Natalie Artzi

In vivo and in vitro tracking of erosion in biodegradable materials using non-invasive fluorescence imaging

The design of erodible biomaterials relies on the ability to program the in vivo retention time, which necessitates real-time monitoring of erosion. However, in vivo performance cannot always be predicted by traditional determination of in vitro erosion, and standard methods sacrifice samples or animals, preventing sequential measures of the same specimen. We harnessed non-invasive fluorescence imaging to sequentially follow in vivo material-mass loss to model the degradation of materials hydrolytically (PEG:dextran hydrogel) and enzymatically (collagen). Hydrogel erosion rates in vivo and in vitro correlated, enabling the prediction of in vivo erosion of new material formulations from in vitro data. Collagen in vivo erosion was used to infer physiologic in vitro conditions that mimic erosive in vivo environments. This approach enables rapid in vitro screening of materials, and can be extended to simultaneously determine drug release and material erosion from a drug-eluting scaffold, or cell viability and material fate in tissue-engineering formulations.

Local triple-combination therapy results in tumour regression and prevents recurrence in a colon cancer model

Conventional cancer therapies involve the systemic delivery of anticancer agents that neither discriminate between cancer and normal cells nor eliminate the risk of cancer recurrence. Here, we demonstrate that the combination of gene, drug and phototherapy delivered through a prophylactic hydrogel patch leads, in a colon cancer mouse model, to complete tumour remission when applied to non-resected tumours and to the absence of tumour recurrence when applied following tumour resection. The adhesive hydrogel patch enhanced the stability and provided local delivery of embedded nanoparticles. Spherical gold nanoparticles were used as a first wave of treatment to deliver siRNAs against Kras, a key oncogene driver, and rod-shaped gold nanoparticles mediated the conversion of near-infrared radiation into heat, causing the release of a chemotherapeutic as well as thermally induced cell damage. This local, triple-combination therapy can be adapted to other cancer cell types and to molecular targets associated with disease progression.

Self-assembled RNA-triple-helix hydrogel scaffold for microRNA modulation in the tumour microenvironment

The therapeutic potential of miRNA (miR) in cancer is limited by the lack of efficient delivery vehicles. Here, we show that a self-assembled dual-colour RNA-triple-helix structure comprising two miRNAs-a miR mimic (tumour suppressor miRNA) and an antagomiR (oncomiR inhibitor)-provides outstanding capability to synergistically abrogate tumours. Conjugation of RNA triple helices to dendrimers allows the formation of stable triplex nanoparticles, which form an RNA-triple-helix adhesive scaffold upon interaction with dextran aldehyde, the latter able to chemically interact and adhere to natural tissue amines in the tumour. We also show that the self-assembled RNA-triple-helix conjugates remain functional in vitro and in vivo, and that they lead to nearly 90% levels of tumour shrinkage two weeks post-gel implantation in a triple-negative breast cancer mouse model. Our findings suggest that the RNA-triple-helix hydrogels can be used as an efficient anticancer platform to locally modulate the expression of endogenous miRs in cancer.

Aldehyde-amine chemistry enables modulated biosealants with tissue-specific adhesion.

Soft-tissue surgical sealants provide an ideal material class for assessment of tissue–material interactions. Sealant adhesion can be rigorously quantified through a series of functional assays that supplement characterizations of tissue reactivity and material fate. A collection of experimental techniques can be exploited to elucidate mechanistic aspects of tissue–material interactions with general implications, extending beyond the immediate scope of adhesive materials. Moreover, though sealants are routinely used in clinical procedures, active questions and limitations force physicians to choose between extremes of adhesion strength and biocompatibility. [1] Common cyanoacrylate derivatives adhere strongly to tissue, but their vigorous and uncontrolled tissue crosslinking along with the release of toxic degradation by-products dramatically impedes healing and regeneration processes. [2] The polymerization of alkylcyanoacrylates occurs via anionic and zwitterionic polymerizations in the presence of weak bases such as alcohols, water, and amino acids encountered in living tissues. [3] Cyanoacrylates with short side alkyl chains (methyl or ethyl) rapidly degrade to form cyanoacetate and formaldehyde, characterized by acute and chronic inflammation. The longer alkyl chains degrade slower, resulting in more limited accumulation of toxic byproducts that may be effectively eliminated by tissues. Histotoxicity depends on the vascularity of tissues, being greater in well-vascularized soft tissues. [4] Fibrin glues represent the opposite polar extreme along the spectrum of sealants [4] eliciting a mild tissue response, but with relatively non-specific and minimally adhesive tissue interaction. [5–7] Though these and all sealants rely on intimate tissue–material interactions for functional adhesion, target-tissue properties have been largely ignored in material design. Instead, one general formulation is proposed for application to the full range of soft tissues across diverse clinical applications. [8–13] Here, we demonstrate that aldehyde-mediated adhesion to tissue strongly depends on target-tissue type and state, and propose a rational approach for the engineering of application-specific surgical sealants. Copolymeric hydrogels featuring aminated star polyethylene glycolandhigh-molecular-weight dextranaldehyde(PEG:dextran) possess a series of physico-chemical properties that can be modified to create a family of materials with tunable tissue adhesion. [14–17] The two polymer constituents of PEG:dextran were prepared as minimally viscous aqueous solutions and consistently polymerized through injection from a dual chamber syringe equipped with a mixing tip. [15,16] The cohesive integrity of PEG:dextran is derived from imine bonds that form through a Schiff base reaction between amines and aldehydes. [14–17] When crosslinked on soft-tissue surfaces, aldehydes not consumed in bulk network formation form analogous bonds with tissue amines to achieve adhesion. Aldehydes in excess of what is required for cohesion or adhesion can induce tissue toxicity. [18] Consequently, material aldehyde density is the key design parameter for informative evaluation of tissue-material adhesion and tissue response. We designed and evaluated a series of PEG:dextran formulations featuring low (8.8%, abbreviated L-PD), medium (14.0%, abbreviated M-PD), and high (20.0%, abbreviated H-PD) levels of dextran aldehyde solid content. Additional design parameters, including dextran molecular weight (10 kDa) and oxidation state (50%), and PEG amine solid content (25%) were identical among formulations, and selected to provide stable and bioreactive networks for evaluation of adhesive

Implantable hydrogel embedded dark-gold nanoswitch as a theranostic probe to sense and overcome cancer multidrug resistance

Significance The integration of biomaterials science, innovative imaging, and cancer biology now enables the design of smart responsive material platforms for cancer theranostics. We show herein that our developed nanovehicle is able to sense and silence a multidrug resistance gene based on its expression in the tumor microenvironment, followed by local chemotherapeutic drug release, with a significant tumor regression not achieved otherwise. This ON/OFF molecular nanoswitch approach can be used to reverse the resistance to many other chemotherapeutic drugs and can serve as a universal gene therapy and drug delivery vehicle for cancer therapy. This disease-responsive platform can revolutionize clinical outcome and cancer patients’ point of care. Multidrug resistance (MDR) in cancer cells is a substantial limitation to the success of chemotherapy. Here, we describe facile means to overcome resistance by silencing the multidrug resistance protein 1 (MRP1), before chemotherapeutic drug delivery in vivo with a single local application. Our platform contains hydrogel embedded with dark-gold nanoparticles modified with 5-fluorouracil (5-FU)-intercalated nanobeacons that serve as an ON/OFF molecular nanoswitch triggered by the increased MRP1 expression within the tumor tissue microenvironment. This nanoswitch can sense and overcome MDR prior to local drug release. The nanobeacons comprise a 5-FU intercalated DNA hairpin, which is labeled with a near-infrared (NIR) dye and a dark-quencher. The nanobeacons are designed to open and release the intercalated drug only upon hybridization of the DNA hairpin to a complementary target, an event that restores fluorescence emission due to nanobeacons conformational reorganization. Despite the cross-resistance to 5-FU, more than 90% tumor reduction is achieved in vivo in a triple-negative breast cancer model following 80% MRP1 silencing compared with the continuous tumor growth following only drug or nanobeacon administration. Our approach can be applied to reverse cross-resistance to other chemotherapeutic drugs and restore treatment efficacy. As a universal nanotheranostic probe, this platform can pave the way to early cancer detection and treatment.

Mechanism of erosion of nanostructured porous silicon drug carriers in neoplastic tissues

Nanostructured porous silicon (PSi) is emerging as a promising platform for drug delivery owing to its biocompatibility, degradability and high surface area available for drug loading. The ability to control PSi structure, size and porosity enables programming its in vivo retention, providing tight control over embedded drug release kinetics. In this work, the relationship between the in vitro and in vivo degradation of PSi under (pre)clinically relevant conditions, using breast cancer mouse model, is defined. We show that PSi undergoes enhanced degradation in diseased environment compared with healthy state, owing to the upregulation of reactive oxygen species (ROS) in the tumour vicinity that oxidize the silicon scaffold and catalyse its degradation. We further show that PSi degradation in vitro and in vivo correlates in healthy and diseased states when ROS-free or ROS-containing media are used, respectively. Our work demonstrates that understanding the governing mechanisms associated with specific tissue microenvironment permits predictive material performance.

Characterization of star adhesive sealants based on PEG/dextran hydrogels.

Swellable PEG amine/dextran aldehyde composite materials are emerging as a controlled, biocompatible tissue adhesive. We explain how preservation of natural tissue amines provides biocompatibility for PEG/dextran that exceeds the stringent, destructive cyanide-based chemistry of cyanoacrylates, and adhere far better than fibrin glue. Strategic variations of material composition allow for the improvement of biocompatibility and adhesion strength. Material variations can be tailored to match the needs of specific tissue beds for an array of clinical applications. PEG/dextran cohesive properties are most responsive to variations in the PEG component (number of arms and solid content), while tissue/material adhesion strength is primarily determined by the number of aldehydes in the dextran.

Hydrogel Doped with Nanoparticles for Local Sustained Release of siRNA in Breast Cancer

Of all the much hyped and pricy cancer drugs, the benefits from the promising siRNA small molecule drugs are limited. Lack of efficient delivery vehicles that would release the drug locally, protect it from degradation, and ensure high transfection efficiency, precludes it from fulfilling its full potential. This work presents a novel platform for local and sustained delivery of siRNA with high transfection efficiencies both in vitro and in vivo in a breast cancer mice model. siRNA protection and high transfection efficiency are enabled by their encapsulation in oligopeptide-terminated poly(β-aminoester) (pBAE) nanoparticles. Sustained delivery of the siRNA is achieved by the enhanced stability of the nanoparticles when embedded in a hydrogel scaffold based on polyamidoamine (PAMAM) dendrimer cross-linked with dextran aldehyde. The combination of oligopeptide-terminated pBAE polymers and biodegradable hydrogels shows improved transfection efficiency in vivo even when compared with the most potent commercially available transfection reagents. These results highlight the advantage of using composite materials for successful delivery of these highly promising small molecules to combat cancer.

Viscoelastic adhesive mechanics of aldehyde-mediated soft tissue sealants

Soft tissue sealants generally sacrifice adhesive strength for biocompatibility, motivating the development of materials which interact with tissue to a predictable and controllable extent. Crosslinked hydrogels comprising aminated star polyethylene glycol and high molecular weight dextran aldehyde polymers (PEG:dextran) display aldehyde-mediated adhesion and readily tunable reactivity with soft tissue ex-vivo. Evaluation of PEG:dextran compositional variants revealed that the burst pressure of repaired intestinal wounds and the extent of material-induced tissue deformation both increase nonlinearly with formulation aldehyde content and are consistently within the desired range established by traditional sealants. Adhesive test elements featuring PEG:dextran and intestinal tissue exhibited considerable viscoelasticity, prompting use of a standard linear solid (SLS) model to describe adhesive mechanics. Model elements were accurately represented as continuous functions of PEG:dextran chemistry, facilitating prediction of adhesive mechanics across the examined range of compositional formulations. SLS models of traditional sealants were also constructed to allow general correlative analyses between viscoelastic adhesive mechanics and metrics of sealant performance. Linear correlation of equilibrium SLS stiffness to sealant-induced tissue deformation indicates that dense adhesive crosslinking restricts tissue expansion, while correlation of instantaneous SLS stiffness to burst pressure suggests that the adhesive stress relaxation capacity of PEG:dextran enhances their overall performance relative to traditional sealants.

Dual-Color Emissive Upconversion Nanocapsules for Differential Cancer Bioimaging In Vivo

Early diagnosis of tumor malignancy is crucial for timely cancer treatment aimed at imparting desired clinical outcomes. The traditional fluorescence-based imaging is unfortunately faced with challenges such as low tissue penetration and background autofluorescence. Upconversion (UC)-based bioimaging can overcome these limitations as their excitation occurs at lower frequencies and the emission at higher frequencies. In this study, multifunctional silica-based nanocapsules were synthesized to encapsulate two distinct triplet-triplet annihilation UC chromophore pairs. Each nanocapsule emits different colors, blue or green, following a red light excitation. These nanocapsules were further conjugated with either antibodies or peptides to selectively target breast or colon cancer cells, respectively. Both in vitro and in vivo experimental results herein demonstrate cancer-specific and differential-color imaging from single wavelength excitation as well as far greater accumulation at targeted tumor sites than that due to the enhanced permeability and retention effect. This approach can be used to host a variety of chromophore pairs for various tumor-specific, color-coding scenarios and can be employed for diagnosis of a wide range of cancer types within the heterogeneous tumor microenvironment.