Magnetic Iron Oxide Nanoparticles for Brain Imaging and Drug Delivery

Central nervous system (CNS) disorders affect as many as 1.5 billion people globally. The limited delivery of most imaging and therapeutic agents into the brain is a major challenge for treatment of CNS disorders. With the advent of nanotechnologies, controlled delivery of drugs with nanoparticles holds great promise in CNS disorders for overcoming the blood-brain barrier (BBB) and improving delivery efficacy. In recent years, magnetic iron oxide nanoparticles (MIONPs) have stood out as a promising theranostic nanoplatform for brain imaging and drug delivery as they possess unique physical properties and biodegradable characteristics. In this review, we summarize the recent advances in MIONP-based platforms as imaging and drug delivery agents for brain diseases. We firstly introduce the methods of synthesis and surface functionalization of MIONPs with emphasis on the inclusion of biocompatible polymers that allow for the addition of tailored physicochemical properties. We then discuss the recent advances in in vivo imaging and drug delivery applications using MIONPs. Finally, we present a perspective on the remaining challenges and possible future directions for MIONP-based brain delivery systems.

Ultrasmall superparamagnetic iron oxide nanoparticles: A next generation contrast agent for magnetic resonance imaging

As a research hotspot, the development of magnetic resonance imaging (MRI) contrast agents has attracted great attention over the past decades for improving the accuracy of diagnosis. Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles with core diameter smaller than 5.0 nm are expected to become a next generation of contrast agents owing to their excellent MRI performance, long blood circulation time upon proper surface modification, renal clearance capacity, and remarkable biosafety profile. On top of these merits, USPIO nanoparticles are used for developing not only T₁ contrast agents, but also T₂ /T₁ switchable contrast agents via assembly/disassembly approaches. In recent years, as a new type of contrast agents, USPIO nanoparticles have shown considerable applications in the diagnosis of various diseases such as vascular pathological changes and inflammations apart from malignant tumors. In this review, we are focusing on the state-of-the-art developments and the latest applications of USPIO nanoparticles as MRI contrast agents to discuss their advantages and future prospects. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

The Intrinsic Biological Identities of Iron Oxide Nanoparticles and Their Coatings: Unexplored Territory for Combinatorial Therapies

Over the last 20 years, iron oxide nanoparticles (IONPs) have been the subject of increasing investigation due to their potential use as theranostic agents. Their unique physical properties (physical identity), ample possibilities for surface modifications (synthetic identity), and the complex dynamics of their interaction with biological systems (biological identity) make IONPs a unique and fruitful resource for developing magnetic field-based therapeutic and diagnostic approaches to the treatment of diseases such as cancer. Like all nanomaterials, IONPs also interact with different cell types in vivo, a characteristic that ultimately determines their activity over the short and long term. Cells of the mononuclear phagocytic system (macrophages), dendritic cells (DCs), and endothelial cells (ECs) are engaged in the bulk of IONP encounters in the organism, and also determine IONP biodistribution. Therefore, the biological effects that IONPs trigger in these cells (biological identity) are of utmost importance to better understand and refine the efficacy of IONP-based theranostics. In the present review, which is focused on anti-cancer therapy, we discuss recent findings on the biological identities of IONPs, particularly as concerns their interactions with myeloid, endothelial, and tumor cells. Furthermore, we thoroughly discuss current understandings of the basic molecular mechanisms and complex interactions that govern IONP biological identity, and how these traits could be used as a stepping stone for future research.

Biohybrid Nanoparticles to Negotiate with Biological Barriers

Incapability of effective cross-talk with biological environments has partly impaired the in vivo functionality of nanoparticles (NPs). Homing, biodistribution, and function of NPs could be engineered through regulating their interactions with in vivo niches. Inspired by communications in biological systems, endowing a "biological identity" to synthetic NPs is one approach to control their biodistribution, and immunonegotiation profiles. This synthetic-biological combination is referred to as biohybrid NPs, which comprise both i) engineerable, readily producible, and trackable synthetic NPs as well as ii) biological moieties with the capability to cross-talk with immunological barriers. Here, the latest understanding on the in vivo interactions of NPs, biological barriers they face, and emerging methods for quantitative measurements of NPs' biodistribution are reviewed. Some key biomolecules that have emerged as negotiators with the immune system in the context of cancer and autoimmunity, and their inspirations on biohybrid NPs are introduced. Critical design considerations for efficient cross-talk between NPs and innate and adaptive immunity followed by hybridization methods are also discussed. Finally, clinical translation challenges and future perspectives regarding biohybrid NPs are discussed.

Label-free plasmonic nanostar probes to illuminate in vitro membrane receptor recognition

Protein-ligand recognition is a key activity where chemical signals are communicated to cells to activate various biochemical pathways, which are important for understanding membrane signaling and drug interactions. Gold nanostars are highly attractive for biological applications due to their readily modified surface chemistry, facile synthesis and optical properties. The increase in electromagnetic field at their branches increases the surface enhanced Raman scattering (SERS) making them ideal candidates as label free in vitro probes that can be used to detect a variety of cellular activities. However, the use of particles in vitro is complicated by the adsorption of proteins, which forms the protein corona. In this paper we demonstrate gold nanostars as label free in vitro probes to study the interaction between αvβ3 integrin and RGD. Nanostars functionalized with cyclic-RDGFC reduced the formation of the protein corona, due to its zwitterionic nature, indicating a small peptide approach to minimizing protein absorption. Additionally, the functionalized nanostars evince a SERS response from their interaction with αvβ3 integrin representative of the amino acids present at the binding site which is also retained in a complex biological matrix. The nanostars were used in vitro to selectively detect αvβ3 integrin on the membrane of human metastatic colon cancer cells. By exploiting the intense SERS and tunable plasmon resonance properties of gold nanostars functionalized with cyclic RGDFC, we have demonstrated a label free approach to investigate the chemical interactions associated with protein-ligand binding from both purified proteins and membrane bound receptors in cells.

Ultrasmall iron oxide nanoparticles: synthesis, surface modification, assembly, and biomedical applications

Ultrasmall iron oxide nanoparticles (USIO NPs) with a size <5nm are a class of emerging nanomaterials. As a result of their intrinsic drawbacks related to poor colloidal stability, low r₁ relaxivity, and lack of functionality, various strategies have been adopted to synthesize USIO NPs with controllable sizes, to surface modify the particles with polymers, and to assemble them in combination with other nanoscale platforms. Here, we review recent progresses in the synthesis, surface modification, and self-assembly of USIO NPs to address key issues in their biomedical application in the field of cancer diagnosis and therapy, in particular magnetic resonance (MR) imaging, dual-modal or multimodal imaging, drug delivery, and theranostics.

Facile preparation of multifunctionalisable ‘stealth’ upconverting nanoparticles for biomedical applications

Hide and Seek. Alendronate-modified upconverting nanoparticles display high colloidal stability, protein corona resistance, bright upconversion luminescence (800 nm excitation), and contain multifunctionalisation sites.

Shedding light on zwitterionic magnetic nanoparticles: limitations for in vivo applications

Over the last few years several studies have dealt with the importance of the surface charge of nanoparticles in prolonging their blood circulation and minimizing their interaction with plasma proteins. These investigations claimed that zwitterionic nanoparticles exhibited a minimal macrophage response and long blood circulation times compared to nanoparticles with other surface charges. These differences in their in vivo behavior are mainly attributed to the interaction of nanoparticles with plasma proteins. Interestingly, most of these studies considered the total surface charge, instead of the outermost layer of the nanomaterial, as being mainly responsible for these undesirable interactions. However, the first contact with plasma proteins is most likely due to the outermost layer on the nanomaterials. Therefore, here we report a detailed study on the effect of the outermost surface charge of magnetic nanoparticles with regard to biodistribution, pharmacokinetics and bioavailability. Magnetic nanoparticles, coated with PEG chains functionalized with neutral, positive or zwitterionic groups, were intravenously injected into mice, followed in vivo by MRI and then quantified by ICP-MS in blood and the main organs. We found that neutral nanoparticles exhibited long blood circulation times, very good stealth properties and the highest bioavailability, whereas zwitterionic nanoparticles were readily recognized by the mononuclear phagocyte system and avidly taken up by the liver. Also, zwitterionic nanoparticles showed high non-specific cell internalization, whereas neutral nanoparticles showed the lowest cellular uptake, indicating that they require active transport to cross the plasma membrane, which is the desirable situation for therapeutic vehicles with low side effects. Thus, neutral nanoparticles exhibit very favorable characteristics for in vivo applications, whereas zwitterionic nanoparticles show important limitations.