Mouse models of human non-small-cell lung cancer: raising the bar

Conditional ERK3 overexpression cooperates with PTEN deletion to promote lung adenocarcinoma formation in mice

ERK3, officially known as mitogen‐activated protein kinase 6 (MAPK6), is a poorly studied mitogen‐activated protein kinase (MAPK). Recent studies have revealed the upregulation of ERK3 expression in cancer and suggest an important role for ERK3 in promoting cancer cell growth and invasion in some cancers, in particular lung cancer. However, it is unknown whether ERK3 plays a role in spontaneous tumorigenesis in vivo. To determine the role of ERK3 in lung tumorigenesis, we created a conditional ERK3 transgenic mouse line in which ERK3 transgene expression is controlled by Cre recombinase. By crossing these transgenic mice with a mouse line harboring a lung tissue–specific Cre recombinase transgene driven by a club cell secretory protein gene promoter (CCSP‐iCre), we have found that conditional ERK3 overexpression cooperates with phosphatase and tensin homolog (PTEN) deletion to induce the formation of lung adenocarcinomas (LUADs). Mechanistically, ERK3 overexpression stimulates activating phosphorylations of erb‐b2 receptor tyrosine kinases 2 and 3 (ERBB2 and ERBB3) by upregulating Sp1 transcription factor (SP1)–mediated gene transcription of neuregulin 1 (NRG1), a potent ligand for ERBB2/ERBB3. Our study has revealed a bona fide tumor‐promoting role for ERK3 using genetically engineered mouse models. Together with previous findings showing the roles of ERK3 in cultured cells and in a xenograft lung tumor model, our findings corroborate that ERK3 acts as an oncoprotein in promoting LUAD development and progression.

p53-inducible SESTRINs might play opposite roles in the regulation of early and late stages of lung carcinogenesis

SESTRINs (SESN1-3) are proteins encoded by an evolutionarily conserved gene family that plays an important role in the regulation of cell viability and metabolism in response to stress. Many of the effects of SESTRINs are mediated by negative and positive regulation of mechanistic target of rapamycin kinase complexes 1 and 2 (mTORC1 and mTORC2), respectively, that are often deregulated in human cancers where they support cell growth, proliferation, and cell viability. Besides their effects on regulation of mTORC1/2, SESTRINs also control the accumulation of reactive oxygen species, cell death, and mitophagy. SESN1 and SESN2 are transcriptional targets of tumor suppressor protein p53 and may mediate tumor suppressor activities of p53. Therefore, we conducted studies based on a mouse lung cancer model and human lung adenocarcinoma A549 cells to evaluate the potential impact of SESN1 and SESN2 on lung carcinogenesis. While we observed that expression of SESN1 and SESN2 is often decreased in human tumors, inactivation of Sesn2 in mice positively regulates tumor growth through a mechanism associated with activation of AKT, while knockout of Sesn1 has no additional impact on carcinogenesis in Sesn2-deficient mice. However, inactivation of SESN1 and/or SESN2 in A549 cells accelerates cell proliferation and imparts resistance to cell death in response to glucose starvation. We propose that despite their contribution to early tumor growth, SESTRINs might suppress late stages of carcinogenesis through inhibition of cell proliferation or activation of cell death in conditions of nutrient deficiency.

Tobacco chemical-induced mouse lung adenocarcinoma cell lines pin the prolactin orthologue proliferin as a lung tumour promoter

Lung adenocarcinoma (LADC) is the leading cause of cancer death worldwide. Nevertheless, syngeneic mouse models of the disease are sparse, and cell lines suitable for transplantable and immunocompetent mouse models of LADC remain unmet needs. We established multiple mouse LADC cell lines by repeatedly exposing two mouse strains (FVB, Balb/c) to the tobacco carcinogens urethane or diethylnitrosamine and by culturing out the resulting lung tumours for prolonged periods of time. Characterization of the resulting cell lines (n = 7) showed that they were immortal and phenotypically stable in vitro, and oncogenic, metastatic and lethal in vivo. The primary tumours that gave rise to the cell lines, as well as secondary tumours generated by transplantation of the cell lines, displayed typical LADC features, such as glandular architecture and mucin and thyroid transcription factor 1 expression. Moreover, these cells exhibited marked molecular similarity with human smokers' LADC, including carcinogen-specific Kras point mutations (KrasQ61R in urethane- and KrasQ61H in diethylnitrosamine-triggered cell lines) and Trp53 deletions and displayed stemness features. Interestingly, all cell lines overexpressed proliferin, a murine prolactin orthologue, which functioned as a lung tumour promoter. Furthermore, prolactin was overexpressed and portended poor prognosis in human LADC. In conclusion, we report the first LADC cell lines derived from mice exposed to tobacco carcinogens. These cells closely resemble human LADC and provide a valuable tool for the functional investigation of the pathobiology of the disease.

BACH1 Stabilization by Antioxidants Stimulates Lung Cancer Metastasis

For tumors to progress efficiently, cancer cells must overcome barriers of oxidative stress. Although dietary antioxidant supplementation or activation of endogenous antioxidants by NRF2 reduces oxidative stress and promotes early lung tumor progression, little is known about its effect on lung cancer metastasis. Here, we show that long-term supplementation with the antioxidants N-acetylcysteine and vitamin E promotes KRAS-driven lung cancer metastasis. The antioxidants stimulate metastasis by reducing levels of free heme and stabilizing the transcription factor BACH1. BACH1 activates transcription of Hexokinase 2 and Gapdh and increases glucose uptake, glycolysis rates, and lactate secretion, thereby stimulating glycolysis-dependent metastasis of mouse and human lung cancer cells. Targeting BACH1 normalized glycolysis and prevented antioxidant-induced metastasis, while increasing endogenous BACH1 expression stimulated glycolysis and promoted metastasis, also in the absence of antioxidants. We conclude that BACH1 stimulates glycolysis-dependent lung cancer metastasis and that BACH1 is activated under conditions of reduced oxidative stress.

p65BTK is a novel potential actionable target in KRAS-mutated/EGFR-wild type lung adenocarcinoma

BACKGROUND

Lung cancer is still the main cause of cancer death worldwide despite the availability of targeted therapies and immune-checkpoint inhibitors combined with chemotherapy. Cancer cell heterogeneity and primary or acquired resistance mechanisms cause the elusive behaviour of this cancer and new biomarkers and active drugs are urgently needed to overcome these limitations. p65BTK, a novel isoform of the Bruton Tyrosine Kinase may represent a new actionable target in non-small cell lung cancer (NSCLC).

METHODS

p65BTK expression was evaluated by immunohistochemistry in 382 NSCLC patients with complete clinico-pathological records including smoking habit, ALK and EGFR status, and in metastatic lymph nodes of 30 NSCLC patients. NSCLC cell lines mutated for p53 and/or a component of the RAS/MAPK pathway and primary lung cancer-derived cells from Kras/Trp53 null mice were used as a preclinical model. The effects of p65BTK inhibition by BTK Tyrosine Kinase Inhibitors (TKIs) (Ibrutinib, AVL-292, RN486) and first-generation EGFR-TKIs (Gefitinib, Erlotinib) on cell viability were evaluated by MTT. The effects of BTK-TKIs on cell growth and clonogenicity were assessed by crystal violet and colony assays, respectively. Cell toxicity assays were performed to study the effect of the combination of non-toxic concentrations of BTK-TKIs with EGFR-TKIs and standard-of-care (SOC) chemotherapy (Cisplatin, Gemcitabine, Pemetrexed).

RESULTS

p65BTK was significantly over-expressed in EGFR-wild type (wt) adenocarcinomas (AdC) from non-smoker patients and its expression was also preserved at the metastatic site. p65BTK was also over-expressed in cell lines mutated for KRAS or for a component of the RAS/MAPK pathway and in tumors from Kras/Trp53 null mice. BTK-TKIs were more effective than EGFR-TKIs in decreasing cancer cell viability and significantly impaired cell proliferation and clonogenicity. Moreover, non-toxic doses of BTK-TKIs re-sensitized drug-resistant NSCLC cell lines to both target- and SOC therapy, independently from EGFR/KRAS status.

CONCLUSIONS

p65BTK results as an emerging actionable target in non-smoking EGFR-wt AdC, also at advanced stages of disease. Notably, these patients are not eligible for EGFR-TKIs-based therapy due to a lack of EGFR mutation. The combination of BTK-TKIs with EGFR-TKIs is cytotoxic for EGFR-wt/KRAS-mutant/p53-null tumors and BTK-TKIs re-sensitizes drug-resistant NSCLC to SOC chemotherapy. Therefore, our data suggest that adding BTK-TKIs to SOC chemotherapy and EGFR-targeted therapy may open new avenues for clinical trials in currently untreatable NSCLC.

Targeting the Complement Pathway as a Therapeutic Strategy in Lung Cancer

Lung cancer is the leading cause of cancer death in men and women. Lung adenocarcinoma (LUAD), represents approximately 40% of all lung cancer cases. Advances in recent years, such as the identification of oncogenes and the use of immunotherapies, have changed the treatment of LUAD. Yet survival rates still remain low. Additionally, there is still a gap in understanding the molecular and cellular interactions between cancer cells and the immune tumor microenvironment (TME). Defining how cancer cells with distinct oncogenic drivers interact with the TME and new strategies for enhancing anti-tumor immunity are greatly needed. The complement cascade, a central part of the innate immune system, plays an important role in regulation of adaptive immunity. Initially it was proposed that complement activation on the surface of cancer cells would inhibit cancer progression via membrane attack complex (MAC)-dependent killing. However, data from several groups have shown that complement activation promotes cancer progression, probably through the actions of anaphylatoxins (C3a and C5a) on the TME and engagement of immunoevasive pathways. While originally shown to be produced in the liver, recent studies show localized complement production in numerous cell types including immune cells and tumor cells. These results suggest that complement inhibitory drugs may represent a powerful new approach for treatment of NSCLC, and numerous new anti-complement drugs are in clinical development. However, the mechanisms by which complement is activated and affects tumor progression are not well understood. Furthermore, the role of local complement production vs. systemic activation has not been carefully examined. This review will focus on our current understanding of complement action in LUAD, and describe gaps in our knowledge critical for advancing complement therapy into the clinic.

Pre-Conditioning the Airways of Mice with Bleomycin Increases the Efficiency of Orthotopic Lung Cancer Cell Engraftment

Lung cancer is a deadly treatment refractory disease that is biologically heterogeneous. To understand and effectively treat the full clinical spectrum of thoracic malignancies, additional animal models that can recapitulate diverse human lung cancer subtypes and stages are needed. Allograft or xenograft models are versatile and enable the quantification of tumorigenic capacity in vivo, using malignant cells of either murine or human origin. However, previously described methods of lung cancer cell engraftment have been performed in non-physiological sites, such as the flank of mice, due to the inefficiency of orthotopic transplantation of cells into the lungs. In this study, we describe a method to enhance orthotopic lung cancer cell engraftment by pre-conditioning the airways of mice with the fibrosis inducing agent bleomycin. As a proof-of-concept experiment, we applied this approach to engraft tumor cells of the lung adenocarcinoma subtype, obtained from either mouse or human sources, into various strains of mice. We demonstrate that injuring the airways with bleomycin prior to tumor cell injection increases the engraftment of tumor cells from 0-17% to 71-100%. Significantly, this method enhanced lung tumor incidence and subsequent outgrowth using different models and mouse strains. In addition, engrafted lung cancer cells disseminate from the lungs into relevant distant organs. Thus, we provide a protocol that can be used to establish and maintain new orthotopic models of lung cancer with limiting amounts of cells or biospecimen and to quantitatively assess the tumorigenic capacity of lung cancer cells in physiologically relevant settings.

Smoking and Lung Cancer: Future Research Directions

The aim of future research in this area is to provide the mechanistic understanding and the tools for effective prevention, early diagnosis, and therapy of lung cancer. With the established causal link between cigarette smoking and the risk of developing lung cancer, the most effective prevention is certainly not to smoke. A much better mechanistic understanding of lung cancer and its variability will support the development and evaluation of potentially reduced risk products for those who maintain smoking as well as for the development of early diagnostic tools and targeted therapies. Because of the complexity of lung cancer and the long duration for its development, nonclinical and clinical research efforts need to complement each other. Recent promising advances in this research area are the understanding of the interaction between genotoxic and epigenetic effects of smoking, the development of laboratory animal models for lung tumorigenesis by smoke inhalation, the unraveling of molecular pathways and signatures in clinical lung cancer research useful for developing diagnostic tools and therapeutic approaches, and the first successful therapy for lung cancer—although less suitable for smokers. The above—in combination with emerging data sets from explorative non-clinical and clinical studies as well as improved modeling approaches—are setting the stage for accelerated progress towards developing successful early diagnostic tools and therapies as well as for the assessment of new consumer products with potentially reduced risk.

The importance of detailed epigenomic profiling of different cell types within organs

The human body consists of hundreds of kinds of cells specified from a single genome overlaid with cell type-specific epigenetic information. Comprehensively profiling the body's distinct epigenetic landscapes will allow researchers to verify cell types used in regenerative medicine and to determine the epigenetic effects of disease, environmental exposures and genetic variation. Key marks/factors that should be investigated include regions of nucleosome-free DNA accessible to regulatory factors, histone marks defining active enhancers and promoters, DNA methylation levels, regulatory RNAs, and factors controlling the three-dimensional conformation of the genome. Here we use the lung to illustrate the importance of investigating an organ's purified cell epigenomes, and outline the challenges and promise of realizing a comprehensive catalog of primary cell epigenomes.

Challenge for 3D culture technology: Application in carcinogenesis studies with human airway epithelial cells

Lung cancer is still one of the major intractable diseases and we urgently need more efficient preventive and curative measures. Recent molecular studies have provided strong evidence that allows us to believe that classically well-known early airway lesions such as hyperplasia, metaplasia, dysplasia and carcinoma in situ are really precancerous lesions progressing toward cancer but not necessarily transient and reversible alteration. This suggests that adequate early control of the precancerous lesions may lead to improved prevention of lung cancer. This knowledge is encouraging in view of the imminent necessity for additional experimental systems to investigate the causal mechanisms of cancers directly in human cells and tissues. There are many questions with regard to various precancerous lesions of the airways. For example, should cells, before reaching a stage of invasive carcinoma, undergo all precancerous stages such as hyperplasia or metaplasia and dysplasia, or is there any shortcut to bypass one or more of the precancerous stages? For the study of such questions, the emerging 3-dimensional (3D) cell culture technology appears to provide an effective and valuable tool. Though a great challenge, it is expected that this in vitro technology will be rapidly and reliably improved to enable the cultures to be maintained in an in vivo-mimicking state of differentiation for much longer than a period of at best a few months, as is currently the case. With the help of a "causes recombination-Lox" (Cre-lox) technology, it has been possible to trace cells giving rise to specific lung tumor types. In this short review we have attempted to assess the future role of 3D technology in the study of lung carcinogenesis.

Ovine pulmonary adenocarcinoma: a large animal model for human lung cancer

Lung cancer is the leading cause of cancer deaths worldwide. Recent progress in understanding the molecular pathogenesis of this disease has resulted in novel therapeutic strategies targeting specific groups of patients. Further studies are required to provide additional advances in diagnosis and treatment. Animal models are valuable tools for studying oncogenesis in lung cancer, particularly during the early stages of disease where tissues are rarely available from human cases. Mice have traditionally been used for studying lung cancer in vivo, and a variety of spontaneous and transgenic models are available. However, it is recognized that other species may also be informative for studies of cancer. Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring lung cancer of sheep caused by retrovirus infection and has several features in common with adenocarcinoma of humans, including a similar histological appearance and activation of common cell signaling pathways. Additionally, the size and organization of human lungs are much closer to those of sheep lungs than to those of mice, which facilitates experimental approaches in sheep that are not available in mice. Thus OPA presents opportunities for studying lung tumor development that can complement conventional murine models. Here we describe the potential applications of OPA as a model for human lung adenocarcinoma with an emphasis on the various in vivo and in vitro experimental systems available.

RAS signaling and anti-RAS therapy: lessons learned from genetically engineered mouse models, human cancer cells, and patient-related studies

Activating mutations of oncogenic RAS genes are frequently detected in human cancers. The studies in genetically engineered mouse models (GEMMs) reveal that Kras-activating mutations predispose mice to early onset tumors in the lung, pancreas, and gastrointestinal tract. Nevertheless, most of these tumors do not have metastatic phenotypes. Metastasis occurs when tumors acquire additional genetic changes in other cancer driver genes. Studies on clinical specimens also demonstrated that KRAS mutations are present in premalignant tissues and that most of KRAS mutant human cancers have co-mutations in other cancer driver genes, including TP53, STK11, CDKN2A, and KMT2C in lung cancer; APC, TP53, and PIK3CA in colon cancer; and TP53, CDKN2A, SMAD4, and MED12 in pancreatic cancer. Extensive efforts have been devoted to develop therapeutic agents that target enzymes involved in RAS posttranslational modifications, that inhibit downstream effectors of RAS signaling pathways, and that kill RAS mutant cancer cells through synthetic lethality. Recent clinical studies have revealed that sorafenib, a pan-RAF and VEGFR inhibitor, has impressive benefits for KRAS mutant lung cancer patients. Combination therapy of MEK inhibitors with either docetaxel, AKT inhibitors, or PI3K inhibitors also led to improved clinical responses in some KRAS mutant cancer patients. This review discusses knowledge gained from GEMMs, human cancer cells, and patient-related studies on RAS-mediated tumorigenesis and anti-RAS therapy. Emerging evidence demonstrates that RAS mutant cancers are heterogeneous because of the presence of different mutant alleles and/or co-mutations in other cancer driver genes. Effective subclassifications of RAS mutant cancers may be necessary to improve patients' outcomes through personalized precision medicine.

Screening for tumor suppressors: Loss of ephrin receptor A2 cooperates with oncogenic KRas in promoting lung adenocarcinoma

Lung adenocarcinoma, a major form of non-small cell lung cancer, is the leading cause of cancer deaths. The Cancer Genome Atlas analysis of lung adenocarcinoma has identified a large number of previously unknown copy number alterations and mutations, requiring experimental validation before use in therapeutics. Here, we describe an shRNA-mediated high-throughput approach to test a set of genes for their ability to function as tumor suppressors in the background of mutant KRas and WT Tp53. We identified several candidate genes from tumors originated from lentiviral delivery of shRNAs along with Cre recombinase into lungs of Loxp-stop-Loxp-KRas mice. Ephrin receptorA2 (EphA2) is among the top candidate genes and was reconfirmed by two distinct shRNAs. By generating knockdown, inducible knockdown and knockout cell lines for loss of EphA2, we showed that negating its expression activates a transcriptional program for cell proliferation. Loss of EPHA2 releases feedback inhibition of KRAS, resulting in activation of ERK1/2 MAP kinase signaling, leading to enhanced cell proliferation. Intriguingly, loss of EPHA2 induces activation of GLI1 transcription factor and hedgehog signaling that further contributes to cell proliferation. Small molecules targeting MEK1/2 and Smoothened hamper proliferation in EphA2-deficient cells. Additionally, in EphA2 WT cells, activation of EPHA2 by its ligand, EFNA1, affects KRAS-RAF interaction, leading to inhibition of the RAS-RAF-MEK-ERK pathway and cell proliferation. Together, our studies have identified that (i) EphA2 acts as a KRas cooperative tumor suppressor by in vivo screen and (ii) reactivation of the EphA2 signal may serve as a potential therapeutic for KRas-induced human lung cancers.

Predictive biomarkers in precision medicine and drug development against lung cancer

The molecular characterization of various cancers has shown that cancers with the same origins, histopathologic diagnoses, and clinical stages can be highly heterogeneous in their genetic and epigenetic alterations that cause tumorigenesis. A number of cancer driver genes with functional abnormalities that trigger malignant transformation and that are required for the survival of cancer cells have been identified. Therapeutic agents targeting some of these cancer drivers have been successfully developed, resulting in substantial improvements in clinical symptom amelioration and outcomes in a subset of cancer patients. However, because such therapeutic drugs often benefit only a limited number of patients, the successes of clinical development and applications rely on the ability to identify those patients who are sensitive to the targeted therapies. Thus, biomarkers that can predict treatment responses are critical for the success of precision therapy for cancer patients and of anticancer drug development. This review discusses the molecular heterogeneity of lung cancer pathogenesis; predictive biomarkers for precision medicine in lung cancer therapy with drugs targeting epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), c-ros oncogene 1 receptor tyrosine kinase (ROS1), and immune checkpoints; biomarkers associated with resistance to these therapeutics; and approaches to identify predictive biomarkers in anticancer drug development. The identification of predictive biomarkers during anticancer drug development is expected to greatly facilitate such development because it will increase the chance of success or reduce the attrition rate. Additionally, such identification will accelerate the drug approval process by providing effective patient stratification strategies in clinical trials to reduce the sample size required to demonstrate clinical benefits.

Lung adenocarcinomas: comparison between mice and men

A few human tumor types have been modeled in mice using genetic or chemical tools. The final goal of these efforts is to establish models that mimic not only the location and cellular origin of human cancers but also their genetic aberrations and morphologic appearances. The latter has been neglected by most investigators, and comparative histopathology of human versus mouse cancers is not readily available. This issue is exacerbated by the fact that some human malignancies comprise a whole spectrum of cancer subtypes that differ molecularly and morphologically. Lung cancer is a paradigm that appears not only as non-small cell and small-cell lung cancer but comprises a plethora of subtypes with distinct morphologic features. This review discusses species-specific and common morphological features of non-small cell lung cancer in mice and humans. Potential inconsistencies and the need for refined genetic tools are discussed in the context of a comparative analysis between commonly employed RAS-induced mouse tumors and human lung cancers.

Requirement for interaction of PI3-kinase p110α with RAS in lung tumor maintenance

RAS proteins directly activate PI3-kinases. Mice bearing a germline mutation in the RAS binding domain of the p110α subunit of PI3-kinse are resistant to the development of RAS-driven tumors. However, it is unknown whether interaction of RAS with PI3-kinase is required in established tumors. The need for RAS interaction with p110α in the maintenance of mutant Kras-driven lung tumors was explored using an inducible mouse model. In established tumors, removal of the ability of p110α to interact with RAS causes long-term tumor stasis and partial regression. This is a tumor cell-autonomous effect, which is improved significantly by combination with MEK inhibition. Total removal of p110α expression or activity has comparable effects, albeit with greater toxicities.

Adult lung stem cells and their contribution to lung tumourigenesis

The isolation and characterization of lung stem and progenitor cells represent an important step towards the understanding of lung repair after injury, lung disease pathogenesis and the identification of the target cells of transformation in lung carcinogenesis. Different approaches using prospective isolation of progenitor cells by flow cytometry or lineage-tracing experiments in mouse models of lung injury have led to the identification of distinct progenitor subpopulations in different morphological regions of the adult lung. Genetically defined mouse models of lung cancer are offering new perspectives on the cells of origin of different subtypes of lung cancer. These mouse models pave the way to further investigate human lung progenitor cells at the origin of lung cancers, as well as to define the nature of the lung cancer stem cells. It will be critical to establish the link between oncogenic driver mutations recently discovered in lung cancers, target cells of transformation and subtypes of lung cancers to enable better stratification of patients for improved therapeutic strategies.

Inhibition of Myc family proteins eradicates KRas-driven lung cancer in mice

The principal reason for failure of targeted cancer therapies is the emergence of resistant clones that regenerate the tumor. Therapeutic efficacy therefore depends on not only how effectively a drug inhibits its target, but also the innate or adaptive functional redundancy of that target and its attendant pathway. In this regard, the Myc transcription factors are intriguing therapeutic targets because they serve the unique and irreplaceable role of coordinating expression of the many diverse genes that, together, are required for somatic cell proliferation. Furthermore, Myc expression is deregulated in most-perhaps all-cancers, underscoring its irreplaceable role in proliferation. We previously showed in a preclinical mouse model of non-small-cell lung cancer that systemic Myc inhibition using the dominant-negative Myc mutant Omomyc exerts a dramatic therapeutic impact, triggering rapid regression of tumors with only mild and fully reversible side effects. Using protracted episodic expression of Omomyc, we now demonstrate that metronomic Myc inhibition not only contains Ras-driven lung tumors indefinitely, but also leads to their progressive eradication. Hence, Myc does indeed serve a unique and nondegenerate role in lung tumor maintenance that cannot be complemented by any adaptive mechanism, even in the most aggressive p53-deficient tumors. These data endorse Myc as a compelling cancer drug target.

Got a light? Illuminating lung cancer

New mouse models shed light on mechanisms of lung cancer progression and pinpoint Rac1b as a potential therapeutic target (Stallings-Mann et al., this issue).

Cross-species functional analysis of cancer-associated fibroblasts identifies a critical role for CLCF1 and IL-6 in non-small cell lung cancer in vivo

Cancer-associated fibroblasts (CAF) have been reported to support tumor progression by a variety of mechanisms. However, their role in the progression of non-small cell lung cancer (NSCLC) remains poorly defined. In addition, the extent to which specific proteins secreted by CAFs contribute directly to tumor growth is unclear. To study the role of CAFs in NSCLCs, a cross-species functional characterization of mouse and human lung CAFs was conducted. CAFs supported the growth of lung cancer cells in vivo by secretion of soluble factors that directly stimulate the growth of tumor cells. Gene expression analysis comparing normal mouse lung fibroblasts and mouse lung CAFs identified multiple genes that correlate with the CAF phenotype. A gene signature of secreted genes upregulated in CAFs was an independent marker of poor survival in patients with NSCLC. This secreted gene signature was upregulated in normal lung fibroblasts after long-term exposure to tumor cells, showing that lung fibroblasts are "educated" by tumor cells to acquire a CAF-like phenotype. Functional studies identified important roles for CLCF1-CNTFR and interleukin (IL)-6-IL-6R signaling in promoting growth of NSCLCs. This study identifies novel soluble factors contributing to the CAF protumorigenic phenotype in NSCLCs and suggests new avenues for the development of therapeutic strategies.

Lung cancer chemoprevention

Lung cancer is the leading cause of cancer death in the United States, and the majority of diagnoses are made in former smokers. Although avoidance of tobacco abuse and smoking cessation clearly will have the greatest impact on lung cancer development, effective chemoprevention could prove to be more effective than treatment of established, advanced-stage disease. Chemoprevention is the use of dietary or pharmaceutical agents to reverse or block the carcinogenic process and has been successfully applied to common malignancies other than lung (including recent reports on the prevention of breast cancer in high-risk individuals). Despite previous studies in lung cancer chemoprevention failing to identify effective agents, our ability to define the highest-risk populations and the understanding of lung tumor and premalignant biology continue to make advances. Squamous cell carcinogenesis in the bronchial epithelium starts with normal epithelium and progresses through hyperplasia, metaplasia, dysplasia, and carcinoma in situ to invasive cancer. Precursor lesions also have been identified for adenocarcinoma, and these premalignant lesions are targeted by chemopreventive agents in current and future trials. Chemopreventive agents can currently only be recommended as part of well-designed clinical trials, and multiple trials have recently been completed or are enrolling subjects.

MEK1/2 inhibition elicits regression of autochthonous lung tumors induced by KRASG12D or BRAFV600E

Genetically engineered mouse (GEM) models of lung tumorigenesis allow careful evaluation of lung tumor initiation, progression, and response to therapy. Using GEM models of oncogene-induced lung cancer, we show the striking similarity of the earliest stages of tumorigenesis induced by KRAS(G12D) or BRAF(V600E). Cre-mediated expression of KRAS(G12D) or BRAF(V600E) in the lung epithelium of adult mice initially elicited benign lung tumors comprising cuboidal epithelial cells expressing markers of alveolar pneumocytes. Strikingly, in a head-to-head comparison, oncogenic BRAF(V600E) elicited many more such benign tumors and did so more rapidly than KRAS(G12D). However, despite differences in the efficiency of benign tumor induction, only mice with lung epithelium expression of KRAS(G12D) developed malignant non-small cell lung adenocarcinomas. Pharmacologic inhibition of mitogen-activated protein (MAP)-extracellular signal-regulated kinase (ERK) kinase (MEK)1/2 combined with in vivo imaging showed that initiation and maintenance of both BRAF(V600E)- or KRAS(G12D)-induced lung tumors was dependent on MEK→ERK signaling. Although the tumors dramatically regressed in response to MEK1/2 inhibition, they regrew following cessation of drug treatment. Together, our findings show that RAF→MEK→ERK signaling is both necessary and sufficient for KRAS(G12D)-induced benign lung tumorigenesis in GEM models. The data also emphasize the ability of KRAS(G12D) to promote malignant lung cancer progression compared with oncogenic BRAF(V600E).

Evidence for type II cells as cells of origin of K-Ras-induced distal lung adenocarcinoma

Identifying the cells of origin of lung cancer may lead to new therapeutic strategies. Previous work has focused upon the putative bronchoalveolar stem cell at the bronchioalveolar duct junction as a cancer cell of origin when a codon 12 K-Ras mutant is induced via adenoviral Cre inhalation. In the present study, we use two "knock-in" Cre-estrogen receptor alleles to inducibly express K-RasG12D in CC10(+) epithelial cells and Sftpc(+) type II alveolar cells of the adult mouse lung. Analysis of these mice identifies type II cells, Clara cells in the terminal bronchioles, and putative bronchoalveolar stem cells as cells of origin for K-Ras-induced lung hyperplasia. However, only type II cells appear to progress to adenocarcinoma.

Reduced cell proliferation by IKK2 depletion in a mouse lung-cancer model

Lung cancer is one of the leading cancer malignancies, with a five-year survival rate of only ~15%. We have developed a lentiviral-vector-mediated mouse model, which enables generation of non-small-cell lung cancer from less than 100 alveolar epithelial cells, and investigated the role of IKK2 and NF-κB in lung-cancer development. IKK2 depletion in tumour cells significantly attenuated tumour proliferation and significantly prolonged mouse survival. We identified Timp1, one of the NF-κB target genes, as a key mediator for tumour growth. Activation of the Erk signalling pathway and cell proliferation requires Timp-1 and its receptor CD63. Knockdown of either Ikbkb or Timp1 by short hairpin RNAs reduced tumour growth in both xenograft and lentiviral models. Our results thus suggest the possible application of IKK2 and Timp-1 inhibitors in treating lung cancer.

Quantitative monitoring of mouse lung tumors by magnetic resonance imaging

Primary lung cancer remains the leading cause of cancer-related death in the Western world, and the lung is a common site for recurrence of extrathoracic malignancies. Small-animal (rodent) models of cancer can have a very valuable role in the development of improved therapeutic strategies. However, detection of mouse pulmonary tumors and their subsequent response to therapy in situ is challenging. We have recently described MRI as a reliable, reproducible and nondestructive modality for the detection and serial monitoring of pulmonary tumors. By combining respiratory-gated data acquisition methods with manual and automated segmentation algorithms described by our laboratory, pulmonary tumor burden can be quantitatively measured in approximately 1 h (data acquisition plus analysis) per mouse. Quantitative, analytical methods are described for measuring tumor burden in both primary (discrete tumors) and metastatic (diffuse tumors) disease. Thus, small-animal MRI represents a novel and unique research tool for preclinical investigation of therapeutic strategies for treatment of pulmonary malignancies, and it may be valuable in evaluating new compounds targeting lung cancer in vivo.

Alpha-fetoprotein-thymidine kinase-luciferase knockin mice: a novel model for dual modality longitudinal imaging of tumorigenesis in liver

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is frequently a lethal disease and one of the few malignancies that is still increasing in incidence around the world. Better animal models are highly desired to investigate the molecular basis of HCC and to develop novel therapeutic strategies. Alpha-fetoprotein (Afp) gene is expressed in fetal liver, silenced soon after birth, and highly re-expressed in hepatocellular carcinomas (HCC). We aimed to take advantage of the dramatic re-expression of the Afp gene in HCC to develop a hepatocarcinogenesis reporter (HCR) mouse model for dual-modality, longitudinal in vivo imaging of liver tumor development, and progression.

METHODS

Knock in mice were established by placing a thymidinekinase (tk)-luciferase (luc) reporter gene cassette under the transcriptional control of the endogenous Afp promoter. DEN, a liver carcinogen, was used to induce liver tumors, which was monitored by both luc-based bioluminescent (BL) and tk-based positron emission tomography (PET) imaging.

RESULTS

The expression profile of luc was identical to that of the endogenous Afp gene during development. As early as 2 months after the exposure to DEN, BLI revealed multifocal signals in the liver, long before the appearance of histologically apparent neoplastic lesions. By 6 months, BL and PET dual imaging showed strong signals in malignant HCC. By serendipity, a strong BL signal was also detected in adult testes, a previously unknown site of Afp expression.

CONCLUSIONS

The HCR model enables longitudinal monitoring of liver tumor development and progression, providing a powerful tool in developing chemoprevention and therapeutic strategies for HCC.

'Model' or 'tool'? New definitions for translational research

The term ‘model’ often describes non-human biological systems that are used to obtain a better understanding of human disorders. According to the most stringent definition, an animal ‘model’ would display exactly the same phenotype as seen in the relevant human disorder; however, this precise correspondence is often not present. In this Editorial, I propose the alternative, broader term ‘tool’ to describe a biological system that does not obviously (or precisely) recapitulate a human disorder, but that nonetheless provides useful insight into the etiology or treatment of that disorder. Applying the term ‘tool’ to biological systems used in disease-related studies will help to identify those systems that can most effectively address mechanisms underlying human disease. Conversely, differentiating ‘models’ from ‘tools’ will help to define more clearly the limitations of biological systems used in preclinical analyses.

A dual role for the immune response in a mouse model of inflammation-associated lung cancer

Lung cancer is the leading cause of cancer death worldwide. Both principal factors known to cause lung cancer, cigarette smoke and asbestos, induce pulmonary inflammation, and pulmonary inflammation has recently been implicated in several murine models of lung cancer. To further investigate the role of inflammation in the development of lung cancer, we generated mice with combined loss of IFN-γ and the β-common cytokines GM-CSF and IL-3. These immunodeficient mice develop chronic pulmonary inflammation and lung tumors at a high frequency. Examination of the relationship between these tumors and their inflammatory microenvironment revealed a dual role for the immune system in tumor development. The inflammatory cytokine IL-6 promoted optimal tumor growth, yet wild-type mice rejected transplanted tumors through the induction of adaptive immunity. These findings suggest a model whereby cytokine deficiency leads to oncogenic inflammation that combines with defective antitumor immunity to promote lung tumor formation, representing a unique system for studying the role of the immune system in lung tumor development.

Wnt/β-catenin signaling accelerates mouse lung tumorigenesis by imposing an embryonic distal progenitor phenotype on lung epithelium

Although mutations in Kras are present in 21% of lung tumors, there is a high level of heterogeneity in phenotype and outcome among patients with lung cancer bearing similar mutations, suggesting that other pathways are important. Wnt/β-catenin signaling is a known oncogenic pathway that plays a well-defined role in colon and skin cancer; however, its role in lung cancer is unclear. We have shown here that activation of Wnt/β-catenin in the bronchiolar epithelium of the adult mouse lung does not itself promote tumor development. However, concurrent activation of Wnt/β-catenin signaling and expression of a constitutively active Kras mutant (KrasG12D) led to a dramatic increase in both overall tumor number and size compared with KrasG12D alone. Activation of Wnt/β-catenin signaling altered the KrasG12D tumor phenotype, resulting in a phenotypic switch from bronchiolar epithelium to the highly proliferative distal progenitors found in the embryonic lung. This was associated with decreased E-cadherin expression at the cell surface, which may underlie the increased metastasis of tumors with active Wnt/β-catenin signaling. Together, these data suggest that activation of Wnt/β-catenin signaling can combine with other oncogenic pathways in lung epithelium to produce a more aggressive tumor phenotype by imposing an embryonic distal progenitor phenotype and by decreasing E-cadherin expression.

Discovery of BRM Targeted Therapies: Novel Reactivation of an Anti-cancer Gene

Drug discovery in the field of oncology has been advanced mainly through the targeting of receptor tyrosine kinases. Both antibodies and small molecule inhibitors have been found to have successful applications in blocking the proliferative functions of these cell surface receptors. Based on these early successes, additional kinases within the cytoplasm have been found to promote cancer and, as such, have been recognized as feasible targets for additional modes of therapies. Unlike these oncogene targets, most tumor suppressors are irreversibly altered during cancer progression and therefore are not feasible targets for therapy. However, a subset of these genes is reversibly epigenetically suppressed. One such gene is BRM, and when it is re-expressed in cancer cells, this gene halts their growth. Moreover, as the key catalytic subunit of the SWI/SNF complex, BRM is centrally important to a host of anticancer pathways and cellular mechanisms, and its status may serve as a biomarker. Restoring its expression will both reconnect a number of growth-controlling pathways and affect cellular adhesion, DNA repair, and immune functions. For these reasons, restoring BRM expression is not only feasible, but potentially a potent form of anticancer therapy. To identify BRM-restoring compounds, we developed a cell-based luciferase assay. In this review, we discuss some of the challenges we encountered, issues related to this type of drug discovery, and our future ambitions. We hope this review will provide insight to this type of endeavor and lead to more investigations pursuing this type of drug research.

Sulf-2: an extracellular modulator of cell signaling and a cancer target candidate

IMPORTANCE OF THE FIELD

Sulf-1 and Sulf-2 are sulfatases that edit the sulfation status of heparan sulfate proteoglycans (HSPGs) on the outside of cells and regulate a number of critical signaling pathways. The Sulfs are dysregulated in many cancers with Sulf-2 in particular implicated as a driver of carcinogenesis in NSCLC, pancreatic cancer and hepatocellular carcinoma.

AREAS COVERED IN THIS REVIEW

This review describes the novel activity of the Sulfs in altering the sulfation pattern of HSPG chains on the outside of cells. Thereby, the Sulfs can change the binding of growth factors to these chains and can either promote (e.g., Wnt) or inhibit (e.g., fibroblast growth factor-2) signaling. The review focuses on the widespread upregulation of both Sulfs in cancers and summarizes the evidence that Sulf-2 promotes the transformed behavior of several types of cancer cells in vitro as well as their tumorigenicity in vivo.

WHAT THE READER WILL GAIN

Sulf-2 is a bonafide candidate as a cancer-causing agent in NSCLC and other cancers in which it is upregulated.

TAKE HOME MESSAGE

Sulf-2 is an extracellular enzyme and as such would be an attractive therapeutic target for the treatment of NSCLC and other cancers.

Suppression of Rev3, the catalytic subunit of Pol{zeta}, sensitizes drug-resistant lung tumors to chemotherapy

Platinum-based chemotherapeutic drugs are front-line therapies for the treatment of non-small cell lung cancer. However, intrinsic drug resistance limits the clinical efficacy of these agents. Recent evidence suggests that loss of the translesion polymerase, Polζ, can sensitize tumor cell lines to cisplatin, although the relevance of these findings to the treatment of chemoresistant tumors in vivo has remained unclear. Here, we describe a tumor transplantation approach that enables the rapid introduction of defined genetic lesions into a preclinical model of lung adenocarcinoma. Using this approach, we examined the effect of impaired translesion DNA synthesis on cisplatin response in aggressive late-stage lung cancers. In the presence of reduced levels of Rev3, an essential component of Polζ, tumors exhibited pronounced sensitivity to cisplatin, leading to a significant extension in overall survival of treated recipient mice. Additionally, treated Rev3-deficient cells exhibited reduced cisplatin-induced mutation, a process that has been implicated in the induction of secondary malignancies following chemotherapy. Taken together, our data illustrate the potential of Rev3 inhibition as an adjuvant therapy for the treatment of chemoresistant malignancies, and highlight the utility of rapid transplantation methodologies for evaluating mechanisms of chemotherapeutic resistance in preclinical settings.

Novel insights into the molecular origins and treatment of lung cancer

Lung cancer is the most common and most deadly cancer worldwide. Because of the aggressive and metastatic nature of many forms of the disease, it is frequently diagnosed late and responds poorly to the therapies currently available. Although our understanding of the molecular origins and evolution of lung cancer is still incomplete, recent research has yielded several developments that may offer opportunities for new, targeted and effective therapy. In this review we first discuss the prevalence and origins of lung cancer, with emphasis on non-small-cell lung cancer and adenocarcinoma, together with current treatments and their efficacy. We then look at a selection of recent papers which between them shed new light on possible therapeutic opportunities, including a novel synthetic interaction with the Kras gene and genomic or proteomic profiling studies that may pave the way for personalized treatment for lung cancer based on specific "signatures" of protein and gene expression. Lung cancer remains the foremost cause of cancer deaths worldwide. Despite advances in both detection and treatment, diagnosis is often late and the prognosis for patients poor. Our understanding of the molecular basis and progression of lung cancer remains incomplete, hampering the design and development of more effective diagnostic tools and therapies for this devastating disease. However, the last twelve months have witnessed the publication of several studies that represent significant advances in our knowledge of lung cancer, and may represent important steps on the road to effective new therapies. In this review we aim to summarize these recent developments, and give our perspectives on the therapeutic possibilities they may offer in the future.

Murine lung tumor response after exposure to cigarette mainstream smoke or its particulate and gas/vapor phase fractions

Knowledge on mechanisms of smoking-induced tumorigenesis and on active smoke constituents may improve the development and evaluation of chemopreventive and therapeutic interventions, early diagnostic markers, and new and potentially reduced-risk tobacco products. A suitable laboratory animal disease model of mainstream cigarette smoke inhalation is needed for this purpose. In order to develop such a model, A/J and Swiss SWR/J mouse strains, with a genetic susceptibility to developing lung adenocarcinoma, were whole-body exposed to diluted cigarette mainstream smoke at 0, 120, and 240 mg total particulate matter per m(3) for 6h per day, 5 days per week. Mainstream smoke is the smoke actively inhaled by the smoker. For etiological reasons, parallel exposures to whole smoke fractions (enriched for particulate or gas/vapor phase) were performed at the higher concentration level. After 5 months of smoke inhalation and an additional 4-month post-inhalation period, both mouse strains responded similarly: no increase in lung tumor multiplicity was seen at the end of the inhalation period; however, there was a concentration-dependent tumorigenic response at the end of the post-inhalation period (up to 2-fold beyond control) in mice exposed to the whole smoke or the particulate phase. Tumors were characterized mainly as pulmonary adenomas. At the end of the inhalation period, epithelial hyperplasia, atrophy, and metaplasia were found in the nasal passages and larynx, and cellular and molecular markers of inflammation were found in the bronchoalveolar lavage fluid. These inflammatory effects were mostly resolved by the end of the post-inhalation period. In summary, these mouse strains responded to mainstream smoke inhalation with enhanced pulmonary adenoma formation. The major tumorigenic potency resided in the particulate phase, which is contrary to the findings published for environmental tobacco smoke surrogate inhalation in these mouse models.

Nek4 status differentially alters sensitivity to distinct microtubule poisons

Microtubule poisons are widely used in cancer treatment, but the factors determining the relative efficacy of different drugs in this class remain obscure. In this study, we identified the NIMA kinase Nek4 in a genetic screen for mediators of the response to Taxol, a chemotherapeutic agent that stabilizes microtubules. After Taxol treatment, Nek4 promoted microtubule outgrowth, whereas Nek4 deficiency impaired G(2)-M arrest and decreased formation of mitotic-like asters. In contrast, Nek4 deficiency sensitized cells to vincristine, which destabilizes microtubules. Therefore, Nek4 deficiency may either antagonize or agonize the effects of microtubule poisons, depending on how they affect microtubule polymerization. Of note, Nek4 gene maps to a commonly deleted locus in non-small cell lung cancer. Thus, Nek4 deletion in this disease may rationalize the use of particular types of microtubule poisons for lung cancer therapy.

Nek4 status differentially alters sensitivity to distinct microtubule poisons

Microtubule poisons are widely used in cancer treatment, but the factors determining the relative efficacy of different drugs in this class remain obscure. In this study, we identified the NIMA kinase Nek4 in a genetic screen for mediators of the response to Taxol, a chemotherapeutic agent that stabilizes microtubules. After Taxol treatment, Nek4 promoted microtubule outgrowth, whereas Nek4 deficiency impaired G(2)-M arrest and decreased formation of mitotic-like asters. In contrast, Nek4 deficiency sensitized cells to vincristine, which destabilizes microtubules. Therefore, Nek4 deficiency may either antagonize or agonize the effects of microtubule poisons, depending on how they affect microtubule polymerization. Of note, Nek4 gene maps to a commonly deleted locus in non-small cell lung cancer. Thus, Nek4 deletion in this disease may rationalize the use of particular types of microtubule poisons for lung cancer therapy.

Genetically engineered mouse models in cancer research

Mouse models of human cancer have played a vital role in understanding tumorigenesis and answering experimental questions that other systems cannot address. Advances continue to be made that allow better understanding of the mechanisms of tumor development, and therefore the identification of better therapeutic and diagnostic strategies. We review major advances that have been made in modeling cancer in the mouse and specific areas of research that have been explored with mouse models. For example, although there are differences between mice and humans, new models are able to more accurately model sporadic human cancers by specifically controlling timing and location of mutations, even within single cells. As hypotheses are developed in human and cell culture systems, engineered mice provide the most tractable and accurate test of their validity in vivo. For example, largely through the use of these models, the microenvironment has been established to play a critical role in tumorigenesis, since tumor development and the interaction with surrounding stroma can be studied as both evolve. These mouse models have specifically fueled our understanding of cancer initiation, immune system roles, tumor angiogenesis, invasion, and metastasis, and the relevance of molecular diversity observed among human cancers. Currently, these models are being designed to facilitate in vivo imaging to track both primary and metastatic tumor development from much earlier stages than previously possible. Finally, the approaches developed in this field to achieve basic understanding are emerging as effective tools to guide much needed development of treatment strategies, diagnostic strategies, and patient stratification strategies in clinical research.

Chemoprevention of lung cancer

Lung cancer is the leading cause of cancer death in the United States, and the majority of diagnoses are made in former smokers. While avoidance of tobacco abuse and smoking cessation clearly will have the greatest impact on lung cancer development, effective chemoprevention could prove to be more effective than treatment of established disease. Chemoprevention is the use of dietary or pharmaceutical agents to reverse or inhibit the carcinogenic process and has been successfully applied to common malignancies other than lung. Despite previous studies in lung cancer chemoprevention failing to identify effective agents, our ability to determine higher risk populations and the understanding of lung tumor and pre-malignant biology continues to advance. Additional biomarkers of risk continue to be investigated and validated. The World Health Organization/International Association for the Study of Lung Cancer classification for lung cancer now recognizes distinct histologic lesions that can be reproducibly graded as precursors of non-small cell lung cancer. For example, carcinogenesis in the bronchial epithelium starts with normal epithelium and progresses through hyperplasia, metaplasia, dysplasia, and carcinoma in situ to invasive squamous cell cancer. Similar precursor lesions exist for adenocarcinoma, and these pre-malignant lesions are targeted by chemopreventive agents in current and future trials. At this time, chemopreventive agents can only be recommended as part of well-designed clinical trials, and multiple trials are currently in progress and additional trials are in the planning stages. This review will discuss the principles of chemoprevention, summarize the completed trials, and discuss ongoing and potential future trials with a focus on targeted pathways.

Conditional mouse osteosarcoma, dependent on p53 loss and potentiated by loss of Rb, mimics the human disease

Osteosarcoma is the most common primary malignant tumor of bone. Analysis of familial cancer syndromes and sporadic cases has strongly implicated both p53 and pRb in its pathogenesis; however, the relative contribution of these mutations to the initiation of osteosarcoma is unclear. We describe here the generation and characterization of a genetically engineered mouse model in which all animals develop short latency malignant osteosarcoma. The genetically engineered mouse model is based on osteoblast-restricted deletion of p53 and pRb. Osteosarcoma development is dependent on loss of p53 and potentiated by loss of pRb, revealing a dominance of p53 mutation in the development of osteosarcoma. The model reproduces many of the defining features of human osteosarcoma including cytogenetic complexity and comparable gene expression signatures, histology, and metastatic behavior. Using a novel in silico methodology termed cytogenetic region enrichment analysis, we demonstrate high conservation of gene expression changes between murine osteosarcoma and known cytogentically rearranged loci from human osteosarcoma. Due to the strong similarity between murine osteosarcoma and human osteosarcoma in this model, this should provide a valuable platform for addressing the molecular genetics of osteosarcoma and for developing novel therapeutic strategies.

Many roads lead to oncogene-induced senescence

Oncogene-induced senescence is a mechanism of tumor suppression that restricts the progression of benign tumors. Important advances have been made toward elucidating the mechanisms that regulate this response; however, there is presently no unified model that integrates all current findings. DNA damage, replicative stress, reactive oxygen species, heterochromatin formation and negative feedback signaling networks have all been proposed to play an integral role in promoting senescence in response to various oncogenic insults. In all cases, these signals have been shown to function through Rb and p53, but utilize different intermediaries. Thus, it appears that senescence is not triggered by a single, linear series of events, but instead is regulated by a complex signaling network. Accordingly, multiple proteins may cooperate to establish a senescence response, but the limiting signal(s) may be dictated by the initiating genetic alteration and/or tissue type. This review will focus on integrating current models and will highlight data that provide new insight into the signals that function to suppress human tumor development.

Identification of the retinoic acid-inducible Gprc5a as a new lung tumor suppressor gene

BACKGROUND

Lung cancers develop via multiple genetic and epigenetic changes, including inactivation of tumor suppressor genes. We previously cloned human G protein-coupled receptor family C type 5A (GPRC5A), whose expression is suppressed in some human lung carcinoma cells, and its mouse homolog Gprc5a.

METHODS

We generated Gprc5a knockout mice by homologous recombination and studied their phenotype by macroscopic observation and microscopic histologic analysis of embryos and lungs of 1- to 2-year-old mice. GPRC5A mRNA expression was analyzed by reverse transcription-polymerase chain reaction in surgical specimens of 18 human lung tumors and adjacent normal tissues and by analyzing previously published data from 186 lung tumor tissues of a variety of histologic types and 17 normal lung samples. Human embryonic kidney, human non-small-cell lung cancer, and mouse lung adenocarcinoma cells were transfected with a GPRC5A expression vector or a control vector, and colony formation in semisolid medium was assayed. Statistical tests were two-sided.

RESULTS

Homozygous knockout mice developed many more lung tumors at 1-2 years of age (incidence: 76% adenomas and 17% adenocarcinomas) than heterozygous (11% adenomas) or wild-type (10% adenomas) mice. Human GPRC5A mRNA levels were lower in most (11 of 18 [61%]) human lung tumors than in adjacent normal tissues. The mean GPRC5A mRNA level in adenocarcinoma (n = 139), squamous cell carcinoma (n = 21), small-cell lung cancer (n = 6), and carcinoid (n = 20) tissues was 46.2% (P = .014), 7.5% (P<.001), 5.3% (P<.001), and 1.8% (P<.001), respectively, that in normal lung tissues (n = 17) GPRC5A transfection suppressed colony formation in semisolid medium of immortalized human embryonic kidney, human non-small-cell lung cancer, and mouse lung adenocarcinoma cells by 91%, 91%, and 68%, respectively, compared with vector controls (all P<.001).

CONCLUSIONS

Gprc5a functions as a tumor suppressor in mouse lung, and human GPRC5A may share this property. The Gprc5a-deficient mouse is a novel model to study lung carcinogenesis and chemoprevention.

What have we learned from mouse models for cystic fibrosis?

Genetically modified mouse strains are important research tools for the study of numerous human diseases. These models provide us with differentiated tissues, which are not often available from human sources. Furthermore, they allow for testing the effects of genetic manipulation and experimental therapeutics on physiology and pathology. Their importance relies on the assumption that biological processes in the mouse very closely resemble those in humans. Cystic fibrosis (CF) is the most common lethal genetic disease in the Caucasian population. CF is a monogenic disease whose phenotype variability is also attributed to genetic variation in other genes, the so-called modifier genes. Modulation of such modifier genes could be a therapeutic strategy to treat CF. CF mice models have been essential not only for understanding the disease better, but also for the discovery of modifier genes and testing of chemical compounds developed to repair the main protein dysfunction in CF, the CF transmembrane conductance regulator. Mice were also indispensable in gene therapy trials and for the study of CF and non-CF lung response to bacterial infections and inflammation challenges, although no spontaneous lung disease is developed in these mice. In this review, mouse models and their most important contribution to the understanding and management of CF will be presented and discussed.

SmgGDS regulates cell proliferation, migration, and NF-kappaB transcriptional activity in non-small cell lung carcinoma

Non-small cell lung carcinoma (NSCLC) is promoted by the increased activities of several small GTPases, including K-Ras4B, Rap1A, Rap1B, RhoC, and Rac1. SmgGDS is an unusual guanine nucleotide exchange factor that activates many of these small GTPases, and thus may promote NSCLC development or progression. We report here that SmgGDS protein levels are elevated in NSCLC tumors, compared with normal lung tissue from the same patients or from individuals without cancer. To characterize SmgGDS functions in NSCLC, we tested the effects of silencing SmgGDS expression by transfecting cultured NSCLC cells with SmgGDS small interfering RNA (siRNA). Cells with silenced SmgGDS expression form fewer colonies in soft agar, do not proliferate in culture due to an arrest in G(1) phase, and exhibit disrupted myosin organization and reduced cell migration. The transcriptional activity of NF-kappaB in NSCLC cells is diminished by transfecting the cells with SmgGDS siRNA, and enhanced by transfecting the cells with a cDNA encoding SmgGDS. Because RhoA is a major substrate for SmgGDS, we investigated whether diminished RhoA expression mimics the effects of diminished SmgGDS expression. Silencing RhoA expression with RhoA siRNA disrupts myosin organization, but only moderately decreases cell proliferation and does not inhibit migration. Our finding that the aggressive NSCLC phenotype is more effectively suppressed by silencing SmgGDS than by silencing RhoA is consistent with the ability of SmgGDS to regulate multiple small GTPases in addition to RhoA. These results demonstrate that SmgGDS promotes the malignant NSCLC phenotype and is an intriguing therapeutic target in NSCLC.

GGTase-I deficiency reduces tumor formation and improves survival in mice with K-RAS-induced lung cancer

Protein geranylgeranyltransferase type I (GGTase-I) is responsible for the posttranslational lipidation of CAAX proteins such as RHOA, RAC1, and cell division cycle 42 (CDC42). Inhibition of GGTase-I has been suggested as a strategy to treat cancer and a host of other diseases. Although several GGTase-I inhibitors (GGTIs) have been synthesized, they have very different properties, and the effects of GGTIs and GGTase-I deficiency are unclear. One concern is that inhibiting GGTase-I might lead to severe toxicity. In this study, we determined the effects of GGTase-I deficiency on cell viability and K-RAS-induced cancer development in mice. Inactivating the gene for the critical beta subunit of GGTase-I eliminated GGTase-I activity, disrupted the actin cytoskeleton, reduced cell migration, and blocked the proliferation of fibroblasts expressing oncogenic K-RAS. Moreover, the absence of GGTase-I activity reduced lung tumor formation, eliminated myeloproliferative phenotypes, and increased survival of mice in which expression of oncogenic K-RAS was switched on in lung cells and myeloid cells. Interestingly, several cell types remained viable in the absence of GGTase-I, and myelopoiesis appeared to function normally. These findings suggest that inhibiting GGTase-I may be a useful strategy to treat K-RAS-induced malignancies.

Genetic determinants of cancer metastasis

Metastasis can be viewed as an evolutionary process, culminating in the prevalence of rare tumour cells that overcame stringent physiological barriers as they separated from their original environment and developmental fate. This phenomenon brings into focus long-standing questions about the stage at which cancer cells acquire metastatic abilities, the relationship of metastatic cells to their tumour of origin, the basis for metastatic tissue tropism, the nature of metastasis predisposition factors and, importantly, the identity of genes that mediate these processes. With knowledge cemented in decades of research into tumour-initiating events, current experimental and conceptual models are beginning to address the genetic basis for cancer colonization of distant organs.

Modeling cancer patient populations in mice: complex genetic and environmental factors

Genetic differences among individuals contribute to differential susceptibility to cancer and, undoubtedly, to variable efficacy and toxicity of pharmacological-based therapeutics. Many of the specific molecular processes involved in human tumorigenesis have been elucidated and accurately modeled in mice. However, the current models used for drug testing do not accurately predict how new treatments will fare in clinical trials. More sophisticated models that treat cancer as a complex disease present within heterogenous patient populations will provide better predictive power to identify patients that may benefit from specific therapies or that may develop potential drug-induced toxicities.