Smoking Cessation after Cancer Diagnosis and Enhanced Therapy Response: Mechanisms and Significance

The adverse effects of smoking on human health have been recognized for several decades, especially in the context of cancer. The ability of tobacco smoke components, including tobacco-specific carcinogens and additive compounds such as nicotine, to initiate or promote tumor growth have been described in hundreds of studies. These investigations have revealed the tumor-promoting activities of nicotine and other tobacco smoke components and have also recognized the ability of these agents to suppress the efficacy of cancer therapy; it is now clear that smoking can reduce the efficacy of most of the widely used therapeutic modalities, including immunotherapy, radiation therapy, and chemotherapy. Several studies examined if continued smoking after cancer diagnosis affected therapy response; it was found that while never smokers or non-smokers had the best response to therapy, those who quit smoking at the time of diagnosis had higher overall survival and reduced side-effects than those who continued to smoke. These studies also revealed the multiple mechanisms via which smoking enhances the growth and survival of tumors while suppressing therapy-induced cell death. In conclusion, smoking cessation during the course of cancer therapy markedly increases the chances of survival and the quality of life.

HDAC11 activity contributes to MEK inhibitor escape in uveal melanoma

We previously demonstrated that pan-HDAC inhibitors could limit escape from MEK inhibitor (MEKi) therapy in uveal melanoma (UM) through suppression of AKT and YAP/TAZ signaling. Here, we focused on the role of specific HDACs in therapy adaptation. Class 2 UM displayed higher expression of HDACs 1, 2, and 3 than Class 1, whereas HDACs 6, 8, and 11 were uniformly expressed. Treatment of UM cells with MEKi led to modulation of multiple HDACs, with the strongest increases observed in HDAC11. RNA-seq analysis showed MEKi to decrease the expression of multiple HDAC11 target genes. Silencing of HDAC11 significantly reduced protein deacetylation, enhanced the apoptotic response to MEKi and reduced growth in long-term colony formation assays across multiple UM cell lines. Knockdown of HDAC11 led to decreased expression of TAZ in some UM cell lines, accompanied by decreased YAP/TAZ transcriptional activity and reduced expression of multiple YAP/TAZ target genes. Further studies showed this decrease in TAZ expression to be associated with increased LKB1 activation and modulation of glycolysis. In an in vivo model of uveal melanoma, silencing of HDAC11 limited the escape to MEKi therapy, an effect associated with reduced levels of Ki67 staining and increased cleaved caspase-3. We have demonstrated a novel role for adaptive HDAC11 activity in UM cells, that in some cases modulates YAP/TAZ signaling leading to MEKi escape.

A Novel PHD2/VHL-mediated Regulation of YAP1 Contributes to VEGF Expression and Angiogenesis

The transcriptional co-activator YAP1 is the major oncogenic component of the Hippo signaling pathway and contributes to the genesis and progression of various tumors, including non-small cell lung cancer (NSCLC). YAP1 levels are regulated by the canonical Hippo kinases, MST1/2 and LATS1/2, which modulate its cytoplasmic retention and proteasomal degradation. While non-canonical regulation of YAP1 has been reported, its role in hypoxic response is not fully elucidated. The studies presented here show that YAP1 levels and function are modulated by VHL and PHD2. YAP1 could regulate multiple genes involved in angiogenesis through E2F1; it also associates with HIF1α in cancer cells under hypoxic conditions, inducing the VEGF-A promoter. Under normoxic conditions, PHD2 associates with and hydroxylates specific proline residues on YAP1, facilitating its interaction with VHL and promoting ubiquitination and subsequent proteasomal degradation. Exposure to hypoxia dissociates YAP1 from PHD2 and VHL, elevating YAP1 levels and enhancing its association with HIF1α. YAP1-HIF1α interaction was higher in NSCLC and RCC samples, indicating a role for this interaction in the genesis of these cancers. Our results thus reveal a novel mode of regulation of YAP1 by PHD2 and VHL in normoxic cells, suggesting that YAP1-mediated induction of VEGF and other genes contributes to hypoxic response in tumors.

Lifetime ovulatory years and ovarian cancer gene expression profiles

BACKGROUND

Greater ovulatory years is associated with increased ovarian cancer risk. Although ovulation leads to an acute pro-inflammatory local environment, how long-term exposure to ovulation impacts ovarian carcinogenesis is not fully understood. Thus, we examined the association between gene expression profiles of ovarian tumors and lifetime ovulatory years to enhance understanding of associated biological pathways.

METHODS

RNA sequencing data was generated on 234 invasive ovarian cancer tumors that were high-grade serous, poorly differentiated, or high-grade endometrioid from the Nurses' Health Study (NHS), NHSII, and the New England Case Control Study. We used linear regression to identify differentially expressed genes by estimated ovulatory years, adjusted for birth decade and cohort, overall and stratified by menopausal status at diagnosis. We used false discovery rates (FDR) to account for multiple testing. Gene set enrichment analysis (GSEA) with Cancer Hallmarks, KEGG, and Reactome databases was used to identify biological pathways associated with ovulatory years.

RESULTS

No individual genes were significantly differentially expressed by ovulatory years (FDR > 0.19). However, GSEA identified several pathways that were significantly associated with ovulatory years, including downregulation of pathways related to inflammation and proliferation (FDR < 1.0 × 10-5). Greater ovulatory years were more strongly associated with downregulation of genes related to proliferation (e.g., E2F targets, FDR = 1.53 × 10-24; G2M checkpoints, FDR = 3.50 × 10-22) among premenopausal versus postmenopausal women at diagnosis. The association of greater ovulatory years with downregulation of genes involved in inflammatory response such as interferon gamma response pathways (FDR = 7.81 × 10-17) was stronger in postmenopausal women.

CONCLUSIONS

Our results provide novel insight into the biological pathways that link ovulatory years to ovarian carcinogenesis, which may lead to development of targeted prevention strategies for ovarian cancer.

Abstract 1523: Novel role of TBK1 in breast cancer EMT

TANK Binding Kinase 1 (TBK1) regulates interferon signaling and NFκB function by acting as a non-canonical IκB kinase. TBK1 also participates in RalB-mediated inflammatory responses and is essential for the survival of non-small cell lung cancers (NSCLC) driven by oncogenic KRAS. Recent evidence suggests a role for TBK1 as a driver of cancer progression and it is overexpressed in breast, colon, lung and pancreatic cancers. Our published results demonstrate that TBK1 is essential for proper microtubule dynamics and regulation of mitosis. Here we show that knockdown of TBK1 results in a decreased expression of mesenchymal genes involved in EMT and a re-distribution of β-catenin in breast cancer cells. Similarly, expression of matrix metalloproteinases 2 and 9 was altered. This led us to hypothesize that TBK1 acts as an EMT driver in cancer. Inhibition of TBK1 resulted in decreased adherence dependent as well as independent colony formation and stem cell self-renewal, while inducing senescence like phenotypes. We propose that TBK1 mediated EMT is mediated through its interaction with the transcription factor E2F1; the interaction was detected in breast cancer cell lines as well as breast cancer Tissue Micro Arrays. To get a holistic view of the changes that take place in the cell after TBK1 knockdown, we performed a global metabolomics and RNAseq analysis of breast cancer cell lines. An integrated analysis of this data suggested significant alterations in glucose, galactose and nucleotide metabolism upon TBK1 knockdown. Two of the genes that were markedly altered were aldoketoreductase1 B10 (AKR1B10) and thymidine phosphorylase (TP); attention was focused on these genes, as both have been reported to be cancer drivers and their over-expression results in poor prognosis. We observed a downregulation of AKR1B10 and TP in response to the TBK1 knockdown. Experiments are under way to investigate whether the pro-cancer role of TBK1 is dependent on AKR1B10 and TP, especially in breast cancer cells. These results suggest that TBK1 mediated EMT might be a function of the altered expression of mesenchymal proteins and the metabolic profile of the cell brought about by TBK1.

Citation Format: Meenu Maan, Mainak Dutta, Neha Jaiswal, Harold Saavedra, Srikumar Chellappan. Novel role of TBK1 in breast cancer EMT [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1523.

Novel HDAC11 inhibitors suppress lung adenocarcinoma stem cell self-renewal and overcome drug resistance by suppressing Sox2

Non-small cell lung cancer (NSCLC) is known to have poor patient outcomes due to development of resistance to chemotherapy agents and the EGFR inhibitors, which results in recurrence of highly aggressive lung tumors. Even with recent success in immunotherapy using the checkpoint inhibitors, additional investigations are essential to identify novel therapeutic strategies for efficacious treatment for NSCLC. Our finding that high levels of histone deacetylase 11 (HDAC11) in human lung tumor tissues correlate with poor patient outcome and that depletion or inhibition of HDAC11 not only significantly reduces self-renewal of cancer stem cells (CSCs) from NSCLC but also decreases Sox2 expression that is essential for maintenance of CSCs, indicates that HDAC11 is a potential target to combat NSCLC. We find that HDAC11 suppresses Sox2 expression through the mediation of Gli1, the Hedgehog pathway transcription factor. In addition, we have used highly selective HDAC11 inhibitors that not only target stemness and adherence independent growth of lung cancer cells but these inhibitors could also efficiently ablate the growth of drug-insensitive stem-like cells as well as therapy resistant lung cancer cells. These inhibitors were found to be efficacious even in presence of cancer associated fibroblasts which have been shown to contribute in therapy resistance. Our study presents a novel role of HDAC11 in lung adenocarcinoma progression and the potential use of highly selective inhibitors of HDAC11 in combating lung cancers.

Chromatin protein PC4 is downregulated in breast cancer to promote disease progression: Implications of miR-29a

The human transcriptional coactivator PC4 has numerous roles to play in the cell. Other than its transcriptional coactivation function, it facilitates chromatin organization, DNA damage repair, viral DNA replication, etc. Although it was found to be an essential protein in vivo, the importance of this multifunctional protein in the regulation of different cellular pathways has not been investigated in details, particularly in oncogenesis. In this study, PC4 downregulation was observed in a significant proportion of mammary tissues obtained from Breast cancer patient samples as well as in a subset of highly invasive and metastatic Breast cancer patient-derived cell lines. We have identified a miRNA, miR-29a which potentially reduce the expression of PC4 both in RNA and protein level. This miR-29a was found to be indeed overexpressed in a substantial number of Breast cancer patient samples and cell lines as well, suggesting one of the key mechanisms of PC4 downregulation. Stable Knockdown of PC4 in MCF7 cells induced its migratory as well as invasive properties. Furthermore, in an orthotopic breast cancer mice model system; we have shown that reduced expression of PC4 enhances the tumorigenic potential substantially. Absence of PC4 led to the upregulation of several genes involved in Epithelial to Mesenchymal Transition (EMT), indicating the possible mechanism of uniform tumour progression in the orthotropic mice. Collectively these data establish the role of PC4 in tumour suppression.

Abstract 378: HDAC inhibition enhances MEK antagonist therapy in uveal melanoma through combined blockade of YAP, AKT and RTK signaling

Around 85-90% of all uveal melanomas harbor driver mutations in GNAQ or GNA11 leading to constitutive activation of numerous signaling pathways, including the MAPK pathway. MEK inhibitors have been evaluated clinically for metastatic uveal melanoma, but the responses are short-lived and the mechanisms of adaptation are poorly understood. In the current study, we performed RNA-seq and activity-based protein profiling (ABPP) to define the adaptive response of uveal melanoma cells to MEK inhibition and to design more effective combination therapy strategies. These analyses showed that MEK inhibition caused cytoskeleton remodeling driven by cortactin/Rho-GTPases with an increase in YAP activity, which in turn allowed therapeutic escape. Cortactin knockdown decreased YAP activity in response to MEK inhibition, increased cell death in vitro and was associated with tumor shrinkage in vivo. The proteomic data showed that MEK inhibition increased HDAC activity and an increase in global protein deacetylation. Co-targeting of HDACs and MEK was associated with increased apoptosis, decreased survival in 2D and 3D cell culture assays and suppression of YAP signaling. As YAP was unlikely to be the only escape pathway, we performed kinome and RTK arrays and demonstrated MEK inhibition also increases ROR1/2 and IGF-1R phosphorylation, leading to downstream PI3K/AKT signaling. At a signal transduction level, the combination of a pan-HDAC inhibitor (panobinostat) with a MEK inhibitor (trametinib) blocked all of the adaptive signaling pathways we identified, including RTKs, AKT, YAP and cortactin. In vivo xenograft studies revealed the MEK/HDAC inhibitor combination to outperform either agent alone, leading to long-term decrease of tumor growth and the suppression of adaptive PI3K/AKT, cortactin and YAP signaling. These findings identify HDAC inhibitors as a promising combination partner for MEK inhibitors in advanced uveal melanoma that may lead to improved systemic responses.

Citation Format: Fernanda Faiao-Flores, Michael Emmons, Michael Durante, Biswarup Saha, Bin Fang, John Koomen, Srikumar Chellappan, Silvya Maria-Engler, Jonathan Licht, William Harbour, Keiran Smalley. HDAC inhibition enhances MEK antagonist therapy in uveal melanoma through combined blockade of YAP, AKT and RTK signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 378.

Abstract 4394: Molecular interplay between Tank-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality in the United States. Lung adenocarcinomas are highly correlated with smoking and are characterized by mutations in KRAS, EGFR, BRAF and other oncogenes. KRAS mutations are widespread in adenocarcinomas among smokers and known to be a key player in various downstream signaling pathways contributing to the tumorigenesis. Recently, a non-canonical IκB kinase, Tank Binding Kinase 1 (TBK1), has been found to contribute in KRAS mutant cancers. TBK1 has well documented functions in immune response, cell survival and in mitosis. While it has been suggested that TBK1-mediated regulation of Akt signaling might facilitate oncogenesis, the molecular mechanisms underlying TBK1 function downstream of KRAS is not fully elucidated.

Yes associated protein 1 (YAP1) is an oncogenic component of the Hippo signaling cascade which could promote KRAS mediated oncogenesis and could substitute for the loss of Kras in mouse models of pancreatic cancer. In our present study, we demonstrate a unique and novel interplay between TBK1 and the oncogenic Hippo effector molecule, YAP1. YAP1 and its paralog, TAZ are known transcriptional co-activators that function to maintain organ size during development and is often activated in cancers.

We find that TBK1 could physically interact with YAP1 and phosphorylate it at T110, T114, S128 and S131 residues in vitro. Knocking down (KD) or knock out (KO) of TBK1 resulted in a significant elevation of YAP1 expression at the protein level; surprisingly, without any effect at the mRNA level. Interestingly, the upregulation of YAP1 upon depletion of TBK1 was restricted to KRAS mutant NSCLC cell-lines and not in EGFR mutant cell lines. This elevation of YAP1 upon TBK1 KD was mainly observed in the nucleus; notably, there were only minimal changes in the levels of MST and LATS, raising the possibility that these changes occur independent of the classic hippo signaling pathway. Treatment with cycloheximide, an inhibitor of protein-translation, could not diminish the elevated level of YAP1 protein in the TBK1 depleted cells, indicating that the increased YAP1 level is due to enhanced protein stability, probably as a result of post-translational modification(s). Depletion of TBK1 also resulted in the induction of EMT-like features, promoting cell-migration in scratch assays and elevated the proportion of stem-like side-population cells, probably in a YAP1-dependent manner. An unbiased RNA-Seq analysis in A549 and H460 cells indicated that MAP kinase (MAPK) pathway is activated upon TBK1 KD, which might also be involved in the YAP1 protein regulation. Our recent experiments further support this argument. The in-depth molecular mechanism(s) by which TBK1 regulates YAP1 in KRAS mutant cells are under investigation, and we hypothesize that this regulatory event contributes to KRAS mediated oncogenesis in NSCLC.

Citation Format: Biswarup Saha, Neha Jaiswal, Namrata Bora-Singhal, Srikumar Chellappan. Molecular interplay between Tank-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4394.

Abstract 2052: A novel PHD2/VHL- mediated regulation of YAP1 and its role in vascular mimicry and tumor angiogenesis

Non-small cell lung cancer (NSCLC) is the leading cause of cancer related death worldwide. In this study, we show that transcriptional co-activator YAP1, the oncogenic component of the Hippo pathway, may contribute to the progression of NSCLC by supporting tumor angiogenesis and vascular mimicry of cancer stem-like cells (CSCs). NSCLC CSCs were found to have higher mRNA expression of VEGF receptor II (KDR) and Angiopoietin-2 (AngPT-2); depletion of YAP1 inhibited the promoter activity as well as the mRNA expression of VEGF, KDR and AngPT-2, with a corresponding reduction in vascular mimicry as well as tumor growth in a mouse xenograft studies. These results suggest a possible mechanism by which YAP1 regulates tumor angiogenesis.

A role for YAP1 in tumor angiogenesis was further supported by the finding that NSCLC cells grown in hypoxic conditions showed higher levels of YAP1. There was little to no changes in the canonical Hippo pathway proteins like LATS1/2, MST1/2, SAV and MOB as well as in the expression of TAZ, an orthologue of YAP1. Elevated YAP1 was found to associate with HIF1α under hypoxic conditions and enhance its transcriptional activity; YAP1 could increase HIF1α-mediated induction of the VEGF promoter confirmed by chromatin immunoprecipitations and transient transfection assays. Elevated levels of YAP1 and HIF1α interaction was detected in lung tumor tissues compared to normal lung tissue, as detected by proximity ligation assay (PLA), suggesting that the higher association of YAP1 with HIF1α and resulting transcriptional activity might have contributed to tumor growth.

An examination of the underlying mechanism by which YAP1 levels are elevated under hypoxic conditions revealed a novel regulation of YAP1 protein by prolyl hydroxylase PHD2 and E3 ubiquitin ligase VHL, which are mainly known to regulate HIF1α under normoxia. PHD2 was found to hydroxylate proline residue(s) of YAP1 between aa 284 to aa 289 as seen by mutational studies. YAP1 was found to directly associate with PHD2 as well as with VHL. Depletion of PHD2 or treatment with DMOG, an inhibitor of prolyl hydroxylases, reduced YAP1 association with VHL ligase. This further elevated YAP1 levels in the nucleus. Interestingly, disruption of the YAP1-PHD2 interaction using a domain specific peptide enhanced the angiogenic tubule formation by endothelial cells. Our data therefore identifies a novel non-canonical pathway of regulation of YAP1 that supports angiogenesis and tumor growth.

Citation Format: Namrata Bora Singhal, Biswarup Saha, Srikumar Chellappan. A novel PHD2/VHL- mediated regulation of YAP1 and its role in vascular mimicry and tumor angiogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2052.

Abstract 1998: Novel interplay between TANK-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality in the United States. Lung adenocarcinomas are highly correlated with smoking and are characterized by mutations in KRAS, EGFR, BRAF and other oncogenes. Among them, KRAS mutations are widespread in adenocarcinomas in smokers and known to be a key player in various downstream signaling pathways contributing to genesis and progression of these tumors. More recently, the non-canonical IκB kinase, Tank Binding Kinase 1 (TBK1), has been found to facilitate tumorigenesis in KRAS mutant cancers. TBK1 has well documented functions in immune response, cell survival as well as in mitosis. While it has been suggested that TBK1-mediated regulation of Akt signaling might facilitate oncogenesis, the molecular mechanisms underlying TBK1 function downstream of KRAS is not fully elucidated. In a similar vein, Yes associated protein 1 (YAP1), the oncogenic component of the Hippo signaling cascade has been found to promote KRAS mediated oncogenesis and could substitute for the loss of Kras in mouse models of pancreatic cancer. In the present study, we have demonstrated a unique and novel molecular interplay between TBK1 and the oncogenic components of Hippo effector molecules, YAP1/TAZ. YAP1 and its ortholog, TAZ are known to be transcriptional co-activators, function to maintain organ size but often get activated in various types of cancer.

We find that TBK1 physically interacts with YAP1, and knock-down (KD) or knocking-out (KO) of TBK1 resulted in a significant elevation of YAP1/TAZ expressions at protein level. We have tested four different KRAS and EGFR mutant NSCLC cell-lines; interestingly, the upregulation of YAP1 upon depletion of TBK1 was only restricted to the KRAS mutant cell-lines. Further, depletion of TBK1 led to the enrichment of YAP1 in the nucleus; notably, there were only minimal changes in the levels of MST1/2 and LATS, raising the possibility that these changes occur independent of the classic hippo signaling pathway. Depletion of TBK1 also resulted in the induction of EMT-like features in these cells, and increased the proportion of stem-like side-population. Mechanistically, TBK1 physically interacts with YAP1 in the cultured cells, and could phosphorylate it in vitro, on T110, T114, S128 and S131 residues. The underlying molecular mechanism(s) by which TBK1 regulates YAP1 expression are under investigation, and we hypothesize that this regulatory event is exclusive to KRAS mediated oncogenesis, especially in the context of NSCLC.

Citation Format: Biswarup Saha, Neha Jaiswal, Namrata Bora-Singhal, Srikumar Chellappan. Novel interplay between TANK-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1998.

Abstract 2310: Targeting transcription-associated CDKs is an effective way to combat glioblastoma and medulloblastoma with minimal effect on primary neurons

Glioblastoma multiforme (GBM) is the most prevalent and malignant brain tumor in adults. Currently there are no effective therapies to manage the disease efficiently. Medulloblastoma is the most common type of pediatric tumor and accounts for approximately 15% of all pediatric brain tumors. We aimed to determine if targeting the transcription-associated cyclin-dependent kinases, cdk7 and cdk9, using specific inhibitors, could interfere with the growth and metastatic properties of glioblastoma and medulloblastoma cell lines. We tested the effectiveness of Flavopiridol, a known inhibitor of cdk4, cdk6, pTEFb and cdk9; THZ1, a cdk7 inhibitor; and SNS032, which is known to inhibit cdk2, cdk7 and cdk9, on U87 and SNB19 glioblastoma, H4 neuroglioma and Daoy medullobastoma cells. Treatment with these pharmacological agents showed very strong cytotoxic effects on these cancer cells as measured by MTT (3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide) assay. Among these agents the cdk7 inhibitor was most effective and showed efficacy at nanomolar concentrations. Additionally, the inhibitors interfered with the cancer cell migration, as measured by wound healing assay, and anchorage independent growth, as measured by soft agar colony formation. In stark contrast, the inhibitors had no cytotoxic effects on primary neurons. Mechanistically, western blot analysis showed that the tumor cells treated with the inhibitors had reduced levels of Pol II C-terminal domain phosphorylation, indicative of its inhibition and suppression of transcription. Furthermore, inhibitor treatment resulted in a significant reduction in p70S6 kinase phosphorylation, suggesting that in addition to the transcriptional machinery, the translational machinery is also affected upon treatment with the aforementioned cdk inhibitors. Immunostaining analysis of the cells showed a marked reduction in the levels of P-Pol II and P-p70S6 kinase upon inhibitor treatment, confirming that the cdk inhibitors indeed interfere with both transcription and translation. These inhibitors appear to be working in a p53-dependent fashion. These novel findings shed light on potential mechanisms that can be targeted to combat both glioblastoma and medulloblastoma effectively. More specifically, our studies imply that cdk7 and cdk9 inhibitors may serve as potential therapies for effective management of brain tumor.

Citation Format: Isha Bhutada, Srikumar Chellappan, Jaya Padmanabhan. Targeting transcription-associated CDKs is an effective way to combat glioblastoma and medulloblastoma with minimal effect on primary neurons [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2310.

Abstract 5063: Beta-arrestin-1 function in CAFs is necessary for enhancement of self-renewal of NSCLC stem-like cells

Cigarette smoking is a major risk factor in the genesis of non-small cell lung cancer (NSCLC), which accounts for 85% of all lung cancer. Nicotine, the addictive component of tobacco smoke, has been shown to induce proliferation, invasion and epithelial-mesenchymal transition (EMT) in NSCLC cells in vitro and promote growth and metastasis of NSCLCs in vivo. These nicotine-induced pro-tumorigenic functions are facilitated through activation of nicotinic acetylcholine receptors (nAChRs). The scaffolding protein β-arrestin-1 (ARRB1), which is involved in the desensitization of signals from activated G-protein-coupled receptors (GPCRs), plays a vital role in mediating the proliferative effects of nicotine through nAChR signaling. Nicotine induces the nuclear translocation of ARRB1 and increases the expression of E2F-regulated proliferative and survival genes to promote the growth and progression of NSCLCs. β-arrestin-1 is also necessary for nicotine-mediated induction of EMT; nicotine could induce a variety of mesenchymal genes including fibronectin, vimentin, ZEB1 and ZEB2 in a β-arrestin-1 dependent manner. Further, nicotine promotes stemness of NSCLCs by inducing SCF (Stem cell factor) in a β-arrestin-1 dependent manner. While all these studies from NSCLC derived cell lines and tumor tissues highlight the significance of β-arrestin-1 in cell-autonomous pro-tumorigenic functions, the role of β-arrestin-1 in NSCLC microenvironment is largely unknown. Cancer associated fibroblasts (CAFs) are shown to promote the self-renewal and proliferation of cancer stem cells in vitro and in vivo. In the present study we address whether β-arrestin-1 is necessary for CAFs to promote self-renewal of stem like cells from NSCLCs.

We generated a GFP expressing KRAS mutant NSCLC cell line A549 (A549-GFP). The side population (SP) cells from A549-GFP was isolated and used in 3D co-culture with lung CAFs in a stem cell selective medium. Our results show that CAFs can promote the self-renewal of SP cells, as measured by a sphere formation assay. Interestingly, depletion of β-arrestin-1 in CAFs significantly impaired the ability of CAFs to promote self-renewal and enhance sphere formation. Experiments are under way to assess the downstream mediators of β-arrestin-1 in CAFs that bring about the impairment in self renewal, which includes signaling molecules like TBK1 and a variety of cytokines. These studies are expected to shed new light on the mechanisms by which CAFs promote self-renewal and tumor growth, enabling identification of actionable pathways downstream of β-arrestin-1 that can potentially be targeted for NSCLC therapy.

Citation Format: Mohan Kumar Durai Raj, Namrata Bora-Singhal, Srikumar Chellappan. Beta-arrestin-1 function in CAFs is necessary for enhancement of self-renewal of NSCLC stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5063.

Abstract 4701: Verteporfin inhibits surface PD-L1 expression in triple-negative breast cancer (TNBC) cells

Background: Programmed death ligand 1 (PDL1) is commonly expressed on the surface of many tumor cells, including breast cancer. The activity of tumor-infiltrating lymphocytes (TIL) is inhibited by PDL1. High PD-L1 basal cells (particularly basal B) overexpress genes involved in invasion, motility, and chemoresistance (Soliman et al., 2014). Targeting and blocking PD-L1 may enhance eradication of aggressive breast cancer cells by the immune system. Verteporfin (VP), a photosensitizer used to treat macular degeneration, was found to inhibit PD-L1 expression in a high-throughput screen. Studies demonstrated VP inhibits YAP activation by disrupting YAP-TEAD interactions and preventing YAP induced oncogenic growth (Zhang et al., 2016). Here we demonstrate the inhibitory effect of VP on PD-L1 expression in TNBC cell lines.

Methods: MDA-MB-231 cells co-cultured with human PBMCs were treated with VP (Sigma) in presence of concanavalin A (ConA) and analyzed using flow cytometry to study levels of CD8+IFNg+ cells. TNBC cell lines (MDA-MB-231, BT-20, HCC-1143, Hs-578T) were treated with VP at doses ranging from 1µM-10µM for 24 hrs. The cells were processed for flow cytometry, Western blot and RT-PCR to check PD-L1 in mechanistic studies looking at manipulation of YAP pathway genes.

Results: When MDA-MB-231 cells were co-cultured with normal human PBMCs in the presence of ConA, the CD8+IFNg+ stained cells were reduced compared to PBMC + ConA alone. Interestingly, in the group treated with VP, rescue of CD8+IFNg+ cells was observed. Moreover, MDA-MB-231, BT-20, HCC-1143 and Hs-578T TNBC cells treated with VP showed a significant dose-dependent inhibition of PD-L1 expression by flow cytometry. Western blot analysis also showed complete clearance of PD-L1 protein band with the lowest dose (1µM) used. However, RT-PCR analysis did not show a significant fold change in mRNA levels of PD-L1 in MDA-MB-231 treated cells. Surprisingly, mechanistic studies performed by silencing YAP1, E2F1, and TBK1 in MDA-MB-231, BT-20 and HS-578 T showed a decline in PD-L1 in E2F1 silenced cells, highlighting a plausible role of E2F1-PDL1 signaling axis. However, no change in PD-L1 expression was seen in cells silenced with YAP1 and TBK1. Further, chromatin-immunoprecipitation assay demonstrated E2F1 binding to PD-L1 promoter.

Conclusion: Our data so far demonstrate that verteporfin treatment leads to inhibition of PD-L1 in TNBC cell lines and improvement in CD8+IFNg+ cells, indicating that VP might have potential for treatment approaches. Our study warrants further attention towards understanding the mechanism of action of VP in inhibiting PD-L1 and the role of E2F1 in the process.

Citation Format: Fatema Khambati, Neha Jaiswal, Srikumar Chellappan, Hatem Soliman. Verteporfin inhibits surface PD-L1 expression in triple-negative breast cancer (TNBC) cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4701.

Abstract 3460: TBK1 regulates mitotic progression by modulating spindle assembly checkpoint in cancer cells

TANK Binding Kinase 1 (TBK1) is a non-canonical IkB kinase that contributes to KRAS-driven lung cancer. It is activated by phosphorylation of Serine-172 by TLR and RIG1 signaling, and this circuit triggers phosphorylation of IRF3 and IRF7, activation of NFκB and the expression of proinflammatory genes and interferons. In addition to its role role in regulating innate immunity, TBK1 also promotes oncogenesis by phosphorylating Akt and enhancing cell survival and by promoting autophagy and mitophagy. TBK1 is also induced under hypoxic conditions and expressed at significant levels in many solid tumors. TBK1 also contributes to prostate cancer dormancy and drug resistance by inhibiting mTOR and to tamoxifen resistance of breast cancer cells by enhancing transcriptional activity of ERα.

Recent studies from our lab revealed a novel role for TBK1 in regulating mitosis. It was found that levels of phospho-TBK1 increases and localizes to centrosomes and the mitotic spindles during mitosis. Depletion of TBK1 was shown to trigger defects in spindle apparatus and prevents mitotic progression (Pillai et al., Nature Communications, 2015). TBK1 physically interacts and phosphorylates centrosomal protein CEP170 and mitotic apparatus protein NuMA. At the same time, it is not clear whether TBK1 regulates mitosis my modulating the Spindle Assembly Checkpoint (SAC).

Our results show that TBK1 colocalizes with Cdc20 on the centrosomes. Additionally, TBK1-inhibited cells showed an increase in the colocalization of BUBR1 and Cdc20, with enhanced recruitment of BUBR1 to kinetochores. To further study how TBK1 affects SAC, lung and breast cancer cells were depleted of TBK1 by CRISPR/Cas9 mediated genome editing. Cells depleted of TBK1 showed very few cells in the mitotic stage; those that entered mitosis had residual levels of TBK1 and showed multipolarity and unusually stable and bundled microtubules. TBK1 knockout cells not only showed aberrant mitotic structures and had elevated levels of SAC components including BUBR1 and Cdc20. Surprisingly, level of mitotic Cyclin B1 remained unchanged in spite of elevated levels of Cdc20 indicating a possible inactivation of Anaphase Promoting complex (APC/C). Also, percentage of Cyclin B1 positive cells was significantly high in mitotic cells enriched using double thymidine block in the presence of TBK1 inhibitor BX795 (R9+BX) and MRT67307 (R9+MRT) as compared to untreated mitotic cells (R9). Further, double thymidine blocked released cells displayed elevated levels of SAC components upon treatment with TBK1 inhibitors. All these findings suggest that TBK1 facilitates mitotic progression through satisfying SAC.

Citation Format: Neha Jaiswal, Smitha Pillai, Namrata BoraSinghal, Srikumar Chellappan. TBK1 regulates mitotic progression by modulating spindle assembly checkpoint in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3460. doi:10.1158/1538-7445.AM2017-3460

Abstract 365: Cross-talk between BRAF and Hippo/YAP1 signaling in melanoma

Hippo/YAP1 signaling pathway is a tumor suppressive pathway that controls the organ size by modulating the cell growth, proliferation and apoptosis and is conserved from Drosophila to mammals. In mammals, the Hippo tumor suppressor pathway consists of cascade of kinases in which MST1/2 phosphorylates and activates LATS1/2. The latter phosphorylates the oncogenic transcriptional coactivators YAP1 and TAZ, leading to their cytoplasmic retention by 14-3-3 proteins and/or degradation. Inactivation of MST and LATS kinases allows YAP1 and/ or TAZ nuclear translocation and subsequent activation of their target genes.

Deregulation of Hippo pathway can induce tumors in model organisms and occurs in wide range of human cancers including melanoma. Merlin, a key component of this pathway which inhibits YAP1, is mutated/deleted in 8% of melanoma. Majority of uveal melanomas are driven by Gq/11 mutations that trigger YAP1 nuclear translocation, promoting tumor growth. High levels of YAP1 in BRAFV600E mutant tumors confer resistance to RAF- and MEK- targeted therapy in patients.

Our results show that YAP1 level is elevated in melanoma and the YAP1 inhibitor verteporfin alone or in combination with B-RAF inhibitor PLX4720 reduces the viability, invasion and anchorage-independent growth of B-RAF V600E mutant SK-MEL-28 and SK-MEL-5 cells. In addition, verteporfin treatment also reduced the viability of PLX4720 resistant 1205 cells. Western blot analysis of verteporfin and PLX4720 treated SK-MEL-28 and SK-MEL-5 cells displayed reduced levels of YAP1, B-RAF, pERK, MEK and pMEK.

We also report a novel physical interaction between YAP1 and B-RAF; this could be detected using double immunofluorescence and immunoprecipitation-western blotting techniques in both B-RAF V600E mutant and N-Ras mutant melanoma cells. Proximity ligation assays on tissue microarray showed that YAP1-B-RAF interaction is elevated in metastatic melanoma compared to normal skin. These novel findings highlight the crosstalk between B-RAF and Hippo/YAP1 signaling which might have a

potential role in melanoma development and progression. Further, experiments are in progress to elucidate the functional significance of YAP1-B-RAF interaction in melanoma.

Citation Format: Mohan Kumar Durai Raj, Jonathan Nguyen, Namrata Bora-singhal, Jane Messina, Geoffrey Gibney, Srikumar Chellappan. Cross-talk between BRAF and Hippo/YAP1 signaling in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 365. doi:10.1158/1538-7445.AM2017-365

Abstract 2145: Regulation of YAP1 during hypoxia and its novel role in vascular mimicry and angiogenesis

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality. As in other solid tumors, angiogenesis is necessary for the growth and progression of NSCLC. Vascular mimicry is a phenomenon in which non-endothelial tumor cells form angiogenic vascular structures. We have shown in the past that NSCLC cancer stem-like cells (CSCs) have unique ability to undergo vascular mimicry. The present study shows that transcriptional co-activator YAP1, the oncogenic component of the Hippo pathway, enables the NSCLC CSCs to form angiogenic tubule-like structures in matrigel. Inhibition of YAP1 or depletion of YAP1 suppressed vascular mimicry of CSCs as well as angiogenic tubule formation by HUVECs in matrigel as well as in a fibrin gel bead assay (FIBA) assay. The NSCLC CSCs were found to have higher mRNA expression of VEGF receptor II (KDR) and Angiopoietin-2 (AngPT-2) and depletion of YAP1 reduced the expression of VEGF, KDR and AngPT-2 mRNA; these promoters were induced by YAP1 in transient transfection assays, suggesting a possible molecular mechanism by which YAP1 regulates angiogenesis. Hypoxia is a strong inducer of tumor angiogenesis, cancer progression and metastasis. Our experiments showed that NSCLC cells grown in hypoxic conditions or treated with hypoxia mimetic DMOG have higher YAP1 mRNA and protein expression. However, such a change was not observed in the expression of YAP1 orthologue, TAZ, nor in the canonical Hippo pathway proteins like LATS1&2, Mst1&2, Sav or Mob. We identified a novel regulation of YAP1 by prolyl hydroxylase PHD2, which is mainly known to regulate HIF1α. PHD2 was found to hydroxylate proline residue(s) in YAP1 in a region between aa 284 to aa 289 as seen by mutational analysis. YAP1 was found to directly bind to PHD2 and depletion of PHD2 or treatment with DMOG which is an inhibitor of prolyl hydroxylases, elevated YAP1 protein levels in the nucleus. Further, YAP1 was found to associate with HIF1α as detected by co-immunoprecipitation experiments and could enhance HIF1α-mediated induction of the VEGF promoter. Proximity ligation assays performed on TMA showed enhanced YAP1 and HIF1α interaction in lung tumor tissues compared to normal cells. Our data suggest a novel regulation of YAP1 in hypoxic environment that supports angiogenesis and tumor growth.

Citation Format: Namrata Bora Singhal, Srikumar Chellappan. Regulation of YAP1 during hypoxia and its novel role in vascular mimicry and angiogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2145. doi:10.1158/1538-7445.AM2017-2145

Abstract 2496: Novel role of YAP1 in tumor angiogenesis and vascular mimicry

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that cancer stem-like cells (CSCs) contribute to the genesis and progression of NSCLC. These cells have been shown to form differentiated tumor cells upon receiving appropriate micro-environmental cues and can give rise to multiple components of the tumor, including the vasculature. We isolated the CSCs from NSCLC cell lines and PDX tumors based on the side population (SP) phenotype. SP cells displayed high self-renewal capacity, were highly drug resistant, and could form metastatic tumors in immunocompromised mice. The present study shows that the transcriptional co-activator YAP1, which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and the ability to form angiogenic tubule-like structures in matrigel, a unique feature of cancer stem-like cells that is also called as vascular mimicry. Inhibition of YAP1 by a small molecule inhibitor Visudyne or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of SP cells. The stem -like SP cells from NSCLC were found to have higher mRNA expression of VEGF receptor II (KDR) and Angiopoietin-2 (AngPT-2) which are crucial genes during angiogenic tubule regression and growth in addition to YAP1. Further, depletion of YAP1 with siRNAs reduced the expression of VEGF, KDR and AngPT-2 mRNA levels. Overexpression of YAP1 resulted in increase in the promoter activity of both KDR and AngPT-2 in transient transfection experiments. This suggests that YAP1 might play a role in regulating VEGF, KDR and AngPT-2 mediated angiogenic functions in cancer cells.

In addition to vascular mimicry, YAP1 appears to play a unique role in regulating the expression of genes involved in angiogenesis. Hypoxia is known to contribute towards angiogenesis as well as cancer progression and metastasis. Preliminary experiments showed that cells grown in hypoxic conditions or treated with hypoxia mimetic compounds like DMOG resulted in increase in YAP1 mRNA and protein expression. However, such an increase was not observed in YAP1 orthologue, TAZ or other canonical Hippo pathway proteins. Hypoxia-inducible factor-1alpha (HIF-1α) is the key transcription factor that regulates the expression of various hypoxia response genes like VEGF. We find that YAP1 directly interacts with HIF-1α as detected by co-immunoprecipitation experiments and proximity ligation assays (PLA). YAP1 also associated with VEGF promoter as seen in ChIP RT-PCRs, and this interaction was elevated under hypoxic environment. Our data suggest a distinct role for YAP1 in regulating hypoxia response, promoting tumor angiogenesis and vascular mimicry.

Citation Format: Namrata Bora Singhal, Srikumar Chellappan. Novel role of YAP1 in tumor angiogenesis and vascular mimicry. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2496.

Gli1-Mediated Regulation of Sox2 Facilitates Self-Renewal of Stem-Like Cells and Confers Resistance to EGFR Inhibitors in Non-Small Cell Lung Cancer

Non–small cell lung cancer (NSCLC) patients have very low survival rates because the current therapeutic strategies are not fully effective. Although EGFR tyrosine kinase inhibitors are effective for NSCLC patients harboring EGFR mutations, patients invariably develop resistance to these agents. Alterations in multiple signaling cascades have been associated with the development of resistance to EGFR inhibitors. Sonic Hedgehog and associated Gli transcription factors play a major role in embryonic development and have recently been found to be reactivated in NSCLC, and elevated Gli1 levels correlate with poor prognosis. The Hedgehog pathway has been implicated in the functions of cancer stem cells, although the underlying molecular mechanisms are not clear. In this context, we demonstrate that Gli1 is a strong regulator of embryonic stem cell transcription factor Sox2. Depletion of Gli1 or inhibition of the Hedgehog signaling significantly abrogated the self-renewal of stem-like side-population cells from NSCLCs as well as vascular mimicry of such cells. Gli1 was found to transcriptionally regulate Sox2 through its promoter region, and Gli1 could be detected on the Sox2 promoter. Inhibition of Hedgehog signaling appeared to work cooperatively with EGFR inhibitors in markedly reducing the viability of NSCLC cells as well as the self-renewal of stem-like cells. Thus, our study demonstrates a cooperative functioning of the EGFR signaling and Hedgehog pathways in governing the stem-like functions of NSCLC cancer stem cells and presents a novel therapeutic strategy to combat NSCLC harboring EGFR mutations.

Nicotine-Mediated Regulation of Nicotinic Acetylcholine Receptors in Non-Small Cell Lung Adenocarcinoma by E2F1 and STAT1 Transcription Factors

Cigarette smoking is the major risk factor for non-small cell lung cancer (NSCLC), which accounts for 80% of all lung cancers. Nicotine, the addictive component of tobacco smoke, can induce proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), angiogenesis, and survival in NSCLC cell lines, as well as growth and metastasis of NSCLC in mice. This nicotine-mediated tumor progression is facilitated through activation of nicotinic acetylcholine receptors (nAChRs), specifically the α7 subunit; however, how the α7 nAChR gene is regulated in lung adenocarcinoma is not fully clear. Here we demonstrate that the α7 nAChR gene promoter is differentially regulated by E2F and STAT transcription factors through a competitive interplay; E2F1 induces the promoter, while STAT transcription factors repress it by binding to an overlapping site at a region -294 through -463bp upstream of the transcription start site. Treatment of cells with nicotine induced the mRNA and protein levels of α7 nAChR; this could be abrogated by treatment with inhibitors targeting Src, PI3K, MEK, α7 nAChR, CDK4/6 or a disruptor of the Rb-Raf-1 interaction. Further, nicotine–mediated induction of α7 nAChR was reduced when E2F1 was depleted and in contrast elevated when STAT1 was depleted by siRNAs. Interestingly, extracts from e-cigarettes, which have recently emerged as healthier alternatives to traditional cigarette smoking, can also induce α7 nAChR expression in a manner similar to nicotine. These results suggest an autoregulatory feed-forward loop that induces the levels of α7 nAChR upon exposure to nicotine, which enhances the strength of the signal. It can be imagined that such an induction of α7 nAChR contributes to the tumor-promoting functions of nicotine.

YAP1 Regulates OCT4 Activity and SOX2 Expression to Facilitate Self-Renewal and Vascular Mimicry of Stem-Like Cells

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that stem-like cells contribute to the genesis and progression of NSCLC. Our results show that the transcriptional coactivator yes-associated protein 1 (YAP1), which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and ability to form angiogenic tubules. Inhibition of YAP1 by a small molecule or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of stem-like cells. These effects of YAP1 were mediated through the embryonic stem cell transcription factor, Sox2. YAP1 could transcriptionally induce Sox2 through a physical interaction with Oct4; Sox2 induction occurred independent of TEAD2 transcription factor, which is the predominant mediator of YAP1 functions. The binding of Oct4 to YAP1 could be detected in cell lines as well as tumor tissues; the interaction was elevated in NSCLC samples compared to normal tissue as seen by proximity ligation assays. YAP1 bound to Oct4 through the WW domain, and a peptide corresponding to this region could disrupt the interaction. Delivery of the WW domain peptide to stem-like cells disrupted the interaction and abrogated Sox2 expression, self-renewal, and vascular mimicry. Depleting YAP1 reduced the expression of multiple epithelial-mesenchymal transition genes and prevented the growth and metastasis of tumor xenografts in mice; overexpression of Sox2 in YAP1 null cells rescued these functions. These results demonstrate a novel regulation of stem-like functions by YAP1, through the modulation of Sox2 expression.

Abstract 2085: Nicotine-mediated regulation of Sox2 and its implications in the biology of non-small cell lung adenocarcinoma stem-like cells

Nicotine, the addictive component of tobacco smoke, is known to promote proliferation, migration, and invasion of multiple cancer cells, including those of the lung and the pancreas. In addition, nicotine can promote the growth and metastasis of such cancers in mouse xenograft models. More recently, nicotine has also been implicated in promotion of cancer stem cell properties such as self-renewal. Our lab has shown that stimulation of lung cancer cells with nicotine results in activation of Src kinase in a β-arrestin-1 dependent manner, resulting in inactivation of the Rb tumor suppressor protein and subsequently the activation of E2F-mediated transcription of proliferative and survival genes. In addition to proliferative and survival genes, the E2F family of transcription factors has been shown to activate genes like matrix metalloproteinases that are involved in invasion and migration, indicating a role for E2F in the growth and metastasis of cancers downstream of nicotine. Our recent studies have shown that E2F1 can also induce genes which promote stemness, such as Stem Cell Factor (SCF/c-kit ligand), promoting nicotine-mediated enhancement of self-renewal of stem-like cells. In addition to these findings, here we demonstrate the ability of nicotine to induce the embryonic stem cell factor Sox2, which is indispensable for self-renewal and maintenance of stem cell properties, as well as the ability of E2F1 transcription factor to regulate Sox2 gene expression in non-small cell lung cancer cells. Western blot analysis revealed an induction of Sox2 protein at 18 and 24 hours post nicotine stimulation, which diminished by 48 hours. Similarly, quantitative real time PCR analysis showed an increase in Sox2 mRNA levels at 18 and24, hours post nicotine stimulation. Analysis of a 1500bp region of the human Sox2 gene promoter revealed multiple predicted E2F binding sites. Chromatin immunoprecipitation assays demonstrated E2F transcription factors to associate with the Sox2 promoter at multiple predicted binding sites. Transient transfection experiments further demonstrated the ability of E2F1 to induce the expression of a Sox2-luciferase reporter. These results suggest that nicotine may enhance lung cancer stem cell properties in part through the induction of Sox2, and this could potentially be mediated via E2F transcriptional activation. Further studies are underway to elucidate the impact of nicotine mediated induction of Sox2 on stemness, the underlying mechanism of activation, and the implications this has for non-small cell lung cancer. These studies can be expected to have a direct impact on our understanding of the molecular mechanism involved in the initiation, growth and metastasis of non-small cell lung cancer, especially in smokers.

Citation Format: Courtney Schaal, Namrata Bora Singhal, Smitha Pillai, Jonathan Nguyen, Srikumar Chellappan. Nicotine-mediated regulation of Sox2 and its implications in the biology of non-small cell lung adenocarcinoma stem-like cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2085. doi:10.1158/1538-7445.AM2015-2085

Abstract 3771: Tank-binding kinase 1 associates with centrosomes and regulates microtubule dynamics and mitosis

TANK Binding Kinase 1 (TBK1) regulates interferon signaling and NFκB function by acting as a non-canonical IκB kinase. TBK1 also participates in RalB-mediated inflammatory responses and contributes to the survival of non-small cell lung cancers (NSCLC) driven by oncogenic KRAS. In addition, TBK1 could phosphorylate and activate Akt, modulate autophagy and alter the autocrine cytokine network in cancer cells indicating oncogenic roles in addition to its immune regulatory functions. Our studies reveal that TBK1 plays a novel and direct role in promoting mitotic progression of lung cancer cells by phosphorylating multiple substrates during mitosis as well as by modulating microtubule dynamics. Levels of active phospho-TBK1 are elevated in mitotic cells where it localized to centrosomes, mitotic spindles and midbody as seen by confocal microscopy. Inhibition of TBK1 by kinase inhibitors such as BX795, Amlexanox, MRT67037 or depletion of TBK1 by shRNA resulted in mitotic defects and decreased the number of mitotic cells. TBK1 could interact with the centrosomal protein CEP170 and the nuclear mitotic apparatus protein NuMA as seen by GST binding assays, immunoprecipitation-western blot assays and proximity ligation assays. In addition, TBK1 could phosphorylate CEP170 and NuMA in in vitro kinase assays; mass spectrometry analysis revealed that TBK1 phosphorylated 12 serine residues and a threonine residue of CEP170 and five serine residues of NuMA. Inhibition or depletion of TBK1 prevented the centrosomal localization of CEP170 and the association of NuMA with the spindle poles. TBK1 depletion in A549 and H1650 cells resulted in more stable microtubules; further, depletion of TBK1 inhibited the interaction of CEP170 with the microtubule depolymerase Kif2b and the binding of NuMA to Dynein, resulting in mitotic abnormalities or mitotic arrest. In addition, inhibition of specific interaction between TBK1 and CEP170 using a 13 amino acid peptide resulted in inhibition of mitosis, enhanced microtubule stability and mitotic defects. These results are paradigm shifting that suggest TBK1 plays a significant role in regulating microtubule dynamics and mitotic progression of cells and this might have significant relevance to cancer as well as innate immune response.

Citation Format: Smitha R. Pillai, Jonathan Nguyen, Joseph Johnson, Eric Haura, Domenico Coppola, Srikumar Chellappan. Tank-binding kinase 1 associates with centrosomes and regulates microtubule dynamics and mitosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3771. doi:10.1158/1538-7445.AM2015-3771

Abstract 1516: YAP1 regulates Oct4 activity and Sox2 expression, facilitating self-renewal and vascular mimicry of stem-like cells

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that cancer stem-like cells (CSCs) contribute to the genesis and progression of NSCLC. These cells have been shown to form differentiated tumor cells upon receiving appropriate microenvironmental cues and can give rise to multiple components of the tumor, including the vasculature. Earlier work from our laboratory had shown that Hoechst 33342 dye excluding side-population (SP) cells are enriched in cells having stem-like properties. SP cells displayed high self-renewal capacity, were highly drug resistant, and could form metastatic tumors in immunocompromised mice. The present study shows that the transcriptional co-activator YAP1, which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and ability to form angiogenic tubules in matrigel. Inhibition of YAP1 by a small molecule inhibitor Visudyne or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of stem-like cells. These effects of YAP1 were mediated through the embryonic stem cell transcription factor Sox2. YAP1 could associate with the Sox2 promoter and could transcriptionally induce Sox2 as seen by qRT-PCRs, ChIP assays and promoter luciferase assays; this induction was through a physical interaction of YAP1 with Oct4 protein. The binding of Oct4 to YAP1 could be detected in cell lines as well as NSCLC tumor tissues as seen by immunofluorescence, proximity ligation assays (PLA), immunoprecipitation-western blot experiments and GST binding assays. Interestingly, the interaction was elevated in NSCLC samples compared to normal tissue as seen by PLA. A peptide that could disrupt the interaction between YAP1 and Oct4 abrogated Sox2 expression, self-renewal and vascular mimicry. Depleting YAP1 reduced the expression of EMT genes and prevented the growth and metastasis of tumor xenografts in mice, while overexpression of Sox2 in YAP1 depleted cells could rescue self-renewal of stem-like cells. In conclusion, our results demonstrate that YAP1 can modulate the stem-like functions of cancer stem cells by regulating Sox2, and this regulatory pathway can potentially be targeted for combating NSCLC.

Citation Format: Namrata Bora Singhal, Jonathan Nguyen, Courtney Schaal, Deepak Perumal, Sandeep Singh, Domenico Coppola, Srikumar Chellappan. YAP1 regulates Oct4 activity and Sox2 expression, facilitating self-renewal and vascular mimicry of stem-like cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1516. doi:10.1158/1538-7445.AM2015-1516

β-arrestin-1 mediates nicotine-induced metastasis through E2F1 target genes that modulate epithelial-mesenchymal transition

Cigarette smoking is a major risk factor in the development of non-small cell lung cancer (NSCLC), which accounts for 80% of all lung cancers. Nicotine, the major addictive component of tobacco smoke, can induce proliferation, invasion, and epithelial-to-mesenchymal transition (EMT) in NSCLC cell lines and promote metastasis of NSCLC in mice. Here, we demonstrate that the scaffolding protein β-arrestin-1 is necessary for nicotine-mediated induction of mesenchymal genes vimentin and fibronectin as well as EMT regulators ZEB1 and ZEB2. Nicotine induced changes in cell morphology and ablate tight junctions consistent with EMT; β-arrestin-1, but not β-arrestin-2, was required for these changes. β-Arrestin-1 promoted the expression of the mesenchymal genes, as well as ZEB1 and ZEB2, through the mediation of the E2F1 transcription factor; this required Src kinase activity. Stimulation of multiple NSCLC cell lines with nicotine led to enhanced recruitment of β-arrestin-1 and E2F1 on vimentin, fibronectin, and ZEB1 and ZEB2 promoters. Furthermore, there was significantly more β-arrestin-1 and E2F1 associated with these promoters in human NSCLC tumors, and β-arrestin-1 levels correlated with vimentin and fibronectin levels in human NSCLC samples. A549-luciferase cells lacking β-arrestin-1 showed a significantly reduced capacity for tumor growth and metastasis when orthotopically implanted into the lungs of SCID-beige mice. Taken together, these studies reveal a novel role for β-arrestin-1 in the growth and metastasis of NSCLC.

Abstract 5001: GATA3 abrogates TGFbeta-mediated breast cancer invasion and metastasis

Transforming growth factor β (TGFβ) is a potent and context dependent regulator of tumor progression. TGFβ promotes the lung metastasis of basal-like (but not the luminal-like) breast cancer. Here, we demonstrated that fascin, a pro-metastasis actin bundling protein, was a direct target of the canonical TGFβ-Smad4 signaling pathway in basal-like breast cancer cells. TGFβ and Smad4 induced fascin overexpression by directly binding to a Smad binding element on the fascin promoter. Through data mining, we identified GATA3, a transcription factor crucial for mammary gland morphogenesis and luminal differentiation, as a potential regulator of fascin overexpression. When ectopically expressed in basal-like breast cancer cells, GATA-3 abrogated Smad4-mediated overexpression of fascin and other TGFβ response genes, invadopodium formation, cell migration and invasion, suggesting suppression of the canonical TGFβ-Smad4 signaling axis. Mechanistically, GATA3 might abrogate TGFβ and Smad4-mediated fascin overexpression by abolishing the interactions between Smad4 and its DNA binding elements, potentially through physical interactions between GATA3 and Smad3/4. Our findings provide mechanistic insight into how TGFβ-mediated cell motility and invasiveness are differentially regulated in breast cancer.

Citation Format: Jianwei Sun, Huifang He, Smitha Pillai, Srikumar Chellappan, Shengyu Yang. GATA3 abrogates TGFbeta-mediated breast cancer invasion and metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5001. doi:10.1158/1538-7445.AM2014-5001

Mammalian lysine histone demethylase KDM2A regulates E2F1-mediated gene transcription in breast cancer cells

It is established that histone modifications like acetylation, methylation, phosphorylation and ubiquitination affect chromatin structure and modulate gene expression. Lysine methylation/demethylation on Histone H3 and H4 is known to affect transcription and is mediated by histone methyl transferases and histone demethylases. KDM2A/JHDM1A/FBXL11 is a JmjC-containing histone demethylase that targets mono- and dimethylated Lys36 residues of Histone H3; its function in breast cancer is not fully understood. Here we show that KDM2A is strongly expressed in myoepithelial cells (MEPC) in breast cancer tissues by immunohistochemistry. Ductal cells from ductal carcinoma in situ (DCIS) and infiltrating ductal carcinoma (IDC) show positive staining for KDM2A, the expression decreases with disease progression to metastasis. Since breast MEPCs have tumor-suppressive and anti-angiogenic properties, we hypothesized that KDM2A could be contributing to some of these functions. Silencing KDM2A with small interfering RNAs demonstrated increased invasion and migration of breast cancer cells by suppressing a subset of matrix metalloproteinases (MMP-2, -9, -14 and -15), as seen by real-time PCR. HUVEC cells showed increased angiogenic tubule formation ability in the absence of KDM2A, with a concomitant increase in the expression of VEGF receptors, FLT-1 and KDR. KDM2A physically bound to both Rb and E2F1 in a cell cycle dependent manner and repressed E2F1 transcriptional activity. Chromatin immunoprecipitation (ChIP) assays revealed that KDM2A associates with E2F1-regulated proliferative promoters CDC25A and TS in early G-phase and dissociates in S-phase. Further, KDM2A could also be detected on MMP9, 14 and 15 promoters, as well as promoters of FLT1 and KDR. KDM2A could suppress E2F1-mediated induction of these promoters in transient transfection experiments. These results suggest a regulatory role for KDM2A in breast cancer cell invasion and migration, through the regulation of E2F1 function.

Nicotine-mediated invasion and migration of non-small cell lung carcinoma cells by modulating STMN3 and GSPT1 genes in an ID1-dependent manner

Background

Inhibitor of DNA binding/Differentiation 1 (ID1) is a helix loop helix transcription factor that lacks the basic DNA binding domain. Over-expression of ID1 has been correlated with a variety of human cancers; our earlier studies had shown that reported ID1 is induced by nicotine or EGF stimulation of non-small cell lung cancer (NSCLC) cells and its down regulation abrogates cell proliferation, invasion and migration. Here we made attempts to identify downstream targets of ID1 that mediate these effects.

Methods

A microarray analysis was done on two different NSCLC cell lines (A549 and H1650) that were transfected with a siRNA to ID1 or a control, non-targeting siRNA. Cells were stimulated with nicotine and genes that were differentially expressed upon nicotine stimulation and ID1 depletion were analyzed to identify potential downstream targets of ID1. The prospective role of the identified genes was validated by RT-PCR. Additional functional assays were conducted to assess the role of these genes in nicotine induced proliferation, invasion and migration. Experiments were also conducted to elucidate the role of ID1, which does not bind to DNA directly, affects the expression of these genes at transcriptional level.

Results

A microarray analysis showed multiple genes are affected by the depletion of ID1; we focused on two of them: Stathmin-like3 (STMN3), a microtubule destabilizing protein, and GSPT1, a protein involved in translation termination; these proteins were induced by both nicotine and EGF in an ID1 dependent fashion. Overexpression of ID1 in two different cell lines induced STMN3 and GSPT1 at the transcriptional level, while depletion of ID1 reduced their expression. STMN3 and GSPT1 were found to facilitate the proliferation, invasion and migration of NSCLC cells in response to nAChR activation. Attempts made to assess how ID1, which is a transcriptional repressor, induces these genes showed that ID1 down regulates the expression of two transcriptional co-repressors, NRSF and ZBP89, involved in the repression of these genes.

Conclusions

Collectively, our data suggests that nicotine and EGF induce genes such as STMN3 and GSPT1 to promote the proliferation, invasion and migration of NSCLC, thus enhancing their tumorigenic properties. These studies thus reveal a central role for ID1 and its downstream targets in facilitating lung cancer progression.

Cationic lipid guided short-hairpin RNA interference of annexin A2 attenuates tumor growth and metastasis in a mouse lung cancer stem cell model

The role of side populations (SP) or cancer stem-like cells (CSC) in promoting the resistance phenotype presents a viable anticancer target. Human-derived H1650 SP cells over-express annexin A2 (AnxA2) and SOX2, and are resistant to conventional cytotoxic chemotherapeutics. AnxA2 and SOX2 bind to proto-oncogenes, c-Myc and c-Src, and AnxA2 forms a functional heterotetramer with S100A10 to promote tumor motility. However, the combined role of AnxA2, S100A10 and SOX2 in promoting the resistant phenotype of SP cells has not been investigated. In the current studies, we examined for the first time a possible role of AnxA2 in regulating SA100A10 and SOX2 in promoting a resistant phenotype of lung tumors derived from H1650 SP cells. The resistance of H1650 SP cells to chemotherapy compared to H1650 MP cells was investigated by cell viability studies. A short hairpin RNA targeting AnxA2 (shAnxA2) was formulated in a liposomal (cationic ligand-guided, CLG) carrier and characterized for size, charge and entrapment and loading efficiencies; CLG carrier uptake by H1650 SP cells was demonstrated by fluorescence microscopy, and knockdown of AnxA2 confirmed by qRT-PCR and Western blot. Targeting of xenograft and orthotopic lung tumors was demonstrated with fluorescent (DiR) CLG carriers in mice. The therapeutic efficacy of CLG-AnxA2, compared to that of placebo, was investigated after 2 weeks of treatment in terms of tumor weights and tumor burden in vivo. Compared to mixed population cells, H1650 SP cells showed exponential resistance to docetaxel (15-fold), cisplatin (13-fold), 5-fluorouracil (31-fold), camptothecin (7-fold), and gemcitabine (16-fold). CLG carriers were nanoparticulate (199nm) with a slight positive charge (21.82mV); CLG-shAnx2 was of similar size (217nm) with decreased charge (12.11mV), and entrapment and loading efficiencies of 97% and 6.13% respectively. Fluorescence microscopy showed high uptake of CLG-shAnxA2 in H1650 SP cells after 2h resulting in a 6-fold reduction in AnxA2 mRNA expression and 92% decreased protein expression. Fluorescence imaging confirmed targeting of tumors and lungs by DiR-CLG carriers with sustained localization up to 4h in mice. CLG-shAnxA2 treatment of mice significantly reduced the weights of lung tumors derived from H1650 SP cells and tumor burden was reduced to only 19% of controls. The loss in tumor weights in response to CLG-shAnxA2 was associated with a significant loss in the relative levels of AnxA2, SOX2, total β-catenin and S100A10, both at the RNA and protein levels. These results suggest the intriguing possibility that AnxA2 may directly or indirectly regulate relative levels of β-catenin, S100A10 and SOX2, and that the combination of these factors may contribute to the resistant phenotype of H1650 SP cells. Thus down-regulating AnxA2 using RNAi methods may provide a useful method for targeting cancer stem cells and help advance therapeutic efficacy against lung cancers.

GATA3 transcription factor abrogates Smad4 transcription factor-mediated fascin overexpression, invadopodium formation, and breast cancer cell invasion

Transforming growth factor β (TGFβ) is a potent and context-dependent regulator of tumor progression. TGFβ promotes the lung metastasis of basal-like (but not the luminal-like) breast cancer. Here, we demonstrated that fascin, a pro-metastasis actin bundling protein, was a direct target of the canonical TGFβ-Smad4 signaling pathway in basal-like breast cancer cells. TGFβ and Smad4 induced fascin overexpression by directly binding to a Smad binding element on the fascin promoter. We identified GATA3, a transcription factor crucial for mammary gland morphogenesis and luminal differentiation, as a negative regulator of TGFβ- and Smad4-induced fascin overexpression. When ectopically expressed in basal-like breast cancer cells, GATA-3 abrogated TGFβ- and Smad4-mediated overexpression of fascin and other TGFβ response genes, invadopodium formation, cell migration, and invasion, suggesting suppression of the canonical TGFβ-Smad signaling axis. Mechanistically, GATA3 abrogated the canonical TGFβ-Smad signaling by abolishing interactions between Smad4 and its DNA binding elements, potentially through physical interactions between the N-terminal of GATA3 and Smad3/4 proteins. Our findings provide mechanistic insight into how TGFβ-mediated cell motility and invasiveness are differentially regulated in breast cancer.

Lung cancer stem cells: Molecular features and therapeutic targets

Lung cancers are highly heterogeneous and resistant to available therapeutic agents, with a five year survival rate of less than 15%. Despite significant advances in our knowledge of the genetic alterations and aberrations in signaling pathways, it has been difficult to determine the basis of lung cancer heterogeneity and drug resistance. Cancer stem cell model has attracted a significant amount of attention in recent years as a viable explanation for the heterogeneity, drug resistance, dormancy and recurrence and metastasis of various tumors. At the same time, cancer stem cells have been relatively less characterized in lung cancers. This review summarizes the current understanding of lung cancer stem cells, including their molecular features and signaling pathways that drive their stemness. This review also discusses the potential startegies to inhibit the signaling pathways driving stemness, in an effort to eradicate these cells to combat lung cancer.

Abstract 2655: Inhibitor of Differentiation/DNA binding (ID) proteins modulate the stem-like features of NSCLC cells by regulating the expression of Oct4, Sox2 and Nanog

Non-small cell lung cancer (NSCLC) accounts for 85% of total lung cancer cases and demonstrates a strong association with tobacco use. The overall survival rate for NSCLC patients diagnosed in the late stages of cancer is very low, demonstrating the need for novel therapeutic strategies to combat this disease. While the genetic changes contributing to lung cancer in smokers and non-smokers are fairly well characterized, the downstream signaling events involved in tumorigenesis are not fully understood. Our laboratory had identified the transcriptional regulator, ID1 (inhibitor of differentiation/DNA binding 1), as a common mediator of oncogenesis in NSCLC, irrespective of the smoking history. NSCLC tumors are heterogeneous and are either refractory to the available treatments or develop resistance to therapy. Cancer stem cells (CSC) hypothesis has emerged as an explanation for tumor initiation, drug resistance and metastasis. CSCs have been shown to have tumor initiating properties.Given that the ID gene family (ID1- ID4) is known to be expressed in the embryonic progenitor cells and have been have been suggested to promote self renewal capacity of embryonic stem cells, and since ID proteins are known to promote the genesis of NSCLC, we examined whether these proteins contribute to the stemness of NSCLC CSCs. Side-population (SP) cells with CSC properties were isolated from four different NSCLC lines using flow cytometric sorting based on Hoechst 33342 exclusion. The mRNA and protein expression of the ID1-4 genes was assessed in the sorted SP cells from these cell lines and compared to the main population (MP) cells. Among the four ID proteins, ID3 expression was found to be comparatively higher in the SP cells compared to MP cells from all the cell lines; there was a difference in the levels of other family members as well. Depletion of ID3 expression by siRNAs led to a decrease in SP frequency; further, this led to a reduced expression of embryonic stem cell transcription factors Sox2, Oct4 and Nanog expression. Similar results were obtained when ID1 was depleted as well. Interestingly, depletion of ID1 or ID3 significantly impaired the ability of SP cells to self-renew, as measured by sphere formation assays. Further analysis suggests that the transcriptional co-repressor ZBP89 might be involved in the ID-mediated repression of the ES cell transcription factors. Our findings suggest that Id proteins might play a role in the maintenance of stem like properties in NSCLC CSCs and this is facilitated by the regulation of ES cell transcription factors in a ZBP89-dependent manner. Our ongoing studies are aimed at elucidating the potential correlation of gene expression levels of ID family members with the survival of NSCLC patients, using microarray datasets.

Citation Format: Namrata Bora Singhal, Deepak Perumal, Srikumar Chellappan. Inhibitor of Differentiation/DNA binding (ID) proteins modulate the stem-like features of NSCLC cells by regulating the expression of Oct4, Sox2 and Nanog. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2655. doi:10.1158/1538-7445.AM2013-2655

Abstract 5446: Nicotinic acetylcholine receptors activate TBK1 in a β-arrestin-1 dependent manner to promote NSCLC growth

Lung cancer is the leading cause of death in the United States. Non-small cell lung cancer (NSCLC) accounts for 85% of total lung cancer cases and demonstrates a strong association with tobacco use. Nicotine, an active component of tobacco smoke has been found to induce proliferation, invasion and epithelial-mesenchymal transition in NSCLC cell lines and promote the metastasis of NSCLC in mouse models. Nicotine induces cell proliferation and EMT utilizing a scaffolding protein, β-arrestin-1, which translocates to nucleus and associates with E2F1 transcription factor in response to nicotine stimulation. TBK1, a non-canonical IκB kinase has been shown to couple pathogen surveillance to induction of host defense mechanisms and contribute to inflammation as well as oncogenesis. These findings raise the possibility that TBK1 contributes to the onset as well as progression of NSCLCs through cell autonomous pathways in cancer cells, and indirectly through activating the inflammatory pathways in the tumor microenvironment. Since nicotinic acetylcholine receptor (nAChR) signaling is thought to augment Ras mediated cell proliferative pathways and confers resistance to apoptosis, attempts were made to assess whether TBK1 is induced by nAChR stimulation. Here we report that activation of nicotinic acetylcholine receptors leads to activation of TBK1 and β-arrestin-1 was required for this. Antagonists of alpha 7 subunit of nAChR such as bungarotoxin or inhibitor of α3/β2 and α4/β2 subunit DhβE abrogated nicotine induced TBK1 phosphorylation; further, depletion of β-arrestin-1 using siRNAs prevented the nicotine-mediated activation of TBK1. Inhibition of Src using dasatinib also could inhibit nicotine induced TBK1 phosphorylation. Interestingly, treatment of NSCLC cell lines with TBK1 inhibitor BX-795 resulted in significant inhibition of nicotine induced S phase entry as seen by BrdU incorporation assays. Cotransfection of TBK1 along with E2F1 significantly enhanced E2F1 mediated induction of E2F target promoters in transient transfection assays. Additionally, in an orthotopic lung cancer model in SCID-beige mice, implantation of A549-luciferase stable cells lacking β-arrestin-1 showed a decrease in primary tumor growth and also resulted in significantly lower levels of nicotine-induced metastasis when compared to controls. Mouse lung tissue sections with β-arrestin-1 depleted cells showed low levels of phosphorylated TBK-1 as compared to lung sections where control cells were implanted. Taken together, these data suggest that TBK1 contributes to nicotine induced growth and progression of NSCLC.

Citation Format: Smitha Pillai, Jonathan Nguyen, Eric Haura, Domenico Coppola, Srikumar Chellappan. Nicotinic acetylcholine receptors activate TBK1 in a β-arrestin-1 dependent manner to promote NSCLC growth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5446. doi:10.1158/1538-7445.AM2013-5446

Abstract 5271: Nicotinic acetylcholine receptors and EGF induce c-Kit ligand/Stem Cell Factor (SCF) in a β-arrestin-1 and E2F1 dependent manner in NSCLC

β-arrestin-1 (ARRB1), a scaffolding protein involved in the termination or desensitization of signals arising from activated G-protein-coupled receptors (GPCRs) has been shown to play a role in invasion and proliferation of many cancers, including nicotine-induced proliferation of human non-small cell lung cancers (NSCLCs). In this study, we carried out microarray analysis of cells lacking β-arrestin-1 which have been rendered quiescent and subsequently stimulated with nicotine or EGF. Nicotine induced and β-arrestin-1 dependent genes from the microarray data were analyzed. We identified 296 genes that were upregulated and 208 that were downregulated by nicotine in a β-arrestin-1 dependent fashion. The functional pathway analysis tool, MetaCoreTM (Genego, MI, USA) was used to obtain curated molecular interactions related to the above selected genes. We selected top 10 genes from both up and down regulated list for prognosis prediction. Prognostic prediction was carried out using a subset of NCI Director's Challenge Set. Kaplan-Meier analyses for 5 year as well as overall survival showed significance for 4 genes namely COL4A4, NFASC, SCF and ZNF137 by log-rank test. We also examined whether the expression of these gens correlated with smoking; it was found that SCF strongly differentiated smokers from non-smokers implying an important role of this gene in lung carcinogenesis induced by smoking.

Stem cell factor (SCF) is the ligand of the c-Kit proto-oncogene product. It is a major human cytokine for the self-renewal, proliferation and differentiation of numerous embryonic, adult hematopoietic and primordial stem cells. Earlier reports show that uncontrolled activity of c-Kit contributes to formation of an array of human tumors. This unregulated activity of c-Kit may be due to overexpression or mutational activation suggesting that SCF-c-Kit signaling can be a potential target for cancer therapy. We elucidate the molecular mechanisms by which nicotine as well as EGF induces the expression of SCF in lung adenocarcinoma cell lines A549 and H1650. ChIP assays and transient transfection experiments showed that transcription factor E2F1 can positively regulate SCF expression at the transcriptional level; depletion of E2F1 or β-arrestin-1 prevented the nicotine-mediated induction of SCF. Given that the binding of SCF to c-Kit leads to activation of multiple downstream signaling pathways including Src, PI3-kinase and MAP/ERK pathways, our data suggest that the SCF/c-Kit pathway plays a central role in lung carcinogenesis, and may be a potential therapeutic target for combating NSCLC.

Citation Format: Deepak Perumal, Smitha Pillai, Srikumar Chellappan. Nicotinic acetylcholine receptors and EGF induce c-Kit ligand/Stem Cell Factor (SCF) in a β-arrestin-1 and E2F1 dependent manner in NSCLC . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5271. doi:10.1158/1538-7445.AM2013-5271

Abstract 1803: Transcriptional regulation of nicotinic acetylcholine receptors (nAChRs) by E2F family transcription factors in non-small cell lung cancer

Nicotine, the addictive component of cigarette smoke, has been shown to promote cell proliferation, migration, invasion, and angiogenesis in multiple cancer types. Earlier studies from our lab had shown that nicotine can promote the growth and metastasis of non-small cell lung carcinoma (NSCLC) in mouse models. While a broad range of nAChRs have been found to be expressed on NSCLC cell lines, nicotine-mediated proliferation, invasion, and migration are facilitated predominantly through the α7 subunit. Consistent with this, α7 nAChR levels are elevated in NSCLC in mice that were administered nicotine. Stimulation of α7 nAChR with nicotine has been reported to activate Src, resulting in inactivation of the retinoblastoma (Rb) tumor suppressor protein and enhancing E2F-mediated transcription. The Rb-E2F transcriptional regulation pathway is known to induce genes involved in cell cycle progression, angiogenesis, and metastasis implicating it in tumor survival and progression. Given this background, attempts were made to elucidate whether nAChR genes are regulated by the Rb-E2F pathway. Analysis of a 2000bp promoter region of the human α7 gene revealed the presence of multiple E2F binding sites. Transient transfection experiments showed α7 to be responsive to multiple E2Fs. E2F1 was found to associate with the α7 promoter via chromatin immunoprecipitation assays. Depletion of E2F genes via small interfering RNA demonstrated a differential regulation of α7 by E2F family members 1-5. These results raise the possibility that exposure to nicotine stimulates the α7 signaling cascade resulting in elevated E2F1-mediated activation of various proliferative promoters, including that of α7 itself in a positive feedback mechanism. In addition to the α7 nAChR, recent genome wide association studies (GWAS) have identified a susceptibility locus for human lung cancer at 15q25.1 which encodes for nAChR subunits α3 and α5. Promoter analysis has revealed that both α3 and α5 have multiple potential E2F binding sites, as well. Preliminary knock down of E2F family members via small interfering RNA has suggested these subunits may also be differentially regulated by the E2F family of transcription factors. Further studies are under way to elucidate the role of E2F in the regulation of nAChR α3 and α5, and how this impacts nicotine signaling as well as growth and progression of NSCLC.

Citation Format: Courtney M. Schaal, Smitha Pillai, Jackie L. Johnson, Srikumar Chellappan. Transcriptional regulation of nicotinic acetylcholine receptors (nAChRs) by E2F family transcription factors in non-small cell lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1803. doi:10.1158/1538-7445.AM2013-1803

α7 nicotinic acetylcholine receptor subunit in angiogenesis and epithelial to mesenchymal transition

Cigarette smoking is strongly correlated with many diseases like cancer, cardiovascular disease and macular degeneration. Nicotine, the main active and addictive component of tobacco smoke has recently been shown to enhance angiogenesis in many experimental systems and animal models. The pro-angiogenic activity of nicotine is mediated by nicotinic acetylcholine receptors, particularly the alpha 7 subunit, that are expressed on a variety of non-neuronal cells including those in the vasculature such as endothelial cells and smooth muscle cells. The present review focuses on the role of α7nAChR in mediating the pro-angiogenic effects of nicotine and describes the molecular mechanisms involved in nicotine-induced angiogenesis as well as epithelial to mesenchymal transition. These observations on nicotine function highlight the therapeutic potential of α7nAChR agonists and antagonists for combating angiogenesis related diseases.

Abstract 3361: Sensitization of chemoresistant H1650 lung cancer stem cells to chemotherapy by combination treatment with novel diindolylmethane compounds

Introduction Effective cancer therapy is hampered by the development of multidrug resistance by most cancer types. Cancer Stem Cells (CSCs) which are Side Population (SP) cells from tumors are attributed to the drug resistance phenotype. Efficient therapies for the successful eradication of tumor would have to employ agent(s) capable of inhibiting the self-renewal pathways and blocking or avoiding the drug-efflux property of these CSCs. Experimental Procedures Cell culture: The H1650 mixed population cells were maintained in DMEM:F12 (50:50) containing 2% PSN and supplemented with 10% fetal bovine serum (FBS) in the presence of 5% CO2 at 37[[Unsupported Character - &#8304;]]C. The H1650 SP cells were cultured in DMEM:F12 (50:50) containing, 1x Nitrogen supplement, 10 µg/mL each of bFGF and EGF. In vitro cytotoxicity studies: The crystal violet dye assay was used to determine the viability of both cell types 72 hours after treatment with test compounds. Cell invasion assay: The invasion of cells through a basement membrane matrix was assessed using the Cultrex 96-well collagen I cell invasion assay from Trevigen according to manufacturer's protocol. Cell migration assay: Migration of cells was determined using the wound healing assay before and after 24 hours of incubation post-treatment. Results The H1650 mixed population cells produced IC50 values of 11.03 µM, 2.68 µM, 8.70 µM, 2.63 µM, 6.48 µM, 5.06 µM, and 6.82 µM after treatment with Cisplatin, Gemcitabine, Doxorubicin, Fluorouracil, Camptothecin, DIM-5 and DIM-8, respectively. Significantly higher IC50 values were observed after similar treatments with Cisplatin (142.01 µM), Gemcitabine (42.68 µM), Doxorubicin (133.76 µM), Fluorouracil (81.01 µM), Camptothecin (48.51 µM), DIM-5 (15.67 µM) and DIM-8(19.69 µM). The invasiveness of the side population cells was seen to be generally diminished following treatment with 25 µM of test compound with percentage invasion ranging between 13.07% and 66.63% and a mean invasion of 37.92%. Further, the side population cells exhibited a much greater migratory index relative to the mixed population cells. Conclusions The resistance of the H1650 stem cells to chemotherapy is evident from the comparatively high IC50 values.; the exception being DIM-5 and DIM-8 exhibiting about 2 to 7 times more anticancer effect. These two agents act on the TR3/Nur77 nuclear receptor as activators and deactivators of the receptor, respectively, with resultant apoptotic events occurring downstream. With such demonstrable anticancer activities, the DIM compound may be potentially useful in sensitizing H1650 stem cells to chemotherapy when given in combination.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3361. doi:1538-7445.AM2012-3361

Abstract 5598: Interaction between BRAF inhibitor PLX-4720 and CDK inhibitors can sensitize melanoma cells with BRAF V600E mutation

BRAF V600E mutation happens in 60% of all melanomas cases and this mutation is responsible to poor prognosis of the disease. BRAF is part of the MAPK signaling pathway and the V600E mutation of BRAF confers full activation of this survival pathway. Several clinical trials are being conducted using mutated BRAF as a target but so far, all this trials works during a certain moment but soon, melanoma cells becomes resistant to treatment by activating some survival pathways that can continues the signal initialized in the MAPK pathway. Our objective is to evaluate if the combination of BRAF inhibitors and CDKs inhibitors can suppress the acquired resistance of V600E melanoma cells to BRAF inhibitors. Two melanoma cell lines were used in this study. The SKMel 28 cell line, which has BRAF V600E mutation, and the SKMel 02, which is wild type to BRAF. Olomoucine and Roscovitine were the CDKs inhibitors used in this study, while PLX-4720 was BRAF inhibitor. Western blot and Real time PCR were used to verify some survival pathways, like the MAP3K8 and the PRKD3 pathway, that are overexpressed after BRAF inhibition and MTT assay was used to verify cell viability with both treatments combined. The combination of Olomoucine and PLX-4720 or Roscovitine and PLX-4720 could sensitize the BRAF V600E mutated melanoma cell line SKMel 28, but not the BRAF wild type melanoma cell line SKMel 02. Two survival pathways (MAP3K8 and PRKD3) which are activated after BRAF inhibition by PLX-4720 were downregulated in the presence of the CDKs inhibitors in the SKMel 28 melanoma cell line. Also, the retinoblastoma protein was not phosphorylated when the SKMel28 melanoma cell line was treated with the BRAF inhibitor together with the CDKs. The treatment with the BRAF inhibitor and the CDKs inhibitors can sensitize BRAF V600E melanoma cells by decreasing cell viability, downregulation of survival pathways induced by the BRAF inhibitor and preventing Rb phosphorylation. This strategy may overcome the acquired resistance of BRAF-mutated melanoma after treatment with its inhibitors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5598. doi:1538-7445.AM2012-5598

Abstract 268: Differential regulation of MMP promoters by E2F transcription factors: Potential role of c-MYC and Id1

The retinoblastoma tumor suppressor, Rb, is the major negative regulator of E2F-1 transcription factor, and the Rb-E2F pathway is altered in most cancers. Further, many oncogenic mutations initiate tumors by targeting the Rb-E2F pathway. E2Fs regulate genes involved in a variety of biological processes, including angiogenesis, apoptosis, and differentiation, but it is unclear whether these molecules contribute to cancer cell invasion and metastasis. To investigate the role of E2F in metastasis, we analyzed the promoters of matrix metalloproteinase genes (MMPs), which are major contributors to the invasion and migration programs. We find that many MMP genes had potential E2F binding sites; we focused on MMP2, MMP9, MMP14, and MMP15 promoter, which have multiple E2F binding sites. Chip assays showed Rb, and E2Fs 1-5 could bind to the each MMP promoter. Transient transfection experiments with MMP promoter-luciferase constructs showed thatMMP9, MMP14, and MMP15-luc promoters were induced by E2Fs, whereas the MMP2 promoter was repressed by E2F1-5 in A549, and H1650 NSCLC cell lines. QRT-PCR showed that MMP2 was upregulated in A549 cells transfected with an siRNA targeting E2F1 and E2F3, whereas other MMPs were downregulated. To determine if MMP2 was repressed in an Rb-dependent manner, A549 cells stably expressing shRNA targeting Rb or a non-targeting control were transiently transfected with MMP2-luc construct and E2F1. In both cases, the MMP2-luc promoter was repressed by E2F1, suggesting that the repression is Rb-independent. Further, cells transfected with MMP2-luc promoter and E2F1 had less luciferase activity than cells transfected with MMP2 alone, independent of BRG-1, YY1, HDAC1, prohibitin-1, mSIN3a, or SUV39h1. Further, depletion of these co-repressors did not enhance MMP2 mRNA levels when compared to cells depleted of E2F1 alone. To determine if this repression is through binding site competition, we examined the effect of depleting transcription factors that have potential binding sites in the MMP2 promoter and were in close proximity to the E2F binding sites. We found that depletion of c-Myc and ID1 significantly enhanced MMP2 luciferase activity, and there was less repression from E2F1 in transient transfection experiments. These data suggest that E2F family members can repress the MMP2 promoter through mechanisms that may involve c-MYC and ID1.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 268. doi:10.1158/1538-7445.AM2011-268

Abstract 4994: Downstream targets of Id1 transcription factor in non-small cell lung cancer

Id1 (Inhibitor of DNA binding/Differentiation) is a helix loop helix (HLH) protein, regulates transcription by binding to bHLH transcription factors and preventing their binding to the DNA. Id1 is especially known to mediate repression of E box proteins and Ets transcription factors. Id1 gene is overexpressed in lung, breast, pancreatic and prostate cancer and it is thought to promote the progression and metastasis of these tumors. At the same time, not much is known about its role in non-small cell lung carcinoma.Preliminary studies from our lab shows that Nicotine as well as EGF induces Id1 in both adenocarcinoma and squamous carcinoma cells and is notably upregulated in metastatic lung cancers. Depletion of Id1 also prevents the proliferation and invasion of NSCLS cells. Attempts were made to understand the downstream effectors of Id1 function in lung cancer progression and metastasis. As a step in this direction, A549 (K-Ras mutant, EGFR wild-type) and H1650 (K-Ras wild-type, EGFR mutant) cells were transfected with short interfering RNA (siRNA) for Id1and stimulated with 1μm Nicotine or 100ng/ml EGF. The samples were subjected to microarray analysis to identify various genes upregulated and downregulated in the Id1 siRNA transfected cell lines. 200 genes were upregulated 2 fold or more by Nicotine and 150 by EGF. Few genes such as stathmin like-3 (STMN3), GSPT1 (G1 to S phase transition), TPD52 (tumor protein D52) were downregulated in the absence of Id1 suggesting those are Id1 regulated genes. The microarray results were validated using Real-time PCR for the above genes. Further depletion of these three genes resulted in decreased cell proliferation, migration and invasion. Indeed STMN3 promoter could be induced by Id1 and Id1 was necessary for Nicotine to induce this gene. These results might reveal the mechanisms by which Id1 promotes tumor progression and metastasis. STMN3 is a microtubule destabilizing phosphoprotein which is overexpressed in adenocarcinoma as well as squamous cell carcinoma and induced tumor cell proliferation, migration and matrix invasion in respective cell lines. GSPT1, which is also known as eukaryotic translation release factor eRF3 and TPD52 are also reported to be over expressed in various kinds of cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4994. doi:10.1158/1538-7445.AM2011-4994

Abstract 4993: Nicotine induced EMT and metastasis of human NSCLC : Role of beta-arrestin-1

Cigarette smoking is a major risk factor in the development of non-small cell lung cancer (NSCLC), which accounts for 80% of all lung cancers. Nicotine, an active component of tobacco smoke has been found to induce proliferation, invasion and epithelial-mesenchymal transition in NSCLC cell lines and promote the metastasis of NSCLC in mice. Nicotine induces cell proliferation utilizing a scaffolding protein, β-arrestin-1, which translocates to nucleus and associates with E2F1 transcription factor in response to nicotine stimulation. Here we demonstrate that mesenchymal markers such as vimentin and fibronectin are E2F1 regulated and β-arrestin-1 is involved in regulating nicotine induced expression of these genes. Vimentin and fibronectin promoters were E2F responsive and E2F1 could be detected on these promoters by chromatin immunoprecipitation (ChIP) assays. Depletion of β-arrestin-1 resulted in down-regulation of vimentin and fibronectin expression as well as inhibition of nicotine induced invasion of cells. Quantitative RT-PCR conducted on patient samples revealed a significant correlation between the levels of β-arrestin-1 and the expression of these genes. A microarray analysis conducted on nicotine stimulated parental A549 cells and those lacking β-arrestin-1 showed that about 290 genes were upregulated in the absence of β-arrestin-1, while 787 genes were downregulated. These included genes for transcription factors, growth factor receptors and signaling molecules. We further analyzed the global association of β-arrestin-1 in the genomic region upon nicotine stimulation by ChIP-sequencing and found that β-arrestin-1 is recruited on the promoters of many genes that regulate EMT such as ZEB2 (Zinc Finger E-box Binding Homeobox-2) as well as other regulatory pathways. ChIP assays conducted on NSCLC cell lines revealed the association of β-arrestin-1 on ZEB1 (Zinc Finger E-box Binding Homeobox-1) and ZEB2 promoters. Depletion of β-arrestin-1 in A549 cells resulted in the downregulation of ZEB1 and ZEB2. Additionally, in an orthotopic lung cancer model in SCID-beige mice, implantation of A549-luciferase stable cells lacking β-arrestin-1 showed a decrease in primary tumor growth and also resulted in significantly lower levels of nicotine-induced metastasis when compared to controls. Taken together, these data suggest that β-arrestin-1 contributes to nicotine induced progression and metastasis of NSCLC, especially in patients exposed to tobacco smoke. Further, β-arrestin-1 and its associated molecules might be targeted for the development of novel agents to combat NSCLC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4993. doi:10.1158/1538-7445.AM2011-4993

Abstract 2108: New analogues of benzyl-isothiourea showed Rb-Raf disruption and anti-cancer activity

The retinoblastoma tumor suppressor protein Rb, is a vital regulator of the mammalian cell cycle which is inactivated by phosphorylation. We had shown that Raf-1 kinase binds and phosphorylates Rb early in the G1 phase facilitating its subsequent phosphorylation by cyclin dependent kinases. This phosphorlation released transcriptionally active E2Fs from Rb to facilitate S-phase entry. Disruption of Rb-Raf protein-protein interaction could prevent proliferation and angiogenesis, leading to inhibition of tumor growth in mouse models. We had earlier identified an orally active small molecule, Rb/Raf-1 disruptor 251 (RRD-251) that potently and selectively disrupts Rb/Raf-1 but not Rb/E2F, Rb/prohibitin, Rb/cyclin E or Rb/HDAC interactions. Here, we have made efforts to analyze additional analogues of RRD251; we focused on XW-19B and XW-35B. These compounds inhibited Rb-Raf interaction in vitro and in vivo as shown by ELISA and Immunoprecipitation-Western blot analysis. They also inhibited cell viability, proliferation, migration, invasion, angiogenesis and adherence-independent growth of human lung cancer cell lines A549. XW-19B inhibited tumor growth significantly in human A549 xenograft model in nude mice, compared to control while XW-35B showed certain amount of toxicity to animals at 50MPK. Overall, these results showed that Rb-Raf disruptors XW-19B and XW-35B have potential anticancer activity. Thus, selective targeting of Rb/Raf-1 interaction seems to be a promising approach for developing novel chemotherapeutic agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2108. doi:10.1158/1538-7445.AM2011-2108

Abstract 4381: EGFR-Src signaling regulates self-renewal of cancer stem like cells from NSCLC through Sox2

NSCLC is the most common form of lung cancer with 5-year survival rate of approximately 10%. Cancer stem cell model has been proposed for tumor-hetrogeniety, carcinogenesis and relapse after therapy. According to this model, cancer stem like cells (CSCs) are defined as self-renewing tumor cells, able to initiate and maintain the tumor. Here, we isolated CSCs based on “side populaton” (SP) phenotype, a functional property of adult stem cells to efflux Hoechst-33352 dye through ABCG2 transporter. Irrespective of genotype of the cells, we observed SP-cells in H358, H292, H1650, H1975, A549 and H460 cell lines. SP phenotype was also displayed by clinical-human xenografts, which could be specifically blocked by ABCG2 inhibitor. Relative tumorigenic potential of SP and MP (main population) cells was determined by subcutaneous or orthotopic xenograft-implantation in SCID mice. As low as 1×103 SP-cells isolated from H1650 cells could form subcutaneous tumor. Similarly, 5×104 SP-cells from A549 could establish orthotopic tumors in lung. Flow-cytometry analysis of subcutaneous tumors demonstrated the asymmetric division of SP-cells generating MP-cells within the tumors. In vitro analysis showed higher expression of ABCG2 and anti-apoptotic protein MCL1 in SP-cells as compared to MP cells. Further, SP-cells displayed higher expression of mesenchymal marker vimentin and lower levels of epithelial marker E-cadherin, suggesting the EMT-like features in SP-cells. SP-cells were found to express embryonic self-renewal factors Oct4, Sox2 and Nanog and demonstrated self-renewal capability by growing as suspended spheres in serum free, stem cell-selective medium. To successfully eliminate these CSCs from tumors, it is necessary to understand the mechanisms facilitating its self-renewal. Based on the favorable clinical outcome of EGFR- and Src-targeted therapy against certain NSCLCs, we hypothesized that the activated EGFR and Src signaling might play important roles in CSCs of NSCLC. This hypothesis was tested using biochemical as well as genetic inhibitor tools against EGFR and Src. SiRNA against EGFR significantly blocked the SP phenotype by downregulating ABCG2 protein levels in all the tested cell lines. Importantly, inhibitor of EGFR (Gefitinib, Erlotinib, BIBW2992) and Src (Dasatinib, PP2) completely blocked the self-renewal capability of SP-cells, as assessed by sphere formation assays. Further, blocking of EGFR and Src signaling by SiRNA or inhibitors resulted in downregulation of the protein levels of Sox2 in SP cells. Importantly, SiRNA against Sox2 significantly blocked the SP phenotype as well as self-renewal capacity of SP-cells. Our findings reveal an important role of EGFR-Src signaling axis in self-renewal and expansion of NSCLC-CSCs by regulating the Sox2 activity in the cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4381. doi:10.1158/1538-7445.AM2011-4381

Rb-Raf-1 interaction disruptor RRD-251 induces apoptosis in metastatic melanoma cells and synergizes with dacarbazine

Metastatic melanoma is an aggressive cancer with very low response rate against conventional chemotherapeutic agents such as dacarbazine (DTIC). Inhibitor of Rb-Raf-1 interaction RRD-251 was tested against the melanoma cell lines SK-MEL-28, SK-MEL-5, and SK-MEL-2. RRD-251 was found to be a potent inhibitor of melanoma cell proliferation, irrespective of V600E B-Raf mutation status of the cell lines. In a SK-MEL-28 xenograft experiment, RRD-251 exerted a significant suppression of tumor growth compared with vehicle (P = 0.003). Similar to in vitro effects, tumors from RRD-251-treated animals showed decreased Rb-Raf-1 interaction in vivo. Growth suppressive effects of RRD-251 were associated with induction of apoptosis as well as a G(1) arrest, with an accompanying decrease in S-phase cells. RRD-251 inhibited Rb phosphorylation and downregulated E2F1 protein levels in these cells. Real-time PCR analysis showed that RRD-251 caused downregulation of cell-cycle regulatory genes thymidylate synthase (TS) and cdc6 as well as the antiapoptotic gene Mcl-1. Combinatorial treatment of RRD-251 and DTIC resulted in a significantly higher apoptosis in DTIC resistant cell lines SK-MEL-28 and SK-MEL-5, as revealed by increased caspase-3 activity and PARP cleavage. Because aberrant Rb/E2F pathway is associated with melanoma progression and resistance to apoptosis, these results suggest that the Rb-Raf-1 inhibitor could be an effective agent for melanoma treatment, either alone or in combination with DTIC.

Small molecule regulators of Rb-E2F pathway as modulators of transcription

The retinoblastoma tumor suppressor protein, Rb, plays a major role in the regulation of mammalian cell cycle progression. It has been shown that Rb function is essential for the proper modulation of G1/S transition and inactivation of Rb contributes to deregulated cell proliferation. Rb exerts its cell cycle regulatory functions mainly by targeting the E2F family of transcription factors and Rb has been shown to physically interact with E2Fs 1, 2 and 3, repressing their transcriptional activity. Multiple genes involved in DNA synthesis and cell cycle progression are regulated by E2Fs, and Rb prevents their expression by inhibiting E2F activity, inducing growth arrest. It has been established that inactivation of Rb by phosphorylation, mutation, or by the interaction of viral oncoproteins leads to a release of the repression of E2F activity, facilitating cell cycle progression. Rb-mediated repression of E2F activity involves the recruitment of a variety of transcriptional co-repressors and chromatin remodeling proteins, including histone deacetylases, DNA methyltransferases and Brg1/Brm chromatin remodeling proteins. Inactivation of Rb by sequential phosphorylation events during cell cycle progression leads to a dissociation of these co-repressors from Rb, facilitating transcription. It has been found that small molecules that prevent the phosphorylation of Rb prevent the dissociation of certain co-repressors from Rb, especially Brg1, leading to the maintenance of Rb-mediated transcriptional repression and cell cycle arrest. Such small molecules have anti-cancer activities and will also act as valuable probes to study chromatin remodeling and transcriptional regulation.

Regulation of vascular endothelial growth factor receptors by Rb and E2F1: role of acetylation

E2F transcription factors regulate a variety of cellular processes, but their role in angiogenesis is not clear. We find that many genes involved in angiogenesis such as FLT-1, KDR, and angiopoietin 2 have potential E2F1 binding sites in their promoter. Chromatin immunoprecipitation (ChIP) assays showed that E2F1 can associate with these promoters and the recruitment of E2F1 was enhanced upon vascular endothelial growth factor (VEGF) stimulation with concomitant dissociation of Rb, leading to the transcriptional activation of these promoters. Transient transfection experiments showed that these promoters were induced by E2F1 and repressed by Rb, whereas depletion of E2F1 decreased their expression. The increased binding of E2F1 to these promoters upon VEGF stimulation correlated with the acetylation of histones and E2F1; this required VEGF receptor function, as seen in ChIP-re-ChIP experiments. This suggests the existence of a positive feedback loop regulating E2F1 acetylation and VEGF receptor expression. Acetylation associated with VEGF signaling seems to be predominantly mediated by P300/CBP-associated factor, and the depletion of histone acetyl transferases disrupted the formation of angiogenic tubules. These results suggest a novel role for E2F1 and acetylation in the angiogenic process.

Abstract 2951: Nicotine induced EMT involves β-arrestin-1 mediated regulation of E2F1 target genes

Cigarette smoking is strongly correlated with the onset of non-small cell lung cancer. Nicotine, an active component of tobacco smoke has been found to induce proliferation, invasion and epithelial-mesenchymal transition in NSCLC cell lines. While nicotine by itself is not carcinogenic, it can induce cell proliferation utilizing a scaffolding protein, β-arrestin-1 which translocates to nucleus and associates with E2F1 transcription factor. In addition, nicotine induces changes in gene expression consistent with epithelial-mesenchymal transition characterized by increase in the levels of mesenchymal proteins like vimentin and fibronectin. In this study we demonstrate that mesenchymal markers such as vimentin and fibronectin are E2F1 regulated and β-arrestin-1 is involved in regulating their expression in response to nicotine stimulation. Analysis of vimentin and fibronectin promoters revealed the presence of potential E2F binding sites. Transient transfection experiments in A549 cells using vimentin and fibronectin promoter constructs showed that these promoters were induced significantly by E2F1 and repressed by Rb. Depletion of E2F1 using siRNAs resulted in down regulation of vimentin and fibronectin as seen by Real-Time PCR. Chromatin immunoprecipitation assays on quiescent as well as nicotine stimulated A549 cells showed a robust recruitment of E2F1 and β-arrestin-1 to vimentin and fibronectin promoters. In addition, depletion of β-arrestin-1 resulted in down regulation of vimentin and fibronectin expression as revealed by western blot and Real-Time PCR. Nicotine stimulation resulted in the induction of vimentin and fibronectin promoters when A549 cells were transfected with reporter constructs while β-arrestin-1 depleted cells did not show promoter induction with nicotine stimulation. Boyden chamber assays conducted on β-arrestin-1 knocked down cells showed that ablation of β-arrestin-1 resulted in the inhibition of nicotine induced migratory and invasive potential of cells. Taken together, these data suggest that β-arrestin-1 contributes to nicotine induced epithelial-mesenchymal transition by regulating E2F1 mediated vimentin and fibronectin expression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2951.

Abstract 4369: MMP9, MMP14, and MMP15 genes are induced by nicotine in an E2F-dependent manner

Cigarette smoking is strongly correlated with the onset of non-small cell lung cancer (NSCLC). Nicotine, the addictive component of cigarettes, has been found to induce proliferation, confer resistance to apoptosis, and induce EMT like changes in breast, pancreatic, and lung cancer cell lines. In addition, nicotine also induces morphological changes characteristic of a migratory, mesenchymal phenotype in NSCLCs. Correspondingly, the exact molecular mechanism for this acquired invasiveness in NSCLCs has been partially elucidated, but still remains somewhat unclear. To determine whether this increased invasion is due to up-regulation of proteolytic proteins, we first examined the mRNA levels of matrix metalloproteinase genes, which are crucial proteins for the mechanical degradation of the ECM, after exposure to nicotine. MMP9, MMP14, and MMP15 mRNA levels were significantly induced by treatment with nicotine when compared to serum starved A549 lung adenocarcinoma cells. Transient transfection experiments in H1650, A549, and MDA-MB-231 cell lines also show that a 2kb MMP9-luc promoter is induced by treatment with nicotine. In order to identify a possible factor responsible for this induction, we next analyzed the promoters of MMP genes. Chip assays show that these MMPs had multiple functional E2F binding sites. Wound healing assays on these cells showed that cells lacking E2F1 were impaired in their ability to migrate on plastic. In addition, cells lacking E2F1 showed a lower capacity for invasion, as determined by Boyden Chamber assays. The effect of depleting E2F1 on MMP expression was assessed by Real-time PCR assays. It was found that MMP 9, 14, and 15 were down-regulated in A549 cells lacking E2F1. Furthermore, these MMP9, 14, and 15 promoter reporters were induced upon co-transfection with either E2F1 or E2F3, both classical E2F activators. These data suggest that the Rb/E2F pathway is a likely downstream target of nicotine and mediates invasion by enhancing the levels of MMPs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4369.

Abstract 4309: Isolation, expansion and molecular characterization of lung cancer stem cells from NSCLC cell lines

Lung cancer is the leading cause of death from cancer worldwide. NSCLC represents the most common subtype of lung cancer with the average five-year survival rate is only 16%. The majorities of these tumors are refractory to chemotherapeutics or acquire resistance to the therapy. In addition, most of the patients develop distant metastases even tough their primary tumors are surgically removed. Cancer stem cell hypothesis has emerged as a possible explanation for tumor growth, recurrence after treatment and metastasis in a variety of cancer. This hypothesis suggests that tumors are maintained by the subset of cancer stem cells (CSCs) that has the ability to self-renew and generate the diverse cells that comprise the tumor. While evidence supporting the existence of CSCs has been demonstrated in many solid cancers, it is largely underdeveloped in lung cancer. Here we have isolated cancer stem like cells from NSCLC cell lines either through isolating the side population (SP) cells based on their property to exclude Hoechst 33342 dye or enriched them by cultivating cancer cells in defined serum free medium containing N2-supplement, EGF and bFGF. Cells obtained from both these methods demonstrated higher clonogenic as well as sphere forming ability which is the typical characteristics associated with CSCs. We further characterized these cells for their ability to express progenitor/stem cell marker genes like Oct4, Sox2 and Nanog. Total RNA from SP cells showed higher expression of these genes as compared to main population. Similarly, the expression of Oct4, Sox2 and Nanog was found elevated after culturing H1650, H358, H322 and H292 cells in defined serum free medium for 10 days. Interestingly, CSCs enriched in this condition also showed the loss of E-cadherin expression and consequent gain of mesenchymal proteins like fibronectin and vimentin. Additionally, ABCG2, which is closely associated with the drug resistance and responsible for side population phenotype, was also upregulated in cancer stem like cells enriched from culturing in serum free defined media. In conclusion, results revealed that lung cancer stem like cells could be isolated and expanded from the established lung cancer cell lines by two different methodologies described here. These cells possess the characteristics of both stem cells and malignant tumors. Therefore, further studies towards targeting these cells may result in effective therapy against lung cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4309.

Nicotine promotes tumor growth and metastasis in mouse models of lung cancer

BACKGROUND

Nicotine is the major addictive component of tobacco smoke. Although nicotine is generally thought to have limited ability to initiate cancer, it can induce cell proliferation and angiogenesis in a variety of systems. These properties might enable nicotine to facilitate the growth of tumors already initiated. Here we show that nicotine significantly promotes the progression and metastasis of tumors in mouse models of lung cancer. This effect was observed when nicotine was administered through intraperitoneal injections, or through over-the-counter transdermal patches.

METHODS AND FINDINGS

In the present study, Line1 mouse adenocarcinoma cells were implanted subcutaneously into syngenic BALB/c mice. Nicotine administration either by intraperitoneal (i.p.) injection or transdermal patches caused a remarkable increase in the size of implanted Line1 tumors. Once the tumors were surgically removed, nicotine treated mice had a markedly higher tumor recurrence (59.7%) as compared to the vehicle treated mice (19.5%). Nicotine also increased metastasis of dorsally implanted Line1 tumors to the lungs by 9 folds. These studies on transplanted tumors were extended to a mouse model where the tumors were induced by the tobacco carcinogen, NNK. Lung tumors were initiated in A/J mice by i.p. injection of NNK; administration of 1 mg/kg nicotine three times a week led to an increase in the size and the number of tumors formed in the lungs. In addition, nicotine significantly reduced the expression of epithelial markers, E-Cadherin and beta-Catenin as well as the tight junction protein ZO-1; these tumors also showed an increased expression of the alpha(7) nAChR subunit. We believe that exposure to nicotine either by tobacco smoke or nicotine supplements might facilitate increased tumor growth and metastasis.

CONCLUSIONS

Our earlier results indicated that nicotine could induce invasion and epithelial-mesenchymal transition (EMT) in cultured lung, breast and pancreatic cancer cells. This study demonstrates for the first time that administration of nicotine either by i.p. injection or through over-the-counter dermal patches can promote tumor growth and metastasis in immunocompetent mice. These results suggest that while nicotine has only limited capacity to initiate tumor formation, it can facilitate the progression and metastasis of tumors pre-initiated by tobacco carcinogens.