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Loss of tumorigenicity of rat glioblastoma
directed by episome-based antisense cDNA transcription of insulin-like growth
factor I
Trojan J, Blossey BK, Johnson TR, Rudin SD, Tykocinski M, Ilan J, Ilan J
Department of Anatomy, Case Western Reserve University, School of
Medicine, Cleveland, OH 44106
Malignant glioma is the most common brain tumor.
The molecular basis of glioma tumorigenicity has not been defined.
Cultured glioma cells accumulate high levels of insulin-like growth factor I
(IGF-I) transcripts.
We asked whether IGF-I expression is coupled to tumorigenicity, using a combined
in vivo/in vitro system employing antisense RNA for IGF-I.
An antisense IGF-I expression construct in an expression vector that
incorporates Epstein-Barr virus replicative signals and the ZnSO4-inducible
metallothionein I transcriptional promoter was assembled.
Stable glioma transfectants were derived from C6 glioma cells, which
constitutively express IGF-I.
B-104 neuroblastoma cells, derived originally from the same tumor but not
expressing IGF-I, were also transfected as controls.
In the absence of ZnSO4, the C6 transfectants expressed high levels of IGF-I
mRNA and protein as detected by in situ hybridization and immunocytochemistry,
respectively.
Addition of ZnSO4 in the culture medium resulted in high levels of antisense
transcript accumulation and dramatically decreased levels of endogenous IGF-I
mRNA and IGF-I protein.
Subcutaneous injection of either nontransfected C6 parental cells or C6 cells
transfected with vector without IGF-I sequences into rats resulted in large
tumors after 2 weeks, as did transfected and nontransfected B-104 cells.
However, the rats injected with transfected C6 cells yielded no tumors after 40
weeks of observation.
Two weeks after injection of the transfected C6 cells a small cyst was apparent
in six rats.
Histologic sections revealed a few glioma cells infiltrated by a large number of
mononuclear cells.
No infiltration of mononuclear cells was apparent in the glioma tumors resulting
from injection of parental (nontransfected) cells, suggesting that the parental
cells, but not the antisense IGF-I transfectants, escape the host immune
response.
PMID: 1594587 [PubMed - indexed for MEDLINE]
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