ECM turnover-stimulated gene delivery through collagen-mimetic peptide-plasmid integration in collagen

Growth factors and growth factor gene therapies for treating chronic wounds

Chronic wounds are an unmet clinical need affecting millions of patients globally, and current standards of care fail to consistently promote complete wound closure and prevent recurrence. Disruptions in growth factor signaling, a hallmark of chronic wounds, have led researchers to pursue growth factor therapies as potential supplements to standards of care. Initial studies delivering growth factors in protein form showed promise, with a few formulations reaching clinical trials and one obtaining clinical approval. However, protein-form growth factors are limited by instability and off-target effects. Gene therapy offers an alternative approach to deliver growth factors to the chronic wound environment, but safety concerns surrounding gene therapy as well as efficacy challenges in the gene delivery process have prevented clinical translation. Current growth factor delivery and gene therapy approaches have primarily used single growth factor formulations, but recent efforts have aimed to develop multi-growth factor approaches that are better suited to address growth factor insufficiencies in the chronic wound environment, and these strategies have demonstrated improved efficacy in preclinical studies. This review provides an overview of chronic wound healing, emphasizing the need and potential for growth factor therapies. It includes a summary of current standards of care, recent advances in growth factor, cell-based, and gene therapy approaches, and future perspectives for multi-growth factor therapeutics.

VEGF-Encoding, Gene-Activated Collagen-Based Matrices Promote Blood Vessel Formation and Improved Wound Repair

Disruption in vascularization during wound repair can severely impair healing. Proangiogenic growth factor therapies have shown great healing potential; however, controlling growth factor activity and cellular behavior over desired healing time scales remains challenging. In this study, we evaluated collagen-mimetic peptide (CMP) tethers for their capacity to control growth factor gene transfer and growth factor activity using our recently developed gene-activated hyaluronic acid-collagen matrix (GAHCM). GAHCM was comprised of DNA/polyethyleneimine (PEI) polyplexes that were retained on hyaluronic acid (HA)-collagen hydrogels using CMPs. We hypothesized that using CMP-collagen tethers to control vascular endothelial growth factor-A (VEGF-A) gene delivery in fibroblasts would provide a powerful strategy to modulate the proangiogenic behaviors of endothelial cells (ECs) for blood vessel formation, resulting in enhanced wound repair. In co-culture experiments, we observed that CMP-modified GAHCM induced tunable gene delivery in fibroblasts as predicted, and correspondingly, VEGF-A produced by the fibroblasts led to increased growth and persistent migration of ECs for at least 7 days, as compared to non-CMP-modified GAHCM. Moreover, when ECs were exposed to fibroblast-containing VEGF-GAHCM with higher levels of CMP modification (50% CMP-PEI, or 50 CP), high CD31 expression was stimulated, resulting in the formation of an interconnected EC network with a significantly higher network volume and a larger diameter network structure than controls. Application of VEGF-GAHCM with 50 CP in murine splinted excisional wounds facilitated prolonged prohealing and proangiogenic responses resulting in increased blood vessel formation, improved granulation tissue formation, faster re-epithelialization, and overall enhanced repair. These findings suggest the benefits of CMP-collagen tethers as useful tools to control gene transfer and growth factor activity for improved treatment of wounds.

Biopolymer-Based Wound Dressings with Biochemical Cues for Cell-Instructive Wound Repair

Regenerative medicine is an active research sphere that focuses on the repair, regeneration, and replacement of damaged tissues and organs. A plethora of innovative wound dressings and skin substitutes have been developed to treat cutaneous wounds and are aimed at reducing the length or need for a hospital stay. The inception of biomaterials with the ability to interact with cells and direct them toward desired lineages has brought about innovative designs in wound healing and tissue engineering. This cellular engagement is achieved by cell cues that can be biochemical or biophysical in nature. In effect, these cues seep into innate repair pathways, cause downstream cell behaviours and, ultimately, lead to advantageous healing. This review will focus on biomolecules with encoded biomimetic, instructive prompts that elicit desired cellular domino effects to achieve advanced wound repair. The wound healing dressings covered in this review are based on functionalized biopolymeric materials. While both biophysical and biochemical cues are vital for advanced wound healing applications, focus will be placed on biochemical cues and in vivo or clinical trial applications. The biochemical cues aforementioned will include peptide therapy, collagen matrices, cell-based therapy, decellularized matrices, platelet-rich plasma, and biometals.

Modified hyaluronic acid-collagen matrices trigger efficient gene transfer and prohealing behavior in fibroblasts for improved wound repair

Growth factor therapy has demonstrated great promise for chronic wound repair, but controlling growth factor activity and cell phenotype over desired time frames remains a critical challenge. In this study, we developed a gene-activated hyaluronic acid-collagen matrix (GAHCM) comprising DNA/polyethylenimine (PEI) polyplexes retained on hyaluronic acid (HA)-collagen hydrogels using collagen mimetic peptides (CMPs). We hypothesized that manipulating both the number of CMP-collagen tethers and the ECM composition would provide a powerful strategy to control growth factor gene transfer kinetics while regulating cell behavior, resulting in enhanced growth factor activity for wound repair. We observed that polyplexes with 50% CMP-modified PEI (50 CP) showed enhanced retention of polyplexes in HCM hydrogels by 2.7-fold as compared to non-CMP modified polyplexes. Moreover, the incorporation of HA in the hydrogel promoted a significant increase in gene transfection efficiency based upon analysis of Gaussia luciferase (GLuc) reporter gene expression, and gene expression could be attenuated by blocking HA-CD44 signaling. Furthermore, when fibroblasts were exposed to vascular endothelial growth factor-A (VEGF-A)-GAHCM, the 50 CP matrix facilitated sustained VEGF-A production for up to 7 days, with maximal expression at day 5. Application of these VEGF-A-50 CP samples stimulated prolonged pro-healing responses, including the TGF-β1-induced myofibroblast-like phenotypes and enhanced closure of murine splinted wounds. Overall, these findings demonstrate the use of ECM-based materials to stimulate efficient gene transfer and regulate cellular phenotype, resulting in improved control of growth factor activity for wound repair. GAHCM have significant potential to overcome key challenges in growth factor therapy for regenerative medicine. STATEMENT OF SIGNIFICANCE: Despite great promise for growth factor therapies in wound treatment, controlling growth factor activity and providing a microenvironment for cells that maximizes growth factor signaling have continued to limit the success of existing formulations. Our GAHCM strategy, combining CMP gene delivery and hyaluronic acid-collagen matrix, enabled enhanced wound healing efficacy via the combination of controlled and localized growth factor expression and matrix-mediated regulation of cell behavior. Incorporation of CMPs and HA in the same matrix synergistically enhanced VEGF activity as compared with simpler matrices. Accordingly, GAHCM will advance our ability to leverage growth factor signaling for wound healing, resulting in new long-term treatments for recalcitrant wounds.

Therapeutic nanocarriers comprising extracellular matrix-inspired peptides and polysaccharides

INTRODUCTION

The extracellular matrix (ECM) is vital for cell and tissue development. Given its importance, extensive work has been conducted to develop biomaterials and drug delivery vehicles that capture features of ECM structure and function.

AREAS COVERED

This review highlights recent developments of ECM-inspired nanocarriers and their exploration for drug and gene delivery applications. Nanocarriers that are inspired by or created from primary components of the ECM (e.g. elastin, collagen, hyaluronic acid (HA), or combinations of these) are explicitly covered. An update on current clinical trials employing elastin-like proteins is also included.

EXPERT OPINION

Novel ECM-inspired nanoscale structures and conjugates continue to be of great interest in the materials science and bioengineering communities. Hyaluronic acid nanocarrier systems in particular are widely employed due to the functional activity of HA in mediating a large number of disease states. In contrast, collagen-like peptide nanocarriers are an emerging drug delivery platform with potential relevance to a myriad of ECM-related diseases, making their continued study most pertinent. Elastin-like peptide nanocarriers have a well-established tolerability and efficacy track record in preclinical analyses that has motivated their recent advancement into the clinical arena.

Physical and mechanical cues affecting biomaterial-mediated plasmid DNA delivery: insights into non-viral delivery systems

BACKGROUND

Whilst traditional strategies to increase transfection efficiency of non-viral systems aimed at modifying the vector or the polyplexes/lipoplexes, biomaterial-mediated gene delivery has recently sparked increased interest. This review aims at discussing biomaterial properties and unravelling underlying mechanisms of action, for biomaterial-mediated gene delivery. DNA internalisation and cytoplasmic transport are initially discussed. DNA immobilisation, encapsulation and surface-mediated gene delivery (SMD), the role of extracellular matrix (ECM) and topographical cues, biomaterial stiffness and mechanical stimulation are finally outlined.

MAIN TEXT

Endocytic pathways and mechanisms to escape the lysosomal network are highly variable. They depend on cell and DNA complex types but can be diverted using appropriate biomaterials. 3D scaffolds are generally fabricated via DNA immobilisation or encapsulation. Degradation rate and interaction with the vector affect temporal patterns of DNA release and transgene expression. In SMD, DNA is instead coated on 2D surfaces. SMD allows the incorporation of topographical cues, which, by inducing cytoskeletal re-arrangements, modulate DNA endocytosis. Incorporation of ECM mimetics allows cell type-specific transfection, whereas in spite of discordances in terms of optimal loading regimens, it is recognised that mechanical loading facilitates gene transfection. Finally, stiffer 2D substrates enhance DNA internalisation, whereas in 3D scaffolds, the role of stiffness is still dubious.

CONCLUSION

Although it is recognised that biomaterials allow the creation of tailored non-viral gene delivery systems, there still are many outstanding questions. A better characterisation of endocytic pathways would allow the diversion of cell adhesion processes and cytoskeletal dynamics, in order to increase cellular transfection. Further research on optimal biomaterial mechanical properties, cell ligand density and loading regimens is limited by the fact that such parameters influence a plethora of other different processes (e.g. cellular adhesion, spreading, migration, infiltration, and proliferation, DNA diffusion and release) which may in turn modulate gene delivery. Only a better understanding of these processes may allow the creation of novel robust engineered systems, potentially opening up a whole new area of biomaterial-guided gene delivery for non-viral systems.

Decellularized extracellular matrix scaffolds identify full-length collagen VI as a driver of breast cancer cell invasion in obesity and metastasis

The extracellular matrix (ECM), a major component of the tumor microenvironment, promotes local invasion to drive metastasis. Here, we describe a method to study whole-tissue ECM effects from disease states associated with metastasis on tumor cell phenotypes and identify the individual ECM proteins and signaling pathways that are driving these effects. We show that decellularized ECM from tumor-bearing and obese mammary glands drives TNBC cell invasion. Proteomics of the ECM from the obese mammary gland led us to identify full-length collagen VI as a novel driver of TNBC cell invasion whose abundance in tumor stroma increases with body mass index in human TNBC patients. Last, we describe the mechanism by which collagen VI contributes to TNBC cell invasion via NG2-EGFR cross-talk and MAPK signaling. Overall, these studies demonstrate the value of decellularized ECM scaffolds obtained from tissues to identify novel functions of the ECM.

Enhanced wound healing via collagen-turnover-driven transfer of PDGF-BB gene in a murine wound model

Wound healing is a complex biological process that requires coordinated cell proliferation, migration, and extracellular matrix production/remodeling, all of which are inhibited/delayed in chronic wounds. In this study, a formulation was developed that marries a fibrin-based, provisional-like matrix with collagen mimetic peptide (CMP)/PDGF gene-modified collagens, leading to the formation of robust gels that supported temporally controlled PDGF expression and facile application within the wound bed. Analysis employing in vitro co-gel scaffolds confirmed sustained and temporally controlled gene release based on matrix metalloproteinase (MMP) activity, with ~30% higher PDGF expression in MMP producing fibroblasts as-compared with non-MMP-expressing cells. The integration of fibrin with the gene-modified collagens resulted in co-gels that strongly supported both fibroblast cell recruitment/invasion as well as multiple aspects of the longer-term healing process. The excisional wound healing studies in mice established faster wound closure using CMP-modified PDGF polyplex-loaded co-gels, which exhibited up to 24% more wound closure (achieved with ~2 orders of magnitude lower growth factor dosing) after 9 days as compared to PDGF-loaded co-gels, and 19% more wound closure after 9 days as compared to CMP-free polyplex loaded co-gels. Moreover, minimal scar formation as well as improved collagen production, myofibroblast activity, and collagen orientation was observed following CMP-modified PDGF polyplex-loaded co-gel application on wounds. Taken together, the combined properties of the co-gels, including their stability and capacity to control both cell recruitment and cell phenotype within the murine wound bed, strongly supports the potential of the co-gel scaffolds for improved treatment of chronic non-healing wounds.

Targeted Drug Delivery via the Use of ECM-Mimetic Materials

The use of drug delivery vehicles to improve the efficacy of drugs and to target their action at effective concentrations over desired periods of time has been an active topic of research and clinical investigation for decades. Both synthetic and natural drug delivery materials have facilitated locally controlled as well as targeted drug delivery. Extracellular matrix (ECM) molecules have generated widespread interest as drug delivery materials owing to the various biological functions of ECM. Hydrogels created using ECM molecules can provide not only biochemical and structural support to cells, but also spatial and temporal control over the release of therapeutic agents, including small molecules, biomacromolecules, and cells. In addition, the modification of drug delivery carriers with ECM fragments used as cell-binding ligands has facilitated cell-targeted delivery and improved the therapeutic efficiency of drugs through interaction with highly expressed cellular receptors for ECM. The combination of ECM-derived hydrogels and ECM-derived ligand approaches shows synergistic effects, leading to a great promise for the delivery of intracellular drugs, which require specific endocytic pathways for maximal effectiveness. In this review, we provide an overview of cellular receptors that interact with ECM molecules and discuss examples of selected ECM components that have been applied for drug delivery in both local and systemic platforms. Finally, we highlight the potential impacts of utilizing the interaction between ECM components and cellular receptors for intracellular delivery, particularly in tissue regeneration applications.

Developing Regenerative Treatments for Developmental Defects, Injuries, and Diseases Using Extracellular Matrix Collagen-Targeting Peptides

Collagen is the most widespread extracellular matrix (ECM) protein in the body and is important in maintaining the functionality of organs and tissues. Studies have explored interventions using collagen-targeting tissue engineered techniques, using collagen hybridizing or collagen binding peptides, to target or treat dysregulated or injured collagen in developmental defects, injuries, and diseases. Researchers have used collagen-targeting peptides to deliver growth factors, drugs, and genetic materials, to develop bioactive surfaces, and to detect the distribution and status of collagen. All of these approaches have been used for various regenerative medicine applications, including neovascularization, wound healing, and tissue regeneration. In this review, we describe in depth the collagen-targeting approaches for regenerative therapeutics and compare the benefits of using the different molecules for various present and future applications.

Gene delivery by peptide-assisted transport

The diverse amino acid chemistries and secondary structures in peptides provide 'minimalist' mimics of motifs in proteins and offer many ideal properties for targeted delivery approaches. Several non-viral vectors (polymers and lipids) have been studied for their potential applications in gene delivery. However, non-specific uptake, lack of targeting, inability to escape endosomes, and inefficient nuclear delivery limit their application. Peptide-assisted trafficking of non-viral vectors can potentially overcome these biological barriers to improve gene delivery through targeted uptake using key cell-surface receptors (e.g., integrins, growth factor receptors, and G-protein coupled receptors); membrane disruption for endosomal escape; and nuclear importation. Furthermore, the capacity of peptides to regulate spatio-temporal control over gene delivery opens multi-faceted avenues for effective gene delivery in a variety of complex applications. Rigorous on-going in vitro and in vivo studies utilizing peptides for targeted and microenvironment-sensitive gene delivery could promote their widespread clinical usage.

Fabrication of a nano polymer wrapping Meg3 ShRNA plasmid for the treatment of cerebral infarction

Cerebral infarction is with poorer prognosis and high rates of mortality. After cerebral infarction, the promoting angiogenesis can accelerate the recovery of neurological function. Long non-coding RNA (LncRNA) maternally expressed gene 3 (Meg3) was overexpressed in cerebral infarction area and the knockdown of Meg3 promotes neovascularization and improves nerve function. In this study, we fabricated a nano-polymer wrapped Meg3 short hairpin RNA (ShRNA) plasmid to knockdown Meg3 and conjugated with OX26 antibody (MPO) to realize the brain targeting for the treatment of cerebral infarction. The MPO particle size was 103 ± 11 nm (PDI = 0.27) detected by dynamic light scattering (DLS) and the zeta potential of MPO was -32 mV. MPO achieved brain microvascular endothelial cell (BMEC) targeting and enhanced endothelial cells migration (p < .05), and tube formation (p < .05) in vitro. MPO realized brain tissue target, reduced the volume of cerebral infarction (p < .05) detected by TTC staining, increased capillary density through the HE staining and increased cerebral cortex micro-vessel through immunofluorescence method in vivo. The angiogenesis associated genes Vegfa, and Vegfr2 were upregulated after the treatment of MPO, compared with Meg3 or control plasmid treated group. This study suggested that MPO could achieve brain target and significantly promoted angiogenesis and became a new treatment method for cerebral infarction.

Histone-targeted gene transfer of bone morphogenetic protein-2 enhances mesenchymal stem cell chondrogenic differentiation

Skeletal tissue regeneration following traumatic injury involves a complex cascade of growth factor signals that direct the differentiation of mesenchymal stem cells (MSCs) within the fracture. The necessity for controlled and localized expression of these factors has highlighted the role gene therapy may play as a promising treatment option for bone repair. However, the design of nanocarrier systems that negotiate efficient intracellular trafficking and nuclear delivery represents a significant challenge. Recent investigations have highlighted the roles histone tail sequences play in directing nuclear delivery and activating DNA transcription. We previously established the ability to recapitulate these natural histone tail activities within non-viral nanocarriers, improving gene transfer and expression by enabling effective navigation to the nucleus via retrograde vesicular trafficking. Herein, we demonstrate that histone-targeting leads to ∼4-fold enhancements in osteogenic bone morphogenetic protein-2 (BMP-2) expression by MSCs over 6 days, as compared with standard polymeric transfection reagents. This improved expression augmented chondrogenesis, an essential first step in fracture healing. Importantly, significant enhancements of cartilage-specific protein expression were triggered by histone-targeted gene transfer, as compared with the response to treatment with equivalent amounts of recombinant BMP-2 protein. In fact, an ∼100-fold increase in recombinant BMP-2 was required to achieve similar levels of chondrogenic gene and protein expression. The enhancements in differentiation achieved using histone-targeting were in part enabled by an increase in transcription factor expression, which functioned to drive MSC chondrogenesis. These novel findings demonstrate the utility of histone-targeted gene transfer strategies to enable substantial reductions in BMP-2 dosing for bone regenerative applications.

STATEMENT OF SIGNIFICANCE

This contribution addresses significant limitations in non-viral gene transfer for bone regenerative applications by exploiting a novel histone-targeting approach for cell-triggered delivery that induces osteogenic BMP-2 expression coincident with the initiation of bone repair. During repair, proliferating MSCs respond to a complex series of growth factor signals that direct their differentiation along cellular lineages essential to mature bone formation. Although these MSCs are ideal targets for enhanced transfection during cellular mitosis, few non-viral delivery approaches exist to enable maximization of this effect. Accordingly, this contribution seeks to utilize our histone-targeted nanocarrier design strategy to stimulate BMP-2 gene transfer in dividing MSCs. This gene-based approach leads to significantly augmented MSC chondrogenesis, an essential first step in bone tissue repair.

Integration of growth factor gene delivery with collagen-triggered wound repair cascades using collagen-mimetic peptides

Growth factors (GFs) play vital roles in wound repair. Many GF therapies have reached clinical trials, but success has been hindered by safety concerns and a lack of efficacy. Previously, we presented an approach to produce protein factors in wound beds through localized gene delivery mediated by biomimetic peptides. Modification of polyethylenimine (PEI) DNA polyplexes with collagen-mimetic peptides (CMPs) enabled tailoring of polyplex release/retention and improved gene transfer activity in a cell-responsive manner. In this work, CMP-mediated delivery from collagen was shown to improve expression of platelet-derived growth factor-BB (PDGF-BB) and promote a diverse range of cellular processes associated with wound healing, including proliferation, extracellular matrix production, and chemotaxis. Collagens were pre-exposed to physiologically-simulating conditions (complete media, 37°C) for days to weeks prior to cell seeding to simulate the environment within typical wound dressings. In cell proliferation studies, significant increases in cell counts were demonstrated in collagen gels containing CMP-modified polyplex versus unmodified polyplex, and these effects became most pronounced following prolonged preincubation periods of greater than a week. Collagen containing CMP-modified polyplexes also induced a twofold increase in gel contraction as well as enhanced directionality and migratory activity in response to cell-secreted PDGF-BB gradients. While these PDGF-BB-triggered behaviors were observed in collagens containing unmodified polyplexes, the responses withstood much longer preincubation periods in CMP-modified polyplex samples (10 days vs. <5 days). Furthermore, enhanced closure rates in an in vitro wound model suggested that CMP-based PDGF-BB delivery may have utility in actual wound repair and other regenerative medicine applications.