Pharmacology of new aromatase inhibitors

Recent investigations of novel aromatase inhibitors have addressed several important questions related to the biochemical effects of this class of drugs. While aromatase inhibitors such as aminoglutethimide, formestane (given by the oral and i.m. route), rogletimide and fadrozole administered at different doses have been found to inhibit in vivo aromatization by 60-93%, the novel aromatase inhibitors, letrozole and anastrozole, are shown to inhibit in vivo aromatization by about 98%. Contrary to previous studies on aromatase inhibitors reporting plasma oestrogens sustained at 30-50% of their control levels letrozole and anastrozole suppress plasma oestrone sulphate by approximately 95%. Future studies should explore cross-resistance of aromatase inhibitors and steroidal antioestrogens and between different types of aromatase inhibitors. A major goal is to evaluate alterations in tissue oestrogen concentration as well as growth factor expression in response to oestrogen deprivation with aromatase inhibitors.