Graduate Researcher, University of Utah
Loading cancer drugs into nanogels for improved tumor-targeting can improve current treatments
Breast cancer is a debilitating disease that will affect 1 out of every 8 women. Current chemotherapy treatments involve the injection of highly toxic compounds through patients' bloodstreams to destroy disseminated cancer cells. Unfortunately, these toxic compounds often devastate healthy tissues and bring about a plethora of side effects. Nanoparticles are often proposed to help improve the transport of chemotherapeutics through the blood, but researchers rarely develop methods that inhibit the passage of such nanoparticle drug delivery systems into healthy tissues.
My research focuses on the development of a completely protein-based nanogel that is too large to readily leave the bloodstream and enter into tissues normally, a process called extravasation. However, the nanogels' elastin units respond to temperature and shrivel when heated. This shriveling causes the chemotherapeutic-carrying nanogels to shrink approximately 50% in size, allowing them to freely extravasate from the bloodstream. Tumors are identified and heated slightly above body temperature, allowing the nanogels to only extravasate at tumor sites. This localized extravasation concentrates the toxic chemotherapeutic drugs near cancer cells and reduces contact with healthy cells, effectively improving treatment efficacy and substantially reducing side effects.
Abstract: Hydrogels consisting of carboxylic acid groups and N-isopropylacrylamide as pendants on their polymeric network usually exhibit volume expansion upon deprotonation or volume contraction when being heated. Demonstrated here is an anti-intuitive case of a hydrogel containing multiple carboxylic acid groups at each crosslinking point in the polymeric network, which shrinks upon increasing pH from 1 to 7 at 37 °C or expands upon heating from 25 to 37 °C at pH 1. The unexpected volume change originates from the high percentage of the crosslinker in the polymers, as detected by solid-state 13C NMR spectroscopy. In addition, the volume changes are thermally reversible. As the first example of the use of functional hyper-crosslinkers to control the pH and thermal responses of nanogels, this work illustrates a new way to design soft materials with unusual behaviors.
Pub.: 27 Jan '17, Pinned: 06 Sep '17
Abstract: This work deals with the scattered light by nanoparticles formed by a temperature sensitive polymer networks, namely nanogel particles. The scattered light is measured as a function of the scattering angle at temperatures below and above the volume phase transition temperature (VPTT) of nanogel particles. Our experimental results indicate that nanogel particles have a core-shell structure, formed by a uniform highly cross-linked core surrounded by a fuzzy shell where the polymer density decays to zero gradually for swollen configurations and sharply for shrunken states. The theoretical fitting of the experimental curves shows that the scattered light at low angle obeys a decreasing power law with the scattering vector, q(-α). The value of exponent α provides information about the radial dependence of the polymer density at the external shell of the particles for swollen nanogels, and about the degree of roughness of the surface for the case of shrunken nanogels. On the one hand, at low temperatures (below the VPPT), the nanogel particle is in the swollen state and the light scattering data show that its shell structure follows a fractal behaviour, with a polymer density that decays as r(α-3), where r is the distance to the particle centre. On the other hand, above the VPPT the results indicate that nanogel collapses into a core of uniform polymer density and a rough shell, with a fractal surface dimension of 2.5.
Pub.: 04 Apr '15, Pinned: 06 Sep '17
Abstract: In this work the equilibrium distribution of ions around a thermo-responsive charged nanogel particle in an electrolyte aqueous suspension is explored using coarse-grained Monte Carlo computer simulations and the Ornstein-Zernike integral equation theory. We explicitly consider the ionic size in both methods and study the interplay between electrostatic and excluded-volume effects for swollen and shrunken nanogels, monovalent and trivalent counterions, and for two different nanogel charges. We find good quantitative agreement between the ionic density profiles obtained using both methods when the excluded repulsive force exerted by the cross-linked polymer network is taken into account. For the shrunken conformation, the electrostatic repulsion between the charged groups provokes a heterogeneous polymer density profile, leading to a nanogel structure with an internal low density hole surrounded by a dense corona. The results show that the excluded-volume repulsion strongly hinders the ion permeation for shrunken nanogels, where volume exclusion is able to significantly reduce the concentration of counterions in the more dense regions of the nanogel. In general, we demonstrate that the thermosensitive behaviour of nanogels, as well as their internal structure, is strongly influenced by the valence of the counterions and also by the charge of the particles. On the one hand, an increase of the counterion valence moves the swelling transition to lower temperatures, and induces a major structuring of the charged monomers into internal and external layers around the crown for shrunken nanogels. On the other hand, increasing the particle charge shifts the swelling curve to larger values of the effective radius of the nanogel.
Pub.: 22 Feb '17, Pinned: 06 Sep '17
Abstract: The adsorption of biomolecules to the surfaces of a nanoparticle (NP) following administration into biological environments is widely recognised. In particular, the "protein corona" is well understood in terms of formation kinetics and its impact upon the biological interactions of NPs. Its presence is an essential consideration in the design of therapeutic NPs. In the present study, the protein corona of six polymeric nanoparticles of prospective therapeutic use, were investigated. These included three colloidal NPs-soft core-multi-shell (CMS) NPs, plus solid cationic Eudragit® RS (EGRS) and anionic ethyl cellulose (EC) nanoparticles-and three nanogels (NGs)-thermoresponsive dendritic-polyglycerol (dPG) nanogels (NGs) and two amino-functionalised dPG-NGs. Following incubation with human plasma, protein coronas were characterised and their biological interactions compared with pristine NPs. All NPs demonstrated protein adsorption and increased hydrodynamic diameters, although the solid EGRS and EC NPs bound notably more protein than the other tested particles. Shifts towards moderately negative surface charges were also observed for all corona bearing NPs, despite varied zeta potentials in their pristine state. While the uptake and cellular adhesion of the colloidal NPs in primary human keratinocytes and HUVECS were significantly decreased when bearing the protein corona, no obvious impact was seen in the NGs. By contrast, corona bearing NGs induced marked increases in cytokine release from primary human macrophages not seen with corona bearing colloidal NPs. Despite this, no apparent enhancement to in vitro toxicity was noted. Finally, drug release from EGRS and EC NPs was assessed, where a decrease was seen in the EGRS NPs alone. Together these results provide a direct comparison of the physical and biological impact the protein corona has on NPs of widely varied character, and in particular highlights a distinction between the corona's effects on NGs and colloidal NPs.
Pub.: 17 May '17, Pinned: 06 Sep '17
Abstract: The development of effective transdermal drug delivery systems based on nanosized polymers requires a better understanding of the behaviour of such nanomaterials at interfaces. N-Isopropylacrylamide-based nanogels synthesized with different percentages of N,N′-methylenebisacrylamide as cross-linker, ranging from 10 to 30%, were characterized at physiological temperature at the air/water interface, using neutron reflectivity (NR), with isotopic contrast variation, and surface tension measurements; this allowed us to resolve the adsorbed amount and the volume fraction of nanogels at the interface. A large conformational change for the nanogels results in strong deformations at the interface. As the percentage of cross-linker incorporated in the nanogels becomes higher, more rigid matrices are obtained, although less deformed, and the amount of adsorbed nanogels is increased. The data provide the first experimental evidence of structural changes of nanogels as a function of the degree of cross-linking at the air/water interface.
Pub.: 16 Dec '15, Pinned: 06 Sep '17
Abstract: We have used neutron reflectivity (NR) measurements in combination with dynamic light scattering (DLS), surface tension and ellipsometry, to study the adsorption behaviour at the air/water interface of N-isopropylacrylamide-based nanogels as a function of concentration. The data provide clear evidence that the nanogels are adsorbed at the interface in a strongly deformed shape and forming a multi-layer where the thickness increases with nanogel concentration in the bulk. The combination of surface characterisation techniques and bulk studies indicate that interfacial film formation is preferred over bulk aggregation. This observation at the air/water interface supports the Derjaguin prediction, that a sphere's interaction with a plane (the thick adsorbed nanogel layer at interface) is much larger than nanogel-nanogel (sphere-sphere) association in the bulk. These findings, in particular the changes in conformations and the thick layer adsorption at the interface as a function of concentration, impact significantly on a number of applications for which nanogels are currently being investigated. These results contribute to the understanding of the behaviour of soft colloids at the interfaces.
Pub.: 24 Jun '17, Pinned: 06 Sep '17
Abstract: Development of nanosized drug delivery systems in cancer therapy is directed towards improving tumor selectivity and minimizing damages of healthy tissue. We introduce a delivery system with synergistic optimization and combination of passive and active targeting strategies. The approach is based on radiopeptide labeled redox sensitive hydrophilic nanogels, which exploit passive targeting by the enhanced permeability and retention effect while avoiding elimination by the mononuclear phagocyte system and fast hepatic and/or renal clearance. The targeting peptide promotes endocytotic uptake of the nanogels by cancer cells. Specific to this delivery system, tumor-specific degradation by the antioxidant glutathione enhances penetration and retention within the tumor tissue. Using in vivo molecular imaging we demonstrate the superiority of combined passive and active targeting with down-sizeable nanogels over exclusive passive targeting. Furthermore, the homogenous tumor distribution of functionalized nanogels compared to the clinically used mere radiopeptide supports the potentially high impact of our targeting concept.
Pub.: 07 Jul '17, Pinned: 06 Sep '17
Abstract: Polymer micellar nanogels are a group of core-shell polymeric micelles with swelling properties in aqueous media. Nanogel systems have proven their potential in controlled, sustained and targetable drug delivery area with no immunological responses. This review includes a comprehensive wide range of self-assembly of polymeric nanogels as delivery systems for anticancer drugs. Nanogels are nanoparticulate drug delivery systems which are specially designed for enhanced target oriented and cellular uptake of drugs with emphasis on chemotherapeutic agents studied in this review. Self-assembling nanogels are based on natural substances or synthetic polymers including: hyaluronic acid, heparin, alginate, cyclodextrins, chondroeitin sulfate, starch, mannan, chitosan, pullulan, poly(N-isopropylacrylamide), polyvynil alcohol, Pluronic F127, polyacrylic acid, poly(hydroxylethyl methacrylate), poly[2- (dimethylamino)ethyl methacrylate and polylactide-co-glycolide-polyethylen glycol amphiphilic di or tri block copolymer used to deliver anticancer drugs are introduced and discussed.
Pub.: 13 Jul '17, Pinned: 06 Sep '17
Abstract: XTEN™ is a class of unstructured hydrophilic, biodegradable protein polymers designed to increase the half-lives of therapeutic peptides and proteins. XTEN polymers and XTEN fusion proteins are typically expressed in Escherichia coli and purified by conventional protein chromatography as monodisperse polypeptides of exact length and sequence. Unstructured XTEN polypeptides have hydrodynamic volumes significantly larger than typical globular proteins of similar mass, thus imparting a bulking effect to the therapeutic payloads attached to them. Since their invention, XTEN polypeptides have been utilized to extend the half-lives of a variety of peptide- and protein-based therapeutics. Multiple clinical and preclinical studies and related drug discovery and development efforts are in progress. This review details the most current understanding of physicochemical properties and biological behavior of XTEN and XTENylated molecules. Additionally, the development path and status of several advanced drug discovery and development efforts are highlighted.
Pub.: 30 Oct '15, Pinned: 25 Aug '17
Abstract: While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment.MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers.This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients.Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications.Several strategies for MMP utilization in targeting - such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes - are addressed.
Pub.: 06 Feb '17, Pinned: 25 Aug '17
Abstract: Radiation-induced proctitis (RIP) is the most common clinical adverse effect for patients receiving radiotherapy as part of the standard course of treatment for ovarian, prostate, colon, and bladder cancers. RIP limits radiation dosage, interrupts treatment, and lowers patients' quality of life. A prophylactic treatment that protects the gastrointestinal tract from deleterious effects of radiotherapy will significantly improve patient quality of life and may allow for higher and more regular doses of radiation therapy. Semi-synthetic glycosaminoglycan (GAG), generated from the sulfation of hyaluronic acid, are anti-inflammatory but have difficulty achieving therapeutic levels in many tissues. To enhance the delivery of GAG, we created an in situ gelling rectal delivery system using silk-elastinlike protein polymers (SELPs). Using solutions of SELP 815K (which contains 6 repeats of blocks comprised of 8 silk-like units, 15 elastin-like units, and 1 lysine-substituted elastin-like unit) with GAG GM-0111, we created an injectable delivery platform that transitioned in <5min from a liquid at room temperature to a hydrogel at body temperature. The hydrogels released 50% of their payload within 30min and enhanced the accumulation of GAG in the rectum compared to traditional enema-based delivery. Using a murine model of radiation-induced proctitis, the prophylactic delivery of a single dose of GAG from a SELP matrix administered prior to irradiation significantly reduced radiation-induced pain after 3, 7, and 21days by 53±4%, 47±10%, and 12±6%, respectively. Matrix-mediated delivery of GAG by SELP represents an innovative method for more effective treatment of RIP and promises to improve quality of life of cancer patients by allowing higher radiotherapy doses with improved safety.
Pub.: 25 Feb '17, Pinned: 25 Aug '17
Abstract: This paper demonstrates the first example of targeting a solid tumor that is externally heated to 42 °C by "heat seeking" drug-loaded polypeptide nanoparticles. These nanoparticles consist of a thermally responsive elastin-like polypeptide (ELP) conjugated to multiple copies of a hydrophobic cancer drug. To rationally design drug-loaded nanoparticles that exhibit thermal responsiveness in the narrow temperature range between 37 and 42 °C, an analytical model was developed that relates ELP composition and chain length to the nanoparticle phase transition temperature. Suitable candidates were designed based on the predictions of the model and tested in vivo by intravital confocal fluorescence microscopy of solid tumors, which revealed that the nanoparticles aggregate in the vasculature of tumors heated to 42 °C and that the aggregation is reversible as the temperature reverts to 37 °C. Biodistribution studies showed that the most effective strategy to target the nanoparticles to tumors is to thermally cycle the tumors between 37 and 42 °C. These nanoparticles set the stage for the targeted delivery of a range of cancer chemotherapeutics by externally applied mild hyperthermia of solid tumors.
Pub.: 18 Apr '14, Pinned: 25 Aug '17
Abstract: Elastin-like polypeptides are biopolymers composed of the pentapeptide repeat Val-Pro-Gly-Xaa-Gly. Elastin-like polypeptides are soluble in aqueous solution below their transition temperature, but they hydrophobically collapse and aggregate when the temperature is raised above the transition temperature. Previous studies have suggested that the aggregation of these polypeptides in response to externally applied hyperthermia may be exploited in the use of elastin-like polypeptide for thermally targeted drug delivery. This work shows the application of elastin-like polypeptide as a delivery vehicle for a short peptide that can inhibit the transcriptional function of a specific oncogene. The coding sequence for elastin-like polypeptide was modified by the addition of the membrane translocating sequence penetratin and a peptide derived from helix 1 of the helix-loop-helix region of c-Myc (H1-S6A,F8A), known to inhibit c-Myc transcriptional function. The designed polypeptide (Pen-ELP-H1) was then expressed and purified from Escherichia coli. Cellular uptake of Pen-ELP-H1 is enhanced by both the penetratin sequence and by the hyperthermia-induced phase transition as shown by flow cytometry studies. Using immunofluorescence and reverse transcription-PCR, we show that Pen-ELP-H1 is able to disrupt the nuclear localization of c-Myc and inhibit transcriptional activation by c-Myc. Cell proliferation studies showed that Pen-ELP-H1 inhibits growth of MCF-7 cells. Furthermore, the use of hyperthermia increased the antiproliferative effect of a thermally responsive Pen-ELP-H1 approximately 2-fold compared with a nonthermally responsive control polypeptide. These studies show that genetically engineered elastin-like polypeptide carriers may provide a new way to thermally target specific oncogene inhibitors to solid tumors.
Pub.: 16 Jul '05, Pinned: 25 Aug '17
Abstract: Silk-elastinlike protein polymers (SELPs) have been effectively used as controlled release matrices for the delivery of viruses for cancer gene therapy in preclinical models. However, the degradability of these polymers needs to be tuned for improved localized intratumoral gene delivery. Using recombinant techniques, systematic modifications in distinct regions of the polymer backbone, namely, within the elastin blocks, silk blocks, and adjacent to silk and elastin blocks, have been made to impart sensitivity to specific matrix metalloproteinases (MMPs) known to be overexpressed in the tumor environment. In this report we investigated the structure-function relationship of MMP-responsive SELPs for viral mediated gene therapy of head and neck cancer. These polymers showed significant degradation in vitro in the presence of MMPs. Their degradation rate was a function of the location of the MMP-responsive sequence in the polymer backbone when in hydrogel form. Treatment efficacy of the adenoviral vectors released from the MMP responsive SELP analogs in a xenograft mouse model of head and neck squamous cell carcinoma (HNSCC) was shown to be polymer structure dependent. These results demonstrate the tunable nature of MMP-responsive SELPs for localized matrix-mediated gene delivery.
Pub.: 23 Jun '15, Pinned: 25 Aug '17
Abstract: Water-soluble triblock copolymers have received much attention in industrial applications and scientific fields. We here show that femtosecond mid-IR pump–probe spectroscopy is useful to study the role of water in the temperature-induced self-assembly of triblock copolymers. Our experimental results suggest two distinct subpopulations of water molecules: those that interact with other water molecules and those involved in the hydration of a triblock copolymer surface. We find that the vibrational dynamics of bulk-like water is not affected by either micellation or gelation of triblock copolymers. The increased population of water interacting with ether oxygen atoms of the copolymer during the unimer to micelle phase transition is important evidence for the entropic role of water in temperature-induced micelle formation at a low copolymer concentration. In contrast, at the critical gelation temperature and beyond, the population of surface-associated water molecules interacting with ether oxygen atoms decreases, which indicates important enthalpic control by water. The present study on the roles of water in the two different phase transitions of triblock copolymers sheds new light on the underlying mechanisms of temperature-induced self-aggregation behaviors of amphiphiles that are ubiquitous in nature.
Pub.: 14 Jun '17, Pinned: 25 Aug '17
Abstract: Silk--elastin-like protein polymers (SELPs), consisting of the repeating units of silk and elastin blocks, combine a set of outstanding physical and biological properties of silk and elastin. Because of the unique properties, SELPs have been widely fabricated into various materials for the applications in drug delivery and tissue engineering. However, little is known about the fundamental self-assembly characteristics of these remarkable polymers. Here we propose a two-step self-assembly process of SELPs in aqueous solution for the first time and report the importance of the ratio of silk-to-elastin blocks in a SELP's repeating unit on the assembly of the SELP. Through precise tuning of the ratio of silk to elastin, various structures including nanoparticles, hydrogels, and nanofibers could be generated either reversibly or irreversibly. This assembly process might provide opportunities to generate innovative smart materials for biosensors, tissue engineering, and drug delivery. Furthermore, the newly developed SELPs in this study may be potentially useful as biomaterials for controlled drug delivery and biomedical engineering.
Pub.: 01 Oct '11, Pinned: 25 Aug '17
Abstract: Silk-elastin-like protein polymers (SELPs) combine the mechanical and biological properties of silk and elastin. These properties have led to the development of various SELP-based materials for drug delivery. However, SELPs have rarely been developed into nanoparticles, partially due to the complicated fabrication procedures, nor assessed for potential as an anticancer drug delivery system. We have recently constructed a series of SELPs (SE8Y, S2E8Y, and S4E8Y) with various ratios of silk to elastin blocks and described their capacity to form micellar-like nanoparticles upon thermal triggering. In this study, we demonstrate that doxorubicin, a hydrophobic antitumor drug, can efficiently trigger the self-assembly of SE8Y (SELPs with silk to elastin ratio of 1:8) into uniform micellar-like nanoparticles. The drug can be loaded in the SE8Y nanoparticles with an efficiency around 6.5% (65 ng doxorubicin/μg SE8Y), S2E8Y with 6%, and S4E8Y with 4%, respectively. In vitro studies with HeLa cell lines demonstrate that the protein polymers are not cytotoxic (IC50 > 200 μg/mL), while the doxorubicin-loaded SE8Y nanoparticles showed a 1.8-fold higher cytotoxicity than the free drug. Confocal laser scanning microscopy (CLSM) and flow cytometry indicate significant uptake of the SE8Y nanoparticles by the cells and suggest internalization of the nanoparticles through endocytosis. This study provides an all-aqueous, facile method to prepare nanoscale, drug-loaded SELPs packages with potential for tumor cell treatments.
Pub.: 18 Feb '14, Pinned: 25 Aug '17