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.