Retracted: Additive antitumor effects of the epidermal growth factor receptor tyrosine kinase inhibitor, gefitinib (Iressa), and the nonsteroidal antiandrogen, bicalutamide (Casodex), in prostate cancer cellsin vitro

High Content Positional Biosensor Assay to Screen for Compounds that Prevent or Disrupt Androgen Receptor and Transcription Intermediary Factor 2 Protein-Protein Interactions

Transcriptional Intermediary Factor 2 (TIF2) is a key Androgen receptor (AR) coactivator that has been implicated in the development and progression of castration resistant prostate cancer (CRPC). This chapter describes the implementation of an AR-TIF2 protein-protein interaction (PPI) biosensor assay to screen for small molecules that can induce AR-TIF2 PPIs, inhibit the DHT-induced formation of AR-TIF2 PPIs, or disrupt pre-existing AR-TIF2 PPIs. The biosensor assay employs high content imaging and analysis to quantify AR-TIF2 PPIs and integrates physiologically relevant cell-based assays with the specificity of binding assays by incorporating structural information from AR and TIF2 functional domains along with intracellular targeting sequences using fluorescent protein reporters. Expression of the AR-Red Fluorescent Protein (RFP) "prey" and TIF2-Green Fluorescent Protein (GFP) "bait" components of the biosensor is directed by recombinant adenovirus (rAV) expression constructs that facilitated a simple co-infection protocol to produce homogeneous expression of both biosensors that is scalable for screening. In untreated cells, AR-RFP expression is localized predominantly to the cytoplasm and TIF2-GFP expression is localized only in the nucleoli of the nucleus. Exposure to DHT induces the co-localization of AR-RFP within the TIF2-GFP positive nucleoli of the nucleus. The AR-TIF2 biosensor assay therefore recapitulates the ligand-induced translocation of latent AR from the cytoplasm to the nucleus, and the PPIs between AR and TIF2 result in the colocalization of AR-RFP within TIF2-GFP expressing nucleoli. The AR-TIF2 PPI biosensor approach offers significant promise for identifying molecules with potential to modulate AR transcriptional activity in a cell-specific manner that may overcome the development of resistance and progression to CRPC.

High-content positional biosensor screening assay for compounds to prevent or disrupt androgen receptor and transcriptional intermediary factor 2 protein-protein interactions

The androgen receptor-transcriptional intermediary factor 2 (AR-TIF2) positional protein-protein interaction (PPI) biosensor assay described herein combines physiologically relevant cell-based assays with the specificity of binding assays by incorporating structural information of AR and TIF2 functional domains along with intracellular targeting sequences and fluorescent reporters. Expression of the AR-red fluorescent protein (RFP) "prey" and TIF2-green fluorescent protein (GFP) "bait" components of the biosensor was directed by recombinant adenovirus constructs that expressed the ligand binding and activation function 2 surface domains of AR fused to RFP with nuclear localization and nuclear export sequences, and three α-helical LXXLL motifs from TIF2 fused to GFP and an HIV Rev nucleolar targeting sequence. In unstimulated cells, AR-RFP was localized predominantly to the cytoplasm and TIF2-GFP was localized to nucleoli. Dihydrotestosterone (DHT) treatment induced AR-RFP translocation into the nucleus where the PPIs between AR and TIF2 resulted in the colocalization of both biosensors within the nucleolus. We adapted the translocation enhanced image analysis module to quantify the colocalization of the AR-RFP and TIF2-GFP biosensors in images acquired on the ImageXpress platform. DHT induced a concentration-dependent AR-TIF2 colocalization and produced a characteristic condensed punctate AR-RFP PPI nucleolar distribution pattern. The heat-shock protein 90 inhibitor 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) and antiandrogens flutamide and bicalutamide inhibited DHT-induced AR-TIF2 PPI formation with 50% inhibition concentrations (IC50s) of 88.5±12.5 nM, 7.6±2.4 μM, and 1.6±0.4 μM, respectively. Images of the AR-RFP distribution phenotype allowed us to distinguish between 17-AAG and flutamide, which prevented AR translocation, and bicalutamide, which blocked AR-TIF2 PPIs. We screened the Library of Pharmacologically Active Compounds (LOPAC) set for compounds that inhibited AR-TIF2 PPI formation or disrupted preexisting complexes. Eleven modulators of steroid family nuclear receptors (NRs) and 6 non-NR ligands inhibited AR-TIF2 PPI formation, and 10 disrupted preexisting complexes. The hits appear to be either AR antagonists or nonspecific inhibitors of NR activation and trafficking. Given that the LOPAC set represents such a small and restricted biological and chemical diversity, it is anticipated that screening a much larger and more diverse compound library will be required to find AR-TIF2 PPI inhibitors/disruptors. The AR-TIF2 protein-protein interaction biosensor (PPIB) approach offers significant promise for identifying molecules with potential to modulate AR transcriptional activity in a cell-specific manner that is distinct from the existing antiandrogen drugs that target AR binding or production. Small molecules that disrupt AR signaling at the level of AR-TIF2 PPIs may also overcome the development of resistance and progression to castration-resistant prostate cancer.

Anti-neoplastic properties of hydralazine in prostate cancer

Prostate cancer (PCa) is a major cause of cancer-related morbidity and mortality worldwide. Although early disease is often efficiently managed therapeutically, available options for advanced disease are mostly ineffective. Aberrant DNA methylation associated with gene-silencing of cancer-related genes is a common feature of PCa. Therefore, DNA methylation inhibitors might constitute an attractive alternative therapy. Herein, we evaluated the anti-cancer properties of hydralazine, a non-nucleoside DNA methyltransferases (DNMT) inhibitor, in PCa cell lines. In vitro assays showed that hydralazine exposure led to a significant dose and time dependent growth inhibition, increased apoptotic rate and decreased invasiveness. Furthermore, it also induced cell cycle arrest and DNA damage. These phenotypic effects were particularly prominent in DU145 cells. Following hydralazine exposure, decreased levels of DNMT1, DNMT3a and DNMT3b mRNA and DNMT1 protein were depicted. Moreover, a significant decrease in GSTP1, BCL2 and CCND2 promoter methylation levels, with concomitant transcript re-expression, was also observed. Interestingly, hydralazine restored androgen receptor expression, with upregulation of its target p21 in DU145 cell line. Protein array analysis suggested that blockage of EGF receptor signaling pathway is likely to be the main mechanism of hydralazine action in DU145 cells. Our data demonstrate that hydralazine attenuated the malignant phenotype of PCa cells, and might constitute a useful therapeutic tool.

Identification of ML-9 as a lysosomotropic agent targeting autophagy and cell death

The growing number of studies suggested that inhibition of autophagy enhances the efficacy of Akt kinase inhibitors in cancer therapy. Here, we provide evidence that ML-9, a widely used inhibitor of Akt kinase, myosin light-chain kinase (MLCK) and stromal interaction molecule 1 (STIM1), represents the ‘two-in-one' compound that stimulates autophagosome formation (by downregulating Akt/mammalian target of rapamycin (mTOR) pathway) and inhibits their degradation (by acting like a lysosomotropic agent and increasing lysosomal pH). We show that ML-9 as a monotherapy effectively induces prostate cancer cell death associated with the accumulation of autophagic vacuoles. Further, ML-9 enhances the anticancer activity of docetaxel, suggesting its potential application as an adjuvant to existing anticancer chemotherapy. Altogether, our results revealed the complex effect of ML-9 on autophagy and indentified ML-9 as an attractive tool for targeting autophagy in cancer therapy through dual inhibition of both the Akt pathway and the autophagy.

Difference in protein expression profile and chemotherapy drugs response of different progression stages of LNCaP sublines and other human prostate cancer cells

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, 80-90% of the patients who receive androgen ablation therapy ultimately develop recurrent tumors in 12-33 months after treatment with a median overall survival time of 1-2 years after relapse. LNCaP is a commonly used cell line established from a human lymph node metastatic lesion of prostatic adenocarcinoma. We previously established two relapsed androgen receptor (AR)-rich androgen-independent LNCaP sublines 104-R1 (androgen depleted for 12 months) and 104-R2 cells (androgen depleted for 24 months) from AR-positive androgen-dependent LNCaP 104-S cells. LNCaP 104-R1 and 104-R2 mimics the AR-positive hormone-refractory relapsed tumors in patients receiving androgen ablation therapy. Androgen treatment stimulates proliferation of 104-S cells, but causes growth inhibition and G1 cell cycle arrest in 104-R1 and 104-R2 cells. We investigated the protein expression profile difference between LNCaP 104-S vs. LNCaP 104-R1, 104-R2, PC-3, and DU-145 cells as well as examined the sensitivity of these prostate cancer cells to different chemotherapy drugs and small molecule inhibitors. Compared to 104-S cells, 104-R1 and 104-R2 cells express higher protein levels of AR, PSA, c-Myc, Skp2, BCL-2, P53, p-MDM2 S166, Rb, and p-Rb S807/811. The 104-R1 and 104-R2 cells express higher ratio of p-Akt S473/Akt, p-EGFR/EGFR, and p-Src/Src, but lower ratio of p-ERK/ERK than 104-S cells. PC-3 and DU-145 cells express higher c-Myc, Skp2, Akt, Akt1, and phospho-EGFR but less phospho-Akt and phospho-ERK. Overexpression of Skp2 increased resistance of LNCaP cells to chemotherapy drugs. Paclitaxel, androgen, and inhibitors for PI3K/Akt, EGFR, Src, or Bcl-2 seem to be potential choices for treatment of advanced prostate cancers. Our study provides rationale for targeting Akt, EGFR, Src, Bcl-2, and AR signaling as a treatment for AR-positive relapsed prostate tumors after hormone therapy.

Role of GLI-1 in epidermal growth factor-induced invasiveness of ARCaPE prostate cancer cells

Epidermal growth factor (EGF) signaling and Hedgehog (HH) signaling are both involved in prostate cancer (PCa) progression, yet the mechanisms through which these two pathways are synergistically linked require elucidation. In the present study, we aimed to ascertain how EGF and the HH signaling transcription factor GLI-1 are linked in prostate cancer invasiveness. ARCaP human prostate cancer cells, which included ARCaPE and ARCaPM cells, were used as a model in the present study. The expression of EGF receptor (EGFR) and the HH signaling transcriptional factor GLI-1 were detected in ARCaPE cells by immunofluorescence, and the ARCaPE cells were treated with human recombinant EGF protein (hrEGF) for 4 consecutive days in vitro. Transwell invasion assays were performed in the ARCaPE cells following treatment with DMSO (vehicle control), hrEGF, GATN61 (GLI-1-specific inhibitor), hrEGF plus GANT61 and in the ARCaPM cells. The expression of phosphorylated extracellular signal regulated kinase (p-ERK), total ERK and GLI-1 was detected by western blotting in ARCaPE cells at different time-points following treatment with hrEGF. The expression of EGFR and GLI-1 was detected in ARCaPE cells, which exhibited a cobblestone-like morphology, while after treatment with hrEGF, the cell morphology was altered to a spindle-shaped mesenchymal cell morphology. Transwell invasion assays demonstrated that hrEGF dramatically enhanced the invasive capability of the ARCaPE cells (p<0.05). Additionally, western blot assay demonstrated that the expression levels of p-ERK and GLI-1 in ARCaPE cells increased in a time-dependent manner after treatment with hrEGF (p<0.05); however, the expression levels of total ERK in the cells remained relatively unchanged. It also demonstrated that the GLI-1 inhibitor GANT61 could reverse the enhanced invasive effect induced by EGF in ARCaPE cells (p<0.05). Our preliminary in vitro study showed that EGF signaling may increase the invasive capability of ARCaPE human prostate cancer cells via upregulation of p-ERK and the HH signaling transcriptional factor GLI-1. Additionally, this enhanced cell invasive effect was reversed by a GLI-1-specific inhibitor in vitro. Consequently, it indicates that both EGF and HH signaling are synergistically involved in the progression of human prostate cancer ARCaP cells, and GlI-1 may be one of the important effectors, which is activated by EGF downstream signaling, to promote the invasiveness of ARCaPE prostate cancer cells.

Prolonging hormone sensitivity in prostate cancer xenografts through dual inhibition of AR and mTOR

BACKGROUND

To determine the mechanisms associated with loss of androgen dependency and disease progression in prostate cancer (PCa), we investigated the relationship between the androgen receptor (AR) and mTOR pathways and the impact of inhibiting both pathways in androgen-dependent and castration-resistant PCa models.

EXPERIMENTAL DESIGN

Androgen-dependent (LNCaP) and castration-resistant PCa (HP-LNCaP) cells were grown as tumours in SCID mice. Once tumours reached 500 mm(3), animals were grouped and injected subcutaneous with vehicle, our novel anti-androgen/androgen synthesis inhibitor, VN/124-1, bicalutamide, and everolimus. Tumour volumes were measured biweekly. The PSA and protein analyses were performed after completion of the treatment.

RESULTS

The addition of everolimus to bicalutamide treatment of resistant tumours significantly reduced tumour growth rates and tumour volumes. Anti-androgen treatment also increased protein expression of multiple signal transduction pathways earlier than vehicle-treated control xenografts. VN/124-1 plus everolimus acted in concert to reduce tumour growth rates in our castration-resistant xenograft model.

CONCLUSIONS

This study suggests that dual inhibition of AR and mTOR in castration-resistant xenograft models can restore sensitivity of tumours to anti-androgen therapy. Furthermore, after bicalutamide failure, dual inhibition with VN/124-1 and everolimus was the most effective treatment.

Serially heterotransplanted human prostate tumours as an experimental model

* Introduction * Serially heterotransplanted human tumours in immunosuppressed mice: similarity to the tumour of origin - Cytological and histological analysis - Karyotype - Marker expression - Other PC markers - Tumour cell proliferation and frequency of mitosis - Vasculature - Stromal compartment - Heterotransplant hormone dependency - Androgen dependent - Partially androgen dependent - Androgen independent - Metastases * Conclusions Preclinical research on prostate cancer (PC) therapies uses several models to represent the human disease accurately. A common model uses patient prostate tumour biopsies to develop a cell line by serially passaging and subsequent implantation, in immunodeficient mice. An alternative model is direct implantation of patient prostate tumour biopsies into immunodeficient mice, followed by serial passage in vivo. The purpose of this review is to compile data from the more than 30 years of human PC serial heterotransplantation research. Serially heterotransplanted tumours are characterized by evaluating the histopathology of the resulting heterotransplants, including cellular differentiation, karyotype, marker expression, hormone sensitivity, cellular proliferation, metastatic potential and stromal and vascular components. These data are compared with the initial patient tumour specimen and, depending on available information, the patient's clinical outcome was compared with the heterotransplanted tumour. The heterotansplant model is a more accurate preclinical model than older generation serially passaged or genetic models to investigate current and newly developed androgen-deprivation agents, antitumour compounds, anti-angiogenic drugs and positron emission tomography radiotracers, as well as new therapeutic regimens for the treatment of PC.

Inhibition of epidermal growth factor receptor signaling by Saussurea involucrata, a rare traditional Chinese medicinal herb, in human hormone-resistant prostate cancer PC-3 cells

Prostate carcinoma is the most frequently diagnosed malignancy and the second leading cause of death of men in the United States. To date, no effective therapeutic treatment allows abrogation of the progression of prostate cancer to more invasive forms. In this study, we identified Saussurea involucrata Kar. et Kir., a rare traditional Chinese medicinal herb, as a potential agent for androgen-independent prostate cancer patients and investigated its biological mechanism as an antineoplastic agent. S. involucrata caused a concentration- and time-dependent inhibition of cell proliferation in human hormone-resistant prostate cancer PC-3 cells. Moreover, in vitro studies in a panel of several types of human cancer cell lines revealed that S. involucrata inhibited cell proliferation with high potency. To evaluate the bioactive compounds, we successively extracted the S. involucrata with fractions of methanol (SI-1), ethyl acetate (SI-2), n-butanol (SI-3), and water (SI-4). Among these extracts, SI-2 contains the most effective bioactivity. SI-2 treatment resulted in significant time-dependent growth inhibition together with G1 phase cell cycle arrest and apoptosis in PC3 cells. In addition, SI-2 treatment strongly induced p21WAF1/CIP and p27KIP1 expression, independent of the p53 pathway, and downregulated expression of cyclin D1 and cyclin-dependent kinase 4 (CDK4). SI-2 treatment increased levels of Bax, cytochrome c, activated caspase-3, and active caspase-9 and decreased Bcl-2 expression level. One of the major targets for the therapy in prostate cancer can be epidermal growth factor receptor (EGFR). SI-2 markedly reduced phosphorylation of EGFR and inhibited activation of AKT and STAT3. Moreover, p.o. administration of SI-2 induced a dose-dependent inhibition of PC-3 tumor growth in vivo. In summary, our study identifies S. involucrata as an effective inhibitor of EGFR signaling in human hormone-resistant prostate cancer PC-3 cells. We suggest that S. involucrata could be developed as an agent for the management of EGFR-positive human cancers.

Exogenous p27KIP1 expression induces anti-tumour effects and inhibits the EGFR/PI3K/Akt signalling pathway in PC3 cells

p27 is a cyclin-dependent kinase inhibitor that regulates the progression of cells from G(1) to S phase of the cell cycle. Loss of p27 has been associated with disease progression and with an unfavourable outcome in prostate cancer. In this study, we investigated whether exogenous p27 expression in the human androgen-independent prostate cancer PC3 cell line had any effect on cell growth, and we studied the molecular mechanisms involved. p27 expression was restored in PC3 cells by plasmid delivery. Cell proliferation and apoptosis were assessed in PC3 cells transfected with p27. We also investigated the effects of p27 on the epidermal growth factor receptor (EGFR)/phosphatidylinositol 3-kinase (PI3K)/Akt signalling pathway in PC3 cells. By restoring p27 expression in PC3 cells, we observed that p27 reduced proliferation and induced arrest in G(0)/G(1) phase. Moreover, p27-transfected PC3 cells underwent apoptosis, as shown by flow cytometric analysis and western blotting analysis of Bcl-2, Bax, Bad, caspase-3 and poly(ADP-ribose)polymerase expression. Furthermore, the p27-induced anti-tumour action correlated with inhibition of the EGFR/PI3K/Akt signalling pathway, as confirmed by western blotting analysis and densitometry of EGFR, PI3K (p85), Akt and p-Akt(S473) expression. Our results suggest that exogenous expression of p27 inhibits the proliferation of PC3 cells through induction of G(1) arrest and apoptosis, and this process correlates with inhibition of the EGFR/PI3K/Akt signalling pathway.

EGFR ligand switch in late stage prostate cancer contributes to changes in cell signaling and bone remodeling

BACKGROUND

Bone metastasis occurs frequently in advanced prostate cancer (PCa) patients; however, it is not known why this happens. The epidermal growth factor receptor (EGFR) ligand EGF is available to early stage PCa; whereas, TGF-alpha is available when PCa metastasizes. Since the microenvironment of metastases has been shown to play a role in the survival of the tumor, we examined whether the ligands had effects on cell survival and proliferation in early and late PCa.

METHODS

We used LNCaP cells as a model of early stage, non-metastatic PCa and the isogenic C4-2B cells as a model of late stage, metastatic PCa.

RESULTS

We found that the proliferation factor MAPK and the survival factor AKT were differentially activated in the presence of different ligands. TGF-alpha induced growth of C4-2B cells and not of the parental LNCaP cells; however, LNCaP cells expressing a constitutively active AKT did proliferate with TGF-alpha. Therefore, AKT appeared to be the TGF-alpha-responsive factor for survival of the late stage PCa cells. LNCaP cells exposed to EGF produced more osteoprotegerin (OPG), an inhibitor of bone remodeling, than C4-2B cells with TGF-alpha, which had increased expression of RANKL, an activator of bone remodeling. In concordance, TGF-alpha-treated C4-2B conditioned medium was able to differentiate an osteoclast precursor line to a greater extent than EGF-treated C4-2B or TGF-alpha-treated LNCaP conditioned media.

CONCLUSION

The switch in EGFR ligand availability as PCa progresses affects cell survival and contributes to bone remodeling.

Bicalutamide demonstrates biologic effectiveness in prostate cancer cell lines and tumor primary cultures irrespective of Her2/neu expression levels

OBJECTIVES

To evaluate the role of Her2/neu as a molecular marker predictive of the treatment response to bicalutamide in prostate cancer (PCa).

METHODS

Four PCa cell lines with graded Her2/neu expression levels and 63 primary tumor cultures derived from men with PCa and selected according to Her2/neu tumor levels were used. Primary tumor cultures and PCa cell lines were treated with bicalutamide (0.1-10 microM) in the presence of dehydrotestosterone (10(-12) M) for 4 days. The presence of a significant correlation between Her2/nue expression and drug efficacy was used to define the role of Her2/neu as molecular predictor of bicalutamide effectiveness. As an indicator of drug effectiveness we used the concentration that inhibits 50% values determined after bicalutamide treatment.

RESULTS

After bicalutamide treatment, no significant differences in the concentration that inhibits 50% were found among the different tumor cell lines (P = .081). In this experimental model, the correlation analysis suggested that the effectiveness of this drug was not influenced by Her2/neu levels (r = 0.053, P = .823). In primary cultures with high Her2/neu levels (43 tumor cultures), the mean value of the concentration that inhibits 50% for bicalutamide was 0.43 +/- 0.13 microM, and in cultures with low Her2/neu levels (20 tumor cultures), the same parameter was 0.5 +/- 0.16 microM (P = .14). The correlation analysis suggested that the effectiveness of this drug was not influenced by Her2/neu levels (r = 0.33, P = .101).

CONCLUSIONS

Our biologic data seem to indicate that the antitumor effect of bicalutamide is independent of Her2/neu levels in preclinical models of PCa. Bicalutamide could be configured as a pharmacologic option to treat patients with high or low levels of Her2/neu.

Functions of normal and malignant prostatic stem/progenitor cells in tissue regeneration and cancer progression and novel targeting therapies

This review summarizes the recent advancements that have improved our understanding of the functions of prostatic stem/progenitor cells in maintaining homeostasis of the prostate gland. We also describe the oncogenic events that may contribute to their malignant transformation into prostatic cancer stem/progenitor cells during cancer initiation and progression to metastatic disease stages. The molecular mechanisms that may contribute to the intrinsic or the acquisition of a resistant phenotype by the prostatic cancer stem/progenitor cells and their differentiated progenies with a luminal phenotype to the current therapies and disease relapse are also reviewed. The emphasis is on the critical functions of distinct tumorigenic signaling cascades induced through the epidermal growth factor system, hedgehog, Wnt/beta-catenin, and/or stromal cell-derived factor-1/CXC chemokine receptor-4 pathways as well as the deregulated apoptotic signaling elements and ATP-binding cassette multidrug transporter. Of particular therapeutic interest, we also discuss the potential beneficial effects associated with the targeting of these signaling elements to overcome the resistance to current treatments and prostate cancer recurrence. The combined targeted strategies toward distinct oncogenic signaling cascades in prostatic cancer stem/progenitor cells and their progenies as well as their local microenvironment, which could improve the efficacy of current clinical chemotherapeutic treatments against incurable, androgen-independent, and metastatic prostate cancers, are also described.

Inhibition of androgen-independent prostate cancer cell growth is enhanced by combination therapy targeting Hedgehog and ErbB signalling

Background

Prostate cancer is a leading cause of male cancer specific mortality. When cure by radical prostatectomy is not possible the next line of prostate cancer treatment is androgen deprivation. However prolonged androgen deprivation often results in relapse and androgen-independent prostate cancer that is inevitably fatal despite optimal chemotherapy. The Hedgehog signalling pathway has recently been implicated in prostate cancer development and metastasis. EGFR or ErbB2 expression has been also correlated with androgen independence, shorter survival and metastasis.

Results

We determined that the Hedgehog and ErbB signalling pathways are active in circulating tumour cells isolated from androgen-independent prostate cancer patients and in the androgen-independent prostate cancer cell line LNCaP C4-2B. As a basis for synergistic chemotherapy protocols combinations of the Hedgehog specific inhibitor cyclopamine and the ErbB signalling inhibitors gefitinib or lapatinib were tested in this study. Androgen-independent prostate cancer cell growth was inhibited by a SMO inhibitor (cyclopamine) which blocks Hedgehog signalling and by ErbB inhibitors (gefitinib and lapatinib). The isobologram and combination index method of Chou and Talalay was used to evaluate drug interactions. Synergistic antiproliferation effects were observed when the Hedgehog and ErbB inhibitors were combined.

Conclusion

Androgen-independent prostate cancer cell proliferation was associated with activity of the Hedgehog and ErbB signalling pathways. Cyclopamine, gefitinib or lapatinib treatment significantly decreased the proliferation of androgen-independent prostate cancer cells. The Hedgehog pathway therefore represents a promising new therapeutic target in androgen-independent prostate cancer. Synergistic effects were observed when Hedgehog and ErbB inhibitors were used together. This study may have clinical implications for improving the treatment of advanced prostate cancer.

Improvement of cytotoxic effects induced by mitoxantrone on hormone-refractory metastatic prostate cancer cells by co-targeting epidermal growth factor receptor and hedgehog signaling cascades

The results of the present study revealed for the first time the possibility to use a combination of mitoxantrone with gefitinib and cyclopamine for inhibiting the growth of epidermal growth factor (EGF), sonic hedgehog- (SHHNp), and serum-stimulated androgen-sensitive LNCaP-C33 and androgen-independent (AI) LNCaP-C81, DU145 and PC3 prostate cancer (PC) cells. The supra-additive anti-proliferative effects of drugs were mediated via a blockade of the PC3 cells in the G(1) and G(2)M phases of the cell cycle. Importantly, the combination of mitoxantrone plus gefitinib and/or cyclopamine also caused a higher rate of apoptotic death of PC cells including enriched fraction of CD44(high) PC3 cell subpopulation as compared to the individual agents or bi-combination of drugs. The cytotoxic effects induced by mitoxantrone, gefitinib and cyclopamine on PC3 cells appear to be at least partly mediated through the depolarization of the mitochondrial membrane, release of cytochrome c into the cytosol, hydrogen peroxide production and activation of caspase cascades. These findings indicate that the simultaneous blockade of EGF-EGFR and sonic hedgehog tumorigenic signaling cascades may represent a promising strategy for improving the efficacy of current mitoxantrone-based therapies against incurable AI and metastatic PCs in the clinics.

Gefitinib combined with endocrine manipulation in patients with hormone-refractory prostate cancer: quality of life and surrogate markers of activity

We investigated efficacy of gefitinib in hormone-refractory prostate cancer. Between March 2003 and December 2004, 23 patients with hormone-refractory prostate cancer were assigned to receive 250 mg oral gefitinib daily in addition to antiandrogen and luteinizing hormone-releasing hormone analogue for at least 2 months or until disease progression. Patients with progression stopped antiandrogen therapy, and received gefitinib and the luteinizing hormone-releasing hormone analogue. Serum HER2 and epidermal growth factor receptor extracellular domain were evaluated every 2 months. Gefitinib treatment did not result in any objective measurable response or responses in prostate-specific antigen. Median time to progression was 70 days (33-336). Median overall survival was 293 days (25-75 percentile: 235-349). HER2 extracellular domain mean value was 9.6 ng/ml (range 6.9-13.3) at basal time and was 10.1 (range 6.0-14.1) after 2 months. Epidermal growth factor receptor mean basal value was 51.0 ng/ml (range 41.4-75.3). After 2 months of treatment the mean value was 51.1 ng/ml (range 41.5-61.4). One patient had reduction in the pain score from baseline without an increase in the analgesic score. Four patients (17%) out of 23 had pain progression with an increase from baseline of at least 25% in the analgesic score. The study was discontinued before target accrual was reached owing to lack of efficacy of the drug. Our results do not support the efficacy of gefitinib in combination with endocrine treatment for hormone-refractory prostate cancer.

Recent advances on the molecular mechanisms involved in the drug resistance of cancer cells and novel targeting therapies

This review summarizes the recent knowledge obtained on the molecular mechanisms involved in the intrinsic and acquired resistance of cancer cells to current cancer therapies. We describe the cascades that are often altered in cancer cells during cancer progression that may contribute in a crucial manner to drug resistance and disease relapse. The emphasis is on the implication of ATP-binding cassette (ABC) multidrug efflux transporters in drug disposition and antiapoptotic factors, including epidermal growth factor receptor cascades and deregulated enzymes in ceramide metabolic pathways. The altered expression and activity of these signaling elements may have a critical role in the resistance of cancer cells to cytotoxic effects induced by diverse chemotherapeutic drugs and cancer recurrence. Of therapeutic interest, new strategies for reversing the multidrug resistance and developing more effective clinical treatments against the highly aggressive, metastatic, and recurrent cancers, based on the molecular targeting of the cancer progenitor cells and their further differentiated progeny, are also described.

Combined targeting of epidermal growth factor receptor and hedgehog signaling by gefitinib and cyclopamine cooperatively improves the cytotoxic effects of docetaxel on metastatic prostate cancer cells

The epidermal growth factor receptor (EGFR) and hedgehog cascades provide a critical role in prostate cancer progression and contribute to the resistance to clinical therapies and disease relapse. Therefore, we evaluated, for the first time, the antiproliferative and cytotoxic effects induced by a combination of selective inhibitors of EGFR tyrosine kinase and smoothened hedgehog signaling element, gefitinib and cyclopamine, with a current chemotherapeutic drug used in the clinics, docetaxel, on some metastatic prostate cancer cell lines. Immunohistochemical analyses revealed that sonic hedgehog (SHH) expression was enhanced in 39% of primary prostatic adenocarcinomas (Gleason scores 4-10) compared with the corresponding normal tissues of the same prostate gland from 32 prostate cancer patients. The confocal microscopy and Western blot analyses have also indicated the high expression levels of SHH and EGFR in metastatic LNCaP, DU145, and PC3 cells. Moreover, the results revealed that the drugs, alone or in combination, at lower concentrations inhibited the growth of EGF plus SHH-stimulated and serum-stimulated androgen-responsive LNCaP-C33 and androgen-independent LNCaP-C81, DU145, and PC3 cells. Importantly, the combined docetaxel, gefitinib, and cyclopamine also caused a higher rate of apoptotic death of prostate cancer cells compared with individual agents. The cytotoxic effects induced by these drugs in PC3 cells seem to be mediated in part through the cellular ceramide production and activation of caspase cascades via a mitochondrial pathway and the release of cytochrome c into the cytosol. Additionally, the combined agents were more effective at suppressing the invasiveness of PC3 cells through Matrigel in vitro than the single drugs. These findings indicate that the combined use of inhibitors of EGF-EGFR and hedgehog signaling with docetaxel could represent a more promising strategy for treatment in patients with metastatic and androgen-independent prostate cancer.

Interplay of distinct growth factors during epithelial mesenchymal transition of cancer progenitor cells and molecular targeting as novel cancer therapies

In this review, we describe the critical functions assumed by the interplay of epidermal growth factor, hedgehog, Wnt/beta-catenin, tumor growth factor-beta and integrin signaling cascades in tumorigenic and migrating cancer progenitor cells and activated stromal cells during carcinogenesis. These growth factors provide an important role for the sustained growth and survival of tumorigenic cancer progenitor cells and their progeny by up-regulating numerous mitotic and antiapoptotic signaling cascades. Furthermore, these potent morphogens may cooperate for inducing the molecular events associated with the epithelial-mesenchymal program in cancer cells including the alterations in epithelial cell shape and motility through the dissociation of intercellular adherens junctions. Of therapeutic interest, new strategies for the development of more effective clinical treatments against the locally aggressive and invasive cancers based on the molecular targeting of deregulated signaling elements in tumorigenic and migrating cancer cells and their local microenvironment are also described.

Management of prostate cancer. Part 3: metastatic disease

Despite the increased detection of prostate cancer at an early stage, men are still dying of this disease. Management of advanced disease focuses on controlling the disease process, palliation of symptoms and improving quality of life. In this review, the basis for androgen deprivation in hormone-dependent disease is discussed and the role of maximum and intermittent androgen deprivation, as well as management options for hormone-refractory disease is addressed. Local radiotherapy continues to be of importance in pain control and the maintenance of quality of life. Radiopharmaceuticals and bisphosphonates also have a role to play, the latter particularly in the reduction of skeletal-related events. Chemotherapy in hormone-refractory disease is now well established following pivotal trials demonstrating a survival benefit with docetaxel. The emergence of novel agents targeting growth factors, angiogenesis and immunotherapy present exciting possibilities for future treatment.

Targeting of EGFR tyrosine kinase by ZD1839 ("Iressa") in androgen-responsive prostate cancer in vitro

EGFR, highly expressed in a variety of human malignancies, is correlated with poor tumour differentiation, high tumour growth and metastatic rate. EGF and several other ligands, such as transforming growth factor-alpha, amphiregulin, heparin-binding EGF, and betacellulin, activate Ras/Raf mitogen-activated protein kinases (MAPKs) and phosphatidyl inositol 3'-kinase (PI3K)/Akt signalling pathways. Therefore, EGFR can regulate multiple processes, i.e., gene expression, cellular proliferation, angiogenesis, and inhibition of apoptosis, which contribute to the development of malignancy. In this review, we discuss the inhibition of EGFR by the specific tyrosine kinase inhibitor Iressa (ZD1839) focusing on its effects in prostate cancer.

Inhibition of EGFR signaling in human prostate cancer PC-3 cells by combination treatment with β-phenylethyl isothiocyanate and curcumin

Many naturally occurring compounds, including beta-phenylethyl isothiocyanate (PEITC) and curcumin, exhibit significant anti-cancer chemopreventive effects. In this study, we investigated the combined effects of PEITC and curcumin in PC-3 human prostate cancer cells and in PC-3 cells that were stably transfected with an NF-kappaB luciferase plasmid (PC-3 C4). We found an additive effect of PEITC and curcumin for the induction of apoptosis. To elucidate the potential mechanisms of this effect, we studied several critical cellular signaling pathways, including the critical NF-kappaB cell survival signal that is hyper-activated in PC-3 cells and many other cancers. PEITC and curcumin additively inhibited NF-kappaB luciferase activity. Furthermore, the combined treatment significantly increased the activity of poly(ADP-Ribose) polymerase and cleavage of caspase-3 in correlation with apoptotic cell death. Studying upstream signaling events, we found that the phosphorylations of IkappaBalpha and Akt (Ser473, Thr308) were significantly attenuated by the combination of PEITC and curcumin. As these events can be downstream of the activation of epidermal growth factor receptor (EGFR), we pretreated PC-3 cells with PEITC and curcumin and then stimulated them with EGF. EGFR phosphorylations (Y845 and Y1068) were dramatically suppressed by PEITC or curcumin, and more so by the combination. Importantly, the degree of Akt and PI3K phosphorylations induced by EGF were also significantly suppressed. We conclude that the simultaneous targeting of EGFR, Akt and NF-kappaB signaling pathways by PEITC and curcumin could be the molecular targets by which PEITC and curcumin exert their additive inhibitory effects on cell proliferation and ultimately lead to programmed cell death of tumor cells.

Recent advances on multiple tumorigenic cascades involved in prostatic cancer progression and targeting therapies

Recent advances on differently-expressed gene products and their functions during the progression from localized androgen-dependent states into androgen-independent and metastatic forms of prostate cancer are reported. The expression levels of numerous oncogenes and tumor suppressor genes in distinct prostatic cancer epithelial cell lines and tissues relative to normal prostate cells are described. This is carried out to identify the signaling elements that are altered during the initiation, progression and metastatic process of prostate cancer. Additional information on the interactions between certain deregulated signaling pathways such as androgen receptor (AR), estrogen receptors, epidermal growth factor receptor (EGFR), hedgehog and Wnt/beta-catenin cascades in controlling the proliferation, survival and invasion of tumor prostate epithelial cells during the disease progression is described. The emphasis is on the critical functions of the AR and EGF-EGFR systems at all stages during prostate carcinogenesis. Of therapeutic interest, new strategies for the diagnosis and treatment of localized and metastatic forms of prostate cancer by targeting multiple tumorigenic signaling elements are also reported.