Abstract 4501: Novel EHE PDX model used for drug sensitivity
Authors: Krishnan Sandhya , Porter Robert , Truong Danh , Lamhamedi-Cherradi Salah-Eddine , Grela Krzysztof , Zielinski Rafal , Landers Sharon , Ravi Vinod , Ludwig Joseph A. 
Published: April 2023

Abstract
EHE is a low-to-intermediate grade angiocentric non-vasogenic tumor that exhibits a wide survival range dependent upon tumor size, stage, and location. Most tumors originate in the lung (37%), soft tissue (20%), or liver (16%), and those with multifocal peritoneal or pleural spread have a 5-year survival rate of ~22%. Solitary lesions are often resected for curative intent. However, treatment options for those with metastatic disease at diagnosis remain less well-defined. Generally, the chemo-resistant slow-growing soft-tissue EHEs can often be observed off therapy for years or decades. In contrast, pleural or peritoneal tumors required rapid intervention with systemic cytotoxic chemotherapies. Given the lack of effective treatments, there remains a significant unmet need.
Unique among all cancer types, more than 90% of EHEs harbor in-frame chromosomal translocations with WWTR1 (TAZ) or YAP1 in the N-terminal domain. Given that YAP and TAZ are two paralogs, which share numerous epigenetic functions as YAP/TEAD or TAZ/TEAD transcriptional coactivators downstream of the Hippo tumor-suppressor pathway, the oncogenic effect of the resulting EHE-associated TAZ-CAMTA1 (TC) or YAP1-TFE (YT) fusion proteins must, with all certainty, continue to depend on the truncated YAP/TAZ proteins. Since no EHE cell lines exist, one cannot predict if the TC FP behaves similarly in human sarcomas that expose different tissue-specific TEAD binding sites.
Trametinib (a MEK inhibitor) was chosen for initial evaluation. We determined the preclinical efficacy of trametinib in the only available EHE patient-derived tumor explant (PDX) in existence, which genetic testing confirmed harbored a TAZ-CAMTA1 translocation. We propagated EHE PDX tumors in mice, then treated with vehicle or trametinib for more than 80 days. Tumor volumes were measured 2-3 times a week, and tumors were collected for further histology and proteomic analysis. Trametinib demonstrated potent antineoplastic activity, consistent with the limited activity observed in recent clinical studies.
A separate 10-day study was conducted to measure early pharmacodynamic studies of a potent, oral, selective small molecule palmitoylation inhibitor of TEAD provided by Ikena Oncology. Edge-Seq RNA sequencing and western blots were performed to validate the TEAD-dependent gene and protein expression. EdgeSeq analysis demonstrated significant down-regulation of multiple TEAD dependent genes, indicating on-target inhibition of TEAD in this model. Western blot protein analysis of YAP, TAZ, TEAD1, TC FP, CTGF, and CYR61, collected for pharmacodynamic analysis, demonstrated reduced CYR61, indicative of possible TEAD inhibitor activity; CTGF protein levels were unchanged. The use of one EHE PDX was a limitation, as this model may not fully recapitulate human tumor biology. Future research, using additional EHE PDX models, will be required in gauge the effect of different inhibitors.
Citation Format: Sandhya Krishnan, Robert Porter, Danh Truong, Salah-Eddine Lamhamedi-Cherradi, Krzysztof Grela, Rafal Zielinski, Sharon Landers, Vinod Ravi, Joseph A. Ludwig. Novel EHE PDX model used for drug sensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4501.