ID #232 Exploiting iron overload to activate ferroptosis and potentiate cisplatin response in pediatric group 3 medulloblastomas

Abstract

Medulloblastomas (MB) are the most common malignant brain tumor of childhood, with group 3 tumors (G3MB) being the most aggressive. Their aggressiveness is linked to the activation of ferroptosis inhibitory genes, like GPX4. Additionally, these tumors activate iron-sulfur (Fe-S) cluster binding and inhibit reactive oxygen species (ROS) generation. ABCB7, the principal Fe-S cluster transporter, is overexpressed in G3MB tumors and associated with poor outcomes.

Our main objective was to investigate whether ferroptosis evasion was a driver of G3MB aggressiveness and whether targeting this driver could potentiate classical chemotherapy. We hypothesized that inhibiting Fe-S cluster export by targeting ABCB7 would induce iron overload, trigger ferroptosis, and ultimately potentiate cisplatin cytotoxicity in G3MBs.

To test our hypothesis, we used a combination of genetic (small interfering RNA, dox-inducible knockdown, and CRISPR knockout) and pharmacologic (artesunate) means to inhibit ABCB7 in two G3MB cancer cell lines (HDMB03, D425). Silencing ABCB7 induced mitochondrial iron overload, oxidative stress, and lipid peroxidation. It enhanced the cytotoxicity of erastin, a ferroptosis inducer, and accelerated cell death in the presence of exogenous iron (FAC). These effects were mitigated by co-treatment with ferrostatin-1, a ferroptosis inhibitor. Mechanistically, disrupting mitochondrial Fe-S cluster export destabilized mitochondrial membrane potential and impaired oxidative phosphorylation. Unexpectedly, silencing ABCB7 abrogated GPX4 expression, concurrently downregulating its principal cofactor, glutathione (GSH). ABCB7 inhibition synergized with cisplatin to abrogate colony formation and significantly reduce tumor burden. Artesunate, an FDA-approved, blood-brain barrier-penetrant, anti-malarial drug that induces ferroptosis, also potentiated cisplatin action in vitro and mitigated tumor burden and prolonged survival in an orthotopic G3MB mouse model. In combination with cisplatin, both drugs reduced ABCB7 and GPX4 levels.

Our study illustrates how inducing iron overload by inhibiting mitochondrial Fe-S cluster transport triggers ferroptosis and potentiates the action of a standard of care chemotherapy agent in G3MB cancer cells and tumors.