Bioresponsive small molecule polyamines as noncytotoxic alternative to polyethylenimine

Nanomedicine therapeutics and diagnostics are the goal

Understanding and exploiting molecular mechanisms in biology is central to chemical biology. In 20 years, chemical biology research has advanced from simple mechanistic studies using isolated biological macromolecules to molecular-level and nanomolecular-level mechanistic studies involving whole organisms. This review documents the best of my personal and collaborative academic research work that has made use of a solid organic chemistry and chemical biology approach toward nanomedicine, in which my focus has been on the design, creation and use of synthetic, self-assembly lipid-based nanoparticle technologies for the functional delivery of active pharmaceutical ingredients to target cells in vivo. This research is now leading to precision therapeutics approaches (PTAs) for the treatment of diseases that may define the future of nanomedicine.

1,2-Dithiolane-Derived Dynamic, Covalent Materials: Cooperative Self-Assembly and Reversible Cross-Linking

The use of dithiolane-containing polymers to construct responsive and dynamic networks is an attractive strategy in material design. Here, we provide a detailed mechanistic study on the self-assembly and gelation behavior of a class of ABA triblock copolymers containing a central poly(ethylene oxide) block and terminal polycarbonate blocks with pendant 1,2-dithiolane functionalities. In aqueous solution, these amphiphilic block copolymers self-assemble into bridged flower micelles at high concentrations. The addition of a thiol initiates the reversible ring-opening polymerizations of dithiolanes in the micellar cores to induce the cross-linking and gelation of the micellar network. The properties of the resulting hydrogels depend sensitively on the structures of 1,2-dithiolanes. While the methyl asparagusic acid-derived hydrogels are highly dynamic, adaptable, and self-healing, those derived from lipoic acid are rigid, resilient, and brittle. The thermodynamics and kinetics of ring-opening polymerization of the two dithiolanes were investigated to provide important insights on the dramatically different properties of the hydrogels derived from the two different dithiolanes. The incorporation of both dithiolane monomers into the block copolymers provides a facile way to tailor the properties of these hydrogels.

Folate-conjugated polyspermine for lung cancer-targeted gene therapy

Biodegradable polyamines have long been studied as potential recombinant viral gene vectors. Spermine (SPE) is an endogenous tetra-amine with excellent biocompatibility yet poor gene condensation capacity. We have previously synthesized a polyspermine based on SPE and poly(ethylene glycol) (PEG) diacrylate (SPE-alt-PEG) for enhanced transfection performance, but the synthesized SPE-alt-PEG still lacked specificity towards cancer cells. In this study, folic acid (FA) was incorporated into SPE-alt-PEG to fabricate a targeted gene delivery vector (FA-SPE-PEG) via an acylation reaction. FA-SPE-PEG exhibited mild cytotoxicity in both cancer cells and normal cells. FA-SPE-PEG possessed higher transfection efficiency than PEI 25 K and Lipofectamine^® 2000 in two tested cancer cell lines at functional weight ratios, and its superiority over untargeted SPE-alt-PEG was prominent in cells with overexpressed folate receptors (FRs). Moreover, in vivo delivery of green fluorescent protein (GFP) with FA-SPE-PEG resulted in highest fluorescent signal intensity of all investigated groups. FA-SPE-PEG showed remarkably enhanced specificity towards cancer cells both in vivo and in vitro due to the interaction between FA and FRs. Taken together, FA-SPE-PEG was demonstrated to be a prospective targeted gene delivery vector with high transfection capacity and excellent biocompatibility.

Suppression of tumor growth in lung cancer xenograft model mice by poly(sorbitol-co-PEI)-mediated delivery of osteopontin siRNA

Small interfering RNA (siRNA)-mediated gene silencing represents a promising strategy for treating diseases such as cancer; however, specific gene silencing requires an effective delivery system to overcome the instability and low transfection efficiency of siRNAs. To address this issue, a polysorbitol-based transporter (PSOT) was prepared by low molecular weight branched polyethylenimine (bPEI) crosslinked with sorbitol diacrylate (SDA). Osteopontin (OPN) gene, which is highly associated with non-small cell lung cancer (NSCLC) was targeted by siRNA therapy using siRNA targeting OPN (siOPN). Characterization study confirmed that PSOT formed compact complexes with siOPN and protected siOPN against degradation by RNase. PSOT/siOPN complexes demonstrated low cytotoxicity and enhanced transfection efficiency in vitro, suggesting that this carrier may be suitable for gene silencing. In the A549 and H460 lung cancer cell lines, PSOT/siOPN complexes demonstrated significant silencing efficiency at both RNA and protein levels. To study in vivo tumor growth suppression, two lung cancer cell-xenograft mouse models were prepared and PSOT/siOPN complexes were delivered into the mice through intravenous injection. The siOPN-treated groups demonstrated significantly reduced OPN expression at both the RNA and protein levels as well as suppression of tumor volume and weight. Taken together, siOPN delivery using PSOT may present an effective and novel therapeutic system for lung cancer treatment.

Thermosensitive, near-infrared-labeled nanoparticles for topotecan delivery to tumors

Liposomal nanoparticles have proven to be versatile systems for drug delivery. However, the progress in clinic has been slower and less efficient than expected. This suggests a need for further development using carefully designed chemical components to improve usefulness under clinical conditions and maximize therapeutic effect. For cancer chemotherapy, PEGylated liposomes were the first nanomedicine to reach the market and have been used clinically for several years. Approaches toward targeted drug delivery using next generation "thermally triggered" nanoparticles are now in clinical trials. However, clinically tested thermosensitive liposomes (TSLs) lack the markers that allow tumor labeling and improved imaging for tissue specific applied hyperthermia. Here we describe the development of optically labeled TSLs for image guidance drug delivery and proof-of-concept results for their application in the treatment of murine xenograft tumors using the anticancer drug topotecan. These labeled TSLs also allow the simultaneous, real-time diagnostic imaging of nanoparticle biodistribution using a near-infrared (NIR; 750-950 nm) fluorophore coupled to a lipidic component of the lipid bilayer. When combined with multispectral fluorescence analysis, this allows for specific and high sensitivity tracking of the nanoparticles in vivo. The application of NIR fluorescence-labeled TSLs could have a transformative effect on future cancer chemotherapy.

Bioreducible polycations in nucleic acid delivery: past, present, and future trends

Polycations that are degradable by reduction of disulfide bonds are developed for applications in delivery of nucleic acids. This Feature Article surveys methods of synthesis of bioreducible polycations and discusses current understanding of the mechanism of action of bioreducible polyplexes. Emphasis is placed on the relationship between the biological redox environment and toxicity, trafficking, transfection activity, and in vivo behavior of bioreducible polycations and polyplexes.

Delivery of RNAi therapeutics: work in progress

RNA interference (RNAi) therapeutics appear to offer substantial opportunities for future therapy. However, post-administration RNAi effectors are typically unable to reach disease target cells in vivo without the assistance of a delivery system or vector. The main focus of this review is on lipid-based nanoparticle (LNP) delivery systems in current research and development that have at least been shown to act as effective delivery systems for functional delivery of RNAi effectors to disease target cells in vivo. The potential utility of these LNP delivery systems is growing rapidly, and LNPs are emerging as the preferred synthetic delivery systems in preclinical studies and current nonviral RNAi effector clinical trials. Moreover, studies on LNP-mediated delivery in vivo are leading to the emergence of useful biophysical parameters and physical organic chemistry rules that provide a framework for understanding in vivo delivery behaviors and outcomes. These same parameters and rules should also suggest ways and means to develop next generations of LNPs with genuine utility and long-term clinical viability.

Delivering the promise of small ncRNA therapeutics

Small non-coding RNA (ncRNA) therapeutics make use of small ncRNA effectors for desired therapeutic purposes that are essentially short (10–20 kD) RNA segments. These small ncRNA effectors are potentially tremendously powerful therapeutic agents, but are typically unable to reach disease target cells in vivo without the assistance of a delivery system or vector. The main focus of this review is the use of lipid-based nanoparticles (LNPs) for the functional delivery of small ncRNA effectors in vivo. LNPs appear to be amongst the most effective delivery systems currently available for this purpose. Moreover, studies on LNP-mediated delivery in vivo are leading to the emergence of useful biophysical parameters and physical organic chemistry rules that provide a framework for understanding LNP-mediated in vivo delivery behaviors and outcomes. These same parameters and rules should also suggest ways and means to develop next generations of LNPs with genuine utility and long-term clinical viability.

Lipid-based nanoparticles in cancer diagnosis and therapy

Today, researchers are constantly developing new nanomaterials, nanodevices, and nanoparticles to meet unmet needs in the delivery of therapeutic agents and imaging agents for cancer therapy and diagnosis, respectively. Of particular interest here are lipid-based nanoparticles (LNPs) that are genuine particles (approximately 100 nm in dimension) assembled from varieties of lipid and other chemical components that act collectively to overcome biological barriers (biobarriers), in order for LNPs to preferentially accumulate in or around disease-target cells for the functional delivery of therapeutic agents for treatment or of imaging agents for diagnosis. The capabilities of these LNPs will clearly vary depending on functional requirements, but the nanoscale allows for an impressive level of diversity in capabilities to enable corresponding LNPs to address an equally diverse range of functional requirements. Accordingly, LNPs should be considered appropriate vehicles to provide an integrated, personalized approach to cancer diagnosis and therapy in future cancer disease management.

pH-triggered nanoparticle mediated delivery of siRNA to liver cells in vitro and in vivo

Recently, we reported for the first time the development of pH-triggered nanoparticles for the functional delivery of small interfering RNA (siRNA) to liver for treatment of hepatitis B virus infections in vivo. Here, we report on systematic formulation and biophysical studies of three different pH-triggered nanoparticle formulations looking for ways to improve on the capabilities of our previous nanoparticle system. We demonstrate how pH-triggered, PEGylated siRNA nanoparticles stable with respect to aggregation in 80% serum can still release siRNA payload at pH 5.5 within 30 min. This capability allows functional delivery to cultured murine hepatocyte cells in vitro, despite a high degree of PEGylation (5 mol %). We also demonstrate that pH-triggered, PEGylated siRNA nanoparticles typically enter cells by clathrin-coated pit endocytosis, but functional delivery requires membrane fusion events (fusogenicity). Biodistribution studies indicate that >70% of our administered nanoparticles are found in liver hepatocytes, post intravenous administration. Pharmacodynamic experiments show siRNA delivery to murine liver effecting maximum knockdown 48 h post administration from a single dose, while control (nontriggered) nanoparticles require 96 h and two doses to demonstrate the same effect. We also describe an anti-hepatitis C virus (HCV) proof-of-concept experiment indicating the possibility of RNAi therapy for HCV infections using pH-triggered, PEGylated siRNA nanoparticles.

Synthesis of the first poly(diaminosulfide)s and an investigation of their applications as drug delivery vehicles

This paper reports the first examples of poly(diaminosulfide)s that were synthesized by the reaction of a sulfur transfer reagent and several secondary diamines. The diaminosulfide group has the general structure of R(2)N-S-NR(2) and, although it has been used in the synthesis of small molecules, it has never been utilized in the synthesis of macromolecules until this report. A series of poly(diaminosulfide)s were synthesized at elevated temperatures, and the molecular weights of the polymers were as high as 12,400 g mol(-1) with conversions for the polymerization reaction up to 99%. The rate constants for the transamination reactions that lead to the polymers were measured in several solvents to provide an understanding the reaction conditions necessary to polymerize the monomers. The degradation of diaminosulfides were studied in D(2)O, C(6)D(6), CD(3)OD, CDCl(3), and DMSO-d(6)/D(2)O to demonstrate that they were very stable in organic solvents but degraded within hours under aqueous conditions. These results clearly demonstrated that diaminosulfides are very stable in organic solvents under ambient conditions. Poly(diaminosulfide)s have sufficient stabilities to be useful for many applications. The ability of these polymers to function as drug delivery vehicles were studied by the fabrication of nanoparticles of a water-insoluble poly(diaminosulfide) with a dye. The microparticles were readily absorbed into human embryonic 293 cells and possessed no measureable toxicity towards these same cells.

Efficient topical delivery of plasmid DNA to lung in vivo mediated by putative triggered, PEGylated pDNA nanoparticles

Non-viral vectors are considered safer than viral vectors and show clinical potential, but remain less efficient in terms of DNA delivery. Here we report how cationic liposomes, prepared from new cationic lipid, N',N',-dioctadecyl-N-4,8-diaza-10-aminodecanoylglycine amide (DODAG) and neutral lipid dioleoyl-L-α-phos-phatidylethanolamine (DOPE), can be formulated with plasmid DNA (pDNA) in the presence of stabilizer cholesteryl-oxycarbonylpolyethlylene glycol(4600) (PEG(4600)-Chol) giving PEGylated pDNA nanoparticles (pDNA-ABC nanoparticles) that are proposed to be half-life triggered nanoparticles. In particular, the PEGylated pDNA nanoparticle formulation DODAG/DOPE/PEG(4600)-Chol (43:43:14, m/m/m)-pDNA (total lipid/pDNA ratio 4:1 w/w) (pTRANSplus nanoparticles) is shown to mediate efficient transfection of murine lung tissue in vivo. Levels of transfection compare well with the results of polyethylenimine (PEI) mediated pDNA transfection in vivo and even of adenovirus mediated transduction. Cryo-EM imaging indicates that pTRANSplus formulations are somewhat heterogeneous but do consist primarily of bilammellar lipoplex nanoparticles with a few multilammellar nanoparticle aggregates. Lung histology confirms that pTRANSplus mediated transfection in vivo targets substantially the epithelial cells of bronchii and bronchioli airway passages. The pTRANSplus nanoparticle system is a useful new starting point for nucleic acid therapeutic strategies to counter lung disorders such as viral infection and possibly cystic fibrosis.