Radionuclide Molecular Imaging of EpCAM Expression in Triple-Negative Breast Cancer Using the Scaffold Protein DARPin Ec1

Efficient treatment of disseminated triple-negative breast cancer (TNBC) remains an unmet clinical need. The epithelial cell adhesion molecule (EpCAM) is often overexpressed on the surface of TNBC cells, which makes EpCAM a potential therapeutic target. Radionuclide molecular imaging of EpCAM expression might permit selection of patients for EpCAM-targeting therapies. In this study, we evaluated a scaffold protein, designed ankyrin repeat protein (DARPin) Ec1, for imaging of EpCAM in TNBC. DARPin Ec1 was labeled with a non-residualizing [¹²⁵I]I-para-iodobenzoate (PIB) label and a residualizing [^99mTc]Tc(CO)₃ label. Both imaging probes retained high binding specificity and affinity to EpCAM-expressing MDA-MB-468 TNBC cells after labeling. Internalization studies showed that Ec1 was retained on the surface of MDA-MB-468 cells to a high degree up to 24 h. Biodistribution in Balb/c nu/nu mice bearing MDA-MB-468 xenografts demonstrated specific uptake of both [¹²⁵I]I-PIB-Ec1 and [^99mTc]Tc(CO)₃-Ec1 in TNBC tumors. [¹²⁵I]I-PIB-Ec1 had appreciably lower uptake in normal organs compared with [^99mTc]Tc(CO)₃-Ec1, which resulted in significantly (p < 0.05) higher tumor-to-organ ratios. The biodistribution data were confirmed by micro-Single-Photon Emission Computed Tomography/Computed Tomography (microSPECT/CT) imaging. In conclusion, an indirectly radioiodinated Ec1 is the preferable probe for imaging of EpCAM in TNBC.

Analysis of Glutamine Deamidation: Products, Pathways, and Kinetics

Spontaneous chemical modifications play an important role in human disease and aging at the molecular level. Deamidation and isomerization are known to be among the most prevalent chemical modifications in long-lived human proteins and are implicated in a growing list of human pathologies, but the relatively minor chemical change associated with these processes has presented a long standing analytical challenge. Although the adoption of high-resolution mass spectrometry has greatly aided the identification of deamidation sites in proteomic studies, isomerization (and the isomeric products of deamidation) remain exceptionally challenging to characterize. Herein, we present a liquid chromatography/mass spectrometry-based approach for rapidly characterizing the isomeric products of Gln deamidation using diagnostic fragments that are abundantly produced and capable of unambiguously identifying both Glu and isoGlu. Importantly, the informative fragment ions are produced through orthogonal fragmentation pathways, thereby enabling the simultaneous detection of both isomeric forms while retaining compatibility with shotgun proteomics. Furthermore, the diagnostic fragments associated with isoGlu pinpoint the location of the modified residue. The utility of this technique is demonstrated by characterizing the isomeric products generated during in vitro aging of a series of glutamine-containing peptides. Sequence-dependent product profiles are obtained, and the abundance of deamidation-linked racemization is examined. Finally, comparisons are made between Gln deamidation, which is relatively poorly understood, and asparagine deamidation, which has been more thoroughly studied.

Chemoenzymatic Synthesis and α-Glucosidase Inhibitory Activity of Dimeric Neolignans Inspired by Magnolol

A chemoenzymatic synthesis of a small library of dimeric neolignans inspired by magnolol (1) is reported. The 2-iodoxybenzoic acid (IBX)-mediated regioselective ortho-hydroxylation of magnolol is described, affording the bisphenols 6 and 7. Further magnolol analogues (12, 13, 15-17, 19-23) were obtained from eugenol (3), tyrosol (4), and homovanillic alcohol (5), through horseradish peroxidase (HRP)-mediated oxidative coupling and regioselective ortho-hydroxylation or ortho-demethylation in the presence of IBX, followed by reductive treatment with Na₂S₂O₄. A chemoselective protection/deprotection of the alcoholic group of 4 and 5 was carried out by lipase-mediated acetylation/deacetylation. The dimeric neolignans, together with 1 and honokiol (2), were evaluated as inhibitors of yeast α-glucosidase, in view of their possible utilization and optimization as antidiabetic drugs. The synthetic analogues of magnolol showed a strong inhibitory activity with IC₅₀ values in the range 0.15-4.1 μM, much lower than those of honokiol and the reference compounds quercetin and acarbose. In particular, a very potent inhibitory activity, with an IC₅₀ of 0.15 μM, was observed for 1,1'-dityrosol-8,8'-diacetate (15), and comparable inhibitory activities were also shown by bisphenols 6 (0.49 μM), 13 (0.50 μM), and 22 (0.86 μM). A kinetic study showed that 15 acts as a competitive inhibitor, with a K_i value of 0.86 μM.

Chemical Genetics Uncovers Novel Inhibitors of Lignification, Including p-Iodobenzoic Acid Targeting CINNAMATE-4-HYDROXYLASE

Plant secondary-thickened cell walls are characterized by the presence of lignin, a recalcitrant and hydrophobic polymer that provides mechanical strength and ensures long-distance water transport. Exactly the recalcitrance and hydrophobicity of lignin put a burden on the industrial processing efficiency of lignocellulosic biomass. Both forward and reverse genetic strategies have been used intensively to unravel the molecular mechanism of lignin deposition. As an alternative strategy, we introduce here a forward chemical genetic approach to find candidate inhibitors of lignification. A high-throughput assay to assess lignification in Arabidopsis (Arabidopsis thaliana) seedlings was developed and used to screen a 10-k library of structurally diverse, synthetic molecules. Of the 73 compounds that reduced lignin deposition, 39 that had a major impact were retained and classified into five clusters based on the shift they induced in the phenolic profile of Arabidopsis seedlings. One representative compound of each cluster was selected for further lignin-specific assays, leading to the identification of an aromatic compound that is processed in the plant into two fragments, both having inhibitory activity against lignification. One fragment, p-iodobenzoic acid, was further characterized as a new inhibitor of CINNAMATE 4-HYDROXYLASE, a key enzyme of the phenylpropanoid pathway synthesizing the building blocks of the lignin polymer. As such, we provide proof of concept of this chemical biology approach to screen for inhibitors of lignification and present a broad array of putative inhibitors of lignin deposition for further characterization.

Photolytic determination of charge state for large proteins and fragments in an ion trap mass spectrometer

RATIONALE

One of the major shortcomings of linear ion trap mass spectrometers is poor resolution. Failure to resolve isotopic peaks makes charge state determination for large proteins very difficult, hindering the ability to perform top-down proteomics.

METHODS

Peptides, proteins and corresponding fragments modified with para-iodobenzoate were trapped and irradiated with 266 nm light from an Nd:YAG laser. Loss of iodine due to photodissociation was then used to assign charge states by measuring the corresponding m/z shifts.

RESULTS

Initial experiments on small peptides illustrate the feasibility of the method. Further studies performed on larger proteins in higher charge states yielded similar results, revealing that fragment ions over a significant mass range either remain in or are quickly cooled to the laser overlap region of the ion trap.

CONCLUSIONS

Rapid charge state assignment for both whole molecules and collision-induced dissociation (CID) fragments can be obtained by photoactivation of chromophores with labile carbon-iodine bonds.

Conformational analysis, spectroscopic study (FT-IR, FT-Raman, UV, 1H and 13C NMR), molecular orbital energy and NLO properties of 5-iodosalicylic acid

In this study, 5-iodosalicylic acid (5-ISA, C7H5IO3) is structurally characterized by FT-IR, FT-Raman, NMR and UV spectroscopies. There are eight conformers, Cn, n=1-8 for this molecule therefore the molecular geometry for these eight conformers in the ground state are calculated by using the ab-initio density functional theory (DFT) B3LYP method approach with the aug-cc-pVDZ-PP basis set for iodine and the aug-cc-pVDZ basis set for the other elements. The computational results identified that the most stable conformer of 5-ISA is the C1 form. The vibrational spectra are calculated DFT method invoking the same basis sets and fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method with PQS program. Total density of state (TDOS) and partial density of state (PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis for C1 conformer were calculated using the same method. The energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT) results complement with the experimental findings. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) are calculated and presented. The NMR chemical shifts ((1)H and (13)C) spectra are recorded and calculated using the gauge independent atomic orbital (GIAO) method. Mulliken atomic charges of the title molecule are also calculated, interpreted and compared with salicylic acid. The optimized bond lengths, bond angles and calculated NMR and UV, vibrational wavenumbers showed the best agreement with the experimental results.

Photochemical synthesis and properties of 1,6- and 1,8-naphthalenophanes

Various 1,6- and 1,8-naphthalenophanes were synthesized by using the Photo-Dehydro-Diels-Alder (PDDA) reaction of bis-ynones. These compounds are easily accessible from ω-(3-iodophenyl)carboxylic acids in three steps. The obtained naphthalenophanes are axially chiral and the activation barrier for the atropisomerization could be determined in some cases by means of dynamic NMR (DNMR) and/or dynamic HPLC (DHPLC) experiments.

Synthesis and structure/antioxidant activity relationship of novel catecholic antioxidant structural analogues to hydroxytyrosol and its lipophilic esters

A large panel of novel catecholic antioxidants and their fatty acid or methyl carbonate esters has been synthesized in satisfactory to good yields through a 2-iodoxybenzoic acid (IBX)-mediated aromatic hydroxylation as the key step. The new catechols are structural analogues of naturally occurring hydroxytyrosol (3,4-DHE). To evaluate structure/activity relationships, the antioxidant properties of all catecholic compounds were evaluated in vitro by ABTS assay and on whole cells by DCF fluorometric assay and compared with that of the corresponding already known hydroxytyrosyl derivatives. Results outline that all of the new catechols show antioxidant capacity in vitro higher than that of the corresponding hydroxytyrosyl derivatives. Less evident positive effects have been detected in whole cells experiments. Cytotoxicity experiments, using MTT assay, on a representative set of compounds evidenced no influence in cell survival.

New protein footprinting: fast photochemical iodination combined with top-down and bottom-up mass spectrometry

We report a new approach for the fast photochemical oxidation of proteins (FPOP) whereby iodine species are used as the modifying reagent. We generate the radicals by photolysis of iodobenzoic acid at 248 nm; the putative iodine radical then rapidly modifies the target protein. This iodine-radical labeling is sensitive, tunable, and site-specific, modifying only histidine and tyrosine residues in contrast to OH radicals that modify 14 amino-acid side chains. We iodinated myoglobin (Mb) and apomyoglobin (aMb) in their native states and analyzed the outcome by both top-down and bottom-up proteomic strategies. Top-down sequencing selects a certain level (addition of one I, two I's) of modification and determines the major components produced in the modification reaction, whereas bottom-up reveals details for each modification site. Tyr146 is found to be modified for aMb but less so for Mb. His82, His93, and His97 are at least 10 times more modified for aMb than for Mb, in agreement with NMR studies. For carbonic anhydrase and its apo form, there are no significant differences of the modification extents, indicating their similarity in conformation and providing a control for this approach. For lispro insulin, insulin-EDTA, and insulin complexed with zinc, iodination yields are sensitive to differences in insulin oligomerization state. The iodine radical labeling is a promising addition to protein footprinting methods, offering higher specificity and lower reactivity than ∙OH and SO(4)(-∙), two other radicals already employed in FPOP.

Room-temperature aromatization of tetrahydro-β-carbolines by 2-iodoxybenzoic acid: utility in a total synthesis of eudistomin U

2-Iodoxybenzoic acid is a convenient reagent for the dehydrogenation of tetrahydro-β-carbolines to their aromatic forms under mild conditions. The utility of the method was demonstrated in a total synthesis of the marine indole alkaloid eudistomin U.

Synthesis and characterization of novel radiopaque poly(allyl amine) nanoparticles

Contrast agents are currently used in a variety of diagnostic imaging techniques, including computer tomography for early cancer detection. Radiopaque nanoparticles have recently been proposed as an alternative method to traditional contrast agents that may allow for long-term image tracking. The aim of this study was the preparation and characterization of aqueous suspensions of radiopaque nanoparticles made of poly(allyl amine) derivatives. Poly(allylamine) (PA) was modified by grafting either 4-iodobenzoyl chloride or 2,3,5-triiodobenzoyl chloride to make the polymer x-ray visible. Nanoparticles of the modified PA were prepared by the nanoprecipitation method and purified with respect to residual organic solvents. Stable suspensions of spherical particles of sub-micronic diameter were characterized by dynamic light scattering and transmission electron microscopy. In addition, the 4.5 wt% suspensions of nanoparticles displayed an x-ray visibility ranging between 185 and 235 HU. The non-clustering ability of the novel PA radiopaque nanoparticles suggests they could be injected via a catheter without clogging or sedimentation.

Convenient synthesis of hydroxytyrosol and its lipophilic derivatives from tyrosol or homovanillyl alcohol

Hydroxytyrosol, a naturally occurred o-phenolic compound exhibiting antioxidant properties, was synthesized by a three-step high-yielding procedure from natural and low-cost compounds such as tyrosol or homovanillyl alcohol. First, the efficient chemoselective protection of the alcoholic group of these compounds was performed by using dimethyl carbonate (DMC) as reagent/solvent; second, the oxidation with 2-iodoxybenzoic acid (IBX) or Dess-Martin periodinane reagent (DMP) and in situ reduction with sodium dithionite (Na2S2O4) allowed the preparation of carboxymethylated hydroxytyrosol; finally, by a mild hydrolytic step, hydroxytyrosol was obtained in high yield and purity, as confirmed by NMR spectra and HPLC profile. By using a similar methodology, lipophilic hydroxytyrosol derivatives, utilized as additives in pharmaceutical, food, and cosmetic preparations, were prepared. In fact, at first the chemoselective protection of the alcoholic group of tyrosol and homovanillyl alcohol was performed by using acyl chlorides without any catalyst to obtain the corresponding lipophilic derivatives, and then these compounds were converted in good yield and high purity into the hydroxytyrosol derivatives by oxidative/reductive pathway with IBX or DMP and Na2S2O4.

Palladium-catalyzed one-step synthesis of isoindole-1,3-diones by carbonylative cyclization of o-halobenzoates and primary amines

The palladium-catalyzed aminocarbonylation of o-halobenzoates produces 2-substituted isoindole-1,3-diones in good yields. This methodology provides a good one-step approach to this important class of heterocycles and tolerates a variety of functional groups, including methoxy, alcohol, ketone, and nitro groups.

Efficient access to orthoquinols and their [4 + 2] cyclodimers via SIBX-mediated hydroxylative phenol dearomatization

SIBX, the nonexplosive formulation of the lambda5-iodane 2-iodoxybenzioc acid (IBX), safely and efficiently mediates the hydroxylative dearomatization of various 2-alkylphenols and napthols into orthoquinols or their [4 + 2] cyclodimers. Reactions are typically run at room temperature using SIBX as a suspension in THF. Using these conditions, natural products such as the cyclodimer of the terpene carvacrol and, for the first time, the shikimate-derived (+/-)-grandifloracin were prepared in one step from their respective phenolic precursor.

A library of noviosylated coumarin analogues

The DNA gyrase inhibitor, novobiocin, was recently shown to inhibit Hsp90 via a previously unrecognized C-terminal ATP-binding site. Previous structure-activity relationship studies identified key moieties that appear important for Hsp90 inhibitory activity. In an effort to provide a more efficacious lead compound, a parallel library of noviosylated coumarin analogues was prepared.

Nickel-Catalyzed Synthesis of Benzocoumarins: Application to the Total Synthesis of Arnottin I

The ring-opening addition of methyl 2,3-dimethoxy-6-iodobenzoate to oxabenzonorbornadienes followed by cyclization in the presence of NiBr2(dppe) and Zn metal powder in acetonitrile at 80 degrees C to give the corresponding benzocoumarin derivatives is described. This methodology was then applied to the synthesis of natural product arnottin I, first isolated from Xanthoxylum arnottianum Maxim, using protecting group chemistry. After deprotection and subsequent ring closure, arnottin I was obtained in 21% overall yield after six steps starting from catechol.

Preparation of N-succinimidyl 3-[*I]iodobenzoate: an agent for the indirect radioiodination of proteins

A procedure for the synthesis of N-succinimidyl 3-iodobenzoate labeled with any iodine isotope ([*I]SIB), which is an agent used in the radioiodination of proteins and peptides, from its tin precursor N-succinimidyl 3-(tri-n-butylstannyl)benzoate (STB) is described. Also included are protocols for the synthesis of an unlabeled standard of SIB and the tin precursor. Radioiododestannylation of STB using tert-butylhydroperoxide as the oxidant gives [*I]SIB in 80% radiochemical yields. The total time for the synthesis of [*I]SIB from STB is approximately 95 min. Use of [*I]SIB yields radioiodinated proteins that are considerably more stable in vivo than those radioiodinated by the direct electrophilic method.

Influence of prosthetic radioiodination on the chemical and biological behavior of chemotactic peptides labeled at high specific activity

The influence of radioiodination made through prosthetic group N-succinimidyl-3-[131I]iodo-benzoate ([131I]SIB) on the behavior of small peptides was investigated using as model the chemotactic hexapeptide Nalpha-for-Nle-Leu-Phe-Nle-Tyr-Lys. No carrier added labeled peptide was isolated by reverse-phase HPLC (RP-HPLC) with coupling efficiencies up to 59-75%. Biodistribution in normal and infected C57 mice showed mainly a hepatobiliary clearance, a very low thyroid uptake and the highest uptake at the infection site was within 1h of injection. Superoxide production and competitive binding assays studies in human polymorphonuclear leukocytes showed a preserved biological activity and high-affinity specific binding. However, the results indicated that the changes observed in the receptor-binding properties with an IC50 almost twice than the unlabeled peptide and the increasing in the hepatobiliary excretion could be the consequence of the increased lipophicity observed due to the presence of the prosthetic group together with a strong influence of the radioisotope per se.

Enhancing 2-iodoxybenzoic acid reactivity by exploiting a hypervalent twist

A rearrangement of hypervalent bonds, or twisting, proves to be the rate-determining step in the 2-iodoxybenzoic acid (IBX) oxidation of alcohols. From this insight, derived from density functional theory calculations, we explain why IBX oxidizes large alcohols faster than small ones and propose a modification to the reagent predicted to make it more active.

Vibrational and microbiological study on alkaline metal picolinates and o-iodobenzoates

FT-IR and Raman experimental data were assigned to appropriate bond vibrations and used to compare the different electronic charge distributions in the aromatic rings and carboxylic anions of various lithium, sodium, potassium, rubidium and caesium o-iodobenzoates and picolinates. Then principal component analysis (PCA) was applied in order to attempt to distinguish the biological activities of these compounds according to selected band wavenumbers. The growth of the bacteria Escherichia coli and Bacillus subtilis and the yeasts Saccharomyces cerevisiae and Hansenula anomala under optimal growth conditions were measured after 24 hours of incubation by the classical plate method. The influence of the picolinates and o-iodobenzoates on the growth of these microorganisms, again after 24 hours of incubation, was also measured and compared to the effect of sodium benzoate, which was used as a reference material. In general, the o-iodobenzoates exhibited more activity against the microorganisms than the picolinates. A statistically significant linear correlation between the spectral data and the degree of influence of a given compound on microorganism growth was established. The correlation coefficients for the o-iodobenzoates were 0.696, -0.628, 0.693 and 0.755 for E. coli, B. subtilis, H. anomala and S. cerevisiae, respectively, and for the picolinates they were 0.818, 0.826, 0.821 and 0.877 for E. coli, B. subtilis, H. anomala and S. cerevisiae, respectively. Therefore, IR spectroscopy is shown to be a rapid and reliable analytical tool for preliminary estimation of the antimicrobial properties of newly synthesized compounds, that can be applied before microbial performance tests.

Esters of 2-Iodoxybenzoic Acid: Hypervalent Iodine Oxidizing Reagents with a Pseudobenziodoxole Structure

Esters of 2-iodoxybenzoic acid (IBX-esters) were prepared by the hypochlorite oxidation of the corresponding 2-iodobenzoate esters and isolated as chemically stable, microcrystalline products. These hypervalent iodine compounds are potentially valuable oxidizing reagents belonging to a new class of pentavalent iodine compounds with a pseudobenziodoxole structure. Methyl 2-iodoxybenzoate can be further converted to the diacetate or a bis(trifluoroacetate) derivative by treatment with acetic anhydride or trifluoroacetic anhydride, respectively. Single-crystal X-ray diffraction analysis of methyl 2-[(diacetoxy)iodosyl]benzoate 8a reveals a pseudobenziodoxole structure with three relatively weak intramolecular I...O interactions. The dimethyl and diisopropyl esters of 2-iodoxyisophthalic acid were prepared by oxidation of the respective iodoarenes with dimethyldioxirane. Single-crystal X-ray diffraction analysis of diisopropyl 2-iodoxyisophthalate 6b showed intramolecular I...O interaction with the carbonyl oxygen of only one of the two carboxylic groups, while NMR spectra in solution indicated equivalency of both ester groups. IBX-esters, methyl 2-[(diacetoxy)iodosyl]benzoate, and 2-iodoxyisophthalate esters can oxidize alcohols to the respective aldehydes or ketones in the presence of trifluoroacetic acid or boron trifluoride etherate. The bis(trifluoroacetate) derivative can oxidize alcohols to carbonyl compounds without acid catalyst.

The relationship between chemical structure and antimicrobial activity of selected nicotinates, p-iodobenzoates, picolinates and isonicotinates

Alkaline metal, calcium and magnesium p-iodobenzoates and alkaline metal nicotinates, as well as sodium and potassium picolinic and isonicotinates were investigated by means of their antimicrobial and chemical properties. The quality estimation of the influence of metal cation coordinated to the carboxylic anion of the series of studied compounds on their antimicrobial activity as well as on the vibrational structure of whole complex in water solution was done. The changes in antimicrobial properties and in charge distribution of the complex along the position of nitrogen atom in the aromatic ring in sodium and potassium complexes were investigated. The analysis of influence of iodine substituent in para position on the change of electronic charge distribution of carboxylate anion and aromatic ring was done. The relationship between electronic properties estimated by vibrational spectroscopy and antimicrobial activity of studied complexes was investigated.

Synthesis of Isocoumarins via Pd/C-Mediated Reactions of o-Iodobenzoic Acid with Terminal Alkynes

The coupling reaction of o-iodobenzoic acid with terminal alkynes by using a catalyst system of 10% Pd/C-Et3N-CuI-PPh3 has been studied in a variety of solvents. 3-Substituted isocoumarins were formed in good yields and with good regioselectivity when the reaction was performed in EtOH.

On the Solid State Structure of 4-Iodobenzoic Acid

The solid-state structure of 4-iodobenzoic acid has been confirmed by variable temperature X-ray diffraction, variable temperature solid-state NMR and differential scanning calorimetry. 4-iodobenzoic acid crystallizes in the space group P2(1)/n, and dimerizes in the solid state about a center of inversion. Using extensive X-ray crystallographic data collections, the placement of the carboxylate H atoms from the residual electron density in difference Fourier maps was determined. The position of the electron density associated with the proton is found to vary with temperature in that the population of the disordered sites changes with varying temperature. Determination of the crystal structure between the temperatures of 248 and 198 K was not possible due to a phase transition, an endothermic event occurring at 230.77 K. The phase transition is also indicated by a change in the relaxation time of the ring carbon atoms in the solid-state NMR data. Though the dominating force in the dimeric unit in the solid state is the presence of strong hydrogen bonds, there are also van der Waals forces present between the iodine atoms. In the layered structure, the iodine-iodine distance is within the van der Waals contact radii, an interaction which causes a deformation in the electron density of the iodine atoms.

Selective binding to transthyretin and tetramer stabilization in serum from patients with familial amyloidotic polyneuropathy by an iodinated diflunisal derivative

In familial amyloidotic polyneuropathy, TTR (transthyretin) variants are deposited as amyloid fibrils. It is thought that this process involves TTR tetramer dissociation, which leads to partially unfolded monomers that aggregate and polymerize into amyloid fibrils. This process can be counteracted by stabilization of the tetramer. Several small compounds, such as diclofenac, diflunisal and flufenamic acid, have been reported to bind to TTR in vitro, in the T4 (thyroxine) binding channel that runs through the TTR tetramer, and consequently are considered to stabilize TTR. However, if these agents bind plasma proteins other than TTR, decreased drug availability will occur, compromising their use as therapeutic agents for TTR amyloidosis. In the present work, we compared the action of these compounds and of new derivatives designed to increase both selectivity of binding to TTR and inhibitory potency in relation to TTR amyloid fibril formation. We found two diflunisal derivatives that, in contrast with diclofenac, flufenamic acid and diflunisal, displaced T4 from TTR in plasma preferentially over binding to albumin and thyroxine binding globulin. The same diflunisal derivatives also had a stabilizing effect on TTR tetramers in plasma, as studied by isoelectric focusing of whole plasma under semi-denaturing conditions. In addition, by transmission electron microscopy, we demonstrated that, in contrast with other proposed TTR stabilizers (namely diclofenac, flufenamic acid and diflunisal), one of the diflunisal derivatives tested efficiently inhibited TTR aggregation. Taken together, our ex vivo and in vitro studies present evidence for the selectivity and efficiency of novel diflunisal derivates as TTR stabilizers and as inhibitors of fibril formation.

Preparation and structure of 2-iodoxybenzoate esters: soluble and stable periodinane oxidizing reagentsElectronic Supplementary Information (ESI) available: synthetic and characterization data for all new compounds; general procedures for the oxidation of alcohols with reagent 4c. See http://www.rsc.org/suppdata/cc/b3/b312961f/

Esters of 2-iodoxybenzoic acid (IBX-esters) are potentially valuable oxidizing reagents belonging to a new class of pentavalent iodine compounds with a pseudo benziodoxole structure.

Synthesis of dendrimer-based biotin radiopharmaceuticals to enhance whole-body clearance

To synthesize a biotin radiopharmaceutical that clears rapidly, dendrimer was used as a carrier and conjugated with succinimidyl 3-[(125)I]iodobenzoate and tetrafluorophenyl norbiotinamidosuccinate. Then, succinic anhydride was used to reduce its pI. In mice, the non-succinylated product showed high liver (67% ID/g) and kidney (44% ID/g) uptakes and whole-body retention (94% ID) at 20 min that persisted for 12 hr. The corresponding organ uptakes (22% and 11% ID/g) and the whole-body retention (47% ID) were drastically reduced by succinylation (p<0.0001). Lysine co-injection further lowered renal uptake.

Optimization of a convenient route to produce N-succinimidyl 4-radiodobenzoate for radioiodination of proteins

The preparation of N-succinimidyl-4-[131I]iodobenzoate (SIB) has been optimized using an alternative technique employing Cu(I)-assisted radioiododebromination that produces p-[131I]iodobenzoic acid. The reaction conditions were optimized and radiochemical purity of more than 90% was obtained when using 160 degrees C, 60 min reaction time and a [CuCl]/[p-bromobenzoic acid] relation of about 10(-2). After purification, the p-[131I]iodobenzoic acid reacted with TSTU to produce the SIB in a radiochemical yield greater than 98%. Protein conjugation using SIB resulted in a relatively low radiochemical yield. Biological distribution studies evidenced the in vivo stability of the labeled protein.

A novel route to radioiodinated [123I]-N-succinimidyl-3-iodobenzoate, a reagent for radioiodination of bioactive peptides

Radiolabeled peptides continue to emerge as potential radiopharmaceuticals for targeting several diseases such as cancer, infection and inflammation and even tissue and organ rejection. The classical method for labeling these molecules has been the electrophilic route. Evidence suggests that most molecules labeled via this route perturb their biological activity. Moreover, this method is not applicable to peptides lacking a tyrosine moiety in their structure. Hence, there is the need to develop alternate methods such as the prosthetic approach. We have optimized a solid-state radioiodination by exchange to produce [123I]-metaiodobenzylguanidine ([123I]-mIBG). The mIBG served as a precursor to obtain an activated N-succinimidyl ester for efficient coupling to amine functions in peptides, preferably the lysine group(s). The method was used to label a model chemotactic peptide and evaluated in vivo.

A simple and advantageous protocol for the oxidation of alcohols with O-iodoxybenzoic acid (IBX)

[reaction: see text] An efficient, user-friendly procedure for the oxidation of alcohols using IBX is described. Simply heating a solution of the alcohol in the presence of suspended IBX followed by filtration and removal of the solvent gives excellent yields of the corresponding carbonyl compounds. We illustrate this procedure with a panel of primary and secondary alcohol substrates and note that it allows recycling and reuse of the oxidant.

Preparation of soluble and insoluble polymer supported IBX reagents

A series of soluble and insoluble polymer supported versions of the versatile oxidizing reagent IBX has been prepared. Each of the reagents were evaluated for their efficiency in the conversion of benzyl alcohol to benzaldehyde. Results from this study were that the soluble, non-crosslinked polystyrene supported IBX reagent gave the best rate of conversion to benzaldehyde, while the macroporous polymer supported IBX resin provided a superior rate of conversion to benzaldehyde when compared with a gel type resin. The macroporous IBX reagent was also shown to convert a series of alcohols to the corresponding aldehydes and ketones.

Facile cleavage of triethylsilyl (TES) ethers using o-iodoxybenzoic acid (IBX) without affecting tert-butyldimethylsilyl (TBS) ethers

[reaction: see text] In DMSO cleavage of triethylsilyl (TES) ethers by o-iodoxybenzoic acid (IBX) was significantly faster than cleavage of tert-butyldimethylsilyl (TBS) ethers or further oxidation into carbonyl compounds. In most cases, TES protecting groups could be removed in good to excellent yields within 1 h, whereas similar TBS protecting groups remained intact under the same conditions. The procedure also could be adapted for direct one-pot conversion of TES ethers into carbonyl compounds.

Iodine(V) reagents in organic synthesis. Part 3. New routes to heterocyclic compounds via o-iodoxybenzoic acid-mediated cyclizations: generality, scope, and mechanism

The discovery and development of the o-iodoxybenzoic acid (IBX) reaction with certain unsaturated N-aryl amides (anilides) to form heterocycles are described. The application of the method to the synthesis of delta-lactams, cyclic urethanes, hydroxy amines, and amino sugars among other important building blocks and intermediates is detailed. In addition to the generality and scope of this cyclization reaction, this article describes a number of mechanistic investigations suggesting a single electron transfer from the anilide functionality to IBX and implicating a radical-based mechanism for the reaction.

Iodine(V) reagents in organic synthesis. Part 4. o-Iodoxybenzoic acid as a chemospecific tool for single electron transfer-based oxidation processes

o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form alpha,beta-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.

Regioselective oxidation of phenols to o-quinones with o-iodoxybenzoic acid (IBX)

[reaction: see text] An efficient regioselective method for oxidation of phenols to o-quinones is reported. When this procedure is combined with a subsequent reduction, it proves to be useful for the construction of a variety of catechols.

Cellular processing of (125)I- and (111)in-labeled epidermal growth factor (EGF) bound to cultured A431 tumor cells

Low molecular weight of epidermal growth factor (EGF) enables better intratumoral penetration in comparison with larger targeting proteins, but the cellular retention of EGF-associated radioactivity is poor for directly iodinated EGF. An attempt was made to improve intracellular retention by the use of metal-diethylenetriaminepentaacetic acid or nonphenolic linker (N-succinimidyl-para-iodobenzoate) as labeling agents. The use of nonphenolic linker did not improve retention of the radioactivity in A431 carcinoma cell line. The use of the radiometal label provided an appreciable prolongation of radioactivity residence inside the cell.

Proprotein convertase PC1/3-related peptides are potent slow tight-binding inhibitors of murine PC1/3 and Hfurin

The proprotein convertase PC1/3 belongs to the subtilisin/kexin-like endoprotease family and is synthesized as a preproenzyme. To investigate the function of its propeptide, murine proPC1/3 and preproPC1/3 were isolated from the inclusion bodies of recombinant preproPC1/3 baculovirus-infected insect cells, rendered soluble with 6 M guanidine HCl and 20 mM dithiothreitol, and purified by gel filtration and metal-binding affinity chromatography. Two NH2-terminal fragments containing the complete propeptide 1-84 region were obtained after CNBr cleavage, purified, and chemically characterized. Progress curve kinetic analysis with enzymatically active murine 71-kDa PC1/3 or 50-kDa human furin demonstrated that both fragments were potent slow tight-binding inhibitors of either enzyme with Ki in the low nanomolar range. Additional cleavages at Trp residues yielded fragment9-71, which no longer represents a potent inhibitor. Upon incubation at pH 5.5 in the presence of excess 71-kDa murine PC1/3, NH2-terminal fragment1-98 is cleaved at two sites, as revealed through Western blotting using NH2-terminal-directed PC1/3 antibodies. Finally, murine PC2 is inhibited by the proPC1/31-98 peptide, albeit at a much lesser extent with a micromolar Ki and in a strictly competitive manner. These results suggest that the proregion of PC1/3 is an important feature in regulating its activity.

Molecular pharmacology of methyl-3,5-diiodo-4 (4'methoxyphenoxy) benzoate (DIME) and its non-hydrolyzible ethanone analog (DIPE) (Review)

A molecular structural relationship of thyroid hormones to methyl-3,5-diiodo-4-(4'-methoxy-phenoxy) benzoate (DIME) and 1-[3,5-diiodo-4-(4'-methoxyphenoxy)-phenyl]-ethanone) (DIPE) and to apoptosis-mediated metamorphogenic mechanisms is postulated. DIME disrupts microtubule assembly already in anaphase, preparing cells for G2/M block, chromosome aggregation and caspase-3 mediated apoptosis. Cooperative action of DIME and vincristine, defining mutually exclusive cellular sites, identifies microtubules as primary drug targets followed by downstream cellular consequences, leading to cell death. Absence of in vivo toxicity of DIME appears to be related to impermeability to DIME of normal cells, but not of tumor cells in vivo. Normal tissue cells hydrolyze DIME but most tumor cells, except lung cancer cells, do not. DIPE, being resistant to enzymatic hydrolysis, is equally effective in all tumor cells.

Method for radioiodination of proteins using N-succinimidyl 3-hydroxy-4-iodobenzoate

A conjugation method has been developed for the radioiodination of proteins which should be adaptable to kit formulation. m-Hydroxybenzoic acid was converted to 3-hydroxy-4-[131I]iodobenzoic acid in 65% radiochemical yield using Chloramine-T as the oxidant. This intermediate was then converted to N-succinimidyl 3-hydroxy-4-[131I]iodobenzoate ([131I]mSHIB) in 75% yield by reaction with N-hydroxysuccinimide and dicyclohexylcarbodiimide in a reaction time of only 10 min. Monoclonal antibody (mAb) 81C6 was labeled in 40-60% yield by reaction with [131I]mSHIB. Performing purifications of radioiodinated compounds using cartridges instead of HPLC did not alter conjugation efficiency, mAb immunoreactivity, or tissue distribution. Thyroid uptake of labeled mAb was low but up to 2.4 times higher than that seen when the mAb was labeled with N-succinimidyl 3-[125I]-iodobenzoate. These results suggest that [131I]mSHIB may be a useful reagent for the radioiodination of proteins, particularly in contexts when less complicated purification methods would be advantageous.

In vivo tissue compatibility of two radio-opaque polymeric biomaterials

Polymeric biomaterials featuring intrinsic radio-opacity continue to attract considerable scientific attention. This work focusses on two polymers that contain covalently bound iodine, rendering the materials radio-opaque. The first material is hard, transparent and glass-like, and consists of methyl methacrylate, 2-(2'-iodobenzoyl)-ethyl methacrylate (1) and 2-hydroxyethyl methacrylate (HEMA), in the molar ratio 65:20:15, respectively. The second material is a cross-linked hydrophilic network, consisting of HEMA and 1, in the molar ratio 80:20, respectively. Both materials were characterized by means of different physico-chemical techniques, including magic-angle-spinning solid state NMR spectroscopy, infrared spectroscopy and differential scanning calorimetry. Moreover, both materials were implanted subcutaneously in rats for 24 days. Upon explanation and histological examination, it appeared that both materials were well tolerated. No tissue necrosis, abscess formation or inflammation were observed. The samples were found to be surrounded by a vascularized capsule consisting of connective tissue cells. The results reveal excellent tissue compatibility for both materials. This is an important observation, since tissue compatibility is absolutely necessary for the applications which are foreseen for this type of radio-opaque biomaterials.

Studies on a new radiopaque polymeric biomaterial

A new radiopaque polymeric biomaterial has been synthesized. The material, which actually represents an entire family of analogous radiopaque materials, is composed of 2-(p-iodobenzoyl)-ethyl methacrylate (compound 1, 21 mol%), methyl methacrylate (MMA, 60 mol%), and 2-hydroxyethyl methacrylate (HEMA, 19 mol%). The terpolymer was synthesized in a radical polymerization reaction at elevated temperature in N,N-dimethylformamide (DMF). The product was subjected to a set of physicochemical characterization techniques (gel permeation chromatography, 500 MHz 1H NMR in deuterated dimethylsulphoxide (d6-DMSO) solution, differential scanning calorimetry, dynamic water contact angle measurements), as well as to an in vitro thrombogenicity assay. Furthermore, scanning electron microscopy was used to study interactions of the material with blood platelets. The most important findings are: (a) the material is a genuine polymer with excellent X-ray visibility, even in the form of thin (0.4 mm) drawn fibres. This was established under realistic conditions. (b) The material exhibits low in vitro thrombogenicity, i.e. comparable to polyvinyl chloride, which is known as a passive material. These observations lead us to the suggestion that this type of radiopaque polymer holds promise with respect to application as a construction material for a new type of endovascular stent. This could be relevant in particular to stents to be used in conjunction with percutaneous transluminal coronary angioplasty (PTCA), also known as Dottering. Currently there is a clear trend away from metallic stents towards all-polymeric stents, since the latter have superior biocompatibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation of critical cysteine residues of type I adenylyl cyclase by o-iodosobenzoate or nitric oxide reversibly inhibits stimulation by calcium and calmodulin

The calmodulin binding domain of the type I adenylyl cyclase has recently been identified as an amino acid sequence (residues 495-522) that contains 2 cysteine residues. Therefore, we examined the effect of several sulfhydryl reagents on the calmodulin sensitivity of the enzyme. Treatment of membranes containing the type I adenylyl cyclase with N-ethylmaleimide rapidly inhibited basal, calcium/calmodulin-stimulated, and forskolin-stimulated adenylyl cyclase activity. When the enzyme was treated with limiting amounts of o-iodosobenzoate, which oxidizes vicinal sulfhydryls to disulfides, stimulation by Ca2+ and calmodulin was eliminated at concentrations which did not affect basal adenylyl cyclase activity. Calmodulin stimulation of the enzyme was restored by treatment with dithiothreitol or glutathione which reduce disulfides to free thiols. NO and sodium nitroprusside also reversible inhibited calmodulin stimulation of the enzyme. We propose that the loss in calmodulin sensitivity caused by these reagents may be due to the oxidation one or more sets of vicinal thiols present in the enzyme.

Effect of plasma binding of ortho- and para-I-benzoates on their distribution in blood and into lymph, biotransformation and excretion in rat urine

Two positional iodine derivatives of benzoic acid, i.e. ortho- (OIB) and para- (PIB), were used alone and in combination with salicylic acid (SA) to study the effects of plasma binding on their pharmacokinetics. Their lymphatic bioavailability (central lymph), their biotransformation and urinary excretion in rats were also studied. Plasma binding of the two benzoates is different, about 95% of PIB and approximately 50% of OIB are bound. The competitive inhibition effect of SA was shown by an increase in the amount of free drug in plasma in both benzoates. Lymphatic binding is lower compared to plasma binding, an effect of SA of the free faction of drug in lymph was shown only with PIB. Kinetic parameters of benzoates are influenced by plasma binding; significant differences were found mainly in total clearance and areas under concentration curves. Lymphatic bioavailability (FL) differs only slightly with different plasma binding; a significant change in FL was, however, found in PIB after SA premedication. Significantly higher urinary excretion of OIB as compared with PIB corresponds to plasma binding of drugs, SA premedication decreases total excretion of both benzoates. SA also changes the proportion of the individual fractions of metabolites of benzoates in urine.

N-succinimidyl 4-methyl-3-(tri-n-butylstannyl)benzoate: synthesis and potential utility for the radioiodination of monoclonal antibodies

N-succinimidyl 4-methyl-3-(tri-n-butylstannyl)benzoate (MATE) was synthesized in two steps from 4-methyl-3-iodobenzoic acid. Radioiododestannylation of MATE proceeded more slowly than N-succinimidyl 3-(tri-n-butylstannyl)benzoate (ATE), but for reaction periods of 10 min or more, identical yields were obtained. Paired-label biodistribution studies were performed in mice with an intact monoclonal antibody and an F(ab')2 fragment labeled using MATE, ATE and Iodogen. Thyroid uptake with MATE was low, comparable to that seen with ATE, and considerably lower than that observed when the Iodogen method was used. With the F(ab')2 fragment, kidney uptake using MATE was 8-fold higher than that observed when either the ATE or Iodogen methods were used.

Radioiodination of proteins using N-succinimidyl 4-hydroxy-3-iodobenzoate

N-Succinimidyl 4-hydroxy-3-[131I]iodobenzoate ([131I]SHIB) was synthesized from 4-hydroxybenzoic acid in two steps. The overall radiochemical yield was 40-56%. A monoclonal antibody (mAb) was labeled in 10-15% yield by reaction with [131I]SHIB. The specific binding of [131I]SHIB mAb to tumor homogenates in vivo was 78 +/- 3%, compared to 84 +/- 3% for the same mAb labeled using N-succinimidyl 3-[125I]iodobenzoate ([125I]SIB). Paired-label studies in normal mice demonstrated similar tissue distributions of 131I and 125I except in thyroid. In thyroid, uptake of the two isotopes was similar on day 1; however, 131I levels increased gradually to 2-3 times those of 125I by day 6. Our results indicate that loss of label in vivo from mAbs labeled using SHIB is somewhat higher than seen with SIB but significantly lower than that observed when direct iodination methods are used.

2-Iodoxybenzoate as a titrant for the determination of some pharmaceutically-important thiol compounds

A simple and reliable method was developed for the determination of five pharmaceutical compounds containing thiol group; namely: N-acetylcysteine, D-penicillamine, 6-mercaptopurine, captopril and thioguanine. The method is based on the use of 2-iodoxybenzoate as a titrant in acid medium. The detection of the end point is accomplished potentiometrically, using platinum/calomel electrode combination. For all the studied compounds, the stoichiometry of the reaction was found to be 2:3 suggesting that, the thiol group is oxidised to the corresponding sulphonic acid. This finding was confirmed through TLC study of the reaction products. The proposed method was successfully applied to the determination of the studied compounds in dosage forms and the results were in good agreement with those given using the official methods.