Daniela S. Basseres

Block of C/EBPα function by phosphorylation in acute myeloid leukemia with FLT3 activating mutations

Mutations constitutively activating FLT3 kinase are detected in ∼30% of acute myelogenous leukemia (AML) patients and affect downstream pathways such as extracellular signal–regulated kinase (ERK)1/2. We found that activation of FLT3 in human AML inhibits CCAAT/enhancer binding protein α (C/EBPα) function by ERK1/2-mediated phosphorylation, which may explain the differentiation block of leukemic blasts. In MV4;11 cells, pharmacological inhibition of either FLT3 or MEK1 leads to granulocytic differentiation. Differentiation of MV4;11 cells was also observed when C/EBPα mutated at serine 21 to alanine (S21A) was stably expressed. In contrast, there was no effect when serine 21 was mutated to aspartate (S21D), which mimics phosphorylation of C/EBPα. Thus, our results suggest that therapies targeting the MEK/ERK cascade or development of protein therapies based on transduction of constitutively active C/EBPα may prove effective in treatment of FLT3 mutant leukemias resistant to the FLT3 inhibitor therapies.

A Transcriptional Profiling Study of CCAAT/Enhancer Binding Protein Targets Identifies Hepatocyte Nuclear Factor 3β as a Novel Tumor Suppressor in Lung Cancer

We showed previously that CCAAT/enhancer binding protein α (C/EBPα), a tissue-specific transcription factor, is a candidate tumor suppressor in lung cancer. In the present study, we have performed a transcriptional profiling study of C/EBPα target genes using an inducible cell line system. This study led to the identification of hepatocyte nuclear factor 3β (HNF3β), a transcription factor known to play a role in airway differentiation, as a downstream target of C/EBPα. We found down-regulation of HNF3β expression in a large proportion of lung cancer cell lines examined and identified two novel mutants of HNF3β, as well as hypermethylation of the HNF3β promoter. We also developed a tetracycline-inducible cell line model to study the cellular consequences of HNF3β expression. Conditional expression of HNF3β led to significant growth reduction, proliferation arrest, apoptosis, and loss of clonogenic ability, suggesting additionally that HNF3β is a novel tumor suppressor in lung cancer. This is the first study to show genetic abnormalities of lung-specific differentiation pathways in the development of lung cancer.

Respiratory Failure Due to Differentiation Arrest and Expansion of Alveolar Cells following Lung-Specific Loss of the Transcription Factor C/EBPα in Mice

ABSTRACT The leucine zipper family transcription factor CCAAT enhancer binding protein alpha (C/EBPα) inhibits proliferation and promotes differentiation in various cell types. In this study, we show, using a lung-specific conditional mouse model of C/EBPα deletion, that loss of C/EBPα in the respiratory epithelium leads to respiratory failure at birth due to an arrest in the type II alveolar cell differentiation program. This differentiation arrest results in the lack of type I alveolar cells and differentiated surfactant-secreting type II alveolar cells. In addition to showing a block in type II cell differentiation, the neonatal lungs display increased numbers of proliferating cells and decreased numbers of apoptotic cells, leading to epithelial expansion and loss of airspace. Consistent with the phenotype observed, genes associated with alveolar maturation, survival, and proliferation were differentially expressed. Taken together, these results identify C/EBPα as a master regulator of airway epithelial maturation and suggest that the loss of C/EBPα could also be an important event in the multistep process of lung tumorigenesis. Furthermore, this study indicates that exploring the C/EBPα pathway might have therapeutic benefits for patients with respiratory distress syndromes.

Frequent downregulation of the transcription factor Foxa2 in lung cancer through epigenetic silencing

PURPOSE We sought to determine the mechanisms of downregulation of the airway transcription factor Foxa2 in lung cancer and the expression status of Foxa2 in non-small-cell lung cancer (NSCLC). METHODS A series of 25 lung cancer cell lines were evaluated for Foxa2 protein expression, FOXA2 mRNA levels, FOXA2 mutations, FOXA2 copy number changes and for evidence of FOXA2 promoter hypermethylation. In addition, 32 NSCLCs were sequenced for FOXA2 mutations and 173 primary NSCLC tumors evaluated for Foxa2 expression using an immunohistochemical assay. RESULTS Out of the 25 cell lines, 13 (52%) had undetectable FOXA2 mRNA. The expression of FOXA2 mRNA and Foxa2 protein were congruent in 19/22 cells (p = 0.001). FOXA2 mutations were not identified in primary NSCLCs and were infrequent in cell lines. Focal or broad chromosomal deletions involving FOXA2 were not present. The promoter region of FOXA2 had evidence of hypermethylation, with an inverse correlation between FOXA2 mRNA expression and presence of CpG dinucleotide methylation (p < 0.0001). In primary NSCLC tumor specimens, there was a high frequency of either absence (42/173, 24.2%) or no/low expression (96/173, 55.4%) of Foxa2. In 130 patients with stage I NSCLC there was a trend towards decreased survival in tumors with no/low expression of Foxa2 (HR of 1.6, 95%CI 0.9-3.1; p = 0.122). CONCLUSIONS Loss of expression of Foxa2 is frequent in lung cancer cell lines and NSCLCs. The main mechanism of downregulation of Foxa2 is epigenetic silencing through promoter hypermethylation. Further elucidation of the involvement of Foxa2 and other airway transcription factors in the pathogenesis of lung cancer may identify novel therapeutic targets.

RUNX1 regulates the CD34 gene in haematopoietic stem cells by mediating interactions with a distal regulatory element

The transcription factor RUNX1 is essential to establish the haematopoietic gene expression programme; however, the mechanism of how it activates transcription of haematopoietic stem cell (HSC) genes is still elusive. Here, we obtained novel insights into RUNX1 function by studying regulation of the human CD34 gene, which is expressed in HSCs. Using transgenic mice carrying human CD34 PAC constructs, we identified a novel downstream regulatory element (DRE), which is bound by RUNX1 and is necessary for human CD34 expression in long‐term (LT)‐HSCs. Conditional deletion of Runx1 in mice harbouring human CD34 promoter–DRE constructs abrogates human CD34 expression. We demonstrate by chromosome conformation capture assays in LT‐HSCs that the DRE physically interacts with the human CD34 promoter. Targeted mutagenesis of RUNX binding sites leads to perturbation of this interaction and decreased human CD34 expression in LT‐HSCs. Overall, our in vivo data provide novel evidence about the role of RUNX1 in mediating interactions between distal and proximal elements of the HSC gene CD34.

Targeted BMI1 inhibition impairs tumor growth in lung adenocarcinomas with low CEBPα expression

In lung cancers with low expression of C/EBPα, BMI1 expression correlates with worse prognosis but can be targeted with a drug. The right drug for the right tumor The expression of a tumor suppressor called C/EBPα is often lost in non–small cell lung cancer, as well as in other cancer types. Yong et al. discovered that lung tumors deficient in C/EBPα often overexpress a particular oncogenic protein, BMI1, and that higher expression of BMI1 correlates with worse prognosis in this group of patients. The authors characterized the role of these two proteins and their interaction in lung cancer development, then used cell lines and a genetic mouse model to test a therapeutic approach, showing that a pharmaceutical inhibitor of BMI1 is effective against non–small cell lung cancer with low C/EBPα and high BMI1. Lung cancer is the most common cause of cancer deaths. The expression of the transcription factor C/EBPα (CCAAT/enhancer binding protein α) is frequently lost in non–small cell lung cancer, but the mechanisms by which C/EBPα suppresses tumor formation are not fully understood. In addition, no pharmacological therapy is available to specifically target C/EBPα expression. We discovered a subset of pulmonary adenocarcinoma patients in whom negative/low C/EBPα expression and positive expression of the oncogenic protein BMI1 (B lymphoma Mo-MLV insertion region 1 homolog) have prognostic value. We also generated a lung-specific mouse model of C/EBPα deletion that develops lung adenocarcinomas, which are prevented by Bmi1 haploinsufficiency. BMI1 activity is required for both tumor initiation and maintenance in the C/EBPα-null background, and pharmacological inhibition of BMI1 exhibits antitumor effects in both murine and human adenocarcinoma lines. Overall, we show that C/EBPα is a tumor suppressor in lung cancer and that BMI1 is required for the oncogenic process downstream of C/EBPα loss. Therefore, anti-BMI1 pharmacological inhibition may offer a therapeutic benefit for lung cancer patients with low expression of C/EBPα and high BMI1.

Aurora kinase targeting in lung cancer reduces KRAS-induced transformation

BackgroundActivating mutations in KRAS are prevalent in lung cancer and have been causally linked to the oncogenic process. However, therapies targeted to oncogenic RAS have been ineffective to date and identification of KRAS targets that impinge on the oncogenic phenotype is warranted. Based on published studies showing that mitotic kinases Aurora A (AURKA) and B (AURKB) cooperate with oncogenic RAS to promote malignant transformation and that AURKA phosphorylates RAS effector pathway components, the aim of this study was to investigate whether AURKA and AURKB are KRAS targets in lung cancer and whether targeting these kinases might be therapeutically beneficial.MethodsIn order to determine whether oncogenic KRAS induces Aurora kinase expression, we used qPCR and western blotting in three different lung cell-based models of gain- or loss-of-function of KRAS. In order to determine the functional role of these kinases in KRAS-induced transformation, we generated KRAS-positive A549 and H358 cells with stable and inducible shRNA-mediated knockdown of AURKA or AURKB and evaluated transformation in vitro and tumor growth in vivo. In order to validate AURKA and/or AURKB as therapeutically relevant KRAS targets in lung cancer, we treated A549 and H358 cells, as well as two different lung cell based models of gain-of-function of KRAS with a dual Aurora kinase inhibitor and performed functional in vitro assays.ResultsWe determined that KRAS positively regulates AURKA and AURKB expression. Furthermore, in KRAS-positive H358 and A549 cell lines, inducible knockdown of AURKA or AURKB, as well as treatment with a dual AURKA/AURKB inhibitor, decreased growth, viability, proliferation, transformation, and induced apoptosis in vitro. In addition, inducible shRNA-mediated knockdown of AURKA in A549 cells decreased tumor growth in vivo. More importantly, dual pharmacological inhibiton of AURKA and AURKB reduced growth, viability, transformation, and induced apoptosis in vitro in an oncogenic KRAS-dependent manner, indicating that Aurora kinase inhibition therapy can specifically target KRAS-transformed cells.ConclusionsOur results support our hypothesis that Aurora kinases are important KRAS targets in lung cancer and suggest Aurora kinase inhibition as a novel approach for KRAS-induced lung cancer therapy.

Development and characterization of miltefosine-loaded polymeric micelles for cancer treatment

Miltefosine presents antineoplastic activity but high hemolytic potential. Its use in cancer has been limited to treating cutaneous metastasis of breast cancer. To decrease hemolytic potential, we developed a formulation of miltefosine-loaded polymeric micelles (PM) of the copolymer Pluronic-F127. A central composite design was applied and the analysis of variance showed that the optimum level of hydrodynamic diameter and polydispersity index predicted by the model and experimentally confirmed were 29nm and 0.105, respectively. Thermal analyses confirmed that miltefosine was molecularly dispersed within PM. Pluronic-F127 PM with miltefosine 80μM presented a significant reduction of hemolytic effect (80%, p<0.05) in comparison to free drug. In vitro assays against HeLa carcinoma cells demonstrated similar cytotoxicity to free miltefosine and PM. Our results suggest that, by lowering hemolytic potential, miltefosine-loaded Pluronic-F127 PM a promising alternative to broaden this drug use in cancer therapy, as well as of other alkylphosphocholines.

Preparation, characterization and in vitro evaluation of ε-polylysine-loaded polymer blend microparticles for potential pancreatic cancer therapy

Abstract Peptide active ingredients show great promise regarding the treatment of various health-endangering diseases. It is reported that L-lysine inhibits the proliferation of several tumour lines in vitro and in vivo. However, proteins and peptide drugs possess certain disadvantages such as in vivo instability and short biological half-life. On the grounds that drug delivery systems can overcome a wide spectrum of bioactive compounds issues, a biopolymeric blend-based microparticulated system capable of delivering ε-polylysine (PLL) was developed. PLL-loaded poly((L)Lactic acid)/poly(D,L-Lactide)-co-poly(ethylene glycol)-based microparticles (PLL-PB-MPs) were prepared and fully characterised exhibiting a narrow size distribution (1.2 ± 0.12 µm), high loading efficiency (81%) and improved thermal stability (Td from 250 °C to 291 °C). The cytotoxicity and antiproliferative effect of PLL-PB-MPs in pancreatic adenocarcinoma cell lines BxPC3 and MIA PaCa-2 were confirmed. Due to their physicochemical and biopharmaceutical properties, PB-MPs constitute a promising carrier to deliver bioactive peptides.

Abstract 1379: IKKβ is a potential anti-angiogenic therapeutic target in KRAS-induced lung cancer

Activating mutations in KRAS are prevalent in cancer, but therapies targeted to oncogenic RAS have been ineffective to date. An alternative route for blocking RAS-driven oncogenic pathways is to target downstream effectors of RAS involved in promoting the oncogenic phenotype. One of the critical characteristics required for tumors to grow and progress is the ability of tumor cells to drive angiogenesis. Interestingly, oncogenic RAS promotes angiogenesis by upregulating the proangiogenic IL-8 cytokine, an NF-kB target gene; and recent studies have shown that oncogenic RAS also activates the NF-κB transcription factor pathway and that KRAS-induced lung tumorigenesis is suppressed by expression of a degradation-resistant form of the IκBα inhibitor or by genetic or pharmacological inhibition of IKKβ or deletion of the RELA/p65 subunit of NF-κB. Therefore, we hypothesized that IKKβ inhibition would reduce KRAS-induced angiogenesis and tumor progression. To test this hypothesis, we used genetic and pharmacological approaches to inhibit IKKβ in K-Ras mutant lung cancer cell lines. Treatment of KRAS-positive A549 e H358 lung cancer cells with the highly specific IKKβ inhibitor Compound A (CmpdA) or siRNA-mediated knockdown of IKKβ in these cells reduced expression and secretion of the proangiogenic IL-8 cytokine. We found that IKKβ targeting also reduced expression and secretion of VEGF, a growth factor involved in promoting angiogenesis, which is also regulated by NF-κB. Moreover, conditioned media from A549 and H358 cells with siRNA-mediated IKKβ knockdown reduced endothelial cell (HUVECS) migration. In order to ascertain whether IKKβ inhibition can directly affect endothelial cell function, we treated HUVECs with CmpdA, which also resulted in reduced HUVEC migration. To evaluate how IKKβ affects endothelial cell function in vivo, we used a mouse model of neonatal retinopathy, where pathological retinal angiogenesis is induced by transient exposure of neonatal mice to hyperoxic conditions. Angiogenesis was significantly reduced in this model when neonatal mice were treated with 3 doses of 10 mg/Kg CmpdA. Finally, IKKβ knockdown in A549 cells also reduced expression of MMP-2 and MMP9 metalloproteases and reduced A549 cell invasion. Taken together, these results suggest that IKKβ inhibition therapy may reduce tumor angiogenesis, as well as invasive properties of KRAS-induced lung tumors, thereby having the potential to result in a sustained therapeutic effect, particularly if combined with other therapeutic approaches. Citation Format: Tatiana C. Lobo, Leila Magalhaes, Laura Cardeal, Ricardo Giordano, Albert Baldwin, Daniela Basseres. IKKβ is a potential anti-angiogenic therapeutic target in KRAS-induced lung 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 1379. doi:10.1158/1538-7445.AM2015-1379