The E1A Gene Therapy: A Two Way Translational Research

Abstract

Adenovirus type 5 E1A is associated with multiple anti-tumor activities and transcriptionally represses HER2/mu. E1A gene therapy induced regression of HER-2/neu-overexpressing cancers in nude mice. To evaluate the feasibility of E1A gene therapy for patient with HER-2/neuoverexpressing cancer, we conducted a phase 1 clinical trial. An E1A/DC-Chol complex was injected weekly into the thoracic or peritoneal cavity of 18 patients with advanced breast and/or ovarian cancers. The most common toxicities were fever, nausea, vomiting, and/or discomfort at the injection sites. After E1A/DC-Chol complex delivery, E1A gene expression was detectable in tumor cells with HER-2/neu downregulation, increased apoptosis, and reduced proliferation. Thus intracavitary E1A gene therapy is a feasible approach resulting m clear proof of preclinical concept. Phase II trials on ovarian cancer are recently initiated under the support of M. D. Anderson Ovarian Spore. In addition to downregulation of HER-2/neu overexpression, we have recently identified molecular mechanisms that provide scientific basis for E1A-mediated antitumor activities independent of HER-2/neu status. These laboratory findings are helpful to understand E1A-associated anti-tumor activity and will be incorporated to the future clinical trials: 1.E1A sensitized TNF α – and ionizing γ – irradiation-induced cell death by inhibition of NF-κB activity. Activation of the transcription factor NF-κB has been shown to play a key role in the anti-apoptotic pathway of TNF α and radiation-induced apoptosis. We have found that TNF α- or radiation-induced activation of NF κB occurred m the cancer cells but was blocked when E1A was expressed. We further showed that this inhibition was through suppression of IκB kinase (IKK) activity and IκB phosphorylation. Since IκB phosphorylation results in degradation of IκB, suppression of IκB phosphorylation leads to increased IκB level that then in turn binds to NF-κB to inbibit NF-κB anti-apoptotic activity. These results open an interesting possibility to combine E1A gene therapy with radation therapy or TNF α therapy. It should also be mentioned that TNF α expression was found to be increased in the body fluid from the treated patients in the Phase 1 trail. The increased TNF α expression may account for the increased apoptosis of cancer cells in the treated patients. In this regards, the E1A/DC-Chol-induced TNF α expression in patients may contribute to its anti-tumor activity. 2.E1A induced bystander effect by inhibiting angiogenesis and inducing apoptosis. To investigate the E1A mediated bystander effect and the mechanisms that may be associated with it. We inoculated nude mice subcutaneously with a mixture of E1A transfectants and parental cells, we found that the E1A transfectants exhibited a bystander effect on inhibition of tumor growth. We further showed that E1A mediated suppression of angiogenesis and induction of apoptosis in the tumors, likely contributing to the bystander effect. 3. E1A inhibits expression of another transforming tyrosine kinase, Axl. To study the mechanism underlying the E1A-mediated tumor suppressing function, we exploited a modified tyrosine kinase profile assay to identify potential tyrosine kinase regulated by E1A. We identified that E1A negatively regulated the expression of the transforming receptor tyrosine kinase Ax1 at the transcriptional level and downregulation of Aχ1 by E1A is required for E1A-mediated growth suppression and induction of apoptosis. These results indicated that downregulation of Ax1 receptor by E1A is involved in E1A-mediated growth suppression and E1A-induced apoptosis and thereby may contribute to E1A’s antitumor activities. Although the clinical trial of E1A gene therapy was initiated by the known mechanism of HER-2/neu downregulation, the above results together with other studies in the literature, indicate that E1A actually associate with multiple mechanisms that may contribute to anti-tumor activity. These results provide scientific basis to open the E1A gene therapy clinical trials for patients without HER-2/neu-verexpressing cancer.