Radiolabeling of an anti-carcinoembryonic antigen antibody Fab' fragment (CEA-Scan) with the positron-emitting radionuclide Tc-94m.

The goal of this work was to test whether an antibody-based agent approved for use as a single-photon-emitting imaging agent when radiolabeled with technetium-99m could be labeled comparably with a positron-emitting nuclide, technetium-94m. "Instant kits" containing lyophilized NP-4 antibody Fab' fragment of an anticarcinoembryonic antigen IgG (CEA-Scan) from the same manufactured lot were reconstituted with either Tc-99m or Tc-94m, as solutions of sodium pertechnetate in isotonic saline solution. Radioanalyses of the labeled Fab' fragments by size-exclusion high-performance chromatography and TLC were carried out. Equivalent results were obtained for radioimmunoconjugates when each was analyzed with both methods. Facile incorporation of Tc-94m into tumor-targeting Fab' antibody fragments will enable investigation of such agents for tumor-specific imaging using positron emission tomography.