Current Medicinal Chemistry - Volume 19, Issue 29, 2012

Current trends in research dealing with methods of developing effective chemotherapy for the two most dangerous killers – breast and colon cancers have been discussed. The input brought by nanotechnology is presented with particular stress on the use of dendrimers. These unique "polymeric compounds" after modification can form intelligent species, transporting drugs into specific areas and at the same time can be used for monitoring the state of organs attacked by cancer cells, as well as the progress of the curing process. They can help to limit the anticancer drugs delivery to designed goals only, eliminating many side effects of chemotherapy. Breast and colon cancer are major problem for public health care in many countries all over the world. During last twenty years a dramatic increase in incidence of both of them has been observed, especially in industrialized countries. Probably, both of them are caused, apart from the hereditary syndromes, by specific point mutation, some hormonal factors in breast cancer and by the strong co-influence of environmental factors and dietary exposure of a patient.

Photodynamic therapy (PDT) is a promising approach to treat certain types of cancer. PDT was proposed as a useful oncology tool more than 30 years ago but it has limitations. The success of PDT depends predominantly on photosensitizers and development of an effective second generation is continuing. Dendrimers possess architecture suitable for incorporating specific functional moieties and are a promising venue for further investigations. This review describes the use of dendrimers in PDT and how they can aid in overcoming obstacles encountered during PDT.

New nano-scale drug carriers offer the possibility of increasing the therapeutic index of drug molecules by increasing their effectiveness, diminishing their toxicity against physiological tissues and achieving controlled therapeutic levels for a prolonged time. This review gives an overview of approaches to the development of these novel complex nanocarriers with emphasis on those involving dendrimers and related systems. The combination of two of more nano-sized units for producing an overall system with unique properties could be advantageous compared to more simple nanotechnology-based carriers. Recent advances in medicinal chemistry offer the possibility of exact tailoring of the properties of such complex systems which, in conjunction with full physicochemical characterization, may lead to novel and highly effective drug products. An assessment is given of the potential of systems such as chimeric advanced Drug Delivery nano Systems (chi-aDDnSs) for the delivery of drugs compared with conventional carriers. Rational synthesis of molecules that can act as modulators of the properties of chi-aDDnSs and may be the future in the design and development of nanocarriers, not only for the delivery of drug molecules but also for genetic material and imaging agents is sought.

Small interfering RNA (siRNA) constitutes an excellent way of knocking down genes. However, it requires the use of delivery systems to reach the target cells, especially to neuronal cells. Dendrimers are one of the most widely used synthetic nanocarriers for siRNA delivery. However, due to the complexity of the dendrimer-siRNA interactions, when a new dendritic carrier is designed it is difficult to predict its efficiency to bind and to deliver siRNA. At the same time it is not easy to understand the origin of eventual limited functionalities. We have modeled the interactions between two dendrimers (TDG-G1 and TDG-G2) and siRNA using molecular dynamics (MD) simulation. The results were compared to experimental physico-chemical parameters such as siRNA complexation, complex stability, size, and zeta potentials and biological effects such as down-regulation of a specific RNA expression in cortical neurons in culture. Data indicate that the combination of rigid core and flexible branches guarantees strong siRNA binding, which is important to have a good transfection profile. However, the successful nanocarrier for siRNA delivery (TDG-G1) is identified not only by a high affinity for siRNA, but by a favorable equilibrium between a strong binding and the ability to release siRNA to exert its biological action. The conditions under which the dendriplex is formed are also relevant for transfection efficiency and biological activity.

Complex functional materials consisting of bioactive molecules immobilized on solid supports present potential applications in biosensoring. Advances in the fabrication of these surface materials are of growing interest for antibody-based diagnosis. This work exploits dendrimers as versatile nanostructures for templating sensor surfaces and the critical role of the immobilization protocol in the solid supports cellulose and zeolites, of organic and inorganic composition respectively. The fabrication and characterization, including the degree of functionalization and reproducibility, of different nanostructured materials are described. To validate the approach, the fabricated supports were further used as a solid phase for developing a radioimmunoassay to detect immunoglobulin E (IgE) specific to penicillin, the antibody involved in immediate allergy responses to this drug. The dendrimer-modified supports provide assays with significantly enhanced sensitivity, as well as increase the availability of biomolecules for specific interaction and minimize nonspecific adsorptions through appropriate functionalization protocols in each case. The manufacturing methodology involved the use of a long, flexible hydrophilic spacer in the cellulose materials, and a higher surface density of the immobilized dendrimers in the zeolite crystals. The ability of hybrid zeolite materials in such biosensing applications was evaluated for the first time. The assays were validated in human serum samples from patients allergic to penicillin and from non-allergic controls. The specificity and improved sensitivity of the dendrimer- modified supports make these strategies versatile for different bioactive molecules and could have significant implications for the quantification of a wide range of specific IgE antibodies and other biomolecules of diagnostic interest.

The diagnosis and treatment of malignant melanoma by means of the formulation of active principles with dendrimeric nanoparticles is an area of great current interest. The identification and understanding of molecular mechanisms which ensure the integration of particular dendrimeric nanostructures in tumor cellular environment can provide valuable guidance in their coupling strategies with antitumor or diagnostic agents. Two structurally distinct maltose-shell modified 5th generation (G5) poly(propylene imine) (PPI) glycodendrimers fluorescently labeled, (a) with open maltose shell, cationic charged G5-PPI-OS and (b) with dense maltose shell and nearly neutral G5-PPI-DS, were tested in relation with several melanoma cell lines. We found that three melanoma cell lines internalize G5-PPI-DS structure more efficiently than non tumoral HEK297T cells. Furthermore, the internalization pathways of G5-PPI-OS and G5-PPI-DS are characteristic for each tumor cell phenotype and include more than one mechanism. As a general trend, large amounts of both G5-PPI-OS and G5-PPI-DS are internalized on cholesterol-dependent pathway in MJS primary melanoma cells and on non conventional pathways in SK28 metastatic melanoma cells. G5-PPI-OS, temporarily retained at plasma membrane in both cell lines, is internalized slower in metastatic than in primary phenotype. Unlike G5-PPI-OS, G5-PPI-DS is immediately endocytosed in both cell lines. The unconventional internalization pathway and trafficking, exclusively used by G5-PPI-DS in metastatic cells, is described at molecular level. The decay kinetics of fluorescent labeled G5-PPI-OS and G5-PPI-DS is distinct in the two cellular phenotypes. Both cationic and neutral maltose G5-PPI glycodendrimeric structures represent molecules based on which designing of new formulations for therapy or/and diagnosis of melanoma can be further developed.

Stem cells and nanomaterials are two new and exciting fields of science that are evolving very fast and that are starting to establish ties. Nanomaterials should, however, be designed to interact with stem cells without compromising their biological characteristics, in other words, without affecting their viability and differentiation potential. In the present report and for the first time, the effects of poly(amidoamine) (PAMAM) dendrimers on the viability and differentiation ability towards the osteogenic and adipogenic lineages of human mesenchymal stem cells (hMSCs) are systematically evaluated. Studies were done as a function of the cell culture media composition and PAMAM dendrimer surface functionalization, generation, and concentration. hMSCs were exposed to amino and hydroxyl (generations 2, 4 and 6), and carboxylate (generations 1.5, 3.5 and 5.5) functionalized dendrimers, at two different concentrations (10 μg/mL and 0.5 μg/mL), for a period of 21 days. Overall, the results revealed that amino functionalized dendrimers can be severely cytotoxic, the extension of cell death being dependent on the concentration of amino groups in solution. However, in all cases, the differentiation of hMSCs towards the osteogenic and adipogenic phenotypes seems not to be affected as demonstrated by staining in in vitro cultures.

The review presents fluorescence spectroscopic studies on the capacities of newly synthesized polypropyleneamine and polyamidoamine fluorescent dendrimers to detect biologically important metal ions. It has been shown that those fluorescent dendrimers whose periphery comprises 1,8-napthalimide fragments are highly sensitive to metal ions which are of great importance to the living organisms.

We describe here the use of anionic carbosilane dendrimers to obtain new copper complexes. UV-Vis and a computer aided analysis of the EPR spectra provided information about the coordination modes of copper depending on the nature of the dendrimer and about the geometry and structure of the complexes in solution. Some of these metallo-dendrimers have been tested “in vitro” as antiviral compounds in the inhibition of HIV infection in pre and post-infection treatment.

Metallodrugs (organometallic complexes) bearing at least one metal-carbon bond - represent original and powerful tools for diverse therapeutic applications based on the development of “bioorganometallic chemistry”. To date, various metallodrugs were described with very interesting biological activities as antimalarials, antibacterials, neuroprotectors, against arthritis, for chemotherapy etc. Anticancer Pt-based drugs are the main complexes used in the treatment of several cancers, but unfortunately these complexes show elicit and severe toxicities and resistance effects. The remarkably unique and tunable properties of dendrimers have made them promising tools for diverse biomedical applications such as diagnostics, gene therapy and drug delivery including in oncology. Recent studies have shown that well designed dendritic carriers overcome such as poor solubility, permeability, biocompatibility, bioavailability and toxicity of the native drug. This review reports on the recent advances for the use of metallodrugs and dendritic based carriers (drug-dendrimer conjugates and drug encapsulation) in oncology. Advantages, limitations and opportunities in oncology of such materials are discussed and compared.

Poly(aminoester) dendrimers are expected to hold great promise as biodegradable nanocarriers for drug delivery due to their advantageous properties allowing their biodegradability, potentially lower toxicity and possibility of diverse chemical conjugations. The synthetic strategies for constructing such dendrimers include the amine branching method, the ester formation method, the combination of both methods as well as the recently emerging click chemistry based synthesis. We present here an overview on the current state of synthesizing poly(aminoester) dendrimers and discuss the benefits and limitations of each strategy with a view to stimulating a fueled interest in the development of efficient and reliable methodologies to synthesize such dendrimers.

This review addresses current and future perspectives of nanogel technology for nanomedicine. The synthetic methodologies and material properties of nanogels prepared by chemical meanings are discussed in detail, and examples that illustrate the different methodologies are presented. Applications in the fields of drug and gene delivery, smart imaging modalities, responsive materials, and multivalency as a therapeutic approach highlight the enormous potential of the functional nanogels as novel polymeric platforms for biomedicine.

Gene therapy, in which oligomeric genetic material is carried into cells by nano-sized gene delivery vehicles to interfere with gene expression, represents a promising approach for preventive therapy against HIV/AIDS pandemic. Herein, we evaluate the usefulness of a phosphorus-containing dendrimer G4(NH+Et2Cl-)96 as a delivery agent of ODNs and siRNAs. G4(NH+Et2Cl-)96 formed stable complexes with ODNs or siRNAs and exhibited very low cytotoxicity in Sup T1 cells or PBMC. Functional validation was performed by using specific siRNA against HIV-1 Nef, siNEF to interfere in HIV-1 replication. G4(NH+Et2Cl-)96/siNEF dendriplex showed a high efficiency in Nef silencing. Furthermore, in vitro treatment of HIV-infected PBMC with G4(NH+Et2Cl-)96/siNEF dendriplex significantly reduced the viral replication. Our results prove the usefulness of phosphorus-containing dendrimers to deliver and transfect siRNA into CD4-T cells as a potential alternative therapy in the HIV-1 infection.

Here we present a synthetic procedure for water-stable carbosilane dendrimers containing ammonium groups at the periphery of type Gn-{[Si(CH2)3N+(Me)(Et)CH2CH2N+Me3]x (CF3SO3 -)y} which have been used as non-viral vectors for transfecting different types of nucleic acids against two different medical problems, HIV and hepatocarcinoma. These systems have shown to be non-toxic in both PBMC and HepG2 cell lines under the experimental conditions and are able to form nanoconjugates with nucleic acids perfectly stable over time and in a wide range of pH values, which leads to the conclusion that the interaction between dendrimer and nucleic acid is very strong. In addition, a high degree of transfection using these nanoconjugates has been observed, ranging from 70-90% depending on the generation and in the particular case of PBMC transfection with anti-HIV oligonucleotides. However, besides of the good properties shown by the dendrimers here prepared as transfecting agents, only moderate effect was observed in functional experiments for hepatocarcinoma, as a result of the strong interaction between dendrimer and nucleic acid. Nevertheless, it is important to mention that an IRS-4 knock-down of 40% in HepG2 achieves an analogous degree of cell sensitization to cancer treatment, which may represent a major advance in the hepatocarcinoma treatment when appropriate dendrimers as transfection agents are used.

Due to the relative easy synthesis and commercial availability, nanovectors based on dendrimers and dendrons are among the most utilized non-viral vectors for gene transfer. Contextually, recent advances in molecular simulations and computer architectures not only allow for accurate predictions of many structural, energetical, and eventual self-assembly features of these nanocarriers per se, but are able to yield vital (and perhaps otherwise unattainable) molecular information about the interactions of these nanovectors with their nucleic acid cargoes. In the present work, we aim at reviewing our own efforts in the field of multiscale molecular modeling of these interesting materials. In particular, our originally developed computational recipes will be presented, and the link between simulations and experiments will be described and discussed in detail. This review is written by computational scientists for experimental scientists, with the specific purpose of illustrating the potentiality of these methodologies and the usefulness of multiscale molecular modeling as an innovative and complementary tool in their current research.

The application of polymers in medicine, as components of drug carriers, as well as their synthetic strategies are considered essential for producing and developing new drug formulations against human deceases. The synthesis of block copolymers is a timeconsuming process with a high cost of the final product, although several block copolymer systems have been already commercialized successfully. The biocompatibility, the biodegradability and the non toxic profile of newly synthesized polymers towards healthy tissues, should be taken into account in order to be acceptable for biomedical applications. In this review article, focus is placed on new approaches and synthetic strategies for preparing novel block copolymers and their utilization as parts of new and advanced Drug Delivery nanoSystems (aDDnSs) with a Modulatory Controlled Release profile (MCR). Such complex and advanced nanosystems can alter the pharmacokinetic properties of the encapsulated drug and consequently its effectiveness. Emphasis is given to the use of living polymerization methodologies and post polymerization chemical transformation reactions for the synthesis of mainly diblock copolymers for novel drug delivery nanosystems. Issues related to self-assembly of block copolymers in solution toward formation of colloidal functional nanostructures that can serve as nanocontainers and nanocarriers, and strategies for controlling encapsulation of specific drugs are also discussed. Specific examples are reported mainly on diblock copolymer systems, including authors’ recent work.

Transfection of genetic material into primary neuronal cultures remains a challenge because of the intrinsic difficulty in transfecting this type of cell. This review covers the recent developments in the use of dendrimers for siRNA and DNA transfection in both neuronal and glial cells. Crossing the blood brain barrier crossing represents a challenge for the effective use of dendrimer-mediated delivery of therapeutic agents to the central nervous system. We will discuss the effectiveness, both in vitro and in vivo, of various dendrimers in delivering genetic material to neural tissue and its ability to cross the blood-brain barrier. In addition, the use of dendrimers as a potential new therapy in the treatment of glioblastoma will be presented.