TET1 reprograms the epithelial ovarian cancer epigenome and reveals casein kinase 2α as a therapeutic target.

Ten-eleven translocation methylcytosine dioxygenase-1, TET1, takes part in active DNA demethylation. However, our understanding of DNA demethylation in cancer biology and its clinical significance remain limited. This study showed that TET1 expression correlated with poor survival in advanced-stage epithelial ovarian carcinoma (EOC), and with cell migration, anchorage-independent growth, cancer stemness, and tumorigenicity. In particular, TET1 was highly expressed in serous tubal intraepithelial carcinoma (STIC), a currently accepted type II EOC precursor, and inversely correlated with TP53 mutations. Moreover, TET1 could demethylate the epigenome and activate multiple oncogenic pathways, including an immunomodulation network having casein kinase II subunit alpha (CK2α) as a hub. Patients with TET1high CK2αhigh EOCs had the worst outcomes, and TET1-expressing EOCs were more sensitive to a CK2 inhibitor, both in vitro and in vivo. Our findings uncover the oncogenic and poor prognostic roles of TET1 in EOC and suggest an unexplored role of epigenetic reprogramming in early ovarian carcinogenesis. Moreover, the immunomodulator CK2α represents a promising new therapeutic target, warranting clinical trials of the tolerable CK2 inhibitor, CX4945, for precision medicine against EOC. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Coupling of the polyamine and iron metabolism pathways in the regulation of proliferation: Mechanistic links to alterations in key polyamine biosynthetic and catabolic enzymes.

Many biological processes result from the coupling of metabolic pathways. Considering this, proliferation depends on adequate iron and polyamines, and although iron-depletion impairs proliferation, the metabolic link between iron and polyamine metabolism has never been thoroughly investigated. This is important to decipher, as many disease states demonstrate co-dysregulation of iron and polyamine metabolism. Herein, for the first time, we demonstrate that cellular iron levels robustly regulate 13 polyamine pathway proteins. Seven of these were regulated in a conserved manner by iron-depletion across different cell-types, with four proteins being down-regulated (i.e., acireductone dioxygenase 1 [ADI1], methionine adenosyltransferase 2α [MAT2α], Antizyme and polyamine oxidase [PAOX]) and three proteins being up-regulated (i.e., S-adenosyl methionine decarboxylase [AMD1], Antizyme inhibitor 1 [AZIN1] and spermidine/spermine-N1-acetyltransferase 1 [SAT1]). Depletion of iron also markedly decreased polyamine pools (i.e., spermidine and/or spermine, but not putrescine). Accordingly, iron-depletion also decreased S-adenosylmethionine that is essential for spermidine/spermine biosynthesis. Iron-depletion additionally reduced 3H-spermidine uptake in direct agreement with the lowered levels of the polyamine importer, SLC22A16. Regarding mechanism, the "reprogramming" of polyamine metabolism by iron-depletion is consistent with the down-regulation of ADI1 and MAT2α, and the up-regulation of SAT1. Moreover, changes in ADI1 (biosynthetic) and SAT1 (catabolic) partially depended on the iron-regulated changes in c-Myc and/or p53. The ability of iron chelators to inhibit proliferation was rescuable by putrescine and spermidine, and under some conditions by spermine. Collectively, iron and polyamine metabolism are intimately coupled, which has significant ramifications for understanding the integrated role of iron and polyamine metabolism in proliferation.

Inactivating ARID1A Tumor Suppressor Enhances TERT Transcription and Maintains Telomere Length in Cancer Cells.

ARID1A is a tumor suppressor gene that belongs to the switch/sucrose non-fermentable chromatin remodeling gene family. It is mutated in many types of human cancer with the highest frequency in endometrium-related ovarian and uterine neoplasms including ovarian clear cell, ovarian endometrioid, and uterine endometrioid carcinomas. We have previously reported that mutations in the promoter of human telomerase reverse transcriptase (TERT) rarely co-occur with the loss of ARID1A protein expression, suggesting a potential role of ARID1A in telomere biology. In this study, we demonstrate that ARID1A negatively regulates TERT transcriptional regulation and activity via binding to the regulatory element of TERT and promotes a repressive histone mode. Induction of ARID1A expression was associated with increased occupancy of SIN3A and H3K9me3, known transcription repressor and histone repressor marks, respectively. Thus, loss of ARID1A protein expression caused by inactivating mutations reactivates TERT transcriptional activity and confers a survival advantage of tumor cells by maintaining their telomeres.

Identification of nonferritin mitochondrial iron deposits in a mouse model of Friedreich ataxia.

There is no effective treatment for the cardiomyopathy of the most common autosomal recessive ataxia, Friedreich ataxia (FA). This disease is due to decreased expression of the mitochondrial protein, frataxin, which leads to alterations in mitochondrial iron (Fe) metabolism. The identification of potentially toxic mitochondrial Fe deposits in FA suggests Fe plays a role in its pathogenesis. Studies using the muscle creatine kinase (MCK) conditional frataxin knockout mouse that mirrors the disease have demonstrated frataxin deletion alters cardiac Fe metabolism. Indeed, there are pronounced changes in Fe trafficking away from the cytosol to the mitochondrion, leading to a cytosolic Fe deficiency. Considering Fe deficiency can induce apoptosis and cell death, we examined the effect of dietary Fe supplementation, which led to body Fe loading and limited the cardiac hypertrophy in MCK mutants. Furthermore, this study indicates a unique effect of heart and skeletal muscle-specific frataxin deletion on systemic Fe metabolism. Namely, frataxin deletion induces a signaling mechanism to increase systemic Fe levels and Fe loading in tissues where frataxin expression is intact (i.e., liver, kidney, and spleen). Examining the mutant heart, native size-exclusion chromatography, transmission electron microscopy, Mössbauer spectroscopy, and magnetic susceptibility measurements demonstrated that in the absence of frataxin, mitochondria contained biomineral Fe aggregates, which were distinctly different from isolated mammalian ferritin molecules. These mitochondrial aggregates of Fe, phosphorus, and sulfur, probably contribute to the oxidative stress and pathology observed in the absence of frataxin.

Hepcidin bound to α2-macroglobulin reduces ferroportin-1 expression and enhances its activity at reducing serum iron levels.

Hepcidin regulates iron metabolism by down-regulating ferroportin-1 (Fpn1). We demonstrated that hepcidin is complexed to the blood transport protein, α2-macroglobulin (α2M) (Peslova, G., Petrak, J., Kuzelova, K., Hrdy, I., Halada, P., Kuchel, P. W., Soe-Lin, S., Ponka, P., Sutak, R., Becker, E., Huang, M. L., Suryo Rahmanto, Y., Richardson, D. R., and Vyoral, D. (2009) Blood 113, 6225-6236). However, nothing is known about the mechanism of hepcidin binding to α2M or the effects of the α2M·hepcidin complex in vivo. We show that decreased Fpn1 expression can be mediated by hepcidin bound to native α2M and also, for the first time, hepcidin bound to methylamine-activated α2M (α2M-MA). Passage of high molecular weight α2M·hepcidin or α2M-MA·hepcidin complexes (≈725 kDa) through a Sephadex G-25 size exclusion column retained their ability to decrease Fpn1 expression. Further studies using ultrafiltration indicated that hepcidin binding to α2M and α2M-MA was labile, resulting in some release from the protein, and this may explain its urinary excretion. To determine whether α2M-MA·hepcidin is delivered to cells via the α2M receptor (Lrp1), we assessed α2M uptake and Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells. Interestingly, α2M·hepcidin or α2M-MA·hepcidin demonstrated similar activities at decreasing Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells, indicating that Lrp1 is not essential for Fpn1 regulation. In vivo, hepcidin bound to α2M or α2M-MA did not affect plasma clearance of α2M/α2M-MA. However, serum iron levels were reduced to a significantly greater extent in mice treated with α2M·hepcidin or α2M-MA·hepcidin relative to unbound hepcidin. This effect could be mediated by the ability of α2M or α2M-MA to retard kidney filtration of bound hepcidin, increasing its half-life. A model is proposed that suggests that unlike proteases, which are irreversibly bound to activated α2M, hepcidin remains labile and available to down-regulate Fpn1.

Nitrogen monoxide (NO) storage and transport by dinitrosyl-dithiol-iron complexes: long-lived NO that is trafficked by interacting proteins.

Nitrogen monoxide (NO) markedly affects intracellular iron metabolism, and recent studies have shown that molecules traditionally involved in drug resistance, namely GST and MRP1 (multidrug resistance-associated protein 1), are critical molecular players in this process. This is mediated by interaction of these proteins with dinitrosyl-dithiol-iron complexes (Watts, R. N., Hawkins, C., Ponka, P., and Richardson, D. R. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 7670-7675; Lok, H. C., Suryo Rahmanto, Y., Hawkins, C. L., Kalinowski, D. S., Morrow, C. S., Townsend, A. J., Ponka, P., and Richardson, D. R. (2012) J. Biol. Chem. 287, 607-618). These complexes are bioavailable, have a markedly longer half-life compared with free NO, and form in cells after an interaction between iron, NO, and glutathione. The generation of dinitrosyl-dithiol-iron complexes acts as a common currency for NO transport and storage by MRP1 and GST P1-1, respectively. Understanding the biological trafficking mechanisms involved in the metabolism of NO is vital for elucidating its many roles in cellular signaling and cytotoxicity and for development of new therapeutic targets.

Melanotransferrin: search for a function.

BACKGROUND: Melanotransferrin was discovered in the 1980s as one of the first melanoma tumour antigens. The molecule is a transferrin homologue that is found predominantly bound to the cell membrane by a glycosyl-phosphatidylinositol anchor. MTf was described as an oncofoetal antigen expressed in only small quantities in normal tissues, but in much larger amounts in neoplastic cells. Several diseases are associated with expression of melanotransferrin, including melanoma and Alzheimer's disease, although the significance of the protein to the pathogenesis of these conditions remains unclear. SCOPE OF REVIEW: In this review, we discuss the roles of melanotransferrin in physiological and pathological processes and its potential use as an immunotherapy. MAJOR CONCLUSIONS: Although the exact biological functions of melanotransferrin remain elusive, a growing number of roles have been attributed to the protein, including iron transport/metabolism, angiogenesis, proliferation, cellular migration and tumourigenesis. GENERAL SIGNIFICANCE: The high expression of melanotransferrin in several disease states, particularly malignant melanoma, remains intriguing and may have clinical significance. Further studies on the biology of this protein may provide new insights as well as potential therapeutic avenues for cancer treatment. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Mitochondrial iron trafficking and the integration of iron metabolism between the mitochondrion and cytosol.

The mitochondrion is well known for its key role in energy transduction. However, it is less well appreciated that it is also a focal point of iron metabolism. Iron is needed not only for heme and iron sulfur cluster (ISC)-containing proteins involved in electron transport and oxidative phosphorylation, but also for a wide variety of cytoplasmic and nuclear functions, including DNA synthesis. The mitochondrial pathways involved in the generation of both heme and ISCs have been characterized to some extent. However, little is known concerning the regulation of iron uptake by the mitochondrion and how this is coordinated with iron metabolism in the cytosol and other organelles (e.g., lysosomes). In this article, we discuss the burgeoning field of mitochondrial iron metabolism and trafficking that has recently been stimulated by the discovery of proteins involved in mitochondrial iron storage (mitochondrial ferritin) and transport (mitoferrin-1 and -2). In addition, recent work examining mitochondrial diseases (e.g., Friedreich's ataxia) has established that communication exists between iron metabolism in the mitochondrion and the cytosol. This finding has revealed the ability of the mitochondrion to modulate whole-cell iron-processing to satisfy its own requirements for the crucial processes of heme and ISC synthesis. Knowledge of mitochondrial iron-processing pathways and the interaction between organelles and the cytosol could revolutionize the investigation of iron metabolism.

Elucidation of the mechanism of mitochondrial iron loading in Friedreich's ataxia by analysis of a mouse mutant.

We used the muscle creatine kinase (MCK) conditional frataxin knockout mouse to elucidate how frataxin deficiency alters iron metabolism. This is of significance because frataxin deficiency leads to Friedreich's ataxia, a disease marked by neurologic and cardiologic degeneration. Using cardiac tissues, we demonstrate that frataxin deficiency leads to down-regulation of key molecules involved in 3 mitochondrial utilization pathways: iron-sulfur cluster (ISC) synthesis (iron-sulfur cluster scaffold protein1/2 and the cysteine desulferase Nfs1), mitochondrial iron storage (mitochondrial ferritin), and heme synthesis (5-aminolevulinate dehydratase, coproporphyrinogen oxidase, hydroxymethylbilane synthase, uroporphyrinogen III synthase, and ferrochelatase). This marked decrease in mitochondrial iron utilization and resultant reduced release of heme and ISC from the mitochondrion could contribute to the excessive mitochondrial iron observed. This effect is compounded by increased iron availability for mitochondrial uptake through (i) transferrin receptor1 up-regulation, increasing iron uptake from transferrin; (ii) decreased ferroportin1 expression, limiting iron export; (iii) increased expression of the heme catabolism enzyme heme oxygenase1 and down-regulation of ferritin-H and -L, both likely leading to increased "free iron" for mitochondrial uptake; and (iv) increased expression of the mammalian exocyst protein Sec15l1 and the mitochondrial iron importer mitoferrin-2 (Mfrn2), which facilitate cellular iron uptake and mitochondrial iron influx, respectively. Our results enable the construction of a model explaining the cytosolic iron deficiency and mitochondrial iron loading in the absence of frataxin, which is important for understanding the pathogenesis of Friedreich's ataxia.

The potent and novel thiosemicarbazone chelators di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone and 2-benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone affect crucial thiol systems required for ribonucleotide reductase activity.

Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone possesses potent and selective antitumor activity. Its cytotoxicity has been attributed to iron chelation leading to inhibition of the iron-containing enzyme ribonucleotide reductase (RR). Thiosemicarbazone iron complexes have been shown to be redox-active, although their effect on cellular antioxidant systems is unclear. Using a variety of antioxidants, we found that only N-acetylcysteine significantly inhibited thiosemicarbazone-induced antiproliferative activity. Thus, we examined the effects of thiosemicarbazones on major thiol-containing systems considering their key involvement in providing reducing equivalents for RR. Thiosemicarbazones significantly (p < 0.001) elevated oxidized trimeric thioredoxin levels to 213 ± 5% (n = 3) of the control. This was most likely due to a significant (p < 0.01) decrease in thioredoxin reductase activity to 65 ± 6% (n = 4) of the control. We were surprised to find that the non-redox-active chelator desferrioxamine increased thioredoxin oxidation to a lower extent (152 ± 9%; n = 3) and inhibited thioredoxin reductase activity (62 ± 5%; n = 4), but at a 10-fold higher concentration than thiosemicarbazones. In contrast, only the thiosemicarbazones significantly (p < 0.05) reduced the glutathione/oxidized-glutathione ratio and the activity of glutaredoxin that requires glutathione as a reductant. All chelators significantly decreased RR activity, whereas the NADPH/NADP(total) ratio was not reduced. This was important to consider because NADPH is required for thiol reduction. Thus, thiosemicarbazones could have an additional mechanism of RR inhibition via their effects on major thiol-containing systems.

The translational regulator eIF3a: the tricky eIF3 subunit!

Regulation of gene expression is a fundamental step in cellular physiology as abnormalities in this process may lead to de-regulated growth and cancer. Translation of mRNA is mainly regulated at the rate-limiting initiation step, where many eukaryotic initiation factors (eIFs) are involved. The largest and most complex initiation factor is eIF3 which plays a role in translational regulation, cell growth and cancer. The largest subunit of eIF3 is eIF3a, although it is not required for the general function of eIF3 in translation initiation. However, eIF3a may play a role as a regulator of a subset of mRNAs and has been demonstrated to regulate the expression of p27(kip1), tyrosinated α-tubulin and ribonucleotide reductase M2 subunit. These molecules have a pivotal role in the regulation of the cell cycle. Moreover, the eIF3a mRNA is ubiquitously expressed in all tissues at different levels and is found elevated in a number of cancer types. eIF3a can modulate the cell cycle and may be a translational regulator for proteins important for entrance into S phase. The expression of eIF3a is decreased in differentiated cells in culture and the suppression of eIF3a expression can reverse the malignant phenotype and change the sensitivity of cells to cell cycle modulators. However, the role of eIF3a in cancer is still unclear. In fact, some studies have identified eIF3a to be involved in cancer development, while other results indicate that it could provide protection against evolution into higher malignancy. Together, these findings highlight the "tricky" and interesting nature of eIF3a.

Hepcidin, the hormone of iron metabolism, is bound specifically to alpha-2-macroglobulin in blood.

Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand. In this study, we identify alpha2-macroglobulin (alpha2-M) as the specific hepcidin-binding molecule in blood. Interaction of 125I-hepcidin with alpha2-M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry. Hepcidin binding to nonactivated alpha2-M displays high affinity (Kd 177 +/- 27 nM), whereas hepcidin binding to albumin was nonspecific and displayed nonsaturable kinetics. Surprisingly, the interaction of hepcidin with activated alpha2-M exhibited a classical sigmoidal binding curve demonstrating cooperative binding of 4 high-affinity (Kd 0.3 microM) hepcidin-binding sites. This property probably enables efficient sequestration of hepcidin and its subsequent release or inactivation that may be important for its effector functions. Because alpha2-M rapidly targets ligands to cells via receptor-mediated endocytosis, the binding of hepcidin to alpha2-M may influence its functions. In fact, the alpha2-M-hepcidin complex decreased ferroportin expression in J774 cells more effectively than hepcidin alone. The demonstration that alpha2-M is the hepcidin transporter could lead to better understanding of hepcidin physiology, methods for its sensitive measurement and the development of novel drugs for the treatment of iron-related diseases.

The MCK mouse heart model of Friedreich's ataxia: Alterations in iron-regulated proteins and cardiac hypertrophy are limited by iron chelation.

There is no effective treatment for the cardiomyopathy of the most common autosomal recessive ataxia, Friedreich's ataxia (FA). The identification of potentially toxic mitochondrial (MIT) iron (Fe) deposits in FA suggests that Fe plays a role in its pathogenesis. This study used the muscle creatine kinase conditional frataxin (Fxn) knockout (mutant) mouse model that reproduces the classical traits associated with cardiomyopathy in FA. We examined the mechanisms responsible for the increased cardiac MIT Fe loading in mutants. Moreover, we explored the effect of Fe chelation on the pathogenesis of the cardiomyopathy. Our investigation showed that increased MIT Fe in the myocardium of mutants was due to marked transferrin Fe uptake, which was the result of enhanced transferrin receptor 1 expression. In contrast to the mitochondrion, cytosolic ferritin expression and the proportion of cytosolic Fe were decreased in mutant mice, indicating cytosolic Fe deprivation and markedly increased MIT Fe targeting. These studies demonstrated that loss of Fxn alters cardiac Fe metabolism due to pronounced changes in Fe trafficking away from the cytosol to the mitochondrion. Further work showed that combining the MIT-permeable ligand pyridoxal isonicotinoyl hydrazone with the hydrophilic chelator desferrioxamine prevented cardiac Fe loading and limited cardiac hypertrophy in mutants but did not lead to overt cardiac Fe depletion or toxicity. Fe chelation did not prevent decreased succinate dehydrogenase expression in the mutants or loss of cardiac function. In summary, we show that loss of Fxn markedly alters cellular Fe trafficking and that Fe chelation limits myocardial hypertrophy in the mutant.

Iron chelator-mediated alterations in gene expression: identification of novel iron-regulated molecules that are molecular targets of hypoxia-inducible factor-1 alpha and p53.

Iron deficiency affects 500 million people, yet the molecular role of iron in gene expression remains poorly characterized. In addition, the alterations in global gene expression after iron chelation remain unclear and are important to assess for understanding the molecular pathology of iron deficiency and the biological effects of chelators. Considering this, we assessed the effect on whole genome gene expression of two iron chelators (desferrioxamine and 2-hydroxy-1-napthylaldehyde isonicotinoyl hydrazone) that have markedly different permeability properties. Sixteen genes were significantly regulated by both ligands, whereas a further 50 genes were significantly regulated by either compound. Apart from iron-mediated regulation of expression via hypoxia inducible factor-1 alpha, it was noteworthy that the transcription factor p53 was also involved in iron-regulated gene expression. Examining 16 genes regulated by both chelators in normal and neoplastic cells, five genes (APP, GDF15, CITED2, EGR1, and PNRC1) were significantly differentially expressed between the cell types. In view of their functions in tumor suppression, proliferation, and apoptosis, these findings are important for understanding the selective antiproliferative effects of chelators against neoplastic cells. Most of the genes identified have not been described previously to be iron-regulated and are important for understanding the molecular and cellular effects of iron depletion.

Generation and characterization of transgenic mice hyper-expressing melanoma tumour antigen p97 (Melanotransferrin): no overt alteration in phenotype.

Melanotransferrin (MTf) is a transferrin homologue that binds iron (Fe) through a high affinity Fe-binding site. MTf has been implicated in diverse processes, e.g., iron metabolism, plasminogen activation, eosinophil differentiation and cancer cell migration, proliferation and tumourigenesis. Our previous studies using a knockout mouse demonstrated that MTf does not have an essential function in Fe metabolism (E.O. Sekyere, L.L. Dunn, Y.S. Rahmanto, D.R. Richardson, Role of melanotransferrin in iron metabolism: studies using targeted gene disruption in vivo, Blood 107 (2006) 2599-2601). However, it does play a role in melanoma cell proliferation and tumourigenesis. In this investigation, we report generation and characterization of transgenic mice bearing the MTf gene (MTf(Tg)) produced via lentiviral delivery. In MTf(Tg) mice, MTf mRNA and protein were hyper-expressed in tissues compared to control mice. These animals exhibited no gross morphological, histological, nor Fe status changes. The MTf(Tg) mice were also born in accordance with classical Mendelian ratios. However, hyper-expression of MTf leads to a mild, but significant decrease in erythrocyte count. This animal provides a novel MTf hyper-expression transgenic model for further investigating the biological function(s) of MTf.

Inactivation of Arid1a in the endometrium is associated with endometrioid tumorigenesis through transcriptional reprogramming.

Somatic inactivating mutations of ARID1A, a SWI/SNF chromatin remodeling gene, are prevalent in human endometrium-related malignancies. To elucidate the mechanisms underlying how ARID1A deleterious mutation contributes to tumorigenesis, we establish genetically engineered murine models with Arid1a and/or Pten conditional deletion in the endometrium. Transcriptomic analyses on endometrial cancers and precursors derived from these mouse models show a close resemblance to human uterine endometrioid carcinomas. We identify transcriptional networks that are controlled by Arid1a and have an impact on endometrial tumor development. To verify findings from the murine models, we analyze ARID1AWT and ARID1AKO human endometrial epithelial cells. Using a system biology approach and functional studies, we demonstrate that ARID1A-deficiency lead to loss of TGF-ß tumor suppressive function and that inactivation of ARID1A/TGF-ß axis promotes migration and invasion of PTEN-deleted endometrial tumor cells. These findings provide molecular insights into how ARID1A inactivation accelerates endometrial tumor progression and dissemination, the major causes of cancer mortality.

Inhibition of the MYC-Regulated Glutaminase Metabolic Axis Is an Effective Synthetic Lethal Approach for Treating Chemoresistant Ovarian Cancers.

Amplification and overexpression of the MYC oncogene in tumor cells, including ovarian cancer cells, correlates with poor responses to chemotherapy. As MYC is not directly targetable, we have analyzed molecular pathways downstream of MYC to identify potential therapeutic targets. Here we report that ovarian cancer cells overexpressing glutaminase (GLS), a target of MYC and a key enzyme in glutaminolysis, are intrinsically resistant to platinum-based chemotherapy and are enriched with intracellular antioxidant glutathione. Deprivation of glutamine by glutamine-withdrawal, GLS knockdown, or exposure to the GLS inhibitor CB-839 resulted in robust induction of reactive oxygen species in high GLS-expressing but not in low GLS-expressing ovarian cancer cells. Treatment with CB-839 rendered GLShigh cells vulnerable to the poly(ADP-ribose) polymerase (PARP) inhibitor, olaparib, and prolonged survival in tumor-bearing mice. These findings suggest consideration of applying a combined therapy of GLS inhibitor and PARP inhibitor to treat chemoresistant ovarian cancers, especially those with high GLS expression. SIGNIFICANCE: Targeting glutaminase disturbs redox homeostasis and nucleotide synthesis and causes replication stress in cancer cells, representing an exploitable vulnerability for the development of effective therapeutics. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/20/4514/F1.large.jpg.

Mechanisms underlying acquired platinum resistance in high grade serous ovarian cancer - a mini review.

BACKGROUND: Advanced epithelial ovarian cancer is one of the hardest human malignancies to treat. Standard treatment involves cytoreductive surgery and platinum-based chemotherapy, however, median progression-free survival for patients diagnosed with advanced stage disease (FIGO stages III and IV) is approximately 18 months. There has been little improvement in overall survival over the past decade and less than half of women with advanced stage disease will be living 5 years after diagnosis. A majority of patients initially have a favourable response to platinum-based chemotherapy, but most will eventually relapse and their disease will become platinum resistant. SCOPE OF REVIEW: Here, we review our current understanding of mechanisms that promote recurrence and acquired resistance in epithelial ovarian cancer with particular focus on studies that describe differences observed between untreated primary tumors and recurrent tumors, post-first-line chemotherapy. Multiple molecular mechanisms contribute to recurrence in patients following initial treatment for advanced epithelial ovarian cancer including those involving the tumor microenvironment, tumor immune status, cancer stem cells, DNA repair/cell survival pathways and extracellular matrix. MAJOR CONCLUSIONS: Due to the adaptive nature of recurrent tumors, the major contributing and specific resistance pattern may largely depend on the nature of the primary tumor itself. GENERAL SIGNIFICANCE: Future work that aims to elucidate the complex pattern of acquired resistance will be useful for predicting chemotherapy response/recurrence following primary diagnosis and to develop novel treatment strategies to improve the survival of patients with advanced epithelial ovarian cancer, especially in tumors not harbouring homologous DNA recombination repair deficiencies.

Therapeutic Inducers of Apoptosis in Ovarian Cancer.

Ovarian cancers remain one of the most common causes of gynecologic cancer-related death in women worldwide. The standard treatment comprises platinum-based chemotherapy, and most tumors develop resistance to therapeutic drugs. One mechanism of developing drug resistance is alterations of molecules involved in apoptosis, ultimately assisting in the cells' capability to evade death. Thus, there is a need to focus on identifying potential drugs that restore apoptosis in cancer cells. Here, we discuss the major inducers of apoptosis mediated through various mechanisms and their usefulness as potential future treatment options for ovarian cancer. Broadly, they can target the apoptotic pathways directly or affect apoptosis indirectly through major cancer-pathways in cells. The direct apoptotic targets include the Bcl-2 family of proteins and the inhibitor of apoptotic proteins (IAPs). However, indirect targets include processes related to homologous recombination DNA repair, micro-RNA, and p53 mutation. Besides, apoptosis inducers may also disturb major pathways converging into apoptotic signals including janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3), wingless-related integration site (Wnt)/ß-Catenin, mesenchymal-epithelial transition factor (MET)/hepatocyte growth factor (HGF), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), and phosphatidylinositol 3-kinase (PI3K)/v-AKT murine thymoma viral oncogene homologue (AKT)/mammalian target of rapamycin (mTOR) pathways. Several drugs in our review are undergoing clinical trials, for example, birinapant, DEBIO-1143, Alisertib, and other small molecules are in preclinical investigations showing promising results in combination with chemotherapy. Molecules that exhibit better efficacy in the treatment of chemo-resistant cancer cells are of interest but require more extensive preclinical and clinical evaluation.

Spleen tyrosine kinase activity regulates epidermal growth factor receptor signaling pathway in ovarian cancer.

BACKGROUND: Spleen tyrosine kinase (SYK) is frequently upregulated in recurrent ovarian carcinomas, for which effective therapy is urgently needed. SYK phosphorylates several substrates, but their translational implications remain unclear. Here, we show that SYK interacts with EGFR and ERBB2, and directly enhances their phosphorylation. METHODS: We used immunohistochemistry and immunoblotting to assess SYK and EGFR phosphorylation in ovarian serous carcinomas. Association with survival was determined by Kaplan-Meier analysis and the log-rank test. To study its role in EGFR signaling, SYK activity was modulated using a small molecule inhibitor, a syngeneic knockout, and an active kinase inducible system. We applied RNA-seq and phosphoproteomic mass spectrometry to investigate the SYK-regulated EGF-induced transcriptome and downstream substrates. FINDINGS: Induced expression of constitutively active SYK130E reduced cellular response to EGFR/ERBB2 inhibitor, lapatinib. Expression of EGFRWT, but not SYK non-phosphorylatable EGFR3F mutant, resulted in paclitaxel resistance, a phenotype characteristic to SYK active ovarian cancers. In tumor xenografts, SYK inhibitor reduces phosphorylation of EGFR substrates. Compared to SYKWT cells, SYKKO cells have an attenuated EGFR/ERBB2-transcriptional activity and responsiveness to EGF-induced transcription. In ovarian cancer tissues, pSYK (Y525/526) levels showed a positive correlation with pEGFR (Y1187). Intense immunoreactivity of pSYK (Y525/526) correlated with poor overall survival in ovarian cancer patients. INTERPRETATION: These findings indicate that SYK activity positively modulates the EGFR pathway, providing a biological foundation for co-targeting SYK and EGFR. FUND: Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, NIH/NCI, Ovarian Cancer Research Foundation Alliance, HERA Women's Cancer Foundation and Roseman Foundation. Funders had no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript and eventually in the decision to submit the manuscript.