Revving up for the Adenoviral-P53 Gene Therapy

 By Curt Herberts, Research Analyst, Frost & Sullivan, North America

While gene therapy has been on the scientific horizon for a few decades, only in the last couple of years has it really taken successful strides in climbing the ominous oncology clinical trial ladder. Despite some serious setbacks, involving the death of one patient and the development of leukaemia in another three, gene therapy has continued to make progress and now has a New Drug Application (NDA) under review at the FDA, and many more in clinical trials. Within the next two to seven years, gene therapy could break the activation energy to finally make it the next big thing in cancer treatment regimes.

IN THE PAST, cancer treatment has involved a mélange of different choices including surgery, radiation, chemotherapy, hormonal therapy, and biologic therapy. However, new discoveries have led to promising technologies within the realms of anti-angiogenesis, monoclonal antibodies, vaccines, and gene therapy. Gene therapy is defined as an “approach to preventing and/or treating disease by replacing, removing or introducing genes or otherwise manipulating genetic material.” Researchers and drug companies alike see this technology as a potential effective therapy to treat different diseases in areas such as: haemophilia, cystic fibrosis, cancer, cardiovascular, pulmonary, neurological, and infectious disease. Gene therapy is applicable across so many different disease states because of its ability to target specific molecular targets on particular cell types within the body. This allows the therapy to directly affect the site of disease, while eliminating extraneous side effects associated with forms of systemic therapy. Currently, there are a number of different techniques to deliver desired gene therapy regimens into specific targeted cells within the body. Some of them include viral vectors, liposomal vectors, ex vivo cell transfection, artificial chromosomes, matrix vectors, genetically engineered cells, gene activators, naked DNA, bacterial vectors, chemical and physical methods, regulation of gene expression, and gene repair.

It has yet to be decided which of these techniques will prove most effective in delivering a specific treatment to the desired location within the body. Many biotechnology and pharmaceutical companies have found significant barriers to commercialisation when trying to develop a gene therapy product. The main problem resides in designing a delivery system that will deliver sufficient quantities of therapeutic DNA into a large enough number of cells, and then express the desired proteins at high enough levels to have a therapeutic effect on the disease. In addition, difficulties lie in the costs and risks associated with clinical trials, financial and logistical difficulties inherent in moving beyond basic research to large-scale manufacture and marketing, as well as research in the sector has generally been taking a much longer time to market than the already lengthy average of seven years for most pharmaceutical drugs. Currently, there are twenty-two new gene therapy candidates in clinical trials for multiple cancer indications. Currently, one of the most promising gene therapies in multiple clinical trials is the Adenoviral p53. Adenoviruses can infect and multiply in cells in which the p53 tumour suppressor gene has been inactivated. Luckily, cancer cells are the only type of cells in the body with an inactivated p53 gene, and about 50 percent of malignant head and neck tumours are composed of cells with the inactivated p53 gene. Therefore, when the adenovirus gets into a cancer cell with an inactivated p53 gene, it replicates, and then lyses (kills) the cancer cell thereby releasing more virus particles to infect neighbouring cancer tissue. With the p53 adenovirus gene therapy in clinical trials for multiple oncology indications, it looks as if it might be the first big leap into the actual application of gene therapy for curing cancer. Many companies such as Introgen/Aventis, Matrix Pharmaceuticals, Schering Plough, and Transgene are currently testing different applications of the p53 tumour suppressor Adenovirus on oncology patients. Phase III trials will hopefully prove whether or not this potential therapeutic will be able to clinically work better than existing therapies and thereby gain a substantial percentage of the skyrocketing cancer market.

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