Rosmarinic acid represses colitis-associated colon cancer: A pivotal involvement of the TLR4-mediated NF-κB-STAT3 axis

Abstract

Previously, we found that rosmarinic acid (RA) exerted anti-inflammatory activities in a dextran sulfate sodium (DSS)-induced colitis model. Here, we investigated the anti-tumor effects of RA on colitis-associated colon cancer (CAC) and the underlying molecular mechanisms. We established an azoxymethane (AOM)/DSS-induced CAC murine model for in vivo studies and used a conditioned media (CM) culture system in vitro. H&E staining, immunohistochemistry, western blot assay, enzyme-linked immunosorbent assay, molecular docking, co-immunoprecipitation, and immunofluorescence assay were utilized to investigate how RA prevented colorectal cancer. In the AOM/DSS-induced CAC murine model, RA significantly reduced colitis severity, inflammation-related protein expression, tumor incidence, and colorectal adenoma development. It significantly modulated toll-like receptor-4 (TLR4)-mediated nuclear factor-kappa B (NF-κB) and signal transducer and activator of transcription 3 (STAT3) activation, thus attenuating the expression of anti-apoptotic factors, which mediate transcription factor-dependent tumor growth. In vitro, RA inhibited CM-induced TLR4 overexpression and competitively inhibited TLR4-myeloid differentiation factor 2 complex in an inflammatory microenvironment. Thus, RA suppressed NF-κB and STAT3 activation in colon cancer cells in an inflammatory microenvironment. Therefore, RA suppressed colitis-associated tumorigenesis in the AOM/DSS-induced CAC murine model and abrogated human colon cancer progression in an inflammatory microenvironment by propitiating TLR4-mediated NF-κB and STAT3 activation, pleiotropically.

Keywords: Colitis-associated colon cancer (CAC); Myeloid differentiation factor 2 (MD-2); Nuclear factor-kappa B (NF-κB); Rosmarinic acid (RA); Signal transducer and activator of transcription 3 (STAT3); Toll-like receptor-4 (TLR4).