Larisa Sheihet

Topical drug delivery by a polymeric nanosphere gel: Formulation optimization and in vitro and in vivo skin distribution studies

Tyrosine-derived nanospheres have demonstrated potential as effective carriers for the topical delivery of lipophilic molecules. In this investigation, a gel formulation containing nanospheres was developed for effective skin application and enhanced permeation. Carbopol and HPMC hydrophilic gels were evaluated for dispersion of these nanospheres. Sparingly water soluble diclofenac sodium (DS) and lipophilic Nile Red were used as model compounds. DS was used to determine the optimum polymer type, viscosity and release properties of the gel while fluorescent Nile Red was used in in vitro and in vivo skin distribution studies. In addition, the effect of a penetration enhancer, Azone, on the skin delivery was investigated. Dispersion of Nile Red-loaded nanospheres in 1% w/v HPMC gel produced a uniform and stable dispersion with suitable rheological properties for topical application, without any short-term cellular toxicity or tissue irritation. In vitro permeation studies using human cadaver skin revealed that the deposition of Nile Red via the nanosphere gel in the upper and lower dermis was 1.4 and 1.8 fold higher, respectively, than the amount of Nile Red deposited via an aqueous nanosphere formulation. In vivo, the HPMC gel containing Nile Red-loaded nanospheres significantly enhanced (1.4 fold) the permeation of Nile Red to the porcine stratum corneum/epidermis compared to the aqueous Nile Red-loaded nanospheres. An additional increase (1.4 fold) of Nile Red deposition in porcine stratum corneum/epidermis was achieved by incorporation of Azone (0.2M) into the nanosphere gel formulation. Therefore, tyrosine-derived nanospheres dispersed in gels offer promise for the topical delivery of lipophilic drugs and personal care agents to skin for treatment of cancers, psoriasis, eczema, and microbial infections.

Polymer-drug interactions in tyrosine-derived triblock copolymer nanospheres: a computational modeling approach.

A combination of molecular dynamics (MD) simulations and docking calculations was employed to model and predict polymer-drug interactions in self-assembled nanoparticles consisting of ABA-type triblock copolymers, where A-blocks are poly(ethylene glycol) units and B-blocks are low molecular weight tyrosine-derived polyarylates. This new computational approach was tested on three representative model compounds: nutraceutical curcumin, anticancer drug paclitaxel and prehormone vitamin D3. Based on this methodology, the calculated binding energies of polymer-drug complexes can be correlated with maximum drug loading determined experimentally. Furthermore, the modeling results provide an enhanced understanding of polymer-drug interactions, revealing subtle structural features that can significantly affect the effectiveness of drug loading (as demonstrated for a fourth tested compound, anticancer drug camptothecin). The present study suggests that computational calculations of polymer-drug pairs hold the potential of becoming a powerful prescreening tool in the process of discovery, development and optimization of new drug delivery systems, reducing both the time and the cost of the process.

Development of paclitaxel-TyroSpheres for topical skin treatment.

A potential topical psoriasis therapy has been developed consisting of tyrosine-derived nanospheres (TyroSpheres) with encapsulated anti-proliferative paclitaxel. TyroSpheres provide enhancement of paclitaxel solubility (almost 4000 times greater than PBS) by effective encapsulation and enable sustained, dose-controlled release over 72 h under conditions mimicking skin permeation. TyroSpheres offer potential in the treatment of psoriasis, a disease resulting from over-proliferation of keratinocytes in the basal layer of the epidermis, by (a) enabling delivery of paclitaxel into the epidermis at concentrations >100 ng/cm(2) of skin surface area and (b) enhancing the cytotoxicity of loaded paclitaxel to human keratinocytes (IC(50) of paclitaxel-TyroSpheres was approximately 45% lower than that of free paclitaxel). TyroSpheres were incorporated into a gel-like viscous formulation to improve their flow characteristics with no impact on homogeneity, release or skin distribution of the payload. The findings reported here confirm that the TyroSpheres provide a platform for paclitaxel topical administration allowing skin drug localization and minimal systemic escape.

Paclitaxel in tyrosine-derived nanospheres as a potential anti-cancer agent: In vivo evaluation of toxicity and efficacy in comparison with paclitaxel in Cremophor

Paclitaxel (PTX) has gained widespread clinical use yet its administration is associated with significant toxicity. In the present study, the toxicity and anti-tumor efficacy of tyrosine-derived nanospheres (NSP) for the delivery of PTX was compared to a clinical formulation of PTX in PBS-diluted Cremophor® EL (PTX-CrEL-D). Maximum tolerated dose was determined using a concentration series of PTX in NSP and CrEL-D, with toxicity assessed by measuring changes in body weight. Healthy mice administered PTX-NSP continued to gain weight normally while treatment with PTX-CrEL-D resulted in significant weight loss that failed to recover following treatment. Even at the dose of 50mg/kg, PTX-NSP showed better tolerance than 25mg/kg of PTX-CrEL-D. Xenograft studies of breast cancer revealed that the anti-tumor efficacy of PTX-NSP was equal to that of PTX-CrEL-D in tumors originating from both MDA-MB-435 and ZR-75-1 cancer lines. Larger volume of distribution and longer half-life were measured for PTX-NSP administration compared to those reported in the literature for a CrEL formulation. This trend suggests the potential for improved therapeutic index of PTX when administered via NSP. The findings reported here confirm that the NSP formulation is an efficient method for PTX administration with significant increase in maximum tolerated dose, offering possible clinical implications in the treatment of breast tumors.

One-step synthesis of biodegradable curcumin-derived hydrogels as potential soft tissue fillers after breast cancer surgery.

A one-step synthesis of a curcumin-derived hydrogel (curcumin content of 25-75 mol %) is reported. Curcumin is incorporated into the hydrogel backbone and cross-linked through biodegradable carbonate linkages. Curcumin as a part of the polymer backbone is protected from oxidation and degradation, while hydrogel hydrolysis results in the release of active curcumin. Nontoxic poly(ethylene glycol) and desaminotyrosyl-tyrosine ethyl ester are used to tune the hydrophilic/hydrophobic hydrogel properties. In this way, hydrogels with a wide range of physical properties including water-uptake (100-550%) and compression moduli (7-100 kPa) were obtained. Curcumin release is swelling-controlled and could be extended to 80 days. In vitro, curcumin-derived hydrogels showed selective cytotoxicity against MDA-MB-231 (IC(50) 9 μM) breast cancer cells but no cytotoxicity to noncancerous quiescent human dermal fibroblasts even at high curcumin concentrations (160 μM). One possible application of these curcumin-derived hydrogels is as soft tissue filler after surgical removal of cancerous tissue.

Multifunctional Albumin Nanoparticles As Combination Drug Carriers for Intra-Tumoral Chemotherapy

Current cancer therapies are challenged by weakly soluble drugs and by drug combinations that exhibit non-uniform biodistribution and poor bioavailability. In this study, we have presented a new platform of advanced healthcare materials based on albumin nanoparticles (ANPs) engineered as tumor penetrating, delivery vehicles of combinatorially applied factors to solid tumors. These materials were designed to overcome three sequential key barriers: tissue level transport across solid tumor matrix; uptake kinetics into individual cancer cells; therapeutic resistance to single chemotherapeutic drugs. The ANPs were designed to penetrate deeper into solid tumor matrices using collagenase decoration and evaluated using a three-dimensional multicellular melanoma tumor spheroid model. Collagenase modified ANPs exhibited 1-2 orders of magnitude greater tumor penetration than unmodified ANPs into the spheroid mass after 96 hours, and showed preferential uptake into individual cancer cells for smaller sized ANPs (<100 nm). For enhanced efficacy, collagenase coated ANPs were modified with two therapeutic agents, curcumin and riluzole, with complementary mechanisms of action for combined cell cycle arrest and apoptosis in melanoma. The collagenase coated, drug loaded nanoparticles induced significantly more cell death within 3-D tumor models than the unmodified, dual drug loaded ANP particles and the kinetics of cytotoxicity was further influenced by the ANP size. Thus, multifunctional nanoparticles can be imbued with complementary size and protease activity features that allow them to penetrate solid tumors and deliver combinatorial therapeutic payload with enhanced cancer cytotoxicity but minimal collateral damage to healthy primary cells.

Functionalized nanospheres for targeted delivery of paclitaxel

Targeted delivery of anti-cancer agents to cancer cells is a mature line of investigation that has yet to realize its full potential. In this study we report on the development of a delivery platform with the future goal of merging two thus far parallel methods for selective elimination of cancer cells: targeted nanospheres and pretargeted radioimmunotherapy. Several clinical trials have shown the promise of pretargeted radioimmunotherapy, which leverages the specificity of antibodies for targeted cell populations and delivers a localized dose of a biotinylated radionuclide that is most often administered following binding of a biotinylated antibody and streptavidin (StA) to the target cells. The work presented here describes the development of biotinylated nanospheres based on an ABA-type copolymer comprised of a tyrosine-derived oligomer as the B-block and poly(ethylene glycol) (PEG) A-blocks. The biotinylated nanospheres encapsulate paclitaxel (PTX) to the same extent as unbiotinylated nanospheres. Efficacy of targeting was shown on CD44 positive cells in the SUM159 breast cancer cell line by incubating the cells sequentially with a biotinylated anti-CD44 antibody, StA and the biotinylated nanospheres encapsulating PTX. Targeted nanospheres achieved the half maximal inhibitory concentration of PTX on SUM159 cells at a 5-10 fold lower concentration than that of PTX applied in either non-targeted nanospheres or free drug approaches. Moreover, targeted nanospheres selectively eliminated CD44 positive SUM159 cells compared to free PTX and untargeted nanospheres. This new generation of nano-sized carrier offers a versatile platform that can be adopted for a wide variety of drug and target specific applications and has the potential to be combined with the clinically emerging method of pretargeted radioimmunotherapy.

Interplay of anionic charge, poly(ethylene glycol), and iodinated tyrosine incorporation within tyrosine‐derived polycarbonates: Effects on vascular smooth muscle cell adhesion, proliferation, and motility

Regulation of smooth muscle cell adhesion, proliferation, and motility on biomaterials is critical to the performance of blood-contacting implants and vascular tissue engineering scaffolds. The goal of this study was to examine the underlying substrate-smooth muscle cell response relations, using a selection of polymers representative of an expansive library of multifunctional, tyrosine-derived polycarbonates. Three chemical components within the polymer structure were selectively varied through copolymerization: (1) the content of iodinated tyrosine to achieve X-ray visibility; (2) the content of poly(ethylene glycol) (PEG) to decrease protein adsorption and cell adhesivity; and (3) the content of desaminotyrosyl-tyrosine (DT), which regulates the rate of polymer degradation. Using quartz crystal microbalance with dissipation, we quantified differential serum protein adsorption behavior because of the chemical components DT, iodinated tyrosine, and PEG: increased PEG content within the polymer structure progressively decreased protein adsorption but the simultaneous presence of both DT and iodinated tyrosine reversed the effects of PEG. The complex interplay of these components was next tested on the adhesion, proliferation, and motility behavior cultured human aortic smooth muscle cells. The incorporation of PEG into the polymer reduced cell attachment, which was reversed in the presence of iodinated tyrosine. Further, we found that as little as 10% DT content was sufficient to negate the PEG effect in polymers containing iodinated tyrosine, whereas in non-iodinated polymers, the PEG effect on cell attachment was reversed. Cross-functional analysis of motility and proliferation revealed divergent substrate chemistry related cell response regimes. For instance, within the series of polymers containing both iodinated tyrosine and 10% of DT, increasing PEG levels lowered smooth muscle cell motility without a change in the rate of cell proliferation. In contrast, for non-iodinated tyrosine and 10% of DT, increasing PEG levels increased cell proliferation significantly while reducing cell motility. Clearly, the polycarbonate polymer library offers a sensitive platform to modulate cell adhesion, proliferation, and motility responses, which, in turn, may have implications for controlling vascular remodeling in vivo. Additionally, our data suggests unique biorelevant properties following the incorporation of iodinated subunits in a polymeric biomaterial as a potential platform for X-ray visible devices.