title: 64Cu-CTS: A Promising Radiopharmaceutical for the Identification of Low-Grade Cardiac Hypoxia by PET.
abstract: The subtle hypoxia underlying chronic cardiovascular disease is an attractive target for PET imaging, but the lead hypoxia imaging agents (64)Cu-2,3-butanedione bis(N4-methylthiosemicarbazone) (ATSM) and (18)F-fluoromisonidazole are trapped only at extreme levels of hypoxia and hence are insufficiently sensitive for this purpose. We have therefore sought an analog of (64)Cu-ATSM better suited to identify compromised but salvageable myocardium, and we validated it using parallel biomarkers of cardiac energetics comparable to those observed in chronic cardiac ischemic syndromes.
  
  
  METHODS
  Rat hearts were perfused with aerobic buffer for 20 min, followed by a range of hypoxic buffers (using a computer-controlled gas mixer) for 45 min. Contractility was monitored by intraventricular balloon, energetics by (31)P nuclear MR spectroscopy, lactate and creatine kinase release spectrophotometrically, and hypoxia-inducible factor 1-α by Western blotting.
  
  
  RESULTS
  We identified a key hypoxia threshold at a 30% buffer O2 saturation that induces a stable and potentially survivable functional and energetic compromise: left ventricular developed pressure was depressed by 20%, and cardiac phosphocreatine was depleted by 65.5% ± 14% (P < 0.05 vs. control), but adenosine triphosphate levels were maintained. Lactate release was elevated (0.21 ± 0.067 mmol/L/min vs. 0.056 ± 0.01 mmol/L/min, P < 0.05) but not maximal (0.46 ± 0.117 mmol/L/min), indicating residual oxidative metabolic capacity. Hypoxia-inducible factor 1-α was elevated but not maximal. At this key threshold, (64)Cu-2,3-pentanedione bis(thiosemicarbazone) (CTS) selectively deposited significantly more (64)Cu than any other tracer we examined (61.8% ± 9.6% injected dose vs. 29.4% ± 9.5% for (64)Cu-ATSM, P < 0.05).
  
  
  CONCLUSIONS
  The hypoxic threshold that induced survivable metabolic and functional compromise was 30% O2. At this threshold, only (64)Cu-CTS delivered a hypoxic-to-normoxic contrast of 3:1, and it therefore warrants in vivo evaluation for imaging chronic cardiac ischemic syndromes.
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and.
authors.forename: Rodolfo A
authors.initials: RA
authors.lastname: Medina
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and.
authors.forename: Erika
authors.initials: E
authors.lastname: Mariotti
authors.affiliation: Centre for Cardiovascular Sciences, School of Clinical and Experimental Medicine, University of Birmingham, Birmingham, United Kingdom.
authors.forename: Davor
authors.initials: D
authors.lastname: Pavlovic
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and.
authors.forename: Karen P
authors.initials: KP
authors.lastname: Shaw
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Eykyn
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Blower
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and richard.southworth@kcl.ac.uk.
authors.forename: Richard
authors.initials: R
authors.lastname: Southworth
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D056831:Coordination Complexes / Q000737:chemistry*; D003301:Copper Radioisotopes / Q000737:chemistry*; D003402:Creatine Kinase / Q000378:metabolism; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D000860:Hypoxia / Q000000981:diagnostic imaging*; D019344:Lactic Acid / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009206:Myocardium / Q000473:pathology*; D009942:Organometallic Compounds / Q000737:chemistry; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals / Q000737:chemistry*; D051381:Rats; D017208:Rats, Wistar; D013882:Thiosemicarbazones / Q000737:chemistry*
chemical_list: C000600261:64Cu-2,3-pentanedione bis(thiosemicarbazone); D056831:Coordination Complexes; D003301:Copper Radioisotopes; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D013882:Thiosemicarbazones; C089548:copper (II) diacetyl-di(N(4)-methylthiosemicarbazone); D019344:Lactic Acid; D000255:Adenosine Triphosphate; D003402:Creatine Kinase
keywords: 64Cu-ATSM; bis(thiosemicarbazones); NMR; PET; bioenergetics; cardiac hypoxia