Multiscale Approach to Investigate Self-Assembly of Telodendrimer Based Nanocarriers for Anticancer Drug Delivery

Delivery of poorly soluble anticancer drugs can be achieved by employing polymeric drug delivery systems, capable of forming stable self-assembled nanocarriers with drug encapsulated within their hydrophobic cores. Computational investigations can aid the design of efficient drug-delivery platforms; however, simulations of nanocarrier self-assembly process are challenging due to high computational cost associated with the large system sizes (millions of atoms) and long time scales required for equilibration. In this work, we overcome this challenge by employing a multiscale computational approach in conjunction with experiments to analyze the role of the individual building blocks in the self-assembly of a highly tunable linear poly­(ethylene glycol)-<i>b</i>-dendritic oligo­(cholic acid) block copolymer called telodendrimer. The multiscale approach involved developing a coarse grained description of the telodendrimer, performing simulations over several microseconds to capture the self-assembly process, followed by reverse mapping of the coarse grained system to atomistic representation for structural analysis. Overcoming the computational bottleneck allowed us to run multiple self-assembly simulations and determine average size, drug-telodendrimer micellar stoichiometry, optimal drug loading capacity, and atomistic details such hydrogen-bonding and solvent accessible area of the nanocarrier. Computed results are in agreement with the experimental data, highlighting the success of the multiscale approach applied here

Drug-Specific Design of Telodendrimer Architecture for Effective Doxorubicin Encapsulation

Designing a versatile nanocarrier platform that can be tailored to deliver specific drug payloads is challenging. In general, effective drug encapsulation, high drug-loading capacity, uniform shape and size distribution, and enhanced stability are among the fundamental attributes of a successful nanocarrier design. These physiochemical features of the nanocarriers are intimately tied to the specific drug payload that they are tasked to deliver. The molecular architecture of the nanocarrier’s scaffold often needs to be tuned for each drug, especially if the target drugs are structurally and chemically distinct as in the case of doxorubicin (DOX) and paclitaxel (PTX). Starting from our previously reported telodendrimeric block copolymer platform optimized for PTX, we analyze three generations of telodendrimer architectures to arrive at the design that is capable of encapsulating another important chemotherapeutic drug, DOX. Multiple long-time-scale self-assembly simulations were performed both in atomistic and coarse-grained resolutions to generate equilibrated DOX-encapsulated nanocarriers. The results show how subtle changes in the molecular architecture of the telodendrimer head groups have profound effects on the nanocarrier size, morphology, and asphericity. The simulation results are in agreement with the experimental data for DOX-encapsulated nanocarriers. This work emphasizes the increasing role of molecular simulations in the rational design of nanocarriers, thereby eliminating the trial and error method that has been prevalent in experimental synthesis. The molecular-level insights gained from the simulations will be used to design the next generation of drug-specific nanocarriers

Photo and Redox Dual Responsive Reversibly Cross-Linked Nanocarrier for Efficient Tumor-Targeted Drug Delivery

To develop a feasible and efficient nanocarrier for potential clinical application, a series of photo and redox dual responsive reversibly cross-linked micelles have been developed for the targeted anticancer drug delivery. The nanocarrier can be cross-linked efficiently via a clean, efficient, and controllable coumarin photodimerization within the nanocarrier, which simplify the formulation process and quality control prior clinical use and improve the in vivo stability for tumor targeting. At the same time, cross-linking of nanocarrier could be cleaved via the responsiveness of the built-in disulfide cross-linkage to the redox tumor microenvironment for on-demand drug release. Coumarin and disulfide bond was introduced into a linear-dendritic copolymer (named as telodendrimer) precisely via peptide chemistry. The engineered nanocarrier possesses good drug loading capacity and stability, and exhibits a safer profile as well as similar anticancer effects compared with free drug in cell culture. The in vivo and ex vivo small animal imaging revealed the preferred tumor accumulation and the prolonged tumor residency of the payload delivered by the cross-linked micelles compared to the non-cross-linked micelles and free drug surrogate because of the increased stability

A Structure–Property Relationship Study of the Well-Defined Telodendrimers to Improve Hemocompatibility of Nanocarriers for Anticancer Drug Delivery

A series of telodendrimer (a linear polyethyelene glycol-<i>block</i>-dendritic oligo-cholic acid) have been synthesized via a bottom-up approach to optimize the hemocompatibility of the nanocarrier. Numbers of hydrophilic glycerol groups were introduced onto the polar surface of cholic acid to reduce the plasma membrane lytic activity of telodendrimers. An interesting result was observed: only an optimum number of glycerol introduced could reduce the hemolytic properties of the nanocarrier; on the contrary, more glycerols or the amino-glycerol substitution onto cholic acid significantly increased the hemolytic properties of the nanocarriers. To further elucidate the structure–property relationship, the molecular dynamic approach was used to simulate the conformation of the subunits of telodendrimers with different glycerol substitution, and the binding energies and the polar surface areas of the hairpin conformations were calculated to explain the membrane activities of nanocarriers. In addition, these telodendrimer subunits were synthesized and their membrane activities were tested directly, which validated the computational prediction and correlated with the observed hemolytic activity of nanocarriers. The glycerol substitution sustained the facial amphiphilicity of cholic acid, maintaining the superior drug loading capacity (paclitaxel and doxorubicin), stability, cell uptake, and anticancer efficacy of payloads. The in vivo optical imaging study indicated that the optimized nanocarriers can specifically deliver drug molecules to the tumor sites more efficiently than free drug administration, which is essential for the enhanced cancer treatment

Block and Random Copolymers Bearing Cholic Acid and Oligo(ethylene glycol) Pendant Groups: Aggregation, Thermosensitivity, and Drug Loading

A series of block and random copolymers consisting of oligo­(ethylene glycol) and cholic acid pendant groups were synthesized via ring-opening metathesis polymerization of their norbornene derivatives. These block and random copolymers were designed to have similar molecular weights and comonomer ratios; both types of copolymers showed thermosensitivity in aqueous solutions with similar cloud points. The copolymers self-assembled into micelles in water as shown by dynamic light scattering and transmission electron microscopy. The hydrodynamic diameter of the micelles formed by the block copolymer is much larger and exhibited a broad and gradual shrinkage from 20 to 54 °C below its cloud point, while the micelles formed by the random copolymers are smaller in size but exhibited some swelling in the same temperature range. Based on <i>in vitro</i> drug release studies, 78% and 24% paclitaxel (PTX) were released in 24 h from micelles self-assembled by the block and random copolymers, respectively. PTX-loaded micelles formed by the block and random copolymers exhibited apparent antitumor efficacy toward the ovarian cancer cells with a particularly low half-maximal inhibitory concentration (IC₅₀) of 27.4 and 40.2 ng/mL, respectively. Cholic acid-based micelles show promise as a versatile and potent platform for cancer chemotherapy

Probing of the Assembly Structure and Dynamics within Nanoparticles during Interaction with Blood Proteins

Fully understanding the influence of blood proteins on the assembly structure and dynamics within nanoparticles is difficult because of the complexity of the system and the difficulty in probing the diverse elements and milieus involved. Here we show the use of site-specific labeling with spin probes and fluorophores combined with electron paramagnetic resonance (EPR) spectroscopy and fluorescence resonance energy transfer (FRET) measurements to provide insights into the molecular architecture and dynamics within nanoparticles. These tools are especially useful for determining nanoparticle stability in the context of blood proteins and lipoproteins and have allowed us to quantitatively analyze the dynamic changes in assembly structure, local stability, and cargo diffusion of a class of novel telodendrimer-based micellar nanoparticles. When combined with human plasma and individual plasma components, we find that non-cross-linked nanoparticles immediately lose their original assembly structure and release their payload upon interaction with lipoproteins. In contrast, serum albumins and immunoglobulin gamma have moderate affects on the integrity of the nanoparticles. Disulfide cross-linked nanoparticles show minimal interaction with lipoproteins and can better retain their assembly structure and payload <i>in vitro</i> and <i>in vivo</i>. We further demonstrate how the enhanced stability and release property of disulfide cross-linked nanoparticles can be reversed in reductive conditions. These findings identify factors that are crucial to the performance of nanomedicines and provide design modes to control their interplay with blood factors

Self-Healing Hydrogels of Low Molecular Weight Poly(vinyl alcohol) Assembled by Host–Guest Recognition

Poly­(vinyl alcohol) (PVA) is a cytocompatible synthetic polymer and has been commonly used to prepare hydrogels. Bile acids and β-cyclodextrin are both natural compounds and they form stable host–guest inclusion complexes. They are attached covalently onto a low molecular weight PVA separately. Self-healing hydrogels can be easily formed by mixing the aqueous solutions of these PVA based polymers. The mechanical properties of the hydrogels can be tuned by varying the molar fractions of bile acid units on PVA. The dynamic inclusion complexation of the host–guest pair of the hydrogel allows the self-healing rapidly under ambient atmosphere and their mechanical properties could recover their original values in 1 min after incision. These PVA based polymers exhibited the good cytocompatibility and high hemocompatibility as shown by their biological evaluations. The use of natural compounds for host–guest interaction make such gels especially convenient to use as biomaterials, an advantage over conventional hydrogels prepared through freeze–thaw method

Generating Encoded Compound Libraries for Fabricating Microarrays as a High-Throughput Protein Ligand Discovery Platform

<div><p></p><p>We demonstrate an effective method for generating libraries of encoded compounds for fabricating large compound microarrays on solid supports. This method is based on one-bead, one-compound synthesis and employs a novel trilayer bead-partition scheme that ensures sufficient quantity of synthesized compounds releasable from each bead for compound microarray fabrication in high-throughput protein–ligand discovery assays.</p> <p>[Supplementary materials are available for this article. Go to the publisher's online edition of <i>Synthetic Communications®</i> for the following free supplemental resource(s): Full experimental and spectral details.]</p> </div

Characterization of lncRNAs involved in cold acclimation of zebrafish ZF4 cells

<div><p>Long non-coding RNAs (lncRNAs) are increasingly regarded as a key role in regulating diverse biological processes in various tissues and species. Although the cold responsive lncRNAs have been reported in plants, no data is available on screening and functional prediction of lncRNAs in cold acclimation in fish so far. Here we compared the expression profile of lncRNAs in cold acclimated zebrafish embryonic fibroblast cells (ZF4) cultured at 18°C for 30 days with that of cells cultured at 28°C as control by high-throughput sequencing. Totally 8,363 novel lncRNAs were identified. Including known and novel lncRNAs, there are 347 lncRNAs up-regulated and 342 lncRNAs down-regulated in cold acclimated cells. Among the differentially expressed lncRNAs, 74 and 61 were detected only in control cells or cold-acclimated cells, respectively. The Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analyses of adjacent genes to the differentially expressed lncRNAs showed that the enriched genes are involved in electron transport, cell adhesion, oxidation-reduction process, and so on. We also predicted the target genes of the differentially expressed lncRNAs by looking for interactions between lncRNAs and mRNAs, and constructed an interaction network. In summary, our genome-wide systematic identification and functional prediction of cold responsive lncRNAs in zebrafish cells suggests a crucial role of lincRNAs in cold acclimation in fish.</p></div

Diagram of PEG^2k-CA4 telodendrimer.

<p>Boc-NH-PEG^2k-CA4 telodendrimer was first synthesized using Boc-NH-PEG-NH₂ (MW, 2000 Da), lysine and cholic acid as building blocks via solution phase condensation reactions. Fmoc peptide chemistry was used to couple Fmoc-Lys(Fmoc)-OH onto the unprotected amino group of PEG for three rounds to generate a third generation of dendritic polylysine.</p