Polyelectrolyte microcapsules templated on poly(styrene sulfonate)-doped CaCO3 particles for loading and sustained release of daunorubicin and doxorubicin

Exploiting the layer-by-layer nanoarchitectonics for the fabrication of polymer capsules: A toolbox to provide multifunctional properties to target complex pathologies

Polymer capsules fabricated via the layer-by-layer (LbL) approach have attracted a great deal of attention for biomedical applications thanks to their tunable architecture. Compared to alternative methods, in which the precise control over the final properties of the systems is usually limited, the intrinsic versatility of the LbL approach allows the functionalization of all the constituents of the polymeric capsules following relatively simple protocols. In fact, the final properties of the capsules can be adjusted from the inner cavity to the outer layer through the polymeric shell, resulting in therapeutic, diagnostic, or theranostic (i.e., combination of therapeutic and diagnostic) agents that can be adapted to the particular characteristics of the patient and face the challenges encountered in complex pathologies. The biomedical industry demands novel biomaterials capable of targeting several mechanisms and/or cellular pathways simultaneously while being tracked by minimally invasive techniques, thus highlighting the need to shift from monofunctional to multifunctional polymer capsules. In the present review, those strategies that permit the advanced functionalization of polymer capsules are accordingly introduced. Each of the constituents of the capsule (i.e., cavity, multilayer membrane and outer layer) is thoroughly analyzed and a final overview of the combination of all the strategies toward the fabrication of multifunctional capsules is presented. Special emphasis is given to the potential biomedical applications of these multifunctional capsules, including particular examples of the performed in vitro and in vivo validation studies. Finally, the challenges in the fabrication process and the future perspective for their safe translation into the clinic are summarized.

Imperative role of electron microscopy in toxicity assessment: A review

Electron microscope (EM) was developed in 1931 and since then microscopical examination of both the biological and non-biological samples has been revolutionized. Modifications in electron microscopy techniques, such as scanning EM and transmission EM, have widened their applicability in the various sectors such as understanding of drug toxicity, development of mechanism, criminal site investigation, and characterization of the nano-molecule. The present review summarizes its role in important aspects such as toxicity assessment and disease diagnosis in special reference to SARS-COV2. In the biological system, EM studies have elucidated the impact of toxicants at the ultra-structural level in various tissue in conformity to physiological alterations. Thus, EM can be concluded as an important tool in toxicity assessment and disease prognosis.

Key Points in Remote-Controlled Drug Delivery: From the Carrier Design to Clinical Trials

The increased research activity aiming at improved delivery of pharmaceutical molecules indicates the expansion of the field. An efficient therapeutic delivery approach is based on the optimal choice of drug-carrying vehicle, successful targeting, and payload release enabling the site-specific accumulation of the therapeutic molecules. However, designing the formulation endowed with the targeting properties in vitro does not guarantee its selective delivery in vivo. The various biological barriers that the carrier encounters upon intravascular administration should be adequately addressed in its overall design to reduce the off-target effects and unwanted toxicity in vivo and thereby enhance the therapeutic efficacy of the payload. Here, we discuss the main parameters of remote-controlled drug delivery systems: (i) key principles of the carrier selection; (ii) the most significant physiological barriers and limitations associated with the drug delivery; (iii) major concepts for its targeting and cargo release stimulation by external stimuli in vivo. The clinical translation for drug delivery systems is also described along with the main challenges, key parameters, and examples of successfully translated drug delivery platforms. The essential steps on the way from drug delivery system design to clinical trials are summarized, arranged, and discussed.

Smart Layer-by-Layer Polymeric Microreactors: pH-Triggered Drug Release and Attenuation of Cellular Oxidative Stress as Prospective Combination Therapy

Polymer capsules fabricated via the layer-by-layer (LbL) approach have emerged as promising biomedical systems for the release of a wide variety of therapeutic agents, owing to their tunable and controllable structure and the possibility to include several functionalities in the polymeric membrane during the fabrication process. However, the limitation of the capsules with a single functionality to overcome the challenges involved in the treatment of complex pathologies denotes the need to develop multifunctional capsules capable of targeting several mediators and/or mechanisms. Oxidative stress is caused by the accumulation of reactive oxygen species [e.g., hydrogen peroxide (H2O2), hydroxyl radicals (•OH), and superoxide anion radicals (•O2-)] in the cellular microenvironment and is a key modulator in the pathology of a broad range of inflammatory diseases. The disease microenvironment is also characterized by the presence of proinflammatory cytokines, increased levels of matrix metalloproteinases, and acidic pH, all of which could be exploited to trigger the release of therapeutic agents. In the present work, multifunctional capsules were fabricated via the LbL approach. Capsules were loaded with an antioxidant enzyme (catalase) and functionalized with a model drug (doxorubicin), which was conjugated to an amine-containing dendritic polyglycerol through a pH-responsive linker. These capsules efficiently scavenge H2O2 from solution, protecting cells from oxidative stress, and release the model drug in acidic microenvironments. Accordingly, in this work, a polymeric microplatform is presented as an unexplored combinatorial approach applicable for multiple targets of inflammatory diseases, in order to perform controlled spatiotemporal enzymatic reactions and drug release in response to biologically relevant stimuli.

Impact of chemistry on the preparation and post-modification of multilayered hollow microcapsules

In the last few years, various chemical bondings and interactions were rationally adopted to develop different multilayered microcapsules, where the empty interior accommodated various important cargoes, including bioactive molecules, nanoparticles, antibodies, enzymes, etc., and the thin membrane protected/controlled the release of the loaded cargo. Eventually, such materials are with immense potential for a wide range of prospective applications related to targeted drug delivery, sensing, bio-imaging, developing biomimetic microreactors, and so on. The emphasis on the use of various chemistries for the development of functional and useful microcapsules is rarely illustrated in the literature in the past. In this feature article, the rational uses of different chemistries for (a) preparing and (b) post-modifying various functional microcapsules are accounted. The appropriate selection of chemical bondings/interactions, including electrostatic interaction, host-guest interaction, hydrogen bonding, and covalent bonding, allowed the integration of essential constituents during the layer-by-layer deposition process for 'in situ' tailoring of the relevant and diverse properties of the hollow microcapsules. Recently, different chemically reactive hollow microcapsules were also introduced through the strategic association of 'click chemistry', ring-opening azlactone reaction, thiol-ene reaction, and 1,4-conjugate addition reaction for facile and desired post covalent modifications of the multilayer membrane. The strategic selection of chemistry remained as the key basis to synthesize smart and useful microcapsules.

Encapsulation of Low-Molecular-Weight Drugs into Polymer Multilayer Capsules Templated on Vaterite CaCO3 Crystals

Polyelectrolyte multilayer capsules (PEMCs) templated onto biocompatible and easily degradable vaterite CaCO₃ crystals via the layer-by-layer (LbL) polymer deposition process have served as multifunctional and tailor-made vehicles for advanced drug delivery. Since the last two decades, the PEMCs were utilized for effective encapsulation and controlled release of bioactive macromolecules (proteins, nucleic acids, etc.). However, their capacity to host low-molecular-weight (LMW) drugs (<1–2 kDa) has been demonstrated rather recently due to a limited retention ability of multilayers to small molecules. The safe and controlled delivery of LMW drugs plays a vital role for the treatment of cancers and other diseases, and, due to their tunable and inherent properties, PEMCs have shown to be good candidates for smart drug delivery. Herein, we summarize recent progress on the encapsulation of LMW drugs into PEMCs templated onto vaterite CaCO₃ crystals. The drug loading and release mechanisms, advantages and limitations of the PEMCs as LMW drug carriers, as well as bio-applications of drug-laden capsules are discussed based upon the recent literature findings.

Cancer Cell Targeting With Functionalized Quantum Dot-Encoded Polyelectrolyte Microcapsules

Imaging agents and drug carriers are commonly targeted toward cancer cell through functionalization with specific recognition molecules. Quantum dots (QDs) are fluorescent semiconductor nanocrystals whose extraordinary brightness and photostability make them attractive for direct fluorescent labeling of biomolecules or optical encoding of the membranes and cells. Here, we analyse the cytotoxicity of QD-encoded microcapsules, validate an approach to the activation of the microcapsule's surface for further functionalization with monoclonal antibody Trastuzumab, a humanized monoclonal antibody targeting the extracellular domain of the human epidermal growth factor receptor 2 (HER2) and already in clinical use for the treatment of HER2 positive breast cancer. In addition, we characterize the cell-specific targeting activity of the resultant bio-conjugate by immunofluorescence assay (IFA) and real-time analysis of interaction of the conjugates with live HER2 overexpressing human breast cancer cells. We demonstrate, that encapsulation of QDs into the polymer shell using the layer-by-layer deposition method yields highly fluorescent polyelectrolyte microcapsules with a homogeneous size distribution and biocompatibility upon in vitro treatment of cancer cells. Carbodiimide surface activation ensures optimal disperse and optical characteristics of the QD-encoded microcapsules before antibody conjugation. The prepared conjugates of the microcapsules with cancer-specific monoclonal antibody targeting HER2 provide sufficiently sensitive and specific antibody-mediated binding of the microcapsules with live cancer cells, which demonstrated their potential as prospective cancer cell–targeting agents.

Mesenchymal Stem Cell Magnetization: Magnetic Multilayer Microcapsule Uptake, Toxicity, Impact on Functional Properties, and Perspectives for Magnetic Delivery

Mesenchymal stem cells (MSCs) are widely used in cell therapy due to their convenience, multiline differentiation potential, reproducible protocols, and biological properties. The potential of MSCs to impregnate magnetic microcapsules and their possible influence on cell function and ability to response to magnetic field have been explored. Interestingly, the cells suspended in media show much higher ability in internalization of microcapsules, then MSCs adhere into the surface. There is no significant effect of microcapsules on cell toxicity compared with other cell line-capsule internalization reported in literature. Due to internalization of magnetic capsules by the cells, such cell engineering platform is responsive to external magnetic field, which allows to manipulate MSC migration. Magnetically sorted MSCs are capable to differentiation as confirmed by their conversion to adipogenic and osteogenic cells using standard protocols. There is a minor effect of capsule internalization on cell adhesion, though MSCs are still able to form spheroid made by dozen of thousand MSCs. This work demonstrates the potential of use of microcapsule impregnated MSCs to carry internalized micron-sized vesicles and being navigated with external magnetic signaling.

Loading and protection of hydrophilic molecules into liposome-templated polyelectrolyte nanocapsules

Compartmentalized systems produced via the layer-by-layer (LbL) self-assembly method have been produced by alternatively depositing alginate and chitosan layers onto cores of liposomes. The combination of dynamic light scattering (DLS), ζ potential, and transmission electron microscopy (TEM) techniques provides detailed information on the stability, dimensions, charge, and wall thickness of these polyelectrolyte globules. TEM microphotographs demonstrate the presence of nanocapsules with an average diameter of below 300 nm and with a polyelectrolyte wall thickness of about 20 nm. The possibility of encapsulating and releasing molecules from this type of nanocapsule was demonstrated by loading FITC-dextrans of different molecular weights in the liposome system. The release of the loaded molecules from the nanocapsule was demonstrated after liposome core dissolution. Even at low molecular weight (20 kDa), the nanocapsules appear to be appropriate for prolonged molecule compartmentalization and protection. By means of the Ritger-Peppas model, non-Fickian transport behavior was detected for the diffusion of dextran through the polyelectrolyte wall. Values of the diffusion coefficient were calculated and yield useful information regarding chitosan/alginate hollow nanocapsules as drug-delivery systems. The influence of the pH on the release properties was also considered. The results indicate that vesicle-templated hollow polyelectrolyte nanocapsules show great potential as novel controllable drug-delivery devices for biomedical and biotechnological applications.

CaCO₃ templated micro-beads and -capsules for bioapplications

Porous CaCO₃ vaterite microparticles have been introduced a decade ago as sacrificial cores and becoming nowadays as one of the most popular templates to encapsulate bioactive molecules. This is due to the following beneficial features: i) mild decomposition conditions, ii) highly developed surface area, and iii) controlled size as well as easy and chip preparation. Such properties allow one to template and design particles with well tuned material properties in terms of composition, structure, functionality -- the parameters crucially important for bioapplications. This review presents a recent progress in utilizing the CaCO₃ cores for the assembly of micrometer-sized beads and capsules with encapsulated both small drugs and large biomacromolecules. Bioapplications of all the particles for drug delivery, biotechnology, and biosensing as well as future perspectives for templating are addressed.

Influence of charge on encapsulation and release behavior of small molecules in self-assembled layer-by-layer microcapsules

The objective of this study is to investigate the influence of charge of model small molecules on their encapsulation and release behavior in layer-by-layer microcapsules (LbL-MC). Poly(styrene sulfonate) and poly(ethylene imine) were sequentially adsorbed on calcium carbonate sacrificial templates to prepare LbL-MC. Model molecules with varying charge, anionic - ascorbic acid, cationic - imatinib mesylate (IM) and neutral - 5-fluorouracil were encapsulated in LbL-MC. Free and encapsulated LbL-MC were characterized using zetasizer, FTIR spectroscope and differential scanning calorimeter. The influence of IM-loaded LbL-MC on cell viability was studied in B16F10 murine melanoma cells. Furthermore, biodistribution of IM-loaded LbL-MC with and without PEGylation was studied in BALB/c mice. Results showed spherical LbL-MC of 3.0 ± 0.4 μm diameter. Encapsulation efficiency of LbL-MC increased linearly (R(2 )= 0.89-0.99) with the increase in solute concentration. Increase in pH from 2 to 6 increased the encapsulation of charged molecules in LbL-MC. Charged molecules showed greater encapsulation efficiency in LbL-MC compared with neutral molecule. In vitro release kinetics showed Fickian and non-Fickian diffusion of small molecules, depending on the nature of molecular interactions with LbL-MC. At 50 μM concentration, free IM showed significantly (p < 0.05) more cytotoxicity compared with IM-loaded LbL-MC. Biodistribution studies showed that PEGylation of LbL-MC decreased the liver and spleen uptake of IM-encapsulated LbL-MC. In conclusion, LbL-MC can be developed as a potential carrier for small molecules depending on their physical and chemical properties.

Exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymers for preparation of robust, multifunctional mesoporous hybrid microcapsules

A facile approach to preparing mesoporous hybrid microcapsules is developed by exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymer. The preparation process contains four steps: segregation of cationic hydrophilic polymer during template formation, cross-linking of the segregated polymer, biomimetic mineralization within cross-linked polymer network, and removal of template to simultaneously generate capsule lumen and mesopores on the capsule wall. Poly(allylamine hydrochloride) (PAH) is chosen as the model polymer, its hydrophilicity renders the segregating capacity and spontaneous enrichment in the near-surface region of CaCO3 microspheres; its biopolyamine-mimic structure renders the mineralization-inducing capacity to produce titania from the water-soluble titanium(IV) precursor. Meanwhile, CaCO3 microspheres serve the dual templating functions in the formation of hollow lumen and mesoporous wall. The thickness of capsule wall can be controlled by changing the polymer segregating and cross-linking conditions, while the pore size on the capsule wall can be tuned by changing the template synthesizing conditions. The robust hybrid microcapsules exhibit desirable efficiency in enzymatic catalysis, wastewater treatment and drug delivery. This approach may open facile, generic, and efficient pathway to designing and preparing a variety of hybrid microcapsules with high and tunable permeability, good stability and multiple functionalities for a broad range of applications.

Polyelectrolyte capsules packaging BSA gels for pH-controlled drug loading and release and their antitumor activity

Polyelectrolyte multilayer capsules, promising candidates for multifunctional drug delivery systems, have recently received increased interest. However, the low encapsulation efficiency of drugs and the lack of reports about animal experiments have greatly slowed down their development for drug delivery. Here, a polyelectrolyte multilayer capsule filled with bovine serum albumin gel (BSA-gel-capsule) was constructed by a layer-by-layer assembly technique and thermally induced gelation of BSA. Owing to the charge variability of BSA with change in pH, BSA-gel-capsules not only showed a pronounced accumulation effect of drugs into capsules, but also displayed excellent pH-controlled loading and release properties. Moreover, a remarkable targeting action to the lung was discovered after intravenous injection of fluorescein isothiocyanate (FITC)-labeled BSA-gel-capsules into mice. After treatment with doxorubicin-loaded BSA-gel-capsules, effective cytotoxicity against B16-F10 cells and inhibition of the pulmonary melanoma growth were revealed. This paper introduces a new type of smart microstructure with notable pH-responsive ability. This material renders feasible the intravenous administration of polyelectrolyte microcapsules, which will be a big step towards their application as drug delivery vehicles.

Tailoring layer-by-layer capsules for biomedical applications

Polymeric capsules have attracted great interest as versatile carrier systems in the area of medicine and pharmaceutics. These capsules are made by stepwise layer-by-layer adsorption of polymers onto a template core, which can be removed to produce hollow capsules. The cavity of these capsules can host various cargo molecules while the capsules’ wall can be functionalized towards desired properties by embedding specific moieties into the multilayers. Tuning of the capsules’ properties influences their interaction with cells and tissues and paves the way towards the development of stimuli-responsive capsules releasing their payload at a target site. In this review, we describe the generation of tailored layer-by-layer capsules and focus hereby on numerous potential applications of this multifunctional delivery platform in biomedical settings. We review the current status in the field and discuss the opportunities, as well as the hurdles, to be overcome to successfully transfer this technology to therapeutic and diagnostic applications.

Introduction to nanocoatings produced by layer-by-layer (LbL) self-assembly

Studies on the adsorption of oppositely charged colloidal particles ultimately resulted in multilayered polyelectrolyte self-assembly. The inception of layer-by-layer constructed particles facilitated the production of multifunctional, stimuli-responsive carrier systems. An array of synthetic and natural polyelectrolytes, metal oxides and clay nanoparticles is available for the construction of multilayered nanocoats on a multitude of substrates or removable cores. Numerous substrates can be encapsulated utilizing this technique including dyes, enzymes, drugs and cells. Furthermore, the outer surface of the particles presents and ideal platform that can be functionalized with targeting molecules or catalysts. Some processing parameters determining the properties of these successive self-assembly constructs are the surface charge density, coating material concentration, rinsing and drying steps, temperature and ionic strength of the medium. Additionally, the simplicity of the layer-by-layer assembly technique and the availability of established characterization methods, render these constructs extremely versatile in applications of sensing, encapsulation and target- and trigger-responsive drug delivery.

Drug-loaded polyelectrolyte microcapsules for sustained targeting of cancer cells

In this review we will overview novel nanotechnological nanocarrier systems for cancer therapy focusing on recent development in polyelectrolyte capsules for targeted delivery of antineoplastic drugs against cancer cells. Biodegradable polyelectrolyte microcapsules (PMCs) are supramolecular assemblies of particular interest for therapeutic purposes, as they can be enzymatically degraded into viable cells, under physiological conditions. Incorporation of small bioactive molecules into nano-to-microscale delivery systems may increase drug's bioavailability and therapeutic efficacy at single cell level giving desirable targeted therapy. Layer-by-layer (LbL) self-assembled PMCs are efficient microcarriers that maximize drug's exposure enhancing antitumor activity of neoplastic drug in cancer cells. They can be envisaged as novel multifunctional carriers for resistant or relapsed patients or for reducing dose escalation in clinical settings.

Target binding influences permeability in aptamer-polyelectrolyte microcapsules

Aptamer-polyelectrolyte microcapsules are prepared for potential use as triggered delivery vehicles and microreactors. The hollow microcapsules are prepared from the sulforhodamine B aptamer and the polyelectrolytes poly(allylamine hydrochloride) and poly(sodium 4-styrene-sulfonate), using layer-by-layer (LbL) film deposition templated on a sacrificial CaCO(3) spherical core. Scanning electron microscopy and confocal microscopy confirm the formation of spherical CaCO(3) cores and LbL-aptamer microcapsules. Colocalization studies with fluorescently-tagged aptamer and sulforhodamine B verify the ability of the aptamer to recognize its cognate target in the presence of the K(+) ions that are required for its characteristic G-quadruplex formation. Fluorescence recovery after photobleaching studies confirms a significant difference in the permeability of the aptamer-polyelectrolyte microcapsules for the sulforhodamine B dye target compared to control microcapsules prepared with a random oligonucleotide. These results suggest that aptamer-based 'smart' responsive films and microcapsules could be applied to problems of catalysis and controlled release.

Preparation and redox-controlled reversible response of ferrocene-modified poly(allylamine hydrochloride) microcapsules

Single-component microcapsules were fabricated by the in situ reaction of ferrocenecarboxaldehyde (Fc-CHO) with poly(allylamine hydrochloride) (PAH) doped inside CaCO(3) microparticles, followed by core removal. The PAH-Fc microcapsules had very thick shells with remnant PAH-Fc inside, leading to a robust capsule structure that is less collapsed in the dry state. This single-component microcapsule is stabilized by the hydrophobic aggregation of Fc moieties and the protection of hydrophilic PAH backbones. Because of the excellent redox properties of Fc, the PAH-Fc microcapsules showed redox sensitivity to oxidation and reduction, as confirmed by UV-vis absorption spectroscopy and confocal laser scanning microscopy, resulting in reversible swelling and shrinking (11.7 vs 5.5 μm) in their size. Consequently, the permeability was also reversibly tuned, leading to the controlled loading and release of desired substances such as dextran.

Mucosal irritation potential of polyelectrolyte multilayer capsules

Polyelectrolyte multilayer capsules have recently gained interest as carriers for drug delivery. When envisioning mucosal administration, one is focused with potential concerns such as tissue irritation and tissue damage, induced by the carrier itself. In this paper we demonstrate the use of a slug-based (Arion lusitanicus) assay to evaluate the mucosal irritation potential of different types of polyelectrolytes, their complexes and multilayer capsules. This assay allows to assess in a simple yet efficient way mucosal tissue irritation without using large numbers of vertebrates such as mice, rabbits or non-human primates. We found that although single polyelectrolyte components do induce tissue irritation, this response is dramatically reduced upon complexation with an oppositely charged polyelectrolyte, rendering fairly inert polyelectrolyte complexes. These findings put polyelectrolyte multilayer capsules further en route towards drug delivery applications.

Emerging trend in nano-engineered polyelectrolyte-based surrogate carriers for delivery of bioactives

IMPORTANCE OF THE FIELD

In recent decades a new colloidal drug delivery system based on layer-by-layer (LbL) technology has emerged, which offers promising means of delivering bioactive agents, specifically biological macromolecules including peptides and DNA. Nano-engineered capsules specifically fabricated from biocompatible and biodegradable polyelectrolytes (PEs) can provide a better option for encapsulation of cells thereby protecting cells from immunological molecules in the body, and their selective permeability can ensure the survival of encapsulated cells.

AREAS COVERED IN THIS REVIEW

This review encompasses a strategic approach to fabricate nano-engineered microcapsules through meticulous selection of polyelectrolytes and core materials based on LbL technology. The content of the article provides evidence for its wide array of applications in medical therapeutics, as indicated by the quantity of research and patents in this area. Recent developments and approaches for tuning drug release, biocompatibility and cellular interaction are discussed thoroughly.

WHAT THE READER WILL GAIN

This review aims to provide an overview on the development of LbL capsules with specific orientation towards drug and macromolecular delivery and its integration with other drug delivery systems, such as liposomes.

TAKE HOME MESSAGE

Selection of PEs for the fabrication of LbL microcapsules has a profound effect on stability, drug release, biocompatibility and encapsulation efficacy. The release can be easily modulated by varying different physicochemical as well as physiological conditions. Scale-up approaches for the fabrication of LbL microcapsules by means of automation must be considered to improve the possibility of application of LbL microcapsules on a large scale.

Mesoporous silica nanotubes coated with multilayered polyelectrolytes for pH-controlled drug release

Two kinds of inorganic/organic hybrid composites based on mesoporous silica nanotubes (MSNTs) and pH-responsive polyelectrolytes have been developed as pH-controlled drug delivery systems via the layer by layer self-assembly technique. One system was based on alternatively loading poly(allylamine hydrochloride) and sodium poly(styrene sulfonate) onto as-prepared MSNTs to load and release the positively charged drug doxorubicin. The other system was synthesized by alternately coating sodium alginate and chitosan onto amine-functionalized MSNTs, which were used as vehicles for the loading and release of the negatively charged model drug sodium fluorescein. Controlled release of the drug molecules from these delivery systems was achieved by changing the pH value of the release medium. The results of in vitro cell cytotoxicity assays indicated that the cell killing efficacy of the loaded doxorubicin against human fibrosarcoma (HT-1080) and human breast adenocarcinoma (MCF-7) cells was pH dependent. Thus, these hybrid composites could be potentially applicable as pH-controlled drug delivery systems.

Imatinib-loaded polyelectrolyte microcapsules for sustained targeting of BCR-ABL+ leukemia stem cells

Aim: The lack of sensitivity of chronic myeloid leukemia (CML) stem cells to imatinib mesylate (IM) commonly leads to drug dose escalation or early disease relapses when therapy is stopped. Here, we report that packaging of IM into a biodegradable carrier based on polyelectrolyte microcapsules increases drug retention and antitumor activity in CML stem cells, also improving the ex vivo purging of malignant progenitors from patient autografts. Materials & methods: Microparticles/capsules were obtained by layer-by-layer (LbL) self-assembly of oppositely charged polyelectrolyte multilayers on removable calcium carbonate (CaCO3) templates and loaded with or without IM. A leukemic cell line (KU812) and CD34+ cells freshly isolated from healthy donors or CML patients were tested. Results & discussion: Polyelectrolyte microcapsules (PMCs) with an average diameter of 3 µm, fluorescently labelled multilayers sensitive to the action of intracellular proteases and 95–99% encapsulation efficiency of IM, were prepared. Cell uptake efficiency of such biodegradable carriers was quantified in KU812, leukemic and normal CD34+ stem cells (range: 70–85%), and empty PMCs did not impact cell viability. IM-loaded PMCs selectively targeted CML cells, by promoting apoptosis at doses that exert only cytostatic effects by IM alone. More importantly, residual CML cells from patient leukapheresis products were reduced or eliminated more efficiently by using IM-loaded PMCs compared with freely soluble IM, with a purging efficiency of several logs. No adverse effects on normal CD34+ stem-cell survival and their clonogenic potential was noticed in long-term cultures of hematopoietic progenitors in vitro. Conclusion: This pilot study provides the proof-of-principle for the clinical application of biodegradable IM-loaded PMC as feasible, safe and effective ex vivo purging agents to target CML stem cells, in order to improve transplant outcome of resistant/relapsed patients or reduce IM dose escalation.

Frozen cyclohexane-in-water emulsion as a sacrificial template for the synthesis of multilayered polyelectrolyte microcapsules

This paper reports the application of frozen cyclohexane-in-water emulsions as sacrificial templates for the fabrication of hollow microcapsules through layer-by-layer assembly of polyelectrolytes, poly(styrenesulfonate sodium salt), and poly(allylamine hydrochloride). Extraction of the cyclohexane phase from frozen emulsions stabilized with 11 polyelectrolyte layers by compatibilization with 30% v/v ethanol leads to the formation of water-filled microcapsules while preserving the spherical geometry. The majority of microcapsules (>90%) are prepared with intact polyelectrolyte membranes as measured by their deformation induced by osmotic pressure. This work provides a new route for the synthesis of hollow multilayered microcapsules under mild operating conditions.