TheProstate69:595^602(2009) Overexpression of 5a -ReductaseType1Increases Sensitivityof Prostate Cancer Cellsto Low Concentrations of Testosterone Lynn N. Thomas, 1 * Robert C. Douglas, 2 Roger S. Rittmaster, 3,4 and Catherine K.L. Too 1,5 1 Departmentof Biochemistry & Molecular Biology,Dalhousie University,Halifax,Nova Scotia,Canada 2 Departmentof Pharmacology,Dalhousie University,Halifax,Nova Scotia,Canada 3 Departmentof Physiology & Biophysics,Dalhousie University,Halifax,Nova Scotia,Canada 4 ResearchandDevelopment,GlaxoSmithKline,RTP,NorthCarolina 5 DepartmentofObstetricsandGynecology,DalhousieUniversity,Halifax,NovaScotia,Canada INTRODUCTION. Conversion of testosterone to dihydrotestosterone (DHT) by the enzymes 5a-reductase types 1 (5aR1) and 2 (5aR2) is important for normal and pathological growth of the prostate. The predominant isoenzyme in normal prostate is 5aR2. However, prostate cancer (PCa) development is accompanied by a decrease in 5aR2 and an increase in 5aR1. The biological significance of increased 5aR1 expression is not fully understood. Therefore, the aim of this study was to determine the effect of overexpression of 5aR1 on growth and prostate-specific antigen (PSA) production in PCa cells. MATERIALS AND METHODS. LNGK-9 PCa cells, transiently transfected with pTRE-5aR1 or pTRE alone, were cultured in the presence or absence of testosterone at varying concentrations. Cell growth and PSA secretion were measured after 4–6 days. Cyclin E1, Ki67, and PSA mRNA levels were evaluated using RT-PCR after 24 hr of treatment. RESULTS. 10 pM testosterone increased growth of pTRE-5aR1 transfectants by 54.1% over cells grown in the absence of testosterone, compared to 25.0% in pTRE transfectants (P < 0.01). Likewise, PSA secretion was increased by 56-fold in pTRE-5aR1 transfectants treated with 10 pM testosterone, compared to 26-fold in pTRE transfectants (P < 0.01). At concentrations of testosterone above 10 pM, the stimulatory effect on growth and PSA secretion was not distinguishable between pTRE-5aR1 and pTRE transfectants. CONCLUSIONS. These results demonstrate that upregulation of 5aR1 enhances the cellular response to low, but not high, concentrations of testosterone. This explains one mechanism by which castration-recurrent PCa can proliferate in the presence of castrate levels of circulating testosterone. Prostate 69: 595 – 602, 2009. # 2009 Wiley-Liss, Inc. KEY WORDS: dihydrotestosterone; finasteride; dutasteride; castration-recurrent pros- tate cancer INTRODUCTION Normal growth, development and secretory activity in the prostate are androgen-dependent. Intracrine con- version of circulating testosterone to the more potent androgen dihydrotestosterone (DHT) by the enzyme 5a-reductase (5aR) is a key step in both normal prostate function and development of prostate cancer (PCa) [1–3]. DHT has about a twofold higher intrinsic potency for stimulating proliferation and secretory Grant sponsor: GlaxoSmithKline. *Correspondence to: Lynn N. Thomas, Department of Biochemistry and Molecular Biology, Dalhousie University, 9D Sir Charles Tupper Building, 5850 College Street, Halifax, NS, Canada B3H 1X5. E-mail: lynn.thomas@dal.ca Received 29 July 2008; Accepted 1 December 2008 DOI 10.1002/pros.20911 Published online 5 January 2009 in Wiley InterScience (www.interscience.wiley.com). ß 2009 Wiley-Liss,Inc.