Local deficiency of Insulin-like growth factor-I receptor (IGF-IR) modulates the initial steps of experimental pheochromocytoma (Pheo) development

MARTIN AYELEN; FERNÁNDEZ MARÍA CELIA; MATHÓ CECILIA; VENARA MARCELA; PENNISI PATRICIA

Milan

Congreso; . 9th Joint Meeting of Pediatric Endocrinology, ESPE, PES, APEG, APPES, ASPAE, JSPE, SLEP; 2013

ESPE, PES, APEG, APPES, ASPAE, JSPE, SLEP

Background: We have shown that circulating IGF-I has a critical role in maintaining tumor phenotype and survival of already transformed pheochromocytoma cells (MPC4/30), and is required for the initial establishment of these tumors. Objective and hypotheses: To investigate the role of the local IGF-I/IGF-IR system that is present in the tumor microenvironment including endothelial cells, fibroblasts and extracellular matrix. Methods: We used a murine model of pheochromocytoma by sc injection of 1x106 MPC4/30 cells in heterozygous IGF-IR knockout mice (IGF-IR+/n). Results: We found that the time of tumor appearance was delayed in IGFIR+/n group (n=53) compared to control IGF-IR+/+ mice (C,n=79) [6 vs 5 weeks,Hazard Ratio:0.27;95%CI:0.16- 0.46]. Additionally, 9.43% of IGFIR+/n mice did not develop tumor (p< 0.0001,Logrank Test,IGF-IR+/nvs.C) while proliferation assessed by BrdU incorporation, vascularization measured as the number of positive endothelial cells for Von Willebrand factor and tumor volume did not differ between the groups. To evaluate the impact of IGF-IR deficiency in the initial steps of pheo development, primary fibroblast cultures from IGF-IR+/n and C mice were used to generate conditioned media (CM) and differential matrix on which MPC4/30 were seeded. In vitro MPC4/30 cell proliferation was higher when cultured with CM from C murine fibroblasts (20±1 vs 13±2 x104cells,C vs IGF-IR+/n,day 7,p= 0.025). Moreover, similar results were obtained when MPC4/30 cell were cultured in differential matrix generated by C murine fibroblasts(23±2 vs 17±1x104cells,C vs IGFIR+/n,day 5,p< 0.05) with a significantly increased of BrdU uptake on day 5 (38±2% vs 28±2% positive nuclei,C vs IGF-IR+/n,p < 0.005). Conclusions: Our data suggest that IGF-I through its type 1 IGF-IR may be involved in early stages of tumor establishment, contributing to tumor cells anchorage by interaction with both matrix and soluble factors produced by tumor microenvironment fibroblasts.