Abstract B09: Evaluating transcription factor networks as targets for the treatment of small cell lung cancer

Abstract

Abstract Achaete-scute homolog 1 (ASCL1) is a transcription factor that is highly expressed in most small cell lung cancer (SCLC) tumors and cell lines and is critical for their proliferation. Inhibiting ASCL1 transcriptional activity may thus be a valid therapeutic strategy for SCLC. However, transcription factors (TFs) have been historically difficult to target. Given that TFs belong to complex regulatory networks, we propose to identify and target multiple components within an ASCL1-transcriptional network rather than ASCL1 alone. We have previously detected ASCL1-bound genomic regions associated with the active chromatin epigenetic mark, H3K27Ac in SCLC cells. Here we report the identification of an ASCL1-containing transcriptional network in SCLC cells and evaluate its targeting by the transcriptional inhibitor, mithramycin. We conducted chromatin immunoprecipitation (ChIP) by immunoprecipitating the H3K27Ac chromatin mark from NCI-H2107 and NCI-H69 SCLCs (5X107 cells) nuclear lysates with10 μg H3K27Ac antibodies (Abcam-Ab4729), and sequenced ChIP libraries on an Illumina High-Seq2000. Further characterization using siRNA transfections, immunoblotting and MTS-cell proliferation assays were conducted following standard procedures. We found 82 overlapping TF genes, including lineage-specific TF genes for ASCL1, Forkhead box protein A2 (FOXA2), and nuclear factor 1 B-type (NFIB), associated with the active chromatin epigenetic marks H3K27Ac in SCLC cell lines. This suggests that ASCL1, FOXA2, and NFIB may belong to the same transcriptional network. siRNA-mediated knockdown of ASCL1 leads to decreased FOXA2 levels, but it has no effect on NFIB levels, implicating ASCL1 as a transcriptional regulator of FOXA2 but not NFIB. Mithramycin stops cell proliferation and reduces ASCL1, FOXA2 but not NFIB protein levels. In conclusion, our studies identify the beginning of a transcriptional network necessary for SCLC proliferation in which ASCL1 regulates FOXA2. Targeting multiple TFs within a network with mithramycin can stop cell proliferation and as such suggests a therapeutic strategy for SCLC. Because of the importance of NFIB in mediating metastatic behavior of SCLC, these data indicate that approaches other than targeting ASCL1 and use of mithramycin will be needed to target NFIB. Citation Format: Karine Pozo, Rahul K. Kollipara, John D. Minna, Adi F. Gazdar, Jane E. Johnson. Evaluating transcription factor networks as targets for the treatment of small cell lung cancer [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr B09.