Thermodynamic Properties of ELP-Labelled Doxorubicin, a Drug Delivery System

Abstract

Macromolecular delivery by hyperthermia and thermal targeting of SynB1-Cys ELP-bound Doxorubicin (Dox) to solid tumors is investigated in animal studies as a means of circumventing multidrug resistance in cancer cells. The structural changes and hydrodynamic properties of ELP below and above its Transition Temperature TT make this construct a useful carrier for the delivery of Dox. At low temperature, the ELPs are soluble and consist of both random coils and β-turn structures. With increasing temperature ELPs undergo weak association, forming repeating type II β-turns and β-spirals. Above the TT, they undergo a cooperative phase transition involving µm size aggregates stabilized by desolvation. Sedimentation velocity (SV) experiments have shown that ELP is a nonideal monomer at low temperature, but with increase in temperature undergoes weak isodesmic self-association. Adding Cell Penetrating Peptides (SynB1) at the N-terminal domain of the ELP decreases its solubility and stabilizes the aggregated state. This study asks how the addition of Dox to SynB1-Cys ELP affects its biophysical and hydrodynamic behavior at physiological conditions, and how these changes influence its potential for aggregation and drug delivery. The preliminary SV results presented here show an increase in self-association of SynB1-Cys ELP-Dox at 20°C relative to the unlabeled construct. The goal of these experiments is to investigate the impact of different labeling efficiencies (10-90%) on self-association and TT. Preliminary turbidity results on unlabeled SynB1-Cys ELP in PBS show that TT decreases linearly with increase in the logarithm of the ELP concentration as solutions are heated from 20 to 60°C. The process is reversible as solutions are cooled to 20°C. The degree of conformational change associated with the TT will also be monitored using CD and FT-IR experiments.