(D)-Amino acid analogues of DT-2 as highly selective and superior inhibitors of cGMP-dependent protein kinase Ialpha

Efficacy and Toxicity Studies of Novel α-MSH Analogues with Antibiofilm Action and β-Lactam Resensitization Potential against MRSA

Methicillin-resistant Staphylococcus aureus (MRSA), a biofilm-forming recalcitrant pathogen with a multidrug-resistant profile, poses a pandemic threat to human health and is the leading cause of severe infections in both healthcare and community settings. In this study, toward designing novel α-MSH-based peptides with enhanced activity and stability against MRSA, particularly its stationary phase and biofilm, we explored a design approach to augment the hydrophobicity of an 8-mer C-terminal α-MSH(6-13)-based peptide Ana-5 through the incorporation of a bulky unnatural amino acid. The designed Ana-peptides overcame the limitation of diminished activity in biological media and exhibited enhanced antistaphylococcal activity and cell selectivity. With membrane rupture as the primary mode of action, the peptides exhibited inhibitory potential against S. aureus biofilms. Importantly, the peptides did not exhibit any adverse effects in the in vivo toxicity studies and were also able to significantly alleviate bacterial infection in a systemic infection mice model study. Additionally, the peptides retained their activity in the presence of serum and displayed a low propensity toward resistance development in MRSA cells. Moreover, the observed synergistic potential of Ana-10 with conventional antibiotics could be vital in resurrecting discarded antibiotics. Thus, this study provides us with an exciting lead, Ana-10, for further development against biofilm-based chronic S. aureus infections.

Targets of cGMP/cGKI in Cardiac Myocytes

The 3',5'-cyclic guanosine monophosphate (cGMP)-dependent protein kinase type I (cGKI aka PKGI) is a major cardiac effector acting downstream of nitric oxide (NO)-sensitive soluble guanylyl cyclase and natriuretic peptides (NPs), which signal through transmembrane guanylyl cyclases. Consistent with the wide distribution of the cGMP-generating guanylyl cyclases, cGKI, which usually elicits its cellular effects by direct phosphorylation of its targets, is present in multiple cardiac cell types including cardiomyocytes (CMs). Although numerous targets of cGMP/cGKI in heart were identified in the past, neither their exact patho-/physiological functions nor cell-type specific roles are clear. Herein, we inform about the current knowledge on the signal transduction downstream of CM cGKI. We believe that better insights into the specific actions of cGMP and cGKI in these cells will help to guide future studies in the search for predictive biomarkers for the response to pharmacological cGMP pathway modulation. In addition, targets downstream of cGMP/cGKI may be exploited for refined and optimized diagnostic and therapeutic strategies in different types of heart disease and their causes. Importantly, key functions of these proteins and particularly sites of regulatory phosphorylation by cGKI should, at least in principle, remain intact, although upstream signaling through the second messenger cGMP is impaired or dysregulated in a stressed or diseased heart state.

Method to generate highly stable D-amino acid analogs of bioactive helical peptides using a mirror image of the entire PDB

Biologics are a rapidly growing class of therapeutics with many advantages over traditional small molecule drugs. A major obstacle to their development is that proteins and peptides are easily destroyed by proteases and, thus, typically have prohibitively short half-lives in human gut, plasma, and cells. One of the most effective ways to prevent degradation is to engineer analogs from dextrorotary (D)-amino acids, with up to 105-fold improvements in potency reported. We here propose a general peptide-engineering platform that overcomes limitations of previous methods. By creating a mirror image of every structure in the Protein Data Bank (PDB), we generate a database of ∼2.8 million D-peptides. To obtain a D-analog of a given peptide, we search the (D)-PDB for similar configurations of its critical-"hotspot"-residues. As a proof of concept, we apply our method to two peptides that are Food and Drug Administration approved as therapeutics for diabetes and osteoporosis, respectively. We obtain D-analogs that activate the GLP1 and PTH1 receptors with the same efficacy as their natural counterparts and show greatly increased half-life.

A computational approach for designing D-proteins with non-canonical amino acid optimised binding affinity

Redesigning protein surface topology to improve target binding holds great promise in the search for highly selective therapeutics. While significant binding improvements can be achieved using natural amino acids, the introduction of non-canonical residues vastly increases sequence space and thus the chance to significantly out-compete native partners. The potency of protein inhibitors can be further enhanced by synthesising mirror image, D-amino versions. This renders them non-immunogenic and makes them highly resistant to proteolytic degradation. Current experimental design methods often preclude the use of D-amino acids and non-canonical amino acids for a variety of reasons. To address this, we build an in silico pipeline for D-protein designs featuring non-canonical amino acids. For a test scaffold we use an existing D-protein inhibitor of VEGF: D-RFX001. We benchmark the approach by recapitulating previous experimental optimisation with canonical amino acids. Subsequent incorporation of non-canonical amino acids allows designs that are predicted to improve binding affinity by up to -7.18 kcal/mol.

Pressure-induced oxidative activation of PKG enables vasoregulation by Ca2+ sparks and BK channels

Activation of Ca²⁺-sensitive, large-conductance potassium (BK) channels in vascular smooth muscle cells (VSMCs) by local, ryanodine receptor-mediated Ca²⁺ signals (Ca²⁺ sparks) acts as a brake on pressure-induced (myogenic) vasoconstriction-a fundamental mechanism that regulates blood flow in small resistance arteries. We report that physiological intraluminal pressure within resistance arteries activated cGMP-dependent protein kinase (PKG) in VSMCs through oxidant-induced formation of an intermolecular disulfide bond between cysteine residues. Oxidant-activated PKG was required to trigger Ca²⁺ sparks, BK channel activity, and vasodilation in response to pressure. VSMCs from arteries from mice expressing a form of PKG that could not be activated by oxidants showed reduced Ca²⁺ spark frequency, and arterial preparations from these mice had decreased pressure-induced activation of BK channels. Thus, the absence of oxidative activation of PKG disabled the BK channel-mediated negative feedback regulation of vasoconstriction. Our results support the concept of a negative feedback control mechanism that regulates arterial diameter through mechanosensitive production of oxidants to activate PKG and enhance Ca²⁺ sparks.

Strategies to Develop Inhibitors of Motif-Mediated Protein-Protein Interactions as Drug Leads

Protein-protein interactions are fundamental for virtually all functions of the cell. A large fraction of these interactions involve short peptide motifs, and there has been increased interest in targeting them using peptide-based therapeutics. Peptides benefit from being specific, relatively safe, and easy to produce. They are also easy to modify using chemical synthesis and molecular biology techniques. However, significant challenges remain regarding the use of peptides as therapeutic agents. Identification of peptide motifs is difficult, and peptides typically display low cell permeability and sensitivity to enzymatic degradation. In this review, we outline the principal high-throughput methodologies for motif discovery and describe current methods for overcoming pharmacokinetic and bioavailability limitations.

Synthetic Peptides as cGMP-Independent Activators of cGMP-Dependent Protein Kinase Iα

PKG is a multifaceted signaling molecule and potential pharmaceutical target due to its role in smooth muscle function. A helix identified in the structure of the regulatory domain of PKG Iα suggests a novel architecture of the holoenzyme. In this study, a set of synthetic peptides (S-tides), derived from this helix, was found to bind to and activate PKG Iα in a cyclic guanosine monophosphate (cGMP)-independent manner. The most potent S-tide derivative (S1.5) increased the open probability of the potassium channel KCa1.1 to levels equivalent to saturating cGMP. Introduction of S1.5 to smooth muscle cells in isolated, endothelium-denuded cerebral arteries through a modified reversible permeabilization procedure inhibited myogenic constriction. In contrast, in endothelium-intact vessels S1.5 had no effect on myogenic tone. This suggests that PKG Iα activation by S1.5 in vascular smooth muscle would be sufficient to inhibit augmented arterial contractility that frequently occurs following endothelial damage associated with cardiovascular disease.

Cardiac Hypertrophy Is Inhibited by a Local Pool of cAMP Regulated by Phosphodiesterase 2

RATIONALE

Chronic elevation of 3'-5'-cyclic adenosine monophosphate (cAMP) levels has been associated with cardiac remodeling and cardiac hypertrophy. However, enhancement of particular aspects of cAMP/protein kinase A signaling seems to be beneficial for the failing heart. cAMP is a pleiotropic second messenger with the ability to generate multiple functional outcomes in response to different extracellular stimuli with strict fidelity, a feature that relies on the spatial segregation of the cAMP pathway components in signaling microdomains.

OBJECTIVE

How individual cAMP microdomains affect cardiac pathophysiology remains largely to be established. The cAMP-degrading enzymes phosphodiesterases (PDEs) play a key role in shaping local changes in cAMP. Here we investigated the effect of specific inhibition of selected PDEs on cardiac myocyte hypertrophic growth.

METHODS AND RESULTS

Using pharmacological and genetic manipulation of PDE activity, we found that the rise in cAMP resulting from inhibition of PDE3 and PDE4 induces hypertrophy, whereas increasing cAMP levels via PDE2 inhibition is antihypertrophic. By real-time imaging of cAMP levels in intact myocytes and selective displacement of protein kinase A isoforms, we demonstrate that the antihypertrophic effect of PDE2 inhibition involves the generation of a local pool of cAMP and activation of a protein kinase A type II subset, leading to phosphorylation of the nuclear factor of activated T cells.

CONCLUSIONS

Different cAMP pools have opposing effects on cardiac myocyte cell size. PDE2 emerges as a novel key regulator of cardiac hypertrophy in vitro and in vivo, and its inhibition may have therapeutic applications.

Cancer-selective targeting of the NF-κB survival pathway with GADD45β/MKK7 inhibitors

Constitutive NF-κB signaling promotes survival in multiple myeloma (MM) and other cancers; however, current NF-κB-targeting strategies lack cancer cell specificity. Here, we identify the interaction between the NF-κB-regulated antiapoptotic factor GADD45β and the JNK kinase MKK7 as a therapeutic target in MM. Using a drug-discovery strategy, we developed DTP3, a D-tripeptide, which disrupts the GADD45β/MKK7 complex, kills MM cells effectively, and, importantly, lacks toxicity to normal cells. DTP3 has similar anticancer potency to the clinical standard, bortezomib, but more than 100-fold higher cancer cell specificity in vitro. Notably, DTP3 ablates myeloma xenografts in mice with no apparent side effects at the effective doses. Hence, cancer-selective targeting of the NF-κB pathway is possible and, at least for myeloma patients, promises a profound benefit.

The oligopeptide DT-2 is a specific PKG I inhibitor only in vitro, not in living cells

BACKGROUND AND PURPOSE

cGMP is involved in the regulation of many cellular processes including cardiac and smooth muscle contractility, aldosterone synthesis and inhibition of platelet activation. Intracellular effects cGMP are mediated by cGMP-dependent PKs, cGMP-regulated PDEs and cGMP-gated ion channels. PKG inhibitors are widely used to discriminate PKG-specific effects. They can be divided into cyclic nucleotide-binding site inhibitors such as Rp-phosphorothioate analogues (Rp-cGMPS), ATP-binding site inhibitors such as KT5823, and substrate binding site inhibitors represented by the recently described DT-oligopeptides. As it has been shown that Rp-cGMPS and KT5823 have numerous non-specific effects, we analysed the pharmacological properties of the oligopeptide (D)-DT-2 described as a highly specific, membrane-permeable, PKG inhibitor.

EXPERIMENTAL APPROACH

Specificity and potency of (D)-DT-2 to inhibit PKG activity was evaluated using biochemical assays in vitro and by substrate phosphorylation analysis in various cell types including human platelets, rat mesangial cells and rat neonatal cardiomyocytes.

KEY RESULTS

Despite potent inhibition of PKGI in vitro, (D)-DT-2 lost specificity for PKG in cell homogenates and particularly in living cells, as demonstrated by phosphorylation of different substrates. Instead, (D)-DT-2 modulated activity of other kinases including ERK, p38, PKB and PKC, thereby inducing unpredicted and often opposing functional effects.

CONCLUSIONS AND IMPLICATIONS

We conclude that DT-oligopeptides, as other inhibitors, cannot be used to specifically inhibit PKG in intact cells. Therefore, no specific pharmacological PKG inhibitors are available, and reliable studies of PKG signalling can only be made by using RNA knockdown or genetic deletion methods.

cGMP-Dependent Protein Kinase Inhibitors in Health and Disease

cGMP-dependent protein kinases (PKG) exhibit diverse physiological functions in the mammalian system e.g., in vascular and gastrointestinal smooth muscles, in platelets, in kidney, in bone growth, nociception and in the central nervous system. Furthermore, PKG were found in insects and in the malaria parasite Plasmodium falciparum. Two different genes of PKG exist: a) the PKG-I gene that is expressed as cytosolic PKG-Iα or PKG-Iβ isoform, and b) the PKG-II gene, which expresses the membrane associated PKG-II protein. The enzyme kinetics, the localization and the substrates of these PKG enzymes differ utilizing different physiological functions. Various inhibitors of PKG were developed directed against diverse functional regions of the kinase. These inhibitors of PKG have been used to analyse the specific functions of these enzymes. The review article will summarize these different inhibitors regarding their specificity and their present applications in vitro and in vivo. Furthermore, it will be discussed that the distinct inhibition of the PKG enzymes could be used as a valuable pharmacological target e.g., in the treatment of cardiovascular diseases, diarrhea, cancer or malaria.

Sub-Nanomolar Sensitivity of Nitric Oxide Mediated Regulation of cGMP and Vasomotor Reactivity in Vascular Smooth Muscle

Nitric oxide (NO) is a potent dilator of vascular smooth muscle (VSM) by modulating intracellular cGMP ([cGMP]_i) through the binding and activation of receptor guanylyl cylases (sGC). The kinetic relationship of NO and sGC, as well as the subsequent regulation of [cGMP]_i and its effects on blood vessel vasodilation, is largely unknown. In isolated VSM cells exposed to both pulsed and clamped NO we observed transient and sustained increases in [cGMP]_i, with sub-nanomolar sensitivity to NO (EC₅₀ = 0.28 nM). Through the use of pharmacological inhibitors of sGC, PDE5, and PKG, a comprehensive VSM-specific modeling algorithm was constructed to elucidate the concerted activity profiles of sGC, PDE5, phosphorylated PDE5, and PDE1 in the maintenance of [cGMP]_i. In small pressure-constricted arteries of the resistance vasculature we again observed both transient and sustained relaxations upon delivery of pulsed and clamped NO, while maintaining a similarly high sensitivity to NO (EC₅₀ = 0.42 nM). Our results propose an intricate dependency of the messengers and enzymes involved in cGMP homeostasis, and vasodilation in VSM. Particularly, the high sensitivity of sGC to NO in primary tissue indicates how small changes in the concentrations of NO, irrespective of the form of NO delivery, can have significant effects on the dynamic regulation of vascular tone.

Adenosine analogue-oligo-arginine conjugates (ARCs) serve as high-affinity inhibitors and fluorescence probes of type I cGMP-dependent protein kinase (PKGIalpha)

INTRODUCTION

Type I cGMP-dependent protein kinase (PKGIalpha) belongs to the family of cyclic nucleotide-dependent protein kinases and is one of the main effectors of cGMP. PKGIalpha is involved in regulation of cardiac contractility, vasorelaxation, and blood pressure; hence, the development of potent modulators of PKGIalpha would lead to advances in the treatment of a variety of cardiovascular diseases.

AIM

Representatives of ARC-type compounds previously characterized as potent inhibitors and high-affinity fluorescent probes of PKA catalytic subunit (PKAc) were tested towards PKGIalpha to determine that ARCs could serve as activity regulators and sensors for the latter protein kinase both in vitro and in complex biological systems.

RESULTS

Structure-activity profiling of ARCs with PKGIalpha in vitro demonstrated both similarities as well as differences to corresponding profiling with PKAc, whereas ARC-903 and ARC-668 revealed low nanomolar displacement constants and inhibition IC(50) values with both cyclic nucleotide-dependent kinases. The ability of ARC-based fluorescent probes to penetrate cell plasma membrane was demonstrated in the smooth muscle tissue of rat cerebellum isolated arteries, and the compound with the highest affinity in vitro (ARC-903) showed also potential for in vivo applications, fully abolishing the PKG1alpha-induced vasodilation.

Development of a proteolytically stable retro-inverso peptide inhibitor of beta-amyloid oligomerization as a potential novel treatment for Alzheimer's disease

The formation of beta-amyloid (Abeta) deposits in the brain is likely to be a seminal step in the development of Alzheimer's disease. Recent studies support the hypothesis that Abeta soluble oligomers are toxic to cells and have potent effects on memory and learning. Inhibiting the early stages of Abeta aggregation could, therefore, provide a novel approach to treating the underlying cause of AD. We have designed a retro-inverso peptide (RI-OR2, H(2)N-r<--G<--k<--l<--v<--f<--f<--G<--r-Ac), based on a previously described inhibitor of Abeta oligomer formation (OR2, H(2)N-R-G-K-L-V-F-F-G-R-NH(2)). Unlike OR2, RI-OR2 was highly stable to proteolysis and completely resisted breakdown in human plasma and brain extracts. RI-OR2 blocked the formation of Abeta oligomers and fibrils from extensively deseeded preparations of Abeta(1-40) and Abeta(1-42), as assessed by thioflavin T binding, an immunoassay method for Abeta oligomers, SDS-PAGE separation of stable oligomers, and atomic force microscopy, and was more effective against Abeta(1-42) than Abeta(1-40). In surface plasmon resonance experiments, RI-OR2 was shown to bind to immobilized Abeta(1-42) monomers and fibrils, with an apparent K(d) of 9-12 muM, and also acted as an inhibitor of Abeta(1-42) fibril extension. In two different cell toxicity assays, RI-OR2 significantly reversed the toxicity of Abeta(1-42) toward cultured SH-SY5Y neuroblastoma cells. Thus, RI-OR2 represents a strong candidate for further development as a novel treatment for Alzheimer's disease.