Abstract 3272: Targeting LIN28 and the RAS/MAP kinase pathway in atypical teratoid rhabdoid tumors
Authors: Rubens Jeffrey , Weingart Melanie , Price Antoinette , Hutt-Cabezas Marianne , Taylor Isabella , Allen Sariah , Orr Brent , Eberhart Charles , Raabe Eric 
Published: August 2015

Abstract
Atypical teratoid rhabdoid tumor (AT/RT) is a highly malignant central nervous system neoplasm that primarily affects very young children and has a very poor prognosis. Aside from presumed founder loss of function mutations in the SMARCB1 (BAF47/INI1/SNF5) chromatin remodeling gene, little is known of molecular drivers of AT/RT. LIN28A and LIN28B are stem cell factors that regulate thousands of RNAs and are expressed in aggressive cancers. One of the canonical downstream targets of LIN28 is the RAS/MEK/ERK pathway. Due to the increased stem cell factor expression in AT/RT, we hypothesized that LIN28 contributes to tumorigenesis in these neoplasms through the regulation of multiple pro-growth, stemness, and metabolic pathways. We identified increased levels of LIN28A in AT/RT primary tumors compared to normal brain using immunohistochemistry (P = 0.026 by Mann-Whitney test). We detected LIN28A or LIN28B in 100% of AT/RT cell lines by western blot or qPCR. Knockdown of LIN28A by lentiviral shRNA in the AT/RT cell lines CHLA-06-ATRT and BT37 inhibited growth, cell proliferation and colony formation and induced apoptosis. Colonies formed by BT37 and CHLA-06 cells with LIN28A knockdown were reduced by between 50 and 90 percent (BT37 p = 0.0002 sh800 vs pLKO, CHLA-06 p = 0.009 sh802 vs pLKO). A Cleaved caspase 3 (CC3) assay for apoptosis showed that LIN28A knockdown in BT37 and CHLA-06 cells led to a 4 to 6 fold increase in the percentage of cells expressing CC3 compared to controls measured by immunofluorescence (BT37 p = 0.0005 sh800 vs pLKO; CHLA-06 p = 0.004 sh802 vs pLKO). Suppression of LIN28A in orthotopic xenograft models led to a more than doubling of median survival compared to empty vector controls (48 vs 115 days - p = 0.007 by Log-rank test) showing that LIN28A is critical to AT/RT cell line tumorigenesis. We found lower KRAS expression in LIN28A knockdown cell lines compared to pLKO control using qPCR. We also found high expression levels of phospho-ERK in AT/RT primary tumors by immunohistochemistry. Increased ERK signaling correlated with LIN28A expression in AT/RT (P = 0.008, r = 0.57 by Spearman correlation). Trametinib is a MEK1 and MEK2 inhibitor that has been developed through phase III clinical trials in adult melanoma. Trametinib inhibited the KRAS pathway in CHLA-06-ATRT and BT37 AT/RT cell lines as measured by suppression of p-ERK by Western blot. Treatment with Trametinib for 5 days suppressed the growth of BT37 and CHLA-06 cells (MTS assay for BT37 p = 0.003 for 1 nM and p = 0.002 for 10 nM vs DMSO control; for CHLA-06 p&lt;0.001 for 1 nM and 10nM vs DMSO control by t-test). These data implicate LIN28/RAS/MAP kinase as key drivers of AT/RT tumorigenesis and indicate that targeting this pathway may serve as a novel therapeutic option in this aggressive pediatric malignancy.
Citation Format: Jeffrey Rubens, Melanie Weingart, Antoinette Price, Marianne Hutt-Cabezas, Isabella Taylor, Sariah Allen, Brent Orr, Charles Eberhart, Eric Raabe. Targeting LIN28 and the RAS/MAP kinase pathway in atypical teratoid rhabdoid tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3272. doi:10.1158/1538-7445.AM2015-3272