Unraveling Aqueous Self-Assembly of Telodendrimers to Shed Light on Their Efficacy in Drug Encapsulation

Human astrocytes and astrocytoma respond differently to resveratrol

A fundamental problem in oncology is that anticancer chemotherapeutics kill both cancer and healthy cells in the surrounding tissues. Resveratrol is a natural antioxidant with intriguing and opposing biological properties: it reduces viability of some cancer cells but not of non-transformed ones (in equimolar concentrations). Therefore, we examined resveratrol in human non-transformed primary astrocytes and astrocytoma. Resveratrol reduced reactive oxygen species in astrocytes, but not in astrocytoma. Such cell-type dependent response is particularly evident with analyses at the single cell level showing clear population difference in high and low glutathione levels. Due to resveratrol's poor aqueous solubility that limits its use in clinics, we incorporated it into stimulus-responsive micelles assembled from miktoarm polymers. This could be an attractive chemotherapeutic delivery strategy in nano-oncology. As a proof of principle, we show that these formulations containing resveratrol markedly decrease astrocytoma viability, particularly in combination with temozolomide, a first line chemotherapeutic for astrocytoma.

Miktoarm Star Polymers with Environment-Selective ROS/GSH Responsive Locations: From Modular Synthesis to Tuned Drug Release through Micellar Partial Corona Shedding and/or Core Disassembly

Branched architectures with asymmetric polymeric arms provide an advantageous platform for the construction of tailored nanocarriers for therapeutic interventions. Simple and adaptable synthetic methodologies to amphiphilic miktoarm star polymers have been developed in which spatial location of reactive oxygen species (ROS) and glutathione (GSH) responsive entities is articulated to be on the corona shell surface or inside the core. The design of such architectures is facilitated through versatile building blocks and selected combinations of ring-opening polymerization, Steglich esterification, and alkyne-azide click reactions. Soft nanoparticles from aqueous self-assembly of these stimuli responsive miktoarm stars have low critical micelle concentrations and high drug loading efficiencies. Partial corona shedding upon response to ROS is accompanied by an increase in drug release, without significant changes to overall micelle morphology. The location of the GSH responsive unit at the core leads to micelle disassembly and complete drug release. Curcumin loaded soft nanoparticles show higher efficiencies in preventing ROS generation in extracellular and cellular environments, and in ROS scavenging in human glioblastoma cells. The ease in synthetic elaboration and an understanding of structure-property relationships in stimuli responsive nanoparticles offer a facile venue for well-controlled drug delivery, based on the extra- and intracellular concentrations of ROS and GSH.

Architectural Change of the Shell-Forming Block from Linear to V-Shaped Accelerates Micellar Disassembly, but Slows the Complete Enzymatic Degradation of the Amphiphiles

Tuning the enzymatic degradation and disassembly rates of polymeric amphiphiles and their assemblies is crucial for designing enzyme-responsive nanocarriers for controlled drug delivery applications. The common methods to control the enzymatic degradation of amphiphilic polymers are to tune the molecular weights and ratios of the hydrophilic and hydrophobic blocks. In addition to these approaches, the architecture of the hydrophilic block can also serve as a tool to tune enzymatic degradation and disassembly. To gain a deeper understanding of the effect of the molecular architecture of the hydrophilic block, we prepared two types of well-defined PEG-dendron amphiphiles bearing linear or V-shaped PEG chains as the hydrophilic blocks. The high molecular precision of these amphiphiles, which emerges from the utilization of dendrons as the hydrophobic blocks, allowed us to study the self-assembly and enzymatic degradation and disassembly of the two types of amphiphiles with high resolution. Interestingly, the micelles of the V-shaped amphiphiles were significantly smaller and disassembled faster than those of the amphiphiles based on linear PEG. However, the complete enzymatic cleavage of the hydrophobic end groups was significantly slower for the V-shaped amphiphiles. Our results show that the V-shaped architecture can stabilize the unimer state and, hence, plays a double role in the enzymatic degradation and the induced disassembly and how it can be utilized to control the release of encapsulated or bound molecular cargo.

Telodendrimers: Promising Architectural Polymers for Drug Delivery

Architectural complexity has played a key role in enhancing the efficacy of nanocarriers for a variety of applications, including those in the biomedical field. With the continued evolution in designing macromolecules-based nanoparticles for drug delivery, the combination approach of using important features of linear polymers with dendrimers has offered an advantageous and viable platform. Such nanostructures, which are commonly referred to as telodendrimers, are hybrids of linear polymers covalently linked with different dendrimer generations and backbones. There is considerable variety in selection from widely studied linear polymers and dendrimers, which can help tune the overall composition of the resulting hybrid structures. This review highlights the advances in articulating syntheses of these macromolecules, and the contributions these are making in facilitating therapeutic administration. Limited progress has been made in the design and synthesis of these hybrid macromolecules, and it is through an understanding of their physicochemical properties and aqueous self-assembly that one can expect to fully exploit their potential in drug delivery.

Telodendrimer-Based Macromolecular Drug Design using 1,3-Dipolar Cycloaddition for Applications in Biology

An architectural polymer containing hydrophobic isoxazole-based dendron and hydrophilic polyethylene glycol linear tail is prepared by a combination of the robust ZnCl2 catalyzed alkyne-nitrile oxide 1,3-dipolar cycloaddition and esterification chemistry. This water soluble amphiphilic telodendrimer acts as a macromolecular biologically active agent and shows concentration dependent reduction of glioblastoma (U251) cell survival.