DESCRIPTION: (Applicant's Description) An initial phase I Clinical Trial was performed using an E1/E3-deleted adenoviral vector containing the Herpes Simplex Thymidine Kinase (HSVtk) gene in 26 patients with unresectable malignant mesothelioma. The results demonstrated that intratumoral HSVtk gene transfer was possible at high titers of vector, but was primarily limited to the superficial cell layers immediately below the pleural space. At current doses of this vector and with large tumors, gene transfer is thus not likely to be effective from a therapeutic standpoint. The primary goals of this project are 1) to optimize gene therapy approaches before proposing to move on to phase II trials, 2) evaluate new imaging techniques to assess therapeutic efficacy and gene transfer in collaboration with another Project optimize ganciclovir administration in collaboration with another Project to test new therapeutic approaches. To achieve these goals, five specific aims are proposed. In the first aim, the phase I clinical trial dose escalation trial will be continued using an E1/E4-deleted adenoviral vector (H5.001RSV.tk). This El/E4 "third generation" adenoviral vector appears to be less hepatotoxic and has a much lower incidence of recombination allowing it to be produced at a substantially lower cost. In addition, information will be collected about the validity of PET-labeled 18F-GCV. In the second aim, a phase I clinical trial of intrapleural Ad.tk after tumor debulking will be performed in order to maximize the vector: tumor cell ratio and improve gene transfer efficiency. In addition, this protocol will be used to obtain information about the pharmacokinetics of GCV administration by measuring GCV levels within tissues after administering varying single intravenous doses of GCV to patients at defined times before their surgical debulking. In the third aim, a clinical trial involving an alternate ganciclovir dosing regimen is proposed. Based on the results of Specific Aims 1 and 2 and Project 2, the best new GCV dosing regimen will be tested in a phase I trial. This will likely involve increased doses of GCV delivered intravenously. In the fourth aim, the toxicity, gene transfer efficacy, and immune responses following the repeated administration of H5.001RSV.tk will be determined. Finally, a phase I Clinical trial using the most promising newly developed vector or vector approach from Project 3 will be implemented. These studies should provide a great deal of valuable information about the use of adenoviral gene therapy for localized malignancy and will hopefully lead to a phase II multi-centered trial aimed at the treatment of mesothelioma.