1. ¹Genetics, LSU Health Sciences Ctr, New Orleans, LA
2. ²Pediatric Pulmonology, University of Pittsburgh Medical Center, Pittsburgh, PA

Abstract

Malignant Mesothelioma (MM) is a rapidly progressing, incurable neoplasm of the pleura or peritoneum. The etiology and development of MM is strongly associated with previous asbestos exposure. Despite the advances made in cancer biology no current therapeutic modality is successful in treating the disease. Given the localized nature of mesothelioma and its confinement to the pleural cavity, makes it an ideal disease in which to evaluate new treatment modalities such as gene therapy. Here, we investigated the use of an HSV-tk gene modified ovarian cancer cell line, PA1STK as a delivery system for this disease by direct administration into the tumor site.

The suicide gene, Herpes Simplex Virus thymidine kinase (HSV-tk) is being explored as part of a novel treatment modality for patients with cancer using different gene delivery systems. HSV thymidine kinase converts the pro-drug ganciclovir (GCV) into GCV-monophosphate (GCVMP) which is incorporated into the newly synthesized DNA and acts as a chain termination molecule leading to cell death. When these cells are exposed to GCV not only are they killed, but adjacent non-infected cells are also killed. This phenomenon known as the |[ldquo]|bystander effect|[rdquo]| involves the transfer of cytotoxic metabolites such as GCVMP through gap junction proteins, which act as connection channels between the cells. The importance of immune mediated mechanisms in this therapy in vivo has been well established in different animal models. We hypothesize immune mediated anti tumor responses to be important in a less immunogenic tumor such as MM. However, it is unknown if similar cytokine responses and cellular are seen in humans, and if these potentially are involved in a possible antitumor response.

We are currently conducting a Phase I clinical trial to assess the therapeutic efficacy of modified PA1STK cells and ganciclovir in the treatment of malignant mesothelioma. The aim of this particular study is to determine if the cytokine profiles of the patient's pleural fluid and blood were altered following treatment with the HSVtk cell line and the accompanying Ganciclovir administration.

Patients received genetically modified PA1STK cells administered intrapleurally; they then received Ganciclovir [GCV] (5mg/kg/day) q12 hrs for 7 days. To characterize the cytokine profiles within the pleural cavity; blood and pleural fluid samples were drawn twice a day, on days 0,2,4 and 6 following administration of the PA!STK cells. The levels of several cytokines, sFas Ligand, GM-CSF, IL-1Beta, IL-2, IL-4, IL-6,IL-8, IL-10,IL-12p70, IL-13,IL-15,IL-18, Interferon gamma, TNF-alpha, TGF-Beta 1 were measured using commercially available Antibodies and ELISA kits. Results of the cytokine analysis showed that IL-2, IL-4,IL-10, IL-12p70 and IL-15 levels increased in the patient's pleural fluid and serum samples, in a cell dose dependent manner. These results suggest that the treatment protocol is modulating the immunological environment of the pleural cavity