STAT3 protects hematopoietic stem cells by preventing activation of a deleterious autocrine type-I interferon response.

Hematopoietic stem and progenitor cells (HSPCs) maintain blood-forming and immune activity, yet intrinsic regulators of HSPCs remain elusive. STAT3 function in HSPCs has been difficult to dissect as Stat3-deficiency in the hematopoietic compartment induces systemic inflammation, which can impact HSPC activity. Here, we developed mixed bone marrow (BM) chimeric mice with inducible Stat3 deletion in 20% of the hematopoietic compartment to avoid systemic inflammation. Stat3-deficient HSPCs were significantly impaired in reconstitution ability following primary or secondary bone marrow transplantation, indicating hematopoietic stem cell (HSC) defects. Single-cell RNA sequencing of Lin-ckit+Sca1+ BM cells (LSKs) revealed aberrant activation of cell cycle, p53, and interferon (IFN) pathways in Stat3-deficient HSPCs. Stat3-deficient LSKs accumulated γH2AX and showed increased expression of DNA sensors and type-I IFN (IFN-I), while treatment with A151-ODN inhibited expression of IFN-I and IFN-responsive genes. Further, the blockade of IFN-I receptor signaling suppressed aberrant cell cycling, STAT1 activation, and nuclear p53 accumulation. Collectively, our results show that STAT3 inhibits a deleterious autocrine IFN response in HSCs to maintain long-term HSC function. These data signify the importance of ensuring therapeutic STAT3 inhibitors are targeted specifically to diseased cells to avoid off-target loss of healthy HSPCs.

Targeting PD-L2-RGMb overcomes microbiome-related immunotherapy resistance.

The gut microbiota is a crucial regulator of anti-tumour immunity during immune checkpoint inhibitor therapy. Several bacteria that promote an anti-tumour response to immune checkpoint inhibitors have been identified in mice1-6. Moreover, transplantation of faecal specimens from responders can improve the efficacy of anti-PD-1 therapy in patients with melanoma7,8. However, the increased efficacy from faecal transplants is variable and how gut bacteria promote anti-tumour immunity remains unclear. Here we show that the gut microbiome downregulates PD-L2 expression and its binding partner repulsive guidance molecule b (RGMb) to promote anti-tumour immunity and identify bacterial species that mediate this effect. PD-L1 and PD-L2 share PD-1 as a binding partner, but PD-L2 can also bind RGMb. We demonstrate that blockade of PD-L2-RGMb interactions can overcome microbiome-dependent resistance to PD-1 pathway inhibitors. Antibody-mediated blockade of the PD-L2-RGMb pathway or conditional deletion of RGMb in T cells combined with an anti-PD-1 or anti-PD-L1 antibody promotes anti-tumour responses in multiple mouse tumour models that do not respond to anti-PD-1 or anti-PD-L1 alone (germ-free mice, antibiotic-treated mice and even mice colonized with stool samples from a patient who did not respond to treatment). These studies identify downregulation of the PD-L2-RGMb pathway as a specific mechanism by which the gut microbiota can promote responses to PD-1 checkpoint blockade. The results also define a potentially effective immunological strategy for treating patients who do not respond to PD-1 cancer immunotherapy.

STAT3 protects HSCs from intrinsic interferon signaling and loss of long-term blood-forming activity.

STAT3 function in hematopoietic stem and progenitor cells (HSPCs) has been difficult to discern as Stat3 deficiency in the hematopoietic system induces systemic inflammation, which can impact HSPC activity. To address this, we established mixed bone marrow (BM) chimeric mice with CreER-mediated Stat3 deletion in 20% of the hematopoietic compartment. Stat3-deficient HSPCs had impaired hematopoietic activity and failed to undergo expansion in BM in contrast to Stat3-sufficient (CreER) controls. Single-cell RNA sequencing of Lin-ckit+Sca1+ BM cells revealed altered transcriptional responses in Stat3-deficient hematopoietic stem cells (HSCs) and multipotent progenitors, including intrinsic activation of cell cycle, stress response, and interferon signaling pathways. Consistent with their deregulation, Stat3-deficient Lin-ckit+Sca1+ cells accumulated γH2AX over time. Following secondary BM transplantation, Stat3-deficient HSPCs failed to reconstitute peripheral blood effectively, indicating a severe functional defect in the HSC compartment. Our results reveal essential roles for STAT3 in HSCs and suggest the potential for using targeted synthetic lethal approaches with STAT3 inhibition to remove defective or diseased HSPCs.

Intestinal toxicity to CTLA-4 blockade driven by IL-6 and myeloid infiltration.

Immune checkpoint blockade (ICB) has revolutionized cancer treatment, yet quality of life and continuation of therapy can be constrained by immune-related adverse events (irAEs). Limited understanding of irAE mechanisms hampers development of approaches to mitigate their damage. To address this, we examined whether mice gained sensitivity to anti-CTLA-4 (αCTLA-4)-mediated toxicity upon disruption of gut homeostatic immunity. We found αCTLA-4 drove increased inflammation and colonic tissue damage in mice with genetic predisposition to intestinal inflammation, acute gastrointestinal infection, transplantation with a dysbiotic fecal microbiome, or dextran sodium sulfate administration. We identified an immune signature of αCTLA-4-mediated irAEs, including colonic neutrophil accumulation and systemic interleukin-6 (IL-6) release. IL-6 blockade combined with antibiotic treatment reduced intestinal damage and improved αCTLA-4 therapeutic efficacy in inflammation-prone mice. Intestinal immune signatures were validated in biopsies from patients with ICB colitis. Our work provides new preclinical models of αCTLA-4 intestinal irAEs, mechanistic insights into irAE development, and potential approaches to enhance ICB efficacy while mitigating irAEs.

Targeting the gut and tumor microbiota in cancer.

Microorganisms within the gut and other niches may contribute to carcinogenesis, as well as shaping cancer immunosurveillance and response to immunotherapy. Our understanding of the complex relationship between different host-intrinsic microorganisms, as well as the multifaceted mechanisms by which they influence health and disease, has grown tremendously-hastening development of novel therapeutic strategies that target the microbiota to improve treatment outcomes in cancer. Accordingly, the evaluation of a patient's microbial composition and function and its subsequent targeted modulation represent key elements of future multidisciplinary and precision-medicine approaches. In this Review, we outline the current state of research toward harnessing the microbiome to better prevent and treat cancer.

Targeting MYC-enhanced glycolysis for the treatment of small cell lung cancer.

INTRODUCTION: The transcription factor MYC is overexpressed in 30% of small cell lung cancer (SCLC) tumors and is known to modulate the balance between two major pathways of metabolism: glycolysis and mitochondrial respiration. This duality of MYC underscores the importance of further investigation into its role in SCLC metabolism and could lead to insights into metabolic targeting approaches. METHODS: We investigated differences in metabolic pathways in transcriptional and metabolomics datasets based on cMYC expression in patient and cell line samples. Metabolic pathway utilization was evaluated by flow cytometry and Seahorse extracellular flux methodology. Glycolysis inhibition was evaluated in vitro and in vivo using PFK158, a small molecular inhibitor of PFKFB3. RESULTS: MYC-overexpressing SCLC patient samples and cell lines exhibited increased glycolysis gene expression directly mediated by MYC. Further, MYC-overexpressing cell lines displayed enhanced glycolysis consistent with the Warburg effect, while cell lines with low MYC expression appeared more reliant on oxidative metabolism. Inhibition of glycolysis with PFK158 preferentially attenuated glucose uptake, ATP production, and lactate in MYC-overexpressing cell lines. Treatment with PFK158 in xenografts delayed tumor growth and decreased glycolysis gene expression. CONCLUSIONS: Our study highlights an in-depth characterization of SCLC metabolic programming and presents glycolysis as a targetable mechanism downstream of MYC that could offer therapeutic benefit in a subset of SCLC patients.

Lung Cancer Models Reveal Severe Acute Respiratory Syndrome Coronavirus 2-Induced Epithelial-to-Mesenchymal Transition Contributes to Coronavirus Disease 2019 Pathophysiology.

INTRODUCTION: Coronavirus disease 2019 is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which enters host cells through the cell surface proteins ACE2 and TMPRSS2. METHODS: Using a variety of normal and malignant models and tissues from the aerodigestive and respiratory tracts, we investigated the expression and regulation of ACE2 and TMPRSS2. RESULTS: We find that ACE2 expression is restricted to a select population of epithelial cells. Notably, infection with SARS-CoV-2 in cancer cell lines, bronchial organoids, and patient nasal epithelium induces metabolic and transcriptional changes consistent with epithelial-to-mesenchymal transition (EMT), including up-regulation of ZEB1 and AXL, resulting in an increased EMT score. In addition, a transcriptional loss of genes associated with tight junction function occurs with SARS-CoV-2 infection. The SARS-CoV-2 receptor, ACE2, is repressed by EMT through the transforming growth factor-ß, ZEB1 overexpression, and onset of EGFR tyrosine kinase inhibitor resistance. This suggests a novel model of SARS-CoV-2 pathogenesis in which infected cells shift toward an increasingly mesenchymal state, associated with a loss of tight junction components with acute respiratory distress syndrome-protective effects. AXL inhibition and ZEB1 reduction, as with bemcentinib, offer a potential strategy to reverse this effect. CONCLUSIONS: These observations highlight the use of aerodigestive and, especially, lung cancer model systems in exploring the pathogenesis of SARS-CoV-2 and other respiratory viruses and offer important insights into the potential mechanisms underlying the morbidity and mortality of coronavirus disease 2019 in healthy patients and patients with cancer alike.

Patterns of transcription factor programs and immune pathway activation define four major subtypes of SCLC with distinct therapeutic vulnerabilities.

Despite molecular and clinical heterogeneity, small cell lung cancer (SCLC) is treated as a single entity with predictably poor results. Using tumor expression data and non-negative matrix factorization, we identify four SCLC subtypes defined largely by differential expression of transcription factors ASCL1, NEUROD1, and POU2F3 or low expression of all three transcription factor signatures accompanied by an Inflamed gene signature (SCLC-A, N, P, and I, respectively). SCLC-I experiences the greatest benefit from the addition of immunotherapy to chemotherapy, while the other subtypes each have distinct vulnerabilities, including to inhibitors of PARP, Aurora kinases, or BCL-2. Cisplatin treatment of SCLC-A patient-derived xenografts induces intratumoral shifts toward SCLC-I, supporting subtype switching as a mechanism of acquired platinum resistance. We propose that matching baseline tumor subtype to therapy, as well as manipulating subtype switching on therapy, may enhance depth and duration of response for SCLC patients.

Lung cancer models reveal SARS-CoV-2-induced EMT contributes to COVID-19 pathophysiology.

COVID-19 is an infectious disease caused by SARS-CoV-2, which enters host cells via the cell surface proteins ACE2 and TMPRSS2. Using a variety of normal and malignant models and tissues from the aerodigestive and respiratory tracts, we investigated the expression and regulation of ACE2 and TMPRSS2. We find that ACE2 expression is restricted to a select population of highly epithelial cells. Notably, infection with SARS-CoV-2 in cancer cell lines, bronchial organoids, and patient nasal epithelium, induces metabolic and transcriptional changes consistent with epithelial to mesenchymal transition (EMT), including upregulation of ZEB1 and AXL, resulting in an increased EMT score. Additionally, a transcriptional loss of genes associated with tight junction function occurs with SARS-CoV-2 infection. The SARS-CoV-2 receptor, ACE2, is repressed by EMT via TGFbeta, ZEB1 overexpression and onset of EGFR TKI inhibitor resistance. This suggests a novel model of SARS-CoV-2 pathogenesis in which infected cells shift toward an increasingly mesenchymal state, associated with a loss of tight junction components with acute respiratory distress syndrome-protective effects. AXL-inhibition and ZEB1-reduction, as with bemcentinib, offers a potential strategy to reverse this effect. These observations highlight the utility of aerodigestive and, especially, lung cancer model systems in exploring the pathogenesis of SARS-CoV-2 and other respiratory viruses, and offer important insights into the potential mechanisms underlying the morbidity and mortality of COVID-19 in healthy patients and cancer patients alike.

WBP11 is required for splicing the TUBGCP6 pre-mRNA to promote centriole duplication.

Centriole duplication occurs once in each cell cycle to maintain centrosome number. A previous genome-wide screen revealed that depletion of 14 RNA splicing factors leads to a specific defect in centriole duplication, but the cause of this deficit remains unknown. Here, we identified an additional pre-mRNA splicing factor, WBP11, as a novel protein required for centriole duplication. Loss of WBP11 results in the retention of ∼200 introns, including multiple introns in TUBGCP6, a central component of the γ-TuRC. WBP11 depletion causes centriole duplication defects, in part by causing a rapid decline in the level of TUBGCP6. Several additional splicing factors that are required for centriole duplication interact with WBP11 and are required for TUBGCP6 expression. These findings provide insight into how the loss of a subset of splicing factors leads to a failure of centriole duplication. This may have clinical implications because mutations in some spliceosome proteins cause microcephaly and/or growth retardation, phenotypes that are strongly linked to centriole defects.

Transferring Fungi to a Deuterium-Enriched Medium Results in Assorted, Conditional Changes in Secondary Metabolite Production.

Deuterium is one of the few stable isotopes that have the capacity to significantly alter a compound's chemical and biological properties. The addition of a single neutron to a protium atom results in the near doubling of its mass, which gives rise to deuterium's characteristic isotope effects. Since the incorporation of deuterium into organic substrates is known to alter enzyme/protein-substrate interactions, we tested the extent to which deuterium enrichment would modify fungal secondary metabolite production. Several fungal cultures were tested, and in all cases their secondary metabolomes were marked by changes in natural product production. Workup of one Aspergillus sp. grown under deuterium-enrichment conditions resulted in the production of several secondary metabolites not previously detected from the fungus. Bioassay testing revealed that in comparison to the inactive crude fungal extract derived from growing the fungus under non-deuterium-enriched conditions, an extract derived from the same isolate cultured in a deuterium-enriched medium inhibited methicillin-resistant Staphylococcus aureus. Using an assortment of NMR and mass spectrometry experiments, we were able to identify the bacterial inhibitor as an isotope-labeled version of pigmentosin A (6). Five additional isotopically labeled metabolites were also obtained from the fungus including brevianamide F (1), stephacidin A (2), notoamide D (3), notoamide L (4), and notoamide C (5). Given the assorted changes observed in the secondary metabolite profiles of this and other fungi grown in deuterium-enriched environments, as well as the fact that 1 and 3-6 had not been previously observed from the Aspergillus sp. isolate used in this study, we propose that deuterium enrichment might offer an effective method for further expanding a fungus's chemical diversity potential.