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.

In the early stages, prostate cancer is androgen- dependent; therefore, medical castration has shown significant results during the initial stages of this pathology. Despite this early effect, advanced prostate cancer is resilient to such treatment. Recent evidence shows that derivatives of Cannabis sativa and its analogs may exert a protective effect against different types of oncologic pathologies. The purpose of the present study was to detect the presence of cannabinoid receptors (CB1 and CB2) on cancer cells with a prostatic origin and to evaluate the effect of the in vitro use of synthetic analogs. In order to do this, we used a commercial cell line and primary cultures derived from prostate cancer and benign prostatic hyperplasia. The presence of the CB1 and CB2 receptors was determined by immunohistochemistry where we showed a higher expression of these receptors in later stages of the disease (samples with a high Gleason score). Later, treatments were conducted using anandamide, 2-arachidonoyl glycerol and a synthetic analog of anandamide, methanandamide. Using the MTT assay, we proved that the treatments produced a cell growth inhibitory effect on all the different prostate cancer cultures. This effect was demonstrated to be dose-dependent. The use of a specific CB1 receptor blocker (SR141716) confirmed that this effect was produced primarily from the activation of the CB1 receptor. In order to understand the MTT assay results, we determined cell cycle distribution by flow cytometry, which showed no variation at the different cell cycle stages in all the cultures after treatment. Treatment with endocannabinoids resulted in an increase in the percentage of apoptotic cells as determined by Annexin V assays and caused an increase in the levels of activated caspase-3 and a reduction in the levels of Bcl-2 confirming that the reduction in cell viability noted in the MTT assay was caused by the activation of the apoptotic pathway. Finally, we observed that endocannabinoid treatment activated the Erk pathway and at the same time, produced a decrease in the activation levels of the Akt pathway. Based on these results, we suggest that endocannabinoids may be a beneficial option for the treatment of prostate cancer that has become nonresponsive to common therapies.

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Prostate cancer (PCa) is the most frequently diagnosed malignancy in men worldwide. Chemotherapy response is very poor and resistance to hormone-based treatments is frequent in advances stages. Recently, tumor-initiating cells or cancer stem cells (CSCs) have been identifi ed in several cancers, including PCa. These cells are thought to be responsible for therapy resistance, relapse and metastasis. In the present work, enriched populations of CSCs were obtained using a mixed procedure that included diff erential clone-forming ability, sphere growing induction (prostatospheres) and magnetic-associated cell sorting (MACS). Also, stem marker expression was determined in PCa biopsies of diff erent histological grades and metastasis samples. The signature for stem markers of the isolated CSCs was CD133+/CD44+/ABCG2+/ CD24-. Expression of stem markers (CD133, CD44, and ABCG2) was higher in medium Gleason biopsies than in lower and higher grades, and lymph-node and bone metastasis samples. These results suggest that the CSCs in PCa reach an important number in medium Gleason grades, when the tumor is still confi ned into the gland. At this stage, the surgical treatment is usually with curative intention. However, an important percentage of patients relapse after treatment. Number and signature of CSCs may be a prognosis factor for PCa recurrence.

Taken together, these findings suggest that Chilean people carrying single or combined GSTM1 and CYP1A1 polymorphisms are more susceptible to prostate cancer.

Cancer stem cells (CSCs) have the ability to self-renew and differentiate to give rise to heterogeneous phenotype of the tumor cells. It is believed that these cells are involved in metastasis, recurrence and therapy resistance in various cancers. CSCs have been identified in prostate cancer (PCa), one of the most diagnosed malignancies in men over the world, for which chemotherapy resistance is a major problem in the treatment of castration-resistant advanced stages. Molecular signatures, gene expression and functional features have been reported for PCa CSCs. Most data come from cell lines which may not represent the actual tumor. In the present work, a CSCs enriched population obtained from PCa explants was functionally characterized and analyzed for drug resistance. Tumorsphere cultures positive for ABCG2 transporter, CD133, CD44, cytokeratins 5 and 18 (CK5 and CK18) and negatives for androgen receptor (AR) and prostate-specific antigen (PSA) showed higher clonogenic capacity, holoclone-forming ability, colony-forming capacity in soft agar and lower proliferative and apoptotic rate than control adherent cell cultures. Furthermore, exposing tumorsphere cultures to ABCG2 substrate drugs resulted in a high survival rate compared with control PCa cells. This high drug resistance was decreased using a selective inhibitor of ABCG2. According to these results, tumorspheres from PCa explants showed a functional stem phenotype and a marked drug resistance, probably mediated by high expression of the ABCG2 transporter, which might be considered as a suitable therapeutic target for CSCs.

Low chemotherapy response in PCa could be explained, in part, by over-expression of functional MDR proteins. Expression and function of these proteins should be evaluated to enhance efficacy of docetaxel-based therapies of patients with hormone-resistant PCa.

Contradictory data have been reported regarding the effect of GnRH agonists and antagonists on cell growth and survival, using prostate cancer-derived cell lines expressing either endogenous or exogenous GnRH receptors. We addressed the issue studying the effect of leuprolide (agonist) and cetrorelix (antagonist) on cell growth, apoptosis and GnRH receptor expression using a primary cell coculture system. Also, binding characteristics of prostate GnRH receptor in this culture system are described. Epithelial and stromal cells were obtained from prostate adenocarcinoma samples and cocultured in a bicameral system. Expression of GnRH receptors was evaluated by semiquantitative RT-PCR (transcript level) and Western blot (protein level). Cell growth was estimated by MTT method and apoptosis by DNA fragmentation using COMET assay. Saturation and competition binding studies were carried out using 125I-GnRH as radioligand. GnRH receptors from cell cultures of prostate cancer exhibited a single class of binding sites with a Kd of 1.11 +/- 0.28 nM and a Bmax of 2.81 +/- 0.37 pmol/mg of membrane protein for GnRH. Leuprolide and cetrorelix showed no effect on GnRH receptor expression. Both analogues showed a significant reduction in cell growth rate and an increase in DNA-fragmented cell number. These effects were dependent on the analogue concentrations (from 5-20 ng/mL). Considering that the culture system used in this work represents more closely the in vivo conditions of tumor cells than metastatic derived cell lines, we conclude that GnRH analogues have a significant inhibitory effect on cell viability of cells expressing GnRH receptors. In addition, GnRH receptors expressed in tumor prostatic cells seem not discriminate between agonist and antagonist, both analogues activating these receptors. Also, leuprolide and cetrorelix treatments did not influence GnRH receptor expression in our culture system. These differences with pituitary receptors may be explained by differences in affinity, transduction mechanism and molecular context in prostatic tissue.