The Molecular Mechanism of Histone Deacetylase (HDAC) Inhibitor PCI-24781 as an Anti-tumor Agent in Neuroblastoma Cells

Neuroblastoma accounts for 7-10% of all childhood cancers, and it is the most common extracranial solid tumor in childhood. The survival rate is less than 40% among children with high-risk neuroblastoma, despite of intensive multi-modality treatment, highlighting the urgent needs for new treatment strategies. Histone deacetylase (HDAC) inhibitors are a new class of promising anti-tumor agents that have been used in clinical trials for various tumor types. Among HDAC inhibitors, PCI-24781 is a novel hydroxamic acid that has high efficacy and safety for cancer treatment. However, the underlying mechanisms of PCI-24781 are not clearly elucidated, especially in neuroblastoma cells.;Different protein expression profiles were further revealed via proteomic analysis between SK-N-DZ cells with or without PCI-24781 exposure. MALDI-TOF MS system identified total 42 differentially expressed proteins. The functional classification revealed that PCI-24781 affected a series of cellular processes, including cytoskeleton organization, energy metabolism, DNA repair, cell cycle and transcriptional regulation. Western blotting confirmed the expression level of five candidate proteins in SK-N-DZ cells, including prohibitin, hHR23a, RuvBL2, TRAP1 and PDCD6IP. Interestingly, expression patterns of the five proteins were totally different in HS-68 cells.;The high abundance of hHR23a and RuvBL2 was found in SK-N-DZ cells but not in HS-68 cells in response to PCI-24781, implying that these two proteins may be functionally important for PCI-24781-mediated cell death. However, selective knockdown of RuvBL2 not hHR23a rescued cells from PCI-24781-induced cell death. Collectively, my current results highlight the important role of RuvBL2 in anti-tumor activity of PCI-24781 in SK-N-DZ cells. The present study confirms the interest in HDAC inhibitors as anti-cancer agents for patients with high-risk neuroblastoma, and even provides a new insight into the potential mechanism of PCI-24781 in SK-N-DZ cell line. However, many efforts are still needed to elucidate differential sensitivity between cancer and normal cells in response to HDAC inhibitors treatment.; In this study, I demonstrated that PCI-24781 treatment significantly inhibited tumor growth at very low doses in neuroblastoma cells SK-N-DZ, not in normal cell line HS-68. However, the accumulation of acetylated histone H3 can be found both in SK-N-DZ and HS-68 cell line in response to PCI-24781. Treatment with PCI-24781 also induced cell cycle arrest in G2/M phase and large amounts of sub-G1 cells in SK-N-DZ cells. Analysis of apoptosis signaling pathways found that both extrinsic and intrinsic pathways were activated by PCI-24781. The increased apoptotic proteins included DR4, p21, p53, caspase3 and cleaved caspase3.