Structure guided drug design to develop kallikrein 5 inhibitors to treat Netherton syndrome

French national protocol for the management of congenital ichthyosis

Congenital ichthyoses (CI) comprise a heterogeneous group of monogenic genetic skin diseases characterized by diffuse scaling, often associated with skin inflammation. Diagnosis of the individual form of ichthyosis is complex and is guided by clinical expertise. CI usually has a major impact on quality of life (QOL) and thus requires lifelong treatment. To date, there are no curative therapies, although various symptomatic treatment options exist. The present protocol for the management of CI has been drawn up in accordance with the recommendations published in 2012 by the French National Authority for Health, based on a literature review, with the help and validation of members of the French network for rare skin diseases (FIMARAD). It provides a summary of evidence and expert-based recommendations and is intended to help clinicians with the management of these rare and often complex diseases.

New developments in the molecular treatment of ichthyosis: review of the literature

Ichthyosis covers a wide spectrum of diseases affecting the cornification of the skin. In recent years, new advances in understanding the pathophysiology of ichthyosis have been made. This knowledge, combined with constant development of pathogenesis-based therapies, such as protein replacement therapy and gene therapy, are rather promising for patients with inherited skin diseases. Several ongoing trials are investigating the potency of these new approaches and various studies have already been published. Furthermore, a lot of case series report that biological therapeutics are effective treatment options, mainly for Netherton syndrome and autosomal recessive congenital ichthyosis. It is expected that some of these new therapies will prove their efficacy and will be incorporated in the treatment of ichthyosis.

Phage Display Selected Cyclic Peptide Inhibitors of Kallikrein-Related Peptidases 5 and 7 and Their In Vivo Delivery to the Skin

Kallikrein-related peptidases 5 (KLK5) and 7 (KLK7) are serine proteases with homeostatic functions in the epidermis that play a critical role in Netherton syndrome (NS), a rare yet life-threatening genetic disorder that currently lacks specific treatment. Previous research suggests that controlling KLKs could lead to the development of NS therapies, but existing synthetic inhibitors have limitations. Herein, we used phage display to screen libraries comprising more than 100 billion different cyclic peptides and found selective, high-affinity inhibitors of KLK5 (K_i = 2.2 ± 0.1 nM) and KLK7 (K_i = 16 ± 4 nM). By eliminating protease-prone sites and conjugating the inhibitors to an albumin-binding peptide, we enhanced the inhibitor stability and prolonged the elimination half-life to around 5 h in mice. In tissue sections taken from mice, a fluorescently labeled peptide was detected in the epidermis, suggesting that the inhibitors can reach the KLKs upon systemic delivery and should be suited to control deregulated protease activity in NS.

Cocktails of KLK5 Protease Inhibitors and Anti-TNFα Therapeutics: an Effective Treatment for Netherton Syndrome

Netherton syndrome (NS) is a rare, severe type of ichthyosis, often lethal in neonates, for which there is no therapy. Spink5^-/- mice recapitulate major NS hallmarks and die homogeneously within 5 h from birth due to severe epidermal barrier defect leading to dehydration. Spink5^-/-Klk5^-/- mice survive neonatal lethality, indicating that KLK5 could be a drug target for NS. Nevertheless, after a week, these mice developed epidermal inflammation and signs of barrier defect leading to lethality. Here we tested whether anti-TNFα strategy in combination with anti-KLK5 could provide a long-term effective therapy for NS. Deletion of Tnfa in Spink5^-/- suppressed the inflammatory phenotype but did not rescue neonatal lethality of Spink5^-/- indicating that anti-TNFα therapy alone would not be sufficient to treat NS. Interestingly, in Spink5^-/-Klk5^-/-Tnfa^-/- mice, NS features were rescued, and mice lived normally for 16-18 months. For the first time, evidence is provided that a combination of anti-TNFα and anti-KLK5 therapeutics represents an effective therapeutic strategy for NS. Notably, anti-TNFα factors are marketed and used widely, while LMW KLK5 inhibitors are being developed.

A Potent and Selective Kallikrein-5 Inhibitor Delivers High Pharmacological Activity in Skin from Patients with Netherton Syndrome

Regulation of proteolytic activity in the skin plays a pivotal role in epidermal homeostasis. This is best exemplified in Netherton syndrome, a severe genetic skin condition caused by loss-of-function mutations in the gene serine protease inhibitor Kazal-type 5 encoding lympho-epithelial Kazal-type-related inhibitor, a serine protease inhibitor that regulates kallikrein (KLK)-related peptidase 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 250 pM for KLK5 and greater than 100-fold selectivity over KLK7 and KLK14. Cocrystal 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 transepidermal water loss, and decreased proinflammatory cytokine expression. GSK951 achieved high concentrations in healthy human epidermis following topical application in a cream formulation. Finally, KLK5 protease activity was increased in stratum corneum of patients with Netherton syndrome and significantly inhibited by GSK951. These findings unveil a KLK5-specific small-molecule inhibitor with a high therapeutic potential for patients with Netherton syndrome.