DIFFERENTIAL TOXICITY OF GANCICLOVIR FOR RAT NEURONS AND ASTROCYTES IN PRIMARY CULTURE FOLLOWING ADENOVIRUS-MEDIATED TRANSFER OF THE HSVTK GENE

The toxicity of the suicide HSVtk gene approach is known to be targete d to DNA synthesis and, consequently, to dividing cells. This system i s therefore useful for the treatment of brain tumors which contain div iding cells surrounded by a quiescent normal tissue. Adenoviruses are efficient vectors for the transfer of the HSVtk gene into the tumor bu t this can lead to the transduction of quiescent cells. In this study, we focused on the toxicity of the HSVtk/ganciclovir treatment for the two main cell types of the normal brain: astrocytes and neurons. Astr ocytes and neurons in primary culture were infected by an adenoviral v ector bearing the HSVtk gene (Ad.tk) and cells were exposed to differe nt concentrations of ganciclovir. After 5 days of treatment, an MTT te st measured a dramatic decrease in cell viability for treated astrocyt es while a small decrease in cell viability was observed for neurons t reated in the same experimental conditions. The differential toxicity of the HSVtk/ganciclovir treatment was also observed in cocultures of astrocytes and neurons: an immunocytochemical analysis of the treated cells showed major morphological modifications for astrocytes but not for neurons. Furthermore, our data suggest that a bystander effect is able to kill all the astrocytes while neurons from the same culture re main unaffected.