title: Hybrid Imaging Labels: Providing the Link Between Mass Spectrometry-Based Molecular Pathology and Theranostics.
abstract: Development of theranostic concepts that include inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) imaging can be hindered by the lack of a direct comparison to more standardly used methods forin vitroandin vivoevaluation; e.g. fluorescence or nuclear medicine. In this study a bimodal (or rather, hybrid) tracer that contains both a fluorescent dye and a chelate was used to evaluate the existence of a direct link between mass spectrometry (MS) andin vitroandin vivomolecular imaging findings using fluorescence and radioisotopes. At the same time, the hybrid label was used to determine whether the use of a single isotope label would allow for MS-based diagnostics.
  
  
  
  A hybrid label that contained both a DTPA chelate (that was coordinated with either165Ho or111In) and a Cy5 fluorescent dye was coupled to the chemokine receptor 4 (CXCR4) targeting peptide Ac-TZ14011 (hybrid-Cy5-Ac-TZ4011). This receptor targeting tracer was used to 1) validate the efficacy of (165Ho-based) mass-cytometry in determining the receptor affinity via comparison with fluorescence-based flow cytometry (Cy5), 2) evaluate the microscopic binding pattern of the tracer in tumor cells using both fluorescence confocal imaging (Cy5) and LA-ICP-MS-imaging (165Ho), 3) comparein vivobiodistribution patterns obtained with ICP-MS (165Ho) and radiodetection (111In) after intravenous administration of hybrid-Cy5-Ac-TZ4011 in tumor-bearing mice. Finally, LA-ICP-MS-imaging (165Ho) was linked to fluorescence-based analysis of excised tissue samples (Cy5).
  
  
  
  Analysis with both mass-cytometry and flow cytometry revealed a similar receptor affinity, respectively 352 ± 141 nM and 245 ± 65 nM (p = 0.08), but with a much lower detection sensitivity for the first modality.In vitroLA-ICP-MS imaging (165Ho) enabled clear discrimination between CXCR4 positive and negative cells, but fluorescence microscopy was required to determine the intracellular distribution.In vivobiodistribution patterns obtained with ICP-MS (165Ho) and radiodetection (111In) of the hybrid peptide were shown to be similar. Assessment of tracer distribution in excised tissues revealed the location of tracer uptake with both LA-ICP-MS-imaging and fluorescence imaging.
  
  
  
  Lanthanide-isotope chelation expands the scope of fluorescent/radioactive hybrid tracers to include MS-based analytical tools such as mass-cytometry, ICP-MS and LA-ICP-MS imaging in molecular pathology. In contradiction to common expectations, MS detection using a single chelate imaging agent was shown to be feasible, enabling a direct link between nuclear medicine-based imaging and theranostic methods.
authors.affiliation: Interventional Molecular Imaging laboratory, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands;; Division of Molecular Pathology, Netherlands Cancer Institute- Antoni van Leeuwenhoek hospital (NKI-AvL), Amsterdam, the Netherlands.
authors.forename: Tessa
authors.initials: T
authors.lastname: Buckle
authors.affiliation: Interventional Molecular Imaging laboratory, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Steffen
authors.initials: S
authors.lastname: van der Wal
authors.affiliation: Department of Analytical Chemistry, Ghent University, Ghent, Belgium.
authors.forename: Stijn J M
authors.initials: SJ
authors.lastname: van Malderen
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany.
authors.forename: Larissa
authors.initials: L
authors.lastname: Müller
authors.affiliation: Interventional Molecular Imaging laboratory, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Joeri
authors.initials: J
authors.lastname: Kuil
authors.affiliation: Department of immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Vincent
authors.initials: V
authors.lastname: van Unen
authors.affiliation: RIKILT Wageningen UR, Wageningen, the Netherlands.
authors.forename: Ruud J B
authors.initials: RJ
authors.lastname: Peters
authors.affiliation: RIKILT Wageningen UR, Wageningen, the Netherlands.
authors.forename: Margaretha E M
authors.initials: ME
authors.lastname: van Bemmel
authors.affiliation: Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Liam A
authors.initials: LA
authors.lastname: McDonnell
authors.affiliation: Interventional Molecular Imaging laboratory, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands;; Laboratory of BioNanoTechnology, Wageningen University, Wageningen, the Netherlands.
authors.forename: Aldrik H
authors.initials: AH
authors.lastname: Velders
authors.affiliation: RIKILT Wageningen UR, Wageningen, the Netherlands.
authors.forename: Frits
authors.initials: F
authors.lastname: Koning
authors.affiliation: Department of Analytical Chemistry, Ghent University, Ghent, Belgium.
authors.forename: Frank
authors.initials: F
authors.lastname: Vanhaeke
authors.affiliation: Interventional Molecular Imaging laboratory, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands;; Laboratory of BioNanoTechnology, Wageningen University, Wageningen, the Netherlands.
authors.forename: Fijs W B
authors.initials: FW
authors.lastname: van Leeuwen
mesh_terms: D000818:Animals; D002232:Carbocyanines / Q000008:administration & dosage; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000008:administration & dosage; D013058:Mass Spectrometry / Q000379:methods*; D051379:Mice; D064847:Multimodal Imaging / Q000379:methods*; D057089:Pathology, Molecular / Q000379:methods*; D004369:Pentetic Acid / Q000008:administration & dosage; D011868:Radioisotopes / Q000008:administration & dosage; D019718:Receptors, CXCR4 / Q000032:analysis*; D000068936:Theranostic Nanomedicine / Q000379:methods*
chemical_list: C514936:CXCR4 protein, mouse; D002232:Carbocyanines; D005456:Fluorescent Dyes; D011868:Radioisotopes; D019718:Receptors, CXCR4; C085321:cyanine dye 5; D004369:Pentetic Acid
keywords: LA-ICP-MS imaging; SPECT.; bimodal; fluorescence; mass cytometry; mass spectrometry; molecular imaging; molecular pathology; radioisotopes