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Combinatorial Cell-Based Screening of Biodegradable Polymer Films and Microspheres: Implications for Vaccine Delivery

Latrisha K. Petersen1, Andrew Adler2, Jennifer H. Wilson3, Michael Wannemuehler3, Rajan Krishna4, Xue Li4, and Balaji Narasimhan1. (1) Chemical and Biological Engineering, Iowa State University, 2114 Sweeney Hall, Ames, IA 50011, (2) Bme, Northwestern University, Evanston, 60208, (3) Veterinary Microbiology & Preventive Medicine, Iowa State University, 2180 Vet Med, Ames, IA 50011, (4) Materials Science and Engineering, Iowa State University, 2220 Hoover Hall, Ames, IA 50011

Surface-erodible polyanhydrides have been thoroughly studied as carriers for drugs, proteins, and vaccines. In general, the focus of these studies has been on structure-function relationships carried out in a “one sample at a time” method. This costly, time consuming, error prone process for studying biomaterial structure-function relationships can be more efficiently investigated and optimized with the use of combinatorial techniques. The polyanhydrides of interest in this work were based on sebacic acid (SA), 1,6-bis(p-carboxyphenoxyhexane) (CPH), and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) copolymers. Within a short amount of time, linearly varying discrete compositional libraries including 25 film chemistries and 11 microsphere chemistries of polyanhydride random copolymers (based on CPH:SA and CPTEG:CPH) were designed, synthesized, and characterized. Both libraries were rapidly screened for cytotoxicity, cytokine production and cell surface marker expression (the latter studies were only performed with microsphere libraries due to limited volume with film libraries). The libraries were incubated with primary antigen presenting cells of the immune system, dendritic cells and macrophages, and rapid screening with the MTT assay showed that these libraries had no pronounced cytotoxic effect for any CPH:SA or CPTEG:CPH composition at a concentration higher than that expected for in vivo biomedical applications. By performing flow cytometry (to assay for cell surface markers) and the Luminex assay (for cytokine production), we were able to clearly identify trends correlating polyanhydride chemistry to cell surface marker expression and cytokine production. There was an observable increase in MHC II, CD86, CD40 and TNFα with an increase in the CPH content of the copolymers (i.e., more hydrophobic polymers) and an evident increase in IL-6 with an increase in the SA content of the copolymers (i.e., less hydrophobic polymers). These trends are important because they dictate the pathway of the immune response to be either cell-mediated or humoral, which is essential knowledge for the rational design of biomaterials as adjuvants for vaccine delivery. We proceeded further to validate the data with the use of informatics and statistical methodologies by performing principal component analysis and model fitting which correlated with previous conventionally determined results. These findings add to the large body of evidence supporting the use of polyanhydrides as drug carriers and vaccine adjuvants. The techniques discussed are amenable to numerous applications in the area of high-throughput polymer synthesis and screening and will enable for future rapid and optimal design of biomaterials.