No potential conflicts of interest were disclosed by the other authors. Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). The costs of publication of this MK-8719 MK-8719 article were defrayed in part by the payment of page charges. new treatment for recurrent SCLC. Significance: These findings identify a novel therapeutic strategy for SCLC using a combination of HDAC6 and BET inhibitors. Introduction Small-cell lung malignancy (SCLC) is a highly malignant neuroendocrine tumor in lung and accounts for 15%C20% of all primary lung cancers (1, 2). SCLC is usually strongly associated with cigarette smoking and displays the highest mortality among all types of lung malignancy (1, 2). The treatment of SCLC continues to be a challenge; although SCLC has a relatively good initial response to chemotherapy and radiotherapy, relapse MK-8719 and disease progression are extremely common, leading to a 5-12 months survival rate of less than 2% (3). In non-SCLC (NSCLC), oncogenic driver mutations have been recognized, making molecular-targeted treatment feasible (4, 5). In contrast, SCLC is not linked to currently targetable oncogenic mutations and, instead, is usually predominantly associated with inactivation of and expression, as well as abnormal histone modifications (6C9). These findings suggest that epigenetic dysregulation may play a major role in this malignancy. Recent strategies to target SCLC by manipulating transcription have shown some efficacy in preclinical models. For example, Christensen and colleagues reported that this transcriptional inhibitor THZ1 inhibits SCLC by targeting super enhancers of certain oncogenic transcriptional factors, including (10). Lenhart and colleagues reported that this BET bromodomain inhibitor JQ1 inhibits SCLC by sequestering BRD4 to prevent docking to the ASCL1 enhancer (11). In addition, Gardner and colleagues recently reported that cisplatin- and etoposide-resistant SCLC in PDX mice undergoes EZH2-mediated hypermethylation on (12). These studies suggest that chromatin regulators can provide manageable drug targets. To explore the potential of F2RL3 epigenetic therapy in SCLC, we required advantage of the technique of synthetic lethality, which has recently contributed to the development of malignancy therapeutics, especially for undrugable targets, such as activation or deletion mutants (13C16), and developed a synthetic lethal screening strategy specifically targeting epigenetic genes in a SCLC xenograft model. As part of our screening strategy, we considered proteins of the bromodomain and extra terminal (BET) family that function as transcriptional coactivators and play functions in transcriptional elongation (17). JQ1 is usually a competitive inhibitor of BET proteins that blocks them from binding to acetylated histones, thus inhibiting gene transcription (18). Inhibition of BET proteins with JQ1 has shown potent antiproliferation effects in hematologic tumors through suppression of c-MYC and downstream target genes (19), in lung adenocarcinoma cells through FOSL1 and its targets (20), as well as in SCLC (11). To maximize the impact of BET inhibition in SCLC, we screened for novel therapeutic targets using a synthetic lethal strategy with BET inhibitor JQ1 and an shRNA library specifically targeting epigenetic genes in a SCLC xenograft model. Our screen recognized HDAC6, which encodes histone deacetylase 6 (HDAC6). HDACs comprise classes I, IIa, IIb, and IV of 18 users and HDAC6 belongs to class IIb (21, 22). HDAC6 is usually phylogenetically close to class I HDACs, but with a distinct dominant cytoplasmic localization (23, 24), although it has been reported to repress transcriptions via association with other transcriptional regulators (25C29). Our identification of HDAC6 and effective suppression of SCLC with inhibitor ACY-1215 and JQ1 shine a light on a potential new treatment for recurrent MK-8719 SCLC. Materials and Methods Cell lines and cell culture The human SCLC NCI-H69 cell collection was obtained from ATCC and the GLC-16 cell collection was from our laboratory (10). Murine SCLC RP501 and RP1328 cell lines were established in our laboratory using lung tumor nodules of genetically designed Rb/p53 mice, and murine RPP41 and RPP394.