Abstract B43: Targeting tumor microenvironment for treatment of K-ras mutant lung cancer

Activating mutations of K-ras are one of the most common molecular alterations associated with lung cancer development. Several attempts to develop therapies directly targeting K-ras have been failed thus far, clearly state the need for new strategies to bring clinical benefits to patients displaying such a molecular profile. Using a conditional K-ras mutant lung cancer mouse model (CC-LR) we previously showed that K-ras mutated lung tumors have intrinsic inflammatory characteristics associated with NF-κB pathway activation. Therefore, CC-LR mice were crossed with IKK-β f/f mice to develop a K-ras mutant mouse with lack of NF-κB activity in airway epithelium. This changed the bronchoalveolar lavage fluid (BALF) cellular component of the CC-LR mice (mostly by reduction of macrophages), and resulted in a ∼70% (3.4-fold) reduction in lung surface tumor number. Lung of CC-LR mice also shows high protein level of IL-6 (downstream to NF-κB activation) and increased STAT3 gene expression (downstream signal to IL-6) plus infiltration of myeloid and Th17 cells. Accordingly, we genetically ablated IL-6 in the CC-LR mice. This significantly inhibited lung cancer development (1.7-fold, 41%) suggesting a role for IL-6 mediated signaling in tumor promotion probably through STAT3 pathway activation. IL-6 and STAT3 are required for differentiation of Th17 cells from naive T cells. Th17 cells mostly produce IL-17A that binds to the IL-17 receptor (IL-17R). IL-17R signaling is required for lung CXC chemokine expression and myeloid cell recruitment. Furthermore, IL-17A induces more production of IL-6 by epithelial cells. So, CC-LR mice were crossed with IL-17A KO mice. Lack of IL-17A in CC-LR mice resulted in a ∼70% (3.4-fold) tumor reduction. It also decreased the expression of pro-inflammatory mediators and reduced recruitment of myeloid cells. These reults suggest that K-ras initiated airway inflammation through NF-κB mediated activation of the IL-6/STAT3/Th17 signaling promotes lung tumorigenesis, and introduce IL-6 as a potential druggable target for lung cancer patients who harbor K-ras mutations. This prompted us to block IL-6 pathway using a monoclonal anti-IL-6 immunotherapy in our K-ras mutant model. Six week old CC-LR mice were injected intraperitoneally with 20 mg/kg dose of an anti-IL-6 monoclonal IgG1 antibody, twice a week, for a period of 8 weeks. Flowcytometry and qPCR analysis of total lung in non-treated CC-LR mice showed 2-fold increase in the population of tumor associated macrophage (TAM) and Arginase-1 mRNA expression (3 fold) during tumor progression from age 6 weeks to 14 weeks suggesting that epithelial signal initiated by K-ras mutation dictates an inflammatory type 2 pro-tumor fate for lung microenvironment. We further found that anti-IL-6 treatment suppressed tumor development by ∼78% (4.6-fold) in CC-LR mice with a significant reduction in the expression levels of Ki-67, VEGF, MMP9, CD31 and phospho-STAT3 in lung tissue. It also reduced TGFβ and KC protein levels in BALF with a significant decrease in Arginase1 mRNA expression (3-fold) and TAM population (5-fold) in total lung homogenate. We conclude that K-ras mutation drives an immunosuppressive pro-tumor response and blocking IL-6 shifts this to an anti-tumor lung microenvironment. Therefore we propose pharmacological targeting of IL-6 as a potential therapeutic strategy alone or in combination with conventional cytotoxic therapy for lung cancer patients with K-ras mutation. Funded by: American Cancer Society, RSG-11-115-01-CNE, and American Lung Association/LUNGevity Foundation, LCD-114696-N Citation Format: Mauricio da Silva Caetano, Seon Hee Chang, Amber M. Cumpian, Soudabeh Daliri, Maria Miguelina De La Garza, Cesar E. Ochoa, Chen Dong, Seyed Javad Moghaddam. Targeting tumor microenvironment for treatment of K-ras mutant lung cancer. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B43. doi: 10.1158/1557-3125.RASONC14-B43