Drug and gene delivery strategies for targeting mechanobiological and biochemical pathways for joint and bone tissue engineering

• Main Author: Atluri, Keerthi
• Other Authors: Salem, Aliasger K.
• Format: Others
• Language: English
• Published: University of Iowa 2019
• Subjects: Bone; Drug Delivery; Fibrosis; Formulation; Gene Delivery; PLGA particles
• Online Access: https://ir.uiowa.edu/etd/6697; https://ir.uiowa.edu/cgi/viewcontent.cgi?article=8196&context=etd

A major challenge in drug development is ensuring that each new candidate drug is delivered to the appropriate location, in a timely manner and at an optimal concentration. Low drug solubility, drug instability, drug degradation, drug toxicity, or rapid clearance from the body can reduce the effectiveness of an otherwise promising drug candidate. Formulations such as nano/microparticles and melt extruded pellets made with synthetic and natural polymers are effective solutions for the advancement of drug delivery technology. These polymeric formulations can provide controlled release of therapeutic agents by delivering constant doses over long periods, cyclic dosages, and tunable release of both hydrophilic and hydrophobic drugs in order to improve the bioavailability and bioactivity of a drug. PLGA-based nanoparticles formed by emulsion or nanoprecipitation techniques can be designed to have a range of degradation times. Particle degradation and drug release kinetics can be controlled by the physiochemical properties of the polymer, such as molecular weight, hydrophobicity, and polydispersity. This study is focused on developing polymeric-based delivery systems for small and large molecules as treatment strategies for arthrofibrosis and bone tissue engineering. In developing arthrofibrotic treatments, several mechanosignaling and biochemical pathways were targeted using small molecule therapeutics such as blebbistatin (a myosin II ATPase inhibitor), paclitaxel (a microtubule stabilizer), sulfasalazine (a kappa B suppressor), beta-aminopropionitrile (a lysyl oxidase inhibitor) and cis-hydroxyproline (inhibits the formation of stable triple helix structure of collagen). The aforementioned drugs were delivered either via PLGA micro/nanoparticles or via pellets formed by melt extrusion. From the studies performed, it was found that blebbistatin delivered by PLGA nanoparticles could reversibly inhibit fibroblast contractile activity and could significantly inhibit collagen synthesis. These findings lay the foundations for further optimization of drug dosing and potentially enabling a new drug delivery technology for treating arthrofibrosis. Sulfasalazine delivered by melt extruded PLGA pellets significantly inhibited myofibroblast numbers as deduced from α-SMA expression and col1A1 gene expression results and thus can be considered a potential treatment for arthrofibrosis. For bone tissue engineering, plasmids encoding differentiation promoting factors or growth factors such as BMP-2 (pBMP-2), FGF-2 (pFGF-2), PDGF (pPDGF) and VEGF (pVEGF) were delivered via polyethylenimine (PEI), a cationic carrier that interacts electrostatically with negatively charged DNA. The formed nanoplexes were either tested directly or by coating them onto biocompatible titanium metal implants and cultured with human bone marrow derived mesenchymal stem cells (hBMSCs). We found that the combinatorial delivery of pBMP-2 and pFGF-2 significantly enhanced bone regeneration as deduced from Runx-2, alkaline phosphatase and osteocalcin gene expression results as well as from data yielded from alizarin red staining assays and atomic absorption spectroscopy where calcium ion levels were measured. It was also found that pBMP-2 nanoplex-coated titanium discs could significantly enhance bone regenerative gene expression for osteocalcin, Runx-2, and alkaline phosphatase as well as enhance calcium ion expression in human adipose derived mesenchymal stem cells (hADMSCs). Thus, it can be concluded that pFGF-2 and pBMP-2 nanoplexes have osteogenic potential and our studies demonstrate a new methodology with the potential to modify titanium disc implant surfaces for the purposes of enhancing osseointegration.