Anti-Cancer Mechanisms of MICA Nanoparticle or PDE4D Inhibitor in Human Cancer CellsAnti-Cancer Mechanisms of MICA Nanoparticle or PDE4D Inhibitor in Human Cancer Cells

Abstract

Glioblastoma multiforme (GBM) and breast cancer are the most prevalent malignant tumors in adults, and both exhibit high fatality rates due to their tumorigenic potentials and limitations of cancer therapy. In this study, I investigated on tumor suppressive and immunostimulatory effects using novel small molecule, CG500354, and natural compound, STB-HO. In the first part of this study, I performed forced differentiation of cancer cells, which is a recently developed approach in developing a cancer therapy. I demonstrated that the novel phosphodiesterase-4 subtype D (PDE4D) inhibitor, CG500354, induces growth arrest and neural differentiation in GBM-derived cells by triggering the activation of cAMP/PKA signaling pathway. Treatment of CG500354 regulated cAMP/PKA signaling pathway by interrupting PDE4 interference and up-regulating phosphorylated protein kinase A (p-PKA) and phosphorylated CREB (p-CREB). Furthermore, PDE4D inhibitor suppressed the expression level of cyclin B1, while up-regulating p21 and p27, which are known to be associated with growth arrest. I next investigated whether PDE4D inhibitor affect neural differentiation of GBM. GFAP, an astrocyte marker, and Tuj-1, a neuronal marker, were significantly increased with p53 expression level in GBM while the expression of nestin, a neural progenitor marker was decreased. These results suggest that CG500354 may play crucial roles in neural differentiation and growth arrest through regulation of cell-cycle-related and neural differentiation markers. In the second part of this study, I investigated on the regulation of interactions between tumor cells and anti-tumor immune cells by treating with mica nanoparticle, STB-HO. Its efficacy and mechanisms in treating various types of tumor are less verified and the mechanistic link between anti-tumor and immunostimulatory effects has not been elucidated. STB-HO was orally administered into MCF-7 xenograft model. The growth of MCF-7 cell in xenograft model was significantly suppressed, whereas STB-HO did not directly affect the proliferation and apoptosis in vitro. Thus, I observed the interactions of MCF-7 and macrophage, dendritic cells (DCs) and natural killer (NK) cells after STB-HO treatment to investigate the discrepancy between in vivo and in vitro. The MHC class I, which is known as an inhibitory factor for NK cell-mediated anti-tumor effect, was down-regulated approximately by 10% when treated with STB-HO. Thus, I induced macrophage-like cells from THP-1 and dendritic cells from CD14+ monocytes to analyze the functional alteration of STB-HO. I observed that IL-12, known for its contribution in NK cell cytotoxicity against tumor cell, was consistently increased by STB-HO treatment. I next isolated NK cells from human blood and performed cytotoxicity test by co-culturing NK cells with fluorescence-labeled MCF-7. The dead cell population of MCF-7 rose up to 2% to 7% and additional STB-HO treatment on co-culture condition rose dead cell proportion up to 16-17% along with the elevation of significant IFN-γ expression. I observed that STB-HO not only increased susceptibility of MCF-7 cells to immune cells, but also stimulated immunocytes in tumor microenviroment to eliminate cancer cells. Taken together, these findings provide insights that CG500354 activated cAMP/PKA signaling pathway by blocking PDE4D, which triggered neural differentiation and growth arrest of glioblastoma-derived cancer cells. STB-HO regulated the interaction of tumor with its immune microenvironment by enhancing the functions of NK cell, macrophage and DCs to attack tumor cells by secreting IFN-γ and IL-12.