Receiver-amplifier, self-immolative dendritic device

Self-immolative dendrimers disassemble through a domino-like chain fragmentation initiated by a single cleavage at the dendrimer core. We have designed and synthesized dendritic molecules that resemble dendritic architectures present in nature. The unique design allows a cleavage signal received by any one of the multiple triggers on one side of the dendrimer to be transferred convergently to a focal point. The signal is divergently amplified through to the other side of the dendrimer, reporter units are released, and fluorescence is emitted. During signal propagation, the dendritic molecule disassembles in a self-immolative manner into small fragments. These compounds are the longest dendritic system ever reported to disassemble through sequential self-immolative reactions. The synthesized dendritic molecules have an architecture and signal-conducting activity related to that of neurons.     

Single-triggered AB6 self-immolative dendritic amplifiers

Self-immolative dendrimers are a unique class of molecules that are able to disassemble upon undergoing a specific triggering reaction through domino-like fragmentations. We have designed and synthesized a novel AB(6) self-immolative dendritic adaptor that amplifies a single cleavage event into the release of six reporter units. The disassembly mechanism is based on a specifically triggered cleavage event followed by elimination of a cyclic urea derivative and six consecutive quinone methide eliminations. The system was disassembled under both organic and aqueous conditions by either chemical or enzymatic triggering. Various reporter molecules and triggering groups were introduced onto the dendritic adaptor to obtaining sensor molecules with enhanced properties for diagnostics and imaging.     

Self‐immolative dendrimers as novel drug delivery platforms

Self‐immolative dendrimers were recently developed and introduced as a potential platform for a single‐triggered multi‐prodrug. These unique structural dendrimers can release all of their tail units through domino‐like chain fragmentation, which is initiated by a single cleavage at the dendrimer core. The incorporation of drug molecules as the tail units and an enzyme substrate as the trigger generates a multi‐prodrug unit that is activated with a single enzymatic cleavage. We have demonstrated several examples of self‐immolative dendritic prodrug systems and have shown significant advantages with respect to the appropriate monomeric prodrug. We anticipate that single‐triggered, dendritic prodrugs will be exploited to further improve selective chemotherapeutic approaches in cancer therapy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1569–1578, 2006     

Molecularly Precise Dendrimer–Drug Conjugates with Tunable Drug Release for Cancer Therapy

The structural preciseness of dendrimers makes them perfect drug delivery carriers, particularly in the form of dendrimer–drug conjugates. Current dendrimer–drug conjugates are synthesized by anchoring drug and functional moieties onto the dendrimer peripheral surface. However, functional groups exhibiting the same reactivity make it impossible to precisely control the number and the position of the functional groups and drug molecules anchored to the dendrimer surface. This structural heterogeneity causes variable pharmacokinetics, preventing such conjugates to be translational. Furthermore, the highly hydrophobic drug molecules anchored on the dendrimer periphery can interact with blood components and alter the pharmacokinetic behavior. To address these problems, we herein report molecularly precise dendrimer–drug conjugates with drug moieties buried inside the dendrimers. Surprisingly, the drug release rates of these conjugates were tailorable by the dendrimer generation, surface chemistry, and acidity.     

Small Targeted Cytotoxics: Current State and Promises from DNA‐Encoded Chemical Libraries

The targeted delivery of potent cytotoxic agents has emerged as a promising strategy for the treatment of cancer and other serious conditions. Traditionally, antibodies against markers of disease have been used as drug‐delivery vehicles. More recently, lower molecular weight ligands have been proposed for the generation of a novel class of targeted cytotoxics with improved properties. Advances in this field crucially rely on efficient methods for the identification and optimization of organic molecules capable of high‐affinity binding and selective recognition of target proteins. The advent of DNA‐encoded chemical libraries allows the construction and screening of compound collections of unprecedented size. In this Review, we survey developments in the field of small ligand‐based targeted cytotoxics and show how innovative library technologies will help develop the drugs of the future.     

Dendronized Triangular Oligo(phenylene ethynylene) Amphiphiles: Nanofibrillar Self‐Assembly and Dye Encapsulation

Triangular‐shaped oligo(phenylene ethynylene) amphiphiles 1 a and 1 b decorated in their periphery with two‐ and four‐branched hydrophilic triethyleneglycol dendron wedges, have been synthesized and their self‐assembling properties in solution and onto surfaces investigated. The steric demand produced by the dendritic substituents induces a face‐to‐face rotated π stacking of the aromatic moieties. Studies on the concentration and temperature dependence confirm this mechanism and provide binding constants of 1.2×10⁵ and 1.7×10⁵ M ^?1 in acetonitrile for 1 a and 1 b , respectively. Dynamic and static light scattering measurements complement the study of the self‐assembly in solution and demonstrate the formation of rod‐like supramolecular structures in aqueous solution. The nanofibers formed in solution can be efficiently transferred onto surfaces. Thus, TEM images reveal the presence of strands of various thickness, with the most common being several micrometers long and with diameters of around 70 nm. Some of these nanofibers present folded edges that are indicative of their ribbon‐like nature. Interestingly, compound 1 b can also form thick filaments with a rope‐like appearance, which points to a chiral arrangement of the fibers. AFM images under highly diluted conditions also reveal long fibers with height profiles that fit well with the molecular dimensions calculated for both amphiphiles. Finally, we have demonstrated the intercalation of the hydrophobic dye Disperse Orange 3 within the filaments and its subsequent release upon increasing the temperature.     

Molecular,Macromolecular, and Supramolecular Glucuronide Prodrugs: Lead Identified for Anticancer Prodrug Monotherapy

In this work, a tumor growth intervention by localized drug synthesis within the tumor volume, using the enzymatic repertoire of the tumor itself, is presented. Towards the overall success, molecular, macromolecular, and supramolecular glucuronide prodrugs were designed for a highly potent toxin, monomethyl auristatin E (MMAE). The lead candidate exhibited a fold difference in toxicity between the prodrug and the drug of 175, had an engineered mechanism to enhance the deliverable payload to tumours, and contained a highly potent toxin such that bioconversion of only a few prodrug molecules created a concentration of MMAE sufficient enough for efficient suppression of tumor growth. Each of these points is highly significant and together afford a safe, selective anticancer measure, making tumor‐targeted glucuronides attractive for translational medicine.     

Self‐Assembled Fluorodendrimers Combine the Features of Lipid and Polymeric Vectors in Gene Delivery

An ideal vector in gene therapy should exhibit high serum stability, excellent biocompatibility, a desired transfection efficacy and permeability into targeted tissues. Here, we describe a class of low‐molecular‐weight fluorodendrimers for efficient gene delivery. These materials self‐assemble into uniform nanospheres and allow for efficient transfection at low charge ratios and very low DNA doses with minimal cytotoxicity. Our results demonstrate that these vectors combine the features of synthetic gene vectors such as liposomes and cationic polymers and present promising potential for clinical gene therapy.     

Self‐Immolative Spacers: Kinetic Aspects,Structure–Property Relationships,and Applications

Self‐immolative spacers are covalent assemblies tailored to correlate the cleavage of two chemical bonds after activation of a protective part in a precursor: Upon stimulation, the protective moiety is removed, which generates a cascade of disassembling reactions leading to the temporally sequential release of smaller molecules. Originally introduced to overcome limitations for drug delivery, self‐immolative spacers have gained wide interest in medicinal chemistry, analytical chemistry, and material science. For most applications, the kinetics of the disassembly of the activated self‐immolative spacer governs functional properties. This Review addresses kinetic aspects of self‐immolation. It provides information for selecting a particular self‐immolative motif for a specific demand. Moreover, it should help researchers design kinetic experiments and fully exploit the rich perspectives of self‐immolative spacers.     

The Self‐Assembly of Anticancer Camptothecin–Dipeptide Nanotubes: A Minimalistic and High Drug Loading Approach to Increased Efficacy

20‐(S)‐Camptothecin (CPT)‐conjugated dipeptides are reported that preassemble into nanotubes with diameters ranging from 80–120 nm. These nanoassemblies maintain a high (～47 %) drug loading and exhibit greater drug stability (i.e., resistance to lactone hydrolysis), and consequently greater efficacy against several human cancer cells (HT‐29, A549, H460, and H23) in vitro compared with the clinically used prodrug irinotecan. A key and defining feature of this system is the use of the CPT‐conjugated dipeptide as both the drug and precursor to the nanostructured carrier, which simplifies the overall fabrication process.     

A Coordinative Dendrimer Achieves Excellent Efficiency in Cytosolic Protein and Peptide Delivery

Cytosolic protein delivery is a prerequisite for the development of protein therapeutics that act on intracellular targets. Proteins are generally membrane‐impermeable and thus need a carrier such as a polymer to facilitate their internalization. However, the efficient binding of proteins with different isoelectric points to polymeric carriers is challenging. In this study, we designed a coordinative dendrimer to solve this problem. The dendrimers modified with dipicolylamine/zinc(II) complex were capable of binding proteins through a combination of ionic and coordination interactions. The best polymer efficiently delivered 30 cargo proteins and peptides into the cytosol, while maintaining their bioactivity after intracellular release. The removal or replacement of zinc ions in the polymer with other transition‐metal ions lead to significantly decreased efficiency in cytosolic protein delivery. This study provides a new strategy to develop robust and efficient polymers for cytosolic protein delivery.