Novel Orthotopic Patient-Derived Xenograft Mouse Models Of Hepatoblastoma That Replicate Tumor Heterogeneity, Chemoresistance, And Refractory Disease.

Abstract Introduction: Hepatoblastoma (HB) is the most common pediatric primary liver tumor and has the fastest rising incidence of all pediatric solid tumors. Patients with high-risk, treatment refractory, or relapse disease have a survival rate of less than 50%. The development of clinically relevant models of these aggressive tumors will facilitate studies to identify drugs that target these cells. Methods: Fresh, whole primary tumor samples were implanted into the livers of immunocompromised mice. Tumor growth was monitored with MRI and ELISA to measure serum human Alpha-fetoprotein (AFP), which is detectable in the blood of tumor-bearing animals. Tumors were validated with immunohistochemistry (IHC) for HB markers Glypican-3 (GPC3) and Beta-catenin; short tandem repeat (STR) DNA validation; next generation sequencing-based mutation profiling of 124 genes involved in pediatric solid tumors; and RNA sequencing (RNA-seq). Cells derived from tumors were grown in vitro and used for high throughput drug screening of candidate agents. Tumors were serially passaged in animals for further in vivo drug testing of novel targeted agents. Results: Nine patient-derived xenograft (PDX) models were generated that represent low- and high-risk tumors, treatment refractory cases, and relapsed tumors. Passaging of these models showed consistent implantation rates at or above 80% with tumors detectable in 2 to 4 weeks. Eight of nine models secrete human serum AFP. All models mimic gene expression and histological patterns of their primary tumor counterparts as well as identical STR DNA profiles. The models also show gene expression consistent with an HB2/high-risk profile according to the Sumazin HB expression signature. Interestingly, two models represent unique sub-clones of a very aggressive HB relapse with different AFP secretion and transcriptomic expression. The nine models also demonstrate a range of DNA mutations with three or four mutations per tumor; all variants present in the original clinical samples were conserved in the PDX models. Drug screening of tumor cells support the efficacy of novel targeted agents and indicate that these tumors are resistant to frontline standard chemotherapy, cisplatin and doxorubicin. More extensive in vivo testing showed the efficacy of a dual MDM2/MDM4 inhibitor (ALRN-6924), a cyclin dependent kinase inhibitor (dinaciclib), and a histone deacetylase inhibitor (panobinostat), and use of an orthotopic animal model also revealed drug toxicities associated with compromised liver function. Conclusions: These novel orthotopic PDX models of HB fully recapitulate the primary tumors and represent a platform for clinically relevant drug screening and testing. Further studies of the sub-clones of disease that grow in the animals will yield information about particularly aggressive HBs. Citation Format: Sarah Elizabeth Woodfield, Roma H. Patel, Samuel R. Larson, Andrew Badachhape, Rohit K. Srivastava, Aayushi P. Shah, Brandon Mistretta, Barry Zorman, Kevin Fisher, Ilavarasi Gandhi, Jacquelyn Reuther, Richard S. Whitlock, Aryana M. Ibarra, Sakuni Rankothgedera, Kimberly R. Holloway, Stephen F. Sarabia, Martin Urbicain, Andras Heczey, Dolores Lopez-Terrada, Angshumoy Roy, Preethi Gunaratne, Pavel Sumazin, Sanjeev A. Vasudevan. Novel orthotopic patient-derived xenograft mouse models of hepatoblastoma that replicate tumor heterogeneity, chemoresistance, and refractory disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2997.