Selective expression of foreign genes in glioma cells: Use of the mouse myelin basic protein gene promoter to direct toxic gene expression

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Abstract
We have previously demonstrated that retrovirusmediated genes were transferred to mouse glioma cells in a meningeal gliomatosis model (Yamada et al.: Japanese Journal of Cancer Research 83:1244–1247, 1992). This retrovirus vector contains the Escherichia coli. β‐galactosidase (β‐gal) gene as a marker for intergration of the lacZ gene, which is controlled by the SV40 early promoter. We investigated whether lacZ genes could be specifically controlled in mouse glioma cells by glial‐specific promoters, including the 2.5 kb 5′ flanking region of the mouse glial fibrillary acidic protein (GFAP) gene, the 1.3 kb 5′ flanking region of the myelin basic protein (MBP) gene, and the 1.5 kb 5′ flanking region of the myelin proteolipid protein (PLP) gene. Psi‐2 packaging cells were transfected with each retrovirus vector (GFAP promoter‐, MBP promoter‐, and PLP promoter‐lacZ) and the infectious virus particles were recovered from the supernatants. Blue staining for β‐gal was detected in various fibroblast, myeloma, and glioma cell lines transduced with the retrovirus BAAG vector. On the other hand, blue staining was only detected in glioma cells after transduction with the lacZ gene‐bearing retrovirus controlled by glial‐specific promoters. The strongest promoter activity was detected after transduction with the retrovirus in which the MBP promoter controlled the lacZ gene. Mouse glioma cells transduced with retrovirus containing the MBP promoter directing the herpes simplex virus type 1 thymidine kinase (HTK) gene wre extremely sensitive to ganciclovir, while the parental cells and cells transduced with retrovirus containing the lacZ gene were not sensitive to ganciclovir. Furthermore, none of the nonglioma cells tested was sensitive to ganciclovir, even when transduced with the MBP promoter‐HTK gene‐containing retrovirus. In conclusion, retrovirus targeted gene therapy of malignant glioma may be applicable with a low risk of side effects such as bone marrow suppression, in constrast to chemotherapy or the use of retroviruses bearing toxic genes controlled by nonspecific promoters.