A new series of gold(I) N-heterocyclic carbene (NHC) complexes based on xanthine ligands have been synthesized and characterized by mass spectrometry, NMR, and X-ray diffraction. The compounds have been tested for their antiproliferative properties in human cancer cells and nontumorigenic cells in vitro, as well as for their toxicity in healthy tissues ex vivo. The bis-carbene complex [Au(caffein-2-ylidene)2][BF4] (complex 4) appeared to be selective for human ovarian cancer cell lines and poorly toxic in healthy organs. To gain preliminary insights into their actual mechanism of action, two biologically relevant in cellulo targets were studied, namely, DNA (more precisely a higher-order DNA structure termed G-quadruplex DNA that plays key roles in oncogenetic regulation) and a pivotal enzyme of the DNA damage response (DDR) machinery (poly-(adenosine diphosphate (ADP)-ribose) polymerase 1 (PARP-1), strongly involved in the cancer resistance mechanism). Our results indicate that complex 4 acts as an efficient and selective G-quadruplex ligand while being a modest PARP-1 inhibitor (i.e., poor DDR impairing agent) and thus provide preliminary insights into the molecular mechanism that underlies its antiproliferative behavior.

Since the initial discovery of the catalytic capability of short DNA fragments, this peculiar enzyme-like property (termed DNAzyme) has continued to garner much interest in the scientific community because of the virtually unlimited applications in developing new molecular devices. Alongside the exponential rise in the number of DNAzyme applications in the last past years, the search for convenient ways to improve its overall efficiency has only started to emerge. Credence has been lent to this strategy by the recent demonstration that the quadruplex-based DNAzyme proficiency can be enhanced by ATP supplements. Herein, we have made a further leap along this path, trying first of all to decipher the actual DNAzyme catalytic cycle (to gain insights into the steps ATP may influence), and subsequently investigating in detail the influence of all the parameters that govern the catalytic efficiency. We have extended this study to other nucleotides and quadruplexes, thus demonstrating the versatility and broad applicability of such an approach. The defined exquisitely efficient DNAzyme protocols were exploited to highlight the enticing advantages of this method via a 96-well plate experiment that enables the detection of nanomolar DNA concentrations in real-time with the naked-eye (see movie as Supplementary Data).

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents.

The end of human telomeres is comprised of a long G-rich single-stranded DNA (known as 3'-overhang) able to adopt an unusual three-dimensional "beads-on-the-string" organization made of consecutively stacked G-quadruplex units (so-called quadruplex multimers). It has been widely demonstrated that, upon interaction with hemin, discrete quadruplexes acquire peroxidase-mimicking properties, oxidizing several organic probes in H(2)O(2)-rich conditions; this property, known as DNAzyme, has found tens of applications in the last two decades. However, little is known about the DNAzyme activity of multimeric quadruplexes; this is an important question to address, especially in light of recent reports that exploit the DNAzyme process to optically assess the activity of an enzyme that elongates the telomeric overhang, the telomerase. Herein, we thoroughly investigate the DNAzyme activity of long telomeric fragments, with a particular focus on both the nature of the hemin/multimeric quadruplex interactions and the putative higher-order fold of the studied fragments; in light of our results, we also propose possible ways that may be followed to improve the use of DNAzyme to evaluate the telomerase activity.

Recent and unambiguous evidences of the formation of DNA and RNA G-quadruplexes in cells has provided solid support for these structures to be considered as valuable targets in oncology. Beyond this, they have lent further credence to the anticancer strategies relying on small molecules that selectively target these higher-order DNA/RNA architectures, referred to as G-quadruplex ligands. They have also shed bright light on the necessity of designing multitasking ligands, displaying not only enticing quadruplex interacting properties (affinity, structural selectivity) but also additional features that make them usable for detecting quadruplexes in living cells, notably for determining whether, when, and where these structures fold and unfold during the cell cycle and also for better assessing the consequences of their stabilization by external agents. Herein, we report a brand new design of such multitasking ligands, whose structure experiences a quadruplex-promoted conformational switch that triggers not only its quadruplex affinity (i.e., smart ligands, which display high affinity and selectivity for DNA/RNA quadruplexes) but also its fluorescence (i.e., smart probes, which behave as selective light-up fluorescent reporters on the basis of a fluorogenic electron redistribution). The first prototype of such multifunctional ligands, termed PyroTASQ, represents a brand new generation of quadruplex ligands that can be referred to as "twice-as-smart" quadruplex ligands.

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An unprecedented strategy to control the quadruplex- vs duplex-DNA selectivity of a ligand is reported. We designed a compound whose structure can rearrange when it interacts with a G-quadruplex, thereby controlling its affinity. Thus, the first "smart G-quadruplex ligand" is reported, since this ligand experiences a structural change in the presence of quadruplexes but not in the presence of duplexes, ensuring a high level of quadruplex selectivity.

The targeting of higher-order DNA structures has been thoroughly developed with G-quadruplex DNA but not with other structures like branched DNA (also known as DNA junctions). Because these alternative higher-order DNA architectures might be of high biological relevance, we implemented a high-throughput version of the FRET melting assay that enabled us to map the interactions of a candidate with four different DNA structures (duplex- and quadruplex DNA, three- and four-way junctions) in a rapid and reliable manner. We also introduce a novel index, the BONDS (branched and other noncanonical DNA selectivity) index, to conveniently quantify this differential affinity.