ABSTRACT
The binding of hormonal steroids to receptors and serum proteins has been a subject of intensive investigation by steroid biochemists. The interaction of primary importance in the design of receptor-binding radiopharmaceuticals is the binding of the agent to the receptor. It is convenient to consider two categories of nonreceptor binding, high affinity nonreceptor binding and low affinity nonreceptor binding. The first category consists of certain binding proteins found in the serum, which for estrogens would be exemplified by rat alpha-fetoprotein and human sex steroid-binding protein. The second category of nonreceptor binding consists of low affinity sites, as are found on serum proteins such as albumin, or in lipoidal phases. More sophisticated biochemical characterization of the receptor interaction of a radiopharmaceutical can also be obtained after in vivo administration. The receptor-specific uptake in the tumors is about 25 to 30% that of the receptor-specific uptake of the mature uterus.
