Biophysical Analysis of a Novel Drug Delivery Vector: ELP[V5G3A2-150

Abstract

Elastin-like Polypeptides (ELPs) are genetically engineered biopolymers that are derived from the endogenous protein Tropoelastin. ELPs are structurally disordered and soluble at low temperatures but transition to a β-spiral and aggregate at a Transition Temperature (TT). This aggregation is being explored as a novel drug delivery vector by thermally targeting systemically delivered ELP-drug conjugates. We are investigating the biophysical properties of ELP[V5G3A2-150] as a means of understanding and predicting the behavior in vivo. We have investigated the hydrodynamic, structural and thermodynamic properties of ELP[V5G3A2-150] through the use of CD, turbidity, DLS, DSC and SV. DLS and SV analyses suggest that ELP[V5G3A2-150] experiences small amounts of weak association below the TT that increase with temperature. CD analyses further indicate that below the TT ELP[V5G3A2-150] consists of both disordered (≈75%) and β-conformation (≈25%) and as the temperature and concentration is increased the % β-conformation increases. The temperature & concentration dependence of β-conformation suggests that the weak association can be attributed to heterogeneous β-sheets. SV revealed that above the TT ELP[V5G3A2-150] exhibits a temperature dependent critical concentration (CC). This CC is consistent with the TT and suggests that the TT may be described as a solubility constant.Assembly in serum raises the TT by ≈ 2.5°C. This is opposite to the expected effect of macromolecular crowding and suggests that certain serum proteins may be associating with ELP[V5G3A2-150]. Investigation of this effect through SV was greatly complicated by the presence of the Johnston-Ogston (J-O) effect. Further investigation suggested additional complexity in systems exhibiting the J-O effect than previously reported. Two of the additional complexities already determined are cross-term hydrodynamic non-ideality and high-concentration convection. Additional research into the effects of attaching CPPs to ELP[V5G3A2-150] will be presented. Work supported by NSF ARRA 0959211 grant.