Abstract 4044: Rapamycin targets Interleukin 6 (IL-6) expression and suppresses endothelial cell invasion stimulated by tumor cells
Authors: Ekshyyan Oleksandr Y. , Rong Xiaohua , Moore-Medlin Tara , Ma Xiaohui , Alexander Jonathan Steven , Nathan Cherie-Ann O. 
Published: July 2016

Background: Previously we demonstrated that mTOR inhibitors have potent antiangiogenic and anti-lymphangiogenic effects in addition to their growth inhibitory effects in head and neck squamous cell carcinoma (HNSCC). Lymphatogenous spread is a significant problem and much more predominant in HNSCC than hematogenous spread. In this study we evaluated the effects of rapamycin on targeting tumor-stroma crosstalk in HNSCC.

Methods: HNSCC tumor cells (FaDu), human blood microvascular endothelial cells (HMEC-1), and human lymphatic endothelial cells (HMEC-1A) were co-cultured in various combinations using transwell cell culture inserts to study tumor-stroma crosstalk and the effects of mTOR inhibitor rapamycin. Cell invasion was assessed using transwell inserts with an 8.0 μm pore size. Levels of various growth factors and cytokines in cell culture media were measured using Milliplex bead immunoassay (EMD Millipore) and ELISA assay (R&D Systems).

Results: We found that conditioned media collected from tumor cells or co-culture with tumor cells significantly increased the invasiveness of lymphatic and blood vascular endothelial cells (p &lt; 0.05), while there was no effect of conditioned media collected from endothelial cell cultures or co-culture with endothelial cells on tumor cell invasiveness. Conditioned media collected from tumor cell cultures increased the invasiveness of endothelial cells by almost two-fold.

Next we evaluated the effects of rapamycin on the baseline and tumor cell stimulated (co-culture or conditioned media) invasiveness of endothelial cells. There was a significant effect of rapamycin on both baseline and tumor cell stimulated invasiveness of endothelial cells. While rapamycin had a moderate effect on the levels of several growth factors and cytokines tested (sVEGFR-1, HGF, FGF-2, TNF-alpha) there was a significant effect of the drug on the levels of IL-6. Importantly the level of IL-6 secreted in media increased significantly in tumor-endothelial cell co-culture compared to monocultures. Rapamycin showed only modest effect on the invasiveness of endothelial cells transfected with rapamycin-resistant mTOR as expected. There was no significant effect of rapamycin on secretion of IL-6 by tumor cells and endothelial cells transfected with rapamycin-resistant mTOR.

Conclusions: HNSCC cells produce chemotactic stimuli that promote endothelial cell invasion toward tumor cells that can stimulate angio- and lymphagiogenesis. Rapamycin effectively reverted the stimulatory effect of cytokines secreted by tumor cells on endothelial cell. IL-6 is being evaluated as an important target in HNSCC and a potential biomarker of response to mTOR inhibitor therapy.

Citation Format: Oleksandr Y. Ekshyyan, Xiaohua Rong, Tara Moore-Medlin, Xiaohui Ma, Jonathan Steven Alexander, Cherie-Ann O. Nathan. Rapamycin targets Interleukin 6 (IL-6) expression and suppresses endothelial cell invasion stimulated by tumor cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4044.