Novel Class of LIM-Kinase 2 Inhibitors for the Treatment of Ocular Hypertension and Associated Glaucoma

Tetrahydropyridine LIMK inhibitors: Structure activity studies and biological characterization

LIM Kinases, LIMK1 and LIMK2, have become promising targets for the development of inhibitors with potential application for the treatment of several major diseases. LIMKs play crucial roles in cytoskeleton remodeling as downstream effectors of small G proteins of the Rho-GTPase family, and as major regulators of cofilin, an actin depolymerizing factor. In this article we describe the conception, synthesis, and biological evaluation of novel tetrahydropyridine pyrrolopyrimidine LIMK inhibitors. Homology models were first constructed to better understand the binding mode of our preliminary compounds and to explain differences in biological activity. A library of over 60 products was generated and in vitro enzymatic activities were measured in the mid to low nanomolar range. The most promising derivatives were then evaluated in cell on cofilin phosphorylation inhibition which led to the identification of 52 which showed excellent selectivity for LIMKs in a kinase selectivity panel. We also demonstrated that 52 affected the cell cytoskeleton by disturbing actin filaments. Cell migration studies with this derivative using three different cell lines displayed a significant effect on cell motility. Finally, the crystal structure of the kinase domain of LIMK2 complexed with 52 was solved, greatly improving our understanding of the interaction between 52 and LIMK2 active site. The reported data represent a basis for the development of more efficient LIMK inhibitors for future in vivo preclinical validation.

Practical Three-Component Regioselective Synthesis of Drug-Like 3-Aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines as Potential Non-Covalent Multi-Targeting Inhibitors To Combat Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are one of the prominent health challenges facing contemporary society, and many efforts have been made to overcome and (or) control it. In this research paper, we described a practical one-pot two-step three-component reaction between 3,4-dihydronaphthalen-1(2H)-one (1), aryl(or heteroaryl)glyoxal monohydrates (2a-h), and hydrazine monohydrate (NH2NH2•H2O) for the regioselective preparation of some 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnoline derivatives (3a-h). After synthesis and characterization of the mentioned cinnolines (3a-h), the in silico multi-targeting inhibitory properties of these heterocyclic scaffolds have been investigated upon various Homo sapiens-type enzymes, including hMAO-A, hMAO-B, hAChE, hBChE, hBACE-1, hBACE-2, hNQO-1, hNQO-2, hnNOS, hiNOS, hPARP-1, hPARP-2, hLRRK-2(G2019S), hGSK-3β, hp38α MAPK, hJNK-3, hOGA, hNMDA receptor, hnSMase-2, hIDO-1, hCOMT, hLIMK-1, hLIMK-2, hRIPK-1, hUCH-L1, hPARK-7, and hDHODH, which have confirmed their functions and roles in the neurodegenerative diseases (NDs), based on molecular docking studies, and the obtained results were compared with a wide range of approved drugs and well-known (with IC50, EC50, etc.) compounds. In addition, in silico ADMET prediction analysis was performed to examine the prospective drug properties of the synthesized heterocyclic compounds (3a-h). The obtained results from the molecular docking studies and ADMET-related data demonstrated that these series of 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines (3a-h), especially hit ones, can really be turned into the potent core of new drugs for the treatment of neurodegenerative diseases (NDs), and/or due to the having some reactionable locations, they are able to have further organic reactions (such as cross-coupling reactions), and expansion of these compounds (for example, with using other types of aryl(or heteroaryl)glyoxal monohydrates) makes a new avenue for designing novel and efficient drugs for this purpose.

Comparative Analysis of Small-Molecule LIMK1/2 Inhibitors: Chemical Synthesis, Biochemistry, and Cellular Activity

LIM domain kinases 1 and 2 (LIMK1 and LIMK2) regulate actin dynamics and subsequently key cellular functions such as proliferation and migration. LIMK1 and LIMK2 phosphorylate and inactivate cofilin leading to increased actin polymerization. As a result, LIMK inhibitors are emerging as a promising treatment strategy for certain cancers and neurological disorders. High-quality chemical probes are required if the role of these kinases in health and disease is to be understood. To that end, we report the results of a comparative assessment of 17 reported LIMK1/2 inhibitors in a variety of in vitro enzymatic and cellular assays. Our evaluation has identified three compounds (TH-257, LIJTF500025, and LIMKi3) as potent and selective inhibitors suitable for use as in vitro and in vivo pharmacological tools for the study of LIMK function in cell biology.

Novel insight into the role of clusterin on intraocular pressure regulation by modifying actin polymerization and extracellular matrix remodeling in the trabecular meshwork

This study provides comprehensive mechanistic evidence for the role of clusterin, a stress-response secretory chaperone protein, in the modulation of intraocular pressure (IOP) by regulating the trabecular meshwork (TM) actin cytoskeleton and the extracellular matrix (ECM). The pathological stressors on TM known to elevate IOP significantly lowered clusterin protein levels indicating stress-related clusterin function loss. Small interfering RNA-mediated clusterin loss in human TM cells in vitro induced actin polymerization and stabilization via protein kinase D1, serine/threonine-protein kinase N2 (PRK2), and LIM kinase 1 (LIMK1), and the recruitment and activation of adhesome proteins including paxillin, vinculin, and integrin αV and β5. A complete loss of clusterin as seen in clusterin knockout mice (Clu-/- ) led to significant IOP elevation at postnatal Day 70. Contrarily, constitutive clusterin expression using adenovirus (AdCLU) in HTM cells resulted in the loss of actin polymerization via decreased PRK2, and LIMK1 and negative regulation of integrin αV and β5. Furthermore, we found that AdCLU treatment in HTM cells significantly decreased the ECM protein expression and distribution by significantly increasing matrix metalloprotease 2 (MMP2) activity and lowering the levels of pro-fibrotic proteins such as transforming growth factor-β2 (TGFβ2), thrombospondin-1 (TSP-1), and plasminogen activator inhibitor-1 (PAI-1). Finally, we found that HTM cells supplemented with recombinant human clusterin attenuated the pro-fibrotic effects of TGFβ2. For the first time this study demonstrates the importance of clusterin in the regulation of TM actin cytoskeleton - ECM interactions and the maintenance of IOP, thus making clusterin an interesting target to reverse elevated IOP.

LIM Kinases, Promising but Reluctant Therapeutic Targets: Chemistry and Preclinical Validation In Vivo

LIM Kinases are important actors in the regulation of cytoskeleton dynamics by controlling microtubule and actin filament turnover. The signaling pathways involving LIM kinases for actin filament remodeling are well established. They are downstream effectors of small G proteins of the Rho-GTPases family and have become promising targets for the treatment of several major diseases because of their position at the lower end of these signaling cascades. Cofilin, which depolymerizes actin filaments, is the best-known substrate of these enzymes. The phosphorylation of cofilin to its inactive form by LIM kinases avoids actin filament depolymerization. The balance between phosphorylated and non-phosphorylated cofilin is thought to play an important role in tumor cell invasion and metastasis. Since 2006, many small molecules have been developed for LIMK inhibition, and in this review article, we will discuss the structure–activity relationships of the few inhibitor families that have been tested in vivo on different pathological models.

Deciphering the conformational transitions of LIMK2 active and inactive states to ponder specific druggable states through microsecond scale molecular dynamics simulation

LIMK2 inhibitors are one of the potential therapeutic modalities for treating various diseases. In the current scenario, there is a paucity of effective LIMK inhibitors that are highly specific with minimal off-target effects. To date, the conformational transitions of LIMK2 from DFG_inαC_in (CIDI) (active) to DFG_outαC_out (CODO) (inactive) states are yet to be probed and are essential for capturing the unique, druggable conformations. Therefore, this study was intended to capture the diverse conformational states of LIMK2 for accelerating the rational identification of conformation specific inhibitors through high-end structural bioinformatics protocols. Hence, in this study, molecular modelling followed by an extensive microsecond timescale of molecular dynamics simulation was performed encompassing perturbation response scanning, metapath, and community analysis towards the conformational sampling of LIMK2. Overall this study precisely identifies the conformational ensemble of LIMK2 the intermediate inactive states namely, CIDO, CinterDinter, CIDinter, CinterDI, CinterDO, CODI, CODinter apart from CIDI and CODO. This also facilitated observing that β8 preceding XDFG, αC (F373, L374), and αD (L413) as the major effectors that may facilitate the regulation of varying conformational transitions among the states. Additionally, the conserved β sheets and the loops namely, C.l, b.l, and G/P.loop were observed to be involved in the metapath for allosteric communication among the intermediates with CIDI and CODO state. Moreover, only the CODO state was observed to have closed type A.l, while the CIDI and other intermediate states except for CIDO were observed to have open-DFG out type A.l, thereby enabling the binding of substrate. Apart from these, the druggable site analysis inferred that the CIDI and CODO states harbor prominent druggable sites spanning the conserved N-lobe, while the intermediates were observed to have unraveled allosteric druggable sites distal from the ATP binding site, majorly spanning the C-lobe of LIMK2. Thus, this study provides potential insights into the intermediate conformational druggable states of LIMK2 and also the druggable conformations, especially the inactive states of LIMK2, as a specific therapeutic targeting mode. Thus, providing a widened avenue to ponder the allosteric sites or the isoform selectivity conformations for targeting LIMK2 in various disease conditions.

The Nature of Diamino Linker and Halogen Bonding Define Selectivity of Pyrrolopyrimidine-Based LIMK1 Inhibitors

The LIM-domain kinase (LIMK) family consists of two isoforms, LIMK1 and LIMK2, which are highly homologous, making selective inhibitor development challenging. LIMK regulates dynamics of the actin cytoskeleton, thereby impacting many cellular functions including cell morphology and motility. Here, we designed and synthesised analogues of a known pyrrolopyrimidine LIMK inhibitor with moderate selectivity for LIMK1 over LIMK2 to gain insights into which features contribute to both activity and selectivity. We incorporated a different stereochemistry around a cyclohexyl central moiety to achieve better selectivity for different LIMK isoforms. Inhibitory activity was assessed by kinase assays, and biological effects in cells were determined using an in vitro wound closure assay. Interestingly, a slight change in stereochemistry alters LIMK isoform selectivity. Finally, a docking study was performed to predict how the new compounds interact with the target.

High-Throughput Screening of Mouse Gene Knockouts Identifies Established and Novel High Body Fat Phenotypes

PURPOSE

Obesity is a major public health problem. Understanding which genes contribute to obesity may better predict individual risk and allow development of new therapies. Because obesity of a mouse gene knockout (KO) line predicts an association of the orthologous human gene with obesity, we reviewed data from the Lexicon Genome5000TM high throughput phenotypic screen (HTS) of mouse gene KOs to identify KO lines with high body fat.

MATERIALS AND METHODS

KO lines were generated using homologous recombination or gene trapping technologies. HTS body composition analyses were performed on adult wild-type and homozygous KO littermate mice from 3758 druggable mouse genes having a human ortholog. Body composition was measured by either DXA or QMR on chow-fed cohorts from all 3758 KO lines and was measured by QMR on independent high fat diet-fed cohorts from 2488 of these KO lines. Where possible, comparisons were made to HTS data from the International Mouse Phenotyping Consortium (IMPC).

RESULTS

Body fat data are presented for 75 KO lines. Of 46 KO lines where independent external published and/or IMPC KO lines are reported as obese, 43 had increased body fat. For the remaining 29 novel high body fat KO lines, Ksr2 and G2e3 are supported by data from additional independent KO cohorts, 6 (Asnsd1, Srpk2, Dpp8, Cxxc4, Tenm3 and Kiss1) are supported by data from additional internal cohorts, and the remaining 21 including Tle4, Ak5, Ntm, Tusc3, Ankk1, Mfap3l, Prok2 and Prokr2 were studied with HTS cohorts only.

CONCLUSION

These data support the finding of high body fat in 43 independent external published and/or IMPC KO lines. A novel obese phenotype was identified in 29 additional KO lines, with 27 still lacking the external confirmation now provided for Ksr2 and G2e3 KO mice. Undoubtedly, many mammalian obesity genes remain to be identified and characterized.

Investigational Rho Kinase Inhibitors for the Treatment of Glaucoma

This review provides a comprehensive update on emerging ROCK inhibitors as an innovative treatment option for lowering intraocular pressure (IOP) in glaucoma and aims to describe the structure, mechanism of action, pharmaceutical characteristics, desirable ocular effects, including side effects for each agent. A literature review was conducted using PubMed, Scopus, clinicaltrials.gov, ARVO journals, Cochrane library and Selleckchem. Databases were searched using "investigational Rho kinase inhibitors," and "glaucoma" as keywords. In addition to this building block strategy, successive fractions were employed to further refine the results. Of the several ROCK inhibitors discovered, only two drugs are currently approved for glaucoma treatment; Netarsudil in the USA and Ripasudil in Japan and China. We identified and reviewed 15 agents currently in laboratory or clinical trials. These agents lower IOP mainly by decreasing outflow resistance through pharmacologic relaxation of the trabecular meshwork (TM) cells and reducing episcleral venous pressure. They have an optimistic safety profile; however, conjunctival hyperemia, conjunctival hemorrhage, pain on instillation, and corneal verticillata are common. Other properties such as neuroprotection (enhancing optic nerve blood flow and promoting axonal regeneration), anti-fibrotic activity, and endothelial cell proliferation may improve the visual prognosis and surgical outcomes in glaucoma. In addition, these agents have the potential to work synergistically with other topical glaucoma medications.

Ocular Disease Therapeutics: Design and Delivery of Drugs for Diseases of the Eye

The ocular drug discovery field has evidenced significant advancement in the past decade. The FDA approvals of Rhopressa, Vyzulta, and Roclatan for glaucoma, Brolucizumab for wet age-related macular degeneration (wet AMD), Luxturna for retinitis pigmentosa, Dextenza (0.4 mg dexamethasone intracanalicular insert) for ocular inflammation, ReSure sealant to seal corneal incisions, and Lifitegrast for dry eye represent some of the major developments in the field of ocular therapeutics. A literature survey also indicates that gene therapy, stem cell therapy, and target discovery through genomic research represent significant promise as potential strategies to achieve tissue repair or regeneration and to attain therapeutic benefits in ocular diseases. Overall, the emergence of new technologies coupled with first-in-class entries in ophthalmology are highly anticipated to restructure and boost the future trends in the field of ophthalmic drug discovery. This perspective focuses on various aspects of ocular drug discovery and the recent advances therein. Recent medicinal chemistry campaigns along with a brief overview of the structure-activity relationships of the diverse chemical classes and developments in ocular drug delivery (ODD) are presented.

LIM kinase 2 (LIMK2) may play an essential role in platelet function

Actin filaments are highly dynamic structures involved in many cellular processes including cell-to-cell/substrate association and cell motility. The actin cytoskeleton is tightly regulated by actin-binding proteins, which include the members of the ADF (actin-depolymerizing factor)/cofilin family. The members of the LIM kinase family of proteins (LIMK1 and 2) regulate actin dynamics by controlling the binding affinity of ADF/cofilin towards actin. LIMK2 has two major splice variants, LMK2a and LIMK2b. We have generated mice lacking LIMK2a expression (LIMK2a KO), to study its specific role in the regulation of the actin cytoskeleton. The LIMK2a KO mice showed a significant prolonged bleeding complication upon injuries compared to wild type mice. This prolonged bleeding prompted us to check the expression of the LIMK2 protein in platelets as it was previously suggested that it is not expressed in platelets. We showed that human and mouse express LIMK2 in platelets and using our LIMK2a KO mice we have identified a potential key role for LIMK2 in platelet functions including platelet spreading, aggregation and thrombus formation.

Development of novel therapeutics for the treatment of glaucoma based on actin-binding kinase inhibition – in silico approach

QSAR modeling with computer-aided drug design were used for the in silico development of novel therapeutics for glaucoma treatment.

Pharmacological inhibition of LIM kinase pathway impairs platelets functionality and facilitates thrombolysis

Actin is highly abundant in platelets, and its function is dependent on its structure. Actin filaments (F-actin) are dynamic structures involved in many cellular processes including platelet shape changes and adhesion. The actin cytoskeleton is tightly regulated by actin-binding proteins, which include members of the actin depolymerising factor (ADF)/cofilin family. LIM kinase (LIMK) and its phosphatase slingshot (SSH-1L) regulate actin dynamics by controlling the binding affinity of ADF/cofilin towards actin. We hypothesised that the inhibition of LIMK activity may prevent the changes in platelet shape and their function during activation by controlling the dynamics of F-actin. Our results demonstrate that in platelet, inhibition of LIMK by small LIMK inhibitors controls the level of filamentous actin leading to decreased platelet adhesion and aggregation. These findings encourage further studies on controlling platelet function via the cytoskeleton.

Targeting Serotonin 2A and Adrenergic α1 Receptors for Ocular Antihypertensive Agents: Discovery of 3,4-Dihydropyrazino[1,2-b]indazol-1(2H)-one Derivatives

Glaucoma affects millions of people worldwide and causes optic nerve damage and blindness. The elevation of the intraocular pressure (IOP) is the main risk factor associated with this pathology, and decreasing IOP is the key therapeutic target of current pharmacological treatments. As potential ocular hypotensive agents, we studied compounds that act on two receptors (serotonin 2A and adrenergic α₁ ) linked to the regulation of aqueous humour dynamics. Herein we describe the design, synthesis, and pharmacological profiling of a series of novel bicyclic and tricyclic N2-alkyl-indazole-amide derivatives. This study identified a 3,4-dihydropyrazino[1,2-b]indazol-1(2H)-one derivative with potent serotonin 2A receptor antagonism, >100-fold selectivity over other serotonin subtype receptors, and high affinity for the α₁ receptor. Moreover, upon local administration, this compound showed superior ocular hypotensive action in vivo relative to the clinically used reference compound timolol.

Recent advances in the rational design and development of LIM kinase inhibitors are not enough to enter clinical trials

LIM kinases are involved in various pathophysiological processes that depend on actin organization. Alteration of microtubule dynamics by LIMK dysregulation is in fact related to tumor progression and metastasis, viral infection, and ocular diseases, such as glaucoma. As a consequence, many efforts have been done in recent years to rationally design small molecules able to inhibit LIMK activity selectively, without affecting other kinases. As a result, compounds optimized in terms of binding affinity and pharmacokinetic parameters have been discovered, that however failed to access clinical trials. In this review, a comprehensive survey of recent LIMK inhibitors is reported, together with SAR considerations and optimization processes.

LIM kinases: cofilin and beyond

LIM kinases are common downstream effectors of several signalization pathways and function as a signaling node that controls cytoskeleton dynamics through the phosphorylation of the cofilin family proteins. These last 10 years, several reports indicate that the functions of LIM kinases are more extended than initially described and, specifically, that LIM kinases also control microtubule dynamics, independently of their regulation of actin microfilament. In this review we analyze the data supporting these conclusions and the possible mechanisms that could be involved in the control of microtubules by LIM kinases. The demonstration that LIM kinases also control microtubule dynamics has pointed to new therapeutic opportunities. Consistently, several new LIM kinase inhibitors have been recently developed. We provide a comprehensive comparison of these inhibitors, of their chemical structure, their specificity, their cellular effects as well as their effects in animal models of various diseases including cancer.

Novel Therapeutics in Glaucoma Management

BACKGROUND

Glaucoma is a progressive optic neuropathy characterized by retinal ganglion cell death and alterations of visual field. Elevated intraocular pressure (IOP) is considered the main risk factor of glaucoma, even though other factors cannot be ruled out, such as epigenetic mechanisms.

OBJECTIVE

An overview of the ultimate promising experimental drugs to manage glaucoma has been provided.

RESULTS

In particular, we have focused on purinergic ligands, KATP channel activators, gases (nitric oxide, carbon monoxide and hydrogen sulfide), non-glucocorticoid steroidal compounds, neurotrophic factors, PI3K/Akt activators, citicoline, histone deacetylase inhibitors, cannabinoids, dopamine and serotonin receptors ligands, small interference RNA, and Rho kinase inhibitors.

CONCLUSIONS

The review has been also endowed of a brief chapter on last reports about potential neuroprotective benefits of anti-glaucoma drugs already present in the market.

Design, synthesis and preliminary biological evaluation of new [1,2,3]triazolo[4,5-d]pyrimidine/thiourea hybrids as antiproliferative agents

A series of new [1,2,3]triazolo[4,5-d]pyrimidine/thiourea hybrids were designed and synthesized through the scaffold replacement/ring cleavage strategy. SARs studies revealed that the N-heteroarene moiety attached to the thiourea is preferred over the phenyl ring for the R² substituents, while the hydrophobic aromatic group is beneficial for improving the activity. Among these compounds, compound 5r significantly inhibited cell growth of lung cancer cell lines H1650 and A549 (IC₅₀ = 1.91, 3.28 μM, respectively), but was less toxic against the normal cell line GES-1 (IC₅₀ = 27.43 μM). Mechanistic studies showed that compound 5r could remarkably inhibit the colony formation of H1650 cells, induced apoptosis possibly through the intrinsic apoptotic pathways, and arrested the cell cycle at G2/M phase. Our studies suggest that the [1,2,3]triazolo[4,5-d]pyrimidine/thiourea hybrids are a new class of chemotypes possessing interesting antiproliferative activity against lung cancer cells and could be potentially utilized for designing new antitumor agents.

Discovery of Novel Small-Molecule Inhibitors of LIM Domain Kinase for Inhibiting HIV-1

A dynamic actin cytoskeleton is necessary for viral entry, intracellular migration, and virion release. For HIV-1 infection, during entry, the virus triggers early actin activity by hijacking chemokine coreceptor signaling, which activates a host dependency factor, cofilin, and its kinase, the LIM domain kinase (LIMK). Although knockdown of human LIM domain kinase 1 (LIMK1) with short hairpin RNA (shRNA) inhibits HIV infection, no specific small-molecule inhibitor of LIMK has been available. Here, we describe the design and discovery of novel classes of small-molecule inhibitors of LIMK for inhibiting HIV infection. We identified R10015 as a lead compound that blocks LIMK activity by binding to the ATP-binding pocket. R10015 specifically blocks viral DNA synthesis, nuclear migration, and virion release. In addition, R10015 inhibits multiple viruses, including Zaire ebolavirus (EBOV), Rift Valley fever virus (RVFV), Venezuelan equine encephalitis virus (VEEV), and herpes simplex virus 1 (HSV-1), suggesting that LIMK inhibitors could be developed as a new class of broad-spectrum antiviral drugs.

IMPORTANCE The actin cytoskeleton is a structure that gives the cell shape and the ability to migrate. Viruses frequently rely on actin dynamics for entry and intracellular migration. In cells, actin dynamics are regulated by kinases, such as the LIM domain kinase (LIMK), which regulates actin activity through phosphorylation of cofilin, an actin-depolymerizing factor. Recent studies have found that LIMK/cofilin are targeted by viruses such as HIV-1 for propelling viral intracellular migration. Although inhibiting LIMK1 expression blocks HIV-1 infection, no highly specific LIMK inhibitor is available. This study describes the design, medicinal synthesis, and discovery of small-molecule LIMK inhibitors for blocking HIV-1 and several other viruses and emphasizes the feasibility of developing LIMK inhibitors as broad-spectrum antiviral drugs.

Regulation of intraocular pressure by microRNA cluster miR-143/145

Glaucoma is a major cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP), which causes optic nerve damage and retinal ganglion cell death, is the primary risk factor for blindness in glaucoma patients. IOP is controlled by the balance between aqueous humor secretion from the ciliary body (CB) and its drainage through the trabecular meshwork (TM). How microRNAs (miRs) regulate IOP and glaucoma in vivo is largely unknown. Here we show that miR-143 and miR-145 expression is enriched in the smooth muscle and trabecular meshwork in the eye. Targeted deletion of miR-143/145 in mice results in significantly reduced IOP, consistent with an ~2-fold increase in outflow facilities. However, aqueous humor production in the same mice appears to be normal based on a microbeads-induced glaucoma model. Mechanistically, we found that miR-143/145 regulates actin dynamics and the contractility of TM cells, consistent with its regulation of actin-related protein complex (ARPC) subunit 2, 3, and 5, as well as myosin light chain kinase (MLCK) in these cells. Our data establish miR-143/145 as important regulators of IOP, which may have important therapeutic implications in glaucoma.

LIM kinase/cofilin dysregulation promotes macrothrombocytopenia in severe von Willebrand disease-type 2B

von Willebrand disease type 2B (VWD-type 2B) is characterized by gain-of-function mutations of von Willebrand factor (vWF) that enhance its binding to platelet glycoprotein Ibα and alter the protein's multimeric structure. Patients with VWD-type 2B display variable extents of bleeding associated with macrothrombocytopenia and sometimes with thrombopathy. Here, we addressed the molecular mechanism underlying the severe macrothrombocytopenia both in a knockin murine model for VWD-type 2B by introducing the p.V1316M mutation in the murine Vwf gene and in a patient bearing this mutation. We provide evidence of a profound defect in megakaryocyte (MK) function since: (a) the extent of proplatelet formation was drastically decreased in 2B MKs, with thick proplatelet extensions and large swellings; and (b) 2B MKs presented actin disorganization that was controlled by upregulation of the RhoA/LIM kinase (LIMK)/cofilin pathway. In vitro and in vivo inhibition of the LIMK/cofilin signaling pathway rescued actin turnover and restored normal proplatelet formation, platelet count, and platelet size. These data indicate, to our knowledge for the first time, that the severe macrothrombocytopenia in VWD-type 2B p.V1316M is due to an MK dysfunction that originates from a constitutive activation of the RhoA/LIMK/cofilin pathway and actin disorganization. This suggests a potentially new function of vWF during platelet formation that involves regulation of actin dynamics.

Role of the Rho GTPase/Rho kinase signaling pathway in pathogenesis and treatment of glaucoma: Bench to bedside research

Glaucoma is a leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is considered to be a predominant risk factor for primary open angle glaucoma, the most prevalent form of glaucoma. Although the etiological mechanisms responsible for increased IOP are not completely clear, impairment in aqueous humor (AH) drainage through the conventional or trabecular pathway is recognized to be a primary cause in glaucoma patients. Importantly, lowering of IOP has been demonstrated to reduce progression of vision loss and is a mainstay of treatment for all types of glaucoma. Currently however, there are limited therapeutic options available for lowering IOP especially as it relates to enhancement of AH outflow through the trabecular pathway. Towards addressing this challenge, bench and bedside research conducted over the course of the last decade and a half has identified the significance of inhibiting Rho kinase for lowering IOP. Rho kinase is a downstream effector of Rho GTPase signaling that regulates actomyosin dynamics in numerous cell types. Studies from several laboratories have demonstrated that inhibition of Rho kinase lowers IOP via relaxation of the trabecular meshwork which enhances AH outflow. By contrast, activation of Rho GTPase/Rho kinase signaling in the trabecular outflow pathway increases IOP by altering the contractile, cell adhesive and permeability barrier characteristics of the trabecular meshwork and Schlemm's canal tissues, and by influencing extracellular matrix production and fibrotic activity. This article, written in honor of the late David Epstein, MD, summarizes findings from both basic and clinical studies that have been instrumental for recognition of the importance of the Rho/Rho kinase signaling pathway in regulation of AH outflow, and in the development of Rho kinase inhibitors as promising IOP- lowering agents for glaucoma treatment.

Discovery of Molecular Therapeutics for Glaucoma: Challenges, Successes, and Promising Directions

Glaucoma, a heterogeneous ocular disorder affecting ∼60 million people worldwide, is characterized by painless neurodegeneration of retinal ganglion cells (RGCs), resulting in irreversible vision loss. Available therapies, which decrease the common causal risk factor of elevated intraocular pressure, delay, but cannot prevent, RGC death and blindness. Notably, it is changes in the anterior segment of the eye, particularly in the drainage of aqueous humor fluid, which are believed to bring about changes in pressure. Thus, it is primarily this region whose properties are manipulated in current and emerging therapies for glaucoma. Here, we focus on the challenges associated with developing treatments, review the available experimental methods to evaluate the therapeutic potential of new drugs, describe the development and evaluation of emerging Rho-kinase inhibitors and adenosine receptor ligands that offer the potential to improve aqueous humor outflow and protect RGCs simultaneously, and present new targets and approaches on the horizon.

Tetrahydro-pyrimido-indoles as selective LIMK inhibitors: synthesis, selectivity profiling and structure–activity studies

Extensive structure–activity studies on three different modification sites resulted in a series of LIM kinase inhibitors, containing a novel tricyclic hinge-binding motif based on the pyrrolopyrimidine scaffold.

Discovery, Development, and SAR of Aminothiazoles as LIMK Inhibitors with Cellular Anti-Invasive Properties

As part of a program to develop a small molecule inhibitor of LIMK, a series of aminothiazole inhibitors were discovered by high throughput screening. Scaffold hopping and subsequent SAR directed development led to a series of low nanomolar inhibitors of LIMK1 and LIMK2 that also inhibited the direct biomarker p-cofilin in cells and inhibited the invasion of MDA MB-231-luc cells in a matrigel inverse invasion assay.

Pathogenic microbes manipulate cofilin activity to subvert actin cytoskeleton

Actin-depolymerizing factor (ADF)/cofilin proteins are key players in controlling the temporal and spatial extent of actin dynamics, which is crucial for mediating host-pathogen interactions. Pathogenic microbes have evolved molecular mechanisms to manipulate cofilin activity to subvert the actin cytoskeletal system in host cells, promoting their internalization into the target cells, modifying the replication niche and facilitating their intracellular and intercellular dissemination. The study of how these pathogens exploit cofilin pathways is crucial for understanding infectious disease and providing potential targets for drug therapies.

Bis-aryl urea derivatives as potent and selective LIM kinase (Limk) inhibitors

The discovery/optimization of bis-aryl ureas as Limk inhibitors to obtain high potency and selectivity and appropriate pharmacokinetic properties through systematic SAR studies is reported. Docking studies supported the observed SAR. Optimized Limk inhibitors had high biochemical potency (IC50 < 25 nM), excellent selectivity against ROCK and JNK kinases (>400-fold), potent inhibition of cofilin phosphorylation in A7r5, PC-3, and CEM-SS T cells (IC50 < 1 μM), and good in vitro and in vivo pharmacokinetic properties. In the profiling against a panel of 61 kinases, compound 18b at 1 μM inhibited only Limk1 and STK16 with ≥80% inhibition. Compounds 18b and 18f were highly efficient in inhibiting cell-invasion/migration in PC-3 cells. In addition, compound 18w was demonstrated to be effective on reducing intraocular pressure (IOP) on rat eyes. Taken together, these data demonstrated that we had developed a novel class of bis-aryl urea derived potent and selective Limk inhibitors.

Discovery of novel inhibitors for the treatment of glaucoma

INTRODUCTION

Glaucoma is a neurodegenerative disease with heterogeneous causes that result in retinal ganglionic cell (RGC) death. The discovery of ocular antihypertensives has shifted glaucoma therapy, largely, from surgery to medical intervention. Indeed, several intraocular pressure (IOP)-lowering drugs, with different mechanisms of action and RGC protective property, have been developed.

AREAS COVERED

In this review, the authors discuss the main new class of kinase inhibitors used as glaucoma treatments, which lower IOP by enhancing drainage and/or lowering production of aqueous humor. The authors include novel inhibitors under preclinical evaluation and investigation for their anti-glaucoma treatment. Additionally, the authors look at treatments that are in clinics now and which may be available in the near future.

EXPERT OPINION

Treatment of glaucoma remains challenging because the exact cause is yet to be delineated. Neuroprotection to the optic nerve head is undisputable. The novel Rho-associated kinase inhibitors have the capacity to lower IOP and provide optic nerve and RGC protection. In particular, the S-isomer of roscovitine has the capacity to lower IOP and provide neuroprotection. Combinations of selected drugs, which can provide maximal and sustained IOP-lowering effects as well as neuroprotection, are paramount to the prevention of glaucoma progression. In the near future, microRNA intervention may be considered as a potential therapeutic target.

Discovery and Development of LX7101, a Dual LIM-Kinase and ROCK Inhibitor for the Treatment of Glaucoma

The structure of LX7101, a dual LIM-kinase and ROCK inhibitor for the treatment of ocular hypertension and associated glaucoma, is disclosed. Previously reported LIM kinase inhibitors suffered from poor aqueous stability due to solvolysis of the central urea. Replacement of the urea with a hindered amide resulted in aqueous stable compounds, and addition of solubilizing groups resulted in a set of compounds with good properties for topical dosing in the eye and good efficacy in a mouse model of ocular hypertension. LX7101 was selected as a clinical candidate from this group based on superior efficacy in lowering intraocular pressure and a good safety profile. LX7101 completed IND enabling studies and was tested in a Phase 1 clinical trial in glaucoma patients, where it showed efficacy in lowering intraocular pressure.

Discovery of a Type III Inhibitor of LIM Kinase 2 That Binds in a DFG-Out Conformation

The first allosteric, type III inhibitor of LIM-kinase 2 (LIMK2) is reported. A series of molecules that feature both an N-phenylsulfonamide and tertiary amide were not only very potent at LIMK2 but also were extremely selective against a panel of other kinases. Enzymatic kinetic studies showed these molecules to be noncompetitive with ATP, suggesting allosteric inhibition. X-ray crystallography confirmed that these sulfonamides are a rare example of a type III kinase inhibitor that binds away from the highly conserved hinge region and instead resides in the hydrophobic pocket formed in the DFG-out conformation of the kinase, thus accounting for the high level of selectivity observed.

Theoretical study on the interaction of pyrrolopyrimidine derivatives as LIMK2 inhibitors: insight into structure-based inhibitor design

LIM kinases (LIMKs), downstream of Rho-associated protein kinases (ROCKs) and p21-activated protein kinases (PAKs), are shown to be promising targets for the treatment of cancers. In this study, the inhibition mechanism of 41 pyrrolopyrimidine derivatives as LIMK2 inhibitors was explored through a series of theoretical approaches. First, a model of LIMK2 was generated through molecular homology modeling, and the studied inhibitors were docked into the binding active site of LIMK2 by the docking protocol, taking into consideration the flexibility of the protein. The binding poses predicted by molecular docking for 17 selected inhibitors with different bioactivities complexed with LIMK2 underwent molecular dynamics (MD) simulations, and the binding free energies for the complexes were predicted by using the molecular mechanics/generalized born surface area (MM/GBSA) method. The predicted binding free energies correlated well with the experimental bioactivities (r(2) = 0.63 or 0.62). Next, the free energy decomposition analysis was utilized to highlight the following key structural features related to biological activity: (1) the important H-bond between Ile408 and pyrrolopyrimidine, (2) the H-bonds between the inhibitors and Asp469 and Gly471 which maintain the stability of the DFG-out conformation, and (3) the hydrophobic interactions between the inhibitors and several key residues (Leu337, Phe342, Ala345, Val358, Lys360, Leu389, Ile408, Leu458 and Leu472). Finally, a variety of LIMK2 inhibitors with a pyrrolopyrimidine scaffold were designed, some of which showed improved potency according to the predictions. Our studies suggest that the use of molecular docking with MD simulations and free energy calculations could be a powerful tool for understanding the binding mechanism of LIMK2 inhibitors and for the design of more potent LIMK2 inhibitors.

Damnacanthal, an effective inhibitor of LIM-kinase, inhibits cell migration and invasion

Damnacanthal is identified as an effective inhibitor of LIM-kinase. It inhibits chemotaxis of T-cells and migration and invasion of breast carcinoma cells in culture and hapten-induced migration of epidermal Langerhans cells in mouse ears. Damnacanthal is a useful tool for investigating the cellular and physiological functions of LIM-kinase.

LIM-kinases (LIMKs) play crucial roles in various cell activities, including migration, division, and morphogenesis, by phosphorylating and inactivating cofilin. Using a bimolecular fluorescence complementation assay to detect the actin–cofilin interaction, we screened LIMK1 inhibitors and identified two effective inhibitors, damnacanthal (Dam) and MO-26 (a pyrazolopyrimidine derivative). These compounds have already been shown to inhibit Lck, a Src family tyrosine kinase. However, in vitro kinase assays revealed that Dam inhibited LIMK1 more effectively than Lck. Dam suppressed LIMK1-induced cofilin phosphorylation and deceleration of actin retrograde flow in lamellipodia in N1E-115 cells. Dam impaired CXCL12-induced chemotactic migration of Jurkat T lymphocytes and Jurkat-derived, Lck-deficient JCaM1.6 cells and also inhibited serum-induced migration and invasion of MDA-MB-231 breast carcinoma cells. These results suggest that Dam has the potential to suppress cell migration and invasion primarily through the inhibition of LIMK kinase activity. Topical application of Dam also suppressed hapten-induced migration of epidermal Langerhans cells in mouse ears. Dam provides a useful tool for investigating cellular and physiological functions of LIMKs and holds promise for the development of agents against LIMK-related diseases. The bimolecular fluorescence complementation assay system used in this study will provide a useful method to screen for inhibitors of various protein kinases.

Morphological and hydrodynamic correlations with increasing outflow facility by rho-kinase inhibitor Y-27632

Abstract Rho-kinase inhibitors affect actomyosin cytoskeletal networks and have been shown to significantly increase outflow facility and lower intraocular pressure in various animal models and human eyes. This article summarizes common morphological changes in the trabecular meshwork induced by Rho-kinase inhibitors and specifically compares the morphological and hydrodynamic correlations with increased outflow facility by Rho-kinase inhibitor, Y-27632, in bovine, monkey, and human eyes under similar experimental conditions. Interspecies comparison has shown that morphological changes in the juxtacanalicular connective tissue (JCT) of these 3 species were different. However, these different morphological changes in the JCT, no matter if it's separation between the JCT and inner wall in bovine eyes, or separation between the JCT cells or between the JCT cells and their matrix in monkey eyes, or even no separation between the inner wall and the JCT but a more subtle expansion of the JCT in human eyes, appear to correlate with the increased percent change of outflow facility. More importantly, these different morphological changes all resulted in an increase in effective filtration area, which was positively correlated with increased outflow facility in all 3 species. These results suggest a link among changes in outflow facility, tissue architecture, and aqueous outflow pattern. Y-27632 increases outflow facility by redistributing aqueous outflow through a looser and larger area in the JCT.

Rho kinase inhibitors for treatment of glaucoma

Affecting 60 million patients, glaucoma is the second leading cause of blindness worldwide. Despite the availability of multiple medical and surgical treatments with effective intraocular pressure lowering, many patients still progress to become visually handicapped from glaucoma due to therapeutic failure. There is therefore a great need for novel therapies to improve the standard of care, and Rho kinase (ROCK) inhibitors represent a promising new class of drugs for treatment of glaucoma. ROCK inhibitors act by increasing facility of fluid outflow from the eye, thereby reducing intraocular pressure. ROCK inhibitors also have a vasodilatory effect on conjunctival vessels, which can lead to eye redness, a less than desirable cosmetic side effect for patients that would use this medication. Although there is promising data to support the clinical potential of this class of drug, the occurrence of conjunctival hyperemia remains a potential deterrent for use by patients. Studies are underway to assess alternative dosing strategies, delivery methods and prodrug formulations that may circumvent this unwanted side effect. This review provides an up-to-date account of the basic scientific data, as well as nonclinical and clinical studies to support use of ROCK inhibitors for treatment of glaucoma.

Novel LIMK2 Inhibitor Blocks Panc-1 Tumor Growth in a mouse xenograft model

LIM kinases (LIMKs) are important cell cytoskeleton regulators that play a prominent role in cancer manifestation and neuronal diseases. The LIMK family consists of two homologues, LIMK1 and LIMK2, which differ from one another in expression profile, intercellular localization, and function. The main substrate of LIMK is cofilin, a member of the actin-depolymerizing factor (ADF) protein family. When phosphorylated by LIMK, cofilin is inactive. LIMKs play a contributory role in several neurodevelopmental disorders and in cancer growth and metastasis. We recently reported the development and validation of a novel LIMK inhibitor, referred to here as T56-LIMKi, using a combination of computational methods and classical biochemistry techniques. Here we report that T56-LIMKi inhibits LIMK2 with high specificity, and shows little or no cross-reactivity with LIMK1. We found that T56-LIMKi decreases phosphorylated cofilin (p-cofilin) levels and thus inhibits growth of several cancerous cell lines, including those of pancreatic cancer, glioma and schwannoma. Because the most promising in-vitro effect of T56-LIMKi was observed in the pancreatic cancer cell line Panc-1, we tested the inhibitor on a nude mouse Panc-1 xenograft model. T56-LIMKi reduced tumor size and p-cofilin levels in the Panc-1 tumors, leading us to propose T56-LIMKi as a candidate drug for cancer therapy.

Myxoma virus oncolytic efficiency can be enhanced through chemical or genetic disruption of the actin cytoskeleton

Myxoma virus (MYXV) is one of many animal viruses that exhibit oncolytic properties in transformed human cells. Compared to orthopoxviruses like vaccinia (VACV), MYXV spreads inefficiently, which could compromise its use in treating tumors and their associated metastases. The VACV F11 protein promotes virus exit and rapid spread by inhibiting Rho signalling, which results in a disruption of cortical actin. We have previously shown that although MYXV lacks an F11 homolog, the F11L gene can be introduced into MYXV promoting the spread of this Leporipoxvirus in natural host cells. Here we show that the F11-encoding (F11L⁺) MYXV strain replicates to higher levels in a number of human cancer cells. We also show that F11L⁺ MYXV induces better tumor control and prolonged survival of mice bearing MDA-MB-231 cancer cells. Furthermore, we show that this virus also spreads more efficiently from the site of growth in one injected tumor, to a second untreated tumor.

While we focused mostly on the use of a modified MYXV we were able to show that the effects of F11 on MYXV growth in cancer cells could be mimicked through the use of pharmacological inhibition or siRNA-mediated silencing of key regulators of cortical actin (RhoA, RhoC, mDia1, or LIMK2). These data suggest that it may be possible to increase the oncolytic efficacy of wild-type MYXV using chemical inhibitors of RhoA/C or their downstream targets. Furthermore, since all viruses must overcome barriers to exit posed by structures like cortical actin, these findings suggest that the oncolytic activity of other viruses may be enhanced through similar strategies.

LIM kinase inhibition reduces breast cancer growth and invasiveness but systemic inhibition does not reduce metastasis in mice

Metastasis is the major cause of morbidity and mortality in cancer patients. An understanding of the genes that regulate metastasis and development of therapies to target these genes is needed urgently. Since members of the LIM kinase (LIMK) family are key regulators of the actin cytoskeleton and are involved in cell motility and invasion, LIMK is considered to be a good therapeutic target for metastatic disease. Here we investigated the consequences of LIMK inhibition on growth and metastasis of human and mouse mammary tumors. LIMK activity was reduced in tumor cells by expression of dominant-negative LIMK1, by RNA interference or with a selective LIMK inhibitor. The extent of phosphorylation of the LIMK substrate, cofilin, of proliferation and invasion in 2D and 3D culture and of tumor growth and metastasis in mice were assessed. Inhibition of LIMK activity efficiently reduced the pro-invasive properties of tumor cells in vitro. Tumors expressing dominant-negative LIMK1 grew more slowly and were less metastatic in mice. However, systemic administration of a LIMK inhibitor did not reduce either primary tumor growth or spontaneous metastasis. Surprisingly, metastasis to the liver was increased after administration of the inhibitor. These data raise a concern about the use of systemic LIMK inhibitors for the treatment of metastatic breast cancer.

Signaling mechanisms and functional roles of cofilin phosphorylation and dephosphorylation

Cofilin and actin-depolymerizing factor (ADF) are actin-binding proteins that play an essential role in regulating actin filament dynamics and reorganization by stimulating the severance and depolymerization of actin filaments. Cofilin/ADF are inactivated by phosphorylation at the serine residue at position 3 by LIM-kinases (LIMKs) and testicular protein kinases (TESKs) and are reactivated by dephosphorylation by the slingshot (SSH) family of protein phosphatases and chronophin. This review describes recent advances in our understanding of the signaling mechanisms regulating LIMKs and SSHs and the functional roles of cofilin phospho-regulation in cell migration, tumor invasion, mitosis, neuronal development, and synaptic plasticity. Accumulating evidence demonstrates that the phospho-regulation of cofilin/ADF is a key convergence point of cell signaling networks that link extracellular stimuli to actin cytoskeletal dynamics and that spatiotemporal control of cofilin/ADF activity by LIMKs and SSHs plays a crucial role in a diverse array of cellular and physiological processes. Perturbations in the normal control of cofilin/ADF activity underlie many pathological conditions, including cancer metastasis and neurological and cardiovascular disorders.

Rho-associated coiled-coil kinase (ROCK) protein controls microtubule dynamics in a novel signaling pathway that regulates cell migration

The two members of the Rho-associated coiled-coil kinase (ROCK1 and 2) family are established regulators of actin dynamics that are involved in the regulation of the cell cycle as well as cell motility and invasion. Here, we discovered a novel signaling pathway whereby ROCK regulates microtubule (MT) acetylation via phosphorylation of the tubulin polymerization promoting protein 1 (TPPP1/p25). We show that ROCK phosphorylation of TPPP1 inhibits the interaction between TPPP1 and histone deacetylase 6 (HDAC6), which in turn results in increased HDAC6 activity followed by a decrease in MT acetylation. As a consequence, we show that TPPP1 phosphorylation by ROCK increases cell migration and invasion via modulation of cellular acetyl MT levels. We establish here that the ROCK-TPPP1-HDAC6 signaling pathway is important for the regulation of cell migration and invasion.