Biology subjects

Limoli, C. L.

Publications and source records attributed to Limoli, C. L..

3 recordsLinked to original sources

bioRxiv2025

Differentiating unirradiated mice from those exposed to conventional or FLASH radiotherapy using MRI

Background and purposeThe FLASH effect expands the therapeutic ratio of tumor control to normal tissue toxicity observed after delivery of ultra-high (>100 Gy/s FLASH-RT) vs. conventional dose rate radiation (CONV-RT). In this first exploratory study, we assessed whether ex-vivo Magnetic Resonance Imaging (MRI) could reveal long-term differences after FLASH-RT and CONV-RT whole-brain irradiation. Materials and methodsFemale C57BL/6 mice were divided into three groups: control (non-irradiated), conventional (CONV-RT 0.1 Gy/s), and ultra-high dose rates (FLASH-RT 1 pulse, 5.5 x 106 Gy/s), and received 10 Gy of whole-brain irradiation in a single fraction at 10 weeks of age. Mice were evaluated by Novel Object Recognition cognitive testing at 10 months post-irradiation and were sampled at 13 months post-irradiation. Ex-vivo brains were imaged with a 14.1 Tesla/26 cm magnet with a multimodal MRI protocol, including T2-weighted TurboRare (T2W) and diffusion-weighted imaging (DWI) sequences. ResultsIn accordance with previous results, cognitive tests indicated that animals receiving CONV-RT exhibited a decline in cognitive function, while FLASH-RT performed similarly to the controls. MRI showed decreased hippocampal mean intensity in the CONV-RT mice compared to controls but not in the FLASH-RT group. Comparing CONV-RT to control, we found significant changes in multiple whole-brain diffusion metrics, including the mean Apparent Diffusion Coefficient (ADC) and Mean Apparent Propagator (MAP) metrics. By contrast, no significant diffusion changes were found between the FLASH-RT and control groups. In an exploratory analysis compared to controls, regional diffusion metrics were primarily altered in the basal forebrain and the insular cortex after CONV-RT, and after FLASH-RT, a trend reduction was also observed. ConclusionThis study presents initial evidence that MRI can uncover clear changes in the brain after CONV-RT but not after FLASH-RT. The MRI results aligned with the observed cognitive protection after FLASH-RT, indicating the potential use of MRI to analyze the FLASH response.

neuroscience↗

bioRxiv2023

FLASH-RT does not affect chromosome translocations and junction structures beyond that of CONV-RT dose-rates

The molecular and cellular mechanisms driving the enhanced therapeutic ratio of ultra-high dose-rate radiotherapy (FLASH-RT) over slower conventional (CONV-RT) radiotherapy dose-rate remain to be elucidated. However, attenuated DNA damage and transient oxygen depletion are among several proposed models. Here, we tested whether FLASH-RT under physioxic (4% O2) and hypoxic conditions ([≤]2% O2) reduces genome-wide translocations relative to CONV-RT and whether any differences identified revert under normoxic (21% O2) conditions. We employed high-throughput rejoin and genome-wide translocation sequencing (HTGTS-JoinT-seq), using S. aureus and S. pyogenes Cas9 "bait" DNA double strand breaks (DSBs), to measure differences in bait-proximal repair and their genome-wide translocations to "prey" DSBs generated by electron beam CONV-RT (0.08-0.13Gy/s) and FLASH-RT (1x102-5x106 Gy/s), under varying ionizing radiation (IR) doses and oxygen tensions. Normoxic and physioxic irradiation of HEK293T cells increased translocations at the cost of decreasing bait-proximal repair but were indistinguishable between CONV-RT and FLASH-RT. Although no apparent increase in chromosome translocations was observed with hypoxia-induced apoptosis, the combined decrease in oxygen tension with IR dose-rate modulation did not reveal significant differences in the level of translocations nor in their junction structures. Thus, Irrespective of oxygen tension, FLASH-RT produces translocations and junction structures at levels and proportions that are indistinguishable from CONV-RT.

molecular biology↗

bioRxiv2022

Hypoxic tumors are sensitive to FLASH radiotherapy

Tumor hypoxia is a major cause of resistance to cancer treatments and especially to radiotherapy (RT) and we wanted to assess whether ultra-high dose rate FLASH RT could overcome this resistance. We engrafted tumor cells of various origins subcutaneously in mice to provide a reliable and rigorous way to modulate oxygen supply via vascular clamping or carbogen breathing. We irradiated tumors using a single 20 Gy fraction at either conventional (CONV) or FLASH dose-rate. Using multiple different subcutaneous tumor models, and in contrast CONV-RT, FLASH-RT retained anti-tumor efficacy under extreme hypoxia. These findings demonstrate that in addition to normal tissue sparing, FLASH-RT overcomes hypoxia-mediated tumor resistance. Follow-up molecular analysis using RNAseq profiling uncovered FLASH-specific inhibition of cell proliferation and translation as well as metabolic shifts that discriminated FLASH-RT from CONV-RT. These data provide new and specific insights into the mechanism of action and identify novel targets for intervention.

cancer biology↗