Advances in prostate cancer

Expression of multidrug resistance proteins in prostate cancer is related with cell sensitivity to chemotherapeutic drugs

BACKGROUND

Multidrug resistance (MDR) proteins have been associated with the lack of chemotherapy response. Expression of these proteins has been described in the prostate, but there is no information about their role in the chemotherapy response of prostate cancer (PC). We studied the gene and protein expression of MDR proteins in primary cell cultures from PC tumors and PC cell lines, their relationship with chemotherapy and their effects on cell survival.

METHODS

Primary cell cultures from PC were obtained from samples provided by our Institutional Hospital. Cell lines LNCaP, PC3, and DU145 were also examined. Cells were treated during 72 hr with several chemotherapeutic drugs. Protein and mRNA expressions of P-glycoprotein (P-Gp), MRP1 and LRP, before and after drug treatment, were evaluated by RT-PCR and Western blot analyses. The effect on cell survival was evaluated by proliferation assays (MTT), and cell cycle and apoptosis by flow cytometry.

RESULTS

Primary PC cultures exhibited higher MDR protein expression and lower drug sensitivity than cell lines, in which P-Gp was not detected. Docetaxel and mitoxantrone displayed the highest apoptotic effect. Exposure to chemotherapeutic drugs increased apoptosis, cell cycle arrest, and MDR expression. Long-term treatment with doxorubicin diminished apoptosis elicited by all drugs examined in this study, suggesting a cross-resistance phenomenon.

CONCLUSIONS

Low chemotherapy response observed in PC primary cultures could be explained, in part, by the high levels of MDR proteins (intrinsic MDR phenotype), and also, by their over-expression induced after long-term exposure to drugs (acquired MDR phenotype), which increase treatment resistance. Prostate 69: 1448-1459, 2009. (c) 2009 Wiley-Liss, Inc.

Evaluation of MENT on primary cell cultures from benign prostatic hyperplasia and prostate carcinoma

7-alpha-Methyl-19-Nortestosterone (MENT) is a synthetic androgen more potent than testosterone (T) and cannot be reduced at 5-alpha position. No important effects of MENT on prostate growth have been reported. However, little is known about the effect of MENT on benign prostatic hyperplasia (BPH) or prostate carcinoma (CaP). We evaluate the effect of MENT, T and dihydrotestosterone (DHT) on secretion, proliferation and gene expression of primary cell cultures from human BPH and CaP. Moreover, the effect of these androgens was examined in the presence of finasteride to determine the influence of the 5-alpha reductase (5-AR) activity on the androgenic potency. BPH and CaP primary cultures were treated with 0, 1, 10 and 100 nM of T, MENT or DHT during 24 and 48 h. Prostate-specific antigen (PSA) was measured by micro particles immunoassay and proliferation rate by spectrophotometric assay (MTT) and by the immunochemical detection of the proliferation marker Ki-67. Gene expression of FGF8b (androgen sensitive gene) was evaluated by semi-quantitative RT-PCR. Results showed that MENT treatments increased PSA secretion and proliferation rate with a potency ranged between T and DHT. Similar effects of MENT were observed in both BPH and CaP cultures. The studies with finasteride showed that in BPH and CaP cells, the conversion of T into DHT significantly contributes to its effect on the proliferation and PSA secretion, and corroborated the resistance of MENT to the 5-AR. The effect of MENT on the gene expression of FGF8b in CaP cells was similar to T and lower than DHT. It is concluded that MENT increases proliferative and secretory activities and gene expression on pathological prostate cells although in less extent than the active metabolite DHT. Furthermore, the fall of endogenous concentration of T during MENT treatment anticipates that this androgen will be of low impact for the prostate.

Pre-clinical evaluation of 1-nitroacridine derived chemotherapeutic agent that has preferential cytotoxic activity towards prostate cancer

Chemotherapy in prostate cancer (CaP) even as an adjunct has not been a success. In this communication, we report the pre-clinical efficacy of a nitroacridine derivative, C-1748 (9[2'-hydroxyethylamino]-4-methyl-1-nitroacridine) in CaP cell culture and human xenograft animal models. C-1748, a DNA intercalating agent has been derived from its precursor C-857 that was a potent anti-cancer drug, but failed clinical development due to "high" systemic toxicities. Chemical modifications such as the introduction of a "methyl" group imparted novel properties, the most interesting of which is the difference in the IC(50) values between LnCaP (22.5 nM), a CaP cell line and HL-60, a leukemia cell line (>100 nM). Using gammaH2AX as an intervention marker of DNA double strand breaks, we concluded that C-1748 is more efficacious in CaP cells than in HL-60 cells. In hormone dependent cells, the androgen receptor (AR) was identified as an additional target of C-1748. In xenograft studies, administration of C-1748 intra-peritoneally inhibited tumor growth by 80-90% with minimal toxicity. These studies identify C-1748 as a novel acridine drug that has a high therapeutic index and low cytotoxicity on myelocytic cells with potential for clinical development.

Immunology and immunotherapy approaches for prostate cancer

Several mechanisms that impair the immune response to promote tumour progression are reported. These mechanisms aim to reduce the ability of antigen-presenting cells to present antigen and activate naïve T cells to support an active immune response or to create a suppressive environment that induce non-functional tumour-associated antigen-specific T cells. Prostate cancer (PC) alone accounts for 33% of incident cancer cases and about 9% of all cancer-related deaths among men in the USA during 2006. Whereas androgen deprivation has remained the first line of therapy for advanced PC, other therapies are still required due to progression to an androgen-resistant state and eventually loss of control in patients receiving hormonal therapy. Immunotherapy seems to be a promising approach to enhance tumour-specific T-cell responses in different cancers including prostate. More importantly, clinical trials in advanced PC patients have shown that immunotherapy may generate significant clinical responses. Immunology and immunotherapy aspects of PC with focus on prostate-specific antigen will be presented.

A Pelvic Drain Can Often Be Avoided After Radical Retropubic Prostatectomy—An Update in 552 Cases

OBJECTIVES

The routine placement of a pelvic drain following radical retropubic prostatectomy (RRP) may not be required. We describe our experience in 552 consecutive RRPs to emphasise the safety of this approach and explain our rationale for avoiding a drain when possible.

METHODS

RRP was performed in 552 consecutive patients with clinically localised adenocarcinoma of the prostate between January 2002 and June 2005. Clinical and pathologic information was documented for each patient. After the prostate was removed and the anastomotic sutures tied, the bladder was gently filled with approximately 50 ml of saline through the urethral catheter. If there was no leak, a drain was not placed.

RESULTS

A drain was not placed in 419 (76%) of the 552 patients. We compared the postoperative complication rates in those with (D+) and without (D-) a drain. There were 27 (5%) immediate postoperative complications and no significant difference between the two groups (D+, 6%; D-, 5%; p=0.629): three (1%) patients who did not have a drain had a urinoma, one (1%) who had a drain had a lymphocele, and two (2%) who had a drain had a small pelvic haematoma.

CONCLUSIONS

If the bladder neck is preserved or meticulously reconstructed, there may be little extravasation and, thus, routine drainage is unnecessary. Our 4-year experience indicates that morbidity is not increased by omitting a drain from the pelvic cavity after RRP in properly selected cases.

Human chorionic gonadotropin modulates prostate cancer cell survival after irradiation or HMG CoA reductase inhibitor treatment

The impact of human chorionic gonadotropin (hCG) on prostate carcinoma viability was investigated. Treatment of LNCaP and PC-3 cells with hCG modestly reduced cell viability within 96 h. Treatment of cells with hCG followed by exposure to ionizing radiation enhanced radiosensitivity. Exposure of LNCaP cells to hCG promoted activation of epidermal growth factor receptor (ERBB1) via a Galpha(i)-, mitogen-activated protein kinase kinase (MEK)1/2-, and metalloprotease-dependent paracrine mechanism, effects that were further enhanced after radiation exposure, and that were causal in prolonged intense activation of poly(ADP-ribose) polymerase (PARP). Inhibition of ERBB1, MEK1, or PARP1 function suppressed the radiosensitizing properties of hCG. Radiosensitization was also, in part, dependent upon c-Jun NH2-terminal kinase 1/2 signaling. PARP1-dependent radiosensitization was suppressed by a pan-caspase inhibitor and by knockdown of apoptosis-inducing factor expression. Inhibition of phosphatidylinositol 3-kinase, expression of dominant-negative AKT, or treatment with the HMG CoA reductase inhibitor lovastatin suppressed AKT phosphorylation and enhanced the cytotoxic effects of hCG. The enhancing effect of lovastatin was reproduced by incubation with a geranylgeranyl transferase inhibitor and blocked by coexposure to geranylgeranyl pyrophosphate. Treatment with hCG and lovastatin decreased expression of BCL-(XL) and XIAP, and increased expression of IkappaB. The cytotoxic effects of hCG were enhanced by expression of dominant-negative IkappaB, and they were abolished by coexpression of activated AKT. Expression of activated AKT maintained BCL-(XL) levels in cells expressing dominant-negative IkappaB. The promotion of hCG lethality by lovastatin was abolished by overexpression of BCL-(XL), and was dependent upon activation of caspase-9. Thus, hCG, in combination with radiation and lovastatin, may represent a novel approach to kill prostate cancer cells.

Prostate cancer cells regulate growth and differentiation of bone marrow endothelial cells through TGFbeta and its receptor, TGFbetaRII

BACKGROUND

The underlying mechanisms permitting prostate cancer bone metastasis are poorly understood. We previously showed that the highly metastatic prostate cancer cell line, PC-3, inhibits bone marrow endothelial (HBME-1) cell growth in collagen gels and induces them to differentiate into cords, resembling angiogenesis in vivo.

METHODS

cDNA microarray analysis was performed to identify cytokines responsible for the effects of PC-3 cells on HBME-1 cells. Cytokine and neutralizing antibody studies were done to further investigate specific angiogenic factors, such as transforming growth factor beta (TGFbeta). TGFbeta RNA and protein were detected by real-time RT-PCR and enzyme-linked immunosorbent assay (ELISA) analysis to measure their production by prostate cancer cell lines. Conditioned media experiments using TGFbeta neutralizing antibodies were used to analyze TGFbeta activation by prostate cancer cells.

RESULTS

PC-3 conditioned media altered the expression of several TGFbeta-regulated or -associated genes in HBME-1 cells. Low concentrations of TGFbeta cytokines inhibited HBME-1 cell growth to a similar level as PC-3 conditioned media and partially induced differentiation. Inhibitors and neutralizing antibodies directed against TGFbeta isoforms and TGFbeta receptor type 2 (TGFbetaRII) reversed the growth inhibition of HBME-1 cells conferred by PC-3 conditioned media. Yet, only TGFbetaRII neutralizing antibodies significantly inhibited HBME-1 differentiation. Also, prostate cancer cell lines produced low levels of TGFbeta RNA and protein, and were shown to activate serum-derived TGFbeta.

CONCLUSIONS

These results suggest that prostate cancer cells mediate growth inhibition and differentiation of bone marrow endothelial cells both through production and activation of TGFbeta as well as alteration of TGFbetaRII-mediated signal transduction. This could contribute to the establishment and growth of bone metastases.

Effect of GnRH analogs on the expression of TrkA and p75 neurotrophin receptors in primary cell cultures from human prostate adenocarcinoma

BACKGROUND

GnRH analogs have antiproliferative and/or apoptotic effects on prostate cancer cells. Also, neurotrophin receptors TrkA and p75 have been reported in normal prostate suggesting a role in the gland growth control. In prostate cancer, TrkA receptors seem to be overexpressed and p75 receptors show a decreased expression. These changes in neurotrophin receptors may be related with unbalanced growth in malignant cells. In the present study we investigate the effects of GnRH analogs (leuprolide and cetrorelix) on the expression of TrkA and p75 neurotrophin receptors in primary cultures of human prostate cancer cells.

METHODS

Tissue was obtained from radical prostatectomies due to prostate adenocarcinoma. Cells were isolated after sequential enzyme digestion and cultured in defined media. Nerve growth factor (NGF) receptors in untreated cultures were estimated by immunofluorescence. Cultures were treated with leuprolide (agonist) or cetrorelix (antagonist) and expression of TrkA and p75 receptors were evaluated by semi quantitative RT-PCR (polymerase chain reaction) and western blot. Cell proliferation was estimated by MTT method and apoptosis through COMET assay.

RESULTS

Both leuprolide and cetrorelix induced a significant increase in p75 receptor gene and protein expression at a concentration that induce apoptosis and decrease proliferation. TrkA receptors showed no changes in presence of GnRH analogs.

CONCLUSIONS

GnRH analogs, leuprolide, and cetrorelix, change the ratio between neurotrophin receptors TrkA and p75 by increasing gene and protein expression of p75 receptor. Considering that TrkA receptor is related with proliferation and p75 with apoptosis, we suggest that our findings may explain, in part, the effect of GnRH analogs on prostate cancer growth.

Approval Summary

PURPOSE

Docetaxel, a taxane previously approved for the treatment of breast cancer and non-small cell lung cancer, was approved by the United States Food and Drug Administration on May 19, 2004 for use in combination with prednisone for the treatment of metastatic androgen-independent (hormone-refractory) prostate cancer. The purpose of this summary is to review the database supporting this approval.

EXPERIMENTAL DESIGN

In a randomized, global study enrolling 1,006 patients, two schedules of docetaxel were compared with mitoxantrone + prednisone as follows: MTZ q 3w, mitoxantrone 12 mg/m2 every 21 days + prednisone 5 mg twice a day for a total of 10 cycles; TXT q 3w, docetaxel 75 mg/m2 every 21 days + prednisone 5 mg twice a day for a total of 10 cycles; and TXT qw, docetaxel 30 mg/m2 days 1, 8, 15, 22, and 29 every 6 weeks + prednisone 5 mg twice a day for a total of 5 cycles.

RESULTS

There was a statistically significant overall survival advantage shown for the TXT q 3w arm over MTZ q 3w (median survival 18.9 months versus 16.5 months, P = 0.0094). No overall survival advantage was shown for TXT qw compared with MTZ q 3w. The most commonly occurring adverse events included anemia, neutropenia, infection, nausea, sensory neuropathy, fluid retention, alopecia, nail changes, diarrhea, and fatigue.

CONCLUSIONS

This report describes the Food and Drug Administration review supporting this first approval of a combination therapy for hormone-refractory prostate cancer based on demonstration of a survival benefit.