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We have investigated the effect of different zwitterionic compounds on DNA precipitation induced by spermine4+. Glycine, beta-alanine, 4-aminobutyric acid, and 6-aminocaproic acid have shown an increasing capacity to attenuate DNA precipitation. This protection effect has been correlated with the dielectric constant increase of their corresponding solutions. Calculations based on these experimental data and counter-ion condensation theory have confirmed the importance of this parameter for DNA-ion interactions and precipitation mechanisms. We have also observed a resolubilization of DNA in the presence of 6-aminocaproic acid at high spermine4+ concentration and in the presence of glycine at high spermidine3+ concentration. This could be explained by an increase of screening effect with polyamine concentration.

A novel delivery modality named "FLASH" radiotherapy (FLASH-RT) has emerged recently. 1 Although radiotherapy facilities are currently set to deliver dose rates around 0.05-0.40 Gy/s (CONV) in 2 Gy daily fractions accumulated to reach the tolerance limit of normal tissues undergoing irradiation, FLASH-RT relies on ultrahigh dose rate facilities and consists of delivering a large dose in a single microsecond pulse, or in a few pulses given over a very short time. FLASH-RT was established using 4-6 MeV electrons with intra-pulse dose rates in the range 10 6 -10 7 Gy/s 1 and was found to spare the lung of C57BL/6J mice exposed to 15 Gy by bilateral thorax irradiation from radiation-induced fibrosis while preserving the antitumor efficacy in xenografted as well as orthotopic, syngeneic models. 1 These features have been confirmed by other teams in adult and juvenile mouse brain, mouse tail, mouse and pig skin, cat muzzle, zebrafish, and mouse intestine (for a review, see the article "Radiobiology of the FLASH effect" in the same issue of the journal). Research groups investigating the feasibility of FLASH-RT with proton beams 2 have found promising results, with gut sparing from necrosis after 18 Gy 230 MeV protons FLASH-RT delivered at 78 Gy/s 3 and reduced lung fibrosis and skin dermatitis after proton FLASH exposures at 40 Gy/s. 4 Corroborating observations made 39 years ago with mouse tail necrosis as an endpoint, 5 Montay-Gruel et al. recently demonstrated that sparing the adult and juvenile mouse brain from radiation-induced gliosis, loss of neural stem cells, and impaired memory by ultrahigh dose rate irradiation is, at least in part, an oxygen-dependent process. 6,7 In support of this idea, carbogen breathing was found to reverse the neuroprotective effect of FLASH-RT. 6 In addition,

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