Abstract 3668: Tumor-associated macrophages (TAMs) promote murine neuroblastoma tumor growth through upregulation of MYC and independent of IL6 expression

Background: The concept of tumor-promoting inflammation is a recognized enabling characteristic of cancers. Our group has demonstrated the significance of inflammation-related genes in poor outcome of children diagnosed with metastatic MYCN non-amplified neuroblastoma (NBL-NA). We investigated the effect of TAMs on neuroblastoma growth using a novel murine model. Methods: We have established a novel 100% penetrant NBL-NA murine model driven by SV40's Large T-antigen (NBL-Tag) and characterized expression of immune-related genes in tumors at various developmental stages. Single cell suspensions of murine tumors were analyzed using flow cytometry for determination of immune cells frequency and IL6 levels. NBL-Tag mice were crossed with IL6 knockout mice (NBL-Tag/IL6-/-) to investigate the role of IL6 in tumor pathogenesis. Results: NBL-Tag tumor growth coincided with IL6 levels becoming detectable and increasing in blood. Immune-related gene expression analysis of NBL-Tag adrenal glands in mice at pre-tumor development age (4, 8 and 12 week old) showed age-dependent increase in expression of IL6 and CCL2 (MCP1) compared to wild-type adrenal glands demonstrating early monocyte chemotaxis and establishment of a pro-inflammatory niche. FACS of tumors showed high expression of IL6, and infiltration by IL6-producing TAMs. In vitro co-culture of peritoneal macrophages from wild type mice increased proliferation of a NBL-Tag mice driven cell line (NBT2) by average of 50% over its basal rate, as measured by Brdu incorporation. This effect coincided with two-fold increase in IL6 protein level in the co-cultured media. However, the proliferative changes were only partially reversed by blocking IL6, suggesting other soluble factors also contribute to the observed effects. IL6 genetic ablation studies were conducted to generate NBL-Tag/IL6-/- mice, which convincingly demonstrated IL6 was not required for tumor growth and development. Macrophages from IL6-/- mice increased in vitro proliferation of tumor to similar levels as those from wild-type mice, while IHC staining of NBL-Tag/IL6-/- tumors revealed similar level of TAM infiltration and positivity for phospo-STAT3, indicating an IL6-independent pathway for STAT3 activation. Lastly, gene expression analyses revealed upregulation of MYC in tumor cells during co-culture and was confirmed by western analysis. Conclusions: This study demonstrates the recruitment and growth-promoting effects of TAMs in early pathogenesis of neuroblastoma in a novel MYCN non-amplified murine model. The macrophage and neuroblastoma cell cross-talk lead to tumor cell proliferation with phosphorylation of STAT3 and MYC upregulation in tumor cells. These effects were found to be independent of IL6 activity. Citation Format: Michael D. Hadjidaniel, Soheila Shirinbak, Sakunthala Muthugounder, Long Hung, Michael Sheard, Janahan Gnanachandran, Jin Kim, Richard Sposto, Hiroyuki Shimada, Shahab Asgharzadeh. Tumor-associated macrophages (TAMs) promote murine neuroblastoma tumor growth through upregulation of MYC and independent of IL6 expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3668. doi:10.1158/1538-7445.AM2014-3668