An injectable and in situ-gelling biopolymer for sustained drug release following perineural administration

Recent advancements in fusion protein technologies in oncotherapy: A review

Cancer is a complicated, adaptable, and heterogeneous disease caused by a wide variety of genetic changes that might impair ability of cells to function normally. The majority of the tumors can only be shrunk using conventional oncology therapies like chemotherapy, radiation, and surgical resection, and the tumor often recurs. The inability of conventional cancer therapies to completely destroy the Cancer Stem Cells (CSCs) that otherwise lead to therapy resistance is thus addressed by therapeutic approaches that concentrate on targeting CSCs and their micro-environmental niche. In this review, we summarize approaches that are used for the development of fusion proteins and their therapeutic applications for treating cancer. The main purpose of making advancements towards the fusion technology instead of using conventional treatment methods is to achieve a prolonged half-life of the therapeutic drugs. The fusion of drugs to the immune response enhancing cytokines or the fusion of antibody and cytokines not only increases half-life but also increase the stability of the anti-tumor drug. Several molecules including different fragments of antibodies, cytokines, Human Serum Albumin, transferrin, XTEN polymers, Elastin-like polypeptides (ELPs) can be employed as a fusion partner and the resulting fusion proteins are reported to show enhanced anti-tumor response.

Novel Protein Therapeutics Created Using the Elastin-Like Polypeptide Platform

Elastin-like polypeptides (ELPs) are bioengineered proteins that have a unique physical property, a thermally triggered inverse phase transition, that can be exploited for drug delivery. ELP-fusion proteins can be used as soluble biologics, thermally targeted drug carriers, self-assembling nanoparticles, and slow-release drug depots. Because of their unique physical characteristics and versatility for delivery of nearly any type of therapeutic, ELP-based drug delivery systems represent a promising platform for biologics development.

Extracellular Matrix-Mimetic Hydrogels for Treating Neural Tissue Injury: A Focus on Fibrin, Hyaluronic Acid, and Elastin-Like Polypeptide Hydrogels

Neurological and functional recovery is limited following central nervous system injury and severe injury to the peripheral nervous system. Extracellular matrix (ECM)-mimetic hydrogels are of particular interest as regenerative scaffolds for the injured nervous system as they provide 3D bioactive interfaces that modulate cellular response to the injury environment and provide naturally degradable scaffolding for effective tissue remodeling. In this review, three unique ECM-mimetic hydrogels used in models of neural injury are reviewed: fibrin hydrogels, which rely on a naturally occurring enzymatic gelation, hyaluronic acid hydrogels, which require chemical modification prior to chemical crosslinking, and elastin-like polypeptide (ELP) hydrogels, which exhibit a temperature-sensitive gelation. The hydrogels are reviewed by summarizing their unique biological properties, their use as drug depots, and their combination with other biomaterials, such as electrospun fibers and nanoparticles. This review is the first to focus on these three ECM-mimetic hydrogels for their use in neural tissue engineering. Additionally, this is the first review to summarize the use of ELP hydrogels for nervous system applications. ECM-mimetic hydrogels have shown great promise in preclinical models of neural injury and future advancements in their design and use can likely lead to viable treatments for patients with neural injury.

New generation of viral nanoparticles for targeted drug delivery in cancer therapy

Nanoscale engineering is one of the novel methods to cure multitudes of diseases, such as types of cancers, neurological disorders, and infectious illnesses. Viruses can play a vital role in nanoscale engineering due to their specific properties like minuscule size, high stability in different body conditions, and large-scale production. Viral-like particles (VLPs) as specific nanoscale scaffolds can encapsulate a wide range of cargos, including nucleic acids, proteins, peptides, and drugs. The Exterior portion of VLPs can be changed by genetical or chemical conjugation as well as targeting ligands or peptides. The aforementioned features of VLPs can be used in several applications, such as drug delivery, bioimaging, tissue engineering, vaccine production, and disease detection. This review article attempts to investigate appearance characteristics, modification strategies, and manufacturing methods of VLPs. Additionally, drug delivery to cancer cells as one of the VLPs applications along with different cellular uptake mechanisms of VLPs by cancer cells are chosen for investigation. This review also tries to gather most of the recent studies of drug delivery to cancer cells by VLPs.

(Macro)molecular self-assembly for hydrogel drug delivery

Hydrogels prepared via self-assembly offer scalable and tunable platforms for drug delivery applications. Molecular-scale self-assembly leverages an interplay of attractive and repulsive forces; drugs and other active molecules can be incorporated into such materials by partitioning in hydrophobic domains, affinity-mediated binding, or covalent integration. Peptides have been widely used as building blocks for self-assembly due to facile synthesis, ease of modification with bioactive molecules, and precise molecular-scale control over material properties through tunable interactions. Additional opportunities are manifest in stimuli-responsive self-assembly for more precise drug action. Hydrogels can likewise be fabricated from macromolecular self-assembly, with both synthetic polymers and biopolymers used to prepare materials with controlled mechanical properties and tunable drug release. These include clinical approaches for solubilization and delivery of hydrophobic drugs. To further enhance mechanical properties of hydrogels prepared through self-assembly, recent work has integrated self-assembly motifs with polymeric networks. For example, double-network hydrogels capture the beneficial properties of both self-assembled and covalent networks. The expanding ability to fabricate complex and precise materials, coupled with an improved understanding of biology, will lead to new classes of hydrogels specifically tailored for drug delivery applications.

Genetically Engineered Elastin-based Biomaterials for Biomedical Applications

Protein-based polymers are some of the most promising candidates for a new generation of innovative biomaterials as recent advances in genetic-engineering and biotechnological techniques mean that protein-based biomaterials can be designed and constructed with a higher degree of complexity and accuracy. Moreover, their sequences, which are derived from structural protein-based modules, can easily be modified to include bioactive motifs that improve their functions and material-host interactions, thereby satisfying fundamental biological requirements. The accuracy with which these advanced polypeptides can be produced, and their versatility, self-assembly behavior, stimuli-responsiveness and biocompatibility, means that they have attracted increasing attention for use in biomedical applications such as cell culture, tissue engineering, protein purification, surface engineering and controlled drug delivery. The biopolymers discussed in this review are elastin-derived protein-based polymers which are biologically inspired and biomimetic materials. This review will also focus on the design, synthesis and characterization of these genetically encoded polymers and their potential utility for controlled drug and gene delivery, as well as in tissue engineering and regenerative medicine.

Utilizing a Kidney-Targeting Peptide to Improve Renal Deposition of a Pro-Angiogenic Protein Biopolymer

Elastin-like polypeptides (ELP) are versatile protein biopolymers used in drug delivery due to their modular nature, allowing fusion of therapeutics and targeting agents. We previously developed an ELP fusion with vascular endothelial growth factor (VEGF) and demonstrated its therapeutic efficacy in translational swine models of renovascular disease and chronic kidney disease. The goal of the current work was to refine renal targeting and reduce off-target tissue deposition of ELP–VEGF. The ELP–VEGF fusion protein was modified by adding a kidney-targeting peptide (KTP) to the N-terminus. All control proteins (ELP, KTP–ELP, ELP–VEGF, and KTP–ELP–VEGF) were also produced to thoroughly assess the effects of each domain on in vitro cell binding and activity and in vivo pharmacokinetics and biodistribution. KTP–ELP–VEGF was equipotent to ELP–VEGF and free VEGF in vitro in the stimulation of primary glomerular microvascular endothelial cell proliferation, tube formation, and extracellular matrix invasion. The contribution of each region of the KTP–ELP–VEGF protein to the cell binding specificity was assayed in primary human renal endothelial cells, tubular epithelial cells, and podocytes, demonstrating that the VEGF domain induced binding to endothelial cells and the KTP domain increased binding to all renal cell types. The pharmacokinetics and biodistribution of KTP–ELP–VEGF and all control proteins were determined in SKH-1 Elite hairless mice. The addition of KTP to ELP slowed its in vivo clearance and increased its renal deposition. Furthermore, addition of KTP redirected ELP–VEGF, which was found at high levels in the liver, to the kidney. Intrarenal histology showed similar distribution of all proteins, with high levels in blood vessels and tubules. The VEGF-containing proteins also accumulated in punctate foci in the glomeruli. These studies provide a thorough characterization of the effects of a kidney-targeting peptide and an active cytokine on the biodistribution of these novel biologics. Furthermore, they demonstrate that renal specificity of a proven therapeutic can be improved using a targeting peptide.

Engineering Adhesive and Antimicrobial Hyaluronic Acid/Elastin-like Polypeptide Hybrid Hydrogels for Tissue Engineering Applications

Hydrogel-based biomaterials have been widely used for tissue engineering applications because of their high water content, swellability, and permeability, which facilitate transport and diffusion of essential nutrients, oxygen, and waste across the scaffold. These characteristics make hydrogels suitable for encapsulating cells and creating a cell supportive environment that promotes tissue regeneration when implanted in vivo. This is particularly important in the context of tissues whose intrinsic regenerative capacity is limited, such as cartilage. However, the clinical translation of hydrogels has been limited by their poor mechanical performance, low adhesive strength, uncontrolled degradation rates, and their susceptibility to bacterial colonization. Here, we introduce an elastic, antimicrobial, and adhesive hydrogel comprised of methacrylated hyaluronic acid (MeHA) and an elastin-like polypeptide (ELP), which can be rapidly photo-cross-linked in situ for the regeneration and repair of different tissues. Hybrid hydrogels with a wide range of physical properties were engineered by varying the concentrations of MeHA and ELP. In addition, standard adhesion tests demonstrated that the MeHA/ELP hydrogels exhibited higher adhesive strength to the tissue than commercially available tissue adhesives. MeHA/ELP hydrogels were then rendered antimicrobial through the incorporation of zinc oxide (ZnO) nanoparticles, and were shown to significantly inhibit the growth of methicillin-resistant Staphylococcus aureus (MRSA), as compared to controls. Furthermore, the composite adhesive hydrogels supported in vitro mammalian cellular growth, spreading, and proliferation. In addition, in vivo subcutaneous implantation demonstrated that MeHA/ELP hydrogels did not elicit any significant inflammatory response, and could be efficiently biodegraded while promoting the integration of new autologous tissue. In summary, we demonstrated for the first time that MeHA/ELP-ZnO hydrogel can be used as an adhesive and antimicrobial biomaterial for tissue engineering applications, because of its highly tunable physical characteristics, as well as remarkable adhesive and antimicrobial properties.

Protein based therapeutic delivery agents: Contemporary developments and challenges

As unique biopolymers, proteins can be employed for therapeutic delivery. They bear important features such as bioavailability, biocompatibility, and biodegradability with low toxicity serving as a platform for delivery of various small molecule therapeutics, gene therapies, protein biologics and cells. Depending on size and characteristic of the therapeutic, a variety of natural and engineered proteins or peptides have been developed. This, coupled to recent advances in synthetic and chemical biology, has led to the creation of tailor-made protein materials for delivery. This review highlights strategies employing proteins to facilitate the delivery of therapeutic matter, addressing the challenges for small molecule, gene, protein and cell transport.

Intranasal administration of elastin-like polypeptide for therapeutic delivery to the central nervous system

Bypassing the blood–brain barrier is one of the primary considerations when designing compounds intended to function in the central nervous system (CNS). Intranasal (IN) administration of otherwise blood–brain barrier impermeable molecules can result in high CNS concentrations and low systemic accumulation, indicating that IN administration may be a useful method of delivering therapeutics to the CNS. Elastin-like polypeptide (ELP) is a large, non-immunogenic, highly manipulable biopolymer with extensive evidence supporting its use as a carrier with the ability to improve drug pharmacokinetics and drug targeting. The ability of ELP to reach the CNS via IN administration has been shown previously. Previous studies have also identified the ability of cell penetrating peptides (CPPs) to increase the uptake of molecules in some instances, including via the IN route. Here, we compared and contrasted the biodistribution of ELPs with or without addition of the CPPs Tat or SynB1 via both the IN and intravenous routes. Administration of ELP via the IN route led to significant accumulation in the brain, especially in the olfactory bulbs. When injected intravenously, <3% of the ELP signal was present outside the vascular compartment. This contrasted with IN administration, which resulted in 79% of the fluorescence signal localized outside the vascular space. The fusion of Tat or SynB1 significantly altered the biodistribution of ELP, decreasing the total CNS accumulation following IN administration. The addition of CPPs to ELP increased their retention in the nasal epithelium. These results suggest ELP may represent an effective CNS delivery vector without further modification and that the addition of a CPP significantly influences biodistribution.

Annular puncture with tumor necrosis factor-alpha injection enhances painful behavior with disc degeneration in vivo

BACKGROUND CONTEXT

Painfulintervertebral disc degeneration is extremely common and costly. Effective treatments are lacking because the nature of discogenic pain is complex with limited capacity to distinguish painful conditions from age-related changes in the spine. Hypothesized sources of discogenic pain include chronic inflammation, neurovascular ingrowth, and structural disruption.

PURPOSE

This study aimed to investigate inflammation, pro-neurovascular growth factors, and structural disruption as sources of painful disc degeneration

STUDY DESIGN/SETTING

This study used an in vivo study to address these hypothesized mechanisms with anterior intradiscal injections of tumor necrosis factor-alpha (TNFα), pro-neurovascular growth factors: nerve growth factor and vascular endothelial growth factor (NGF and VEGF), and saline with additional sham surgery and naïve controls. Depth of annular puncture was also evaluated for its effects on structural and painful degeneration.

METHODS

Rat lumbar discs were punctured (shallow or deeper puncture) and intradiscally injected with saline, TNFα, or NGF and VEGF. Structural disc degeneration was assessed using X-ray, magnetic resonance imaging (MRI), and histology. The rat painful condition was evaluated using Von Frey hyperalgesia measurements, and substance P immunostaining in dorsal root ganglion (DRG) was performed to determine the source of pain.

RESULTS

Saline injection increased painful responses with degenerative changes in disc height, MRI intensity, and morphologies of disc structure and cell. TNFα and NGF/VEGF accelerated painful behavior, and TNFα-injected animals had increased substance P in DRGs. Deeper punctures led to more severe disc degeneration. Multiple regression analysis showed that the painful behavior was correlated with disc height loss.

CONCLUSIONS

We concluded that rate and severity of structural disc degeneration was associated with the amount of annular disruption and puncture depth. The painful behavior was associated with disc height loss and discal inflammatory state, whereas pro-inflammatory cytokines might play a more important role in the level of pain, which might have resulted from enhanced DRG sensitization. These in vivo painful disc degeneration models with different severities of structural changes may be useful for investigating discogenic pain mechanisms and for screening therapies, although interpretations must note the differences between all surgically induced animal models and the human condition.

Elastin-like polypeptides in drug delivery

The use of recombinant elastin-like materials, or elastin-like recombinamers (ELRs), in drug-delivery applications is reviewed in this work. Although ELRs were initially used in similar ways to other, more conventional kinds of polymeric carriers, their unique properties soon gave rise to systems of unparalleled functionality and efficiency, with the stimuli responsiveness of ELRs and their ability to self-assemble readily allowing the creation of advanced systems. However, their recombinant nature is likely the most important factor that has driven the current breakthrough properties of ELR-based delivery systems. Recombinant technology allows an unprecedented degree of complexity in macromolecular design and synthesis. In addition, recombinant materials easily incorporate any functional domain present in natural proteins. Therefore, ELR-based delivery systems can exhibit complex interactions with both their drug load and the tissues and cells towards which this load is directed. Selected examples, ranging from highly functional nanocarriers to macrodepots, will be presented.

Fabricated Elastin

The mechanical stability, elasticity, inherent bioactivity, and self-assembly properties of elastin make it a highly attractive candidate for the fabrication of versatile biomaterials. The ability to engineer specific peptide sequences derived from elastin allows the precise control of these physicochemical and organizational characteristics, and further broadens the diversity of elastin-based applications. Elastin and elastin-like peptides can also be modified or blended with other natural or synthetic moieties, including peptides, proteins, polysaccharides, and polymers, to augment existing capabilities or confer additional architectural and biofunctional features to compositionally pure materials. Elastin and elastin-based composites have been subjected to diverse fabrication processes, including heating, electrospinning, wet spinning, solvent casting, freeze-drying, and cross-linking, for the manufacture of particles, fibers, gels, tubes, sheets and films. The resulting materials can be tailored to possess specific strength, elasticity, morphology, topography, porosity, wettability, surface charge, and bioactivity. This extraordinary tunability of elastin-based constructs enables their use in a range of biomedical and tissue engineering applications such as targeted drug delivery, cell encapsulation, vascular repair, nerve regeneration, wound healing, and dermal, cartilage, bone, and dental replacement.

Challenges and new strategies for therapeutic peptide delivery to the CNS

Therapeutic peptides represent a largely untapped resource in medicine today, especially in the central nervous system. Despite their ease of design and remarkably high target specificity, it is difficult to deliver them beyond the blood-brain barrier or into the required intracellular compartments. In addition, the instability of these peptides in vivo precludes their use to combat the symptoms of numerous neurological disorders including Alzheimer's disease and spinocerebellar ataxia. In this review, we aim to characterize recent advances in the delivery of therapeutic peptides to the central nervous system past the blood-brain barrier and discuss the advantages and disadvantages of the examined methods as well as explore new potential directions.

Therapeutic opportunities to prevent post-traumatic arthritis: Lessons from the natural history of arthritis after articular fracture

An estimated 12% of patients seeking surgical intervention for symptomatic arthritis have an etiology of post-traumatic arthritis (PTA). The onset of PTA is rapid in the setting of articular fracture (AF). The investigation began with development of a murine model of a closed AF that develops PTA. In the process of characterizing this model a technique was developed for assessing quantitative synovial fluid biomarker concentrations. The work began with observations of the natural history of PTA development in the C57BL/6 strain of mice. A species of mice (MRL/MpJ) was found that is protected from PTA after AF. Further work identified key differences between mouse strains that did and did not develop PTA. This knowledge led to an intervention based on anti-cytokine (interleukin 1 receptor antagonist, (IL-1Ra) delivery in the C57BL/6 strain of mice that successfully prevented PTA following AF. This success in preventing PTA in the murine model has elucidated several important clinical implications: 1) Pro-inflammatory cytokines play an important role in the development of PTA after joint injury, 2) Pharmacologic intervention can lessen the severity of PTA after an AF, and 3) The murine AF model of joint injury provides a novel means of studying mechanisms of PTA development.

Delivery systems for the treatment of degenerated intervertebral discs

The intervertebral disc (IVD) is the most avascular and acellular tissue in the body and therefore prone to degeneration. During IVD degeneration, the balance between anabolic and catabolic processes in the disc is deregulated, amongst others leading to alteration of extracellular matrix production, abnormal enzyme activities and production of pro-inflammatory substances like cytokines. The established treatment strategy for IVD degeneration consists of physiotherapy, pain medication by drug therapy and if necessary surgery. This approach, however, has shown limited success. Alternative strategies to increase and prolong the effects of bioactive agents and to reverse the process of IVD degeneration include the use of delivery systems for drugs, proteins, cells and genes. In view of the specific anatomy and physiology of the IVD and depending on the strategy of the therapy, different delivery systems have been developed which are reviewed in this article.

Applications of elastin-like polypeptides in drug delivery

Elastin-like polypeptides (ELPs) are biopolymers inspired by human elastin. Their lower critical solution temperature phase transition behavior and biocompatibility make them useful materials for stimulus-responsive applications in biological environments. Due to their genetically encoded design and recombinant synthesis, the sequence and size of ELPs can be exactly defined. These design parameters control the structure and function of the ELP with a precision that is unmatched by synthetic polymers. Due to these attributes, ELPs have been used extensively for drug delivery in a variety of different embodiments-as soluble macromolecular carriers, self-assembled nanoparticles, cross-linked microparticles, or thermally coacervated depots. These ELP systems have been used to deliver biologic therapeutics, radionuclides, and small molecule drugs to a variety of anatomical sites for the treatment of diseases including cancer, type 2 diabetes, osteoarthritis, and neuroinflammation.

The role of cytokines in posttraumatic arthritis

The development of arthritis after joint injury is commonly known as posttraumatic arthritis (PTA). The inciting traumatic event may range from cartilage contusion and bone bruise combined with meniscus or ligament tear, to intra-articular fracture. End-stage PTA is often indistinguishable from primary osteoarthritis. However, knowing the time of the inciting traumatic event in a patient with PTA provides an opportunity to understand the events following joint injury that lead to the progression of arthritis. Joint injury often leads to mechanical alterations in loading of the injured joint, and restoration of joint mechanics through surgical repair remains an important aspect of treatment. However, the accuracy of joint reduction by itself does not account for the variability in outcome following joint injury, as evidenced by the fact that PTA remains a significant clinical problem. Emerging research in animal models and human subjects indicates that several inflammatory cytokines and related inflammatory mediators are elevated following joint injury. Data from animal studies and early clinical trials suggest that early inhibition of the intra-articular inflammatory response may improve clinical outcomes.

A genetically engineered thermally responsive sustained release curcumin depot to treat neuroinflammation

Radiculopathy, a painful neuroinflammation that can accompany intervertebral disc herniation, is associated with locally increased levels of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFα). Systemic administration of TNF antagonists for radiculopathy in the clinic has shown mixed results, and there is growing interest in the local delivery of anti-inflammatory drugs to treat this pathology as well as similar inflammatory events of peripheral nerve injury. Curcumin, a known antagonist of TNFα in multiple cell types and tissues, was chemically modified and conjugated to a thermally responsive elastin-like polypeptide (ELP) to create an injectable depot for sustained, local delivery of curcumin to treat neuroinflammation. ELPs are biopolymers capable of thermally-triggered in situ depot formation that have been successfully employed as drug carriers and biomaterials in several applications. ELP-curcumin conjugates were shown to display high drug loading, rapidly release curcumin in vitro via degradable carbamate bonds, and retain in vitro bioactivity against TNFα-induced cytotoxicity and monocyte activation with IC50 only two-fold higher than curcumin. When injected proximal to the sciatic nerve in mice via intramuscular (i.m.) injection, ELP-curcumin conjugates underwent a thermally triggered soluble-insoluble phase transition, leading to in situ formation of a depot that released curcumin over 4days post-injection and decreased plasma AUC 7-fold.

Preparation and characterization of elastin-like polypeptide scaffolds for local delivery of antibiotics and proteins

Tissue engineering applications could benefit from simultaneous release of growth factors, signaling molecules, and antibiotics to obtain optimal healing of tissues. Elastin-like polypeptides (ELPs) are genetically engineered polymers that possess good biocompatibility, are biodegradable, and exhibit mechanical properties similar to natural elastin. In addition, ELPs exhibit a characteristic inverse phase transition temperature (T(t)). This T(t) behavior is widely exploited in hyperthermia mediated drug delivery. The objectives of this research were to prepare ELP hydrogel scaffolds using a novel ultrasonication method and to investigate the release of a model protein (bovine serum albumin, BSA) and a commonly used antibiotic in periodontal therapy (doxycycline) from the scaffolds at two different temperatures (25 °C <T(t) vs. 37 °C >T(t)). Both BSA and doxycycline showed a gradual time dependent release and showed a trend of higher release fractions with higher loading doses. Based on the comparison between the release profiles at the two selected temperatures, the release was higher at 37 °C compared to that at 25 °C for both the loading concentrations of doxycycline (0.05 and 0.1 % v/v) and only one of the loading concentrations of BSA (0.5 % v/v) studied, while the release was higher at 25 °C compared to that at 37 °C only for the other loading concentration of BSA (1 % v/v) studied. These results suggested that the drug molecular weight and loading concentration were significant factors that affected the release kinetics. The experiments in this study demonstrated that the ELP hydrogel scaffolds can successfully release proteins and antibiotics critical to tissue engineering.

Thermoresponsive nanogels for prolonged duration local anesthesia

Nanogels based on poly(N-isopropylacrylamide) are attractive vehicles for prolonged duration local anesthesia because of their tunable size, number of functional groups, thermoresponsiveness and anionic charge. Nerve block durations of up to 9h were achieved using acrylic acid-loaded nanogels loaded with bupivacaine. Increasing the anionic charge density of the nanogels or (for more highly acid-functionalized nanogels) decreasing the nanogel size facilitated longer duration of anesthetic release. Small (<300 nm diameter) nanogels formed dense aggregates upon injection in vivo and induced only mild inflammatory responses, while large (>500 nm diameter) nanogels typically remained as liquid-like residues in vivo and induced more severe inflammatory reactions.

Elastomeric polypeptides

Elastomeric polypeptides are very interesting biopolymers and are characterized by rubber-like elasticity, large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Their useful properties have motivated their use in a wide variety of materials and biological applications. This chapter focuses on elastin and resilin - two elastomeric biopolymers - and the recombinant polypeptides derived from them (elastin-like polypeptides and resilin-like polypeptides). This chapter also discusses the applications of these recombinant polypeptides in the fields of purification, drug delivery, and tissue engineering.

Attenuation of inflammatory events in human intervertebral disc cells with a tumor necrosis factor antagonist

STUDY DESIGN

The inflammatory responses of primary human intervertebral disc (IVD) cells to tumor necrosis factor α (TNF-α) and an antagonist were evaluated in vitro.

OBJECTIVE

To investigate an ability for soluble TNF receptor type II (sTNFRII) to antagonize TNF-α-induced inflammatory events in primary human IVD cells in vitro.

SUMMARY OF BACKGROUND DATA

TNF-α is a known mediator of inflammation and pain associated with radiculopathy and IVD degeneration. sTNFRs and their analogues are of interest for the clinical treatment of these IVD pathologies, although information on the effects of sTNFR on human IVD cells remains unknown.

METHODS

IVD cells were isolated from surgical tissues procured from 15 patients and cultured with or without 1.4 nmol/L TNF-α (25 ng/mL). Treatment groups were coincubated with varying doses of sTNFRII (12.5-100 nmol/L). Nitric oxide (NO), prostaglandin E₂ (PGE₂), and interleukin-6 (IL6) levels in media were quantified to characterize the inflammatory phenotype of the IVD cells.

RESULTS

Across all patients, TNF-α induced large, statistically significant increases in NO, PGE₂, and IL6 secretion from IVD cells compared with controls (60-, 112-, and 4-fold increases, respectively; P < 0.0001). Coincubation of TNF-α with nanomolar doses of sTNFRII significantly attenuated the secretion of NO and PGE₂ in a dose-dependent manner, whereas IL6 levels were unchanged. Mean IC₅₀ values for NO and PGE₂ were found to be 35.1 and 20.5 nmol/L, respectively.

CONCLUSION

Nanomolar concentrations of sTNFRII were able to significantly attenuate the effects of TNF-α on primary human IVD cells in vitro. These results suggest this sTNFR to be a potent TNF antagonist with potential to attenuate inflammation in IVD pathology.

Thermoresponsive polymeric radionuclide delivery system--an injectable brachytherapy

Brachytherapy is of increasing popularity in clinical oncology for the local therapy of solid tumors due to high radiation doses delivered to malignant tissue while keeping the whole-body radiation burden low. Pronounced dose-dependent tumor growth reduction was achieved by single dose of injectable intratumoral brachytherapy with iodine-131-labeled thermoresponsive polymer [poly(N-isopropyl acrylamide)] in murine xenograft model (PC3 human prostate adenocarcinoma). The two doses of radionuclide were used, 2 MBq/mouse and 25 MBq/mouse. The higher dose caused gradual tumor volume reduction and 2 of 6 mice from this group were cured. The lower dose caused tumor growth retardation only. In both cases there were no signs of inflammation. The effects of both doses were statistically significant compared to untreated controls. Such injectable system should keep advantages of brachytherapy while making system administration easier and less invasive (injection instead of implantation), patient-tailored (splitting of doses into several depoes) and bioerodable.

Recombinant elastin-mimetic biomaterials: Emerging applications in medicine

Biomaterials derived from protein-based block copolymers are increasingly investigated for potential application in medicine. In particular, recombinant elastin block copolymers provide significant opportunities to modulate material microstructure and can be processed in various forms, including particles, films, gels, and fiber networks. As a consequence, biological and mechanical responses of elastin-based biomaterials are tunable through precise control of block size and amino acid sequence. In this review, the synthesis of a set of elastin-mimetic triblock copolymers and their diverse processing methods for generating material platforms currently applied in medicine will be discussed.

Quantitative model of the phase behavior of recombinant pH-responsive elastin-like polypeptides

Quantitative models are required to engineer biomaterials with environmentally responsive properties. With this goal in mind, we developed a model that describes the pH-dependent phase behavior of a class of stimulus responsive elastin-like polypeptides (ELPs) that undergo reversible phase separation in response to their solution environment. Under isothermal conditions, charged ELPs can undergo phase separation when their charge is neutralized. Optimization of this behavior has been challenging because the pH at which they phase separate, pHt, depends on their composition, molecular weight, concentration, and temperature. To address this problem, we developed a quantitative model to describe the phase behavior of charged ELPs that uses the Henderson-Hasselbalch relationship to describe the effect of side-chain ionization on the phase-transition temperature of an ELP. The model was validated with pH-responsive ELPs that contained either acidic (Glu) or basic (His) residues. The phase separation of both ELPs fit this model across a range of pH. These results have important implications for applications of pH-responsive ELPs because they provide a quantitative model for the rational design of pH-responsive polypeptides whose transition can be triggered at a specified pH.

Evaluating intra-articular drug delivery for the treatment of osteoarthritis in a rat model

Osteoarthritis (OA) is a degenerative joint disease that can result in joint pain, loss of joint function, and deleterious effects on activity levels and lifestyle habits. Current therapies for OA are largely aimed at symptomatic relief and may have limited effects on the underlying cascade of joint degradation. Local drug delivery strategies may provide for the development of more successful OA treatment outcomes that have potential to reduce local joint inflammation, reduce joint destruction, offer pain relief, and restore patient activity levels and joint function. As increasing interest turns toward intra-articular drug delivery routes, parallel interest has emerged in evaluating drug biodistribution, safety, and efficacy in preclinical models. Rodent models provide major advantages for the development of drug delivery strategies, chiefly because of lower cost, successful replication of human OA-like characteristics, rapid disease development, and small joint volumes that enable use of lower total drug amounts during protocol development. These models, however, also offer the potential to investigate the therapeutic effects of local drug therapy on animal behavior, including pain sensitivity thresholds and locomotion characteristics. Herein, we describe a translational paradigm for the evaluation of an intra-articular drug delivery strategy in a rat OA model. This model, a rat interleukin-1beta overexpression model, offers the ability to evaluate anti-interleukin-1 therapeutics for drug biodistribution, activity, and safety as well as the therapeutic relief of disease symptoms. Once the action against interleukin-1 is confirmed in vivo, the newly developed anti-inflammatory drug can be evaluated for evidence of disease-modifying effects in more complex preclinical models.

Elastin-like polypeptides revolutionize recombinant protein expression and their biomedical application

Elastin-like polypeptides (ELPs) are highly biocompatible and exhibit a potentially highly useful property: that of a thermally responsive reversible phase transition. These characteristics make ELPs attractive for drug delivery, appealing as materials for tissue repair or engineering, and improve the efficiency with which recombinant proteins can be purified. ELP fusion proteins (referred to as ELPylation) inherit the reversible phase transition property. ELPylation technology recently has been extended to plant cells, and a number of plant-based expression systems have been evaluated for the production of ELPylated proteins. Here, we discuss recent developments in ELP technology and the substantial potential of ELPs for the deployment of transgenic plants as bioreactors to synthesize both biopharmaceuticals and industrial proteins.

Sustained release of antibiotics from injectable and thermally responsive polypeptide depots

Biodegradable polymeric scaffolds are of interest for delivering antibiotics to local sites of infection in orthopaedic applications, such as bone and diarthrodial joints. The objective of this study was to develop a biodegradable scaffold with ease of drug loading in aqueous solution, while providing for drug depot delivery via syringe injection. Elastin-like polypeptides (ELPs) were used for this application, biopolymers of repeating pentapeptide sequences that were thermally triggered to undergo in situ depot formation at body temperature. ELPs were modified to enable loading with the antibiotics, cefazolin, and vancomycin, followed by induction of the phase transition in vitro. Cefazolin and vancomycin concentrations were monitored, as well as bioactivity of the released antibiotics, to test an ability of the ELP depot to provide for prolonged release of bioactive drugs. Further tests of formulation viscosity were conducted to test suitability as an injectable drug carrier. Results demonstrate sustained release of therapeutic concentrations of bioactive antibiotics by the ELP, with first-order time constants for drug release of approximately 25 h for cefazolin and approximately 500 h for vancomycin. These findings illustrate that an injectable, in situ forming ELP depot can provide for sustained release of antibiotics with an effect that varies across antibiotic formulation. ELPs have important advantages for drug delivery, as they are known to be biocompatible, biodegradable, and elicit no known immune response. These benefits suggest distinct advantages over currently used carriers for antibiotic drug delivery in orthopedic applications.

Treatment of neuroinflammation by soluble tumor necrosis factor receptor Type II fused to a thermally responsive carrier

OBJECT

Biochemical irritation of the dorsal root ganglion (DRG) after intervertebral disc herniation contributes to radiculopathy through tumor necrosis factor-alpha (TNFalpha)-mediated inflammation. Soluble TNF receptor Type II (sTNFRII) sequesters this cytokine, providing clinical benefit. Previous work involving conjugation of sTNFRII with thermally responsive elastin-like polypeptide (ELP) yielded a chimeric protein (ELP-sTNFRII) with in vitro anti-TNFalpha bioactivity. Furthermore, temperature-triggered ELP aggregation into a "depot" prolongs protein residence time following perineural injection. In this study the authors evaluated the inflammatory phenotype of DRG explants after TNFalpha stimulation, and assessed the abilities of sTNFRII or ELP-sTNFRII to attenuate these neuro-inflammatory changes.

METHODS

Rat lumbar DRGs (35 animals) were treated in 6 groups, as follows: control; TNFalpha (25 ng/ml); TNFalpha with low-(0.2 microg/ml) or high-dose (1 microg/ml) sTNFRII; and TNFalpha with low-(52.5 microg/ml) or high-dose (262.5 microg/ml) ELP-sTNFRII. After 24 hours, supernatant was evaluated for inflammatory cytokines (interleukin [IL]-1, IL-6, and IL-10); prostaglandin E2; and metabolites (glutamate, lactate, and pyruvate). Single-factor analysis of variance with post hoc Dunn analysis (alpha = 0.05) was used to assess treatment differences.

RESULTS

Incubation of explants with TNFalpha caused metabolic stress reflected by an increased lactate/pyruvate ratio (1.8 +/- 0.5-fold) and extracellular glutamate (79 +/- 8% increase). Inflammatory activation was observed with heightened IL-6 release (5.2 +/- 1.4-fold) and prostaglandin E2 production (14 +/- 3-fold). An autoregulatory response occurred with an 11.8 +/- 0.6-fold increase in sTNFRI shedding. Treatment with high doses of sTNFRII or ELP-sTNFRII reversed all changes. Values are expressed as the mean +/- standard deviation.

CONCLUSIONS

These results demonstrate that TNFalpha stimulation of DRG explants yields a phenotype of neurotoxic metabolite release and inflammatory mediator expression. Coincubation with either sTNFRII or ELP-sTNFRII antagonizes TNFalpha activity to abrogate these changes, suggesting potential for therapeutic intervention to treat peripheral nerve inflammatory disease.

Synthesis and characterization of a thermally-responsive tumor necrosis factor antagonist

Numerous antagonists of tumor necrosis factor alpha (TNFalpha) have been developed to attenuate inflammation and accompanying pain in many disease processes. Soluble TNF receptor type II (sTNFRII) is one such antagonist that sequesters TNFalpha away from target receptors and attenuates its activity. Systemic delivery of soluble TNF receptors or other antagonists may have deleterious side effects associated with immune suppression, so that strategies for locally targeted drug delivery are of interest. Elastin-like polypeptides (ELPs) are biopolymers capable of in situ drug depot formation through thermally-driven supramolecular complexes at physiological temperatures. A recombinant fusion protein between ELP and sTNFRII was designed and evaluated for retention of bivalent functionality. Thermal sensitivity was observed by formation of supramolecular submicron-sized particles at 32 degrees C, with gradual resolubilization from the depot observed at physiological temperatures. In vitro refolding of the sTNFRII domain was required and the purified product exhibited an equilibrium dissociation constant for interacting with TNFalpha that was seven-fold higher than free sTNFRII. Furthermore, anti-TNF activity was observed in inhibiting TNFalpha-mediated cytotoxicity in the murine L929 fibrosarcoma assay. Potential advantages of this ELP-sTNFRII fusion protein as an anti-TNFa drug depot include facility of injection, in situ depot formation, low endotoxin content, and functionality against TNFalpha.