Gene Therapy Trials
Gene therapy involves the introduction of normal or modified genes into somatic cells, in an epichromosomal location, of a target organ to correct or modify cell functions with the ultimate goal of treating or preventing disorders. A large number of clinical trials are underway assessing the potential use of gene therapy for the treatment of a number of different diseases, including hereditary disorders, cardiovascular disease and cancer. In vivo gene therapy relies on a vector to introduce the gene into the cell. Vectors currently in use include plasmids, adeno- and retroviruses as well as adeno-associated viruses. AdGV11TNF-a (TNFerade) uses a replication-deficient adenovirus type 5 vector, which provides a high gene transfer efficiency.
TNF-a is a soluble cytokine and mediator of the cellular immune response. When injected into tumor-bearing mice, it was found to cause severe tumor necrosis, which generated interest in its use as an anticancer agent. TNF-a induces adhesiveness of vascular endothelium to neutrophils and platelets and decreases thrombomodulin production. The result is clot formation in tumor vasculature, resulting in hemorrhagic necrosis in tumors in vivo. TNF-a has also been shown to be directly cytotoxic to a number of cell lines, through the production of hydroxyl radicals with resulting damage of the DNA. As radiation therapy (RT) also produces cell damage by free radical formation, a synergistic interaction between TNF-a and radiation is conceivable.
A number of studies have evaluated the interaction between ionizing radiation and TNF-a. In one study of twelve cell lines, TNF-a was directly cytotoxic to ten. Importantly, the addition of radiation (700 cGy) toTNF-a produced synergistic or additive effects in seven of ten tumor cell lines. This interaction was observed only when TNF-a was given 4-12 hours prior to irradiation.
In another study, TNF-a was used systemically as a radiosensitizer in patients with locally advanced primary and metastatic tumors. Of 20 evaluated patients, TNF-a in conjunction with local radiation therapy (30-60 Gy) produced complete regression of disease in four patients and a partial response in an additional four patients, indicating a potentially promising role of TNF-a as a radiosensitizer. However, this treatment regimen caused significant toxicity, which has limited further work with systemic administration of TNF-a. Major toxicity, requiring 7 patients to withdraw from the study, was found to be independent of TNF-a dose and included angina, hypotension, respiratory distress, atrial fibrillation, allergic reaction and progressive leukopenia. In other clinical trials using systemic administration of TNF-a, the primary dose-limiting toxicity was hypotension.
Due to these severe systemic toxicities, mechanisms of administering TNF-a locally have been investigated. A study delivering high-dose TNF-a, melphalan and low-dose interferon-g, via isolated limb perfusion, in a group of 29 patients with extremity melanoma and sarcoma, resulted in a complete response in 26 patients and a partial response in 3, for an overall response rate of 100%. This was an improvement over the use of melphalan alone, which in a group of 120 patients resulted in an overall repose rate of 79%. Several studies have been conducted delivering TNF-a to the liver via isolated hepatic perfusion. In a phase I study using TNF-a and melphalan, six patients were treated by delivering TNF-a through both the portal vein and hepatic artery. Five of the six patients treated demonstrated a partial response; however, all patients developed significant hepatotoxicity. Another trial delivering TNF-a and melphalan via isolated hepatic perfusion found an overall response rate of 75% (1 complete response and 26 partial responses) with approximately 75% of patients experiencing grade III (using the National Cancer Institute Common Toxicity Criteria) or greater hepatic toxicities that were reversible, with the exception of one patient who developed hepatic venoocclusive disease. However, these local treatment modalities are cumbersome in that they require surgery. Also, substantial toxicities have occurred when isolated liver perfusion has been used.
A novel means of selective delivery of TNF-a to tumor cells was pioneered by Weichselbaum et al. using gene therapy. To maximize local delivery and to minimize extratumoral toxicity, a portion of the Egr-1 promoter gene, inducible by ionizing radiation, was ligated upstream to a TNF-a cDNA and incorporated into a replication-deficient adenovirus type 5 (Ad5). Transfection of tumor cells with this construct provided spatial and temporal control of the radiosensitivity and cytotoxicity provided by TNF-a. This construct was tested in xenograft models of human laryngeal squamous cell carcinoma, human glioma, prostate cancer and epidermoid cancer. A high level of activity was found in terms of anticancer activity, and in all these studies TNFerade acted synergistically with RT. Observed toxicity was reported as mild with local effects limited to mild edema and fibrosis. No systemic toxicity was observed attesting to the local effect of TNF-a combined with RT. Intramuscular injections into the hind limbs of non-tumor bearing mice combined with radiation did not cause the vascular thrombosis in normal tissue seen in treated tumors, suggesting that the interaction between radiation and TNF-a occurs only in tumor tissue. At Montefiore, we are pioneering the clinical effort - An open-label, phase I, dose escalation study of AdGV11TNF-a (TNFerade) gene therapy with radiation therapy for locally advanced, recurrent, or metastatic solid tumors.
