Targeting and killing of prostate cancer cells using lentiviral constructs containing a sequence recognized by translation factor eIF4E and a prostate-specific promoter

Strategies to Improve the Safety of iPSC-Derived β Cells for β Cell Replacement in Diabetes

Allogeneic islet transplantation allows for the re-establishment of glycemic control with the possibility of insulin independence, but is severely limited by the scarcity of organ donors. However, a new source of insulin-producing cells could enable the widespread use of cell therapy for diabetes treatment. Recent breakthroughs in stem cell biology, particularly pluripotent stem cell (PSC) techniques, have highlighted the therapeutic potential of stem cells in regenerative medicine. An understanding of the stages that regulate β cell development has led to the establishment of protocols for PSC differentiation into β cells, and PSC-derived β cells are appearing in the first pioneering clinical trials. However, the safety of the final product prior to implantation remains crucial. Although PSC differentiate into functional β cells in vitro, not all cells complete differentiation, and a fraction remain undifferentiated and at risk of teratoma formation upon transplantation. A single case of stem cell-derived tumors may set the field back years. Thus, this review discusses four approaches to increase the safety of PSC-derived β cells: reprogramming of somatic cells into induced PSC, selection of pure differentiated pancreatic cells, depletion of contaminant PSC in the final cell product, and control or destruction of tumorigenic cells with engineered suicide genes.

Promoter-Operating Targeted Expression of Gene Therapy in Cancer: Current Stage and Prospect

The technique of targeted expression of interesting genes, including distinct delivery systems and specific gene promoter-operating expression, is an important strategy for gene therapy against cancers. Up to now, extensive literature documented the efficacy of distinct delivery systems, such as the liposome system, nano-particle system, polyetherimide (PEI) system, and so on, in cancer gene therapy. However, a related document on the potential value of using a specific gene promoter, such as a tumor suppressor, in cancer gene therapy was still scary. The main obstacle might be that the selection of an ideal gene promoter to operate interesting gene expression in cancer gene therapy is still not fully understood. Therefore, many efforts need to be done in order to make it a real power tool for the human clinical treatment of cancer patients. The purpose of this review is to clarify the current state and some problematics in development of promoter-operating targeted expression of interesting genes and highlight its potential in cancer gene therapy.

Targeting of protein translation as a new treatment paradigm for prostate cancer

PURPOSE OF REVIEW

The current overview will summarize some of the developments in the area of protein translation, including their relation to the therapeutic targeting of prostate cancer.

RECENT FINDINGS

Translational control, mediated by the rate-limiting eukaryotic translation initiation factor 4E (eIF4E), drives selective translation of several oncogenic proteins, thereby contributing to tumor growth, metastasis, and treatment resistance in various cancers, including prostate cancer. As an essential regulatory hub, several oncogenic hyperactive signaling pathways appear to converge on eIF4E to promote tumorigenesis. Several approaches that target the eIF4E-dependent protein translation network are being actively studied, and it is likely that some may ultimately emerge as promising anticancer therapeutics.

SUMMARY

An array of inhibitors has shown promise in targeting specific components of the translational machinery in several preclinical models of prostate cancer. It is hoped that some of these approaches may ultimately have relevance in improving the clinical outcomes of patients with advanced prostate cancer.

Simultaneous targeting of androgen receptor (AR) and MAPK-interacting kinases (MNKs) by novel retinamides inhibits growth of human prostate cancer cell lines

Androgen receptor (AR) and MNK activated eIF4E signaling promotes the development and progression of prostate cancer (PCa). In this study, we report that our Novel Retinamides (NRs) target both AR signaling and eIF4E translation in androgen sensitive and castration resistant PCa cells via enhancing AR and MNK degradation through ubiquitin-proteasome pathway. Dual blockade of AR and MNK initiated eIF4E activation by NRs in turn induced cell cycle arrest, apoptosis, and inhibited cell proliferation. NRs also inhibited cell migration and invasion in metastatic cells. Importantly, the inhibitory effects of NRs on AR signaling, eIF4E translation initiation and subsequent oncogenic program were more potent than that observed with clinically relevant retinoids, established MNK inhibitors, and the FDA approved PCa drugs. Our findings provide the first preclinical evidence that simultaneous inhibition of AR and eIF4E activation is a novel and efficacious therapeutic approach for PCa, and that NRs hold significant promise for treatment of advanced prostate cancer.

Safeguarding clinical translation of pluripotent stem cells with suicide genes

The generation of human induced pluripotent stem cells (hiPSCs) opens a new avenue in regenerative medicine. However, transplantation of hiPSC-derived cells carries a risk of tumor formation by residual pluripotent stem cells. Numerous adaptive strategies have been developed to prevent or minimize adverse events and control the in vivo behavior of transplanted stem cells and their progeny. Among them, the application of suicide gene modifications, which is conceptually similar to cancer gene therapy, is considered an ideal means to control wayward stem cell progeny in vivo. In this review, the choices of vectors, promoters, and genes for use in suicide gene approaches for improving the safety of hiPSCs-based cell therapy are introduced and possible new strategies for improvements are discussed. Safety-enhancing strategies that can selectively ablate undifferentiated cells without inducing virus infection or insertional mutations may greatly aid in translating human pluripotent stem cells into cell therapies in the future.

AKT/mTOR as Novel Targets of Polyphenol Piceatannol Possibly Contributing to Inhibition of Proliferation of Cultured Prostate Cancer Cells

The polyphenol piceatannol has shown inhibition against tyrosine and serine/threonine kinases. Whether piceatannol also exerts activity on the mammalian target of rapamycin (mTOR), a kinase involved in growth control of eukaryotic cells, is not known. In this study, we tested the effects of piceatannol on proliferation of androgen-dependent (AD) LNCaP and androgen-independent (AI) DU145 and PC-3 prostate cancer (CaP) cells. Suppression of AD and AI CaP cell growth by piceatannol was accompanied by cell cycle blockade in G(1)/S and S phases for LNCaP and PC-3 and induction of apoptosis in DU145 cells. Induction of apoptosis by piceatannol in DU145 cells was evident by reduced expression of poly(ADP-ribose) polymerase (PARP), cleavage of caspase 3 and apoptosis inducing factor AIF, and an increase in cytochrome c. The apoptotic changes occurred in concordance with DNA damage, supported by increased phosphorylated histone H2AX. Immunoblot analyses showed that exposure of different-stage CaP cells to piceatannol also resulted in cell-type-specific downregulation of mTOR and its upstream and downstream effector proteins, AKT and eIF-4E-BP1. We propose that the observed AKT and mTOR changes are new targets of piceatannol possibly contributing to its inhibitory activities on proliferation of CaP cells.

Fibroblast growth factor and ornithine decarboxylase 5'UTRs enable preferential expression in human prostate cancer cells and in prostate tumors of PTEN(-/-) transgenic mice

In this study, we have taken advantage of over-expression of eukaryotic translation initiation factor 4E (eIF4E) in prostate cancer cells to design a viral-based targeting system of prostate cancer. Three different lengths of 5'-untranslated regions (5'UTRs) derived from either fibroblast growth factor-2 (FU-FGF2-GW) or ornithine decarboxylase (FU-ODC149-GW and FU-ODC274-GW) were inserted upstream of enhanced green fluorescent protein (GFP) gene in a lentiviral backbone. Both nonmalignant control (PNT1B and BPH-1) and neoplastic (LNCaP, C4-2, DU145 and PC-3) prostate cell lines were transfected with each plasmid or virus alone, or in the presence of siRNA against eIF4E, and their expression was monitored via GFP protein levels. Two 5'UTRs (FU-FGF2-GW and FU-ODC-GW) were selected as being most sensitive to eIF4E status. Lentiviruses containing these sequences were injected directly into the prostates of PTEN(-/-) (tumor-bearing) and control mice. Immunofluorescence data and western blot analyses determined that a lentivirus containing a 5'UTR derived from FGF-2 is the best candidate for directing selective gene expression in the prostate tumors of PTEN(-/-) mice in vivo. This study demonstrates that judicious selection of a complex 5'UTR can enhance selective targeting of viral-based gene therapies for prostate cancer.

Translational control gone awry: a new mechanism of tumorigenesis and novel targets of cancer treatments

Translational control is one of primary regulation mechanisms of gene expression. Eukaryotic translational control mainly occurs at the initiation step, the speed-limiting step, which involves more than ten translation initiation factors [eIFs (eukaryotic initiation factors)]. Changing the level or function of these eIFs results in abnormal translation of specific mRNAs and consequently abnormal growth of cells that leads to human diseases, including cancer. Accumulating evidence from recent studies showed that the expression of many eIFs was associated with malignant transformation, cancer prognosis, as well as gene expression regulation. In the present paper, we perform a critical review of recent advances in understanding the role and mechanism of eIF action in translational control and cancer as well as the possibility of targeting eIFs for therapeutic development.

Progranulin deficiency leads to enhanced cell vulnerability and TDP-43 translocation in primary neuronal cultures

Null mutations in the progranulin gene (PGRN) have been identified as a major cause of frontotemporal dementia with ubiquitinated inclusions. In this disorder, ubiquitinated, aggregated protein inclusions of a normally nuclear-located RNA processing protein called TAR DNA binding protein (TDP-43) accumulate in the neuronal cytoplasm (FTLD-TDP). To determine whether aspects of this clinical pathology can be established in primary cultures of mouse cortical neurons, PGRN levels were knocked down in neuronal cultures using lentiviral vectors to introduce mouse PGRN-siRNA constructs and subsequently rescued by overexpressing PGRN using a human PGRN-expressing lentiviral vector. The depletion of PGRN enhanced caspase-3 activation, and the PGRN-deficient neurons demonstrated enhanced vulnerability to normally sublethal doses of N-methyl-D-aspartic acid (NMDA) and hydrogen peroxide (H(2)O(2)). TDP-43 protein levels were markedly increased in the cytoplasm of PGRN-deficient neurons relative to nuclear levels, which is similar to observations in the brains of FTLD-TDP patients. Our results establish a neuronal culture model of the PGRN deficiency, which displays some of the important phenotypic characteristics of the early stages of the disease. The results further suggest that the seeds of this form of frontotemporal dementia may be sown early in life.

Bioengineered viral vectors for targeting and killing prostate cancer cells

Enabling the transduction of therapeutic gene expression exclusively in diseased sites is the key to developing more effective treatments for advanced prostate cancer using viral-based therapy. While prostate cancers that express high levels of HER-2 are resistant to the killing effects of trastuzumab, they can be targeted for selective gene expression and destruction by lentiviruses with envelope proteins engineered to bind to this therapeutic antibody. More importantly, after intravenous injection, this trastuzumab-bound lentivirus is able to target castration-resistant prostate tumor xenografts, albeit with low efficiency. This proof of principle opens up multiple possibilities for the prevention and treatment of prostate cancer using a viral-based therapy. However, to be safe and more effective, the viral vectors must target prostate cancer cells more selectively and efficiently. A higher degree of specificity and efficiency of cancer cell targeting can be achieved by engineering viral vectors to bind to a specific cell surface marker and by controlling the expression of the therapeutic payload at transcriptional level, with a tissue-specific promoter, and at the translational level, with a regulatory sequences inserted into either the 5'UTR or 3'UTR regions of the therapeutic gene(s). The latter would be designed to ensure that translation of this mRNA occurs exclusively in malignant cells. Furthermore, in order to obtain a potent anti-tumor effect, viral vectors would be engineered to express pro-apoptotic genes, intra-cellar antibodies/nucleotide aptamers to block critical proteins, or siRNAs to knockdown essential cellular mRNAs. Alternatively, controlled expression of an essential viral gene would restore replication competence to the virus and enable selective oncolysis of tumor cells. Successful delivery of such bioengineered viruses may provide a more effective way to treat advanced prostate cancer.

Transcriptional and translational dual-regulated oncolytic herpes simplex virus type 1 for targeting prostate tumors

The aim of this project was to demonstrate that an oncolytic herpes simplex virus type 1 (HSV-1) can replicate in a tissue- and tumor-specific fashion through both transcriptional (prostate-specific promoter, ARR(2)PB) and translational (5'-untranslated regions (5'UTRs) of rFGF-2) regulation of an essential viral gene, ICP27. We generated two recombinant viruses, ARR(2)PB-ICP27 (A27) and ARR(2)PB-5'UTR-ICP27 (AU27) and tested their efficacy and toxicity both in vitro and in vivo. The ARR(2)PB promoter caused overexpression of ICP27 gene in the presence of activated androgen receptors (ARs) and increased viral replication in prostate cells. However, this transcriptional upregulation was effectively constrained by the 5'UTR-mediated translational regulation. Mice bearing human prostate LNCaP tumors, treated with a single intravenous injection of 5 x 10(7) plaque-forming units (pfu) of AU27 virus exhibited a >85% reduction in tumor size at day 28 after viral injection. Although active viral replication was readily evident in the tumors, no viral DNA was detectable in normal organs as measured by real-time PCR analyses. In conclusion, a transcriptional and translational dual-regulated (TTDR) viral essential gene expression can increase both viral lytic activity and tumor specificity, and this provides a basis for the development of a novel tumor-specific oncolytic virus for systemic treatment of locally advanced and metastatic prostate cancers.

Molecular and traditional chemotherapy: a united front against prostate cancer

Castrate resistant prostate cancer (CRPC) is essentially incurable. Recently though, chemotherapy demonstrated a survival benefit ( approximately 2months) in the treatment of CRPC. While this was a landmark finding, suboptimal efficacy and systemic toxicities at the therapeutic doses warranted further development. Smart combination therapies, acting through multiple mechanisms to target the heterogeneous cell populations of PC and with potential for reduction in individual dosing, need to be developed. In that, targeted molecular chemotherapy has generated significant interest with the potential for localized treatment to generate systemic efficacy. This can be further enhanced through the use of oncolytic conditionally replicative adenoviruses (CRAds) to deliver molecular chemotherapy. The prospects of chemotherapy and molecular-chemotherapy as single and as components of combination therapies are discussed.

Targeting of prostate cancer cells by a cytotoxic lentiviral vector containing a prostate stem cell antigen (PSCA) promoter

BACKGROUND

The efficacy of prostate cancer gene therapy is limited by the inefficiency of prostate-specific promoters as compared to ubiquitous viral promoters. The purpose of this investigation was to evaluate the specificity and efficacy of a lentiviral vector driven by a PSCA promoter.

METHODS

Prostate cancer (LNCap, C42-B, and LAPC-4) and non-prostate cancer (HeLa, MB231, and MCF-7) cells were transduced with a lentiviral vector expressing either the luciferase or the HSV-TK suicide gene and driven by a short PSCA promoter. Specificity and efficacy were evaluated in vitro and in vivo.

RESULTS

Luciferase expression was only detected in prostate cancer cells and was comparable to the universal CMV promoter. Luciferase expression in prostate cancer cells cultured with androgen was higher than that in cells cultured without androgen. In subsequent cytotoxicity experiments in which the luciferase marker gene was replaced with the HSV-TK gene, the lentiviral vector harboring the PSCA promoter induced cytotoxicity in prostate cancer cell lines while demonstrating a minimal effect on non-prostate cells. Cellular toxicity was correlated to increasing concentrations of the prodrug ganciclovir. Androgen had a positive effect on the cytotoxicity of this lentiviral construct. Intratumoral injection of prostate cancer xenografts with the lentiviral construct induced tumor growth inhibition versus saline controls.

CONCLUSION

Our results indicate that a lentiviral gene therapy vector driven by a short PSCA promoter can induce prostate-specific cellular toxicity in vivo and in vitro and may provide a strategy to selectively treat local and advanced metastatic prostate cancer. Prostate 69: 1422-1434, 2009. (c) 2009 Wiley-Liss, Inc.

MicroRNA regulation of oncolytic herpes simplex virus-1 for selective killing of prostate cancer cells

PURPOSE

Advanced castration-resistant prostate cancer, for which there are few treatment options, remains one of the leading causes of cancer death. MicroRNAs (miRNA) have provided a new opportunity for more stringent regulation of tumor-specific viral replication. The purpose of this study was to provide a proof-of-principle that miRNA-regulated oncolytic herpes simplex virus-1 (HSV-1) virus can selectively target cancer cells with reduced toxicity to normal tissues.

EXPERIMENTAL DESIGN

We incorporated multiple copies of miRNA complementary target sequences (for miR-143 or miR-145) into the 3'-untranslated region (3'-UTR) of an HSV-1 essential viral gene, ICP4, to create CMV-ICP4-143T and CMV-ICP4-145T amplicon viruses and tested their targeting specificity and efficacy both in vitro and in vivo.

RESULTS

Although miR-143 and miR-145 are highly expressed in normal tissues, they are significantly down-regulated in prostate cancer cells. We further showed that miR-143 and miR-145 inhibited the expression of the ICP4 gene at the translational level by targeting the corresponding 3'-UTR in a dose-dependent manner. This enabled selective viral replication in prostate cancer cells. When mice bearing LNCaP human prostate tumors were treated with these miRNA-regulated oncolytic viruses, a >80% reduction in tumor volume was observed, with significantly attenuated virulence to normal tissues in comparison with control amplicon viruses not carrying these 3'-UTR sequences.

CONCLUSION

Our study is the first to show that inclusion of specific miRNA target sequences into the 3'-UTR of an essential HSV-1 gene is a viable strategy for restricting viral replication and oncolysis to cancer cells while sparing normal tissues.

Receptor-DNA interactions: EMSA and footprinting

Defining the precise promoter DNA sequence motifs where nuclear receptors and other transcription factors bind is an essential prerequisite for understanding how these proteins modulate the expression of their specific target genes. The purpose of this chapter is to provide the reader with a detailed guide with respect to the materials and the key methods required to perform this type of DNA-binding analysis. Irrespective of whether starting with purified DNA-binding proteins or somewhat crude cellular extracts, the tried-and-true procedures described here will enable one to accurately access the capacity of specific proteins to bind to DNA as well as to determine the exact sequences and DNA contact nucleotides involved. For illustrative purposes, we primarily have used the interaction of the androgen receptor with the rat probasin proximal promoter as our model system.

An internal polyadenylation signal substantially increases expression levels of lentivirus-delivered transgenes but has the potential to reduce viral titer in a promoter-dependent manner

In lentiviral gene delivery systems, transgene expression cassettes are commonly cloned without a polyadenylation signal to prevent disruption of full-length lentiviral genomes on mRNA maturation in producer cells. The lack of the polyadenylation signal, however, has the potential to reduce stability and translation efficiency of transgene mRNA. Therefore, we have assessed the effect of a strong internal polyadenylation [poly(A)] signal on both transgene expression levels in virus-infected cells and functional viral titer, in a series of eight self-inactivating lentiviruses expressing the mOrange transgene under the control of the constitutive cytomegalovirus (CMV), elongation factor 1alpha (EF1alpha), and beta-actin promoters or the highly tissue-specific prostate-specific antigen/probasin hybrid (PSA/Pb) promoter with or without a simian virus 40 (SV40) early polyadenylation signal downstream of the mOrange-coding sequence. We show that mOrange expression levels in virus-infected HEK-293, LNCaP, and primary prostate epithelial cells were increased 3- to 6.5-fold when an internal polyadenylation signal was present. When the CMV and EF1alpha promoters were used, functional viral titer decreased 8- to 9-fold in the presence of the polyadenylation signal, but titer was not affected when transgene expression was driven by the beta-actin promoter or tissue-specific PSA/Pb promoter. We therefore conclude that an internal polyadenylation signal in lentiviral vectors has a highly beneficial effect on transgene expression, but reduces viral titer in a promoter-dependent manner.

Carboxypeptidase-G2-based gene-directed enzyme-prodrug therapy: a new weapon in the GDEPT armoury

Gene-directed enzyme-prodrug therapy (GDEPT) aims to improve the therapeutic ratio (benefit versus toxic side-effects) of cancer chemotherapy. A gene encoding a 'suicide' enzyme is introduced into the tumour to convert a subsequently administered non-toxic prodrug into an active drug selectively in the tumour, but not in normal tissues. Significant effects can now be achieved in vitro and in targeted experimental models, and GDEPT therapies are entering the clinic. Our group has developed a GDEPT system that uses the bacterial enzyme carboxypeptidase G2 to convert nitrogen mustard prodrugs into potent DNA crosslinking agents, and a clinical trial of this system is pending.

An HSV-1 amplicon system for prostate-specific expression of ICP4 to complement oncolytic viral replication for in vitro and in vivo treatment of prostate cancer cells

The aim of the present study was to determine whether a prostate-specific amplicon, containing a probasin-derived promoter (ARR(2)PB) upstream of an essential Herpes simplex virus-1 (HSV-1) viral gene, infected-cell polypeptide 4 (ICP4), could complement an HSV-1 helper virus with this gene deleted (ICP4-) and cause lytic replication specifically in prostate cancer cells. Two amplicon constructs, CMV-ICP4 and ARR(2)PB-ICP4, were packaged by a replication-deficient ICP4- helper virus. The amplicon viruses could complement ICP4- helper viruses to efficiently replicate and cause cell lysis in prostate cancer cells. Intratumoral injection of LNCaP human prostate cancer xenografts with either amplicon/helper virus resulted in >75% reduction in tumor volume and serum prostate specific antigen (PSA). Histological and Q-PCR (quantitative PCR) analyses indicated that the toxicity in nontumor tissues was much lower with ARR(2)PB-ICP4 than with CMV-ICP4 amplicon/helper virus. In conclusion, a replication-deficient HSV-1 virus could be complemented by an amplicon virus to restore its oncolytic activity in a tissue-specific and low toxicity fashion, illustrating that this approach could be a potentially useful strategy for developing an oncolytic viral therapy for prostate cancer.

Mechanisms of translational deregulation in human tumors and therapeutic intervention strategies

Analysis of the recurrent genetic aberrations present in human tumors provides insight into how normal cells escape appropriate proliferation and survival cues. Commonly mutated genes encode proteins that monitor DNA damage (e.g., p53), proteins that regulate the cell cycle (such as Rb), and proteins that regulate signal transduction pathways (such as APC, PTEN and Ras). Analysis of the relevant targets and downstream events of these genes in normal and tumor cells will clearly highlight important pathways for tumorigenesis. However, more infrequent mutations are also informative in defining events critical for the process of tumorigenesis, and often delineate important pathways lying downstream of commonly mutated oncogenes and tumor suppressors. Together, these studies have led to the conclusion that deregulated protein synthesis plays an important role in human cancer. This review will discuss the evidence implicating mRNA translation as an important downstream consequence of signal transduction pathways initiated by mutated oncogenes and tumor suppressors, as well as additional genetic findings implicating the importance of global and specific translational control in human cancer. It will also discuss therapeutic strategies that take advantage of differences in translational regulation between normal and tumor cells.

Novel gene-directed enzyme prodrug therapies against prostate cancer

There is no effective cure for late-stage hormone (androgen) refractory prostate cancer. Although chemotherapy offers palliation to these late-stage patients, it also leads to systemic toxicities leading to poor quality of life. Clearly, the focus is on the development and evaluation of novel biologically relevant alternatives such as cytoreductive gene-directed enzyme prodrug therapy (GDEPT). With the current limitations of effective gene delivery in vivo, the in situ amplification of cytotoxicity due to bystander effects of GDEPT has special attraction for patients with prostate cancer, the prostate being dispensable. This review focuses on the development, application and potential of various GDEPTs for treating prostate cancer. The current status of research related to the issues of enhancement of in situ GDEPT delivery and prostate cancer-specific targeting of vectors (especially viral vectors) is assessed. Finally, the scope and progress of synergies between GDEPT and other treatment modalities, both traditional and alternate, are discussed.

Viral Vaccines for Cancer Immunotherapy

The understanding that tumor cells can be recognized and eliminated by the immune system has led to intense interest in the development of cancer vaccines. Viruses are naturally occurring agents that cause human disease but have the potential to prevent disease when attenuated forms or subunits are used as vaccines before exposure. A large number of viruses have been engineered as attenuated vaccines for the expression of tumor antigens, immunomodulatory molecules, and as vehicles for direct destruction of tumor cells or expression of highly specific gene products. This article focuses on the major viruses that are under development as cancer vaccines, including the poxviruses, adenoviruses, adeno-associated viruses, herpesviruses, retroviruses, and lentiviruses. The biology supporting these viruses as vaccines is reviewed and clinical progress is reported.