Use of the probasin promoter ARR(2)PB to express Bax in androgen receptor-positive prostate cancer cells

Background: Adenovirus-mediated overexpression of the apoptosis-inducing pr otein Bax can induce apoptosis in prostate cancer cell lines. Constitutive overexpression of Bax could result in unwanted apoptosis in every site of a ccidental Bax accumulation in vivo. Therefore, we developed an adenoviral c onstruct (Av-ARR(2)PB-Bax) in which the probasin promoter, modified to cont ain two androgen response elements, drives Bax expression. This promoter wo uld be expected to limit expression of Bax to cells expressing the androgen receptor. Methods: A variety of androgen receptor (AR)-positive and -negat ive cell lines of prostatic or nonprostatic origin were infected with Av-AR R2PB-Bax or a control virus, Av-ARR(2)PB-CAT, in which the same promoter dr ives expression of the chloramphenicol acetyl transferase-reporter gene. Ba x expression and apoptosis in vitro were assessed by western blot analysis. Tumor size and apoptosis in vivo were assessed after four weekly injection s of Av-ARR(2)PB-Bax or Av-ARR(2)PB-CAT into subcutaneous LNCaP xenografts growing in uncastrated male mice. All statistical tests were two-sided. Res ults: Bax was overexpressed in an androgen-dependent way in AR-positive cel l lines of prostatic origin but not in AR-positive cells of nonprostatic or igin or in AR-negative cell lines of either prostatic or nonprostatic origi n. The androgen dihydrotestosterone activated apoptosis in LNCaP cells infe cted with Av-ARR2PB-Bax but not in those infected with Av-ARR(2)-PB-CAT. Av -ARR(2)PB-Bax-injected LNCaP xenograft tumors decreased in tumor size from 34.1 mm(3) (95% confidence interval [CI] = 25.1 mm(3) to 43.1 mm(3)) to 24. 6 mm(3) (95% CI = -2.5 mm(3) to 51.7 mm(3)), but the difference was not sta tistically significant (P = .5). Tumors injected with Av-ARR(2)PB-CAT incre ased in size, from 28.9 mm(3) (95% CI = 12.7 mm(3) to 45.1 mm(3)) to 206 mm (3) (95% CI = 122 mm(3) to 290 mm(3)) (P = .002) and contained statisticall y significant more apoptotic cells (23.3% [95% CI = 21.1% to 25.6%] versus 9.5% [95% CI = 8.0% to 11.1]) (P < .001). Conclusions: Av-ARR2PB-Bax induce s androgen-dependent therapeutic apoptosis in vitro and in vivo by activati ng apoptosis in AR-positive cells derived specifically from prostatic epith elium and does not affect nonprostatic cells.