Impact of IUdR on Rat 9L glioma cell survival for 25-35 keV photon-activated auger electron therapy

Radiosensitizing Effect of Dextran-Coated Iron Oxide Nanoparticles on Malignant Glioma Cells

The potential of standard methods of radiation therapy is limited by the dose that can be safely delivered to the tumor, which could be too low for radical treatment. The dose efficiency can be increased by using radiosensitizers. In this study, we evaluated the sensitizing potential of biocompatible iron oxide nanoparticles coated with a dextran shell in A172 and Gl-Tr glioblastoma cells in vitro. The cells preincubated with nanoparticles for 24 h were exposed to ionizing radiation (X-ray, gamma, or proton) at doses of 0.5-6 Gy, and their viability was assessed by the Resazurin assay and by staining of the surviving cells with crystal violet. A statistically significant effect of radiosensitization by nanoparticles was observed in both cell lines when cells were exposed to 35 keV X-rays. A weak radiosensitizing effect was found only in the Gl-Tr line for the 1.2 MeV gamma irradiation and there was no radiosensitizing effect in both lines for the 200 MeV proton irradiation at the Bragg peak. A slight (ca. 10%) increase in the formation of additional reactive oxygen species after X-ray irradiation was found when nanoparticles were present. These results suggest that the nanoparticles absorbed by glioma cells can produce a significant radiosensitizing effect, probably due to the action of secondary electrons generated by the magnetite core, whereas the dextran shell of the nanoparticles used in these experiments appears to be rather stable under radiation exposure.

Auger electrons and DNA double-strand breaks studied by using iodine-containing chemicals

Irradiation of high Z elements such as iodine, gold, gadolinium with monochromatic X-rays causes photoelectric effects that include the release of Auger electrons. Decay of radioactive iodine such as I-123 and I-125 also results in multiple events and some involve the generation of Auger electrons. These electrons have low energy and travel only a short distance but have a strong effect on DNA damage including the generation of double-strand breaks. In this chapter, we focus on iodine and discuss various studies that used iodine-containing chemicals to generate Auger electrons and cause DNA double-strand breaks. First, DNA synthesis precursors containing iodine were used to place iodine on DNA. DNA binding dyes such as iodine Hoechst were investigated for Auger electron generation and DNA breaks. More recently, iodine containing nanoparticles were developed. We describe our study using tumor spheroids loaded with iodine nanoparticles and synchrotron-generated monochromatic X-rays. This study led to the demonstration that an optimum effect on DNA double-strand break formation is observed with a 33.2keV X-ray which is just above the K-edge energy of iodine.

Iodine containing porous organosilica nanoparticles trigger tumor spheroids destruction upon monochromatic X-ray irradiation: DNA breaks and K-edge energy X-ray

X-ray irradiation of high Z elements causes photoelectric effects that include the release of Auger electrons that can induce localized DNA breaks. We have previously established a tumor spheroid-based assay that used gadolinium containing mesoporous silica nanoparticles and synchrotron-generated monochromatic X-rays. In this work, we focused on iodine and synthesized iodine-containing porous organosilica (IPO) nanoparticles. IPO were loaded onto tumor spheroids and the spheroids were irradiated with 33.2 keV monochromatic X-ray. After incubation in CO₂ incubator, destruction of tumor spheroids was observed which was accompanied by apoptosis induction, as determined by the TUNEL assay. By employing the γH2AX assay, we detected double strand DNA cleavages immediately after the irradiation. These results suggest that IPO first generate double strand DNA breaks upon X-ray irradiation followed by apoptosis induction of cancer cells. Use of three different monochromatic X-rays having energy levels of 33.0, 33.2 and 33.4 keV as well as X-rays with 0.1 keV energy intervals showed that the optimum effect of all three events (spheroid destruction, apoptosis induction and generation of double strand DNA breaks) occurred with a 33.2 keV monochromatic X-ray. These results uncover the preferential effect of K-edge energy X-ray for tumor spheroid destruction mediated by iodine containing nanoparticles.

Enhancement radiation-induced apoptosis in C6 glioma tumor-bearing rats via pH-responsive magnetic graphene oxide nanocarrier

5-iodo-2-deoxyuridine (IUdR) has been demonstrated to induce an appreciable radiosensitizing effect on glioblastoma patients, but due to the short circulation half-life times and failure to pass through the blood-brain barrier (BBB), its clinical use is limited. Accordingly, in this study, we used magnetic graphene oxide (NGO/SPIONs) nanoparticles coated with PLGA polymer as a dynamic nanocarrier for IUdR and, evaluated its sensitizing enhancement ratio in combination with a single dose X-ray at clinically megavoltage energies for treatment of C6 glioma rats. Nanoparticles were characterized using Zetasizer and TEM microscopy, and in vitro biocompatibility of nanoparticles was assessed with MTT assay. IUdR/MNPs were intravenously administered under a magnetic field (1.3 T) on day 13 after the implantation of C6 cells. After a day following the injection, rats exposed with radiation (8 Gy). ICP-OES analysis data indicated an effective magnetic targeting, leading to remarkably improved penetration through the BBB. In vivo release analysis with HPLC indicated sustained release of IUdR and, prolonged the lifespan in plasma (P < .01). In addition, our findings revealed a synergistic effect for IUdR/MNPs coupled with radiation, which significantly inhibited the tumor expansion (>100%), prolonged the survival time (>100%) and suppressed the anti-apoptotic response of glioma rats by increasing Bax/Bcl-2 ratio (2.13-fold) in compared with the radiation-only. In conclusion, besides high accumulation in targeted tumor sites, the newly developed IUdR/MNPs, also exhibited the ability of IUdR/MNPs to significantly enhance radiosensitizing effect, improve therapeutic efficacy and increase toxicity for glioma-bearing rats.

Bromopyridone Nucleotide Analogues, Anoxic Selective Radiosensitizing Agents That Are Incorporated in DNA by Polymerases

Ionizing radiation is frequently used to kill tumor cells. However, hypoxic solid tumor cells are more resistant to this treatment, providing the impetus to develop molecules that sensitize cells to ionizing radiation. 5-Bromo-2'-deoxyuridine (BrdU) has been investigated as a radiosensitizing agent in the lab and clinic for almost 5 decades. Recent reports that BrdU yields DNA interstrand cross-links (ICLs) in non-base-paired regions motivated us to develop radiosensitizing agents that generate cross-links in duplex DNA selectively under anoxic conditions. 4-Bromo- and 5-bromopyridone analogues of BrdU were synthesized and incorporated into oligonucleotides via solid-phase synthesis. Upon irradiation, these molecules yield DNA interstrand cross-links under anaerobic conditions. The respective nucleotide triphosphates are substrates for some DNA polymerases. ICLs are produced upon irradiation under anoxic conditions when the 4-bromopyridone is present in a PCR product. Because the nucleoside analogue is a poor phosphorylation substrate for human deoxycytidine kinase, a pro-nucleotide form of the 4-bromopyridone was used to incorporate this analogue into cellular DNA. Despite these efforts, the 4-bromopyridone nucleotide was not detected in cellular DNA. Although these molecules are improvements over previously reported nucleotide analogues designed to be hypoxic radiosensitizing agents, additional advances are needed to create molecules that function in cells.