Enhancement of IUdR Radiosensitization by Low-Energy Photons Results from Increased and Persistent DNA Damage

Technical note: Evaluation of the dose enhancement effect for a novel transmission-type x-ray tube using the Monte Carlo method

PURPOSE

Transmission-target x-ray tubes generate more x-rays than reflection thick-target x-ray tubes. A transmission x-ray tube combined with radiosensitizers has a better radiation enhancement effect. This study investigated the feasibility of using a transmission x-ray tube with radiosensitizers in clinical radiotherapy and its effect on radiation dose enhancement.

METHODS

This study used MCNP6.2 to simulate the model of a transmission x-ray tube and Co-60 beam.   The radiation enhancement effect of radiosensitizers was examined with iodine-127 (I-127), radioiodinated iododeoxyuridine (IUdR), and gold nanoparticles (GNPs).

RESULTS

The study results showed that the dose enhancement factor (DEF) of the transmission x-ray tube with GNPs was 10.27, which was higher than that of I-127 (6.46) and IUdR (3.08). The DEF of the Co-60 beam with GNPs, I-127, and IUdR was 1.23, 1.19, and 1.2, respectively. The Auger electron flux of the transmission x-ray tube with GNPs was 1.19E+05 particles/cm2 .

CONCLUSIONS

This study found that a transmission x-ray tube with appropriate radiosensitizers could produce a high rate of Auger electrons to fulfill the radiation enhancement effect, and this procedure has the potential to become a radiotherapy modality.

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 of Radio-Thermo-Sensitivity of 5-Iodo-2-Deoxyuridine-Loaded Polymeric-Coated Magnetic Nanoparticles Triggers Apoptosis in U87MG Human Glioblastoma Cancer Cell Line

Introduction

With an emphasis on the radioresistant nature of glioblastoma cells, the aim of the present study was to evaluate the radio-thermo-sensitizing effects of PCL-PEG-coated Superparamagnetic iron oxide nanoparticles (SPIONs) as a carrier of 5-iodo-2-deoxyuridine (IUdR) in monolayer culture of U87MG human glioma cell line.

Methods

Following monolayer culture of U87MG cells, nanoparticle uptake was assessed using Prussian blue staining and ICP-OES method. The U87MG cells were treated with an appropriate concentration of free IUdR and PCL-PEG-coated SPIONs (MNPs) loaded with IUdR (IUdR/MNPs) for 24 h, subjected to hyperthermia (water bath and alternating magnetic field (AMF)) at 43 °C, and exposed to X-ray (2 Gy, 6 MV). The combined effects of hyperthermia with or without magnetic nanoparticles on radiosensitivity of the U87MG cells were evaluated using colony formation assay (CFA) and Flowcytometry.

Results

Prussian blue staining and ICP-OES showed that the nanoparticles were able to enter the cells. The results also indicated that IUdR/MNPs combined with X-ray radiation and hyperthermia significantly decreased the colony formation ability of monolayer cells (1.11, 1.41 fold) and increased the percentage of apoptotic (2.47, 4.1 fold) and necrotic cells (12.28, 29.34 fold), when compared to IUdR combined with X-ray and hyperthermia or IUdR/MNPs + X-ray. MTT results revealed that the presence of IUdR/MNPs significantly increased the toxicity of AMF hyperthermia compared to the water bath method.

Conclusions

Our study showed that SPIONs/PCL-PEG, as a carrier of IUdR, can enhance the cytotoxic effects of radiotherapy and hyperthermia and act as a radio-thermo-sensitizing agent.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00675-y.

Advancements in the use of Auger electrons in science and medicine during the period 2015-2019

Auger electrons can be highly radiotoxic when they are used to irradiate specific molecular sites. This has spurred basic science investigations of their radiobiological effects and clinical investigations of their potential for therapy. Focused symposia on the biophysical aspects of Auger processes have been held quadrennially. This 9th International Symposium on Physical, Molecular, Cellular, and Medical Aspects of Auger Processes at Oxford University brought together scientists from many different fields to review past findings, discuss the latest studies, and plot the future work to be done. This review article examines the research in this field that was published during the years 2015-2019 which corresponds to the period since the last meeting in Japan. In addition, this article points to future work yet to be done. There have been a plethora of advancements in our understanding of Auger processes. These advancements range from basic atomic and molecular physics to new ways to implement Auger electron emitters in radiopharmaceutical therapy. The highly localized doses of radiation that are deposited within a 10 nm of the decay site make them precision tools for discovery across the physical, chemical, biological, and medical sciences.

Fast dose fractionation using ultra-short laser accelerated proton pulses can increase cancer cell mortality, which relies on functional PARP1 protein

Radiotherapy is a cornerstone of cancer management. The improvement of spatial dose distribution in the tumor volume by minimizing the dose deposited in the healthy tissues have been a major concern during the last decades. Temporal aspects of dose deposition are yet to be investigated. Laser-plasma-based particle accelerators are able to emit pulsed-proton beams at extremely high peak dose rates (~10⁹ Gy/s) during several nanoseconds. The impact of such dose rates on resistant glioblastoma cell lines, SF763 and U87-MG, was compared to conventionally accelerated protons and X-rays. No difference was observed in DNA double-strand breaks generation and cells killing. The variation of the repetition rate of the proton bunches produced an oscillation of the radio-induced cell susceptibility in human colon carcinoma HCT116 cells, which appeared to be related to the presence of the PARP1 protein and an efficient parylation process. Interestingly, when laser-driven proton bunches were applied at 0.5 Hz, survival of the radioresistant HCT116 p53^−/− cells equaled that of its radiosensitive counterpart, HCT116 WT, which was also similar to cells treated with the PARP1 inhibitor Olaparib. Altogether, these results suggest that the application modality of ultrashort bunches of particles could provide a great therapeutic potential in radiotherapy.

Effect of X-ray minibeam radiation therapy on clonogenic survival of glioma cells

The goal is to compare, in vitro, the efficiency of minibeam radiotherapy (MBRT) and standard RT in inducing clonogenic cell death in glioma cell lines. With this aim, we report on the first in vitro study performed in an X-ray Small Animal Radiation Research Platform (SARRP) modified for minibeam irradiations. F98 rat and U87 human glioma cells were irradiated with either an array of minibeams (MB) or with conventional homogeneous beams (broad beam, BB). A specially designed multislit collimator was used to generate the minibeams with a with of a center-to-center distance of 1465 (±10) μm, and a PVDR value of 12.4 (±2.3) measured at 1 cm depth in a water phantom. Cells were either replated for clonogenic assay directly (immediate plating, IP) or 24 h after irradiation (delayed plating, DP) to assess the effect of potentially lethal damage repair (PLDR) on cell survival. Our hypothesis is that with MBRT, a similar level of clonogenic cell death can be reached compared to standard RT, when using equal mean radiation doses. To prove this, we performed dose escalations to determine the minimum integrated dose needed to reach a similar level of clonogenic cell death for both treatments. We show that this minimum dose can vary per cell line: in F98 cells a dose of 19 Gy was needed to obtain similar levels of clonogenic survival, whereas in U87 cells there was still a slightly increased survival with MB compared to BB 19 Gy treatment. The results suggest also an impairment of DNA damage repair in F98 cells as there is no difference in clonogenic cell survival between immediately and delayed plated cells for each dose and irradiation mode. For U87 cells, a small IP-DP effect was observed in the case of BB irradiation up to a dose of 17 Gy. However, at 19 Gy BB, as well as for the complete dose range of MB irradiation, U87 cells did not show a difference in clonogenic survival between IP and DP. We therefore speculate that MBRT might influence PLDR. The current results show that X-ray MBRT is a promising method for treatment of gliomas: future preclinical and clinical studies should aim at reaching a minimum radiation (valley) dose for effective eradication of gliomas with increased sparing of normal tissues compared to standard RT.

Enhancement of radiosensitivity of oral carcinoma cells by iodinated chlorin p6 copper complex in combination with synchrotron X-ray radiation

The combination of synchrotron X-ray radiation and metal-based radiosensitizer is a novel form of photon activation therapy which offers the advantage of treating malignant tumors with greater efficacy and higher precision than conventional radiation therapy. In this study the anticancer cytotoxic efficacy of a new chlorophyll derivative, iodinated chlorin p₆ copper complex (ICp₆-Cu), combined with synchrotron X-ray radiation (8-10 keV) in two human oral cancer cell lines is explored. Pre-treatment of cells with 20 µM and 30 µM ICp₆-Cu for 3 h was found to enhance the X-ray-induced cytotoxicity with sensitization enhancement ratios of 1.8 and 2.8, respectively. ICp₆-Cu localized in cytoplasm, mainly in lysosomes and endoplasmic reticulum, and did not cause any cytotoxicity alone. The radiosensitization effect of ICp₆-Cu accompanied a significant increase in the level of reactive oxygen species, damage to lysosomes, inhibition of repair of radiation-induced DNA double-strand breaks, increase in cell death and no significant effect on cell cycle progression. These results demonstrate that ICp₆-Cu is a potential agent for synchrotron photon activation therapy of cancer.