Targeted intracellular codelivery of chemotherapeutics and nucleic acid with a well-defined dendrimer-based nanoglobular carrier.

Codelivery of different therapeutics has a potential to efficaciously treat human diseases via their synergetic effects. We have recently developed a new class dendrimers, poly(l-lysine) dendrimers with a silsesquioxane cubic core (nanoglobules). These dendrimers have compact globular and well-defined structures and highly functionalized surfaces, and can be used as versatile carriers for biomedical applications. In this study, a generation-3 (G3) nanoglobular dendrimer was used to conjugate a peptide c(RGDfK) with a PEG spacer for codelivery of doxorubicin (DOX) and siRNA. Doxorubicin (DOX) was coupled to the RGD targeted nanoglobule via a degradable disulfide spacer to give G3-[PEG-RGD]-[DOX]. G3-[PEG-RGD]-[DOX] showed higher cytotoxicity than free DOX at high doses in glioblastoma U87 cells. G3-[PEG-RGD]-[DOX] was further complexed with siRNA and such complexes were readily internalized by U87 cells as shown by confocal microscopy. The siRNA complexes of the targeted conjugate resulted in significantly higher gene silencing efficiency in U87-Luc cells than those of control conjugates G3-[PEG-RGD] and G3-[DOX]. The nanoglobules are promising carriers for the codelivery of nucleic acids and chemotherapeutic agents.

Synthesis, characterization, and gene delivery of poly-L-lysine octa(3-aminopropyl)silsesquioxane dendrimers: nanoglobular drug carriers with precisely defined molecular architectures.

Macromolecules with defined nanosizes--nanoglobules--were synthesized and characterized as novel drug carriers with precise molecular architectures. Poly-L-lysine dendrimers with a cubic octa(3-aminopropyl)silsesquioxane (OAS) core, (L-lysine 8-OAS, (L-lysine) 16-(L-lysine) 8-OAS, (L-lysine) 32-(L-lysine) 16-(L-lysine) 8-OAS, and (L-lysine) 64-(L-lysine) 32-(L-lysine) 16-(L-lysine) 8-OAS, were divergently synthesized by solution phase peptide chemistry in good yield and purity. Matrix-assisted laser desorption time of flight (MALDI-TOF) mass spectrometry showed complete substitution of the surface amino groups of lower generation dendrimers during synthesis, as well as precisely defined molecular architectures of the nanoglobules. The structures of the nanoglobules were further characterized by (1)H- and (13)C-NMR and 2D-NMR (correlation spectroscopy (COSY) and pulsed-field-gradient heteronuclear multiple quantum correlation (gHMQC)) spectroscopy. The (1)H-NMR spectroscopy revealed that the nanoglobules had a relatively rigid molecular architecture. Cytotoxicity studies showed that these nanoglobules exhibited a size-dependent toxicity, but it was much lower than that of linear poly-L-lysine. Preliminary in vitro nucleic acid delivery studies have shown that these globular dendrimers can efficiently deliver plasmid DNA to MDA-MB-231 cells. These nanoglobules hold much promise as safe drug carriers with precisely defined molecular architecture.

Gd-DTPA L-cystine bisamide copolymers as novel biodegradable macromolecular contrast agents for MR blood pool imaging.

PURPOSE: The purpose of this study was to synthesize biodegradable Gd-DTPA L-cystine bisamide copolymers (GCAC) as safe and effective, macromolecular contrast agents for magnetic resonance imaging (MRI) and to evaluate their biodegradability and efficacy in MR blood pool imaging in an animal model. METHODS: Three new biodegradable GCAC with different substituents at the cystine bisamide [R = H (GCAC), CH2CH2CH3 (Gd-DTPA L-cystine bispropyl amide copolymers, GCPC), and CH(CH3)2 (Gd-DTPA cystine bisisopropyl copolymers, GCIC)] were prepared by the condensation copolymerization of diethylenetriamine pentaacetic acid (DTPA) dianhydride with cystine bisamide or bisalkyl amides, followed by complexation with gadolinium triacetate. The degradability of the agents was studied in vitro by incubation in 15 microM cysteine and in vivo with Sprague-Dawley rats. The kinetics of in vivo contrast enhancement was investigated in Sprague-Dawley rats on a Siemens Trio 3 T scanner. RESULTS: The apparent molecular weight of the polydisulfide Gd(III) chelates ranged from 22 to 25 kDa. The longitudinal (T1) relaxivities of GCAC, GCPC, and GCIC were 4.37, 5.28, and 5.56 mM(-1) s(-1) at 3 T, respectively. The polymeric ligands and polymeric Gd(III) chelates readily degraded into smaller molecules in incubation with 15 microM cysteine via disulfide-thiol exchange reactions. The in vitro degradation rates of both the polymeric ligands and macromolecular Gd(III) chelates decreased as the steric effect around the disulfide bonds increased. The agents readily degraded in vivo, and the catabolic degradation products were detected in rat urine samples collected after intravenous injection. The agents showed strong contrast enhancement in the blood pool, major organs, and tissues at a dose of 0.1 mmol Gd/kg. The difference of their in vitro degradability did not significantly alter the kinetics of in vivo contrast enhancement of the agents. CONCLUSION: These novel GCAC are promising contrast agents for cardiovascular and tumor MRI, which are later cleaved into low molecular weight Gd(III) chelates and rapidly cleared from the body.