ESTRO 2024 - Abstract Book

S5377

Radiobiology - Tumour biology

ESTRO 2024

standard biochemical assays. The Fluorescence Ubiquitin Cell Cycle Indicator system was used to monitor phase of the cell cycle. Key pathways in the DNA damage response (DDR) were inhibited genetically or pharmacologically.

Results:

The first cell death wave occurred 24-48 hours after ART in cells irradiated in S- or G2-phase with a threshold ~8Gy, coinciding with prolonged mitotic duration. This wave was dependent on intrinsic apoptosis and was driven by spindle assembly checkpoint-dependent mitotic arrest. Homologous recombination (HR) promoted the first wave of cell death, and restoration of BRCA2 (a key component of HR) restored mitotic cell death after ART in a patient-derived cell line which had spontaneously lost and subsequently re-gained BRCA2. The second wave, delayed lethality, occurred days after ART, in the G1-phase irradiated cells, following at least one cell division with chromosome segregation errors. Death occurred after combined non-homologous end joining, microhomology-mediated end joining, and single strand annealing repair that enabled first cell cycle survival at the cost of chromosome segregation errors. These activated the innate immune response via DNA and RNA sensing pathways and promoted paracrine interferon signalling and STAT1-dependent extrinsic apoptosis. ART induced senescence in cells with intact TP53. Altering the spectrum of cell death outcomes through inhibition of specific DNA repair pathways corresponded to reduced interferon signalling when mitotic death was promoted, with the potential to decrease synergy with immunotherapy. Conversely, interferon signalling increased when mitotic death was rescued with one exception; targeting RAD51 promoted mitotic survival of ART-treated cells, but corresponding enhanced autophagy suppressed interferon.

Conclusion:

ART of p53-compromised cancer cells induced two distinct waves of cell death regulated through cell cycle-dependent DSB repair, with only the second wave expected to synergise with immunotherapy. Pharmacological manipulation of DDR pathways at key timings may potentially increase ART and immunotherapy synergy.

Keywords: Ablative radiotherapy cell death immunotherapy

1514

Digital Poster

Combining TiO2 loaded gel with radiotherapy to enhance anticancer effect for glioblastoma

Pei-An Chu, Hsiang-Kuang Tony Liang

National Taiwan University, Department of biomedical engineering, Taipei, Taiwan