The effect of iodine-131 beta-particles in combination with A-966492 and Topotecan on radio-sensitization of glioblastoma: An in-vitro study

by Selleckchem | Oct 25 2023

Glioblastoma tumors are resistant to radiotherapy, and the need for drugs to induce radio-sensitization in tumor cells has always been a challenge. Besides, radiotherapy using targeted radionuclide would be effective even for resistant tumors. It has been shown topoisomerase I and poly (ADP-ribose) polymerase (PARP) enzymes have critical roles in the repair process of DNA injury in cells. Therefore, the inhibition of the activity of these enzymes can halt this process and result in the accumulation of damaged DNA in cells and the induction of cell death in tumors. In the present research, the impact of beta-particles of iodine-131 in combination with Topotecan (TPT), as the inhibitor of topoisomerase I, and A-966492, as the inhibitor of the PARP enzyme on the possible increase of radio-sensitivity of glioblastoma cells was assessed. For this purpose, a human glioblastoma cell line, U87MG, was cultured in flasks coated with Poly-Hema to achieve 300 μm-diameter spheroids. Then, nontoxic concentrations of A-966492 and TPT were applied in the cell culture media. The viability of the cells treated with iodine131 in combination with A-966492 and TPT was determined by the clonogenic assay. The expression rate of gamma-H2AX, as a biomarker of DNA double-strand breaks, was analyzed using immunofluorescence microscopy to unravel the effect of TPT, A-966492 (1 μM), and radiation on the cell death induction. The combination of each TPT or A-966492 with radiation resulted in the increased rate of cell death, and the ratios of sensitizer enhancement at 50% survival (SER50) were elevated by 1.45 and 1.25, respectively. Chemo- and radio-sensitization were promoted when iodine-131 was combined with A-966492 and TPT, with the SER50 of 1.68. Also, the expression of γ-H2AX was significantly increased in cells treated with A-966492 and TPT combined with radiation. The results demonstrated that iodine-131, in combination with A-966492 and TPT, had marked effects on radio-sensitizing and can be used as a targeted radionuclide for targeting radiotherapy in combination with topoisomerase I and PARP inhibitors to enhance radiotherapy in clinics.

Comments:

The present research aimed to investigate the potential of using a combination of iodine-131, Topotecan (TPT), and A-966492 to increase the radio-sensitivity of glioblastoma cells. Glioblastoma tumors are known to be resistant to radiotherapy, so finding effective drugs to enhance the response of tumor cells to radiation has been a challenge.

The study utilized a human glioblastoma cell line called U87MG, which was cultured as spheroids with a diameter of 300 μm. Non-toxic concentrations of A-966492 and TPT were added to the cell culture media. The viability of the cells treated with iodine-131 in combination with A-966492 and TPT was evaluated using the clonogenic assay, a method that assesses the ability of individual cells to form colonies.

The researchers also examined the expression of gamma-H2AX, a biomarker associated with DNA double-strand breaks, using immunofluorescence microscopy. This analysis aimed to determine the effect of TPT, A-966492 (at a concentration of 1 μM), and radiation on the induction of cell death.

The results of the study indicated that the combination of either TPT or A-966492 with radiation led to an increased rate of cell death compared to radiation alone. The sensitization enhancement ratios at 50% survival (SER50) were elevated by 1.45 and 1.25, respectively, when TPT or A-966492 was combined with radiation. Furthermore, the combination of iodine-131 with A-966492 and TPT resulted in an SER50 of 1.68, demonstrating enhanced chemo- and radio-sensitization.

The expression of gamma-H2AX was significantly increased in cells treated with the combination of A-966492 and TPT along with radiation, suggesting an accumulation of DNA damage. This finding indicates that the inhibition of topoisomerase I and PARP enzymes may interfere with the repair process of DNA damage, leading to the accumulation of damaged DNA and subsequent cell death in tumors.

Based on these results, the authors concluded that iodine-131, in combination with A-966492 and TPT, exhibits significant effects in sensitizing glioblastoma cells to radiotherapy. They suggest that iodine-131 can be utilized as a targeted radionuclide in combination with topoisomerase I and PARP inhibitors to enhance the efficacy of radiotherapy in clinical settings.