PIM kinase inhibitor, PIM447, decreases cancer cell stemness and exhibits synergy with cisplatin in hepatoblastoma

Background: Current chemotherapy regimens for hepatoblastoma include platinum-based combinations that have remained virtually unchanged over the last twenty years. The overall survival for children with advanced stage or recurrent disease utilizing these regimens remains poor. We have previously shown that Proviral Integration site for Moloney murine leukemia virus (PIM) kinases act as oncoproteins promoting hepatoblastoma cell survival and the cancer stem cell phenotype, which may contribute to chemoresistance. We hypothesized that PIM inhibition utilizing a novel PIM inhibitor, PIM447, would decrease the hepatoblastoma stem cell phenotype and potentiate the activity of cisplatin.

Methods: The hepatoblastoma patient-derived xenograft (PDX), COA67, and human hepatoblastoma cell line, HuH6, were utilized. COA67 cells were treated with PIM447 and the expression of CD133, a marker of hepatoblastoma cell stemness, was detected by flow cytometry. Sphere-forming ability was assessed using in vitro limiting dilution assays. For synergy experiments, COA67 and HuH6 cells were treated with cisplatin and PIM447 in combination, and viability assessed using alamarBlue™ assays. Isobolograms were constructed and combination indices (CIs) calculated using Chou-Talalay method. Data were analyzed using Student’s t-test with p≤0.05 considered significant.

Results: PIM447 significantly reduced cell surface expression of CD133 in COA67 cells by 20% (p=0.04, treated versus untreated cells). PIM447 also led to a significant decrease in the ability of COA67 cells to form tumorspheres, indicating decreased stemness (Figure 1 A). When used in combination with cisplatin, PIM447 significantly decreased the median lethal dose (LD50) for cisplatin in both HuH6 and COA67 cells and the CIs were less than 1, indicating synergy between the two drugs (Figure 1 B-C).

Conclusion: PIM447 diminished the stemness of COA67 hepatoblastoma PDX cells and potentiated the in vitro activity of cisplatin against HuH6 hepatoblastoma cell line and COA67 hepatoblastoma PDX. These data support further investigation of PIM447 as a therapeutic agent for hepatoblastoma.