Steric stabilization of bioactive nanoparticles using elastin-like polypeptides

Elastin-like polypeptides (ELP) are versatile, thermo-responsive polymers that can be conjugated to virtually any therapeutic cargo. Derived from short amino-acid sequences and abundant in humans, certain ELPs display low immunogenicity. Substrates for endogenous proteases, ELPs are biodegradable and thus, are candidate biomaterials. Peptides and proteins can be directly coupled with ELPs through genetic engineering, while other polymers and small molecules can be appended through covalent bioconjugation or non-covalent complexation. ELPs that phase separate at physiological temperatures can form the core of nano assemblies; however, ELPs that remain soluble can sterically stabilize the corona of a variety of nanoparticles. Nanoparticles with ELPs at their corona promote colloids with favorable pharmacokinetic (PK) properties that enables therapeutic efficacy with intermittent administration. This review highlights a comprehensive spectrum of ELP fusions shown to stabilize the solubility, and sometimes bioactivity, of their cargo - with a focus on biophysical properties that underlie their therapeutic effects.

Pharmacokinetic model of human exposure to ciprofloxacin through consumption of fish

Fluoroquinolones are broad-spectrum antibiotics that accumulate in the environment. To assess human exposure through the food chain, we developed a pharmacokinetic model of fluoroquinolone accumulation in fish and a human pharmacokinetic model to predict gastrointestinal concentrations of ciprofloxacin, a common fluoroquinolone, following consumption of fish. At 70 ng/L ciprofloxacin, the average in North American surface waters, the fish steady-state concentration was calculated to be 7.5 × 10-6 µg/g. Upon human consumption of the FDA-recommended portion of 113 g of fish containing this ciprofloxacin level, the predicted human intestinal concentration was 2 × 10-6 µg/mL. At 4 × 106 ng/L (4 µg/mL) ciprofloxacin, the highest recorded environmental measurement, these numbers were 0.42 µg/g in fish and 0.1 µg/mL in the human intestine. Thus, based on the ciprofloxacin MIC for E. coli of 0.13 µg/mL, background environmental ciprofloxacin levels are unlikely to be problematic, but environmental pollution can result in high intestinal levels that may cause gut dysbiosis and antibiotic resistance.

Noncovalent Conjugation of OVA323 to ELP Micelles Increases Immune Response

Subunit vaccines would benefit from a safe particle-based adjuvant. Elastin-like polypeptide (ELP)-based micelles are interesting candidate adjuvants due to their well-defined size and easy modification with protein-based cargo. Coiled coils can facilitate noncovalent modifications, while potentially enhancing antigen delivery through interaction with cell membranes. ELP micelles comprise ELP diblock copolymers that self-assemble above a critical micelle temperature. In this study, an amphiphilic ELP was conjugated to peptide "K", which forms a heterodimeric coiled-coil complex with peptide "E". Self-assembled "covalent" micelles containing ELP-OVA323 (i.e., model antigen OVA323 conjugated to ELP), "coiled-coil" micelles containing ELP-K/E-OVA323 and "hybrid" micelles containing ELP-K and ELP-OVA323 were shown to be monodisperse and spherical. Dendritic cells (DCs) were exposed to all micelle compositions, and T-cell proliferation was investigated. The presence of ELP-K enhanced micelle uptake and subsequent DC maturation, resulting in enhanced CD4+ T-cell proliferation, which makes ELPs with coiled coil-associated antigens a promising vaccine platform.

αB-Crystallin Peptide Fused with Elastin-like Polypeptide: Intracellular Activity in Retinal Pigment Epithelial Cells Challenged with Oxidative Stress

BACKGROUND

Oxidative stress-induced retinal degeneration is among the main contributing factors of serious ocular pathologies that can lead to irreversible blindness. αB-crystallin (cry) is an abundant component of the visual pathway in the vitreous humor, which modulates protein and cellular homeostasis. Within this protein exists a 20 amino acid fragment (mini-cry) with both chaperone and antiapoptotic activity. This study fuses this mini-cry peptide to two temperature-sensitive elastin-like polypeptides (ELP) with the goal of prolonging its activity in the retina.

METHODS

The biophysical properties and chaperone activity of cry-ELPs were confirmed by mass spectrometry, cloud-point determination, and dynamic light scattering 'DLS'. For the first time, this work compares a simpler ELP architecture, cry-V96, with a previously reported ELP diblock copolymer, cry-SI. Their relative mechanisms of cellular uptake and antiapoptotic potential were tested using retinal pigment epithelial cells (ARPE-19). Oxidative stress was induced with H2O2 and comparative internalization of both cry-ELPs was made using 2D and 3D culture models. We also explored the role of lysosomal membrane permeabilization by confocal microscopy.

RESULTS

The results indicated successful ELP fusion, cellular association with both 2D and 3D cultures, which were enhanced by oxidative stress. Both constructs suppressed apoptotic signaling (cleaved caspase-3); however, cry-V96 exhibited greater lysosomal escape.

CONCLUSIONS

ELP architecture is a critical factor to optimize delivery of therapeutic peptides, such as the anti-apoptotic mini-cry peptide; furthermore, the protection of mini-cry via ELPs is enhanced by lysosomal membrane permeabilization.

Biomimetic SARS-CoV-2 Spike Protein Nanoparticles

COVID-19 is an infectious respiratory disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This virus contains a crucial coat protein that engages with target cells via a receptor binding domain (RBD) on its spike protein. To better study the RBD and its therapeutic opportunities, we genetically engineered a simple fusion with a thermo-responsive elastin-like polypeptide (ELP). These fusions express in Escherichia coli at a high yield in the soluble fraction and were easily purified using ELP-mediated phase separation (79 mg/L culture). Interestingly, they assembled peptide-based nanoparticles (Rh = 71.4 nm), which was attributed to oligomerization of RBDs (25.3 kDa) counterbalanced by steric stabilization by a soluble ELP (73.4 kDa). To investigate their biophysical properties, we explored the size, shape, and binding affinity for the human angiotensin-converting enzyme 2 (hACE2) and cellular uptake. Biomimetic nanoparticles such as these may enable future strategies to target the same cells, tissues, and cell-surface receptors as those harnessed by SARS-CoV-2.

Protein and polypeptide mediated delivery to the eye

Hybrid or recombinant protein-polymers, peptide-based biomaterials, and antibody-targeted therapeutics are widely explored for various ocular conditions and vision correction. They have been noted for their potential biocompatibility, potency, adaptability, and opportunities for sustained drug delivery. Unique to peptide and protein therapeutics, their production by cellular translation allows their precise modification through genetic engineering. To a greater extent than drug delivery to other systems, delivery to the eye can benefit from the combination of locally-targeted administration and protein-based specificity. Consequently, a range of delivery platforms and administration methods have been exploited to address the ocular delivery of peptide and protein biomaterials. This review discusses a sample of preclinical and clinical opportunities for peptide-based drug delivery to the eye.

Hydra-Elastin-like Polypeptides Increase Rapamycin Potency When Targeting Cell Surface GRP78

Rapalogues are powerful therapeutic modalities for breast cancer; however, they suffer from low solubility and dose-limiting side effects. To overcome these challenges, we developed a long-circulating multiheaded drug carrier called 5FA, which contains rapamycin-binding domains linked with elastin-like polypeptides (ELPs). To target these "Hydra-ELPs" toward breast cancer, we here linked 5FA with four distinct peptides which are reported to engage the cell surface form of the 78 kDa glucose-regulated protein (csGRP78). To determine if these peptides affected the carrier solubility, this library was characterized by light scattering and mass spectrometry. To guide in vitro selection of the most potent functional carrier for rapamycin, its uptake and inhibition of mTORC1 were monitored in a ductal breast cancer model (BT474). Using flow cytometry to track cellular association, it was found that only the targeted carriers enhanced cellular uptake and were susceptible to proteolysis by SubA, which specifically targets csGRP78. The functional inhibition of mTOR was monitored by Western blot for pS6K, whereby the best carrier L-5FA reduced mTOR activity by 3-fold compared to 5FA or free rapamycin. L-5FA was further visualized using super-resolution confocal laser scanning microscopy, which revealed that targeting increased exposure to the carrier by ∼8-fold. This study demonstrates how peptide ligands for GRP78, such as the L peptide (RLLDTNRPLLPY), may be incorporated into protein-based drug carriers to enhance targeting.

Supra-lacrimal protein-based carriers for cyclosporine A reduce Th17-mediated autoimmunity in murine model of Sjögren's syndrome

Sjögren's syndrome (SS) is a multifactorial autoimmune disease with principal symptoms including inflammation and loss of function of lacrimal glands (LG) and salivary glands. While glandular infiltrates includes both B- and T-cells, CD4+ T cells are strongly implicated. Utilizing the male non-obese diabetic (NOD) mouse model of SS, this work: 1) identifies clinically-relevant elevations in cytokines (IL-17A, IL-2) in LG-derived CD4+ T cells; and 2) explores tissue-specific immunosuppression of SS using a novel protein-based drug carrier to concentrate cyclosporine A (CsA) directly in the LG. As a potent immunosuppressant, topical ophthalmic CsA is approved for dry eye disorders; however, it cannot effectively resolve inflammation due to limited accumulation in the LG. Systemic CsA has dose-limiting side effects that also limit its ability to block LG inflammation. Using elastin-like polypeptides (ELPs) fused genetically to cyclophilin, the intracellular cognate receptor of CsA, this manuscript reports a sustained-release formulation of CsA that maintains therapeutic drug concentrations in the LG and extends intervals between doses. This formulation blocked both in vitro Th17 cell differentiation and IL-17A secretion. In vivo treatment significantly decreased the abundance of Th17.1 cells, a helper cell population sharing phenotypes of both Th17 and Th1, in the LG of diseased NOD mice. Treatment with even a single dose of the sustained-release formulation was effective enough to improve basal levels of tear production. Thus, this sustained-release formulation suppressed local LG inflammation driven through IL-17 dependent pathways, while improving ocular surface function.

Intracellular Dynamin Elastin-like Polypeptides Assemble into Rodlike, Spherical, and Reticular Dynasomes

Dynamin (DNM) is a family of large GTPases possessing a unique mechanical ability to "pinch" off vesicles entering cells. DNM2 is the most ubiquitously expressed member of the DNM family. We developed a novel tool based on elastin-like polypeptide (ELP) technology to quickly, precisely, and reversibly modulate the structure of DNM2. ELPs are temperature-sensitive biopolymers that self-assemble into microdomains above sharp transition temperatures. When linked together, DNM2 and a temperature-sensitive ELP fusion organize into a range of distinct temperature-dependent structures above a sharp transition temperature, which were not observed with wild-type DNM2 or a temperature-insensitive ELP fusion control. The structures comprised three different morphologies, which were prevalent at different temperature ranges. The size of these structures was influenced by an inhibitor of the DNM2 GTPase activity, dynasore; furthermore, they appear to entrap co-expressed cytosolic ELPs. Having demonstrated an unexpected diversity of morphologically distinct structures, DNM2-ELP fusions may have applications in the exploration of dynamin-dependent biology.

Bet v 1-displaying elastin-like polypeptide nanoparticles induce a strong humoral and weak CD4+ T-cell response against Bet v 1 in a murine immunogenicity model

There is growing concern about the toxicity of colloidal aluminum salts used as adjuvants in subcutaneous allergen immunotherapy (SCIT). Therefore, alternative adjuvants and delivery systems are being explored to replace alum in SCIT. We applied micellar elastin-like polypeptides (ELPs), a type of self-assembling protein, to replace alum as vaccine adjuvant in birch pollen SCIT. ELP and an ELP-Bet v 1 fusion protein were expressed in E. coli and purified by immuno-affinity chromatography and inverse-transition cycling (ITC). Nanoparticles self-assembled from ELP and a 9:1 ELP/ELP-Bet v 1 mixture were characterized by using dynamic light scattering and atomic force microscopy. Allergenicity was assessed by measuring mediator release from rat basophilic leukemia cells transformed with the human FcϵR1 and sensitized with sera derived from human birch pollen allergic patients. Humoral and T-cell immunity were investigated by immunizing naïve mice with the ELP/ELP-Bet v 1 nanoparticles or alum-adsorbed Bet v 1, both containing 36 µg Bet v 1. ELP and ELP/ELP-Bet v 1 self-assembled at 37°C into spherically shaped micelles with a diameter of ~45 nm. ELP conjugation made Bet v 1 hypo-allergenic (10-fold). Compared to alum-adsorbed Bet v 1, ELP/ELP-Bet v 1 nanoparticles induced stronger IgG responses with an earlier onset. Additionally, ELP/ELP-Bet v 1 did not induce Th2 skewing cytokines and IgE. The hypoallergenic character and strong humoral immune response in the absence of a Th2-skewing T-cell response make ELP-based nanoparticles a promising candidate to replace alum in SCIT.

Intralacrimal Sustained Delivery of Rapamycin Shows Therapeutic Effects without Systemic Toxicity in a Mouse Model of Autoimmune Dacryoadenitis Characteristic of Sjögren's Syndrome

Sjögren's syndrome (SS) is an autoimmune disease associated with severe exocrinopathy, which is characterized by profound lymphocytic infiltration (dacryoadenitis) and loss of function of the tear-producing lacrimal glands (LGs). Systemic administration of Rapamycin (Rapa) significantly reduces LG inflammation in the male Nonobese Diabetic (NOD) model of SS-associated autoimmune dacryoadenitis. However, the systemic toxicity of this potent immunosuppressant limits its application. As an alternative, this paper reports an intra-LG delivery method using a depot formulation comprised of a thermoresponsive elastin-like polypeptide (ELP) and FKBP, the cognate receptor for Rapa (5FV). Depot formation was confirmed in excised whole LG using cleared tissue and observation by both laser-scanning confocal and lightsheet microscopy. The LG depot was evaluated for safety, efficacy, and intra-LG pharmacokinetics in the NOD mouse disease model. Intra-LG injection with the depot formulation (5FV) retained Rapa in the LG for a mean residence time (MRT) of 75.6 h compared to Rapa delivery complexed with a soluble carrier control (5FA), which had a MRT of 11.7 h in the LG. Compared to systemic delivery of Rapa every other day for 2 weeks (seven doses), a single intra-LG depot of Rapa representing 16-fold less total drug was sufficient to inhibit LG inflammation and improve tear production. This treatment modality further reduced markers of hyperglycemia and hyperlipidemia while showing no evidence of necrosis or fibrosis in the LG. This approach represents a potential new therapy for SS-related autoimmune dacryoadenitis, which may be adapted for local delivery at other sites of inflammation; furthermore, these findings reveal the utility of optical imaging for monitoring the disposition of locally administered therapeutics.

Live long and active: Polypeptide-mediated assembly of antibody variable fragments

Antibodies possess multiple biologically relevant features that have been engineered into new therapeutic formats. Two examples include the adaptable specificity of their variable (Fv) region and the extension of plasma circulation times through their crystallizable (Fc) region. Since the invention of the single chain variable fragment (scFv) in 1988, antibody variable regions have been re-engineered into a wide variety of multifunctional nanostructures. Among these strategies, peptide-mediated self-assembly of variable regions through heterologous expression has become a powerful method to produce homogenous, functional biomaterials. This manuscript reviews recent reports of antibody fragments assembled through fusion with peptides and proteins, including elastin-like polypeptides (ELPs), collagen-like polypeptides (CLPs), albumin, transmembrane proteins, leucine zippers, silk protein, and viruses. This review further discusses the current clinical status of engineered antibody fragments and challenges to overcome.

Adaptable antibody Nanoworms designed for non-Hodgkin lymphoma

Despite advancements in antibody-based therapies for non-Hodgkin lymphoma (NHL), at least two major therapeutic needs remain unmet: i) heterogenous activation of host immunity towards B cell NHL; and ii) lack of antibody-based therapeutics for T cell NHL. This study explores the molecular characteristics of an adaptable modality called antibody Nanoworms and demonstrates their receptor clustering activity as a means to overcome and address abovementioned needs. To test this, four selected therapeutic receptors of B cell (CD19, CD20, HLA-DR10) and T cell (CD3) NHL were targeted by Nanoworms. Regardless of the target or the cell type, Nanoworms inherently clustered bound receptors on the cell-surface through their multivalency and activated intracellular signaling without any secondary crosslinker. As a sole agent, Nanoworms induced apoptosis by clustering CD20 or HLA-DR10, and arrested the cell cycle upon CD19 clustering. Interestingly, CD3 clustering was particularly advantageous in inducing activation-induced cell death (AICD) in an aggressive form of T cell NHL named Sézary syndrome that is fatal, limited in antibody-based therapeutics, and has poor outcomes to traditional chemotherapy. As Nanoworms can be easily designed to target any receptor for which a scFv is available, they may provide solutions and add therapeutic novelty to underserved diseases.

Anti-CD99 scFv-ELP nanoworms for the treatment of acute myeloid leukemia

CD99 is a transmembrane glycoprotein shown to be upregulated in various malignancies. We have previously reported CD99 to be highly upregulated and present a viable therapeutic target in acute myeloid leukemia (AML). Currently, no therapy against CD99 is under clinical investigation. As a surface molecule, CD99 can be targeted with an antibody-based approach. Here, we have developed a new modality to target CD99 by engineering a fusion protein composed of a single-chain variable fragment antibody (anti-CD99 scFv) conjugated with a high molecular weight elastin-like polypeptide (ELP), A192: α-CD99-A192. This fusion protein assembles into multi-valent nanoworm with optimal physicochemical properties and favorable pharmacokinetic parameters (half-life: 16 h). α-CD99-A192 nanoworms demonstrated excellent in vitro and in vivo anti-leukemic effects. α-CD99-A192 induced apoptotic cell death in AML cell lines and primary blasts and prolonged overall survival of AML xenograft mouse model.

Human Granulocyte-Macrophage Colony-Stimulating Factor Fused to Elastin-Like Polypeptides Assembles Biologically-Active Nanoparticles

Human granulocyte-macrophage colony-stimulating factor (hGMCSF) is crucial in the immune system as it stimulates survival, proliferation, differentiation, and functional activation of myeloid hematopoietic cells. hGMCSF is integral to approved therapies, including monoclonal antibodies against checkpoint inhibitors, chimeric antigen receptors, and prevention of chemotherapy-induced neutropenia. Recombinant hGMCSF can be purified from Escherichia. coli; however, it forms inclusion bodies that require solubilization and refolding. Alternatively, this manuscript describes its fusion with an elastin-like polypeptide (ELP). Previously reported as purification tags and solubility enhancers, ELPs are recombinant polypeptides that undergo reversible temperature-dependent phase separation. This report is the first to show that fusion to an ELP enables direct purification of hGMCSF fusions from the soluble fraction of bacterial lysate. Surprisingly, these ELP-fusions assemble stable, small, spherical nanoparticles that maintain pro-mitotic activity of hGMCSF. These nanoparticles exhibit ELP-mediated phase separation; however, nanoparticle assembly significantly increases the entropic and enthalpic cost of phase separation compared to ELP alone. The attachment of a high molecular weight ELP to a difficult-to-express protein, like hGMCSF, appears to be a useful strategy to stabilize bioactive, protein-based nanoparticles, which may have broad applications in medicine and biology.

A Multivalent ICAM-1 Binding Nanoparticle which Inhibits ICAM-1 and LFA-1 Interaction Represents a New Tool for the Investigation of Autoimmune-Mediated Dry Eye

The autoimmune disorder, Sjögren’s syndrome (SS), is characterized by lymphocytic infiltration and loss of function of exocrine glands such as the lacrimal gland (LG) and salivary gland. SS-associated changes in the LG are associated with the development of autoimmune-mediated dry eye disease. We have previously reported the accumulation of intercellular adhesion molecule 1 (ICAM-1) in the LG of Non-Obese Diabetic (NOD) mice, a murine model of autoimmune-mediated dry eye in SS, in both LG acinar cells and infiltrating lymphocytes. ICAM-1 initiates T-cell activation and can trigger T-cell migration through binding to lymphocyte function-associated 1 antigen (LFA). To modulate this interaction, this study introduces a new tool, a multivalent biopolymeric nanoparticle assembled from a diblock elastin-like polypeptide (ELP) using the S48I48 (SI) ELP scaffold fused with a mouse ICAM-1 targeting peptide to form IBP-SI. IBP-SI forms a multivalent, monodisperse nanoparticle with a radius of 21.9 nm. Unlike the parent SI, IBP-SI binds mouse ICAM-1 and is internalized by endocytosis into transfected HeLa cells before it accumulates in lysosomes. In vitro assays measuring lymphocyte adhesion to Tumor Necrosis Factor TNF-α-treated bEnd.3 cells, which express high levels of ICAM-1, show that adhesion is inhibited by IBP-SI but not by SI, with IC₅₀ values of 62.7 μM and 81.2 μM, respectively, in two different assay formats. IBP-SI, but not SI, also blocked T-cell proliferation in a mixed lymphocyte reaction by 74% relative to proliferation in an untreated mixed cell reaction. These data suggest that a biopolymeric nanoparticle with affinity for ICAM-1 can disrupt ICAM-1 and LFA interactions in vitro and may have further utility as an in vivo tool or potential therapeutic.

Molecular Targeting of Immunosuppressants Using a Bifunctional Elastin-Like Polypeptide

Elastin-Like Polypeptides (ELP) are environmentally responsive protein polymers which are easy to engineer and biocompatible, making them ideal candidates as drug carriers. Our team has recently utilized ELPs fused to FKBP12 to carry Rapamycin (Rapa), a potent immunosuppressant. Through high affinity binding to Rapa, FKBP carriers can yield beneficial therapeutic effects and reduce the off-site toxicity of Rapa. Since ICAM-1 is significantly elevated at sites of inflammation in diverse diseases, we hypothesized that a molecularly targeted ELP carrier capable of binding ICAM-1 might have advantageous properties. Here we report on the design, characterization, pharmacokinetics, and biodistribution of a new ICAM-1-targeted ELP Rapa carrier (IBPAF) and its preliminary characterization in a murine model exhibiting elevated ICAM-1. Lacrimal glands (LG) of male NOD mice, a disease model recapitulating the autoimmune dacryoadenitis seen in Sjögren's Syndrome patients, were analyzed to confirm that ICAM-1 was significantly elevated in the LG relative to control male BALB/c mice (3.5-fold, p < 0.05, n = 6). In vitro studies showed that IBPAF had significantly higher binding to TNF-α-stimulated bEnd.3 cells which overexpress surface ICAM-1, relative to nontargeted control ELP (AF)(4.0-fold, p < 0.05). A pharmacokinetics study in male NOD mice showed no significant differences between AF and IBPAF for plasma half-life, clearance, and volume of distribution. However, both constructs maintained a higher level of Rapa in systemic circulation compared to free Rapa. Interestingly, in the male NOD mouse, the accumulation of IBPAF was significantly higher in homogenized LG extracts compared to AF at 2 h (8.6 ± 6.6% versus 1.3 ± 1.3%, respectively, n = 5, p < 0.05). This accumulation was transient with no differences detected at 8 or 24 h. This study describes the first ICAM-1 targeted protein-polymer carrier for Rapa that specifically binds to ICAM-1 in vitro and accumulates in ICAM-1 overexpressing tissue in vivo, which may be useful for molecular targeting in diverse inflammatory diseases where ICAM-1 is elevated.

Generation of a Monoclonal Antibody to Detect Elastin-like Polypeptides

The identification and use of antibodies dominate the biologic, clinical diagnostic, and therapeutic landscapes. In particular, antibodies have become essential tools in a variety of protein analytical experiments and to study the disposition of biologic therapeutics. One emerging class of peptide biologics is known as the elastin-like polypeptides (ELPs), which are repetitive protein polymers inspired by human tropoelastin. A major limitation in the clinical translation of ELP biologics has been a lack of a monoclonal antibody (mAb) to characterize their identity during expression. To facilitate these studies, we successfully generated a new mAb that is specific toward ELPs and ELP fusion proteins. A purified antibody was evaluated in an ELISA, western blotting, and immunofluorescence assay. The optimal anti-ELP mAb proved to be highly reactive and specific toward ELPs. Moreover, they were able to detect ELPs with a variety of aliphatic guest residues. ELPs phase-separate in response to heating; furthermore, when incubated at a great excess of ELPs, the anti-ELP mAb partially blocks phase separation. These findings are direct evidence that novel murine mAbs can be raised against purified ELPs. This new reagent will enable purification, experimental detection, and characterization of these biopolymers.

Inhibition of Cathepsin S Reduces Lacrimal Gland Inflammation and Increases Tear Flow in a Mouse Model of Sjögren's Syndrome

Cathepsin S (CTSS) is highly increased in Sjögren's syndrome (SS) patients tears and in tears and lacrimal glands (LG) of male non-obese diabetic (NOD) mice, a murine model of SS. To explore CTSS's utility as a therapeutic target for mitigating ocular manifestations of SS in sites where CTSS is increased in disease, the tears and the LG (systemically), the peptide-based inhibitor, Z-FL-COCHO (Z-FL), was administered to 14-15 week male NOD mice. Systemic intraperitoneal (i.p.) injection for 2 weeks significantly reduced CTSS activity in tears, LG and spleen, significantly reduced total lymphocytic infiltration into LG, reduced CD3+ and CD68+ cell abundance within lymphocytic infiltrates, and significantly increased stimulated tear secretion. Topical administration of Z-FL to a different cohort of 14-15 week male NOD mice for 6 weeks significantly reduced only tear CTSS while not affecting LG and spleen CTSS and attenuated the disease-progression related reduction of basal tear secretion, while not significantly impacting lymphocytic infiltration of the LG. These findings suggest that CTSS inhibitors administered either topically or systemically can mitigate aspects of the ocular manifestations of SS.

Berunda Polypeptides: Biheaded Rapamycin Carriers for Subcutaneous Treatment of Autoimmune Dry Eye Disease

The USFDA-approved immunosuppressive drug rapamycin (Rapa), despite its potency, is limited by poor bioavailability and a narrow therapeutic index. In this study, we sought to improve bioavailability of Rapa with subcutaneous (SC) administration and to test its therapeutic feasibility and practicality in a murine model of Sjögren's syndrome (SS), a systemic autoimmune disease with no approved therapies. To improve its therapeutic index, we formulated Rapa with a carrier termed FAF, a fusion of the human cytosolic FK506-binding protein 12 (FKBP12) and an elastin-like polypeptide (ELP). The resulting 97 kDa FAF (i) has minimal burst release, (ii) is "humanized", (iii) is biodegradable, (iv) solubilizes two Rapa per FAF, and (v) avoids organic solvents or amphiphilic carriers. Demonstrating high stability, FAF remained soluble and monodisperse with a hydrodynamic radius of 8 nm at physiological temperature. A complete pharmacokinetic (PK) analysis of FAF revealed that the bioavailability of SC FAF was 60%, with significantly higher blood concentration during the elimination phase compared to IV FAF. The plasma concentration of Rapa delivered by FAF was 8-fold higher with a significantly increased plasma-to-whole blood ratio relative to free Rapa, 24 h after injection. To evaluate therapeutic effects, FAF-Rapa was administered SC every other day for 2 weeks to male non-obese diabetic (NOD) mice, which develop an SS-like autoimmune-mediated lacrimal gland (LG) inflammation and other characteristic features of SS. Both FAF-Rapa and free Rapa exhibited immunomodulatory effects by significantly suppressing lymphocytic infiltration, gene expression of IFN-γ, MHC II, type I collagen and IL-12a, and cathepsin S (CTSS) activity in LG compared to controls. Serum chemistry and histopathological analyses in major organs revealed no apparent toxicity of FAF-Rapa. Given its improved PK and equipotent therapeutic efficacy compared to free Rapa, FAF-Rapa is of further interest for systemic treatments for autoimmune diseases like SS.

Thermally-Responsive Loading and Release of Elastin-Like Polypeptides from Contact Lenses

Contact lenses are widely prescribed for vision correction, and as such they are an attractive platform for drug delivery to the anterior segment of the eye. This manuscript explores a novel strategy to drive the reversible adsorption of peptide-based therapeutics using commercially available contact lenses. To accomplish this, thermo-sensitive elastin-like polypeptides (ELPs) alone or tagged with a candidate ocular therapeutic were characterized. For the first time, this manuscript demonstrates that Proclear Compatibles^TM contact lenses are a suitable platform for ELP adsorption. Two rhodamine-labelled ELPs, V96 (thermo-sensitive) and S96 (thermo-insensitive), were employed to test temperature-dependent association to the contact lenses. During long-term release into solution, ELP coacervation significantly modulated the release profile whereby more than 80% of loaded V96 retained with a terminal half-life of ~4 months, which was only 1–4 days under solubilizing conditions. A selected ocular therapeutic candidate lacritin-V96 fusion (LV96), either free or lens-bound LV96, was successfully transferred to HCE-T cells. These data suggest that ELPs may be useful to control loading or release from certain formulations of contact lenses and present a potential for this platform to deliver a biologically active peptide to the ocular surface via contact lenses.

Tunable assembly of protein-microdomains in living vertebrate embryos

Subcellular events such as trafficking and signaling are regulated by self-assembled protein complexes inside the cell. The ability to rapidly and reversibly manipulate these protein complexes would likely enhance studies of their mechanisms and their roles in biological function and disease manifestation.^{[1, 2]} This manuscript reports that thermally-responsive elastin-like polypeptides (ELPs) linked to fluorescent proteins can regulate the self-assembly and disassembly of protein microdomains within the individual cells of zebrafish embryos. By exploring a library of fluorescent ELP proteins, this reports demonstrates that ELPs can co-assemble different fluorescent proteins inside of embryos. By tuning ELP length and sequence, fluorescent protein microdomains can be assembled at different temperatures, in varying sizes, or for desired periods of time. For the first time in a multicellular living embryo, these studies demonstrate that temperature-mediated ELP assembly can reversibly manipulate assembly of subcellular protein complexes, which may have applications in the study and manipulation of in vivo biological functions.

NOD and NOR mice exhibit comparable development of lacrimal gland secretory dysfunction but NOD mice have more severe autoimmune dacryoadenitis

The male Non-Obese Diabetic (NOD) mouse is an established model of autoimmune dacryoadenitis characteristic of Sjögren's Syndrome (SS), but development of diabetes may complicate studies. The Non-Obese Diabetes Resistant (NOR) mouse is a MHC-II matched diabetes-resistant alternative, but development of autoimmune dacryoadenitis is not well-characterized. We compare features of SS in male NOD and NOR mice at 12 and 20 weeks. Stimulated tear secretion was decreased in 12 week NOD relative to BALB/c mice (p < 0.05), while by 20 weeks both NOD and NOR showed decreased stimulated tear secretion relative to BALB/c mice (p < 0.001). Tear CTSS activity was elevated in NOD and NOR relative to BALB/c mice (p < 0.05) at 12 and 20 weeks. While NOD and NOR lacrimal glands (LG) showed increased LG lymphocytic infiltration at 12 and 20 weeks relative to BALB/c mouse LG (p < 0.05), the percentage in NOD was higher relative to NOR at each age (p < 0.05). Gene expression of CTSS, MHC II and IFN-γ in LG were significantly increased in NOD but not NOR relative to BALB/c at 12 and 20 weeks. Redistribution of the secretory effector, Rab3D in acinar cells was observed at both time points in NOD and NOR, but thinning of myoepithelial cells at 12 weeks in NOD and NOR mice was restored by 20 weeks in NOR mice. NOD and NOR mice share features of SS-like autoimmune dacryoadenitis, suggesting common disease etiology. Other findings suggest more pronounced lymphocytic infiltration in NOD mouse LG including increased pro-inflammatory factors that may be unique to this model.

Intra-vitreal αB crystallin fused to elastin-like polypeptide provides neuroprotection in a mouse model of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe and irreversible central vision loss, and the primary site of AMD pathology is the retinal pigment epithelium (RPE). Geographic atrophy (GA) is an advanced form of AMD characterized by extensive RPE cell loss, subsequent degeneration of photoreceptors, and thinning of retina. This report describes the protective potential of a peptide derived from the αB crystallin protein using a sodium iodate (NaIO₃) induced mouse model of GA. Systemic NaIO₃ challenge causes degeneration of the RPE and neighboring photoreceptors, which have similarities to retinas of GA patients. αB crystallin is an abundant ocular protein that maintains ocular clarity and retinal homeostasis, and a small peptide from this protein (mini cry) displays neuroprotective properties. To retain this peptide for longer in the vitreous, mini cry was fused to an elastin-like polypeptide (ELP). A single intra-vitreal treatment by this crySI fusion significantly inhibits retinal degeneration in comparison to free mini cry. While mini cry is cleared from the eye with a mean residence time of 0.4 days, crySI is retained with a mean residence time of 3.0 days; furthermore, fundus photography reveals evidence of retention at two weeks. Unlike the free mini cry, crySI protects the RPE against NaIO₃ challenge for at least two weeks after administration. CrySI also inhibits RPE apoptosis and caspase-3 activation and protects the retina from cell death up to 1-month post NaIO₃ challenge. These results show that intra-ocular ELP-linked peptides such as crySI hold promise as protective agents to prevent RPE atrophy and progressive retinal degeneration in AMD.

Bifunctional Elastin-like Polypeptide Nanoparticles Bind Rapamycin and Integrins and Suppress Tumor Growth in Vivo

Recombinant protein-polymer scaffolds such as elastin-like polypeptides (ELPs) offer drug-delivery opportunities including biocompatibility, monodispersity, and multifunctionality. We recently reported that the fusion of FK-506 binding protein 12 (FKBP) to an ELP nanoparticle (FSI) increases rapamycin (Rapa) solubility, suppresses tumor growth in breast cancer xenografts, and reduces side effects observed with free-drug controls. This new report significantly advances this carrier strategy by demonstrating the coassembly of two different ELP diblock copolymers containing drug-loading and tumor-targeting domains. A new ELP nanoparticle (ISR) was synthesized that includes the canonical integrin-targeting ligand (Arg-Gly-Asp, RGD). FSI and ISR mixed in a 1:1 molar ratio coassemble into bifunctional nanoparticles containing both the FKBP domain for Rapa loading and the RGD ligand for integrin binding. Coassembled nanoparticles were evaluated for bifunctionality by performing in vitro cell-binding and drug-retention assays and in vivo MDA-MB-468 breast tumor regression and tumor-accumulation studies. The bifunctional nanoparticle demonstrated superior cell target binding and similar drug retention to FSI; however, it enhanced the formulation potency, such that tumor growth was suppressed at a 3-fold lower dose compared to an untargeted FSI-Rapa control. This data suggests that ELP-mediated scaffolds are useful tools for generating multifunctional nanomedicines with potential activity in cancer.

Berunda Polypeptides: Multi-Headed Fusion Proteins Promote Subcutaneous Administration of Rapamycin to Breast Cancer In Vivo

Recombinant Elastin-Like Polypeptides (ELPs) serve as attractive scaffolds for nanoformulations because they can be charge-neutral, water soluble, high molecular weight, monodisperse, biodegradable, and decorated with functional proteins. We recently reported that fusion of the FK-506 binding protein 12 (FKBP) to an ELP nanoparticle (FSI) reduces rapamycin (Rapa) toxicity and enables intravenous (IV) therapy in both a xenograft breast cancer model and a murine autoimmune disease model. Rapa has poor solubility, which leads to variable oral bioavailability or drug precipitation following parenteral administration. While IV administration is routine during chemotherapy, cytostatic molecules like Rapa would require repeat administrations in clinical settings. To optimize FKBP/Rapa for subcutaneous (SC) administration, this manuscript expands upon first-generation FSI nanoparticles (R_h ~ 25 nm) and compares them with two second-generation carriers (FA and FAF) that: i) do not self-assemble; ii) retain a hydrodynamic radius (R_h ~ 7 nm) above the renal filtration cutoff; iii) increase tumor accumulation; and iv) have either one (FA) or two (FAF) drug-binding FKBP domains per ELP protein. Methods: The carriers were compared and evaluated for temperature-concentration phase behavior by UV-Vis spectrophotometry; equilibrium binding and thermodynamics by Isothermal Titration Calorimetry; drug retention and formulation stability by Dialysis and Dynamic Light Scattering; in vitro efficacy using a cell proliferation assay; in vivo efficacy in human MDA-MB-468 orthotopic breast cancer xenografts; downstream target inhibition using western blot; tissue histopathology; and bio-distribution via optical imaging in the orthotopic xenograft mouse model. Results: Named after the two-headed bird in Hindu mythology, the 'Berunda polypeptide' FAF with molecular weight of 97 kDa and particle size, R_h ~ 7 nm demonstrated polypeptide conformation of a soluble hydrated coiled polymer, retained formulation stability for one month post Rapa loading, eliminated toxicity observed with free Rapa after SC administration, suppressed tumor growth, decreased phosphorylation of a downstream target, and increased tumor accumulation in orthotopic breast tumor xenografts. Conclusion: This comprehensive manuscript demonstrates the versatility of recombinant protein-polymers to investigate drug carrier architectures. Furthermore, their facilitation of SC administration of poorly soluble drugs, like Rapa, may enable chronic self-administration in patients.

Elastin-like polypeptide switches: A design strategy to detect multimeric proteins

Elastin-Like Polypeptides (ELPs) reversibly phase separate in response to changes in temperature, pressure, concentration, pH, and ionic species. While powerful triggers, biological microenvironments present a multitude of more specific biological cues, such as antibodies, cytokines, and cell-surface receptors. To develop better biosensors and bioresponsive drug carriers, rational strategies are required to sense and respond to these target proteins. We recently reported that noncovalent association of two ELP fusion proteins to a "chemical inducer of dimerization" small molecule (1.5 kDa) induces phase separation at physiological temperatures. Having detected a small molecule, here we present the first evidence that ELP multimerization can also detect a much larger (60 kDa) protein target. To demonstrate this strategy, ELPs were biotinylated at their amino terminus and mixed with tetrameric streptavidin. At a stoichiometric ratio of [4:1], two to three biotin-ELPs associate with streptavidin into multimeric complexes with an apparent K_d of 5 nM. The increased ELP density around a streptavidin core strongly promotes isothermal phase separation, which was tuned to occur at physiological temperature. This phase separation reverses upon saturation with excess streptavidin, which only favors [1:1] complexes. Together, these findings suggest that ELP association with multimeric biomolecules is a viable strategy to deliberately engineer ELPs that respond to multimeric protein substrates.

Rapamycin Eye Drops Suppress Lacrimal Gland Inflammation In a Murine Model of Sjögren's Syndrome

Purpose

To evaluate the efficacy of topical rapamycin in treating autoimmune dacryoadenitis in a mouse model of Sjögren's syndrome.

Methods

We developed rapamycin in a poly(ethylene glycol)-distearoyl phosphatidylethanolamine (PEG-DSPE) micelle formulation to maintain solubility. Rapamycin or PEG-DSPE eye drops (vehicle) were administered in a well-established Sjögren's syndrome disease model, the male nonobese diabetic (NOD) mice, twice daily for 12 weeks starting at 8 weeks of age. Mouse tear fluid was collected and tear Cathepsin S, a putative tear biomarker for Sjögren's syndrome, was measured. Lacrimal glands were retrieved for histological evaluation, and quantitative real-time PCR of genes associated with Sjögren's syndrome pathogenesis. Tear secretion was measured using phenol red threads, and corneal fluorescein staining was used to assess corneal integrity.

Results

Lymphocytic infiltration of lacrimal glands from rapamycin-treated mice was significantly (P = 0.0001) reduced by 3.8-fold relative to vehicle-treated mice after 12 weeks of treatment. Rapamycin, but not vehicle, treatment increased tear secretion and decreased corneal fluorescein staining after 12 weeks. In rapamycin-treated mice, Cathepsin S activity was significantly reduced by 3.75-fold in tears (P < 0.0001) and 1.68-fold in lacrimal gland lysates (P = 0.003) relative to vehicle-treated mice. Rapamycin significantly altered the expression of several genes linked to Sjögren's syndrome pathogenesis, including major histocompatibility complex II, TNF-α, IFN-γ, and IL-12a, as well as Akt3, an effector of autophagy.

Conclusions

Our findings suggest that topical rapamycin reduces autoimmune-mediated lacrimal gland inflammation while improving ocular surface integrity and tear secretion, and thus has potential for treating Sjögren's syndrome–associated dry eye.

Elastin-like polypeptides: Therapeutic applications for an emerging class of nanomedicines

Elastin-like polypeptides (ELPs) constitute a genetically engineered class of 'protein polymers' derived from human tropoelastin. They exhibit a reversible phase separation whereby samples remain soluble below a transition temperature (Tt) but form amorphous coacervates above Tt. Their phase behavior has many possible applications in purification, sensing, activation, and nanoassembly. As humanized polypeptides, they are non-immunogenic, substrates for proteolytic biodegradation, and can be decorated with pharmacologically active peptides, proteins, and small molecules. Recombinant synthesis additionally allows precise control over ELP architecture and molecular weight, resulting in protein polymers with uniform physicochemical properties suited to the design of multifunctional biologics. As such, ELPs have been employed for various uses including as anti-cancer agents, ocular drug delivery vehicles, and protein trafficking modulators. This review aims to offer the reader a catalogue of ELPs, their various applications, and potential for commercialization across a broad spectrum of fields.

Image-driven pharmacokinetics: nanomedicine concentration across space and time

Clinical pharmacokinetics (PK) primarily measures the concentration of drugs in the blood. For nanomedicines it may be more relevant to determine concentration within a target tissue. The emerging field of image-driven PK, which utilizes clinically accepted molecular imaging technology, empirically and noninvasively, measures concentration in multiple tissues. Image-driven PK represents the intersection of PK and biodistribution, combining to provide models of concentration across space and time. Image-driven PK can be used both as a research tool and in the clinic. This review explores the history of pharmacokinetics, technologies used in molecular imaging (especially positron emission tomography) and research using image-driven pharmacokinetic analysis. When standardized, image-driven PK may have significant implications in preclinical development as well as clinical optimization of targeted nanomedicines.

Tear-mediated delivery of nanoparticles through transcytosis of the lacrimal gland

Rapid clearance from the tears presents a formidable obstacle to the delivery of peptide drugs to the eye surface. This impedes therapies for ocular infections, wound healing, and dry-eye disease that affect the vision of millions worldwide. To overcome this challenge, this manuscript explores a novel strategy to reach the ocular surface via receptor-mediated transcytosis across the lacrimal gland (LG), which produces the bulk of human tears. The LG abundantly expresses the coxsackievirus and adenovirus receptor (CAR); furthermore, we recently reported a peptide-based nanoparticle (KSI) that targets CAR on liver cells. This manuscript reports the unexpected finding that KSI both targets and transcytoses into the LG acinar lumen, which drains to tear ducts. When followed using ex vivo live cell imaging KSI rapidly accumulates in lumen formed by LG acinar cells. LG transduction with a myosin Vb tail, which is dominant negative towards transcytosis, inhibits lumenal accumulation. Transcytosis of KSI was confirmed in vivo by confocal and TEM imaging of LG tissue following administration of KSI nanoparticles. These findings suggest that it is possible to target nanomaterials to the tears by targeting certain receptors on the LG. This design strategy represents a new opportunity to overcome barriers to ocular delivery.

Engineering structure and function using thermoresponsive biopolymers

Self-assembly enables exquisite control at the smallest scale and generates order among macromolecular-building blocks that remain too small to be manipulated individually. Environmental cues, such as heating, can trigger the organization of these materials from individual molecules to multipartixcle assemblies with a variety of compositions and functions. Synthetic as well as biological polymers have been engineered for these purposes; however, biological strategies can offer unparalleled control over the composition of these macromolecular-building blocks. Biologic polymers are macromolecules composed of monomeric units that can be precisely tailored at the genetic level; furthermore, they can often utilize endogenous biodegradation pathways, which may enhance their potential clinical applications. DNA (nucleotides), polysaccharides (carbohydrates), and proteins (amino acids) have all been engineered to self-assemble into nanostructures in response to a change in temperature. This focus article reviews the growing body of literature exploring temperature-dependent nano-assembly of these biological macromolecules, summarizes some of their physical properties, and discusses future directions.

Lacritin-mediated regeneration of the corneal epithelia by protein polymer nanoparticles

The avascular corneal epithelium plays an important role in maintaining normal vision and protecting the corneal interior from environmental infections. Delayed recovery of ocular wounds caused by trauma or refractive surgery strengthens the need to accelerate corneal wound healing and better restore the ocular surface. To address this need, we fused elastin-like polypeptide (ELP) based nanoparticles SI with a model mitogenic protein called lacritin. Lacritin fused at the N-terminus of the SI diblock copolymer is called LSI. This LSI fusion protein undergoes thermo-responsive assembly of nanoparticles at physiologically relevant temperatures. In comparison to ELP nanoparticles without lacritin, LSI showed potent signs of lacritin specific effects on a human corneal epithelial cell line (HCE-T), which included enhancement of cellular uptake, calcium-mediated signaling, and closure of a scratch. In vivo, the corneas of non-obese diabetic mice (NOD) were found to be highly responsive to LSI. Fluorescein imaging and corneal histology suggested that topical administration of LSI onto the ocular surface significantly promoted corneal wound healing and epithelial integrity compared to mice treated with or without plain ELP. Most interestingly, it appears that ELP-mediated assembly of LSI is essential to produce this potent activity. This was confirmed by comparison to a control lacritin ELP fusion called LS96, which does not undergo thermally-mediated assembly at relevant temperatures. In summary, fusion of a mitogenic protein to ELP nanoparticles appears to be a promising new strategy to bioengineer more potent biopharmaceuticals with potential applications in corneal wound healing.

A thermo-responsive protein treatment for dry eyes

Millions of Americans suffer from dry eye disease, and there are few effective therapies capable of treating these patients. A decade ago, an abundant protein component of human tears was discovered and named lacritin (Lacrt). Lacrt has prosecretory activity in the lacrimal gland and mitogenic activity at the corneal epithelium. Similar to other proteins placed on the ocular surface, the durability of its effect is limited by rapid tear turnover. Motivated by the rationale that a thermo-responsive coacervate containing Lacrt would have better retention upon administration, we have constructed and tested the activity of a thermo-responsive Lacrt fused to an elastin-like polypeptide (ELP). Inspired from the human tropoelastin protein, ELP protein polymers reversibly phase separate into viscous coacervates above a tunable transition temperature. This fusion construct exhibited the prosecretory function of native Lacrt as illustrated by its ability to stimulate β-hexosaminidase secretion from primary rabbit lacrimal gland acinar cells. It also increased tear secretion from non-obese diabetic (NOD) mice, a model of autoimmune dacryoadenitis, when administered via intra-lacrimal injection. Lacrt ELP fusion proteins undergo temperature-mediated assembly to form a depot inside the lacrimal gland. We propose that these Lacrt ELP fusion proteins represent a potential therapy for dry eye disease and the strategy of ELP-mediated phase separation may have applicability to other diseases of the ocular surface.

Flipping the Switch on Clathrin-Mediated Endocytosis using Thermally Responsive Protein Microdomains

A ubiquitous approach to study protein function is to knock down activity (gene deletions, siRNA, small molecule inhibitors, etc) and study the cellular effects. Using a new methodology, this manuscript describes how to rapidly and specifically switch off cellular pathways using thermally responsive protein polymers. A small increase in temperature stimulates cytosolic elastin-like polypeptides (ELPs) to assemble microdomains. We hypothesize that ELPs fused to a key effector in a target macromolecular complex will sequester the complex within these microdomains, which will bring the pathway to a halt. To test this hypothesis, we fused ELPs to clathrin-light chain (CLC), a protein associated with clathrin-mediated endocytosis. Prior to thermal stimulation, the ELP fusion is soluble and clathrin-mediated endocytosis remains 'on.' Increasing the temperature induces the assembly of ELP fusion proteins into organelle-sized microdomains that switches clathrin-mediated endocytosis 'off.' These microdomains can be thermally activated and inactivated within minutes, are reversible, do not require exogenous chemical stimulation, and are specific for components trafficked within the clathrin-mediated endocytosis pathway. This temperature-triggered cell switch system represents a new platform for the temporal manipulation of trafficking mechanisms in normal and disease cell models and has applications for manipulating other intracellular pathways.

An amphipathic alpha-helical peptide from apolipoprotein A1 stabilizes protein polymer vesicles

L4F, an alpha helical peptide inspired by the lipid-binding domain of the ApoA1 protein, has potential applications in the reduction of inflammation involved with cardiovascular disease as well as an antioxidant effect that inhibits liver fibrosis. In addition to its biological activity, amphipathic peptides such as L4F are likely candidates to direct the molecular assembly of peptide nanostructures. Here we describe the stabilization of the amphipathic L4F peptide through fusion to a high molecular weight protein polymer. Comprised of multiple pentameric repeats, elastin-like polypeptides (ELPs) are biodegradable protein polymers inspired from the human gene for tropoelastin. Dynamic light scattering confirmed that the fusion peptide forms nanoparticles with a hydrodynamic radius of approximately 50nm, which is unexpectedly above that observed for the free ELP (~5.1nm). To further investigate their morphology, conventional and cryogenic transmission electron microscopy were used to reveal that they are unilamellar vesicles. On average, these vesicles are 49nm in radius with lamellae 8nm in thickness. To evaluate their therapeutic potential, the L4F nanoparticles were incubated with hepatic stellate cells. Stellate cell activation leads to hepatic fibrosis; furthermore, their activation is suppressed by anti-oxidant activity of ApoA1 mimetic peptides. Consistent with this observation, L4F nanoparticles were found to suppress hepatic stellate cell activation in vitro. To evaluate the in vivo potential for these nanostructures, their plasma pharmacokinetics were evaluated in rats. Despite the assembly of nanostructures, both free L4F and L4F nanoparticles exhibited similar half-lives of approximately 1h in plasma. This is the first study reporting the stabilization of peptide-based vesicles using ApoA1 mimetic peptides fused to a protein polymer; furthermore, this platform for peptide-vesicle assembly may have utility in the design of biodegradable nanostructures.

Multimeric disintegrin protein polymer fusions that target tumor vasculature

Recombinant protein therapeutics have increased in number and frequency since the introduction of human insulin, 25 years ago. Presently, proteins and peptides are commonly used in the clinic. However, the incorporation of peptides into clinically approved nanomedicines has been limited. Reasons for this include the challenges of decorating pharmaceutical-grade nanoparticles with proteins by a process that is robust, scalable, and cost-effective. As an alternative to covalent bioconjugation between a protein and nanoparticle, we report that biologically active proteins may themselves mediate the formation of small multimers through steric stabilization by large protein polymers. Unlike multistep purification and bioconjugation, this approach is completed during biosynthesis. As proof-of-principle, the disintegrin protein called vicrostatin (VCN) was fused to an elastin-like polypeptide (A192). A significant fraction of fusion proteins self-assembled into multimers with a hydrodynamic radius of 15.9 nm. The A192-VCN fusion proteins compete specifically for cell-surface integrins on human umbilical vein endothelial cells (HUVECs) and two breast cancer cell lines, MDA-MB-231 and MDA-MB-435. Confocal microscopy revealed that, unlike linear RGD-containing protein polymers, the disintegrin fusion protein undergoes rapid cellular internalization. To explore their potential clinical applications, fusion proteins were characterized using small animal positron emission tomography (microPET). Passive tumor accumulation was observed for control protein polymers; however, the tumor accumulation of A192-VCN was saturable, which is consistent with integrin-mediated binding. The fusion of a protein polymer and disintegrin results in a higher intratumoral contrast compared to free VCN or A192 alone. Given the diversity of disintegrin proteins with specificity for various cell-surface integrins, disintegrin fusions are a new source of biomaterials with potential diagnostic and therapeutic applications.

Genetically engineered nanocarriers for drug delivery

Cytotoxicity, low water solubility, rapid clearance from circulation, and off-target side-effects are common drawbacks of conventional small-molecule drugs. To overcome these shortcomings, many multifunctional nanocarriers have been proposed to enhance drug delivery. In concept, multifunctional nanoparticles might carry multiple agents, control release rate, biodegrade, and utilize target-mediated drug delivery; however, the design of these particles presents many challenges at the stage of pharmaceutical development. An emerging solution to improve control over these particles is to turn to genetic engineering. Genetically engineered nanocarriers are precisely controlled in size and structure and can provide specific control over sites for chemical attachment of drugs. Genetically engineered drug carriers that assemble nanostructures including nanoparticles and nanofibers can be polymeric or non-polymeric. This review summarizes the recent development of applications in drug and gene delivery utilizing nanostructures of polymeric genetically engineered drug carriers such as elastin-like polypeptides, silk-like polypeptides, and silk-elastin-like protein polymers, and non-polymeric genetically engineered drug carriers such as vault proteins and viral proteins.

Triggered sorting and co-assembly of genetically engineered protein microdomains in the cytoplasm

Elastin-like polypeptides (ELPs) are genetically encoded protein polymers that reversibly phase separate in response to stimuli. They respond sharply to small shifts in temperature and form dense microdomains in the living eukaryotic cytosol. For the first time, this communication illustrates how to tune the ELP sequence and architecture for either co-assembly or sorting of distinct proteins into microdomains within a living cell.

Kinetic quantification of protein polymer nanoparticles using non-invasive imaging

Protein polymers are repetitive amino acid sequences that can assemble monodisperse nanoparticles with potential applications as cancer nanomedicines. Of the currently available molecular imaging methods, positron emission tomography (PET) is the most sensitive and quantitative; therefore, this work explores microPET imaging to track protein polymer nanoparticles over several days. To achieve reliable imaging, the polypeptides were modified by site-specific conjugation using a heterobifunctional sarcophagine chelator, AmBaSar, which was subsequently complexed with (64)Cu. AmBaSar/(64)Cu was selected because it can label particles in vivo over periods of days, which is consistent with the timescales required to follow long-circulating nanotherapeutics. Using an orthotopic model of breast cancer, we observed four elastin-like polypeptides (ELPs)-based protein polymers of varying molecular weight, amino acid sequence, and nanostructure. To analyze this data, we developed a six-compartment image-driven pharmacokinetic model capable of describing their distribution within individual subjects. Surprisingly, the assembly of an ELP block copolymer (78 kD) into nanoparticles (R(h) = 37.5 nm) minimally influences pharmacokinetics or tumor accumulation compared to a free ELP of similar length (74 kD). Instead, ELP molecular weight is the most important factor controlling the fate of these polymers, whereby long ELPs (74 kD) have a heart activity half-life of 8.7 hours and short ELPs (37 kD) have a half-life of 2.1 hours. These results suggest that ELP-based protein polymers may be a viable platform for the development of multifunctional therapeutic nanoparticles that can be imaged using clinical PET scanners.

Switchable elastin-like polypeptides that respond to chemical inducers of dimerization

Elastin-like polypeptides (ELPs) are protein polymers that reversibly phase separate in response to increased temperature, pressure, concentration, ionic strength, and molecular weight. If it were possible to engineer their phase separation to respond to specific molecular substrates, ELP fusion proteins might be engineered as biosensors, smart biomaterials, diagnostic imaging agents, and targeted therapies. What has been lacking is a strategy to design ELPs to respond to specific substrates. To address this deficiency, we report that ELP fusion proteins phase separate in response to chemical inducers of dimerization (CID). The rationale is that ELP phase separation depends on molecular weight, concentration, and local hydrophobicity; therefore, processes that affect these properties, including noncovalent dimerization, can be tuned to produce isothermal phase separation. To test this hypothesis, constructs were evaluated consisting of an immunophilin: human FK-506 binding protein 12 (FKBP) attached to an ELP. Under stoichiometric binding of a CID, the fusion protein homodimerizes and triggers phase separation. This dimerization is reversible upon saturation with excess CID or competitive binding of a small lipophilic macrolide to FKBP. By modulating the ELP molecular weight, phase separation was tuned for isothermal response to CID at physiological ionic strength and temperature (37 °C). To interpret the relationship between transition temperature and equilibrium binding constants, an empirical mathematical model was employed. To the best of our knowledge, this report is the first demonstration of reversible ELP switching in response to controlled dimerization. Due to its simplicity, this strategy may be useful to design ELP fusion proteins that respond to specific dimeric biological entities.

Elastin-like peptide amphiphiles form nanofibers with tunable length

Peptide amphiphiles (PAs) self-assemble nanostructures with potential applications in drug delivery and tissue engineering. Some PAs share environmentally responsive behavior with their peptide components. Here we report a new type of PAs biologically inspired from human tropoelastin. Above a lower critical solution temperature (LCST), elastin-like polypeptides (ELPs) undergo a reversible inverse phase transition. Similar to other PAs, elastin-like PAs (ELPAs) assemble micelles with fiber-like nanostructures. Similar to ELPs, ELPAs have inverse phase transition behavior. Here we demonstrate control over the ELPAs fiber length and cellular uptake. In addition, we observed that both peptide assembly and nanofiber phase separation are accompanied by a distinctive secondary structure attributed primarily to a type-1 β turn. We also demonstrate increased solubility of hydrophobic paclitaxel (PAX) in the presence of ELPAs. Due to their biodegradability, biocompatibility, and environmental responsiveness, elastin-inspired biopolymers are an emerging platform for drug and cell delivery; furthermore, the discovery of ELPAs may provide a new and useful approach to engineer these materials into stimuli-responsive gels and drug carriers.

Biodegradation of elastin-like polypeptide nanoparticles

Protein polymers are repetitive polypeptides produced by ribosomal biosynthetic pathways; furthermore, they offer emerging opportunities in drug and biopharmaceutical delivery. As for any polymer, biodegradation is one of the most important determinants affecting how a protein polymer can be utilized in the body. This study was designed to characterize the proteolytic biodegradation for a library of protein polymers derived from the human tropoelastin, the Elastin-like polypeptides (ELPs). ELPs are of particular interest for controlled drug delivery because they reversibly transition from soluble to insoluble above an inverse phase transition temperature (T(t)). More recently, ELP block copolymers have been developed that can assemble into micelles; however, it remains unclear if proteases can act on these ELP nanoparticles. For the first time, we demonstrate that ELP nanoparticles can be degraded by two model proteases and that comparable proteolysis occurs after cell uptake into a transformed culture of murine hepatocytes. Both elastase and collagenase endopeptidases can proteolytically degrade soluble ELPs. To our surprise, the ELP phase transition was protective against collagenase but not to elastase activity. These findings enhance our ability to predict how ELPs will biodegrade in different physiological microenvironments and are essential to develop protein polymers into biopharmaceuticals.

Design and cellular internalization of genetically engineered polypeptide nanoparticles displaying adenovirus knob domain

Hepatocytes and acinar cells exhibit high-efficiency, fiber-dependent internalization of adenovirus; however, viral capsids have unpredictable immunological effects and are challenging to develop into targeted drug carriers. To exploit this internalization pathway and minimize the use of viral proteins, we developed a simple gene product that self assembles nanoparticles decorated with the knob domain of adenovirus serotype 5 fiber protein. The most significant advantages of this platform include: (i) compatibility with genetic engineering; (ii) no bioconjugate chemistry is required to link fusion proteins to the nanoparticle surface; and (iii) it can direct the reversible assembly of large nanoparticles, which are monodisperse, multivalent, and biodegradable. These particles are predominantly composed from diblock copolymers of elastin-like polypeptide (ELP). ELPs have unique phase transition behavior, whereby they self-assemble above a transition temperature that is simple to control. The diblock ELP described contains two motifs with distinct transition temperatures, which assemble nanoparticles at physiological temperatures. Analysis by non-denaturing-PAGE demonstrated that the purified knob-ELP formed trimers or dimers, which is a property of the native knob/fiber protein. Dynamic light scattering indicated that the diblock copolymer, with or without knob, is able to self assemble into nanoparticles ~40 nm in diameter. To examine the functionality of knob-ELP, their uptake was assessed in a hepatocyte cell-line that expresses the receptor for adenovirus serotype 5 fiber and knob, the coxsackievirus and adenovirus receptor (CAR). Both plain ELP and knob-ELP were bound to the outside of hepatocytes; however, the knob-ELP fusion protein exhibits more internalization and localization to lysosomes of hepatocytes. These findings suggest that functional fusion proteins may only minimally influence the assembly temperature and diameter of ELP nanoparticles. These results are a proof-of-principal that large fusion proteins (>10 kDa) can be assembled by diblock ELPs without the need for bioconjugate chemistry, which greatly simplifies the design and evaluation of targeted drug carriers.

Imaging and drug delivery using theranostic nanoparticles

Nanoparticle technologies are significantly impacting the development of both therapeutic and diagnostic agents. At the intersection between treatment and diagnosis, interest has grown in combining both paradigms into clinically effective formulations. This concept, recently coined as theranostics, is highly relevant to agents that target molecular biomarkers of disease and is expected to contribute to personalized medicine. Here we review state-of-the-art nanoparticles from a therapeutic and a diagnostic perspective and discuss challenges in bringing these fields together. Major classes of nanoparticles include, drug conjugates and complexes, dendrimers, vesicles, micelles, core-shell particles, microbubbles, and carbon nanotubes. Most of these formulations have been described as carriers of either drugs or contrast agents. To observe these formulations and their interactions with disease, a variety of contrast agents have been used, including optically active small molecules, metals and metal oxides, ultrasonic contrast agents, and radionuclides. The opportunity to rapidly assess and adjust treatment to the needs of the individual offers potential advantages that will spur the development of theranostic agents.