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Covalently binding molecules are frequently regarded as being generally promiscuous. In a recent study, binding selectivities and cellular target proteins of a wide variety of reactive fragments are examined in a proteome-wide context.

There is a lack of current treatment options for ovarian clear cell carcinoma (CCC) and the cancer is often resistant to platinum-based chemotherapy. Hence there is an urgent need for novel therapeutics. The transcription factor hepatocyte nuclear factor 1β (HNF1β) is ubiquitously overexpressed in CCC and is seen as an attractive therapeutic target. This was validated through shRNA-mediated knockdown of the target protein, HNF1β, in five high- and low-HNF1β-expressing CCC lines. To inhibit the protein function, cell-permeable, non-helical constrained proteomimetics to target the HNF1β–importin α protein–protein interaction were designed, guided by X-ray crystallographic data and molecular dynamics simulations. In this way, we developed the first reported series of constrained peptide nuclear import inhibitors. Importantly, this general approach may be extended to other transcription factors.

Import ban: The transcription factor HNF1β is ubiquitously overexpressed in ovarian clear cell carcinoma. Guided by X-ray crystallographic data and molecular dynamics simulations, cell-permeable, non-helical constrained proteomimetics (orange) were designed to target the HNF1β–importin α protein–protein interaction and thereby inhibit the nuclear import of HNF1β. This general approach may be extended to other transcription factors.

A supramolecular approach was undertaken to create functionally activatable cell-penetrating peptides. Two tetra-arginines were assembled into an active cell-penetrating peptide by heterodimerizing leucine zippers. Three different leucine-zipper pairs were evaluated: activation was found to depend on the association constant of the coiled-coil peptides. The weaker-binding peptides required an additional disulfide linkage to induce cell-penetrating capability, whereas for the most-stable coiled-coil no additional stabilization was needed. The latter zipper pair was used to show that the induced formation of the coiled coils allows control over the uptake of an oligoarginine CPP-conjugated cargo protein.

Springing into action: Activation of a cell-penetrating peptide can be established through noncovalent coiled-coil formation. Three different leucine-zipper peptide pairs were tested for their cell-penetration upon association by fluorescence analysis. This approach can be extended to whole proteins such GFP.

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a family of sequence-selective DNA minor-groove binding agents that form a covalent aminal bond between their C11-position and the C2-NH₂ groups of guanine bases. The first example of a PBD monomer, the natural product anthramycin, was discovered in the 1960s, and the best known PBD dimer, SJG-136 (also known as SG2000, NSC 694501 or BN2629), was synthesized in the 1990s and has recently completed Phase II clinical trials in patients with leukaemia and ovarian cancer. More recently, PBD dimer analogues are being attached to tumor-targeting antibodies to create antibody–drug conjugates (ADCs), a number of which are now in clinical trials, with many others in pre-clinical development. This Review maps the development from anthramycin to the first PBD dimers, and then to PBD-containing ADCs, and explores both structure–activity relationships (SARs) and the biology of PBDs, and the strategies for their use as payloads for ADCs.

PBDs as payloads for ADCs: The pyrrolobenzodiazepines (PBDs) are a family of DNA-interactive antitumor agents that bind to guanine bases in the DNA minor groove in a sequence-selective manner. They have potent cytotoxicity, and are being used as payloads for antibody–drug conjugates (ADCs). This Review outlines their development from the discovery of the natural product anthramycin through to the use of PBD dimer payloads in ADCs.

Microemulsions (MEs) are ideal for obtaining high-quality inorganic nanoparticles. As thermodynamically stable systems with a nanometer-sized droplet phase that serves as a nanoreactor, MEs have obvious advantages for the synthesis of nanoparticles. MEs also have disadvantages, such as their complexity as multicomponent systems, the low amount of obtainable nanoparticles, their limited thermal stability, the fact that hydrolyzable or oxidizable compounds are often excluded from synthesis, the partly elaborate separation of nanoparticles, as well as the removal of surface-adhered surfactants subsequent to synthesis. This Review presents some strategies to further expand the options of ME-based synthesis of inorganic nanoparticles. This comprises the crystallization of nanoparticles in “high-temperature MEs”, the synthesis of hollow nanospheres, the use of hydrogen peroxide or liquid ammonia as the polar droplet phase, and the synthesis of base metals and nitrides in MEs.

Nanoreactors in microemulsions are ideal for the synthesis of high-quality inorganic nanoparticles, including bimetals, hollow nanospheres, base metals, peroxides, and metal nitrides. This Review illustrates some options beyond the standard microemulsion synthesis of nanoparticles.

The copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction has proven to be a pivotal advance in chemical ligation strategies with applications ranging from polymer fabrication to bioconjugation. However, application in vivo has been limited by the inherent toxicity of the copper catalyst. Herein, we report the application of heterogeneous copper catalysts in azide–alkyne cycloaddition processes in biological systems ranging from cells to zebrafish, with reactions spanning from fluorophore activation to the first reported in situ generation of a triazole-containing anticancer agent from two benign components, opening up many new avenues of exploration for CuAAC chemistry.

Localized drug synthesis: Biocompatible copper nanoparticle catalysts were synthesized and employed in the activation of a profluorophore in living cells and in zebrafish embryos. Furthermore, an anticancer drug was synthesized in situ from two benign components, leading to apoptosis in ovarian cancer cells.

Many DNA binding proteins utilize one-dimensional (1D) diffusion along DNA to accelerate their DNA target recognition. Although 1D diffusion of proteins along DNA has been studied for decades, a quantitative understanding is only beginning to emerge and few chemical tools are available to apply 1D diffusion as a design principle. Recently, we discovered that peptides can bind and slide along DNA—even transporting cargo along DNA. Such molecules are known as molecular sleds. Here, to advance our understanding of structure–function relationships governing sequence nonspecific DNA interaction of natural molecular sleds and to explore the potential for controlling sliding activity, we test the DNA binding and sliding activities of chemically modified peptides and analogs, and show that synthetic small molecules can slide on DNA. We found new ways to control molecular sled activity, novel small-molecule synthetic sleds, and molecular sled activity in N-methylpyrrole/N-methylimidazole polyamides that helps explain how these molecules locate rare target sites.

Synthetic small molecules with a wide range of chemical functionality can slide on DNA, and specific modifications can be used to tune crucial properties like DNA affinity and sliding speed. The picture shows a polyamide bound to DNA and its trajectory when sliding on DNA.

We report a comprehensive study on novel, highly efficient, and biodegradable hybrid molecular transporters. To this end, we designed a series of cell-penetrating, cube-octameric silsesquioxanes (COSS), and investigated cellular uptake by confocal microscopy and flow cytometry. A COSS with dense spatial arrangement of guanidinium groups displayed fast uptake kinetics and cell permeation at nanomolar concentrations in living HeLa cells. Efficient uptake was also observed in bacteria, yeasts, and archaea. The COSS-based carrier was significantly more potent than cell-penetrating peptides (CPPs) and displayed low toxicity. It efficiently delivered a covalently attached cytotoxic drug, doxorubicin, to living tumor cells. As the uptake of fluorescently labeled carrier remained in the presence of serum, the system could be considered particularly attractive for the in vivo delivery of therapeutics.

COSS and effect: New-generation molecular transporters are based on cell-penetrating cube-octameric silsesquioxanes (COSS). These nanoscale hybrid carriers are biodegradable, low-toxic, and show efficient uptake in living cells of all three domains of life.