Antibody-cytosine Deaminase Conjugate

With years of experience in antibody-cytosine deaminase conjugate for targeted immunotherapy, Creative Biolabs is able to offer high-quality antibody-directed enzyme prodrug therapy (ADEPT) development services for global clients. We have a full range of linkers and optimized conjugation strategies, and we are confident in providing clients world-class antibody-cytosine deaminase conjugate develop and production service.

Cytosine Deaminase

Cytosine deaminase is an enzyme that catalyzes cytosine within the water condition transformed into uracil and NH3. Therefore, the substrates of cytosine deaminase are cytosine and H2O. However, its two products are uracil and NH3. This enzyme is one of the hydrolases within the hydrolases family, those acting on carbon-nitrogen bonds specifically in cyclic amidines other than peptide bonds. The systematic name of this enzyme class is cytosine aminohydrolase. This enzyme is also referred to as isocytosine deaminase and involved in pyrimidine metabolism.

(a) The ribbon diagram of the bCD (bacterial cytosine deaminase) showing the hotspot residues (highlighted with different colors) chosen for in silico mutagenesis. (b) Zoomed in image of the protein for a clear view of the hotspot residues. Fig.1 (a) The ribbon diagram of the bCD (bacterial cytosine deaminase) showing the hotspot residues (highlighted with different colors) chosen for in silico mutagenesis. (b) Zoomed in image of the protein for a clear view of the hotspot residues. (Kohila, 2012)

MOA of Cytosine Deaminase

Cytosine deaminase catalyzes the hydrolytic cleavage of a prodrug and has the ability to convert the clinically used antifungal agent 5-fluorocytosine into the known antitumor drug 5-fluorouracil. Cytosine deaminase catalyzes the prodrug losing the NH3 and becoming a potent drug upon the enzyme entering a targeted tumor site to treat the tumor disease. 5-fluorouracil and its deoxyribonucleoside derivative, which are toxic and frequently cause leukopenia and gastrointestinal disorders, are extensively used for the treatment of metastatic cancer. However, Cytosine deaminase catalyzes the noncytotoxic prodrug 5-fluorocytosine into 5-fluorouracil, which can present in the fungal cells but not in mammalian cells without antineoplastic activity. Thus, the antibody-cytosine deaminase conjugate targets 5-fluorocytosine prodrug can be used in humans for the treatment of fungal infections.

Cytosine deaminase catalyzes 5-fluorocytosine prodrug to drug 5-fluorouracil. Fig.2 Cytosine deaminase catalyzes 5-fluorocytosine prodrug to drug 5-fluorouracil.

Antibody-cytosine Deaminase Conjugate-based ADEPT

ADEPT is an attractive molecule for cancer treatment. Cytosine deaminase (CD) has been used as an enzyme in the ADEPT system. Anti-gpA33 single-chain variable fragment (scFv) against the gpA33 antigen present on more than 95% of colorectal tumor cells was fused to bacterial CD (A33scFv: CD). Initial in vitro studies revealed enhanced selective toxicity of the prodrug to gpA33+ tumor cells of 300-fold when compared with the active drug alone. However, the bacterially expressed A33scFv: CD fusion protein presented significantly reduced catalytic activity when compared with nonfused CD. In addition, the yeast-expressed A33scFv: CDy had ten-times toxic than the bacterially produced protein. Therapeutic experiments with A33scFv: CDy/5-FC showed significant tumor regressions in mice bearing colorectal carcinoma xenografts.

Creative Biolabs is dedicated to helping clients develop antibody-cytosine deaminase conjugate using readily available or customized linkers or direct antibody-enzyme fusion proteins in a timely and cost-effective manner. Our customarily tailored services and high-quality products will contribute greatly to the success of your projects. Please contact us for more information.


  1. Kohila, V.; et al. Rationally designed Escherichia coli cytosine deaminase mutants with improved specificity towards the prodrug 5-fluorocytosine for potential gene therapy applications. MedChemComm. 2012, 3(10), 1316-1322.

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