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Epithelial ovarian cancer (EOC) has a unique mode of metastasis, where cells shed from the primary tumour, form aggregates called spheroids to evade anoikis, spread through the peritoneal cavity, and adhere to secondary sites. We previously showed that the master kinase Liver kinase B1 (LKB1) is required for EOC spheroid viability and metastasis. We have identified novel (nua) kinase 1 (NUAK1) as a top candidate LKB1 substrate in EOC cells and spheroids using a multiplex inhibitor beads-mass spectrometry approach. We confirmed that LKB1 maintains NUAK1 phosphorylation and promotes its stabilization. We next investigated NUAK1 function in EOC cells. Ectopic NUAK1-overexpressing EOC cell lines had increased adhesion, whereas the reverse was seen in OVCAR8-NUAK1KO cells. In fact, cells with NUAK1 loss generate spheroids with reduced integrity, leading to increased cell death after long-term culture. Following transcriptome analysis, we identified reduced enrichment for cell interaction gene expression pathways in OVCAR8-NUAK1KO spheroids. In fact, the FN1 gene, encoding fibronectin, exhibited a 745-fold decreased expression in NUAK1KO spheroids. Fibronectin expression was induced during native spheroid formation, yet this was completely lost in NUAK1KO spheroids. Co-incubation with soluble fibronectin restored the compact spheroid phenotype to OVCAR8-NUAK1KO cells. In a xenograft model of intraperitoneal metastasis, NUAK1 loss extended survival and reduced fibronectin expression in tumours. Thus, we have identified a new mechanism controlling EOC metastasis, through which LKB1-NUAK1 activity promotes spheroid formation and secondary tumours via fibronectin production.

Epithelial ovarian cancer (EOC) spreads by direct dissemination of malignant cells and multicellular clusters, known as spheroids, into the peritoneum followed by implantation and growth on abdominal surfaces. Using a spheroid model system of EOC metastasis, we discovered that Liver kinase B1 (LKB1), encoded by the STK11 gene, and its canonical substrate AMP-activated protein kinase (AMPK) are activated in EOC spheroids, yet only LKB1 is required for cell survival. We have now generated STK11-knockout cell lines using normal human FT190 cells and three EOC cell lines, OVCAR8, HeyA8, and iOvCa147. STK11KO did not affect growth and viability in adherent culture, but it decreased anchorage-independent growth of EOC cells. EOC spheroids lacking LKB1 had markedly impaired growth and viability, whereas there was no difference in normal FT190 spheroids. To test whether LKB1 loss affects EOC metastasis, we performed intraperitoneal injections of OVCAR8-, HeyA8-, and iOvCa147-STK11KO cells, and respective controls. LKB1 loss exhibited a dramatic reduction on tumor burden and metastatic potential; in particular, OVCAR8-STK11KO tumors had evidence of extensive necrosis, apoptosis, and hypoxia. Interestingly, LKB1 loss did not affect AMPKα phosphorylation in EOC spheroids and tumor xenografts, indicating that LKB1 signaling to support EOC cell survival in spheroids and metastatic tumor growth occurs via other downstream mediators. We identified the dual-specificity phosphatase DUSP4 as a commonly upregulated protein due to LKB1 loss; indeed, DUSP4 knockdown in HeyA8-STK11KO cells partially restored spheroid formation and viability. Implications: LKB1 possesses key tumor-promoting activity independent of downstream AMPK signaling during EOC metastasis.

Epithelial ovarian cancer (EOC) cells form multicellular aggregates, or spheroids, and enter a dormant state during intraperitoneal metastasis. Dormant spheroids reduce anabolic metabolism and cell proliferation, which are linked to chemo-resistance. Liver kinase B1 (LKB1), encoded by the STK11 gene, is a critical regulator of stress metabolic signaling; LKB1 phosphorylates the downstream substrates AMP-activated protein kinase (AMPK) and AMPK-related kinases (ARKs) to mediate stress signaling. We have demonstrated that LKB1 expression and activity is required for EOC spheroid cell survival, yet knockdown of AMPKα1/α2 has no effect on viability. In addition, we have preliminary data demonstrating that phosphorylated AMPK is still maintained in EOC spheroids generated from CRISPR-mediated STK11-deleted cells, which completely lack LKB1 expression. Taken together, these results implicate the importance of other AMPK-independent effectors of LKB1 signaling in spheroid cell viability. Therefore, to identify critical downstream targets of LKB1-mediated signaling in EOC spheroids, we employed multiplex inhibitor beads/mass spectrometry (MIB/MS) using OVCAR8 STK11-knockout cells and OVCAR8 control cells grown in adherent and spheroid culture conditions. Using this proteomic approach, we identified NUAK1 as the sole ARK out of 12 different family members that is negatively affected by LKB1 loss. In fact, both phosphorylated and total NUAK1 protein expression are decreased in STK11-knockout cells and spheroids. NUAK1 can negatively control cell growth and proliferation by direct regulation of cell cycle checkpoint proteins in several cell systems; however, it has been relatively understudied in EOC. In analysis of the serous ovarian carcinoma data from TCGA, NUAK1 is infrequently altered ( Citation Format: Parima Saxena, Olga Collins, Yudith Ramos Valdes, Adrian Buensuceso, Kyle Francis, Kevin Brown, Karen Colwill, Anne-Claude Gingras, Robert Rottapel, Gabriel E. DiMattia, Trevor G. Shepherd. NUAK1 acts as a growth suppressor in epithelial ovarian cancer. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A17.

Background Epithelial ovarian cancer exhibits extensive interpatient and intratumoral heterogeneity, which can hinder successful treatment strategies. Herein, we investigated the efficacy of an emerging oncolytic, Maraba virus (MRBV), in an in vitro model of ovarian tumour heterogeneity. Methods Four ovarian high-grade serous cancer (HGSC) cell lines were isolated and established from a single patient at four points during disease progression. Limiting-dilution subcloning generated seven additional subclone lines to assess intratumoral heterogeneity. MRBV entry and oncolytic efficacy were assessed among all 11 cell lines. Low-density receptor (LDLR) expression, conditioned media treatments and co-cultures were performed to determine factors impacting MRBV oncolysis. Results Temporal and intratumoral heterogeneity identified two subpopulations of cells: one that was highly sensitive to MRBV, and another set which exhibited 1000-fold reduced susceptibility to MRBV-mediated oncolysis. We explored both intracellular and extracellular mechanisms influencing sensitivity to MRBV and identified that LDLR can partially mediate MRBV infection. LDLR expression, however, was not the singular determinant of sensitivity to MRBV among the HGSC cell lines and subclones. We verified that there were no apparent extracellular factors, such as type I interferon responses, contributing to MRBV resistance. However, direct cell-cell contact by co-culture of MRBV-resistant subclones with sensitive cells restored virus infection and oncolytic killing of mixed population. Conclusions Our data is the first to demonstrate differential efficacy of an oncolytic virus in the context of both spatial and temporal heterogeneity of HGSC cells and to evaluate whether it will constitute a barrier to effective viral oncolytic therapy. Electronic supplementary material The online version of this article (10.1186/s12885-017-3600-2) contains supplementary material, which is available to authorized users.

// Teresa Peart 1, 2 , Yudith Ramos Valdes 1 , Rohann J. M. Correa 1, 3 , Elena Fazio 1, 2 , Monique Bertrand 1, 4, 5 , Jacob McGee 1, 4 , Michel Prefontaine 1, 4 , Akira Sugimoto 1, 4, 5 , Gabriel E. DiMattia 1, 3, 4, 5 , Trevor G. Shepherd 1, 2, 4, 5 1 Translational Ovarian Cancer Research Program, London Regional Cancer Program, London, Ontario, Canada 2 Departments of Anatomy & Cell Biology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada 3 Departments of Biochemistry, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada 4 Departments of Obstetrics & Gynaecology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada 5 Departments of Oncology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada Correspondence to: Trevor G. Shepherd, e-mail: tshephe6@uwo.ca Keywords: ovarian cancer, spheroid, LKB1, AMPK, tumour cell dormancy Received: May 14, 2015 Accepted: May 23, 2015 Published: June 05, 2015 ABSTRACT Metastatic epithelial ovarian cancer (EOC) cells can form multicellular spheroids while in suspension and disperse directly throughout the peritoneum to seed secondary lesions. There is growing evidence that EOC spheroids are key mediators of metastasis, and they use specific intracellular signalling pathways to control cancer cell growth and metabolism for increased survival. Our laboratory discovered that AKT signalling is reduced during spheroid formation leading to cellular quiescence and autophagy, and these may be defining features of tumour cell dormancy. To further define the phenotype of EOC spheroids, we have initiated studies of the Liver kinase B1 (LKB1)-5′-AMP-activated protein kinase (AMPK) pathway as a master controller of the metabolic stress response. We demonstrate that activity of AMPK and its upstream kinase LKB1 are increased in quiescent EOC spheroids as compared with proliferating adherent EOC cells. We also show elevated AMPK activity in spheroids isolated directly from patient ascites. Functional studies reveal that treatment with the AMP mimetic AICAR or allosteric AMPK activator A-769662 led to a cytostatic response in proliferative adherent ovarian cancer cells, but they fail to elicit an effect in spheroids. Targeted knockdown of STK11 by RNAi to reduce LKB1 expression led to reduced viability and increased sensitivity to carboplatin treatment in spheroids only, a phenomenon which was AMPK-independent. Thus, our results demonstrate a direct impact of altered LKB1-AMPK signalling function in EOC. In addition, this is the first evidence in cancer cells demonstrating a pro-survival function for LKB1, a kinase traditionally thought to act as a tumour suppressor.

Epithelial ovarian cancer (EOC) generates multicellular aggregates called spheroids that detach from the primary tumor and disseminate through ascites. Spheroids possess a number of characteristics of tumor dormancy including withdrawal from the cell cycle and resistance to chemotherapeutics. This report systematically analyzes the effects of RNAi depletion of 21 genes that are known to contribute to negative regulation of the cell cycle in 10 ovarian cancer cell lines. Interestingly, spheroid cell viability was compromised by loss of some cyclin-dependent kinase inhibitors such as p57Kip2, as well as Dyrk1A, Lin52, and E2F5 in most cell lines tested. Many genes essential for EOC spheroid viability are pertinent to the mammalian DREAM repressor complex. Mechanistically, the data demonstrate that DREAM is assembled upon the induction of spheroid formation, which is dependent upon Dyrk1A. Loss of Dyrk1A results in retention of the b-Myb–MuvB complex, elevated expression of DREAM target genes, and increased DNA synthesis that is coincident with cell death. Inhibition of Dyrk1A activity using pharmacologic agents Harmine and INDY compromises viability of spheroids and blocks DREAM assembly. In addition, INDY treatment improves the response to carboplatin, suggesting this is a therapeutic target for EOC treatment. Implications: Loss of negative growth control mechanisms in cancer dormancy lead to cell death and not proliferation, suggesting they are an attractive therapeutic approach. Mol Cancer Res; 15(4); 371–81. ©2016 AACR.

Most epithelial ovarian cancer (EOC) patients with metastatic disease initially respond to cytotoxic chemotherapy, yet almost all will relapse with resistant disease. Thus, improving patient outcomes will require novel approaches to limit metastasis and overcome chemo-resistance. Liver Kinase B1 (LKB1), encoded by the STK11 gene, is a key intracellular regulator of metabolic stress and is considered a putative tumor suppressor in some cancers. However, we have demonstrated that LKB1 is intact and required for EOC cell viability and growth in an in vitro spheroid model of ovarian cancer metastasis. We propose that LKB1 signaling enables malignant EOC cells to maintain viability and survive in metabolically challenging environments like that encountered during intraperitoneal metastasis. To further investigate the therapeutic potential of targeting LKB1 activity in metastatic EOC, we generated STK11-knockout cell lines—normal FT190 cells, and EOC cell lines OVCAR8, HeyA8, and iOvCa147—using CRISPR technology. STK11KO resulted in decreased malignant properties of EOC cells in vitro, including clonogenicity and anchorage-independent growth; however, loss of LKB1 in FT190 cells had no effect on cell proliferation, clonogenicity, or anchorage-independent growth, indicating LKB1 does not likely act as a tumor suppressor in EOC. Loss of LKB1 sensitized EOC cells to the growth-inhibiting effects of specific metabolic stresses. OVCAR8-STK11KO cells were more sensitive to nutrient deprivation in adherent culture, and to carboplatin and paclitaxel treatment in spheroid culture, as compared with OVCAR8 cells. Among the three EOC cell lines, STK11KO yielded variable sensitivity to inhibition of mitochondrial ATP production via oligomycin treatment. Interestingly, STK11KO did not affect induction of AMP-activated protein kinase (AMPK) phosphorylation in EOC spheroids, indicating that metabolic stress signaling to support EOC cell survival in spheroids during metastasis may occur via alternative pathways. In support of our previous knockdown results, EOC spheroids completely lacking LKB1 had markedly impaired growth in suspension culture compared to parental cell controls. In contrast, FT190 spheroids exhibited rapid cell attrition in spheroid culture regardless of LKB1 status. These results indicate that LKB1 may be specifically required in EOC cells to evade anoikis during metastatic spread. Finally, to test directly whether loss of LKB1 activity affects the metastatic potential of EOC cells, we performed intraperitoneal injections of OVCAR8-STK11KO and HeyA8-STK11KO cells with their respective parental cell controls. Loss of LKB1 in both aggressive EOC cell lines exhibited a dramatic reduction on tumor burden. STK11KO significantly decreased the establishment of large, solid tumor masses, reduced adhesion of OVCAR8 tumor nodules, and even changed the metastatic trajectory of HeyA8 cells with evidence of tumor cell growth only as a thin layer on peritoneal walls. Histologic analysis revealed evidence of extensive necrosis in STK11KO tumors, which was likely the major contributor to reduced tumor burden. These results strongly indicate that loss of LKB1 activity abrogates the metabolic stress response necessary during EOC metastasis both in spheroids and establishment of intraperitoneal tumors. Overall, LKB1 or its AMPK-independent signaling mediators represent unique yet very potent therapeutic vulnerabilities in metastatic EOC. Citation Format: Adrian Buensuceso, Yudith R. Valdes, Rene Figueredo, Gabriel E. DiMattia, Trevor G. Shepherd. The metabolic stress mediator LKB1 is required for ovarian cancer metastasis. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A12.

Epithelial ovarian cancer is unique among most carcinomas in that metastasis occurs by direct dissemination of malignant cells traversing throughout the intraperitoneal fluid. Accordingly, we test new therapeutic strategies using an in vitro three-dimensional spheroid suspension culture model that mimics key steps of this metastatic process. In the present study, we sought to uncover the differential oncolytic efficacy among three different virusesâMyxoma virus, double-deleted vaccinia virus, and Maraba virusâusing three ovarian cancer cell lines in our metastasis model system. Herein, we demonstrate that Maraba virus effectively infects, replicates, and kills epithelial ovarian cancer (EOC) cells in proliferating adherent cells and with slightly slower kinetics in tumor spheroids. Myxoma virus and vaccinia viruses infect and kill adherent cells to a much lesser extent than Maraba virus, and their oncolytic potential is almost completely attenuated in spheroids. Myxoma virus and vaccinia are able to infect and spread throughout spheroids, but are blocked in the final stages of the lytic cycle, and oncolytic-mediated cell killing is reactivated upon spheroid reattachment. Alternatively, Maraba virus has a remarkably reduced ability to initially enter spheroid cells, yet rapidly infects and spreads throughout spheroids generating significant cell killing effects. We show that low-density lipoprotein receptor expression in ovarian cancer spheroids is reduced and this controls efficient Maraba virus binding and entry into infected cells. Taken together, these results are the first to implicate the potential impact of differential viral oncolytic properties at key steps of ovarian cancer metastasis.

Background Autophagy is a conserved cellular self-digestion mechanism that can either suppress or promote cancer in a context-dependent manner. In ovarian cancer, prevalent mono-allelic deletion of BECN1 (a canonical autophagy-inducer) suggests that autophagy is impaired to promote carcinogenesis and that Beclin-1 is a haploinsufficient tumor suppressor. Nonetheless, autophagy is known to be readily inducible in ovarian cancer cells. We sought to clarify whether Beclin-1 expression is in fact disrupted in ovarian cancer and whether this impacts autophagy regulation. Methods BECN1 expression levels were assessed using The Cancer Genome Atlas (TCGA) datasets from 398 ovarian high-grade serous cystadenocarcinomas (HGSC) and protein immunoblot data from HGSC samples obtained at our institution. Knockdown of BECN1 and other autophagy-related gene expression was achieved using siRNA in established human ovarian cancer cell lines (CaOV3, OVCAR8, SKOV3, and HeyA8) and a novel early-passage, ascites-derived cell line (iOvCa147-E2). LC3 immunoblot, autophagic flux assays, transmission electron microscopy and fluorescence microscopy were used to assess autophagy. Results We observed prevalent mono-allelic BECN1 gene deletion (76 %) in TCGA tumors, yet demonstrate for the first time that Beclin-1 protein expression remains relatively unaltered in these and additional samples generated at our institution. Surprisingly, efficient siRNA-mediated Beclin-1 knockdown did not attenuate autophagy induction, whereas knockdown of other autophagy-related genes blocked the process. Beclin-1 knockdown instead decreased cell viability without inducing apoptosis. Conclusions Taken together, these data demonstrate that despite its sustained expression, Beclin-1 is dispensable for autophagy induction in ovarian tumor cells in vitro, yet may be retained to promote cell viability by a mechanism independent of autophagy or apoptosis regulation. Overall, this work makes novel observations about tumor expression of Beclin-1 and challenges the accepted understanding of its role in regulating autophagy in ovarian cancer. Electronic supplementary material The online version of this article (doi:10.1186/s13048-015-0182-y) contains supplementary material, which is available to authorized users.

Aberrant cell metabolism is rapidly establishing itself as a critical hallmark of human malignancies. Cancer cells are faced with huge metabolic demands to support rapid tumor growth, yet are commonly starved for nutrients. In response, cancer cells hijack alternative signaling pathways during these times of energy and metabolic stress to sustain viability. Metastatic epithelial ovarian cancer (EOC) cells are faced with additional stressors during transcoelomic spread, such as detachment from a matrix substratum and inhospitable conditions in peritoneal fluid. However, EOC cells have a natural ability to aggregate when in suspension to form multicellular aggregates, or spheroids, which supports a survival advantage for cells when transiting the peritoneal space during metastatic progression. Therefore, we utilize an in vitro spheroid culture model system to investigate signaling pathways altered in EOC cells that may be implicated in ovarian cancer pathobiology and promote metastasis. For example, we have shown that spheroid formation induces cellular quiescence and autophagy, two disparate processes which promote EOC cell survival and resistance to platinum-based chemotherapeutics. In addition, we discovered that EOC spheroids have significantly reduced mitochondrial activity and ATP levels compared with matched proliferating adherent cells. Liver kinase B1 (LKB1) acts as a chief responder to intracellular stress due to reduced energy and nutrients by eliciting general growth suppression during these starvation-like conditions. Thus, we hypothesized that LKB1 activity is increased in EOC spheroids to promote tumor cell dormancy and cell survival. Although the STK11 gene encoding LKB1 is heterozygously deleted in 84% of serous ovarian tumors, we demonstrate that almost all ovarian tumor cells and established EOC cell lines retain intact LKB1 expression. In fact, LKB1 protein expression increases when EOC cells form spheroids and this coincides with induced serine-428 phosphorylation, a modification that is required for LKB1 growth suppressive activity. To address the potential functional requirement of LKB1 in EOC spheroids, we first performed transient knockdown of STK11 to block LKB1 expression. Indeed, reduced LKB1 renders spheroids susceptible to cell death and increases sensitivity to carboplatin. Next, we utilized Cas9-mediated genome editing of the STK11 locus to completely ablate LKB1 expression in HEYA8 and OVCAR8 cells. STK11-knockout HEYA8 and OVCAR8 cells yielded significantly decreased spheroid number and viability compared with parental cell lines. In a reciprocal fashion, forced re-expression of LKB1 in CaOV3 and TOV21G cells—two EOC cell lines which harbor inactivating STK11 mutations—reduces cell growth and colony formation in proliferating adherent culture. Proliferation and dispersion of CaOV3-LKB1 and TOV21G-LKB1 cells from re-attached spheroids are also reduced. Taken together, LKB1 has growth suppressive effects in EOC cells, yet it serves the additional purpose to promote cell survival in spheroids. The canonical target of LKB1 is AMP-activated protein kinase (AMPK), which is thought to elicit the majority of LKB1 growth suppressive effects during stress metabolism signaling. As expected, AMPK phosphorylation at threonine-172 is also induced upon spheroid formation. Using STK11-knockout EOC cells, however, we demonstrate that LKB1 is not required to phosphorylate AMPK in spheroids; more importantly, knockdown of PRKAA1 encoding the catalytic alpha-subunit of AMPK has no effect on spheroid cell viability. Thus, our results suggest that LKB1 utilizes alternative mechanisms to regulate the dormancy phenotype in EOC spheroids. Future work will entail direct experiments testing whether LKB1-mediated stress metabolism signaling has the potential to promote EOC metastasis and recurrence of chemo-resistant disease. Citation Format: Trevor G. Shepherd, Yudith Ramos Valdes, Teresa Peart, Meera Shah, Gabriel E. DiMattia. Stress management: LKB1 controls growth and survival of dormant epithelial ovarian cancer spheroid cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B51.

Epithelial ovarian cancer (EOC) cells have the ability to form multi-cellular aggregates in malignant ascites which dramatically alters cell signalling, survival, and metastatic potential. Herein, we demonstrate that patient ascites-derived EOC cells down-regulate endogenous bone morphogenetic protein (BMP) signalling by decreasing BMP ligand expression when grown in suspension culture to form spheroids. Enforced BMP signalling in these cells via constitutively-active BMP type I ALK3(QD) receptor expression causes the formation of smaller, more loosely-aggregated spheroids. Additionally, ALK3(QD)-expressing spheroids have an increased rate of adhesion and dispersion upon reattachment to substratum. Inhibition of endogenous BMP signalling using recombinant Noggin or small molecule inhibitor LDN-193189, on the other hand, opposed these phenotypic changes. To identify potential targets that impact the phenotype of EOC spheroids due to activated BMP signalling, we performed genome-wide expression analyses using Affymetrix arrays. Using the online Connectivity Map resource, the BMP signalling gene expression signature revealed that the AKT pathway is induced by activated BMP signalling in EOC cells; this finding was further validated by phospho-AKT immuno-blotting. In fact, treatment of EOC spheroids with an AKT inhibitor, Akti-1/2, reduced BMP-stimulated cell dispersion during reattachment as compared to controls. Thus, we have identified AKT as being one important downstream component of activated BMP signalling on EOC spheroid pathobiology, which may have important implications on the metastatic potential of this malignancy.

Epithelial ovarian cancer (EOC) metastasis proceeds by an intra-peritoneal route, involving detachment of cells from the primary tumor and dissemination throughout the peritoneal cavity as multicellular aggregates, or spheroids. Herein, we demonstrate that ascites-derived cells upregulate the process of macroautophagy (autophagy), a highly-conserved self-digestion mechanism that functions to mitigate cellular stresses. Both non-adherent culture of these cells to form in vitro spheroids as well as exposure to an allosteric AKT inhibitor stimulated this process, as evidenced by Western blot and immunofluorescence staining for the autophagy marker MAP1LC3B (LC3). Likewise, expression of an eGFP-labeled LC3 protein revealed a shift from diffuse to ‘punctate’ cytoplasmic localization, demonstrating the formation of intracellular autophagic vesicles (autophagosomes). Additionally, we performed transmission electron microscopy and autophagy flux assays, confirming that autophagic degradation proceeded to completion. To determine the role of autophagy upregulation, we attempted to block this process using siRNAs targeting critical autophagy-related (ATG) genes. Interestingly, we found that depletion of Beclin1/ATG6 had no effect on autophagy, despite its role as a canonical inducer of the process. Conversely, depletion of the autophagy regulators ATG5 & ATG7 efficiently blocked LC3 processing and autophagosome formation. Likewise, autophagy was also blocked pharmacologically using the classical inhibitor Chloroquine and the novel agent Spautin-1 (the first targeted autophagy inhibitor to be published). Autophagy blockade by any of these mechanisms reduced EOC cell viability in both adherent and spheroid cultures, suggesting that the upregulation of this process serves to promote cell survival. Moreover, when autophagy blockade was combined with AKT inhibition, a synergistic reduction in cell survival was observed based on combination index analysis. Taken together, this work describes spheroid formation as a stimulus for a non-canonical, Beclin1-independent autophagy program, but also reveals autophagy to be a promoter of tumor cell survival during ovarian cancer metastasis, particularly in cells subjected to AKT/mTOR inhibition. In light of these findings, we propose that clinical autophagy inhibition could enhance the effectiveness of current or investigational ovarian cancer therapies. Citation Format: Rohann Correa, Yudith Ramos-Valdes, Teresa Peart, Elena Fazio, Monique Bertrand, Jacob McGee, Michel Préfontaine, Akira Sugimoto, Trevor G. Shepherd, Gabriel E. DiMattia. Beclin1-independent autophagy promotes the survival of metastatic ovarian cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A45.

Metastatic epithelial ovarian cancer (EOC) cells can form multicellular spheroids while in suspension and disperse throughout the peritoneum via ascites to seed secondary lesions. We hypothesize that EOC spheroids are key mediators of metastasis, which use specific signaling pathways to alter cell metabolism for increased survival. Our lab discovered that AKT signaling is reduced during spheroid formation leading to cellular quiescence and autophagy. Given the induction of quiescence and autophagy in EOC spheroids, we are studying the 5′-AMP-activated protein kinase (AMPK) pathway as a master controller of the metabolic stress response and dormant phenotype of EOC spheroids. We demonstrate AMPK activity and its upstream kinase LKB1 are increased in quiescent EOC spheroids compared with proliferating adherent EOC cells. We also show elevated AMPK activity in spheroids isolated directly from patient ascites. Targeted knockdown of STK11, encoding LKB1, reduces cell viability in ovarian cancer cell line spheroids; PRKAA1 (AMPKα1) knockdown has little to no effect on EOC cell or spheroid viability. Combination of STK11 knockdown with carboplatin treatment leads to a synergistic enhancement in EOC spheroid cell death. In contrast, AICAR treatment of proliferating adherent ovarian cancer cell lines and primary EOC cells induces AMPK activity and causes either cytostasis or cell death. In addition, AICAR treatment of spheroids during reattachment decreases the dispersion capacity of migrating EOC cells. These results offer a glimpse of the potential important contributions of LKB1-AMPK pathway in stress signaling related to EOC cell survival during metastasis. In addition, downstream effectors of upregulated LKB1-AMPK signalling may provide additional mechanisms by which EOC evades chemotherapy. It is foreseeable that these findings will allow us to identify new therapeutic targets within this pathway critical to EOC progression for ultimate translation to the clinic. Citation Format: Teresa Peart, Elena Fazio, Yudith Ramos-Valdes, Monique Bertrand, Jacob McGee, Michel Prefontaine, Akira Sugimoto, Gabriel E. DiMattia, Trevor G. Shepherd. The LKB1-AMPK pathway mediates the metabolic stress response of dormant ovarian cancer spheroids. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A47.