ESTRO 2024 - Abstract Book


Radiobiology - Microenvironment

ESTRO 2024

Keywords: Fibroblast ; FGFR2 ; radioresistance


Proffered Paper

Overcoming the Hypoxia Challenge: Hydrogen Peroxide as Radiosensitizer for Solid Tumors

Febe Geirnaert 1 , Lisa Kerkhove 1 , Amir L Rifi 1 , Hugo Vandenplas 1 , Cyril Corbet 2 , Thierry Gevaert 1 , Inès Dufait 1 , Mark De Ridder 1 1 UZ Brussel, VUB, Radiotherapy, Brussels, Belgium. 2 UCLouvain, Pole of Pharmacology and Therapeutics, Brussels, Belgium


The hypoxic microenvironment is the primary factor responsible for radioresistance in solid tumors. While free radicals, including hydrogen peroxide (H 2 O 2 ), are well-known radiosensitizers due to their ability to mimic oxygen, the mechanism of action of H 2 O 2 has traditionally been limited to induction of apoptosis. Concerns about local irritation associated with intact H 2 O 2 administration have halted further clinical studies. To address this issue, intratumoral injection of Kochi Oxydol for Unresectable Carcinomas (KORTUC) has been developed, which combines H 2 O 2 with sodium hyaluronate (SH) (1). While these recent advances in controlled drug delivery hold promise in a clinical setting, there is a lack of comprehensive studies that elucidate the mechanistic pathways involved. This project aims to investigate the underlying effects of H 2 O 2 when used alone or in combination with SH.


Murine CT26 colorectal and 4T1 breast cancer cells were briefly exposed to H 2 O 2 /KORTUC, and toxicity levels were determined using MTT, Incucyte and CellTiter-Glo assays. The radiomodulatory properties of H 2 O 2 /KORTUC were evaluated by colony formation assay (2D) under 0.1% O 2 and in multicellular tumor spheroids (3D). Reactive oxygen species (ROS) levels (measured using DCFDA/MitoSOX), DNA damage (assessed through γH2AX), apoptosis (determined via Annexin-V/7-AAD), and ferroptosis (evaluated using C11BODIPY) were measured using flow cytometry. Oxygen consumption rate and mitochondrial complex activity were assessed with a Seahorse Analyzer. Partial oxygen pressure after H 2 O 2 /KORTUC injections was investigated using fiber-optic sensors under hypoxic conditions in a tissue mimetic culture system (TMCS). Subcutaneous CT26 tumors in BALB/c mice received intratumoral KORTUC administration prior to radiation (3x3Gy). The effect of KORTUC on hypoxia in CT26 tumors was assessed through pimonidazole immunohistochemistry (IHC) staining.


Non-toxic concentrations of H 2 O 2 were determined and subsequently utilized. KORTUC displayed toxicity on cultured cells and was therefore diluted for downstream in vitro experiments. While SH alone exhibited radioprotective properties, the combination of SH and H 2 O 2 in KORTUC sensitized hypoxic CT26 and 4T1 cells, resulting in an enhancement ratio of 2.6 and 2.5, respectively. The enhanced radioresponse of H 2 O 2 /KORTUC was further confirmed in a 3D model.

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