Induction of transferrin receptor 1-mediated ferroptosis by ultrasound-triggered microbubble destruction sensitizes glioblastoma to radiotherapy.

Ultrasound-triggered microbubble destruction (UTMD), a non-invasive technique, has been proposed as a promising means of improving the efficacy of radiotherapy against glioblastoma (GBM); however, the underlying mechanisms remain to be fully clarified. Here, UTMD was shown to induce ferroptosis, an iron-dependent form of regulated cell death, in ionizing radiation (IR)-treated GL261 and 1016B cells, as evidenced by decreased cell viability, glutathione, and glutathione peroxidase 4 levels, and increased total reactive oxygen species (ROS), lipid ROS, iron/Fe2+, malondialdehyde contents, acyl-CoA synthetase long-chain family member 4 expression and cell death. Suppression of ferroptosis by ferrostatin-1 or deferoxamine abolished UTMD-induced radiosensitization in GBM cells, whereas blockade of apoptosis, autophagy, or necroptosis showed no significant effect. Conversely, induction of ferroptosis using erastin, RAS-selective lethal 3, and ferric ammonium citrate further promoted UTMD-mediated radiosensitivity of GBM cells. Mechanistically, UTMD markedly increased transferrin receptor 1 (TFR1) expression in IR-exposed GBM cells. TFR1 downregulation reversed UTMD-caused increase of intracellular Fe2+, subsequently inhibiting UTMD-induced ferroptosis and radiosensitivity of GBM cells, which were augmented by TFR1 overexpression. In GBM-bearing C57BL/6J and NOD-SCID mouse models, UTMD similarly upregulated TFR1 expression, triggered ferroptosis, and sensitized tumors to IR, and these effects were reversed by TFR1 knockdown. In conclusion, UTMD promoted the radiosensitivity of GBM partially by induction of TFR1-mediated ferroptosis, providing novel insights into the mechanism underlying UTMD-mediated radiosensitization.