Abstract LB-037: Upregulation of Rab, a member of the Ras gene family, is associated with accelerated lung tumor progression in mice exposed in utero to secondhand smoke

Abstract

Abstract Rationale: While second-hand smoke (SHS) exposure is responsible for more than 7,000 lung cancer deaths annually among US nonsmokers, it is unclear whether there is an association between in utero SHS and lung cancer. We have reported that lungs of mice exposed in utero to SHS and as adults to ovalbumin exhibited up-regulation of miR-155-5p, miR-21-3p and miR-18a-5p and down-regulation of 16 tumor suppressor genes, all predicted targets of these 3 miRNAs, which have been characterized as oncogenic miRNAs. In this pilot study, we investigated whether in utero SHS exposure promotes an oncogenic milieu in lungs of adult mice. Methods: Pregnant Balb/c mice were exposed from gestational days 6 - 19 to 10 mg/m3 of SHS or filtered air. From 16-19 weeks of age, male offspring were treated with 4 weekly intraperitoneal injections of urethane (1 g/kg) or saline. At 44 weeks of age, mice were sacrificed. Broncho-alveolar lavage fluids (BALF) were collected for assessment of inflammatory responses and oxidative stress. Tumors were analyzed for number, size, volume, and histopathological classification. Lung RNA sequencing was also performed. Results: In utero SHS-adult urethane (SU) treatment significantly (p < 0.05) increased the number of tumors larger than 2 mm, and their volumes, compared to their respective air-urethane (AU)-treated controls. Lungs of SU mice also showed significant increases in percentages of BALF lymphocytes and levels of 8-isoprostane, a biomarker of oxidative stress. Bronchial-alveolar carcinomas were present in all SU mice (mean = 3.8 carcinomas/mouse) compared to 85% of AU mice (mean = 2.2 carcinomas/mouse). Moreover, 5 intrapulmonary metastases were observed in the SU group vs. 1 in the AU group. A total of 24 genes were differently expressed in lungs of SU vs. AU mice. These dysregulated genes clustered mainly into 3 functional groups: regulation of cellular processes, protein binding and intracellular signaling cascade. Of these genes, 13 were up-regulated, including the Ras-associated binding GTPase (Rab), a member of the Ras oncogene family-like 2A, which showed a 5-fold increase in SU mice. Conclusion: In this lung cancer model, in utero SHS exposure accelerated tumor growth, created chronic inflammation, increased oxidative stress levels, and promoted the development of carcinomas and intrapulmonary metastases. Our results also suggest that the mechanisms by which in utero SHS exposure accelerates lung tumor progression and malignant transformation are associated with 3 functional clusters of genes that include the over-expression of Rab. Overall, our data indicate that in utero SHS exposure aggravates adult responses to carcinogenic stimuli by promoting an oncogenic milieu in lungs of male mice. Citation Format: Alexandra Noel, Rui Xiao, Zakia Perveen, Viviana Le Donne, Daniel B. Paulsen, Arthur L. Penn. Upregulation of Rab, a member of the Ras gene family, is associated with accelerated lung tumor progression in mice exposed in utero to secondhand smoke. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-037.