Animal models of lung cancer characterization and use for chemoprevention research

Opportunities and Challenges of Kava in Lung Cancer Prevention

Lung cancer is the leading cause of cancer-related deaths due to its high incidence, late diagnosis, and limited success in clinical treatment. Prevention therefore is critical to help improve lung cancer management. Although tobacco control and tobacco cessation are effective strategies for lung cancer prevention, the numbers of current and former smokers in the USA and globally are not expected to decrease significantly in the near future. Chemoprevention and interception are needed to help high-risk individuals reduce their lung cancer risk or delay lung cancer development. This article will review the epidemiological data, pre-clinical animal data, and limited clinical data that support the potential of kava in reducing human lung cancer risk via its holistic polypharmacological effects. To facilitate its future clinical translation, advanced knowledge is needed with respect to its mechanisms of action and the development of mechanism-based non-invasive biomarkers in addition to safety and efficacy in more clinically relevant animal models.

Human bronchial carcinoid tumor initiating cells are targeted by the combination of acetazolamide and sulforaphane

Background

Bronchial carcinoids are neuroendocrine tumors that present as typical (TC) and atypical (AC) variants, the latter being more aggressive, invasive and metastatic. Studies of tumor initiating cell (TIC) biology in bronchial carcinoids has been hindered by the lack of appropriate in-vitro and xenograft models representing the bronchial carcinoid phenotype and behavior.

Methods

Bronchial carcinoid cell lines (H727, TC and H720, AC) were cultured in serum-free growth factor supplemented medium to form 3D spheroids and serially passaged up to the 3rd generation permitting expansion of the TIC population as verified by expression of stemness markers, clonogenicity in-vitro and tumorigenicity in both subcutaneous and orthotopic (lung) models. Acetazolamide (AZ), sulforaphane (SFN) and the AZ + SFN combination were evaluated for targeting TIC in bronchial carcinoids.

Results

Data demonstrate that bronchial carcinoid cell line 3rd generation spheroid cells show increased drug resistance, clonogenicity, and tumorigenic potential compared with the parental cells, suggesting selection and expansion of a TIC fraction. Gene expression and immunolabeling studies demonstrated that the TIC expressed stemness factors Oct-4, Sox-2 and Nanog. In a lung orthotopic model bronchial carcinoid, cell line derived spheroids, and patient tumor derived 3rd generation spheroids when supported by a stroma, showed robust tumor formation. SFN and especially the AZ + SFN combination were effective in inhibiting tumor cell growth, spheroid formation and in reducing tumor formation in immunocompromised mice.

Conclusions

Human bronchial carcinoid tumor cells serially passaged as spheroids contain a higher fraction of TIC exhibiting a stemness phenotype. This TIC population can be effectively targeted by the combination of AZ + SFN. Our work portends clinical relevance and supports the therapeutic use of the novel AZ+ SFN combination that may target the TIC population of bronchial carcinoids.

The Effect of Mouse Strain, Sex, and Carcinogen Dose on Toxicity and the Development of Lung Dysplasia and Squamous Cell Carcinomas in Mice

In order to translate new treatments to the clinic, it is necessary to use animal models that closely recapitulate human disease. Lung cancer develops after extended exposure to carcinogens. It has one of the highest mutation rates of all cancer and is highly heterogenic. Topical treatment with N-nitrosotris-(2-chloroethyl)urea (NTCU) induces lung squamous cell carcinoma (SCC) with nonsynonymous mutation rates similar to those reported for human non-small cell lung cancer. However, NTCU induces lung cancer with variable efficacy and toxicity depending on the mouse strain. A detailed characterization of the NTCU model is needed. We have compared the effect of three different NTCU doses (20, 30, and 40 mmol/L) in female and male of NIH Swiss, Black Swiss, and FVB mice on tumor incidence, survival, and toxicity. The main findings in this study are (1) NIH Swiss mice present with a higher incidence of SCC and lower mortality compared with Black Swiss and FVB mice; (2) 30 mmol/L NTCU dose induces SCC at the same rate and incidence as the 40 mmol/L dose with lower mortality; (3) female mice present higher grade and incidence of preinvasive lesions and SCC compared with males; (4) NTCU-induced transformation is principally within the respiratory system; and (5) NTCU treatment does not affect the ability to elicit a specific adaptive immune response. This study provides a reference point for experimental designs to evaluate either preventive or therapeutic treatments for lung SCC, including immunotherapies, before initiating human clinical trials.

Mouse models in squamous cell lung cancer: impact for drug discovery

INTRODUCTION

Squamous cell lung cancer (SQCLC) is the second most common subtype of non-small cell lung cancer (NSCLC) and has limited therapeutic options. Its development is likely a result of a multistep process in response to chronic tobacco exposure, involving sequential metaplasia, dysplasia and invasive carcinoma. Its complex genomic landscape has recently been revealed but no driver mutations have been validated that could lead to molecularly targeted therapy as have emerged in lung adenocarcinoma. Few preclinical murine models exist for testing and developing novel therapeutics in SQCLC. Areas covered: This review discusses the pathophysiology and molecular underpinnings of SQCLC that have limited the development of animal models. It then explores the advantages and limitations of a variety of existing mouse models and illustrates their potential application in drug discovery and chemoprevention. Expert opinion: There are several challenges in the development of mouse models for SQCLC, such as lack of validated driver genetic alterations, unclear cell of origin, and difficulty in reproducing the sophisticated tumor microenvironment of human disease. Nevertheless, several successful SQCLC murine models have emerged, especially Patient Derived Xenografts (PDXs) and Genetically Engineered Mouse Models (GEMMs). Continued efforts are needed to generate more SQCLC animal models to better understand its carcinogenesis and metastasis and to further test novel therapeutic strategies.

Sex-related differences of urethane and sodium valproate effects on Ki-67 expression in urethane-induced lung tumors of mice

The aim of the present study was to evaluate sex differences in tumorigenesis by assessing the number of Ki-67-positive cells [Ki-67(+)] in urethane-induced mice lung tumors and the effect of sodium valproate (NaVP) in BALB/c mice. Gonad-intact and gonadectomized female and male mice were divided into the following groups: i) Treated with urethane, ii) treated with urethane and NaVP and iii) gonad-intact or gonadectomized control. Urethane (total 50 mg/mouse) was injected intraperitoneally. The NaVP 0.4% solution was administered orally for 6 months. Histologically, lung tumors were divided into adenomas and adenocarcinomas and assessed immunohistochemically using antibodies against Ki-67. The Ki-67(+) was calculated per one mm² of a tumor. In adenomas, Ki-67(+) in the urethane-treated gonad-intact males was significantly higher than in females (P=0.001) and in castrated males (P<0.01); Ki-67(+) in adenomas of the urethane-treated gonad-intact males was significantly higher than in urethane-NaVP-treated ones (P<0.04). No significant differences were found in analogous female groups. In adenocarcinomas, Ki-67(+) in urethane-treated gonad-intact males was significantly higher than in females and gonadectomized mice of both sexes (P<0.001), and in ovariectomized females was significantly higher than in ovary-intact group (P=0.01). A significantly higher number of Ki-67(+) cells were observed in gonad-intact adenocarcinomas of the urethane-NaVP-treated females compared with the urethane-treated ones (P<0.001). Comparing between urethane-NaVP-treated gonadectomized males and females in adenocarcinomas, determined that Ki-67(+) was significantly lower in females (P=0.005). In adenocarcinomas, Ki-67(+) in urethane-NaVP-treated gonadectomized males and females was significantly lower than in gonad-intact mice of the same sex (P<0.001). In summary, gonadectomy with NaVP treatment decreased Ki-67(+) in adenocarcinomas for mice of both sexes. The results of the present study indicate sex-related differences in mice lung tumorigenesis, and a sex-related effect of NaVP on progression in urethane-induced BALB/c mice lung tumors.

Optimizing mouse models for precision cancer prevention

As cancer has become increasingly prevalent, cancer prevention research has evolved towards placing a greater emphasis on reducing cancer deaths and minimizing the adverse consequences of having cancer. 'Precision cancer prevention' takes into account the collaboration of intrinsic and extrinsic factors in influencing cancer incidence and aggressiveness in the context of the individual, as well as recognizing that such knowledge can improve early detection and enable more accurate discrimination of cancerous lesions. However, mouse models, and particularly genetically engineered mouse (GEM) models, have yet to be fully integrated into prevention research. In this Opinion article, we discuss opportunities and challenges for precision mouse modelling, including the essential criteria of mouse models for prevention research, representative success stories and opportunities for more refined analyses in future studies.

Organotypic culture of breast tumor explants as a multicellular system for the screening of natural compounds with antineoplastic potential

Breast cancer is the leading cause of death in women worldwide. The search for novel compounds with antitumor activity, with less adverse effects and higher efficacy, and the development of methods to evaluate their toxicity is an area of intense research. In this study we implemented the preparation and culture of breast tumor explants, which were obtained from precision-cut breast tumor slices. In order to validate the model we are proposing to screen antineoplastic effect of natural compounds, we selected caffeic acid, ursolic acid, and rosmarinic acid. Using the Krumdieck tissue slicer, precision-cut tissue slices were prepared from breast cancer samples; from these slices, 4 mm explants were obtained and incubated with the selected compounds. Viability was assessed by Alamar Blue assay, LDH release, and histopathological criteria. Results showed that the viability of the explants cultured in the presence of paclitaxel (positive control) decreased significantly (P < 0.05); however, tumor samples responded differently to each compound. When the explants were coincubated with paclitaxel and compounds, a synergic effect was observed. This study shows that ex vivo culture of breast cancer explants offers a suitable alternative model for evaluating natural or synthetic compounds with antitumor properties within the complex microenvironment of the tumor.

Dietary diindolylmethane suppresses inflammation-driven lung squamous cell carcinoma in mice

Inflammatory conditions of the lung such as chronic obstructive pulmonary disease (COPD) are known to increase lung cancer risk, particularly lung squamous cell carcinoma (LSCC). In the present study, we developed a mouse model of inflammation-driven LSCC that was induced by N-nitroso-trischloroethylurea (NTCU) and enhanced by lipopolysaccharide (LPS), a potent proinflammatory agent contained in tobacco and tobacco smoke, and determined the chemopreventive effects of BioResponse diindolylmethane (DIM) in the same model. Compared with mice treated with NTCU alone, mice treated with the combination of NTCU and LPS had a 9-fold increase in the number of bronchioles with LSCC. Also, compared with mice treated with LPS alone, mice treated with NTCU plus LPS showed significantly increased expression of the inflammatory cytokines IL1α, IL6, and TNFα (all three increased about 7-fold). Parallel to the increased cytokine gene expression, the NTCU plus LPS-treated group exhibited significantly enhanced activation of NF-κB, STAT3, ERK, p-38, and Akt, expression of p53, COX-2, and Mcl-1, and NF-κB- and STAT3-DNA binding in the lung. Dietary administration of DIM (10 μmol/g diet or 2,460 ppm) to mice treated with NTCU plus LPS reduced the incidence of LSCC by 2-fold, suppressed activation/expression of proinflammatory and procarcinogenic proteins and NF-κB- and STAT3-DNA binding, but not the expression of cytokines and p53. This study highlights the potential significance of our mouse model to identify promising drugs or dietary agents for the chemoprevention of human LSCC and that DIM is a very good candidate for clinical lung cancer chemoprevention trials.

Honokiol inhibits lung tumorigenesis through inhibition of mitochondrial function

Honokiol is an important bioactive compound found in the bark of Magnolia tree. It is a nonadipogenic PPARγ agonist and capable of inhibiting the growth of a variety of tumor types both in vitro and in xenograft models. However, to fully appreciate the potential chemopreventive activity of honokiol, a less artificial model system is required. To that end, this study examined the chemopreventive efficacy of honokiol in an initiation model of lung squamous cell carcinoma (SCC). This model system uses the carcinogen N-nitroso-trischloroethylurea (NTCU), which is applied topically, reliably triggering the development of SCC within 24 to 26 weeks. Administration of honokiol significantly reduced the percentage of bronchial that exhibit abnormal lung SCC histology from 24.4% bronchial in control to 11.0% bronchial in honokiol-treated group (P = 0.01) while protecting normal bronchial histology (present in 20.5% of bronchial in control group and 38.5% of bronchial in honokiol-treated group. P = 0.004). P63 staining at the SCC site confirmed the lung SCCs phenotype. In vitro studies revealed that honokiol inhibited lung SCC cells proliferation, arrested cells at the G1-S cell-cycle checkpoint, while also leading to increased apoptosis. Our study showed that interfering with mitochondrial respiration is a novel mechanism by which honokiol changed redox status in the mitochondria, triggered apoptosis, and finally leads to the inhibition of lung SCC. This novel mechanism of targeting mitochondrial suggests honokiol as a potential lung SCC chemopreventive agent.

Lung tumors in mice induced by "whole-life" inorganic arsenic exposure at human-relevant doses

In mice, inorganic arsenic in the drinking water in the parts per million range via the dam during in utero life or with whole-life exposure is a multi-site carcinogen in the offspring. However, human arsenic exposure is typically in the parts per billion (ppb) range. Thus, we studied "whole-life" inorganic arsenic carcinogenesis in mice at levels more relevant to humans. Breeder male and female CD1 mice were exposed to 0, 50, 500 or 5,000 ppb arsenic (as sodium arsenite) in the drinking water for 3 weeks prior to breeding, during pregnancy and lactation, and after weaning (at week 3) groups of male and female offspring (initial n = 40) were exposed for up to 2 years. Tumors were assessed in these offspring. Arsenic exposure had no effect on pregnant dam weights or water consumption, litter size, offspring birthweight or weight at weaning compared to control. In male offspring mice, arsenic exposure increased (p < 0.05) bronchiolo-alveolar tumor (adenoma or carcinoma) incidence at 50-ppb group (51 %) and 500-ppb group (54 %), but not at 5,000-ppb group (28 %) compared to control (22 %). These arsenic-induced bronchiolo-alveolar tumors included increased (p < 0.05) carcinoma at 50-ppb group (27 %) compared to controls (8 %). An increase (p < 0.05) in lung adenoma (25 %) in the 50-ppb group compared to control (11 %) occurred in female offspring. Thus, in CD1 mice whole-life arsenic exposure induced lung tumors at human-relevant doses (i.e., 50 and 500 ppb).

The HDAC inhibitor, MPT0E028, enhances erlotinib-induced cell death in EGFR-TKI-resistant NSCLC cells

Epidermal growth factor receptor (EGFR), which promotes cell survival and division, is found at abnormally high levels on the surface of many cancer cell types, including many cases of non-small cell lung cancer. Erlotinib (Tarceva), an oral small-molecule tyrosine kinase inhibitor, is a so-called targeted drug that inhibits the tyrosine kinase domain of EGFR, and thus targets cancer cells with some specificity while doing less damage to normal cells. However, erlotinib resistance can occur, reducing the efficacy of this treatment. To develop more effective therapeutic interventions by overcoming this resistance problem, we combined the histone deacetylase inhibitor, MPT0E028, with erlotinib in an effort to increase their antitumor effects in erlotinib-resistant lung adenocarcinoma cells. This combined treatment yielded significant growth inhibition, induced the expression of apoptotic proteins (PARP, γH2AX, and caspase-3), increased the levels of acetylated histone H3, and showed synergistic effects in vitro and in vivo. These effects were independent of the mutation status of the genes encoding EGFR or K-Ras. MPT0E028 synergistically blocked key regulators of the EGFR/HER2 signaling pathways, attenuating multiple compensatory pathways (e.g., AKT, extracellular signal-regulated kinase, and c-MET). Our results indicate that this combination therapy might be a promising strategy for facilitating the effects of erlotinib monotherapy by activating various networks. Taken together, our data provide compelling evidence that MPT0E028 has the potential to improve the treatment of heterogeneous and drug-resistant tumors that cannot be controlled with single-target agents.

Chemoprevention of lung squamous cell carcinoma by ginseng

Ginseng has been used as a medicinal herb to maintain physical vitality for thousands of years, and it has also been shown to be a nonorgan-specific cancer preventive agent by several epidemiologic studies. However, the chemopreventive effects of Korea white ginseng (KWG) in lung squamous cell carcinoma (SCC) have not been tested. In this study, we investigated the chemopreventive activity of KWG in a mouse lung SCC model. N-nitroso-trischloroethylurea (NTCU) was used to induce lung tumors in female Swiss mice, and KWG was given orally. KWG significantly reduced the percentage of lung SCCs from 26.5% in the control group to 9.1% in the KWG group and in the meantime, increased the percentage of normal bronchial and hyperplasia. KWG was also found to greatly reduce squamous cell lung tumor area from an average of 9.4% in control group to 1.5% in the KWG group. Treatment with KWG decreased Ki-67 staining, suggesting that the lung tumor inhibitory effects of KWG were partly through inhibition of proliferation. High-performance liquid chromatography/mass spectrometry identified 10 ginsenosides from KWG extracts, Rb1 and Rd being the most abundant as detected in mouse blood and lung tissue. The tumor inhibitory effects of KWG are mediated by inhibition of activator protein (AP-1), as showed by in vitro study conducted on AP-1/NF-κB-dependent mouse non-small cell lung carcinoma cell lines. Western blotting of lung tissues also indicated that NTCU upregulated AP-1 through phosphorylation of c-jun-NH2-kinase, which was downregulated by KWG in concurrence with its chemoprevention function. These results suggest that KWG could be a potential chemopreventive agent for lung SCC.

Lung cancer chemoprevention: difficulties, promise and potential agents?

INTRODUCTION

In a variety of cancers there is evidence that specific regimens can prevent or significantly delay the development of cancer. Thus, for breast cancer (ER+) use of SERMs or aromatase inhibitors can substantially decrease tumor incidence. For cervical cancer, HPV vaccination will inhibit long term cancer incidence. For colon cancer, the second greatest cancer killer, administration of aspirin and other NSAIDs decreases advanced colon adenomas in Phase II trials and epidemiologic data support their ability to prevent colon cancer. To date prevention trials in the area of lung cancer have shown minimal efficacy.

AREAS COVERED

The paper examines and discusses in greater detail certain promising agents which the authors have tested either preclinically and or in early phase clinical trials. These agents include RXR agonists, EGFr inhibitors, NSAIDs and Triterpenoids. Other agents including glucocorticoids, pioglitazone and iloprost are briefly mentioned. In addition, the paper presents various types of potential Phase II lung cancer prevention trials and describes their strengths and weaknesses. The potential use of various biomarkers as endpoints in trials e.g. histopathology, non-specific biomarkers (e.g., Ki67, cyclin D expression, apoptosis) and molecular biomarkers (e.g. specific phosphorylated proteins, gene expression etc.) is presented. Finally, we examine at least one approach, the use of aerosols, which may diminish the systemic toxicity associated with certain of these agents.

EXPERT OPINION

The manuscript presents: a) a number of promising agents which appear applicable to further Phase II prevention trials; b) approaches to defining potential preventive agents as well; c) approaches which might mitigate the side effects associated with potential agents most specifically the use of aerosols. Finally, we discuss biomarker studies both preclinical and clinical which might help support potential Phase II trials. The particular appeal to the preclinical studies is that they can be followed to a tumor endpoint. We hope that this will give the reader further background and allow one to appreciate the potential and some of the hurdles associated with lung cancer chemoprevention.