Targeting FACT complex suppresses mammary tumorigenesis in Her2/neu transgenic mice

Chromatin as an old and new anticancer target

Recent genome-wide analyses identified chromatin modifiers as one of the most frequently mutated classes of genes across all cancers. However, chemotherapies developed for cancers involving DNA damage remain the standard of care for chromatin-deranged malignancies. In this review we address this conundrum by establishing the concept of 'chromatin damage': the non-genetic damage to protein-DNA interactions induced by certain small molecules. We highlight anthracyclines, a class of chemotherapeutic agents ubiquitously applied in oncology, as an example of overlooked chromatin-targeting agents. We discuss our current understanding of this phenomenon and explore emerging chromatin-damaging agents as a basis for further studies to maximize their impact in modern cancer treatment.

Comparison of cell response to chromatin and DNA damage

DNA-targeting drugs are widely used for anti-cancer treatment. Many of these drugs cause different types of DNA damage, i.e. alterations in the chemical structure of DNA molecule. However, molecules binding to DNA may also interfere with DNA packing into chromatin. Interestingly, some molecules do not cause any changes in DNA chemical structure but interfere with DNA binding to histones and nucleosome wrapping. This results in histone loss from chromatin and destabilization of nucleosomes, a phenomenon that we call chromatin damage. Although the cellular response to DNA damage is well-studied, the consequences of chromatin damage are not. Moreover, many drugs used to study DNA damage also cause chromatin damage, therefore there is no clarity on which effects are caused by DNA or chromatin damage. In this study, we aimed to clarify this issue. We treated normal and tumor cells with bleomycin, nuclease mimicking drug which cut predominantly nucleosome-free DNA and therefore causes DNA damage in the form of DNA breaks, and CBL0137, which causes chromatin damage without direct DNA damage. We describe similarities and differences between the consequences of DNA and chromatin damage. Both agents were more toxic for tumor than normal cells, but while DNA damage causes senescence in both normal and tumor cells, chromatin damage does not. Both agents activated p53, but chromatin damage leads to the accumulation of higher levels of unmodified p53, which transcriptional activity was similar to or lower than that of p53 activated by DNA damage. Most importantly, we found that while transcriptional changes caused by DNA damage are limited by p53-dependent activation of a small number of p53 targets, chromatin damage activated many folds more genes in p53 independent manner.

Comparison of cell response to chromatin and DNA damage

DNA-targeting drugs may damage DNA or chromatin. Many anti-cancer drugs damage both, making it difficult to understand their mechanisms of action. Using molecules causing DNA breaks without altering nucleosome structure (bleomycin) or destabilizing nucleosomes without damaging DNA (curaxin), we investigated the consequences of DNA or chromatin damage in normal and tumor cells. As expected, DNA damage caused p53-dependent growth arrest followed by senescence. Chromatin damage caused higher p53 accumulation than DNA damage; however, growth arrest was p53-independent and did not result in senescence. Chromatin damage activated the transcription of multiple genes, including classical p53 targets, in a p53-independent manner. Although these genes were not highly expressed in basal conditions, they had chromatin organization around the transcription start sites (TSS) characteristic of most highly expressed genes and the highest level of paused RNA polymerase. We hypothesized that nucleosomes around the TSS of these genes were the most sensitive to chromatin damage. Therefore, nucleosome loss upon curaxin treatment would enable transcription without the assistance of sequence-specific transcription factors. We confirmed this hypothesis by showing greater nucleosome loss around the TSS of these genes upon curaxin treatment and activation of a p53-specific reporter in p53-null cells by chromatin-damaging agents but not DNA-damaging agents.

Human FACT subunits coordinate to catalyze both disassembly and reassembly of nucleosomes

The histone chaperone FACT (facilitates chromatin transcription) enhances transcription in eukaryotic cells, targeting DNA-protein interactions. FACT, a heterodimer in humans, comprises SPT16 and SSRP1 subunits. We measure nucleosome stability and dynamics in the presence of FACT and critical component domains. Optical tweezers quantify FACT/subdomain binding to nucleosomes, displacing the outer wrap of DNA, disrupting direct DNA-histone (core site) interactions, altering the energy landscape of unwrapping, and increasing the kinetics of DNA-histone disruption. Atomic force microscopy reveals nucleosome remodeling, while single-molecule fluorescence quantifies kinetics of histone loss for disrupted nucleosomes, a process accelerated by FACT. Furthermore, two isolated domains exhibit contradictory functions; while the SSRP1 HMGB domain displaces DNA, SPT16 MD/CTD stabilizes DNA-H2A/H2B dimer interactions. However, only intact FACT tethers disrupted DNA to the histones and supports rapid nucleosome reformation over several cycles of force disruption/release. These results demonstrate that key FACT domains combine to catalyze both nucleosome disassembly and reassembly.

The FACT complex facilitates expression of lysosomal and antioxidant genes through binding to TFEB and TFE3

TFEB (transcription factor EB) and TFE3 (transcription factor binding to IGHM enhancer 3) orchestrate the cellular response to a variety of stressors, including nutrient deprivation, oxidative stress and pathogens. Here we describe a novel interaction of TFEB and TFE3 with the FAcilitates Chromatin Transcription (FACT) complex, a heterodimeric histone chaperone consisting of SSRP1 and SUPT16H that mediates nucleosome disassembly and assembly, thus facilitating transcription. Extracellular stimuli, such as nutrient deprivation or oxidative stress, induce nuclear translocation and activation of TFEB and TFE3, which then associate with the FACT complex to regulate stress-induced gene transcription. Depletion of FACT does not affect TFEB activation, stability, or binding to the promoter of target genes. In contrast, reduction of FACT levels by siRNA or treatment with the FACT inhibitor curaxin, severely impairs induction of numerous antioxidant and lysosomal genes, revealing a crucial role of FACT as a regulator of cellular homeostasis. Furthermore, upregulation of antioxidant genes induced by TFEB over-expression is significantly reduced by curaxin, consistent with a role of FACT as a TFEB transcriptional activator. Together, our data show that chromatin remodeling at the promoter of stress-responsive genes by FACT is important for efficient expression of TFEB and TFE3 targets, thus providing a link between environmental changes, chromatin modifications and transcriptional regulation.Abbreviations: ADNP2, ADNP homeobox 2; ATP6V0D1, ATPase H+ transporting V0 subunit d1; ATP6V1A, ATPase H+ transporting V1 subunit A; ATP6V1C1, ATPase H+ transporting V1 subunit C1; CSNK2/CK2, casein kinase 2; CLCN7, chloride voltage-gated channel 7; CTSD, cathepsin D; CTSZ, cathepsin Z; EBSS, earle's balanced salt solution; FACT complex, facilitates chromatin transcription complex; FOXO3, forkhead box O3; HEXA, hexosaminidase subunit alpha; HIF1A, hypoxia inducible factor 1 subunit alpha; HMOX1, heme oxygenase 1; LAMP1, lysosomal associated membrane protein 1; MAFF, MAF bZIP transcription factor F; MAFG, MAF bZIP transcription factor G; MCOLN1, mucolipin TRP cation channel 1; MTORC1, mechanistic target of rapamycin kinase complex 1; NaAsO_2, sodium arsenite; POLR2, RNA polymerase II; PPARGC1A, PPARG coactivator 1 alpha; PYROXD1, pyridine nucleotide-disulfide oxidoreductase domain 1; RRAGC, Ras related GTP binding C; SEC13, SEC13 homolog, nuclear pore and COPII coat complex component; SLC38A9, solute carrier family 38 member 9; SSRP1, structure specific recognition protein 1; SUPT16H, SPT16 homolog, facilitates chromatin remodeling subunit; TFEB, transcription factor EB; TFE3, transcription factor binding to IGHM enhancer 3; TXNRD1, thioredoxin reductase 1; UVRAG, UV radiation resistance associated; WDR59, WD repeat domain 59.

Physiologic Targets and Modes of Action for CBL0137, a Lead for Human African Trypanosomiasis Drug Development

CBL0137 is a lead drug for human African trypanosomiasis, caused by Trypanosoma brucei Herein, we use a four-step strategy to 1) identify physiologic targets and 2) determine modes of molecular action of CBL0137 in the trypanosome. First, we identified fourteen CBL0137-binding proteins using affinity chromatography. Second, we developed hypotheses of molecular modes of action, using predicted functions of CBL0137-binding proteins as guides. Third, we documented effects of CBL0137 on molecular pathways in the trypanosome. Fourth, we identified physiologic targets of the drug by knocking down genes encoding CBL0137-binding proteins and comparing their molecular effects to those obtained when trypanosomes were treated with CBL0137. CBL0137-binding proteins included glycolysis enzymes (aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphofructokinase, phosphoglycerate kinase) and DNA-binding proteins [universal minicircle sequence binding protein 2, replication protein A1 (RPA1), replication protein A2 (RPA2)]. In chemical biology studies, CBL0137 did not reduce ATP level in the trypanosome, ruling out glycolysis enzymes as crucial targets for the drug. Thus, many CBL0137-binding proteins are not physiologic targets of the drug. CBL0137 inhibited 1) nucleus mitosis, 2) nuclear DNA replication, and 3) polypeptide synthesis as the first carbazole inhibitor of eukaryote translation. RNA interference (RNAi) against RPA1 inhibited both DNA synthesis and mitosis, whereas RPA2 knockdown inhibited mitosis, consistent with both proteins being physiologic targets of CBL0137. Principles used here to distinguish drug-binding proteins from physiologic targets of CBL0137 can be deployed with different drugs in other biologic systems. SIGNIFICANCE STATEMENT: To distinguish drug-binding proteins from physiologic targets in the African trypanosome, we devised and executed a multidisciplinary approach involving biochemical, genetic, cell, and chemical biology experiments. The strategy we employed can be used for drugs in other biological systems.

The Current Status of SSRP1 in Cancer: Tribulation and Road Ahead

Methods

We search PubMed and Web of Sciences with keywords “SSRP1” and “Cancer.” Only English literature was included, and conference papers and abstract were all excluded.

Results

Transcription factors are classified into three groups based on their DNA binding motifs: simple helix-loop-helix (bHLH), classical zinc fingers (ZF-TFs), and homeodomains. The tumor-suppressive miR-497 (microRNA-497) acted as an undesirable regulator of SSRP1 upregulation, which led to tumor growth. The siRNA (small interfering RNA) knockdown of SSRP1 hindered cell proliferation along with incursion and glioma cell migration. Through the AKT (also known as protein kinase B) signaling pathway, SSRP1 silencing affected cancer apoptosis and cell proliferation.

Conclusion

The MAPK (mitogen-activated protein kinase) signaling pathway's phosphorylation was suppressed when SSRP1 was depleted. The effect of curaxins on p53 and NF-B (nuclear factor-κB), and their toxicity to cancer cells, is attributable to the FACT (facilitates chromatin transcription) complex's chromatin trapping.

The FAcilitates Chromatin Transcription (FACT) complex: Its roles in DNA repair and implications for cancer therapy

Genomic DNA in the nucleus is wrapped around nucleosomes, a repeating unit of chromatin. The nucleosome, consisting of octamer of core histones, is a barrier for several cellular processes that require access to the naked DNA. The FAcilitates Chromatin Transcription (FACT), a histone chaperone complex, is involved in nucleosome remodeling via eviction or assembly of histones during transcription, replication, and DNA repair. Increasing evidence suggests that FACT plays an important role in multiple DNA repair pathways including transcription-coupled nucleotide excision repair (TC-NER) of UV-induced damage, DNA single- and double-strand breaks (DSBs) repair, and base excision repair (BER) of oxidized or alkylated damaged bases. Further, studies have shown overexpression of FACT in multiple types of cancer and its association with drug resistance and patients' poor prognosis. In this review, we discuss how FACT is accumulated at the damage site and what functions it performs. We describe the known mechanisms by which FACT facilitates repair of different types of DNA damage. Further, we highlight the recent advances in a class of FACT inhibitors, called curaxins, which show promise as a new adjuvant therapy to sensitize multiple types of cancer to chemotherapy and radiation.

SSRP1 Affects Growth and Apoptosis of Gastric Cancer Cells Through AKT Pathway

Background: We aimed to figure out the SSRP1's potential influence on the apoptosis and proliferation of gastric cancer (GC) cells and its regulatory mechanism. Methods: SSRP1 expression in GC cells and tissues was detected via quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The interrelation between clinicopathological characteristics of GC patients and SSRP1 expression was analyzed via χ2 test, and the correlation between SSRP1 expression and overall survival rate was analyzed using Kaplan-Meier survival analysis. After knockdown of SSRP1 in AGS cells, the SSRP1 expression, colony formation ability, cell viability, cell cycle changes, apoptosis rate, and migration and invasion ability were detected through qRT-PCR, colony formation assay, CCK8 assay, flow cytometry and transwell test, respectively. Finally, the effects of down-regulation of SSRP1 on the expressions of phosphorylated-protein kinase B (p-AKT), B-cell lymphoma-2 (Bcl-2) and Bcl-2 associated X protein (Bax) were explored using Western blotting. Results: SSRP1 displayed a high expression in GC cells and tissues. SSRP1 expression was closely interrelated to the TNM stage, lymph node metastasis and tumor size. The survival rate of patients was markedly shorter in high expression group than the lower expression group. After the knockdown of SSRP1 in cells, the viability and colony formation ability of AGS cells were inhibited. In addition, cell ration in the G1 phase was increased, while that in the S phase declined, and the cell invasion and migration were obviously weakened. It was found from Western blotting that the knockdown of SSRP1 could evidently suppress the protein levels of Bcl-2 and p-AKT, but promote the protein expression of Bax, indicating that silencing SSRP1 can inhibit the proliferative capacity and increase the number of GC cells through incativating AKT signaling pathway. Conclusion: SSRP1 rose up in GC tissues and cells. Reduction of SSRP1 can inhibit the proliferative capacity and increase the number of GC cells through inactiving AKT signaling pathway.

Stimulation of an anti-tumor immune response with "chromatin-damaging" therapy

Curaxins are small molecules that bind genomic DNA and interfere with DNA-histone interactions leading to the loss of histones and decondensation of chromatin. We named this phenomenon 'chromatin damage'. Curaxins demonstrated anti-cancer activity in multiple pre-clinical tumor models. Here, we present data which reveals, for the first time, a role for the immune system in the anti-cancer effects of curaxins. Using the lead curaxin, CBL0137, we observed elevated expression of several group of genes in CBL0137-treated tumor cells including interferon sensitive genes, MHC molecules, some embryo-specific antigens suggesting that CBL0137 increases tumor cell immunogenicity and improves recognition of tumor cells by the immune system. In support of this, we found that the anti-tumor activity of CBL0137 was reduced in immune deficient SCID mice when compared to immune competent mice. Anti-tumor activity of CBL0137 was abrogated in CD8+ T cell depleted mice but only partially lost when natural killer or CD4+ T cells were depleted. Further support for a key role for the immune system in the anti-tumor activity of CBL0137 is evidenced by an increased antigen-specific effector CD8+ T cell and NK cell response, and an increased ratio of effector T cells to Tregs in the tumor and spleen. CBL0137 also elevated the number of CXCR3-expressing CTLs in the tumor and the level of interferon-γ-inducible protein 10 (IP-10) in serum, suggesting IP-10/CXCR3 controls CBL0137-elicited recruitment of effector CTLs to tumors. Our collective data underscores a previously unrecognized role for both innate and adaptive immunity in the anti-tumor activity of curaxins.

Dual targeting of the epigenome via FACT complex and histone deacetylase is a potent treatment strategy for DIPG

Diffuse intrinsic pontine glioma (DIPG) is an aggressive and incurable childhood brain tumor for which new treatments are needed. CBL0137 is an anti-cancer compound developed from quinacrine that targets facilitates chromatin transcription (FACT), a chromatin remodeling complex involved in transcription, replication, and DNA repair. We show that CBL0137 displays profound cytotoxic activity against a panel of patient-derived DIPG cultures by restoring tumor suppressor TP53 and Rb activity. Moreover, in an orthotopic model of DIPG, treatment with CBL0137 significantly extends animal survival. The FACT subunit SPT16 is found to directly interact with H3.3K27M, and treatment with CBL0137 restores both histone H3 acetylation and trimethylation. Combined treatment of CBL0137 with the histone deacetylase inhibitor panobinostat leads to inhibition of the Rb/E2F1 pathway and induction of apoptosis. The combination of CBL0137 and panobinostat significantly prolongs the survival of mice bearing DIPG orthografts, suggesting a potential treatment strategy for DIPG.

Proteasomal Regulation of Mammalian SPT16 in Controlling Transcription

FACT (facilitates chromatin transcription), an essential and evolutionarily conserved heterodimer from yeast to humans, controls transcription and is found to be upregulated in various cancers. However, the basis for such upregulation is not clearly understood. Our recent results deciphering a new ubiquitin-proteasome system regulation of the FACT subunit SPT16 in orchestrating transcription in yeast hint at the involvement of the proteasome in controlling FACT in humans, with a link to cancer. To test this, we carried out experiments in human embryonic kidney (HEK293) cells, which revealed that human SPT16 undergoes ubiquitylation and that its abundance is increased following inhibition of the proteolytic activity of the proteasome, thus implying proteasomal regulation of human SPT16. Furthermore, we find that the increased abundance/expression of SPT16 in HEK293 cells alters the transcription of genes, including ones associated with cancer, and that the proteasomal degradation of SPT16 is impaired in kidney cancer (Caki-2) cells to upregulate SPT16. Like human SPT16, murine SPT16 in C2C12 cells also undergoes ubiquitylation and proteasomal degradation to regulate transcription. Collectively, our results reveal a proteasomal regulation of mammalian SPT16, with physiological relevance in controlling transcription, and implicate such proteasomal control in the upregulation of SPT16 in cancer.

SSRP1 Is a Prognostic Biomarker Correlated with CD8+ T Cell Infiltration in Hepatocellular Carcinoma (HCC)

Background

Hepatocellular carcinoma (HCC), one of the most common primary malignancies, is theoretically an epitope candidate for immune checkpoint inhibitors, and therefore, the identification of HCC biomarkers is important. Structure-specific recognition protein 1 (SSRP1) is involved in almost all chromatin-related processes, including DNA replication, repair, and transcription. However, its role in HCC remains to be elucidated.

Methods

This study investigated the expression of SSRP1 in HCCDB, Oncomine, HPA, and other databases. The prognostic value of SSRP1 in HCC and its relationship with clinical characteristics were then explored using Kaplan-Meier plotter. At the same time, SSRP1 coexpression genes were explored and functionally annotated in the LinkedOmics database. Finally, the correlation between the SSRP1 expression and HCC immune cell infiltration was explored in TIMER and online single-cell sequencing database.

Results

Significantly elevated transcriptional and proteomic SSRP1 expressions were found in HCC. Increased SSRP1 mRNA expression was significantly correlated with relevant clinicopathological parameters such as immune cells. Notably, the SSRP1 expression was positively correlated with the infiltration levels of Treg and CD8⁺ T cells, especially exhausted CD8⁺ T cells. Interestingly, the SSRP1 expression was higher in both tumor Treg and exhausted CD8⁺ T cells than in adjacent tissues.

Conclusion

SSRP1, as a new prognostic marker for HCC, promotes HCC development by influencing the infiltration of depleted CD8⁺ T cells and may influence the effect of immunotherapy.

Transcription-facilitating histone chaperons interact with genomic and synthetic G4 structures

Affinity for G-quadruplex (G4) structures may be a common feature of transcription-facilitating histone chaperons (HCs). This assumption is based on previous unmatched studies of HCs FACT, nucleolin (NCL), BRD3, and ATRX. We verified this assumption and considered its implications for the therapeutic applications of synthetic (exogenous) G4s and the biological significance of genomic G4s. First, we questioned whether exogenous G4s that recognize cell-surface NCL and could trap other HCs in the nucleus are usable as anticancer agents. We performed in vitro binding assays and selected leading multi-targeted G4s. They exhibited minor effects on cell viability. The presumed NCL-regulated intracellular transport of G4s was inefficient or insufficient for tumor-specific G4 delivery. Next, to clarify whether G4s in the human genome could recruit HCs, we compared available HC ChIP-seq data with G4-seq/G4-ChIP-seq data. Several G4s, including the well-known c-Myc quadruplex structure, were found to be colocalized with HC occupancy sites in cancer cell lines. As evidenced by our molecular modeling data, c-Myc G4 might interfere with the HC function of BRD3 but is unlikely to prevent the BRD3-driven assembly of the chromatin remodeling complex. The c-Myc case illustrates the intricate role of genomic G4s in chromatin remodeling, nucleosome remodeling, and transcription.

Suppressor of Ty 16 promotes lung cancer malignancy and is negatively regulated by miR-1227-5p

Suppressor of Ty 16 (Spt16) is a component of the facilitates chromatin transcription (FACT) complex, which is a histone chaperone and involved in gene transcription, DNA replication, and DNA repair. Previous studies showed that FACT is highly expressed in cancer, and cancer cells are more reliant on FACT than normal cells. However, the relationship between Spt16 and lung cancer remains unclear. In this study, we explored the functions of Spt16 in lung cancer cells. The effects of Spt16 on lung cancer cell proliferation, cell cycle progression, apoptosis, migration, and invasion were examined. We found that knockdown of Spt16 led to obvious decreases of both Rb and MCM7, and further activated the DNA damage response (DDR) pathway. In addition, a novel micro‐RNA, miR‐1227‐5p, directly targeted the 3′‐UTR of Spt16 and regulated the mRNA levels of Spt16. Furthermore, we found that CBL0137, the functional inhibitor of FACT, showed similar effects as loss of Spt16. Together, our data indicated that Spt16 is likely to be an essential regulator for lung cancer malignancy and is negatively regulated by miR‐1227‐5p.

Histone chaperone FACT is essential to overcome replication stress in mammalian cells

The histone chaperone FACT is upregulated during mammary tumorigenesis and necessary for the viability and growth of breast tumor cells. We established that only proliferating tumor cells are sensitive to FACT knockdown, suggesting that FACT functions during DNA replication in tumor cells but not in normal cells. We hypothesized that the basal level of replication stress defines the FACT dependence of cells. Using genetic and chemical tools, we demonstrated that FACT is needed to overcome replication stress. In the absence of FACT during replication stress, the MCM2-7 helicase dissociates from chromatin, resulting in the absence of ssDNA accumulation, RPA binding, and activation of the ATR/CHK1 checkpoint response. Without this response, stalled replication forks are not stabilized, and new origin firing cannot be prevented, leading to the accumulation of DNA damage and cell death. Thus, we propose a novel role for FACT as a factor preventing helicase dissociation from chromatin during replication stress.

Unresolved Complexity in the Gene Regulatory Network Underlying EMT

Epithelial to mesenchymal transition (EMT) is the process whereby a polarized epithelial cell ceases to maintain cell-cell contacts, loses expression of characteristic epithelial cell markers, and acquires mesenchymal cell markers and properties such as motility, contractile ability, and invasiveness. A complex process that occurs during development and many disease states, EMT involves a plethora of transcription factors (TFs) and signaling pathways. Whilst great advances have been made in both our understanding of the progressive cell-fate changes during EMT and the gene regulatory networks that drive this process, there are still gaps in our knowledge. Epigenetic modifications are dynamic, chromatin modifying enzymes are vast and varied, transcription factors are pleiotropic, and signaling pathways are multifaceted and rarely act alone. Therefore, it is of great importance that we decipher and understand each intricate step of the process and how these players at different levels crosstalk with each other to successfully orchestrate EMT. A delicate balance and fine-tuned cooperation of gene regulatory mechanisms is required for EMT to occur successfully, and until we resolve the unknowns in this network, we cannot hope to develop effective therapies against diseases that involve aberrant EMT such as cancer. In this review, we focus on data that challenge these unknown entities underlying EMT, starting with EMT stimuli followed by intracellular signaling through to epigenetic mechanisms and chromatin remodeling.

OTU deubiquitinase 5 inhibits the progression of non-small cell lung cancer via regulating p53 and PDCD5

Non-small cell lung cancer (NSCLC) has the highest morbidity and mortality worldwide. OTU deubiquitinase 5 (OTUD5), a deubiquitinating enzyme, can enhance the stability of p53 and programmed cell death 5 (PDCD5), a protein related to the apoptosis, by deubiquitination. This study aimed to explore the biological function and underlying mechanism of OTUD5 in NSCLC. Western blot and qRT-PCR were used to detect the expression of OTUD5 protein and mRNA in NSCLC tissues and cells, respectively. RNAi was adopted to construct an OTUD5 low-expression model while the plasmids overexpressing p53 and PDCD5 were used to establish the overexpression models, respectively. CCK-8 assay, transwell assay, and apoptosis assay were carried out to analyze the changes in the proliferation, migration, and chemoresistance of A549 and HCC827 cells. The mechanism of OTUD5 in NSCLC was studied by Western blot. Down-regulated OTUD5 in NSCLC tissues was significantly correlated to a poor prognosis. The knockdown of OTUD5 inactivated p53 and PDCD5, promoting the proliferation and metastasis of NSCLC cells while inhibiting their apoptosis. OTUD5 knockdown also enhanced the resistance of NSCLC cells to doxorubicin and cisplatin. OTUD5 acted as a tumor suppressor in NSCLC by regulating the p53 and PDCD5 pathways.

CPF impedes cell cycle re-entry of quiescent lung cancer cells through transcriptional suppression of FACT and c-MYC

Blockade of cell cycle re‐entry in quiescent cancer cells is a strategy to prevent cancer progression and recurrence. We investigated the action and mode of action of CPF mixture (Coptis chinensis, Pinellia ternata and Fructus trichosanthis) in impeding a proliferative switch in quiescent lung cancer cells. The results indicated that CPF impeded cell cycle re‐entry in quiescent lung cancer cells by reduction of FACT and c‐MYC mRNA and protein levels, with concomitant decrease in H3K4 tri‐methylation and RNA polymerase II occupancy at FACT and c‐MYC promoter regions. Animals implanted with quiescent cancer cells that had been exposed to CPF had reduced tumour volume/weight. Thus, CPF suppresses proliferative switching through transcriptional suppression of FACT and the c‐MYC, providing a new insight into therapeutic target and intervention method in impeding cancer recurrence.

Histone Chaperone FACT and Curaxins: Effects on Genome Structure and Function

The histone chaperone FACT plays important roles in essentially every chromatin-associated process and is an important indirect target of the curaxin class of anti-cancer drugs. Curaxins are aromatiс compounds that intercalate into DNA and can trap FACT in bulk chromatin, thus interfering with its distribution and its functions in cancer cells. Recent studies have provided mechanistic insight into how FACT and curaxins cooperate to promote unfolding of nucleosomes and chromatin fibers, resulting in genome-wide disruption of contact chromatin domain boundaries, perturbation of higher order chromatin organization, and global disregulation of gene expression. Here, we discuss the implications of these insights for cancer biology.

Prevention of Colorectal Carcinogenesis by DNA-Binding Small-Molecule Curaxin CBL0137 Involves Suppression of Wnt Signaling

Chemoprevention is considered a valid approach to reduce the incidence of colorectal cancer, one of the most common malignancies worldwide. Here, we investigated the tumor-preventive activity of curaxin CBL0137. This compound represents a new class of nonmutagenic DNA-binding small molecules that alter chromatin stability and inhibit the function of the histone chaperone FACT. Among downstream effects of CBL0137 treatment are activation of p53 and type I interferons and inhibition of NFκB, HSF1, and MYC. In addition, our data show that in both human and mouse colorectal cancer cells in vitro, CBL0137 inhibits the APC/WNT/β-catenin signaling pathway, which plays a key role in colon carcinogenesis. Using quantitative RT-PCR and microarray hybridization, we have demonstrated decreased expression of multiple components and downstream targets of the WNT pathway in colon cancer cells treated with CBL0137. At the same time, CBL0137 induced expression of WNT antagonists. Inhibition of WNT signaling activity by CBL0137 was also confirmed by luciferase reporter assay. Tumor-preventive activity of CBL0137 in vivo was tested in a murine model of colorectal carcinogenesis induced by 1,2-dimethylhydrazine (DMH), which is known to involve WNT pathway dysregulation. After DMH subcutaneous treatment, mice were administered CBL0137 in drinking water. Efficacy of CBL0137 in suppressing development of colorectal cancer in this model was evidenced by reduced incidence of adenocarcinomas and adenomas in both males and females and decrease in tumor multiplicity. These data support the prospective use of CBL0137 in chemoprevention of colorectal cancer as well as of other malignances associated with activated WNT signaling.

Targeting Histone Chaperone FACT Complex Overcomes 5-Fluorouracil Resistance in Colon Cancer

Fluorouracil (5-FU) remains a first-line chemotherapeutic agent for colorectal cancer. However, a subset of colorectal cancer patients who have defective mismatch-repair (dMMR) pathway show resistance to 5-FU. Here, we demonstrate that the efficacy of 5-FU in dMMR colorectal cancer cells is largely dependent on the DNA base excision repair (BER) pathway. Downregulation of APE1, a key enzyme in the BER pathway, decreases IC₅₀ of 5-FU in dMMR colorectal cancer cells by 10-fold. Furthermore, we discover that the facilitates chromatin transcription (FACT) complex facilitates 5-FU repair in DNA via promoting the recruitment and acetylation of APE1 (AcAPE1) to damage sites in chromatin. Downregulation of FACT affects 5-FU damage repair in DNA and sensitizes dMMR colorectal cancer cells to 5-FU. Targeting the FACT complex with curaxins, a class of small molecules, significantly improves the 5-FU efficacy in dMMR colorectal cancer in vitro (∼50-fold decrease in IC₅₀) and in vivo xenograft models. We show that primary tumor tissues of colorectal cancer patients have higher FACT and AcAPE1 levels compared with adjacent nontumor tissues. Additionally, there is a strong clinical correlation of FACT and AcAPE1 levels with colorectal cancer patients' response to chemotherapy. Together, our study demonstrates that targeting FACT with curaxins is a promising strategy to overcome 5-FU resistance in dMMR colorectal cancer patients.

Repurposing quinacrine for treatment-refractory cancer

Quinacrine, also known as mepacrine, has originally been used as an antimalarial drug for close to a century, but was recently rediscovered as an anticancer agent. The mechanisms of anticancer effects of quinacrine are not well understood. The anticancer potential of quinacrine was discovered in a screen for small molecule activators of p53, and was specifically shown to inhibit NFκB suppression of p53. However, quinacrine can cause cell death in cells that lack p53 or have p53 mutations, which is a common occurrence in many malignant tumors including high grade serous ovarian cancer. Recent reports suggest quinacrine may inhibit cancer cell growth through multiple mechanisms including regulating autophagy, FACT (facilitates chromatin transcription) chromatin trapping, and the DNA repair process. Additional reports also suggest quinacrine is effective against chemoresistant gynecologic cancer. In this review, we discuss anticancer effects of quinacrine and potential mechanisms of action with a specific focus on gynecologic and breast cancer where treatment-refractory tumors are associated with increased mortality rates. Repurposing quinacrine as an anticancer agent appears to be a promising strategy based on its ability to target multiple pathways, its selectivity against cancer cells, and the synergistic cytotoxicity when combined with other anticancer agents with limited side effects and good tolerability profile.

Potent antileukemic activity of curaxin CBL0137 against MLL-rearranged leukemia

Around 10% of acute leukemias harbor a rearrangement of the MLL/KMT2A gene, and the presence of this translocation results in a highly aggressive, therapy-resistant leukemia subtype with survival rates below 50%. There is a high unmet need to identify safer and more potent therapies for MLL-rearranged (MLL-r) leukemia that can be combined with established chemotherapeutics to decrease treatment-related toxicities. The curaxin, CBL0137, has demonstrated nongenotoxic anticancer and chemopotentiating effects in a number of preclinical cancer models and is currently in adult Phase I clinical trials for solid tumors and hematological malignancies. The aim of our study was to investigate whether CBL0137 has potential as a therapeutic and chemopotentiating compound in MLL-r leukemia through a comprehensive analysis of its efficacy in preclinical models of the disease. CBL0137 decreased the viability of a panel of MLL-r leukemia cell lines (n = 12) and xenograft cells derived from patients with MLL-r acute lymphoblastic leukemia (ALL, n = 3) in vitro with submicromolar IC50s. The small molecule drug was well-tolerated in vivo and significantly reduced leukemia burden in a subcutaneous MV4;11 MLL-r acute myeloid leukemia model and in patient-derived xenograft models of MLL-r ALL (n = 5). The in vivo efficacy of standard of care drugs used in remission induction for pediatric ALL was also potentiated by CBL0137. CBL0137 exerted its anticancer effect by trapping Facilitator of Chromatin Transcription (FACT) into chromatin, activating the p53 pathway and inducing an Interferon response. Our findings support further preclinical evaluation of CBL0137 as a new approach for the treatment of MLL-r leukemia.

SSRP1 promotes colorectal cancer progression and is negatively regulated by miR-28-5p

In this study, microarray data analysis, real‐time quantitative PCR and immunohistochemistry were used to detect the expression levels of SSRP1 in colorectal cancer (CRC) tissue and in corresponding normal tissue. The association between structure‐specific recognition protein 1 (SSRP1) expression and patient prognosis was examined by Kaplan‐Meier analysis. SSRP1 was knocked down and overexpressed in CRC cell lines, and its effects on proliferation, cell cycling, migration, invasion, cellular energy metabolism, apoptosis, chemotherapeutic drug sensitivity and cell phenotype‐related molecules were assessed. The growth of xenograft tumours in nude mice was also assessed. MiRNAs that potentially targeted SSRP1 were determined by bioinformatic analysis, Western blotting and luciferase reporter assays. We showed that SSRP1 mRNA levels were significantly increased in CRC tissue. We also confirmed that this upregulation was related to the terminal tumour stage in CRC patients, and high expression levels of SSRP1 predicted shorter disease‐free survival and faster relapse. We also found that SSRP1 modulated proliferation, metastasis, cellular energy metabolism and the epithelial‐mesenchymal transition in CRC. Furthermore, SSRP1 induced apoptosis and SSRP1 knockdown augmented the sensitivity of CRC cells to 5‐fluorouracil and cisplatin. Moreover, we explored the molecular mechanisms accounting for the dysregulation of SSRP1 in CRC and identified microRNA‐28‐5p (miR‐28‐5p) as a direct upstream regulator of SSRP1. We concluded that SSRP1 promotes CRC progression and is negatively regulated by miR‐28‐5p.

Chromatin Stability as a Target for Cancer Treatment

In this essay, I propose that DNA-binding anti-cancer drugs work more via chromatin disruption than DNA damage. Success of long-awaited drugs targeting cancer-specific drivers is limited by the heterogeneity of tumors. Therefore, chemotherapy acting via universal targets (e.g., DNA) is still the mainstream treatment for cancer. Nevertheless, the problem with targeting DNA is insufficient efficacy due to high toxicity. I propose that this problem stems from the presumption that DNA damage is critical for the anti-cancer activity of these drugs. DNA in cells exists as chromatin, and many DNA-targeting drugs alter chromatin structure by destabilizing nucleosomes and inducing histone eviction from chromatin. This effect has been largely ignored because DNA damage is seen as the major reason for anti-cancer activity. I discuss how DNA-binding molecules destabilize chromatin, why this effect is more toxic to tumoral than normal cells, and why cells die as a result of chromatin destabilization.

Curaxin CBL0137 Exerts Anticancer Activity via Diverse Mechanisms

Chemotherapy with or without radiation remains the first choice for most cancers. However, intolerant side effects and conventional drug resistance restrict actual clinical efficacy. Curaxin CBL0137 is designed to regulate p53 and nuclear factor-κB simultaneously and to prevent the resistance caused by a single target. Functionally, CBL0137 exhibits an antitumor activity in multiple cancers, including glioblastoma, renal cell carcinoma, melanoma, neuroblastoma, and small cell lung cancer (SCLC). Mechanistically, CBL0137 is originally identified to act by facilitates chromatin transcription (FACT) complex. Further investigations reveal that several pathways, such as NOTCH1 and heat shock factor 1 (HSF1), are involved in the process. CBL0137 has been reported to target cancer stem cells (CSCs) and enhance chemotherapy/monotherapy efficacy. The translational advance of CBL0137 into clinical practice is expected to provide a promising future for cancer treatment.

Mechanism of FACT removal from transcribed genes by anticancer drugs curaxins

Human FACT (facilitates chromatin transcription) is a multifunctional protein complex that has histone chaperone activity and facilitates nucleosome survival and transcription through chromatin. Anticancer drugs curaxins induce FACT trapping on chromatin of cancer cells (c-trapping), but the mechanism of c-trapping is not fully understood. Here, we show that in cancer cells, FACT is highly enriched within the bodies of actively transcribed genes. Curaxin-dependent c-trapping results in redistribution of FACT from the transcribed chromatin regions to other genomic loci. Using a combination of biochemical and biophysical approaches, we have demonstrated that FACT is bound to and unfolds nucleosomes in the presence of curaxins. This tight binding to the nucleosome results in inhibition of FACT-dependent transcription in vitro in the presence of both curaxins and competitor chromatin, suggesting a mechanism of FACT trapping on bulk nucleosomes (n-trapping).

Structure and function of the histone chaperone FACT - Resolving FACTual issues

FAcilitates Chromatin Transcription (FACT) has been considered essential for transcription through chromatin mostly based on cell-free experiments. However, FACT inactivation in cells does not cause a significant reduction in transcription. Moreover, not all mammalian cells require FACT for viability. Here we synthesize information from different organisms to reveal the core function(s) of FACT and propose a model that reconciles the cell-free and cell-based observations. We describe FACT structure and nucleosomal interactions, and their roles in FACT-dependent transcription, replication and repair. The variable requirements for FACT among different tumor and non-tumor cells suggest that various FACT-dependent processes have significantly different levels of relative importance in different eukaryotic cells. We propose that the stability of chromatin, which might vary among different cell types, dictates these diverse requirements for FACT to support cell viability. Since tumor cells are among the most sensitive to FACT inhibition, this vulnerability could be exploited for cancer treatment.

The FACT inhibitor CBL0137 Synergizes with Cisplatin in Small-Cell Lung Cancer by Increasing NOTCH1 Expression and Targeting Tumor-Initiating Cells

Traditional treatments of small-cell lung cancer (SCLC) with cisplatin, a standard-of-care therapy, spare the tumor-initiating cells (TIC) that mediate drug resistance. Here we report a novel therapeutic strategy that preferentially targets TICs in SCLC, in which cisplatin is combined with CBL0137, an inhibitor of the histone chaperone facilitates chromatin transcription (FACT), which is highly expressed in TICs. Combination of cisplatin and CBL0137 killed patient-derived and murine SCLC cell lines synergistically. In response to CBL0137 alone, TICs were more sensitive than non-TICs, in part, because CBL0137 increased expression of the tumor suppressor NOTCH1 by abrogating the binding of negative regulator SP3 to the NOTCH1 promoter, and in part because treatment decreased the high expression of stem cell transcription factors. The combination of cisplatin and CBL0137 greatly reduced the growth of a patient-derived xenograft in mice and also the growth of a syngeneic mouse SCLC tumor. Thus, CBL0137 can be a highly effective drug against SCLC, especially in combination with cisplatin.Significance: These findings reveal a novel therapeutic regimen for SCLC, combining cisplatin with an inhibitor that preferentially targets tumor-initiating cells. Cancer Res; 78(9); 2396-406. ©2018 AACR.

TRAIN (Transcription of Repeats Activates INterferon) in response to chromatin destabilization induced by small molecules in mammalian cells

Cellular responses to the loss of genomic stability are well-established, while how mammalian cells respond to chromatin destabilization is largely unknown. We previously found that DNA demethylation on p53-deficient background leads to transcription of repetitive heterochromatin elements, followed by an interferon response, a phenomenon we named TRAIN (Transcription of Repeats Activates INterferon). Here, we report that curaxin, an anticancer small molecule, destabilizing nucleosomes via disruption of histone/DNA interactions, also induces TRAIN. Furthermore, curaxin inhibits oncogene-induced transformation and tumor growth in mice in an interferon-dependent manner, suggesting that anticancer activity of curaxin, previously attributed to p53-activation and NF-kappaB-inhibition, may also involve induction of interferon response to epigenetic derepression of the cellular 'repeatome'. Moreover, we observed that another type of drugs decondensing chromatin, HDAC inhibitor, also induces TRAIN. Thus, we proposed that TRAIN may be one of the mechanisms ensuring epigenetic integrity of mammalian cells via elimination of cells with desilenced chromatin.

Level of FACT defines the transcriptional landscape and aggressive phenotype of breast cancer cells

Although breast cancer (BrCa) may be detected at an early stage, there is a shortage of markers that predict tumor aggressiveness and a lack of targeted therapies. Histone chaperone FACT, expressed in a limited number of normal cells, is overexpressed in different types of cancer, including BrCa. Recently, we found that FACT expression in BrCa correlates with markers of aggressive BrCa, which prompted us to explore the consequences of FACT inhibition in BrCa cells with varying levels of FACT.

FACT inhibition using a small molecule or shRNA caused reduced growth and viability of all BrCa cells tested. Phenotypic changes were more severe in high- FACT cells (death or growth arrest) than in low-FACT cells (decreased proliferation). Though inhibition had no effect on the rate of general transcription, expression of individual genes was changed in a cell-specific manner. Initially distinct transcriptional profiles of BrCa cells became similar upon equalizing FACT expression. In high-FACT cells, FACT supports expression of genes involved in the regulation of cell cycle, DNA replication, maintenance of an undifferentiated cell state and regulated by the activity of several proto-oncogenes. In low-FACT cells, the presence of FACT reduces expression of genes encoding enzymes of steroid metabolism that are characteristic of differentiated mammary epithelia.

Thus, we propose that FACT is both a marker and a target of aggressive BrCa cells, whose inhibition results in the death of BrCa or convertion of them to a less aggressive subtype.

SSRP1 silencing inhibits the proliferation and malignancy of human glioma cells via the MAPK signaling pathway

Structure-specific recognition protein 1 (SSRP1) has been considered as a potential biomarker, since aberrant high expression of SSRP1 has been detected in numerous malignant tumors. However, the correlation between the expression level of SSRP1 and glioma remains unclear. The present study attempted to investigate the role of SSRP1 in the pathogenesis of glioma. In the present study, our data revealed that SSRP1 overexpression was detected in glioma tissues at both the mRNA and protein levels using quantitative real-time RT-PCR and immunohistochemical analysis. We also demonstrated that the upregulated expression of SSRP1 was correlated with the World Health Organization (WHO) grade of glioma. The knockdown of SSRP1 by siRNA not only resulted in the inhibition of cell proliferation, but also significantly inhibited glioma cell migration and invasion. Mechanistic analyses revealed that SSRP1 depletion suppressed the activity of the phosphorylation of the MAPK signaling pathway. In conclusion, the present study indicated that SSRP1 regulated the proliferation and metastasis of glioma cells via the MAPK signaling pathway.

Anticancer drug candidate CBL0137, which inhibits histone chaperone FACT, is efficacious in preclinical orthotopic models of temozolomide-responsive and -resistant glioblastoma

Background

The survival rate for patients with glioblastoma (GBM) remains dismal. New therapies targeting molecular pathways dysregulated in GBM are needed. One such clinical-stage drug candidate, CBL0137, is a curaxin, small molecules which simultaneously downregulate nuclear factor-kappaB (NF-ĸB) and activate p53 by inactivating the chromatin remodeling complex, Facilitates Chromatin Transcription (FACT).

Methods

We used publicly available databases to establish levels of FACT subunit expression in GBM. In vitro, we evaluated the toxicity and effect of CBL0137 on FACT, p53, and NF-ĸB on U87MG and A1207 human GBM cells. In vivo, we implanted the cells orthotopically in nude mice and administered CBL0137 in various dosing regimens to assess brain and tumor accumulation of CBL0137, its effect on tumor cell proliferation and apoptosis, and on survival of mice with and without temozolomide (TMZ).

Results

FACT subunit expression was elevated in GBM compared with normal brain. CBL0137 induced loss of chromatin-unbound FACT, activated p53, inhibited NF-ĸB-dependent transcription, and was toxic to GBM cells. The drug penetrated the blood-brain barrier and accumulated in orthotopic tumors significantly more than normal brain tissue. It increased apoptosis and suppressed proliferation in both U87MG and A1207 tumors. Intravenous administration of CBL0137 significantly increased survival in models of early- through late-stage TMZ-responsive and -resistant GBM, with a trend toward significantly increasing the effect of TMZ in TMZ-responsive U87MG tumors.

Conclusion

CBL0137 targets GBM according to its proposed mechanism of action, crosses the blood-brain barrier, and is efficacious in both TMZ-responsive and -resistant orthotopic models, making it an attractive new therapy for GBM.

Prognostic value of histone chaperone FACT subunits expression in breast cancer

Understanding the underlying reasons for tumor aggressiveness, such as why some tumors grow slowly and locally, while others rapidly progress to a lethal metastatic disease, is still limited. This is especially critical in breast cancer (BrCa) due to its high prevalence and also due to the possibility that it can be detected early. Several oncogenes and tumor suppressors have been identified and are used in the prognosis and treatment of BrCa. However, even with these markers, the outcome within BrCa subtypes is highly variable. Chromatin organization has long been acknowledged as a factor that plays an important role in tumor progression, but molecular mechanisms defining chromatin dynamics are largely missing. We have recently found that histone chaperone FACT (facilitates chromatin transcription) is overexpressed in ~18–20% of BrCa cases. FACT is elevated upon transformation of mammary epithelial cells and is essential for viability of tumor cells. BrCa cells with high FACT have a more aggressive transcriptional program than those with low FACT cells. Based on this we propose that FACT may be a marker of aggressive BrCa. In this study, we aimed to comprehensively characterize the pattern of FACT expression in BrCa in relation to other molecular and clinical prognostic markers. We developed and tested an assay for the detection and quantitation of protein levels of both FACT subunits, SSRP1, and SPT16, in clinical samples. We compared the value of mRNA and protein as potential markers of disease aggressiveness using a large cohort of patients (n=1092). We demonstrated that only SSRP1 immunohistochemical staining is a reliable indicator of FACT levels in tumor samples. High SSRP1 correlated with known markers of poor prognosis, such as negative hormone receptor status, presence of Her2, high-grade tumors, and tumors of later clinical stage. At the same time, no strong correlation between SSRP1 expression and survival was detected when all samples were analyzed together. Clear trend toward longer survival of patients with low or no SSRP1 expression in tumor samples was seen in several subgroups of patients, and most importantly significant association of high SSRP1 expression with shorter disease-free survival was detected in patients with early-stage and low-grade BrCa, the category of patients with the highest demand in predictive marker of disease progression.

SSRP1 Cooperates with PARP and XRCC1 to Facilitate Single-Strand DNA Break Repair by Chromatin Priming

DNA single-strand breaks (SSB) are the most common form of DNA damage, requiring repair processes that to initiate must overcome chromatin barriers. The FACT complex comprised of the SSRP1 and SPT16 proteins is important for maintaining chromatin integrity, with SSRP1 acting as an histone H2A/H2B chaperone in chromatin disassembly during DNA transcription, replication, and repair. In this study, we show that SSRP1, but not SPT16, is critical for cell survival after ionizing radiation or methyl methanesulfonate-induced single-strand DNA damage. SSRP1 is recruited to SSB in a PARP-dependent manner and retained at DNA damage sites by N-terminal interactions with the DNA repair protein XRCC1. Mutational analyses showed how SSRP1 function is essential for chromatin decondensation and histone H2B exchange at sites of DNA strand breaks, which are both critical to prime chromatin for efficient SSB repair and cell survival. By establishing how SSRP1 facilitates SSB repair, our findings provide a mechanistic rationale to target SSRP1 as a general approach to selectively attack cancer cells. Cancer Res; 77(10); 2674-85. ©2017 AACR.

Preclinical Validation of a Single-Treatment Infusion Modality That Can Eradicate Extremity Melanomas

Isolated limb perfusion (ILP) with the chemotherapeutic agent melphalan is an effective treatment option for extremity in-transit melanoma but is toxic and technically challenging to deliver locoregionally. CBL0137 is an experimental clinical drug with broad anticancer activity in animal models, owing to its ability to bind DNA in a nongenotoxic manner and inactivate the FACT chromatin modulator essential for tumor cell viability. Here, we report that CBL0137 delivered by ILP in a murine melanoma model is as efficacious as melphalan, displaying antitumor activity at doses corresponding to only a fraction of the systemic MTD of CBL0137. The ability to bind DNA quickly combined with a favorable safety profile made it possible to substitute CBL0137 in the ILP protocol, using an intra-arterial infusion method, to safely achieve effective tumor suppression. Our findings of a preclinical proof of concept for CBL0137 and its administration via intra-arterial infusion as a superior treatment compared with melphalan ILP allows for locoregional treatment anywhere a catheter can be placed. Cancer Res; 76(22); 6620-30. ©2016 AACR.

Discovery of a Carbazole-Derived Lead Drug for Human African Trypanosomiasis

The protozoan parasite Trypanosoma brucei causes the fatal illness human African trypanosomiasis (HAT). Standard of care medications currently used to treat HAT have severe limitations, and there is a need to find new chemical entities that are active against infections of T. brucei. Following a "drug repurposing" approach, we tested anti-trypanosomal effects of carbazole-derived compounds called "Curaxins". In vitro screening of 26 compounds revealed 22 with nanomolar potency against axenically cultured bloodstream trypanosomes. In a murine model of HAT, oral administration of compound 1 cured the disease. These studies established 1 as a lead for development of drugs against HAT. Pharmacological time-course studies revealed the primary effect of 1 to be concurrent inhibition of mitosis coupled with aberrant licensing of S-phase entry. Consequently, polyploid trypanosomes containing 8C equivalent of DNA per nucleus and three or four kinetoplasts were produced. These effects of 1 on the trypanosome are reminiscent of "mitotic slippage" or endoreplication observed in some other eukaryotes.

Blockage of SSRP1/Ets-1/Pim-3 signalling enhances chemosensitivity of nasopharyngeal carcinoma to docetaxel in vitro

Nasopharyngeal carcinoma (NPC) is a rare cancer in most parts of the world, but is prevalent in South China area. Besides, therapeutic outcome is still unsatisfactory for patients with refractory and relapsed NPC, even though receiving a second line of docetaxel-based chemotherapy. These reasons require a better understanding of mechanisms underlying the carcinogenesis, malignancy and chemoresistance. In the basis of our previous finding of SSRP1 over-expression in NPC cell lines, this study continuously discovered up-regulated Ets-1, phosphor-Ets-1 and Pim-3 in NPC tissues with immunohistochemistry assay and revealed a close correlation of these up-regulated proteins with NPC proliferation and invasion. Using gene-silencing technology followed by western blot and immunocytochemistry detections, SSRP1 was found to facilitate the translocation of phosphor-Ets-1 from cytoplasm to cell nucleus, but have marginal effect on Ets-1 expression and phosphorylation. Pim-3 was positively regulated by Ets-1. In NPC HNE-1 cells, all SSRP1, Ets-1 and Pim-3 knockdown diminished the cell proliferation, enhanced the apoptosis, as well as inhibited the autophagy, invasion and clonogenicity in the presence or absence of docetaxel at IC25. Exposure of HNE-1 cells to docetaxel (IC25) alone had modest effect on cell proliferation and autophagy, and was not as effective as docetaxel treatment after knockdown of SSRP1, Ets-1 or Pim-3 on induction of the apoptosis and on inhibition of the invasion and clonogenicity. Our data indicate that SSRP1/Ets-1/Pim-3 signalling is tightly associated with the proliferation, apoptosis, autophagy, invasion and clonogenicity of NPC cells, and blockage of this signalling facilitates chemosensitivity of the cells to docetaxel.

Pharmacological Targeting of the Histone Chaperone Complex FACT Preferentially Eliminates Glioblastoma Stem Cells and Prolongs Survival in Preclinical Models

The nearly universal recurrence of glioblastoma (GBM) is driven in part by a treatment-resistant subpopulation of GBM stem cells (GSC). To identify improved therapeutic possibilities, we combined the EGFR/HER2 inhibitor lapatinib with a novel small molecule, CBL0137, which inhibits FACT (facilitates chromatin transcription), a histone chaperone complex predominantly expressed in undifferentiated cells. Lapatinib and CBL0137 synergistically inhibited the proliferation of patient-derived GBM cells. Compared with non-stem tumor cells (NSTC) enriched from the same specimens, the GSCs were extremely sensitive to CBL0137 monotherapy or FACT knockdown. FACT expression was elevated in GSCs compared with matched NSTCs and decreased in GSCs upon differentiation. Acute exposure of GSCs to CBL0137 increased asymmetric cell division, decreased GSC marker expression, and decreased the capacity of GSCs to form tumor spheres in vitro and to initiate tumors in vivo Oral administration of CBL0137 to mice bearing orthotopic GBM prolonged their survival. Knockdown of FACT reduced the expression of genes encoding several core stem cell transcription factors (SOX2, OCT4, NANOG, and OLIG2), and FACT occupied the promoters of these genes. FACT expression was elevated in GBM tumors compared with non-neoplastic brain tissues, portended a worse prognosis, and positively correlated with GSC markers and stem cell gene expression signatures. Preferential targeting of GSCs by CBL0137 and synergy with EGFR inhibitors support the development of clinical trials combining these two agents in GBM. Cancer Res; 76(8); 2432-42. ©2016 AACR.

SSRP1 Contributes to the Malignancy of Hepatocellular Carcinoma and Is Negatively Regulated by miR-497

The aim of this study is to clarify the clinical implication and functional role of structure specific recognition protein 1 (SSRP1) in hepatocellular carcinoma (HCC) and explore the underlying mechanism of aberrant high expression of SSRP1 in cancers. In the present investigation, we validated that SSRP1 was upregulated in HCC samples. We also demonstrated that its upregulation was associated with several clinicopathologic features such as higher serum AFP level, larger tumor size, and higher T stage of HCC patients; and its high expression indicated shorter overall survival and faster recurrence. To investigate the role of SSRP1 in HCC progression, both loss- and gain-function models were established. We demonstrated that SSPR1 modulated both proliferation and metastasis of HCC cells in vitro and vivo. Furthermore, we demonstrated that SSRP1-modulated apoptosis process and its knockdown increased the sensitivity of HCC cells to doxorubicin, 5-Fluorouracil, and cisplatin. We also identified microRNA-497 (miR-497) as a posttranscriptional regulator of SSRP1. Ectopic expression of miR-497 inhibited 3'-untranslated-region–coupled luciferase activity and suppressed endogenous SSRP1 expression at both messenger RNA and protein levels. For the first time, we proved that SSRP1 upregulation contributed to HCC development and the tumor-suppressive miR-497 served as its negative regulator.

CUL4A contributes to the biology of basal-like breast tumors through modulation of cell growth and antitumor immune response

The CUL4A E3 ubiquitin ligase is involved in the regulation of many cellular processes and its amplification and/or overexpression has been observed in breast cancer. The 13q34 amplification, which is associated with the basal-like breast cancer subtype, has been proposed as one of the mechanism behind CUL4A up-regulation. However, the specific contribution of CUL4A to the biology of basal-like breast tumors has not yet been elucidated. In this work, by using cellular models of basal phenotype, we show the inhibitory effect of CUL4A silencing in the proliferation and growth of breast cancer cells both, in vitro and in vivo. We also demonstrate the transforming capacity of CUL4A exogenous overexpression in the 184B5 human mammary epithelial cells in vitro. Our results suggest a synergistic effect between CUL4A high levels and the activation of the RAS pathway in the tumorigenesis of basal-like breast cancer tumors. In addition, by using a proteomics approach we have defined novel candidate proteins and pathways that might mediate the oncogenic effect of CUL4A. In particular, we report a putative role of CUL4A in bypassing the immune system in breast cancer through the down-regulation of several molecules involved in the immune surveillance. These findings provide insight into the oncogenic properties of CUL4A in basal-like breast cancer and highlight the therapeutic opportunities to target CUL4A.

Epigenetic plasticity: a central regulator of epithelial-to-mesenchymal transition in cancer

Tumor metastasis is the major cause of mortality and morbidity in most solid cancers. A growing body of evidence suggests that the epithelial-to-mesenchymal transition (EMT) plays a central role during tumor metastasis and frequently imparts a stem cell-like phenotype and therapeutic resistance to tumor cells. The induction of EMT is accompanied by a dynamic reprogramming of the epigenome involving changes in DNA methylation and several post-translational histone modifications. These changes in turn promote the expression of mesenchymal genes or repress those associated with an epithelial phenotype. Importantly, in order for metastatic colonization and the formation of macrometastases to occur, tumor cells frequently undergo a reversal of EMT referred to as the mesenchymal-to-epithelial transition (MET). Thus, a high degree of epigenetic plasticity is required in order to induce and reverse EMT during tumor progression. In this review, we describe various epigenetic regulatory mechanisms employed by tumor cells during EMT and elaborate on the importance of the histone code in controlling both the expression and activity of EMT-associated transcription factors. We propose that a more thorough understanding of the epigenetic mechanisms controlling EMT may provide new opportunities which may be harnessed for improved and individualized cancer therapy based on defined molecular mechanisms.

A role for FACT in repopulation of nucleosomes at inducible genes

Xenobiotic drugs induce Pleiotropic Drug Resistance (PDR) genes via the orthologous Pdr1/Pdr3 transcription activators. We previously identified the Mediator transcription co-activator complex as a key target of Pdr1 orthologs and demonstrated that Pdr1 interacts directly with the Gal11/Med15 subunit of the Mediator complex. Based on an interaction between Pdr1 and the FACT complex, we show that strains with spt16 or pob3 mutations are sensitive to xenobiotic drugs and display diminished PDR gene induction. Although FACT acts during the activation of some genes by assisting in the nucleosomes eviction at promoters, PDR promoters already contain nucleosome-depleted regions (NDRs) before induction. To determine the function of FACT at PDR genes, we examined the kinetics of RNA accumulation and changes in nucleosome occupancy following exposure to a xenobiotic drug in wild type and FACT mutant yeast strains. In the presence of normal FACT, PDR genes are transcribed within 5 minutes of xenobiotic stimulation and transcription returns to basal levels by 30–40 min. Nucleosomes are constitutively depleted in the promoter regions, are lost from the open reading frames during transcription, and the ORFs are wholly repopulated with nucleosomes as transcription ceases. While FACT mutations cause minor delays in activation of PDR genes, much more pronounced and significant defects in nucleosome repopulation in the ORFs are observed in FACT mutants upon transcription termination. FACT therefore has a major role in nucleosome redeposition following cessation of transcription at the PDR genes, the opposite of its better-known function in nucleosome disassembly.

Facilitates chromatin transcription complex is an "accelerator" of tumor transformation and potential marker and target of aggressive cancers

The facilitates chromatin transcription (FACT) complex is involved in chromatin remodeling during transcription, replication, and DNA repair. FACT was previously considered to be ubiquitously expressed and not associated with any disease. However, we discovered that FACT is the target of a class of anticancer compounds and is not expressed in normal cells of adult mammalian tissues, except for undifferentiated and stem-like cells. Here, we show that FACT expression is strongly associated with poorly differentiated aggressive cancers with low overall survival. In addition, FACT was found to be upregulated during in vitro transformation and to be necessary, but not sufficient, for driving transformation. FACT also promoted survival and growth of established tumor cells. Genome-wide mapping of chromatin-bound FACT indicated that FACT's role in cancer most likely involves selective chromatin remodeling of genes that stimulate proliferation, inhibit cell death and differentiation, and regulate cellular stress responses.