Androgen-independent Prostate Tumor Cell Research Articles

Using microfluidic models to evaluate whether monocyte preconditioning plays a role in tumor-associated macrophage mediated resistance to hormone therapy in men with prostate cancer.

228 Background: While men with metastatic castrate-resistant prostate cancer benefit greatly from 2nd generation androgen targeted therapies (ATTs), the utility of these therapies is inevitably limited by the development of resistance. Tumor associated macrophages (TAMs) are a myeloid immune cell population within the prostate tumor microenvironment (TME) that have been shown to play an integral role in development of ATT-resistance. However, the pathways that underlie TAM-mediated ATT resistance remain under investigation. In particular, many TAMs within the TME are derived from circulating monocytes and it is not yet clear whether the pathways driving TAM-mediated resistance are activated exclusively within the TME or if the activation of critical resistance pathways begins while the cells are circulating as monocytes. In this study, we utilized novel microscale technologies to investigate the transcriptome of monocytes and macrophages derived from patients progressing and responding to ATTs as well as the degree to which the macrophages promote ATT resistance in prostate tumor models. Methods: Primary monocytes were isolated from 22 men with prostate cancer who were either progressing or responding to 2ndgeneration ATTs. A portion of the monocytes from each patient were isolated for transcriptome analysis and the rest were differentiated into monocyte-derived macrophages (MDMs). MDMs were then cultured in monoculture or in co-culture with androgen-independent prostate tumor cells (22Rv1 and C42B). Each culture was then left untreated or treated with enzalutamide therapy. Following culture/treatment, each macrophage condition was isolated for transcriptome analysis and tumor cell populations from each condition were evaluated for treatment cytotoxicity. Results: Viability data from MDM-C42B co-culture demonstrated a 20% increase in tumor cell viability following enzalutamide treatment when C42B cells were cultured with primary MDMs from castrate-sensitive patients as compared to MDMs from castrate-resistant patients. Subsequent transcriptome analysis demonstrated key signatures in monocyte/macrophage populations that were associated ATT response. Conclusions: Leveraging a novel microfluidic culture platform known as Stacks, we were able to utilize primary, patient-derived cells to demonstrate that the role of TAMs in ATT resistance within the prostate TME is dependent, at least in part, on factors that are present prior to extravasation into the TME. Transcriptome analysis identified candidate pathways, which may be driving TAM-mediated differences in ATT response. These findings have the potential to lead to future use of circulating monocytes as a predictive biomarker as well as lead to the identification and targeting of ATT resistance pathways in patients.

KMT9 monomethylates histone H4 lysine 12 and controls proliferation of prostate cancer cells.

Histone lysine methylation is generally performed by SET domain methyltransferases and regulates chromatin structure and gene expression. Here, we identify human C21orf127 (HEMK2, N6AMT1, PrmC), a member of the seven-β-strand family of putative methyltransferases, as a novel histone lysine methyltransferase. C21orf127 functions as an obligate heterodimer with TRMT112, writing the methylation mark on lysine 12 of histone H4 (H4K12) in vitro and in vivo. We characterized H4K12 recognition by solving the crystal structure of human C21orf127-TRMT112, hereafter termed 'lysine methyltransferase 9' (KMT9), in complex with S-adenosyl-homocysteine and H4K12me1 peptide. Additional analyses revealed enrichment for KMT9 and H4K12me1 at the promoters of numerous genes encoding cell cycle regulators and control of cell cycle progression by KMT9. Importantly, KMT9 depletion severely affects the proliferation of androgen receptor-dependent, as well as that of castration- and enzalutamide-resistant prostate cancer cells and xenograft tumors. Our data link H4K12 methylation with KMT9-dependent regulation of androgen-independent prostate tumor cell proliferation, thereby providing a promising paradigm for the treatment of castration-resistant prostate cancer.

PRK1/PKN1 controls migration and metastasis of androgen-independent prostate cancer cells.

The major threat in prostate cancer is the occurrence of metastases in androgen-independent tumor stage, for which no causative cure is available. Here we show that metastatic behavior of androgen-independent prostate tumor cells requires the protein-kinase-C-related kinase (PRK1/PKN1) in vitro and in vivo. PRK1 regulates cell migration and gene expression through its kinase activity, but does not affect cell proliferation. Transcriptome and interactome analyses uncover that PRK1 regulates expression of migration-relevant genes by interacting with the scaffold protein sperm-associated antigen 9 (SPAG9/JIP4). SPAG9 and PRK1 colocalize in human cancer tissue and are required for p38-phosphorylation and cell migration. Accordingly, depletion of either ETS domain-containing protein Elk-1 (ELK1), an effector of p38-signalling or p38 depletion hinders cell migration and changes expression of migration-relevant genes as observed upon PRK1-depletion. Importantly, a PRK1 inhibitor prevents metastases in mice, showing that the PRK1-pathway is a promising target to hamper prostate cancer metastases in vivo. Here we describe a novel mechanism controlling the metastatic behavior of PCa cells and identify PRK1 as a promising therapeutic target to treat androgen-independent metastatic prostate cancer.

Anticancer Agents from the Australian Tropical Rainforest: Spiroacetals EBC‐23, 24, 25, 72, 73, 75 and 76

EBC-23, 24, 25, 72, 73, 75 and 76 were isolated from the fruit of Cinnamomum laubatii (family Lauraceae) in the Australian tropical rainforests. EBC-23 (1) was synthesized stereoselectively, in nine linear steps in 8 % overall yield, to confirm the reported relative stereochemistry and determine the absolute stereochemistry. Key to the total synthesis was a series of Tietze-Smith linchpin reactions. The novel spiroacetal structural motif, exemplified by EBC-23 (1), was found to inhibit the growth of the androgen-independent prostate tumor cell line DU145 in the mouse model, indicating potential for the treatment of refractory solid tumors in adults.

Dysregulated expression of MIC-1/PDF in human prostate tumor cells

As a part of the study to identify genes associated with hormone-refractory stage of human prostate cancer, we have recently identified several genetic and epigenetic changes that seem to be associated with the progression of androgen-sensitive to androgen-independent prostate tumor cells. In the present study, we report a novel gene, macrophage inhibitory cytokine-1 ( MIC-1) also known as prostate derived factor ( PDF), that was highly expressed in androgen-independent LNCaP-C81 cells and its metastatic variant LNCaP-Ln3 compared to androgen-sensitive LNCaP-C33 cells. The MIC-1/PDF expression was dysregulated (very low to non-detectable) in the androgen-independent PC3 and DU145 cells. Interestingly, serum factors demonstrated a differential regulation of MIC-1/PDF in the androgen-sensitive and the androgen-independent cells of LNCaP cells. Immunohistochemical analysis on 15 prostatic adenocarcinomas showed a weak staining in the benign prostatic glandular area (intensity score 2.38 ± 0.25; n=13), while the immunoreactivity was significantly stronger ( p<0.05) in areas of adenocarcinoma (score 7.33 ± 0.88; n=15). Altogether, these data suggest that the serum factors (including androgens and cytokines) might contribute to the regulation of the MIC-1/PDF gene that seems to be associated with the progression of prostate cancer.

Constitutive activation of IkappaB kinase alpha and NF-kappaB in prostate cancer cells is inhibited by ibuprofen.

Apoptotic pathways controlled by the Rel/NF-kappaB family of transcription factors may regulate the response of cells to DNA damage. Here, we have examined the NF-kappaB status of several prostate tumor cell lines. In the androgen-independent prostate tumor cells PC-3 and DU-145, the DNA-binding activity of NF-kappaB was constitutively activated and IkappaB-alpha levels were decreased. In contrast, the androgen-sensitive prostate tumor cell line LNCaP had low levels of NF-kappaB which were upregulated following exposure to cytokines or DNA damage. The activity of the IkappaB-alpha kinase, IKKalpha, which mediates NF-kappaB activation, was also measured. In PC-3 cells, IKKalpha activity was constitutively active, whereas LNCaP cells had minimal IKKalpha activity that was activated by cytokines. The anti-inflammatory agent ibuprofen inhibited the constitutive activation of NF-kappaB and IKKalpha in PC-3 and DU-145 cells, and blocked stimulated activation of NF-kappaB in LNCaP cells. However, ibuprofen did not directly inhibit IkappaB-alpha kinase. The results demonstrate that NF-kappaB is constitutively activated in the hormone-insensitive prostate tumor cell lines PC-3 and DU-145, but not in the hormone responsive LNCaP cell line. The constitutive activation of NF-kappaB in prostate tumor cells may increase expression of anti-apoptotic proteins, thereby decreasing the effectiveness of anti-tumor therapy and contributing to the development of the malignant phenotype.

Luteinizing hormone-releasing hormone agonists interfere with the mitogenic activity of the insulin-like growth factor system in androgen-independent prostate cancer cells.

We have previously shown that LHRH agonists exert a direct and specific inhibitory action on the proliferation of the androgen-independent DU 145 prostate cancer cell line; however, the cellular mechanisms mediating this antiproliferative action are not well defined. It is well known that the insulin-like growth factor (IGF) system plays a crucial role in the local regulation of the growth of androgen-independent prostate cancer. The present experiments were performed to evaluate whether LHRH agonists might exert their antimitogenic effect by interfering with the activity of the locally expressed IGF system. To this purpose, the effects of the LHRH agonist Zoladex (LHRH-A) on 1) the mitogenic action of IGF-I, 2) the tyrosine phosphorylation of type 1 IGF-I receptor (IGF-IR), 3) the concentration of IGF-IR, and 4) the secretion of IGF-binding protein-3 were studied. The results obtained show that in DU 145 cells, LHRH-A 1) counteracts the mitogenic action of IGF-I in a dose-dependent manner, 2) prevents the IGF-I-induced tyrosine phosphorylation of the IGF-IR, 3) reduces the concentration of IGF-IR without affecting its Kd value, and 4) does not affect the secretion of IGF-binding protein-3 in the conditioned medium from these cells. These data suggest that LHRH agonists may inhibit the proliferation of human androgen-independent prostate tumor cells by interfering with some of the cellular mechanisms mediating the stimulatory action of the IGF system.

Calcium signaling in prostate cancer cells: evidence for multiple receptors and enhanced sensitivity to bombesin/GRP.

Cellular calcium is an important second messenger for growth regulation. We sought to identify potentially important receptors on prostate tumor cells by screening over 20 agonists for their ability to increase intracellular free calcium ([Ca2+]i) in several human prostate tumor cell lines. Intracellular calcium mobilization was detected using fura-2. We found bombesin, GRP, ATP/UTP, lysophosphatidic acid, thrombin, endothelin, histamine, and bradykinin increased [Ca2+]i in the advanced tumor cell lines DU-145, PC3, and PPC-1. Bombesin failed to elevate [Ca2+]i in an immortalized human prostate cell line. Rank-order of potency studies suggested the presence of P2U nucleotide receptors for ATP/UTP on prostate epithelial cells. Potency studies also revealed GRP > > bombesin > > neuromedin B at elevating [Ca2+]i in responding tumor cells. These findings indicate that androgen independent prostate tumor cell lines express multiple receptors capable of elevating intracellular calcium, and suggest that GRP receptors may be selectively expressed and/or coupled to calcium signaling during prostate tumor progression. Calcium sensitive cellular events may therefore contribute to the progression of prostate cancer.

Anti-proliferative effect of the kinase inhibitor K252a on human prostatic carcinoma cell lines.

Members of the K252 family of kinase inhibitors have been demonstrated to inhibit a number of neurotrophin-mediated cellular responses, and to preferentially inhibit the activity of neurotrophin receptors. In this study, we examined the effects of K252a and K252b on the growth of human prostate carcinoma cells, whose growth is, in part, mediated by a prostatic nerve growth factor(NGF)-like protein(s). K252a inhibited [3H]thymidine incorporation by three androgen-independent prostate tumor cell lines (TSU-pr1, DU-145, and PC-3), under basal growth conditions, and in response to growth stimulation by human prostatic stromal (hPS) cell proteins and serum. K252b, which does not readily penetrate cell membranes, had no significant effect on [3H]thymidine incorporation by the prostate tumor cell lines. The decrease in [3H]thymidine incorporation by the cell lines in response to K252a did not appear to be the result of K252a cytotoxicity at concentrations as high as 100 nM, as measured by the Trypan blue assay for cell viability. Treatment of cells for 25 hours with 100 nM K252a resulted in accumulation of TSU-pr1, DU-145, and PC-3 cells in G0/G1, concurrent with a substantial decrease in cells synthesizing DNA. Treatment of androgen-responsive LNCaP prostatic carcinoma cells for 25 hours with 100 nM K252a also resulted in a significant decrease in DNA synthesis. Human recombinant NGF-mediated phosphorylation of a 140-kDa Trk NGF receptor in the TSU-pr1 cell line was inhibited by treatment with 100 nM K252a. Hence, K252a inhibition of Trk phosphorylation most probably contributed, in part, to the inhibition of prostate tumor cell growth in vitro. These results suggest that the mechanism of K252a action may be useful in the design of potential therapies for prostate cancer treatment.

Signal‐transduction pathways in androgen‐dependent and androgen‐independent prostate tumor cells

AbstractWe have investigated the differential responses of androgen‐dependent prostate tumor cell line LNCaP and androgen‐independent prostate tumor cell line PC‐3 to various effectors at the level of mitogen‐activated protein kinase (MAPK) signal‐transduction intermediates. We have examined the change in protein levels of ras, raf, mek1,2, and erk1,2 in LNCaP and PC‐3 cells following treatment with dihydrotestosterone (DHT), estradiol (E2), ionizing radiation, tumor necrosis factor alpha (TNFα), ZnSO4, and CdSO4, DHT treatment of androgen‐dependent LNCaP cells resulted in an increase in cellular ras protein levels by 1 hour after treatment, whereas ras levels decreased 0.5 hours after DHT treatment of androgen‐independent PC‐3 cells. These data indicate that, in fact, DHT does invoke a differential response in androgen‐dependent compared to androgenindependent prostate tumor cells. E2 treatment resulted in a change in ras levels for LNCaP cells, but not for PC‐3 cells, which is further evidence of a differential response in these prostate tumor cells. Ionizing radiation, TNFα, and CdSO4 treatment showed no effect on signal‐transduction intermediates; however, ZnSO4 treatment of LNCaP cells resulted in an increase in ras protein levels and a decrease in raf‐1 protein levels. No change in ras levels was observed in PC‐3 cells upon ZnSO4 treatment. Our data show few differences in the signal‐transduction intermediates of the MAPK pathway in LNCaP and PC‐3 prostate tumor cells in response to tested stimuli. These results and the observation that cellular mek1,2 and erk1,2 protein levels were constituitively elevated support the hypothesis that MAPK‐independent signal transduction may be occurring in these prostate cells. © 1995 Wiley‐Liss, Inc.

The androgen receptor: Functional structure and expression in transplanted human prostate tumors and prostate tumor cell lines

The growth of the majority of prostate tumors is androgen-dependent, for which the presence of a functional androgen receptor is a prerequisite. Tumor growth can be inhibited by blockade of androgen receptor action. However, this inhibition is transient. To study the role of the androgen receptor in androgen-dependent and androgen-independent prostate tumor cell growth, androgen receptor mRNA expression was monitored in six different human prostate tumor cell lines and tumors, which were grown either in vitro or by transplantation on (male) nude mice. Androgen receptor mRNA was clearly detectable in three androgen-dependent (sensitive) tumors and absent or low in three androgen-independent tumors. Growth of the LNCaP prostate tumor cell line can be stimulated both by androgens and by fetal calf serum. In the former situation androgen receptor mRNA expression is downregulated, whereas in the latter no effect on androgen receptor mRNA levels can be demonstrated. Sequence analysis showed that the androgen receptor gene from LNCaP cells contains a point mutation in the region encoding the steroid-binding domain, which confers an ACT coVon encoding a threonine residue to GCT, encoding alanine.