GSBS Dissertations and Theses

ORCID ID

0000-0003-0460-0647

Publication Date

2020-03-20

Document Type

Doctoral Dissertation

Academic Program

Cancer Biology, MD/PhD

Department

RNA Therapeutics Institute, MD/PhD Program, Cancer Biology

First Thesis Advisor

Wen Xue

Keywords

Therapeutic Differentiation, Targeted Therapy, Pediatric Cancer, Oncogene, Liver cancer, Mouse Model, Conditional Model, Genetic, Inducible, Hepatoblastoma, Oncogene Addiction, Tumor Dormancy, Drug Discovery, YAP, B-Catenin, Hydrodynamic Injection, Sleeping Beauty System, Tranposase, Lineage Tracing

Abstract

Background & Aims: Despite advances in surgical care and chemotherapeutic regimens, the five-year survival rate for Stage IV Hepatoblastoma (HB), the predominant pediatric liver tumor, remains at 27%. YAP1 and β-Catenin co-activation occurs in 80% of children’s HB; however, a lack of conditional genetic models precludes exploration of tumor maintenance and therapeutic targets. Thus, the clinical need for a targeted therapy remains unmet. Given the predominance of YAP1 and β-catenin activation in children’s tumors, I sought to evaluate YAP1 as a therapeutic target in HB.

Approach & Results: Herein, I engineered the first conditional murine model of HB using hydrodynamic injection to deliver transposon plasmids encoding inducible YAP1S127A, constitutive β-CateninDelN90, and a luciferase reporter to murine liver. Tumor regression was evaluated using in vivo bioluminescent imaging, and tumor landscape characterized using RNA sequencing, ATAC sequencing and DNA foot-printing. Here I show that YAP1 withdrawal in mice mediates >90% tumor regression with survival for 230+ days. Mechanistically, YAP1 withdrawal promotes apoptosis in a subset of tumor cells and in remaining cells induces a cell fate switch driving therapeutic differentiation of HB tumors into Ki-67 negative “hbHep cells.” hbHep cells have hepatocyte-like morphology and partially restored mature hepatocyte gene expression. YAP1 withdrawal drives formation of hbHeps by modulating liver differentiation transcription factor (TF) occupancy. Indeed, tumor-derived hbHeps, consistent with their reprogrammed transcriptional landscape, regain partial hepatocyte function and can rescue liver damage in mice.

Conclusions: YAP1 withdrawal, without modulation of oncogenic β-Catenin, significantly regresses hepatoblastoma, providing the first in vivo data to support YAP1 as a therapeutic target for HB. Modulating YAP1 expression alone is sufficient to drive long-term regression in hepatoblastoma because it promotes cell death in a subset of tumor cells and modulates transcription factor occupancy to reverse the fate of residual tumor cells to mimic functional hepatocytes.

DOI

10.13028/3cd6-va15

Rights and Permissions

Copyright is held by the author, with all rights reserved.

Available for download on Sunday, April 24, 2022

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