Malignant gliomas and glioblastomas are the most common type of primary brain tumors. The treatment of malignant glioma involves surgery, radiation, and chemotherapy. These therapies have not been successful in curing malignant glioma and typically associated with dismal prognosis. Therefore, we can investigate thymidine kinase activity and cytotoxic effect after transfer suicide gene in U-251 glioma cells. We assessed expression patterns of green fluorescence protein(GFP) after infected with adenovirus in U-251 cells. After infection of HSV-tk in U-251 cells, we observed thymidine kinase activity with [3H]-penciclovir and cytotoxic effect by treated with ganciclovir.
We could observe that expression level of GFP was increased according to infected concentrations in U-251 cells. GFP was not expressed in 1moi and 10moi, and slightly expressed in 30moi. Expression level of GFP was largely increased in 50moi and almost cells expressed GFP in 100moi. GFP expression has shown clear image in 100moi compared with other concentrations. We also investigated thymidine kinase activity using [3H]-penciclovir after infection of suicide gene HSV-tk into U-251 cells. Thymidine kinase activity increased in 10moi concentration compared with empty adenovirus infection. We could find that thymidine kinase activity was elevated proportional to HSV-tk infection amount in 30moi and 50moi. For evaluation of cellular cytotoxic effect of HSV-tk, we treated ganciclovir to U-251 cells and assessed cytotoxicity by using MTT assay. We could identifiy that cytotoicity appeared in very low concentration of HSV-tk compared with cancer cells originated with other organs. Cytotoxic effect was shown about 15% of U-251 cells of total cells in 5moi. By infection 10moi of HSV-tk, cytotoxic effect was intensively increased and about 60% of U-251 cells became extinct. About 70% cells exhibited cytotoxic effect in 30moi and more than 80% cells also appeared cytotoxic effect by infection of HSV-tk in 50moi, 100moi, and 200moi. Therefore, we could confirm to gene expression in U-251 cells was increased proportional to infected gene concentrations. Also we
could find that thymidine kinase activity elevated with according to infected concentration and cellular cytotoxic effect was shown in very low concentration and higher cytotoxic effect also appeared by infection of suicide gene HSV-tk into U-251 glioma cells. These results suggest that gene therapy with suicide gene will be successful in curing brain tumors containing malignant glioma and glioblastoma.

• 홍승희(신한대학교 식품조리과학부) | Seung Hee Hong Correspondence