Inhibition of chemomigration of a human prostatic carcinoma cell (TSU-pr1) line by inhibition of epidermal growth factor receptor function

Tyrosine kinase inhibitors in the treatment of prostate cancer: taking the next step in clinical development

INTRODUCTION

Prostate cancer (PCa) is the most frequently diagnosed, non-cutaneous malignancy in Western countries. Until recently, few therapeutic options were available for patients with advanced PCa. Although these treatments may delay progression of disease, none are curative. Therefore, research continues to investigate other treatments for advanced PCa. Tyrosine kinase inhibitors (TKIs) have been extensively studied as a treatment for multiple malignancies and may represent an additional strategy. In addition to limiting cellular proliferation and metastasis, there is also growing interest in using these treatments to impact the bone microenvironment and reduce associated morbidity from PCa.

AREAS COVERED

Several TKIs have been evaluated in the preclinical setting in advanced PCa. Targets reviewed include the epidermal growth factor family, VEGF receptor, c-Src family kinases, platelet-derived growth factor and c-Met.

EXPERT OPINION

Despite strong biological rationale for the use of TKIs therapy for the treatment of PCa, Phase III clinical trials have produced disappointing results. As TKI strategies move forward, the failures of past trials need to be better understood. New approaches with these treatments will also have to take into account modern anti-androgens and a treatment landscape that now includes immunotherapy.

Erlotinib has moderate single-agent activity in chemotherapy-naïve castration-resistant prostate cancer: final results of a phase II trial

OBJECTIVES

To investigate the efficacy and toxicity of single-agent erlotinib in chemotherapy-naive castration-resistant prostate cancer.

METHODS

Eligible patients received erlotinib at 150 mg daily until disease progression. Toxicity was assessed every 2 weeks and responses every 8 weeks. Primary end point was assessing the overall clinical benefit measured as the sum of stable disease, partial response, and complete response. Secondary end points included time to disease progression, overall survival, and toxicity using the National Cancer Institute Common Toxicity Criteria version 3.0.

RESULTS

A total of 29 patients were enrolled in this study. Median age was 77 and median prostate-specific antigen was 66.3 ng/mL. Of 22 evaluable patients, 2 met the criteria for partial response and 5 demonstrated stable disease for an overall clinical benefit of 31%. PSA-doubling time improved in all responding patients to a median of 6 months from 3 months before entry into the study. One patient remained in study at 28 months, and 2 had > 50% decrease in their serum PSA level. Median time to disease progression was 2 months, but at 12 months, 9% of patients were progression-free. Median overall survival was 16.3 months, with 1- and 2-year survival rates of 58% and 27%, respectively. Erlotinib was well tolerated, with only 2 patients requiring dose reductions. Adverse events were as expected with grade 3 or 4 diarrhea, fatigue, and rash occurring in 10%, 6%, and 6% of patients, respectively.

CONCLUSIONS

Erlotinib has moderate activity in chemotherapy-naive castration-resistant prostate cancer, with some patients showing biochemical response. Future studies investigating this agent in combination are warranted. (This trial was registered at http://NCI.gov, NCT00272038).

Epidermal growth factor upregulates motility of Mat-LyLu rat prostate cancer cells partially via voltage-gated Na+ channel activity

The main aim of this investigation was to determine whether a functional relationship existed between epidermal growth factor (EGF) and voltage-gated sodium channel (VGSC) upregulation, both associated with strongly metastatic prostate cancer cells. Incubation with EGF for 24 h more than doubled VGSC current density. Similar treatment with EGF significantly and dose-dependently enhanced the cells' migration through Transwell filters. Both the patch clamp recordings and the migration assay suggested that endogenous EGF played a similar role. Importantly, co-application of EGF and tetrodotoxin, a highly selective VGSC blocker, abolished 65% of the potentiating effect of EGF. It is suggested that a significant portion of the EGF-induced enhancement of migration occurred via VGSC activity.

The metastatic cascade in prostate cancer

Morbidity and mortality due to prostate cancer are mainly a result of prostate cancer metastases. After the initial neoplastic transformation of cells, the process of metastasis involves a series of sequential steps, which involve neoangiogenesis and lymphangiogenesis, loss of adhesion with migration away from the primary tumour and entry into the systemic vasculature or lymphatics. Metastatic growth in sites such as lymph nodes and bone marrow then involves the specific non-random homing of prostate cancer cells. An appreciation and understanding of this metastatic cascade in relation to prostate cancer is clinically important in order to stratify men with prostate cancer into prognostic groups. Moreover, it is crucial in the future development of therapies that can prevent metastases.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Prostate cancer cell proliferation is strongly reduced by the epidermal growth factor receptor tyrosine kinase inhibitor ZD1839 in vitro on human cell lines and primary cultures

PURPOSE

To investigate the effects of the epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) ZD1839 ('Iressa') on the cellular proliferation of androgen-sensitive and androgen-independent human prostatic cancer cell lines and primary cultures in vitro.

EXPERIMENTAL DESIGN

In this study, we investigated the effects of the quinazoline ZD1839, a potent, selective EGFR-TKI, on the EGFR autophosphorylation and cellular proliferation of androgen-sensitive (ND1, LNCaP, and ALVA-31) and androgen-independent (PC3, DU145, and TSU-Pr1) human prostatic cancer cell lines and 20 primary cultures derived from human prostatic cancer tissue.

RESULTS

EGFR was present and phosphorylated in all cell lines tested. ZD1839 reduced EGFR autophosphorylation in intact cell lines with IC(50)s of 0.46-0.97 microM, and inhibited cellular proliferation with IC(50)s of 0.37-1.03 microM. Constitutive EGFR autophosphorylation was low in primary cell cultures, but addition of EGF (50 ng/ml) caused marked EGFR autophosphorylation; cellular proliferation in the presence of EGF was inhibited by ZD1839 with a mean IC(50) of 0.45 microM. At doses >1 microM, ZD1839 induced apoptosis in both androgen-dependent and androgen-independent PCa cell lines. CONCLUSION. Our experiments suggest that EGFR-TKIs such as ZD1839 may have potential in blocking the growth and progression of human prostatic cancers even in early phases of the disease.

Neurotrophin receptor p75(NTR) suppresses growth and nerve growth factor-mediated metastasis of human prostate cancer cells

The loss of tumor- and/or metastasis-suppressor gene function contributes to the transformation of human prostate epithelial cells to a malignant pathology. Such a putative tumor-suppressor and metastasis-suppressor gene(s) has been mapped to the region of 17q21, which coincidentally is in the vicinity of the human gene locus for the neurotrophin receptor p75(NTR). The p75(NTR) is expressed in normal human prostate epithelial cells and exhibits an inverse association of p75(NTR) expression with the malignant progression of the prostate, consistent with a pathologic role of the p75(NTR) as a putative tumor and metastasis suppressor. Utilizing stable transfectants of the TSU-pr1 and PC-3 human prostate tumor cell lines that exhibit a rank order (dose-dependent) increase in p75(NTR) protein expression, we investigated the effects of the p75(NTR) in combination with its predominant ligand, nerve growth factor (NGF), on tumor cell growth. A rank order (dose-dependent) increase in p75(NTR) expression was found to suppress the growth of prostate tumors in severe combined immunodeficient (SCID) mice. Treatment of these tumors with NGF stimulated both proliferation as indicated by PCNA expression and apoptosis as indicated by TUNEL assay, the net result of which was no change in the overall growth of the tumors. However, NGF was found to increase the formation of satellite tumors, both contiguous and noncontiguous with respect to the primary tumor mass, indicating dose-dependent induction of metastasis. Significantly, the formation of satellite tumors was suppressed by the expression of p75(NTR). This suggests that p75(NTR) is a tumor suppressor of growth and a metastasis suppressor of NGF-stimulated migration of human prostate tumor cells.

Myosin II heavy chain isoforms are phosphorylated in an EGF-dependent manner

To explore the involvement and regulation of the nonmuscle myosin II heavy chains isoforms, MHC-A and MHC-B in the chemotaxis of metastatic tumor cells,we analyzed the changes in phosphorylation and cellular localization of these isoforms upon stimulation of prostate tumor cells with epidermal growth factor(EGF). EGF stimulation of prostate tumor cells resulted in transient increases in MHC-A and MHC-B phosphorylation and subcellular localization with quite different kinetics. Furthermore, the kinetics of subcellular localization correlated with the in vivo kinetics of MHC-B phosphorylation but not of MHC-A phosphorylation, suggesting different modes of regulation for these myosin II isoforms. We further showed that protein kinase C (PKC) is involved in the EGF-dependent phosphorylation of MHC-A and MHC-B. To our knowledge, this is the first report demonstrating that MHC phosphorylation might regulate its subcellular localization and that the EGF signal is transmitted to MHC-A and MHC-B via PKC. The correlation between MHC-B phosphorylation and localization in response to EGF stimulation might suggest that MHC-B is the myosin II isoform that is involved in chemotaxis.

Fatty Acid Regulation of Protein Kinase C Isoforms in Prostate Cancer Cells

Polyunsaturated fatty acids influence the aetiology of prostate cancer. Their effects on cellular mechanisms regulating prostate tumorigenesis are unclear. Using prostate cancer cells (LNCaP), we determined effects of n-9-OA, n-6-LA, and n-3-EPA on total PKC and its isoforms in relation to cell proliferation and PSA production. PKC-alpha, delta, gamma, iota, mu, and zeta were present in LNCaP cells; PKC-beta, epsilon, eta, and theta isoforms were not. PKC-alpha was detected only in cytosol; PKC-delta, iota, gamma, and mu were present in cytosol and in membranes. Fatty acids increased cell proliferation, total PKC activity and elicited pro-proliferative effects on specific PKC isoforms (PKC-delta and -iota). EPA and LA increased total PKC activity and reduced membrane-abundance of PKC-delta. OA reduced cytosolic and membrane PKC-delta. Only EPA reduced PKC-gamma membrane abundance. Fatty acids enhanced cytosolic PKC-iota abundance but only EPA and to a lesser extent LA increased its membrane content. Changes in PKC-delta, -iota, and -gamma did not affect PSA production.

Two classes of androgen receptor elements mediate cooperativity through allosteric interactions

Genes uniquely regulated by the androgen receptor (AR) typically contain multiple androgen response elements (AREs) that in isolation are of low DNA binding affinity and transcriptional activity. However, specific combinations of AREs in their native promoter context result in highly cooperative DNA binding by AR and high levels of transcriptional activation. We demonstrate that the natural androgen-regulated promoters of prostate specific antigen and probasin contain two classes of AREs dictated by their primary nucleotide sequence that function to mediate cooperativity. Class I AR-binding sites display conventional guanine contacts. Class II AR-binding sites have distinctive atypical sequence features and, upon binding to AR, the DNA structure is dramatically altered through allosteric interactions with the receptor. Class II sites stabilize AR binding to adjacent class I sites and result in synergistic transcriptional activity and increased hormone sensitivity. We have determined that the specific nucleotide variation within the AR binding sites dictate differential functions to the receptor. We have identified the role of individual nucleotides within class II sites and predicted consensus sequences for class I and II sites. Our data suggest that this may be a universal mechanism by which AR achieved unique regulation of target genes through complex allosteric interactions dictated by primary binding sequences.

Low-dose staurosporine suppresses proliferation and induces neurites in human prostatic cancer TSU-Pr1 cells

BACKGROUND

Despite the beneficial effects of androgen ablation therapy in patients with prostate carcinoma, advancing prostate cancer usually becomes hormone-refractory. We attempted to establish a new prostate cancer therapy by controlling the malignancy of tumor cells through the induction of differentiation in vitro.

METHODS

We examined the ability of staurosporine to induce differentiation of human prostate cancer TSU-Pr1 cells into the cells with neuronal characteristics.

RESULTS

At low concentrations, staurosporine remarkably suppressed proliferation of human prostate cancer TSU-Pr1 cells without increasing dead cell number. TSU-Pr1 cells treated with 10(-8) M staurosporine began to extend neurites within 1 day, and approximately 80% of cells were changed to a neuronal morphology at 3 days. The expression of mRNA of tau, a microtubule-associated protein that is one of the essential components of neurite outgrowth, time-dependently increased in the cells treated with 10(-8) M staurosporine. Similarly, the amount of acetylcholinesterase increased. Colony-forming activity of TSU-Pr1 cells treated with 10(-8) M staurosporine for 7 days was 40% that of control cells. The invasive ability of TSU-Pr1 cells treated with staurosporine to penetrate through a reconstituted basement membrane of Matrigel was 20% that of untreated cells.

CONCLUSIONS

These results suggest that staurosporine might induce differentiation of human prostate cancer TSU-Pr1 cells to cells with neuronal characteristics.

Epidermal growth factor receptor inhibition in cancer therapy: biology, rationale and preliminary clinical results

The epidermal growth factor receptor (EGFR), a growth factor receptor involved in the regulation of cellular differentiation and proliferation, is highly expressed by many tumor cells. In light of a relationship between overexpression of EGFR and clinically aggressive malignant disease, EGFR has emerged as a promising target for cancer therapy. In recent years, several molecular strategies have been explored to modulate either the EGFR itself, or the downstream signal beyond the cell surface receptor. One of the most promising current strategies involves the use of anti-EGFR monoclonal antibodies (mAbs), either alone or in combination with conventional cytotoxic modalities such as chemotherapy or radiotherapy. This review focuses primarily on recent progress in the development of anti-EGFR mAbs, and examines their potential in the treatment of cancer.

Early effects of protein kinase modulators on DNA synthesis in rat cerebral cortex

By using tissue miniunits, protein kinase modulators, and topoisomerase inhibitors in short-term incubation (0-90 min) we studied (1) the role of protein phosphorylation in the immediate control of DNA replication in the developing rat cerebral cortex and (2) the mechanism of action for genistein-mediated DNA synthesis inhibition. Genistein decreased the DNA synthesis within less than 30 min. None of the other protein kinase inhibitors examined (herbimycin A, staurosporine, calphostin-C) or the protein phosphatase inhibitor sodium orthovanadate inhibited DNA synthesis and they did not affect the genistein-mediated inhibition. The selective topoisomerase inhibitors camptothecin and etoposide decreased the DNA synthesis to an extent similar to that of genistein and within less than 30 min. In addition, the effects of these substances on topoisomerase I and II were studied. Etoposide and genistein but not herbimycin A, staurosporine, or calphostin-C strongly inhibited the activity of topoisomerase II. Our results (1) strongly suggest that the net rate of DNA replication during the S phase of the cell cycle is independent of protein phosphorylation and (2) indicate that the early inhibitory effect of genistein on DNA synthesis is mediated by topoisomerase II inhibition rather than protein tyrosine kinase inhibition.

Human breast cancer cell metastasis to long bone and soft organs of nude mice: a quantitative assay

Bone is a common metastatic site in human breast cancer (HBC). Since bone metastasis occurs very rarely from current spontaneous or experimental metastasis models of HBC cells in nude mice, an arterial seeding model involving the direct injection of the cells into the left ventricle has been developed to better understand the mechanisms involved in this process. We present here a sensitive polymerase chain reaction (PCR) method to detect and quantitate bone and soft organ metastasis in nude mice which have been intracardially inoculated with Lac Z transduced HBC cells. Amplification of genomically incorporated Lac Z sequences in MDA-MB-231-BAG HBC cells enables us to specifically detect these cells in mouse organs and bones. We have also created a competitive template to use as an internal standard in the PCR reactions, allowing us to better quantitate levels of HBC metastasis. The results of this PCR detection method correlate well with cell culture detection from alternate long bones from the same mice, and are more sensitive than gross Lac Z staining with X-gal or routine histology. Comparable qualitative results were obtained with PCR and culture in a titration experiment in which mice were inoculated with increasing numbers of cells, but PCR is more quantifiable, less time consuming, and less expensive. This assay can be employed to study the molecular and cellular aspects of bone metastasis, and could easily be used in conjunction with RT-PCR-based analyses of gene products which may be involved with HBC metastasis.

Two peptides derived from the nerve growth factor precursor are biologically active

This report provides evidence that the proregion of the NGF precursor protein contains two novel bioactive peptides. The presence of pairs of basic amino acid (aa) residues in the NGF proregion suggests that two or three peptides other than NGF may be generated by proteolytic cleavage. Synthetic peptides of 29 aa (LIP1) and 38aa (LIP2) corresponding to the sequences -71 to -43 and -40 to -3 of the proNGF, respectively, were used in this study. ELISA specific for these two peptides revealed their presence in the rat intestine. LIP1 was localized by immunohistochemistry in endocrine cells of the intestinal epithelium, and LIP2 was immunoprecipitated from an intestinal extract. We also provide evidence for the presence of specific receptors for LIP2 in several cell lines. Scatchard analysis indicated the presence of a low affinity binding site with a Kd of approximately 10(-7) M and a high affinity binding site of 10(-9) M. Cross-linking studies revealed receptor forms of about 140 kD and 93 kD in a prostatic adenocarcinoma cell line. LIP1 and LIP2 induced rapid F-actin redistribution in PC12 cells within 2 min of incubation, which suggests a role of LIP1 and LIP2 in the process of neurite outgrowth. Furthermore, both propeptides induced rapid tyrosine phosphorylation of the Trk protein in both prostatic adenocarcinoma cells and PC12 cells, thus implicating trk in their mechanism of action. These results support our hypothesis that two peptides within the NGF precursor protein are biologically active.