Vascular endothelial-cadherin is an important determinant of microvascular integrity in vivo

In the present paper, we characterize an antibody, mAb BV13, directed to mouse vascular endothelial (VE)-cadherin, a major adhesive protein of interendothelial adherens junctions. When added to cultured endothelial cells, BV13 induces a redistribution of VE-cadherin from intercellular junctions. VE-cadherin redistribution did not change the localization of platelet endothelial cell adhesion molecule or tight junction markers such as zonula occludens 1, cingulin, and junctional adhesion molecule. Intravenous administration of mAb BV13 induced a concentration- and time-dependent increase in vascular permeability in heart and lungs. By electron microscopy, interstitial edema and accumulation of mixed types of inflammatory cells in heart and lungs were observed. Injection of (rhodamine-labeled) Ricinus communis I lectin showed focal spots of exposed basement membrane in the alveolar capillaries and in some larger pulmonary vessels. These data indicate that VE-cadherin is required for vascular integrity and normal organ functions.

Differences in the protein composition of bovine retinal rod outer segment disk and plasma membranes isolated by a ricin-gold-dextran density perturbation method

The plasma membrane and disk membranes of bovine retinal rod outer segments (ROS) have been purified by a novel density-gradient perturbation method for analysis of their protein compositions. Purified ROS were treated with neuraminidase to expose galactose residues on plasma membrane-specific glycoproteins and labeled with ricin-gold-dextran particles. After the ROS were lysed in hypotonic buffer, the plasma membrane was dissociated from the disks by either mild trypsin digestion or prolonged exposure to low ionic strength buffer. The dense ricin-gold-dextran-labeled plasma membrane was separated from disks by sucrose gradient centrifugation. Electron microscopy was used to follow this fractionation procedure. The dense red pellet primarily consisted of inverted plasma membrane vesicles containing gold particles; the membrane fraction of density 1.13 g/cc consisted of unlabeled intact disks and vesicles. Ricin-binding studies indicated that the plasma membrane from trypsin-treated ROS was purified between 10-15-fold. The protein composition of plasma membranes and disks was significantly different as analyzed by SDS gels and Western blots labeled with lectins and monoclonal antibodies. ROS plasma membrane exhibited three major proteins of 36 (rhodopsin), 38, and 52 kD, three ricin-binding glycoproteins of 230, 160, and 110 kD, and numerous minor proteins in the range of 14-270 kD. In disk membranes rhodopsin appeared as the only major protein. A 220-kD concanavalin A-binding glycoprotein and peripherin, a rim-specific protein, were also present along with minor proteins of 43 and 57-63 kD. Radioimmune assays indicated that the ROS plasma membrane contained about half as much rhodopsin as disk membranes.

Immunotoxins in cancer therapy

Immunotoxins are composed of a protein toxin connected to a binding ligand such as an antibody or growth factor. These molecules bind to surface antigens (which internalize) and kill cells by catalytic inhibition of protein synthesis within the cell cytosol. Immunotoxins have recently been tested clinically in hematologic malignancies and solid tumors and have demonstrated potent clinical efficacy in patients with malignant diseases that are refractory to surgery, radiation therapy and chemotherapy - the traditional modalities of cancer treatment. This therapy is thus evolving into a separate modality of cancer treatment, capable of rationally targeting cells on the basis of surface markers. Efforts are underway to obviate impediments to clinical efficacy, including immunogenicity and toxicity to normal tissues. Immunotoxins are now being developed to new antigens for the treatment of cancer.

Suicide transport: destruction of neurons by retrograde transport of ricin, abrin, and modeccin

Certain toxic lectins, including ricin, are retrogradely transported along neuronal processes to the cell body where they inactivate ribosomes, resulting in neuronal death. This process of "suicide transport" suggests a powerful new experimental strategy for solving neurobiological problems.

Distribution of saccharide residues on membrane fragments from a myeloma-cell homogenate: its implications for membrane biogenesis

Ferritin conjugates of two plant agglutinins, concanavalin A and ricin, have been used as specific electron microscopic stains for covalently-bound saccharide residues on membrane fragments from a myeloma-cell homogenate. The results indicate that different saccharide residues are uniformly localized to a single surface of each membrane fragment. In particular, the ferritin-concanavalin A conjugate binds exclusively to the cisternal side of membrane fragments of the rough endoplasmic reticulum. If it is postulated that the biogenesis of eukaryotic plasma membranes involves an assembly-line process from precursor intracellular membranes, these observed asymmetric distributions of saccharides on cell membranes can be explained.

Microglia in the giant cell encephalitis of acquired immune deficiency syndrome: proliferation, infection and fusion

The autopsied brains of three homosexual men with acquired immune deficiency syndrome (AIDS), progressive encephalopathy and widespread multinucleated giant cell encephalitis were investigated by lectin and immunohistochemical methods to ascertain the cellular distribution of a human immunodeficiency virus (HIV) core protein, p25. Abundant viral antigen was present in all brains, limited to perivascular macrophages, microglial and multinucleated cells, some bearing elongated cytoplasmic processes. The multinucleated cells were consistently labelled by the lectin Ricinus communis agglutinin-1, a marker for microglia, which demonstrated process-bearing variants of these cells. The prominent staining of microglia for viral antigen and the morphological suggestion that they fuse with other microglia and/or macrophages to form the multinucleated cells characteristic of HIV encephalitis indicate that microglia are probably direct targets of HIV infection and serve to propagate and amplify this retroviral encephalitis.

Evidence that glutamic acid 167 is an active-site residue of Shiga-like toxin I

Escherichia coli Shiga-like toxin I, a close relative of Shiga toxin and a distant relative of the ricin family of plant toxins, inhibits eukaryotic protein synthesis by catalyzing the depurination of adenosine 4324 in 28S rRNA. By comparing the crystallographic structure of ricin with amino acids conserved between the Shiga and ricin toxin families, we identified seven potential active-site residues of Shiga-like toxin I. The structural gene encoding Shiga-like toxin I A chain (Slt-IA), the enzymatically active subunit, was engineered for high expression in E. coli. Oligonucleotide-directed mutagenesis of the gene for Slt-IA was used to change glutamic acid 167 to aspartic acid. As measured by an in vitro assay for inhibition of protein synthesis, the specific activity of mutant Slt-IA was decreased by a factor of 1000 compared to wild-type Slt-IA. Immunoblots showed that mutant and wild-type Slt-IA were synthesized as full-length proteins and were processed correctly by signal peptidase. Both proteins were equally susceptible to trypsin digestion, suggesting that the amino acid substitution did not produce a major alteration in Slt-IA conformation. We conclude that glutamic acid 167 is critical for activity of the Shiga-like toxin I A chain and may be located at the active site.

Binding of galactose and lactose to ricin. Equilibrium studies

The interaction of ricin, one of the two lectins of Ricinus sanguineus, with its specific ligands galactose and lactose (4-O-beta-D-galactopyranosyl-D-glucopyranose) has been studied by means of equilibrium dialysis, analytical ultracentrifugation and fluorescence polarization. In the studied concentration range, only one molecule of galactose is bound per molecule of ricin with an association constant, Ka = 6900 m-1 at 4 degrees C. Scatchard plots of equilibrium dialysis data show that two molecules of lactose bind to one molecule of ricin, without modification of molecular weight of the lectin. Together with results of microcalorimetric experiments and agglutination of erythrocytes by ricin, equilibrium dialysis data indicate that the lectin contains two distinct saccharide binding sites. Regardless of the existence of extended sites, it is not possible to select between the two models: (a) two independent sites (Ka1 = 35 000 M-1, Ka2 = 2800 M-1 at 4 degrees C) or (b) two identical sites with negative cooperativity.

Expression of choline acetyltransferase and nerve growth factor receptor within hypoglossal motoneurons following nerve injury

In the present study we employed light microscopic immunocytochemical techniques in order to investigate the temporal response of choline acetyltransferase (ChAT) and nerve growth factor receptor (NGFr) within hypoglossal motoneurons following unilateral transection or crushing of the XII nerve or after intraneural injections of ricin into the nerve. In control rats (i.e., sham operated) virtually all the motoneurons of the XII nucleus displayed intense immunolabeling for ChAT and were devoid of NGFr immunoreactivity. As early as 3 days post-operative the intensity and the number of ChAT-labeled neurons were reduced on the axotomized side compared to the non-lesioned side. This decrease was maximal approximately two weeks post-operative when virtually no ChAT-labeled cells were present on the lesioned side. In contrast, no loss of hypoglossal neurons was found using Nissl stains. This absence of ChAT immunolabeling persisted for several days, yet by 30 days many of the motoneurons had begun to re-express the enzyme. In contrast to the decrease in ChAT immunoreactivity, transection of the XII nerve also resulted in the expression of NGFr immunoreactivity within the lesioned motoneurons. This response was detected as early as one day post-operatively and continued throughout all time points thus far examined including times after many of the motoneurons had begun to re-express ChAT. Crushing of the XII nerve effected the expression of ChAT and NGFr in a manner comparable to, yet less intense than, that observed following transection. Ricin injected directly into the XII nerve resulted in the loss of hypoglossal motoneurons as demonstrated both in immunohistochemical and Nissl-stained tissue preparations. The cell loss was readily apparent 3 days post-operatively, and ChAT immunoreactivity permanently disappeared. NGFr immunolabeling was seen only in scattered surviving neurons but not in ricin poisoned cells. The possible mechanisms underlying the differential expression of ChAT and NGFr are discussed.

Improved tumor-specific immunotoxins in the treatment of CNS and leptomeningeal neoplasia

A novel antibody-toxin conjugate has been developed for use in cancer therapy. This report demonstrates that this new reagent selectively kills glioblastoma- and medulloblastoma-derived cell lines, medulloblastoma cells in primary culture, and cell lines derived from tumors commonly metastatic to the cerebrospinal fluid (CSF). Efficient killing of human tumor cells occurred at concentrations between 3.9 X 10(-13) M and 1.1 X 10(-10) M, whereas guinea pigs and rhesus monkeys tolerated intrathecal levels of 2 X 10(-9) M. Cerebrospinal fluid from normal humans and from brain-tumor patients does not inhibit the in vitro efficacy of this reagent. The wide therapeutic window, extreme potency, and general applicability of this antibody-toxin conjugate against CSF-borne primary or metastatic tumors warrants clinical trials.

The removal of carbohydrates from ricin with endoglycosidases H, F and D and alpha-mannosidase

Recently, several investigators have explored the possibility of targeting ricin to designated cell types in animals by its linkage to specific antibodies. There is evidence, however, that the mannose-containing oligosaccharide chains on ricin are recognised by reticuloendothelial cells in the liver and spleen and so cause the immunotoxins to be removed rapidly from the blood stream. In the present study we analysed the carbohydrate composition of ricin and examined enzymic methods for removing the carbohydrate. The carbohydrate analysis ricin A-chain revealed the presence of one residue of xylose and one of fucose in addition to mannose and N-acetylglucosamine which had been detected previously. The B-chain contained only mannose and N-acetylglycosamine. Ricin A-chain is heterogeneous containing two components of molecular weight 30 000 and 32 000. Strong evidence was found that the heavier form of the A-chain contains an extra carbohydrate unit which is heterogeneous with respect to concanavalin A binding and sensitivity to endoglycosidase H. The lower molecular weight form of A-chain did not bind concanavalin A and was insusceptible to endoglycosidases. Only one of the two high mannose oligosaccharide units on the isolated B-chain could be removed by endoglycosidases H or F, whereas both were removable after denaturation of the polypeptide by SDS. Both the isolated A- and B-chains were sensitive to alpha-mannosidase. Intact ricin was resistant to endoglycosidase treatment and was only slightly sensitive to alpha-mannosidase. The addition of SDS allowed endoglycosidase H to remove both of the B-chain oligosaccharides from intact ricin and increased the toxin's sensitivity to alpha-mannosidase. In conclusion, extensive enzymic deglycosylation of ricin may only be possible if the A- and B-chains are first separated, treated with enzymes and then recombined to form the toxin.

The effect of a "bisecting" N-acetylglucosaminyl group on the binding of biantennary, complex oligosaccharides to concanavalin A, Phaseolus vulgaris erythroagglutinin (E-PHA), and Ricinus communis agglutinin (RCA-120) immobilized on agarose

The effect of a "bisecting" 2-acetamido-2-deoxy-beta-D-glucopyranosyl group, linked (1----4) to the beta-D-mannopyranosyl group of asparagine-linked complex and hybrid oligosaccharides, on the binding of [14C]acetylated glycopeptides to columns of immobilized concanavalin A (Con A), Phaseolus vulgaris erythroagglutinin (E-PHA), and Ricinus communis agglutinin-120 (RCA-120) was investigated. The presence of this "bisecting" GlcNAc group caused significant inhibition of the binding to ConA-agarose of biantennary complex glycopeptides in which the two branches are terminated at their nonreducing ends by two GlcNAc groups, or by a Gal and a GlcNAc group, or by two Gal groups, or by a Man and a GlcNAc group. Binding of biantennary, complex glycopeptides to E-PHA-agarose required a "bisecting" GlcNAc group, a Gal group at the nonreducing terminus of the alpha-D-Man-p-(1----6) branch, and a terminal or internal GlcNAc residue linked beta-(1----2) to the alpha-D-Manp-(1----3) branch. Binding to RCA-120-agarose occurred only when at least one nonreducing terminal Gal group was present, and increased as the proportion of terminal Gal groups increased; the presence of a "bisecting" GlcNAc group caused either enhancement or inhibition of these binding patterns. It is concluded that a "bisecting" GlcNAc group affects the binding of glycopeptides to all three lectin columns.

Ber-H2 (anti-CD30)-saporin immunotoxin: a new tool for the treatment of Hodgkin's disease and CD30+ lymphoma: in vitro evaluation

An immunotoxin containing an anti-CD30 monoclonal antibody (Ber-H2) and saporin, a ribosome-inactivating protein type 1, is described. It specifically inhibits protein synthesis by Hodgkin derived target cell lines with a very high efficiency (IC50 ranging from 5 x 10(-12) M to 5 x 10(-14) M, as saporin), while irrelevant immunotoxins do not. Present results suggest that this immunotoxin could be used for in vivo therapy as well as for ex vivo bone marrow purging in Hodgkin's disease and CD30+ lymphomas.

New strategy in glycopolymer synthesis. Preparation of antigenic water-soluble poly(acrylamide-co-p-acrylamidophenyl beta-lactoside)

Stereospecific phase-transfer-catalyzed glycosidation of acetobromolactose 3 with p-nitrophenoxide gave the peracetylated 1,2-trans-beta-D-4-nitrophenyl lactoside 4. Functionalization of 4 into an N-acryloyl monomer was achieved by catalytic transfer hydrogenation of the nitro group, followed by N-acryloylation of the resulting amino group, on both O-acetyl-protected and unprotected disaccharides. Copolymerization of 4-acrylamidophenyl beta-lactoside (9) with acrylamide, initiated by ammonium persulfate, afforded a water-soluble carbohydrate copolymer (glycopolymer). The antigenicity of the new polymer was demonstrated by agar gel diffusion with Arachis hypogaea (peanut) and Ricinus communis (castor bean) lectins. Quantitative precipitation and enzyme linked lectin assays (ELLA) were also performed with peanut lectin.

Central oxytocin inhibition of salt appetite in rats: evidence for differential sensing of plasma sodium and osmolality

Sodium chloride ingestion is stimulated during conditions of sodium deficiency to maintain body fluid and electrolyte balance. Recent studies have indicated that salt appetite in rats is often inversely related to peripheral and central secretion of the hormone oxytocin (OT). We studied the potential role of central OT on salt and water ingestion by treating rats intracerebroventricularly with OT conjugated to the A chain of the plant cytotoxin ricin (rAOT) to produce a chronic selective inactivation of brain cells containing OT-receptive elements. The rats treated with rAOT and control rats treated with the ricin A chain alone were given 5-hr two-bottle (water and 0.5 M NaCl) drinking tests 30 min after they were made hyperosmolar by injections of hypertonic (2M) mannitol solution, which elevated plasma osmolality but reduced plasma Na+ concentration. In the control rats only water intake was stimulated in response to the induced hyperosmolality, but in the rAOT-treated rats hypertonic mannitol caused a robust salt appetite as well as thirst. Analogous results were obtained in rats treated with two different OT-receptor antagonists prior to induction of hyperosmolality with mannitol. In contrast to these results, when hyperosmolality was induced by administration of equivalently hypertonic (1M) NaCl, which elevated both plasma osmolality and plasma Na+ concentration, only water intake but not salt intake was stimulated in both control and OT-receptor antagonist-treated rats. When salt appetite was stimulated by the physiological stimulus of polyethylene glycol-induced hypovolemia, hypertonic mannitol similarly inhibited salt ingestion in control animals but not in rAOT-treated rats, whereas hypertonic NaCl inhibited subsequent salt ingestion in both groups. These results suggest that salt appetite is regulated by both Na(+)- and osmolality-sensing mechanisms in rats. In addition, they indicate that central OT likely mediates a significant component of osmolality-related inhibition of salt appetite but does not appear to be essential for Na(+)-related inhibition of this important homeostatic behavior.

Effects of administration of an anti-CD5 plus immunoconjugate in rheumatoid arthritis. Results of two phase II studies. The CD5 Plus Rheumatoid Arthritis Investigators Group

OBJECTIVE

To evaluate the safety and activity of an immunoconjugate of ricin A chain and anti-CD5 monoclonal antibody (anti-CD5 IC), with and without concomitant methotrexate and/or azathioprine, in the treatment of rheumatoid arthritis (RA).

METHODS

Seventy-nine patients with active RA were enrolled in 2 prospective open-label protocols.

RESULTS

Using composite criteria, response rates were 50-68% at 1 month and 22-25% at 6 months. Transient depletion of CD3/CD5 T cells was observed on days 2 and 5 of treatment, with reconstitution on day 15 or day 29. Treatment-associated adverse effects were common but resolved rapidly without sequelae.

CONCLUSION

These findings suggest activity of anti-CD5 IC in active RA and warrant confirmation in a multicenter randomized study (currently underway).

Biological and chemical agents: a brief synopsis

The objective of this article is to provide a concise overview of the most likely biological and chemical agents that could be used as biochemical weapons. The diagnosis, pathology, prevention, decontamination, treatment, and disposition of these biological and chemical agents are presented in a tabular format for quick reference purposes. The information provided outlines the bare essentials needed to deal with any emergency or catastrophic event involving these agents.

Developmental expression of cell type-specific markers in mouse cerebellar cells in vitro

The expression of several cell type-specific markers was studied by indirect immunofluorescence in discontinuous BSA gradient fractionated and unfractionated mouse cerebellar cells cultured for 3 days in vitro from embryonic day 13 through postnatal day 9. Cell surface antigen NS-4 and tetanus toxin receptors are present at all ages studied. Thy-1 first detected on neurons with large cell bodies (Purkinje and/or Golgi Type II.neurons) onpostnatal day 3, but absent from all neurons with small cell bodies (granule, basket, and stellate cells). At all ages Thy-1 antigen is absent from astro- and oligodendroglia, and fibroblasts or fibroblast-like cells. Fibroblast-like cells express fibronectin at all ages studied. Astroglia expressing glial fibrillary acidic (GFA) protein are first detectable in cultures from 16-day-old embryos. Their number increases at later ages. At all ages studied fluorescein conjugated Ricinus communis agglutinin 120 brightly labels the cell surfaces of fibroblastic cells and large neurons, less brightly those of astrocytes, bu not those of small neurons. Oligodendroglia become detectable in cerebellar cultures from 16- and 17-day-old embryos maintained in vitro for 3 days using antibodies to 04 antigen and bovine corpus callosum, respectively. At embryonic ages BSA step gradient procedures do not result in enrichment of particular cell types as recognized by the available markers. From birth onward, however, enrichment of cell populations was obtained corresponding to the ones characterized at postnatal day 6 as described in the companion paper (Schnitzer and Schachner 1981b).

Importance of the antigen-binding valency and the nature of the cross-linking bond in ricin A-chain conjugates with antibody

As a continuation of our work on toxin A-chain conjugates with antitumor antibodies for selective delivery of the toxin to the target cells, four ricin A-chain conjugates were prepared by linking A-chain to Fab' or F(ab')2 of rabbit IgG against L1210 with or without employing a cross-linking agent, N,N'-o-phenylenedimaleimide (PDM), N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) or N-succinimidyl m-(N-maleimido)benzoate (SMB), and the effects of antigen-binding valency and of the nature of the cross-linking bond on their in vitro cytotoxicity were studied. The relative potencies of the conjugates in terms of IC94's were as follows: F(ab')2-SPDP-A-chain, 100; Fab'-S-S-A-chain, 21; F(ab')2-SMB-A-chain, 1.3; Fab'-PDM-A-chain 0.38. Among the four conjugates, F(ab')2-SPDP-A-chain and Fab'-S-S-A-chain can be cleaved into the homing and the cytotoxic components with 2 mM 2-mercaptoethanol. These results suggest that divalency in antigen-binding and susceptibility of the cross-linking bond to cleavage by mercapto reagent are desirable for high potency. Protein synthesis in a cell-free system of rabbit reticulocyte lysate was inhibited by Fab'-S-S-A-chain and by Fab'-PDM-A-chain as effectively as by free A-chain, indicating that the liberation of A-chain is not important, at least on ribosomes, but it is important for the A-chain to reach a ribosome after binding of the conjugates to the cell-surface.

Synthesis and biochemical evaluation of RNA containing an intrahelical disulfide crosslink

BACKGROUND

Several factors impede the elucidation of RNA structure and function by X-ray and NMR methods, including the complexity of folded RNA motifs, the tendency of RNA to aggregate, and its ability to fold into multiple isomeric structures. The ability to constrain the process of RNA folding to give a single, homogeneous product would assist these investigations. We therefore set out to develop a synthetic procedure for the site-specific insertion of a disulfide crosslink into oligoribonucleotides. We also examined the ability of a crosslinked species to serve as a substrate for ricin, an RNA glycosylase.

RESULTS

A convertible nucleoside derivative (C) suitable for the site-specific introduction of N4-alkylcytidine residues into RNA has been developed. The corresponding C phosphoramidite was employed in the synthesis of an 8-mer oligonucleotide, 5'-CGGA-GACG-3', which was then efficiently converted to an 8-mer containing two S-protected N4-(2-thioethyl)C residues. Upon deprotection and air oxidation, the 8-mer efficiently formed an intramolecular disulfide bond, yielding a GAGA tetraloop presented on a two-base-pair CpG disulfide crosslinked ministem. We show that this ministem-loop is an excellent substrate for ricin. Control 8-mers lacking the disulfide crosslink were substantially poorer substrates for ricin.

CONCLUSIONS

The nucleoside chemistry described here should be generally useful for the site-specific introduction of a range of non-native functional groups into RNA. We have used this chemistry to constrain an RNA ministem through introduction of an intrahelical disulfide crosslink. That this tetraloop substrate linked to a two base-pair ministem is efficiently processed by ricin is clear evidence that ricin makes all of its energetically favorable contacts to the extreme end of the stem-loop structure, and that the two base pairs of the stem abutting the loop remain intact during recognition and processing by ricin.