Identifying Context-Specific Synthetic Lethal miRNA Inhibition in Non-Small Cell Lung Cancer




Borkowski, Robert John

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Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related fatalities in the US. This is due in part to a lack of highly effective therapies for advanced cases, and this is of special concern as most NSCLC cases are not diagnosed until they are in an advanced, later stage. Recent successes in developing genotypically-targeted therapies with potency only in a well-defined subpopulation of tumors suggests that identifying targeted therapies for additional common NSCLC genotypes will improve patient survival. In this study I utilized a library of inhibitors to microRNAs, a class of post-transcriptional gene regulators, to identify novel synthetic lethal miRNA inhibition:molecular mechanism interactions in NSCLC. I accomplished this by screening a panel of 13 NSCLC and immortalized normal lung epithelium (HBEC) cell lines in two phases to identify miRNA inhibitors with selective toxicity in the NSCLC cell lines that were also benign in an HBEC cell line. Two inhibitors, the miR-92a and miR-1226* inhibitors, met these criteria. I then collected toxicity data in an expanded panel of 29 total cell lines. This expanded toxicity data was used to identify p53 loss as a molecular mechanism correlated with sensitivity to the miR-92a and miR-1226* inhibitors in NSCLC cell lines. This was recapitulated by demonstrating sensitivity after knockdown of p53 in the previously resistant HBEC30KT cell line. I determined that the inhibitors were toxic in a very sequence-specific manner and that they down-regulated the miR-17~92 polycistron. Down-regulation of the polycistron was toxic in a context-specific manner, and the down-regulation of the miR-17~92 cluster in sensitive cell lines mimicked activation of a 1α, 25-dihydroxyvitamin D3 response in NSCLC cell lines in a manner consistent with sensitivity to the miR-92a inhibitor. The results of this investigation demonstrate that the screening approach utilized in this study was capable of identifying a synthetic lethal miRNA inhibition:molecular mechanism interaction, and that I was then able to use a genetically defined model of the mechanism to identify a relevant mechanism of action for the toxic inhibitors.

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