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Chronic inflammation plays a crucial role in the carcinogenesis process and, in particular, in smoking-related carcinogenesis. Therefore, anti-inflammatory agents provide an interesting perspective in the prevention of smoking-associated cancers. Among nonsteroidal anti-inflammatory drugs (NSAIDs), licofelone is a triple inhibitor of both cyclooxygenases (COX-1 and COX-2) and of 5-lipooxygenase (5-LOX) that has shown some encouraging results in cancer prevention models. We previously showed that the dietary administration of licofelone, starting after weanling, to Swiss H mice exposed for 4 months to mainstream cigarette smoke since birth attenuated preneoplastic lesions of inflammatory nature in both lung and urinary tract, and had some effects on the yield of lung tumors at 7.5 months of age. The present study aimed at evaluating the early modulation by licofelone of pulmonary DNA and RNA alterations either in smoke-free or smoke-exposed H mice after 10 weeks of exposure. Licofelone protected the mice from the smoke-induced loss of body weight and significantly attenuated smoke-induced nucleotide alterations by decreasing the levels of bulky DNA adducts and 8-hydroxy-2'-deoxyguanosine in mouse lung. Moreover, the drug counteracted dysregulation by smoke of several pulmonary microRNAs involved in stress response, inflammation, apoptosis, and oncogene suppression. However, even in smoke-free mice administration of the drug had significant effects on a broad panel of microRNAs and, as assessed in a subset of mice used in a parallel cancer chemoprevention study, licofelone even enhanced the smoke-induced systemic genotoxic damage after 4 months of exposure. Therefore, caution should be paid when administering licofelone to smokers for long periods., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Cigarette smoke (CS) is known to dysregulate microRNA expression profiles in the lungs of mice, rats, and humans, thereby modulating several pathways involved in lung carcinogenesis and other CS-related diseases. We designed a study aimed at evaluating (a) the expression of 1135 microRNAs in the lung of Swiss H mice exposed to mainstream CS during the first 4 months of life and thereafter kept in filtered air for an additional 3.5 months, (b) the relationship between lung microRNA profiles and histopathological alterations in the lung, (c) intergender differences in microRNA expression, and (d) the comparison with microRNA profiles in blood serum. CS caused multiple histopathological alterations in the lung, which were almost absent in sham-exposed mice. An extensive microRNA dysregulation was detected in the lung of CS-exposed mice. Modulation of microRNA profiles was specifically related to the histopathological picture, no effect being detected in lung fragments with non-neoplastic lung diseases (emphysema or alveolar epithelial hyperplasia), whereas a close association occurred with the presence and multiplicity of preneoplastic lesions (microadenomas) and benign lung tumors (adenomas). Three microRNAs regulating estrogen and HER2-dependent mechanisms were modulated in the lung of adenoma-bearing female mice. Blood microRNAs were also modulated in mice affected by early neoplastic lesions. However, there was a poor association between lung microRNAs and circulating microRNAs, which can be ascribed to an impaired release of mature microRNAs from the damaged lung. Studies in progress are evaluating the feasibility of analyzing blood microRNAs as a molecular tool for lung cancer secondary prevention.

Both ethanol and cigarette smoke are classified as human carcinogens. They can synergize, especially in tissues of the upper aerodigestive tract that are targeted by both agents. The main objective of the present study was to evaluate the individual and combined effects of ethanol and smoke in the respiratory tract, either following transplacental exposure and/or postnatal exposure. We designed two consecutive studies in mouse models by exposing Swiss H mice to oral ethanol and/or inhaled mainstream cigarette smoke for up to 4 months, at various prenatal and postnatal life stages. Clastogenic effects and histopathological alterations were evaluated after 4 and 8 months, respectively. Ethanol was per se devoid of clastogenic effects in mouse peripheral blood erythrocytes. However, especially in mice exposed both transplacentally throughout pregnancy and in the postnatal life, ethanol administration was associated not only with liver damage but also with pro-angiogenetic effects in the lung by stimulating the proliferation of blood vessels. In addition, these mice developed pulmonary emphysema, alveolar epithelial hyperplasias, microadenomas, and benign tumors. On the other hand, ethanol interfered in the lung carcinogenesis process resulting from the concomitant exposure of mice to smoke. In fact, ethanol significantly attenuated some smoke-related preneoplastic and neoplastic lesions in the respiratory tract, such as alveolar epithelial hyperplasia, microadenomas, and even malignant tumors. In addition, ethanol attenuated cigarette smoke clastogenicity. In conclusion, preclinical studies provide evidence that, in spite of its pulmonary toxicity, ethanol may mitigate some noxious effects of cigarette smoke in the respiratory tract., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

The role of nonsteroidal anti-inflammatory drugs (NSAIDs) in smoke-related lung carcinogenesis is still controversial. We have developed and validated a murine model for evaluating the tumorigenicity of mainstream cigarette smoke (MCS) and its modulation by chemopreventive agents. In the present study, the protective effects of the nonselective cyclooxygenase inhibitors aspirin and naproxen were investigated by using a total of 277 Swiss H neonatal mice of both genders. Groups of mice were exposed whole-body to MCS during the first 4 months of life, followed by an additional 3.5 months in filtered air in order to allow a better growth of tumors. Aspirin (1600 mg/kg diet) and naproxen (320 mg/kg diet) were given after weanling until the end of the experiment. After 4 months of exposure, MCS significantly enhanced the frequency of micronucleated normochromatic erythrocytes in the peripheral blood of mice, and naproxen prevented such systemic genotoxic damage in female mice. After 7.5 months, exposure of mice to MCS resulted in the formation of lung tumors, both benign and malignant, and in several other histopathological lesions detectable both in the respiratory tract and in the urinary tract. Aspirin and, even more sharply, naproxen significantly inhibited the formation of lung tumors in MCS-exposed mice, but this protective effect selectively occurred in female mice only. These results lend support to the views that estrogens are involved in smoke-related pulmonary carcinogenesis and that NSAIDs have antiestrogenic properties. The two NSAIDs proved to be safe and efficacious in the experimental model used.

Many drugs in common use possess pleiotropic properties that make them capable of interfering with carcinogenesis mechanisms. We discuss here the ability of pharmacological agents to mitigate the pulmonary carcinogenicity of mainstream cigarette smoke. The evaluated agents include anti-inflammatory drugs (budesonide, celecoxib, aspirin, naproxen, licofelone), antidiabetic drugs (metformin, pioglitazone), antineoplastic agents (lapatinib, bexarotene, vorinostat), and other drugs and supplements (phenethyl isothiocyanate, myo-inositol, N-acetylcysteine, ascorbic acid, berry extracts). These drugs have been evaluated in mouse models mimicking interventions either in current smokers or in ex-smokers, or in prenatal chemoprevention. They display a broad spectrum of activities by attenuating either smoke-induced preneoplastic lesions or benign tumors and/or malignant tumors. Together with epidemiological data, these findings provide useful information to predict the potential effects of pharmacological agents in smokers., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Chemoprevention provides an important strategy for cancer control in passive smokers. Due to the crucial role played by smoke-related chronic inflammation in lung carcinogenesis, of special interest are extensively used pharmacological agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs). We evaluated the ability of aspirin and naproxen, inhibitors of both cyclooxygenase-1 and cyclooxygenase -2, to modulate environmental cigarette smoke (ECS)-induced lung carcinogenesis in A/J mice of both genders. Based on a subchronic toxicity study in 180 postweaning mice, we used 1600 mg/kg diet aspirin and 320 mg/kg diet naproxen. In the tumor chemoprevention study, using 320 mice, exposure to ECS started soon after birth and administration of NSAIDs started after weaning. At 10 weeks of life, the NSAIDs did not affect the presence of occult blood in feces. As assessed in a subset of 40 mice, bulky DNA adducts and 8-hydroxy-2'-deoxyguanosine levels were considerably increased in ECS-exposed mice and, irrespective of gender, both NSAIDs remarkably inhibited these nucleotide alterations. After exposure for 4 months followed by 5 months in filtered air, ECS induced a significant increase in the yield of surface lung tumors, the 43.7% of which were adenomas and the 56.3% were adenocarcinomas. Oct-4 (octamer-binding transcription factor 4), a marker of cell stemness, was detected in some adenocarcinoma cells. The NAIDs attenuated the yield of lung tumors, but prevention of ECS-induced lung adenomas was statistically significant only in female mice treated with aspirin, which supports a role for estrogens in ECS-related lung carcinogenesis and highlights the antiestrogenic properties of NSAIDs., (© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Lapatinib, a dual tyrosine kinase inhibitor targeting the epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER-2), is prescribed for the treatment of patients with metastatic breast cancer overexpressing HER-2. Involvement of this drug in pulmonary carcinogenesis has been poorly investigated. We used murine models suitable to evaluate cigarette smoke-related molecular and histopathological alterations. A total of 481 Swiss H mice were used. The mice were exposed to mainstream cigarette smoke (MCS) during the first four months of life. After 10 weeks, MCS caused an elevation of bulky DNA adducts, oxidative DNA damage and an extensive downregulation of microRNAs in lung. After four months, an increase in micronucleus frequency was observed in peripheral blood erythrocytes. After 7.5 months, histopathological alterations were detected in the lung, also including benign tumors and malignant tumors, and in the urinary tract. A subchronic toxicity study assessed the non-toxic doses of lapatinib, administered daily with the diet after weaning. After 10 weeks, lapatinib significantly attenuated the MCS-related nucleotide changes and upregulated several low-intensity microRNAs in lung. The drug poorly affected the MCS systemic genotoxicity and had modest protective effects on MCS-induced preneoplastic lesions in lung and kidney, when administered under conditions that temporarily mimicked interventions either in current smokers or ex-smokers. On the other hand, it caused some toxicity to the liver. Thus, on the whole, lapatinib appears to have a low impact in the smoke-related lung carcinogenesis models used, especially in terms of tumorigenic response., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The anti-diabetic drug metformin is endowed with anti-cancer properties. Epidemiological and experimental studies, however, did not provide univocal results regarding its role in pulmonary carcinogenesis. We used Swiss H mice of both genders in order to detect early molecular alterations and tumors induced by mainstream cigarette smoke. Based on a subchronic toxicity study, oral metformin was used at a dose of 800 mg/kg diet, which is 3.2 times higher than the therapeutic dose in humans. Exposure of mice to smoke for 4 months, starting at birth, induced a systemic clastogenic damage, formation of DNA adducts, oxidative DNA damage, and extensive downregulation of microRNAs in lung after 10 weeks. Preneoplastic lesions were detectable after 7.5 months in both lung and urinary tract along with lung tumors, both benign and malignant. Modulation by metformin of 42 of 1281 pulmonary microRNAs in smoke-free mice highlighted a variety of mechanisms, including modulation of AMPK, stress response, inflammation, NFκB, Tlr9, Tgf, p53, cell cycle, apoptosis, antioxidant pathways, Ras, Myc, Dicer, angiogenesis, stem cell recruitment, and angiogenesis. In smoke-exposed mice, metformin considerably decreased DNA adduct levels and oxidative DNA damage, and normalized the expression of several microRNAs. It did not prevent smoke-induced lung tumors but inhibited preneoplastic lesions in both lung and kidney. In conclusion, metformin was able to protect the mouse lung from smoke-induced DNA and microRNA alterations and to inhibit preneoplastic lesions in lung and kidney but failed to prevent lung adenomas and malignant tumors induced by this complex mixture., (© 2014 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)

Assessing the correlation between molecular endpoints and cancer induction or prevention aims at validating the use of intermediate biomarkers. We previously developed murine models that are suitable to detect both the carcinogenicity of mainstream cigarette smoke (MCS) and the induction of molecular alterations. In this study, we used 931 Swiss mice in two parallel experiments and in a preliminary toxicity study. The chemopreventive agents included vorinostat, myo-inositol, bexarotene, pioglitazone and a combination of bexarotene and pioglitazone. Pulmonary micro-RNAs and proteins were evaluated by microarray analyses at 10 weeks of age in male and female mice, either unexposed or exposed to MCS since birth, and either untreated or receiving each one of the five chemopreventive regimens with the diet after weaning. At 4 months of age, the frequency of micronucleated normochromatic erythrocytes was evaluated. At 7 months, the lungs were subjected to standard histopathological analysis. The results showed that exposure to MCS significantly downregulated the expression of 79 of 694 lung micro-RNAs (11.4%) and upregulated 66 of 1164 proteins (5.7%). Administration of chemopreventive agents modulated the baseline micro-RNA and proteome profiles and reversed several MCS-induced alterations, with some intergender differences. The stronger protective effects were produced by the combination of bexarotene and pioglitazone, which also inhibited the MCS-induced clastogenic damage and the yield of malignant tumors. Pioglitazone alone increased the yield of lung adenomas. Thus, micro-RNAs, proteins, cytogenetic damage and lung tumors were closely related. The molecular biomarkers contributed to evaluate both protective and adverse effects of chemopreventive agents and highlighted the mechanisms involved.

Cigarette smoke (CS) and dietary factors play a major role in cancer epidemiology. At the same time, however, the diet is the richest source of anticancer agents. Berries possess a broad array of health protective properties and were found to attenuate the yield of tumors induced by individual carcinogens in the rodent digestive tract and mammary gland but failed to prevent lung tumors induced by typical CS components in mice. We exposed whole-body Swiss ICR mice to mainstream CS, starting at birth and continuing daily for 4 months. Aqueous extracts of black chokeberry and strawberry were given as the only source of drinking water, starting after weaning and continuing for 7 months, thus mimicking an intervention in current smokers. In the absence of berries, CS caused a loss of body weight, induced early cytogenetical damage in circulating erythrocytes and histopathological alterations in lung (emphysema, blood vessel proliferation, alveolar epithelial hyperplasia and adenomas), liver (parenchymal degeneration) and urinary bladder (epithelial hyperplasia). Both berry extracts inhibited the CS-related body weight loss, cytogenetical damage, liver degeneration, pulmonary emphysema and lung adenomas. Protective effects were more pronounced in female mice, which may be ascribed to modulation by berry components of the metabolism of estrogens implicated in lung carcinogenesis. Interestingly, both the carcinogen and the chemopreventive agents tested are complex mixtures that contain a multitude of components working through composite mechanisms., (Copyright © 2012 UICC.)

Cigarette smoke (CS) plays a dominant role in the epidemiology of human cancer. However, it is difficult to reproduce its carcinogenicity in laboratory animals. Recently, we showed that CS becomes a potent carcinogen in mice when exposure starts soon after birth. In our study, we comparatively evaluated the carcinogenic response to mainstream CS in mice at different ages. Neonatal mice were exposed daily for 4 months to CS, starting within 12 hr after birth, and sacrificed at 8 months. Adult mice were exposed for the same time period (3-7 months) and sacrificed at 11 months. Other mice were exposed transplacentally or both transplacentally and early in life. A total of 351 neonatal mice and 80 adult Swiss H mice were used. With varying intensity depending on age, CS induced pulmonary emphysema, bronchial and alveolar epithelial hyperplasia, blood vessel proliferation and hemangiomas and microadenomas in lung as well as parenchymal degeneration of liver. Histopathological alterations of kidney were only observed in mice exposed to CS early in life. Lung adenomas and malignant tumors of various histopathological nature were detected in neonatally exposed mice but not in adults. Transplacental CS induced the formation of lung adenomas in the offspring 8 months after birth. Previous exposure during pregnancy attenuated CS-related alveolar epithelial hyperplasia induced after birth. In conclusion, the carcinogenic response to CS varies depending on the developmental stage. The early postnatal life and the prenatal life are particularly at risk for the later development of CS-related tumors., (Copyright © 2011 UICC.)

We have investigated alterations of microRNA expression profiles in the apparently healthy lung of mice and rats as an early response to exposure to cigarette smoke, either mainstream (MCS) or environmental, and/or to treatment with chemopreventive agents. Further on, we evaluated microRNA alterations at a later stage, when lung tumors were detectable in MCS-exposed mice. Lung samples were available from previous studies, in which strain H mice had been exposed to MCS for 4 months, starting immediately after birth, and then kept in filtered air for an additional 3 months. Some samples were from MCS-exposed mice treated either with N-acetyl-l-cysteine during pregnancy or with phenethyl isothiocyanate after weaning. The analysis of 576 mouse microRNAs showed that MCS strongly dysregulated microRNA expression and that both chemopreventive agents efficiently attenuated this trend, especially in noncancer tissue. MicroRNA expression was affected by histopathology, with specific signatures related to occurrence of pneumonia, adenoma, or bronchoalveolar carcinoma. Within pairs of samples from individual mice, microRNA analysis discriminated adenomatous tissue and especially carcinomatous tissue from the surrounding normal appearing tissue. A series of microRNA alterations characterized the sequential stages of pulmonary carcinogenesis. The involved functions included oncogene activation, inhibition of oncosuppressor genes, recruitment of undifferentiated stem cells, inflammation, inhibition of gap-junctional intercellular communications, angiogenesis, invasiveness, and metastatization. Thus, microRNA expression profiles in lung are dysregulated by MCS along all steps of the carcinogenesis process and depend on the interplay among exposure to noxious agents, treatment with dietary and pharmacological agents, and occurrence of pulmonary diseases., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Lung cancer is the most important cause of death among neoplastic diseases worldwide, and cigarette smoke (CS) is the major risk factor for cancer. Complementarily to avoidance of exposure to CS, chemoprevention will lower the risk of cancer in passive smokers, ex-smokers, and addicted current smokers who fail to quit smoking. Unfortunately, chemoprevention clinical trials have produced disappointing results to date and, until recently, a suitable animal model evaluating CS carcinogenicity was not available. We previously demonstrated that mainstream CS induces a potent carcinogenic response when exposure of mice starts at birth. In the present study, neonatal mice (strain H) were exposed to CS for 120 consecutive days, starting at birth. The chemopreventive agents budesonide (2.4 mg/kg diet), phenethyl isothiocyanate (PEITC, 1,000 mg/kg diet), and N-acetyl-L-cysteine (NAC, 1,000 mg/kg body weight) were administered orally according to various protocols. The experiment was stopped after 210 days. Exposure to CS resulted in a high incidence and multiplicity of benign lung tumors and in significant increases of malignant lung tumors and other histopathological alterations. All three chemopreventive agents, administered to current smokers after weaning, were quite effective in protecting both male and female mice from CS pulmonary carcinogenicity. When given to ex-smokers after withdrawal of exposure to CS, the protective capacity of budesonide was unchanged, while PEITC lost part of its cancer chemopreventive activity. In conclusion, the proposed experimental model provides convincing evidence that it is possible to prevent CS-induced lung cancer by means of dietary and pharmacological agents.

Certain adult diseases may have their origin early in life, and perinatal exposures may contribute to cancers both during childhood and later in life. We recently demonstrated that mainstream cigarette smoke (MCS) induces a potent carcinogenic response in mice when exposure starts soon after birth. We also showed that the antioxidant N-acetylcysteine (NAC) prevents the extensive nucleotide and gene expression alterations that occur 'physiologically' at birth in mouse lung. The present study was designed to evaluate whether administration of NAC during pregnancy may affect the yield of tumors in mice exposed to MCS, starting after birth and continuing for 120 days. The results obtained showed that 210 days after birth, one adenoma only was detectable in sham-exposed mice. In contrast, as much as the 61.1% (33/54) of MCS-exposed mice born from untreated dams had lung tumors, including both benign tumors and bronchoalveolar carcinomas. Treatment with NAC during pregnancy strikingly inhibited the formation of benign lung tumors and totally prevented occurrence of carcinomas. In addition, prenatal NAC inhibited the MCS-induced hyperplasia of the urinary bladder epithelium. These findings demonstrate for the first time that treatment during pregnancy with an antioxidant chemopreventive agent can affect the induction of tumors consequent to exposure to a carcinogen after birth.

Our discovery that the perinatal period involves nucleotide modifications and gene overexpression in mouse lung prompted us to evaluate whether mice may become more susceptible to cigarette smoke when exposure starts immediately after birth. We previously showed that mainstream cigarette smoke is a quite potent carcinogen in neonatal mice. Further on, we showed that exposure of mice to environmental cigarette smoke (ECS), starting at birth, results in alterations of a variety of intermediate biomarkers. However, after 4 months of exposure to ECS followed by 7 months of recovery in filtered air, the lung tumor yield was rather low. In the present study, we evaluated the protective effects of the glucocorticoid budesonide and of the dietary agent phenethyl isothiocyanate in mice exposed to ECS for 9 months followed by 2 months of recovery. After weanling, the mice exposed to ECS since birth underwent a variety of alterations of molecular and cytogenetical end points, and 11 months after birth, they exhibited significant histopathologic changes, such as pulmonary anthracosis, emphysema, hemorrhagic areas, alveolar bronchiolarization, bronchial hyperplasia, and tumors, both benign and malignant. The carcinogenic response was less evident in dams exposed to ECS under identical conditions. Both phenethyl isothiocyanate and budesonide, administered daily with the diet after weanling, attenuated several alterations of ECS-related biomarkers and moderately protected the lungs from histopathologic alterations, including tumors. Thus, although not as efficiently as the bioassay in mainstream cigarette smoke-exposed mice, the model in neonatal mice is suitable to evaluate both ECS carcinogenicity and its modulation by chemopreventive agents.

It is difficult to reproduce the carcinogenicity of cigarette smoke (CS) in animal models. Recently, we showed that exposure of mice to mainstream CS (MCS) for 120 days, starting immediately after birth, resulted in an early and potent carcinogenic response. In parallel, we implemented studies evaluating intermediate biomarkers and tumors in mice exposed to environmental CS (ECS). To this purpose, we used 263 newborn CD-1 mice born from 27 dams. The whole-body exposure to ECS for 120 days, starting within 12 hr after birth, resulted in an early appearance of preneoplastic lesions in lung, which however tended to attenuate after discontinuing exposure. When the experiment was stopped, after 330 days, the number of lung adenomas was higher in ECS-exposed mice as compared to sham-exposed mice, but such increase was statistically significant only in mice co-exposed to smoke and halogen light mimicking solar irradiation. Moreover, exposure to ECS produced extensive histopathological changes, mainly parenchymatous degeneration, in liver. The alterations produced in both lung and liver require that exposure to ECS starts immediately after birth, no effect being observed when exposure started 8 days later. In contrast, induction by ECS of alterations in the urinary tract, such as microadenomas and adenomas in renal pelvis and kidney, papillary hyperplasia of urothelium, and urinary bladder papillomas, were unrelated to the exposure time after birth. The results obtained with ECS cannot be directly compared to those previously obtained with MCS, since the latter involved shorter daily exposures to more massive CS doses.

Post-genomic methodologies have provided novel tools for evaluating safety and efficacy of cancer chemopreventive agents. We exposed rats to environmental cigarette smoke (ECS) for 28 days, with or without oral administration of N-acetylcysteine (NAC). As assessed by 32P-postlabelling, ECS caused a 10-fold increase of DNA adduct levels, which were significantly reduced by NAC. Of 518 proteins tested by antibody microarray, ECS stimulated 56 activities involved in stress response, protein removal, cell replication, apoptosis, phagocytosis, and immune response. NAC alone did not change the amounts of any protein, whereas it significantly decreased the amounts of 6 ECS-induced proteins. The intensity of expression of 278 related genes, assessed by cDNA microarray, was significantly correlated with protein amounts. These observed molecular alterations, which can be attenuated by NAC, represent in part adaptive responses and in part reflect mechanisms contributing to the pathogenesis of smoke-related diseases, including lung cancer, asthma, chronic bronchitis, and emphysema.

Cigarette smoke plays a major role in the epidemiology of lung cancer, and smoke components have extensively been investigated in carcinogenicity and chemoprevention studies in experimental animals. However, it is much more difficult to reproduce the tumorigenicity of the whole complex mixture in preclinical models. The authors review here some results obtained in their laboratories, dealing with the induction of lung tumors, and genomic and transciptional alterations in smoke-exposed mice. The authors were successful in inducing lung tumors in 4 strains of mice exposed whole-body to environmental cigarette smoke, including Swiss albino, A/J, SKH-1 hairless, and p53 mutant (UL533 x A/J)F1 mice. However, the tumorigenic response was rather weak in all strains. Much more intense were the smoke-induced alterations of a variety of intermediate biomarkers, such as cytogenetic end points in pulmonary alveolar macrophages, bone marrow and peripheral blood erythrocytes; apoptosis, p53 oncoprotein, and proliferating cell nuclear antigen in the bronchial epithelium; bulky DNA adducts, 8-hydroxy-2-deoxyguanosine; multigene expression, and thiobarbituric acid-reactive aldehydes in whole lung and several other organs. Smoke-induced genomic and transcriptional alterations were suitable for evaluating their modulation by chemopreventive agent, as shown in studies using the thiol N-acetylcysteine and the nonsteroidal anti-inflammatory drug sulindac.

Mutations and deletions in p53 are the most common genetic lesions in human cancer,and an extraordinarily high incidence of lung cancer occurs in smokers suffering from Li-Fraumeni syndrome, which is characterized by germ-line inactivation of one p53 allele. In contrast, p53 mutations are infrequent in lung tumors formed in A/J mice. Moreover, despite the dominant role of cigarette smoke in the epidemiology of human lung cancer, it is very difficult to reproduce the lung tumorigenicity of this complex mixture in animal models. We used a transgenic mouse with a dominant-negative p53 mutation to examine the effects of a mutant p53 on smoke-induced lung carcinogenesis in mice. p53 mutant (UL53-3 x A/J)F(1) mice of both genders and their wild-type (wt) littermate controls were exposed whole-body to environmental cigarette smoke (ECS) for up to 9.5 months. Untreated mutant mice of both genders underwent an early stimulus of bronchial cell proliferation, and an age-related formation of DNA adducts in lung and heart. In males, there was an age-related increase of micronucleated normochromatic erythrocytes in peripheral blood and an impairment of body weight gain. These findings underscore a physiological protective role of p53 in wt A/J mice. The response of wt and mutant mice to ECS was similar in terms of oxidative DNA damage in lung and heart, proliferation of the bronchial epithelium, and levels of p53 oncoprotein, as assessed after exposure for 28 days. In contrast, ECS-exposed mutant mice underwent a lower induction of apoptosis in bronchial epithelium, a greater formation of DNA adducts in lung and heart, and a more intense cytogenetic damage, shown by a higher frequency of micronuclei in pulmonary alveolar macrophages and in peripheral blood normochromatic erythrocytes. Interestingly, at the end of the experiment, DNA adducts were not repaired in either wt or mutant mice after discontinuing exposure to ECS for 1 week. A weak but significant increase of lung tumor incidence and multiplicity was induced in p53 mutant (UL53-3 x A/J)F(1) mice after exposure to ECS for either 5 months, followed by recovery in air for 4.5 months, or 9.5 continuative months. Conversely, no tumorigenic effect was observed in their wt littermate controls, carrying a 99.9% A/J background and 5% FVB genome. This contrasts with the weakly positive results obtained in previous studies using wt A/J mice. Thus, in agreement with the results of previous lung tumorigenicity studies performed with the smoke carcinogens benzo(a)pyrene and 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone, (UL53-3 x A/J)F(1) mice carrying a mutant p53 transgene appear to be more sensitive to ECS than the corresponding wt littermate controls. These findings provide evidence that p53 mutations play a role in smoke-related carcinogenesis not only in humans but also in A/J mice.