Genetic influence on type 2 or Clara cell origin of pulmonary adenomas in urethan-treated mice

Verification and Defined Dosage of Sodium Pentobarbital for a Urodynamic Study in the Possibility of Survival Experiments in Female Rat

Objectives

To evaluate the effects of pentobarbital dosages on lower urinary tract function and to define an appropriate dosage of sodium pentobarbital that would be suitable for urodynamic studies in which recovery from anesthesia and long term survive were needed for subsequent experiment.

Methods

Twenty-four 8-week-old, female, virgin, Sprague-Dawley rats (200-250 g) were used in this study. Rats in study groups received gradient doses of pentobarbital intraperitoneally, and those in the control group received urethane intraperitoneally. External urethral sphincter electromyography (EUS-EMG) was recorded simultaneously during cystometry and leak point pressure tests. The toe-pinch reflex was used to determine the level of anesthesia.

Results

Micturition was normally induced in both the urethane group and 32 mg/kg pentobarbital group. However, in groups of 40 mg/kg or 36 mg/kg pentobarbital, micturition failed to be induced; instead, nonvoiding contractions accompanied by EUS-EMG tonic activity were observed. There were no significant differences in leak point pressure or EUS-EMG amplitude or frequency between the urethane and 32 mg/kg pentobarbital groups.

Conclusions

This study confirmed significant dose-dependent effects of pentobarbital on lower urinary tract function and 32 mg/kg pentobarbital as an appropriate dosage for recovery urodynamic testing, which enable the achievement of expected essential micturition under satisfactory anesthesia in female rats.

Chronic Obstructive Pulmonary Disease and Lung Cancer: Underlying Pathophysiology and New Therapeutic Modalities

Chronic obstructive pulmonary disease (COPD) and lung cancer are major lung diseases affecting millions worldwide. Both diseases have links to cigarette smoking and exert a considerable societal burden. People suffering from COPD are at higher risk of developing lung cancer than those without, and are more susceptible to poor outcomes after diagnosis and treatment. Lung cancer and COPD are closely associated, possibly sharing common traits such as an underlying genetic predisposition, epithelial and endothelial cell plasticity, dysfunctional inflammatory mechanisms including the deposition of excessive extracellular matrix, angiogenesis, susceptibility to DNA damage and cellular mutagenesis. In fact, COPD could be the driving factor for lung cancer, providing a conducive environment that propagates its evolution. In the early stages of smoking, body defences provide a combative immune/oxidative response and DNA repair mechanisms are likely to subdue these changes to a certain extent; however, in patients with COPD with lung cancer the consequences could be devastating, potentially contributing to slower postoperative recovery after lung resection and increased resistance to radiotherapy and chemotherapy. Vital to the development of new-targeted therapies is an in-depth understanding of various molecular mechanisms that are associated with both pathologies. In this comprehensive review, we provide a detailed overview of possible underlying factors that link COPD and lung cancer, and current therapeutic advances from both human and preclinical animal models that can effectively mitigate this unholy relationship.

NLRP3 deletion inhibits inflammation-driven mouse lung tumorigenesis induced by benzo(a)pyrene and lipopolysaccharide

Background

Inflammatory micro-environment has been proposed to play a critical role in lung tumorigenesis. NLRP3 is known as an intracellular receptor involving inflammation and has been reported which is increasingly associated with tumor development, but the role in inflammation-driven lung cancer has not been fully clarified. In this study, we investigated whether lipopolysaccharide (LPS)-induced pulmonary inflammation could contribute to lung tumorigenesis induced by benzo(a)pyrene [B(a)p] in C57BL/6J mice and the role of NLRP3 in the pathogenesis.

Methods

NLRP3−/− mice and C57BL/6J mice (wide-type, WT) were instilled intratracheally with B(a)p (1 mg/mouse) once a week for 4 times [the week of the last time of B(a)p treatment named Week 0], and mice were then instilled intratracheally with LPS at Week 3, 2.5 μg/mouse, once every three weeks for 5 times. At Week 30, the incidence, number, size and histopathology of lung tumor were analyzed.

Results

Mice exposed to B(a)p or B(a)p plus LPS could induce lung tumors, whereas LPS or vehicles treatment could not induce lung tumorigenesis. In WT mice, B(a)p plus LPS exposure significantly increased tumor incidence, mean tumor count and tumor size of visible tumors of lungs compared with B(a)p treatment alone, and NLRP3 deletion inhibited lung tumorigenesis induced by B(a)p or B(a)p plus LPS. Histopathological examination found LPS-induced pulmonary inflammatory changes enhanced lung tumorigenesis induced by B(a)p in WT mice, deletion of NLRP3 improved the inflammatory changes induced by LPS and the number and size of pathological tumor nests induced by B(a)p or B(a)p plus LPS. In addition, we found B(a)p treatment and B(a)p plus LPS treatment predominately induced the development of adenoma.

Conclusion

LPS enhanced B(a)p-induced lung tumorigenesis in WT and NLRP3−/− mice of C57BL/6J strain, and NLRP3 deletion inhibits lung tumorigenesis induced by B(a)p or B(a)p plus LPS.

Bronchioloalveolar lung tumors induced in “mice only” by non-genotoxic chemicals are not useful for quantitative assessment of pulmonary adenocarcinoma risk in humans

Chemicals classified as known human carcinogens by International Agency for Research on Cancer (IARC) show a low level of concordance between rodents and humans for induction of pulmonary carcinoma. Rats and mice exposed via inhalation for 2 years show a low level of concordance in both tumor development and organ site location. In 2-year inhalation studies using rats and mice, when pulmonary tumors are seen in only male or female mice or both, but not in either sex of rat, there is a high probability that the murine pulmonary tumor has been produced via Clara cell or club cell (CC) metabolism of the inhaled chemical to a cytotoxic metabolite. Cytotoxicity-induced mitogenesis increases mutagenesis via amplification of the background mutation rate. If the chemical being tested is also negative in the Ames Salmonella mutagenicity assay, and only mouse pulmonary tumors are induced, the probability that this pulmonary tumor is not relevant to human lung cancer risk goes even higher. Mice have a larger percentage of CCs in their distal airways than rats, and a much larger percentage than in humans. The CCs of mice have a much higher concentration of metabolic enzymes capable of metabolizing xenobiotics than CCs in either rats or humans. A principal threat to validity of extrapolating from the murine model lies in the unique capacity of murine CCs to metabolize a significant spectrum of xenobiotics which in turn produces toxicants not seen in rat or human pulmonary pathophysiology.

Proliferative and nonproliferative lesions of the rat and mouse respiratory tract

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the respiratory tract of laboratory rats and mice, with color photomicrographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for respiratory tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Pulmonary inflammation and tumor induction in lung tumor susceptible A/J and resistant C57BL/6J mice exposed to welding fume

Background

Welding fume has been categorized as "possibly carcinogenic" to humans. Our objectives were to characterize the lung response to carcinogenic and non-carcinogenic metal-containing welding fumes and to determine if these fumes caused increased lung tumorigenicity in A/J mice, a lung tumor susceptible strain. We exposed male A/J and C57BL/6J, a lung tumor resistant strain, by pharyngeal aspiration four times (once every 3 days) to 85 μg of gas metal arc-mild steel (GMA-MS), GMA-stainless steel (SS), or manual metal arc-SS (MMA-SS) fume, or to 25.5 μg soluble hexavalent chromium (S-Cr). Shams were exposed to saline vehicle. Bronchoalveolar lavage (BAL) was done at 2, 7, and 28 days post-exposure. For the lung tumor study, gross tumor counts and histopathological changes were assessed in A/J mice at 48 and 78 weeks post-exposure.

Results

BAL revealed notable strain-dependent differences with regards to the degree and resolution of the inflammatory response after exposure to the fumes. At 48 weeks, carcinogenic metal-containing GMA-SS fume caused the greatest increase in tumor multiplicity and incidence, but this was not different from sham. By 78 weeks, tumor incidence in the GMA-SS group versus sham approached significance (p = 0.057). A significant increase in perivascular/peribronchial lymphoid infiltrates for the GMA-SS group versus sham and an increased persistence of this fume in lung cells compared to the other welding fumes was found.

Conclusion

The increased persistence of GMA-SS fume in combination with its metal composition may trigger a chronic, but mild, inflammatory state in the lung possibly enhancing tumorigenesis in this susceptible mouse strain.

Tumor signaling to the bone marrow changes the phenotype of monocytes and pulmonary macrophages during urethane-induced primary lung tumorigenesis in A/J mice

Little is known about how the composition of stromal cells within the lung cancer microenvironment varies during tumor progression. We examined by immunohistochemistry each of six different stromal cell populations during the development of chemically induced primary lung cancer in mice. Blood vessels were seen even in microscopic lesions, and their numbers increased with tumor size. Neutrophils infiltrated the alveoli of tumor-bearing lungs and within the periphery of macroscopic adenomas and adenocarcinomas. The numbers of peritumoral lymphocytes and macrophages increased during oncogeny, but quantitative changes in mast cells and fibroblasts were not evident. Because macrophage depletion reduces tumor growth and these cells are thus important to tumorigenesis, we also investigated their phenotype. Pulmonary macrophages expressed arginase I (subtype M2) but not inducible nitric-oxide synthase in lungs with premalignant lesions, whereas macrophages in carcinoma-bearing lungs expressed inducible nitric-oxide synthase (subtype M1) but not arginase I. Local pulmonary stimuli did not seem responsible for this shift in macrophage activation state because monocytes still residing within the bone marrow adopted these expression patterns before entering the circulation, presumably in response to tumor-derived signals. These biochemical markers of macrophage activation states would have diagnostic and/or therapeutic value if analogous systemic shifts occur in humans.

Lung tumor location and lymphocyte infiltration in mice are genetically determined

Lung cancer is a heterogeneous disease with individual differences in histological type, rate of progression, and response to therapy. Definition of the molecular and genetic basis of specific tumor characteristics would provide a better assessment of prognosis and a basis for a more individualized therapy. Here the authors compare the quantitative and qualitative phenotypes of lung tumors in mice of O20/A and OcB-9/Dem strains subjected to 2 regimens of N-ethyl-N-nitrosourea (ENU) treatment: (1) prenatal tumor induction by a single intraperitoneal (IP) injection of 40 mg/kg body weight into pregnant females and (2) after the same prenatal induction, the progeny received on weeks 9 and 11 additional IP ENU injections. The numbers, size, and histological characteristics of tumors were determined microscopically in semiserial lung sections. Unexpectedly, the authors observed very highly significant strain differences in a novel polymorphic phenotype-peribronchial versus nonperibronchial location of lung tumors, as well as in frequency of lymphocyte infiltration. To assess the reproducibility of these genetic differences, the authors classified both tumor location and lymphocyte infiltration also in an independent set of lung tumors that were induced in these strains in experiments performed more than 10 years ago in a different mouse facility and found the same strain differences. These results indicate that these qualitative phenotypes are very robust (P(c) 5.52 x 10(-6) and 2.27 x 10(-8), respectively) and relatively independent of environmental influences. They likely reflect different stages of lung differentiation at the time of tumor induction and differences in molecules involved in intercellular signaling, respectively. The definition of genes controlling these traits will provide novel insights into the determination of tumor phenotype.

Role of inflammation in mouse lung tumorigenesis: a review

Peritumoral and intratumoral macrophages are associated with human and mouse lung cancer The mouse model allows manipulation of the macrophage population to experimentally evaluate its contribution to tumor growth. Genetic and pharmacologic strategies also permit testing the invol vement of specific inflammatory mediators in tumor progression. Among those endogenous mediators thus identified are interleukin (IL)-10, glucocorticoids, prostacyclin, nitric oxide, and surfactant apoprotein D (SP-D); serum SP-D levels are a useful biomarker to monitor tumor growth rate. The importance of understanding the mutually antagonistic roles of individual prostaglandins downstream from cycloxygenase (COX) and how this affects the efficacy of COX-inhibitory drugs is discussed. Promising drug candidates include synthetic glucocorticoids such as budesonide and the sulfone derivative of sulindac, apotosyn.

Mouse models for human lung cancer

In recent years several new mouse models for lung cancer have been described. These include models for both non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC). Tumorigenesis in these conditional mouse tumor models can be initiated in adult mice through Cre-recombinase-induced activation of oncogenic mutations in a subset of the cells. They present a marked improvement over mouse models that depend on carcinogen induction of tumors. These models permit us to study the consecutive steps involved in initiation and progression and allow us to address questions like the cell of origin, and the role of cancer stem cells in the maintenance of these tumors. They now need to be validated as suitable preclinical models for intervention studies in which questions with respect to therapy response and resistance can be addressed.

Immunohistochemical analysis of Clara cell secretory protein expression in a transgenic model of mouse lung carcinogenesis

Immunohistochemical methods have been widely used to determine the histogenesis of spontaneous and chemically-induced mouse lung tumors. Typically, antigens for either alveolar Type II cells or bronchiolar epithelial Clara cells are studied. In the present work, the morphological and immunohistochemical phenotype of a transgenic mouse designed to develop lung tumors arising from Clara cells was evaluated. In this model, Clara cell-specific transformation is accomplished by directed expression of the SV40 large T antigen (TAg) under the mouse Clara cell secretory protein (CC10) promoter. In heterozygous mice, early lesions at 1 month of age consisted of hyperplastic bronchiolar epithelial cells. These progressed to adenoma by 2 months as proliferating epithelium extended into adjacent alveolar spaces. By 4 months, a large portion of the lung parenchyma was composed of tumor masses. Expression of constitutive CC10 was diminished in transgenic animals at all time points. Only the occasional cell or segment of the bronchiolar epithelium stained positively for CC10 by immunohistochemistry, and all tumors were found to be uniformly negative for staining. These results were corroborated by Western blotting, where CC10 was readily detectable in whole lung homogenate from nontransgenic animals, but not detected in lung from transgenic animals at any time point. Tumors were also examined for expression of surfactant apoprotein C (SPC), an alveolar Type II cell-specific marker, and found to be uniformly negative for staining. These results indicate that, in this transgenic model, expression of CC10, which is widely used to determine whether lung tumors arise from Clara cells, was reduced and subsequently lost during Clara cell tumor progression.

Studies using structural analogs and inbred strain differences to support a role for quinone methide metabolites of butylated hydroxytoluene (BHT) in mouse lung tumor promotion

Chronic treatment of BALB and GRS mice with BHT (2,6-di-tert-butyl-4-methylphenol) following a single urethane injection increases lung tumor multiplicity, but this does not occur in CXB4 mice. Previous data suggest that promotion requires the conversion of BHT to a tert-butyl-hydroxylated metabolite (BHTOH) in lung and the subsequent oxidation of this species to an electrophilic quinone methide. To obtain additional evidence for the importance of quinone methide formation, structural analogs that form less reactive quinone methides were tested and found to lack promoting activity in BHT-responsive mice. The possibility that promotion-unresponsive strains are unable to form BHTOH was tested by substituting this compound for BHT in the promotion protocol using CXB4 mice. No promotion occurred, and in-vitro work demonstrated that CXB4 mice are, in fact, capable of producing BHTOH and its quinone methide, albeit in smaller quantities. Incubations with BALB lung microsomes and radiolabeled substrates confirmed that more covalent binding to protein occurs with BHTOH than with BHT and, in addition, BHTOH quinone methide is considerably more toxic to mouse lung epithelial cells than BHT quinone methide. These data are consistent with the hypothesis that a two-step oxidation process, i.e. hydroxylation and quinone methide formation, is required for the promotion of mouse lung tumors by BHT.

Enhanced tumorigenesis and reduced transforming growth factor-beta type II receptor in lung tumors from mice with reduced gene dosage of transforming growth factor-beta1

To elucidate the role of transforming growth factor-beta1 (TGF-beta1) and the TGF-beta type II receptor (TGF-beta RII) as tumor-suppressor genes in lung carcinogenesis, we mated C57BL/6 mice heterozygous (HT) for deletion of the TGF-beta1 gene with A/J mice to produce AJBL6 TGF-beta1 HT progeny and their wild-type (WT) littermates. Immunohistochemical staining, in situ hybridization, and northern blot analyses showed lower staining and hybridization for TGF-beta1 protein and mRNA, respectively, in the lungs of normal HT mice versus WT mice. Competitive reverse transcription-polymerase chain reaction (CRT-PCR) amplification showed the level of TGF-beta1 mRNA in the lungs of HT mice to be fourfold lower than the level in WT lung. When challenged with ethyl carbamate, lung adenomas were detected in 55% of HT mice by 4 mo but only in 25% of WT littermates at this time. Whereas all HT mice had adenomas by 6 mo, it was not until 10 mo before all WT mice had adenomas. After 12 mo, the average number of adenomas was fivefold higher in HT lungs than in WT lungs. Most dramatic was the appearance of lung carcinomas in HT mice 8 mo before they were visible in WT mice. Thus, the AJBL6 TGF-beta1 HT mouse provides an excellent model system to examine carcinogen-induced lung tumorigenesis by increasing progressive lesion incidence and multiplicity relative to their WT littermates. Immunohistochemical staining showed expression of the TGF-beta type I receptor (TGF-beta RI) at moderate to strong levels in lung adenomas and carcinomas in HT and WT mice. In contrast, whereas weak immunostaining for TGF-beta RII was detected in 67% of HT carcinomas at 12 mo, only 22% of WT carcinomas showed weak staining for this protein. Individual lung carcinomas showing reduced TGF-beta RII expression and adjacent normal bronchioles were excised from HT lungs using laser capture microdissection, and CRT-PCR amplification of the extracted RNA showed 12-fold less TGF-beta RII mRNA in these carcinomas compared with bronchioles. Decreasing TGF-beta RII mRNA levels occurred with increasing tumorigenesis in lung hyperplasias, adenomas, and carcinomas, with carcinomas having fourfold and sevenfold lower levels of TGF-beta RII mRNA than adenomas and hyperplasias, respectively. These data show enhanced ethyl carbamate-induced lung tumorigenesis in AJBL6 HT mice compared with WT mice, suggesting that both TGF-beta1 alleles are necessary for tumor-suppressor activity. Reduction of TGF-beta RII mRNA expression in progressive stages of lung tumorigenesis in HT mice suggests that loss of TGF-beta RII may play an important role in the promotion of lung carcinogenesis in mice with reduced TGF-beta1 gene dosage when challenged with carcinogen.

Surfactant protein C expression in urethane-induced murine pulmonary tumors

Mice injected with urethane develop tumors with distinct histological patterns, which are classified as solid, papillary, or a mixture of these two patterns within the same tumor. Most investigators agree that solid tumors arise from alveolar type II cells, but the cellular origin of papillary tumors is less certain, being attributed to either type II cells or nonciliated bronchiolar epithelial (Clara) cells. To characterize the state of differentiation of these tumors more precisely and to provide additional information on gene expression, we used immunocytochemistry and/or in situ hybridization to determine the cellular localization of surfactant-associated proteins A (SP-A), SP-B, SP-C, and SP-D; Clara cell-associated protein CC-10; and thyroid transcription factor-1. In normal mouse lung, the messenger RNAs (mRNAs) for SP-A, SP-B, and SP-D were expressed in both type II cells and Clara cells. SP-C mRNA, however, was expressed only in type II cells, and CC-10 expression of mRNA was restricted to Clara cells. All tumors examined, both solid and papillary, expressed SP-A, SP-B, SP-C, SP-D, and thyroid transcription factor-1, but not CC-10. However, SP-C expression was slightly diminished in larger (older) papillary tumors. These results demonstrate that urethane-induced murine lung tumors express the type II cell phenotype.

Activation of extracellular signal-regulated kinase in lung tissues of mice treated with carcinogen

The activation of extracellular signal-regulated kinase (ERK) in lung tissues of mice, as determined by the appearance of phosphorylated form, was observed on day 30 after urethane injection, and the activation also occurred in urethane-induced lung tumors. Immunohistochemical analysis using anti-phosphorylated ERK antibody indicated that the active form of ERK localized in alveolar epithelial cells. Furthermore, we confirmed by immunoprecipitation and immunoblot analysis that other essential components of the ERK cascade, that is, Ras, Raf and MEK (known as ERK kinase) were activated. These results indicate that the activation of the ERK signal in alveolar epithelial cells at the early stage of urethane-induced lung carcinogenesis is an important factor to develop lung tumors.

Genetics of quantitative and qualitative aspects of lung tumorigenesis in the mouse: multiple interacting Susceptibility to lung cancer (Sluc) genes with large effects

Inbred strains of mice exhibit large differences in their susceptibility to various complex quantitative genetic traits, among which is the susceptibility to lung cancer. These differences are caused by the combined effects of multiple quantitative trait loci (QTLs). Due to their multiplicity, it is relatively difficult and laborious to study the effects of individual QTLs. To dissect complex genetic traits the authors make use of recombinant congenic strains (RCS), a system of mouse inbred strains in which the genetic complexity is reduced. The susceptibility to lung cancer is studied by using the series of O20-congenic-B10.O20 (OcB) RC strains. They are derived from the parental background strain O20 and the parental donor strain B10.O20, two mouse inbred strains that differ from each other in both quantitative and qualitative aspects of lung tumorigenesis. This study describes the segregation of lung tumor number, size, and histology among the OcB RC strains, and indicates that these traits are influenced by multiple interacting QTLs with considerable individual effects. The results suggest that some of the susceptibility loci to lung cancer affect the susceptibility to other types of cancer as well, possibly by functioning systematically.

Expression of human Krev-1 gene in lungs of transgenic mice and subsequent reduction in multiplicity of ethyl carbamate-induced lung adenomas

Mice of the A/J strain are useful models of lung cancer because they develop tumors spontaneously or after treatment with ethyl carbamate. These tumors are thought to arise from either Clara cells (papillary tumors) or alveolar type 2 cells (alveolar tumors); like many human lung adenocarcinomas, the mouse tumors involve Kiras activation. Transformation with Ki-ras can be reversed by coexpression of the Krev-1 gene in tissue culture. To test the tumor suppressor activity of Krev-1 in vivo, we produced transgenic A/J mice expressing Krev-1 under the control of the rabbit uteroglobin promoter, which directs expression of heterologous genes to the lung Clara cells. Krev-1 was expressed specifically in the lungs of transgenic mice. Sixty-six mice (35 transgenic and 31 nontransgenic) from three lines were given ethyl carbamate, and the numbers of resulting lung tumors were compared between transgenic and nontransgenic animals. The mean number (+/-standard deviation) of ethyl carbamate-induced lung tumors was 21.7 +/- 1.3 in transgenic mice and 26.9 +/- 1.3 in their nontransgenic littermates (P < 0.01). Sequencing of polymerase chain reaction-amplified ras DNA from 15 transgenic mouse tumors and 16 nontransgenic mouse tumors (controls) detected mutations in codon 61 in 13 tumors from the transgenic group and 11 tumors in the control group, whereas mutations in codon 12 were detected in only one tumor in the transgenic group and in four tumors in the controls. Together, these data demonstrate for the first time the tumor suppressor activity of Krev-1 in vivo and suggest that Krev-1 tumor suppressor activity may be specific for cells harboring mutations in codon 12 of ras.

Comparison of pulmonary O6-methylguanine DNA adduct levels and Ki-ras activation in lung tumors from resistant and susceptible mouse strains

The role of O6-methylguanine (O6MG) DNA adduct formation and persistence in the formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors from resistant C57BL/6 and susceptible A/J mice was investigated. In addition, the frequencies of pulmonary tumor formation and Ki-ras activation were defined in C57BL/6 mice treated with NNK or vinyl carbamate (VC), and the role of the p53 gene in pulmonary carcinogenesis in these resistant mice was examined. One day after treatment with 100 mg/kg NNK, O6MG adduct concentrations were twofold to eightfold higher in Clara cells and type II cells than in small cells or whole lungs from both mouse strains. The concentrations of O6MG in isolated cells decreased at a similar rate in the two strains of mice. Lung tumors were detected by 27 mo of age in 18% of the C57BL/6 mice after a single 100 mg/kg dose of NNK and in 46% of these mice after a single 60 mg/kg dose of VC. In contrast, the tumor incidence in untreated C57BL/6 mice was 4%. Only one of 22 lung tumors from C57BL/6 mice treated with NNK contained an activated Ki-ras gene that was associated with an O6MG DNA adduct, whereas previous studies detected activated Ki-ras oncogenes in most of the NNK-induced lung tumors analyzed from susceptible A/J and resistant C3H mice. The small differences in formation and persistence of the O6MG adduct in whole lung or isolated lung cells from A/J and C57BL/6 strains do not account for the differences in either susceptibility for tumor formation or activation of the Ki-ras gene between these strains. In contrast to the low number of NNK-induced tumors with Ki-ras mutations in the resistant mice, 11 of 20 lung tumors from VC-treated mice contained activated Ki-ras genes. Neither p53 tumor suppressor gene mutations nor overexpression of the p53 protein were detected in spontaneous or chemically induced lung tumors in C57BL/6 mice. Thus, although Ki-ras activation was detected in some tumors, pathways independent of ras activation and p53 inactivation also appear to be involved in lung tumorigenesis in this resistant mouse strain.

The effect of butylated hydroxytoluene, with and without cortisol, on stimulated lymphocytes

In the present work we undertook to ascertain whether butylated hydroxytoluene (BHT), which is used in food as an antioxidant, is capable of either inhibiting human lymphocyte stimulation or acting synergistically with cortisol and prednisolone to the same end. BHT cytotoxicity was observed at concentrations higher than 100 micrograms/ml. In the concentration range of 0.0 to 60.0 micrograms/mL, BHT showed no effect on the uptake of 3H-thymidine by PHA stimulated lymphocytes. However, at 50 micrograms/mL BHT suppressed mixed lymphocyte reaction (MLR). A synergistic effect with regard to suppression of PHA stimulated lymphocytes was observed when the cells were incubated with BHT in the presence of either cortisol or prednisolone.

Lung adenoma structure among inbred strains of mice: the pulmonary adenoma histologic type (Pah) genes

Urethane-induced, lung adenoma multiplicity and histologic type vary among mouse strains. We asked whether the Pas genes which control multiplicity also determine adenoma structure. Lung adenomas from inbred mice, F1 hybrids, and recombinant inbred mice were classified by growth pattern as either solid or papillary. Since no correlation was observed between adenoma multiplicity and histologic type, no linkage apparently exists between the Pas genes and adenoma morphology. We propose the name Pah (Pulmonary Adenoma Histologic type) for the genes controlling lung adenoma growth patterns. Genetic analysis indicated dominance of the papillary phenotype, and that two or more Pah genes determine adenoma structure.

Cells of origin of primary pulmonary neoplasms in mice: morphologic and histochemical studies

Urethane-induced pulmonary adenomas in mice have two distinct histologic growth patterns--solid and papillary. The development of these tumors between 14 and 56 weeks was investigated in A/J mice. Solid tumor multiplicity remained constant from 14 to 56 weeks, whereas papillary and total tumor multiplicities increased in parallel between 14 and 28 weeks and remained constant through 56 weeks. The simplest explanation of these results is that solid and papillary adenomas arise independently, possibly from different cell types. The cell type of origin of these primary mouse lung tumors was investigated histochemically. Succinate dehydrogenase (SDH) histochemistry readily stained bronchiolar epithelial cells, but alveolar epithelial cells exhibited only slight enzymatic activity. Urethane-induced papillary adenomas exhibited intense SDH staining, whereas solid adenomas stained very lightly. Since Clara cells and type II pneumocytes are the only cells capable of proliferation in the bronchiolar and alveolar epithelia, respectively, the relative SDH activities of these adenomas is consistent with a hypothesis that solid tumors arise from type II pneumocytes and papillary tumors arise from Clara cells.

MHC and non-MHC genes in lung tumor susceptibility in the mouse: implications for the study of the different lung tumor types and their cell of origin

Lung tumorigenesis in the mouse is controlled by multiple genes, which until now largely escaped detection because of the limitations of the available genetic tools. Therefore, we have developed the Recombinant Congenic Strains (RCS), which can be used to separate and map individual tumor susceptibility genes. The two strains, B10.O20/Dem and O20/A (used to produce the RCS series O20.c.B10.O20/Dem) differ in number, type, and degree of malignancy of lung tumors. Thus the genetic control of the different aspects of lung tumorigenesis can now be analyzed using RCS. The tests on the role of the Major Histocompatibility Complex (MHC; H-2 in mice) in lung tumorigenesis show that the H-2 influence is different for alveolar tumors and papillary tumors. In addition, only the development of papillary tumors is influenced by glucocorticoid administration concomitant with the transplacental carcinogen treatment. The MHC influence on lung tumor development is probably related to H-2 effects on the regulation of lung differentiation. In the H-2 congenic strains used papillary tumors developed early, whereas alveolar tumors appeared later, if at all. This differential impact of genetic and hormonal factors on the development of alveolar and papillary tumors suggests that they arise either from different cell types or from a common cell type at different stages of differentiation.

Effect of lung development on the histological pattern of lung tumors induced by ethylnitrosourea in the C3HeB/FeJ mouse

The number, size, and histological pattern of lung tumors collected 6 months after being induced in C3HeB/FeJ mice by ethylnitrosourea (ENU) treatment on one of days 13-19 of gestation, or days 5, 15, or 35 after birth, or as 9-month-old adults was investigated. The number of lung tumors induced increased when treatment occurred between days 13-16 and then decreased when treatment occurred on days 17-19 of gestation. There was a marked increase in lung tumor numbers induced on day 5 after birth, which decreased to much lower levels on days 15 and 35 after birth and in the treated adult mice. The size of lung tumors was greater in males than females in all groups and decreased as the age at the time of ENU treatment increased. A greater proportion (60-65%) of papillary tumors were induced following treatment on days 13-16 whereas, with one exception, alveolar lining tumors were the predominant histological type when treatment occurred after day 16. When treatment occurred on day 5 after birth, papillary tumors were once again the predominant type (66%) induced. The changes in tumor numbers induced and in the histological type of tumor induced occur at periods when major shifts in the histological development of the lung occur. The results indicate that the histological type of tumor induced by ENU treatment is developmentally regulated and suggests that alveolar lining and papillary tumors behave as two separate populations of tumors.

Strain A/J mouse lung adenoma growth patterns vary when induced by different carcinogens

The histogenesis of mouse lung adenomas is currently being investigated in several laboratories. Based upon studies of a limited number of carcinogens in different mouse strains, some investigators suggest that all lung adenomas in mice are derived from alveolar type II cells, whereas others suggest a Clara cell origin for a majority of the tumors. This report differs from previous investigations in that 12 different carcinogens were evaluated for the types of lung tumor growth patterns they induced in a single mouse strain (strain A mice). The carcinogens aflatoxin B1 (AFB1), benzo(a)pyrene (BP), 1,2-dimethylhydrazine (DMH), 3-methylcholanthrene (MCA), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and N-nitrosomethylurea (MNU) induced tumors with a predominantly solid/alveolar growth pattern, whereas N-nitrosodiethylamine (NDEA) induced predominantly papillary tumors. Most of the other carcinogens induced a higher proportion of lung tumors with the solid/alveolar growth pattern than with the papillary growth pattern; however, ratios between the 2 growth patterns varied. If, as suggested by others, solid tumors are derived from alveolar type II cells and papillary tumors from Clara cells, then carcinogens may differ with respect to their ability to transform one cell type or the other.

Fetal mouse alveolar type II cells in culture express several type II cell characteristics found in vivo, together with major histocompatibility antigens

Alveolar type II cells were isolated from fetal mouse lung by differential adherence and obtained in monolayer culture. Cultures display a high degree of purity as shown by histochemical and immunocytochemical staining procedures. Seventy-five percent of cells stained positive with specific anti-lavage serum mouse (SALS-M), an antiserum specific for (pre)alveolar type II cells of the mouse, and osmiophilic bodies were present in 82% of cells. These and other characteristics of type II cells in culture correspond to those of alveolar type II cells in fetal mouse lung. The pattern of reactivity of these cells with various anti-cytokeratin antibodies is described, and we show that, in contrast to rat type II cells, they do not exhibit alkaline phosphatase activity. Identity of the type II cell cultures was shown by their specific phospholipid composition and surfactant protein A (SP-A) content. The fetal alveolar type II cells in culture were found to synthesize and express class I but not class II major histocompatibility complex (MHC) antigens. The possibility to culture fetal alveolar type II cells of the mouse and the availability of genetically well-defined inbred and transgenic mouse strains opens ways to study the genetics of type II cell differentiation and function. Also, the in vitro availability of alveolar type II cells, the progenitor cells of mouse lung tumors, will enable us to study in vitro several of the processes involved in lung tumorigenesis in the mouse.

Differential staining of normal and neoplastic mouse lung epithelia by succinate dehydrogenase histochemistry

The cell type of origin of primary mouse lung tumors was investigated histochemically. Succinate dehydrogenase (SDH) histochemistry readily differentiated bronchiolar epithelial (Clara and ciliated) cells from alveolar type II pneumocytes in mice aged 10 days through adult. Correspondingly, freshly-isolated Clara cells stained intensely but type II cells did not. Urethane-induced papillary adenomas exhibited intense SDH staining while alveolar adenomas stained very lightly. The relative SDH activities of these two types of pulmonary adenomas is consistent with the hypothesis that alveolar tumors arise from type II pneumocytes and papillary tumors from Clara cells.

Specific Ki-ras codon 61 mutations may determine the development of urethan-induced mouse lung adenomas or adenocarcinomas

In A/J strain mice, the carcinogen urethan induces lung adenomas and adenocarcinomas that contain Ki-ras-activating mutations primarily in codon 61. These mutations affect the middle adenine in codon 61 resulting in the substitution of either arginine (AT----GC transition) or leucine (AT----TA transversion) for the wild-type glutamine. To analyze the expression of the wild-type and mutant Ki-ras mRNAs in primary mouse lung tumors and transformed mouse lung cell lines, we utilized reverse transcription of total mRNA and DNA amplification by the polymerase chain reaction. The wild-type allele of codon 61 was expressed in all normal lung and primary tumor samples and in all transformed cell lines, except one. Significantly, the leucine-substituted allele was expressed primarily in very small lung adenomas, whereas the arginine-substituted allele was expressed in large lung adenocarcinomas and transformed lung cell lines. The relative amounts of expression of the mutant versus wild-type Ki-ras alleles and the total Ki-ras mRNA expression was similar in both lung adenomas and adenocarcinomas. Further, the arginine mutant allele was present in adenocarcinomas having either alveolar or papillary tumor morphologies. These results suggest that the specific activating Ki-ras mutation is more critical to either lung adenoma or adenocarcinoma development than is the tumor's cell of origin or the extent to which the mutant alleles are expressed. A distinct role of the specific activating Ki-ras mutations in affecting lung tumor growth or malignant potential is indicated.

Enhancing effect of high fat diet on 4-nitroquinoline 1-oxide-induced pulmonary tumorigenesis in ICR male mice

The effects of dietary high fat on 4-nitroquinoline 1-oxide (4NQO)-induced lung tumorigenesis were investigated in male ICR mice. Two groups of mice were initially given a single subcutaneous injection of 4NQO at a dose of 15 mg/kg and, thereafter, fed either 20% corn oil-supplemented diet or a standard basal diet. Two further groups were maintained on the high fat diet or standard diet without administration of 4NQO. Mice were killed at weeks 15, 18 and 25 and the incidence of lung tumors at each time point was found to be significantly increased in the 4NQO/high fat diet group as compared to the 4NQO/standard diet group in terms of both incidence of tumor-bearing mice and the number of lesions per mouse. The results thus indicate that dietary high fat can enhance 4NQO-induced lung tumorigenesis in mice.

The genetic basis of susceptibility to lung tumors in mice

This is the first in a series of review articles describing the current state of research on mouse lung tumorigenesis. The system is valuable as a biological model for studying stages of tumor development and the interaction of genetic and environmental factors which dispose towards neoplasia. Additionally, these tumors are analagous to bronchiolo-alveolar cancer in man. Three pulmonary adenoma susceptibility (Pas) genes regulate susceptibility; 1 of these is the proto-oncogene, K-ras2. Candidates for the other 2 genes include the H-2 histocompatibility locus and genes which regulate the basal proliferative rate of the cells from which these tumors arise. Tumor development is favored by a depressed immune system, immature age, and decreased levels of circulating corticosterone.

Pulmonary adenoma and endocrine cell hyperplasia in Syrian golden hamster treated with 4-nitroquinoline 1-oxide

Chronic effects of 4-nitroquinoline 1-oxide (4 NQO) on the lungs of Syrian golden hamsters were studied. 4 NQO was subcutaneously injected weekly for 3 weeks at a dose of 20 mg/kg body weight. The animals were sacrificed at the 65th and 80th experimental weeks. Two cases of pulmonary adenomas were demonstrated in the 10 4 NQO-treated animals at the 80th week, and the tumor cells contained cytoplasmic lamellar inclusion bodies. In a previous study, we reported 4 NQO- induced pulmonary endocrine cell hyperplasias in the 4 NQO-treated hamster after the 20th experimental week (Jpn. J. Cancer Res., 77, 1986). In the present study, 12 pulmonary endocrine cell hyperplasias were recognized in serial sections of the 24 treated animals. The hyperplastic lesions showed positive immunoreactivity to calcitonin. The hyperplastic lesion did not develop to pulmonary endocrine cell neoplasm.

Decreased incorporation of the photoaffinity probe 8N3-[gamma-32P]-GTP into a 45kD protein in lung tumors

Photoincorporation of 8N3-[gamma-32P]-GTP into tissue and cell extracts was examined using gel electrophoresis and autoradiography. Decreased photoincorporation into a 45kD band was observed in extracts from mouse lung tumors as compared to normal mouse lung, and in extracts from lung tumor-derived cell lines when compared to isolated bronchiolar epithelial cells. Decreased 45kD photolabelling was also observed in extracts of S49 lymphoma cyc- cells (deficient in Gs alpha, a 45kD GTP binding protein of receptor-coupled adenylate cyclase) when compared to wild type S49 cells. This, and the observation that there was no cholera toxin-catalyzed ADP-ribosylation in the 45kD band of lung tumor extracts, suggests that the 45kD band contains Gs alpha.