The cell cycle-coupled expression of topoisomerase IIalpha during S phase is regulated by mRNA stability and is disrupted by heat shock or ionizing radiation

The Bisdioxopiperazine ICRF-193 Attenuates LPS-induced IL-1β Secretion by Macrophages

Inhibiting pathological secretion of Interleukin-1β has shown beneficial effects in disease models and in the clinic and thus there is interest in finding inhibitors that can reduce its release from macrophages in response to their activation by foreign pathogens. We used an in vitro human macrophage model to investigate whether ICRF-193, a Topoisomerase II inhibitor could modulate IL1B mRNA expression and IL-1β secretion. These macrophage-like cells readily secrete IL-1β in response to Lipopolysaccharide (LPS). Upon exposure to a non-toxic dose of ICRF-193, IL-1β secretion was diminished by ~ 40%; however, level of transcription of IL1B was unaffected. We show that there was no Topoisomerase 2B (TOP2B) binding to several IL1B gene sites, which may explain why ICRF-193 does not alter IL1B mRNA levels. Hence, we show for the first time that ICRF-193 can reduce IL-1β secretion. Its low cost and the development of water-soluble prodrugs of ICRF-193 warrants its further investigation in the modulation of pathological secretion of this cytokine for the treatment of inflammatory disorders. (165 words).

Synthesis and biological evaluation of 1-phenyl-4,6-dihydrobenzo[b]pyrazolo[3,4-d]azepin-5(1H)-one/thiones as anticancer agents

Cancer is associated with uncontrolled cell proliferation invading adjoining tissues and organs. Despite the availability of several chemotherapeutic agents, the constant search for newer approaches and drugs is necessitated owing to the ever-growing challenge of resistance. Over the years, DNA has emerged as an important druggable therapeutic drug due to its role in critical cellular processes such as cell division and maintenance. Further, evading apoptosis stands out as a hallmark of cancer. Hence, designing new compounds that would target DNA and induce apoptosis plays an important role in cancer therapy. In the current work, we carried out the synthesis and anticancer evaluation of 1-aryl-4,6-dihydrobenzo[b]pyrazolo[3,4-d]azepin-5(1H)-ones/thiones (26 compounds) against selected human cancer cell lines. Among these, compounds 8ae, 8ad, 8cf, 10ad and Kenpaullone have shown good inhibitory properties against HeLa cells (IC₅₀ < 2 µM) with good selectivity over the non-cancerous human embryonic kidney (Hek293T) cells. In cell cycle analysis, the compounds 8ad and 8cf have exhibited G₂/M cell cycle arrest in HeLa cells. In addition, the compounds 8ad and 8cf induced apoptosis in a dose-dependent manner in the Annexin-V FITC staining assay. The DAPI staining clearly demonstrated the condensed and fragmented nuclei in 8ad, 8cf, 8ae and Kenpaullone-treated HeLa cells. In addition, these compounds strongly suppressed the healing after 48 h in in vitro cell migration assay. The DNA binding experiments indicated that compounds 8ae, 8cf, and 8ad as well as Kenpaullone interact with double-stranded DNA by binding in grooves which may interrupt the DNA replication and kill fast-growing cells. Molecular docking studies revealed the binding pose of 8ad and Kenpaullone at HT1 binding pocket of double-stranded DNA. Compounds 8ad and 8cf demonstrated moderate topo II inhibition which could be a possible reason for their anticancer properties. Compounds 8ad and 8cf may cause the topo II and DNA covalent complex, which leads to the inhibition of DNA replication and transcription. This eventually increases the DNA damage in cells and promotes cell apoptosis. With the above interesting biological profile, the new 1-aryl-2,6-dihydrobenzo[b]pyrazolo[3,4-d]azepin-5(4H)-one/thione derivatives have emerged as promising leads for the discovery of new anticancer agents.

Adaptive resistance is not responsible for long-term drug resistance in a cellular model of triple negative breast cancer

Resistance to cancer therapeutics represents a leading cause of mortality and is particularly important in cancers, such as triple negative breast cancer, for which no targeted therapy is available, as these are only treated with traditional chemotherapeutics. Cancer, as well as bacterial, drug resistance can be intrinsic, acquired or adaptive. Adaptive cancer drug resistance is gaining attention as a mechanism for the generation of long-term drug resistance as is the case with bacterial antibiotic resistance. We have used a cellular model of triple negative breast cancer (CAL51) and its drug resistance derivative (CALDOX) to gain insight into genome-wide expression changes associated with long-term doxorubicin (a widely used anthracycline for cancer treatment) resistance and doxorubicin-induced stress. Previous work indicates that both naïve and resistance cells have a functional p53-p21 axis controlling cell cycle at G1, although this is not a driver for drug resistance, but down-regulation of TOP2A (topoisomerase IIα). As expected, CALDOX cells have a signature characterized, in addition to down-regulation of TOP2A, by genes and pathways associated with drug resistance, metastasis and stemness. Both CAL51 and CALDOX stress signatures share 12 common genes (TRIM22, FAS, SPATA18, SULF2, CDKN1A, GDF15, MYO6, CXCL5, CROT, EPPK1, ZMAT3 and CD44), with roles in the above-mentioned pathways, indicating that these cells have similar functional responses to doxorubicin relaying on the p53 control of apoptosis. Eight genes are shared by both drug stress signatures (in CAL51 and CALDOX cells) and CALDOX resistant cells (FAS, SULF2, CDKN1A, CXCL5, CD44, SPATA18, TRIM22 and CROT), many of them targets of p53. This corroborates experimental data indicating that CALDOX cells, even in the absence of drug, have activated, at least partially, the p53-p21 axis and DNA damage response. Although this eight-gene signature might be an indicator of adaptive resistance, as this transient phenomenon due to short-term stress may not revert to its original state upon withdrawal of the stressor, previous experimental data indicates that the p53-p21 axis is not responsible for doxorubicin resistance. Importantly, TOP2A is not responsive to doxorubicin treatment and thus absent in both drug stress signatures. This indicates that during the generation of doxorubicin resistance, cells acquire genetic changes likely to be random, leading to down regulation of TOP2A, but selected during the generation of cells due to the presence of drug in the culture medium. This poses a considerable constraint for the development of strategies aimed at avoiding the emergence of drug resistance in the clinic.

Predictive value of topoisomerase II alpha protein for clinicopathological characteristics and prognosis in early breast cancer

PURPOSE

Topoisomerase II alpha (TOP2A) has been identified as a proliferation marker, of which the most common method for detection is immunohistochemistry (IHC). However, the optimal cut-off of TOP2A expression regarding prognostic value remains controversial. This study was to identify the optimal cut-off value of TOP2A expression and its correlation with clinicopathological variables and prognosis in early stage breast cancer in China.

METHODS

Between January 2013 and January 2015, a total of 1084 early breast cancer patients were enrolled. The optimal cut-off of TOP2A expression was assessed using the minimum P value approach. Correlations between TOP2A expression and clinicopathological characteristics were explored by the Spearman's correlation analysis, while the impact of TOP2A expression on disease-free survival (DFS) and overall survival (OS) was evaluated by the Kaplan-Meier methods. Univariate and multivariate Cox regression analyses were executed to identify statistically significant prognostic factors.

RESULTS

The optimal cut-off value of TOP2A was recommended as 15%. Overall, 603 (55.6%) patients were TOP2A over-expression and 481 (44.4%) patients were TOP2A low expression. TOP2A over-expression was in positive associations with a higher Ki67 index (r = 0.83, P < 0.001), HER2 positive (r = 0.26, P < 0.001), a larger tumor size (r = 0.14, P < 0.001), and a higher histologic grade (r = 0.59, P < 0.001), and in a significantly negative correlation with hormone receptor (HR) positive expression (r =  - 0.40, P < 0.001) in early breast cancer. TOP2A over-expression significantly associated with worse DFS (P = 0.001) and OS (P < 0.001) and was an independent prognostic factor for both DFS (hazard ratio [HR] = 2.04; 95% confidence interval [95% CI] 1.30-3.18, P = 0.0018) and OS (HR = 3.54; 95%CI 1.53-8.23, P = 0.003) in stage I-II breast cancer patients.

CONCLUSION

To our knowledge, this is the first study to recommend the optimal cut-off value of TOP2A expression in breast cancer. The TOP2A expression is significantly correlated with HER2 status, Ki67 index, tumor size, histologic grade and HR status, and could be a surrogate indicator for poor prognosis of early breast cancer.

The regulation of DNA supercoiling across evolution

DNA supercoiling controls a variety of cellular processes, including transcription, recombination, chromosome replication, and segregation, across all domains of life. As a physical property, DNA supercoiling alters the double helix structure by under- or over-winding it. Intriguingly, the evolution of DNA supercoiling reveals both similarities and differences in its properties and regulation across the three domains of life. Whereas all organisms exhibit local, constrained DNA supercoiling, only bacteria and archaea exhibit unconstrained global supercoiling. DNA supercoiling emerges naturally from certain cellular processes and can also be changed by enzymes called topoisomerases. While structurally and mechanistically distinct, topoisomerases that dissipate excessive supercoils exist in all domains of life. By contrast, topoisomerases that introduce positive or negative supercoils exist only in bacteria and archaea. The abundance of topoisomerases is also transcriptionally and post-transcriptionally regulated in domain-specific ways. Nucleoid-associated proteins, metabolites, and physicochemical factors influence DNA supercoiling by acting on the DNA itself or by impacting the activity of topoisomerases. Overall, the unique strategies that organisms have evolved to regulate DNA supercoiling hold significant therapeutic potential, such as bactericidal agents that target bacteria-specific processes or anticancer drugs that hinder abnormal DNA replication by acting on eukaryotic topoisomerases specialized in this process. The investigation of DNA supercoiling therefore reveals general principles, conserved mechanisms, and kingdom-specific variations relevant to a wide range of biological questions.

Cell Cycle-Dependent Control and Roles of DNA Topoisomerase II

Type II topoisomerases are ubiquitous enzymes in all branches of life that can alter DNA superhelicity and unlink double-stranded DNA segments during processes such as replication and transcription. In cells, type II topoisomerases are particularly useful for their ability to disentangle newly-replicated sister chromosomes. Growing lines of evidence indicate that eukaryotic topoisomerase II (topo II) activity is monitored and regulated throughout the cell cycle. Here, we discuss the various roles of topo II throughout the cell cycle, as well as mechanisms that have been found to govern and/or respond to topo II function and dysfunction. Knowledge of how topo II activity is controlled during cell cycle progression is important for understanding how its misregulation can contribute to genetic instability and how modulatory pathways may be exploited to advance chemotherapeutic development.

Topoisomerases as anticancer targets

Many cancer type-specific anticancer agents have been developed and significant advances have been made toward precision medicine in cancer treatment. However, traditional or nonspecific anticancer drugs are still important for the treatment of many cancer patients whose cancers either do not respond to or have developed resistance to cancer-specific anticancer agents. DNA topoisomerases, especially type IIA topoisomerases, are proved therapeutic targets of anticancer and antibacterial drugs. Clinically successful topoisomerase-targeting anticancer drugs act through topoisomerase poisoning, which leads to replication fork arrest and double-strand break formation. Unfortunately, this unique mode of action is associated with the development of secondary cancers and cardiotoxicity. Structures of topoisomerase-drug-DNA ternary complexes have revealed the exact binding sites and mechanisms of topoisomerase poisons. Recent advances in the field have suggested a possibility of designing isoform-specific human topoisomerase II poisons, which may be developed as safer anticancer drugs. It may also be possible to design catalytic inhibitors of topoisomerases by targeting certain inactive conformations of these enzymes. Furthermore, identification of various new bacterial topoisomerase inhibitors and regulatory proteins may inspire the discovery of novel human topoisomerase inhibitors. Thus, topoisomerases remain as important therapeutic targets of anticancer agents.

Retinoic acid signaling regulates Krt5 and Krt14 independently of stem cell markers in submandibular salivary gland epithelium

BACKGROUND

Retinoic acid (RA), the active metabolite of vitamin A, has been demonstrated to be important for growth and branching morphogenesis of mammalian embryonic salivary gland epithelium. However, it is not known whether RA functions directly within epithelial cells or in associated tissues that influence morphogenesis of salivary epithelium. Moreover, downstream targets of RA regulation have not been identified.

RESULTS

Here, we show that canonical RA signaling occurs in multiple tissues of embryonic mouse salivary glands, including epithelium, associated parasympathetic ganglion neurons, and nonneuronal mesenchyme. By culturing epithelium explants in isolation from other tissues, we demonstrate that RA influences epithelium morphogenesis by direct action in that tissue. Moreover, we demonstrate that inhibition of RA signaling represses cell proliferation and expression of FGF10 signaling targets, and upregulates expression of basal epithelial keratins Krt5 and Krt14. Importantly, we show that the stem cell gene Kit is regulated inversely from Krt5/Krt14 by RA signaling.

CONCLUSIONS

RA regulates Krt5 and Krt14 expression independently of stem cell character in developing salivary epithelium. RA, or chemical inhibitors of RA signaling, could potentially be used for modulating growth and differentiation of epithelial stem cells for the purpose of re-populating damaged glands or generating bioengineered organs. Developmental Dynamics 246:135-147, 2017. © 2016 Wiley Periodicals, Inc.

Long-term exposure to estrogen enhances chemotherapeutic efficacy potentially through epigenetic mechanism in human breast cancer cells

Chemotherapy is the most common clinical option for treatment of breast cancer. However, the efficacy of chemotherapy depends on the age of breast cancer patients. Breast tissues are estrogen responsive and the levels of ovarian estrogen vary among the breast cancer patients primarily between pre- and post-menopausal age. Whether this age-dependent variation in estrogen levels influences the chemotherapeutic efficacy in breast cancer patients is not known. Therefore, the objective of this study was to evaluate the effects of natural estrogen 17 beta-estradiol (E2) on the efficacy of chemotherapeutic drugs in breast cancer cells. Estrogen responsive MCF-7 and T47D breast cancer cells were long-term exposed to 100 pg/ml estrogen, and using these cells the efficacy of chemotherapeutic drugs doxorubicin and cisplatin were determined. The result of cell viability and cell cycle analysis revealed increased sensitivities of doxorubicin and cisplatin in estrogen-exposed MCF-7 and T47D cells as compared to their respective control cells. Gene expression analysis of cell cycle, anti-apoptosis, DNA repair, and drug transporter genes further confirmed the increased efficacy of chemotherapeutic drugs in estrogen-exposed cells at molecular level. To further understand the role of epigenetic mechanism in enhanced chemotherapeutic efficacy by estrogen, cells were pre-treated with epigenetic drugs, 5-aza-2-deoxycytidine and Trichostatin A prior to doxorubicin and cisplatin treatments. The 5-aza-2 deoxycytidine pre-treatment significantly decreased the estrogen-induced efficacy of doxorubicin and cisplatin, suggesting the role of estrogen-induced hypermethylation in enhanced sensitivity of these drugs in estrogen-exposed cells. In summary, the results of this study revealed that sensitivity to chemotherapy depends on the levels of estrogen in breast cancer cells. Findings of this study will have clinical implications in selecting the chemotherapy strategies for treatment of breast cancer patients depending on the serum estrogen levels that varies among pre- and post-menopausal age of the patients.

Optimising the combination dosing strategy of abemaciclib and vemurafenib in BRAF-mutated melanoma xenograft tumours

BACKGROUND

Resistance to BRAF inhibition is a major cause of treatment failure for BRAF-mutated metastatic melanoma patients. Abemaciclib, a cyclin-dependent kinase 4 and 6 inhibitor, overcomes this resistance in xenograft tumours and offers a promising drug combination. The present work aims to characterise the quantitative pharmacology of the abemaciclib/vemurafenib combination using a semimechanistic pharmacokinetic/pharmacodynamic modelling approach and to identify an optimum dosing regimen for potential clinical evaluation.

METHODS

A PK/biomarker model was developed to connect abemaciclib/vemurafenib concentrations to changes in MAPK and cell cycle pathway biomarkers in A375 BRAF-mutated melanoma xenografts. Resultant tumour growth inhibition was described by relating (i) MAPK pathway inhibition to apoptosis, (ii) mitotic cell density to tumour growth and, under resistant conditions, (iii) retinoblastoma protein inhibition to cell survival.

RESULTS

The model successfully described vemurafenib/abemaciclib-mediated changes in MAPK pathway and cell cycle biomarkers. Initial tumour shrinkage by vemurafenib, acquisition of resistance and subsequent abemaciclib-mediated efficacy were successfully captured and externally validated. Model simulations illustrate the benefit of intermittent vemurafenib therapy over continuous treatment, and indicate that continuous abemaciclib in combination with intermittent vemurafenib offers the potential for considerable tumour regression.

CONCLUSIONS

The quantitative pharmacology of the abemaciclib/vemurafenib combination was successfully characterised and an optimised, clinically-relevant dosing strategy was identified.

Collision of Trapped Topoisomerase 2 with Transcription and Replication: Generation and Repair of DNA Double-Strand Breaks with 5' Adducts

Topoisomerase 2 (Top2) is an essential enzyme responsible for manipulating DNA topology during replication, transcription, chromosome organization and chromosome segregation. It acts by nicking both strands of DNA and then passes another DNA molecule through the break. The 5′ end of each nick is covalently linked to the tyrosine in the active center of each of the two subunits of Top2 (Top2cc). In this configuration, the two sides of the nicked DNA are held together by the strong protein-protein interactions between the two subunits of Top2, allowing the nicks to be faithfully resealed in situ. Top2ccs are normally transient, but can be trapped by cancer drugs, such as etoposide, and subsequently processed into DSBs in cells. If not properly repaired, these DSBs would lead to genome instability and cell death. Here, I review the current understanding of the mechanisms by which DSBs are induced by etoposide, the unique features of such DSBs and how they are repaired. Implications for the improvement of cancer therapy will be discussed.

Heat Stress-Induced DNA Damage

Although the heat-stress response has been extensively studied for decades, very little is known about its effects on nucleic acids and nucleic acid-associated processes. This is due to the fact that the research has focused on the study of heat shock proteins and factors (HSPs and HSFs), their involvement in the regulation of transcription, protein homeostasis, etc. Recently, there has been some progress in the study of heat stress effects on DNA integrity. In this review, we summarize and discuss well-known and potential mechanisms of formation of various heat stress-induced DNA damage.

Reconsidering plant memory: Intersections between stress recovery, RNA turnover, and epigenetics

Plants grow in dynamic environments where they can be exposed to a multitude of stressful factors, all of which affect their development, yield, and, ultimately, reproductive success. Plants are adept at rapidly acclimating to stressful conditions and are able to further fortify their defenses by retaining memories of stress to enable stronger or more rapid responses should an environmental perturbation recur. Indeed, one mechanism that is often evoked regarding environmental memories is epigenetics. Yet, there are relatively few examples of such memories; neither is there a clear understanding of their duration, considering the plethora of stresses in nature. We propose that this field would benefit from investigations into the processes and mechanisms enabling recovery from stress. An understanding of stress recovery could provide fresh insights into when, how, and why environmental memories are created and regulated. Stress memories may be maladaptive, hindering recovery and affecting development and potential yield. In some circumstances, it may be advantageous for plants to learn to forget. Accordingly, the recovery process entails a balancing act between resetting and memory formation. During recovery, RNA metabolism, posttranscriptional gene silencing, and RNA-directed DNA methylation have the potential to play key roles in resetting the epigenome and transcriptome and in altering memory. Exploration of this emerging area of research is becoming ever more tractable with advances in genomics, phenomics, and high-throughput sequencing methodology that will enable unprecedented profiling of high-resolution stress recovery time series experiments and sampling of large natural populations.

Semi-mechanistic pharmacokinetic/pharmacodynamic modeling of the antitumor activity of LY2835219, a new cyclin-dependent kinase 4/6 inhibitor, in mice bearing human tumor xenografts

PURPOSE

Selective inhibition of cyclin-dependent kinases 4 and 6 (CDK4/6) represents a promising therapeutic strategy. However, despite documented evidence of clinical activity, limited information is available on the optimal dosing strategy of CDK4/6 inhibitors. Here, we present an integrated semi-mechanistic pharmacokinetic/pharmacodynamic model to characterize the quantitative pharmacology of LY2835219, a CDK4/6 inhibitor, in xenograft tumors.

EXPERIMENTAL DESIGN

LY2835219 plasma concentrations were connected to CDK4/6 inhibition and cell-cycle arrest in colo-205 human colorectal xenografts by incorporating the biomarkers, phospho-(ser780)-Rb, topoisomerase II α, and phosphohistone H3, into a precursor-dependent transit compartment model. This biomarker model was then connected to tumor growth inhibition (TGI) by: (i) relating the rate of tumor growth to mitotic cell density, and (ii) incorporating a concentration-dependent mixed cytostatic/cytotoxic effect driving quiescence and cell death at high doses. Model validation was evaluated by predicting LY2835219-mediated antitumor effect in A375 human melanoma xenografts.

RESULTS

The model successfully described LY2835219-mediated CDK4/6 inhibition, cell-cycle arrest, and TGI in colo-205, and was validated in A375. The model also demonstrated that a chronic dosing strategy achieving minimum steady-state trough plasma concentrations of 200 ng/mL is required to maintain durable cell-cycle arrest. Quiescence and cell death can be induced by further increasing LY2835219 plasma concentrations.

CONCLUSIONS

Our model provides mechanistic insight into the quantitative pharmacology of LY2835219 and supports the therapeutic dose and chronic dosing strategy currently adopted in clinical studies.

Preclinical characterization of the CDK4/6 inhibitor LY2835219: in-vivo cell cycle-dependent/independent anti-tumor activities alone/in combination with gemcitabine

The G1 restriction point is critical for regulating the cell cycle and is controlled by the Rb pathway (CDK4/6-cyclin D1-Rb-p16/ink4a). This pathway is important because of its inactivation in a majority of human tumors. Transition through the restriction point requires phosphorylation of retinoblastoma protein (Rb) by CDK4/6, which are highly validated cancer drug targets. We present the identification and characterization of a potent CDK4/6 inhibitor, LY2835219. LY2835219 inhibits CDK4 and CDK6 with low nanomolar potency, inhibits Rb phosphorylation resulting in a G1 arrest and inhibition of proliferation, and its activity is specific for Rb-proficient cells. In vivo target inhibition studies show LY2835219 is a potent inhibitor of Rb phosphorylation, induces a complete cell cycle arrest and suppresses expression of several Rb-E2F-regulated proteins 24 hours after a single dose. Oral administration of LY2835219 inhibits tumor growth in human tumor xenografts representing different histologies in tumor-bearing mice. LY2835219 is effective and well tolerated when administered up to 56 days in immunodeficient mice without significant loss of body weight or tumor outgrowth. In calu-6 xenografts, LY2835219 in combination with gemcitabine enhanced in vivo antitumor activity without a G1 cell cycle arrest, but was associated with a reduction of ribonucleotide reductase expression. These results suggest LY2835219 may be used alone or in combination with standard-of-care cytotoxic therapy. In summary, we have identified a potent, orally active small-molecule inhibitor of CDK4/6 that is active in xenograft tumors. LY2835219 is currently in clinical development.

DNA topoisomerase II-dependent control of the cell cycle progression in root meristems of Allium cepa

The catalytic ability of DNA topoisomerases (Topo) to generate short-term DNA breaks allow these enzymes to play crucial functions in managing DNA topology during S-phase replication, transcription, and chromatin-remodelling processes required to achieve commitment for the onset and transition through mitosis. Our experiments on root meristem cells of onion (Allium cepa) were designed to gain insight into the contribution of Topo II to plant-specific progression throughout interphase and mitosis. Irrespective of the position of the cell in interphase, the immunofluorescence of Topo II revealed similar nuclear labelling pattern with well defined signals dispersed in the nucleoplasm and the cortical zone of the nucleolus. Only weak labelling was detected in metaphase and anaphase chromosomes. Experiments with two potent anti-Topo II agents, doxorubicin (DOX, an anthracycline) and a bisdioxopiperazine derivative, ICRF-193, suggest that the inhibition-mediated increase in Topo II immunofluorescence may represent a compensatory mechanism, by which an up-regulated expression of the enzyme tends to counteract the drug-induced loss of indispensable catalytic and relaxation functions. γ-H2AX immunolabelling seems to indicate that both DOX- and ICRF-193-induced alterations in cell cycle progression reflect primarily the activity of the G2/M DNA damage checkpoint. Our findings provide evidence for the plant-specific cell cycle control mechanism induced by Topo II inhibitors under DNA stress conditions.

Replication-dependent and transcription-dependent mechanisms of DNA double-strand break induction by the topoisomerase 2-targeting drug etoposide

Etoposide is a DNA topoisomerase 2-targeting drug widely used for the treatment of cancer. The cytoxicity of etoposide correlates with the generation of DNA double-strand breaks (DSBs), but the mechanism of how it induces DSBs in cells is still poorly understood. Catalytically, etoposide inhibits the re-ligation reaction of Top2 after it nicks the two strands of DNA, trapping it in a cleavable complex consisting of two Top2 subunits covalently linked to the 5' ends of DNA (Top2cc). Top2cc is not directly recognized as a true DSB by cells because the two subunits interact strongly with each other to hold the two ends of DNA together. In this study we have investigated the cellular mechanisms that convert Top2ccs into true DSBs. Our data suggest that there are two mechanisms, one dependent on active replication and the other dependent on proteolysis and transcription. The relative contribution of each mechanism is affected by the concentration of etoposide. We also find that Top2α is the major isoform mediating the replication-dependent mechanism and both Top2α and Top2 mediate the transcription-dependent mechanism. These findings are potentially of great significance to the improvement of etoposide's efficacy in cancer therapy.

Gene transfection enhanced by ultrasound exposure combined with drug treatment guided by gene chip analysis

PURPOSE

Heterogeneous bioeffects have been reported in previous studies of ultrasound-mediated gene delivery. The goal of this study is to identify the differences between cells that take up plasmid DNA (pDNA) after sonication but are not transfected and cells that similarly take up pDNA but are transfected. We used these findings to select drugs that regulate intracellular processes expected to enhance gene transfection in combination with US.

MATERIALS AND METHODS

Gene expression among DU145 human prostate cancer cells after ultrasound-mediated transfection was analyzed using Affymetrix GeneChip Human Genome U133 Plus 2.0 Arrays. Drug treatments suggested by the microarray analysis were combined with US exposure to regulate the corresponding intracellular processes. Cell viability and transfection efficiency were determined by flow cytometry to analyze the effects of US combined with drug treatment.

RESULTS

Genes such as GADD45α (growth arrest and DNA-damage inducible, alpha) and Topoisomerase IIα were found to be associated with successful transfection. Drugs that regulate GADD45α and Topoisomerase IIα (e.g., ethyl methanesulfomate, amsacrine and chloroquine) were shown to increase ultrasound-mediated transfection efficiency by up to 2 fold.

CONCLUSIONS

Among cells with pDNA uptake after sonication, we found that genes are differentially expressed among transfected cells versus non-transfected cells. Regulation of the expression level of GADD45α and TOP2α and other intracellular processes can yield higher efficiency of ultrasound-mediated gene transfection. This suggests that a strategy to increase gene transfection efficiency involving the combination of sonication and regulation of intracellular processes using drugs could further enhance US-mediated gene transfection.

Topoisomerase 2 alpha: a real predictor of anthracycline efficacy?

Anthracyclines are frequently used in the adjuvant setting for breast cancer treatment since it is considered that anthracycline-based chemotherapy treatment benefits breast cancer patients. Nonetheless, these drugs are associated with severe side effects and predictive factors, for sensitivity to anthracyclines, are warranted in clinical practice. Topoisomerase 2 alpha (TOP2A) is considered to be the molecular target of these drugs. The potential predictive value of TOP2A amplification and overexpression has been extensively studied in breast cancer patients treated with anthracyclines. However, results are not conclusive. In this paper, we review some of the published studies addressing the predictive value of TOP2A as well as the cellular functions of this enzyme and its status in breast cancer tissue.

Target genes of Topoisomerase IIβ regulate neuronal survival and are defined by their chromatin state

Topoisomerases are essential for DNA replication in dividing cells, but their genomic targets and function in postmitotic cells remain poorly understood. Here we show that a switch in the expression from Topoisomerases IIα (Top2α) to IIβ (Top2β) occurs during neuronal differentiation in vitro and in vivo. Genome-scale location analysis in stem cell-derived postmitotic neurons reveals Top2β binding to chromosomal sites that are methylated at lysine 4 of histone H3, a feature of regulatory regions. Indeed Top2β-bound sites are preferentially promoters and become targets during the transition from neuronal progenitors to neurons, at a time when cells exit the cell cycle. Absence of Top2β protein or its activity leads to changes in transcription and chromatin accessibility at many target genes. Top2β deficiency does not impair stem cell properties and early steps of neuronal differentiation but causes premature death of postmitotic neurons. This neuronal degeneration is caused by up-regulation of Ngfr p75, a gene bound and repressed by Top2β. These findings suggest a chromatin-based targeting of Top2β to regulatory regions in the genome to govern the transcriptional program associated with neuronal differentiation and longevity.

Correlations of TOP2A gene aberrations and expression of topoisomerase IIα protein and TOP2A mRNA expression in primary breast cancer: a retrospective study of 86 cases using fluorescence in situ hybridization and immunohistochemistry

Our aim in this study was to assess the status of TOP2A gene aberrations (no change/amplification or deletion) and its correlations with topoisomerase IIα (Topo IIα) protein and TOP2A mRNA expression, respectively. TOP2A amplification, Topo IIα protein expression and TOP2A mRNA expression were assessed using samples of 86 cases of breast cancer by fluorescence in fluorescence in situ hybridization, quantitative real-time polymerase chain reaction and immunohistochemistry, respectively. Twenty two (22.57%) had amplification/deletion of TOP2A gene. Twenty eight (32.56%) tumor samples were 17q polysomy or monosomy. Topo IIα protein was expressed in 57 cases (66.27%, 57/86): 22 cases (38.62%, 22/57) and 35 cases (61.40%, 35/57) had amplification/deletion and no change of TOP2A gene, respectively. These three groups showed significant differences by one-way analysis of variance (P < 0.001). The average Ct values of TOP2A mRNA expression in the tumors with deletion, amplification and no change of TOP2A gene were 27.00, 27.33 and 31.66, respectively. We demonstrated that the TOP2A gene was amplified or deleted in breast cancer, with a significant correlation with high expressions of Topo IIα protein and TOP2A mRNA expression. Ki-67 expression index (mean = 14.9) decreased significantly in cases wherein TOP2A gene had no change and Her2/neu protein expression was weakly positive (0-1+, P < 0.001).

Topo IIα gene alterations correlated with survival in patients with diffuse large B-cell lymphoma

BACKGROUND

Topoisomerase IIα (topo IIα) protein expression has prognostic significance in many cancers. However, it is still unclear whether topo IIα protein expression and gene alterations play roles as prognostic factors in diffuse large B-cell lymphoma (DLBCL).

MATERIALS AND METHODS

We selected 102 patients with DLBCL who were homogeneously treated with CHOP chemotherapy and followed up. Using tissue microarray technology, all of the cases, consisting of 25 germinal centre B-cell-like (GCB) and 77 nongerminal centre B-cell-like (non-GCB) types, were studied. Topo IIα protein expression was detected by immunohistochemistry. Gene copy number of topo IIα was analysed by chromogenic in situ hybridization. Cox regression, chi-square test and Kaplan-Meier statistics were performed using SPSS 15·0.

RESULTS

Topo IIα protein overexpression was found in 91 (91/102, 89·2%) cases, while topo IIα gene amplification was absent in all cases. Chromosome 17 deletion was identified in 3 (3/102, 2·9%) cases, diploid in 66 (66/102, 64·7%) cases and aneuploidy in 33 (33/102, 32·4%) cases. By multivariate analysis, no significant differences in progression-free survival (PFS) and overall survival (OS) were observed in patients with topo IIα protein overexpression (P > 0·05), while chromosome 17 aneuploidy predicted worse PFS and OS (P < 0·001).

CONCLUSIONS

These results suggested that chromosome 17 aneuploidy, but not topo IIα protein expression, could predict worse survival in patients with DLBCL.

Combined experimental and computational analysis of DNA damage signaling reveals context-dependent roles for Erk in apoptosis and G1/S arrest after genotoxic stress

Following DNA damage, cells display complex multi-pathway signaling dynamics that connect cell-cycle arrest and DNA repair in G1, S, or G2/M phase with phenotypic fate decisions made between survival, cell-cycle re-entry and proliferation, permanent cell-cycle arrest, or cell death. How these phenotypic fate decisions are determined remains poorly understood, but must derive from integrating genotoxic stress signals together with inputs from the local microenvironment. To investigate this in a systematic manner, we undertook a quantitative time-resolved cell signaling and phenotypic response study in U2OS cells receiving doxorubicin-induced DNA damage in the presence or absence of TNFα co-treatment; we measured key nodes in a broad set of DNA damage signal transduction pathways along with apoptotic death and cell-cycle regulatory responses. Two relational modeling approaches were then used to identify network-level relationships between signals and cell phenotypic events: a partial least squares regression approach and a complementary new technique which we term 'time-interval stepwise regression.' Taken together, the results from these analysis methods revealed complex, cytokine-modulated inter-relationships among multiple signaling pathways following DNA damage, and identified an unexpected context-dependent role for Erk in both G1/S arrest and apoptotic cell death following treatment with this commonly used clinical chemotherapeutic drug.

RECQL5 cooperates with Topoisomerase II alpha in DNA decatenation and cell cycle progression

DNA decatenation mediated by Topoisomerase II is required to separate the interlinked sister chromatids post-replication. SGS1, a yeast homolog of the human RecQ family of helicases interacts with Topoisomerase II and plays a role in chromosome segregation, but this functional interaction has yet to be identified in higher organisms. Here, we report a physical and functional interaction of Topoisomerase IIα with RECQL5, one of five mammalian RecQ helicases, during DNA replication. Direct interaction of RECQL5 with Topoisomerase IIα stimulates the decatenation activity of Topoisomerase IIα. Consistent with these observations, RECQL5 co-localizes with Topoisomerase IIα during S-phase of the cell cycle. Moreover, cells with stable depletions of RECQL5 display a slow proliferation rate, a G2/M cell cycle arrest and late S-phase cycling defects. Metaphase spreads generated from RECQL5-depleted cells exhibit undercondensed and entangled chromosomes. Further, RECQL5-depleted cells activate a G2/M checkpoint and undergo apoptosis. These phenotypes are similar to those observed when Topoisomerase II catalytic activity is inhibited. These results reveal an important role for RECQL5 in the maintenance of genomic stability and a new insight into the decatenation process.

Application of mRNA regulatory regions to improve tumor specificity of transgene expression

Efficiency and specificity are two key attributes of anti-cancer drugs including genetic therapeutic agents. We suggest a way to improve specificity of gene therapy drugs based on the ability of 3'-untranslated regions (UTR) of some mRNAs selectively stabilize transcripts only during cell division. The mRNAs of genes encoding DNA methyltransferase I (DNMT1) and topoisomerase IIα (TOP2A) are among such transcripts. When inserted into genetic constructs designed to produce therapeutic protein in tumor cells, such 3'-UTR would lead to diminished effect of therapeutic protein on normal cells, which are characterized by low or absent proliferative activity. However, when included in gene expression cassette, these 3'-UTR might result in decreased transgene expression, thus, overweighting the advantage of increased specificity of expression. We showed that DNMT1 and to the lesser extent TOP2A 3'-UTR do not alter significantly therapeutic transgene expression level in tumor cells, thus, confirming the functionality of the proposed approach.

Topoisomerase IIalpha maintains genomic stability through decatenation G(2) checkpoint signaling

Topoisomerase IIalpha (topoIIalpha) is an essential mammalian enzyme that topologically modifies DNA and is required for chromosome segregation during mitosis. Previous research suggests that inhibition of topoII decatenatory activity triggers a G(2) checkpoint response, which delays mitotic entry because of insufficient decatenation of daughter chromatids. Here we examine the effects of both topoIIalpha and topoIIbeta on decatenatory activity in cell extracts, DNA damage and decatenation G(2) checkpoint function, and the frequencies of p16(INK4A) allele loss and gain. In diploid human fibroblast lines, depletion of topoIIalpha by small-interfering RNA was associated with severely reduced decatenatory activity, delayed progression from G(2) into mitosis and insensitivity to G(2) arrest induced by the topoII catalytic inhibitor ICRF-193. Furthermore, interphase nuclei of topoIIalpha-depleted cells showed increased frequencies of losses and gains of the tumor suppressor genetic locus p16(INK4A). This study shows that the topoIIalpha protein is required for decatenation G(2) checkpoint function, and inactivation of decatenation and the decatenation G(2) checkpoint leads to abnormal chromosome segregation and genomic instability.

Prognostic significance of cyclooxygenase-2 and DNA topoisomerase IIalpha expression in oral carcinoma

BACKGROUND

Despite recent advances in the diagnosis and treatment of oral carcinoma, outcomes remain disappointing. The identification of new prognostic factors is necessary to improve survival. To determine the prognostic significance of cyclooxygenase (COX)-2 and DNA topoisomerase (DNA-Topo) IIalpha expression in patients with oral carcinoma, we immunohistochemically examined these enzymes and studied their relation to overall 5-year survival.

METHODS

Surgical specimens were obtained from 160 patients with oral carcinoma, 80 with and 80 without regional lymph node metastasis. The specimens were immunostained for COX-2 and DNA-Topo IIalpha as an index of cell proliferative activity. COX-2 immunoreactivity and clinicopathological data were analyzed, and 5-year survival was calculated by the Kaplan-Meier method.

RESULTS

COX-2 expression in primary lesions was higher in cases with lymph node metastasis than in those without lymph node metastasis. An increase in tumor size was associated with increased COX-2 expression. In most cases with lymph node metastasis, COX-2 expression was higher in metastatic lesions than in primary lesions. As COX-2 expression increased, the DNA-Topo IIalpha labeling index significantly increased and the overall 5-year survival rate decreased.

CONCLUSION

Expression of COX-2 and DNA-Topo IIalpha were related to lymph node metastasis, cell proliferative activity, and overall 5-year survival rate in oral carcinoma. These enzymes may therefore be valuable diagnostic and prognostic indices in oral carcinoma.

A redox cycle within the cell cycle: ring in the old with the new

In recent years, the intracellular oxidation-reduction (redox) state has gained increasing attention as a critical mediator of cell signaling, gene expression changes and proliferation. This review discusses the evidence for a redox cycle (i.e., fluctuation in the cellular redox state) regulating the cell cycle. The presence of redox-sensitive motifs (cysteine residues, metal co-factors in kinases and phosphatases) in several cell cycle regulatory proteins indicate periodic oscillations in intracellular redox state could play a central role in regulating progression from G0/G1 to S to G2 and M cell cycle phases. Fluctuations in the intracellular redox state during cell cycle progression could represent a fundamental mechanism linking oxidative metabolic processes to cell cycle regulatory processes. Proliferative disorders are central to a variety of human pathophysiological conditions thought to involve oxidative stress. Therefore, a more complete understanding of redox control of the cell cycle could provide a biochemical rationale for manipulating aberrant cell proliferation.

Germline variations of the topoisomerase IIα gene as risk factors for primary gastric B-cell lymphoma

We investigated if germline variations of the Topoisomerase II alpha gene could predispose patients with chronic Helicobacter pylori infection to develop gastric lymphoma and conducted a mutation detection of the entire promoter region. Single marker and haplotype analysis did not reveal any associations with development of gastric lymphoma in general, histological grade or stage of disease (P>0.05). No genetic variations in the promotor region were found in 92 chromosomes of lymphoma patients and controls and linkage disequilibrium indicated a highly conserved genomic region. The results of our work exclude genetic variations as predisposing factors of primary gastric B-cell lymphoma development.

Protein kinase C delta activates topoisomerase IIalpha to induce apoptotic cell death in response to DNA damage

DNA topoisomerase II is an essential nuclear enzyme that modulates DNA processes by altering the topological state of double-stranded DNA. This enzyme is required for chromosome condensation and segregation; however, the regulatory mechanism of its activation is largely unknown. Here we demonstrate that topoisomerase IIalpha is activated in response to genotoxic stress. Concomitant with the activation, the expression of topoisomerase IIalpha is increased following DNA damage. The results also demonstrate that the proapoptotic kinase protein kinase C delta (PKCdelta) interacts with topoisomerase IIalpha. This association is in an S-phase-specific manner and is required for stabilization and catalytic activation of topoisomerase IIalpha in response to DNA damage. Conversely, inhibition of PKCdelta activity attenuates DNA damage-induced activation of topoisomerase IIalpha. Finally, aberrant activation of topoisomerase IIalpha by PKCdelta is associated with induction of apoptosis upon exposure to genotoxic agents. These findings indicate that PKCdelta regulates topoisomerase IIalpha and thereby cell fate in the genotoxic stress response.

The products of the herpes simplex virus type 1 immediate-early US1/US1.5 genes downregulate levels of S-phase-specific cyclins and facilitate virus replication in S-phase Vero cells

Herpes simplex virus type 1 ICP22-/U(S)1.5- mutants initiate viral gene expression in all cells; however, in most cell types, the replication process stalls due to an inability to express gamma2 late proteins. Although the function of ICP22/U(S)1.5 has not been established, it has been suggested that these proteins activate, induce, or repress the activity of cellular proteins during infection. In this study, we hypothesized that cell cycle-associated proteins are targets of ICP22/U(S)1.5. For this purpose, we first isolated and characterized an ICP22-/U(S)1.5- mutant virus, 22/n199. Like other ICP22-/U(S)1.5- mutants, 22/n199 replicates in a cell-type-specific manner and fails to induce efficient gamma2 late gene expression in restrictive cells. Although synchronization of restrictive human embryonic lung cells in each phase of the cell cycle did not overcome the growth restrictions of 22/n199, synchronization of permissive Vero cells in S phase rendered them less able to support 22/n199 plaque formation and replication. Consistent with this finding, expression of cellular S-phase cyclins was altered in an ICP22/U(S)1.5-dependent manner specifically when S-phase Vero cells were infected. Collectively, these observations support the notion that ICP22/U(S)1.5 deregulates the cell cycle upon infection of S-phase permissive cells by altering expression of key cell cycle regulatory proteins either directly or indirectly.

Combined static and dynamic analysis for determining the quality of time-series expression profiles

Expression profiling of time-series experiments is widely used to study biological systems. However, determining the quality of the resulting profiles remains a fundamental problem. Because of inadequate sampling rates, the effect of arrest-and-release methods and loss of synchronization, the measurements obtained from a series of time points may not accurately represent the underlying expression profiles. To solve this, we propose an approach that combines time-series and static (average) expression data analysis--for each gene, we determine whether its temporal expression profile can be reconciled with its static expression levels. We show that by combining synchronized and unsynchronized human cell cycle data, we can identify many cycling genes that are missed when using only time-series data. The algorithm also correctly distinguishes cycling genes from genes that specifically react to an environmental stimulus even if they share similar temporal expression profiles. Experimental validation of these results shows the utility of this analytical approach for determining the accuracy of gene expression patterns.

Type II topoisomerase activities in both the G1 and G2/M phases of the dinoflagellate cell cycle

Dinoflagellate genomes are large (up to 200 pg) and are encoded in histoneless chromosomes that are quasi-permanently condensed. This unique combination of chromosomal characteristics presents additional topological and cell cycle control problems for a eukaryotic cell, potentially exhibiting novel regulatory requirements of topoisomerase II. The heterotrophic dinoflagellate Crypthecodinium cohnii was used in this study. The topoisomerase II activities throughout its cell cycle were investigated by DNA flow cytometry following enzyme deactivation. Fluorescence microscopy was also used for studying the chromosome morphology of the treated cells. Two classes of topoisomerase II inhibitors were applied in our study, both of which caused G1 delay as well as G2/M arrest in the C. cohnii cell cycle. At high doses, the topoisomerase poisons amsacrine and ellipticine induced DNA fragmentation in C. cohnii cells. Topoisomerase II activities, as measured by the ability to decatenate kinetoplastid DNA (kDNA), are normally detected throughout the cell cycle in C. cohnii. Our results suggest that the requirement of type II topoisomerase activities during the G1 phase of the cell cycle may relate to the unwinding of quasi-permanently condensed chromosomes for the purpose of transcription. This was also the first time that topoisomerase II activity in dinoflagellate cells was detected.

Topo IIα reporter mice reveal proliferative regions in the epidermis and small intestine

We investigated topoisomerase II alpha promoter activity in epithelia. In confluent human keratinocytes the promoter (-557 to+90 bp) was upregulated by oncogenic Ras. In transgenic mice expressing GFP via the promoter, GFP expression in undamaged epidermis was confined to growing hair follicles. GFP was also expressed in intestinal crypts. GFP expression was upregulated in epidermis following wounding or phorbol ester treatment. In each situation GFP expression correlated with high endogenous topoisomerase II alpha expression and high proliferation. The mice therefore provide a useful model for non-invasive imaging of regions of high proliferation in normal or damaged epidermis.

Quantitative analysis of topoisomerase IIα to rapidly evaluate cell proliferation in brain tumors

Immunohistochemical cell proliferation analyses have come into wide use for evaluation of tumor malignancy. Topoisomerase IIalpha (topo IIalpha), an essential nuclear enzyme, has been known to have cell cycle coupled expression. We here show the usefulness of quantitative analysis of topo IIalpha mRNA to rapidly evaluate cell proliferation in brain tumors. A protocol to quantify topo IIalpha mRNA was developed with a real-time RT-PCR. It took only 3 h to quantify from a specimen. A total of 28 brain tumors were analyzed, and the level of topo IIalpha mRNA was significantly correlated with its immuno-staining index (p<0.0001, r=0.9077). Furthermore, it sharply detected that topo IIalpha mRNA decreased in growth-inhibited glioma cell. These results support that topo IIalpha mRNA may be a good and rapid indicator to evaluate cell proliferate potential in brain tumors.

CD26/dipeptidyl peptidase IV enhances expression of topoisomerase II alpha and sensitivity to apoptosis induced by topoisomerase II inhibitors

CD26/dipeptidyl peptidase IV (DPPIV) is a cell surface-bound ectopeptidase with important roles in T-cell activation and tumour biology. We now report that CD26/DPPIV enhances sensitivity to apoptosis induced by the antineoplastic agents doxorubicin and etoposide. In particular, CD26/DPPIV presence is associated with increased susceptibility to the mitochondrial pathway of apoptosis, documented by enhanced cleavage of poly (ADP ribose) polymerase (PARP), caspase-3 and caspase-9, Bcl-xl, and Apaf-1, as well as increased expression of death receptor 5 (DR5). We also show that the caspase-9-specific inhibitor z-LEHD-fmk inhibits drug-mediated apoptosis, leading to decreased PARP and caspase-3 cleavage, and reduced DR5 expression. Importantly, through detailed studies that demonstrate the association between topoisomerase II alpha expression and DPPIV activity, our data provide further evidence of the key role played by CD26 in biological processes.

Expression of cyclins A, E and topoisomerase II alpha correlates with centrosome amplification and genomic instability and influences the reliability of cytometric S-phase determination

BACKGROUND

The progression of normal cells through the cell cycle is meticulously regulated by checkpoints guaranteeing the exact replication of the genome during S-phase and its equal division at mitosis. A prerequisite for this achievement is synchronized DNA-replication and centrosome duplication. In this context the expression of cyclins A and E has been shown to play a principal role.

RESULTS

Our results demonstrated a correlation between centrosome amplification, cell cycle fidelity and the level of mRNA and protein expression of cyclins A and E during the part of the cell cycle defined as G1-phase by means of DNA content based histogram analysis. It is shown that the normal diploid breast cell line HTB-125, the genomically relatively stable aneuploid breast cancer cell line MCF-7, and the genomically unstable aneuploid breast cancer cell line MDA-231 differ remarkably concerning both mRNA and protein expression of the two cyclins during G1-phase. In MDA-231 cells the expression of e.g. cyclin A mRNA was found to be ten times higher than in MCF-7 cells and about 500 times higher than in HTB-125 cells. Topoisomerase II alpha showed high mRNA expression in MDA compared to MCF-7 cells, but the difference in protein expression was small. Furthermore, we measured centrosome aberrations in 8.4% of the MDA-231 cells, and in only 1.3% of the more stable aneuploid cell line MCF-7. MDA cells showed 27% more incorporation of BrdU than reflected by S-phase determination with flow cytometric DNA content analysis, whereas these values were found to be of the same size in both HTB-125 and MCF-7 cells.

CONCLUSIONS

Our data indicate that the breast cancer cell lines MCF-7 and MDA-231, although both DNA-aneuploid, differ significantly regarding the degree of cell cycle disturbance and centrosome aberrations, which partly could explain the different genomic stability of the two cell lines. The results also question the reliability of cytometric DNA content based S-phase determination in genomically unstable tumor cell populations.

DR1-like element in human topoisomerase IIalpha gene involved in enhancement of etoposide-induced apoptosis by PPARgamma ligand

OBJECTIVE

The nuclear peroxisome proliferator-activated receptor gamma (PPARgamma) ligands may enhance the etoposide-induced apoptosis by modulating the topoisomerase (Topo) IIalpha expression through binding to direct repeat 1 (DR1)-like element.

METHODS

To investigate the effect of etoposide-induced apoptosis by PPARgamma ligands, leukemia cell lines were treated with troglitazone and 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) in the presence of etoposide and studied about various biological responses.

RESULTS

We found the enhancement of etoposide-induced apoptosis by PPARgamma ligands in several leukemia cell lines, which was dependent on the expression of PPARgamma and specific for TopoIIalpha inhibitor. We also observed the increased expression of TopoIIalpha protein by 15d-PGJ2 in Jurkat and HUVEC cells, which might lead to the increased sensitivity to etoposide. Furthermore, we demonstrated that 15d-PGJ2 enhanced the promoter activity of human TopoIIalpha promoter construct with a DR1-like site by sevenfold when expressed with PPARgamma and RXRalpha. The mutation of DR1-like site decreased the promoter activity, although the direct binding between DR1-like site and PPARgamma/RXRalpha heterodimer was not demonstrated.

CONCLUSIONS

We conclude that the induction of TopoIIalpha expression by PPARgamma ligands via DR1-like site is an important mechanism for the enhancement of etoposide-induced apoptosis and a DR1-like site in TopoIIalpha promoter is involved in transcriptional regulation dependent on PPARgamma ligands and PPARgamma/RXRalpha heterodimer.

Modification of topoisomerase genes copy number in newly diagnosed childhood acute lymphoblastic leukemia

Topoisomerase genes were analyzed at both DNA and RNA levels in 25 cases of newly diagnosed childhood acute lymphoblastic leukemia (ALL). The results of molecular analysis were compared to risk group classification of children in order to identify molecular characteristics associated with response to therapy. At diagnosis, allelic imbalance at topo-isomerase IIalpha (TOP2A) gene locus was found in 75% of informative cases whereas topoisomerase I and IIbeta gene loci are altered in none or only one case, respectively. By semi-quantitative Polymerase chain reaction, we found a 2.5 to 8-fold TOP2A gene amplification in 72% of the children, which was correlated to gene overexpression in every case. These results show that TOP2A gene amplification is a frequent event in ALL at diagnosis. Interestingly, we also identified a small population of children that do not present TOP2A gene amplification or gene overexpression and who are significantly associated with very high risk classified patients showing glucocorticoid resistance. In conclusion, characterization of TOP2A gene status in childhood ALL at diagnosis provides useful complementary information for risk assessment.

Use of positron emission tomography in pharmacokinetic studies to investigate therapeutic advantage in a phase I study of 120-hour intravenous infusion XR5000

PURPOSE

XR5000 (N-[2-(dimethylamino)ethyl]acridine-4-carboxamide) is a topoisomerase I and II inhibitor. Because the cytotoxicity of XR5000 increases markedly with prolonged exposure, we performed a phase I study of weekly XR5000 by 120-hour continuous infusion over 3 weeks.

PATIENTS AND METHODS

Twenty-four patients with advanced solid cancer were treated at seven dose levels (700 to 4,060 mg/m2/120 hrs) for a total of 67 cycles. Three patients underwent positron emission tomography (PET) studies at the maximum-tolerated dose (MTD) to evaluate normal tissue and tumor carbon-11 radiolabeled XR5000 ([11C]XR5000) pharmacokinetics.

RESULTS

The dose-limiting toxicity was National Cancer Institute Common Toxicity Criteria (version 1) grade 4 chest and abdominal pain affecting the single patient receiving 4,060 mg/m2/120 hours, and the MTD was 3,010 mg/m2/120 hours. Other grade 3-4 toxicities, affecting single patients at the MTD, were myelosuppression (grade 4), raised bilirubin, vomiting, and somnolence (all grade 3). There was one partial response (adenocarcinoma of unknown primary); the remainder had progressive disease. [11C]XR5000 distributed well into the three tumors studied by PET. Tumor uptake (maximum concentration or area under the concentration versus time curve [AUC]) was less than in normal tissue in which the tumors were located. Tumor exposure (AUC; mean +/- SD in m2/mL/sec) increased when [(11)C]XR5000 was administered during an infusion of XR5000 (0.242 +/- 0.4), compared with [11C]XR5000 given alone (0.209 +/- 0.04; P <.05), indicating that tumor drug exposure was not saturated [corrected].

CONCLUSION

The recommended dose for XR5000 in phase II studies is 3,010 mg/m2/120 hours. PET studies with 11C-labeled drug were feasible and demonstrated in vivo distribution into tumors. Saturation of tumor exposure was not reached at the MTD.

Identification of genes periodically expressed in the human cell cycle and their expression in tumors

The genome-wide program of gene expression during the cell division cycle in a human cancer cell line (HeLa) was characterized using cDNA microarrays. Transcripts of >850 genes showed periodic variation during the cell cycle. Hierarchical clustering of the expression patterns revealed coexpressed groups of previously well-characterized genes involved in essential cell cycle processes such as DNA replication, chromosome segregation, and cell adhesion along with genes of uncharacterized function. Most of the genes whose expression had previously been reported to correlate with the proliferative state of tumors were found herein also to be periodically expressed during the HeLa cell cycle. However, some of the genes periodically expressed in the HeLa cell cycle do not have a consistent correlation with tumor proliferation. Cell cycle-regulated transcripts of genes involved in fundamental processes such as DNA replication and chromosome segregation seem to be more highly expressed in proliferative tumors simply because they contain more cycling cells. The data in this report provide a comprehensive catalog of cell cycle regulated genes that can serve as a starting point for functional discovery. The full dataset is available at http://genome-www.stanford.edu/Human-CellCycle/HeLa/.

ATF is important to late S phase-dependent regulation of DNA topoisomerase IIalpha gene expression in HeLa cells

DNA topoisomerase IIalpha (Topo IIalpha) is regulated in late S phase-dependent manner. To identify late S phase-dependent cis-acting elements of Topo IIalpha gene, we have investigated the synchronized HeLa cells with chloramphenicol acetyltransferase and DNase I footprinting assays. The level of Topo IIalpha mRNA increased after release from aphidicolin block and reached a maximum in 8h (late S phase) in HeLa cells, and Topo II unknotting activity was also in parallel with the level of Topo IIalpha mRNA. The late S phase-regulatory element was found to be located in the region containing ATF-binding element between -290 and -90bp and the region was required for a maximal stimulation during late S phase. DNase I footprinting assay showed that ATF-binding element and novel cis-acting element (Topo IIalpha-specific sequence) were the principal protein-binding sites and the proteins interacting with these elements were induced during late S phase. One DNA-protein complex was formed by DNA mobility shift assay when ATF-binding site was incubated with nuclear extract prepared from late S phase cells, but no protein bound in non-S phase cells. Taken together, these results suggest that ATF may be essential transacting factor for maximal expression of Topo IIalpha gene during late S phase in HeLa cells.