[Cancer gene therapy by direct intratumoral injection: gene expression and intratumoral pharmacokinetics of plasmid DNA].

Pharmacokinetic properties and gene expression of naked plasmid DNA and its cationic liposome complexes after intratumoral injection were studied. Using Walker 256 tissue-isolated tumor perfusion system, we quantified the recovery of naked plasmid DNA and cationic liposome complexes in the tumor, leakage from the tumor surface and the venous outflow after intratumoral injection. Approximately 50% of naked plasmid DNA was eliminated from the tumor at 2 hr after injection, while more than 90% of plasmid DNA was retained in the tumor when complexed with cationic liposome. However, distribution of these complexes in the tumor was restricted only in the vicinity of the injection site. Furthermore, we have examined the expression of chloramphenicol acetyltransferase (CAT) DNA constructs (naked pCMV-CAT) and its cationic liposome (DC-chol) complexes after intratumoral injection into subcutaneous rat Walker 256 carcinosarcoma. Significant gene expression was observed in both cases, but localization of gene expressing cells in the tumor tissue was limited to the vicinity of the injection site. Thus the pharmacokinetic and gene expression studies have demonstrated that in vivo gene expression in the tumor can be achieved by direct injection of naked plasmid DNA. In addition, there is a possibility that restricted localization of naked DNA and its cationic liposome complexes in tumor inhibits gene expression.