Identification by in silico and in vitro screenings of small organic molecules acting as reversible inhibitors of kallikreins

Assessing the performance of docking, FEP, and MM/GBSA methods on a series of KLK6 inhibitors

Kallikrein 6 (KLK6) is an attractive drug target for the treatment of neurological diseases and for various cancers. Herein, we explore the accuracy and efficiency of different computational methods and protocols to predict the free energy of binding (ΔG_bind) for a series of 49 inhibitors of KLK6. We found that the performance of the methods varied strongly with the tested system. For only one of the three KLK6 datasets, the docking scores obtained with rDock were in good agreement (R² ≥ 0.5) with experimental values of ΔG_bind. A similar result was obtained with MM/GBSA (using the ff14SB force field) calculations based on single minimized structures. Improved binding affinity predictions were obtained with the free energy perturbation (FEP) method, with an overall MUE and RMSE of 0.53 and 0.68 kcal/mol, respectively. Furthermore, in a simulation of a real-world drug discovery project, FEP was able to rank the most potent compounds at the top of the list. These results indicate that FEP can be a promising tool for the structure-based optimization of KLK6 inhibitors.

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.

Specifically targeting cancer proliferation and metastasis processes: the development of matriptase inhibitors

Matriptase is a type II transmembrane serine protease, which has been suggested to play critical roles in numerous pathways of biological developments. Matriptase is the activator of several oncogenic proteins, including urokinase-type plasminogen activator (uPA), hepatocyte growth factor (HGF) and protease-activated receptor 2 (PAR-2). The activations of these matriptase substrates subsequently lead to the generation of plasmin, matrix metalloproteases (MMPs), and the triggers for many other signaling pathways related to cancer proliferation and metastasis. Accordingly, matriptase is considered an emerging target for the treatments of cancer. Thus far, inhibitors of matriptase have been developed as potential anti-cancer agents, which include small-molecule inhibitors, peptide-based inhibitors, and monoclonal antibodies. This review covers established literature to summarize the chemical and biochemical aspects, especially the inhibitory mechanisms and structure-activity relationships (SARs) of matriptase inhibitors with the goal of proposing the strategies for their future developments in anti-cancer therapy.

Discovery and structure-activity relationship of imidazolinylindole derivatives as kallikrein 7 inhibitors

A series of imidazolinylindole derivatives were discovered as novel kallikrein 7 (KLK7, stratum corneum chymotryptic enzyme) inhibitors. Structure-activity relationship (SAR) studies led to the identification of potent human KLK7 inhibitors. By further modification of the benzenesulfonyl moiety to overcome species differences in inhibitory activity, potent inhibitors against both human and mouse KLK7 were identified. Furthermore, the complex structure of 25 with mouse KLK7 could explain the SAR and the cause of the species differences in inhibitory activity.

Jizanpeptins, Cyanobacterial Protease Inhibitors from a Symploca sp. Cyanobacterium Collected in the Red Sea

Jizanpeptins A-E (1-5) are micropeptin depsipeptides isolated from a Red Sea specimen of a Symploca sp. cyanobacterium. The planar structures of the jizanpeptins were established using NMR spectroscopy and mass spectrometry and contain 3-amino-6-hydroxy-2-piperidone (Ahp) as one of eight residues in a typical micropeptin motif, as well as a side chain terminal glyceric acid sulfate moiety. The absolute configurations of the jizanpeptins were assigned using a combination of Marfey's methodology and chiral-phase HPLC analysis of hydrolysis products compared to commercial and synthesized standards. Jizanpeptins A-E showed specific inhibition of the serine protease trypsin (IC50 = 72 nM to 1 μM) compared to chymotrypsin (IC50 = 1.4 to >10 μM) in vitro and were not overtly cytotoxic to HeLa cervical or NCI-H460 lung cancer cell lines at micromolar concentrations.

Kallikrein-related peptidase 7 is a potential target for the treatment of pancreatic cancer

Pancreatic cancer is one of the deadliest cancers with very poor prognosis, and the five-year survival rate of the patients is less than 5% after diagnosis. Kallikrein-related peptidases (KLKs) belong to a serine protease family with 15 members that play important roles in cellular physiological behavior and diseases. The high expression level of KLK7 in pancreatic cancer tissues is considered to be a marker for the poor prognosis of this disease. In this work, we set out to investigate whether KLK7 could be a target for the treatment of pancreatic cancer. Short hairpin RNAs (shRNAs) were designed and constructed in lentivirus to knock down KLK7 in pancreatic cancer cell line PANC-1, and the real time cellular analysis (RTCA) was used to evaluate cell proliferation, migration and invasion abilities. Small molecules inhibiting KLK7 were discovered by computer-aided drug screening and used to inhibit PANC-1 cells. Our results confirmed that KLK7 is significantly up-regulated in pancreatic cancer tissue, and knocking down or inhibiting KLK7 efficiently inhibited the proliferation, migration and invasion of pancreatic cancer cells. This study suggested that KLK7 could be a potential chemotherapy target for treatment of pancreatic cancer, which would provide us a novel strategy for the treatment of this disease.

Discovery and structure-activity relationship study of 1,3,6-trisubstituted 1,4-diazepane-7-ones as novel human kallikrein 7 inhibitors

Compound 1, composed of a 1,3,6-trisubstituted 1,4-diazepane-7-one, was discovered as a novel human kallikrein 7 (KLK7, stratum corneum chymotryptic enzyme, SCCE) inhibitor, and its derivatives were synthesized and evaluated. Structure-activity relationship studies of the amidoxime unit and benzoic acid part of this new scaffold led to the identification of 25 and 34, which were more potent than the hit compound, 1. The X-ray co-crystal structure of compound 25 and human KLK7 revealed the characteristic interactions and enabled explanations of the structure-activity relationship.

The kallikrein-related peptidase family: Dysregulation and functions during cancer progression

Cancer is the second leading cause of death with 14 million new cases and 8.2 million cancer-related deaths worldwide in 2012. Despite the progress made in cancer therapies, neoplastic diseases are still a major therapeutic challenge notably because of intra- and inter-malignant tumour heterogeneity and adaptation/escape of malignant cells to/from treatment. New targeted therapies need to be developed to improve our medical arsenal and counter-act cancer progression. Human kallikrein-related peptidases (KLKs) are secreted serine peptidases which are aberrantly expressed in many cancers and have great potential in developing targeted therapies. The potential of KLKs as cancer biomarkers is well established since the demonstration of the association between KLK3/PSA (prostate specific antigen) levels and prostate cancer progression. In addition, a constantly increasing number of in vitro and in vivo studies demonstrate the functional involvement of KLKs in cancer-related processes. These peptidases are now considered key players in the regulation of cancer cell growth, migration, invasion, chemo-resistance, and importantly, in mediating interactions between cancer cells and other cell populations found in the tumour microenvironment to facilitate cancer progression. These functional roles of KLKs in a cancer context further highlight their potential in designing new anti-cancer approaches. In this review, we comprehensively review the biochemical features of KLKs, their functional roles in carcinogenesis, followed by the latest developments and the successful utility of KLK-based therapeutics in counteracting cancer progression.

Face-to-face with anti-inflammatory therapy for rosacea

In the past, our understanding of rosacea has been inadequate and limited to descriptions of factors that exacerbate and improve the disease. While the pathophysiology of rosacea is complex and multifactorial, cathelicidin peptides have emerged as key players in the pathogenesis of this common dermatological disorder. This article correlates recent findings in abnormal cathelicidin production and proteolytic processing in rosacea with therapeutic actions of current treatment options and, in this way, highlights potential points of intervention for the development of efficient therapeutic alternatives.

Pyrido-imidazodiazepinones as a new class of reversible inhibitors of human kallikrein 7

The human tissue kallikrein-7 (KLK7) is a chymotryptic serine protease member of tissue kallikrein family. KLK7 is involved in skin homeostasis and inflammation. Excess of KLK7 activity is also associated with tumor metastasis processes, especially in ovarian carcinomas, prostatic and pancreatic cancers. Development of Kallikrein 7 inhibitors is thus of great interest in oncology but also for treating skin diseases. Most of the developed synthetic inhibitors present several drawbacks such as poor selectivity and unsuitable physico-chemical properties for in vivo use. Recently, we described a practical sequence for the synthesis of imidazopyridine-fused [1,3]-diazepines. Here, we report the identification of pyrido-imidazodiazepinone core as a new potential scaffold to develop selective and competitive inhibitors of kallikrein-related peptidase 7. Structure-activity relationships (SAR), inhibition mechanisms and selectivity as well as cytotoxicity against selected cancer cell lines were investigated.

Cytotoxic metabolites from the endophytic fungus Penicillium chermesinum: discovery of a cysteine-targeted Michael acceptor as a pharmacophore for fragment-based drug discovery, bioconjugation and click reactions

A novel tetracyclic polyketide uniquely spiro-attached with a γ-lactone ring and a potent cytotoxic agent possessing a thiol-reactive pharmacophore were isolated from the mangrove endophytic fungus Penicillium chermesinum.

Toward the first class of suicide inhibitors of kallikreins involved in skin diseases

The inhibition of kallikreins 5 and 7, and possibly kallikrein 14 and matriptase, (that initiates the kallikrein proteolytic cascade) constitutes an innovative way to treat some skin diseases such as Netherton syndrome. We present here the inhibitory properties of coumarin-3-carboxylate derivatives against these enzymes. Our small collection of these versatile organic compounds was enriched by newly synthesized derivatives in order to obtain molecules selective against one, two, three enzymes or acting on the four ones. We evidenced a series of compounds with IC50 values in the nanomolar range. A suicide mechanism was observed against kallikrein 7 whereas the inactivation was either definitive (suicide type) or transient for kallikreins 5 and 14, and matriptase. Most of these potent inhibitors were devoid of cytotoxicity toward healthy human keratinocytes. In situ zymography investigations on skin sections from human kallikrein 5 transgenic mouse revealed significant reduction of the global proteolytic activity by several compounds.