Copper–zinc superoxide dismutase 1 (SOD1) has long been recognized as a major redox enzyme in scavenging superoxide radicals. However, there is little information on its non-canonical role and metabolic implications. Using a protein complementation assay (PCA) and pull-down assay, we revealed novel protein–protein interactions (PPIs) between SOD1 and tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein zeta (YWHAZ) or epsilon (YWHAE) in this research. Through site-directed mutagenesis of SOD1, we studied the binding conditions of the two PPIs. Forming the SOD1 and YWHAE or YWHAZ protein complex enhanced enzyme activity of purified SOD1 in vitro by 40% (p < 0.05) and protein stability of over-expressed intracellular YWHAE (18%, p < 0.01) and YWHAZ (14%, p < 0.05). Functionally, these PPIs were associated with lipolysis, cell growth, and cell survival in HEK293T or HepG2 cells. In conclusion, our findings reveal two new PPIs between SOD1 and YWHAE or YWHAZ and their structural dependences, responses to redox status, mutual impacts on the enzyme function and protein degradation, and metabolic implications. Overall, our finding revealed a new unorthodox role of SOD1 and will provide novel perspectives and insights for diagnosing and treating diseases related to the protein.

Background: The potent topoisomerase I inhibitor SN-38, the active metabolite of irinotecan, is limited in clinical application due to severe systemic toxicity. Prodrug strategies enabling selective activation in the tumor microenvironment offer a promising approach to improve its therapeutic index. This study aims to rationally design, synthesize, and systematically evaluate novel disulfide-based SN-38 prodrugs engineered for redox-responsive activation in hypoxic tumors. Methods: Two novel disulfide-based SN-38 prodrugs (SN-38-CSS and SN-38-LSS) were designed and synthesized; SN-38-CSS incorporates a constrained cis-piperazine-fused six-membered cyclic disulfide linker, while SN-38-LSS contains a linear disulfide tether, to differentially exploit the upregulated thioredoxin (Trx/TrxR) system in hypoxic tumor microenvironments. Results: Both prodrugs demonstrated high stability under physiological pH conditions and in human plasma, minimizing premature release. Crucially, they exhibited selective, rapid degradation in the presence of dithiol reductants (TCEP and DTT), mimicking Trx system activity, while remaining stable towards monothiols (GSH, L-Cys). In vitro cytotoxicity assays revealed that the prodrugs exhibited significantly reduced toxicity compared to SN-38 under normoxic conditions across most tested cell lines. However, under hypoxic conditions, their activity was significantly restored. Specifically, SN-38-CSS exhibited cytotoxicity comparable to SN-38 against MCF-7 and NCI-N87 cells, whereas SN-38-LSS showed lower activation efficiency. Conclusions: SN-38-CSS is identified as a promising redox and hypoxia dual-responsive prodrug candidate, highlighting the strategic use of cyclic disulfide linkers for achieving high selectivity and controlled drug release within the tumor microenvironment.