ENGINEERING ARYLBORONATE – MODIFIED DEXTRAN POLYMERS FOR USE AS BIOCOMPATIBLE, BIODEGRADABLE MATERIALS IN MICROPARTICULATE IMMUNOTHERAPY
Date
2019-06-18
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Abstract
Microparticulate immunotherapy holds promise to vaccinate against difficult targets like cancer. Many vehicles exist, but triggering is often based on pH or passive hydrolysis. The most effective cells at promoting an immune response are dendritic cells. The lysosomes of these cells are highly oxidizing relative to acidifying, so an oxidation-sensitive vehicle could be a significant advancement in this field. One promising class of materials being developed toward this end are aryl boronate- modified dextran polymers. Boronic esters for oxidation-sensitive delivery vehicles are typically made using pinacol (Pin) as a diol. However, Pin- based aryl boronate-modified polymers are prone to interchain transesterification that restricts their solubility and ability to be tuned and synthesized. This phenomenon also inhibits the polymers ability to be processed into discrete particles. To solve this, the diol used in the modified polymer was varied in order to develop a pattern for how the structural properties of different diols affect the behavior of the molecule as a whole. In addition to pinacol, (-)-pinanediol, norbornenediol, and cis- 1,2-cyclopentanediol were tested using 1H-NMR to track the formation and disappearance of key elements of interactions between their ester forms and dextran. The stability of these diols in other contexts have been assessed, but those conclusions have not yet been applied to the addition of those diols as boronic esters onto polymer backbones. It was confirmed that in accordance with patterns developed in literature, pinanediol formed the most stable boronic ester of the four analyzed and retained its stability when incorporated into a dextran polymer. This behavior is due to pinanediol’s cyclic nature, rigidity, and high degree of steric hindrance.
Subsequently, the synthesis of a new aryl-boronate modified dextran polymer was achieved using pinanediol (PD) to replace Pin (PDB- Dex). This modified dextran improves upon Pin-based materials by maintaining its solubility in organic solvents and resulting in smooth, discrete, microparticles that are consistent in size. Microparticles were prepared and analyzed using SEM and DLS methods. Degradation of particles was triggered with hydrogen peroxide and tracked using 1H-NMR to confirm the mechanism of degradation. A standard BCA Assay was adapted to measure the rate of degradation under physiologically relevant conditions, and it was found that PDB-Dex is sensitive to peroxide levels as low as 0.01 mM. Preliminary biological assays and in vitro studies show low cytotoxicity and the ability to deliver an immunostimulatory agent.
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chemistry, biochemistry, chemical biology, polymers