Gene therapy of thyroid cancer via retrovirally-driven combined expression of human interleukin-2 and herpes simplex virus thymidine kinase

Interleukins in Thyroid Cancer: From Basic Researches to Applications in Clinical Practice

Inflammation is crucial to tumorigenesis and progression of many cancers. Inflammatory molecules in tumor microenvironment exert pro- or anti-tumor effects. Among them, interleukin, mainly produced by CD3+ and CD4+ T lymphocytes, is a class of small molecule proteins which play an important role in intercellular communication. Numerous studies have confirmed that interleukins are closely related to thyroid cancer. Interleukins regulate the proliferation and migration of thyroid cancer cells and they have prospects in discriminating benign and malignant thyroid diseases, predicting the risk of tumorigenesis, evaluating the prognosis and monitoring the recurrence of thyroid cancer. Besides, the effective application of interleukins in treatment of thyroid cancer has been confirmed by some cell and animal researches. The present review will introduce the potential mechanisms of interleukins in thyroid cancer and focus on the applications of interleukins in clinical practice of thyroid cancer, which will help update understanding of the progress of interleukins researches in thyroid cancer.

Comparison of analytic methods for quantitative real-time polymerase chain reaction data

Polymerase chain reaction (PCR) is a laboratory procedure to amplify and simultaneously quantify targeted DNA molecules, and then detect the product of the reaction at the end of all the amplification cycles. A more modern technique, real-time PCR, also known as quantitative PCR (qPCR), detects the product after each cycle of the progressing reaction by applying a specific fluorescence technique. The quantitative methods currently used to analyze qPCR data result in varying levels of estimation quality. This study compares the accuracy and precision of the estimation achieved by eight different models when applied to the same qPCR dataset. Also, the study evaluates a newly introduced data preprocessing approach, the taking-the-difference approach, and compares it to the currently used approach of subtracting the background fluorescence. The taking-the-difference method subtracts the fluorescence in the former cycle from that in the latter cycle to avoid estimating the background fluorescence. The results obtained from the eight models show that taking-the-difference is a better way to preprocess qPCR data compared to the original approach because of a reduction in the background estimation error. The results also show that weighted models are better than non-weighted models, and that the precision of the estimation achieved by the mixed models is slightly better than that achieved by the linear regression models.

Novel approaches in anaplastic thyroid cancer therapy

Anaplastic thyroid cancer (ATC), accounting for less than 2% of all thyroid cancer, is responsible for the majority of death from all thyroid malignancies and has a median survival of 6 months. The resistance of ATC to conventional thyroid cancer therapies, including radioiodine and thyroid-stimulating hormone suppression, contributes to the very poor prognosis of this malignancy. This review will cover several cellular signaling pathways and mechanisms, including RET/PTC, RAS, BRAF, Notch, p53, and histone deacetylase, which are identified to play roles in the transformation and dedifferentiation process, and therapies that target these pathways. Lastly, novel approaches and agents involving the Notch1 pathway, nuclear factor κB, Trk-fused gene, cancer stem-like cells, mitochondrial mutation, and tumor immune microenvironment are discussed. With a better understanding of the biological process and treatment modality, the hope is to improve ATC outcome in the future.

Progress in oncolytic virotherapy for the treatment of thyroid malignant neoplasm

Thyroid malignant neoplasm develops from follicular or parafollicular thyroid cells. A higher proportion of anaplastic thyroid cancer has an adverse prognosis. New drugs are being used in clinical treatment. However, for advanced thyroid malignant neoplasm such as anaplastic thyroid carcinoma, the major impediment to successful control of the disease is the absence of effective therapies. Oncolytic virotherapy has significantly progressed as therapeutics in recent years. The advance is that oncolytic viruses can be designed with biological specificity to infect, replicate and lyse tumor cells. Significant advances in virotherapy have being achieved to improve the accessibility, safety and efficacy of the treatment. Therefore, it is necessary to summarize and bring together the main areas covered by these investigations for the virotherapy of thyroid malignant neoplasm. We provide an overview of the progress in virotherapy research and clinical trials, which employ virotherapy for thyroid malignant neoplasm as well as the future prospect for virotherapy of thyroid malignant neoplasms.

Current advances in retroviral gene therapy

There have been major changes since the incidents of leukemia development in X-SCID patients after the treatments using retroviral gene therapy. Due to the risk of oncogenesis caused by retroviral insertional activation of host genes, most of the efforts focused on the lentiviral therapies. However, a relative clonal dominance was detected in a patient with β-thalassemia Major, two years after the subject received genetically modified hematopoietic stem cells using lentiviral vectors. This disappointing result of the recent clinical trial using lentiviral vector tells us that the current and most advanced vector systems does not have enough safety. In this review, various safety features that have been tried for the retroviral gene therapy are introduced and the possible new ways of improvements are discussed. Additional feature of chromatin insulators, co-transduction of a suicidal gene under the control of an inducible promoter, conditional expression of the transgene only in appropriate target cells, targeted transduction, cell type-specific expression, targeted local administration, splitting of the viral genome, and site specific insertion of retroviral vector are discussed here.

Improvement of different vaccine delivery systems for cancer therapy

Cancer vaccines are the promising tools in the hands of the clinical oncologist. Many tumor-associated antigens are excellent targets for immune therapy and vaccine design. Optimally designed cancer vaccines should combine the best tumor antigens with the most effective immunotherapy agents and/or delivery strategies to achieve positive clinical results. Various vaccine delivery systems such as different routes of immunization and physical/chemical delivery methods have been used in cancer therapy with the goal to induce immunity against tumor-associated antigens. Two basic delivery approaches including physical delivery to achieve higher levels of antigen production and formulation with microparticles to target antigen-presenting cells (APCs) have demonstrated to be effective in animal models. New developments in vaccine delivery systems will improve the efficiency of clinical trials in the near future. Among them, nanoparticles (NPs) such as dendrimers, polymeric NPs, metallic NPs, magnetic NPs and quantum dots have emerged as effective vaccine adjuvants for infectious diseases and cancer therapy. Furthermore, cell-penetrating peptides (CPP) have been known as attractive carrier having applications in drug delivery, gene transfer and DNA vaccination. This review will focus on the utilization of different vaccine delivery systems for prevention or treatment of cancer. We will discuss their clinical applications and the future prospects for cancer vaccine development.

HSV-TK/IL-2 gene therapy for glioblastoma multiforme

We performed a clinical trial of gene therapy in patients with recurrent glioblastoma multiforme based on retroviral vector-mediated combined delivery of interleukin-2 and thymidine kinase of herpes simplex virus (HSV)-1. Treatment consisted of intratumor injection of retroviral vector-producing cells, followed by intravenous ganciclovir administration. The primary endpoints of the study were the evaluation of the safety of the treatment and demonstration of transduction of tumor cells. Here, we report details on the clinical protocol and the methods used.

Gene therapy via inducible nitric oxide synthase: a tool for the treatment of a diverse range of pathological conditions

Nitric oxide (NO(.)) is a reactive nitrogen radical produced by the NO synthase (NOS) enzymes; it affects a plethora of downstream physiological and pathological processes. The past two decades have seen an explosion in the understanding of the role of NO(.) biology, highlighting various protective and damaging modes of action. Much of the controversy surrounding the role of NO(.) relates to the differing concentrations generated by the three isoforms of NOS. Both calcium-dependent isoforms of the enzyme (endothelial and neuronal NOS) generate low-nanomolar/picomolar concentrations of NO(.). By contrast, the calcium-independent isoform (inducible NOS (iNOS)) generates high concentrations of NO(.), 2-3 orders of magnitude greater. This review summarizes the current literature in relation to iNOS gene therapy for the therapeutic benefit of various pathological conditions, including various states of vascular disease, wound healing, erectile dysfunction, renal dysfunction and oncology. The available data provide convincing evidence that manipulation of endogenous NO(.) using iNOS gene therapy can provide the basis for future clinical trials.

Combined HSV-TK/IL-2 gene therapy in patients with recurrent glioblastoma multiforme: biological and clinical results

Following our pilot clinical study of combined IL-2/HSV-TK gene therapy for recurrent glioblastoma multiforme (GBM), we extended the protocol to a larger population of patients and evaluated safety, feasibility, and biological activity of treatment. A total of 12 patients received intratumor injection of retroviral vector-producing cells (RVPCs), followed by intravenous ganciclovir (GCV). Treatment was well tolerated with only minor adverse events. Transduction of tumor cells was demonstrated in tumor biopsies. A marked and persistent increase of intratumor and plasma Th1 cytokine levels was demonstrated after RVPC injection. At magnetic resonance imaging evaluation, two patients had a partial response (including a patient showing disappearance of a distant noninjected tumor mass), four had a minor response, four had stable disease, and two had progressive disease. The 6- and 12-month progression-free survival rates were 47 and 14%, respectively. The 6- and 12-month overall survival rates were 58 and 25%, respectively. In conclusion, the results of our clinical protocol of gene therapy for recurrent GBM, based on combined delivery of a suicide and a cytokine gene, demonstrate that intratumor injection of RVPCs was safe, provided effective transduction of the therapeutic genes to target tumor cells, and activated a systemic cytokine cascade, with tumor responses in 50% of cases.

Interventional bronchoscopy in the treatment of tracheal obstruction secondary to advanced thyroid cancer

BACKGROUND

Surgery is the choice treatment for symptomatic tracheal obstruction due to malignant thyroid disease. Few additional therapeutic alternatives are available: radiotherapy (RT), chemotherapy (CT) or radioiodine therapy (1311). Only few studies on interventional bronchoscopy (IB) as well as alternative or palliative procedures have been reported so far. This study is a retrospective report of results of IB performed in patients with severe tracheal obstruction due to advanced thyroid cancer.

SETTING

Pulmonary and Endocrinology Units of a University Hospital.

PATIENTS AND INTERVENTIONS

From January 2, 2000 to March 1, 2004 14 consecutive patients [5 males, mean age: 62.2+/-10.7 (SD) yr] underwent IB due to tracheal obstruction for anaplastic (ATC: 7 patients), differentiated (DTC: 5), medullary (MTC: 1) and non-epithelial malignant (NEMN: 1) thyroid cancer. Eight out of 14 patients had local advanced inoperable disease, 6 had local relapse after surgery, 1311 or RT. Ten out of 14 patients suffered from severe dyspnea. In 4 patients airway patency was maintained by insertion of a stent; in 3 the tracheal lesion was removed by Nd-YAG laser; in 7 both procedures were performed.

RESULTS

All 10 patients with dyspnea showed an improvement in symptoms. Early and late complications were observed in 4 and in 3 patients, respectively. All but 4 DTC patients died 11.9+/-14.2 months after the diagnosis (4.20+/-5.1 after IB). In 4 DTC patients still alive 90.7+/-59.2 since diagnosis and 16.7+/-9.2 months since IB, the airway dilatations allowed further treatments like 131-I and/or RT.

CONCLUSIONS

Interventional bronchoscopy, including Nd-YAG laser and airways stenting are alternatives to surgery in inoperable thyroid-induced tracheal obstruction. Moreover, airway dilatation improves dyspnea and may allow further treatment.

Efficacy and safety evaluation of human reovirus type 3 in immunocompetent animals: racine and nonhuman primates

PURPOSE

Human reovirus type 3 has been proposed to kill cancer cells with an activated Ras signaling pathway. The purpose of this study was to investigate the efficacy of reovirus in immunocompetent glioma animal models and safety/toxicity in immunocompetent animals, including nonhuman primates.

EXPERIMENTAL DESIGN

Racine glioma cells 9L and RG2 were implanted s.c. or intracranially in Fisher 344 rats with or without reovirus antibodies, followed by treatment of reovirus. To study whether reovirus kills contralateral tumors in the brain and to determine viral distribution, we established an in situ dual tumor model followed by reovirus intratumoral inoculation only into the ipsilateral tumor. To evaluate neurotoxicity/safety of reovirus, Cynomolgus monkeys and immunocompetent rats were given intracranially with reovirus, and pathological examination and/or behavioral studies were done. Viral shedding and clinical biochemistry were systematically studied in monkeys.

RESULTS

Intratumorally given reovirus significantly suppressed the growth of both s.c. and intracranially tumors and significantly prolonged survival. The presence of reovirus-neutralizing antibodies did not abort the reovirus' antitumor effect. Reovirus inhibited glioma growth intracranially in the ipsilateral but not the contralateral tumors; viral load in ipsilateral tumors was 15 to 330-fold higher than the contralateral tumors. No encephalitis or behavioral abnormalities were found in monkeys and rats given reovirus intracranially. No treatment-related clinical biochemistry changes or diffuse histopathological abnormality were found in monkeys inoculated intracranially with Good Manufacturing Practice prepared reovirus. Microscopic changes were confined to the region of viral inoculation and were dose related, suggesting reovirus intracranially was well tolerated in nonhuman primates.

CONCLUSIONS

These data show the efficacy and safety of reovirus when it is used in the treatment of gliomas in immunocompetent hosts. Inoculation of reovirus into the brain of nonhuman primates did not produce significant toxicities.

Systemic efficacy of combined suicide/cytokine gene therapy in a murine model of hepatocellular carcinoma

BACKGROUND/AIMS

Gene therapy might be a promising therapeutic approach for advanced hepatocellular carcinoma (HCC) not amenable to any effective traditional treatment. The aim of the study was to evaluate the in vitro and in vivo efficacy of combined gene therapy of HCC with two different MoMLV-derived retroviral vectors, an MFG- and a LXSN-derived vector, both containing HSV-TK and hIL-2.

RESULTS

In vitro experiments on HCC cells showed efficient killing of transduced cells and efficient bystander effect after ganciclovir (GCV) treatment, with higher antitumor activity when the MFG-based vector was used. In vivo studies in a murine syngenic model of HCC demonstrated that treatment with GCV led to complete regression of tumors composed of transduced cells and regression of distant non-transduced tumors. Tumor transduction and efficacy of treatment was also demonstrated after in vivo delivery of vectors. Microarray analysis of tumor samples in mice receiving gene therapy showed up-regulation of genes involved in immune response and signal transduction.

CONCLUSIONS

We demonstrated the in vitro and in vivo efficacy of combined retroviral-mediated gene therapy for HCC, with significant systemic therapeutic efficacy in vivo.

A pilot study of combined suicide/cytokine gene therapy in two patients with end-stage anaplastic thyroid carcinoma

This study represents the first report of gene therapy for anaplastic thyroid carcinoma, one of the most aggressive solid tumors in humans. Two patients with end-stage anaplastic thyroid carcinoma were treated by direct intratumor injection of retroviral vector producer cells followed by ganciclovir. The retroviral vector carried the human IL-2 gene and the suicide gene thymidine kinase of herpes simplex virus type 1. Treatment was safe and associated with only mild adverse events. Transduction of tumor cells and production of T helper type 1 cytokines was demonstrated in tumor biopsies. Gene therapy led also to a marked increase in T helper type 1 cytokine expression in peripheral blood mononuclear cells. Radiological evaluation of injected tumor masses demonstrated local tumor necrosis.

Engineered E. coli delivers therapeutic genes to the colonic mucosa

Taking advantage of the proximity of bowel mucosa to luminal bacteria, we have attempted to deliver a therapeutic gene to the colonic mucosa by oral administration of an invasive and non-pathogenic Escherichia coli. E. coli diamenopimelate (dap) auxotroph, harboring plasmid pGB2Omegainv-hly, express the inv gene from Yersinia pseudotubercolosis that confers the ability to invade nonprofessional phagocytic cells and the hly gene from Listeria monocytogenes that allows expression of lystreriolysin O, a perforin cytolysin able to perfore phagosomal membranes. This bacterial vector invades and transfers functional DNA to epithelial cells in vitro. We have shown that this strain carrying a therapeutic gene (pC1OmegaTGF-beta1) can significantly reduce the severity of experimental colitis in mice. However, as a consequence of mucosal barrier disruption during colitis, vector-specific mRNA transcripts could be recovered from the colon and also from extra-colonic tissues. We therefore replaced the constitutive CMV promoter in pC1OmegaTGF-beta1 by the inflammation-inducible interleukin-8 promoter generating plasmid pC1OmegaTGF-beta1IND. Plasmid-specific TGF-beta1 mRNA transcripts were detectable in mouse CMT-93 epithelial cells incubated with E. coli BM2710/pGB2Omegainv-hly carrying pC1OmegaTGF-beta1IND following exposure to inflammatory cytokines. Furthermore, the transcripts were detectable only within inflamed tissues and the therapeutic effects were comparable to those in animals treated with E. coli BM2710/pGB2Omegainv-hly+pC1OmegaTGF-beta1. In summary, engineered enteric bacteria can efficiently deliver in vivo therapeutic genes to the intact intestinal mucosa and regulation expression of the therapeutic gene by an inflammation-inducible promoter prevents its dissemination during colitis.

Gene therapy for thyroid cancer

Thyroid carcinomas are suitable targets for gene therapy because they can be highly lethal on one hand, while being susceptible to specific tumour targeting on the other hand. Several gene therapy modalities have been evaluated so far in experimental models of thyroid cancer, including tumour suppressor gene replacement, oncogene inhibition, suicide gene therapy, immunotherapy, antiangiogenesis, and viral oncolysis. All of these strategies have shown promising results, but clinical studies are lacking. Based on the clinical experience achieved in a pilot study in patients with advanced thyroid cancer and on clinical results in other types of solid cancer, it is suggested that combined gene therapy approaches, as well as multimodality therapeutic regimens, including gene therapy and conventional treatments, should be pursued to achieve clinically significant results.

Modulation of retrovirally driven therapeutic genes by mutant TP53 in anaplastic thyroid carcinoma

We previously demonstrated that restoration of TP53 activity in anaplastic thyroid carcinoma inhibits cell growth and induces expression of thyroid differentiation markers. Here, we investigated whether TP53 status may condition the expression of therapeutic genes driven by retroviral LTR or tissue-specific enhancer elements. The TP53-defective ARO anaplastic thyroid carcinoma cells were transfected with TP53(Val135), which exhibits wild-type activity at 32 degrees C, and transduced with retroviral vectors, in which therapeutic genes were driven either by wild-type LTR or by a reshuffled LTR containing thyroglobulin (TG) enhancer. Both at 37 and 32 degrees C, expression of transgenes driven by TG enhancer was 10-fold lower than that obtained with wild-type LTR retroviral vector. TP53(Val135) transfer into ARO cells repressed transcription from wild-type LTR but increased expression of TG-driven therapeutic genes. This effect was markedly enhanced by cell culture at 32 degrees C and by TSH treatment. Cytotoxic effects shown after ganciclovir treatment paralleled therapeutic gene expression levels. In conclusion, TP53 status in the tumor cell can influence expression of therapeutic genes. When using retroviral-vector-based gene therapy, wild-type LTR vectors should be employed to target TP53-defective tumors, whereas thyroid-specific promoters should be used for transcriptional targeting of thyroid carcinomas carrying wild-type TP53.

Real-time Fluorescent PCR Techniques to Study Microbial-Host Interactions

This chapter describes how real-time polymerase chain reaction (PCR) performs and how it may be used to detect microbial pathogens and the relationship they form with their host. Research and diagnostic microbiology laboratories contain a mix of traditional and leading-edge, in-house and commercial assays for the detection of microbes and the effects they impart upon target tissues, organs, and systems. The PCR has undergone significant change over the last decade, to the extent that only a small proportion of scientists have been able or willing to keep abreast of the latest offerings. The chapter reviews these changes. It discusses the second-generation of PCR technology-kinetic or real-time PCR, a tool gaining widespread acceptance in many scientific disciplines but especially in the microbiology laboratory.

An overview of current delivery systems in cancer gene therapy

The main objective in gene therapy is the development of efficient, non-toxic gene carriers that can encapsulate and deliver foreign genetic materials into specific cell types such as cancerous cells. During the past two decades, enormous research in the area of gene delivery has been conducted worldwide, in particular for cancer gene therapy application. Viral vectors are biological systems derived from naturally evolved viruses capable of transferring their genetic materials into the host cells. Many viruses including retrovirus, adenovirus, herpes simplex virus (HSV), adeno-associated virus (AAV) and pox virus have been modified to eliminate their toxicity and maintain their high gene transfer capability. The limitations associated with viral vectors, however, in terms of their safety, particularly immunogenicity, and in terms of their limited capacity of transgenic materials, have encouraged researchers to increasingly focus on non-viral vectors as an alternative to viral vectors. Non-viral vectors are generally cationic in nature. They include cationic polymers such as poly(ethylenimine) (PEI) and poly(L-lysine) (PLL), cationic peptides and cationic liposomes. The newly described liposomal preparation LPD (liposomes/protamine/DNA), for example, has shown superiority over conventional liposomes/DNA complexes (lipoplexes). Although non-viral vectors are less efficient than viral ones, they have the advantages of safety, simplicity of preparation and high gene encapsulation capability. This article reviews the most recent studies highlighting the advantages and the limitations of various types of gene delivery systems used in cancer gene therapy.

Spontaneous and Controllable Activation of Suicide Gene Expression Driven by the Stress-InducibleGrp78Promoter Resulting in Eradication of Sizable Human Tumors

GRP78 is a stress-inducible chaperone protein with antiapoptotic properties that is overexpressed in transformed cells and cells under glucose starvation, acidosis, and hypoxic conditions that persist in poorly vascularized tumors. Previously we demonstrated that the Grp78 promoter is able to eradicate tumors using murine cells in immunocompetent models by driving expression of the HSV-tk suicide gene. Here, through the use of positron emission tomography (PET) imaging, we provide direct evidence of spontaneous in vivo activation of the HSV-tk suicide gene driven by the Grp78 promoter in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner. In this report, we evaluated whether this promoter can be applied to human cancer therapy. We observed that the Grp78 promoter, in the context of a retroviral vector, was highly activated by stress and PDT in three different types of human breast carcinomas independent of estrogen receptor and p53. Complete regression of sizable human tumors was observed after prodrug ganciclovir treatment of the xenografts in immunodeficient mice. In addition, the Grp78 promoter-driven suicide gene is strongly expressed in a variety of human tumors, including human osteosarcoma. In contrast, the activity of the murine leukemia virus (MuLV) long-terminal repeat (LTR) promoter varied greatly in different human breast carcinoma cell lines, and in some cases, stress resulted in partial suppression of the LTR promoter activity. In transgenic mouse models, the Grp78 promoter-driven transgene is largely quiescent in major adult organs but highly active in cancer cells and cancer-associated macrophages, which can diffuse to tumor necrotic sites devoid of vascular supply and facilitate cell-based therapy. Thus, transcriptional control through the use of the Grp78 promoter offers multiple novel approaches for human cancer gene therapy.

Gene therapy for thyroid cancer: current status and future prospects

Despite multimodality treatment for thyroid cancer, including surgical resection, radioiodine therapy, thyrotropin (TSH)-suppressive thyroxine treatment, and chemotherapy/radiotherapy, survival rates have not improved over the last decades. Therefore, development and evaluation of novel treatment strategies, including gene therapy, are urgently needed. A variety of gene therapy approaches have been evaluated for the treatment of follicular cell-derived and medullary thyroid cancer, including corrective gene therapy (p53 restoration, expression of a dominant negative RET mutant), cytoreductive gene therapy (suicide gene/prodrug strategy herpes simplex virus-thymidine kinase [HSV-tk]/ganciclovir, antiangiogenic therapy with endostatin) and immunomodulatory gene therapy (expression of interleukin (IL)-2 and IL-12). Furthermore, cloning of the sodium iodide symporter (NIS) gene has paved the way for the development of a novel cytoreductive gene therapy strategy based on NIS gene transfer followed by the application of radioiodine therapy ((131)I). NIS gene delivery into medullary and follicular cell-derived thyroid cancer cells has been shown to be capable of establishing or restoring radioiodine accumulation and might therefore represent an effective therapy for medullary and dedifferentiated thyroid tumors that lack iodide accumulating activity. The data summarized in this review article clearly demonstrate that the currently available strategies represent potentially curative novel therapeutic approaches for future gene therapy of thyroid cancer. The combination of different therapeutic genes has been demonstrated to be very useful to enhance therapeutic efficacy and seems to have a promising role at least as part of a multimodality approach for advanced thyroid cancer.

Highly selective toxic and proapoptotic effects of two dimeric ribonucleases on thyroid cancer cells compared to the effects of doxorubicin

The lack of selectivity of conventional antitumour drugs against cancer cells is responsible for their high toxicity. The development of new tumour-specific drugs is therefore highly needed. We tested the cytotoxic effects and the nature of cell death induced by a naturally dimeric bovine RNase and a newly engineered dimeric human RNase upon three genetically well-defined normal and malignant thyroid cell systems. RNases effects were compared with those of doxorubicin, a conventional antineoplastic drug. Our results show significant and selective proapoptotic effects exerted on tumour cells by both RNases, the strength of their cytotoxic and apoptotic activity being directly related to the degree of cell malignancy. No toxic effects were observed upon normal cells. Doxorubicin showed, instead, cytotoxic and apoptotic effects also against normal cells. The in vitro results were corroborated by the antitumour action of both dimeric RNases towards a malignant human thyroid tumour grown in nude mice. These results indicate a selective action of dimeric RNases against cancer cells and suggest the potential application of these molecules or their derivatives to the treatment of aggressive subtypes of thyroid cancer.

Thyroid cancer immuno-therapy with retroviral and adenoviral vectors expressing granulocyte macrophage colony stimulating factor and interleukin-12 in a rat model

BACKGROUND

Introduction of genes encoding immuno-stimulatory cytokine(s) into cancer cells is well known to enhance anti-tumour immunity.

AIM

The present studies were designed to evaluate the therapeutic efficacy of retroviral- and adenoviral-mediated delivery of IL-12 and/or granulocyte macrophage colony-stimulating factor (GM-CSF) genes for thyroid cancer in an immuno-competent rat model.

METHODS

A rat thyroid cancer cell line FRTL-Tc syngeneic to Fisher rat was used.

RESULTS

Expression of these exogenous cytokines did not affect in vitro cell growth. Subcutaneous injection of FRTL-Tc cells retrovirally transduced with IL-12 or GM-CSF genes formed significantly smaller tumours than that of the parental cells, but had little effect on growth of distant tumours, suggesting no vaccine effect. Similarly, injection of the cells infected with adenovirus expressing IL-12 or GM-CSF (AdIL-12 or AdGM-CSF) almost completely abolished tumourigenicity and injection of AdGM-CSF into pre-established tumours significantly inhibited growth of the tumours injected; neither, however, showed a systemic vaccine affect. On the other hand, injection of AdIL-12 into the pre-established tumours significantly inhibited growth of not only the tumours injected but also distant tumours, indicating induction of systemic anti-tumour immunity. Serum IL-12 was detectable only in this approach. There was neither a synergistic or additive effect of these two cytokines.

CONCLUSIONS

Our data demonstrate in a rat thyroid cancer model that only injection of AdIL-12 into the pre-established tumours elicited systemic anti-tumour immunity, but injection of AdGM-CSF or injection of the cells expressing IL-12 or GM-CSF elicited only local effect, indicating that in situdelivery of IL-12 gene with adenovirus appears most efficacious but may still require adjuvant modalities to enhance the anti-tumour effect.

Gene therapy: theoretical and bioethical concepts

Gene therapy holds great promise. Somatic gene therapy has the potential to treat a wide range of disorders, including inherited conditions, cancers, and infectious diseases. Early progress has already been made in the treatment of a range of disorders. Ethical issues surrounding somatic gene therapy are primarily those concerned with safety. Germline gene therapy is theoretically possible but raises serious ethical concerns concerning future generations.