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Catalytic activity of an in vivo tumor targeted anti-CEA scFv::carboxypeptidase G2 fusion protein.

Abstract
Antibody-directed enzyme prodrug therapy (ADEPT) targets an enzyme selectively to a tumor where it converts a relatively non-toxic prodrug to a potent cytotoxic drug. Previous clinical work using antibody-enzyme chemical conjugates has been limited by the moderate efficiency of tumor targeting of these molecules. To address this a recombinant fusion protein composed of MFE-23, an anti-carcinoembryonic antigen (CEA) single chain Fv (scFv) antibody, fused to the amino-terminus of the enzyme carboxypeptidase G2 (CPG2) has been constructed to achieve ADEPT in CEA-producing tumors. MFE-23::CPG2 fusion protein was overexpressed in Escherichia coli and purified using CEA affinity chromatography. Efficacy of MFE-23::CPG2 delivery to tumors in vivo was assessed by measuring catalytic activity after intravenous injection of purified MFE-23::CPG2 into nude mice bearing CEA-positive LS174T human colon adenocarcinoma xenografts. Recombinant MFE-23::CPG2 cleared rapidly from circulation and catalytic activity in extracted tissues showed tumor to plasma ratios of 1.5:1 (6 hr), 10:1 (24 hr), 19:1 (48 hr) and 12:1 (72 hr). (125)I-MFE-23::CPG2 was retained in kidney, liver and spleen but MFE-23::CPG2 catalytic activity was not, resulting in excellent tumor to normal tissue enzyme ratios 48 hr after injection. These were 371:1 (tumor to liver), 450:1 (tumor to lung), 562:1 (tumor to kidney), 1,477:1 (tumor to colon) and 1,618:1 (tumor to spleen). Favorable tumor : normal tissue ratios occurred at early time points when there was still 21% (24 hr) and 9.5% (48 hr) of the injected activity present per gram of tumor tissue. The high tumor concentrations and selective tumor retention of active enzyme delivered by MFE-23::CPG2 establish that this recombinant fusion protein has potential to give improved clinical efficiency for ADEPT.
AuthorsJ Bhatia, S K Sharma, K A Chester, R B Pedley, R W Boden, D A Read, G M Boxer, N P Michael, R H Begent
JournalInternational journal of cancer (Int J Cancer) Vol. 85 Issue 4 Pg. 571-7 (Feb 15 2000) ISSN: 0020-7136 [Print] United States
PMID10699932 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
CopyrightCopyright 2000 Wiley-Liss, Inc.
Chemical References
  • Carcinoembryonic Antigen
  • Immunoglobulin Variable Region
  • Prodrugs
  • Recombinant Fusion Proteins
  • gamma-Glutamyl Hydrolase
Topics
  • Animals
  • Carcinoembryonic Antigen (immunology)
  • Cloning, Molecular
  • Colonic Neoplasms (drug therapy, metabolism)
  • Escherichia coli
  • Humans
  • Immunoglobulin Variable Region (immunology)
  • Mice
  • Mice, Nude
  • Prodrugs (pharmacokinetics, therapeutic use)
  • Recombinant Fusion Proteins (pharmacokinetics, therapeutic use)
  • Tissue Distribution
  • Transplantation, Heterologous
  • gamma-Glutamyl Hydrolase (metabolism, therapeutic use)

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