Abstract 1483: Metastatic characteristics and radiosensitivity of thyroid carcinoma cells depends on HIF-1 and PI3K signaling in vitro and in vivo
Authors: Burrows Natalie , Babur Muhammad , Ridsdale Sophie , Williams Joseph , Williams Kaye J. , Resch Julia , Brabant Georg 
Published: June 2012

The purpose of this study was to determine the importance of the HIF-1 and PI3K pathways in the development of a) a metastatic phenotype and b) desensitization to radiotherapy, in thyroid carcinomas.

In vitro scratch wound migration assays and cell spreading assays were performed under various oxygen tensions in the presence or absence of two PI3K inhibitors PI-103 and GDC-0941 (GDC-0941 is currently in clinical trials). The role of HIF-1α and PI3K on these processes was also assessed via genetic inhibition of HIF-1α and PI3K by use of a dominant negative variant (dnHIF) and by over expressing WT PTEN in PTEN-null FTC133 cells. For in vivo studies, follicular (FTC133) and anaplastic (8505c) thyroid carcinoma cells were manufactured to stably express eGFP and implanted sub-cutaneously. Mice were treated with PI-103 and GDC-0941 by intra-peritoneal injection and oral gavage. Spontaneous metastatic colonization to the lungs was confirmed by viewing eGFP postive colonies cultured from digested lung tissue and further by immuno-blotting for eGFP. For irradiation studies, cells were exposed to 0,2,4,6 GY external beam radiation.

Both PI3K and hypoxia increased cell migration, cell adhesion and cell spreading on extra-cellular matrix molecules. These processes are key in the development of a metastatic phenotype. Genetic and pharmacological inhibition of both PI3K and HIF-1α reduced the migratory, adhesive and cell spreading potential of thyroid carcinoma cells under varying oxygen tensions. Additionally, pharmacological and genetic inhibition of PI3K and HIF-1α reduced both PI3K and HIF-1 activity resulting in reduced activation of PI3K target proteins (pAKT, pGSK-3β) and reduced expression of HIF-1 target genes (CA-9, VEGF, LDH-A, GLUT-1). In vivo, PI-103 and GDC-0941 reduced PI3K and HIF-1α activity as well as PI3K and HIF-1 target genes in primary follicular and anaplastic tumors. Importantly, mice bearing dnHIF-FTC133 tumors and those treated with GDC-0941 had reduced number of metastatic colonies in the lungs of follicular thyroid tumor bearing mice.

Radiation induced HIF-1α activity and expression. GDC-0941 combined with radiation blocked HIF-1 induction, prolonged DNA double-strand breaks and reduced clonogenic survival suggesting a radio-sensitising effect.

These data link PI3K, HIF-1 activation and aggressive disease in thyroid carcinoma and suggest PI3K may be an important therapeutic target. One attractive approach would be combination therapy with external beam radiation. The latter is the first line treatment in patients suffering from anaplastic thyroid carcinoma but is seldom successful. With the known desensitizing effects of HIF-1 and PI3K activity on radiation treatment, a combined approach involving both radiation and a PI3K inhibitor may improve both the therapeutic response within the local tumor and reduce metastatic potential.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1483. doi:10.1158/1538-7445.AM2011-1483