A significant problem in high-throughput drug screening is the disproportionate number of false hits associated with drug candidates that form colloidal aggregates. Such molecules, referred to as promiscuous inhibitors, nonspecifically inhibit multiple enzymes and are thus not useful as potential drugs. Here, we report a printable hydrogel-based drug-screening platform capable of non-ambiguously differentiating true enzyme inhibitors from promiscuous aggregating inhibitors, critical for accelerating the drug discovery process. The printed hydrogels can both immobilize as well as support the activity of entrapped enzymes against drying or treatment with a protease or chemical denaturant. Furthermore, the printed hydrogel can be applied in a high-throughput microarray-based screening platform (consistent with current practice) to rapidly ( <25 min) and inexpensively identify only clinically promising lead compounds with true inhibitory potential as well as to accurately quantify the dose–response relationships of those inhibitors, all while using 95% less sample than required for a solution assay.

Injectable, degradable hydrogels based on cross-linking between aldehyde-functionalized dextran, hydrazide-functionalized dextran, and hydrazide-functionalized beta-cyclodextrin (bCD) were developed for hydrophobic drug delivery. bCD functions as both the in situ-gelling agent driving hydrogel formation as well as the binding site for the hydrophobic model drug, dexamethasone. In hydrogel systems where bCD is primarily covalently attached to the polymer network through cross-linking, the amount of drug release per sampling point is independent of the time between samples, the solubility of drug in the release medium, and the cross-link density of the hydrogel; instead, drug release is controlled primarily by partitioning of free (water-solubilized) drug between the hydrogel and the release medium. When the concentration of the hydrazide-functionalized dextran polymer was increased and more hydrazide groups were available to compete with bCD reactive sites for cross-linking the polymers, greater than ten-fold more drug was released from the hydrogel during the 20 day sampling period. Mobile, noncross-linked bCD increases the solubility of the drug and facilitates rapid drug release by diffusion, as confirmed by quenching bCD-bound hydrazide groups. In this way, via a very subtle change in the composition of the injectable hydrogel, both the kinetics of drug release as well as the mechanism of drug release can be tuned over a wide range. Together with the low cytotoxicity of the materials, these results suggest that injectable bCD-based hydrogels have potential for facilitating controlled release of hydrophobic drugs over multiple time scales by controlling the mobility of bCD within the hydrogel network.

No abstract