Abstract 4537: Interaction with wild-type (wt) androgen receptor (AR) alters the function of AR splice-variants and response to AR-ligand binding domain inhibition
Authors: Sun Shihua , Sprenger Cynthia T. , Haugk Kathy , Mostaghel Elahe , Plymate Stephen 
Published: June 2012

Abstract
Introduction: Androgen ablation induces splicing of AR pre-mRNA to produce constitutively active AR-variants. However, these variants usually co-exist in a cell with wtAR and may form heterodimers with the wtAR. This dimerization results in the activity of the variant being directed via ligand activated AR. In contrast, the AR splice variants may act independent of their association with wtAR. Clinically differentiating these two potential activities is crucial since the former activity would respond to agents targeting the ligand-binding domain (LBD) while the latter would not respond.
Purpose: To determine if wtAR accounts for the activity of AR splice variants in cells and the effect co-existence of both variants has on therapy directed at the AR LBD.
Methods: We expressed AR splice variants V7 or ARv567es along with wtAR at various ratios in M12 AR-null cells or the variants alone at graded concentrations in LNCaP or CWR22Rv1 cells. AR activity was determined by probasin AR-luciferase in all cells and PSA and TMPRSS2 mRNA in LNCaP and CWR22Rv1 cells. Response to LBD inhibition was determined by the addition of MDV-3100. Expression ratios of wt and variant AR were determined by qt-RTPCR and Western immunoblot.
Results: WtAR or AR variants were expressed at ratios ranging from 1:10 to 10:1 in M12 cells. In the absence of wtAR, there was marked elevation ARE-reporter activity when either V7 or ARv567es were expressed and there were no differences in reporter activity when either DHT or MDV-3100 were added_consistent with these variants being constitutively active. WtAR showed minimal ARE-LUC activity until DHT was added. MDV-3100 blocked the DHT-induced ARE-LUC activity in wtAR transfected cells by &gt;95%. As increased concentrations of wtAR were expressed in cells transfected with AR variants, the ligand-independent activity of AR variants was suppressed. However, MDV-3100 could not suppress the constitutive AR activity. Similar results were seen in LNCaP cells. In contrast, for CWR22Rv1 cells, which express primarily the V7 AR variant but have no ligand-independent AR activity and transactivate AR with DHT, MDV-3100 completely suppressed ARE-LUC activity. However, transfection with ARv567es resulted in a &gt;100 fold increase in basal ARE-LUC activity that was not affected by MDV-3100.
Summary: These data indicate that the presence of wtAR suppresses AR V7 and ARv567es ligand-independent activity by heterodimerization as previously described. This effect imbues partial responsiveness to MDV-3100. However, as the proportion of AR variant to wtAR is increased, response to MDV-3100 is lost.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4537. doi:10.1158/1538-7445.AM2011-4537