Abstract 1885: Targeting the FOXO1/KLF6 transcriptional network to modulate response to anti-EGFR based therapy

Epidermal growth factor receptor (EGFR) activation is both a key molecular driver of disease progression and the target of a broad class of molecular agents designed to treat advanced cancer. Nevertheless, resistance develops through several mechanisms including constitutive activation of AKT signaling. Additional molecular characterization of the downstream mediators of EGFR signaling may lead to the development of new classes of targeted molecular therapies to treat resistant disease. Here we identify a transcriptional network involving the KLF6 and FOXO1 tumor suppressor genes that negatively regulate activated EGFR signaling and that can be reactivated using the combination of two FDA approved agents in both cell culture and in vivo models of the disease. In both murine models and patient derived lung adenocarcinoma samples, EGFR activation is associated with FOXO1 mislocalization and decreased KLF6 expression. Furthermore, in a Kras driven mouse model, KLF6 expression is not significantly changed whereas AKT activation seen in the Pten/Mmac1+/− heterozygous mouse model results in FOXO1 mislocalization and decreased KLF6 expression. Consistent with these findings, inhibition of AKT signaling promotes increase in nuclear FOXO1 resulting in transactivation of the KLF6 tumor suppressor gene in lung adenocarcinoma cell lines. Correspondingly, the EGFRL858R mouse model demonstrates spontaneous tumor regression when treated with the anti-EGFR based therapy, erlotinib, an FDA-approved small-molecule inhibitor of EGFR signaling. We analyzed L858R mouse tumors samples treated with erlotinib and found increased KLF6 expression following EGFR inhibition. Conversely, targeted reduction of KLF6 resulted in decreased erlotinib response in both cell culture and in vivo models of disease suggesting a direct link between KLF6 upregulation and the induction of apoptosis by anti-EGFR based therapy. Therefore, we hypothesized that acquired resistance to anti-EGFR based therapies could be overcome by restoring downstream function of the FOXO1/KLF6 transcriptional network. Here we demonstrate that an FDA-approved drug, trifluoperazine hydrochloride (TFP), which has been shown to inhibit FOXO1 nuclear export, restores sensitivity to AKT-driven erlotinib-resistance through modulation of the KLF6/FOXO1 signaling cascade in both cell culture and xenograft models. Furthermore, silencing of FOXO1 blunts apoptosis mediated through combination erlotinib and TFP treatment suggesting