title: Specific tumour localisation of a huA33 antibody--carboxypeptidase A conjugate and activation of methotrexate-phenylalanine.
abstract: In antibody-directed enzyme-prodrug therapy (ADEPT), antibody-enzyme conjugates specifically activate non-toxic prodrugs in tumour tissue. The A33 cognate antigen is a promising target for immunotherapy of gastrointestinal cancers. We have explored A33-based ADEPT with carboxypeptidase A (CPA) and the prodrug, methotrexate-phenylalanine (MTX-Phe). In A33-positive SW1222 cells, the toxicity of MTX-Phe was about 3 logarithms lower compared to MTX. Preincubation with a huA33 antibody-CPA conjugate (huA33-CPA), but not with an isotypic control conjugate, rendered MTX-Phe equally toxic to MTX. No toxicity was observed in mice receiving MTX-Phe in 8-fold the LD50 of MTX. Nude mice bearing A33-positive SW1222 colon carcinoma xenografts were injected intravenously (IV) with 125I-labeled huA33-CPA. The conjugate localised to the tumour with a maximum from 6-24 h. Pre-treating these mice with excess A33 substantially reduced subsequent conjugate uptake, demonstrating immunologic specificity of tumour-uptake. Total tumour uptake and ratios of tumour over blood or normal tissues, however, were lower than with unconjugated A33. This may explain in part why no significant tumour responses were observed in xenografted mice. In summary, our results demonstrate in principle the feasibility of A33-based enzyme targeting, but they call for small recombinant antibody-enzyme constructs to facilitate tumour penetration and clearance from the bloodstream.
authors.affiliation: Medizinische Klinik III - Haematology, Oncology and Transfusion Medicine, Charité - Campus Benjamin Franklin, D-12200 Berlin, Germany. markus.deckert@charite.de
authors.forename: P Markus
authors.initials: PM
authors.lastname: Deckert
authors.forename: William G
authors.initials: WG
authors.lastname: Bornmann
authors.forename: Gerd
authors.initials: G
authors.lastname: Ritter
authors.forename: Clarence
authors.initials: C
authors.lastname: Williams
authors.forename: Juergen
authors.initials: J
authors.lastname: Franke
authors.forename: Ulrich
authors.initials: U
authors.lastname: Keilholz
authors.forename: Eckhard
authors.initials: E
authors.lastname: Thiel
authors.forename: Lloyd J
authors.initials: LJ
authors.lastname: Old
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Bertino
authors.forename: Sydney
authors.initials: S
authors.lastname: Welt
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism* / Q000494:pharmacology; D000951:Antigens, Neoplasm / Q000276:immunology; D043422:Carboxypeptidases A / Q000378:metabolism* / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000276:immunology / Q000378:metabolism / Q000628:therapy*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins / Q000276:immunology*; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D008819:Mice, Nude; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D011355:Prodrugs / Q000378:metabolism* / Q000494:pharmacology; D015996:Survival Rate; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; C104258:GPA33 protein, human; C504395:Gpa33 protein, mouse; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D011355:Prodrugs; C091716:methotrexate-alpha-phenylalanine; D010649:Phenylalanine; D043422:Carboxypeptidases A; D008727:Methotrexate