Self-assembly of the octapeptide lanreotide and lanreotide-based derivatives: the role of the aromatic residues

The relationship between the tyrosine residue 850-830 cm-1 Raman doublet intensity ratio and the aromatic side chain χ1 torsion angle

Tyrosine (Tyr) residue in a peptide chain is characterized by the presence of seven Raman markers, referred to as Yi (i = 1, …, 7), distributed over the middle wavenumber spectral region. Particularly, the changes observed in the relative intensity of Y5 and Y6 markers, appearing as a side by side doublet at ca. 850-830 cm-1, has received a great attention. Primarily assigned to a Fermi-resonance effect between phenol ring planar and nonplanar modes, former density functional theory calculations led us to affiliate the Y5-Y6 doublet to two distinct fundamental modes. Furthermore, despite the previous assumptions, it was evidenced that the reversal of the doublet intensity ratio cannot be solely explained by hydrogen bonding on the phenol hydroxyl group involved in Tyr. Herein, upon analyzing the observed and theoretical data collected from the cationic species of the tripeptide Gly-Tyr-Gly, the crucial effect of the aromatic side chain orientation, especially that of the χ1 torsion angle defined around the CαCβ bond, on the Tyr doublet intensity ratio has been evidenced.

Aggregation Behavior of Structurally Similar Therapeutic Peptides Investigated by 1H NMR and All-Atom Molecular Dynamics Simulations

Understanding of peptide aggregation propensity is an important aspect in pharmaceutical development of peptide drugs. In this work, methodologies based on all-atom molecular dynamics (AA-MD) simulations and ¹H NMR (in neat H₂O) were evaluated as tools for identification and investigation of peptide aggregation. A series of structurally similar, pharmaceutically relevant peptides with known differences in aggregation behavior (D-Phe⁶-GnRH, ozarelix, cetrorelix, and degarelix) were investigated. The ¹H NMR methodology was used to systematically investigate variations in aggregation with peptide concentration and time. Results show that ¹H NMR can be used to detect the presence of coexisting classes of aggregates and the inclusion or exclusion of counterions in peptide aggregates. Interestingly, results suggest that the acetate counterions are included in aggregates of ozarelix and cetrorelix but not in aggregates of degarelix. The peptides investigated in AA-MD simulations (D-Phe⁶-GnRH, ozarelix, and cetrorelix) showed the same rank order of aggregation propensity as in the NMR experiments. The AA-MD simulations also provided molecular-level insights into aggregation dynamics, aggregation pathways, and the influence of different structural elements on peptide aggregation propensity and intermolecular interactions within the aggregates. Taken together, the findings from this study illustrate that ¹H NMR and AA-MD simulations can be useful, complementary tools in early evaluation of aggregation propensity and formulation development for peptide drugs.

Self-Assembling Peptides: From Design to Biomedical Applications

Self-assembling peptides could be considered a novel class of agents able to harvest an array of micro/nanostructures that are highly attractive in the biomedical field. By modifying their amino acid composition, it is possible to mime several biological functions; when assembled in micro/nanostructures, they can be used for a variety of purposes such as tissue regeneration and engineering or drug delivery to improve drug release and/or stability and to reduce side effects. Other significant advantages of self-assembled peptides involve their biocompatibility and their ability to efficiently target molecular recognition sites. Due to their intrinsic characteristics, self-assembled peptide micro/nanostructures are capable to load both hydrophobic and hydrophilic drugs, and they are suitable to achieve a triggered drug delivery at disease sites by inserting in their structure's stimuli-responsive moieties. The focus of this review was to summarize the most recent and significant studies on self-assembled peptides with an emphasis on their application in the biomedical field.

Synthesis, Characterization and Evaluation of Peptide Nanostructures for Biomedical Applications

There is a challenging need for the development of new alternative nanostructures that can allow the coupling and/or encapsulation of therapeutic/diagnostic molecules while reducing their toxicity and improving their circulation and in-vivo targeting. Among the new materials using natural building blocks, peptides have attracted significant interest because of their simple structure, relative chemical and physical stability, diversity of sequences and forms, their easy functionalization with (bio)molecules and the possibility of synthesizing them in large quantities. A number of them have the ability to self-assemble into nanotubes, -spheres, -vesicles or -rods under mild conditions, which opens up new applications in biology and nanomedicine due to their intrinsic biocompatibility and biodegradability as well as their surface chemical reactivity via amino- and carboxyl groups. In order to obtain nanostructures suitable for biomedical applications, the structure, size, shape and surface chemistry of these nanoplatforms must be optimized. These properties depend directly on the nature and sequence of the amino acids that constitute them. It is therefore essential to control the order in which the amino acids are introduced during the synthesis of short peptide chains and to evaluate their in-vitro and in-vivo physico-chemical properties before testing them for biomedical applications. This review therefore focuses on the synthesis, functionalization and characterization of peptide sequences that can self-assemble to form nanostructures. The synthesis in batch or with new continuous flow and microflow techniques will be described and compared in terms of amino acids sequence, purification processes, functionalization or encapsulation of targeting ligands, imaging probes as well as therapeutic molecules. Their chemical and biological characterization will be presented to evaluate their purity, toxicity, biocompatibility and biodistribution, and some therapeutic properties in vitro and in vivo. Finally, their main applications in the biomedical field will be presented so as to highlight their importance and advantages over classical nanostructures.

Multistimuli-responsive drug vehicles based on gold nanoflowers for chemophotothermal synergistic cancer therapy

AIM

To design and synthesize a novel multistimuli-responsive drug vehicle based on gold nanoflowers (AuNFs) for chemophotothermal synergistic cancer therapy.

MATERIALS & METHODS

Multistimuli-responsive drug-delivery system based on doxorubicin (DOX)/polydopamine (PDA)-functionalized AuNFs (Lan-AuNFs@PDA/DOX) was prepared. The structural characteristics, photothermal properties and stimuli-responsive drug release properties of Lan-AuNFs@PDA/DOX were evaluated. Antitumor studies in vivo and in vitro were performed.

RESULTS

Lan-AuNFs@PDA/DOX exhibited uniform morphology, excellent biocompatibility and photothermal conversion efficiency, which could also respond to stimulus including near infrared light and pH to trigger on demand drug release. The excellent synergistic therapeutic efficacy was confirmed both in vitro and in vivo.

CONCLUSION

Lan-AuNFs@PDA/DOX would be a promising drug carrier, endowing a great potential for multistimuli-responsive chemophotothermal synergistic cancer therapy.

Tracking the amyloidogenic core of IAPP amyloid fibrils: Insights from micro-Raman spectroscopy

Human islet amyloid polypeptide (hIAPP) is the major protein component of extracellular amyloid deposits, located in the islets of Langerhans, a hallmark of type II diabetes. The underlying mechanisms of IAPP aggregation have not yet been clearly defined, although the highly amyloidogenic sequence of the protein has been extensively studied. Several segments have been highlighted as aggregation-prone regions (APRs), with much attention focused on the central 8-17 and 20-29 stretches. In this work, we employ micro-Raman spectroscopy to identify specific regions that are contributing to or are excluded from the amyloidogenic core of IAPP amyloid fibrils. Our results demonstrate that both the N-terminal region containing a conserved disulfide bond between Cys residues at positions 2 and 7, and the C-terminal region containing the only Tyr residue are excluded from the amyloid core. Finally, by performing detailed aggregation assays and molecular dynamics simulations on a number of IAPP variants, we demonstrate that point mutations within the central APRs contribute to the reduction of the overall amyloidogenic potential of the protein but do not completely abolish the formation of IAPP amyloid fibrils.

Lanreotide Depot: An Antineoplastic Treatment of Carcinoid or Neuroendocrine Tumors

Purpose

Peptide drugs for antineoplastic therapies usually have low oral bioavailability and short in vivo half-lives, requiring less preferred delivery methods. Lanreotide depot is a sustained-release somatostatin analog (SSA) formulation produced via an innovative peptide self-assembly method. Lanreotide is approved in the USA and Europe to improve progression-free survival (PFS) in patients with unresectable gastroenteropancreatic neuroendocrine tumors (GEP-NETs) and also approved in Europe for symptom control in carcinoid syndrome associated with GEP-NETs. This review discusses how the distinct molecule and formulation of lanreotide depot provide advantages to patients and health care providers, as well as the most recent clinical evidence demonstrating the safety and efficacy of lanreotide depot in inhibiting tumor growth and controlling hormonal symptoms in GEP-NETs.

Methodology and Results

The lanreotide depot formulation confers a remarkable pharmacokinetic profile with no excipients, comprised only of lanreotide acetate and water. Of note, lanreotide depot constitutes an example for peptide self-assembly based formulations, providing insights that could help future development of sustained-release formulations of other antineoplastic peptides. Most patients with GEP-NETs will present with inoperable or incurable disease; thus, medical management for symptoms and tumor control plays a crucial role. Recent long-term clinical studies have demonstrated that lanreotide depot is well tolerated, prolongs PFS in GEP-NET patients, and significantly reduces symptoms related to carcinoid syndrome.

Conclusions

The unique depot formulation and delivery method of lanreotide confer advantages in the treatment of metastatic GEP-NETs, contributing to improvements in NET-related symptoms and PFS without reducing quality of life in this patient population.

Fabrication of gold nanocages and nanoshells using lanreotide acetate and a comparison study of their photothermal antitumor therapy

Functional gold nanoshells and nanocages were synthesized via self-assembly of lanreotide acetate.

Directing peptide crystallization through curvature control of nanotubes

In the absence of efficient crystallization methods, the molecular structures of fibrous assemblies have so far remained rather elusive. In this paper, we present a rational method to crystallize the lanreotide octapeptide by modification of a residue involved in a close contact. Indeed, we show that it is possible to modify the curvature of the lanreotide nanotubes and hence their diameter. This fine tuning leads to crystallization because the radius of curvature of the initially bidimensional peptide wall can be increased up to a point where the wall is essentially flat and a crystal is allowed to grow along a third dimension. By comparing X-ray diffraction data and Fourier transform Raman spectra, we show that the nanotubes and the crystals share similar cell parameters and molecular conformations, proving that there is indeed a structural continuum between these two morphologies. These results illustrate a novel approach to crystallization and represent the first step towards the acquisition of an Å-resolution structure of the lanreotide nanotubes β-sheet assembly.

Control of peptide nanotube diameter by chemical modifications of an aromatic residue involved in a single close contact

Supramolecular self-assembly is an attractive pathway for bottom-up synthesis of novel nanomaterials. In particular, this approach allows the spontaneous formation of structures of well-defined shapes and monodisperse characteristic sizes. Because nanotechnology mainly relies on size-dependent physical phenomena, the control of monodispersity is required, but the possibility of tuning the size is also essential. For self-assembling systems, shape, size, and monodispersity are mainly settled by the chemical structure of the building block. Attempts to change the size notably by chemical modification usually end up with the loss of self-assembly. Here, we generated a library of 17 peptides forming nanotubes of monodisperse diameter ranging from 10 to 36 nm. A structural model taking into account close contacts explains how a modification of a few Å of a single aromatic residue induces a fourfold increase in nanotube diameter. The application of such a strategy is demonstrated by the formation of silica nanotubes of various diameters.

Elucidation of the self-assembly pathway of lanreotide octapeptide into beta-sheet nanotubes: role of two stable intermediates

Nanofabrication by molecular self-assembly involves the design of molecules and self-assembly strategies so that shape and chemical complementarities drive the units to organize spontaneously into the desired structures. The power of self-assembly makes it the ubiquitous strategy of living organized matter and provides a powerful tool to chemists. However, a challenging issue in the self-assembly of complex supramolecular structures is to understand how kinetically efficient pathways emerge from the multitude of possible transition states and routes. Unfortunately, very few systems provide an intelligible structure and formation mechanism on which new models can be developed. Here, we elucidate the molecular and supramolecular self-assembly mechanism of synthetic octapeptide into nanotubes in equilibrium conditions. Their complex hierarchical self-assembly has recently been described at the mesoscopic level, and we show now that this system uniquely exhibits three assembly stages and three intermediates: (i) a peptide dimer is evidenced by both analytical centrifugation and NMR translational diffusion experiments; (ii) an open ribbon and (iii) an unstable helical ribbon are both visualized by transmission electron microscopy and characterized by small angle X-ray scattering. Interestingly, the structural features of two stable intermediates are related to the final nanotube organization as they set, respectively, the nanotube wall thickness and the final wall curvature radius. We propose that a specific self-assembly pathway is selected by the existence of such preorganized and stable intermediates so that a unique final molecular organization is kinetically favored. Our findings suggests that the rational design of oligopeptides can encode both molecular- and macro-scale morphological characteristics of their higher-order assemblies, thus opening the way to ultrahigh resolution peptide scaffold engineering.

Molecular origin of the self-assembly of lanreotide into nanotubes: a mutational approach

Lanreotide, a synthetic, therapeutic octapeptide analog of somatostatin, self-assembles in water into perfectly hollow and monodisperse (24-nm wide) nanotubes. Lanreotide is a cyclic octapeptide that contains three aromatic residues. The molecular packing of the peptide in the walls of a nanotube has recently been characterized, indicating four hierarchical levels of organization. This is a fascinating example of spontaneous self-organization, very similar to the formation of the gas vesicle walls of Halobacterium halobium. However, this unique peptide self-assembly raises important questions about its molecular origin. We adopted a directed mutation approach to determine the molecular parameters driving the formation of such a remarkable peptide architecture. We have modified the conformation by opening the cycle and by changing the conformation of a Lys residue, and we have also mutated the aromatic side chains of the peptide. We show that three parameters are essential for the formation of lanreotide nanotubes: i), the specificity of two of the three aromatic side chains, ii), the spatial arrangement of the hydrophilic and hydrophobic residues, and iii), the aromatic side chain in the beta-turn of the molecule. When these molecular characteristics are modified, either the peptides lose their self-assembling capability or they form less-ordered architectures, such as amyloid fibers and curved lamellae. Thus we have determined key elements of the molecular origins of lanreotide nanotube formation.