Fibroblast growth factor receptors (FGFRs) mediate the tumourigenic effects of FGFs in prostate cancer. These receptors are therefore potential therapeutic targets in the development of inhibitors to this pathway. To identify the most relevant targets, we simultaneously investigated FGFR1-4 expression using a prostate cancer tissue microarray (TMA) and in laser capture microdissected (LCM) prostate epithelial cells. In malignant prostates (n = 138) we observed significant FGFR1 and FGFR4 protein over-expression in comparison with benign prostates (n = 58; p < 0.0001). FGFR1 was expressed at high levels in the majority of tumours (69% of grade 3 or less, 74% of grade 4 and 70% of grade 5), while FGFR4 was strongly expressed in 83% of grade 5 cancers but in only 25% of grade 1-3 cancers (p < 0.0001). At the transcript level we observed a similar pattern, with FGFR1 and FGFR4 mRNA over-expressed in malignant epithelial cells compared to benign cells (p < 0.0005 and p < 0.05, respectively). While total FGFR2 was increased in some cancers, there was no association between expression and tumour grade or stage. Transcript analysis, however, revealed a switch in the predominant isoform expressed from FGFR2IIIb to FGFR2IIIc among malignant epithelial cells. In contrast, protein and transcript expression of FGFR3 was very similar between benign and cancer biopsies. The functional effect of targeting FGFR4 in prostate cancer cells has not previously been investigated. In in vitro experiments, suppression of FGFR4 by RNA interference effectively blocked prostate cancer cell proliferation (p < 0.0001) and invasion (p < 0.001) in response to exogenous stimulation. This effect was evident regardless of whether the cells expressed the FGFR4 Arg388 or Gly388 allele. In parallel experiments, FGFR3 suppression had no discernible effect on cancer cell behaviour. These results suggest evidence of selective over-expression of FGFR1 and FGFR4 in clinical prostate cancer and support the notion of targeted inhibition of these receptors to disrupt FGF signalling.

Abnormal intracellular signaling contributes to carcinogenesis and may represent novel therapeutic targets. mitogen/extracellular signal-regulated kinase kinase-5 (MEK5) overexpression is associated with aggressive prostate cancer. In this study, we examined the role of extracellular signal-regulated kinase (ERK5, an MAPK and specific substrate for MEK5) in prostate cancer. ERK5 immunoreactivity was significantly upregulated in high-grade prostate cancer when compared to benign prostatic hyperplasia (Po0.0001). Increased ERK5 cytoplasmic signals correlated closely with Gleason sum score (Po0.0001), bony metastases (P ¼ 0.0044) and locally advanced disease at diagnosis (P ¼ 0.0023), with a weak association with shorter disease-specific survival (P ¼ 0.036). A subgroup of patients showed strong nuclear ERK5 localization, which correlated with poor diseasespecific survival and, on multivariant analysis, was an independent prognostic factor (Po0.0001). Analysis of ERK5 expression in matched tumor pairs (before and after hormone relapse, n ¼ 26) revealed ERK5 nuclear expression was significantly associated with hormoneinsensitive disease (P ¼ 0.0078). Similarly, ERK5 protein expression was increased in an androgen-independent LNCaP subline. We obtained the following in vitro and in vivo evidence to support the above expression data: (1) cotransfection of ERK5wt and MEK5D constructs in PC3 cells results in predominant ERK5 nuclear localization, similar to that observed in aggressive clinical disease; (2) ERK5-overexpressing PC3 cells have enhanced proliferative, migrative and invasive capabilities in vitro (Po0.0001), and were dramatically more efficient in forming tumors, with a shorter mean time for tumors to reach a critical volume of 1000 mm 3 , in vivo (Po0.0001); (3) the MEK1 inhibitor, PD184352, blocking ERK1/2 activation at low dose, did not suppress proliferation but did significantly decrease proliferation at a higher dose required to inhibit ERK5 activation. Taken together, our results establish the potential importance of ERK5 in aggressive prostate cancer.

Zebrafish MITF-low melanoma models human MITF-low melanoma. While the bulk of the tumor is dependent on MITF activity, MITF-independent cells preexist and arise de novo in residual disease.

The microphthalmia-associated transcription factor (MITF) is the “master melanocyte transcription factor” with a complex role in melanoma. MITF protein levels vary between and within clinical specimens, and amplifications and gain- and loss-of-function mutations have been identified in melanoma. How MITF functions in melanoma development and the effects of targeting MITF in vivo are unknown because MITF levels have not been directly tested in a genetic animal model. Here, we use a temperature-sensitive mitf zebrafish mutant to conditionally control endogenous MITF activity. We show that low levels of endogenous MITF activity are oncogenic with BRAFV600E to promote melanoma that reflects the pathology of the human disease. Remarkably, abrogating MITF activity in BRAFV600Emitf melanoma leads to dramatic tumor regression marked by melanophage infiltration and increased apoptosis. These studies are significant because they show that targeting MITF activity is a potent antitumor mechanism, but also show that caution is required because low levels of wild-type MITF activity are oncogenic.

Overexpression of fibroblast growth factors (FGFs) has been implicated in prostate carcinogenesis. FGFs function via their high-affinity interactions with receptor tyrosine kinases, FGFR1 -4. Expression of FGFR1 and FGFR2 in prostate cancer (CaP) was not found to be associated with clinical parameters. In this report, we further investigated for abnormal FGFR expression in prostate cancer and explore their significance as a potential target for therapy. The expression levels of FGFR3 and FGFR4 in CaP were examined and corroborated to clinical parameters. FGFR3 immunoreactivity in benign prostatic hyperplasia (BPH) and CaP (n ¼ 26 and 57, respectively) had similar intensity and pattern. Overall, FGFR4 expression was significantly upregulated in CaP when compared to BPH. A significant positive correlation between FGFR4 expression and Gleason score was noted: Gleason score 7 -10 tumours compared to BPH (Po0.0001, Fisher's exact test), Gleason score 4 -6 tumours compared to BPH (Po0.0004), and Gleason 7 -10 compared to Gleason 4 -6 tumours (Po0.005). FGFR4 overexpression was associated with an unfavourable outcome with decreased disease-specific survival (Po0.04, log rank test). FGF-induced signalling is targeted using soluble FGF receptor (sFGFR), potent inhibitor of FGFR function. We have previously shown that sFGFR expression via a replication-deficient adenoviral vector (AdlllcRl) suppresses in vitro FGF-induced signalling and function in human CaP DU145 cells. We tested the significance of inhibiting FGF function along with conventional therapeutic modalities in CaP, and confirmed synergistic effects on in vitro cell growth (proliferation and colony formation) by combining sFGFR expression and treatment with either Paclitaxel (Taxol s ) or g-irradiation. In summary, our data support the model of FGF system as valid target for therapy in CaP. Prostate cancer is the commonest cancer in men and the second commonest cause of cancer-related death in men, and its incidence is increasing (Woolf, 1995;Boyle et al, 1996). Prostate cancer is an enigmatic disease. It is histologically present in 80% of men over the age of 80 years, but will only clinically manifest itself in about 10%. Increasing use of serum measurement of prostate-specific antigen is facilitating early diagnosis of prostate cancer. There are currently limited prognostic markers that may allow patients found to have early prostate cancer to be stratified into different management plans. Hence, new methods of predicting disease progression are urgently needed.Abnormal expression of peptide growth factors and their highaffinity receptor tyrosine kinases are important in the development and progression of prostate cancer. These mitogens enhance tumour proliferation and invasion while inhibiting apoptosis. Several peptide growth factors have been implicated in prostate cancer development and progression, including insulin-like growth factors, epidermal growth factor and members of the fibroblast growth factors (Byrne et al, 1996;Tennant et al, 1996;Dorkin et...