Overexpression of 5 alpha-reductase type 1 increases sensitivity of prostate cancer cells to low concentrations of testosterone.

INTRODUCTION: Conversion of testosterone to dihydrotestosterone (DHT) by the enzymes 5 alpha-reductase types 1 (5 alpha R1) and 2 (5 alpha R2) is important for normal and pathological growth of the prostate. The predominant isoenzyme in normal prostate is 5 alpha R2. However, prostate cancer (PCa) development is accompanied by a decrease in 5 alpha R2 and an increase in 5 alpha R1. The biological significance of increased 5 alpha R1 expression is not fully understood. Therefore, the aim of this study was to determine the effect of overexpression of 5 alpha R1 on growth and prostate-specific antigen (PSA) production in PCa cells. MATERIALS AND METHODS: LNGK-9 PCa cells, transiently transfected with pTRE-5 alpha R1 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-5 alpha R1 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-5 alpha R1 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-5 alpha R1 and pTRE transfectants. CONCLUSIONS: These results demonstrate that upregulation of 5 alpha R1 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.

Levels of 5alpha-reductase type 1 and type 2 are increased in localized high grade compared to low grade prostate cancer.

PURPOSE: In the prostate testosterone is converted to dihydrotestosterone by 5alpha-reductase type 1 and/or 2. Although 5alpha-reductase type 2 is predominant in normal prostates, type 1 is increased in cancer vs benign tissue. It is unclear whether 5alpha-reductase type 1/2 levels correlate with cancer grade. We compared the relative expression of 5alpha-reductase type 1 and 2 in localized high and low grade prostate cancer. MATERIALS AND METHODS: Immunostaining for 5alpha-reductase type 1/2 was evaluated in 64 prostate tissues from untreated men with localized prostate cancer. The percent of tumor area with moderate-high intensity staining was estimated for each Gleason pattern in the tissues. Adjacent benign tissue was evaluated in 26 prostate cancer specimens. RESULTS: Moderate-high staining for 5alpha-reductase type 1 increased from 18.8% +/- 2.9% (mean +/- SEM) in 34 Gleason pattern 3 cancers to 31.0% +/- 4.1% in 30 Gleason pattern 4/5 cancers (p = 0.016). Staining for 5alpha-reductase type 2 increased from 22.9% +/- 3.0% in 34 Gleason pattern 3 cancers to 39.2% +/- 4.1% in 30 Gleason pattern 4/5 cancers (p = 0.002). Compared to benign prostatic hyperplasia tissues staining for 5alpha-reductase type 1 was greater than 3-fold higher and staining for 5alpha-reductase type 2 was significantly lower in benign tissue adjacent to cancer (p = 0.006 and 0.0236, respectively). CONCLUSIONS: Levels of 5alpha-reductase type 1 and 2 are increased in localized high vs low grade prostate cancer. Levels of 5alpha-reductase type 1 are higher in benign tissue adjacent to cancer than in benign prostatic hyperplasia. These results raise the possibility that increased 5alpha-reductase type 1 in localized high grade cancers may contribute to the decreased effectiveness of the 5alpha-reductase type 2 selective inhibitor finasteride against high grade prostate cancer in the Prostate Cancer Prevention Trial.

Type 1 and type 2 5alpha-reductase expression in the development and progression of prostate cancer.

OBJECTIVES: Both normal and pathological growth of the prostate is dependent on dihydrotestosterone (DHT) synthesis, which is catalysed by two 5alpha-reductase (5alphaR) isoenzymes, 5alphaR1 and 5alphaR2, of which only 5alphaR2 has traditionally been viewed as important in the prostate. The objective of this study was to evaluate the role of both isoenzymes during development/progression of prostate cancer. METHODS: A thorough literature search was performed with the MEDLINE database to identify studies that have assessed expression of 5alphaR1/2 in prostate tissue. RESULTS: DHT suppression data for the 5alphaR2-specific inhibitor, finasteride, and the dual 5alphaR1/2 inhibitor, dutasteride, show that both isoenzymes are active in benign prostate. Furthermore, immunostaining studies have shown that 5alphaR1 expression increases and 5alphaR2 expression decreases in prostatic intraepithelial neoplasia (PIN) and prostate cancer, compared with nonmalignant prostate tissue. Both isoenzymes appear increased in high-grade compared with low-grade localised cancer. Dual inhibition of both isoenzymes with dutasteride may, therefore, be effective in preventing or delaying the growth of prostate cancer. The 4-yr REduction by DUtasteride of prostate Cancer Events (REDUCE) trial is underway to test this hypothesis. Androgen-withdrawal therapy can reverse prostate tumour growth by reducing circulating testosterone. However, 5alphaR-catalysed DHT synthesis within the prostate can continue and most tumours eventually develop resistance to androgen-deprivation therapy. Full assessment of the role of a 5alphaR inhibitor in this scenario is warranted. CONCLUSIONS: The consensus of evidence to date shows that 5alphaR1 is present in the prostate, and that levels are higher in malignant compared with benign prostate hyperplasia tissue.