Endocrine Abstracts

Background: Anaplastic thyroid-carcinomas (ATC) and a subset of papillary (PTC) and follicular (FTC) thyroid carcinomas behave aggressively showing metastatic spread and radio-resistance. Both the PI3K and HIF pathways are associated with aggressiveness and metastasis in thyroid carcinoma.

Aims: To assess if the PI3K/HIF pathways contribute to radio-resistance and assess the effect of PI3K/HIF inhibition on radio-sensitivity and metastatic behaviour of thyroid-carcinoma cells (8505c, FTC133, WRO, BcPAP) in vitro and in vivo. Methods:PI3K was inhibited pharmacologically (via PI-103/GDC-0941) and genetically (via PTEN rescue in PTEN-null FTC133 cells). HIF-1 activity was inhibited using a dominant-negative variant of HIF-1α (dnHIF). Cells were irradiated with 0,2,4 and 6Gy with/without PI-103/GDC-0941 under normoxia/hypoxia (1% oxygen)/anoxia. In vitro DNA double-stranded breaks (DSBs) were assessed by γH2AX expression, HIF-1α activity by use of luciferase reporter assays and migration by use of the scratch-wound migration method. Activity of PI3K and ATM, a protein critically involved in the DNA damage response, was analysed by pAKT/pATM expression. In vivo, mice bearing FTC-xenografts were exposed to 5×2Gy with/without GDC-0941 (orally), tumour pAKT expression and volumes were assessed. Spontaneous-lung metastasis was quantified by clonogenic assay.

Results: GDC-0941, dnHIF and PTEN rescue increased and prolonged radiation-induced DNA-DSBs under normoxia/anoxia in carcinoma cells and had no effect on immortalised ‘normal’ thyroid cells. Mechanistically this was via inhibition of pATM, with the degree of inhibition being dependent on oxygen environment and cell-type. Radiation-induced HIF-1alpha activity/expression in normoxic/anoxia FTC133s. GDC-0941 reduced HIF-1α activity and clonogenicity in irradiated FTC133 and 8505c cells. Radiation increased FTC migration, which has important therapeutic implications. PI-103/GDC-041 and PTEN rescue inhibited migration in irradiated cells. GDC-0941 increased growth delay of irradiated tumours and reduced radiation-induced pAKT and metastasis in FTC-xenografted mice. Conclusions: These data link PI3K/HIF and ATM in radio-resistance of thyroid-carcinoma. PI3K inhibitors combined with radiotherapy may improve therapeutic response two-fold: By radio-sensitising thyroid-tumour cells and inhibiting metastasis.

Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding: Declaration of Funding: Cancer Research UK (C7820/ A8696), EU FP7 Metoxia Grant agreement no. 222741.