Adenovirus mediated prostate specific enzyme prodrug gene therapy using prostate specific antigen promoter enhanced by the Cre-loxP system

Applications of tissue-specific and cancer-selective gene promoters for cancer diagnosis and therapy

Current treatment of solid tumors with standard of care chemotherapies, radiation therapy and/or immunotherapies are often limited by severe adverse toxic effects, resulting in a narrow therapeutic index. Cancer gene therapy represents a targeted approach that in principle could significantly reduce undesirable side effects in normal tissues while significantly inhibiting tumor growth and progression. To be effective, this strategy requires a clear understanding of the molecular biology of cancer development and evolution and developing biological vectors that can serve as vehicles to target cancer cells. The advent and fine tuning of omics technologies that permit the collective and spatial recognition of genes (genomics), mRNAs (transcriptomics), proteins (proteomics), metabolites (metabolomics), epiomics (epigenomics, epitranscriptomics, and epiproteomics), and their interactomics in defined complex biological samples provide a roadmap for identifying crucial targets of relevance to the cancer paradigm. Combining these strategies with identified genetic elements that control target gene expression uncovers significant opportunities for developing guided gene-based therapeutics for cancer. The purpose of this review is to overview the current state and potential limitations in developing gene promoter-directed targeted expression of key genes and highlights their potential applications in cancer gene therapy.

A Winning New Combination? Toward Clinical Application in Oncology

Immunotherapy has substantial attention in oncology due to the success of CTLA-4 and PD-1 inhibitors in the treatment of melanoma, lung cancer, head and neck cancer, renal cell carcinoma, and Hodgkin's lymphoma. A deeper understanding of interaction of tumor with its environment and the immune system provides best guide for oncology research. Recent studies in oncology have explained how a tumor alters antigen presentation, avoids detection, and activation of the host immune system to live and develop. Understanding the connections between the tumor and the immune system has resulted in several innovative therapy options. The extensive field of gene therapy has provided a number of cutting-edge medicines that are expected to play an important role in lowering cancer-related mortality. This article explains the history, important breakthroughs, and future prospects for three separate gene therapy treatment modalities: immunotherapy, oncolytic virotherapy, and gene transfer. Immunotherapies have completely changed how cancer is treated, especially for individuals whose condition was previously thought to be incurable. Examples include ACT (adoptive cell therapy) and ICB (immune checkpoint blockade). This review article will discuss the relationship between the immune response to cancer and the mechanisms of immunotherapy resistance. It will cover combination drugs authorized by the US Food and Drug Administration and provide a thorough overview of how these drugs are doing clinically right now. Cytokines, vaccines, and other soluble immunoregulatory agents, innate immune modifiers, ACT, virotherapy, and other treatment modalities will all be covered in detail.

World Trade Center dust exposure promotes cancer in PTEN-deficient mouse prostates

During the 9/11 attacks individuals were exposed to World Trade Center (WTC) dust which contained a complex mixture of carcinogens. Epidemiological studies have revealed the increased incidence of prostate and thyroid cancer in WTC survivors and responders. While reports have shown that WTC-dust associates with the increased prevalence of inflammatory related disorders, studies to date have not determined whether this exposure impacts cancer progression. In this study, we have used genetically engineered mouse (GEM) models with prostate specific deletion of the PTEN tumor suppressor to study the impact of WTC-dust exposure on deposition of dust particles, inflammation, and cancer progression. In normal C57/BL6 mice, dust exposure increased cellular expression of inflammatory genes with highest levels in the lung and peripheral blood. In normal and tumor bearing GEM mice, increased immune cell infiltration to the lungs was observed. Pathological evaluation of mice at different time points showed that WTC-dust exposure promoted PI3K-AKT activation, increased epithelial proliferation and acinar invasion in prostates with heterozygous and homozygous Pten loss. Using autochthonous and transplant GEM models of prostate cancer we demonstrated that dust exposure caused reduced survival as compared to control cohorts. Finally, we used imaging mass cytometry (IMC) to detect elevated immune cell infiltration and cellular expression of inflammatory markers in prostate tumors isolated from human WTC survivors. Collectively, our study shows that chronic inflammation, induced by WTC dust exposure, promotes more aggressive cancer in genetically predisposed prostates and potentially in patients.

Enhanced Vector Design for Cancer Gene Therapy with Hierarchical Enhancement of Therapeutic Transgene Expression

A set of vectors for Cre recombinase-dependent expression of the hybrid suicidal FCU1 transgene was constructed, including a two-plasmid system wherein the FCU1 and Cre transgenes reside in separate vectors, and single-plasmid variants in which a single plasmid bears both transgenes. To improve the safety profile and specificity in cancer gene therapy applications, as well as to ensure stable propagation of plasmids in bacterial cells, the Cre/LoxP system components were optimized. A bicistronic vector with the Cre expression cassette placed between the LoxP sites unidirectionally with FCU1 cDNA resulted in higher therapeutic efficiency compared with the double-plasmid system in an enzyme-prodrug suicide cancer gene therapy scheme. Therefore, the feasibility of a single-plasmid approach in the development of cancer gene therapy with hierarchical enhancement of therapeutic transgene expression has been demonstrated.

Targeted prodrug approaches for hormone refractory prostate cancer

Due to the propensity of relapse and resistance with prolonged androgen deprivation therapy (ADT), there is a growing interest in developing non-hormonal therapeutic approaches as alternative treatment modalities for hormone refractory prostate cancer (HRPC). Although the standard treatment for HRPC consists of a combination of ADT with taxanes and anthracyclines, the clinical use of chemotherapeutics is limited by systemic toxicity stemming from nondiscriminatory drug exposure to normal tissues. In order to improve the tumor selectivity of chemotherapeutics, various targeted prodrug approaches have been explored. Antibody-directed enzyme prodrug therapy (ADEPT) and gene-directed enzyme prodrug therapy (GDEPT) strategies leverage tumor-specific antigens and transcription factors for the specific delivery of cytotoxic anticancer agents using various prodrug-activating enzymes. In prostate cancer, overexpression of tumor-specific proteases such as prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) is being exploited for selective activation of anticancer prodrugs designed to be activated through proteolysis by these prostate cancer-specific enzymes. PSMA- and PSA-activated prodrugs typically comprise an engineered high-specificity protease peptide substrate coupled to a potent cytotoxic agent via a linker for rapid release of cytotoxic species in the vicinity of prostate cancer cells following proteolytic cleavage. Over the past two decades, various such prodrugs have been developed and they were effective at inhibiting prostate tumor growth in rodent models; several of these prodrug approaches have been advanced to clinical trials and may be developed into effective therapies for HRPC.

High-level expression by tissue/cancer-specific promoter with strict specificity using a single-adenoviral vector

Tissue-/cancer-specific promoters for use in adenovirus vectors (AdVs) are valuable for elucidating specific gene functions and for use in gene therapy. However, low activity, non-specific expression and size limitations in the vector are always problems. Here, we developed a 'double-unit' AdV containing the Cre gene under the control of an α-fetoprotein promoter near the right end of its genome and bearing a compact 'excisional-expression' unit consisting of a target cDNA 'upstream' of a potent promoter between two loxPs near the left end of its genome. When Cre was expressed, the expression unit was excised as a circular molecule and strongly expressed. Undesired leak expression of Cre during virus preparation was completely suppressed by a dominant-negative Cre and a short-hairpin RNA against Cre. Using this novel construct, a very strict specificity was maintained while achieving a 40- to 90-fold higher expression level, compared with that attainable using a direct specific promoter. Therefore, the 'double-unit' AdV enabled us to produce a tissue-/cancer-specific promoter in an AdV with a high expression level and strict specificity.

Prodrug cancer gene therapy

There is no effective treatment for late stage and metastatic cancers of colorectal, prostate, pancreatic, breast, glioblastoma and melanoma cancers. Novel treatment modalities are needed for these late stage patients because cytotoxic chemotherapy offers only palliation, usually accompanied with systemic toxicities and poor quality of life. Gene directed enzyme prodrug therapy (GDEPT), which concentrates the cytotoxic effect in the tumor site may be one alternative. This review provides an explanation of the GDEPT principle, focusing on the development, application and potential of various GDEPTs. Current gene therapy limitations are in efficient expression of the therapeutic gene and in tumor-specific targeting. Therefore, the current status of research related to the enhancement of in situ GDEPT delivery and tumor-specific targeting of vectors is assessed. Finally, GDEPT versions of stem cell based gene therapy as another potential treatment modality for progressed tumors and metastases are discussed. Combinations of traditional, targeted, and stem cell directed gene therapy could significantly advance the treatment of cancer.

The tumorigenicity diversification in human embryonic kidney 293 cell line cultured in vitro

The Human Embryonic Kidney (HEK) 293 cell line is widely used in research work such as vaccine production, adenovirus and adeno-associated viral vectors, and gene therapy. However, little attention was drawn to the passage level of 293 cells. We first claim that the tumorigenicity of the HEK 293 cell line reached 100% when the passage exceeded 65, whereas using low-passage (<52) HEK 293 cell line no tumor could be induced under the same condition. Results from nude mice assay, tumor tissue histological examination, primary culture, PCR and isoenzyme analysis showed that the tumor in nude mice could only be induced by viable high-passage 293 cells. This suggests that more attention should be paid to the passage level of the HEK 293 cell line, especially for vaccine production but the low-passage HEK 293 cell line should be acceptable to regulatory authorities for recombinant virus vector, vaccines, and gene therapy. Meanwhile, we also find that high-passage HEK 293 can be employed as a highly malignant tumor model as its tumorigenicity increases significantly.

Reversible transfection of human melanocytes mediated by Cre/loxP site-specific recombination system and SV40 large T antigen

OBJECTIVE

To study the reversible transfection of human melanocytes mediated by simian virus 40 large T antigen (SV40LTAg) and Cre/loxP site-specific recombination system.

METHODS

The reconstructed SV40LTAg-EGFP-neo-loxP vector was transfected into primary cultured human melanocytes with Sofast(TM) transfection reagent and the positive cells were selected using G418. After expanding culture of these positive cell clones, the expression of SV40LTAg was detected by polymerase chain reaction (PCR), reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescent method. After that, these positive cells were infected by virus supernatant of Cre-ER(T2) retrovirus vector and Cre recombinase was induced to act by tamoxifen. On the 6th and 10th day after Cre recombinase acting, the expression of SV40LTAg was detected using the same methods as above, and cell tumorigenicity was studied using soft agar assay, athymic mouse study and karyotype analysis. On 10th day after tamoxifen treatment, cell biological characters were identified with immunofluorescent staining and transmission electron microscopy. Then these cells were transplanted into vitiligo animal model to observe their melanogenesis ability in vivo.

RESULTS

The genome DNA and total RNA were isolated from the positive cells transfected by SV40LTAg (designated as MCT) and specific 288 bp fragment was amplificated using PCR and RT-PCR methods. The results of immunofluorescence confirmed the expression of SV40LTAg in cell nucleus. On the 6th day after tamoxifen treatment in infected cells by Cre-ER(T2) retrovirus vector (designated as MCT-Cre), there could be detected SV40LTAg expression, but on 10th day, there could not be detected SV40LTAg expression in cells. These results showed that the excised efficiency of Cre recombinase increased along with time prolongation, and would obtain complete recombination efficiency. The identification of MCT-Cre cell biological characters showed that these cells had normal parent-cell-like cell phenotype and no tumorigenicity in vitro. The pigmentation started in 4 weeks and formed black macula in 3 months after grafting. The pathological results showed that there had been significant melanocytes and melanin accumulation in epidermis and some hair follicle in transplanted area, which confirmed that MCT-Cre had melanogenesis function in vivo.

CONCLUSION

Human melanocytes could be mediated by reversible transfection by SV40LTAg and Cre/loxP site-specific recombination system, which had stable parent-cell-like phenotypic characters and no tumorigenicity in vitro; moreover, these cells still had melanogenesis function in vivo.

Effective ablation of pancreatic cancer cells in SCID mice using systemic adenoviral RIP-TK/GCV gene therapy

BACKGROUND

Studies have demonstrated that adenovirus subtype 5 mediated rat insulin promoter directed thymidine kinase (A-5-RIP-TK)/ganciclovir (GCV) gene therapy resulted in significant enhanced cytotoxicity to both PANC-1 and MIA PaCa2 pancreatic cancer cells in vitro. However, little is known about the effect in vivo. In this study we examine the in vivo safety and efficacy of intravenous A-5-RIP-TK/GCV gene therapy.

MATERIALS AND METHODS

1 x 10(6) Mia PaCa2 cells were injected intraperitoneally (i.p.) into SCID mice to create a mouse model of human pancreatic cancer. A-5-RIP-TK gene construct was administered intravenously (i.v.), followed by i.p. GCV administration. Intravenous injection of A-5-RIP-lacZ reporter gene constructs was used for evaluation of Ad-RIP-gene expression in tumors and other tissues. Optimal adenoviral and GCV doses and treatment duration were determined. Tumor volume, serum insulin, and glucose levels were measured. Immunohistochemical staining of pancreata and tumors were performed to assess morphology and hormone expression and apoptotic rates were determined.

RESULTS

All A-5-RIP-TK/GCV-treated mice had reduced tumor volume compared with controls, but maximal tumor volume reduction was observed with 10(8) vp followed by GCV treatment for 4 wk. A-5-RIP-TK/GCV gene therapy contributed to significant survival advantage in MIA PaCa2 bearing mice, and the greatest survival benefit was observed with 10(8) vp and was not affected by length of treatment of GCV. A-5-RIP-TK/GCV therapy increased PDX-1 expression and tumor cells apoptosis, and altered islet morphology. However, A-5-RIP-TK/GCV gene therapy caused diabetes associated with islet cell apoptosis, increased delta-cells and reduced pancreatic polypeptide (PP)-cell numbers.

CONCLUSIONS

Systemically administered A-5-RIP-TK/GCV is an effective treatment of pancreatic cancer. A-5-RIP-TK/GCV cytotoxicity to malignant cells varies with adenoviral dose and length of GCV treatment. However, A-5-RIP-TK/GCV is associated with islet cell toxicity and diabetogenesis. The type of diabetes observed is distinct from Types 1 and 2 and is associated with islet cell apoptosis and reduced delta- and PP-cells.

Advances in preclinical investigation of prostate cancer gene therapy

Treating recurrent prostate cancer poses a great challenge to clinicians. Research efforts in the last decade have shown that adenoviral vector-based gene therapy is a promising approach that could expand the arsenal against prostate cancer. This maturing field is at the stage of being able to translate many preclinical discoveries into clinical practices. At this juncture, it is important to highlight the promising strategies including prostate-targeted gene expression, the use of oncolytic vectors, therapy coupled to reporter gene imaging, and combined treatment modalities. In fact, the early stages of clinical investigation employing combined, multimodal gene therapy focused on loco-regional tumor eradication and showed promising results. Clinicians and scientists should seize the momentum of progress to push forward to improve the therapeutic outcome for the patients.

Two-step transcriptional amplification-lipid-based nanoparticles using PSMA or midkine promoter for suicide gene therapy in prostate cancer

A two-step transcriptional amplification system (TSTA) was used to enhance the efficacy of suicide gene therapy for treatment of prostate cancer. We designed a TSTA system and constructed two types of plasmid: one containing GAL4-VP16 fusion protein under the control of a tumor-specific promoter, the other containing luciferase or herpes simplex virus thymidine kinase (HSV-tk) under the control of a synthetic promoter. The TSTA systems using nanoparticles based on lipids were evaluated by measuring the amount of induced luciferase activity as a function of prostate-specific membrane antigen (PSMA) and midkine (Mk) promoters, specific for LNCaP and PC-3 prostate cancer cells, respectively. In LNCaP cells that were PSMA-positive, the TSTA system featuring the PSMA enhancer and promoter exhibited activity that was 640-fold greater than a system consisting of one-step transcription with the PSMA promoter. In contrast, this difference in activity did not occur in PSMA-negative PC-3 cells. In Mk-positive PC-3 cells, the TSTA system with the Mk promoter exhibited a five-fold increase in activity over one-step transcription, but such activity was not induced in Mk-negative LNCaP cells. When using HSV-tk for suicide gene therapy, TSTA systems featuring the PSMA or Mk promoter inhibited in vitro cell growth in the presence of ganciclovir. Furthermore, the TSTA system featuring the Mk promoter suppressed in vivo growth of PC-3 tumor xenografts to a greater extent than one-step transcription. These findings show that TSTA systems can enhance PSMA and Mk promoter activities and selectively inhibit PC-3 cell growth in tumors. This suggests that TSTA systems featuring tumor-specific promoters are suitable for cancer treatment by gene therapy.

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.

Properties of a telomerase-specific Cre/Lox switch for transcriptionally targeted cancer gene therapy

Telomerase expression represents a good target for cancer gene therapy. The promoters of the core telomerase catalytic [human telomerase reverse transcriptase (hTERT)] and RNA [human telomerase RNA (hTR)] subunits show selective activity in cancer cells but not in normal cells. This property can be harnessed to express therapeutic transgenes in a wide range of cancer cells. Unfortunately, weak hTR and hTERT promoter activities in some cancer cells could limit the target cell range. Therefore, strategies to enhance telomerase-specific gene therapy are of interest. We constructed a Cre/Lox reporter switch coupling telomerase promoter specificity with Cytomegalovirus (CMV) promoter activity, which is generally considered to be constitutively high. In this approach, a telomerase-specific vector expressing Cre recombinase directs excisive recombination on a second vector, removing a transcriptional blockade to CMV-dependent luciferase expression. We tested switch activation in cell lines over a wide range of telomerase promoter activities. However, Cre/Lox-dependent luciferase expression was not enhanced relative to expression using hTR or hTERT promoters directly. Cell-specific differences between telomerase and CMV promoter activities and incomplete sigmoid switch activation were limiting factors. Notably, CMV activity was not always significantly stronger than telomerase promoter activity. Our conclusions provide a general basis for a more rational design of novel recombinase switches in gene therapy.

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.

Highly specific expression of luciferase gene in lungs of naïve nude mice directed by prostate-specific antigen promoter

PSA promoter has been demonstrated the utility for tissue-specific toxic gene therapy in prostate cancer models. Characterization of foreign gene overexpression in normal animals elicited by PSA promoter should help evaluate therapy safety. Here we constructed an adenovirus vector (AdPSA-Luc), containing firefly luciferase gene under the control of the 5837 bp long prostate-specific antigen promoter. A charge coupled device video camera was used to non-invasively image expression of firefly luciferase in nude mice on days 3, 7, 11 after injection of 2 x 10(9)PFU of AdPSA-Luc virus via tail vein. The result showed highly specific expression of the luciferase gene in lungs of mice from day 7. The finding indicates the potential limitations of the suicide gene therapy of prostate cancer based on selectivity of PSA promoter. By contrary, it has encouraging implications for further development of vectors via PSA promoter to enable gene therapy for pulmonary diseases.

Conditional animal models: a strategy to define when oncogenes will be effective targets to treat cancer

The ability to model cancer in the mouse has provided a robust methodology to dissect the molecular etiology of cancer. These models serve as potentially powerful platforms to preclinically evaluate novel therapeutics. In particular, the recent development of strategies to conditionally induce the or knockout the function of genes in a tissue specific manner has enabled investigators to engineer mice to demonstrate that the targeted inactivation of specific oncogenes can be effective in inducing sustained regression of tumors. Thus, these animal models will be useful to define the specific genes that will be therapeutically useful to target for the treatment of particular human cancers.

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.