Fragment-Drug Conjugation (FDC)

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As a leading CRO, BOC Sciences has been supporting customers at the forefront of drug conjugation. Compared to antibody drug conjugate, fragment drug conjugate uses a smaller molecular weight antibody fragment as the targeting fraction, which is more conducive to penetrating solid tumors and is easily bioengineered. We provide fragment-drug conjugation services to meet unique project needs of our clients. Our scientific team will work with you to create a scope of work to complete the project on time and within specifications.

Find out more with Drug Conjugation Services.


Antibody fragment drug conjugates (FDCs) are a class of conjugated drugs with the ability to target tumor molecules by replacing antibody macromolecules of antibody fragments in ADC drugs. Compared with ADC, FDC has a smaller molecular weight, which is more conducive to penetrating solid tumors, and shorter biological half-life, which can effectively reduce the toxicity and side effects caused by high systemic accumulation. In addition, FDCs are easier to discover and can be easily bioengineered with multiple drug molecules for higher drug loading.

FDCs are composed of humanized antibody fragments, cytotoxic loads and linkers. The antibody fragments are coupled with cytotoxic drugs through linkers, which together endow FDC cells with targeting and cell killing efficacy. The biggest difference from ADC is the target part, FDC contains smaller antibody fragments, such as antigen binding fragment (Fab), single domain antibody (sdAb), single chain variable fragment (scFv), small immune protein (SIP), diabody, etc. By changing the chemical structure and length of the linker and adding PEG polymers to the conjugated drugs, they can precisely control the PK, toxin/antibody fragment loading ratio (DAR), druggability, efficacy and safety of FDC drugs.

Classification of FDCs

Several representative antibody fragment conjugates are briefly introduced below.

  • Antigen-binding fragment drug conjugates

Fabs contain the constant and variable domains of IGg, linked by a single disulfide bond located at the C-terminus, ideal for drug conjugation via bisalkylation conjugation. Generally, enzymes such as papain, pepsin, and IdeS can be applied to the hydrolysis of site-specific IgG proteins.

  • Single domain antibodies drug conjugates

sdAbs refer to a class of heavy-chain antibodies that are naturally deficient in the light and heavy chain constant regions of antibodies found in camelid animals, exhibiting high antigen-binding activity and low autoimmunity. Specific single-domain antibodies against specific antigens can be obtained by immunizing camelid animals or phage display technology.

  • Single chain fragment variable drug conjugates

ScFv antibodies contain a variable heavy chain and a variable light chain region, which are linked by a synthetic flexible peptide linker between the two variable regions. Similar to Fabs, scFvs have the potential for low-cost prokaryotic expression and increased tissue penetration, but exhibit short in vivo half-lives, rapid clearance, and lack of effector functions. For instance, ANT-043 is a scFv conjugated drug for the treatment of refractory solid tumors which is superior to ADCs for reaching hard-to-access solid tumors. In preclinical studies, compared with Herceptin-based ADC drugs, ANT-043 has stronger tumor penetration and more flexible PK profile.


Compared with antibody-drug conjugates, antibody fragment drug conjugates offer more efficient delivery of cytotoxic payloads to solid tumors, faster clearance and higher therapeutic windows, which largely make up for the therapeutic defects of antibody conjugates, increase anticancer efficacy, and have broader application space as well as clinical benefits in the treatment of solid tumors.

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