Mahesh L. Patil

A novel internally quaternized and surface-acetylated poly(amidoamine) generation four dendrimer (QPAMAM-NHAc) was synthesized and evaluated for intracellular delivery of siRNA. The proposed dendrimer as a nanocarrier possesses the following advantages: (1) modified neutral surface of the dendrimer for low cytotoxicity and enhanced cellular internalization; (2) existence of cationic charges inside the dendrimer (not on the outer surface) resulting in highly organized compact nanoparticles, which can potentially protect nucleic acids from degradation. The properties of this dendrimer were compared with PAMAM-NH 2 dendrimer, possessing surface charges, and with an internally quaternized charged and hydroxyl-terminated QPAMAM-OH dendrimer. Atomic force microscopy studies revealed that internally charged and surface neutral dendrimers, QPAMAM-OH and QPAMAM-NHAc, formed well-condensed, spherical particles (polyplexes) with siRNA, while PAMAM-NH 2 resulted in the formation of nanofibers. The modification of surface amine groups to amide significantly reduced cytotoxicity of dendrimers with QPAMAM-NHAc dendrimer showing the lowest toxicity. Confocal microscopy demonstrated enhanced cellular uptake and homogeneous intracellular distribution of siRNA delivered by the proposed QPAMAM-NHAc nanocarrier. The results clearly demonstrated distinct advantages of developed QPAMAM-NHAc/siRNA polyplexes over the existing nucleic acid dendrimeric carriers.

A novel cancer targeted, internally cationic and surface neutral polyamidoamine (PAMAM) dendrimer, was designed, synthesized, and evaluated as a nanocarrier for the targeted intracellular delivery of siRNA. The dendrimer contained a synthetic analog of Luteinizing hormone-releasing hormone as cancer targeting moiety. The proposed delivery system possesses the following advantages: (1) internal cationic charges for complexation with siRNA and enhanced siRNA protection; (2) low cytotoxicity; (3) lesser degree of quaternization offering free tertiary amines for potential proton sponge effect; and (4) targeting specifically to cancer cells for enhancing siRNA uptake and efficiency and potential limitation of adverse side effects of chemotherapy on healthy organs. Both nontargeted and targeted dendrimer-siRNA complexes formed compact nanometer size spherical particles, exhibited very low cytotoxicity even at the higher concentration, and efficiently penetrated cancer cells in vitro. However, only the targeted dendrimer-siRNA complex was able to substantially decrease the expression of a targeted BCL2 gene.

A novel triblock poly(amido amine)-poly(ethylene glycol)-poly-l-lysine (PAMAM-PEG-PLL) nanocarrier was designed, synthesized, and evaluated for the delivery of siRNA. The design of the nanocarrier is unique and provides a solution to most of the common problems associated with the delivery and therapeutic applications of siRNA. Every component in the triblock nanocarrier plays a significant role and performs multiple functions: (1) tertiary amine groups in the PAMAM dendrimer work as a proton sponge and play a vital role in the endosomal escape and cytoplasmic delivery of siRNA; (2) PEG, a linker connecting PLL and PAMAM dendrimers renders nuclease stability and protects siRNA in human plasma; (3) PLL provides primary amines to form polyplexes with siRNA through electrostatic interaction and also acts as penetration enhancer; and (4) conjugation to PEG and PAMAM reduced toxicity of PLL and the entire triblock nanocarrier PAMAM-PEG-PLL. The data obtained show that the polyplexes resulted from the conjugation of siRNA, and the proposed nanocarriers were effectively taken up by cancer cells and induced the knock down of the target BCL2 gene. In addition, triblock nanocarrier/siRNA polyplexes showed excellent stability in human plasma.

The prevention of cyto- and genotoxicity of nanocarriers is an important task in nanomedicine. In the present investigation, we, at the first time using similar experimental conditions, compared genotoxicity of nanocarriers with different composition, architecture, size, molecular weight and charge. Poly(ethylene glycol) polymers, neutral and cationic liposomes, micelles, poly(amindo amine) and poly(propyleneimine) dendrimers, quantum dots, mesoporous silica, and supermagnetic iron oxide (SPIO) nanoparticles were studied. All nanoparticles were used in non-cytotoxic concentrations. However, even in these concentrations, positively charged cationic liposomes, dendrimers, and SPIO nanoparticles induced genotoxicity leading to the significant formation of micronuclei in cells. Negatively charged and neutral nanocarriers were not genotoxic. A strong positive correlation was found between the number of formed micronuclei and the positive charge of nanocarriers. We proposed modifications of both types of dendrimers and SPIO nanoparticles that substantially decreased their genotoxicity and allowed for an efficient intracellular delivery of nucleic acids.

[reaction: see text] Novel chiral imidazolium salts have been synthesized as examples of chiral ionic liquids with a spiro skeleton. Effects of N-substituents and counteranions on the melting point of spiro imidazolium salts and their chiral discrimination abilities are described.