COTI-2 reactivates mutant p53 and inhibits growth of triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) currently lacks an approved targeted therapy. The tumour suppressor TP53 gene is mutated in approximately 80% of TNBC cases. COTI-2 is a third-generation thiosemicarbazone engineered for high efficacy and low toxicity which acts by reactivating mutant p53 to a WT form. The aim of this study was to investigate COTI-2 as a targeted therapy for TNBC patients. Using a panel of 18 breast cell lines, we carried out MTT assay. p53 protein folding was determined by immunofluorescent staining with the p53 mutant-specific antibody PAb240 and the p53 WT-specific PAb1620. Surface plasmon resonance was used to determine binding affinity of COTI-2 to full length (FL) p53, and the DNA-binding domain (DBD). Flow cytometry was used to measure apoptosis. TNBC cell lines were significantly more responsive to COTI-2 than non-TNBC cell lines (p = 0.04). Furthermore, lower IC50 values were found in p53 mutant compared to p53 WT cells (p = 0.001). COTI-2 was shown to bind to FL and DBD of mutant p53. Treatment resulted in an increase in staining with PAb1620 which coincided with a decrease in staining with PAb240, suggesting refolding of the mutant protein. In addition, COTI-2 was found to induce apoptosis in TNBC cell lines. We conclude that targeting mutant p53 with COTI-2 is a potential approach for treating p53-mutated TNBC.