Human lung cancer harbors spatially organized stem-immunity hubs associated with response to immunotherapy.

The organization of immune cells in human tumors is not well understood. Immunogenic tumors harbor spatially localized multicellular 'immunity hubs' defined by expression of the T cell-attracting chemokines CXCL10/CXCL11 and abundant T cells. Here, we examined immunity hubs in human pre-immunotherapy lung cancer specimens and found an association with beneficial response to PD-1 blockade. Critically, we discovered the stem-immunity hub, a subtype of immunity hub strongly associated with favorable PD-1-blockade outcome. This hub is distinct from mature tertiary lymphoid structures and is enriched for stem-like TCF7+PD-1+CD8+ T cells, activated CCR7+LAMP3+ dendritic cells and CCL19+ fibroblasts as well as chemokines that organize these cells. Within the stem-immunity hub, we find preferential interactions between CXCL10+ macrophages and TCF7-CD8+ T cells as well as between mature regulatory dendritic cells and TCF7+CD4+ and regulatory T cells. These results provide a picture of the spatial organization of the human intratumoral immune response and its relevance to patient immunotherapy outcomes.

Unprocessed genomic uracil as a source of DNA replication stress in cancer cells.

Alterations of bases in DNA constitute a major source of genomic instability. It is believed that base alterations trigger base excision repair (BER), generating DNA repair intermediates interfering with DNA replication. Here, we show that genomic uracil, a common type of base alteration, induces DNA replication stress (RS) without being processed by BER. In the absence of uracil DNA glycosylase (UNG), genomic uracil accumulates to high levels, DNA replication forks slow down, and PrimPol-mediated repriming is enhanced, generating single-stranded gaps in nascent DNA. ATR inhibition in UNG-deficient cells blocks the repair of uracil-induced gaps, increasing replication fork collapse and cell death. Notably, a subset of cancer cells upregulates UNG2 to suppress genomic uracil and limit RS, and these cancer cells are hypersensitive to co-treatment with ATR inhibitors and drugs increasing genomic uracil. These results reveal unprocessed genomic uracil as an unexpected source of RS and a targetable vulnerability of cancer cells.

Single-Cell Sequencing Illuminates Thymic Development: An Updated Framework for Understanding Thymic Epithelial Tumors.

Thymic epithelial tumors (TETs) are rare tumors for which treatment options are limited. The ongoing need for improved systemic therapies reflects a limited understanding of tumor biology as well as the normal thymus. The essential role of the thymus in adaptive immunity is largely effected by its epithelial compartment, which directs thymocyte (T-cell) differentiation and immunologic self-tolerance. With aging, the thymus undergoes involution whereby epithelial tissue is replaced by adipose and other connective tissue, decreasing immature T-cell production. Against this natural drive toward involution, a fraction of thymuses will instead undergo oncologic transformation, leading to the formation of TETs, including thymoma and thymic carcinoma. The rarity of these tumors restricts investigation of the mechanisms of tumorigenesis and development of rational treatment options. To this end, the development of technologies which allow deep molecular profiling of individual tumor cells permits a new window through which to view normal thymic development and contrast the malignant changes that result in oncogenic transformation. In this review, we describe the findings of recent illuminating studies on the diversity of cell types within the epithelial compartment through thymic differentiation and aging. We contextualize these findings around important unanswered questions regarding the spectrum of known somatic tumor alterations, cell of origin, and tumor heterogeneity. The perspectives informed by single-cell molecular profiling offer new approaches to clinical and basic investigation of thymic epithelial tumors, with the potential to accelerate development of improved therapeutic strategies to address ongoing unmet needs in these rare tumors.

Deacetylase-independent function of HDAC3 in transcription and metabolism requires nuclear receptor corepressor.

Histone deacetylases (HDACs) are believed to regulate gene transcription by catalyzing deacetylation reactions. HDAC3 depletion in mouse liver upregulates lipogenic genes and results in severe hepatosteatosis. Here we show that pharmacologic HDAC inhibition in primary hepatocytes causes histone hyperacetylation but does not upregulate expression of HDAC3 target genes. Meanwhile, deacetylase-dead HDAC3 mutants can rescue hepatosteatosis and repress lipogenic genes expression in HDAC3-depleted mouse liver, demonstrating that histone acetylation is insufficient to activate gene transcription. Mutations abolishing interactions with the nuclear receptor corepressor (NCOR or SMRT) render HDAC3 nonfunctional in vivo. Additionally, liver-specific knockout of NCOR, but not SMRT, causes metabolic and transcriptomal alterations resembling those of mice without hepatic HDAC3, demonstrating that interaction with NCOR is essential for deacetylase-independent function of HDAC3. These findings highlight nonenzymatic roles of a major HDAC in transcriptional regulation in vivo and warrant reconsideration of the mechanism of action of HDAC inhibitors.

Anti-PD-1 Immunotherapy-Induced Flare of a Known Underlying Relapsing Vasculitis Mimicking Recurrent Cancer.

Safe use of immune checkpoint blockade in patients with cancer and autoimmune disorders requires a better understanding of the pathophysiology of immunologic activation. We describe the immune correlates of reactivation of granulomatosis with polyangiitis (GPA)-an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis-in a patient with metastatic urothelial carcinoma treated with pembrolizumab. After PD-1 blockade, an inflammatory pulmonary nodule demonstrated a granulomatous, CD4+ T-cell infiltrate, correlating with increased CD4+ and CD8+ naïve memory cells in the peripheral blood without changes in other immune checkpoint receptors. Placed within the context of the existing literature on GPA and disease control, our findings suggest a key role for PD-1 in GPA self-tolerance and that selective strategies for immunotherapy may be needed in patients with certain autoimmune disorders. We further summarize the current literature regarding reactivation of autoimmune disorders in patients undergoing immune checkpoint blockade, as well as potential immunosuppressive strategies to minimize the risks of further vasculitic reactivation upon rechallenge with anti-PD-1 blockade. KEY POINTS: Nonspecific imaging findings in patients with cancer and rheumatological disorders may require biopsy to distinguish underlying pathology.Patients with rheumatologic disorders have increased risk of reactivation with PD-(L)1 immune checkpoint blockade, requiring assessment of disease status before starting treatment.Further study is needed to evaluate the efficacy of treatment regimens in preventing and controlling disease reactivation.

International, evidence-based consensus diagnostic criteria for HHV-8-negative/idiopathic multicentric Castleman disease.

Human herpesvirus-8 (HHV-8)-negative, idiopathic multicentric Castleman disease (iMCD) is a rare and life-threatening disorder involving systemic inflammatory symptoms, polyclonal lymphoproliferation, cytopenias, and multiple organ system dysfunction caused by a cytokine storm often including interleukin-6. iMCD accounts for one third to one half of all cases of MCD and can occur in individuals of any age. Accurate diagnosis is challenging, because no standard diagnostic criteria or diagnostic biomarkers currently exist, and there is significant overlap with malignant, autoimmune, and infectious disorders. An international working group comprising 34 pediatric and adult pathology and clinical experts in iMCD and related disorders from 8 countries, including 2 physicians that are also iMCD patients, was convened to establish iMCD diagnostic criteria. The working group reviewed data from 244 cases, met twice, and refined criteria over 15 months (June 2015 to September 2016). The proposed consensus criteria require both Major Criteria (characteristic lymph node histopathology and multicentric lymphadenopathy), at least 2 of 11 Minor Criteria with at least 1 laboratory abnormality, and exclusion of infectious, malignant, and autoimmune disorders that can mimic iMCD. Characteristic histopathologic features may include a constellation of regressed or hyperplastic germinal centers, follicular dendritic cell prominence, hypervascularization, and polytypic plasmacytosis. Laboratory and clinical Minor Criteria include elevated C-reactive protein or erythrocyte sedimentation rate, anemia, thrombocytopenia or thrombocytosis, hypoalbuminemia, renal dysfunction or proteinuria, polyclonal hypergammaglobulinemia, constitutional symptoms, hepatosplenomegaly, effusions or edema, eruptive cherry hemangiomatosis or violaceous papules, and lymphocytic interstitial pneumonitis. iMCD consensus diagnostic criteria will facilitate consistent diagnosis, appropriate treatment, and collaborative research.

APOBEC3A efficiently deaminates methylated, but not TET-oxidized, cytosine bases in DNA.

AID/APOBEC family enzymes are best known for deaminating cytosine bases to uracil in single-stranded DNA, with characteristic sequence preferences that can produce mutational signatures in targets such as retroviral and cancer cell genomes. These deaminases have also been proposed to function in DNA demethylation via deamination of either 5-methylcytosine (mC) or TET-oxidized mC bases (ox-mCs), which include 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine. One specific family member, APOBEC3A (A3A), has been shown to readily deaminate mC, raising the prospect of broader activity on ox-mCs. To investigate this claim, we developed a novel assay that allows for parallel profiling of activity on all modified cytosines. Our steady-state kinetic analysis reveals that A3A discriminates against all ox-mCs by >3700-fold, arguing that ox-mC deamination does not contribute substantially to demethylation. A3A is, by contrast, highly proficient at C/mC deamination. Under conditions of excess enzyme, C/mC bases can be deaminated to completion in long DNA segments, regardless of sequence context. Interestingly, under limiting A3A, the sequence preferences observed with targeting unmodified cytosine are further exaggerated when deaminating mC. Our study informs how methylation, oxidation, and deamination can interplay in the genome and suggests A3A's potential utility as a biotechnological tool to discriminate between cytosine modification states.

Plasma proteomics identifies a 'chemokine storm' in idiopathic multicentric Castleman disease.

Human Herpesvirus-8 (HHV-8)-negative/idiopathic multicentric Castleman disease (iMCD) is a poorly understood disease involving polyclonal lymphoproliferation with dysmorphic germinal centers, constitutional symptoms, and multi-organ failure. Patients can experience thrombocytopenia, anasarca, reticulin fibrosis, renal dysfunction, organomegaly, and normal immunoglobulin levels, - iMCD-TAFRO. Others experience thrombocytosis, milder effusions, and hypergammaglobulinemia, -iMCD-Not Otherwise Specified (iMCD-NOS). Though the etiology is unknown in both subtypes, iMCD symptoms and disease progression are believed to be driven by a cytokine storm, often including interleukin-6 (IL-6). However, approximately two-thirds of patients do not respond to anti-IL-6 therapy; alternative drivers and signaling pathways are not known for anti-IL-6 nonresponders. To identify potential mediators of iMCD pathogenesis, we quantified 1129 proteins in 13 plasma samples from six iMCD patients during flare and remission. The acute phase reactant NPS-PLA2 was the only significantly increased protein (P = .017); chemokines and complement were significantly enriched pathways. Chemokines represented the greatest proportion of upregulated cytokines, suggesting that iMCD involves a chemokine storm. The chemokine CXCL13, which is essential in homing B cells to germinal centers, was the most upregulated cytokine across all patients (log2 fold-change = 3.22). Expression of CXCL13 was also significantly increased in iMCD lymph node germinal centers compared to controls in a stromal meshwork pattern. We observed distinct proteomic profiles between the two iMCD-TAFRO patients, who both failed anti-IL-6-therapy, and the four iMCD-NOS patients, in whom all three treated with anti-IL-6-therapy responded, suggesting that differing mechanisms may exist. This study reveals proteomic differences between flare and remission and the potential to molecularly define iMCD subgroups.

DNA Methyltransferases Demonstrate Reduced Activity against Arabinosylcytosine: Implications for Epigenetic Instability in Acute Myeloid Leukemia.

Arabinosylcytosine (araC) is a mainstay in the initial treatment of acute myeloid leukemia (AML), although relapses are common. Given the recent recognition of altered DNA methylation patterns in relapsed AML, we considered whether araC, which acts by incorporation into DNA, could itself perturb methylation dynamics. To explore this possibility, we examined several DNA methyltransferases and find that araC embedded in DNA is consistently methylated with an efficiency diminished relative to that of deoxycytidine. Importantly, with the human maintenance methyltransferase DNMT1, the extent of araC methylation is reduced by more than ∼200-fold. These observations support a model whereby araC treatment may itself contribute to locus-specific, passive DNA demethylation in relapsed AML.

Tet2 Catalyzes Stepwise 5-Methylcytosine Oxidation by an Iterative and de novo Mechanism.

Modification of cytosine-guanine dinucleotides (CpGs) is a key part of mammalian epigenetic regulation and helps shape cellular identity. Tet enzymes catalyze stepwise oxidation of 5-methylcytosine (mC) in CpGs to 5-hydroxymethylcytosine (hmC), or onward to 5-formylcytosine (fC) or 5-carboxylcytosine (caC). The multiple mC oxidation products, while intricately linked, are postulated to play independent epigenetic roles, making it critical to understand how the products of stepwise oxidation are established and maintained. Using highly sensitive isotope-based studies, we newly show that Tet2 can yield fC and caC by iteratively acting in a single encounter with mC-containing DNA, without release of the hmC intermediate, and that the modification state of the complementary CpG has little impact on Tet2 activity. By revealing Tet2 as an iterative, de novo mC oxygenase, our study provides insight into how features intrinsic to Tet2 shape the epigenetic landscape.

HHV-8-negative, idiopathic multicentric Castleman disease: novel insights into biology, pathogenesis, and therapy.

Multicentric Castleman's disease (MCD) describes a heterogeneous group of disorders involving proliferation of morphologically benign lymphocytes due to excessive proinflammatory hypercytokinemia, most notably of interleukin-6. Patients demonstrate intense episodes of systemic inflammatory symptoms, polyclonal lymphocyte and plasma cell proliferation, autoimmune manifestations, and organ system impairment. Human herpes virus-8 (HHV-8) drives the hypercytokinemia in all HIV-positive patients and some HIV-negative patients. There is also a group of HIV-negative and HHV-8-negative patients with unknown etiology and pathophysiology, which we propose referring to as idiopathic MCD (iMCD). Here, we synthesize what is known about iMCD pathogenesis, present a new subclassification system, and propose a model of iMCD pathogenesis. MCD should be subdivided into HHV-8-associated MCD and HHV-8-negative MCD or iMCD. The lymphocyte proliferation, histopathology, and systemic features in iMCD are secondary to hypercytokinemia, which can occur with several other diseases. We propose that 1 or more of the following 3 candidate processes may drive iMCD hypercytokinemia: systemic inflammatory disease mechanisms via autoantibodies or inflammatory gene mutations, paraneoplastic syndrome mechanisms via ectopic cytokine secretion, and/or a non-HHV-8 virus. Urgent priorities include elucidating the process driving iMCD hypercytokinemia, identifying the hypercytokine-secreting cell, developing consensus criteria for diagnosis, and building a patient registry to track cases.

Clinicopathologic analysis of TAFRO syndrome demonstrates a distinct subtype of HHV-8-negative multicentric Castleman disease.

Multicentric Castleman disease (MCD) describes a heterogeneous group of disorders involving systemic inflammation, characteristic lymph node histopathology, and multi-organ dysfunction because of pathologic hypercytokinemia. Whereas Human Herpes Virus-8 (HHV-8) drives the hypercytokinemia in a cohort of immunocompromised patients, the etiology of HHV-8-negative MCD is idiopathic (iMCD). Recently, a limited series of iMCD cases in Japan sharing a constellation of clinical features, including thrombocytopenia (T), anasarca (A), fever (F), reticulin fibrosis (R), and organomegaly (O) has been described as TAFRO syndrome. Herein, we report clinicopathological findings on 25 patients (14 males and 11 females; 23 Japanese-born and two US-born), the largest TAFRO syndrome case series, including the first report of cases from the USA. The median age of onset was 50 years old (range: 23-72). The frequency of each feature was as follows: thrombocytopenia (21/25), anasarca (24/25), fever (21/25), organomegaly (25/25), and reticulin fibrosis (13/16). These patients frequently demonstrated abdominal pain, elevated serum alkaline phosphatase levels, and acute kidney failure. Surprisingly, none of the cases demonstrated marked hypergammoglobulinemia, which is frequently reported in iMCD. Lymph node biopsies revealed atrophic germinal centers with enlarged nuclei of endothelial cells and proliferation of endothelial venules in interfollicular zone. 23 of 25 cases were treated initially with corticosteroids; 12 patients responded poorly and required further therapy. Three patients died during the observation period (median: 9 months) because of disease progression or infections. TAFRO syndrome is a unique subtype of iMCD that demonstrates characteristic clinicopathological findings. Further study to clarify prognosis, pathophysiology, and appropriate treatment is needed.

Nucleic acid determinants for selective deamination of DNA over RNA by activation-induced deaminase.

Activation-induced deaminase (AID), a member of the larger AID/APOBEC family, is the key catalyst in initiating antibody somatic hypermutation and class-switch recombination. The DNA deamination model accounting for AID's functional role posits that AID deaminates genomic deoxycytosine bases within the immunoglobulin locus, activating downstream repair pathways that result in antibody maturation. Although this model is well supported, the molecular basis for AID's selectivity for DNA over RNA remains an open and pressing question, reflecting a broader need to elucidate how AID/APOBEC enzymes engage their substrates. To address these questions, we have synthesized a series of chimeric nucleic acid substrates and characterized their reactivity with AID. These chimeric substrates feature targeted variations at the 2'-position of nucleotide sugars, allowing us to interrogate the steric and conformational basis for nucleic acid selectivity. We demonstrate that modifications to the target nucleotide can significantly alter AID's reactivity. Strikingly, within a substrate that is otherwise DNA, a single RNA-like 2'-hydroxyl substitution at the target cytosine is sufficient to compromise deamination. Alternatively, modifications that favor a DNA-like conformation (or sugar pucker) are compatible with deamination. AID's closely related homolog APOBEC1 is similarly sensitive to RNA-like substitutions at the target cytosine. Inversely, with unreactive 2'-fluoro-RNA substrates, AID's deaminase activity was rescued by introducing a trinucleotide DNA patch spanning the target cytosine and two nucleotides upstream. These data suggest a role for nucleotide sugar pucker in explaining the molecular basis for AID's DNA selectivity and, more generally, suggest how other nucleic acid-modifying enzymes may distinguish DNA from RNA.

AID/APOBEC deaminases disfavor modified cytosines implicated in DNA demethylation.

Activation-induced deaminase (AID)/APOBEC-family cytosine deaminases, known to function in diverse cellular processes from antibody diversification to mRNA editing, have also been implicated in DNA demethylation, a major process for transcriptional activation. Although oxidation-dependent pathways for demethylation have been described, pathways involving deamination of either 5-methylcytosine (5mC) or 5-hydroxymethylcytosine (5hmC) have emerged as alternatives. Here we address the biochemical plausibility of deamination-coupled demethylation. We found that purified AID/APOBECs have substantially reduced activity on 5mC relative to cytosine, their canonical substrate, and no detectable deamination of 5hmC. This finding was explained by the reactivity of a series of modified substrates, where steric bulk was increasingly detrimental to deamination. Further, upon AID/APOBEC overexpression, the deamination product of 5hmC was undetectable in genomic DNA, whereas oxidation intermediates remained detectable. Our results indicate that the steric requirements for cytosine deamination are one intrinsic barrier to the proposed function of deaminases in DNA demethylation.

Metabolite profiling of human renal cell carcinoma reveals tissue-origin dominance in nutrient availability.

The tumor microenvironment is a determinant of cancer progression and therapeutic efficacy, with nutrient availability playing an important role. Although it is established that the local abundance of specific nutrients defines the metabolic parameters for tumor growth, the factors guiding nutrient availability in tumor compared to normal tissue and blood remain poorly understood. To define these factors in renal cell carcinoma (RCC), we performed quantitative metabolomic and comprehensive lipidomic analyses of tumor interstitial fluid (TIF), adjacent normal kidney interstitial fluid (KIF), and plasma samples collected from patients. TIF nutrient composition closely resembles KIF, suggesting that tissue-specific factors unrelated to the presence of cancer exert a stronger influence on nutrient levels than tumor-driven alterations. Notably, select metabolite changes consistent with known features of RCC metabolism are found in RCC TIF, while glucose levels in TIF are not depleted to levels that are lower than those found in KIF. These findings inform tissue nutrient dynamics in RCC, highlighting a dominant role of non-cancer-driven tissue factors in shaping nutrient availability in these tumors.

Cancer cells convert nutrients into energy differently compared to healthy cells. This difference in metabolism allows them to grow and divide more quickly and sometimes to migrate to different areas of the body. The environment around cancer cells ­ known as the tumor microenvironment ­ contains a variety of different cells and blood vessels, which are bathed in interstitial fluid. This microenvironment provides nutrients for the cancer cells to metabolize, and therefore influences how well a tumor grows and how it might respond to treatment. Recent advances with techniques such as mass spectrometry, which can measure the chemical composition of a substance, have allowed scientists to measure nutrient levels in the tumor microenvironments of mice. However, it has been more difficult to conduct such studies in humans, as well as to compare the tumor microenvironment to the healthy tissue the tumors arose from. Abbott, Ali, Reinfeld et al. aimed to fill this gap in knowledge by using mass spectrometry to measure the nutrient levels in the tumor microenvironment of 55 patients undergoing surgery to remove kidney tumors. Comparing the type and levels of nutrients in the tumor interstitial fluid, the neighboring healthy kidney and the blood showed that nutrients in the tumor and healthy kidney were more similar to each other than those in the blood. For example, both the tumor and healthy kidney interstitial fluids contained less glucose than the blood. However, the difference between nutrient composition in the tumor and healthy kidney interstitial fluids was insignificant, suggesting that the healthy kidney and its tumor share a similar environment. Taken together, the findings indicate that kidney cancer cells must adapt to the nutrients available in the kidney, rather than changing what nutrients are available in the tissue. Future studies will be required to investigate whether this finding also applies to other types of cancer. A better understanding of how cancer cells adapt to their environments may aid the development of drugs that aim to disrupt the metabolism of tumors.

Metabolite profiling of human renal cell carcinoma reveals tissue-origin dominance in nutrient availability.

The tumor microenvironment is a determinant of cancer progression and therapeutic efficacy, with nutrient availability playing an important role. Although it is established that the local abundance of specific nutrients defines the metabolic parameters for tumor growth, the factors guiding nutrient availability in tumor compared to normal tissue and blood remain poorly understood. To define these factors in renal cell carcinoma (RCC), we performed quantitative metabolomic and comprehensive lipidomic analyses of tumor interstitial fluid (TIF), adjacent normal kidney interstitial fluid (KIF), and plasma samples collected from patients. TIF nutrient composition closely resembles KIF, suggesting that tissue-specific factors unrelated to the presence of cancer exert a stronger influence on nutrient levels than tumor-driven alterations. Notably, select metabolite changes consistent with known features of RCC metabolism are found in RCC TIF, while glucose levels in TIF are not depleted to levels that are lower than those found in KIF. These findings inform tissue nutrient dynamics in RCC, highlighting a dominant role of non-cancer driven tissue factors in shaping nutrient availability in these tumors.

Spatial analysis of human lung cancer reveals organized immune hubs enriched for stem-like CD8 T cells and associated with immunotherapy response.

The organization of immune cells in human tumors is not well understood. Immunogenic tumors harbor spatially-localized multicellular 'immunity hubs' defined by expression of the T cell-attracting chemokines CXCL10/CXCL11 and abundant T cells. Here, we examined immunity hubs in human pre-immunotherapy lung cancer specimens, and found that they were associated with beneficial responses to PD-1-blockade. Immunity hubs were enriched for many interferon-stimulated genes, T cells in multiple differentiation states, and CXCL9/10/11 + macrophages that preferentially interact with CD8 T cells. Critically, we discovered the stem-immunity hub, a subtype of immunity hub strongly associated with favorable PD-1-blockade outcomes, distinct from mature tertiary lymphoid structures, and enriched for stem-like TCF7+PD-1+ CD8 T cells and activated CCR7 + LAMP3 + dendritic cells, as well as chemokines that organize these cells. These results elucidate the spatial organization of the human intratumoral immune response and its relevance to patient immunotherapy outcomes.

Histone Deacetylase 6 Inhibition Exploits Selective Metabolic Vulnerabilities in LKB1 Mutant, KRAS Driven NSCLC.

INTRODUCTION: In KRAS-mutant NSCLC, co-occurring alterations in LKB1 confer a negative prognosis compared with other mutations such as TP53. LKB1 is a tumor suppressor that coordinates several signaling pathways in response to energetic stress. Our recent work on pharmacologic and genetic inhibition of histone deacetylase 6 (HDAC6) revealed the impaired activity of numerous enzymes involved in glycolysis. On the basis of these previous findings, we explored the therapeutic window for HDAC6 inhibition in metabolically-active KRAS-mutant lung tumors. METHODS: Using cell lines derived from mouse autochthonous tumors bearing the KRAS/LKB1 (KL) and KRAS/TP53 mutant genotypes to control for confounding germline and somatic mutations in human models, we characterize the metabolic phenotypes at baseline and in response to HDAC6 inhibition. The impact of HDAC6 inhibition was measured on cancer cell growth in vitro and on tumor growth in vivo. RESULTS: Surprisingly, KL-mutant cells revealed reduced levels of redox-sensitive cofactors at baseline. This is associated with increased sensitivity to pharmacologic HDAC6 inhibition with ACY-1215 and blunted ability to increase compensatory metabolism and buffer oxidative stress. Seeking synergistic metabolic combination treatments, we found enhanced cell killing and antitumor efficacy with glutaminase inhibition in KL lung cancer models in vitro and in vivo. CONCLUSIONS: Exploring the differential metabolism of KL and KRAS/TP53-mutant NSCLC, we identified decreased metabolic reserve in KL-mutant tumors. HDAC6 inhibition exploited a therapeutic window in KL NSCLC on the basis of a diminished ability to compensate for impaired glycolysis, nominating a novel strategy for the treatment of KRAS-mutant NSCLC with co-occurring LKB1 mutations.

Ebolavirus proteins suppress the effects of small interfering RNA by direct interaction with the mammalian RNA interference pathway.

Cellular RNA interference (RNAi) provides a natural response against viral infection, but some viruses have evolved mechanisms to antagonize this form of antiviral immunity. To determine whether Ebolavirus (EBOV) counters RNAi by encoding suppressors of RNA silencing (SRSs), we screened all EBOV proteins using an RNAi assay initiated by exogenously delivered small interfering RNAs (siRNAs) against either an EBOV or a reporter gene. In addition to viral protein 35 (VP35), we found that VP30 and VP40 independently act as SRSs. Here, we present the molecular mechanisms of VP30 and VP35. VP30 interacts with Dicer independently of siRNA and with one Dicer partner, TRBP, only in the presence of siRNA. VP35 directly interacts with Dicer partners TRBP and PACT in an siRNA-independent fashion and in the absence of effects on interferon (IFN). Taken together, our findings elucidate a new mechanism of RNAi suppression that extends beyond the role of SRSs in double-stranded RNA (dsRNA) binding and IFN antagonism. The presence of three suppressors highlights the relevance of host RNAi-dependent antiviral immunity in EBOV infection and illustrates the importance of RNAi in shaping the evolution of RNA viruses.