Targeting thioredoxin reductase 1 in novel combination therapies in p53 mutant triple negative breast cancer

Background: The TP53 gene is frequently mutated in human cancers including triple negative breast cancers (TNBCs) (∼84% patients). Although TP53 mutation is the only oncogenic driver in TNBCs, no targeted therapies for mutant p53 (mtp53) TNBCs are available. We aim to identify novel therapeutic targets and combination therapies for mtp53 TNBCs. Methods: A large-scale genomic analysis was performed using the TCGA database to analyse the expression of various antioxidant genes in Mt and wild-type (wt) p53 BC cells. Thioredoxin reductase 1 (TrxR1) protein levels and redox activity were measured by western blot and DTNB reduction assay, respectively. Mt and wt p53 cells were treated with gold-based TrxR1 inhibitor and APR-246 and subsequently analysed for cell proliferation, apoptosis, and cell cycle progression. Phospho-histone H3 (pHH3) Ser10 expression was analysed by FACS. Results: We observed significant upregulation of TrxR1, a redox gene, in mtp53 BC patients compared to wt patients. TrxR1 protein levels and redox activity were higher in mtp53 cells compared to wt cells. Notably, TrxR1 inhibition selectively induced apoptosis in mtp53 BC cells, but not in wt cells. Upon treatment with TrxR1 inhibitor, a significant proportion of mtp53 cells arrested in the G2/M phase with a concomitant increase in pHH3 Ser10, a marker of mitotic chromatin condensation. Thus, TrxR1 inhibition may lead to mtp53 TNBC cell death by causing mitotic catastrophe. APR-246, known to restore wild-type activity of mtp53 in many cancers, alone failed to induce apoptosis in mtp53 BC cells. However, co-treatment of APR-246 with a sub-lethal concentration of TrxR1 inhibitor resulted in a synergistic effect in mtp53 cells. Conclusions: Inhibiting TrxR1 may represent an effective therapeutic strategy for mtp53 TNBCs. These results warrant the clinical evaluation of a novel combination therapy using APR-246 and TrxR1 inhibitors for mtp53 TNBC patients. Legal entity responsible for the study: QIMR Berghofer Medical Research Institute Funding: National Health and Medical Research Council, Australia Disclosure: All authors have declared no conflicts of interest.