Layer-by-Layer Polymer Functionalization Improves Nanoparticle Penetration and Glioblastoma Targeting in the Brain.

Glioblastoma is characterized by diffuse infiltration into surrounding healthy brain tissues, which makes it challenging to treat. Complete surgical resection is often impossible, and systemically delivered drugs cannot achieve adequate tumor exposure to prevent local recurrence. Convection-enhanced delivery (CED) offers a method for administering therapeutics directly into brain tumor tissue, but its impact has been limited by rapid clearance and off-target cellular uptake. Nanoparticle (NP) encapsulation presents a promising strategy for extending the retention time of locally delivered therapies while specifically targeting glioblastoma cells. However, the brain's extracellular structure poses challenges for NP distribution due to its narrow, tortuous pores and a harsh ionic environment. In this study, we investigated the impact of NP surface chemistry using layer-by-layer (LbL) assembly to design drug carriers for broad spatial distribution in brain tissue and specific glioblastoma cell targeting. We found that poly-l-glutamate and hyaluronate were effective surface chemistries for targeting glioblastoma cells in vitro. Coadsorbing either polymer with a small fraction of PEGylated polyelectrolytes improved the colloidal stability without sacrificing cancer cell selectivity. Following CED in vivo, gadolinium-functionalized LbL NPs enabled MRI visualization and exhibited a distribution volume up to three times larger than liposomes and doubled the retention half-time up to 13.5 days. Flow cytometric analysis of CED-treated murine orthotopic brain tumors indicated greater cancer cell uptake and reduced healthy cell uptake for LbL NPs compared to nonfunctionalized liposomes. The distinct cellular outcomes for different colayered LbL NPs provide opportunities to tailor this modular delivery system for various therapeutic applications.

Surface Presentation of Hyaluronic Acid Modulates Nanoparticle-Cell Association.

Nanoparticle (NP) drug carriers have revolutionized medicine and increased patient quality of life. Clinically approved formulations typically succeed because of reduced off-target toxicity of the cargo. However, increasing carrier accumulation at disease sites through precise targeting remains one of the biggest challenges in the field. Novel multivalent ligand presentations and self-assembled constructs can enhance cell association, but an inability to draw direct comparisons across formulations has hindered progress. Furthermore, how nanoparticle structure influences function often is unclear. In this report, we leverage the well-characterized hyaluronic acid (HA)-CD44 binding pair to investigate how the surface architecture of modified NPs impacts their association with ovarian cancer cells that overexpress CD44. We functionalized anionic liposomes with 5 kDa HA by either covalent conjugation via surface coupling or electrostatic self-assembly using the layer-by-layer (LbL) adsorption method. Comparing these two methods, we observed a consistent enhancement of NP-cell association with the self-assembly LbL technique, particularly with higher molecular weight (≥10 kDa) HA. To further optimize association, we increased the surface-available HA. We synthesized a bottlebrush glycopolymer composed of a polynorbornene backbone and pendant 5 kDa HA and layered this macromolecule onto NPs. Flow cytometry revealed that the LbL HA bottlebrush NP outperformed the LbL linear display of HA. Cellular visualization by deconvolution optical microscopy corroborated results from all three constructs. Using exogenous HA to block NP-CD44 interactions, we found the LbL HA bottlebrush NP had a 4-fold higher binding avidity than the best-performing LbL linear HA NP. We further observed that decreasing the density of HA bottlebrush side chains to 75% had minimal impact on LbL NP stability or cell association, though we did see a reduction in binding avidity with this side-chain-modified NP. Our studies indicate that LbL surfaces are highly effective for multivalent displays, and the mode in which they present a targeting ligand can be optimized for NP cell targeting.

Directed Evolution Enables Simultaneous Controlled Release of Multiple Therapeutic Proteins from Biopolymer-Based Hydrogels.

With the advent of increasingly complex combination strategies of biologics, independent control over their delivery is the key to their efficacy; however, current approaches are hindered by the limited independent tunability of their release rates. To overcome these limitations, directed evolution is used to engineer highly specific, low affinity affibody binding partners to multiple therapeutic proteins to independently control protein release rates. As a proof-of-concept, specific affibody binding partners for two proteins with broad therapeutic utility: insulin-like growth factor-1 (IGF-1) and pigment epithelium-derived factor (PEDF) are identified. Protein-affibody binding interactions specific to these target proteins with equilibrium dissociation constants (KD ) between 10-7 and 10-8 m are discovered. The affibodies are covalently bound to the backbone of crosslinked hydrogels using click chemistry, enabling sustained, independent, and simultaneous release of bioactive IGF-1 and PEDF over 7 days. The system is tested with C57BL/6J mice in vivo, and the affibody-controlled release of IGF-1 results in sustained activity when compared to bolus IGF-1 delivery. This work demonstrates a new, broadly applicable approach to tune the release of therapeutic proteins simultaneously and independently and thus the way for precise control over the delivery of multicomponent therapies is paved.

Reengineering biocatalysts: Computational redesign of chondroitinase ABC improves efficacy and stability.

Maintaining biocatalyst stability and activity is a critical challenge. Chondroitinase ABC (ChABC) has shown promise in central nervous system (CNS) regeneration, yet its therapeutic utility is severely limited by instability. We computationally reengineered ChABC by introducing 37, 55, and 92 amino acid changes using consensus design and forcefield-based optimization. All mutants were more stable than wild-type ChABC with increased aggregation temperatures between 4° and 8°C. Only ChABC with 37 mutations (ChABC-37) was more active and had a 6.5 times greater half-life than wild-type ChABC, increasing to 106 hours (4.4 days) from only 16.8 hours. ChABC-37, expressed as a fusion protein with Src homology 3 (ChABC-37-SH3), was active for 7 days when released from a hydrogel modified with SH3-binding peptides. This study demonstrates the broad opportunity to improve biocatalysts through computational engineering and sets the stage for future testing of this substantially improved protein in the treatment of debilitating CNS injuries.

Inverse Electron-Demand Diels-Alder Methylcellulose Hydrogels Enable the Co-delivery of Chondroitinase ABC and Neural Progenitor Cells.

A hydrogel that can deliver both proteins and cells enables the local microenvironment of transplanted cells to be manipulated with a single injection. Toward this goal, we designed a hydrogel suitable for the co-delivery of neural stem cells and chondroitinase ABC (ChABC), a potent enzyme that degrades the glial scar that forms after central nervous system (CNS) injury. We leveraged the inverse electron-demand Diels-Alder reaction between norbornene and methylphenyltetrazine to form rapidly gelling (<15 min) crosslinked methylcellulose (MC) hydrogels at physiological temperature and pH, with Young's modulus similar to that of brain tissue (1-3 kPa), and degradable, disulfide-containing crosslinkers. To achieve tunable, affinity-controlled release of a ChABC-Src homology 3 (SH3) fusion protein, we immobilized norbornene-functionalized SH3-binding peptides onto MC-methylphenyltetrazine and observed release of bioactive ChABC-SH3 over 4 days. We confirmed cytocompatibility by evaluating neural progenitor cell survival and proliferation. The combined encapsulation of neural stem cells and chondroitinase ABC from one hydrogel lays the framework for future in vivo studies to treat CNS injuries.

Local delivery of stabilized chondroitinase ABC degrades chondroitin sulfate proteoglycans in stroke-injured rat brains.

Central nervous system (CNS) injuries, such as stroke and spinal cord injuries, result in the formation of a proteoglycan-rich glial scar, which acts as a barrier to axonal regrowth and limits the regenerative capacity of the CNS. Chondroitinase ABC (ChABC) is a potent bacterial enzyme that degrades the chondroitin sulfate proteoglycan (CSPG) component of the glial scar and promotes tissue recovery; however, its use is significantly limited by its inherent instability at physiological temperatures. Here, we demonstrate that ChABC can be stabilized using site-directed mutagenesis and covalent modification with poly(ethylene glycol) chains (i.e. PEGylation). Rosetta protein structure modeling was used to screen >20,000 single point mutations, and four potentially stabilizing mutations were tested in vitro. One of the mutations, N1000G (asparagine ➔ glycine at residue 1000), significantly improved the long-term activity of the protein, doubling its functional half-life. PEGylation of this ChABC mutant inhibited unfolding and aggregation and resulted in prolonged bioactivity with a 10-fold increase in activity compared to the unmodified protein after two days. Local, affinity-controlled release of the modified protein (PEG-N1000G-ChABC) was achieved by expressing it as a fusion protein with Src homology 3 (SH3) and delivering the protein from a methylcellulose hydrogel modified with SH3 binding peptides. This affinity-based release strategy provided sustained PEG-N1000G-ChABC-SH3 release over several days in vitro. Direct implantation of the hydrogel delivery vehicle containing stabilized PEG-N1000G-ChABC-SH3 onto the rat brain cortex in a sub-acute model of stroke resulted in significantly reduced CSPG levels in the penumbra of 49% at 14 and 40% at 28 days post-injury compared to animals treated with the vehicle alone.