Clinical Research Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N. PO Box 19024 Seattle, WA.
Abiraterone is a potent inhibitor of the steroidogenic enzyme CYP17A1 and suppresses tumor growth in patients with castration-resistant prostate cancer (CRPC). The effectiveness of abiraterone in reducing tumor androgens is not known, nor have mechanisms contributing to abiraterone resistance been established.
We treated human CRPC xenografts with abiraterone and measured tumor growth, tissue androgens, androgen receptor (AR) levels, and steroidogenic gene expression vs. controls.
Abiraterone suppressed serum PSA levels and improved survival in two distinct CRPC xenografts: median survival of LuCaP35CR improved from 17 to 39 days (HR 3.6, p=0.0014) and LuCaP23CR from 14 to 24 days (HR 2.5, p=0.0048). Abiraterone strongly suppressed tumor androgens, with testosterone (T) decreasing from 0.49 + 0.05 to 0.07 + 0.04 pg/mg (p< 0.0001), and from 0.69 + 0.11 to 0.22 + 0.08 pg/mg (p=0.002) in abirater-one-treated 23CR and 35CR, respectively, with comparable decreases in tissue DHT. Treatment was associated with increased expression of full length AR (ARFL) and trun-cated AR variants (ARFL 2.3 fold, p=0.008 and ARdel567es 2.7 fold, p=0.036 in 23CR; ARFL 3.4 fold, p=0.001 and ARV7 3.1 fold, p=0.0003 in 35CR), and increased expression of the abiraterone target CYP17A1 (~2.1 fold, p=0.0001and p=0.028 in 23CR and 35CR, respectively) and transcript changes in other enzymes modulating steroid metabolism.
These studies indicate that abiraterone reduces CRPC growth via suppression of intratumoral androgens and that resistance to abiraterone may occur through mechanisms that include upregulation of CYP17A1, and/or induction of AR and AR splice variants that confer ligand-independent AR transactivation.
Mostaghel EA, Marck B, Plymate S, Vessella RL, Balk SP, Matsumoto AM, Nelson PS, Montgomery B. Are you the author?
Reference: Clin Cancer Res. 2011 Aug 1. Epub ahead of print.