Garcinolic Acid Distinguishes Between GACKIX Domains and Modulates Interaction Networks.

Natural products are often uniquely suited to modulate protein-protein interactions (PPIs) due to their architectural and functional group complexity relative to synthetic molecules. Here we demonstrate that the natural product garcinolic acid allosterically blocks the CBP/p300 KIX PPI network and displays excellent selectivity over related GACKIX motifs. It does so via a strong interaction (KD 1 µM) with a non-canonical binding site containing a structurally dynamic loop in CBP/p300 KIX. Garcinolic acid engages full-length CBP in the context of the proteome and in doing so effectively inhibits KIX-dependent transcription in a leukemia model. As the most potent small-molecule KIX inhibitor yet reported, garcinolic acid represents an important step forward in the therapeutic targeting of CBP/p300.

Electron-deficient p-benzoyl-l-phenylalanine derivatives increase covalent chemical capture yields for protein-protein interactions.

The photoactivatable amino acid p-benzoyl-l-phenylalanine (pBpa) has been used for the covalent capture of protein-protein interactions (PPIs) in vitro and in living cells. However, this technique often suffers from poor photocrosslinking yields due to the low reactivity of the active species. Here we demonstrate that the incorporation of halogenated pBpa analogs into proteins leads to increased crosslinking yields for protein-protein interactions. The analogs can be incorporated into live yeast and upon irradiation capture endogenous PPIs. Halogenated pBpas will extend the scope of PPIs that can be captured and expand the toolbox for mapping PPIs in their native environment.

Pharmaceutical solvate formation for the incorporation of the antimicrobial agent hydrogen peroxide.

Antimicrobial functionality is introduced into a pharmaceutical formulation of miconazole while improving solubility. The work leverages hydrate formation propensity in order to produce hydrogen peroxide solvates. The ubiquity of hydrate formation suggests that hydrogen peroxide can be broadly deployed in pharmaceuticals, rendering a liquid excipient suitable for solid pharmaceutical formulations.

Modulating the masters: chemical tools to dissect CBP and p300 function.

Dysregulation of transcription is found in nearly every human disease, and as a result there has been intense interest in developing new therapeutics that target regulators of transcription. CREB binding protein (CBP) and its paralogue p300 are attractive targets due to their function as `master coactivators'. Although inhibitors of several CBP/p300 domains have been identified, the selectivity of many of these compounds has remained underexplored. Here, we review recent successes in the development of chemical tools targeting several CBP/p300 domains with selectivity acceptable for use as chemical probes. Additionally, we highlight recent studies which have used these probes to expand our understanding of interdomain interactions and differential coactivator usage.

A Bifunctional Amino Acid Enables Both Covalent Chemical Capture and Isolation of in Vivo Protein-Protein Interactions.

In vivo covalent chemical capture by using photoactivatable unnatural amino acids (UAAs) is a powerful tool for the identification of transient protein-protein interactions (PPIs) in their native environment. However, the isolation and characterization of the crosslinked complexes can be challenging. Here, we report the first in vivo incorporation of the bifunctional UAA BPKyne for the capture and direct labeling of crosslinked protein complexes through post-crosslinking functionalization of a bioorthogonal alkyne handle. Using the prototypical yeast transcriptional activator Gal4, we demonstrate that BPKyne is incorporated at the same level as the commonly used photoactivatable UAA pBpa and effectively captures the Gal4-Gal80 transcriptional complex. Post-crosslinking, the Gal4-Gal80 adduct was directly labeled by treatment of the alkyne handle with a biotin-azide probe; this enabled facile isolation and visualization of the crosslinked adduct from whole-cell lysate. This bifunctional amino acid extends the utility of the benzophenone crosslinker and expands our toolbox of chemical probes for mapping PPIs in their native cellular environment.

Exquisitely specific bisubstrate inhibitors of c-Src kinase.

We have developed a modular approach to bisubstrate inhibition of protein kinases. We apply our methodology to c-Src and identify a highly selective bisubstrate inhibitor for this target. Our approach has yielded the most selective c-Src inhibitor to date, and the methodology to render the bisubstrate inhibitor cell-permeable provides a highly valuable tool for the study of c-Src signaling. In addition, we have applied our bisubstrate inhibitor to develop a novel screening methodology to identify non-ATP-competitive inhibitors of c-Src. Using this methodology, we have discovered the most potent non-ATP-competitive inhibitor reported to date. Our methodology is designed to be general and could be applicable to additional kinases inhibited by the promiscuous ATP-competitive fragment used in our studies.

Small molecule substrate phosphorylation site inhibitors of protein kinases: approaches and challenges.

Protein kinases are important mediators of cellular communication and attractive drug targets for many diseases. Although success has been achieved with developing ATP-competitive kinase inhibitors, the disadvantages of ATP-competitive inhibitors have led to increased interest in targeting sites outside of the ATP binding pocket. Kinase inhibitors with substrate-competitive, ATP-noncompetitive binding modes are promising due to the possibility of increased selectivity and better agreement between biochemical and in vitro potency. However, the difficulty of identifying these types of inhibitors has resulted in significantly fewer small molecule substrate phosphorylation site inhibitors being reported compared to ATP-competitive inhibitors. This review surveys reported substrate phosphorylation site inhibitors and methods that can be applied to the discovery of such inhibitors, including a discussion of the challenges inherent to these screening methods.

Substrate activity screening with kinases: discovery of small-molecule substrate-competitive c-Src inhibitors.

Substrate-competitive kinase inhibitors represent a promising class of kinase inhibitors, however, there is no methodology to selectively identify this type of inhibitor. Substrate activity screening was applied to tyrosine kinases. By using this methodology, the first small-molecule substrates for any protein kinase were discovered, as well as the first substrate-competitive inhibitors of c-Src with activity in both biochemical and cellular assays. Characterization of the lead inhibitor demonstrates that substrate-competitive kinase inhibitors possess unique properties, including cellular efficacy that matches biochemical potency and synergy with ATP-competitive inhibitors.

Effects of Experimental Sarcocystis neurona-Induced Infection on Immunity in an Equine Model.

Sarcocystis neurona is the most common cause of Equine Protozoal Myeloencephalitis (EPM), affecting 0.5-1% horses in the United States during their lifetimes. The objective of this study was to evaluate the equine immune responses in an experimentally induced Sarcocystis neurona infection model. Neurologic parameters were recorded prior to and throughout the 70-day study by blinded investigators. Recombinant SnSAG1 ELISA for serum and CSF were used to confirm and track disease progression. All experimentally infected horses displayed neurologic signs after infection. Neutrophils, monocytes, and lymphocytes from infected horses displayed significantly delayed apoptosis at some time points. Cell proliferation was significantly increased in S. neurona-infected horses when stimulated nonspecifically with PMA/I but significantly decreased when stimulated with S. neurona compared to controls. Collectively, our results suggest that horses experimentally infected with S. neurona manifest impaired antigen specific response to S. neurona, which could be a function of altered antigen presentation, lack of antigen recognition, or both.

Novel inhibitors of bacterial virulence: development of 5,6-dihydrobenzo[h]quinazolin-4(3H)-ones for the inhibition of group A streptococcal streptokinase expression.

Resistance to antibiotics is an increasingly dire threat to human health that warrants the development of new modes of treating infection. We recently identified 1 (CCG-2979) as an inhibitor of the expression of streptokinase, a critical virulence factor in Group A Streptococcus that endows blood-borne bacteria with fibrinolytic capabilities. In this report, we describe the synthesis and biological evaluation of a series of novel 5,6-dihydrobenzo[h]quinazolin-4(3H)-one analogs of 1 undertaken with the goal of improving the modest potency of the lead. In addition to achieving an over 35-fold increase in potency, we identified structural modifications that improve the solubility and metabolic stability of the scaffold. The efficacy of two new compounds 12c (CCG-203592) and 12k (CCG-205363) against biofilm formation in Staphylococcus aureus represents a promising additional mode of action for this novel class of compounds.

A photoreactive crystalline quasiracemate.

Rationally designed racemic and quasiracemic sulfonamidecinnamic acids assemble to give hydrogen-bonded dimers with coplanar alignment of neighboring olefins. The quasiracemate phase contains near inversion-related motifs with chemically distinct components forming supramolecular heterodimers that undergo asymmetric photodimerization.

Discovery and development of a small molecule library with lumazine synthase inhibitory activity.

(E)-5-Nitro-6-(2-hydroxystyryl)pyrimidine-2,4(1H,3H)-dione (9) was identified as a novel inhibitor of Schizosaccharomyces pombe lumazine synthase by high-throughput screening of a 100000 compound library. The K(i) of 9 vs Mycobacterium tuberculosis lumazine synthase was 95 microM. Compound 9 is a structural analogue of the lumazine synthase substrate 5-amino-6-(d-ribitylamino)-2,4-(1H,3H)pyrimidinedione (1). This indicates that the ribitylamino side chain of the substrate is not essential for binding to the enzyme. Optimization of the enzyme inhibitory activity through systematic structure modification of the lead compound 9 led to (E)-5-nitro-6-(4-nitrostyryl)pyrimidine-2,4(1H,3H)-dione (26), which has a K(i) of 3.7 microM vs M. tuberculosis lumazine synthase.