A tandemly repeated thyroglobulin core promoter has potential to enhance efficacy for tissue-specific gene therapy for thyroid carcinomas

miR-122a-regulated expression of a suicide gene prevents hepatotoxicity without altering antitumor effects in suicide gene therapy

The combined use of adenovirus (Ad) vectors expressing herpes simplex virus thymidine kinase (HSVtk) and ganciclovir (GCV) offers a potential therapeutic strategy against cancer. However, intratumorally injected Ad vectors are disseminated into the systemic circulation and efficiently transduce the liver, resulting in severe hepatotoxicity. In order to overcome this problem, an Ad vector carrying a microRNA (miRNA)-regulated expression system was developed by inserting into the 3'-untranslated region (3'-UTR) of the expression cassette four tandem copies of sequences with perfect complementarity to miR-122a, which exhibits liver-specific expression. Transgene expression from the Ad vector carrying the miR-122a target sequences was 7- to 70-fold lower in cells with high miR-122a expression as compared to expression from a conventional Ad vector. Intratumoral injection of the Ad vector containing the miR-122a target sequences resulted in a 130- to 1,500-fold reduction in hepatic transgene products (without affecting the transgene expression in the tumor) when compared with those from a conventional Ad vector. In suicide gene therapy, the inclusion of the miR-122a target sequences in the HSVtk expression cassette achieved not only significant antitumor effects, but also a dramatic reduction in HSVtk/GCV-induced hepatotoxicity. These results indicate that Ad vectors that mediate miR-122a-regulated HSVtk expression provide a safe and efficient suicide gene therapy strategy.

Eukaryotic expression vectors and immunoconjugates for cancer therapy

This review considers ways to address specificity to therapeutic targeted anticancer agents. These include transcriptional activation of tissue- and tumor-specific promoters in eukaryotic expression vectors and use of antitumor-directed immunoconjugates. The review deals with analysis of strategies used for selection of targeted promoters and examples of antibody fusion proteins exhibiting antitumor activity. A new direction in antitumor treatment pooling together methods of gene therapy and antibody therapy has appeared. This direction is based on the development of vectors encoding secreted forms of immunoconjugates. After vector introduction into a cell, the latter is capable of synthesizing and secreting antibody fusion protein composed of a therapeutic anticancer agent and antibody specifically targeted to cancer cells.

Gene therapy for thyroid cancer

Although most thyroid cancers may be cured by surgery and ¹³¹I therapy, approximately 10-20% of patients die from advanced differentiated and anaplastic tumors that are unresponsive to conventional treatments. Thus, alternative approaches such as gene therapy are of interest, especially using targeted therapeutic gene delivery. Several strategies have been designed specifically for thyroid cancer and some have proven to be feasible in preclinical studies. In particular, 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. The recent discovery of new markers of thyroid cancer should improve the efficacy of gene therapy.

Variable expression of coxsackie-adenovirus receptor in thyroid tumors: implications for adenoviral gene therapy

Adenoviral gene therapy represents a novel approach for the treatment of aggressive thyroid carcinomas. Both coxsackie-adenovirus receptor (CAR) and integrins have been shown to be the major determinants for adenoviral infectivity in many types of cancer cells, yet conflicting results have been reported. In this report we examine these factors mediating adenoviral infection in thyroid cells and to evaluate CAR expression in various types of thyroid cancer. We found that neither expression levels of CAR nor integrins are solely predictive of adenoviral infectivity in thyroid cells. However, the absence of CAR was associated with poor adenoviral infectivity in immortalized rat FRTL-5 cells. Moreover, preincubation with alpha-CAR antibody decreased infectivity in FTC 238 cells, a human thyroid tumor line. These results indicate that CAR does play a role in adenoviral infection of thyroid cells. Immunohistochemical analysis revealed that CAR is expressed at the cell surface in the majority of malignant thyroid tumors. We further show that adenoviral infectivity in some thyroid cancer cells can be improved by poly-L-lysine. Our study warrants a functional method to evaluate adenoviral infectivity should be developed and instituted prior to clinical trials of adenoviral gene therapy in patients with advanced thyroid cancer.

Antiviral Drug-Induced Nephrotoxicity

Drug-induced kidney injury is a major side effect in clinical practice, frequently leading to acute renal failure (ARF). It accounts for more than 2% to 15% of cases of ARF in patients admitted to the hospital or in the intensive care unit, respectively. The exact frequency of nephrotoxicity induced by antiviral drugs is difficult to determine. Antiviral drugs cause renal failure through a variety of mechanisms. Direct renal tubular toxicity has been described with a number of new medications with unique effects on epithelial cells of the kidney. These include cidofovir, adefovir dipivoxil, and tenofovir, as well as acyclovir. Additionally, crystal deposition in the kidney may promote the development of renal failure. Several different drugs have been described to induce crystal nephropathy, including acyclovir and the protease inhibitor indinavir. Renal injury associated with antiviral drugs involves diverse processes having effects on the renal transporters, as well as on tubule cells. In this article, we review the pathogenesis of antiviral drug-induced kidney injury, common nephrotoxic renal syndromes, and strategies for preventing kidney injury.

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.

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.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.