Maternally expressed gene 3 (MEG3, mouse homolog Gtl2) encodes a long noncoding RNA (lncRNA) that is expressed in many normal tissues, but is suppressed in various cancer cell lines and tumors, suggesting it plays a functional role as a tumor suppressor. Hypermethylation has been shown to contribute to this loss of expression. We now demonstrate that MEG3 expression is regulated by the retinoblastoma protein (Rb) pathway and correlates with a change in cell proliferation. Microarray analysis of mouse embryonic fibroblasts (MEFs) isolated from mice with genetic deletion of all three Rb family members (TKO) revealed a significant silencing of Gtl2/MEG3 expression compared to WT MEFs, and re-expression of Gtl2/MEG3 caused decrease in cell proliferation and increased apoptosis. MEG3 levels also were suppressed in A549 lung cancer cells compared with normal human bronchial epithelial (NHBE) cells, and, similar to the TKO cells, re-constitution of MEG3 led to a decrease in cell proliferation and elevated apoptosis. Activation of pRb by treatment of A549 and SK-MES-1 cells with palbociclib, a CDK4/6 inhibitor, increased the expression of MEG3 in a dose-dependent manner, while knockdown of pRb/p107 attenuated this effect. In addition, expression of phosphorylation-deficient mutant of pRb increased MEG3 levels in both lung cancer cell types. Treatment of these cells with palbociclib also decreased the expression of pRb-regulated DNA methyltransferase 1 (DNMT1), while conversely, knockdown of DNMT1 resulted in increased expression of MEG3. As gene methylation has been suggested for MEG3 regulation, we found that palbociclib resulted in decreased methylation of the MEG3 locus similar to that observed with 5-aza-deoxycytidine. Anti-sense oligonucleotide silencing of drug-induced MEG3 expression in A549 and SK-MES-1 cells partially rescued the palbociclib-mediated decrease in cell proliferation, while analysis of the TCGA database revealed decreased MEG3 expression in human lung tumors harboring a disrupted RB pathway. Together, these data suggest that disruption of the pRb-DNMT1 pathway leads to a decrease in MEG3 expression, thereby contributing to the pro-proliferative state of certain cancer cells.

KRAS mutant ( KRAS mut ) lung adenocarcinoma is a refractory cancer without available targeted therapy. The current study explored the possibility to develop coxsackievirus type B3 (CVB3) as an oncolytic agent for the treatment of KRAS mut lung adenocarcinoma. In cultured cells, we discovered that CVB3 selectively infects and lyses KRAS mut lung adenocarcinoma cells (A549, H2030, and H23), while sparing normal lung epithelial cells (primary, BEAS2B, HPL1D, and 1HAEo) and EGFR mut lung adenocarcinoma cells (HCC4006, PC9, H3255, and H1975). Using stable cells expressing a single driver mutation of either KRAS G12V or EGFR L858R in normal lung epithelial cells (HPL1D), we further showed that CVB3 specifically kills HPL1D- KRAS G12V cells with minimal harm to HPL1D- EGFR L858R and control cells. Mechanistically, we demonstrated that aberrant activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and compromised type I interferon immune response in KRAS mut lung adenocarcinoma cells serve as key factors contributing to the sensitivity to CVB3-induced cytotoxicity. Lastly, we conducted in vivo xenograft studies using two immunocompromised mouse models. Our results revealed that intratumoral injection of CVB3 results in a marked tumor regression of KRAS mut lung adenocarcinoma in both non-obese diabetic (NOD) severe combined immunodeficiency (SCID) gamma (NSG) and NOD-SCID xenograft models. Together, our findings suggest that CVB3 is an excellent candidate to be further developed as a targeted therapy for KRAS mut lung adenocarcinoma.

Lung cancer is a heterogeneous disease consisting of multiple histological subtypes each driven by unique genetic alterations. Despite the development of targeted therapies that inhibit the oncogenic mutations driving a subset of lung cancer cases, there is a paucity of effective treatments for the majority of lung cancer patients and new strategies are urgently needed. In recent years, the concept of synthetic lethality has been established as an effective approach for discovering novel cancer-specific targets as well as a method to improve the efficacy of existing drugs which provide partial but insufficient benefits for patients. In this review, we discuss the concept of synthetic lethality, the various types of synthetic lethal interactions in the context of oncology and the approaches used to identify these interactions, including recent advances that have transformed the ability to discover novel synthetic lethal combinations on a global scale. Lastly, we describe the specific synthetic lethal interactions identified in lung cancer to date and explore the pharmacological challenges and considerations in translating these discoveries to the clinic.

Nodal is a member of the transforming growth factor-β (TGF-β) superfamily that plays critical roles during embryogenesis. Recent studies in ovarian, breast, prostate, and skin cancer cells suggest that Nodal also regulates cell proliferation, apoptosis, and invasion in cancer cells. However, it appears to exert both tumor-suppressing and tumor-promoting effects, depending on the cell type. To further understand the role of Nodal in tumorigenesis, we examined the effect of Nodal in glioblastoma cell growth and spheroid formation using U87 cell line. Treatment of U87 with recombinant Nodal significantly increased U87 cell growth. In U87 cells stably transfected with the plasmid encoding Nodal, Smad2 phosphorylation was strongly induced and cell growth was significantly enhanced. Overexpression of Nodal also resulted in tight spheroid formation. On the other hand, the cells stably transfected with Nodal siRNA formed loose spheroids. Nodal is known to signal through activin receptor-like kinase 4 (ALK4) and ALK7 and the Smad2/3 pathway. To determine which receptor and Smad mediate the growth promoting effect of Nodal, we transfected siRNAs targeting ALK4, ALK7, Smad2, or Smad3 into Nodal-overexpressing cells and observed that cell growth was significantly inhibited by ALK4, ALK7, and Smad3 siRNAs. Taken together, these findings suggest that Nodal may have tumor-promoting effects on glioblastoma cells and these effects are mediated by ALK4, ALK7, and Smad3.

Background: Pulmonary large cell carcinoma (LCC) was an undifferentiated and marker-null non-small cell lung January 2017 Abstracts S533