Protocells Capable of Generating a Cytoskeleton-like Structure from intracellular Membrane-active Artificial Organelles.

The intricate nature of eukaryotic cells with differently viscous intracellular compartments provides (membrane-active) enzymes to trigger time- and concentration-dependent processes in the intra-/extracellular matrix. Herein, we capitalize on membrane-active artificial organelles (AOs) to develop fluidic and stable proteinaceous membrane-based protocells. AOs in protocells induce the self-assembly of oligopeptides into an artificial cytoskeleton that underline their influence on the structure and functionality of protocells. A series of microscopical tools is used to validate the intracellular assembly and distribution of cytoskeleton, the changing protocells morphology, and AOs inclusion within cytoskeletal growth. Thus, the dynamics, diffusion and viscosity of intracellular components in the presence of cytoskeleton are evaluated by fluorescence tools and enzymatic assay. Membrane-active alkaline phosphatase in polymersomes as AOs fulfills the requirements of biomimetic eukaryotic cells to trigger intracellular environment, mobility, viscosity, diffusion and enzymatic activity itself as well as high mechanical stability and high membrane fluidity of protocells. Thus membrane-active AOs in protocells thoroughly provide a variable reaction space in a changing intracellular environment and underline their regulatory role in the fabrication of complex protocell architectures and functions. This study demonstrates an important contribution to effective biomimicry of cell-like structures, shapes and functions.

Crosslinked and Multi-Responsive Polymeric Vesicles as a Platform to Study Enzyme-Mediated Undocking Behavior: Toward Future Artificial Organelle Communication.

Various cellular functions are successfully mimicked, opening the door to the next generation of therapeutic approaches and systems biology. Herein, the first steps are taken toward the construction of artificial organelles for mimicking cell communication by docking and undocking of cargo in the membrane of swollen artificial organelles. Stimuli-responsive and crosslinked polymeric vesicles are used to allow docking processes at acidic pH at which ferrocene units in the swollen membrane state can undergo desired specific host-guest interaction using ß-cyclodextrin as model cargo. The release of the cargo mediated by two different enzymes, glucose oxidase and α-amylase, is investigated, triggered by distinct enzymatic undocking mechanisms. Different release times for a useful transport are shown that can be adapted to different communication pathways. In addition, Förster resonance energy transfer (FRET) experiments further support the hypotheses of host-guest inclusion complexation formation and their time-dependent breakdown. This work paves a way to a platform based on polymeric vesicles for synthetic biology, cell functions mimicking, and the construction of multifunctional cargo delivery system.

Probing Crowdedness of Artificial Organelles by Clustering Polymersomes for Spatially Controlled and pH-Triggered Enzymatic Reactions.

Most sophisticated biological functions and features of cells are based on self-organization, and the coordination and connection between their cell organelles determines their key functions. Therefore, spatially ordered and controllable self-assembly of polymersomes to construct clusters to simulate complex intracellular biological functions has attracted widespread attention. Here, we present a simple one-step copper-free click strategy to cross-link nanoscale pH-responsive and photo-cross-linked polymersomes (less than 100 nm) to micron-level clusters (more than 90% in 0.5-2 µm range). Various influencing factors in the clustering process and subsequent purification methods were studied to obtain optimal clustered polymeric vesicles. Even when polymeric vesicles separately loaded with different enzymes (glucose oxidase and myoglobin) are coclustered, the overall permeability of the clusters can still be regulated through tuning the pH values on demand. Compared with simple blending of those enzyme-loaded polymersomes, the rate of enzymatic cascade reaction increased significantly due to the interconnected complex microstructure established. The connection of catalytic nanocompartments into clusters confining different enzymes of a cascade reaction provides an excellent platform for the development of artificial systems mimicking natural organelles or cells.

Poly(2-ethyl-2-oxazoline)-doxorubicin conjugate-based dual endosomal pH-sensitive micelles with enhanced antitumor efficacy.

Dual endosomal pH-sensitive micelles were designed and fabricated to deliver doxorubicin (DOX) for treating breast cancer based on a poly(2-ethyl-2-oxazoline) (PEOz)-DOX (PEOz-hyd-DOX) conjugate. PEOz-hyd-DOX was successfully synthesized by connecting DOX to PEOz via an acid cleavable hydrazone linker and self-assembled into nanosized micelles, which further physically encapsulated DOX. The conjugate and DOX-loaded conjugate micelles displayed faster release of DOX at pH 5.0 than at pH 7.4. This pH-dependent release behavior might assist the quick diffusion of DOX from acidic endosomes or lysosomes and the intracellular transfer into the nucleus after internalization, which was confirmed by confocal laser scanning microscopy images. As expected, PEOz-hyd-DOX conjugate and DOX-loaded conjugate micelles maintained cytotoxicity of DOX. In addition, the dual endosomal pH-sensitive micelles were found to substantially enhance antitumor efficacy and reduce side effects compared with free DOX. Therefore, PEOz-hyd-DOX conjugate-based micelles might be potential drug delivery vehicles of DOX for safe and effective breast cancer therapy.

Cell Free Expression in Proteinosomes Prepared from Native Protein-PNIPAAm Conjugates.

Towards the goal of building synthetic cells from the bottom-up, the establishment of micrometer-sized compartments that contain and support cell free transcription and translation that couple cellular structure to function is of critical importance. Proteinosomes, formed from crosslinked cationized protein-polymer conjugates offer a promising solution to membrane-bound compartmentalization with an open, semi-permeable membrane. Critically, to date, there has been no demonstration of cell free transcription and translation within water-in-water proteinosomes. Herein, a novel approach to generate proteinosomes that can support cell free transcription and translation is presented. This approach generates proteinosomes directly from native protein-polymer (BSA-PNIPAAm) conjugates. These native proteinosomes offer an excellent alternative as a synthetic cell chassis to other membrane bound compartments. Significantly, the native proteinosomes are stable under high salt conditions that enables the ability to support cell free transcription and translation and offer enhanced protein expression compared to proteinosomes prepared from traditional methodologies. Furthermore, the integration of native proteinosomes into higher order synthetic cellular architectures with membrane free compartments such as liposomes is demonstrated. The integration of bioinspired architectural elements with the central dogma is an essential building block for realizing minimal synthetic cells and is key for exploiting artificial cells in real-world applications.

Biomimetic Protocells Featuring Macrophage-Like Capture and Digestion of Protein Pathogens.

Modern medical research develops interest in sophisticated artificial nano- and microdevices for future treatment of human diseases related to biological dysfunctions. This covers the design of protocells capable of mimicking the structure and functionality of eukaryotic cells. The authors use artificial organelles based on trypsin-loaded pH-sensitive polymeric vesicles to provide macrophage-like digestive functions under physiological conditions. Herein, an artificial cell is established where digestive artificial organelles (nanosize) are integrated into a protocell (microsize). With this method, mimicking crossing of different biological barriers, capture of model protein pathogens, and compartmentalized digestive function are possible. This allows the integration of different components (e.g., dextran as stabilizing block) and the diffusion of pathogens in simulated cytosolic environment under physiological conditions. An integrated characterization approach is carried out, with identifying electrospray ionization mass spectrometry as an excellent detection method for the degradation of a small peptide such as ß-amyloid. The degradation of model enzymes is measured by enzyme activity assays. This work is an important contribution to effective biomimicry with the design of cell-like functions having potential for therapeutic action.

Programmable synthetic cell networks regulated by tuneable reaction rates.

Coupled compartmentalised information processing and communication via molecular diffusion underpin network based population dynamics as observed in biological systems. Understanding how both compartmentalisation and communication can regulate information processes is key to rational design and control of compartmentalised reaction networks. Here, we integrate PEN DNA reactions into semi-permeable proteinosomes and characterise the effect of compartmentalisation on autocatalytic PEN DNA reactions. We observe unique behaviours in the compartmentalised systems which are not accessible under bulk conditions; for example, rates of reaction increase by an order of magnitude and reaction kinetics are more readily tuneable by enzyme concentrations in proteinosomes compared to buffer solution. We exploit these properties to regulate the reaction kinetics in two node compartmentalised reaction networks comprised of linear and autocatalytic reactions which we establish by bottom-up synthetic biology approaches.

Detection of subtle extracellular glucose changes by artificial organelles in protocells.

Feedback-controlled detection of subtle changes of extracellular biomolecules as known from cells is also needed in protocells. Artificial organelles, located in protocells, detect the small variation in pH which is triggered by different amounts of invading glucose, converted by glucose-oxidase into gluconic acid. The approach paves the way for using pH fluctuations-detecting artificial organelles in the lumen of protocells.

Concurrently suppressing multidrug resistance and metastasis of breast cancer by co-delivery of paclitaxel and honokiol with pH-sensitive polymeric micelles.

To concurrently suppress multidrug resistance (MDR) and metastasis of breast cancer cells, paclitaxel (PTX) and honokiol (HNK) were coencapsulated into pH-sensitive polymeric micelles based on poly(2-ethyl-2-oxazoline)-poly(d,l-lactide) (PEOz-PLA). The physicochemical properties of dual drug-loaded PEOz-PLA micelles were characterized in size, drug loading and in vitro release. The efficiency of MDR reversal for the micelles was testified by synergetic enhancement of cytotoxicity and uptake by MCF-7/ADR cells. The flow cytometry and fluorescence polarization measurement results reinforced the conclusion that down-regulation of P-gp expression and increase of plasma membrane fluidity appeared to be possible mechanisms of MDR reversal by dual drug-loaded PEOz-PLA micelles. Further, the efficient inhibition of tumor metastasis by dual drug-loaded PEOz-PLA micelles was demonstrated by in vitro anti-invasion and anti-migration assessment in MDA-MB-231 cells and in vivo bioluminescence imaging in nude mice. The suppression of MDR and metastasis by the micelles was assigned to synergistic effects of pH-triggered drug release and HNK/PEOz-PLA-aroused P-gp inhibition, and pH-triggered drug release and PTX/HNK-aroused MMPs inhibition, respectively. In conclusion, our findings strengthen the usefulness of co-delivery of PTX and HNK by pH-responsive polymeric micelles for suppression of tumor MDR and metastasis. STATEMENT OF SIGNIFICANCE: Multidrug resistance (MDR) and metastasis are considered to be two of the major barriers for successful chemotherapy. The combination of a chemotherapeutic drug with a modulator has emerged as a promising strategy for efficiently treating MDR cancer and preventing tumor metastasis. Herein, a dual drug (paclitaxel and honokiol)-loaded pH-sensitive polymeric micelle system based on PEOz-PLA was successfully fabricated to ensure that tumor MDR and metastasis could be concurrently suppressed, therefore achieving distinguishing endo/lysosomal pH from physiological pH by accelerating drug release and then enhancing the cytotoxicity of paclitaxel to drug-resistant tumor cells MCF-7/ADR by increasing cellular uptake of paclitaxel, preventing in vitro invasion and migration for MDA-MB-231 cells and in vivo metastasis in nude mice. Further, the mechanism of MDR reversal by dual drug-loaded PEOz-PLA micelles was elucidated to be down-regulation of P-gp expression and increase of plasma membrane fluidity of MCF-7/ADR cells. The present findings strengthen the usefulness of co-delivery of PTX and HNK by pH-responsive polymeric micelles for suppression of tumor MDR and metastasis.

Mechanisms of pH-Sensitivity and Cellular Internalization of PEOz-b-PLA Micelles with Varied Hydrophilic/Hydrophobic Ratios and Intracellular Trafficking Routes and Fate of the Copolymer.

pH-responsive polymeric micelles have shown promise for the targeted and intracellular delivery of antitumor agents. The present study aimed to elucidate the possible mechanisms of pH-sensitivity and cellular internalization of PEOz-b-PLA micelles in detail, further unravel the effect of hydrophilic/hydrophobic ratio of the micelles on their cellular internalization, and examine the intracellular trafficking routes and fate of PEOz-b-PLA after internalization of the micelles. The results of variations in the size and Zeta potential of PEOz-b-PLA micelles and cross-sectional area of PEOz-b-PLA molecules with pH values suggested that electrostatic repulsion between PEOz chains resulting from ionization of the tertiary amide groups along PEOz chain at pH lower than its pKa was responsible for pH-sensitivity of PEOz-b-PLA micelles. Furthermore, the studies on internalization of PEOz-b-PLA micelles by MCF-7 cells revealed that the uptake of PEOz-b-PLA micelles was strongly influenced by their structural features, and showed that PEOz-b-PLA micelles with hydrophilic/hydrophobic ratio of 1.7-2.0 exhibited optimal cellular uptake. No evident alteration in cellular uptake of PEOz-b-PLA micelles was detected by flow cytometry upon the existence of EIPA and chlorpromazine. However, the intracellular uptake of the micelles in the presence of MßCD and genistein was effectively inhibited. Hence, the internalization of such micelles by MCF-7 cells appeared to proceed mainly through caveolae/lipid raft-mediated endocytosis without being influenced by their hydrophilic/hydrophobic ratio. Confocal micrographs revealed that late endosomes, mitochondria and endoplasmic reticulum were all involved in the intracellular trafficking of PEOz-b-PLA copolymers following their internalization via endocytosis, and then part of them was excreted from tumor cells to extracellular medium. These findings provided valuable information for developing desired PEOz-b-PLA micelles to improve their therapeutic efficacy and reducing the potential safety risks associated with their intracellular accumulation.

Bovine serum albumin nanoparticles for delivery of tacrolimus to reduce its kidney uptake and functional nephrotoxicity.

The purpose of the present study was to develop a new nanoparticulate formulation for delivery of tacrolimus to reduce its kidney distribution and functional nephrotoxicity. Tacrolimus (TAC)-loaded bovine serum albumin (BSA) nanoparticles (TAC-BSA-NPs) were prepared by emulsification-dispersion technique. The obtained TAC-BSA-NPs, with 189.50±7.15 nm of diameter and -20.86±0.45 mV of Zeta potential determined by DLS, were spherical in shape observed by TEM. The drug loading content and encapsulation efficiency were (1.7±0.13)% and (85±3.0)%, respectively. The in vitro release of TAC-BSA-NPs exhibited biphasic drug release pattern with an initial burst release and subsequently sustained release. Pharmacokinetic analysis displayed that TAC-BSA-NPs could enhance the drug blood level and prolong the circulation time in comparison to Prograf(®). Meanwhile, compared with Prograf(®), TAC-BSA-NPs could deliver less TAC to kidney and simultaneously reduce the functional nephrotoxicity of TAC to kidney. In conclusion, BSA nanoparticles might be a more safe carrier for delivery of hydrophobic drug TAC.

pH-responsive polymeric micelles based on poly(2-ethyl-2-oxazoline)-poly(D,L-lactide) for tumor-targeting and controlled delivery of doxorubicin and P-glycoprotein inhibitor.

The combination of a chemotherapeutic drug with a P-glycoprotein (P-gp) inhibitor has emerged as a promising strategy for treating multidrug resistance (MDR) cancer. To ensure that two drugs can be co-delivered to the tumor region and quickly released in tumor cells, tumor-targeted and pH-sensitive polymeric micelles were designed and prepared by combining cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EOz) with anionic ring-opening polymerization of D,L-lactide (LA), and then encapsulating doxorubicin (DOX) and D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS1000) into the micelles self-assembled by poly(2-ethyl-2-oxazoline)-poly(D,L-lactide) (PEOz-PLA) and DSPE-PEG-folate. PEOz-PLA exhibited a low critical micelle concentration and negligible cytotoxicity. The micelles enabled the rapid release of DOX when pH decreased from 7.4 to 5.0. The targeting ability of the micelles was demonstrated by in vitro flow cytometry in KBv cells and in vivo real time near-infrared fluorescence imaging in KBv tumor-bearing nude mice. The efficiency of MDR reversion for the micelles was testified by enhancement of intracellular DOX accumulation and cytotoxicity. The efficient drug delivery by the micelles was attributed to synergistic effects of folate-mediated targeting, pH-triggered drug release and TPGS1000-aroused P-gp inhibition. Therefore, the designed multifunctional polymeric micelles may have significant promise for therapeutic application of MDR cancer.