Abstract B66: miRNA 3’UTR activity driven enrichment of ovarian tumor-initiating cells (TICs) to overcome the barriers of heterogeneity and TIC plasticity

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy. Tumor recurrence is a major barrier towards improving patient outcome in EOC. Tumor-initiating cells (TICs) survive platinum-based therapies and contribute to tumor recurrence, at which stage the tumor is often difficult to eradicate, and thus TICs form the root cause of poor patient survival in EOC. Unfortunately, no TIC-targeting drugs to date are being evaluated in EOC patient trials. Isolating majority of TIC clones present in EOC tumors for functional analysis remains elusive to date and hence, understanding the complexity of TIC functioning remains a hurdle to be overcome in TIC therapeutics. TIC regulators can differ between tumors across patients and also in tumors within a patient. Tumor heterogeneity and TIC plasticity are the major challenges towards deciphering TIC functioning in EOC. Studying EOC cell populations with TIC properties is often limited to approaches driven by enrichment based on expression of stem-cell markers, which do not faithfully reflect TIC functioning in the context of heterogeneity and plasticity. Hence, pathway-based enrichment of TICs provide a reliable approach to functionally enrich for TIC subpopulations in EOC. miRNAs are small RNA molecules that regulate post-transcriptional gene silencing by binding mostly to the 3’UTR of their potential targets and targeting them for degradation through miRNA-induced silencing complexes (miRISCs). Isolation and characterization of TIC subpopulations in EOC based on miRNA activity can offer a reliable approach to functionally enrich for TICs in EOC. We have developed a novel miRNA-sensor based functional platform driven by miR-181a 3’UTR activity with mCHERRY fluorescence as the readout. miR-181a expression was upregulated in primary recurrent EOC tumors that were clinically resistant to platinum chemotherapy, suggesting a potential role for this miRNA in regulating TIC properties in EOC. Accordingly, miR-181a high subpopulation isolated from both cisplatin-sensitive and cisplatin-resistant/recurrent primary high-grade serous (HGSOC) ovarian tumor cells using miR-181a sensor were enriched in TIC properties in vitro and in vivo. Cisplatin treatment of primary EOC cells enriched miR-181a high subpopulation and reprogrammed miR-181a low non-TICs into miR-181a high TICs. Mechanistically, Wnt signaling was upregulated in miR-181a high ovarian tumor cells, showing that miRNA sensor platform can enrich TICs based on stem-cell pathway activity. Taken together, we provide the first evidence of TIC enrichment and analysis in EOC based on miRNA 3’UTR activity that provides with a valuable tool to broaden the understanding of TIC regulatory mechanisms in EOC in “real time,” with potential extension to other cancers by overcoming the barriers of tumor heterogeneity and TIC plasticity. miRNA sensor platform will provide a TIC pharmacologic screening tool to enable the discovery of novel miRNA-inhibiting TIC-targeting drugs in EOC. Citation Format: Anil Belur Nagaraj, Peronne Joseph, Matthew Knarr, Olga Kovalenko, Arshia Surti, Analisa DiFeo. miRNA 3’UTR activity driven enrichment of ovarian tumor-initiating cells (TICs) to overcome the barriers of heterogeneity and TIC plasticity. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr B66.