Antisense c-myc retroviral vector suppresses established human prostate cancer

Comparison of prostate-specific promoters and the use of PSP-driven virotherapy for prostate cancer

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of cancer deaths in men today. Although virus-based gene therapy is a promising strategy to combat advanced prostate cancer, its current effectiveness is limited partially due to inefficient cellular transduction in vivo. To overcome this obstacle, conditional oncolytic viruses (such as conditional replication adenovirus (CRAD)) are developed to specifically target prostate without (or with minimal) systemic toxicity due to viral self-replication. In this study, we have analyzed and compared three prostate-specific promoters (PSA, probasin, and MMTV LTR) for their specificity and activity both in vitro and in vivo. Both mice model with xenograft prostate tumor model and canine model were used. The best PSP was selected to construct a prostate-specific oncolytic adenovirus (CRAD) by controlling the adenoviral E1 region. The efficacy and specificity of CRAD on prostate cancer cells were examined in cell culture and animal models.

Translational Approaches towards Cancer Gene Therapy: Hurdles and Hopes

INTRODUCTION

Of the cancer gene therapy approaches, gene silencing, suicide/apoptosis inducing gene therapy, immunogene therapy and targeted gene therapy are deemed to sub-stantially control the biological consequences of genomic changes in cancerous cells. Thus, a large number of clinical trials have been conducted against various malignancies. In this review, we will discuss recent translational progresses of gene and cell therapy of cancer.

METHODS

Essential information on gene therapy of cancer were reviewed and discussed towards their clinical translations.

RESULTS

Gene transfer has been rigorously studied in vitro and in vivo, in which some of these gene therapy endeavours have been carried on towards translational investigations and clinical applications. About 65% of gene therapy trials are related to cancer therapy. Some of these trials have been combined with cell therapy to produce personalized medicines such as Sipuleucel-T (Provenge®, marketed by Dendreon, USA) for the treatment of asymptomatic/minimally symptomatic metastatic hormone-refractory prostate cancer.

CONCLUSION

Translational approach links two diverse boundaries of basic and clinical researches. For successful translation of geno-medicines into clinical applications, it is essential 1) to have the guidelines and standard operating procedures for development and application of the genomedicines specific to clinically relevant biomarker(s); 2) to conduct necessary animal experimental studies to show the "proof of concept" for the proposed genomedicines; 3) to perform an initial clinical investigation; and 4) to initiate extensive clinical trials to address all necessary requirements. In short, translational researches need to be refined to accelerate the geno-medicine development and clinical applications.

Targeted inhibition of SRC kinase signaling attenuates pancreatic tumorigenesis

Elevated Src expression correlates with malignant potential and metastatic disease in many tumors including pancreatic cancer. We sought to characterize the molecular effects of Src kinase inhibition with dasatinib (BMS-354825), a novel, multitargeted kinase inhibitor that targets Src family kinases in pancreatic ductal adenocarcinoma (PDA). We identified sensitive and resistant PDA cell lines to dasatinib treatment and tested the molecular effects of Src inhibition in vitro and in vivo. We show for the first time that cellular localization of Src expression affects survival in patients with PDA. Pancreatic tumors with increased membranous expression of Src resulted in decreased survival compared with tumors that had increased cytoplasmic Src expression. Src kinase inhibition with dasatinib markedly inhibits cell proliferation, migration, invasion, cell cycle progression and anchorage-independent growth, and stimulates apoptosis. This was accompanied by decreased phosphorylation of Src, focal adhesion kinase, paxillin, AKT, signal transducers and activators of transcription 3 (STAT3), extracellular signal-regulated kinase, and mitogen-activated protein kinase (MAPK), as well as decreased cyclin D1 expression in a time- and concentration-dependent manner. Furthermore, small interfering RNA to Src results in a significant decrease in cell proliferation, invasion, and migration of pancreatic cancer cells. Dasatinib treatment also inhibits in vivo pancreatic tumor growth. Mechanisms of resistance to Src inhibition seem to be related to a lack of inhibition of STAT3 and MAPK signaling. These results establish a mechanistic rationale for Src inhibition with dasatinib as a therapeutic target in the treatment of pancreatic cancer and identify potential biomarkers of resistance to Src inhibition.

Transcriptionally regulated, prostate-targeted gene therapy for prostate cancer

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of cancer deaths in American males today. Novel and effective treatment such as gene therapy is greatly desired. The early viral based gene therapy uses tissue-nonspecific promoters, which causes unintended toxicity to other normal tissues. In this chapter, we will review the transcriptionally regulated gene therapy strategy for prostate cancer treatment. We will describe the development of transcriptionally regulated prostate cancer gene therapy in the following areas: (1) Comparison of different routes for best viral delivery to the prostate; (2) Study of transcriptionally regulated, prostate-targeted viral vectors: specificity and activity of the transgene under several different prostate-specific promoters were compared in vitro and in vivo; (3) Selection of therapeutic transgenes and strategies for prostate cancer gene therapy (4) Oncolytic virotherapy for prostate cancer. In addition, the current challenges and future directions in this field are also discussed.

The knockdown of c-myc expression by RNAi inhibits cell proliferation in human colon cancer HT-29 cells in vitro and in vivo

We investigated the effects of RNA interference-mediated silencing of the c-myc gene on celluar proliferation and apoptosis in human colon cancer HT-29 cells in vitro and in vivo. A small interfering RNA (siRNA) targeting c-myc was designed, the DNA template was synthesized, and the siRNA was obtained by in vitro transcription. After siRNA transfection into HT-29 and human neuroblastoma IMR-32 cells with Lipofectamine 2000™, the proliferation of the HT-29 and IMR-32 cells was assessed via 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) colorimetry, and Hoechst 33258 staining was used to observe cell apoptosis. Following gene transfer to HT-29 cells, the expression of c-myc mRNA was examined via reverse transcription polymerase chain reaction, and the level of the protein via Western blot assay. Growth curves were constructed and in vivo experiments were performed on nude mice to assess the effects of c-myc silencing on tumor growth. The c-myc expression in the tumor tissue was measured by reverse transcription polymerase chain reaction and subsequently by immunohistochemistry. Our paper demonstrates that the delivery of siRNA directed against c-myc not only efficiently down-regulated the expression of c-myc, inhibited the proliferation of HT-29 cells and induced apoptosis in vitro, but also suppressed the growth of colon cancer cells in vivo.

Molecular markers in prostate cancer. Part II: potential roles in management

Predicting treatment responses in advanced prostate cancer (PCa) currently centres on prostate-specific antigen (PSA) kinetics and on being able to visualize measurable changes in imaging modalities. New molecular markers have emerged as potential diagnostic and prognostic indicators; these were summarized in Part I of this review in the Asian Journal of Andrology. A number of molecular markers are now being used to enhance PCa imaging and staging. However, management options for advanced and hormone-resistant PCa (HRPC) are limited and additional therapeutic options are needed. Molecular markers have been proposed as potential therapeutic targets using gene therapy and immunomodulation. Additionally, markers identified in early PCa and precursor lesions may offer novel targets for chemoprevention and vaccine development. This review summarizes the current advances regarding the roles of these markers in the management of PCa.

Src family kinase oncogenic potential and pathways in prostate cancer as revealed by AZD0530

Prostate cancer is the most frequently diagnosed cancer in American men. We have previously demonstrated that Src mediates androgen-independent proliferation in prostate cancer. We sought to investigate the Src-mediated oncogenic pathways and tumor biology using AZD0530, a novel Src family kinase/Abl dual-kinase inhibitor that is entering phase II clinical trials. We show that while both Src and Abl are expressed in all prostate cancer cell lines, Src but not Abl is activated in the prostate. Furthermore, Src activation is inhibited by AZD0530 in a rapid and dose-dependent manner. We show that Src mediates cell proliferation in DU145 and PC3 cells at the G1 phase of cell cycle. Src inhibition resulted in decreased binding of beta-catenin to the promoters of G1 phase cell cycle regulators cyclin D1 and c-Myc. C-Myc may also be regulated at the protein level by extracellular signal-regulated kinase 1/2 and GSK3beta. Cell motility factors focal adhesion kinase, p130CAS and paxillin activation in DU145 and PC3 cells were also inhibited. Administration of AZD0530 in mice reduced orthotopic DU145 xenograft growth by 45%. We have further delineated the Src-mediated oncogenic growth and migration pathways in prostate cancer and established mechanistic rationale for Src inhibition as novel therapy in the treatment of prostate cancer.

c-Myc-induced chemosensitization is mediated by suppression of cyclin D1 expression and nuclear factor-kappa B activity in pancreatic cancer cells

PURPOSE

Pancreatic cancer is a highly aggressive disease that remains refractory to various chemotherapeutic agents. Because the proto-oncogene c-myc can modulate apoptosis in response to cytotoxic insults and is commonly overexpressed in pancreatic cancer, we investigated the value of c-myc as a potential modulator of cellular response to various chemotherapeutic agents.

EXPERIMENTAL DESIGN

Stable overexpression or small interfering RNA (siRNA)-mediated knockdown of c-myc and restoration of cyclin D1 were done in the Ela-myc pancreatic tumor cell line. Cell viability after cisplatin treatment of c-myc-overexpressing, control, and siRNA-transfected cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and drug-induced apoptosis was measured by DNA fragmentation, sub-G(1), and poly(ADP-ribose) polymerase cleavage analyses. Protein expression profile after cisplatin treatment was determined by Western blotting and DNA binding activity of nuclear factor-kappaB was examined by electrophoretic mobility shift assay.

RESULTS

Ectopic overexpression of c-myc in murine and human pancreatic cancer cell lines, Ela-myc and L3.6pl, respectively, resulted in increased sensitivity to cisplatin and other chemotherapeutic drugs. Increased sensitivity to cisplatin in c-myc-overexpressing cells was due, in part, to the marked increase in cisplatin-induced apoptosis. Conversely, down-regulation of c-myc expression in stable c-myc-overexpressing cells by c-myc siRNA resulted in decreased sensitivity to cisplatin-induced cell death. These results indicate an important role of c-myc in chemosensitivity of pancreatic cancer cells. The c-myc-induced cisplatin sensitivity correlated with inhibition of nuclear factor kappaB activity, which was partially restored by ectopic cyclin D1 overexpression.

CONCLUSIONS

Our results suggest that the c-myc-dependent sensitization to chemotherapy-induced apoptosis involves suppression of cyclin D1 expression and nuclear factor kappaB activity.

Future innovations in treating advanced prostate cancer

Many novel techniques for the treatment of prostate cancer are being aggressively investigated because prostate cancer is prevalent in the population and the current treatments for advanced prostate cancer are woefully inadequate. Although the current treatment options prolong life, most patients will eventually experience local recurrence or develop advanced disease. A greater understanding of the molecular events underlying cancer has enabled investigators to explore gene therapy approaches that are targeted against these molecular events. This article discusses antiangiogenic therapy, immune based therapy, and gene therapy. Any of these experimental modalities could be developed to replace hormone ablation therapy which causes unpleasant side effects, decreases the quality of life of the patient, and only temporarily controls the disease.

Gene therapy for prostate cancer: current strategies and new cell-based approaches

Prostate cancer is the most commonly diagnosed cancer in adult males in the Western world. It accounts for one in ten cancer cases and is the second leading cause of cancer death in men, after lung cancer. A number of curative treatments are available for patients with localized prostate cancer such as radical prostatectomy, radiotherapy, or brachytherapy. However, a proportion of these men will develop progressive disease, and some will present de novo with advanced and metastatic prostate cancer, which is amenable to palliation only with androgen-withdrawal therapy. Most of these patients will eventually develop hormone refractory disease which is incurable, and for whom gene therapy, if feasible may develop as an alternative treatment option. In this review we discuss the gene therapy vectors and strategies that are currently in use, new cell-based approaches, discuss their advantages and disadvantages, and review the potential or proven pre-clinical and clinical efficacy in prostate cancer models/patients.

Gene delivery and gene therapy of prostate cancer

Surgery, radiation or hormonal therapy are not adequate to control prostate cancer. Clearly, other novel treatment approaches, such as gene therapy, for advanced/recurrent disease are desperately needed to achieve long-term local control and particularly to develop effective systemic therapy for metastatic prostate cancer. In the last decade, significant progress in gene therapy for the treatment of localised prostate cancer has been demonstrated. A broad range of different gene therapy approaches, including cytolytic, immunological and corrective gene therapy, have been successfully applied for prostate cancer treatment in animal models, with translation into early clinical trials. In addition, a wide variety of viral and nonbiological gene delivery systems are available for basic and clinical research. Gene therapy approaches that have been developed for the treatment of prostate cancer are summarised.

Adeno-associated virus 2-mediated intratumoral prostate cancer gene therapy: long-term maspin expression efficiently suppresses tumor growth

Maspin is a member of the serine protease inhibitors and the maspin gene, a tumor suppressor gene, is down-regulated in a large fraction of prostate cancers. We evaluated the use of adeno-associated virus (AAV, serotype 2) vector encoding maspin as a means for in vivo gene therapy for human prostate cancer. TUNEL assay of subcutaneously formed LNCaP or DU145 tumors in nude mice showed that intratumoral AAV-mediated maspin expression significantly upregulated the number of apoptotic cells compared with AAV-LacZ treatment. Immunofluorescence double staining for maspin protein and apoptosis in LNCaP tumors showed that the percentage of apoptotic cells in AAV-maspin-mediated maspin-expressing cells was significantly high compared with that in AAV-GFP-mediated GFP-expressing cells. Moreover, significantly fewer CD31-positive microvessels were observed in AAV-maspin-treated tumors compared with the control tumors. These therapeutic responses were highly correlated to persistent maspin expression in tumors, confirmed by Western blot analysis until at least day 56 after treatment. Finally, intratumoral delivery of AAV-maspin significantly suppressed growth of LNCaP and DU145 tumors and improved survival of mice. We conclude that AAV-mediated prolonged maspin expression efficiently suppresses human prostate tumor growth in vivo by apoptosis induction and inhibition of angiogenesis.

Knockdown of c-Myc expression by RNAi inhibits MCF-7 breast tumor cells growth in vitro and in vivo

Introduction

Breast cancer is the leading cause of cancer death in women worldwide. Elevated expression of c-Myc is a frequent genetic abnormality seen in this malignancy. For a better understanding of its role in maintaining the malignant phenotype, we used RNA interference (RNAi) directed against c-Myc in our study. RNAi provides a new, reliable method to investigate gene function and has the potential for gene therapy. The aim of the study was to examine the anti-tumor effects elicited by a decrease in the protein level of c-Myc by RNAi and its possible mechanism of effects in MCF-7 cells.

Method

A plasmid-based polymerase III promoter system was used to deliver and express short interfering RNA (siRNA) targeting c-myc to reduce its expression in MCF-7 cells. Western blot analysis was used to measure the protein level of c-Myc. We assessed the effects of c-Myc silencing on tumor growth by a growth curve, by soft agar assay and by nude mice experiments in vivo. Standard fluorescence-activated cell sorter analysis and TdT-mediated dUTP nick end labelling assay were used to determine apoptosis of the cells.

Results

Our data showed that plasmids expressing siRNA against c-myc markedly and durably reduced its expression in MCF-7 cells by up to 80%, decreased the growth rate of MCF-7 cells, inhibited colony formation in soft agar and significantly reduced tumor growth in nude mice. We also found that depletion of c-Myc in this manner promoted apoptosis of MCF-7 cells upon serum withdrawal.

Conclusion

c-Myc has a pivotal function in the development of breast cancer. Our data show that decreasing the c-Myc protein level in MCF-7 cells by RNAi could significantly inhibit tumor growth both in vitro and in vivo, and imply the therapeutic potential of RNAi on the treatment of breast cancer by targeting overexpression oncogenes such as c-myc, and c-myc might be a potential therapeutic target for human breast cancer.

Is gene therapy the answer for prostate cancer?

Prostate cancer is the third most common cancer, accounting for one in 10 cancer diagnoses in men worldwide during 2000. Despite this high burden of morbidity, there is a lack of curative treatments for locally advanced and metastatic disease. Good anatomical accessibility of the prostate combined with substantial molecular understanding of the disease makes prostate cancer an attractive target for gene therapy. Considerable progress has been made in the development of suitable gene transfer vectors and prostate-targeting strategies. Therapeutic approaches being explored fall into two broad categories: corrective and cytoreductive/cytolytic. There are currently 63 prostate cancer gene therapy clinical trials based on these approaches registered in the United States and United Kingdom. Although significant hurdles remain to be overcome, early clinical trial results are encouraging, suggesting that gene therapy may become an important treatment option for prostate cancer.

Gene-based therapy in prostate cancer

Prostate cancer is one of the commonest causes of illness and death from cancer. Radical prostatectomy, radiotherapy, and hormonal therapy are the main conventional treatments. However, gene therapy is emerging as a promising adjuvant to conventional strategies, and several clinical trials are in progress. Here, we outline several approaches to gene therapy for prostate cancer that have been investigated. Methods of gene delivery are described, particularly those that have commonly been used in research on prostate cancer. We discuss efforts to achieve tissue-specific gene delivery, focusing on the use of tissue-specific gene promoters. Finally, the present use of gene therapy for prostate cancer is evaluated. The ability to deliver gene-therapy vectors directly to prostate tissue, and to regulate gene expression in a tissue-specific manner, offers promise for the use of gene therapy in prostate cancer.

The future of antisense therapy: combination with anticancer treatments

The current direction in cancer research is rational drug design, which is based on the evidence that transformed cells are characterized by alterations of genes devoted to the regulation of both cell proliferation and apoptosis. A variety of approaches have been carried out to develop new agents selective for cancer cells. Among these, antisense oligonucleotides (ASOs) are one of such class of new agents able to inhibit specifically the synthesis of a particular cancer-associated protein by binding to protein-encoding RNA, thereby preventing RNA function. In the past decade, several ASOs have been developed and tested in preclinical and clinical studies. Many have shown convincing in vitro reduction in target gene expression and promising activity against a wide variety of tumors. However, because of the multigenic alterations of tumors, the use of ASOs as single agents does not seem to be effective in the treatment of malignancies. Antisense therapy that interferes with signaling pathways involved in cell proliferation and apoptosis are particularly promising in combination with conventional anticancer treatment. An overview of the progress of ASOs used in combination therapy is provided.

Suppression of LNCaP prostate cancer xenograft tumors by a prostate-specific protein tyrosine phosphatase, prostatic acid phosphatase

BACKGROUND

Although the molecular mechanism of androgen-independent prostate cancer growth and progression has been gradually elucidated, there is limited effective treatment for this prevalent disease. Human prostatic acid phosphatase (PAcP), a major protein tyrosine phosphatase in prostate epithelium, plays a critical role in regulating the growth of prostate cancer cells. In prostate carcinomas, the expression of cellular PAcP decreases. To explore directly the possible therapeutic potential of cellular PAcP, we investigated the suppression effect of PAcP by utilizing cDNA direct intratumoral administration in androgen-independent LNCaP xenograft tumors.

METHODS

An androgen-independent LNCaP cell model (C-33 and C-81 cells) and stable subclones of PAcP cDNA-transfected C-81 cells (LNCaP-23 and LNCaP-34 cells) were used for the experiments. We examined the growth property and expression of PAcP and c-ErbB-2 of these different LNCaP cells in vitro and in vivo. We subsequently investigated the growth suppression effect of PAcP cDNA intratumoral injection in pre-established C-81 xenograft tumors, and analyzed the expression of PAcP, prostate-specific antigen (PSA), proliferating cell nuclear antigen (PCNA), and c-ErbB-2 in the tumors by immunohistochemistry and Western blotting.

RESULTS

The different LNCaP cells exhibited different growth property and tumorigenicity, both in cell culture and xenograft. Biochemical characterizations revealed that the level of cellular PAcP correlated negatively with the growth property of different LNCaP cells, while the level of tyrophosphorylated c-ErbB-2 had an inverse correlation with cellular PAcP. The single intratumoral administration of the wild type PAcP cDNA showed a significant suppression effect on C-81 xenograft tumor growth, compared to vector alone-injected control (P<0.05). In the tumors injected with this PAcP cDNA, the PAcP expression was detected 1 week (wk) after injection, but was undetectable at 6 wk, which inversely correlated with the level of tyrophosphorylated c-ErbB-2 and the degree of cell proliferation indicated by PCNA staining.

CONCLUSIONS

Our results clearly demonstrated that cellular PAcP has a suppression effect on the growth of androgen-independent LNCaP xenograft tumors. This effect occurs at least partly through the dephosphorylation of c-ErbB-2 by PAcP, the prostate-specific protein tyrosine phosphatase. The data indicates that human PAcP could be utilized in the corrective gene therapy for a subgroup of androgen-independent human prostate cancer cells that lack cellular PAcP expression.

Synthesis and application of functional peptides as cell nucleus-directed molecules in the treatment of malignant diseases

The unique functions of biomolecules, including transport across biological membranes (e.g. the cell membrane, the nuclear envelope), modulation of protein function, gene transcription, reconstitution of the malignant transformation, and viral, bacterial and fungal activities underlie a high pharmaceutical potential. The development of combinatorial functional peptide modules in this important area has been slow, in contrast to the rapid development in the synthesis of small biopolymers. The conjugation of a short transmembrane transport peptide module with a cell nucleus address peptide module and with any substance is attractive for preparation of BioShuttle-based peptides because of the well-established automated synthesis of peptides. Variation of the different functional modules for drug targeting and the choice of substances can be combined to create novel bioconjugates with unique properties. This article provides an overview of previous work on the BioShuttle technology and outlines the promising use of this approach in combinatorial peptide synthesis and drug discovery.

Inhibition of human chorionic gonadotropin beta-subunit modulates the mitogenic effect of c-myc in human prostate cancer cells

BACKGROUND

Amplification of the proto-oncogene c-myc has been identified as one of the most common genetic alterations in prostate cancer, thus making it an attractive therapeutic target. However, certain prostate cancer cells are unresponsive to c-Myc inhibition. The purpose of this study was to test the hypothesis that effective growth inhibition in the refractory cancer cells can be achieved by blocking c-myc along with a growth factor using a novel phosphorodiamidate morpholino antisense oligomer-based approach. Human chorionic gonadotropin, a growth factor implicated in neoplasm, causes activation of c-myc through a G-protein-coupled pathway of signal transduction.

METHODS

In this study, the effect of inhibition of beta-hCG and c-myc singly or in combination was evaluated in DU145 (RB -/-, p53-/-, androgen-independent) and LNCaP (Rb+/+, p53 +/+, androgen-sensitive) human prostate cancer cell lines and in a DU145 subcutaneous xenograft murine model.

RESULTS

Antisense phosphorodiamidate morpholino oligomers directed against beta-hCG and c-myc caused a specific decrease of the target protein levels. Unlike LNCaP cells, DU145 cell growth was refractory to c-Myc inhibition. Unresponsiveness to c-myc inhibition in DU145 cells was overcome by targeting both beta-hCG and c-myc genes, resulting in potentiation of the antiproliferative effect seen with inhibition of beta-hCG alone.

CONCLUSIONS

The inhibition of beta-hCG sensitizes prostate cancer cells to the antiproliferative effects of c-Myc inhibition, including tumors that are refractory to c-Myc decrease alone.

Prostate cancer gene therapy

Numerous gene therapy trials in the United States and throughout the world using various strategies are in progress for the treatment of locally advanced and metastatic prostate cancer. Although vector technology advances at a rapid pace, progress in elucidating the molecular pathways critical for the development and progression of prostate cancer has been slower and more deliberate. Thus far, prostate gene therapy appears to be safe and well tolerated. Through these early clinical trials, the safety and efficacy of gene therapy alone or in combination with more conventional therapy as a basis for the treatment of prostate cancer will ultimately be determined.

Gene therapy for prostate cancer

Prostate cancer is the most common noncutaneous cancer in man. When confined to the prostate it can be cured by radical prostatectomy or irradiation therapy. However, there are no curative therapies for locally advanced, recurrent or metastatic disease. Prostate cancer gene therapy has recently transition from preclinical studies to clinical trials with the goal of developing novel treatments for prostate cancer. The greatest challenge in treating advanced prostate cancer is therapeutic access to and the elimination of metastases. This review details two aspects of prostate cancer gene therapy, the types of delivery systems under development and specific categories of therapeutic genes available with an emphasis on the mechanism of action of specific gene therapy strategies.

p53 and PTEN/MMAC1/TEP1 gene therapy of human prostate PC-3 carcinoma xenograft, using transferrin-facilitated lipofection gene delivery strategy

We previously reported that supplementation of a cationic liposome with transferrin (Tf) greatly enhanced lipofection efficiency (P.-W. Cheng, Hum. Gene Ther. 1996;7:275-282). In this study, we examined the efficacy of p53 and PTEN tumor suppressor gene therapy in a mouse xenograft model of human prostate PC-3 carcinoma cells, using a vector consisting of dimyristoyloxypropyl-3-dimethylhydroxyethyl ammonium bromide (DMRIE)-cholesterol (DC) and Tf. When the volume of the tumors grown subcutaneously in athymic nude mice reached 50-60 mm(3), three intratumoral injections of the following four formulations were performed during week 1 and then during week 3: (1) saline, (2) DC + Tf + pCMVlacZ, (3) DC + Tf + pCMVPTEN, and (4) DC + Tf + pCMVp53 (standard formulation). There was no significant difference in tumor volume and survival between group 1 and group 2 animals. As compared with group 1 controls, group 3 animals had slower tumor growth during the first 3 weeks but thereafter their tumor growth rate was similar to that of the controls. By day 2 posttreatment, group 4 animals had significantly lower tumor volume relative to initial tumor volume as well as controls at the comparable time point. Also, animals treated with p53 survived longer. Treatment with DC, Tf, pCMVp53, DC + pCMVp53, or Tf + pCMVp53 had no effect on tumor volume or survival. Expression of p53 protein and apoptosis were detected in tumors treated with the standard formulation, thus associating p53 protein expression and apoptosis with efficacy. However, p53 protein was expressed in only a fraction of the tumor cells, suggesting a role for bystander effects in the efficacy of p53 gene therapy. We conclude that intratumoral gene delivery by a nonviral vector consisting of a cationic liposome and Tf can achieve efficacious p53 gene therapy of prostate cancer.

Gene therapy for prostate cancer: current status and future prospects

PURPOSE

Locally advanced, relapsed and metastatic prostate cancer has a dismal prognosis with conventional therapies offering no more than palliation. In recent years advances achieved in understanding the molecular biology of cancer have afforded clinicians and scientists the opportunity to develop a range of novel genetic therapies for this disease.

MATERIALS AND METHODS

We performed a detailed review of published reports of gene therapy for prostate cancer. Particular emphasis was placed on recent developments in the arena of nonviral (plasmid DNA, DNA coated gold particles, liposomes and polymer DNA complexes) and viral (adenovirus, retrovirus, adeno-associated virus, herpes virus and pox virus) vectors. Therapeutic strategies were categorized as corrective, cytoreductive and immunomodulatory gene therapy for the purpose of data analysis and comparison.

RESULTS

Locoregional administration of nonviral and viral vectors can yield impressive local gene expression and therapeutic effects but to our knowledge no efficient systemically delivered vector is available to date. Corrective gene therapy to restore normal patterns of tumor suppressor gene (p53, Rb, p21 and p16) expression or negate the effect of mutated tumor promoting oncogenes (ras, myc, erbB2 and bcl-2) have efficacy in animal models but this approach suffers from the fact that each cancer cell must be targeted. A wide variety of cytoreductive strategies are under development, including suicide, anti-angiogenic, radioisotopic and pro-apoptotic gene therapies. Each approach has strengths and weaknesses, and may best be suited for use in combination. Immunomodulatory gene therapy seeks to generate an effective local immune response that translates to systemic antitumor activity. Currently most studies involve immunostimulatory cytokine genes, such as granulocyte-macrophage colony-stimulating factor, or interleukin-2 or 12.

CONCLUSIONS

Various therapeutic genes have proved activity against prostate cancer in vitro and in vivo. However, the chief challenge facing clinical gene therapy strategies is the lack of efficient gene delivery by local and systemic routes. For the foreseeable future vector development may remain a major focus of ongoing research. Despite this caveat it is anticipated that gene therapy approaches may significantly contribute to the management of prostate cancer in the future.

Gene therapy for prostate cancer

Basic research continues to unravel the molecular complexity of normal and abnormal biologic processes. The development of means to affect the expression level of genes that promote or contribute to cellular transformation, invasion, and metastasis has spawned the concept of gene therapy. This relatively new field seeks to reverse or suspend the pathologic progression of a variety of diseases including the malignant transformation of prostatic epithelial cells. Initial clinical trials for prostate cancer have thus far shown gene therapy to be relatively safe, although definitive evidence of durable therapeutic efficacy remains to be demonstrated. In this article, recent preclinical research, current therapeutic strategies, and recent results of gene therapy clinical trials for the treatment of prostate cancer are reviewed.

Suppression of melanoma cell proliferation by histidine decarboxylase specific antisense oligonucleotides

Histidine decarboxylase (HDC) is expressed by the cells of melanoma, in which the histamine content tends to be relatively high. This study shows that elevated expression of HDC was found by western blot analysis of primary and metastatic melanoma tissue using a polyclonal HDC specific antibody. The specificity of anti-HDC antibody was confirmed by inhibition of HDC translation (i.e., immunopositivity) in melanoma cells by HDC-specific antisense oligonucleotide. Moreover, the decrease in proliferation caused by HDC antisense oligonucleotides indicates considerable functional relevance of histamine synthesis in melanoma growth and suggests a possible in situ application of specific antisense oligonucleotides for HDC in melanoma therapy.

Reduction of c-myc expression by an antisense approach under Cre/loxP switching induces apoptosis in human liver cancer cells

c-Myc has been documented to be both a positive and a negative signal for the induction of apoptosis. It is well known that overexpression of the c-myc gene induces apoptosis of normal cells, but the result of a reduction in its expression is not fully understood. We examined whether a reduction in c-myc expression would induce apoptosis in human liver cancer cells. Specifically, antisense and sense oligodeoxynucleotides (oligos) against the human c-myc mRNA were synthesized, mixed with a liposome reagent at various ratios, and were applied to the liver cancer-derived cell lines, HCC-T, HepG2, and PLC/PRF/5. To exclude effects resulting from using oligos, plasmid vectors expressing the full-length c-myc cDNA in both sense and antisense orientations under the control of the Cre/loxP system were generated. Monoclonal cell lines including these plasmid vectors were produced and Cre was supplied by adenovirus infection. Apoptosis was determined morphologically and c-Myc and Bcl-2 expression was examined by Western blotting. The antisense myc significantly inhibited the proliferation of the cells within two days, while neither the liposome reagent alone nor sense myc did so. Most of the cells were rounded up by the antisense-treatment and nuclear fragmentation and DNA ladder formation were detected after two days in antisense c-myc-treated cells. Antisense c-myc largely reduced c-Myc and partially Bcl-2 expression; overexpression of Bcl-2 partially rescued from apoptosis in HCC-T and HepG2 cells. These results suggest that the massive reduction in c-myc mRNA induces apoptosis in liver cancer cell lines and consequent decrease in Bcl-2 enhances the cell death. c-Myc reduction under the Cre/loxP switching system may be a useful tool for the clarification of c-myc-related cellular mechanisms in differentiation and proliferation.

Gene therapy for prostate cancer

Basic research continues to unravel the molecular complexity of normal and abnormal biologic processes. The development of means to affect the expression level of genes that promote or contribute to cellular transformation, invasion, and metastasis has spawned the concept of gene therapy. This relatively new field seeks to reverse or suspend the pathologic progression of a variety of diseases including the malignant transformation of prostatic epithelial cells. Initial clinical trials for prostate cancer have thus far shown gene therapy to be relatively safe, although definitive evidence of durable therapeutic efficacy remains to be demonstrated. In this article, recent preclinical research, current therapeutic strategies, and recent results of gene therapy clinical trials for the treatment of prostate cancer are reviewed.

Prostate cancer gene therapy

Cancer-specific gene therapy is still in its infancy. Although the first gene therapy trials were initiated in the late 1980s, it was only more recently that the first successful treatment of a genetic disease was reported.3 The current problems with low efficiency of gene transfer coupled with the immunologic difficulties with certain vectors indicate that more effort needs to be directed at the basic science of gene transfer. Ultimately, successful cancer-specific gene therapy will require combinations of the lessons learned from the ex vivo and in vivo paradigms. The next generation of gene therapy trials likely will focus on combination therapy with conventional chemotherapeutic agents, differentiating agents, or radiation therapy. The obstacles to the development of gene-based human therapeutics (i.e., molecular medicine) are formidable, but the benefits are so great that eventually the technical issues of gene transfer methodology will be worked out, and ultimately this will become the standard of care, not only for inborn errors of metabolism, but also for cancer.

Mxi1, a Myc antagonist, suppresses proliferation of DU145 human prostate cells

BACKGROUND

Mxi1, an antagonist of c-Myc, maps to human chromosome 10q24-q25, a region altered in a substantial fraction of prostate tumors. Mice deficient for Mxi1 exhibit significant prostate hyperplasia. We studied the ability of Mxi1 to act as a growth suppressor in prostate tumor cells.

METHODS

We infected DU145 prostate carcinoma cells with an Mxi1-expressing adenovirus (AdMxi1) in vitro, and measured Mxi1 expression, cell proliferation, soft agar colony formation, and cell cycle distribution. To explore mechanisms of Mxi1-induced growth arrest, we performed gene expression analysis.

RESULTS

AdMxi1 infection resulted in reduced cell proliferation, reduced soft agar colony formation, and a higher proportion of cells in the G(2)/M phase of the cell cycle. This G(2)/M growth arrest was associated with elevated levels of cyclin B, and reduced levels of c-MYC and MDM2.

CONCLUSIONS

The ability of AdMxi1 to suppress prostate tumor cell proliferation supports a role for Mxi1 loss in the pathogenesis of a subset of human prostate cancers. Prostate 47:194-204, 2001.

In situ gene therapy for prostate cancer: immunomodulatory approaches

The development of effective treatments for prostate cancer is thwarted by the natural history of the disease. The biological and clinical potential of most individual cancers is uncertain. In many cases the disease will not progress to clinical significance but experimental and clinical studies indicate that prostate cancer can and may metastasis early in the course of the disease from relatively small foci (i.e., not necessarily the largest or index cancer). Localised prostate cancer is potentially curable with localised therapies (radical prostatectomy or irradiation therapy). However, there are no curative therapies for metastatic prostate cancer. Gene therapy, especially those approaches with an immunomodulatory component, may provide additional therapeutic options with the potential to affect both localised and systemic disease. We have pioneered the development and application of in situ gene therapy protocols using adenoviral vectors to transduce specific genes that generate cytotoxic activity and/or a systemic antitumour immune response. In addition we have completed initial studies that demonstrate the therapeutic potential of adenoviral vector-mediated gene modified cell-based vaccines. Our review discusses preclinical studies focused on the development of immunostimulatory in situ gene therapy approaches that hopefully will provide novel and effective treatments for localised and metastatic prostate cancer.

Making decisions through Myc

c-Myc is a transcriptional regulator involved in carcinogenesis through its role in growth control and cell cycle progression. Here we attempt to relate its role in stimulating the G1-S transition to the ability to affect functioning of key cell cycle regulators, and we focus on how its property of modulating transcription of a wide range of target genes could explain its capacity to affect multiple pathways leading to proliferation, apoptosis, growth, and transformation.

p16/MTS1/INK4A suppresses prostate cancer by both pRb dependent and independent pathways

Tumor suppressor gene p16 is a cyclin-dependent kinase inhibitor and an important negative cell cycle regulator. The inactivation of p16 appears to be a common event in prostate cancer. Replacement of p16 inhibits prostate tumor cell growth, but the mechanism is not known. Human prostate cancer cell lines PPC-1, which has an inactivated p16, and DU145, which has a nonfunctional retinoblastoma Rb protein (pRb), were used to determine the possible mechanism of p16 mediated growth inhibition. PPC-1 cells treated with 5-aza-2'-deoxycytidine (5-aza-dC), a demethylating agent, induced p16 expression, inhibited cell growth, and induced senescence. Similarly, PPC-1 cells transduced by an adenoviral vector containing the p16 gene (AdRSVp16) produced a p16 protein that suppressed cellular proliferation and induced senescence. Co-staining of AdRSVp16-transduced PPC-1 cells by p16 immunohistochemistry and by beta-galactosidase substrate X-gal showed that the morphologically enlarged cells expressed both p16 and senescence-associated beta-galactosidase. In contrast, AdRSVp16 did not induce senescence in DU145 cells, but did inhibit its growth. However, when wild-type pRb was introduced in DU145 cells, AdRSVp16 was able to induce senescence. Thus, the mechanism by which p16 suppressed prostate cancer was dependent on the pRb functional status of cells whereby p16 caused pRb+ cells to undergo inhibition by senescence, whereas pRb- cells were also inhibited, but not by senescence.

Recent developments in the virus therapy of cancer

Cancer is one of the leading causes of death in the United States. Although there has been significant progress in the areas of cancer etiology, diagnostic techniques, and cancer prevention, adequate therapeutic approaches for many cancers have lagged behind. One promising line of investigation is the virus therapy of cancer. This approach entails the use of viruses, such as retroviruses, adenovirus, and vaccinia virus, to modify tumor cells so that they become more susceptible to being killed by the host immune response, chemotherapeutic agents, or programmed cell death. This review discusses recent advances in the virus therapy of cancer from both basic science and clinical perspectives. Given the potential of viruses to kill tumor cells directly or transduce desired gene products to allow a vigorous host antitumor immune response, the virus therapy of cancer holds great promise in the treatment of cancer.

Coamplification of prostate stem cell antigen (PSCA) and MYC in locally advanced prostate cancer

Gain of sequences on chromosome arm 8q is a common feature of prostate cancer that may correlate with metastatic and androgen-independent progression. The target gene(s) for this gain is not known, although MYC is amplified in a subset of advanced tumors and is one potential candidate. Prostate stem cell antigen (PSCA) is a prostate-specific cell surface protein that maps to chromosome region 8q24.2 and is overexpressed in prostate cancer. Our aim in this study was to test the hypothesis that PSCA overexpression may result from overrepresentation of chromosome arm 8q. Twenty locally advanced prostate cancers were analyzed by dual-probe fluorescence in situ hybridization (FISH) for alterations of MYC and PSCA. Extra copies of MYC were found in 12/20 (60%) tumors, including 5 (25%) with simple gain (no increase in MYC copy number relative to the chromosome 8 centromere) and 7 (35%) with an additional increase (AI or overrepresentation) in MYC copy number relative to the centromere. In the five cases with simple gain of MYC, there was a concomitant gain of PSCA. PSCA was overrepresented in 5/7 (71%) cases with AI of MYC. Immunohistochemical staining of the 20 tumors with monoclonal antibodies specific for PSCA showed a high degree of correlation between PSCA gene overrepresentation and protein overexpression. Four of 5 tumors with AI of PSCA overexpressed PSCA protein, compared with only 2/15 tumors with a normal PSCA copy number or simple gain of PSCA (P = 0.014). These results demonstrate that PSCA is co-overrepresented with MYC in a majority of cases, but may not be a necessary part of the 8q amplicon. PSCA protein overexpression can result from AI of PSCA and might be useful as a cell surface marker on prostate cancer cells with 8q overrepresentation. Genes Chromosomes Cancer 27:95-103, 2000.

Clinical significance of alterations of chromosome 8 in high-grade, advanced, nonmetastatic prostate carcinoma

BACKGROUND

Chromosome 8 alterations, including loss of 8p21-22 and gain of 8q24, are commonly observed in prostate carcinoma. We examined whether these alterations are associated with poor prognosis in prostate cancer.

METHODS

We used dual-probe fluorescence in situ hybridization and DNA probes for 8p22 (lipoprotein lipase gene), centromere 8 (8cen), and 8q24 (c-myc gene) to determine the corresponding copy numbers in tumor samples from 144 patients with high-grade, advanced (stage III) prostate carcinoma. Cox models were used for multivariate analysis of systemic progression or patient death from prostate cancer. All statistical tests are two-sided.

RESULTS

We classified the 8p22, 8cen, and c-myc copy number as normal, loss, and gain. An additional increase (AI) category of c-myc relative to the centromere copy number (i.e., overrepresentation and amplification of c-myc) was also used. Alterations of 8p22 were not statistically significantly associated with either systemic progression or patient death. Alterations of c-myc were associated with both systemic progression (P =.024) and patient death (P =.039); AI of c-myc showed the poorest outcome. We also evaluated the prognostic relevance of the combined 8p22-8cen-c-myc loci anomaly pattern for the following six patterns: normal-normal-normal, loss-any 8cen-normal, loss-gain-gain, gain-gain-gain, non-loss-any 8cen-AI, and loss-any 8cen-AI, where any 8cen is normal, loss, or gain of the chromosome 8 centromere. Patients with the loss-any 8cen-AI pattern had earlier systemic progression (P =.009) and earlier cause-specific death (P =.013) than did patients with other patterns. Multivariate analyses demonstrated that the loss-any 8cen-AI pattern was an independent risk factor for systemic progression (P<.001) and cause-specific death (P =.002).

CONCLUSIONS

Genetic alterations of chromosome 8 appear to accumulate in parallel with the progression of prostate carcinomas. AI of the c-myc gene, especially with loss of 8p22, appears to be associated with poor patient prognosis.

Gene therapy for prostate cancer. New perspectives on an old problem

Recent advances in molecular biology have made the prospect of gene therapy for prostate cancer a reality. A wide variety of genetic strategies, vector designs, and delivery modalities are currently in use. This article examines the state of the art prostate cancer gene therapy and details the various options available to clinicians.