Size control of core-shell-type polymeric micelle with a nanometer precision

Theranostics Using Indocyanine Green Lactosomes

Lactosomes™ are biocompatible nanoparticles that can be used for cancer tissue imaging and drug delivery. Lactosomes are polymeric micelles formed by the self-assembly of biodegradable amphiphilic block copolymers composed of hydrophilic polysarcosine and hydrophobic poly-L-lactic acid chains. The particle size can be controlled in the range of 20 to 100 nm. Lactosomes can also be loaded with hydrophobic imaging probes and photosensitizers, such as indocyanine green. Indocyanine green-loaded lactosomes are stable for long-term circulation in the blood, allowing for accumulation in cancer tissues. Such lactosomes function as a photosensitizer, which simultaneously enables fluorescence diagnosis and photodynamic therapy. This review provides an overview of lactosomes with respect to molecular design, accumulation in cancer tissue, and theranostics applications. The use of lactosomes can facilitate the treatment of cancers in unresectable tissues, such as glioblastoma and head and neck cancers, which can lead to improved quality of life for patients with recurrent and unresectable cancers. We conclude by describing some outstanding questions and future directions for cancer theranostics with respect to clinical applications.

Prospects of Using Biocatalysis for the Synthesis and Modification of Polymers

Trends in the dynamically developing application of biocatalysis for the synthesis and modification of polymers over the past 5 years are considered, with an emphasis on the production of biodegradable, biocompatible and functional polymeric materials oriented to medical applications. The possibilities of using enzymes not only as catalysts for polymerization but also for the preparation of monomers for polymerization or oligomers for block copolymerization are considered. Special attention is paid to the prospects and existing limitations of biocatalytic production of new synthetic biopolymers based on natural compounds and monomers from biomass, which can lead to a huge variety of functional biomaterials. The existing experience and perspectives for the integration of bio- and chemocatalysis in this area are discussed.

A Novel 89Zr-labeled DDS Device Utilizing Human IgG Variant (scFv): "Lactosome" Nanoparticle-Based Theranostics for PET Imaging and Targeted Therapy

“Theranostics,” a new concept of medical advances featuring a fusion of therapeutic and diagnostic systems, provides promising prospects in personalized medicine, especially cancer. The theranostics system comprises a novel ⁸⁹Zr-labeled drug delivery system (DDS), derived from the novel biodegradable polymeric micelle, “Lactosome” nanoparticles conjugated with specific shortened IgG variant, and aims to successfully deliver therapeutically effective molecules, such as the apoptosis-inducing small interfering RNA (siRNA) intracellularly while offering simultaneous tumor visualization via PET imaging. A 27 kDa-human single chain variable fragment (scFv) of IgG to establish clinically applicable PET imaging and theranostics in cancer medicine was fabricated to target mesothelin (MSLN), a 40 kDa-differentiation-related cell surface glycoprotein antigen, which is frequently and highly expressed by malignant tumors. This system coupled with the cell penetrating peptide (CPP)-modified and photosensitizer (e.g., 5, 10, 15, 20-tetrakis (4-aminophenyl) porphyrin (TPP))-loaded Lactosome particles for photochemical internalized (PCI) driven intracellular siRNA delivery and the combination of 5-aminolevulinic acid (ALA) photodynamic therapy (PDT) offers a promising nano-theranostic-based cancer therapy via its targeted apoptosis-inducing feature. This review focuses on the combined advances in nanotechnology and material sciences utilizing the “⁸⁹Zr-labeled CPP and TPP-loaded Lactosome particles” and future directions based on important milestones and recent developments in this platform.

Collapse Behavior of Polyion Complex (PIC) Micelles upon Salt Addition and Reforming Behavior by Dialysis and Its Temperature Responsivity

Temperature-responsive polyion complex (PIC) micelles were prepared by using two diblock copolymers composed of a sulfobetaine chain (poly(sulfopropyldimethylammonium propylacrylamide), PSPP) and ionic chains (poly(sodium styrenesulfonate), PSSNa, or poly(3-(methacrylamido)propyltrimethylammonium chloride), PMAPTAC). Because the core is PIC and the shell is sulfobetaine with UCST-type temperature response, the corona expands and contracts in response to temperature. To control the size and uniformity of the PIC micelles, the collapse of PIC micelles by salt addition and the reforming behavior by dialysis were investigated by transmittance, DLS, TEM, AFM, and ¹H NMR measurements. Investigation of the ionic species dependence of the added salt in the collapse behavior of PIC micelles revealed that it was dependent on the anionic species, although no dependence on the cationic species was observed. Its effectiveness was in the order of I^- > Br^- > Cl^- > F^-, which is in agreement with the order of ionic species with strong structural destruction in the Hofmeister series. Heterogeneous and large PIC micelles were formed by the simple mixing method. They collapsed by salt addition and were reformed by the dialysis method to form uniform and smaller PIC micelles. This is considered to be because a uniform and smaller micelle is formed to reform in equilibrium state by dialysis. The temperature response of PIC micelles formed by the simple mixing method and PIC micelles reformed by dialysis showed nearly the same temperature-transmittance curves. These results indicate that the temperature response of PIC micelles is affected by the concentration rather than the hydrodynamic radius. Furthermore, the stability of PIC micelles was found to be affected by the concentration temperature (the temperature at the time of concentration).

Design and preparation of nanostructures based on Krafft point of nonionic amphiphiles for delivery of poorly water-soluble compounds

Micellar solubilization can effectively dissolve low water-soluble compounds in aqueous environment, however, the micellar systems are not able to withstand dilution and maintain solubilization of poorly water-soluble drugs below critical micelle concentration. To overcome the drawbacks of conventional micellar solubilization, nonionic polyoxyethylated surfactants with Krafft points at or higher than body temperature were chosen to create novel micelle-based nanostructures as a delivery vehicle for poorly water-soluble compounds. A technique "thermo-spray process" was developed for the preparation of the nanostructures-containing formulation, in which the drug-containing micelle solution was first prepared and maintained at the elevated temperature above the Krafft point of the surfactant, then spray dried to solidify the obtained micelle-like nanostructure at room temperature. Lactose was used as an excipient to embed the nanostructures in the thermo-spray products. Water insoluble spherical nanoparticles with size range from 80 to 250 nm were obtained after reconstitution of the product at the temperature lower than Krafft point. When paclitaxel was used as model drug, the micelle-like nanostructures exhibited similar drug entrapment efficiency, solubility enhancement and drug release facilitation as conventional micelles, but provided lower critical micellar concentration at body temperature, and good encapsulation stability upon storage and dilution. These findings indicated that the developed thermo-spray product can serve as a promising delivery platform for drugs with low aqueous solubility.

Effect of Formulation and Processing Parameters on the Size of mPEG- b-p(HPMA-Bz) Polymeric Micelles

Micelles composed of block copolymers of poly(ethylene glycol)- b-poly( N-2-benzoyloxypropyl methacrylamide) (mPEG- b-p(HPMA-Bz)) have shown great promise as drug-delivery carriers due to their excellent stability and high loading capacity. In the present study, parameters influencing micelle size were investigated to tailor sizes in the range of 25-100 nm. Micelles were prepared by a nanoprecipitation method, and their size was modulated by the block copolymer properties such as molecular weight, their hydrophilic-to-hydrophobic ratio, homopolymer content, as well as formulation and processing parameters. It was shown that the micelles have a core-shell structure using a combination of dynamic light scattering and transmission electron microscopy analysis. By varying the degree of polymerization of the hydrophobic block ( N_B) between 68 and 10, at a fixed hydrophilic block mPEG_5k ( N_A = 114), it was shown that the hydrophobic core of the micelle was collapsed following the power law of ( N_B × N_agg)^1/3. Further, the calculated brush height was similar for all the micelles examined (10 nm), indicating that crew-cut micelles were made. Both addition of homopolymer and preparation of micelles at lower concentrations or lower rates of addition of the organic solvent to the aqueous phase increased the size of micelles due to partitioning of the hydrophobic homopolymer chains to the core of the micelles and lower nucleation rates, respectively. Furthermore, it was shown that by using different solvents, the size of the micelles substantially changed. The use of acetone, acetonitrile, ethanol, tetrahydrofuran, and dioxane resulted in micelles in the size range of 45-60 nm after removal of the organic solvents. The use of dimethylformamide and dimethylsulfoxide led to markedly larger sizes of 75 and 180 nm, respectively. In conclusion, the results show that by modulating polymer properties and processing conditions, micelles with tailorable sizes can be obtained.

Cisplatin-Encapsulated Polymeric Nanoparticles with Molecular Geometry-Regulated Colloidal Properties and Controlled Drug Release

Encapsulation of chemotherapeutic agents inside a nanoscale delivery platform can provide an attractive therapeutic strategy with many pharmaceutical benefits, such as increased plasma solubility, prolonged in vivo circulation, and reduced acute toxicity. Given that the biological activities of polymeric nanoparticles are highly dependent on their colloidal structures, the molecular geometry-regulated programming of self-assembled nanoscale architecture is of great interest for chemical design of an ideal delivery platform. In this report, we demonstrate that the molecular geometry of block-copolymer excipients can govern the level of drug-loading capacity and core hydrophobicity of polymeric nanoparticles, which can eventually control the pH-sensitive drug-release property. Atom-transfer radical polymerization was employed as a controlled synthetic method for the copolymer excipients, which contain the metal-chelating poly(acrylic acid) block linked to either a small mPEG-grafted poly(methacrylate) to generate a bulky brush-like chains or a simple linear mPEG segment. During the coordination of cis-diammineplatinum(II) as an active pharmacophore of cisplatin, aqueous-phase size-exclusion chromatography analyses exhibited highly different self-association kinetic regimes prompted by versatile molecular geometry of copolymer excipients, which further allows us to explore the molecular geometry-colloidal property relationship.

Polymeric Micelle of A₃B-Type Lactosome as a Vehicle for Targeting Meningeal Dissemination

Polymeric micelle of the A₃B-type lactosome comprising (poly(sarcosine))₃-b-poly(l-lactic acid) was labeled with ¹¹¹In. The ¹¹¹In-labeled A₃B-type lactosome was administered to the model mice bearing meningeal dissemination and bone metastasis at mandible. With single-photon emission computed tomography (SPECT) imaging, the meningeal dissemination was identified successfully by ¹¹¹In-labeled A₃B-type lactosome, which was superior to ²⁰¹TlCl in regard of the imaging contrast. The ¹¹¹In-labeled A₃B-type lactosome was also potential in imaging selectively of bone metastasis at mandible, whilst a nonspecific imaging of the whole bone was obtained by the SPECT imaging using ^99mTc-HMDP. The polymeric micelle of the A₃B-type lactosome was therefore found to be effective as a vehicle of ¹¹¹In to be targeted to meningeal dissemination and bone metastasis.

Immune responses against Lewis Y tumor-associated carbohydrate antigen displayed densely on self-assembling nanocarriers

Immune responses against Lewis Y (LY) displayed at varying densities on the nanocarriers were studied.

Aqueous solution behaviour of novel water-soluble amphiphilic copolymers with elevated hydrophobic unit content

The synthesis and aqueous solution behaviour of water-soluble copolymers poly(OEGMA-stat-styrene)-b-PDMAPMA with a relatively high content of styrene units were explored.

Factors influencing in vivo disposition of polymeric micelles on multiple administrations

Lactosome is a polymeric micelle composed of amphiphilic polydepsipeptide, poly(sarcosine)64-block-poly(l-lactic acid)30 (AB-type), which accumulates in solid tumors through the enhanced permeability and retention (EPR) effect. However, lactosome on multiple administrations changed its pharmacokinetics from accumulation in tumors to liver due to the production of antilactosome IgM, which was triggered by the first administration. This phenomenon is called the accelerated blood clearance (ABC). In order to reduce the production of antilactosome IgM, a novel nanoparticle composed of (poly(sarcosine)23)3-block-poly(l-lactic acid)30 (A3B-type) was prepared. The A3B-type lactosome at the second administration showed an in vivo disposition similar to that at the first administration due to suppression of antibody production. This study involving the AB- and A3B-type lactosomes, with variation of conditions, revealed that the high local density of poly(sarcosine) chains of the A3B-type lactosome should relate to the prevention of a polymeric micelle from interacting B-cell receptors.

pH-sensitive short worm-like micelles targeting tumors based on the extracellular pH

We developed novel photosensitizing drug-carrying worm-like micelles using a pH-sensitive AB₂ miktoarm block copolymer consisting of one methoxy-poly(ethylene glycol) (mPEG) block (A) and two 3-diethylaminopropylated poly(l-lysine) [poly(Lys-DEAP)] blocks (B₂).