Dna Damage of Glioblastoma Multiform Cells Induced By Beta Radiation of Iodine-131 in the Presence Or Absence of Topotecan: A Picogreen and Colonogenic Assay

Objective: glioblastoma multiforme (gbm), one of the most common and aggressivemalignant brain tumors, is highly resistant to radiotherapy. numerous approaches havebeen pursued to find new radiosensitizers. we used a picogreen and colonogenic assayto appraise the dna damage and cell death in a spheroid culture of gbm cells caused byiodine-131 (i-131) beta radiation in the presence of topotecan (tpt).materials and methods: u87mg cells were cultured as spheroids with approximatediameters of 300 ?m. cells were treated with beta radiation of i-131 (at a dose of 2 gy)and/ or tpt (1 ?g/ml for 2 hours). the numbers of cells that survived were compared withuntreated cells using a colonogenic assay. in addition, we evaluated possible dna damagesby the picogreen method. the relation between dna damage and cell death wasassessed in the experimental study of groups.results: the findings showed that survival fraction (sf) in the i-131+tpt group(39%) was considerably less than the i-131 group (58.92%; p < 0.05). the number ofsingle strand breaks (ssb) and double strand breaks (dsb), in the dna of u87mgcells treated with beta radiation of i-131 and tpt (i-131+tpt) significantly increasedcompared to cells treated with only i-131 or tpt (p < 0.05). the amount of ssb repairwas more than dsb repair (p < 0.05). the relationship between cell death anddna damage was close (r?0.6) and significant (p < 0.05) in the irradiated and treatedgroups. also the maximum rate of dna repair occurred 24 hours after the treatments.a significant difference was not observed on other days of the restoration.conclusion: the findings in the present study indicated that tpt can sensitizeu87mg cells to radiation and increase dna damages. potentially, tpt can causean increase in damage from dsb and ssb by its inhibitory effects on topoisomeraseenzyme and the cell cycle. the increased complex damages following the use of agenotoxic agent and beta i-131 radiation, causes a significant increase the cell deathbecause of the difficult repair process. by assessing the relationship between dnadamage and cell death, the picogreen method can be useful in predicting colonogenicassay. consequently, it is suggested that co-treatment with i-131 beta radiation andtpt can improve gbm treatment.