The linkers are designed to be stable in the bloodstream and then release the active drug from the targeting ligand when the SMDC is taken up by the diseased cell.
The drug payloads are highly active molecules that are too toxic to be administered in their untargeted forms at therapeutic dose levels[citation needed].
This modular approach allows varying targeting ligands, linker systems and drug payloads and generate SMDCs for different diseases.
[1] The most advanced SMDC is vintafolide, a derivative of the anti-mitotic chemotherapy drug vinblastine which is chemically linked to folic acid.
[2] Potent, bioactive natural products like triptolide that inhibit mammalian transcription has been recently reported as a glucose conjugate for targeting hypoxic cancer cells with increased glucose transporter expression.