Design and Discovery of Novel NLRP3 Inhibitors and PET Imaging Radiotracers Based on a 1,2,3-Triazole-Bearing Scaffold

The NOD-like receptor (NLR) family pyrin-domain-containing 3 (NLRP3) inflammasome, an essential component of the innate immune system, has been emerging as a viable drug target and a potential biomarker for human diseases. In our efforts to develop novel small molecule NLRP3 inhibitors, a 1-(5-chloro-2-methoxybenzyl)-4-phenyl-1H-1,2,3-triazole scaffold was designed via a rational approach based on our previous leads. Structure-activity relationship studies and biophysical studies identified a new lead compound 8 as a potent (IC50: 0.55 ± 0.16 μM), selective, and direct NLRP3 inhibitor. Positron emission tomography (PET) imaging studies of [11C]8 demonstrated its rapid and high brain uptake as well as fast washout in mice and rhesus macaque. Notably, plasma kinetic analysis of this radiotracer from the PET/magnetic resonance imaging studies in rhesus macaque suggested radiometabolic stability. Collectively, our data not only encourage further studies of this lead compound but also warrant further optimization to generate additional novel NLRP3 inhibitors and suitable central nervous system PET radioligands with translational promise.

A patent review of NLRP3 inhibitors to treat autoimmune diseases

INTRODUCTION

NOD-like receptor family pyrin domain containing 3 (NLRP3) can sense a plethora of exogenous and endogenous dangers. Upon activation, a multimeric protein complex, the NLRP3 inflammasome, is formed to initiate the innate immune responses. Emerging studies have implicated the pathophysiological roles of this protein complex in human disorders, highlighting that it represents a druggable target for therapeutics development.

AREAS COVERED

The current review summarizes the functional facets of the NLRP3 inflammasome, its association with autoimmune diseases, and recent patents on the development of NLRP3 inhibitors. Literature search was conducted using SciFinder and Google Patents with the key word NLRP3 and NLRP3 inhibitors.

EXPERT OPINION

Although significant advances have been made in understanding the NLRP3 inflammasome, more studies are still needed to elucidate the molecular mechanisms underlying its roles in autoimmune diseases. A number of NLRP3 inhibitors have been patented, however, none of them have been approved for clinical use. Due to the complex nature of the NLRP3 inflammasome, novel screening assays along with target engagement methods could benefit the drug discovery and clinical translation. In addition, clinical trials on NLRP3 inhibitors are still in their early stages, and continuous investigations are needed to fully assess their safety and effectiveness.

Development of sulfonamide-based NLRP3 inhibitors: Further modifications and optimization through structure-activity relationship studies

NLRP3 inflammasome dysregulation has been observed in many human diseases including neurodegenerative disorders. Thus, development of small molecule inhibitors targeting this protein complex represents a promising strategy to achieve disease intervention. In our continuing efforts to develop NLRP3 inhibitors, a recently identified lead inhibitor, YQ128, was further modified and optimized. The structure-activity relationship studies of this lead compound suggested its flexibility for structural modifications while the sulfonamide and benzyl moiety demonstrated being important for selectivity. Additionally, the systematic SAR studies also provided insights for designing NLRC4 and AIM2 inflammasome inhibitors. A new lead inhibitor, 19, was identified with improved potency (IC₅₀: 0.12 ± 0.01 μM) and binding affinity (K_D: 84 nM). Further characterization of this lead compound using wild type and nlrp3^-/- mice confirmed its in vivo selective target engagement. PET studies using a radiotracer based on the structure of 19 also demonstrated its improved brain penetration compared to previous lead compounds. These results strongly encourage further testing of 19 in disease models.

The NLRP3 Inflammasome Pathway: A Review of Mechanisms and Inhibitors for the Treatment of Inflammatory Diseases

The NLRP3 inflammasome is a multiprotein complex that plays a pivotal role in regulating the innate immune system and inflammatory signaling. Upon activation by PAMPs and DAMPs, NLRP3 oligomerizes and activates caspase-1 which initiates the processing and release of pro-inflammatory cytokines IL-1β and IL-18. NLRP3 is the most extensively studied inflammasome to date due to its array of activators and aberrant activation in several inflammatory diseases. Studies using small molecules and biologics targeting the NLRP3 inflammasome pathway have shown positive outcomes in treating various disease pathologies by blocking chronic inflammation. In this review, we discuss the recent advances in understanding the NLRP3 mechanism, its role in disease pathology, and provide a broad review of therapeutics discovered to target the NLRP3 pathway and their challenges.

Novel Positron Emission Tomography Radiotracers for Imaging Mitochondrial Complex I

Mitochondrial dysfunction has been indicated in neurodegenerative and other disorders. The mitochondrial complex I (MC-I) of the electron transport chain (ETC) on the inner membrane is the electron entry point of the ETC and is essential for the production of reactive oxygen species. Based on a recently identified β-keto-amide type MC-I modulator from our laboratory, an ¹⁸F-labeled positron emission tomography (PET) tracer, ¹⁸F-2, was prepared. PET/CT imaging studies demonstrated that ¹⁸F-2 exhibited rapid brain uptake without significant wash out during the 60 min scanning time. In addition, the binding of ¹⁸F-2 was higher in the regions of the brain stem, cerebellum, and midbrain. The uptake of ¹⁸F-2 can be significantly blocked by its parent compound. Collectively, the results strongly suggest successful development of MC-I PET tracers from this chemical scaffold that can be used in future mitochondrial dysfunction studies of the central nervous system.