Using glycosaminoglycan/chemokine interactions for the long-term delivery of 5P12-RANTES in HIV prevention

Improvement of wound healing by the development of ECM-inspired biomaterial coatings and controlled protein release

Implant design has evolved from biochemically inert substrates, minimizing cell and protein interaction, towards sophisticated bioactive substrates, modulating the host response and supporting the regeneration of the injured tissue. Important aspects to consider are the control of cell adhesion, the discrimination of bacteria and non-local cells from the desired tissue cell type, and the stimulation of implant integration and wound healing. Here, the extracellular matrix acts as a role model providing us with inspiration for sophisticated designs. Within this scope, small bioactive peptides have proven to be miscellaneously deployable for the mediation of surface, cell and matrix interactions. Combinations of adhesion ligands, proteoglycans, and modulatory proteins should guide multiple aspects of the regeneration process and cooperativity between the different extracellular matrix components, which bears the chance to maximize the therapeutic efficiency and simultaneously lower the doses. Hence, efforts to include multiple of these factors in biomaterial design are well worth. In the following, multifunctional implant coatings based on bioactive peptides are reviewed and concepts to implement strong surface anchoring for stable cell adhesion and a dynamic delivery of modulator proteins are discussed.

Integrative Model to Coordinate the Oligomerization and Aggregation Mechanisms of CCL5

CC-type chemokine ligand 5 (CCL5) is involved in the pathogenesis of many inflammatory conditions. Under physiological conditions, CCL5 oligomerization and aggregation are considered to be responsible for its inflammatory properties. The structural basis of CCL5 oligomerization remains controversial because the current oligomer models contain no consensus interactions. In this study, NMR and biophysical analyses proposed evidence that the CC-type CCL5 dimer acts as the basic unit to constitute the oligomer and that CCL5 oligomerizes alternatively through E66-K25 and E66-R44/K45 interactions. In addition, a newly determined trimer structure, constituted by CCL5 and the E66S mutant, reported an interfacial interaction through the N-terminal ¹²FAY¹⁴ sequence. The interaction contributes to CCL5 aggregation and precipitation but not to oligomerization. In accordance with the observations, an integrative model explains the CCL5 oligomerization and aggregation mechanism in which CCL5 assembly consists of two types of dimer-dimer interactions and one aggregation mechanism. For full-length CCL5, the molecular accumulation triggers oligomerization through the E66-K25 and E66-R44/K45 interactions, and the ¹²FAY¹⁴ interaction acts as a secondary effect to derive aggregation and precipitation. In contrast, the E66-R44/K45 interaction might dominate in CCL5 N-terminal truncations, and the interaction would lead to the filament-like formation in solution.

Pharmacokinetics of the Protein Microbicide 5P12-RANTES in Sheep following Single-Dose Vaginal Gel Administration

5P12-RANTES, a chemokine analogue that potently blocks the HIV CCR5 coreceptor, is being developed as both a vaginal and rectal microbicide for prevention of sexual transmission of HIV. Here, we report the first pharmacokinetic data for 5P12-RANTES following single-dose vaginal gel administration in sheep. Aqueous gel formulations containing low (1.24-mg/ml), intermediate (6.18-mg/ml), and high (32.0-mg/ml; suspension-type gel) concentrations of 5P12-RANTES were assessed via rheology, syringeability, and in vitro release testing. Following vaginal gel administration to sheep, 5P12-RANTES concentrations were measured in vaginal fluid, vaginal tissue, and serum over a 96-h period. All gels showed non-Newtonian pseudoplastic behavior, with the high-concentration gels exhibiting a greater viscosity and cohesive structure than the intermediate- and low-concentration gels. In in vitro release testing, >90% 5P12-RANTES was released from the low- and intermediate-concentration gels after 72 h. For the high-concentration gel, ∼50% 5P12-RANTES was detected, attributed to protein denaturation during lyophilization and/or subsequent solvation of the protein within the gel matrix. In sheep, 5P12-RANTES concentrations in vaginal fluid, vaginal tissue, and serum increased in a dose-dependent manner. The highest concentrations were measured in vaginal fluid (10⁵ to 10⁷ ng/ml), followed by vaginal tissue (10⁴ to 10⁶ ng/ml). Both of these concentration ranges are several orders of magnitude above the reported half-maximal inhibitory concentrations. The lowest concentration was measured in serum (<10² ng/ml). The 5P12-RANTES pharmacokinetic data are similar to those reported previously for other candidate microbicides. These data, coupled with 5P12-RANTES's potency at picomolar concentrations, its strong barrier to resistance, and the full protection that it was observed to provide in a rhesus macaque vaginal challenge model, support the continued development of 5P12-RANTES as a microbicide.

Glycosaminoglycan Interactions with Chemokines Add Complexity to a Complex System

Chemokines have two types of interactions that function cooperatively to control cell migration. Chemokine receptors on migrating cells integrate signals initiated upon chemokine binding to promote cell movement. Interactions with glycosaminoglycans (GAGs) localize chemokines on and near cell surfaces and the extracellular matrix to provide direction to the cell movement. The matrix of interacting chemokine–receptor partners has been known for some time, precise signaling and trafficking properties of many chemokine–receptor pairs have been characterized, and recent structural information has revealed atomic level detail on chemokine–receptor recognition and activation. However, precise knowledge of the interactions of chemokines with GAGs has lagged far behind such that a single paradigm of GAG presentation on surfaces is generally applied to all chemokines. This review summarizes accumulating evidence which suggests that there is a great deal of diversity and specificity in these interactions, that GAG interactions help fine-tune the function of chemokines, and that GAGs have other roles in chemokine biology beyond localization and surface presentation. This suggests that chemokine–GAG interactions add complexity to the already complex functions of the receptors and ligands.

Local Affinity Release

The use of hydrogels for therapeutic delivery is a burgeoning area of investigation. These water-swollen polymer matrices are ideal platforms for localized drug delivery that can be further combined with specific ligands or nanotechnologies to advance the controlled release of small-molecule drugs and proteins. Due to the advantage of hydrophobic, electrostatic, or specific extracellular matrix interactions, affinity-based strategies can overcome burst release and challenges associated with encapsulation. Future studies will provide innovative binding tools, truly stimuli-responsive systems, and original combinations of emerging technologies to control the release of therapeutics spatially and temporally. Local drug delivery can be achieved by directly injecting a therapeutic to its site of action and is advantageous because off-target effects associated with systemic delivery can be minimized. For prolonged benefit, a vehicle that provides sustained drug release is required. Hydrogels are versatile platforms for localized drug release, owing to the large library of biocompatible building blocks from which they can be formed. Injectable hydrogel formulations that gel quickly in situ and provide sustained release of therapeutics are particularly advantageous to minimize invasiveness. The incorporation of polymers, ligands or nanoparticles that have an affinity for the therapeutic of interest improve control over the release of small-molecule drugs and proteins from hydrogels, enabling spatial and temporal control over the delivery. Such affinity-based strategies can overcome drug burst release and challenges associated with protein instability, allowing more effective therapeutic molecule delivery for a range of applications from therapeutic contact lenses to ischemic tissue regeneration.

Local release from affinity-based polymers increases urethral concentration of the stem cell chemokine CCL7 in rats

The protein chemokine (C-C motif) ligand 7 (CCL7) is significantly over-expressed in urethral and vaginal tissues immediately following vaginal distention in a rat model of stress urinary incontinence. Further evidence, in this scenario and other clinical scenarios, indicates CCL7 stimulates stem cell homing for regenerative repair. This CCL7 gradient is likely absent or compromised in the natural repair process of women who continue to suffer from SUI into advanced age. We evaluated the feasibility of locally providing this missing CCL7 gradient by means of an affinity-based implantable polymer. To engineer these polymers we screened the affinity of different proteoglycans, to use them as CCL7-binding hosts. We found heparin to be the strongest binding host for CCL7 with a 0.323 nM dissociation constant. Our experimental approach indicates conjugation of heparin to a polymer backbone (using either bovine serum albumin or poly (ethylene glycol) as the base polymer) can be used as a delivery system capable of providing sustained concentrations of CCL7 in a therapeutically useful range up to a month in vitro. With this approach we are able to detect, after polymer implantation, significant increase in CCL7 in the urethral tissue directly surrounding the polymer implants with only trace amounts of human CCL7 present in the blood of the animals. Whole animal serial sectioning shows evidence of retention of locally injected human mesenchymal stem cells (hMSCs) only in animals with sustained CCL7 delivery, 2 weeks after affinity-polymers were implanted.

Chemokine and chemokine receptor structure and interactions: implications for therapeutic strategies

The control of cell migration by chemokines involves interactions with two types of receptors: seven transmembrane chemokine-type G protein-coupled receptors and cell surface or extracellular matrix-associated glycosaminoglycans. Coordinated interaction of chemokines with both types of receptors is required for directional migration of cells in numerous physiological and pathological processes. Accumulated structural information, culminating most recently in the structure of a chemokine receptor in complex with a chemokine, has led to a view where chemokine oligomers bind to glycosaminoglycans through epitopes formed when chemokine subunits come together, while chemokine monomers bind to receptors in a pseudo two-step mechanism of receptor activation. Exploitation of this structural knowledge has and will continue to provide important information for therapeutic strategies, as described in this review.