Targeting gene expression to
cancer cells remains a challenge for the development of gene and viral
therapy for
gliomas. Recent studies have highlighted transcriptional targeting as one of the possible solutions to overcome this limitation. In this context,
melanoma associated
antigens (MAAs) are usually over-expressed in
brain tumors in comparison to normal brain tissue. For this reason, we investigated the use of the
tyrosinase promoter as a transcriptional
element to target oncolytic
therapy for
gliomas.
Tyrosinase mRNA expression was evaluated by qRT-PCR in normal human brain tissue as well as in human
glioma specimens. We found that this gene was significantly over-expressed in
glioma cell lines and in primary
glioma samples.
Tyrosinase expression correlated with the grade of the
tumor (p-value range: 0.05-0.001). Furthermore, transfection of several cell cultures with human and mouse
tyrosinase promoters driving a
luciferase reporter gene confirmed the activity of this promoter in mouse and human cells. To evaluate whether
tyrosinase-activated conditionally replicative adenoviruses (CRAds) could induce toxicity in
glioma cells, two vectors (Ad h/m and Ad24TYR) were tested in a mouse
glioma model. C57BL/6 mice underwent intracranial injection of tumor cell line GL261. Survival was used to evaluate efficacy of the tested vectors. Mice receiving 1 x 10(9) MOI of Ad h/m and Ad24TYR following intracranial
tumor implants had a median survival of 46+/-3 days (p<0.05); in contrast, those treated with medium had a median survival of 31+/-2 days. These results suggest that injection of
tyrosinase CRAds leads to prolongation of survival in mice with experimental
brain tumors. The
tyrosinase promoter stands as a proof of principle of the potential use of MAA over-expression patterns for targeting novel anti-
glioma therapies.