Abstract 2954: TWIST1 is a critical mediator of KRAS mutant tumorigenesis in human non-small cell lung cancer

Abstract

Abstract A large fraction of non-small cell lung cancers (NSCLC) have mutant KRAS, which is associated with poor response to current cytotoxic therapy and a poor prognosis. Although the KRAS signaling pathway has been well characterized, no current therapies target this critical oncogene. Several studies have demonstrated that bypass of senescence in Kras-mediated adenocarcinoma mouse models is essential for tumorigenesis. Therefore, activation of senescence in KRAS mutant NSCLC may be an effective therapeutic strategy. We recently demonstrated that the basic helix loop helix transcription factor Twist1 cooperates with mutant Kras to induce lung adenocarcinoma in transgenic mouse models and that inhibition of Twist1 in these models led to activation of Kras-induced senescence and tumor stasis. In the current study, we examine the role of TWIST1 in KRAS mutant human NSCLC. Silencing of TWIST1 in multiple KRAS mutant NSCLC cell lines resulted in dramatic growth inhibition and either reactivation of oncogene-induced senescence or in some cases, apoptosis. Similar effects were also observed in four KRAS wild type lines, including cell lines with key driver mutations including a cell line with an activating EGFR mutation and a cell line with c-Met amplification. Gene set enrichment analysis of NSCLC cell lines after silencing of TWIST1 revealed a striking cell cycle arrest gene signature. Growth inhibition by silencing of TWIST1 was independent of p53 or Rb/p16 mutational status. Furthermore, activation of oncogene-induced senescence by TWIST1 silencing did not require previously defined mediators of senescence, p21 and p27, nor could this phenotype be rescued by overexpression of SKP2. To extend these observations in vivo, TWIST1 was silenced in both KRAS mutant and wildtype cell lines and these cells were implanted in NOD-SCID mice to assess tumor formation. Interestingly, silencing of TWIST1 in xenograft models preferentially inhibited KRAS mutant tumor formation suggesting that TWIST1 plays a critical in mediating KRAS tumorigenesis. Finally, inducible silencing of TWIST1 resulted in significant growth inhibition of established xenograft KRAS mutant tumors. Together these findings suggest TWIST1 is essential for the establishment and maintenance of KRAS mutant NSCLC tumors and silencing of TWIST1 in KRAS mutant NSCLC represents a novel and promising therapeutic strategy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2954. doi:1538-7445.AM2012-2954