ObjectiveThe NLRP3 inflammasome is closely linked to the pathophysiology of a wide range of inflammatory diseases. This study was undertaken to identify small molecules that directly bind to NLRP3 in order to develop pharmacologic interventions for NLRP3‐related diseases.MethodsA structure‐based virtual screening analysis was performed with ~62,800 compounds to select efficient NLRP3 inhibitors. The production of caspase 1‐p10 and interleukin‐1β (IL‐1β) was measured by immunoblotting and enzyme‐linked immunosorbent assay to examine NLRP3 inflammasome activation. Two gouty arthritis models and an air pouch inflammation model induced by monosodium urate monohydrate (MSU) crystal injection were used for in vivo experiments. Primary synovial fluid cells from gout patients were used to determine the relevance of NLRP3 inflammasome inhibition in human gout.ResultsBeta‐carotene (provitamin A) suppressed the NLRP3 inflammasome activation induced by various activators, including MSU crystals, in mouse bone marrow–derived primary macrophages (P < 0.05). Surface plasmon resonance analysis demonstrated the direct binding of β‐carotene to the pyrin domain (PYD) of NLRP3 (KD = 3.41 × 10−6). Molecular modeling and mutation assays revealed the interaction mode between β‐carotene and the NLRP3 PYD. Inflammatory symptoms induced by MSU crystals were attenuated by oral administration of β‐carotene in gouty arthritis mouse models (P < 0.05), correlating with its suppressive effects on the NLRP3 inflammasome in inflamed tissues. Furthermore, β‐carotene reduced IL‐1β secretion from human synovial fluid cells isolated from gout patients (P < 0.05), showing its inhibitory efficacy in human gout.ConclusionOur results present β‐carotene as a selective and direct inhibitor of NLRP3, and the binding of β‐carotene to NLRP3 PYD as a novel pharmacologic strategy to combat NLRP3 inflammasome–driven diseases, including gouty arthritis.

Tumor microenvironment favors tumor cells to promote tumor growth, migration, invasion, and angiogenesis. IL-1beta, one of the inflammatory cytokines associated with tumor microenvironment, plays an important role in the development and progress of tumor. The activation of inflammasome is critical to secrete mature IL-1beta through stepwise reactions to activate capspase-1. Therefore, we investigated whether the metastatic potential of breast cancer cells was regulated by NLRP3 inflammasome activation of macrophages in tumor microenvironment. The activation of NLRP3 inflammasome was induced by ATP in bone marrow-derived primary mouse macrophages. The metastatic potential of 4T1 breast cancer cells was determined by migration and invasion assays with transwell system. Conditioned media from ATP-stimulated wild-type macrophages increased the migration and invasion of breast cancer cells (4T1) while conditioned media from NLRP3 knockout macrophages stimulated with ATP failed to induce the migration and invasion of breast cancer cells. Celastrol, an inhibitor of NLRP3 inflammasome, reduced the potency of macrophages to stimulate the migration and invasion of 4T1 breast cancer cells. The suppression of NLRP3 inflammasome by celastrol was mediated by the blockade of potassium efflux. The results demonstrate that the activation of NLRP3 inflammasome in macrophages leads to the enhancement of metastatic potential of breast cancer cells. The results would provide a novel anticancer strategy to modulate tumor microenvironment by suppressing NLRP3 inflammasome and consequently reducing IL-1beta production. (This study was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (Bio & Medical Technology Development Program, NRF-2017M3A9F5028608; Basic Research Laboratory Program, NRF-2017R1A4A1015036.) Citation Format: Jin Y. Lee, Hye E. Lee, Joo Y. Lee. The metastatic potential of breast cancer cells was suppressed by NLRP3 inflammasome inhibition in macrophages [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A26.