In vivo amplification of the androgen receptor gene and progression of human prostate cancer.

Overexpression of amplified genes is often associated with the acquisition of resistance to cancer therapeutic agents in vitro. We have identified a similar molecular mechanism in vivo for endocrine treatment failure in human prostate cancer which involves amplification of the androgen receptor (AR) gene. Comparative genomic hybridization shows that amplification of the Xq11-q13 region (the location), is common in tumours recurring during androgen deprivation therapy. We found high-level AR amplification in seven of 23 (30%) recurrent tumours, but in none of the specimens taken from the same patients prior to therapy. Our results suggest that AR amplification emerges during androgen deprivation therapy by facilitating tumour cell growth in low androgen concentrations.

Evidence for a prostate cancer susceptibility locus on the X chromosome.

Over 200,000 new prostate cancer cases are diagnosed in the United States each year, accounting for more than 35% of all cancer cases affecting men, and resulting in 40,000 deaths annually. Attempts to characterize genes predisposing to prostate cancer have been hampered by a high phenocopy rate, the late age of onset of the disease and, in the absence of distinguishing clinical features, the inability to stratify patients into subgroups relative to suspected genetic locus heterogeneity. We previously performed a genome-wide search for hereditary prostate cancer (HPC) genes, finding evidence of a prostate cancer susceptibility locus on chromosome 1 (termed HPC1; ref. 2). Here we present evidence for the location of a second prostate cancer susceptibility gene, which by heterogeneity estimates accounts for approximately 16% of HPC cases. This HPC locus resides on the X chromosome (Xq27-28), a finding consistent with results of previous population-based studies suggesting an X-linked mode of HPC inheritance. Linkage to Xq27-28 was observed in a combined study population of 360 prostate cancer families collected at four independent sites in North America, Finland and Sweden. A maximum two-point lod score of 4.60 was observed at DXS1113, theta=0.26, in the combined data set. Parametric multipoint and non-parametric analyses provided results consistent with the two-point analysis. Significant evidence for genetic locus heterogeneity was observed, with similar estimates of the proportion of linked families in each separate family collection. Genetic mapping of the locus represents an important initial step in the identification of an X-linked gene implicated in the aetiology of HPC.

Changes in circulating microRNA levels associated with prostate cancer.

BACKGROUND: The aim of this study was to investigate the hypothesis that changes in circulating microRNAs (miRs) represent potentially useful biomarkers for the diagnosis, staging and prediction of outcome in prostate cancer. METHODS: Real-time polymerase chain reaction analysis of 742 miRs was performed using plasma-derived circulating microvesicles of 78 prostate cancer patients and 28 normal control individuals to identify differentially quantified miRs. RESULTS: A total of 12 miRs were differentially quantified in prostate cancer patients compared with controls, including 9 in patients without metastases. In all, 11 miRs were present in significantly greater amounts in prostate cancer patients with metastases compared with those without metastases. The association of miR-141 and miR-375 with metastatic prostate cancer was confirmed using serum-derived exosomes and microvesicles in a separate cohort of patients with recurrent or non-recurrent disease following radical prostatectomy. An analysis of five selected miRs in urine samples found that miR-107 and miR-574-3p were quantified at significantly higher concentrations in the urine of men with prostate cancer compared with controls. CONCLUSION: These observations suggest that changes in miR concentration in prostate cancer patients may be identified by analysing various body fluids. Moreover, circulating miRs may be used to diagnose and stage prostate cancer.

Single-cell ATAC and RNA sequencing reveal pre-existing and persistent cells associated with prostate cancer relapse.

Prostate cancer is heterogeneous and patients would benefit from methods that stratify those who are likely to respond to systemic therapy. Here, we employ single-cell assays for transposase-accessible chromatin (ATAC) and RNA sequencing in models of early treatment response and resistance to enzalutamide. In doing so, we identify pre-existing and treatment-persistent cell subpopulations that possess regenerative potential when subjected to treatment. We find distinct chromatin landscapes associated with enzalutamide treatment and resistance that are linked to alternative transcriptional programs. Transcriptional profiles characteristic of persistent cells are able to stratify the treatment response of patients. Ultimately, we show that defining changes in chromatin and gene expression in single-cell populations from pre-clinical models can reveal as yet unrecognized molecular predictors of treatment response. This suggests that the application of single-cell methods with high analytical resolution in pre-clinical models may powerfully inform clinical decision-making.

Prostate cancer evolution from multilineage primary to single lineage metastases with implications for liquid biopsy.

The evolutionary progression from primary to metastatic prostate cancer is largely uncharted, and the implications for liquid biopsy are unexplored. We infer detailed reconstructions of tumor phylogenies in ten prostate cancer patients with fatal disease, and investigate them in conjunction with histopathology and tumor DNA extracted from blood and cerebrospinal fluid. Substantial evolution occurs within the prostate, resulting in branching into multiple spatially intermixed lineages. One dominant lineage emerges that initiates and drives systemic metastasis, where polyclonal seeding between sites is common. Routes to metastasis differ between patients, and likely genetic drivers of metastasis distinguish the metastatic lineage from the lineage that remains confined to the prostate within each patient. Body fluids capture features of the dominant lineage, and subclonal expansions that occur in the metastatic phase are non-uniformly represented. Cerebrospinal fluid analysis reveals lineages not detected in blood-borne DNA, suggesting possible clinical utility.

Expression Analysis of Platinum Sensitive and Resistant Epithelial Ovarian Cancer Patient Samples Reveals New Candidates for Targeted Therapies.

Ovarian cancer has the highest mortality rate of all gynecologic malignancies. Identification of new biomarkers is highly needed due to its late diagnosis and high recurrence rate. The objective of this study was to identify mechanisms of therapy resistance and potential biomarkers by analyzing mRNA and protein expression from samples derived from patients with platinum-sensitive and -resistant ovarian cancer (total cohort n = 53). The data revealed new candidates for targeted therapies, such as GREB1 and ROR2. We showed that the development of platinum resistance correlated with upregulation of ROR2, whereas GREB1 was downregulated. Moreover, we demonstrated that high levels of ROR2 in platinum-resistant samples were associated with upregulation of Wnt5a, STAT3 and NF-kB levels, suggesting that a crosstalk between the non-canonical Wnt5a-ROR2 and STAT3/NF-kB signaling pathways. Upregulation of ROR2, Wnt5a, STAT3 and NF-kB was further detected in a platinum-resistant cell-line model. The results of the present study provided insight into molecular mechanisms associated with platinum resistance that could be further investigated to improve treatment strategies in this clinically challenging gynecological cancer.

The methyl-CpG-binding protein MECP2 is required for prostate cancer cell growth.

The incidence of prostate cancer is increasing in western countries because of population aging. Prostate cancer begins as an androgen-dependent disease, but it can become androgen independent at a later stage or in tumors recurring after an antihormonal treatment. Although many genetic events have been described to be involved in androgen-dependent and/or -independent prostate cancer growth, little is known about the contribution of epigenetic events. Here we have examined the possibility that the methyl-CpG-binding protein MECP2 might play a role in controlling the growth of prostate cancer cells. Inhibition of MECP2 expression by stable short hairpin RNA stopped the growth of both normal and cancer human prostate cells. In addition, ectopic expression of the MECP2 conferred a growth advantage to human prostate cancer cells. More importantly, this expression allowed androgen-dependent cells to grow independently of androgen stimulation and to retain tumorigenic properties in androgen-depleted conditions. Analysis of signaling pathways showed that this effect is independent of androgen receptor signaling. Instead, MECP2 appears to act by maintaining a constant c-myc level during antihormonal treatment. We further show that MECP2-expressing cells possess a functional p53 pathway and are still responsive to chemotherapeutic drugs.

Association of overexpression of tumor suppressor protein p53 with rapid cell proliferation and poor prognosis in node-negative breast cancer patients.

BACKGROUND: Recent evidence indicates that a subset of axillary node-negative (ANN) breast cancer patients can benefit from adjuvant therapy. Reliable prognostic markers are needed, however, to help clinicians identify these patients and arrive at more rational treatment decisions. PURPOSE: Mutations of the p53 tumor suppressor gene often result in overexpression of the p53 protein. In this study, we evaluated the prognostic significance of p53 protein overexpression in patients with ANN breast cancer. We also studied the association between the tumor cell proliferation rate and overexpression of the p53 and c-erbB-2 proteins, both of which have been implicated in cell cycle control. The c-erbB-2 protein is the product of the ERBB2 gene. METHODS: Two hundred eighty-nine ANN cases were randomly selected from a population-based cohort of patients who had not received any kind of adjuvant chemotherapy or endocrine therapy. Overexpression of the p53 and c-erbB-2 proteins was studied immunohistochemically in archival paraffin-embedded tumor samples, using the CM-1 polyclonal and the TAb 250 monoclonal antibodies, respectively. The tumor cell proliferation rate was measured as the S-phase fraction by DNA flow cytometry. Statistical analyses were performed using BMDP software. RESULTS: High-level p53 protein overexpression, found in 41 of the 289 tumors, was most common in tumors with high histologic grade, negative estrogen receptor status, c-erbB-2 protein overexpression, DNA index greater than 1.3, or high S-phase fraction. The lowest S-phase levels were found in tumors with neither p53 nor c-erbB-2 protein overexpression; the highest levels were seen in tumors showing overexpression of both proteins (P less than .0001). Both p53 and c-erbB-2 overexpression, as well as tumor size, had independent prognostic value in multivariate analysis. Eight-year survival of patients with p53 protein overexpression was 56% compared with 81% in patients with no overexpression (relative risk, 3.7; P less than .0001). If the S-phase fraction was included in a Cox regression analysis, however, only the tumor size and the S-phase fraction emerged as independent predictors of survival. CONCLUSIONS: Overexpression of the p53 and c-erbB-2 proteins indicates a high malignant potential in ANN breast cancer, but it is not a significant prognostic factor independent of the cell proliferation rate. The correlation between overexpression of these proteins and an increased S-phase fraction suggests that they may confer a proliferative advantage to cancer cells in vivo.

Small subgroup of aggressive, highly proliferative prostatic carcinomas defined by p53 accumulation.

BACKGROUND: Mutations in the p53 gene resulting in the accumulation of altered p53 proteins with prolonged half-life have been found in a large variety of human malignancies. PURPOSE: We studied the significance of p53 protein accumulation in prostatic carcinoma. METHODS: The material consisted of 137 paraffin-embedded, primary prostatic carcinomas. Accumulation of p53 protein was studied by immunohistochemical staining using a polyclonal p53-specific CM-1 antibody. Proliferation activity was determined by DNA flow cytometry and by immunohistochemical detection of proliferative cell nuclear antigen (PCNA) using a monoclonal PC10 antibody. RESULTS: Eight (6%) of the tumors showed intense p53 staining in more than 20% of the tumor cells, 15 (11%) had only lower level immunoreactivity, and 114 (83%) showed no staining. High-level p53 accumulation was associated with high histologic grade (P less than .001), DNA aneuploidy (P less than .05), and high cell proliferation rate as defined by flow cytometric S-phase analysis (P less than .01) or PCNA expression (P less than .01). High-level p53 accumulation predicted short, progression-free interval (P less than .01) and poor survival (P less than .001), with about a 12-fold relative risk of death as compared with p53-negative cases. Low-level p53 accumulation had no prognostic significance. CONCLUSIONS: Accumulation of p53 confers proliferative advantage for prostatic carcinoma cells and defines a small subgroup of highly malignant carcinomas.

Amplification and overexpression of androgen receptor gene in hormone-refractory prostate cancer.

The expression level of the androgen receptor (AR) gene in androgen-dependent and -independent prostate cancer was determined by using real-time quantitative reverse transcription-PCR assay. Eight benign prostate hyperplasias, 33 untreated and 13 hormone-refractory locally recurrent carcinomas, as well as 10 prostate cancer xenografts, were analyzed. All hormone-refractory tumors expressed AR and showed, on average, 6-fold higher expression than androgen-dependent tumors or benign prostate hyperplasias (P < 0.001). Four of 13 (31%) hormone-refractory tumors contained AR gene amplification detected by fluorescence in situ hybridization. Androgen-independent tumors with gene amplification expressed, on average, a 2-fold higher level of AR than the refractory tumors without the gene amplification. Two xenografts (LuCaP 35 and 69) showed amplification and high-level expression of the AR gene. These xenografts are the first prostate cancer model systems containing the gene amplification. The findings demonstrate that AR is highly expressed in androgen-independent prostate cancer, suggesting that the AR signaling pathway is important in the progression of prostate cancer during endocrine treatment. The two xenografts with the AR gene amplification will enable studies evaluating the functional significance of the amplification and development of new treatment strategies based on high-level expression of AR.

Amplification of urokinase gene in prostate cancer.

Prostate cancer is the most common male malignancy in the United States as well as in many European countries. It is curable as long as it is localized, but the invasion of prostate cancer and formation of metastasis turn it into a life-threatening disease. Urokinase-type plasminogen activator (uPA) is believed to play a key role in tissue degradation and cell migration under various normal and pathological conditions, including cancer invasion and metastasis. Increased expression of uPA has been reported in various malignancies including prostate cancer. However, the mechanisms of the overexpression have remained poorly understood. Here, we report increased copy number of uPA gene in 3 of 13 hormone-refractory prostate carcinomas, including 1 high-level amplification. Real-time quantitative reverse transcription-PCR showed that the increased expression of uPA coincided with the amplification of the gene in these tumors. Matrigel invasion assay showed that prostate cancer cell line PC-3, containing amplification of the uPA gene, was more sensitive to the urokinase inhibitor, amiloride, than DU145 or LNCaP cell lines, which do not have the amplification. The findings suggest that one of the mechanisms underlying the overexpression of the uPA is the amplification of the gene, which is associated with the increased invasive potential of the cells.

Direct visualization of the clonal progression of primary cutaneous melanoma: application of tissue microdissection and comparative genomic hybridization.

Human cutaneous malignant melanoma progresses through a series of well defined clinical and histopathological stages. It has been assumed that the neoplastic progression of this disease advances from a common acquired nevus or dysplastic nevus through the primary radial growth phase (RGP), primary vertical growth phase (VGP), and finally to distant metastasis. However, it has never been directly shown that VGP is clonally derived from RGP. Furthermore, it has not been possible previously to conduct a detailed genetic analysis on pure tumor cells from archival material because the lesions are a heterogeneous mixture of normal and neoplastic cells, and the entire specimen must be excised and fixed for clinical diagnosis. This report describes a new approach designed to identify DNA copy number changes in tumor cells from a series of progressive primary stages of cutaneous melanoma archival biopsies. Under direct high-power visualization, cells are procured with a sterile needle from highly specific areas of the tissue section. DNA is extracted from microdissected cells (normal, RGP, and VGP), PCR amplified, fluorescently labeled, and examined by comparative genomic hybridization to determine DNA copy number changes. Data obtained from three representative cases suggest a clonal derivation of VGP cells from RGP. This approach could be useful in identifying the sequence of genetic changes in progressive cutaneous melanoma stages.

Genetic changes in primary and recurrent prostate cancer by comparative genomic hybridization.

Genetic changes leading to the development of prostate cancer and factors that underlie the clinical progression of the disease are poorly characterized. Here, we used comparative genomic hybridization (CGH) to screen for DNA sequence copy number changes along all chromosomes in 31 primary and 9 recurrent uncultured prostate carcinomas. The aim of the study was to identify those chromosome regions that contain genes important for the development of prostate cancer and to identify genetic markers of tumor progression. CGH analysis indicated that 74% of primary prostate carcinoma showed DNA sequence copy number changes. Losses were 5 times more common than gains and most often involved 8p (32%), 13q (32%), 6q (22%), 16q (19%), 18q (19%), and 9p (16%). Allelic loss studies with 5 polymorphic microsatellite markers for 4 different chromosomes were done from 13 samples and showed a 76% concordance with CGH results. In local recurrences that developed during endocrine therapy, there were significantly more gains (P < 0.001) and losses (P < 0.05) of DNA sequences than in primary tumors, with gains of 8q (found in 89% of recurrences versus 6% of primary tumors), X (56% versus 0%), and 7 (56% versus 10%), as well as loss of 8p (78% versus 32%), being particularly often involved. In conclusion, our CGH results indicate that losses of several chromosomal regions are common genetic changes in primary tumors, suggesting that deletional inactivation of putative tumor suppressor genes in these chromosomal sites is likely to underlie development of prostate cancer. Furthermore, the pattern of genetic changes seen in recurrent tumors with the frequent gains of 7, 8q, and X suggests that the progression of prostate cancer and development of hormone-independent growth may have a distinct genetic basis. These chromosome aberrations may have diagnostic utility as markers of prostate cancer progression.

Androgen receptor gene amplification: a possible molecular mechanism for androgen deprivation therapy failure in prostate cancer.

Progression of prostate cancer during endocrine therapy is a major clinical problem, the molecular mechanisms of which remain poorly understood. Amplification of the androgen receptor (AR) gene was recently described in recurrent prostate carcinomas from patients who had failed androgen deprivation therapy. To evaluate the hypothesis that amplification of the AR gene is a cause for the failure of androgen deprivation therapy in prostate cancer, we studied whether AR amplification leads to gene overexpression, whether the amplified AR gene is structurally intact, and whether tumors with AR amplification have distinct biological and clinical characteristics. Tumor specimens were collected from 54 prostate cancer patients at the time of a local recurrence following therapy failure. In 26 cases, paired primary tumor specimens from the same patients prior to therapy were also available. Fifteen (28%) of the recurrent therapy-resistant tumors, but none of the untreated primary tumors, contained AR gene amplification as determined by fluorescence in situ hybridization. According to single-stranded conformation polymorphism analysis, the AR gene was wild type in all but one of the 13 AR amplified cases studied. In one tumor, a presumed mutation in the hormone-binding domain at codon 674 leading to a Gly --> Ala substitution was found, but functional studies indicated that this mutation did not change the transactivational properties of the receptor. AR amplification was associated with a substantially increased level of mRNA expression of the gene by in situ hybridization. Clinicopathological correlations indicated that AR amplification was most likely to occur in tumors that had initially responded well to endocrine therapy and whose response duration was more than 12 months. Tumors that recurred earlier or those that showed no initial therapy response did not contain AR amplification. The median survival time after recurrence was two times longer for patients with AR amplification in comparison to those with no amplification (P = 0.03, Willcoxon-Breslow test). In conclusion, failure of conventional androgen deprivation therapy in prostate cancer may be caused by a clonal expansion of tumor cells that are able to continue androgen-dependent growth despite of the low concentrations of serum androgens. Amplification and the increased expression of a wild-type AR gene may play a key role in this process.

Tumor features and survival after radical prostatectomy among antidiabetic drug users.

BACKGROUND: To evaluate the association between use of metformin and other antidiabetic drugs with tumor characteristics and survival in surgically managed prostate cancer (PCa) patients. METHODS: The study population included 1314 men who underwent radical prostatectomy at the Tampere University Hospital during 1995-2009. Causes of deaths were collected from the Finnish Cancer Registry. Individual-level data on medication use during 1995-2009 was obtained from national prescription database. Fasting blood glucose and hemoglobin A1c values during the study period were gathered from hospital district database. Gleason grade and pathological stage were compared by drug use before surgery and separately by metformin usage. Risk of biochemical recurrence, all-cause death and PCa-specific death were calculated using Cox proportional hazard regression with adjustment for age, tumor characteristics, glycemic control and use of other drug groups. RESULTS: High-grade tumors were more common among antidiabetic drug users (P=0.032), including metformin users (P=0.012). Despite this, no difference in PSA levels was observed. Men who had used antidiabetic drugs before surgery had an increased risk of Gleason 7-10 disease (odds ratio (OR) 1.83, 95% confidence interval (CI) 1.04-3.23). The risk of high-grade PCa was higher among metformin users compared with other antidiabetic drug users (OR 3.11, 95% CI 1.16-8.33). During the median follow-up of 8.6 years after surgery, 551 men had biochemical recurrence and 244 died, 32 owing to PCa. Generally, no association with risk of disease recurrence was observed. Risk of death was increased by preoperative use of antidiabetic drugs (hazard ratio 1.81 95% CI 1.03-3.19), but no survival associations for postoperative use of antidiabetic drugs or metformin were observed. CONCLUSION: Diabetic men have more high-grade PCa at lower PSA levels, but that does not have a clear impact on disease-specific survival in the short term even when glycemic control is being considered.

Cathepsin D expression detected by immunohistochemistry has independent prognostic value in axillary node-negative breast cancer.

PURPOSE: Increased expression of the lysosomal protease cathepsin D (CD) has been implicated in the metastatic progression of breast cancer. This study was designed to determine the prognostic significance of CD expression in axillary node-negative (ANN) breast cancer. The relationship of CD expression and onset of soft tissue recurrences and visceral metastatases was also studied. PATIENTS AND METHODS: We analyzed a population-based group of 262 ANN breast cancer patients, none of whom had received any adjuvant chemotherapy or endocrine therapy. An immunohistochemical method based on a new monoclonal antibody (1C11) with a distinct epitope specificity made it possible to study CD expression from archival paraffin-embedded specimens and to distinguish staining in tumor cells from the high-level expression found in tumor-infiltrating macrophages. RESULTS: High-level CD expression, as defined by cytoplasmic immunoreactivity in greater than 10% of the cancer cells, was found in 95 cases (36%). High-level CD expression was associated with large primary tumor size (P = .014), but not with histologic grade, estrogen and progesterone receptors, DNA index, or S-phase fraction, or with c-erbB-2 and p53 overexpression. Patients with CD-positive tumors developed significantly more often both soft tissue recurrences and visceral metastases (P = .0007) and had a significantly shorter disease-free survival (P < .0001). Eight-year overall survival of patients with high-level CD expression was 64% as compared with 90% in those with low-level expression (relative risk, 2.97; 95% confidence interval [Cl], 1.6 to 4.4; P < .0001). According to a Cox multivariate model and a regression-tree analysis, high-level CD expression was an independent predictor of poor overall survival in conjunction with tumor size and S-phase fraction. CONCLUSION: These results indicate that CD expression determined by immunohistochemistry is a powerful prognostic factor in ANN breast cancer. The most significant prognostic information was obtained when CD expression (predicting metastatic activity) was combined with estimate of cell-proliferation rate (S-phase fraction).

Gene Copy Number Analysis by Fluorescence in Situ Hybridization and Comparative Genomic Hybridization

Fluorescence in situ hybridization (FISH) with gene- and locus-specific probes provides a rapid means to assess copy numbers of specific sequences in individual interphase nuclei. Recent technical improvements have made FISH applicable to the analysis of both fresh and archival tissue specimens in research as well as in diagnostic laboratories. FISH is limited to analysis of one or a few loci at a time, making genome-wide surveys impractical. Comparative genomic hybridization (CGH) was developed as a means to screen entire genomes for DNA sequence copy number changes. CGH is based on the cohybridization of differentially labeled test and reference DNAs to normal metaphase chromosomes. Measurement of the test to reference fluorescence ratios along all chromosomes provides information on chromosomal regions that are over- or underrepresented in the test genome. The use of these two techniques will be illustrated in the analysis of genetic changes in solid tumors. The techniques are complementary to one another and have proven to be highly useful for identification of previously unknown genetic changes and genes that play an important role in tumor progression.

miR-25 Modulates Invasiveness and Dissemination of Human Prostate Cancer Cells via Regulation of αv- and α6-Integrin Expression.

Altered microRNA (miRNA; miR) expression is associated with tumor formation and progression of various solid cancers. A major challenge in miRNA expression profiling of bulk tumors is represented by the heterogeneity of the subpopulations of cells that constitute the organ, as well as the tumor tissue. Here, we analyzed the expression of miRNAs in a subpopulation of epithelial stem/progenitor-like cells in human prostate cancer [prostate cancer stem cell (PCSC)] and compared their expression profile to more differentiated cancer cells. In both cell lines and clinical prostate cancer specimens, we identified that miR-25 expression in PCSCs was low/absent and steadily increased during their differentiation into cells with a luminal epithelial phenotype. Functional studies revealed that overexpression of miR-25 in prostate cancer cell lines and selected subpopulation of highly metastatic and tumorigenic cells (ALDH(high)) strongly affected the invasive cytoskeleton, causing reduced migration in vitro and metastasis via attenuation of extravasation in vivo. Here, we show, for the first time, that miR-25 can act as a tumor suppressor in highly metastatic PCSCs by direct functional interaction with the 3'-untranslated regions of proinvasive αv- and α6-integrins. Taken together, our observations suggest that miR-25 is a key regulator of invasiveness in human prostate cancer through its direct interactions with αv- and α6-integrin expression.

Human prostate carcinoma cells as targets for herpes simplex virus thymidine kinase-mediated suicide gene therapy.

To evaluate human prostate carcinoma cells as targets for herpes simplex virus thymidine kinase (HSV-TK) -mediated gene therapy, we tested the utility of different viral vectors on three human cell lines DU-145, LNCaP, and PC-3. Our viral vectors were carrying a fusion gene of HSV-TK and green fluorescent protein for accurate determination of the gene transfer rate and its contribution to the treatment outcome in each case. We observed that adenoviral and lentiviral vectors were efficient vehicles for all the cell lines, whereas Semliki Forest virus and Sindbis virus vectors yielded only a few percent of transgene-positive cells. Despite sufficient gene transfer rates (25-45%) in the ganciclovir (GCV) sensitivity experiment, only DU-145 cells were efficiently destroyed under clinically relevant GCV concentrations. This was shown to be due to low level of "bystander effect" in PC-3 and LNCaP cells. Our data demonstrate that human prostate tumors can be good targets for adenovirus- or lentivirus-mediated HSV-TK/GCV gene therapy, but each tumor should be investigated for gene transfer rate and bystander effect to warrant a sufficient treatment result.