Growth factors and their receptors in prostate cancer

Increase in prostate stem cell antigen expression in prostatic hyperplasia induced by testosterone and 17β-estradiol in C57BL mice

Estradiol (E2) is known to act synergistically with testosterone (T) for the development of prostatic hyperplasia in rats and dogs, but murine prostate is less responsive to hormonal stimulation. However, a recent study revealed that the combined administration of E2 and T induced prostatic hyperplasia with bladder outlet obstruction in C57BL mice. To understand the mechanisms underlying the hormonal induction of prostatic hyperplasia, the expression of growth factors and their receptors, androgen receptor, estrogen receptor (ER), and prostatic secretory proteins was investigated. Ten-week-old male C57BL mice were treated with T (30mg) or T+E2 (0.5mg) for 10 weeks, and prostatic lobes were dissected and subjected to quantitative RT-PCR and immunoblotting analysis. T administration appeared to induce glandular prostatic growth, while with T+E2 administration this growth was greater and accompanied by extreme bladder enlargement. The expression of prostate stem cell antigen (PSCA) mRNA and protein was increased in prostate tissue in the T group. The combined administration of E2 with T prominently enhanced PSCA expression, along with increased insulin growth factor 1 mRNA levels and decreased estrogen receptor β mRNA expression. The synergistic effect of E2 on the expression of PSCA suggests that this protein may play an important role in the hormone-induced development of prostatic hyperplasia.

Furin as proprotein convertase and its role in normal and pathological biological processes

Furin belongs to serine intracellular Ca2+-dependent endopeptidases of the subtilisin family, also known as proprotein convertase (PC). Human furin is synthesized as zymogen with a molecular weight of 104 kDa, which is then activated by autocatalytic in two stages. This process can occur when zymogen migrates from the endoplasmic reticulum to the Golgi apparatus, where a large part of furin is accumulated. The molecular weigh t of the active furin is 98 kDa. Furin relates to enzymes with a narrow substrate specificity: it hydrolyzes peptide bonds at the site of paired basic amino acids and furin activity exhibits in a wide pH range 5-8. Its main biological function is activation of the functionally important protein precursors. It is accompanied by the launch of a cascade of reactions, which lead to appearance of biologically active molecules involved in realization of specific biological functions both in normal and in some patologicheskih processes. Furin substrates are biologically important proteins such as enzymes, hormones, growth factors and differentiation, receptors, adhesion proteins, proteins of blood plasma. Furin plays an important role in the development of processes such as proliferation, invasion, cell migration, survival, maintenance of homeostasis, embryogenesis, as well as the development of a number of pathologies, including cardiovascular, oncologic and neurodegenerative diseases. Furin and furin-like proprotein convertases participate as key factors in the realization of the regulatory functions of proteolytic enzymes, the value of which is currently being evaluated as most important in comparison with the degradative function of proteases.

Cabozantinib Inhibits Abiraterone's Upregulation of IGFIR Phosphorylation and Enhances Its Anti-Prostate Cancer Activity

PURPOSE

Abiraterone improves the overall survival of men with metastatic castration-resistant prostate cancer. However, de novo or adaptive resistance to abiraterone limits its activity. Rational combinations of drugs with different mechanisms of action that overcome resistance mechanisms may improve the efficacy of therapy. To that end, we studied the molecular and phenotypic effects of the combination of cabozantinib plus abiraterone.

EXPERIMENTAL DESIGN

Three prostate cancer cell lines were used to interrogate the in vitro molecular and antiproliferative effects of the single agents and combination of cabozantinib and abiraterone. The in vivo impact of the combination was assessed using the LAPC4-CR xenograft mouse model.

RESULTS

In vitro proliferation studies demonstrated single-agent doses between 2 μmol/L and 10 μmol/L for abiraterone and cabozantinib inhibit prostate cancer cell proliferation in a dose-dependent manner, and the anticancer activity of abiraterone is enhanced when combined with cabozantinib. In vivo LAPC4-CR xenograft mouse studies also showed that cabozantinib can improve the antitumor activity of abiraterone. Cabozantinib, a multiple receptor tyrosine kinase inhibitor, enhances the ability of abiraterone to inhibit AR activity in a cell line-dependent manner. In addition, our cell line studies demonstrate abiraterone-stimulated insulin-like growth factor I receptor (IGFIR) phosphorylation with downstream activation of MEK1/2 and ERK1/2, and that this potential adaptive resistance mechanism was inhibited by cabozantinib.

CONCLUSIONS

Cabozantinib can enhance the efficacy of abiraterone by blocking multiple compensatory survival mechanisms, including IGFIR activation, and supports the assessment of the combination in a clinical trial.

Randomized phase II study of nintedanib in metastatic castration-resistant prostate cancer postdocetaxel

This open-label, phase II trial assessed the efficacy and safety of two doses of nintedanib, a triple angiokinase inhibitor targeting vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor signaling, in patients with metastatic castration-resistant prostate cancer (mCRPC) following progression on docetaxel-based regimens. Patients were randomized to nintedanib 150 mg (arm A, n=40) or 250 mg (arm B, n=41) twice daily for 6 months unless disease progression or adverse events (AEs) led to discontinuation. The primary endpoint was the prostate-specific antigen (PSA) response rate (confirmed PSA decline of ≥20% from baseline). Eighty-one patients were enrolled. The PSA response rate was 0% (0/32) in arm A versus 11.1% (4/36) in arm B (P=0.12); 5.6% of patients (2/36) in arm B showed a PSA reduction of at least 50%. In arm B, the rate of PSA increase was significantly decelerated on treatment versus before treatment (P=0.002). The median progression-free survival was 73.5 and 76.0 days for arm A and arm B, respectively (P=0.3). AEs included gastrointestinal disorders, asthenia, hypertension, and reversible elevated transaminases. The incidence of drug-related serious AEs (no drug-related deaths) was 20.0% (arm A) and 24.4% (arm B). The primary endpoint was not met. Nintedanib (250 mg) showed only modest activity with manageable AEs in patients with mCRPC post-docetaxel.

A phase II trial of dasatinib in patients with metastatic castration-resistant prostate cancer treated previously with chemotherapy

There is a need for efficacious therapies for metastatic castration-resistant prostate cancer (mCRPC) after disease progression on docetaxel. The SRC tyrosine kinase and its related family members may be important drivers of prostate cancer and can be inhibited by dasatinib. mCRPC patients, after one previous chemotherapy, started dasatinib at 70 mg twice daily, amended to 100 mg daily. The primary endpoint was the disease control (DC) rate, defined as complete response (CR), partial response (PR), or stable disease (SD) in prostate specific antigen (PSA), RECIST, bone scan, and FACT-P score. Up to 41 patients were to be accrued (two-stage design, 21+20) to rule out a null-hypothesized effect of 5 versus 20% (α=0.05, β=0.1). Secondary endpoints included progression-free survival, toxicity, and pharmacokinetic and pharmacodynamic correlatives. Of 38 patients, 27 were evaluable for response or toxicity. The median duration of therapy was 55 days (6-284). Five patients showed DC after 8 weeks of therapy (18.5% DC, 95% CI: 6.3-38.1%). One PR (3.7% response rate, 95% CI: 0.1-19.0%) was observed in a patient treated for 284 days. Twelve patients (43%) discontinued treatment for toxicity. Dasatinib induced a decrease in phytohemagglutinin-stimulated CSF2, CD40L, GZMB, and IL-2 mRNAs in blood cells, indicating target engagement. Decreases in plasma IL-6 and bone alkaline phosphatase, and in urinary N-telopeptide, were associated with DC. Dasatinib has definite but limited activity in advanced mCRPC, and was poorly tolerated. The observation of a patient with prolonged, objective, clinically significant benefit warrants molecular profiling to select the appropriate patient population.

The antitumor lignan Nortrachelogenin sensitizes prostate cancer cells to TRAIL-induced cell death by inhibition of the Akt pathway and growth factor signaling

Prostate cancer cells frequently develop resistance toward androgen-deprivation and chemotherapy. To identify new approaches to treat androgen-dependent prostate cancer, we have performed a structure-activity analysis of lignan polyphenols for cancer cell specific sensitization to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a death ligand that has ability to induce tumor-specific cell death. In this study, we report that the lignan nortrachelogenin (NTG) is the most efficient of the 27 tested lignan compounds in sensitizing prostate cancer cells to TRAIL-induced apoptosis. Importantly, pretreatment with NTG does not sensitize a non-malignant prostate cell line to TRAIL-induced cell death. The structural comparison of lignans reveals that the dibenzylbutyrolactone skeleton is required for the apoptosis-sensitizing activity, while substitutions at the aromatic rings do not seem to play a critical role in this lignan function. Our study also characterizes the cellular effects and molecular mechanisms involved in NTG anticancer activity. We previously reported that specific lignans inhibit the Akt survival-signaling pathway in concert with TRAIL sensitization. While NTG is also shown to be a effective inhibitor of Akt signaling, in this study we further demonstrate that NTG potently inhibits tyrosine kinase (RTK) activation in response to growth factors, such as insulin and insulin-like growth factor I (IGF-I). Our results identify NTG as a novel agent for prostate cancer therapy with ability to inhibit Akt membrane localization and activity as well as the activation of growth factor receptors (GFRs), thereby efficiently synergizing with TRAIL exposure.

Evidence for the Possible Biological Significance of the igf-1 Gene Alternative Splicing in Prostate Cancer

Insulin-like growth factor-I (IGF-I) has been implicated in the pathogenesis of prostate cancer (PCa), since it plays a key role in cell proliferation, differentiation, and apoptosis. The IGF-I actions are mediated mainly via its binding to the type I IGF receptor (IGF-IR), however IGF-I signaling via insulin receptor (IR) and hybrid IGF-I/IR is also evident. Different IGF-I mRNA splice variants, namely IGF-IEa, IGF-IEb, and IGF-IEc, are expressed in human cells and tissues. These transcripts encode several IGF-I precursor proteins which contain the same bioactive product (mature IGF-I), however, they differ by the length of their signal peptides on the amino-terminal end and the structure of the extension peptides (E-peptides) on the carboxy-terminal end. There is an increasing interest in the possible different role of the IGF-I transcripts and their respective non-(mature)IGF-I products in the regulation of distinct biological activities. Moreover, there is strong evidence of a differential expression profile of the IGF-I splice variants in normal versus PCa tissues and PCa cells, implying that the expression pattern of the various IGF-I transcripts and their respective protein products may possess different functions in cancer biology. Herein, the evidence that the IGF-IEc transcript regulates PCa growth via Ec peptide specific and IGF-IR/IR-independent signaling is discussed.

Plasma and tissue insulin-like growth factor-I receptor (IGF-IR) as a prognostic marker for prostate cancer and anti-IGF-IR agents as novel therapeutic strategy for refractory cases: a review

Cancer database analysis indicates that prostate cancer is one of the most seen cancers in men meanwhile composing the leading cause of morbidity and mortality among developed countries. Current available therapies are surgery, radiotherapy and androgene ablation for prostate carcinoma. The response rate is as high nearly 90% however, most of these recur or become refractory and androgene independent (AI). Therefore recent studies intensified on molecular factors playing role on development of prostate carcinoma and novel treatment strategies targetting these factors and their receptors. Insulin-like growth factor-I (IGF-I) and its primary receptor insulin-like growth factor receptor-I (IGF-IR) are among these factors. Biologic functions and role in malign progression are primarily achieved via IGF-IR which is a type 2 tyrosine kinase receptor. IGF-IR plays an important role in mitogenesis, angiogenesis, transformation, apoptosis and cell motility. It also generates intensive proliferative signals leading to carcinogenesis in prostate tissue. So IGF-IR and its associated signalling system have provoked considerable interest over recent years as a novel therapeutic target in cancer. In this paper it is aimed to sum up the lately published literature searching the relation of IGF-IR and prostate cancer in terms of incidence, pathologic features, and prognosis. This is followed by a discussion of the different possible targets within the IGF-1R system, and drugs developed to interact at each target. A systems-based approach is then used to review the in vitro and in vivo data in the published literature of the following compounds targeting IGF-1R components using specific examples: growth hormone releasing hormone antagonists (e.g. JV-1-38), growth hormone receptor antagonists (e.g. pegvisomant), IGF-1R antibodies (e.g. CP-751,871, AVE1642/EM164, IMC-A12, SCH-717454, BIIB022, AMG 479, MK-0646/h7C10), and IGF-1R tyrosine kinase inhibitors (e.g. BMS-536942, BMS-554417, NVP-AEW541, NVP-ADW742, AG1024, potent quinolinyl-derived imidazo (1,5-a)pyrazine PQIP, picropodophyllin PPP, nordihydroguaiaretic acid Insm-18/NDGA). And the other end point is to yield an overview on the recent progress about usage of this receptor as a novel anticancer agent of targeted therapies in treatment of prostate carcinoma.

Gene amplification and mutation analysis of epidermal growth factor receptor in hormone refractory prostate cancer

BACKGROUND

Amplification and mutation of the epidermal growth factor receptor (EGFR) and Her-2 genes were analyzed in both hormone sensitive and hormone refractory prostate cancer (HRPC).

METHODS

Gene amplifications of EGFR and Her-2 were analyzed by fluorescence in situ hybridization (FISH) with direct sequencing. Studies were performed on a total of 10 patients; tissues were sampled at the time of initial diagnosis and after the conversion to HRPC (a total of 20 tissue samples). Direct sequencing was performed on exons 18-24 of EGFR and exons 19 and 20 of Her-2. Amplification and mutation were compared with clinicopathologic features.

RESULTS

Gene amplification of EGFR was observed in 6 (30%) out of 20 samples. A total of six EGFR mutations in exons 18 and 19 were detected in three pairs of tissues (three patients). One patient, with hormone refractory status, had a novel deletion mutation in EGFR exon 19. EGFR mutations were associated with the acinar type of prostate cancer but were not associated with the ductal type. No significant correlation was found between mutation change and hormone sensitive or refractory status. However, the time to convert to HRPC was significantly shorter in the patients with a mutation in the EGFR gene (P = 0.017). There were no Her-2 gene amplifications or mutations found in any of the samples.

CONCLUSIONS

EGFR gene mutation and amplification occurred frequently in advanced prostate cancer cases. EGFR mutations do not appear to play a significant role in the hormone refractory pathway but are associated with prognosis.

Prognostic significance of plasma scatter factor/hepatocyte growth factor levels in patients with metastatic hormone- refractory prostate cancer: results from cancer and leukemia group B 150005/9480

BACKGROUND

Scatter factor, also known as hepatocyte growth factor (SF/HGF), is a polypeptide growth factor thought to be important in the growth and spread of prostatic carcinoma.

PATIENTS AND METHODS

Scatter factor/HGF levels in pretreatment plasma samples from 171 men with metastatic hormone-refractory prostate cancer enrolled in CALGB 9480 were quantified by solid-phase, enzyme-linked immunosorbent assay.

RESULTS

The Cox proportional hazards model was used to assess the prognostic importance of SF/HGF with adjustment for established prognostic factors. Median SF/HGF was 991 pg/mL (range, 212-2733 pg/mL). In a univariate analysis, although plasma SF/HGF levels above versus below the median value did not reach statistical significance (P = 0.0862), the cutoff point of > 935 pg/mL was associated with a significant reduction in overall survival (P = 0.0334). Patients with SF/HGF levels > 935 pg/mL experienced a median survival of 15 months compared with 19 months for men with SF/HGF levels < or = 935 pg/mL. In a multivariate analysis, adjusting for SF/HGF, prostate-specific antigen, lactate dehydrogenase, and performance status, only plasma alkaline phosphatase was significantly associated with overall survival (hazard ratio, 1.7; 95% confidence interval, 1.2-2.5; P = 0.0017).

CONCLUSION

Higher plasma levels of SF/HGF in men with hormone-refractory prostate cancer are associated with a decreased patient survival. Currently, SF/HGF levels do not appear to be of value as a contributor to multivariate models for prediction of outcome, but the association with decreased survival suggests that SF/HGF might be a potential target for therapy.

Transforming growth factor beta and prostate cancer

The TGF-beta superfamily is the most versatile considering the ability of its members to regulate proliferation, growth arrest, differentiation, and apoptosis of prostatic stromal and epithelial cells as well as the formation of osteoblastic metastases. TGF-beta mediated action in prostate cells follows a complex signaling pathway from binding and phosphorylation of receptor type II to the TbetaRI kinase to Smad activation, resulting in ligand-induced transcription. TGF-beta as an indirect tumor suppressor, its role of regulating tumor induction, as well as tumor suppression depending on the tissue microenvironment merits further exploration. The rationale for targeting growth factors and their receptors for therapeutic intervention is based upon the fact that these proteins represent the most proximate component of the signal transduction cascade. The alternate targeting of intracellular effectors in the signal transduction may be thwarted by cross talk between signaling pathways (such as the Smads in a dynamic interplay with the androgen receptor). TGF-beta within the context of its well-documented apoptosis regulatory actions in the prostate and the significance its key receptor TbetaRII as a potential tumor suppressor, provides a highly attractive candidate for such targeting with high clinical significance for the treatment and diagnosis of prostate cancer.

Angiotensin II-mediated calcium signals and mitogenesis in human prostate stromal cell line hPCPs

Western blots and immunocytochemistry were used to detect angiotensin 1 (AT(1)) and angiotensin 2 (AT(2)) receptors in human primary cultures of the prostate stromal compartment (hPCPs). Immunohistochemistry was performed on human prostate tissue-embedded paraffin. In addition, pharmacological tools were applied in combination with photometry experiments to characterize the physiological activity of AT(1) and AT(2) receptors in hPCPs cell culture. A proliferation assay was used to describe the mitogenic activity of angiotensin II (Ang II) on hPCPs cells. Only the AT(1) receptor was detected in Western blot analysis. Immunocytochemistry of hPCPs cells showed that the AT(1) receptor is present in both the smooth muscle type and the fibroblastic type. In the stromal compartment of human prostate tissue, immunoreaction with antibodies against the AT(1) receptor was detectable.Fura-2-loaded hPCPs cells showed an instantaneous and linear rise in free intracellular calcium ion concentration ([Ca(2+)](i)) after local perfusion with Ang II in concentrations of 10 nM. Removing of external calcium or emptying intracellular calcium stores before Ang II application diminished or abolished this [Ca(2+)](i) response. The response to Ang II was also diminished when hPCPs cells were perfused with the AT(1) receptor inhibitor losartan prior to Ang II application. No inhibition of the [Ca(2+)](i) increase was detectable after perfusion with PD 123319, a specific inhibitor of the AT(2) receptor.hPCPs cells were stimulated with Ang II in various concentrations over a period of 2 days. The subsequently performed proliferation assay revealed a mitogenic effect of Ang II on hPCPs in concentrations starting at 10 nM. This effect could be inhibited by losartan.

Molecular biology of prostate cancer

Development of any cancer reflects a progressive accumulation of alterations in various genes. Oncogenes, tumour suppressor genes, DNA repair genes and metastasis suppressor genes have been investigated in prostate cancer. Here, we review current understanding of the molecular biology of prostate cancer. Detailed understanding of the molecular basis of prostate cancer will provide insights into the aetiology and prognosis of the disease, and suggest avenues for therapeutic intervention in the future.

Pyrrolopyrimidine c-Src inhibitors reduce growth, adhesion, motility and invasion of prostate cancer cells in vitro

Two bona fide c-Src inhibitors, denominated CGP77675 and CGP76030, reduced in a time- and concentration-dependent manner (i) the proliferation of the PC3 prostate carcinoma cell line, as assessed by the [3H]-thymidine incorporation test, (ii) the capacity of PC3 cells to adhere and spread on Matrigel substrate, as determined by crystal violet staining, (iii) the ability of PC3 cells to migrate through a gelatine boundary and invade a Matrigel substrate. The latter effect was not due to a decrease of urokinase-type plasminogen activator (uPA), nor of metalloproteinase-2 (MMP-2) activities. The MMP-9 activity, along with the expression of the Tissue Inhibitor of Metalloproteinases (TIMP)-1 and TIMP-2, were reduced by the two inhibitors, consistent with the ability of c-Src to enhance MMP-9 and TIMP expression levels. Collectively, these data demonstrate that the pyrrolopyrimidine-derived c-Src inhibitors significantly reduced PC3 cell activities associated with their malignant phenotype.

Altered localization and activity of the intracellular tyrosine kinase BRK/Sik in prostate tumor cells

Breast tumor kinase (BRK) is an intracellular tyrosine kinase expressed in differentiating epithelial cells of the gastrointestinal tract and skin, and in several epithelial cancers including carcinomas of the breast and colon. We examined expression of BRK and its mouse ortholog Src-related intestinal kinase (Sik) in prostate tissues and detected it in the nuclei of normal luminal prostate epithelial cells. BRK localization was then examined in 58 human prostate biopsy samples representing various grades of prostate cancer. While nuclear localization of BRK was present in well-differentiated tumors, it was absent in poorly differentiated tumors. However localization of Sam68, a nuclear substrate of BRK/Sik, was unaltered in all prostate tumors examined. Consistent with these results, nuclear BRK was detected in the more differentiated androgen-responsive LNCaP human prostate cancer cell line that is poorly tumorigenic in host animals, but it was primarily cytoplasmic in the undifferentiated androgen-unresponsive PC3 prostate cancer cell line that forms aggressive tumors. While PC3 cells expressed higher levels of endogenous BRK than LNCaP cells, BRK was less active in these cells. Our data suggest that BRK plays a role in differentiation of prostate epithelial cells. Altered BRK localization and/or activity may provide a prognostic indicator for prostate tumor progression and be a potential target for therapeutic intervention.

Chemosensitization of human prostate cancer using antisense agents targeting the type 1 insulin-like growth factor receptor

OBJECTIVE

To assess the effect of the downregulation of type 1 insulin-like growth factor receptor (IGF1R) on the chemosensitivity of prostate cancer cells. IGF1R is overexpressed by prostate cancer compared with benign prostatic epithelium and IGF1R expression commonly persists in androgen-independent metastatic disease at levels comparable to those in the primary.

MATERIALS AND METHODS

Human androgen-independent DU145 prostate cancer cells were transfected with IGF1R antisense oligonucleotides or antisense RNA. Transfected cultures were treated with cisplatin, mitoxantrone, paclitaxel or vehicle control, and survival measured using a clonogenic assay.

RESULTS

Both antisense strategies suppressed IGF1R protein levels to 30-50% of those in control cultures. This was associated with 1.5-2-fold enhancement of sensitivity to cisplatin, mitoxantrone and paclitaxel, and an increase in cisplatin-induced apoptosis.

CONCLUSION

This approach has potential for development as a clinical treatment for advanced prostate cancer and other chemoresistant tumours.