Human FGF-21 Is a Substrate of Fibroblast Activation Protein.

FGF-21 is a key regulator of metabolism and potential drug candidate for the treatment of type II diabetes and other metabolic disorders. However, the half-life of active, circulating, human FGF-21 has recently been shown to be limited in mice and monkeys by a proteolytic cleavage between P171 and S172. Here, we show that fibroblast activation protein is the enzyme responsible for this proteolysis by demonstrating that purified FAP cleaves human FGF-21 at this site in vitro, and that an FAP-specific inhibitor, ARI-3099, blocks the activity in mouse, monkey and human plasma and prolongs the half-life of circulating human FGF-21 in mice. Mouse FGF-21, however, lacks the FAP cleavage site and is not cleaved by FAP. These findings indicate FAP may function in the regulation of metabolism and that FAP inhibitors may prove useful in the treatment of diabetes and metabolic disorders in humans, but pre-clinical proof of concept studies in rodents will be problematic

Human FGF-21 is digested by FAP but not PREP.

<p>(A) Human FGF-21 is cleaved by FAP. Recombinant human FGF-21 was digested by recombinant human FAP and visualized by Coomassie staining of SDS-Page gel. (B) Time course of FGF-21 digestion by FAP quantified by LC/MS extracted ion integration of peaks corresponding to intact (1–181) and cleaved (1–171) forms of FGF-21 (n = 3 per time point per group). Values are mean ± SEM with one phase decay curve fit superimposed. (C) FAP cleavage of FGF-21 is prevented by ARI-3099. ARI-3099 was pre-incubated with recombinant FAP for 30 minutes prior to addition of FGF-21. Reaction products were visualized by Coomassie staining of SDS-Page gel. (D) Recombinant PREP does not cleave FGF-21. Recombinant human PREP was added to recombinant FGF-21 and visualized by Coomassie staining of SDS-Page gel.</p

Effect of FAP inhibition on FGF-21 digestion in plasma.

<p>(A) FAP cleaves human FGF-21 in mouse, monkey and human plasma. Recombinant FGF-21 was added to plasma to a final concentration of 1 μM in the presence or absence of 16 μM ARI-3099 followed by assessment of intact FGF-21 by sandwich ELISA (n = 3 per group). Values are mean ± SEM. *P < .05 ***P < .001 by <i>ANOVA</i>. (B) FAP activity of mouse, monkey and human plasma as assessed by the FAP-specific fluorescent substrate ARI-3144.</p

Inhibition of FAP prolongs the half-life of human FGF-21 in mice.

<p>(A) ARI-3099 was administered to mice at 80 mg/kg via oral gavage. FAP activity in plasma samples was determined using the FAP-specific fluorescent substrate ARI-3144 (n = 3 per group). Values are mean ± SEM. (B) Mice were pre-treated with vehicle or 80 mg/kg ARI-3099 followed by injection of 0.5 mg/kg human FGF-21 (n = 4 per group). Plasma samples were assessed for intact FGF-21 concentrations by sandwich ELISA. Values are mean ± SEM. *P < .05 by <i>t</i>-test.</p

A high-throughput, multiplexed assay for superfamily-wide profiling of enzyme activity

The selectivity of an enzyme inhibitor is a key determinant of its usefulness as a tool compound or its safety as a drug. Yet selectivity is never assessed comprehensively in the early stages of the drug discovery process, and only rarely even in the later stages, because technical limitations prohibit doing otherwise. Here, we report EnPlex, an efficient, high-throughput method for simultaneously assessing inhibitor potency and specificity, and pilot its application to 96 serine hydrolases. EnPlex analysis of widely used serine hydrolase inhibitors revealed numerous previously unrecognized off-target interactions, some of which may help to explain previously confounding adverse effects. In addition, EnPlex screening of a hydrolase-directed library of boronic acid- and nitrile-containing compounds provided dual potency/selectivity structure-activity relationships from which lead candidates could be more effectively prioritized. Follow-up of a series of dipeptidyl peptidase 4 (DPP4) inhibitors showed that EnPlex indeed predicted efficacy and safety in animal models. These results demonstrate the feasibility and value of high-throughput, superfamily-wide selectivity profiling, and suggest such profiling can be incorporated into the earliest stages of drug discovery

A General Method for Making Peptide Therapeutics Resistant to Serine Protease Degradation: Application to Dipeptidyl Peptidase IV Substrates

Bioactive peptides have evolved to optimally fulfill specific biological functions, a fact which has long attracted attention for their use as therapeutic agents. While there have been some recent commercial successes fostered in part by advances in large-scale peptide synthesis, development of peptides as therapeutic agents has been significantly impeded by their inherent susceptibility to protease degradation in the bloodstream. Here we report that incorporation of specially designed amino acid analogues at the P1′ position, directly C-terminal of the enzyme cleavage site, renders peptides, including glucagon-like peptide-1 (7–36) amide (GLP-1) and six other examples, highly resistant to serine protease degradation without significant alteration of their biological activity. We demonstrate the applicability of the method to a variety of proteases, including dipeptidyl peptidase IV (DPP IV), dipeptidyl peptidase 8 (DPP8), fibroblast activation protein α (FAPα), α-lytic protease (αLP), trypsin, and chymotrypsin. In summary, the “P1′ modification” represents a simple, general, and highly adaptable method of generating enzymatically stable peptide-based therapeutics