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Clin Cancer Res. 2011 Sep 15;17(18):5913-25. doi: 10.1158/1078-0432.CCR-11-0728. Epub 2011 Aug 1.

Resistance to CYP17A1 inhibition with abiraterone in castration-resistant prostate cancer: induction of steroidogenesis and androgen receptor splice variants.

Author information

  • 1Division of Clinical Research and Human Biology, Fred Hutchinson Cancer Research Center; Department of Medicine, University of Washington, Seattle, Washington, USA. emostagh@fhcrc.org

Abstract

PURPOSE:

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.

EXPERIMENTAL DESIGN:

We treated human CRPC xenografts with abiraterone and measured tumor growth, tissue androgens, androgen receptor (AR) levels, and steroidogenic gene expression versus controls.

RESULTS:

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 ± 0.22 to 0.03 ± 0.01 pg/mg (P < 0.0001), and from 0.69 ± 0.36 to 0.03 ± 0.01 pg/mg (P = 0.002) in abiraterone-treated 23CR and 35CR, respectively, with comparable decreases in tissue DHT. Treatment was associated with increased expression of full-length AR (AR(FL)) and truncated AR variants (AR(FL) 2.3-fold, P = 0.008 and AR(del567es) 2.7-fold, P = 0.036 in 23 CR; AR(FL) 3.4-fold, P = 0.001 and AR(V7) 3.1-fold, P = 0.0003 in 35CR), and increased expression of the abiraterone target CYP17A1 (∼2.1-fold, P = 0.0001 and P = 0.028 in 23CR and 35CR, respectively) and transcript changes in other enzymes modulating steroid metabolism.

CONCLUSIONS:

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.

©2011 AACR.

PMID:
21807635
[PubMed - indexed for MEDLINE]
PMCID:
PMC3184252
Free PMC Article

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