G1 Cell Cycle Checkpoint Research Articles

A novel function of HER2/Neu in the activation of G2/M checkpoint in response to γ-irradiation.

In response to γ-irradiation (IR)-induced DNA damage, activation of cell cycle checkpoints results in cell cycle arrest, allowing time for DNA repair before cell cycle re-entry. Human cells contain G1 and G2 cell cycle checkpoints. While G1 checkpoint is defective in most cancer cells, commonly due to mutations and/or alterations in the key regulators of G1 checkpoint (for example, p53, cyclin D), G2 checkpoint is rarely impaired in cancer cells, which is important for cancer cell survival. G2 checkpoint activation involves activation of ataxia telangiectasia-mutated (ATM)/ATM- and rad3-related (ATR) signalings, which leads to the inhibition of Cdc2 kinase and subsequent G2/M cell cycle arrest. Previous studies from our laboratory show that G2 checkpoint activation following IR exposure of MCF-7 breast cancer cells is dependent on the activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) signaling. As HER receptor tyrosine kinases (RTKs), which have important roles in cell proliferation and survival, have been shown to activate ERK1/2 signaling in response to various stimuli, we investigated the role of HER RTKs in IR-induced G2/M checkpoint response in breast cancer cells. Results of the present studies indicate that IR exposure resulted in a striking increase in the phosphorylation of HER1, HER2, HER3 and HER4 in MCF-7 cells, indicative of activation of these proteins. Furthermore, specific inhibition of HER2 using an inhibitor, short hairpin RNA and dominant-negative mutant HER2 abolished IR-induced activation of ATM/ATR signaling, phosphorylation of Cdc2-Y15 and subsequent induction of G2/M arrest. Moreover, the inhibition of HER2 also abrogated IR-induced ERK1/2 phosphorylation. In contrast, inhibition of HER1 using specific inhibitors or decreasing expression of HER3 or HER4 using short hairpin RNAs did not block the induction of G2/M arrest following IR. These results suggest an important role of HER2 in the activation of G2/M checkpoint response following IR.

The Roles of MAPKs in Rabbit Nucleus Pulposus Cell Apoptosis Induced by High Osmolality

Earlier work has suggested that the p38 MAPK, JNK1/2 and ERK1/2 signal pathway existed in nucleus pulposus cells and the cell growth, differentiation and apoptosis were regulated by them. Because osmotic fluctuations are inevitable in the physicochemical environment of intervertebral disc cells, high osmolality could activate p38 MAPK, JNK1/2 and ERK1/2 signal pathway. The effects of high osmolality on the catabolic program and proliferation of nucleus pulposus cells are still not clear. To explore the possible roles of MAPKs in rabbit nucleus pulposus cell apoptosis induced by high osmolality. Rabbit nucleus pulposus cells were cultured and divided into different group at random. The cells were pretreated with inhibitor for p38 MAPK, JNK1/2 and ERK1/2 signal pathway respectively. In next step, the cells were cultured in different osmolality environment for different time at 37°C in 5% carbon dioxide incubator. After treatments, ratio of apoptosis was measured by flow cytometry, and western blotting was performed to quantify the expression of the activated forms of p38 MAPK, JNK1/2 and ERK1/2. Furthermore, immunofluorescence analysis with confocal microscopy was performed to confirm the hyperosmolality effects on activation of p38 MAPK, JNK1/2 and ERK1/2 signal pathways in nucleus pulposus cells. Our results show that in 500 and 600 mOsm/kg medium, rabbit nucleus pulposus cell apoptosis increased, and a persistent phosphorylation of p38 MAPK, JNK1/2 and ERK1/2 proteins were observed. In the same condition, the apoptotic cells death remarkably decreased when the p38 MAPK and JNK1/2 signal pathways were blocked by their inhibitors SB203580, SP600125 repectively. On the other side, the apoptotic cells death rate reraised greatly when the ERK1/2 signal pathways were blocked by its inhibitor PD98059. High osmolality activated p38MAPK, JNK1/2 and ERK1/2 in rabbit nucleus pulposus cell, and the activated p38 MAPK and JNK1/2 induced cell apoptosis, on the contrary, the activated ERK1/2 made the cell survived.

G1 checkpoint establishment in vivo during embryonic liver development.

BackgroundThe DNA damage-mediated cell cycle checkpoint is an essential mechanism in the DNA damage response (DDR). During embryonic development, the characteristics of cell cycle and DNA damage checkpoint evolve from an extremely short G1 cell phase and lacking G1 checkpoint to lengthening G1 phase and the establishment of the G1 checkpoint. However, the regulatory mechanisms governing these transitions are not well understood. In this study, pregnant mice were exposed to ionizing radiation (IR) to induce DNA damage at different embryonic stages; the kinetics and mechanisms of the establishment of DNA damage-mediated G1 checkpoint in embryonic liver were investigated.ResultsWe found that the G2 cell cycle arrest was the first response to DNA damage in early developmental stages. Starting at E13.5/E15.5, IR mediated inhibition of the G1 to S phase transition became evident. Concomitantly, IR induced the robust expression of p21 and suppressed Cdk2/cyclin E activity, which might involve in the initiation of G1 checkpoint. The established G1 cell cycle checkpoint, in combination with an enhanced DNA repair capacity at E15.5, displayed biologically protective effects of repairing DNA double-strand breaks (DSBs) and reducing apoptosis in the short term as well as reducing chromosome deletion and breakage in the long term.ConclusionOur study is the first to demonstrate the establishment of the DNA damage-mediated G1 cell cycle checkpoint in liver cells during embryogenesis and its in vivo biological effects during embryonic liver development.

Identification of Preferred Chemotherapeutics for Combining with a CHK1 Inhibitor

Here we report that GNE-783, a novel checkpoint kinase-1 (CHK1) inhibitor, enhances the activity of gemcitabine by disabling the S- and G2 cell-cycle checkpoints following DNA damage. Using a focused library of 51 DNA-damaging agents, we undertook a systematic screen using three different cell lines to determine which chemotherapeutics have their activity enhanced when combined with GNE-783. We found that GNE-783 was most effective at enhancing activity of antimetabolite-based DNA-damaging agents; however, there was a surprisingly wide range of activity within each class of agents. We, next, selected six different therapeutic agents and screened these in combination with GNE-783 across a panel of cell lines. This revealed a preference for enhanced chemopotentiation of select agents within tumor types, as, for instance, GNE-783 preferentially enhanced the activity of temozolomide only in melanoma cell lines. Additionally, although p53 mutant status was important for the overall response to combinations with some agents; our data indicate that this alone was insufficient to predict synergy. We finally compared the ability of a structurally related CHK1 inhibitor, GNE-900, to enhance the in vivo activity of gemcitabine, CPT-11, and temozolomide in xenograft models. GNE-900 significantly enhanced activity of only gemcitabine in vivo, suggesting that strong chemopotentiation in vitro can translate into chemopotentiation in vivo. In conclusion, our results show that selection of an appropriate agent to combine with a CHK1 inhibitor needs to be carefully evaluated in the context of the genetic background and tumor type in which it will be used.

Abstract A47: Study of promoter methylation pattern of 14-3-3 sigma gene in serum of patients with breast cancer: A potential biomarker for diagnostic anf prognostic factor.

Abstract Background: Expression of 14-3-3 σ is a tumor suppressor gene induced in response to DNA damage, and has been implicated in G2/M cell cycle arrest by p53. Hypermethylation of CpG islands located in the promoter regions of tumor suppressor genes is now firmly established as an important mechanism for gene inactivation. Objective: To correlation methylation levels of promoter 14-3-3σ with association prognostic factors in breast cancer. Material and Methods: This is a prospective study we quantified methylation levels of promoter 14-3-3σ gene in 107 women with breast cancer and 108 control subjects by real time QMS-PCR SYBR green and analyzed association with prognostics factor in breast cancer. Results: Median age was 58 years (32-88); 69% were postmenopausal women.Nodal involvement N0;63%,N1;30%,N2;7%), tumor size (T1;58%,T2;35%,T3;4%,T4;4%) and grade G1; 20%, G2; 37%, G3; 30%). The methylation of 14-3-3σ were 60% of sporadic breast cancer patients and were 34% of normal breast (p=0.0047).The methylation of 14-3-3σ gene in serum was markedly related with T3-4 stage (p<0.05),nodal positive status (p<0.05) and poor outcome. With a median follow up 6 years we saw more probability of developing distance metastasis in patients with methylation 14-3-3σ (p>0.05). Conclusions: Hypermethylation of the 14-3-3σ a promoter is an early and frequent event in breast neoplastic transformation, leading to the suggestion that silencing of 14-3-3σ may be an important event in tumor progression and particularly in breast carcinogenesis.Therefore, it is possible that loss of σ expression contributes to malignant transformation by impairing the G2 cell cycle checkpoint function, thus allowing an accumulation of genetic defects. Perhaps in the detection of CpG methylation of 14-3-3σ may be used for diagnostic and prognostic purposes. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A47. Citation Format: Martínez-Galán Joaquina, Juan Ramón Delgado, Blanca Torres-Torres, Rosario Del Moral, Sandra Rios, M. Isabel Núñez. Study of promoter methylation pattern of 14-3-3 sigma gene in serum of patients with breast cancer: A potential biomarker for diagnostic anf prognostic factor. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A47.

Panobinostat Synergistically Enhances the Cytotoxic Effects of Cisplatin, Doxorubicin or Etoposide on High-Risk Neuroblastoma Cells

High-risk neuroblastoma remains a therapeutic challenge with a long-term survival rate of less than 40%. Therefore, new agents are urgently needed to overcome chemotherapy resistance so as to improve the treatment outcome of this deadly disease. Histone deacetylase (HDAC) inhibitors (HDACIs) represent a novel class of anticancer drugs. Recent studies demonstrated that HDACIs can down-regulate the CHK1 pathway by which cancer cells can develop resistance to conventional chemotherapy drugs. This prompted our hypothesis that combining HDACIs with DNA damaging chemotherapeutic drugs for treating neuroblastoma would result in enhanced anti-tumor activities of these drugs. Treatment of high-risk neuroblastoma cell lines with a novel pan-HDACI, panobinostat (LBH589), resulted in dose-dependent growth arrest and apoptosis in 4 high-risk neuroblastoma cell lines. Further, the combination of panobinostat with cisplatin, doxorubicin, or etoposide resulted in highly synergistic antitumor interactions in the high-risk neuroblastoma cell lines, independent of the sequence of drug administration. This was accompanied by cooperative induction of apoptosis. Furthermore, panobinostat treatment resulted in substantial down-regulation of CHK1 and its downstream pathway and abrogation of the G2 cell cycle checkpoint. Synergistic antitumor interactions were also observed when the DNA damaging agents were combined with a CHK1-specific inhibitor, LY2603618. Contrary to panobinostat treatment, LY2603618 treatments neither resulted in abrogation of the G2 cell cycle checkpoint nor enhanced cisplatin, doxorubicin, or etoposide-induced apoptosis in the high-risk neuroblastoma cells. Surprisingly, LY2603618 treatments caused substantial down-regulation of total CDK1. Despite this discrepancy between panobinostat and LY2603618, our results indicate that suppression of the CHK1 pathway by panobinostat is at least partially responsible for the synergistic antitumor interactions between panobinostat and the DNA damaging agents in high-risk neuroblastoma cells. The results of this study provide a rationale for clinical evaluation of the combination of panobinostat and cisplatin, doxorubicin, or etoposide for treating children with high-risk neuroblastoma.

Targeting p53 mutant ovarian cancer: Phase I results of the WEE1 inhibitor MK-1775 with carboplatin plus paclitaxel in patients (pts) with platinum-sensitive, p53-mutant ovarian cancer (OC).

5518 Background: MK-1775 is a highly selective, investigational oral tyrosine kinase inhibitor of WEE1, which regulates G2 cell cycle checkpoint. Functional p53 mutation impairs G1 checkpoint; hence, targeting G2 checkpoint with MK-1775 in p53 mutants should induce synthetic lethality. Methods: Pts with platinum-sensitive disease-recurrent OC who had measurable disease (RECIST 1.1) with loss of function (LOF) p53 mutations by Roche AmpliChip were eligible. All pts received MK-1775 225mg twice daily (BID) D1-D3 (5 doses) plus carboplatin AUC5 + paclitaxel 175mg/m2 every 21 days (CP) for 6 cycles. The objective for the phase I run-in portion of the study was to determine the recommended phase II dose based on safety data. A Toxicity Probability Interval method [Ji et al, Clin Trials 2010; 7(6):653-63] would determine if additional lower doses should be explored. A randomized phase II portion, assessing the efficacy of the combination vs placebo, would start if ≥5 radiological responses and <5 dose-limiting toxicities (DLTs) were observed among the first 13 pts. Results: Of 76 pts screened (26 wt, 43 mutant [24 nonfunctional], 7 undetermined), 19 women had LOF p53 mutations and were eligible. Fifteen consented and were enrolled in the Phase I: median age was 57 (range 38-77); ECOG 0:1 ratio 9:6 pts. Three DLTs were observed: G3 febrile neutropenia, G4 neutropenia, and G4 thrombocytopenia. Diarrhea (84.6%), nausea (76.9%), and fatigue (76.9%) were the most common adverse events (AEs). Seven of 13 pts completed treatment (2 ongoing). Three pts discontinued due to AEs and 3 patients withdrew consent prior to completing treatment. Of 14 evaluable pts by RECIST 1.1 there were 11 partial responses (PRs; 6 confirmed, 5 unconfirmed) and 3 had stable disease; 7 pts were evaluable by CA125 with 3 complete responses and 4 PRs. MK-1775 PK results were similar to those reported for monotherapy studies. Conclusions: The combination of MK-1775 225mg BID x 5 doses with CP is well tolerated, with a preliminary radiological response rate of 78.6%, and has met the safety and efficacy bar for randomized phase II assessment in part 2 of the study. Clinical trial information: NCT01357161.

In vitro and in vivo radiosensitization induced by hydroxyapatite nanoparticles

Previous study showed that hydroxyapatite nanoparticles (nano-HAPs) inhibited glioma growth in vitro and in vivo; and in a drug combination, they could reduce adverse reactions. We investigated the possible enhancement of radiosensitivity induced by nano-HAPs. In vitro radiosensitization of nano-HAPs was measured using a clonogenic survival assay in human glioblastoma U251 and breast tumor brain metastatic tumor MDA-MB-231BR cells. DNA damage and repair were measured using γH2AX foci, and mitotic catastrophe was determined by immunostaining. The effect of nano-HAPs on in vivo tumor radiosensitivity was investigated in a subcutaneous and an orthotopic model. Nano-HAPs enhanced each cell line's radiosensitivity when the exposure was 1 h before irradiation, and they had no significant effect on irradiation-induced apoptosis or on the activation of the G2 cell cycle checkpoint. The number of γH2AX foci per cell was significantly large at 24 h after the combination modality of nano-HAPs + irradiation compared with single treatments. Mitotic catastrophe was also significantly increased at an interval of 72 h in tumor cells receiving the combined modality compared with the individual treatments. In a subcutaneous model, nano-HAPs caused a larger than additive increase in tumor growth delay. In an orthotopic model, nano-HAPs significantly reduced tumor growth and extended the prolongation of survival induced by irradiation. These results show that nano-HAPs can enhance the radiosensitivity of tumor cells in vitro and in vivo through the inhibition of DNA repair, resulting in an increase in mitotic catastrophe.

WEE1 Kinase Inhibition Enhances the Radiation Response of Diffuse Intrinsic Pontine Gliomas

Diffuse intrinsic pontine glioma (DIPG) is a fatal pediatric disease. Thus far, no therapeutic agent has proven beneficial in the treatment of this malignancy. Therefore, conventional DNA-damaging radiotherapy remains the standard treatment, providing transient neurologic improvement without improving the probability of overall survival. During radiotherapy, WEE1 kinase controls the G(2) cell-cycle checkpoint, allowing for repair of irradiation (IR)-induced DNA damage. Here, we show that WEE1 kinase is one of the highest overexpressed kinases in primary DIPG tissues compared with matching non-neoplastic brain tissues. Inhibition of WEE1 by MK-1775 treatment of DIPG cells inhibited the IR-induced WEE1-mediated phosphorylation of CDC2, resulting in reduced G(2)-M arrest and decreased cell viability. Finally, we show that MK-1775 enhances the radiation response of E98-Fluc-mCherry DIPG mouse xenografts. Altogether, these results show that inhibition of WEE1 kinase in conjunction with radiotherapy holds potential as a therapeutic approach for the treatment of DIPG.

Assessing the Radiation Response of Lung Cancer with Different Gene Mutations Using Genetically Engineered Mice

Purpose: Non-small cell lung cancers (NSCLC) are a heterogeneous group of carcinomas harboring a variety of different gene mutations. We have utilized two distinct genetically engineered mouse models of human NSCLC (adenocarcinoma) to investigate how genetic factors within tumor parenchymal cells influence the in vivo tumor growth delay after one or two fractions of radiation therapy (RT).Materials and Methods: Primary lung adenocarcinomas were generated in vivo in mice by intranasal delivery of an adenovirus expressing Cre-recombinase. Lung cancers expressed oncogenic KrasG12D and were also deficient in one of two tumor suppressor genes: p53 or Ink4a/ARF. Mice received no radiation treatment or whole lung irradiation in a single fraction (11.6 Gy) or in two 7.3 Gy fractions (14.6 Gy total) separated by 24 h. In each case, the biologically effective dose (BED) equaled 25 Gy10. Response to RT was assessed by micro-CT 2 weeks after treatment. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemical staining were performed to assess the integrity of the p53 pathway, the G1 cell-cycle checkpoint, and apoptosis.Results: Tumor growth rates prior to RT were similar for the two genetic variants of lung adenocarcinoma. Lung cancers with wild-type (WT) p53 (LSL-Kras; Ink4a/ARFFL/FL mice) responded better to two daily fractions of 7.3 Gy compared to a single fraction of 11.6 Gy (P = 0.002). There was no statistically significant difference in the response of lung cancers deficient in p53 (LSL-Kras; p53FL/FL mice) to a single fraction (11.6 Gy) compared to 7.3 Gy × 2 (P = 0.23). Expression of the p53 target genes p21 and PUMA were higher and bromodeoxyuridine uptake was lower after RT in tumors with WT p53.Conclusion: Using an in vivo model of malignant lung cancer in mice, we demonstrate that the response of primary lung cancers to one or two fractions of RT can be influenced by specific gene mutations.

S-adenosylmethionine limitation induces p38 mitogen activated protein kinase and triggers cell cycle arrest in G1

The primary methyl group donor S-adenosylmethionine (SAM) is important for a plethora of cellular pathways including methylation of nucleic acids, proteins, and the 5' cap structure of mRNAs, as well as biosynthesis of phospholipids and polyamines. In addition, because it is the cofactor for chromatin methylation, SAM is an important metabolite for the establishment and maintenance of epigenetic marks. Here, we demonstrate that cells halt proliferation when SAM levels become low. Cell cycle arrest occurs primarily in the G1 phase of the cell cycle and is accompanied by activation of the mitogen-activated protein kinase p38 (MAPK14) and subsequent phosphorylation of MAPK-activated protein kinase-2 (MK2). Surprisingly, Cdk4 activity remains high during cell cycle arrest, whereas Cdk2 activity decreases concomitantly with cyclin E levels. Cell cycle arrest was induced by both pharmacological and genetic manipulation of SAM synthesis through inhibition or downregulation of methionine adenosyltransferase, respectively. Depletion of methionine, the precursor of SAM, from the growth medium induced a similar cell cycle arrest. Unexpectedly, neither methionine depletion nor inhibition of methionine adenosyltransferase significantly affected mTORC1 activity, suggesting that the cellular response to SAM limitation is independent from this major nutrient-sensing pathway. These results demonstrate a G1 cell cycle checkpoint that responds to limiting levels of the principal cellular methyl group donor S-adenosylmethionine. This metabolic checkpoint might play important roles in maintenance of epigenetic stability and general cellular integrity.

Implications prognostics of methylation 14-3-3 sigma promoter in peripheral blood cell DNA with nodal involvement status and tumor size for breast cancer patients.

33 Background: Expression of 14-3-3 σ is a tumor suppressor gene induced in response to DNA damage, and has been implicated in G2/M cell cycle arrest by p53. Hypermethylation of CpG islands located in the promoter regions of tumor suppressor genes is now firmly established as an important mechanism for gene inactivation. To correlation methylation levels of promoter 14-3-3σ with association prognostic factors in breast cancer. Methods: This is a prospective study we quantified methylation levels of promoter 14-3-3σ gene in 107 women with breast cancer and 108 control subjects by Real Time QMS-PCR SYBR green and analyzed association with prognostics factor in breast cancer. Results: Median age was 58 years (32-88); 69% were postmenopausal women. Nodal involvement N0; 63%,N1;30%,N2;7%), tumor size (T1;58%,T2;35%,T3;4%,T4;4%) and grade G1; 20%,G2;37%,G3;30%). The methylation of 14-3-3σ were 60% of sporadic breast cancer patients and were 34% of normal breast (p=0.0047). The methylation of 14-3-3σ gene in serum was markedly related with T3-4 stage (p<0.05),nodal positive status (p<0.05) and poor outcome. With a median follow up 6 years we saw more probability of developing distance metastasis in patients with methylation 14-3-3σ (p>0.05). Conclusions: Hypermethylation of the 14-3-3σ a promoter is an early and frequent event in breast neoplastic transformation, leading to the suggestion that silencing of 14-3-3σ may be an important event in tumor progression and particularly in breast carcinogenesis.Therefore, it is possible that loss of σ expression contributes to malignant transformation by impairing the G2 cell cycle checkpoint function, thus allowing an accumulation of genetic defects. Perhaps in the detection of CpG methylation of 14-3-3σ may be used for diagnostic and prognostic purposes.

Regulation of cell cycle checkpoint kinase WEE1 by miR-195 in malignant melanoma

WEE1 kinase has been described as a major gate keeper at the G2 cell cycle checkpoint and to be involved in tumour progression in different malignant tumours. Here we analysed the expression levels of WEE1 in a series of melanoma patient samples and melanoma cell lines using immunoblotting, quantitative real-time PCR and immunohistochemistry. WEE1 expression was significantly downregulated in patient samples of metastatic origin as compared with primary melanomas and in melanoma cell lines of high aggressiveness as compared with cell lines of low aggressiveness. Moreover, there was an inverse correlation between the expression of WEE1 and WEE1-targeting microRNA miR-195. Further analyses showed that transfection of melanoma cell lines with miR-195 indeed reduced WEE1 mRNA and protein expression in these cells. Reporter gene analysis confirmed direct targeting of the WEE1 3' untranslated region (3'UTR) by miR-195. Overexpression of miR-195 in SK-Mel-28 melanoma cells was accompanied by WEE1 reduction and significantly reduced stress-induced G2-M cell cycle arrest, which could be restored by stable overexpression of WEE1. Moreover, miR-195 overexpression and WEE1 knockdown, respectively, increased melanoma cell proliferation. miR-195 overexpression also enhanced migration and invasiveness of melanoma cells. Taken together, the present study shows that WEE1 expression in malignant melanoma is directly regulated by miR-195. miR-195-mediated downregulation of WEE1 in metastatic lesions may help to overcome cell cycle arrest under stress conditions in the local tissue microenvironment to allow unrestricted growth of tumour cells.

Synthesis and biological evaluation of analogs of the marine alkaloids granulatimide and isogranulatimide

A series of pyrrolic analogs and two series of regioisomeric pyrazolic analogs of the marine alkaloids granulatimide and isogranulatimide were prepared. The synthesis of the two first ones was based on the condensation reaction of diversely 5-substituted 3-bromoindoles with pyrrole or pyrazole followed by addition of the intermediates on maleimide or dibromomaleimide, respectively, the so-obtained acyclic adducts being finally photocyclized to the desired analogs. Compounds of the last series were obtained by reacting different 5-substituted-indole-3-glyoxylates with N-Boc-pyrazole-3-acetamide and subsequent photochemical cyclization of the adducts. All the compounds were evaluated for their in vitro growth inhibitory properties toward eight cancer cell lines. Several compounds were also assayed for their ability to abrogate the G2-cell cycle checkpoint or to inhibit a panel of Ser/Thr kinases. Lastly, computer-assisted phase-contrast microscopy (quantitative videomicroscopy) revealed that the three most potent compounds (4a, 9a, 9e), with IC50 growth inhibitory concentrations ranging between 10 and 20μM, displayed cytostatic, not cytotoxic, anticancer effects.

The Role of Exogenous Stresses on the Proliferation of Intervertebral Disk Cells

Introduction The native microenvironment of intervertebral disk (IVD) cells is characterized by adverse physicochemical conditions. Low cellularity and proliferation rate is a hallmark of the disk, possibly resulting from the absence of vascularization, which leads to the insufficient nutrition of its cells. Nutrients diffuse from the vessels of the endplates, which may sometimes be several mm away from the IVD and especially from nucleus pulposus cells. On the other hand, the IVD is confronted with several stresses, that is, mechanical load, a constant higher osmolality in comparison to other organs of the body, and oxidative stress. Our aim in the present study was to investigate the effect of the aforementioned exogenous stresses on disk cells’ proliferation and the underlying mechanisms of the observed phenomena. Materials and Methods Primary cultures of IVD cells were established. Cellular proliferation was estimated by tritiated thymidine and bromodeoxyuridine incorporation into DNA, as well as by direct cell counting. Western blot analysis was used to examine the activation of several signaling pathways. Cell cycle analysis was performed by flow cytometry. DNA damage and repair was assessed by comet assay, immunofluorescence for γH2A.X, and the host cell reactivation assay. Finally, reactive oxygen species’ production was measured using DCFH-DA. Results We showed that hyperosmotic treatment reduced nucleus pulposus cells’ proliferation by activating the G2 and G1 cell cycle checkpoints. p38 MAPK was found to participate in the manifestation of the G2 arrest under conditions of increased osmolality, since inhibition of its activity released the cells from G2 phase into mitosis. High osmolality resulted in the ATM-mediated phosphorylation of p53 on Ser15, the upregulation of p21WAF1 and the hypophosphorylation of the retinoblastoma protein in accordance to the observed G1 arrest. Furthermore, comet assay revealed the presence of DNA damage after hyperosmotic treatment, possibly attributed to the abrupt alterations in chromatin configuration observed early after exposure of the cells to this stress. Under these conditions, the histone H2A.X was phosphorylated on Ser139, a classical marker of DNA double strand breaks. In addition, when the DNA repair efficiency of the cells was directly measured by a host cell reactivation of luciferase activity assay, it was found to be significantly increased under hyperosmotic pressure. To shed light in the origin of the response, an ionic NaCl/KCl solution, the compatible osmolyte sorbitol, and the readily permeant urea were used. In contrast to urea, high salt and sorbitol were found to activate the same molecular pathways, indicating that the osmo-regulatory response of nucleus pulposus cells stems rather from cell volume alterations mediated by hypertonicity than from elevated intracellular ionic concentration. The antiproliferative effect of high osmolality was confirmed by the reduced growth factor-mediated novel DNA synthesis and ERK and Akt activation. On the other hand, the recurrent mechanical load of the cells resulted in the activation of MEK/ERK and PI3K/Akt pathways, though no actual effect on cellular proliferative potential was observed. Finally, oxidative stress led to cell cycle arrest through p38MAPK, DNA damage, and the subsequent induction of the ATM-p53-p21WAF1-pRb axis. Overall, oxidative stress was shown to induce similar intracellular mechanisms to those induced by osmotic stress and to also restrain cellular proliferation. Conclusion Our findings indicate that exogenous stresses impose a strict control in IVD cells’ proliferation, thus possibly participating in the maintenance of tissue homeostasis. Understanding disk cells’ physiology—especially after taking into consideration the conditions of their in vivo physicochemical environment—has important implications for targeted treatments against disk degeneration and back pain, as those cells are utterly responsible for the retention of the dynamic equilibrium between synthesis and degradation of the extracellular matrix. Supported by the European Union FP7 (“GENODISC”, grant agreement no. HEALTH-F2-2008-201626) I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared

Abstract 3113: Effects of an up-regulated ATR-CHEK1 pathway in head and neck squamous cell carcinomas

Abstract Background: The ATR-CHEK1 pathway is upregulated in a subset of head and neck squamous cell carcinoma (HNSCC) cell lines with loss of the G1 cell cycle checkpoint. We hypothesized that the upregulated ATR-CHEK1 pathway protects HNSCC from mitotic catastrophe (cell death) by enhancing the G2M phase checkpoint and that inhibition of this pathway may sensitize HNSCC to DNA damaging agents. Methods and Results: In HNSCC, we observed gain, amplification or translocation of the ATR gene in 8 of 20 cell lines studied; whereas the CHEK1 gene is partially lost in 12 of 20 cell lines. ATR and CHEK1 FISH in paraffin sections of primary head and neck squamous cell carcinomas confirmed our findings in HNSCC cell lines. We observed that both ATR and CHEK1 are overexpressed by quantitative PCR in five of eight HNSCC cell lines with loss of the G1 cell cycle checkpoint. Inhibition of ATR and CHEK1 with caffeine or specific inhibition with the respective siRNAs results in increased susceptibility of HNSCC to ionizing radiation by clonogenic cell survival assay. siRNA-mediated ATR or CHEK1 knockdown leads to loss of G2M checkpoint accumulation and increased sub-G0 apoptotic population by flow cytometric analysis. The mechanism of cell death after ATR and CHEK1 knockdown is by mitotic catastrophe, as evidenced by increased premature chromatin condensation. Conclusions: The ATR-CHEK1 pathway is up-regulated in a subset of HNSCC with loss of G1 phase cell cycle checkpoint. The up-regulated ATR-CHEK1 pathway protects these HNSCC from mitotic catastrophe by enhancing the G2M phase cell cycle checkpoints and inhibition of ATR and/or CHEK1 increase the sensitivity of the HNSCC to ionizing radiation. We conclude that inhibition of the up-regulated ATR-CHEK1 pathway in HNSCC may potentiate or increase the efficacy of the current therapeutic modalities for HNSCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3113. doi:1538-7445.AM2012-3113

Abstract B82: High frequency of hypermethylation at the 14-3-3 sigma to gene silencing in breast cancer.

Abstract Background: Expression of 14-3-3 sigma is induced in response to DNA damage, and causes cells to arrest in G(2). Hypermethylation of CpG islands located in the promoter regions of tumor suppressor genes is now firmly established as an important mechanism for gene inactivation. Objetive: To study the relation of 14-3-3 sigma gene promoter hypermethylation and its transcription expression levels in sporadic breast carcinogenesis. Material and Methods:This is a prospective study we quantified methylation levels of promoter 14-3-3 gene in 107 women with breast cancer and 108 control subjects by Real Time QMS-PCR SYBR green and analyzed association with prognostics factor in breast cancer. Results: Median age was 58 years (32-88); 69% were postmenopausal women. Nodal involvement N0; 63%, N1;30%, N2;7%), tumor size (T1;58%, T2;35%, T3;4%, T4;4%) and grade G1; 20%, G2;37%, G3;30%). The methylation of 14-3-3σ were 60% of sporadic breast cancer patients and were 34% of normal breast (p=0.0047). The methylation of 14-3-3σ gene in serum was markedly related with T3-4 stage (p<0.05), nodal positive status (p<0.05) and poor outcome. With a median follow up 6 years we saw more probability of developing distance metastasis in patients with methylation 14-3-3σ (p>0.05). Conclusions: The recent identification of novel 14-3-3sigma-associated proteins by a targeted proteomics approach implies that 14-3-3sigma regulates diverse cellular processes, which may become deregulated after silencing of 14-3-3sigma expression in cancer cells. Therefore, it is possible that loss of σ expression contributes to malignant transformation by impairing the G2 cell cycle checkpoint function, thus allowing an accumulation of genetic defects. Perhaps in the detection of CpG methylation of 14-3-3σ may be used for diagnostic and prognostic purposes Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B82.

Mitotic Catastrophe Occurs in the Absence of Apoptosis in p53-Null Cells with a Defective G1 Checkpoint

Cell death occurring during mitosis, or mitotic catastrophe, often takes place in conjunction with apoptosis, but the conditions in which mitotic catastrophe may exhibit features of programmed cell death are still unclear. In the work presented here, we studied mitotic cell death by making use of a UV-inactivated parvovirus (adeno-associated virus; AAV) that has been shown to induce a DNA damage response and subsequent death of p53-defective cells in mitosis, without affecting the integrity of the host genome. Osteosarcoma cells (U2OSp53DD) that are deficient in p53 and lack the G1 cell cycle checkpoint respond to AAV infection through a transient G2 arrest. We found that the infected U2OSp53DD cells died through mitotic catastrophe with no signs of chromosome condensation or DNA fragmentation. Moreover, cell death was independent of caspases, apoptosis-inducing factor (AIF), autophagy and necroptosis. These findings were confirmed by time-lapse microscopy of cellular morphology following AAV infection. The assays used readily revealed apoptosis in other cell types when it was indeed occurring. Taken together the results indicate that in the absence of the G1 checkpoint, mitotic catastrophe occurs in these p53-null cells predominantly as a result of mechanical disruption induced by centrosome overduplication, and not as a consequence of a suicide signal.

WEE1 Kinase Targeting Combined with DNA-Damaging Cancer Therapy Catalyzes Mitotic Catastrophe

WEE1 kinase is a key molecule in maintaining G₂-cell-cycle checkpoint arrest for premitotic DNA repair. Whereas normal cells repair damaged DNA during G₁-arrest, cancer cells often have a deficient G₁-arrest and largely depend on G₂-arrest. The molecular switch for the G₂-M transition is held by WEE1 and is pushed forward by CDC25. WEE1 is overexpressed in various cancer types, including glioblastoma and breast cancer. Preclinical studies with cancer cell lines and animal models showed decreased cancer cell viability, reduced tumor burden, and improved survival after WEE1 inhibition by siRNA or small molecule inhibitors, which is enhanced by combination with conventional DNA-damaging therapy, such as radiotherapy and/or cytostatics. Mitotic catastrophe results from premature entry into mitosis with unrepaired lethal DNA damage. As such, cancer cells become sensitized to conventional therapy by WEE1 inhibition, in particular those with insufficient G₁-arrest due to deficient p53 signaling, like glioblastoma cells. One WEE1 inhibitor has now reached clinical phase I studies. Dose-limiting toxicity consisted of hematologic events, nausea and/or vomiting, and fatigue. The combination of DNA-damaging cancer therapy with WEE1 inhibition seems to be a rational approach to push cancer cells in mitotic catastrophe. Its safety and efficacy are being evaluated in clinical studies.

WEE1 inhibition sensitizes osteosarcoma to radiotherapy

BackgroundThe use of radiotherapy in osteosarcoma (OS) is controversial due to its radioresistance. OS patients currently treated with radiotherapy generally are inoperable, have painful skeletal metastases, refuse surgery or have undergone an intralesional resection of the primary tumor. After irradiation-induced DNA damage, OS cells sustain a prolonged G2 cell cycle checkpoint arrest allowing DNA repair and evasion of cell death. Inhibition of WEE1 kinase leads to abrogation of the G2 arrest and could sensitize OS cells to irradiation induced cell death.MethodsWEE1 expression in OS was investigated by gene-expression data analysis and immunohistochemistry of tumor samples. WEE1 expression in OS cell lines and human osteoblasts was investigated by Western blot. The effect of WEE1 inhibition on the radiosensitivity of OS cells was assessed by cell viability and caspase activation analyses after combination treatment. The presence of DNA damage was visualized using immunofluorescence microscopy. Cell cycle effects were investigated by flow cytometry and WEE1 kinase regulation was analyzed by Western blot.ResultsWEE1 expression is found in the majority of tested OS tissue samples. Small molecule drug PD0166285 inhibits WEE1 kinase activity. In the presence of WEE1-inhibitor, irradiated cells fail to repair their damaged DNA, and show higher levels of caspase activation. The inhibition of WEE1 effectively abrogates the irradiation-induced G2 arrest in OS cells, forcing the cells into premature, catastrophic mitosis, thus enhancing cell death after irradiation treatment.ConclusionWe show that PD0166285, a small molecule WEE1 kinase inhibitor, can abrogate the G2 checkpoint in OS cells, pushing them into mitotic catastrophe and thus sensitizing OS cells to irradiation-induced cell death. This suggests that WEE1 inhibition may be a promising strategy to enhance the radiotherapy effect in patients with OS.