No abstract

After more than a century, aspirin remains one of the most commonly used drugs in western medicine. Although mainly used for its anti-thrombotic, anti-pyretic, and analgesic properties, a multitude of clinical studies have provided convincing evidence that regular, low-dose aspirin use dramatically lowers the risk of cancer. These observations coincide with recent studies showing a functional relationship between platelets and tumors, suggesting that aspirin’s chemopreventive properties may result, in part, from direct modulation of platelet biology and biochemistry. Here, we present a review of the biochemistry and pharmacology of aspirin with particular emphasis on its cyclooxygenase-dependent and cyclooxygenase-independent effects in platelets. We also correlate the results of proteomic-based studies of aspirin acetylation in eukaryotic cells with recent developments in platelet proteomics to identify non-cyclooxygenase targets of aspirin-mediated acetylation in platelets that may play a role in its chemopreventive mechanism.

There is a pressing need for new molecular tools to target protein surfaces with high affinity and specificity. Here, we describe cyclic messenger RNA display with a trillion-member covalent peptide macrocycle library. Using this library, we have designed a number of high-affinity, redoxinsensitive, cyclic peptides that target the signaling protein Gαi1. In addition to cyclization, our library construction took advantage of an expanded genetic code, utilizing nonsense suppression to insert N-methylphenylalanine as a 21st amino acid. The designed macrocycles exhibit several intriguing features. First, the core motif seen in all of the selected variants is the same and shares an identical context with respect to the macrocyclic scaffold, consistent with the idea that selection simultaneously optimizes both the cyclization chemistry and the structural placement of the binding epitope. Second, detailed characterization of one molecule, cyclic Gαi binding peptide (cycGiBP), demonstrates substantially enhanced proteolytic stability relative to that of the parent linear molecule. Third and perhaps most important, the cycGiBP peptide binds the target with very high affinity (K i ≈ 2.1 nM), similar to those of many of the best monoclonal antibodies and higher than that of the βγ heterodimer, an endogenous Gαi1 ligand. Overall the work provides a general route to design novel, low-molecular-weight, high-affinity ligands that target protein surfaces.Although networks of protein-protein interactions control function inside cells, it is increasingly clear that many of these players cannot be targeted using traditional druglike molecules (1). High-affinity, high-specificity ligands targeting protein surfaces are thus of considerable interest as tools for chemical genetics, as potential lead/surrogate compounds, and as new drugs. Nanotechnology could also greatly benefit from such molecules, particularly robust, inexpensive, low-molecular-weight ligands that could replace monoclonal antibodies (2). Designing these ligands still remains a significant challenge despite the tremendous advances in structural biology and computational chemistry.Our laboratory has been working to design new peptide ligands that target heterotrimeric Gprotein signaling. We have previously used messenger RNA (mRNA) display (3) to isolate new linear peptides that target Gαi1 (4-6). Gαi1 is a member of the Gα subunit family and serves as a molecular router, connecting the cell-surface G-protein-coupled receptors (GPCR) to down-stream effector pathways (see ref 7 for a review of GPCR signaling). Gα subunits function by collaboration with the Gβγ heterodimer and a transmembrane receptor. The Gαβγ heterotrimer associates with the cytosolic portion of GPCRs with GDP bound in the nucleotide pocket of Gα. Extracellular ligand binding to the GPCR results in

Synthesis of Aminoacylated tRNAThe pdCpA dinucleotide (tetrabutylammonium salt) and a sample of αOH-Phenylalanyl-dCA were obtained as a gift from Neurion Pharmaceuticals (Pasadena, CA). Subsequent preparation of αOH-Phenylalanyl-dCA was carried out according to the protocols in references 17-18. An example synthesis is described below. Synthesis of αOH-Phenylalanine cyanomethyl ester (1)L-phenylactic acid (266 mg, 1.6 mmol) was dissolved in 3 mL DMF. To this was added chloroacetonitrile (3 mL, 47.4 mmol) and TEA (651 μL, 4.6 mmol). The reaction was allowed to proceed under nitrogen at room temperature overnight. The desired product was purified by flash chromatography (silica gel, 3:7 EtOAc:Hexanes). The final yield (amber oil) was 18.9 mg (68% Synthesis of αOH-Phenylalanine-dCA (2)αOH-Phenylalanine cyanomethyl ester (11 mg, 54 μmol) was dissolved in 400 μL DMF and added to the tetrabutyl ammonium salt of pdCpA (9 μmol) in the presence of a catalytic amount of TBA-acetate. The reaction was allowed to proceed under nitrogen for 4 hr. at room temperature. The aminoacylated dinucleotide was purified by RP-HPLC using a gradient from 25 mM NH 4 OAc (pH=4.5) to CH 3 CN. Following lyophilization of the pooled fractions, the product was dissolved in 10 mM HOAc and lyophilized again. The final yield was determined by absorbance at 260 nm. and found to be 97 nmol (1%). The product was analyzed by ESI- In vitro Transcription of THG73 tRNAThe plasmid harboring the THG73 gene was linearized with FokI and transcribed with T7 RNA polymerase. The transcription product was gel-purified by Urea-PAGE, dissolved in dH 2 O, and quantitated by absorbance at 260 nm.Ligation to THG73 tRNA 20 μg THG73 tRNA (8 μL in dH 2 O) in HEPES (22 μL, 10 mM, pH=7.5) was heated to 94 ºC for 3 min and allowed to cool slowly at room temperature. 8 μL αOH-Phenylalanine-dCA (3 mM in DMSO), 32 μL 2.5 X Reaction Buffer (25 μL 400 mM HEPES pH=7.5, 10 μL 100 mM DTT, 25 μL 200 mM MgCl 2 , 3.75 μL 10 mM ATP, 10 μL S1 5 mg/mL BSA, 26.25 μL dH 2 O), 7 μL water, and 4 μL T4 RNA Ligase (N.E.B.). After incubation at 37 ºC for 1 hr, the reaction was extracted once with an equal volume of phenol (saturated with 300 mM NaOAc, pH=5.0:CHCl 3 :isoamyl alcohol (25:24:1)) and ethanol precipitated. The pellet was washed with 70% EtOH, dried under vacuum, and dissolved in 1 mM NaOAc to a concentration of 2 μg/μL. Construction of Fusion Templates (Phe(K), UAG(K), UAG(V))These dsDNA templates were created by PCR using overlapping primers: (Forward primer = Gen-FP: 5'-TAATACGACTCACTATAGGGACAATTACTATTTACAATTACA-3') and a unique reverse primer (Phe(K)- hr. The mRNA-DNA template was gel purified by Urea-PAGE, dissolved in water, and quantitated by absorbance at 260 nm. Construction of MK(n) Library Templates (MK0, MK2, MK4, MK6, MK8, MK10)Antisense ssDNA templates were synthesized at the Keck Oligonucleotide Synthesis Facility (Yale). The sequences for the MK Library ssDNA templates are as follows: MK library dsDNA was amplified by PCR using the forward primer Gen-FP (5'-TAATACG...

Special agents for protein capture: Iterative in situ click chemistry (see scheme for the tertiary ligand screen) and the one‐bead–one‐compound method for the creation of a peptide library enable the fragment‐based assembly of selective high‐affinity protein‐capture agents. The resulting ligands are water‐soluble and stable chemically, biochemically, and thermally. They can be produced in gram quantities through copper(I)‐catalyzed cycloaddition.