Simple Modifications of Branched PEI Lead to Highly Efficient siRNA Carriers with Low Toxicity

Polymer carriers like PEI which proved their efficiency in DNA delivery were found to be far less effective for the applications with siRNA. In the current study, we generated a number of nontoxic derivates of branched PEI through modification of amines by ethyl acrylate, acetylation of primary amines, or introduction of negatively charged propionic acid or succinic acid groups to the polymer structure. The resulting products showed high efficiency in siRNA-mediated knockdown of target gene. In particular, succinylation of branched PEI resulted in up to 10-fold lower polymer toxicity in comparison to unmodified PEI. Formulations of siRNA with succinylated PEI were able to induce remarkable knockdown (80% relative to untreated cells) of target luciferase gene at the lowest tested siRNA concentration of 50 nM in Neuro2ALuc cells. The polyplex stability assay revealed that the efficiency of formulations which are stable in physiological saline is independent of the affinity of siRNA to the polymer chain. The improved properties of modified PEI as siRNA carrier are largely a consequence of the lower polymer toxicity. In order to achieve significant knockdown of target gene, the PEI-based polymer has to be applied at higher concentrations, required most probably for sufficient accumulation and proton sponge effects in endosomes. Unmodified PEI is highly toxic at such polymer concentrations. In contrast, the far less toxic modified analogues can be applied in concentrations required for the knockdown of target genes without side effects

Improved Synthesis Strategy of Poly(amidoamine)s for Biomedical Applications: Catalysis by “Green” Biocompatible Earth Alkaline Metal Salts

Poly(amidoamine)s (PAAs) have received significant attention due to their good biocompatibility and fast biodegradation profile which gives these polymers high potential in biomedical applications. Conventional synthesis of PAAs via aza-type Michael addition reaction of primary amines to bis-acrylamides often proceeds slowly and takes several days, which does not allow fast and extensive screening of PAA libraries for their bioactivity. Current investigation was dedicated to the development of catalytic synthesis procedures in order to decrease the polymerization times. The salts of several transition metals, as well as earth alkali metals were studied for their catalytic activity in the polymerization reaction. It was found that the salts of earth alkali metals showed the highest potential in the catalysis of polymerization, whereas the salts of transition metals showed either no effect or even resulted in slowing down the reaction. In particular, the addition of CaCl2 to the reaction mixtures resulted in remarkable increase of the reaction rate as compared to the system without catalyst. PAAs synthesized by the conventional procedure and those obtained by using CaCl2 as a catalyst showed no difference in physico-chemical properties as well as in biological activity. The novel synthetic method for PAAs, using catalysts based on earth alkali metals, represents an attractive alternative to currently applied methods. Characteristics of earth alkali metals such as low toxicity and good biocompatibility make them especially useful in the preparation of these polymers for biomedical application

Drug Nanocarriers Labeled With Near-infrared-emitting Quantum Dots (Quantoplexes): Imaging Fast Dynamics of Distribution in Living Animals

The knowledge of the biodistribution of macromolecular drug formulations is a key to their successful development for specific tissue- and tumor-targeting after systemic application. Based on the polyplex formulations, we introduce novel drug nanocarriers, which we denote as “quantoplexes” incorporating near-infrared (IR)-emitting cadmium telluride (CdTe) quantum dots (QDs), polyethylenimine (PEI), and a macromolecular model drug [plasmid DNA (pDNA)], and demonstrate the ability of tracking these bioactive compounds in living animals. Intravenous application of bare QD into nude mice leads to rapid accumulation in the liver and peripheral regions resembling lymph nodes, followed by clearance via the liver within hours to days. Quantoplexes rapidly accumulate in the lung, liver, and spleen and the fluorescent signal is detectable for at least a week. Tracking quantoplexes immediately after intravenous injection shows rapid redistribution from the lung to the liver within 5 minutes, depending on the PEI topology and quantoplex formulation used. With polyethyleneglycol (PEG)-modified quantoplexes, blood circulation and passive tumor accumulation was measured in real time. The use of quantoplexes will strongly accelerate the development of tissue and tumor-targeted macromolecular drug carriers