Electric Charge Influence of Dextran Derivatives on their Tumor Accumulation After Intravenous Injection

Tailoring the surface charges of iron-crosslinked dextran nanogels towards improved tumor-associated macrophage targeting

Tumor-associated macrophages (TAMs) have emerged as therapeutic interests in cancer nanomedicine because TAMs play a pivotal role in the immune microenvironment of solid tumors. Dextran and its derived nanocarriers are among the most promising nanomaterials for TAM targeting due to their intrinsic affinities towards macrophages. Various dextran-based nanomaterials have been developed to image TAMs. However, the effects of physiochemical properties especially for surface charges of dextran nanomaterials on TAM-targeting efficacy were ambiguous in literature. To figure out the surface charge effects on TAM targeting, here we developed a facile non-covalent self-assembly strategy to construct oppositely charged dextran nanogels (NGs) utilizing the coordination interaction of ferric ions, chlorine e6 (Ce6) dye and three dextran derivatives, diethylaminoethyl-, sulfate sodium- and carboxymethyl-dextran. The acquired dextran NGs exhibit different charges but similar hydrodynamic size, Ce6 loading and mechanical stiffness, which enables a side-by-side comparison of the effects of NG surface charges on TAM targeting monitored by the Ce6 fluorescence imaging. Compared with negative NGs, the positive NG clearly displays a superior TAM targeting in murine breast cancer model. This study identifies that positively charged dextran NG could be a promising approach to better engineer nanomedicine towards an improved TAM targeting.

Nanomedicines Meet Disordered Proteins: A Shift from Traditional Materials and Concepts to Innovative Polymers

Water-soluble nanomedicines have been widely studied for the targeted delivery of drugs for a very long time. As a notable example, biomaterials based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers have been under investigation for nearly half a century. In particular, anticancer drug carriers have been developed under the assumption that the leading mechanism with a therapeutic impact on solid tumors is the enhanced permeability and retention (EPR) effect, which dates back more than three decades. Nevertheless, these (and other) materials and concepts have encountered several barriers in their successful translation into clinical practice, and future nanomedicines need improvements in both passive and active targeting to their site of action. Notions borrowed from recent studies on intrinsically disordered proteins (IDPs) seem promising for enhancing the self-assembly, stimuli-responsiveness, and recognition properties of protein/peptide-based copolymers. Accordingly, IDP-based nanomedicines are ready to give new impetus to more traditional research in this field.

Thaw-Induced Gelation of Alginate Hydrogels for Versatile Delivery of Therapeutics

Alginate hydrogels have been extensively used and successfully validated as delivery vehicles of bioactive factors in many tissue engineering applications. This work describes and characterizes a singular alternative method to create alginate hydrogels designated as thaw-induced gelation (TIG). The TIG method involves gelation through the time-dependent release of the polymer or crosslinker by melting into solution. Alginate TIG hydrogels were validated for spatial-temporal control delivery of different cargos including albumin, dextran, and doxorubicin. Chitosan was incorporated into TIG hydrogels to investigate the electrostatic interactions between alginate and the tested cargos. Interestingly, while 90% of doxorubicin was released after 8 h from hydrogels formed with frozen calcium, hydrogels formulated from frozen alginate took 72 h. In addition, the storage modulus of TIG hydrogels prepared from frozen alginate was double that of a hydrogel formed without freezing alginate. Therefore, the utility of TIG strategies are particularly promising for the delivery of therapeutic cargos smaller than the mesh size of the alginate hydrogel, as it enables controlled release of these cargos without any further chemical modifications of the hydrogels. These TIG alginate hydrogels with tunable mechanical properties and control over the delivery of smaller cargos could be useful in many tissue engineering applications.

Evaluation of affibody charge modification identified by synthetic consensus design in molecular PET imaging of epidermal growth factor receptor

Tumor overexpression of epidermal growth factor receptor (EGFR) correlates to therapeutic response in select patient populations. Thus, molecular positron emission tomography (PET) imaging of EGFR could stratify responders versus non-responders. We previously demonstrated effectiveness of a "synthetic consensus" design principle to identify six neutralizing mutations within a 58-amino acid EGFR-targeted affibody domain. Herein, we extend the approach to identify additional neutralized variants that vary net charge from -2 to either -4 or +4 while retaining high affinity (1.6 ± 1.2 nM and 2.5 ± 0.7 nM), specific binding to EGFR, secondary structure, and stability (T_m = 68 °C and 59 °C). We radiolabeled the resultant collection of five charge variants with ⁶⁴Cu and evaluated PET imaging performance in murine models with subcutaneously xenografted EGFR^high and EGFR^low tumors. All variants exhibited good EGFR^high tumor imaging as early as 1 h, with EA35S (+3/-5) achieving 7.7 ± 1.4 %ID/g tumor at 4 h with 1.5 ± 0.3%ID/g EGFR^low tumor, 34 ± 5 tumor:muscle and 12 ± 3 tumor:blood ratios. The positively charged EA62S mutant (+6/-2) exhibited 2.2-3.3-fold higher liver signal than the other variants (p<0.01). The EA68 variant with higher charge density was more stable to human and mouse serum than neutralized variants. In a comparison of radiometal chelators, 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) exhibited superior physiological specificity to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). In total, these studies comparatively evaluated a set of EGFR-targeted affibodies varying in net charge and charge density, which revealed functional variations that are useful in engineering an ideal probe for translational studies.

A mechanistic compartmental model for total antibody uptake in tumors

Antibodies are under development to treat a variety of cancers, such as lymphomas, colon, and breast cancer. A major limitation to greater efficacy for this class of drugs is poor distribution in vivo. Localization of antibodies occurs slowly, often in insufficient therapeutic amounts, and distributes heterogeneously throughout the tumor. While the microdistribution around individual vessels is important for many therapies, the total amount of antibody localized in the tumor is paramount for many applications such as imaging, determining the therapeutic index with antibody drug conjugates, and dosing in radioimmunotherapy. With imaging and pretargeted therapeutic strategies, the time course of uptake is critical in determining when to take an image or deliver a secondary reagent. We present here a simple mechanistic model of antibody uptake and retention that captures the major rates that determine the time course of antibody concentration within a tumor including dose, affinity, plasma clearance, target expression, internalization, permeability, and vascularization. Since many of the parameters are known or can be estimated in vitro, this model can approximate the time course of antibody concentration in tumors to aid in experimental design, data interpretation, and strategies to improve localization.

Pharmacokinetics and tumor dynamics of the nanoparticle IT-101 from PET imaging and tumor histological measurements

IT-101, a cyclodextrin polymer-based nanoparticle containing camptothecin, is in clinical development for the treatment of cancer. Multiorgan pharmacokinetics and accumulation in tumor tissue of IT-101 is investigated by using PET. IT-101 is modified through the attachment of a 1,4,7,10-tetraazacyclododecane-1,4,7-Tris-acetic acid ligand to bind (64)Cu(2+). This modification does not affect the particle size and minimally affects the surface charge of the resulting nanoparticles. PET data from (64)Cu-labeled IT-101 are used to quantify the in vivo biodistribution in mice bearing Neuro2A s.c. tumors. The (64)Cu-labeled IT-101 displays a biphasic plasma elimination. Approximately 8% of the injected dose is rapidly cleared as a low-molecular-weight fraction through the kidneys. The remaining material circulates in plasma with a terminal half-life of 13.3 h. Steadily increasing concentrations, up to 11% injected dose per cm(3), are observed in the tumor over 24 h, higher than any other tissue at that time. A 3-compartment model is used to determine vascular permeability and nanoparticle retention in tumors, and is able to accurately represent the experimental data. The calculated tumor vascular permeability indicates that the majority of nanoparticles stay intact in circulation and do not disassemble into individual polymer strands. A key assumption to modeling the tumor dynamics is that there is a "sink" for the nanoparticles within the tumor. Histological measurements using confocal microscopy show that IT-101 localizes within tumor cells and provides the sink in the tumor for the nanoparticles.

Antibody tumor penetration: transport opposed by systemic and antigen-mediated clearance

Antibodies have proven to be effective agents in cancer imaging and therapy. One of the major challenges still facing the field is the heterogeneous distribution of these agents in tumors when administered systemically. Large regions of untargeted cells can therefore escape therapy and potentially select for more resistant cells. We present here a summary of theoretical and experimental approaches to analyze and improve antibody penetration in tumor tissue.

Tumor vascular permeability, accumulation, and penetration of macromolecular drug carriers

BACKGROUND

Delivery of anticancer therapeutic agents to solid tumors is problematic. Macromolecular drug carriers are an attractive alternative drug delivery method because they appear to target tumors and have limited toxicity in normal tissues. We investigated how molecular weight influences the accumulation of a model macromolecular drug carrier, dextran covalently linked to a fluorophore, in tumors.

METHODS

We used dextrans with molecular weights from 3.3 kDa to 2 MDa. Vascular permeability, accumulation, and three-dimensional penetration of these dextrans were simultaneously measured in solid tumors via a dorsal skin fold window chamber, intravital laser-scanning confocal microscopy, and custom image analysis.

RESULTS

Increasing the molecular weight of dextran statistically significantly reduced its vascular permeability by approximately two orders of magnitude (i.e., from 154 x 10(-7) cm/s, 95% confidence interval [CI] = 134 to 174 x 10(-7) cm/s, for 3.3-kDa dextran to 1.7 x 10(-7) cm/s, 95% CI = 0.7 to 2.6 x 10(-7) cm/s for 2-MDa dextran; P < .001, two-sided Kruskal-Wallis test) but increased its plasma half-life, which provided ample time for extravasation (i.e., to enter tumor tissue from the vasculature). Tumor accumulation was maximal for dextrans with molecular weights between 40 and 70 kDa. Dextrans of 3.3 and 10 kDa penetrated deeply (greater than 35 microm) and homogeneously into tumor tissue from the vessel wall. After a 30-minute period, a high concentration was observed only approximately 15 microm from the vessel wall for 40- to 70-kDa dextrans and only 5 microm for 2-MDa dextrans.

CONCLUSIONS

Increasing the molecular weight of dextran statistically significantly reduced its tumor vascular permeability. Dextrans of 40 and 70 kDa had the highest accumulation in solid tumors but were largely concentrated near the vascular surface.

Drug delivery systems for vitreoretinal diseases

The eye has an environment that is specific unto itself in terms of pharmacokinetics: the inner and outer blood-retinal barriers separate the retina and the vitreous from the systemic circulation and vitreous body, which physiologically has no cellular components, occupies the vitreous cavity, an inner space of the eye, and reduces practical convection of molecules. Considering this, development of a drug delivery system (DDS) is becoming increasingly important in the treatment of vitreoretinal diseases not only to facilitate drug efficacy but also to attenuate adverse effects. The DDS has three major goals: enhances drug permeation (e.g., iontophoresis and transscleral DDS), controls release of drugs (e.g., microspheres, liposomes, and intraocular implants), and targets drugs (e.g., prodrugs with high molecular weight and immunoconjugates). Comprehensive knowledge of these should lead to development of innovative treatment modalities.

RETRACTED: PEGylation enhances tumor targeting of plasmid DNA by an artificial cationized protein with repeated RGD sequences, Pronectin®

The objective of this study is to investigate feasibility of a non-viral gene carrier with repeated RGD sequences (Pronectin F+) in tumor targeting for gene expression. The Pronectin F+ was cationized by introducing spermine (Sm) to the hydroxyl groups to allow to polyionically complex with plasmid DNA. The cationized Pronectin F+ prepared was additionally modified with poly(ethylene glycol) (PEG) molecules which have active ester and methoxy groups at the terminal, to form various PEG-introduced cationized Pronectin F+. The cationized Pronectin F+ with or without PEGylation at different extents was mixed with a plasmid DNA of LacZ to form respective cationized Pronectin F+-plasmid DNA complexes. The plasmid DNA was electrophoretically complexed with cationized Pronectin F+ and PEG-introduced cationized Pronectin F+, irrespective of the PEGylation extent, although the higher N/P ratio of complexes was needed for complexation with the latter Pronectin F+. The molecular size and zeta potential measurements revealed that the plasmid DNA was reduced in size to about 250 nm and the charge was changed to be positive by the complexation with cationized Pronectin F+. For the complexation with PEG-introduced cationized Pronectin F+, the charge of complex became neutral being almost 0 mV with the increasing PEGylation extents, while the molecular size was similar to that of cationized Pronectin F+. When cationized Pronectin F+-plasmid DNA complexes with or without PEGylation were intravenously injected to mice carrying a subcutaneous Meth-AR-1 fibrosarcoma mass, the PEG-introduced cationized Pronectin F+-plasmid DNA complex specifically enhanced the level of gene expression in the tumor, to a significantly high extent compared with the cationized Pronectin F+-plasmid DNA complexes and free plasmid DNA. The enhanced level of gene expression depended on the percentage of PEG introduced, the N/P ratio, and the plasmid DNA dose. A fluorescent microscopic study revealed that the localization of plasmid DNA in the tumor tissue was observed only for the PEG-introduced cationized Pronectin F+-plasmid DNA complex injected. We conclude that the PEGylation of cationized Pronectin F+ is a promising way to enable the plasmid DNA to target to the tumor for gene expression.

Tumor targeting of gene expression through metal-coordinated conjugation with dextran

Tumor targeting of plasmid DNA was achieved through the conjugation of dextran derivatives with chelate residues based on metal coordination. Diethylenetriamine pentaacetic acid (DTPA), spermidine (Sd), and spermine (Sm) were chemically introduced to the hydroxyl groups of dextran to obtain dextran-DTPA, dextran-Sd and dextran-Sm derivatives. Conjugation of the dextran derivative by Zn(2+) coordination decreased the apparent size of the plasmid DNA, depending on the derivative type. The negative zeta potential of plasmid DNA became almost 0 mV after Zn(2+)-coordinated conjugation with dextran-Sm. When the dextran derivative-plasmid DNA conjugates with Zn(2+) coordination were intravenously injected subcutaneously into mice bearing Meth-AR-1 fibrosarcoma, the dextran-Sm-plasmid DNA conjugate significantly enhanced the level of gene expression in the tumor, in contrast to the conjugate of other dextran derivatives and free plasmid DNA. The enhanced gene expression produced by the Zn(2+)-coordinated dextran-Sm-plasmid DNA conjugate was specific to the tumor, whereas a simple mixture of dextran-Sm and plasmid DNA was not effective. The level of gene expression depended on the percentage of chelate residues introduced, the mixing weight ratio of the plasmid DNA/Sm residue used for conjugate preparation, and the plasmid DNA dose. A fluorescent microscopic study revealed that localization of plasmid DNA in the tumor tissue was observed only after injection of the dextran-Sm-plasmid DNA conjugate with Zn(2+) coordination. In addition, the gene expression induced by the conjugate lasted for more than 10 days after the injection. We conclude that Zn(2+)-coordinated dextran-Sm conjugation is a promising way to enable plasmid DNA to target the tumor in gene expression as well as to prolong the duration of gene expression.

Biodistribution and antitumour efficacy of long-circulating N-(2-hydroxypropyl)methacrylamide copolymer-doxorubicin conjugates in nude mice

The aim of this study was to evaluate the influence of the molecular weight (mol. wt) of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (DOX) conjugates (P-DOX) on biodistribution and therapeutic efficacy in nu/nu mice bearing human ovarian carcinoma OVCAR-3 xenografts. Copolymerisation of HPMA, a polymerisable derivative of DOX (N-methacryloylglycylphenylalanylleucylglycyl doxorubicin) and a newly designed crosslinking agent, N(2),N(5)-bis(N-methacryloylglycylphenylalanyl-leucylglycyl)ornithine methyl ester monomers resulted in novel, high mol. wt, branched, water-soluble P-DOX containing lysosomally degradable oligopeptide sequences as crosslinks and side-chains terminated in DOX. Four conjugates with mol. wt of 22, 160, 895 and 1230 kDa were prepared. The results indicated that the half-life in blood and the elimination rate from the tumour were up to 28 times longer and 25 times slower, respectively, for P-DOX (mol. wt=1230 kDa) than for free DOX. Treatment with P-DOX (mol. wt > or = 160 kDa) inhibited tumour growth more efficiently than that of 22 kDa P-DOX or free DOX (P<0.02) at a 2.2 mg/kg DOX equivalent dose. In conclusion, the administration of long circulating P-DOX resulted in enhanced tumour accumulation with a concomitant increase in therapeutic efficacy.

Active drug targeting with immunoconjugates to choroidal neovascularization

PURPOSE

Active drug targeting with monoclonal antibody to neovascular vessels may be a potential treatment for choroidal neovascularization (CNV) in age-related macular degeneration (AMD). Endoglin (CD105) is a proliferating endothelial cell marker with excellent potential for targeting. The goals of this study were to investigate the expression of CD105 in CNV membranes surgically excised from patients with AMD and CNV lesions induced by intense laser photocoagulation in a cynomolgus monkey and to evaluate the in vitro effect of immunoconjugates on endothelial cells.

METHODS

CNV membranes were surgically excised from 10 patients with AMD. Experimental CNV was induced by intense laser photocoagulation in a cynomolgus monkey. Immunolocalization of CD105 on frozen sections of CNV lesions was studied by immunohistochemical evaluation. Anti-von Willebrand's factor antibody was used as an endothelial cell marker. The cytotoxic effect of immunoconjugates of anti-CD105 monoclonal antibody and dextran binding mitomycin C on human umbilical vein endothelial cells (HUVECs) was evaluated in vitro.

RESULTS

Endothelial cells demonstrated strong immunoreactivity of CD105 in all surgically excised CNV membranes. In the monkey eye, CD105-positive cells were detected only in CNV lesions but not in normal chorioretinal tissues. Immunoconjugates with anti-CD105 monoclonal antibody showed a specific inhibitory effect on proliferating HU-VECs.

CONCLUSIONS

These results suggest that anti-CD105 monoclonal antibody-mediated drug targeting has a potential to treat CNV in AMD.

Targeting of tumor necrosis factor to tumor by use of dextran and metal coordination

Tumor targeting of recombinant human tumor necrosis factor alpha (TNF) and consequently an enhanced anti-tumor effect were achieved through conjugation with dextran having metal chelating, diethylenetriaminepentaacetic acid (DTPA) residues based on metal coordination. A simple mixing with the DTPA-dextran in an aqueous solution containing Cu2+ enabled TNF to coordinately conjugate to dextran. Following intravenous (i.v.) injection into tumor-bearing mice, the TNF-DTPA-dextran conjugate caused a significantly higher tumor accumulation of TNF and the longer retention period than free TNF or its mixture with the DTPA-dextran. Intravenous injection of the TNF-DTPA-dextran conjugate suppressed tumor growth to a significantly greater extent than that of free TNF at a lower injection dose. It is concluded that dextran conjugation based on Cu2+ coordination is a promising way to enhance the anti-tumor effect of TNF as a result of its passive tumor targeting.