Mutually enhancing anti-inflammatory activities of dimethyl fumarate and NF-κB inhibitors – implications for dose-sparing combination therapies

Fumaric acid esters, dimethyl fumarate (DMF) in particular, have been established for the therapy of psoriasis and, more recently, multiple sclerosis. In the light of therapy-limiting dose-dependent side effects, such as gastrointestinal irritation, reducing the effective doses of FAE is a worthwhile goal. In search of strategies to maintain the anti-inflammatory activity of DMF at reduced concentrations, we found that NF-κB inhibition augmented key anti-inflammatory effects of DMF in two complementary experimental settings in vitro. At non-toxic concentrations, both proteasome inhibition with bortezomib as well as blocking NF-κB activation through KINK-1, a small molecule inhibitor of IKKβ-profoundly enhanced DMF-dependent inhibition of nuclear NF-κB translocation in TNFα-stimulated human endothelial cells. This resulted in significant and selective co-operative down-regulation of endothelial adhesion molecules crucial for leucocyte extravasation, namely E-selectin (CD62E), VCAM-1 (CD106) and ICAM-1 (CD54), on both mRNA and protein levels. Functionally, these molecular changes led to synergistically decreased rolling and firm adhesion of human lymphocytes on TNF-activated endothelial cells, as demonstrated in a dynamic flow chamber system. If our in vitro findings can be translated into clinical settings, it is conceivable that anti-inflammatory effects of DMF can be achieved with lower doses than currently used, thus potentially reducing unwanted side effects.