The synthesis of 16α-[ 131I]iodo-oestradiol and evaluation of its use as a radiotracer for oestrogen receptor positive breast tumours

Abstract

16α-Iodo-oestradiol binds with high affinity to the oestrogen receptor and has been shown to accumulate in oestrogen sensitive tissues in many test systems. We have prepared the compound labelled with 131I at four specific activities. Using these preparations we have attempted to image human primary and metastatic breast cancer deposits at various times from 15 min to 24 h post injection by external gamma scintigraphy. Clinical studies were conducted on 10 post-menopausal patients. The receptor status was determined in seven cases, four were positive and three negative. The imaging results were very poor, in only two cases were images obtained, these were very faint and only of the primary, never of the metastatic deposits. The oestrogen receptor status was only available in one of these cases, it was positive. Dynamic studies in vivo revealed that the compound is cleared rapidly from the circulation during the first 5 min and thereafter undergoes extensive enterohepatic recycling. Studies of the radiochemical identity of the circulating species revealed that the injected compound was extensively metabolised. Neither an increase in specific activity of injected radiotracer nor imaging at shorter times after injection improved the results.