Technetium (99mTc) arcitumomab

Technetium (^99mTc) arcitumomab is a drug used for the diagnostic imaging of colorectal cancers, marketed by Immunomedics. It consists of the Fab' fragment of a monoclonal antibody (arcitumomab, trade name CEA-Scan) and a radionuclide, technetium-99m.

Chemistry

Technetium (^99mTc) arcitumomab is an immunoconjugate. Arcitumomab is a Fab' fragment of IMMU-4, a murine IgG1 monoclonal antibody extracted from the ascites of mice. The enzyme pepsin cleaves the F(ab')₂ fragment off the antibody. From this, the Fab' fragment is prepared by mild reduction.

Before application, arcitumomab is reconstituted with a solution of the radioactive agent sodium pertechnetate (^99mTc) from a technetium generator.

Mechanism of action

Arcitumomab recognizes carcinoembryonic antigen (CEA), an antigen over-expressed in 95% of colorectal cancers. Consequently, the antibody accumulates in such tumours together with the radioisotope, which emits photons. Via single photon emission computed tomography (SPECT), high-resolution images showing localisation, remission or progression, and metastases of the tumour can be obtained.

Contraindications

Technetium (^99mTc) arcitumomab is contraindicated for patients with known allergies or...
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