Emergence of metastatic hormone-refractory disease in prostate cancer after anti-androgen therapy

The anti-androgens used in prostate cancer therapy have been designed to interfere with the normal androgen receptor (AR)-mediated processes that ensure prostate cell survival, triggering tumor cells to undergo programmed cell death. While anti-androgens were originally designed to treat advanced disease, they have recently been used to debulk organ-confined prostate tumors, to improve positive margins prior to surgery, and for chemoprevention in patients at high risk for prostate cancer. However, tumors treated with anti-androgens frequently become hormone refractory and acquire a more aggressive phenotype. Progression toward metastatic hormone-refractory disease has often been regarded as the outgrowth of a small number of hormone-independent cells that emerge from a hormone-dependent tumor during anti-androgen treatment by natural selection. While a number of selective advantages have recently been identified, there is also considerable evidence suggesting that the progression toward metastatic hormone-refractory disease is an dynamic process which involves abrogation of programmed cell death as a result of the attenuation of DNA fragmentation and maintenance of mitochondrial membrane potential in tumor cells; the upregulation of stromal-mediated growth factor signaling pathways; and the upregulation of extracellular matrix (ECM) protease expression.     

Treatment options for hormone-refractory prostate cancer

Hormone-refractory prostate cancer is a disease that includes a variety of patients and represents a treatment dilemma for the practicing physician. Because of the diversity of this group, management strategies must be targeted to the clinical situations of the individual patients and their wishes. This article outlines a logical progression of treatment choices that currently exist in this rapidly evolving field, and the landmark chemotherapy trials involving docetaxel (SWOG 9916 and TAX 327) are reviewed. Although significant progress has been made in understanding and treating hormone-refractory prostate cancer, current treatments do not yet provide a cure, and important clinical trials continue to recruit patients.     

The role of the urologist in treating patients with hormone-refractory prostate cancer

Objectives: To ascertain what percentage of urologists' oncology practice is dedicated to the care of prostate cancer patients and to determine urologists' attitudes towards the treatment of patients with metastatic and hormone-refractory prostate cancer (HRPC). An additional objective is to determine urologists' interest in administering various types of chemotherapy in HRPC patients.Materials and Methods: The American Urological Association (AUA) directory of practicing urologists was obtained, and 3000 randomly selected members of the AUA, as well as the complete list of 168 Society of Urologic Oncology (SUO) members, were chosen for the mailing of a 16-item questionnaire. The urologists were asked about how many of their patients have prostate cancer, how many have metastatic disease, and how many have HRPC and are currently receiving intravenous (IV) chemotherapy. In addition, the urologists were queried regarding their level of interest in learning about chemotherapy options as well as learning how to administer chemotherapy.Results: A total of 654 survey questionnaires were completed and returned for tabulation, resulting in a 21% effective response rate. Sixty-four percent of the responding urologists' cancer patients had prostate cancer, 21% had metastatic disease, and 19% had HRPC; only 4% of the urologists currently administer IV chemotherapy themselves. When asked to describe their interest in learning how to deliver and be reimbursed for IV chemotherapy, 26% expressed an extremely low level of interest, 23% a low level of interest, 31% a high level of interest, and 17% an extremely high level of interest. The results of other questions are presented and correlated with the number of years the urologists have been in practice and other demographic data.Conclusions: The management of prostate cancer comprises a major portion of urologists' practices. Almost one half (48%) of the urologists in this survey were interested in administering and being reimbursed for IV chemotherapy. Several chemotherapy regimens have been shown to improve quality of life in patients with HRPC, yet only about 30% of these patients were referred for chemotherapy. If more urologists were able to deliver these drugs, then the number of patients referred for chemotherapy would likely increase, as would accrual to important clinical trials in HRPC. The results of this survey suggest that methods to implement the training and reimbursement of urologists in the use of chemotherapy regimens should be investigated.     

Orchidectomy versus Zoladex plus Eulexin in patients with metastatic prostate cancer (EORTC 30853)

A total of 327 patients with metastatic prostate cancer have been randomized to either orchidectomy or treatment with goserelin (Zoladez^®) 3.6 mg depot preparation combined with flutamide (Eulexin^®) 250 mg t.i.d. in a phase III study (EORTC 30853). A small but statistically significant difference in time to subjective and objective progression of disease was found in favour of the combination treatment. However, time from objective progression to death was longer in the group initially allocated to orchidectomy. Thus no difference was found in overall survival between the two treatment groups. The clinical significance of these differences requires further follow up and analysis.     

Docetaxel for the treatment of hormone-refractory prostate cancer

Chemotherapy has historically proven toxic and ineffective for the treatment of metastatic hormone-refractory prostate cancer (HRPC), a disease with substantial morbidity and mortality. Progress has been made in symptom relief, and the combination of mitoxantrone and prednisone is considered the palliative standard of care. The effects of a variety of chemotherapeutic agents, both alone and in combination, on prostate-specific antigen decline rates, measurable disease response, and survival have been examined in numerous phase I and II trials. Results suggest that combining vinblastine or paclitaxel with estramustine confers a survival advantage over either agent alone. In addition, docetaxel-based therapy has been found to be effective and well tolerated, and phase III trials will soon determine whether docetaxel-based therapy should replace mitoxantrone-based therapy as the standard of care for HRPC.     

Loss of mir-146a function in hormone-refractory prostate cancer

The pattern of microRNA (miRNA) expression is associated with the degree of tumor cell differentiation in human prostate cancer. MiRNAs bind complementarily to either oncogenes or tumor suppressor genes, which are consequently silenced, resulting in alterations of tumorigenecity. We have detected eight down-regulated and three up-regulated known miRNAs in androgen-independent human prostate cancer cells compared to those in androgen-dependent cells, using miRNA microarray analyses. These identified miRNAs showed the same expression patterns in hormone-refractory prostate carcinomas (HRPC) compared to androgen-sensitive noncancerous prostate epithelium as determined by fluorescent in situ hybridization assays in human prostate cancer tissue arrays. One of the eight down-regulated miRNAs, mir-146a, was selected and constitutively expressed to examine its effects on suppression of prostate cancer transformation from androgen-dependent to -independent cells as determined by in vitro tumorigenecity assays. Transfection of mir-146a, which perpetually express the miRNA, suppressed >82% of the expression of the targeted protein-coding gene, ROCK1, in androgen-independent PC3 cells, consequently markedly reducing cell proliferation, invasion, and metastasis to human bone marrow endothelial cell monolayers. Given that ROCK1 is one of the key kinases for the activation of hyaluronan (HA)-mediated HRPC transformation in vivo and in PC3 cells, mir-146a may function as a tumor-suppressor gene in modulating HA/ROCK1-mediated tumorigenecity in androgen-dependent prostate cancer.     

The treatment of hormone-refractory prostate cancer: docetaxel and beyond

Two randomized clinical trials demonstrated a survival benefit of 20% to 24% with docetaxel-based therapy when compared with survival with mitoxantrone and prednisone after failure of androgen ablation therapy. These studies supported the approval of docetaxel-based therapy for the treatment of metastatic hormone-refractory prostate cancer by the US Food and Drug Administration in May 2005. Clinical trials in hormone-refractory prostate cancer are now focused on building on the survival improvement seen with docetaxel-based therapy. This article presents a summary of some of the more promising treatments and regimens for advanced prostate cancer.     

A multidisciplinary approach to the management of hormone-refractory prostate cancer

The patient with hormone-refractory prostate cancer (HRPC) presents unique management challenges for both the urologist and the medical oncologist. Because of a lack of effective treatment options, the management of patients with HRPC has historically been palliative. Over the past 10 years, the advent of relatively efficacious chemotherapeutic regimens, particularly taxane-based chemotherapy, has resulted in a desire to treat patients with HRPC more aggressively. The complex needs of these patients have made a multidisciplinary approach, inclusive of specialists with expertise in disease processes directly affecting the patient, the optimal means of treating HRPC. An understanding of the natural history and complications of HRPC, combined with a systemic evaluative process, can allow the multidisciplinary team to comprehensively address the needs of the individual patient with HRPC.     

Mitotic catastrophe and apoptosis induced by docetaxel in hormone-refractory prostate cancer cells

Studies performed in different experimental and clinical settings have shown that Docetaxel (Doc) is effective in a wide range of tumors and that it exerts its activity through multiple mechanisms of action. However, the sequence of events induced by Doc which leads to cell death is still not fully understood. Moreover, it is not completely clear how Doc induces mitotic catastrophe and whether this process is an end event or followed by apoptosis or necrosis. We investigated the mechanisms by which Doc triggers cell death in hormone-refractory prostate cancer cells by analyzing cell cycle perturbations, apoptosis-related marker expression, and morphologic cell alterations. Doc induced a transient increase in G2/M phase followed by the appearance of G0/1 hypo- and hyperdiploid cells and increased p21 expression. Time- and concentration-dependent apoptosis was induced in up to 70% of cells, in concomitance with Bcl-2 phosphorylation, which was followed by caspase-2 and -3 activation. In conclusion, Doc would seem to trigger apoptosis in hormone-refractory prostate cancer cells via mitotic catastrophe through two forms of mitotic exit, in concomitance with increased p21 expression and caspase-2 activation.     

Induction of Tc2 cells with specificity for prostate-specific antigen from patients with hormone-refractory prostate cancer

Prostate-specific antigen (PSA) is a potentially useful antigen for targeted T-cell immunotherapy of prostate cancer (CaP). Our laboratory has identified a synthetic nonamer peptide (PSA 146-154) homologue of PSA, which binds to the prevalent human leukocyte antigen, HLA-A2, and elicits specific cytotoxic T-lymphocyte (CTL) responses from normal individuals of the HLA-A2 phenotype. In the present study, we report on the induction of CTL from peripheral blood mononuclear cells (PBMC) of patients with hormone-refractory CaP, which exhibit the same specificity. T-cell lines were established from two patients by stimulation of PBMC with PSA 146-154 peptide in vitro. The T-cell lines exhibited specific cytolytic activity against T2 cells pulsed with PSA 146-154 peptide, but not a control HLA-A2 binding peptide (HIV-RT 476-484) via chromium release assay (CRA). The T-cell lines also showed PSA 146-154 peptide-specific IL-4 responses, but no detectable interferon-gamma (IFN-gamma) responses via enzyme-linked immuno-spot assays. Magnetic immuno-selection studies of one of the T-cell lines demonstrated that both cytolytic and interleukin-4 (IL-4) responses were mediated by CD8(+), but not by CD4(+) T cells. This Tc2 line was further characterized for the ability to recognize endogenously processed PSA epitopes. The line specifically secreted IL-4 in response to HLA-A2(+) target cells transfected to express PSA and specifically lysed the PSA(+) target cells, but not control transfected cells. The results indicate that the PSA 146-154 peptide emulates a naturally processed and presented peptide epitope of PSA that is within the T-cell repertoire of HLA-A2(+)patients with CaP.     

MicroRNAs associated with metastatic prostate cancer

Objective

Metastasis is the most common cause of death of prostate cancer patients. Identification of specific metastasis biomarkers and novel therapeutic targets is considered essential for improved prognosis and management of the disease. MicroRNAs (miRNAs) form a class of non-coding small RNA molecules considered to be key regulators of gene expression. Their dysregulation has been shown to play a role in cancer onset, progression and metastasis, and miRNAs represent a promising new class of cancer biomarkers. The objective of this study was to identify down- and up-regulated miRNAs in prostate cancer that could provide potential biomarkers and/or therapeutic targets for prostate cancer metastasis.

Methods

Next generation sequencing technology was applied to identify differentially expressed miRNAs in a transplantable metastatic versus a non-metastatic prostate cancer xenograft line, both derived from one patient''s primary cancer. The xenografts were developed via subrenal capsule grafting of cancer tissue into NOD/SCID mice, a methodology that tends to preserve properties of the original cancers (e.g., tumor heterogeneity, genetic profiles).

Results

Differentially expressed known miRNAs, isomiRs and 36 novel miRNAs were identified. A number of these miRNAs (21/104) have previously been reported to show similar down- or up-regulation in prostate cancers relative to normal prostate tissue, and some of them (e.g., miR-16, miR-34a, miR-126*, miR-145, miR-205) have been linked to prostate cancer metastasis, supporting the validity of the analytical approach.

Conclusions

The use of metastatic and non-metastatic prostate cancer subrenal capsule xenografts derived from one patient''s cancer makes it likely that the differentially expressed miRNAs identified in this study include potential biomarkers and/or therapeutic targets for human prostate cancer metastasis.     

Current standard and investigational approaches to the management of hormone-refractory prostate cancer

Prostate cancer is a common cause of death in men and remains incurable in the metastatic setting. In 2004, 2 landmark trials using docetaxel-based chemotherapy, TAX 327 and SWOG 99-16, showed a survival benefit for the first time in metastatic, hormone-refractory prostate cancer. Current research suggests that several distinct mechanisms of androgen-refractory disease may converge in patients with disease progression on androgen deprivation therapy. These findings have identified several potential targets for therapeutic intervention. Current standard and investigational treatment options for this disease are discussed, including chemotherapy and rapidly evolving therapies in phase II/III trials involving antiangiogenic therapies, signal transduction inhibitors, immunomodulatory agents, and nuclear receptor targets. In light of a growing array of treatment options and an increasingly chronic natural history, this review supports a multidisciplinary care approach to these patients, including medical oncologists, urologists, and radiation oncologists, to optimize survival and quality of life.     

Changes in extracellular matrix (ECM) and ECM-associated proteins in the metastatic progression of prostate cancer

Prostate cancer (PCa) is no exception to the multi-step process of metastasis. As PCa progresses, changes occur within the microenvironments of both the malignant cells and their targeted site of metastasis, enabling the necessary responses that result in successful translocation. The majority of patients with progressing prostate cancers develop skeletal metastases. Despite advancing efforts in early detection and management, there remains no effective, long-term cure for metastatic PCa. Therefore, the elucidation of the mechanism of PCa metastasis and preferential establishment of lesions in bone is an intensive area of investigation that promises to generate new targets for therapeutic intervention. This review will survey what is currently know concerning PCa interaction with the extracellular matrix (ECM) and the roles of factors within the tumor and ECM microenvironments that contribute to metastasis. These will be discussed within the context of changes in expression and functional heterodimerization patterns of integrins, changes in ECM expression and reorganization by proteases facilitating invasion. In this context we also provide a brief summary of how growth factors (GFs), cytokines and regulatory signaling pathways favor PCa metastasis to bone.     

Treating metastatic prostate cancer with microRNA-145

Prostate cancer (PCa) is an incurable disease at the metastatic stage. Although there are different options for treatment, the results are limited. MicroRNAs (miRNAs) are a group of small, noncoding, regulatory RNAs with important roles in regulating gene expression. miR-145 is reported to be a key tumor suppressor miRNA (tsmiR) that controls important oncogenes, such as MYC and RAS. In this study, in vitro studies were performed to show the control of MYC and RAS by miR-145. Flow cytometry was used to analyze cell proliferation and apoptosis. The efficacy of miR-145 in treating metastatic PCa was tested in nude mice using a model of bone metastasis promoted by intraventricular injection of PC-3MLuc-C6 cells. Tumor growth was evaluated by an in vivo bioluminescence system. After the full establishment of metastases on day 21, six animals were treated with three intravenous doses of miR-145 (on days 21, 24 and 27), and six were injected with scramble miRNA as controls. Compared to the controls, tumor growth was significantly reduced in animals receiving miR-145, most importantly on day 7 after the third and last dose of miRNA. After discontinuing the treatment, tumor growth resumed, becoming similar to the group of non-treated animals. A decrease in MYC and RAS expression was observed in all cell lines after treatment with miR-145, although statistical significance was achieved only in experiments with LNCaP and PC3 cell lines, with a decrease in 56% (p?=?0.012) and 31% (p?=?0.013) of RAS expression, respectively. Our results suggest that miR-145 is a potential molecule to be tested for treatment of metastatic, castration-resistant PCa.