Comparative studies of Iodo-bead and chloramine-T methods for the radioiodination of human alpha-fetoprotein

Synthesis of Radioiodinated Compounds. Classical Approaches and Achievements of Recent Years

This review demonstrates the progress in the synthesis of radioiodinated compounds over the past decade. The possibilities and limitations of radiopharmaceuticals with different iodine isotopes, as well as the synthesis of low and high molecular weight compounds containing radioiodine, are discussed. An analysis of synthesis strategies, substrate frameworks, isolation methods, and metabolic stability, and the possibility of industrial production of radioiodinated organic derivatives which can find applications in the synthesis of drugs and diagnostics are presented.

Binding of phenochalasin A, an inhibitor of lipid droplet formation in mouse macrophages, on G-actin

Phenochalasin A, a unique phenol-containing cytochalasin produced by the marine-derived fungus Phomopsis sp. FT-0211, was originally discovered in a cell morphological assay of observing the inhibition of lipid droplet formation in mouse peritoneal macrophages. To investigate the mode of action and binding proteins, phenochalasin A was radio-labeled by ¹²⁵I. Iodinated phenochalasin A exhibited the same biological activity as phenochalasin A. [¹²⁵I]Phenochalasin A was found to be associated with an approximately 40 kDa protein, which was identified as G-actin. Furthermore, detail analyses of F-actin formation in Chinese hamster ovary cells (CHO-K1 cells) indicated that phenochalasin A (2 µM) caused elimination of F-actin formation on the apical site of the cells, suggesting that actin-oriented specific function(s) in cytoskeletal processes are affected by phenochalasin A.

Radioiodine Labeling Reagents and Methods for New Chemical Entities and Biomolecules

Several radioisotopes of iodine (¹²³I, ¹²⁴I, ¹²⁵I, and ¹³¹I) are available for medical use. One of them can be used, depending on the application, for radioiodine labeling of New Chemical Entities (NCEs) and biomolecules (peptides, proteins, protein fragments, monoclonal antibodies, etc.) for the development of novel imaging and therapeutic pharmaceuticals. Direct, using inorganic and organic oxidizing agents and enzyme catalysts, and indirect, using prosthetic groups, radioiodine-labeling methods have been used routinely in the past. In this report, a comprehensive review of the physical properties of various iodine radionuclides, their medical applications, and a summary of various radioiodine labeling reagents and methods for NCEs and biomolecules are provided.

Hepatoma-Targeted Radionuclide Immune Albumin Nanospheres: (131)I-antiAFPMcAb-GCV-BSA-NPs

An effective strategy has been developed for synthesis of radionuclide immune albumin nanospheres (¹³¹I-antiAFPMcAb-GCV-BSA-NPs). In vitro as well as in vivo targeting of ¹³¹I-antiAFPMcAb-GCV-BSA-NPs to AFP-positive hepatoma was examined. In cultured HepG2 cells, the uptake and retention rates of ¹³¹I-antiAFPMcAb-GCV-BSA-NPs were remarkably higher than those of ¹³¹I alone. As well, the uptake rate and retention ratios of ¹³¹I-antiAFPMcAb-GCV-BSA-NPs in AFP-positive HepG2 cells were also significantly higher than those in AFP-negative HEK293 cells. Compared to ¹³¹I alone, ¹³¹I-antiAFPMcAb-GCV-BSA-NPs were much more easily taken in and retained by hepatoma tissue, with a much higher T/NT. Due to good drug-loading, high encapsulation ratio, and highly selective affinity for AFP-positive tumors, the ¹³¹I-antiAFPMcAb-GCV-BSA-NPs are promising for further effective radiation-gene therapy of hepatoma.

S5a/Rpn10, a UIM-protein, as a universal substrate for ubiquitination

The assay of the activity of ubiquitin (Ub) ligases (E3s) and screens for pharmacological agents that alter their function are a continual challenge for basic investigators as well as in drug development. The assay of different E3s requires distinct detection methods and reagents (e.g., specific antibodies against each E3 or substrate). So, a single assay applicable to many E3s could be very useful. Here, we demonstrate that S5a/Rpn10 binds to the growing polyUb chain formed on a substrate (or on the Ub ligase during autoubiquitination) and then itself becomes extensively ubiquitinated. S5a thus can serve as a universal substrate for ubiquitination. This biochemical property of S5a provides a method for measuring the enzymatic activity of any E3. This approach is valuable when substrates are not known or not available and when multiple ubiquitination reactions are being studied (e.g., in high-throughput screens).

Uptake of apolipoprotein E fragment coupled liposomes by cultured brain microvessel endothelial cells and intact brain capillaries

The suitability of surface modified liposomes as drug carriers for brain-specific targeting was investigated using apolipoprotein E fragments as brain-directed vectors. Liposomes coated with polyethylene glycol-2000 (sterically stabilized, PEGylated liposomes) were prepared from hydrogenated egg phosphatidylcholine, cholesterol, and a PEG-derivatized phospholipid. Liposomes were covalently coupled to a peptide of 26 amino acids length, derived from the binding site of human apolipoprotein E4 (ApoE4) and a peptide of random amino acid sequence, respectively. Rhodamine-labeled dipalmitoylphosphatidylethanolamine was incorporated into the lipid bilayer in order to visualize the liposomal interaction with brain capillary endothelial cell monolayers. The interaction of the liposomes with monolayers of porcine brain capillary endothelial cells (BCEC), the rodent cell line RBE4, and freshly isolated porcine brain capillaries was studied by means of confocal laser scanning fluorescence microscopy. In contrast to random peptide coupled liposomes, the ApoE4-fragment coupled liposomes were rapidly taken up by cultured BCECs and RBE4 cells. Uptake could be inhibited by ApoE4, free peptide, and antibodies against the LDL receptor in a concentration-dependent manner. The results indicate that the liposomes are internalized via the LDL receptor, which is expressed at the blood-brain barrier. In conclusion, liposomes coupled to ApoE4 fragments are taken up into brain endothelium via an endocytotic pathway and may therefore be a suitable carrier for drug delivery to the brain.

Fluorescein isothiocyanate–hapten immunoassay for determination of peptide–cell interactions

We have developed a fluorescein isothiocyanate (FITC)-hapten immunoassay, where a FITC-labeled peptide binding to a cell is assayed as the amount of immunoreactive fluorescein present in a cell lysate. An antifluorescein-horseradish peroxidase conjugate binds to either a fluoresceinated peptide in the lysate or a fluorescein attached to the wells of a microtiter plate in a competitive fashion. After washing, solid-phase peroxidase activity is measured and inversely related to the amount of FITC-labeled peptide present. To demonstrate the assay, the interaction of a FITC-labeled bombesin-like peptide with the gastrin-releasing peptide receptor on PC-3 and HT-29 cells was investigated. Using PC-3 cells, we obtained similar displacement curves and numbers of binding sites per cell by both the FITC-hapten immunoassay and a reference radioreceptor assay. The FITC-hapten immunoassay is a sensitive and versatile method, since the same commercially available reagents can be used to assess interactions between any peptide and any receptor. In addition, the FITC-labeled peptide can be used to visualize receptors in fluorescent-activated cell sorting or fluorescent microscopy.

Characterization of the oligomeric behavior of a 16.5 kDa peanut oleosin by chromatography and electrophoresis of the iodinated form

Oleosins are amphipathic proteins associated with oil bodies in seeds. We purified the major 16,500 peanut oleosin by preparative SDS-PAGE. Autoradiography after SDS-PAGE separation of the iodinated oleosin revealed covalently bound oligomers with Mr of 21,000, 33,000, 44,000 and 51,000. The strong capacity of these oligomers to form aggregates and to be incorporated into large-sized detergent micelles was demonstrated by gel permeation and isoelectric focusing. A 50% ethanol concentration was necessary to elute the 16,500 oleosin from octyl groups in hydrophobic interaction chromatography showing its natural tendency to interact with lipid acyl chains. This oligomerization behavior in aqueous solution is an indirect reflection of the interactions that occur in the oil body.

Perturbation of epidermal growth factor clearance after radioiodination and its implications

The clearance of human epidermal growth factor (hEGF1-53) has been thought to be mediated mainly by a high-capacity receptor system, yet relatively low in vivo clearance rates (<10 mL/min/kg) and long terminal elimination half-lives (>120 min) have been observed in rats receiving the peptide that was iodinated by the oxidative chloramine-T (CT) method. We investigated if a mild, less oxidative iodination by the lactoperoxidase (Enzymobeads, EB) method, which is known to yield an iodinated peptide with receptor-binding equivalence, could produce a labeled peptide that behaves pharmacokinetically similar to the native material. For comparison, a parallel study was also conducted with EB-125I-hEGF1-48, which in its native form has a much reduced receptor binding activity due to the loss of the C-terminal pentapeptide. Plasma radioactivity concentrations were determined by trichloroacetic acid (TCA) precipitation and immunoprecipitation. Rats cleared unlabeled hEGF1-53 and hEGF1-48 markedly faster (CL(tot) > 120 mL/min/kg) than their radiolabeled counterparts. Approximately 96% of the hEGF1-53 dose was cleared during the initial phase (0-4 min), as opposed to only 5-14% for the iodinated peptide. Similar change was also observed for EB-125I-hEGF1-48 and CT-125I-hEGF1-53. The pharmacokinetic behavior of EB-125I-hEGF1-53 was, in fact, comparable to that of CT-125I-hEGF1-53. These observations indicate that receptor-binding equivalence does not have direct relationship with in vivo EGF clearance. Both iodination methods (oxidative CT and less oxidative EB) might have perturbed one or more steps in the cascade of ligand-receptor internalization and intracellular procession, which in turn modified the disposition of the peptides. In addition, the two independent precipitation techniques for the same peptide generated different kinetic outcomes. The overall experimental results suggest that it is unacceptable to use an iodinated form to characterize the disposition of peptides/proteins like EGF with a specific receptor system mediating its clearance.

Tissue targeting and plasma clearance of cobra venom factor in mice

The tissue targeting and rate of clearance of cobra venom factor (CVF) from the circulation was studied in mice by intravenous or intraperitoneal injection of radioiodinated CVF. In both modes of administrations, CVF was targeted mainly to liver. CVF injected directly into the blood was cleared from the circulation with a plasma half life of about 10 h, whereas CVF injected into the peritoneal cavity was slowly absorbed into the blood stream reaching a maximum level at approximately 6 h, and it was then cleared from the circulation with a plasma half life of about 18 h. The rate of plasma clearance of CVF was markedly decreased upon removal of the terminal alpha-galactosyl residues of the oligosaccharide chains; the plasma half lives for intravenously and intraperitoneally administered de-alpha-galactosylated CVF were approximately 5 and approximately 10 h, respectively. However, the clearance rate was not affected by complete deglycosylation using N-glycanase or by chemical modification of the terminal galactosyl residues. Together, these data demonstrate that the terminal alpha-galactosyl residues of CVF mask the Lewis X-dependent uptake of CVF by liver.

Virus-encoded serine proteinase inhibitor SERP-1 inhibits atherosclerotic plaque development after balloon angioplasty

BACKGROUND

Recurrent atherosclerotic plaque growth, restenosis, is a significant clinical problem after interventional procedures. Initiation of restenosis involves activation of inflammatory and thrombotic cascades, which are regulated by serine proteinase enzymes and inhibitors. We have investigated the use of a viral serine proteinase inhibitor, SERP-1, to reduce plaque development after primary balloon angioplasty. This is the first experimental report of the use of a viral anti-inflammatory protein for the prevention of atherosclerosis.

METHODS AND RESULTS

Seventy-four cholesterol-fed rabbits were treated with either local or systemic infusions of SERP-1 protein (or control solutions) after balloon-mediated injury. Sites of SERP-1 infusion in rabbits had dramatically reduced plaque compared with control infusions at the 4-week follow-up. At low-dose infusions (30 to 300 pg), only the primary infusion site had a demonstrable decrease in plaque, whereas at higher-dose infusions (> 3000 pg), a generalized reduction in plaque development was detected. An associated decrease in mononuclear cell infiltration of the arterial wall was detected after SERP-1 infusion within the first 24 hours. Infusion of an active-site mutant of SERP-1 (P1-P1', ala-ala) lacking serine proteinase inhibitory activity failed to prevent plaque growth.

CONCLUSIONS

Purified SERP-1, a virus-encoded secreted glycoprotein, reduces plaque growth after primary balloon-mediated injury. Plaque development is decreased by inhibition of serine proteinase activity and is associated with a focal reduction in macrophage infiltration immediately after injury. Investigation of serine proteinase inhibitors may provide new insight into the regulation of arterial responses to injury.

Staphylococcus aureus binding to human nasal mucin

Colonization of human nasal mucosa with Staphylococcus aureus sets the stage for subsequent systemic infection. This study characterizes S. aureus adhesion to nasal mucosa in vitro and investigates the interaction of S. aureus with human nasal mucin. S. aureus binding to cell-associated and cell-free mucus was greater than to nonmucin-coated epithelial cells. Scanning electron microscopy of S. aureus incubated with human nasal mucosal tissue showed minimal binding to ciliated respiratory epithelium. In a solid-phase assay, S. aureus bound to purified human nasal mucin-coated wells significantly more than to bovine serum albumin-coated microtiter wells. Binding to mucin was saturable in a dose- and time-dependent fashion. Staphylococcal adherence to human nasal mucin was inhibited by bovine submaxillary mucin but not by fibrinogen. Pretreatment of mucin with periodate but not with pronase reduced adherence. Trypsin treatment of the bacteria significantly reduced adherence to mucin. 125I-labelled nasal mucin bound to two surface proteins (138 and 127 kDa) of lysostaphin-solubilized S. aureus. Binding to human nasal mucin occurs in part via specific adhesin-receptor interactions involving bacterial proteins and the carbohydrate moiety in mucin. These experiments suggest that S. aureus binding to mucin may be critical for colonization of the nasopharyngeal mucosa.

T cell activation by Theileria annulata-infected macrophages correlates with cytokine production

A major feature of the pathology induced by Theileria annulata is acute lymphocytic proliferation, and this study investigates the mechanisms underlying the intrinsic ability of T. annulata-infected monocytes to induce naive autologous T cells to proliferate. Different T. annulata-infected clones expressed different but constant levels of MHC class II, varying from < 1.0 x 10(5) to 1.5 x 10(6) molecules/cell, as measured by saturation binding. However, no correlation was found between the level of MHC class II expression and levels of induced T cell proliferation. Theileria annulata-infected cell lines and clones were assayed for cytokine mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR). The infected cells assayed produced mRNA specific for IL-1 alpha, IL-1 beta, IL-6, IL-10 and tumour necrosis factor-alpha (TNF-alpha), but not IL-2 or IL-4. One clone (clone G) did not produce mRNA for TNF-alpha. The degree of T cell proliferation induced by infected cells was directly correlated with the amount of mRNA produced for the T cell stimulatory cytokines IL-1 alpha and IL-6, as assessed by a semiquantitative technique. In contrast, cells infected with the related parasite T. parva produced mRNA for IL-1 alpha, IL-2, IL-4, IL-10 and interferon-gamma (IFN-gamma). Since T. parva-infected cells also induce naive autologous T cell proliferation, it seems likely that the production of IL-1 alpha by cells infected with either parasite is a major signal for the induction of non-specific T cell proliferation.

Prion protein (PrP) synthetic peptides induce cellular PrP to acquire properties of the scrapie isoform

Conversion of the cellular isoform of prion protein (PrPC) into the scrapie isoform (PrPSc) involves an increase in the beta-sheet content, diminished solubility, and resistance to proteolytic digestion. Transgenetic studies argue that PrPC and PrPSc form a complex during PrPSc formation; thus, synthetic PrP peptides, which mimic the conformational pluralism of PrP, were mixed with PrPC to determine whether its properties were altered. Peptides encompassing two alpha-helical domains of PrP when mixed with PrPC produced a complex that displayed many properties of PrPSc. The PrPC-peptide complex formed fibrous aggregates and up to 65% of complexed PrPC sedimented at 100,000 x g for 1 h, whereas PrPC alone did not. These complexes were resistant to proteolytic digestion and displayed a high beta-sheet content. Unexpectedly, the peptide in a beta-sheet conformation did not form the complex, whereas the random coil did. Addition of 2% Sarkosyl disrupted the complex and rendered PrPC sensitive to protease digestion. While the pathogenic A117V mutation increased the efficacy of complex formation, anti-PrP monoclonal antibody prevented interaction between PrPC and peptides. Our findings in concert with transgenetic investigations argue that PrPC interacts with PrPSc through a domain that contains the first two putative alpha-helices. Whether PrPC-peptide complexes possess prion infectivity as determined by bioassays remains to be established.

Modulation of iron metabolism in monocyte cell line U937 by inflammatory cytokines: changes in transferrin uptake, iron handling and ferritin mRNA

We have investigated the effects of the pro-inflammatory cytokines interleukin 1 beta (IL-1 beta), tumour necrosis factor alpha (TNF alpha) and interferon gamma (IFN gamma) on the iron metabolism of the human monocytic cell line U937. Cells were treated with each cytokine for up to 24 h, and then iron uptake from diferric transferrin was determined. The intracellular distribution of this iron, the expression of the transferrin receptor and levels of mRNA for the two ferritin subunits were also studied. IL-1 beta, TNF alpha and IFN gamma all decreased transferrin-iron uptake into cells, and all three cytokines had effects on the proportion of iron associated with ferritin. With TNF alpha there was a marked enhancement of the fraction incorporated into ferritin. Transferrin-receptor expression was diminished by TNF alpha and IL-1 beta, but not IFN gamma, suggesting different effector mechanisms. Both TNF alpha and IFN gamma increased the amount of cellular mRNA for ferritin H-chain, but not the L-chain; IL-1 beta affected mRNA for neither ferritin. These data demonstrate that cytokines, which can be present at high concentrations in inflammation, have the capacity to affect macrophage iron uptake, transferrin receptor expression, intracellular iron handling and the relative abundance of ferritin-subunit mRNA, and may therefore be important mediators in the observed perturbations of iron metabolism in inflammatory diseases.

Interaction of insulin with Pseudomonas pseudomallei

Pseudomonas pseudomallei is the causative agent of melioidosis, a disease being increasingly recognized as an important cause of morbidity and mortality in many regions of the world. An intriguing observation regarding melioidosis is that a significant percentage of patients who develop the disease have preexisting diabetes mellitus. In this regard, we have tested the hypothesis that insulin may modulate the growth of P. pseudomallei. We have demonstrated that insulin markedly inhibits the growth of P. pseudomallei in vitro and in vivo. The growth rate of P. pseudomallei in minimal medium containing human recombinant insulin was significantly lower than that of control cultures containing no insulin. P. pseudomallei grew at an increased rate in serum samples obtained from diabetic rats compared with that in serum samples obtained from control animals. When the insulin level was restored by the addition of human recombinant insulin, the growth rate was reduced to a level similar to that seen in control serum. P. pseudomallei also grew significantly better in insulin-depleted human serum than control human serum. 125I-insulin binding studies demonstrated that P. pseudomallei possesses a specific, high-affinity binding site for human insulin. In in vivo studies, rats made diabetic by streptozotocin injection (80 mg/kg of body weight, intraperitoneally) were significantly more susceptible to P. pseudomallei septicemia than control rats. Thus, it appears that serum insulin levels may play a significant role in modulating the pathogenesis of P. pseudomallei septicemic infections.

Structure of the major oligosaccharide of cobra venom factor

Cobra venom factor (CVF), the complement-activating glycoprotein in cobra venom, contains three or possibly four N-linked oligosaccharide chains per molecule and is devoid of O-linked saccharides. Analysis by lectin-affinity staining revealed the presence of complex-type oligosaccharides containing non-reducing terminal alpha-galactosyl residues and fucose residues linked to the proximal N-acetylglucosamine. Sialic acid residues could not be detected. For their structural analysis, the oligosaccharides were released by hydrazinolysis and fractionated on Bio-Gel P-4. Approximately 80% of the eluted oligosaccharides have a size equivalent of 17 +/- 2 glucose units. The major oligosaccharide representing about 45% of the total carbohydrate present in CVF was purified to homogeneity by MicroPak AX-5 HPLC and its structure was analyzed by sequential exoglycosidase digestion. The positions of the glycosidic linkages of the sugar residues were established by methylation analysis of CVF-derived glycopeptides. The data of these analyses indicated that the major oligosaccharide has a symmetrical fucosylated biantennary complex-type structure terminating with unusual alpha-galactosyl residues.

Structural features of carbohydrate moieties in snake venom glycoproteins

The structures of the carbohydrate moieties of glycoproteins in snake venoms are largely unknown. In the present study, we have analyzed venoms of several species of snakes as well as plasma and tissue glycoproteins from one species of cobra (Naja naja kaouthia) by lectin affinity staining of Western blots. The data demonstrate that glycoproteins in cobra venom invariably contain terminal alpha-galactosyl residues with negligible proportions of sialic acids. Interestingly, however, terminal alpha-galactosyl residues are present in significantly lower proportions in cobra tissues such as brain, liver, lung, kidney, spleen, muscle, and totally absent in cobra plasma glycoproteins. In sharp contrast to cobras, venom glycoproteins of other snakes do not contain terminal alpha-galactosyl residues but do contain terminal 2,3- and/or 2,6-linked sialic acids as well as beta-galactosyl residues. Cobra venom also contains high molecular weight heavily glycosylated proteins bearing poly-N-acetyllactosaminyl oligosaccharides, the majority of which appear to be linked to the protein core via O-glycosidic bonds.

Binding proteins for a peptide hormone in the shrimp, Sicyonia ingentis: evidence from photoaffinity labeling with red pigment concentrating hormone analogs

Two photoaffinity analogs of the crustacean erythrophore (red pigment) concentrating hormone (RPCH) have been synthesized and shown to cause pigment concentration in the shrimp Sicyonia ingentis. These two modified oligopeptides have azidosalicylamide groups which allow introduction of an 125I label and enable photochemically induced covalent attachment to a specific binding site. Incubation of [125I]-ASA-Glu1-CC-2 with the 100,000g membrane pellet and cytosol fraction from epidermis, eyestalks, muscle, and central nervous system (CNS), followed by irradiation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography results in covalent modification of certain protein bands in the membranes of selected tissues. Two such proteins were observed in neural tissues and showed competitive displacement by excess RPCH, indicative of specific high-affinity binding. This is the first report of peptide hormone-binding proteins in an invertebrate and provides further evidence of a role for RPCH as a neurotransmitter in the CNS.

SDS-soluble and peptidoglycan-bound proteins in the outer membrane-peptidoglycan complex of Brucella abortus

Outer membrane-peptidoglycan complex from Brucella abortus was separated from cytoplasmic membrane and cytosol by either sucrose density gradient fractionation or differential (rate) centrifugation of surface labeled cells disrupted by sonication without the use of detergents. The outer membrane-peptidoglycan complex had a buoyant density of 1.22 gm/ml and contained 67 labeled SDS-soluble proteins when examined by SDS-PAGE. Included were four major bands exhibiting molecular masses of 88k, 40k, 35.7k and 26k daltons corresponding to previously described group 1, 2 and 3 outer membrane proteins. Lysozyme treatment of outer membrane-peptidoglycan complex increased its buoyant density to 1.25 gm/ml and released eight additional peptidoglycan-linked proteins.

A carbohydrate-directed heterobifunctional cross-linking reagent for the synthesis of immunoconjugates

A novel, highly water-soluble, heterobifunctional cross-linking reagent, S-(2-thiopyridyl)-L-cysteine hydrazide (TPCH), was synthesized which contains a hydrazide moiety for coupling to aldehyde groups generated in the carbohydrate residues of antibodies by mild periodate oxidation, and a pyridyl disulfide moiety for coupling to molecules with a free sulfhydryl group. Since the carbohydrate moieties are distal to the antigen binding region of antibodies, derivatization with this cross-linker minimizes impairment of the antigen binding function. Derivatization of the human monoclonal IgM antibody 16-88 against human colon carcinoma cells with as many as 16 TPCH cross-linker molecules did not impair its antigen binding capability. Using mild oxidation conditions for antibody derivatization, sialic acid residues were identified as attachment sites for the cross-linker molecules, since after desialylation of antibody 16-88 by neuraminidase virtually no cross-linker molecules could be incorporated. Comparison of TPCH with S-(2-thiopyridyl)mercaptopropionic acid hydrazide and S-(2-thiopyridyl)-L-cysteine, two related cross-linking reagents, revealed that TPCH is most efficiently incorporated into periodate-treated antibody. Based on the structural differences of the cross-linkers, the more efficient incorporation of TPCH appears to be a function of the presence of a hydrazide moiety with an adjacent amino group. When three to four molecules of pyridyl disulfide-derivatized barley toxin were coupled to TPCH-derivatized antibody 16-88, the antigen binding capability remained uncompromised. In addition, no significant impairment of toxin activity upon coupling to the antibody was observed. Based on these data, TPCH may be very useful for the synthesis of immuno-conjugates with no or only minimal impairment of the antigen binding function.

A method for separating bound versus unbound label during radioiodination

An inexpensive, highly effective, and safe method for the removal of bound versus unbound label during radiolabeling of proteins is described. The technique employs the use of membrane ultrafiltration technology and returns in one step a highly reproducible product of quality superior to that attained by gel chromatography. Advantages of this technique are a reduction in the quantity of liquid and solid radioactive waste and a significant limitation of potentially harmful manipulation and exposure times.

Further analysis on the structural proteins of infectious pancreatic necrosis virus

The structural proteins of infectious pancreatic necrosis virus (IPNV) have been analyzed. Two-dimensional gel electrophoresis showed that IPNV proteins are slightly acidic with apparent pIs ranging from 5.8 to 6.6. To identify the IPNV surface-located proteins, purified virus was labelled either with fluorescein isothiocyanate (FITC) or with Na 125I. After analysis by SDS-PAGE, only the major viral protein, VP2, was labelled by either procedure. The accessibility of VP2 to these reagents suggests that this protein is externally located. In addition, using Concanavalin A conjugated with FITC and IPNV labelling with 3H-mannose, evidence is present that VP2 contains carbohydrate residues.

The role of protein-linked oligosaccharide in the bilayer stabilization activity of glycophorin A for dioleoylphosphatidylethanolamine liposomes

The importance of the protein-linked carbohydrates for the stabilization of dioleoylphosphatidylethanolamine (DOPE) bilayers has been investigated using glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, as a stabilizer. Two major types of glycophorin, differing in the sialic acid content, were used in the study. Type MM contains 19.2 +/- 2.5 sialic residues per molecule of glycophorin, and type NN contains 10.8 +/- 1.2. Type MM could stabilize DOPE bilayers at 0.5 mol%, whereas type NN was unable to do so even at 1 mol%. The importance of the sialic acid content to the stabilization activity of glycophorin was further confirmed by the observation that the neuraminidase-treated type MM showed a lower stabilization activity than the untreated type. Since type NN had no stabilizing activity, we attempted to couple a trisaccharide, NeuNAc----Gal----Glc, to type NN by reductive amination. 2.5 +/- 0.8 saccharide chains were added per molecule of type NN. The trisaccharide-attached type NN showed a greater stabilization activity than the parent type NN molecule, indicating again that the sialic acid content of the stabilizer molecule determines the stabilization activity. Addition of wheat-germ agglutinin (WGA), which binds to the sialic acid residues of a glycoprotein, to type MM-stabilized liposomes caused rapid aggregation and destabilization of liposomes, resulting in leakage of an entrapped marker, calcein. The aggregation increased with increasing amount of the lectin; however, the leakage rate was maximum at an optimum concentration of WGA. These results are discussed in terms of the role of sialic acid in the interfacial hydration and charge repulsion which determines the DOPE bilayer stability.

Labeling of monoclonal antibodies with radionuclides

Antibodies, specifically monoclonal antibodies, are potentially very useful and powerful carriers of therapeutic agents to target tissues and diagnostic agents. The loading or charging of antibodies with agents, especially radiotracers, is reviewed here. The choice of radioisotope for immunodetection and/or immunotherapy is based on its availability, half-life, nature of the radiation emitted, and the metabolic pathways of the radionuclide in the body. Most important of all are the derivatization techniques available for labeling the antibody with the given radionuclide. Isotopes of iodine and divalent metal ions are the most commonly used radionuclides. Antibodies labeled with iodine at tyrosine residues are metabolized rapidly in vivo. This leads to the incorporation of metabolized radioactive iodine into various tissues, mainly the thyroid gland and stomach, and to the accumulation of high levels of circulating iodine in the blood, which masks tumor uptake considerably. To overcome these limitations, the use of iodohippurate as an iodine-anchoring molecule to the protein should be considered. When divalent or multivalent metal ions are used as the preferred radionuclide, bifunctional chelating reagents such as ethylenediaminepentaacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) are first coupled to the protein or antibody. These chelating molecules are attached to the protein by formation of an isopeptide linkage between the carboxylate of the chelating reagent and the amino group of the protein. Several procedures are available to generate the isopeptide linkage. When the anchoring of the chelating agent through isopeptide linkage results in the inactivation of the antibody, periodate oxidation of the carbohydrate moiety of the antibody, followed by reductive coupling of chelator, could be considered as an alternative. There is still a need for better, simpler, and more direct methods for labeling antibodies with radionuclides.