Effect of finasteride on serum androstenedione and risk of prostate cancer within the prostate cancer prevention trial: differential effect on high- and low-grade disease

OBJECTIVE

To evaluate the effect of finasteride on serum androst-4-ene-3,17-dione (androstenedione) and its association with prostate cancer risk among subjects who participated in the Prostate Cancer Prevention Trial.

METHODS

We analyzed serum androstenedione levels in 317 prostate cancer cases and 353 controls, nested in the Prostate Cancer Prevention Trial, a randomized placebo-controlled trial that found finasteride decreased prostate cancer risk. Androstenedione is the second most important circulating androgen in men besides testosterone and also a substrate for 5α-reductase enzyme.

RESULTS

We observed a 22% increase in androstenedione levels compared with the baseline values in subjects who were treated with finasteride for 3 years. This significant increase did not vary by case-control status. Adjusted odds ratio and 95% confidence interval for the third tertile of absolute change in androstenedione levels compared with the first tertile were 0.42 (95% confidence interval, 0.19-0.94) for low-grade (Gleason score <7) cases. Similar results were observed when analyzed using percent change. There were no significant associations between serum androstenedione levels and the risk of high-grade disease.

CONCLUSION

The results of this nested case-control study confirm that finasteride blocks the conversion of testosterone to dihydrotestosterone (DHT) and of androstenedione to 5α-androstanedione-3,17-dione, which also leads to the reduction of DHT formation. This decrease in DHT may help reduce the risk of low-grade prostate cancer in men. Our data on a differential effect of androstenedione also suggest that some high-grade prostate cancers may not require androgen for progression.

5α-reductase type 3 enzyme in benign and malignant prostate

BACKGROUND

Currently available 5α-reductase inhibitors are not completely effective for treatment of benign prostate enlargement, prevention of prostate cancer (CaP), or treatment of advanced castration-recurrent (CR) CaP. We tested the hypothesis that a novel 5α-reductase, 5α-reductase-3, contributes to residual androgen metabolism, especially in CR-CaP.

METHODS

A new protein with potential 5α-reducing activity was expressed in CHO-K1 cellsandTOP10 E. coli for characterization. Protein lysates and total mRNA were isolated from preclinical and clinical tissues. Androgen metabolism was assessed using androgen precursors and thin layer chromatography or liquid chromatography tandem mass spectrometry.

RESULTS

The relative mRNA expression for the three 5α-reductase enzymes in clinical samples of CR-CaP was 5α-reductase-3 ≫ 5α-reductase-1> 5α-reductase-2. Recombinant 5α-reductase-3 protein incubations converted testosterone, 4-androstene-3,17-dione (androstenedione) and 4-pregnene-3,20-dione (progesterone) to dihydrotestosterone, 5α-androstan-3,17-dione, and 5α-pregnan-3,20-dione, respectively. 5α-Reduced androgen metabolites were measurable in lysates from androgen-stimulated (AS) CWR22 and CR-CWR22 tumors and clinical specimens of AS-CaP and CR-CaP pre-incubated with dutasteride (a bi-specific inhibitor of 5α-reductase-1 and 2).

CONCLUSION

Human prostate tissues contain a third 5α-reductase that was inhibited poorly by dutasteride at high androgen substrate concentration in vitro, and it may promote DHT formation in vivo, through alternative androgen metabolism pathways when testosterone levels are low.

Assessment of steroidogenesis and steroidogenic enzyme functions

There is some confusion in the literature about steroidogenesis in endocrine glands and steroidogenesis in peripheral intracrine tissues. The objective of the present review is to bring some clarifications and better understanding about steroidogenesis in these two types of tissues. Concerns about substrate specificity, kinetic constants and place of enzymes in the pathway have been discussed. The role of 17α-hydroxylase/17-20 lyase (CYP17A1) in the production of dehydroepiandrosterone and back-door pathways of dihydrotestosterone biosynthesis is also analyzed. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Aldo-keto reductases AKR1C1, AKR1C2 and AKR1C3 may enhance progesterone metabolism in ovarian endometriosis

Endometriosis is a very common disease that is characterized by increased formation of estradiol and disturbed progesterone action. This latter is usually explained by a lack of progesterone receptor B (PR-B) expression, while the role of pre-receptor metabolism of progesterone is not yet fully understood. In normal endometrium, progesterone is metabolized by reductive 20α-hydroxysteroid dehydrogenases (20α-HSDs), 3α/β-HSDs and 5α/β-reductases. The aldo-keto reductases 1C1 and 1C3 (AKR1C1 and AKR1C3) are the major reductive 20α-HSDs, while the oxidative reaction is catalyzed by 17β-HSD type 2 (HSD17B2). Also, 3α-HSD and 3β-HSD activities have been associated with the AKR1C isozymes. Additionally, 5α-reductase types 1 and 2 (SRD5A1, SRD5A2) and 5β-reductase (AKR1D1) are responsible for the formation of 5α- and 5β-reduced pregnanes. In this study, we examined the expression of PR-AB and the progesterone metabolizing enzymes in 31 specimens of ovarian endometriosis and 28 specimens of normal endometrium. Real-time PCR analysis revealed significantly decreased mRNA levels of PR-AB, HSD17B2 and SRD5A2, significantly increased mRNA levels of AKR1C1, AKR1C2, AKR1C3 and SRD5A1, and negligible mRNA levels of AKR1D1. Immunohistochemistry staining of endometriotic tissue compared to control endometrium showed significantly lower PR-B levels in epithelial cells and no significant differences in stromal cells, there were no significant differences in the expression of AKR1C3 and significantly higher AKR1C2 levels were seen only in stromal cells. Our expression analysis data at the mRNA level and partially at the cellular level thus suggest enhanced metabolism of progesterone by SRD5A1 and the 20α-HSD and 3α/β-HSD activities of AKR1C1, AKR1C2 and AKR1C3.