De Novo Design and Development of a Nutrient-Rich Perfusate for Ex Vivo Lung Perfusion with Cell Culture Models.

Ex vivo lung perfusion (EVLP) has increased donor lung utilization through assessment of "marginal" lungs prior to transplantation. To develop it as a donor lung reconditioning platform, prolonged EVLP is necessary, and new perfusates are required to provide sufficient nutritional support. Human pulmonary microvascular endothelial cells and epithelial cells were used to test different formulas for basic cellular function. A selected formula was further tested on an EVLP cell culture model, and cell confluence, apoptosis, and GSH and HSP70 levels were measured. When a cell culture medium (DMEM) was mixed with a current EVLP perfusate-Steen solution, DMEM enhanced cell confluence and migration and reduced apoptosis in a dose-dependent manner. A new EVLP perfusate was designed and tested based on DMEM. The final formula contains 5 g/L Dextran-40 and 7% albumin and is named as D05D7A solution. It inhibited cold static storage and warm reperfusion-induced cell apoptosis, improved cell confluence, and enhanced GSH and HSP70 levels in human lung cells compared to Steen solution. DMEM-based nutrient-rich EVLP perfusate could be a promising formula to prolong EVLP and support donor lung repair, reconditioning and further improve donor lung quality and quantity for transplantation with better clinical outcome.

L-alanyl-L-glutamine modified perfusate improves human lung cell functions and extend porcine ex vivo lung perfusion.

BACKGROUND: The clinical application of normothermic ex vivo lung perfusion (EVLP) has increased donor lung utilization for transplantation through functional assessment. To develop it as a platform for donor lung repair, reconditioning and regeneration, the perfusate should be modified to support the lung during extended EVLP. METHODS: Human lung epithelial cells and pulmonary microvascular endothelial cells were cultured, and the effects of Steen solution (commonly used EVLP perfusate) on basic cellular function were tested. Steen solution was modified based on screening tests in cell culture, and further tested with an EVLP cell culture model, on apoptosis, GSH, HSP70, and IL-8 expression. Finally, a modified formula was tested on porcine EVLP. Physiological parameters of lung function, histology of lung tissue, and amino acid concentrations in EVLP perfusate were measured. RESULTS: Steen solution reduced cell confluence, induced apoptosis, and inhibited cell migration, compared to regular cell culture media. Adding L-alanyl-L-glutamine to Steen solution improved cell migration and decreased apoptosis. It also reduced cold preservation and warm perfusion-induced apoptosis, enhanced GSH and HSP70 production, and inhibited IL-8 expression on an EVLP cell culture model. L-alanyl-L-glutamine modified Steen solution supported porcine lungs on EVLP with significantly improved lung function, well-preserved histological structure, and significantly higher levels of multiple amino acids in EVLP perfusate. CONCLUSIONS: Adding L-alanyl-L-glutamine to perfusate may provide additional energy support, antioxidant, and cytoprotective effects to lung tissue. The pipeline developed herein, with cell culture, cell EVLP, and porcine EVLP models, can be used to further optimize perfusates to improve EVLP outcomes.

Tellurophene-Tagging of Teniposide Facilitates Monitoring by Mass Cytometry.

Target engagement and the biodistribution of exogenously administered small molecules is rarely homogenous. Methods to determine the biodistribution at the cellular level are limited by the ability to detect the small molecule and simultaneously identify the cell types or tissue structures with which it is associated. The highly multiplexed nature of mass cytometry could facilitate these studies provided a heavy isotope label was available in the molecule of interest. Here we show it is possible to append a tellurophene to a known chemotherapeutic, teniposide, to follow this molecule in vivo. A semi-synthetic approach offers an efficient route to the teniposide analogue which is found to have similar characteristics when compared with the parent teniposide in vitro. Using mass cytometry we find the teniposide analogue has significant nonspecific binding to cells. In vivo the tellurium bearing teniposide produces the expected DNA damage in a PANC-1 xenograft model. The distribution of Te in the tissue is near the limits of detection and further work will be required to characterize the localization of this analogue with respect to cell type distributions.

Salicylic acid modulates ACS, NHX1, sos1 and HKT1;2 expression to regulate ethylene overproduction and Na+ ions toxicity that leads to improved physiological status and enhanced salinity stress tolerance in tomato plants cv. Pusa Ruby.

Tomato is an important crop for its high nutritional and medicinal properties. The role of salicylic acid (SA) in 1-aminocyclopropane-1-carboxylate synthase (ACS), sodium-hydrogen exchanger (NHX1), salt overly sensitive 1 (sos1) and high-affinity K+ transporter (HKT1;2) transcripts, and ACS enzyme activity and ethylene (ET) production, and growth and physiological attributes was evaluated in tomato cv. Pusa Ruby under salinity stress. Thirty days-old seedlings treated with 0 mM NaCl, 250 mM NaCl, 250 mM NaCl plus 100 µM SA were assessed for different growth and physiological parameters at 45 DAS. Results showed ACS, NHX1, sos1 and HKT1;2 transcripts were significantly changed in SA treated plants. The ACS enzyme activity and ET content were considerably decreased in SA treated plants. Shoot length (SL), root length (RL), number of leaves (NL), leaf area per plant (LA), shoot fresh weight (SFW) and root fresh weight (RFW) were also improved under SA treatment. Conversely, the electrolyte leakage and sodium ion (Na+) content were significantly reduced in SA treated plants. In addition, the endogenous proline and potassium ion (K+) content, and K+/Na+ ratio were considerably increased under SA treatment. Likewise, antioxidant enzymes (SOD, CAT, APX and GR) profile were better in SA treated plant. The present findings suggest that SA reverse the negative effects of salinity stress and stress induced ET production by modulating ACS, NHX, sos1 and HKT1;2 transcript level, and improving various growth and physiological parameters, and antioxidants enzymes profile. This will contribute to a better understanding of salinity stress tolerance mechanisms of tomato plants involving SA and ET cross talk and ions homeostasis to develop more tolerant plant.

Mammary epithelial cells have lineage-rooted metabolic identities.

Cancer metabolism adapts the metabolic network of its tissue of origin. However, breast cancer is not a disease of a single origin. Multiple epithelial populations serve as the culprit cell of origin for specific breast cancer subtypes, yet our knowledge of the metabolic network of normal mammary epithelial cells is limited. Using a multi-omic approach, here we identify the diverse metabolic programmes operating in normal mammary populations. The proteomes of basal, luminal progenitor and mature luminal cell populations revealed enrichment of glycolysis in basal cells and of oxidative phosphorylation in luminal progenitors. Single-cell transcriptomes corroborated lineage-specific metabolic identities and additional intra-lineage heterogeneity. Mitochondrial form and function differed across lineages, with clonogenicity correlating with mitochondrial activity. Targeting oxidative phosphorylation and glycolysis with inhibitors exposed lineage-rooted metabolic vulnerabilities of mammary progenitors. Bioinformatics indicated breast cancer subtypes retain metabolic features of their putative cell of origin. Thus, lineage-rooted metabolic identities of normal mammary cells may underlie breast cancer metabolic heterogeneity and targeting these vulnerabilities could advance breast cancer therapy.

GLUT1 inhibition blocks growth of RB1-positive triple negative breast cancer.

Triple negative breast cancer (TNBC) is a deadly form of breast cancer due to the development of resistance to chemotherapy affecting over 30% of patients. New therapeutics and companion biomarkers are urgently needed. Recognizing the elevated expression of glucose transporter 1 (GLUT1, encoded by SLC2A1) and associated metabolic dependencies in TNBC, we investigated the vulnerability of TNBC cell lines and patient-derived samples to GLUT1 inhibition. We report that genetic or pharmacological inhibition of GLUT1 with BAY-876 impairs the growth of a subset of TNBC cells displaying high glycolytic and lower oxidative phosphorylation (OXPHOS) rates. Pathway enrichment analysis of gene expression data suggests that the functionality of the E2F pathway may reflect to some extent OXPHOS activity. Furthermore, the protein levels of retinoblastoma tumor suppressor (RB1) strongly correlate with the degree of sensitivity to GLUT1 inhibition in TNBC, where RB1-negative cells are insensitive to GLUT1 inhibition. Collectively, our results highlight a strong and targetable RB1-GLUT1 metabolic axis in TNBC and warrant clinical evaluation of GLUT1 inhibition in TNBC patients stratified according to RB1 protein expression levels.

Metabolic Regulation of the Epigenome Drives Lethal Infantile Ependymoma.

Posterior fossa A (PFA) ependymomas are lethal malignancies of the hindbrain in infants and toddlers. Lacking highly recurrent somatic mutations, PFA ependymomas are proposed to be epigenetically driven tumors for which model systems are lacking. Here we demonstrate that PFA ependymomas are maintained under hypoxia, associated with restricted availability of specific metabolites to diminish histone methylation, and increase histone demethylation and acetylation at histone 3 lysine 27 (H3K27). PFA ependymomas initiate from a cell lineage in the first trimester of human development that resides in restricted oxygen. Unlike other ependymomas, transient exposure of PFA cells to ambient oxygen induces irreversible cellular toxicity. PFA tumors exhibit a low basal level of H3K27me3, and, paradoxically, inhibition of H3K27 methylation specifically disrupts PFA tumor growth. Targeting metabolism and/or the epigenome presents a unique opportunity for rational therapy for infants with PFA ependymoma.

Identifying the murine mammary cell target of metformin exposure.

The heterogeneity of breast cancer makes current therapies challenging. Metformin, the anti-diabetic drug, has shown promising anti-cancer activities in epidemiological studies and breast cancer models. Yet, how metformin alters the normal adult breast tissue remains elusive. We demonstrate metformin intake at a clinically relevant dose impacts the hormone receptor positive (HR+) luminal cells in the normal murine mammary gland. Metformin decreases total cell number, progenitor capacity and specifically reduces DNA damage in normal HR+ luminal cells, decreases oxygen consumption rate and increases cell cycle length of luminal cells. HR+ luminal cells demonstrate the lowest levels of mitochondrial respiration and capacity to handle oxidative stress compared to the other fractions, suggesting their intrinsic susceptibility to long-term metformin exposure. Uncovering HR+ luminal cells in the normal mammary gland as the major cell target of metformin exposure could identify patients that would most benefit from repurposing this anti-diabetic drug for cancer prevention/therapy purposes.

TePhe, a tellurium-containing phenylalanine mimic, allows monitoring of protein synthesis in vivo with mass cytometry.

Protein synthesis is central to maintaining cellular homeostasis and its study is critical to understanding the function and dysfunction of eukaryotic systems. Here we report L-2-tellurienylalanine (TePhe) as a noncanonical amino acid for direct measurement of protein synthesis. TePhe is synthetically accessible, nontoxic, stable under biological conditions, and the tellurium atom allows its direct detection with mass cytometry, without postexperiment labeling. TePhe labeling is competitive with phenylalanine but not other large and aromatic amino acids, demonstrating its molecular specificity as a phenylalanine mimic; labeling is also abrogated in vitro and in vivo by the protein synthesis inhibitor cycloheximide, validating TePhe as a translation reporter. In vivo, imaging mass cytometry with TePhe visualizes translation dynamics in the mouse gut, brain, and tumor. The strong performance of TePhe as a probe for protein synthesis, coupled with the operational simplicity of its use, suggests TePhe could become a broadly applied molecule for measuring translation in vitro and in vivo.

A chemical toolbox for the study of bromodomains and epigenetic signaling.

Bromodomains (BRDs) are conserved protein interaction modules which recognize (read) acetyl-lysine modifications, however their role(s) in regulating cellular states and their potential as targets for the development of targeted treatment strategies is poorly understood. Here we present a set of 25 chemical probes, selective small molecule inhibitors, covering 29 human bromodomain targets. We comprehensively evaluate the selectivity of this probe-set using BROMOscan and demonstrate the utility of the set identifying roles of BRDs in cellular processes and potential translational applications. For instance, we discovered crosstalk between histone acetylation and the glycolytic pathway resulting in a vulnerability of breast cancer cell lines under conditions of glucose deprivation or GLUT1 inhibition to inhibition of BRPF2/3 BRDs. This chemical probe-set will serve as a resource for future applications in the discovery of new physiological roles of bromodomain proteins in normal and disease states, and as a toolset for bromodomain target validation.

ONECUT2 is a driver of neuroendocrine prostate cancer.

Neuroendocrine prostate cancer (NEPC), a lethal form of the disease, is characterized by loss of androgen receptor (AR) signaling during neuroendocrine transdifferentiation, which results in resistance to AR-targeted therapy. Clinically, genomically and epigenetically, NEPC resembles other types of poorly differentiated neuroendocrine tumors (NETs). Through pan-NET analyses, we identified ONECUT2 as a candidate master transcriptional regulator of poorly differentiated NETs. ONECUT2 ectopic expression in prostate adenocarcinoma synergizes with hypoxia to suppress androgen signaling and induce neuroendocrine plasticity. ONEUCT2 drives tumor aggressiveness in NEPC, partially through regulating hypoxia signaling and tumor hypoxia. Specifically, ONECUT2 activates SMAD3, which regulates hypoxia signaling through modulating HIF1α chromatin-binding, leading NEPC to exhibit higher degrees of hypoxia compared to prostate adenocarcinomas. Treatment with hypoxia-activated prodrug TH-302 potently reduces NEPC tumor growth. Collectively, these results highlight the synergy between ONECUT2 and hypoxia in driving NEPC, and emphasize the potential of hypoxia-directed therapy for NEPC patients.

The mTOR Targets 4E-BP1/2 Restrain Tumor Growth and Promote Hypoxia Tolerance in PTEN-driven Prostate Cancer.

The mTOR signaling pathway is a central regulator of protein synthesis and cellular metabolism in response to the availability of energy, nutrients, oxygen, and growth factors. mTOR activation leads to phosphorylation of multiple downstream targets including the eukaryotic initiation factor 4E (eIF4E) binding proteins-1 and -2 (EIF4EBP1/4E-BP1 and EIF4EBP2/4E-BP2). These binding proteins inhibit protein synthesis, but are inactivated by mTOR to stimulate cell growth and metabolism. However, the role of these proteins in the context of aberrant activation of mTOR, which occurs frequently in cancers through loss of PTEN or mutational activation of the PI3K/AKT pathway, is unclear. Here, even under conditions of aberrant mTOR activation, hypoxia causes dephosphorylation of 4E-BP1/4E-BP2 and increases their association with eIF4E to suppress translation. This is essential for hypoxia tolerance as knockdown of 4E-BP1 and 4E-BP2 decreases proliferation under hypoxia and increases hypoxia-induced cell death. In addition, genetic deletion of 4E-BP1 and 4E-BP2 significantly accelerates all phases of cancer development in the context of PTEN loss-driven prostate cancer in mice despite potent PI3K/AKT and mTOR activation. However, even with a more rapid onset, tumors that establish in the absence of 4E-BP1 and 4E-BP2 have reduced levels of tumor hypoxia and show increased cell death within hypoxic tumor regions. Together, these data demonstrate that 4E-BP1 and 4E-BP2 act as essential metabolic breaks even in the context of aberrant mTOR activation and that they are essential for the creation of hypoxia-tolerant cells in prostate cancer. Mol Cancer Res; 16(4); 682-95. ©2018 AACR.

Metabolic targeting of HIF-dependent glycolysis reduces lactate, increases oxygen consumption and enhances response to high-dose single-fraction radiotherapy in hypoxic solid tumors.

BACKGROUND: A high rate of glycolysis leading to elevated lactate content has been linked to poor clinical outcomes in patients with head and neck and cervical cancer treated with radiotherapy. Although the biological explanation for this relationship between lactate and treatment response remains unclear, there is a continued interest in evaluating strategies of targeting metabolism to enhance the effectiveness of radiotherapy. The goal of this study was to investigate the effect of metabolic-targeting through HIF-1α inhibition and the associated changes in glycolysis, oxygen consumption and response on the efficacy of high-dose single-fraction radiotherapy (HD-SFRT). METHODS: HIF-1α wild-type and HIF-1α knockdown FaDu and ME180 xenograft tumors were grown in the hind leg of mice that were placed in an environmental chamber and exposed to different oxygen conditions (air-breathing and hypoxia). Ex vivo bioluminescence microscopy was used to measure lactate and ATP levels and the hypoxic fraction was measured using EF5 immunohistochemical staining. The oxygen consumption rate (OCR) in each cell line in response to in vitro hypoxia was measured using an extracellular flux analyzer. Tumor growth delay in vivo was measured following HD-SFRT irradiation of 20 Gy. RESULTS: Targeting HIF-1α reduced lactate content, and increased both oxygen consumption and hypoxic fraction in these tumors after exposure to short-term continuous hypoxia. Tumors with intact HIF-1α subjected to HD-SFRT immediately following hypoxia exposure were less responsive to treatment than tumors without functional HIF-1α, and tumors irradiated under air breathing conditions regardless of HIF-1α status. CONCLUSIONS: Blocking the HIF1 response during transient hypoxic stress increased hypoxia, reduced lactate levels and enhanced response to HD-SFRT. This strategy of combining hypofractionated radiotherapy with metabolic reprogramming to inhibit anaerobic metabolism may increase the efficacy of HD-SFRT through increased oxygen consumption and complementary killing of radiosensitive and hypoxic, radioresistant cells.

MATE2 Expression Is Associated with Cancer Cell Response to Metformin.

BACKGROUND: There is great interest in repurposing the commonly prescribed anti-diabetic drug metformin for cancer therapy. Intracellular uptake and retention of metformin is affected by the expression of organic cation transporters (OCT) 1-3 and by multidrug and toxic compound extrusion (MATE) 1-2. Inside cells, metformin inhibits mitochondrial function, which leads to reduced oxygen consumption and inhibition of proliferation. Reduced oxygen consumption can lead to improved tumor oxygenation and radiation response. PURPOSE: Here we sought to determine if there is an association between the effects of metformin on inhibiting oxygen consumption, proliferation and expression of OCTs and MATEs in a panel of 19 cancer cell lines. RESULTS: There was relatively large variability in the anti-proliferative response of different cell lines to metformin, with a subset of cell lines being very resistant. In contrast, all cell lines demonstrated sensitivity to the inhibition of oxygen consumption by metformin, with relatively small variation. The expression of OCT1 correlated with expression of both OCT2 and OCT3. OCT1 and OCT2 were relatively uniformly expressed, whereas expression of OCT3, MATE1 and MATE2 showed substantial variation across lines. There were statistically significant associations between resistance to inhibition of proliferation and MATE2 expression, as well as between sensitivity to inhibition of oxygen consumption and OCT3 expression. One cell line (LNCaP) with high OCT3 and low MATE2 expression in concert, had substantially higher intracellular metformin concentration than other cell lines, and was exquisitely sensitive to both anti-proliferative and anti-respiratory effects. In all other cell lines, the concentration of metformin required to inhibit oxygen consumption acutely in vitro was substantially higher than that achieved in the plasma of diabetic patients. However, administering anti-diabetic doses of metformin to tumor-bearing mice resulted in intratumoral accumulation of metformin and reduced hypoxic tumor fractions. CONCLUSIONS: All cancer cells are susceptible to inhibition of oxygen consumption by metformin, which results in reduced hypoxic tumor fractions beneficial for the response to radiotherapy. High MATE2 expression may result in resistance to the anti-proliferative effect of metformin and should be considered as a negative predictive biomarker in clinical trials.

Isotopologous Organotellurium Probes Reveal Dynamic Hypoxia In Vivo with Cellular Resolution.

Changes in the oxygenation state of microenvironments within solid tumors are associated with the development of aggressive cancer phenotypes. Factors that influence cellular hypoxia have been characterized; however, methods for measuring the dynamics of oxygenation at a cellular level in vivo have been elusive. We report a series of tellurium-containing isotopologous probes for cellular hypoxia compatible with mass cytometry (MC)-technology that allows for highly parametric interrogation of single cells based on atomic mass spectrometry. Sequential labeling with the isotopologous probes (SLIP) in pancreatic tumor xenograft models revealed changes in cellular oxygenation over time which correlated with the distance from vasculature, the proliferation of cell populations, and proximity to necrosis. SLIP allows for capture of spatial and temporal dynamics in vivo using enzyme activated probes.

Identification of P450 Oxidoreductase as a Major Determinant of Sensitivity to Hypoxia-Activated Prodrugs.

Hypoxia is a prevalent feature of many tumors contributing to disease progression and treatment resistance, and therefore constitutes an attractive therapeutic target. Several hypoxia-activated prodrugs (HAP) have been developed, including the phase III candidate TH-302 (evofosfamide) and the preclinical agent SN30000, which is an optimized analogue of the well-studied HAP tirapazamine. Experience with this therapeutic class highlights an urgent need to identify biomarkers of HAP sensitivity, including enzymes responsible for prodrug activation during hypoxia. Using genome-scale shRNA screens and a high-representation library enriched for oxidoreductases, we identified the flavoprotein P450 (cytochrome) oxidoreductase (POR) as the predominant determinant of sensitivity to SN30000 in three different genetic backgrounds. No other genes consistently modified SN30000 sensitivity, even within a POR-negative background. Knockdown or genetic knockout of POR reduced SN30000 reductive metabolism and clonogenic cell death and similarly reduced sensitivity to TH-302 under hypoxia. A retrospective evaluation of head and neck squamous cell carcinomas showed heterogeneous POR expression and suggested a possible relationship between human papillomavirus status and HAP sensitivity. Taken together, our study identifies POR as a potential predictive biomarker of HAP sensitivity that should be explored during the clinical development of SN30000, TH-302, and other hypoxia-directed agents.

CHCHD2 Is Coamplified with EGFR in NSCLC and Regulates Mitochondrial Function and Cell Migration.

UNLABELLED: Coiled-coil-helix-coiled-coil-helix domain-containing 2, a mitochondrial protein, encoded by CHCHD2 is located at chromosome 7p11.2 and proximal to the EGFR gene. Here, bioinformatic analyses revealed that CHCHD2 is consistently coamplified with EGFR in non-small cell lung carcinoma (NSCLC). In addition, CHCHD2 and EGFR protein expression levels were positively correlated and upregulated relative to normal lung in NSCLC tumor-derived xenografts. Knockdown of CHCHD2 expression in NSCLC cells attenuated cell proliferation, migration, and mitochondrial respiration. CHCHD2 protein-protein interactions were assessed by the complementary approaches of affinity purification mass spectrometry and in vivo proximity ligation. The CHCHD2 interactome includes the apparent hub proteins C1QBP (a mitochondrial protein) and YBX1 (an oncogenic transcription factor), and an overlapping set of hub-associated proteins implicated in cell regulation. IMPLICATIONS: CHCHD2 influences mitochondrial and nuclear functions and contributes to the cancer phenotype associated with 7p11.2 amplification in NSCLC.

Identification of hypoxic cells using an organotellurium tag compatible with mass cytometry.

Mass cytometry (MC) offers unparalleled potential for the development of highly parameterized assays for characterization of single cells within heterogeneous populations. Current reagents compatible with MC analysis employ antibody-metal-chelating polymer conjugates to report on the presence of biomarkers. Here, we expand the utility of MC by developing the first activity-based probe designed specifically for use with the technology. A compact MC-detectable telluroether is linked to a bioreductively sensitive 2-nitroimidazole scaffold, thereby generating a probe sensitive to cellular hypoxia. The probe exhibits low toxicity and is able to selectively label O2-deprived cells. A proof-of-concept experiment employing metal-bound DNA intercalators demonstrates that a heterogeneous mixture of cells with differential exposure to O2 can be effectively discriminated by the quantity of tellurium-labeling. The organotellurium reagents described herein provide a general approach to the development of a large toolkit of MC-compatible probes for activity-based profiling of single cells.

Constitutive optimized production of streptokinase in Saccharomyces cerevisiae utilizing glyceraldehyde 3-phosphate dehydrogenase promoter of Pichia pastoris.

A novel expression vector constructed from genes of Pichia pastoris was applied for heterologous gene expression in Saccharomyces cerevisiae. Recombinant streptokinase (SK) was synthesized by cloning the region encoding mature SK under the control of glyceraldehyde 3-phosphate dehydrogenase (GAP) promoter of Pichia pastoris in Saccharomyces cerevisiae. SK was intracellularly expressed constitutively, as evidenced by lyticase-nitroanilide and caseinolytic assays. The functional activity was confirmed by plasminogen activation assay and in vitro clot lysis assay. Stability and absence of toxicity to the host with the recombinant expression vector as evidenced by southern analysis and growth profile indicate the application of this expression system for large-scale production of SK. Two-stage statistical approach, Plackett-Burman (PB) design and response surface methodology (RSM) was used for SK production medium optimization. In the first stage, carbon and organic nitrogen sources were qualitatively screened by PB design and in the second stage there was quantitative optimization of four process variables, yeast extract, dextrose, pH, and temperature, by RSM. PB design resulted in dextrose and peptone as best carbon and nitrogen sources for SK production. RSM method, proved as an efficient technique for optimizing process conditions which resulted in 110% increase in SK production, 2352 IU/mL, than for unoptimized conditions.

New small molecule inhibitors of UPR activation demonstrate that PERK, but not IRE1α signaling is essential for promoting adaptation and survival to hypoxia.

BACKGROUND AND PURPOSE: The unfolded protein response (UPR) is activated in response to hypoxia-induced stress in the endoplasmic reticulum (ER) and consists of three distinct signaling arms. Here we explore the potential of targeting two of these arms with new potent small-molecule inhibitors designed against IRE1α and PERK. METHODS: We utilized shRNAs and small-molecule inhibitors of IRE1α (4µ8c) and PERK (GSK-compound 39). XBP1 splicing and DNAJB9 mRNA was measured by qPCR and was used to monitor IRE1α activity. PERK activity was monitored by immunoblotting eIF2α phosphorylation and qPCR of DDIT3 mRNA. Hypoxia tolerance was measured using proliferation and clonogenic cell survival assays of cells exposed to mild or severe hypoxia in the presence of the inhibitors. RESULTS: Using knockdown experiments we show that PERK is essential for survival of KP4 cells while knockdown of IRE1α dramatically decreases the proliferation and survival of HCT116 during hypoxia. Further, we show that in response to both hypoxia and other ER stress-inducing agents both 4µ8c and the PERK inhibitor are selective and potent inhibitors of IRE1α and PERK activation, respectively. However, despite potent inhibition of IRE1α activation, 4µ8c had no effect on cell proliferation or clonogenic survival of cells exposed to hypoxia. This was in contrast to the inactivation of PERK signaling with the PERK inhibitor, which reduced tolerance to hypoxia and other ER stress inducing agents. CONCLUSIONS: Our results demonstrate that IRE1α but not its splicing activity is important for hypoxic cell survival. The PERK signaling arm is uniquely important for promoting adaptation and survival during hypoxia-induced ER stress and should be the focus of future therapeutic efforts.