Background Delta‐like protein 3 (DLL3) is a Notch ligand that has an important role in the tumorigenesis of small cell lung cancer (SCLC). Recently, rovalpituzumab tesirine (Rova‐T), a DLL3‐targeted antibody‐drug conjugate, has been developed for treating SCLC. DLL3 is a transcriptional target of the achaete‐scute homolog‐1 (ASCL1) transcription factor, which is involved in pulmonary neuroendocrine cell development. However, the relationship between DLL3 and/or ASCL1 expression and the clinical features of SCLC remains unknown, especially for early‐stage resected SCLC. This study aimed to investigate the expression of DLL3 and ASCL1 in resected SCLC samples using immunohistochemical analysis. Materials and Methods We collected 95 surgically resected SCLC samples, which were formalin fixed and paraffin embedded. Immunohistochemistry staining was performed to investigate the correlation between the expression of either DLL3 or ASCL1 and clinicopathological features of study patients. Results Seventy‐seven (83%) of 93 immunohistochemically evaluable samples were positive for DLL3 (expression in ≥1% of tumor cells), and DLL3‐high expression (≥75%) was observed in 44 samples (47%). Sixty‐one (64%) of 95 samples were positive for ASCL1 (expression in ≥5% of tumor cells). A positive correlation was observed between DLL3 and ASCL1 expression. DLL3 and ASCL1 expression were not associated with survival in SCLC patients. DLL3 was more prevalent in patients with advanced clinical disease. Conclusion DLL3 and ASCL1 were highly expressed in patients with surgically resected SCLC. DLL3 and ASCL1 may be targets for the treatment of SCLC. Implications for Practice This article examines the relationship between delta‐like protein 3 (DLL3) and achaete‐scute homolog‐1 (ASCL1) protein expression with the clinical features of 95 surgically resected small cell lung cancer (SCLC). DLL3 is attracting attention because rovalpituzumab tesirine (Rova‐T), a DLL3‐targeted antibody‐drug conjugate, was developed recently. DLL3 and ASCL1 were highly expressed in patients with surgically resected SCLC. DLL3 and ASCL1 may be targets for the treatment of early‐stage SCLC, including with Rova‐T.

Delta‐like protein 3 ( DLL 3) is a ligand of Notch signaling, which mediates cell‐fate decisions and is tumor‐suppressive or oncogenic depending on the cellular context. Previous studies show that DLL 3 is highly expressed in small cell lung cancer ( SCLC ) but not in normal lung tissue, suggesting that DLL 3 might be associated with neuroendocrine tumorigenesis. However, its role in SCLC remains unclear. To investigate the role of DLL 3 in tumorigenesis in SCLC , we performed loss‐of‐function and gain‐of‐function assays using SCLC cell lines. In vitro analysis of cell migration and invasion by transwell assay showed that DLL 3 knockdown reduced migration and invasion of SCLC cells, whereas DLL 3 overexpression increased these activities. In addition, DLL 3 positively regulated SNAI 1 expression and knockdown of SNAI 1 attenuated the migration and invasion ability of SCLC cells. Moreover, upregulated DLL 3 expression induced subcutaneous tumor growth in mouse models. These results indicate that DLL 3 promoted tumor growth, migration and invasion in an SCLC model by modulating SNAI 1/Snail.

Bromodomain and extraterminal domain (BET) inhibitors are broadly active against distinct types of cancer, including nonsmall cell lung cancer (NSCLC). Previous studies have addressed the effect of BET‐inhibiting drugs on the expression of oncogenes such as c‐Myc, but DNA damage repair pathways have also been reported to be involved in the efficacy of these drugs. AZD1775, an inhibitor of the G2‐M cell cycle checkpoint kinase WEE1, induces DNA damage by promoting premature mitotic entry. Thus, we hypothesized that BET inhibition would increase AZD1775‐induced cytotoxicity by impairing DNA damage repair. Here, we demonstrate that combined inhibition of BET and WEE1 synergistically suppresses NSCLC growth both in vitro and in vivo. Two BET inhibitors, JQ1 and AZD5153, increased and prolonged AZD1775‐induced DNA double‐strand breaks (DSBs) and concomitantly repressed genes related to nonhomologous end joining (NHEJ), including XRCC4 and SHLD1. Furthermore, pharmaceutical inhibition of BET or knockdown of the BET protein BRD4 markedly diminished NHEJ activity, and the BET‐inhibitor treatment also repressed myelin transcription factor 1 (MYT1) expression and promoted mitotic entry with subsequent mitotic catastrophe when combined with WEE1 inhibition. Our findings reveal that BET proteins, predominantly BRD4, play an essential role in DSB repair through the NHEJ pathway, and further suggest that combined inhibition of BET and WEE1 could serve as a novel therapeutic strategy for NSCLC.

Notch signaling in tumorigenesis functions as an oncogene or tumor suppressor according to the type of malignancy. Numb represses intracellular Notch signaling. Previous studies have demonstrated that Notch signaling suppresses the proliferation of small cell lung cancer (SCLC) cell lines. However, in SCLC, the association between Notch1 and Numb expression and clinicopathological factors or prognosis has remained unclear. In this study, we evaluated the expression of Notch1 and Numb in SCLC. We immunohistochemically assessed 125 SCLCs that were surgically resected at 16 institutions participating in either the Hokkaido Lung Cancer Clinical Study Group Trial (HOT) or the Fukushima Investigative Group for Healing Thoracic Malignancy (FIGHT) between 2003 and 2013. Correlations between Notch1 or Numb expression and various clinicopathological features were evaluated. Notch1 expression was associated with ECOG performance status. Numb expression was associated with age, sex, and pathological histology (SCLC or Combined SCLC). Analysis of cellular biological expression did not demonstrate a significant correlation between the expression of Notch1 and of Numb. Multivariate Cox regression analysis showed that high Notch1 expression was an independent favorable prognostic factor for SCLC(hazard ratio = 0.503, P = 0.023). High Notch1 expression, but not Numb expression, is associated with favorable prognosis in SCLC.

Some reports suggest that Numb is a potential tumor suppressor. However, its role in non-small cell lung cancer remains unclear. Non-small cell lung cancer comprises two major histological subtypes, adenocarcinoma and squamous cell carcinoma. To investigate the role of Numb in tumorigenesis of lung adenocarcinoma and squamous cell carcinoma, we firstly performed loss-of-function and gain-of-function assays. Moreover, Numb expression was investigated in surgically resected lung adenocarcinoma and squamous cell carcinoma tissues by immunohistochemistry and correlations with prognosis were analyzed. Numb suppressed the proliferation, migration, and invasion of adenocarcinoma cells and inhibited Notch signaling and epithelial-mesenchymal transition in vitro. Numb overexpression also inhibited subcutaneous adenocarcinoma tumor growth. In contrast, Numb promoted the proliferation, migration, and invasion of squamous cell carcinoma cells, but did not induce any consistent changes in Notch signaling. High Numb expression was associated with favorable prognosis in patients with lung adenocarcinoma, but not in those with squamous cell carcinoma. Collectively, our data demonstrate that Numb plays distinct roles in lung adenocarcinoma and squamous cell carcinoma. In lung adenocarcinoma, Numb impairs tumor growth and inhibits the Notch pathway and epithelial-mesenchymal transition, whereas in lung squamous cell carcinoma it may promote proliferation.