Driver Of Proliferation Research Articles

The Changing Face of Nuclear Proliferation

Abstract A rich literature has identified a number of important drivers of nuclear proliferation. Most of this work, however, treats the determinants of proliferation as constant over the entire nuclear age—the factors leading to proliferation are assumed to be the same in 2010 as they were in 1945. But there are reasons to suspect that the drivers of proliferation have changed over this time: nuclear technology is easier to come by, the global strategic environment has shifted, and the nuclear nonproliferation regime has come into being. To examine changes in the dynamics of nuclear proliferation, I adapt a cross-validation technique frequently used in the machine learning literature. I create a rolling window of training data with which statistical models of proliferation are built, and I then test the predictive power of these models against data from other time periods. The result of this analysis is a temporal map of how the determinants of proliferation have changed over time. My findings suggest that the underlying dynamics of nuclear proliferation have indeed shifted, with important implications both for the literature on nuclear proliferation and for policymakers interested in limiting the future spread of nuclear weapons.

KMT2C methyltransferase domain regulated INK4A expression suppresses prostate cancer metastasis

BackgroundFrequent truncation mutations of the histone lysine N-methyltransferase KMT2C have been detected by whole exome sequencing studies in various cancers, including malignancies of the prostate. However, the biological consequences of these alterations in prostate cancer have not yet been elucidated.MethodsTo investigate the functional effects of these mutations, we deleted the C-terminal catalytic core motif of Kmt2c specifically in mouse prostate epithelium. We analysed the effect of Kmt2c SET domain deletion in a Pten-deficient PCa mouse model in vivo and of truncation mutations of KMT2C in a large number of prostate cancer patients.ResultsWe show here for the first time that impaired KMT2C methyltransferase activity drives proliferation and PIN formation and, when combined with loss of the tumour suppressor PTEN, triggers loss of senescence, metastatic dissemination and dramatically reduces life expectancy. In Kmt2c-mutated tumours we show enrichment of proliferative MYC gene signatures and loss of expression of the cell cycle repressor p16INK4A. In addition, we observe a striking reduction in disease-free survival of patients with KMT2C-mutated prostate cancer.ConclusionsWe identified truncating events of KMT2C as drivers of proliferation and PIN formation. Loss of PTEN and KMT2C in prostate cancer results in loss of senescence, metastatic dissemination and reduced life expectancy. Our data demonstrate the prognostic significance of KMT2C mutation status in prostate cancer patients. Inhibition of the MYC signalling axis may be a viable treatment option for patients with KMT2C truncations and therefore poor prognosis.

Estrogen Receptor-Beta2 (ERβ2)-Mutant p53-FOXM1 Axis: A Novel Driver of Proliferation, Chemoresistance, and Disease Progression in High Grade Serous Ovarian Cancer (HGSOC).

Simple SummaryHigh grade serous ovarian cancer (HGSOC) is the most common and lethal subtype of ovarian cancer without effective therapeutic options. The high prevalence of mutations (~96%) in tumor suppressor p53 is a hallmark of HGSOC. Estrogen receptor-beta (ERβ) has been reported to be another important player in HGSOC, although the pro-versus anti-tumorigenic role of its different isoforms remains unclear. The aim of this study was to analyze the crosstalk between ERβ and mutant p53 and its impact on the pro-tumorigenic processes in HGSOC. Using the HGSOC cell line models and patient tumor tissue specimens, we demonstrated functional interaction between the ERβ2 isoform and mutant p53 and their ability to co-dependently increase FOXM1 gene transcription, decrease cell death, increase cell proliferation, and mediate resistance to carboplatin treatment. Furthermore, high levels of ERβ2 as well as FOXM1 correlated with worse patient survival. Collectively, our data suggest that the ERβ2-mutant p53-FOXM1 axis could be a novel therapeutic target for HGSOC.High grade serous ovarian cancer (HGSOC) is the most common and lethal subtype of epithelial ovarian cancer. Prevalence (~96%) of mutant p53 is a hallmark of HGSOC. Estrogen receptor-beta (ERβ) has been reported to be another important player in HGSOC, although the pro-versus anti-tumorigenic role of its different isoforms remains unsettled. However, whether there is functional interaction between ERβ and mutant p53 in HGSOC is unknown. ERβ1 and ERβ2 mRNA and protein analysis in HGSOC cell lines demonstrated that ERβ2 is the predominant isoform in HGSOC. Specificity of ERβ2 antibody was ascertained using cells depleted of ERβ2 and ERβ1 separately with isoform-specific siRNAs. ERβ2-mutant p53 interaction in cell lines was confirmed by co-immunoprecipitation and in situ proximity ligation assay (PLA). Expression levels of ERβ2, ERα, p53, and FOXM1 proteins and ERβ2-mutant p53 interaction in patient tumors were determined by immunohistochemistry (IHC) and PLA, respectively. ERβ2 levels correlate positively with FOXM1 levels and negatively with progression-free survival (PFS) and overall survival (OS). Quantitative chromatin immunoprecipitation (qChIP) and mRNA expression analysis revealed that ERβ2 and mutant p53 co-dependently regulated FOXM1 gene transcription. The combination of ERβ2-specific siRNA and PRIMA-1MET that converts mutant p53 to wild type conformation increased apoptosis. Our work provides the first evidence for a novel ERβ2-mutant p53-FOXM1 axis that can be exploited for new therapeutic strategies against HGSOC.

Abstract 14033: Inhibition of the Prolyl Isomerase Pin1 Improves Endothelial Function and Attenuates Vascular Remodelling in Pulmonary Hypertension by Inhibiting TGF-β Signalling

Introduction: Pulmonary arterial hypertension (PAH) is a devastating disease, characterized by obstructive pulmonary vascular remodelling ultimately leading to right ventricular (RV) failure and death. Disturbed transforming growth factor-β (TGF-β) / bone morphogenetic protein (BMP) signalling, endothelial cell dysfunction, increased proliferation of smooth muscle cells and fibroblasts, and inflammation contribute to this abnormal remodelling. Peptidyl prolyl isomerase Pin1 has been identified as a critical driver of proliferation and inflammation in vascular cells, but its role in the disturbed TGF-β/BMP signalling, endothelial cell dysfunction and vascular remodelling in PAH is unknown. Methods and Results: Pin1 expression is increased in cultured pulmonary microvascular endothelial cells (MVECs) and lung tissue of PAH patients. Pin1 inhibitor, juglone significantly decreased TGF-β signalling, increased BMP signalling, normalized their hyper-proliferative, and inflammatory phenotype. Juglone treatment reversed vascular remodelling through reducing TGF-β signalling in monocrotaline + shunt-PAH rat model. Juglone treatment decreased Fulton index, but did not affect or harm cardiac function and remodelling in rats with RV pressure load induced by pulmonary artery banding. Conclusions: Our study demonstrates that inhibition of Pin1 reversed the PAH phenotype in PAH-MVECs in vitro and in PAH rats in vivo, potentially through modulation of TGF-β/BMP signalling pathways. Selective inhibition of Pin1 could be a novel therapeutic option for the treatment of PAH.

The Eye in Internal Medicine: Diabetic retinopathy

Diabetic retinopathy has seen tremendous progress in diagnostic tools and treatment in recent 15 years. Sight threatening stages like proliferative diabetic retinopathy (PDR) and diabetic macular edema (DME) can be treated much more effectively now. The recognition of vascular endothelial growth factor (VEGF) as a driver of proliferation and macular edema has led to the development of VEGF inhibiting drugs such as antibodies (Bevacizumab), fragments of an antibody (Ranibizumab), or a so called VEGF trap (Aflibercept). Laser treatment is no longer a gold standard. Today laser therapy is part of a combined treatment strategy. DME can be monitored quantitatively by ocular coherence tomography (OCT) measurements. For non-responders to VEGF inhibiting drugs, we have secondline corticosteroidal implants. However, screening examinations and early diagnosis of DME and PDR remain crucial. The same accounts for the collaboration of opthalmologists, general practioners, and diabetologists. Good control of diabetes and blood pressure is still important.

Clinical CDK4/6 inhibitors induce selective and immediate dissociation of p21 from cyclin D-CDK4 to inhibit CDK2

Since their discovery as drivers of proliferation, cyclin-dependent kinases (CDKs) have been considered therapeutic targets. Small molecule inhibitors of CDK4/6 are used and tested in clinical trials to treat multiple cancer types. Despite their clinical importance, little is known about how CDK4/6 inhibitors affect the stability of CDK4/6 complexes, which bind cyclins and inhibitory proteins such as p21. We develop an assay to monitor CDK complex stability inside the nucleus. Unexpectedly, treatment with CDK4/6 inhibitors—palbociclib, ribociclib, or abemaciclib—immediately dissociates p21 selectively from CDK4 but not CDK6 complexes. This effect mediates indirect inhibition of CDK2 activity by p21 but not p27 redistribution. Our work shows that CDK4/6 inhibitors have two roles: non-catalytic inhibition of CDK2 via p21 displacement from CDK4 complexes, and catalytic inhibition of CDK4/6 independent of p21. By broadening the non-catalytic displacement to p27 and CDK6 containing complexes, next-generation CDK4/6 inhibitors may have improved efficacy and overcome resistance mechanisms.

In vivo screen identifies a SIK inhibitor that induces β cell proliferation through a transient UPR.

It is known that β cell proliferation expands the β cell mass during development and under certain hyperglycemic conditions in the adult, a process that may be used for β cell regeneration in diabetes. Here, through a new high-throughput screen using a luminescence ubiquitination-based cell cycle indicator (LUCCI) in zebrafish, we identify HG-9-91-01 as a driver of proliferation and confirm this effect in mouse and human β cells. HG-9-91-01 is an inhibitor of salt-inducible kinases (SIKs), and overexpression of Sik1 specifically in β cells blocks the effect of HG-9-91-01 on β cell proliferation. Single-cell transcriptomic analyses of mouse β cells demonstrate that HG-9-91-01 induces a wave of activating transcription factor (ATF)6-dependent unfolded protein response (UPR) before cell cycle entry. Importantly, the UPR wave is not associated with an increase in insulin expression. Additional mechanistic studies indicate that HG-9-91-01 induces multiple signalling effectors downstream of SIK inhibition, including CRTC1, CRTC2, ATF6, IRE1 and mTOR, which integrate to collectively drive β cell proliferation.

DTX3 copy number increase in breast cancer: a study of associations to molecular subtype, proliferation and prognosis

PurposeThe degree of cell proliferation is important for subclassification of breast cancers into prognostic and therapeutic groups. DTX3 has been identified as a driver of proliferation in luminal breast cancer. In this study, we describe DTX3 copy number in breast cancer primary tumours and corresponding axillary lymph node metastases, and studied associations with molecular subtype, proliferation and prognosis.MethodsUsing fluorescence in situ hybridization, we assessed DTX3 and chromosome 12 centromere (CEP12) copy number in 542 primary breast cancers and 117 lymph node metastases, from a well-described cohort of Norwegian breast cancer patients. Proliferation was expressed as mitotic counts and Ki67 score. Associations between DTX3 copy number and molecular subtype and proliferation were assessed using Pearson’s χ2 test. We studied the effect of copy number increase on prognosis estimating cumulative incidence of breast cancer death and hazard ratios.ResultsMean DTX3 copy number ≥ 4 was found in 23 tumours (4%), and mean ≥ 5 in 9 tumours (1.7%). Copy number increase was found within all molecular subtypes except the 5 negative phenotype and the Luminal B (HER2 +) subtype. DTX3 copy number increase was not accompanied by an increase in CEP12. Point estimates showed that there were associations between DTX3 copy number increase and high proliferation and poor prognosis; however, precision depended on copy number cut-off.ConclusionsDTX3 copy number increase was present in a small proportion of breast cancer cases. There was an association between copy number increase and high tumour cell proliferation and poor prognosis.

In situ river experiments to explore variability in Microcoleus autumnalis mat expansion

Proliferations of benthic mats dominated by anatoxin-producing Microcoleus autumnalis (basionym Phormidium autumnale) pose an increasing health risk to human and animals worldwide. This study assessed M. autumnalis mats in two in situ experiments undertaken at three spatial scales: (1) reach-scale along a river; (2) reach-scale, focusing on two sites upstream and downstream of a tributary with substantial differences in naturally occurring M. autumnalis; and (3) patch-scale differences in light intensity. Most studies exploring drivers of proliferation have surveyed natural populations with correlative analyses; these in situ experiments aimed to validate previously hypothesised drivers. In experiment one, M. autumnalis mat area and expansion tended to increase downstream. This longitudinal variation was partially associated with increases in dissolved inorganic nitrogen, fine sediment and associated biologically available phosphorus. M. autumnalis mat area differed markedly at sites above and below the most downstream tributary. A second experiment with additional parameters (metals, grazing and light) was undertaken in this reach. None of the parameters conclusively explained differences in mat area, although numerous metals were identified for further investigation with a controlled experimental approach. These results posit that there are multiple non-linear drivers of M. autumnalis proliferation and their hierarchy of importance varies amongst sites.

Paradoxical activation of AMPK by glucose drives selective EP300 activityin colorectal cancer.

Coordination of gene expression with nutrient availability supports proliferation and homeostasis and is shaped by protein acetylation. Yet how physiological/pathological signals link acetylation to specific gene expression programs and whether such responses are cell-type–specific is unclear. AMP-activated protein kinase (AMPK) is a key energy sensor, activated by glucose limitation to resolve nutrient supply–demand imbalances, critical for diabetes and cancer. Unexpectedly, we show here that, in gastrointestinal cancer cells, glucose activates AMPK to selectively induce EP300, but not CREB-binding protein (CBP). Consequently, EP300 is redirected away from nuclear receptors that promote differentiation towards β-catenin, a driver of proliferation and colorectal tumorigenesis. Importantly, blocking glycogen synthesis permits reactive oxygen species (ROS) accumulation and AMPK activation in response to glucose in previously nonresponsive cells. Notably, glycogen content and activity of the ROS/AMPK/EP300/β-catenin axis are opposite in healthy versus tumor sections. Glycogen content reduction from healthy to tumor tissue may explain AMPK switching from tumor suppressor to activator during tumor evolution.

MRPS23 amplification and gene expression in breast cancer; association with proliferation and the non-basal subtypes

PurposeMRPS23 is recognized as a driver of proliferation in luminal breast cancer. The aims of the present study were to describe MRPS23 copy number change in breast cancer, and to assess associations between MRPS23 copy number change and molecular subtype, proliferation and prognosis, and between MRPS23 gene expression and molecular subtype and prognosis.MethodsUsing fluorescence in situ hybridization (FISH), we examined MRPS23 and centromere 17 copy number in 590 formalin-fixed, paraffin-embedded primary tumours and 144 corresponding lymph node metastases from a cohort of Norwegian breast cancer patients. Furthermore, we analysed MRPS23 gene expression data in 1971 primary breast cancer tumours from the METABRIC dataset. We used Pearson’s χ2 test to assess associations between MRPS23 copy number and molecular subtype and proliferation, and between MRPS23 expression and molecular subtype. We studied prognosis by estimating hazard ratios and cumulative incidence of death from breast cancer according to MRPS23 copy number and MRPS23 expression status.ResultsWe found MRPS23 amplification (mean MRPS23 copy number ≥ 6 and/or MRPS23/chromosome 17 ratio ≥ 2) in 8% of primary tumours. Copy number increase associated with non-basal subtypes and higher tumour cell proliferation (Ki67). Higher MRPS23 expression associated with the Luminal B subtype. We found no significant association between MRPS23 amplification or MRSP23 gene expression, and prognosis.ConclusionAmplification of MRPS23 is associated with higher proliferation and non-basal subtypes in breast cancer. High MRPS23 expression is associated with the Luminal B subtype.

Autonomous Ca2+ Oscillations Reflect Oncogenic Signaling in B-ALL Cells

Background: Engagement of the B-cell receptor (BCR) results in Ca2+ flux and is linked to B-cell survival based on store-operated Ca2+ entry (SOCE), which is triggered by ORAI1 and stromal interaction molecule-1 (STIM1). While normal B-cells release Ca2+ only in response to external stimuli (e.g. BCR-engagement), we recently observed that transformed B-cells exhibit autonomous oscillatory Ca2+ signals that are linked to oncogene activity. Studying a novel dual biosensor system to concurrently measure Ca2+ fluctuations and oncogenic kinase activity in the same B-ALL cells, we discovered that oncogenic kinase- and Ca2+-signals alternate between On- and Off-phases, during which kinase and Ca2+ signals are mutually exclusive. Results: Consistent with a scenario in which autonomous Ca2+-signaling is linked to oncogenic signaling, we observed that high mRNA levels of Orai1 and Stim1 in patients with B-ALL were linked to poor clinical outcomes. To study the role of SOCE and its effectors Orai1 and Stim1 in oncogene signaling, we developed mouse models for inducible deletion of Orai1 and Stim1/2 in BCR-ABL1- and NRASG12D-driven B-ALL. Tamoxifen-inducible activation of Cre in Orai1fl/fl and Stim1/2 fl/fl BCR-ABL1- and NRASG12D-driven B-ALL cells induced excision of both SOCE-mediators and induced near-complete loss of Ca2+-signaling competence. While treatment with the Ca2+ pump inhibitor, thapsigargin, elicited a strong SOCE signal, Ca2+-signaling was entirely muted upon Orai1-deletion, while deletion of Stim1 diminished and substantially delayed the residual Ca2+-signal. Studying autonomous Ca2+-signaling activity in B-ALL cells, Orai1-deletion resulted in a complete loss of oscillatory Ca2+-signaling, while deletion of Stim1/2 distorted the morphology of the Ca2+-signals with lowered amplitude and greatly extended signal duration. While both Orai1 and Stim1 contribute to SOCE, these observations highlight distinct roles of the two molecules in autonomous Ca2+ oscillation. For both BCR-ABL1- and NRASG12D-driven B-ALL, ablation of both Orai1- and Stim1/2 had profound effects on cell viability and the ability to form leukemic colonies. These results are consistent with the hypothesis that SOCE and autonomous Ca2+-oscillations are essential for oncogenic signaling in B-ALL and thus enable colony formation, proliferation and survival. To elucidate a functional link between autonomous Ca2+-oscillations and oncogenic signaling in B-ALL, we studied activation of Nfatc1, a central regulator of oncogene signaling and frequency-dependent decoder of Ca2+-oscillations. Upon Cre-mediated deletion of Orai1 and Stim1/2, however, Nfatc1 no longer translocated to the nucleus and was subject to increased proteasomal degradation. Establishing a functional link between Nfatc1-activation and survival and proliferation signaling in B-ALL cells, inducible activation of Nfatc1-deletion in BCR-ABL1-transformed Nfatc1flfl B-ALL cells phenocopied the effects observed with genetic deletion of Orai1 and Stim1/2. Interestingly, the NFATC1-inhibitor INCA6 exhibited strong cytotoxic responses in human B-ALL cells with strong Ca2+-oscillations, while Hodgkin's lymphoma and myeloma cells, lacking Ca2+-oscillations, were resistant to INCA6. To directly determine how oncogenic signaling impinges on Ca2+-oscillations, we developed a dual biosensor to concurrently measure Ca2+ fluctuations (RCaMP; red) and oncogenic BCR-ABL1 kinase activity (CRKL-phosphorylation; green) in the same B-ALL cells. Simultaneous measurement of Ca2+ (red) and kinase (green) activity revealed that B-ALL cells continuously alternated between Red-only and Green-only, suggesting that kinase and Ca2+ signals both oscillate in a mutually exclusive manner. Conclusions: Our findings show central roles of SOCE-effector genes, Orai1 and Stim1/2, in oncogenic signaling of B-ALL cells and activation of Nfatc1 as a driver of proliferation and survival signaling. Engineering of a dual biosensor for concurrent measurement of Ca2+ and oncogenic kinase activity revealed that B-ALL cells continuously alternate between Ca2+ and oncogenic kinase activity, with Ca2+-peaks marking the off-state of the oncogenic kinase. Disclosures No relevant conflicts of interest to declare.

Highly Potent BTK Degradation Induced By NRX0492 As a Therapeutic Strategy for CLL

B-cell receptor (BCR) signaling plays an essential role in normal B-cell development and is a key driver of proliferation and survival of chronic lymphocytic leukemia (CLL) B cells. BCR signals through BTK to NF-ĸB. Targeted inhibition of BTK with ibrutinib, a first-in-class covalent BTK inhibitor, is highly effective in treating CLL and related B-cell malignancies. However, progressive disease on continuous therapy with ibrutinib has been associated with mutations in BTK and PLCG2. Most patients with acquired resistance and progressive CLL on ibrutinib have mutations in BTK affecting the cysteine at position 481 (C481) to which ibrutinib covalently binds. The common C481S mutation increases IC50 with ibrutinib from low nM to μM concentrations. The emergence of specific BTK mutations in ibrutinib resistant CLL further validate BTK as a valuable therapeutic target in CLL. Therefore, agents that can target C481 mutant BTK are of great interest, and non-covalent BTK inhibitors have entered clinical trials. Here we investigated an alternative approach using a chimeric targeting molecule: NRX0492. NRX0492 combines two molecules: a "hook" that binds BTK with a "harness" that recruits ubiquitin ligases that mediate proteasome-dependent degradation of BTK. In cell line models, NRX0492 induce both wild-type and C481S mutant BTK degradation efficiently and specifically. Here we sought to define the on-target effects of NRX0492 in primary CLL cells in vitro and in vivo and to test NRX0492 against ibrutinib-resistant primary CLL cells. CLL cells were treated at densities of 5 × 106 cells/ml in 24-well plates with NRX0492, ibrutinib, the "hook" moiety devoid of the ubiquitin ligase binding moiety, or DMSO. BTK levels were quantified by Western blotting and flow cytometry. The mean ED50 and ED90 of NRX0492 for BTK degradation at 4 hours was 0.18nM and 0.5nM, respectively. At ED90 concentrations, mean cell viability of cultures treated with NRX0492 was 97.5%, and not different from viability of controls. Incubation at ED50 up to 24 hours also did not induce cell death. A lack of substantial cytotoxic activity with BTK degradation is in line with observations with BTK inhibitors under similar conditions. BTK degradation was achieved rapidly; in time-course experiments of CLL cells treated with 0.2nM NRX0492 the mean half-live of BTK protein was 2.7 hours (range 2.4h-3h), and at 2nM 99% of BTK was degraded within 4 hours. Next, we tested the rate of recovery of BTK expression after drug washout. After 0.2nm NRX0492 treatment for 4 hours, mean BTK levels were 55% of pre-treatment. After washout and continued culture of cells in complete medium for 96 hours, BTK levels were 41% of pre-treatment. In additional experiments with washout of NRX0492 after 4 hours, we found the lowest levels of BTK 48hours post-treatment, indicating a sustained drug effect. There was no significant difference in the efficacy of BTK degradation between CLL samples subdivided by IGHV mutation status or FISH categories. At 0.2nM NRX0492 for 4 hours, mean remaining BTK was 54% in IGHV mutated and 55% in IGHV unmutated samples (P =0.78), and 60% vs 50% for del(13q) vs del(17p) (P =0.18). Next, we studied samples from two patients progressing on ibrutinib with classic C481S mutations at cancer cell fractions of 50% and 84%, respectively. Both patients remained on ibrutinib at the time of sample collection. After 4 hours of treatment with 0.2nM NRX0492, BTK levels were 50% and 15% of DMSO-treated controls, respectively, consistent with degradation of mutant but not ibrutinib bound BTK. Wild-type BTK bound by ibrutinib is not degraded because ibrutinib prevents NRX0492 binding to BTK. In conclusion, we find NRX0492 is highly effective in degrading BTK in CLL cells. NRX0492 is effective at sub nM concentrations with ED50 ~0.2nM and ED90 ~0.5nM in primary CLL cells. Onset of BTK degradation was rapid and sustained for days after drug washout. NRX0492 was effective across CLL risk groups and equally effective in degrading wild-type BTK and C481S-mutant BTK. Studies testing NRX0492 in vivo in PDX models are ongoing and will inform dosing regimens for clinical studies. Disclosures Kelly: Nurix Therapeutics: Employment. Robbins:Nurix Therapeutics: Employment. Tan:Nurix Therapeutics: Employment. Ingallinera:Nurix Therapeutics: Employment. Sands:Nurix Therapeutics: Employment. Baskar:NIH: Patents & Royalties: ROR1 mAb 2A2. Wiestner:Pharmayclics: Research Funding; Acerta: Research Funding; Merck: Research Funding; Nurix: Research Funding.

ROCK2 promotes osteosarcoma growth and metastasis by modifying PFKFB3 ubiquitination and degradation

Rho-associated coiled-coil-containing protein kinase 2 (ROCK2) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) are widely involved in cell biological activities and play a key role in controlling various cell phenomena. However, the underlying mechanisms connecting ROCK2 and PFKFB3 in osteosarcoma growth and metastasis are poorly understood. In this study, we explored and analysed the role and molecular mechanism of ROCK2 and PFKFB3 in osteosarcoma. We analysed ROCK2 and PFKFB3 protein expression in 51 surgical specimens from osteosarcoma patients and determined the correlation between ROCK2 and PFKFB3. In addition, we used Transwell and wound-healing assays to detect cell invasion and migration and CCK8 and EdU assays to assess cell proliferation. Herein, we confirmed that ROCK2 and PFKFB3 proteins were significantly upregulated in osteosarcoma compared with adjacent normal tissues. Further studies revealed that knockdown of ROCK2 significantly decreased the expression levels of PFKFB3; moreover, growth and metastasis were decreased in shROCK2 osteosarcoma cells. Additionally, upregulation of PFKFB3 rescued the decreased proliferation and metastasis induced by ROCK2 knockdown, whereas knockdown of PFKFB3 decreased ROCK2-enhanced osteosarcoma proliferation and metastasis. These results suggest that PFKFB3 is essential for ROCK2-mediated proliferation and metastasis of osteosarcoma cells. Mechanistically, ROCK2 stabilizes PFKFB3 expression by modifying its ubiquitination and degradation. Taken together, our results link two drivers of proliferation and metastasis in osteosarcoma and identify a novel pathway for PFKFB3 regulation. Thus, we provide new evidence of the biological and clinical significance of PFKFB3 as a potential biomarker for osteosarcoma.

Evidence for activated Lck protein tyrosine kinase as the driver of proliferation in acute myeloid leukemia cell, CTV-1

Acute myeloid leukemia (AML) is a heterogeneous group of fast growing cancers of myeloid progenitor cells, for which effective treatments are still lacking. Identification of signaling inhibitors that block their proliferation could reveal the proliferative mechanism of a given leukemia cell, and provide small molecule drugs for targeted therapy for AML. In this study, kinase inhibitors that block the majority of cancer signaling pathways are evaluated for their inhibition of two AML cell lines of the M5 subtypes, CTV-1 and THP-1. While THP-1 cells do not respond to any of these inhibitors, CTV-1 cells are potently inhibited by dasatinib, bosutinib, crizotinib, A-770041, and WH-4-23, all potent inhibitors for Lck, a Src family kinase. CTV-1 cells contain a kinase activity that phosphorylates an Lck-specific peptide substrate in an Lck inhibitor-sensitive manner. Furthermore, the Lck gene is over-expressed in CTV-1, and it contains four mutations, two of which are located in regions critical for Lck negative regulation, and are confirmed to activate Lck. Collectively, these results provide strong evidence that mutated and overexpressed Lck is driving CTV-1 proliferation. While Lck activation and overexpression is rare in AML, this study provides a potential therapeutic strategy for treating patients with a similar oncogenic mechanism.

Pharmacokinetic drug evaluation of palbociclib for the treatment of breast cancer

ABSTRACTIntroduction: Cyclin-dependent kinases (CDKs) 4 and 6 regulate the transition from G0/G1-phase to S-phase of the cell cycle and have been identified as key drivers of proliferation in hormone receptor (HR)-positive breast cancer. The CDK4/6 inhibitor palbociclib in combination with endocrine therapy has been approved for treatment of HR-positive/HER2-negative breast cancer patients.Areas covered: In this article, we provide an update of the data on pharmacodynamics, pharmacokinetics, preclinical, and clinical studies of palbociclib in breast cancer. We performed a search of data on palbociclib in the PubMed and the clinicaltrials.gov databases, in the FDA website and in the ASCO and AACR proceedings.Expert opinion: In order to optimize the clinical outcome of HR-positive breast cancer patients treated with palbociclib, predictive biomarkers allowing patient selection are urgently needed. A recent study suggested that early dynamics of PIK3CA mutations in circulating tumor DNA might be a potential predictive biomarker for CDK4/6 inhibitors. Several clinical trials are ongoing with the aim to explore the activity of combinations of palbociclib with targeted agents and/or immunotherapy in the different subtypes of breast cancer in both metastatic and early phases of the disease. These combinations might allow improving the sensitivity and overcoming mechanisms of resistance.

Abstract B42: Identification of CPT1A as a novel driver of proliferation in luminal breast cancer

Abstract Clinically, approximately two-thirds of the nearly 250,000 breast cancer cases diagnosed each year in the United States are hormone receptor-positive, luminal breast tumors. Slower-growing luminal breast tumors are often successfully treated using endocrine-based therapies, resulting in a relatively good prognosis for these patients. However, more highly proliferative luminal tumors, even with the recent approval of CDK4/6 inhibitors, are often resistant, or become resistant, to current therapies, leading to a worse outcome for these women. Therefore, it is necessary to identify genetic events responsible for tumorigenesis and to identify potential druggable genetic alterations and/or pathways in order to improve clinical outcome. To address this question, we recently developed and used an innovative genomics-based strategy to interrogate orthogonal genome-wide data from more than 2,500 patients from the TCGA and METABRIC studies. By using an 11-gene mRNA-based gene expression signature of proliferation as a conceptual framework, we identified DNA copy number alterations and somatic mutations associated with luminal breast cancer proliferation. In order to identify the subset of amplified genes that are essential for cell viability, we analyzed a dataset of 27 breast cancer cell lines with available mRNA expression and genome-wide shRNA proliferation data. By integrating DNA copy number and shRNA analyses, we identified amplified carnitine palmitoyltransferase 1A (CPT1A) as a novel driver of proliferation in luminal breast cancer. CPT1A was found to be amplified in 40.2% of highly proliferative (top quartile) luminal tumors compared to 24.7% of all other samples and CPT1A DNA copy number status correlated with mRNA expression levels. Importantly, CPT1A was shown to be essential in luminal breast cancer cell lines with a high proliferation signature score. By analyzing RPPA data from luminal breast tumors, we confirmed CPT1A amplified tumors have increased expression of protein markers of proliferation. Since CPT1A is the rate-limiting enzyme responsible for fatty acid import into the mitochondria during fatty acid β oxidation (FAO), these data indicate that highly proliferative luminal tumors may utilize FAO as a prominent energy source. Interestingly, our analyses of RNA-seq data (n=1,031) demonstrated that highly proliferative luminal tumors have significantly higher CPT1A mRNA expression than either basal-like, which are largely synonymous with TNBC, or less proliferative luminal tumors, suggesting that these tumors may have a greater dependency on CPT1A activity. CPT1A has two major variants: cytoplasmic Variant 1 is the rate-limiting enzyme responsible for fatty acid import into the mitochondria during FAO while nuclear Variant 2 is purported to mediate histone deacetylase activity. Analyses of RNAseq data (n=819) demonstrated that Variant 1 represents >99.2% of CPT1A mRNA transcripts in a given tumor, suggesting the FAO-associated role of CPT1A is the more critical function of this protein in breast cancer. Consistent with this observation, we determined that breast cancer cell lines with high CPT1A protein expression are significantly more sensitive to etomoxir, a CPT1A-specific inhibitor known to repress FAO, when compared to cell lines with low CPT1A protein levels. Finally, we determined that under glucose-depleted conditions, cell lines with high CPT1A expression showed no difference in etomoxir response whereas cells with low CPT1A become significantly more sensitive. Collectively, these data suggest that CPT1A amplification and overexpression contribute to proliferation. Given that a number of approved or experimental drugs target CPT1A or FAO, our data suggest that CPT1A and/or FAO may represent a novel therapeutic target for luminal breast cancer. Citation Format: Kristina Mastrioanni, Kimberly Parker, Michael L. Gatza. Identification of CPT1A as a novel driver of proliferation in luminal breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B42.

The combination of epigenetic drugs SAHA and HCI-2509 synergistically inhibits EWS-FLI1 and tumor growth in Ewing sarcoma.

PurposeEpigenetic regulation is crucial in mammalian development and maintenance of tissue-cell specific functions. Perturbation of epigenetic balance may lead to alterations in gene expression, resulting in cellular transformation and malignancy. Previous studies in Ewing sarcoma (ES) have shown that the Nucleosome Remodeling Deacetylase (NuRD) complex binds directly to EWS-FLI1 oncoprotein and modulates its transcriptional activity. The role of EWS-FLI1 as a driver of proliferation and transformation in ES is widely known, but the effect of epigenetic drugs on fusion activity remains poorly described. The present study evaluated the combination effects of the histone deacetylases inhibitor suberoylanilide hydroxamic acid (SAHA) and Lysine-specific demethylase1 inhibitor (HCI-2509) on different biological functions in ES and in comparison to monotherapy treatments.ResultsThe study of proliferation and cell viability showed a synergistic effect in most ES cell lines analyzed. An enhanced effect was also observed in the induction of apoptosis, together with accumulation of cells in G1 phase and a blockage of the migratory capacity of ES cell lines. Treatment, either in monotherapy or in combination, caused a significant decrease of EWS-FLI1 mRNA and protein levels and this effect is mediated in part by fusion gene promoter regulation. The anti-tumor effect of this combination was confirmed in patient-derived xenograft mouse models, in which only the combination treatment led to a statistically significant decrease in tumor volume.ConclusionsThe combination of SAHA and HCI-2509 is proposed as a novel treatment strategy for ES patients to inhibit the essential driver of this sarcoma and tumor growth.

Abstract 4310: Condensin II complex as a potential driver of cancer proliferation

Abstract BACKGROUND The Condensin II complex's known function is in chromosomal segregation and assembly. Leiserson et al. demonstrated that Condensin II was enriched for mutations in a pan-cancer sweep, particularly lung cancer; one gene, NCAPH2, had a notable mutation cluster. Venet et al. created metaPCNA, a robust proliferation-based gene expression (GE) signature from 36 tissues, which includes 4 Condensin genes. This suggests that Condensin II expression is correlated with proliferation. We hypothesize that Condensin II influences cancer proliferation in two ways, and demonstrate evidence for the first: 1) rare stabilizing subunit mutations or 2) pairing of high Condensin II expression with a driver mutation that affects pathways controlling Condensin II activity. METHODS Using the TCGA lung adenocarcinoma (LUAD) gene expression dataset (n=571), we calculated the Condensin II index (mean expression of 5 genes) and the metaPCNA index (median expression of 131 genes). Pearson correlation between indices was calculated to assess information overlap between gene signatures. For outcome assessments, scores were split into tertile labels (high, middle, low). Linear-by-linear testing was assessed for score agreement. Unsupervised hierarchical clustering of the top 2,500 most variant genes with samples labeled by index tertile inclusion was completed for both indices. After noting the similarity between indices, we tested Condensin II as a driver of proliferation by running overexpression assays using the rate limiting subunit of the complex, NCAPH2. Plasmids with NCAPH2, both wildtype and engineered to have the R551P mutation identified by Leiserson, were transfected into RPE1 cells, a telomere elongation immortalized cell line with a ‘normal' proliferation profile. We had 3 conditions 1) myc-tagged control, 2) wild-type NCAPH2, and 3) R551P mutated NCAPH2, utilizing Incucyte imaging for 3 days after a 1-day rest to assess the proliferation of cells. RESULTS The Condensin II index and metaPCNA index were strongly associated (correlation = 0.85). Cluster analysis by either the metaPCNA or Condensin II index demonstrated that the lowest tertile tends to separate from the middle and highest tertile. Samples had a high overlap of tertile labels between the 2 indices (n labels matched =406, n not matched = 165, z= 18.57, p= <2.2*10-16). A 72-hour time course of the 3 transfected cell lines demonstrated that overexpression of R551P mutated NCAPH2was associated with an increase in proliferation, while wild-type NCAPH2did not differ significantly from the myc-tagged control. CONCLUSIONS Condensin II index is a simple, 5-gene signature strongly associated with a known proliferation signature and tumor expression patterns. A potentially stabilizing mutation to NCAPH2, R551P, increases proliferation potential in cell line experimentation, but overexpression of wild-type NCAPH2does not. Condensin II may be a driver of cancer proliferation. Citation Format: Ellen L. Nutter, Emily S. Weyburne, Jeffrey Thompson, Jennifer A. Doherty, Giovanni Bosco. Condensin II complex as a potential driver of cancer proliferation [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 4310.

Abstract LB-240: LSD1 activates a lethal prostate cancer gene network independently of its demethylase function

Abstract Background: Medical castration that interferes with androgen receptor (AR) function is the principal treatment for advanced prostate cancer. However, clinical progression is universal, and tumors with AR-independent resistance mechanisms appear to be increasing in frequency. Consequently, there is an urgent need to develop new treatments targeting molecular pathways enriched in lethal prostate cancer. Lysine specific demethylase 1 (LSD1) is a histone demethylase and important regulator of gene expression. Here we describe a distinct role of LSD1 as a driver of proliferation and survival of castration-resistant prostate cancer (CRPC) cells independently of its demethylase function and of the AR. Methods: We used loss of function studies to determine the importance of LSD1 for survival of prostate cancer cells. To identify transcriptional networks that contribute to cell survival, we suppressed LSD1 with RNAi and performed gene expression profiling. To determine the importance of LSD1's demethylase function in regulation of target genes, we measured LSD1's canonical histone substrates (H3K4me2 and H3K9me2) using genome-wide chromatin immunoprecipitation-sequencing and measured the effect of ectopically expressed wild type or catalytically deficient LSD1 on cell survival and target gene expression. We used mass spectrometry (MS) to identify important LSD1 protein complex members. Finally, we used multiple biochemical and cellular assays and an in vivo study to confirm the mechanism of action of a small molecule inhibitor that targets critical, non-canonical functions of LSD1 in CRPC cells. Results: Cell viability assays demonstrated that LSD1 is important for proliferation and survival of CRPC cells independently of the AR. Gene expression profiles demonstrated that LSD1 activates androgen-independent genes that are enriched in lethal human tumors. Importantly, our global epigenomic studies and biochemical experiments demonstrated that LSD1's demethylase function was dispensable for these effects, while our MS studies identified cooperating LSD1 binding proteins. Finally, we identified a reversible small molecule inhibitor of LSD1 that blocked critical, demethylase-independent functions in vitro and in vivo. Conclusions: Our results demonstrate that LSD1 promotes survival of prostate cancer cells, including those that are castration-resistant, independently of its demethylase function and of the AR. Importantly, this effect is explained in part by activation of a lethal prostate cancer gene network in collaboration with specific binding proteins. Finally, that a reversible small molecule LSD1 inhibitor blocks important demethylase-independent functions and suppresses CRPC cell viability demonstrates the potential of LSD1 inhibition in this disease. Citation Format: Archana Sehrawat, Dae-Hwan Kim, Lina Gao, Yuliang Wang, Armand Bankhead, Shannon McWeeney, Carly J. King, Jacob Schwartzman, Junior Tayou, Joshua Urrutia, William H. Bisson, Daniel J. Coleman, Sunil K. Joshi, David A. Sampson, Sheila Weinmann, Bhaskar VS Kallakury, Deborah L. Berry, Reina Haque, Stephen K. Van Den Eeden, Sunil Sharma, Jared Bearss, Tomasz M. Beer, George V. Thomas, Laura M. Heiser, Joshi J. Alumkal. LSD1 activates a lethal prostate cancer gene network independently of its demethylase function [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 LB-240.