Design and synthesis of engineered peptides to target undruggable PPIs: from in silico to in vitro studies

[eng] Major unsolved diseases such as Cancer, cardiopathies or neurodegenerative disorders are frequently related with the malunction of complex protein networks. These networks are integrated by the interaction of multiple proteins that in case of a misregulation can trigger an undesired effect. Therefore, disruption of protein-protein interactions (PPIs), that are involucrated in a protein signalling cascade which is relevant for a particular diseases, is a hot topic in pharmaceutical industry. Unfortunately, traditional small molecules have been found to not be the most suitable inhibitiors of these therapeutic targets as PPI interfaces are characterized by a flat area with a lack of cavities that can fit a small molecule. In this scenario, peptides has called the attention in the drug discovery field for be a more appropiate candidates to target PPIs. Peptides are found in the chemical space between small molecules and antibodies, usullay contain between 2-50 amino acids and have an approximated weight of 250-10.000 Da. Then, their medium size allows a efficient recognition of the target protein without the need of well formed cavieties on the protein surface. However, peptides are characterized by a poor permeability and low stability in blood stream which had limited their therapeutic application in the past. Opportunately, introduction of non-natural amino acids and D-amino acids, N-alkylations of peptide backbone, cyclization and N-terminal and C-terminal modified cappings improve the biophysical properties along with the affinity for the receptor protein. Then, the use of engineered peptides, so-called peptidomimetics, is a promissing approach to target PPIs that can improve the binding potency of natural peptides and overcoming their major drawbacks at the same time. This thesis was carried out at Iproteos, a biotech company positioned in the use of peptidomimetics to target intracellular PPIs. The company has developed an in-house technology coined IPROTech, which is a platform that applys different in silico tools that are focused in the design of peptidomimetics, which are synthesized manually, quantified and finally evaluated in vitro. The experimental results are reintroduced in the platform and the process is repeated iteratively until achieve a final lead candidate. Hence, in the present work, IPROTech was applied to found de novo peptidomimetic molecules that inhibit the interaction of 4 different PPIs that are considered of therapeutic importance, Talin- Vinculin (Cancer), Rad51-BRCA2 (Cancer), Ras-Effectors (Cancer) and Retromer-L2 (HPVs infection). For each PPI, a collabration project with an academic group expert in field was setted up. Iproteos was in charge of the in silico studies of the target protein in order to design and synthesized a set peptidomimetic sequences that were predicted to disrupt the PPI of interest. On the other hand, the collaborators were responsible of the experimental evualtion of the synthesized compounds. In this terms, at least 1 hit was found for each PPI when evaluated in vitro, demonstrating an outsanding overall succes-rate of 31 % when all synthesized peptidomimetics were evaluated in vitro. Additinoally, the inclusion of new fancy builduing blocks into the compounds sintheysis, N-alkylation of the peptidomimetics backbone, pearmeability across biological barriers or the use of cyclodextrins as solvating excipient were other points studied as well.[cat] Trobar nous fàrmacs capaços de trencar interaccions proteïna-proteïna, que d’alguna manera estan involucrades amb una malaltia, és de gran interès en el camp de la indústria farmacèutica. No obstant això, aquest tipus de diana terapèutica normalment no presenten cap cavitat ben definida a la seva superfície, característica necessària per albergar les tradicionals molècules petites. Per aquest motiu, la utilització de pèptids com a possibles fàrmacs és una aproximació molt prometedora perquè en tenir una mida molecular superior poden establir més interaccions amb la proteïna receptora afavorint així la seva unió. Però, aquesta aproximació està limitada per les propietats bioquímiques dels pèptids, ja que normalment són poc permeables i amb una baixa estabilitat un cop administrats. Afortunadament, els avanços fets en la síntesi de pèptids ha permès afegir modificacions sobre la seqüència dels pèptids per tal de millora les seves propietats, això inclou amino àcids no naturals, N-alquilacions, diferent tipus de N-terminals i C-terminals, entre altres. Els compostos obtinguts quan s’aplica aquesta enginyeria es coneixen com a peptidomimetics. Aquesta tesi es va realitzar a Iproteos. Iproteos és una petita empresa biotecnològica, focalitzada en l’ús de peptidomimetics per tal d’inhibir IPPs relacionades amb alguna malaltia. Per fer possible aquesta tasca, Iproteos ha creat una tecnologia, IPROTech, que agrupa tècniques computacionals per tal de cribrar la proteïna d’interès i genera estructures peptidometiques que més tard són sintetitzades, purificades i quantificades. Per aquesta tesi, es va aplicar la tecnologia IPROTech per trobar peptidomimetics amb la capacitat d’inhibir quatre IPP de rellevància terapèutica, Talina-Vinculina (càncer), Rad51- BRCA2 (càncer), Ras-Effectors (càncer) i Retromer-L2 (HPVs). Per cadascuna d’aquestes dianes, a Iproteos es va realitzar els estudis in silico i la síntesi dels peptidomimetics mentre que l'avaluació experimental la van fer grups acadèmics experts en cada camp. En tots els casos es va trobar almenys un compost capaç de trencar amb la interacció. Addicionalment propietats com la solubilitat, permeabilitat o estabilitat van ser avaluades per aquells compostos actius. Finalment, gràcies a les dades generades, alguns d’aquests compostos es van poder optimitzar obtenint un candidat final més potent encara

Azacyclopeptide synthesis and their neuroprotective activity against Aβ toxicity

Le mauvais repliement et l’agrégation des protéines représentent une cause fondamentale des pathologies amyloïdes. Des dépôts de protéines sous la forme de fibrilles amyloïdes sont une composante caractéristique de plus de vingt maladies neurodégénératives incluant la maladie d’Alzheimer, la maladie de Parkinson et la maladie d’Huntington. Des nanotubes composés de peptides-α -D,L cycliques synthétiques peuvent mimer les propriétés structurelles et biochimiques des protéines amyloïdes. L’introduction de résidus aza-aminés dans des peptides α -D,L cycliques a été étudiée dans le but d’augmenter les interactions hydrogènes intermoléculaires entre les différents macrocycles superposés composant le nanotube. Les peptides aza-α-D,L cycliques devraient aussi posséder une meilleure capacité d’interaction avec les feuillets des oligomères amyloïdes. Le peptide d’intérêt CP-2 possède la séquence [l-J-w-H-s-K], où les lettres minuscules et majuscules font référence respectivement aux acides aminés D et L, les crochets indiquent une structure cyclique et la lettre « J » représente la norleucine. En exploitant la capacité des semicarbazides d’accroitre les ponts hydrogènes intermoléculaires, nous avons remplacés successivement chacun des acides aminés de la séquence CP-2 par un résidu aza-glycine, obtenant une librairie d’azapeptides cycliques. Ces peptides ont été testés pour leur propriété neuroprotectrice contre les amyloïdes en utilisant un essai de viabilité cellulaire (essai MTT). Le peptide où la D-serine a été remplacée par une aza-glycine, CP-2 (4), s’est avéré plus efficace que CP-2. Il s’agit du premier exemple d’introduction d’un résidu aza-aminé dans un peptide α-D,L cyclique, et ces résultats pourraient être extrapolés à d’autres peptides α-D,L cycliques d’intérêt thérapeutique.Protein misfolding and aggregation are the fundamental causes of amyloid diseases. Deposits of proteins in the form of amyloid fibrils and plaques are the characteristic features of more than twenty degenerative conditions, including Alzheimer’s, Parkinson’s, and Huntington’s diseases. Synthetic cyclic D,L-α-peptide nanotubes can mimic the structural and biochemical properties of amyloid proteins. The introduction of aza-residues into cyclic D,L-α-peptides was studied to enhance intermolecular hydrogen bonding between stacked rings within the tube structures. The resulting cyclic aza-D,L-α-peptides were also expected to exhibit enhanced propensity to interact with the sheet structures of amyloid oligomers. The lead peptide CP-2 features the sequence [l-J-w-H-s-K] in which lower and upper-case letters indicate D- and L-amino acids, respectively, square brackets designate a cyclic structure, and J denotes norleucine. There are no reports for introduction of aza-residues into cyclic D,L-α-peptides. Considering the potential for semicarbazides to enhance intermolecular hydrogen bonding, we performed an aza-glycine scan of the CP-2 sequence by preparing a focused library of azapeptides. All the cyclic aza-glycine peptides were tested for neuroprotective activity against amyloid using cell viability assay (MTT assay). The aza-glycine replacing D-serine i.e., [azaG2]-CP-2 (4) was found to be more potent than CP-2. This is the first example of introducing an aza-amino residue into a cyclic D, L-α-peptide, and these results could be extrapolated to other cyclic D, L-α-peptides of therapeutic interest

TARGETING THE NRF2/KEAP1 INTERACTION

The Nrf2/Keap1 protein-protein interaction (PPI) regulates activity of the Nrf2 antioxidant and anti-inflammatory pathway. The transcription factor Nrf2 has been found to be a key mediator in the resolution of inflammation and the progression of chronic diseases. Most known inducers of the Nrf2 pathway act by covalent modification of Keap1 via electrophilic functional groups. Controlled induction of the Nrf2 pathway via specific disruption of the Nrf2/Keap1 interaction is an attractive therapeutic target. This work describes a cell penetrating, TAT-Nrf2 peptide which targets the Nrf2/Keap1 interaction in vitro. Induction of downstream genes is both sequence and dose dependent. In an established model of bacterial sepsis, the peptide reduces pro-inflammatory mediators. Investigation of both cell penetrating and Keap1 binding sequences has identified the requirements for effective Nrf2 induction in cell based assays. An in vitro purified protein, fluorescence polarisation (FP) assay was established in order to rapidly characterise these peptides. Based on the secondary structure of the Keap1 binding portion of Nrf2, further peptides were designed to constrain the conformation and mimic the full protein, while reducing overall size. Synthesis of cyclic peptides has identified the minimal sequence required for efficient binding and provides significant improvement in affinity over linear sequences. Several macrocyclisation techniques were explored in an attempt to retain biological activity, without the need for cell penetration sequences. Initially, disulfide bridge formation was used to produce peptides with affinities for Keap1 similar to the TAT-Nrf2 peptides at considerably reduced size. Subsequently, both head-to-tail cyclisation and peptide stapling were examined in order to restore potency in cell based assays. Finally, an alternative method for identification of Nrf2/Keap1 disruptors was explored. In silico docking calculations were used to identify potential novel PPI disruptors through library screening. Extracted hits were assessed using the FP assay, validating its use for high throughput screening

A computational study of cyclic peptides with vibrational circular dichroism

Cyclic peptides are a class of molecules that has shown antimicrobial potential. These are complex compounds to investigate with their large conformational space and multiple chiral centers. A technique that can be used to investigate both conformational preferences and absolute configuration (AC) is vibrational circular dichroism (VCD). To extract information from the experimental VCD spectra a comparison with calculated spectra is often needed and this is the focus of this thesis: the calculation of VCD spectra. The VCD spectra are very sensitive to small structural changes, and to accurately calculate the spectra, all important conformers need to be identified. The first part of this thesis has been to establish a reliable computational protocol using meta-dynamics to sample the conformational space and ab initio methods to calculate the spectra for cyclic peptides. Using our protocol, we have investigated if VCD alone can determine the AC of cyclic tetra- and hexapeptides. We show that it is possible to determine the AC of the cyclic peptides with two chiral centers while for the peptides with three and four chiral centers, VCD is at best able to reduce the number of possible ACs and further investigation with other techniques is needed. Further, we investigated four cyclic hexapeptides with antimicrobial potential. These peptides, in contrast to the ones used for validating the protocol, consist of several amino acids with long and positively charged side chains. For these peptides, a molecular dynamics based approach provided VCD spectra in better agreement with experiment than our protocol. Reasons for this may be the lack of atomistic detail in the solvent model used during the conformational search and insufficient description of dispersion interactions during the meta-dynamics simulation

The design, synthesis and evaluation of Nrf2-Keap1 PPI inhibitors: a modular, virtual screening-led approach

Nrf2 (nuclear factor erythroid 2-related factor 2) is a cap’n’collar bZIP transcription factor and is the main activator of the transcription of over 100 genes that play roles in responses to oxidative stress and detoxifying xenobiotics. The main control of Nrf2 levels is exercised by Keap1 (Kelchlike ECH-associated protein 1) which facilitates the ubiquitination of Nrf2 and therefore its degradation. Keap1 is oxidation-sensitive and upon exposure to oxidants, it changes its conformation and binds Nrf2 tightly. Consequently, de novo-synthesised Nrf2 can accumulate. Following its discovery, Nrf2 received most attention in relation to cancer. Over the time, however, its implication in other pathologies have been more and more acknowledged, namely in inflammation and most importantly in neurodegenerative diseases. Especially Parkinson’s disease (PD), which is the second most common neurodegenerative disease, caused by the progressive loss of dopaminergic neurons in the substantia nigra, has been linked to oxidative stress. The role Nrf2 plays has been demonstrated in animal models of α-synuclein aggregation or chemically induced parkinsonism, where an increase in Nrf2 expression provided neuroprotection and a slowing of disease progression. Therefore, the inhibition of Keap1- mediated Nrf2 degradation presents a promising strategy for the mechanistic study and the therapy of PD. Several structures showing high potency towards Keap1 inhibition have been described, with activities in the nanomolar range. However, these compounds are large, or hydrophilic and charged. In order to develop new scaffolds, extensive virtual screening assays have been conducted which resulted in hits with promising molecular scaffolds. At the same time, chemical modifications on a known triazole structure have been performed in order to elucidate structure-activity relationships. In this thesis, the molecular modelling lead, as well the synthetic approach to both project components are described. Finally, the results of a competitive fluorescence polarisation (FP) assay for the second set of compounds are presented

COMPUTATIONAL TECHNIQUES TO EVALUATE AT ATOMIC LEVEL THE MECHANISM OF MOLECULAR BINDING

Integrins are an important class of transmembrane receptors that relay signals bidirectionally across the plasma membrane, regulating several cell functions and playing a key role in diverse pathological processes. Specifically, integrin subtype \u3b1IIb\u3b23 is involved in thrombosis and stroke, while subtypes \u3b1v\u3b23 and \u3b15\u3b21 play an important role in angiogenesis and tumor progression. They therefore emerged as attractive pharmacological targets. In the past decades several peptides and peptidomimetics targeting these proteins and based on the integrin recognition motif RGD (Arg-Gly-Asp) have been developed, whereby their affinity and selectivity for a specific integrin subtype have been fine-tuned by modulation of RGD flanking residues, by cyclization or by introduction of chemical modifications. Thus far, the design and development of RGD-based cyclopeptides have been mainly based on empirical approaches, requiring expensive and time-consuming synthesis campaigns. In this field, the employment of computational tools, that could be valuable to accelerate the drug design and optimization process, has been limited by the inherent difficulties to predict in silico the three-dimensional structure and the inhibitory activity of cyclopeptides. However, recent improvements in both computational resources and in docking and modeling techniques are expected to open new perspectives in the development of cyclopeptides as modulators of protein-protein interactions and, particularly, as integrin inhibitors. Within this PhD project, I have investigated the applicability of computational techniques in predicting and rationalizing how the environment of the recognition-motif in cyclopeptides (i.e. flanking residues and introduction of chemical modification) could influence their integrin affinity and selectivity. These features can regulate integrin affinity both by favoring direct interactions with the receptor and/or by modulating the three-dimensional conformation properties of the recognition motif. To take into account both these aspects, I have proposed and optimized a multi-stage computational protocol in which an exhaustive conformational sampling of the investigated cyclopeptides is followed by docking calculations and re-scoring techniques. Specifically: i) the exhaustive sampling could be achieved by using Metadynamics in its Bias Exchange variant (BE-META), an enhanced sampling technique which represents a valuable methodology for the acceleration of rare events, allowing to cross the high free energy barriers characteristic of cyclopeptides and providing reliable estimations of the populations of the accessible conformers. ii) The docking calculations, complemented with the re-scoring technique MM-GB/SA (Molecular Mechanics Generalized Born Surface Area) and the cluster analysis of the decoy poses, allow to evaluate the ability of each peptide to engage interactions with the receptors and to rank the docking poses according to their binding ability; iii) a joint analysis of the previous outcomes results in a reliable ranking of cyclopeptides based on their binding affinity and in the rationalization of their structure-activity relationship. This computational protocol has been exploited in two different applications, illustrated within the thesis. In the first application the protocol has been applied to rationalize how the introduction of chemical modifications, specifically backbone N-methylation, impacts on the equilibrium conformation and consequently on the integrin affinity of five RGD containing cyclic hexapeptides, which were previously generated by the group of professor Kessler to modulate their selectivity for \u3b1IIb\u3b23 integrin. The study revealed that backbone N-methylation affects the preferences of the \u3c6 dihedral angle of the methylated residue, specifically favoring the adoption of additional conformations, characterized by a 180\ub0 twist of the peptide bond plane preceding the methylated residue. These twists of dihedral angles were found to have relevant consequences on the cyclopeptides conformation, influencing the formation of intra-molecular hydrogen bonds as well as some structural features which are known to be fundamental in integrin binding. Both structural analysis and docking calculations allowed to identify the \u201cbioactive\u201d conformation (i.e. an extended RGD conformation able to recapitulate the canonical electrostatic and the additional stabilizing hydrophobic interactions). Of note, the cyclopeptides that are pre-organized, already in their free state, in this bioactive conformation are the ones displaying the best \u3b1IIb\u3b23 binding affinity in terms of IC50 values, confirming that pre-organization of cyclopeptides in solution can strongly affect their binding strength to the receptor and demonstrating that the knowledge of their conformational equilibrium is fundamental to provide reliable affinity predictions. In the second application, I have focused my attention on cyclopeptides harboring a recently discovered integrin recognition motif: isoDGR (isoAsp-Gly-Arg), deriving from the spontaneous deamidation of NGR (Asp-Gly-Arg) sequence present in integrin natural ligands. As a preliminary step, I have systematically tested the accuracy of eight Molecular Mechanics force fields in reproducing the equilibrium properties of isoDGR-based cyclopeptides, for which NMR experiments have been acquired. The comparison between simulated and NMR-derived data (i.e. chemical shifts and J scalar couplings) revealed that, while most of the investigated force fields can properly reproduce the equilibrium conformational properties of cyclic peptides, only two of them (i.e. the AMBER force fields ff99sb-ildn and ff99sb*-ildn) are able to recover the NMR observables characteristics of the non-standard residue isoAspartate with an accuracy close to the systematic uncertainty. Overall, these results suggest that the transferability of force field parameters to non standard amino acids is not straightforward. However, two force fields allowed to obtain a satisfactory accuracy and have been therefore employed for the subsequent investigation. I thus applied the computational protocol to rationalize the diverse selectivity and affinity profiles for integrins \u3b1v\u3b23 and \u3b15\u3b21, both related to cancer, displayed by three isoDGR-based cyclic hexapeptides. These molecules differ in the residues flanking the isoDGR motif and show appealing tumor-homing properties; specifically it has been shown that one of these, c(CGisoDGRG), can be coupled with human serum albumin through a chemical linker to be used as a drug delivery agent for functionalized gold nanoparticles. Herein, I investigated the role of the chemical linker in improving affinity and selectivity of c(CGisoDGRG) for \u3b1v\u3b23. The application of the multi-stage protocol allowed to propose an explanation for the different selectivity profiles displayed by these molecules, where the direct interactions engaged by the flanking residues and/or their steric hindrance seem to be largely responsible for the observed different affinities. As a last result, through the combination of MD and NMR techniques, I demonstrated that the chemical linker improved the \u3b1v\u3b23 affinity of c(CGisoDGRG) by engaging direct interactions with the receptor and I proposed two possible complex models, which well-reproduce data from Saturation Transfer Difference experiments. Overall, in this PhD work I have shown that the combination of different computational techniques, BE-META, docking and MM-GB/SA re-scoring, could be a reliable approach to perform structure-activity relationship studies in cyclopeptides. Specifically, the proposed protocol is able to predict the influence of the recognition motif environment (i.e. chemical modification and flanking residues) on integrin affinities. These two features regulate integrin affinity differently: the first one by conformational modulation of the recognition motif, the second by engaging direct interactions with the receptor. Of note, the approach can deal with both these mechanisms of affinity modulation. We expect that the protocol herein described could be used in future to screen novel peptides library or to complement biochemical experiments during the drug optimization stages, assisting organic chemists in the design of more effective integrin-targeting peptides

Review on bibliography related to antimicrobials

In this report, a bibliographic research has been done in the field of antimicrobials.In this report, a bibliographic research has been done in the field of antimicrobials. Not all antimicrobials have been included, but those that are being subject of matter in the group GBMI in Terrassa, and others of interest. It includes chitosan and other biopolymers. The effect of nanoparticles is of great interest, and in this sense, the effect of Ag nanoparticles and antibiotic nanoparticles (nanobiotics) has been revised. The report focuses on new publications and the antimicrobial effect of peptides has been considered. In particular, the influence of antimicrobials on membranes has deserved much attention and its study using the Langmuir technique, which is of great utility on biomimetic studies. The building up of antimicrobials systems with new techniques (bottom-up approach), as the Layer-by-Layer technique, can also be found in between the bibliography. It has also been considered the antibiofilm effect, and the new ideas on quorem sensing and quorum quenching.Preprin

Development of an Electrochemical Technique for Oxidative Surface Mapping to Investigate Solution-Phase Protein Dynamics with High Performance Mass Spectrometry and Advanced Informatics

Oxidative protein surface mapping has gained popularity over recent years within the mass spectrometry (MS) community for gleaning information about the solvent accessibility of folded protein structures. The hydroxyl radical targets a wide breadth of reactive amino acids with a stable mass tag that withstands subsequent MS analysis. A variety of techniques exist for generating hydroxyl radicals, with most requiring sources of radiation or caustic oxidizing reagents. The purpose of this research was to evaluate the novel use of electrochemistry for accomplishing a comparable probe of protein structure with a more accessible tool. Two different working electrode types were tested across a range of experimental parameters, including voltage, flow rate, and solution electrolyte composition, to affect the extent of oxidation on intact proteins. Results indicated that the boron-doped diamond electrode was most valuable for protein research due to its capacity to produce hydroxyl radicals and its relatively low adsorption profile. Oxidized proteins were collected from the electrochemical cell for intact protein and peptide level MS analysis. Peptide mass spectral data were searched by two different “hybrid” software packages that incorporate de novo elements into a database search to accommodate the challenge of searching for more than forty possible oxidative mass shifts. Preliminary data showed reasonable agreement between amino acid solvent accessibility and the resulting oxidation status of these residues in aqueous solution, while more buried residues were found to be oxidized in “non-native” solution. Later experiments utilized higher flow rates to reduce protein residence time inside the electrochemical flow chamber, along with a different cell activation approach to improve controllability of the intact protein oxidation yield. A multidimensional chromatographic strategy was employed to improve dynamic range for detecting oxidation of lower reactivity residues. Along with increased levels of oxidation around “reactive hotspot” sites, the enhanced sensitivity of these measurements uncovered a significant level of background oxidation in control proteins. While further work is needed to determine the full utility that BDD electrochemistry can lend protein structural studies, the experimental refinements reported here pave the way for improvements that could lead to a high-throughput structural pipeline complementary to predictive modeling efforts

Synthetic Peptides and Peptidomimetics: From Basic Science to Biomedical Applications

This Special Issue, entitled "Synthetic Peptides and Peptidomimetics: From Basic Science to Biomedical Applications", has included both reviews and original research contributions focused on the chemical design and biomedical applications of structurally modified bioactive peptides. The papers collected show how successful this class of molecules still is, both as model molecules for studying the structure of proteins and as potential therapeutics and diagnostics, and also as laboratory tools for advanced basic and applied studies. The large scientific community working in this field is in fact very active and productive, and is making the most of the potential and versatility of these molecules to generate increasingly interesting and innovative molecules of therapeutic interest and to understand the fundamental molecular mechanisms of life