Oesophageal adenocarcinoma (OAC) is a deadly disease with limited and largely ineffective treatment options. TP53 is mutated in up to 80% of OAC, resulting in resistance to chemo-radiotherapies and poor patient survival. In this study, we evaluated the potential therapeutic effects of restoring wild-type activity to mutant p53 protein in OAC, using the small molecular compound APR-246.

APR-246 inhibited cell proliferation and clonogenic survival, and induced cell cycle arrest (G1/S and G2/M) as well as apoptosis in OAC cells harbouring p53 mutations but not wild type p53 or p53 null cell lines. This corresponded to up-regulation of wild-type p53 target genes including cell cycle (p21, Gadd45α) and apoptosis regulators (PUMA and NOXA). Sensitivity to APR-246 correlated with intrinsic cellular levels of mutant p53 protein. Furthermore, ectopic expression of mutant p53 cDNA sensitised p53-null cells to APR-246, whilst p53 gene knockdown (siRNA) and knockout (CRSIPR/Cas9 mediated) diminished drug activity. Significantly, p53 knockout abolished cell cycle arrest by APR-246, whilst attenuating apoptosis induction. These data confirm the presence of p53-independent activities of APR-246 recently reported by others, at least in the induction of apoptosis.

Importantly, APR-246 synergistically enhanced the inhibitory effects of cisplatin, 5-flurouracil and epirubicin (commonly used in the treatment of OAC) in a mutant p53 dependent manner through upregulation of p53 protein and enhanced activation of apoptotic pathways. Synergism with cisplatin and 5-flurouracil was abolished by inhibiting p53 upregulation with siRNA, demonstrating. Finally, APR-246 demonstrated potent anti-tumour activity in both cell line and patient derived xenograft models, and restored chemo-sensitivity to a cisplatin/5-flurouracil resistant xenograft model.

Thus, we have convincingly demonstrated that APR-246 has significant anti-tumour activity in OAC. Recent Phase I data demonstrates that APR-246 is safe and tolerable. Therefore, our study provides proof-of-concept that APR-246 can be translated into improving the clinical outcomes of patients with OAC.