Treatment Options in Androgen-Independent Prostate Cancer

CXCL13 in Cancer and Other Diseases: Biological Functions, Clinical Significance, and Therapeutic Opportunities

The development of cancer is a multistep and complex process involving interactions between tumor cells and the tumor microenvironment (TME). C-X-C chemokine ligand 13 (CXCL13) and its receptor, CXCR5, make crucial contributions to this process by triggering intracellular signaling cascades in malignant cells and modulating the sophisticated TME in an autocrine or paracrine fashion. The CXCL13/CXCR5 axis has a dominant role in B cell recruitment and tertiary lymphoid structure formation, which activate immune responses against some tumors. In most cancer types, the CXCL13/CXCR5 axis mediates pro-neoplastic immune reactions by recruiting suppressive immune cells into tumor tissues. Tobacco smoke and haze (smohaze) and the carcinogen benzo(a)pyrene induce the secretion of CXCL13 by lung epithelial cells, which contributes to environmental lung carcinogenesis. Interestingly, the knockout of CXCL13 inhibits benzo(a)pyrene-induced lung cancer and azoxymethane/dextran sodium sulfate-induced colorectal cancer in mice. Thus, a better understanding of the context-dependent functions of the CXCL13/CXCR5 axis in tumor tissue and the TME is required to design an efficient immune-based therapy. In this review, we summarize the molecular events and TME alterations caused by CXCL13/CXCR5 and briefly discuss the potentials of agents targeting this axis in different malignant tumors.

Repositioning "old" drugs for new causes: identifying new inhibitors of prostate cancer cell migration and invasion

The majority of prostate cancer (PCa) deaths occur due to the metastatic spread of tumor cells to distant organs. Currently, there is a lack of effective therapies once tumor cells have spread outside the prostate. It is therefore imperative to rapidly develop therapeutics to inhibit the metastatic spread of tumor cells. Gain of cell motility and invasive properties is the first step of metastasis and by inhibiting motility one can potentially inhibit metastasis. Using the drug repositioning strategy, we developed a cell-based multi-parameter primary screening assay to identify drugs that inhibit the migratory and invasive properties of metastatic PC-3 PCa cells. Following the completion of the primary screening assay, 33 drugs were identified from an FDA approved drug library that either inhibited migration or were cytotoxic to the PC-3 cells. Based on the data obtained from the subsequent validation studies, mitoxantrone hydrochloride, simvastatin, fluvastatin and vandetanib were identified as strong candidates that can inhibit both the migration and invasion of PC-3 cells without significantly affecting cell viability. By employing the drug repositioning strategy instead of a de novo drug discovery and development strategy, the identified drug candidates have the potential to be rapidly translated into the clinic for the management of men with aggressive forms of PCa.

Androgen receptor degradation by the E3 ligase CHIP modulates mitotic arrest in prostate cancer cells

The androgen receptor (AR) has a vital role in the onset and progression of prostate cancer by promoting G1-S progression, possibly by functioning as a licensing factor for DNA replication. We here report that low dose 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, induces mitotic arrest in prostate cancer cells involving activation of the E3 ligase CHIP (C-terminus of Hsp70-interacting protein) and degradation of the AR. Depletion of the AR by small interfering RNA (siRNA) eliminates 2-ME-induced arrest and introducing AR into PC3-M cells confers 2-ME-induced mitotic arrest. Knockdown of CHIP or MDM2 (mouse homolog of double minute 2 protein) individually or in combination reduced AR degradation and abrogated M phase arrest induced by 2-ME. Our data link AR degradation via ubiquitination to mitotic arrest. Targeting the AR by activating E3 ligases such as CHIP represents a novel strategy for the treatment of prostate cancer.

Bevacizumab plus 5-fluorouracil induce growth suppression in the CWR-22 and CWR-22R prostate cancer xenografts

Prostate cancer is the most common malignancy in men. Although patients with metastatic prostate cancer can benefit from androgen ablation, most of them will die of prostate cancer progression to an androgen-refractory state. In the present study, the effects of docetaxel, bevacizumab, 5-fluorouracil (5-FU), bevacizumab plus docetaxel, and bevacizumab plus 5-FU on the growth of human CWR-22 (androgen-dependent) and CWR-22R (androgen-independent) prostate carcinoma xenografts were investigated. We report that i.p. administration of 10 mg/kg docetaxel at 1-week interval, 5 mg/kg/ bevacizumab once every 2 weeks, or 12.5 mg/kg 5-FU, bevacizumab/docetaxel, or bevacizumab/5-FU weekly to severe combined immunodeficient mice bearing prostate cancer xenografts (12 mice per treatment group) for 21 days resulted in 22.5 +/- 8%, 23 +/- 7%, 31 +/- 8%, 22 +/- 6%, and 81 +/- 5% growth inhibition, respectively. Greatest growth suppression was observed in bevacizumab/5-FU treatment. Bevacizumab/5-FU-induced growth suppression was associated with reduction in microvessel density, inhibition of cell proliferation; up-regulation of phosphatase and tensin homologue, p21(Cip1/Waf1), p16(INK4a), and p27(Kip1); hypophosphorylation of retinoblastoma protein; and inhibition of Akt/mammalian target of rapamycin pathway. Our data indicate that bevacizumab/5-FU effectively inhibits angiogenesis and cell cycle progression and suggest that bevacizumab/5-FU may represent an alternative treatment for patients with prostate cancer.

Androgen receptor levels in prostate cancer epithelial and peritumoral stromal cells identify non-organ confined disease

BACKGROUND

Although up to 30% of men who undergo radical prostatectomy for clinically organ-confined prostate cancer will relapse with disseminated disease, currently it is not possible to predict these patients.

METHODS

Androgen receptor (AR) immunoreactivity in stromal and epithelial compartments of tumor foci was evaluated by video image analysis in 53 radical prostatectomy specimens. Kaplan-Meier and Cox Regression analyses were used to determine whether AR immunostaining was related to rate and risk of relapse, respectively.

RESULTS

Ninety-eight percent (52/53) of the tumors contained AR positive malignant epithelial cells. Kaplan-Meier analysis indicated that patients with high AR levels (>64% AR positive nuclear area) in the malignant epithelial cells or low AR levels (<or=45% AR positive nuclear area) in the peritumoral stroma cells, were more likely to relapse earlier following radical prostatectomy. The shortest time to relapse and the highest relapse rate was for patients with both high AR in the malignant epithelial cells and low AR in the peritumoral stromal cells.

CONCLUSIONS

These findings suggest that AR is an important determinant of disease relapse in early stage prostate cancer, and that altered AR levels in the malignant epithelial cells or in the peritumoral stroma is indicative of non-organ confined prostate cancer.

2-Chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) inhibits prostate carcinoma cell growth via p53-dependent and p53-independent pathways

BACKGROUND

Prostate carcinoma is the most commonly occurring malignancy in men. Although 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU), an analog of the chloroethylnitrosoureas, has been used in the treatment of advanced solid tumors, the molecular mechanisms underlying the antineoplastic activity of this agent are not well understood. In the current study, the authors sought to investigate the effects of SarCNU on prostate carcinoma cell growth in vivo and in vitro.

METHODS

Male SCID mice underwent subcutaneous implantation (on both flanks) of human CWR-22 and CWR-22R prostate carcinoma xenografts. Mice were treated with either vehicle or 60 or 80 mg SarCNU per kg body weight for 5 days, with tumor growth being assessed every 3 days. Animals were sacrificed 21 days after the final injection, and tumors subsequently were collected, weighed, and processed for analysis. Immunohistochemical analyses were performed to obtain data on the localization of p53 and p21Cip1/Waf1. Cell counting, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) assays, cell cycle analyses, Western blotting, and in vitro kinase assays were performed to determine the effects of SarCNU on growth, apoptosis, cell cycle arrest, cell cycle-regulated protein levels, and Cdc-2 activity, respectively.

RESULTS

SarCNU reduced tumor incidence and inhibited the growth of CWR-22 and CWR-22R xenografts. In addition, treatment with this agent led to increases in p21Cip1/Waf1 levels and p53 phosphorylation at Ser15. In vitro administration of SarCNU to cells with wild-type p53 (LNCaP and primary CWR-22 cells) and cells with mutant p53 (PC-3 cells) resulted in G2/M arrest and the reduction of cellular Cdc-2 activity. Up-regulation of p53 levels, p53 phosphorylation at Ser15, and p21Cip1/Waf1 levels in primary CWR-22 and LNCaP cells, as well as up-regulation of Cdc-2 phosphorylation at Tyr15 in PC-3 cells, was detected.

CONCLUSIONS

SarCNU induced G2/M arrest in prostate carcinoma cells via p53-dependent up-regulation of p21Cip1/Waf1 and p53-independent phosphorylation of Cdc-2 at Tyr15. These findings suggest a potential role for SarCNU in the treatment of prostate malignancies.

Lysophosphatidic acid promotes survival of androgen-insensitive prostate cancer PC3 cells via activation of NF-kappaB

BACKGROUND

Dysregulated cell survival contributes to the poor efficacy of many chemotherapeutic regimens for patients with advanced prostate cancer. In this study we examined ability of the lipid growth factor lysophosphatidic acid (LPA), a G protein-coupled receptor (GPCR) ligand, to promote prostate cell survival.

METHODS

PC3 cells were used as a model to study mechanisms involved in survival of androgen-insensitive prostate cancer cells. Cell survival was measured by FACS analysis of cell cycle parameters after propidium iodide or annexin V and 7-AAD immunostaining. Activation state of nuclear facor-kappaB (NF-kappaB) was determined biochemically by nuclear translocation and transcriptional activation. Human tissue was analyzed for nuclear expression of NF-kappaB by immunohistochemistry.

RESULTS

Molecular dissection of the LPA-regulated PC3 cell survival revealed the sequential phosphorylation of Akt, IkappaB, and transcriptional activation of NF-kappaB. Both Akt and NF-kappaB were required to escape serum deprivation-induced cell death since their inhibition abrogated the LPA-mediated PC3 cell survival. Data from archival human tissue show that NF-kappaB is constitutively activated in prostate cancers, but not in benign prostate tissues.

CONCLUSIONS

Targeted disruption of the LPA receptor-Akt-NF-kappaB signaling axis may be effective for the treatment of androgen-insensitive prostate cancer.

Par-4 transcriptionally regulates Bcl-2 through a WT1-binding site on the bcl-2 promoter

Elevated expression levels of the bcl-2 proto-oncogene have been extensively correlated with the appearance of androgen independence in prostate cancer. Although bcl-2 was first cloned as the t(14:18) translocation breakpoint from human follicular B cell lymphoma, the mechanism of overexpression of bcl-2 is largely undefined for advanced prostate cancer because there are no gross alterations in the gene structure. We investigated the role of the product of the prostate apoptosis response gene-4 (Par-4) and the product of the Wilms' tumor 1 gene (WT1) in the regulation of Bcl-2 expression in prostate cancer cell lines. We observed growth arrest and apoptosis, upon decreasing Bcl-2 protein and transcript in the high Bcl-2-expressing, androgen-independent prostate cancer cell line, by all-trans-retinoic acid treatment (ATRA), but this did not occur in the androgen-dependent cell line expressing low levels of Bcl-2. The decrease in the Bcl-2 protein and transcript following all-trans-retinoic acid treatment was accompanied by changes in localization of Par-4 and an induction in the expression of WT1 protein. In stable clones expressing ectopic Par-4 and in ATRA-treated cells, we observed decreased Bcl-2 protein and transcript. This was accompanied by an induction in WT1 expression. The involvement of WT1 in the Par-4-mediated down-modulation of Bcl-2 was further defined by blocking endogenous WT1 expression, which resulted in an increase in Bcl-2 expression. Finally, we detected Par-4 and WT1 proteins binding to a previously identified WT1-binding site on the bcl-2 promoter both in vitro and in vivo leading to a decrease in transcription from the bcl-2 promoter. We conclude that Par-4 regulates Bcl-2 through a WT1-binding site on the bcl-2 promoter. These data also identify Par-4 nuclear localization as a novel mechanism for ATRA-mediated bcl-2 regulation.

HER-2/neu is overexpressed infrequently in patients with prostate carcinoma. Results from the California Cancer Consortium Screening Trial

BACKGROUND

The overexpression of HER-2/neu is found in 20-30% of patients with breast carcinoma and is an adverse prognostic factor. HER-2 overexpression also has been reported in up to 60% of patients with hormone-refractory prostate carcinoma (HRPC) and was correlated with shortened survival. Trastuzumab (Herceptin) is a humanized monoclonal antibody that binds to the HER-2 receptor and has antitumor activity in patients with HER-2-overexpressing breast carcinoma. The authors report the results of HER-2 screening from a Phase II trial of chemotherapy with trastuzumab and docetaxel in patients with HER-2-overexpressing prostate carcinoma.

METHODS

Archival paraffin embedded tumor tissue was obtained from potentially eligible patients and was screened for HER-2 expression by immunohistochemistry (IHC) using a specialized test kit. Shed HER-2 antigen in serum also was determined using an enzyme-linked immunosorbent assay (ELISA). HER-2 gene amplification was assessed by fluorescent in situ hybridization (FISH). Patients with IHC scores of 2+ or 3+ were considered to have HER-2 overexpression and were eligible for the trial. To date, 62 patients with HRPC have been screened.

RESULTS

The median patient age was 72 years, and Gleason scores were < 5 in 1 patients, 5-7 in 24 patients, > 7 in 23 patients, and not specified in 14 patients. IHC HER-2 expression was 0 in 28 patients, 1+ in 14 patients, 2+ in 4 patients, and 3+ in 1 patients. Fifteen patients had either suboptimal tissue (13 patients) for interpretation or had pending results (2 patients). Therefore, 8% of all patients screened (5 of 62 patients) had HER-2 overexpression by IHC. Quantitative ELISA for shed HER-2 was available in 32 patients; this level was elevated (> 15 ng/mL) in only 2 patients, and neither had HER-2 expression by IHC. Of the 5 patients with 2+ or 3+ HER-2 expression by IHC, none had elevated shed HER-2 antigen levels by ELISA. FISH for HER-2 amplification was performed on 12 specimens; 5 of these specimens were uninterpretable due to specimen artifact, and none of the remaining 7 specimens had HER-2 amplification, defined as a ratio > 1. Patient age and Gleason score were not correlated with HER-2 status.

CONCLUSIONS

Unlike breast carcinoma and contrary to prior reports, HER-2 overexpression by IHC in archival prostate tissue from patients who eventually developed hormone-refractory disease was infrequent. There did not appear to be any correlation between HER-2 overexpression by IHC and shed HER-2 antigen levels in serum by ELISA in this tumor type. Whether trastuzumab possesses single-agent activity or modulates chemotherapy response in tumor types other than breast carcinoma remains to be determined.

Prostate cancer and the androgen receptor: strategies for the development of novel therapeutics

The early demonstrations that prostate cancer was hormone-sensitive initiated a therapeutic strategy of hormone ablation that is still in use today. Although chemical or surgical castration reduces androgen stimulation of the androgen receptor (AR) and produces tumor regression, little survival benefit is achieved. Patients with metastatic cancer eventually relapse as their tumors progress to hormone independence. The AR is a member of the steroid receptor family; however, it manifests many unique features including: N-terminal, C-terminal interactions and antiparallel dimerization, unique N-terminal domains for co-factor recruitment, AR-specific co-activators and upstream promoter/enhancer response elements that amplify AR-mediated responses. The AR is regulated by phosphorylation and cross-talk with several signaling pathways, including MAP kinases, PKA and PKC. Non-genomic effects of AR to regulate transcription factors elk-1 and -2 have also been demonstrated. These unique features suggest mechanisms by which novel therapeutics might target and influence AR-mediated actions. Progress in this direction has been realized with the recent synthesis of non-steroidal androgen agonists that may have tissue-selective effects.

Chemotherapy in advanced androgen-independent prostate cancer 1990-1999: a decade of progress?

BACKGROUND AND PURPOSE

A great number of clinical research studies have been reported in the field of chemotherapy for advanced androgen-independent prostate cancer during the last ten years. The aims of the present review were to assess their impact on management of the disease and on survival of patients.

METHODS

The review of full published reports was facilited by the use of a MEDLINE computer search.

RESULTS

Clinical research studies have focused on defining guidelines for eligibility criteria and accurate endpoints for patients to be enrolled onto clinical trials and developing new agents or combination of drugs including estramustine phosphate. Any combination of current chemotherapy has no impact on overall survival of patients. Among drugs in development, only the promising activity observed with docetaxel deserves randomized trials to assess its impact on survival. The major innovative advance of the 90s is the demonstration of the impact of chemotherapy (mitoxantrone + prednisone) on quality of life as compared to prednisone alone. A greater and longer-lasting improvement in quality of life along with a concomitant decrease in costs was observed.

CONCLUSIONS

At the present time, chemotherapy should be considered as a palliative treatment in patients with symptomatic androgen-independent disease. The enrollment of patients into clinical trials dealing with quality of life as primary endpoint is strongly solicited. A standard methodology should be used in phase II trials with a primary goal of selection of agents which should progress to randomized trials using survival as an endpoint. Hopefully new specific strategies targeted to reverse the molecular changes that underlie prostate tumorigenesis should rapidly impact the multimodality management of AIPC in the third millenium.

The novel heterodinucleoside dimer 5-FdU-NOAC is a potent cytotoxic drug and a p53-independent inducer of apoptosis in the androgen-independent human prostate cancer cell lines PC-3 and DU-145

BACKGROUND

We analyzed the cytotoxic properties of the new heterodinucleoside phosphate dimer 5-FdU-NOAC, which is composed of the cytotoxic drugs 5-FdU and N(4)-octadecyl-1-beta-D-arabinofuranosylcytosine (NOAC) against human prostate tumor cells.

METHODS

5-FdU-NOAC effects on cell proliferation, cell cycle distribution, thymidylate synthase activity, and apoptosis were investigated in vitro in the two human prostate carcinoma cell lines DU-145 and PC-3 and compared to cells treated with the corresponding single drugs 5-FdU and NOAC.

RESULTS

Treatment of the cells with 5-FdU-NOAC resulted in IC(50) values of 3.9-5 microM and in a complete inhibition of cell proliferation at 200 microM after 96 hr compared to 5-FdU, where 10% of the cells remained resistant. Flow cytometric analysis revealed cell cycle perturbations in S-phase only in the DU-145 cells. 5-FdU-NOAC caused 50% inhibition of thymidylate synthase after 90 min at 0.6 microM in both cell lines. Apoptotic cell fractions in DU-145 (66%) and in PC-3 (34%) cells were found after treatment with 5-FdU-NOAC for 96 hr. DNA fragmentation further confirmed the induction of apoptosis.

CONCLUSIONS

5-FdU-NOAC inhibits thymidylate synthase and cell cycle progression causing proliferation arrest and apoptosis in DU-145 and PC-3 cells, suggesting a potential role of 5-FdU-NOAC for the treatment of prostate cancer.