Metal-Organic Frameworks for Drug Delivery: A Design Perspective

The use of metal-organic frameworks (MOFs) in biomedical applications has greatly expanded over the past decade due to the precision tunability, high surface areas, and high loading capacities of MOFs. Specifically, MOFs are being explored for a wide variety of drug delivery applications. Initially, MOFs were used for delivery of small-molecule pharmaceuticals; however, more recent work has focused on macromolecular cargos, such as proteins and nucleic acids. Here, we review the historical application of MOFs for drug delivery, with a specific focus on the available options for designing MOFs for specific drug delivery applications. These options include choices of MOF structure, synthetic method, and drug loading. Further considerations include tuning, modifications, biocompatibility, cellular targeting, and uptake. Altogether, this Review aims to guide MOF design for novel biomedical applications.

Targeting receptor-mediated endocytotic pathways with nanoparticles: rationale and advances

Targeting of drugs and their carrier systems by using receptor-mediated endocytotic pathways was in its nascent stages 25 years ago. In the intervening years, an explosion of knowledge focused on design and synthesis of nanoparticulate delivery systems as well as elucidation of the cellular complexity of what was previously-termed receptor-mediated endocytosis has now created a situation when it has become possible to design and test the feasibility of delivery of highly specific nanoparticle drug carriers to specific cells and tissue. This review outlines the mechanisms governing the major modes of receptor-mediated endocytosis used in drug delivery and highlights recent approaches using these as targets for in vivo drug delivery of nanoparticles. The review also discusses some of the inherent complexity associated with the simple shift from a ligand-drug conjugate versus a ligand-nanoparticle conjugate, in terms of ligand valency and its relationship to the mode of receptor-mediated internalization.

Nanoparticles in Cancer Treatment: Opportunities and Obstacles

In the United States, the estimated number of new cancer cases in 2018 will be approx. 1.7 million. Historically, combination chemotherapy has been the primary choice of treatment. However, chemotherapeutics have pharmaceutical limitations, among which include problems with stability and aqueous solubility. Likewise, dose limiting toxicity is significant with nonspecific toxicity to healthy cells, hair loss, loss of appetite, peripheral neuropathy and diarrhea being typical side effects. The emergence of Multidrug resistance (MDR) also presents s a significant challenge for the successful treatment of cancer whereby cancer cells become cross resistant to many of the chemotherapeutic agents used. Nanotechnology presents a new frontier for cancer treatment. It holds potential in minimizing systemic toxicity through the development of functionalized particles for targeted treatment. They also provide an alternative strategy to circumvent multidrug resistance as they have a capacity to by-pass the drug efflux mechanism associated with this phenotype. Aside from the advantages they offer in treatment, nanoparticles are also emerging to be valuable diagnostic entities. This article highlights the various ways nanotechnology is being used to improve the treatment and management of cancer. We also discuss the opportunities and obstacles in this area and provide an up to date review of progress in the treatment of cancer.

Importance of having low-density functional groups for generating high-performance semiconducting polymer dots

Semiconducting polymers with low-density side-chain carboxylic acid groups were synthesized to form stable, functionalized, and highly fluorescent polymer dots (Pdots). The influence of the molar fraction of hydrophilic side-chains on Pdot properties and performance was systematically investigated. Our results show that the density of side-chain carboxylic acid groups significantly affects Pdot stability, internal structure, fluorescence brightness, and nonspecific binding in cellular labeling. Fluorescence spectroscopy, single-particle imaging, and a dye-doping method were employed to investigate the fluorescence brightness and the internal structure of the Pdots. The results of these experiments indicate that semiconducting polymers with low density of side-chain functional groups can form stable, compact, and highly bright Pdots as compared to those with high density of hydrophilic side-chains. The functionalized polymer dots were conjugated to streptavidin (SA) by carbodiimide-catalyzed coupling and the Pdot-SA probes effectively and specifically labeled the cancer cell-surface marker Her2 in human breast cancer cells. The carboxylate-functionalized polymer could also be covalently modified with small functional molecules to generate Pdot probes for click chemistry-based bio-orthogonal labeling. This study presents a promising approach for further developing functional Pdot probes for biological applications.

Crystal structure of a PP2A B56-BubR1 complex and its implications for PP2A substrate recruitment and localization

Protein phosphatase 2A (PP2A) accounts for the majority of total Ser/Thr phosphatase activities in most cell types and regulates many biological processes. PP2A holoenzymes contain a scaffold A subunit, a catalytic C subunit, and one of the regulatory/targeting B subunits. How the B subunit controls PP2A localization and substrate specificity, which is a crucial aspect of PP2A regulation, remains poorly understood. The kinetochore is a critical site for PP2A functioning, where PP2A orchestrates chromosome segregation through its interactions with BubR1. The PP2A-BubR1 interaction plays important roles in both spindle checkpoint silencing and stable microtubule-kinetochore attachment. Here we present the crystal structure of a PP2A B56-BubR1 complex, which demonstrates that a conserved BubR1 LxxIxE motif binds to the concave side of the B56 pseudo-HEAT repeats. The BubR1 motif binds to a groove formed between B56 HEAT repeats 3 and 4, which is quite distant from the B56 binding surface for PP2A catalytic C subunit and thus is unlikely to affect PP2A activity. In addition, the BubR1 binding site on B56 is far from the B56 binding site of shugoshin, another kinetochore PP2A-binding protein, and thus BubR1 and shugoshin can potentially interact with PP2A-B56 simultaneously. Our structural and biochemical analysis indicates that other proteins with the LxxIxE motif may also bind to the same PP2A B56 surface. Thus, our structure of the PP2A B56-BubR1 complex provides important insights into how the B56 subunit directs the recruitment of PP2A to specific targets.

Functionalization of Reduced Graphene Oxide via Thiol-Maleimide "Click" Chemistry: Facile Fabrication of Targeted Drug Delivery Vehicles

Materials based on reduced graphene oxide (rGO) have shown to be amenable to noncovalent functionalization through hydrophobic interactions. The scaffold, however, does not provide sufficient covalent linkage given the low number of reactive carboxyl and alcohol groups typically available on the rGO. The integration of clickable groups, particularly the ones that can undergo efficient conjugation without any metal catalyst, would allow facile functionalization of these materials. This study reports on the noncovalent association of a maleimide-containing catechol (dopa-MAL) surface anchor onto the rGO. Thiol-maleimide chemistry allows thereafter the facile attachment of thiol-containing molecules under ambient metal-free conditions. Although the attachment of glutathione and 6-(ferrocenyl)hexanethiol was used as model thiols, the attachment of a cancer cell targeting cyclic peptide, c(RGDfC), opened the possibility of using the dopa-MAL-modified rGO as a targeted drug delivery system for doxorubicin (DOX). Although free DOX showed to be more effective at killing the human cervical cancer cells (HeLa) over human breast adenocarcinoma cancer cells (MDA-MB-231), the DOX-loaded rGO/dopa-MAL-c (RGDfC) nanostructure showed an opposite effect being notably more effective at targeting and killing the MDA-MB-231 cells. The effect is enhanced upon laser irradiation for 10 min at 2 W cm^-2. The facile fabrication and functionalization to readily obtain a functional material in a modular fashion make this clickable-rGO construct an attractive platform for various applications.

Improving the Anticancer Efficacy of Laminin Receptor-Specific Therapeutic Ruthenium Nanoparticles (RuBB-Loaded EGCG-RuNPs) via ROS-Dependent Apoptosis in SMMC-7721 Cells

Functionalization can promote the uptake of nanoparticles into cancer cells via receptor-mediated endocytosis, enabling them to exert their therapeutic effects. In this paper, epigallocatechin gallate (EGCG), which has a high binding affinity to 67 kDa laminin receptor (67LR) overexpressed in HCC cells, was employed in the present study to functionalized ruthenium nanoparticles (RuNPs) loaded with luminescent ruthenium complexes to achieve antiliver cancer efficacy. [Ru(bpy)2(4-B)] (ClO4)2·2H2O (RuBB)-loaded EGCG-RuNPs (bpy = 2,2'-bipyridine) showed small particle size with narrow distribution, better stability, and high selectivity between liver cancer and normal cells. The internalization of RuBB-loaded EGCG-RuNPs was inhibited by 67LR-blocking antibody or laminin, suggesting that 67LR-mediated endocytosis played an important role in the uptake into HCC cells. Moreover, transmission electron microscopy and confocal microscopic images showed that RuBB-loaded EGCG-RuNPs accumulated in the cytoplasm of SMMC-7721 cells. Furthermore, our results indicated that the EGCG-functionalized nanoparticles displayed enhanced anticancer effects in a target-specific manner. Concentrations of RuBB-loaded EGCG-RuNPs, nontoxic in normal L-02 cells, showed direct reactive oxygen species-dependent cytotoxic, pro-apoptotic, and anti-invasive effects in SMMC-7721 cells. Furthermore, in vivo animal study demonstrated that RuBB-loaded EGCG-RuNPs possessed high antitumor efficacy on tumor-bearing nude mice. It is encouraging to conclude that the multifunctional RuNPs may form the basis of new strategies on the treatment of liver cancer and other malignancies.

Correlative Light-Electron Microscopy Shows RGD-Targeted ZnO Nanoparticles Dissolve in the Intracellular Environment of Triple Negative Breast Cancer Cells and Cause Apoptosis with Intratumor Heterogeneity

ZnO nanoparticles (NPs) are reported to show a high degree of cancer cell selectivity with potential use in cancer imaging and therapy. Questions remain about the mode by which the ZnO NPs cause cell death, whether they exert an intra- or extracellular effect, and the resistance among different cancer cell types to ZnO NP exposure. The present study quantifies the variability between the cellular toxicity, dynamics of cellular uptake, and dissolution of bare and RGD (Arg-Gly-Asp)-targeted ZnO NPs by MDA-MB-231 cells. Compared to bare ZnO NPs, RGD-targeting of the ZnO NPs to integrin αvβ3 receptors expressed on MDA-MB-231 cells appears to increase the toxicity of the ZnO NPs to breast cancer cells at lower doses. Confocal microscopy of live MDA-MB-231 cells confirms uptake of both classes of ZnO NPs with a commensurate rise in intracellular Zn(2+) concentration prior to cell death. The response of the cells within the population to intracellular Zn(2+) is highly heterogeneous. In addition, the results emphasize the utility of dynamic and quantitative imaging in understanding cell uptake and processing of targeted therapeutic ZnO NPs at the cellular level by heterogeneous cancer cell populations, which can be crucial for the development of optimized treatment strategies.

Plant mitochondrial protein import: the ins and outs

The majority of the mitochondrial proteome, required to fulfil its diverse range of functions, is cytosolically synthesised and translocated via specialised machinery. The dedicated translocases, receptors, and associated proteins have been characterised in great detail in yeast over the last several decades, yet many of the mechanisms that regulate these processes in higher eukaryotes are still unknown. In this review, we highlight the current knowledge of mitochondrial protein import in plants. Despite the fact that the mechanisms of mitochondrial protein import have remained conserved across species, many unique features have arisen in plants to encompass the developmental, tissue-specific, and stress-responsive regulation in planta. An understanding of unique features and mechanisms in plants provides us with a unique insight into the regulation of mitochondrial biogenesis in higher eukaryotes.

Self-adjuvanting bacterial vectors expressing pre-erythrocytic antigens induce sterile protection against malaria

Genetically inactivated, Gram-negative bacteria that express malaria vaccine candidates represent a promising novel self-adjuvanting vaccine approach. Antigens expressed on particulate bacterial carriers not only target directly to antigen-presenting cells but also provide a strong danger signal thus circumventing the requirement for potent extraneous adjuvants. E. coli expressing malarial antigens resulted in the induction of either Th1 or Th2 biased responses that were dependent on both antigen and sub-cellular localization. Some of these constructs induced higher quality humoral responses compared to recombinant protein and most importantly they were able to induce sterile protection against sporozoite challenge in a murine model of malaria. In light of these encouraging results, two major Plasmodium falciparum pre-erythrocytic malaria vaccine targets, the Cell-Traversal protein for Ookinetes and Sporozoites (CelTOS) fused to the Maltose-binding protein in the periplasmic space and the Circumsporozoite Protein (CSP) fused to the Outer membrane (OM) protein A in the OM were expressed in a clinically relevant, attenuated Shigella strain (Shigella flexneri 2a). This type of live-attenuated vector has previously undergone clinical investigations as a vaccine against shigellosis. Using this novel delivery platform for malaria, we find that vaccination with the whole-organism represents an effective vaccination alternative that induces protective efficacy against sporozoite challenge. Shigella GeMI-Vax expressing malaria targets warrant further evaluation to determine their full potential as a dual disease, multivalent, self-adjuvanting vaccine system, against both shigellosis, and malaria.

Layer-by-Layer Polymer Functionalization Improves Nanoparticle Penetration and Glioblastoma Targeting in the Brain

Glioblastoma is characterized by diffuse infiltration into surrounding healthy brain tissues, which makes it challenging to treat. Complete surgical resection is often impossible, and systemically delivered drugs cannot achieve adequate tumor exposure to prevent local recurrence. Convection-enhanced delivery (CED) offers a method for administering therapeutics directly into brain tumor tissue, but its impact has been limited by rapid clearance and off-target cellular uptake. Nanoparticle (NP) encapsulation presents a promising strategy for extending the retention time of locally delivered therapies while specifically targeting glioblastoma cells. However, the brain's extracellular structure poses challenges for NP distribution due to its narrow, tortuous pores and a harsh ionic environment. In this study, we investigated the impact of NP surface chemistry using layer-by-layer (LbL) assembly to design drug carriers for broad spatial distribution in brain tissue and specific glioblastoma cell targeting. We found that poly-l-glutamate and hyaluronate were effective surface chemistries for targeting glioblastoma cells in vitro. Coadsorbing either polymer with a small fraction of PEGylated polyelectrolytes improved the colloidal stability without sacrificing cancer cell selectivity. Following CED in vivo, gadolinium-functionalized LbL NPs enabled MRI visualization and exhibited a distribution volume up to three times larger than liposomes and doubled the retention half-time up to 13.5 days. Flow cytometric analysis of CED-treated murine orthotopic brain tumors indicated greater cancer cell uptake and reduced healthy cell uptake for LbL NPs compared to nonfunctionalized liposomes. The distinct cellular outcomes for different colayered LbL NPs provide opportunities to tailor this modular delivery system for various therapeutic applications.

Protein quality control at the ribosome: focus on RAC, NAC and RQC

The biogenesis of new polypeptides by ribosomes and their subsequent correct folding and localization to the appropriate cellular compartments are essential key processes to maintain protein homoeostasis. These complex mechanisms are governed by a repertoire of protein biogenesis factors that directly bind to the ribosome and chaperone nascent polypeptide chains as soon as they emerge from the ribosomal tunnel exit. This nascent chain 'welcoming committee' regulates multiple co-translational processes including protein modifications, folding, targeting and degradation. Acting at the front of the protein production line, these ribosome-associated protein biogenesis factors lead the way in the cellular proteostasis network to ensure proteome integrity. In this article, I focus on three different systems in eukaryotes that are critical for the maintenance of protein homoeostasis by controlling the birth, life and death of nascent polypeptide chains.

Regulation and function of elF2B in neurological and metabolic disorders

Eukaryotic initiation factor 2B, eIF2B is a guanine nucleotide exchange, factor with a central role in coordinating the initiation of translation. During stress and disease, the activity of eIF2B is inhibited via the phosphorylation of its substrate eIF2 (p-eIF2α). A number of different kinases respond to various stresses leading to the phosphorylation of the alpha subunit of eIF2, and collectively this regulation is known as the integrated stress response, ISR. This targeting of eIF2B allows the cell to regulate protein synthesis and reprogramme gene expression to restore homeostasis. Advances within structural biology have furthered our understanding of how eIF2B interacts with eIF2 in both the productive GEF active form and the non-productive eIF2α phosphorylated form. Here, current knowledge of the role of eIF2B in the ISR is discussed within the context of normal and disease states focusing particularly on diseases such as vanishing white matter disease (VWMD) and permanent neonatal diabetes mellitus (PNDM), which are directly linked to mutations in eIF2B. The role of eIF2B in synaptic plasticity and memory formation is also discussed. In addition, the cellular localisation of eIF2B is reviewed and considered along with the role of additional in vivo eIF2B binding factors and protein modifications that may play a role in modulating eIF2B activity during health and disease.

Cellular Targeting of Oligonucleotides by Conjugation with Small Molecules

Drug candidates derived from oligonucleotides (ON) are receiving increased attention that is supported by the clinical approval of several ON drugs. Such therapeutic ON are designed to alter the expression levels of specific disease-related proteins, e.g., by displaying antigene, antisense, and RNA interference mechanisms. However, the high polarity of the polyanionic ON and their relatively rapid nuclease-mediated cleavage represent two major pharmacokinetic hurdles for their application in vivo. This has led to a range of non-natural modifications of ON structures that are routinely applied in the design of therapeutic ON. The polyanionic architecture of ON often hampers their penetration of target cells or tissues, and ON usually show no inherent specificity for certain cell types. These limitations can be overcome by conjugation of ON with molecular entities mediating cellular 'targeting', i.e., enhanced accumulation at and/or penetration of a specific cell type. In this context, the use of small molecules as targeting units appears particularly attractive and promising. This review provides an overview of advances in the emerging field of cellular targeting of ON via their conjugation with small-molecule targeting structures.

Targeting protein function: the expanding toolkit for conditional disruption

A major objective in biological research is to understand spatial and temporal requirements for any given gene, especially in dynamic processes acting over short periods, such as catalytically driven reactions, subcellular transport, cell division, cell rearrangement and cell migration. The interrogation of such processes requires the use of rapid and flexible methods of interfering with gene function. However, many of the most widely used interventional approaches, such as RNAi or CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 (CRISPR-associated 9), operate at the level of the gene or its transcripts, meaning that the effects of gene perturbation are exhibited over longer time frames than the process under investigation. There has been much activity over the last few years to address this fundamental problem. In the present review, we describe recent advances in disruption technologies acting at the level of the expressed protein, involving inducible methods of protein cleavage, (in)activation, protein sequestration or degradation. Drawing on examples from model organisms we illustrate the utility of fast-acting techniques and discuss how different components of the molecular toolkit can be employed to dissect previously intractable biochemical processes and cellular behaviours.

Connexin 43-targeted T1 contrast agent for MRI diagnosis of glioma

Glioblastoma multiforme is the most aggressive form of brain tumor. Early and accurate diagnosis of glioma and its borders is an important step for its successful treatment. One of the promising targets for selective visualization of glioma and its margins is connexin 43 (Cx43), which is highly expressed in reactive astrocytes and migrating glioma cells. The purpose of this study was to synthesize a Gd-based contrast agent conjugated with specific antibodies to Cx43 for efficient visualization of glioma C6 in vivo. We have prepared stable nontoxic conjugates of monoclonal antibody to Cx43 and polylysine-DTPA ligands complexed with Gd(III), which are characterized by higher T1 relaxivity (6.5 mM(-1) s(-1) at 7 T) than the commercial agent Magnevist® (3.4 mM(-1) s(-1)). Cellular uptake of Cx43-specific T1 contrast agent in glioma C6 cells was more than four times higher than the nonspecific IgG-contrast agent, as detected by flow cytometry and confocal analysis. MRI experiments showed that the obtained agents could markedly enhance visualization of glioma C6 in vivo after their intravenous administration. Significant accumulation of Cx43-targeted contrast agents in glioma and the peritumoral zone led not only to enhanced contrast but also to improved detection of the tumor periphery. Fluorescence imaging confirmed notable accumulation of Cx43-specific conjugates in the peritumoral zone compared with nonspecific IgG conjugates at 24 h after intravenous injection. All these features of Cx43-targeted contrast agents might be useful for more precise diagnosis of glioma and its borders by MRI.

Glycolaldehyde and maleyl conjugated human serum albumin as potential macrophage-targeting carriers for molecular imaging purposes

Maleylated bovine serum albumin is a known ligand for targeting macrophages and has potential as a carrier for molecular imaging purposes. We present a novel synthesis of glycolaldehyde-conjugated human serum albumin (GA-HSA) and maleylated human serum albumin (Mal-HSA). Seventeen modifications of fluorescently tagged GA-HSA and Mal-HSA molecules with different degrees of conjugation were prepared. The comparative uptake studies, using 12 of these modifications, were done in vitro on mouse monocytes/macrophages (RAW264.7), and evaluated qualitatively by confocal microscopy and quantitatively by flow cytometry. The GA modifications are taken up by the macrophages approximately 40% better than the maleyl modifications at low concentrations (≤ 3 μM), while at higher concentrations it appears that the maleyl modifications are taken up around 25-44% better than the GA-modified HSA. However, high uptake at low concentrations will be beneficial for in vivo localizing inflammation in areas with low penetration of the probe as in an atherosclerotic plaque. Further, another advantage of GA-HSA is that GA competes less than the maleyl group for the free reactive amine sites that are to be used for conjugation of metal chelating ligands (e.g. tetraazacyclododecanetetraacetic acid and triazacyclononanetriacetic acid). Metal ions such as Gd(3+) and Mn(2+) can be chelated for positive Magnetic Resonance (MR) contrast and positron emitting ions such as (64) Cu(2+) and (68) Ga(3+) for Positron Emission Tomography (PET) imaging. These are important properties, especially, when considering the MR contrast possibilities owing to the low sensitivity of the technique, and would motivate the use of GA-HSA before Mal-HSA.

SLC26A9 is selected for endoplasmic reticulum associated degradation (ERAD) via Hsp70-dependent targeting of the soluble STAS domain

SLC26A9, a member of the solute carrier protein family, transports chloride ions across various epithelia. SLC26A9 also associates with other ion channels and transporters linked to human health, and in some cases these heterotypic interactions are essential to support the biogenesis of both proteins. Therefore, understanding how this complex membrane protein is initially folded might provide new therapeutic strategies to overcome deficits in the function of SLC26A9 partners, one of which is associated with Cystic Fibrosis. To this end, we developed a novel yeast expression system for SLC26A9. This facile system has been used extensively with other ion channels and transporters to screen for factors that oversee protein folding checkpoints. As commonly observed for other channels and transporters, we first noted that a substantial fraction of SLC26A9 is targeted for endoplasmic reticulum associated degradation (ERAD), which destroys folding-compromised proteins in the early secretory pathway. We next discovered that ERAD selection requires the Hsp70 chaperone, which can play a vital role in ERAD substrate selection. We then created SLC26A9 mutants and found that the transmembrane-rich domain of SLC26A9 was quite stable, whereas the soluble cytosolic STAS domain was responsible for Hsp70-dependent ERAD. To support data obtained in the yeast model, we were able to recapitulate Hsp70-facilitated ERAD of the STAS domain in human tissue culture cells. These results indicate that a critical barrier to nascent membrane protein folding can reside within a specific soluble domain, one that is monitored by components associated with the ERAD machinery.

Targeted Cancer Therapy: Correlative Light-Electron Microscopy Shows RGD-Targeted ZnO Nanoparticles Dissolve in the Intracellular Environment of Triple Negative Breast Cancer Cells and Cause Apoptosis with Intratumor Heterogeneity (Adv. Healthcare Mater. 11/2016)

On page 1310 J. S. Merzaban, A. E. Porter, and co-workers present fluorescently labeled RGD-targeted ZnO nanoparticles (NPs; green) for the targeted delivery of cytotoxic ZnO to integrin αvβ3 receptors expressed on triple negative breast cancer cells. Correlative light-electron microscopy shows that NPs dissolve into ionic Zn(2+) (blue) upon uptake and cause apoptosis (red) with intra-tumor heterogeneity, thereby providing a possible strategy for targeted breast cancer therapy. Cover design by Ivan Gromicho.

Therapeutic Applications of Programmable DNA Nanostructures

Deoxyribonucleic acid (DNA) nanotechnology, a frontier in biomedical engineering, is an emerging field that has enabled the engineering of molecular-scale DNA materials with applications in biomedicine such as bioimaging, biodetection, and drug delivery over the past decades. The programmability of DNA nanostructures allows the precise engineering of DNA nanocarriers with controllable shapes, sizes, surface chemistries, and functions to deliver therapeutic and functional payloads to target cells with higher efficiency and enhanced specificity. Programmability and control over design also allow the creation of dynamic devices, such as DNA nanorobots, that can react to external stimuli and execute programmed tasks. This review focuses on the current findings and progress in the field, mainly on the employment of DNA nanostructures such as DNA origami nanorobots, DNA nanotubes, DNA tetrahedra, DNA boxes, and DNA nanoflowers in the biomedical field for therapeutic purposes. We will also discuss the fate of DNA nanostructures in living cells, the major obstacles to overcome, that is, the stability of DNA nanostructures in biomedical applications, and the opportunities for DNA nanostructure-based drug delivery in the future.