Shrinkage of a rapidly growing tumor by drug-loaded polymersomes: pH-triggered release through copolymer degradation

Polymersome delivery of siRNA and antisense oligonucleotides

siRNA and antisense oligonucleotides, AON, have similar size and negative charge and are often packaged for in vitro delivery with cationic lipids or polymers-but exposed positive charge is problematic in vivo. Here we demonstrate loading and functional delivery of RNAi and AON with non-ionic, nano-transforming polymersomes. These degradable carriers are taken up passively by cultured cells after which the vesicles transform into micelles that allow endolysosomal escape and delivery of either siRNA into cytosol for mRNA knockdown or else AON into the nucleus for exon skipping within pre-mRNA. Polymersome-mediated knockdown appears as efficient as common cationic-lipid transfection and about half as effective as Lenti-virus after sustained selection. For AON, initial results also show that intramuscular injection into a mouse model of muscular dystrophy leads to the expected protein expression, which occurs along the entire length of muscle. The lack of cationic groups in antisense polymersomes together with initial tests of efficacy suggests broader utility of these non-viral carriers.

Receptor targeted polymers, dendrimers, liposomes: which nanocarrier is the most efficient for tumor-specific treatment and imaging?

To compare the influence of different characteristics of nanocarriers on the efficacy of chemotherapy and imaging, we designed, characterized, and evaluated three widely used nanocarriers: linear polymer, dendrimer and liposome in vitro and in vivo. These nanocarriers delivered the same anticancer drug (paclitaxel) and/or imaging agent (Cy5.5). A synthetic analog of LHRH peptide targeted to receptors overexpressed on the membrane of cancer cells was attached to the nanocarriers as a tumor targeting moiety. Significant differences were found between various studied non-targeted carriers in their cellular internalization, cytotoxicity, tumor and organ distribution and anticancer efficacy. LHRH peptide substantially enhanced intratumoral accumulation and anticancer efficacy of all delivery systems and minimized their adverse side effects. For the first time, the present study revealed that the targeting of nanocarriers to tumor-specific receptors minimizes the influence of the architecture, composition, size and molecular mass of nanocarriers on the efficacy of imaging and cancer treatment.

Polymersomes: a new multi-functional tool for cancer diagnosis and therapy

Nanoparticles are being developed as delivery vehicles for therapeutic pharmaceuticals and contrast imaging agents. Polymersomes (mesoscopic polymer vesicles) possess a number of attractive biomaterial properties that make them ideal for these applications. Synthetic control over block copolymer chemistry enables tunable design of polymersome material properties. The polymersome architecture, with its large hydrophilic reservoir and its thick hydrophobic lamellar membrane, provides significant storage capacity for both water soluble and insoluble substances (such as drugs and imaging probes). Further, the brush-like architecture of the polymersome outer shell can potentially increase biocompatibility and blood circulation times. A further recent advance is the development of multi-functional polymersomes that carry pharmaceuticals and imaging agents simultaneously. The ability to conjugate biologically active ligands to the brush surface provides a further means for targeted therapy and imaging. Hence, polymersomes hold enormous potential as nanostructured biomaterials for future in vivo drug delivery and diagnostic imaging applications.

PEG-b-PPS diblock copolymer aggregates for hydrophobic drug solubilization and release: cyclosporin A as an example

Micelles formed from amphiphilic block copolymers have been explored in recent years as carriers for hydrophobic drugs. In an aqueous environment, the hydrophobic blocks form the core of the micelle, which can host lipophilic drugs, while the hydrophilic blocks form the corona or outer shell and stabilize the interface between the hydrophobic core and the external medium. In the present work, mesophase behavior and drug encapsulation were explored in the AB block copolymeric amphiphile composed of poly(ethylene glycol) (PEG) as a hydrophile and poly(propylene sulfide) PPS as a hydrophobe, using the immunosuppressive drug cyclosporin A (CsA) as an example of a highly hydrophobic drug. Block copolymers with a degree of polymerization of 44 on the PEG and of 10, 20 and 40 on the PPS respectively (abbreviated as PEG44-b-PPS10, PEG44-b-PPS20, PEG44-b-PPS40) were synthesized and characterized. Drug-loaded polymeric micelles were obtained by the cosolvent displacement method as well as the remarkably simple method of dispersing the warm polymer melt, with drug dissolved therein, in warm water. Effective drug solubility up to 2 mg/mL in aqueous media was facilitated by the PEG- b-PPS micelles, with loading levels up to 19% w/w being achieved. Release was burst-free and sustained over periods of 9-12 days. These micelles demonstrate interesting solubilization characteristics, due to the low glass transition temperature, highly hydrophobic nature, and good solvent properties of the PPS block.

Recent advances in nanooncology

Nanobiotechnology is playing an important role in advances in oncology and currently nanooncology is the most important chapter of nanomedicine. Nanobiotechnologies have refined molecular diagnostics and enabled early detection of tumors and discovery of biomarkers of cancer. Various nanoparticles are the basis of diagnostic assays for cancer as well as contrast materials for MRI. Nanobiotechnology is facilitating the discovery and development of drugs for cancer. Several nanobiotechnologies, mostly based on nanoparticles, have been described to facilitate drug delivery in cancer, which is important for optimizing the effect of drugs and reducing toxic side effects. Nanoparticles for targeted drug delivery in cancer enable combination of diagnostics and therapeutics and act as adjuncts to hyperthermia and photodynamic therapy. Several applications of nanobiotechnology in cancer surgery include use of nanoparticles to visualize tumor during surgery as aid to proper removal, and nanorobotics for remotely controlled diagnostics combined with therapeutics. Selected new developments in nanooncology have been highlighted in this review and these point to an important role in development of personalized oncology.

Releasable PEGylation of proteins with customized linkers

Releasable PEGylation employs customized linkers that reversibly tether a therapeutic moiety with polyethylene glycol polymers. The choice of releasable PEG linkers may have numerous applications that are insufficiently addressed by stable polymer attachment. Releasable PEGylation provides regeneration of authentic and fully active drug and allows tailored design of critical pharmacological parameters such as the maximal drug concentration and total drug exposure. This provides a prodrug format that combines beneficial attributes of PEGylation with controlled release. The linker release mechanisms are shown to be kinetically controlled by the design of a hydrolytically labile center and side chains for the steric modulation of the intramolecular elimination reactions and linker self-immolation. Recent reports have described both aromatic and aliphatic based customized linkers that release the unaltered original drug under physiological conditions and at therapeutically useful release rates. These studies have examined bioconjugates of cytokines, peptide hormones, immunotoxins, enzymes, and reporter proteins.

Nanocarriers as an emerging platform for cancer therapy

Nanotechnology has the potential to revolutionize cancer diagnosis and therapy. Advances in protein engineering and materials science have contributed to novel nanoscale targeting approaches that may bring new hope to cancer patients. Several therapeutic nanocarriers have been approved for clinical use. However, to date, there are only a few clinically approved nanocarriers that incorporate molecules to selectively bind and target cancer cells. This review examines some of the approved formulations and discusses the challenges in translating basic research to the clinic. We detail the arsenal of nanocarriers and molecules available for selective tumour targeting, and emphasize the challenges in cancer treatment.

Emerging Applications of Polymersomes in Delivery: from Molecular Dynamics to Shrinkage of Tumors

Polymersomes are self-assembled shells of amphiphilic block copolymers that are currently being developed by many groups for fundamental insights into the nature of self-assembled states as well as for a variety of potential applications. While recent reviews have highlighted distinctive properties - particularly stability - that are strongly influenced by both copolymer type and polymer molecular weight, here we first review some of the more recent developments in computational molecular dynamics (MD) schemes that lend insight into assembly. We then review polymersome loading, in vivo stealthiness, degradation-based disassembly for controlled release, and even tumor-shrinkage in vivo. Comparisons of polymersomes with viral capsids are shown to encompass and inspire many aspects of current designs.

Micelles of different morphologies--advantages of worm-like filomicelles of PEO-PCL in paclitaxel delivery

PURPOSE

Worm-like and spherical micelles are both prepared here from the same amphiphilic diblock copolymer, poly(ethylene oxide)-b-poly (epsilon-caprolactone) (PEO [5 kDa]-PCL [6.5 kDa]) in order to compare loading and delivery of hydrophobic drugs.

MATERIALS AND METHODS

Worm-like micelles of this degradable copolymer are nanometers in cross-section and spontaneously assemble to stable lengths of microns, resembling filoviruses in some respects and thus suggesting the moniker 'filomicelles'. The highly flexible worm-like micelles can also be sonicated to generate kinetically stable spherical micelles composed of the same copolymer.

RESULTS

The fission process exploits the finding that the PCL cores are fluid, rather than glassy or crystalline, and core-loading of the hydrophobic anticancer drug delivery, paclitaxel (TAX) shows that the worm-like micelles load and solubilize twice as much drug as spherical micelles. In cytotoxicity tests that compare to the clinically prevalent solubilizer, Cremophor EL, both micellar carriers are far less toxic, and both types of TAX-loaded micelles also show fivefold greater anticancer activity on A549 human lung cancer cells.

CONCLUSION

PEO-PCL based worm-like filomicelles appear to be promising pharmaceutical nanocarriers with improved solubilization efficiency and comparable stability to spherical micelles, as well as better safety and efficacy in vitro compared to the prevalent Cremophor EL TAX formulation.

Acid-Labile Polyvinylamine Micro- and Nanogel Capsules

Hollow nanoparticles represent an emerging area of development for the encapsulation of active ingredients. Expanding the capabilities of these nanomaterials will require continued efforts to infill properties such as size control, biodegradability, and environmental responsiveness. Acid-labile poly(N-vinylformamide) (PNVF) nanocapsules were synthesized by free radical polymerization of N-vinylformamide on the surface of silica nanoparticles. Polymerization in the presence of a novel crosslinker that contains an acid-labile ketal facilitated stable etching of silica nanoparticle templates using sodium hydroxide and recovery of degradable PNVF nanocapsules. The formamido side group of PNVF was then hydrolyzed by extended exposure to sodium hydroxide to produce polyvinylamine (PVAm) micro- and nanocapsules. Both capsule types demonstrated an increasing dissolution rate as pH decreased. In addition, PVAm nanocapsules exhibited swelling in proportion to the relative charge density of the PVAm network (a function of the degree of formamide hydrolysis and pH), presumably due to the repulsion of positively charged amino groups within the elastic shell network. The synthetic approaches reported provide methods to endow nanocapsules with key attributes such as size control, pH sensitive degradation, swelling in response to pH, and amine functionality.

PEG-SS-PPS: reduction-sensitive disulfide block copolymer vesicles for intracellular drug delivery

Under appropriate conditions, block copolymeric macroamphiphiles will self-assemble in water to form vesicles, referred to as polymersomes. We report here polymersomes that can protect biomolecules in the extracellular environment, are taken up by endocytosis, and then suddenly burst within the early endosome, releasing their contents prior to exposure to the harsh conditions encountered after lysosomal fusion. Specifically, block copolymers of the hydrophile poly(ethylene glycol) (PEG) and the hydrophobe poly(propylene sulfide) (PPS) were synthesized with an intervening disulfide, PEG17-SS-PPS30. Polymersomes formed from this block copolymer were demonstrated to disrupt in the presence of intracellular concentrations of cysteine. In cellular experiments, uptake, disruption, and release were observed within 10 min of exposure to cells, well within the time frame of the early endosome of endolysosomal processing. This system may be useful in cytoplasmic delivery of biomolecular drugs such as peptides, proteins, oligonucleotides, and DNA.

Shape effects of filaments versus spherical particles in flow and drug delivery

Interaction of spherical particles with cells and within animals has been studied extensively, but the effects of shape have received little attention. Here we use highly stable, polymer micelle assemblies known as filomicelles to compare the transport and trafficking of flexible filaments with spheres of similar chemistry. In rodents, filomicelles persisted in the circulation up to one week after intravenous injection. This is about ten times longer than their spherical counterparts and is more persistent than any known synthetic nanoparticle. Under fluid flow conditions, spheres and short filomicelles are taken up by cells more readily than longer filaments because the latter are extended by the flow. Preliminary results further demonstrate that filomicelles can effectively deliver the anticancer drug paclitaxel and shrink human-derived tumours in mice. Although these findings show that long-circulating vehicles need not be nanospheres, they also lend insight into possible shape effects of natural filamentous viruses.

Polymersomes

Polymersomes are self-assembled polymer shells composed of block copolymer amphiphiles. These synthetic amphiphiles have amphiphilicity similar to lipids, but they have much larger molecular weights, so for this reason--along with others reviewed here--comparisons of polymersomes with viral capsids composed of large polypeptide chains are highly appropriate. We summarize the wide range of polymers used to make polymersomes along with descriptions of physical properties such as stability and permeability. We also elaborate on emerging studies of in vivo stealthiness, programmed disassembly for controlled release, targeting in vitro, and tumor-shrinkage in vivo. Comparisons of polymersomes with viral capsids are shown to encompass and inspire many aspects of current designs.

Biodegradable polymersomes loaded with both paclitaxel and doxorubicin permeate and shrink tumors, inducing apoptosis in proportion to accumulated drug

Cytotoxicity can in principle be maximized if drugs with different activities can be delivered simultaneously to the same cell. However, combination therapy with drugs having distinct properties such as solubility generally requires use of multiple carriers or solvents, limiting the likelihood of simultaneous delivery. In this brief report, we describe the in vivo use of biodegradable polymersomes for systemic delivery of an anticancer cocktail. These polymer-based shells exploit a thick hydrophobic membrane and an aqueous lumen to efficiently carry both hydrophobic and hydrophilic drugs, respectively paclitaxel and doxorubicin. Polymersomes are long-circulating in vivo but also degrade and release their drugs on a time scale of about 1 day, by which time the tumors treated here will otherwise have almost doubled in volume. A single systemic injection of the dual drug combination shows a higher maximum tolerated dose than the free drug cocktail and shrinks tumors more effectively and more sustainably than free drug: 50% smaller tumors are seen at 5 days with polymersomes. The polymersomes cause two-fold higher cell death in tumors than free drug and show quantitatively similar increases in maximum tolerated dose and drug accumulation within the tumors-suggesting promise for multi-drug delivery.