The Pharmacokinetics and Biodistribution of a 64 kDa PolyPEG Star Polymer After Subcutaneous and Pulmonary Administration to Rats

Lipidated brush-PEG polymers as low molecular weight pulmonary drug delivery platforms

OBJECTIVES

Nanomedicines are being actively developed as inhalable drug delivery systems. However, there is a distinct utility in developing smaller polymeric systems that can bind albumin in the lungs. We therefore examined the pulmonary pharmacokinetic behavior of a series of lipidated brush-PEG (5 kDa) polymers conjugated to 1C2, 1C12 lipid or 2C12 lipids.

METHODS

The pulmonary pharmacokinetics, patterns of lung clearance and safety of polymers were examined in rats. Permeability through monolayers of primary human alveolar epithelia, small airway epithelia and lung microvascular endothelium were also investigated, along with lung mucus penetration and cell uptake.

RESULTS

Polymers showed similar pulmonary pharmacokinetic behavior and patterns of lung clearance, irrespective of lipid molecular weight and albumin binding capacity, with up to 30% of the dose absorbed from the lungs over 24 h. 1C12-PEG showed the greatest safety in the lungs. Based on its larger size, 2C12-PEG also showed the lowest mucus and cell membrane permeability of the three polymers. While albumin had no significant effect on membrane transport, the cell uptake of C12-conjugated PEGs were increased in alveolar epithelial cells.

CONCLUSION

Lipidated brush-PEG polymers composed of 1C12 lipid may provide a useful and novel alternative to large nanomaterials as inhalable drug delivery systems.

Novel Pt(IV) prodrug self-assembled nanoparticles with enhanced blood circulation stability and improved antitumor capacity of oxaliplatin for cancer therapy

Pt(IV) compounds are regarded as prodrugs of active Pt(II) drugs (i.e. cisplatin, carboplatin, and oxaliplatin) and burgeoned as the most ideal candidates to substitute Pt(II) anticancer drugs with severe side effects. Nanoparticle drug delivery systems have been widely introduced to deliver Pt(IV) prodrugs more effectively and safely to tumors, but clinical outcomes were unpredictable owing to limited in vivo pharmacokinetics understanding. Herein, a novel Pt(IV) prodrug of oxaliplatin(OXA) was synthesized and prepared as self-assembled micellar nanoparticles(PEG-OXA NPs). In vitro, PEG-OXA NPs rapidly released biologically active OXA within 5 min in tumor cells while remaining extremely stable in whole blood or plasma. Importantly, the pharmacokinetic results showed that the AUC_0-∞, and t_1/2 values of PEG-OXA NPs were 1994 ± 117 h·µg/mL and 3.28 ± 0.28 h, respectively, which were much higher than that of free OXA solution (2.03 ± 0.55 h·µg/mL and 0.16 ± 0.07 h), indicating the longer drug circulation of PEG-OXA NPs in vivo. The altered pharmacokinetic behavior of PEG-OXA NPs remarkably contributed to improve antitumor efficacy, decrease systemic toxicity and increase tumor growth inhibition compared to free OXA. These findings establish that PEG-OXA NPs have the potential to offer a desirable self-delivery platform of platinum drugs for anticancer therapeutics.

Nitroxide-functional PEGylated nanostars arrest cellular oxidative stress and exhibit preferential accumulation in co-cultured breast cancer cells

The limited application of traditional antioxidants to reducing elevated levels of reactive oxygen species (ROS) is potentially due to their lack of stability and biocompatibility when tested in a biological milieu. For instance, the poor biological antioxidant performance of small molecular nitroxides arises from their limited diffusion across cell membranes and their significant side effects when applied at high doses. Herein, we describe the use of nanostructured carriers to improve the antioxidant activity of a typical nitroxide derivative, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). Polymers with star-shaped structures were synthesised and were further conjugated to TEMPO moieties via amide linkages. The TEMPO-loaded stars have small hydrodynamic sizes (<20 nm), and are better tolerated by cells than free TEMPO in a breast cancer-fibroblast co-culture, a system exhibiting elevated ROS levels. At a well-tolerated concentration, the polymer with the highest TEMPO-loading capacity successfully downregulated ROS production in co-cultured cells (a significant decrease of up to 50% vs. basal ROS levels), which was accompanied by a specific reduction in superoxide anion generation in the mitochondria. In contrast, the equivalent concentration of free TEMPO did not achieve the same outcome. Further investigation showed that the TEMPO-conjugated star polymers can be recycled inside the cells, thus providing longer term scavenging activity. Cell association studies demonstrated that the polymers can be taken up by both cell types in the co-culture, and are found to co-locate with the mitochondria. Interestingly the stars exhibited preferential mitochodria targeting in the co-cultured cancer cells compared to accompanying fibroblasts. The data suggest the potential of TEMPO-conjugated star polymers to arrest oxidative stress for various applications in cancer therapy.

The Impact of Polymer Size and Cleavability on the Intravenous Pharmacokinetics of PEG-Based Hyperbranched Polymers in Rats

A better understanding of the impact of molecular size and linkers is important for PEG-based hyperbranched polymers (HBPs) intended as tailored drug delivery vehicles. This study aimed to evaluate the effects of crosslinker chemistry (cleavable disulphide versus non-cleavable ethylene glycol methacrylate (EGDMA) linkers) and molecular weight within the expected size range for efficient renal elimination (22 vs. 48 kDa) on the intravenous pharmacokinetic and biodistribution properties of 89Zr-labelled HBPs in rats. All HBPs showed similar plasma pharmacokinetics over 72 h, despite differences in linker chemistry and size. A larger proportion of HBP with the cleavable linker was eliminated via the urine and faeces compared to a similar-sized HBP with the non-cleavable linker, while size had no impact on the proportion of the dose excreted. The higher molecular weight HBPs accumulated in organs of the mononuclear phagocyte system (liver and spleen) more avidly than the smaller HBP. These results suggest that HBPs within the 22 to 48 kDa size range show no differences in plasma pharmacokinetics, but distinct patterns of organ biodistribution and elimination are evident.

Thiol-Reactive Star Polymers Functionalized with Short Ethoxy-Containing Moieties Exhibit Enhanced Uptake in Acute Lymphoblastic Leukemia Cells

Purpose

Directing nanoparticles to cancer cells without using antibodies is of great interest. Subtle changes to the surface chemistry of nanoparticles can significantly affect their biological fate, including their propensity to associate with different cell populations. For instance, nanoparticles functionalized with thiol-reactive groups can potentially enhance association with cells that over-express cell-surface thiol groups. The potential of such an approach for enhancing drug delivery for childhood acute lymphoblastic leukemia (ALL) cells has not been investigated. Herein, we investigate the impact of thiol-reactive star polymers on the cellular association and the mechanisms of uptake of the nanoparticles.

Methods

We prepared fluorescently labeled star polymers functionalized with an mPEG brush corona and pyridyl disulfide to examine how reactivity to exofacial thiols impacts cellular association with ALL cells. We also studied how variations to the mPEG brush composition could potentially be used as a secondary method for controlling the extent of cell association. Specifically, we examined how the inclusion of shorter diethylene glycol brush moieties into the nanoparticle corona could be used to further influence cell association.

Results

Star polymers incorporating both thiol-reactive and diethylene glycol brush moieties exhibited the highest cellular association, followed by those functionalized solely with thiol reactive groups compared to control nanoparticles in T and B pediatric ALL patient-derived xenografts harvested from the spleens and bone marrow of immunodeficient mice. Transfection of cells with an early endosomal marker and imaging with correlative light and electron microscopy confirmed cellular uptake. Endocytosis inhibitors revealed dynamin-dependent clathrin-mediated endocytosis as the main uptake pathway for all the star polymers.

Conclusion

Thiol-reactive star polymers having an mPEG brush corona that includes a proportion of diethylene glycol brush moieties represent a potential strategy for improved leukemia cell delivery.

Synthesis of multifunctional miktoarm star polymers via an RGD peptide-based RAFT agent

A “grafting from” approach for facile access of multifunctional miktoarm star polymers containing peptide arms.

Linker chemistry dictates the delivery of a phototoxic organometallic rhenium(i) complex to human cervical cancer cells from core crosslinked star polymer nanoparticles

We have investigated core-crosslinked star polymer nanoparticles designed with tunable release chemistries as potential nanocarriers for a photoactive Re(i) organometallic complex. The nanoparticles consisted of a brush poly(oligo-ethylene glycol)methyl ether acrylate (POEGA) corona and a cross-linked core of non-biodegradable N,N'-methylenebis(acrylamide) (MBAA) and either pentafluorophenyl acrylate (PFPA), 3-vinyl benzaldehyde (VBA) or diacetone acrylamide (DAAM). Each star was modified with an amine functionalized photodynamic agent (i.e. a rhenium(i) organometallic complex) resulting in the formation of either a stable amide bond (POEGA-star-PFPA), or hydrolytically labile aldimine (POEGA-star-VBA) or ketimine bonds (POEGA-star-DAAM). These materials revealed linker dependent photo- and cytotoxicity when tested in vitro against non-cancerous lung fibroblast MRC-5 cells and HeLa human cervical cancer cells: the toxicity results correlated with final intracellular Re concentrations.

A tunable one-pot three-component synthesis of an125I and Gd-labelled star polymer nanoparticle for hybrid imaging with MRI and nuclear medicine

Bimodal radioiodine/Gd labelled polymeric nanoparticles prepared using a versatile one-step three-component click reaction.

Nano-Star-Shaped Polymers for Drug Delivery Applications

With the advancement of polymer engineering, complex star-shaped polymer architectures can be synthesized with ease, bringing about a host of unique properties and applications. The polymer arms can be functionalized with different chemical groups to fine-tune the response behavior or be endowed with targeting ligands or stimuli responsive moieties to control its physicochemical behavior and self-organization in solution. Rheological properties of these solutions can be modulated, which also facilitates the control of the diffusion of the drug from these star-based nanocarriers. However, these star-shaped polymers designed for drug delivery are still in a very early stage of development. Due to the sheer diversity of macromolecules that can take on the star architectures and the various combinations of functional groups that can be cross-linked together, there remain many structure-property relationships which have yet to be fully established. This review aims to provide an introductory perspective on the basic synthetic methods of star-shaped polymers, the properties which can be controlled by the unique architecture, and also recent advances in drug delivery applications related to these star candidates.

Thiol-Reactive Star Polymers Display Enhanced Association with Distinct Human Blood Components

Directing nanoparticles to specific cell types using nonantibody-based methods is of increasing interest. Thiol-reactive nanoparticles can enhance the efficiency of cargo delivery into specific cells through interactions with cell-surface proteins. However, studies to date using this technique have been largely limited to immortalized cell lines or rodents, and the utility of this technology on primary human cells is unknown. Herein, we used RAFT polymerization to prepare pyridyl disulfide (PDS)-functionalized star polymers with a methoxy-poly(ethylene glycol) brush corona and a fluorescently labeled cross-linked core using an arm-first method. PDS star polymers were examined for their interaction with primary human blood components: six separate white blood cell subsets, as well as red blood cells and platelets. Compared with control star polymers, thiol-reactive nanoparticles displayed enhanced association with white blood cells at 37 °C, particularly the phagocytic monocyte, granulocyte, and dendritic cell subsets. Platelets associated with more PDS than control nanoparticles at both 37 °C and on ice, but they were not activated in the duration examined. Association with red blood cells was minor but still enhanced with PDS nanoparticles. Thiol-reactive nanoparticles represent a useful strategy to target primary human immune cell subsets for improved nanoparticle delivery.

Synthesis of Star Polymers by RAFT Polymerization as Versatile Nanoparticles for Biomedical Applications

The precise control of polymer chain architecture has been made possible by developments in polymer synthesis and conjugation chemistry. In particular, the synthesis of polymers in which at least three linear polymeric chains (or arms) are tethered to a central core has yielded a useful category of branched architecture, so-called star polymers. Fabrication of star polymers has traditionally been achieved using either a core-first technique or an arm-first approach. Recently, the ability to couple polymeric chain precursors onto a functionalized core via highly efficient coupling chemistry has provided a powerful new methodology for star synthesis. Star syntheses can be implemented using any of the living polymerization techniques using ionic or living radical intermediates. Consequently, there are innumerable routes to fabricate star polymers with varying chemical composition and arm numbers. In comparison with their linear counterparts, star polymers have unique characteristics such as low viscosity in solution, prolonged blood circulation, and high accumulation in tumour regions. These advantages mean that, far beyond their traditional application as rheology control agents, star polymers may also be useful in the medical and pharmaceutical sciences. In this account, we discuss recent advances made in our laboratory focused on star polymer research ranging from improvements in synthesis through to novel applications of the product materials. Specifically, we examine the core-first and arm-first preparation of stars using reversible addition–fragmentation chain transfer (RAFT) polymerization. Further, we also discuss several biomedical applications of the resulting star polymers, particularly those made by the arm-first protocol. Emphasis is given to applications in the emerging area of nanomedicine, in particular to the use of star polymers for controlled delivery of chemotherapeutic agents, protein inhibitors, signalling molecules, and siRNA. Finally, we examine possible future developments for the technology and suggest the further work required to enable clinical applications of these interesting materials.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.