Clinical and Molecular Effects of Interleukin-17 Pathway Blockade in Psoriasis

The interleukin-17 (IL-17) pathway plays a crucial role in the development of psoriasis. Briefly, naive T cells differentiate into helper T (Th17) cells through interaction with activated dendritic cells in the presence of IL-23, Th17 cells produce IL-17 cytokines, and keratinocytes stimulated by IL-17 ligands lead to aberrant differentiation and proliferation that promote production of proinflammatory chemokines and further recruitment of inflammatory cells, setting up a positive feedback loop. Currently, 3 US Food and Drug Administration–approved agents to treat psoriasis affect the IL-17 pathway: brodalumab, secukinumab, and ixekizumab. Brodalumab is a fully human IL-17 receptor A antagonist that blocks signaling of multiple downstream inflammatory cytokines involved in psoriasis. Secukinumab and ixekizumab selectively bind to and neutralize only IL-17A. Pharmacologic effects in patients with psoriasis include decreased keratinocyte hyperproliferation, reduced epidermal thickening, decreased inflammatory markers, and resolution of histologic and genomic features of psoriasis. In clinical trials, therapeutic doses of brodalumab, secukinumab, and ixekizumab have demonstrated skin clearance efficacy by psoriasis area and severity index and static physician’s global assessment scores at 12 weeks. The immunomodulation of these agents is associated with a favorable safety profile. Overall, the clinical improvement and normalization of genetic hallmarks of psoriasis provide a strong case for the unique role of IL-17 receptor blocking as a therapeutic mechanism of action to treat psoriasis. Understanding the unique mechanisms by which treatments interact with the IL-17 pathway to inhibit downstream proinflammatory signal cascade can help physicians make informed treatment decisions when selecting the appropriate medication for patients. J Drugs Dermatol. 2020;19(2)138-143. doi:10.36849/JDD.2020.4645