The pharmacological landscape and therapeutic potential of serine hydrolases

Abstract

Serine hydrolases perform crucial roles in many biological processes, and several of these enzymes are targets of approved drugs for indications such as type 2 diabetes, Alzheimer's disease and infectious diseases. Despite this, most of the human serine hydrolases (of which there are more than 200) remain poorly characterized with respect to their physiological substrates and functions, and the vast majority lack selective, in vivo-active inhibitors. Here, we review the current state of pharmacology for mammalian serine hydrolases, including marketed drugs, compounds that are under clinical investigation and selective inhibitors emerging from academic probe development efforts. We also highlight recent methodological advances that have accelerated the rate of inhibitor discovery and optimization for serine hydrolases, which we anticipate will aid in their biological characterization and, in some cases, therapeutic validation.

Figure 1. Schematic representation of the serine hydrolase catalytic cycle

A base-activated serine nucleophile attacks the carbonyl carbon of the scissile bond, forming a covalent intermediate and releasing the first reaction product. A water molecule then hydrolyzes the covalent intermediate to release the second reaction product and regenerate the active enzyme. X= N, O, or S.

Figure 2. The human serine hydrolases

A dendrogram showing the ~240 predicted human serine hydrolases with branch length depicting sequence relatedness. The metabolic serine hydrolases are colored blue. The remaining enzymes are serine proteases, with chymotrypsin-like enzymes colored black, subtilisin-like enzymes colored red, and other, smaller serine protease clans colored green.

Figure 3. Overview of the current pharmacological toolkit for serine hydrolases

The electrophilic moieties of each compound, if applicable, are colored red.

Figure 4. Activity-based protein profiling (ABPP) for enzyme and inhibitor discovery

(a) Schematic representation of an activity-based probe. (b) A fluorophosphonate (FP) reactive group can be coupled to a tag (e.g., rhodamine, biotin, or alkyne) to covalently label and then detect, enrich, and identify active serine hydrolases. (c) In a typical competitive ABPP experiment, a cell or animal model is treated with an inhibitor (or vehicle control), after which proteomes are prepared and incubated with an activity-based probe. SDS-PAGE separation for fluorophore-tagged probes or mass spectrometry analysis of affinity-enriched biotin-tagged probes enables detection and identification, respectively, of the active enzymes in a biological sample. Note that an enzyme that is the target of an inhibitor will show reduced signals in the inhibitor-treated samples relative to vehicle controls (“<”).