Temperature Triggered Self-Assembly of Polypeptides into Multivalent Spherical Micelles

Abstract

We report herein thermally responsive elastin-like polypeptides (ELPs) in a linear AB diblock architecture with an N-terminal peptide ligand that self-assemble into spherical micelles when heated slightly above body temperature. A series of 10 ELP block copolymers (ELP BC s) with different molecular weights and hydrophilic-to-hydrophobic block ratios were genetically synthesized by recursive directional ligation. The self-assembly of these polymers from unimers into micelles was investigated by light scattering, fluorescence spectroscopy and cryo-TEM. These ELP BC s undergo two phase transitions as a function of solution temperature: a unimer to spherical micelle transition at an intermediate temperature, and a micelle to bulk aggregate transition at a higher temperature when the hydrophilic-to-hydrophobic block ratio is between 1:2 and 2:1. The critical micelle temperature is controlled by the length of the hydrophobic block and the size of the micelle is controlled by both the total ELP BC length and hydrophilic-to-hydrophobic block ratio. These polypeptide micelles display a critical micelle concentration in the range of 4-8 μM demonstrating high stability of these structures. These studies have also identified a subset of ELP BC s bearing terminal peptide ligands that are capable of forming multivalent spherical micelles that present multiple copies of the ligand on their corona in the clinically relevant temperature range of 37-42 °C and target cancer cells. These ELP BC s may be useful for drug targeting by thermally triggered multivalency. More broadly, the design rules uncovered by this study should be applicable to the design of other thermally reversible nanoparticles for diverse applications in medicine and biology.

Peptide-based biopolymers in biomedicine and biotechnology

“…The turbidity (line) and DLS (points) data show the progression of the ELP from monomer to aggregate. [182] Diagram of pH-sensitive (A) micelles and (B) vesicles formed from poly(butadiene-b)-poly (glutamic acid) diblock copolymers. The hydrophilic to hydrophobic ratio of the blocks determines whether a micelle or vesicle will form.…”

Quantitative Side-Chain Modifications of Methionine-Containing Elastin-Like Polypeptides as a Versatile Tool to Tune Their Properties

“…8,9 This solubility switch has proven to be a major advantage for the purification of recombinant ELPs from bacterial lysates, 10 as well as for the controlled self-assembly of individual ELP blocks. 11,12 This property has also been used to develop nanocarriers for drug-delivery systems, the resulting micellar systems being able to self-assemble spontaneously with temperature and to load different drugs. 11,[13][14][15] Post-polymerization modifications of ELPs reported so far have mostly involved their chain ends.…”

“…11,12 This property has also been used to develop nanocarriers for drug-delivery systems, the resulting micellar systems being able to self-assemble spontaneously with temperature and to load different drugs. 11,[13][14][15] Post-polymerization modifications of ELPs reported so far have mostly involved their chain ends. Different ELP sequences have been conjugated to small organic molecules, 16 oligonucleotides, 17 drugs, 18,19 or PEG.…”

Nanotechnological Approaches to Therapeutic Delivery Using Elastin-Like Recombinamers

“…This CMT can be controlled by varying the length and composition of the hydrophobic block, whereas the size of the micelle can be controlled by varying the ELR length and the hydrophilic-to-hydrophobic block ratio. 59 The high versatility in the design of ELR diblocks even allows control over whether self-assembly results in micelles or hollow vesicles by varying the block arrangement and length. This conclusion was reached in studies with different ELR constructs comprising glutamic acid and alanine blocks, as described by Martin et al 55 ELR diblocks can be functionalized for different purposes by genetically inserting protein domains into their sequence.…”