Pharmacological ascorbate combined with rucosopasem selectively radio-chemo-sensitizes NSCLC via generation of H₂O₂

Differences in cancer and normal cell oxidative metabolism provide a unique therapeutic opportunity for developing combined modality approaches with redox-active small molecules as radio-chemosensitizers that are well-tolerated by normal tissues. Pentaazamacrocyclic Mn (II)-containing (MnPAM) superoxide dismutase (SOD) mimetics and pharmacological ascorbate given IV to achieve [mM] plasma levels (pharmacological ascorbate: P-AscH‾) have been shown to act individually as cancer cell radio- and chemosensitizers via the generation of H₂O₂in vivo. The current study shows that the combination of newly developed MnPAM dismutase mimetic, rucosopasem manganese (RUC) with P-AscH‾ radio-sensitizes non-small cell lung cancer cells (NSCLC) and increases steady state levels of intracellular H₂O₂ with no additional toxicity to normal human bronchial epithelial cells (HBECs). Conditional over expression of catalase (CAT) in H1299T CATc15 cells demonstrates that the combination of RUC and P-AscH‾ causes radio-sensitization through an H₂O₂-dependent mechanism. Interestingly, RUC combined with P-AscH‾ demonstrates more than additive cytotoxicity in both H1299T and A549 NSCLC cells, but conditional over-expression of ferritin heavy chain (FtH) protected only the H1299T, and not the A549, from this toxicity. Most importantly, the combination of RUC + P-AscH‾ was found to sensitize both H1299T and A549 cell types to radio-chemotherapy with cisplatin (CIS) + etoposide (ETOP). Finally, in H1299T NSCLC xenografts the combination of RUC + P-AscH‾ with CIS + ETOP and 12 × 2 Gy radiation significantly inhibits tumor growth and increased median overall over survival. These results support the hypothesis that selective MnPAM dismutase mimetic + P-AscH‾ enhances the efficacy of radio-chemotherapy in NSCLC through a mechanism governed by redox active metals and H₂O₂ production.