction of expected human protection from in vitro rate constant and initial enzyme level measurements is the ultimate goal for this work. The enhanced model predicts the LD50 from rate constants of the OP agent's binding reactions with AChE, carboxylesterase (CaE) and a stoichiometric scavenger (S); a first-order OP elimination rate (including a contribution due to a catalytic scavenger); and whole body estimates of AChE, CaE and S. The ratio of the scavenger-treated LD50 estimate to the scavenger-free LD50 estimate provided a theoretical expression describing the scavenger's contributions to the protective ratio. Published in vivo protective ratios for two stoichiometric scavengers (fetal bovine serum AChE and human utyrylcholinesterase) against challenge by several OP agents in mice were compared with ratios predicted by the model. A linear regression analysis of in vivo protective ratios in mice versus the ratios predicted by the model from the in vitro measurements resulted in an R(2) value of 0.902. The catalytic scavenger portion of the theory could not be validated due to a lack of published data. We conclude that the one-compartment model can be used to make reasonable estimates of the protective ratio attributable to stoichiometric scavengers, but can make no conclusions regarding the ability of the model to predict catalytic scavenger protection ratios.     

The 1.15A crystal structure of the Staphylococcus aureus methionyl-aminopeptidase and complexes with triazole based inhibitors

Methionyl aminopeptidases (MetAPs) represent a unique class of protease that are responsible for removing the N-terminal methionine residue from proteins and peptides. There are two major classes of MetAPs (type I and type II) described and each class can be subdivided into two subclasses. Eukaryotes contain both the type I and type II MetAPs, whereas prokaryotes possess only the type I enzyme. Due to the physiological importance of these enzymes there is considerable interest in inhibitors to be used as antiangiogenic and antimicrobial agents. Here, we describe the 1.15A crystal structure of the Staphylococcus aureus MetAP-I as an apo-enzyme and its complexes with various 1,2,4-triazole-based derivatives at high-resolution. The protein has a typical "pita-bread" fold as observed for the other MetAP structures. The inhibitors bind in the active site with the N1 and N2 atoms of the triazole moiety complexing two divalent ions. The 1,2,4-triazols represent a novel class of potent non-peptidic inhibitors for the MetAP-Is.     

Targeted expression of tetanus neurotoxin interferes with behavioral responses to sensory input in Drosophila.

Targeted inactivation of neurons by expression of toxic gene products is a useful tool to assign behavioral functions to specific neurons or brain structures. Of a variety of toxic gene products tested, tetanus neurotoxin light chain (TNT) has the least severe side effects and can completely block chemical synapses. By using the GAL4 system to drive TNT expression in a subset of chemo- and mechanosensory neurons, we detected walking and flight defects consistent with blocking of relevant sensory information. We also found, for the first time, an olfactory behavioral phenotype associated with blocking of a specific subset of antennal chemoreceptors. Similar behavioral experiments with GAL4 lines expressing in different subsets of antennal chemoreceptors should contribute to an understanding of olfactory coding in Drosophila. To increase the utility of the GAL4 system for such purposes, we have designed an inducible system that allows us to circumvent lethality caused by TNT expression during early development.     

Selective inhibition of prostaglandin biosynthesis by gold salts and phenylbutazone

Gold salts and phenylbutazone selectively inhibit the synthesis of PGF_2α and PGE₂ respectively. Lowered production of one prostaglandin species is accompanied by an increased production of the other. Selective inhibition by these drugs was observed in the presence of adrenaline, reduced glutathione and copper sulphate under conditions when most anti-inflammatory compounds inhibited PGE₂ and PGF_2α syntheses equally. It is postulated that selective inhibitors may have a different mode of action and beneficial effects may be related to the endogenous ratio of PGE to PGF required for normal function.     

FREEZE-FRACTURED CHLOROPLAST MEMBRANES OF GONYAULAX POLYEDRA (PYRROPHYTA)1

The chloroplast membranes of Gonyaulax polyedra Stein were studied in replicas of rapidly frozen and fractured cells. The thylakoid EF_s face lacked the large 15–16 nm particles characteristic of plants with the light-harvesting chlorophyll a/b protein, presumably because the principal light-harvesting protein of Gonyaulax is the small water-soluble peridinin-chlorophyll-protein and the chlorophyll a/b protein is absent. As in other plants, the EF_s thylakoid fracture face carried more particles (4 ×) than EF_uface. The PF faces of the thylakoid showed twice as many particles as did the EF_s faces. No circadian differences in the number or size of thylakoid membrane particles could be detected. Three membranes comprise the chloroplast envelope in Gonyaulax. They could be clearly differentiated in freeze-fractured cells. The middle envelope membrane carried many fewer particles on both the EF and PF faces than did the other two envelope membranes. The PF faces of both the outer and inner envelope membranes showed more particles than the EF faces, as do many other membranes which have been examined.