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Altered expression of mitochondrial DNA (mtDNA) occurs in ageing and a range of human pathologies (for example, inborn errors of metabolism, neurodegeneration and cancer). Here we describe first-in-class specific inhibitors of mitochondrial transcription (IMTs) that target the human mitochondrial RNA polymerase (POLRMT), which is essential for biogenesis of the oxidative phosphorylation (OXPHOS) system 1 – 6 . The IMTs efficiently impair mtDNA transcription in a reconstituted recombinant system and cause a dose-dependent inhibition of mtDNA expression and OXPHOS in cell lines. To verify the cellular target, we performed exome sequencing of mutagenized cells and identified a cluster of amino acid substitutions in POLRMT that cause resistance to IMTs. We obtained a cryo-electron microscopy (cryo-EM) structure of POLRMT bound to an IMT, which further defined the allosteric binding site near the active centre cleft of POLRMT. The growth of cancer cells and the persistence of therapy-resistant cancer stem cells has previously been reported to depend on OXPHOS 7 – 17 , and we therefore investigated whether IMTs have anti-tumour effects. Four weeks of oral treatment with an IMT is well-tolerated in mice and does not cause OXPHOS dysfunction or toxicity in normal tissues, despite inducing a strong anti-tumour response in xenografts of human cancer cells. In summary, IMTs provide a potent and specific chemical biology tool to study the role of mtDNA expression in physiology and disease. Inhibitors of mitochondrial transcription that target human mitochondrial RNA polymerase provide a chemical biology tool for studying the role of mitochondrial DNA expression in a wide range of pathologies.

The E3 ligase Cbl-b acts on TAM tyrosine kinase receptors and has a critical role in the regulation of natural killer (NK) cell rejection of metastatic tumours; a small molecule TAM kinase inhibitor is shown to enhance the anti-metastatic NK cell activity. Controlling NK cell anti-metastatic activity This study describes a previously unknown role for the E3 ubiquitin ligase Cbl-b as part of a regulatory pathway in innate natural killer (NK) cells that licenses them to spontaneously reject cancer metastases. Genetic loss of Cbl-b or inactivation of its E3 ligase activity in mice allows NK cells to suppress growth of both multiple primary tumours and distant tumour metastases. The effect is mediated via members of the TAM family tyrosine kinase receptors, and treatment of wild-type NK cells with a small-molecule TAM inhibitor conferred therapeutic NK cell activity against metastatic melanomas. This suggests a possible approach for NK-cell-based anti-metastatic therapy in humans and at the same time explains the anti-metastatic properties of the widely used anticoagulant warfarin. Tumour metastasis is the primary cause of mortality in cancer patients and remains the key challenge for cancer therapy 1 . New therapeutic approaches to block inhibitory pathways of the immune system have renewed hopes for the utility of such therapies 2 . Here we show that genetic deletion of the E3 ubiquitin ligase Cbl-b (casitas B-lineage lymphoma-b) or targeted inactivation of its E3 ligase activity licenses natural killer (NK) cells to spontaneously reject metastatic tumours. The TAM tyrosine kinase receptors Tyro3, Axl and Mer (also known as Mertk) were identified as ubiquitylation substrates for Cbl-b. Treatment of wild-type NK cells with a newly developed small molecule TAM kinase inhibitor conferred therapeutic potential, efficiently enhancing anti-metastatic NK cell activity in vivo . Oral or intraperitoneal administration using this TAM inhibitor markedly reduced murine mammary cancer and melanoma metastases dependent on NK cells. We further report that the anticoagulant warfarin exerts anti-metastatic activity in mice via Cbl-b/TAM receptors in NK cells, providing a molecular explanation for a 50-year-old puzzle in cancer biology 3 . This novel TAM/Cbl-b inhibitory pathway shows that it might be possible to develop a ‘pill’ that awakens the innate immune system to kill cancer metastases.

Reversible palmitoylation controls the localization and signaling of Ras. Development of a potent and specific small molecule inhibitor of the thioesterase APT1 reveals that this enzyme depalmitoylates Ras in cells. Inhibition of APT1 led to redistribution and altered activity of HRas, NRas and an oncogenic mutant Ras. Cycles of depalmitoylation and repalmitoylation critically control the steady-state localization and function of various peripheral membrane proteins, such as Ras proto-oncogene products. Interference with acylation using small molecules is a strategy to modulate cellular localization—and thereby unregulated signaling—caused by palmitoylated Ras proteins. We present the knowledge-based development and characterization of a potent inhibitor of acyl protein thioesterase 1 (APT1), a bona fide depalmitoylating enzyme that is, so far, poorly characterized in cells. The inhibitor, palmostatin B, perturbs the cellular acylation cycle at the level of depalmitoylation and thereby causes a loss of the precise steady-state localization of palmitoylated Ras. As a consequence, palmostatin B induces partial phenotypic reversion in oncogenic HRasG12V-transformed fibroblasts. We identify APT1 as one of the thioesterases in the acylation cycle and show that this protein is a cellular target of the inhibitor.

Natural product–inspired compounds are primed to interact with and manipulate biological processes, but obtaining these complex molecules poses synthetic challenges. The development of a 12-step, 1-pot cascade reaction leads to the 'centrocountins', tetrahydroindoloquinolizines that modulate mitosis by targeting the centrosome-associated proteins nucleophosmin and Crm1. In biology-oriented synthesis, the scaffolds of biologically relevant compound classes inspire the synthesis of focused compound collections enriched in bioactivity. This criterion is, in particular, met by the scaffolds of natural products selected in evolution. The synthesis of natural product–inspired compound collections calls for efficient reaction sequences that preferably combine multiple individual transformations in one operation. Here we report the development of a one-pot, twelve-step cascade reaction sequence that includes nine different reactions and two opposing kinds of organocatalysis. The cascade sequence proceeds within 10–30 min and transforms readily available substrates into complex indoloquinolizines that resemble the core tetracyclic scaffold of numerous polycyclic indole alkaloids. Biological investigation of a corresponding focused compound collection revealed modulators of centrosome integrity, termed centrocountins, which caused fragmented and supernumerary centrosomes, chromosome congression defects, multipolar mitotic spindles, acentrosomal spindle poles and multipolar cell division by targeting the centrosome-associated proteins nucleophosmin and Crm1.

T-cell prolymphocytic leukemia (T-PLL) is an aggressive malignancy characterized by chemotherapy resistance and a median survival of less than 2 years. Here, we investigated the pharmacological effects of the novel highly specific cyclin-dependent kinase 9 (CDK9) inhibitor LDC526 and its clinically used derivate atuveciclib employing primary T-PLL cells in an ex vivo drug sensitivity testing platform. Importantly, all T-PLL samples were sensitive to CDK9 inhibition at submicromolar concentrations, while conventional cytotoxic drugs were found to be largely ineffective. At the cellular level LDC526 inhibited the phosphorylation at serine 2 of the RNA polymerase II C-terminal domain resulting in decreased de novo RNA transcription. LDC526 induced apoptotic leukemic cell death through down-regulating MYC and MCL1 both at the mRNA and protein level. Microarray-based transcriptomic profiling revealed that genes down-modulated in response to CDK9 inhibition were enriched for MYC and JAK-STAT targets. By contrast, CDK9 inhibition increased the expression of the tumor suppressor FBXW7, which may contribute to decreased MYC and MCL1 protein levels. Finally, the combination of atuvecliclib and the BCL2 inhibitor venetoclax exhibited synergistic anti-leukemic activity, providing the rationale for a novel targeted-agent-based treatment of T-PLL.