Chemical End Group Modified Diblock Copolymers Elucidate Anchor and Chain Mechanism of Membrane Stabilization

Abstract

Block copolymers can be synthesized in an array of architectures and compositions to yield diverse chemical properties. The triblock copolymer Poloxamer 188 (P188), the family archetype, consisting of a hydrophobic poly(propylene oxide) core flanked by hydrophilic poly(ethylene oxide) chains, can stabilize cellular membranes during stress. However, little is known regarding the molecular basis of membrane interaction by copolymers in living organisms. By leveraging diblock architectural design, discrete end-group chemistry modifications can be tested. Here we show evidence of an anchor and chain mechanism of interaction wherein titrating poly(propylene oxide) block end group hydrophobicity directly dictates membrane interaction and stabilization. These findings, obtained in cells and animals in vivo, together with molecular dynamics simulations, provide new insights into copolymer–membrane interactions and establish the diblock copolymer molecular architecture as a valuable platform to inform copolymer–biological membrane interactions. These results have implications for membrane stabilizers in muscular dystrophy and for other biological applications involving damaged cell membranes.

Quantifying Binding of Ethylene Oxide–Propylene Oxide Block Copolymers with Lipid Bilayers

“…A previous in-vivo study of membrane stabilization by block copolymers by Houang et al demonstrated that the replacement of a hydroxyl endgroup by a tert -butyl endgroup on the PPO block of a diblock analog to F68 could significantly enhance the stabilization efficacy of polymers on the dystrophic membrane. 58 This result also confirmed the importance of the endgroup, despite the fact that it is less significant in our case.…”

PEO–PPO Diblock Copolymers Protect Myoblasts from Hypo-Osmotic Stress In Vitro Dependent on Copolymer Size, Composition, and Architecture

“…The ability of PEO-PPO diblock copolymers to effectively protect damaged membranes from enzyme leakage in vitro demonstrates that the second hydrophilic PEO segment – present in triblock P188 – is not required for efficacy, in agreement with Houang, et al . 54 This result, and the impacts of composition and size, are consistent with a model in which the hydrophobic segment anchors the copolymer to the membrane while the hydrophilic segment interacts with the lipid head groups and the aqueous extracellular environment.…”

“…The membrane protection effects of varying copolymer size, composition, and architecture can be compared across the current myoblast LDH release assay and concurrent studies on liposomal integrity under free radical challenge 53 and maintenance of muscle torque in dystrophin-deficient (Dmd mdx ) mice under mechanical stress 54 . A slight protective efficacy of diblock E 75 P 16 m was also observed in mdx mice upon intraperitoneal injection though not upon subcutaneous injection, inverse of the result for triblock E 75 P 30 E 75 .…”

“…Recently, we discovered that a PEO-PPO diblock copolymer, with a composition and size corresponding to essentially one half of P188, can protect a model lipid membrane 53 as well as skeletal muscles from mechanical stress in vivo 54 . Also, PEO-poly(butylene oxide) diblock copolymers (73% hydrophilic; 2700 g/mol) were shown to effectively interact with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers with surface activity increasing with longer poly(butylene oxide) segments.…”

Rational design of block copolymer self-assemblies in photodynamic therapy

“…They showed that the copolymer inserted itself in the membrane, leading to the formation of hybrid membrane with better mechanical properties. Houang et al [170] compared the results obtained with MD simulations and with physiological studies. They used PEO-PPO copolymers with different PPO end groups and tested them as membrane stabilizer both in silico and in vitro.…”