Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor. It has a WHO grade of IV, which is the highest classification of tumors regarding their rate of growth and spreading. Additionally, GBM is a particularly difficult cancer to treat due to its high resistance to both radio- and chemotherapy. Patients with GBM who receive normal treatment have a median survival rate of 15-16 months (for untreated patients, this number is 3 months); however, no developments in treatments for this cancer have been put into clinical use since 2005, and the median survival rate in treated patients has not changed. Our lab has determined that treating GBM cells with Na2S (which releases H2S) before the cells undergo radiation increases the rate of tumor cell death, while Na2S does not kill or enhance the radiosensitivity of a cerebral endothelial cell line. This is important due to the pleomorphic nature of GBM (also reflected in its WHO grading). We have also discovered the addition of H2S increases DNA damage in GBM cells after exposure of the GBM to radiation. However, the mechanism for this is unknown. One idea is that H2S inhibits DNA double strand break repair, which increases DNA damage and therefore cell death in the tumor. To investigate this, T98G cells (from GBM cells) were transfected with plasmid DNA that was linearized in order to test the cell’s ability to repair its DNA through double strand break repair mechanisms. This plasmid expresses green fluorescent protein (GFP) after the DNA undergoes double strand break repair by the non-homologous end joining (NHEJ-I) repair mechanism. Cells were pre-treated with Na2S, transfected with the linear plasmid and a circular plasmid that expresses red fluorescent protein (RFP), and then treated with the Na2S for two more hours. The RFP expression plasmid was used to normalize for the transfection efficiency between samples. Cells were examined 24 hrs and 32 hrs after transfection using fluorescent microscopy to determine the number of GFP or RFP expressing T98G cells. The GFP/RFP ratio was calculated for two transfections. These initial experiments suggest that the Na2S treatment may increase DNA repair. However, further experiments are required to determine whether Na2S does increase double strand break repair. These results also suggest that the increased damage introduced by the Na2S treatment into the T98G cells is likely due to increased production of damaging radicals.

Does hydrogen sulfide inhibit DNA double strand break repair?

2019 Spring National Meeting

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