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Glioma stem‐cells are associated with the brain vasculature. However, the way in which this vascular niche regulates stem‐cell renewal and fate remains unclear. Here, we show that factors emanating from brain endothelial cells positively control the expansion of long‐term glioblastoma stem‐like cells. We find that both pharmacological inhibition of and RNA interference with the mammalian target of rapamycin (mTOR) pathway reduce their spheroid growth. Conversely, the endothelial secretome is sufficient to promote this mTOR‐dependent survival. Thus, interfering with endothelial signals might present opportunities to identify treatments that selectively target malignant stem‐cell niches. Endothelial cells provide a permissive microenvironment for glioblastoma stem‐like cell (GSC) identity. Secreted factors from brain endothelial cells are shown here to be sufficient for the propagation and mTOR‐dependent survival of GSC in culture.

Triple negative breast cancer (TNBC) is a deadly form of breast cancer due to the development of resistance to chemotherapy affecting over 30% of patients. New therapeutics and companion biomarkers are urgently needed. Recognizing the elevated expression of glucose transporter 1 (GLUT1, encoded by SLC2A1 ) and associated metabolic dependencies in TNBC, we investigated the vulnerability of TNBC cell lines and patient-derived samples to GLUT1 inhibition. We report that genetic or pharmacological inhibition of GLUT1 with BAY-876 impairs the growth of a subset of TNBC cells displaying high glycolytic and lower oxidative phosphorylation (OXPHOS) rates. Pathway enrichment analysis of gene expression data suggests that the functionality of the E2F pathway may reflect to some extent OXPHOS activity. Furthermore, the protein levels of retinoblastoma tumor suppressor (RB1) strongly correlate with the degree of sensitivity to GLUT1 inhibition in TNBC, where RB1-negative cells are insensitive to GLUT1 inhibition. Collectively, our results highlight a strong and targetable RB1-GLUT1 metabolic axis in TNBC and warrant clinical evaluation of GLUT1 inhibition in TNBC patients stratified according to RB1 protein expression levels. Triple negative breast cancer is a deadly form of breast cancer with limited therapeutic options. Here the authors show the efficacy of GLUT1 pharmacological inhibition against a subset of tumors expressing RB1, thereby identifying RB1 protein level as a biomarker of sensitivity to anti-GLUT1 therapy.

Cancer stem cells are thought to be resistant to anticancer therapies and are able to repopulate tumors and sustain tumor growth. The authors establish BMI-1 as a crucial regulator of cancer cell stemness in colorectal tumors and develop a chemical inhibitor that targets cancer stem cell renewal by reducing the levels of BMI-1. This strategy affords antitumor effects in vitro and in vivo and may pave the way for the precise targeting of elusive cancer stem cells. Tumor recurrence following treatment remains a major clinical challenge. Evidence from xenograft models and human trials indicates selective enrichment of cancer-initiating cells (CICs) in tumors that survive therapy. Together with recent reports showing that CIC gene signatures influence patient survival, these studies predict that targeting self-renewal, the key 'stemness' property unique to CICs, may represent a new paradigm in cancer therapy. Here we demonstrate that tumor formation and, more specifically, human colorectal CIC function are dependent on the canonical self-renewal regulator BMI-1. Downregulation of BMI-1 inhibits the ability of colorectal CICs to self-renew, resulting in the abrogation of their tumorigenic potential. Treatment of primary colorectal cancer xenografts with a small-molecule BMI-1 inhibitor resulted in colorectal CIC loss with long-term and irreversible impairment of tumor growth. Targeting the BMI-1–related self-renewal machinery provides the basis for a new therapeutic approach in the treatment of colorectal cancer.

Bromodomains (BRDs) are conserved protein interaction modules which recognize (read) acetyl-lysine modifications, however their role(s) in regulating cellular states and their potential as targets for the development of targeted treatment strategies is poorly understood. Here we present a set of 25 chemical probes, selective small molecule inhibitors, covering 29 human bromodomain targets. We comprehensively evaluate the selectivity of this probe-set using BROMO scan and demonstrate the utility of the set identifying roles of BRDs in cellular processes and potential translational applications. For instance, we discovered crosstalk between histone acetylation and the glycolytic pathway resulting in a vulnerability of breast cancer cell lines under conditions of glucose deprivation or GLUT1 inhibition to inhibition of BRPF2/3 BRDs. This chemical probe-set will serve as a resource for future applications in the discovery of new physiological roles of bromodomain proteins in normal and disease states, and as a toolset for bromodomain target validation. Bromodomains are conserved protein interaction modules that recognize acetyl-lysine modifications. Here the authors present a set of 25 selective small molecule inhibitors covering 29 human bromodomain targets and comprehensively evaluate the selectivity of this probe-set.

A pyrrolidine-based small-molecule inhibitor competes with H3K27me3 for binding to EED leading to inactivation of PRC2 and global reduction in H3K27me3 levels. Polycomb repressive complex 2 (PRC2) is a regulator of epigenetic states required for development and homeostasis. PRC2 trimethylates histone H3 at lysine 27 (H3K27me3), which leads to gene silencing, and is dysregulated in many cancers. The embryonic ectoderm development (EED) protein is an essential subunit of PRC2 that has both a scaffolding function and an H3K27me3-binding function. Here we report the identification of A-395, a potent antagonist of the H3K27me3 binding functions of EED. Structural studies demonstrate that A-395 binds to EED in the H3K27me3-binding pocket, thereby preventing allosteric activation of the catalytic activity of PRC2. Phenotypic effects observed in vitro and in vivo are similar to those of known PRC2 enzymatic inhibitors; however, A-395 retains potent activity against cell lines resistant to the catalytic inhibitors. A-395 represents a first-in-class antagonist of PRC2 protein–protein interactions (PPI) for use as a chemical probe to investigate the roles of EED-containing protein complexes.

Robust, generalizable approaches to identify compounds efficiently with undesirable mechanisms of action in complex cellular assays remain elusive. Such a process would be useful for hit triage during high-throughput screening and, ultimately, predictive toxicology during drug development. Here we generate cell painting and cellular health profiles for 218 prototypical cytotoxic and nuisance compounds in U-2 OS cells in a concentration-response format. A diversity of compounds that cause cellular damage produces bioactive cell painting morphologies, including cytoskeletal poisons, genotoxins, nonspecific electrophiles, and redox-active compounds. Further, we show that lower quality lysine acetyltransferase inhibitors and nonspecific electrophiles can be distinguished from more selective counterparts. We propose that the purposeful inclusion of cytotoxic and nuisance reference compounds such as those profiled in this resource will help with assay optimization and compound prioritization in complex cellular assays like cell painting. Cellular nuisance compounds are a burden in chemical biology and drug screening. Here the authors profile prototypical cytotoxic and nuisance compounds using the cell painting assay to systematically characterise cellular morphologies associated with compound-dependent cellular injury and nuisance activity.

High mortality and low response rates in lung cancer patients call for novel therapeutic targets. Data mining of whole-genome genetic dependency screens suggest Cell Division Cycle 40 (CDC40) to be an essential protein for lung cancer cell survival. We characterized CDC40 knockdown effects in multiple lung cancer cell lines, revealing induced cell cycle defects that resulted in strong growth inhibition and activation of apoptosis. Global transcriptional and splicing changes were also investigated, where CDC40 knockdown resulted in perturbation of splicing- and translation-related genes as well as more transcripts with intron retention. In the transcript of the cell cycle regulatory protein CDCA5, CDC40 knockdown was shown to induce retention of the first intron, leading to an increase in the unspliced CDCA5 transcript and subsequent decrease in CDCA5 protein expression. Additionally, protein–protein interactions of CDC40 were explored and spliceosome components were found to be its main binding partners, further highlighting the role of CDC40 in splicing. CDC40 mutation analysis suggests that it may be difficult to disrupt key interactions using small molecules within a large complex. Our results demonstrate that CDC40 is essential for lung cancer cell growth, and that its inhibition may represent a viable therapeutic strategy for lung cancer.

In embryonic stem cells, promoters of key lineage-specific differentiation genes are found in a bivalent state, having both activating H3K4me3 and repressive H3K27me3 histone marks, making them poised for transcription upon loss of H3K27me3. Whether cancer-initiating cells (C-ICs) have similar epigenetic mechanisms that prevent lineage commitment is unknown. Here we show that colorectal C-ICs (CC-ICs) are maintained in a stem-like state through a bivalent epigenetic mechanism. Disruption of the bivalent state through inhibition of the H3K27 methyltransferase EZH2, resulted in decreased self-renewal of patient-derived C-ICs. Epigenomic analyses revealed that the promoter of Indian Hedgehog ( IHH ), a canonical driver of normal colonocyte differentiation, exists in a bivalent chromatin state. Inhibition of EZH2 resulted in de-repression of IHH, decreased self-renewal, and increased sensitivity to chemotherapy in vivo. Our results reveal an epigenetic block to differentiation in CC-ICs and demonstrate the potential for epigenetic differentiation therapy of a solid tumour through EZH2 inhibition. The presence of bivalent epigenetic active and repressive histone marks control lineage-specific differentiation in embryonic stem cells. Here, the authors reveal that bivalent marks repress the differentiation gene IHH in colorectal cancer-initiating cells, and can be targeted by EZH2 inhibition

PRDM9 is a PR domain containing protein which trimethylates histone 3 on lysine 4 and 36. Its normal expression is restricted to germ cells and attenuation of its activity results in altered meiotic gene transcription, impairment of double-stranded breaks and pairing between homologous chromosomes. There is growing evidence for a role of aberrant expression of PRDM9 in oncogenesis and genome instability. Here we report the discovery of MRK-740, a potent (IC50: 80 ± 16 nM), selective and cell-active PRDM9 inhibitor (Chemical Probe). MRK-740 binds in the substrate-binding pocket, with unusually extensive interactions with the cofactor S-adenosylmethionine (SAM), conferring SAM-dependent substrate-competitive inhibition. In cells, MRK-740 specifically and directly inhibits H3K4 methylation at endogenous PRDM9 target loci, whereas the closely related inactive control compound, MRK-740-NC, does not. The discovery of MRK-740 as a chemical probe for the PRDM subfamily of methyltransferases highlights the potential for exploiting SAM in targeting SAM-dependent methyltransferases.

The tumour suppressor PTEN (phosphatase and tensin deleted on chromosome 10) regulates major cellular functions via lipid phosphatase‐dependent and ‐independent mechanisms. Despite its fundamental pathophysiological importance, how PTEN's cellular activity is regulated has only been partially elucidated. We report that the scaffolding proteins β‐arrestins (β‐arrs) are important regulators of PTEN. Downstream of receptor‐activated RhoA/ROCK signalling, β‐arrs activate the lipid phosphatase activity of PTEN to negatively regulate Akt and cell proliferation. In contrast, following wound‐induced RhoA activation, β‐arrs inhibit the lipid phosphatase‐independent anti‐migratory effects of PTEN. β‐arrs can thus differentially control distinct functional outputs of PTEN important for cell proliferation and migration. This paper discovers β‐arrestins as novel binding partner for PTEN. With functional implications for Rho and AKT signalling, the paper adds new insight into the regulation of PTEN by cell surface receptor signalling pathways.