The Effect of Angiogenesis Inhibition on Tumor-Associated Granulocytes in an Orthotopic Model of High-Risk Neuroblastoma

Background: Neuroblastoma is the most common extracranial solid tumor in children. The survival rate in high-risk neuroblastoma is less than 50 % despite intensive multimodal therapy, and there is thus an immense need for new treatment options. In a previous preclinical study conducted at Uppsala University, treatment with sunitinib was found to inhibit tumor growth and angiogenesis in an orthotopic model of high-risk neuroblastoma. Aim: The present study aimed to further explore the effect of sunitinib on tumor stroma, focusing on whether it was possible to detect and quantify tumor-associated neutrophils (TANs) in tumor sections from the above-mentioned study using immunohistochemistry (IHC). Methods: Tissue sections from formalin-fixated paraffin-embedded tumors were stained with anti-Ly-6G/Ly-6C, anti-ITGAM, or hematoxylin-eosin, and the number of granulocytes was quantified manually using a light microscope. An independent samples two-tailed t-test was used for statistical analysis. Results: The average number of granulocytes increased by 40 % in animals treated with sunitinib compared to control animals (p = 0.003) in hematoxylin-eosin stained tumor sections of orthotopic neuroblastomas. The results from the staining with anti-Ly-6G/Ly-6C or anti-ITGAM, on the other hand, were impossible to quantify due to the high background staining despite the concentration of antibody used. Conclusion: In conclusion, this report indicates that the density of TANs in an orthotopic murine neuroblastoma model is increased by treatment with sunitinib. However, to confirm this result, the study should be repeated once a reliable IHC method for the detection of TANs has been developed