Abstract 3587: Polycyclic aromatic hydrocarbons exhibit differential tumor promoting properties through mitogen activated protein kinases and inhibition of gap junctions in murine lung cells.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants as well as major components of tobacco smoke. Exposure to PAHs represents a significant health concern due to their association with a variety of cancer endpoints. While a majority of research has focused on the ability of the high molecular weight PAHs to act as carcinogens through their ability to bind and adduct DNA, recent evidence suggests that the low molecular weight PAHs, two to four ring compounds, may act through distinct mechanisms to promote, rather than initiate, neoplasia. We evaluated five sidestream smoke PAHs, 1-Methylanthracene (1-MeA) and 2 Methlyanthracene (2-MeA), Phenanthrene (Phe) and Anthracene (A) and Fluoranthene (Flthn) for their ability to (1) inhibit gap junction intercellular communication (GJIC), (2) with a concomitant effect on the gap junction protein Connexin 43 (Cxn43) and (3) to activate mitogen activated protein kinases (MAPK) in murine lung cells. Since both dysregulation of GJIC and activation of MAPK have been previously reported to contribute to tumor promotion, these pathways represent potential mechanistic targets for PAH perturbation. Murine C10 cells (a non-tumorigenic type II alveolar pneumocyte, and progenitor cell type of lung adenocarcinoma) were used to assess the effects of these low molecular weight PAHs on GJIC and MAPKs over a time course of 15 minutes to 4 hours. Detection of MAPKs and Connexin 43 protein was determined by immunoblot, and GJIC was assessed by a scrap-load dye transfer assay. Pathway specific antagonists were used to further elucidate the mechanism by which 1-MeA 2-MeA, Phe, A, and Flthn inhibited GJIC in a dose and time dependent manner while the isomers, 2-MeA and A, did not. With 1-MeA, this inhibition was prevented by blocking either the phosphotidylcholine-phospholipase or p38 pathway, while inhibiting the MAP kinase kinase (MEK) pathway had no effect. Treatment with 1-MeA also activated ERK1/2 and p38 MAP kinases and also decreased the overall amount of Connexin 43, the major lung connexin, in a time-dependent manner. The ability of 1-MeA to both inhibit GJIC as well as activate MAPKs supports a role for low molecular weight tobacco-smoke PAHs to act as tumor promoters in lung cells, and is consistent with previous studies that suggest these compounds may act as tumor promoters in liver cells. The differences observed between 1-MeA and 2-MeA and Phe and A suggests that the ability of low molecular weight PAHs to inhibit GJIC and activate MAPKs is highly dependent on chemical structure. Such structure-activity relationships are often indicative of discrete toxicological mechanisms. Citation Format: Ross S. Osgood, Thomas Hill, Katherine L. Helms, Pavel Babica, Brad L. Upham, Alison K. Bauer. Polycyclic aromatic hydrocarbons exhibit differential tumor promoting properties through mitogen activated protein kinases and inhibition of gap junctions in murine lung cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3587. doi:10.1158/1538-7445.AM2013-3587