Abstract 2616: The immunoproteasome subunit LMP2 as a novel therapeutic target for non-small cell lung cancer

Introduction: Lung cancer, although not the most commonly diagnosed form of cancer, is the leading cause of cancer deaths in the US. Unfortunately, standard chemotherapeutic treatments for lung cancer are largely ineffective and, thus, novel approaches are urgently needed to improve clinical outcomes. Targeted therapies are currently being explored, including combining bortezomib, a general proteasome inhibitor, with other therapies. The immunoproteasome is an alternative form of the proteasome and has been shown to play an important role in a number of diseases including cancer. We have previously developed ‘UK-101’, a small molecule that selectively inhibits the immunoproteasome catalytic subunit LMP2. In our present study, we investigate the therapeutic potential of the LMP2-targeting approach in lung cancer. Experimental Procedures: The expression and cellular localization of LMP2 was evaluated in primary non-small cell lung cancer (NSCLC) tissues via immunohistochemistry (IHC). Established lung cancer cell lines were likewise examined using western blotting (WB) and immunofluorescence (IF). A panel of NSCLC cell lines were selected for further analysis using UK-101 and the general proteasome inhibitors epoxomicin and bortezomib. Upon treatment with these inhibitors, cell viability was measured using the MTS assay while proteasome activity was interrogated using Suc-LLVY-aminoluciferin. Apoptosis markers were examined to determine the mechanism of UK-101-induced loss of cell viability. Finally, the presence of a naturally occurring LMP2 genetic polymorphism (Arg>His at codon 60) in the NSCLC cell lines was determined using restriction fragment length polymorphism analysis. Data Summary: Our WB and IHC analyses indicated that LMP2 is substantially upregulated in primary NSCLC tissues as well as established NSCLC cell lines compared to nonmalignant lung tissues and small cell lung cancer cell lines. IF and IHC analyses showed LMP2 localization throughout the cells, including overlap with nuclear staining in both. UK-101 treatment led to a covalent modification of LMP2 and decreased proteasomal activity. In addition, UK-101 decreased cell viability and induced apoptotic cell death in NSCLC cells expressing LMP2. The LMP2 polymorphism at codon 60 did not appear to influence the proteasomal activity or cellular sensitivity to UK-101, epoxomicin, or bortezomib in these NSCLC cell lines. Conclusion: Our results show that LMP2 is upregulated in NSCLC and that the targeted inhibition of LMP2 using UK-101 induces apoptotic cell death in NSCLC cell lines. Taken together, these results suggest that LMP2 may be a potential therapeutic target for the treatment of NSCLC with lesser systemic toxicity than general proteasome inhibitors. Further studies are warranted to identify molecular factors impacting the effectiveness of the immunoproteasome-targeting approaches in NSCLC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2616. doi:10.1158/1538-7445.AM2011-2616