Iron-oxide nanoparticles selectively enhance the toxicity of pharmacological ascorbate through hydrogen peroxide-dependent DNA damage in non-small cell lung cancer (NSCLC)

Pharmacological ascorbate (IV delivery, to plasma levels ≈ 15–20 mM) has been shown to be selectively toxic to cancer vs. normal cells as well as inducing radio-chemo-sensitization in non-small cell lung cancer (NSCLC) via increased generation of hydrogen peroxide (H₂O₂) and increased intracellular redox-active iron (Fe²⁺). The current study shows that 24 h pretreatment with an FDA-approved iron-oxide nanoparticle, Ferumoxytol (FMX), enhances the toxicity of P-AscH^- in human NSCLC cells (H1299T and A549), but not in primary human bronchiolar epithelial cells (HBEpC). In H1299TCat15 cells engineered to overexpress doxycycline inducible catalase, FMX + P-AscH^- also induced cell killing and carboplatin-induced radio-chemo-sensitization that was inhibited by exposure to doxycycline, demonstrating the dependence of the biological effects on H₂O₂. P-AscH^- + FMX induced increases in intracellular redox active Fe²⁺ in H1299TCat15 cells, that was partially inhibited by doxycycline-inducible catalase overexpression, demonstrating that both P-AscH^- and H₂O₂ participate in the intracellular release of redox active Fe²⁺ from FMX. Finally, H1299TCat15 cells treated with P-AscH^- + FMX demonstrated increased single- and double-strand DNA damage, that was not seen in HBEpCs and was inhibited by doxycycline induced expression of catalase. This study represents the first demonstration that FMX combined with P-AscH^- selectively sensitize NSCLC cells (relative to normal cells) to ascorbate toxicity and chemo-radio-sensitization through enhancing H₂O₂-dependent DNA damage, that is accompanied by increased release of intracellular Fe²⁺. These results support the hypothesis that FMX can be used to selectively enhance therapy responses to P-AscH^- in NSCLC.