Highly selective inhibitors of monoacylglycerol lipase bearing a reactive group that is bioisosteric with endocannabinoid substrates

Abstract

The endocannabinoids 2-arachidonoyl glycerol (2-AG) and N-arachidonoyl ethanolamine (anandamide) are principally degraded by monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), respectively. The recent discovery of O-aryl carbamates such as JZL184 as selective MAGL inhibitors has enabled functional investigation of 2-AG signaling pathways in vivo. Nonetheless, JZL184 and other reported MAGL inhibitors still display low-level cross-reactivity with FAAH and peripheral carboxylesterases, which can complicate their use in certain biological studies. Here, we report a distinct class of O-hexafluoroisopropyl (HFIP) carbamates that inhibits MAGL in vitro and in vivo with excellent potency and greatly improved selectivity, including showing no detectable cross-reactivity with FAAH. These findings designate HFIP carbamates as a versatile chemotype for inhibiting MAGL and should encourage the pursuit of other serine hydrolase inhibitors that bear reactive groups resembling the structures of natural substrates.

Figure 1. Discovery of HFIP carbamates as potent and selective MAGL inhibitors

(A) Structures of 2-AG, representative O-aryl carbamate inhibitors of endocannabinoid hydrolases, and HFIP carbamate analogues of these inhibitors, showing the bioisosteric nature of the HFIP group compared to the glycerol head group of MAGL substrate 2-AG. (B) Competitive ABPP gels comparing the potency and selectivity of JZL184, KML29, JW642 and JW618 against MAGL, ABHD6, and FAAH in mouse brain proteomes. See Figure S1 for full gel profiles of each inhibitor. See also Table 1 for IC₅₀ values calculated from gel-based ABPP experiments. Note that MAGL migrates as two bands in the mouse brain likely due to alternative spliced isoforms (Karlsson et al., 2001). (C) Full competitive ABPP gel showing KML29 activity against mouse brain serine hydrolase activities, which revealed selective inhibition of MAGL at inhibitor concentrations of 1 μM of less and inhibition of ABHD6 at concentrations > 1 μM. No inhibition of FAAH was detected at any tested concentration of KML29. (D) Blockade of MAGL and FAAH by KML29 in mouse brain proteomes as measured by hydrolysis of 2-AG and AEA, respectively. Data are presented as means ± SEM of three independent experiments. Gels are representative images from three independent experiments (n = 3).

Figure 2. Characterization of KML29-mediated inactivation of MAGL

(A) Proposed mechanism of MAGL inactivation by KML29. The catalytic serine (Ser122) of MAGL attacks the activated carbamate of KML29, releasing hexafluoroisopropanol and forming a stable, carbamylated KML29-MAGL covalent adduct. (B) Extracted ion chromatograms for +4 (m/z = 1408.2310) and +5 (m/z = 1126.7862) charge states corresponding to the KML29-modified adduct of the active site tryptic peptide from DMSO-treated and KML29-treated recombinant, purified human MAGL. (C) Proposed docking mode of KML29 (green) to MAGL (grey) illustrated in views of the whole protein (left image) and the active site (right image). When the catalytic Ser122 is positioned for nucleophilic attack at the carbonyl of KML29, His121 and Tyr194, which are predicted to interact with 2-AG’s head group (Bertrand et al., 2010), show potentially favorable interactions with the KML29’s HFIP leaving group. RosettaLigand 3.3 (http://www.ncbi.nlm.nih.gov/pubmed/19041878) was used to perform the docking and the MAGL structure used for docking was 3JWE from the protein data bank (Bertrand et al., 2010).

Figure 3. In vivo characterization of KML29 activity in mice

(A) Competitive ABPP gel of FP-Rh labeling of brain serine hydrolase activities from mice treated with JZL184 or KML29 at the indicated dose (1–40 mg kg⁻¹, p.o.) for 4 h. (B) Brain lipid profile for 2-AG, AA, AEA, PEA, OEA across the indicated dose-range of KML29 (p.o.). 2-AG and AEA hydrolytic activity of brain tissue isolated from KML29 treated mice (far right graph). (C) Competitive ABPP gels of serine hydrolase activities in liver and lung tissues from mice treated with either JZL184 or KML29 (1–40 mg kg⁻¹, p.o.) for 4 h. Red boxes mark various CES enzymes that show differential sensitivity to JZL184 versus KML29. Also see Figure S2 for in vitro inhibition of CESs by JZL184 and KML29 in lung proteomes and ABPP gels from spleen proteomes isolated from mice treated with JZL184 and KML29. Data are presented as means ± SEM, n = 3 mice per group. *, P < 0.05; **, P < 0.01; ***, P < 0.001 for vehicle-treated versus inhibitor-treated mice.

Figure 4. Characterization of serine hydrolase activities and endocannabinoid metabolism in mice treated chronically with KML29 and JZL184

(A) Competitive ABPP gels of serine hydrolase activities in brain from mice chronically treated with vehicle, JZL184, or KML29 (40 mg kg⁻¹ day⁻¹, p.o., 6 days). (B) Competitive ABPP gels of serine hydrolase activities in liver, lung and spleen from mice chronically treated with vehicle, JZL184, or KML29. Red boxes mark various off-targets that show differential sensitivity to JZL184 versus KML29. (C) Brain lipid profiles and endocannabinoid hydrolytic activities measured from mice chronically treated with vehicle, JZL184, or KML29.

Figure 5. Inhibition of rat and human MAGL enzymes by KML29

(A) Competitive ABPP gels comparing the potency and selectivity of JZL184, KML29, JW642 and JW618 against MAGL, ABHD6 and FAAH in rat brain proteomes. See Figure S3 for full gel profiles of each inhibitor. See also Table 1 for IC₅₀ values calculated from gel-based ABPP experiments. (B) Full competitive ABPP gel showing KML29 activity against rat brain serine hydrolase activities, which revealed selective inhibition of MAGL at inhibitor concentrations of 1 μM or less and inhibition of ABHD6 at concentrations > 1 μM. No inhibition of FAAH was detected at any tested concentration of KML29. (C) Competitive ABPP gel of brain serine hydrolase activities from rats treated with KML29 (1–40 mg kg⁻¹, i.p.) for 4 h. Also see Figure S3 for gel profiles of liver, lung and spleen from rats treated with KML29. (D) Brain lipid profile of 2-AG, AA, AEA, PEA, OEA from rats treated with KML29 (1–40 mg kg⁻¹, i.p.). (E) Brain MAGL and FAAH activity from rats treated with KML29 (1–40 mg kg⁻¹, i.p.) as measured by 2-AG and AEA hydrolysis, respectively. (F) Activity of JZL184, KML29, JW642, and JW618 against recombinant human MAGL and FAAH by gel-based competitive ABPP (upper gel panels) and substrate hydrolysis (lower graph) assays. See also Table 1 for IC₅₀ values calculated from gel-based ABPP experiments. Data are presented as means ± SEM, n = 3 rats per group. *, P < 0.05; **, P < 0.01; ***, P < 0.001 for vehicle-treated versus inhibitor-treated rats.