Chemoprevention of prostate cancer

When Is Enough, Enough? When Are More Observational Epidemiologic Studies Needed to Resolve a Research Question: Illustrations Using Biomarker-Cancer Associations

BACKGROUND

Research reproducibility is vital for translation of epidemiologic findings. However, repeated studies of the same question may be undertaken without enhancing existing knowledge. To identify settings in which additional research is or is not warranted, we adapted research synthesis metrics to determine number of additional observational studies needed to change the inference from an existing meta-analysis.

METHODS

The fail-safe number (FSN) estimates number of additional studies of average weight and null effect needed to drive a statistically significant meta-analysis to null (P ≥ 0.05). We used conditional power to determine number of additional studies of average weight and equivalent heterogeneity to achieve 80% power in an updated meta-analysis to detect the observed summary estimate as statistically significant. We applied these metrics to a curated set of 98 meta-analyses on biomarkers and cancer risk.

RESULTS

Both metrics were influenced by number of studies, heterogeneity, and summary estimate size in the existing meta-analysis. For the meta-analysis on Helicobacter pylori and gastric cancer with 15 studies [OR = 2.29; 95% confidence interval (CI), 1.71-3.05], FSN was 805 studies, supporting futility of further study. For the meta-analysis on dehydroepiandrosterone sulfate and prostate cancer with 7 studies (OR = 1.29; 95% CI, 0.99-1.69), 5 more studies would be needed for 80% power, suggesting further study could change inferences.

CONCLUSIONS

Along with traditional assessments, these metrics could be used by stakeholders to decide whether additional studies addressing the same question are needed.

IMPACT

Systematic application of these metrics could lead to more judicious use of resources and acceleration from discovery to population-health impact.

Drug development for cancer chemoprevention: focus on molecular targets

With biomolecular evidence accumulating at an exponential rate, there will be a surge in the development of targeted cancer prevention drugs and interventions in the next decade. Promising results from clinical treatment trials identify a spectrum of targeted cancer therapies in several broad categories. These include both small molecule inhibitors of either key receptors or enzyme binding sites, as well as intravenously delivered monoclonal antibodies that block a specific binding interaction between ligands and their receptors. These targeted interventions conform to a basic translational algorithm: biomarker present, biomarker modulated, and biomarker clinically relevant. A review of solid tumor targets provides a manageable list of factors that are critical to cancer cell survival. As such, these targets represent factors that are not only clinically relevant but also may play a critical role in early tumor development prior to the evolution of frank invasive malignancy. This possibility qualifies these targets for consideration in the development of cancer prevention interventions. Among solid tumors, the treatment of breast cancer with targeted drugs has a long record benchmarked by the initial US Food and Drug Administation (FDA) approval of tamoxifen for metastatic breast cancer treatment in 1977. Since then, the list of oncology drug targets has expanded to include aromatase, androgen receptor, the epidermal growth factor receptor (EGFR) family, and others. It is not surprising that tamoxifen was the first of the modern targeted therapies to be approved for cancer risk reduction and additional approvals are anticipated. The focus of this review is the pharmacologic manipulation of targets within epithelial tumor cells and the implication of those targets for intervening to suppress and eliminate premalignant cells in human tissue. Major obstacles to prevention drug development can be addressed by attention to two important areas. One of these is the refinement of early phase prevention trials to identify drug targets in epithelial cells that are at demonstrated risk of evolving into cancer cells, ie, cells from a developmental niche in cancer ontogeny. Early results suggest that molecular risk signatures may allow the investigational identification of molecular targets in premalignant tissue, with the possibility that chemoprevention agents can be used to eliminate the risk signature. To the extent that this approach can be developed, it will allow for cancer risk reduction in a way that is analogous to the measurement of tumor response to treatment. Even with improvements in the efficiency of clinical trials that come from using molecular risk signatures, there is an ever-growing list of chemoprevention agents that are candidates for evaluation. Improved prevention drug screening methodologies are therefore needed to prioritize agents for clinical testing. In addition to drug targets located in epithelial tumor cells, another list of malignancy-associated targets could be generated by considering targets in tumor-associated stromal and endothelial cells (eg, fibroblast growth factor [FGF], vascular endothelial growth factor [VEGF]), as well as targets related to a systemic reservoir of circulating cells that can be recruited to carcinogenic influence by inflammatory factors such as nuclear factor (NF)kappaB. The complementarities of target-related processes within tumors cells, in the tumor microenvironment, and beyond suggests that there is great potential for multi-targeted approaches that may be more effective than single agents and also less prone to resistance. Additional options, related to drug dose and schedule, remain to be established. As long as multiple agents can be used in combination for optimal effect with acceptable toxicity, the co-targeting of the epithelial cell compartment along with other compartments of oncogenic activity is expected to expand the dimensions of targeted prevention and enhance the overall opportunity to eliminate precancer or cells at risk of eventually transitioning to invasive cancer.

Prevention of prostate cancer

Prostate cancer is an ideal candidate for chemoprevention because of its high prevalence, long latency time, hormone dependency, precursor lesions, and its unique serum marker, PSA. Chemoprevention is the administration of drugs or other agents which aim to prevent the induction or inhibit/delay cancer progression. Large-scale studies favor environmental rather than genetic factors as key determinants of prostate cancer development. Among these environmental factors, nutrition certainly has a leading role. Numerous basic science studies but also clinical studies indicate that dietary compounds or diet modifications may ultimately play a major role in prostate cancer promotion and inhibition. Definitive proofs are often difficult because of methodological problems and complex triggering cascades. New pharmaceutical drugs with minimal toxicity are also currently evaluated.

Inhibition of arachidonate 5-lipoxygenase triggers prostate cancer cell death through rapid activation of c-Jun N-terminal kinase

Previously, we reported that inhibition of arachidonate 5-lipoxygenase triggers massive apoptosis in both androgen-sensitive (LNCaP) and androgen-refractory (PC3) human prostate cancer cells within hours of treatment [Proc. Natl. Acad. Sci. USA 95 (1998) 13182-13187]. Apoptosis was prevented by exogenous 5(S)-HETE, a product of 5-lipoxygenase, indicating a role of this eicosanoid as an essential survival/anti-apoptotic factor for prostate cancer cells. However, nothing was clearly known about details of the underlying molecular mechanisms or events mediating the induction of fulminating apoptosis in these cells. This report documents the fact that inhibition of arachidonate 5-lipoxygenase induces rapid activation of c-Jun N-terminal kinase (JNK) in human prostate cancer cells which is prevented by the 5-lipoxygenase metabolite, 5(S)-HETE. Activation of JNK is unaffected by the cell-permeable tetra-peptide inhibitors of caspase 8 or caspase 3 (IETD-FMK and DEVD-FMK), though these inhibitors effectively blocked apoptosis triggering, suggesting that activation of JNK is independent or upstream of caspase activation. Both 5-lipoxygenase inhibition-induced activation of JNK and induction of apoptosis are prevented by curcumin, an inhibitor of JNK-signaling pathway. Apoptosis is also blocked by SP600125, a specific inhibitor of JNK activity, indicating that JNK activity is required for the induction of apoptosis in these cells. These findings suggest that the metabolites of arachidonate 5-lipoxygenase promote survival of prostate cancer cells involving down-regulation of stress-activated protein kinase.

5alpha-reductase inhibitors: what role should they play?

The development of finasteride (PROSCAR, Merck & Co., Whitehouse Station, NJ) for the treatment of benign prostatic hyperplasia (BPH) has had variable results. Numerous short-term and long-term studies comparing finasteride with placebo have been reported. The results suggest that, physiologically, treatment with finasteride significantly decreases levels of both serum and intraprostatic dihydrotestosterone about 70% to 80% from baseline. In addition, total gland size decreases significantly-about 15% to 25% from baseline-particularly in the area of the periurethral zone of the prostate after finasteride treatment. Baseline prostate size has been found to have a relation to efficacy of finasteride treatment. The larger the prostate at baseline, the greater the urinary flow rate increase and symptom score decrease compared with placebo. Health-related quality-of-life parameters improved in those taking finasteride. In studies evaluating combination therapy, no significant differences were noted between those treated with an alpha blocker, such as terazosin or doxazosin in combination with finasteride, and those receiving an alpha blocker alone. Long-term finasteride versus placebo studies, such as the PROSCAR Long-Term Efficacy and Safety Study (PLESS), suggest that long-term medical therapy with finasteride affects the natural history of the disease as manifested by the decrease in rates of acute urinary retention and surgery. In patients who are "therapeutic responders," the degree of symptomatic improvement in those treated with finasteride appears to be equal to that seen in patients receiving alpha blockers. Prostate cancer detection rates did not differ between those treated with finasteride and those receiving a placebo. The results of these studies suggest that physicians must evaluate what role finasteride plays in the spectrum of available options for the treatment of BPH and lower urinary tract symptoms. Baseline parameters, such as prostate volume, prostate-specific antigen values, and whether to administer finasteride in combination with alpha blockers, are among the factors that will determine the appropriateness of such therapy.

Detection and cloning of a protein recognized by anti-human prostate-specific antigen (PSA) antibody in the rat ventral prostate

Prostate-specific antigen (PSA), a 33 kDa glycoprotein produced in the epithelium of the human prostate, has become established as a useful tumor marker for prostate cancer in man. Since reports of homologous proteins in animals other than primates have been lacking, the present investigation was carried out to identify any PSA-like protein in rats. Immunoblot analysis using a specific monoclonal anti-human PSA antibody detected a 32 kDa immunoreactive protein in the ventral lobe of the rat prostate, but not in other lobes or in other tissues. Positive immunostaining was observed only for the luminal surface of the glandular epithelium and the intraductal fluid in the ventral prostate. Sequence analysis of a cDNA for the rat PSA-like protein, cloned by immunoscreening of an expression cDNA library prepared from the ventral lobe, revealed identity to the rat submaxillary gland S3 kallikrein. Human PSA also belongs to the kallikrein family. Thus, this protein produced in the rat ventral prostate was suggested to be a possible counterpart of human PSA.

Psychological and screening profiles of first-degree relatives of prostate cancer patients

The purpose of the present study was to systematically compare the psychological and screening profiles of first-degree relatives (FDRs) of prostate cancer patients versus non-FDRs. FDRs (n = 56) and non-FDRs (n = 100), recruited through prostate cancer index cases and newspaper advertisements, completed questionnaires via mail. FDRs reported feeling at greater risk for prostate cancer, estimated that they were at higher average lifetime risk for the disease, agreed more strongly that prostate cancer is inherited, and that less can be done to prevent the development of the disease. Increased age, but not FDR status, was associated with more frequent screening behavior. Taken together, the results indicate that FDRs are characterized by greater perceived vulnerability to prostate cancer and lower expectations about disease prevention. Yet, they are no more likely to be screened than non-FDRs. These findings underscore the importance of developing, and evaluating, evidence-based health communication protocols to promote screening adherence among at-risk patients.

Inhibitory effect of silibinin on ligand binding to erbB1 and associated mitogenic signaling, growth, and DNA synthesis in advanced human prostate carcinoma cells

We recently showed the inhibitory effect of a flavonoid antioxidant, silymarin, on erbB1-Shc activation in prostate cancer (PCA) DU145 cells. In the present study, we performed more detailed mechanistic and molecular modeling studies with pure silibinin to assess and define its effect on membrane signaling related to erbB1 activation in human PCA LNCaP and DU145 cells. Studies also were performed to establish the biologic responses toward extracellular signal-regulated protein kinase 1/2 (ERK1/2) activation, cell growth, and DNA synthesis. Treatment of serum-starved cells with various doses of silibinin for 2 h followed by (125)I-epidermal growth factor (EGF) showed 30-75% inhibition in ligand binding and 55-95% inhibition in its internalization in LNCaP cells and 20-64% and 12-27% inhibition in these two events in DU145 cells. Time-response studies showed similar effects. In further studies, treatment of serum-starved cultures with silibinin followed by EGF showed strong inhibitory effects on membrane and cytoplasmic signaling molecules. In the case of erbB1 activation, silibinin showed a 58-75% decrease in LNCaP and a 40-100% decrease in DU145 cells at 50, 75, and 100-microg/mL doses. Inhibitory effects of silibinin also were evident on ERK1/2 activation (20-80% inhibition) in both cell lines. Treatment of serum-starved cultures with silibinin resulted in 20-40% and 30-55% inhibition of LNCaP and DU145 cell growth, respectively, at similar doses after 1-3 d of treatment, and 10-50% cell death in both cell lines. Under 10% serum conditions, identical silibinin treatments resulted in 20-65% inhibition of cell growth in LNCaP and DU145 cells but did not cause any cell death. Similar doses of silibinin treatments for 24 h also resulted in 25-60%, 35-40%, and 36-50% inhibition of DNA synthesis when cells were cultured in 10% serum, totally serum starved, and serum starved plus stimulated with EGF, respectively. Molecular modeling of silibinin showed that it is a highly lipophilic compound, suggesting that it interacts with lipid-rich plasma membrane, including binding with erbB1, thereby competing with the EGF-erbB1 interaction. Because the ligand-erbB1 autocrine-loop is causally involved in advanced and androgen-independent PCA, the observed effects of silibinin and its strong lipophilic nature could be useful in developing this agent for the prevention and therapy of PCA.

A medical hypothesis: phosphorus balance and prostate cancer

Over the last three decades the mortality rate for prostatic carcinoma has steadily increased. Carcinoma of prostate (CaP), the most common malignancy in men, is also the second most common cause of cancer deaths in men. However, few epidemiologic studies have been done, and there are scant clues to the etiology/pathogenesis of CaP. As treatment failures for advanced carcinoma continue to frustrate clinicians, more emphasis has recently been focused on strategies to prevent invasive CaP. Prostatic hyperplasia is a universal phenomenon in aging men. Mechanism and signals causing this growth are not understood. Thus, prostatic diseases affect men over the age of 45 and increase in frequency with age so that by the eighth decade more than 90% of men have benign prostatic hyperplasia, of which some progress to CaP. Data from several studies support that higher levels of active metabolite of vitamin D, 1,25-(OH)2-D, reduce the risk of prostatic hyperplasia and CaP. Men with high serum levels of 1,25-(OH)2-D have a reduced risk of poorly differentiated and clinically advanced CaP. Receptor for vitamin D has been reported in both normal and cancer prostate cells. 1,25-(OH)2-D inhibits proliferation and induces differentiation of normal and neoplastic cells. Hypercalcemic activity of 1,25-(OH)2-D or its analogues, however, thwart their use for therapy in humans. 1,25-(OH)2-D also has an established role in phosphorus homeostasis. Low dietary intake of phosphorus leads to an increase in serum concentration of 1,25-(OH)2-D. In addition, dietary fructose reduces plasma phosphate levels by 30 to 50% for more than 3 hr due to a rapid shift of phosphate from extracellular to intracellular compartment. Fruit intake has been shown to be associated with reduced risk of CaP, particularly the advanced type. Put together, these observations support that dietary determinants of hypophosphatemia, leading to increased plasma levels of 1,25-(OH)2-D, could reduce the risk of aging men to develop prostatic diseases, both benign prostatic hyperplasia and CaP.

Advances in the systemic treatment of cancers in the elderly

Cancer is a disease of the elderly. More than 50% of all cancers and deaths occur in people over 65 years. Older cancer patients are less likely to be referred to centers or to be given adequate chemotherapy. The elderly are under-represented in Phase I and II trials. Some of this hesitancy to give chemotherapy is related to the increased presence of co-morbid conditions in the elderly. Toxicity is another concern. This review summarizes data from literature on the effectiveness, outcome, and toxicity of chemotherapy in selected tumors. Information is presented on age related effects. In addition, a summary of new agents and biologics is presented that needs to be looked at for age related effects. Some comments are made on the pharmacokinetic impact of physiologic changes in the elderly on chemotherapy drugs. As the world's population ages, we need to include the elderly in trials to get data on age related effects. Most of the information presented shows that effective chemotherapy can be given safely to the elderly and the outcomes and toxicity are equivalent for many of the common solid tumors.

Prostate cancer screening: promise and peril--a review

This review summarizes the current status of and recommendations for prostate cancer screening with prostate-specific antigen in light of recent reductions in prostate cancer incidence and mortality. It describes how the uncertain effectiveness of aggressive treatment for prostate cancer and a reservoir of unsuspected indolent cancers make prostate cancer fit poorly into conventional screening models. The large proportion of men with unsuspected prostate cancers that may not cause morbidity or mortality and are unlikely to benefit from aggressive treatment decrease the effectiveness of a screening program. In addition, indolent, unsuspected prostate cancers in the screening population accentuate the detrimental effects of length bias on studies evaluating the effectiveness of prostate cancer screening. Screening tests for prostate cancer will continue to improve, but chemoprevention or nutritional prevention with vitamins and micronutrients such as tocopherols or selenium may prove to be effective methods of reducing prostate cancer incidence and should be aggressively investigated.

Does long-term finasteride therapy affect the histologic features of benign prostatic tissue and prostate cancer on needle biopsy? PLESS Study Group. Proscar Long-Term Efficacy and Safety Study

OBJECTIVES

Finasteride, a common agent used to treat benign prostatic hyperplasia (BPH), inhibits 5-alpha-reductase. Testosterone is converted by 5-alpha-reductase to the more potent dihydrotestosterone, which is the primary androgen in the prostate. Leuprolide is a stronger antiandrogen that is used to downstage prostate cancer before radical prostatectomy. Leuprolide induces marked atrophy of prostate carcinoma cells, which sometimes makes pathologic diagnosis of cancer difficult, although evaluation at radical prostatectomy is easier than at biopsy. It is unknown whether finasteride produces similar changes, which would result in greater diagnostic difficulty because such changes would be seen on biopsy to rule out cancer in men with suspicious clinical findings treated for BPH. The current study investigated the histologic effects of finasteride therapy on human prostate cancer and benign prostatic tissue on needle biopsy.

METHODS

In blinded manner, we reviewed 53 needle biopsy specimens showing prostate carcinoma (35 treated with finasteride, 18 with placebo). Also reviewed in blinded manner were 50 benign needle biopsy specimens (25 treated with finasteride, 25 with placebo). The Gleason score, number of cores involved, percentage cancer involvement in a core, percentage of atrophic changes in cancer cells, presence of mitoses, blue-tinged mucinous secretions, prominent nucleoli, and high-grade prostatic intraepithelial neoplasia were documented for each case in the cancer group. The percentage of atrophy, basal cell hyperplasia, transitional metaplasia, chronic inflammation, and stromal proliferation was documented for each case in the benign group.

RESULTS

No significant histologic differences were present in either the benign or cancer group between cases treated with finasteride and placebo.

CONCLUSIONS

We conclude that finasteride treatment for BPH does not cause difficulty in the diagnosis of cancer in prostate needle specimens. It is possible that there are severely atrophic areas resulting from finasteride treatment that are undersampled. However, the conclusion that cancer seen on needle biopsy in men treated with finasteride is unaltered and readily identified as cancer remains valid.

Effects of a soybean isoflavone mixture on carcinogenesis in prostate and seminal vesicles of F344 rats

Several epidemiological studies have suggested an inverse association between the risk of prostate cancer and intake of soybeans and their products. In vitro data pointing to possible anti-carcinogenic properties of the soybean isoflavone, genistein, led us to investigate the chemopreventive potential of soybean isoflavones in a rat carcinogenesis model induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) and testosterone propionate (TP). Animals received DMAB s.c. injections at 2-week intervals for the first 20 weeks and implanted silicon tubes containing 40 mg of TP, replaced at 6-week intervals throughout the experiment. The soybean isoflavone mixture consisting of 74% genistein and 21% daidzein was mixed in basal diet (AIN-76A) at concentrations of 100 and 400 ppm and fed to F344 male rats throughout the experiment. Rats treated with carcinogens and administered isoflavone mixture at 100 and 400 ppm developed adenocarcinomas at incidences of 35% and 29%, respectively, in the prostate and seminal vesicles, whereas the figure was 60% for those maintained on control diet. Feeding of the isoflavone mixture at 100 and 400 ppm significantly inhibited the number of argyrophilic nucleolar organizer regions (AgNORs) in adenocarcinomas of the accessory sex glands as compared to those of rats fed control diet. No influence on the development of neoplastic lesions originating in other organs was noted. The results of this study provide evidence that soybean isoflavones may have potential as chemopreventive agents against carcinogenesis in the prostate.

Inhibition of arachidonate 5-lipoxygenase triggers massive apoptosis in human prostate cancer cells

Diets high in fat are associated with an increased risk of prostate cancer, although the molecular mechanism is still unknown. We have previously reported that arachidonic acid, an omega-6 fatty acid common in the Western diet, stimulates proliferation of prostate cancer cells through production of the 5-lipoxygenase metabolite, 5-HETE (5-hydroxyeicosatetraenoic acid). We now show that 5-HETE is also a potent survival factor for human prostate cancer cells. These cells constitutively produce 5-HETE in serum-free medium with no added stimulus. Exogenous arachidonate markedly increases the production of 5-HETE. Inhibition of 5-lipoxygenase by MK886 completely blocks 5-HETE production and induces massive apoptosis in both hormone-responsive (LNCaP) and -nonresponsive (PC3) human prostate cancer cells. This cell death is very rapid: cells treated with MK886 showed mitochondrial permeability transition between 30 and 60 min, externalization of phosphatidylserine within 2 hr, and degradation of DNA to nucleosomal subunits beginning within 2-4 hr posttreatment. Cell death was effectively blocked by the thiol antioxidant, N-acetyl-L-cysteine, but not by androgen, a powerful survival factor for prostate cancer cells. Apoptosis was specific for 5-lipoxygenase-programmed cell death was not observed with inhibitors of 12-lipoxygenase, cyclooxygenase, or cytochrome P450 pathways of arachidonic acid metabolism. Exogenous 5-HETE protects these cells from apoptosis induced by 5-lipoxygenase inhibitors, confirming a critical role of 5-lipoxygenase activity in the survival of these cells. These findings provide a possible molecular mechanism by which dietary fat may influence the progression of prostate cancer.

Decreased incidence of prostate cancer with selenium supplementation: results of a double-blind cancer prevention trial

OBJECTIVE

To test if supplemental dietary selenium is associated with changes in the incidence of prostate cancer.

PATIENTS AND METHOD

A total of 974 men with a history of either a basal cell or squamous cell carcinoma were randomized to either a daily supplement of 200 microg of selenium or a placebo. Patients were treated for a mean of 4.5 years and followed for a mean of 6.5 years.

RESULTS

Selenium treatment was associated with a significant (63%) reduction in the secondary endpoint of prostate cancer incidence during 1983-93. There were 13 prostate cancer cases in the selenium-treated group and 35 cases in the placebo group (relative risk, RR=0.37, P=0.002). Restricting the analysis to the 843 patients with initially normal levels of prostate-specific antigen (< or = 4 ng/mL), only four cases were diagnosed in the selenium-treated group and 16 cases were diagnosed in the placebo group after a 2 year treatment lag, (RR=0.26 P=0.009). There were significant health benefits also for the other secondary endpoints of total cancer mortality, and the incidence of total, lung and colorectal cancer. There was no significant change in incidence for the primary endpoints of basal and squamous cell carcinoma of the skin. In light of these results, the 'blinded' phase of this trial was stopped early.

CONCLUSIONS

Although selenium shows no protective effects against the primary endpoint of squamous and basal cell carcinomas of the skin, the selenium-treated group had substantial reductions in the incidence of prostate cancer, and total cancer incidence and mortality that demand further evaluation in well-controlled prevention trials.

Immunolocalization of apolipoprotein D, androgen receptor and prostate specific antigen in early stage prostate cancers

PURPOSE

To determine the cellular distribution and levels of immunohistochemical staining for apolipoprotein D (Apo-D), prostate specific antigen (PSA) and androgen receptor (AR) in early stage prostate cancers.

MATERIALS AND METHODS

Cellular distribution of Apo-D, PSA and AR in 30 stage A/B prostate cancers and in non-malignant glandular tissue contained in the same sections was detected immunohistochemically, and staining was evaluated by computerized video image analysis.

RESULTS

Staining for Apo-D (percentage positive cellular area) was significantly increased in tumor cells of early stage prostate cancers compared with non-malignant glandular tissue. PSA and AR were present at high levels in both early stage prostate tumors and non-malignant prostate.

CONCLUSIONS

Malignant transformation in the prostate is associated with increased cellular levels of Apo-D.

Arachidonic acid stimulates prostate cancer cell growth: critical role of 5-lipoxygenase

Arachidonic acid (5,8,11,14-eicosatetraenoic acid), a member of the omega-6 poly-unsaturated fatty acids, was found to be an effective stimulator of human prostate cancer cell growth in vitro at micromolar concentrations. Selective blockade of the different metabolic pathways of arachidonic acid (e.g. ibuprofen for cyclooxygenase, SKF-525A for cytochrome P-450, baicalein and BHPP for 12-lipoxygenase, AA861 and MK886 for 5-lipoxygenase, etc.) revealed that the growth stimulatory effect of arachidonic acid is inhibited by the 5-lipoxygenase specific inhibitors, AA861 and MK886, but not by others. Addition of the eicosatetraenoid products of 5-lipoxygenase (5-HETEs) showed stimulation of prostate cancer cell growth similar to that of arachidonic acid, whereas the leukotrienes were ineffective. Moreover, the 5-series of eicosatetraenoids could reverse the growth inhibitory effect of MK886. Finally, prostate cancer cells fed with arachidonic acid showed a dramatic increase in the production of 5-HETEs which is effectively blocked by MK886. These experimental observations suggest that arachidonic acid needs to be metabolized through the 5-lipoxygenase pathway to produce 5-HETE series of eicosatetraenoids for its growth stimulatory effects on human prostate cancer cells.

Molecular carcinogenesis of prostate cancer: potential clinical relevance and nursing implications

OBJECTIVES

Describe the current state of knowledge on the molecular basis of prostate carcinogenesis, potential clinical relevance of findings, and nursing implications.

DATA SOURCES

Published research articles, clinical summaries, proceedings of conferences, and personal communication with investigators.

CONCLUSION

The understanding of the molecular basis of prostate cancer lags behind that of other common solid tumors. Until recently, much research was reliant on cell line and animal data. Epidemiologic studies, a recently recognized hereditary variant, and cytogenetic analysis of human prostate tissue have provided insight into prostate carcinogenesis. Like other cancers, prostate cancer results from combined somatic and genetic mutations, gene activations, and interplay of genetic and environmental factors. To date, the most consistent changes are those of allelic loss events with the majority of tumors examined showing loss of alleles from at least one chromosomal arm. No specific genes have yet been identified. Clinical applications of these findings are still in developmental stages or early stages of clinical trials.

IMPLICATIONS FOR NURSING PRACTICE

An understanding of the molecular basis of cancer is requisite to the provision of up-to-date patient education and to understanding newly developing diagnostic, treatment, and preventive strategies.

Prospective evaluation plan for randomised trials of prostate cancer screening. The International Prostate Cancer Screening Trial Evaluation Group

To enable pooled analyses of continuing and planned randomised trials of prostate cancer screening, guidelines for minimal data required for such analyses were developed in the recent meeting of the International Prostate Screening Trial Evaluation Group (IPSTEG). The aim of the pooled analysis with data on individual level will be: (a) Estimation of the effect of screening on prostate cancer mortality with greater precision than individual studies (b) Assessment of optimal screening procedures and interval (c) Identification of subgroups within the populations that might receive most benefit from screening (d) Evaluation of the quality of life effects and cost effectiveness of screening. All studies included in the combined analysis share a common core protocol with minimum data requirements. The protocol allows, however, adaptation of the procedures to local circumstances within defined options. It should be noted that the process is continuing and the protocol is subject to evaluation and revision in the meetings of the IPSTEG on a regular basis.

Hormone therapy for prostate cancer: a topical perspective

Evolution of the roles proposed for antiandrogenic agents in prostatic disease has been rapid. Since the early suggestions by Labrie and his colleagues that the nonsteroidal antiandrogen flutamide could be used in combination with medical or surgical castration to provide superior care for patients with metastatic prostate cancer, and subsequent substantiation of the theory in a number of clinical trials, we have observed an increasing tendency to test the use of antiandrogens (alone or in combination with other interventions) earlier in the disease process. At least in part, this tendency is a consequence of our increased ability to detect prostate cancer earlier in the disease process. At the present time, flutamide is the only nonsteroidal antiandrogen available for the treatment of prostate cancer in general clinical practice in the United States. However, two other nonsteroidal antiandrogens currently await decisions on their efficacy and safety by the Food and Drug Administration: nilutamide and bicalutamide. Will either of these agents offer clinical benefits beyond those offered by flutamide? Will the safety, activity, and dosing profiles of the nonsteroidal antiandrogens allow us to use them to treat even earlier stages of prostate cancer and perhaps even prostatic intraepithelial dysplasia in patients at high risk of prostate cancer? What are the potential future roles for bicalutamide and other nonsteroidal antiandrogens in the management of prostatic disorders? This article will attempt to lay out the key questions that await definitive answers as we expand our understanding of the possible future roles for antiandrogens in the management of prostate cancer and related conditions.

Finasteride: a clinical review

Finasteride is the first of a new class of 5 alpha-reductase inhibitors which allows selective androgen deprivation affecting dihydrotestosterone (DHT) levels in target organs such as the prostate and scalp hair without effecting circulating levels of testosterone thus preserving the desired androgen mediated effects on muscle strength, bone density and sexual function. Finasteride has been demonstrated to produce significant effects in men with an enlarged prostate gland. The long-term data now emerging suggests that progression of benign prostatic hyperplasia (BPH) may be arrested providing additional long term benefits. Experimental uses in prostate cancer prevention and male pattern baldness offer new and exciting possibilities for this class of compounds.