Special Issue: "Functional Dendrimers"

Recent advances in multifunctional dendrimer-based complexes for cancer treatment

The application of nanotechnology in biological and medical fields have resulted in the creation of new devices, supramolecular systems, structures, complexes, and composites. Dendrimers are relatively new nanotechnological polymers with unique features; they are globular in shape, with a topological structure formed by monomeric subunit branches diverging to the sides from the central nucleus. This review analyzes the main features of dendrimers and their applications in biology and medicine regarding cancer treatment. Dendrimers have applications that include drug and gene carriers, antioxidant agents, imaging agents, and adjuvants, but importantly, dendrimers can create complex nanosized constructions that combine features such as drug/gene carriers and imaging agents. Dendrimer-based nanosystems include different metals that enhance oxidative stress, polyethylene glycol to provide biosafety, an imaging agent (a fluorescent, radioactive, magnetic resonance imaging probe), a drug or/and nucleic acid that provides a single or dual action on cells or tissues. One of major benefit of dendrimers is their easy release from the body (in contrast to metal nanoparticles, fullerenes, and carbon nanotubes), allowing the creation of biosafe constructions. Some dendrimers are already clinically approved and are being used as drugs, but many nanocomplexes are currently being studied for clinical practice. In summary, dendrimers are very useful tool in the creation of complex nanoconstructions for personalized nanomedicine. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Dendrimer nanoplatforms for veterinary medicine applications: A concise overview

Within the nanoparticle (NP) space, dendrimers are becoming increasingly important in the field of nanomedicine, not only to treat human diseases, but also in veterinary medicine, which represents a new therapeutic approach. Major applications include using dendrimers to tackle highly contagious foot-and-mouth disease virus (FMDV) and swine fever virus (SFV) in pigs, FMDV in cattle, hypothermic circulatory arrest (HCA) in dogs, rabies, and H9N2 avian influenza virus in chickens. As we review here, intramuscular (im) subcutaneous (sc), intravenous (iv), and intraperitoneal (ip) routes of administration can be used for the successful application of dendrimers in animals.

Ferrocenyl-terminated polyphenylene-type "click" dendrimers as supports for efficient gold and palladium nanocatalysis

Although dendrimer supports have been known as key parts of nanocatalysts, the capability of rigid dendrimers for this function has not yet been reported. Here, the study is focused on ferrocenylmethylenetriazolyl-terminated dendrimers (FcMTPD) as supports of remarkably efficient nanogold and nanopalladium catalysts. A biphasic system is elaborated to evaluate the catalytic activity of FcMTPD-supported Au and Pd nanoparticles (NPs) for the reduction of 4-nitrophenol to 4-aminophenol by NaBH₄ at 20 °C, and FcMTPD-supported PdNPs are found to be the best nanocatalysts with a rate constant k_app = 7.8 × 10^-2 s^-1. Excellent catalytic results are also obtained in this reaction for FcMTPD-supported AuNPs with a rate constant k_app = 5.6 × 10^-2 s^-1. For both Pd NPs and AuNPs, the kinetic results are shown to strongly depend on the method of preparation of these NPs that influences the NP size and thus their catalytic efficiency. The FcMTPD-stabilized PdNPs are easily recovered and reused at least 13 times, and their catalytic performance displays only a slight decrease during the first seven runs.

Dendrimer- and polymeric nanoparticle-aptamer bioconjugates as nonviral delivery systems: a new approach in medicine

Aptamers are RNA or DNA oligonucleotides interacting to form unique 3D target conformations with high affinity and specificity, and are emerging as a powerful class of ligands for therapeutic applications. In addition, dendrimers are well-defined nano-sized symmetric polymeric molecules. In this review, we provide an analysis of the use of dendrimers modified with aptamers as nonviral vectors to specifically target tumor cells. Various anticancer agents have been encapsulated with dendrimers complexing with aptamers, including epirubicin, camptothecin, Bcl-xL short hairpin (sh)RNA, and 5-fluorouracil rhodamine-labeled dextran. Other types of polymeric nanoparticle (NP)-aptamer bioconjugates have also been developed and loaded with Pt(IV) derivatives, to target specific tumor cells.

Cylindrical micelles of a POSS amphiphilic dendrimer as nano-reactors for polymerization

A low generation amphiphilic dendrimer, POSS-AD, which has a POSS core and eight amphiphilic arms, was synthesized and used as a nano-reactor to produce well-defined polymer nano-cylinders. Confirmed by small-angle X-ray scattering (SAXS), Raman and NMR spectrometry, monodispersed cylindrical micelles that contain a hydrophilic cavity with a diameter of 2.09 nm and a length of 4.26 nm were produced via co-assembling POSS-AD with hydrophilic liquids, such as H₂O and HEMA in hydrophobic solvents. Taking the HEMA/POSS-AD cylindrical micelles as nano-reactors, polymerization of HEMA within the micelles results in polymer nano-cylinders (POSS-ADNPs) with a diameter of 2.24 nm and a length of 5.02 nm. The study confirmed that despite the inability to maintain specific shape in solution, low generation dendrimers form well-defined nano-containers or nano-reactors, which relies on co-assembling with hydrophilic guest molecules. These nano-reactors are robust enough to maintain their shape during the polymerization of the guest molecules. Polymer nano-cylinders with dimensions less than 10 nm can thus be produced from the HEMA/POSS-AD micelles. Since the chemical structure of low-generation dendrimers and the contents of the co-assembled nano-reactors can be easily adjusted, the concept holds the potential for the further developments of low-generation amphiphilic dendrimers.

Dendrimers, Carotenoids, and Monoclonal Antibodies

Dendrimers are unimolecular architectural nano- or microparticle entities that can accommodate various nutraceuticals and pharmaceuticals between their branches (dendrons) and provide targeted delivery of biomimetics into different tissues upon addition of functionalized groups to the dendrimer's surface. Covalent binding, hydrogen bonds, and electrostatic interactions between dendrimer-composing molecules are known to form and stabilize dendrimer structure. Carotenoids have recently been shown to form dendrimer-like structures and promote targeted delivery of "cargo" molecules into organs characterized by high-carotenoid uptake (adrenal glands, prostate, liver, and brain). The use of carotenoid dendrimers, in particular lycosome particles loaded with various xenobiotics (resveratrol, cocoa flavanols, and HMG-CoA reductase inhibitors), reportedly has a beneficial effect in diabetic foot syndrome, prehypertension, and cardiovascular disease. New applications for carotenoid dendrimers may arise from the use of complexes formed by carotenoid dendrimers and monoclonal antibodies (mAbs). The internalization of carotenoid dendrimer-mAb complexes through receptor-mediated mechanisms may prevent interactions of dendrimer-incorporated xenobiotics with membrane-associated P-glycoprotein, a major factor of drug resistance in tumor cells. The incorporation of mAb fragments with higher binding capacity to the membrane receptors and higher affinity to the target molecule may further increase the bioavailability of "cargo" molecules transported by the carotenoid dendrimer-mAb complexes and open new doors in nanodelivery technologies.

Click Co sandwich-terminated dendrimers as polyhydride reservoirs and micellar templates

Neutral click metallodendrimers with [Co^I(η⁴-cyclopentadiene)(η⁵-cyclopentadienyl)] termini are synthesized by reduction of dendrimers with 9, 27 or 81 cobalticenium termini and serve as polyhydride reservoirs and reductants; for instance, they reduce proton sources to H₂ and Au^III to micellized capsules of gold nanoparticles.

Time-Resolved Fluorescence Spectroscopy and Fluorescence Lifetime Imaging Microscopy for Characterization of Dendritic Polymer Nanoparticles and Applications in Nanomedicine

The emerging field of nanomedicine provides new approaches for the diagnosis and treatment of diseases, for symptom relief and for monitoring of disease progression. One route of realizing this approach is through carefully constructed nanoparticles. Due to the small size inherent to the nanoparticles a proper characterization is not trivial. This review highlights the application of time-resolved fluorescence spectroscopy and fluorescence lifetime imaging microscopy (FLIM) for the analysis of nanoparticles, covering aspects ranging from molecular properties to particle detection in tissue samples. The latter technique is particularly important as FLIM allows for distinguishing of target molecules from the autofluorescent background and, due to the environmental sensitivity of the fluorescence lifetime, also offers insights into the local environment of the nanoparticle or its interactions with other biomolecules. Thus, these techniques offer highly suitable tools in the fields of particle development, such as organic chemistry, and in the fields of particle application, such as in experimental dermatology or pharmaceutical research.