Andrea M. Zuhl

NNMT promotes epigenetic remodeling in cancer by creating a metabolic methylation sink

Nicotinamide N-methyltransferase (NNMT) is overexpressed in a variety of human cancers, where it contributes to tumorigenesis by a still poorly understood mechanism. Here, we show using metabolomics that NNMT impairs the methylation potential of cancer cells by consuming methyl units from S-adenosyl methionine to create the stable metabolic product 1-methylnicotinamide. As a result, NNMT-expressing cancer cells possess an altered epigenetic state that includes hypomethylated histones and other cancer-related proteins combined with heightened expression of pro-tumorigenic gene products. Our findings thus point to a direct mechanistic link between the deregulation of a metabolic enzyme and widespread changes in the methylation landscape of cancer cells.

Total Synthesis of (+)-Fendleridine (Aspidoalbidine) and (+)-1-Acetylaspidoalbidine

A total synthesis of the Aspidosperma alkaloids (+)-fendleridine and (+)-1-acetylaspidoalbidine is detailed, providing access to both enantiomers of the natural products and establishing their absolute configuration. Central to the synthetic approach is a powerful intramolecular [4+2]/[3+2] cycloaddition cascade of a 1,3,4-oxadiazole in which the pentacyclic skeleton and all the stereochemistry of the natural products are assembled in a reaction that forms three rings, four C-C bonds, and five stereogenic centers including three contiguous quaternary centers, and introduces the correct oxidation state at C19 in a single synthetic operation. The final tetrahydrofuran bridge is subsequently installed in one step, enlisting an intramolecular alcohol addition to an iminium ion generated by nitrogen-assisted opening of the cycloadduct oxido bridge, with a modification that permits release of useful functionality (a ketone) at the cleavage termini.

Discovery and optimization of sulfonyl acrylonitriles as selective, covalent inhibitors of protein phosphatase methylesterase-1.

The serine hydrolase protein phosphatase methylesterase-1 (PME-1) regulates the methylesterification state of protein phosphatase 2A (PP2A) and has been implicated in cancer and Alzheimers disease. We recently reported a fluorescence polarization-activity-based protein profiling (fluopol-ABPP) high-throughput screen for PME-1 that uncovered a remarkably potent and selective class of aza-β-lactam (ABL) PME-1 inhibitors. Here, we describe a distinct set of sulfonyl acrylonitrile inhibitors that also emerged from this screen. The optimized compound, 28 (AMZ30), selectively inactivates PME-1 and reduces the demethylated form of PP2A in living cells. Considering that 28 is structurally unrelated to ABL inhibitors of PME-1, these agents, together, provide a valuable set of pharmacological probes to study the role of methylation in regulating PP2A function. We furthermore observed that several serine hydrolases were sensitive to analogues of 28, suggesting that more extensive structural exploration of the sulfonyl acrylonitrile chemotype may result in useful inhibitors for other members of this large enzyme class.

Competitive Activity-Based Protein Profiling Identifies Aza-β- Lactams as a Versatile Chemotype for Serine Hydrolase Inhibition

Serine hydrolases are one of the largest and most diverse enzyme classes in Nature. Most serine hydrolases lack selective inhibitors, which are valuable probes for assigning functions to these enzymes. We recently discovered a set of aza-β-lactams (ABLs) that act as potent and selective inhibitors of the mammalian serine hydrolase protein-phosphatase methylesterase-1 (PME-1). The ABLs inactivate PME-1 by covalent acylation of the enzymes serine nucleophile, suggesting that they could offer a general scaffold for serine hydrolase inhibitor discovery. Here, we have tested this hypothesis by screening ABLs more broadly against cell and tissue proteomes by competitive activity-based protein profiling (ABPP), leading to the discovery of lead inhibitors for several serine hydrolases, including the uncharacterized enzyme α,β-hydrolase domain-containing 10 (ABHD10). ABPP-guided medicinal chemistry yielded a compound ABL303 that potently (IC(50) ≈ 30 nM) and selectively inactivated ABHD10 in vitro and in living cells. A comparison of optimized inhibitors for PME-1 and ABHD10 indicates that modest structural changes that alter steric bulk can tailor the ABL to selectively react with distinct, distantly related serine hydrolases. Our findings, taken together, designate the ABL as a versatile reactive group for creating first-in-class serine hydrolase inhibitors.

Selective Inhibitor of Platelet-Activating Factor Acetylhydrolases 1b2 and 1b3 That Impairs Cancer Cell Survival

Platelet-activating factor acetylhydrolases (PAFAHs) 1b2 and 1b3 are poorly characterized serine hydrolases that form a complex with a noncatalytic protein (1b1) to regulate brain development, spermatogenesis, and cancer pathogenesis. Determining physiological substrates and biochemical functions for the PAFAH1b complex would benefit from selective chemical probes that can perturb its activity in living systems. Here, we report a class of tetrahydropyridine reversible inhibitors of PAFAH1b2/3 discovered using a fluorescence polarization-activity-based protein profiling (fluopol-ABPP) screen of the NIH 300,000+ compound library. The most potent of these agents, P11, exhibited IC50 values of ∼40 and 900 nM for PAFAH1b2 and 1b3, respectively. We confirm selective inhibition of PAFAH1b2/3 in cancer cells by P11 using an ABPP protocol adapted for in situ analysis of reversible inhibitors and show that this compound impairs tumor cell survival, supporting a role for PAFAH1b2/3 in cancer.

Chemoproteomic profiling reveals that cathepsin D off-target activity drives ocular toxicity of β-secretase inhibitors

Inhibition of β-secretase BACE1 is considered one of the most promising approaches for treating Alzheimers disease. Several structurally distinct BACE1 inhibitors have been withdrawn from development after inducing ocular toxicity in animal models, but the target mediating this toxicity has not been identified. Here we use a clickable photoaffinity probe to identify cathepsin D (CatD) as a principal off-target of BACE1 inhibitors in human cells. We find that several BACE1 inhibitors blocked CatD activity in cells with much greater potency than that displayed in cell-free assays with purified protein. Through a series of exploratory toxicology studies, we show that quantifying CatD target engagement in cells with the probe is predictive of ocular toxicity in vivo. Taken together, our findings designate off-target inhibition of CatD as a principal driver of ocular toxicity for BACE1 inhibitors and more generally underscore the power of chemical proteomics for discerning mechanisms of drug action.

Rapid development of a potent photo-triggered inhibitor of the serine hydrolase RBBP9.

The serine hydrolases constitute a large class of enzymes that play important roles in physiology. There is great interest in the development of potent and selective pharmacological inhibitors of these proteins. Traditional active‐site inhibitors often have limited selectivity within this superfamily and are tedious and expensive to discover. Using the serine hydrolase RBBP9 as a model target, we designed a rapid and relatively inexpensive route to highly selective peptoid‐based inhibitors that can be activated by visible light. This technology provides rapid access to photo‐activated tool compounds capable of selectively blocking the function of particular serine hydrolases.