Coupled, connected.
A molecule created by fusing together (e.g., via recombination or chemically) two unlike (different) molecules. The purpose of this is to create a molecule in which one of the original molecules has one function, for example, a toxic, cell-killing function, while the other original molecule has another function, such as targeting the toxin to a specific site which might include cancerous cells. For example, molecules of interleukin-2 (IL-2) have been fused with molecules of diphtheria toxin to create a conjugate that does the following:
- It enters leukemia and lymphoma cells. Because these two types of cancer cells possess IL-2 receptors on their surfaces, the IL-2 (targeting function) binds to that receptor and is internalized.
- The diphtheria toxin (killing function) then shuts down protein synthesis within the cancer cells.
- It then kills the cancerous cells. This type of approach is widespread and there are many different types of conjugates. One type of conjugate consists of enzymes used in the treatment of certain molecular diseases attached covalently to polyethylene glycol (PEG). In this case the PEG greatly diminishes both the immunogenicity (the ability to induce an immune reaction) and the antigenicity (the ability to react with preformed antibodies). Antibodies may be used as vectors to carry both relatively small molecules of destructive chemicals or proteins to specific sites (cells) within the body. Antibodies may be coupled to enzymes, toxins, and/or ribosome-inhibiting proteins, as well as to radioisotopes. These conjugates are known collectively as immunoconjugates.