Genotoxic Damage to Glioblastoma Cells Treated with 6 MV X-Radiation in The Presence or Absence of Methoxy Estradiol, IUDR or Topotecan

Objective

To explore the cumulative genotoxic damage to glioblastoma (GBM) cells, grown as multicellular spheroids, following exposure to 6 MV X-rays (2 Gy, 22 Gy) with or without, 2- methoxy estradiol (2ME2), iododeoxyuridine (IUDR) or topotecan (TPT), using the Picogreen assay.

Materials and Methods

The U87MG cells cultured as spheroids were treated with 6 MV X-ray using linear accelerator. Specimens were divided into five groups and irradiated using X-ray giving the dose of 2 Gy after sequentially incubated with one of the following three drug combinations: TPT, 2-ME2/TPT, IUDR/TPT or 2ME2/IUDR/ TPT. One specimen was used as the irradiated only sample (R). The last group was also irradiated with total dose of 22 Gy (each time 2 Gy) of 6 MV X-ray in 11 fractions and treated for three times. DNA damage was evaluated using the Picogreen method in the experimental study.

Results

R/TPT treated group had more DNA damage [double strand break (DSB)/single strand break (SSB)] compared with the untreated group (P<0.05). Moreover the R/ TPT group treated with 2ME2 followed by IUDR had maximum DNA damage in spheroid GBM indicating an augmented genotoxicity in the cells. The DNA damage was induced after seven fractionated irradiation and two sequential treatments with 2ME2/IUDR/TPT. To ensure accuracy of the slope of dose response curve the fractionated radiation was calculated as 7.36 Gy with respect to α/β ratio based on biologically effective dose (BED) formulae.

Conclusion

Cells treated with 2ME2/IUDR showed more sensitivity to radiation and accumulative DNA damage. DNA damage was significantly increased when GBM cells treated with TPT ceased at S phase due to the inhibition of topoisomerase enzyme and phosphorylation of Chk1 enzyme. These results suggest that R/TPT- treated cells increase sensitivity to 2ME2 and IUDR especially when they are used together. Therefore, due to an increase in the level of DNA damage (SSB vs. DSB) and impairment of DNA repair machinery, more cell death will occur. This in turn may improve the treatment of GBM.

Evaluation of the Combined Effect of 2ME2 and (60)Co on the Inducement of DNA Damage by IUdR in a Spheroid Model of the U87MG Glioblastoma Cancer Cell Line Using Alkaline Comet Assay

OBJECTIVE

In this study, we investigated the combined effect of 2-Methoxyestradiol (2ME2) and (60)Co on the cytogenetic damage of iododeoxyuridine (IUdR) in the spheroid model of U87MG glioblastoma cancer cell lines by alkaline comet assay.

MATERIALS AND METHODS

U87MG cells were cultured as spheroids with diameters of 350 µm. As control, the spheroids of one plate were not treated. Other cultures were pretreated with 2ME2 (250 µM) for one volume doubling time (1 VDT). After this time, the subsequent treatments were performed according to the following groups: Vehicle (this sample was not treated in the 2(nd) VDT) Treated with 2ME2 (250 µM) for 1 VDT Treated simultaneously with 2ME2 (250 µM) and IUdR (1 µM) for 1 VDT Treated with 2ME2 (250 µM) for 1 VDT then irradiated with (60)Co (2 Gy) Treated simultaneously with 2ME2 (250 µM) and IUdR (1 µM) for 1 VDT then irradiated with (60)Co (2 Gy) Then the DNA damage was evaluated using the alkaline comet assay method.

RESULTS

The results showed that 2ME2 in combination with gamma irradiation of (60)Co significantly (p<0.001) increased the DNA damage by IUdR as compared to the control group. Thus the combination of these two agents increased the cytogenetic effects of IUdR in the spheroid culture model of U87MG glioblastoma cell lines.

CONCLUSION

By inhibiting the HIF-1α protein and preventing the G0 phase arrest, 2ME2 causes an increased progression into S phase and increases the IUdR absorption. Then the DNA damage in the spheroid cells increases as the uptake of IUdR is increased. These results suggest that the combined use of 2ME2 and (60)Co can increase the radiosensitization effect of IUdR.