Role of X-Linked Inhibitor of Apoptosis as a Prognostic Marker and Therapeutic Target in Papillary Thyroid Carcinoma.

CONTEXT Papillary thyroid cancer (PTC) is the second most common cancer in females in Saudi Arabia. However, the pathogenesis of PTC is still not fully elucidated. OBJECTIVE To identify potential genes that play important role in progression of PTC, we studied the role of X-linked inhibitor of apoptosis protein (XIAP) as a potential prognostic marker and therapeutic target in a large cohort of PTC samples and cell lines. DESIGN A DNA microarray chip was used to screen for gene copy number. XIAP expression was assessed by immunohistochemistry in a tissue microarray format on a cohort of 1022 clinical samples. In vitro and in vivo studies were performed using Embelin and/or LY294002 on PTC cell lines. RESULTS XIAP was found to be amplified in 14 of 29 and overexpressed in 48.8% of PTC cases. XIAP overexpression was significantly associated with old age, extrathyroidal extension, tumor size, nodal involvement, tall-cell variant, advanced stage disease, and significantly poor disease-free survival (P = .0341). XIAP was also significantly associated with phosphorylated AKT (P < .0001), Bcl-Xl (P < .0001), and Ki67 (P = .0006) proteins. Embelin treatment caused growth inhibition and apoptosis in PTC cell lines and induced tumor regression in PTC xenograft in nude mice. Finally, the combination of suboptimal doses of Embelin and LY294002 induced a synergistic apoptotic response in PTC cells. CONCLUSION XIAP dysregulation in PTC confers an aggressive phenotype with poor outcome. In vitro and in vivo studies using an XIAP inhibitor suggest that this subgroup of PTC with overexpression of XIAP can be therapeutically targeted, either alone or in combination, to induce efficient apoptosis in these cancers.