Limited efficacy of gene transfer in herpes simplex virus-thymidine kinase/ganciclovir gene therapy for brain tumors.
OBJECTIVE
Low efficacy of gene transfer, transient gene expression, and toxicity of viral vectors are the major hurdles in successful anticancer gene therapy. The authors conducted in vitro (U87MG cell line) and in vivo (xenograft, tumor-bearing rodent model) studies to address the stability of transduction by using the adenoassociated virus serotype-2 (AAV2)-thymidine kinase (TK) vector over time.


METHODS
Standard methods for cell growth and a ganciclovir (GCV) cytotoxicity assay were applied. The AAV2-TK was infused into implanted tumors in athymic rats via convection-enhanced delivery (CED). Thymidine kinase expression was evaluated through immunohistochemical analysis, and the distribution volumes of the transduced tumors were calculated. Twenty-four hours following the viral infusions, animals were treated with GCV (50 mg/kg intraperitoneally every day for 10 days; six rats) or phosphate-buffered saline (six rats). A rapid decrease in TK expression over time was observed both in vitro and in vivo. A large volume of the tumor (up to 39%) was transduced with AAV2-TK following CED. Administration of GCV resulted in limited therapeutic effects (survival of 25.8 compared with 21.3 days).


CONCLUSIONS
Rapid elimination of TK expression from dividing tumor cells and focal transduction of the brain tumor were most likely responsible for the limited bystander effect in this approach. Immediate administration of GCV is crucial to assure maximal efficacy in the elimination of cancer cells. In addition, the complete or diffused transduction of a brain tumor with TK may be required for its total eradication.
Hadaczek
Piotr
P
Molecular Therapy Laboratory, Brain Tumor Research Center, Department of Neurological Surgery, University of California, San Francisco, California 94103, USA. piotr@itsa.ucsf.edu
Mirek
Hanna
H
Berger
Mitchel S
MS
Bankiewicz
Krystof
K
D000818:Animals; D001921:Brain / Q000473:pathology; D001932:Brain Neoplasms / Q000235:genetics / Q000473:pathology / Q000628:therapy*; D045744:Cell Line, Tumor; D018481:Convection; D000229:Dependovirus / Q000235:genetics*; D015774:Ganciclovir; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D041722:Genes, Transgenic, Suicide / Q000235:genetics*; D005909:Glioblastoma / Q000235:genetics / Q000473:pathology / Q000628:therapy*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009368:Neoplasm Transplantation; D051381:Rats; D011923:Rats, Nude; D018139:Simplexvirus / Q000235:genetics*; D013937:Thymidine Kinase / Q000235:genetics*; D014183:Transplantation, Heterologous
D013937:Thymidine Kinase; D015774:Ganciclovir