Marina Gobbo

The development of theranostic tools for the early detection and localization of tumors represents a major challenge in oncology. Among emerging strategies, the targeting of Programmed Death Ligand-1 (PD-L1), a key immune checkpoint protein overexpressed in many tumor types, has gained significant attention. In this work, we report design and development of theranostic gold nanostructures functionalized with PD-L1-targeting peptides (PTP, sPTP, and rPTP) whose sequences were identified combining structural analysis of the PD-1/PD-L1 interaction interface and molecular dynamics simulations. This is because the design of functional nanostructures for protein targeting requires a precise understanding of how molecular recognition is affected by ligand organization at interfaces; therefore, peptide design was guided not only by the selection of key residues involved in binding but also by the evaluation of peptide assemblies to explicitly account for the collective effects governing target recognition. Indeed, beyond conventional evaluation of protein/single-peptide interaction, peptide clusters and surface-anchored monolayers were investigated to consider features like peptide assembly, organization, and reduced conformational freedom in the nanostructure/PD-L1 interaction. Results indicate that peptide sequence and orientation critically determine monolayer organization and accessibility of the PD-L1 binding motif. The computational predictions were experimentally validated by synthesizing peptide-functionalized gold nanostructures and evaluating their targeting performance against MDA-MB-231 breast cancer cells over-expressing PD-L1, using the surface-enhanced Raman scattering technique: NS functionalized with PTPs achieved the targeting of approximately 85% of MDA-MB-231 cells at 100 pM nanostructure concentration, compared to 23% for those functionalized with rPTP, demonstrating a nearly four-fold difference attributable exclusively to peptide orientation on the nanostructure surface. The specific system investigated in this work establishes a computational framework for the rational design of peptide-functionalized nanostructures, providing insights into the collective behavior of peptide monolayers and offering a smart methodology that, while demonstrated here for targeting PD-L1, is in principle applicable to other protein targets.

PD-L1 (programmed cell death ligand-1) is a protein located on the surface of regulatory cells. It has an immunosuppressive role as it binds specifically to the protein programmed cell death-1 (PD-1), a checkpoint glycoprotein, present on the surface of immune cells such as T and B lymphocytes. Many tumor cells block the immune response by overexpressing PD-L1 on their surface; therefore, targeting PD-L1 represents a powerful strategy that allows tumor localization. To determine the presence of PD-L1 in cells, the use of ad hoc functionalized peptides that bind to PD-L1 can be exploited. One of them is the peptide CLP002 (Trp-His-Arg-Ser-Tyr-Tyr-Thr-Trp-Asn-Leu-Asn-Thr), which, bound to surface-enhanced Raman scattering (SERS) gold nanostructures via a suitable linker, was shown to be highly effective in recognizing MDA-MB-231 breast cancer cells and, importantly, this recognition can be measured by SERS experiments. To characterize, on a molecular scale, the interaction between PD-L1 and peptide functionalized nanostructures, we performed molecular dynamics (MDs) simulations, studying the features of peptide monolayers bound on gold surfaces in the absence and presence of PD-L1. The results obtained allow us to explain why the nature of the linker plays a fundamental role in the binding and why a peptide carrying the same amino acids as CPL002 but with a different sequence (scrambled) is much less active than CLP002. These results open the way to an in silico evaluation of the key parameters that regulate the binding of PD-L1 useful for cancer recognition.

We demonstrate that the triplet state of I ₂ BODIPY can be employed as a spin label for EPR distance determination using magnetophotoselection for increased orientational selectivity.

Engineered peptides on plasmonic nanostructures show a good targeting activity against the immune checkpoint programmed death ligand 1 protein (PD-L1) expressed by tumor cells. SERS signals allow quantitative evaluation of the targeting activity.

Cationic porphyrins exhibit an amazing variety of binding modes and inhibition mechanisms of 20S proteasome. Depending on the spatial distribution of their electrostatic charges, they can occupy different sites on α rings of 20S proteasome by exploiting the structural code responsible for the interaction with regulatory proteins. Indeed, they can act as competitive or allosteric inhibitors by binding at the substrate gate or at the grooves between the α subunits, respectively. Moreover, the substitution of a charged moiety in the peripheral arm with a hydrophobic moiety revealed a “new” 20S functional state with higher substrate affinity and catalytic efficiency. In the present study, we expand our structure–activity relationship (SAR) analysis in order to further explore the potential of this versatile class of 20S modulators. Therefore, we have extended the study to additional macrocyclic compounds, displaying different structural features, comparing their interaction behavior on the 20S proteasome with previously investigated compounds. In particular, in order to evaluate how the introduction of a peptidic chain can affect the affinity and the interacting mechanism of porphyrins, we investigate the MTPyApi, a porphyrin derivatized with an Arg–Pro-rich antimicrobial peptide. Moreover, to unveil the role played by the porphyrin core, this was replaced with a corrole scaffold, a “contracted” version of the tetrapyrrolic ring due to the lack of a methine bridge. The analysis has been undertaken by means of integrated kinetic, Nuclear Magnetic Resonance, and computational studies. Finally, in order to assess a potential pharmacological significance of this type of investigation, a preliminary attempt has been performed to evaluate the biological effect of these molecules on MCF7 breast cancer cells in dark conditions, envisaging that porphyrins may indeed represent a powerful tool for the modulation of cellular proteostasis.

Cell targeting has been considered an important strategy in diagnostic and therapeutic applications. Among different targeting units, peptides have emerged for their ability to bind to many different cellular targets, their scarce immunogenicity and the possibility of introducing multiple copies on nanosystems, providing high avidity for the target. However, their sensitivity to proteases strongly limits their applications in vivo. Here, we show that when presented on the surface of nanostructures, peptide stability to proteolysis is strongly improved without reducing the targeting activity. We prepared plasmonic nanostructures functionalized with a dodecapeptide (GE11) which targets EGFR, a protein overexpressed on different types of tumors. Two types of nanosystems were prepared in which the targeting unit was either directly linked to gold nanoparticles or through a PEG chain, resulting in a different peptide density on the surface of nanostructures. The peptide was rapidly degraded in 20% human serum or in the presence of isolated serine proteases, whereas no significant proteolytic fragments were detected during incubation of the nanosystems and after 24 h digestion, the nanostructures maintained their targeting activity and selectivity on colon cancer cells. Molecular dynamic calculations of the interaction of the nanostructure with chymotrypsin suggest that the formation of the enzyme–peptide complex, the first step in the mechanism of peptide hydrolysis, is highly unlikely because of the constraint imposed by the link of the peptide to the nanoparticle. These results support the utilization of peptides as active targeting units in nanomedicine.

We explore the potential of orientation-resolved pulsed dipolar spectroscopy (PDS) in light-induced versions of the experiment. The use of triplets as spin-active moieties for PDS offers an attractive tool for studying biochemical systems containing optically active cofactors. Cofactors are often rigidly bound within the protein structure, providing an accurate positional marker. The rigidity leads to orientation selection effects in PDS, which can be analyzed to give both distance and mutual orientation information. Herein we present a comprehensive analysis of the orientation selection of a full set of light-induced PDS experiments. We exploit the complementary information provided by the different light-induced techniques to yield atomic-level structural information. For the first time, we measure a 2D frequency-correlated laser-induced magnetic dipolar spectrum, and we are able to monitor the complete orientation dependence of the system in a single experiment. Alternatively, the summed spectrum enables an orientation-independent analysis to determine the distance distribution.

We present a new technique, light-induced triplet–triplet electron resonance spectroscopy (LITTER), which measures the dipolar interaction between two photoexcited triplet states, enabling both the distance and angular distributions between the two triplet moieties to be determined on a nanometer scale. This is demonstrated for a model bis-porphyrin peptide that renders dipolar traces with strong orientation selection effects. Using simulations and density functional theory calculations, we extract distance distributions and relative orientations of the porphyrin moieties, allowing the dominant conformation of the peptide in a frozen solution to be identified. LITTER removes the requirement of current light-induced electron spin resonance pulse dipolar spectroscopy techniques to have a permanent paramagnetic moiety, becoming more suitable for in-cell applications and facilitating access to distance determination in unmodified macromolecular systems containing photoexcitable moieties. LITTER also has the potential to enable direct comparison with Förster resonance energy transfer and combination with microscopy inside cells.

Laser synthesis emerges as a suitable technique to produce ligand-free nanoparticles, alloys and functionalized nanomaterials for catalysis, imaging, biomedicine, energy and environmental applications. In the last decade, laser ablation and nanoparticle generation in liquids has proven to be a unique and efficient technique to generate, excite, fragment and conjugate a large variety of nanostructures in a scalable and clean way. In this work, we give an overview on the fundamentals of pulsed laser synthesis of nanocolloids and new information about its scalability towards selected applications. Biomedicine, catalysis and sensing are the application areas mainly discussed in this review, highlighting advantages of laser-synthesized nanoparticles for these types of applications and, once partially resolved, the limitations to the technique for large-scale applications.

The biological light-harvesting process offers an unlimited source of inspiration. The high level of control, adaptation capability, and efficiency challenge humankind to create artificial bio-mimicking nanoarchitectures with the same performances to respond to our energy needs. Here, in the extensive search for design principles at the base of efficient artificial light-harvesters, an approach based on self-assembly of pigment-peptide conjugates is proposed. The solvent-driven and controlled aggregation of the peptide moieties promotes the formation of a dense network of interacting pigments, giving rise to an excitonic network characterized by intense and spectrally wide absorption bands. The ultrafast dynamics of the nanosystems studied through 2D electronic spectroscopy reveals that the excitation energy is funneled in an ultrafast time range (hundreds of femtoseconds) to a manifold of long-living dark states, thus suggesting the considerable potentiality of the systems as efficient harvesters.