Cell proliferation and apoptosis during prostatic tumor xenograft involution and regrowth after castration

The impact of biological clock and sex hormones on the risk of disease

Molecular clocks are responsible for defining 24-h cycles of behaviour and physiology that are called circadian rhythms. Several structures and tissues are responsible for generating these circadian rhythms and are named circadian clocks. The suprachiasmatic nucleus of the hypothalamus is believed to be the master circadian clock receiving light input via the optic nerve and aligning internal rhythms with environmental cues. Studies using both in vivo and in vitro methodologies have reported the relationship between the molecular clock and sex hormones. The circadian system is directly responsible for controlling the synthesis of sex hormones and this synthesis varies according to the time of day and phase of the estrous cycle. Sex hormones also directly interact with the circadian system to regulate circadian gene expression, adjust biological processes, and even adjust their own synthesis. Several diseases have been linked with alterations in either the sex hormone background or the molecular clock. So, in this chapter we aim to summarize the current understanding of the relationship between the circadian system and sex hormones and their combined role in the onset of several related diseases.

Bone Health Management in the Continuum of Prostate Cancer Disease

Prostate cancer (PCa) is the second-leading cause of cancer-related deaths in men. PCa cells require androgen receptor (AR) signaling for their growth and survival. Androgen deprivation therapy (ADT) is the preferred treatment for patients with locally advanced and metastatic PCa disease. Despite their initial response to androgen blockade, most patients eventually will develop metastatic castration-resistant prostate cancer (mCRPC). Bone metastases are common in men with mCRPC, occurring in 30% of patients within 2 years of castration resistance and in >90% of patients over the course of the disease. Patients with mCRPC-induced bone metastasis develop lesions throughout their skeleton; the 5-year survival rate for these patients is 47%. Bone-metastasis-induced early changes in the bone that proceed the osteoblastic response in the bone matrix are monitored and detected via modern magnetic resonance and PET/CT imaging technologies. Various treatment options, such as targeting osteolytic metastasis with bisphosphonates, prednisone, dexamethasone, denosumab, immunotherapy, external beam radiation therapy, radiopharmaceuticals, surgery, and pain medications are employed to treat prostate-cancer-induced bone metastasis and manage bone health. However, these diagnostics and treatment options are not very accurate nor efficient enough to treat bone metastases and manage bone health. In this review, we present the pathogenesis of PCa-induced bone metastasis, its deleterious impacts on vital organs, the impact of metastatic PCa on bone health, treatment interventions for bone metastasis and management of bone- and skeletal-related events, and possible current and future therapeutic options for bone management in the continuum of prostate cancer disease.

Standing Variations Modeling Captures Inter-Individual Heterogeneity in a Deterministic Model of Prostate Cancer Response to Combination Therapy

Sipuleucel-T (Provenge) is the first live cell vaccine approved for advanced, hormonally refractive prostate cancer. However, survival benefit is modest and the optimal combination or schedule of sipuleucel-T with androgen depletion remains unknown. We employ a nonlinear dynamical systems approach to modeling the response of hormonally refractive prostate cancer to sipuleucel-T. Our mechanistic model incorporates the immune response to the cancer elicited by vaccination, and the effect of androgen depletion therapy. Because only a fraction of patients benefit from sipuleucel-T treatment, inter-individual heterogeneity is clearly crucial. Therefore, we introduce our novel approach, Standing Variations Modeling, which exploits inestimability of model parameters to capture heterogeneity in a deterministic model. We use data from mouse xenograft experiments to infer distributions on parameters critical to tumor growth and to the resultant immune response. Sampling model parameters from these distributions allows us to represent heterogeneity, both at the level of the tumor cells and the individual (mouse) being treated. Our model simulations explain the limited success of sipuleucel-T observed in practice, and predict an optimal combination regime that maximizes predicted efficacy. This approach will generalize to a range of emerging cancer immunotherapies.

Epidemiology of Prostate Cancer

Prostate cancer is the second most frequent cancer diagnosis made in men and the fifth leading cause of death worldwide. Prostate cancer may be asymptomatic at the early stage and often has an indolent course that may require only active surveillance. Based on GLOBOCAN 2018 estimates, 1,276,106 new cases of prostate cancer were reported worldwide in 2018, with higher prevalence in the developed countries. Differences in the incidence rates worldwide reflect differences in the use of diagnostic testing. Prostate cancer incidence and mortality rates are strongly related to the age with the highest incidence being seen in elderly men (> 65 years of age). African-American men have the highest incidence rates and more aggressive type of prostate cancer compared to White men. There is no evidence yet on how to prevent prostate cancer; however, it is possible to lower the risk by limiting high-fat foods, increasing the intake of vegetables and fruits and performing more exercise. Screening is highly recommended at age 45 for men with familial history and African-American men. Up-to-date statistics on prostate cancer occurrence and outcomes along with a better understanding of the etiology and causative risk factors are essential for the primary prevention of this disease.

Population pharmacokinetic-pharmacodynamic modelling of the relationship between testosterone and prostate specific antigen in patients with prostate cancer during treatment with leuprorelin

AIMS

This investigation aimed to quantitatively characterize the relationship between the gonadotropin-releasing hormone agonist leuprorelin, testosterone (T) and prostate specific antigen (PSA) concentrations over time, to aid identification of a target T concentration that optimises the balance of the benefits of T suppression whilst reducing the risk of side effects related to futile over-suppression.

METHODS

Data from a single dose study to investigate the effect of leuprorelin in a 6-month depot formulation on T and PSA in prostate cancer patients were analysed using a population pharmacokinetic-pharmacodynamic modelling approach. The developed model was qualified using external data from 3 studies, in which the effect of different formulations of leuprorelin on T and PSA was evaluated in prostate cancer patients.

RESULTS

The effect of leuprorelin on the relationship between T and PSA was adequately characterized by the Romero model with minor modifications, combined with a turnover model to describe the delay in response between T and PSA. The data were significantly better described when assuming a minimum PSA level that is independent on the treatment-related reduction in T, as compared to a model with a proportional reduction in PSA and T.

CONCLUSIONS

The model-based analysis suggests that on a population level, reducing T concentrations below 35 ng/dL does not result in a further decrease in PSA levels (>95% of the minimal PSA level is reached). More data are required to support this relationship in the lower T and PSA range.

Redox Responsive Hyaluronic Acid Nanogels for Treating RHAMM (CD168) Over-expressive Cancer, both Primary and Metastatic Tumors

It remains a substantial challenge to targetedly deliver drug to both primary tumors and metastatic lesions employing a single nanoparticle delivery system. Here aiming at the receptor for hyaluronic acid mediated motility (RHAMM or CD168), a specific receptor for hyaluronic acid (HA), the bioreductive responsive HA nanogels loaded doxorubicin were prepared. The targeting effects of HA nanogels in high RHAMM-expressed cancer cells, primary and metastatic tumors were investigated. It was found that HA nanogels show a strong in vitro and in vivo RHAMM-mediated cellular uptake and drug delivery. The cellular uptake of HA nanogels in high RHAMM-expressed LNCaP and H22 cells was far more than the uptake in low RHAMM-expressed NIH3T3 cells. The IC50 value of drug-loaded HA nanogels against H22 cells was lower than that of free drug. In vivo antitumor activity examinations showed that the HA nanogels not only had significantly superior antitumor efficacy in murine H22 and human LNCaP tumor-bearing mice but also exhibited much deep tumor penetration. The drug delivery of lymph node metastasis by systemically administering HA nanogels demonstrated that the HA nanogels could sufficiently increase drug concentration in metastatic lymph node by RHAMM-HA interaction and inhibit the growth of metastatic lymph node, even completely heal malignant lymph node metastasis. Thus, RHAMM-directed drug delivery is a promising therapy route for treating both primary and metastatic tumors.

Testosterone and prostate cancer: an evidence-based review of pathogenesis and oncologic risk

Testosterone plays a central role in male development and health. Likewise, androgen deficiency, or hypogonadism, is associated with a variety of symptoms including decreased energy, diminished libido and erectile dysfunction, among others. Male androgen levels steadily decline with age, and, in a subset of symptomatic older men, can result in late-onset hypogonadism (LOH). Over the last decade, increased awareness of hypogonadism among patients and providers has led to a significant rise in the use of testosterone replacement therapy (TRT) for hypogonadism, and especially in LOH. Accompanying the rise in TRT are concerns of potential adverse effects, including cardiovascular risks and the promotion of prostate cancer. The 'androgen hypothesis' asserts that prostate cancer development and progression is driven by androgens, and thus TRT has the theoretical potential to drive prostate cancer development and progression. In this review, we examine existing data surrounding testosterone and prostate cancer. There is significant evidence that androgens promote prostate cancer in experimental systems. However, there is no clear evidence that elevations in endogenous testosterone levels promote the development of prostate cancer in humans. As a result of experimental and historical data on the progression of prostate cancer following TRT, there has been widespread belief that TRT will promote disease progression in prostate cancer patients. Despite these fears, there are a growing number of studies demonstrating no increase in prostate cancer incidence among men on TRT. Furthermore, in studies involving a small number of patients, there has been no discernable increase in disease progression in prostate cancer patients on TRT. While data from large, prospective, randomized, controlled trials are absent, TRT in select prostate cancer patients is likely safe. In the end, the use of TRT in prostate cancer patients is still considered experimental and should only be offered after well-informed shared decision making and with close monitoring.

Parameter estimation and optimal scheduling algorithm for a mathematical model of intermittent androgen suppression therapy for prostate cancer

We propose an algorithm based on cross-entropy to determine parameters of a piecewise linear model, which describes intermittent androgen suppression therapy for prostate cancer. By comparing with clinical data, the parameter estimation for the switched system shows good fitting accuracy and efficiency. We further optimize switching time points for the piecewise linear model to obtain a feasible therapeutic schedule. The simulation results of therapeutic effect are superior to those of previous strategy.

Androgen deprivation induces senescence characteristics in prostate cancer cells in vitro and in vivo

BACKGROUND

The treatment of non-localized prostate cancer involves androgen deprivation (AD) therapy which results in tumor regression. Apoptosis has been implicated in the tumor response to AD, but constitutes a small fraction of the total tumor at any time. Cellular senescence is a response to sub-lethal stress in which cells are persistently growth arrested and develop distinct morphological and biochemical characteristics. The occurrence of senescence in prostate tumor tissue after AD therapy has not previously been investigated.

METHODS

Phenotypic and molecular characteristics of senescence were examined in models of androgen-sensitive prostate cancer after AD and compared with androgen-intact controls.

RESULTS

In vitro in LNCaP cells, AD induced elevated senescence-associated β-galactosidase (SA-β-gal) staining, decreased proliferation, and increased flow cytometric side scatter while minimally affecting cell viability. The increased expression of the senescence-related proteins Glb1, the cyclin-dependent kinase inhibitor p27(Kip1) and chromatin-regulating heterochromatin protein 1γ (HP1γ) were detected in LNCaP cells after AD in vitro by immunoblot and immunofluorescence microscopy. In mice bearing LuCaP xenograft tumors in vivo, surgical castration similarly increased SA-β-gal staining, increased expression of p27(Kip1) and HP1γ, and decreased expression of the proliferation marker KI-67, with minimal induction of apoptosis identified by detection of cleaved caspase 3 and TUNEL. Immunohistochemical analysis of human prostate tumors removed after AD shows similar induction of Glb1, HP1γ and decreased KI-67.

CONCLUSIONS

We conclude that AD induces characteristics consistent with cellular senescence in androgen-sensitive prostate cancer cells. This finding may explain incomplete tumor regression in response to AD.

Targeting ErbB3: the New RTK(id) on the Prostate Cancer Block

Most prostate cancers (PCa) are critically reliant on functional androgen receptor (AR) signaling. At its onset, PCa is androgen-dependent and although temporarily halted by surgically or pharmacologically blocking the AR (androgen ablation), the disease ultimately recurs as an aggressive, fatal castration resistant prostate cancer (CRPC). FDA-approved treatments like docetaxel, a chemotherapeutic agent, and Provenge, a cancer vaccine, extend survival by a scant 3 and 4 months, respectively. It is clear that more effective drugs targeting CRPC are urgently needed. The ErbB family (EGFR/ErbB1, ErbB2/HER2/neu, ErbB3/HER3 and ErbB4/HER4) of receptor tyrosine kinases (RTKs) have long been implicated in PCa initiation and progression, but inhibitors of ErbB1 and ErbB2 (prototypic family members) fared poorly in PCa clinical trials. Recent research suggests that another family member ErbB3 abets emergence of the castration-resistant phenotype. Considerable efforts are being directed towards understanding ErbB3-mediated molecular mechanisms of castration resistance and searching for novel ways of inhibiting ErbB3 activity via rational drug design. Antibody-based therapy that prevents ligand binding to ErbB3 appears promising and fully-humanized antibodies that inhibit ligand-induced phosphorylation of ErbB3 are currently in early development. Small molecule tyrosine kinase inhibitors are also being vigorously pursued, as are siRNA-based approaches and combination treatment strategies- the simultaneous suppression of ErbB3 and its signaling partners or downstream effectors - with the primary purpose of undermining the resiliency of ErbB3-mediated signal transduction. This review summarizes the existing literature and reinforces the importance of ErbB3 as a therapeutic target in the clinical management of prostate cancer.

Plasma testosterone and sex hormone-binding globulin concentrations and the risk of prostate cancer among Japanese men: a nested case-control study

Sex hormones, particularly androgens, have been implicated in prostate carcinogenesis. Overall, however, prospective studies have reported no association between circulating levels of sex hormones and the risk of prostate cancer. However, despite the possible difference in the effects of hormones on prostate cancer risk by stage, age, body mass index (BMI) and isoflavones, evidence for these is sparse. Moreover, few studies have been conducted in Asian populations, who are relatively lean and have high isoflavone consumption. We examined the hypothesis that plasma concentrations of circulating testosterone and sex hormone-binding globulin (SHBG) are associated with the risk of prostate cancer in a case-control study nested in the Japan Public Health Center-based Prospective Study. Concentrations of total testosterone and SHBG were measured in plasma samples from 201 patients with prostate cancer and 402 matched control participants, and concentrations of free testosterone were calculated. No overall association between the plasma levels of any hormone and total prostate cancer was observed. Odds ratios (95% confidence interval [CI]) in the highest versus lowest group were 0.71 (95% CI = 0.36-1.41, Ptrend = 0.43) for total testosterone, 0.70 (95% CI = 0.39-1.27, Ptrend = 0.08) for free testosterone and 1.38 (95% CI = 0.69-2.77, Ptrend = 0.23) for SHBG. When stratified by cancer stage, age, BMI and plasma isoflavone level, free testosterone was inversely associated with localized cancers and equol producers, while SHBG was associated with an increased risk of prostate cancer in younger men. In conclusion, in this nested case-control study, concentrations of circulating total testosterone, free testosterone or SHBG were not strongly associated with a risk for total 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.

Comparison of ACINUS, caspase-3, and TUNEL as apoptotic markers in determination of tumor growth rates of clinically localized prostate cancer using image analysis

BACKGROUND

The balance between apoptotic and proliferative processes determines the enlargement of a tumor. Accurate measurement of apoptotic and proliferative rates from diagnostic prostate biopsies would allow calculation of tumor growth rates in a population-based prostate cancer (CaP) study. Automated image analysis may be used if proliferation and apoptotic biomarkers provide clearly resolved immunostained images.

METHODS

Clinical CaP aggressiveness was assigned as low, intermediate or high using clinical criteria for 46 research subjects with newly diagnosed CaP. Diagnostic biopsy sections from the research subjects were dual-labeled for proliferation biomarker, Ki-67 and apoptotic biomarker, apoptotic chromatin condensation inducer in the nucleus (ACINUS). Apoptotic biomarkers, caspase-3 and terminal deoxyribonucleotidyltransferase mediated dUTP-biotin nick end labeling (TUNEL) were labeled separately. Images from immunostained sections were analyzed using automated image analysis and tumor growth rates computed. Association between clinical CaP aggressiveness and tumor growth rates was explored.

RESULTS

Sixteen subjects had high, 17 had intermediate, and 13 had low clinical CaP aggressiveness. Positive immunostaining was localized to the nucleus for Ki-67, ACINUS, and TUNEL. A statistically significant linear trend across clinical CaP aggressiveness categories was found when tumor growth rates were calculated using ACINUS (P = 0.046). Logistic regression and ROC plots generated showed ACINUS (AUC = 0.677, P = 0.048) and caspase-3 (AUC = 0.694, P = 0.038) to be better predictors than TUNEL (AUC = 0.669, P = 0.110).

CONCLUSIONS

ACINUS met the criteria for automated image analysis and for calculation of apoptotic rate. Tumor growth rates determined using automated image analysis should be evaluated for clinical prediction of CaP aggressiveness, treatment response, recurrence, and mortality.

Androgens and prostate cancer risk

Androgens have been implicated in prostate tumourigenesis. However, no association between circulating levels of androgens and prostate cancer risk was found in a recent large pooled analysis of prospective studies. A decreased risk of prostate cancer among men treated with finasteride, a 5 alpha-reductase inhibitor which reduces levels of dihydrotestosterone, was observed in the Prostate Cancer Prevention Trial (PCPT), a large clinical trial. In the PCPT, a higher number of high-grade tumours was found in the finasteride group than in the control group; the reason for this finding is still unclear. Treatment of symptoms of late-onset hypogonadism - such as decreased muscle and bone mass and decreased cognition and libido - has become more prevalent with the advent of new forms of administration of testosterone replacement therapy. One small placebo-controlled study showed no increase in incidence of prostate cancer after 6 months of testosterone therapy, but data on the safety of testosterone replacement therapy remain limited.

Intermittent versus continuous androgen suppression for prostatic cancer

BACKGROUND

After lung cancer, prostate cancer is the most common cause of death among males. The aim of treatment is to prevent disease-related morbidity and mortality while minimizing intervention-related adverse events. Androgen suppression therapy (AST) to reduce circulating serum testosterone and disease progression is considered a mainstay of treatment for men with advanced prostate cancer. It has been increasingly utilized for early stage disease despite a lack of evidence of effectiveness.

OBJECTIVES

Evaluate the effectiveness and safety of intermittent androgen suppression (IAS) compared to continuous androgen suppression for treating prostatic cancer.

SEARCH STRATEGY

The following databases were searched to identify randomised or quasi-randomised, controlled trials comparing intermittent and continuous androgen suppression in the treatment of any stage of prostate cancer: the Cochrane Central Register of Controlled Trials; EMBASE and LILACS.

SELECTION CRITERIA

Studies were included if they were randomised or quasi-randomized, and compare the effects of IAS versus CAS.

DATA COLLECTION AND ANALYSIS

Two reviewers selected relevant trials, assessed methodological quality and extracted data.

MAIN RESULTS

Five randomized studies involving 1382 patients were included in this review. All the included studies involved advanced (T3 or T4) prostate cancer, had relatively small populations, and were of short duration. Few events were reported and did not assess disease-specific survival or metastatic disease. Only one study (N = 77) evaluated biochemical outcomes. A subgroup analysis found no significant differences in biochemical progression (defined by the authors as PSA >/= 10 ng/mL) between IAS and CAS for Gleason scores 4 - 6, 7, and 8 - 10. For patients with a Gleason score > 6, reduction in biochemical progression favoured the IAS group (RR 0.10, 95% CI 0.01 to 0.67, P = 0.02). Studies primarily reported on adverse events. One trial (N = 43) found no difference in adverse effects (gastrointestinal, gynecomastia and asthenia) between IAS ( two events) and CAS (five events), with the exception of impotence, which was significantly lower in the IAS group (RR 0.72, 95% CI 0.56 to 0.92, P = 0.008).

AUTHORS' CONCLUSIONS

Data from RCTs comparing IAS to CAS are limited by small sample size and short duration. There are no data for the relative effectiveness of IAS versus CAS for overall survival, prostate cancer-specific survival, or disease progression. Limited information suggests IAS may have slightly reduced adverse events. Overall, IAS was also as effective as CAS for potency, but was superior during the interval of cycles (96%).

Cellular Changes in Prostate Cancer Cells Induced by Intermittent Androgen Suppression

OBJECTIVES

This study used tumour specimens from a clinical trial on intermittent androgen suppression (IAS) to study the effects of castration on tissue morphology, cell proliferation, apoptosis, and the expression of androgen receptor (AR).

METHODS

A total of 113 representative needle biopsy specimens were available from 29 patients for evaluation of the Gleason score as well as Ki-67, cleaved caspase-3, and AR immunostaining.

RESULTS

At 6 mo from the beginning of the first androgen withdrawal, cell proliferation activity was significantly (p = 0.002) reduced, whereas no effect on apoptosis was found. A nonsignificant trend to an increase in Gleason score after castration was found. Subsequent cycles of withdrawals had no significant effect on any of the measured parameters. The Gleason score, proliferation activity, and apoptosis rate showed only heterogeneous, nonsignificant changes after the first progression. Strong nuclear AR staining was evident in all cancer specimens.

CONCLUSIONS

The findings suggest that the long-term (months) effect of androgen withdrawal on tumour growth is due to the inhibition of proliferation. Because the tumours seem to become resistant to castration at the first cycle of treatment withheld, it is possible that IAS does not postpone the emergence of ablation-resistant tumours. There was no consistent sign of increased proliferation or Gleason score during the treatment, suggesting that the biologic aggressiveness of a particular tumour is defined already at an early stage of disease. The constant nuclear expression of AR in cancer cells indicates that the AR signalling remains active despite of the androgen withdrawal.

Androgens and prostate cancer risk: a prospective study

BACKGROUND

Androgens have been implicated in prostate tumorigenesis, but prospective studies have overall reported no association between circulating levels of androgens and risk of prostate cancer. However, some recent studies have shown that a high level of testosterone increase the risk of non-aggressive tumors but is associated with a decreased risk of aggressive tumors.

METHODS

We prospectively measured plasma levels of total testosterone, androstanediol glucuronide (A-diol-g) and sex hormone binding globuline (SHBG) and calculated estimated levels of free testosterone, in a nested case-control study of 392 cases and 392 matched controls.

RESULTS

None of the studied hormones were significantly associated with prostate cancer risk in the full study group or in subgroups according to tumor aggressiveness. Odds ratios in the full study group, for top versus bottom quartile, was for total testosterone 1.25 (95% CI = 0.79-2.00; P(trend) = 0.51); free testosterone, 1.31 (95% CI = 0.82-2.07; P(trend) = 0.35); A-diol-g, 0.88 (95% CI = 0.59-1.33; P(trend) = 0.77); and for SHBG, 1.01 (95% CI = 0.64-1.58; P(trend) = 0.94).

CONCLUSIONS

We found no significant associations between androgen levels and risk of prostate cancer in this population-based, non-screened cohort.

Inhibition of androgen-independent prostate cancer by estrogenic compounds is associated with increased expression of immune-related genes

The clinical utility of estrogens for treating prostate cancer (CaP) was established in the 1940s by Huggins. The classic model of the anti-CaP activity of estrogens postulates an indirect mechanism involving the suppression of androgen production. However, clinical and preclinical studies have shown that estrogens exert growth-inhibitory effects on CaP under low-androgen conditions, suggesting additional modes whereby estrogens affect CaP cells and/or the microenvironment. Here we have investigated the activity of 17beta estradiol (E2) against androgen-independent CaP and identified molecular alterations in tumors exposed to E2. E2 treatment inhibited the growth of all four androgen-independent CaP xenografts studied (LuCaP 35V, LuCaP 23.1AI, LuCaP 49, and LuCaP 58) in castrated male mice. The molecular basis of growth suppression was studied by cDNA microarray analysis, which indicated that multiple pathways are altered by E2 treatment. Of particular interest are changes in transcripts encoding proteins that mediate immune responses and regulate androgen receptor signaling. In conclusion, our data show that estrogens have powerful inhibitory effects on CaP in vivo in androgen-depleted environments and suggest novel mechanisms of estrogen-mediated antitumor activity. These results indicate that incorporating estrogens into CaP treatment protocols could enhance therapeutic efficacy even in cases of advanced disease.

Molecular profile of androgen-independent prostate cancer xenograft LuCaP 23.1

After castration or therapeutic hormone deprivation, most cancer of the prostate (CaP) cells develop androgen-independent (AI) growth. In this work, we studied the effect of androgen depletion (castration) on the growth of experimental model LuCaP 23.1 xenograft. A total of 101 nude mice were implanted and analysed for their growth profile before experimental period 1 (11 weeks) and after castration experimental period 2 (15 weeks). For specific periods, tumors were harvested and assessed for molecular marker expression specific for CaP. Taking into account tumor dynamic growth, prior to castration we found 37 fast growing (FG) tumors (948.9+/-76.9 mm3) and 63 slow growing (SG) tumors (229.6+/-18.4 mm3). Real-time quantitative RT-PCR showed that in comparison to SGs, FGs contained elevated expression of epidermal growth factor receptor type 1 (HER1), urokinase plasminogen activator (uPA), thymidine phosphorylase (TP) and thymidilate synthase (TS) mRNAs expression and low levels of 5alpha-reductase 2 (5alpha-R2) mRNA. After castration all FG tumors progressed rapidly (by 5 weeks) to AI growth (FG-P). In SG castrated tumors, 66% of tumors showed retarded progression (by 12 weeks) to AI (SG-P), whereas 34% responded to castration (SG-R). Molecular analysis demonstrated distinct molecular profiles integrating different pathways associated with AI progression. The progressive tumors FG-P, and some tumors of SG-P subgroup, presented significantly high levels of HER1, epidermal growth factor receptor type 2 (HER2), TS, uPA, TP, tumor necrosis factor superfamily member 6 (FAS) and peptidylglycine alpha-amidating mono-oxygenase (PAM) mRNA all of which correlated with androgen receptor (AR) mRNA. The second subgroup of SG-P tumors showed a high expression of the anti-apoptotic gene Bcl-2. A third subgroup of SG-P tumors showed significant expression of hypoxia-related genes such as adrenomedullin (AM) after castration. LuCaP 23.1 xenograft represent a useful dynamic model to study pre-clinically new therapeutic molecules and evaluate non-randomized therapeutics protocols combining different target inhibition specific to each AI pathways.

Testosterone as a predictor of pathological stage in clinically localized prostate cancer

PURPOSE

Substantial controversy exists in the literature regarding the association between pretreatment testosterone and disease outcome in patients with prostate cancer. We explored the relationship between preoperative total testosterone, and pathological stage and progression in patients with clinically localized prostate cancer treated with radical prostatectomy.

MATERIALS AND METHODS

We retrospectively reviewed the records of consecutive patients with clinically localized prostate cancer treated with radical prostatectomy between January 1990 and June 2003. A total of 326 patients with pretreatment testosterone levels available were eligible for this analysis. Biochemical progression (BCR) was defined by postoperative prostate specific antigen (PSA) greater than 0.4 ng/ml with a confirmatory increase and it occurred in 41 men. No men received adjuvant therapy. Univariate and multivariate logistic regression analyses were done to examine whether pretreatment testosterone was associated with pathological stage. Cox regression was used to assess the association of testosterone and BCR.

RESULTS

Median PSA was 6.01 ng/ml (range 0.13 to 86), testosterone was 385 ng/dl (range 133 to 998) and followup was 36 months (range 4 to 136). In 245 patients (75%) disease was organ confined. Lower testosterone correlated with adverse pathological stage on multivariate analysis (p = 0.01), as did clinical stage, biopsy grade and PSA. However, we found no relationship between testosterone and BCR after adjusting for covariates. Furthermore, we found no evidence of an interaction between PSA and testosterone (p = 0.4).

CONCLUSIONS

On multivariate analysis low preoperative total testosterone was associated with advanced pathological stage but not with BCR. Future studies are warranted with data on more patients who have progressed.

A mathematical investigation of the multiple pathways to recurrent prostate cancer: comparison with experimental data

Considerable research is aimed at determining the mechanisms by which hormone-refractory prostate cancer develops. In an effort to assist in the understanding of recurrent prostate cancer and the cellular processes that mediate this disease, a mathematical model is presented that describes both the pretreatment growth and the posttherapy relapse of human prostate cancer xenografts. Our goal is to evaluate the interplay between the multiple mechanisms that have been postulated as causes of androgen-independent relapse. Simulations of the model show that molecular events that render the androgen receptor irrelevant to disease progression, such as upregulation of BCL2, can result in relapse after androgen deprivation therapy. However, decreased apoptosis of androgen-independent cells alone overestimates the effects of hormone therapy when compared to experimental data. When decreased apoptosis is combined with continual androgen receptor activation, the posttherapy growth dynamics are in excellent correlation with experimental observations of the growth of LuCaP xenografts. Furthermore, the mathematical model predicts that upregulation of the androgen receptor, together with its increased activation, is alone sufficient to result in the androgen-independent growth of LNCaP xenografts. Recent experimental studies that suggest that the posttherapy increase in and continual activation of the androgen receptor are common and crucial features of recurrent prostate cancer provide validation of the model predictions. This approach provides a framework for using mathematical techniques to study novel therapeutic strategies aimed at controlling this disease.

The effect of osteoprotegerin administration on the intra-tibial growth of the osteoblastic LuCaP 23.1 prostate cancer xenograft

Osteoprotegerin (OPG) plays a central role in controlling bone resorption. Exogenous administration of OPG has been shown to be effective in preventing osteolysis and limiting the growth of osteolytic metastasis. The objective of this study was to investigate the effects of OPG on osteoblastic prostate cancer (CaP) metastases in an animal model. LuCaP 23.1 cells were injected intra-tibially and Fc-OPG (6.0 mg/kg) was administered subcutaneously three times a week starting either 24 hours prior to cell injection (prevention regimen) or at 4 weeks post-injection (treatment regimen). Changes in bone mineral density at the tumor site were determined by dual x-ray absorptiometry. Tumor growth was monitored by evaluating serum prostate specific antigen (PSA). Fc-OPG did not inhibit establishment of osteoblastic bone lesions of LuCaP 23.1, but it decreased growth of the tumor cells, as determined by decreases in serum PSA levels of 73.0 +/- 44.3% (P < 0.001) and 78.3 +/- 25.3% (P < 0.001) under the treatment and prevention regimens, respectively, compared to the untreated tumor-bearing animals. Administration of Fc-OPG decreased the proliferative index by 35.0% (P = 0.1838) in the treatment group, and 75.2% (P = 0.0358) in the prevention group. The results of this study suggest a potential role for OPG in the treatment of established osteoblastic CaP bone metastases.

Cell proliferation and apoptosis in prostate tumors and adjacent non-malignant prostate tissue in patients at different time-points after castration treatment

BACKGROUND

Androgen ablation is the standard treatment for advanced prostate cancer but the short-term cellular effects are largely unknown.

METHODS

Sextant prostate biopsies were taken from 77 prostate cancer patients before and 1-10 days after castration treatment. Apoptosis, cell proliferation, and morphology were studied in malignant and non-malignant tissue, using stereological and immunohistochemical methods.

RESULTS

Epithelial cell proliferation was significantly decreased both in non-malignant and malignant epithelium already 1 day after therapy. It remained low until day 7, but increased thereafter in the remaining non-malignant epithelial cells and in some tumors. Epithelial cell apoptosis was significantly increased during the first week and then returned to basal levels. The maximal apoptotic indexes, seven- and two-times the intact levels in the non-malignant and malignant glands, respectively, were found at days 3-4 or even earlier in the tumors. Signs of tumor shrinkage such as glandular collapse and decreased tumor cell size were observed from day 3 in most tumors.

DISCUSSION

The present study shows that the magnitude and kinetics of the response to castration in the normal human prostate is very similar to the response previously described in rodents. We also demonstrate that most human prostate tumors rapidly respond to castration indicating the need for further evaluation of when and how to best monitor the effects of hormone ablation therapy in prostate cancer patients.

Characterization of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) as a model to study effects of castration therapy

BACKGROUND

In order to learn more about short- and long-term effects of castration therapy, relevant model systems for prostate cancer are required. In this study, we examined whether the transgenic adenocarcinoma of the mouse prostate (TRAMP) tumor response to castration in C57BL/6 mice mimics that seen in patients.

METHODS

Transgenic animals were examined before and 3 days after castration, at the ages of 17, 24, and 36 weeks. Moreover, 24-weeks old animals were castrated and followed for 6 months. Immunohistochemistry (IHC) and stereology were used to evaluate epithelial cell proliferation and death, blood vessel volume, androgen receptor (AR) expression, and transgenic expression of SV40 large T.

RESULTS

Cancer developed preferentially in the dorso-lateral prostate lobe. Tumor burden and incidence of metastases increased with age. The majority of tumors were well differentiated, while poorly differentiated, large tumors and macroscopic metastases developed in 8% of the animals. Well and moderately differentiated tumors responded to castration with cessation of proliferation and induction of apoptosis. Poorly differentiated tumors and metastases did not respond. Castration prevented local tumor growth for at least 6 months in 82% of the cases. Although, 45% of the treated animals developed wide-spread metastatic disease suggesting that castration may enhance growth of distant metastases.

CONCLUSIONS

The C57Bl/6 TRAMP tumor in several ways mimics how prostate cancer in patients responds to castration both in the short and long term, but some differences may also exist. This model can preferably be used to elucidate how this treatment works, and to test how it can be improved by additional therapies.

Molecular analysis integrating different pathways associated with androgen-independent progression in LuCaP 23.1 xenograft

After therapeutic hormone deprivation, most prostate cancer (PrCa) cells develop androgen-independent (AI) growth. PrCa is highly heterogeneous and multifocal, suggesting that several molecular processes or pathways may be contributing to AI. The human LuCaP 23.1 xenograft model retains clinical hallmarks of PrCa, including heterogeneous growth, PSA production, androgen-responsiveness and progression to AI. In this work, we studied the effect of androgen depletion (castration) on the growth of LuCaP 23.1 xenografts. A total of 100 nude mice were implanted and analysed for their growth profiles before and after castration. By 11 and 15 weeks, tumours were harvested and assessed for molecular marker expression specific for PrCa. Prior to castration we found 37 fast growing (FG) tumours (948.9+/-76.9 mm(3)) and 63 slow growing (SG) tumours (229.6+/-18.4 mm(3)), a previously undescribed result for this PrCa model. Quantitative RT-PCR showed that in comparison to SGs, FGs contained high HER1, uPA and thymidilate synthetase (TS) expression with low levels of 5alpha-reductase 2 mRNA. All FG tumours progressed rapidly to AI growth 5 weeks after castration (FG-P). In SG castrated tumours, 66% of tumours (SG-P) showed retarded progression (by 12 weeks) to AI, whereas 34% responded to castration (SG-R). Molecular analysis permitted us to define distinct molecular profiles integrating different pathways associated with AI progression. FG-P, and a subgroup of SG-P tumours, presented significantly high levels of peptidylglycine alpha-amidating monooxygenase (PAM), HER1, HER2, TS, and uPA mRNA, all of which correlated with AR expression. The second subgroup of SG-P tumours showed overexpression of the antiapoptotic gene Bcl-2. A third subgroup of SG-P tumours showed significant expression of hypoxia-related gene (adrenomedullin) after castration. This work permitted to define distinct molecular profiles related to different AI growth in the LuCaP 23.1 xenograft.

Long-Term Outcomes in Patients with Prostate Cancer Managed with Intermittent Androgen Suppression

OBJECTIVES

To assess the long-term outcomes of patients with prostate cancer managed with intermittent androgen suppression (IAS) following their enrollment in an open, non-randomised feasibility study initiated 10 years ago.

PATIENTS AND METHODS

Patients with prostate cancer who developed marked side effects following androgen deprivation were considered for entry into the study. All patients were required to have been managed with androgen deprivation for a minimum of 9 months and to have achieved PSA remissions to levels <4 ng/ml or falls to greater than 90% of pre-treatment levels. Patients remained off treatment until PSA values rose to >20 ng/ml or individuals became symptomatic--at which stage a 9-month cycle of androgen suppression was repeated. Such on-off cycling continued until hormone-resistant disease developed and patients proceeded (off trial) to second-line therapies.

RESULTS

75 patients were recruited to the study following an initial referral with treatment-related side effects specifically associated with androgen deprivation. 86% of these remain alive at a median of 134 months (11 years) since initial histological diagnosis. Survival times and times to hormone resistance (from first cycle hormone deprivation) have also been calculated. Overall there is a median survival time of 95 months (8 years) from initial (first-cycle) androgen deprivation in those presenting with localised or locally advanced disease and a median survival time of 87 months (7 years) for those presenting with metastatic disease. There exists a median of 83 months to hormone resistance in the localised and locally advanced group and a median of 50 months in those presenting with metastatic disease. We have calculated a 100% 5-year actuarial survival rate for those presenting with localised or locally advanced disease (from time of first cycle hormone ablation) and a 70% 5-year actuarial survival rate for those presenting with metastatic.

CONCLUSIONS

Long-term outcome figures and actuarial survival rates presented here provide further support for a pulsed or intermittent approach to androgen ablation in patients with prostate cancer. In addition, they serve as valuable extended outcome data for patients managed in this way. Likewise, data presented here suggests that apparent survival advantages appear related, at least in part, to a delay in the onset of androgen resistance and that such a management approach is both safe and effective in those presenting with both metastatic disease as well as those with more localised pathology.

Progression to androgen-independent LNCaP human prostate tumors: cellular and molecular alterations

Lethal phenotypes of human prostate cancer are characterized by progression to androgen-independence and metastasis. For want of a clinically relevant animal model, mechanisms behind this progression remain unclear. Our study used an in vivo model of androgen-sensitive LNCaP human prostate cancer cell xenografts in male SCID mice to study the cellular and molecular biology of tumor progression. Primary tumors were established orthotopically, and the mice were then surgically castrated to withdraw androgens. Five generations of androgen-independent tumors were developed using castrated host mice. Tumor samples were used to determine expressions of cellular and molecular markers. Androgen-independent tumors had increased proliferation and decreased apoptosis compared to androgen-sensitive tumors, outcomes associated with elevated expression of p53, p21/waf1, bcl-2, bax and the bcl-2/bax ratio. Blood vessel growth in androgen-independent tumor was associated with increased expression of vascular endothelial growth factor. Overexpression of androgen receptor mRNA and reduced expression of androgen receptor protein in androgen-independent tumors suggest that the androgen receptor signaling pathway may play an important role in the progression of human prostate cancer to androgen-independence. The in vivo orthotopic LNCaP tumor model described in our study mimics the clinical course of human prostate cancer progression. As such, it can be used as a model for defining the molecular mechanisms of prostate cancer progression to androgen-independence and for evaluating the effect of preventive or therapeutic regimens for androgen-independent human prostate cancer.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Apoptosis levels increase after castration in the CWR22 human prostate cancer xenograft

BACKGROUND

The role of apoptosis in the regression of human prostate cancer after androgen deprivation therapy remains controversial. Detection of caspase-3, an ubiquitous effector of apoptosis, is a highly specific technique for in vivo evaluation of apoptosis.

METHODS

Apoptotic rates were evaluated in the androgen-dependent CWR22 human prostate cancer xenograft in tumors that represented time points throughout the progression from androgen-stimulated to recurrent prostate cancer. Caspase-3 levels in formalin-fixed, paraffin-embedded specimens were quantified using immunohistochemical detection and video image analysis. Western blot analysis was used to confirm the results of immunodetection.

RESULTS

Expression of caspase-3 reached a maximum on day 2 after castration, decreased on day 6, and remained low until tumor recurrence. The percentage of tumor area expressing caspase-3 increased from 2.51 +/- 0.44% in tumors from intact mice to 20.84 +/- 1.75% on day 2 after castration. Among immunopositive cells, the intensity of caspase-3 expression measured using the mean optical density (MOD) increased 45% (0.3762 +/- 0.003 to 0.5461 +/- 0.001) on day 2 after castration compared to levels detected in tumors from intact mice.

CONCLUSIONS

Apoptosis contributes to tumor regression after castration in the CWR22 human prostate cancer xenograft model.

Interrelationships between plasma testosterone, SHBG, IGF-I, insulin and leptin in prostate cancer cases and controls

Despite strong indirect evidence that androgens stimulate prostate cancer development, data from most analytical studies on this association have been negative. To further investigate this issue, we studied the interrelationships between androgenicity and insulin-like growth factor I (IGF-I), insulin and leptin. Within a prospective cohort study, we measured testosterone, sex hormone-binding globulin (SHBG) and IGF-I, IGF-binding protein (IGFBP)-1, IGFBP-3, insulin and leptin, in plasma from 149 cases and 298 controls. Testosterone correlated positively with SHBG, whereas testosterone and SHBG correlated inversely with IGF-I, IGFBP-3, insulin, leptin and body mass index (BMI). Indices of free testosterone showed an inverse linear correlation with leptin (P<0.01), and a strong drop in the 5th quintile of BMI. However, levels of free testosterone showed non-linear relationships over quintiles of insulin and IGF-I, with a significant increase in the second quintile of IGF-I compared with other levels. The absence of an association between plasma levels of androgens and prostate cancer risk in analytical studies, despite the strong indirect evidence of their tumour-stimulating effects, may reflect the complex and mostly inverse associations of androgenicity to IGF-I, insulin and leptin which are hormones that have also been implicated as risk factors for prostate cancer.

High levels of circulating testosterone are not associated with increased prostate cancer risk: A pooled prospective study

Androgens stimulate prostate cancer in vitro and in vivo. However, evidence from epidemiologic studies of an association between circulating levels of androgens and prostate cancer risk has been inconsistent. We investigated the association of serum levels of testosterone, the principal androgen in circulation, and sex hormone-binding globulin (SHBG) with risk in a case-control study nested in cohorts in Finland, Norway and Sweden of 708 men who were diagnosed with prostate cancer after blood collection and among 2,242 men who were not. In conditional logistic regression analyses, modest but significant decreases in risk were seen for increasing levels of total testosterone down to odds ratio for top vs. bottom quintile of 0.80 (95% CI = 0.59-1.06; p(trend) = 0.05); for SHBG, the corresponding odds ratio was 0.76 (95% CI = 0.57-1.01; p(trend) = 0.07). For free testosterone, calculated from total testosterone and SHBG, a bell-shaped risk pattern was seen with a decrease in odds ratio for top vs. bottom quintile of 0.82 (95% CI = 0.60-1.14; p(trend) = 0.44). No support was found for the hypothesis that high levels of circulating androgens within a physiologic range stimulate development and growth of prostate cancer.

Castration-induced reduction of vascular endothelial growth factor expression in benign human prostate tissue is lost in advanced prostate cancer

OBJECTIVE

To determine the role of vascular response in the castration-induced regression of benign and malignant human prostate tissue, as recent studies show that castration rapidly decreases blood flow and induces endothelial cell death, which may be important for subsequent epithelial cell death and involution of the glandular tissue of the prostate.

MATERIALS AND METHODS

The expression of vascular endothelial growth factor (VEGF) and its receptors was analysed using the quantitative reverse transcriptase-polymerase chain reaction, in benign and tumour areas of core biopsies taken before, and approximately 1 week after castration therapy. The castration-induced VEGF response was related to therapy-induced changes in tumour cell apoptotic index and subsequent response in serum prostate-specific antigen (PSA). In another set of patients, serum VEGF was quantified by enzyme-linked immunosorbent assay before, and at 3--6 months after castration therapy.

RESULTS

VEGF mRNA was down-regulated after castration in benign prostate tissue (P < or = 0.05), whereas in tumour tissue, VEGF levels were reduced in some of the patients but unchanged or increased in others. In most patients whose tumour tissue responded with VEGF reduction, there was a corresponding increase in tumour cell apoptosis. Serum VEGF levels were not significantly changed after castration. Almost all patients responded with a substantial reduction in serum PSA after castration.

CONCLUSION

Castration reduces VEGF mRNA expression in benign prostate tissue and generally in those prostate tumours where castration also induces tumour cell apoptosis. This suggests that a therapy-induced down-regulation of VEGF could be important for tumour cell death.

Intermittent androgen deprivation

Intermittent androgen deprivation is a controversial approach to management of prostate cancer. Preclinical models have demonstrated delay in time to prostate-specific antigen (PSA) progression in athymic mice bearing LNCaP tumors and a delay in time to androgen independence in androgen-dependent Shionogi carcinoma tumors in castrated animals exposed to intermittent androgen. Phase II clinical trials have demonstrated improved sexual function and quality of life in men discontinuing androgen deprivation. The average percentage of time spent off androgen deprivation ranges from 37% to 58%. Most men respond to retreatment with hormonal therapy. Current ongoing phase III clinical trials of intermittent versus continuous androgen deprivation in men with metastatic disease or recurrent disease after localized therapy will assess the comparative impact on quality of life and survival. Final analyses of these critical trials will define the ultimate role of this approach in prostate cancer. In the interim, intermittent androgen deprivation should be considered an experimental approach.

Prolonged response to a single androgen suppression phase in a subpopulation of prostate cancer patients

BACKGROUND

In an intermittent androgen suppression therapy (IAS) trial we observed regular cycles of tumor suppression and regrowth in the majority of patients (17 +/- 2.6 month), with a subpopulation of patients (14 of 72) exhibiting a prolonged response of 28 +/- 7 month (range 18-64+ month) to the first eight-month androgen suppression cycle.

PURPOSE

To compare clinical data and laboratory tests (testosterone, prostate-specific antigen, and tissue polypeptide-specific antigen) of matched IAS patients showing either regular treatment cycles (n = 16) or prolonged response (n = 14).

RESULTS

Periods of androgen suppression resulted in reversible reduction of serum testosterone (< 1 nmol/l), PSA (< 1 ng/ml) indicating partial growth arrest and apoptotic regression of the tumors. The long-term response subgroup showed significantly lower mean values of tumor gradings, of pretreatment PSA values (11.36 +/- 4.54 vs. 47.5 +/- 12.4 ng/ml PSA), of PSA nadirs during androgen suppression (0.5 vs. 1 ng/ml PSA), and of overall testosterone values (3.9 +/- 1.14 vs. 6.6 +/- 1.18 mmol/l pretreatment) associated with low TPS values.

CONCLUSIONS

Patients exhibiting prolonged response to a single cycle of androgen suppression during IAS are characterized by a lower tumor burden, slow growing and less aggressive tumors, lower testosterone serum concentrations and lower absolute PSA nadirs during androgen suppression compared to a matched control group of short-term responders.

Intermittent androgen suppression in the LuCaP 23.12 prostate cancer xenograft model

BACKGROUND

Intermittent androgen suppression (IAS) has been proposed as a method of delaying the onset of androgen-independent growth in prostate cancer. While several pilot studies have demonstrated the feasibility of such a treatment, no study to date has defined the effect of IAS on survival.

METHODS

We developed an IAS protocol for mice bearing the LuCaP 23.12 human prostate cancer xenograft, with each cycle consisting of 1 week of androgen replacement with a testosterone pellet followed by 3 weeks of androgen withdrawal. Mice that responded to castration with a 40% or greater decrease in serum prostate-specific antigen (PSA) were randomized to treatment with either continuous androgen suppression (CAS) or IAS. Serum PSA, tumor volume, and overall survival were monitored.

RESULTS

A total of 75 mice met the randomization criteria. There was no significant difference of survival between animals treated with CAS or IAS (185 vs. 239 days, P = 0.1835). Serum PSA showed evidence of cycling with hormonal manipulation. No cycling was noted in tumor volume.

CONCLUSIONS

IAS is not associated with a decrease in survival compared to CAS, yet in patients may offer quality-of-life improvements. Further studies of IAS in the setting of Institutional Review Board (IRB) approved clinical trials should be encouraged. Prostate 43:63-70, 2000. Published 2000 Wiley-Liss, Inc.

The early supra-additive apoptotic response of R3327-G prostate tumors to androgen ablation and radiation is not sustained with multiple fractions

PURPOSE

The treatment of R3327-G tumor-bearing rats with androgen ablation (AA) via castration results in a supra-additive increase in apoptosis when 2-8 Gy gamma-irradiation (RT) is given as a single dose 3-14 days afterwards. We report here the dose response and effect of multiple fractions on this supra-additive apoptotic response.

MATERIALS AND METHODS

Dunning R3327-G tumors were grown in the flanks of Copenhagen rats and the experiments were initiated at a tumor volume of 1.0-1.5 cc. Androgen ablation was achieved by castration 3 days prior to gamma-irradiation. Apoptosis was measured with a terminal deoxynucleotidyl transferase dUTP-biotin nick end-labeling assay 6-h after RT, unless otherwise specified.

RESULTS

The dose response of the supra-additive apoptotic response was assessed by irradiating castrated animals with single doses of 2, 4, 8, or 16 Gy (n = 5 per group); tumor cell apoptosis at 6-h following irradiation was 2.4%+/-0.7% (+/- SEM), 4.2%+/-0.8%, 6.5%+/-1.4%, and 1.6%+/-0.3%, respectively. The RT only and AA only controls had < 1% apoptosis. The effect of fractionated RT on apoptosis was investigated to determine if the supra-additive apoptotic response was sustained with repeated 2-8 Gy fractions. When tumor-bearing animals were treated with repeated daily 2-Gy fractions, there was a reduction in the level of the supra-additive apoptotic response. After five 2-Gy fractions at 24-h intervals, apoptosis in the combined treated tumors was at levels seen in the AA controls. This raised the possibility that more than 24 h are required for recovery of the high supra-additive apoptotic levels seen after one fraction. When the interfraction interval was extended to 96 h, there was no significant increase in apoptosis over the additive effect of AA and RT. Although there was a decline in supra-additive apoptosis with repeated fractions, a dose response for tumor growth delay was evident for RT alone using 2.5-Gy fractions. Moreover, the combination of AA + fractionated RT resulted in a supra-additive enhancement in tumor growth delay to 5 cc.

CONCLUSION

The early supra-additive apoptotic response from AA and single fraction radiation is not seen at high single fraction doses and is not sustained with repeated fractions. Therefore, the classical apoptotic response that occurs within 24 h of irradiation is not likely to be the main mechanism responsible for any clinical benefit seen with this combination.

Molecular cloning and characterization of prostase, an androgen-regulated serine protease with prostate-restricted expression

The identification of genes with selective expression in specific organs or cell types provides an entry point for understanding biological processes that occur uniquely within a particular tissue. Using a subtraction approach designed to identify genes preferentially expressed in specific tissues, we have identified prostase, a human serine protease with prostate-restricted expression. The prostase cDNA encodes a putative 254-aa polypeptide with a conserved serine protease catalytic triad and an amino-terminal pre-propeptide sequence, indicating a potential secretory function. The genomic sequence comprises five exons and four introns and contains multiple copies of a chromosome 19q-specific minisatellite repeat. Northern analysis indicates that prostase mRNA is expressed in hormonally responsive normal and neoplastic prostate epithelial tissues, but not in prostate stromal constituents. Prostase shares 35% amino acid identity with prostate-specific antigen (PSA) and 78% identity with the porcine enamel matrix serine proteinase 1, an enzyme involved in enamel matrix degradation and with a putative role in the disruption of intercellular junctions. Radiation-hybrid-panel mapping localized prostase to chromosome 19q13, a region containing several other serine proteases, including protease M, pancreatic/renal kallikrein hK1, and the prostate-specific kallikreins hK2 and hK3 (PSA). The sequence homology between prostase and other well-characterized serine proteases suggests several potential functional roles for the prostase protein that include the degradation of extracellular matrix and the activation of PSA and other proteases.

Current status of intermittent androgen suppression in the treatment of prostate cancer

Treatment of advanced prostate cancer by continuous androgen suppression results in excellent short-term response but poor long-term survival. Intermittent androgen suppression (IAS) aims to maintain androgen responsiveness of tumor cells by regular cycles of treatment cessations and tumor regrowth to specific prostate-specific antigen limits. First clinical trials demonstrate consistent responses and improved quality of life in most patients on androgen suppression retreatment for up to five cycles, with mean off-treatment periods of approximately 5 to 16 months. Most patients with metastatic disease exhibit early disease progression or androgen independency under IAS, but a subgroup including patients with metastatic disease respond to a single androgen suppression cycle with off-treatment times for up to 48 months. In conclusion, IAS improves the quality of life in patients with primarily hormone-dependent tumors without adverse effects and seems to be most effective in patients with prostate cancer with asymptomatic biochemical progression and low tumor burden. Patients should be treated within the framework of randomized trials and characterized for survival and prognostic factors associated with response to IAS treatment.

Study of free and complexed prostate-specific antigen in mice bearing human prostate cancer xenografts

BACKGROUND

Our objective was to evaluate five preclinical prostate cancer (CaP) xenograft models to determine whether (1) prostate-specific antigen (PSA) formed complexes in murine serum, (2) the percentage of free PSA (f-PSA) was characteristic of a given xenograft line, and (3) the percentage of f-PSA was similar to that in the patient at time of tumor harvest. Our fourth objective was to identify which murine serpin(s) bind(s) to PSA in vivo.

METHODS

Xenografts were established from metastatic foci. The percentage of f-PSA, and total PSA (t-PSA) in serum of animals bearing CaP xenografts was determined by immunoassay. Size exclusion high-performance liquid chromatography and Western blots were used to evaluate the presence of PSA complexes in murine serum. Edman degradation was used to determine the N-terminal sequence of complexed proteins.

RESULTS

PSA was detected as both free and complexed forms in murine serum from all mice bearing the CaP xenografts. Three xenografts (related sublines) produced PSA that resulted in low mean percentages of f-PSA (1.9-6.4%). In sera from the other two xenografts, the mean percentages of f-PSA were high (>25%); patient sera, where available at time of tumor acquisition, were in agreement. Western blots showed that murine protease inhibitors formed complexes with PSA. Edman degradation yielded a sequence with 80% homology over 15 amino acids with that of murine alpha1-protease inhibitor (alpha1-PI).

CONCLUSIONS

Our data have shown that the majority of PSA secreted by these CaP xenografts complexes in murine serum with a protease inhibitor with high homology to murine alpha1-PI and that the percentage of f-PSA is a characteristic of each xenograft line tested, which is in agreement with patient values at time of tumor harvest. These CaP xenografts offer opportunities for study of human PSA biology and phenomenology.

Growth factor involvement in progression of prostate cancer

Understanding how the regulation of growth factor pathways alters during prostate cancer (PC) progression may enable researchers to develop targeted therapeutic strategies for advanced disease. PC progression involves the shifting of cells from androgen-dependent growth to an androgen-independent state, sometimes with the loss or mutation of the androgen receptors in PC cells. Both autocrine and paracrine pathways are up-regulated in androgen-independent tumors and may replace androgens as primary growth stimulatory factors in cancer progression. Our discussion focuses on growth factor families that maintain homeostasis between epithelial and stromal cells in the normal prostate and that undergo changes as PC progresses, often making stromal cells redundant. These growth factors include fibroblast growth factor, insulin-like growth factors, epidermal growth factor, transforming growth factor α, retinoic acid, vitamin D3, and the transforming growth factor β families. We review their role in normal prostate development and in cancer progression, using evidence from clinical specimens and models of PC cell growth.

Short-term cellular effects induced by castration therapy in relation to clinical outcome in prostate cancer

To explore the relationship between short-term effects of castration therapy and clinical response, biopsies obtained before and a week after castration therapy from 15 responding and 13 non-responding patients with prostate cancer were investigated. The biopsies were assessed for regressive morphology, apoptotic index by morphological criteria, nuclear area, and immunoreactivity (IR) for Ki-67, p53, bcl-2, bax and Fas. The index was defined as the percentage of immunoreactive cells in a tumour. Regressive morphology was observed in 14 out of 15 responding tumours after therapy, compared with 4 out of 13 non-responders (P < 0.001). Median tumour epithelial cell nuclear area and Ki-67 index decreased equally in both groups. The median apoptotic index increased from 2.6 to 3.5 after castration among responders (P < 0.05), whereas it remained at 2.8 among non-responders. p53 IR was present in three tumours before castration; after therapy p53 reactivity was seen in three additional tumours belonging to the responding group. Median bcl-2 index increased in responders from 1.5 to 10.0 (P < 0.05), and in non-responders from 0.08 to 2.7 (P < 0.05). Bax IR and Fas IR were present in all tumours before therapy and unchanged after therapy. Thus, regressive morphology and an increase in apoptotic index were related to a favourable clinical response. These data suggest that it might be possible to predict the effect of castration therapy by examining tumour biopsies shortly after treatment.