Macrophage targeted N-(2-hydroxypropyl)methacrylamide conjugates for magnetic resonance imaging

Role of Liposome Size, Surface Charge, and PEGylation on Rheumatoid Arthritis Targeting Therapy

Rheumatoid arthritis (RA) is a chronic, systemic, progressive autoimmune disease. The vascular permeability of inflamed joints in RA makes it a natural candidate for passive targeting, similar to the enhanced permeability and retention (EPR) effect in solid tumors. Thus, various therapeutic drugs have been encapsulated in nanocarriers to achieve longer in vivo circulation times and improve RA targeting. Although liposomes are the most widely used nanocarriers for RA treatment, the effects of physical and chemical characteristics of liposomes, such as particle sizes, surface charge, polyethylene glycol (PEG) chain length, and PEG concentration, on their passive RA targeting effect have not been fully elucidated. Here, we systematically investigated the effects of physical and chemical properties of liposomes on circulation time and conducted preliminary studies on their passive targeting mechanisms. A series of liposomes with different particle sizes (70, 100, 200, and 350 nm), surface charges (positive, negative, slight positive, and slight negative), PEG chain lengths (1, 2, and 5 kDa), and concentrations (5, 10, and 20% w/w of total lipid) were prepared by lipid film dispersion and extrusion. The pharmacokinetics of liposomes with different formulas were evaluated with a fluorescence microplate reader. A collagen-induced arthritis (CIA) mouse model was utilized to mimic RA pathological conditions and to evaluate the targeting and efficacy of liposomes with different properties using a near-infrared fluorescence imaging system. Uptake of fluorescent liposomes by various synovial cells was measured by flow cytometry. The results indicated that liposomes with 100 nm diameter, a slight negative charge, and 10% incorporation of 5 kDa PEG had better in vivo circulation time and inflamed joint targeting than did other liposomes. Dexamethasone (Dex) was encapsulated into optimized liposomes as an active ingredient for RA treatment. Pharmacodynamic studies demonstrated that Dex liposomes could significantly improve the antiarthritic efficacy of Dex in a CIA mouse model of RA. This study also found that the retention mechanism of RA was mainly increased because of the uptake of liposomes by fibroblasts and macrophages in inflamed joints. This study provides a persuasive explanation for passive RA targeting by liposomes and advances our ability to treat RA with nanomedicine.

Overcoming the Blood-Brain Barrier: The Role of Nanomaterials in Treating Neurological Diseases

Therapies directed toward the central nervous system remain difficult to translate into improved clinical outcomes. This is largely due to the blood-brain barrier (BBB), arguably the most tightly regulated interface in the human body, which routinely excludes most therapeutics. Advances in the engineering of nanomaterials and their application in biomedicine (i.e., nanomedicine) are enabling new strategies that have the potential to help improve our understanding and treatment of neurological diseases. Herein, the various mechanisms by which therapeutics can be delivered to the brain are examined and key challenges facing translation of this research from benchtop to bedside are highlighted. Following a contextual overview of the BBB anatomy and physiology in both healthy and diseased states, relevant therapeutic strategies for bypassing and crossing the BBB are discussed. The focus here is especially on nanomaterial-based drug delivery systems and the potential of these to overcome the biological challenges imposed by the BBB. Finally, disease-targeting strategies and clearance mechanisms are explored. The objective is to provide the diverse range of researchers active in the field (e.g., material scientists, chemists, engineers, neuroscientists, and clinicians) with an easily accessible guide to the key opportunities and challenges currently facing the nanomaterial-mediated treatment of neurological diseases.

Multifunctional PHPMA-Derived Polymer for Ratiometric pH Sensing, Fluorescence Imaging, and Magnetic Resonance Imaging

In this paper, we report synthesis and characterization of a novel multimodality (MRI/fluorescence) probe for pH sensing and imaging. A multifunctional polymer was derived from poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) and integrated with a naphthalimide-based-ratiometric fluorescence probe and a gadolinium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid complex (Gd-DOTA complex). The polymer was characterized using UV-vis absorption spectrophotometry, fluorescence spectrofluorophotometry, magnetic resonance imaging (MRI), and confocal microscopy for optical and MRI-based pH sensing and cellular imaging. In vitro labeling of macrophage J774 and esophageal CP-A cell lines shows the polymer's ability to be internalized in the cells. The transverse relaxation time (T₂) of the polymer was observed to be pH-dependent, whereas the spin-lattice relaxation time (T₁) was not. The pH probe in the polymer shows a strong fluorescence-based ratiometric pH response with emission window changes, exhibiting blue emission under acidic conditions and green emission under basic conditions, respectively. This study provides new materials with multimodalities for pH sensing and imaging.

Microinjection for the ex Vivo Modification of Cells with Artificial Organelles

Microinjection is extensively used across fields to deliver material intracellularly. Here we address the fundamental aspects of introducing exogenous organelles into cells to endow them with artificial functions. Nanocarriers encapsulating biologically active cargo or extreme intraluminal pH were injected directly into the cytosol of cells, where they bypassed subcellular processing pathways and remained intact for several days. Nanocarriers' size was found to dictate their intracellular distribution pattern upon injection, with larger vesicles adopting polarized agglomerated distributions and smaller colloids spreading evenly in the cytosol. This in turn determined the symmetry or asymmetry of their dilution following cell division, ultimately affecting the intracellular dose at a cell population level. As an example of microinjection's applicability, a cell type relevant for cell-based therapies (dendritic cells) was injected with vesicles, and its migratory properties were studied in a co-culture system mimicking lymphatic capillaries.

The evolution of gadolinium based contrast agents: from single-modality to multi-modality

Gadolinium-based contrast agents are extensively used as magnetic resonance imaging (MRI) contrast agents due to their outstanding signal enhancement and ease of chemical modification. However, it is increasingly recognized that information obtained from single modal molecular imaging cannot satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research, due to its limitation and default rooted in single molecular imaging technique itself. To compensate for the deficiencies of single function magnetic resonance imaging contrast agents, the combination of multi-modality imaging has turned to be the research hotpot in recent years. This review presents an overview on the recent developments of the functionalization of gadolinium-based contrast agents, and their application in biomedicine applications.

Avoiding compositional drift during the RAFT copolymerization of N-(2-hydroxypropyl)methacrylamide and N-acryloxysuccinimide: towards uniform platforms for post-polymerization modification

Compositionally uniform copolymers: avoiding compositional drift during RAFT copolymerization by controlling monomer feed ratio and conversion.

MR imaging techniques for nano-pathophysiology and theranostics

The advent of nanoparticle DDSs (drug delivery systems, nano-DDSs) is opening new pathways to understanding physiology and pathophysiology at the nanometer scale. A nano-DDS can be used to deliver higher local concentrations of drugs to a target region and magnify therapeutic effects. However, interstitial cells or fibrosis in intractable tumors, as occurs in pancreatic or scirrhous stomach cancer, tend to impede nanoparticle delivery. Thus, it is critical to optimize the type and size of nanoparticles to reach the target. High-resolution 3D imaging provides a means of "seeing" the nanoparticle distribution and therapeutic effects. We introduce the concept of "nano-pathophysiological imaging" as a strategy for theranostics. The strategy consists of selecting an appropriate nano-DDS and rapidly evaluating drug effects in vivo to guide the next round of therapy. In this article we classify nano-DDSs by component carrier materials and present an overview of the significance of nano-pathophysiological MRI.

Gadolinium-labeled peptide dendrimers with controlled structures as potential magnetic resonance imaging contrast agents

Gadolinium (Gd(3+)) based dendrimers with precise and tunable nanoscopic sizes are excellent candidates as magnetic resonance imaging (MRI) contrast agents. Control of agents' sensitivity, biosafety and functionality is key to the successful applications. We report the synthesis of Gd(III)-based peptide dendrimers possessing highly controlled and precise structures, and their potential applications as MRI contrast agents. These agents have no obvious cytotoxicity as verified by in vitro studies. One of the dendrimer formulations with mPEG modification showed a 9-fold increase in T(1) relaxivity to 39.2 Gd(III) mM(-1) s(-1) comparing to Gd-DTPA. In vivo studies have shown that the mPEGylated Gd(III)-based dendrimer provided much higher signal intensity enhancement (SI) in mouse kidney, especially at 60 min post-injection, with 54.8% relatively enhanced SI. The accumulations of mPEGylated dendrimer in mouse liver and kidney were confirmed through measurement of gadolinium by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Meanwhile, mPEGylated dendrimer showed much higher Gd(III) concentration in blood with 38 μg Gd(III)/g blood at 1 h post-injection comparing to other dendrimer formulations. These findings provide an attractive alternative strategy to the design of multifunctional gadolinium-based dendrimers with controlled structures, and open up possibilities of using the Gd(III)-based peptide dendrimers as MRI probes.

Cell-mediated drug delivery

INTRODUCTION

Drug targeting to sites of tissue injury, tumor or infection with limited toxicity is the goal for successful pharmaceutics. Immunocytes (including mononuclear phagocytes (dendritic cells, monocytes and macrophages), neutrophils and lymphocytes) are highly mobile; they can migrate across impermeable barriers and release their drug cargo at sites of infection or tissue injury. Thus, immune cells can be exploited as Trojan horses for drug delivery.

AREAS COVERED

This paper reviews how immunocytes laden with drugs can cross the blood-brain or blood-tumor barriers to facilitate treatments for infectious diseases, injury, cancer, or inflammatory diseases. The promises and perils of cell-mediated drug delivery are reviewed, with examples of how immunocytes can be harnessed to improve therapeutic end points.

EXPERT OPINION

Using cells as delivery vehicles enables targeted drug transport and prolonged circulation times, along with reductions in cell and tissue toxicities. Such systems for drug carriage and targeted release represent a new disease-combating strategy being applied to a spectrum of human disorders. The design of nanocarriers for cell-mediated drug delivery may differ from those used for conventional drug delivery systems; nevertheless, engaging different defense mechanisms in drug delivery may open new perspectives for the active delivery of drugs.

Development of a macromolecular prodrug for the treatment of inflammatory arthritis: mechanisms involved in arthrotropism and sustained therapeutic efficacy

Introduction

The purpose of the present manuscript is to test the hypothesis that arthrotropic localization and synovial cell internalization account for the unique capacity of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-dexamethasone conjugate (P-Dex, a macromolecular prodrug of dexamethasone) to induce sustained amelioration of joint inflammation and inhibition of tissue damage in an animal model of inflammatory arthritis.

Methods

Rats with adjuvant-induced arthritis (AA) were treated with P-Dex, free dexamethasone, saline or HPMA homopolymer. To define the biodistribution of P-Dex, conjugates with different imaging labels were given to AA rats and analyzed. Isolated joint tissues were evaluated by fluorescence-activated cell sorting (FACS) and immunohistochemical staining. Cellular uptake of P-Dex and its effects on apoptosis and production of proinflammatory cytokines were examined using human monocyte-macrophages and fibroblasts.

Results

A single systemic administration of P-Dex completely suppressed AA for >20 days. Magnetic resonance imaging demonstrated higher HPMA copolymer influx into the inflamed joints than the normal joints. Immunohistochemistry and FACS analyses of arthritic joints revealed extensive uptake of the polymer conjugate by synovial fibroblasts and myeloid lineage cells. The capacity of P-Dex to suppress inflammation was confirmed in monocyte-macrophage cultures in which P-Dex treatment resulted in suppression of lipopolysaccharide-induced IL-6 and TNFα release. Similarly, TNFα-induced expression of matrix metalloproteinases (MMP1 and MMP3) in synovial fibroblasts from a rheumatoid arthritis patient was suppressed by P-Dex. P-Dex showed no detectable effect on monocyte apoptosis.

Conclusions

P-Dex provides superior and sustained amelioration of AA compared with an equivalent dose of free dexamethasone. The arthrotropism and local retention of P-Dex is attributed to the enhanced vascular permeability in arthritic joints and the internalization of P-Dex by synovial cells. The uptake and processing of P-Dex by macrophages and fibroblasts, and downregulation of proinflammatory mediators, provides an explanation for the sustained anti-inflammatory efficacy of P-Dex in this model of inflammatory arthritis.

Noninvasive monitoring of HPMA copolymer-RGDfK conjugates by magnetic resonance imaging

PURPOSE

To evaluate the tumor targeting potential of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-gadolinium(Gd)-RGDfK conjugates by magnetic resonance (MR) T1-mapping.

METHODS

HPMA copolymers with and without RGDfK were synthesized to incorporate side chains for Gd chelation. The conjugates were characterized by their side-chain contents and r(1) relaxivity. In vitro integrin-binding affinities of polymeric conjugates were assessed via competitive cell binding assays on HUVEC endothelial cells and MDA-MB-231 breast cancer cells. In vivo MR imaging was performed on MDA-MB-231 tumor-bearing SCID mice at different time points using non-targetable and targetable polymers. The specificity of alphavbeta3 targeting was assessed by using non-paramagnetic targetable polymer to block alphavbeta3 integrins followed by injection of paramagnetic targetable polymers after 2 h.

RESULTS

The polymer conjugates showed relaxivities higher than Gd-DOTA. Endothelial cell binding studies showed that IC(50) values for the copolymer with RGDfK binding to alphavbeta3 integrin-positive HUVEC and MDA-MB-231 cells were similar to that of free peptide. Significantly lower T1 values were observed at the tumor site after 2 h using targetable conjugate (p < 0.012). In vivo blocking study showed significantly higher T1 values (p < 0.045) compared to targetable conjugate.

CONCLUSION

These results demonstrate the potential of this conjugate as an effective targetable MR contrast agent for tumor imaging and therapy monitoring.

HPMA copolymer-doxorubicin-gadolinium conjugates: synthesis, characterization, and in vitro evaluation

This study describes the synthesis, characterization, and in vitro evaluation of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-gadolinium (Gd)-doxorubicin (Dox) conjugates. Copolymers of HPMA were derivatized to incorporate side chains for Gd chelation and Dox conjugation. The conjugates were characterized by their side chain contents, T(1) relaxivity (r(1)), stability, and in vitro cytotoxicity. High stability and relaxivity of these conjugates coupled with low toxicity show their potential for monitoring the in vivo fate of HPMA-based drug delivery systems by magnetic resonance imaging techniques.

Cell-based drug delivery

Drug delivery has been greatly improved over the years by means of chemical and physical agents that increase bioavailability, improve pharmacokinetic and reduce toxicities. At the same time, cell based delivery systems have also been developed. These possesses a number of advantages including prolonged delivery times, targeting of drugs to specialized cell compartments and biocompatibility. Here we'll focus on erythrocyte-based drug delivery. These systems are especially efficient in releasing drugs in circulations for weeks, have a large capacity, can be easily processed and could accommodate traditional and biologic drugs. These carriers have also been used for delivering antigens and/or contrasting agents. Carrier erythrocytes have been evaluated in thousands of drug administration in humans proving safety and efficacy of the treatments. Erythrocyte-based delivery of new and conventional drugs is thus experiencing increasing interests in drug delivery and in managing complex pathologies especially when side effects could become serious issues.