Synthesis of Biocompatible Polymers. 1. Homopolymerization of 2-Methacryloyloxyethyl Phosphorylcholine via ATRP in Protic Solvents: An Optimization Study

Enhancement of cellular uptake and antitumor efficiencies of micelles with phosphorylcholine

Internalization of drug delivery micelles into cancer cells is a crucial step for antitumor therapeutics. Novel amphiphilic star-shaped copolymers with zwitterionic phosphorylcholine (PC) block, 6-arm star poly(ε-caprolactone)-b-poly(2-methacryloyloxyethyl phosphorylcholine) (6sPCL-b-PMPC), have been developed for encapsulation of poorly water-soluble drugs and enhancement of their cellular uptake. The star-shaped copolymers were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The copolymers self-assembled to form spherical micelles with low critical micelle concentration (CMC). The sizes of the micelles range from 80 to 170 nm and increase 30 ≈ 80% after paclitaxel (PTX) loading. Labeled with fluorescein isothiocyanate (FITC), the micelles were confirmed by fluorescence microscopy to have been internalized efficiently by tumor cells. Direct visualization of the micelles within tumor cells by transmission electron microscopy (TEM) confirmed that the 6sPCL-b-PMPC micelles were more efficiently uptaken by tumor cells compared to PCL-b-PEG micelles. When incorporated with PTX, the 6sPCL-b-PMPC micelles show much higher cytotoxicity against Hela cells than PCL-b-PEG micelles, in response to the higher efficiency of cellular uptake.

Synthesis of rhodamine 6G-based compounds for the ATRP synthesis of fluorescently labeled biocompatible polymers

Facile derivatization of rhodamine 6G in the 2' position by direct reaction with secondary amines is reported. If the secondary amine contains a hydroxy group, the hydroxyl-functional intermediate can be readily esterified to give either fluorescent initiators for atom transfer radical polymerization (ATRP) or a fluorescent methacrylic comonomer. In contrast to rhodamine dyes functionalized using primary amines, which are only fluorescent at low pH, these compounds are highly fluorescent at physiological pH. These new compounds were subsequently used to prepare a range of fluorescently labeled biocompatible polymers based on the biomimetic monomer, 2-(methacryloyloxy)ethyl phosphorylcholine (MPC), for biomedical studies.

Internalization and biodistribution of polymersomes into oral squamous cell carcinoma cells in vitro and in vivo

The prognosis for oral squamous cell carcinoma (OSCC) is not improving despite advances in surgical treatment. As with many cancers, there is a need to deliver therapeutic agents with greater efficiency into OSCC to improve treatment and patient outcome. The development of polymersomes offers a novel way to deliver therapy directly into tumor cells. Here we examined the internalization and biodistribution of two different fluorescently labeled polymersome formulations; polyethylene oxide (PEO)-poly 2-(diisopropylamino)ethyl methacrylate (PDPA) and poly 2-(methacryloyloxy)ethyl phosphorylcholine (PMPC)-PDPA, into SCC4 OSCC cells in vitro and in vivo. In vitro SCC4 monolayers internalized PMPC-PDPA and PEO-PDPA at similar rates. However, in vivo PMPC-PDPA polymersomes penetrated deeper and were more widely dispersed in SCC4 tumors than PEO-PDPA polymersomes. In the liver and spleen PMPC-PDPA mainly accumulated in tissue macrophages. However, in tumors PMPC-PDPA was found extensively in the nucleus and cytoplasm of tumor cells as well as in tumor-associated macrophages. Use of PMPC-PDPA polymersomes may enhance polymersome-mediated antitumor therapy.

Essential Factors to Make Excellent Biocompatibility of Phospholipid Polymer Materials

Recently, much attention has been attracted to bio/blood compatible materials to suppress undesirable biological reactions that determine the fate of living organisms and materials. A phospholipid polymer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) unit, which is designed by inspiration of cell membrane surface structure, is the most promising polymer biomaterial with excellent bio/blood compatibility. Progress in living radical polymerization method initiated from the surface enables preparation of a dense polymer chains on the surface, which is called as a polymer brush. The polymer brush structure has narrow molecular weight distribution and controlled chain length. So, it is ideal surface to clarify the interactions between the biomolecules and biomaterial surface that has never done. In these regards, the poly(MPC) brush surfaces are expected to be a novel class of biomaterials, and have been extensively studied its unusual properties. In this review, surface-initiated living radical polymerization of MPC and the characteristics of the poly(MPC) brush surfaces are summarized from a viewpoint of biomaterials science.

Biomimetic surface modification of honeycomb films via a "grafting from" approach

Hydrophobic isoporous membranes were fabricated using the "breath figure" method from polystyrene stars synthesized via ATRP. The living polymer chain ends at the surface of the films were then used, without further modification, in a "grafting-from" approach to grow surface-linked polyglycidyl methacrylate chains under conditions that maintained the regular honeycomb structure. This versatile functional surface was then used as a platform to build a small library of surfaces using a variety of simple chemistries: (i) the acid hydrolysis of the epoxide to form bis-alcohol groups and (ii) utilizing the "click-like" epoxide-amine reaction to functionalize the surface with a model biomolecule-(biotinamido)pentylamine. The successful modifications were confirmed by a combination of spectroscopic and biological means. Changes in the growth characteristics of nonmotile Psychrobacter sp. strain, SW5, on the honeycomb films, provided further evidence confirming changes in the hydrophobicity of the surface upon grafting.

Co-nonsolvency effects for surface-initiated poly(2-(methacryloyloxy)ethyl phosphorylcholine) brushes in alcohol/water mixtures

Surface-initiated atom transfer radical polymerization (SI-ATRP) has been used to grow brushes of poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) from silicon wafers using a polyelectrolytic macroinitiator on planar silicon wafers. Film thicknesses of up to 450 nm were possible within 21 h, and the effect of adding activator and deactivator species on the brush growth rate was studied. The solvation of PMPC brushes in mixed alcohol/water solvents was investigated using in situ ellipsometry. Co-nonsolvency (a re-entrant swelling transition) behavior was observed in water/ethanol binary mixtures; that is, the PMPC brushes were highly swollen in either pure ethanol or water but became deswollen at specific ethanol-rich solvent compositions. A similar effect was obtained with water/2-propanol mixtures, except that in this case pure 2-propanol was not a particularly good solvent for the PMPC chains. However, co-nonsolvency was not observed for water/methanol binary mixtures, since the brushes remained well swollen at all solvent compositions. This is consistent with prior reports of co-nonsolvency effects in both PMPC gels and linear PMPC chains. However, this is the first report of this phenomenon for PMPC brushes and one of the first examples of co-nonsolvency observed for any polymer brush system. A direct comparison of brush and gel swelling reveals an approximate power-law relationship between the equilibrium volumes of these two systems at various solvent compositions, which is interpreted by treating the brush layer as a surface-attached gel. We believe this to be the first quantitative comparison of brush and gel swelling using the same polymer under the same conditions. The kinetics of the PMPC brush response to adjustment of the alcohol/water composition is relatively fast, with the brush volume change occurring on time scales of less than 1 min as judged by in situ ellipsometry.

Molecular recognition at the exterior surface of a zwitterionic telomer brush

3-Sulfo-N,N-dimethyl-N-(2'-methacryloyloxyethyl)propanaminium inner salt (SPB) was polymerized on a glass plate with a surface-confined initiator of atom transfer radical polymerization (ATRP) having a 2-bromoisobutyryl group. The glass plate modified with a brush of sulfobetaine telomer (PSPB) was highly hydrophilic and showed a strong resistance against nonspecific adsorption of proteins such as lysozyme and albumin. Through the polymerization from the free surface of PSPB chain by ATRP, furthermore, N-methacryloyloxysuccinimide (MAOSu) residues were introduced, and the incubation of the telomer (PSPB-b-PMAOSu)-modified glass chip with a lectin (concanavalin A, Con A) gave a glass chip covered with the Con-A-modified PSPB brush. The Con A fixed to the zwitterionic telomer brush pursued specific binding of mannose residues accumulated on the surface of Au colloidal particles, resulting in the increase in absorbance at 550 nm ascribable to localized surface plasmon resonance, while the nonspecific adsorption of proteins to the surface of the glass chip was still largely suppressed. The present results indicate usefulness of the zwitterionic telomer surface with antibiofouling properties as a scaffold for specific sensing devices.

Polymeric phosphorylcholine-camptothecin conjugates prepared by controlled free radical polymerization and click chemistry

Novel polymer-drug conjugates, consisting of zwitterionic poly(methacryloyloxyethyl phosphorylcholine) (polyMPC) as the polymer component, and camptothecin (CPT) as the drug, were prepared by two methods. In one case, CPT was transformed by acylation into a functional initiator for copper catalyzed atom transfer radical polymerization (ATRP), and polyMPC was grown from this therapeutic initiator. In the other case, a one-pot ATRP-"click" conjugation strategy was employed to synthesize novel polyMPC structures containing multiple copies of the drug pendant to the zwitterionic polymer chain. The latter method allows polyMPC-graft-CPT conjugates to be prepared with a high weight percent drug loading (up to 14% CPT) with excellent solubility in pure water (>250 mg/mL). The linkage chemistry chosen between the polyMPC backbone and the pendant drugs proved critically important for assuring drug release within a time frame reasonable to consider these structures as a platform for injectable cancer therapeutics. Liberation of the drug from the polymer backbone was monitored by high-performance liquid chromatography, using size-exclusion and reverse-phase columns, and the toxicity of the polymer-drug conjugates was examined in cell culture against breast (MCF7), ovarian (OVCAR-3), and colorectal (COLO 205) cancer cell lines.

Synthesis of biocompatible sterically-stabilized poly(2-(methacryloyloxy)ethyl phosphorylcholine) latexes via dispersion polymerization in alcohol/water mixtures

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) is soluble in either 2-propanol or water but becomes insoluble in certain alcohol-rich 2-propanol/water mixtures. We have exploited this unusual cononsolvency behavior in order to prepare new biocompatible sterically stabilized PMPC latexes via nonaqueous dispersion polymerization in 2-propanol/water mixtures. All polymerizations were conducted in the presence of monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA) as a reactive stabilizer, with some formulations including ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Under optimized conditions, unimodal size distributions could be obtained with a mean latex diameter of approximately 1 microm, as judged by laser diffraction and DLS. The mean latex diameter depended on both the PEGMA and initiator concentration but was almost independent of the cross-linking density. Smaller PMPC latexes were obtained by increasing the alcohol content of the dispersion medium. On dilution with water, these latexes acquired microgel character. The microgel solution viscosity was insensitive to added salt due to the so-called "antipolyelectrolyte" effect, which is characteristic of polyzwitterions. Finally, copolymerization of MPC with a fluorescein-based methacrylic comonomer produced fluorescently labeled PMPC latexes, which may have potential biomedical applications.

Bioinspired interface for nanobiodevices based on phospholipid polymer chemistry

This review paper describes novel biointerfaces for nanobiodevices. Biocompatible and non-biofouling surfaces are designed largely based on cell membrane structure, and the preparation and functioning of the bioinspired interface are evaluated and compared between living and artificial systems. A molecular assembly of polymers with a phospholipid polar group has been developed as the platform of the interface. At the surface, protein adsorption is effectively reduced and the subsequent bioreactions are suppressed. Through this platform, biomolecules with a high affinity to the specific molecules are introduced under mild conditions. The activity of the biomolecules is retained even after immobilization. This bioinspired interface is adapted to construct bionanodevices, that is, microfluidic chips and nanoparticles for capturing target molecules and cells. The interface functions well and has a very high efficiency for biorecognition. This bioinspired interface is a promising universal platform that integrates various fields of science and has useful applications.

A novel biomimetic polymer as amphiphilic surfactant for soluble and biocompatible carbon nanotubes (CNTs)

Novel amphiphilic diblock copolymer, cholesterol-end-capped poly(2-methacryloyloxyethyl phosphorylcholine) (CPMPC), which has poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) as hydrophilic segment and cholesterol as hydrophobic segment, was specially designed as amphiphilic surfactant to achieve water-soluble and biocompatible carbon nanotubes (CNTs). The pristine CNTs were facilely dispersed via non-covalently binding the zwitterionic phosphorylcholine-based amphiphile onto the surfaces of the CNTs. It is interesting to find that CPMPC shows better CNTs solubilizing ability compared with the surfactant of pyrene-end-capped poly(2-methacryloyloxyethyl phosphorylcholine) (PPMPC). The biocompatibility of the CPMPC stabilized CNTs was evaluated using cholesterol-end-capped poly(2-(dimethylamino) ethyl methacrylate) (CPDMAEMA), cholesterol-end-capped poly(acrylic acid) (CPAA) and cholesterol-end-capped poly(ethylene oxide) (CPEG) as surfactants for CNTs as controls. While CPDMAEMA stabilized CNTs and CPAA stabilized CNTs showed obvious cytotoxicity, cytotoxicity of this novel zwitterionic phosphorylcholine-based amphiphile stabilized CNTs was not observed as indicated by cell culture. The biocompatible CNTs represent an excellent nano-object for potential biomedical applications.