title: Insertion of a lysosomal enzyme cleavage site into the sequence of a radiolabeled neuropeptide influences cell trafficking in vitro and in vivo.
abstract: Radiolabeled neuropeptides are widely explored for targeting tumours for either imaging or radiotherapeutic purposes. After binding to their receptors, these peptides are rapidly internalized into lysosomes, where they are degraded by proteolytic enzymes, such as cathepsins. The aim of this study was to investigate the effect of the inclusion of specific cleavage sites for cathepsin B into the peptide sequence. The cleavage site, GFLG, together with a series of dipeptides for pharmacokinetic modification of radiometabolites, were, therefore, inserted into a peptide that binds to the gastrin/CCK2 receptor. The receptor binding of the peptides was explored in AR42J cells, rates of internalization, and externalization of the radionuclide were measured and the nature of the radiometabolites explored. The effects of the modifications on biodistribution in tumor-bearing mice was explored by high-resolution single-photon emission computed tomography imaging. Differences in rates of externalization from tumor cells in vitro and in the rates of washout from tumor and kidney in vivo were observed. These results indicate that insertion of an enzymatic cleavage site, such as that for cathepsin B, into a neuropeptide appears to have an influence on the intracellular processing, which results in a change in the rate of egress of radioactivity from target and nontarget tissues.
authors.affiliation: Center for Molecular Oncology and Imaging, Institute of Cancer, Queen Mary University of London, Barts and the London School of Medicine and Dentistry, London, United Kingdom.
authors.forename: Syed Ali Raza
authors.initials: SA
authors.lastname: Naqvi
authors.forename: Torkjel
authors.initials: T
authors.lastname: Matzow
authors.forename: Ciara
authors.initials: C
authors.lastname: Finucane
authors.forename: Saeed A
authors.initials: SA
authors.lastname: Nagra
authors.forename: Malik M
authors.initials: MM
authors.lastname: Ishfaq
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Mather
authors.forename: Jane
authors.initials: J
authors.lastname: Sosabowski
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D020134:Catalytic Domain; D002401:Cathepsin B / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry* / Q000493:pharmacokinetics; D007553:Isotope Labeling; D008247:Lysosomes / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D009479:Neuropeptides / Q000737:chemistry* / Q000493:pharmacokinetics; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000737:chemistry* / Q000493:pharmacokinetics; D051381:Rats
chemical_list: D007205:Indium Radioisotopes; D009479:Neuropeptides; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; D002401:Cathepsin B