Dendritic Molecular Transporters Provide Control of Delivery to Intracellular Compartments

Intracellular delivery and deep tissue penetration of nucleoside triphosphates using photocleavable covalently bound dendritic polycations

Nucleoside triphosphates (NTPs) are essential in various biological processes. Cellular or even organismal controlled delivery of NTPs would be highly desirable, yet in cellulo and in vivo applications are hampered owing to their negative charge leading to cell impermeability. NTP transporters or NTP prodrugs have been developed, but a spatial and temporal control of the release of the investigated molecules remains challenging with these strategies. Herein, we describe a general approach to enable intracellular delivery of NTPs using covalently bound dendritic polycations, which are derived from PAMAM dendrons and their guanidinium derivatives. By design, these modifications are fully removable through attachment on a photocage, ready to deliver the native NTP upon irradiation enabling spatiotemporal control over nucleotide release. We study the intracellular distribution of the compounds depending on the linker and dendron generation as well as side chain modifications. Importantly, as the polycation is bound covalently, these molecules can also penetrate deeply into the tissue of living organisms, such as zebrafish.

Mannosylated Polycations Target CD206+ Antigen-Presenting Cells and Mediate T-Cell-Specific Activation in Cancer Vaccination

Immunotherapy is deemed one of the most powerful therapeutic approaches to treat cancer. However, limited response and tumor specificity are still major challenges to address. Herein, mannosylated polycations targeting mannose receptor- are developed as vectors for plasmid DNA (pDNA)-based vaccines to improve selective delivery of genetic material to antigen-presenting cells and enhance immune cell activation. Three diblock glycopolycations (M₁₅A₁₂, M₂₉A₂₅, and M₅₈A₄₅) and two triblock copolymers (M₂₉A₂₉B₉ and M₆₂A₅₂B₃₂) are generated by using mannose (M), agmatine (A), and butyl (B) derivatives to target CD206, complex nucleic acids, and favor the endosomal escape, respectively. All glycopolycations efficiently complex pDNA at N/P ratios <5, protecting the pDNA from degradation in a physiological milieu. M₅₈A₄₅ and M₆₂A₅₂B₃₂ complexed with plasmid encoding for antigenic ovalbumin (pOVA) trigger the immune activation of cultured dendritic cells, which present the SIINFEKL antigenic peptide via specific major histocompatibility complex-I. Importantly, administration of M₅₈A₄₅/pOVA elicits SIINFEKL-specific T-cell response in C56BL/6 mice bearing the melanoma tumor model B16-OVA, well in line with a reduction in tumor growth. These results qualify mannosylation as an efficient strategy to target immune cells in cancer vaccination and emphasize the potential of these glycopolycations as effective delivery vehicles for nucleic acids.

Improving cellular uptake of therapeutic entities through interaction with components of cell membrane

Efficient cellular delivery of biologically active molecules is one of the key factors that affect the discovery and development of novel drugs. The plasma membrane is the first barrier that prevents direct translocation of chemic entities, and thus obstructs their efficient intracellular delivery. Generally, hydrophilic small molecule drugs are poor permeability that reduce bioavailability and thus limit the clinic application. The cellular uptake of macromolecules and drug carriers is very inefficient without external assistance. Therefore, it is desirable to develop potent delivery systems for achieving effective intracellular delivery of chemic entities. Apart from of the types of delivery strategies, the composition of the cell membrane is critical for delivery efficiency due to the fact that cellular uptake is affected by the interaction between the chemical entity and the plasma membrane. In this review, we aimed to develop a profound understanding of the interactions between delivery systems and components of the plasma membrane. For the purpose, we attempt to present a broad overview of what delivery systems can be used to enhance the intracellular delivery of poorly permeable chemic entities, and how various delivery strategies are applied according to the components of plasma membrane.

Cytotoxicity of Dendrimers

Drug delivery systems are molecular platforms in which an active compound is packed into or loaded on a biocompatible nanoparticle. Such a solution improves the activity of the applied drug or decreases its side effects. Dendrimers are promising molecular platforms for drug delivery due to their unique properties. These macromolecules are known for their defined size, shape, and molecular weight, as well as their monodispersity, the presence of the void space, tailorable structure, internalization by cells, selectivity toward cells and intracellular components, protection of guest molecules, and controllable release of the cargo. Dendrimers were tested as carriers of various molecules and, simultaneously, their toxicity was examined using different cell lines. It was discovered that, in general, dendrimer cytotoxicity depended on the generation, the number of surface groups, and the nature of terminal moieties (anionic, neutral, or cationic). Higher cytotoxicity occurred for higher-generation dendrimers and for dendrimers with positive charges on the surface. In order to decrease the cytotoxicity of dendrimers, scientists started to introduce different chemical modifications on the periphery of the nanomolecule. Dendrimers grafted with polyethylene glycol (PEG), acetyl groups, carbohydrates, and other moieties did not affect cell viability, or did so only slightly, while still maintaining other advantageous properties. Dendrimers clearly have great potential for wide utilization as drug and gene carriers. Moreover, some dendrimers have biological properties per se, being anti-fungal, anti-bacterial, or toxic to cancer cells without affecting normal cells. Therefore, intrinsic cytotoxicity is a comprehensive problem and should be considered individually depending on the potential destination of the nanoparticle.

Biofilm dispersal using nitric oxide loaded nanoparticles fabricated by photo-PISA: influence of morphology

The morphology of nitric oxide loaded polymeric nanoparticles is a significant parameter that influence the nitric oxide release and dispersal of bacterial biofilms.

Development of protein mimics for intracellular delivery

Designing delivery agents for therapeutics is an ongoing challenge. As treatments and desired cargoes become more complex, the need for improved delivery vehicles becomes critical. Excellent delivery vehicles must ensure the stability of the cargo, maintain the cargo's solubility, and promote efficient delivery and release. In order to address these issues, many research groups have looked to nature for design inspiration. Proteins, such as HIV-1 trans-activator of transcription (TAT) and Antennapedia homeodomain protein, are capable of crossing cellular membranes. However, due to the complexities of their structures, they are synthetically challenging to reproduce in the laboratory setting. Being able to incorporate the key features of these proteins that enable cell entry into simpler scaffolds opens up a wide range of opportunities for the development of new delivery reagents with improved performance. This review charts the development of protein mimics based on cell-penetrating peptides (CPPs) and how structure-activity relationships (SARs) with these molecules and their protein counterparts ultimately led to the use of polymeric scaffolds. These scaffolds deviate from the normal peptide backbone, allowing for simpler, synthetic procedures to make carriers and tune chemical compositions for application specific needs. Successful design of polymeric protein mimics would allow researchers to further understand the key features in proteins and peptides necessary for efficient delivery and to design the next generation of more efficient delivery reagents.

Intracellular neutralization of a virus using a cell-penetrating molecular transporter

Aims: Antibodies are the principal mediator of immunity against reinfection with viruses. Antibodies typically neutralize viruses by binding to virion particles in solution prior to attachment to susceptible cells. Once viruses enter cells, conventional antibodies cannot inhibit virus infection or replication. It is desirable to develop an efficient and nontoxic method for the introduction of virus-inhibiting antibodies into cells. Materials & methods: In this article, we report a new method for the delivery of small recombinant antibody fragments into virus-infected cells using a dendrimer-based molecular transporter. Results & conclusion: The construct penetrated virus-infected cells efficiently and inhibited virus replication. This method provides a novel approach for the immediate delivery of inhibitory antibodies directed to virus proteins that are exposed only in the intracellular environment. This approach circumvents the current and rather complicated expression of inhibitory antibodies in cells following gene transfer.

Original submitted 9 March 2013; Revised submitted 8 July 2013

Fifteen years of cell-penetrating, guanidinium-rich molecular transporters: basic science, research tools, and clinical applications

All living systems require biochemical barriers. As a consequence, all drugs, imaging agents, and probes have targets that are either on, in, or inside of these barriers. Fifteen years ago, we initiated research directed at more fully understanding these barriers and at developing tools and strategies for breaching them that could be of use in basic research, imaging, diagnostics, and medicine. At the outset of this research and now to a lesser extent, the "rules" for drug design biased the selection of drug candidates mainly to those with an intermediate and narrow log P. At the same time, it was becoming increasingly apparent that Nature had long ago developed clever strategies to circumvent these "rules." In 1988, for example, independent reports documented the otherwise uncommon passage of a protein (HIV-Tat) across a membrane. A subsequent study implicated a highly basic domain in this protein (Tat49-57) in its cellular entry. This conspicuously contradictory behavior of a polar, highly charged peptide passing through a nonpolar membrane set the stage for learning how Nature had gotten around the current "rules" of transport. As elaborated in our studies and discussed in this Account, the key strategy used in Nature rests in part on the ability of a molecule to change its properties as a function of microenvironment; such molecules need to be polarity chameleons, polar in a polar milieu and relatively nonpolar in a nonpolar environment. Because this research originated in part with the protein Tat and its basic peptide domain, Tat49-57, the field focused heavily on peptides, even limiting its nomenclature to names such as "cell-penetrating peptides," "cell-permeating peptides," "protein transduction domains," and "membrane translocating peptides." Starting in 1997, through a systematic reverse engineering approach, we established that the ability of Tat49-57 to enter cells is not a function of its peptide backbone, but rather a function of the number and spatial array of its guanidinium groups. These function-oriented studies enabled us and others to design more effective peptidic agents and to think beyond the confines of peptidic systems to new and even more effective nonpeptidic agents. Because the function of passage across a cell membrane is not limited to or even best achieved with the peptide backbone, we referred to these agents by their shared function, "cell-penetrating molecular transporters." The scope of this molecular approach to breaching biochemical barriers has expanded remarkably in the past 15 years: enabling or enhancing the delivery of a wide range of cargos into cells and across other biochemical barriers, creating new tools for research, imaging, and diagnostics, and introducing new therapies into clinical trials.

Dendritic surface functionalization of nanomaterials: controlling properties and functions for biomedical applications

A wide variety of nanomaterials have demonstrated promise in medical applications such as drug delivery and imaging. In these applications, the surface chemistry of the materials is critical as it plays an important role in determining the toxicity and biodistribution behavior of the material. We review here the functionalization of nanomaterials with dendrons as an efficient method to alter the surface chemistry of the materials, introducing new properties and functions. Described here is the functionalization of superparamagnetic iron oxide nanoparticles (SPIO) with dendritic guanidines to enhance their transport into cells for magnetic resonance imaging applications. The introduction of dendrons bearing peripheral hydroxyls, amines, guanidines, carbohydrates and Gd(III) chelates to polymer vesicles (polymersomes) is also described. These dendritic moieties allow for modulation of toxicity, cell uptake, protein binding, and contrast agent efficiency, while at the same time allowing the stabilities of the polymersomes to be maintained. Thus, this approach holds promise for the development of a wide range of multifunctional materials for pharmaceutical applications.

Modification of a dioxygen carrier, hemoCD, with PEGylated dendrons for extension of circulation time in the bloodstream

A supramolecular diatomic receptor, hemoCD, was modified with PEGylated dendrons to extend its circulation time in the bloodstream. The core component was 4-oxo-4-[[4-(10,15,20-tris(4-sulfonatophenyl)-21H,23H-porphin-5-yl)phenyl]amino]butanoic acid (Por-COOH). The building block of the dendrons was Fmoc-4-amino-4-(2-carboxyethyl)heptanedioic acid (FmocTA), which was condensed with α-amino-ω-methoxy-poly(ethylene glycol) (PEG(5000)-NH(2)) to yield an FmocG1-dendron. After deprotection, the G1-dendron was condensed with Por-COOH to yield G1-Por. A precursor (FmocNA) of an FmocG2-dendron was prepared via a condensation reaction of 4-amino-4-(2-t-butoxycarbonylethyl)heptanedioic acid di-t-butyl ester (TA-E) with FmocTA followed by hydrolysis of the resultant nona-carboxylic acid nona-t-butyl ester. Condensation of FmocNA with PEG(5000)-NH(2) yielded an FmocG2-dendron. After deprotection, the G2-dendron was condensed with Por-COOH to yield G2-Por. The ferrous complexes of G1- and G2-Pors formed stable 1:1 inclusion complexes with Py3CD, a per-O-methylated β-cyclodextrin dimer with a pyridine linker, in aqueous solution yielding supramolecular complexes designated as G1-hemoCD and G2-hemoCD, respectively. Both G1- and G2-hemoCDs bound molecular oxygen, with the O(2) affinities (P(1/2)) of hemoCD, G1-, and G2-hemoCDs at pH 7.4 and 37 °C being 22, 20, and 20 Torr, respectively. The modification of hemoCD with the dendrons did not cause destabilization of the O(2) adducts via autoxidation, as indicated by their half-lives (t(1/2)) of 6.8, 6.1, and 5.5 h for hemoCD, G1-, and G2-hemoCDs, respectively. The blood concentration-time curves of G1- and G2-hemoCDs injected into the bloodstream of rats exhibited two phases, with the half-lives of the fast and slow decays being 0.45 and 5.3 h, respectively, for G1-hemoCD, and 0.20 and 12.8 h, respectively, for G2-hemoCD. The half-lives of hemoCD were 0.02 and 0.50 h, respectively. The circulation time of hemoCD was markedly extended by its modification with the PEGylated dendrons, which was very effective in protecting hemoCD against opsonization for uptake by the reticuloendothelial system.

Dendrimer functionalization with a membrane-interacting domain of herpes simplex virus type 1: towards intracellular delivery

A poly(amide)-based dendrimer was synthesized and functionalized with the membrane-interacting peptide gH(625-644) (gH625) derived from the herpes simplex virus type 1 (HSV-1) envelope glycoprotein H, which has previously been shown to assist in delivering large cargoes across the cellular membrane. We demonstrate that the attachment of the gH625 peptide sequence to the termini of a dendrimer allows the conjugate to penetrate into the cellular matrix, whereas the unfunctionalized dendrimer is excluded from translocation. The peptide-functionalized dendrimer is rapidly taken into the cells mainly through a non-active translocation mechanism. Our results suggest that the presented peptidodendrimeric scaffold may be a promising material for efficient drug delivery.

Beyond Cell Penetrating Peptides: Designed Molecular Transporters

Inspired originally by peptides that traverse biological barriers, research on molecular transporters has since identified the key structural requirements that govern cellular entry, leading to new, significantly more effective and more readily available agents. These new drug delivery systems enable or enhance cellular and tissue uptake, can be targeted, and provide numerous additional advantages of significance in imaging, diagnostics and therapy.

A novel mitotropic oligolysine nanocarrier: Targeted delivery of covalently bound D-Luciferin to cell mitochondria

New and emerging therapeutic approaches focus on the targeted delivery of therapeutic agents to cell mitochondria with high specificity. Herein we present a novel mitotropic nanocarrier based on an oligolysine scaffold by addition of two triphenylphosphonium cations per oligomer. Although the parent oligolysine failed to enter healthy cells, the triphenylphosphonium modified carrier, with or without D-Luciferin, attached as cargo molecule, demonstrated striking mitochondrial specificity. Furthermore, the oligolysine bound d-Luciferin exhibited chemiluminescence, of lower intensity than free d-Luciferin, yet of remarkably longer steady-state temporal profile.

Cell delivery of therapeutic nanoparticles

Nanomedicine seeks to manufacture drugs and other biologically relevant molecules that are packaged into nanoscale systems for improved delivery. This includes known drugs, proteins, enzymes, and antibodies that have limited clinical efficacy based on delivery, circulating half-lives, or toxicity profiles. The <100 nm nanoscale physical properties afford them a unique biologic potential for biomedical applications. Hence they are attractive systems for treatment of cancer, heart and lung, blood, inflammatory, and infectious diseases. Proposed clinical applications include tissue regeneration, cochlear and retinal implants, cartilage and joint repair, skin regeneration, antimicrobial therapy, correction of metabolic disorders, and targeted drug delivery to diseased sites including the central nervous system. The potential for cell and immune side effects has necessitated new methods for determining formulation toxicities. To realize the potential of nanomedicine from the bench to the patient bedside, our laboratories have embarked on developing cell-based carriage of drug nanoparticles to improve clinical outcomes in infectious and degenerative diseases. The past half decade has seen the development and use of cells of mononuclear phagocyte lineage, including dendritic cells, monocytes, and macrophages, as Trojan horses for carriage of anti-inflammatory and anti-infective medicines. The promise of this new technology and the perils in translating it for clinical use are developed and discussed in this chapter.

Investigation of polyethylenimine-grafted-triamcinolone acetonide as nucleus-targeting gene delivery systems

BACKGROUND

Nuclear membrane is one of the main barriers in polymer mediated intracellular gene delivery. To improve the transgenic activity and safety of nonviral vector, triamcinolone acetonide (TA) as a nuclear localization signal was conjugated with different molecular weight polyethylenimine (PEI).

METHODS

Different molecular weight PEI [600, 1800, 25,000 (25k)] was conjugated with TA to synthesize PEI-TA by two-step reaction. Their physicochemical characteristics, in vitro cytotoxicity and transfection efficiency were evaluated. To investigate the difference of transfection efficiency of various molecular weight PEI-TA, their transfection mechanism was further investigated by confocal microscopy and competition assay. Transgenic expression in vivo was evaluated by injection into hepatic portal vein of mice.

RESULTS

All PEI-TA could form nanosize polyplexes with DNA and their physicochemical properties resemble each other. Their cytotoxicities were negligible compared to PEI 25k. The order of transfection efficiency was PEI 1800-TA > PEI 600-TA > PEI 25k-TA. A transfection mechanism study displayed that TA could inhibit considerably the transgenic activity of PEI 1800-TA and PEI 600-TA, but that of PEI 25k-TA was not inhibited. It was suggested that PEI 1800-TA and PEI 600-TA might translocate into the nucleus. Confocal microscopy investigation verified this suggestion. The data strongly suggested that the transfection efficiency of PEI 1800-TA in vivo was much higher than that of PEI 25k, which was consistent with the results obtained in vitro.

CONCLUSIONS

Low molecular weight PEI-TA could translocate into the nucleus efficiently. PEI 1800-TA presented higher transgenic activity and it has a great potential for gene therapy as a nonviral carrier.

Dendritic Guanidines as Efficient Analogues of Cell Penetrating Peptides

The widespread application of cell penetrating agents to clinical therapeutics and imaging agents relies on the ability to prepare them on a large scale and to readily conjugate them to their cargos. Dendritic analogues of cell penetrating peptides, with multiple guanidine groups on their peripheries offer advantages as their high symmetry allows them to be efficiently synthesized, while orthogonal functionalities at their focal points allow them to be conjugated to cargo using simple synthetic methods. Their chemical structures and properties are also highly tunable as their flexibility and the number of guanidine groups can be tuned by altering the dendritic backbone or the linkages to the guanidine groups. This review describes the development of cell-penetrating dendrimers based on several different backbones, their structure-property relationships, and comparisons of their efficacies with those of known cell penetrating peptides. The toxicities of these dendritic guanidines are also reported as well as their application towards the intracellular delivery of biologically significant cargos including proteins and nanoparticles.

A guanidinylated bioreducible polymer with high nuclear localization ability for gene delivery systems

Guanidinylated bioreducible polymer (GBP) was developed for gene delivery systems utilizing cellular penetrating ability of guanidine groups. GBP could retard pDNA from a weight ratio of 5 completely in agarose gel electrophoresis but pDNA was released from GBP polyplexes even at a weight ratio of 20 in reducing condition (2.5mm DTT) due to their biodegradation. GBP also could construct 200 nm-sized and positively charged (approximately 30 mV) polyplex nanoparticles with pDNA. The cytotoxicity of GBP was found to be minimal and GBP showed about 8 folds improved transfection efficiency than a scaffold polymer, poly(cystaminebisacrylamide-diaminohexane) (poly(CBA-DAH)) and even higher transfection efficiency than PEI25k in mammalian cell lines. Its high cellular uptake efficiency (96.1%) and strong nuclear localization ability for pDNA delivery due to the structural advantage of bioreducible polymer and guanidine groups were also identified, suggesting GBP is a promising candidate for efficient gene delivery systems.

Guanidinylated dendritic molecular transporters: prospective drug delivery systems and application in cell transfection

In the present review the crucial role of the guanidinium functional group in facilitating the transport of dendritic polymers through liposomal and cell membranes is discussed, along with other structural features of guanidinylated dendritic polymers that fine-tune their transport properties, and even determine their subcellular destinations. In this context, an ideal dendritic molecular transporter would need to possess a dendritic scaffold of the appropriate size and degree of guanidinylation, flexibility of the guanidinium moiety, and should exhibit a proper balance between hydrophilic and hydrophobic moieties located on the dendritic surface. All of the above are illustrated through selected paradigms from the relevant literature, which give a valuable insight into forging successful dendritic delivery systems for both drugs and genes. The main challenge for the future focus of the field is identified as the determination of the key structural and functional characteristics that will enhance cell internalisation, and secure localisation in specific subcellular organelles.

Molecular dendritic transporter nanoparticle vectors provide efficient intracellular delivery of peptides

We present the synthesis of a modular delivery system that is composed of two main macromolecular building blocks, dendritic molecular transporter molecules and a polymeric scaffold in a size dimension of 5-10 nm. The conjugated dendritic molecular transporter units proved to be critical for the delivery of the polymer nanoparticle into 3T3 cells and illustrates the dendritic molecular transporter promoted intracellular uptake of polymer particles derived from intramolecular chain collapse processes. In a sequence of modification steps, pyridinyldithio linker was introduced to undergo thiol-disulfide exchange reactions with peptide sequences containing cysteine amino acid units to furnish peptide-nanoparticle conjugates with cleavable disulfide linkers. The intracellular uptake of the nanoparticle conjugates and the delivery of the peptidic cargo were studied via dual labeling of the nanoparticle with Alexa Fluor 568 dye and fluorescein (FITC) markers on the peptide in mammalian cell lines such as NIH 3T3 cells via confocal microscopy. In this work, we have demonstrated the assembly of a novel nanoscopic delivery system in which the conjugated dendritic molecular transporter molecules facilitated the rapid cellular uptake of a nanoparticle-peptide conjugate with up to 25 copies of peptidic cargo to establish new venues for the implementation of protein and oligonucleotide drugs.

Design and synthesis of dendritic molecular transporter that achieves efficient in vivo delivery of morpholino antisense oligo

Safe and efficient in vivo delivery of Morpholino antisense oligos was probably the last and most difficult challenge for the broad application of antisense in animal research and therapeutics. Several arginine-rich peptides effective for in vivo delivery of Morpholino antisense oligos require rather complex and expensive procedures for synthesis and conjugation. This work describes the design and synthesis of a dendritic transporter in a most concise manner where the selection of the core scaffold, functional group multiplication, orthogonal protecting group manipulation, solid phase conjugation, and off-resin perguanidinylation of the transporter structure are all orchestrated for efficient assembly. We utilized triazine as a core to provide a site for on-column conjugation to the Morpholino oligo and to anchor functional side arms which, after extension, multiplication, and deprotection, are subsequently converted from primary amines to the eight guanidinium headgroups that serve for transport across cell membranes. Intravenous administration of the delivery-enabled Morpholino into a splice-reporter strain of transgenic living mice results in de novo expression of splice-corrected green fluorescent protein in a broad range of tissues and organs in those treated mice. This rigorously demonstrates that this new dendritic transporter achieves effective delivery of a Morpholino oligo into the cytosol/nuclear compartment of cells systemically in vivo. The practical conjugation process may overcome any availability limitation for routine use by the scientific community, and the efficient delivery ability of this transporter may advance the application of Morpholino antisense technology in animals.

A polymeric domain that promotes cellular internalization

Polymers have emerged as powerful biological tools; however, their ability to gain access to the intracellular environment is limited. To expand the biological utility of polymer scaffolds, we have synthesized an internalization domain using the ring-opening metathesis polymerization (ROMP). A polymer functionalized with guanidinium groups is effectively internalized by cells and localized in both vesicles and the cytoplasm. Because the synthesis of such materials is modular, we anticipate that compounds of this type can be fashioned that facilitate the delivery of cargo via end-cap derivatization or block copolymer synthesis.

Methodological and cellular aspects that govern the internalization mechanisms of arginine-rich cell-penetrating peptides

Peptides including HIV-1 Tat peptide and oligoarginines represent arginine-rich membrane-permeable vectors that attain efficient intracellular delivery of bioactive molecules. The importance of the arginine residues or their guanidino functions is now appreciated for efficient internalization of the Tat peptide, and based on this, various novel arginine/guanidino-rich vectors have now been developed. However, molecular detail of their method(s) of internalization are still debated. This review summarizes our current understandings of endocytic and non-endocytic aspects of internalization of arginine-rich peptide vectors. We highlight the possibility of simultaneous employment of multiple internalization pathways, the contribution of which is dependent on a number of factors. Similarities and dissimilarities among the internalization methods of typical peptide vectors and other guanidino-rich vectors including branched-chain, beta-peptide, and sugar-based vectors, are also discussed.

The design of guanidinium-rich transporters and their internalization mechanisms

The ability of a drug or probe to cross a biological barrier has historically been viewed to be a function of its intrinsic physical properties. This view has largely restricted drug design and selection to agents within a narrow log P range. Molecular transporters offer a strategy to circumvent these restrictions. In the case of guanidinium-rich transporters (GRTs), a typically highly water-soluble conjugate is found to readily pass through the non-polar membrane of a cell and for some across tissue barriers. This activity opens a field of opportunities for the use of GRTs to enable delivery of polar and non-polar drugs or probes as well as to enhance uptake of those of intermediate polarity. The field of transporter enabled or enhanced uptake has grown dramatically in the last decade. Some GRT drug conjugates have been advanced into clinical trials. This review will provide an overview of recent work pertinent to the design and mechanism of uptake of GRTs.

Monofunctionalization of dendrimers with use of microwave-assisted 1,3-dipolar cycloadditions

Monofunctionalized polyamide-based dendrimers containing either a terminal azide or alkyne moiety have been designed and synthesized via a convergent synthetic approach. The monofunctionalization allows for the single attachment of a functional moiety in quantitative yields by using 1,3-dipolar cycloadditions, thereby opening the possibility for targeted dendrimer functionalization.