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BackgroundNovel therapies are urgently needed for ovarian cancer (OC), the fifth deadliest cancer in women. Preclinical work has shown that DNA methyltransferase inhibitors (DNMTis) can reverse the immunosuppressive tumor microenvironment in OC. Inhibiting DNA methyltransferases activate transcription of double-stranded (ds)RNA, including transposable elements. These dsRNAs activate sensors in the cytoplasm and trigger type I interferon (IFN) signaling, recruiting host immune cells to kill the tumor cells. Adenosine deaminase 1 (ADAR1) is induced by IFN signaling and edits mammalian dsRNA with an A-to-I nucleotide change, which is read as an A-to-G change in sequencing data. These edited dsRNAs cannot be sensed by dsRNA sensors, and thus ADAR1 inhibits the type I IFN response in a negative feedback loop. We hypothesized that decreasing ADAR1 editing would enhance the DNMTi-induced immune response.MethodsHuman OC cell lines were treated in vitro with DNMTi and then RNA-sequenced to measure RNA editing. Adar1 was stably knocked down in ID8Trp53-/-mouse OC cells. Control cells (shGFP) or shAdar1 cells were tested with mock or DNMTi treatment. Tumor-infiltrating immune cells were immunophenotyped using flow cytometry and cell culture supernatants were analyzed for secreted chemokines/cytokines. Mice were injected with syngeneic shAdar1 ID8Trp53-/-cells and treated with tetrahydrouridine/DNMTi while given anti-interferon alpha and beta receptor 1, anti-CD8, or anti-NK1.1 antibodies every 3 days.ResultsWe show that ADAR1 edits transposable elements in human OC cell lines after DNMTi treatment in vitro. Combining ADAR1 knockdown with DNMTi significantly increases pro-inflammatory cytokine/chemokine production and sensitivity to IFN-β compared with either perturbation alone. Furthermore, DNMTi treatment and Adar1 loss reduces tumor burden and prolongs survival in an immunocompetent mouse model of OC. Combining Adar1 loss and DNMTi elicited the most robust antitumor response and transformed the immune microenvironment with increased recruitment and activation of CD8+ T cells.ConclusionIn summary, we showed that the survival benefit from DNMTi plus ADAR1 inhibition is dependent on type I IFN signaling. Thus, epigenetically inducing transposable element transcription combined with inhibition of RNA editing is a novel therapeutic strategy to reverse immune evasion in OC, a disease that does not respond to current immunotherapies.

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Pancreatic cancer adenocarcinoma (PDAC) has been reported to be the third highest cause of cancer-related deaths in the United States. PDAC is known for its high proportion of stroma which accounts for 90% of the tumor mass. The stroma is made up of extracellular matrix (ECM) and non-malignant cells such as inflammatory cells, cancer-associated fibroblasts (CAF), and lymphatic and blood vessels. Here, we decoupled the roles of the extracellular matrix on PDAC cell lines by investigating the effects of different ECM proteins on the cell lines. Our data showed that primary lines have different morphology that depends on the ECM proteins on which they are cultured, while metastatic PDAC lines’ morphology does not change with respect to different ECM proteins. Next, we examined how these ECM proteins affect the cell response to the gemcitabine’s cytotoxicity. Lastly, transcriptomics analysis of the cells cultured on different ECM reveals the regulation of various pathways, such as cell cycle, cell adhesion molecules, and focal adhesion, including the regulation of several integrin genes that are essential for ECM recognition.