Cisplatin inhibits synthesis of ribosomal RNA in vivo

Analysis of Giardia lamblia Nucleolus as Drug Target: A Review

Giardia lamblia (G. lamblia) is the main causative agent of diarrhea worldwide, affecting children and adults alike; in the former, it can be lethal, and in the latter a strong cause of morbidity. Despite being considered a predominant disease in low-income and developing countries, current migratory flows have caused an increase in giardiasis cases in high-income countries. Currently, there is a wide variety of chemotherapeutic treatments to combat this parasitosis, most of which have potentially serious side effects, such as genotoxic, carcinogenic, and teratogenic. The necessity to create novel treatments and discover new therapeutic targets to fight against this illness is evident. The current review centers around the controversial nucleolus of G. lamblia, providing a historical perspective that traces its apparent absence to the present evidence supporting its existence as a subnuclear compartment in this organism. Additionally, possible examples of ncRNAs and proteins ubiquitous to the nucleolus that can be used as targets of different therapeutic strategies are discussed. Finally, some examples of drugs under research that could be effective against G. lamblia are described.

Stress-responsive Gdf15 counteracts renointestinal toxicity via autophagic and microbiota reprogramming

The integrated stress response (ISR) plays a pivotal role in the cellular stress response, primarily through global translational arrest and the upregulation of cellular adaptation-linked molecules. Growth differentiation factor 15 (Gdf15) is a potent stress-responsive biomarker of clinical inflammatory and metabolic distress in various types of diseases. Herein, we assess whether ISR-driven cellular stress contributes to pathophysiological outcomes by modulating Gdf15. Clinical transcriptome analysis demonstrates that PKR is positively associated with Gdf15 expression in patients with renal injury. Gdf15 expression is dependent on protein kinase R (PKR)-linked ISR during acute renointestinal distress in mice and genetic ablation of Gdf15 aggravates chemical-induced lesions in renal tissues and the gut barrier. An in-depth evaluation of the gut microbiota indicates that Gdf15 is associated with the abundance of mucin metabolism-linked bacteria and their enzymes. Moreover, stress-responsive Gdf15 facilitates mucin production and cellular survival via the reorganization of the autophagy regulatory network. Collectively, ISR-activated Gdf15 counteracts pathological processes via the protective reprogramming of the autophagic network and microbial community, thereby providing robust predictive biomarkers and interventions against renointestinal distress.

Paiteling induces apoptosis of cervical cancer cells by down-regulation of the E6/E7-Pi3k/Akt pathway: A network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Human papillomavirus (HPV) infection is considered to be the main pathogen causing intraepithelial neoplasia. Paiteling (PTL) has been used to treat intraepithelial neoplasia caused by human papillomavirus (HPV) infection for more than 20 years in China, but its specific mechanism of action is not very clear, and further research is still needed.

OBJECTIVE

This study designed a comprehensive strategy to study the pharmacological mechanism of paiteling in regulating cervical cancer cell apoptosis by integrating LC-MS/MS, network pharmacology and pharmacological experiments.

METHODS

We used liquid chromatography-tandem mass spectrometry to detect the active substances in PTL and performed protein-protein interaction analysis on the intersection of the targets of these key compounds and the targets of intraepithelial neoplasia. Additionally, by using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes (KEGG), the potential pathway of PTL against HPV-induced intraepithelial neoplasia was predicted. Finally, we used HeLa and Ect1/E6E7 cells for experimental verification.

RESULTS

The protein-protein interaction network predicted that AKT1, TP53, MYC, STAT3, MTOR, and MAPK were pivotal targets for PTL to inhibit epithelial neoplasia. KEGG enrichment analysis showed that the Pi3k/Akt pathway and HPV infection had scientific significance. Compared to the control group, after PTL diluent stimulated HeLa and Ect1/E6E7 cells for 24 h, cell viability, migration, and invasion capabilities were significantly reduced, and cell apoptosis was significantly increased, conforming to a dose-effect relationship and time-effect relationship. PCR, cellular immunohistochemistry, and western blot experiments showed that PTL reduced the expression of E6, Pi3k, E7, Akt, Bcl-xl, while increasing the expression of Bad in HeLa and Ect1/E6E7 cells.

CONCLUSION

PTL can induce cervical cancer cell apoptosis by inhibiting the E6/E7-Pi3k/Akt signaling pathway. It may provide an effective alternative strategy of traditional Chinese medicine for the treatment of epithelial neoplasia caused by HPV infection.

Targeting PEA3 transcription factors to mitigate small cell lung cancer progression

Small cell lung cancer (SCLC) remains a lethal disease with a dismal overall survival rate of 6% despite promising responses to upfront combination chemotherapy. The key drivers of such rapid mortality include early metastatic dissemination in the natural course of the disease and the near guaranteed emergence of chemoresistant disease. Here, we found that we could model the regression and relapse seen in clinical SCLC in vitro. We utilized time-course resolved RNA-sequencing to globally profile transcriptome changes as SCLC cells responded to a combination of cisplatin and etoposide-the standard-of-care in SCLC. Comparisons across time points demonstrated a distinct transient transcriptional state resembling embryonic diapause. Differential gene expression analysis revealed that expression of the PEA3 transcription factors ETV4 and ETV5 were transiently upregulated in the surviving fraction of cells which we determined to be necessary for efficient clonogenic expansion following chemotherapy. The FGFR-PEA3 signaling axis guided the identification of a pan-FGFR inhibitor demonstrating in vitro and in vivo efficacy in delaying progression following combination chemotherapy, observed inhibition of phosphorylation of the FGFR adaptor FRS2 and corresponding downstream MAPK and PI3K-Akt signaling pathways. Taken together, these data nominate PEA3 transcription factors as key mediators of relapse progression in SCLC and identify a clinically actionable small molecule candidate for delaying relapse of SCLC.

Targeting Ribosome Biogenesis in Cancer: Lessons Learned and Way Forward

Simple Summary

Cells need to produce ribosomes to sustain continuous proliferation and expand in numbers, a feature that is even more prominent in uncontrollably proliferating cancer cells. Certain cancer cell types are expected to depend more on ribosome biogenesis based on their genetic background, and this potential vulnerability can be exploited in designing effective, targeted cancer therapies. This review provides information on anti-cancer molecules that target the ribosome biogenesis machinery and indicates avenues for future research.

Abstract

Rapid growth and unrestrained proliferation is a hallmark of many cancers. To accomplish this, cancer cells re-wire and increase their biosynthetic and metabolic activities, including ribosome biogenesis (RiBi), a complex, highly energy-consuming process. Several chemotherapeutic agents used in the clinic impair this process by interfering with the transcription of ribosomal RNA (rRNA) in the nucleolus through the blockade of RNA polymerase I or by limiting the nucleotide building blocks of RNA, thereby ultimately preventing the synthesis of new ribosomes. Perturbations in RiBi activate nucleolar stress response pathways, including those controlled by p53. While compounds such as actinomycin D and oxaliplatin effectively disrupt RiBi, there is an ongoing effort to improve the specificity further and find new potent RiBi-targeting compounds with improved pharmacological characteristics. A few recently identified inhibitors have also become popular as research tools, facilitating our advances in understanding RiBi. Here we provide a comprehensive overview of the various compounds targeting RiBi, their mechanism of action, and potential use in cancer therapy. We discuss screening strategies, drug repurposing, and common problems with compound specificity and mechanisms of action. Finally, emerging paths to discovery and avenues for the development of potential biomarkers predictive of therapeutic outcomes across cancer subtypes are also presented.

Ribosomal proteins and human diseases: molecular mechanisms and targeted therapy

Ribosome biogenesis and protein synthesis are fundamental rate-limiting steps for cell growth and proliferation. The ribosomal proteins (RPs), comprising the structural parts of the ribosome, are essential for ribosome assembly and function. In addition to their canonical ribosomal functions, multiple RPs have extra-ribosomal functions including activation of p53-dependent or p53-independent pathways in response to stress, resulting in cell cycle arrest and apoptosis. Defects in ribosome biogenesis, translation, and the functions of individual RPs, including mutations in RPs have been linked to a diverse range of human congenital disorders termed ribosomopathies. Ribosomopathies are characterized by tissue-specific phenotypic abnormalities and higher cancer risk later in life. Recent discoveries of somatic mutations in RPs in multiple tumor types reinforce the connections between ribosomal defects and cancer. In this article, we review the most recent advances in understanding the molecular consequences of RP mutations and ribosomal defects in ribosomopathies and cancer. We particularly discuss the molecular basis of the transition from hypo- to hyper-proliferation in ribosomopathies with elevated cancer risk, a paradox termed "Dameshek's riddle." Furthermore, we review the current treatments for ribosomopathies and prospective therapies targeting ribosomal defects. We also highlight recent advances in ribosome stress-based cancer therapeutics. Importantly, insights into the mechanisms of resistance to therapies targeting ribosome biogenesis bring new perspectives into the molecular basis of cancer susceptibility in ribosomopathies and new clinical implications for cancer therapy.

Early nucleolar responses differentiate mechanisms of cell death induced by oxaliplatin and cisplatin

Recent reports provide evidence that the platinum chemotherapeutic oxaliplatin causes cell death via ribosome biogenesis stress, while cisplatin causes cell death via the DNA damage response (DDR). Underlying differences in mechanisms that might initiate disparate routes to cell death by these two broadly used platinum compounds have not yet been carefully explored. Additionally, prior studies had demonstrated that cisplatin can also inhibit ribosome biogenesis. Therefore, we sought to directly compare the initial influences of oxaliplatin and cisplatin on nucleolar processes and on the DDR. Using pulse-chase experiments, we found that at equivalent doses, oxaliplatin but not cisplatin significantly inhibited ribosomal RNA (rRNA) synthesis by Pol I, but neither compound affected rRNA processing. Inhibition of rRNA synthesis occurred as early as 90 min after oxaliplatin treatment in A549 cells, concurrent with the initial redistribution of the nucleolar protein nucleophosmin (NPM1). We observed that the nucleolar protein fibrillarin began to redistribute by 6 h after oxaliplatin treatment and formed canonical nucleolar caps by 24 h. In cisplatin-treated cells, DNA damage, as measured by γH2AX immunofluorescence, was more extensive, whereas nucleolar organization was unaffected. Taken together, our results demonstrate that oxaliplatin causes early nucleolar disruption via inhibition of rRNA synthesis accompanied by NPM1 relocalization and subsequently causes extensive nucleolar reorganization, while cisplatin causes early DNA damage without significant nucleolar disruption. These data support a model in which, at clinically relevant doses, cisplatin kills cells via the canonical DDR, and oxaliplatin kills cells via ribosome biogenesis stress, specifically via rapid inhibition of rRNA synthesis.

Ribosomal RNA Transcription Regulation in Breast Cancer

Ribosome biogenesis is a complex process that is responsible for the formation of ribosomes and ultimately global protein synthesis. The first step in this process is the synthesis of the ribosomal RNA in the nucleolus, transcribed by RNA Polymerase I. Historically, abnormal nucleolar structure is indicative of poor cancer prognoses. In recent years, it has been shown that ribosome biogenesis, and rDNA transcription in particular, is dysregulated in cancer cells. Coupled with advancements in screening technology that allowed for the discovery of novel drugs targeting RNA Polymerase I, this transcriptional machinery is an increasingly viable target for cancer therapies. In this review, we discuss ribosome biogenesis in breast cancer and the different cellular pathways involved. Moreover, we discuss current therapeutics that have been found to affect rDNA transcription and more novel drugs that target rDNA transcription machinery as a promising avenue for breast cancer treatment.

Unexpected therapeutic effects of cisplatin

Cisplatin is a widely used chemotherapeutic agent that is clinically approved to fight both carcinomas and sarcomas. It has relatively high efficiency in treating ovarian cancers and metastatic testicular cancers. It is generally accepted that the major mechanism of cisplatin anti-cancer action is DNA damage. However, cisplatin is also effective in metastatic cancers and should, therefore, affect slow-cycling cancer stem cells in some way. In this review, we focused on the alternative effects of cisplatin that can support a good therapeutic response. First, attention was paid to the effects of cisplatin at the cellular level such as changes in intracellular pH and cellular mechanical properties. Alternative cellular targets of cisplatin, and the effects of cisplatin on cancer cell metabolism and ER stress were also discussed. Furthermore, the impacts of cisplatin on the tumor microenvironment and in the whole organism context were reviewed. In this review, we try to reveal possible causes of the unexpected effectiveness of this anti-cancer drug.

Accumulation of Nucleolar Inorganic Polyphosphate Is a Cellular Response to Cisplatin-Induced Apoptosis

The chemotherapeutic drug cisplatin, which targets DNA, serves as one of the main staples in cancer treatment. Yet, the therapeutic application of cisplatin is limited by two major challenges: the occurrence of reversible and irreversible side effects due to non-specific toxicity, and the intrinsic or developing resistance of tumor cells toward cisplatin. Here we demonstrate that cancer cells respond to cisplatin treatment with the nucleolar accumulation of inorganic polyphosphate (polyP), a universally conserved high-energy compound. PolyP accumulation positively correlates with the levels of activated caspase-3, suggesting a novel role of polyP in cisplatin-mediated apoptosis. In support of this finding, we discovered that administration of exogenous polyP increases cisplatin-induced toxicity in select cancer cell lines, raising the exciting possibility that enhancing endogenous polyP levels might be a novel mechanism to sensitize cancer cells to cisplatin treatment.

The nucleolus: a central response hub for the stressors that drive cancer progression

The nucleolus is a sub-nuclear body known primarily for its role in ribosome biogenesis. Increased number and/or size of nucleoli have historically been used by pathologists as a prognostic indicator of cancerous lesions. This increase in nucleolar number and/or size is classically attributed to the increased need for protein synthesis in cancer cells. However, evidences suggest that the nucleolus plays critical roles in many cellular functions in both normal cell biology and disease pathologies, including cancer. As new functions of the nucleolus are elucidated, there is mounting evidence to support the role of the nucleolus in regulating additional cellular functions, particularly response to cellular stressors, maintenance of genome stability, and DNA damage repair, as well as the regulation of gene expression and biogenesis of several ribonucleoproteins. This review highlights the central role of the nucleolus in carcinogenesis and cancer progression and discusses how cancer cells may become "addicted" to nucleolar functions.

APE1 and NPM1 protect cancer cells from platinum compounds cytotoxicity and their expression pattern has a prognostic value in TNBC

Background

Triple negative breast cancer (TNBC) is a breast cancer subgroup characterized by a lack of hormone receptors’ expression and no HER2 overexpression. These molecular features both drastically reduce treatment options and confer poor prognosis. Platinum (Pt)-salts are being investigated as a new therapeutic strategy. The base excision repair (BER) pathway is important for resistance to Pt-based therapies. Overexpression of APE1, a pivotal enzyme of the BER pathway, as well as the expression of NPM1, a functional regulator of APE1, are associated with poor outcome and resistance to Pt-based therapies.

Methods

We evaluated the role of NPM1, APE1 and altered NPM1/APE1 interaction in the response to Pt-salts treatment in different cell lines: APE1 knockout (KO) cells, NPM1 KO cells, cell line models having an altered APE1/NPM1 interaction and HCC70 and HCC1937 TNBC cell lines, having different levels of APE1/NPM1. We evaluated the TNBC cells response to new chemotherapeutic small molecules targeting the endonuclease activity of APE1 or the APE1/NPM1 interaction, in combination with Pt-salts treatments. Expression levels’ correlation between APE1 and NPM1 and their impact on prognosis was analyzed in a cohort of TNBC patients through immunohistochemistry. Bioinformatics analysis, using TCGA datasets, was performed to predict a molecular signature of cancers based on APE1 and NPM1 expression.

Results

APE1 and NPM1, and their interaction as well, protect from the cytotoxicity induced by Pt-salts treatment. HCC1937 cells, having higher levels of APE1/NPM1 proteins, are more resistant to Pt-salts treatment compared to the HCC70 cells. A sensitization effect by APE1 inhibitors to Pt-compounds was observed. The association of NPM1/APE1 with cancer gene signatures highlighted alterations concerning cell-cycle dependent proteins.

Conclusions

APE1 and NPM1 protect cancer cells from Pt-compounds cytotoxicity, suggesting a possible improvement of the activity of Pt-based therapy for TNBC, using the NPM1 and APE1 proteins as secondary therapeutic targets. Based on positive or negative correlation with APE1 and NPM1 gene expression levels, we finally propose several TNBC gene signatures that should deserve further attention for their potential impact on TNBC precision medicine approaches.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1294-9) contains supplementary material, which is available to authorized users.

Targeting RNA polymerase I transcription machinery in cancer cells by a novel monofunctional platinum-based agent

Aberrant ribosome biogenesis and enlarged nucleoli have long been used by pathologists as a marker of aggressive tumors. Suppression of RNA polymerase I (Pol I) transcription machinery within the nucleolus could be a direct way to trigger the nucleolar stress and to inhibit the rapid proliferation of cancer cells. Here we modified cisplatin with an analogue of the selective inhibitor of RNA polymerase I-mediated transcription BMH-21 to develop a novel platinum-based Pol I selective inhibitor. We show that this novel monofunctional platinum-based agent, P1-B1, had enhanced antitumor activity of up to 17-fold greater than the clinical drug cisplatin in cisplatin-resistant non-small cell lung cancer cells. P1-B1 also had significantly lower cytotoxicity compared to cisplatin as well as the Pol I selective inhibitor BMH-21 in MRC-5 normal lung fibroblast cells, and the selectivity index (SI) greatly increases. Mechanistic investigations revealed that P1-B1 displayed significant nucleolar accumulation, selectively inhibited Pol I transcription, and induced nucleolar stress, leading to S-phase arrest and apoptosis. Our results suggest that the effects of P1-B1 are mechanistically distinct from those of conventional platinum agents and the recently described non-classical platinum compounds and that functionalizing platinum-based agents with directly Pol I transcription inhibition properties may represent an improved modality for cancer treatment.

Monitoring Subcellular Stress Response via a Cell-permeant Rotor Dye

Monitoring the response of cells to environmental challenges, e.g. after exposure to oxidative stress or pharmaceutical substances, not only provides clues for fundamental biological processes but can also serve as a valuable tool in drug development. Obtaining such insights on the subcellular level in a rapid and simple manner is therefore of major importance. Ideally, such an approach not only reports on compartment-specific responses but also allows for an inherent subcellular segmentation using the same data set. Here, we propose such a method based on fluorescence lifetimes of a single cell-permeant rotor dye with a broad emission spectrum. Using a k-means clustering approach, a straightforward, unsupervised, and rapid segmentation protocol allows for subcellular segmentation in addition to monitoring the differential response of these compartments to environmental stress, e.g. induced by hydrogen peroxide or the widely used chemotherapeutic cisplatin. Based on our data we suggest that our automatable approach can be a valuable and robust tool for pharmaceutical screening applications.

A novel triazolonaphthalimide induces apoptosis and inhibits tumor growth by targeting DNA and DNA-associated processes

DNA and DNA-associated processes have been classes of the most important targets of chemotherapeutic drugs. As classic DNA intercalators and topoisomerase inhibitors, naphthalimides have been extensively investigated as potential anti-cancer drugs. We recently synthesized a novel series of triazolonaphthalimides with excellent anti-cancer activities. In the present study, one of the most potent triazolonaphthalimides, LSS-11, was investigated. LSS-11 bound to DNA in vitro and in cell mainly by minor groove binding and significantly increased the stability of DNA, which could be fundamental for the biological activities of LSS-11. In addition to inhibiting DNA topoisomerase II-catalyzed decatenation of knotted circulated DNA, LSS-11 dramatically inhibited DNA replication mediated by polymerase chain reaction and isothermal helicase-dependent amplification, as well as the expression of luciferase driven by a minimal TA promoter in cell. Furthermore, LSS-11 exhibited strong cytotoxicity in selected human colon cancer cell lines by inducing cell cycle arrest and apoptosis, which was accompanied by DNA damage response. Finally, LSS-11 potently inhibited the growth of S180 murine sarcoma and SW480 human colorectal cancer xenografts in vivo without significant major toxicities. These results suggest that LSS-11 deserves further research and development as a novel anti-cancer agent, and provided new understandings of mechanisms by which LSS-11 inhibited multiple DNA-associated processes and tumor growth.

Differences in cisplatin distribution in sensitive and resistant ovarian cancer cells: a TEM/NanoSIMS study

Cisplatin is a widely used anti-cancer drug, but its effect is often limited by acquired resistance to the compound during treatment. Here, we use a combination of transmission electron microscopy (TEM) and nanoscale-secondary ion mass spectrometry (NanoSIMS) to reveal differences between cisplatin uptake in human ovarian cancers cells, which are known to be susceptible to acquired resistance to cisplatin. Both cisplatin sensitive and resistant cell lines were studied, revealing markedly less cisplatin in the resistant cell line. In cisplatin sensitive cells, Pt was seen to distribute diffusely in the cells with hotspots in the nucleolus, mitochondria, and autophagosomes. Inductively coupled plasma mass spectrometry (ICP-MS) was used to validate the NanoSIMS results.

Ixr1 Regulates Ribosomal Gene Transcription and Yeast Response to Cisplatin

Ixr1 is a Saccharomyces cerevisiae HMGB protein that regulates the hypoxic regulon and also controls the expression of other genes involved in the oxidative stress response or re-adaptation of catabolic and anabolic fluxes when oxygen is limiting. Ixr1 also binds with high affinity to cisplatin-DNA adducts and modulates DNA repair. The influence of Ixr1 on transcription in the absence or presence of cisplatin has been analyzed in this work. Ixr1 regulates other transcriptional factors that respond to nutrient availability or extracellular and intracellular stress stimuli, some controlled by the TOR pathway and PKA signaling. Ixr1 controls transcription of ribosomal RNAs and genes encoding ribosomal proteins or involved in ribosome assembly. qPCR, ChIP, and 18S and 25S rRNAs measurement have confirmed this function. Ixr1 binds directly to several promoters of genes related to rRNA transcription and ribosome biogenesis. Cisplatin treatment mimics the effect of IXR1 deletion on rRNA and ribosomal gene transcription, and prevents Ixr1 binding to specific promoters related to these processes.

Common Chemical Inductors of Replication Stress: Focus on Cell-Based Studies

DNA replication is a highly demanding process regarding the energy and material supply and must be precisely regulated, involving multiple cellular feedbacks. The slowing down or stalling of DNA synthesis and/or replication forks is referred to as replication stress (RS). Owing to the complexity and requirements of replication, a plethora of factors may interfere and challenge the genome stability, cell survival or affect the whole organism. This review outlines chemical compounds that are known inducers of RS and commonly used in laboratory research. These compounds act on replication by direct interaction with DNA causing DNA crosslinks and bulky lesions (cisplatin), chemical interference with the metabolism of deoxyribonucleotide triphosphates (hydroxyurea), direct inhibition of the activity of replicative DNA polymerases (aphidicolin) and interference with enzymes dealing with topological DNA stress (camptothecin, etoposide). As a variety of mechanisms can induce RS, the responses of mammalian cells also vary. Here, we review the activity and mechanism of action of these compounds based on recent knowledge, accompanied by examples of induced phenotypes, cellular readouts and commonly used doses.

ARF Confers a Context-Dependent Response to Chemotherapy in Muscle-Invasive Bladder Cancer

Muscle-invasive bladder cancer (MIBC) generally responds poorly to treatment and tends to exhibit significant mortality. Here we show that expression of the tumor suppressor p14ARF (ARF) is upregulated in aggressive subtypes of MIBC. Accumulation of ARF in the nucleolus is associated with poor outcome and attenuated response to chemotherapy. In both genetically engineered mouse models and murine xenograft models of human MIBC, we demonstrate that tumors expressing ARF failed to respond to treatment with the platinum-based chemotherapy agent cisplatin. Resistance was mediated in part by the integrin-binding protein ITGB3BP (CENPR) and reflected ARF-dependent impairment of protein translation, which was exaggerated by drug treatment. Overall, our results highlight a context-dependent role for ARF in modulating the drug response of bladder cancer. Cancer Res; 77(4); 1035-46. ©2017 AACR.

Depletion of the cisplatin targeted HMGB-box factor UBF selectively induces p53-independent apoptotic death in transformed cells

Cisplatin-DNA adducts act as strong decoys for the Upstream Binding Factor UBF (UBTF) and have been shown to inhibit transcription of the ribosomal RNA genes by RNA polymerase I. However, it is unclear if this plays a significant role in the chemotherapeutic activity of cis- or carboplatin. We find that cisplatin in fact induces a very rapid displacement of UBF from the ribosomal RNA genes and strong inhibition of ribosomal RNA synthesis, consistent with this being an important factor in its cytotoxicity. Using conditional gene deletion, we recently showed that UBF is an essential factor for transcription of the ribosomal RNA genes and for ribosome biogenesis. We now show that loss of UBF arrests cell proliferation and induces fully penetrant, rapid and synchronous apoptosis, as well as nuclear disruption and cell death, specifically in cells subjected to oncogenic stress. Apoptosis is not affected by homozygous deletion of the p53 gene and occurs equally in cells transformed by SV40 T antigens, by Myc or by a combination of Ras & Myc oncogenes. The data strongly argue that inhibition of UBF function is a major factor in the cytotoxicity of cisplatin. Hence, drug targeting of UBF may be a preferable approach to the use of the highly toxic platins in cancer therapy.

RNA disruption is associated with response to multiple classes of chemotherapy drugs in tumor cell lines

BACKGROUND

Cellular stressors and apoptosis-inducing agents have been shown to induce ribosomal RNA (rRNA) degradation in eukaryotic cells. Recently, RNA degradation in vivo was observed in patients with locally advanced breast cancer, where mid-treatment tumor RNA degradation was associated with complete tumor destruction and enhanced patient survival. However, it is not clear how widespread chemotherapy induced "RNA disruption" is, the extent to which it is associated with drug response or what the underlying mechanisms are.

METHODS

Ovarian (A2780, CaOV3) and breast (MDA-MB-231, MCF-7, BT474, SKBR3) cancer cell lines were treated with several cytotoxic chemotherapy drugs and total RNA was isolated. RNA was also prepared from docetaxel resistant A2780DXL and carboplatin resistant A2780CBN cells following drug exposure. Disruption of RNA was analyzed by capillary electrophoresis. Northern blotting was performed using probes complementary to the 28S and 18S rRNA to determine the origins of degradation bands. Apoptosis activation was assessed by flow cytometric monitoring of annexin-V and propidium iodide (PI) binding to cells and by measuring caspase-3 activation. The link between apoptosis and RNA degradation (disruption) was investigated using a caspase-3 inhibitor.

RESULTS

All chemotherapy drugs tested were capable of inducing similar RNA disruption patterns. Docetaxel treatment of the resistant A2780DXL cells and carboplatin treatment of the A2780CBN cells did not result in RNA disruption. Northern blotting indicated that two RNA disruption bands were derived from the 3'-end of the 28S rRNA. Annexin-V and PI staining of docetaxel treated cells, along with assessment of caspase-3 activation, showed concurrent initiation of apoptosis and RNA disruption, while inhibition of caspase-3 activity significantly reduced RNA disruption.

CONCLUSIONS

Supporting the in vivo evidence, our results demonstrate that RNA disruption is induced by multiple chemotherapy agents in cell lines from different tissues and is associated with drug response. Although present, the link between apoptosis and RNA disruption is not completely understood. Evaluation of RNA disruption is thus proposed as a novel and effective biomarker to assess response to chemotherapy drugs in vitro and in vivo.

The Nucleolus: Structure and Function

The nucleolus is the largest nuclear organelle and is the primary site of ribosome subunit biogenesis in eukaryotic cells. It is assembled around arrays of ribosomal DNA genes, forming specific chromosomal features known as nucleolar organizing regions (NORs) which are the sites of ribosomal DNA transcription. While the nucleolus main activity involve different steps of ribosome biogenesis, the presence of proteins with no obvious relationship with ribosome subunit production suggests additional functions for the nucleolus, such as regulation of mitosis, cell cycle progression, stress response and biogenesis of multiple ribonucleoprotein complexes. The many novel factors and separate classes of proteins identified within the nucleolus support this view that the nucleolus may perform additional functions beyond its known role in ribosome subunit biogenesis. Here we review our knowledge of the nucleolar functions and will provide a detailed picture of how the nucleolus is involved in many cellular pathways.

Role of platinum DNA damage-induced transcriptional inhibition in chemotherapy-induced neuronal atrophy and peripheral neurotoxicity

Platinum-based anticancer drugs cause peripheral neurotoxicity by damaging sensory neurons within the dorsal root ganglia (DRG), but the mechanisms are incompletely understood. The roles of platinum DNA binding, transcription inhibition and altered cell size were investigated in primary cultures of rat DRG cells. Click chemistry quantitative fluorescence imaging of RNA-incorporated 5-ethynyluridine showed high, but wide ranging, global levels of transcription in individual neurons that correlated with their cell body size. Treatment with platinum drugs reduced neuronal transcription and cell body size to an extent that corresponded to the amount of preceding platinum DNA binding, but without any loss of neuronal cells. The effects of platinum drugs on neuronal transcription and cell body size were inhibited by blocking platinum DNA binding with sodium thiosulfate, and mimicked by treatment with a model transcriptional inhibitor, actinomycin D. In vivo oxaliplatin treatment depleted the total RNA content of DRG tissue concurrently with altering DRG neuronal size. These findings point to a mechanism of chemotherapy-induced peripheral neurotoxicity, whereby platinum DNA damage induces global transcriptional arrest leading in turn to neuronal atrophy. DRG neurons may be particularly vulnerable to this mechanism of toxicity because of their requirements for high basal levels of global transcriptional activity. Findings point to a new stepwise mechanism of chemotherapy-induced peripheral neurotoxicity, whereby platinum DNA damage induces global transcriptional arrest leading in turn to neuronal atrophy. Dorsal root ganglion neurons may be particularly vulnerable to this neurotoxicity because of their high global transcriptional outputs, demonstrated in this study by click chemistry quantitative fluorescence imaging.

Therapeutic interventions to disrupt the protein synthetic machinery in melanoma

Control of the protein synthetic machinery is deregulated in many cancers, including melanoma, to increase the protein production. Tumor suppressors and oncogenes play key roles in protein synthesis from the transcription of rRNA and ribosome biogenesis to mRNA translation initiation and protein synthesis. Major signaling pathways are altered in melanoma to modulate the protein synthetic machinery, thereby promoting tumor development. However, despite the importance of this process in melanoma development, involvement of the protein synthetic machinery in this cancer type is an underdeveloped area of study. Here, we review the coupling of melanoma development to deregulation of the protein synthetic machinery. We examine existing knowledge regarding RNA polymerase I inhibition and mRNA translation focusing on their inhibition for therapeutic applications in melanoma. Furthermore, the contribution of amino acid biosynthesis and involvement of ribosomal proteins are also reviewed as future therapeutic strategies to target deregulated protein production in melanoma.

Ribosomal proteins: functions beyond the ribosome

Although ribosomal proteins are known for playing an essential role in ribosome assembly and protein translation, their ribosome-independent functions have also been greatly appreciated. Over the past decade, more than a dozen of ribosomal proteins have been found to activate the tumor suppressor p53 pathway in response to ribosomal stress. In addition, these ribosomal proteins are involved in various physiological and pathological processes. This review is composed to overview the current understanding of how ribosomal stress provokes the accumulation of ribosome-free ribosomal proteins, as well as the ribosome-independent functions of ribosomal proteins in tumorigenesis, immune signaling, and development. We also propose the potential of applying these pieces of knowledge to the development of ribosomal stress-based cancer therapeutics.

Imaging of nucleolar RNA in living cells using a highly photostable deep-red fluorescent probe

A new crescent-shape fluorescent probe (named here as CP) that selectively stains RNA in nucleoli of living cells is prepared. CP shows a deep-red emission (658 nm) and a large Stokes shift because of the introduction of rigid-conjugated coumarin moiety into the molecular structure. Cell imaging experiments indicate that CP can rapidly stain nucleoli in living cells by binding with nucleolar RNA, showing performance superior to commercially available nucleoli dye SYTO RNASelect in terms of high photostability and selectivity. More significantly, these excellent properties together with low cytotoxicity enable CP to monitor nucleolar RNA changes during mitosis, and after treating with anti-cancer drugs cisplatin, actinomycin D and α-amanitin. Thus, CP could be a potential tool for real-time, long-term visualization of the dynamic changes for nucleolar RNA and evaluation of the therapeutic effect for anti-cancer drugs that targeted RNA polymerase I (Pol I).

The nucleolus as a fundamental regulator of the p53 response and a new target for cancer therapy

BACKGROUND

Recent studies have highlighted the fundamental role that key oncogenes such as MYC, RAS and PI3K occupy in driving RNA Polymerase I transcription in the nucleolus. In addition to maintaining essential levels of protein synthesis, hyperactivated ribosome biogenesis and nucleolar function plays a central role in suppressing p53 activation in response to oncogenic stress. Consequently, disruption of ribosome biogenesis by agents such as the small molecule inhibitor of RNA Polymerase I transcription, CX-5461, has shown unexpected, potent, and selective effects in killing tumour cells via disruption of nucleolar function leading to activation of p53, independent of DNA damage.

SCOPE OF REVIEW

This review will explore the mechanism of DNA damage-independent activation of p53 via the nucleolar surveillance pathway and how this can be utilised to design novel cancer therapies.

MAJOR CONCLUSION AND GENERAL SIGNIFICANCE

Non-genotoxic targeting of nucleolar function may provide a new paradigm for treatment of a broad range of oncogene-driven malignancies with improved therapeutic windows. This article is part of a Special Issue entitled: Translation and Cancer.

Platinum-RNA modifications following drug treatment in S. cerevisiae identified by click chemistry and enzymatic mapping

With the importance of RNA-based regulatory pathways, the potential for targeting noncoding and coding RNAs by small molecule therapeutics is of great interest. Platinum(II) complexes including cisplatin (cis-diamminedichloroplatinum(II)) are widely prescribed anticancer compounds that form stable adducts on nucleic acids. In tumors, DNA damage from Pt(II) initiates apoptotic signaling, but this activity is not necessary for cytotoxicity (e.g., Yu et al., 2008), suggesting accumulation and consequences of Pt(II) lesions on non-DNA targets. We previously reported an azide-functionalized compound, picazoplatin, designed for post-treatment click labeling that enables detection of Pt complexes (White et al., 2013). Here, we report in-gel fluorescent detection of Pt-bound rRNA and tRNA extracted from picazoplatin-treated S. cerevisiae and labeled using Cu-free click chemistry. These data provide the first evidence that cellular tRNA is a platinum drug substrate. We assess Pt(II) binding sites within rRNA from cisplatin-treated S. cerevisiae, in regions where damage is linked to significant downstream consequences including the sarcin-ricin loop (SRL) Helix 95. Pt-RNA adducts occur on the nucleotide substrates of ribosome-inactivating proteins, as well as on the bulged-G motif critical for elongation factor recognition of the loop. At therapeutically relevant concentrations, Pt(II) also binds robustly within conserved cation-binding pockets in Domains V and VI rRNA at the peptidyl transferase center. Taken together, these results demonstrate a convenient click chemistry methodology that can be applied to identify other metal or covalent modification-based drug targets and suggest a ribotoxic mechanism for cisplatin cytotoxicity.

Turning a new page on nucleostemin and self-renewal

A quintessential trait of stem cells is embedded in their ability to self-renew without incurring DNA damage as a result of genome replication. One key self-renewal factor is the nucleolar GTP-binding protein nucleostemin (also known as guanine-nucleotide-binding protein-like 3, GNL3, in invertebrate species). Several studies have recently pointed to an unexpected role of nucleostemin in safeguarding the genome integrity of stem and cancer cells. Since its discovery, the predominant presence of nucleostemin in the nucleolus has led to the notion that it might function in the card-carrying event of the nucleolus--the biogenesis of ribosomes. As tantalizing as this might be, a ribosomal role of nucleostemin is refuted by evidence from recent studies, which argues that nucleostemin depletion triggers a primary event of DNA damage in S phase cells that then leads to ribosomal perturbation. Furthermore, there have been conflicting reports regarding the p53 dependency of nucleostemin activity and the cell cycle arrest profile of nucleostemin-depleted cells. In this Commentary, I propose a model that explains how the many contradictory observations surrounding nucleostemin can be reconciled and suggest that this protein might not be as multi-tasking as has been previously perceived. The story of nucleostemin highlights the complexity of the underlying molecular events associated with the appearance of any cell biological phenotype and also signifies a new understanding of the genome maintenance program in stem cells.

Mechanistic studies on the anticancer activity of 2,4-disubstituted quinazoline derivative

BACKGROUND

Accelerated proliferation of solid tumor and hematologic cancer cells is related to accelerated transcription of ribosomal DNA by the RNA polymerase I to produce elevated level of ribosomal RNA. Therefore, down-regulation of RNA polymerase I transcription in cancer cells is an important anticancer therapeutic strategy.

METHODS

A variety of methods were used, including cloning, expression and purification of protein, electrophoretic mobility shift assay (EMSA), circular dichroic (CD) spectroscopy, CD-melting, isothermal titration calorimetry (ITC), chromatin immunoprecipitation (Ch-IP), RNA interference, RT-PCR, Western blot, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell assay.

RESULTS

Our results showed that 2,4-disubstituted quinazoline derivative Sysu12d could down-regulate c-myc through stabilization of c-myc promoter G-quadruplex, resulting in down-regulation of nucleolin expression. Sysu12d could also disrupt nucleolin/G-quadruplex complex. Both of the above contributed to the down-regulation of ribosomal RNA synthesis, followed by activation of p53 and then cancer cell apoptosis.

CONCLUSIONS

These mechanistic studies set up the basis for further development of Sysu12d as a new type of lead compound for cancer treatment.

GENERAL SIGNIFICANCE

2,4-Disubstituted quinazoline derivatives may have multi-functional effect for cancer treatment.

Functional ribosome biogenesis is a prerequisite for p53 destabilization: impact of chemotherapy on nucleolar functions and RNA metabolism

The production and processing of ribosomal RNA is a complex and well-coordinated nucleolar process for ribosome biogenesis. Progress in understanding nucleolar structure and function has lead to the unexpected discovery of the nucleolus as a highly sensitive sensor of cellular stress and an important regulator of the tumor suppressor p53. Inhibition of ribosomal RNA metabolism has been shown to activate a signaling pathway for p53 induction. This review elucidates the potential of classical and recently developed chemotherapeutic drugs to stabilize p53 by inhibiting nucleolar functions.

Connecting the nucleolus to the cell cycle and human disease

Long known as the center of ribosome synthesis, the nucleolus is connected to cell cycle regulation in more subtle ways. One is a surveillance system that reacts promptly when rRNA synthesis or processing is impaired, halting cell cycle progression. Conversely, the nucleolus also acts as a first-responder to growth-related stress signals. Here we review emerging concepts on how these "infraribosomal" links between the nucleolus and cell cycle progression operate in both forward and reverse gears. We offer perspectives on how new cancer therapeutic designs that target this infraribosomal mode of cell growth control may shape future clinical progress.

Sky1 regulates the expression of sulfur metabolism genes in response to cisplatin

Cisplatin is commonly used in cancer therapy and yeast cells are also sensitive to this compound. We present a transcriptome analysis discriminating between RNA changes induced by cisplatin treatment, which are dependent on or independent of SKY1 function – a gene whose deletion increases resistance to the drug. Gene expression changes produced by addition of cisplatin to W303 and W303-Δsky1 cells were recorded using DNA microarrays. The data, validated by quantitative PCR, revealed 122 differentially expressed genes: 69 upregulated and 53 downregulated. Among the upregulated genes, those related to sulfur metabolism were over-represented and partially dependent on Sky1. Deletions of MET4 or other genes encoding co-regulators of the expression of sulfur-metabolism-related genes, with the exception of MET28, did not modify the cisplatin sensitivity of yeast cells. One of the genes with the highest cisplatin-induced upregulation was SEO1, encoding a putative permease of sulfur compounds. We also measured the platinum, sulfur and glutathione content in W303, W303-Δsky1 and W303-Δseo1 cells after cisplatin treatment, and integration of the data suggested that these transcriptional changes might represent a cellular response that allowed chelation of cisplatin with sulfur-containing amino acids and also helped DNA repair by stimulating purine biosynthesis. The transcription pattern of stimulation of sulfur-containing amino acids and purine synthesis decreased, or even disappeared, in the W303-Δsky1 strain.

Effects of four chemotherapeutic agents, bleomycin, etoposide, cisplatin, and cyclophosphamide, on DNA damage and telomeres in a mouse spermatogonial cell line

Treatment with chemotherapeutics agents may induce persistent DNA damage in male germ cells with the possibility of long-term consequences on fertility and progeny outcome. Telomeres, specialized structures at the physical ends of chromosomes, play an important role in the maintenance of genetic stability and in the response of somatic cells to anticancer drugs. Our objective was to test the hypothesis that exposure to bleomycin, etoposide, or cisplatin (the drugs used to treat testicular cancer) or cyclophosphamide (an anticancer agent and immunosuppressant) targets telomeres in the male germ line. C18-4 spermatogonial cells were exposed to bleomycin, etoposide, cisplatin, or 4-hydroperoxycyclophosphamide (4OOH-CPA, a preactivated analog of cyclophosphamide). All four anticancer drugs induced a significant increase in DNA damage in C18-4 cells, as assessed by gamma-H2AX immunofluorescence. Interestingly, the gamma-H2AX signal was localized to telomeres after treatment with bleomycin, cisplatin, and 4OOH-CPA, but not etoposide. Mean telomere lengths, the intensity of the telomere fluorescence in situ hybridization signal, telomerase activity, and the expression of the telomerase enzyme mRNA components, Tert and Terc, were reduced by exposure to cisplatin and 4OOH-CPA, but not by bleomycin or etoposide. Thus, although all four anticancer drugs induced DNA damage in this spermatogonial cell line, telomeres were not specifically affected by etoposide and only the two alkylating agents, cisplatin and 4OOH-CPA, induced telomere dysfunction. This telomere dysfunction may contribute to infertility and developmental defects in the offspring.

Nucleolar control of p53: a cellular Achilles' heel and a target for cancer therapy

Nucleoli perform a crucial cell function, ribosome biogenesis, and of critical relevance to the subject of this review, they are also extremely sensitive to cellular stresses, which can cause loss of function and/or associated structural disruption. In recent years, we have learned that cells take advantage of this stress sensitivity of nucleoli, using them as stress sensors. One major protein regulated by this role of nucleoli is the tumor suppressor p53, which is activated in response to diverse cellular injuries in order to exert its onco-protective effects. Here we discuss a model of nucleolar regulation of p53, which proposes that key steps in the promotion of p53 degradation by the ubiquitin ligase MDM2 occur in nucleoli, thus providing an explanation for the observed link between nucleolar disruption and p53 stability. We review current evidence for this compartmentalization in p53 homeostasis and highlight current limitations of the model. Interestingly, a number of current chemotherapeutic agents capable of inducing a p53 response are likely to do so by targeting nucleolar functions and these compounds may serve to inform further improved therapeutic targeting of nucleoli.

Investigating the cellular fate of a DNA-targeted platinum-based anticancer agent by orthogonal double-click chemistry

Confocal fluorescence microscopy was used to study a platinum-based anticancer agent in intact NCI-H460 lung cancer cells. Orthogonal copper-catalyzed azide-alkyne cycloaddition (click) reactions were used to simultaneously determine the cell-cycle-specific localization of the azide-functionalized platinum-acridine agent 1 and monitor its effects on nucleic acid metabolism. Copper-catalyzed postlabeling showed advantages over copper-free click chemistry using a dibenzocyclooctyne (DIBO)-modified reporter dye, which produced high background levels in microscopic images and failed to efficiently label platinum adducts in chromatin. Compound 1 was successfully labeled with the fluorophore DIBO to yield 1* (characterized by in-line high-performance liquid chromatography/electrospray mass spectrometry). 1 and 1* show a high degree of colocalization in the confocal images, but the ability of 1* to target the (compacted) chromatin was markedly reduced, most likely owing to the steric bulk introduced by the DIBO tag. Nuclear platinum levels correlated inversely with the ability of the cells to synthesize DNA and cause cell cycle arrest, as confirmed by bivariate flow cytometry analysis. In addition, a decrease in the level of cellular transcription, shrinkage of the nucleolar regions, and redistribution of RNA into the cytosol were observed. Postlabeling in conjunction with colocalization experiments is a useful tool for studying the cell killing mechanism of this type of DNA-targeted agent.

Targeting the nucleolus for cancer intervention

The contribution of the nucleolus to cancer is well established with respect to its traditional role in facilitating ribosome biogenesis and proliferative capacity. More contemporary studies however, infer that nucleoli contribute a much broader role in malignant transformation. Specifically, extra-ribosomal functions of the nucleolus position it as a central integrator of cellular proliferation and stress signaling, and are emerging as important mechanisms for modulating how oncogenes and tumor suppressors operate in normal and malignant cells. The dependence of certain tumor cells to co-opt nucleolar processes to maintain their cancer phenotypes has now clearly been demonstrated by the application of small molecule inhibitors of RNA Polymerase I to block ribosomal DNA transcription and disrupt nucleolar function (Bywater et al., 2012 [1]). These drugs, which selectively kill tumor cells in vivo while sparing normal cells, have now progressed to clinical trials. It is likely that we have only just begun to scratch the surface of the potential of the nucleolus as a new target for cancer therapy, with "suppression of nucleolar stress" representing an emerging "hallmark" of cancer. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.

The cell's nucleolus: an emerging target for chemotherapeutic intervention

The transient nucleolus plays a central role in the up-regulated synthesis of ribosomal RNA (rRNA) to sustain ribosome biogenesis, a hallmark of aberrant cell growth. This function, in conjunction with its unique pathohistological features in malignant cells and its ability to mediate apoptosis, renders this sub-nuclear structure a potential target for chemotherapeutic agents. In this Minireview, structurally and functionally diverse small molecules are discussed that have been reported to either interact with the nucleolus directly or perturb its function indirectly by acting on its dynamic components. These molecules include all major classes of nucleic-acid-targeted agents, antimetabolites, kinase inhibitors, anti-inflammatory drugs, natural product antibiotics, oligopeptides, as well as nanoparticles. Together, these molecules are invaluable probes of structure and function of the nucleolus. They also provide a unique opportunity to develop novel strategies for more selective and therefore better-tolerated chemotherapeutic intervention. In this regard, inhibition of RNA polymerase-I-mediated rRNA synthesis appears to be a promising mechanism for killing cancer cells. The recent development of molecules targeted at G-quadruplex-forming rRNA gene sequences, which are currently undergoing clinical trials, seems to attest to the success of this approach.

The nucleolus: an emerging target for cancer therapy

For over 100 years, pathologists have utilised an increase in size and number of nucleoli, the subnuclear site of ribosome synthesis, as a marker of aggressive tumours. Despite this, the contribution of the nucleolus and ribosomal RNA synthesis to cancer has been largely overlooked. This concept has recently changed with the demonstration that the nucleolus indirectly controls numerous other cellular functions, in particular, the cellular activity of the critical tumour suppressor protein, p53. Moreover, selective inhibition of ribosomal gene transcription in the nucleolus has been shown to be an effective therapeutic strategy to promote cancer-specific activation of p53. This article reviews the largely untapped potential of the nucleolus and ribosomal gene transcription as exciting new targets for cancer therapy.

DNA damage-induced inhibition of rRNA synthesis by DNA-PK and PARP-1

RNA synthesis and DNA replication cease after DNA damage. We studied RNA synthesis using an in situ run-on assay and found ribosomal RNA (rRNA) synthesis was inhibited 24 h after UV light, gamma radiation or DNA cross-linking by cisplatin in human cells. Cisplatin led to accumulation of cells in S phase. Inhibition of the DNA repair proteins DNA-dependent protein kinase (DNA-PK) or poly(ADP-ribose) polymerase 1 (PARP-1) prevented the DNA damage-induced block of rRNA synthesis. However, DNA-PK and PARP-1 inhibition did not prevent the cisplatin-induced arrest of cell cycle in S phase, nor did it induce de novo BrdU incorporation. Loss of DNA-PK function prevented activation of PARP-1 and its recruitment to chromatin in damaged cells, suggesting regulation of PARP-1 by DNA-PK within a pathway of DNA repair. From these results, we propose a sequential activation of DNA-PK and PARP-1 in cells arrested in S phase by DNA damage causes the interruption of rRNA synthesis after DNA damage.

Effects of intratumoral administration of a hyaluronan-cisplatin nanoconjugate to five dogs with soft tissue sarcomas

OBJECTIVE

To determine the effects of intratumoral injection of a hyaluronan-cisplatin nanoconjugate on local and systemic platinum concentrations and systemic toxicosis.

ANIMALS

5 dogs with spontaneous soft tissue sarcomas (STSs).

PROCEDURES

For each dog, approximately 1.5 mL of hyaluronan nanocarrier conjugated with 20 mg of cisplatin was injected into an external STS. Blood samples were collected immediately before (0 hours) and at 0.5, 1, 2, 3, 4, 24, and 96 hours after hyaluronan-cisplatin injection for pharmacokinetic analyses. Urine samples were obtained at 0 and at 96 hours after hyaluronan-cisplatin injection for urinalysis. Each treated STS and its sentinel lymph nodes were surgically removed 96 hours after the hyaluronan-cisplatin injection. Inductively coupled plasma mass spectrometry was used to measure platinum concentrations in blood samples, tumors, and lymph nodes.

RESULTS

No tissue reactions were detected 96 hours after hyaluronan-cisplatin injection. Mean ± SD area under the curve, peak concentration, and terminal half-life for unbound (plasma) and total (serum) platinum were 774.6 ± 221.1 ng•h/mL and 3,562.1 ± 2,031.1 ng•h/mL, 56.5 ± 20.9 ng/mL and 81.6 ± 40.4 ng/mL, and 33.6 ± 16.1 hours and 51.2 ± 29.1 hours, respectively. Platinum concentrations ranged from 3,325 to 8,229 ng/g in STSs and 130 to 6,066 ng/g in STS-associated lymph nodes.

CONCLUSIONS AND CLINICAL RELEVANCE

Intratumoral injection of the hyaluronan-cisplatin nanoconjugate was well tolerated in treated dogs. Following intratumoral hyaluronan-cisplatin injection, platinum concentration was 1,000-fold and 100-fold greater within treated tumors and tumor-draining lymphatics, respectively, compared with that in plasma.

Melatonin Suppresses the Expression of 45S Preribosomal RNA and Upstream Binding Factor and Enhances the Antitumor Activity of Puromycin in MDA-MB-231 Breast Cancer Cells

Since the dysregulation of ribosome biogenesis is closely associated with tumor progression, in the current study, the critical role of ribosome biogenesis related signaling was investigated in melatonin and/or puromycin induced apoptosis in MDA-MB-231 breast cancer cells. Despite its weak cytotoxicity, melatonin from 3 mM attenuated the expression of 45S pre-ribosomal RNA (pre-rRNA), UBF as a nucleolar transcription factor, and fibrillarin at mRNA level and consistently downregulated nucleolar proteins such as UBF and fibrillarin at protein level in MDA-MB-231 cells. Furthermore, immunofluorescence assay revealed that UBF was also degraded by melatonin in MDA-MB-231 cells. In contrast, melatonin attenuated the expression of survival genes such as Bcl-xL, Mcl-1, cyclinD1, and cyclin E, suppressed the phosphorylation of AKT, mTOR, and STAT3, and cleaved PARP and activated caspase 3 only at a high concentration of 12 mM. However, combined treatment of melatonin (3 mM) and puromycin (1 μM) synergistically inhibited viability, attenuated the expression of 45S pre-rRNA and UBF, and consistently downregulated UBF, XPO1 and IPO7, procaspase 3, and Bcl-xL in MDA-MB 231 cells. Overall, these findings suggest that melatonin can be a cancer preventive agent by combination with puromycin via the inhibition of 45S pre-rRNA and UBF in MDA-MB 231 breast cancer cells.

P19ARF and RasV¹² offer opposing regulation of DHX33 translation to dictate tumor cell fate

DHX33 is a pivotal DEAH-box RNA helicase in the multistep process of RNA polymerase I-directed transcription of the ribosomal DNA locus. We explored the regulation of DHX33 expression by Ras(V12) and ARF to determine DHX33's role in sensing these opposing signals to regulate ribosome biogenesis. In wild-type primary fibroblasts, Ras(V12) infection induced a transient increase in DHX33 protein level, as well as an rRNA transcriptional rate that was eventually suppressed by a delayed activation of the ARF/p53 pathway. DHX33 expression was exclusively controlled at the level of translation. ARF caused a dramatic reduction in polysome-associated DHX33 mRNAs, while Ras(V12) led to a complete shift of existing DHX33 mRNAs to actively translating polysomes. The translation of DHX33 by Ras(V12) was sensitive to inhibitors of phosphatidylinositol 3-kinase, mTOR, and mitogen-activated protein and was pivotal for enhanced rRNA transcription and enhanced overall cellular protein translation. In addition, DHX33 knockdown abolished Ras(V12)-induced rRNA transcription and protein translation and prevented both the in vitro and in vivo transforming properties of oncogenic Ras(V12). Our results directly implicate DHX33 as a crucial player in establishing rRNA synthesis rates in the face of Ras(V12) or ARF signals, adjusting ribosome biogenesis to match the appropriate growth or antigrowth signals.

Silencing of GLUT-1 inhibits sensitization of oral cancer cells to cisplatin during hypoxia

BACKGROUND

During tumor development, cells are exposed to a hypoxic microenvironment. Tumor hypoxia also has a profound influence on the sensitivity of cancer chemotherapy. The objective of this study was to investigate the mechanism of cisplatin (CDDP) resistance of oral squamous cell carcinoma (OSCC) cells under hypoxia by analyzing gene expression profiles to identify key genes and factors involved.

METHODS

Cell viability was measured following culture of the cells in the presence or absence of CDDP, under normoxic or hypoxic conditions, using a CCK-8 assay. Analysis of the expression of HIF target genes in hypoxia-treated cells was performed using an HIF-regulated cDNA plate array. Changes in the mRNA expression of selected HIF target genes were analyzed using RT-PCR, and changes in the protein levels of these genes were analyzed by Western blotting. Tumor cell apoptosis was assessed by flow cytometry.

RESULTS

The OSCC cell lines responded differently to CDDP under normoxic and hypoxic conditions. The expression of glucose transporter protein-1 (GLUT-1) was up-regulated in human squamous cell carcinoma of mouth (HSC-2) cells under hypoxia. Furthermore, there was little correlation between the cisplatin sensitivity of human squamous cell carcinoma of tongue (SAS) in normoxia and hypoxia. After GLUT-1 knockdown, CDDP treatment resulted in increased rates of apoptosis under hypoxia as compared with normoxia in cell lines HSC-2, Ca9-22, and SAS (P = 0.025).

CONCLUSION

The results of this study suggest that knockdown of GLUT-1 inhibits sensitization of oral squamous cells to CDDP during hypoxia in HSC-2, Ca9-22, and SAS cells.

Hepatitis B virus X protein and c-Myc cooperate in the upregulation of ribosome biogenesis and in cellular transformation

Viral and cellular oncogenes are well known to enhance rRNA synthesis, leading to increased ribosome biogenesis and cell proliferation. Our study on the molecular underpinnings of the interaction between viral HBx and c-Myc, which is implicated in the development of hepatocellular carcinoma, showed a marked increase in the biosynthesis of rRNA, ribosomes and protein in hepatoma cells. A profound alteration in the nucleolar morphology and biochemical content of these cells was also observed. Increased biosynthetic activity was associated with increased cell proliferation and transformation of immortalized human hepatocytes. Furthermore, inhibition of RNA polymerase III activity impaired the proliferative advantage of hepatoma cells and transformation of immortalized hepatocytes as effectively as cisplatin treatment. These findings were corroborated in a transgenic HBx-myc microenvironment, in which an elevated hepatic level of rRNA was associated with conspicuous morphological and biochemical changes in the hepatocytic nucleoli. Thus, HBx and c-Myc seem to work cooperatively to support ribosome biogenesis and cellular transformation.

Non-coding rRNA-mediated preferential killing in cancer cells is enhanced by suppression of autophagy in non-transformed counterpart

Interest to anticancer agents targeting rRNA biogenesis is growing. Cis-non-coding rRNAs, alternative to primary rRNA, have been shown to regulate rRNA biogenesis. We have recently detected bidirectional non-coding rRNAs that carry ribozyme-like properties. Anti-antisense oligonucleotides complementary to antisense non-coding rRNAs markedly stabilized the bidirectional transcripts and induced cell death in mouse lung cells. Here, we demonstrated that the same oligonucleotide killed mouse lung-cancer cells preferentially, compared with non-cancer sister lines, suggesting its potential utility for cancer treatment. A human version of anti-antisense oligonucleotide, complementary to an rDNA intergenic site, mediated apoptosis primarily in cancer cells. Autophagic activation was largely undifferentiable between the anti-antisense and other oligonucleotides and accounted for the undesired cytotoxicity in non-cancer cells. Co-treatment with chloroquine, an autophagy inhibitor, reduced cytotoxicity in the non-cancer cells, but retained the anti-antisense-mediated killings in cancer cells. Furthermore, the anti-antisense oligonucleotide stabilized bidirectional non-coding rRNAs predominantly in human cancer cells and perturbed rRNA biogenesis. Contributions of non-coding rRNAs to cell death were proven by transfection of in –vitro-synthesized transcripts. Taken together, cancer/non-cancer cells respond differently to stabilization of non-coding rRNAs, and such differential responses provide a window of opportunity to enhance anticancer efficacy.