Supramolecular self-assembled peptide-engineered nanofibers: A propitious proposition for cancer therapy

Cancer is a devastating disease that causes a substantial number of deaths worldwide. Current therapeutic interventions for cancer include chemotherapy, radiation therapy, or surgery. These conventional therapeutic approaches are associated with disadvantages such as multidrug resistance, destruction of healthy tissues, and tissue toxicity. Therefore, there is a paradigm shift in cancer management wherein nanomedicine-based novel therapeutic interventions are being explored to overcome the aforementioned disadvantages. Supramolecular self-assembled peptide nanofibers are emerging drug delivery vehicles that have gained much attention in cancer management owing to their biocompatibility, biodegradability, biomimetic property, stimuli-responsiveness, transformability, and inherent therapeutic property. Supramolecules form well-organized structures via non-covalent linkages, the intricate molecular arrangement helps to improve tissue permeation, pharmacokinetic profile and chemical stability of therapeutic agents while enabling targeted delivery and allowing efficient tumor imaging. In this review, we present fundamental aspects of peptide-based self-assembled nanofiber fabrication their applications in monotherapy/combinatorial chemo- and/or immuno-therapy to overcome multi-drug resistance. The role of self-assembled structures in targeted/stimuli-responsive (pH, enzyme and photo-responsive) drug delivery has been discussed along with the case studies. Further, recent advancements in peptide nanofibers in cancer diagnosis, imaging, gene therapy, and immune therapy along with regulatory obstacles towards clinical translation have been deliberated.

Metal-Assembled Collagen Peptide Microflorettes as Magnetic Resonance Imaging Agents

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents.

Engineered Nonviral Protein Cages Modified for MR Imaging

Diagnostic medical imaging utilizes magnetic resonance (MR) to provide anatomical, functional, and molecular information in a single scan. Nanoparticles are often labeled with Gd(III) complexes to amplify the MR signal of contrast agents (CAs) with large payloads and high proton relaxation efficiencies (relaxivity, r1). This study examined the MR performance of two structurally unique cages, AaLS-13 and OP, labeled with Gd(III). The cages have characteristics relevant for the development of theranostic platforms, including (i) well-defined structure, symmetry, and size; (ii) the amenability to extensive engineering; (iii) the adjustable loading of therapeutically relevant cargo molecules; (iv) high physical stability; and (v) facile manufacturing by microbial fermentation. The resulting conjugates showed significantly enhanced proton relaxivity (r1 = 11-18 mM-1 s-1 at 1.4 T) compared to the Gd(III) complex alone (r1 = 4 mM-1 s-1). Serum phantom images revealed 107% and 57% contrast enhancements for Gd(III)-labeled AaLS-13 and OP cages, respectively. Moreover, proton nuclear magnetic relaxation dispersion (1H NMRD) profiles showed maximum relaxivity values of 50 mM-1 s-1. Best-fit analyses of the 1H NMRD profiles attributed the high relaxivity of the Gd(III)-labeled cages to the slow molecular tumbling of the conjugates and restricted local motion of the conjugated Gd(III) complex.

The Value of CTA Based on Gold Nanorod Contrast Agent in Coronary Artery Diagnosis and Plaque Property Analysis

Coronary CT angiography (CTA) with the characteristics of noninvasive and simple operation is widely used in the diagnosis of coronary artery stenosis. The choice of contrast agent exerts an important impact on the imaging quality of CTA. Conventional iodine contrast agents are easily excreted by the kidneys, from which the imaging window is short, and the imaging quality is poor. Metal nanomaterials have unique optical properties and have broad application prospects in imaging. Our aim is to explore the value of gold nanorod contrast agent in the diagnosis of coronary heart disease. A gold nanorod suspension was first prepared, and the prepared gold nanorod was uniform and had good dispersibility. It can be seen from the light absorption curve that there are two obvious peaks on the UV absorption peak of the gold nanorods. The gold nanorods were cultured in different solutions, and it was found that the particle size of the gold nanorods did not change significantly within 72 hours, indicating that the prepared gold nanorods had good stability. When observing the damage degree of mouse kidney tissue, it was shown that the damage degree of gold nanorod contrast agent to mouse kidney tissue was less than that of iodine contrast agent. The above results indicate that the gold nanorod contrast agent has good stability and safety. Therefore, our study demonstrated that the gold nanorod contrast agent has high value in the diagnosis of coronary arteries and the analysis of plaque properties.

Self-assembly of peptide nanofibers for imaging applications

Pathological stimuli-responsive self-assembly of peptide nanofibers enables selective accumulation of imaging agent cargos in the stimuli-rich regions of interest. It provides enhanced imaging signals, biocompatibility, and tumor/disease accessibility and retention, thereby promoting smart, precise, and sensitive tumor/disease imaging both in vitro and in vivo. Considering the remarkable significance and recent encouraging breakthroughs of self-assembled peptide nanofibers in tumor/disease diagnosis, this reivew is herein proposed. We emphasize the recent advances particularly in the past three years, and provide an outlook in this field.

Simple Host-Guest Assembly for High-Resolution Magnetic Resonance Imaging of Microvasculature

Magnetic resonance angiography (MRA) is an important imaging technique that can be used to identify and characterize various types of vascular diseases. However, currently used molecular contrast agents are unsuitable for MRA due to the short intravascular retention time, the whole-body distribution, and the relatively low contrast effect. In this study, we developed a vascular analysis contrast agent (i.e., VasCA) for MRA, which is a simple and biocompatible 1:1 host-guest assembly of PEGylated β-cyclodextrin and gadolinium chelate with renal clearable size and high relaxivity (r1 = 9.27 mM-1 s-1). Its biocompatibility was confirmed by in vivo animal studies as well as in vitro 3D cell culture. In a tumor-bearing rat model, VasCA circulated in the blood vessels much longer (4.3-fold increase) than gadoterate meglumine (Dotarem) and was mainly excreted by the renal system after intravenous injection. This feature of VasCA allows characterization of tumor microvasculature (e.g., feeding and draining vessels) as well as visualization of small vessels in the brain and body organs. Furthermore, after treatment with an angiogenesis inhibitor (i.e., sorafenib), VasCA revealed the vessel normalization process and allowed the assessment of viable and necrotic tumor regions. Our study provides a useful tool for diverse MRA applications, including tumor characterization, early-stage evaluation of drug efficacy, and treatment planning, as well as diagnosis of cardiovascular diseases.

Strategies for the design of nanoparticles: starting with long-circulating nanoparticles, from lab to clinic

Short half-life is one of the main causes of drug attrition in clinical development, which also leads to the failure of many leading compounds and hits to become drug candidates. Nowadays, nanomaterials have been applied to drug development to address this problem. In fact, the clinical application of nanoparticles (NPs) is severely limited due to their rapid elimination by the reticuloendothelial system (RES) in vivo. In this paper, we aim to summarize representative strategies on prolonging the circulation time for bridging the gap between excellent pharmaceutics and proper half-life and encourage clinical translation.

Harnessing amphiphilic polymeric micelles for diagnostic and therapeutic applications: Breakthroughs and bottlenecks

Amphiphilic block copolymers are widely utilized in the design of formulations owing to their unique physicochemical properties, flexible structures and functional chemistry. Amphiphilic polymeric micelles (APMs) formed from such copolymers have gained attention of the drug delivery scientists in past few decades for enhancing the bioavailability of lipophilic drugs, molecular targeting, sustained release, stimuli-responsive properties, enhanced therapeutic efficacy and reducing drug associated toxicity. Their properties including ease of surface modification, high surface area, small size, and enhanced permeation as well as retention (EPR) effect are mainly responsible for their utilization in the diagnosis and therapy of various diseases. However, some of the challenges associated with their use are premature drug release, low drug loading capacity, scale-up issues and their poor stability that need to be addressed for their wider clinical utility and commercialization. This review describes comprehensively their physicochemical properties, various methods of preparation, limitations followed by approaches employed for the development of optimized APMs, the impact of each preparation technique on the physicochemical properties of the resulting APMs as well as various biomedical applications of APMs. Based on the current scenario of their use in treatment and diagnosis of diseases, the directions in which future studies need to be carried out to explore their full potential are also discussed.

Vascular-targeted micelles as a specific MRI contrast agent for molecular imaging of fibrin clots and cancer cells

Molecular medical imaging is intended to increase the accuracy of diagnosis, particularly in cardiovascular and cancer-related diseases, where early detection could significantly increase the treatment success rate. In this study, we present mixed micelles formed from four building blocks as a magnetic resonance imaging targeted contrast agent for the detection of atheroma and cancer cells. The building blocks are a gadolinium-loaded DOTA ring responsible for contrast enhancement, a fibrin-specific CREKA pentapeptide responsible for targeting, a fluorescent dye and DSPE-PEG₂₀₀₀. The micelles were fully characterized in terms of their size, zeta potential, stability, relaxivity and toxicity. Target binding assays performed on fibrin clots were quantified by fluorescence and image signal intensities and proved the binding power. An additional internalization assay showed that the micelles were also designed to specifically enter into cancer cells. Overall, these multimodal mixed micelles represent a potential formulation for MRI molecular imaging of atheroma and cancer cells.

Tumor Acid Microenvironment-Triggered Self-Assembly of ESIONPs for T1/T2 Switchable Magnetic Resonance Imaging

Smart magnetic resonance imaging (MRI) contrast agents (CAs), whose MRI contrasting enhancement is variable in response to the specific stimulus from tumor tissues, possess great potential in precise tumor diagnosis. Herein, we design a type of extremely small iron oxide nanoparticle (ESIONP)-based pH-responsive system for activatable T₂ MRI in the tumor acid microenvironment. The ESIONP system is composed of ESIONP-PEG-PGA and ESIONP-PEG-PDC, which were respectively constructed through the surface modification with poly (l-glutamic acid) (PGA) and poly(N-{N'-[N″-(2-carbox aminoethyl)]-2-aminoethyl}glutamide) (PDC) on the surface of ESIONP. The pH-responsive system exhibits the dispersed state under the neutral condition, and when it is exposed to the weakly acid environment, ESIONP-PEG-PDC switches from the neutral to positive charge, finally leading to the aggregation by the electrostatic interaction between the positively charged ESIONP-PEG-PDC and negatively charged ESIONP-PEG-PGA. On the basis of the aggregation, the T₁ contrasting effect of the pH-responsive system switches to a T₂ contrasting effect, which can be employed to realize the selective enhancement of imaging contrast at the tumor location owing to the weakly acid microenvironment. Moreover, on the basis of size increase originated from the aggregation effect, the residence time of extremely small iron oxide nanoparticles (ESIONPs) in the tumor site is effectively prolonged, which is beneficial for the MRI of tumors. Therefore, the pH-responsive system based on the ESIONPs is a potential smart MRI contrast agent for accurate tumor diagnosis.

Erythrocyte membrane concealed paramagnetic polymeric nanoparticle for contrast-enhanced magnetic resonance imaging

Recent progress in bioimaging nanotechnology has a great impact on the diagnosis, treatment, and prevention of diseases by enabling early intervention. Among different types of bioimaging modalities, contrast-enhanced magnetic resonance imaging using paramagnetic gadolinium-based molecular contrast agents (GBCAs) are most commonly used in clinic. However, molecular GBCAs distribute rapidly between plasma and interstitial spaces with short half-lives limiting its clinical impacts. To improve the properties of GBCAs, herein an effort has been put forth by incorporating GBCA into nanoscale system mimicking the property of red blood cell (RBC) that could facilitate contrast enhancement and prolong intraluminal retention in the body. The proposed nanoconstruct is made up of polymeric-core labeled with lipid conjugated GBCA followed by the imprint of the RBC membrane concealment layer to enhance stability and biocompatibility. Meanwhile, the confinement strategy of GBCA was implemented to accelerate magnetic properties of nanoconstruct providing longitudinal-relaxivity (r₁) to 12.78 ± 0.29 (mM s)^-1. Such improvement in r₁ was further confirmed by enhanced contrast in the vascular angiography of the murine model. Given higher colloidal stability and tunable magnetic properties, nanoconstruct proposed herein is a promising platform technology for the applications where enhanced plasma residence time and magnetic properties are necessary for diagnosis and therapy.

Peptide-Based Soft Hydrogels Modified with Gadolinium Complexes as MRI Contrast Agents

Poly-aromatic peptide sequences are able to self-assemble into a variety of supramolecular aggregates such as fibers, hydrogels, and tree-like multi-branched nanostructures. Due to their biocompatible nature, these peptide nanostructures have been proposed for several applications in biology and nanomedicine (tissue engineering, drug delivery, bioimaging, and fabrication of biosensors). Here we report the synthesis, the structural characterization and the relaxometric behavior of two novel supramolecular diagnostic agents for magnetic resonance imaging (MRI) technique. These diagnostic agents are obtained for self-assembly of DTPA(Gd)-PEG8-(FY)3 or DOTA(Gd)-PEG8-(FY)3 peptide conjugates, in which the Gd-complexes are linked at the N-terminus of the PEG8-(FY)3 polymer peptide. This latter was previously found able to form self-supporting and stable soft hydrogels at a concentration of 1.0% wt. Analogously, also DTPA(Gd)-PEG8-(FY)3 and DOTA(Gd)-PEG8-(FY)3 exhibit the trend to gelificate at the same range of concentration. Moreover, the structural characterization points out that peptide (FY)3 moiety keeps its capability to arrange into β-sheet structures with an antiparallel orientation of the β-strands. The high relaxivity value of these nanostructures (~12 mM⁻¹·s⁻¹ at 20 MHz) and the very low in vitro cytotoxicity suggest their potential application as supramolecular diagnostic agents for MRI.

Pharmacokinetics and biodistribution study of self-assembled Gd-micelles demonstrating blood-pool contrast enhancement for MRI

Magnetic resonance angiography (MRA) requires the use of contrast agents (CAs) to enable accurate diagnosis. There are currently no CAs on the market with appropriate pharmacokinetic (PK) parameters, namely long persistence in the blood, that can be easily used for MRA. We have recently synthesized amphiphilic building blocks loaded with gadolinium (Gd), which self-assemble into Gd-micelles in aqueous media, and have evaluated their potential as a blood-pool contrast agent (BPCA) in vivo. To assess the short and long term PK of Gd-micelles, the blood and organs of the mice were analyzed at t = 30 min, 1, 2, 3 h, 7, 14 and 21 days. Gd-DOTA was used as a control because it is the gold-standard CA for MRA despite its rapid clearance from the blood compartment. Gd-micelles circulated in the blood for more than 3 h postinjection whereas Gd-DOTA was eliminated less than half an hour postinjection. No side effects were observed in the mice up to the end of the study at 21 days and no accumulation of Gd was observed in the brain or bones. The Magnetic Resonance Imaging (MRI) parameters and the results of this in vivo study indicate the true BCPA properties of Gd-micelles and warrant further development.

Nanoparticle-Based Paramagnetic Contrast Agents for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive medical imaging modality that is routinely used in clinics, providing anatomical information with micron resolution, soft tissue contrast, and deep penetration. Exogenous contrast agents increase image contrast by shortening longitudinal (T 1) and transversal (T 2) relaxation times. Most of the T 1 agents used in clinical MRI are based on paramagnetic lanthanide complexes (largely Gd-based). In moving to translatable formats of reduced toxicity, greater chemical stability, longer circulation times, higher contrast, more controlled functionalisation and additional imaging modalities, considerable effort has been applied to the development of nanoparticles bearing paramagnetic ions. This review summarises the most relevant examples in the synthesis and biomedical applications of paramagnetic nanoparticles as contrast agents for MRI and multimodal imaging. It includes the most recent developments in the field of production of agents with high relaxivities, which are key for effective contrast enhancement, exemplified through clinically relevant examples.

Development and characterization of lanthanide-HPDO3A-C16-based micelles as CEST-MRI contrast agents

The synthesis and characterization of a novel HPDO3A-based ligand having a C16 alkyl chain and its Eu³⁺, Gd³⁺and Yb³⁺complexes are reported.