FGF2-Targeted adenovirus encoding platelet-derived growth factor-B enhances de novo tissue formation

Future Drug Targets in Periodontal Personalised Medicine—A Narrative Review

Periodontal disease is an infection-driven inflammatory disease characterized by the destruction of tooth-supporting tissues. The establishment of chronic inflammation will result in progressive destruction of bone and soft tissue changes. Severe periodontitis can lead to tooth loss. The disease has complex pathogenesis with an interplay between genetic, environmental, and host factors and pathogens. Effective management consists of plaque control and non-surgical interventions, along with adjuvant strategies to control inflammation and disrupt the pathogenic subgingival biofilms. Recent studies have examined novel approaches for managing periodontal diseases such as modulating microbial signaling mechanisms, tissue engineering, and molecular targeting of host inflammatory substances. Mounting evidence suggests the need to integrate omics-based approaches with traditional therapy to address the disease. This article discusses the various evolving and future drug targets, including proteomics, gene therapeutics, vaccines, and nanotechnology in personalized periodontal medicine for the effective management of periodontal diseases.

Tumor-Associated Fibroblast-Targeting Nanoparticles for Enhancing Solid Tumor Therapy: Progress and Challenges

Even though nanoparticle drug delivery systems (nanoDDSs) have improved antitumor efficacy by delivering more drugs to tumor sites compared to free and unencapsulated therapeutics, achieving satisfactory distribution and penetration of nanoDDSs inside solid tumors, especially in stromal fibrous tumors, remains challenging. As one of the most common stromal cells in solid tumors, tumor-associated fibroblasts (TAFs) not only promote tumor growth and metastasis but also reduce the drug delivery efficiency of nanoparticles through the tumor's inherent physical and physiological barriers. Thus, TAFs have been emerging as attractive targets, and TAF-targeting nanotherapeutics have been extensively explored to enhance the tumor delivery efficiency and efficacy of various anticancer agents. The purpose of this Review is to opportunely summarize the underlying mechanisms of TAFs on obstructing nanoparticle-mediated drug delivery into tumors and discuss the current advances of a plethora of nanotherapeutic approaches for effectively targeting TAFs.

The pharmacology of plant virus nanoparticles

The application of nanoparticles for medical purposes has made enormous strides in providing new solutions to health problems. The observation that plant virus-based nanoparticles (VNPs) can be repurposed and engineered as smart bio-vehicles for targeted drug delivery and imaging has launched extensive research for improving the therapeutic and diagnostic management of various diseases. There is evidence that VNPs are promising high value nanocarriers with potential for translational development. This is mainly due to their unique features, encompassing structural uniformity, ease of manufacture and functionalization by means of expression, chemical biology and self-assembly. While the development pipeline is moving rapidly, with many reports focusing on engineering and manufacturing aspects to tailor the properties and efficacy of VNPs, fewer studies have focused on gaining insights into the nanotoxicity of this novel platform nanotechnology. Herein, we discuss the pharmacology of VNPs as a function of formulation and route of administration. VNPs are reviewed in the context of their application as therapeutic adjuvants or nanocarrier excipients to initiate, enhance, attenuate or impede the formulation's toxicity. The summary of the data however also underlines the need for meticulous VNP structure-nanotoxicity studies to improve our understanding of their in vivo fates and pharmacological profiles to pave the way for translation of VNP-based formulations into the clinical setting.

Is Viral Vector Gene Delivery More Effective Using Biomaterials?

Gene delivery has been extensively investigated for introducing foreign genetic material into cells to promote expression of therapeutic proteins or to silence relevant genes. This approach can regulate genetic or epigenetic disorders, offering an attractive alternative to pharmacological therapy or invasive protein delivery options. However, the exciting potential of viral gene therapy has yet to be fully realized, with a number of clinical trials failing to deliver optimal therapeutic outcomes. Reasons for this include difficulty in achieving localized delivery, and subsequently lower efficacy at the target site, as well as poor or inconsistent transduction efficiency. Thus, ongoing efforts are focused on improving local viral delivery and enhancing its efficiency. Recently, biomaterials have been exploited as an option for more controlled, targeted and programmable gene delivery. There is a growing body of literature demonstrating the efficacy of biomaterials and their potential advantages over other delivery strategies. This review explores current limitations of gene delivery and the progress of biomaterial-mediated gene delivery. The combination of biomaterials and gene vectors holds the potential to surmount major challenges, including the uncontrolled release of viral vectors with random delivery duration, poorly localized viral delivery with associated off-target effects, limited viral tropism, and immune safety concerns.

Localised non-viral delivery of nucleic acids for nerve regeneration in injured nervous systems

Axons damaged by traumatic injuries are often unable to spontaneously regenerate in the adult central nervous system (CNS). Although the peripheral nervous system (PNS) has some regenerative capacity, its ability to regrow remains limited across large lesion gaps due to scar tissue formation. Nucleic acid therapy holds the potential of improving regeneration by enhancing the intrinsic growth ability of neurons and overcoming the inhibitory environment that prevents neurite outgrowth. Nucleic acids modulate gene expression by over-expression of neuronal growth factor or silencing growth-inhibitory molecules. Although in vitro outcomes appear promising, the lack of efficient non-viral nucleic acid delivery methods to the nervous system has limited the application of nucleic acid therapeutics to patients. Here, we review the recent development of efficient non-viral nucleic acid delivery platforms, as applied to the nervous system, including the transfection vectors and carriers used, as well as matrices and scaffolds that are currently used. Additionally, we will discuss possible improvements for localised nucleic acid delivery.

Gene delivery from polymer scaffolds for tissue engineering

The combination of gene therapy with tissue engineering offers the potential to direct progenitor cell proliferation and differentiation into functional tissue replacements. Many approaches to engineering tissue replacements feature a polymer scaffold to create and maintain a space, support cell adhesion, and organize tissue formation. Polymer scaffolds, either natural, synthetic, or a combination of the two, have also been adapted to serve as delivery vehicles for viral and nonviral vectors, which can induce the expression of tissue inductive factors. Gene delivery is a versatile approach, capable of targeting any cellular process through localized expression of tissue inductive factors. The design and application of tissue engineering scaffolds for localized gene transfer are reviewed. Scaffolds are designed either to release the vector into the local tissue environment or maintain the vector at the polymer surface, which is regulated by the effective affinity of the vector for the polymer. Polymeric delivery can enhance gene transfer locally, promote and extend transgene expression, avoid vector distribution to distant tissues, and reduce the immune response to the vector. Scaffolds capable of controlled DNA delivery can provide a fundamental tool for directing progenitor cell function, which has applications with the engineering of numerous types of tissue. The utility of this approach will increase with the development of design parameters that correlate release and transgene expression, and with continued research into the biology of tissue formation.

A slow-release fibrin matrix increases adeno-associated virus transduction of wound repair cells in vivo

Virus-mediated gene therapy is a promising strategy for numerous tissue engineering applications. Fibrin-based scaffolds have been previously used as vehicles for localised delivery of adenovirus to wound sites. However, their utility in the delivery of adeno-associated viruses to wound repair cells has not yet been determined. The influence of fibrin concentration on efficacy of delivery of AAV-2 to wound tissue was assessed in this study. Fibrin scaffolds containing recombinant AAV-2 encoding for β-galactosidase were polymerised in porous polyurethane discs and implanted subcutaneously in rats. A fibrin scaffold with a concentration of 50 mg/ml showed significantly elevated levels of β-galactosidase activity within explanted discs at 10 days compared to 10 mg/ml and 25 mg/ml fibrin. These findings inform efforts to optimise biodegradable scaffolds for the localised delivery of AAV in tissue engineering.

Tissue engineering and regenerative medicine -where do we stand?

Tissue Engineering (TE) in the context of Regenerative Medicine (RM) has been hailed for many years as one of the most important topics in medicine in the twenty-first century. While the first clinically relevant TE efforts were mainly concerned with the generation of bioengineered skin substitutes, subsequently TE applications have been continuously extended to a wide variety of tissues and organs. The advent of either embryonic or mesenchymal adult stem-cell technology has fostered many of the efforts to combine this promising tool with TE approaches and has merged the field into the term Regenerative Medicine. As a typical example in translational medicine, the discovery of a new type of cells called Telocytes that have been described in many organs and have been detected by electron microscopy opens another gate to RM. Besides cell-therapy strategies, the application of gene therapy combined with TE has been investigated to generate tissues and organs. The vascularization of constructs plays a crucial role besides the matrix and cell substitutes. Therefore, novel in vivo models of vascularization have evolved allowing axial vascularization with subsequent transplantation of constructs. This article is intended to give an overview over some of the most recent developments and possible applications in RM through the perspective of TE achievements and cellular research. The synthesis of TE with innovative methods of molecular biology and stem-cell technology appears to be very promising.

Controlled delivery of recombinant adeno-associated virus serotype 2 using pH-sensitive poly(ethylene glycol)-poly-L-histidine hydrogels

Loading of viral vectors in synthetic polymers is a promising strategy for overcoming hurdles associated with viral gene delivery. For enhanced gene expression at a specific site, gene transfer by using hydrogels represents a versatile approach. In this study, adeno-associated virus serotype 2 containing the green fluorescent protein gene (rAAV2-GFP) were loaded into poly(ethylene glycol) (PEG) hydrogels, with and without incorporation of poly-L-hisditine (polyHis). Inclusion of polyHis created pH responsive hydrogels in a physiological range of tissues, containing the damaged vasculature and activated phagocytosis. The fraction of polyHis used controlled the degree of swelling, water uptake and subsequent degradation of the hydrogels and release rate of rAAV2-GFP. The swelling ratio of the PEG-polyHis hydrogels increased inversely with environment pH. As pH declined from 7.4 to 6.0, PEG-polyHis hydrogel swelling ratio and degradation rate increased 875% and 135%, respectively. As a result, release and transduction efficiency of the rAAV2-GFP from PEG-polyHis hydrogel in human HT-1080 fibrosarcoma cells increased significantly compared to a PEG hydrogel. Transduction rate can be controlled by the hydrogels' polyHis concentration and is sensitive to localized decreases in pH consistent with inflammation. This is relevant to optimizing parameters for wound care and regenerative medicine applications.

Dual-targeting non-viral vector based on polyethylenimine improves gene transfer efficiency

Polyethylenimine (PEI) is the polymer most commonly used for transferring plasmids into eukaryotes, but its gene-transfer efficiency is lower compared to viral vectors. Receptors targeting PEI combined with ligands can enhance efficiency of gene transfer into the corresponding receptor-positive cells. Using the double-receptor-mediated pathway of viral infection, in this study we synthesized a novel non-viral vector based on PEI combined with two peptides recognizing FGF receptors (peptide YC25) and integrins (peptide CP9) on the cell surface. The dual targeting vector showed a physicochemical character similar to that of PEI, such as pDNA formation, particle size, zeta potential and lower toxicity. In vitro gene transfer showed that the dual-receptor targeted vector (YC25-PEI-CP9) exhibited a markedly higher transgene efficiency in cell lines with positive expression of FGF receptors and integrins, compared with single-peptide-modified PEI or unmodified PEI. In the cells with only integrin-positive expression, YC25-PEI-CP9 mediated a higher transgene expression than PEI but lower than CP9-PEI. The corresponding free peptides could inhibit the transgene efficiency of the peptide-coupled PEI. In vivo gene transfer in tumor-bearing nude mice also demonstrated that the dual-targeting vectors showed a significantly enhanced transfection efficiency in tumors with positive expression of FGF receptors and integrins. The synthesized polymer YC25-PEI-CP9 has the prospect to act as a novel kind of non-viral vector in gene therapy.

Silk-elastinlike protein polymers improve the efficacy of adenovirus thymidine kinase enzyme prodrug therapy of head and neck tumors

BACKGROUND

Adenoviral-directed enzyme prodrug therapy is a promising approach for head and neck cancer gene therapy. The challenges faced by this approach, however, comprise transient gene expression and dissemination of viruses to distant organs.

METHODS

We used recombinant silk-elastinlike protein polymer (SELP) matrices for intratumoral delivery of adenoviruses containing both thymidine kinase-1 and luciferase genes in a nude mouse model of JHU-022 head and neck tumor. Hydrogels made from two SELP analogues (47K and 815K), with similar silk to elastinlike block ratios but different block lengths, were studied for intratumoral viral delivery. Tumor-bearing mice were followed up for tumor progression and luciferase gene expression concomitantly for 5 weeks. Polymer safety was evaluated through body weight change, blood count, and liver and kidney functions, in addition to gross and microscopic histological examination.

RESULTS

SELP-815K analogues efficiently controlled the duration and extent of transfection in tumors for up to 5 weeks with no detectable spread to the liver. An approximately five-fold greater reduction in tumor volume was obtained with matrix-mediated delivery compared to intra-tumoral injection of adenoviruses in saline. SELP matrix proved safe in all injected mice compared to the control group.

CONCLUSIONS

The SELP-controlled gene delivery approach could potentially improve the anticancer activity of virus-mediated gene therapy at the same time as limiting viral spread to normal organs.

Fibrin-mediated lentivirus gene transfer: implications for lentivirus microarrays

We employed fibrin hydrogel as a bioactive matrix for lentivirus mediated gene transfer. Fibrin-mediated gene transfer was highly efficient and exhibited strong dependence on fibrinogen concentration. Efficient gene transfer was achieved with fibrinogen concentration between 3.75 and 7.5mg/ml. Lower fibrinogen concentrations resulted in diffusion of virus out of the gel while higher concentrations led to ineffective fibrin degradation by target cells. Addition of fibrinolytic inhibitors decreased gene transfer in a dose-dependent manner suggesting that fibrin degradation by target cells may be necessary for successful gene delivery. Under these conditions transduction may be limited only to cells interacting with the matrix thereby providing a method for spatially-localized gene delivery. Indeed, when lentivirus-containing fibrin microgels were spotted in an array format gene transfer was confined to virus-containing fibrin spots with minimal cross-contamination between neighboring sites. Collectively, our data suggest that fibrin may provide an effective matrix for spatially-localized gene delivery with potential applications in high-throughput lentiviral microarrays and in regenerative medicine.

Adenovirus encoding human platelet-derived growth factor-B delivered to alveolar bone defects exhibits safety and biodistribution profiles favorable for clinical use

Platelet-derived growth factor (PDGF) gene therapy offers promise for tissue engineering of tooth-supporting alveolar bone defects. To date, limited information exists regarding the safety profile and systemic biodistribution of PDGF gene therapy vectors when delivered locally to periodontal osseous defects. The aim of this preclinical study was to determine the safety profile of adenovirus encoding the PDGF-B gene (AdPDGF-B) delivered in a collagen matrix to periodontal lesions. Standardized alveolar bone defects were created in rats, followed by delivery of matrix alone or containing AdPDGF-B at 5.5 x 10(8) or 5.5 x 10(9) plaque-forming units/ml. The regenerative response was confirmed histologically. Gross clinical observations, hematology, and blood chemistries were monitored to evaluate systemic involvement. Bioluminescence and quantitative polymerase chain reaction were used to assess vector biodistribution. No significant histopathological changes were noted during the investigation. Minor alterations in specific hematological and blood chemistries were seen; however, most parameters were within the normal range for all groups. Bioluminescence analysis revealed vector distribution at the axillary lymph nodes during the first 2 weeks with subsequent return to baseline levels. AdPDGF-B was well contained within the localized osseous defect area without viremia or distant organ involvement. These results indicate that AdPDGF-B delivered in a collagen matrix exhibits acceptable safety profiles for possible use in human clinical studies.

Lentivirus immobilization to nanoparticles for enhanced and localized delivery from hydrogels

Hydrogels can provide a controllable cell microenvironment for numerous applications in regenerative medicine, and delivery of gene therapy vectors can be employed to enhance their bioactivity. We investigated the delivery of lentiviral vectors from hydrogels, and employed the immobilization of lentivirus to hydroxylapatite (HA) nanoparticles as a means to retain and stabilize vectors within hydrogels, and thereby increase delivery efficiency. Entrapment of the vector alone within the hydrogel maintained the activity of the virus more effectively compared to the absence of a hydrogel, and release was slowed with an increasing solid content of the hydrogel. Association of the lentivirus with HA increased the activity of the complexes, with HA increasing the virus activity for 72 hours. Cells seeded onto lentivirus-HA-loaded hydrogels had a decreased number of infected cells outside of the hydrogel relative to the absence of HA. In vivo studies with collagen hydrogels loaded with lentivirus and HA-lentivirus demonstrated sustained and localized transgene expression for at least 4 weeks, with increased expression using the lentivirus-HA complex. This strategy of nanoparticle immobilization to stabilize and retain vectors is broadly applicable to hydrogels, and may provide a versatile tool to combine gene therapy and biomaterials for applications in regenerative medicine.

The noninvasive, quantitative, in vivo assessment of adenoviral-mediated gene delivery in skin wound biomaterials

Because there are few reports using gene delivery in clinically-approved synthetic matrices, we examined the feasibility of using a noninvasive imaging system to study the kinetics of luciferase gene expression when delivered in an adenoviral vector. Using a mouse model of full thickness injury, we quantified the kinetics of gene expression, determined the optimal dose of particle delivery, and established the temporal importance of drug delivery in obtaining optimal gene expression. Specifically, we found that the ideal time to deliver adenovirus to a graft is during the early phase of graft wound closure (days 0-3 post-operatively) for a peak of gene expression to occur 7 days after delivery. Under these conditions, there is a saturating dose of 6 x 10(8) adenoviral particles per graft. In light of these findings, we examined whether the efficacy of delivery could be increased by modulating the composition of the grafts. When a collagen gene-activated matrix (GAM) containing basic fibroblast growth factor (FGF2) was compared to matrix alone, a significant increase in gene expression is observed when identical amounts of vector are delivered (p<0.05). Taken together, these results show how a noninvasive and quantitative assessment of gene expression can be used to optimize gene delivery and that the composition of matrices can dramatically influence gene expression in the wound bed.

Polymers for viral gene delivery

BACKGROUND

The development of viral vectors capable of providing efficient gene transfer in diseased tissues without causing any pathogenic effects is pivotal for overcoming the many challenges facing gene therapy.

OBJECTIVE

Immune responses against viral vectors, inadequate gene expression and inefficient targeting to specific cells in vivo are some of the major problems limiting the clinical utility of viral gene therapy.

METHODS

This review will focus on recent progress in strategic polymer-based modifications to improve the performance and biocompatibility of a variety of viral vectors. We will discuss the preclinical development of four approaches involving injectable polymers, polyelectrolytes, polymer microspheres and polymer-virus conjugates.

RESULTS/CONCLUSION

Much progress has been made in creating 'hybrid' gene delivery vectors that combine the strengths of polymers and viruses. With further optimization, these hybrid vectors, which may be safer and more effective, are likely to succeed in clinical applications.

The use of therapeutic gene eNOS delivered via a fibrin scaffold enhances wound healing in a compromised wound model

Diabetic healing is marked by a reduced nitric oxide (NO) production at the wound site. This study aimed to investigate whether a fibrin scaffold would enhance the delivery of adenovirus encoding endothelial nitric oxide synthase (eNOS), one of the enzymes responsible for NO production, resulting in more NO production, and enhanced healing. An alloxan rabbit ear ulcer model was used to investigate healing, in response to the following treatments: fibrin containing AdeNOS, AdeNOS alone, fibrin alone and no treatment. Immunohistochemistry to detect eNOS expression and histological evaluation of healing were assessed at 7 and 14 days. eNOS expression was significantly greater in the fibrin containing AdeNOS group at 14 days compared to all other groups. Furthermore, this group showed a significantly faster rate of epithelialisation than all other groups. The volume of inflammatory cells was highest in the fibrin containing AdeNOS group at 7 days, which dropped significantly by 14 days. Likewise, the surface area and length of vessels reduced significantly in the fibrin containing AdeNOS group between 7 and 14 days indicating tissue remodelling, but remained stable in all other groups. Regression analysis showed that the epithelialisation rate was significantly affected by change in eNOS expression, inflammation, and surface area and length of vessels over time in the fibrin containing AdeNOS group. It was concluded that fibrin delivery of AdeNOS resulted in enhanced eNOS expression, inflammatory response, and a faster rate of re-epithelialisation.

Creating thick linear scar by inserting a gelatin sponge into rat excisional wounds

The rat incisional wound is an important model for wound scarring research, but it is also difficult to mimic thick human incisional scarring. We hypothesized that such a thick linear scarring can be generated by inserting a gelatin sponge into a rat excisional wound. The results demonstrated that the new wound model could generate 11 times wider wound width (at day 7) and 4-5 times wider scar width (at days 14, 21, and 60), respectively, than the widths of incisional wounds (p<0.05) in adult Sprague-Dawley rats. The thick linear scar created was grossly apparent in contrast to the grossly unobvious scar of the incisional wound, and a regular linear shape could be achieved with a similar scar width along the wound. The mechanism study revealed several factors that might contribute to the enhanced scarring, including delayed wound healing, enhanced inflammation, increased expression of fibrotic factors, and abnormal wound remodeling due to the insertion of the gelatin sponge. These results indicate that the new wound model of thick linear scar might be valuable for clinically relevant study of scar manipulation. Moreover, this model may serve as a tool for studying gene-mediated tissue regeneration during wound repair using inserted gelatin sponge as a gene carrier.

Gene transfer strategies in tissue engineering

Aiming for regeneration of severed or lost parts of the body, the combined application of gene therapy and tissue engineering has received much attention by regenerative medicine. Techniques of molecular biology can enhance the regenerative potential of a biomaterial by co-delivery of therapeutic genes, and several different strategies have been used to achieve that goal. Possibilities for application are many-fold and have been investigated to regenerate tissues such as skin, cartilage, bone, nerve, liver, pancreas and blood vessels. This review discusses advantages and problems encountered with the different gene delivery strategies as far as they relate to tissue engineering, analyses the positive aspects of polymeric gene delivery from matrices and discusses advances and future challenges of gene transfer strategies in selected tissues.

Matrices and scaffolds for DNA delivery in tissue engineering

Regenerative medicine aims to create functional tissue replacements, typically through creating a controlled environment that promotes and directs the differentiation of stem or progenitor cells, either endogenous or transplanted. Scaffolds serve a central role in many strategies by providing the means to control the local environment. Gene delivery from the scaffold represents a versatile approach to manipulating the local environment for directing cell function. Research at the interface of biomaterials, gene therapy, and drug delivery has identified several design parameters for the vector and the biomaterial scaffold that must be satisfied. Progress has been made towards achieving gene delivery within a tissue engineering scaffold, though the design principles for the materials and vectors that produce efficient delivery require further development. Nevertheless, these advances in obtaining transgene expression with the scaffold have created opportunities to develop greater control of either delivery or expression and to identify the best practices for promoting tissue formation. Strategies to achieve controlled, localized expression within the tissue engineering scaffold will have broad application to the regeneration of many tissues, with great promise for clinical therapies.

In vitro chondrogenesis of mesenchymal stem cells in recombinant silk-elastinlike hydrogels

PURPOSE

In this study the chondrocytic differentiation and cartilage matrix accumulation of human mesenchymal stem cells (hMSCs) were investigated after encapsulation in a genetically engineered silk-elastinlike protein polymer SELP-47 K as an injectable matrix for delivery of cell-based therapeutics.

MATERIALS AND METHODS

hMSCs were encapsulated in SELP-47 K and cultured for 4 weeks in chondrogenic medium with or without transforming growth factor-beta3 (TGF). Chondrogenic differentiation was evaluated by histological, RNA and biochemical analyses for the expression of cartilage extracellular matrix components.

RESULTS

Histological and immunohistochemical staining revealed that the cells acquired a rounded morphology and were embedded in significant amounts of chondrogenic extracellular matrix. Reverse transcriptase (RT)-PCR showed an up-regulation in aggrecan, type II and type X collagen and SOX9 in presence of TGF-beta3. By day 28, constructs cultured in the presence of TGF-beta3 exhibited significant increase in sulfated glycosaminoglycan and total collagen content up to 65 and 300%, respectively.

CONCLUSIONS

This study demonstrates that SELP-47 K hydrogel can be used as a scaffold for encapsulation and chondrogenesis of hMSCs. The ability to use recombinant techniques to precisely control SELP structure enables the investigation of injectable protein polymer scaffolds for soft-tissue engineering with varied physicochemical properties.

Adenoviral Gene Delivery to Solid Tumors by Recombinant Silk–Elastinlike Protein Polymers

PURPOSE

The purpose of this study was to investigate the potential of silk-elastinlike protein polymers (SELPs) in controlling the release rate of adenoviruses in vitro and in vivo while preserving their bioactivity.

MATERIALS AND METHODS

A hydrogel system composed of SELP/adenovirus mixture was prepared. The release of the adenovirus particles from the hydrogels was quantified by Real Time-PCR and the bioactivity of the released viruses was evaluated using confocal microscopy and beta-galactosidase assay. To demonstrate the ability of SELP in entrapping virus cargo and releasing it over a prolonged period of time in vivo, a SELP/adenovirus mixture was prepared and injected directly into xenograft tumor models of breast and head and neck cancer in mice. At various time points mice were sacrificed, tumors dissected, and tissue sections studied under confocal microscope.

RESULTS

In vitro studies demonstrated that SELP hydrogels release viruses over a period of 4 weeks while preserving their bioactivity. After intratumoral injection, a prolonged and localized expression of adenoviruses was observed.

CONCLUSIONS

These results suggest the potential of SELPs in local adenoviral delivery to solid tumors as an alternative approach to intratumoral virus infusion.

Strategies to enhance transductional efficiency of adenoviral-based gene transfer to primary human fibroblasts and keratinocytes as a platform in dermal wounds

Genetically modified keratinocytes and fibroblasts are suitable for delivery of therapeutic genes capable of modifying the wound healing process. However, efficient gene delivery is a prerequisite for successful gene therapy of wounds. Whereas adenoviral vectors (Ads) exhibit superior levels of in vivo gene transfer, their transductional efficiency to cells resident within wounds may nonetheless be suboptimal, due to deficiency of the primary adenovirus receptor, coxsackie-adenovirus receptor (CAR). We explored CAR-independent transduction to fibroblasts and keratinocytes using a panel of CAR-independent fiber-modified Ads to determine enhancement of infectivity. These fiber-modified adenoviral vectors included Ad 3 knob (Ad5/3), canine Ad serotype 2 knob (Ad5CAV-2), RGD (Ad5.RGD), polylysine (Ad5.pK7), or both RGD and polylysine (Ad5.RGD.pK7). To evaluate whether transduction efficiencies of the fiber-modified adenoviral vectors correlated with the expression of their putative receptors on keratinocytes and fibroblasts, we analyzed the mRNA levels of CAR, alpha upsilon integrin, syndecan-1, and glypican-1 using quantitative polymerase chain reaction. Analysis of luciferase and green fluorescent protein transgene expression showed superior transduction efficiency of Ad5.pK7 in keratinocytes and Ad5.RGD.pK7 in fibroblasts. mRNA expression of alpha upsilon integrin, syndecan-1 and glypican-1 was significantly higher in primary fibroblasts than CAR. In keratinocytes, syndecan-1 expression was significantly higher than all the other receptors tested. Significant infectivity enhancement was achieved in keratinocytes and fibroblasts using fiber-modified adenoviral vectors. These strategies to enhance infectivity may help to achieve higher clinical efficacy of wound gene therapy.

Receptor-mediated gene delivery using polyethylenimine (PEI) coupled with polypeptides targeting FGF receptors on cells surface

OBJECTIVE

To construct a novel kind of nonviral gene delivery vector based on polyethylenimine (PEI) conjugated with polypeptides derived from ligand FGF with high transfection efficiency and according to tumor targeting ability.

METHODS

The synthetic polypeptides CR16 for binding FGF receptors was conjugated to PEI and the characters of the polypeptides including DNA condensing and particle size were determined. Enhanced efficiency and the targeting specificity of the synthesized vector were investigated in vitro and in vivo.

RESULTS

The polypeptides were successfully coupled to PEI. The new vectors PEI-CR16 could efficiently condense pDNA into particles with around 200 nm diameter. The PEI-CR16/pDNA polyplexes showed significantly greater transgene activity than PEI/pDNA in FGF receptors positive tumor cells in vitro and in vivo gene transfer, while no difference was observed in FGF receptors negative tumor cells. The enhanced transfection efficiency of PEI-CR16 could be blocked by excess free polypeptides.

CONCLUSION

The synthesized vector could improve the efficiency of gene transfer and targeting specificity in FGF receptors positive cells. The vector had good prospect for use in cancer gene therapy.

Gene-modified tissue-engineered skin: the next generation of skin substitutes

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases.

Biomimetic approaches to protein and gene delivery for tissue regeneration

Novel therapeutic strategies that promote wound healing seek to mimic the response of the body to wounding, to regenerate rather than repair injured tissues. Many synthetic or natural biomaterials have been developed for this purpose and are used to deliver wound therapeutics in a controlled manner that prevents unwanted and potentially harmful side-effects. Here, we review the natural and synthetic biomaterials that have been developed for protein and gene delivery to enhance tissue regeneration. Particular emphasis is placed on novel biomimetic materials that respond to environmental stimuli or release their cargo according to cellular demand. Engineering biomaterials to release therapeutic agents in response to physiologic signals mimics the natural healing process and can promote faster tissue regeneration and reduce scarring in severe acute or chronic wounds.

Recombinant polymers for cancer gene therapy: A minireview

A major challenge for successful cancer gene therapy is the development of safe and effective gene delivery vectors. Gene delivery vectors can be viral or nonviral. Among nonviral vectors various polymeric vectors have shown potential in gene delivery. However, much work needs to be done in order to correlate polymer structure with gene release at the target site and transfection efficiency. This article is a brief introduction into cancer gene therapy, barriers and methods for gene transfer with emphasis on the applications of recombinant polymers for cancer gene therapy.

Bone induction by AdBMP-2/collagen implants

BACKGROUND

Demineralized bone matrix and recombinant human bone morphogenetic protein-2 or 7 (BMP-2 or BMP-7)-containing collagenous matrix have been shown to induce new bone formation in orthotopic and heterotopic sites. We examined the ability of subcutaneous implants of collagen combined with adenoviral vector containing the BMP-2 gene (AdBMP-2) to induce bone formation in rats. We also evaluated whether targeting the AdBMP-2 vector through an alternative receptor pathway, fibroblast growth factor (FGF), would increase the vector's potency.

METHODS

In a time-course study, rat subcutaneous sites were implanted with (1) AdBMP-2 in rat-bone-derived collagen or (2) rat-bone-derived collagen alone. Samples were collected three, seven, fourteen, or thirty-five days after treatment. In a dose-response study, bone induction by AdBMP-2 in collagen (AdBMP-2/collagen) or by AdBMP-2 and FGF2 Fab' anti-adenovirus knob protein antibody in collagen (FGF2-AdBMP-2/collagen) was tested at fourteen days. Viral vector doses of 1 x 10(9) PN (viral particle number), 3 x 10(9) PN, 1 x10(10) PN, 3 x 10(10) PN, or 1 x 10(11) PN per implant were used. Equal amounts of collagen (25 mg) were used to formulate all implants. Explanted tissues were evaluated histologically to determine bone formation, specific activity of alkaline phosphatase, and calcium content.

RESULTS

AdBMP-2/collagen implants induced robust bone formation. New bone was formed by the fourteenth day after implantation. In contrast, little or no bone was induced by the implant containing collagen alone. FGF2-AdBMP-2/collagen implants stimulated significantly more bone formation (p < 0.05) than did AdBMP-2/collagen implants, regardless of the dose of viral particles.

CONCLUSIONS

Local delivery of AdBMP-2 in a collagen matrix rapidly induces bone formation, and targeting the virus through FGF receptors enhances the osteogenic potential of AdBMP-2.

Gene transfer to epidermal stem cells: implications for tissue engineering

The skin is an attractive target for gene therapy because it is easily accessible and shows great potential as an ectopic site for protein delivery in vivo. Genetically modified epidermal cells can be used to engineer three-dimensional skin substitutes, which when transplanted can act as in vivo 'bioreactors' for delivery of therapeutic proteins locally or systemically. Although some gene transfer technologies have the potential to afford permanent genetic modification, differentiation and eventual loss of genetically modified cells from the epidermis results in temporary transgene expression. Therefore, to achieve stable long-term gene expression, it is critical to deliver genes to epidermal stem cells, which possess unlimited growth potential and self-renewal capacity. This review discusses the recent advances in epidermal stem cell isolation, gene transfer and engineering of skin substitutes. Recent efforts that employ gene therapy and tissue engineering for the treatment of genetic diseases, chronic wounds and systemic disorders, such as leptin deficiency or diabetes, are reviewed. Finally, the use of gene-modified tissue-engineered skin as a biological model for understanding tissue development, wound healing and epithelial carcinogenesis is also discussed.

Delivery systems for small molecule drugs, proteins, and DNA: the neuroscience/biomaterial interface

Manipulation of cellular processes in vivo by the delivery of drugs, proteins or DNA is of paramount importance to neuroscience research. Methods for the presentation of these molecules vary widely, including direct injection (either systemic or stereotactic), osmotic pump-mediated chronic delivery, or even implantation of cells engineered to indefinitely secrete a factor of interest. Biomaterial-based delivery systems represent an alternative to more traditional approaches, with the possibility of increased efficacy. Drug-releasing biomaterials, either as injectable microspheres or as three-dimensional implants, can deliver a molecule of interest (including small molecule drugs, biologically active proteins, or DNA) over a more prolonged period of time than by standard bolus injection, avoiding the need for repeated administration. Furthermore, sustained-release systems can maintain therapeutic concentrations at a target site, thus reducing the chance for toxicity. This review summarizes applications of polymer-based delivery of small molecule drugs, proteins, and DNA specifically relevant to neuroscience research. We detail the fabrication procedures for the polymeric systems and their utility in various experimental models. The biomaterial field offers unique experimental tools with downstream clinical application for the study and treatment of neurologic disease.

Biotinylated GHK peptide incorporated collagenous matrix: A novel biomaterial for dermal wound healing in rats

Matrikines are small peptide fragments of extracellular matrix proteins that display potent tissue repair activities. Difficulties in achieving sustained delivery of bioactive concentration of matrikines in the affected area limits their therapeutic use. The present study evaluates the effects biotinylated matrikine peptide (bio-glycyl-histidyl-lysine) incorporated collagen membrane for dermal wound healing processes in rats. Biotinylated peptide incorporated collagen matrix (PIC) showed better healing when compared to wounds treated with collagen matrix [CF (collagen film)] and without collagen [CR (control)]. Binding studies indicate that biotinylated GHK (Bio-GHK) binds effectively to the collagen matrix and red blood cell (RBC) membrane when compared with t-butyloxycarbonyl substituted GHK (Boc-GHK). Wound contraction, increased cell proliferation, and high expression of antioxidant enzymes in PIC treated group indicate enhanced wound healing activity when compared to CF and CR groups. Interestingly Bio-GHK incorporated collagen increases the copper concentration by ninefold at the wound site indicating the wound healing property of Bio-GHK can also be linked with both copper localization and matrikine activities. These results demonstrate the possibility of using Bio-GHK incorporated collagen film as a therapeutic agent in the wound healing process.

Alpha-crystallin-incorporated collagen matrices as an aid for dermal wound healing

This study evaluated the effects of noncovalently incorporated crystallin into the collagen matrix for dermal wound-healing processes in rats. Crystallin-incorporated collagen matrix (CIC) showed better healing when compared to wounds treated with collagen matrix (CS) and without collagen (CR). Biochemical parameters and histological analysis revealed that increased wound contraction enhanced cell proliferation and efficient radical scavenging in the CIC group. The higher shrinkage temperature of CIC films when compared to CS groups suggested increased hydrothermal stability for the former material. An in vitro release study of CIC has showed sustained and time-dependent release of crystallin from the collagen matrix. These results demonstrate the possibility of using crystallin as therapeutic protein in the wound-healing process.

Genetically engineered polymers: status and prospects for controlled release

Genetic engineering methodology has enabled the synthesis of protein-based polymers with precisely controlled structures. Protein-based polymers have well-defined molecular weights, monomer compositions, sequences and stereochemistries. The incorporation of tailor-made motifs at specified locations by recombinant techniques allows the formation of hydrogels, sensitivity to environmental stimuli, complexation with drugs and nucleic acids, biorecognition and biodegradation. Accordingly, a special interest has emerged for the use of protein-based polymers for controlled drug and gene delivery, tissue engineering and other biomedical applications. This article is a review of genetically engineered polymers, their physicochemical characteristics, synthetic strategies used to produce them and their biomedical applications with emphasis on controlled release.

Controlled release systems for DNA delivery

Adapting controlled release technologies to the delivery of DNA has the potential to overcome extracellular barriers that limit gene therapy. Controlled release systems can enhance gene delivery and increase the extent and duration of transgene expression relative to more traditional delivery methods (e.g., injection). These systems typically deliver vectors locally, which can avoid distribution to distant tissues, decrease toxicity to nontarget cells, and reduce the immune response to the vector. Delivery vehicles for controlled release are fabricated from natural and synthetic polymers, which function either by releasing the vector into the local tissue environment or by maintaining the vector at the polymer surface. Vector release or binding is regulated by the effective affinity of the vector for the polymer, which depends upon the strength of molecular interactions. These interactions occur through nonspecific binding based on vector and polymer composition or through the incorporation of complementary binding sites (e.g., biotin-avidin). This review examines the delivery of nonviral and viral vectors from natural and synthetic polymers and presents opportunities for continuing developments to increase their applicability.

In vitro and in vivo evaluation of recombinant silk-elastinlike hydrogels for cancer gene therapy

The objectives of this study were to evaluate: (i). the influences of hydrogel geometry, DNA molecular weight, and DNA conformation on DNA release from a silk-elastinlike protein polymer (SELP) hydrogel, (ii). the bioactivity and transfection efficiency of encapsulated DNA over time in vitro, (iii). the delivery and transfection of a reporter gene in a murine model of human breast cancer in vivo, and (iv). the in vitro release and bioactivity of adenovirus containing the green fluorescent protein (gfp) gene as a marker of gene transfer. Plasmid DNA was released from SELP hydrogels in a size-dependent manner, with the average effective diffusivity ranging from 1.70+/-0.52 x 10(-12) cm(2)/s for a larger plasmid (11 kbp) to 2.55+/-0.51 x 10(-10) cm(2)/s for a smaller plasmid (2.6 kbp). Plasmid conformation also influenced the rate of release, with the rank order linear>supercoiled>open-circular. DNA retained bioactivity in vitro, after encapsulation in a SELP hydrogel for up to 28 days. Delivery of pRL-CMV from a SELP hydrogel resulted in increased transfection in a murine model of human breast cancer by 1-3 orders of magnitude, as compared to naked DNA. The release of a bioactive adenoviral vector was related to the concentration of the polymer in the hydrogel. These studies indicate that genetically engineered SELP hydrogels have potential as matrices for controlled nonviral and viral gene delivery.

Adenovirus Encoding Human Platelet-Derived Growth Factor-B Delivered in Collagen Exhibits Safety, Biodistribution, and Immunogenicity Profiles Favorable for Clinical Use

We have developed a therapeutic approach to wound repair involving immobilization of gene transfer vectors within biocompatible matrices (gene-activated matrix, or GAM). The matrix also serves as a scaffold for cellular in-growth and subsequent gene uptake and expression. An adenoviral vector encoding human platelet-derived growth factor-B delivered in collagen (AdPDGF-B/GAM) has demonstrated efficacy in models of wound repair. The safety, biodistribution, and immunogenicity profiles of AdPDGF-B/GAM were examined using a rabbit dermal wound model. Four weekly doses at 1 x 10(10) and 1 x 10(11) viral particles/cm2 of wound surface stimulated dose-related increases in granulation tissue formation and cell proliferation. In situ hybridization and immunostaining demonstrated concordant expression of human PDGF-B mRNA and protein. No treatment-related changes in hematology, serum chemistry, or histopathology were observed. Although AdPDGF-B DNA and PDGF-B mRNA were detected in wounds and axillary lymph nodes of treated animals, no AdPDGF-B was detected in blood or other organs. No immunologic responses against collagen were observed; however, as expected, IgG responses to AdPDGF-B and human PDGF-BB protein were detected. In adenovirus-preimmunized rats, attenuation of the wound healing response was modest (approximately 16%). Collectively, these observations indicate that repeat doses of AdPDGF-B/GAM are well tolerated and lead to robust, localized tissue repair.

Delivery and Protection of Adenoviruses Using Biocompatible Hydrogels for Localized Gene Therapy

Localized gene delivery for repair of bone defects requires appropriate carriers for the gene therapy vectors. The objective of this study was to determine if hydrogels can control temporal and spatial delivery of adenovirus for localized gene therapy. Adenovirus expressing beta-galactosidase was suspended in liquid or fibrin or collagen gels of varied concentrations and incubated prior to testing its bioactivity. The bioactivity of the virus was determined by exposing fibroblasts to the medium, the gels, or the elution medium from the gels. Bioactivity of adenovirus suspended in medium or collagen decreased to half-maximal activity after 15 h of incubation. In contrast, virus suspended in fibrin exhibited a threefold extension of bioactivity and did not reach half-maximal activity for 45 h. Bioactivity of adenovirus in hydrogels was determined to be a function of the gel concentration. In vivo experiments involved intramuscular implantation of BMP-7-expressing adenovirus in collagen, fibrin, or liquid in nude mice for 1, 2, or 4 weeks. Bone formation was observed only after 4 weeks, with bone formation occurring in 80% of muscles implanted with fibrin or collagen and 50% of muscles implanted with liquid. Fibrin gel also led to significantly larger ossicles, indicating that fibrin may offer protection from loss of infectivity both in vivo and in vitro. These results demonstrated that hydrogels may be used as carriers to control delivery of the virus and resultant tissue regeneration.

Gene therapy for tissue regeneration

Tissue repair and regeneration are the normal biological responses of many different tissues in the body to injury. During the healing process, profound changes occur in cell composition and extracellular matrix (ECM) formation. Fibroblasts and equivalent reparative cells migrate to the wounded area and subsequently proliferate. These cells and reparative cells from the surrounding tissue are responsible for the rapid repair which results in tissue regeneration. Growth factors, one of which is transforming growth factor-beta (TGF-beta), stimulate fibroblasts and smooth muscle cells to proliferate and synthesize ECM proteins. This process of early repair provides a rapid way to restore new tissue and mechanical integrity. This early tissue repair process is normally followed by involution, which requires the production and activation of proteases, tissue maturation and remodeling, reorganization and finally regeneration. Alternately, failure to replace the critical components of the ECM, including elastin and basement membrane, results in abnormal regeneration of the epithelial cell layer. Although remodeling should occur during healing, provisional repair may be followed by excessive synthesis and deposition of collagen, which results in irreversible fibrosis and scarring. This excessive fibrosis which occurs in aberrant healing is at least in part mediated by persistent TGF-beta. Because of the central role of collagen in the wound healing process, the pharmacological control of collagen synthesis has been of paramount importance as a possible way to abrogate aberrant healing and prevent irreversible fibrosis. Fibrosis is an abnormal response to tissue injury.

Targeted adenoviral vectors

Replication-defective vectors based on human adenovirus serotypes 2 and 5 (Ad2 and Ad5) possess a number of attributes which favor their use as gene delivery vehicles in gene therapy applications. However, the widespread distribution of the primary cellular receptor for Ad, the coxsackievirus and adenovirus receptor (CAR), allows Ad vectors to infect a broad range of cells in the host. Conversely, a number of tissues which represent important targets for gene therapy, such as the airway epithelium and cancer cells, are refractory to Ad infection due a paucity of CAR. Thus, there is a strong rationale for the development of CAR-independent Ad vectors capable of enhanced specificity and efficiency of gene transfer to target cells. In this article we review the approaches which have been employed to generate tropism-modified Ad vectors. These targeting strategies have led to improvements in the safety and efficacy of Ad vectors and have the potential to yield an increased therapeutic benefit in the human clinical context.

Adenoviral gene transfer of PDGF downregulates gas gene product PDGFalphaR and prolongs ERK and Akt/PKB activation

The delivery of platelet-derived growth factor (PDGF) for tissue engineering of skin and periodontal wounds has become an active area of interest. However, little is known regarding the extended effects of PDGF on cell signaling via gene therapy and how such an approach facilitates the exiting of cells from growth arrest and entry to competence required for cell cycling. We show in vitro expression and secretion of PDGF-AA by recombinant adenovirus encoding the PDGF-A gene (Ad-PDGF-A). The bioactive PDGF-AA protein released induces sustained downregulation of PDGFalphaR that is encoded by a growth arrest-specific (gas) gene. Ad-PDGF-A induces sustained phosphorylation of PDGFalphaR as well as prolonged phosphorylation of downstream extracellular signal-regulated kinase 1/2 and Akt signaling pathways. Furthermore, the phosphorylation of PDGFalphaR is abolished by cotransducing cells with adenovirus encoding a dominant negative mutant of the PDGF-A gene that disrupts PDGF bioactivity. These findings demonstrate the prolonged effects of adenoviral delivery of PDGF and aid in the better understanding of sustained PDGF signaling.

Gene delivery to pig coronary arteries from stents carrying antibody-tethered adenovirus

Deployment of coronary stents to relieve atherosclerotic obstruction has benefitted millions of patients. However, gene therapy to prevent in-stent restenosis, while promising in experimental studies, remains a challenge. Conventional strategies for viral vector administration utilize catheters that deliver infusions of viral suspensions, which result in suboptimal localization and potentially dangerous distal spread of vector. Stent-based gene delivery may circumvent this problem. We hypothesized that site-specific delivery of adenoviral gene vectors from a stent could be achieved through a mechanism involving anti-viral antibody tethering. Stents were formulated with a collagen coating. Anti-adenoviral monoclonal antibodies were covalently bound to the collagen surface. These antibodies enabled tethering of replication defective adenoviruses through highly specific antigen-antibody affinity. We report for the first time successful stent-based gene delivery using antibody-tethered adenovirus encoding green fluorescent protein (GFP), demonstrating efficient and highly localized gene delivery to arterial smooth muscle cells in both cell culture and pig coronary arteries. Overall arterial wall transduction efficiency in pigs was 5.9 +/- 1.1% of total cells. However, neointimal transduction was more than 17% of total cells in this region. Importantly, when specific antibody was used to tether adenovirus, no distal spread of vector was detectable by PCR, in either distal organs, or in the downstream segments of the stented arteries. Control adenovirus stents, with nonspecific antibody plus adenovirus, demonstrated only a few isolated foci of transduction, and poor site-specific transduction with distal spread of vector. We conclude that a vascular stent is a suitable platform for a localizable viral vector delivery system that also prevents systemic spread of vector. Gene delivery using stent-based anti-viral antibody tethering of vectors should be suitable for a wide array of single or multiple therapeutic gene strategies.