Galeterone (VN 124) is an orally bioavailable small-molecule androgen receptor modulator and CYP17 lyase inhibitor with potential antiandrogen activity. Galeterone exhibits three distinct mechanisms of action: 1) as an androgen receptor antagonist, 2) as a CYP17 lyase inhibitor and 3) by decreasing overall androgen receptor levels in prostate cancer tumors, all of which may result in a decrease in androgen-dependent growth signaling. Localized to the endoplasmic reticulum (ER), the cytochrome P450 enzyme CYP17 (P450C17 or CYP17A1) exhibits both 17alpha-hydroxylase and 17, 20-lyase activities, and plays a key role in the steroidogenic pathway that produces progestins, mineralocorticoids, glucocorticoids, androgens, and estrogens.

Androgen receptor:384 nM, CYP17:300 nM

Galeterone在阻止[3H]-R1881与突变LNCaP AR (T877A)的结合方面有效，IC50为845 nM。Galeterone以剂量依赖性方式抑制DHT诱导的LNCaP和LAPC4细胞增殖，其IC50分别为6μM和3.2μM。[1] Galeterone还能抑制[3H]-R1881与PC3细胞中T575A突变AR的结合，IC50为454 nM。Galeterone在没有DHT刺激的情况下强效抑制LNCaP和LAPC4细胞增殖，其IC50分别为2.6μM和4μM。此外，Galeterone治疗以剂量依赖性方式增加AR降解率。[2] Galeterone强效抑制雄激素独立细胞系PC-3和DU-145的增长，以剂量依赖性方式，其GI50分别为7.82μM和7.55μM。Galeterone诱导内质网应激反应，导致cyclin D1蛋白表达下调和cyclin E2 mRNA下调。[3] Galeterone有效抑制HP-LNCaP和C4-2B细胞系的增殖，IC50分别为2.9μM和9.7μM。1μM的Galeterone治疗有效抑制LNCaP细胞（50%）和HP-LNCaP细胞（70%）的雄激素受体激活。Galeterone 1μM和411 nM的IC50分别降低LNCaP细胞和HP-LNCaP细胞的雄激素受体激活，并在24小时治疗后通过50%下调雄激素受体蛋白表达。[4] Galeterone降低AR蛋白和mRNA表达，对抗由雄激素诱导的AR依赖性启动子激活，并显著降低phospho-4EBP1水平。[6]

给予Galeterone（50 mg/kg，每日两次）极其有效地抑制了依赖雄激素的LAPC4人类前列腺肿瘤异种移植物的生长，与对照组相比，最终平均肿瘤体积减少了93.8%，其效果也明显优于去势手术。[1] 通过每日两次给予Galeterone（0.13 mM/kg）或Galeterone（0.13 mmol/kg）加上去势手术，可以使SCID小鼠体内的LAPC4肿瘤异种移植物分别退缩26.55%和60.67%。Galeterone单独使用或结合去势治疗，分别可使AR蛋白的表达量显著降低10倍和5倍。[2]

In vitro assay of CYP17: The in vitro CYP17 inhibitory activity of Galeterone is evaluated using rapid acetic acid releasing assay (AARA), utilizing intact P450c17-expressing E. coli as the enzyme source. It involves the use of [21-3H]-17α-hydroxypregnenolone as the substrate, and CYP17 activity is measured by the amount of tritiated acetic acid formed during the cleavage of the C-21 side chain of the substrate. IC50 value is obtained directly from plots relating percentage inhibition versus inhibitor concentration over appropriate ranges.

Cells are seeded in 24 well multi-well plates. Cells are treated with the increasing concentration of Galeterone in steroid free medium with or without 1 nM DHT (LNCaP), or 10 nM DHT (LAPC4) and allowed to grow for 7 days. The number of viable cells is compared by MTT assay (LAPC4) or XTT assay (LNCaP) on the 7th day. (Only for Reference)