Advances of phenylboronic acid-containing materials in drug delivery

Phenylboronic acid (PBA) and its derivatives are a kind of synthetic chemicals which can recognize diols via reacting reversibly with them in aqueous solutions. Recently, based on the reversible covalent PBA/diol complexes, strategies to construct drug delivery system for diabetes treatments and cancer therapy have made enormous progress. Diabetis mellitus have greatly increased all over the world in recent decades. With the regular use of insulin in diabetes treatment, there is a high demand of insulin self-regulated release system responding to glucose concentration in vivo. Since the apparent pKa value of PBA and its derivatives is around 8.2-8.6, which is higher than human physiological pH 7.4, efficient glucose-responsiveness of PBA-based polymer materials could not be obtained at physiological pH and glucose level. Recently, studies to construct this insulin release system based on PBA polymer materials have made enormous progress, such as reducing the pKa of the PBA group, achieving "on-off" release of insulin according to the change of glucose concentration and so on. Similar to diabetes treatments, significant efforts have recently been made to develop drug delievery system based on PBA polymer materials in cancer therapy. Traditional chemotherapy has disadvantages such as poor permeability, short resident time, and toxic side effects. Therefore, the ideal drug delivery carrier should possess tumor targeting ability to prolong the retention time and enhance the aggregation of carriers in tumors. Inaddition, carriers should release drugs and degrade in response to intracellular triggers when inside the cancer cells, in order to increase delivery efficiency and reduce toxicity. The recognition ability of boronic acid to polyol residues in cell membranes enables PBA-functionalized nanocarriers to specific target to sialic acid groups, which are overexpressed on tumor cells. The high affinity and specificity of PBA to SA could significantly improve drug accumulation and retention in tumor, and increase the cellular uptake of carriers. Moreover, the reversible covalent PBA/diol complexes provide three modes of stimuli-responsive features of PBA polymer materials. Firstly, the reversible covalent of PBA with diols depends on the pH, and the PBA-diols bond will be weak at acidic pH such as within endosomes and lysosome. So this pH-responsiveness of PBA-modified carriers could be used to release drugs and genes accurately inside tumor tissues as well as cancer cells. Secondly, one diols complex with PBA could easily be replaced by another diols having better thermodynamic stability complex with PBA. Adenosine triphosphate (ATP) with a cis-diol moiety is abundant inside cells, and the PBA-sugar complex could be exchanged by more stable PBA-ATP formation. Finally, many types of tumor tissues and cancer cells have increased levels of reactive oxygen species (ROS), and PBA ester can react with these ROS such as H2O2, thus PBA ester can be used as the oxidation-responsive trigger during the drug delievery process. Herein, the responsiveness to stimuli of PBA polymer materials has been well studied, including glucose, pH, adenosine triphosphate (ATP), and H2O2 sensitive. This paper reviews recent research on drug delivery system for diabetes treatments and cancer therapy based on PBA polymer materials, and the possible development in the future is predicated. © 2016, Science Press. All right reserved.