The Role of PIM3 Kinase in Promoting Tumorigenesis, Tumor Metastasis, and Cancer Cell Stemness in Human Hepatoblastoma

Hepatoblastoma is the most common primary liver tumor in children. Despite an increasing incidence and major advances in care for other pediatric solid tumors, therapy for hepatoblastoma has remained virtually unchanged for the last 20 years, and children with metastatic or relapsed disease continue to suffer from a dismal prognosis. Treatment strategies primarily rely on cisplatin, due to its role as the most active single agent in hepatoblastoma treatment. However, chemoresistance remains a significant challenge with 54-80% of patients developing resistance to chemotherapy after 4-5 cycles of treatment. We have previously demonstrated that Proviral Integration site in Maloney murine leukemia virus (PIM) kinases, specifically PIM3, are overexpressed in hepatoblastoma and function to promote tumorigenesis. In this dissertation, we aimed to elucidate the role of PIM3 kinase in promoting hepatoblastoma metastasis and mediating resistance to cisplatin chemotherapy. As a result of these studies, we have established the following:

(i) Described the development of cisplatin-resistant hepatoblastoma xenograft models and showed that cisplatin-resistant cells are enriched for stem cell-like cancer cells (SCLCCs) and have higher expression of PIM3 kinase.

(ii) Demonstrated that PIM inhibition overcomes hepatoblastoma chemoresistance by sensitizing cisplatin-resistant cells to cisplatin, enhancing cisplatin-mediated apoptosis, and reducing the SCLCC phenotype seen with cisplatin resistance.(iii) Used CRISPR/Cas9 gene editing with dual gRNAs to achieve stable PIM3 knockout in hepatoblastoma cells. Using this novel cell line, we confirmed the role of PIM3 kinase in promoting hepatoblastoma proliferation, cell survival, migration and invasion, cell-cycle progression, and cancer cell stemness.

(iv) Demonstrated that PIM3 kinase promoted hepatoblastoma tumor growth and formation of lung metastasis in vivo, and identified CXCR4 as a plausible mechanism in mediating PIM3’s promotion of hepatoblastoma metastasis.

(v) We established a metastatic hepatoblastoma cell line to further delineate the role of PIM3 kinase and CXCR4 chemokine receptor in metastatic hepatoblastoma.

This dissertation adds fundamental knowledge to our understanding of hepatoblastoma metastasis and chemoresistance, and the role of PIM3 kinase in promoting tumorigenesis, tumor metastasis, and chemoresistance in hepatoblastoma. The findings presented in these studies provide evidence for targeting PIM3 as a potential novel therapeutic strategy in the treatment of hepatoblastoma patients.