Design and Synthesis of Highly Potent and Specific ABHD6 Inhibitors

Fine-tuning than complete disruption of 2-arachidonoylglycerol (2-AG) metabolism in the brain represents a promising pharmacological approach to limit potential untoward effects associated with complete blockade of monoacylglycerol lipase (MGL), the primary hydrolase of 2-AG. This could be achieved through a/b-hydrolase domain containing 6 (ABHD6) inhibition, which will provide a smaller and safer contribution to 2-AG regulation in the brain. Pharmacological studies with ABHD6 inhibitors have recently been reported, where modulation of ABHD6 activity either through CB1R-dependent or CB1R-independent processes showed promise in preclinical models of epilepsy, neuropathic pain and inflammation. Furthermore in the periphery, ABHD6 modulates 2-AG and other fatty acid monoacylglycerols (MAGs) and is implicated in Type-2 diabetes, metabolic syndrome and potentially other diseases. Herein, we report the discovery of single-digit nanomolar potent and highly specific ABHD6 inhibitors with >1000-fold selectivity against MGL and FAAH. The new ABHD6 inhibitors provide early leads to develop therapeutics for neuroprotection and the treatment of inflammation and diabetes.

Abstract 518: AB801 is a highly potent and selective AXL kinase inhibitor that demonstrates significant anti-tumor activity

Background: AXL receptor tyrosine kinase (AXL) is overexpressed in a variety of tumors and correlates with poor prognosis in cancer patients. AXL is expressed in cancer, stromal, and select immune cells, and has been implicated in the development of resistance to chemotherapy, targeted therapies & immunotherapies. Activation of AXL can be mediated by its ligand, growth arrest specific protein 6 (GAS6), or via ligand-independent homo/hetero-dimerization, both of which facilitate AXL phosphorylation, initiation of signaling cascades that promote cancer cell proliferation, survival, and an immunosuppressive microenvironment. Here we present the discovery and characterization of a novel, highly potent and selective AXL inhibitor, AB801.

Materials and Methods: The potency and selectivity of AB801 against AXL and other kinases were determined using a panel of HTRF KinEASE-TK assays and via a competition binding assay utilizing DNA-tagged kinases. The effects of AB801 were further assessed by a cell-based phospho-AXL ELISA. The pharmacokinetic (PK) profile of the molecule was evaluated in preclinical species. AB801 was characterized in routine in vitro safety assays, including hERG inhibition. Downstream signaling of AXL was evaluated by phospho-array, Western blot, and qPCR. Pharmacodynamics (PD) and anti-tumor efficacy in combination with standard of care (SOC) therapies were assessed in murine cancer models.

Results: The novel AXL inhibitor AB801 is potent, reversible, and selective. AB801 exhibits cellular activity at low nanomolar concentrations and retains significant activity in 100% human serum. Excellent selectivity was observed against MERTK (860x), TYRO3 (1,400x), and the overall kinome. Importantly, AB801 does not show significant CYP450 or hERG inhibition. Favorable preclinical PK is consistent with projected once-a-day oral administration in humans. AB801 increases sensitivity to SOC therapeutics such as chemotherapy, and results in increased DNA damage. Moreover, AB801 treatment sensitizes tumors to checkpoint blockade by increasing immune cell activation. Significant anti-tumor efficacy is observed in combination SOC therapies in multiple in vivo models.

Conclusions: AXL inhibition is a promising therapeutic mechanism for impairing the growth of tumors resistant to SOC therapeutics. AB801 exhibits improved potency, selectivity, and safety profiles compared to other AXL inhibitors currently advancing into clinical development.

Citation Format: Susan Lee Paprcka, Armon Goshayeshi, Suan Liu, Ruben Flores, Lauren Rocha, Jhansi L. Leslie, Dillon H. Miles, Corinne N. Foley, Shiwei Qu, Manjunath Lamani, Srinivas Paladugu, Hsin-Ting Huang, Nidhi Tribewal, Ada Chen, Joseph Kulusich, Stefan Garrido-Shaqfeh, Patricia Fabila, Salema Jafri, Anuja Devarajan, Ester Fernandez-Salas. AB801 is a highly potent and selective AXL kinase inhibitor that demonstrates significant anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 518.

The endocannabinoid 2-arachidonoylglycerol and dual ABHD6/MAGL enzyme inhibitors display neuroprotective and anti-inflammatory actions in the in vivo retinal model of AMPA excitotoxicity

The endocannabinoid system has been shown to be a putative therapeutic target for retinal disease. Here, we aimed to investigate the ability of the endocannabinoid 2-arachidonoylglycerol (2-AG) and novel inhibitors of its metabolic enzymes, α/β-hydrolase domain-containing 6 (ABHD6) and monoacylglycerol lipase (MAGL), a) to protect the retina against excitotoxicity and b) the mechanisms involved in the neuroprotection. Sprague-Dawley rats, wild type and Akt2^-/- C57BL/6 mice were intravitreally administered with phosphate-buffered saline or (RS)-α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hydrobromide (AMPA). 2-AG was intravitreally co-administered with AMPA in the absence and presence of AM251 or AM630 (cannabinoid 1 and 2 receptor antagonists, respectively) or Wortmannin [Phosphoinositide 3-Kinase (PI3K)/Akt inhibitor]. Inhibitors of ABHD6 and dual ABHD6/MAGL (AM12100 and AM11920, respectively) were co-administered with AMPA intravitreally in rats. Immunohistochemistry was performed using antibodies raised against retinal neuronal markers (bNOS), microglia (Iba1) and macroglia (GFAP). TUNEL assay and real-time PCR were also employed. The CB2 receptor was expressed in rat retina (approx. 62% of CB1 expression). 2-AG attenuated the AMPA-induced increase in TUNEL⁺ cells. 2-AG activation of both CB1 and CB2 receptors and the PI3K/Akt downstream signaling pathway, as substantiated by the use of Akt2^-/- mice, afforded neuroprotection against AMPA excitotoxicity. AM12100 and AM11920 attenuated the AMPA-induced glia activation and produced a dose-dependent partial neuroprotection, with the dual inhibitor AM11920 being more efficacious. These results show that 2-AG has the pharmacological profile of a putative therapeutic for retinal diseases characterized by neurodegeneration and neuroinflammation, when administered exogenously or by the inhibition of its metabolic enzymes.

Design and synthesis of cyanamides as potent and selective N-acylethanolamine acid amidase inhibitors

N-acylethanolamine acid amidase (NAAA) inhibition represents an exciting novel approach to treat inflammation and pain. NAAA is a cysteine amidase which preferentially hydrolyzes the endogenous biolipids palmitoylethanolamide (PEA) and oleoylethanolamide (OEA). PEA is an endogenous agonist of the nuclear peroxisome proliferator-activated receptor-α (PPAR-α), which is a key regulator of inflammation and pain. Thus, blocking the degradation of PEA with NAAA inhibitors results in augmentation of the PEA/PPAR-α signaling pathway and regulation of inflammatory and pain processes. We have prepared a new series of NAAA inhibitors exploring the azetidine-nitrile (cyanamide) pharmacophore that led to the discovery of highly potent and selective compounds. Key analogs demonstrated single-digit nanomolar potency for hNAAA and showed >100-fold selectivity against serine hydrolases FAAH, MGL and ABHD6, and cysteine protease cathepsin K. Additionally, we have identified potent and selective dual NAAA-FAAH inhibitors to investigate a potential synergism between two distinct anti-inflammatory molecular pathways, the PEA/PPAR-α anti-inflammatory signaling pathway,^1-4 and the cannabinoid receptors CB1 and CB2 pathways which are known for their antiinflammatory and antinociceptive properties.^5-8 Our ligand design strategy followed a traditional structure-activity relationship (SAR) approach and was supported by molecular modeling studies of reported X-ray structures of hNAAA. Several inhibitors were evaluated in stability assays and demonstrated very good plasma stability (t_1/2 > 2 h; human and rodents). The disclosed cyanamides represent promising new pharmacological tools to investigate the potential role of NAAA inhibitors and dual NAAA-FAAH inhibitors as therapeutic agents for the treatment of inflammation and pain.

Piperidine and piperazine inhibitors of fatty acid amide hydrolase targeting excitotoxic pathology

FAAH inhibitors offer safety advantages by augmenting the anandamide levels "on demand" to promote neuroprotective mechanisms without the adverse psychotropic effects usually seen with direct and chronic activation of the CB1 receptor. FAAH is an enzyme implicated in the hydrolysis of the endocannabinoid N-arachidonoylethanolamine (AEA), which is a partial agonist of the CB1 receptor. Herein, we report the discovery of a new series of highly potent and selective carbamate FAAH inhibitors and their evaluation for neuroprotection. The new inhibitors showed potent nanomolar inhibitory activity against human recombinant and purified rat FAAH, were selective (>1000-fold) against serine hydrolases MGL and ABHD6 and lacked any affinity for the cannabinoid receptors CB1 and CB2. Evaluation of FAAH inhibitors 9 and 31 using the in vitro competitive activity-based protein profiling (ABPP) assay confirmed that both inhibitors were highly selective for FAAH in the brain, since none of the other FP-reactive serine hydrolases in this tissue were inhibited by these agents. Our design strategy followed a traditional SAR approach and was supported by molecular modeling studies based on known FAAH cocrystal structures. To rationally design new molecules that are irreversibly bound to FAAH, we have constructed "precovalent" FAAH-ligand complexes to identify good binding geometries of the ligands within the binding pocket of FAAH and then calculated covalent docking poses to select compounds for synthesis. FAAH inhibitors 9 and 31 were evaluated for neuroprotection in rat hippocampal slice cultures. In the brain tissue, both inhibitors displayed protection against synaptic deterioration produced by kainic acid-induced excitotoxicity. Thus, the resultant compounds produced through rational design are providing early leads for developing therapeutics against seizure-related damage associated with a variety of disorders.

Total synthesis of myceliothermophins C, D, and E

The total synthesis of cytotoxic polyketides myceliothermophins E (1), C (2), and D (3) through a cascade-based cyclization to form the trans-fused decalin system is described. The convergent synthesis delivered all three natural products through late-stage divergence and facilitated unambiguous C21 structural assignments for 2 and 3 through X-ray crystallographic analysis, which revealed an interesting dimeric structure between its enantiomeric forms.