7-Dehydrocholesterol is an endogenous suppressor of ferroptosis

Ferroptosis is a form of cell death that has received considerable attention not only as a means to eradicate defined tumour entities but also because it provides unforeseen insights into the metabolic adaptation that tumours exploit to counteract phospholipid oxidation1,2. Here, we identify proferroptotic activity of 7-dehydrocholesterol reductase (DHCR7) and an unexpected prosurvival function of its substrate, 7-dehydrocholesterol (7-DHC). Although previous studies suggested that high concentrations of 7-DHC are cytotoxic to developing neurons by favouring lipid peroxidation3, we now show that 7-DHC accumulation confers a robust prosurvival function in cancer cells. Because of its far superior reactivity towards peroxyl radicals, 7-DHC effectively shields (phospho)lipids from autoxidation and subsequent fragmentation. We provide validation in neuroblastoma and Burkitt's lymphoma xenografts where we demonstrate that the accumulation of 7-DHC is capable of inducing a shift towards a ferroptosis-resistant state in these tumours ultimately resulting in a more aggressive phenotype. Conclusively, our findings provide compelling evidence of a yet-unrecognized antiferroptotic activity of 7-DHC as a cell-intrinsic mechanism that could be exploited by cancer cells to escape ferroptosis.

LRP8-mediated selenocysteine uptake is a targetable vulnerability in MYCN-amplified neuroblastoma

Ferroptosis has emerged as an attractive strategy in cancer therapy. Understanding the operational networks regulating ferroptosis may unravel vulnerabilities that could be harnessed for therapeutic benefit. Using CRISPR-activation screens in ferroptosis hypersensitive cells, we identify the selenoprotein P (SELENOP) receptor, LRP8, as a key determinant protecting MYCN-amplified neuroblastoma cells from ferroptosis. Genetic deletion of LRP8 leads to ferroptosis as a result of an insufficient supply of selenocysteine, which is required for the translation of the antiferroptotic selenoprotein GPX4. This dependency is caused by low expression of alternative selenium uptake pathways such as system Xc- . The identification of LRP8 as a specific vulnerability of MYCN-amplified neuroblastoma cells was confirmed in constitutive and inducible LRP8 knockout orthotopic xenografts. These findings disclose a yet-unaccounted mechanism of selective ferroptosis induction that might be explored as a therapeutic strategy for high-risk neuroblastoma and potentially other MYCN-amplified entities.

A Dynamic rRNA Ribomethylome Drives Stemness in Acute Myeloid Leukemia

The development and regulation of malignant self-renewal remain unresolved issues. Here, we provide biochemical, genetic, and functional evidence that dynamics in ribosomal RNA (rRNA) 2'-O-methylation regulate leukemia stem cell (LSC) activity in vivo. A comprehensive analysis of the rRNA 2'-O-methylation landscape of 94 patients with acute myeloid leukemia (AML) revealed dynamic 2'-O-methylation specifically at exterior sites of ribosomes. The rRNA 2'-O-methylation pattern is closely associated with AML development stage and LSC gene expression signature. Forced expression of the 2'-O-methyltransferase fibrillarin (FBL) induced an AML stem cell phenotype and enabled engraftment of non-LSC leukemia cells in NSG mice. Enhanced 2'-O-methylation redirected the ribosome translation program toward amino acid transporter mRNAs enriched in optimal codons and subsequently increased intracellular amino acid levels. Methylation at the single site 18S-guanosine 1447 was instrumental for LSC activity. Collectively, our work demonstrates that dynamic 2'-O-methylation at specific sites on rRNAs shifts translational preferences and controls AML LSC self-renewal.

SIGNIFICANCE

We establish the complete rRNA 2'-O-methylation landscape in human AML. Plasticity of rRNA 2'-O-methylation shifts protein translation toward an LSC phenotype. This dynamic process constitutes a novel concept of how cancers reprogram cell fate and function. This article is highlighted in the In This Issue feature, p. 247.

Mitochondrial inhibitors circumvent adaptive resistance to venetoclax and cytarabine combination therapy in acute myeloid leukemia

Therapy resistance represents a major clinical challenge in acute myeloid leukemia (AML). Here we define a 'MitoScore' signature, which identifies high mitochondrial oxidative phosphorylation in vivo and in patients with AML. Primary AML cells with cytarabine (AraC) resistance and a high MitoScore relied on mitochondrial Bcl2 and were highly sensitive to venetoclax (VEN) + AraC (but not to VEN + azacytidine). Single-cell transcriptomics of VEN + AraC-residual cell populations revealed adaptive resistance associated with changes in oxidative phosphorylation, electron transport chain complex and the TP53 pathway. Accordingly, treatment of VEN + AraC-resistant AML cells with electron transport chain complex inhibitors, pyruvate dehydrogenase inhibitors or mitochondrial ClpP protease agonists substantially delayed relapse following VEN + AraC. These findings highlight the central role of mitochondrial adaptation during AML therapy and provide a scientific rationale for alternating VEN + azacytidine with VEN + AraC in patients with a high MitoScore and to target mitochondrial metabolism to enhance the sensitivity of AML cells to currently approved therapies.

Bladder cancer incidence and predictions: Observational Study (Monastir, Tunisia: (2002-2030)

Background

Bladder cancer is a highly prevalent disease and is associated with substantial morbidity, mortality if not treated optimally. We aimed to describe bladder cancer incidence and trends from 2002 to 2013 and to estimate predictions up to 2030.

Methods

We performed an observational study from 2002 to 2013. Incidence was estimated by the crude incidence rate (CIR) and standardized incidence rate (SIR). Poisson regression model was used to calculate the slope 'b' in order to describe trends and was performed to estimate incidence projection for 2030. Data were verified and analyzed using IBM SPSS Statistics version 22.0 software.

Results

A total of 1024 cases of bladder cancer was declared from 2002 to 2013 predominately among males with a rate of 90.4%. CIR was 16.79/100,000 inhabitants (inh) and SIR was 21.38/100,000 inh. By gender, SIR was 41.3/100,000 inh and 7.73/100,000 inh for males and females respectively. During our study period a significant positive trend was noted with a (b = 0.042, p < 10-4). In 2030, the predicted incidence rate would increase to 28.4/100,000 inh.

Conclusions

The findings have highlighted the positive trend and the increased predicted incidence of bladder cancer in 2030. Thus, developing primary prevention strategies is crucial.

Key messages

Our results are important for health-care professionals to improve planning policies related to bladder cancer. Identifying associated factors is crucial to guide preventive strategies measures.

Prostate cancer incidence and predictions: Observational Study (Monastir, Tunisia: 2002-2030)

Introduction

Cancer is an eminent public health issue in the developing countries. The risk factors incriminated in cancer higher incidence are multiple such as the growing population rates, increasing tobacco consumption, the changes of diet and lifestyle. In Tunisia, there are three population-based cancer registries at the present time providing data on cancer incidence and survival. According to the data published by WHO International Agency for Research on Cancer (IACR) (GLOBOCAN 2018), prostate cancer in Tunisia ranks fifth among cancers with almost 819 new cases per year. The aim of this study was to we report trends in the cancer incidence during the span of time between 2002 and 2013 from the population-based cancer registry of the centre of Tunisia, and to predict the future number of cancer cases by 2030.

Methods

The cancer incidence data were collected from the Center cancer registries from 2003 to 2012.The data were stratified by cancer site, sex and age. We used SPSS software in order to calculate the crude incidence rates and age-standardized incidence rates. SPSS software was used in order to estimate the future number of cancer cases by 2030.

Results

A total of 725 cases of prostate cancer were enregistrated. The mean age of patients was 71.6 ±10.61years. The crude incidence rates were estimated 23.537. The standardized incidence rate was 33.92. A significant positive trend was noted with a b = 0133 and p < 10-3. 1033 new cases are predicted by 2030

Conclusions

The data of the cancer register of the center shows that the incidence of cancer is rising, and it is consistent with the National cancer intelligence, but some cancer incidence showed slightly higher, such as thyroid cancer and prostate cancer. In order to face this alarming situation, many preventive steps should be done such as strengthening early screening and diagnosis of cancer, improving clinical research in order to better control the risks factors.

Key messages

Prediction of the future number of cancer cases is of great interest to society. Prostate cancer in Tunisia ranks fifth among cancers.

Gastric cancer incidence and predictions: Observational Study (Monastir, Tunisia: 2002-2030)

Introduction

Gastric cancer is a major health burden worldwide. Based on GLOBOCAN 2018 data, stomach cancer is the fifth most common neoplasm and the third most deadly cancer, with an estimated 783,000 deaths in 2018. Unfortunately, only a few countries have set up extensive programs of early screening. In Tunisia the gastric cancer ranks among the ten most frequent cancers with more than 637 new cases per year. The aim of this study was to we report trends in the gastric cancer incidence during the span of time between 2002 and 2013 from the population-based cancer registry of the centre of Tunisia, and to predict the future number of cancer cases by 2030.

Methods

The cancer incidence data were collected from the cancer register of the Tunisian Center from 2003 to 2012.The data were stratified by cancer site, sex and age. We used SPSS software in order to calculate the crude incidence rates and standardized incidence rates. SPSS software was used in order to estimate the future number of cancer cases by 2030.

Results

During our study period, 326 cases of gastric cancer were observed. 53.1% of our patients were male with a sex ratio male to female 1.13.The crude incidence rates were 5.71 for male patients and 5.43 for females. The standardized incidence rates were 7.22 and 6.3 respectively for male and female patients. A stable trend was observed. Only 28 cases of gastric cancer are predicted by 2030.

Conclusions

Over the recent, there has been a slight decrease in gastric cancer rates. Many preventive steps should be encouraged in order to maintain this decreasing trend such as changing dietary habits by encouraging the consumption of fresh fruit and vegetables, as well as decreasing the use of tobacco and salt.

Key messages

Gastric cancer is a major health burden worldwide, only a few countries have set up extensive programs of early screening. Changingdietary habits by encouraging the consumption of fresh fruit and vegetables, as well as decreasing the use of tobacco and salt.

Extracellular ATP and CD39 Activate cAMP-Mediated Mitochondrial Stress Response to Promote Cytarabine Resistance in Acute Myeloid Leukemia

Relapses driven by chemoresistant leukemic cell populations are the main cause of mortality for patients with acute myeloid leukemia (AML). Here, we show that the ectonucleotidase CD39 (ENTPD1) is upregulated in cytarabine-resistant leukemic cells from both AML cell lines and patient samples in vivo and in vitro. CD39 cell-surface expression and activity is increased in patients with AML upon chemotherapy compared with diagnosis, and enrichment in CD39-expressing blasts is a marker of adverse prognosis in the clinics. High CD39 activity promotes cytarabine resistance by enhancing mitochondrial activity and biogenesis through activation of a cAMP-mediated adaptive mitochondrial stress response. Finally, genetic and pharmacologic inhibition of CD39 ecto-ATPase activity blocks the mitochondrial reprogramming triggered by cytarabine treatment and markedly enhances its cytotoxicity in AML cells in vitro and in vivo. Together, these results reveal CD39 as a new residual disease marker and a promising therapeutic target to improve chemotherapy response in AML. SIGNIFICANCE: Extracellular ATP and CD39-P2RY13-cAMP-OxPHOS axis are key regulators of cytarabine resistance, offering a new promising therapeutic strategy in AML.This article is highlighted in the In This Issue feature, p. 1426.

Targeting Myeloperoxidase Disrupts Mitochondrial Redox Balance and Overcomes Cytarabine Resistance in Human Acute Myeloid Leukemia

Chemotherapies alter cellular redox balance and reactive oxygen species (ROS) content. Recent studies have reported that chemoresistant cells have an increased oxidative state in hematologic malignancies. In this study, we demonstrated that chemoresistant acute myeloid leukemia (AML) cells had a lower level of mitochondrial and cytosolic ROS in response to cytarabine (AraC) and overexpressed myeloperoxidase (MPO), a heme protein that converts hydrogen peroxide to hypochlorous acid (HOCl), compared with sensitive AML cells. High MPO-expressing AML cells were less sensitive to AraC in vitro and in vivo. They also produced higher levels of HOCl and exhibited an increased rate of mitochondrial oxygen consumption when compared with low MPO-expressing AML cells. Targeting MPO expression or enzyme activity sensitized AML cells to AraC treatment by triggering oxidative damage and sustaining oxidative stress, particularly in high MPO-expressing AML cells. This sensitization stemmed from mitochondrial superoxide accumulation, which impaired oxidative phosphorylation and cellular energetic balance, driving apoptotic death and selective eradication of chemoresistant AML cells in vitro and in vivo. Altogether, this study uncovers a noncanonical function of MPO enzyme in maintaining redox balance and mitochondrial energetic metabolism, therefore affecting downstream pathways involved in AML chemoresistance. SIGNIFICANCE: These findings demonstrate the role of myeloperoxidase in the regulation of ROS levels and sensitivity of AML cells to cytarabine, an essential chemotherapeutic backbone in the therapy of AML.

Chemotherapy-Resistant Human Acute Myeloid Leukemia Cells Are Not Enriched for Leukemic Stem Cells but Require Oxidative Metabolism

Chemotherapy-resistant human acute myeloid leukemia (AML) cells are thought to be enriched in quiescent immature leukemic stem cells (LSC). To validate this hypothesis in vivo, we developed a clinically relevant chemotherapeutic approach treating patient-derived xenografts (PDX) with cytarabine (AraC). AraC residual AML cells are enriched in neither immature, quiescent cells nor LSCs. Strikingly, AraC-resistant preexisting and persisting cells displayed high levels of reactive oxygen species, showed increased mitochondrial mass, and retained active polarized mitochondria, consistent with a high oxidative phosphorylation (OXPHOS) status. AraC residual cells exhibited increased fatty-acid oxidation, upregulated CD36 expression, and a high OXPHOS gene signature predictive for treatment response in PDX and patients with AML. High OXPHOS but not low OXPHOS human AML cell lines were chemoresistant in vivo. Targeting mitochondrial protein synthesis, electron transfer, or fatty-acid oxidation induced an energetic shift toward low OXPHOS and markedly enhanced antileukemic effects of AraC. Together, this study demonstrates that essential mitochondrial functions contribute to AraC resistance in AML and are a robust hallmark of AraC sensitivity and a promising therapeutic avenue to treat AML residual disease.Significance: AraC-resistant AML cells exhibit metabolic features and gene signatures consistent with a high OXPHOS status. In these cells, targeting mitochondrial metabolism through the CD36-FAO-OXPHOS axis induces an energetic shift toward low OXPHOS and strongly enhanced antileukemic effects of AraC, offering a promising avenue to design new therapeutic strategies and fight AraC resistance in AML. Cancer Discov; 7(7); 716-35. ©2017 AACR.See related commentary by Schimmer, p. 670This article is highlighted in the In This Issue feature, p. 653.