Development of a portable hypoxia chamber for ultra-high dose rate laser-driven proton radiobiology applications

Combining a noble gas with radiotherapy: glutamate receptor antagonist xenon may act as a radiosensitizer in glioblastoma

BACKGROUND

Ionotropic glutamate receptors α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) modulate proliferation, invasion and radioresistance in glioblastoma (GB). Pharmacological targeting is difficult as many in vitro-effective agents are not suitable for in patient applications. We aimed to develop a method to test the well tolerated AMPAR- and NMDAR-antagonist xenon gas as a radiosensitizer in GB.

METHODS

We designed a diffusion-based system to perform the colony formation assay (CFA), the radiobiological gold standard, under xenon exposure. Stable and reproducible gas atmosphere was validated with oxygen and carbon dioxide as tracer gases. After checking for AMPAR and NMDAR expression via immunofluorescence staining we performed the CFA with the glioblastoma cell lines U87 and U251 as well as the non-glioblastoma derived cell line HeLa. Xenon was applied after irradiation and additionally tested in combination with NMDAR antagonist memantine.

RESULTS

The gas exposure system proved compatible with the CFA and resulted in a stable atmosphere of 50% xenon. Indications for the presence of glutamate receptor subunits were present in glioblastoma-derived and HeLa cells. Significantly reduced clonogenic survival by xenon was shown in U87 and U251 at irradiation doses of 4-8 Gy and 2, 6 and 8 Gy, respectively (p < 0.05). Clonogenic survival was further reduced by the addition of memantine, showing a significant effect at 2-8 Gy for both glioblastoma cell lines (p < 0.05). Xenon did not significantly reduce the surviving fraction of HeLa cells until a radiation dose of 8 Gy.

CONCLUSION

The developed system allows for testing of gaseous agents with CFA. As a proof of concept, we have, for the first time, unveiled indications of radiosensitizing properties of xenon gas in glioblastoma.

Emerging technologies for cancer therapy using accelerated particles

Cancer therapy with accelerated charged particles is one of the most valuable biomedical applications of nuclear physics. The technology has vastly evolved in the past 50 years, the number of clinical centers is exponentially growing, and recent clinical results support the physics and radiobiology rationale that particles should be less toxic and more effective than conventional X-rays for many cancer patients. Charged particles are also the most mature technology for clinical translation of ultra-high dose rate (FLASH) radiotherapy. However, the fraction of patients treated with accelerated particles is still very small and the therapy is only applied to a few solid cancer indications. The growth of particle therapy strongly depends on technological innovations aiming to make the therapy cheaper, more conformal and faster. The most promising solutions to reach these goals are superconductive magnets to build compact accelerators; gantryless beam delivery; online image-guidance and adaptive therapy with the support of machine learning algorithms; and high-intensity accelerators coupled to online imaging. Large international collaborations are needed to hasten the clinical translation of the research results.

Induction of DNA strand breaks and oxidative base damages in plasmid DNA by ultra-high dose rate proton irradiation

PURPOSE

Radiation cancer therapy with ultra-high dose rate (UHDR) exposure, so-called FLASH radiotherapy, appears to reduce normal tissue damage without compromising tumor response to therapy. The aim of this study was to clarify whether a 59.5 MeV proton beam at an UHDR of 48.6 Gy/s could effectively reduce the DNA damage of pBR322 plasmid DNA in solution compared to the conventional dose rate (CONV) of 0.057 Gy/s.

MATERIALS AND METHODS

A simple system, consisting of pBR322 plasmid DNA in 1× Tris-EDTA buffer, was initially employed for proton beam exposure. We then used formamidopyrimidine-DNA glycosylase (Fpg) enzymes. which convert oxidative base damages of oxidized purines to DNA strand breaks, to quantify DNA single strand breaks (SSBs) and double strand breaks (DSBs) by agarose gel electrophoresis.

RESULTS

Our findings showed that the SSB induction rate (SSB per plasmid DNA/Gy) at UHDR and the induction of Fpg enzyme sensitive sites (ESS) were significantly reduced in UHDR compared to CONV. However, there was no significant difference in DSB induction and non-DSB cluster damages.

CONCLUSIONS

UHDR of a 59.5 MeV proton beam could reduce non-clustered, non-DSB damages, such as SSB and sparsely distributed ESS. However, this effect may not be significant in reducing lethal DNA damage that becomes apparent only in acute radiation effects of mammalian cells and in vivo studies.

Cellular irradiations with laser-driven carbon ions at ultra-high dose rates

Objective.Carbon is an ion species of significant radiobiological interest, particularly in view of its use in cancer radiotherapy, where its large Relative Biological Efficiency is often exploited to overcome radio resistance. A growing interest in highly pulsed carbon delivery has arisen in the context of the development of the FLASH radiotherapy approach, with recent studies carried out at dose rates of 40 Gy s^-1. Laser acceleration methods, producing ultrashort ion bursts, can now enable the delivery of Gy-level doses of carbon ions at ultra-high dose rates (UHDRs), exceeding 10⁹Gy s^-1. While studies at such extreme dose rate have been carried out so far using low LET particles such as electrons and protons, the radiobiology of high-LET, UHDR ions has not yet been explored. Here, we report the first application of laser-accelerated carbon ions generated by focussing 10²⁰W cm^-2intense lasers on 10-25 nm carbon targets, to irradiate radioresistant patient-derived Glioblastoma stem like cells (GSCs).Approach.We exposed GSCs to 1 Gy of 9.5 ± 0.5 MeV/n carbon ions delivered in a single ultra-short (∼400-picosecond) pulse, at a dose rate of 2 × 10⁹Gy s^-1, generated using the ASTRA GEMINI laser of the Central Laser Facility at the Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK. We quantified carbon ion-induced DNA double strand break (DSB) damage using the 53BP1 foci formation assay and used 225 kVp x-rays as a reference radiation.Main Results.Laser-accelerated carbon ions induced complex DNA DSB damage, as seen through persistent 53BP1 foci (11.5 ± 0.4 foci/cell/Gy) at 24 h and significantly larger foci (1.69 ± 0.07μm²) than x-rays induced ones (0.63 ± 0.02μm²). The relative foci induction value for laser-driven carbon ions relative to conventional x-rays was 3.2 ± 0.3 at 24 h post-irradiation also confirming the complex nature of the induced damage.Significance.Our study demonstrates the feasibility of radiobiology investigations at unprecedented dose rates using laser-accelerated high-LET carbon ions in clinically relevant models.