Co-expression of interleukin 12 enhances antitumor effects of a novel chimeric promoter-mediated suicide gene therapy in an immunocompetent mouse model

Potential Alternatives to Conventional Cancer Therapeutic Approaches: The Way Forward

onventional cancer therapeutic approaches broadly include chemotherapy, radiation therapy and surgery. These established approaches have evolved over several decades of clinical experience. For a complex disease like cancer, satisfactory treatment remains an enigma for the simple fact that the causal factors for cancer are extremely diverse. In order to overcome existing therapeutic limitations, consistent scientific endeavors have evolved several potential therapeutic approaches, majority of which focuses essentially on targeted drug delivery, minimal concomitant ramification, and selective high cytotoxicity. The current review focuses on highlighting some of these potential alternatives that are currently in various stages of in vitro, in vivo, and clinical trials. These include physical, chemical and biological entities that are avidly being explored for therapeutic alternatives. Some of these entities include suicide gene, micro RNA, modulatory peptides, ultrasonic waves, free radicals, nanoparticles, phytochemicals, and gene knockout, and stem cells. Each of these techniques may be exploited exclusively and in combination with conventional therapeutic approaches thereby enhancing the therapeutic efficacy of the treatment. The review intends to briefly discuss the mechanism of action, pros, and cons of potential alternatives to conventional therapeutic approaches.

Chapter seven--Cancer treatment with gene therapy and radiation therapy

Radiation therapy methods have evolved remarkably in recent years which have resulted in more effective local tumor control with negligible toxicity of surrounding normal tissues. However, local recurrence and distant metastasis often occur following radiation therapy mostly due to the development of radioresistance through the deregulation of the cell cycle, apoptosis, and inhibition of DNA damage repair mechanisms. Over the last decade, extensive progress in radiotherapy and gene therapy combinatorial approaches has been achieved to overcome resistance of tumor cells to radiation. In this review, we summarize the results from experimental cancer therapy studies on the combination of radiation therapy and gene therapy.

Therapeutic efficacy of an hTERT promoter-driven oncolytic adenovirus that expresses apoptin in gastric carcinoma

The efficacy and specificity of treatment are the major challenges for cancer gene therapy. Oncolytic virotherapy is an attractive drug delivery platform of cancer gene therapy. Previous studies have determined that apoptin is a p53-independent, Bcl-2-insensitive apoptotic protein that has the ability to induce apoptosis specifically in tumor cells. In this study, we show that the administration of a dual cancer-specific oncolytic adenovirus construct, Ad-hTERT-E1a-apoptin [in which the adenovirus early region 1a (E1a) gene is driven by the cancer-specific promoter of human telomerase reverse transcriptase (hTERT) and that expresses apoptin simultaneously], suppresses tumor growth in gastric carcinoma cells in vitro and reduces the tumor burden in vivo in xenografted nude mice. The observation that infection with the Ad-hTERT-E1a-apoptin construct significantly inhibited the growth of gastric cancer cells and protected normal human gastric epithelium from growth inhibition confirmed the induction of cancer cell-selective adenovirus replication, growth inhibition and apoptosis by this therapeutic approach. In vivo assays were performed using BALB/c nude mice that had established primary tumors. Subcutaneous primary tumor volume was reduced not only in the intratumoral injection group but also in the systemic delivery mice following treatment with Ad-hTERT-E1a-apoptin. Furthermore, treatment of primary models with Ad-hTERT-E1a-apoptin increased the mouse survival time. These data reinforce previous research and highlight the potential therapeutic application of Ad-hTERT-E1a-apoptin for the treatment of neoplastic diseases in clinical trials.

Suicide gene therapy in cancer: where do we stand now?

Suicide gene therapy is based on the introduction into tumor cells of a viral or a bacterial gene, which allows the conversion of a non-toxic compound into a lethal drug. Although suicide gene therapy has been successfully used in a large number of in vitro and in vivo studies, its application to cancer patients has not reached the desirable clinical significance. However, recent reports on pre-clinical cancer models demonstrate the huge potential of this strategy when used in combination with new therapeutic approaches. In this review, we summarize the different suicide gene systems and gene delivery vectors addressed to cancer, with particular emphasis on recently developed systems and associated bystander effects. In addition, we review the different strategies that have been used in combination with suicide gene therapy and provide some insights into the future directions of this approach, particularly towards cancer stem cell eradication.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.