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Drug Delivery

Drug Delivery - Poster Session A

Poster J5 - Controlled Release of Small Molecule Therapeutics from a Self-Assembling Boronate Ester Release Peptide Hydrogel Platform

Thursday, October 24, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Boronic acid-containing small molecule (BACSM) therapeutics are of growing interest for cancer and infectious disease treatment. Five BACSMs are already FDA-approved and many more are in development. However, many of these drugs have short biological half-lives and require frequent dosing, which reduces patient adherence. Frequent, often daily, dosing can be particularly challenging when combatting chronic diseases, such as latent tuberculosis. A potential solution is the use of a multidomain peptide (MDP) hydrogel delivery system. The biocompatibility and shear-thinning ability of MDP hydrogels makes them enticing for drug delivery applications; however, limitations in their ability to slow the release of small and uncharged molecules poses many challenges. Nanofibrous MDP hydrogels modified with boronic acid-binding motifs (BABMs) could overcome these issues by acting as a platform for controlled BACSM drug release. BABMs take advantage of dynamic covalent boronate ester bonding between the BACSM and diol motif on BABMs to temporarily and reversibly attach to the hydrogel, delaying the otherwise diffusion-mediated release of drug from our hydrogels. We demonstrate that this Self-Assembling Boronate Ester Release (SABER) hydrogel platform significantly delays the release of the clinically relevant BACSM drugs bortezomib, ixazomib, tavaborole, and ganfeborole. Further, we show that the SABER platform can be used to control the release of small molecules that do not natively contain a boronic acid. The extension of drug release without a large initial burst achieved by SABER hydrogels could reduce dosing frequency, thereby improving adherence and patient outcomes for both novel and current BACSMs.

Materials and

Methods:  MDPs were manually synthesized using solid-phase peptide synthesis. BABMs are added as N-terminal modifications to the self-assembling MDPs KK(SL)6KK, termed K2, and EE(SL)6EE, termed E2. A three-step design process was developed and tested for engineering the hydrogel-based platform for BACSM drug delivery. A competition assay was used to determine the binding constants of BACSMs to the BABMs salicylhydroxamic acid (SHA), a catechol (Cat), and a nitro-catechol (nitroCat) in vitro. Alizarin Red S (ARS) was used as a fluorescence indicator to calculate the equilibrium constant for interactions between BACSMs and BABMs using the Benesi-Hildebrand equation. Serial dilutions of BACSM and BABM were performed and fluorescence output measured using a plate reader was graphed to determine equilibrium constants. This allows us to quickly screen the effectiveness of BABM-modified hydrogels with minimal material. To investigate the release of small molecules that do not natively contain a boronic acid, 1V209 modified with phenylboronic acid (1V209-PBA) was tested by evaluating its ability to activate its target relative to the parent drug, 1V209.

In vitro drug release studies were performed with SABER hydrogels loaded with BACSM. Samples were plated in a custom 3D-printed 48 well-plate and media was sampled with replacement over 24 hours. To evaluate the effect of SABER hydrogels in vivo, female BALB/c mice were subcutaneously injected with SABER hydrogels loaded with BACSM and the concentration of circulating drug was measured over time. Blood was collected from the saphenous vein and liquid chromatography-mass spectrometry was used to quantify drug release.

Results, Conclusions, and Discussions: In vitro drug release results generally correlated well with competition assay data as BACSM-BABM combinations that had larger equilibrium constants exhibited slower BACSM release from corresponding SABER hydrogels. Thus, this assay can be used to screen BACSM and BABM combinations for further testing. Pharmacokinetics studies with SABER hydrogels reflected in vitro release trends with high fidelity. SABER hydrogels significantly enhanced the pharmacokinetics of two BACSM drugs tested, bortezomib and ganfeborole. The peak concentration of systemic bortezomib was 4-fold lower when released from SABER hydrogels than as bolus injection (Figure 1a). We also observed higher concentrations of systemic ganfeborole after two weeks when released from SABER hydrogels compared to a bolus injection, extending the time it remains above the effective treatment concentration by almost 10-fold (Figure 1b). In a mouse model of tuberculosis, subjects that received ganfeborole loaded in SABER hydrogels saw a 10-fold reduction in tuberculosis colony forming units in their lungs compared to a 10-day oral dosing regimen delivered over 2 weeks (Figure 1c).

Since there are relatively few therapeutics in the market containing boronic acids, we sought to demonstrate that our SABER system can also control the release of small molecules that do not natively contain boronic acids. For this, we modified 1V209, a small molecule toll-like receptor 7 agonist, with phenylboronic acid to create 1V209-PBA and confirmed that it retained its bioactivity in vitro. We then investigated its release characteristics, finding that SABER hydrogels were able to significantly delay the release of 1V209-PBA in vitro (Figure 1d). This highlighted the versatility of this delivery platform as boronic acids can be intentionally added to small molecules to prolong their release from SABER hydrogels.

SABER hydrogels overcome challenges such as burst release and rapid release kinetics of small and uncharged particles from hydrogels. We have demonstrated that modifying MDPs with BABMs allows them to dynamically bond with BACSMs to form boronate esters, prolonging drug release, while retaining the biocompatibility and shear-thinning ability that make MDPs enticing. SABER hydrogels appear to be a versatile drug delivery platform that holds promise for clinical development.

Acknowledgements (Optional):