GENE-THERAPY OF EXPERIMENTAL MALIGNANT MESOTHELIOMA USING ADENOVIRUS VECTORS ENCODING THE HSVTK GENE

Replication-defective adenovirus vectors were generated in which the g ene of interest (lacZ, luciferase or HSV-tk) is driven by the adenovir us major late promoter (MLP) or the human cytomegalovirus immediate-ea rly gene promoter/enhancer (CMV). In vitro experiments with rat (II-45 ) and human (MERO 25) mesothelioma cell lines revealed that the CMV pr omoter was stronger than the MLP promoter regarding levels of expressi on of the luciferase reporter gene and ganciclovir (GCV) killing effic iency after tk gene transfer. Following administration of IG.Ad.CMV.la cZ recombinant adenovirus (Introgene, IG) into the pleural cavity of F ischer rats with established mesothelioma, a widespread distribution o f infectious virus particles through the thorax contents was demonstra ted However, a relatively small proportion of tumor cells were transdu ced. Nevertheless, a strong tumor growth inhibition observed following treatment with IG.AdCMV.TK recombinant adenovirus and GCV. Separate g roups of rats inoculated on day 0 with 10(5) II-45 cells into the pleu ral cavity, received 7 x 10(9) infectious particles of IG.AD.CMV.TK on day 1, day 2, day 4 or day 8. One day after virus adminstration, 25 m g/kg GCV or PBS (controls) was injected i.p. (intraperitoneally) twice daily. On day 15, all animals were killed. Significant tumor regressi on, equivalent to 5 log cell kill, occurred in the treated rats sugges ting an impressive bystander effect. In a survival study, animals were treated 9 days after inoculation of 10(5) tumor cells with IG.Ad.CMV. TK and a 14 days course of GCV. This treatment prolonged symptom-free survival time from 19 days in the controls to 33 days in the treated g roup. These responses can be best explained by assuming continued tk e xpression in or around the tumor tissue during GCV treatment. Our resu lts confirm and extend earlier findings with the same model and demons trate the potential of the herpes simplex virus thymidine kinase suici de gene therapy as a local treatment for malignant mesothelioma.