A potent and selective Kallikrein-5 inhibitor delivers high pharmacological activity in Netherton Syndrome patient skin.

ABSTRACT Regulation of proteolytic activity in the skin plays a pivotal role in epidermal homeostasis. This is best exemplified in Netherton Syndrome (NS), a severe genetic skin condition caused by loss-of-function mutations in SPINK5 encoding LEKTI, a serine protease inhibitor which regulates kallikrein-related peptidase (KLK) 5, 7 and 14 activities. KLK5 plays a central role in stratum corneum shedding and inflammatory cell signaling, activates KLK7 and KLK14 and is therefore an optimal therapeutic target. We aimed to identify a potent and selective small molecule inhibitor of KLK5 amenable to epidermal delivery. GSK951 was identified using a structure-based design strategy and showed a half maximal inhibitory concentration of 250pM for KLK5 and greater than 100-fold selectivity over KLK7 and KLK14. Co-crystal structure analysis identified the critical catalytic site interactions to a surrogate for KLK5. Topical application of GSK951-containing cream inhibited KLK5 activity in TgKLK5 mouse skin, reduced trans-epidermal water loss and decreased pro-inflammatory cytokine expression. GSK951 achieved high concentrations in healthy human epidermis following topical application in a cream formulation. Finally, KLK5 protease activity was increased in NS-patient stratum corneum and significantly inhibited by GSK951. These findings unveil a KLK5-specific small molecule inhibitor with a high therapeutic potential for NS patients.