The nonapoptotic pathway mediating thymidine kinase/ganciclovir toxicity is reduced by signal from adenovirus type 5 early region 4.
Suicide gene therapy using thymidine kinase/ganciclovir (Tk/GCV) yields highly variable results, in vitro and in vivo. To determine the reasons for such variations, we examined cellular mechanisms mediating its cytotoxicity in view of their interaction with adenoviral vectors (Ad) used for gene delivery. Here we report that the presence of adenovirus early region 4 (AdE4)-encoded viral proteins significantly decreases toxicity of Tk/GCV. The E4 region-encoded proteins exerted this effect when found on the adenoviral delivery vector and when provided in trans in Tk retrovirally transduced cells. The apoptotic response was assessed in GCV-treated cells. The decrease in toxicity caused by AdE4 proteins was not correlated with apoptotic response, as measured by internucleosomal DNA degradation and TUNEL assays. Our results indicate that apoptosis is not the only mechanism of Tk/GCV-induced cell death and that other mechanisms equally important in determining the success of such a gene therapy strategy should be considered when optimizing treatment conditions.
Katabi
Maha
M
McGill Center for Translational Research in Cancer, Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Quebec, H3T 1E2, Canada.
Yuan
Shala
S
Chan
Helen
H
Galipeau
Jacques
J
Batist
Gerald
G
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D005260:Female; D015774:Ganciclovir / Q000494:pharmacology*; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D013937:Thymidine Kinase / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000502:physiology*
D000970:Antineoplastic Agents; C121517:E4orf4 protein, adenovirus; D014764:Viral Proteins; D013937:Thymidine Kinase; D015774:Ganciclovir