Abstract 1907: Multi-step microRNA control of pancreatic neuroendocrine tumors metastatic cascade

Abstract MicroRNAs (miRs) are implicated in the pathogenesis of various malignancies, including pancreatic cancer, and may represent key players in the metastatic process. In a previous study (Olson et al., 2009), we identified two unique miR signatures associated with tumour metastasis in the mouse model of pancreatic neuroendocrine tumour (PNET), RIP-Tag2. The first signature was characteristic of rare liver metastases. Intriguingly, the second signature, identified in a subset of primary PNET, had overlap with the liver metastasis signature. This signature was denoted “met-like primary” (referred to as MLP-miRs). Bioinformatic analysis revealed that three MLP-miRs (miR-181, miR-137, and miR-132), as well as three metastasis-specific miRs (miR-23b, miR-27b, and miR-24-1) are also upregulated in human PNET MLP samples. To examine the potential pro-metastatic role of the aforementioned miRs, we generated PNET cancer cell lines (β-TC) that stably express single miRs or combinations. We first audited their effect using orthotopic studies. MiR-181 caused a significant delay in the tumor progression, while the rest of the miRs did not affect tumor growth. Notably, the orthotopic tumors overexpressing miR-137 and miR-132 were characterized by markedly enhanced invasion into adjacent normal tissue. Then, using experimental metastasis assays we examined potential roles in distant metastasis. Overexpression of the miR-23b cluster (miR-23b, -27b and -24-1) caused a dramatic increase in the number of liver metastatic foci, indicating that they play a significant role in seeding distant metastases. The aforementioned pro-invasive miRs had little activity in this assay. Using an inducible system we went on to demonstrate that the three miRs comprising the 23b cluster act together in a synergistic manner during the early stages of distant colonization. Transcriptome analysis of miRNA isolated from β-TC expressing cell lines revealed enrichment of genes involved in axonal guidance, actin nucleation and integrin signaling in the case of miR-137, and of glutamate receptor signaling and EMT in the case of miR-23b cluster. Overall, our results suggest a multi-step miRNA control of the PNET metastatic cascade, during which miR-137 and miR-132 enables PNET cancer cells to invade,, while the miR-23b cluster plays an important role in distant metastasis. Using miR gene target prediction algorithms applied to mouse and human PNET transcriptome datasets, we are in the process of identifying and validating possible effector genes involved in distinctive aspects of the invasion-metastasis cascade, potentially guiding the design of new therapeutic strategies to target metastasis. Citation Format: Iacovos P. Michael, Douglas Hanahan. Multi-step microRNA control of pancreatic neuroendocrine tumors metastatic cascade. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1907.