A Polycation Scaffold Presenting Tunable “Click” Sites: Conjugation to Carbohydrate Ligands and Examination of Hepatocyte-Targeted pDNA Delivery

GalNAc- or Mannose-PEG-Functionalized Polyplexes Enable Effective Lectin-Mediated DNA Delivery

A cationic, dendrimer-like oligo(aminoamide) carrier with four-arm topology based on succinoyl tetraethylene pentamine and histidines, cysteines, and N-terminal azido-lysines was screened for plasmid DNA delivery on various cell lines. The incorporated azides allow modification with various shielding agents of different polyethylene glycol (PEG) lengths and/or different ligands by copper-free click reaction, either before or after polyplex formation. Prefunctionalization was found to be advantageous over postfunctionalization in terms of nanoparticle formation, stability, and efficacy. A length of 24 ethylene oxide repetition units and prefunctionalization of ≥50% of azides per carrier promoted optimal polyplex shielding. PEG shielding resulted in drastically reduced DNA transfer, which could be successfully restored by active lectin targeting via novel GalNAc or mannose ligands, enabling enhanced receptor-mediated endocytosis of the carrier system. The involvement of the asialoglycoprotein receptor (ASGPR) in the uptake of GalNAc-functionalized polyplexes was confirmed in the ASGPR-positive hepatocarcinoma cell lines HepG2 and Huh7. Mannose-modified polyplexes showed superior cellular uptake and transfection efficacy compared to unmodified and shielded polyplexes in mannose-receptor-expressing dendritic cell-like DC2.4 cells.

Developing a Library of Mannose-Based Mono- and Disaccharides: A General Chemoenzymatic Approach to Monohydroxylated Building Blocks

Regioselective deprotection of acetylated mannose-based mono- and disaccharides differently functionalized in anomeric position was achieved by enzymatic hydrolysis. Candida rugosa lipase (CRL) and Bacillus pumilus acetyl xylan esterase (AXE) were immobilized on octyl-Sepharose and glyoxyl-agarose, respectively. The regioselectivity of the biocatalysts was affected by the sugar structure and functionalization in anomeric position. Generally, CRL was able to catalyze regioselective deprotection of acetylated monosaccharides in C6 position. When acetylated disaccharides were used as substrates, AXE exhibited a marked preference for the C2, or C6 position when C2 was involved in the glycosidic bond. By selecting the best enzyme for each substrate in terms of activity and regioselectivity, we prepared a small library of differently monohydroxylated building blocks that could be used as intermediates for the synthesis of mannosylated glycoconjugate vaccines targeting mannose receptors of antigen presenting cells.

Nonviral Gene Delivery with Cationic Glycopolymers

The field of gene therapy, which aims to treat patients by modulating gene expression, has come to fruition and has landed several landmark FDA approvals. Most gene therapies currently rely on viral vectors to deliver nucleic acid cargo into cells, but there is significant interest in moving toward chemical-based methods, such as polymer-based vectors, due to their low cost, immunocompatibility, and tunability. The full potential of polymer-based delivery systems has yet to be realized, however, because most polymeric transfection reagents are either too inefficient or too toxic for use in the clinic. In this Account, we describe developments in carbohydrate-based cationic polymers, termed glycopolymers, for enhanced nonviral gene delivery. As ubiquitous components of biological systems, carbohydrates are a rich class of compounds that can be harnessed to improve the biocompatibility of non-native polymers, such as linear polyamines used for promoting transfection. Reineke et al. developed a new class of carbohydrate-based polymers called poly(glycoamidoamine)s (PGAAs) by step-growth polymerization of linear monosaccharides with linear ethyleneamines. These glycopolymers were shown to be both efficient and biocompatible transfection reagents. Systematic modifications of the structural components of the PGAA system revealed structure-activity relationships important to its function, including its ability to degrade in situ. Expanding upon the development of step-growth glycopolymers, monosaccharides, such as glucose, were functionalized as vinyl-based monomers for the formation of diblock copolymers via radical addition-fragmentation chain-transfer (RAFT) polymerization. Upon complexation with plasmid DNA, the glucose-containing block creates a hydrophilic shell that promotes colloidal stability as effectively as PEG functionalization. An N-acetyl-d-galactosamine variant of this diblock polymer yields colloidally stable particles that show increased receptor-mediated uptake by liver hepatocytes in vitro and promotes liver targeting in mice. Finally, the disaccharide trehalose was incorporated into polycationic structures using both step-growth and RAFT techniques. It was shown that these trehalose-based copolymers imparted increased colloidal stability and yielded plasmid and siRNA polyplexes that resist aggregation upon lyophilization and reconstitution in water. The aforementioned series of glycopolymers use carbohydrates to promote effective and safe delivery of nucleic acid cargo into a variety of human cells types by promoting vehicle degradation, tissue-targeting, colloidal stabilization, and stability toward lyophilization to extend shelf life. Work is currently underway to translate the use of glycopolymers for safe and efficient delivery of nucleic acid cargo for gene therapy and gene editing applications.

A novel galactose-PEG-conjugated biodegradable copolymer is an efficient gene delivery vector for immunotherapy of hepatocellular carcinoma

Successful immunogene therapy depends not only on the therapeutic gene but also on the gene delivery vector. In this study, we synthesized a novel copolymer consisting of low-molecular-weight polyethylenimine (PEI) cross-linked by myo-inositol (INO) and conjugated with a galactose-grafted PEG chain, named LA-PegPI. We characterized the chemical structure and molecular weight of the copolymer and particle properties of LA-PegPI/pDNA. Furthermore, we showed that LA-PegPI/pDNA polyplexes possessed excellent stability in physiological salt solution, low cytotoxicity, and high transfection efficiency in the asialoglycoprotein receptor (ASGPR)-positive liver cells in vitro. Importantly, we also showed that through intraperitoneal injection of LA-PegPI/pDNA nanoparticles, the reporter gene was forcefully expressed in the liver hepatocytes of mice. Finally, we documented that intraperitoneal injection of LA-PegPI/pIL15 nanoparticles effectively suppressed tumor growth and prolonged survival time of tumor-bearing mice via activation of CD8⁺ T cells and NK cells and upregulation of the cytokines IFN-γ, TNF, and IL12 in an orthotopic hepatocellular carcinoma mouse model. Interestingly, LA-PegPI/pluc nanoparticles could effectively stimulate the proliferation of NK cells and inhibit tumor growth in this model. In summary, LA-PegPI is a useful gene vector for immunogene therapy of hepatocellular carcinoma, and its potential for clinical application warrants further study.

Recent advances in ligand targeted therapy

BACKGROUND

Ligand targeted therapy (LTT) is a powerful pharmaceutical strategy to achieve selective drug delivery to pathological cells, for both therapeutic and diagnostic purposes, with the advantage of limited side effects and toxicity. This active drug targeting approach is based on the discovery that there are receptors overexpressed on pathological cells, compared to their expression in normal tissues.

PURPOSE

The purpose of this article is to review recently published data on LTT with applications, both in the field of cancer therapy and other diseases. Moreover, data on LTT exploiting receptors overexpressed at cytoplasmatic level are also reviewed.

METHODS

Data were deduced from Medline (PubMed) and SciFinder and their selections were made with preference to papers where the most relevant receptors were involved.

RESULTS

Several groups have reported improved delivery of targeted nanocarriers, as compared to nontargeted ones, to pathological cells. LTT offers several advantages, but there are also limitations in the development of this strategy. Moreover, LTT have shown encouraging results in in vitro and in animal models in vivo; hence their clinical potential awaits investigation.

CONCLUSION

Recent studies highlight that the ligand density plays an important role in targeting efficacy. Furthermore, LTT applications in diseases different from cancer and those exploiting receptors overexpressed at cytoplasmatic level are growing.