Blockade of tumor necrosis factor-α converting enzyme (TACE) enhances IL-1β and IFN-γ via caspase-1 activation: a probable cause for loss of efficacy of TACE inhibitors in humans?

TNF-α converting enzyme (TACE) is a member of the ADAM (a disintegrin and metalloproteinase) family and is known as ADAM17, which processes precursor TNF-α in order to release soluble TNF-α (sTNF-α). Inhibition of TACE has been effective as a strategy to inhibit arthritis in animal models; however, it has not been translated in the clinic due to lack of efficacy or toxicity. We hypothesized that inhibition of TACE may activate a different pro-inflammatory pathway in human. To investigate this, we studied the effect of TACE inhibitor DPC-333 on cytokine levels in concanavalin A (Con A) activated human peripheral blood mononuclear cells (hPBMC). We have also studied the effects of DPC-333 on Con A induced cytokine levels in mice in vivo or in vitro in whole blood assay. DPC-333 treatment significantly up-regulated IL-1β and IFN-γ in Con A activated hPBMC. In contrast, pre-treatment with DPC-333 effectively suppressed IL-1β and IFN-γ in mice in vivo or in vitro. Interestingly, DPC-333 was found to up-regulate mRNA expression of caspase-1 in hPBMC in a dose dependent fashion and selective caspase-1 inhibitor completely restored DPC-333 induced IL-1β and IFN-γ. Furthermore, selective IL-1β receptor antagonist (anakinra) prevented DPC-333 induced IFN-γ. In conclusion, our data demonstrates that blockade of TACE enhances IL-1β in a caspase-1 dependent manner in vitro in hPBMC and the elevation of IFN-γ is secondarily mediated via IL-1β. This novel finding might explain the possible cause behind the loss of efficacy of TACE inhibitors in human.