Identification and evaluation of small-molecule inhibitors against the dNTPase SAMHD1 via a comprehensive screening funnel

SAMHD1 is a dNTP triphosphohydrolase governing nucleotide pool homeostasis and can detoxify chemotherapy metabolites controlling their clinical responses. To understand SAMHD1 biology and investigate the potential of targeting SAMHD1 as neoadjuvant to current chemotherapies, we set out to discover selective small-molecule inhibitors. Here, we report a discovery pipeline encompassing a biochemical screening campaign and a set of complementary biochemical, biophysical, and cell-based readouts for rigorous characterization of the screen output. The identified small molecules, TH6342 and analogs, accompanied by inactive control TH7126, demonstrated specific, low μM potency against both physiological and oncology-drug-derived substrates. By coupling kinetic studies with thermal shift assays, we reveal the inhibitory mechanism of TH6342 and analogs, which engage pre-tetrameric SAMHD1 and deter oligomerization and allosteric activation without occupying nucleotide-binding pockets. Altogether, our study diversifies inhibitory modes against SAMHD1, and the discovery pipeline reported herein represents a thorough framework for future SAMHD1 inhibitor development.

Photo-physical characterization of high triplet yield brominated fluoresceins by transient state (TRAST) spectroscopy

Photo-induced dark transient states of fluorophores can pose a problem in fluorescence spectroscopy. However, their typically long lifetimes also make them highly environment sensitive, suggesting fluorophores with prominent dark-state formation yields to be used as microenvironmental sensors in bio-molecular spectroscopy and imaging. In this work, we analyzed the singlet-triplet transitions of fluorescein and three synthesized carboxy-fluorescein derivatives, with one, two or four bromines linked to the anthracence backbone. Using transient state (TRAST) spectroscopy, we found a prominent internal heavy atom (IHA) enhancement of the intersystem crossing (ISC) rates upon bromination, inferred by density functional theory calculations to take place via a higher triplet state, followed by relaxation to the lowest triplet state. A corresponding external heavy atom (EHA) enhancement was found upon adding potassium iodide (KI). Notably, increased KI concentrations still resulted in lowered triplet state buildup in the brominated fluorophores, due to relatively lower enhancements in ISC, than in the triplet decay. Together with an antioxidative effect on the fluorophores, adding KI thus generated a fluorescence enhancement of the brominated fluorophores. By TRAST measurements, analyzing the average fluorescence intensity of fluorescent molecules subject to a systematically varied excitation modulation, dark state transitions within very high triplet yield (>90%) fluorophores can be directly analyzed under biologically relevant conditions. These measurements, not possible by other techniques such as fluorescence correlation spectroscopy, opens for bio-sensing applications based on high triplet yield fluorophores, and for characterization of high triplet yield photodynamic therapy agents, and how they are influenced by IHA and EHA effects.

Enhanced cytotoxicity of a novel family of ATPase inhibitors in colorectal cancer cells with high NAT2 activity

Loss of heterozygosity (LOH) is a hallmark feature of cancer genomes that reduces allelic variation, thereby creating tumor specific vulnerabilities which could be exploited for therapeutic purposes. We previously reported that loss of drug metabolic arylamine N-acetyltransferase 2 (NAT2) activity following LOH at 8p22 could be targeted for collateral lethality anticancer therapy in colorectal cancer (CRC). Here, we report a novel compound CBK034026C that exhibits specific toxicity towards CRC cells with high NAT2 activity. Connectivity Map analysis revealed that CBK034026C elicited a response pattern related to ATPase inhibitors. Similar to ouabain, a potent inhibitor of the Na⁺/K⁺-ATPase, CBK034026C activated the Nf-kB pathway. Further metabolomic profiling revealed downregulation of pathways associated with antioxidant defense and mitochondrial metabolism in CRC cells with high NAT2 activity, thereby weakening the protective response to oxidative stress induced by CBK034026C. The identification of a small molecule targeting metabolic vulnerabilities caused by NAT2 activity provides novel avenues for development of anticancer agents.

Pharmacological targeting of MTHFD2 suppresses acute myeloid leukemia by inducing thymidine depletion and replication stress

The folate metabolism enzyme MTHFD2 (methylenetetrahydrofolate dehydrogenase/cyclohydrolase) is consistently overexpressed in cancer but its roles are not fully characterized, and current candidate inhibitors have limited potency for clinical development. In the present study, we demonstrate a role for MTHFD2 in DNA replication and genomic stability in cancer cells, and perform a drug screen to identify potent and selective nanomolar MTHFD2 inhibitors; protein cocrystal structures demonstrated binding to the active site of MTHFD2 and target engagement. MTHFD2 inhibitors reduced replication fork speed and induced replication stress followed by S-phase arrest and apoptosis of acute myeloid leukemia cells in vitro and in vivo, with a therapeutic window spanning four orders of magnitude compared with nontumorigenic cells. Mechanistically, MTHFD2 inhibitors prevented thymidine production leading to misincorporation of uracil into DNA and replication stress. Overall, these results demonstrate a functional link between MTHFD2-dependent cancer metabolism and replication stress that can be exploited therapeutically with this new class of inhibitors.

Glioblastoma cytotoxicity conferred through dual disruption of endolysosomal homeostasis by Vacquinol-1

Background

Increased membrane trafficking is observed in numerous cancer types, including glioblastoma. Targeting the oncogenic driven acquired alterations in membrane trafficking by synthetic cationic amphiphilic small molecules has recently been shown to induce death of glioblastoma cells, although the molecular targets are unknown.

Methods

The mechanism of action of the cationic amphiphilic drug Vacquinol-1 (Vacq1)-induced cytotoxicity was investigated using cell biology, biochemistry, functional experiments, chemical biology, unbiased antibody-based post-translation modification profiling, and mass spectrometry-based chemical proteomic analysis on patient-derived glioblastoma cells.

Results

Vacq1 induced two types of abnormal endolysosomal vesicles, enlarged vacuoles and acidic vesicle organelles (AVOs). Mechanistically, enlarged vacuoles were formed by the impairment of lysosome reformation through the direct interaction and inhibition of calmodulin (CaM) by Vacq1, while AVO formation was induced by Vacq1 accumulation and acidification in the endosomal compartments through its activation of the v-ATPase. As a consequence of v-ATPase activation, cellular ATP consumption markedly increased, causing cellular energy shortage and cytotoxicity. This effect of Vacq1 was exacerbated by its inhibitory effects on calmodulin, causing lysosomal depletion and a failure of acidic vesicle organelle clearance.

Conclusion

Our study identifies the targets of Vacq1 and the mechanisms underlying its selective cytotoxicity in glioblastoma cells. The dual function of Vacq1 sets in motion a glioblastoma-specific vicious cycle of ATP consumption resulting in cellular energy crisis and cell death.

Identification of a novel compound that simultaneously impairs the ubiquitin-proteasome system and autophagy

The ubiquitin-proteasome system (UPS) and macroautophagy/autophagy are the main proteolytic systems in eukaryotic cells for preserving protein homeostasis, i.e., proteostasis. By facilitating the timely destruction of aberrant proteins, these complementary pathways keep the intracellular environment free of inherently toxic protein aggregates. Chemical interference with the UPS or autophagy has emerged as a viable strategy for therapeutically targeting malignant cells which, owing to their hyperactive state, heavily rely on the sanitizing activity of these proteolytic systems. Here, we report on the discovery of CBK79, a novel compound that impairs both protein degradation by the UPS and autophagy. While CBK79 was identified in a high-content screen for drug-like molecules that inhibit the UPS, subsequent analysis revealed that this compound also compromises autophagic degradation of long-lived proteins. We show that CBK79 induces non-canonical lipidation of MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) that requires ATG16L1 but is independent of the ULK1 (unc-51 like autophagy activating kinase 1) and class III phosphatidylinositol 3-kinase (PtdIns3K) complexes. Thermal preconditioning of cells prevented CBK79-induced UPS impairment but failed to restore autophagy, indicating that activation of stress responses does not allow cells to bypass the inhibitory effect of CBK79 on autophagy. The identification of a small molecule that simultaneously impairs the two main proteolytic systems for protein quality control provides a starting point for the development of a novel class of proteostasis-targeting drugs.

Inhibition of the ubiquitin-proteasome system by an NQO1-activatable compound

Malignant cells display an increased sensitivity towards drugs that reduce the function of the ubiquitin-proteasome system (UPS), which is the primary proteolytic system for destruction of aberrant proteins. Here, we report on the discovery of the bioactivatable compound CBK77, which causes an irreversible collapse of the UPS, accompanied by a general accumulation of ubiquitylated proteins and caspase-dependent cell death. CBK77 caused accumulation of ubiquitin-dependent, but not ubiquitin-independent, reporter substrates of the UPS, suggesting a selective effect on ubiquitin-dependent proteolysis. In a genome-wide CRISPR interference screen, we identified the redox enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1) as a critical mediator of CBK77 activity, and further demonstrated its role as the compound bioactivator. Through affinity-based proteomics, we found that CBK77 covalently interacts with ubiquitin. In vitro experiments showed that CBK77-treated ubiquitin conjugates were less susceptible to disassembly by deubiquitylating enzymes. In vivo efficacy of CBK77 was validated by reduced growth of NQO1-proficient human adenocarcinoma cells in nude mice treated with CBK77. This first-in-class NQO1-activatable UPS inhibitor suggests that it may be possible to exploit the intracellular environment in malignant cells for leveraging the impact of compounds that impair the UPS.

Optimization of Tetrahydroindazoles as Inhibitors of Human Dihydroorotate Dehydrogenase and Evaluation of Their Activity and In Vitro Metabolic Stability

Human dihydroorotate dehydrogenase (DHODH), an enzyme in the de novo pyrimidine synthesis pathway, is a target for the treatment of rheumatoid arthritis and multiple sclerosis and is re-emerging as an attractive target for cancer therapy. Here we describe the optimization of recently identified tetrahydroindazoles (HZ) as DHODH inhibitors. Several of the HZ analogues synthesized in this study are highly potent inhibitors of DHODH in an enzymatic assay, while also inhibiting cancer cell growth and viability and activating p53-dependent transcription factor activity in a reporter cell assay. Furthermore, we demonstrate the specificity of the compounds toward the de novo pyrimidine synthesis pathway through supplementation with an excess of uridine. We also show that induction of the DNA damage marker γ-H2AX after DHODH inhibition is preventable by cotreatment with the pan-caspase inhibitor Z-VAD-FMK. Additional solubility and in vitro metabolic stability profiling revealed compound 51 as a favorable candidate for preclinical efficacy studies.

Irreversible TrxR1 inhibitors block STAT3 activity and induce cancer cell death

Because of its key role in cancer development and progression, STAT3 has become an attractive target for developing new cancer therapeutics. While several STAT3 inhibitors have progressed to advanced stages of development, their underlying biology and mechanisms of action are often more complex than would be expected from specific binding to STAT3. Here, we have identified and optimized a series of compounds that block STAT3-dependent luciferase expression with nanomolar potency. Unexpectedly, our lead compounds did not bind to cellular STAT3 but to another prominent anticancer drug target, TrxR1. We further identified that TrxR1 inhibition induced Prx2 and STAT3 oxidation, which subsequently blocked STAT3-dependent transcription. Moreover, previously identified inhibitors of STAT3 were also found to inhibit TrxR1, and likewise, established TrxR1 inhibitors block STAT3-dependent transcriptional activity. These results provide new insights into the complexities of STAT3 redox regulation while highlighting a novel mechanism to block aberrant STAT3 signaling in cancer cells.

A drug screening assay on cancer cells chronically adapted to acidosis

Background

Drug screening for the identification of compounds with anticancer activity is commonly performed using cell lines cultured under normal oxygen pressure and physiological pH. However, solid tumors are characterized by a microenvironment with limited access to nutrients, reduced oxygen supply and acidosis. Tumor hypoxia and acidosis have been identified as important drivers of malignant progression and contribute to multicellular resistance to different forms of therapy. Tumor acidosis represents an important mechanism mediating drug resistance thus the identification of drugs active on acid-adapted cells may improve the efficacy of cancer therapy.

Methods

Here, we characterized human colon carcinoma cells (HCT116) chronically adapted to grow at pH 6.8 and used them to screen the Prestwick drug library for cytotoxic compounds. Analysis of gene expression profiles in parental and low pH-adapted cells showed several differences relating to cell cycle, metabolism and autophagy.

Results

The screen led to the identification of several compounds which were further selected for their preferential cytotoxicity towards acid-adapted cells. Amongst 11 confirmed hits, we primarily focused our investigation on the benzoporphyrin derivative Verteporfin (VP). VP significantly reduced viability in low pH-adapted HCT116 cells as compared to parental HCT116 cells and normal immortalized epithelial cells. The cytotoxic activity of VP was enhanced by light activation and acidic pH culture conditions, likely via increased acid-dependent drug uptake. VP displayed the unique property to cause light-dependent cross-linking of proteins and resulted in accumulation of polyubiquitinated proteins without inducing inhibition of the proteasome.

Conclusions

Our study provides an example and a tool to identify anticancer drugs targeting acid-adapted cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0645-5) contains supplementary material, which is available to authorized users.

High-affinity recognition of the human C-reactive protein independent of phosphocholine

A high-affinity polypeptide conjugate 4-C25L22-DQ, has been developed for the molecular recognition of the human C-reactive protein, CRP, a well-known inflammation biomarker. CRP is one of the most frequently quantified targets in diagnostic applications and a target in drug development. With the exception of antibodies, most molecular constructs take advantage of the known affinity for CRP of phosphocholine that depends on Ca²⁺ for its ability to bind. 4-C25L22-DQ which is unrelated to phosphocholine binds in the absence of Ca²⁺ with a dissociation constant of 760 nM, an order of magnitude lower than that of phosphocholine, the K_D of which is 5 μM. The small organic molecule 2-oxo-1,2-dihydroquinoline-8-carboxylic acid (DQ) was designed based on the structural similarities between three hits from a set of compounds selected from a building block collection and evaluated with regards to affinity for CRP by NMR spectroscopy. 4-C25L22-DQ was shown in a competition experiment to bind CRP three orders of magnitude more strongly than DQ itself, and in a pull-down experiment 4-C25L22-DQ was shown to extract CRP from human serum. The development of a robust and phosphocholine-independent recognition element provides unprecedented opportunities in bioanalytical applications in vivo and in vitro under conditions where the concentration of Ca²⁺ ions is low, or where Ca²⁺ binding agents such as EDTA or heparin are needed to prevent blood coagulation. The identification from a compound library of a small organic molecule and its conjugation to a small set of polypeptides, none of which were previously known to bind CRP, illustrates a convenient and general route to selective high-affinity binders for proteins with dissociation constants in the μM to nM range for which no small molecule ligands are known.

Identification of inhibitors of Tartrate-resistant acid phosphatase (TRAP/ACP5) activity by small-molecule screening

Tartrate-resistant acid phosphatase (TRAP/ACP5) occurs as two isoforms-TRAP 5a with low enzymatic activity due to a loop interacting with the active site and the more active TRAP isoform 5b generated upon proteolytic cleavage of this loop. TRAP has been implicated in several diseases, including cancer. Thus, this study set out to identify small-molecule inhibitors of TRAP activity. A microplate-based enzymatic assay for TRAP 5b was applied in a screen of 30,315 compounds, resulting in the identification of 90 primary hits. After removal of promiscuous compounds, unwanted groups, and false positives by orthogonal assays and three-concentration validation, the properties of 52 compounds were further investigated to better understand their mechanism of action. Full-concentration-response curves for these compounds were established under different enzyme concentrations and (pre)incubation times to remove compounds with inconsistent results and low potencies. Full-concentration-response curves were also performed for both isoforms, to examine isoform prevalence. Filtering led to six prioritized compounds, representing different clusters. One of these, CBK289001 or (6S)-6-[3-(2H-1,3-benzodioxol-5-yl)-1,2,4-oxadiazol-5-yl]-N-(propan-2-yl)-1H,4H,5H,6H,7H-imidazo[4,5-c]pyridine-5-carboxamide, demonstrated efficacy in a migration assay and IC₅₀ values from 4 to 125 μm. Molecular docking studies and analog testing were performed around CBK289001 to provide openings for further improvement toward more potent blockers of TRAP activity.

A DHODH inhibitor increases p53 synthesis and enhances tumor cell killing by p53 degradation blockage

The development of non-genotoxic therapies that activate wild-type p53 in tumors is of great interest since the discovery of p53 as a tumor suppressor. Here we report the identification of over 100 small-molecules activating p53 in cells. We elucidate the mechanism of action of a chiral tetrahydroindazole (HZ00), and through target deconvolution, we deduce that its active enantiomer (R)-HZ00, inhibits dihydroorotate dehydrogenase (DHODH). The chiral specificity of HZ05, a more potent analog, is revealed by the crystal structure of the (R)-HZ05/DHODH complex. Twelve other DHODH inhibitor chemotypes are detailed among the p53 activators, which identifies DHODH as a frequent target for structurally diverse compounds. We observe that HZ compounds accumulate cancer cells in S-phase, increase p53 synthesis, and synergize with an inhibitor of p53 degradation to reduce tumor growth in vivo. We, therefore, propose a strategy to promote cancer cell killing by p53 instead of its reversible cell cycle arresting effect.

Identification of novel small molecules that inhibit STAT3-dependent transcription and function

Activation of Signal Transducer and Activator of Transcription 3 (STAT3) has been linked to several processes that are critical for oncogenic transformation, cancer progression, cancer cell proliferation, survival, drug resistance and metastasis. Inhibition of STAT3 signaling has shown a striking ability to inhibit cancer cell growth and therefore, STAT3 has become a promising target for anti-cancer drug development. The aim of this study was to identify novel inhibitors of STAT-dependent gene transcription. A cellular reporter-based system for monitoring STAT3 transcriptional activity was developed which was suitable for high-throughput screening (Z’ = 0,8). This system was used to screen a library of 28,000 compounds (the ENAMINE Drug-Like Diversity Set). Following counter-screenings and toxicity studies, we identified four hit compounds that were subjected to detailed biological characterization. Of the four hits, KI16 stood out as the most promising compound, inhibiting STAT3 phosphorylation and transcriptional activity in response to IL6 stimulation. In silico docking studies showed that KI16 had favorable interactions with the STAT3 SH2 domain, however, no inhibitory activity could be observed in the STAT3 fluorescence polarization assay. KI16 inhibited cell viability preferentially in STAT3-dependent cell lines. Taken together, using a targeted, cell-based approach, novel inhibitors of STAT-driven transcriptional activity were discovered which are interesting leads to pursue further for the development of anti-cancer therapeutic agents.

CETSA screening identifies known and novel thymidylate synthase inhibitors and slow intracellular activation of 5-fluorouracil

Target engagement is a critical factor for therapeutic efficacy. Assessment of compound binding to native target proteins in live cells is therefore highly desirable in all stages of drug discovery. We report here the first compound library screen based on biophysical measurements of intracellular target binding, exemplified by human thymidylate synthase (TS). The screen selected accurately for all the tested known drugs acting on TS. We also identified TS inhibitors with novel chemistry and marketed drugs that were not previously known to target TS, including the DNA methyltransferase inhibitor decitabine. By following the cellular uptake and enzymatic conversion of known drugs we correlated the appearance of active metabolites over time with intracellular target engagement. These data distinguished a much slower activation of 5-fluorouracil when compared with nucleoside-based drugs. The approach establishes efficient means to associate drug uptake and activation with target binding during drug discovery.

Abstract 5509: A drug-screening model to identify compounds active in cells under metabolic stress

Background and aim: Promising anticancer compounds often fail in vivo due to lack of efficacy. Drug screenings to identify anticancer agents are usually performed in culture conditions that very poorly represent the complex metabolic tumor environment. Tumor tissues are characterised by low oxygen (hypoxia) and acidic extracellular pH (acidosis). A screen of a drug-library for compounds able to induce cell death in acidic/hypoxic conditions may lead to discover effective drugs targeting quiescent/hypoxic cells, normally considered responsible for tumor relapses after therapy. Methods: The colon carcinoma cell line HCT-116 has been adapted to grow in low pH conditions (pH 6.8). The Prestwick compound library (1200 FDA-approved compounds) was used to validate the assay. Cell viability was measured using the acid phosphatase assay after 48 hours exposure to test compounds. The assay was validated in HCT-116 cells cultured in normoxic and hypoxic conditions. Multicellular spheroids (MCS) were used to evaluate the sensitivity to hit compounds confirmed at least three times in 2D culture conditions. Results: The assay was optimized to perform the screening at pH 6.8 in normoxic and hypoxic conditions. Experiments have demonstrated the ability of cells to survive and grow in hypoxic conditions (1% oxygen) for at least 4 days. The test was optimized in terms of number of plated cells and serum concentration. Hit compounds were identified based on the mean values for quality control plus 3 standard deviations of untreated samples. The screen led to identify 20 hits for both conditions and 11 hits were further confirmed for hypoxic/acidic conditions. Auranofin and Verteporfin showed to better induce cell death in cells adapted or acutely exposed to low pH compared to parental cells and immortalized epithelial cells (RPE1). Both drugs showed cytotoxic effects on cells grown as MCS, suggesting a potential good efficacy of the therapeutic agent in vivo. In addition, the screening of about 10000 compounds of the LCBKI library is ongoing and about 100 hits have been identified. Conclusions: The screening validation on the Prestwick library will hopefully lead to identify potential “off-label” effects of already approved drugs. The screening of larger drug-libraries will hopefully lead to find and characterize more compounds able to target slow proliferating and therapy resistant cells.

Citation Format: Paola Pellegrini, Martin Haraldsson, Annika Jenmalm Jensen, Thomas Lundbäck, Angelo De Milito. A drug-screening model to identify compounds active in cells under metabolic stress. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5509. doi:10.1158/1538-7445.AM2015-5509

[Meningeal carcinomatosis. A case report.]

We describe a 69 year old man presenting with acute confusional state as the first symptom of meningeal carcinomatosis complicating adenocarcinoma of the lung. For three weeks preceding the admission the patient was intermittently and increasingly confused and short term memory was clearly impaired but normal in-between. The patient stopped working one week prior to admission because of the mental changes. He also had two months history of increasing neck pain. He was otherwise well except for history of mild hypertension. General physical examination and neurological examination were essentially unremarkable except for somewhat distant affect and he was fully oriented and without aphasia. The patient was somewhat uncooperative and left the emergency room against medical advice after a spinal tap had been done. The cerebrospinal fluid was markedly abnormal showing slight increase in mono-nucleated white cells (22/M1), markedly elevated protein (3.4 g/1 (0.2-0.4)) and decreased glucose con notcentration (0.8 mmol/1 (2.5-4.0)). The patient was immediately readmitted to the hospital and the differential diagnosis of fungal, tuberculous or neoplastic meningitis was considered based on the cerebrospinal fluid (CSF) findings. Chest X-ray demonstrated a lesion in the right upper lobe and repeated CSF exa notmination showed neoplastic cells forming gland like structures. Lung biopsy demonstrated adenocarcinoma. The clinical condition of the patient worsened rapidly and he died five days after admission.

[A prospective study of oral anticoagulation therapy monitored with the P&P-test.]

OBJECTIVE

To analyze the outcome of patients on oral anticoagulation therapy who are monitored with the prothrombin proconvertin time (P&P-test, PP).

MATERIAL AND METHODS

The prothrombin-proconvertin time was used to adjust anticoagulant intensity in a prospective study of 326 patients treated with oral anticoagulants for a study period of 121 patient years. The goal intensity INR was 2.0-3.0 for all patients. The main indications were: artificial heart valves 26%, venousthromboembolism 25%, atrial fibrillation 23%, atherosclerotic disease 14% and systemic arterial embolism of uncertain etiology 7%.

RESULTS

INR calculated directly from the PP correlated well with INR calculated from the PT. The mean time adjusted anticoagulant intensity was 2.3 and did not differ significantly according to indication. Six major bleedings, including one fatal, occurred in five patients during the study period. The INR was 1.8 in one patient who bled from a duodenal ulcer, but 6.8,7.9,8.6,11.6 (died) and 15.5 at five other events. The INR was <4.5 during 97% of the treatment time of the whole group and 1% of treat notment time were at an INR>6.0. The bleeders had a different pattern with 18% of the treatment time at INR>6.0. The risk of bleeding was one for every 73 days at that intensity or an almost 600 fold risk increase compared to an INR<4.5. One patient anticoagulated for systemic embolism had cerebral infarction with an event related INR of 2.0. Two patients with atrial fibrillation died from acute myocardial infarction but event related INR's were not available. One patient anticoagulated for venous thromboembolism died suddenly but was not autopsied. No embolic events occurred in patients with artificial heart valves in spite of the low intensity anticoagulation.

CONCLUSION

Despite a relatively low intensity in all patient groups in this study thromboembolic events were rare. The risk of bleeding increased markedly at INR>6.0. The mortality rate of the ariticoagulated population was comparable to the expected age adjusted Icelandic mortality rate.

Correlations of splitting and phobic anxiety with dreaming

Dream characteristics of 28 women from a graduate counseling program were correlated with measures of phobic anxiety, splitting, and sleepiness. Significant correlations between splitting and recurrent nightmares (.68), agoraphobia and dreams about death (.44), and global phobia and recurrent nightmares (.56) were obtained. Results are discussed in terms of how phobic anxieties and splitting may relate to traumatic content and the dream process.

Effect on human liver glycosidases and short syntheses of 1 alpha,2 alpha,6 alpha,7 alpha,7a beta-1,2,6,7-tetrahydroxypyrrolizidine from D-glycero-D-gulo-heptono-1,4-lactone

The synthesis of 1 alpha,2 alpha,6 alpha,7 alpha,7a beta-1,2,6,7-tetrahydroxypyrrolizidine (1) from D-glycero-D-gulo-heptono-1,4-lactone (6) by two different routes is reported. The effects of 1 on the inhibition of 15 human liver glycosidases are described.

Binding and precipitating activities of Erythrina lectins with complex type carbohydrates and synthetic cluster glycosides. A comparative study of the lectins from E. corallodendron, E. cristagalli, E. flabelliformis, and E. indica

Erythrina lectins possess similar structural and carbohydrate binding properties. Recently, tri- and tetra-antennary complex type carbohydrates with non-reducing terminal galactose residues have been shown to be precipitated as tri- and tetravalent ligands, respectively, with certain Erythrina lectins [Bhattacharyya L, Haraldsson M, Brewer CF (1988) Biochemistry 27:1034-41]. The present work describes a comparative study of the binding and precipitating activities of four Erythrina lectins, viz., E. corallodendron, E. cristagalli, E. flabelliformis, and E. indica, with multi-antennary complex type carbohydrates and synthetic cluster glycosides. The results show that though their binding affinities are very similar, the Erythrina lectins show large differences in their precipitating activities with the carbohydrates. The results also indicate significant dependence of the precipitating activities of the lectins on the core structure of the carbohydrates. These findings provide a new dimension to the structure-activity relationship of the lectins and their interactions with asparagine-linked carbohydrates.

Precipitation of galactose-specific lectins by complex-type oligosaccharides and glycopeptides: studies with lectins from Ricinus communis (agglutinin I), Erythrina indica, Erythrina arborescens, Abrus precatorius (agglutinin), and Glycine max (soybean)

We have recently demonstrated that certain oligomannose and bisected hybrid type glycopeptides and bisected complex type oligosaccharides are bivalent for binding to concanavalin A and can precipitate the lectin [Bhattacharyya, L., Ceccarini, C., Lorenzoni, P., & Brewer, C.F. (1987) J. Biol. Chem. 262, 1288-1293; Bhattacharyya, L., Haraldsson, M., & Brewer, C.F. (1987) J. Biol. Chem. 262, 1294-1299]. The present results show that tri- and tetraantennary complex type oligosaccharides containing nonreducing terminal galactose residues, and a related triantennary glycopeptide, precipitate the D-galactose-specific lectins from Ricinus communis (agglutinin I) (RCA-I), Erythrina indica (EIL), Erythrina arborescens (EAL), and Glycine max (soybean) (SBA). Nonbisected and bisected biantennary complex type oligosaccharides can precipitate SBA, which is a tetrameric lectin, but not RCA-I, EIL, or EAL, which are dimeric lectins. The relative affinities of the oligosaccharides and glycopeptide were determined by hemagglutination inhibition measurements and their valencies by quantitative precipitin analyses. The equivalence points of the precipitin curves indicate that the tri- and tetraantennary oligosaccharides are tri- and tetravalent, respectively, for EIL, EAL, and SBA binding. However, the oligosaccharides are all trivalent for RCA-I binding due apparently to the larger size of the monomeric subunit of the lectin. The triantennary glycopeptide was also trivalent for RCA-I and EIL binding. Biantennary oligosaccharides with adequate chain lengths were found to be bivalent for binding to SBA; those with shorter chains did not precipitate the lectin.(ABSTRACT TRUNCATED AT 250 WORDS)

Concanavalin A interactions with asparagine-linked glycopeptides. Bivalency of bisected complex type oligosaccharides

In the preceding paper (Bhattacharyya, L., Ceccarini, C., Lorenzoni, P., and Brewer, C.F. (1987) J. Biol. Chem. 262, 1288-1293), we have demonstrated that certain high mannose and bisected hybrid type glycopeptides are bivalent for concanavalin A (ConA) binding. In the present study, we have investigated the interactions of ConA with a series of synthetic nonbisected and bisected complex type oligosaccharides and related glycopeptides. The modes of binding of the carbohydrates were studied by nuclear magnetic relaxation dispersion techniques, and their affinities were determined by hemagglutination inhibition measurements. We find that certain bisected complex type oligosaccharides are capable of binding and precipitating the lectin. The corresponding nonbisected analogs, however, bind but do not precipitate the protein. The stoichiometries of the precipitin reactions were investigated by quantitative precipitation analyses. The equivalence zones (regions of maximum precipitation) of the precipitin curves indicate that the bisected complex type oligosaccharides are bivalent for lectin binding. Data for the nonbisected analogs are consistent with their being univalent. The nuclear magnetic relaxation dispersion and precipitation data indicate that nonbisected and bisected complex type carbohydrates bind with different mechanisms and conformations. The former class binds by extended site interactions with the protein involving the 2 alpha-mannose residues on the alpha(1-6) and alpha(1-3) arms of the core beta-mannose residue. The latter class binds by only 1 of these 2 mannose residues, which leaves the other mannose residue free to bind to a second ConA molecule. The role of the bisecting GlcNAc residue in affecting the binding properties of complex type carbohydrates to ConA is discussed, and the results are related to the possible structure-function properties of complex type glycopeptides on the surface of cells.

Binding of synthetic oligosaccharides to the hepatic Gal/GalNAc lectin. Dependence on fine structural features

A series of synthetic oligosaccharides, resembling natural N-acetyllactosamine type glycans, were tested for their ability to inhibit the binding of labeled ligand to the mammalian hepatic lectin on rabbit hepatocytes at 2 degrees C. A dramatic hierarchy of inhibitory potency (tetraantennary greater than triantennary much greater than biantennary much greater than monoantennary) could be demonstrated. The range of concentration required for 50% inhibition of labeled ligand binding extended from approximately 1 mM, for the monoantennary oligosaccharides, to approximately 1 nM for triantennary oligosaccharides, even though the absolute Gal concentration increased only 3-fold. It was found that the number of Gal residues/cluster and their branching mode are major determinants of binding affinity of ligands to the hepatic lectin on the surface of hepatocytes.

Synthesis of three oligosaccharides that form part of the complex type of carbohydrate moiety of glycoproteins

Silver trifluoromethanesulfonate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl bromide with benzyl 3,6-di-O-benzyl-alpha-D-mannopyranoside and benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside gave the protected 2,4- and 2,6-linked trisaccharides in yields of 54 and 32%, respectively. After exchanging the 2-deoxy-2-phthalimido groups for 2-acetamido-2-deoxy groups and de-blocking, the trisaccharides 2,4-di-O-(2-deoxy-beta-D-glucopyranosyl)-D-mannose and 2,6-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-D-mannose were obtained. Similar condensation of 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-beta-D-glucopyranosyl bromide with benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside gave a pentasaccharide derivative in 52% yield. After transformations analogous to those applied to the trisaccharides, 2,6-di-O-[beta-D-galactopyranosyl-(1 leads to 4)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)]-D-mannose was obtained.