Cyclin-dependent Kinase 2 Activity Research Articles

A novel function for CDK2 activity at meiotic crossover sites.

Genetic diversity in offspring is induced by meiotic recombination, which is initiated between homologs at >200 sites originating from meiotic double-strand breaks (DSBs). Of this initial pool, only 1–2 DSBs per homolog pair will be designated to form meiotic crossovers (COs), where reciprocal genetic exchange occurs between parental chromosomes. Cyclin-dependent kinase 2 (CDK2) is known to localize to so-called “late recombination nodules” (LRNs) marking incipient CO sites. However, the role of CDK2 kinase activity in the process of CO formation remains uncertain. Here, we describe the phenotype of 2 Cdk2 point mutants with elevated or decreased activity, respectively. Elevated CDK2 activity was associated with increased numbers of LRN-associated proteins, including CDK2 itself and the MutL homolog 1 (MLH1) component of the MutLγ complex, but did not lead to increased numbers of COs. In contrast, reduced CDK2 activity leads to the complete absence of CO formation during meiotic prophase I. Our data suggest an important role for CDK2 in regulating MLH1 focus numbers and that the activity of this kinase is a key regulatory factor in the formation of meiotic COs.

Targeting CDK9: A novel biomarker inthetreatment of endometrial cancer.

Endometrial cancer is one of the three major malignant tumors of the female reproductive system. Although cyclin-dependent kinase 9 (CDK9) has a definitive pathogenic role in various types of cancer, little is known concerning its function in endometrial cancer. Our study was conducted to evaluate the expression and therapeutic potential of CDK9 in endometrial cancer. CDK9 expression was determined by immunohistochemistry in endometrial cancer tissues constructed with paired primary, metastatic, and recurrent tumor tissues from 32 endometrial cancer patients. Small interfering RNA (siRNA) and inhibitors of CDK9 were used to evaluate the effect of CDK9 inhibition on the anti-apoptotic activity and proliferation in endometrial cancer cells. Colony formation assay and wound-healing assays were adopted to assess clonal formation and migratory capacity. The results of the immunohistochemistry demonstrated that CDK9 was highly expressed in the human endometrial cancer cell lines; moreover, it was elevated in metastatic and recurrent endometrial tumor tissue compared when compared with that in patient-matched primary endometrial tumor tissue. Knockdown of CDK9 with siRNA and inhibition of CDK9 activity with the inhibitor suppressed cell proliferation and promoted apoptosis in endometrial cancer. In conclusion, our results provide evidence that CDK9 may be a potential prognostic biomarker and a promising therapeutic target for the treatment of endometrial cancer in the future.

Abstract 5826: Molecular mechanism of OLIG2-CDK2 interaction in glioma cells

Abstract Oligodendrocyte transcription factor 2 (Olig2) promotes proliferation of normal neural stem/progenitor cells and glioma cells. However, the mechanisms underlying the regulation of Olig2 remain largely unknown. Here we identified Olig2 as a critical phosphorylation target for cyclin-dependent kinase 2 (CDK2). CDK2-mediated Olig2 phosphorylation stabilizes Olig2 protein from proteasomal degradation. Phosphorylated Olig2 binds to the E-Box regions of p27 promoter and represses p27 transcription, which in turn activates CDK2 in positive feedback manner. CDK2-mediated Olig2 phosphorylation promotes cell cycle progression, cell proliferation, and tumorigenesis. Olig2 inhibition disrupted cell cycle control mechanism by decreasing CDK2 and elevating apoptosis-related molecules. Inhibition of CDK2 activity disrupted Olig2-CDK2 interactions and attenuated Olig2 protein stability. In addition, Olig2-high glioma initiating cells are highly sensitive to CDK2 inhibitor treatment, indicating that Olig2 can be a biomarker for personalized treatment for glioblastoma patients with CDK2 inhibitors. Further investigation on these mechanisms may lead to novel targeted therapy on GBMs with high Olig2 expression. Citation Format: Norihiko Saito, Nozomi Hirai, Sho Sato, Yu Hiramoto, Satoshi Fujita, Haruo Nakayama, Morito Hayashi, Takatoshi Sakurai, Satoshi Iwabuchi. Molecular mechanism of OLIG2-CDK2 interaction in glioma cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5826.

Screening and analysis of bioactive food compounds for modulating the CDK2 protein for cell cycle arrest: Multi-cheminformatics approaches for anticancer therapeutics

The cyclin-dependent kinase-2 (CDK2) belongs to the protein kinase family and its overexpression leads to an unusual regulation of cell-cycle which directly linked with hyperproliferation in many cancer cell types. CDK2 activation spontaneously promotes the cell cycle progression and also involved in a large number of cellular processes including cell cycle regulation, DNA replication, DNA damage response and apoptotic pathways, therefore targeting the CDK2 can be reemerged as a therapeutic boulevard to restrain cancer cell proliferation. For the last two decades, emerging evidences suggested that CDK2 inhibition draws out some antitumor/anticancer activity, which has driven the research possibility for developing next-generation newer or cost-effective inhibitors with greater specificity to CDK2. In the current work, compounds from the FooDB - a world’s largest food constituents database was retrieved and curated and followed by multi-pharmacoinformatics approaches adopted to find out potential CDK2 inhibitors. The curated dataset was considered for screening through “Virtual Screening Workflow” (VSW) employed in Schrödinger suite. The numbers of cost-effective food constituents were reduced by removing low potential molecules in terms of interaction affinity and further explored for pharmacokinetics analysis. Based on strong binding interaction profiles with the lowest binding interactions affinity and energy values, four food compounds were proposed as CDK2 inhibitors. A number of key analyzing parameters from molecular dynamics (MD) simulations studies were successfully substantiated that all four proposed food compounds can act as CDK2 inhibitors based on their proficient structural and molecular interactions integrity with CDK2 protein following in the active site cavity. Furthermore, the binding free energy was calculated using the MM-PBSA (Molecular Mechanics Poisson-Boltzmann Surface Area) approach from the entire trajectory frames derived in MD simulation revealed strong interaction affinity. The binding free energy was found to be in the range of −991.831 to −210.452 kJ/mol. High binding free energy was undoubtedly explained that all molecules possess strong affection towards CDK2. Hence, proposed molecules may be crucial to stop the hyperproliferation in cancer cells subjected to experimental validation.

Network mechanisms and dysfunction within an integrated computational model of progression through mitosis in the human cell cycle.

The cellular protein-protein interaction network that governs cellular proliferation (cell cycle) is highly complex. Here, we have developed a novel computational model of human mitotic cell cycle, integrating diverse cellular mechanisms, for the purpose of generating new hypotheses and predicting new experiments designed to help understand complex diseases. The pathogenic state investigated is infection by a human herpesvirus. The model starts at mitotic entry initiated by the activities of Cyclin-dependent kinase 1 (CDK1) and Polo-like kinase 1 (PLK1), transitions through Anaphase-promoting complex (APC/C) bound to Cell division cycle protein 20 (CDC20), and ends upon mitotic exit mediated by APC/C bound to CDC20 homolog 1 (CDH1). It includes syntheses and multiple mechanisms of degradations of the mitotic proteins. Prior to this work, no such comprehensive model of the human mitotic cell cycle existed. The new model is based on a hybrid framework combining Michaelis-Menten and mass action kinetics for the mitotic interacting reactions. It simulates temporal changes in 12 different mitotic proteins and associated protein complexes in multiple states using 15 interacting reactions and 26 ordinary differential equations. We have defined model parameter values using both quantitative and qualitative data and using parameter values from relevant published models, and we have tested the model to reproduce the cardinal features of human mitosis determined experimentally by numerous laboratories. Like cancer, viruses create dysfunction to support infection. By simulating infection of the human herpesvirus, cytomegalovirus, we hypothesize that virus-mediated disruption of APC/C is necessary to establish a unique mitotic collapse with sustained CDK1 activity, consistent with known mechanisms of virus egress. With the rapid discovery of cellular protein-protein interaction networks and regulatory mechanisms, we anticipate that this model will be highly valuable in helping us to understand the network dynamics and identify potential points of therapeutic interventions.

The Photorhabdus Virulence Cassettes RRSP-Like Effector Interacts With Cyclin-Dependent Kinase 1 and Causes Mitotic Defects in Mammalian Cells.

The “Photorhabdus virulence cassettes” (PVCs) secreted by Photorhabdus are defined as “extracellular contractile injection systems” (eCISs) and can deliver effectors to eukaryotic hosts for cytotoxicity. Previously, we demonstrated the cryogenic electron microscopy (cryo-EM) structure and assembly process of an intact PVC particle from Photorhabdus asymbiotica. In this work, we characterized the biological functions of a PVC effector, which is defined as a homologous protein of Ras/Rap1-specific endopeptidase domain (RRSP) in the multifunctional autoprocessing repeats-in-toxin (MARTX) toxin from Vibrio vulnificus. In this work, we found that the RRSP homologous protein (RRSPPa) was associated with inhibition of cell proliferation and increased cell apoptosis and death of HeLa cells. Furthermore, we discovered that RRSPPa disturbed mitotic progression, including the induction of cell cycle alteration, retardation of cell abscission time, and regression of the cleavage furrow. In addition, we revealed that RRSPPa could target the cyclin-dependent kinase 1 (CDK1) protein and block activation of CDK1 through inhibition of Thr161 phosphorylation, which partially explained the crucial role of this effector in cell mitosis.

Identification of High-Affinity Inhibitors of Cyclin-Dependent Kinase 2 Towards Anticancer Therapy.

Cyclin-dependent kinase 2 (CDK2) is an essential protein kinase involved in the cell cycle regulation. The abnormal activity of CDK2 is associated with cancer progression and metastasis. Here, we have performed structure-based virtual screening of the PubChem database to identify potent CDK2 inhibitors. First, we retrieved all compounds from the PubChem database having at least 90% structural similarity with the known CDK2 inhibitors. The selected compounds were subjected to structure-based molecular docking studies to investigate their pattern of interaction and estimate their binding affinities with CDK2. Selected compounds were further filtered out based on their physicochemical and ADMET properties. Detailed interaction analysis revealed that selected compounds interact with the functionally important residues of the active site pocket of CDK2. All-atom molecular dynamics simulation was performed to evaluate conformational changes, stability and the interaction mechanism of CDK2 in-complex with the selected compound. We found that binding of 6-N,6-N-dimethyl-9-(2-phenylethyl)purine-2,6-diamine stabilizes the structure of CDK2 and causes minimal conformational change. Finally, we suggest that the compound (PubChem ID 101874157) would be a promising scaffold to be further exploited as a potential inhibitor of CDK2 for therapeutic management of cancer after required validation.

Analog-sensitive cell line identifies cellular substrates of CDK9.

Transcriptional cyclin-dependent kinases regulate all phases of transcription. Cyclin-dependent kinase 9 (CDK9) has been implicated in the regulation of promoter-proximal pausing of RNA polymerase II and more recently in transcription termination. Study of the substrates of CDK9 has mostly been limited to in vitro approaches that lack a quantitative assessment of CDK9 activity. Here we analyzed the cellular phosphoproteome upon inhibition of CDK9 by combining analog-sensitive kinase technology with quantitative phosphoproteomics in Raji B-cells. Our analysis revealed the activity of CDK9 on 1102 phosphosites quantitatively, and we identified 120 potential cellular substrates. Furthermore, a substantial number of CDK9 substrates were described as splicing factors, highlighting the role of CDK9 in transcription-coupled splicing events. Based on comparison to in vitro data, our findings suggest that cellular context fundamentally impacts the activity of CDK9 and specific selection of its substrates.

CBMT-04. MOLECULAR MECHANISM OF OLIG2-CDK2 INTERACTION IN GLIOMA CELLS

Abstract Oligodendrocyte transcription factor 2 (OLIG2) promotes proliferation of normal neural stem/progenitor cells and glioma cells. However, the mechanisms underlying the regulation of OLIG2 remain largely unknown. Here we identified OLIG2 as a critical phosphorylation target for cyclin-dependent kinase 2 (CDK2). CDK2-mediated OLIG2 phosphorylation stabilizes OLIG2 protein from proteasomal degradation. Phosphorylated OLIG2 binds to the E-Box regions of p27 promoter and represses p27 transcription, which in turn activates CDK2 in positive feedback manner. CDK2-mediated OLIG2 phosphorylation promotes cell cycle progression, cell proliferation, and tumorigenesis. OLIG2 inhibition disrupted cell cycle control mechanism by decreasing CDK2 and elevating apoptosis-related molecules. Inhibition of CDK2 activity disrupted OLIG2-CDK2 interactions and attenuated OLIG2 protein stability. In addition, OLIG2-high glioma initiating cells are highly sensitive to CDK2 inhibitor treatment, indicating that OLIG2 can be a biomarker for personalized treatment for glioblastoma patients with CDK2 inhibitors. Further investigation on these mechanisms may lead to novel targeted therapy on GBMs with high OLIG2 expression.

Synthesis, Docking Studies into CDK-2 and Anticancer Activity of New Derivatives Based Pyrimidine Scaffold and Their Derived Glycosides.

New diaryl-substituted pyrimidinedione compounds, their thioxo derivatives as well as their bicyclic thiazole compounds were synthesized and characterized. The glycosylamino derivatives of the synthesized disubstituted derivatives of the pyrimidine scaffold were also prepared via reaction of the N3-amino derivatives with a number of monosaccharides followed by acetylation. The anticancer activity of the synthesized compounds was studied against human liver cancer (HepG2) and RPE-1cell lines. Compounds 2a, 2b, 3a and 12 showed potent activities with IC50 results comparable to that of doxorubicin. Docking investigations into Cyclin-dependent kinase 2 (CDK-2) enzyme, a potential target for cancer medication, were also reported showing the possible binding interaction into the enzyme active site to support their activity behavior.

Mitotic Kinases Choreograph Receptor Storage and Redistribution During Asymmetric Cell Division

Endosomal trafficking of receptors and associated proteins plays a critical role in signal processing. Until recently, it was thought that trafficking was shut down during cell division. Thus, remarkably, the regulation of trafficking during division remains poorly characterized. Here we delineate the role of mitotic kinases in receptor trafficking during asymmetric division. Targeted perturbations reveal that Cyclin Dependent Kinase 1 (CDK1) and Aurora Kinase promote storage of Fibroblast Growth Factor Receptors (FGFRs) by suppressing endosomal degradation and recycling pathways. As cells progress through metaphase, loss of CDK1 activity permits differential degradation and targeted recycling of stored receptors, leading to asymmetric induction. Mitotic receptor storage, as delineated in this study, may facilitate rapid reestablishment of signaling competence in nascent daughter cells. However, mutations that limit or enhance the release of stored signaling components could alter daughter cell fate or behavior thereby promoting oncogenesis.

Abstract 2956: Inhibition of CHK1 sensitizes Ewing sarcoma cells to CDK1-dependent cell death in S-phase

Abstract Ewing sarcoma is a highly aggressive bone and soft tissue cancer that is caused by the EWS-FLI1 fusion protein. The treatment of Ewing sarcoma has changed very little in the past two decades and novel treatment approaches are needed. We recently identified that Ewing sarcoma cells are uniquely vulnerable to inhibitors of ribonucleotide reductase (RNR), the rate limiting enzyme in the synthesis of deoxyribonucleotides. We subsequently found that the inhibition of checkpoint kinase 1 (CHK1) increases the sensitivity of Ewing sarcoma cells to inhibitors of RNR, such as gemcitabine. The ATR-CHK1 pathway, from a mechanistic standpoint, regulates multiple stages of the cell cycle, including S-phase, the G2/M transition, and M phase. In the current work, we used cell synchronization to identify that the inhibition of CHK1 in S-phase cells results in premature entry into mitosis and cell death. Similarly, the inhibition of ATR serine/threonine kinase (ATR), the upstream activator of CHK1, also causes Ewing sarcoma cells to inappropriately enter mitosis. Moreover, we have found in Ewing sarcoma cells that this aberrant entry into mitosis is mediated, in part, by cyclin dependent kinase 1 (CDK1). In addition, activation of CDK1 by inhibiting the WEE1 kinase with AZD1775 also results in entry into mitosis and cell death in Ewing sarcoma cells. Currently, ongoing work is focused on the in vivo testing of gemcitabine in combination with CHK1 and WEE1 inhibitors as a novel therapeutic approach for the treatment of Ewing sarcoma. Citation Format: David Gordon, Kelli Goss, Stacia Koppenhafer. Inhibition of CHK1 sensitizes Ewing sarcoma cells to CDK1-dependent cell death in S-phase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2956.

Allosteric Regulation of Cyclin-B Binding by the Charge State of Catalytic Lysine in CDK1 Is Essential for Cell-Cycle Progression

Cyclin-dependent kinase 1 (CDK1) is essential for cell-cycle progression. While dependence of CDK activity on cyclin levels is well established, molecular mechanisms that regulate their binding are less understood. Here, we report for the first time that CDK1:cyclin-B binding is not default but rather determined by the evolutionarily conserved catalytic residue, lysine-33 in CDK1. We demonstrate that the charge state of this lysine allosterically remodels the CDK1:cyclin-B interface. Cell cycle-dependent acetylation of lysine-33 or its mutation to glutamine, which mimics acetylation, abrogates cyclin-B binding. Using biochemical approaches and atomistic molecular dynamics simulations, we have uncovered both short-range and long-range effects of perturbing the charged state of the catalytic lysine, which lead to inhibition of kinase activity. Specifically, although loss of the charge state of catalytic lysine did not impact ATP binding significantly, it altered its orientation in the active site. In addition, the catalytic lysine also acts as an intra-molecular electrostatic tether at the active site to orient structural elements interfacing with cyclin-B. Physiologically, opposing activities of SIRT1 and P300 regulate acetylation and thus control the charge state of lysine-33. Importantly, cells expressing acetylation mimic mutant of Cdc2/CDK1 in yeast are arrested in G2 and fail to divide, indicating the requirement of the deacetylated state of the catalytic lysine for cell division. Thus, by illustrating the molecular role of the catalytic lysine and cell cycle-dependent deacetylation as a determinant of CDK1:cyclin-B interaction, our results redefine the current model of CDK1 activation and cell-cycle progression.

Cyclin-dependent kinase 9 (CDK9) is a novel prognostic marker and therapeutic target in osteosarcoma.

BackgroundCyclin-dependent protein kinase 9 (CDK9) has been shown to play an important role in the pathogenesis of malignant tumors. However, the expression and function of CDK9 remain unknown in osteosarcomas. The purpose of this study is to assess the expression, function and clinical prognostic relationship of CDK9 in osteosarcomas.MethodsA tissue microarray of 70 patient specimens was analyzed by immunohistochemistry to measure CDK9 expression, which was further investigated for correlation with patient clinical characteristics. CDK9 expression in osteosarcoma cell lines and patient tissues was also evaluated by Western blotting. CDK9-specific siRNA and the CDK9 inhibitor were applied to determine the effect of CDK9 inhibition on osteosarcoma cell proliferation and anti-apoptotic activity. The clonogenicity and migration activity were also examined using clonogenic and wound healing assays. A 3D cell culture model was performed to mimic the in vivo osteosarcoma environment to further validate the effect of CDK9 inhibition on osteosarcoma cells.FindingsWe demonstrated that higher CDK9-expression is associated with significantly shortened patient survival by immunohistochemistry. Expression of CDK9 is inversely correlated to the percent of tumor necrosis post-neoadjuvant chemotherapy, which is the most important predictive factor of disease outcome for osteosarcoma patients. Knockdown of CDK9 with siRNA and inhibition of CDK9 activity with inhibitor decreased cell proliferation and induced apoptosis in osteosarcoma.InterpretationHigh expression of CDK9 is an independent predictor of poor prognosis in osteosarcoma patients. Our results suggest that CDK9 is a novel prognostic marker and a promising therapeutic target for osteosarcomas.

Cyclin-Dependent Kinase 2 Inhibitors in Cancer Therapy: An Update.

Cyclin-dependent kinase 2 (CDK2) drives the progression of cells into the S- and M-phases of the cell cycle. CDK2 activity is largely dispensable for normal development, but it is critically associated with tumor growth in multiple cancer types. Although the role of CDK2 in tumorigenesis has been controversial, emerging evidence proposes that selective CDK2 inhibition may provide a therapeutic benefit against certain tumors, and it continues to appeal as a strategy to exploit in anticancer drug development. Several small-molecule CDK2 inhibitors have progressed to the clinical trials. However, a CDK2-selective inhibitor is yet to be discovered. Here, we discuss the latest understandings of the role of CDK2 in normal and cancer cells, review the core pharmacophores used to target CDK2, and outline strategies for the rational design of CDK2 inhibitors. We attempt to provide an outlook on how CDK2-selective inhibitors may open new avenues for cancer therapy.

Development and Use of Clinical Pharmacodynamic Assays to Demonstrate Target Engagement for AZD4573, a Selective and Potent CDK9 Inhibitor Currently in Phase I Clinical Trials

CDK9 (cyclin-dependent kinase 9) regulates RNA transcription through its phosphorylation of RNA polymerase II and subsequent release from a “paused” elongation state, resulting in transcriptional activity. A transient inhibition of CDK9 activity will significantly impact transcripts with a short half-life, which includes the transcript for MCL1, an anti-apoptotic protein. AZD4573 is a highly potent and selective CDK9 inhibitor. We have previously reported that AZD4573 treatment results in dose-dependent inhibition of pSer2 of RNA polymerase II, reductions in MCL1 mRNA and protein, and an increase in cleaved caspase 3, resulting in cell death of hematological tumor cell lines and regressions in AML/DLBCL in vivo models [Cidado et. al., AACR Annual Meeting, Abstract 310 (2018)].AZD4573 is currently being evaluated in a Phase I all-comers relapsed/refractory hematological malignancy trial (NCT03263637). To generate clinical evidence that the compound is inhibiting its target and having the expected downstream effects, we have developed pharmacodynamic biomarker (PD) assays for clinical use to measure the changes in pSer2/RNApol II, MCL1 protein, cleaved Caspase 3 and cleaved PARP. We have chosen a capillary electrophoresis platform which allows quantification and multiplexing while requiring lower sample quantities (<20ng/capillary) than Western blotting. Data from AZD4573-treated MV4,11 AML cells using the clinical assays were similar to what had been shown previously with Western blotting, i.e. similar dose-dependence across 0.1nM to 1uM and >80% inhibition of both pSer2 and MCL1 at 100nM (in 10% FCS). Next, we validated the use of these assays with human peripheral blood mononuclear cells (PBMCs) since we expected that some patients from the trial are likely to have significant numbers of circulating tumor cells (i.e. AML/CLL). After incubation of human whole blood with 1uM AZD4573 for different times, PBMCs were isolated and analyzed using the capillary electrophoresis assays. These results showed at least ~80% inhibition of pSer2 at 2h, consistent with preclinical efficacy modeling and predicted clinically achievable levels. In addition, we optimized the PBMC isolation protocol for the clinical sites and showed that compound washout during the procedure did not diminish AZD4573-mediated effects. In another study, we mimicked potential clinical conditions (e.g. 30 min, 1h, and 2h between blood collection and PBMC isolation, ambient vs 37°C storage conditions) and demonstrated that significant ex vivo apoptosis (i.e. activation of cleaved caspase 3) was unlikely to occur if PBMCs were isolated within 1-2h of blood collection. Finally, by showing that AZD4573 target engagement and pathway inhibition can be measured in normal PBMCs, these assays will be informative for all patients, including those without circulating tumor cells (e.g. many lymphomas).Here we describe the development and characterization of a suite of pharmacodynamic assays for clinical use with blood samples for our CDK9 program. Preliminary data from our Phase I study demonstrate successful implementation of these assays and support that AZD4573 inhibits CDK9 with the expected downstream effects, in the clinical setting. Updated results will be presented at the meeting. DisclosuresYeh:AstraZeneca: Employment, Equity Ownership. O'Connor:AstraZeneca: Employment, Equity Ownership. Cidado:AstraZeneca: Employment, Equity Ownership. Barrett:AstraZeneca: Employment, Equity Ownership.

Pevonedistat, a Small Molecule Inhibitor of NEDD8-Activating Enzyme (NAE), Induces Cell Cycle Deregulation, Anaphase Catastrophe, and Apoptosis in T-Cell Lymphoma Cells

Introduction: Despite the significant progress of targeted therapies in B-cell malignancies, T-cell lymphomas remain an area of unmet medical need. Most patients are diagnosed at an advanced stage and have limited treatment options. Moreover, most patients who relapse following initial chemotherapy ultimately succumb to disease. Recent successes of targeting the proteasome (i.e., bortezomib) and E3 ligases (i.e., lenalidomide) identify the ubiquitin-proteasome system (UPS) as a tractable target in lymphoma. Pevonedistat, an investigational small molecule inhibitor of NEDD8-activating enzyme (NAE), interferes with activation of NEDD8, a ubiquitin-like modifier. This interference ultimately leads to decreased activity of cullin-RING (E3) ligases and accumulation of their substrates, including inhibitor of NFκB (IκB), the replication licensing protein Cdt1, and p27. We previously demonstrated that targeting NAE affected primary neoplastic B cells via several mechanisms: disruption of NFκB activity as well as induction of Cdt1, DNA damage, and cell cycle arrest. Here, we demonstrate that targeting NAE in T-cell lymphoma cells mediates apoptosis via cell cycle deregulation, accompanied by induction of Cdt1 and p27, and induction of anaphase catastrophe.Methods: Experiments were performed in T-cell lymphoma cell lines (SR, HH, Jurkat, and SUP-T1) as well as circulating primary cells from patients with peripheral T-cell lymphoma and Sezary syndrome. Pevonedistat (TAK-924) was obtained from Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda Pharmaceutical Company Limited (Cambridge, MA). Apoptosis was assessed by Annexin V staining.Results: SR (PTCL) cells and primary T-cell lymphoma cells were the most sensitive to pevonedistat (IC50of ~250nM at 24 hours); Jurkat and SUP-T1 cells demonstrated low/intermediate sensitivity, whereas HH (CTCL) cells were resistant. Targeting NAE disrupted cullin neddylation in a dose-dependent manner across all tested cell lines and primary neoplastic T cells, followed by accumulation of phospho-IκBα. Upregulation of phospho-IκBα was notable within 2 hours of pevonedistat treatment across both sensitive and resistant cell lines and primary cells. Concomitantly, we observed induction of p27 and Cdt1. Upregulation of Cdt1 was attenuated in HH cells compared with SR, consistent with the low proliferation rate of the former. Treatment of SR cells with pevonedistat led to DNA damage as evidenced by γH2AX and G2/M arrest.Chromosomal instability is a prominent feature in cancer and poorly studied as a therapeutic target. We have previously shown that cancer cells undergo multipolar anaphase in response to inhibition of cyclin-dependent kinase-2 (CDK2), an interphase CDK, followed by apoptosis and termed this event anaphase catastrophe (Hu et al., 2015; Danilov et al., 2016). As we observed robust accumulation of the endogenous CDK inhibitor p27 in cells treated with pevonedistat, an event presumed to lead to attenuated CDK2 activity, we studied anaphase catastrophe in this setting. We visualized anaphase catastrophe by immunofluorescent staining for nuclear material (DAPI) and γ-tubulin, and scored it in 50 cells per condition. NAE inhibition with pevonedistat induced anaphase catastrophe in SR and Jurkat cells. Upon 24-hour exposure to 250 nM pevonedistat, 9.8±6.0% of SR and 18±4.4% of Jurkat cells demonstrated multipolar anaphases, compared with 1±0.8% and 3.0±2.6% with vehicle control, respectively.Conclusions: Inhibiting NAE with pevonedistat induces apoptosis of T-cell lymphoma cells. We propose deregulation of Cdt1 and p27, followed by anaphase catastrophe, as a key mechanistic event implicated in pevonedistat-induced apoptosis in neoplastic T cells. Our work provides rationale to further investigate neddylation as a therapeutic target in T-cell lymphoma. DisclosuresDanilov:Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy; Genentech: Consultancy, Research Funding; Takeda Oncology: Research Funding; Gilead Sciences: Consultancy, Research Funding; Astra Zeneca: Consultancy; Aptose Biosciences: Research Funding; Bayer Oncology: Consultancy, Research Funding.

High Spy1 expression predicts poor prognosis in colorectal cancer.

BackgroundSpy1 (SPDYA) is a new discovered cell cycle protein capable of promoting cell proliferation dependent on cyclin-dependent kinase-2 activation. However, to the best of our knowledge, the expression of Spy1 in colorectal cancer (CRC) tissues remains virtually unknown.Materials and methodsIn this retrospective study, we investigated the mRNA and protein expression levels of Spy1 in CRC tissues and corresponding non-cancerous tissues with the analyses of quantitative real-time polymerase chain reaction, western blotting, and immunohistochemistry. In our research, the prognostic significances of Spy1 expression were further explored by univariate and multivariate survival analyses of 203 patients who were followed up.ResultsThe results demonstrated that the levels of Spy1 mRNA were significantly higher in CRC tissues compared with corresponding non-cancerous tissues (p=0.0002). The results of immunohistochemistry demonstrated that the expressions of Spy1 were significantly associated with clinicopathological parameters, including T stage (χ2=7.126, p=0.028) and TNM stage (χ2=9.461, p=0.009). Kaplan-Meier analysis results indicated that high Spy1 expression (HR=2.573, p<0.001) and TNM stage (HR=1.494, p=0.011) were independent factors to predict poor prognosis for patients with CRC.ConclusionWe concluded that high Spy1 expression is significantly associated with unfavorable prognosis in CRC and could serve as a potential prognostic marker in clinical diagnosis of CRC.

Abstract 2436: Anti-cancer effect by combination treatment of CDK and HSP90 inhibitors through HIF1α inhibition

Abstract Hypoxia-inducible factor 1α (HIF1α) is the main mediator of the adaptive response to intra-tumoral hypoxia. HIF1α overexpression contributes to tumor angiogenesis, cancer cell survival and metastasis. Thus, targeting HIF1α provides new opportunities for cancer therapy. We have previously shown that cyclin-dependent kinase 1 (CDK1) stabilizes HIF1α through direct phosphorylation of its Ser668 residue in a Von Hippel-Lindau (VHL)-independent or p53-independent manner both under hypoxia and at G2/M under normoxia (Warfel et al., Cell Cycle, 2013). Because heat shock protein 90 (HSP90) is a VHL-independent HIF1α stabilizer, we hypothesized CDK and CDK inhibitor effects in the stabilization/destabilization mechanism. We found that CDK1 inhibition disrupts the interaction between HSP90 and HIF1α. Moreover, administration of the CDK1 inhibitor, Ro-3306, partially reversed a heat shock (40°C) response dependent increase in the level of HIF1α, which suggests that CDK1 activity may contribute to HSP90-mediated HIF1α stabilization. Combination treatment with both HSP90 inhibitor and CDK1 inhibition/knockdown decreased HIF1α level more robustly than either single treatment. Dual inhibition of CDK1 and HSP90 not only synergistically decreased cell viability but also remarkably reduced colony formation of HCT116 colon cancer cells. Previously we have also shown that similar to CDK1, CDK4 plays a role in HIF1α stabilization as well. This led us to investigate the effect of CDK4/HSP90 dual inhibition on colorectal cancer cells. The combination treatment of CDK4 knockdown/inhibition and HSP90 inhibition reduced the level of HIF1α in various cancer cell lines (e.g., colorectal, glioblastoma, prostate cancers). The FDA-approved CDK4 inhibitor palbociclib along with ganetespib synergistically inhibited cell viability in SW480 colon cancer cells under hypoxia or normoxia. No reduction in cell viability was noted in WI38 normal cells under normoxia at similar concentrations. In addition, we tested the therapeutic potential of the dual CDKi/HSP90i therapy in vivo. The combination treatment of palbociclib and ganetespib inhibited tumor growth in the HT29 colon cancer cell xenograft mouse model at relatively low doses. Immunohistochemistry staining of the tumor samples revealed higher levels of apoptosis, lower levels of VEGF expression and reduced microvessel formation in the combination treatment group. Our findings provide a compelling rationale for a therapeutic strategy to target HIF1α through the combination of CDK and HSP90 inhibitors in cancer therapy. Citation Format: Shuai Zhao, Lanlan Zhou, David T. Dicker, Wafik S. El-Deiry. Anti-cancer effect by combination treatment of CDK and HSP90 inhibitors through HIF1α inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2436.

Fibroblast growth factor 2 induces proliferation and fibrosis via SNAI1-mediated activation of CDK2 and ZEB1 in corneal endothelium

Investigating stimulation of endogenous wound healing in corneal endothelial cells (CECs) may help address the global shortage of donor corneas by decreasing the number of transplants performed for blindness because of endothelial dysfunction. We previously reported that IL-1β stimulation leads to fibroblast growth factor (FGF2) expression, enhancing migration and proliferation of mammalian CECs. However, FGF2 also promotes the endothelial-mesenchymal transition, which can lead to retrocorneal membrane formation and blindness. This prompted us to investigate downstream FGF2 signaling targets that could be manipulated to prevent retrocorneal membrane formation. FGF2 stimulation altered cell morphology and induced expression of mesenchymal transition marker genes such as snail family transcriptional repressor 1 (SNAI1), SNAI2, zinc finger E-box-binding homeobox 1 (ZEB1), and ZEB2 This, in turn, induced expression of fibronectin, vimentin, and type I collagen, and suppressed E-cadherin in CECs in vitro and ex vivo siRNA-mediated SNAI1 knockdown revealed that SNAI1 induces ZEB1 expression, in turn inducing expression of type I collagen, the major component of retrocorneal membranes, and of cyclin-dependent kinase 2 (CDK2) and cyclin E1, promoting cell proliferation. siRNA-mediated knockdown of SNAI1 or ZEB1, but not of CDK2, inhibited FGF2-dependent expression of fibronectin, vimentin, and type I collagen and of suppression of E-cadherin expression. We conclude that SNAI1 is a key regulator of FGF2-dependent mesenchymal transition in human ex vivo corneal endothelium, with ZEB1 regulating type I collagen expression and CDK2 regulating cell proliferation. These results suggest that SNAI1 promotes fibrosis and cell proliferation in human corneal endothelium through ZEB1 and CDK2.