The N-hydroxysuccinimide ester of Boc-[S-(3-nitro-2-pyridinesulfenyl)]-cysteine: a heterobifunctional cross-linking agent

Synthetic cysteine-containing peptides were unidirectionally conjugated to albumin via disulfide bonds using the S-(3-nitro-2-pyridinesulfenyl) derivative of cysteine. This method employs the N-hydroxysuccinimide ester of Boc-[S-(3-nitro-2-pyridinesulfenyl)]-cysteine, a protected amino acid derivative used in peptide synthesis, as a heterobifunctional cross-linking agent. The disulfide bonds in the conjugates are formed by the reaction of free thiols with S-(3-nitro-2-pyridinesulfenyl) groups. Bovine albumin was conjugated in this manner to several synthetic peptides derived from human fibrin. Amino acid analysis of these conjugates demonstrated incorporations of from 6 to 11 peptide molecules per molecule of protein.     

Chemoenzymatic synthesis of optically active, biodegradable polymers based on phenyl- and naphthyl-ethanols esterified with divinyladipate

For the purpose of developing a new synthetic polymer containing an asymmetric molecule branch, three racemic alcohols, i.e. 1-phenylethanol, 1-(4-methylphenyl)ethanol and 1-(2-naphthyl)ethanol, were esterified enzymatically with divinyladipate using a lipase from Pseudomonas cepacia. The enzymatic acylation of alcohols produced monoacylated products. Optically active polymerizable monomers, (R)-vinyl adipic acid (phenyl-1-yl) ethyl ester, (R)-vinyl adipic acid (4-methylphenyl-1-yl) ethyl ester and (R)-vinyl adipic acid (2-naphthyl-1-yl) ethyl ester with enantiometric excesses over 99%, 96% and 99%, respectively, were obtained. Each optically active monomer was then subjected to free radical polymerization, to give polymers having a number average molecular weight of 2.9 x 10(3) - 2.2 x 10(4). These polymers are considered useful as optically active polymers having biodegradability.     

Serum albumin leads to false-positive results in the XTT and the MTT assay

Tetrazolium salts like 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) or sodium 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) that form formazans after reduction are widely used to investigate cell viability. Besides cellular enzymes, some constituents of cell media and other substances reduce tetrazolium salts, thereby interfering with these assays. We describe here that different preparations of serum albumin from bovine or human origin can lead to a concentration-dependent increase in the signals of the XTT assay; therefore leading to an overestimation of cell numbers and to an underestimation of potential cytotoxic effects of compounds to be tested. The same effect was seen in the MTT assay with human serum albumin (HSA). We demonstrate that this reductive activity cannot be inactivated by proteolytic digestion, but that it is due to the free cysteine residue in albumin, and is also observed when cysteine or glutathione (GSH) are used. Binding of N-ethylmaleimide (NEM) to the free cysteine residue leads to a decrease of the albumin interference in the XTT assay.     

Development of a solid-phase enzyme immunoassay for ursodeoxycholic acid: application to plasma disappearance of injected ursodeoxycholic acid in the rabbit.

A bile acid disappearance test using an enzyme immunoassay for ursodeoxycholic acid (UDCA) is presented. The immunoassay employs an antiserum produced in rabbits with UDCA coupled by amide linkage to egg albumin. An antigen (UDCA)-enzyme (beta-D-galactosidase) complex was prepared by adding the N-hydroxy-succinimide ester of UDCA to beta-D-galactosidase in a molar ratio of 5000:1. The anti-UDCA serum was coupled to glass beads and a competitive reaction between bile acids and UDCA coupled to the enzyme on the glass beads was measured by determining enzyme activity. One bead was used for each test tube. Thus it was convenient to wash and transfer the bead to a fresh test tube after incubation. The procedure requires 2.5 hr at 30 degrees C for the competitive reaction and enzyme assay. Using a 1:100 dilution of anti-serum, the intensity of fluorescence of 4-methylumbelliferone produced from 4-methylumbelliferyl-beta-D-galactoside by the enzyme decreased linearly with a logarithmic increase of UDCA concentration over a range of from 0.1 to 10 pmnd taurine conjugates, and good recovery data were obtained. The development of the enzyme immunoassay using glass beads shortens analysis time; furthermore, the method makes it possible to detect obstructive jaundice in rabbits before the serum bilirubin level is elevated.     

Synthesis and selective cytotoxicity of a hyaluronic acid-antitumor bioconjugate.

A cell-targeted prodrug was developed for the anti-cancer drug Taxol, using hyaluronic acid (HA) as the drug carrier. HA-Taxol bioconjugates were synthesized by linking the Taxol 2'-OH via a succinate ester to adipic dihydrazide-modified HA (HA-ADH). The coupling of Taxol-NHS ester and HA-ADH provided several HA bioconjugates with different levels of ADH modification and different Taxol loadings. A fluorescent BODIPY-HA was also synthesized to illustrate cell targeting and uptake of chemically modified HA using confocal microscopy. HA-Taxol conjugates showed selective toxicity toward the human cancer cell lines (breast, colon, and ovarian) that are known to overexpress HA receptors, while no toxicity was observed toward a mouse fibroblast cell line at the same concentrations used with the cancer cells. The drug carrier HA-ADH was completely nontoxic. The selective cytotoxicity is consistent with the results from confocal microscopy, which demonstrated that BODIPY-HA only entered the cancer cell lines.     

Radioimmunoassays of 3,4,5-trimethoxyphenethylamine (mescaline) and 2,5-dimethoxy-4-methylphenyl-isopropylamine(DOM)

Mescaline (3,4,5-trimethoxyphenethylamine) and N-succinylmescaline were coupled to human serum albumin with carbodiimide. DOM (2,5-dimethoxy-4-methylphenylisopropylamine) was linked to human serum albumin by reaction with glutaraldehyde. These conjugates were used for immunization of rabbits. Derivatives of mescaline [N-(3′,4′,5′-trimethoxyphenethyl)-4-hydroxyphenylacetamide] and of DOM [N-(2′,5′-dimethoxy-4′-methylphenylisopropyl)-4-hydroxyphenylacetamide], which could be iodinated to high specific activity, were synthesized. The antibodies bound specifically to these iodinated compounds. In competition experiments with a mescaline antiserum, 6 pmoles of mescaline inhibited 50%; with a DOM antiserum, 50% inhibition was observed with 118 pmoles of DOM. Thus, 100 pg of mescaline and 2 ng of DOM can be detected. The specificity of both antibodies is such that structurally related molecules, such as p-methoxy-phenethylamine or 3-methoxytyramine, are several orders of magnitude less effective as inhibitors than the parent molecules. With the use of antimescaline, it was determined that mescaline administered intravenously to rabbits disappeared rapidly from the circulation. The acid was identified as the major metabolite in the serum and urine of these animals.     

Assay of penicillin acylase in organic media

Summary The synthetic substrate 6-nitro-3-(phenylacetamido) benzoic acid (NIPAB) is an appropriate substrate for assaying penicillin acylase activity in reversed micellar systems of Aerosol - OT in isooctane. Accumulation of 6-nitro-3-aminobenzoic acid (NABA) produced by the enzymatic hydrolysis of NIPAB, followed by the increase in absorbance at 405 nm, was linear at 4 to 20 mM for up to 30 minutes and 15 °C to 40 °C.Abbreviations PA penicillin acylase (penicillin amidohydrolase EC 3.5.1.11) - AOT Aerosol OT (sodium bis- (2-ethylhexyl) sulfosuccinate) - NIPAB 6-nitro-3-(phenylacetamido)-benzoic acid - NABA 6-nitro-3-aminobenzoic acid - BSA bovine serum albumin     

Preparation of novel conjugates involving immunomodulating peptidoglycan monomer.

Peptidoglycan monomer, the disaccharide pentapeptide beta-D-Glcp-N-Ac-(1-->4)-D-Murp-N-Ac-L-Ala-D-mesoA2pm- (epsilonN H2)-D-Ala-D-Ala (PGM) is an immunomodulator. PGM and/or its derivative N-tert-butyloxycarbonyl-L-tyrosyl peptidoglycan monomer (Boc-Tyr-PGM) were coupled to two polysaccharides: the glucuronoxylomannan (GXM) from Cryptococcus neoformans, type B, solubilized by ultrasonic irradiation (MW 12-400 kDa) and to the dextran FP 70 (MW 70 kDa). Both polysaccharides were activated by CNBr. Initially, unprotected PGM was coupled via its amino group to GXM. The reactions yielded 42%-52% of the conjugate, containing only 0.18%-0.31% of PGM. In another approach Boc-Tyr-PGM (having its amino group blocked) was reacted via its free carboxyl group. Both CNBr-activated polysaccharides were first coupled to adipic acid dihydrazide (ADH) and then subsequently coupled to Boc-Tyr-PGM. The dextran conjugate (approximately 80% yield ) contained 6.3% of Boc-Tyr-PGM. The isolation of GXM conjugate required several modifications and it was obtained in lower yield (approximately 30%) but contained 13.7% of Boc-Tyr-PGM. Both conjugates were water soluble and apyrogenic and suitable for further testing of biological activity.     

Synthesis and cytotoxic activities of beta-carboline amino acid ester conjugates

Beta-carboline represents a class of compounds with potent anti-tumor activity by intercalating with DNA. To further enhance the cytotoxic potency and bioavailability of beta-carboline, a series of novel beta-carboline amino acid ester conjugates were designed and synthesized, and the cytotoxic activities of these compounds were tested using a panel of human tumor cell lines. In addition, the membrane permeability of these compounds was evaluated in vitro using a Caco-2 cell monolayer model. The beta-carboline amino acid ester conjugates demonstrated improved cytotoxic activity compared to the parental beta-carbolines. In particular, the Lys/Arg conjugates were the most potent analogs with an IC(50) value of 4 and 1 microM against human cervical carcinoma cells. The low interaction energy of Arg conjugate based on molecular modeling may contribute to its enhanced cytotoxicity. Taken together, this study provided new insights into structure-activity relationships in the beta-carboline amino acid ester conjugates and identified the beta-carboline Lys/Arg conjugates as promising lead compounds for further in vivo biological and molecular evaluation.     

Evaluation of synthetic schemes to prepare immunogenic conjugates of Vibrio cholerae O139 capsular polysaccharide with chicken serum albumin

Vibrio cholerae serotype O139 is a new etiologic agent of epidemic cholera. There is no vaccine available against cholera caused by this serotype. V. cholerae O139 is an encapsulated bacterium, and its polysaccharide capsule is an essential virulent factor and likely protective antigen.This study evaluated several synthetic schemes for preparation of conjugates of V. cholerae O139 capsular polysaccharide (CPS) with chicken serum albumin as the carrier protein (CSA) using 1-ethyl-3(3-dimethylaminopropyl)carbodiimide (EDC) or 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) as activating agents. Four conjugates described here as representative of many experiments were synthesized in 2 steps: 1) preparation of adipic acid hydrazide derivative of CPS (CPS_AH) or of CSA (CSA_AH), and 2) binding of CPS_AH to CSA or of CPS to CSA_AH. Although all conjugates induced CPS antibodies, the conjugate prepared by EDC-mediated binding of CPS and CSA_AH (EDC:CPS-CSA_AH) was statistically significantly less immunogenic than the other three conjugates. Representative sera from mice injected with these three conjugates contained antibodies that mediated the lysis of V. cholerae O139 inoculum.Evaluation of the different synthetic schemes and reaction conditions in relation to the immunogenicity of the resultant conjugates provided the basis for the preparation of a V. cholerae O139 conjugate vaccine with a medically useful carrier protein such as diphtheria toxin mutant.     

Synthesis and biological activity of ester derivatives of mycophenolic acid and acridines/acridones as potential immunosuppressive agents

Improved derivatives of mycophenolic acid (MPA) are necessary to reduce the frequency of adverse effects, this drug exerts in treated patients. In this study, MPA was coupled with N-(ω-hydroxyalkyl)-9-acridone-4-carboxamides or N-(ω-hydroxyalkyl)acridine-4-carboxamides to give respective ester conjugates upon Yamaguchi protocol. This esterification required protection of phenol group in MPA. Designed conjugates revealed higher potency in vitro than parent MPA. Acridine derivatives were more active than acridone analogs and length of the alkyl linker between MPA and heterocyclic units influenced the observed cytotoxicity. Derivatives 2b, 2d, 3a, 3b displayed the most promising immunosuppressive activity.     

Synthesis and characterization of protein and polylysine conjugates of sulfamethoxazole and sulfanilic acid for investigation of sulfonamide drug allergy

Conjugates of sulfamethoxazole (SMX) with human serum albumin (HSA), transferrin (TR), and poly(L-lysine) (PL, degrees of polymerization 16 and 430) have been prepared. As a model, succinylSMX-glycine methyl ester was synthesized by carbodiimide and active ester routes. The proteins and PL were acylated with succinylSMX succinimido ester, affording conjugates (succinylSMX)2-21-HSA, (succinylSMX)17,27-TR, (succinylSMX)11-Lys16, and (succinylSMX)71-Lys430 in which SMX was linked by a spacer chain of four carbons. This represents substitution of up to 35, 46, 65, and 17% of the amino groups of HSA, TR, PL16, and PL430, respectively. HSA was also acylated with the succinimido esters of succinylSMX-glycine and succinylSMX-epsilon-aminohexanoic acid, affording conjugates (succinylSMX-Gly)53-HSA and (succinylSMX-epsilon-NH2hex)51-HSA. In these conjugates SMX was linked by a spacer chain of 7 and 11 carbons, respectively, and almost all the amino groups of HSA were substituted. Factors apparently influencing the extent of conjugation to HSA were the stability of the active ester and the solubility of the conjugation reaction mixture. A sulfanilic acid (SA) conjugate, containing 12 mol of ligand/mol of HSA, was also prepared. The route of synthesis involved acylation of HSA with sulfanilyl fluoride. N-epsilon-Sulfanilyl-L-lysine dihydrochloride, required for quantitation of bound SA, was synthesized by a new route starting from alpha-Boc-L-lysine. Conjugates (sulfanilyl)12-HSA and (succinylSMX)13-HSA, differing in molecular weight from HSA by only 2.6 and 6.5%, were distinguishable from HSA by gel-filtration HPLC, as were the more highly substituted conjugates from their respective unsubstituted materials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Design and synthesis of ferrocene probe molecules for detection by electrochemical methods

A series of ferrocenyl conjugates to fatty acids have been designed and synthesized to establish the key properties required for use in biomolecular binding studies. Amperometric detection of the ferrocene conjugates was sought in the region of 0.3 V (vs Ag/AgCl) for use in protein/blood solutions. Different linkers and solubilizing moieties were incorporated to produce a conjugate with optimal electrochemical properties. In electrochemical studies, the linker directly attached to the ferrocene was found to affect significantly the E(1/2) value and the stability of the ferrocenium cation. Ester-linked ferrocene conjugates had E(1/2) ranging from +400 to +410 mV, while amide-linked compounds ranged from +350 to +370 mV and the amines +260 to +270 mV. Folding of long-chain substituents around the ferrocene, also significantly affected by the choice of linker, was inferred as a secondary effect that increased E(1/2). The stability of the ferrocenium cation decreased systematically as E(1/2) increased. Disubstituted ferrocene ester and amide conjugates, with oxidation potentials of +640 and +570 mV, respectively, showed only a barely discernible reduction wave in cyclic voltammetry at 50 mV/s. Electrochemical measurements identified two lead compounds with the common structural characteristics of an amide and carbamate linker (compounds 17 and 21) with a C(11) fatty acid chain attached. It is envisaged that such molecules can be used to mimic and study the biomolecular binding interaction between fatty acids and molecules such as human serum albumin.     

Bisphosphonate conjugation to proteins as a means to impart bone affinity

Growth factors are endogenous proteins capable of stimulating new bone formation, but their clinical benefit for systemic stimulation of bone mass has not been demonstrated. The critical challenge is to deliver a significant dose of the proteins to bone after intravenous injection. This challenge may be overcome by derivatizing proteins with ligands that exhibit a high bone affinity (e.g., bisphosphonates). To demonstrate the feasibility of this approach, 1-amino-1,1-diphosphonate methane (aminoBP) was conjugated to a model protein, albumin. The conjugation was performed by (1) converting the amino group of aminoBP to a thiol group using 2-iminothiolane, (2) derivatizing the albumin amino groups with a thiol-reactive sulfosuccinimidyl-4-(N-maleimidomethyl)-1-cyclohexane carboxylate, and (3) reacting the derivatized albumin with thiolated aminoBP. Typically, 1-4 aminoBP molecules per albumin were obtained. The conjugated albumin exhibited a high affinity to hydroxyapatite that was proportional to the extent of conjugation. The conjugates were shown to exhibit a high affinity to bone matrix in vitro in a serum-containing medium. Once bound to bone matrix, the conjugates were found to desorb more slowly than the unmodified albumin, especially from bone whose organic matrix was removed by ashing. In conclusion, conjugation of bisphosphonates to albumin was shown to impart a high bone affinity to the protein, and such conjugates can be potentially targeted to bone.     

Synthesis of pH-sensitive amphotericin B-poly(ethylene glycol) conjugates and study of their controlled release in vitro

New intravenous conjugates of amphotericin B (AMB) with poly(ethylene glycols) (PEG) (M=5000, 10,000, 20,000) have been synthesized and characterised. The intermediate PEGs possess a 1,4-disubstituted benzene ring with aldehyde group at the end of the chain. The benzene ring is connected with PEG at its 4-position (with respect to the aldehyde group) by various functional groups (ether, amide, ester). Reaction of terminal aldehyde group of the substituted PEGs with AMB gave conjugates containing a pH-sensitive imine linkage, which can be presumed to exhibit antimycotic effect at sites with lowered pH value. All types of the conjugates are relatively stable in phosphate buffer at physiological conditions of pH 7.4 (37 degrees C), less than 5 mol% AMB being split off from them within 24 h. For a model medium of afflicted tissue was used a phosphate buffer (pH 5.5, 37 degrees C), in which controlled release of AMB from the conjugates takes place. The imine linkage is split to give free AMB with half-lives of 2-45 min. The rate of acid catalysed hydrolysis depends upon substitution of the benzene ring; however, it does not depend on molecular weights of the PEGs used. The conjugates with ester linkage undergo enzymatic splitting in human blood plasma and/or blood serum at pH 7.4 (37 degrees C) with half-lives of 2-5 h depending on molecular weights of the PEGs used (M = 5000, 10,000, 20,000). At first, the splitting of ester linkage produces the relatively stable pro-drug, that is, 4-carboxybenzylideniminoamphotericin B, which is decomposed to AMB and 4-formylbenzoic acid in a goal-directed manner only at pH 7 (t1/2 = 2 min, pH 5.5, 37 degrees C). A goal-directed release of AMB is only achieved by acid catalysed hydrolysis of imine linkage, either from the polymeric conjugate or from the pro-drug released thereof. The LD50 values determined in vivo (mouse) are 20.7 mg/kg and 40.5 mg/kg for the conjugates with ester linkage (M = 10,000 and 5000, respectively), which means that they are ca. 6-11 times less toxic than free AMB.     

Conjugation of N-acylated amino sugars to protein by reductive alkylation using sodium cyanoborohydride: application to an azo derivative of alpha-amanitin.

Reductive alkylation mediated by cyanoborohydride is an attractive approach to the conjugation of small molecules, such as drugs, to proteins. This reaction is specific for protein amino groups and can be conducted under mild conditions with little risk of protein polymerization. However, the lability of the aldehyde function that is needed in such reactions presents a difficulty. We have investigated the use of derivatives of D-galactosamine and D-glucosamine in reductive alkylation, since these sugars contain aldehyde groups that are inherently protected and that may be readily linked to other molecules through their amino groups. The amino groups of these sugars were acylated with N-4-nitro-benzoylglycylglycine. Studies of the reductive coupling of the resultant adducts to bovine serum albumin revealed that conjugation to albumin is strongly dependent on cyanoborohydride, is much faster in the presence of borate, and shows a marked increase in rate between pH 7.0 and 9.0. In the presence of borate, the glucosamine derivative coupled much more rapidly than did the galactosamine derivative. The aryl nitro group of the glucosamine adduct was selectively reduced to an amine, diazotized, and reacted with alpha-amanitin to form an azo compound. This azo derivative was reductively coupled to form conjugates that inhibit calf thymus RNA polymerase II.     

P4 cap modified tetrapeptidyl alpha-ketoamides as potent HCV NS3 protease inhibitors

We describe herein the design, syntheses, and biological evaluation of new series of P4 tetrazole and adipic acid, ester, amide capped tetrapeptidyl alpha-ketoamide based HCV protease inhibitors.     

Radiolabeled affibody-albumin bioconjugates for HER2-positive cancer targeting

Affibody molecules have received significant attention in the fields of molecular imaging and drug development. However, Affibody scaffolds display an extremely high renal uptake, especially when modified with chelators and then labeled with radiometals. This unfavorable property may impact their use as radiotherapeutic agents in general and as imaging probes for the detection of tumors adjacent to kidneys in particular. Herein, we present a simple and generalizable strategy for reducing the renal uptake of Affibody molecules while maintaining their tumor uptake. Human serum albumin (HSA) was consecutively modified by 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA-NHS ester) and the bifunctional cross-linker sulfosuccinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (Sulfo-SMCC). The HER2 Affibody analogue, Ac-Cys-Z(HER2:342), was covalently conjugated with HSA, and the resulting bioconjugate DOTA-HSA-Z(HER2:342) was further radiolabeled with ??Cu and 111In and evaluated in vitro and in vivo. Radiolabeled DOTA-HSA-Z(HER2:342) conjugates displayed a significant and specific cell uptake into SKOV3 cell cultures. Positron emission tomography (PET) investigations using ??Cu-DOTA-HSA-Z(HER2:342) were performed in SKOV3 tumor-bearing nude mice. High tumor uptake values (>14% ID/g at 24 and 48 h) and high liver accumulations but low kidney accumulations were observed. Biodistribution studies and single-photon emission computed tomography (SPECT) investigations using 111In-DOTA-HSA-Z(HER2:342) validated these results. At 24 h post injection, the biodistribution data revealed high tumor (16.26% ID/g) and liver (14.11% ID/g) uptake but relatively low kidney uptake (6.06% ID/g). Blocking studies with coinjected, nonlabeled Ac-Cys-Z(HER2:342) confirmed the in vivo specificity of HER2. Radiolabeled DOTA-HSA-Z(HER2:342) Affibody conjugates are promising SPECT and PET-type probes for the imaging of HER2 positive cancer. More importantly, DOTA-HSA-Z(HER2:342) is suitable for labeling with therapeutic radionuclides (e.g., ??Y or 1??Lu) for treatment studies. The approach of using HSA to optimize the pharmacokinetics and biodistribution profile of Affibodies may be extended to the design of many other targeting molecules.     

Use of Water-soluble Carbodiimide (EDC) for Immobilization of EDC-sensitive Dextranase

Water-soluble carbodiimide [EDC: (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide)] is a useful reagent for chemical modification of carboxyl group of various proteins. Model experiments to establish detailed conditions for the cross-linking reaction with EDC were conducted. Since the reactivity of hexamethylenediamine as a nucleophile was almost comparable to that of glycine ethyl ester, AH-Sephadex and the carboxyl group of aspartylphenylalanine methyl ester were coupled by EDC. From the hydrolyzate of the isolated gel, aspartic acid and phenylalanine methyl ester were identified. When bovine serum albumin (BSA) was incubated with AH-Sephadex and EDC, about 90 % of the BSA was coupled to the gel by 3 hr incubation. Moreover, BSA was effectively coupled with the carboxymethyl cellulose (CMC) after activation of the carboxyl groups of CMC with EDC followed by the removal of excess EDC. The latter case would be useful for cross-linking the enzyme molecules to the matrix because of the very mild reaction conditions. For example, endodextranase, which readily lost its activity upon being incubated with EDC (suggesting that a carboxyl group was essential for the enzyme activity), was effectively immobilized to CMC with EDC. This improved reaction step for the cross-linking seemed to be especially useful for the glycosylases, because in most of these enzymes carboxyl groups play a role in the catalytic residue.