What is radioimmunotherapy?Radioimmunotherapy is a relatively new treatment for cancer patients. The aim is to generate a high dose of radioactive radiation in the vicinity of the tumor cells, which kills the tumor cells.
One uses so-called conjugated radiopharmaceuticals. It is a combination of a carrier molecule and a radioisotope. The carrier molecules are usually antigens or peptides.
These dock specifically at surface structures of the tumor cells, whereupon the radioisotope, usually a short-range beta emitter, destroys the tumor cell.
The antibody must be structured so that it binds exclusively to tumor cells and spares healthy tissue. The coupling of the two components takes place via an intermediate molecule.
Function, effect & goals
In the case of chemotherapy, all rapidly dividing cells of the body are attacked. In addition to the tumor cells, these include the mucous membrane cells of the mouth, stomach and intestine as well as cells of the hair roots. Almost always comes to strong side effects such as diarrhea, hair loss, mucous membrane diseases and blood cell changes.
Irradiation of the tumor from the outside by means of X-rays, electron or proton radiation usually also damages parts of the surrounding, healthy tissue. In addition, certain organs each bear only a certain tolerance dose that must not be exceeded. In the meantime, radiation therapy often uses several weak rays which intersect and add up in the tumor to be treated. But the burden on healthy tissue remains significant in many cases.
In the case of radioimmunotherapy, the antibodies injected into the bloodstream specifically target the tumor cells throughout the body. Thus, the conjugated radiopharmaceuticals can also find previously undetected cancerous foci in the body of the patient through imaging and clinical examinations, as the entire body is scanned via the bloodstream. The tumor cells are irradiated in the interior of the body from close proximity and are therefore exposed to a particularly high radiation dose, while sparing healthy tissue. Since the radioisotopes attach directly to the tumor cells, one generally needs a lower radiation intensity because of the smaller distance to the radiation source.
In addition, tumor cells in the adjacent lymph nodes, which can not be reached via antigens, are also reached by the radiation. This is called a "cross fire effect". The radioactive substance used sheds with a half-life of typically hours or days and is largely excreted in the urine via the kidneys.
In some cases additional medication and fluids are given to protect the kidneys.
For a radioimmunotherapy to be possible, a surface structure of the tumor cell must first be found which occurs exclusively there. Then an antigen must be produced which binds only to this type of surface structure. The finding of such specific surface structures on the respective tumor cells and the production of suitable antigens are the main difficulties in the development of this therapy.
This has been successful for some types of tumors, such as non-Hodgkin's lymphoma. The surface structure in this case is the CD-20 structure and the beta emitter used is yttrium. In this case the treatment can even be done on an outpatient basis.
There are promising approaches to combine radioimmunotherapy with chemotherapy. Only very few cancers have been known to date for which radioimmunotherapy has been successfully applied. The first and long only one was non-Hodgkin's lymphoma. Radioimmunotherapy is a fairly new therapy that has been used regularly for the treatment of cancer since the beginning of the 21st century. In many preclinical and, more recently, some clinical studies, it has proven to be more efficient compared to chemotherapy.
It is a promising concept for the future of tumor treatment and is the subject of intensive research worldwide. The main focus here is on the exploration of new possibilities in the production of carrier molecules.
Risks & Side Effects
The most common side effect is nausea. Overall, the expected side effects are usually less severe compared to chemotherapy and radiation.