Liquid, Injectable, Hydrophobic and Biodegradable Polymers as Drug Delivery Vehicles

Formulation parameters governing sustained protein delivery from degradable viscous liquid aliphatic polycarbonates

Viscous liquid degradable polymers have advantages as drug depots for sustained protein delivery. We have created a new aliphatic polycarbonate for this purpose, poly(trimethylene carbonate-co-5-hydroxy trimethylene carbonate), which upon degradation retains a near neutral micro-environmental pH. As such, this copolymer is highly suited to the delivery of acid sensitive proteins. We show that the mechanism of protein release from this liquid copolymer is consistent with the formation of super-hydrated regions as a result of the osmotic activity of the solution formed upon distributed protein particle dissolution. Protein release can be manipulated by controlling polymer hydrophobicity which can be adjusted by molecular weight and choice of initiator. Moreover, protein release is highly dependent on protein solubility which impacts the osmotic activity of the solution formed upon dissolution of the protein particles while protein molecular size and isoelectric point are not as influential. As demonstrated by the release of highly bioactive vascular endothelial growth factor, formulations of this copolymer are suitable for prolonged delivery of protein therapeutics.

Corelease of bioactive VEGF and HGF from viscous liquid poly(5-ethylene ketal ε-caprolactone-co-D,L-lactide)

The potential of a viscous liquid injectable delivery system composed of poly(5-ethylene ketal ε-caprolactone-co-D,L-lactide) (PEKCDLLA) to release bioactive vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) using an osmotic pressure release mechanism for the purpose of treating critical limb ischemia was investigated. VEGF and HGF were lyophilized separately with trehalose and bovine serum albumin (BSA) and incorporated into the polymer by simple mixing. VEGF and HGF were released by convective flow through superhydrated regions formed within the polymer as a result of the osmotic activity generated upon dissolution of the particles, along with the contributions of polymer degradation at later time points. A sustained release of highly bioactive VEGF and HGF for over 40 days with minimal burst was achieved under conditions of multidirectional delivery. The solubility of the growth factors in the concentrated trehalose solution formed upon dissolution of the particle within the polymer was determined to be a key parameter governing the rate and extent of growth factor release. This formulation approach, of using a low viscosity polymer delivery vehicle, is potentially useful for localized delivery of acid and temperature sensitive proteins, such as VEGF and HGF. This system may also serve as a platform for controlled and predictable delivery patterns for other therapeutic proteins in other clinical settings.

Emerging technologies for enabling proangiogenic therapy

Ischemic disease causes a large number of deaths and significant clinical problems worldwide. Therapeutic angiogenesis, strengthened by advances in growth-factor-based therapies, is a promising solution to ischemic pathologies. Major challenges in therapeutic angiogenesis are the lack of stability of native angiogenic proteins and also providing sustained delivery of biologically active proteins at the ischemic sites. This paper will discuss various protein engineering strategies to develop stabilized proangiogenic proteins and several biomaterial technologies used to amplify the angiogenic outcome by delivering biologically active growth factors in a sustained manner.