BRAFV600E-mutant metastatic NSCLC: disease overview and treatment landscape

In this review, we cover the current understanding of BRAF mutations and associated clinical characteristics in patients with metastatic NSCLC, approved and emerging treatment options, BRAF sequencing approaches, and unmet needs. The BRAFV600E mutation confers constitutive activity of the MAPK pathway, leading to enhanced growth, proliferation, and survival of tumor cells. Testing for BRAF mutations enables patients to be treated with therapies that directly target BRAFV600E and the MAPK pathway, but BRAF testing lags behind other oncogene testing in metastatic NSCLC. Additional therapies targeting BRAFV600E mutations provide options for patients with metastatic NSCLC. Emerging therapies and combinations under investigation could potentially overcome issues of resistance and target non-V600E mutations. Therefore, because targeted therapies with enhanced efficacy are on the horizon, being able to identify BRAF mutations in metastatic NSCLC may become even more important.

Preclinical Modeling of Pathway-Targeted Therapy of Human Lung Cancer in the Mouse

Animal models, particularly genetically engineered mouse models (GEMMs), continue to have a transformative impact on our understanding of the initiation and progression of hematological malignancies and solid tumors. Furthermore, GEMMs have been employed in the design and optimization of potent anticancer therapies. Increasingly, drug responses are assessed in mouse models either prior, or in parallel, to the implementation of precision medical oncology, in which groups of patients with genetically stratified cancers are treated with drugs that target the relevant oncoprotein such that mechanisms of drug sensitivity or resistance may be identified. Subsequently, this has led to the design and preclinical testing of combination therapies designed to forestall the onset of drug resistance. Indeed, mouse models of human lung cancer represent a paradigm for how a wide variety of GEMMs, driven by a variety of oncogenic drivers, have been generated to study initiation, progression, and maintenance of this disease as well as response to drugs. These studies have now expanded beyond targeted therapy to include immunotherapy. We highlight key aspects of the relationship between mouse models and the evolution of therapeutic approaches, including oncogene-targeted therapies, immunotherapies, acquired drug resistance, and ways in which successful antitumor strategies improve on efficiently translating preclinical approaches into successful antitumor strategies in patients.

Transposon Mutagenesis Reveals RBMS3 Silencing as a Promoter of Malignant Progression of BRAFV600E-Driven Lung Tumorigenesis

Mutationally activated BRAF is detected in approximately 7% of human lung adenocarcinomas, with BRAFT1799A serving as a predictive biomarker for treatment of patients with FDA-approved inhibitors of BRAFV600E oncoprotein signaling. In genetically engineered mouse (GEM) models, expression of BRAFV600E in the lung epithelium initiates growth of benign lung tumors that, without additional genetic alterations, rarely progress to malignant lung adenocarcinoma. To identify genes that cooperate with BRAFV600E for malignant progression, we used Sleeping Beauty-mediated transposon mutagenesis, which dramatically accelerated the emergence of lethal lung cancers. Among the genes identified was Rbms3, which encodes an RNA-binding protein previously implicated as a putative tumor suppressor. Silencing of RBMS3 via CRISPR/Cas9 gene editing promoted growth of BRAFV600E lung organoids and promoted development of malignant lung cancers with a distinct micropapillary architecture in BRAFV600E and EGFRL858R GEM models. BRAFV600E/RBMS3Null lung tumors displayed elevated expression of Ctnnb1, Ccnd1, Axin2, Lgr5, and c-Myc mRNAs, suggesting that RBMS3 silencing elevates signaling through the WNT/β-catenin signaling axis. Although RBMS3 silencing rendered BRAFV600E-driven lung tumors resistant to the effects of dabrafenib plus trametinib, the tumors were sensitive to inhibition of porcupine, an acyltransferase of WNT ligands necessary for their secretion. Analysis of The Cancer Genome Atlas patient samples revealed that chromosome 3p24, which encompasses RBMS3, is frequently lost in non-small cell lung cancer and correlates with poor prognosis. Collectively, these data reveal the role of RBMS3 as a lung cancer suppressor and suggest that RBMS3 silencing may contribute to malignant NSCLC progression.

SIGNIFICANCE

Loss of RBMS3 cooperates with BRAFV600E to induce lung tumorigenesis, providing a deeper understanding of the molecular mechanisms underlying mutant BRAF-driven lung cancer and potential strategies to more effectively target this disease.

Overview of Current Developments in Biobutanol Production Methods and Future Perspectives

Renewable biobutanol production is receiving more attention toward substituting fossil-based nonrenewable fuels. Biobutanol is recognized as the top most biofuel with extraordinary properties as compared with gasoline. The demand for biobutanol production is increasing enormously due to application in various industries as chemical substituent. Biobutanol production technology has attracted many researchers toward implementation of replacing cost-effective substrate and easy method to recover from the fermentation broth. Sugarcane bagasse, algal biomass, crude glycerol, and lignocellulosic biomass are potential cost-effective substrates which could replace consistent glucose-based substrates. The advantages and limitations of these substrates have been discussed in this chapter. Moreover, finding the integrated biobutanol recovery methods is an important factor parameter in production of biobutanol. This chapter also concentrated on possibilities and drawbacks of obtainable integrated biobutanol recovery methods. Thus, successful process involving cost-effective substrate and biobutanol recovery methods could help to implementation of biobutanol production industry. Overall, this chapter has endeavored to increase the viability of industrial production of biobutanol.

Abstract 3769: Combined TRKA and MEK1/2 Inhibition Forestalls the Onset of Acquired Resistance in a New Preclinical Model of NTRK1+ Pancreatic Cancer

NTRK1 gene fusions encode oncoprotein (TRKA) kinases that are actionable drivers of a number of human malignancies including a subset of pancreatic cancers. Here, we describe a new preclinical model of pancreatic cancer in which a TPR-NTRK1 fusion gene is expressed in conditionally immortalized mouse pancreatic ductal epithelial (IMPE) cells. Indeed, expression of TPR-NTRK1 in IMPE cells is sufficient to transform these cells without any additional engineered genetic alterations. Other oncogenes tested in this model include KRAS and EGFR, but neither were unable to replicate this one-hit model of transformation. This striking result may be explained by the differential levels of MAPK pathway activation produced by different oncogenes, and a “goldilocks zone” required to drive pancreatic cellular transformation. These data suggest NTRK1 is a unique and powerful driver of transformation in pancreatic epithelial cells. NTRK1-driven IMPE cells form fast growing tumors in immunocompromised mice both subcutaneously, and orthotopically in the mouse pancreas. Importantly, TPR-NTRK1-driven IMPE cell derived tumors are exquisitely sensitive to targeted inhibition of TRKA kinase activity. However, as also observed in pancreatic cancer patients treated with entrectinib, this therapeutic response is transient and tumors eventually develop resistance to single-agent TRKA inhibition. This model revealed that short drug treatments (2 hours) are sufficient to block autophosphorylation of the oncoprotein target, as well as blockade of the downstream MAPK signaling pathway. Critically, we observed that long-term drug treatments (24 hours) result in downstream MAPK pathway reactivation despite maintained drug activity against the target, TRKA. Consistent with this, the targeted inhibition of TRKA, which transiently blocks MAPK signaling results in a subsequent elevation of BIM protein expression, a pro-apoptotic member of the BCL2 family. Indeed, CRISPR/CAS9-mediated abrogation of BIM expression significantly diminishes the response of TPR-NTRK1-driven IMPE tumors to inhibition of TRKA kinase activity. In an effort to delay acquired resistance to single-agent TRKA inhibitors, we reasoned that combined vertical inhibition of both TRKA and MAPK signaling with the combination of an TRKA plus a MEK1/2 inhibitor might increase the durability of response in this model and counteract the observed pathway reactivation. To that end, we treated mice bearing TPR-NTRK-driven IMPE tumors with either a TRKA inhibitor, a MEK1/2 inhibitor or the combination of both therapeutic agents. Mice treated with the entrectinib/cobimetinib combination revealed the durability of the tumor regression was significantly increased compared to single-agent entrectinib. Importantly, no toxicity or adverse side effects were observed in mice receiving the combination. Additionally, the combined therapies also induced more stable expression of BIM than the single-agent, by delaying degradation of BIM by the proteasome following BIM phosphorylation. Collectively, these data provide a compelling rationale for the clinical deployment of the targeted combination of TRKA inhibition plus MEK1/2 inhibition first-line in patients whose cancers are driven by NTRK1 gene fusions.

Citation Format: Aria Vaishnavi, Michael T. Scherzer, Conan Kinsey, Ignacio Garrido-Laguna, Martin McMahon. Combined TRKA and MEK1/2 Inhibition Forestalls the Onset of Acquired Resistance in a New Preclinical Model of NTRK1+ Pancreatic Cancer [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 3769.

Inhibition of MEK1/2 Forestalls the Onset of Acquired Resistance to Entrectinib in Multiple Models of NTRK1-Driven Cancer

NTRK1 gene fusions are actionable drivers of numerous human malignancies. Here, we show that expression of the TPR-NTRK1 fusion kinase in immortalized mouse pancreatic ductal epithelial (IMPE) (pancreas) or mouse lung epithelial (MLE-12) cells is sufficient to promote rapidly growing tumors in mice. Both tumor models are exquisitely sensitive to targeted inhibition with entrectinib, a tropomyosin-related kinase A (TRKA) inhibitor. Initial regression of NTRK1-driven tumors is driven by induced expression of BIM, such that BIM silencing leads to a diminished response to entrectinib in vivo. However, the emergence of drug-resistant disease limits the long-term durability of responses. Based on the reactivation of RAF>MEK>ERK signaling observed in entrectinib-treated tumors, we show that the combination of entrectinib plus the MEK1/2 inhibitor cobimetinib dramatically forestalls the onset of drug resistance in vivo. Collectively, these data provide a mechanistic rationale for rapid clinical deployment of combined inhibition of TRKA plus MEK1/2 in NTRK1-driven cancers.

Abstract A29: The CUTO panel of patient-derived NSCLC cell lines reveals unique molecular characteristics and responses to targeted therapies

Cell lines generated from human tumors have been an invaluable tool in dissecting the underlying molecular mechanisms of cancer biology and for cancer drug development. The large library of original human lung cancer cell lines established by Minna and Gazdar, though instrumental in investigating various aspect of lung cancer biology, lacks examples of some of the diverse mutations responsible for this cancer. The CUTO (Colorado University Thoracic Oncology) cell line series, initiated in 2011, had the goal of curating a new panel of cells derived from NSCLC patients with distinct oncogenic drivers. By generating multiple, unique cell lines representing each oncogene driver subset, we believe that these lines would allow study of interpatient variability that underlie differential patient responses and duration of response to targeted therapies. The current CUTO panel consist of 33 cell lines with either 1) gene rearrangements in ALK, RET, ROS1 or NTRK1; 2) activating mutations in the ERBB gene family including exon 20 insertions in EGFR and ERBB2 (HER2) as well as rare mutations in EGFR; and 3) inactivation of the NF1 gene either as a concurrent mutation with other oncogenic alterations or as the sole driver mutation. For cells harboring gene rearrangements we have amassed four EML4-ALK lines, two KIF5B-RET cell lines, five ROS1 fusion lines (3 CD74-ROS1, 1 SDC4-ROS1, and 1 TPM3-ROS1), and one MPRIP-NTRK1 cell line. Our ERBB mutant lines include one cell line with HER2 exon 20 insertion, three lines with different exon 20 insertions in EGFR, and two EGFR mutant cell lines with compound mutations. We present our characterization of these cell lines in terms of their proliferation profiles and molecular signaling pathways in the presence of targeted inhibition. The derivation and characterization of these cell lines have facilitated the study of cell signaling in oncogene-driven cancer, have helped identify new resistance mechanisms, and have facilitated drug development for rare oncogenes such as NTRK1 gene fusions and EGFR exon 20 insertions. We expect that this growing library of cell lines will continue to further our understanding of oncogenic-driven tumor biology and provide mechanistic insight towards the development of novel therapeutics and drug combinations.

Citation Format: Anh Tuan Le, Adriana Estrada-Bernal, Laura Schubert, Andrea Doak, Nan Chen, Kurtis Davies, Aria Vaishnavi, Mary Jackson, Vignesh Narayana, Kimi Kondo, John Mitchell, Michael Weyant, Tom Purcell, Paul Bunn, Ross Camidge, Janet Freeman-Daly, Robert Doebele. The CUTO panel of patient-derived NSCLC cell lines reveals unique molecular characteristics and responses to targeted therapies [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr A29.

EGFR Mediates Responses to Small-Molecule Drugs Targeting Oncogenic Fusion Kinases

Oncogenic kinase fusions of ALK, ROS1, RET, and NTRK1 act as drivers in human lung and other cancers. Residual tumor burden following treatment of ALK or ROS1⁺ lung cancer patients with oncogene-targeted therapy ultimately enables the emergence of drug-resistant clones, limiting the long-term effectiveness of these therapies. To determine the signaling mechanisms underlying incomplete tumor cell killing in oncogene-addicted cancer cells, we investigated the role of EGFR signaling in drug-naïve cancer cells harboring these oncogene fusions. We defined three distinct roles for EGFR in the response to oncogene-specific therapies. First, EGF-mediated activation of EGFR blunted fusion kinase inhibitor binding and restored fusion kinase signaling complexes. Second, fusion kinase inhibition shifted adaptor protein binding from the fusion oncoprotein to EGFR. Third, EGFR enabled bypass signaling to critical downstream pathways such as MAPK. While evidence of EGFR-mediated bypass signaling has been reported after ALK and ROS1 blockade, our results extended this effect to RET and NTRK1 blockade and uncovered the other additional mechanisms in gene fusion-positive lung cancer cells, mouse models, and human clinical specimens before the onset of acquired drug resistance. Collectively, our findings show how EGFR signaling can provide a critical adaptive survival mechanism that allows cancer cells to evade oncogene-specific inhibitors, providing a rationale to cotarget EGFR to reduce the risks of developing drug resistance. Cancer Res; 77(13); 3551-63. ©2017 AACR.

An Oncogenic NTRK Fusion in a Patient with Soft-Tissue Sarcoma with Response to the Tropomyosin-Related Kinase Inhibitor LOXO-101

Oncogenic TRK fusions induce cancer cell proliferation and engage critical cancer-related downstream signaling pathways. These TRK fusions occur rarely, but in a diverse spectrum of tumor histologies. LOXO-101 is an orally administered inhibitor of the TRK kinase and is highly selective only for the TRK family of receptors. Preclinical models of LOXO-101 using TRK-fusion-bearing human-derived cancer cell lines demonstrate inhibition of the fusion oncoprotein and cellular proliferation in vitro, and tumor growth in vivo. The tumor of a 41-year-old woman with soft-tissue sarcoma metastatic to the lung was found to harbor an LMNA-NTRK1 gene fusion encoding a functional LMNA-TRKA fusion oncoprotein as determined by an in situ proximity ligation assay. In a phase I study of LOXO-101 (ClinicalTrials.gov no. NCT02122913), this patient's tumors underwent rapid and substantial tumor regression, with an accompanying improvement in pulmonary dyspnea, oxygen saturation, and plasma tumor markers.

SIGNIFICANCE

TRK fusions have been deemed putative oncogenic drivers, but their clinical significance remained unclear. A patient with a metastatic soft-tissue sarcoma with an LMNA-NTRK1 fusion had rapid and substantial tumor regression with a novel, highly selective TRK inhibitor, LOXO-101, providing the first clinical evidence of benefit from inhibiting TRK fusions.

TRKing down an old oncogene in a new era of targeted therapy

The use of high-throughput next-generation sequencing techniques in multiple tumor types during the last few years has identified NTRK1, 2, and 3 gene rearrangements encoding novel oncogenic fusions in 19 different tumor types to date. These recent developments have led us to revisit an old oncogene, Trk (originally identified as OncD), which encodes the TPM3-NTRK1 gene fusion and was one of the first transforming chromosomal rearrangements identified 32 years ago. However, no drug has yet been approved by the FDA for cancers harboring this oncogene. This review will discuss the biology of the TRK family of receptors, their role in human cancer, the types of oncogenic alterations, and drugs that are currently in development for this family of oncogene targets.

SIGNIFICANCE

Precision oncology approaches have accelerated recently due to advancements in our ability to detect oncogenic mutations in tumor samples. Oncogenic alterations, most commonly gene fusions, have now been detected for the genes encoding the TRKA, TRKB, and TRKC receptor tyrosine kinases across multiple tumor types. The scientific rationale for the targeting of the TRK oncogene family will be discussed here.

Abstract 5255: EGFR is a conspiring kinase in gene fusion positive lung cancer

The use of kinase inhibitors directed at dominant oncogenes has proven a successful treatment strategy for non-small cell lung cancer (NSCLC) harboring ALK gene fusions, but intrinsic or acquired drug resistance limits clinical benefit. We recently identified a novel class of oncogenes generated by translocations of the NTRK1 gene, which encodes the TRKA receptor tyrosine kinase. ROS1 and RET gene fusions represent additional oncogene targets in lung cancer and gene fusion positive tumors currently comprise ∼10% of lung adenocarcinomas. Previous results from our laboratory have demonstrated that EGFR signaling can mediate both intrinsic and acquired resistance in a ROS1+ NSCLC cell line. We asked whether EGFR might play a common role in other NSCLC cell lines harboring gene fusions with the aim of developing combination therapies that may delay drug resistance to oncogene-targeted kinase inhibitors in these tumors. We have observed high protein expression of the epidermal growth factor receptor (EGFR) in NSCLC cell lines positive for ALK (H3122, H2228, and STE-1), ROS1 (HCC78 and CUTO-2), RET (LC-2/Ad), and NTRK1 gene fusions (CUTO-3), and in a NTRK1 patient-derived xenograft (PDX) model. We observed increased inhibition of downstream signaling and in vitro cellular proliferation with the addition of EGFR tyrosine kinase inhibitors in these gene fusion positive cell lines. Furthermore, stimulation of EGFR with EGF rescues targeted inhibition with oncogene-specific kinase inhibitors in the critical downstream signaling pathways such as PI3K/AKT and MEK/ERK. Inhibition of cellular proliferation of these cell lines using oncogene-specific kinase inhibitors was also rescued by stimulation of EGFR. Interestingly, we observed transactivation of the TRKA and RET kinase domains by EGFR stimulation in the CUTO-3 and LC-2/Ad cell lines, respectively, despite treatment with a TRKA or RET kinase inhibitor. Additionally, co-immunoprecipitation experiments show that EGFR and the chimeric protein RIP-TRKA (encoded by the fusion gene MPRIP-NTRK1) associate in the CUTO-3 cells or when ectopically expressed in 293T cells. Collectively, these data demonstrate a critical role for EGFR in gene fusion positive lung cancer and suggest that signaling via this receptor may provide a survival mechanism for cancer cells treated with an oncogene-specific kinase inhibitor. Further investigation of EGFR inhibition in addition to oncogene-specific kinase inhibitors may be warranted.

Citation Format: Aria Vaishnavi, Anh T. Le, Stephen B. Keysar, Christine M. Lovly, Severine Kako, Marileila Varella-Garcia, Antonio Jimeno, Robert C. Doebele. EGFR is a conspiring kinase in gene fusion positive lung cancer. [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 5255. doi:10.1158/1538-7445.AM2014-5255

Resistance to ROS1 inhibition mediated by EGFR pathway activation in non-small cell lung cancer

The targeting of oncogenic ‘driver’ kinases with small molecule inhibitors has proven to be a highly effective therapeutic strategy in selected non-small cell lung cancer (NSCLC) patients. However, acquired resistance to targeted therapies invariably arises and is a major limitation to patient care. ROS1 fusion proteins are a recently described class of oncogenic driver, and NSCLC patients that express these fusions generally respond well to ROS1-targeted therapy. In this study, we sought to determine mechanisms of acquired resistance to ROS1 inhibition. To accomplish this, we analyzed tumor samples from a patient who initially responded to the ROS1 inhibitor crizotinib but eventually developed acquired resistance. In addition, we generated a ROS1 inhibition-resistant derivative of the initially sensitive NSCLC cell line HCC78. Previously described mechanisms of acquired resistance to tyrosine kinase inhibitors including target kinase-domain mutation, target copy number gain, epithelial-mesenchymal transition, and conversion to small cell lung cancer histology were found to not underlie resistance in the patient sample or resistant cell line. However, we did observe a switch in the control of growth and survival signaling pathways from ROS1 to EGFR in the resistant cell line. As a result of this switch, ROS1 inhibition-resistant HCC78 cells became sensitive to EGFR inhibition, an effect that was enhanced by co-treatment with a ROS1 inhibitor. Our results suggest that co-inhibition of ROS1 and EGFR may be an effective strategy to combat resistance to targeted therapy in some ROS1 fusion-positive NSCLC patients.

Oncogenic and drug-sensitive NTRK1 rearrangements in lung cancer

We identified novel gene fusions in patients with lung cancer harboring the kinase domain of the NTRK1 gene that encodes the TRKA receptor. Both the MPRIP-NTRK1 and CD74-NTRK1 fusions lead to constitutive TRKA kinase activity and are oncogenic. Treatment of cells expressing NTRK1 fusions with inhibitors of TRKA kinase activity inhibited autophosphorylation of TRKA and cell growth. Three of 91 lung cancer patients (3.3%), without known oncogenic alterations, assayed by NGS or FISH demonstrated evidence of NTRK1 gene fusions.

NTRK1 gene fusions as a novel oncogene target in lung cancer

8023

Background: The identification and therapeutic targeting of oncogenic drivers in lung adenocarcinoma has led to significant clinical improvements for patients with EGFR mutations or ALK fusions. However, many lung cancer patients do not yet have an identified oncogenic driver and the discovery of new actionable oncogenic drivers is thus an active area of investigation. Methods: Tumor samples from 36 ‘pan-negative’ (EGFR, KRAS, ALK, and ROS1) lung adenocarcinoma patients were analyzed using a next generation sequencing (NGS) test performed in a CLIA-certified lab (Foundation Medicine, Cambridge, MA). Fluorescence in situ hybridization (FISH) screening using a novel NTRK1 break-apart assay was performed on an additional 61 pan-negative samples. Cells expressing the novel NTRK1 fusions were assayed for transformation and pharmacologic inhibition. Results: Two tumor samples were identified with gene fusions containing the kinase domain of TrkA, encoded by NTRK1, including one each with an MPRIP-NTRK1 (M21;N14) and CD74-NTRK1 (C8;N12) fusion. RT-PCR confirmed mRNA expression and identity of the fusion partner and FISH analysis detected split 5’/3’ signals corresponding to the NTRK1 gene. A third sample was identified by FISH analysis. Cloning and expression of MPRIP- and CD74-NTRK1 into NIH3T3 and Ba/F3 cells show constitutive activation of the TrkA kinase domain and transformation. Treatment of cells expressing NTRK1 fusions with several candidate pan-Trk inhibitors (ARRY-772, -523, and -470) as well as CEP-701 and crizotinib demonstrate decreased phosphorylation of the fusion oncoprotein and inhibition of cell proliferation. Treatment of the index patient harboring the MPRIP-NTRK1fusion with crizotinib led to minor transient tumor shrinkage. Conclusions: We identified a novel class of oncogenes, NTRK1 fusions, in lung adenocarcinomas that can be detected by NGS or FISH. Additional studies to determine the frequency and characteristics of NTRK1 fusions in lung cancer are ongoing. Our findings suggest prospective clinical trials of Trk inhibitors in NTRK1 fusion positive patients may be warranted. Support: CO Bioscience Discovery and Evaluation Grant and CO Clinical and Translational Sciences Institute Grant.

Organ-specific gene expression: the bHLH protein Sage provides tissue specificity to Drosophila FoxA

FoxA transcription factors play major roles in organ-specific gene expression, regulating, for example, glucagon expression in the pancreas, GLUT2 expression in the liver, and tyrosine hydroxylase expression in dopaminergic neurons. Organ-specific gene regulation by FoxA proteins is achieved through cooperative regulation with a broad array of transcription factors with more limited expression domains. Fork head (Fkh), the sole Drosophila FoxA family member, is required for the development of multiple distinct organs, yet little is known regarding how Fkh regulates tissue-specific gene expression. Here, we characterize Sage, a bHLH transcription factor expressed exclusively in the Drosophila salivary gland (SG). We show that Sage is required for late SG survival and normal tube morphology. We find that many Sage targets, identified by microarray analysis, encode SG-specific secreted cargo, transmembrane proteins, and the enzymes that modify these proteins. We show that both Sage and Fkh are required for the expression of Sage target genes, and that co-expression of Sage and Fkh is sufficient to drive target gene expression in multiple cell types. Sage and Fkh drive expression of the bZip transcription factor Senseless (Sens), which boosts expression of Sage-Fkh targets, and Sage, Fkh and Sens colocalize on SG chromosomes. Importantly, expression of Sage-Fkh target genes appears to simply add to the tissue-specific gene expression programs already established in other cell types, and Sage and Fkh cannot alter the fate of most embryonic cell types even when expressed early and continuously.

Abstract B29: Oncogenic K-ras addiction in NSCLC switches PKCδ from a pro-apoptotic to a pro-survival signal

Oncogenic mutations in K-ras occur in about 25% of lung cancers, however only a subset of lung tumors with KRAS mutations are functionally dependent upon oncogenic K-ras for survival. Our previous studies show that the function of Protein Kinase C-δ (PKCδ), a serine/threonine kinase that regulates apoptosis in non-transformed cells, is altered in non-small cell lung cancers (NSCLC) that are dependent on oncogenic K-ras, such that these cells now require PKCδ for survival and transformed growth (Symonds et al, Cancer Research, 2011). The purpose of the current studies was to determine if this switch in PKCδ function alters the response of lung cancer cells to chemotherapeutic drugs. We analyzed apoptosis and PKCδ function in five NSCLC cells lines previously characterized in our laboratory as dependent on oncogenic K-ras for survival, and five NSCLC cell lines characterized as K-ras independent. Our results show that NSCLC cell lines that are functionally dependent on K-ras are highly resistant to apoptosis induced by DNA damaging agents such as etoposide. In contrast, K-ras independent NSCLC cell lines are highly sensitive to apoptosis. Our previous studies have shown that PKCδ translocates to the nucleus in response to apoptotic agents and that nuclear localization of PKCδ is essential for apoptosis. To determine the mechanism underlying the switch in PKCδ function from pro-apoptotic to pro-survival, we analyzed PKCδ expression and cytoplasmic/nuclear localization in apoptosis sensitive (K-ras independent) and apoptosis resistant (K-ras dependent) NCSCL cells. Relative to insensitive NSCLC cells, apoptosis sensitive cells showed increased expression of PKCδ by qrtPCR, a reduced cytoplasmic:nuclear ratio of PKCδ under basal conditions, and increased nuclear import of PKCδ in response to etoposide. This suggests that PKCδ may be a pro-apoptotic signal in K-ras independent cells, similar to what we have shown for non-transformed cells. In contrast, nuclear import of PKCδ in response to etoposide was suppressed in K-ras dependent/apoptosis resistant NSCLC cells as was phosphorylation of PKCδ on tyrosines Y64 and Y155, which we have previously shown is required for importin -α binding and nuclear import. Exclusion of PKCδ from the nucleus may explain the resistance of K-ras dependent cells to apoptotic agents. To probe the contribution of PKCδ to these two phenotypes more directly, we depleted PKCδ from K-ras independent/apoptosis sensitive A549 and K-ras dependent/apoptosis resistant H2009 cells using an lentivirus delivered shRNA to PKCδ or a scrambled shRNA control. Depletion of PKCδ in A549 cells resulted in suppression of etoposide-induced apoptosis, similar to what we have previously reported in non-transformed cells. Suppression of apoptosis was accompanied by increased activation of the Akt and MEK/ERK cell survival pathways in A549 cells. In contrast, depletion of PKCδ in H2009 cells resulted in increased apoptosis in response to etoposide, and suppression of the Akt and MEK/ERK cell survival pathways. Our studies suggest NSCLC cells functionally dependent on oncogenic K-ras may be resistant to chemotherapeutic agents in part due to loss of the pro-apoptotic function of PKCδ.

Erosive oesophagitis: outcome of repeated long term maintenance treatment with low dose omeprazole 10 mg or placebo

AIMS

To investigate the efficacy of daily maintenance treatment with omeprazole 10 mg in reducing the relapse rate of healed erosive oesophagitis.

METHODS

Three hundred patients with erosive oesophagitis (grade 2 or greater) received omeprazole 20 mg daily for 12 weeks, followed by 40 mg daily for a further 12 weeks if required. After healing, patients were randomised to double blind treatment with omeprazole 10 mg daily or placebo for up to 18 months. On relapse the treatment cycle was repeated.

RESULTS

The cumulative healing rate at 12 weeks in the initial healing period was 95%, and 96% and 98% on rehealing courses after relapse in the first and second maintenance periods respectively. After 12 weeks of treatment, 98% of patients were free from heartburn and 97% were free of all reflux related symptoms. Relapse in the subgroup of patients who relapsed in both maintenance periods was infrequent on omeprazole 20 mg daily: only 9% at two years. Gastrin concentrations rose above normal in one third of patients. One patient had linear hyperplasia of endocrine cells and another had micronodular hyperplasia. There were no side effects definitely attributable to omeprazole.

CONCLUSION

Maintenance treatment with omeprazole 10 mg daily keeps about 60% of patients with erosive oesophagitis in prolonged remission. Patients relapsing once are likely to do so again; they can subsequently be treated effectively with omeprazole 20 mg daily.

Histamine H2 receptor antagonist-refractory oesophagitis: the efficacy of long-term omeprazole maintenance treatment

BACKGROUND

Erosive oesophagitis refractory to high dose histamine H2 receptor antagonists (definition: failure to heal fully after > or = 3 months' treatment with cimetidine 3.2 g or ranitidine 0.9 g) responds well to omeprazole 40 mg daily but frequently relapses when the patients are put back on maintenance H2 receptor antagonists at medium or even high dose (e.g. cimetidine 1.6 g and 3.2 g, respectively).

AIM

To investigate the efficacy of maintenance omeprazole 20 mg daily in refractory erosive oesophagitis.

PATIENTS & METHODS

In this open, sequential study, patients with H2 receptor antagonist-refractory oesophagitis were healed on omeprazole 40 mg daily and then put on maintenance H2 receptor antagonists (cimetidine 1.6 g or 3.2 g). Relapses were re-treated with omeprazole 40 mg; upon rehealing, patients were put on maintenance omeprazole 20 mg daily for up to 4.5 years.

RESULTS

Healing on omeprazole occurred in 38 out of 39 patients (97%) at 12 weeks. Only six of the 38 patients (16%) relapsed (asymptomatic in half) during subsequent maintenance treatment, whereas all had relapsed earlier on high dose H2 receptor antagonists.

CONCLUSION

Within the limits of interpretation of an open study, omeprazole 20 mg daily seems effective in maintaining prolonged remission in this group of patients with H2 receptor antagonist-refractory oesophagitis.