Combination of EZH2 and ATM inhibition in BAP1-deficient mesothelioma.

BACKGROUND: More than half of mesothelioma tumours show alterations in the tumour suppressor gene BAP1. BAP1-deficient mesothelioma is shown to be sensitive to EZH2 inhibition in preclinical settings but only showed modest efficacy in clinical trial. Adding a second inhibitor could potentially elevate EZH2i treatment efficacy while preventing acquired resistance at the same time. METHODS: A focused drug synergy screen consisting of 20 drugs was performed by combining EZH2 inhibition with a panel of anti-cancer compounds in mesothelioma cell lines. The compounds used are under preclinical investigation or already used in the clinic. The synergistic potential of the combinations was assessed by using the Bliss model. To validate our findings, in vivo xenograft experiments were performed. RESULTS: Combining EZH2i with ATMi was found to have synergistic potential against BAP1-deficient mesothelioma in our drug screen, which was validated in clonogenicity assays. Tumour growth inhibition potential was significantly increased in BAP1-deficient xenografts. In addition, we observe lower ATM levels upon depletion of BAP1 and hypothesise that this might be mediated by E2F1. CONCLUSIONS: We demonstrated the efficacy of the combination of ATM and EZH2 inhibition against BAP1-deficient mesothelioma in preclinical models, indicating the potential of this combination as a novel treatment modality using BAP1 as a biomarker.

Bioactive molecules from fungal endophytes and their applications in pharmaceutical industries: challenges and future scope.

Medicinal plants are an important source of bioactive compounds and have been used to isolate various bioactive compounds having industrial applications. The demand for plants derived bioactive molecules is increasing gradually. However, the extensive use of these plants to extract bioactive molecules has threatened many plant species. Moreover, extracting bioactive molecules from these plants is laborious, costly, and time-consuming. So, some alternative sources and strategies are urgently needed to produce these bioactive molecules similar to that of plant origin. However, the interest in new bioactive molecules has recently shifted from plants to endophytic fungi because many fungi produce bioactive molecules similar to their host plant. Endophytic fungi live in mutualistic association within the healthy plant tissue without causing disease symptoms to the host plant. These fungi are a treasure house of novel bioactive molecules having broad pharmaceutical, industrial, and agricultural applications. The rapid increase in publications in this domain over the last three decades proves that natural product biologists and chemists are paying great attention to the natural bioactive products from endophytic fungi. Though endophytes are source of novel bioactive molecules but there is need of advanced technologies like clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR-Cas9) and epigenetic modifiers to enhance the production of compounds having industrial applications. This review provides an overview of the various industrial applications of bioactive molecules produced by endophytic fungi and the rationale behind selecting specific plants for fungal endophyte isolation. Overall, this study presents the current state of knowledge and highlights the potential of endophytic fungi for developing alternative therapies for drug-resistant infections.

Long noncoding RNA-mediated maintenance of DNA methylation and transcriptional gene silencing.

Establishment of silencing by noncoding RNAs (ncRNAs) via targeting of chromatin remodelers is relatively well investigated; however, their role in the maintenance of silencing is poorly understood. Here, we explored the functional role of the long ncRNA Kcnq1ot1 in the maintenance of transcriptional gene silencing in the one mega-base Kcnq1 imprinted domain in a transgenic mouse model. By conditionally deleting the Kcnq1ot1 ncRNA at different stages of mouse development, we suggest that Kcnq1ot1 ncRNA is required for the maintenance of the silencing of ubiquitously imprinted genes (UIGs) at all developmental stages. In addition, Kcnq1ot1 ncRNA is also involved in guiding and maintaining the CpG methylation at somatic differentially methylated regions flanking the UIGs, which is a hitherto unknown role for a long ncRNA. On the other hand, silencing of some of the placental-specific imprinted genes (PIGs) is maintained independently of Kcnq1ot1 ncRNA. Interestingly, the non-imprinted genes (NIGs) that escape RNA-mediated silencing are enriched with enhancer-specific modifications. Taken together, this study illustrates the gene-specific maintenance mechanisms operational at the Kcnq1 locus for tissue-specific transcriptional gene silencing and activation.

Combined Inhibition of EZH2 and FGFR is Synergistic in BAP1-deficient Malignant Mesothelioma.

Malignant mesothelioma is a highly aggressive tumor with a survival of only 4-18 months after diagnosis. Treatment options for this disease are limited. Immune checkpoint blockade using ipilimumab and nivolumab has recently been approved as a frontline therapy, but this led to only a small improvement in overall patient survival. As more than half of patients with mesothelioma have alterations in the gene encoding for BAP1 this could be a potential marker for targeted therapies. In this study, we investigated the synergistic potential of combining EZH2 inhibition together with FGFR inhibition for treatment of BAP1-deficient malignancies. The efficacy of the combination was evaluated using human and murine preclinical models of mesothelioma and uveal melanoma in vitro. The efficacy of the combination was further validated in vivo by using BAP1-deficient mesothelioma xenografts and autochthonous mouse models. In vitro data showed sensitivity to the combined inhibition in BAP1-deficient mesothelioma and uveal melanoma tumor cell lines but not for BAP1-proficient subtypes. In vivo data showed susceptibility to the combination of BAP1-deficient xenografts and demonstrated an increase of survival in autochthonous models of mesothelioma. These results highlight the potential of this novel drug combination for the treatment of mesothelioma using BAP1 as a biomarker. Given these encouraging preclinical results, it will be important to clinically explore dual EZH2/FGFR inhibition in patients with BAP1-deficient malignant mesothelioma and justify further exploration in other BAP1 loss-associated tumors. SIGNIFICANCE: Despite the recent approval of immunotherapy, malignant mesothelioma has limited treatment options and poor prognosis. Here, we observe that EZH2 inhibitors dramatically enhance the efficacy of FGFR inhibition, sensitising BAP1-mutant mesothelioma and uveal melanoma cells. The striking synergy of EZH2 and FGFR inhibition supports clinical investigations for BAP1-mutant tumors.

Characterization of the RNA content of chromatin.

Noncoding RNA (ncRNA) constitutes a significant portion of the mammalian transcriptome. Emerging evidence suggests that it regulates gene expression in cis or trans by modulating the chromatin structure. To uncover the functional role of ncRNA in chromatin organization, we deep sequenced chromatin-associated RNAs (CARs) from human fibroblast (HF) cells. This resulted in the identification of 141 intronic regions and 74 intergenic regions harboring CARs. The intronic and intergenic CARs show significant conservation across 44 species of placental mammals. Functional characterization of one of the intergenic CARs, Intergenic10, revealed that it regulates gene expression of neighboring genes through modulating the chromatin structure in cis. Our data suggest that ncRNA is an integral component of chromatin and that it may regulate various biological functions through fine-tuning of the chromatin architecture.

Kcnq1ot1 noncoding RNA mediates transcriptional gene silencing by interacting with Dnmt1.

A long noncoding RNA, Kcnq1ot1, regulates the expression of both ubiquitously and tissue-specific imprinted genes within the Kcnq1 domain. However, the functional sequences of the Kcnq1ot1 RNA that mediate lineage-specific imprinting are unknown. Here, we have generated a knockout mouse with a deletion encompassing an 890-bp silencing domain (Delta890) downstream of the Kcnq1ot1 promoter. Maternal transmission of the Delta890 allele has no effect on imprinting, whereas paternal inheritance of the deletion leads to selective relaxation of the imprinting of ubiquitously imprinted genes to a variable extent in a tissue-specific manner. Interestingly, the deletion affects DNA methylation at somatically acquired differentially methylated regions (DMRs), but does not affect the histone modifications of the ubiquitously imprinted genes. Importantly, we found that Kcnq1ot1 recruits Dnmt1 to somatic DMRs by interacting with Dnmt1, and that this interaction was significantly reduced in the Delta890 mice. Thus, the ubiquitous and placental-specific imprinting of genes within the Kcnq1 domain might be mediated by distinct mechanisms, and Kcnq1ot1 RNA might mediate the silencing of ubiquitously imprinted genes by maintaining allele-specific methylation through its interactions with Dnmt1.

Genetic screens reveal new targetable vulnerabilities in BAP1-deficient mesothelioma.

More than half of patients with malignant mesothelioma show alterations in the BAP1 tumor-suppressor gene. Being a member of the Polycomb repressive deubiquitinating (PR-DUB) complex, BAP1 loss results in an altered epigenome, which may create new vulnerabilities that remain largely unknown. Here, we performed a CRISPR-Cas9 kinome screen in mesothelioma cells that identified two kinases in the mevalonate/cholesterol biosynthesis pathway. Furthermore, our analysis of chromatin, expression, and genetic perturbation data in mesothelioma cells suggests a dependency on PR complex 2 (PRC2)-mediated silencing. Pharmacological inhibition of PRC2 elevates the expression of cholesterol biosynthesis genes only in BAP1-deficient mesothelioma, thereby sensitizing these cells to the combined targeting of PRC2 and the mevalonate pathway. Finally, by subjecting autochthonous Bap1-deficient mesothelioma mice or xenografts to mevalonate pathway inhibition (zoledronic acid) and PRC2 inhibition (tazemetostat), we demonstrate a potent anti-tumor effect, suggesting a targeted combination therapy for Bap1-deficient mesothelioma.

Long Non-Coding RNAs: Tools for Understanding and Targeting Cancer Pathways.

The regulatory nature of long non-coding RNAs (lncRNAs) has been well established in various processes of cellular growth, development, and differentiation. Therefore, it is vital to examine their contribution to cancer development. There are ample examples of lncRNAs whose cellular levels are significantly associated with clinical outcomes. However, whether these non-coding molecules can work as either key drivers or barriers to cancer development remains unknown. The current review aims to discuss some well-characterised lncRNAs in the process of oncogenesis and extrapolate the extent of their decisive contribution to tumour development. We ask if these lncRNAs can independently initiate neoplastic lesions or they always need the modulation of well characterized oncogenes or tumour suppressors to exert their functional properties. Finally, we discuss the emerging genetic approaches and appropriate animal and humanised models that can significantly contribute to the functional dissection of lncRNAs in cancer development and progression.

Regulation of the mammalian epigenome by long noncoding RNAs.

Genomic analyses have demonstrated that although less than 2% of the mammalian genome encodes proteins, at least two thirds is transcribed. Many nontranslated RNAs have now been characterized, and several long transcripts, ranging from 0.5 to over 100 kb, have been shown to regulate gene expression by modifying chromatin structure. Functions uncovered at a few well characterized loci demonstrate a wide diversity of mechanisms by which long noncoding RNAs can regulate chromatin over a single promoter, a gene cluster, or an entire chromosome, in order to activate or silence genes in cis or in trans. In reviewing the activities of these ncRNAs, we will look for common features in their interactions with the chromatin modifying machinery, and highlight new experimental approaches by which to address outstanding issues in ncRNA-dependent regulation of gene expression in development, disease and evolution.

Combined deletion of Bap1, Nf2, and Cdkn2ab causes rapid onset of malignant mesothelioma in mice.

We have generated mouse models of malignant mesothelioma (MM) based upon disruption of the Bap1, Nf2, and Cdkn2ab tumor suppressor loci in various combinations as also frequently observed in human MM. Inactivation of all three loci in the mesothelial lining of the thoracic cavity leads to a highly aggressive MM that recapitulates the histological features and gene expression profile observed in human patients. The tumors also show a similar inflammatory phenotype. Bap1 deletion alone does not cause MM but dramatically accelerates MM development when combined with Nf2 and Cdkn2ab (hereafter BNC) disruption. The accelerated tumor development is accompanied by increased Polycomb repression and EZH2-mediated redistribution of H3K27me3 toward promoter sites with concomitant activation of PI3K and MAPK pathways. Treatment of BNC tumor-bearing mice with cisplatin and pemetrexed, the current frontline treatment, prolongs survival. This makes the autochthonous mouse model described here very well suited to explore the pathogenesis of MM and validate new treatment regimens for MM, including immunotherapy.

EZH2 Is Overexpressed in BRCA1-like Breast Tumors and Predictive for Sensitivity to High-Dose Platinum-Based Chemotherapy.

PURPOSE: BRCA1-deficient breast cancers carry a specific DNA copy-number signature ("BRCA1-like") and are hypersensitive to DNA double-strand break (DSB) inducing compounds. Here, we explored whether (i) EZH2 is overexpressed in human BRCA1-deficient breast tumors and might predict sensitivity to DSB-inducing drugs; (ii) EZH2 inhibition potentiates cisplatin efficacy in Brca1-deficient murine mammary tumors. EXPERIMENTAL DESIGN: EZH2 expression was analyzed in 497 breast cancers using IHC or RNA sequencing. We classified 370 tumors by copy-number profiles as BRCA1-like or non-BRCA1-like and examined its association with EZH2 expression. Additionally, we assessed BRCA1 loss through mutation or promoter methylation status and investigated the predictive value of EZH2 expression in a study population of breast cancer patients treated with adjuvant high-dose platinum-based chemotherapy compared with standard anthracycline-based chemotherapy. To explore whether EZH2 inhibition by GSK126 enhances sensitivity to platinum drugs in EZH2-overexpressing breast cancers we used a Brca1-deficient mouse model. RESULTS: The highest EZH2 expression was found in BRCA1-associated tumors harboring a BRCA1 mutation, BRCA1-promoter methylation or were classified as BRCA1 like. We observed a greater benefit from high-dose platinum-based chemotherapy in BRCA1-like and non-BRCA1-like patients with high EZH2 expression. Combined treatment with the EZH2 inhibitor GSK126 and cisplatin decreased cell proliferation and improved survival in Brca1-deficient mice in comparison with single agents. CONCLUSIONS: Our findings demonstrate that EZH2 is expressed at significantly higher levels in BRCA1-deficient breast cancers. EZH2 overexpression can identify patients with breast cancer who benefit significantly from intensified DSB-inducing platinum-based chemotherapy independent of BRCA1-like status. EZH2 inhibition improves the antitumor effect of platinum drugs in Brca1-deficient breast tumors in vivo.

Long noncoding RNAs and neuroblastoma.

Neuroblastoma is a disease that affects infants and despite intense multimodal therapy, high-risk patients have low survival rates (<50%). In recent years long noncoding RNAs (lncRNAs) have become the cutting edge of cancer research with inroads made in understanding their roles in multiple cancer types, including prostate and breast cancers. The roles of lncRNAs in neuroblastoma have just begun to be elucidated. This review summarises where we are with regards to lncRNAs in neuroblastoma. The known mechanistic roles of lncRNAs during neuroblastoma pathogenesis are discussed, as well as the relationship between lncRNA expression and the differentiation capacity of neuroblastoma cells. We speculate about the use of some of these lncRNAs, such as those mapping to the 6p22 hotspot, as biomarkers for neuroblastoma prognosis and treatment. This novel way of thinking about both neuroblastoma and lncRNAs brings a new perspective to the prognosis and treatment of high-risk patients.

Temporal separation of replication and transcription during S-phase progression.

Transcriptional events during S-phase are critical for cell cycle progression. Here, by using a nascent RNA capture assay coupled with high-throughput sequencing, we determined the temporal patterns of transcriptional events that occur during S-phase. We show that genes involved in critical S-phase-specific biological processes such as nucleosome assembly and DNA repair have temporal transcription patterns across S-phase that are not evident from total RNA levels. By comparing transcription timing with replication timing in S-phase, we show that early replicating genes show increased transcription late in S-phase whereas late replicating genes are predominantly transcribed early in S-phase. Global anti-correlation between replication and transcription timing was observed only based on nascent RNA but not total RNA. Our data provides a detailed view of ongoing transcriptional events during the S-phase of cell cycle, and supports that transcription and replication are temporally separated.

The risk-associated long noncoding RNA NBAT-1 controls neuroblastoma progression by regulating cell proliferation and neuronal differentiation.

Neuroblastoma is an embryonal tumor of the sympathetic nervous system and the most common extracranial tumor of childhood. By sequencing transcriptomes of low- and high-risk neuroblastomas, we detected differentially expressed annotated and nonannotated long noncoding RNAs (lncRNAs). We identified a lncRNA neuroblastoma associated transcript-1 (NBAT-1) as a biomarker significantly predicting clinical outcome of neuroblastoma. CpG methylation and a high-risk neuroblastoma associated SNP on chromosome 6p22 functionally contribute to NBAT-1 differential expression. Loss of NBAT-1 increases cellular proliferation and invasion. It controls these processes via epigenetic silencing of target genes. NBAT-1 loss affects neuronal differentiation through activation of the neuronal-specific transcription factor NRSF/REST. Thus, loss of NBAT-1 contributes to aggressive neuroblastoma by increasing proliferation and impairing differentiation of neuronal precursors.