Patient-Derived Xenograft Models of Non-Small Cell Lung Cancer and Their Potential Utility in Personalized Medicine

Traditional preclinical studies of cancer therapeutics have relied on the use of established human cell lines that have been adapted to grow in the laboratory and, therefore, may deviate from the cancer they were meant to represent. With the emphasis of cancer drug development shifting from non-specific cytotoxic agents to rationally designed molecularly targeted therapies or immunotherapy comes the need for better models with predictive value regarding therapeutic activity and response in clinical trials. Recently, the diversity and accessibility of immunodeficient mouse strains has greatly enhanced the production and utility of patient-derived xenograft (PDX) models for many tumor types, including non-small cell lung cancer (NSCLC). Combined with next-generation sequencing, NSCLC PDX mouse models offer an exciting tool for drug development and for studying targeted therapies while utilizing patient samples with the hope of eventually aiding in clinical decision-making. Here, we describe NSCLC PDX mouse models generated by us and others, their ability to reflect the parental tumors’ histomorphological characteristics, as well as the effect of clonal selection and evolution on maintaining genomic integrity in low-passage PDXs compared to the donor tissue. We also raise vital questions regarding the practical utility of PDX and humanized PDX models in predicting patient response to therapy and make recommendations for addressing those questions. Once collaborations and standardized xenotransplantation and data management methods are established, NSCLC PDX mouse models have the potential to be universal and invaluable as a preclinical tool that guides clinical trials and standard therapeutic decisions.

SOX9 is targeted for proteasomal degradation by the E3 ligase FBW7 in response to DNA damage

SOX9 encodes a transcription factor that governs cell fate specification throughout development and tissue homeostasis. Elevated SOX9 is implicated in the genesis and progression of human tumors by increasing cell proliferation and epithelial-mesenchymal transition. We found that in response to UV irradiation or genotoxic chemotherapeutics, SOX9 is actively degraded in various cancer types and in normal epithelial cells, through a pathway independent of p53, ATM, ATR and DNA-PK. SOX9 is phosphorylated by GSK3β, facilitating the binding of SOX9 to the F-box protein FBW7α, an E3 ligase that functions in the DNA damage response pathway. The binding of FBW7α to the SOX9 K2 domain at T236-T240 targets SOX9 for subsequent ubiquitination and proteasomal destruction. Exogenous overexpression of SOX9 after genotoxic stress increases cell survival. Our findings reveal a novel regulatory mechanism for SOX9 stability and uncover a unique function of SOX9 in the cellular response to DNA damage. This new mechanism underlying a FBW7-SOX9 axis in cancer could have implications in therapy resistance.

Abstract 4544: FBW7 induces S-phase arrest caused by DNA double strand breaks through targeting SOX9 for proteasomal degradation

SOX9 encodes a transcription factor that governs cell fate specification throughout development and tissue homeostasis. Elevated SOX9 is implicated in the genesis or progression of many human tumors through increasing cell proliferation and epithelial-mesenchymal transition. We observed that, in response to UV irradiation or certain chemotherapeutic agents, SOX9 is actively and rapidly degraded by a ubiquitin pathway dependent mechanism across several different tumor types including lung cancer, colon cancer, osteosarcoma and melanoma, as well as normal human bronchial epithelial cells. We found that SOX9 is phosphorylated by GSK3β at Ser-236, facilitating the direct binding and degradation of SOX9 via the F box protein, FBW7α. We also determined that the de-ubiquitinase, USP28, stabilizes SOX9 under normal conditions by sequestering FBW7, but is released from FBW7 after UV irradiation, allowing FBW7 to bind SOX9 and target it for destruction. DNA damage-induced SOX9 degradation was independent of p53, ATM, ATR and MAPK pathways. Failure to deplete SOX9 attenuated the DNA damage-induced intra-S-phase checkpoint and increased long-term cell survival. Moreover, mutations within the FBW7 phosphodegron binding site of SOX9 prevented SOX9 degradation after DNA damage, and incurred resistance of non-small cell lung cancer (NSCLC) cells to cisplatin in vivo. We found that cancer patients with tumors expressing high Sox9 and low Fbw7 levels exhibit inferior survival. Our discovery reveals a novel function of SOX9 in the cellular response to DNA damage. Induced degradation of SOX9 may be part of the protection mechanisms to maintain genomic stability. This new regulatory mechanism of the FBW7-SOX9 axis in cancer could have diagnostic and therapeutic implications.

Citation Format: Xuehui Hong, Wenyu Liu, Ruipeng Song, Hiroyuki Inuzuka, Hatem E. Sabaawy, Katherine M. Morgan, Jamie J. Shah, Samuel F. Bunting, Xing Feng, Chi-Kwan Tsang, Zhiyuan Shen, X. F. Steven Zheng, LianXin Liu, Sharon R. Pine. FBW7 induces S-phase arrest caused by DNA double strand breaks through targeting SOX9 for proteasomal degradation. [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 4544.

Abstract 4834: Preclinical analysis of the Notch gamma secretase inhibitor BMS-906024 in combination with chemotherapy in the treatment of lung adenocarcinoma

Notch signaling is aberrantly activated in approximately one third of non-small cell lung cancer (NSCLC) cases, primarily through loss of the endogenous Notch inhibitor, Numb, or via gain-of-function mutations in the Notch1 receptor. Notch activity is associated with poor overall survival among NSCLC patients whose tumors are wildtype for TP53. Here, we characterized the interaction between BMS-906024, a clinically relevant gamma secretase inhibitor (GSI) that inhibits Notch activation, and front-line chemotherapy in preclinical models of NSCLC. MTS drug synergy assays consisting of treatment with BMS-906024, cisplatin or paclitaxel, or the combination of GSI and chemotherapy were performed on a panel of human NSCLC cell lines, most of which were derived from adenocarcinomas. Analysis of the drug effects with CalcuSyn yielded significantly lower CI values for the GSI BMS-906024 combined with paclitaxel than with cisplatin (average CI = 0.54 vs 0.85, respectively; P = 0.001). The synergy between BMS-906024 and paclitaxel was significantly greater in Kras-wildtype than Kras-mutant cells (average CI = 0.39 vs 0.68, respectively; P = 0.009), while there was no correlation with EGFR or TP53 status. Treatment of lung adenocarcinoma xenografts in NOD scid gamma mice confirmed enhanced antitumor activity for the combination treatment of BMS-906024 and paclitaxel by mechanisms currently under investigation. These results are a step toward identification of the optimal combination of the GSI BMS-906024 with standard chemotherapies, as well as potential biomarkers that could be used to predict patient response to Notch-targeted therapy.

Citation Format: Katherine M. Morgan, Francis Lee, Erin Michaud, Bruce S. Fischer, Sharon R. Pine. Preclinical analysis of the Notch gamma secretase inhibitor BMS-906024 in combination with chemotherapy in the treatment of lung adenocarcinoma. [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 4834.

Differential Serum Cytokine Levels and Risk of Lung Cancer Between African and European Americans

BACKGROUND

African Americans have a higher risk of developing lung cancer than European Americans. Previous studies suggested that certain circulating cytokines were associated with lung cancer. We hypothesized that variations in serum cytokine levels exist between African Americans and European Americans, and increased circulating cytokine levels contribute to lung cancer differently in the two races.

METHODS

Differences in 10 serum cytokine levels, IL1β, IL4, IL5, IL6, IL8, IL10, IL12, granulocyte macrophage colony-stimulating factor, IFNγ, and TNFα, between 170 African-American and 296 European-American controls from the National Cancer Institute-Maryland (NCI-MD) case-control study were assessed. Associations of the serum cytokine levels with lung cancer were analyzed. Statistically significant results were replicated in the prospective Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial and the Wayne State University Karmanos Cancer Institute case-control study.

RESULTS

Six cytokines, IL4, IL5, IL8, IL10, IFNγ, and TNFα, were significantly higher among European-American as compared with African-American controls. Elevated IL6 and IL8 levels were associated with lung cancer among both races in all three studies. Elevated IL1β, IL10, and TNFα levels were associated with lung cancer only among African Americans. The association between elevated TNFα levels and lung cancer among European Americans was significant after adjustment for additional factors.

CONCLUSIONS

Serum cytokine levels vary by race and might contribute to lung cancer differently between African Americans and European Americans.

IMPACT

Future work examining risk prediction models of lung cancer can measure circulating cytokines to accurately characterize risk within racial groups.

Abstract 1957: Negative regulation of Sox9 by glycogen synthase kinase 3 beta phosphorylation and SCFFbw7-dependent ubiquitination in cancer

Sox9 is a member of the SOX [Sry-related high-mobility group (HMG) box] family of transcription factors, with known functions in proliferation, epithelial-mesenchymal transition (EMT), stem cell maintenance and senescence. Sox9 protein levels are elevated in several different cancer types, including lung cancer and osteosarcoma. Furthermore, Sox9 overexpression is associated with poor survival in both cancer types. We recently reported that Sox9 is a direct transcriptional target of the Notch signaling pathway and mediates Notch1-induced EMT in lung cancer (Capaccione et al., Oncotarget, 2014). Fbxw7 (F-box and WD repeat domain-containing 7) is a member of the SCFFbw7E3 ubiquitin ligase complexthat targets several oncogenic proteins for degradation, including Notch1. We hypothesized that Sox9 is targeted for degradation by SCFFbw7. Knocking down or overexpressingFbxw7 significantly increasedor decreased, respectively, endogenous Sox9 protein levels in lung cancer and osteosarcoma cell lines. In addition, overexpression of Fbxw7 resulted in active degradation of ectopic Sox9 protein levels, when assessed in combination with cycloheximide, and did so in a dose dependent-manner.Furthermore, both Sox9 and FBXW7 were detected in immunoblots after the reciprocal protein was immunoprecipitated. Because substrate degradation by SCFFbw7 is typically phosphorylation-dependent, frequently by glycogen synthase kinase (GSK)3-beta, we examined whether modulation of GSK3-beta could affect FBXW7-induced Sox9 degradation. Treatment of cells with the GSK3-beta inhibitor, CHIR99021, completely abolished Sox9 degradation by ectopically overexpressed FBXW7, in a dose-dependent manner. We next identified four putative phosphorylation sites within potential FBXW7 degron motifs in Sox9.Mass spectrophotometric analysis confirmed these sites within Sox9 are indeed phosphorylated.In summary, we found that the E3 ubiquitin ligase complex (SCFFbw7) targets Sox9 for ubiquitin-mediated degradation in a GSK3-beta-mediated Sox9 phosphorylation-dependent manner. As a result, this negative regulation of Sox9 by GSK3-beta/FBXW7 could lead to inhibition of Sox9-mediated proliferation, EMT and stemness. This new regulatory mechanism of Sox9 could have diagnostic and therapeutic implications for lung cancer, osteosarcoma, as well as other cancers.

Citation Format: Xuehui Hong, Wenyu Liu, Hiroyuki Inuzuka, Lianxin Liu, Sharon R. Pine. Negative regulation of Sox9 by glycogen synthase kinase 3 beta phosphorylation and SCFFbw7-dependent ubiquitination in cancer. [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 1957. doi:10.1158/1538-7445.AM2015-1957

Abstract 2535: Synergistic anti-tumor activity of the Notch gamma secretase inhibitor BMS-906024 and paclitaxel in the treatment of lung adenocarcinoma

Notch signaling is aberrantly activated in approximately one third of non-small cell lung cancer cases, primarily through loss of the endogenous Notch inhibitor, Numb, or via gain-of-function mutations in the Notch1 receptor. Notch activity is associated with poor overall survival among non-small cell lung cancer patients whose tumors are wildtype for TP53. We set out to evaluate the combination of Notch-targeted therapy with front-line chemotherapy as an effective treatment for non-small cell lung cancer. Our study focused on lung adenocarcinoma, the most common histological subtype in lung cancer. To target Notch, we utilized the gamma secretase inhibitor (GSI) BMS-906024 which inhibits Notch activation. BMS-906024 is currently in Phase 1 clinical trials for patients with T-cell acute lymphoblastic leukemia and metastatic solid tumors, including lung cancer. Human cell lines representing the major genetic subtypes of lung cancer, most of which were derived from adenocarcinomas, underwent MTS drug synergy assays consisting of treatment with BMS-906024, cisplatin or paclitaxel, or the combination of GSI and chemotherapy. The dosing and timing for BMS-906024 administration were optimized by examination of maximal Notch1 inhibition. Analysis of the drug effects with CalcuSyn yielded Combination Index (CI) values, in which a CI of 0.5 or less was considered as strong synergism for the drug combination. We found that there were significantly lower CI values for the GSI BMS-906024 combined with paclitaxel than with cisplatin (average CI = 0.54 vs 0.85, respectively; P = 0.001). We then grouped the cell lines by major genetic subtype (wildtype versus mutant or null for EGFR, Kras or TP53). The synergy between BMS-906024 and paclitaxel was significantly greater in Kras-wildtype than Kras-mutant cells (average CI = 0.39 vs 0.68, respectively; P = 0.009), while there was no correlation with EGFR or TP53 status. These results are a step toward identification of potential biomarkers that could be used to predict patient response to Notch-targeted therapy, which could have a positive impact on the care of lung adenocarcinoma patients and be informative for treatment decisions.

Citation Format: Katherine M. Morgan, Francis Lee, Erin Michaud, Joseph R. Bertino, Bruce S. Fischer, Sharon R. Pine. Synergistic anti-tumor activity of the Notch gamma secretase inhibitor BMS-906024 and paclitaxel in the treatment of lung adenocarcinoma. [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 2535. doi:10.1158/1538-7445.AM2015-2535

Sox9 mediates Notch1-induced mesenchymal features in lung adenocarcinoma

Sox9 has gained increasing importance both functionally and as a prognostic factor in cancer. We demonstrate a functional role for Sox9 in inducing a mesenchymal phenotype in lung ADC. We show that Sox9 mRNA and protein are overexpressed in lung ADC, particularly those with KRAS mutations. Sox9 expression correlated with the Notch target gene Hes1, and numerous other Notch pathway components. We observed that Sox9 is a potent inducer of lung cancer cell motility and invasion, and a negative regulator of E-cadherin, a key protein that is lost during epithelial-mesenchymal transition (EMT). Moreover, we show that Notch1 signaling directly regulates Sox9 expression through a SOX9 promoter binding site, independently of the TGF-β pathway, and that Sox9 participates in Notch-1 induced cell motility, cell invasion, and loss of E-cadherin expression. Together, the results identify a new functional role for a Notch1-Sox9 signaling axis in lung ADC that may explain the correlation of Sox9 with tumor progression, higher tumor grade, and poor lung cancer survival. In addition to Notch and TGF-β, Sox9 also acts downstream of NF-κB, BMP, EGFR, and Wnt/β-catenin signaling. Thus, Sox9 could potentially act as a hub to mediate cross-talk among key oncogenic pathways in lung ADC. Targeting Sox9 expression or transcriptional activity could potentially reduce resistance to targeted therapy for lung ADC caused by pathway redundancy.

Identification of a functional SNP in the 3'UTR of CXCR2 that is associated with reduced risk of lung cancer

Global changes in gene expression accompany the development of cancer. Thus, inherited variants in miRNA-binding sites are likely candidates for conferring inherited susceptibility. Using an in silico approach, we compiled a comprehensive list of SNPs predicted to modulate miRNA binding in genes from several key lung cancer pathways. We then investigated whether these SNPs were associated with lung cancer risk in two independent populations. In general, SNPs in miRNA-binding sites are rare. However, some allelic variation was observed. We found that rs1126579 in CXCR2 was associated with a reduced risk of lung cancer in both European American [ORTT vs. CC 0.56 (0.37-0.88); P = 0.008] and Japanese [ORTT vs. CC 0.62 (0.38-1.00); P = 0.049] populations. Furthermore, we found that the SNP disrupted a novel binding site for miR-516a-3p, led to a moderate increase in CXCR2 mRNA and protein expression, and increased MAPK signaling. Moreover, analysis of rs1126579 with serum levels of IL8, its endogenous ligand, supported an interaction whereby rs1126579-T and high serum IL8 conferred synergistic protection from lung cancer. Our findings demonstrate a function for a 3'UTR SNP in modulating CXCR2 expression, signaling, and susceptibility to lung cancer.

A combined prognostic serum interleukin-8 and interleukin-6 classifier for stage 1 lung cancer in the prostate, lung, colorectal, and ovarian cancer screening trial

BACKGROUND

The advent of low-dose helical computed tomography for lung cancer screening will likely lead to an increase in the detection of stage I lung cancer. Presently, these patients are primarily treated with surgery alone and approximately 30% will develop recurrence and die. Biomarkers that can identify patients for whom adjuvant chemotherapy would be a benefit could significantly reduce both patient morbidity and mortality. Herein, we sought to build a prognostic inflammatory-based classifier for stage I lung cancer.

METHODS

We performed a retrospective analysis of 548 European American lung cancer cases prospectively enrolled in the Prostate, Lung, Colorectal and Ovarian study. C-reactive protein, interleukin (IL)-6, IL-8, tumor necrosis factor-α, and IL-1β were measured using an ultrasensitive electrochemiluminescence immunoassay in serum samples collected at the time of study entry.

RESULTS

IL-6 and IL-8 were each associated with significantly shorter survival (hazard ratio [HR], 1.33; 95% confidence interval [CI], 1.08-1.64; p = 0.007; and HR, 1.3; 95% CI, 1.09-1.67; p = 0.005, respectively). Moreover, a combined classifier of IL-6 and IL-8 were significantly associated with poor outcome in stage I lung cancer patients (HR, 3.39; 95% CI, 1.54-7.48, p = 0.002) and in stage 1 patients with more than or equal to 30 pack-years of smoking (HR, 3.15; 95% CI, 1.54-6.46, p = 0.002).

CONCLUSIONS

These results further support the association between inflammatory markers and lung cancer outcome and suggest that a combined serum IL-6/IL-8 classifier could be a useful tool for guiding therapeutic decisions in patients with stage I lung cancer.

Abstract 1149: The role of the novel Notch1-Sox9 signaling axis in NSCLC progression and EMT

Sox9 plays critical roles in the specification and differentiation of numerous progenitor and differentiated cell types during embryonic and fetal development. Sox9 is overexpressed in 40 - 50% of lung adenocarcinomas and associated with poor prognosis in lung cancer patients. We set out to identify upstream pathways that regulate Sox9 expression in lung cancer, as well as the role of Sox9 in lung adenocarcinoma progression. Several developmental and stem cell pathways are known to induce Sox9 transcription during carcinogenesis, including the TGB-β, Wnt/β-catenin, Sonic Hedgehog, and NF-κB signaling. Sox9 has also been shown to be a transcriptional target of the Notch pathway during mouse development, although the binding sites for Notch within the mouse Sox9 promoter are not conserved in humans. We mined gene expression data from three publicly available datasets and found that Hes1, a known Notch target gene, is co-expressed with Sox9 in lung adenocarcinoma. Furthermore, Sox9 mRNA and protein levels were upregulated over 100-fold as early as 14 days after Notch1 induction in the Notch1-induced mouse model of lung cancer, suggesting that Sox9 overexpression is an early event during lung cancer development. Through a series of in vitro assays, we determined that Sox9 is downstream of Notch1 in lung adenocarcinoma cell lines. By ChIP we determined that Sox9 is a direct target of Notch1 and using luciferase reporter assays, we located the previously unidentified human RBP-Jκ binding site, the principle effector of canonical Notch1 signaling, immediately upstream of the Sox9 transcriptional start site. We also examined TGF-β, a known inducer of epithelial-to-mesenchymal transition (EMT) in lung cancer. We determined that induction of Sox9 expression by Notch1 is independent of TGF-β signaling and that TGF-β and Notch1 cooperate in their regulation of Sox9 expression. Loss of Notch1 expression led to an induced MET phenotype, characterized by decreased cell invasion/migration, MET-like morphological changes, and increased E-cadherin expression, which were rescued by Sox9 overexpression. Our data also demonstrate that Sox9 contributes to Notch1-induced EMT in lung adenocarcinoma. These results establish Sox9 as a key Notch1 target gene mediating Notch1-induced EMT independent of TGF-β, leading to poor survival in lung adenocarcinoma.

Citation Format: Kathleen M. Capaccione, Xuehui Hong, Katherine M. Morgan, Thaddeus D. Allen, Gregory D. Miles, Elke K. Markert, J. Michael Bishop, Sharon R. Pine. The role of the novel Notch1-Sox9 signaling axis in NSCLC progression and EMT. [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 1149. doi:10.1158/1538-7445.AM2014-1149

Asymmetric cell division and template DNA co-segregation in cancer stem cells

During tissue homeostasis, normal stem cells self-renew and repopulate the diverse cell types found within the tissue via a series of carefully controlled symmetric and asymmetric cell divisions (ACDs). The notion that solid tumors comprise a subset of cancer stem cells (CSCs) with dysregulated self-renewal and excessive symmetric cell divisions has led to numerous studies aimed to elucidate the mechanisms regulating ACD under steady-state conditions, during stem-cell expansion and in cancer. In this perspective, we focus on a type of asymmetry that can be established during ACD, called non-random co-segregation of template DNA, which has been identified across numerous species, cell types, and cancers. We discuss the role of p53 loss in maintaining self-renewal in both normal and malignant cells. We then review our current knowledge of the mechanisms underlying co-segregation of template DNA strands and the stem-cell pathways associated with it in normal and CSCs.

Abstract B17: Sox9 mediates Notch pathway-induced epithelial-mesenchymal transition (EMT) in lung adenocarcinoma

Background: Sox9 plays critical roles in the specification and differentiation of numerous progenitor and differentiated cell types during embryonic and fetal development. Sox9 is overexpressed in 40 - 50% of lung adenocarcinomas and associated with poor prognosis in lung cancer patients. We set out to identify the upstream pathways that regulate Sox9 expression in lung cancer as well as the role of Sox9 in lung adenocarcinoma progression. Several developmental and stem cell pathways are known induce Sox9 transcription during carcinogenesis, including the TGB-β, Wnt/β-catenin, Sonic Hedgehog, and NF-κB signaling pathways. SOX9 has also been shown to be a transcriptional target of the Notch pathway during mouse development, although the binding sites for Notch within the mouse SOX9 promoter are not conserved in humans.

Results: We mined gene expression data from three publicly available datasets and found that Hes1, a known Notch target gene, is co-expressed with Sox9 in lung adenocarcinoma. We validated the data by identifying significant overlap in Sox9 and Hes1 protein expression levels in a human lung cancer tissue microarray. Furthermore, Sox9 mRNA and protein levels were upregulated over 100-fold as early as 14 days after Notch1 induction in the Notch1-induced mouse model of lung cancer, suggesting that Sox9 overexpression is an early event during lung cancer development. Through a series of in vitro assays, we determined that Sox9 is immediately downstream of Notch1, but not Notch3, in lung adenocarcinoma cell lines. By ChIP and luciferase reporter assays, we located the previously unidentified human RBPjk binding site, the principle effector of canonical Notch1 signaling, immediately upstream of the SOX9 transcriptional start site. We also examined TGF-β, a known inducer of epithelial-to-mesenchymal transition (EMT) in lung cancer. We determined that induction of Sox9 expression by Notch1 is independent of TGF-β signaling, that TGF-β upregulates both Sox9 and Notch1 expression, and that TGF-β and Notch1 cooperate in their regulation of Sox9 expression. Sox9 overexpression led to an induced EMT phenotype, characterized by increased cell invasion/migration, and EMT-related gene expression changes. Sox9 mRNA expression correlated with EMT-like gene expression signatures in several gene expression microarray datasets, and Sox9 protein levels were negatively correlated with expression of the epithelial marker, E-cadherin, in a lung cancer tissue microarray. Our data also demonstrate that Notch1-induced EMT in lung adenocarcinoma is mediated, at least partly, through Sox9.

Conclusion: These results establish Sox9 as a key Notch1 target gene mediating Notch1- and TGF-β- induced EMT, leading to poor survival in lung adenocarcinoma.

Citation Format: Kathleen Capaccione, Xuehui Hong, Katherine M. Morgan, Wenyu Liu, Thaddeus Allen, J. Michael Bishop, Sharon R. Pine. Sox9 mediates Notch pathway-induced epithelial-mesenchymal transition (EMT) in lung adenocarcinoma. [abstract]. In: Proceedings of the AACR-IASLC Joint Conference on Molecular Origins of Lung Cancer; 2014 Jan 6-9; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2014;20(2Suppl):Abstract nr B17.

p53 isoforms regulate aging- and tumor-associated replicative senescence in T lymphocytes

Cellular senescence contributes to aging and decline in tissue function. p53 isoform switching regulates replicative senescence in cultured fibroblasts and is associated with tumor progression. Here, we found that the endogenous p53 isoforms Δ133p53 and p53β are physiological regulators of proliferation and senescence in human T lymphocytes in vivo. Peripheral blood CD8+ T lymphocytes collected from healthy donors displayed an age-dependent accumulation of senescent cells (CD28-CD57+) with decreased Δ133p53 and increased p53β expression. Human lung tumor-associated CD8+ T lymphocytes also harbored senescent cells. Cultured CD8+ blood T lymphocytes underwent replicative senescence that was associated with loss of CD28 and Δ133p53 protein. In poorly proliferative, Δ133p53-low CD8+CD28- cells, reconstituted expression of either Δ133p53 or CD28 upregulated endogenous expression of each other, which restored cell proliferation, extended replicative lifespan and rescued senescence phenotypes. Conversely, Δ133p53 knockdown or p53β overexpression in CD8+CD28+ cells inhibited cell proliferation and induced senescence. This study establishes a role for Δ133p53 and p53β in regulation of cellular proliferation and senescence in vivo. Furthermore, Δ133p53-induced restoration of cellular replicative potential may lead to a new therapeutic paradigm for treating immunosenescence disorders, including those associated with aging, cancer, autoimmune diseases, and HIV infection.

Asymmetric segregation of template DNA strands in basal-like human breast cancer cell lines

BACKGROUND AND METHODS

Stem or progenitor cells from healthy tissues have the capacity to co-segregate their template DNA strands during mitosis. Here, we set out to test whether breast cancer cell lines also possess the ability to asymmetrically segregate their template DNA strands via non-random chromosome co-segregation, and whether this ability correlates with certain properties attributed to breast cancer stem cells (CSCs). We quantified the frequency of asymmetric segregation of template DNA strands in 12 human breast cancer cell lines, and correlated the frequency to molecular subtype, CD44+/CD24-/lo phenotype, and invasion/migration ability. We tested if co-culture with human mesenchymal stem cells, which are known to increase self-renewal, can alter the frequency of asymmetric segregation of template DNA in breast cancer.

RESULTS

We found a positive correlation between asymmetric segregation of template DNA and the breast cancer basal-like and claudin-low subtypes. There was an inverse correlation between asymmetric segregation of template DNA and Her2 expression. Breast cancer samples with evidence of asymmetric segregation of template DNA had significantly increased invasion and borderline significantly increased migration abilities. Samples with high CD44+/CD24-/lo surface expression were more likely to harbor a consistent population of cells that asymmetrically segregated its template DNA; however, symmetric self-renewal was enriched in the CD44+/CD24-/lo population. Co-culturing breast cancer cells with human mesenchymal stem cells expanded the breast CSC pool and decreased the frequency of asymmetric segregation of template DNA.

CONCLUSIONS

Breast cancer cells within the basal-like subtype can asymmetrically segregate their template DNA strands through non-random chromosome segregation. The frequency of asymmetric segregation of template DNA can be modulated by external factors that influence expansion or self-renewal of CSC populations. Future studies to uncover the underlying mechanisms driving asymmetric segregation of template DNA and dictating cell fate at the time of cell division may explain how CSCs are maintained in tumors.

The Notch signaling pathway as a mediator of tumor survival

The Notch signaling pathway is evolutionarily conserved and responsible for cell fate determination in the developing embryo and mature tissue. At the molecular level, ligand binding activates Notch signaling by liberating the Notch intracellular domain, which then translocates into the nucleus and activates gene transcription. Despite the elegant simplicity of this pathway, which lacks secondary messengers or a signaling cascade, Notch regulates gene expression in a highly context- and cell-type-dependent manner. Notch signaling is frequently dysregulated, most commonly by overactivation, across many cancers and confers a survival advantage on tumors, leading to poorer outcomes for patients. Recent studies demonstrate how Notch signaling increases tumor cell proliferation and provide evidence that active Notch signaling maintains the cancer stem-cell pool, induces epithelial-mesenchymal transition and promotes chemoresistance. These studies imply that pharmacological inhibition of Notch signaling may refine control of cancer therapy and improve patient survival. Gamma secretase inhibitors (GSIs) are drugs that inhibit Notch signaling and may be successful in controlling cancer cell growth in conjunction with standard chemotherapy, but substantial side effects have hampered their widespread use. Recent efforts have been aimed at the development of antibodies against specific Notch receptors and ligands with the hope of limiting side effects while providing the same therapeutic benefit as GSIs. Together, studies characterizing Notch signaling and modulation have offered hope that refined methods targeting Notch may become powerful tools in anticancer therapeutics.

MDM2 SNP285 does not antagonize the effect of SNP309 in lung cancer

Conflicting reports exist regarding the contribution of SNP309 in MDM2 to cancer risk. Recently, SNP285 was shown to act as an antagonist to SNP309 by overriding the effect of SNP309 on SP1-mediated transcription. Moreover, SNP285 modified the relationship between SNP309 and risk of breast, ovarian and endometrial cancer. We assessed whether SNP285 confounded the effect of SNP309 in lung cancer in a cohort of 720 controls and 556 cases. Our cohort included both Caucasians and African Americans. Neither SNP309 nor SNP285 was associated with lung cancer risk or survival. In addition, removal of individuals who carried the variant C allele of SNP285 did not modify the association between SNP309 with either lung cancer risk or survival. Although an effect of SNP285 has been demonstrated in breast, ovarian and endometrial cancer, our findings do not support a role for this SNP in lung cancer and raise the possibility that the effect of SNP285 is restricted to cancers in women.

Delineation of breast cancer cell hierarchy identifies the subset responsible for dormancy

The bone marrow (BM) is a major organ of breast cancer (BC) dormancy and a common source of BC resurgence. Gap junctional intercellular communication (GJIC) between BC cells (BCCs) and BM stroma facilitates dormancy. This study reports on a hierarchy of BCCs with the most immature subset (Oct4^hi/CD44^hi/med/CD24^−/+) demonstrating chemoresistance, dormancy, and stem cell properties: self-renewal, serial passaging ability, cycling quiescence, long doubling time, asymmetric division, high metastatic and invasive capability. In vitro and in vivo studies indicated that this subset was responsible for GJIC with BM stroma. Similar BCCs were detected in the blood of patients despite aggressive treatment and in a patient with a relatively large tumor but no lymph node involvement. In brief, these findings identified a novel BCC subset with stem cell properties, with preference for dormancy and in the circulation of patients. The findings establish a working cellular hierarchy of BCCs based on phenotype and functions.

Abstract B1: p53 isoforms, Δ133p53 and p53β, regulate aging-associated T lymphocyte senescence

Normal human cells undergo finite divisions and reach a state of cellular senescence, which is a critical barrier for tumor progression in vivo and contributes to organismal aging. CD8+ T lymphocytes are an excellent model to study cellular senescence in vivo. The decreased proliferative potential and cellular senescence of CD8+ T lymphocytes are associated with loss of CD28 and gain of CD57 cell surface antigens, but the mechanisms regulating these phenotypic changes are unknown. The natural isoforms of human p53 protein, Δ133p53 and p53β, play important roles in regulating replicative cellular senescence in vitro (e.g., in normal human fibroblasts) and in vivo (e.g., in colon adenomas) and in different cell types (mesenchymal and epithelial origins). In this study we show that Δ133p53 and p53β are associated with and regulate replicative cellular senescence in CD8+ T lymphocytes (hematopoietic origin), which represent a physiological setting of in vivo cellular senescence. Loss of CD28 and gain of CD57 in CD8+ T lymphocytes were associated with increased donor age in normal individuals. When stimulated to proliferate in vitro, the FACS sorted CD28+/CD57− subsets of CD8+ T lymphocytes showed highest proliferation rate, whereas CD28−/CD57+ subsets showed lowest. The loss of proliferative potential of the CD28−/CD57+ cells was also associated with the shorter telomere length than the CD28+/CD57− subsets. Importantly, Δ133p53 and p53β expression levels were significantly changed during cellular senescence of CD8+ T lymphocytes, as observed in human fibroblasts and colon adenomas. Δ133p53 levels were decreased and p53β levels were increased in the senescent CD28−/CD57+ subset compared with the proliferative CD28+/CD57− subset. During in vitro culture, FACS sorted CD8+ T lymphocytes became senescent and lost Δ133p53 expression, which was associated with the loss of CD28 expression. Moreover, in overexpression experiments, p53β cooperated with full-length p53 to inhibit cellular proliferation, and Δ133p53 enhanced the proliferative potential of the CD8+ T lymphocytes, suggesting that the p53 isoforms regulate cellular proliferation and senescence in CD8+ T lymphocytes. Our study provides insight toward understanding the mechanisms regulating physiological aging of normal human circulating T lymphocytes and thus proposes a novel approach for reinstating replicative potential and immune function of the senescent CD8+ T lymphocytes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B1.

Increased levels of circulating interleukin 6, interleukin 8, C-reactive protein, and risk of lung cancer

BACKGROUND

Previous studies that were based primarily on small numbers of patients suggested that certain circulating proinflammatory cytokines may be associated with lung cancer; however, large independent studies are lacking.

METHODS

Associations between serum interleukin 6 (IL-6) and interleukin 8 (IL-8) levels and lung cancer were analyzed among 270 case patients and 296 control subjects participating in the National Cancer Institute-Maryland (NCI-MD) case-control study. Results were validated in 532 case patients and 595 control subjects in a nested case-control study within the prospective Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. Association with C-reactive protein (CRP), a systemic inflammation biomarker, was also analyzed. Associations between biomarkers and lung cancer were estimated using logistic regression models adjusted for smoking, stage, histology, age, and sex. The 10-year standardized absolute risks of lung cancer were estimated using a weighted Cox regression model.

RESULTS

Serum IL-6 and IL-8 levels in the highest quartile were associated with lung cancer in the NCI-MD study (IL-6, odds ratio [OR] = 3.29, 95% confidence interval [CI] = 1.88 to 5.77; IL-8, OR = 2.06, 95% CI = 1.19 to 3.57) and with lung cancer risk in the PLCO study (IL-6, OR = 1.48, 95% CI = 1.04 to 2.10; IL-8, OR = 1.57, 95% CI = 1.10 to 2.24), compared with the lowest quartile. In the PLCO study, increased IL-6 levels were only associated with lung cancer diagnosed within 2 years of blood collection, whereas increased IL-8 levels were associated with lung cancer diagnosed more than 2 years after blood collection (OR = 1.57, 95% CI = 1.15 to 2.13). The 10-year standardized absolute risks of lung cancer in the PLCO study were highest among current smokers with high IL-8 and CRP levels (absolute risk = 8.01%, 95% CI = 5.77% to 11.05%).

CONCLUSIONS

Although increased levels of both serum IL-6 and IL-8 are associated with lung cancer, only IL-8 levels are associated with lung cancer risk several years before diagnosis. Combination of IL-8 and CRP are more robust biomarkers than either marker alone in predicting subsequent lung cancer.

Admixture mapping of lung cancer in 1812 African-Americans

Lung cancer continues to be the leading cause of cancer death in the USA and the best example of a cancer with undisputed evidence of environmental risk. However, a genetic contribution to lung cancer has also been demonstrated by studies of familial aggregation, family-based linkage, candidate gene studies and most recently genome-wide association studies (GWAS). The African-American population has been underrepresented in these genetic studies and has patterns of cigarette use and linkage disequilibrium that differ from patterns in other populations. Therefore, studies in African-Americans can provide complementary data to localize lung cancer susceptibility genes and explore smoking dependence-related genes. We used admixture mapping to further characterize genetic risk of lung cancer in a series of 837 African-American lung cancer cases and 975 African-American controls genotyped at 1344 ancestry informative single-nucleotide polymorphisms. Both case-only and case-control analyses were conducted using ADMIXMAP adjusted for age, sex, pack-years of smoking, family history of lung cancer, history of emphysema and study site. In case-only analyses, excess European ancestry was observed over a wide region on chromosome 1 with the largest excess seen at rs6587361 for non-small-cell lung cancer (NSCLC) (Z-score = -4.33; P = 1.5 × 10⁻⁵) and for women with NSCLC (Z-score = -4.82; P = 1.4 × 10⁻⁶). Excess African ancestry was also observed on chromosome 3q with a peak Z-score of 3.33 (P = 0.0009) at rs181696 among ever smokers with NSCLC. These results add to the findings from the GWAS in Caucasian populations and suggest novel regions of interest.

C-reactive protein and risk of lung cancer

PURPOSE

Chronic inflammation could play a role in lung carcinogenesis, underscoring the potential for lung cancer prevention and screening. We investigated the association of circulating high-sensitivity C-reactive protein (CRP, an inflammation biomarker) and CRP single nucleotide polymorphisms (SNPs) with prospective lung cancer risk.

PATIENTS AND METHODS

We conducted a nested case-control study of 592 lung cancer patients and 670 controls with available prediagnostic serum and 378 patients and 447 controls with DNA within the screening arm of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (N = 77,464). Controls were matched to patients on age, sex, entry year, follow-up time, and smoking. We measured CRP levels in baseline serum samples and genotyped five common CRP SNPs.

RESULTS

Elevated CRP levels were associated with increased lung cancer risk (odds ratio [OR], 1.98; 95% CI, 1.35 to 2.89; P-trend < .001 for fourth quartile [Q4, > or = 5.6 mg/L] v Q1 [< 1.0 mg/L]). The CRP association did not differ significantly by histology, follow-up time, or smoking status, but was most apparent for squamous cell carcinomas (OR, 2.92; 95% CI, 1.30 to 6.54), 2 to 5 years before lung cancer diagnosis (OR, 2.33; 95% CI, 1.24 to 4.39), and among former smokers (OR, 2.48; 95% CI, 1.53 to 4.03) and current smokers (OR, 1.90; 95% CI, 1.06 to 3.41). Although CRP SNPs and haplotypes were associated with CRP levels, they were not associated with lung cancer risk. Ten-year standardized absolute risks of lung cancer were higher with elevated CRP levels among former smokers (Q4: 2.55%; 95% CI, 1.98% to 3.27% v Q1: 1.39%; 95% CI, 1.07% to 1.81%) and current smokers (Q4: 7.37%; 95% CI, 5.81% to 9.33% v Q1: 4.03%; 95% CI, 3.01% to 5.40%).

CONCLUSION

Elevated CRP levels are associated with subsequently increased lung cancer risk, suggesting an etiologic role for chronic pulmonary inflammation in lung carcinogenesis.

Abstract 4238: Human non-small cell lung cancer cells asymmetrically divide their template DNA strands and cell fate proteins

Certain subpopulations of tumor cells are capable of both self-renewal and regeneration of phenotypically heterogeneous tumors. These observations suggest that tumor initiation and maintenance are linked to asymmetric cell divisions of tumor stem cells. However, cell progeny of symmetric divisions could adopt different cell fates, possibly through interactions between the daughter cells and their microenvironments. We set out to determine if human lung cancer primary tumor cells and cell lines asymmetrically divide their template DNA strands exclusively to only one daughter cell during cell division, and further, if the process is linked to cell fate. By performing pulse-chase experiments with halogenated thymidine analogs, we observed that 0.7-6.0% of cells within human lung cancer cell lines and 15-25% of short-term culture cells from primary lung tumor samples asymmetrically divide their template DNA strands. The data was confirmed by examination of asymmetrically dividing cells by two-color DNA analogs and visualization in real-time. Furthermore, cells that asymmetrically divide the lung cancer stem cell marker CD133 are 10-fold more likely to asymmetrically divide their labeled template DNA strands than cells that symmetrically divide CD133, and in each case, the CD133 co-segregates with the older DNA strands. The lung adenocarcinoma differentiation marker pro-surfactant protein C (SPC) is passed to the opposing daughter cell in 93% of cell divisions that asymmetrically divide both the DNA and SPC, suggesting a correlation between asymmetric division of template DNA and cell fate. To gain insight into the mechanisms regulating asymmetric cell division in lung cancer, we subjected cell lines to conditions known to enhance self-renewal. We observed that the frequency of template DNA co-segregation decreases 2- to 3-fold at lower cell densities as well as during serum deprivation and hypoxic conditions. These data indicate that a switch from asymmetric to symmetric cell divisions is one mechanism by which tumor cells increase self-renewal. Furthermore, the process requires cell-cell contact, suggesting that the niche participating in self-renewal regulation is provided by direct signaling from neighboring tumor cells. Our results demonstrate that a hierarchical cellular pattern within human lung tumors may be regulated, in part, by an orchestrated mechanism of self-renewal and differentiation involving co-segregation of template DNA and cell fate markers. An in-depth examination of intercellular and environmental response signaling pathways are needed to decipher exactly how neighboring cells and the environment influence cancer cell fate decisions. Examination of genes known to disrupt asymmetric cell division in lower organisms in human cancers could elucidate novel pathways controlling cancer maintenance and provide novel therapeutic targets.

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 4238.

Abstract 2915: p53 isoforms Δ133p53 and p53β are endogenous regulators of replicative cellular senescence

The finite proliferative potential of normal human cells leads to replicative cellular senescence, which is a critical barrier to tumor progression in vivo. The p53 signaling pathway plays central roles in the regulation of cellular senescence. Humans, as well as Drosophila and zebrafish, have p53 isoforms; however, their regulation and function are poorly understood. We here examine the expression profiles of two human p53 isoforms, p53β (lacking the C-terminal oligomerization domain due to an alternative mRNA splicing) and Δ133p53 (lacking the N-terminal transactivation and proline-rich domains due to the transcription from an alternative promoter in intron 4), during in vitro and in vivo cellular senescence and their biological activities in regulating cellular senescence. Induced p53β and diminished Δ133p53 were associated with replicative senescence, but not oncogene-induced senescence, in normal human fibroblasts. The replicatively senescent fibroblasts also expressed increased levels of miR-34a, a p53-induced microRNA, the antisense inhibition of which delayed the onset of replicative senescence. The siRNA-mediated knockdown of endogenous Δ133p53 induced cellular senescence, which was attributed to the regulation of p21WAF1 and other p53 transcriptional target genes. In overexpression experiments, while p53β cooperated with full-length p53 to accelerate cellular senescence, Δ133p53 repressed miR-34a expression and extended cellular replicative lifespan, providing a functional connection of this microRNA to the p53 isoform-mediated regulation of senescence. The senescence-associated signature of p53 isoform expression (i.e., elevated p53β and reduced Δ133p53) was observed in vivo in colon adenomas with senescent phenotypes. The decreased p53β and increased Δ133p53 expression found in colon carcinomas might signal an escape from the senescence barrier during the progression from premalignant to malignant tumors in vivo. This study shows that natural p53 isoforms constitute an endogenous regulatory mechanism for p53-mediated replicative senescence and may open up a new p53-based, senescence-mediated strategy to manipulate carcinogenesis and aging. The molecular details of the senescence-associated Δ133p53 repression and p53β induction are currently under investigation.

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 2915.