Towards a characterization of the structural determinants of specificity in the macrocyclizing thioesterase for deoxyerythronolide B biosynthesis.

Type I polyketide synthases (PKSs) are giant multidomain proteins that synthesize many therapeutics and other natural products. The synthesis proceeds by a thiotemplate mechanism whereby intermediates are covalently attached to the PKS. The release of the final polyketide is catalyzed by the terminal thioesterase (TE) domain through hydrolysis, transesterification, or macrocyclization. The PKS 6-deoxyerythronolide B synthase (DEBS) produces the 14-membered macrolide core of the clinically important antibiotic erythromycin. The TE domain of DEBS (DEBS TE) has well-established, empirically-defined specificities for hydrolysis or macrocyclization of native and modified substrates. We present efforts towards understanding the structural basis for the specificity of the thioesterase reaction in DEBS TE using a set of novel diphenyl alkylphosphonates, which mimic substrates that are specifically cyclized or hydrolyzed by DEBS TE. We have determined structures of a new construct of DEBS TE alone at 1.7Å, and DEBS TE bound with a simple allylphosphonate at 2.1Å resolution. Other, more complex diphenyl alkylphosphonates inhibit DEBS TE, but we were unable to visualize these faithful cyclization analogs in complex with DEBS TE. This work represents a first step towards using DEBS TE complexed with sophisticated substrate analogs to decipher the specificity determinants in this important reaction.

N,N'-methylenediimidazolium salts: from self-assembly to an efficient DNAse protection system.

We have developed N,N'-dialkylmethylenediimidazolium salts ([C(n)C(n)DIM][X]2) that self-organize into multilayered cationic vesicles and can interact with DNA. These preorganized systems form complexes with linear DNA and protect it from DNase I cleavage.

Photolabeling of tissue transglutaminase reveals the binding mode of potent cinnamoyl inhibitors.

We have recently developed a new class of cinnamoyl derivatives as potent tissue transglutaminase (TG2) inhibitors. Herein, we report the synthesis of a diazirine derivative of these inhibitors and its application to the photolabeling of its binding site on guinea pig liver transglutaminase. Two novel homology models were generated for this commonly studied TG2, which differ in the conformational state they represent. Tryptic digest and mass spectrometric analysis of the photolabeling experiment showed that only residue Cys230 was labeled, and our homology models were used to visualize these results. This visualization suggested that Cys230 is somewhat more solvent-exposed in the "closed" conformation of TG2, compared to the "open" conformation. Docking experiments suggested binding modes consistent with the labeling pattern that would block access to the tunnel leading to the active site, consistent with the observed mode of inhibition. However, while these modeling simulations favored the closed conformation as the target of our cinnamoyl inhibitors, native PAGE experiments indicated the open conformation of the enzyme in fact predominates in the presence of our photolabeling derivative. These results are important for understanding the binding modes of TG2 inhibitors in general and will be critical for the structure-based design of future inhibitors.

Cinnamoyl inhibitors of tissue transglutaminase.

Transglutaminases (TGases) catalyze the intermolecular cross-linking of certain proteins and tissue TGases (TG2) are involved in diverse biological processes. Unregulated, high TGase activities have been implicated in several physiological disorders, but few reversible inhibitors of TG2 have been reported. Herein, we report the synthesis of a series of novel trans-cinammoyl derivatives, discovered to be potent inhibitors of guinea pig liver transglutaminase. The most effective inhibitors evaluated can be sorted into two subclasses: substituted cinnamoyl benzotriazolyl amides and the 3-(substituted cinnamoyl)pyridines, referred to more commonly as azachalcones. Kinetic evaluation of both of these subclasses revealed that they display reversible inhibition and are competitive with acyl donor TGase substrates at IC50 values as low as 18 microM. An analysis of structure-activity relationships within these series of inhibitors permitted the identification of potentially important binding interactions. Further testing of some of the most potent inhibitors demonstrated their selectivity for TG2 and their potential for further development.

Poly(vinyl alcohol)-graft-poly(ethylene glycol) resins and their use in solid-phase synthesis and supported TEMPO catalysis.

New poly(vinyl alcohol)-graft-poly(ethylene glycol) (PVA-g-PEG) resins with various PEG chain lengths, which have high loadings and good swelling both in water and organic solvents, have been prepared via an anionic polymerization of ethylene oxide onto PVA beads and applied in solid-phase synthesis, supported TEMPO catalysis and in HR-MAS 1H NMR spectral analysis.

Development of new scaffolds as reversible tissue transglutaminase inhibitors, with improved potency or resistance to glutathione addition.

Previous studies within our group have yielded a class of cinnamoyl-based competitive reversible inhibitors for tissue transglutaminase (TG2), with Ki values as low as 1.0 µM (compound CP4d). However, due to the electrophilic nature of their alkene moiety, this class of inhibitors is susceptible to nucleophilic attack by glutathione, a key element in cellular metabolism and toxicity response. To address this issue, we made several modifications to the inhibitor scaffold, ultimately showing that a bis(triazole) scaffold increased resistance to nucleophilic attack, with compound 27d being the most potent (Ki = 10 µM). In the process of reducing reactivity, we also prepared a new class of inhibitors, replacing the alkene of CP4d with an alkyne, leading to a significant increase in potency for compound 22b (Ki = 420 nM).

First-in-class small molecule potentiators of cancer virotherapy.

The use of engineered viral strains such as gene therapy vectors and oncolytic viruses (OV) to selectively destroy cancer cells is poised to make a major impact in the clinic and revolutionize cancer therapy. In particular, several studies have shown that OV therapy is safe and well tolerated in humans and can infect a broad range of cancers. Yet in clinical studies OV therapy has highly variable response rates. The heterogeneous nature of tumors is widely accepted to be a major obstacle for OV therapeutics and highlights a need for strategies to improve viral replication efficacy. Here, we describe the development of a new class of small molecules for selectively enhancing OV replication in cancer tissue. Medicinal chemistry studies led to the identification of compounds that enhance multiple OVs and gene therapy vectors. Lead compounds increase OV growth up to 2000-fold in vitro and demonstrate remarkable selectivity for cancer cells over normal tissue ex vivo and in vivo. These small molecules also demonstrate enhanced stability with reduced electrophilicity and are highly tolerated in animals. This pharmacoviral approach expands the scope of OVs to include resistant tumors, further potentiating this transformative therapy. It is easily foreseeable that this approach can be applied to therapeutically enhance other attenuated viral vectors.

Analysis of aminofluorescein-fatty acid derivatives by capillary electrophoresis with laser-induced fluorescence detection at the attomole level: application to mycobacterial fatty acids.

A method based on capillary electrophoresis coupled to laser-induced fluorescence detection was developed for the characterization of fatty acids including palmitic, stearic, oleic and tuberculostearic acids. The fatty acids were tagged by 4-aminofluorescein (AF) via a carboxylic acid-amine condensation promoted by N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) in non-aqueous solution. Using the optimized derivatization conditions, the fluorophore labeling of the fatty acids was achieved at the nanomolar level. The separation of palmitic, stearic, oleic and tuberculostearic-AF derivatives was achieved in less than 10 min, using 25 mM sodium borate buffer containing 30% of acetonitrile as running electrolyte. The concentration detection limit was found to be 5 nM while the minimum mass limit detection is around 30 attomol. This method was successfully applied to identification of mycobacteria via the characterization of tuberculostearic acid and found to be suitable for the detection of a minimum of 10(6) mycobacteria.

Site-specific protein labelling and immobilization mediated by microbial transglutaminase.

Microbial transglutaminase (mTG) shows broad substrate specificity that is amenable to in vitro bio-conjugation applications. Herein, test proteins were genetically fused with peptide tags, followed by mTG-mediated propargylation of their reactive Gln residues. The propargylated proteins were subjected to copper-assisted azide-alkyne cycloaddition to demonstrate either fluorescent labelling or immobilization.

Uncovering new properties of imidazolium salts: Cl- transport and supramolecular regulation of their transmembrane activity.

We report the Cl(-) transport activity for three imidazolium-based transporters. We present significant findings regarding the use of α-cyclodextrin and cucurbit[7]uril macrocycles to form inclusion complexes with these salts and to inhibit their membrane activity.

Multivalent DR5 peptides activate the TRAIL death pathway and exert tumoricidal activity.

Ongoing clinical trials are exploring anticancer approaches based on signaling by TRAIL, a ligand for the cell death receptors DR4 and DR5. In this study, we report on the selective apoptotic effects of multivalent DR5 binding peptides (TRAIL(mim/DR5)) on cancer cells in vitro and in vivo. Surface plasmon resonance revealed up to several thousand-fold increased affinities of TRAIL(mim/DR5)-receptor complexes on generation of divalent and trivalent molecules, the latter of which was achieved with a conformationally restricted adamantane core. Notably, only multivalent molecules triggered a substantial DR5-dependent apoptotic response in vitro. In tumor models derived from human embryonic kidney cells or primary foreskin fibroblasts, TRAIL(mim/DR5) peptides exerted a cancer cell-selective action that could synergize with resveratrol in a manner independent of p53. In a xenograft model of human colon cancer, a divalent TRAIL(mim/DR5) peptide inhibited tumor growth. Our results offer a proof-of-principle for the development of synthetic small molecules to trigger the TRAIL apoptosis pathway for cancer therapy.

Reversible and competitive cinnamoyl triazole inhibitors of tissue transglutaminase.

A series of 15 cinnamoyl triazole derivatives was prepared by Cu(I)-catalyzed azide/alkyne [3+2]-cycloaddition reactions and examined as inhibitors of guinea-pig liver transglutaminase. Several compounds exhibited activity as reversible inhibitors that were competitive with acyl donor transglutaminase substrates. For example, triazole 4d has a K(i) value of 174 nM and represents one of the most potent reversible transglutaminase inhibitors reported to date.

Preparation, characterization, and application of poly(vinyl alcohol)-graft-poly(ethylene glycol) resins: novel polymer matrices for solid-phase synthesis.

Spherical crosslinked poly(vinyl alcohol) (PVA) beads with good mechanical stability were prepared by reverse-suspension polymerization, using dimethyl sulfoxide (DMSO) as a cosolvent in an aqueous phase. Poly(ethylene glycol)s with varying chain lengths were grafted onto the PVA beads by anionic polymerization of ethylene oxide. The thermal behavior, morphology, and swelling were evaluated for each of the new polymer matrices. High loading and good swelling in water and organic solvents were characteristic of the PEG-grafted PVA beads. The polymer beads also exhibited good mechanical and chemical stability and were unaffected by treatment with 6 N HCl and with 6 N NaOH. The hydroxyl groups of the PVA-PEG beads were converted into aldehyde, carboxylic acid, and isocyanate functions to provide scavenger resins and were extended by way of a benzyl alcohol in a Wang linker. The transglutaminase substrates dipeptides (Z-Gln-Gly) and heptapeptides (Pro-Asn-Pro-Gln-Leu-Pro-Phe) were synthesized on PVA-PEG_5, PVA-PEG_20, and the Wang linker-derivatized PVA-PEG resins. The cleavage of the peptides from the resins using MeOH/NH3 mixture at different temperatures (0 degrees C and room temp) and 50% TFA/DCM provided, respectively, peptide methyl esters, amides, and acids in good yields and purity as assessed by LC-MS analysis.

Synthesis and evaluation of peptidic irreversible inhibitors of tissue transglutaminase.

Herein we report the synthesis and the evaluation of eight novel compounds as irreversible inhibitors of transglutaminase (TGase). These compounds are based on a minimal peptidic scaffold shown previously [Chem. Biol.2005, 12, 469-475] to confer affinity for the TGase active site and bear electrophilic groups such as alpha,beta-unsaturated amide, chloroacetamide or maleimide; their general structure being Cbz-Phe-spacer-electrophile. The affinity conferred by the Cbz-Phe scaffold was determined by comparison to N-propylacrylamide and the length of the spacer was also varied to evaluate its importance. The inhibitory efficiencies (k(inact)/K(I)) of these compounds vary up to 10(5)M(-1)min(-1), among the highest reported for derivatives based on this simple Cbz-Phe peptidic scaffold.