946. Effect of Androgen Receptor Suppression Using Dominant Negative Inhibition on Castration-Resistant Prostate Cancer
Authors: Brian J. Zeithaml, Mark Titus, Karin Haack, Adam Cockrell, Angela Ponguta, Elizabeth Wilson, James Mohler, Tal Kafri
Journal: Molecular Therapy (2006)

An American dies from CaP every 17 minutes. Advanced prostate cancer almost always responds to androgen deprivation therapy but inevitably recurs as castration-resistant prostate cancer. Recent evidence suggests that the growth of most cases of castration-resistant prostate cancer depends upon androgen receptor (AR) activation 1 and that AR activation may be due to a combination of AR hypersensitization2-6 and low levels of dihydrotestosterone and/ortestosterone (DHT/T), 7,8 intracellular testicular androgens produced by intracrine metabolism from cholesterol or adrenal androgens. The role of AR in castration-resistant prostate cancer can be studied using an AR dominant negative mutant, ΔTR (Wilson unpublished) and CWR-R1, a castration-resistant prostate cancer cell line9. ΔTR contains a deletion in the NH2-terminal region that results in loss of the AR transactivating domain and inhibits wild type AR possibly due to dimerization and loss of binding of one or more coactivators. Activation of ΔTR appears to require binding of DHT and/or T for interaction with and transactivational inhibition of endogeneous AR. Past evidence reveals that CWR-R1 cells express high levels of AR, grow in the absence of DHT/T when supplemented with EGF, and increase cell proliferation when supplied with DHT9. Suppressing AR using ΔTR delivered via lentiviral vectors tested the hypothesis that CaP recurrence can be delayed or prevented by interfering with AR function. Lentiviral vectors achieved high level expression of ΔTR which decreased endogenous hK2 (an AR- regulated gene product) expression, decreased plasmid luciferase expression from the MMTV promoter (an AR target promoter), decreased CWR-R1 cell proliferation in culture, and inhibited xenografted CWR-R1 tumor growth in castrated mice with DHT pellet implants (all unpublished). ΔTR must require higher amounts of DHT or other cofactors than AR for activation since in vivo CWR-R1 tumor growth rates were slowed but not eliminated. To address this question, ligand-independent shRNA will be used to knockdown AR independent of the need for DHT/T for ΔTR dimerization and effect. CWR-R1 proliferation and in vivo tumor growth of the ΔTR-transduced and AR-targeted shRNA-transduced cells will further enlarge our understanding of the role of AR in castration-resistant prostate cancer.1Debes JD and Tindall DJ. (2004) N Engl J Med. 315, 1488-90.2Tapin ME et al. (1995) N Engl J Med. 332, 1392-8.3Shi X et al. (2002) Cancer Res. 62, 1496-1502.4Culig Z et al. (1993) Mol Endocrinol. 7, 1541-50.5Peterziel H et al. (1995) Int J Cancer. 63, 544-50.6Tan JA et al. (1997) Mol Endocrinol. 11, 450-9.7Mohler JL et al. (2004) Clin Cancer Res. 10, 440-48.8Titus MA et al. (2005) Clin Cancer Res. 11, 4365-71.9Gregory CW et al. (2001) Cancer Res. 61, 2892-8. An American dies from CaP every 17 minutes. Advanced prostate cancer almost always responds to androgen deprivation therapy but inevitably recurs as castration-resistant prostate cancer. Recent evidence suggests that the growth of most cases of castration-resistant prostate cancer depends upon androgen receptor (AR) activation 1 and that AR activation may be due to a combination of AR hypersensitization2-6 and low levels of dihydrotestosterone and/ortestosterone (DHT/T), 7,8 intracellular testicular androgens produced by intracrine metabolism from cholesterol or adrenal androgens. The role of AR in castration-resistant prostate cancer can be studied using an AR dominant negative mutant, ΔTR (Wilson unpublished) and CWR-R1, a castration-resistant prostate cancer cell line9. ΔTR contains a deletion in the NH2-terminal region that results in loss of the AR transactivating domain and inhibits wild type AR possibly due to dimerization and loss of binding of one or more coactivators. Activation of ΔTR appears to require binding of DHT and/or T for interaction with and transactivational inhibition of endogeneous AR. Past evidence reveals that CWR-R1 cells express high levels of AR, grow in the absence of DHT/T when supplemented with EGF, and increase cell proliferation when supplied with DHT9. Suppressing AR using ΔTR delivered via lentiviral vectors tested the hypothesis that CaP recurrence can be delayed or prevented by interfering with AR function. Lentiviral vectors achieved high level expression of ΔTR which decreased endogenous hK2 (an AR- regulated gene product) expression, decreased plasmid luciferase expression from the MMTV promoter (an AR target promoter), decreased CWR-R1 cell proliferation in culture, and inhibited xenografted CWR-R1 tumor growth in castrated mice with DHT pellet implants (all unpublished). ΔTR must require higher amounts of DHT or other cofactors than AR for activation since in vivo CWR-R1 tumor growth rates were slowed but not eliminated. To address this question, ligand-independent shRNA will be used to knockdown AR independent of the need for DHT/T for ΔTR dimerization and effect. CWR-R1 proliferation and in vivo tumor growth of the ΔTR-transduced and AR-targeted shRNA-transduced cells will further enlarge our understanding of the role of AR in castration-resistant prostate cancer. 1Debes JD and Tindall DJ. (2004) N Engl J Med. 315, 1488-90. 2Tapin ME et al. (1995) N Engl J Med. 332, 1392-8. 3Shi X et al. (2002) Cancer Res. 62, 1496-1502. 4Culig Z et al. (1993) Mol Endocrinol. 7, 1541-50. 5Peterziel H et al. (1995) Int J Cancer. 63, 544-50. 6Tan JA et al. (1997) Mol Endocrinol. 11, 450-9. 7Mohler JL et al. (2004) Clin Cancer Res. 10, 440-48. 8Titus MA et al. (2005) Clin Cancer Res. 11, 4365-71. 9Gregory CW et al. (2001) Cancer Res. 61, 2892-8.