A highly selective, cell-permeable furin inhibitor BOS-318 rescues key features of cystic fibrosis airway disease

In cystic fibrosis (CF), excessive furin activity plays a critical role in the activation of the epithelial sodium channel (ENaC), dysregulation of which contributes to airway dehydration, ineffective mucociliary clearance (MCC), and mucus obstruction. Here, we report a highly selective, cell-permeable furin inhibitor, BOS-318, that derives selectivity by eliciting the formation of a new, unexpected binding pocket independent of the active site catalytic triad. Using human ex vivo models, BOS-318 showed significant suppression of ENaC, which led to enhanced airway hydration and an ∼30-fold increase in MCC rate. Furin inhibition also protected ENaC from subsequent activation by neutrophil elastase, a soluble protease dominant in CF airways. Additional therapeutic benefits include protection against epithelial cell death induced by Pseudomonas aeruginosa exotoxin A. Our findings demonstrate the utility of selective furin inhibition as a mutation-agnostic approach that can correct features of CF airway pathophysiology in a manner expected to deliver therapeutic value.

Discovery of a first-in-class reversible DNMT1-selective inhibitor with improved tolerability and efficacy in acute myeloid leukemia

DNA methylation, a key epigenetic driver of transcriptional silencing, is universally dysregulated in cancer. Reversal of DNA methylation by hypomethylating agents, such as the cytidine analogs decitabine or azacytidine, has demonstrated clinical benefit in hematologic malignancies. These nucleoside analogs are incorporated into replicating DNA where they inhibit DNA cytosine methyltransferases DNMT1, DNMT3A and DNMT3B through irreversible covalent interactions. These agents induce notable toxicity to normal blood cells thus limiting their clinical doses. Herein we report the discovery of GSK3685032, a potent first-in-class DNMT1-selective inhibitor that was shown via crystallographic studies to compete with the active-site loop of DNMT1 for penetration into hemi-methylated DNA between two CpG base pairs. GSK3685032 induces robust loss of DNA methylation, transcriptional activation and cancer cell growth inhibition in vitro. Due to improved in vivo tolerability compared with decitabine, GSK3685032 yields superior tumor regression and survival mouse models of acute myeloid leukemia.

Characterization of Apo-Form Selective Inhibition of Indoleamine 2,3-Dioxygenase*

Indoleamine-2,3-dioxygenase 1 (IDO1) is a heme-containing enzyme that catalyzes the rate-limiting step in the kynurenine pathway of tryptophan (TRP) metabolism. As it is an inflammation-induced immunoregulatory enzyme, pharmacological inhibition of IDO1 activity is currently being pursued as a potential therapeutic tool for the treatment of cancer and other disease states. As such, a detailed understanding of the mechanism of action of IDO1 inhibitors with various mechanisms of inhibition is of great interest. Comparison of an apo-form-binding IDO1 inhibitor (GSK5628) to the heme-coordinating compound, epacadostat (Incyte), allows us to explore the details of the apo-binding inhibition of IDO1. Herein, we demonstrate that GSK5628 inhibits IDO1 by competing with heme for binding to a heme-free conformation of the enzyme (apo-IDO1), whereas epacadostat coordinates its binding with the iron atom of the IDO1 heme cofactor. Comparison of these two compounds in cellular systems reveals a long-lasting inhibitory effect of GSK5628, previously undescribed for other known IDO1 inhibitors. Detailed characterization of this apo-binding mechanism for IDO1 inhibition might help design superior inhibitors or could confer a unique competitive advantage over other IDO1 inhibitors vis-à-vis specificity and pharmacokinetic parameters.

Discovery of piperazic acid peptide deformylase inhibitors with in vivo activity for respiratory tract and skin infections

The discovery of a novel series of peptide deformylase inhibitors incorporating a piperazic acid amino acid found in nature is described. These compounds demonstrated potent in vitro enzymatic potency and antimicrobial activity. Crystal structure analysis revealed the piperazic acid optimized a key contact with the PDF protein that accounted for the increased enzymatic potency of these compounds. We describe lead optimization of the P3' region of the series that resulted in a compound with good potency against three target organisms. One molecule showed in vivo efficacy in a rat respiratory infection model but ultimately did not meet candidate progression criteria.

BacMam production and crystal structure of nonglycosylated apo human furin at 1.89 Å resolution

Furin, also called proprotein convertase subtilisin/kexin 3 (PCSK3), is a calcium-dependent serine endoprotease that processes a wide variety of proproteins involved in cell function and homeostasis. Dysregulation of furin has been implicated in numerous disease states, including cancer and fibrosis. Mammalian cell expression of the furin ectodomain typically produces a highly glycosylated, heterogeneous protein, which can make crystallographic studies difficult. Here, the expression and purification of nonglycosylated human furin using the BacMam technology and site-directed mutagenesis of the glycosylation sites is reported. Nonglycosylated furin produced using this system retains full proteolytic activity indistinguishable from that of the glycosylated protein. Importantly, the nonglycosylated furin protein reliably forms extremely durable apo crystals that diffract to high resolution. These crystals can be soaked with a wide variety of inhibitors to enable a structure-guided drug-discovery campaign.

Identification and Optimization of Novel Small c-Abl Kinase Activators Using Fragment and HTS Methodologies

Abelson kinase (c-Abl) is a ubiquitously expressed, nonreceptor tyrosine kinase which plays a key role in cell differentiation and survival. It was hypothesized that transient activation of c-Abl kinase via displacement of the N-terminal autoinhibitory "myristoyl latch", may lead to an increased hematopoietic stem cell differentiation. This would increase the numbers of circulating neutrophils and so be an effective treatment for chemotherapy-induced neutropenia. This paper describes the discovery and optimization of a thiazole series of novel small molecule c-Abl activators, initially identified by a high throughput screening. Subsequently, a scaffold-hop, which exploited the improved physicochemical properties of a dihydropyrazole analogue, identified through fragment screening, delivered potent, soluble, cell-active c-Abl activators, which demonstrated the intracellular activation of c-Abl in vivo.

Identification of an antibody-based immunoassay for measuring direct target binding of RIPK1 inhibitors in cells and tissues

Therapies that suppress RIPK1 kinase activity are emerging as promising therapeutic agents for the treatment of multiple inflammatory disorders. The ability to directly measure drug binding of a RIPK1 inhibitor to its target is critical for providing insight into pharmacokinetics, pharmacodynamics, safety and clinical efficacy, especially for a first‐in‐class small‐molecule inhibitor where the mechanism has yet to be explored. Here, we report a novel method for measuring drug binding to RIPK1 protein in cells and tissues. This TEAR1 (Target Engagement Assessment for RIPK1) assay is a pair of immunoassays developed on the principle of competition, whereby a first molecule (ie, drug) prevents the binding of a second molecule (ie, antibody) to the target protein. Using the TEAR1 assay, we have validated the direct binding of specific RIPK1 inhibitors in cells, blood and tissues following treatment with benzoxazepinone (BOAz) RIPK1 inhibitors. The TEAR1 assay is a valuable tool for facilitating the clinical development of the lead RIPK1 clinical candidate compound, GSK2982772, as a first‐in‐class RIPK1 inhibitor for the treatment of inflammatory disease.

Discovery of a First-in-Class Receptor Interacting Protein 1 (RIP1) Kinase Specific Clinical Candidate (GSK2982772) for the Treatment of Inflammatory Diseases

RIP1 regulates necroptosis and inflammation and may play an important role in contributing to a variety of human pathologies, including immune-mediated inflammatory diseases. Small-molecule inhibitors of RIP1 kinase that are suitable for advancement into the clinic have yet to be described. Herein, we report our lead optimization of a benzoxazepinone hit from a DNA-encoded library and the discovery and profile of clinical candidate GSK2982772 (compound 5), currently in phase 2a clinical studies for psoriasis, rheumatoid arthritis, and ulcerative colitis. Compound 5 potently binds to RIP1 with exquisite kinase specificity and has excellent activity in blocking many TNF-dependent cellular responses. Highlighting its potential as a novel anti-inflammatory agent, the inhibitor was also able to reduce spontaneous production of cytokines from human ulcerative colitis explants. The highly favorable physicochemical and ADMET properties of 5, combined with high potency, led to a predicted low oral dose in humans.

Discovery of a Novel 2,6-Disubstituted Glucosamine Series of Potent and Selective Hexokinase 2 Inhibitors

A novel series of potent and selective hexokinase 2 (HK2) inhibitors, 2,6-disubstituted glucosamines, has been identified based on HTS hits, exemplified by compound 1. Inhibitor-bound crystal structures revealed that the HK2 enzyme could adopt an "induced-fit" conformation. The SAR study led to the identification of potent HK2 inhibitors, such as compound 34 with greater than 100-fold selectivity over HK1. Compound 25 inhibits in situ glycolysis in a UM-UC-3 bladder tumor cell line via (13)CNMR measurement of [3-(13)C]lactate produced from [1,6-(13)C2]glucose added to the cell culture.

Long-Range Inhibitor-Induced Conformational Regulation of Human IRE1α Endoribonuclease Activity

Activation of the inositol-requiring enzyme-1 alpha (IRE1α) protein caused by endoplasmic reticulum stress results in the homodimerization of the N-terminal endoplasmic reticulum luminal domains, autophosphorylation of the cytoplasmic kinase domains, and conformational changes to the cytoplasmic endoribonuclease (RNase) domains, which render them functional and can lead to the splicing of X-box binding protein 1 (XBP 1) mRNA. Herein, we report the first crystal structures of the cytoplasmic portion of a human phosphorylated IRE1α dimer in complex with (R)-2-(3,4-dichlorobenzyl)-N-(4-methylbenzyl)-2,7-diazaspiro(4.5)decane-7-carboxamide, a novel, IRE1α-selective kinase inhibitor, and staurosporine, a broad spectrum kinase inhibitor. (R)-2-(3,4-dichlorobenzyl)-N-(4-methylbenzyl)-2,7-diazaspiro(4.5)decane-7-carboxamide inhibits both the kinase and RNase activities of IRE1α. The inhibitor interacts with the catalytic residues Lys599 and Glu612 and displaces the kinase activation loop to the DFG-out conformation. Inactivation of IRE1α RNase activity appears to be caused by a conformational change, whereby the αC helix is displaced, resulting in the rearrangement of the kinase domain-dimer interface and a rotation of the RNase domains away from each other. In contrast, staurosporine binds at the ATP-binding site of IRE1α, resulting in a dimer consistent with RNase active yeast Ire1 dimers. Activation of IRE1α RNase activity appears to be promoted by a network of hydrogen bond interactions between highly conserved residues across the RNase dimer interface that place key catalytic residues poised for reaction. These data implicate that the intermolecular interactions between conserved residues in the RNase domain are required for activity, and that the disruption of these interactions can be achieved pharmacologically by small molecule kinase domain inhibitors.

Discovery of Small Molecule RIP1 Kinase Inhibitors for the Treatment of Pathologies Associated with Necroptosis

Potent inhibitors of RIP1 kinase from three distinct series, 1-aminoisoquinolines, pyrrolo[2,3-b]pyridines, and furo[2,3-d]pyrimidines, all of the type II class recognizing a DLG-out inactive conformation, were identified from screening of our in-house kinase focused sets. An exemplar from the furo[2,3-d]pyrimidine series showed a dose proportional response in protection from hypothermia in a mouse model of TNFα induced lethal shock.

Acylprolinamides: a new class of peptide deformylase inhibitors with in vivo antibacterial activity

A new class of PDF inhibitor with potent, broad spectrum antibacterial activity is described. Optimization of blood stability and potency provided compounds with improved pharmacokinetics that were suitable for in vivo experiments. Compound 5c, which has robust antibacterial activity, demonstrated efficacy in two respiratory tract infection models.

Understanding the origins of time-dependent inhibition by polypeptide deformylase inhibitors

The continual bacterial adaptation to antibiotics creates an ongoing medical need for the development of novel therapeutics. Polypeptide deformylase (PDF) is a highly conserved bacterial enzyme, which is essential for viability. It has previously been shown that PDF inhibitors represent a promising new area for the development of antimicrobial agents, and that many of the best PDF inhibitors demonstrate slow, time-dependent binding. To improve our understanding of the mechanistic origin of this time-dependent inhibition, we examined in detail the kinetics of PDF catalysis and inhibition by several different PDF inhibitors. Varying pH and solvent isotope led to clear changes in time-dependent inhibition parameters, as did inclusion of NaCl, which binds to the active site metal of PDF. Quantitative analysis of these results demonstrated that the observed time dependence arises from slow binding of the inhibitors to the active site metal. However, we also found several metal binding inhibitors that exhibited rapid, non-time-dependent onset of inhibition. By a combination of structural and chemical modification studies, we show that metal binding is only slow when the rest of the inhibitor makes optimal hydrogen bonds within the subsites of PDF. Both of these interactions between the inhibitor and enzyme were found to be necessary to observe time-dependent inhibition, as elimination of either leads to its loss.

Structure-based design of potent and selective 3-phosphoinositide-dependent kinase-1 (PDK1) inhibitors

Phosphoinositide-dependent protein kinase-1(PDK1) is a master regulator of the AGC family of kinases and an integral component of the PI3K/AKT/mTOR pathway. As this pathway is among the most commonly deregulated across all cancers, a selective inhibitor of PDK1 might have utility as an anticancer agent. Herein we describe our lead optimization of compound 1 toward highly potent and selective PDK1 inhibitors via a structure-based design strategy. The most potent and selective inhibitors demonstrated submicromolar activity as measured by inhibition of phosphorylation of PDK1 substrates as well as antiproliferative activity against a subset of AML cell lines. In addition, reduction of phosphorylation of PDK1 substrates was demonstrated in vivo in mice bearing OCl-AML2 xenografts. These observations demonstrate the utility of these molecules as tools to further delineate the biology of PDK1 and the potential pharmacological uses of a PDK1 inhibitor.

Aminoindazole PDK1 Inhibitors: A Case Study in Fragment-Based Drug Discovery

Fragment screening of phosphoinositide-dependent kinase-1 (PDK1) in a biochemical kinase assay afforded hits that were characterized and prioritized based on ligand efficiency and binding interactions with PDK1 as determined by NMR. Subsequent crystallography and follow-up screening led to the discovery of aminoindazole 19, a potent leadlike PDK1 inhibitor with high ligand efficiency. Well-defined structure-activity relationships and protein crystallography provide a basis for further elaboration and optimization of 19 as a PDK1 inhibitor.

Synthesis and SAR of potent LXR agonists containing an indole pharmacophore

A novel series of 1H-indol-1-yl tertiary amine LXR agonists has been designed. Compounds from this series were potent agonists with good rat pharmacokinetic parameters. In addition, the crystal structure of an LXR agonist bound to LXRalpha will be disclosed.

Structure-guided design of N-phenyl tertiary amines as transrepression-selective liver X receptor modulators with anti-inflammatory activity

A cocrystal structure of T1317 (3) bound to hLXRbeta was utilized in the design of a series of substituted N-phenyl tertiary amines. Profiling in binding and functional assays led to the identification of LXR modulator GSK9772 ( 20) as a high-affinity LXRbeta ligand (IC 50 = 30 nM) that shows separation of anti-inflammatory and lipogenic activities in human macrophage and liver cell lines, respectively. A cocrystal structure of the structurally related analog 19 bound to LXRbeta reveals regions within the receptor that can affect receptor modulation through ligand modification. Mechanistic studies demonstrate that 20 is greater than 10-fold selective for LXR-mediated transrepression of proinflammatory gene expression versus transactivation of lipogenic signaling pathways, thus providing an opportunity for the identification of LXR modulators with improved therapeutic indexes.

Discovery of Substituted Maleimides as Liver X Receptor Agonists and Determination of a Ligand-Bound Crystal Structure

Substituted 3-(phenylamino)-1H-pyrrole-2,5-diones were identified from a high throughput screen as inducers of human ATP binding cassette transporter A1 expression. Mechanism of action studies led to the identification of GSK3987 as an LXR ligand. GSK3987 recruits the steroid receptor coactivator-1 to human LXRalpha and LXRbeta with EC(50)s of 40 nM, profiles as an LXR agonist in functional assays, and activates LXR though a mechanism that is similar to first generation LXR agonists.

3-hydroxy-3-methylglutaryl-CoA synthase intermediate complex observed in "real-time"

The formation of carbon-carbon bonds via an acyl-enzyme intermediate plays a central role in fatty acid, polyketide, and isoprenoid biosynthesis. Uniquely among condensing enzymes, 3-hydroxy-3-methylglutaryl (HMG)-CoA synthase (HMGS) catalyzes the formation of a carbon-carbon bond by activating the methyl group of an acetylated cysteine. This reaction is essential in Gram-positive bacteria, and represents the first committed step in human cholesterol biosynthesis. Reaction kinetics, isotope exchange, and mass spectroscopy suggest surprisingly that HMGS is able to catalyze the "backwards" reaction in solution, where HMG-CoA is cleaved to form acetoacetyl-CoA (AcAc-CoA) and acetate. Here, we trap a complex of acetylated HMGS from Staphylococcus aureus and bound acetoacetyl-CoA by cryo-cooling enzyme crystals at three different times during the course of its back-reaction with its physiological product (HMG-CoA). This nonphysiological "backwards" reaction is used to understand the details of the physiological reaction with regards to individual residues involved in catalysis and substrate/product binding. The structures suggest that an active-site glutamic acid (Glu-79) acts as a general base both in the condensation between acetoacetyl-CoA and the acetylated enzyme, and the hydrolytic release of HMG-CoA from the enzyme. The ability to trap this enzyme-intermediate complex may suggest a role for protein dynamics and the interplay between protomers during the normal course of catalysis.

Staphylococcus aureus 3-Hydroxy-3-methylglutaryl-CoA Synthase

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase, a member of the family of acyl-condensing enzymes, catalyzes the first committed step in the mevalonate pathway and is a potential target for novel antibiotics and cholesterol-lowering agents. The Staphylococcus aureus mvaS gene product (43.2 kDa) was overexpressed in Escherichia coli, purified to homogeneity, and shown biochemically to be an HMG-CoA synthase. The crystal structure of the full-length enzyme was determined at 2.0-A resolution, representing the first structure of an HMG-CoA synthase from any organism. HMG-CoA synthase forms a homodimer. The monomer, however, contains an important core structure of two similar alpha/beta motifs, a fold that is completely conserved among acyl-condensing enzymes. This common fold provides a scaffold for a catalytic triad made up of Cys, His, and Asn required by these enzymes. In addition, a crystal structure of HMG-CoA synthase with acetoacetyl-CoA was determined at 2.5-A resolution. Together, these structures provide the structural basis for an understanding of the mechanism of HMG-CoA synthase.

Structural characterization of the enzyme-substrate, enzyme-intermediate, and enzyme-product complexes of thiamin phosphate synthase

Thiamin phosphate synthase catalyzes the formation of thiamin phosphate from 4-amino-5-(hydroxymethyl)-2-methylpyrimidine pyrophosphate and 5-(hydroxyethyl)-4-methylthiazole phosphate. Several lines of evidence suggest that the reaction proceeds via a dissociative mechanism. The previously determined crystal structure of thiamin phosphate synthase in complex with the reaction products, thiamin phosphate and magnesium pyrophosphate, provided a view of the active site and suggested a number of additional experiments. We report here seven new crystal structures primarily involving crystals of S130A thiamin phosphate synthase soaked in solutions containing substrates or products. We prepared S130A thiamin phosphate synthase with the intent of characterizing the enzyme-substrate complex. Surprisingly, in three thiamin phosphate synthase structures, the active site density cannot be modeled as either substrates or products. For these structures, the best fit to the electron density is provided by a model that consists of independent pyrimidine, pyrophosphate, and thiazole phosphate fragments, consistent with a carbenium ion intermediate. The resulting carbenium ion is likely to be further stabilized by proton transfer from the pyrimidine amino group to the pyrophosphate to give the pyrimidine iminemethide, which we believe is the species that is observed in the crystal structures.

[Renal arteriovenous fistulas after renal biopsy. Percutaneous embolization]

PURPOSE

We report our experience relative to transcatheter percutaneous embolization of post-biopsy renal intraparenchymal arteriovenous fistulas in patients with chronic renal insufficiency.

MATERIAL AND METHODS

We observed 5 patients affected with post-bioptic fistulas for possible embolization. In three cases the symptoms were represented by intermittent macro-microhematuria; one patient had hypertension of nephrovascular origin and one patient was asymptomatic. In all cases we performed angiography and it was possible to catheterize the peripheral afferent branch of the fistula with a superselective technique using a hydrophilic guide of 0.035 F and a hydrophilic Cobra catheter of 4-5 F. The occlusion was obtained by the positioning of Granturco metal coils: in 1 case we adapted a coil of 3 mm diameter and 1 cm length; in 3 cases 2 coils of 3 mm and in 1 case 2 coils of 3 mm and 1 coil of 5 mm diameter and 1 cm length were necessary. The success of the procedure was always checked with an immediate angiogram and color Doppler US after 48 hrs.

RESULTS

The diagnosis of arteriovenous fistulas was always confirmed by a preliminary angiography that demonstrated the normal anatomic disposition of the renal arteries except in one case in which the fistula was fed by a peripheral branch originating from an inferior polar artery. All the lesions were localized in the inferior pole, the site of biopsy, and ranged from 3 mm to 2.5 cm in diameter. We never had any difficulties in the positioning and placement of the coils. The arterial occlusion and exclusion of the fistula was accomplished in all cases. The induced parenchymal loss ranged from 10 to 30% of the renal volume. There was a complete disappearance of symptoms in 3 of the patients, with hematuria without any modification of the blood pressure values in the patient with hypertension. Considering the patient status renal function did not worsen after the embolization. Each patient was followed-up with color Doppler US every two months.

CONCLUSIONS

The intrarenal arteriovenous fistula represents a relative frequent complication of renal needle biopsy in patients with arterial hypertension and nephroangiosclerosis as risk factors. Embolization is a valid alternative therapeutic option to surgical treatments. The use of small size catheters permits the successful embolization also of peripheral lesions, reducing the induced parenchymal ischemia. We believe that among the embolization material available metal coils represent a valid solution as they are easily positioned and permit definitive occlusion without any risks of systemic venous microembolization.

Primary renal lymphoma does exist: case report and review of the literature

Primary renal lymphoma (PRL) is a controversial and rare disease and there is still no agreement on its existence. Many cases have been reported in the literature, but clear diagnostic criteria have not yet been established. Most of the reported cases are questionable because of incomplete staging or the presence of extrarenal disease. Here we report a new case and a review of the literature based on a critical examination of the diagnostic procedure. Thus, probably only 29 cases, ours included, should be recognized as PRL, because only these cases fulfil the three diagnostic criteria and underwent complete diagnostic screening, including renal biopsy, bone marrow biopsy and thoraco-abdominal computerised tomography (CT).

Crystal structure of 4-methyl-5-beta-hydroxyethylthiazole kinase from Bacillus subtilis at 1.5 A resolution

4-Methyl-5-beta-hydroxyethylthiazole kinase (ThiK) catalyzes the phosphorylation of the hydroxyl group of 4-methyl-5-beta-hydroxyethylthiazole (Thz). This enzyme is a salvage enzyme in the thiamin biosynthetic pathway and enables the cell to use recycled Thz as an alternative to its synthesis from 1-deoxy-D-xylulose-5-phosphate, cysteine, and tyrosine. The structure of ThiK in the rhombohedral crystal form has been determined to 1.5 A resolution and refined to a final R-factor of 21. 6% (R-free 25.1%). The structures of the enzyme/Thz complex and the enzyme/Thz-phosphate/ATP complex have also been determined. ThiK is a trimer of identical subunits. Each subunit contains a large nine-stranded central beta-sheet flanked by helices. The overall fold is similar to that of ribokinase and adenosine kinase, although sequence similarity is not immediately apparent. The area of greatest similarity occurs in the ATP-binding site where several key residues are highly conserved. Unlike adenosine kinase and ribokinase, in which the active site is located between two domains within a single subunit, the ThiK active site it formed at the interface between two subunits within the trimer. The structure of the enzyme/ATP/Thz-phosphate complex suggests that phosphate transfer occurs by an inline mechanism. Although this mechanism is similar to that proposed for both ribokinase and adenosine kinase, ThiK lacks an absolutely conserved Asp thought to be important for catalysis in the other two enzymes. Instead, ThiK has a conserved cysteine (Cys198) in this position. When this Cys is mutated to Asp, the enzymatic activity increases 10-fold. Further sequence analysis suggests that another thiamin biosynthetic enzyme (ThiD), which catalyzes the formation of 2-methyl-4-amino-5-hydroxymethylpyrimidine pyrophosphate by two sequential phosphorylation reactions, belongs to the same family of small molecule kinases.

Thiamin biosynthesis in prokaryotes

Twelve genes involved in thiamin biosynthesis in prokaryotes have been identified and overexpressed. Of these, six are required for the thiazole biosynthesis (thiFSGH, thil, and dxs), one is involved in the pyrimidine biosynthesis (thiC), one is required for the linking of the thiazole and the pyrimidine (thiE), and four are kinase genes (thiD, thiM, thiL, and pdxK). The specific reactions catalyzed by ThiEF, Dxs, ThiDM, ThiL, and PdxK have been reconstituted in vitro and ThiS thiocarboxylate has been identified as the sulfur source. The X-ray structures of thiamin phosphate synthase and 5-hydroxyethyl-4-methylthiazole kinase have been completed. The genes coding for the thiamin transport system (thiBPQ) have also been identified. Remaining problems include the cloning and characterization of thiK (thiamin kinase) and the gene(s) involved in the regulation of thiamin biosynthesis. The specific reactions catalyzed by ThiC (pyrimidine formation), and ThiGH and ThiI (thiazole formation) have not yet been identified.

Crystal structure of thiaminase-I from Bacillus thiaminolyticus at 2.0 A resolution

Thiaminase-I catalyzes the replacement of the thiazole moiety of thiamin with a wide variety of nucleophiles, such as pyridine, aniline, catechols, quinoline, and cysteine. The crystal structure of the enzyme from Bacillus thiaminolyticus was determined at 2.5 A resolution by multiple isomorphous replacement and refined to an R factor of 0.195 (Rfree = 0.272). Two other structures, one native and one containing a covalently bound inhibitor, were determined at 2.0 A resolution by molecular replacement from a second crystal form and were refined to R factors of 0.205 and 0.217 (Rfree = 0.255 and 0.263), respectively. The overall structure contains two alpha/beta-type domains separated by a large cleft. At the base of the cleft lies Cys113, previously identified as a key active site nucleophile. The structure with a covalently bound thiamin analogue, which functions as a mechanism-based inactivating agent, confirms the location of the active site. Glu241 appears to function as an active site base to increase the nucleophilicity of Cys113. The mutant Glu241Gln was made and shows no activity. Thiaminase-I shows no sequence identity to other proteins in the sequence databases, but the three-dimensional structure shows very high structural homology to the periplasmic binding proteins and the transferrins.

Crystallization and preliminary X-ray analysis of thiaminase I from Bacillus thiaminolyticus: space group change upon freezing of crystals

Thiaminase I (Mr = 42 100) from B. thiaminolyticus, expressed in E. coli, has been crystallized by the vapor-diffusion method. Three crystal forms, two of which grew from 0.1 M sodium acetate (pH = 4.6), 0.2 M ammonium sulfate and 30%(w/v) PEG 2000, have been examined by X-ray analysis. One crystal form diffracted to 2.5 A at room temperature, was orthorhombic, and had unit-cell edges of a = 87.7, b = 120.5 and c = 76.7 A with space group P212121. A self-Patterson map showed a strong peak indicating noncrystallographic translational pseudosymmetry with (u, v, w) = (0.03, 0.0, 0.5). When these crystals were frozen at liquid-nitrogen temperatures, a second crystal form was observed which had unit-cell dimensions a = 85.5, b = 117.5 and c = 36.6 A with space group P21212. A third crystal form grew from 0.1 M Tris (pH = 8.5), 0.2 M sodium acetate trihydrate and 28%(w/v) PEG 6000 to produce orthorhombic crystals of space group P212121 with cell edges of a = 114.4, b = 123.1 and c = 92.5 A.

[Echography in the diagnosis and follow-up of renal biopsy complications]

The introduction of echography represented a focal step in the management of renal biopsy, resulting in easier and faster procedures. Chiefly, echography allows the diagnosis and monitoring of complications of bioptic procedure. Here we present a series of 722 consecutive echo-guided renal biopsies, carried out from 1990 to 1995, 97 of which on kidney allografts. Echographic examination, performed 24 to 48 hours after renal biopsy, enable to diagnose the presence of perirenal hematoma in 30% of patients. Of these, only 10% presented with clinical symptoms and/or signs (reduction of Hct and arterial pressure, local pain). Our protocol comprises an echographic follow-up to control the evolution of hematoma, that usually resolves within 15-40 days, according to the initial size of the lesion. One time we observed an intra-parenchimal hematoma, which resulted in kidney rupture and consequent nephrectomy. 14% of all patients complained with macrohematuria: in 10% of these cases, echography showed the presence of coaguli in the urinary tract, which was associated with the clinical features of renal colic pain. Only in two cases of persistent macrohematuria, the echography together with echo- and color-doppler, allowed the diagnosis of the arterio-venous fistula. In conclusion, our experience demonstrates that the echographic examination allows not only to simplify the bioptic procedure, but also to early diagnose the complications due to this invasive manouvre.

[Monoclonal antibodies in the diagnosis and therapy of lung cancer]

The discovery of monoclonal antibodies (MoAbs) by Köhler and Milstein in 1975 has marked a fundamental step accounting for the present development of immuno-oncology. The use of MoAbs in the study of lung carcinoma has allowed to enlarge our knowledge on the biology and natural history of this tumor, on the diagnostic procedures both in vitro and in vivo, on the monitoring of patients as well as on the therapeutic potentialities. A number of MoAbs have been produced, directed either to the small cell lung carcinoma or to the other histotypes which are altogether defined as non-small cell lung carcinoma. Although these reagents are not specific sensu strictiori, their use has been shown to be of partial utility for tumor imaging by immunoscintigraphy and for immunotherapeutic procedures based on the administration of MoAbs conjugated with radioactive isotopes or immunotoxins. Several attempts are presently under way aiming at the production of MoAbs endowed with a more defined specificity and larger potentialities. In this context, a special mention deserve the so-called third-generation MoAbs, anti-idiotype MoAbs, the cocktails of MoAbs, and chimeric antibodies also termed humanized MoAbs.

Treatment of adult patients with idiopathic thrombocytopenic purpura with intravenous immunoglobulin: effects on circulating T cell subsets and PWM-induced antibody synthesis in vitro

Eight adult patients with idiopathic thrombocytopenic purpura (ITP) were given two 5-d courses of intermediate (250 mg/kg body weight/d) to high dose (400 mg/kg body weight/d) intravenous infusions of human plasmin-cleaved Ig, at 15-30 d intervals. Three patients also were given single booster infusions (400 mg/kg body weight for 1 d) of a different preparation, S-sulfonated Ig. As expected, significant though transient rises in the platelet count were consistently observed in all patients. The mean platelet count increase was 95 600/mm3 after the first course, and 143 500/mm3 after the second course. Similar effects of lower magnitude were obtained several times in the patients given single booster doses. In three patients, platelet-bound IgG levels were decreased in association with Ig therapy. Phenotypic analysis of T cell subsets before starting Ig therapy and at the end of the second high dose course of intravenous Ig treatment revealed significant reductions in the proportion of T4+ lymphocytes in five patients and relative increases in the percentage of T8+ cells after therapy. As the overall proportion of T3+ cells remained unchanged, the T4+/T8+ ratio was therefore decreased. The total number of circulating lymphocytes was also decreased following therapy. In addition, PWM-driven Ig biosynthesis in vitro was significantly impaired after therapy in most patients, the capacity to synthesize IgG being mainly affected. It is concluded that, in addition to the reported transient blockade of the reticuloendothelial system, non-specific suppression of polyclonal Ig biosynthesis induced by the high dose Ig infusions also contributes to the net increase in platelet count.

Immunoglobulin secretion by peripheral blood and bone marrow B cells in patients with multiple myeloma. Studies by the reverse haemolytic plaque assay

The reverse haemolytic plaque assay (RHPA) was used to enumerate circulating and bone marrow (BM) immunoglobulin secreting cells (ISC) in patients with multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS), as well as in normal controls. Significantly greater quantities of plaque forming cells (PFC) secreting the same isotype of the serum M component were detected in the peripheral blood of MM patients than in the blood of MGUS patients or normal subjects. Comparative analysis of the numbers of monoclonal PFC in both peripheral blood (PB) and BM at diagnosis usually showed a higher number as well as more precocious chemotherapy-induced variations of ISC in the BM compartment than in the PB. Although large individual variations were observed during follow-up studies of MM patients, persistently increased or decreased levels of monoclonal PFC were often found to accompany (and sometimes to precede by months) the phases of relapse or remission, respectively. Similarly to IgG-MGUS patients, a distorted ratio of IgG kappa to IgG lambda secreting cells was consistently detected in patients with smouldering MM, although the total number (IgG kappa plus IgG lambda) of ISC appeared within normal limits. It is suggested that, in addition to other clinical and laboratory criteria, the RHPA may be of value in the diagnosis and follow-up of patients with monoclonal gammopathies.

Analogues in immunology

A number of immunological functions has been found to be endowed with biological rhythmicity. Variations of peripheral blood lymphocytes, immediate and delayed hypersensitivity responses, and reactivity of the immune system to antigenic challenge have consistently shown circadian bioperiodicity. By employing a panel of monoclonal antibodies specific for the various lymphocyte subsets, we have been able to detect rhythmic variations in the number of total T lymphocytes, as well as of the T helper (TH) and the T suppressor/cytotoxic (Ts) subsets. Available evidence clearly indicates such circadian variations to be due to compartmentalization of circulating lymphocytes in several lymphoid organs. Biological rhythms (circadian, circaseptan, etc.) have been demonstrated in several immunological situations of clinical interest, including variations of TH and Ts cells in patients with rheumatoid arthritis incidence of allograft rejections, antitumoral effectiveness of chemoimmunotherapy, and allergic symptoms. In addition, the recent availability of synthetic analogues of some thymic peptide hormones and of the synthetic ACTH 1-17 (Synchrodyn 1-17 is greatly contributing to the elucidation of the role of such hormones in the immune regulation process. A preliminary account is reported of the experiments performed with the aim of raising conventional rabbit antisera to the peptide analogue ACTH 1-17, as well as of the consistently negative results which were obtained when 578 human serum samples (from patients treated with such synthetic peptide) were screened by a radioimmunoassay for the occurrence of anti-ACTH 1-17 antibodies. It is emphasized that the recognition of the rhythmic variations of several immunological mechanisms and of the crucial role played by the analogues of adrenal corticotropic and thymic hormones in immune regulation has favoured significant advances in the fast growing area of chronoimmunology.