title: Radiolabelling of glycosylated MFE-23::CPG2 fusion protein (MFECP1) with 99mTc for quantitation of tumour antibody-enzyme localisation in antibody-directed enzyme pro-drug therapy (ADEPT).
abstract: MFECP1 is a glycosylated recombinant fusion protein composed of MFE-23, a high-affinity anti-carcinoembryonic antigen (CEA) single chain Fv (scFv), fused to the enzyme carboxypeptidase G2 (CPG2), and has been constructed for use in antibody-directed enzyme pro-drug therapy (ADEPT). Radiolabelling of glycosylated MFECP1 with technetium-99m was developed for the purpose of determining tumour localisation of MFECP1 in a phase I ADEPT clinical study. The method used was 99mTc-carbonyl [99mTc(H2O)3(CO)3]+ (abbreviated to TcCO) mediated labelling of 99mTc to the hexahistidine (His) tag of MFECP1. MFECP1 fusion protein was labelled with TcCO under a variety of conditions, and this was shown to be a relatively simple and robust method. Tissue biodistribution was assessed in a CEA-expressing LS174T (human colon carcinoma) nude mouse xenograft model. Tissues were taken at 1, 4 and 6 h for assessment of distribution of radioactivity and for measurement of CPG2 enzyme levels. The amount of radioactivity retained by the tumour proved to be an accurate estimation of actual measured enzyme activity, indicating that this radiolabelling method does not appear to damage the antibody-antigen binding or the enzyme activity of MFECP1. However, correlation between CPG2 enzyme activity and measured radioactivity in liver, spleen and kidney was poor, indicating retention of radioactivity in non-tumour sites but loss of enzyme activity. The high retention of technetium radioisotope in normal tissues may limit the clinical applicability of this radiolabelling method for MFECP1; however, these results suggest that this technique does have applicability for measuring the biodistribution of His-tagged recombinant proteins.
authors.affiliation: Cancer Research UK Targeting and Imaging Group, Royal Free Campus of Royal Free and University College Medical School, NW3 2PF, London, UK.
authors.forename: R J
authors.initials: RJ
authors.lastname: Francis
authors.forename: S J
authors.initials: SJ
authors.lastname: Mather
authors.forename: K
authors.initials: K
authors.lastname: Chester
authors.forename: S K
authors.initials: SK
authors.lastname: Sharma
authors.forename: J
authors.initials: J
authors.lastname: Bhatia
authors.forename: R B
authors.initials: RB
authors.lastname: Pedley
authors.forename: R
authors.initials: R
authors.lastname: Waibel
authors.forename: A J
authors.initials: AJ
authors.lastname: Green
authors.forename: R H J
authors.initials: RH
authors.lastname: Begent
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000378:metabolism; D000818:Animals; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007167:Immunotherapy / Q000379:methods; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000737:chemistry / Q000493:pharmacokinetics*; D011355:Prodrugs / Q000627:therapeutic use; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D011993:Recombinant Fusion Proteins / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics*; D013667:Technetium / Q000737:chemistry / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D011623:gamma-Glutamyl Hydrolase / Q000378:metabolism*
chemical_list: D015609:Organotechnetium Compounds; D011355:Prodrugs; D019275:Radiopharmaceuticals; D011993:Recombinant Fusion Proteins; C496669:technetium Tc 99m MFECP1 protein; D013667:Technetium; D011623:gamma-Glutamyl Hydrolase