Exploring the prognostic value of circular RNAs in pancreatic ductal adenocarcinoma using genome-wide expression profiling.

BACKGROUND/OBJECTIVES: Median survival of pancreatic ductal adenocarcinoma (PDAC) is around eight months and new prognostic tools are needed. Circular RNAs (circRNAs) have gained interest in different types of cancer. However, only a few studies have evaluated their potential in PDAC. We aimed to identify the most differentially expressed circRNAs in PDAC compared to controls and to explore their potential as prognostic markers. METHODS: Using frozen specimens with PDAC and controls, we performed RNA sequencing and identified 20,440 unique circRNAs. A custom code set of capture- and reporter probes for NanoString nCounter analysis was designed to target 152 circRNAs, based on abundancy, differential expression and a literature study. Expression of these 152 circRNAs was examined in 108 formalin-fixed and paraffin-embedded surgical PDAC specimens and controls. The spatial expression of one of the most promising candidates, ciRS-7 (hsa_circ_0001946), was evaluated by chromogenic in situ hybridization (CISH) using multi-punch tissue microarrays (TMAs) and digital imaging analysis. RESULTS: Based on circRNA expression profiles, we identified different PDAC subclusters. The 30 most differentially expressed circRNAs showed log2 fold changes from -3.43 to 0.94, where circNRIP1 (hsa_circ_0004771), circMBOAT2 (hsa_circ_0007334) and circRUNX1 (hsa_circ_0002360) held significant prognostic value in multivariate analysis. CiRS-7 was absent in PDAC cells but highly expressed in the tumor microenvironment. CONCLUSIONS: We identified several new circRNAs with biomarker potential in surgically treated PDAC, three of which showed an independent prognostic value. We also found that ciRS-7 is absent in cancer cells but abundant in tumor microenvironment and may hold potential as marker of activated stroma.

The Transcriptional Landscape of Coding and Noncoding RNAs in Recurrent and Nonrecurrent Colon Cancer.

A considerable number of colon cancer patients with local or local advanced disease suffer from recurrence and there is an urgent need for better prognostic biomarkers in this setting. Here, the transcriptomic landscape of mRNAs, long noncoding RNAs, snRNAs, small nucleolar RNAs (snoRNAs), small Cajal body-specific RNAs, pseudogenes, and circular RNAs, as well as RNAs denoted as miscellaneous RNAs, was profiled by total RNA sequencing. In addition to well-known coding and noncoding RNAs, differential expression analysis also uncovered transcripts that have not been implicated previously in colon cancer, such as RNA5SP149, RNU4-2, and SNORD3A. Moreover, there was a profound global up-regulation of snRNA pseudogenes, snoRNAs, and rRNA pseudogenes in more advanced tumors. A global down-regulation of circular RNAs in tumors relative to normal tissues was observed, although only a few were expressed differentially between tumor stages. Many previously undescribed transcripts, including RNU6-620P, RNU2-20P, VTRNA1-3, and RNA5SP60, indicated strong prognostic biomarker potential in receiver operating characteristics analyses. In summary, this study unveiled numerous differentially expressed RNAs across various classes between recurrent and nonrecurrent colon cancer. Notably, there was a significant global up-regulation of snRNA pseudogenes, snoRNAs, and rRNA pseudogenes in advanced tumors. Many of these newly discovered candidates demonstrated a strong prognostic potential for stage II colon cancer.

Concurrent Inhibition of Akt and ERK Using TIC-10 Can Overcome Venetoclax Resistance in Mantle Cell Lymphoma.

Venetoclax, a BCL-2 inhibitor, has proven to be effective in several hematological malignancies, including mantle cell lymphoma (MCL). However, development of venetoclax resistance is inevitable and understanding its underlying molecular mechanisms can optimize treatment response. We performed a thorough genetic, epigenetic and transcriptomic analysis of venetoclax-sensitive and resistant MCL cell lines, also evaluating the role of the stromal microenvironment using human and murine co-cultures. In our model, venetoclax resistance was associated with abrogated TP53 activity through an acquired mutation and transcriptional downregulation leading to a diminished apoptotic response. Venetoclax-resistant cells also exhibited an upregulation of the PI3K/Akt pathway, and pharmacological inhibition of Akt and ERK with TIC-10 led to cell death in all venetoclax-resistant cell lines. Overall, we highlight the importance of targeted therapies, such as TIC-10, against venetoclax resistance-related pathways, which might represent future therapeutic prospects.

The emerging roles of circRNAs in cancer and oncology.

Over the past decade, circular RNAs (circRNAs) have emerged as a large class of primarily non-coding RNA molecules, many of which have key roles in cancer development and progression through diverse mechanisms of action. CircRNAs often have tissue-restricted and cancer-specific expression patterns, and accumulating data suggest that these molecules are of potential clinical relevance and utility. In particular, circRNAs have strong potential as diagnostic, prognostic and predictive biomarkers, which is underscored by their detectability in liquid biopsy samples such as in plasma, saliva and urine. However, technical issues in the detection and assessment of circRNAs as well as biological knowledge gaps need to be addressed to move this relatively young field of research forward and bring circRNAs to the forefront of clinical practice. Herein, we review the current knowledge regarding circRNA biogenesis, regulation and functions in cancer as well as their clinical potential as biomarkers, therapeutic agents and drug targets.

Genome-Wide Circular RNA Expression Patterns Reflect Resistance to Immunomodulatory Drugs in Multiple Myeloma Cells.

Immunomodulatory drugs (IMiDs), such as lenalidomide and pomalidomide, may induce significant remissions in multiple myeloma (MM) patients, but relapses are frequently observed and the underlying molecular mechanisms for this are not completely understood. Circular RNAs (circRNAs) constitute an emerging class of non-coding RNAs with important roles in cancer. Here, we profiled genome-wide expression patterns of circRNAs in IMiD-sensitive MM cells and their resistant counterparts as well as in IMiD-resistant cells treated with specific epigenetic drugs alone or in combination. We found that genome-wide circRNA expression patterns reflect IMiD sensitivity and ciRS-7 (also known as CDR1as) was the most downregulated circRNA upon acquired resistance. The depletion of ciRS-7 correlated with increased methylation levels of the promoter CpG island of its host gene, LINC00632. Expression of LINC00632 and ciRS-7 was partly restored by treatment with a combination of an EZH2 inhibitor (EPZ-6438) and a DNA methyl transferase inhibitor (5-azacytidine), which also restores the IMiD sensitivity of the cells. However, knockdown of ciRS-7 did not affect IMiD sensitivity and we found that ciRS-7 also becomes epigenetically silenced after prolonged cell culture without drug-exposure. In conclusion, we found that genome-wide circRNA expression patterns reflect IMiD sensitivity in an in vitro model of acquired resistance.

Spatial expression analyses of the putative oncogene ciRS-7 in cancer reshape the microRNA sponge theory.

Circular RNAs (circRNAs) have recently gained substantial attention in the cancer research field where most, including the putative oncogene ciRS-7 (CDR1as), have been proposed to function as competitive endogenous RNAs (ceRNAs) by sponging specific microRNAs. Here, we report the first spatially resolved cellular expression patterns of ciRS-7 in colon cancer and show that ciRS-7 is completely absent in the cancer cells, but highly expressed in stromal cells within the tumor microenvironment. Additionally, our data suggest that this generally apply to classical oncogene-driven adenocarcinomas, but not to other cancers, including malignant melanoma. Moreover, we find that correlations between circRNA and mRNA expression, which are commonly interpreted as evidence of a ceRNA function, can be explained by different cancer-to-stromal cell ratios among the studied tumor specimens. Together, these results have wide implications for future circRNA studies and highlight the importance of spatially resolving expression patterns of circRNAs proposed to function as ceRNAs.