title: A peptide-based positron emission tomography probe for in vivo detection of caspase activity in apoptotic cells.
abstract: OBJECTIVE
  Apoptosis, or programmed cell death, can be leveraged as a surrogate measure of response to therapeutic interventions in medicine. Cysteine aspartic acid-specific proteases, or caspases, are essential determinants of apoptosis signaling cascades and represent promising targets for molecular imaging. Here, we report development and in vivo validation of [(18)F]4-fluorobenzylcarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone ([(18)F]FB-VAD-FMK), a novel peptide-based molecular probe suitable for quantification of caspase activity in vivo using positron emission tomography (PET).
  
  
  METHODS
  Supported by molecular modeling studies and subsequent in vitro assays suggesting probe feasibility, the labeled pan-caspase inhibitory peptide, [(18)F]FB-VAD-FMK, was produced in high radiochemical yield and purity using a simple two-step, radiofluorination. The biodistribution of [(18)F]FB-VAD-FMK in normal tissue and its efficacy to predict response to molecularly targeted therapy in tumors was evaluated using microPET imaging of mouse models of human colorectal cancer.
  
  
  RESULTS
  Accumulation of [(18)F]FB-VAD-FMK was found to agree with elevated caspase-3 activity in response to Aurora B kinase inhibition as well as a multidrug regimen that combined an inhibitor of mutant BRAF and a dual PI3K/mTOR inhibitor in (V600E)BRAF colon cancer. In the latter setting, [(18)F]FB-VAD-FMK PET was also elevated in the tumors of cohorts that exhibited reduction in size.
  
  
  CONCLUSIONS
  These studies illuminate [(18)F]FB-VAD-FMK as a promising PET imaging probe to detect apoptosis in tumors and as a novel, potentially translatable biomarker for predicting response to personalized medicine.
authors.affiliation: Authors' Affiliations: Interdisciplinary Materials Science Program, Department of Physics & Astronomy, Departments of Biochemistry, Pathology, Cell and Developmental Biology, and Biomedical Engineering; Vanderbilt University Center for Structural Biology (CSB), Vanderbilt University; Vanderbilt University Institute of Imaging Science (VUIIS); Departments of Radiology and Radiological Sciences and Neurosurgery; Vanderbilt-Ingram Cancer Center (VICC); Program in Chemical and Physical Biology, Vanderbilt University Medical Center; Department of Medicine, Vanderbilt University Medical School; and Department of Veterans Affairs Medical Center, Nashville, Tennessee.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Hight
authors.forename: Yiu-Yin
authors.initials: YY
authors.lastname: Cheung
authors.forename: Michael L
authors.initials: ML
authors.lastname: Nickels
authors.forename: Eric S
authors.initials: ES
authors.lastname: Dawson
authors.forename: Ping
authors.initials: P
authors.lastname: Zhao
authors.forename: Samir
authors.initials: S
authors.lastname: Saleh
authors.forename: Jason R
authors.initials: JR
authors.lastname: Buck
authors.forename: Dewei
authors.initials: D
authors.lastname: Tang
authors.forename: M Kay
authors.initials: MK
authors.lastname: Washington
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Coffey
authors.forename: H Charles
authors.initials: HC
authors.lastname: Manning
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000737:chemistry / Q000493:pharmacokinetics; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism*; D061945:Caspase Inhibitors / Q000493:pharmacokinetics; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D005260:Female; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics; D005464:Fluorobenzenes / Q000737:chemistry; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D015151:Immunoblotting; D007150:Immunohistochemistry; D007211:Indoles / Q000494:pharmacology; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D010755:Organophosphates / Q000494:pharmacology; D010455:Peptides / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography / Q000379:methods*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D013449:Sulfonamides / Q000494:pharmacology; D014018:Tissue Distribution; D023041:Xenograft Model Antitumor Assays
chemical_list: C520647:2-((3-((4-((5-(2-((3-fluorophenyl)amino)-2-oxoethyl)-1H-pyrazol-3-yl)amino)quinazolin-7-yl)oxy)propyl)(ethyl)amino)ethyl dihydrogen phosphate; D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D005462:Fluorine Radioisotopes; D005464:Fluorobenzenes; D007093:Imidazoles; D007211:Indoles; D010755:Organophosphates; C528407:PLX 4720; D010455:Peptides; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D011804:Quinolines; D019275:Radiopharmaceuticals; D013449:Sulfonamides; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D053148:Caspase 3; C531198:dactolisib