Phenotypic effects of overexpression of the MMAC1 gene in prostate epithelial cells

Olaparib is effective in combination with, and as maintenance therapy after, first-line endocrine therapy in prostate cancer cells

A number of prostate cancer (PCa)‐specific genomic aberrations (denominated BRCAness genes) have been discovered implicating sensitivity to PARP inhibition within the concept of synthetic lethality. Recent clinical studies show favorable results for the PARP inhibitor olaparib used as single agent for treatment of metastatic castration‐resistant PCa. Using 2D and 3D cell culture models mimicking the different treatment and progression stages of PCa, we evaluated a potential use for olaparib in combination with first‐line endocrine treatments, androgen deprivation, and complete androgen blockade, and as a maintenance therapy following on from endocrine therapy. We demonstrate that the LNCaP cell line, possessing multiple aberrations in BRCAness genes, is sensitive to olaparib. Additive effects of olaparib combined with endocrine treatments in LNCaP are noted. In contrast, we find that the TMPRSS2:ERG fusion‐positive cell lines VCaP and DuCaP do not show signs of synthetic lethality, but are sensitive to cytotoxic effects caused by olaparib. In consequence, additive effects of olaparib with endocrine therapy were not observable in these cell lines, showing the need for synthetic lethality in combination treatment regimens. Additionally, we show that PCa cells remain sensitive to olaparib treatment after initial androgen deprivation implicating a possible use of olaparib as maintenance therapy. In sum, our preclinical data recommend olaparib as a synthetic lethal treatment option in combination or sequenced to first‐line endocrine therapy for PCa patients with diagnosed BRCAness.

ProstaCaid Induces G2/M Cell Cycle Arrest and Apoptosis in Human and Mouse Androgen-Dependent and-Independent Prostate Cancer Cells

The anticancer effects of ProstaCaid, a novel integrative blend of vitamins, minerals, multiherb extracts, and derivatives, were tested in human and mouse androgen—dependent (AD) and —independent (AI) prostate cancer cell lines. ProstaCaid shows growth inhibitory effects on both human and mouse AD prostate cancer cells (LNCaP and CASP 2.1) and AI prostate cancer cells (PC3 and CASP 1.1) in a dose-/time-dependent manner. Consistently, long-term treatment with ProstaCaid also reduced colony formation capacities of prostate cancer cells. Flow cytometry assays revealed that ProstaCaid induces G2/M arrest and apoptosis in LNCaP and PC3 cells after 72 hours of treatment. Immunoblotting assay demonstrated that 25 µg/mL of ProstaCaid treatment resulted in (1) the reduction of cyclin D1, cyclin B1, and Cdc2 expression in a time-dependent way; (2) increase in p21WAF1/Cip1 as early as 12 hours after the treatments in PC3 cells and reduction to base line at the 72-hour time point; and (3) repression of Bcl-2, BclxL, and induction of Bim as well as the cleavages of caspase-3 and poly(ADP-ribose) polymerase (PARP) at 72 hours of treatment, suggesting caspase-3-dependent apoptosis. Moreover, ProstaCaid suppressed activation of AKT and MAPK signaling pathways in PC3 and LNCaP cells by reducing phosphorylation levels of AKT, its downstream target S6 ribosomal protein and GSK3β, and ERK1/2, respectively. In summary, these findings strongly suggest that ProstaCaid may be a potential chemopreventive and therapeutic agent for both AD and, more importantly, AI prostate cancer.

PTEN-mediated G1 cell-cycle arrest in LNCaP prostate cancer cells is associated with altered expression of cell-cycle regulators

BACKGROUND

The tumor suppressor PTEN regulates many biological processes. A well-known downstream effector of PTEN is phospho-Akt. Although PTEN is the most frequently inactivated gene in prostate cancer, its mode of action is not fully understood. We studied the association of regulated PTEN expression with changes in biological function and gene expression profiles.

METHODS

PTEN-negative LNCaP cells were stably transfected with wild-type PTEN cDNA under inducible control, resulting in LNCaP/PTEN cells. Microarray analysis was used to monitor gene expression changes upon induction of PTEN. Expression of selected individual genes was studied in Q-PCR and siRNA experiments. Cell-cycle distribution was analyzed by flow cytometry.

RESULTS

Induced expression of PTEN in LNCaP/PTEN cells significantly inhibited cell proliferation, at least partly due to cell-cycle arrest at the G1 phase. Expression profiling combined with pathway analysis revealed that PTEN-dependent G1 growth arrest was associated with an altered mRNA expression of the G1 cell-cycle regulators Cdc25a, E2F2, cyclin G2, and RBL2/p130. Specific inhibition of Akt signaling by siRNA resulted in downregulation of both E2F2 and Cdc25a mRNA expression and upregulation of the FOXO target cyclin G2, similar to the effect observed by PTEN induction. However, Akt did not mediate the PTEN-dependent RBL2/p130 mRNA expression in LNCaP/PTEN cells.

CONCLUSIONS

The results indicate that PTEN dependent gene expression is important in cell-cycle regulation and is mediated by both Akt-dependent and -independent mechanisms.

The TGF-beta, PI3K/Akt and PTEN pathways: established and proposed biochemical integration in prostate cancer

A key to the development of improved pharmacological treatment strategies for cancer is an understanding of the integration of biochemical pathways involved in both tumorigenesis and cancer suppression. Furthermore, genetic markers that may predict the outcome of targeted pharmacological intervention in an individual are central to patient-focused treatment regimens rather than the traditional 'one size fits all' approach. Prostate cancer is a highly heterogeneous disease in which a patient-tailored care program is a holy grail. This review will describe the evidence that demonstrates the integration of three established pathways: the tumour-suppressive TGF-beta (transforming growth factor-beta) pathway, the tumorigenic PI3K/Akt (phosphoinositide 3-kinase/protein kinase B) pathway and the tumour-suppressive PTEN (phosphatase and tensin homologue deleted on chromosome 10) pathway. It will discuss gene polymorphisms and somatic mutations in relevant genes and highlight novel pharmaceutical agents that target key points in these integrated pathways.

Pharmacological targeting of the integrated protein kinase B, phosphatase and tensin homolog deleted on chromosome 10, and transforming growth factor-beta pathways in prostate cancer

Prostate cancer is a highly heterogenous disease in which a patient-tailored care program is much desired. Central to this goal is the development of novel targeted pharmacological interventions. To develop these treatment strategies, an understanding of the integration of cellular pathways involved in both tumorigenesis and tumor suppression is crucial. Of further interest are the events elicited by drug treatments that exploit the underlying molecular pathology in cancer. This review briefly describes the evidence that suggests integration of three established pathways: the tumorigenic phosphoinositide 3-kinase/protein kinase B (AKT) pathway, the tumor suppressive phosphatase and tensin homolog deleted on chromosome 10 pathway, and the tumor suppressive transforming growth factor-beta pathway. More importantly, we discuss novel pharmaceutical agents that target key points of integration in these three pathways. These new therapeutic strategies include the use of agents that target iron to inhibit proliferation via multiple mechanisms and suppression of AKT by cytosolic phospholipase A(2)-alpha inhibitors.

Regulation of protein kinase B activity by PTEN and SHIP2 in human prostate-derived cell lines

Protein Kinase B (PKB/Akt) is a key regulator of cell proliferation, motility and survival. The activation status of PKB is regulated by phosphatidylinositol 3-kinase (PI3K) via the synthesis of phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3, PIP3). PTEN antagonises PI3K by degrading PIP3 to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). Deregulation of PKB through loss of functional PTEN has frequently been implicated in the progression of tumours, including prostate cancer, and the PTEN-negative prostate cancer cell lines LNCaP and PC3 have been widely used as models for this mechanism of constitutive PKB activation. However, other enzymes in addition to PTEN can antagonise PI3K, including SHIP2, which degrades PIP3 to phosphatidylinositol-3,4-bisphosphate (PI(3,4)P2). We investigated the role of PTEN and SHIP2 in the regulation of PKB phosphorylation in a panel of human prostate-derived epithelial cell lines. In the PTEN-positive prostate-derived cell lines PNT2, PNT1a and P4E6, PI3K inhibition by LY294002 caused rapid dephosphorylation of PKB at ser473 (T(1/2)<2 min), leading to its inactivation. In the PTEN-null line LNCaP, LY294002-induced PKB dephosphorylation was much slower (T(1/2)>20 min), but in PC3 cells (also PTEN-null) it was only slightly slower than in PTEN-positive cells (T(1/2)=3 min). PKB dephosphorylation paralleled loss of plasma membrane PIP3. PNT1a, P4E6 and PC3, but not PNT2 or LNCaP, expressed SHIP2. SiRNA-mediated knockdown of SHIP2 expression markedly slowed PKB inactivation in response to LY294002 in PC3 but not in other SHIP2-positive cells, whereas knockdown of PTEN expression in PNT2, PNT1a and P4E6 resulted in higher steady-state levels of PKB phosphorylation and slowed, but did not prevent, LY294002-induced PKB inactivation. Thus SHIP2 substitutes for PTEN in the acute regulation of PKB in PC3 cells but not other prostate cell lines, where PTEN may share this role with further PIP3-degrading mechanisms.

Invasive characteristics of human prostatic epithelial cells: understanding the metastatic process

Prostate cancer has a predilection to metastasise to the bone marrow stroma (BMS) by an as yet uncharacterised mechanism. We have defined a series of coculture models of invasion, which simulate the blood/BMS boundary and allow the elucidation of the signalling and mechanics of trans-endothelial migration within the complex bone marrow environment. Confocal microscopy shows that prostate epithelial cells bind specifically to bone marrow endothelial-to-endothelial cell junctions and initiate endothelial cell retraction. Trans-endothelial migration proceeds via an epithelial cell pseudopodial process, with complete epithelial migration occurring after 232±43 min. Stromal-derived factor-1 (SDF-1)/CXCR4 signalling induced PC-3 to invade across a basement membrane although the level of invasion was 3.5-fold less than invasion towards BMS (P=0.0007) or bone marrow endothelial cells (P=0.004). Maximal SDF-1 signalling of invasion was completely inhibited by 10 μM of the SDF-1 inhibitor T140. However, 10 μM T140 only reduced invasion towards BMS and bone marrow endothelial cells by 59% (P=0.001) and 29% (P=0.011), respectively. This study highlights the need to examine the potential roles of signalling molecules and/or inhibitors, not just in single-cell models but in coculture models that mimic the complex environment of the bone marrow.

Clusterin overexpression in both malignant and nonmalignant prostate epithelial cells induces cell cycle arrest and apoptosis

Expression of the castration-induced clusterin protein is incompatible with the survival of human prostate cancer cells in tissues and in cell culture. To investigate the fate of human prostate epithelial cells, when engineered to maintain expression of clusterin protein, we have used an IRES-hyg vector and hygromycin selection. PC-3 prostate tumour cells were substantially more sensitive to clusterin expression than nonmalignant PNT1a cells, showing multiple phenotypic changes including cell cycle arrest and increased apoptosis. The results strengthen the hypothesis that clusterin expression is proapoptotic. Expression of exogenous clusterin in both cell types resulted in its relocation from the cytoplasm and a nuclear accumulation of the protein, as was also seen in the same cells when apoptosis was induced by etoposide treatment. To survive clusterin expression, the PC-3 tumour cells developed apoptosis-inhibitory properties. This could have significance for the resistance of prostate cancers to chemo/radiotherapy, where clusterin overexpression is observed.

Molecular genetic evidence for different clonal origins of epithelial and stromal components of phyllodes tumor of the prostate

Phyllodes tumor of the prostate is a rare neoplasm, composed of epithelium-lined cysts and channels embedded in a variably cellular stroma. The pathogenetic relationship of the epithelium and stroma is unknown and whether each is a clonal neoplastic element is uncertain. We studied the clonality of phyllodes tumors from six patients who underwent either enucleation or transurethral resection as their initial treatment. This was followed by total prostatectomy in three of the patients. Laser-assisted microdissection was performed to extract epithelial and stromal components of phyllodes tumor from formalin-fixed, paraffin-embedded tissue. Polymerase chain reaction was used to amplify genomic DNA at specific loci on chromosome 7q31 (D7S522), 8p21.3-q11.1 (D8S133, D8S137), 8p22 (D8S261), 10q23 (D10S168, D10S571), 17p13 (TP53), 16q23.2 (D16S507), 12q11-12 (D12S264), 17q (D17S855), 18p11.22-p11 (D18S53), and 22q11.2 (D22S264). In each tumor, stroma and epithelium were analyzed separately. Gel electrophoresis with autoradiography was used to detect loss of heterozygosity. All tumors showed allelic loss in one or more loci of both the epithelial and stromal components. The frequency of allelic loss in the epithelial component was 2 of 5 (40%) at D7S522, 2 of 6 (33%) at D8S133, 1 of 5 (20%) at D8S137, 3 of 6 (50%) at D8S261, 4 of 4 (100%) at D10S168, 4 of 6 (67%) at TP53, 2 of 6 (33%) at D10S571, 6 of 6 (100%) at D16S507, 1 of 5 (20%) at D12S264, 1 of 6 (17%) at D17S855, 2 of 6 (33%) at D18S53, and 2 of 5 (40%) at D22S264. The frequency of allelic loss in the stromal component was 2 of 5 (40%) at D7S522, 1 of 6 (17%) at D8S133, 2 of 5 (40%) at D8S137, 3 of 6 (50%) at D8S261, 1 of 4 (25%) at D10S168, 3 of 6 (50%) at TP53, 2 of 6 (33%) at D10S571, 3 of 6 (50%) at D16S507, 1 of 5 (20%) at D12S264, 0 of 6 (0%) at D17S855, 1 of 6 (17%) at D18S53, and 0 of 5 (0%) at D22S264. The pattern of allelic loss is significantly different in both stroma and epithelium statistically; completely concordant allelic loss patterns were not seen in any tumor examined. Our data demonstrate that both epithelial and stromal components of phyllodes tumor of the prostate are clonal, supporting the hypothesis that both elements are neoplastic. While both epithelium and stroma are clonal proliferations, they appear to have different clonal origins.

The significance of key regulators of apoptosis in the development and prognosis of prostate carcinoma. II. Products of suppressor genes Rb and PTEN, CDKI, Fas

The molecular basis for the transition of carcinoma of the prostate from androgen-dependent to androgen-independent growth is largely unknown. Currently for example, it is not clear whether the androgen-independent phenotype is a result of selection of a subgroup of genetically distinct prostate tumour cells which are already hormone-resistant or a genetic adaptation of prostate tumour cells to the hormone therapy itself. It has also been established that prostate tumour transformation is a result of homeostatic control defects, a line of thinking directed toward elucidating the apoptotic profile of prostate tumour cells that may be important in determining prognosis, response to therapy and illness progression. Main consideration in this part of rewiev is given to the role of tumour suppressor genes pRb and PTEN and also the natural inhibitors of cyclin dependent kinases - proteins p21(Waf1/Cip1) and p27(Kip1). Attention is also given to the role of FAS-mediated pathways in apoptosis induction.

p53 and PTEN/MMAC1/TEP1 gene therapy of human prostate PC-3 carcinoma xenograft, using transferrin-facilitated lipofection gene delivery strategy

We previously reported that supplementation of a cationic liposome with transferrin (Tf) greatly enhanced lipofection efficiency (P.-W. Cheng, Hum. Gene Ther. 1996;7:275-282). In this study, we examined the efficacy of p53 and PTEN tumor suppressor gene therapy in a mouse xenograft model of human prostate PC-3 carcinoma cells, using a vector consisting of dimyristoyloxypropyl-3-dimethylhydroxyethyl ammonium bromide (DMRIE)-cholesterol (DC) and Tf. When the volume of the tumors grown subcutaneously in athymic nude mice reached 50-60 mm(3), three intratumoral injections of the following four formulations were performed during week 1 and then during week 3: (1) saline, (2) DC + Tf + pCMVlacZ, (3) DC + Tf + pCMVPTEN, and (4) DC + Tf + pCMVp53 (standard formulation). There was no significant difference in tumor volume and survival between group 1 and group 2 animals. As compared with group 1 controls, group 3 animals had slower tumor growth during the first 3 weeks but thereafter their tumor growth rate was similar to that of the controls. By day 2 posttreatment, group 4 animals had significantly lower tumor volume relative to initial tumor volume as well as controls at the comparable time point. Also, animals treated with p53 survived longer. Treatment with DC, Tf, pCMVp53, DC + pCMVp53, or Tf + pCMVp53 had no effect on tumor volume or survival. Expression of p53 protein and apoptosis were detected in tumors treated with the standard formulation, thus associating p53 protein expression and apoptosis with efficacy. However, p53 protein was expressed in only a fraction of the tumor cells, suggesting a role for bystander effects in the efficacy of p53 gene therapy. We conclude that intratumoral gene delivery by a nonviral vector consisting of a cationic liposome and Tf can achieve efficacious p53 gene therapy of prostate cancer.