Abstract 4843: Inhibition of autophagy for the treatment of lung cancer
Authors: Roos Rebecca , Peyton Michael , Zachariah Sunny , Minna John D. 
Published: February 2011

Recent studies indicate that autophagy plays an important role in cancer pathogenesis, and therefore may be a good target for cancer therapies. However, the role of autophagy is complex and it is possible that early in pathogenesis autophagy plays a role in tumor suppression while in later stages it may play a role in tumor progression. One hypothesis is that cancer cells use autophagy as a protective mechanism to overcome stress induced by chemotherapy. While there has been some success in enhancing the efficacy of chemotherapy treatment by targeting autophagy in some cancer types, very little is known about the potential benefits of autophagy targeting drugs in the treatment of lung cancer. In order to determine the efficacy of autophagy inhibition in the treatment of lung cancer, the autophagy inhibitor chloroquine was used in combination with several standard chemotherapy agents to treat a panel of non-small cell lung cancer (NSCLC) lines. Drug response to chloroquine alone, as well as in combination with cisplatin, erlotinib, or paclitaxel was determined using a five day MTS assay performed in 96 well microtiter plates. Synergy, additivity, or antagonism was determined by calculating the combination index for combined chloroquine (using both 1 and 10 uM) plus chemotherapy or EGFR targeted treatments. In tests of chloroquine as a single agent in 50 NSCLC lines (representing the complete spectrum of oncogenotypes such as KRAS, EGFR, STK11/LKB1, PTEN, and p53 mutations) IC50 values ranged from 9 to 125uM. Autophagosome formation can be observed with immunoblotting by monitoring the conversion of the protein LC3 to its membrane bound phosphatidylethanolamine (PE) conjugated form. Western blotting experiments were performed to demonstrate that in every case NSCLCs treated with 1uM chloroquine showed inhibition of the degradation of autophagosomes, thereby preventing autophagic flux. Of the NSCLCs tested with combined chloroquine + chemotherapy, only a few showed sensitization to cisplatin (2/12) or to erlotinib (3/8, two with EGFR mutations), while no sensitization was found to paclitaxel. Liquid colony formation assays verified the results found by mass culture MTS assay, except in one case where sensitization to cisplatin was not seen with chloroquine addition, but was seen by MTS assay. In all cases the sensitization was &lt;10 fold. Studies of standard doublet chemotherapy for NSCLC (carboplatin + paclitaxel, cisplatin + gemcitabine, and cisplatin + pemetrexed) with chloroquine are underway. We conclude that: chloroquine at clinically achievable concentrations (1 uM) inhibits autophagy in NSCLCs; NSCLCs representing all oncogenotypes demonstrate a narrow spectrum of response to chloroquine alone; and that only occasional NSCLCs show chloroquine sensitization to single agent chemotherapy or erlotinib, indicating the need for biomarker signatures predicting which NSCLCs would benefit from chloroquine treatment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4843.