Epigenetic modifications mediated by histone deacetylases (HDACs) play important roles in the mechanisms of different neurologic diseases and HDAC inhibitors (HDACIs) have shown promise in therapy. However, pharmacodynamic profiles of many HDACIs in the brain remain largely unknown due to the lack of validated methods for noninvasive imaging of HDAC expression-activity. In this study, dynamic PET/CT imaging was performed in 4 rhesus macaques using [(18)F]FAHA, a novel HDAC substrate, and [(18)F]fluoroacetate, the major radio-metabolite of [(18)F]FAHA, and fused with corresponding MR images of the brain. Quantification of [(18)F]FAHA accumulation in the brain was performed using a customized dual-tracer pharmacokinetic model. Immunohistochemical analyses of brain tissue revealed the heterogeneity of expression of individual HDACs in different brain structures and cell types and confirmed that PET/CT/MRI with [(18)F]FAHA reflects the level of expression-activity of HDAC class IIa enzymes. Furthermore, PET/CT/MRI with [(18)F]FAHA enabled non-invasive, quantitative assessment of pharmacodynamics of HDAC inhibitor SAHA in the brain.
Brain/enzymology , Brain/metabolism , Fluorine Radioisotopes/pharmacokinetics , Histone Deacetylases/metabolism , Magnetic Resonance Imaging/methods , Molecular Imaging/methods , Positron-Emission Tomography/methods , Anilides , Animals , Epigenesis, Genetic/physiology , Female , Gene Expression Regulation, Enzymologic/physiology , Macaca mulatta , Male , Subtraction Technique
The importance of the EGF receptor (EGFR) signaling pathway in the development and progression of nonsmall cell lung carcinomas (NSCLC) is widely recognized. Gene sequencing studies revealed that a majority of tumors responding to EGFR kinase inhibitors harbor activating mutations in the EGFR kinase domain. This underscores the need for novel biomarkers and diagnostic imaging approaches to identify patients who may benefit from particular therapeutic agents and approaches with improved efficacy and safety profiles. To this goal, we developed 4-[(3-iodophenyl)amino]-7-{2-[2-{2-(2-[2-{2-([(18)F]fluoroethoxy)-ethoxy}-ethoxy]-ethoxy)-ethoxy}-ethoxy]-quinazoline-6-yl-acrylamide ([(18)F]F-PEG6-IPQA), a radiotracer with increased selectivity and irreversible binding to the active mutant L858R EGFR kinase. We show that PET with [(18)F]F-PEG6-IPQA in tumor-bearing mice discriminates H3255 NSCLC xenografts expressing L858R mutant EGFR from H441 and PC14 xenografts expressing EGFR or H1975 xenografts with L858R/T790M dual mutation in EGFR kinase domain, which confers resistance to EGFR inhibitors (i.e., gefitinib). The T790M mutation precludes the [(18)F]F-PEG6-IPQA from irreversible binding to EGFR. These results suggest that PET with [(18)F]F-PEG6-IPQA could be used for the selection of NSCLC patients for individualized therapy with small molecular inhibitors of EGFR kinase that are currently used in the clinic and have a similar structure (i.e., iressa, gefitinib, and erlotinib).
Carcinoma, Non-Small-Cell Lung/metabolism , ErbB Receptors/metabolism , Lung Neoplasms/metabolism , Molecular Imaging/methods , Mutant Proteins/metabolism , Amino Acid Substitution , Animals , Binding, Competitive , Blotting, Western , Carcinoma, Non-Small-Cell Lung/drug therapy , Carcinoma, Non-Small-Cell Lung/pathology , Cell Line, Tumor , Cell Proliferation/drug effects , ErbB Receptors/genetics , Fluorodeoxyglucose F18/metabolism , Humans , Lung Neoplasms/drug therapy , Lung Neoplasms/pathology , Mice , Mice, Nude , Mutant Proteins/genetics , Mutation , Positron-Emission Tomography/methods , Protein Binding , Protein Kinase Inhibitors/pharmacology , Quinazolines/metabolism , Radiopharmaceuticals/metabolism , Tomography, X-Ray Computed/methods , Xenograft Model Antitumor Assays
INTRODUCTION: Previous studies demonstrated that the lactose-binding protein (hepatocellular carcinoma-intestine-pancreas and pancreatitis-associated proteins (HIP/PAP)) is upregulated >130 times in peritumoral pancreatic tissue as compared to normal pancreatic tissue. Therefore, we developed a new radiolabeled ligand of HIP/PAP, the ethyl-ß-D-galactopyranosyl-(1,4')-2'-deoxy-2'-[¹8F]fluoro-ß-D-glucopyranoside (Et-[¹8F]FDL) for noninvasive imaging of pancreatic carcinoma using positron emission tomography and computerized tomography (PET/CT). METHODS: The novel precursor and radiolabeling methods for synthesis of Et-[¹8F]FDL produced no isomers; the average decay-corrected radiochemical yield was 68%, radiochemical purity >99%, and specific activity >74 GBq/µmol. The radioligand properties of Et-[¹8F]FDL were evaluated using an ex vivo autoradiography and immunohistochemistry in pancreatic tissue sections obtained from mice-bearing orthotopic pancreatic tumor xenografts. RESULTS AND DISCUSSION: Et-[¹8F]FDL binding to peritumoral pancreatic tissue sections strongly correlated with HIP/PAP expression (r = 0.81) and could be completely blocked by treatment with 1 mM lactose. CONCLUSION: These results suggest that Et-[¹8F]FDL is a promising agent which should be evaluated for detection of early pancreatic carcinomas by PET/CT imaging.
Autoradiography/methods , Disaccharides/chemical synthesis , Early Detection of Cancer , Glucosides/chemical synthesis , Lactose/metabolism , Neoplasm Proteins/metabolism , Pancreatic Neoplasms/diagnostic imaging , Positron-Emission Tomography , Animals , Antigens, Neoplasm/metabolism , Biomarkers, Tumor/metabolism , Chromatography, High Pressure Liquid , Disaccharides/chemistry , Disaccharides/isolation & purification , Glucosides/chemistry , Glucosides/isolation & purification , Halogenation , Immunohistochemistry , Lectins, C-Type/metabolism , Ligands , Mice , Pancreatitis-Associated Proteins , Radiopharmaceuticals/chemical synthesis , Radiopharmaceuticals/chemistry
