C4-2 Human Prostate Cancer Cells Research Articles

In vivo Knockdown of the Androgen Receptor Results in Growth Inhibition and Regression of Well-Established, Castration-Resistant Prostate Tumors

Progression to the castration-resistant state is the incurable and lethal end stage of prostate cancer, and there is strong evidence that androgen receptor (AR) still plays a central role in this process. We hypothesize that knocking down AR will have a major effect on inhibiting growth of castration-resistant tumors. Castration-resistant C4-2 human prostate cancer cells stably expressing a tetracycline-inducible AR-targeted short hairpin RNA (shRNA) were generated to directly test the effects of AR knockdown in C4-2 human prostate cancer cells and tumors. In vitro expression of AR shRNA resulted in decreased levels of AR mRNA and protein, decreased expression of prostate-specific antigen (PSA), reduced activation of the PSA-luciferase reporter, and growth inhibition of C4-2 cells. Gene microarray analyses revealed that AR knockdown under hormone-deprived conditions resulted in activation of genes involved in apoptosis, cell cycle regulation, protein synthesis, and tumorigenesis. To ensure that tumors were truly castration-resistant in vivo, inducible AR shRNA expressing C4-2 tumors were grown in castrated mice to an average volume of 450 mm(3). In all of the animals, serum PSA decreased, and in 50% of them, there was complete tumor regression and disappearance of serum PSA. Whereas castration is ineffective in castration-resistant prostate tumors, knockdown of AR can decrease serum PSA, inhibit tumor growth, and frequently cause tumor regression. This study is the first direct evidence that knockdown of AR is a viable therapeutic strategy for treatment of prostate tumors that have already progressed to the castration-resistant state.

Effects of Naturally Occurring and Synthetic Organoselenium Compounds on Protein Profiling in Androgen Responsive and Androgen Independent Human Prostate Cancer Cells

Prostate cancer represents a major clinical public health challenge. Both epidemiological and clinical intervention studies support the protective role of selenium against development of prostate cancer. However, the mechanisms responsible for the inhibitory activity by this micronutrient remain elusive. Furthermore, literature reports consistently have shown that the dose and form of selenium are important factors in cancer chemoprevention. Thus, in the present investigation using androgen responsive (AR) lymph node carcinoma of the prostate (LNCaP) and its androgen-independent clone (AI) LNCaP C4-2 human prostate cancer cells, we compared the effects of selenomethionine (SM) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) on cell growth, DNA synthesis, and on proteomic profiles. p-XSC (5–20 μ M) significantly inhibited cell growth in both cell types in a dose-dependent manner; SM was also effective but at much higher doses (50–100 μ M). We hypothesize that the inhibition of cell growth is due, in part, to selenium interaction with redox-sensitive proteins. Using 2D gel electrophoresis, both organoselenium compounds altered the expression, to a varied extent, of several unrecognized selenium-responsive proteins. Employing matrix-assisted laser-desorption ionization (MALDI) and time-of-flight (TOF; MALDI-TOF) followed by tandem mass spectrometric analysis, we identified the following proteins: cofilin-2, heterogeneous nuclear ribonucleoprotein, single-stranded mitochondrial DNA binding protein, chaperonin 10, nucleoside diphosphate kinase 6, and chain A Horf 6 human peroxidase enzyme. This is the first report showing that SM and p-XSC are capable of altering these proteins; their roles in prostate cancer prevention warrant further investigations.

S-phase checkpoints regulate Apo2 ligand/TRAIL and CPT-11–induced apoptosis of prostate cancer cells

As S-phase checkpoints play critical roles in maintaining genomic integrity and replicating the human genome correctly, understanding the molecular mechanism by which they regulate the therapeutic response is of great interest. Previously, we reported that the cytotoxic effect of a zinc-bound form of Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL), which is currently evaluated in clinical trials, in combination with low-dose CPT-11, induces apoptosis of C4-2 human prostate cancer cells and tissues. Here, we show that apoptosis, induced synergistically by this combination treatment, was associated with accumulation of cells in early S phase, indicated by cell cycle analyses, increased proliferating cell nuclear antigen, and Chk2-Thr(68) phosphorylation in tumors xenografted in mice. The combination treatment induced an S-phase checkpoint response through activation of Chk2 and Chk1 by the ataxia telangiectasia mutated and ataxia telangiectasia mutated and Rad3 related kinases, leading to phosphorylation and decreased Cdc25A levels. Cdc25A-dependent regulation of cyclin-dependent kinase 2 (Cdk2) and changes in association of p21(WAF1/CIP1) and hSpy1 with Cdk2 resulted in inhibition of Cdk2-associated kinase activity. Knockdown of ataxia telangiectasia mutated/Chk2 and ataxia telangiectasia mutated and Rad3 related/Chk1 by small inhibitory RNAs abrogated the S-phase checkpoint and accelerated apoptosis, resulting in caspase-3 activation and poly(ADP-ribose) polymerase 1 cleavage following combination treatment. Thus, Apo2L/TRAIL + CPT-11 treatment-induced apoptosis is regulated through an S-phase checkpoint controlled by the Chk2-Cdc25A and Chk1-Cdc25A pathways and inhibition of Cdk2-associated kinase activity. Low-dose CPT-11 and aphidicolin increased the proportion of S-phase cells and sensitized cells to Apo2L/TRAIL, by inducing phosphatidylserine externalization, caspase activation, and poly(ADP-ribose) polymerase 1 cleavage. Combinations with S-phase arrest-inducing chemotherapeutic drugs may represent promising avenues for clinical development of Apo2L/TRAIL.

Sensitization of prostate carcinoma cells to Apo2L/TRAIL by a Bcl-2 family protein inhibitor

Overexpression of anti-apoptotic Bcl-2 family proteins may play an important role in the aggressive behavior of prostate cancer cells and their resistance to therapy. The Bcl-2 homology 3 domain (BH3) is a uniquely important functional element within the pro-apoptotic class of the Bcl-2-related proteins, mediating their ability to dimerize with other Bcl-2-related proteins and promote apoptosis. The BH3 inhibitors (BH3Is) function by disrupting the interactions mediated by the BH3 domain between pro- and anti-apoptotic members of the Bcl-2 family and liberating more Bax/Bak to induce mitochondrial membrane permeabilization. LNCaP-derived C4-2 human prostate cancer cells are quite resistant to non-tagged, human recombinant soluble Apo2 ligand [Apo2L, also Tumor necrosis factor (TNF)-related apoptosis-inducing ligand, TRAIL], a tumor specific drug that is now in clinical trials. However, when Apo2L/TRAIL was combined with the Bcl-xL inhibitor, BH3I-2', it induced apoptosis synergistically through activation of Caspase-8 and the proapoptotic Bcl-2 family member Bid, resulting in the activation of effector Caspase-3 and proteolytic cleavage of Poly(ADP-ribose) polymerase, events that were blocked by the pan-caspase inhibitor zVAD-fmk. Our data indicate that, in combination with the BH3 mimetic, BH3I-2', Apo2L/TRAIL synergistically induces apoptosis in C4-2 human prostate cancer cells through both the extrinsic and intrinsic apoptotic pathways.

SERIAL TISSUE POLYPEPTIDE SPECIFIC ANTIGEN DETERMINATIONS IN THE FOLLOWUP OF HORMONE TREATED CARCINOMA OF THE PROSTATE

We determined the impact of serum cytokeratin-18-related tissue polypeptide specific antigen (TPS) in monitoring hormone treated carcinoma of the prostate. From 1991 to 1996, serial TPS and prostate specific antigen (PSA) determinations (3,882) in 443 hormone treated prostate carcinoma patients were correlated with the clinical course for a mean of 22 months. Elevated TPS levels were significantly associated with disease progression in hormone treated stage M1 carcinoma of the prostate (p = 0.001), even in high grade, PSA negative tumors. Post-therapy TPS declines following second line therapy in hormone refractory prostate cancer patients (92) correlated significantly with subjective response (p = 0.001, PSA p = 0.02) and progression-free survival time (r(s) = -0.76, PSA r(s) = -0.32). A TPS decrease of more than 50% coincided with palliation in 90% of patients (PSA 64%) and predicted the best chance of a longer progression of free survival (p < 0.00005, PSA p = 0.036). Vice versa, rising TPS levels (more than 20%) coincided with subjective response in only 1 of 37 patients (PSA 9 of 33). TPS may be a useful adjunct to PSA in monitoring hormone refractory, metastasized prostate cancer.