title: Targeting MT1-MMP as an ImmunoPET-Based Strategy for Imaging Gliomas.
abstract: BACKGROUND
  A critical challenge in the management of Glioblastoma Multiforme (GBM) tumors is the accurate diagnosis and assessment of tumor progression in a noninvasive manner. We have identified Membrane-type 1 matrix metalloproteinase (MT1-MMP) as an attractive biomarker for GBM imaging since this protein is actively involved in tumor growth and progression, correlates with tumor grade and is closely associated with poor prognosis in GBM patients. Here, we report the development of an immunoPET tracer for effective detection of MT1-MMP in GBM models.
  
  
  METHODS
  An anti-human MT1-MMP monoclonal antibody (mAb), LEM2/15, was conjugated to p-isothiocyanatobenzyl-desferrioxamine (DFO-NCS) for 89Zr labeling. Biodistribution and PET imaging studies were performed in xenograft mice bearing human GBM cells (U251) expressing MT1-MMP and non-expressing breast carcinoma cells (MCF-7) as negative control. Two orthotopic brain GBM models, patient-derived neurospheres (TS543) and U251 cells, with different degrees of blood-brain barrier (BBB) disruption were also used for PET imaging experiments.
  
  
  RESULTS
  89Zr labeling of DFO-LEM2/15 was achieved with high yield (>90%) and specific activity (78.5 MBq/mg). Biodistribution experiments indicated that 89Zr-DFO-LEM2/15 showed excellent potential as a radiotracer for detection of MT1-MMP positive GBM tumors. PET imaging also indicated a specific and prominent 89Zr-DFO-LEM2/15 uptake in MT1-MMP+ U251 GBM tumors compared to MT1-MMP- MCF-7 breast tumors. Results obtained in orthotopic brain GBM models revealed a high dependence of a disrupted BBB for tracer penetrance into tumors. 89Zr-DFO-LEM2/15 showed much higher accumulation in TS543 tumors with a highly disrupted BBB than in U251 orthotopic model in which the BBB permeability was only partially increased. Histological analysis confirmed the specificity of the immunoconjugate in all GBM models.
  
  
  CONCLUSIONS
  A new anti MT1-MMP-mAb tracer, 89Zr-DFO-LEM2/15, was synthesized efficiently. In vivo validation showed high-specific-contrast imaging of MT1-MMP positive GBM tumors and provided strong evidence for utility of MT1-MMP-targeted immunoPET as an alternate to nonspecific imaging of GBM.
authors.affiliation: Biomedical Application of Radioisotopes Unit, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain.
authors.forename: A G
authors.initials: AG
authors.lastname: de Lucas
authors.affiliation: Seve Ballesteros Foundation Brain Tumour Group, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
authors.forename: A J
authors.initials: AJ
authors.lastname: Schuhmacher
authors.affiliation: Biomedical Application of Radioisotopes Unit, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Oteo
authors.affiliation: Biomedical Application of Radioisotopes Unit, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Romero
authors.affiliation: Molecular Imaging Unit, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Cámara
authors.affiliation: Histopathology Unit, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: de Martino
authors.affiliation: Matrix Metalloproteases Lab, Spanish National Center for Cardiovascular Research (CNIC), Madrid Spain.
authors.forename: A G
authors.initials: AG
authors.lastname: Arroyo
authors.affiliation: Biomedical Application of Radioisotopes Unit, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain.
authors.forename: M Á
authors.initials: MÁ
authors.lastname: Morcillo
authors.affiliation: Seve Ballesteros Foundation Brain Tumour Group, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Squatrito
authors.affiliation: Proteomics Unit, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Martinez-Torrecuadrada
authors.affiliation: Molecular Imaging Unit, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Mulero
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D014408:Biomarkers, Tumor / Q000378:metabolism; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000201:enzymology; D045744:Cell Line, Tumor; D005909:Glioblastoma / Q000000981:diagnostic imaging* / Q000201:enzymology; D006801:Humans; D053511:Matrix Metalloproteinase 14 / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D055114:X-Ray Microtomography
chemical_list: D000911:Antibodies, Monoclonal; D014408:Biomarkers, Tumor; D053511:Matrix Metalloproteinase 14