ABSTRACT
Purpose: Hypoxia-inducible factor-2α (HIF2α) is regarded as a preferential target for individualized hepatocellular carcinoma (HCC) treatment and sorafenib resistance. Our study aimed to identify the regulatory mechanisms of HIF2α activity under hypoxic conditions. We sought to determine whether the COX-2/PGE2 axis is involved in the regulatory mechanisms of HIF2α activity and of sorafenib resistance in hypoxic HCC cells.Experimental Design: The cell viability, migration, and invasion abilities were measured to analyze the effects of HIF2α on hypoxic HCC cells. Both in vitro and in vivo HCC models were used to determine whether the COX-2/PGE2 axis is a driver of HIF2α level and activity, which then reduces the sensitivity of sorafenib treatment in hypoxic HCC cells.Results: Under hypoxic conditions, the COX-2/PGE2 axis effectively stabilized HIF2α and increased its level and activity via decreasing von Hippel-Lindau protein (p-VHL) level, and also enhanced HIF2α activity by promoting HIF2α nuclear translocation via MAPK pathway. The activation of HIF2α then led to the enhanced activation of VEGF, cyclin D1, and TGFα/EGFR pathway to mediate HCC development and reduce the sensitivity of sorafenib. More importantly, COX-2-specific inhibitors synergistically enhanced the antitumor activity of sorafenib treatment.Conclusions: Our data obtained demonstrate that the COX/PGE2 axis acts as a regulator of HIF2α expression and activity to promote HCC development and reduce sorafenib sensitivity by constitutively activating the TGFα/EGFR pathway. This study highlights the potential of COX-2-specific inhibitors for HCC treatment and particularly for enhancing the response to sorafenib treatment. Clin Cancer Res; 24(13); 3204-16. ©2018 AACR.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/metabolism , Carcinoma, Hepatocellular/drug therapy , Carcinoma, Hepatocellular/metabolism , Cyclooxygenase 2/metabolism , Dinoprostone/metabolism , Liver Neoplasms/drug therapy , Liver Neoplasms/metabolism , Sorafenib/therapeutic use , Animals , Antineoplastic Agents/pharmacology , Antineoplastic Agents/therapeutic use , Apoptosis/drug effects , Carcinoma, Hepatocellular/pathology , Cell Line, Tumor , Cell Survival/drug effects , Cyclin D1/metabolism , Disease Models, Animal , Drug Resistance, Neoplasm , Humans , Hypoxia/metabolism , Liver Neoplasms/pathology , Mice , Neovascularization, Pathologic/metabolism , Protein Kinase Inhibitors/pharmacology , Protein Kinase Inhibitors/therapeutic use , Proteolysis , Signal Transduction/drug effects , Sorafenib/pharmacology , Xenograft Model Antitumor AssaysABSTRACT
We demonstrate a systematic visualization of the unique photophysical and fluorescence anisotropic properties of polyfluorene coplanar conformation (ß-conformation) using time-resolved scanning confocal fluorescence imaging (FLIM) and fluorescence anisotropy imaging microscopy (FAIM) measurements. We observe inhomogeneous morphologies and fluorescence decay profiles at various micrometer-sized regions within all types of polyfluorene ß-conformational spin-coated films. Poly(9,9-dioctylfluorene-2,7-diyl) (PFO) and poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF) ß-domains both have shorter lifetime than those of the glassy conformation for the longer effective conjugated length and rigid chain structures. Besides, ß-conformational regions have larger fluorescence anisotropy for the low molecular rotational motion and high chain orientation, while the low anisotropy in glassy conformational regions shows more rotational freedom of the chain and efficient energy migration from amorphous regions to ß-conformation as a whole. Finally, ultrastable ASE threshold in the PODPF ß-conformational films also confirms its potential application in organic lasers. In this regard, FLIM and FAIM measurements provide an effective platform to explore the fundamental photophysical process of conformational transitions in conjugated polymer.
