Controlling antibody delivery, mechanical properties, and cell response of alginate-chitosan polyelectrolyte complexes

Abstract

Therapeutic antibodies have become attractive treatment options for numerous diseases, including various cancers, based on their ability to target and bind to specific proteins or antigens. The antiangiogenic antibody, bevacizumab, targets and binds to VEGF to prevent angiogenesis. Bevacizumab has been approved for the treatment of recurrent glioblastoma, with concurrent radiation and chemotherapy, however the clinical efficacy of bevacizumab is still debated. As a large molecule therapeutic, bevacizumab cannot readily cross the blood brain barrier (BBB) to reach the tumor site. A local, injectable biopolymer delivery system that provided controlled, sustained release of bevacizumab directly to the tumor site would have significant advantages to intravenous administration. In this thesis, biodegradable polysaccharides were used to develop an injectable delivery system for sustained release of therapeutic antibodies. The anionic polysaccharide alginate and cationic polysaccharide chitosan readily form ionic bonds in solution to form a polyelectrolyte complex (PEC). It was demonstrated that the release rate of non-specific IgG antibody could be tailored by altering the ratio of alginate to chitosan or the concentration of CaSO4 in the PEC, with the 50:50 alginate-chitosan PEC having a sustained release of IgG for up to 7 weeks. It is believed that the sustained release of IgG was a result of electrostatic interactions between the antibodies and the chitosan chains in the PEC. Based on these initial release studies, a PEC was designed to target a 30-day release of anti-VEGF antibody (bevacizumab) and the released antibody was shown to inhibit VEGF induced proliferation and angiogenesis in vitro in human umbilical vein endothelial cells (HUVECs). The alginate-chitosan PEC delivery system shows tremendous promise for local, sustained release of therapeutic antibodies. iv It was also discovered that the mechanical properties of the alginate-chitosan PECs can be tailored by altering gelation temperature or ionic interactions within the complex. Increasing gelation temperature from 37°C to 50°C increased the storage modulus of the gel 6.5-fold. The stiffer gel, formed at 50°C, demonstrated increased cell proliferation, indicating manipulation of hydrogel mechanical properties could effectively alter biological response. It was also observed that gel stiffness increase as chitosan content was reduced when a glutamate counterion was present in the PEC. It is believed that the glutamate counterion fundamentally alters PEC formation, resulting in different mechanical behavior.