Inhibition Of Mitochondrial Electron Transport Chain Research Articles

N-acetylcysteine amide and di- N-acetylcysteine amide protect retinal cells in culture via an antioxidant action

Reactive oxygen species (ROS) play a significant role in toxicity to the retina in a variety of diseases. N-acetylcysteine (NAC), N-acetylcysteine amide (NACA) and the dimeric di-N-acetylcysteine amide (diNACA) were evaluated in terms of protecting retinal cells, in vitro, in a variety of stress models.Three types of rat retinal cell cultures were utilized in the study: macroglial-only cell cultures, neuron-only retinal ganglion cell (RGC) cultures, and mixed cultures containing retinal glia and neurons. Ability of test agents to attenuate oxidative stress in all cultures was ascertained. In addition, capability of agents to protect against a variety of alternate clinically-relevant stressors, including excitotoxins and mitochondrial electron transport chain inhibitors, was also evaluated. Capacity of test agents to elevate cellular levels of reduced glutathione under normal and compromised conditions was also determined.NAC, NACA and diNACA demonstrated concentration-dependent cytoprotection against oxidative stress in all cultures. These three compounds, however, had differing effects against a variety of alternate insults to retinal cells. The most protective agent was NACA, which was most potent against the most stressors (including oxidative stress, mitochondrial impairment by antimycin A and azide, and glutamate-induced excitotoxicity). Similar to NAC, NACA increased glutathione levels in non-injured cells, although diNACA did not, suggesting a different, unknown mechanism of antioxidant activity for the latter. In support of this, diNACA was the only agent to attenuate rotenone-induced toxicity in mitochondria.NAC, NACA and diNACA exhibited varying degrees of antioxidant activity, i.e., protected cultured rat retinal cells from a variety of stressors which were designed to mimic aspects of the pathology of different retinal diseases. A general rank order of activity was observed: NACA ≥ diNACA > NAC. These results warrant further exploration of NACA and diNACA as antioxidant therapeutics for the treatment of retinal diseases, particularly those involving oxidative stress. Furthermore, we have defined the battery of tests carried out as the “Wood, Chidlow, Wall and Casson (WCWC) Retinal Antioxidant Indices”; we believe that these are of great value for screening molecules for potential to reduce retinal oxidative stress in a range of retinal diseases.

Heat stress upregulates arachidonic acid to trigger autophagy in sertoli cells via dysfunctional mitochondrial respiratory chain function

As a key factor in determining testis size and sperm number, sertoli cells (SCs) play a crucial role in male infertility. Heat stress (HS) reduces SCs counts, negatively impacting nutrient transport and supply to germ cells, and leading to spermatogenesis failure in humans and animals. However, how HS affects the number of SCs remains unclear. We hypothesized that changes in SC metabolism contribute to the adverse effects of HS. In this study, we first observed an upregulation of arachidonic acid (AA), an unsaturated fatty acid after HS exposure by LC-MS/MS metabolome detection. By increasing ROS levels, expression of KEAP1 and NRF2 proteins as well as LC3 and LAMP2, 100 µM AA induced autophagy in SCs by activating oxidative stress (OS). We observed adverse effects of AA on mitochondria under HS with a decrease of mitochondrial number and an increase of mitochondrial membrane potential (MMP). We also found that AA alternated the oxygen transport and absorption function of mitochondria by increasing glycolysis flux and decreasing oxygen consumption rate as well as the expression of mitochondrial electron transport chain (ETC) proteins Complex I, II, V. However, pretreatment with 5 mM NAC (ROS inhibitor) and 2 µM Rotenone (mitochondrial ETC inhibitor) reversed the autophagy induced by AA. In summary, AA modulates autophagy in SCs during HS by disrupting mitochondrial ETC function, inferring that the release of AA is a switch-like response, and providing insight into the underlying mechanism of high temperatures causing male infertility.

Cyclin-dependent kinase 12 deficiency reprogrammes cellular metabolism to alleviate ferroptosis potential and promote the progression of castration-resistant prostate cancer.

Cyclin-dependent kinase 12 (CDK12)-deficient prostate cancer defines a subtype of castration-resistant prostate cancer (CRPC) with a poor prognosis. Current therapy, including PARP inhibitors, shows minimal treatment efficacy for this subtype of CRPC, and the underlying mechanism remains elusive. Based on bioinformatics analysis, we evaluated the relationship between CDK12 deficiency and prostate cancer patient's prognosis and treatment resistance. Furthermore, we used CRISPR-Cas9 technology and mass spectrometry-based metabolomic profiling to reveal the metabolic characteristics of CDK12-deficient CRPC. To elucidate the specific mechanisms of CDK12 deficiency-mediated CRPC metabolic reprogramming, we utilized cell RNA-seq profiling and other molecular biology techniques, including cellular reactive oxygen species probes, mitochondrial function assays, ChIP-qPCR and RNA stability analyses, to clarify the role of CDK12 in regulating mitochondrial function and its contribution to ferroptosis. Finally, through in vitro drug sensitivity testing and in vivo experiments in mice, we identified the therapeutic effects of the electron transport chain (ETC) inhibitor IACS-010759 on CDK12-deficient CRPC. CDK12-deficient prostate cancers reprogramme cellular energy metabolism to support their aggressive progression. In particular, CDK12 deficiency enhanced the mitochondrial respiratory chain for electronic transfer and ATP synthesis to create a ferroptosis potential in CRPC cells. However, CDK12 deficiency downregulated ACSL4 expression, which counteracts the lipid oxidation stress, leading to the escape of CRPC cells from ferroptosis. Furthermore, targeting the ETC substantially inhibited the proliferation of CDK12-deficient CRPC cells in vitro and in vivo, suggesting a potential new target for the therapy of CDK12-deficient prostate cancer. Our findings show that energy and lipid metabolism in CDK12-deficient CRPC work together to drive CRPC progression and provide a metabolic insight into the worse prognosis of CDK12-deficient prostate cancer patients. CDK12 deficiency promotes castration-resistant prostate cancer (CRPC) progression by reprogramming cellular metabolism. CDK12 deficiency in CRPC leads to a more active mitochondrial electron transport chain (ETC), ensuring efficient cell energy supply. CDK12 phosphorylates RNA Pol II to ensure the transcription of ACSL4 to regulate ferroptosis. Mitochondrial ETC inhibitors exhibit better selectivity for CDK12-deficient CRPC cells, offering a promising new therapeutic approach for this subtype of CRPC patients.

Ether lipid biosynthesis promotes lifespan extension and enables diverse pro-longevity paradigms in Caenorhabditis elegans.

Biguanides, including the world's most prescribed drug for type 2 diabetes, metformin, not only lower blood sugar, but also promote longevity in preclinical models. Epidemiologic studies in humans parallel these findings, indicating favorable effects of metformin on longevity and on reducing the incidence and morbidity associated with aging-related diseases. Despite this promise, the full spectrum of molecular effectors responsible for these health benefits remains elusive. Through unbiased screening in Caenorhabditis elegans, we uncovered a role for genes necessary for ether lipid biosynthesis in the favorable effects of biguanides. We demonstrate that biguanides prompt lifespan extension by stimulating ether lipid biogenesis. Loss of the ether lipid biosynthetic machinery also mitigates lifespan extension attributable to dietary restriction, target of rapamycin (TOR) inhibition, and mitochondrial electron transport chain inhibition. A possible mechanistic explanation for this finding is that ether lipids are required for activation of longevity-promoting, metabolic stress defenses downstream of the conserved transcription factor skn-1/Nrf. In alignment with these findings, overexpression of a single, key, ether lipid biosynthetic enzyme, fard-1/FAR1, is sufficient to promote lifespan extension. These findings illuminate the ether lipid biosynthetic machinery as a novel therapeutic target to promote healthy aging.

Transcriptional landscape of mitochondrial electron transport chain inhibition in renal cells

Analysis of the transcriptomic alterations upon chemical challenge, provides in depth mechanistic information on the compound’s toxic mode of action, by revealing specific pathway activation and other transcriptional modulations. Mapping changes in cellular behaviour to chemical insult, facilitates the characterisation of chemical hazard. In this study, we assessed the transcriptional landscape of mitochondrial impairment through the inhibition of the electron transport chain (ETC) in a human renal proximal tubular cell line (RPTEC/TERT1). We identified the unfolded protein response pathway (UPR), particularly the PERK/ATF4 branch as a common cellular response across ETC I, II and III inhibitions. This finding and the specific genes elaborated may aid the identification of mitochondrial liabilities of chemicals in both legacy data and prospective transcriptomic studies.Graphical abstract

Imidazopyridine Amides: Synthesis, Mycobacterium smegmatis CIII2CIV2 Supercomplex Binding, and In Vitro Antimycobacterial Activity.

Q203 (telacebec) is an imidazopyridine amide (IPA) targeting the respiratory CIII2CIV2 supercomplex of the mycobacterial electron transport chain (ETC). Aiming for a better understanding of the molecular mechanism of action of IPA, 27 analogues were prepared through a seven-step synthetic scheme. Oxygen consumption assay was designed to test the inhibition of purified Mycobacterium smegmatis CIII2CIV2 by these compounds. The assay results generally supported structure-activity relationship information obtained from the structure of M. smegmatis CIII2CIV2 bound to Q203. The IC50 of Q203 and compound 27 was 99 ± 32 and 441 ± 138 nM, respectively. All IPAs including Q203 showed no inhibition of mitochondrial ETC, proving their selectivity against mycobacteria. In vitro Mycobacterium tuberculosis growth inhibition and M. smegmatis CIII2CIV2 binding did not correlate perfectly. These observations suggest that further investigation into the mechanisms of resistance in different mycobacterial species is needed to understand the lack of the correlation pattern between CIII2CIV2 inhibition and cellular activity.

EFSA Pilot Project on New Approach Methodologies (NAMs) for Tebufenpyrad Risk Assessment. Part 1. Development of Physiologically‐Based Kinetic (PBK) Model Coupled With Pulmonary and Dermal Exposure

Tebufenpyrad is a pesticide active substance used as insecticide, for which the mechanism of action is an inhibition Complex I of the Mitochondrial Electron Transport Chain (ETC). In vitro experimental data demonstrated that Tebufenpyrad-induced inhibition of ETC's complex I leads to oxidative damage, reduction of oxygen consumption rates with increasing in mitochondrial stress level and dysfunction in dopaminergic neuronal cells (Charli et al. 2016; Chen et al. 2017; Delp et al. 2021). This inhibition of Complex I has been included as a molecular initiating event (MIE) in an adverse outcome pathway (AOP) for Parkinsonian motor deficits. A set of in vitro mechanistic data are available along the AOP (Part 2 of this project) and their interpretation with regards to potential neurotoxicity need to estimate brain exposure to Tebufenpyrad in human, considering its intended uses as plant protection product. To this end, ANSES developed a Physiologically-Based Kinetic (PBK) model supporting several objectives. First objective explores the feasibility of PBK development for Tebufenpyrad when this is accomplished by means of NAMs only. Learnings from this case study will serve as ways to improve active substance dossiers for internal exposure assessment. Second objective relates to the possibility of interpreting the aforementioned AOP when in vitro data are produced on mitochondrial ETC inhibition and whether this inhibition may or may not occur in human too and therefore whether it is possible to discard neurological effects of Tebufenpyrad. This second objective is also intended to support Tebufenpyrad toxicological evaluation during its renewal process. The third objective is to better evaluate uncertainties related to the development of such PBK model, harvest the performed work to support further improvements and potentially seek guidance for harmonization.

Influence of Mitochondrial Electron Transport Chain Inhibitors on Respiration and Gene Expression of Respiratory Components in a Greening Wheat Leaf

Influence of Mitochondrial Electron Transport Chain Inhibitors on Respiration and Gene Expression of Respiratory Components in a Greening Wheat Leaf

Mitochondrial Alterations in Neurons Derived from the Murine AppNL-F Knock-In Model of Alzheimer's Disease.

Alzheimer's disease (AD) research has relied on mouse models overexpressing human mutant A βPP; however, newer generation knock-in models allow for physiological expression of amyloid-β protein precursor (AβPP) containing familial AD mutations where murine AβPP is edited with a humanized amyloid-β (Aβ) sequence. The AppNL-F mouse model has shown substantial similarities to AD brains developing late onset cognitive impairment. In this study, we aimed to characterize mature primary cortical neurons derived from homozygous AppNL-F embryos, especially to identify early mitochondrial alterations in this model. Primary cultures of AppNL-F neurons kept in culture for 12-15 days were used to measure Aβ levels, secretase activity, mitochondrial functions, mitochondrial-ER contacts, synaptic function, and cell death. We detected higher levels of Aβ42 released from AppNL-F neurons as compared to wild-type neurons. AppNL-F neurons, also displayed an increased Aβ42/Aβ40 ratio, similar to adult AppNL-F mouse brain. Interestingly, we found an upregulation in mitochondrial oxygen consumption with concomitant downregulation in glycolytic reserve. Furthermore, AppNL-F neurons were more susceptible to cell death triggered by mitochondrial electron transport chain inhibition. Juxtaposition between ER and mitochondria was found to be substantially upregulated, which may account for upregulated mitochondrial-derived ATP production. However, anterograde mitochondrial movement was severely impaired in this model along with loss in synaptic vesicle protein and impairment in pre- and post-synaptic function. We show that widespread mitochondrial alterations can be detected in AppNL-F neurons in vitro, where amyloid plaque deposition does not occur, suggesting soluble and oligomeric Aβ-species being responsible for these alterations.

Siccanin Is a Dual-Target Inhibitor of Plasmodium falciparum Mitochondrial Complex II and Complex III

Plasmodium falciparum contains several mitochondrial electron transport chain (ETC) dehydrogenases shuttling electrons from the respective substrates to the ubiquinone pool, from which electrons are consecutively transferred to complex III, complex IV, and finally to the molecular oxygen. The antimalarial drug atovaquone inhibits complex III and validates this parasite’s ETC as an attractive target for chemotherapy. Among the ETC dehydrogenases from P. falciparum, dihydroorotate dehydrogenase, an essential enzyme used in de novo pyrimidine biosynthesis, and complex III are the two enzymes that have been characterized and validated as drug targets in the blood-stage parasite, while complex II has been shown to be essential for parasite survival in the mosquito stage; therefore, these enzymes and complex II are considered candidate drug targets for blocking parasite transmission. In this study, we identified siccanin as the first (to our knowledge) nanomolar inhibitor of the P. falciparum complex II. Moreover, we demonstrated that siccanin also inhibits complex III in the low-micromolar range. Siccanin did not inhibit the corresponding complexes from mammalian mitochondria even at high concentrations. Siccanin inhibited the growth of P. falciparum with IC50 of 8.4 μM. However, the growth inhibition of the P. falciparum blood stage did not correlate with ETC inhibition, as demonstrated by lack of resistance to siccanin in the yDHODH-3D7 (EC50 = 10.26 μM) and Dd2-ELQ300 strains (EC50 = 18.70 μM), suggesting a third mechanism of action that is unrelated to mitochondrial ETC inhibition. Hence, siccanin has at least a dual mechanism of action, being the first potent and selective inhibitor of P. falciparum complexes II and III over mammalian enzymes and so is a potential candidate for the development of a new class of antimalarial drugs.

Structural and Biophysical Characterization of Purified Recombinant Arabidopsis thaliana's Alternative Oxidase 1A (rAtAOX1A): Interaction With Inhibitor(s) and Activator.

In higher plants, alternative oxidase (AOX) participates in a cyanide resistant and non-proton motive electron transport pathway of mitochondria, diverging from the ubiquinone pool. The physiological significance of AOX in biotic/abiotic stress tolerance is well-documented. However, its structural and biophysical properties are poorly understood as its crystal structure is not yet revealed in plants. Also, most of the AOX purification processes resulted in a low yield/inactive/unstable form of native AOX protein. The present study aims to characterize the purified rAtAOX1A protein and its interaction with inhibitors, such as salicylhydroxamic acid (SHAM) and n-propyl gallate (n-PG), as well as pyruvate (activator), using biophysical/in silico studies. The rAtAOX1A expressed in E. coli BL21(DE3) cells was functionally characterized by monitoring the respiratory and growth sensitivity of E. coli/pAtAOX1A and E. coli/pET28a to classical mitochondrial electron transport chain (mETC) inhibitors. The rAtAOX1A, which is purified through affinity chromatography and confirmed by western blotting and MALDI-TOF-TOF studies, showed an oxygen uptake activity of 3.86 μmol min−1 mg−1 protein, which is acceptable in non-thermogenic plants. Circular dichroism (CD) studies of purified rAtAOX1A revealed that >50% of the protein content was α-helical and retained its helical absorbance signal (ellipticity) at a wide range of temperature and pH conditions. Further, interaction with SHAM, n-PG, or pyruvate caused significant changes in its secondary structural elements while retaining its ellipticity. Surface plasmon resonance (SPR) studies revealed that both SHAM and n-PG bind reversibly to rAtAOX1A, while docking studies revealed that they bind to the same hydrophobic groove (Met191, Val192, Met195, Leu196, Phe251, and Phe255), to which Duroquinone (DQ) bind in the AtAOX1A. In contrast, pyruvate binds to a pocket consisting of Cys II (Arg174, Tyr175, Gly176, Cys177, Val232, Ala233, Asn294, and Leu313). Further, the mutational docking studies suggest that (i) the Met195 and Phe255 of AtAOX1A are the potential candidates to bind the inhibitor. Hence, this binding pocket could be a ‘potential gateway' for the oxidation-reduction process in AtAOX1A, and (ii) Arg174, Gly176, and Cys177 play an important role in binding to the organic acids like pyruvate.

Mitochondrial electron transport chain is necessary for NLRP3 inflammasome activation

The NLRP3 inflammasome is linked to sterile and pathogen-dependent inflammation, and its dysregulation underlies many chronic diseases. Mitochondria have been implicated as regulators of the NLRP3 inflammasome through several mechanisms including generation of mitochondrial reactive oxygen species (ROS). Here, we report that mitochondrial electron transport chain (ETC) complex I, II, III and V inhibitors all prevent NLRP3 inflammasome activation. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI1) or Ciona intestinalis alternative oxidase, which can complement the functional loss of mitochondrial complex I or III, respectively, without generation of ROS, rescued NLRP3 inflammasome activation in the absence of endogenous mitochondrial complex I or complex III function. Metabolomics revealed phosphocreatine (PCr), which can sustain ATP levels, as a common metabolite that is diminished by mitochondrial ETC inhibitors. PCr depletion decreased ATP levels and NLRP3 inflammasome activation. Thus, the mitochondrial ETC sustains NLRP3 inflammasome activation through PCr-dependent generation of ATP, but via a ROS-independent mechanism.

Mechanism of hepatobiliary toxicity of the LPA1 antagonist BMS-986020 developed to treat idiopathic pulmonary fibrosis: Contrasts with BMS-986234 and BMS-986278

In a Phase 2 clinical trial, BMS-986020, a lysophosphatidic acid receptor-1 (LPA1) antagonist, produced hepatobiliary toxicity (increased ALT, AST, and ALP; cholecystitis) and increases in plasma bile acids (BA). Nonclinical investigations conducted to identify a potential mechanism(s) for this toxicity examined BMS-986020 and two LPA1 antagonists structurally distinct from BMS-986020 (BMS-986234 and BMS-986278). BMS-986020 inhibited hepatic BA efflux transporters BSEP (IC50 1.8 μM), MRP3 (IC50 22 μM), and MRP4 (IC50 6.2 μM) and inhibited BA canalicular efflux in human hepatocytes (68% at 10 μM). BMS-986020 inhibited mitochondrial function (basal and maximal respiration, ATP production, and spare capacity) in human hepatocytes and cholangiocytes at ≥10 μM and inhibited phospholipid efflux in human hepatocytes (MDR3 IC50 7.5 μM). A quantitative systems toxicology analysis (DILIsym®), considering pharmacokinetics, BA homeostasis, mitochondrial function, oxidative phosphorylation, and reactive intermediates performed for BMS-986020 recapitulated clinical findings ascribing the effects to BA transporter and mitochondrial electron transport chain inhibition. BMS-986234 and BMS-986278 minimally inhibited hepatic BA transporters (IC50 ≥20 μM) and did not inhibit MDR3 activity (IC50 >100 μM), nor did BMS-986234 inhibit BA efflux (≤50 μM) or mitochondrial function (≤30 μM) (BMS-986278 not evaluated). Multiple mechanisms may be involved in the clinical toxicity observed with BMS-986020. The data indicate that this toxicity was unrelated to LPA1 antagonism since the mechanisms that likely influenced the adverse clinical outcome of BMS-986020 were not observed with equipotent LPA1 antagonists BMS-986234 and BMS-986278. This conclusion is consistent with the lack of hepatobiliary toxicity in nonclinical and clinical safety studies with BMS-986278.

A conserved expression signature predicts growth rate and reveals cell & lineage-specific differences.

Isogenic cells cultured together show heterogeneity in their proliferation rate. To determine the differences between fast and slow-proliferating cells, we developed a method to sort cells by proliferation rate, and performed RNA-seq on slow and fast proliferating subpopulations of pluripotent mouse embryonic stem cells (mESCs) and mouse fibroblasts. We found that slowly proliferating mESCs have a more naïve pluripotent character. We identified an evolutionarily conserved proliferation-correlated transcriptomic signature that is common to all eukaryotes: fast cells have higher expression of genes for protein synthesis and protein degradation. This signature accurately predicted growth rate in yeast and cancer cells, and identified lineage-specific proliferation dynamics during development, using C. elegans scRNA-seq data. In contrast, sorting by mitochondria membrane potential revealed a highly cell-type specific mitochondria-state related transcriptome. mESCs with hyperpolarized mitochondria are fast proliferating, while the opposite is true for fibroblasts. The mitochondrial electron transport chain inhibitor antimycin affected slow and fast subpopulations differently. While a major transcriptional-signature associated with cell-to-cell heterogeneity in proliferation is conserved, the metabolic and energetic dependency of cell proliferation is cell-type specific.

Mitochondrial Electron Transport Chain Inhibition Promotes Resistance to Proteasome Inhibitors in Multiple Myeloma

INTRODUCTIONProteasome inhibitors (PI) such as bortezomib (Velcade), carfilzomib (Kyprolis) and ixazomib (Ninlaro)) have been shown to be efficacious in multiple myeloma (MM) therapy. However, despite being an effective first line therapy, resistance to PI usually develops, leading to relapse and refractory disease. Previous studies have implicated a role of OXPHOS, glycolysis, antioxidants and serine metabolism in PI resistance. Mitochondrial metabolism plays a central role in malignant progression not only by generating ATP but also by providing precursors for synthesis of several biomolecules such as proteins, nucleotides, fatty acids and antioxidants that can influence the efficacy of MM therapies. We previously determined reduced mitochondrial electron transport chain (ETC) activity promotes sensitivity to the BCL-2 antagonist, venetoclax. However, the relationship between the metabolic state of the mitochondria and proteasome inhibitor (PI) sensitivity is not fully understood. Unexpectedly, we found ETC inhibition or reduced ETC activity to promote resistance to PIs. Here, we investigate the mechanistic basis for divergent effects of mitochondrial stress on sensitivity to PIs and venetoclax.METHODSWe have used RNA-Seq and carbon isotope tracing using labeled U 13C-glucose or U 13C-glutamine, flow cytometry and western blot analysis in MM cell lines treated with mitochondrial Complex I inhibitor, IACS-010759 (IACS) +/- Bortezomib; and immunostaining of MM patient samples and interrogation of Multiple Myeloma Research Foundation's CoMMpass Study (NCT01454297, Interim Analysis 15).RESULTSWe find that mitochondrial ETC (complex I-V) inhibition antagonizes bortezomib (BTZ) and carfilzomib (CFZ) induced cell death in MM in contrast to promoting sensitivity to venetoclax. Additionally, cell lines exhibiting intrinsically reduced ETC activity were more resistant to PI in comparison to cell lines with higher ETC activity. Evaluation of CoMMpass MM trial (NCT0145429, IA15) and serial samples from 50 patients before PI treatment and after relapse, show pathways related to OXPHOS and TCA cycle to be downregulated in poor survival patients, corroborating our in vitro observations on reduced ETC activity promoting resistance to PI. To elucidate the mechanistic basis of ETC-inhibition induced PI resistance we performed RNA-Seq and U 13C-glucose and glutamine tracing in L363 cells treated with the ETC Complex I inhibitor IACS +/- BTZ. RNA-Seq analysis and further confirmation by western blot analysis reveals integrated stress response (ISR) upregulation, ATF4 induction, and suppression of protein translation and global protein ubiquitination levels, likely responsible for resistance to proteasome inhibition in cells co-treated with IACS and BTZ compared to BTZ alone. Stable isotope tracing reveals an upregulation of reductive carboxylation; while RNA-Seq data and flow cytometry demonstrate increase in the cystine/glutamate transporter SLC7A11. The ensuing metabolic rewiring in mitochondrially suppressed MM induces several metabolic vulnerabilities including sensitivity to the SLC7A11 inhibitor, erastin. We also show that knockdown of ATF4 re-sensitizes ETC-inhibited cells to BTZ while ablating sensitivity to venetoclax (previously reported). Furthermore, examination of patient samples demonstrates inter-cellular heterogeneity in ATF4 expression. Our results thus, support the role ATF4 as key determinants of PI and BCL-2 antagonist efficacy.CONCLUSIONWe show mitochondrial ETC inhibition induces ISR mediated resistance to PI. These ETC-inhibited cells are however sensitive to BCL-2 antagonists and afford additional metabolic vulnerabilities that can be capitalized upon to target metabolic heterogeneity in MM. Our study underscores the need for implementing combinatorial regimens in MM cognizant of mitochondrial metabolic heterogeneity-mediated resistance. DisclosuresLonial: Janssen: Consultancy, Honoraria, Research Funding; BMS/Celgene: Consultancy, Honoraria, Research Funding; AMGEN: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Merck: Honoraria. Boise: AstraZeneca: Consultancy, Research Funding; Abbvie: Consultancy. Jaye: Stemline Therapeutics: Honoraria. Nooka: Janssen Oncology: Consultancy, Research Funding; GlaxoSmithKline: Consultancy, Other: Travel expenses; Sanofi: Consultancy; Bristol-Myers Squibb: Consultancy; Takeda: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Oncopeptides: Consultancy; Adaptive technologies: Consultancy; Karyopharm Therapeutics: Consultancy.

Circulating syndecan-1 is reduced in pregnancies with poor fetal growth and its secretion regulated by matrix metalloproteinases and the mitochondria

Fetal growth restriction is a leading cause of stillbirth that often remains undetected during pregnancy. Identifying novel biomarkers may improve detection of pregnancies at risk. This study aimed to assess syndecan-1 as a biomarker for small for gestational age (SGA) or fetal growth restricted (FGR) pregnancies and determine its molecular regulation. Circulating maternal syndecan-1 was measured in several cohorts; a large prospective cohort collected around 36 weeks’ gestation (n = 1206), a case control study from the Manchester Antenatal Vascular service (285 women sampled at 24–34 weeks’ gestation); two prospective cohorts collected on the day of delivery (36 + 3–41 + 3 weeks’ gestation, n = 562 and n = 405 respectively) and a cohort who delivered for preterm FGR (< 34 weeks). Circulating syndecan-1 was consistently reduced in women destined to deliver growth restricted infants and those delivering for preterm disease. Syndecan-1 secretion was reduced by hypoxia, and its loss impaired proliferation. Matrix metalloproteinases and mitochondrial electron transport chain inhibitors significantly reduced syndecan-1 secretion, an effect that was rescued by coadministration of succinate, a mitochondrial electron transport chain activator. In conclusion, circulating syndecan-1 is reduced among cases of term and preterm growth restriction and has potential for inclusion in multi-marker algorithms to improve detection of poorly grown fetuses.

Artemisinin-resistant K13 mutations rewire Plasmodium falciparum\u2019s intra-erythrocytic metabolic program to enhance survival

The emergence and spread of artemisinin resistance, driven by mutations in Plasmodium falciparum K13, has compromised antimalarial efficacy and threatens the global malaria elimination campaign. By applying systems-based quantitative transcriptomics, proteomics, and metabolomics to a panel of isogenic K13 mutant or wild-type P. falciparum lines, we provide evidence that K13 mutations alter multiple aspects of the parasite’s intra-erythrocytic developmental program. These changes impact cell-cycle periodicity, the unfolded protein response, protein degradation, vesicular trafficking, and mitochondrial metabolism. K13-mediated artemisinin resistance in the Cambodian Cam3.II line was reversed by atovaquone, a mitochondrial electron transport chain inhibitor. These results suggest that mitochondrial processes including damage sensing and anti-oxidant properties might augment the ability of mutant K13 to protect P. falciparum against artemisinin action by helping these parasites undergo temporary quiescence and accelerated growth recovery post drug elimination.

Abstract PO-041: Genome-wide CRISPR/Cas9 screen reveals mitochondrial gene mutation as a driver for drug resistance in Ewing sarcoma

Abstract Ewing sarcoma is a pediatric bone cancer caused by a chromosomal translocation event that generates the pathognomonic fusion protein, EWS/FLI, which acts as aberrant transcription factor. EWS/FLI is responsible for activating and repressing important genes to drive oncogenic transformation and tumorigenesis. EWS/FLI is notoriously difficult to target with small molecule inhibitors based on its lack of enzymatic activity and intrinsically disordered EWS domain, thus rational drug design is presently unfeasible. Other potential therapeutic targets are interacting partners of EWS/FLI, including epigenetic modulators, such as lysine specific demethylase-1 (LSD1). Inhibition of LSD1 by a reversible, non-competitive inhibitor, SP-2509, has been shown to cause extensive changes to gene expression and induce apoptosis in Ewing sarcoma cells. A Phase I clinical trial (NCT03600649) is currently ongoing to study the effect an SP-2509 analog, Seclidemstat (SP-2577), on patients with recurrent or refractory Ewing sarcoma tumors. Thus, understanding potential drug resistance mechanisms is vital to ensure maximal efficacy of Seclidemstat treatment for patients in the present, and in future clinical trials with this targeted therapeutic drug. Preliminary investigation using a genome-wide CRISPR/Cas9 knock-out (GeCKo) screen has revealed that the loss of genes important to mitochondrial function, specifically in the electron transport chain (ETC), play a distinct role in SP-2509 drug-resistance in Ewing sarcoma cells. We validated the GeCKo screen using cell viability assays in an Ewing sarcoma cell line (A673) via knockout (KO) of mitochondrial genes that were identified by the GeCKo screen. Consistent with the screen, we found select mitochondrial genes led to an increase in IC50 values (i.e. drug-resistance) to SP-2509, compared to WT A673 cells. We found that drug resistance could be enhanced even greater by generating monoclonal cell populations containing complete mitochondrial gene KO. We performed RNA-sequencing and metabolomics analyses to examine SP-2509 response differences between WT and our generated drug resistance cell lines. We similarly determined that treating A673 cells with mitochondrial ETC inhibitors recapitulated drug resistance. Currently, the mechanism that links mitochondrial dysfunction in Ewing sarcoma cells and resistance to the epigenetic drug SP-2509 is incompletely understood. However, our ongoing studies aim to uncover this link and ultimately provide consequential information that will help patients overcome Ewing sarcoma. Citation Format: Jack P. Tokarsky, Jesse Crow, Lillian Guenther, Emily Theisen, Kimberly Stegmaier, Stephen Lessnick. Genome-wide CRISPR/Cas9 screen reveals mitochondrial gene mutation as a driver for drug resistance in Ewing sarcoma [abstract]. In: Abstracts: AACR Special Virtual Conference on Epigenetics and Metabolism; October 15-16, 2020; 2020 Oct 15-16. Philadelphia (PA): AACR; Cancer Res 2020;80(23 Suppl):Abstract nr PO-041.

Cytochrome oxidase and alternative oxidase pathways of mitochondrial electron transport chain are important for the photosynthetic performance of pea plants under salinity stress conditions

The flexible plant mitochondrial electron transport chain with cytochrome c oxidase (COX) and alternative oxidase (AOX) pathways is known to be modulated by abiotic stress conditions. The effect of salinity stress on the mitochondrial electron transport chain and the importance of COX and AOX pathways for optimization of photosynthesis under salinity stress conditions is not clearly understood. In the current study, importance of COX and AOX pathways for photosynthetic performance of pea plants (Pisum sativum L. Pea Arkel cv) was analysed by using the mitochondrial electron transport chain inhibitors Antimycin A (AA) and salicylhydroxamic acid (SHAM) which restrict the electron flow through COX and AOX pathways respectively. Salinity stress resulted in decreased CO2 assimilation rates, leaf stomatal conductance, transpiration and leaf intercellular CO2 concentration in a stress dependent manner. Superimposition of leaves of salt stressed plants with AA and SHAM caused cellular H2O2 and O2− accumulation along with cell death. Additionally, aggravation in decrease of CO2 assimilation rates, leaf stomatal conductance, transpiration and leaf intercellular CO2 concentration upon superimposition with AA and SHAM during salinity stress suggests the importance of mitochondrial oxidative electron transport for photosynthesis. Increased expression of AOX1a and AOX2 transcripts along with AOX protein levels indicated up regulation of AOX pathway in leaves during salinity stress. Chlorophyll fluorescence measurements revealed enhanced damage to Photosystem (PS) II in the presence of AA and SHAM during salinity stress. Results suggested the beneficial role of COX and AOX pathways for optimal photosynthetic performance in pea leaves during salinity stress conditions.

Reactive oxygen species production by BP-1,6-quinone and its effects on the endothelial dysfunction: Involvement of the mitochondria

Strong epidemiological evidence supports the association between increased air pollution and the risk of developing atherosclerotic cardiovascular diseases (CVDs). However, the mechanism remains unclear. As an environmental air pollutant and benzo-a-pyrene (BP) metabolite, BP-1,6-quinone (BP-1,6-Q) is present in the particulate phase of air pollution. This study was undertaken to examine the redox activity of BP-1,6-Q and mechanisms associated with it using EA.hy926 endothelial cells. BP-1,6-Q at 0.01–1 μM significantly stimulated the production of reactive oxygen species (ROS)·in intact cells and isolated mitochondria. Furthermore, BP-1,6-Q-induced ROS was altered by mitochondrial electron transport chain (METC) inhibitors of complex I (rotenone) and complex III (antimycin A), denoting the involvement of mitochondrial electron transport chain (METC) in BP-1,6-Q mediated ROS production. In METC deficient cells, interestingly, BP-1,6-Q-mediated ROS production was enhanced, suggesting that overproduction of ROS by BP-1,6-Q is not only produced from mitochondria but can also be from the cell outside of mitochondria (extramitochondrial). BP-1,6-Q also triggered endothelial-monocyte interaction and stimulated expression of vascular adhesion molecule-1 (VCAM-1). In conclusion, these results demonstrate that BP-1,6-Q can generate ROS within both mitochondria and outside of mitochondria, resulting in stimulation of adhesion of monocytes to endothelial cells, a key event in the pathogenesis of atherosclerosis.