Nicholas Bruchovsky

Intermittent androgen suppression in the treatment of prostate cancer: A preliminary report

OBJECTIVES To test the feasibility of using intermittent androgen suppression in the treatment of prostate cancer by taking advantage of the reversible action of medical castration. METHODS Observations were made on a group of 47 patients (clinical Stage D2, 14; D1, 10; C, 19; B2, 2; and A2, 2) with a mean follow-up time of 125 weeks. Treatment was initiated with combined androgen blockade and continued for at least 6 months until a serum prostate-specific antigen (PSA) nadir was observed. Medication was then withheld until the serum PSA increased to a mean value between 10 and 20 ng/mL. This cycle of treatment and no treatment was repeated until the regulation of serum PSA became androgen independent. RESULTS The first two treatment cycles lasted 73 and 75 weeks, with a mean time off therapy of 30 and 33 weeks and an overall mean percentage time off therapy of 41% and 45%, respectively. The mean time to achieve a nadir level of serum PSA was 20 weeks in cycle 1 and 18 weeks in cycle 2. Serum testosterone returned to the normal range within 8 weeks (range, 1 to 26) of stopping treatment. The off-treatment period in both cycles was associated with an improvement in sense of well-being and the recovery of libido and potency in the men who reported normal or near-normal sexual function before the start of therapy. In 7 patients with Stage D2 disease, the cancer progressed to an androgen-independent state. The mean and median times to progression were 128 weeks and 108 weeks, respectively. Seven patients have died, 1 from a noncancer-related illness, with mean and median overall survival times of 210 weeks and 166 weeks, respectively. CONCLUSIONS Prostate cancer is amenable to control by intermittent androgen suppression. This approach affords an improved quality of life when the patient is off therapy. It also results in reduced toxicity and cost of treatment and possibly delays tumor progression. Whether survival is affected in a beneficial or adverse way remains to be studied in a randomized, prospective study.

Intermittent androgen suppression delays progression to androgen-independent regulation of prostate-specific antigen gene in the LNCaP prostate tumour model

In most patients with prostate cancer, continuous androgen suppression (CAS) therapy causes tumour regression and an accompanying decrease in serum prostate specific antigen (PSA). However, with tumour progression, regulation of both tumour growth and PSA gene expression becomes androgen-independent. Because androgen resistance develops, in part, from adaptive cell survival mechanisms activated by androgen withdrawal, we hypothesize that intermittent re-exposure to androgens may prolong time to androgen-independent progression. The objective of this study was to determine whether intermittent androgen suppression (IAS) could delay the onset of androgen-independent PSA gene regulation in LNCaP prostate tumour model when compared to CAS. Five or six cycles of IAS were possible before progression developed. IAS prolonged time to androgen-independent PSA gene regulation from an average of 26 days in CAS to 77 days in IAS. Serum PSA increased above pre-castrate levels in all mice treated with CAS by 28 days post-castration, but remained below pre-castrate levels in 75% of IAS-treated mice by 60 days post-castration. By 15 weeks post-castration, serum PSA levels increased 7-fold above pre-castrate levels in CAS-treated mice compared to 1.9-fold increase in IAS-treated mice. PSA mRNA expression levels highly correlated with serum PSA levels in both groups. Maintenance of androgen dependency through IAS may be due to androgen-induced differentiation and/or down-regulation of androgen-suppressed gene expression.

Androgenic Induction of Prostate-specific Antigen Gene Is Repressed by Protein-Protein Interaction between the Androgen Receptor and AP-1/c-Jun in the Human Prostate Cancer Cell Line LNCaP

In exploring the possible mechanisms of androgen independence of prostate-specific antigen (PSA) gene expression, we investigated the effect of elevating AP-1 by both 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment and transfection of the c-Jun expression vector in LNCaP cells. Transcription of PSA is initiated when ligand-activated androgen receptor (AR) binds to a region in the PSA promoter that contains an androgen-responsive element (ARE). It was found that TPA inhibited androgen-induced PSA gene expression by a mechanism that did not alter nuclear levels of AR protein. Overexpression of AP-1 (junand fos proteins) also inhibited androgen-induced PSA promoter activity. These observations were apparently related to the disruption of AR·ARE complexes as demonstrated by the results of electrophoretic mobility shift assays. Specifically, c-Jun inhibited the formation of AR·ARE complexes and conversely that AR-glutathioneS-transferase proteins inhibited the formation of c-Jun·TPA-responsive element (TRE) complexes. Consistent with the inhibitory effect of both proteins, anti-c-Jun antibody blocked the inhibition of AR·ARE complex formation by c-Jun. A similar, but less marked, effect was obtained when anti-AR antibody was used to prevent AR inhibition of c-Jun·TRE complex formation. These findings together with results obtained from co-immunoprecipitation experiments strongly suggest that mutual repression of DNA binding activity is due to direct interaction between the two proteins and that the degree of repression may be determined by the ratio of AR to c-Jun. The mechanism of repression studied in mutant analysis experiments yielded evidence of an interaction between the DNA- and ligand-binding domains of AR and the leucine zipper region of c-Jun. Thus, the AR is similar to other nuclear receptors in its ability to interact with AP-1. This association provides a link between AP-1 and AR signal transduction pathways and may play a role in the regulation of the androgen-responsive PSA gene.

Intermittent Androgen Suppression for Prostate Cancer: Rationale and Clinical Experience

The rationale behind intermittent androgen suppression (IAS) is based on: (1) observations that androgen ablation is palliative, not curative, in most patients with prostate cancer, and that quality of life must be considered; (2) the assumption that immediate androgen ablation is superior to delayed therapy in improving survival; (3) the hypothesis that if tumour cells surviving androgen withdrawal are forced into a normal pathway of differentiation by androgen replacement, then apoptotic potential might be restored and progression to androgen independence delayed. Several centres have now tested the feasibility of IAS therapy in non-randomized groups of prostate cancer patients using serum of prostate-specific antigen levels as trigger points. Clinical data suggest that prostate cancer is amenable to control by IAS and offers clinicians an opportunity to improve patients’ quality of life by balancing the benefits of immediate androgen ablation (delayed progression and prolonged survival) while reducing treatment-related side effects and expense. Whether time to progression and survival is affected in a beneficial or adverse way is being studied in randomized, prospective protocols.

Development of a mathematical model that predicts the outcome of hormone therapy for prostate cancer

We propose a mathematical model that quantitatively reproduces the dynamics of the serum prostate-specific antigen (PSA) level under intermittent androgen suppression (IAS) for prostate cancer. Taking into account the biological knowledge that there are reversible and irreversible changes in a malignant cell, we constructed a piecewise-linear dynamical model where the testosterone dynamics are modelled with rapid shifts between two levels, namely the normal and castrate concentrations of the male hormone. The validity of the model was supported by patient data obtained from a clinical trial of IAS. It accurately reproduced the kinetics of the therapeutic reduction of PSA and predicted the future nadir level correctly. The coexistence of reversible and irreversible changes within the malignant cell provided the best explanation of early progression to androgen independence. Finally, since the model identified patients for whom IAS was effective, it potentially offers a novel approach to individualized therapy requiring the input of time sequence values of PSA only.

Characterization of 5α-reductase gene expression in stroma and epithelium of human prostate

The expression of 5alpha-reductase type 1 and type 2 isoenzymes in hyperplastic human prostate tissue and several human prostate cell lines was investigated by Northern blot analyses, reverse transcription-polymerase chain reaction (RT-PCR), and enzyme activity. Separation of stroma and epithelium was confirmed histologically and only preparations with no apparent contamination were employed in the subsequent studies. Poly(A)+ RNA was isolated from stromal and epithelial fractions and analysed by Northern blot and RT-PCR. Inhibition of epithelial and stromal 5alpha-reductase activities by 17beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5alpha-androstan- 3-one (4MA) was assessed using a range of concentrations between 10(-13) and 10(-5) M. Results from Northern blot analyses and RT-PCR showed that the prostate stroma expressed 5alpha-reductase type 1 and type 2 isoenzymes, whereas the prostate epithelium only expressed 5alpha-reductase type 1. This was consistent with biphasic inhibition of 5alpha-reductase activity by 4MA in stroma and monophasic inhibition in epithelium. Cultured epithelial cells derived from human prostate only expressed 5alpha-reductase type 1 and had Vmax and Km values that approximated the lower end of the range reported for surgically removed prostate epithelium. The foregoing data explains the disparate activities of 5alpha-reductase, previously reported, in stroma and epithelium. The differential localization of these isoenzymes in the prostate suggests that future therapy of androgen-sensitive disease may be more successful through the use of selective inhibitors of the different 5alpha-reductase isoenzymes.

Locally advanced prostate cancer: Biochemical results from a prospective phase II study of intermittent androgen suppression for men with evidence of prostate-specific antigen recurrence after radiotherapy

Biochemical results from a prospective Phase II trial of intermittent androgen suppression for recurrent prostate cancer after radiotherapy were analyzed for correlations to the onset of hormone‐refractory disease.

Final results of the Canadian prospective phase II trial of intermittent androgen suppression for men in biochemical recurrence after radiotherapy for locally advanced prostate cancer: clinical parameters.

This prospective Phase II study was undertaken to evaluate intermittent androgen suppression as a form of therapy in men with localized prostate cancer who failed after they received external beam irradiation.

Osteoblast-Derived Factors Induce Androgen-Independent Proliferation and Expression of Prostate-Specific Antigen in Human Prostate Cancer Cells

Purpose: Prostate cancer metastasizes to the skeleton to form osteoblastic lesions. Androgen ablation is the current treatment for metastatic prostate cancer. This therapy is palliative, and the disease will return in an androgen-independent form that is preceded by a rising titer of prostate-specific antigen (PSA). Here, we investigated the possibility that human osteoblasts might secrete factors that contribute to the emergence of androgen-independent prostate cancer. Experimental Design: Primary cultures of human osteoblasts were used as a source of conditioned medium (OCM). Proliferation, expression of androgen-regulated genes, and transactivation of the androgen receptor (AR) were monitored in LNCaP human prostate cancer cells in response to OCM using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Northern blot analysis, and reporter gene constructs. Levels of interleukin-6 (IL-6) present in OCM were measured, and its contribution to proliferation and expression of PSA were investigated by neutralization studies with anti IL-6 antibodies. Results: OCM increased the proliferation and expression of PSA at both the protein and RNA levels in LNCaP cells. Synergistic increases in the activities of PSA (6.1 kb)- and pARR3-tk-luciferase reporters were measured in cells cotreated with both OCM and androgen. OCM targeted the NH2-terminal domain of the AR. The effect of OCM on transcriptional activity of the AR was inhibited by an antiandrogen. Neutralizing antibodies to IL-6 blocked proliferation and expression of PSA by OCM. Conclusion: Osteoblasts secrete factors, such as IL-6, that cause androgen-independent induction of PSA gene expression and proliferation of prostate cancer cells by a mechanism that partially relies on the AR. Identifying such molecular mechanisms may lead to improved clinical management of metastatic prostate cancer.

Mathematical modelling of prostate cancer growth and its application to hormone therapy

Hormone therapy in the form of androgen deprivation is a major treatment for advanced prostate cancer. However, if such therapy is overly prolonged, tumour cells may become resistant to this treatment and result in recurrent fatal disease. Long-term hormone deprivation also is associated with side effects poorly tolerated by patients. In contrast, intermittent hormone therapy with alternating on- and off-treatment periods is a possible clinical strategy to delay progression to hormone-refractory disease with the advantage of reduced side effects during the off-treatment periods. In this paper, we first overview previous studies on mathematical modelling of prostate tumour growth under intermittent hormone therapy. The model is categorized into a hybrid dynamical system because switching between on-treatment and off-treatment intervals is treated in addition to continuous dynamics of tumour growth. Next, we present an extended model of stochastic differential equations and examine how well the model is able to capture the characteristics of authentic serum prostate-specific antigen (PSA) data. We also highlight recent advances in time-series analysis and prediction of changes in serum PSA concentrations. Finally, we discuss practical issues to be considered towards establishment of mathematical model-based tailor-made medicine, which defines how to realize personalized hormone therapy for individual patients based on monitored serum PSA levels.