Protein kinase A in complex with Rho-kinase inhibitors Y-27632, Fasudil, and H-1152P: structural basis of selectivity

The novel ROCK2 selective inhibitor NRL-1049 preserves the blood-brain barrier after acute injury

Endothelial blood-brain barrier (BBB) dysfunction is critical in the pathophysiology of brain injury. Rho-associated protein kinase (ROCK) activation disrupts BBB integrity in the injured brain. We aimed to test the efficacy of a novel ROCK2 inhibitor in preserving the BBB after acute brain injury. We characterized the molecular structure and pharmacodynamic and pharmacokinetic properties of a novel selective ROCK2 inhibitor, NRL-1049, and its first metabolite, 1-hydroxy-NRL-1049 (referred to as NRL-2017 hereon) and tested the efficacy of NRL-1049 on the BBB integrity in rodent models of acute brain injury. Our data show that NRL-1049 and NRL-2017 both inhibit ROCK activity and are 44-fold and 17-fold more selective towards ROCK2 than ROCK1, respectively. When tested in a mouse model of cortical cryoinjury, NRL-1049 significantly attenuated the increase in water content. Interestingly, 60% of the mice in the vehicle arm developed seizures within 2 hours after cryoinjury versus none in the NRL-1049 arm. In spontaneously hypertensive rats, NRL-1049 attenuated the dramatic surge in Evans Blue extravasation compared with the vehicle arm after transient middle cerebral artery occlusion. Hemorrhagic transformation was also reduced. We show that NRL-1049, a selective ROCK2 inhibitor, is a promising drug candidate to preserve the BBB after brain injury.

Rho-Associated Protein Kinase Activity Is Required for Tissue Homeostasis in the Xenopus laevis Ciliated Epithelium

Lung epithelial development relies on the proper balance of cell proliferation and differentiation to maintain homeostasis. When this balance is disturbed, it can lead to diseases like cancer, where cells undergo hyperproliferation and then can undergo migration and metastasis. Lung cancer is one of the deadliest cancers, and even though there are a variety of therapeutic approaches, there are cases where treatment remains elusive. The rho-associated protein kinase (ROCK) has been thought to be an ideal molecular target due to its role in activating oncogenic signaling pathways. However, in a variety of cases, inhibition of ROCK has been shown to have the opposite outcome. Here, we show that ROCK inhibition with y-27632 causes abnormal epithelial tissue development in Xenopus laevis embryonic skin, which is an ideal model for studying lung cancer development. We found that treatment with y-27632 caused an increase in proliferation and the formation of ciliated epithelial outgrowths along the tail edge. Our results suggest that, in certain cases, ROCK inhibition can disturb tissue homeostasis. We anticipate that these findings could provide insight into possible mechanisms to overcome instances when ROCK inhibition results in heightened proliferation. Also, these findings are significant because y-27632 is a common pharmacological inhibitor used to study ROCK signaling, so it is important to know that in certain in vivo developmental models and conditions, this treatment can enhance proliferation rather than lead to cell cycle suppression.

Isoform selectivities of novel 4-hydroxycoumarin imines as inhibitors of myosin II

Muscle myosin inhibition could be used to treat many medical conditions involving hypercontractile states, including muscle spasticity, chronic musculoskeletal pain, and hypertrophic cardiomyopathy. A series of 13 advanced analogs of 3-(N-butylethanimidoyl)ethyl)-4-hydroxy-2H-chromen-2-one (BHC) were synthesized to explore extended imine nitrogen side chains and compare aldimines vs. ketimines. None of the new analogs inhibit nonmuscle myosin in a cytokinesis assay. ATPase structure-activity relationships reveal that selectivity for cardiac vs. skeletal myosin can be tuned with subtle structural changes. None of the compounds inhibited smooth muscle myosin II. Docking the compounds to homology models of cardiac and skeletal myosin II gave rationales for the effects of side arm length on inhibition selectivity and for cardiac vs. skeletal myosin. Properties including solubility, stability and toxicity, suggest that certain BHC analogs may be useful as candidates for preclinical studies or as lead compounds for advanced candidates for drugs with cardiac or skeletal muscle myosin selectivity.

Reduction of Phosphorylated Tau in Alzheimer's Disease Induced Pluripotent Stem Cell-Derived Neuro-Spheroids by Rho-Associated Coiled-Coil Kinase Inhibitor Fasudil

BACKGROUND

Alzheimer's disease (AD) is the most predominant form of dementia. Rho-associated coiled coil kinase (ROCK) inhibitor, fasudil, is one of the candidate drugs against the AD progression.

OBJECTIVE

We aimed to investigate possible changes of AD associated markers in three-dimensional neuro-spheroids (3D neuro-spheroids) generated from induced pluripotent stem cells derived from AD patients or healthy control subjects (HC) and to determine the impact of pharmacological intervention with the ROCK inhibitor fasudil.

METHODS

We treated 3D neuro-spheroids with fasudil and tested the possible effect on AD markers by ELISA, transcriptomic and proteomic analyses.

RESULTS

Transcriptomic analysis revealed a reduction in the expression of AKT serine/threonine-protein kinase 1 (AKT1) in AD neuro-spheroids, compared to HC. This decrease was reverted in the presence of fasudil. Proteomic analysis showed up- and down-regulation of proteins related to AKT pathway in fasudil-treated neuro-spheroids. We found an evident increase of phosphorylated tau at four different residues (pTau181, 202, 231, and 396) in AD compared to HC-derived neuro-spheroids. This was accompanied by a decrease of secreted clusterin (clu) and an increase of intracellular clu levels in AD patient-derived neuro-spheroids. Increases of phosphorylated tau in AD patient-derived neuro-spheroids were suppressed in the presence of fasudil.

CONCLUSIONS

Fasudil modulates clu protein levels and enhances AKT1 that results in the suppression of AD associated tau phosphorylation.

Hsp70–Bag3 Module Regulates Macrophage Motility and Tumor Infiltration via Transcription Factor LITAF and CSF1

Simple Summary

Patients’ normal cells, such as lymphocytes, fibroblasts, or macrophages, can either suppress or facilitate tumor growth. Macrophages can infiltrate tumors and secrete molecules that enhance the proliferation of cancer cells and their invasion into neighboring tissues and blood. Here, we investigated the mechanism of action of a novel small molecule that suppresses the infiltration of macrophages into tumors and demonstrates potent anticancer activity. We identified the entire pathway that links the intracellular protein Hsp70, which is inhibited by this small molecule, with the macrophage motility system. This study will lay the basis for a novel approach to cancer treatment via targeting tumor-associated macrophages.

Abstract

The molecular chaperone Hsp70 has been implicated in multiple stages of cancer development. In these processes, a co-chaperone Bag3 links Hsp70 with signaling pathways that control cancer development. Recently, we showed that besides affecting cancer cells, Hsp70 can also regulate the motility of macrophages and their tumor infiltration. However, the mechanisms of these effects have not been explored. Here, we demonstrated that the Hsp70-bound co-chaperone Bag3 associates with a transcription factor LITAF that can regulate the expression of inflammatory cytokines and chemokines in macrophages. Via this interaction, the Hsp70–Bag3 complex regulates expression levels of LITAF by controlling its proteasome-dependent and chaperone-mediated autophagy-dependent degradation. In turn, LITAF regulates the expression of the major chemokine CSF1, and adding this chemokine to the culture medium reversed the effects of Bag3 or LITAF silencing on the macrophage motility. Together, these findings uncover the Hsp70–Bag3–LITAF–CSF1 pathway that controls macrophage motility and tumor infiltration.

Carbon-11 patents (2012-2022): synthetic methodologies and novel radiotracers for PET imaging

INTRODUCTION

Carbon-11 is a short-lived radionuclide with versatile applications in synthetic methodologies to develop a variety of novel PET radiotracers. Different primary and secondary carbon-11 precursors are generated from cyclotron produced [¹¹C]CO₂ and used to insert carbon-11 radionuclide into the target specific bioactive molecules.

AREAS COVERED

In this review, the patents as well as specific research articles on carbon-11 radiotracer synthesis and PET imaging applications in various diseases are mentioned since 2012 to 2022 through SciFinder database.

EXPERT OPINION

Carbon-11 is generally easier to insert into more organic scaffolds as a greater variety of functional groups. Despite the short half-life of carbon-11 radionuclide (t_1/2 = 20.4 min), it is widely used in PET radiotracer development due to its direct insertion into bioactive compounds and less isotopic dilution unlike other positron emitters like fluorine-18. Various synthons can be easily generated using the primary and secondary carbon-11 precursors like [¹¹C]CO₂, [¹¹C]CH₄, ¹¹CH₃I, ¹¹CO, ¹¹COCl_2, ¹¹CN, ¹¹CS_2, and ¹¹CH₃OTf etc. that would be useful to develop any PET radiotracers by adapting various organic methods. The carbon-11 radiotracers provide target-oriented information associated with the pharmacology, and physiological conditions of the disease status. Various protocols and automated methods were adapted for easy and convenient synthesis of carbon-11 radiotracers. The PET advances drug development and clinical trials by revealing biological target engagement, proof of mechanism, pharmacokinetic, and pharmacodynamic profiles of new drug candidates using selective radiotracers.

Acetyl-L-carnitine improves erectile function in bilateral cavernous nerve injury rats via promoting cavernous nerve regeneration

BACKGROUND

Neurogenic erectile dysfunction (NED) caused by cavernous nerve (CN) injury is a typical complication after pelvic surgery, which lacks efficient treatments. Acetyl-L-carnitine (ALCAR) has been proven to promote nerve repair.

OBJECTIVES

To investigate the effect and potential mechanism of ALCAR in the treatment of NED.

MATERIALS AND METHODS

Thirty-two rats were randomly divided into bilateral cavernous nerve injury (BCNI) group, BCNI + lower-dose ALCAR (50 mg/kg/day) group, BCNI + higher-dose (100 mg/kg/day) group and sham-operated group. Erectile function was assessed 14 days after daily intraperitoneal injection of ALCAR or placebo. The penile tissues were gathered for subsequent histological and molecular biological analysis. Rat Schwann cell (SC) line S16 was used to verify the mechanism of ALCAR in vitro.

RESULTS

We found that the erectile function of the rats in BCNI group was severely impaired, which was improved considerably in both BCNI+ALCAR-LD and BCNI+ALCAR-HD groups. Also, we observed decreased smooth muscle and increased collagen content in corpus cavernosum in BCNI group. The expressions of fibrosis markers TGF-β, CTGF, and Smad 2/3 were significantly up-regulated in the BCNI group. The above changes were alleviated after the administration of lower and higher-dose ALCAR. Meanwhile, the NO/cGMP pathway was promoted and the RhoA/ROCK pathway was inhibited in the corpus cavernosum of BCNI rats after ALCAR treatment, accompanied by increased nNOS and down-regulated Tyrosine Hydroxylase. In vitro, ALCAR promoted the migration and proliferation of SC, and increased the expression of Pmp22 and NGF. Further, rats treated with ALCAR had high expression of ATF3 and S100 in the distal nerve tissues of the CN extrusion site.

DISCUSSION AND CONCLUSION

ALCAR could promote nerve repair and regeneration, inhibit penile fibrosis and improve penile erection by promoting the proliferation and migration of SC and the secretion of NGF. Our study confirms that ALCAR may be a potential treatment strategy for NED. This article is protected by copyright. All rights reserved.

Rho Kinases in Embryonic Development and Stem Cell Research

The Rho-associated coiled-coil containing kinases (ROCKs or Rho kinases) belong to the AGC (PKA/PKG/PKC) family of serine/threonine kinases and are major downstream effectors of small GTPase RhoA, a key regulator of actin-cytoskeleton reorganization. The ROCK family contains two members, ROCK1 and ROCK2, which share 65% overall identity and 92% identity in kinase domain. ROCK1 and ROCK2 were assumed to be functionally redundant, based largely on their major common activators, their high degree kinase domain homology, and study results from overexpression with kinase constructs or chemical inhibitors. ROCK signaling research has expanded to all areas of biology and medicine since its discovery in 1996. The rapid advance is befitting ROCK’s versatile functions in modulating various cell behavior, such as contraction, adhesion, migration, proliferation, polarity, cytokinesis, and differentiation. The rapid advance is noticeably driven by an extensive linking with clinical medicine, including cardiovascular abnormalities, aberrant immune responsive, and cancer development and metastasis. The rapid advance during the past decade is further powered by novel biotechnologies including CRISPR-Cas and single cell omics. Current consensus, derived mainly from gene targeting and RNA interference approaches, is that the two ROCK isoforms have overlapping and distinct cellular, physiological and pathophysiology roles. In this review, we present an overview of the milestone discoveries in ROCK research. We then focus on the current understanding of ROCK signaling in embryonic development, current research status using knockout and knockin mouse models, and stem cell research.

Structural Insights into Protein Regulation by Phosphorylation and Substrate Recognition of Protein Kinases/Phosphatases

Protein phosphorylation is one of the most widely observed and important post-translational modification (PTM) processes. Protein phosphorylation is regulated by protein kinases, each of which covalently attaches a phosphate group to an amino acid side chain on a serine (Ser), threonine (Thr), or tyrosine (Tyr) residue of a protein, and by protein phosphatases, each of which, conversely, removes a phosphate group from a phosphoprotein. These reversible enzyme activities provide a regulatory mechanism by activating or deactivating many diverse functions of proteins in various cellular processes. In this review, their structures and substrate recognition are described and summarized, focusing on Ser/Thr protein kinases and protein Ser/Thr phosphatases, and the regulation of protein structures by phosphorylation. The studies reviewed here and the resulting information could contribute to further structural, biochemical, and combined studies on the mechanisms of protein phosphorylation and to drug discovery approaches targeting protein kinases or protein phosphatases.

Current Insights and Advancements in Head and Neck Cancer: Emerging Biomarkers and Therapeutics with Cues from Single Cell and 3D Model Omics Profiling

Head and neck cancer (HNC) is among the ten leading malignancies worldwide, with India solely contributing one-third of global oral cancer cases. The current focus of all cutting-edge strategies against this global malignancy are directed towards the heterogeneous tumor microenvironment that obstructs most treatment blueprints. Subsequent to the portrayal of established information, the review details the application of single cell technology, organoids and spheroid technology in relevance to head and neck cancer and the tumor microenvironment acknowledging the resistance pattern of the heterogeneous cell population in HNC. Bioinformatic tools are used for study of differentially expressed genes and further omics data analysis. However, these tools have several challenges and limitations when analyzing single-cell gene expression data that are discussed briefly. The review further examines the omics of HNC, through comprehensive analyses of genomics, transcriptomics, proteomics, metabolomics, and epigenomics profiles. Patterns of alterations vary between patients, thus heterogeneity and molecular alterations between patients have driven the clinical significance of molecular targeted therapies. The analyses of potential molecular targets in HNC are discussed with connotation to the alteration of key pathways in HNC followed by a comprehensive study of protein kinases as novel drug targets including its ATPase and additional binding pockets, non-catalytic domains and single residues. We herein review, the therapeutic agents targeting the potential biomarkers in light of new molecular targeted therapies. In the final analysis, this review suggests that the development of improved target-specific personalized therapies can combat HNC's global plight.

GraphDTI: A robust deep learning predictor of drug-target interactions from multiple heterogeneous data

Traditional techniques to identify macromolecular targets for drugs utilize solely the information on a query drug and a putative target. Nonetheless, the mechanisms of action of many drugs depend not only on their binding affinity toward a single protein, but also on the signal transduction through cascades of molecular interactions leading to certain phenotypes. Although using protein-protein interaction networks and drug-perturbed gene expression profiles can facilitate system-level investigations of drug-target interactions, utilizing such large and heterogeneous data poses notable challenges. To improve the state-of-the-art in drug target identification, we developed GraphDTI, a robust machine learning framework integrating the molecular-level information on drugs, proteins, and binding sites with the system-level information on gene expression and protein-protein interactions. In order to properly evaluate the performance of GraphDTI, we compiled a high-quality benchmarking dataset and devised a new cluster-based cross-validation protocol. Encouragingly, GraphDTI not only yields an AUC of 0.996 against the validation dataset, but it also generalizes well to unseen data with an AUC of 0.939, significantly outperforming other predictors. Finally, selected examples of identified drugtarget interactions are validated against the biomedical literature. Numerous applications of GraphDTI include the investigation of drug polypharmacological effects, side effects through offtarget binding, and repositioning opportunities.

Drugging the Undruggable: How Isoquinolines and PKA Initiated the Era of Designed Protein Kinase Inhibitor Therapeutics

In 1984, Japanese researchers led by the biochemist Hiroyoshi Hidaka described the first synthetic protein kinase inhibitors based on an isoquinoline sulfonamide structure (Hidaka et al. Biochemistry, 1984 Oct 9; 23(21): 5036-41. doi: 10.1021/bi00316a032). These led to the first protein kinase inhibitor approved for medical use (fasudil), an inhibitor of the AGC subfamily Rho kinase. With potencies strong enough to compete against endogenous ATP, the isoquinoline compounds established the druggability of the ATP binding site. Crystal structures of their protein kinase complexes, including with cAMP-dependent protein kinase (PKA), showed interactions that, on the one hand, could mimic ATP but, on the other hand, could be optimized for high potency binding, kinase selectivity, and diversification away from adenosine. They also showed the flexibility of the glycine-rich loop, and PKA became a major prototype for crystallographic and nuclear magnetic resonance (NMR) studies of protein kinase mechanism and dynamic activity control. Since fasudil, more than 70 kinase inhibitors have been approved for clinical use, involving efforts that progressively have introduced new paradigms of data-driven drug discovery. Publicly available data alone comprise over 5000 protein kinase crystal structures and hundreds of thousands of binding data. Now, new methods, including artificial intelligence techniques and expansion of protein kinase targeting approaches, together with the expiration of patent protection for optimized inhibitor scaffolds, promise even greater advances in drug discovery. Looking back to the time of the first isoquinoline hinge binders brings the current state-of-the-art into stark contrast. Appropriately for this Perspective article, many of the milestone papers during this time were published in Biochemistry (now ACS Biochemistry).

Pharmacological Modulators of Small GTPases of Rho Family in Neurodegenerative Diseases

Classical Rho GTPases, including RhoA, Rac1, and Cdc42, are members of the Ras small GTPase superfamily and play essential roles in a variety of cellular functions. Rho GTPase signaling can be turned on and off by specific GEFs and GAPs, respectively. These features empower Rho GTPases and their upstream and downstream modulators as targets for scientific research and therapeutic intervention. Specifically, significant therapeutic potential exists for targeting Rho GTPases in neurodegenerative diseases due to their widespread cellular activity and alterations in neural tissues. This study will explore the roles of Rho GTPases in neurodegenerative diseases with focus on the applications of pharmacological modulators in recent discoveries. There have been exciting developments of small molecules, nonsteroidal anti-inflammatory drugs (NSAIDs), and natural products and toxins for each classical Rho GTPase category. A brief overview of each category followed by examples in their applications will be provided. The literature on their roles in various diseases [e.g., Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Frontotemporal dementia (FTD), and Multiple sclerosis (MS)] highlights the unique and broad implications targeting Rho GTPases for potential therapeutic intervention. Clearly, there is increasing knowledge of therapeutic promise from the discovery of pharmacological modulators of Rho GTPases for managing and treating these conditions. The progress is also accompanied by the recognition of complex Rho GTPase modulation where targeting its signaling can improve some aspects of pathogenesis while exacerbating others in the same disease model. Future directions should emphasize the importance of elucidating how different Rho GTPases work in concert and how they produce such widespread yet different cellular responses during neurodegenerative disease progression.

A high-content screen identifies the vulnerability of MYC-overexpressing cells to dimethylfasudil

A synthetic lethal effect arises when a cancer-associated change introduces a unique vulnerability to cancer cells that makes them unusually susceptible to a drug’s inhibitory activity. The synthetic lethal approach is attractive because it enables targeting of cancers harboring specific genomic or epigenomic alterations, the products of which may have proven refractory to direct targeting. An example is cancer driven by overexpression of MYC. Here, we conducted a high-content screen for compounds that are synthetic lethal to elevated MYC using a small-molecule library to identify compounds that are closely related to, or are themselves, regulatory-approved drugs. The screen identified dimethylfasudil, a potent and reversible inhibitor of Rho-associated kinases, ROCK1 and ROCK2. Close analogs of dimethylfasudil are used clinically to treat neurologic and cardiovascular disorders. The synthetic lethal interaction was conserved in rodent and human cell lines and could be observed with activation of either MYC or its paralog MYCN. The synthetic lethality seems specific to MYC overexpressing cells as it could not be substituted by a variety of oncogenic manipulations and synthetic lethality was diminished by RNAi-mediated depletion of MYC in human cancer cell lines. Collectively, these data support investigation of the use of dimethylfasudil as a drug that is synthetic lethal for malignancies that specifically overexpress MYC.

Chemotherapy-Enriched THBS2-Deficient Cancer Stem Cells Drive Hepatocarcinogenesis through Matrix Softness Induced Histone H3 Modifications

The physical microenvironment is a critical mediator of tumor behavior. However, detailed biological and mechanistic insight is lacking. The present study reveals the role of chemotherapy-enriched CD133+ liver cancer stem cells (CSCs) with THBS2 deficiency. This subpopulation of cells contributes to a more aggressive cancer and functional stemness phenotype in hepatocellular carcinoma (HCC) by remodeling the extracellular matrix (ECM) through the regulation of matrix metalloproteinase (MMP) activity, collagen degradation, and matrix stiffness. The local soft spots created by these liver CSCs can enhance stemness and drug resistance and provide a route of escape to facilitate HCC metastasis. Interestingly, a positive feed-forward loop is identified where a local soft spot microenvironment in the HCC tumor is enriched with CD133 expressing cells that secrete markedly less ECM-modifying THBS2 upon histone H3 modification at its promoter region, allowing the maintenance of a localized soft spot matrix. Clinically, THBS2 deficiency is also correlated with low HCC survival, where high levels of CSCs with low THBS2 expression in HCC are associated with decreased collagen fiber deposits and an invasive tumor front. The findings have implications for the treatment of cancer stemness and for the prevention of tumor outgrowth through disseminated tumor cells.

ADP-ribose and analogues bound to the deMARylating macrodomain from the bat coronavirus HKU4

Macrodomains are proteins that recognize and hydrolyze ADP ribose (ADPR) modifications of intracellular proteins. Macrodomains are implicated in viral genome replication and interference with host cell immune responses. They are important to the infectious cycle of Coronaviridae and Togaviridae viruses. We describe crystal structures of the conserved macrodomain from the bat coronavirus (CoV) HKU4 in complex with ligands. The structures reveal a binding cavity that accommodates ADPR and analogs via local structural changes within the pocket. Using a radioactive assay, we present evidence of mono-ADPR (MAR) hydrolase activity. In silico analysis presents further evidence on recognition of the ADPR modification for hydrolysis. Mutational analysis of residues within the binding pocket resulted in diminished enzymatic activity and binding affinity. We conclude that the common structural features observed in the macrodomain in a bat CoV contribute to a conserved function that can be extended to other known macrodomains.

Two Methods, One Goal: Structural Differences between Cocrystallization and Crystal Soaking to Discover Ligand Binding Poses

In lead optimization, protein crystallography is an indispensable tool to analyze drug binding. Binding modes and non-covalent interaction inventories are essential to design follow-up synthesis candidates. Two protocols are commonly applied to produce protein-ligand complexes: cocrystallization and soaking. Because of its time and cost effectiveness, soaking is the more popular method. Taking eight ligand hinge binders of protein kinase A, we demonstrate that cocrystallization is superior. Particularly for flexible proteins, such as kinases, and larger ligands cocrystallization captures more reliable the correct binding pose and induced protein adaptations. The geometrical discrepancies between soaking and cocrystallization appear smaller for fragment-sized ligands. For larger flexible ligands that trigger conformational changes of the protein, soaking can be misleading and underestimates the number of possible polar interactions due to inadequate, highly impaired positions of protein amino-acid side and main chain atoms. Thus, if applicable cocrystallization should be the gold standard to study protein-ligand complexes.

New insights into RhoA/Rho-kinase signaling: a key regulator of vascular contraction

While Rho-signalling controlling vascular contraction is a canonical mechanism, with the modern approaches used in research, we are advancing our understanding and details into this pathway are often uncovered. RhoA-mediated Rho-kinase is the major regulator of vascular smooth muscle cells and a key player manoeuvring other functions in these cells. The discovery of new interactions, such as oxidative stress and hydrogen sulphide with Rho signalling are emerging addition not only in the physiology of the smooth muscle, but especially in the pathophysiology of vascular diseases. Likewise, the interplay between ageing and Rho-kinase in the vasculature has been recently considered. Importantly, in smooth muscle contraction, this pathway may also be affected by sex hormones, and consequently, sex-differences. This review provides an overview of Rho signalling mediating vascular contraction and focuses on recent topics discussed in the literature affecting this pathway such as ageing, sex differences and oxidative stress.

Liraglutide Ameliorates Erectile Dysfunction via Regulating Oxidative Stress, the RhoA/ROCK Pathway and Autophagy in Diabetes Mellitus

Background

Erectile dysfunction (ED) occurs more frequently and causes a worse response to the first-line therapies in diabetics compared with nondiabetic men. Corpus cavernosum vascular dysfunction plays a pivotal role in the occurrence of diabetes mellitus ED (DMED). The aim of this study was to investigate the protective effects of glucagon-like peptide-1 (GLP-1) analog liraglutide on ED and explore the underlying mechanisms in vivo and in vitro.

Methods

Type 1 diabetes was induced in rats by streptozotocin, and the apomorphine test was for screening the DMED model in diabetic rats. Then they were randomly treated with subcutaneous injections of liraglutide (0.3 mg/kg/12 h) for 4 weeks. Erectile function was assessed by cavernous nerve electrostimulation. The corpus cavernosum was used for further study. In vitro, effects of liraglutide were evaluated by primary corpus cavernosum smooth muscle cells (CCSMCs) exposed to low or high glucose (HG)-containing medium with or without liraglutide and GLP-1 receptor (GLP-1R) inhibitor. Western blotting, fluorescent probe, immunohistochemistry, and relevant assay kits were performed to measure the levels of target proteins.

Results

Administration of liraglutide did not significantly affect plasma glucose and body weights in diabetic rats, but improved erectile function, reduced levels of NADPH oxidases and ROS production, downregulated expression of Ras homolog gene family (RhoA) and Rho-associated protein kinase (ROCK) 2 in the DMED group dramatically. The liraglutide treatment promoted autophagy further and restored expression of GLP-1R in the DMED group. Besides, cultured CCSMCs with liraglutide exhibited a lower level of oxidative stress accompanied by inhibition of the RhoA/ROCK pathway and a higher level of autophagy compared with HG treatment. These beneficial effects of liraglutide effectively reversed by GLP-1R inhibitor.

Conclusion

Liraglutide exerts protective effects on ED associated with the regulation of smooth muscle dysfunction, oxidative stress and autophagy, independently of a glucose- lowering effect. It provides new insight into the extrapancreatic actions of liraglutide and preclinical evidence for a potential treatment for DMED.

Rho-kinase (ROCK) Inhibitors - A Neuroprotective Therapeutic Paradigm with a Focus on Ocular Utility

BACKGROUND

Glaucoma is a progressive optic neuropathy causing visual impairment and Retinal Ganglionic Cells (RGCs) death gradually posing a need for neuroprotective strategies to minimize the loss of RGCs and visual field. It is recognized as a multifactorial disease, Intraocular Pressure (IOP) being the foremost risk factor. ROCK inhibitors have been probed for various possible indications, such as myocardial ischemia, hypertension, kidney diseases. Their role in neuroprotection and neuronal regeneration has been suggested to be of value in the treatment of neurological diseases, like spinal-cord injury, Alzheimer's disease and multiple sclerosis but recently Rho-associated Kinase inhibitors have been recognized as potential antiglaucoma agents.

EVIDENCE SYNTHESIS

Rho-Kinase is a serine/threonine kinase with a kinase domain which is constitutively active and is involved in the regulation of smooth muscle contraction and stress fibre formation. Two isoforms of Rho-Kinase, ROCK-I (ROCK β) and ROCK-II (ROCK α) have been identified. ROCK II plays a pathophysiological role in glaucoma and hence the inhibitors of ROCK may be beneficial to ameliorate the vision loss. These inhibitors decrease the intraocular pressure in the glaucomatous eye by increasing the aqueous humour outflow through the trabecular meshwork pathway. They also act as anti-scarring agents and hence prevent post-operative scarring after the glaucoma filtration surgery. Their major role involves axon regeneration by increasing the optic nerve blood flow which may be useful in treating the damaged optic neurons. These drugs act directly on the neurons in the central visual pathway, interrupting the RGC apoptosis and therefore serve as a novel pharmacological approach for glaucoma neuroprotection.

CONCLUSION

Based on the results of high-throughput screening, several Rho kinase inhibitors have been designed and developed comprising of diverse scaffolds exhibiting Rho kinase inhibitory activity from micromolar to subnanomolar ranges. This diversity in the scaffolds with inhibitory potential against the kinase and their SAR development will be intricated in the present review. Ripasudil is the only Rho kinase inhibitor marketed to date for the treatment of glaucoma. Another ROCK inhibitor AR-13324 has recently passed the clinical trials whereas AMA0076, K115, PG324, Y39983 and RKI-983 are still under trials. In view of this, a detailed and updated account of ROCK II inhibitors as the next generation therapeutic agents for glaucoma will be discussed in this review.

Discovery of strong inhibitory properties of a monoclonal antibody of PKA and use of the antibody and a competitive photoluminescent orthosteric probe for analysis of the protein kinase

We show that the antibody, clone mAb(D38C6), of the α isoform of the catalytic subunit of PKA (PKAcα) inhibits the kinase-catalyzed phosphorylation with low-nanomolar inhibitory potency (K_i = 2.4 nM). This property of the antibody was established by its capacity to displace a synthetic small-molecule active site-binding (orthosteric) photoluminescent ARC-Lum(Fluo) probe from the complex with PKAcα. Likely, the competitiveness of association of the two binders with the protein is coming from two excluding conformations of PKAcα to which the binders bind. mAb(D38C6) possesses a linear peptide epitope and it binds to the disordered C-tail of unliganded inactive conformer of PKAcα. ARC-Lum(Fluo) probes bind to the ordered and active conformation of PKAcα with Phe327 residue from the C-tail taking part in the formation of the active core. Consecutive application of these competitive PKAcα binders was used to develop an immunoassay allowing the determination of PKAcα concentration in complex biological solutions. At first, PKAcα was captured from the solution by the isoform-specific antibody and thereafter a high-affinity ARC-Lum(Fluo) probe was used to displace PKAcα from the binary complex. The developed immunoassay could be used for quantification of small amounts (starting from 93 pg, 2.3 fmol) of PKAcα in cell lysates.

Surprising Non-Additivity of Methyl Groups in Drug-Kinase Interaction

Drug optimization is guided by biophysical methods with increasing popularity. In the context of lead structure modifications, the introduction of methyl groups is a simple but potentially powerful approach. Hence, it is crucial to systematically investigate the influence of ligand methylation on biophysical characteristics such as thermodynamics. Here, we investigate the influence of ligand methylation in different positions and combinations on the drug-kinase interaction. Binding modes and complex structures were analyzed using protein crystallography. Thermodynamic signatures were measured via isothermal titration calorimetry (ITC). An extensive computational analysis supported the understanding of the underlying mechanisms. We found that not only position but also stereochemistry of the methyl group has an influence on binding potency as well as the thermodynamic signature of ligand binding to the protein. Strikingly, the combination of single methyl groups does not lead to additive effects. In our case, the merger of two methyl groups in one ligand leads to an entirely new alternative ligand binding mode in the protein ligand complex. Moreover, the combination of the two methyl groups also resulted in a nonadditive thermodynamic profile of ligand binding. Molecular dynamics (MD) simulations revealed distinguished characteristic motions of the ligands in solution explaining the pronounced thermodynamic changes. The unexpected drastic change in protein ligand interaction highlights the importance of crystallographic control even for minor modifications such as the introduction of a methyl group. For an in-depth understanding of ligand binding behavior, MD simulations have shown to be a powerful tool.

Design of a potent anticancer lead inspired by natural products from traditional Indian medicine

Among the plant constituents of Clerodendrum colebrookianum Walp., acteoside, martinoside, and osmanthuside β6 interact with ROCK, a drug target for cancer. In this study, aglycone fragments of these plant constituents (caffeic acid, ferulic acid, and p-coumaric acid) along with the homopiperazine ring of fasudil (standard ROCK inhibitor) were used to design hybrid molecules. The designed molecules interact with the key hinge region residue Met156/Met157 of ROCK I/II in a stable manner according to our docking and molecular dynamics simulations. These compounds were synthesized and tested in vitro in SW480, MDA-MB-231, and A-549 cancer cell lines. The most promising compound was chemically optimized to obtain a thiourea analog, 6a (IC₅₀ = 25 µM), which has >3-fold higher antiproliferative activity than fasudil (IC₅₀ = 87 µM) in SW480 cells. Treatment with this molecule also inhibits the migration of colon cancer cells and induces cell apoptosis. Further, SPR experiments suggests that the binding affinity of 6a with ROCK I protein is better than that of fasudil. Hence, the drug-like natural product analog 6a constitutes a highly promising new anticancer lead.Communicated by Ramaswamy H. Sarma.

Rho-Associated Coiled-Coil Kinase (ROCK) in Molecular Regulation of Angiogenesis

Identified as a major downstream effector of the small GTPase RhoA, Rho-associated coiled-coil kinase (ROCK) is a versatile regulator of multiple cellular processes. Angiogenesis, the process of generating new capillaries from the pre-existing ones, is required for the development of various diseases such as cancer, diabetes and rheumatoid arthritis. Recently, ROCK has attracted attention for its crucial role in angiogenesis, making it a promising target for new therapeutic approaches. In this review, we summarize recent advances in understanding the role of ROCK signaling in regulating the permeability, migration, proliferation and tubulogenesis of endothelial cells (ECs), as well as its functions in non-ECs which constitute the pro-angiogenic microenvironment. The therapeutic potential of ROCK inhibitors in angiogenesis-related diseases is also discussed.

PAK4 crystal structures suggest unusual kinase conformational movements

In order for protein kinases to exchange nucleotide they must open and close their catalytic cleft. These motions are associated with rotations of the N-lobe, predominantly around the 'hinge region'. We conducted an analysis of 28 crystal structures of the serine-threonine kinase, p21-activated kinase 4 (PAK4), including three newly determined structures in complex with staurosporine, FRAX486, and fasudil (HA-1077). We find an unusual motion between the N-lobe and C-lobe of PAK4 that manifests as a partial unwinding of helix αC. Principal component analysis of the crystal structures rationalizes these movements into three major states, and analysis of the kinase hydrophobic spines indicates concerted movements that create an accessible back pocket cavity. The conformational changes that we observe for PAK4 differ from previous descriptions of kinase motions, and although we observe these differences in crystal structures there is the possibility that the movements observed may suggest a diversity of kinase conformational changes associated with regulation.

AUTHOR SUMMARY

Protein kinases are key signaling proteins, and are important drug targets, therefore understanding their regulation is important for both basic research and clinical points of view. In this study, we observe unusual conformational 'hinging' for protein kinases. Hinging, the opening and closing of the kinase sub-domains to allow nucleotide binding and release, is critical for proper kinase regulation and for targeted drug discovery. We determine new crystal structures of PAK4, an important Rho-effector kinase, and conduct analyses of these and previously determined structures. We find that PAK4 crystal structures can be classified into specific conformational groups, and that these groups are associated with previously unobserved hinging motions and an unusual conformation for the kinase hydrophobic core. Our findings therefore indicate that there may be a diversity of kinase hinging motions, and that these may indicate different mechanisms of regulation.

Effects of eupatilin on the contractility of corpus cavernosal smooth muscle through nitric oxide-independent pathways

Eupatilin (5,7-dihydroxy-3,4,6-trimethoxyflavone) is one of the main compounds present in Artemisia species. Eupatilin has both antioxidative and anti-inflammatory properties and a relaxation effect on vascular contraction regardless of endothelial function. We evaluated the relaxant effects of eupatilin on the corpus cavernosum (CC) of rabbits and the underlying mechanisms of its activity in human corpus cavernosum smooth muscle (CCSM) cells. Isolated rabbit CC strips were mounted in an organ bath system. A conventional whole-cell patch clamp technique was used to measure activation of calcium-sensitive K⁺ -channel currents in human CCSM cells. The relaxation effect of eupatilin was evaluated by cumulative addition (10^-5  m ~ 3 × 10^-4  m) to CC strips precontracted with 10^-5  m phenylephrine. Western blotting analysis was performed to measure myosin phosphatase targeting subunit 1 (MYPT1) and protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17-kDa (CPI-17) expression and to evaluate the effect of eupatilin on the RhoA/Rho-kinase pathway. Eupatilin effectively relaxed the phenylephrine-induced tone in the rabbit CC strips in a concentration-dependent manner with an estimated EC₅₀ value of 1.2 ± 1.6 × 10^-4  m (n = 8, p < 0.05). Iberiotoxin and tetraethylammonium significantly reduced the relaxation effect (n = 8, p < 0.001 and p = 0.003, respectively). Removal of the endothelium or the presence of L-NAME or indomethacin did not affect the relaxation effect of eupatilin. In CCSM cells, the extracellular application of eupatilin 10^-4  m significantly increased the outward currents, and the eupatilin-stimulated currents were significantly attenuated by treatment with 10^-7  m iberiotoxin (n = 13, p < 0.05). Eupatilin reduced the phosphorylation level of MYPT1 at Thr853 of MLCP and CPI-17 at Thr38. Eupatilin-induced relaxation of the CCSM cells via NO-independent pathways. The relaxation effects of eupatilin on CCSM cells were partially due to activation of BK_Ca channels and inhibition of RhoA/Rho-kinase.

Crucial Role of ROCK2-Mediated Phosphorylation and Upregulation of FHOD3 in the Pathogenesis of Angiotensin II-Induced Cardiac Hypertrophy

Cardiac hypertrophy is characterized by increased myofibrillogenesis. Angiotensin II (Ang-II) is an essential mediator of the pressure overload-induced cardiac hypertrophy in part through RhoA/ROCK (small GTPase/Rho-associated coiled-coil containing protein kinase) pathway. FHOD3 (formin homology 2 domain containing 3), a cardiac-restricted member of diaphanous-related formins, is crucial in regulating myofibrillogenesis in cardiomyocytes. FHOD3 maintains inactive through autoinhibition by an intramolecular interaction between its C- and N-terminal domains. Phosphorylation of the 3 highly conserved residues (1406S, 1412S, and 1416T) within the C terminus (CT) of FHOD3 by ROCK1 is sufficient for its activation. However, it is unclear whether ROCK-mediated FHOD3 activation plays a role in the pathogenesis of Ang-II-induced cardiac hypertrophy. In this study, we detected increases in FHOD3 expression and phosphorylation in cardiomyocytes from Ang-II-induced rat cardiac hypertrophy models. Valsartan attenuated such increases. In cultured neonate rat cardiomyocytes, overexpression of phosphor-mimetic mutant FHOD3-DDD, but not wild-type FHOD3, resulted in myofibrillogenesis and cardiomyocyte hypertrophy. Expression of a phosphor-resistant mutant FHOD3-AAA completely abolished myofibrillogenesis and attenuated Ang-II-induced cardiomyocyte hypertrophy. Pretreatment of neonate rat cardiomyocytes with ROCK inhibitor Y27632 reduced Ang-II-induced FHOD3 activation and upregulation, suggesting the involvement of ROCK activities. Silencing of ROCK2, but not ROCK1, in neonate rat cardiomyocytes, significantly lessened Ang-II-induced cardiomyocyte hypertrophy. ROCK2 can directly phosphorylate FHOD3 at both 1412S and 1416T in vitro and is more potent than ROCK1. Both kinases failed to phosphorylate 1406S. Coexpression of FHOD3 with constitutively active ROCK2 induced more stress fiber formation than that with constitutively active ROCK1. Collectively, our results demonstrated the importance of ROCK2 regulated FHOD3 expression and activation in Ang-II-induced myofibrillogenesis, thus provided a novel mechanism for the pathogenesis of Ang-II-induced cardiac hypertrophy.

Heterogeneous Impact of ROCK2 on Carotid and Cerebrovascular Function

Rho kinase (ROCK) has been implicated in physiological and pathophysiological processes, including regulation of vascular function. ROCK signaling is thought to be a critical contributor to cardiovascular disease, including hypertension and effects of angiotensin II (Ang II). Two isoforms of ROCK (1 and 2) have been identified and are expressed in vascular cells. In this study, we examined the importance of ROCK2 in relation to vessel function using several models and a novel inhibitor of ROCK2. First, incubation of carotid arteries with the direct RhoA activator CN-03 or Ang II impaired endothelium-dependent relaxation by ≈40% to 50% (P<0.05) without altering endothelium-independent relaxation. Both CN-03- and Ang II-induced endothelial dysfunction was prevented by Y-27632 (an inhibitor of both ROCK isoforms) or the selective ROCK2 inhibitor SLX-2119. In contrast, SLX-2119 had little effect on contraction of carotid arteries to receptor-mediated agonists (serotonin, phenylephrine, vasopressin, or U46619). Second, in basilar arteries, SLX-2119 inhibited constriction to Ang II by ≈90% without significantly affecting responses to serotonin or KCl. Third, in isolated pressurized brain parenchymal arterioles, SLX-2119 inhibited myogenic tone in a concentration-dependent manner (eg, 1 μmol/L SLX-2119 dilated by 79±4%). Finally, SLX-2119 dilated small pial arterioles in vivo, an effect that was augmented by inhibition of nitric oxide synthase. These findings suggest that ROCK2 has major, but heterogeneous, effects on function of endothelium and vascular muscle. The data support the concept that aberrant ROCK2 signaling may be a key contributor to select aspects of large and small vessel disease, including Ang II-induced endothelial dysfunction.

Rho Kinase Inhibition Is Essential During In Vitro Neurogenesis and Promotes Phenotypic Rescue of Human Induced Pluripotent Stem Cell-Derived Neurons With Oligophrenin-1 Loss of Function

: Rho-GTPases have relevant functions in various aspects of neuronal development, such as differentiation, migration, and synaptogenesis. Loss of function of the oligophrenin-1 gene (OPHN1) causes X-linked intellectual disability with cerebellar hypoplasia and leads to hyperactivation of the rho kinase (ROCK) pathway. ROCK mainly acts through phosphorylation of the myosin phosphatase targeting subunit 1, triggering actin-myosin contractility. We show that during in vitro neurogenesis, ROCK activity decreases from day 10 until terminal differentiation, whereas in OPHN1-deficient human induced pluripotent stem cells (h-iPSCs), the levels of ROCK are elevated throughout differentiation. ROCK inhibition favors neuronal-like appearance of h-iPSCs, in parallel with transcriptional upregulation of nuclear receptor NR4A1, which is known to induce neurite outgrowth. This study analyzed the morphological, biochemical, and functional features of OPHN1-deficient h-iPSCs and their rescue by treatment with the ROCK inhibitor fasudil, shedding light on the relevance of the ROCK pathway during neuronal differentiation and providing a neuronal model for human OPHN1 syndrome and its treatment.

SIGNIFICANCE

The analysis of the levels of rho kinase (ROCK) activity at different stages of in vitro neurogenesis of human induced pluripotent stem cells reveals that ROCK activity decreases progressively in parallel with the appearance of neuronal-like morphology and upregulation of nuclear receptor NR4A1. These results shed light on the role of the ROCK pathway during early stages of human neurogenesis and provide a neuronal stem cell-based model for the treatment of OPHN1 syndrome and other neurological disorders due to ROCK dysfunction.

Structure-Based Design, Synthesis, and Biological Evaluation of Highly Selective and Potent G Protein-Coupled Receptor Kinase 2 Inhibitors

G protein-coupled receptors (GPCRs) are central to many physiological processes. Regulation of this superfamily of receptors is controlled by GPCR kinases (GRKs), some of which have been implicated in heart failure. GSK180736A, developed as a Rho-associated coiled-coil kinase 1 (ROCK1) inhibitor, was identified as an inhibitor of GRK2 and co-crystallized in the active site. Guided by its binding pose overlaid with the binding pose of a known potent GRK2 inhibitor, Takeda103A, a library of hybrid inhibitors was developed. This campaign produced several compounds possessing high potency and selectivity for GRK2 over other GRK subfamilies, PKA, and ROCK1. The most selective compound, 12n (CCG-224406), had an IC50 for GRK2 of 130 nM, >700-fold selectivity over other GRK subfamilies, and no detectable inhibition of ROCK1. Four of the new inhibitors were crystallized with GRK2 to give molecular insights into the binding and kinase selectivity of this class of inhibitors.

Planar cell polarity gene expression correlates with tumor cell viability and prognostic outcome in neuroblastoma

BACKGROUND

The non-canonical Wnt/Planar cell polarity (PCP) signaling pathway is a major player in cell migration during embryonal development and has recently been implicated in tumorigenesis.

METHODS

Transfections with cDNA plasmids or siRNA were used to increase and suppress Prickle1 and Vangl2 expression in neuroblastoma cells and in non-tumorigenic cells. Cell viability was measured by trypan blue exclusion and protein expression was determined with western blotting. Transcriptional activity was studied with luciferase reporter assay and mRNA expression with real-time RT-PCR. Immunofluorescence stainings were used to study the effects of Vangl2 overexpression in non-tumorigenic embryonic cells. Statistical significance was tested with t-test or one-way ANOVA.

RESULTS

Here we show that high expression of the PCP core genes Prickle1 and Vangl2 is associated with low-risk neuroblastoma, suppression of neuroblastoma cell growth and decreased Wnt/β-catenin signaling. Inhibition of Rho-associated kinases (ROCKs) that are important in mediating non-canonical Wnt signaling resulted in increased expression of Prickle1 and inhibition of β-catenin activity in neuroblastoma cells. In contrast, overexpression of Vangl2 in MYC immortalized neural stem cells induced accumulation of active β-catenin and decreased the neural differentiation marker Tuj1. Similarly, genetically modified mice with forced overexpression of Vangl2 in nestin-positive cells showed decreased Tuj1 differentiation marker during embryonal development.

CONCLUSIONS

Our experimental data demonstrate that high expression of Prickle1 and Vangl2 reduce the growth of neuroblastoma cells and indicate different roles of PCP proteins in tumorigenic cells compared to normal cells. These results suggest that the activity of the non-canonical Wnt/PCP signaling pathway is important for neuroblastoma development and that manipulation of the Wnt/PCP pathway provides a possible therapy for neuroblastoma.

Novel Insights into the Roles of Rho Kinase in Cancer

Rho-associated coiled-coil kinase (ROCK) is a major downstream effector of the small GTPase RhoA. The ROCK family, consisting of ROCK1 and ROCK2, plays a central role in the organization of the actin cytoskeleton, and is involved in a wide range of fundamental cellular functions such as contraction, adhesion, migration, proliferation, and apoptosis. Since the discovery of effective inhibitors such as fasudil and Y27632, the biological roles of ROCK have been extensively explored in numerous diseases, including cancer. Accumulating evidence supports the concept that ROCK plays important roles in tumor development and progression through regulating many key cellular functions associated with malignancy, including tumorigenicity, tumor growth, metastasis, angiogenesis, tumor cell apoptosis/survival and chemoresistance as well. This review focuses on the new advances of the most recent 5 years from the studies on the roles of ROCK in cancer development and progression; the discussion is mainly focused on the potential value of ROCK inhibitors in cancer therapy.

Rho-associated kinase signalling and the cancer microenvironment: novel biological implications and therapeutic opportunities

The Rho/ROCK pathway is involved in numerous pivotal cellular processes that have made it an area of intense study in cancer medicine, however, Rho-associated coiled-coil containing protein kinase (ROCK) inhibitors are yet to make an appearance in the clinical cancer setting. Their performance as an anti-cancer therapy has been varied in pre-clinical studies, however, they have been shown to be effective vasodilators in the treatment of hypertension and post-ischaemic stroke vasospasm. This review addresses the various roles the Rho/ROCK pathway plays in angiogenesis, tumour vascular tone and reciprocal feedback from the tumour microenvironment and explores the potential utility of ROCK inhibitors as effective vascular normalising agents. ROCK inhibitors may potentially enhance the delivery and efficacy of chemotherapy agents and improve the effectiveness of radiotherapy. As such, repurposing of these agents as adjuncts to standard treatments may significantly improve outcomes for patients with cancer. A deeper understanding of the controlled and dynamic regulation of the key components of the Rho pathway may lead to effective use of the Rho/ROCK inhibitors in the clinical management of cancer.

Rho kinase is required to prevent retinal axons from entering the contralateral optic nerve

To grow out to contact target neurons an axon uses its distal tip, the growth cone, as a sensor of molecular cues that help the axon make appropriate guidance decisions at a series of choice points along the journey. In the developing visual system, the axons of the output cells of the retina, the retinal ganglion cells (RGCs), cross the brain midline at the optic chiasm. Shortly after, they grow past the brain entry point of the optic nerve arising from the contralateral eye, and extend dorso-caudally through the diencephalon towards their optic tectum target. Using the developing visual system of the experimentally amenable model Xenopus laevis, we find that RGC axons are normally prevented from entering the contralateral optic nerve. This mechanism requires the activity of a Rho-associated kinase, Rock, known to function downstream of a number of receptors that recognize cues that guide axons. Pharmacological inhibition of Rock in an in vivo brain preparation causes mis-entry of many RGC axons into the contralateral optic nerve, and this defect is partially phenocopied by selective disruption of Rock signaling in RGC axons. These data implicate Rock downstream of a molecular mechanism that is critical for RGC axons to be able to ignore a domain, the optic nerve, which they previously found attractive.

The oncogene c-Jun impedes somatic cell reprogramming

Oncogenic transcription factors are known to mediate the conversion of somatic cells to tumour or induced pluripotent stem cells (iPSCs). Here we report c-Jun as a barrier for iPSC formation. c-Jun is expressed by and required for the proliferation of mouse embryonic fibroblasts (MEFs), but not mouse embryonic stem cells (mESCs). Consistently, c-Jun is induced during mESC differentiation, drives mESCs towards the endoderm lineage and completely blocks the generation of iPSCs from MEFs. Mechanistically, c-Jun activates mesenchymal-related genes, broadly suppresses the pluripotent ones, and derails the obligatory mesenchymal to epithelial transition during reprogramming. Furthermore, inhibition of c-Jun by shRNA, dominant-negative c-Jun or Jdp2 enhances reprogramming and replaces Oct4 among the Yamanaka factors. Finally, Jdp2 anchors 5 non-Yamanaka factors (Id1, Jhdm1b, Lrh1, Sall4 and Glis1) to reprogram MEFs into iPSCs. Our studies reveal c-Jun as a guardian of somatic cell fate and its suppression opens the gate to pluripotency.

Assessing protein kinase target similarity: Comparing sequence, structure, and cheminformatics approaches

In just over two decades, structure based protein kinase inhibitor discovery has grown from trial and error approaches, using individual target structures, to structure and data driven approaches that may aim to optimize inhibition properties across several targets. This is increasingly enabled by the growing availability of potent compounds and kinome-wide binding data. Assessing the prospects for adapting known compounds to new therapeutic uses is thus a key priority for current drug discovery efforts. Tools that can successfully link the diverse information regarding target sequence, structure, and ligand binding properties now accompany a transformation of protein kinase inhibitor research, away from single, block-buster drug models, and toward "personalized medicine" with niche applications and highly specialized research groups. Major hurdles for the transformation to data driven drug discovery include mismatches in data types, and disparities of methods and molecules used; at the core remains the problem that ligand binding energies cannot be predicted precisely from individual structures. However, there is a growing body of experimental data for increasingly successful focussing of efforts: focussed chemical libraries, drug repurposing, polypharmacological design, to name a few. Protein kinase target similarity is easily quantified by sequence, and its relevance to ligand design includes broad classification by key binding sites, evaluation of resistance mutations, and the use of surrogate proteins. Although structural evaluation offers more information, the flexibility of protein kinases, and differences between the crystal and physiological environments may make the use of crystal structures misleading when structures are considered individually. Cheminformatics may enable the "calibration" of sequence and crystal structure information, with statistical methods able to identify key correlates to activity but also here, "the devil is in the details." Examples from specific repurposing and polypharmacology applications illustrate these points. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.

RAGE Mediates the Pro-Migratory Response of Extracellular S100A4 in Human Thyroid Cancer Cells

BACKGROUND

Expression of the small calcium-binding protein S100A4 is associated with poor prognosis in patients with thyroid cancer (TC). The authors have previously shown that S100A4 is a target for relaxin and insulin-like peptide 3 signaling in TC cells and that S100A4 is secreted from human TC cells. Although the pro-migratory role of intracellular S100A4 in binding to non-muscle myosin is well known, this study investigated here whether extracellular S100A4 contributes to TC migration.

METHODS

Human cell lines of follicular, papillary, and undifferentiated thyroid cancer, primary patient TC cells, and TC tissues were utilized to discover the presence of the receptor of advanced glycation end products (RAGE) in TC cells and TC tissues. Fluorescence imaging, protein pull-down assays, Western blot, siRNA protein silencing, small GTPase inhibitors, cell proliferation, and cell migration assays were used to investigate the interaction of extracellular S100A4 with RAGE in promoting a TC migratory response.

RESULTS

It was demonstrated that RAGE served as receptor for extracellular S100A4 mediating cell migration in TC cells. The RAGE-mediated increase in cell migration was dependent on the intracellular RAGE signaling partner diaphanous-1 (Dia-1) and involved the activation of the small GTPases Cdc42 and RhoA. Although extracellular S100A4 consistently activated ERK signaling in TC cells, it was shown that ERK signaling was not mediated by RAGE and not essential for the migratory response in TC cells.

CONCLUSION

The data have identified the RAGE/Dia-1 signaling system as a mediator for the pro-migratory response of extracellular S100A4 in human TC. Thus, therapeutic targeting of the RAGE/Dia-1/small GTPases signaling may successfully reduce local invasion and metastasis in TC.

Molecular basis for small molecule inhibition of G protein-coupled receptor kinases

Small molecules that inhibit the protein kinase A, G, and C (AGC) family of serine/threonine kinases can exert profound effects on cell homeostasis and thereby regulate fundamental processes such as heart rate, blood pressure, and metabolism, but there is not yet a clinically approved drug in the United States selective for a member of this family. One subfamily of AGC kinases, the G protein-coupled receptor (GPCR) kinases (GRKs), initiates the desensitization of active GPCRs. Of these, GRK2 has been directly implicated in the progression of heart failure. Thus, there is great interest in the identification of GRK2-specific chemical probes that can be further developed into therapeutics. Herein, we compare crystal structures of small molecule inhibitors in complex with GRK2 to those of highly selective compounds in complex with Rho-associated coiled-coil containing kinase 1 (ROCK1), a closely related AGC kinase. This analysis suggests that reduced hydrogen-bond formation with the hinge of the kinase domain, occupation of the hydrophobic subsite, and, consequently, higher buried surface area are key drivers of potency and selectivity among GRK 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.

Identification of new hit scaffolds by INPHARMA-guided virtual screening

INPHARMA, an NMR-based method that determines ligand binding poses, allows finding novel scaffolds as inhibitors of a target protein.

Understanding and targeting the Rho kinase pathway in erectile dysfunction

Erectile dysfunction (ED) is a common disorder that affects a quarter of US men, and has many causes, including endothelial impairment, low testosterone levels, prior surgical manipulation, and/or psychogenic components. Penile erection is a complex process requiring neurally mediated relaxation of arteriolar smooth muscle and engorgement of cavernosal tissues, mediated by nitric oxide (NO). Current medical therapies for ED largely seek to maximize endogenous NO signalling. Certain aetiologies, including diabetes, are difficult to treat with current modalities, emphasizing the need for new molecular targets. Research has demonstrated the importance of RhoA-Rho-associated protein kinase (ROCK) signalling in maintaining a flaccid penile state, and inhibition of RhoA-ROCK signalling potentiates smooth-muscle relaxation in an NO-independent manner. The mechanisms and effects of RhoA-ROCK signalling and inhibition suggest that the RhoA-ROCK pathway could prove to be a new therapeutic target for the treatment of ED.

Induction of oligodendrocyte differentiation and in vitro myelination by inhibition of rho-associated kinase

In inflammatory demyelinating diseases such as multiple sclerosis (MS), myelin degradation results in loss of axonal function and eventual axonal degeneration. Differentiation of resident oligodendrocyte precursor cells (OPCs) leading to remyelination of denuded axons occurs regularly in early stages of MS but halts as the pathology transitions into progressive MS. Pharmacological potentiation of endogenous OPC maturation and remyelination is now recognized as a promising therapeutic approach for MS. In this study, we analyzed the effects of modulating the Rho-A/Rho-associated kinase (ROCK) signaling pathway, by the use of selective inhibitors of ROCK, on the transformation of OPCs into mature, myelinating oligodendrocytes. Here we demonstrate, with the use of cellular cultures from rodent and human origin, that ROCK inhibition in OPCs results in a significant generation of branches and cell processes in early differentiation stages, followed by accelerated production of myelin protein as an indication of advanced maturation. Furthermore, inhibition of ROCK enhanced myelin formation in cocultures of human OPCs and neurons and remyelination in rat cerebellar tissue explants previously demyelinated with lysolecithin. Our findings indicate that by direct inhibition of this signaling molecule, the OPC differentiation program is activated resulting in morphological and functional cell maturation, myelin formation, and regeneration. Altogether, we show evidence of modulation of the Rho-A/ROCK signaling pathway as a viable target for the induction of remyelination in demyelinating pathologies.

Antitumoral effect of a selective Rho-kinase inhibitor Y-27632 against Ehrlich ascites carcinoma in mice

BACKGROUND

The Rho proteins and Rho-kinase (ROCK) enzymes are responsible for signal transduction, and cause cell permeability, contractility, differentiation, migration, proliferation or apoptosis depending on cell types. All of these functions are vital for cancer initiation and progression. In this study, the preventive and protective effects of a selective ROCK inhibitor Y-27632 against Ehrlich ascites carcinoma in Swiss albino mice were investigated.

METHODS

Adult male albino mice were divided into five equal groups, and Y-27632 (0.1, 1, and 10 mg/kg) was given to groups as two steps; before (pre-carcinoma) and after inoculation of carcinoma cell suspensions (post-carcinoma). At the end of the experiments (at day 15), cardiac blood samples, the ascitic fluid, and intestinal specimens were collected for histopathology and biochemical investigation.

RESULTS

Significant decreases in the body weight and immunostaining scores in small and large intestine for ROCK2, preservation of serum glutathione (GSH) levels, and an increase in tumor level of nitric oxide were recorded in groups pretreated with Y-27632. However, treatment with Y-27632 after tumor inoculation did not affect body weight and ROCK2 immunostaining scores, increased serum MDA levels, and decreased GSH levels.

CONCLUSIONS

This is the first study on the effectiveness of Y-27632 in this experimental tumor model. Our findings provided direct evidence for ROCK involvement in tumor development. These data suggest that pretreatment with Y-27632 has a protective effect against tumor formation.