Nanostructuring Lipophilic Dyes in Water Using Stable Vesicles, Quatsomes, as Scaffolds and Their Use as Probes for Bioimaging

NIR-II Conjugated Electrolytes as Biomimetics of Lipid Bilayers for In Vivo Liposome Tracking

Liposomes serve as promising and versatile vehicles for drug delivery. Tracking these nanosized vesicles, particularly in vivo, is crucial for understanding their pharmacokinetics. This study introduces the design and synthesis of three new conjugated electrolyte (CE) molecules, which emit in the second near-infrared window (NIR-II), facilitating deeper tissue penetration. Additionally, these CEs, acting as biomimetics of lipid bilayers, demonstrate superior compatibility with lipid membranes compared to commonly used carbocyanine dyes like DiR. To counteract the aggregation-caused quenching effect, CEs employ a twisted backbone, as such their fluorescence intensities can effectively enhance after a fluorophore multimerization strategy. Notably, a "passive" method was employed to integrate CEs into liposomes during the liposome formation, and membrane incorporation efficiency was significantly promoted to nearly 100%. To validate the in vivo tracking capability, the CE-containing liposomes were functionalized with cyclic arginine-glycine-aspartic acid (cRGD) peptides, serving as tumor-targeting ligands. Clear fluorescent images visualizing tumor site in living mice were captured by collecting the NIR-II emission. Uniquely, these CEs exhibit additional emission peak in visible region, enabling in vitro subcellular analysis using routine confocal microscopy. These results underscore the potential of CEs as a new-generation of membrane-targeting probes to facilitate the liposome-based medicine research.

Evaluation of Quatsome Morphology, Composition, and Stability for Pseudomonas aeruginosa Biofilm Eradication

Biofilm infections are a major cause of food poisoning and hospital-acquired infections. Quaternary ammonium compounds are a group of effective disinfectants widely used in industry and households, yet their efficacy is lessened when used as antibiofilm agents compared to that against planktonic bacteria. It is therefore necessary to identify alternative formulations of quaternary ammonium compounds to achieve an effective biofilm dispersal. Quaternary ammonium amphiphiles can form vesicular structures termed "quatsomes" in the presence of cholesterol. In addition to their intrinsic antimicrobial properties, quatsomes can also be used for the delivery of other types of antibiotics or biomarkers. In this study, quatsomes were prepared from binary mixtures of cholesterol and mono- or dialkyl-quaternary ammonium compounds; then, the integrity and stability of their vesicular structure were assessed and related to monomer chain number and chain length. The quatsomes were used to treat Pseudomonas aeruginosa biofilms, showing effective antibiofilm abilities comparable to those of their monomers. A systematic liquid chromatography-mass spectrometry method for quantifying quatsome vesicle components was also developed and used to establish the significance of cholesterol in the quatsome self-assembly processes.

Nanomedical research and development in Spain: improving the treatment of diseases from the nanoscale

The new and unique possibilities that nanomaterials offer have greatly impacted biomedicine, from the treatment and diagnosis of diseases, to the specific and optimized delivery of therapeutic agents. Technological advances in the synthesis, characterization, standardization, and therapeutic performance of nanoparticles have enabled the approval of several nanomedicines and novel applications. Discoveries continue to rise exponentially in all disease areas, from cancer to neurodegenerative diseases. In Spain, there is a substantial net of researchers involved in the development of nanodiagnostics and nanomedicines. In this review, we summarize the state of the art of nanotechnology, focusing on nanoparticles, for the treatment of diseases in Spain (2017-2022), and give a perspective on the future trends and direction that nanomedicine research is taking.

Quatsomes Loaded with Squaraine Dye as an Effective Photosensitizer for Photodynamic Therapy

Photodynamic therapy is a non-invasive therapeutic strategy that combines external light with a photosensitizer (PS) to destroy abnormal cells. Despite the great progress in the development of new photosensitizers with improved efficacy, the PS's photosensitivity, high hydrophobicity, and tumor target avidity still represent the main challenges. Herein, newly synthesized brominated squaraine, exhibiting intense absorption in the red/near-infrared region, has been successfully incorporated into Quatsome (QS) nanovesicles at different loadings. The formulations under study have been characterized and interrogated in vitro for cytotoxicity, cellular uptake, and PDT efficiency in a breast cancer cell line. The nanoencapsulation of brominated squaraine into QS overcomes the non-water solubility limitation of the brominated squaraine without compromising its ability to generate ROS rapidly. In addition, PDT effectiveness is maximized due to the highly localized PS loadings in the QS. This strategy allows using a therapeutic squaraine concentration that is 100 times lower than the concentration of free squaraine usually employed in PDT. Taken together, our results reveal the benefits of the incorporation of brominated squaraine into QS to optimize their photoactive properties and support their applicability as photosensitizer agents for PDT.

Fluorescent Multifunctional Organic Nanoparticles for Drug Delivery and Bioimaging: A Tutorial Review

Fluorescent organic nanoparticles (FONs) are a large family of nanostructures constituted by organic components that emit light in different spectral regions upon excitation, due to the presence of organic fluorophores. FONs are of great interest for numerous biological and medical applications, due to their high tunability in terms of composition, morphology, surface functionalization, and optical properties. Multifunctional FONs combine several functionalities in a single nanostructure (emission of light, carriers for drug-delivery, functionalization with targeting ligands, etc.), opening the possibility of using the same nanoparticle for diagnosis and therapy. The preparation, characterization, and application of these multifunctional FONs require a multidisciplinary approach. In this review, we present FONs following a tutorial approach, with the aim of providing a general overview of the different aspects of the design, preparation, and characterization of FONs. The review encompasses the most common FONs developed to date, the description of the most important features of fluorophores that determine the optical properties of FONs, an overview of the preparation methods and of the optical characterization techniques, and the description of the theoretical approaches that are currently adopted for modeling FONs. The last part of the review is devoted to a non-exhaustive selection of some recent biomedical applications of FONs.

Hierarchical Quatsome-RGD Nanoarchitectonic Surfaces for Enhanced Integrin-Mediated Cell Adhesion

The synthesis and study of the tripeptide Arg-Gly-Asp (RGD), the binding site of different extracellular matrix proteins, e.g., fibronectin and vitronectin, has allowed the production of a wide range of cell adhesive surfaces. Although the surface density and spacing of the RGD peptide at the nanoscale have already shown a significant influence on cell adhesion, the impact of its hierarchical nanostructure is still rather unexplored. Accordingly, a versatile colloidal system named quatsomes, based on fluid nanovesicles formed by the self-assembling of cholesterol and surfactant molecules, has been devised as a novel template to achieve hierarchical nanostructures of the RGD peptide. To this end, RGD was anchored on the vesicle's fluid membrane of quatsomes, and the RGD-functionalized nanovesicles were covalently anchored to planar gold surfaces, forming a state of quasi-suspension, through a long poly(ethylene glycol) (PEG) chain with a thiol termination. An underlying self-assembled monolayer (SAM) of a shorter PEG was introduced for vesicle stabilization and to avoid unspecific cell adhesion. In comparison with substrates featuring a homogeneous distribution of RGD peptides, the resulting hierarchical nanoarchitectonic dramatically enhanced cell adhesion, despite lower overall RGD molecules on the surface. The new versatile platform was thoroughly characterized using a multitechnique approach, proving its enhanced performance. These findings open new methods for the hierarchical immobilization of biomolecules on surfaces using quatsomes as a robust and novel tissue engineering strategy.

Ultrabright Föster Resonance Energy Transfer Nanovesicles: The Role of Dye Diffusion

The development of contrast agents based on fluorescent nanoparticles with high brightness and stability is a key factor to improve the resolution and signal-to-noise ratio of current fluorescence imaging techniques. However, the design of bright fluorescent nanoparticles remains challenging due to fluorescence self-quenching at high concentrations. Developing bright nanoparticles showing FRET emission adds several advantages to the system, including an amplified Stokes shift, the possibility of ratiometric measurements, and of verifying the nanoparticle stability. Herein, we have developed Förster resonance energy transfer (FRET)-based nanovesicles at different dye loadings and investigated them through complementary experimental techniques, including conventional fluorescence spectroscopy and super-resolution microscopy supported by molecular dynamics calculations. We show that the optical properties can be modulated by dye loading at the nanoscopic level due to the dye's molecular diffusion in fluid-like membranes. This work shows the first proof of a FRET pair dye's dynamism in liquid-like membranes, resulting in optimized nanoprobes that are 120-fold brighter than QDot 605 and exhibit >80% FRET efficiency with vesicle-to-vesicle variations that are mostly below 10%.

Quatsomes Formulated with l-Prolinol-Derived Surfactants as Antibacterial Nanocarriers of (+)-Usnic Acid with Antioxidant Activity

The efficacy of the treatment of bacterial infection is seriously reduced because of antibiotic resistance; thus, therapeutic solutions against drug-resistant microbes are necessary. Nanoparticle-based solutions are particularly promising for meeting this challenge because they can offer intrinsic antimicrobial activity and sustained drug release at the target site. Herein, we present a newly developed nanovesicle system of the quatsome family, composed of l-prolinol-derived surfactants and cholesterol, which has noticeable antibacterial activity even on Gram-negative strains, demonstrating great potential for the treatment of bacterial infections. We optimized the vesicle stability and antibacterial activity by tuning the surfactant chain length and headgroup charge (cationic or zwitterionic) and show that these quatsomes can furthermore serve as nanocarriers of pharmaceutical actives, demonstrated here by the encapsulation of (+)-usnic acid, a natural substance with many pharmacological properties.

DELOS Nanovesicles-Based Hydrogels: An Advanced Formulation for Topical Use

Topical delivery has received great attention due to its localized drug delivery, its patient compliance, and its low risk for side effects. Recent developments have focused on studying new drug delivery systems as a strategy for addressing the challenges of current topical treatments. Here we describe the advances on an innovative drug delivery platform called DELOS nanovesicles for topical drug delivery. Previously, the production of DELOS nanovesicles demonstrated potentiality for the topical treatment of complex wounds, achieving well-tolerated liquid dispersions by this route. Here, research efforts have been focused on designing these nanocarriers with the best skin tolerability to be applied even to damaged skin, and on exploring the feasibility of adapting the colloidal dispersions to a more suitable dosage form for topical application. Accordingly, these drug delivery systems have been efficiently evolved to a hydrogel using Methocel^TM K4M, presenting proper stability and rheological properties. Further, the integrity of these nanocarriers when being gellified has been confirmed by cryo-transmission electron microscopy and by Förster resonance energy transfer analysis with fluorescent-labeled DELOS nanovesicles, which is a crucial characterization not widely reported in the literature. Additionally, in vitro experiments have shown that recombinant human Epidermal Growth Factor (rhEGF) protein integrated into gellified DELOS nanovesicles exhibits an enhanced bioactivity compared to the liquid form. Therefore, these studies suggest that such a drug delivery system is maintained unaltered when hydrogellified, becoming the DELOS nanovesicles-based hydrogels, an advanced formulation for topical use.

Engineering pH-Sensitive Stable Nanovesicles for Delivery of MicroRNA Therapeutics

MicroRNAs (miRNAs) are small non-coding endogenous RNAs, which are attracting a growing interest as therapeutic molecules due to their central role in major diseases. However, the transformation of these biomolecules into drugs is limited due to their unstability in the bloodstream, caused by nucleases abundantly present in the blood, and poor capacity to enter cells. The conjugation of miRNAs to nanoparticles (NPs) could be an effective strategy for their clinical delivery. Herein, the engineering of non-liposomal lipid nanovesicles, named quatsomes (QS), for the delivery of miRNAs and other small RNAs into the cytosol of tumor cells, triggering a tumor-suppressive response is reported. The engineered pH-sensitive nanovesicles have controlled structure (unilamellar), size (<150 nm) and composition. These nanovesicles are colloidal stable (>24 weeks), and are prepared by a green, GMP compliant, and scalable one-step procedure, which are all unavoidable requirements for the arrival to the clinical practice of NP based miRNA therapeutics. Furthermore, QS protect miRNAs from RNAses and when injected intravenously, deliver them into liver, lung, and neuroblastoma xenografts tumors. These stable nanovesicles with tunable pH sensitiveness constitute an attractive platform for the efficient delivery of miRNAs and other small RNAs with therapeutic activity and their exploitation in the clinics.

The Secret Lives of Fluorescent Membrane Probes as Revealed by Molecular Dynamics Simulations

Fluorescent probes have been employed for more than half a century to study the structure and dynamics of model and biological membranes, using spectroscopic and/or microscopic experimental approaches. While their utilization has led to tremendous progress in our knowledge of membrane biophysics and physiology, in some respects the behavior of bilayer-inserted membrane probes has long remained inscrutable. The location, orientation and interaction of fluorophores with lipid and/or water molecules are often not well known, and they are crucial for understanding what the probe is actually reporting. Moreover, because the probe is an extraneous inclusion, it may perturb the properties of the host membrane system, altering the very properties it is supposed to measure. For these reasons, the need for independent methodologies to assess the behavior of bilayer-inserted fluorescence probes has been recognized for a long time. Because of recent improvements in computational tools, molecular dynamics (MD) simulations have become a popular means of obtaining this important information. The present review addresses MD studies of all major classes of fluorescent membrane probes, focusing in the period between 2011 and 2020, during which such work has undergone a dramatic surge in both the number of studies and the variety of probes and properties accessed.

Dye-Loaded Quatsomes Exhibiting FRET as Nanoprobes for Bioimaging

Fluorescent organic nanoparticles (FONs) are emerging as an attractive alternative to the well-established fluorescent inorganic nanoparticles or small organic dyes. Their proper design allows one to obtain biocompatible probes with superior brightness and high photostability, although usually affected by low colloidal stability. Herein, we present a type of FONs with outstanding photophysical and physicochemical properties in-line with the stringent requirements for biomedical applications. These FONs are based on quatsome (QS) nanovesicles containing a pair of fluorescent carbocyanine molecules that give rise to Förster resonance energy transfer (FRET). Structural homogeneity, high brightness, photostability, and high FRET efficiency make these FONs a promising class of optical bioprobes. Loaded QSs have been used for in vitro bioimaging, demonstrating the nanovesicle membrane integrity after cell internalization, and the possibility to monitor the intracellular vesicle fate. Taken together, the proposed QSs loaded with a FRET pair constitute a promising platform for bioimaging and theranostics.

Super-resolution Imaging of Structure, Molecular Composition, and Stability of Single Oligonucleotide Polyplexes

The successful application of gene therapy relies on the development of safe and efficient delivery vectors. Cationic polymers such as cell-penetrating peptides (CPPs) can condense genetic material into nanoscale particles, called polyplexes, and induce cellular uptake. With respect to this point, several aspects of the nanoscale structure of polyplexes have remained elusive because of the difficulty in visualizing the molecular arrangement of the two components with nanometer resolution. This limitation has hampered the rational design of polyplexes based on direct structural information. Here, we used super-resolution imaging to study the structure and molecular composition of individual CPP-mRNA polyplexes with nanometer accuracy. We use two-color direct stochastic optical reconstruction microscopy (dSTORM) to unveil the impact of peptide stoichiometry on polyplex structure and composition and to assess their destabilization in blood serum. Our method provides information about the size and composition of individual polyplexes, allowing the study of such properties on a single polyplex basis. Furthermore, the differences in stoichiometry readily explain the differences in cellular uptake behavior. Thus, quantitative dSTORM of polyplexes is complementary to the currently used characterization techniques for understanding the determinants of polyplex activity in vitro and inside cells.

Tetrazine- trans-Cyclooctene Chemistry Applied to Fabricate Self-Assembled Fluorescent and Radioactive Nanoparticles for in Vivo Dual Mode Imaging

Multimodal imaging agents combine two or more imaging modalities into one probe. Self-assembling fluorescent nanoparticles are a promising class of modular multimodal imaging probes as they can allow easy blending of imaging and targeting modalities. Our group recently developed a class of self-assembling and intrinsically fluorescent small molecule-based nanoparticles (SMNPs) with excellent optical properties. In this article, we describe the efficient radiolabeling of these SMNPs via a two-step bioconjugation strategy involving the inverse-electron-demand Diels-Alder ligation between a tetrazine (Tz)-tagged radiolabel and a trans-cyclooctene (TCO)-tagged fluorescent small molecule building block of the SMNPs. Studies in mice revealed that the SMNPs are well tolerated and could be monitored by both radioactivity and fluorescence, thereby demonstrating the potential of SMNPs in optical and dual-mode imaging in vivo. The work also testifies to the utility of the Tz-TCO conjugation chemistry for the labeling of self-assembled nanoparticles.

Insights into the structure and nanomechanics of a quatsome membrane by force spectroscopy measurements and molecular simulations

Quatsomes (QS) are unilamellar nanovesicles constituted by quaternary ammonium surfactants and sterols in defined molar ratios. Unlike conventional liposomes, QS are stable upon long storage such as for several years, they show outstanding vesicle-to-vesicle homogeneity regarding size and lamellarity, and they have the structural and physicochemical requirements to be a potential platform for site-specific delivery of hydrophilic and lipophilic molecules. Knowing in detail the structure and mechanical properties of the QS membrane is of great importance for the design of deformable and flexible nanovesicle alternatives, highly pursued in nanomedicine applications such as the transdermal administration route. In this work, we report the first study on the detailed structure of the cholesterol : CTAB QS membrane at the nanoscale, using atomic force microscopy (AFM) and spectroscopy (AFM-FS) in a controlled liquid environment (ionic medium and temperature) to assess the topography of supported QS membranes (SQMs) and to evaluate the local membrane mechanics. We further perform molecular dynamics (MD) simulations to provide an atomistic interpretation of the obtained results. Our results are direct evidence of the bilayer nature of the QS membrane, with characteristics of a fluid-like membrane, compact and homogeneous in composition, and with structural and mechanical properties that depend on the surrounding environment. We show how ions alter the lateral packing, modifying the membrane mechanics. We observe that according to the ionic environment and temperature, different domains may coexist in the QS membranes, ascribed to variations in molecular tilt angles. Our results indicate that QS membrane properties may be easily tuned by altering the lateral interactions with either different environmental ions or counterions.

Coarse-grained molecular dynamics simulation of the interface behaviour and self-assembly of CTAB cationic surfactants

We study surfactant molecules at interfaces, micelles and their self-assembly with different models (all atomic and coarse grained).