YM-511

Aromatase (CYP19) is a rate-limiting enzyme that catalyzes the biosynthesis of estrogens. Imaging agents based on aromatase inhibitors (AIs) have been developed for a PET/SPECT study. A series of compounds was synthesized based on YM511, which has previously been used for breast cancer treatment. Two examples of these derivatives, 4-(((4-iodophenyl)methyl)-4H-1,2,4-triazol-4-yl-amino)-benzonitrile (5) and 4-((1H-imidazol-1-yl)(4-iodobenzyl)amino)benzonitrile (11), displayed potent binding affinities to human aromatase (IC₅₀ = 0.17 and 0.04 nM, respectively). Biodistribution and autoradiographic studies revealed that [¹²⁵I]5 and [¹²⁵I]11 were highly accumulated in the stomach (16.21 and 10.88% dose/g, respectively) and ovaries (8.56 and 3.32% dose/g, respectively) of female rats. Log P of [¹²⁵I]5 was 2.49, meaning good brain penetration. Autoradiograms of brain sections showed a high uptake in the bed nucleus of the stria terminalis and amygdala. These results suggest that [¹²⁵I]5 and [¹²⁵I]11 are potent probes for aromatase imaging in both the brain and peripheral organs.

Estrogens and androgens are instrumental in the maturation of many hormone-dependent cancers. Consequently, the enzymes involved in their synthesis are cancer therapy targets. One such enzyme, steroid sulfatase (STS), hydrolyses estrone sulfate, and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone respectively. These are the precursors to the formation of biologically active estradiol and androstenediol. This review focuses on three aspects of STS inhibitors: 1) chemical development, 2) biological activity, and 3) clinical trials. The aim is to discuss the importance of estrogens and androgens in many cancers, the developmental history of STS inhibitor synthesis, the potency of these compounds in vitro and in vivo and where we currently stand in regards to clinical trials for these drugs. STS inhibitors are likely to play an important future role in the treatment of hormone-dependent cancers. Novel in vivo models have been developed that allow pre-clinical testing of inhibitors and the identification of lead clinical candidates. Phase I/II clinical trials in postmenopausal women with breast cancer have been completed and other trials in patients with hormone-dependent prostate and endometrial cancer are currently active. Potent STS inhibitors should become therapeutically valuable in hormone-dependent cancers and other non-oncological conditions.