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Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions

Published: October 10th, 2016



1Leslie Dan Faculty of Pharmacy, University of Toronto

The key steps of living anionic polymerization of phenyl glycidyl ether (PheGE) on methoxy-polyethylene glycol (mPEG-b-PPheGE) are described. The resulting block copolymer micelles (BCMs) were loaded with doxorubicin 14% (wt%) and sustained release of drug over 4 days under physiologically relevant conditions was obtained.

In this study, an amphiphilic copolymer that includes a core-forming block with phenyl groups was synthesized by living anionic polymerization of phenyl glycidyl ether (PheGE) on methoxy-polyethylene glycol (mPEG-b-PPheGE). Characterization of the copolymer revealed a narrow molecular distribution (PDI < 1.03) and confirmed the degree of polymerization of mPEG122-b-(PheGE)15. The critical micelle concentration of the copolymer was evaluated using an established fluorescence method with the aggregation behavior evaluated by dynamic light scattering and transmission electronic microscopy. The potential of the copolymer for use in drug delivery applications was evaluated in a preliminary manner including in vitro biocompatibility, loading and release of the hydrophobic anti-cancer drug doxorubicin (DOX). A stable micelle formulation of DOX was prepared with drug loading levels up to 14% (wt%), drug loading efficiencies > 60% (w/w) and sustained release of drug over 4 days under physiologically relevant conditions (acidic and neutral pH, presence of albumin). The high drug loading level and sustained release is attributed to stabilizing π-π interactions between DOX and the core-forming block of the micelles.

In aqueous media, amphiphilic block copolymers assemble to form nano-sized block copolymer micelles (BCMs) that consist of a hydrophobic core surrounded by a hydrophilic shell or corona. The micelle core can serve as a reservoir for the incorporation of hydrophobic drugs; while, the hydrophilic corona provides an interface between the core and the external medium. Poly(ethylene glycol) (PEG) and its derivatives are one of the most important classes of polymers and one of the most widely used in drug formulation.1-3 BCMs have proven to be a worthy drug delivery platform with several formulations relying on this technology now in late stage clinical developme....

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Figure 1
Figure 1. Schematic showing the nine key steps in the preparation of the mPEG-b-PPheGE copolymer. Please click here to view a larger version of this figure.

1. Preparation of the Reagents under Dry Conditions

  1. Preparation of the reagents.
    1. Weigh 15 g of mPEG-5K.......

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Figure 3
Figure 3. Illustration of the anionic polymerization of phenyl glycidyl ether on mPEG macroinitiator to produce mPEG-b-(PheGE)15 for preparation of block copolymer micelles for loading of doxorubicin. The schematic illustrates the deprotonation of the hydroxyl group of mPEG using naphthalene potassium as a radical-anion, followed.......

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Due to the good control that anionic polymerization provides over molecular weight it is one of the most applied processes in the industry for the preparation of polymers based on oxirane monomers (PEG and PPG). Optimal and stringent conditions must be used for successful polymerization to be achieved. Rigorous purification of all reagents and appropriate apparatus are essential for the living character of the synthesis. Limitations of the current setup are mostly associated with the transfer technique that relies on can.......

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CA acknowledges a Discovery grant from the Natural Sciences and Engineering Research Council of Canada. CA acknowledges a Chair in Pharmaceutics and Drug Delivery from GSK. The authors declare no competing financial interest.


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Name Company Catalog Number Comments
DMEM/HAMF12 Gibco, Life Technologies 12500 Supplemented with 10%FBS. Warm in 37 °C water bath
Trypsin-EDTA(0.25%) Sigma-Aldrich T4049 Warm in 37 °C water bath 
Fetal bovine serum (FBS) Sigma-Aldrich F1051 Canada origin
MDA-MB-468 cell line ATCC HTB-132
MTS tetrazolium reagent PROMEGA G111B
Phenazine ethosulfate (PES) Sigma-Aldrich P4544 >95%
mPEG5K (Mn 5400 g/mol) Sigma-Aldrich 81323 PDI=1.02
Dimethylsolfoxide (DMSO) Sigma-Aldrich D4540 >99.5%
Naphthalene Sigma-Aldrich 147141 >99%
Phenyl glycidyl ether Sigma-Aldrich A32608 >85%
Benzophenone Sigma-Aldrich 427551 >99%
Potassium Sigma-Aldrich 451096 >98%
Tetrahydrofuran Caledon Laboratory Chemicals 8900 1 ACS
Hexane Caledon Laboratory Chemicals 5500 1 ACS
Calcium hydride (CaH2) ACP C-0460 >99.5%
Diethyl Ether Caledon Laboratory Chemicals 1/10/4800 ACS
Microplate reader BioTek Instruments
Differential scanning calorimetry (DSC) TA Instruments Inc DSC Q100
Gel permeation chromatography (GPC) Waters 2695 separation moldule / 2414 detector  2 Columns: Agilent Plgel 5µm Mixed-D
NMR spectroscopy Varian Mercury 400MHz
Chloroform-d Sigma-Aldrich 151858 99.96%
DMSO-d Sigma-Aldrich 156914 99.96%
Vaccum pump  Gardner Denver Welch Vacuum Tech, Inc. Ultimate  pressure 1.10-4 torr
Drierit with indicator, 8 mesh Sigma-Aldrich 238988 Regenerated at 230°C for 2 hrs

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