ASH1Gene Is a Specific Therapeutic Target for Lung Cancers with Neuroendocrine Features

Genomic profiling of small-cell lung cancer: the era of targeted therapies

The molecular profiling of small-cell lung cancer is challenging because of the difficulty in obtaining suitable tumor samples for integrative genomic analysis. While an urgent need exists for well-defined and effective therapeutic targets in small-cell lung cancer, no significant improvement has been made in treating this disease over the past 30 years. Recently, three reports describing comprehensive genomic analyses of small-cell lung cancer have been published. These reports have provided a framework of biologically relevant genes in small-cell lung cancer and have demonstrated that the genomic landscape of small-cell lung cancer was almost equivalent between Asian and Caucasian populations. Of note, these three comprehensive genomic analyses and other molecular analyses of small-cell lung cancer have contributed to the identification of patient populations that may benefit from promising targeted agents, such as those affecting the PI3K/AKT/mTOR pathway, FGFR1, RET or AURORA kinase inhibitors. Targeting small-cell lung cancer cells with tumor suppressor gene alteration based on synthetic lethality is also promising. The present review provides an overview of the biologically relevant genetic alterations and targeted therapies of small-cell lung cancer focusing on recent discoveries that could impact the management of small-cell lung cancer.

Targeting transcriptional addictions in small cell lung cancer with a covalent CDK7 inhibitor

Small cell lung cancer (SCLC) is an aggressive disease with high mortality, and the identification of effective pharmacological strategies to target SCLC biology represents an urgent need. Using a high-throughput cellular screen of a diverse chemical library, we observe that SCLC is sensitive to transcription-targeting drugs, in particular to THZ1, a recently identified covalent inhibitor of cyclin-dependent kinase 7. We find that expression of super-enhancer-associated transcription factor genes, including MYC family proto-oncogenes and neuroendocrine lineage-specific factors, is highly vulnerability to THZ1 treatment. We propose that downregulation of these transcription factors contributes, in part, to SCLC sensitivity to transcriptional inhibitors and that THZ1 represents a prototype drug for tailored SCLC therapy.

Different micro-RNA expression profiles distinguish subtypes of neuroendocrine tumors of the lung: results of a profiling study

MicroRNAs (miRNAs) are a class of small (∼22 nucleotides), non-coding, highly conserved single-stranded RNAs with posttranscriptional regulatory features, including the regulation of cell proliferation, differentiation, survival, and apoptosis. They are deregulated in a broad variety of tumors showing characteristic expression patterns and can, thus, be used as a diagnostic tool. In contrast to non-small cell carcinoma of the lung neuroendocrine lung tumors, encompassing typical and atypical carcinoids, small cell lung cancer and large cell neuroendocrine lung cancer, no data about deregulation of tumor entity-specific miRNAs are available to date. miRNA expression differences might give useful information about the biological characteristics of these tumors, as well as serve as helpful markers.In 12 pulmonary neuroendocrine tumors classified as either typical carcinoid, atypical, large cell neuroendocrine or small cell lung cancer, screening for 763 miRNAs known to be involved in pulmonary cancerogenesis was conducted by performing 384-well TaqMan low-density array real-time qPCR. In the entire cohort, 44 miRNAs were identified, which showed a significantly different miRNA expression. For 12 miRNAs, the difference was highly significant (P<0.01). Eight miRNAs showed a negative (miR-22, miR-29a, miR-29b, miR-29c, miR-367*; miR-504, miR-513C, miR-1200) and four miRNAs a positive (miR-18a, miR-15b*, miR-335*, miR-1201) correlation to the grade of tumor biology. The miRNAs let-7d; miR-19; miR-576-5p; miR-340*; miR-1286 are significantly associated with survival. Members of the miR-29 family seem to be extremely important in this group of tumors. We found a number of miRNAs, which showed a highly significant deregulation in pulmonary neuroendocrine tumors. Moreover, some of these deregulated miRNAs seem to allow discrimination of the various subtypes of pulmonary neuroendocrine tumors. Thus, the analysis of specific sets of miRNAs can be proposed as diagnostic and/or predictive markers in this group of neoplasias.

ASCL1 is a lineage oncogene providing therapeutic targets for high-grade neuroendocrine lung cancers

Aggressive neuroendocrine lung cancers, including small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC), represent an understudied tumor subset that accounts for approximately 40,000 new lung cancer cases per year in the United States. No targeted therapy exists for these tumors. We determined that achaete-scute homolog 1 (ASCL1), a transcription factor required for proper development of pulmonary neuroendocrine cells, is essential for the survival of a majority of lung cancers (both SCLC and NSCLC) with neuroendocrine features. By combining whole-genome microarray expression analysis performed on lung cancer cell lines with ChIP-Seq data designed to identify conserved transcriptional targets of ASCL1, we discovered an ASCL1 target 72-gene expression signature that (i) identifies neuroendocrine differentiation in NSCLC cell lines, (ii) is predictive of poor prognosis in resected NSCLC specimens from three datasets, and (iii) represents novel "druggable" targets. Among these druggable targets is B-cell CLL/lymphoma 2, which when pharmacologically inhibited stops ASCL1-dependent tumor growth in vitro and in vivo and represents a proof-of-principle ASCL1 downstream target gene. Analysis of downstream targets of ASCL1 represents an important advance in the development of targeted therapy for the neuroendocrine class of lung cancers, providing a significant step forward in the understanding and therapeutic targeting of the molecular vulnerabilities of neuroendocrine lung cancer.

Proneural bHLH genes in development and disease

Proneural genes encode evolutionarily conserved basic-helix-loop-helix transcription factors. In Drosophila, proneural genes are required and sufficient to confer a neural identity onto naïve ectodermal cells, inducing delamination and subsequent neuronal differentiation. In vertebrates, proneural genes are expressed in cells that already have a neural identity, but they are still required and sufficient to initiate neurogenesis. In all organisms, proneural genes control neurogenesis by regulating Notch-mediated lateral inhibition and initiating the expression of downstream differentiation genes. The general mode of proneural gene function has thus been elucidated. However, the regulatory mechanisms that spatially and temporally control proneural gene function are only beginning to be deciphered. Understanding how proneural gene function is regulated is essential, as aberrant proneural gene expression has recently been linked to a variety of human diseases-ranging from cancer to neuropsychiatric illnesses and diabetes. Recent insights into proneural gene function in development and disease are highlighted herein.

ASCL1 and RET expression defines a clinically relevant subgroup of lung adenocarcinoma characterized by neuroendocrine differentiation

ASCL1 is an important regulatory transcription factor in pulmonary neuroendocrine (NE) cell development, but its value as a biomarker of NE differentiation in lung adenocarcinoma (AD) and as a potential prognostic biomarker remains unclear. We examined ASCL1 expression in lung cancer samples of varied histologic subtype, clinical outcome and smoking status and compared with expression of traditional NE markers. ASCL1 mRNA expression was found almost exclusively in smokers with AD, in contrast to non-smokers and other lung cancer subtypes. ASCL1 protein expression by immunohistochemical (IHC) analysis correlated best with synaptophysin compared with chromogranin and CD56/NCAM. Analysis of a compendium of 367 microarray-based gene expression profiles in stage I lung adenocarcinomas identified significantly higher expression levels of the RET oncogene in ASCL1-positive tumors (ASCL1(+)) compared with ASCL1(-) tumors (q-value <10(-9)). High levels of RET expression in ASCL1(+) but not in ASCL1(-) tumors was associated with significantly shorter overall survival (OS) in stage 1 (P=0.007) and in all AD (P=0.037). RET protein expression by IHC had an association with OS in the context of ASCL1 expression. In silico gene set analysis and in vitro experiments by ASCL1 shRNA in AD cells with high endogenous expression of ASCL1 and RET implicated ASCL1 as a potential upstream regulator of the RET oncogene. Also, silencing ASCL1 in AD cells markedly reduced cell growth and motility. These results suggest that ASCL1 and RET expression defines a clinically relevant subgroup of ∼10% of AD characterized by NE differentiation.

Human ASH-1 promotes neuroendocrine differentiation in androgen deprivation conditions and interferes with androgen responsiveness in prostate cancer cells

BACKGROUND

Neuroendocrine differentiation in prostate cancer is a dynamic process associated to the onset of hormone-refractory disease in vivo. The molecular mechanisms underlying this process are poorly recognized. Our study aimed at testing in vitro the role of hASH-1, a transcription factor implicated in neuroendocrine differentiation, in the onset of neuroendocrine phenotype in prostate cancer cells.

METHODS

Androgen sensitive LNCAP, androgen insensitive PC-3, and three immortalized prostate cancer cell lines were cultured in standard and androgen deprivation conditions. Expression of hASH-1 was modulated by either specific lentiviral transduction or shRNA interference. Inhibitors of WNT-11, a WNT family member associated to the development of neuroendocrine differentiation in prostate cancer, were also used. Cell viability was measured using the MTS method. Neuroendocrine phenotype was assessed by morphology, immunohistochemistry and real time PCR for several neuroendocrine markers.

RESULTS

hASH-1 was up-modulated by androgen deprivation in LNCaP cells and in androgen-sensitive immortalized prostate cancer cells, and associated with the onset of a neuroendocrine phenotype. Silencing of hASH-1 prevented neuroendocrine differentiation, as did also the selective interference with the WNT-11 pathway. Moreover, hASH-1 over-expression in LNCaP cells was sufficient to promote neuroendocrine differentiation and increased cell viability at basal and androgen-deprived growth conditions.

CONCLUSION

In summary, the present data support previous evidence that the acquisition of a neuroendocrine phenotype is linked to androgen responsiveness profiles and suggest a pivotal role of hASH-1 transcription factor, whose activity might be explored as a potential therapeutic target in prostate cancer, with special reference to hormone refractory disease.

Adenovirus-mediated RNA interference targeting FOXM1 transcription factor suppresses cell proliferation and tumor growth of nasopharyngeal carcinoma

BACKGROUND

The Forkhead Box M1 (FOXM1) transcription factor, which regulates the expression of genes essential for cell proliferation and transformation, is implicated in tumorigenesis and tumor progression. FOXM1 has attracted much attention as a potential target for the prevention and/or therapeutic intervention in human carcinomas.

METHODS

The levels of FOXM1 expression in clinical tissue specimens and cell lines of human malignant nasopharyngeal carcinoma (NPC) were measured. Knockdown of FOXM1 expression was performed by small interfering RNA in NPC cells. An adenovirus vector (named AdFOXM1shRNA) was constructed to express a short hairpin RNA specific to FOXM1. The efficacy of AdFOXM1shRNA for tumor gene therapy in NPC cells and an in vivo NPC grafting model was assessed.

RESULTS

A strong expression of FOXM1 was observed in clinical tissue specimens and cell lines of human NPC. Knockdown of FOXM1 expression by FOXM1 specific small interfering RNA diminished the NPC cell proliferation. The infection of AdFOXM1shRNA in NPC cells resulted in the knockdown of FOXM1 mRNA and protein levels, correlated with the reduction of proliferation and anchorage-independent growth of the cancer cells. The growth of NPC tumors was significantly suppressed when inoculated mice were injected with AdFOXM1shRNA in the tumor.

CONCLUSIONS

Together, our results suggest that FOXM1 is a potential therapeutic target for NPC and AdFOXM1shRNA may be an additional gene therapeutic intervention to be evaluated in future treatment strategies for patients with NPC.

NKX2-1/TTF-1: an enigmatic oncogene that functions as a double-edged sword for cancer cell survival and progression

Emerging evidence indicates that NKX2-1, a homeobox-containing transcription factor also known as TTF-1, plays a role as a "lineage-survival" oncogene in lung adenocarcinomas. In T cell acute lymphoblastic leukemia, gene rearrangements lead to aberrant expression of NKX2-1/TTF-1. Despite accumulating evidence supporting its oncogenic role, it has become apparent that NKX2-1/TTF-1 expression also has biological and clinical functions in the opposite direction that act against tumor progression. Herein, we review recent findings showing these enigmatic double-edged characteristics, with special attention given to the roles of NKX2-1/TTF-1 in lung development and carcinogenesis.

Involvement of intermediate filament nestin in cell growth of small-cell lung cancer

BACKGROUND

Nestin is a class VI intermediate filament protein expressed in stem/progenitor cells during the development of the central nervous system. Nestin is detected in various types of tumors and is involved in malignant processes. This study investigated the expression and function of nestin in small-cell lung cancer (SCLC).

METHODS

Expression of nestin and achaete-scute homolog 1 (ASH1) was studied in 21 lung cancer cell lines. To assess the function of nestin, a short hairpin RNA (shRNA) targeting nestin was transfected into two SCLC cell lines (DMS53 and SBC3), and cloned cells that showed apparent down-regulation of nestin were obtained. Nestin expression was also studied immunohistochemically in surgically resected SCLC primary tumors and metastatic SCLC tumors obtained from autopsy cases.

RESULT

Nestin was expressed in nine of 10 SCLC cell lines. The nestin expression level was significantly higher in SCLC cell lines than in NSCLC cell lines (P < 0.01). There was a statistically significant positive correlation between the expression levels of nestin and ASH1 in SCLC cell lines. Nestin knock-down cells created by transfection with shRNA exhibited decreased invasion and cell proliferation capabilities. Furthermore, nestin was detected in SCLC tumor cells and tumor vessels in all clinical tumor specimens.

CONCLUSION

Nestin is expressed in SCLC in association with neuroendocrine features and participates in malignant phenotypes, including cell growth. Therefore, nestin may be a novel therapeutic target for SCLC.

RNA interference--a silent but an efficient therapeutic tool

RNA interference (RNAi) is an evolutionary conserved gene regulation pathway that has emerged as an important discovery in the field of molecular biology. One of the important advantages of RNAi in therapy is that it brings about efficient downregulation of gene expression by targeting complementary transcripts in comparison with other antisense-based techniques. RNAi can be can be achieved by introducing chemically synthesized small interfering RNAs (siRNAs) into a cell system. A more stable knockdown effect can be brought about by the use of plasmid or viral vectors encoding the siRNA. RNAi has been used in reverse genetics to understand the function of specific genes and also as a therapeutic tool in treating human diseases. This review provides a brief insight into the therapeutic applications of RNAi against debilitating diseases.

Inhibition of FOXM1 transcription factor suppresses cell proliferation and tumor growth of breast cancer

The forkhead box M1 (FOXM1) transcription factor regulates the expression of genes essential for cell proliferation and transformation and is implicated in tumorigenesis and tumor progression. FOXM1 has been considered as a potential target for the prevention and/or therapeutic intervention in human carcinomas. In this study, we observed a strong expression of FOXM1 in clinical tissue specimens and cell lines of human breast cancer and a correlation between FOXM1 levels and the proliferation ability in the tested MCF-7, MDA-MB-231 and ZR-75-30 cells. By using an adenovirus vector (named AdFOXM1shRNA) that expresses a short hairpin RNA (shRNA) to downregulate FOXM1 expression specifically, we found that the knockdown of FOXM1 expression diminished the proliferation and anchorage-independent growth of the breast cancer cells. The FOXM1 silencing in ZR-75-30 cells dramatically prevented the tumorigenicity of the AdFOXM1shRNA-treated cells in vitro and in vivo. Furthermore, the efficacy of AdFOXM1shRNA for tumor gene therapy was assessed with the breast cancer xenograft mouse model and the tumor growth was significantly suppressed when inoculated mice were injected with AdFOXM1shRNA in the tumors. Together, our results suggest that FOXM1 is a potential therapeutic target for breast cancer and AdFOXM1shRNA may be an additional gene therapeutic intervention for breast cancer treatment.

Co-delivery of doxorubicin and siRNA using octreotide-conjugated gold nanorods for targeted neuroendocrine cancer therapy

A multifunctional gold (Au) nanorod (NR)-based nanocarrier capable of co-delivering small interfering RNA (siRNA) against achaete-scute complex-like 1 (ASCL1) and an anticancer drug (doxorubicin (DOX)) specifically to neuroendocrine (NE) cancer cells was developed and characterized for combined chemotherapy and siRNA-mediated gene silencing. The Au NR was conjugated with (1) DOX, an anticancer drug, via a pH-labile hydrazone linkage to enable pH-controlled drug release, (2) polyarginine, a cationic polymer for complexing siRNA, and (3) octreotide (OCT), a tumor-targeting ligand, to specifically target NE cancer cells with overexpressed somatostatin receptors. The Au NR-based nanocarriers exhibited a uniform size distribution as well as pH-sensitive drug release. The OCT-conjugated Au NR-based nanocarriers (Au-DOX-OCT, targeted) exhibited a much higher cellular uptake in a human carcinoid cell line (BON cells) than non-targeted Au NR-based nanocarriers (Au-DOX) as measured by both flow cytometry and confocal laser scanning microscopy (CLSM). Moreover, Au-DOX-OCT-ASCL1 siRNA (Au-DOX-OCT complexed with ASCL1 siRNA) resulted in significantly higher gene silencing in NE cancer cells than Au-DOX-ASCL1 siRNA (non-targeted Au-DOX complexed with ASCL1 siRNA) as measured by an immunoblot analysis. Additionally, Au-DOX-OCT-ASCL1 siRNA was the most efficient nanocarrier at altering the NE phenotype of NE cancer cells and showed the strongest anti-proliferative effect. Thus, combined chemotherapy and RNA silencing using NE tumor-targeting Au NR-based nanocarriers could potentially enhance the therapeutic outcomes in treating NE cancers.

Comprehensive genomic characterization of squamous cell lung cancers

Lung squamous cell carcinoma is a common type of lung cancer, causing approximately 400,000 deaths per year worldwide. Genomic alterations in squamous cell lung cancers have not been comprehensively characterized, and no molecularly targeted agents have been specifically developed for its treatment. As part of The Cancer Genome Atlas, here we profile 178 lung squamous cell carcinomas to provide a comprehensive landscape of genomic and epigenomic alterations. We show that the tumour type is characterized by complex genomic alterations, with a mean of 360 exonic mutations, 165 genomic rearrangements, and 323 segments of copy number alteration per tumour. We find statistically recurrent mutations in 11 genes, including mutation of TP53 in nearly all specimens. Previously unreported loss-of-function mutations are seen in the HLA-A class I major histocompatibility gene. Significantly altered pathways included NFE2L2 and KEAP1 in 34%, squamous differentiation genes in 44%, phosphatidylinositol-3-OH kinase pathway genes in 47%, and CDKN2A and RB1 in 72% of tumours. We identified a potential therapeutic target in most tumours, offering new avenues of investigation for the treatment of squamous cell lung cancers.

Insights into the achaete-scute homolog-1 gene (hASH1) in normal and neoplastic human lung

Achaete-scute homolog-1 (ASH1) is pivotal for the development of pulmonary neuroendocrine (NE) cells. We examined human ASH1 (hASH1) expression across a comprehensive panel of human lung cancer cell lines, primary human lung tumors and normal fetal and post-natal lungs. While hASH1 was a cardinal feature of NE carcinomas, a subgroup of non-NE lung cancers also exhibited expression of this factor. Twenty lung cancer cell lines out of 33 were positive for hASH1 mRNA by reverse transcription PCR, including 6/6 small cell carcinomas (SCLC), 5/5 carcinoids, 6/7 non-SCLC with NE features, and 3/14 other non-SCLC. Among human primary tumors, 2/2 SCLC, 5/5 pulmonary carcinoids, and 10/41 non-SCLC (only 4 of which had NE features) were positive for hASH1 by immunohistochemistry and RNA-RNA in situ hybridization. In normal human fetal lung, the expression of hASH1 and the neural marker synaptophysin was highly concordant in neuroepithelial bodies and solitary NE cells, while the rest of the epithelium was negative. In childhood and adulthood, the markers became progressively discordant, with a majority of hASH1-immunoreactive foci (69%) being negative for synaptophysin in adults, potentially representing dormant NE cell progenitors. We conclude that hASH1 provides an early indication of NE program in human lung.

Notch signaling in lung development and disease

Notch signaling plays an essential role in development and homeostasis of multiple organs including the lung. Dysregulation of Notch signaling has been implicated in various lung diseases including lung cancer. Here we review functions of Notch signaling in coordinating events during lung development, such as early proximodistal fate generation and branching, airway epithelial cell fate specification, alveogenesis and pulmonary vascular development. We also discuss roles of Notch in chronic obstructive pulmonary disease, progressive pulmonary fibrosis, pulmonary arterial hypertension, asthma and lung cancer.

NKX2-1/TITF1/TTF-1-Induced ROR1 is required to sustain EGFR survival signaling in lung adenocarcinoma

We and others previously identified NKX2-1, also known as TITF1 and TTF-1, as a lineage-survival oncogene in lung adenocarcinomas. Here we show that NKX2-1 induces the expression of the receptor tyrosine kinase-like orphan receptor 1 (ROR1), which in turn sustains a favorable balance between prosurvival PI3K-AKT and pro-apoptotic p38 signaling, in part through ROR1 kinase-dependent c-Src activation, as well as kinase activity-independent sustainment of the EGFR-ERBB3 association, ERBB3 phosphorylation, and consequential PI3K activation. Notably, ROR1 knockdown effectively inhibited lung adenocarcinoma cell lines, irrespective of their EGFR status, including those with resistance to the EGFR tyrosine kinase inhibitor gefitinib. Our findings thus identify ROR1 as an "Achilles' heel" in lung adenocarcinoma, warranting future development of therapeutic strategies for this devastating cancer.

miR-375 is activated by ASH1 and inhibits YAP1 in a lineage-dependent manner in lung cancer

Lung cancers with neuroendocrine (NE) features are often very aggressive but the underlying molecular mechanisms remain elusive. The transcription factor ASH1/ASCL1 is a master regulator of pulmonary NE cell development that is involved in the pathogenesis of lung cancers with NE features (NE-lung cancers). Here we report the definition of the microRNA miR-375 as a key downstream effector of ASH1 function in NE-lung cancer cells. miR-375 was markedly induced by ASH1 in lung cancer cells where it was sufficient to induce NE differentiation. miR-375 upregulation was a prerequisite for ASH1-mediated induction of NE features. The transcriptional coactivator YAP1 was determined to be a direct target of miR-375. YAP1 showed a negative correlation with miR-375 in a panel of lung cancer cell lines and growth inhibitory activities in NE-lung cancer cells. Our results elucidate an ASH1 effector axis in NE-lung cancers that is functionally pivotal in controlling NE features and the alleviation from YAP1-mediated growth inhibition.

A novel function of the proneural factor Ascl1 in progenitor proliferation identified by genome-wide characterization of its targets

Proneural genes such as Ascl1 are known to promote cell cycle exit and neuronal differentiation when expressed in neural progenitor cells. The mechanisms by which proneural genes activate neurogenesis--and, in particular, the genes that they regulate--however, are mostly unknown. We performed a genome-wide characterization of the transcriptional targets of Ascl1 in the embryonic brain and in neural stem cell cultures by location analysis and expression profiling of embryos overexpressing or mutant for Ascl1. The wide range of molecular and cellular functions represented among these targets suggests that Ascl1 directly controls the specification of neural progenitors as well as the later steps of neuronal differentiation and neurite outgrowth. Surprisingly, Ascl1 also regulates the expression of a large number of genes involved in cell cycle progression, including canonical cell cycle regulators and oncogenic transcription factors. Mutational analysis in the embryonic brain and manipulation of Ascl1 activity in neural stem cell cultures revealed that Ascl1 is indeed required for normal proliferation of neural progenitors. This study identified a novel and unexpected activity of the proneural gene Ascl1, and revealed a direct molecular link between the phase of expansion of neural progenitors and the subsequent phases of cell cycle exit and neuronal differentiation.

Nicotinic acetylcholine receptor-mediated mechanisms in lung cancer

Despite the known adverse health effects associated with tobacco use, over 45 million adults in the United States smoke. Cigarette smoking is the major etiologic factor associated with lung cancer. Cigarettes contain thousands of toxic chemicals, many of which are carcinogenic. Nicotine contributes directly to lung carcinogenesis through the activation of nicotinic acetylcholine receptors (nAChRs). nAChRs are ligand-gated ion channels, expressed in both normal and lung cancer cells, which mediate the proliferative, pro-survival, angiogenic, and metastatic effects of nicotine and its nitrosamine derivatives. The underlying molecular mechanisms involve increases in intracellular calcium levels and activation of cancer signal transduction pathways. In addition, acetylcholine (ACh) acts as an autocrine or paracrine growth factor in lung cancer. Other neurotransmitters and neuropeptides also activate similar growth loops. Recent genetic studies further support a role for nAChRs in the development of lung cancer. Several nAChR antagonists have been shown to inhibit lung cancer growth, suggesting that nAChRs may serve as valuable targets for biomarker-guided lung cancer interventions.

Expression of RNA interference triggers from an oncolytic herpes simplex virus results in specific silencing in tumour cells in vitro and tumours in vivo

Background

Delivery of small interfering RNA (siRNA) to tumours remains a major obstacle for the development of RNA interference (RNAi)-based therapeutics. Following the promising pre-clinical and clinical results with the oncolytic herpes simplex virus (HSV) OncoVEX^GM-CSF, we aimed to express RNAi triggers from oncolytic HSV, which although has the potential to improve treatment by silencing tumour-related genes, was not considered possible due to the highly oncolytic properties of HSV.

Methods

To evaluate RNAi-mediated silencing from an oncolytic HSV backbone, we developed novel replicating HSV vectors expressing short-hairpin RNA (shRNA) or artificial microRNA (miRNA) against the reporter genes green fluorescent protein (eGFP) and β-galactosidase (lacZ). These vectors were tested in non-tumour cell lines in vitro and tumour cells that are moderately susceptible to HSV infection both in vitro and in mice xenografts in vivo. Silencing was assessed at the protein level by fluorescent microscopy, x-gal staining, enzyme activity assay, and western blotting.

Results

Our results demonstrate that it is possible to express shRNA and artificial miRNA from an oncolytic HSV backbone, which had not been previously investigated. Furthermore, oncolytic HSV-mediated delivery of RNAi triggers resulted in effective and specific silencing of targeted genes in tumour cells in vitro and tumours in vivo, with the viruses expressing artificial miRNA being comprehensibly more effective.

Conclusions

This preliminary data provide the first demonstration of oncolytic HSV-mediated expression of shRNA or artificial miRNA and silencing of targeted genes in tumour cells in vitro and in vivo. The vectors developed in this study are being adapted to silence tumour-related genes in an ongoing study that aims to improve the effectiveness of oncolytic HSV treatment in tumours that are moderately susceptible to HSV infection and thus, potentially improve response rates seen in human clinical trials.

[Expression and clinicopathologic significance of human achaete-scute homolog 1 in pulmonary neuroendocrine tumors]

BACKGROUND AND OBJECTIVE

Human achaete-scute homolog 1 (hASH1) gene plays a critical role in development of the central nervous system, automatic nervous system, adrenal medullary chromaffin cells, thyroid C cells and pulmonary neuroendocrine cells. The aim of this study is to determine hASH1 gene expression in the normal lung tissue and various types of lung tumors, to analyze whether its expression correlated with pulmonary neuroendocrine markers, and to explore the possibility of hASH1 as clinical pathological markers in the neuroendocrine tumors compared with previous neuroendocrine tumor markers.

METHODS

hASH1, Chromogranin A, Synaptophysin and CD56 expression were examined in lung tumor specimens (lung inflammatory pseudotumor, squamous cell carcinoma, adenocarcinomas, large cell carcinoma, typical carcinoids, atypical carcinoids, large cell neuroendocrine carcinomas and small cell lung carcinoma and corresponding normal lung specimens) using immunohistochemistry (S-P method). Western blot and reverse transcription polymerase chain reaction (RT-PCR) assay were applied to detect the expressions of hASH1 protein and mRNA in lung cancer tissues.

RESULTS

hASH1 expression was positive in 2/16 (12.5%) typical carcinoids, 15/20 (75%) atypical carcinoids, 6/10 (60%) large cell neuroendocrine carcinomas and 31/40 (77.5%) small cell lung carcinoma, respectively, but not in any normal lung tissue (0/10), lung inflammatory pseudotumor (0/49), squamous cell carcinoma (0/30), adenocarcinomas (0/30) or large cell carcinoma (0/20). There was a significant difference in hASH1 expression between typical carcinoids and atypical carcinoids (P < 0.01), but not in large cell neuroendocrine carcinomas and small cell lung carcinoma (P > 0.05). hASH1 expression highly closely correlated with Chromogranin A, Synaptophysin and CD56 expression (P < 0.05).

CONCLUSION

hASH1 is a new kind of highly specific markers of pulmonary neuroendocrine tumours, and may be applied to clinical pathology diagnosis of the pulmonary neuroendocrine tumors.

Prognostic role of neuroendocrine differentiation in prostate cancer, putting together the pieces of the puzzle

Neuroendocrine (NE) differentiation is a common feature in prostate cancer (PC). The clinical significance of this phenomenon is controversial; however preclinical and clinical data are in favor of an association with poor prognosis and early onset of a castrate resistant status. NE PC cells do not proliferate, but they can stimulate the proliferation of the exocrine component through the production of paracrine growth factors. The same paracrine signals may favor the outgrowth of castrate adapted tumors through androgen receptor dependent or independent mechanisms. Noteworthy, NE differentiation in PC is not a stable phenotype, being stimulated by several agents including androgen deprivation therapy, radiation therapy, and chemotherapy. The proportion of NE positive PC, therefore, is destined to increase during the natural history of the disease. This may complicate the assessment of the prognostic significance of this phenomenon. The majority of clinical studies have shown a significant correlation between NE differentiation and disease prognosis, confirming the preclinical rationale. In conclusion the NE phenotype is a prognostic parameter in PC. Whether this phenomenon is a pure prognostic factor or whether it can influence the prognosis by favoring the onset of a castrate resistance status is a matter of future research.

Achaete-scute homologue-1 tapers neuroendocrine cell differentiation in lungs after exposure to naphthalene

The basic helix-loop-helix transcription factor achaete-scute homologue-1 (ASH1) plays a critical role in regulating the neuroendocrine (NE) phenotype in normal and neoplastic lung. Transgenic (TG) mice that constitutively express human ASH1 (hASH1) under control of the Clara cell 10-kDa protein (CC10) promoter in non-NE airway lining cells display progressive epithelial hyperplasia and bronchiolar metaplasia or bronchiolization of the alveoli (BOA). However, little is known about the involvement of hASH1 in regeneration of the conducting airway. In this study, we investigated the impact of hASH1 on airway cell injury and repair in the TG mice following an intraperitoneal injection of naphthalene, which specifically ablates bronchiolar Clara cells and induces pulmonary NE cell hyperplasia. We discovered an overall attenuation of NE maturation coupled with increased proliferation in TG mice during post-naphthalene repair. In addition, BOA lesions revealed enhanced epithelial cell proliferation while preserving Clara cell markers CC10 and the principal naphthalene-metabolizing enzyme cytochrome P4502F2. These data suggest that ASH1 may play an important role in maintaining a progenitor phenotype that promotes renewal of both NE and epithelial cells. Moreover, ASH1 may propagate a stem cell microenvironment in BOA where epithelium becomes resistant to naphthalene toxicity.

The nicotinic acetylcholine receptor CHRNA5/A3/B4 gene cluster: dual role in nicotine addiction and lung cancer

More than 1 billion people around the world smoke, with 10 million cigarettes sold every minute. Cigarettes contain thousands of harmful chemicals including the psychoactive compound, nicotine. Nicotine addiction is initiated by the binding of nicotine to nicotinic acetylcholine receptors, ligand-gated cation channels activated by the endogenous neurotransmitter, acetylcholine. These receptors serve as prototypes for all ligand-gated ion channels and have been extensively studied in an attempt to elucidate their role in nicotine addiction. Many of these studies have focused on heteromeric nicotinic acetylcholine receptors containing α4 and β2 subunits and homomeric nicotinic acetylcholine receptors containing the α7 subunit, two of the most abundant subtypes expressed in the brain. Recently however, a series of linkage analyses, candidate-gene analyses and genome-wide association studies have brought attention to three other members of the nicotinic acetylcholine receptor family: the α5, α3 and β4 subunits. The genes encoding these subunits lie in a genomic cluster that contains variants associated with increased risk for several diseases including nicotine dependence and lung cancer. The underlying mechanisms for these associations have not yet been elucidated but decades of research on the nicotinic receptor gene family as well as emerging data provide insight on how these receptors may function in pathological states. Here, we review this body of work, focusing on the clustered nicotinic acetylcholine receptor genes and evaluating their role in nicotine addiction and lung cancer.

ASCL1 regulates the expression of the CHRNA5/A3/B4 lung cancer susceptibility locus

Tobacco contains a variety of carcinogens as well as the addictive compound nicotine. Nicotine addiction begins with the binding of nicotine to its cognate receptor, the nicotinic acetylcholine receptor (nAChR). Genome-wide association studies have implicated the nAChR gene cluster, CHRNA5/A3/B4, in nicotine addiction and lung cancer susceptibility. To further delineate the role of this gene cluster in lung cancer, we examined the expression levels of these three genes as well as other members of the nAChR gene family in lung cancer cell lines and patient samples using quantitative reverse transcription-PCR. Overexpression of the clustered nAChR genes was observed in small-cell lung carcinoma (SCLC), an aggressive form of lung cancer highly associated with cigarette smoking. The overexpression of the genomically clustered genes in SCLC suggests their coordinate regulation. In silico analysis of the promoter regions of these genes revealed putative binding sites in all three promoters for achaete-scute complex homolog 1 (ASCL1), a transcription factor implicated in the pathogenesis of SCLC, raising the possibility that this factor may regulate the expression of the clustered nAChR genes. Consistent with this idea, knockdown of ASCL1 in SCLC, but not in non-SCLC, led to a significant decrease in expression of the alpha 3 and beta 4 genes without having an effect on any other highly expressed nAChR gene. Our data indicate a specific role for ASCL1 in regulating the expression of the CHRNA5/A3/B4 lung cancer susceptibility locus. This regulation may contribute to the predicted role that ASCL1 plays in SCLC tumorigenesis.

[In vivo delivery of siRNA]

RNA interference (RNAi) is a mechanism of posttranscriptional gene silencing mediated by small interfering RNA (siRNA). The ability of synthetic siRNA to silence genes in vivo has made it well suited as therapeutic drug, but the instability and polarity of siRNA and the complexity of in vivo circumstances retarded rapid development of RNAi-based therapies. In this review, a summary of the advances on in vivo siRNA delivery is presented and discussed.

[Small cell lung cancer: pathology and molecular pathology]

In the current WHO classification, together with the subtype of combined small cell lung cancer, small cell lung cancers (SCLC) are listed as a special tumour entity. Their microscopic appearance is characterised by small tumour cells with scant cytoplasm and frequently hypodiploid nuclei. For the precise histological diagnosis of SCLC, especially for the diagnostic differentiation from pulmonary NHL infiltrates, additional immunohistochemical investigations are recommended. The presented core classification of lung cancer is intended to facilitate the semi-quantitative registration of "atypical" SCLC. Genetically SCLC is especially characterised by manifold chromosomal deletions with losses of whole chromosomes or chromosome arms, associated with the inactivation of numerous tumour suppressor genes. Whereas the extensive DNA losses may explain the marked sensitivity of SCLC to anti-neoplastic chemotherapy or radiotherapy, its considerable chromosomal instability is correlated with the development of resistance to therapy.

Achaete-scute complex homologue 1 regulates tumor-initiating capacity in human small cell lung cancer

The basic helix-loop-helix transcription factor achaete-scute complex homologue 1 (ASCL1) is essential for the development of normal lung neuroendocrine cells as well as other endocrine and neural tissues. Small cell lung cancer (SCLC) and non-SCLC with neuroendocrine features express ASCL1, where the factor may play a role in the virulence and primitive neuroendocrine phenotype of these tumors. In this study, RNA interference knockdown of ASCL1 in cultured SCLC resulted in inhibition of soft agar clonogenic capacity and induction of apoptosis. cDNA microarray analyses bolstered by expression studies, flow cytometry, and chromatin immunoprecipitation identified two candidate stem cell marker genes, CD133 and aldehyde dehydrogenase 1A1 (ALDH1A1), to be directly regulated by ASCL1 in SCLC. In SCLC direct xenograft tumors, we detected a relatively abundant CD133(high)-ASCL1(high)-ALDH1(high) subpopulation with markedly enhanced tumorigenicity compared with cells with weak CD133 expression. Tumorigenicity in the CD133(high) subpopulation depended on continued ASCL1 expression. Whereas CD133(high) cells readily reconstituted the range of CD133 expression seen in the original xenograft tumor, CD133(low) cells could not. Our findings suggest that a broad range of SCLC cells has tumorigenic capacity rather than a small discrete population. Intrinsic tumor cell heterogeneity, including variation in key regulatory factors such as ASCL1, can modulate tumorigenicity in SCLC.

Terminal and progenitor lineage-survival oncogenes as cancer markers

Tumour classification has traditionally focused on differentiation and cellular morphology, and latterly on the application of genomic approaches. By combining chromatin immunoprecipitation with expression array, it has been possible to identify direct gene targets for transcription factors for nuclear hormone receptors. At the same time, there have been great strides in deriving stem and progenitor cells from tissues. It is therefore timely to propose that pairing the isolation of these cell subpopulations from tissues and tumours with these genomics approaches will reveal conserved gene targets for transcription factors. By focusing on transcription factors (lineage-survival oncogenes) with roles in both organogenesis and tumourigenesis at multiple organ sites, we suggest that this comparative genomics approach will enable developmental biology to be used more fully in relation to understanding tumour progression and will reveal new cancer markers. We focus here on neurogenesis and neuroendocrine differentiation in tumours.

YAP1 is involved in mesothelioma development and negatively regulated by Merlin through phosphorylation

We previously reported the results of bacterial artificial chromosome array comprehensive genomic hybridization of malignant pleural mesotheliomas (MPMs), including two cases with high-level amplification in the 11q22 locus. In this study, we found that the YAP1 gene encoding a transcriptional coactivator was localized in this amplified region and overexpressed in both cases, suggesting it as a candidate oncogene in this region. We analyzed the involvement of YAP1 in MPM proliferation, as well as its functional and physical interaction with Merlin encoded by the neurofibromatosis type 2 (NF2) tumor suppressor gene, which is frequently mutated in MPMs. YAP1-RNA interference suppressed growth of a mesothelioma cell line NCI-H290 with NF2 homozygous deletion, probably through cell-cycle arrest and apoptosis induction, whereas YAP1 transfection promoted the growth of MeT-5A, an immortalized mesothelial cell line. We also found that the introduction of NF2 into NCI-H290 induced phosphorylation at serine 127 of YAP1, which was accompanied by reduction of nuclear localization of YAP1, whereas nuclear localization of a YAP1 S 127A mutant was not affected. Furthermore, results of immunoprecipitation and in vitro pull-down assays indicated a physical interaction between Merlin and YAP1. These results suggest that YAP1 is involved in mesothelial cell growth and that the transcriptional coactivator activity of YAP1 is functionally inhibited by Merlin through the induction of phosphorylation and cytoplasmic retention of YAP1. This is the first report of negative regulatory signaling from Merlin to YAP1 in mammalian cells. Future studies of transcriptional targets of YAP1 in MPMs may shed light on the molecular mechanisms of MPM development and lead to new therapeutic strategies.

Human ASH1 expression in prostate cancer with neuroendocrine differentiation

Neuroendocrine differentiation in prostate cancer correlates with overall prognosis and disease progression after androgen-deprivation therapy, although its specific mechanisms are currently poorly understood. A role of Notch pathway has been reported in determining neuroendocrine phenotype of normal and neoplastic tissues. The aim of this study was to analyze whether this pathway might affect neuroendocrine differentiation in prostate cancer. Human achaete-scute homolog 1 (hASH1), a pivotal member of the Notch pathway, was investigated in 80 prostate cancers selected and grouped according to chromogranin A immunohistochemistry, as follows: prostate cancers without neuroendocrine differentiation, untreated (25 cases); prostate cancers with neuroendocrine differentiation, untreated (40 cases); prostate cancers with previous androgen-deprivation therapy, all having neuroendocrine differentiation (15 cases). Human ASH1 protein was analyzed by immunohistochemistry, whereas the presence of hASH1 mRNA transcripts was investigated on paraffin material by real-time PCR. By immunohistochemistry, hASH1 was colocalized with chromogranin A in neuroendocrine cells of normal prostatic gland. It was absent in all but one prostate cancers without neuroendocrine differentiation, whereas it was positive in 25% of prostate cancers with neuroendocrine differentiation/untreated, with a significant correlation with the extent of neuroendocrine features (P=0.02). Moreover, comparing untreated and treated prostate cancers with neuroendocrine differentiation, a positive association with androgen-deprivation therapy was observed (P=0.01). In prostate cancers with neuroendocrine differentiation, RNA analysis confirmed the association of higher transcript levels in androgen deprivation-treated compared with untreated patients (P=0.01). In addition, hASH1 mRNA analysis in microdissected chromogranin A-positive and chromogranin A-negative areas within the same tumor demonstrated a two- to sevenfold increase of hASH1 mRNA expression in chromogranin A-positive tumor cell populations.

Roles of achaete-scute homologue 1 in DKK1 and E-cadherin repression and neuroendocrine differentiation in lung cancer

The proneural basic-helix-loop-helix protein achaete-scute homologue 1 (ASH1) is expressed in a very limited spectrum of normal and cancerous cells in a lineage-specific manner, including normal pulmonary neuroendocrine cells and lung cancer cells with neuroendocrine features. Our previous results indicated that ASH1 may play a crucial role in the growth and survival of lung cancers with neuroendocrine features, which prompted us to investigate the molecular function of ASH1 in relation to its involvement in carcinogenic processes. Herein, we report for the first time that ASH1 functions as a dual transcription factor by activating neuroendocrine differentiation markers and also repressing putative tumor suppressors. This protein was found to inactivate DKK1 and DKK3, negative regulators of Wnt/beta-catenin signaling, E-cadherin, and integrin beta1 through ASH1-mediated deacetylation and repressive trimethylation of lysine 27 (H3K27me3) of histone H3 in the promoter regions of DKK1 and E-cadherin. In addition, ASH1-transduced A549 adenocarcinoma cells exhibited markedly altered morphology characteristics compared with lung cancer cells with neuroendocrine features both in vitro and in vivo and also grew faster in vivo. Our results provide important clues for a better understanding of the molecular and cellular biological roles of ASH1 in the process of carcinogenesis of lung cancers with neuroendocrine features and warrant future investigations to shed light on the lineage-specific dependency of this transcription factor with dual functions.

Tumor suppressor role of Notch-1 signaling in neuroendocrine tumors

A growing body of literature is demonstrating that Notch signaling is a more complex process than originally thought. Contradictory findings of notch-1 acting as an oncogene or a tumor suppressor revealed that its role is very specific to the cellular context. In this review we focus on the tumor suppressor role of Notch-1 signaling in neuroendocrine tumors (NETs) such as carcinoid and medullary thyroid cancers. NETs secrete various bioactive hormones that can cause debilitating symptoms. Surgery is the only potential curative treatment for the patients with NETs. Notch-1 signaling is absent in these tumors and activation of Notch-1 significantly reduces tumor growth in vitro. Therefore, identification of compound(s) that activate the Notch-1 pathway in NETs could be a potential strategy to treat patients with NETs.

Neuro-endocrine tumours of the lung. A review of relevant pathological and molecular data

Neuroendocrine (NE) tumours of the lung include pure and mixed forms. In the former group, a continuum of lesions is recognised ranging from benign typical carcinoids to atypical carcinoids (having a low-grade behaviour, although often associated with regional and distant metastases), to the highly aggressive poorly differentiated carcinomas of the small and large cell types. In the mixed tumour group, the NE component is extensively represented in association with any of the non-small cell carcinoma subtypes (so-called combined carcinomas), or the NE component is restricted to a cell population scattered among adenocarcinoma cells (or more rarely within squamous or large cell carcinomas). The molecular profile of NE tumours has been widely investigated to identify features helpful for the diagnosis, prognosis and even therapy for this special lung tumour category. Specific chromosomal alterations, oncogene mutations and cell cycle molecule disregulation has been documented in NE tumours of the lung, as well as the expression of specific receptors or enzymes implicated in the response to biotherapies or to chemotherapeutic agents. The "molecular classification" of NE tumours should be integrated to morphology, for a better definition of the different histological types and a more appropriate selection of the therapeutic strategy.

Lineage-Specific Dependency of Lung Adenocarcinomas on the Lung Development Regulator TTF-1

Emerging evidence, although currently very sparse, suggests the presence of "lineage-specific dependency" in the survival mechanisms of certain cancers. TTF-1 has a decisive role as a master regulatory transcription factor in lung development and in the maintenance of the functions of terminal respiratory unit (TRU) cells. We show that a subset of lung adenocarcinoma cell lines expressing TTF-1, which presumably represent those derived from the TRU lineage, exhibit marked dependence on the persistent expression of TTF-1. The inhibition of TTF-1 by RNA interference (RNAi) significantly and specifically induced growth inhibition and apoptosis in these adenocarcinoma cell lines. Furthermore, a fraction of TTF-1-expressing tumors and cell lines displayed an increase in the gene dosage of TTF-1 in the analysis of 214 patients with non-small-cell lung cancer, including 174 adenocarcinomas, showing a tendency of higher frequency of increased gene copies at metastatic sites than at primary sites (P=0.07, by two-sided Fisher's exact test). These findings strongly suggest that in addition to the development and maintenance of TRU lineages in normal lung, sustained TTF-1 expression may be crucial for the survival of a subset of adenocarcinomas that express TTF-1, providing credence for the lineage-specific dependency model.

Achaete-scute homolog-1 linked to remodeling and preneoplasia of pulmonary epithelium

The basic helix-loop-helix protein achaete-scute homolog-1 (ASH1) is involved in lung neuroendocrine (NE) differentiation and tumor promotion in SV40 transgenic mice. Constitutive expression of human ASH-1 (hASH1) in mouse lung results in hyperplasia and remodeling that mimics bronchiolization of alveoli (BOA), a potentially premalignant lesion of human lung carcinomas. We now show that this is due to sustained cellular proliferation in terminal bronchioles and resistance to apoptosis. Throughout the airway epithelium the expression of anti-apoptotic Bcl-2 and c-Myb was increased and Akt/mTOR pathway activated. Moreover, the expression of matrix metalloproteases (MMPs) including MMP7 was specifically enhanced at the bronchiolo-alveolar duct junction and BOA suggesting that MMPs play a key role in this microenvironment during remodeling. We also detected MMP7 in 70% of human BOA lesions. Knockdown of hASH1 gene in human lung cancer cells in vitro suppressed growth by increasing apoptosis. We also show that forced expression of hASH1 in immortalized human bronchial epithelial cells decreases apoptosis. We conclude that the impact of hASH1 is not limited to cells with NE phenotype. Rather, constitutive expression of hASH1 in lung epithelium promotes remodeling through multiple pathways that are commonly activated during lung carcinogenesis. The collective results suggest a novel model of BOA formation via hASH1-induced suppression of the apoptotic pathway. Our study yields a promising new preclinical tool for chemoprevention of peripheral lung carcinomas.

RNA interference as a novel and powerful tool in immunopharmacological research

RNA interference (RNAi), as an evolutionarily conserved mechanism for silencing gene expression, is realized through the actions of both small interference RNA (siRNA) and microRNA. Since its discovery, siRNA has been rapidly deployed not only for the elucidation of gene function, but also for identification of drug targets and as a powerful therapeutic approach for a variety of diseases. In this review, we briefly introduce the mechanisms of RNAi, methods of siRNA design and delivery, and summarized recent researches on the therapeutic potential of RNAi for immune diseases.

Functional facets of the pulmonary neuroendocrine system

Pulmonary neuroendocrine cells (PNECs) have been around for 60 years in the scientific literature, although phylogenetically they are ancient. Their traditionally ascribed functions include chemoreception and regulation of lung maturation and growth. There is recent evidence that neuroendocrine (NE) differentiation in the lung is regulated by genes and pathways that are conserved in the development of the nervous system from Drosophila to humans (such as achaete-scute homolog-1), or implicated in the carcinogenesis of the nervous or NE system (such as the retinoblastoma tumor suppressor gene). In addition, complex neural networks are in place to regulate chemosensory and other functions. Even solitary PNECs appear to be innervated. For the first time ever, we have mouse models for lung NE carcinomas, including the most common and virulent small cell lung carcinoma. Moreover, PNECs may be important for inflammatory responses, and pivotal for lung stem cell niches. These discoveries signify an exciting new era for PNECs and are likely to have therapeutic and diagnostic applications.