Development of resistance to chemotherapy was linked to persistence of cancer stem cells (CSCs). CSCs are characterized by the ability to self-renew, grow as spheres, differentiate and generate tumors in immunodeficient mice. They are resistant to traditional forms of treatment, including chemo and radio-therapy. Building on our previous work showing that ovarian CSCs residual after treatment with platinum display increased DNA methylation, we hypothesized that other epigenetic modifications occur, promote a stem-like phenotype, and render CSCs vulnerable to epigenome modifying agents. To begin to address this question, we used partial wave spectroscopy to visualize chromatin at the nanoscale level, the Assay for Transposase Accessible Chromatin with high-throughput sequencing (ATAC-seq) to map accessible promoter regions, and proteomic analysis to measure histone marks in CSCs vs. non-CSCs. We found less open chromatin associated with repressive histone marks in CSCs vs. non-CSC and identified increased expression of the H379 histone methyl transferase Dot1L in CSCs vs. non-CSCs. Our preliminary data show that Dot1L inhibitors blocked stemness features. FOXK2, one of the transcription factors found to have an open promoter by ATAC-Seq in CSCs vs. non-CSCs was shown to be a Dot1L target gene and was highly expressed in ovarian CSCs. These preliminary observations led us to propose dissecting the link between Dot1L-induced H3K79 methylation, cancer stemness, and platinum-resistance by addressing three main objectives.
Aim 1 : Determine whether H3K79 methylation regulated by Dot1L is a mark and a target in OCSCs. H3K79 mono-, di-, and trimethylation will be mapped to chromatin extracted from OCSCs vs. non-CSCs by using chromatin-immunoprecipitation (ChIP)-sequencing. Effects of Dot-1L inhibitors and Dot-1L knock-down on stem cell characteristics and response to platinum will be assessed in vitro and in vivo.
Aim 2 : Determine whether H3K79 methylation is altered in platinum-resistant OC models and tumors. Paired parental and platinum resistant cell lines, xenografts and patient-derived xenograft models (PDX) developed by our group will be used to measure DOT1L expression and H3K79methylation. Expression and function of Dot1L will be measured in human ovarian tumors sensitive or persistent after platinum-based chemotherapy. Effects of genetic and pharmacological inhibitory strategies on response to platinum will be investigated in vitro and in vivo.
Aim 3 : Determine the function of FOXK2, a Dot1L target in ovarian CSCs. FOXK2 expression will be measured in platinum-resistant vs. platinum-nave models and in human ovarian tumors. Knock-in and knock- out experiments will determine its function on transcription regulation in ovarian CSCs. In summary, the proposed studies will address an important biological question with direct clinical applications. Our preliminary data and extensive expertise on cancer stem cell biology and platinum resistance strongly support the project?s feasibility and impact. We will use state of the art technologies to propel the development of new epigenome-directed strategies, such as Dot1L inhibitors, to target ovarian CSCs. Our proven track record of bench-to-clinic interventions will facilitate translation of our findings to clinical applications. The results of this project will be immediately applicable to ovarian cancer, but may have broader implications for other platinum- resistant solid tumors. In all, this project will bridge a gap of knowledge in platinum-resistant malignancies that affect a significant number of US Veterans and US military.
This innovative project will study epigenomic modifications in cancer cells and their link to stemness and drug resistance. We hypothesize that treatment with platinum induces chromatin modifications promoting a cancer stem-like phenotype and vulnerability to epigenome modifiers. We propose to tackle this question by using next generation sequencing adapted to the study of rare cell populations, by focusing on the enzyme Dot1L and the target gene, FoxK2. Successful demonstration of this concept will provide the rationale for pursuing Dot1L inhibitors to restore response to platinum in ovarian cancer. We envision that this strategy will increase sensitivity to platinum and impact clinical outcomes. Our findings could be translated to other treatment- resistant solid tumors. As platinum-resistant cancer kills a significant number of US Veterans and military personnel, this project is highly relevant to the Department of Veterans Affairs.
| Condello, Salvatore; Sima, Livia; Ivan, Cristina et al. (2018) Tissue Tranglutaminase Regulates Interactions between Ovarian Cancer Stem Cells and the Tumor Niche. Cancer Res 78:2990-3001 |
| Li, Junjie; Condello, Salvatore; Thomes-Pepin, Jessica et al. (2017) Lipid Desaturation Is a Metabolic Marker and Therapeutic Target of Ovarian Cancer Stem Cells. Cell Stem Cell 20:303-314.e5 |
| Lee, Jiyoon; Yakubov, Bakhtiyor; Ivan, Cristina et al. (2016) Tissue Transglutaminase Activates Cancer-Associated Fibroblasts and Contributes to Gemcitabine Resistance in Pancreatic Cancer. Neoplasia 18:689-698 |
| Lee, Jiyoon; Condello, Salvatore; Yakubov, Bakhtiyor et al. (2015) Tissue Transglutaminase Mediated Tumor-Stroma Interaction Promotes Pancreatic Cancer Progression. Clin Cancer Res 21:4482-93 |
| Mitra, Anirban K; Davis, David A; Tomar, Sunil et al. (2015) In vivo tumor growth of high-grade serous ovarian cancer cell lines. Gynecol Oncol 138:372-7 |
