Abstract 2274: Deregulated Hippo pathway is a potential therapeutic target for advanced gallbladder cancer
Authors: Bizama Carolina , García Patricia , Espinoza Jaime A , Elgueta Nicole , Riquelme Ismael , Alfaro Francisca , Romero Diego , Weber Helga , Leal Pamela , Retamal Javier , Rosa Lorena , Roa Juan Carlos 
Published: July 2016

Gallbladder cancer (GBC) is lethal and aggressive disease characterized by late diagnosis, poor prognosis and lack of effective therapeutic options. An excellent candidate for targeting therapy in cancer is the Hippo signaling pathway that has been reported to be deregulated in different types of cancer and recently has emerged as a master regulator that plays a critical role in multiple processes such as tumorigenesis, apoptosis, tumor stem cell phenotype, drug cell resistance and metastatic potential. However, little is known about the status of the Hippo kinase pathway in human GBC. The aim of this study is determinate the Hippo pathway activity in GBC and evaluate the potential therapeutic role of YAP1 siRNA and the pharmacological inhibitor Verteporfin, a small molecule that inhibit TEAD-YAP interaction. Immunohistochemistry was used to analyze the expression of YAP1 and Survivin, a major downstream effector and transcriptional target gene of Hippo signaling pathway, in tissue microarray containing 198 advanced GBC samples. Then, we performed an exploratory analysis of Hippo pathway activity by qRT- PCR in advanced GBC and cholecystitis samples. The levels of expression of the Hippo core kinase proteins in GBC cell lines was studied by western blot and the inhibition of YAP1 was performed thought specific siRNA and Verteporfin. Immunohistochemistry showed high nuclear expression of YAP1 in vast majority of advanced GBC, which is correlated significantly with nuclear Survivin expression. The 5-year survival rates of patients with survivin-positive cancer were significantly lower compared with survivin-negative cancer patients (p&lt;0.05, Log-rank test). The gene expression analysis showed a significant down-regulation of the Hippo kinase core suppressor genes STK3 (MST2), STK4 (MST1), SAV1, LATS2 and up-regulation of GPCR5A and BIRC5 in GBC tissues compared with cholecystitis. In addition, western blot analysis show high levels of nuclear YAP1 in 4 GBC cells and its expression were associated with a reduction in the phosphorylation status of LATS1 and MOB. Our findings indicate that targeting YAP1 with siRNA reduced mRNA and protein levels of this oncogene in almost 80% and inhibited the clonogenic capacity of GBC cell lines. Otherwise, the in vitro pharmacological inhibition of YAP1 with Verterporfin reduces YAP1 protein in a dose-dependent manner and was associated with down-regulation of survivin. Our results showed that the Hippo- pathway is deregulated in advanced GBC and mediates its oncogenic effects through of attenuation of their suppressor core components, nuclear translocation of YAP1 and up-regulation of survivin expression. Targeting YAP1 by siRNA and Verteporfin leads to inactivation of YAP1 and survivin affecting cancer cell survival capacity. Targeting the Hippo/YAP has the potential to provide a novel strategy for GBC therapy. Research supported by FONDECYT 3140426, 1130204, 11130515, 3140308.

Citation Format: Carolina Bizama, Patricia García, Jaime A Espinoza, Nicole Elgueta, Ismael Riquelme, Francisca Alfaro, Diego Romero, Helga Weber, Pamela Leal, Javier Retamal, Lorena Rosa, Juan Carlos Roa. Deregulated Hippo pathway is a potential therapeutic target for advanced gallbladder cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2274.