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The first large genome fully sequenced by next-generation sequencing (NGS) was that of a bacteriophage using sequencing by synthesis (SBS) as a paradigm. SBS in NGS is underpinned by ‘reversible-terminator chemistry’. To grow from proof of concept to being both affordable and practical, SBS needed to overcome a series of challenges, each of which required the invention of new chemistries. These included the design and synthesis of unnatural deoxynucleotide triphosphates (dNTPs), engineering a suitable polymerase, a new surface chemistry and an ingenious molecular solution to neutralize copying errors inherent to all polymerases. In this historical Perspective, we discuss how NGS was developed from Sanger sequencing, highlighting the chemistry behind this technology, which has impacted biology in unprecedented ways. A historical perspective on how next-generation sequencing chemistry was developed.

Down-regulation and mutations of the nuclear-architecture proteins lamin A and C cause misshapen nuclei and altered chromatin organization associated with cancer and laminopathies, including the premature-aging disease Hutchinson-Gilford progeria syndrome (HGPS). Here, we identified the small molecule \"Remodelin\" that improved nuclear architecture, chromatin organization, and fitness of both human lamin A/C–depleted cells and HGPS-derived patient cells and decreased markers of DNA damage in these cells. Using a combination of chemical, cellular, and genetic approaches, we identified the acetyl-transferase protein NAT10 as the target of Remodelin that mediated nuclear shape rescue in laminopathic cells via microtubule reorganization. These findings provide insights into how NAT10 affects nuclear architecture and suggest alternative strategies for treating laminopathies and aging.

Cancer stem cells (CSCs) represent a subset of cells within tumours that exhibit self-renewal properties and the capacity to seed tumours. CSCs are typically refractory to conventional treatments and have been associated to metastasis and relapse. Salinomycin operates as a selective agent against CSCs through mechanisms that remain elusive. Here, we provide evidence that a synthetic derivative of salinomycin, which we named ironomycin (AM5), exhibits a more potent and selective activity against breast CSCs in vitro and in vivo , by accumulating and sequestering iron in lysosomes. In response to the ensuing cytoplasmic depletion of iron, cells triggered the degradation of ferritin in lysosomes, leading to further iron loading in this organelle. Iron-mediated production of reactive oxygen species promoted lysosomal membrane permeabilization, activating a cell death pathway consistent with ferroptosis. These findings reveal the prevalence of iron homeostasis in breast CSCs, pointing towards iron and iron-mediated processes as potential targets against these cells. Cancer stem cells are typically refractory to conventional treatments. Now, an unprecedented mechanism has been discovered by which salinomycin and derivatives can sequester iron in lysosomes leading to cytoplasmic iron depletion and the subsequent production of reactive oxygen species that are lethal to the cell. This discovery of the importance of iron in cancer stem cell maintenance provides an opportunity for developing new therapeutics.

Nucleic acids containing stretches of tandem guanines can fold into four-stranded structures called G-quadruplexes. The existence of such sequences in genomic DNA suggests the occurrence of these motifs in cells, with potential implications in a number of biological processes relevant to cancer. Small molecules have proven to be valuable tools to dissect cell circuitry. Here, we describe a synthetic small molecule derived from an N , N ′- bis (2-quinolinyl)pyridine-2,6-dicarboxamide, which is designed to mediate the selective isolation of G-quadruplex nucleic acids. The methodology was successfully applied to a range of DNA and RNA G-quadruplexes in vitro . We demonstrate the general applicability of the method by isolating telomeric DNA-containing G-quadruplex motifs from cells. We show that telomeres are targets for the probe, providing further evidence of the formation of G-quadruplexes in human cells. A small-molecule-affinity tag has been designed to mediate the selective isolation of G-quadruplex nucleic acids in a structure-dependant manner. This concept has been applied to the pull-down of G-quadruplex-containing fragments from human cells, and the methodology holds promise for the elucidation of their putative biological functions.

Natural products and synthetic small molecules can be used to perturb, dissect and manipulate biological processes, thereby providing the basis for drug development. Over the past decades, the evolution of molecular biology protocols and microscopy techniques has made it possible to visually detect proteins in living systems with valuable spatiotemporal resolution, in which dynamic topological information has proved to be insightful. By contrast, although small molecules have become essential for biological studies, general methods to track them in cells remain underexplored. In this Review, we discuss how bioorthogonal chemistry, and click chemistry in particular, can be exploited to label and visualize almost any biologically active small molecule in cells and tissues. We review recent developments, highlighting cases in which visualizing small molecules has provided crucial mechanistic insights. This methodology is facile to implement, is versatile and is illuminating. Click chemistry enables efficient chemical labelling of small molecules in cells, providing a powerful method to visualize almost any biologically active compound. This versatile methodology can provide valuable information about the mechanisms of action of small molecules in various biological settings.

Transcription factors are proteins that bind specifically to defined DNA sequences to promote gene expression. Targeting transcription factors with small molecules to modulate the expression of certain genes has been notoriously difficult to achieve. The natural product thiostrepton is known to reduce the transcriptional activity of FOXM1, a transcription factor involved in tumorigenesis and cancer progression. Herein we demonstrate that thiostrepton interacts directly with FOXM1 protein in the human breast cancer cells MCF-7. Biophysical analyses of the thiostrepton–FOXM1 interaction provide additional insights on the molecular mode of action of thiostrepton. In cellular experiments, we show that thiostrepton can inhibit the binding of FOXM1 to genomic target sites. These findings illustrate the potential druggability of transcription factors and provide a molecular basis for targeting the FOXM1 family with small molecules. The natural product thiostrepton is known to have anticancer properties but its mechanism of action is not known. Here, it is shown that thiostrepton binds to the protein FOXM1, preventing its interaction with several gene promoters and inhibits their expression. This illustrates the druggability of transcription factors, and provides a molecular basis for targeting FOXM1.

Key Points Small molecules can target protein and nucleic acid components of chromatin at specific genomic sites and perturb cellular processes. Click chemistry relies on bio-orthogonal chemical reactivity that enables the introduction of a fluorophore to visualize small molecules in cells or the introduction of an affinity reagent that can be used for the purpose of target isolation. High-throughput sequencing can be used to identify where small molecules influence the genome, which in some cases has provided new insights into drug responses. Small molecules can be functionalized with affinity reagents to allow the isolation of DNA and characterization of genomic target sites by means of deep sequencing in a protocol known as Chem–seq. A combination of experimental approaches — including ChIP–seq, Chem–seq and genome-wide gene expression analysis — can be used to delineate genome targeting with small molecules and might be useful for predicting cellular responses in the context of personalized medicine. Chromatin influences genomic targeting with small molecules, thereby providing the opportunity for epigenome-targeting drugs to regulate and potentially reprogramme the response of certain drugs that operate at the genomic level. Various small molecules, including numerous anticancer agents, act by targeting DNA or protein components of chromatin. This Review describes how various complementary technologies use high-throughput sequencing to delineate drug responses, from identifying the genomic binding sites of drugs or their targets, to the ensuing changes to chromatin states and gene expression. These insights should facilitate the rational use of these therapies. Small molecules — including various approved and novel cancer therapeutics — can operate at the genomic level by targeting the DNA and protein components of chromatin. Emerging evidence suggests that functional interactions between small molecules and the genome are non-stochastic and are influenced by a dynamic interplay between DNA sequences and chromatin states. The establishment of genome-wide maps of small-molecule targets using unbiased methodologies can help to characterize and exploit drug responses. In this Review, we discuss how high-throughput sequencing strategies, such as ChIP–seq (chromatin immunoprecipitation followed by sequencing) and Chem–seq (chemical affinity capture and massively parallel DNA sequencing), are enabling the comprehensive identification of small-molecule target sites throughout the genome, thereby providing insights into unanticipated drug effects.

Ligands that stabilize the formation of telomeric DNA G-quadruplexes have potential as cancer treatments, because the G-quadruplex structure cannot be extended by telomerase, an enzyme over-expressed in many cancer cells. Understanding the kinetic, thermodynamic and mechanical properties of small-molecule binding to these structures is therefore important, but classical ensemble assays are unable to measure these simultaneously. Here, we have used a laser tweezers method to investigate such interactions. With a force jump approach, we observe that pyridostatin promotes the folding of telomeric G-quadruplexes. The increased mechanical stability of pyridostatin-bound G-quadruplex permits the determination of a dissociation constant K d of 490 ± 80 nM. The free-energy change of binding obtained from a Hess-like process provides an identical K d for pyridostatin and a K d of 42 ± 3 µM for a weaker ligand RR110 . We anticipate that this single-molecule platform can provide detailed insights into the mechanical, kinetic and thermodynamic properties of liganded bio-macromolecules, which have biological relevance. G-quadruplex structures in telomeric DNA inhibit the action of telomerase — an enzyme over-expressed in many cancer cells. Small molecules that stabilize the formation of G-quadruplex structures are therefore of interest as potential cancer treatments. Here, a platform is described that allows the interactions between small-molecule ligands and human telomeric G-quadruplexes to be measured at the single-molecule level.

Inflammation is a complex physiological process triggered in response to harmful stimuli 1 . It involves cells of the immune system capable of clearing sources of injury and damaged tissues. Excessive inflammation can occur as a result of infection and is a hallmark of several diseases 2 – 4 . The molecular bases underlying inflammatory responses are not fully understood. Here we show that the cell surface glycoprotein CD44, which marks the acquisition of distinct cell phenotypes in the context of development, immunity and cancer progression, mediates the uptake of metals including copper. We identify a pool of chemically reactive copper (ii) in mitochondria of inflammatory macrophages that catalyses NAD(H) redox cycling by activating hydrogen peroxide. Maintenance of NAD + enables metabolic and epigenetic programming towards the inflammatory state. Targeting mitochondrial copper (ii) with supformin (LCC-12), a rationally designed dimer of metformin, induces a reduction of the NAD(H) pool, leading to metabolic and epigenetic states that oppose macrophage activation. LCC-12 interferes with cell plasticity in other settings and reduces inflammation in mouse models of bacterial and viral infections. Our work highlights the central role of copper as a regulator of cell plasticity and unveils a therapeutic strategy based on metabolic reprogramming and the control of epigenetic cell states. Cellular uptake of copper( ii ) by CD44 has a key role in regulating cellular plasticity via copper( ii )-dependent downstream signalling events.