The PET Radiochemistry Laboratory of NIBIB has had a productive year of research. The majority of our effort has focused on projects that are collaborations with other NIH investigators. We have continued to expand our efforts on the imaging of the human epidermal growth factor receptor family (HER2 and EGFR) using specific Affibody molecules. The studies have been conducted with an extensive small animal PET imaging program using a human breast cancer xenograft model in athymic nude mice. This is a collaborative project among the NIBIB PET Radiochemistry Laboratory, the group of Jacek Capala in NCI's Radiation Oncology Branch, and Affibody AG (CRADA partner of Dr. Jacek Capala). The Affibody molecules were prepared for us with a C-terminal cysteine residue. This allows coupling with a 18Ffluoromaleimide (18FFBEM). We have developed a semi automated radiosynthetic procedure for preparing this radiolabeled maleimide using a commercial radiochemical synthesis apparatus. In this project year we explored the ability of the tracer to quantify HER2 receptor changes as a function of therapy. In addition we began our initial studies with an Affibody with specificity for EGFR. We have determined that a longer half-life radionuclide will be required for the EGFR Affibody because of the slow biological clearance from the blood stream. In our collaborative project with NIAID investigator, Dr. Michele di Mascio, on the development of an F-18 radiolabeled nucleoside analog reverse transcriptase inhibitor (FPMPA--1-(6-amino-9H-9-yl)-3-fluoropropan-2-yloxy)methylphosphonic acid), we prepared a manuscript describing the very similar biodistribution of 18FFPMPA compared with 14CPMPA. The manuscript concludes that the biodistribution and clearance in rat is very similar between the two compounds with the exception of the lungs and the kidney. In collaboration with Kenneth Jacobson, NIDDK senior investigator, our exploration of adenosine receptor ligands has continued. We published the biodistribution data of two Br-76 radiolabeled adenosine A3 ligands, which have potential utility in the study of inflammation processes (inflammation, tumor infiltration, etc). We began the exploration of a 18FFluoroethyl analog of SCH442416, a high affinity A2A anatagonist. The A2A receptor is up-regulated in the same brain regions where dopamine D2 decreases in Parkinsons disease. Thus, we will study this compound in the hemi-Parkinsons rat. Last year, in collaboration with Dr. Kenner Rice, NIDA senior investigator, we prepared corticotropin releasing hormone ligands labeled with Br-76. This year, fluorinated analogues were prepared in radiolabeled form. We are planning a comparative biological study of the various radiolabeled compound to determine which to investigate in imaging studies. An extensive collaborative project, with NIAID investigator Dr. Josh Farber and his post-doctoral associate Dr. Ido Weiss, on the study of chemokine receptor ligands has proven very productive. The initial work has focused on the CXCR4 chemokine receptor that plays a role in HIV infection, tumor proliferation, and tumor metastases. 64CuAMD3100, the Cu-64 form of a drug used to increase stem cell harvest from donors, has been prepared and shown to localize selectively in tumors that express high levels of the receptor. The nuclear decay properties of Cu-64 may be appropriate for radiotherapy with this compound and we have begun a study of therapeutic Cu-64 AMD. Peptide ligands for the CXCR4 receptor are known. We have prepared a fluorine 18 labeled analog and begun the study of its in vivo properties. The phospholipase A2 is an important enzyme in the arachadonic acid second messenging system. The enzyme is responsible for the release of arachadonic acid from the sn2 position of phospholipids. The activity of the enzyme is upregulated in neuroinflammatory disease and in peripheral inflammation. There is a rat model of neuroinflammation generated by brain ventricle injection of lipopolysaccharide. The enzyme levels are increased following treatment with NMDA. In collaboration with Dr. Stanley Rapoport of the NIA, we have explored one radiolabeled inhibitor of phospholipase A2. The compound was radiolabeled with fluorine-18 and shown to be poorly taken up in the brain of normal rats. Biodistribution studies and imaging studies in the inflammation model are currently being analyzed.
