Combined treatment of Dunning R3327 rat prostatic tumor with the 5alpha-reductase inhibitor PNU 157706 and the antiandrogen bicalutamide

Transgenic mouse model for rapid pharmacodynamic evaluation of antiandrogens

Persistent androgen receptor signaling has been implicated as a critical factor in prostate cancer progression even at the hormone-refractory stage and provides strong rationale for developing novel androgen receptor antagonists. Traditional models for in vivo evaluation of antiandrogens are cumbersome because they rely on physiologic end points, such as the size of androgen-dependent tissues. Here, we describe a transgenic mouse (ARR2 Pb-Lux) that expresses luciferase specifically in the prostate in an androgen-dependent fashion. This signal is reduced by castration or by treatment with bicalutamide and can be quantified through noninvasive bioluminescent imaging. ARR2 Pb-Lux mice provide a novel method for rapid pharmacodynamic evaluation of novel pharmacologic compounds designed to inhibit androgen receptor signaling.

Differential alterations in 5alpha-reductase type 1 and type 2 levels during development and progression of prostate cancer

BACKGROUND

In the prostate, conversion of testosterone to dihydrotestosterone (DHT), by the enzymes 5alpha-reductase types 1 and 2 (5alphaR1, 5alphaR2) is required for normal growth and probably also for development of prostate cancer (PCa). Finasteride, a 5alphaR2 inhibitor, was shown to reduce the prevalence of PCa in the Prostate Cancer Prevention Trial. However, inhibition of both 5alphaR isoenzymes causes a greater decrease in serum DHT. The aim of this study was to assess differential expression of these enzymes at various stages of PCa development.

METHODS

Immunostaining for 5alphaR1 and 5alphaR2, using specific, well-validated antibodies, was evaluated in 26 benign prostatic hyperplasia (BPH) (16 for 5alphaR2), 53 primary PCa (21 for 5alphaR2), 18 prostatic intraepithelial neoplasia (PIN), 12 primary PCa treated with neoadjuvant androgen ablation, 15 locally recurrent PCa specimens, and 18 PCa metastases.

RESULTS

The mean area of moderate plus high intensity staining for 5alphaR1 increased from 4.8 +/- 2.8% of total epithelial area in BPH, to 18.9 +/- 5.7% in PIN, 17.0 +/- 3.2% in primary cancer, 38.0 +/- 7.3% in recurrent cancer, and 55.8 +/- 8.5% in PCa metastases. The mean staining area for 5alphaR2 decreased from 58.8 +/- 7.2% in BPH, to 21.1 +/- 5.5% in PIN and 34.8 +/- 6.7% in primary PCa. Staining for 5alphaR2 was increased in recurrent cancer and PCa metastases compared to primary PCa, at 58.7 +/- 5.2% and 69.2 +/- 8.7%, respectively.

CONCLUSIONS

5alphaR1 immunostaining is increased and 5alphaR2 immunostaining is decreased during development of PCa. In addition, there is increased expression of both 5alphaR isozymes in recurrent and metastatic cancers, suggesting that both isozymes may be important in the development and progression of PCa.

Biochemical recurrence after definitive prostate cancer therapy. Part II: Treatment strategies for biochemical recurrence of prostate cancer*

PURPOSE OF REVIEW

Through the prostate-specific antigen era, the proportion of men less than 55 years old with newly diagnosed prostate cancer more than doubled to almost 15%. As increasing numbers of men are living longer with prostate cancer, larger proportions will eventually present to our collective practices with rising prostate-specific antigen levels. Such prostate-specific antigen relapses, conservatively estimated to affect approximately 50 000 men each year, have become the most common form of advanced prostate cancer in the current period.

RECENT FINDINGS

Increasing evidence suggests that early hormonal therapy improves progression-free survival and may alter the cancer-specific survival. However, there is a cost to pay in side-effects when androgen deprivation is administered over prolonged periods. The non-steroidal anti-androgen bicalutamide may offer an equivalent progression-free survival to castration without the complications of androgen deprivation. Observational data seem to indicate that high-risk individuals (i.e. those with high-grade, high-stage disease or a prostate-specific antigen doubling time less than 12 months) may also receive benefit from early therapy.

SUMMARY

The definition of advanced prostate cancer has changed. Multimodal therapy improves cancer-specific outcomes especially in men with high-risk disease. The potential opportunities for novel therapeutic agents with low associated morbidity are great.

Rising prostate-specific antigen after primary prostate cancer therapy

An estimated 20-40% of men experience a biochemical recurrence within 10 years of definitive prostate cancer treatment. No single prostate-specific antigen (PSA) value is invariably associated with clinical metastasis or cancer-specific survival; PSA kinetics might prove to be a more important predictor of eventual progression-free survival and cancer-specific survival than absolute PSA level alone. With only one-third of patients progressing from biochemical recurrence to clinical disease, therapeutic morbidity should not outpace risk of disease progression. Salvage radiation therapy following radical prostatectomy has widely variable long-term biochemical control rates (from 18 to 64% depending on the follow-up period). Early hormonal therapy delivered as castration or complete androgen blockade might delay clinical metastasis in patients with high-risk pathologic disease; however, the adverse effects and morbidity of long-term therapy must not be underestimated. Non-steroidal antiandrogens as monotherapy for early biochemical recurrence, particularly for younger men who wish to preserve their libido and sexual potency, have received considerable attention, but there are conflicting data on long-term outcomes. Because of their favorable adverse-effect profiles, non-traditional therapies that exert localized hormonal or cellular effects are receiving considerable attention for treatment of early, PSA-only recurrence. Data from animal models provide a rationale for the use of these therapies, but there is a lack of evidence to support prolongation of progression-free survival or cancer-specific survival.