Synthesis, Biological Evaluation and Docking Studies of Ring-Opened Analogues of Ipomoeassin F.

The plant-derived macrocyclic resin glycoside ipomoeassin F (Ipom-F) binds to Sec61α and significantly disrupts multiple aspects of Sec61-mediated protein biogenesis at the endoplasmic reticulum, ultimately leading to cell death. However, extensive assessment of Ipom-F as a molecular tool and a therapeutic lead is hampered by its limited production scale, largely caused by intramolecular assembly of the macrocyclic ring. Here, using in vitro and/or in cellula biological assays to explore the first series of ring-opened analogues for the ipomoeassins, and indeed all resin glycosides, we provide clear evidence that macrocyclic integrity is not required for the cytotoxic inhibition of Sec61-dependent protein translocation by Ipom-F. Furthermore, our modeling suggests that open-chain analogues of Ipom-F can interact with multiple sites on the Sec61α subunit, most likely located at a previously identified binding site for mycolactone and/or the so-called lateral gate. Subsequent in silico-aided design led to the discovery of the stereochemically simplified analogue 3 as a potent, alternative lead compound that could be synthesized much more efficiently than Ipom-F and will accelerate future ipomoeassin research in chemical biology and drug discovery. Our work may also inspire further exploration of ring-opened analogues of other resin glycosides.

Inhibition of the SEC61 translocon by mycolactone induces a protective autophagic response controlled by EIF2S1-dependent translation that does not require ULK1 activity.

The Mycobacterium ulcerans exotoxin, mycolactone, is responsible for the immunosuppression and tissue necrosis that characterizes Buruli ulcer. Mycolactone inhibits SEC61-dependent co-translational translocation of proteins into the endoplasmic reticulum and the resultant cytosolic translation triggers degradation of mislocalized proteins by the ubiquitin-proteasome system. Inhibition of SEC61 by mycolactone also activates multiple EIF2S1/eIF2α kinases in the integrated stress response (ISR). Here we show mycolactone increased canonical markers of selective macroautophagy/autophagy LC3B-II, ubiquitin and SQSTM1/p62 in diverse disease-relevant primary cells and cell lines. Increased formation of puncta positive for the early autophagy markers WIPI2, RB1CC1/FIP200 and ATG16L1 indicates increased initiation of autophagy. The mycolactone response was SEC61A1-dependent and involved a pathway that required RB1CC1 but not ULK. Deletion of Sqstm1 reduced cell survival in the presence of mycolactone, suggesting this response protects against the increased cytosolic protein burden caused by the toxin. However, reconstitution of baseline SQSTM1 expression in cells lacking all autophagy receptor proteins could not rescue viability. Translational regulation by EIF2S1 in the ISR plays a key role in the autophagic response to mycolactone. Mycolactone-dependent induction of SQSTM1 was reduced in eif2ak3-/-/perk-/- cells while the p-EIF2S1 antagonist ISRIB reversed the upregulation of SQSTM1 and reduced RB1CC1, WIPI2 and LC3B puncta formation. Increased SQSTM1 staining could be seen in Buruli ulcer patient skin biopsy samples, reinforcing genetic data that suggests autophagy is relevant to disease pathology. Since selective autophagy and the ISR are both implicated in neurodegeneration, cancer and inflammation, the pathway uncovered here may have a broad relevance to human disease.Abbreviations: ATF4: activating transcription factor 4; ATG: autophagy related; BAF: bafilomycin A1; ATG16L1: autophagy related 16 like 1; BU: Buruli ulcer; CQ: chloroquine; EIF2AK3: eukaryotic translation initiation factor 2 alpha kinase 3; CALCOCO2: calcium binding and coiled-coil domain 2; DMSO: dimethyl sulfoxide; EIF2S1: eukaryotic translation initiation factor 2 subunit alpha; ER: endoplasmic reticulum; GFP: green fluorescent protein; HDMEC: human dermal microvascular endothelial cells; HFFF: human fetal foreskin fibroblasts; ISR: integrated stress response; ISRIB: integrated stress response inhibitor; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MEF: mouse embryonic fibroblast; Myco: mycolactone; NBR1: NBR1 autophagy cargo receptor; NFE2L2: nuclear factor, erythroid 2 like 2; OPTN: optineurin; PFA: paraformaldehyde; PtdIns3P: phosphatidylinositol-3-phosphate; RB1CC1: RB1-inducible coiled coil 1; SQSTM1: sequestosome 1; TAX1BP1: Tax1 binding protein 1; ULK: unc-51 like autophagy activating kinase; UPS: ubiquitin-proteasome system; WIPI: WD repeat domain, phosphoinositide interacting; WT: wild type.

Murine Norovirus Infection Results in Anti-inflammatory Response Downstream of Amino Acid Depletion in Macrophages.

Murine norovirus (MNV) infection results in a late translation shutoff that is proposed to contribute to the attenuated and delayed innate immune response observed both in vitro and in vivo. Recently, we further demonstrated the activation of the α subunit of eukaryotic initiation factor 2 (eIF2α) kinase GCN2 during MNV infection, which has been previously linked to immunomodulation and resistance to inflammatory signaling during metabolic stress. While viral infection is usually associated with activation of double-stranded RNA (dsRNA) binding pattern recognition receptor PKR, we hypothesized that the establishment of a metabolic stress in infected cells is a proviral event, exploited by MNV to promote replication through weakening the activation of the innate immune response. In this study, we used multi-omics approaches to characterize cellular responses during MNV replication. We demonstrate the activation of pathways related to the integrated stress response, a known driver of anti-inflammatory phenotypes in macrophages. In particular, MNV infection causes an amino acid imbalance that is associated with GCN2 and ATF2 signaling. Importantly, this reprogramming lacks the features of a typical innate immune response, with the ATF/CHOP target GDF15 contributing to the lack of antiviral responses. We propose that MNV-induced metabolic stress supports the establishment of host tolerance to viral replication and propagation. IMPORTANCE During viral infection, host defenses are typically characterized by the secretion of proinflammatory autocrine and paracrine cytokines, potentiation of the interferon (IFN) response, and induction of the antiviral response via activation of JAK and Stat signaling. To avoid these and propagate, viruses have evolved strategies to evade or counteract host sensing. In this study, we demonstrate that murine norovirus controls the antiviral response by activating a metabolic stress response that activates the amino acid response and impairs inflammatory signaling. This highlights novel tools in the viral countermeasures arsenal and demonstrates the importance of the currently poorly understood metabolic reprogramming occurring during viral infections.

The One That Got Away: How Macrophage-Derived IL-1ß Escapes the Mycolactone-Dependent Sec61 Blockade in Buruli Ulcer.

Buruli ulcer (BU), caused by Mycobacterium ulcerans, is a devastating necrotizing skin disease. Key to its pathogenesis is mycolactone, the exotoxin virulence factor that is both immunosuppressive and cytotoxic. The discovery that the essential Sec61 translocon is the major cellular target of mycolactone explains much of the disease pathology, including the immune blockade. Sec61 inhibition leads to a loss in production of nearly all cytokines from monocytes, macrophages, dendritic cells and T cells, as well as antigen presentation pathway proteins and costimulatory molecules. However, there has long been evidence that the immune system is not completely incapable of responding to M. ulcerans infection. In particular, IL-1ß was recently shown to be present in BU lesions, and to be induced from M. ulcerans-exposed macrophages in a mycolactone-dependent manner. This has important implications for our understanding of BU, showing that mycolactone can act as the "second signal" for IL-1ß production without inhibiting the pathways of unconventional secretion it uses for cellular release. In this Perspective article, we validate and discuss this recent advance, which is entirely in-line with our understanding of mycolactone's inhibition of the Sec61 translocon. However, we also show that the IL-1 receptor, which uses the conventional secretory pathway, is sensitive to mycolactone blockade at Sec61. Hence, a more complete understanding of the mechanisms regulating IL-1ß function in skin tissue, including the transient intra-macrophage stage of M. ulcerans infection, is urgently needed to uncover the double-edged sword of IL-1ß in BU pathogenesis, treatment and wound healing.

Ipomoeassin F Binds Sec61α to Inhibit Protein Translocation.

Ipomoeassin F is a potent natural cytotoxin that inhibits growth of many tumor cell lines with single-digit nanomolar potency. However, its biological and pharmacological properties have remained largely unexplored. Building upon our earlier achievements in total synthesis and medicinal chemistry, we used chemical proteomics to identify Sec61α (protein transport protein Sec61 subunit alpha isoform 1), the pore-forming subunit of the Sec61 protein translocon, as a direct binding partner of ipomoeassin F in living cells. The interaction is specific and strong enough to survive lysis conditions, enabling a biotin analogue of ipomoeassin F to pull down Sec61α from live cells, yet it is also reversible, as judged by several experiments including fluorescent streptavidin staining, delayed competition in affinity pulldown, and inhibition of TNF biogenesis after washout. Sec61α forms the central subunit of the ER protein translocation complex, and the binding of ipomoeassin F results in a substantial, yet selective, inhibition of protein translocation in vitro and a broad ranging inhibition of protein secretion in live cells. Lastly, the unique resistance profile demonstrated by specific amino acid single-point mutations in Sec61α provides compelling evidence that Sec61α is the primary molecular target of ipomoeassin F and strongly suggests that the binding of this natural product to Sec61α is distinctive. Therefore, ipomoeassin F represents the first plant-derived, carbohydrate-based member of a novel structural class that offers new opportunities to explore Sec61α function and to further investigate its potential as a therapeutic target for drug discovery.

Megazol and its bioisostere 4H-1,2,4-triazole: comparing the trypanocidal, cytotoxic and genotoxic activities and their in vitro and in silico interactions with the Trypanosoma brucei nitroreductase enzyme

Megazol (7) is a 5-nitroimidazole that is highly active against Trypanosoma cruzi and Trypanosoma brucei, as well as drug-resistant forms of trypanosomiasis. Compound 7 is not used clinically due to its mutagenic and genotoxic properties, but has been largely used as a lead compound. Here, we compared the activity of 7 with its 4H-1,2,4-triazole bioisostere (8) in bloodstream forms of T. brucei and T. cruzi and evaluated their activation by T. brucei type I nitroreductase (TbNTR) enzyme. We also analysed the cytotoxic and genotoxic effects of these compounds in whole human blood using Comet and fluorescein diacetate/ethidium bromide assays. Although the only difference between 7 and 8 is the substitution of sulphur (in the thiadiazole in 7) for nitrogen (in the triazole in 8), the results indicated that 8 had poorer antiparasitic activity than 7 and was not genotoxic, whereas 7 presented this effect. The determination of Vmax indicated that although 8 was metabolised more rapidly than 7, it bounds to the TbNTR with better affinity, resulting in equivalent kcat/KM values. Docking assays of 7 and 8 performed within the active site of a homology model of the TbNTR indicating that 8 had greater affinity than 7.

The pathogenic mechanism of the Mycobacterium ulcerans virulence factor, mycolactone, depends on blockade of protein translocation into the ER.

Infection with Mycobacterium ulcerans is characterised by tissue necrosis and immunosuppression due to mycolactone, the necessary and sufficient virulence factor for Buruli ulcer disease pathology. Many of its effects are known to involve down-regulation of specific proteins implicated in important cellular processes, such as immune responses and cell adhesion. We have previously shown mycolactone completely blocks the production of LPS-dependent proinflammatory mediators post-transcriptionally. Using polysome profiling we now demonstrate conclusively that mycolactone does not prevent translation of TNF, IL-6 and Cox-2 mRNAs in macrophages. Instead, it inhibits the production of these, along with nearly all other (induced and constitutive) proteins that transit through the ER. This is due to a blockade of protein translocation and subsequent degradation of aberrantly located protein. Several lines of evidence support this transformative explanation of mycolactone function. First, cellular TNF and Cox-2 can be once more detected if the action of the 26S proteasome is inhibited concurrently. Second, restored protein is found in the cytosol, indicating an inability to translocate. Third, in vitro translation assays show mycolactone prevents the translocation of TNF and other proteins into the ER. This is specific as the insertion of tail-anchored proteins into the ER is unaffected showing that the ER remains structurally intact. Fourth, metabolic labelling reveals a near-complete loss of glycosylated and secreted proteins from treated cells, whereas cytosolic proteins are unaffected. Notably, the profound lack of glycosylated and secreted protein production is apparent in a range of different disease-relevant cell types. These studies provide a new mechanism underlying mycolactone's observed pathological activities both in vitro and in vivo. Mycolactone-dependent inhibition of protein translocation into the ER not only explains the deficit of innate cytokines, but also the loss of membrane receptors, adhesion molecules and T-cell cytokines that drive the aetiology of Buruli ulcer.

Patient attitudes towards chemotherapy and survival: a prospective observational study in advanced non-small cell lung cancer.

This multicenter, non-interventional, prospective, observational study aimed to determine whether patients' attitude to chemotherapy is an independent prognostic factor for survival in patients with advanced non-small cell lung cancer (NSCLC) who are treated with gemcitabine-platinum. Chemonaive patients (n=1895) with stage IIIB or IV NSCLC not amenable to curative surgery or radiotherapy were treated with a combination of gemcitabine plus cisplatin/carboplatin and followed for a maximum of 18 months. Patients' attitude to treatment was measured on a 5-point scale and responses were used to assign patients to one of the three need categories: A, maximum extension of survival with the acceptance of high toxicity (60.0% of patients); B, maximum extension of survival only if coupled with normal lifestyle (26.1%); C, relief of symptoms (13.8%). Median survival varied significantly among the need categories (A=13.00 months, B=15.70 months, C=15.33 months; log-rank test P=0.0415). Patient attitude to treatment (need categories) was not a significant prognostic factor for survival after adjusting for known prognostic factors (P=0.0503). After adjusting for baseline differences, patients in this study had a significantly lower risk of death than patients in three randomized trials (hazard ratio 0.879; 95% confidence interval: 0.775, 0.998; P=0.0458). In conclusion, in this observational study, patient attitude to chemotherapy was not an independent prognostic factor of survival.

Gemcitabine and cisplatin treatment over a 3-week versus a 4-week dosing schedule: a randomized trial conducted in Chinese patients with nonsmall cell lung cancer.

BACKGROUND: Gemcitabine plus cisplatin is a standard treatment for stages IIIB and IV nonsmall cell lung cancer (NSCLC). This randomized phase II study evaluated a 3-week versus a 4-week schedule of gemcitabine-cisplatin as first line treatment for Chinese patients with advanced NSCLC. METHODS: Patients were randomized to receive cisplatin 75 mg/m(2) on day 1 plus either gemcitabine 1250 mg/m(2) on days 1 and 8 of a 21-day cycle (3-week group) or gemcitabine 1000 mg/m(2) on days 1, 8 and 15 of a 28-day cycle (4-week group). RESULTS: One hundred patients were enrolled in this study. The response rate was 24% (12/51 patients) in the 3-week group and 27% (13/49 patients) in the 4-week group. There were no statistically significant differences between the two treatment groups in survival (hazard ratio: 1.19; 95% CI: 0.68 - 2.09) with a median survival of 12.1 months and 13.8 months in the 3-week group and the 4-week group respectively. The rate of grade 3/4 toxicity in the 3-week group was 55% compared with 86% in the 4-week group (P = 0.001). The difference in the incidence of grade 3/4 haematological toxicities did not reach statistical significance (3-week: 37%, 4-week: 57%), however grade 3/4 drug related neutropenia (3-week: 27%, 4-week: 51%) and thrombocytopenia (3-week: 8%, 4-week: 31%) were significantly lower in the 3-week group. Grade 3/4 nonhaematological toxicities were less in the 3-week group (33% cf 63%; P = 0.005). CONCLUSIONS: The differences in the efficacy endpoints were all in favour of the 4-week schedule of gemcitabine plus cisplatin, however these differences did not reach statistical significance. Fewer grade 3/4 toxicities were observed in the 3-week group compared with the 4-week group.

Gemcitabine administered as a short infusion versus a fixed dose rate in combination with cisplatin for the treatment of patients with advanced non-small cell lung cancer.

Previous studies have indicated that, in combination with cisplatin, fixed dose rate gemcitabine may be more efficacious than standard infusion gemcitabine. This open-label, randomised phase II study was aimed to compare the efficacy and safety of these regimens as treatment for advanced non-small cell lung cancer (NSCLC) in Latin American patients. Sixty-four patients were randomised to receive up to six cycles of treatment with cisplatin 75 mg/m(2) on Day 1 plus either gemcitabine 1000 mg/m(2) over 30 min on Days 1 and 8 of a 21-day cycle (standard arm, N=33) or gemcitabine 1000 mg/m(2) at a fixed dose rate of 10 mg/m(2)/min on Days 1 and 8 of a 21-day cycle (FDR arm, N=31). In the standard arm, 9 of 33 (27%) patients responded compared with 6 of 30 (20%) patients in the FDR arm (odds ratio: 0.67, 95% CI, 0.21-2.2; p=0.56). Median overall survival was 7.5 months in the standard arm and 9.9 months in the FDR arm. One-year survival rates were 35% and 37% in the standard arm and the FDR arm, respectively. Patients in the FDR arm experienced more grade 3/4 haematological toxicity than those in the standard arm (48% versus 21%). The results of this trial do not support FDR administration of gemcitabine in preference to the standard administration in Latin American patients with NSCLC.