Abstract B32: High-throughput chemical screening reveals YAP-mediated alterations in drug sensitivities
Authors: Bondesson Andrew J. , Miyaki Aya , Shin Stella , Ceribelli Michele , Thomas Craig J. , Gujral Taran S. 
Published: September 2020

Abstract
The Hippo pathway is evolutionarily conserved and plays a critical role in determining organ size and in tumorigenesis. Aberrant genetic alterations in the Hippo pathway genes including LATS1/2, NF2, and STK11, as well as increased expression and activity of YAP have been found in some human cancers. Loss of function of Hippo genes results in increased nuclear localization of YAP, which promotes cell proliferation, migration, and invasion. Despite our increasing understanding of molecular phenotypes associated with Hippo aberration and excess YAP activity, there are as yet no FDA-approved therapies targeting this pathway, representing a large, unmet patient need. Previous work from our lab has established an additional role for the pathway in altering cellular response to gemcitabine in pancreatic cancer (PNAS 2017). To uncover therapeutic vulnerabilities caused by increased YAP activity, we performed a quantitative, high-throughput screen using the Mechanism Interrogation PlatE (MIPE) library of compounds. All the drugs in this library are relevant for clinical use in cancer and have known mechanisms of action. Annotated gene families represented in the MIPE library include kinases, GPCRs, and ion channels as well as broad cellular mechanisms including modulators of nuclear receptor transcription factors, lipid metabolism, histone epigenetic machinery, and apoptosis. The screen was carried out in twenty 1,536-well plates consisting of 2,154 compounds at nine different doses on both Panc02.13 cells expressing GFP or constitutively active YAP (YAPS6A). Preliminary data have confirmed our previous work in YAP’s role in increasing sensitivity to gemcitabine and several other chemotherapeutics. Pathway enrichment analysis of drugs based on similar mechanism of action allowed us to identify specific signaling nodes and cellular processes that present points of vulnerability or resistance caused by excess YAP activity. We discovered a profound increase in cellular resistance to MEK inhibitors. AC50 values for seventeen out of eighteen MEK inhibitors tested were on average more than four-fold higher in YAPS6A-expressing cells. We have validated these results in several other pancreatic cell lines in both 2D and 3D spheroid assays. Molecular analysis revealed that nuclear YAP causes sustained PI3K/AKT activation, providing a plausible compensatory pathway for cell survival. Moreover, treatment with PI3K/AKT inhibitors can abrogate this YAP-induced resistance to MEK inhibitors. Overall our data are consistent with previous findings that increases in PI3K and AKT signaling function as an escape mechanism to MEK inhibition. Our data suggest that increased YAP activity may represent a distinct molecular mechanism for how this escape is accomplished in refractory cancers. Cotargeting PI3K/AKT may thus provide therapeutic options for patients carrying mutations in Hippo pathway genes.
Citation Format: Andrew J. Bondesson, Aya Miyaki, Stella Shin, Michele Ceribelli, Craig J. Thomas, Taran S. Gujral. High-throughput chemical screening reveals YAP-mediated alterations in drug sensitivities [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr B32.