Abstract C78: The mu opioid receptor regulates Lewis lung carcinoma tumor growth and metastasis

Abstract

Abstract Introduction: Expression of the mu opioid receptor (MOR) is increased in patients with non-small cell lung cancer (NSCLC), a disease with poor prognosis and limited therapies. Previous work by our laboratory and others suggested a role of opioids in several aspects of tumor growth (Anticancer Res 2009;29:3195–3205, Mol Cancer Ther 2008;7:1669–1679, Cancer Res 2002;62:4491–4498). In this study, we investigated MOR as a potential therapeutic target for lung carcinoma. Methods: Lewis lung carcinoma (LLC) cells were treated with MOR siRNA or the peripheral MOR antagonist, methylnaltrexone (MNTX, 250 nM), prior to the addition of EGF (10 ng/ml), IGF (10 ng/ml), DAMGO (1 nM), morphine (1 nM) or serum (1, 5 or 10%). In vitro functional (cell proliferation and invasion) and biochemical studies (immunoblotting) were then conducted. For in vivo assays, C57BL/6J mice were injected intravenously with dual color (GFP-RFP labeled) LLC cells, with or without MOR siRNA treatment. In another experiment, MOR knockout as well as wildtype control mice were injected with LLC cells (subcutaneously into the flank) and followed for 12 weeks. In a parallel experiment, LLC tumor bearing C57BL/6J mice received continuous infusion of MNTX (10 mg/kg/day) for 2 weeks. Tumor growth and lung metastasis were evaluated using tumor volume measurements and/or in vivo fluorescent microscopy (Olympus OV-100) with or without intravenous injection of ProSense and/or MMP Sense probes. Results: Our data indicate that LLC cells have ∼5 fold increased expression of MOR (compared to primary lung epithelial or BEAS-2B cells). Inhibition of MOR with siRNA or MNTX treatment reduced in vitro LLC proliferation (90%) and invasion (50–75%). In vivo lung metastasis was reduced by ∼75% in wildtype C57BL/6J mice with LLC lacking MOR (siRNA) versus control siRNA-treated LLC (3 weeks post-i.v. injection, quantitated with OV-100). In addition, primary LLC tumor volume was substantially reduced (>90%) in MOR knockout mice compared to wildtype mice (flank injection). Finally, we observed that continuous infusion of MNTX (10 mg/kg/day) in mice with pre-existing LLC primary tumors attenuates further tumor growth. Conclusion: We have shown that MOR is a potential therapeutic target for inhibition of LLC proliferation, invasion and metastasis. In addition, MNTX can attenuate LLC primary tumor growth. Further study of MNTX as a potential therapeutic agent is warranted. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C78.