Macromolecule Loading on PLGA Particles through Surface Adsorption

The advent of biotherapeutics have impacted the ways in which diseases are treated. In many instances development of recombinant proteins and oligonucleotides into therapeutics are slowed by poor stability of the candidate drugs. Progress has been made in using polymeric particles as carriers of macromolecule drugs. Historically the method is to encapsulate biological drugs into spherical polymeric matrices. Owing to its biocompatible and biodegradable nature, poly (d,l-lactic-co-glycolic acid) (PLGA) has been used extensively in formulating biological drugs into nano- and micro-sized particles. The development of PLGA biologic formulations, however, has been hampered by matrix acidification; the hydrolysis of the polymer generates non-diffusive acid fragments by which the interior pH can be driven to as low as 2, a condition unfavorable for proteins and oligonucleotides to remain intact. In addition, loading of proteins through encapsulation can lead to substantial loss of activity because of homogenization or sonication-induced denaturation. To circumvent these limitations yet still take advantage of the proven safety of PLGA in humans, I proposed to load macromolecules onto the surface of PLGA particles functionalized with biotin (“PLGA-biotin”). The specific binding between avidin and biotin (or desthiobiotin) was employed to enable surface adsorption. The pair has the strongest known non-covalent affinity, an interaction that is relatively insensitive to temperature and pH. PLGA-biotin particles were prepared by co-emulsifying the lipid DSPE-PEG-biotin with PLGA into a matrix. The tetravalent feature of avidin was used to bridge biotinylated proteins or oligonucleotides onto PLGA- biotin particles. The hypothesis of this project is that solvent-accessible biotin molecules are displayed on PLGA-biotin particles. The rationale for my hypothesis is that the co- emulsification of the biotinylated lipid DSPE-PEG-biotin and the polymer matrix PLGA has the potential to generate PLGA particles functionalized with biotin molecules embedded on the surface. As a result, the interaction between biotin and avidin can be utilized to load macromolecules onto the surface of these modified PLGA particles through adsorption, circumventing the challenges to the stability and bioactivity of the biological drugs caused by the encapsulation process and the acidic environment inside PLGA particles during the degradation of the polymer matrix. Two specific aims were carried out. In aim 1, the presence of biotin in PLGA-biotin particles was verified and the physical attributes of the particles, namely particle size and zeta potential, were characterized. Spectroscopic and biochemical studies indicated the presence of biotin on the particle surface. In aim 2, the amount of biotin accessible on PLGA-biotin particles was quantified. Taken together, the data generated in this thesis support the notion that surface adsorption is a general method for loading macromolecules onto PLGA particles. The work presented is a step toward a new platform in formulating biotherapeutics

Product market relationships and cost of bank loans: evidence from strategic alliances

This paper examines the effects of strategic alliances on non-financial firms’ bank loan financing. We construct several measures to capture firms’ alliance activities using the frequency of alliance activities, the prominence of the alliance partner and the relative networking position in the overall alliance network. We find that firms with active alliance involvement experience a lower cost of debt from banks. We also document that allying with a prestigious partner (ie S&P 500 firms) can provide an endorsement effect and benefit the borrowers by reducing the price of bank loans. Moreover, a borrowing firm positioned at the centre of an alliance network enjoys a lower cost of bank loans. Finally, we find that borrowing firms with alliance experience are less likely to use collateral and covenants in their loan contracts.cost of bank loans; strategic alliances; product market relationships