Editorial Cite This: Mol. Pharmaceutics 2018, 15, 703−704
Pharmacology by Chemical Biology
T
he real voyage of discovery consists not in seeking new landscapes, but in having new eyes.
co-workers report the effects of carboxylate NSAIDs and their metabolites (NSAID-CoAs) on lysine acetyltransferase (KAT) activity. They find that while carboxylate-containing NSAID chemotypes inhibit KATs with modest potency, metabolism to their cognate NSAID-CoA thioesters greatly increases their inhibitory potential. To test whether this metabolic mechanism influences cellular acetylation, the authors focus on ibuprofen, which is known to undergo stereoselective metabolism in cells. While ibuprofen forms NSAID-CoAs and inhibits histone acetylation in cells, this effect appears to be independent of the molecule’s stereochemistry, suggesting that it may not depend on NSAID-CoA formation. These studies provide new insights into the epigenetic mechanisms of NSAIDs, and further demonstrate how pharmacological insights can be exploited to study the biological activity of drug metabolites. Modified mRNAs (mRNAs) represent an emerging avenue for the production of therapeutic protein cargoes in diseased cells. However, efficient delivery remains a rate-limiting step in the development of this therapeutic paradigm. To facilitate these goals, Devaraj and co-workers demonstrate the compatibility of modified mRNAs with a recently developed site-specific bioorthogonal RNA labeling methodology. Utilizing in vitro transcription they produce mRNAs which incorporate the modified nucleobases 5-methylcytidine and pseudouridine, which can positively impact mRNA stability, as well as an Escherichia coli tRNA guainine transglycosylase (TGT) recognition sequence. Incubation of this mRNA with bacterial TGT and a PreQ1 analogue results in introduction of a tetrazine tag into the mRNA, which can be labeled subsequently using a cyclooctene-conjugated fluorophore. Interestingly, while different modified bases are accommodated in the TGT recognition sequence, they are found to alter labeling efficiency. These studies highlight new opportunities for optimization of the TGT method via enzyme or substrate engineering, as well as future applications for small molecule− RNA hybrids prepared by this technique. Chemoproteomics represents a central chemical biology approach that has found powerful applications in the discovery and optimization of small molecules. One specific method that is finding increasingly broad application is reactivity-based profiling of functional protein cysteine residues. This methodology utilizes affinity tagged iodoacetamides which are reacted with proteomic cysteines, conjugated to isotopically labeled biotin handles using biorthogonal chemistry, enriched with streptavidin, and analyzed via LC−MS/MS to provide a quantitative comparison of cysteine reactivity between two samples (e.g., drug-treated and control). One technical challenge in these studies is obtaining the cleavable isotopically labeled biotin tag used in these experiments, which are not commercially available and whose synthesis is tedious and lowyielding. To expand the accessibility of this method, Weerapana and co-workers report a clever variation of their original
Marcel Proust
Pharmacology is a science deeply rooted not only in manipulating physiology but also in defining the mechanism of therapeutic compounds so that they may be more precisely deployed. For example, studies by Sydney Farber revealed the potential of antifolates as drugs for the treatment of childhood leukemia, which led to mechanistic efforts that defined dihydrofolate reductase as a drug target. This discovery in turn enabled the development of novel anticancer and antibacterial agents, as well as new methods for probing biology using inducible dimerization. In this special issue of Molecular Pharmaceutics, “Pharmacology by Chemical Biology”, we highlight a diverse collection of chemical advances which may be used to treat disease or study drug action, and thus impact our understanding of pharmacology. Metabolic glycoengineering using hexosamine analogues represents one of the pioneering successes of chemical biology, with important applications in imaging, proteomics, immunity, and therapy. However, optimizing these molecules for in vivo applications represents an impediment due to the combinatorial challenge of exploring the thousands of potential modification patterns that may be accommodated by ester-linked monosaccharide scaffolds. In this issue Yarema and co-workers use a dual in silico/experimental approach to address this challenge, systematically defining the impact of variables such as acyl chain length and ester regiochemistry on important pharmacological parameters including solubility and hERG ion channel binding. These studies represent a critical step toward utilizing esterlinked hexosamines as clinical agents, and also may have important implications for in vivo applications which utilize biorthogonal glycan precursors. The invention of novel formulations represents another important approach to translate small molecules for in vivo applications. Toward this goal, the Hsu laboratory at the University of Virginia reports in this issue the development of a liposomal strategy to deliver inhibitors of diacylglycerol lipase-β (DAGL-β), a serine hydrolase important in inflammatory signaling. By tailoring an encapsulation vehicle to the hydrophobic structure of their inhibitor they are able to increase its potency in a model of LPS-induced allodynia ∼20fold. Importantly, the authors also demonstrate that the augmented potency of these formulated inhibitors is paralleled by increased in vivo target occupancy using competitive activity-based protein profiling. In addition to the utility of the DAGL-β inhibitors themselves, this study provides a valuable example of how in vivo target occupancy studies can be used to assess how formulation and delivery impact the ontarget effects of small molecules. In contrast to DAGL-β inhibitors, many clinically utilized drugs have pleiotropic mechanisms of action of which new aspects are being continuously defined. Building on the recent discovery that the nonsteroidal anti-inflammatory drug (NSAID) salicylate can inhibit histone acetylation, Meier and This article not subject to U.S. Copyright. Published 2018 by the American Chemical Society
Special Issue: Pharmacology by Chemical Biology Published: March 5, 2018 703
DOI: 10.1021/acs.molpharmaceut.8b00067 Mol. Pharmaceutics 2018, 15, 703−704
Molecular Pharmaceutics
Editorial
method, which utilizes an isotopically labeled biorthogonal iodoacetamide. These reagents are prepared via a facile fourstep synthesis, and enable profiling of >900 reactive cysteines in a single chemoproteomic experiment. In addition to representing a new and useful addition to the current chemoproteomic arsenal, the general approach utilized may be readily extendable to other classes of reactivity-based profiling reagents, for example, recently reported lysine probes. The use of fluorescent probes to guide surgical resection of solid tumors is a rapidly emerging approach. Developing probe molecules suitable for in vivo use is an interdisciplinary effort that spans organic synthesis to in vivo tumor biology. Understanding the link between chemical structure and in vivo pharmacology of these constructs is a critical, and largely unaddressed, component of these efforts. An article by Bogyo and co-workers describes a strategy using protease-activated near-infrared FRET pairs that are selectively activated within the tumor microenvironment. Careful optimization of the fluorophore component of these probes dramatically improves tumor signal. This paper provides important insights regarding dosing, optics, and probe components as these approaches progress toward clinical application. Another emerging area of chemical biology is the development of advanced fluorescence-driven high-throughput assays. A report by Bruchez and co-workers details the discovery of a novel assay that reports on the location of the cystic fibrosis transmembrane regulator (CFTR). Rescuing the cell surface trafficking of CFTR is a long-standing therapeutic goal. This rescue event can now be readily visualized using the fluorogenactivating-protein (FAP) technology pioneered in this group. The new assay is used to identify kinase targets that synergize with a therapeutic candidate for the treatment of cystic fibrosis. These studies will enable large scale screening efforts that target the development of novel small molecules for this pressing disease need. The enediyne natural products represent a uniquely potent class of cytotoxic compounds. The clinical application of these molecules is tempered by significant toxicity. The development of enediynes that can be locally activated using light as an external stimulus has been a long-standing goal. The methods applied to this challenging chemical endeavor have been reviewed by Alabugin and co-workers. The various strategies examined include metal complexes, photocaging approaches, the use of cyclopropenone-substituted enediynes, and direct photoactivation. This review highlights the diverse range of creative approaches being brought to bear on this problem. The complex photochemistry and biological activity of pterin and pterin-containing biomolecules such as folate has been a long-standing topic of interest. To study the photochemistry of molecules in organic solvents, as well as to prepare liposomal formulations of these molecules, Greer, Thomas, and coworkers describe the synthesis and photochemical characterization of lipophilic analogues of pterin. Going forward, these studies will enable the development of new vesicle-based therapies using these molecules. We began with this editorial with the quote: “The real voyage of discovery consists not in seeking new landscapes, but in having new eyes.” This collection of articles is united by their potential to significantly impact pharmacology by providing “new eyes”, through which to consider the discovery and deployment of therapeutic agents. As such, we hope you find them inspiring and useful.
Martin J. Schnermann,* Guest Editor
■
National Cancer Institute, Frederick, Maryland 21702 United States
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Jordan L. Meier: 0000-0002-0537-7101 Martin J. Schnermann: 0000-0002-0503-0116 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
Jordan L. Meier,* Guest Editor 704
DOI: 10.1021/acs.molpharmaceut.8b00067 Mol. Pharmaceutics 2018, 15, 703−704
