Elucidation of the anti-inflammatory activity and molecular mechanisms of the novel compound Taxamairin B for development as an inflammatory bowel disease therapeutic agent

Abstract

Uncontrolled inflammation is a major cause of various chronic diseases, including inflammatory bowel disease (IBD), cancer, cardiovascular disease, and autoimmune disorders, which are leading causes of mortality worldwide. Notably, these diseases have no effective treatment and thus, there is an urgent need for the discovery of novel effective entities that reduce inflammation, to decrease the burden of various inflammatory diseases. Natural products are a rich source of anti-inflammatory compounds. In my ongoing search for novel anti-inflammatory small molecules, I have identified Taxamairin A (TaxA), a non-taxane diterpenoid first isolated from the dried bark of Taxus mairei (Lemee et Lev.) S.Y.Hu (Taxaceae). In this study, I first demonstrated the anti-inflammatory activities of TaxA, in vitro and in vivo. Based on the anti-inflammatory potential of TaxA and using it as a lead compound, I designed and synthesized over twenty chemical derivatives. I further assessed the anti-inflammatory activities of these compounds, and among the tested compounds, TaxB (WT-17) exhibited the highest anti-inflammatory activity with low toxicity, therefore, I focused on further investigation of TaxB. In in vitro studies, I demonstrated that TaxB effectively suppressed the activation of macrophages, one of the main effectors of inflammation. TaxB inhibited the production of a broad range of cytokines and chemokines, and activation of NF-κB, MAPK, AKT, STAT3, and NLRP3 inflammasome signaling, promising targets for the treatment of many inflammatory diseases. I further demonstrated the in vivo anti-inflammatory activity of TaxB using the DSS-induced acute colitis mouse model. TaxB significantly ameliorated the severity of DSS-induced acute colitis and exhibited increased efficacy when compared to 5-aminosalicylic acid (5-ASA), one of the first-line drugs for IBD. In line with my in vitro results, TaxB reduced cytokine production and pro-inflammatory signaling in the colon tissues of DSS-induced mice. Taking into consideration potential clinical applications, I examined the combinatory effect of TaxB with 5-ASA at sub-clinical doses. Results revealed that combined treatment increased efficacy when compared to 5-ASA or TaxB treatment alone, and the enhanced inhibition was potentially mediated through inhibition of STAT3 signaling. Importantly, no observable adverse interactions between the two drugs were observed in the mice. The above findings provide a solid base of evidence for the clinical advancement of TaxB as an anti-inflammatory treatment for IBD. Lastly, I identified CD14, most well recognized as a co-receptor of TLR4 for the recognition of LPS, as a molecular target of the anti-inflammatory activity of TaxB. TaxB treatment was found to decrease CD14 protein expression while increasing the co-localization of CD14 to lysosomes in LPS-induced macrophages. We, therefore, propose two potential mechanisms where TaxB, (1) competes for membrane CD14 binding with LPS; (2) binds CD14, inducing accumulation of CD14 and lysosomal degradation of CD14, resulting in reduced availability of CD14 for binding LPS and the triggering of inflammatory responses. To conclude, this study presents for the first time, the anti-inflammatory activity, signaling pathway involvement, and CD14 as a molecular target of TaxB, and highlights its potential as an effective therapeutic agent against IBD.