Discovery of natural-product-derived sequanamycins as potent oral anti-tuberculosis agents.

The emergence of drug-resistant tuberculosis has created an urgent need for new anti-tubercular agents. Here, we report the discovery of a series of macrolides called sequanamycins with outstanding in vitro and in vivo activity against Mycobacterium tuberculosis (Mtb). Sequanamycins are bacterial ribosome inhibitors that interact with the ribosome in a similar manner to classic macrolides like erythromycin and clarithromycin, but with binding characteristics that allow them to overcome the inherent macrolide resistance of Mtb. Structures of the ribosome with bound inhibitors were used to optimize sequanamycin to produce the advanced lead compound SEQ-9. SEQ-9 was efficacious in mouse models of acute and chronic TB as a single agent, and it demonstrated bactericidal activity in a murine TB infection model in combination with other TB drugs. These results support further investigation of this series as TB clinical candidates, with the potential for use in new regimens against drug-susceptible and drug-resistant TB.

How Far Can Life Cycle Assessment Be Simplified? A Protocol to Generate Simple and Accurate Models for the Assessment of Energy Systems and Its Application to Heat Production from Enhanced Geothermal Systems.

Life cycle assessments (LCAs) quantify environmental impacts of systems and support decision-making processes. LCAs are however time-consuming and difficult to conduct for nonexperts, thus calling for simplified approaches for multicriteria environmental assessments. In this paper, a five-step protocol is presented to generate simplified arithmetic equations from a reference parametrized LCA model of an energy system and its application illustrated for an enhanced geothermal system for heat generation with very low direct emissions in continental Europe. The simplified models estimate seven environmental impacts (climate change, freshwater ecotoxicity, human health, minerals and metals, and fossil resources depletion, and acidification) based on six technological parameters: number of injection and production wells, power of the production and injection pump, average well length, thermal power output, and eight background parameters defining the European electricity mix. A global sensitivity analysis identified these parameters as influencing the variance of the environmental impacts the most. Ensuring the representativeness of the reference LCA model and the validity of the simplified models requires thorough assessment. This protocol allows to develop relevant alternatives to detailed LCAs for quick and multicriteria environmental impact assessments of energy systems, showing that LCAs can be simplified to system-specific equations based on few, easily quantified, parameters.

From LCAs to simplified models: a generic methodology applied to wind power electricity.

This study presents a generic methodology to produce simplified models able to provide a comprehensive life cycle impact assessment of energy pathways. The methodology relies on the application of global sensitivity analysis to identify key parameters explaining the impact variability of systems over their life cycle. Simplified models are built upon the identification of such key parameters. The methodology is applied to one energy pathway: onshore wind turbines of medium size considering a large sample of possible configurations representative of European conditions. Among several technological, geographical, and methodological parameters, we identified the turbine load factor and the wind turbine lifetime as the most influent parameters. Greenhouse Gas (GHG) performances have been plotted as a function of these key parameters identified. Using these curves, GHG performances of a specific wind turbine can be estimated, thus avoiding the undertaking of an extensive Life Cycle Assessment (LCA). This methodology should be useful for decisions makers, providing them a robust but simple support tool for assessing the environmental performance of energy systems.

Endosome-to-cytosol transport of viral nucleocapsids.

During viral infection, fusion of the viral envelope with endosomal membranes and nucleocapsid release were thought to be concomitant events. We show here that for the vesicular stomatitis virus they occur sequentially, at two successive steps of the endocytic pathway. Fusion already occurs in transport intermediates between early and late endosomes, presumably releasing the nucleocapsid within the lumen of intra-endosomal vesicles, where it remains hidden. Transport to late endosomes is then required for the nucleocapsid to be delivered to the cytoplasm. This last step, which initiates infection, depends on the late endosomal lipid lysobisphosphatidic acid (LBPA) and its putative effector Alix/AIP1, and is regulated by phosphatidylinositol-3-phosphate (PtdIns3P) signalling via the PtdIns3P-binding protein Snx16. We conclude that the nucleocapsid is exported into the cytoplasm after the back-fusion of internal vesicles with the limiting membrane of late endosomes, and that this process is controlled by the phospholipids LBPA and PtdIns3P and their effectors.

Global trends of whole-genome duplications revealed by the ciliate Paramecium tetraurelia.

The duplication of entire genomes has long been recognized as having great potential for evolutionary novelties, but the mechanisms underlying their resolution through gene loss are poorly understood. Here we show that in the unicellular eukaryote Paramecium tetraurelia, a ciliate, most of the nearly 40,000 genes arose through at least three successive whole-genome duplications. Phylogenetic analysis indicates that the most recent duplication coincides with an explosion of speciation events that gave rise to the P. aurelia complex of 15 sibling species. We observed that gene loss occurs over a long timescale, not as an initial massive event. Genes from the same metabolic pathway or protein complex have common patterns of gene loss, and highly expressed genes are over-retained after all duplications. The conclusion of this analysis is that many genes are maintained after whole-genome duplication not because of functional innovation but because of gene dosage constraints.

Targeting Tumor Angiogenesis with the Selective VEGFR-3 Inhibitor EVT801 in Combination with Cancer Immunotherapy.

The receptor tyrosine kinase VEGFR-3 plays a crucial role in cancer-induced angiogenesis and lymphangiogenesis, promoting tumor development and metastasis. Here, we report the novel VEGFR-3 inhibitor EVT801 that presents a more selective and less toxic profile than two major inhibitors of VEGFRs (i.e., sorafenib and pazopanib). As monotherapy, EVT801 showed a potent antitumor effect in VEGFR-3-positive tumors, and in tumors with VEGFR-3-positive microenvironments. EVT801 suppressed VEGF-C-induced human endothelial cell proliferation in vitro and tumor (lymph)angiogenesis in different tumor mouse models. In addition to reduced tumor growth, EVT801 decreased tumor hypoxia, favored sustained tumor blood vessel homogenization (i.e., leaving fewer and overall larger vessels), and reduced important immunosuppressive cytokines (CCL4, CCL5) and myeloid-derived suppressor cells (MDSC) in circulation. Furthermore, in carcinoma mouse models, the combination of EVT801 with immune checkpoint therapy (ICT) yielded superior outcomes to either single treatment. Moreover, tumor growth inhibition was inversely correlated with levels of CCL4, CCL5, and MDSCs after treatment with EVT801, either alone or combined with ICT. Taken together, EVT801 represents a promising anti(lymph)angiogenic drug for improving ICT response rates in patients with VEGFR-3 positive tumors. Significance: The VEGFR-3 inhibitor EVT801 demonstrates superior selectivity and toxicity profile than other VEGFR-3 tyrosine kinase inhibitors. EVT801 showed potent antitumor effects in VEGFR-3-positive tumors, and tumors with VEGFR-3-positive microenvironments through blood vessel homogenization, and reduction of tumor hypoxia and limited immunosuppression. EVT801 increases immune checkpoint inhibitors' antitumor effects.

Bactericidal Disruption of Magnesium Metallostasis in Mycobacterium tuberculosis Is Counteracted by Mutations in the Metal Ion Transporter CorA.

A defining characteristic of treating tuberculosis is the need for prolonged administration of multiple drugs. This may be due in part to subpopulations of slowly replicating or nonreplicating Mycobacterium tuberculosis bacilli exhibiting phenotypic tolerance to most antibiotics in the standard treatment regimen. Confounding this problem is the increasing incidence of heritable multidrug-resistant M. tuberculosis A search for new antimycobacterial chemical scaffolds that can kill phenotypically drug-tolerant mycobacteria uncovered tricyclic 4-hydroxyquinolines and a barbituric acid derivative with mycobactericidal activity against both replicating and nonreplicating M. tuberculosis Both families of compounds depleted M. tuberculosis of intrabacterial magnesium. Complete or partial resistance to both chemotypes arose from mutations in the putative mycobacterial Mg2+/Co2+ ion channel, CorA. Excess extracellular Mg2+, but not other divalent cations, diminished the compounds' cidality against replicating M. tuberculosis These findings establish depletion of intrabacterial magnesium as an antimicrobial mechanism of action and show that M. tuberculosis magnesium homeostasis is vulnerable to disruption by structurally diverse, nonchelating, drug-like compounds.IMPORTANCE Antimycobacterial agents might shorten the course of treatment by reducing the number of phenotypically tolerant bacteria if they could kill M. tuberculosis in diverse metabolic states. Here we report two chemically disparate classes of agents that kill M. tuberculosis both when it is replicating and when it is not. Under replicating conditions, the tricyclic 4-hydroxyquinolines and a barbituric acid analogue deplete intrabacterial magnesium as a mechanism of action, and for both compounds, mutations in CorA, a putative Mg2+/Co2+ transporter, conferred resistance to the compounds when M. tuberculosis was under replicating conditions but not under nonreplicating conditions, illustrating that a given compound can kill M. tuberculosis in different metabolic states by disparate mechanisms. Targeting magnesium metallostasis represents a previously undescribed antimycobacterial mode of action that might cripple M. tuberculosis in a Mg2+-deficient intraphagosomal environment of macrophages.

Opposing reactions in coenzyme A metabolism sensitize Mycobacterium tuberculosis to enzyme inhibition.

Mycobacterium tuberculosis (Mtb) is the leading infectious cause of death in humans. Synthesis of lipids critical for Mtb's cell wall and virulence depends on phosphopantetheinyl transferase (PptT), an enzyme that transfers 4'-phosphopantetheine (Ppt) from coenzyme A (CoA) to diverse acyl carrier proteins. We identified a compound that kills Mtb by binding and partially inhibiting PptT. Killing of Mtb by the compound is potentiated by another enzyme encoded in the same operon, Ppt hydrolase (PptH), that undoes the PptT reaction. Thus, loss-of-function mutants of PptH displayed antimicrobial resistance. Our PptT-inhibitor cocrystal structure may aid further development of antimycobacterial agents against this long-sought target. The opposing reactions of PptT and PptH uncover a regulatory pathway in CoA physiology.

Desensitization of platelet-derived growth factor receptor-beta by oxidized lipids in vascular cells and atherosclerotic lesions: prevention by aldehyde scavengers.

The platelet-derived growth factor receptor-beta (PDGFRbeta) signaling pathway regulates smooth muscle cell (SMC) migration and proliferation and plays a role in the vascular wall response to injury. Oxidized low-density lipoprotein (oxLDL) in atherosclerotic lesions can activate the PDGFRbeta pathway, but the long-term effects of oxLDL on PDGFRbeta function are not well understood. We found that oxLDL induced a dual effect on PDGFRbeta signaling. Initial activation of the PDGFR was followed by desensitization of the receptor. PDGFRbeta desensitization was not attributable to PDGFRbeta degradation or changes in localization to the caveolae but instead resulted from decreased PDGF binding and inhibition of PDGFRbeta tyrosine kinase activity. This inhibition was associated with formation of (4HNE)- and acrolein-PDGFRbeta adducts and was mimicked by preincubation of cells with 4HNE. These PDGFRbeta adducts were also detected in aortae of apolipoprotein-deficient mice and hypercholesterolemic rabbits and in human carotid plaques. The aldehyde scavengers DNPH and Hydralazine prevented both oxLDL- and 4HNE-induced structural modification and PDGFRbeta signaling dysfunction in cells and in vivo. OxLDL inhibition of PDGF signaling may contribute to defective SMC proliferation and decrease the stability of a vulnerable plaque.

High coding density on the largest Paramecium tetraurelia somatic chromosome.

Paramecium, like other ciliates, remodels its entire germline genome at each sexual generation to produce a somatic genome stripped of transposons and other multicopy elements. The germline chromosomes are fragmented by a DNA elimination process that targets heterochromatin to give a reproducible set of some 200 linear molecules 50 kb to 1 Mb in size. These chromosomes are maintained at a ploidy of 800n in the somatic macronucleus and assure all gene expression. We isolated and sequenced the largest megabase somatic chromosome in order to explore its organization and gene content. The AT-rich (72%) chromosome is compact, with very small introns (average size 25 nt), short intergenic regions (median size 202 nt), and a coding density of at least 74%, higher than that reported for budding yeast (70%) or any other free-living eukaryote. Similarity to known proteins could be detected for 57% of the 460 potential protein coding genes. Thirty-two of the proteins are shared with vertebrates but absent from yeast, consistent with the morphogenetic complexity of Paramecium, a long-standing model for differentiated functions shared with metazoans but often absent from simpler eukaryotes. Extrapolation to the whole genome suggests that Paramecium has at least 30,000 genes.

LCA of emerging technologies: addressing high uncertainty on inputs' variability when performing global sensitivity analysis.

In the life cycle assessment (LCA) context, global sensitivity analysis (GSA) has been identified by several authors as a relevant practice to enhance the understanding of the model's structure and ensure reliability and credibility of the LCA results. GSA allows establishing a ranking among the input parameters, according to their influence on the variability of the output. Such feature is of high interest in particular when aiming at defining parameterized LCA models. When performing a GSA, the description of the variability of each input parameter may affect the results. This aspect is critical when studying new products or emerging technologies, where data regarding the model inputs are very uncertain and may cause misleading GSA outcomes, such as inappropriate input rankings. A systematic assessment of this sensitivity issue is now proposed. We develop a methodology to analyze the sensitivity of the GSA results (i.e. the stability of the ranking of the inputs) with respect to the description of such inputs of the model (i.e. the definition of their inherent variability). With this research, we aim at enriching the debate on the application of GSA to LCAs affected by high uncertainties. We illustrate its application with a case study, aiming at the elaboration of a simple model expressing the life cycle greenhouse gas emissions of enhanced geothermal systems (EGS) as a function of few key parameters. Our methodology allows identifying the key inputs of the LCA model, taking into account the uncertainty related to their description.

Two distinct calcium-dependent mitochondrial pathways are involved in oxidized LDL-induced apoptosis.

OBJECTIVE: Oxidized low-density lipoprotein (oxLDL)-induced apoptosis of vascular endothelial cells may contribute to plaque erosion and rupture. We aimed to clarify the relationship between the oxLDL-induced calcium signal and induction of apoptotic pathways. METHODS AND RESULTS: Apoptosis was evaluated by biochemical methods, including studies of enzyme activities, protein processing, release of proapoptotic factors, chromatin cleavage, and especially by morphological methods that evaluate apoptosis/necrosis by SYTO-13/propidium iodide fluorescent labeling. The oxLDL-induced sustained calcium rise activated 2 distinct calcium-dependent mitochondrial apoptotic pathways in human microvascular endothelial cells. OxLDLs induced calpain activation and subsequent Bid cleavage and cytochrome C release, which were blocked by calpeptin. Cyclosporin-A inhibited cytochrome C release, possibly by inhibiting the opening of the mitochondrial permeability transition pore (mPTP). Calcineurin, another cyclosporin-sensitive step, was not implicated, because oxLDLs inhibited calcineurin and FK-506 treatment was ineffective. Cytochrome C release in turn induced caspase-3 activation. In addition, oxLDLs triggered release and nuclear translocation of mitochondrial apoptosis-inducing factor through a mechanism dependent on calcium but independent of calpains, mPTP, and caspases. CONCLUSIONS: OxLDL-induced apoptosis involves 2 distinct calcium-dependent pathways, the first mediated by calpain/mPTP/cytochrome C/caspase-3 and the second mediated by apoptosis-inducing factor, which is cyclosporin-insensitive and caspase-independent.

Mildly oxidized LDL particle subspecies are distinct in their capacity to induce apoptosis in endothelial cells: role of lipid hydroperoxides.

The risk of atherosclerosis is intimately related to the heterogeneity of low-density lipoprotein (LDL) particles. The potential relationship between oxidative modification of distinct LDL subspecies and induction of apoptosis in arterial wall cells is indeterminate. The capacity of light LDL3 versus dense LDL5 to induce cytotoxicity in endothelial cells as a function of the degree of copper-mediated oxidation was compared. Mildly oxidized LDL3 (oxLDL3) exerted potent cytotoxicity, which was intimately related to both the degree of oxidation and the oxLDL3 concentration based on either cholesterol content or particle number. In contrast, dense LDL5 particles exerted a minor effect on cell viability. Cells incubated with oxLDL3 exhibited apoptotic features, with cytoplasmic condensation, cell or nuclear fragmentation, and accumulation of DNA fragments. OxLDL3-induced apoptosis involved cytoplasmic release of cytochrome c, with a concomitant increase in caspase-3-like protease activity. OxLDL3 particles were uniquely distinct from oxLDL5 particles in their elevated content of lipid hydroperoxides. Hydroperoxide removal by NaBH4 markedly reduced oxLDL3-induced cytotoxicity, leading to an increase in cell viability. Lipid hydroperoxide content of oxidatively modified LDL subclasses is therefore a major determinant of the induction of apoptosis in endothelial cells. These data are highly relevant to atherogenic hypercholesterolemia, in which the LDL phenotype is dominated by elevated concentrations of light LDL3.

Unusual pattern of Sonic hedgehog expression in the polydactylous mouse mutant Hemimelic extra-toes.

We have examined the dynamic expression of Sonic hedgehog (Shh) in limb buds of the Hemimelic extra-toes (Hx) mutant. An ectopic domain of expression appears in the limb bud at embryonic day 11.5, which is not restricted to the anterior mesenchyme as in other polydactylous mutants, but extends along the entire apical ectodermal ridge. No difference in expression was observed between heterozygotes and homozygotes. This ectopic expression domain forms later and is maintained longer than the normal one. We verified that the Shh signal is properly transduced in the ectopic expression domain by analysing the expression of downstream target genes and provide evidence that the ectopic domain is functional. Interactions between Msx1 and Hx were investigated by constructing a double mutant strain. Embryos from this strain exhibit little difference in Shh expression compared to Hx simple mutants. However, homozygous Msx1/Hx double mutants exhibit a postaxial polydactyly at birth, demonstrating that the two genes interact.

Oxidized LDL and 4-hydroxynonenal modulate tyrosine kinase receptor activity.

Among the diverse risk factors involved in atherosclerosis, LDL are thought to become atherogenic after undergoing oxidative modifications, characterized by oxidized lipid formation and structural alterations of apoB. Oxidized LDL alter various signaling pathways and exhibit a broad range of biological responses including inflammation, gene expression, cell proliferation or apoptosis. The biological effects of oxidized LDL are related to the presence of peroxidation products such as hydroperoxides, lysophosphatidylcholines, oxysterols and aldehydes.4-Hydroxynonenal (HNE) is one of the most abundant aldehydes formed during the oxidation of polyunsaturated fatty acids in LDL and in membranes. It is able to react with thiols and free amino group residues of proteins. HNE is involved in apoB modifications that alter LDL metabolism and cell protein-adduct formation which may mediate in part the biological effects of oxidized LDL. We report here that HNE delivered to cells by oxidized LDL reacts with cellular proteins, for instance with tyrosine kinase receptors (RTK) such as EGFR and PDGFR. HNE induces in vitro derivatization and tyrosine phosphorylation of RTK (the fine molecular mechanism and conformational changes remain to be elucidated). In intact living cells, oxidized LDL (and pure HNE) trigger HNE-adduct formation and activation of PDGFR and EGFR, through an antioxidant-insensitive and reactive oxygen species independent mechanism. The presence of HNE-PDGFR adducts in atherosclerotic areas lead one to hypothesize that oxidized lipids may also react in vivo with membrane RTK, thereby disturbing their cellular functions.

[Juvenile polyposis coli. The usefulness of a genetic study and the role of surgical treatment]. / Polypose juvénile familiale. Intérêt de l'etude génétique et place du traitement chirurgical.

We report two cases of familial juvenile polyposis coli. SMAD4 gene mutation was found in our two patients, leading to the definite diagnosis. Colonic cancer occurred in the first patient. Long-term outcome was favorable after colectomy. In the second patient, prophylactic total colectomy was performed. Rectal bleeding, diarrhea, stomach obstruction and vomiting developed during the follow-up. Proctectomy, distal partial gastrectomy and total gastrectomy were successively performed.

Specific Inhibition of the VEGFR-3 Tyrosine Kinase by SAR131675 Reduces Peripheral and Tumor Associated Immunosuppressive Myeloid Cells.

Myeloid derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) represent prominent components in cancer progression. We previously showed that inhibition of the VEGFR-3 pathway by SAR131675 leads to reduction of TAM infiltration and tumor growth. Here, we found that treatment with SAR131675 prevents the accumulation of immunosuppressive blood and splenic MDSCs which express VEGFR-3, in 4T1 tumor bearing mice. Moreover we showed that soluble factors secreted by tumor cells promote MDSCs proliferation and differentiation into M2 polarized F4/80+ macrophages. In addition, cell sorting and transcriptomic analysis of tumor infiltrating myeloid cells revealed the presence of a heterogeneous population that could be divided into 3 subpopulations: (i) immature cells with a MDSC phenotype (GR1+/CD11b+/F4/80-); (ii) "immuno-incompetent" macrophages (F4/80high/CD86neg/MHCIILow) strongly expressing M2 markers such as Legumain, CD206 and Mgl1/2 and (iii) "immuno-competent"-M1 like macrophages (F4/80Low/CD86+/MHCIIHigh). SAR131675 treatment reduced MDSCs in lymphoid organs as well as F4/80High populations in tumors. Interestingly, in the tumor SAR131675 was able to increase the immunocompetent M1 like population (F4/80low). Altogether these results demonstrate that the specific VEGFR-3 inhibitor SAR131675 exerts its anti tumoral activity by acting on different players that orchestrate immunosuppression and cancer progression in a tumoral context: MDSCs in peripheral lymphoid organs and TAMs infiltrating the tumor.

Inhibition of tumor angiogenesis and growth by a small-molecule multi-FGF receptor blocker with allosteric properties.

Receptor tyrosine kinases (RTK) are targets for anticancer drug development. To date, only RTK inhibitors that block orthosteric binding of ligands and substrates have been developed. Here, we report the pharmacologic characterization of the chemical SSR128129E (SSR), which inhibits fibroblast growth factor receptor (FGFR) signaling by binding to the extracellular FGFR domain without affecting orthosteric FGF binding. SSR exhibits allosteric properties, including probe dependence, signaling bias, and ceiling effects. Inhibition by SSR is highly conserved throughout the animal kingdom. Oral delivery of SSR inhibits arthritis and tumors that are relatively refractory to anti-vascular endothelial growth factor receptor-2 antibodies. Thus, orally-active extracellularly acting small-molecule modulators of RTKs with allosteric properties can be developed and may offer opportunities to improve anticancer treatment.

SAR131675, a potent and selective VEGFR-3-TK inhibitor with antilymphangiogenic, antitumoral, and antimetastatic activities.

SAR131675 is a potent and selective VEGFR-3 inhibitor. It inhibited VEGFR-3 tyrosine kinase activity and VEGFR-3 autophosphorylation in HEK cells with IC(50) values of 20 and 45 nmol/L, respectively. SAR131675 dose dependently inhibited the proliferation of primary human lymphatic cells, induced by the VEGFR-3 ligands VEGFC and VEGFD, with an IC(50) of about 20 nmol/L. SAR131675 was found to be highly selective for VEGFR-3 versus 107 receptors, enzymes, ion channels, and 65 kinases. However, it was moderately active on VEGFR-2 with a VEGFR-3/VEGFR-2 ratio of about 10. SAR131675 had no antiproliferative activity on a panel of 30 tumors and primary cells, further showing its high specificity and indicating that SAR131675 is not a cytotoxic or cytostatic agent. SAR131675 was very well tolerated in mice and showed a potent antitumoral effect in several orthotopic and syngenic models, including mammary 4T1 carcinoma and RIP1.Tag2 tumors. Interestingly, it significantly reduced lymph node invasion and lung metastasis, showing its antilymphangiogenic activity in vivo. Moreover, treatment of mice before resection of 4T1 primary tumors was sufficient to prevent metastasis. Tumor-associated macrophages (TAM) play an important role in tumor growth and metastasis. The expression of VEGFR-3 on TAMs has been recently described. F4/80 immunostaining clearly showed that SAR131675 significantly reduced TAM infiltration and aggregation in 4T1 tumors. Taken together, SAR131675 is the first highly specific VEGFR-3-TK inhibitor described to date, displaying significant antitumoral and antimetastatic activities in vivo through inhibition of lymphangiogenesis and TAM invasion.

Late endosomal cholesterol accumulation leads to impaired intra-endosomal trafficking.

BACKGROUND: Pathological accumulation of cholesterol in late endosomes is observed in lysosomal storage diseases such as Niemann-Pick type C. We here analyzed the effects of cholesterol accumulation in NPC cells, or as phenocopied by the drug U18666A, on late endosomes membrane organization and dynamics. METHODOLOGY/PRINCIPAL FINDINGS: Cholesterol accumulation did not lead to an increase in the raft to non-raft membrane ratio as anticipated. Strikingly, we observed a 2-3 fold increase in the size of the compartment. Most importantly, properties and dynamics of late endosomal intralumenal vesicles were altered as revealed by reduced late endosomal vacuolation induced by the mutant pore-forming toxin ASSP, reduced intoxication by the anthrax lethal toxin and inhibition of infection by the Vesicular Stomatitis Virus. CONCLUSIONS/SIGNIFICANCE: These results suggest that back fusion of intralumenal vesicles with the limiting membrane of late endosomes is dramatically perturbed upon cholesterol accumulation.