Assessment of the Integrity of Poly(caprolactone)-b-poly(ethylene oxide) Micelles under Biological Conditions:  A Fluorogenic-Based Approach

Abstract

The integrity of block copolymer micelles is important for their effectiveness and successful delivery of the incorporated drugs. Here we evaluate the integrity of poly(caprolactone)-b-poly(ethylene oxide) micelles in media of varying chemical complexity and in cells by using fluorogenic micelles. Fluorogenic dye fluorescein-5-carbonyl azide diacetate was covalently attached to the micelle-core-forming part of the block copolymer, poly(caprolactone). The fluorescence was not detectable unless the poly(caprolactone)21-b-poly(ethylene oxide)45 micelles were destroyed and the fluorogenic dye was activated by deesterification. The fluorescence of the activated dye from destroyed micelles was easily detectable in various media and in cells. Micelles were stable in simple media such as phosphate-buffered saline but disassembled to varying extents with increasing chemical complexity of the media and addition of serum. The integrity of the internalized micelles within the cells showed a time-dependent decrease but remained largely preserved (80%) after 20 h of incubation with cells. A proof of principle was also demonstrated in vivo in mice. The fluorogenic approach to micelle integrity assessment presented herein should lend itself to other block copolymer micelles and assessments of their integrity in complex biological systems in vitro and in vivo.

Investigation on design of stable etoposide-loaded PEG-PCL micelles: effect of molecular weight of PEG-PCL diblock copolymer on thein vitroandin vivoperformance of micelles

“…If micelles dissociate into unimers immediately after intravenous injection due to poor in vivo stability, the loaded hydrophobic drug would be immediately released out and precipitated. Hence, the purpose of higher drug accumulation to tumor by EPR effect will be badly affected and will create suspicion about stability of micelles (Savic et al, 2006). Therefore, in addition to CMC determination, it is necessary to investigate the in vitro performance of prepared micellar formulation thoroughly before it goes to preclinical or clinical stage.…”

Formulation of a geldanamycin prodrug in mPEG-b-PCL micelles greatly enhances tolerability and pharmacokinetics in rats

“…This indicates that mPEG-b-PCL micelles were significantly stable in blood, allowing for sustained release and conversion of 17′GAC 16 Br over 48-h without leading to significant systemic toxicities, especially evident at the high dosage of 200 mg/kg. mPEG-b-PCL micelle stability in blood is further justified by recent work which has shown that a significant portion of these block-copolymers do indeed remain intact as micelles in vivo [29,30]. There was evidence of rapid release in serum for 17′GAOH at 10 and 200 mg/kg 17′GAC16Br loadedmicelles, which was not apparent during in vitro characterizations in ddH 2 O at 37°C and pH 7.4 [15].…”

“…The advantage with mPEG-b-PCL micelles is that they are usually characterized by low critical micelle concentrations (CMCs) which are indicative of high stability leading to sustained drug release in the plasma [27,28], and are kinetically stable in vivo following i.v. injections into animals [29,30]. Recently, we reported on the use of micelles composed of mPEG-b-PCL (MW 5000:10000 g/mol) as biocompatible nanocarriers for a series of lipophilic GA prodrugs [15].…”

Lactic acid‐ and carbonate‐based crosslinked polymeric micelles for drug delivery

“…Micelles have also been shown to become unstable once they encounter blood components. 11,36,38 Instability may result from protein adsorption, protein penetration, or drug extraction. 36 As the most abundant protein in blood plasma is serum albumin, we investigated the effect of physiological simulating concentrations of BSA (45 mg/mL) on Cm and NCM stability using DLS to observe time-dependent changes in micelle size.…”

“…[5][6][7] Nonetheless, poor in vivo stability resulting in premature dissociation and subsequent untimely drug release has limited their clinical application. [8][9][10][11] Polymeric micelles become unstable either due to destabilization by plasma proteins (kinetic instability) or dilutions below their CMC (thermodynamic instability) upon systemic administration.…”