Design of radiopharmaceuticals

Abstract

The major objective in the design of a radiopharmaceutical is to assure that it accumulates in and is eliminated from the target organ/tissue, blood and whole body. Since a radiopharmaceutical is made up of two components — radionuclide and non-radioactive compound — the design criteria must take into account the biologic activity not only of the individual component but also of the product, the radiopharmaceutical. When the biologic activity resides only in the radionuclide, the radiopharmaceutical is either an element (133Xe) or a completely ionized molecule (99mTcO−4, 123I− or 201Tl+), in which case the non-radioactive component serves as a co-ion (Na+ or Cl−). When the biologic activity resides only in the non-radioactive component (antibodies, MDP, colloids or MAA), the radionuclide serves only as a tag (99mTc) for external monitoring. When the biologic activity is shared by both the radionuclide and the non-radioactive compound, a coordinated complex with the radionuclide as the central atom is formed (99mTc-IDA derivates, 99mTc-d,l-HMPAO or 99mTc-sestamibi). To design the above categories of radiopharmaceuticals rationally, a number of processes are involved, and these are grouped together under radionuclide, chemistry, biology, human studies and registration.