In Vivo Biodistribution of Dendrimers and Dendrimer Nanocomposites — Implications for Cancer Imaging and Therapy

Dendritic systems in drug delivery applications

The design of well-defined particulate carrier systems with controlled size, shapes and physicochemical characteristics is becoming a focal point in the field of biomedicine and drug delivery. Dendrimers are one of the emerging technologies of recent times and have served as a unique platform to achieve the development as novel drug delivery scaffolds. Dendrimers may be engineered to meet the specific needs of biologically active agents, which can either be encapsulated within dendrimers or chemically attached to these units. The large number of active functional groups on the surface of dendrimers allows them to be meticulously tailored and to act as nano-scaffolds or nano-containers of various categories of drugs. The architecture of modified dendrimers has posed a challenge to drug delivery, in particular with respect to their in vivo metabolic fate. The drug delivery applications of dendrimers presented in this article provide an insight of their potential and substantiate the major roles for the future of these nanoconstructs.

Studies on polyamidoamine dendrimers as efficient gene delivery vector

Non-viral methods of gene delivery are attractive alternatives compared to virus-based gene delivery. Polyamidoamine (PAMAM) dendrimers are a new class of highly branched spherical polymers and have a unique surface of positively charged primary amine groups. They can form complex with DNA by electrostatic interaction, and deliver gene into cells. The ability of G5 PAMAM dendrimers binding and transferring DNA to cells has been investigated, and the effect of this complex to cell viability has been evaluated. G5 PAMAM dendrimers can bind DNA and transfer it to cultured cells efficiently, and have low cytotoxicity. The complex of PAMAM dendrimer-DNA can remain intact in a broad pH range, and also can prevent DNA from being degraded by restriction enzyme. Using the EGFP-C2 gene as marker genes, PAMAM dendrimers can deliver it to many organs after intravenous injection and have high expression in liver, kidney, lung, and spleen. Polyamidoamine- DNA complex can bind selectively plasma proteins, which may be correlated with its transportation in vivo. Polyamidoamine dendrimers' high-efficiency, low-cytotoxicity gene vector, appear to have potential for fundamental research and genetic therapy in vitro and in vivo.

Synthesis and characterization of PAMAM dendrimer-based multifunctional nanodevices for targeting alphavbeta3 integrins

We have synthesized a stable and clinically relevant nanodevice (cRGD-BT-ND; ND for short) that exhibits superior binding to the biologic target alphavbeta3 integrins, when either compared to the same free cRGD peptide or to the biotinylated nanodevice without covalently attached peptides (BT-ND). Selective targeting of alphavbeta3 integrins was achieved by coupling cyclic cRGD peptides to the nanodevice (ND) surface, while biotin groups (BT) were used for amplified detection of bound cRGD-BT-ND by anti-biotin antibody or avidin linked to horseradish peroxidase after binding. The synthesis involved the following steps: the amino-terminated ethylenediamine core generation 5 poly(amidoamine) (PAMAM_E5.NH2) dendrimer was first partially acetylated and then biotinylated, and residual primary amine termini were converted to succinamic acid groups (SAH), some of which finally were conjugated with cRGD peptide residues through the amino group of the lysine side chain. The starting material and all derivatives were extensively characterized by polyacrylamide gel electrophoresis (PAGE), size exclusion chromatography (SEC), potentiometric acid-base titration, MALDI-TOF, and NMR. Cytotoxicity of all dendrimer derivatives was examined in B16F10 melanoma cell cultures using the XTT colorimetric assay for cellular viability. Binding of nanodevices to the biological target was determined using plates coated with human alphavbeta3 integrin and alphavbeta3 receptor expressing human dermal microvascular endothelial cells (HDMECs). The PAMAM_E5.(NHAc)72(NHBT)8(NHSAH)35(NHSA-cR GD)4 nanodevice is nontoxic within physiologic concentration ranges and specifically binds to the alphavbeta3 integrins, apparently much stronger than the cyclic cRGD peptide itself.

Analysis of fullerene-based nanomaterial in serum matrix by CE

With the increasing interest in using nanoparticles as vehicles for drug delivery and image contrast agents, there is a need to develop assays for their detection and quantitation in complex matrices to facilitate monitoring their biodistribution. In this study, we developed a CE approach for the analysis of two nanoparticles: carboxyfullerene (C3) and dendrofullerene (DF1) in both standard solutions and a serum matrix. These highly soluble, charged C(60) derivatives were characterized by CZE using either a bare or dynamically coated fused-silica capillaries. The resolution of both nanoparticles was slightly lower with the coated capillary; however, their migration times were faster. While separation of the DF1 nanoparticles using MEKC resulted in a greater number of observable peaks, the peak profile of C3 was basically unchanged regardless of whether SDS micelles were added to the running buffers or not. The MEKC and/or CZE assays were then used to quantitate the C3 and DF1 nanoparticles in spiked human serum samples. The quantitation of the nanoparticles was linear from 0-500 microg/mL with detection limits ranging from 0.5 to 6 microg/mL.

Monte Carlo simulations of a charged dendrimer with explicit counterions and salt ions

Static properties of a dendrimer with generation g = 5 with positively charged terminal groups in an athermal solvent are studied by lattice Monte Carlo simulations using the cooperative motion algorithm as the tossing scheme. The calculations are performed both for a salt-free system with neutralizing counterions and for a small amount of added monovalent and divalent salt. The full Coulomb potential and the excluded volume interactions between ions and beads are taken explicitly into account with the reduced temperature tau, the number of salt cations (anions) n(s), and salt valence z(s) as the simulation parameters. The bahaviour of the systems is analyzed by the mean effective charge per end-bead <Q>, Coulomb mean energy <E>, mean-square radius of gyration <R(g)(2)>, pair correlation functions g(alphabeta), and charge density rho(ch). The simulations show that for n(s)> or = 0 and decreasing tau: (a) there is encapsulation in the dendrimer and condensation onto the terminal groups of anions accompanied by a monotonic decrease in <Q> and <E> and by subsequent swelling and shrinking of the molecule; (b) encapsulation, condensation and shrinking are the most significant and swelling weaker for |z(s)| = 2; (c) penetration of salt cations into the dendrimer is minor when compared to that of anions; (d) rho(ch) is reduced and becomes negative close to the center of mass of the dendrimer and on its periphery; (e) for the considered n(s) > 0, unlike divalent salt ions the monovalent ones cause slight effects when compared to the salt-free case.