TERT activation targets DNA methylation and multiple aging hallmarks.

Insufficient telomerase activity, stemming from low telomerase reverse transcriptase (TERT) gene transcription, contributes to telomere dysfunction and aging pathologies. Besides its traditional function in telomere synthesis, TERT acts as a transcriptional co-regulator of genes pivotal in aging and age-associated diseases. Here, we report the identification of a TERT activator compound (TAC) that upregulates TERT transcription via the MEK/ERK/AP-1 cascade. In primary human cells and naturally aged mice, TAC-induced elevation of TERT levels promotes telomere synthesis, blunts tissue aging hallmarks with reduced cellular senescence and inflammatory cytokines, and silences p16INK4a expression via upregulation of DNMT3B-mediated promoter hypermethylation. In the brain, TAC alleviates neuroinflammation, increases neurotrophic factors, stimulates adult neurogenesis, and preserves cognitive function without evident toxicity, including cancer risk. Together, these findings underscore TERT's critical role in aging processes and provide preclinical proof of concept for physiological TERT activation as a strategy to mitigate multiple aging hallmarks and associated pathologies.

An Activity-Guided Map of Electrophile-Cysteine Interactions in Primary Human T Cells.

Electrophilic compounds originating from nature or chemical synthesis have profound effects on immune cells. These compounds are thought to act by cysteine modification to alter the functions of immune-relevant proteins; however, our understanding of electrophile-sensitive cysteines in the human immune proteome remains limited. Here, we present a global map of cysteines in primary human T cells that are susceptible to covalent modification by electrophilic small molecules. More than 3,000 covalently liganded cysteines were found on functionally and structurally diverse proteins, including many that play fundamental roles in immunology. We further show that electrophilic compounds can impair T cell activation by distinct mechanisms involving the direct functional perturbation and/or degradation of proteins. Our findings reveal a rich content of ligandable cysteines in human T cells and point to electrophilic small molecules as a fertile source for chemical probes and ultimately therapeutics that modulate immunological processes and their associated disorders.

Synthesis of portimines reveals the basis of their anti-cancer activity.

Marine-derived cyclic imine toxins, portimine A and portimine B, have attracted attention because of their chemical structure and notable anti-cancer therapeutic potential1-4. However, access to large quantities of these toxins is currently not feasible, and the molecular mechanism underlying their potent activity remains unknown until now. To address this, a scalable and concise synthesis of portimines is presented, which benefits from the logic used in the two-phase terpenoid synthesis5,6 along with other tactics such as exploiting ring-chain tautomerization and skeletal reorganization to minimize protecting group chemistry through self-protection. Notably, this total synthesis enabled a structural reassignment of portimine B and an in-depth functional evaluation of portimine A, revealing that it induces apoptosis selectively in human cancer cell lines with high potency and is efficacious in vivo in tumour-clearance models. Finally, practical access to the portimines and their analogues simplified the development of photoaffinity analogues, which were used in chemical proteomic experiments to identify a primary target of portimine A as the 60S ribosomal export protein NMD3.

Chemoproteomics reveals microbiota-derived aromatic monoamine agonists for GPRC5A.

The microbiota generates diverse metabolites to modulate host physiology and disease, but their protein targets and mechanisms of action have not been fully elucidated. To address this challenge, we explored microbiota-derived indole metabolites and developed photoaffinity chemical reporters for proteomic studies. We identified many potential indole metabolite-interacting proteins, including metabolic enzymes, transporters, immune sensors and G protein-coupled receptors. Notably, we discovered that aromatic monoamines can bind the orphan receptor GPRC5A and stimulate ß-arrestin recruitment. Metabolomic and functional profiling also revealed specific amino acid decarboxylase-expressing microbiota species that produce aromatic monoamine agonists for GPRC5A-ß-arrestin recruitment. Our analysis of synthetic aromatic monoamine derivatives identified 7-fluorotryptamine as a more potent agonist of GPRC5A. These results highlight the utility of chemoproteomics to identify microbiota metabolite-interacting proteins and the development of small-molecule agonists for orphan receptors.

Human Hsp70 Substrate-Binding Domains Recognize Distinct Client Proteins.

The 13 Hsp70 proteins in humans act on unique sets of substrates with diversity often being attributed to J-domain-containing protein (Hsp40 or JDP) cofactors. We were therefore surprised to find drastically different binding affinities for Hsp70-peptide substrates, leading us to probe substrate specificity among the 8 canonical Hsp70s from humans. We used peptide arrays to characterize Hsp70 binding and then mined these data using machine learning to develop an algorithm for isoform-specific prediction of Hsp70 binding sequences. The results of this algorithm revealed recognition patterns not predicted based on local sequence alignments. We then showed that none of the human isoforms can complement heat-shocked DnaK knockout Escherichia coli cells. However, chimeric Hsp70s consisting of the human nucleotide-binding domain and the substrate-binding domain of DnaK complement during heat shock, providing further evidence in vivo of the divergent function of the Hsp70 substrate-binding domains. We also demonstrated that the differences in heat shock complementation among the chimeras are not due to loss of DnaJ binding. Although we do not exclude JDPs as additional specificity factors, our data demonstrate substrate specificity among the Hsp70s, which has important implications for inhibitor development in cancer and neurodegeneration.

A metabolite-derived protein modification integrates glycolysis with KEAP1-NRF2 signalling.

Mechanisms that integrate the metabolic state of a cell with regulatory pathways are necessary to maintain cellular homeostasis. Endogenous, intrinsically reactive metabolites can form functional, covalent modifications on proteins without the aid of enzymes1,2, and regulate cellular functions such as metabolism3-5 and transcription6. An important 'sensor' protein that captures specific metabolic information and transforms it into an appropriate response is KEAP1, which contains reactive cysteine residues that collectively act as an electrophile sensor tuned to respond to reactive species resulting from endogenous and xenobiotic molecules. Covalent modification of KEAP1 results in reduced ubiquitination and the accumulation of NRF27,8, which then initiates the transcription of cytoprotective genes at antioxidant-response element loci. Here we identify a small-molecule inhibitor of the glycolytic enzyme PGK1, and reveal a direct link between glycolysis and NRF2 signalling. Inhibition of PGK1 results in accumulation of the reactive metabolite methylglyoxal, which selectively modifies KEAP1 to form a methylimidazole crosslink between proximal cysteine and arginine residues (MICA). This posttranslational modification results in the dimerization of KEAP1, the accumulation of NRF2 and activation of the NRF2 transcriptional program. These results demonstrate the existence of direct inter-pathway communication between glycolysis and the KEAP1-NRF2 transcriptional axis, provide insight into the metabolic regulation of the cellular stress response, and suggest a therapeutic strategy for controlling the cytoprotective antioxidant response in several human diseases.

A Cell Type Selective YM155 Prodrug Targets Receptor-Interacting Protein Kinase 2 to Induce Brain Cancer Cell Death.

Glioblastoma (GBM) is the most prevalent and aggressive primary central nervous system (CNS) malignancy. YM155 is a highly potent broad-spectrum anti-cancer drug that was derived from a phenotypic screen for functional inhibitors of survivin expression, but for which the relevant biomolecular target remains unknown. Presumably as a result of its lack of cell-type selectivity, YM155 has suffered from tolerability issues in the clinic. Based on its structural similarity to the GBM-selective prodrug RIPGBM, here, we report the design, synthesis, and characterization of a prodrug form of YM155, termed aYM155. aYM155 displays potent cell killing activity against a broad panel of patient-derived GBM cancer stem-like cells (IC50 = 0.7-10 nM), as well as EGFR-amplified and EGFR variant III-expressing (EGFRvIII) cell lines (IC50 = 3.8-36 nM), and becomes activated in a cell-type-dependent manner. Mass spectrometry-based analysis indicates that enhanced cell-type selectivity results from relative rates of prodrug activation in transformed versus non-transformed cell types. The prodrug strategy also facilitates transport into the brain (brain-to-plasma ratio, aYM155 = 0.56; YM155 = BLQ). In addition, we determine that the survivin-suppressing and apoptosis-inducing activities of YM155 involve its interaction with receptor-interacting protein kinase 2 (RIPK2). In an orthotopic intracranial GBM xenograft model, aYM155 prodrug significantly inhibits brain tumor growth in vivo, which correlates with cell-type selective survivin-based pharmacodynamic effects.

Optimization of 3-aminotetrahydrothiophene 1,1-dioxides with improved potency and efficacy as non-electrophilic antioxidant response element (ARE) activators.

Activating NRF2-driven transcription with non-electrophilic small molecules represents an attractive strategy to therapeutically target disease states associated with oxidative stress and inflammation. In this study, we describe a campaign to optimize the potency and efficacy of a previously identified bis-sulfone based non-electrophilic ARE activator 2. This work identifies the efficacious analog 17, a compound with a non-cytotoxic profile in IMR32 cells, as well as ARE activators 18 and 22, analogs with improved cellular potency. In silico drug-likeness prediction suggested the optimized bis-sulfones 17, 18, and 22 will likely be of pharmacological utility.

A cell type-selective apoptosis-inducing small molecule for the treatment of brain cancer.

Glioblastoma multiforme (GBM; grade IV astrocytoma) is the most prevalent and aggressive form of primary brain cancer. A subpopulation of multipotent cells termed GBM cancer stem cells (CSCs) play a critical role in tumor initiation, tumor maintenance, metastasis, drug resistance, and recurrence following surgery. Here we report the identification of a small molecule, termed RIPGBM, from a cell-based chemical screen that selectively induces apoptosis in multiple primary patient-derived GBM CSC cultures. The cell type-dependent selectivity of this compound appears to arise at least in part from redox-dependent formation of a proapoptotic derivative, termed cRIPGBM, in GBM CSCs. cRIPGBM induces caspase 1-dependent apoptosis by binding to receptor-interacting protein kinase 2 (RIPK2) and acting as a molecular switch, which reduces the formation of a prosurvival RIPK2/TAK1 complex and increases the formation of a proapoptotic RIPK2/caspase 1 complex. In an orthotopic intracranial GBM CSC tumor xenograft mouse model, RIPGBM was found to significantly suppress tumor formation in vivo. Our chemical genetics-based approach has identified a drug candidate and a potential drug target that provide an approach to the development of treatments for this devastating disease.

Towards an Understanding of the Molecular Mechanisms of Variable Unnatural Base-Pair Behavior: A Biophysical Analysis of dNaM-dTPT3.

The series of unnatural base pairs (UBPs) developed by the Romesberg lab, which pair via hydrophobic and packing interactions have been replicated, transcribed, and translated inside of a living organism. However, as to why these UBPs exhibit variable fidelity and efficiency when used in different contexts is not clear. In an effort to gain some insights, we investigated the thermal stability and pairing selectivity of the (d)NaM-(d)TPT3 UBP in 11nt duplexes via UV spectroscopy and the effects on helical structure via CD spectroscopy. We observed that while the duplexes containing a UBP are less stable than fully natural duplexes, they are generally more stable than duplexes containing natural mispairs. This work provides the first insights connecting the thermal stability of the (d)NaM-(d)TPT3 UBP to the molecular mechanisms for varying replication fidelity in different sequence contexts in DNA, asymmetrical transcription fidelity, and codon:anticodon interactions and can assist in future UBP development.

Modulators of immunoregulatory exonucleases PLD3 and PLD4 identified by high-throughput screen.

PLD3 and PLD4 have recently been revealed to be endosomal exonucleases that regulate the innate immune response by digesting the ligands of nucleic acid sensors. These enzymes can suppress RNA and DNA innate immune sensors like toll-like receptor 9, and PLD4-deficent mice exhibit inflammatory disease. Targeting these immunoregulatory enzymes presents an opportunity to indirectly regulate innate immune nucleic acid sensors that could yield immunotherapies, adjuvants, and nucleic acid drug stabilizers. To aid in delineating the therapeutic potential of these targets, we have developed a high-throughput fluorescence enzymatic assay to identify modulators of PLD3 and PLD4. Screening of a diversity library (N = 17952) yielded preferential inhibitors of PLD3 and PLD4 in addition to a PLD3 selective activator. The modulation models of these compounds were delineated by kinetic analysis. This work presents an inexpensive and simple method to identify modulators of these immunoregulatory exonucleases.

Synthetic fluorescent MYC probe: Inhibitor binding site elucidation and development of a high-throughput screening assay.

We report the discovery of a fluorescent small molecule probe. This probe exhibits an emission increase in the presence of the oncoprotein MYC that can be attenuated by a competing inhibitor. Hydrogen-deuterium exchange mass spectrometry analysis, rationalized by induced-fit docking, suggests it binds to the "coiled-coil" region of the leucine zipper domain. Point mutations of this site produced functional MYC constructs resistant to inhibition in an oncogenic transformation assay by compounds that displace the probe. Utilizing this probe, we have developed a high-throughput assay to identify MYC inhibitor scaffolds. Screening of a diversity library (N = 1408, 384-well) and a library of pharmacologically active compounds (N = 1280, 1536-well) yielded molecules with greater drug-like properties than the probe. One lead is a potent inhibitor of oncogenic transformation and is specific for MYC relative to resistant mutants and transformation-inducing oncogenes. This method is simple, inexpensive, and does not require protein modification, DNA binding, or the dimer partner MAX. This assay presents an opportunity for MYC inhibition researchers to discover unique scaffolds.

Discovery and SAR studies of 3-amino-4-(phenylsulfonyl)tetrahydrothiophene 1,1-dioxides as non-electrophilic antioxidant response element (ARE) activators.

The transcription factor NRF2 controls resistance to oxidative insult and is thus a key therapeutic target for treating a number of disease states associated with oxidative stress and aging. We previously reported CBR-470-1, a bis-sulfone which activates NRF2 by increasing the levels of methylglyoxal, a metabolite that covalently modifies NRF2 repressor KEAP1. Here, we report the design, synthesis, and structure activity relationship of a series of bis-sulfones derived from this unexplored chemical template. We identify analogs with sub-micromolar potencies, 7f and 7g, as well as establish that efficacious NRF2 activation can be achieved by non-toxic analogs 7c, 7e, and 9, a key limitation with CBR-470-1. Further efforts to identify non-covalent NRF2 activators of this kind will likely provide new insight into revealing the role of central metabolism in cellular signaling.

Metabolomics-based discovery of a metabolite that enhances oligodendrocyte maturation.

Endogenous metabolites play essential roles in the regulation of cellular identity and activity. Here we have investigated the process of oligodendrocyte precursor cell (OPC) differentiation, a process that becomes limiting during progressive stages of demyelinating diseases, including multiple sclerosis, using mass-spectrometry-based metabolomics. Levels of taurine, an aminosulfonic acid possessing pleotropic biological activities and broad tissue distribution properties, were found to be significantly elevated (∼20-fold) during the course of oligodendrocyte differentiation and maturation. When added exogenously at physiologically relevant concentrations, taurine was found to dramatically enhance the processes of drug-induced in vitro OPC differentiation and maturation. Mechanism of action studies suggest that the oligodendrocyte-differentiation-enhancing activities of taurine are driven primarily by its ability to directly increase available serine pools, which serve as the initial building block required for the synthesis of the glycosphingolipid components of myelin that define the functional oligodendrocyte cell state.

A vimentin binding small molecule leads to mitotic disruption in mesenchymal cancers.

Expression of the transcription factor FOXC2 is induced and necessary for successful epithelial-mesenchymal transition, a developmental program that when activated in cancer endows cells with metastatic potential and the properties of stem cells. As such, identifying agents that inhibit the growth of FOXC2-transformed cells represents an attractive approach to inhibit chemotherapy resistance and metastatic dissemination. From a high throughput synthetic lethal screen, we identified a small molecule, FiVe1, which selectively and irreversibly inhibits the growth of mesenchymally transformed breast cancer cells and soft tissue sarcomas of diverse histological subtypes. FiVe1 targets the intermediate filament and mesenchymal marker vimentin (VIM) in a mode which promotes VIM disorganization and phosphorylation during metaphase, ultimately leading to mitotic catastrophe, multinucleation, and the loss of stemness. These findings illustrate a previously undescribed mechanism for interrupting faithful mitotic progression and may ultimately inform the design of therapies for a broad range of mesenchymal cancers.

Small molecule-mediated inhibition of myofibroblast transdifferentiation for the treatment of fibrosis.

Fibrosis, a disease in which excessive amounts of connective tissue accumulate in response to physical damage and/or inflammatory insult, affects nearly every tissue in the body and can progress to a state of organ malfunction and death. A hallmark of fibrotic disease is the excessive accumulation of extracellular matrix-secreting activated myofibroblasts (MFBs) in place of functional parenchymal cells. As such, the identification of agents that selectively inhibit the transdifferentiation process leading to the formation of MFBs represents an attractive approach for the treatment of diverse fibrosis-related diseases. Herein we report the development of a high throughput image-based screen using primary hepatic stellate cells that identified the antifungal drug itraconazole (ITA) as an inhibitor of MFB cell fate in resident fibroblasts derived from multiple murine and human tissues (i.e., lung, liver, heart, and skin). Chemical optimization of ITA led to a molecule (CBR-096-4) devoid of antifungal and human cytochrome P450 inhibitory activity with excellent pharmacokinetics, safety, and efficacy in rodent models of lung, liver, and skin fibrosis. These findings may serve to provide a strategy for the safe and effective treatment of a broad range of fibrosis-related diseases.

A regenerative approach to the treatment of multiple sclerosis.

Progressive phases of multiple sclerosis are associated with inhibited differentiation of the progenitor cell population that generates the mature oligodendrocytes required for remyelination and disease remission. To identify selective inducers of oligodendrocyte differentiation, we performed an image-based screen for myelin basic protein (MBP) expression using primary rat optic-nerve-derived progenitor cells. Here we show that among the most effective compounds identifed was benztropine, which significantly decreases clinical severity in the experimental autoimmune encephalomyelitis (EAE) model of relapsing-remitting multiple sclerosis when administered alone or in combination with approved immunosuppressive treatments for multiple sclerosis. Evidence from a cuprizone-induced model of demyelination, in vitro and in vivo T-cell assays and EAE adoptive transfer experiments indicated that the observed efficacy of this drug results directly from an enhancement of remyelination rather than immune suppression. Pharmacological studies indicate that benztropine functions by a mechanism that involves direct antagonism of M1 and/or M3 muscarinic receptors. These studies should facilitate the development of effective new therapies for the treatment of multiple sclerosis that complement established immunosuppressive approaches.

Identification of a small molecule inhibitor of 3-phosphoglycerate dehydrogenase to target serine biosynthesis in cancers.

Cancer cells reprogram their metabolism to promote growth and proliferation. The genetic evidence pointing to the importance of the amino acid serine in tumorigenesis is striking. The gene encoding the enzyme 3-phosphoglycerate dehydrogenase (PHGDH), which catalyzes the first committed step of serine biosynthesis, is overexpressed in tumors and cancer cell lines via focal amplification and nuclear factor erythroid-2-related factor 2 (NRF2)-mediated up-regulation. PHGDH-overexpressing cells are exquisitely sensitive to genetic ablation of the pathway. Here, we report the discovery of a selective small molecule inhibitor of PHGDH, CBR-5884, identified by screening a library of 800,000 drug-like compounds. CBR-5884 inhibited de novo serine synthesis in cancer cells and was selectively toxic to cancer cell lines with high serine biosynthetic activity. Biochemical characterization of the inhibitor revealed that it was a noncompetitive inhibitor that showed a time-dependent onset of inhibition and disrupted the oligomerization state of PHGDH. The identification of a small molecule inhibitor of PHGDH not only enables thorough preclinical evaluation of PHGDH as a target in cancers, but also provides a tool with which to study serine metabolism.