Improving bone healing using polymeric nanoparticle mediated delivery of wnt agonists

Abstract

Bone fractures and their complications are prevalent medical issues with high financial costs and loss in quality of life. Pharmaceutical treatments to aid bone fracture repair are not yet available in clinic, despite their potential for improving fracture outcomes. Therapeutic candidates such as Wnt agonists may improve the quality and rate of healing by boosting key signalling involved in fracture repair. However, these therapies are limited by off-target effects and poor bioavailability at the injury site. Polymeric nanoparticles (polymersomes; PMs) may provide a solution by enabling controlled spatio-temporal drug delivery. This research aimed to develop a PM drug delivery therapeutic for the controlled and localised delivery of a Wnt agonist to a bone injury site, in order to promote bone repair and ultimately improve fracture healing outcomes. In this study, the efficiency of PMs for encapsulating Wnt agonists BIO and CHIR and achieving in vitro induction of a Wnt signalling response was assessed using techniques of UVVis spectroscopy and a luciferase reporter cell line. Here PMs were successfully produced with a sufficient dose of BIO and CHIR to induce Wnt signalling. In contrast to free compounds, PM-encapsulated BIO and CHIR prevented cytotoxicity when incubated with primary bone cells. This study also assessed the in vivo localisation of PMs using an IVIS imaging method which semi-quantified a fluorescent PM payload distribution within a mouse bone injury model. It was found that following injury, either immediate or a 7- day delayed IV administration of PMs resulted in passive accumulation at a target bone injury site. Additionally, a preliminary study using a clodronate liposome pre-treatment to deplete the macrophage population of MPS organs found no significant change in PM accumulation to a target bone injury site. Finally, this study tests the hypothesis that PM-encapsulated BIO can induce Wnt signalling activity and osteogenic differentiation in vivo. RT-qPCR analysis of tissues of high PM accumulation extracted 24 or 48 hours following IV treatment of PM-BIO revealed disparate in vivo gene expression of Wnt signalling inhibitors (Axin2 and Dkk1) depending on the presence of a bone injury, as well as the induction of early osteogenic gene expression (Runx2) at a target injured bone. Overall the findings presented in this thesis demonstrate that PM delivery of a Wnt agonist provides a viable bone-promoting therapeutic which could improve fracture healing outcomes.

More information

Identifiers

Catalogue record

Export record