Preclinical Testing of Recombinant Adenoviral Herpes Simplex Virus-Thymidine Kinase Gene Therapy for Central Nervous System Malignancies

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Abstract
Adenoviral gene transfer and killing efficiency using the thymidine kinase (TK)/ganciclovir (CO mechanism was evaluated in human cancer cells occurring as central nervous system tumors. The effectivenes of this approach was tested in vitro and in experimental models for brain tumor and leptomeningeal metastase in rats in vivo. Recombinant adenoviruses with different promoters were compared. Adenoviral vectors harboring a marker (lacZ) or a TK gene were constructed. Transcription of genes wai under the control of either the adenovirus Type 2 major late promoter (MLP) or the human cytomegaloviru (CMV) immediate early gene promoter. lacZ expression and GCV killing efficiency after TK gene transfer in several human tumor cells was evaluated in vitro. The 9L rat brain tumor and leptomeningeal metastases model were used to determine the effectiveness of adeno-TK and subsequent GCV treatment in vivo. MLP and CMV containing adenoviral vectors were compared. Gene expression and the killing of tumor cells were very efficient in all human tumor cell lines tested. The adenovirus containing the CMV promoter showed cytopathic effects in cultured tumor cells at high multiplied of infections but also greater cell killing efficiency after TK/GCV treatment, as compared to the MLP promote' Although both the MLP and CMV vectors showed a significant dose-dependent therapeutic effect, animals treatei with recombinant adenovirus containing the CMV promoter showed significantly longer survival time (bran1 tumors) or symptom-free periods (leptomeningeal metastases). This study demonstrates the therapeutic efficiency and feasibility of the TK/GCV approach in experimental brain tumors and leptomeningeal metastases. It also demonstrates that the promoter driving tht transgene in an adenoviral vector influences toxicity and efficiency of treatment.